Plastics play an enormous role in modern manufacturing, but the extraction and refining of raw materials, followed by the synthesis of plastics themselves, represents an enormous energy investment into a product that is all too often simply “thrown away” into a landfill after a single use. Microwave-assisted pyrolysis is a recycling technique that allows the recovery of chemical value from plastic waste by breaking down polymers into useful smaller hydrocarbons using microwave heat in the absence of oxygen. This dissertation examines the use of a catalytic activated carbon bed in this procedure, using high density polyethylene (HDPE) as a model plastic. Initial tests with the batch input of HDPE produced a condensed pyrolysis oil comprising 35.5–45.3% aromatics, with the remainder primarily short-chain aliphatics. This oil was approximately three times lighter than that produced in the absence of catalyst, with a narrower range of molecular masses that matched those of the liquid transport fuels petrol and diesel (C5–C21). The non-condensable gases that resulted were short-chain aliphatics that could be used as feedstock for the creation of new chemicals (such as virgin HDPE), or fuels such as natural gas and LPG. The development of apparatus capable of adding sample in a continuous fashion enabled the processing of larger quantities of HDPE, and resulted in condensed products with a significantly higher aromatic content (>80% at 450°C), and which encompassed a somewhat narrower range of molecular masses compared with those produced in the batch mode; this was due to differences in kinetics and residence time that resulted from the different modes of sample introduction. As a result of processing larger quantities of HDPE it became apparent that the activated carbon deactivated over time, with a bed able to process around 3.5 times its mass in HDPE at 450°C before any significant changes in output products occurred. The decomposition of HDPE proceeds via thermal scission and radical-mediated mechanisms; high energy surface active sites facilitate the transfer of hydrogen and radicals, and this enhances overall cracking and lowers the activation energy for the formation of aromatics. Analysis of material deposited on the surface of the activated carbon confirmed that deactivation occurred through coking, with both cracking and deactivation thought to be enhanced by the formation of microwave-induced microplasmas. Overall, the microwave-assisted pyrolysis of HDPE using activated carbon produces a much narrower range of more valuable products compared with non-catalytic processing. While the process is not likely to be economic in its current form owing to the relatively rapid deactivation of the activated carbon, future configurations incorporating online reactivation may be able to economically provide a second use cycle for these materials, avoiding expending energy to extract and process increasingly scarce new raw material from the surface of the earth.

The products arising from the liquid-phase pyrolyses of 3,5-dimethyl-3-carbomethoxy-1-pyrazoline and 4,5-dimethyl-3-carbomethoxy-2- pyrazoline have been isolated and identified. The pyrolysis of 3,5-dimethyl-3-carbomethoxy-1-pyrazoline has been found to yield a mixture of 5 isomers consisting of 15% methyl trans-2-methyl-2-pentenoate, 10% methyl cis-2-methyl-2-pentenoate, 3% methyl trans-2-methyl-3-pentenoate. 45% methyl cis-1,2-dimethylcyclopropane-1-carboxylate and 27% methyl trans-1,2-dimethylcyclopropane-1-carboxylate. The pyrolysis of 4,5-dimethyl-3-carbomethoxy-2-pyrazoline yielded a mixture of 7 isomers consisting of 25.5% methyl trans-3-methy1-2-pentenoate, 26% methyl cis-3-methyl-2-pentenoate, 3% methyl trans-3-methyl-3-pentenoate, 2% methyl cis-3-methyl-3-pentenoate, 26% methyl trans-1,2-dimethylcyclo-propane-3-carboxylate, 16% methyl cis-1,2-dimethylcyclopropane-3-trans-carboxylate and 0.8% methyl 3-ethyl-3-butenoate. Pyrolysis of both pyrazolines has also been obtained in the vapour-phase and under these conditions a higher proportion of cyclopropanecarboxylic esters was formed than that obtained in the liquid-phase pyrolysis: 3,5-dimethyl-3-carbo-methoxy-1-pyrazoline yielded a mixture containing 94.5% cyclopropane carboxylic esters and 4,5-dimethyl-3-carbomethoxy-2-pyrazoline yields a mixture containing 67% of cyclopropane carboxylic esters. The vapour-phase pyrolysis of the 1-pyrazoline occurred readily at 200° whereas the vapour-phase pyrolysis of the 2-pyrazoline was found to require a catalyst. This catalyst is believed to facilitate the transformation of the 2-pyrazoline to the readily pyrolisable 1-pyrazoline form. Studies have been made of the equilibration of the unsaturated, esters arising from the pyrolysis of the pyrazolines and have shown that the composition of the olefin portion of the pyrolysis mixture in general is not an equilibrium mixture. A mechanism for the pyrolysis is suggested. The unsaturated esters arising from the pyrolysis of 4,5-dimethyl-3-carbomethoxy-2-pyrazoline have been synthesised and identified and structural assignments have been made. / Science, Faculty of / Chemistry, Department of / Graduate

This thesis presents a comparison analysis between various pyrolysis techniques performed on kraft lignin. Numerous literature studies of pyrolysis techniques performed on kraft lignin are reviewed and analysed where different operation temperatures, catalysts and different heating methods are used to pyrolyze kraft lignin. Based on the collected data from the reviewed literature, calculations are performed to determine energy efficiency of each pyrolysis technique. The energy efficiencies are used to establish a comparison between various pyrolysis techniques. Energy efficiencies of all pyrolysis techniques are determined by using series of equations. Dissimilarities of products composition are investigated between various pyrolysis techniques. Environmental impacts caused by lignin pyrolysis are reviewed and discussed. Uses of products produced from lignin pyrolysis are discussed to highlight the potential of using lignin as an energy resource to produce biooil, biochar and non-condensable gases (NCG). Results show that energy efficiencies differ significantly between various pyrolysis techniques, where microwave-assisted pyrolysis (MAP) shows the highest energy efficiency. Products produced from pyrolysis show a wide range of uses in many industrial applications. Lignin based products have the potential to replace many petroleum-based products which may contribute significantly to decrease pollutants in nature and gas emissions caused by combusting fossil fuels.

The study of the ignition of wood and other cellulosic materials has resulted in the publication of a large amount of literature. As an aid in the planning and interpretation of future research, it was felt that a survey of a representative body of literature should be made. With this as its motivation, the present work was initiated.

Bio-oil is produced by the rapid pyrolysis of biomass and is a source of renewable fuel. The increase in viscosity during storage is a major problem that can be controlled by the addition of methanol or other alcohols. The objective of this research was to determine how alcohols stabilize bio-oil by investigating the reactions of alcohols with low molecular weight aldehydes and acids. The reaction of methanol with hydroxyacetaldehyde (HA) and acetic acid to form the respective acetal or ester was catalyzed by the 7 x 10-4 M strong acids such as sulfuric, hydrochloric, p-toluene sulfonic acid, and methylsulfonic acid. HA formed 2,2-dimethoxyethanol (DME) and AT 60°C, equilibrium was reached in less than one hour. Smaller amounts of DME were formed in the absence of strong acid. HA, acetaldehyde, and propanal formed their corresponding acetals when reacted with methanol, ethanol, 1-propanol or 1-butanol. Esters of acetic acid and hydroxyacetic acid were observed from reactions with these same four alcohols. Other acetals and esters were observed by GC/MS analysis of the reaction products. The results from accelerated aging experiments at 90°C suggest that the presence of methanol slows polymerization by formation of acetals and esters from low molecular weight aldehydes and organic acids. The other objective of this study was to improve the bio-oil quality as fuel in a single step by adding methanol to the pyrolysis gases. Therefore, a methanol/sulphuric acid mixture was injected into the pyrolysis vapor zone prior to the water cooled condensers of the auger reactor. The chemical and physical properties of bio-oils were determined and the results of these tests were compared with the results of tests with raw bio-oils. The amount of methanol injection varied from 1 to 20 wt % with and without catalysts. The results showed that the addition of 10% methanol was required for stability with the accelerated aging test. The bio-oil viscosity was reduced to 11.7 cSt from 15.45 cSt with the 10% methanol addition and after 5 days of ageing at 90°C the viscosity only increased by 17% whereas raw bio-oil turned into a highly viscous phase separated material. GC/MS analysis indicated the formation of the esters and quantified the amount of methanol present in the bio-oil after the reaction. The acid value was 87 compared to 99.8 for raw bio-oil. The lower acid value of the esterified bio-oil supports the hypothesis that the formation of esters lowered the amount of free acids present. The flash point of the bio-oil was improved to 37°C and it burned intensely in the waste oil burner. A Principal component analysis supported these findings by indicating that the esterified bio-oil properties differed significantly from the raw bio-oil.

No description available.

No description available.

In the search for fossil fuel alternatives the production of bio-oil through the pyrolysis of biomass is one method which has shown evidence of scalability, meaning that the technology could be scaled up for the processing of biomass on the order of tons per day. Pyrolysis is the thermal degradation of compounds in the absence of oxygen. Of particular interest is the pyrolysis of sustainable energy crops such as Loblolly pine (Pinus taeda). The goal of this study is to develop a new method of characterizing the fast pyrolysis of biomass for the advancement of reactor design. The objectives are to determine bulk kinetic coefficients for the isothermal fast pyrolysis of biomass, evaluate the interchangeability of fast and slow pyrolysis kinetic parameters and compare generally accepted pyrolysis mechanisms derived from a common data set. A technical objective is to apply the most suitable derived kinetic parameters to model pyrolysis within a moving bed reactor. A novel fast pyrolysis micro-reactor is presented along with its design and development process. The micro-reactor allows for the control over both temperature and residence time of the reacting biomass. This system provides the experimental data for the characterization of biomass pyrolysis kinetic parameters. Thermal validation tests are presented and experimental yield results are given for raw Loblolly Pine, Avicel cellulose and Beechwood xylan for the derivation of kinetic descriptors. Cellulose and xylan results show good agreement with literature when the proper experimental conditions are met and whole wood pyrolysis results clearly demonstrate the dissimilarity between fast and slow pyrolysis apparent kinetic rates. The experimental results are then used to evaluate five different pyrolysis kinetic model configurations: single component global pyrolysis, two component global pyrolysis, product based pyrolysis, pseudo-component based pyrolysis and pseudo-component pyrolysis with an intermediate solid compound. Pseudo-component models are of particular interest because they may provide a generalized model, parameterized by the fractional composition of cellulose, hemicellulose and lignin in biomass species. Lignin pyrolysis yields are calculated to evaluate the suitability of a pseudo-component parallel non-competing superposition pyrolysis model. Lignin yields are estimated by taking the difference between whole wood pyrolysis and predicted cellulose and hemicellulose pyrolysis behaviors. The five models are then evaluated by comparison of predicted yields to the results for the pyrolysis of Scots pine (Pinus sylvestris) and Norway spruce (Picea abies). Model evaluations show that pseudo-component superposition is not suitable as a generic pyrolysis model for the fast pyrolysis of biomass observed using the micro-reactor. Further analytical evaluations indicate that the assumption of parallel non-competing reactions between pseudo-components is not valid. Among the other models investigated the intermediate solid compound model showed the best fit to the verification experimentation results followed closely by the two component global model. Finally, the derived kinetic parameters are applied to the design of moving bed vacuum pyrolysis reactors which provide for the separation of heat and mass transfer pathways, resulting in the reduction of char entrainment and secondary reactions within collected bio-oils. Reaction kinetics and porous bed heat and mass transfer are accounted for within the bed model. Model development and predictive results are presented and sensitivity to activation energy variations investigated.

The diploma thesis is focused on the energy utilization of sewage sludge before and after microwave pyrolysis process. The first part of the thesis deals with sludge management, treatment of sludge and its subsequent use or disposal. In the second part of the thesis prepared and modified samples of sludge from WWTP 1 and WWTP 2 are subjected to microwave pyrolysis process. Subsequently, samples are taken for analyzes to determine the total organic carbon, the specific surface area, the heavy metal content and the calorific values. The resulting data was processed in Microsoft Office Excel and presented at work. At the end of the thesis two case studies are then proposed for a specific design of the conceptual location of microwave pyrolysis for the sludge drying process and the drying process of the sewage sludge in the direct combustion boiler room.

The plasticity of coal during pyrolysis is of significant importance, since it affects the reactivity, porosity, particle size and the density of the char and thus also the behaviour of the char during further utilisation processes. The main focus of this study was to characterize the chemical and physical changes which the thermally treated coal undergoes, in order to better understand the pyrolysis process of caking and non-caking South African coals. The pyrolysis behaviour of three South African coals with different caking indices was investigated. The coal samples included; (1) Highveld (TWD), a medium rank C coal with a free swelling index (FSI) of 0, (2) Grootegeluk (GG), also a medium rank C coal, with a FSI of 6.5, and (3) Tshikondeni (TSH), a medium rank B coal with the highest FSI of 9. The three coal samples were classified as vitrinite-rich coals consisting of mainly aliphatic structures. Thermogravimetric experiments were used to determine the different temperatures relating to specific percentages of mass loss using set conditions. The pyrolysis process was stopped at various percentages of mass loss (thus at various stages of the reactions) to characterize the chemical structural changes that occurred at the specific mass loss percentages. The results obtained from characterization analyses indicated that the three coals differ in chemical composition and thus were expected to behave differently during pyrolysis. The coal samples consist of different amounts of macerals and minerals according to X-ray Fluorescence (XRF) and X-ray Diffraction (XRD) analyses. The Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFT) results indicated that some of the functional groups within the coal samples evolved with the increase in temperature. The highly caking coal (TSH) exhibited the highest aromaticity and ring condensation. The surface areas were determined by CO2 adsorption and an increase in surface area was observed with an increase in temperature. The surface area of the GG and TSH coal-derived char samples decreased at some stage, which is an indication of thermoplastic behaviour and subsequent swelling of the coal samples. Scanning electron microscopy (SEM) images confirm the plastic stage of caking coals at specific temperatures and volatile matter release via the multiple bubble mechanism. All these results are given and discussed extensively in this dissertation. / MSc (Chemistry), North-West University, Potchefstroom Campus, 2015