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Experiments were conducted to study the absorption reaction of hydrogen sulphide with zinc oxide forming zinc sulphide and water. The reaction is of commercial importance for the removal of hydrogen sulphide from reactor feed streams and from natural gas. Most of the experiments were performed on a commercial ICI zinc oxide-based absorbent prepared by calcination of basic zinc carbonate but a number of experiments were also performed on samples of basic zinc carbonate or of zinc oxide prepared by different treatments. The reactions were carried out in a shallow bed flow reactor containing 0.2-0.6g of absorbent at a pressure just above atmospheric and at temperatures in the range 0 to 45<SUP>0</SUP>C. Feed gases containing 0.06-0.7% v/v hydrogen sulphide and 0-0.5% v/v water in nitrogen were used. On-line gaseuos analysis was performed using a Thermal Conductivity Detector with complementary information provided by sulphur analysis and electron microprobe analysis of the discharged partially sulphided absorbent. The specific reaction rate was observed to be very high initially but to decline to a much slower pseudo-steady state (pss) rate. The pattern of this decline was found to be a function of particle size, with larger particles exhibiting slower, diffusion-limited rates in the initial period but higher pss rates than smaller particles. This latter result was attributed to an enhanced water concentration in the centre of larger particles. Microprobe analysis indicated uniform sulphiding at about 20% absorbent conversion whereas at low conversions an outer sulphided shell surrounds a central unreacted core. The conversion of the absorbent at pss (in the range 9-23%) was observed to increase with increasing partial pressures of water and of hydrogen sulphide in the feed. A marked dependence of the pss rate upon water partial pressure and a decrease in the rate with increasing temperature were observed and interpreted as indicative of an autocatalytic reaction. The role of water in facilitating solid rearrangement is consistent with the results of interrupted experiments which showed enhanced water adsorption and reaction rate after isolation. The pss rate was found to be insensitive to hydrogen sulphide concentration in the range studied. There appears to be an optimal calcination temperature of the absorbent precursor although this may not correspond with the temperature yielding maximal specific surface area. The effects of some impurities in the commercial absorbent were also investigated.

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This thesis describes the application of solid catalysis to the Flash Vacuum Pyrolysis (FVP) and Flow Pyrolysis techniques in order to develop preparative scale processes for specific transformations. The development of a dehydration protocol for the transformation of amides to the corresponding nitriles has been successfully achieved. This involves the use of commercially available molecular sieves under FVP conditions. The conditions have been optimised and extended to the analogous dehydration of oximes and utilised in the preparation of a number of aromatic, aliphatic and heteroaromatic nitriles in generally excellent yields of 59-99%. The role of the molecular sieves in the process has been extensively investigated in working towards truly catalytic conditions. Dehydrogeneration-aromatisation of hydroaromatic compounds has been studied under FVP conditions by the use of molybdenum oxide based catalysts. Again, after optimisation, the conditions have been applied to the preparation of a number of aromatic and heteroaromatic compounds. The mechanism of the reaction has been investigated by the application of the method to substrates with appropriate substitution. Because substituents are generally retained in the products formed, it suggests that the dehydrogenation mechanism does not involve discrete free radical intermediates. The so-called "anthranilate rearrangement" of 2-nitrotoluene to anthranilic acid has been investigated. Several stages of the mechanism of this process in the gas-phase have been elucidated using both Flash Vacuum Pyrolysis and Flow Pyrolysis. Various flow pyrolytic conditions have been developed in an attempt to identify and overcome the problem steps of this reaction and to work towards a preparatively useful process.

Kinetic processes involving the low-lying metastable electronically excited states of the group VI atoms, oxygen and sulphur, and diatomics, 02, S2 and SO have been investigated. Singlet molecular oxygen, 02(1Ag) was generated by the reaction of hydrogen peroxide with sodium hypochlorite and its subsequent decay monitored by the 'dimol' emission at A = 633 run. A simple experimental arrangement is described for determining the rate constants for quenching of 02(1Ag) by 02(3? g) and H20. it was shown that conditions were readily obtainable under which the decay of 02(1Ag) in the bubbles was controlled by quenching in the gas phase, and where gas-surface interactions were negligible. Singlet sulphur monoxide, SO( 1A), was produced by the reaction of 0(21 D2) atoms with OCS. The initially rapid removal of ozone in this system was accounted for by the reaction of S0(IA) with 03. Rate constants for the reactions of both SO(1A) and S0(3? ) with 03 were obtained by computer modelling. Photolysis of OCS (A > 200 nm) yields S(31D2) atoms, which react on almost every collision with carbonyl sulphide to produce singlet molecular sulphur, S2(1Ag). Both S2(1Ag) and S2(3?g ) were observed in absorption using kinetic spectroscopy. A rate constant for quenching of S2(lAg) by OCS was obtained from the formation kinetics of ground state sulphur, S2(3?g ). This process is discussed qualitatively in terms of electronic to vibrational energy transfer. Photolysis of 03,(Au.v. < 310 nm) was employed as a source of O(21D2)atoms. The primary and secondary reactions which follow ozone photolysis were investigated. Ozone was monitored by kinetic absorption spectrophotometry at A = 253.7 mm. Computer modelling studies were carried out and these provided a better understanding of the processes involved, and in particular, with regard to the reaction of 0(21D2) atoms with ozone. The reactions of 0(21 D2) atoms with several chlorofluoromethanes in the presence of ozone were studied. Schemes are presented to account for the observed removal of ozone obtained for CF3C1 and CF 2C12.

The application of zoelites as catalysts for a number of organic, liquid-phase, acid-promoted reactions is discussed with reference to zeolite acidity and structure on product yield and selectivity. The zeolites described are predominantly high silica materials including Nu-2, ZSM-5, Nu-10 and EU-1 structures. Examination of the Claisen rearrangement of allyl phenyl ether has shown that it is promoted by zeolites relative to the thermal reaction and that the extent of conversion increases with zeolite acidity. In addition to the expected products, 2-allylphenol and the cyclic 2-methyldihydrobenzofuran, small quantities of the <i>para</i>-product, 4-allylphenol are detected over H-Nu-2 and (Cu(II),H)-Y zeolites. 4-Allylphenol is not detected in the thermal rearrangement and its formation in the present work is attributed to an intermolecular mechanism <i>via</i> ether cleavage. Also examined is the Fries rearrangement of phenyl acetate and phenyl benzoate. The product selectivity is compared with that over Nafion-H, an acidic, non-porous, perfluorinated ion-exchange resin. Both rearrangements are more <i>para</i>-selective when performed in the presence of zeolites. In the rearrangement of phenyl acetate a number of by-products in addition to the expected 2- and 4-hydroxyacetophenones are observed. The aldol self-condensation of acetophenone to yield β-methylchalcone and of acetophenone and benzaldehyde to yield chalcone is promoted by H-Nu-2 zeolite. The ring closure of 2-benzoylbenzoic acid to anthraquinone takes place quantitatively over H-Nu-2. The cyclisation is monitored by i.r. to completion and the product isolated by extraction or sublimation. Of those zeolites examined, H-Nu-2 is likely to be most widely applicable as a catalyst in organic synthesis because of its relatively large pore dimensions, high silica content (thermal stability) and high acidity.

The problem of liquid evaporating/condensing from/to its surface is of importance in a wide variety of engineering applications. These can be classified into naturally occurring processes and those that came out of technological advancement. Of the naturally occurring processes the important problems are loss of water due to evaporation in dams, evaporation from moist material to dry it, condensation in droplets required for cloud formation etc. The processes which became important due to technological advancement are evaporation in freeze drying processes, evaporation and condensation required to produce thin films using vacuum coating techniques, drying processes required at ordinary temperatures and pressure to prevent chemical degradation at high temperature and the evaporation process which produce the cooling effect in evaporative cooling towers. The problem in which continuum concepts are valid are analysed using the Fick's Diffusion model. It involves the experimental determination of the diffusion coefficient in each case. Cases where evaporation took place under free molecular regime could not be analysed using the Fick's model. In the present study a Kinetic Theory approach is made to analyse the problem. The analysis is made in two stages. In the first stage, the evaporation from a free liquid surface to its own vapour is studied. In the second stage the study is extended to the case where noncondensable gas is also present along with the vapour. The analysis is carried out using the Boltzmann transport equation. The collision terms in the equation are obtained using the model suggested by Bhatnagar Gross and Krook and now known as the BGK equation. The numerical schemes are developed for both the cases and solutions are obtained for the net rate of evaporation. The distribution of temperature, pressure and molecular number density are also plotted for the region close to the interface. The evaporation coefficient introduced in the theoretical model is obtained by comparison with experimental data. Experiments are conducted with water as the fluid and nitrogen as the inert gas. The correlations are made and the results are presented. The evaporation coefficient was found to be in the range 0.0005 to 0.0007 for the single component case and for the twocomponent case it is found to be in the range 0.0009 to 0.00135. These values can be used for engineering design applications

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