The reaction kinetics of Iroko and Mahogany were studied using TGA. The pyrolysis process was achieved using six different heating rates of 2,5,8,12,15 and 20˚C. A 15˚C/min heating rate was used for gasification in steam at different temperatures while varying the concentrations of nitrogen and steam in the process. The kinetic parameters, activation energy and pre exponential factor, were obtained by implementing two chosen kinetic models. These models are: Friedman’s Iso-conversional Method, Flynn-Wall-Ozawa Method (FWO). There were substantial differences in the values of the kinetic triplets found from the experiments. Due to the substantial differences in the values, it was not the best way to perform this kind of analysis (which is the traditional way) but instead to use pure regression analysis; but using it for the whole data set (that means for all heating rates) and minimize the difference with experimental data.

Thesis (PhD)--Stellenbosch University, 2012. / ENGLISH ABSTRACT: Gasification provides a proven alternative to the dependence on petroleum for the production of high value products such as liquid fuels and chemicals. Syngas, the main product from gasification can be converted to fuels and chemicals via a number of possible synthesis processes. Coal and natural gas are currently the main feedstock used for syngas production. In South Africa (SA), Sasol operates the largest commercial coal-to-liquids conversion process in the world, based on updraft fixed bed gasification of low grade coal to syngas. Co-utilizing alternative and more sustainable feedstock (such as biomass and wastes) with coal in existing coal-based plants offers a realistic approach to reducing the costs and risks associated with setting up dedicated biomass conversion plants. An experimental and modelling investigation was performed to assess the impacts of co-gasifying two of the most commonly available agricultural wastes in SA (sugarcane bagasse and corn residue) with typical low grade SA coals, on the main products of updraft fixed bed gasification, i.e. liquid condensates and syngas. Condensates are produced in the pyrolysis section of the updraft gasifier, whereas syngas is a result of residual char conversion. An experimental set-up that simulates the pyrolysis section of the gasifier was employed to investigate the yield and composition of devolatilized products at industrially relevant conditions of 26 bars and 400-600°C. The results show that about 15 wt% of coal and 70 wt% of biomass are devolatilized during the pyrolysis process. The biomass derived condensates were determined to comprise of significantly higher quantities of oxygenates such as organic acids, phenols, ketones, and alcohols, whereas coal derived hydrocarbon condensates were dominated by polycyclic aromatic hydrocarbons, creosotes and phenols. Results of investigation into the influence of coal-biomass feedstock mix ratio on yields of products from pyrolysis show limited evidence of non-additive or synergistic behaviour on the overall distribution of solid, liquid and gas yields. On the other hand, in terms of the distribution of specific liquid phase hydrocarbons, there was significant evidence in favour of non-additive pyrolysis behaviour, as indicated by the non-additive yield distribution of specific chemicals. Synergistic trends could also be observed in the thermogravimetric (TGA) study of pyrolysis under kinetically controlled non-isothermal conditions. Model free and model fitting kinetic analysis of the TGA data revealed activation energies ranging between 94-212 kJ mol-1 for the biomass fuels and 147-377 kJ mol-1 for coal. Synergistic interactions may be linked to the increased presence of hydrogen in biomass fuels which partially saturates free radicals formed during earlier stages of devolatilization, thereby preventing secondary recombination reactions that would have produced chars, allowing for the increased formation of volatile species instead. Analysis of char obtained from the co-pyrolysis experiments revealed that the fixed carbon and volatile content of the blended chars is is proportional to the percentage of biomass and coal in the mixture. CO2 reactivity experiments on the chars showed that the addition of biomass to coal did not impose any kinetic limitation on the gasification of blended chars. The blended chars decomposed at approximately the same rate as when coal was gasified alone, even at higher biomass concentrations in the original feedstock blend. Based on these observations, a semi-empirical equilibrium based simulation of syngas production for co-gasification of coalbiomass blends at various mix ratios was developed using ASPEN Plus. The model showed that H2/CO ratio was relatively unaffected by biomass addition to the coal fuel mix, whereas syngas heating value and thermal efficiency were negatively affected. Subsequent evaluation of the production cost of syngas at biomass inputs ranging between 0-20 wt% of coal reflected the significant additional cost of pretreating biomass (3.3% of total capital investment). This resulted in co-gasification derived syngas production costs of ZAR146/tonne (ZAR12.6/GJ) at 80:20 coalbiomass feedstock ratio, compared to a baseline (coal only) cost of ZAR130/tonne (ZAR10.7/GJ). Sensitivity analysis that varied biomass costs from ZAR0 ZAR470 revealed that syngas production costs from co-gasification remained significantly higher than baseline costs, even at low to zero prices of the biomass feedstock. This remained the case even after taking account of a carbon tax of up to ZAR117/tCO2. However, for range of carbon tax values suggested by the SA treasury (ZAR70 tCO2 to ZAR200 tCO2), the avoided carbon tax due to co-feeding biomass can offset between 40-96% of the specific retrofitting cost at 80:20 coal-biomass feedstock mass ratio. In summary, this dissertation has showed that in addition to the widely recognized problems of ash fouling and sintering, co-feeding of biomass in existing coal based updraft gasification plants poses some challenges in terms of impacts on condensates and syngas quality, and production costs. Further research is required to investigate the potential in ameliorating some of these impacts by developing new high value product streams (such as acetic acid) from the significant fraction of condensates derived from biomass. / AFRIKAANSE OPSOMMING: Vergassing bied 'n beproefde alternatief vir die afhanklikheid van petroleum vir die produksie van hoë waarde produkte soos vloeibare brandstof en chemikalieë. Sintese gas, die belangrikste produk van vergassing, kan omgeskakel word na brandstof en chemikalieë deur 'n aantal moontlike sintese prosesse. Steenkool en aardgas is tans die belangrikste grondstowwe wat gebruik word vir sintese gas produksie. In Suid-Afrika (SA) bedryf Sasol die grootste kommersiële steenkool-totvloeistof omskakelingsproses in die wêreld, gebaseer op stygstroom vastebed vergassing van laegraadse steenkool na sintese gas. Die gebruik van alternatiewe en meer volhoubare grondstowwe (soos biomassa en afval) saam met steenkool in die bestaande steenkool-gebaseerde aanlegte bied 'n realistiese benadering tot die vermindering van die koste en risiko's wat verband hou met die oprigting van toegewyde biomassa omskakelingsaanlegte. 'n Eksperimentele en modelleringsondersoek is uitgevoer om die impak van gesamentlike vergassing van twee van die mees algemeen beskikbare landbouafvalprodukte in Suid-Afrika (suikerriet bagasse en mieliereste) met tipiese laegraadse SA steenkool op die vernaamste produkte van stygstroom vastebed vergassing, dws vloeistof kondensate en sintese gas, te evalueer. Kondensate word geproduseer in die piroliese gedeelte van die stygstroomvergasser, terwyl sintese gas 'n resultaat is van die omskakeling van oorblywende houtskool. 'n Eksperimentele opstelling wat die piroliese gedeelte van die vergasser simuleer is gebruik om die opbrengs en die samestelling van produkte waarvan die vlugtige komponente verwyder is by industrie relevante toestande van 26 bar en 400-600°C te ondersoek. Die resultate toon dat ongeveer 15% (massabasis) van die steenkool en 70% (massabasis) van die biomassa verlore gaan aan vlugtige komponente tydens die piroliese proses. Daar is vasgestel dat die kondensate afkomstig van biomassa uit aansienlik hoër hoeveelhede suurstofryke verbindings soos organiese sure, fenole, ketone, en alkohole bestaan, terwyl koolwaterstofkondensate afkomstig uit steenkool oorwegend bectaan uit polisikliese aromatise verbindings, kreosote en fenole. Die resultate van die ondersoek na die invloed van die verhouding van steenkool tot biomassa grondstof op piroliese opbrengste toon beperkte bewyse van nie-toevoegende of sinergistiese gedrag op die algehele verspreiding van soliede, vloeistof en gas opbrengste. Aan die ander kant, in terme van die verspreiding van spesifieke vloeibare fase koolwaterstowwe, was daar beduidende bewyse ten gunste van 'n sinergistiese piroliese gedrag. Sinergistiese tendense is ook waargeneem in die termogravimetriese (TGA) studie van piroliese onder kineties beheerde nieisotermiese toestande. Modelvrye en modelpassende kinetiese analise van die TGA data het aan die lig gebring dat aktiveringsenergieë wissel tussen 94-212 kJ mol-1 vir biomassa brandstof en 147-377 kJ mol-1 vir steenkool. Ontleding van die houtskool verkry uit die gesamentlike piroliese eksperimente het aan die lig gebring dat die onmiddellike kenmerke van die gemengde houtskool die geweegde gemiddelde van die individuele waardes vir steenkool en biomassa benader. CO2 reaktiwiteitseksperimente op die houtskool het getoon dat die byvoeging van biomassa by steenkool nie enige kinetiese beperking op die vergassing van gemengde houtskool plaas nie. Die gemengde houtskool ontbind teen ongeveer dieselfde tempo as wanneer steenkool alleen vergas is, selfs teen hoër biomassa konsentrasies in die oorspronklike grondstofmengsel. Op grond van hierdie waarnemings is 'n semi-empiriese ewewig-gebaseerde simulasie van sintese gas produksie vir gesamentlike vergassing van steenkool-biomassa-mengsels vir verskeie mengverhoudings ontwikkel met behulp van Aspen Plus. Die model het getoon dat die H2/CO verhouding relatief min geraak is deur biomassa by die steenkool brandstofmengsel te voeg, terwyl sintese gas se verhittingswaarde en termiese doeltreffendheid negatief geraak is. Daaropvolgende evaluering van die produksiekoste van sintese gas vir biomassa insette wat wissel tussen 0-20% (massabasis) van die hoeveelheid steenkool het die aansienlike addisionele koste van die vooraf behandeling van biomassa (3.3% van die totale kapitale belegging) gereflekteer. Dit het gelei tot 'n produksiekoste van ZAR146/ton (ZAR12.6/GJ) vir sintese gas afkomstig uit gesamentlike-vergassing van 'n 80:20 steebkool-biomassa grondstof mengesl, in vergelyking met 'n basislyn (steenkool) koste van ZAR130/ton (ZAR10.7/GJ). Sensitiwiteitsanalise wat biomassa koste van ZAR0 - ZAR470 gevarieër het, het aan die lig gebring dat sintese gas produksiekoste van gesamentlike vergassing aansienlik hoër bly as die basislyn koste, selfs teen 'n lae of nul prys van biomassa grondstof. Dit bly die geval selfs nadat koolstof belasting van tot ZAR117/tCO2 in ag geneem is. In opsomming het hierdie verhandeling getoon dat, bykomend tot die wyd-erkende probleme van as besoedeling en sintering, die gesamentlike gebruik van biomassa in bestaande steenkool stygstroom vergassingsaanlegte groot uitdagings inhou in terme van die impak op die kwaliteit van kondensate en sintese gas, asook produksiekoste. Verdere navorsing is nodig om die potensiaal te ondersoek vir die verbetering van sommige van hierdie impakte deur die ontwikkeling van nuwe hoë waarde produkstrome (soos asynsuur) uit die beduidende breukdeel van kondensate wat verkry word uit biomassa.

No description available.

published_or_final_version / Chemistry / Master / Master of Philosophy

Synthesis and flash vacuum pyrolysis (FVP) of stabilised phosphorus ylides containing an o-amino functionalised benzene ring has been examined for the first time. Model studies using N-methyl-N-tosyl and N-mesyl-N-methyl ylides showed that the ylides could be prepared, although yields were variable, and had the expected spectroscopic properties. Upon FVP, however, the expected loss of Ph₃PO and the sulfonyl group was accompanied by unexpected transfer of the reactive site from nitrogen to carbon giving 3- substituted quinolines rather than the expected indole products. Moving to ylides with an α-cinnamoyl group (or heterocyclic analogue) did, however, result in the originally planned tandem cyclisation leading to ring-fused carbazole products. N-Benzyl was also found to be a suitable thermally labile group and a series of α-cinnamoyl N-benzyl-N-methyl ylides were prepared and characterised. For their synthesis, use of N-cinnamoylbenzotriazoles was found to be preferable to cinnamoyl chloride, requiring only half the amount of amino-functionalised phosphonium salt. While FVP of some of these ylides led to benzo-, furo- and thienocarbazoles in good yield, others again gave quinoline-type products pointing to a fine balance between the two alternative modes of cyclisation. It was noted that one of the furocarbazole products was very similar to a natural product, Eustifoline D, isolated from the medicinally active shrub Murraya euchrestifolia from Taiwan and its synthesis was planned. With a view to producing the required N-H carbazole, N,N-dibenzylamino amino ylides were prepared and were found to exhibit restricted rotation leading to broad NMR signals. Their FVP again led to both quinoline and carbazole products, with the former having usually, but not always, lost a phenyl group. Mechanistic pathways for the formation of the various products are proposed. Complete assignment of the complex ¹H NMR spectra of the various fused-ring heterocyclic products was achieved, assisted by simulations in many cases. The ylide precursor required for Eustifoline D was prepared in five steps and 10% overall yield from 5-methylanthranilic acid. The final FVP step gave a quinoline as the major product, but the minor product was Eustifoline D, spectroscopically identical to the natural product.

Routes to N-amino heterocycles were reviewed and findings applied to generate flash vacuum pyrolysis (FVP) precursors of two types - ketene generators and azol-1-yl radical generators. N-Amino heterocycles can be used as nitrogen radical generators, the N-N bond being homolytically cleaved at furnace temperatures of approximately 850 °C. A number of 2-substituted benzimidazoles were synthesised and subsequently Naminated. The 2-arylbenzimidazole precursors 1-amino-2-(2-methylphenyl)-1Hbenzimidazole and 1-amino-2-(2-ethylphenyl)-1H-benzimidazole were synthesised and subjected to FVP. The hydrogen transfer processes of the resulting azol-1-yl radicals were investigated. Pyrolysis of 1-amino-2-(2-methylphenyl)-1Hbenzimidazole resulted in three products; 2-(2-methylphenyl)-1H-benzimdazole, 11H-benzo[4,5]imidazo[1,2-a]isoindole and 1-(2-methylphenyl)-1Hbenzo[ d]imidazol-2-amine. Pyrolysis of 1-amino-2-(2-ethylphenyl)-1Hbenzimidazole resulted in five products, four of which have been successfully isolated and identified as 2-(2-ethylphenyl)-1H-benzimidazole, 5,6- dihydrobenzo[4,5]imidazo[2,1-a]isoquinoline, 1-(2-ethylphenyl)-1Hbenzo[ d]imidazol-2-amine and 11-methyl-11H-benzo[4,5]imidazo[2,1-a]isoindole. The mechanism of formation of most products is initiated by hydrogen atom transfer to the azol-1-yl radical position. N-Aminopyrazole was reacted with 5-methoxymethylene-2,2-dimethyl-1,3-dioxane- 4,6-dione to form the corresponding 5-(N-aminopyrazolyl)methylene derivative, which, when subjected to FVP, eliminates acetone and carbon dioxide to form a methyleneketene. This subsequently undergoes a [1,3]-hydrogen shift giving an imidoylketene which can collapse onto the neighbouring nitrogen atom forming pyrazolo[1,2-a][1,2,3]triazin-5-ium-4-olate (a novel heterocyclic mesomeric betaine system) or cyclise onto the adjacent carbon atom to yield a pyrazolopyridazinone. On variation of the furnace temperature it was apparent the former forms at relatively moderate temperatures (~500 °C) whereas the latter begins to predominate as the furnace temperature increases (~700 °C). The relationship between these kinetic and thermodynamic products was modelled using DFT calculations. By using substituted pyrazole precursors, substituents could be incorporated into all three available positions around the pyrazole ring. Using substituted acrylic esters as alternative imidoylketene generators, substituents could also be incorporated into both available positions in the pyridazinone ring. All corresponding betaine and pyrazolopyridazinone products were isolated and characterised.

Submitted to School of Chemical and Metallurgical Engineering, Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, South Africa June, 2016 / The main objective of this study is to produce biofuel from waste animal fat (collected from abattoirs) using the pyrolysis (thermal cracking) method. To achieve this goal, the study investigated the effects of temperature and heating rate on the yield and quality of the bio-oil produced. Also investigated was the effect of zeolite nano-catalyst(s) on the quality of the bio-oil produced. Animal waste fat (tallow) was pyrolyzed in a laboratory fixed bed reactor of volume 2200 cm3 at final temperatures (FT), 450oC, 500oC, 530oC and 580oC using heating rates (HR) of 4oC/min, 5oC/min and 6oC/min. The properties of the resultant bio-oils were tested and analyzed. The maximum bio-oil yield of 82.78 % was achieved at 530oC FT and 6oC /min HR while the highest calorific value, 52.41 MJ/kg, was recorded from the bio-oil produced at the FT of 580oC and 6oC/min HR. The molecular components of each of the bio-oil samples was analyzed using the Gas Chromatography – Molecular Spectrograph (GC-MS) which indicated the predominant presence of alkanes, alkenes, carboxylic acids and alkyl esters in the bio-oils produced without a catalyst. The introduction of zeolites in nano-form yielded relatively more cyclo-alkanes and aromatics. A maximum yield of 58% was recorded when 1% of the zeolite nano-catalyst was used to pyrolyse the tallow at 530oC FT and 6oC/min HR but with lots of coking and gas formation. The viscosity improved with a 35% reduction for the samples produced with 1% zeolites (C1 and C2). The viscosity of the bio-oil produced with 2% zeolites improved with a resultant 34% reduction in value. For pyrolysis done at 530oC FT and 6oC/min HR, the bio-oils with 1% (C1) and 2% zeolite (C3) resulted in a reduction in acid value of 32% and 30%, respectively. Acid value is the mass of potassium hydroxide (KOH) in milligrams that is required to neutralize one gram of chemical substance. / MT2016

A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg 10th of October 2016 / Thermal pyrolysis is one of the viable technologies suitable for the management of organic solid waste, which has become a global challenge over the years. This is due to the non-biodegradability of these materials and their continuous usage across all segments of man’s daily activities. Effectiveness of the method is in converting these materials under controlled process conditions, that enable the optimization of the fraction of interest, such as the liquid fraction also referred to as pyrolytic oil with a near zero pollution effect on the environment. The main setback in the production of the liquid fraction include low yield, presence of sulphur and other aromatic compounds which have been linked to environmental pollution and health complications. This study focuses on improving the liquid fraction yield and composition obtainable from pyrolysis process. Latex natural rubber (obtained from Hevea Brasiliensis) was pyrolysed and its products compared with that of the used tyres. The production of pyrolytic oil from used tyres and natural rubber was performed using thermal and catalytic pyrolysis processes. The operating temperature range of 375 to 750 oC (at an interval of 75 oC) at a heating rate of 15oC/min and feed material particle sizes of 2, 4, 6, 8 and 10 mm were used. In addition, Zeolite NaY was synthesized from Lawani Benin River Kaolin (LBK) at a synthesis time and temperature of 9 h and 100 oC respectively, using hydrothermal synthesis method, and used for catalytic pyrolysis. The chemical characterisation revealed pyrolytic oil composition to be a complex mixture of aliphatic, aromatics, polycyclic aromatic hydrocarbons and other oxygen, nitrogen, sulphur and chlorinated compounds in small proportions. The non-catalysed and catalysed pyrolysis using natural rubber resulted in pyrolytic oil with 80 and 66% of aliphatic, 12 and 15% aromatic (with polycyclic aromatic hydrocarbons concentration of 2 and 1%). The non-catalysed and catalysed pyrolysis using used tyres yielded pyrolytic oil with 42 and 32% of aliphatic, 34 and 39% aromatic (with polycyclic aromatic hydrocarbons concentrations of 18 and 23%). The kinetics of the thermal degradation with the aid of a thermogravimetry and differential thermogravimetry analyzer was performed over a temperature range of 30 to 800 oC at a heating rate of 15, 20 and 30oC/min. Results showed that natural rubber displayed higher activation energy than used tyres, with respect to the heating rates. This is an indication that natural rubber is more difficult to thermally decompose than used tyres. The distillation temperature of the distillates was within the temperature range of the conventional petrol and diesel. The composition of the distillates revealed carbon chain length of C5-C30 with majority being C8 – C10. A spark ignition generator engine was used to perform the combustion tests for the various pyrolytic oil distillates and petrol blended in the ratio 0, 5, 10, 15 and 20% successfully without engine modification. For the fuel consumption with respect to generator run time, it was observed that an optimum of 20% natural rubber pyrolytic oil distillates (NRPD)-Petrol blend gave comparative fuel consumption behavior with that of commercial petrol. Furthermore, the 20% NRPD distillates gave optimum fuel consumption and power. Hence, a significant yield improvement and combustion performance were observed for the pyrolytic oil derived from natural rubber than that of used tyres. Further treatment of the pyrolytic oil distillates could pave the way for effective use of the oil as chemical feedstock for industries, or as substitutes for fossil fuel. It was also requisite to develop a mathematical model which adopts thermogravimetry analyser (TGA) as a dynamic apparatus to predict weight change of a material as it degrades with time at a fixed temperature. The proposed models were in three consecutive phases which were classified into three time zones 0 ≤ t ≤ t1, t1 ≤ t ≤ t2 and t ≤ t2. The general model equation for the first phase of degradation was 2 0 1 2 0 ( ) t T w t w e   , while the second phase model was and at the third phase, it is assumed that the limit of weight loss (in the second phase equation) as t tends to ∞ gives a value k , at which change in weight loss with time is negligible. The proposed model was used to plot graph of weight loss versus time at different fixed temperature which fitted well with the experimental TGA and had a characteristic pattern fitted closely to the second phase degradation of the fixed bed reactor. / MT2017

A novel process for single-pot conversion of biomass to biofuels was developed called the molten salt catalytic pyrolysis (MSCP) method. The proposed single-pot MSCP process proved to be an inherently more efficient and cost-effective methodology for converting lignocellulosic biomass. In this study, several parameters that affect yield of bio-oil were investigated including carrier gas flow rate; pyrolysis temperature; feed particle size; varying types of molten salt and catalysts. Use of molten salt as the reaction medium offered higher liquid yield and experiments containing ZnCl2 showed higher yield than other chloride salts. The highest yield of bio-oil was up to 66% obtained in a ZnCl2-KCl-LiCl ternary molten salt system compared with 32.2% at the same condition without molten salts. In addition, the effect of molten salt on the composition of bio-oil was also studied. It was observed that molten salt narrowed the product distribution of bio-oil with furfural and acetic acid as the only two main components in the liquid with the exception of water. Finally, a thermogravimetric kinetic study on the pyrolysis of biomass in MSCP was conducted.

Waste plastic treatment was a global issue currently. A sustainable recycling process was required to recovery the monomer units from the polymer, thus avoiding environmental impacts due to disposal and enhancing the economic benefit from the recovered products. Pyrolysis was one of the promising process and previous MQP group has studied the pyrolysis with molten salts. In this work, a standardized and optimized pyrolysis reaction process of polystyrene was developed, based on the previous work on molten salt pyrolysis 5. The literature of pyrolysis mechanism and catalytic effects were reviewed as a guide process design. The orientation of the reactor was standardized to be consistent with literature record of preceding work. The positioning of the flow tube for the carrier gas and thermocouple were standardized in locations to provide mixing process of the reactant, the removal of products, and the accurate measurement of reaction temperature. The product collection system was also investigated and optimized to maximize collection efficiency while avoiding excessively low temperatures. The experiment results with standardized reaction configuration showed an improved styrene yield, 65%, compared with a previous yield of 44%. Then with the standardized reaction configuration, the catalytic effects of molten salt were studied at 400℃ pyrolysis temperature. Quantitative analysis indicated that the molten salt improved the styrene selectivity of the monomer compared to the dimer. Analysis of product composition and mass balance indicated formation of heavy non-GC detectable species in the liquid products. Gas phase secondary reaction during pyrolysis, and re-polymerization inside the liquid products, were discussed to explain the different styrene yield and the existence of heavy species. Based on the current results, recommendations for the pyrolysis temperature, initial reactants loading, and condenser temperature and analysis strategies were provided for further study of the molten salt pyrolysis of polystyrene.