An investigation has been made of the pyrolysis of n-pentane, isopentane and neo-pentane in a static system at temperatures near 500°C. Both uninhibited and inhibited reactions were investigated. Of principal concern has been the effect of variation of initial pressure of hydrocarbon on the decomposition products for the uninhibited reaction. The effect of variation in surface-to-volume ratio on rates and on the distribution of the products has been also a point of concern. Structural effects on rates as well as the variation of energy of activation and frequency factors with pressure have been considered of importance. Investigations of orders of reaction provide information as far as the mechanism is concerned. As a final point the most important task for the uninhibited reaction was a mechanism explaining the results obtained, and offering logical reasons for the similarities and differences between the isomeric pentanes. For the inhibited reaction the points of principal concern considered have been: the effect of nitric oxide on the product distribution; the effect of packing on both rates and products, the behavior of NO. The investigation has as a main purpose to determine whether the role of nitric oxic5e as an inhibitor involves homogeneous or heterogeneous reactions. Whether NO was consumed or not was also an important question. As a final point a mechanism is also proposed for inhibited reactions which accounts for the experimental results and attempts to give a logical explanation of the inhibition phenomenon. / Science, Faculty of / Chemistry, Department of / Graduate

The kinetics for the liquid-phase thermal decomposition of a number of 1-pyrazolines have been determined. Factors determining the relative rates of decomposition were: i) the nature of the polar substituent at the C-3 position; ii) the position and stereochemistry of alkyl substitution on positions C-4 and C-5; and iii) the polarity of the solvent employed. The pyrolysis rates were found to increase with the increasing electron-withdrawing ability of the C-3 substituent. Alkyl substitution at C-4 decreased the rate of pyrolysis relative to hydrogen at C-4 but this decrease also depended on the stereochemistry of the C-4 substituted pyrazoline. Alkyl substitution at C-5 increased the rate of pyrolysis relative to hydrogen at C-5 but the stereochemistry of substitution at C-5 had little effect on the rates. A drastic polarity increase upon going from n-butyl phthalate to formamide solvent decreased the rate of pyrolysis of 3-cyano and 3-carbomethoxy substituted 1-pyrazolones by a factor of about two. However, the rate of pyrolysis of 3-acetyl substituted 1-pyrazolines was increased by a factor of about two upon going from n-butyl phthalate to formamide solvent. These results are discussed in relation to the current views on pyrazoline pyrolysis. Deuterium substitution at the C-5 position was found to decrease the pyrolysis rate due to a secondary deuterium kinetic isotope effect. A comparison of the magnitudes of these effects with those found for similar systems indicated that there is considerable breakage of the C (5)-N bond in the transition states for pyrolysis in both n-butyl phthalate and formamide solvents. Deuterium substitution at C-5 had very little effect on the product distribution. A pyrazoline with deuterium at the C-4 position was prepared, 3-mothyl-: 3-carbomethoxy- 1-pyrazolone-4, 4-d₂, The product distribution, compared to the natural compound, showed that olefin formation was decreased due to the deuterium substitution. The kinetic isotope effect on the rate of pyrolysis was found to be 1. 36 in n-butylphthalate solvent. It has been previously suggested that there may be separate transition states for olefin and cyclopropane formation. Calculations using the above isotope effect and the product distributions for the deuterated and natural pyrazoline gave a value of 1. 94 for the deuterium isotope effect on the olefin-forming reaction. This supports a mechanism for olefin formation where the migration of a C-4 hydrogen to the C-5 position is concerted with breakage of the carbon-nitrogen bond. In formamide solvent, however, the kinetic isotope effect was found to be only 1. 06. This was taken as an indication that C (4)-H bond breakage was not advanced in the transition state for pyrazoline pyrolysis in this polar solvent. However, the effect of deuterium substitution on the product distribution suggests that a nitrogen-free intermediate is formed in the rate-determining step. The deuterium isotope effect on the olefin forming step, largely primary, was estimated to be 2.2. The synthesis and decomposition products of a new pyrazoline, 3, 5, 5, -trimethyl-3-acetyl-1-pyrazoline, are described. The preparations of the deuterated pyrazolones are described and their nuclear magnetic resonance spectra arc discussed in detail. / Science, Faculty of / Chemistry, Department of / Graduate

The geometric stereoisomers of 3-carbomethoxy-3-methyl-4-bromo-1-pyrazoline have been prepared. Both compounds have been found to be highly unstable and are transformed readily into the hydrobromide salt of 3-methyl-4-carbomethoxypyrazole. This transformation requires preferential migration of a carbomethoxy group over a methyl group. A stepwise mechanism is proposed for this rearranagement. Pyrolysis of 3-carbomethoxy-3-cyano-4-methyl-4-aryl-1-pyrazoline, (Z)-and (E)- gives predominantly the olefin expected for concerted migration with elimination of nitrogen. The transition state is described by a structure in which there is no bond breaking of C(5)-N bond. This mechanism is supported by (i) the lack of a C(5) secondary ⍺-deuterium kinetic isotope effect, (ii) the negative value of the entropy of activation, and (iii) the migratory aptitudes between various substituted aryl groups. The possibility of a short-lived intermediate is not completely ruled out. However, the lack of a large effect of solvent polarity on the rate of reaction and the stereospecificity of the reaction suggest the intermediate of the pyrazoline pyrolysis cannot be a zwitterion with free rotation about the C(3)-C(4) bond. / Science, Faculty of / Chemistry, Department of / Graduate

A series of tetrasubstituted 1-pyrazolines uniquely substituted at all three carbon centers has been prepared and decomposed thermally. The 1-pyrazolines in which three of the substituents occupy a pseudo equatorial position and the remaining substituent occupies a pseudo axial position give as the major product the cyclopropane with retention of configuration. On the other hand,the 1-pyrazolines in which two substituents are pseudo equatorial and two are pseudo axial give a random distribution of cyclopropanes. Evidence is presented that the former set of pyrazolines have a larger degree of folding between the two planes defined by C-3, C-4, C-5 and C-5, N-1, N-2, C-3. This suggests that the larger the degree of folding in the pyrazoline molecule the more stereospecificity there is. Two mechanisms are proposed to account for the cyclopropane formed with retention of configuration - one involving a concerted mechanism and the other involving an intermediate resembling a pyramidal diradical. In the case of one pair of C-5 isomeric pyrazolines, the pyrazoline in which three substituents are pseudo equatorial and one is pseudo axial gave 99% cyclopropane products whereas the C-5 isomer in which there are two substituents both equatorial and axial gave 67% olefin products. This supports the mechanism involving concerted migration of the hydrogen at C-4 that is trans to the leaving nitrogen. / Science, Faculty of / Chemistry, Department of / Graduate

Pyrolysis of biomass is the thermochemical conversion process whereby the long lignocellulosic polymers in biomass are cracked into several higher-value products such as bio-oil, bio-char and combustible non-condensable gases (NCG). Fast pyrolysis in particular is aimed at maximising the yield of crude liquid bio-oil, with the production of bio-char and NCG as co-products. Since a large quantity of under-utilised biomass is produced in the forestry sector annually, as by-product from harvesting, this sector has shown particular interest in this process. Furthermore, the continuing drive for renewable and sustainable energy production, particularly of drop-in liquid biofuels, has urged the development of such technology on a commercial scale. The main purpose of this investigation was to evaluate the technical feasibility and performance of the scalable dual fluidised bed (DFB) reactor system designed and constructed at the University of Pretoria by Swart in 2012. The sub-objectives of this study were as follows: • Biomass pre-treatment equipment was implemented to ensure that the physical characteristics of the biomass feedstock meet the pyrolysis process requirements. • The scalable DFB reactor system, including all sub-systems and ancillary equipment, was commissioned to ensure satisfactory operation of the complete system. • Continuous, steady-state experimental runs were conducted to produce fast pyrolysis products in the scalable DFB reactor system. • The fast pyrolysis products were quantified and characterised to evaluate the technical feasibility of the DFB reactor system. • A material and energy balance was conducted over the pyrolysis fluidised bed (PFB) reactor to quantify its performance. Eucalyptus grandis raw material, as received from Sappi Southern Africa’s Ngodwana mill, was successfully converted to bio-oil, bio-char and NCG in the scalable DFB reactor system. Fast pyrolysis was conducted at a pyrolysis temperature of 500 °C, a vapour residence time of 4 s and a sawdust feed rate of 2.0 kg/h. The PFB reactor temperature could be controlled easily, at the desired setpoint (500 °C), by continuously circulating hot solids between the two bubbling fluidised beds. The excellent temperature control of the PFB reactor makes the DFB system a suitable reactor system for the fast pyrolysis of biomass on a commercial scale. At these PFB reactor conditions the yield of fast pyrolysis products, on a dry feedstock basis, was determined as 36.3, 14.0 and 49.7 weight % for bio-oil, NCG and bio-char respectively. High-value process heat, in the form of hot flue gas (450–500 °C), was produced in the combustion fluidised bed Although the crude liquid bio-oil contained highly oxygenated compounds (including organic acids, water, alcohols, esters, sugars, aldehydes, ketones, furans, pyrans and phenolics) it may be utilised for heat generation when co-fired with conventional fossil fuels, including heavy furnace oil. However, the scalable DFB reactor system allows for integrated catalytic fast pyrolysis, which would enable catalytic cracking of the biomass feedstock, and the subsequent pyrolysis vapours, to selectively produce deoxygenated bio-oil compounds, compatible with conventional refinery streams. The DFB reactor system allowed easy separation of bio-char from the pyrolysis vapours by means of the bio-char cyclone. The bio-char had a high heating value of only 17.0 MJ/kg because of an unexpectedly high inorganic content of 54.4 weight % on a dry basis. However, 77.0 weight % of the inorganics were identified as entrained silica sand fines. Notwithstanding the entrained silica fines, the bio-char carbon content was determined as approximately 55 weight % on a dry basis, which would result in a high heating value of approximately 29 MJ/kg. Combustible NCG (including carbon monoxide, methane, ethane, ethylene, acetylene and propene) were produced as co-product from the fast pyrolysis of E. grandis sawdust in the DFB reactor system. The high heating value of the NCG was estimated at 7.3 MJ/kg or 8.3 MJ/Nm3 . Furthermore, it was demonstrated that both the solid bio-char residue and NCG could be combusted in the CFB reactor to supplement its energy demand. At the sawdust feed rate of 2 000 g/h and silica sand circulation rate of 50 kg/h, the production rate of pyrolysis products was estimated at 687.8, 265.2 and 940.0 g/h for bio-oil, NCG and bio-char respectively. However, only 13.0 g/h of bio-char was collected from the bio-char cyclone, with the balance (i.e. 927.0 g/h) understood to have been transferred to the CFB with the silica sand heat carrier. The recycle rate of the NCG was determined as 7 689.7 g/h. The total energy input from the feedstock and recycled NCG was determined as 150 W, while the energy supplied to the PFB by means of the hot silica sand was determined as 3 889 W. The pyrolysis reaction energy demand, at the feed rate of 2 000 g/h, was determined as 1 000 W. The pyrolysis reactor freeboard temperature was found to be much lower than the fluidised bed temperature (± 195 °C vs. ± 500 °C) as a result of heat loss. Therefore, the energy output from the pyrolysis products was determined as only 344 W. The overall heat loss from the PFB reactor was estimated at a very high 2 696 W, which implies that approximately 69% of the total energy supplied to this reactor by means of the hot silica sand was dissipated to the surrounding atmosphere. From a heat loss evaluation, it was concluded that the biomass throughput could be increased by as much as five to ten times by mitigating the heat loss. / Dissertation (MEng)--University of Pretoria, 2015. / Chemical Engineering / MEng / Unrestricted

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In order to meet growing demands for alternatives to fossil fuels, biomass pyrolysis is a method that has been explored in depth as a method to develop new liquid fuels. Fast pyrolysis is a subtype of pyrolysis reaction in which a specimen is heated at rates in excess of 10C/s in an oxygen-free environment, causing the specimen to thermally degrade and release a volatile bio-oil. The goal of this thesis is to design and commission a novel reactor for the continuous isothermal fast pyrolysis of ground biomass. The reactor design utilizes a vibrating plate heated to a set pyrolysis temperature. Analytical and empirically-derived vibratory transport models are presented for ground Pinus taeda (loblolly pine) to assist in setting the desired pyrolysis reaction time. A condenser system was designed to rapidly evacuate and chill the volatiles to prevent tar formation and secondary reactions. Commissioning tests were run at a pair of temperatures and biomass residence times to determine the degree of agreement between the reactor yields and two-component volatile formation data derived from batch fast pyrolysis of Pinus taeda.

Due to the migration of scientists towards green chemistry, landfilling and incineration will no longer be acceptable options for plastics waste disposal in the future. Consequently new methods for recycling plastics and plastic products such as carpets are being researched. This study serves as a preliminary effort to study the catalytic feedstock recycling of polyolefins, specifically PP and PE, as source for gasoline range fuels, as well as an alternative for plastic waste disposal. Several studies have been conducted on the pyrolysis of waste polyolefins using commercial cracking catalysts (FCC), however, the effect of catalyst size and mode of catalyst dispersion have been studied sparsely. This thesis proposes to study these effects in the catalytic pyrolysis of polypropylene (PP), a component of carpets, using both fresh and used FCC catalysts. The same study will be applied to polyethylene (PE), which accounts for an enormous amount of municipal solid waste in the US today. Furthermore, the catalytic impact of calcium carbonate, a filler component of tufted carpet, will be investigated. Using thermogravimetric analysis, the global kinetics of the PP pyrolysis using various FCC catalysts will be derived and applied in the modeling of the pyrolysis reaction in a twin screw extruder. Furthermore, an economic analysis on the catalytic pyrolysis of PP is presented.

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Chapter one provides a brief history and current state of knowledge of the chemistry of organosilicon reactive intermediates relevant to this thesis. Chapter two outlines the experimental techniques used in the majority of work carried out in this thesis. Chapter three describes an experimental investigation of the pyrolysis of 4-dimethylsilylbut-l-ene and 5-dimethylsilylpent-l-ene, with and without excess methylchloride as a silyl radical trap. The results of computer modelling of the pyrolysis of 4-dimethylsilylbut-1-ene with excess methylchloride are described, in which information concerning the isomerisation of an alpha-silyl radical to a silyl radical via a hydrogen shift is obtained. Chapter four describes the results of an experimental investigation of the reactions of dimethylsilene and dimethylsilylene with anions. Chapters five and six contain the results of computer modelling of three related pyrolysis mechanisms composed of complex series of unimolecular rearrangements of silylenes, silenes, disilenes and disilacyclopropanes. Chapter seven describes an experimental determination of Arrhenius parameters for the trapping of dimethylsilene by butadiene, together with the results of pyrolysis of butadiene adducts of methylsilene, dimethylsilene and dimethylsilylene. Chapter eight is an experimental investigation of the pyrolysis of cis and trans dimethy1(1-propenyl)vinylsilane with excess 2,3-dimethylbutadiene as a silylene trap. Interpretation of the results as a cis-trans isomerisation and decomposition of the cis isomer via a silacyclopropane intermediate are reinforced by the results of computer modelling of both systems. Chapter nine describes an experimental investigation of the pyrolysis of 1, 2-dimethyldisilane with and without butadiene as a silylene trap. Computer modelling of the pyrolysis with the absence of butadiene is used to clarify the pyrolysis mechanism. Chapter ten is an experimental investigation of the pyrolysis of silacyclobutane and methylsilacyclobutane with excess butadiene to trap silylene intermediates and thus suppress secondary decomposition. Arrhenius parameters for the primary decomposition pathways are determined.