In the transition to a sustainable energy supply there is an increasing need to use biomass for replacement of fossil fuel. A key challenge is to utilize biomass conversion technologies in an environmentally sound manner. Important aspects are to minimize potential formation of persistent organic pollutants (POPs) such as dioxins and dioxin-like compounds. This thesis involves studies of formation characteristics of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and naphthalenes (PCNs) in microwave-assisted pyrolysis (MAP) and torrefaction using biomass as feedstock. The research focuses are on their levels, distributions, fingerprints (homologue profiles and isomer patterns) and the underlying formation pathways. The study also included efforts to optimize methods for extracting chlorinated aromatic compounds from thermally treated biomass. The overall objective was to contribute better understanding on the formation of dioxins and dioxin-like compounds in low temperature thermal processes. The main findings include the following: Pressurized liquid extraction (PLE) is applicable for simultaneous extraction of PCDDs, PCDFs, PCNs, polychlorinated phenols and benzenes from thermally treated wood. The choice of solvent for PLE is critical, and the extraction efficiency depends on the degrees of biomass carbonization. In MAP experiments PCDDs, PCDFs and PCNs were predominantly found in pyrolysis oils, while in torrefaction experiments they were mainly retained in solid chars with minor fractions in volatiles. In both cases, highly chlorinated congeners with low volatility tended to retain on particles whereas the less chlorinated congeners tended to volatize into the gas phase. Isomer patterns of PCDDs, PCDFs and PCNs generated in MAP were more selective than those reported in combustion processes. The presence of isomers with low thermodynamic stability suggests that the pathway of POPs formation in MAP may be governed not only by thermodynamic stabilities but also by kinetic factors. Formation of PCDDs, PCDFs and PCNs depends not only on the chlorine contents in biomass but also the presence of metal catalysts and organic/metal-based preservatives. Overall, the results provide information on the formation characteristics of PCDDs, PCDFs and PCNs in MAP and torrefaction. The obtained knowledge is useful regarding management and utilization of thermally treated biomass with minimum environmental impact.

Thesis (MScEng)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In recent times, governments around the world have placed increasing focus on cleaner technologies and sustainable methods of power generation in an attempt to move away from fossil fuel derived power, which is deemed unsustainable and unfriendly to the environment. This trend has also been supported by the South African government, with clear intentions to diversify the country’s power generation by including, among others, biomass as a renewable resource for electricity generation. Woody biomass and associated forestry residues in particular, could potentially be used as such a renewable resource when considering the large amount of fast growing hardwood species cultivated in South Africa. Approximately 6.3 million ton of Eucalyptus grandis is sold annually for pulp production while a further 7 million ton of Eucalyptus species are sold as round wood. With these tree species reaching commercial maturity within 7 – 9 years in the South African climate, there is real potential in harnessing woody biomass as a renewable energy source. In this study, pyrolysis was investigated as a method to condense and upgrade E.grandis into energy and chemical rich products. The pyrolysis of E.grandis is the study of the thermal degradation of the biomass, in the absence of oxygen, to produce char and bio-oil. The thermal degradation behaviour of E.grandis was studied using thermo-gravimetric analysis (TGA) at the Karlsruhe Institute of Technology (KIT) in Germany and subsequently used to determine the isoconversional kinetic constants for E.grandis and its main lignocellulosic components. Slow, Vacuum and Fast Pyrolysis were investigated and optimised to maximise product yields and to identify the key process variables affecting product quality. The Fast Pyrolysis of E.grandis was investigated and compared on bench (KIT0.1 kg/h), laboratory (SU1 kg/h) and pilot plant scale (KIT10 kg/h), using Fast Pyrolysis reactors at Stellenbosch University (SU) in South Africa and at KIT in Germany. The Slow and Vacuum Pyrolysis of E.grandis was investigated and compared using a packed bed reactor at Stellenbosch University. The TGA revealed that biomass particle size had a negligible effect on the thermal degradation behaviour of E.grandis at a heating rate set point of 50 °C/min. It was also shown that increasing the furnace heating rates shifted the thermo-gravimetric (TG) and differential thermo-gravimetric (DTG) curves towards higher temperatures while also increasing the maximum rate of volatilisation. Lignin resulted in the largest specific char yield and also reacted across the widest temperature range of all the samples investigated. The average activation energies found for the samples investigated were 177.8, 141.0, 106.2 and 170.4 kJ/mol for holocellulose, alpha-cellulose, Klason lignin and raw E.grandis, respectively. Bio-oil yield was optimised at 76 wt. % (daf) for the SU1 kg/h Fast Pyrolysis plant using an average biomass particle size of 570 μm and a reactor temperature of 470 °C. Differences in the respective condensation chains of the various Fast Pyrolysis reactor configurations investigated resulted in higher gas and char yields for the KIT reactor configurations compared to the SU1 kg/h Fast Pyrolysis plant. Differences in the vapour residence time between Slow (>400 s) and Vacuum Pyrolysis (< 2 s) resulted in a higher liquid and lower char yield for Vacuum Pyrolysis. Local liquid yield maxima of 41.1 and 64.4 wt. % daf were found for Slow and Vacuum Pyrolysis, respectively (achieved at a reactor temperature of 450 °C and a heating rate of 17 °C/min). Even though char yields were favoured at low reactor temperatures (269 – 300 °C), the higher heating values of the char were favoured at high reactor temperatures (29 – 34 MJ/kg for 375 – 481 °C). Reactor temperature had the most significant effects on product yield and quality for the respective Slow and Vacuum Pyrolysis experimental runs. The bio-oils yielded for SP and VP were found to be rich in furfural and acetic acid. / AFRIKAANSE OPSOMMING: Regerings regoor die wêreld het in die afgelope tyd toenemende fokus geplaas op skoner tegnologie en volhoubare metodes van kragopwekking in 'n poging om weg te beweeg van fossielbrandstof gebasseerde energie, wat geag word as nie volhoubaar nie en skadelik vir die omgewing. Hierdie tendens is ook ondersteun deur die Suid-Afrikaanse regering, met 'n duidelike bedoeling om die land se kragopwekking te diversifiseer deur, onder andere, biomassa as 'n hernubare bron vir die opwekking van elektrisiteit te gebruik. Houtagtige biomassa en verwante bosbou afval in die besonder, kan potensieel gebruik word as so 'n hernubare hulpbron, veral aangesien ‘n groot aantal vinnig groeiende hardehout spesies tans in Suid-Afrika verbou word. Ongeveer 6,3 miljoen ton Eucalyptus grandis word jaarliks verkoop vir pulp produksie, terwyl 'n verdere 7 miljoen ton van Eucalyptus spesies verkoop word as paal hout. Met hierdie boom spesies wat kommersiële volwassenheid bereik binne 7 - 9 jaar in die Suid-Afrikaanse klimaat, is daar werklike potensiaal vir die benutting van houtagtige biomassa as 'n hernubare energiebron. In hierdie studie is pirolise ondersoek as 'n metode om E.grandis te kondenseer en op te gradeer na energie en chemikalie ryke produkte. Die pirolise van E.grandis is die proses van termiese afbreking van die biomassa, in die afwesigheid van suurstof, om houtskool en bio-olie te produseer. Die termiese afbrekingsgedrag van E.grandis is bestudeer deur gebruik te maak van termo-gravimetriese analise (TGA) by die Karlsruhe Instituut van Tegnologie in Duitsland en daarna gebruik om die kinetiese konstantes vir die iso-omskakeling van E.grandis en sy hoof komponente te bepaal. Stadige, Vakuum en Snel pirolise is ondersoek en geoptimiseer om produk opbrengste te maksimeer en die sleutel proses veranderlikes wat die kwaliteit van die produk beïnvloed te identifiseer. Die Snel Pirolise van E.grandis is ondersoek en vergelyk op bank- (KIT0.1 kg / h), laboratorium- (SU1 kg / h) en proefaanlegskaal (KIT10 kg / h) deur gebruik te maak van Snel pirolise reaktore by die Universiteit van Stellenbosch (US) in Suid-Afrika en die Karlsruhe Instituut van Tegnologie (KIT) in Duitsland. Die Stadige en Vakuum Pirolise van E.grandis is ondersoek en vergelyk met behulp van 'n gepakte bed reaktor aan die Universiteit van Stellenbosch. Die TGA studie het openbaar dat biomassa deeltjiegrootte 'n onbeduidende uitwerking op die termiese afbrekingsgedrag van E.grandis het by 'n verhittings tempo van 50 ° C / min. Dit is ook bewys dat die verhoging van die oond verwarming tempo die termo-gravimetriese (TG) en differensiële termo-gravimetriese (DTG) kurwes na hoër temperature verskuif, terwyl dit ook die maksimum tempo van vervlugtiging laat toeneem het. Lignien het gelei tot die grootste spesifieke houtskool opbrengs en het ook oor die wydste temperatuur interval gereageer van al die monsters wat ondersoek is. Die gemiddelde aktiveringsenergieë vir die monsters wat ondersoek is, was 177,8, 141,0, 106,2 en 170,4 kJ / mol, onderskeidelik vir holosellulose, alpha-sellulose, Klason lignien en rou E.grandis. Bio-olie opbrengs is geoptimeer teen 76 wt. % (DAF) vir die SU1 kg / h Snel Pirolise aanleg met behulp van 'n gemiddelde biomassa deeltjiegrootte van 570 μm en 'n reaktor temperatuur van 470 ° C. Verskille in die onderskeie kondensasie kettings van die verskillende Snel Pirolise aanlegte wat ondersoek is, het gelei tot hoër gas- en houtskool opbrengste vir die KIT reaktor konfigurasies in vergelyking met die SU1kg/h FP plant. Verskille in die damp retensie tyd tussen Stadige (> 400 s) en Vakuum pirolise (<2 s) het gelei tot 'n hoër vloeistof en laer houtskool opbrengs vir Vakuum Pirolise. Plaaslike vloeistof opbrengs maksima van 41,1 en 64,4 wt. % (daf) is gevind vir Stadig en Vakuum pirolise onderskeidelik, bereik by 'n reaktor temperatuur van 450 ° C en 'n verhittingstempo van 17 ° C / min. Selfs al is houtskool opbrengste bevoordeel by lae reaktor temperature (269 - 300 ° C), is die hoër warmte waardes van die houtskool bevoordeel deur hoë reaktor temperature (29 - 34 MJ / kg vir 375 - 481 ° C). Reaktor temperatuur het die mees beduidende effek op die produk opbrengs en kwaliteit vir die onderskeie Stadige Pirolise en Vakuum Pirolise eksperimentele lopies gehad. Die bio-olies geproduseer tydens Stadige en Vakuum Pirolise was ryk aan furfuraal en asynsuur.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2005. / Biomass is a significant renewable energy source and much research is currently being done to enable the production of biofuels and chemicals from biomass. This study looks at vacuum pyrolysis, a technology which has the potential to turn biomass, amongst other waste materials, into commercially valuable commodities. Vacuum pyrolysis is the thermal degradation of a feedstock in the absence of oxygen and under low pressure, to produce a bio-oil and char as main products, together with water and non-condensable gases. Both the oil and char have a high energy content and may be used as fuels. An incredible number of chemical compounds are also found in the oil and these compounds can be extracted and sold as high value chemicals.

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: Increasing oil prices along with the climate change threat have forced governments, society and the energy sector to consider alternative fuels. Biofuel presents itself as a suitable replacement and has received much attention over recent years. Thermochemical conversion processes such as pyrolysis is a topic of interest for conversion of cheap agricultural wastes into clean energy and valuable products. Fast pyrolysis of biomass is one of the promising technologies for converting biomass into liquid fuels and regarded as a promising feedstock to replace petroleum fuels. Corn residues, corn cob and corn stover, are some of the largest agricultural waste types in South Africa amounting to 8 900 thousand metric tonnes annually (1.7% of world corn production) (Nation Master, 2005). This study looked at the pyrolysis kinetics, the characterisation and quality of by-products from fast pyrolysis of the corn residues and the upgrading of bio-oil. The first objective was to characterise the physical and chemical properties of corn residues in order to determine the suitability of these feedstocks for pyrolytic purposes. Secondly, a study was carried out to obtain the reaction kinetic information and to characterise the behaviour of corn residues during thermal decomposition. The knowledge of biomass pyrolysis kinetics is of importance in the design and optimisation of pyrolytic reactors. Fast pyrolysis experiments were carried out in 2 different reactors: a Lurgi twin screw reactor and a bubbling fluidised bed reactor. The product yields and quality were compared for different types of reactors and biomasses. Finally, a preliminary study on the upgrading of bio-oil to remove the excess water and organics inorder to improve the quality of this liquid fuel was performed. Corn residues biomass are potential thermochemical feedstocks, with the following properties (carbon 50.2 wt. %, hydrogen 5.9 wt. % and Higher heating value 19.14 MJ/kg) for corn cob and (carbon 48.9 wt. %, hydrogen 6.01 wt. % and Higher heating value 18.06 MJ/kg) for corn stover. Corn cobs and corn stover contained very low amounts of nitrogen (0.41-0.57 wt. %) and sulphur (0.03-0.05 wt. %) compared with coal (nitrogen 0.8-1.9 wt. % and sulphur 0.7-1.2 wt. %), making them emit less sulphur oxides than when burning fossil fuels. The corn residues showed three distinct stages in the thermal decomposition process, with peak temperature of pyrolysis shifting to a higher value as the heating rate increased. The activation energies (E) for corn residues, obtained by the application of an iso-conversional method from thermogravimetric tests were in the range of 220 to 270 kJ/mol. The products obtained from fast pyrolysis of corn residues were bio-oil, biochar, water and gas. Higher bio-oil yields were produced from fast pyrolysis of corn residues in a bubbling fluidised bed reactor (47.8 to 51.2 wt. %, dry ash-free) than in a Lurgi twin screw reactor (35.5 to 37 wt. %, dry ash-free). Corn cobs produced higher bio-oil yields than corn stover in both types of reactors. At the optimised operating temperature of 500-530 °C, higher biochar yields were obtained from corn stover than corn cobs in both types of reactors. There were no major differences in the chemical and physical properties of bio-oil produced from the two types of reactors. The biochar properties showed some variation in heating values, carbon content and ash content for the different biomasses. The fast pyrolysis of corn residues produced energy products, bio-oil (Higher heating value = 18.7-25.3 MJ/kg) and biochar (Higher heating value = 19.8-29.3 MJ/kg) comparable with coal (Higher heating value = 16.2-25.9 MJ/kg). The bio-oils produced had some undesirable properties for its application such as acidic (pH 3.8 to 4.3) and high water content (21.3 to 30.5 wt. %). The bio-oil upgrading method (evaporation) increased the heating value and viscosity by removal of light hydrocarbons and water. The corn residues biochar produced had a BET Brynauer-Emmet-Teller (BET) surface area of 96.7 to 158.8 m2/g making it suitable for upgrading for the manufacture of adsorbents. The gas products from fast pyrolysis were analysed by gas chromatography (GC) as CO2, CO, H2, CH4, C2H4, C2H6, C3H8 and C5+ hydrocarbons. The gases had CO2 and CO of more than 80% (v/V) and low heating values (8.82-8.86 MJ/kg). / AFRIKAANSE OPSOMMING: Die styging in olie pryse asook dreigende klimaatsveranderinge het daartoe gelei dat regerings, die samelewing asook die energie sektor alternatiewe energiebronne oorweeg. Biobrandstof as alternatiewe energiebron het in die afgope paar jaar redelik aftrek gekry. Termochemiese omskakelingsprosesse soos pirolise word oorweeg vir die omskakeling van goedkoop landbou afval na groen energie en waardevolle produkte. Snel piroliese van biomassa is een van die mees belowende tegnologië vir die omskakeling van biomassa na vloeibare brandstof en word tans gereken as ’n belowende kandidaat om petroleum brandstof te vervang. Mielieafval, stronke en strooi vorm ’n reuse deel van die Suid Afrikaanse landbou afval. Ongeveer 8900 duisend metrieke ton afval word jaarliks geproduseer wat optel na ongeveer 1.7% van die wêreld se mielie produksie uitmaak (Nation Master, 2005). Hierdie studie het gekk na die kinetika van piroliese, die karakterisering en kwaliteit van by-produkte van snel piroliese afkomstig van mielie-afval asook die opgradering van biobrandstof. Die eerste mikpunt was om die fisiese en chemiese karakteristieke van mielie-afval te bepaal om sodoende die geskiktheid van hierdie afval vir die gebruik tydens piroliese te bepaal. Tweendens is ’n kinetiese studie onderneem om reaksie parameters te bepaal asook die gedrag tydens termiese ontbinding waar te neem. Kennis van die piroliese kinetika van biomassa is van belang juis tydens die ontwerp en optimering van piroliese reaktore. Snel piroliese ekspermente is uitgevoer met behulp van twee verskillende reaktore: ’n Lurgi twee skroef reaktor en ’n borrelende gefluidiseerde-bed reaktor. Die produk opbrengs en kwaliteit is vergelyk. Eindelik is ’n voorlopige studie oor die opgradering van bio-olie uitgevoer deur te kyk na die verwydering van oortollige water en organiese materiaal om die kwaliteit van hierdie vloeibare brandstof te verbeter. Biomassa afkomstig van mielie-afval is ’n potensiële termochemiese voerbron met die volgende kenmerke: mielie stronke- (C - 50.21 massa %, H – 5.9 massa %, HHV – 19.14 MJ/kg); mielie strooi – (C – 48.9 massa %, H – 6.01 massa %, HHV – 18.06 MJ/kg). Beide van hierdie materiale bevat lae hoeveelhede N (0.41-0.57 massa %) and S (0.03-0.05 massa %) in vergelyking met steenkool N (0.8-1.9 massa %) and S (0.7-1.2 massa %). Dit beteken dat hieride bronne van biomassa laer konsentrasies van swael oksiedes vrystel in vergelyking met fossielbrandstowwe. Drie kenmerkende stadia is waargeneem tydens die termiese afbraak van mielie-afval, met die temperatuur piek van piroliese wat skuif na ’n hoër temperatuur soos die verhittingswaarde toeneem. Die waargenome aktiveringsenergie (E) van mielie-afval bereken met behulp van die iso-omskakelings metode van TGA toetse was in die bestek: 220 tot 270 kJ/mol. Die produkte verkry deur Snel Piroliese van mielie-afval was bio-olie, bio-kool en gas. ’n Hoër opbrengs van bio-olie is behaal tydens Snel Piroliese van mielie-afval in die borrelende gefluidiseerde-bed reakctor (47.8 na 51.2 massa %, droog as-vry) in vergelyking met die Lurgi twee skroef reakctor (35.5 na 37 massa %, droog as-vry). Mielie stronke sorg vir ’n hoër opbrengs van bio-olie as mielie strooi in beide reaktore. By die optimum bedryfskondisies is daar in beide reaktor ’n hoër bio-kool opbrengs verkry van mielie stingels teenoor mielie stronke. Geen aansienlike verskille is gevind in die chemise en fisiese kenmerke van van die bio-olie wat geproduseer is in die twee reaktore nie. Daar is wel variasie getoon in die bio-kool kenmerkte van die verskillende Snel Piroliese prosesse. Snel piroliese van mielie-afval lewer energie produkte, bio-olie (HVW = 18.7-25.3MJ/kg) en bio-kool (HVW = 19.8-29.3 MJ/kg) vergelykbaar met steenkool (HVW = 16.2-25.9 MJ/kg). Die bio-olies geproduseer het sommige ongewenste kenmerke getoon byvoorbeeld suurheid (pH 3.8-4.3) asook hoë water inhoud (21.3 – 30.5 massa %). Die metode (indamping) wat gebruik is vir die opgradering van bio-olie het gelei tot die verbetering van die verhittingswaarde asook die toename in viskositeit deur die verwydering van ligte koolwaterstowwe en water. Die mielie-afval bio-kool toon ’n BET (Brunauer-Emmet-Teller) oppervlakte area van 96.7-158.8 m2/g wat dit toepaslik maak as grondstof vir absorbante. The gas geproduseer tydens Snel Piroliese is geanaliseer met behulp van gas chromotografie (GC) as CO2, CO, H2, CH4, C2H4, C2H6, C3H8 and C5+ koolwaterstowwe. Die vlak van CO2 en CO het 80% (v/V) oorskry en met lae verhittingswaardes (8.82-8.86 MJ/kg).

Thesis (MScEng)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: According to recent studies, biochar has the potential to improve soil fertility, mitigate climate change, reduce off-site pollution and assist in managing wastes. The application of biochar to soil is not a new concept; Amazonian dark earths are carbon-rich soils with high soil fertility that were created before 1541. Vacuum pyrolysis is a thermo-chemical conversion technique in which biomass is transformed into bio-oil, biochar and non-condensable gas. The objective of this work was to investigate the chemical and physical properties of biochar produced from vacuum pyrolysis of black wattle, vineyard annual prunings and sugar cane bagasse for their potential as soil amendment and adsorbent. The vacuum pyrolysis of black wattle, vineyard prunings and sugar cane bagasse (pyrolysis temperature: 460°C, pressure: 8kPaabs, heating rate: 17°C/min) resulted in biochar yields of 23.5%, 31.0% and 19.7% on a weight basis, respectively. The nature of the biomass had a substantial effect on yields of the products. High ash content combined with high lignin composition led to higher biochar yields for vineyard prunings. The highest surface acidity was observed for sugar cane bagasse (2.3 mmol/g), whereas the lowest surface acidity was observed for vineyard biochar (1.67 mmol/g). Consequently, the pH of the biochars was in the order: vineyard (10.43)> black wattle (9.74)> sugar cane bagasse (6.56). The cation exchange capacities (CEC) of biochars were 122 cmol/kg, 101 cmol/kg and 65 cmol/kg for sugar cane bagasse, black wattle and vineyard, respectively. The electrical conductivities (EC) were highly correlated with feedstock nature. The Ca and K rich vineyard biochar resulted in the highest EC (0.83 dS/m), whilst EC values of black wattle and sugar cane bagasse were 0.67 dS/m and 0.17 dS/m, respectively. Biochars contained substantial amounts of plant-available nutrients, while being low in toxic inorganic content (Pb, As, Cd). The BET surface areas of sugar cane bagasse, black wattle and vineyard were 259 mª/g, 241 mª/g and 91 mª/g, respectively. The adsorption capacity was found to increase with increased contact time and initial solution concentration. The experimental equilibrium time were found to be 3505 min, 1350 min and 150 min for adsorption of 20 mg/L methylene blue solution for vineyard, black wattle and sugar cane bagasse, respectively. Equilibrium data were well fitted to Langmuir and Freundlich isotherms. The maximum adsorption capacities were found to be 15.15 mg/g, 14.49 mg/g and 19.23 mg/g for vineyard, black wattle and sugar cane bagasse when modelled with Langmuir isotherms. The adsorption kinetics was found to follow the pseudo-second order kinetic model. In summary, biochar from sugar cane bagasse is a promising adsorbent for the removal of basic dyes due to its high surface area and microporous structure. This biochar can be applied to slightly acidic soils for nutrient retention and the exchange of nutrients. On the other hand, possessing high amounts of nutrients, biochars from black wattle and vineyard are potential soil amendentment agents. Biochar from black wattle is more beneficial compared to biochar from vineyard due to its higher surface area, microporosity and cation exchange capacity. / AFRIKAANSE OPSOMMING: Volgens onlangse studies, het houtskool die potensiaal om grond vrugbaarheid te verbeter, klimaat verandering te versag, besoedeling te verlaag en ondersteuning te verleen in die bestuur van afval. Die toevoeging van houtskool in grond is nie ‘n nuwe konsep nie; Amazone donker gronde is koolstof ryk gronde met hoë vrugbaarheid wat voor 1541 geskep is. Vakuum pirolise is ‘n termo-chemiese omskakelings tegniek waarin biomassa afgebreek word na bio-olie, houtskool en nie-kondenseerbare gasse. Die doelwit van hierdie werk was om die chemiese en fisiese eienskappe van houtskool, wat geproduseer is deur die vakuum pirolise van swart wattel, jaarlikse wingerd snoeisels, en suikerriet bagasse, vir hulle potensiaal vir grond verbetering en adsorpsie toepassings te ondersoek. Die vakuum pirolise van swart wattel, jaarlikse wingerd snoeisels, en suikerriet bagasse (pirolise temperatuur: 460°C, druk: 8kPaabs, verhittingstempo: 17°C/min) het houtskool opbrengste van 23.5%, 31.0% en 19.7% op massa basis, respektiewelik tot gevolg. Die tipe biomassa het ‘n beduidende effek op die opbrengs van die produkte. Hoë as-inhoud, gekombineer met hoë lignien inhoud, lei tot hoër houtskool opbrengste vir wingerd snoeisels. Die hoogste oppervlak suurheid is gevind vir suikerriet bagasse (2.3 mmol/g), terwyl die laagste waarde gevind is vir die wingerd snoeisels (1.67 mmol/g). Gevolglik, is die pH van die houtskole in die volgorde van: wingerd (10.43) > swart wattle (9.74) > suikerriet bagasse (6.56). Die katioon uitruiling vermoë (CEC) van die houtskole was 122 cmol/kg, 101 cmol/kg and 65 cmol/kg vir suikerriet bagasse, swart wattel en wingerd snoeisels respektiewelik. Die elektriese konduktiwiteite (EC) is gekorreleer met die eienskappe van die biomassas. Die Ca en K ryke wingerd snoeisel houtskool het die hoogste EC waarde (0.83 dS/m) tot gevolg, terwyl die EC waardes vir swart wattel en suikerriet bagasse bepaal is as 0.67 dS/ 0.16 dS/m respektiewelik. Die houtskole het groot hoeveelhede plant-beskikbare voedingstowwe bevat, terwyl dit laag was in toksiese anorganiese stowwe (Pb, As, Cd). Die BET oppervlak areas van suikerriet bagasse, swart wattel en wingerd snoeisels was 259 mª/g, 241 mª/g en 91 mª/g respektiewelik. Daar is gevind dat die adsorpsie kapasiteit toeneem met toenemende kontak tyd met die aanvanklike oplossing. Die eksperimentele ewewigs tye is gevind as 350 min, 1350 min en 150 min vir die adsorpsie van ‘n 20 mg/L metileen blou oplossing vir wingerd snoeisels, swart wattel en suikerriet bagasse, respektiewelik. Die ewewigs data het die Langmuir en Freundlich isoterme goed gepas. Die maksimum adsorpsie kapasiteite is gevind as 15.15 mg/g, 14.9 mg/g en 19.23 mg/g vir wingerd snoeisels, swart wattel en suikerriet bagasse wanneer dit gemodeleer is met Langmuir isoterme. Daar is bevind dat die adsorpsie kinetika ‘n pseudo-tweede orde kintika model volg. In opsomming, houtskool van suikerriet bagasse is ‘n veelbelowende adsorpsie middel vir die verwydering van basiese kleurstowwe, as gevolg van die hoë oppervlak area en mikroporie-struktuur van hierdie houtskool. Dié houtskool kan gebruik word op effense suur gronde vir voedingstof behoud en uitruiling. Aan die ander kant, houtskole van swart wattel en wingerd snoeisels wat hoë hoeveelhede voedingsstowwe bevat, is potensiële grond verbeterings middels. Houtskool afkomstig van swart wattel is meer voordelig as die van wingerd snoeisels, as gevolg van die hoër oppervlak area, mikroporositeit en katioon uitruilings vermoë van die swart wattel houtskool.

Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010. / ENGLISH ABSTRACT: The world’s depleting fossil fuels and increasing greenhouse gas emissions have given rise to much research into renewable and cleaner energy. Biomass is unique in providing the only renewable source of fixed carbon. Agricultural residues such as Sugarcane Bagasse (SB) are feedstocks for ‘second generation fuels’ which means they do not compete with production of food crops. In South Africa approximately 6 million tons of raw SB is produced annually, most of which is combusted onsite for steam generation. In light of the current interest in bio-fuels and the poor utilization of SB as energy product in the sugar industry, alternative energy recovery processes should be investigated. This study looks into the thermochemical upgrading of SB by means of pyrolysis. Biomass pyrolysis is defined as the thermo-chemical decomposition of organic materials in the absence of oxygen or other reactants. Slow Pyrolysis (SP), Vacuum Pyrolysis (VP), and Fast Pyrolysis (FP) are studied in this thesis. Varying amounts of char and bio-oil are produced by the different processes, which both provide advantages to the sugar industry. Char can be combusted or gasified as an energy-dense fuel, used as bio-char fertilizer, or upgraded to activated carbon. High quality bio-oil can be combusted or gasified as a liquid energy-dense fuel, can be used as a chemical feedstock, and shows potential for upgrading to transport fuel quality. FP is the most modern of the pyrolysis technologies and is focused on oil production. In order to investigate this process a 1 kg/h FP unit was designed, constructed and commissioned. The new unit was tested and compared to two different FP processes at Forschungszentrum Karlsruhe (FZK) in Germany. As a means of investigating the devolatilization behaviour of SB a Thermogravimetric Analysis (TGA) study was conducted. To investigate the quality of products that can be obtained an experimental study was done on SP, VP, and FP. Three distinct mass loss stages were identified from TGA. The first stage, 25 to 110°C, is due to evaporation of moisture. Pyrolitic devolatilization was shown to start at 230°C. The final stage occurs at temperatures above 370°C and is associated with the cracking of heavier bonds and char formation. The optimal decomposition temperatures for hemicellulose and cellulose were identified as 290°C and 345°C, respectively. Lignin was found to decompose over the entire temperature range without a distinct peak. These results were confirmed by a previous study on TGA of bagasse. SP and VP of bagasse were studied in the same reactor to allow for accurate comparison. Both these processes were conducted at low heating rates (20°C/min) and were therefore focused on char production. Slow pyrolysis produced the highest char yield, and char calorific value. Vacuum pyrolysis produced the highest BET surface area chars (>300 m2/g) and bio-oil that contained significantly less water compared to SP bio-oil. The short vapour residence time in the VP process improved the quality of liquids. The mechanism for pore formation is improved at low pressure, thereby producing higher surface area chars. A trade-off exists between the yield of char and the quality thereof. FP at Stellenbosch University produced liquid yields up to 65 ± 3 wt% at the established optimal temperature of 500°C. The properties of the bio-oil from the newly designed unit compared well to bio-oil from the units at FZK. The char properties showed some variation for the different FP processes. At the optimal FP conditions 20 wt% extra bio-oil is produced compared to SP and VP. The FP bio-oil contained 20 wt% water and the calorific value was estimated at 18 ± 1 MJ/kg. The energy per volume of FP bio-oil was estimated to be at least 11 times more than dry SB. FP was found to be the most effective process for producing a single product with over 60% of the original biomass energy. The optimal productions of either high quality bio-oil or high surface area char were found to be application dependent. / AFRIKAANSE OPSOMMING: As gevolg van die uitputting van fossielbrandstofreserwes, en die toenemende vrystelling van kweekhuisgasse word daar tans wêreldwyd baie navorsing op hernubare en skoner energie gedoen. Biomassa is uniek as die enigste bron van hernubare vaste koolstof. Landbouafval soos Suikerriet Bagasse (SB) is grondstowwe vir ‘tweede generasie bio-brandstowwe’ wat nie die mark van voedselgewasse direk affekteer nie. In Suid Afrika word jaarliks ongeveer 6 miljoen ton SB geproduseer, waarvan die meeste by die suikermeulens verbrand word om stoom te genereer. Weens die huidige belangstelling in bio-brandstowwe en ondoeltreffende benutting van SB as energieproduk in die suikerindustrie moet alternatiewe energie-onginningsprosesse ondersoek word. Hierdie studie is op die termo-chemiese verwerking van SB deur middel van pirolise gefokus. Biomassa pirolise word gedefinieer as die termo-chemiese afbreking van organiese bio-materiaal in die afwesigheid van suurstof en ander reagense. Stadige Pirolise (SP), Vakuum Pirolise (VP), en Vinnige Pirolise word in hierdie tesis ondersoek. Die drie prosesse produseer veskillende hoeveelhede houtskool en bio-olie wat albei voordele bied vir die suikerindustrie. Houtskool kan as ‘n vaste energie-digte brandstof verbrand of vergas word, as bio-houtskoolkompos gebruik word, of kan verder tot geaktiveerde koolstof geprosesseer word. Hoë kwaliteit bio-olie kan verbrand of vergas word, kan as bron vir chemikalië gebruik word, en toon potensiaal om in die toekoms opgegradeer te kan word tot vervoerbrandstof kwaliteit. Vinnige pirolise is die mees moderne pirolise tegnologie en is op bio-olie produksie gefokus. Om die laasgenoemde proses te toets is ‘n 1 kg/h vinnige pirolise eenheid ontwerp, opgerig en in werking gestel. Die nuwe pirolise eenheid is getoets en vegelyk met twee verskillende vinnige pirolise eenhede by Forschungszentrum Karlsruhe (FZK) in Duitsland. Termo-Gravimetriese Analise (TGA) is gedoen om die ontvlugtigingskenmerke van SB te bestudeer. Eksperimentele werk is verrig om die kwaliteit van produkte van SP, VP, vinnige pirolise te vergelyk. Drie duidelike massaverlies fases van TGA is geïdentifiseer. Die eerste fase (25 – 110°C) is as gevolg van die verdamping van vog. Pirolitiese ontvlugtiging het begin by 230°C. Die finale fase (> 370°C) is met die kraking van swaar verbindings en die vorming van houtskool geassosieer. Die optimale afbrekingstemperatuur vir hemisellulose en sellulose is as 290°C en 345°C, respektiewelik, geïdentifiseer. Daar is gevind dat lignien stadig oor die twede en derde fases afgebreek word sonder ‘n duidelike optimale afbrekingstemperatuur. Die resultate is deur vorige navorsing op TGA van SB bevestig. SP en VP van bagasse is in dieselfde reaktor bestudeer, om ‘n akkurate vergelyking moontlik te maak. Beide prosesse was by lae verhittingstempo’s (20°C/min) ondersoek, wat gevolglik op houtskoolformasie gefokus is. SP het die hoogste houtskoolopbrengs, met die hoogste verbrandingsenergie, geproduseer. VP het hootskool met die hoogste BET oppervlakarea geproduseer, en die bio-olie was weens ‘n dramatiese afname in waterinhoud van beter gehalte. Die meganisme vir die vorming van ‘n poreuse struktuur word deur lae atmosferiese druk verbeter. Daar bestaan ‘n inverse verband tussen die kwantiteit en kwaliteit van die houtskool. Vinnige pirolise by die Universiteit van Stellenbosch het ‘n bio-olie opbrengs van 65 ± 3 massa% by ‘n vooraf vasgestelde optimale temperatuur van 500°C geproduseer. Die eienskappe van bio-olie wat deur die nuwe vinnige pirolise eenheid geproduseer is het goed ooreengestem met die bio-olie afkomstig van FZK se pirolise eenhede. Die houtskool eienskappe van die drie pirolise eenhede het enkele verskille getoon. By optimale toestande vir vinnige pirolise word daar 20 massa% meer bio-olie as by SP en VP geproduseer. Vinnige pirolise bio-olie het ‘n waterinhoud van 20 massa% en ‘n verbrandingswarmte van 18 ± 1 MJ/kg. Daar is gevind dat ten opsigte van droë SB die energie per enheidsvolume van bio-olie ongeveer 11 keer meer is. Vinnige pirolise is die mees doeltreffende proses vir die vervaardiging van ‘n produk wat meer as 60% van die oorspronklike biomassa energie bevat. Daar is gevind dat die optimale hoeveelhede van hoë kwaliteit bio-olie en hoë oppervlakarea houtskool doelafhanklik is.

This research investigates the decomposition and burning behaviours of polyurethane foams experimentally and compares the experimental results obtained with the numerical results from the pyrolysis model of Fire Dynamics Simulator, Version 5 (FDS 5). Based on the comparison of model and experimental heat release rates, the accuracy of the pyrolysis model is quantified. In total, this research tested seven polyurethane foams consisting of three non-fire retardant (NFR) and four fire retardant (FR) foams. According to the simultaneous differential scanning calorimetry and thermogravimetric analysis (SDT) experiments, the decomposition behaviour of polyurethane foams under nitrogen environment is represented by two pyrolysis reactions. The first reaction consists of foam decomposition into melts and gases while the second reaction consists of the decomposition of the remaining melts into gases. The kinetic properties which govern the rate of decomposition are the activation energy (E), pre-exponential factor (A), reaction order (n) and heat of reaction (Δhr). Using graphical techniques, E, A and n of the first and second reactions are determined from the thermogravimetric analysis (TGA) results. Through analysing the differential scanning calorimetry (DSC) results, Δhr is determined from the changes in heat flow and sample mass. The thermophysical properties govern the heat transfer through material and these are the thermal conductivity (λ) and specific heat (cp) which are measured experimentally at ambient temperature through the Hot Disk method. Through the Sample Feeding Vertical Cone, the decomposition and melting behaviours of polyurethane foams in a vertical orientation are investigated and the foams tested can be categorised into those which produce melts only after ignition and those which produce melts and char after ignition. The 1-dimensional burning behaviour of foams is obtained from the cone calorimeter experiments. The NFR foams show a change from plateau burning behaviour at low heat flux to two stage burning behaviour at high heat flux while the FR foams consistently show two stage burning behaviour. The combustion property governs the amount of heat released when fuel combusts and this is the effective heat of combustion (Δhc,eff) which is determined from the heat released and mass consumed in the cone experiment. The 1-dimensional burning behaviour is simulated using the pyrolysis model of FDS 5 and two different modelling approaches are considered. The direct method uses the material properties determined experimentally as FDS 5 inputs while the refined method uses the genetic algorithm of Gpyro to refine the kinetic properties which are later used as FDS 5 inputs. The heat release rate of the model and experiment are compared through linear regression analysis which quantifies the accuracy of both methods. The accuracy is defined as the percentage of data points within the boundary of acceptance which is bounded by 25 % of the greatest experimental heat release rate. This assessment method places greater emphasis on the accuracy of developed burning phases and lesser emphasis on the accuracy of initial growth and final decay. The accuracy of the direct method is found to be 56 % while the refined method with estimated kinetic properties achieves a higher accuracy of 75 %. The 2-dimensional burning behaviours are investigated in the foam slab experiments for two different slab thicknesses, 120 and 100 mm. The opposed-flow spread of 120 mm slab is more intense and rapid while for the 100 mm slab, the flame spread is less intense and slow. FDS 5 is used to simulate the experimental results but when the material properties either developed experimentally or refined by Gpyro are used as inputs, the model fails to produce flame spread. This is because FDS 5 does not yet have the features which address the dynamics of foam melting and the reactive nature of the flame. In order to produce flame spread in the model, E of the reactions have been reduced to increase the decomposition rate.

Gas-phase electron diffraction (GED) is the only viable technique for the accurate structural study of gas-phase molecules that contain more than ~10 atoms. Recent advances in Edinburgh have made it possible to study larger, more complex, stable molecules using the SARACEN method. This thesis is concerned with obtaining the structures of unstable species, using both standard GED techniques and by developing a new method in which ash vacuum pyrolysis is used to generate short-lived species in situ. In the first part of this thesis nine primary phosphines (R-PH2) with different substituents (R = methyl, vinyl, ethynyl, allenyl, allyl, propargyl, phenyl, benzyl and chloromethyl) are studied by GED. Vinylarsine and vinyldichloroarsine are also studied. Primary phosphines and arsines appear infrequently in the literature owing to their toxicity and high reactivity, especially of the unsaturated systems. The conformational behaviour in these molecules and trends throughout the series are rationalised. As appropriate, comparisons are made to analogous amines and the differences found are discussed. Tertiary phosphines (R3P) are routinely protected by complexation with borane (BH3) and it has been proposed that this technique could be extended to primary phosphines. As an extension of the initial investigation, the GED study of methylphosphine-borane offers an insight into structural changes that occur upon complexation, although attempts to study larger phosphine-borane complexes by GED proved dificult. The structures and bonding trends in a series of phosphineborane adducts are discussed, mainly using the results of ab initio calculations. The second part of the thesis details the implementation of a new, very high temperature nozzle, which allows the generation of short-lived species by pyrolysis. The workings of this nozzle are discussed and the study of the structure of ketene, generated from three different precursors, is detailed. The benzyl radical has also been studied, and a preliminary GED structure is presented. As a result of this work the molecular structures of Meldrum's acid and dibenzylsulfone are also presented, having been determined in the gas phase for the first time.

Chemical and allied industries produce significant quantities of chlorinated wastes each year. Thermal treatnent of these chlorinated wastes has a long and controversial history. The most common and contentious method of waste destruction is incineration. Although waste incinerators are designed to provide greater control over the combustion process, toxic products are inevitably formed from incomplete combustion and released in stack gases and other residues. The most notable group belonging to the products of incomplete combustion (PICs) are dioxins and furans. The fact that oxygen is an integral part of the molecular structure of dioxins and furans suggests that the formation of these particular PICs may be reduced or avoided by minimizing or completely excluding oxygen from thermal waste treatment. Pyrolysis using induction heating is a relatively new technology that has shown much promise from the initial work performed by Pillay (2001). This research was an extension of that study, and investigated equipment and process optimization as well as macroscopic modeling of different systems. The objective of this study was to establish the technology of pyrolysis using induction heating as a competitive alternative to existing waste destruction systems. The novel approach of pyrolysing compounds using induction heating was demonstrated by destroying chlorinated aliphatic, aromatic and a mixture of these compounds. These experiments were conducted at atmospheric pressure in a tubular laminar flow reactor (5.2cm I.D) under a thermally transparent argon atmosphere. In this system heat was generated in an embedded graphite tube using induction heating. Thermal degradation occurred through the bombardment of the compounds by the photons emitted from the heated graphite tube. The compounds were pyrolysed at temperatures ranging from 330°C to 1000°C and at mean residence times from 0.47s to 2.47s. In addition to these process variables the effects of reactant concentration and additives were investigated The major species formed from this thermal treatment were solid carbon black and gaseous hydrogen chloride. Destruction efficiencies (DE) of the order of 99.9999% (six nines) and greater were obtained for the different feed mixtures at their respective operating conditions. A minimum DE of six nines adequately satisfies the regulation set by the Environmental Protection Agency (EPA) for successful waste destruction. / Thesis (M.Sc.Eng.)-University of KwaZulu-Natal, Durban, 2004.

Biochars have been created and characterized from a variety livestock manure biomass including poultry, dairy, and swine. However, no research has been conducted on the physical and chemical makeup of biochar pyrolyzed from horse muck. Two horse muck derived biochars containing either straw (HS) or woodchip (HW) bedding were pyrolyzed at 700°C and characterized for their physical and chemical properties. Tests revealed both biochars had high alkalinity, moderate specific conductivity, and low surface area as compared to other biochars in the literature. HS contained more mineral structures than HW. Scanning electron microscopy presented differences in particle shape, size, and presence of xylemic structures. The chemical makeup of both biochars was similar, while HW contained about 23% more C than HS while HS contained more calcium and magnesium. The effect of biochar-amended soils on the transport of two Escherichia coli isolates was studied using saturated soil columns. The results show that HW significantly reduced the transport of isolate SP2B07 over the Soil control, and reduced the transport of isolate SP2B07 more than isolate SP1H01. Horse muck biochars may show promise in reducing bacterial transport though agricultural soils.