This thesis examines two important physical phenomena that occur when solid fuels are exposed to external radiative heating: (1) the pyrolysis process in reaching ignition conditions and (2) the natural convection around one or more radiatively heated fuel samples. A vegetation fire (bushfire, wildfire, or forest fire) preheating the vegetation which is in its path is a particular example which occurs in nature. However there are many more applications where modelling the pyrolysis process and/or the natural convection is of practical use. For the pyrolysis phenomena, a one-dimensional time dependent pyrolysis model is proposed. The mathematical model is solved numerically and results are used to analyse the influence of the size of a wood-based fuel sample, the heating rate it is exposed to, and its initial moisture content in the process of the sample reaching the conditions where it can produce enough pyrolysate vapour to support a flame (flash point). In many pyrolysis models in the open literature it is assumed that the fuel samples are dry. In the present study it is found that the initial moisture content has a marked effect for a fuel sample reaching its flash point. For the convection phenomena, a two-dimensional steady model, which explores the natural convection around one or more solid fuels, is also presented. The flame front is represented by a radiating panel. This means that the solid fuels receive a non-uniform heating rate depending on their geometry and location in relation to the panel. Changes in temperature and velocity profiles are monitored for varying heating rates and sample sizes (or, equivalently, the Rayleigh number Ra). Additionally, in the case of multiple fuel samples, changes in the distance between the fuels is also taken into account. For multiple fuels in arbitrary locations it is possible that one sample will block some of the radiation from the panel from reaching another sample. This means that the fuel sample will receive a reduced heating rate. This reduction in heating is also incorporated in the natural convection model. Both the pyrolysis and natural convection models are solved numerically using the finite element software package COMSOL Multiphysics. A comparison of COMSOL is performed with benchmark solutions provided by the open literature. A good agreement in the numerical results is observed.

Pyrolysis of a New Brunswick oil shale has been studied in a 12.8cm diameter spouted bed reactor. The aim of the project was to study the effect of pyrolysis temperature, shale particle size, feed rate and bed material on oil yield. Gas and spent shale yields were also determined. Shale of different particle size ranging from 0.5mm to 4mm was studied using an electrically heated reactor containing sand or spent shale which was spouted with nitrogen or nitrogen/carbon dioxide mixtures. For a given particle size and feed rate, there is a maximum in oil yield with temperature. For particles of 1-2mm at a feed rate of about 1.4kg/hr, the optimum temperature is at 475°C with an oil yield of 7.1% which represents 89.3% of the modified Fischer Assay yield. For the 2-4mm and the same feed rate, the optimum temperature is 505°C with an oil yield equal to 7.4% which is 94.3% of the modified Fischer Assay value. At a fixed temperature of about 500°C, the oil yield increases with increasing particle size. This trend is in agreement with the Fischer Assay values which showed oil yields increasing from 5.2% to about 8% as the particle size was increased. In the spouted bed, the oil yield decreases as the oil shale feed rate increases at a given temperature. The use of spent shales as the spouting solids in the bed also has a negative effect on oil yield. The gas yields which were low (less than 2.1%) and difficult to measure do not seem to be affected by particle sizes, feed rate and bed material. Hydrogen, methane and other hydrocarbons are produced in very small amounts. C0₂ and CO are not released in measurable yield in the experiments. The trend of the spent shale yield has not been successfully understood due to the unreliability of the particle collection results. Attrition of the spent shale appears to be a serious problem. Results of the experiments are rationalized with the aid of a kinetic model in which the kerogen in the oil shale decomposes to yield a bitumen and other by products and the bitumen undergoes further decomposition into oil. The spouted bed is treated as a backmixed reactor with respect to the solids. A heat transfer model is used to predict the temperature rise of the shale entering the pyrolyzer. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

Coal pyrolysis has been studied in a 12.8 cm diameter continuous spouted bed reactor with the aim of determining conditions for maximum liquid yields from Western Canadian coals. Coals studied included two British Columbia bituminous coals and one Alberta sub-bituminous coal. The basic characteristics of the spouted bed pyrolyzer were determined by carrying out experiments over a range of spouting gas velocities and composition, coal feed rates and particle size, reactor temperatures, and bed heights. The process was assessed by measuring the yields and compositions of the tar, char, and gas. Nitrogen and nitrogen/carbon dioxide mixtures and coal of size - 3.36 + 1.19 mm were fed at atmospheric pressure to an electrically heated reactor containing sand. The tar yield was determined by sampling the outlet gas through a series of cooled impingers. The spouted bed pyrolyzer behaves in a manner similar to a fluidized bed unit, and shows a maximum tar yield with temperature at a fixed feed rate. At a given pyrolyzer temperature, the tar yield was inversely proportional to the coal feed rate over the range 0.4 to 7.6 kg/h. This effect is attributed to the detrimental effect on tar yield of the increasing amounts of char present in the reactor as coal feed rate increases. Coal type strongly influenced the liquid yields as expected. Sukunka bituminous coal from the Peace River coal field gave a maximum tar yield at 600°C of 31% wt/wt MAF coal. The corresponding gas yield was 3.6%, and the char yield was 64%. The maximum tar yield from Balmer bituminous coal from Crowsnest coal field was 19.4% wt/wt MAF coal at 580°C while that from a high-ash Balmer bituminous coal was 12.1% at 620°C. Forestburg sub-bituminous coal from the Edmonton formation gave a maximum tar yield of 21% at 530°C and significantly higher gas yields of 20% versus 6% for the bituminous coals due to higher C02 production. With Sukunka coal, a steady increase in tar yield from 20.4 to 26.7% wt/wt MAF coal at 580°C was found as the average coal particle size was reduced from 2.28 to 0.65 mm. No significant effects on tar yield were found for variations in spouted bed depth, or vapour residence time over the range 0.68 -1.15 s. No serious problems were encountered with agglomeration. Composition of gas, tar and char are presented for conditions of maximum tar yield for the various coals tested. The H/C atomic ratio of the tars was as high as twice that of the parent coal. Oxygen, sulphur and nitrogen together represent up to 10 wt% of the bituminous coal tars, which suggests considerable upgrading will be necessary to produce liquids of quality comparable to petroleum oils. The total volatiles yield data were well represented by a first order kinetic model. An activation energy of 4.71 kcal/mole was obtained for the sub-bituminous coal while that for the bituminous coals was 14.1 kcal/mole. / Applied Science, Faculty of / Chemical and Biological Engineering, Department of / Graduate

The threat to the environment and human health posed by the emission of soot particles and their precursors during the combustion process has attracted widespread attention for some time. Generation of soot particles includes the precursor’s formation, particle nucleation, and the growth and oxidation of soot particles; these processes are experimentally and numerically studied in this dissertation. Fuel composition is one of the most important parameters in the study of the combustion emissions. In the first portion of this research, quantified soot precursors were detected in a jet stirred reactor and a flow reactor of several gasoline surrogates, which covered various fuel compositions and different MON numbers. A kinetic model was made to capture the polycyclic aromatic formations and help to clarify the chemistry behind them. Major reaction pathways were discussed, as well as the role of important intermediate species, such as acetylene, and resonantly stabilized radicals like allyl, propargyl, cyclopentadienyl, and benzyl in the formation of polycyclic aromatic hydrocarbons. In the second section, a Fourier-transform ion cyclotron resonance mass spectrometry was first used to probe the chemical constituents of soot particles. By examining the soot particle generated in the early stage of nucleation, some information about the nucleation process was gained. The aromatics in the infant soot particles were all peri-condensed, of a size and shape easily linked by Van der Waals forces to form aromatic dimers and bigger clusters under the specified flame conditions. Compositions in the mature soot particles indicated that soot particles grow through the carbonization process. As a hydrogen carrier, ammonia was considered a good additive for controlling soot formation. In the third portion of this work, chemical effects of ammonia on soot formation were studied. Ammonia can suppress soot formation by reducing the precursor’s formation. Chemical kinetic analysis revealed that C-N species generated in ethylene-ammonia flames removed carbon from participating in soot precursor formation, thereby reducing soot formation, however, high concentrations of toxic hydrogen cyanide may be formed, which warrants further investigation.

Pyrolysis oil is produced from biomass when a feedstock is rapidly heated in a non-oxidizing environment during a short residence time. While pyrolysis oil is inexpensive, major issues prevent the facile use of this oil product ‘as produced’. Principally, since the rapid condensation results in a product not in thermodynamic equilibrium, the oil components continue to react until equilibrium is reached. Understanding how and why these reactions—including polymerization—occur in pyrolysis oil is important in designing treatments to stabilize or transform pyrolysis oil before further upgrading. Physical and chemical changes in pyrolysis oils are investigated as a function of temperature and time to simulate the aging process during storage. The effects of alcohol addition on pyrolysis oil stability during high temperature treatment are investigated. The pretreatment of pyrolysis oil with low-cost alcohols is promising prior to hydrotreating or catalytic cracking.

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A better understanding of the chemistry of terphenyls production is required due to its contribution to the petrochemical industry and its usage in the production of useful raw materials. A benzene pyrolysis study was conducted with pure benzene, benzene with biphenyl and acetylene and benzene with CO2 mixed with N2 as diluent. This study aims to provide better insights into the effect of additives on terphenyls through pyrolyzing different fuels which were carried out in a jet-stirred reactor under atmospheric pressure, temperature range of 700-1250 K and residence time of 3s. The experimental data were measured by GC (gas chromatography) and plotted versus the temperature range provided four different kinetic models were simulated to compare with the experimental data of the reactants and products. Numerical analyses were conducted to gain a deep understanding of the main pathways that affect terphenyl isomers. A significant amount of soot was noticed at high temperatures (1200-1250 K) which was considered a soot area where the measurements may have affected. The addition of biphenyl and acetylene to benzene pyrolysis speeds the benzene consumption at high temperatures provided it showed a boost in m-terphenyl formation compared to pure benzene. In addition, acetylene addition increases the production of small hydrocarbons and the production of m-terphenyl was inhibited due to the change in the chemistry that acetylene follows. In the comparison of the experimental data with simulations, a good agreement was noticed for some compounds. Biphenyl addition is less sensitive toward H-abstraction reaction compared to pure benzene. Additionally, kinetic simulations of different residence times and pressures show an increase with increasing both factors and vice versa, based on the selected model. A shift in the speciation profiles was seen where the effect on reactants was noted at lower temperatures for higher residence time and pressure.

This research explores the ion chemistry and pyrolysis of a selection of formates. Alternative fuels have become increasingly popular over the past decade, one of particular interest is biofuels. Biofuels contain a variety of oxygenated compounds that are not present in traditional crude-oil fuels such as formates. Therefore, knowing the pyrolysis and ion chemistry of a selection of formates is of particular interest in being able to determine the environmental implications of switching to biofuels. The pyrolysis in particular for these formates have largely been studied using shock-tube experiments where both unimolecular and bimolecular reactions occur. This study employs the use of a micro-reactor coupled to imaging photoelectron photoion coincidence spectroscopy (iPEPICO) using synchrotron vacuum ultra-violet (VUV) radiation at the Swiss Light Source (SLS). The sample is introduced in the dilute-gas phase to optimise for unimolecular reactions. This thesis therefore presents the unimolecular pyrolysis chemistry of methyl formate, ethyl formate and methyl chloroformate and the ion chemistry of methyl chloroformate, phenyl formate and phenyl chloroformate. In chapter 3, the thermal dissociation of the atmospheric constituent methyl formate was probed by coupling pyrolysis with iPEPICO. The pyrolysis products of dilute methyl formate, CH₃OC(O)H, were elucidated to be CH₃OH⁺, CO, 2 CH₂O and CH₄ + CO₂ as in part distinct from the dissociation of the radical cation (CH₃OH⁺˙ + CO and CH₂OH⁺ + HCO). Density functional theory, CCSD(T), and CBS-QB3 calculations were used to describe the experimentally observed reaction mechanisms, and the thermal decomposition kinetics and the competition between the reaction channels are addressed in a statistical model. One result of the theoretical model is that CH₂O formation was predicted to come directly from methyl formate at temperatures below 1200 K, while above 1800 K, it is formed primarily from the thermal decomposition of methanol. Chapter 4 utilises the same techniques but expands on it by taking advantage of threshold photoionization and ion imaging, parent ions of neutral pyrolysis products and dissociative photoionization products could be distinguished, and multiple spectral carriers could be identified in several ms-TPES. The TPES and mass-selected TPES for ethyl formate are reported for the first time and appear to correspond to ionization of the lowest energy conformation having a cis configuration of the O=C(H)-O-C(H₂)-CH₃ and trans configuration of the O=C(H)-O-C(H₂)-CH₃ dihedral angles. We observed the following ethyl formate pyrolysis products: CH₃CH₂OH, CH₃CHO, C₂H₆, C₂H₄, HC(O)OH, CH₂O, CO₂, and CO, with HC(O)OH and C₂H₄ pyrolyzing further, forming CO + H₂O and C₂H₂ + H₂. The reaction paths and energetics leading to these products, together with the products of two homolytic bond cleavage reactions, CH₃CH₂O˙ + ˙CHO and CH₃CH₂˙ + HC(O)O˙, were studied computationally at the M06-2X-GD3/aug-cc-pVTZ and SVECV-f12 levels of theory, complemented by further theoretical methods for comparison. The calculated reaction pathways were used to derive Arrhenius rate parameters for each reaction. The reaction rate constants and branching ratios are discussed in terms of the residence time and suggest carbon monoxide as a competitive primary fragmentation product at high temperatures. Chapter 5 explores the pyrolysis chemistry of methyl chloroformate (MCF) in a similar manner but also introduces the study of the ion chemistry. The TPES for MCF was acquired for the first time; the geometry change upon ionization of MCF results in a broad, poorly defined TPES. Franck-Condon simulations are consistent with an ionisation energy (IE) of 10.90 ± 0.05 eV. Ionized MCF dissociated by the expected loss of Cl with a measured appearance energy (AE) of 11.30 ± 0.01 eV. Together with the above IE, this AE suggests a reaction barrier of 0.40 eV, consistent with that found from SVECV-f12 calculations (0.41 eV). At higher internal energies, the loss of CH₃O˙ becomes competitive due to its more favourable entropy of activation. Pyrolysis of neutral MCF formed the anticipated major products of CH₃Cl + CO₂ (R1) and the minor products HCl + CO + CH₂O (R2), all species being confirmed by their mass-selected TPES. Several possible reactions were computationally explored but these two were confirmed to be the dominant reaction channels. R1 proceeds by a concerted Cl atom migration via a 4-membered transition state in agreement with that proposed in the literature. R2 is a two-step reaction proceeding first by loss of HCl to make 2-oxiranone which then decomposes to CH₂O and CO. Kinetic modelling of the neutral decomposition could be made to simulate the observed reactions only if the vibrational temperature of the MCF was assumed not to cool during the expansion. Chapter 6 further expands on the ion chemistry study by exploring the ion dissociation of phenyl formate (PF) and phenyl chloroformate (PCF). Imaging photoelectron photoion coincidence (iPEPICO) spectroscopy and tandem mass spectrometry were employed to explore the ionisation and dissociative ionisation of phenyl formate (PF) and phenyl chloroformate (PCF). The threshold photoelectron spectra of both compounds are featureless and lack a definitive origin transition, owing to the internal rotation of the formate functional group relative to the benzene ring, active upon ionisation. CBS-QB3 calculations yield ionisation energies of 8.88 and 9.03 eV for PF and PCF, respectively. Ionised PF dissociates by the loss of CO via a transition state composed of a phenoxy cation and a HCO moieties. The dissociation of PCF ions involves the competing losses of CO (m/z 128/130), Cl (m/z 121), and CO₂ (m/z 112/114), with Cl loss also shown to occur from the second excited state in a non-statistical process. The primary CO- and Cl-loss fragment ions undergo sequential reactions leading to fragment ions at m/z 98 and 77. The mass-analysed ion kinetic energy (MIKE) spectrum of PCF⁺ showed that the loss of CO₂ occurs with a large reverse energy barrier, which is consistent with the computationally derived minimum energy reaction pathway. Chapter 7 highlights the conclusions drawn from across the chapters 3-6 and brings chapter 1 back into focus with how these findings can help to inform future studies on pyrolysis. Furthermore, chapter 7 discusses how future technologies for biofuels can be shaped with the understanding of the pyrolysis products of these biofuel related compounds.

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