Thesis (PhD (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: There is growing interest to utilise xylan as speciality biopolymers in similar ways as high molecular weight polysaccharides such as starch and cellulose. The need to utilise xylan as alternative to cellulose and starch has increased because the cellulose and starch have many other competing uses. Unlike cellulose and starch, xylans are heteropolymers with higher degree of substitution and are of lower molecular mass and therefore, do not readily become insoluble to form hydrogels and biofilms. Consequently, xylans do not suit applications of starch and cellulose as speciality biodegradable additives and coatings in the food, pharmaceutical, pulp and paper and textile and many other industries. This study was conducted to develop an enzyme technology, based on recombinant α-L-arabinofuranosidase and purified α-D-glucuronidase with polymeric xylan substrate specificity, for controlled reduction of the solubility of water soluble polymeric xylan, leading to formation of insoluble nanohydrogels. Although xylan is available in abundance, a large proportion of it is currently wasted in lignocellulose process waste streams with little prospects for recovery and addition of value. Lignocellulosic materials including Eucalyptus grandis, Pinus patula, Bambusa balcooa (bamboo) and sugarcane (Saccharum officinarum L) bagasse (bagasse) found in South Africa were investigated as sources of water soluble xylan for enzyme modification. Two mild alkali-low temperature methods (alkali charge of < 14% and temperature of < 80ºC), one with ultrapurification denoted as the Hoije and the other with ethanol precipitation, denoted as Lopez method, were evaluated for their selective extraction of water soluble xylans from the specified lignocellulosic materials. The water soluble xylans were extracted from P. patula, bagasse, E. grandis and bamboo by the Hoije method with extraction efficiencies of 71.0, 66.0, 35.0 and 20.0% respectively. Using the Lopez method, the xylans from bagasse and E. grandis were extracted with extraction efficiencies of 28.0 and 12.0% respectively. The xylans extracted from P. patula, bamboo and bagasse were identified as arabinoglucuronoxylans, which were substituted with arabinose and 4-O-methyl-D- glucuronic acid (MeGlcA) side chains, whereas, the xylan extracted from E. grandis were identified as 4-O-methyl-β-D-glucuronoxylan (glucuronoxylan) substituted with MeGlcA groups on the main xylan chain. In addition, the glucuronoxylans contained some traces of arabinose and rhaminose sugar residues. The extracted xylan fractions had degree of polymerisation (DP) of > 10 and were water soluble, which suited the required properties of xylans for customised enzyme modification. The selective removal of the arabinose, MeGlcA and acetyl groups to create linear regions of xylose units in xylans that causes intra and inter-polymer bonding is considered to be the key process for reducing the solubility of water soluble xylans. The α-L-arabinofuranosidase of Aspergillus niger (AbfB) and α-D-glucuronidase of Schizophyllum commune (AguA) are special enzymes so far identified with the ability to selectively remove arabinose and MeGlcA side chains respectively, from water soluble xylans. Large scale application of the AbfB and AguA for reducing solubility of the water soluble xylans would require their extracellular production in large quantities and free of contamination from the xylan main chain degrading enzymes including the endo-1,4-β -xylanase. Selective production of the AbfB free of xylanase activity was achieved in recombinant A. niger D15 [abfB] strain under the transcriptional control of the glyceraldehyde-3-phosphate dehydrogenase promoter (gpdP) and glucoamylase terminator (glaAT). The recombinant AbfB was secreted extracellulary in 125 mL shake flasks and 10 L bioreactor fermentation cultures with volumetric activities of up to 10.0 and 8.0 nkat mL-1 respectively, against para-nitrophenol arabinofuranoside (pNPA). The secretion of the recombinant AbfB was growth associated and therefore, increased up to 2.5 times with addition of concentrate corn steep liquor (CCSL) as an additional source of nitrogen in the 2 x minimal standard cultivation media. The biomass specific activity of the recombinant AbfB against the pNPA substrate was approximately 366 nkat g-1 (dry weight basis). The recombinant AbfB displayed a single pure species band on 10% SDS-PAGE stained with Coomassie blue and had an estimated molecular mass of 67 kDa. In addition, the recombinant AbfB showed optimal activity at 40-55ºC and pH 3.0-5.0 and was stable under cultivation, storage and operating conditions at temperatures between 30-60ºC and pH 3.0-6.0. Furthermore, the recombinant AbfB showed broad substrate specificity selectively removing arabinose side groups from low viscosity wheat and oat spelt arabinoxylans, larchwood arabinogalactan, debranched arabinan and arabiglucuronoxylans extracted from bagasse, bamboo and P. patula found in South Africa,. The recombinant AbfB was able to precipitate xylans extracted from bagasse, bamboo and oat spelt but not from P. patula. Over 95% of the activity of the recombinant AbfB against the pNPA was recyclable after selective hydrolysis of the xylan at 40ºC for 16 h. On the other hand, the purified AguA enzyme could only precipitate the birch glucuronoxylan but not the glucuronoxylan extracted from E. grandis and arabinoglucuronoxylans extracted from bagasse, bamboo and P. patula. The synergetic action of the recombinant AbfB and the purified AguA increased the removal of the arabinose side chains from bagasse xylan by 22% and from bamboo xylan by 33%, whereas, the removal of the MeGlcA side chains from bagasse xylan increased by only 5% and that from bamboo xylan decreased by 13%. The selective removal of the arabinose side chains from oat spelt, bagasse and bamboo xylans by the recombinant AbfB had higher apparent viscosity relative the corresponding untreated xylans. However, the apparent viscosity of both the treated and untreated xylans reduced with increased shear rate. The viscosity had an overall negative correlation with arabinose side chain removal reaching a minimum of 2.03 mPa.s for hydrolysis of oat spelt xylan that was performed for 9.0 h at a temperature of 45.8ºC with recombinant AbfB xylan specific dosage of 400.0 nkat g-1substrate . The alteration of the viscosity of the xylans by the selective removal of the side chains is of special interest in the production of speciality emulsifying, thickening and antifoaming agents. The optimal values for hydrolysis time, enzyme dosage and temperature for maximum degree of removal of arabinose side chains from oat spelt xylan by the recombinant AbfB and of the removal of MeGlcA side chains from birch xylan by the purified AguA were determined by the Box-Benhken response surface method (RSM). The experimental region covered the xylan specific dosage for the recombinant AbfB between 18.0 and 540.0 nkatg-1substrate and for the purified AguA xylan between 2.0 and 18.0 μkatg-1substrate at temperatures between 30 and 50ºC and hydrolysis time between 1 and 16 h. The temperature, enzyme xylan specific dosage and hydrolysis time had significant effect (p<0.05) on both the selective removal of arabinose from oat spelt xylan by the recombinant AbfB and the selective removal of MeGlcA from birch xylan by the purified AguA. However, the interaction of these hydrolysis parameters were significant (p<0.05) on only the removal of arabinose side chains from oat spelt xylan by the recombinant AbfB. The optimal values for hydrolysis time, temperature and xylan specific dosage were estimated to be 14-16 h, 38-45ºC and 607.0 nkatg-1substrate respectively, for maximum removal of 43% of the available arabinose in oat spelt xylan by the recombinant AbfB. Whereas, the optimal values for hydrolysis time, temperature and xylan specific dosage for maximum removal of 0.5% of the available MeGlcA side chains from the birch xylan by the purified AguA were estimated to be 11 h, 38ºC and 18.0 μkatg-1substrate respectively. The optimal values of the hydrolysis parameters for both the removal of the arabinose from oat spelt xylan by the recombinant AbfB and of MeGlcA side chains from birch by the purified AguA could be predicted using quadratic models that fitted the response surface plots with regression coefficients of > 0.9. The effects of in situ selective removal of arabinose and MeGlcA side chains by AbfB and AguA respectively, from water soluble xylans, on their precipitation and adsorption onto cotton lint were investigated. The cotton lint was treated with xylans extracted from bagasse, bamboo, P. patula and E. grandis using the Hoije method in the presence of the recombinant AbfB, AguA and the cocktail of the two enzymes. The effects of in situ selective hydrolysis of model xylans including birch, oat spelt and H2O2 bleached bagasse and E. grandis xylan gel by the enzymes on their adsorption onto cotton lint were used for reference purposes. The purified AguA increased the adsorption of arabinoglucuronoxylans extracted from bagasse bamboo and P. Patula using the Hoije method onto cotton lint the most compared to the effect of the recombinant AbfB and the cocktail of the recombinant AbfB and purified AguA. The purified AguA increased the adsorption of the xylans extracted from bagasse and E. grandis xylans by 334 and 29% respectively, but decreased that of E. grandis xylan gel and H2O2 bleached bagasse xylan by 31 and 6% respectively. Similarly, the presence of the recombinant AbfB increased the adsorption of the bamboo, P. Patula and oat spelt xylans by 31, 44 and 900% respectively, but decreased the adsorption of the xylan extracted from bagasse and the H2O2 bleached bagasse xylan by 13 and 30% respectively. Furthermore, different xylan-cellulose interactions and water adsorption capacities of the cotton lint were observed with the in situ modification and adsorption of the xylans extracted from bagasse, bamboo, E. grandis and P. patula in the presence of the recombinant AbfB and purified AguA. Therefore, the enzyme aided adsorption of xylans could be used to alter or improve functional properties of cellulosic materials. The performance of enzymatically formed xylan nanohydrogels as encapsulation matrices for slow delivery of bioactive agents was evaluated. Insoluble xylan nanohydrogels formed by selective removal of arabinose side chains from water soluble oat spelt xylan by the recombinant AbfB were characterized for particle size distribution, surface charge (zeta potential), morphology stability and ability to encapsulate and slowly release the HRP. The enzymatically formed oat spelt xylan hydrogels were spherical in shape with particle sizes ranging from 18 nm to > 10 000 nm. The xylan nanohydrogels exhibited a negative zeta potential of up to -19 mV and displayed self assembling behaviour when formed at xylan concentrations of higher than 1.5% (w/v) and hydrolysis time beyond 17 h. The xylan concentration significantly (P < 0.05) influenced both the particle size and zeta potential of the oat spelt xylan nanohydrogels whereas the recombinant AbfB hydrolysis time was significant (P < 0.05) on the zeta potential. The oat spelt xylan nanohydrogels successfully encapsulated the HRP enzyme both during and after formation of the oat spelt xylan nanohydrogels and the release of the encapsulated HRP in active form, was sustained for a period of 180 min. Therefore, the xylan side chain removing enzymes have a role in preparation of biodegradable nanoencapsulation devices. Overall, the AbfB and AguA have presented a novel tool for functionalising water soluble xylans to be used as speciality additives, coating and implantation or encapsulation matrices, with reduced impact on the environment. This will advance processing and expand the product spectrum of lignocellulosic materials. / AFRIKAANSE OPSOMMING: Daar is ‘n toenemende belangstelling om spesialiteit biopolimere uit xilaan ontwikkel, en op soortgelyke wyse as hoë molekulêre massa polisakkariede soos stysel en sellulose te benut. Die behoefte om xilaan biodegradeerbare polimere as ‘n alternatief tot sellulose en stysel te gebruik neem toe omdat laasgenoemde baie ander kompeterende gebruike het. Anders as sellulose en stysel is uit xilaan heteropolimere met ‘n hoë graad van substitusie in die hoofketling met sygroepe en lae molekulêre massas, en raak daarom nie geredelik onoplosbaar om hidrojel en biofilms te vorm nie. Gevolglik is xilaan nie geskik vir toepassings van stysel en sellulose as spesialiteit biodegradeerbare bymiddels en bedekkings in die voedsel-, farmaseutiese-, pulp en papier-, tekstiel-, en vele ander industrieë nie. Hierdie studie is uitgevoer om ‘n ensiemtegnologie te ontwikkel gebaseer op rekombinante α-L-arabinofuranosidase en gesuiwerde α-D-glukuronidase met polimeriese xilaan substraat spesifisiteit, vir beheerde vermindering van die oplosbaarheid van wateroplosbare polimeriese xilaan wat lei tot die vorming van onoplosbare nanohidrojels. Alhoewel xilaan volop beskikbaar is, word ‘n groot deel daarvan tans vermors in afvalstrome uit lignosellulose prosessering, primêr verpulping, met min vooruitsigte vir herwinning en toevoeging van waarde. Lignosellulose materiaal wat in Suid-Afrika geproduseer word, insluitend Eucalyptus grandis (E. grandis), Pinus patula (P. patula), Bambusa balcooa (bamboes) en suikerriet (Saccharum officinarum L) (bagasse), is ondersoek as bronne van wateroplosbare xilaan vir ensiem modifikasie. Twee gematigde, lae temperatuur alkali-metodes (‘nalkali lading van < 14% en temperatuur van < 80°C), een met ultrasuiwering aangedui as Hoije en die ander met etanolpresipitasie aangedui as Lopez metode, is evalueer vir selektiewe ekstraksie van wateroplosbare xilaan vanuit die genoemde lignosellulose materiale. Die wateroplosbare xilaan is ge-ekshaheer vanuit P. patula, bagasse, E. grandis en bamboes met die Hoije metode met ekstraksie doeltreffendhede van 71.0, 66.0, 35.0, en 20.0%, onderskeidelik. Met die Lopez metode is xilaan vanuit bagasse en E. grandis geëkstraheer met ekstraksie doeltreffendhede van 28.0% en 12.0%, onderskeidelik. Die xilaan wat vanuit P. patula, bamboes, en bagasse ekstraheer is, is as arabinoglukuronoxilaan geïdentifiseer, wat met arabinose en 4-O-metiel-D glukuronsuur sykettings vervang is, terwyl die xilaan wat vanuit E. grandis ekstraheer is as 4-O-metiel--D-glukuronoxilaan (glukuronoxilaan), met substitusie met MeGlcA en asetiel-groepe op die hoof xilaan-ketting (ruggraat) is. Die glukuronoxilaan het verder spore van arabinose en rhaminose funksionele groepe bevat. Die geëkstraheerde xilaan fraksies het grade van polimerisasie > 10 gehad en was wateroplosbaar, wat die vereiste eienskappe van die xilaan vir doelgemaakte ensiem modifikasies bevredig het. Die selektiewe verwydering van die arabinose, MeGlcA, en asetiel-groepe om xilose eenhede sonder substitusie in polimeriese xilaan te vorm, wat intra- en inter-polimeer binding veroorsaak, word beskou as die belangrikste proses vir die vermindering van die oplosbaarheid van wateroplosbare xilaan. Die α-L-arabinofuranosidase van Aspergillus niger (AbfB) en α-D-glukuronidase van Schizophyllum commune (AguA) is spsialiteutsensieme wat tot dusver is met die vermoë om selektief die arabinose en MeGlcA sykettings, onderskeidelik, vanaf wateroplosbare xilaan te verwyder. Grootskaalse toepassing van die AbfB en AguA ensieme, vir die vermindering van die oplosbaarheid van wateroplosbare xilaan , sal ekstrasellulêre produksie deur mikrobes in groot hoeveelhede en vry van kontaminasie van die xilaan hoofketting degraderende ensieme insluitend die endo-1,4--xilanase vereis. Selektiewe produksie van die AbfB vry van xilanase aktiwiteit is verkry deur kultivering van rekombinante A. niger D15 [abfB], met transkipsie van die abfB-geen beheer deur die gliseraldehied-3-fosfaat dehidrogenase promotor (gpdp) en glukoamilase termineerder (glaAT). Die rekombinante AbfB ensiem is ekstrasellulêr geproduseer in 125 mL skudflesse en ‘n10 L bioreaktor fermentasiekulture met volumetriese aktiwiteite van tot 10.0 en 8.0 nkat mL-1, onderskeidelik, teen para-nitrofenol arabinofuranosied (pNPA). Die uitskeiding van die rekombinante AbfB was groei geassosieerd en het daarom tot 2.5 keer toegeneem met die byvoeging van gekonsentreerde mielieweekvloeistof as ‘n addisionele bron van stikstof in die 2 x minimale standaard kwekingsmedium. Die biomassa spesifieke aktiwiteit van die rekombinante AbfB teen die pNPA substraat was ongeveer 366 nkat g-1 (droë massa basis). Die rekombinante AbfB het ‘n enkele suiwer spesie band getoon op 10% SDS-PAGE gevlek met Coomassie blou en het ‘n beraamde molekulêre massa van 67 kDa gehad. Die rekombinante AbfB het verder optimale aktiwiteit by 40-55°C en pH 3.0-5.0 getoon en was stabiel onder kweking-, storing-, en bedryfstoestande by temperature tussen 30-60°C en pH 3.0-6.0. Die rekombinante AbfB het ook wye substraatspesifisiteit getoon om arabinose sy-groepe selektief te verwyder vanaf lae viskositeit koring-en hawerbiopolimere, lariks arabinogalaktaan, onvertakte arabinaan, en arabinoglukuronoxilaan biopolimere, geëkstraheer vanaf bagasse, bamboes en P.patula wat in Suid-Afrika aangetief word. Die rekombinante AbfB kon xilaan, ge-ekshaheer vanaf bagasse, bamboes en hawer onoplosbaar maak, maar die xilaan geëkstraheer vanaf P. patula nie. Meer as 95% van die aktiwiteit van die rekombinante AbfB teen die pNPA kon hersirkuleer word na selektiewe hidrolise van die xilaan by 40°C vir 16 h. Aan die ander kant kon die gesuiwerde AguA-ensiem slegs berkehout glukuronoxilaan onoplosbaar maak, maar nie glukuronoxilaan wat vanaf E. grandis geëkstraheer is of arabinoglukuronoxilaan wat vanaf bagasse, bamboes en P. patula geëkstraheer is nie. Die sinergistiese aksie van die rekombinante AbfB en die gesuiwerde AguA het die verwydering van die arabinose sykettings vanaf bagassexilaan met 22% vermeerder en met 33% in die geval van bamboesxilaan. Die verwydering van MeGlcA sykettings vanaf bagassexilaan is met slegs 5% vermeerder, terwyl dit met 13% verminder het in die geval van bamboesxilaan. Die selektiewe verwydering van die arabinose sykettings vanaf xilaan van hawer, bagasse, en bamboes deur die rekombinante AbfB het hoër skynbare viskositeit gehad relatief tot die ooreenstemmende onbehandelde xilaan . Die skynbare viskositeit van beide die behandelde en onbehandelde xilaan het egter verminder met toenemende skuiftempo. Die viskositeit het ‘n algehele negatiewe korrelasie met arabinose syketting verwydering gehad en het ‘n minimum van 2.03 mPa.s bereik vir hidrolise van hawerxilaan wat uitgevoer is vir 9.0 h by ‘n temperatuur van 45.8°C met rekombinante AbfB xilaan met ‘n spesifieke dosering van 400.0 nkat g-1substraat. Die wysiging van die viskositeit van die xilaan deur die selektiewe verwydering van die sykettings is van besondere belang in die produksie van spesialiteit emulsifisering, verdikking- en skuimweermiddels. Die optimale waardes vir hidrolisetyd, ensiemdosering en temperatuur vir maksimum graad van arabinose syketting verwydering vanaf hawerxilaan met die rekombinante AbfB, en van MeGlcA syketting verwydering vanaf berkehout xilaan met die gesuiwerde AguA, is vasgestel deur middel van die Box-Benhken responsie oppervlak metode. Die eksperimentele gebied het die xilaanspesifieke dosering met die rekombinante AbfB tussen 18.0 en 540.0 nkat g-1substraat en vir die gesuiwerde AguA xilaan tussen 2.0 en 18.0 μkat g-1substraat by temperature tussen 30 en 50°C en hidrolisetye tussen 1 en 16 h gedek. Die temperatuur, ensiem xilaan spesifieke dosering en hidrolise tyd het elk ‘n beduidende invloed (p<0.05) gehad op beide die selektiewe verwydering van arabinose vanaf hawerxilaan met die rekombinante AbfB en die selektiewe verwydering van MeGlcA vanaf berkehout xilaan met die gesuiwerde AguA. Die interaksie van hierdie hidroliseparameters was egter net beduidend (p<0.05) in die geval van arabinose syketting verwydering vanaf hawer xilaan met die rekombinante AbfB. Die optimale waardes vir die hidrolise tyd, temperatuur, en xilaan spesifieke dosering is beraam om gelyk aan 14-16 h, 38-45°C, en 607.0 nkat g-1substraat, onderskeidelik, te wees vir maksimale verwydering van 43% van die beskikbare arabinose in die hawer xilaan met die rekombinante AbfB. Die optimale waardes vir die hidrolise tyd, temperatuur en xilaan spesifieke dosering vir maksimale verwydering van 0.5% van die beskikbare MeGlcA sykettings vanaf die berkehout xilaan met die gesuiwerde AguA is beraam om gelyk aan 11 h, 38°C, en 18.0 μkat g-1substraat, onderskeidelik, te wees. Die optimale waardes van die hidrolise parameters, vir beide die verwydering van die arabinose vanaf hawer xilaan met die rekombinante AbfB en van MeGlcA sykettings vanaf berkehout met die gesuiwerde AguA, kon voorspel word deur gebruik te maak van kwadratiese modelle wat die responsie-oppervlak grafieke met regressie koeffisiënte > 0.9 gepas het. Die effek van in situ selektiewe verwydering van arabinose en MeGlcA sykettings met rekombinante AbfB en gesuiwerde AguA, onderskeidelik, vanaf wateroplosbare xilaan op hulle presipitasie en adsorpsie op katoen lint is ondersoek. Die katoenlint is behandel met xilaan ge-ekstraheer vanuit bagasse, bamboes, P. patula, en E. grandis deur gebruik te maak van die Hoije metode in die teenwoordigheid van die rekombinante AbfB, AguA, en ‘n mengsel van die twee ensieme. Die effek van in situ selektiewe hidrolise, deur die ensieme van model xilaan insluitende berkehout, hawer en H2O2-gebleikte bagasse en E. grandis xilaan jel, op hulle adsorpsie op katoen lint is gebruik vir verwysingsdoeleindes. Die gesuiwerde AguA het die adsorpsie van arabinoglukuronoxilaan , wat vanuit bagasse, bamboes en P. patula ekstraheer is deur middel van die Hoije metode, op katoenlint die meeste laat toeneem in vergelyking met die effek van die rekombinante AbfB en die mengsel van die rekombinante AbfB en die gesuiwerde AguA. Die gesuiwerde AguA het die adsorpsie van die xilaan wat vanuit bagasse en E. grandis ekstraheer is met 334 en 29%, onderskeidelik, laat toeneem, maar het die adsorpsie van E. grandis xilaanjel en H2O2 gebleikte bagasse xilaan met 31 en 6%, onderskeidelik, laat afneem. Op ‘n soortgelyke wyse het die teenwoordigheid van die rekombinante AbfB die adsorpsie van die bamboes, P. Patula en hawer xilaan met 31, 44, en 900%, onderskeidelik, laat toeneem, maar die adsorpsie van die xilaan ekstraheer vanuit bagasse en die H2O2 gebleikte bagasse xilaan met 13 en 30%, onderskeidelik, laat afneem. Verskillende xilaan-sellulose interaksies en water adsorpsie kapasiteite van die katoen lint is opgemerk met die in situ modifikasie en adsorpsie van die xilaan ekstraheer vanuit die bagasse, bamboes, E. grandis en P. patula in die teenwoordigheid van die rekombinante AbfB en gesuiwerde AguA. Die ensiem bygestaande adsorpsie van xilaan kon daarom gebruik word om die funksionele eienskappe van die sellulose materiaal aan te pas of te verbeter. Die wekverrigting van ensimaties gevormde xilaan nanohidrojels as enkapsuleringmatrikse vir stadige vrystelling van bioaktiewe middels is geevalueer. Onoplosbare xilaan nanohidrojels wat gevorm is deur selektiewe verwydering van arabinose sykettings vanaf wateroplosbare hawer xilaan met die rekombinante AfbA, is gekarakteriseer vir partikelgrootteverspreiding, oppervlaklading (zeta potensiaal), morfologiese stabiliteit, en die vermoë om die ramenas peroksidase te enkapsuleer en stadig vry te stel. Die ensimaties gevormde hawer xilaan hidrojels het ‘n sferiese vorm gehad met partikelgroottes wat gewissel het van 18 nm tot > 10 000 nm. Die xilaan nanohidrojels het ‘n negatiewe zeta potensiaal van tot -19 mV getoon, en het self-vormings gedrag vir partikels ten toon gestel indien dit by xilaankonsentrasies hoër as 1.5% (m/v) en hidrolise tye langer as 17 h gevorm is. Die xilaan konsentrasie het beide die partikelgrootte en die zeta potensiaal van die hawerxilaan nanohidrojels beduidend (P < 0.05) beïnvloed terwyl die rekombinante AbfB hidrolise tyd beduidend (P < 0.05) was op die zeta potensiaal. Die hawer xilaan nanohidrojels, het die ramenasperoksidase ensiem suksesvol enkapsuleer, beide gedurende en na die vorming van die hawer xilaan nanohidrojels en die vrystelling van die geënkapsuleerde ramenas peroksidase in aktiewe vorm is volgehou vir ‘n periode van 180 min. Die ensieme wat die syketting van die xilaan verwyder het, het dus ‘n rol in die voorbereiding van biodegadeerbare nano-enkapsulasie geedskap. In die geheel veskaf die rekombinante AbfB en gesuiwerde AguA ‘n nuwe stel manier voor om wateroplosbare xilaan te funksionaliseer om as spesialiteit bymiddels, bedekking, en inplanting of enkapsulasiematrikse gebruik te word met ‘n verminderde impak op die omgewing. Dit sal prosessering bevorder en die produkspektrum van lignosellulose materiale uitbrei.

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Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Sulphuric acid/oxygen pressure leaching is typically employed on Base Metal Refineries (BMRs) to selectively dissolve base metals from platinum group metal (PGM) bearing nickelcopper matte. Optimal operation of this processing step requires an understanding of the system chemistry and the effects of process variables on base metal and PGM leaching behaviour. This project aimed to aid in the development of an improved understanding of the high pressure leaching system. The effects of temperature, pressure, acid concentration, and solid to liquid ratio on the leaching behaviour were determined experimentally using a two litre autoclave. For conditions comparable to that typically used at the Western Platinum Ltd. BMR, changes in the acid concentration had the largest effect on the copper leaching behaviour. Increasing the initial acid concentration from 140 g H2SO4/ℓ to 165 g H2SO4/ℓ resulted in the copper dissolution decreasing from 88.7% to 75.3% on average for the experiments performed at different temperatures (116°C, 130°C) and pressures (7 bar, 9 bar), and with different solids contents (80 g/ℓ, 130 g/ℓ). In the case of the other precious metals (OPMs), temperature was determined to be the process variable with the largest effect on the leaching kinetics. The average percentage rhodium dissolution achieved after seven hours of leaching at different conditions (pressure, acid concentration, and solids content were varied) increased from 58.3% at 116°C to 83.6% at 130°C. Similar effects were observed for ruthenium (96.2% dissolution at 130°C; 79.4% dissolution at 116°C) and iridium (81.8% dissolution at 130°C; 46.9% dissolution at 116°C). The rate of copper leaching was found to be limited by the rate of oxygen transfer from the gaseous phase to the liquid phase, while the remainder of the reactions were chemical reaction limited. The extent of OPM leaching was found to be dependent on the rate and extent of copper leaching. A set of 21 chemical reactions was proposed to describe the leaching behaviour, and the shape factors and reaction rate constants were determined by the method of least squares to minimise the error between the predicted concentrations and the experimental data. Apart from direct base metal leaching reactions, six cationic exchange reactions contribute to the leaching of copper sulphides and nickel sulphides by precipitation of OPM oxides. Three leaching reactions for each of the OPMs (one for sulphide phases, one for metallic phases, and one for oxide phases) resulted in satisfactory modelling of the system behaviour. Activation energies of -26.2 kJ/mol and -5.9 kJ/mol were calculated for the digenite acid leaching reaction and the covellite direct oxidation reaction, respectively, which confirmed that the rates of these reactions were mass transfer limited. The activation energies for the remainder of the base metal leaching reactions exceeded 30 kJ/mol. The activation energies of the reactions accounting for rhodium sulphide leaching, rhodium leaching, and rhodium oxide leaching, were calculated to be 64.2 kJ/mol, 138.5 kJ/mol, and 116.2 kJ/mol, respectively. Similar activation energies were calculated for the respective Ru and Ir leaching reactions. The rate of OPM sulphide leaching was typically an order of magnitude and three orders of magnitude larger than the rate of OPM leaching reactions and OPM oxide leaching reactions, respectively. The autoclave at the Western Platinum Ltd. BMR was modelled assuming a monosized distribution of the feed and approximating the autoclave as four ideal continuously stirred tank reactors. The steady state solution employed the sequential modular approach in MATLAB, while the dynamic simulation involved solving a set of 217 differential equations derived from mass and energy balances simultaneously in MATLAB. The model was used successfully to evaluate the effects that changes in the leaching temperature, leaching pressure, acid feed rate, and solids feed rate have on the extent of base metal and OPM leaching in the autoclave. The optimum operating conditions depend on the flow rates and compositions of the feed streams. A feed stream containing 10.3 wt% solids (825 kg solids/h) and an acid addition rate of 28.6 kg/h were considered as typical operating conditions for model-based analysis. More than 95% copper dissolution and no OPM dissolution were predicted when performing the pressure leaching at a pressure of 8 bar and a temperature of approximately 123°C. Decreasing the pressure resulted in lower copper dissolution when OPM leaching started to occur. Increasing the temperature resulted in reduced copper leaching, while decreasing the temperature resulted in a longer OPM leaching period and hence higher OPM dissolution. Model-based analysis furthermore showed that the relative amounts and relative leaching rates of digenite and covellite significantly influence the percentage copper dissolution achieved when noticeable OPM leaching start to occur. / AFRIKAANSE OPSOMMING: Swawelsuur/suurstof hoë druk loging word tipies op Basis Metaal Raffinaderye (BMRe) gebruik om basis metale selektief op te los vanuit platinum groep metaal (PGM) bevattende nikkel-koper mat. Optimale bedryf van hierdie prosesstap vereis ʼn begrip van die sisteem se chemie en die effekte wat proses veranderlikes op die logingsgedrag van basis metale en PGMe het. Hierdie projek het ten doel gehad om ʼn beter begrip van die hoë druk loging sisteem te ontwikkel. Die effekte van temperatuur, druk, suur konsentrasie, en vastestof tot vloeistof verhouding op die logingsgedrag is eksperimenteel met behulp van ʼn twee liter outoklaaf bepaal. Vir toestande vergelykbaar met dié wat tipies by die Western Platinum Bpk. BMR gebruik word, het veranderinge in die suurkonsentrasie die grootste effek op die logingsgedrag van koper gehad. Verhoging van die aanvanklike suurkonsentrasie van 140 g H2SO4/ℓ na 165 g H2SO4/ℓ het tot gevolg gehad dat die gemiddelde koper oplossing afgeneem het van 88.7% na 75.3% vir die eksperimente wat by verskillende temperature (116°C, 130°C) en drukke (7 bar, 9 bar), en met verskillende vastestof inhoud (80 g/ℓ, 130 g/ℓ), uitgevoer is. In die geval van die ander edelmetale (AEM) is bevind dat die temperatuur die prosesveranderlike met die grootste effek op die logingskinetika is. Die gemiddelde persentasie rodium oplossing wat na sewe ure se loging by verskillende toestande (druk, suurkonsentrasie, en vastestof inhoud is varieer) behaal is, het toegeneem van 58.3% by 116°C na 83.6% by 130°C. Soortgelyke effekte is waargeneem vir rutenium (96.2% oplossing by 130°C; 79.4% oplossing by 116°C) en iridium (81.8% oplossing by 130°C; 46.9% oplossing by 116°C). Dit is bevind dat die tempo van koper loging beperk is deur die tempo van suurstof oordrag vanaf die gas na die vloeistoffase, terwyl chemiese reaksies beperkend was vir die res van die reaksies. Die mate van AEM loging was afhanklik van die tempo en mate van koper loging. ʼn Stel van 21 reaksies is voorgestel om die logingsgedrag te beskryf, en die vorm faktore en reaksie tempo konstantes is bepaal deur middel van die metode van kleinste kwadrate om die fout tussen die voorspelde konsentrasies en die eksperimentele data te minimeer. Afgesien van die direkte basis metaal logingsreaksies het ses kationiese uitruilingsreaksies bygedra tot die loging van kopersulfiede en nikkelsulfiede deur presipitasie van AEM oksiede. Drie logingsreaksies vir elk van die AEMe (een vir die sulfied fase, een vir die metaal fase, en een vir die oksied fase) het bevredigende modellering van die sisteem se gedrag tot gevolg gehad. Aktiveringsenergieë van -26.2 kJ/mol en -5.9 kJ/mol is bereken vir die Cu1.8S suur logingsreaksie en die CuS direkte oksidasie reaksie, onderskeidelik, wat bevestig het dat die tempo’s van hierdie reaksies deur massa oordrag beperk is. Die aktiveringsenergieë vir die res van die basis metaal logingsreaksies het 30 kJ/mol oorskry. Die aktiveringsenergieë vir die reaksies wat die rodiumsulfied loging, rodium loging, en rodiumoksied loging beskryf is as 64.2 kJ/mol, 138.5 kJ/mol, en 116.2 kJ/mol, onderskeidelik, bereken. Soortgelyke aktiveringsenergieë is bereken vir die onderskeie Ru en Ir logingsreaksies. Die tempo van AEM sulfied loging was tipies ʼn ordegrootte en drie ordegroottes groter as die tempo van AEM logingsreaksie en AEM oksied logingsreaksies, onderskeidelik. Die outoklaaf by die Western Platinum Bpk. BMR is gemodelleer deur ʼn enkelgrootte verspreiding vir die voer te aanvaar en die outoklaaf as vier ideale kontinu geroerde tenk reaktore te benader. Die oplossing vir gestadige toestande het die sekwensiële modulêre benadering toegepas in MATLAB, terwyl die dinamiese simulasie die gelyktydige oplos van 217 differensiale vergelykings, wat vanaf massa- en energiebalanse afgelei is, in MATLAB behels het. Die model is suksesvol gebruik om die effekte wat veranderinge in die logingstemperatuur, logingsdruk, suur voertempo, en vastestof voertempo op die mate van basis metaal en AEM loging in die outoklaaf het, te bepaal. Die optimale bedryfstoestande is afhanklik van die vloeitempo’s en samestellings van die voerstrome. ʼn Voerstroom wat 10.3 massa% vastestof (825 kg vastestof per uur) bevat en ʼn suur voertempo van 28.6 kg/h is as tipiese bedryfstoestande beskou vir model-gebaseerde analises. Meer as 95% koper oplossing sonder enige AEM oplossing is voorspel wanneer die loging by ʼn druk van 8 bar en ʼn temperatuur van ongeveer 123°C uitgevoer word. ʼn Vermindering van die druk het tot gevolg gehad dat laer koper loging behaal is toe AEM loging begin plaasvind het. ʼn Verhoging in die temperatuur het laer koper loging tot gevolg gehad, terwyl laer temperature ʼn langer AEM logingsperiode en gevolglik hoër AEM loging tot gevolg het. Model-gebaseerde analises het verder getoon dat die relatiewe hoeveelhede en relatiewe tempo’s van loging van Cu1.8S en CuS ʼn beduidende invloed het op die persentasie koper wat geloog is wanneer beduidende AEM loging begin plaasvind.

Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: Conventional, advanced and fractionation pretreatment technologies were employed to recover and/or enhance the efficacy of the main constituents present in lignocellulosic biomass. Bamboo and triticale bran are novel feedstocks and hence their response towards treatment is unknown. Thus, to assist with the characterisation of these feedstock, in terms of the amount of sugar released during acid and enzymatic hydrolysis, use were made of conventional pretreatment technologies. Pretreatment involved the use of either the conventional single-stage dilute-acid or the conventional acid-catalysed steam-explosion process at times, temperatures and acid concentration ranging between 5 to 40 min, 120 to 214°C, and 0.002 to 0.055 (H3O+) gmol/L, respectively. For additional comparison, results were also obtained from an established feedstock namely sugarcane bagasse, by subjecting it to the single-stage dilute-acid process, at similar pretreatment conditions employed during the treatment of the other feedstocks. Sugarcane bagasse and bamboo, upon pretreatment and enzymatic hydrolysis, both yielded a similar combined sugar recovery yield of 78.0% and 81.2%, respectively. Alternatively, only 55.3% (w/w) of the total sugar content in triticale bran could be recovered. Triticale bran consists predominantly of hemicellulose which, compared to cellulose, the main constituent in sugarcane bagasse and bamboo, is more susceptible to degradation. Thus, to enhance the combined sugar recovery yield, it is recommended that triticale bran be treated at less severe pretreatment conditions, in order to preserve the hemicellulose. To further enhance the amount of sugar (i.e. cellulose and hemicellulose) that can be recovered from sugarcane bagasse, the use of a two- rather than one-stage dilute acid process was proposed. The single-stage dilute acid process, despite being the subject of many research efforts, failed to recover more than 83% (w/w) of the total sugar content in sugarcane bagasse. Following an extensive literature study, it was concluded that sugarcane bagasse comprises a hemicellulose and cellulose fraction which dictates the use of different pretreatment conditions in order to ensure their effective recovery. The use of a more advance two-step dilute acid process was therefore proposed as it allows for multiple-sets of pretreatment conditions which accommodate the requirements set forth by each of the polysaccharides present in sugarcane bagasse. With the assistance of response surface methodology, a 4.8% (w/w) improvement over the single-stage method was calculated for the two-stage process, by assuming both pretreatment technologies operated at optimum pretreatment conditions. This improvement, which is similar to the 7.7% (w/w) obtained with substrates other than sugarcane bagasse, was accredited to the use of multiple-sets of pretreatment conditions. Both low and high severity pretreatment conditions were applied to maximise the recovery of hemicellulose and cellulose, respectively. In the case of bamboo however, little can be gained by using the two- in lieu of the one-stage method, as similar pretreatment conditions are required to maximise both hemicellulose and cellulose recovery. Alternatively, a three- rather than a two-stage process needs to be applied, when treating triticale bran, to accommodate for an additional set of pretreatment conditions required to recover arabinan, a third polysaccharide. In order to realise the full potential of sugarcane bagasse, use was made of a fractionation method, which in addition to the recovery of polysaccharide (i.e. cellulose and hemicellulose), also allowed for the recovery of the polyphenolic content (i.e. lignin) thereof. Limited by the complexity of the fractionation process, sugarcane bagasse was selected as the preferred substrate to be subjected to fractionation, mainly because of its availability in the South African (established sugar milling industry), and ease of treatment using both conventional (e.g. single-stage) and advanced (e.g. two-stage) pretreatment technologies. A novel fractionation technology, involving the use of the ionic liquid 1-butyl-3- mehylimidazolium methyl sulphate ([BMiM]MeSO4), was devised to separate the main constituents of sugarcane bagasse. Although other ionic liquid fractionation examples also exist in literature, processes used caused production of multi-component product streams with 34% (w/w) of the original lignin and hemicellulose being recovered in the same product stream. Tests conducted during the present study confirmed these results and further indicated that the production of multi-constituent product streams could not be avoided by using acetone, an acetone-water mixture or a sodium hydroxide solution as the solvent in a subsequent solvent extraction step. Hence, to avoid the production of multi-component product streams, a hemicellulose pre-extraction step, comprising the single-stage dilute acid process, was introduced to extract and recover 75% (w/w) of the hemicellulose content. The remaining solid was subjected to ionic liquid treatment whereafter it was effectively separated into cellulose and lignin enriched product streams through solvent extraction. Up to 73% (w/w) of the original lignin and cellulose content was recovered using optimum operating conditions (120 min; 125°C). Comparison of the novel ionic liquid ([BMiM]MeSO4) with 1-ethyl-3-methylimidazolium acetate, an established ionic liquid, identified the former to be the superior delignification solvent whereas the latter contributed more towards the digestibility of the residual solids. In conclusion, methods for the effective recovery of polysaccharides and polyphenol units from established (i.e. sugarcane bagasse) and novel (i.e. bamboo, triticale bran) lignocellulosic feedstocks have been demonstrated through the application of conventional (single-stage), advanced (two-stage) and fractionation pretreatment technologies. Economic improvement is promised through the application of these constituents as they may serve as precursor chemicals for the production of value-added products that may replace the fuel and chemicals currently derived from fossil carbon resources. / AFRIKAANSE OPSOMMING: Konvensionele, gevorderde en fraksionering voorafbehandeling tegnologieë is gebruik om die herwinning en gebruiksaamheid van die hoofbestanddele wat in lignosellulose biomassa aanwesig is, te verbeter. Bamboes en tritikale semels is nuwe rou materiale en dus is hul reaksie op behandeling onbekend. Ten einde die karaktereienskappe van hierdie rou materiale, in terme van die hoeveelheid suiker wat gedurende die suur- en suiker ensimatiese-hidrolise vrygestel word, te bepaal, is gebruik gemaak van konvensionele voorbehandeling tegnologieë. Voorbehandeling behels die gebruik van óf die konvensionele enkelstadium vedunde-suur óf die konvensionele suur-gekataliseerde stoomontploffingsproses; by tye, temperature en suurladings wat wissel tusen 5 en 40 minute, 120 tot 214°C, en 0.002 tot 0.055 (H3O+)gmol/L, onderskeidelik. Vir verdere vergelykings is resultate vanaf ’n gevestigde rou materiaal, naamlik suikerriet reste, verkry, deur dit te onderwerp aan ’n enkelstadium verdunde suur proses met dieselfde voorbehandeling toestande wat gegeld het gedurende die behandeling van die ander roumateriale. Tydens voorbehandeling en ensimaties-hidrolise het suikerriet reste en bamboes ’n gelyke gekombineerde terugwinnings opbrengs van 78.0% en 81.2% suiker, onderskeidelik, gelewer. Daar kon egter net 55.3% (w/w) van die totale suikerinhoud van tritikale semels herwin word. Tritikale semels bestaan hoofsaaklik uit hemisellulose, wat meer vatbaar is vir degradasie ten opsigte van sellulose, die hoof bestanddeel van suikerriet reste en bamboes. Om dus die gekombineerde suikerherwinnings-opbrengs te verbeter, word daar voorgestel dat tritikale semels aan minder strawwe toestande onderwerp word, om sodoende die hemisellulose te bewaar. Om verder die hoeveelheid suiker (d.w.s glukose en xilose) wat vanuit suikerriet reste herwin kan word, te verbeter, is die gebruik van ’n twee- in plaas van ’n eenstadium verdunde suur proses, voorgestel. Die enkelstadium verdunde suur proses het, ten spyte daarvan dat dit al die onderwerp van verskillende navorsing projekte was, nie daarin geslaag om meer as 83% (w/w) van die totale suikerinhoud vanuit die suikerriet reste te herwin nie. Na ’n uitgebreide literatuurstudie is daar tot die slotsom gekom dat suikerriet reste bestaan uit ’n hemisellulose deel en ’n sellulose deel wat die gebruik van verskillende voorbehandeling toestande noodsaak, om sodoende effektiewe herwinning daarvan te verseker. Die aanwending van ’n meer gevorderde twee-stap verdunde suur proses is dus voorgestel, aangesien dit van veelvoudige-stelle voorbehandelings toestande, soos vereis deur die polisakkariedes in suikerriet reste, gebruik maak. Deur die toepassing van reaksie oppervlakte metodologie, is ’n 4.2% verbetering op die enkel-stadium metode vir die twee-stadium proses behaal deur aan te neem dat beide van hierdie prosesse, by optimum kondisies vir maksimale suiker herwinning, uitgevoer is. Hierdie verbetering is soortgelyk aan die 7.7% (w/w) verbetering wat voorheen met andersoortige substrate (uitgesonder suikerriet reste) verkry is. Sodanige verhoging word toegeskryf aan die gebruik van veelvoudige stelle van voorbehandeling toestande, wat beide meer en minder strawwe toestande insluit, om sodoende die herwinning van xilose en glukose onderskeidelik te maksimeer. In die geval van bamboes, is die twee-stadium metode nie superieur tot die een-stadium metode nie, aangesien soortgelyke voorbehandeling-toestande benodig word om beide die herwinning van xilose en glukose te maksimeer. Alternatiewelik moet ’n drie-stadium in plaas van ’n twee-stadium proses gebruik word wanneer tritikale semels behandel word aangesien ’n bykomende stel voorbehandeling toestande benodig word om arabinan, ’n derde polisakkaried, te herwin. Om sodoende die volle potensiaal van suikerriet reste te ontgin, is gebruik gemaak van ʼn fraksioneringstegnologie. Waar konvensionele voorbehandeling metodes slegs fokus op die herwinning van polisakkariedes (naamlik sellulose en hemisellulose), kan die fraksioneringsproses ook die poli-fenoliese inhoud (naamlik lignien) in lignosellulose, herwin. Weens die ingewikkeldheid van die fraksioneringsproses, is suikerriet reste gekies as die mees geskikte substraat vir fraksionering, hoofsaaklik omdat dit veral in die Suid- Afrikaanse konteks, maklik beskikbaar is en omdat dit ook maklik is om met beide die konvensionele (bv. die enkel-stadium) en die gevorderde (bv. die twee-stadium) voorbehandeling proses behandel te word. ʼn Nuut ontwikkelde fraksionering tegnologie wat gebruik maak van die ioniese vloeistof 1-butiel-3-metielimidazolium metielsulfaat ([BMiM]MeSO4) is ontwikkel, om die hoofbestanddele in suikerriet reste van mekaar te skei. Literatuur bevat verskeie voorbeelde waar ioniese vloeistowe gebruik word vir fraksionering. Die doeltreffendheid van hierdie prosesse is egter deur die produksie van multi-komponent produkstrome, waartydens tot en met ekwivalente hoeveelhede hemisellulose en lignien in dieselfde produkstrome herwin is, beperk. Hierdie resultate is tydens die studie deur middel van toetse bevestig. Sodanige toetse het ook aangedui dat die produksie van multi-komponent produkstrome nie deur die gebruikmaking van asetoon, ʼn asetoon-water mengsel of ʼn natrium hidroksied oplosmiddel, wat deel maak van ʼn opvolgende oplossing-ekstraksie-stap, vermy kon word nie. Om gevolglik die vervaardiging van multi-komponent produkstrome te vermy, is ʼn hemisellulose vooraf-ekstraksie stap, bestaande uit die enkel-stap verdunde suur proses, gebruik, om sodoende 75% (w/w) van die hemisellulose inhoud in suikerriet reste, te herwin. Die oorblywende vastestof was onderwerp aan ioniese vloeistof behandeling waarna dit effektiewelik geskei is in onderskeidelik, sellulose en lignien verrykte produkstrome, verkry deur gebruikmaking van ʼn oplossing-ekstraksie-stap. Tot en met 73% (w/w) van die oorspronklike lignien en sellulose inhoud was herwin deur gebruik te maak van optimale behandelingskondisies (120 min, 125°C). ʼn Vergelyking tussen die nuut-geïdentifiseerde ioniese vloeistof ([BMiM]MeSO4) en 1-etiel-3-metielimidazolium asetaat, ʼn gevestigde ioniese vloeistof, het aangetoon dat eersgenoemde ʼn superieure delignifikasie oplosmiddel is terwyl laasgenoemde ʼn groter bydra tot die verteerbarheid van die oorblywende reste lewer. Ten slotte het hierdie studie, metodes vir die effektiewe herwinning van polisakkariedes en poli-fenoliese eenhede, vanaf gevestigde (bv. Suikerriet reste) en nuwe (bv. bamboes en tritikale semels) lignosellulose rou materiale, gedemonstreer, deur telkens van konvensionele (enkel-stadium), gevorderde (twee-stadium) en fraksionerings voorbehandeling tegnologieë gebruik te maak. Ekonomiese verbetering kan dus verwag word indien hierdie bestanddele as voorloper chemikalieë vir die produksie van waarde toegevoegde produkte aangewend word, aangesien sodanige produkte die plek kan inneem van brandstof en chemikalieë wat tans vanuit fossielbronne vervaardig word.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Distillation continues to be the most widely used method of separation in the processing industry, in spite of its inherently low thermodynamic efficiency. Two of the critical distillation research needs that arose from the US-Initiative Vision 2020 were to develop a better understanding of the physical phenomena as well as developing better predictive models. Also, characterisation of modern packing materials is required to assist in the CO2 capture optimisation. This thesis deals with both these aspects by establishing a facility that can accurately measure the hydraulic capacity of packed columns. This setup eliminates mass transfer and specific attention can be given to the hydrodynamic behaviour of packed columns. Two phenomena that have a large impact on the mass transfer efficiency of packing materials are the loading and flooding point. The loading point is signified by the following: a.) where the packed column hold-up increases, b.) higher increase in pressure drop, and c.) a decrease in Height Equivalent to a Theoretical Plate (HETP). The onset of flooding is where the shear forces between the gas and liquid become so large (relative to the gravitational forces) that a net upwards movement of liquid occurs, resulting in liquid droplets being heavily entrained. This is normally accompanied by a sharp increase in HETP, pressure drop and liquid hold-up. The prediction of these operating limits is of great value but, despite the many contributions that were made from 1960 to 2010, there is still room for improvement. The operating region of particular interest is between the loading and flooding point, especially for fluids with physical properties significantly different from that of water. In the past, this operating region was not of great importance, but industries are constantly striving to increase their production with minimal capital expenditure. Thus, packed columns are being pushed to their limits and a good understanding of the phenomena occurring near these operational limits is now required. A 400 mm diameter glass packed bed setup (with a bed height of 3000 mm) was designed and constructed to test the effect of the following parameters on packed bed pressure drop and liquid hold-up: · Gas and liquid physical properties · Gas and liquid rates · Type of packing (either random or structured) The experimental setup has been designed so that in the future the influences of the above mentioned parameters on entrainment can also be measured. Initially, hydrodynamic tests on random packing materials (1.5” Pall® Rings, 1.5” IMTP®, 1.5” Intalox® Ultra™) were conducted over a liquid range of 6 - 122 m3/(m2·h). Through a thorough literature study it was found that the most likely semi-theoretical model, that would be able to predict the pressure drop and the liquid hold-up over most of the random packing test range, was the model developed by Billet [1991; 1993; 1995; 1999]. The other models found throughout the literature had at least one of the following deficiencies: · Limited to only the pre-loading region. · Tested (and thus applicable) only over a very select group of packing materials with no attempt to generalise. · Lacked the proper validation of significantly variable fluid properties over multitudes of liquid and gas rates especially, at higher gas and liquid rates. The experimental setup was successfully commissioned, noting the following maximum experimental errors: Vapour flow factor - 2.6 %; liquid rate - 0.75 %; packed bed pressure drop - 0.75 %; liquid hold-up - 1.25 % and entrainment - 1.05 %. Significant deviations were observed between the experimental hold-up and the hold-up from the predictive model of Billet (using Pall® Rings). Careful inspection revealed that this predictive model potentially uses two definitions for hold-up at flooding, one which has a theoretical basis and the other purely empirical. Upon substituting the theoretical value with the empirical value, a significant improvement was observed between the measured and predicted results. Deviations were still observed near the flooding point and were attributed to the difficulty of obtaining reliable flooding data. The range of liquid hold-up prediction by Billet was only verified up to a liquid rate of 82 m3/(m2·h) and the pressure drop prediction only verified up to a liquid rate of 60 m3/(m2·h). This reinforces the need for high liquid, high gas rate data. Due to the empirical nature of the liquid hold-up at flooding prediction, and since pressure drop prediction is directly linked to liquid hold-up, another model was used to compare the experimental pressure drop data. The KG-TOWER® simulator was used to predict IMTP® data and compare it to the experimentally measured values. It was found that the experimental IMTP® data followed the same trends as those from KG-TOWER® within the operating limits of the program. Thus, since the experimental data follows similar trends as models found in the literature, as well as falling within their reliable limits, the experimental setup can correctly measure the parameters in question. The experimental data from the different random packings were compared to one another by using a statistical method to determine the loading point and onset of flooding. This method uses prediction confidence intervals by fitting empirical curves to each operating region and was found to be useful in determining these critical points from experimental hydraulic data (in the absence of HETP data).The only useful comparison was between IMTP® and Intalox® Ultra™ as they both have roughly the same density, size and void fraction. It was found that, on average, the pressure drop of Intalox® Ultra™ is 20 % lower than that of IMTP® over the entire operating range. The hydraulic operating range of Intalox® Ultra™ was found to be on average 16 % larger than that of IMTP®. It is recommended that further testing should be done to investigate the influence of fluid properties (specifically liquid viscosity and to a lesser extent surface tension) on the hydraulic capacity of packed columns. Also, high gas and high liquid rate data should be generated to assist current modelling techniques. Lastly, a comparative characterisation between Intalox® Ultra™ and Raschig Super-Rings would serve as a benchmark for fourth generation random packings. / AFRIKAANSE OPSOMMING: Distillasie is vandag nog die skeidingsproses wat die meeste gebruik word in the prosesnywerhede ten spyte van ‘n lae termodinamiese effektiwiteit. Twee van die kritieke distillasie navorsing behoeftes wat vanuit die US-Initiative Vision 2020 ontstaan het, was om die fisiese verskynsels beter te verstaan, asook om beter voorspellende modelle te ontwikkel. Die karakterisering van moderne pakking materiale is ook nodig vir die optimering van die verwydering van CO2 uit uitlaatstrome. Hierdie tesis spreek beide van hierdie faktore aan deur ‘n fasiliteit op te rig wat die hidrouliese kapasiteit van gepakte kolomme akkuraat kan meet. Hierdie opstelling elimineer massa-oordrag en dus kan spesifieke aandag gegee word aan die hidrodinamiese gedrag van gepakte kolomme. Twee verskynsels wat ‘n groot impak het op die massaoordrag effektiwiteit van pakkingsmateriale is die ladingspunt en die vloedpunt. Die ladingspunt word deur die volgende gekenmerk: a.) waar die vloeistof inhoud in die gepakte bed toeneem, b.) ‘n toename in drukval en c.) ‘n afname in die hoogte ekwivalent aan ‘n teoretiese plaat (HETP). Die vloed gebied word gekenmerk waar die skuifkragte tussen die vloeistof en gas so groot raak (relatief tot die gravitasionele kragte), dat daar ‘n netto opwaartse beweging van vloeistof druppels in die kolom is. Hierdie gaan normaalweg gepaard met ‘n skerp toename in HETP, drukval en vloeistof inhoud. Die voorspelling van hierdie bedryfslimiete is baie waardevol, maar ten spyte van die bydrae wat tussen 1960 en 2010 gemaak was, is daar nog steeds ruimte vir verbetering. Die spesifieke bedryfsgebied van belang is die gebied tussen die ladingspunt en die vloedpunt en spesifiek vir sisteme waar die fisiese eienskappe van die vloeistowwe drasties verskil van die van water. In die verlede was hierdie gebied van minder belang gewees, maar maatskappye probeer deesdae hul produksie opstoot met minimale kapitale uitleg. Dus is ‘n goeie kennis van massa-oordrag verskynsels naby aan die bedryfslimiete van kardinale belang. ‘n 400 mm Diameter gepakte kolom (met ‘n bed hoogte van 3000 mm en bestaande uit glas) opstelling is ontwerp en gebou om die effek van die volgende parameters te toets op gepakte bed drukval en vloeistof inhoud: · Gas en vloeistof fisiese eienskappe · Gas vloeistof vloeitempos · Tipe pakking (beide ongeordend en gestruktureerd) Die eksperimentele opstelling is ontwerp om die bogenoemde eienskappe op vloeistofmeesleuring te meet vir toekomstige navorsing. Hidrodinamiese toetse op ongeordende pakkingsmateriale (1.5” Pall® Ringe, 1.5” IMTP®, 1.5” Intalox® Ultra™) is uitgevoer vir vloeistof vloeitempos tussen 6 en 122 m3/(m2·h). Vanuit ‘n deeglike literatuurstudie is daar gevind dat die mees toepaslike semi-teoretiese model, wat die drukval sowel as die vloeistof inhoud kan voorspel oor al die bedryfsgebiede, is die model wat deur Billet [1991; 1993; 1995; 1999] ontwikkel is. Die ander modelle in die literatuur het ten minste een van die volgende tekortkominge gehad: · Is slegs van toepassing in die voor-ladings gebied. · Is slegs van toepassing vir ‘n paar pakkingsmateriale en geen poging is aangewend om dit te veralgemeen nie. · Is nie geldig waar die vloeistof eienskappe drasties verskil van ‘n lug/water sisteem nie, sowel as by hoë gas en vloeistof vloeitempos. Die eksperimentele opstelling is suksesvol in werking gestel met die volgende waargenome eksperimentele foute: Gas vloei faktor – 2.6 %; vloeistof vloeitempo – 0.75 %; gepakte bed drukval – 0.75 %; vloeistof inhoud – 1.25 %; vloeistof-meesleuring tempo – 1.05 %. Noemenswaardige verskille is waargeneem tussen die eksperimentele en teoretiese vloeistof inhoud (deur Pall® Ringe te gebruik). Na gelang van noukeurige inspeksie, is daar gevind dat die Billet-model twee moontlike definisies voorstel vir die voorspelling van vloeistofinhoud by die vloedpunt. Een van hierdie is teoreties van aard en die ander een suiwer empiries. ‘n Vervanging van die teoretiese waardes met die empiriese waardes het gelei tot ‘n merkwaardige verbetering tussen die eksperimentele en teoretiese voorspellings. Daar was nog steeds verskille naby aan die vloedpunt, maar dit kon toegeskryf word aan die feit dat min betroubare data naby aan die vloedpunt beskikbaar is. Die voorspelling van vloeistof inhoud deur Billet is slegs gekontroleer tot ‘n vloeistof vloeitempo van 82 m3/(m2·h) en die drukval slegs tot ‘n vloeistof vloeitempo van 60 m3/(m2·h). Die bogenoemde bewys dus die tekort aan hoë gas- en hoë vloeistofvloeitempo data. Die voorspellende model se drukval is gekoppel aan die vloeistof inhoud, en dus is ‘n ander model gebruik om die eksperimentele drukval data teen te vergelyk. Die KG-TOWER® simulasie program is gebruik om die IMTP® drukval te voorspel en dit het goed vergelyk met die eksperimentele data. Dus, aangesien die eksperimentele data dieselfde tendens toon as dié van die modelle in die literatuur en aangesien dit binne die modelle se foutbande val, kan die eksperimentele opstelling die verlangde parameters akkuraat meet. Die eksperimentele data van al drie pakkingsmateriale is teenoor mekaar vergelyk deur gebruik te maak van ‘n statistiese metode wat die ladings- en vloedpunt bepaal. Hierdie metode maak gebruik van voorspellings vertroue intervalle deur empiriese kurwes op die eksperimentele data in elke bedryfsgebied te pas. Hierdie metode is ontwikkel om toepaslike te wees in die afwesigheid van HETP data. Die enigste nuttige vergelyking is tussen IMTP® en Intalox® Ultra™ omdat albei dieselfde pakkingsdigtheid, grootte en pakkings oop ruimte het. Daar is gevind dat die drukval van Intalox® Ultra™ ‘n gemiddeld van 20 % laer is as dié van IMTP® oor die hele bedryfsgebied. Die hidrouliese bedryfsgebied van Intalox® Ultra™ is 16 % groter as dié van IMTP®. Daar word voorgestel dat bykomende toetswerk gedoen moet word om die invloed van vloeistof eienskappe (spesifiek vloeistof viskositeit en vloeistof oppervlak spanning) op die hidrouliese kapasiteit van gepakte kolomme te ondersoek. Bykomende toestwerk by hoë gas- en hoë vloeistofvloeitempo word benodig om die bestaande modelle aan te vul. Laastens, sal ‘n vergelykende studie tussen Intalox® Ultra™ en Raschig Super-Rings die grondslag lewer vir die karakterisering van vierde generasie ongeordende pakkingsmateriale.

Thesis (MScEng)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: The objective of this study is the assessment of the usefulness of an industrial machine vision system for laboratory studies of especially flotation froths and other foams. With this in mind it was attempted to meet three objectives. The first objective is the adjudication of the machine vision system's ability through image analysis to differentiate between characteristics of two-phase and three-phase systems. Secondly, through the use of image analysis the effect of varying surfactant concentration, as well as the addition of quartz particles on the foam/froth stability was quantified and thirdly it was attempted to define the nature of foam decay as stochastic or deterministic. While not as important in the industrial setting, the last objective is quite important when a laboratory system is concerned, even more so owing to the difficulty of quantifying the collapse or decay of foams and froths. Two experimental set-ups were used to attain above-mentioned objectives. A Leeds flotation cell was used for the flotation of the quartz with cetyltrimethylammonium bromide (CTAB) and octadecylamine (ODA) and as well as for the characterisation of the CTAB and ODA foam. A glass column was used to investigate the CTAB foam column decay. In both set-ups the foam/froth structures were monitored with an ELMO charged coupled device (CCD). The CCD was connected to a personal computer equipped with frame grabber, which captured and digitised the images. The following conclusions can be drawn from the experimental results: The machine vision system can differentiate accurately between surfactant groups of different concentration and thus groups with unique characteristics. 11 The stability of foam is highly correlated with all other foam variables extracted from the image analysis system. In particular, the movement of the foam/froth in the flotation cell has a substantial influence on the stability values obtained for the foam/froth. III As far as the experimental system was concerned, small quartz particles (- 75 urn) stabilised the froth, while coarser particles (75-106 urn, 106-150 urn and 150+ urn) destabilised the froth. IV Likewise, the decay of CTAB foam in a column was non-linear and deterministic. When observed manually, the decay of long life foams follow the same trend as short-life foams and short-life emulsions in that a specific decay constant can be calculated for a specific surfactant system. V The machine vision system is a viable alternative for current stability measurements. Firstly, no data processing need to be done to calculate a indirect stability parameter as it computes a direct stability parameter and secondly it also computes the bubble size distribution of the sample. The following recommendations are made: The experimental design of the system needs to be altered to minimise the effect the experimental environment has on results. The possibility of a different camera set-up must be investigated. The focus of the camera on the foam surface needs to be accurate as the computation of the stability value depends on the quality of the image obtained. Il The four factors that affect the stability of a flotation froth, namely solid concentration, particle size, particle type and particle hydrophobicity should be investigated in the same study. There exists many conflicting studies on this subject as many studies for different particles with a variety of sizes, hydrophobicity and concentration are performed. One study should be conducted where all four these factors are investigated under the same experimental conditions. III The method with which the image analysis system deal with fine froth need to be addressed. In laboratory systems a typical system investigated will show a dense foam with small bubble distributions as in the case of CTAB. The extent to which the grouping of fine froth as one bubble influence the instability values obtained needs to be investigated . / AFRIKAANSE OPSOMMING: Die doelwit van hierdie studie is die evaluering van die toepassing van 'n industriële masjienvisiesisteem in 'n laboratorium studie van hoofsaaklik flottasie skuim. Die doel van hierdie toepassing is drie-ledig. Die eerste doelwit is om die onderskeidingsvermoë van die masjienvisiesisteem tussen groepe met verskillende eienskappe te evalueer deur intydse beeld verwerking. Tweedens is die invloed van oppervlakmiddelkonsentrasie veranderinge asook die byvoeging van kwarts partikels op die stabiliteit van die skuim ondersoek. Derdens is die aard van die skuim verval ondersoek om vas te stelof die proses deterministies of stochasties is. Alhoewel laasgenoemde doelwit nie so belangrik is in die industriële toepassing nie, is dit van uiterse belang in die laboratorium studies, veral as gevolg van die probleme wat ondervind word in die kwantifisering van skuimverval. Twee eksperimentele opstellings is gebruik om bogenoemde doelwitte te bereik. 'n Leeds flottasiesel is gebruik vir die flottasie van kwarts met CTAB en ODA asook vir die karakterisering van CTAB en ODA skuimeienskappe. 'n Glaskolom is gebruik vir die ondersoek van die aard van skuimverval. In beide opstellings is die beelde gemonitor deur 'n ELMO CCD. Die CCD is verbind met 'n rekenaar wat toegerus is met 'n raam-vanger wat die beelde vang en digitiseer. Die volgende gevolgtrekkings kan uit die eksperimentele resultate gemaak word: Die masjienvisiesisteem differensieer akkuraat tussen oppervlakmiddel groepe van verskillende konsentrasies en dus ook tussen groepe met unieke eienskappe. 11 Die skuim stabiliteit korreleer met die ander skuim eienskappe naamlik gemiddelde area, gemiddelde omtrek, aantal borrels, fynheid van die beeld (SNE), beweging van die skuim en kleur van die skuim. Veral die beweging van die skuim in die flottasiesel het 'n beduidende invloed op die skuimstabiliteit. 111 In die genoemde eksperimentele sisteem IS gevind dat klein kwartspartikels (-75 urn) skuim stabiliseer terwyl groter partikels (75-106 urn, 106-150 urn en 150+ urn) skuim destabiliseer. IV Die verval van CTAB skuim in 'n kolom is nie-lineêr en deterministies. In die geval waar die verval van die CTAB met die hand gemeet is, is gevind dat die verval van 'n lang-lewe skuim dieselfde tendens as kort-lewe skuim en kort-lewe emulsies volg. 'n Spesifieke verval konstante kan bereken word vir 'n spesifieke oppervlakmiddel sisteem. v Die masjienvisiesisteem IS 'n werkbare alternatief in die meting van skuimstabiliteit. Anders as in bestaande stabiliteitsmetings waar 'n indirekte stabiliteitsparameter bereken moet word, bereken die sisteem 'n direkte stabiliteitsparameter asook die borrelverspreiding van die skuim monster. Die volgende aanbevelings kan gemaak word: Die eksperimentele ontwerp van die sisteem moet aangepas word om sodoende die invloed van eksperimentele kondisies op die resultate te verminder. Die moontlikheid van 'n alternatiewe kamera opstelling moet ook ondersoek word, aangesien die verkrygde stabiliteitswaardes afhanklik is van die kwaliteit van die skuimbeelde. 11 Daar is talle teenstrydige studies ten opsigte van die vier faktore wat die stabiliteit van flotasie skuim beinvloed naamlik erts tipe, partikel grootte, partikel hidrofobisiteit en vastestof konsentrasie. Hierdie faktore moet gelyktydig in 'n studie ondersoek word onder dieselfde eksperimentele kondisies. 111 Die masjienvisiesisteem groepeer fyn skuim gedeeltes saam as een borrel. Hierdie wyse van fyn skuim hantering moet aangespreek word aangesien 'n tipiese oppervlakmiddel sisteem in die laboratorium, soos in die geval van CTAB, digte skuim met 'n fyn borrelverspreiding toon. Die mate waarin die onvermoë van die sisteem om fyn borrels te herken die stabiliteitswaardes beïnvloed, moet ondersoek word.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: Hydrocarbons provide excellent feed stocks for bioconversion processes to produce value added products using various micro-organisms. However, hydrocarbon-based aerobic bioprocesses may exhibit transport problems where the bioconversion is limited by oxygen supply rather than reaction kinetics. Consequently, the overall volumetric oxygen transfer coefficient (KLa) becomes critical in designing, operating and scaling up of these processes. In view of KLa importance in hydrocarbon-based processes, this work evaluated KLa measurement methodologies as well as quantification of KLa behavior in aerated agitated alkane-solid-aqueous dispersions. A widely used KLa measurement methodology, the gassing out procedure (GOP) was improved. This improvement was done to account for the dissolved oxygen (DO) transfer resistances associated with probe. These resistances result in a lag in DO response during KLa measurement. The DO probe response lag time, was incorporated into the GOP resulting in the GOP (lag) methodology. The GOP (lag) compared well with the pressure step procedure (PSP), as documented in literature, which also incorporated the probe response lag time. Using the GOP (lag), KLa was quantified in alkane-solid-aqueous dispersions, using either inert compounds (corn flour and CaCO3) or inactive yeast cells as solids to represent the micro-organisms in a hydrocarbon bioprocess. Influences of agitation, alkane concentration, solids loading and solids particle sizes and their interactions on KLa behavior in these systems were quantified. In the application of an accurate KLa measurement methodology, the DO probe response lag time was investigated. Factors affecting the lag, which included process conditions such as agitation (600-1200rpm), alkane concentration (2.5-20% (v/v), alkane chain length (n-C10-13 and n-C14-20), inert solids loading (1-10g/L) and solids particle sizes (3-14μm) as well as probe characteristics such as membrane age and electrolyte age (5 day usage), were investigated. Kp, the oxygen transfer coefficient of the probe, was determined experimentally as the inverse of the time taken for the DO to reach 63.2% of saturation after a step change in DO concentration. Kp dependence on these factors was defined using 22 factorial design experiments. Kp decreased on increased membrane age with an effect double that of Kp decrease due to electrolyte age. Additionally, increased alkane concentration decreased Kp with an effect 7 times higher compared to that of Kp decrease due to increased alkane chain length. This was in accordance to Pareto charts quantification. KLa was then calculated, using the GOP (lag), according to equation [1] which incorporates the influence of Kp. Equation 1 is derived from the simultaneous solution of the models which describe the response of the system and of the probe to a step change in DO. 1 1 * L p p p K at K t L p p La C K e K ae C K K = -  - - -  -   [1] The KLa values documented in literature from the PSP and KLa calculated by the GOP (lag) showed only a 1.6% difference. However KLa values calculated by the GOP (lag) were more accurate than KLa calculated by the GOP, with up to >40% error observed in the latter according to t-tests analyses. These results demonstrated that incorporating Kp markedly improved KLa accuracy. Consequently, the GOP (lag) was chosen as the preferred KLa measurement methodology. KLa was determined in n-C14-20-inert solid-aqueous dispersions. Experiments were conducted in a stirred tank reactor with a 5L working volume at constant aeration of 0.8vvm, 22ºC and 101.3kPa. KLa behavior across a range of agitations (600- 1200rpm), alkane concentrations (2.5-20% (v/v)), inert solids loadings (1-10g/L) and solids particle sizes (3-14μm) was defined using a 24 factorial design experiment. In these dispersions, KLa increased significantly on increased agitation with an effect 5 times higher compared to that of KLa increase due to interaction of increased alkane concentration and inert solids loading. Additionally, KLa decreased significantly on increased alkane concentration with an effect 4 times higher compared to both that of increased solids particle sizes and the interaction of increased agitation and solids particle size. In n-C14-20-yeast-aqueous dispersions, KLa was determined under narrowed process conditions better representing typical bioprocess conditions. KLa behavior across a range of agitations (600-900rpm), alkane concentrations (2.5-11.25% (v/v)) and yeast loadings (1-5.5g/L) using a 5μm-yeast cell was defined using a 23 factorial design experiment. In these dispersions, KLa increased significantly on increased agitation. Additionally, KLa decreased significantly on increased yeast loading with an effect 1.2 times higher compared to that of KLa decrease due to interaction of increased alkane concentration and yeast loading. In this study, the importance of Kp for accurate KLa measurement in alkane based systems has been quantified and an accurate and less complex methodology for its measurement applied. Further, KLa behavior in aerated alkane-solid-aqueous dispersions was quantified, demonstrating KLa enhancement on increased agitation and KLa depression on increased alkane concentration, solids loading and solids particle sizes. / AFRIKAANSE OPSOMMING: Koolwaterstowwe dien as uitstekende voervoorraad vir ´n verskeidenheid van mikroorganismes wat aangewend word in biologiese omsettingsprosesse ter vervaardiging van waardetoevoegende produkte. Hierdie biologiese omsettingsprosesse word egter vertraag weens die gebrek aan suurstoftoevoer onder aerobiese toestande. Die tempo van omsetting word dus beheer deur die volumetriese suurstofoordragkoeffisiënt (KLa) eerder as die toepaslike reaksiekinetika. Die bepaling van ´n akkurate KLa word dus krities tydens die ontwerp en opskalering van hierdie prosesse. Met dit in gedagte het hierdie studie die huidige metodes om KLa te bepaal geëvalueer en die gedrag van KLa in goed vermengde en belugde waterige alkaanmengsels met inerte vastestowwe, soos gisselle, in suspensie ondersoek. ´n Deesdae populêre metode om KLa te bepaal, die sogenaamde gasvrylatingsprosedure (GOP) is in hierdie studie verbeter. Die verbetering berus op die ontwikkeling van ´n prosedure om die suurstofoordragsweerstand van die pobe wat die hoeveelheid opgeloste suurstof (DO) meet, in berekening te bring. Hierdie weerstand veroorsaak ´n vertragin in the responstyd van die probe. Die verbeterde metode, GOP (lag), vergelyk goed met die gepubliseerde resultate van die drukstaptegniek (PSP) wat ook die responstyd in ag neem. GOP (lag) is ingespan om KLa te gekwantifiseer vir waterige alkaan-vastestof suspensies. Inerte componente soos mieliemeel, kalsiumkarbonaat en onaktiewe gisselle het gedien as die vastestof in suspensie verteenwoordigend van die mikroörganismes in ´n koolwaterstof bio-proses. Die invloed van vermengingstempo, alkaan konsentrasie, vastestof konsentrasie en partikelgrootte asook die interaksie van al die bogenoemde op KLa is kwatitatief bepaal in hierdie studie. Faktore wat die responstyd van die DO probe beïnvloed is ondersoek. Hierdie faktore is onder meer vermengingstempo (600-1200opm), alkaankonsentrasie (2.5-20% (v/v)), alkaankettinglengte (n-C10-13 en n-C14-20), vastestofkonsentrasie (1-10g/L) en partikelgrootte (3-14 μm). Faktore wat die eienskappe van die probe beïnvoed, naamlik membraan-en elektrolietouderdom (5 dae verbruik), is ook ondersoek. Kp, die suurstofoordragskoeffisiënt, is bepaal deur ´n inkrementele verandering in die suurstofkonsentrasie van die mengsel te maak en die tyd vir 63.2% versadiging van die probelesing te noteer. Die genoteerde tyd is die response tyd van die probe en Kp, die inverse van hierdie tyd. Die afhanklikheid van Kp op die bogenoemde faktore is ondersoek in ´n 22 faktorieël ontwerpte reeks eksperimente. Kp toon ´n afname met ´n toename in membraanouderdom. Hierdie afname is dubbel in grootte as dit vergelyk word met die afname relatief tot die toename in elektrolietouderdom. Verder toon Kp ´n afname met ´n toename in alkaankonsentrasie. Hierdie afname is 7 keer groter relatief tot die afname gesien met die toename in alkaan kettinglengte. Hierdie is in goeie ooreenstemming met Pareto kaarte as kwantifiseringsmetode. KLa is bereken met die inagname van Kp volgens vergelyking [1]: 1 1 * L p p p K at K t L p p La C K e K ae C K K = -  - - -  -   [1] Vergelyking [1] is afgelei vanaf die gelyktydige oplossing van die bestaande modelle wat die responstyd van die pobe vir ´n stapverandering in DO bereken. Die KLa waardes van die PSP metode uit literatuur verskil in die orde van 1.6% van dié bereken deur vergelyking [2]. Hierdie verskil is weglaatbaar. Die KLa waardes verkry uit die GOP metode wat nie Kp in berekening bring nie, verskil met meer as 40% van die huidige, verbeterde metode volgens die statistiese t-test analiese. Dit bewys dat die inagname van Kp ´n merkwaardige verbetering in die akuraatheid van KLa teweeg bring. GOP (lag) kry dus voorkeur vir die berekening van KLa verder aan in hierdie studie. KLa is bereken vir n-C14-20-water mengsels met inerte vastestofsuspensies. Die eksperimente is uitgevoer in ´n 5L geroerde reaktor met ´n konstante belugting van 0.8vvm (volume lug per volume supensie per minuut), 22ºC en 101.3kPa. Die gedrag van KLa met betrekking tot vermengingstempo (600-1200opm), alkaankonsentrasie (2.5-20% (v/v)), vastestofkonsentrasie (1-10g/L) en partikelgrootte (3-14μm) is ondersoek in ´n 24 faktorieël ontwerpte reeks eksperimente. Verder is die invloed van vloeistofviskositeit en oppervlakspanning op KLa ondersoek in ´n 23 faktorieël ontwerpte reeks eksperimente. KLa het ´n beduidende toename getoon met ´n toename in vermengingstempo. Hierdie toename was 5 keer groter as die toename relatief tot die interaksie van alkaan-en vastestofkonsentrasie. KLa het ook beduidend afgeneem met ´n toename in alkaankonsentrasie. Die toename was 4 keer groter as die toename relatief tot die toename in partikelgrootte en die interaksie van vermengingstempo en partikelgrootte. In n-C14-20-water mengsels met gisselsuspensies is KLa bepaal onder kondisies verteenwoordigend van tipiesie biologiese omsettingsprosesse. Die gedrag van KLa met betrekking tot vermengingstempo (600-900opm), alkaankonsentrasie (2.5-11.25% (v/v)) en giskonsentrasie (1-5.5g/L) met ´n partikelgroote van 5μm is ondersoek in ´n 23 faktorieël ontwerpte reeks eksperimente. Hierdie eksperimente het ´n beduidende toename in KLa met ´n toename in vermengingstempo getoon sowel as ´n beduidende afname met ´n toename in giskonsentrasie. Hierdie afname is in die orde van 1.2 keer groter in vergelyking met die interaksie van alkeen- en giskonsentrasie. Hierdie studie bring die kritieke rol wat Kp speel in die akkurate bepaling van KLa in waterige alkaansisteme met inerte vastestofsuspensies na vore. Dit stel verder ´n metodiek voor vir die akurate meting van en kwantifisering van beide Kp en KLa onder aerobiese toestande met betrekking tot vermengingstempo, alkaankonsentrasie, vastestofkonsentrasie en partikelgrootte.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / Thesis presented in partial fulfilment of the requirements for the degree MASTER OF SCIENCE IN ENGINEERING (EXTRACTIVE METALLURGICAL ENGINEERING) in the Department of Process Engineering at the University of Stellenbosch / ENGLISH ABSTRACT: Flotation is an important processing step in the mineral processing industry wherein valuable minerals are extracted. Flotation is a difficult process to control due to its complexity, meaning that the reversal of series of changes will not necessarily bring the process back to its original state. Expert knowledge is incorporated in flotation control through operator experience and intervention, which is subject to many challenges, creating the need for improvement in control. The performance of a flotation cell is often determined by evaluating froth appearance. The application of image analysis to capture, evaluate and monitor froth appearance poses multiple benefits such as consistent and reliable froth appearance evaluation. The objective for this study was to conduct a laboratory study for the collection of froth images with the purpose of evaluating the feasibility of using image information to predict platinum froth grade. Laboratory test work was performed according to a fractional factorial experimental design. Six variables were considered: air flowrate, pulp level and collector, activator, frother and depressant dosages. The laboratory study results were quantified by assay analysis. Analysis of variance only revealed the significant effect of pulp height and collector addition on flotation performance. Data pre-processing revealed information regarding feature correlations and variance contributions. Data analysis from captured images achieved reliable froth grade predictions using random forest classification and artificial neural network (ANN) regression techniques. Random forest classification accuracies of 86.8% and 75.5% were achieved for the following respective datasets: image data of each individual experiment (average of all experiments) and all image data. The applied ANN models achieved R2 values 0.943 and 0.828 for the same 2 datasets. An industrial case study was done wherein a series of step changes in air flowrate was made on a specific flotation cell. The limited industrial case study results supported laboratory study results. Multiple linear regression performed very well, reaching Rª values up to 0.964. Neural networks achieved slightly better with R2 values of up to 0.997. Based on the findings, the following main conclusions were drawn from this study: - Reliable predictions using classification and regression models on image data were proved possible in concept by the laboratory study, and supported by results from an industrial case study on a narrow system. The following main recommendations were made for further investigation: - Research over a larger range of operating conditions is needed to find a more comprehensive solution. - Investigations should be conducted to determine hardware requirements and specifications in terms of minimum resolution, lighting requirements, sampling frequency and data storage. Software requirements, specifications and maintenance challenges should also be investigated for implementation purposes once a more comprehensive solution has been found. - Strategies in terms of camera placement and model building will need to follow, giving special attention to a strategy to handle ore composition change. / AFRIKAANSE OPSOMMING: Flotasie is ‘n belangrike proses in die mineraal proseseringsbedryf vermoeid met die ontginning van waardevolle minerale. Die proses is moelik om te beheer vanweë sy kompleksiteit, wat verwys na die onvermoë om die proses terug te bring na sy oorspronklike toestand deur ‘n reeks veranderinge om te keer. In die algemeen word spesialis kennis deel van prosesbeheer deur die toepassing van operateurs se ervaring en ingryping, wat opsigself verskeie uitdagings bied wat die behoefte aan verbeterde beheertoestelle en strategieë daarstel. Die werkverrigting van flotasieselle word gereeld beoordeel op grond van die voorkoms van die skuim. Die gebruik van beeldverwerking om dié inligting vas te vang vir monitering en evaluering doeleindes hou verskeie voordele in, bv. konsikwente en betroubare evaluasie van die skuimvoorkoms. Die doelwitte vir hierdie studie was om ‘n laboratorium studie te loods vir die opname van skuimbeelde, met die doel om die bruikbaarheid van beeldinligting vir die voorspelling van die flotasieprodukkwaliteit, te ondersoek. Die laboratorium gevallestudie is uitgevoer aan die hand van ‘n fraksionele faktoriale eksperimentele ontwerp. Ses veranderlikes was ondersoek naamlik, lugvloeitempo, pulphoogte en versamelaar aktiveerder en depressant toevoeging. Die studie se resultate is gekwantifiseer deur die analise van die skuim inhoud. ‘n Analise van variansie het slegs die invloed van pulphoogte en versamelaartoevoeging op die flotasievertoning uitgelig. Data voorverwerking het inligting uitgelig rondom die veranderlikes se verhouding met mekaar. Data analise metodes, naamlik lukrake klassifiseringswoude en neurale netwerk regressie, is toegepas op die versamelde beelddata en het belowende resultate gelewer. Lukrake klassifiseringswoude het klasse gedentifiseer met akkuraathede van 86.8% en 75.5% vir die volgende onderskeie datastelle: individuele eksperimente se beeld data (gemiddeld oor alle eksperimentele lopies), alle beelddata as een stel. Die neurale netwerke het Rª waardes van 0.943 rn 0.828 gelewer vir dieselfde 2 datastelle. Die beperkte nywerheidsgevallestudie het verandering in lugvloeitempo toegelaat vir ‘n enkele flotasie sel. Die resultate het die bevindinge van die laboratorium gevallestudie gesteun. Veelvoudige lineere regressie het Rª waardes van tot en met 0.964 gelewer. Neurale netwerke het daarop verbeter met waardes tot en met 0.997. Die volgende hoof gevolgtrekkinge was duidelik vanuit die resultate: - Betroubare voorspellings was moontlik met die toepassing van klassifikasie en regressie modelle op die laboratorium studie data. Die resultate is ondersteun deur soortgelyke resultate van die beperkte nywerheidsgevallestudie. Die volgende hoof aanbevelings was gemaak vir verdere navorsing: - Navorsing oor ‘n wyer reeks proseskondisies is nodig om ‘n meer omvattende oplossing te vind. - ‘n Ondersoek moet geloods word om die hardeware vereistes en spesifikasies in terme van die minimum beeld resolusie, beligting vereistes, monsterneming tempo en die berging van data te bepaal. Sagteware vereistes, spesifikasies en instandhouding uitdagings moet ook ondersoek word vir implementasie doeleindes sodra ‘n meer omvattende oplossing gevind is. - Strategieë in verband met die plasing van kamers en die ontwikkeling van modelle is nodig, waarin spesiale aandag gegee moet word om die probleem van veranderende ertssamestelling op te los.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: The extraction of mineral values from ore requires liberation of the minerals followed by separation. Liberation is achieved by size reduction operations which are inefficient processes typically accounting for up to 70% of the energy consumption in a mineral concentrator (Tromans, 2008). As the grade of ores reserves declines, future viability of mineral operations will be determined by the costs of comminution. Recent work has shown that microwave treatment of secondary crusher product at specific microwave energy consumption of the order of 1 kWh/t reduces the work index of the ore and increases grade and recovery in batch flotation tests. Improved liberation at coarse sizes was also demonstrated (Kingman, 2006). Based on these findings work is ongoing to commercialise the technology. The objective of this study is to develop a modelling framework to determine the value proposition of microwave treatment of ore. It was noted that various models exist in literature for modelling of mineral processing flotation flow sheets, but these models do not incorporate the feed ore liberation property as an input variable in their calculations. Thus, a fundamentally derived property based model was identified as appropriate for flow sheet modelling of microwave treated ore, as it utilised liberation as an indirect variable in calculating the flotation rate constant through the use of contact angle to describe particle surface hydrophobicity. The model was successfully incorporated into the flotation flow sheet units developed in HSC Chemistry and used with Mineral Liberation Analyser (MLA) data to investigate the effects of changes in feed ore liberation on rougher cell flotation recovery. Different liberation scenarios based around modification of porphyry copper flotation feed were created. A sensitivity analysis of the various feed stream liberation scenarios was carried out to test the ability of the model to effectively model the differences in downstream processing of microwave treated and untreated ores. For a single flotation cell of size 85 m3 with a solids feed flow rate of 890 tph, it was observed that below a certain size (120 μm in the case of the porphyry copper ore) changes in flotation feed liberation had no significant effect on value mineral recovery. Significant differences in value mineral recovery were observed only at coarser sizes above 120 μm. The results indicated that improvement in recovery of value minerals due to improved liberation from applying microwave technology has size limits and is significantly dependent on the feed grind size. Feed grind size sensitivity analysis was then carried on the same single cell flow sheet utilising feeds with the same mineralogy but with different grind sizes. The results indicated that maximum benefits from the application of microwave technology would be best obtained by utilising coarse grinding at sizes between P70 = 200 μm and P70 = 300 μm for the porphyry copper ores considered in this study. Coarse grinding appears to be the best way to exploit improved liberation in downstream processing of microwave treated ores. Investigations similar to those carried out on the single cell flotation flow sheet were then carried out on a continuous plant rougher flotation flow sheet. The flow sheet consisted of nine rougher cells in series each with a volume of 85 m3 with a solids feed flow rate of 890 tph into the bank of rougher cells. The results indicated that there was no significant difference in final rougher bank overall cumulative recovery at fine grind sizes below a P70 grind size of 120 μm with improvements in feed ore liberation. Feed grind size sensitivity analysis showed a significant variation in cumulative recovery at coarse grind sizes of above P70 = 129 μm .This variation was attributed to improvements in flotation feed ore value mineral liberation from locked composite particles to the maximum possible theoretical liberation scenario of fully liberated value mineral particles. A 7.2 percentage point improvement in cumulative value mineral overall recovery and a 2 to 3 percentage point improvement in enrichment ratio was also observed above the P70 = 250 μm grind sizes after improving the flotation feed ore value mineral particle liberation of a typical flotation plant feed to a maximum. The increases in grade and cumulative recovery at coarse sizes were attributed to improvements to the flotation plant feed ore value mineral particle liberation. From the results, it was concluded that microwave technology application will offer greater benefits in downstream processing of coarse ground ores. / AFRIKAANSE OPSOMMING: Die ekstraksie van mineraalwaardes uit erts vereis bevryding van die minerale gevolg deur skeiding. Bevryding word bereik deur verkleiningsprosedures wat ondoeltreffende prosesse is en wat gewoonlik vir tot 70% van die energieverbruik in ʼn mineraalkonsentreerder verantwoordelik is (Tromans, 2008). Algaande die graad van ertsreserwes afneem, sal toekomstige lewensvatbaarheid van mineraalprosesse bepaal word deur die koste van vergruising. Onlangse werk het getoon dat mikrogolfbehandeling van sekondêre vergruiserproduk by spesifieke mikrogolf-energieverbruik van ongeveer 1 kWh/t die werkindeks van die erts verminder en die graad en opbrengs in lotflottasietoetse verhoog. Verbeterde bevryding by growwer groottes is ook aangetoon (Kingman, 2006). Werk gaan voort op grond van hierdie bevindinge ten einde die tegnologie te kommersialiseer. Die doel van hierdie navorsing is om ʼn modelleringsraamwerk te ontwikkel om die waardeproposisie van mikrogolfbehandeling van erts te bepaal. Daar is in die literatuur afgekom op verskeie modelle vir die modellering van vloeidiagramme vir flottasie van mineraalverwerking, maar hierdie modelle inkorporeer nie die voerertsbevrydingseienskap as ʼn insetveranderlike in hulle berekeninge nie. ʼn Fundamentele afgeleide eienskapgebaseerde model is geïdentifiseer as geskik vir vloeidiagrammodellering van mikrogolfbehandelde erts, aangesien dit bevryding as ʼn indirekte veranderlike by die berekening van die flotteertempokonstante aangewend het deur die gebruik van kontakhoek om hidrofobisiteit van die deeltjieoppervlak te beskryf. Die model is suksesvol in eenhede van die flottasievloeidiagram wat in HSC Chemistry ontwikkel is, geïnkorporeer en tesame met data van die mineraalbevrydingsontleder (MBO) gebruik om die gevolge van veranderinge in voerertsbevryding op die opbrengs van voorskeiselflottasie te ondersoek. Verskillende bevrydingscenario’s is geskep wat óm die modifisering van porfierkoperflotteringstoevoer heen gebaseer is. ʼn Sensitiwiteitsontleding van die verskillende voerstroombevrydingscenario’s is uitgevoer om die vermoë van die model om die verskille in stroomaf-verwerking van mikrogolfbehandelde en onbehandelde ertse te toets, doeltreffend te modelleer. In die geval van ʼn enkele flottasiesel van 85 m3 groot met ʼn vastestof-toevoervloeitempo van 890 tph, is waargeneem dat veranderinge in flottasietoevoer-bevryding benede ʼn sekere grootte (120 μm in die geval van die porfierkopererts) geen beduidende uitwerking op die opbrengs van die waardemineraal gehad het nie. Beduidende verskille in die opbrengs van die waardemineraal is slegs by growwer groottes bo 120 μm waargeneem. Die resultate het daarop gedui dat verbetering in die opbrengs van waardeminerale as gevolg van verbeterde bevryding ná die toepassing van mikrogolftegnologie beperkinge ten opsigte van grootte het en opvallend afhanklik is van die toevoermaalgrootte. Sensitiwiteitstoetsing van toevoermaalgrootte is daarna op dieselfde enkele selvloeidiagram wat voerders met dieselfde mineralogie gebruik uitgevoer, maar met verskillende maalgroottes. Die resultate het daarop gedui dat maksimum voordele van die toepassing van mikrogolftegnologie die beste verkry sou word deur gebruik van growwe maling by groottes tussen P70 = 200 μm en P70 = 300 μm vir die porfierkoperertse wat in hierdie navorsing in oorweging geneem is. Growwe maling skyn die beste manier te wees om verbeterde bevryding in stroomaf-verwerking van mikrogolfbehandelde ertse te eksploiteer. Ondersoeke soortgelyk aan dié wat op die vloeidiagram van die enkelselflottasie uitgevoer is, is toe op ʼn deurlopende vloeidiagram van die aanlegvoorskeierflottasie uitgevoer. Die vloeidiagram het bestaan uit nege voorskeiselle in serie elk met ʼn volume van 85 m3 met ʼn vastestof-toevoervloeitempo van 890 tph in die ry voorskeiselle. Die resultate het daarop gedui dat daar geen aanmerklike verskil in algemene kumulatiewe opbrengs van die finale voorskeiry by fyn maalgroottes benede ʼn P70-maalgrootte van 120 μm met verbeteringe in voerertsbevryding was nie. Sensitiwiteitsontleding van voermaalgrootte het ʼn beduidende variasie in kumulatiewe opbrengs by growwe maalgroottes van bo P70 = 129 μm getoon. Hierdie variasie is toegeskryf aan verbeteringe in waardemineraalbevryding van flottasietoevoererts uit geslote saamgestelde deeltjies tot die maksimum moontlike teoretiese bevrydingscenario van ten volle bevryde waardemineraaldeeltjies. ʼn Persentasiepuntverbetering van 7.2 in die kumulatiewe algemene opbrengs van waardemineraal en ʼn persentasiepuntverbetering van 2 tot 3 in die verrykingsratio is ook bo die P70 = 250 μmmaalgroottes waargeneem ná verbetering van die bevryding van die waardemineraaldeeltjies van die flottasietoevoererts van ʼn tipiese flottasieaanlegtoevoer tot die maksimum. Die toenames in graad en kumulatiewe opbrengs by growwe groottes is toegeskryf aan verbeteringe in die bevryding van die waardemineraaldeeltjies van die flottasietoevoererts. Op grond van die resultate is daar tot die gevolgtrekking gekom dat toepassing van mikrogolftegnologie groter voordele in stroomaf-verwerking van grofgemaalde ertse sal bied.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2011. / Please refer to full text for abstracts