A catalytic reactor for the trapping of free radicals from gas phase oxidation reactions

A catalytic reactor for the trapping of free radicals originating from gas phase catalytic reactions is described and discussed. Radical trapping and identification were initially carried out using a known radical generator such as dicumyl peroxide. The trapping of radicals was further demonstrated by investigating genuine radical oxidation processes, e.g., benzaldehyde oxidation over manganese and cobalt salts. The efficiency of the reactor was finally proven by the partial oxidation of cyclohexane over MoO3, Cr2O3, and WO3, which allowed the identification of all the radical intermediates responsible for the formation of the products cyclohexanol and cyclohexanone. Assignment of the trapped radicals was carried out using spin trapping technique and X -band electron paramagnetic resonance spectroscopy. © 2010 American Institute of Physics.

Gas-liquid-solid flow modelling in a bubble column

An alternative approach to the modelling of solid-liquid and gas-liquid-solid flows for a 5:1 height to width aspect ratio bubble column is presented here. A modified transport equation for the volume fraction of a dispersed phase has been developed for the investigation of turbulent buoyancy driven flows (Chem. Eng. Proc., in press). In this study, a modified transport equation has been employed for discrete phase motion considering both solid-liquid and gas-liquid-solid flows. The modelling of the three-phase flow in a bubble column was achieved in the following case: injecting a slug of solid particles into the column for 10 s at a velocity of 0.1 m s-1 and then the gas phase flow was initiated with a superficial gas velocity of 0.02 cm s-1. © 2003 Elsevier B.V. All rights reserved.

Organometallic precursors for pillared clay synthesis

The synthetic hectorite, laponite has been used within the paper industry to produce mildly conducting paper for use in electrographic printing. The aim of this research was to modify laponite in order to improve the electrical conductivity. In a continuation of a previous investigation involving organotin intercalation of laponite, the organotin precursor (p-CH3,OC6H4)4Sn was synthesised and characterised using Mass Spectroscopy, Infrared Spectroscopy and elemental analysis. Results of intercalation with this compound and a range of organobismuth and organoantimony compounds suggested that a halide content within the precursor was necessary for improvement in conductivity to be observed. Organometallic intercalation of a range of organotellurium compounds with laponite provided evidence that a hydrolysis reaction on the clay surface followed by the release of hydrochloric acid was an important first step if a reaction was to occur with the clay. Atomic Absorption Spectroscopy studies have shown that the acid protons underwent exchange with the interlayer sodium ions in the clay to varying degrees. Gas-liquid Chromatography and Infrared Spectroscopy revealed that the carbon-tellurium bond remained intact. Powder X-ray diffraction revealed that there had been no increase in the basal spacing. The a.c. conductivity of the modified clays in the form of pressed discs was studied over a frequency range of 12Hz - 100kHz using two electrode systems, silver paste and stainless steel. The a.c. conductivity consists of two components, ionic and reactive. The conductivity of laponite was increased by intercalation with organometallic compounds. The most impressive increase was gained using the organotellurium precursor (p-CH3OC6H4)2TeCl2. Conductivity investigations using the stainless steel electrode where measurements are made under pressure showed that in the case of laponite, where poor particle-particle contact exists at ambient pressure, there is a two order of magnitude increase in the measured a.c. conductivity. This significant increase was not seen in modified laponites where the particle-particle contact had already been improved upon. Investigations of the clay surface using Scanning Electron Microscopy suggested that the improvement in particle-particle contact is the largest factor in the determination of the conductivity. The other important factor is the nature and the concentration of the interlayer cations. A range of clays were synthesised in order to increase the concentration of sodium interlayer cations. A sol-gel method was employed to carry out these syntheses. A conductivity evaluation showed that increasing the concentration of the sodium cations within the clay led to an increase in the conductivity.

Chemical studies of plasma etchants used in integrated circuit manufacture

Plasma or "dry" etching is an essential process for the production of modern microelectronic circuits. However, despite intensive research, many aspects of the etch process are not fully understood. The results of studies of the plasma etching of Si and Si02 in fluorine-containing discharges, and the complementary technique of plasma polymerisation are presented in this thesis. Optical emission spectroscopy with argon actinometry was used as the principle plasma diagnostic. Statistical experimental design was used to model and compare Si and Si02 etch rates in CF4 and SF6 discharges as a function of flow, pressure and power. Etch mechanisms m both systems, including the potential reduction of Si etch rates in CF4 due to fluorocarbon polymer formation, are discussed. Si etch rates in CF4 /SF6 mixtures were successfully accounted for by the models produced. Si etch rates in CF4/C2F6 and CHF3 as a function of the addition of oxygen-containing additives (02, N20 and CO2) are shown to be consistent with a simple competition between F, 0 and CFx species for Si surface sites. For the range of conditions studied, Si02 etch rates were not dependent on F-atom concentration, but the presence of fluorine was essential in order to achieve significant etch rates. The influence of a wide range of electrode materials on the etch rate of Si and Si02 in CF4 and CF4 /02 plasmas was studied. It was found that the Si etch rate in a CF4 plasma was considerably enhanced, relative to an anodised aluminium electrode, in the presence of soda glass or sodium or potassium "doped" quartz. The effect was even more pronounced in a CF4 /02 discharge. In the latter system lead and copper electrodes also enhanced the Si etch rate. These results could not be accounted for by a corresponding rise in atomic fluorine concentration. Three possible etch enhancement mechanisms are discussed. Fluorocarbon polymer deposition was studied, both because of its relevance to etch mechanisms and its intrinsic interest, as a function of fluorocarbon source gas (CF4, C2F6, C3F8 and CHF3), process time, RF power and percentage hydrogen addition. Gas phase concentrations of F, H and CF2 were measured by optical emission spectroscopy, and the resultant polymer structure determined by X-ray photoelectron spectroscopy and infrared spectroscopy. Thermal and electrical properties were measured also. Hydrogen additions are shown to have a dominant role in determining deposition rate and polymer composition. A qualitative description of the polymer growth mechanism is presented which accounts for both changes in growth rate and structure, and leads to an empirical deposition rate model.

The Single drop drying of heat-sensitive materials

The literature relating to the principles and practice of drying of materials, particularly those susceptible to thermal degradation or undesirable loss of volatile components, has been reviewed. Single droplets of heat-sensitive materials were dried whilst suspended in a horizontal wind tunnel from a specially-designed, rotating thermocouple which enabled direct observation of drying behaviour and continuous measurement of droplet temperature as drying progressed. The effects of drying air temperature and initial solids concentration on the potency of various antibiotics, viz. ampicillin, chloramphenicol, oxytetracycline, streptomycin and tetracycline, were assessed using a modified Drug Sensitivity Testing technique. Only ampicillin was heat-sensitive at temperatures above 100°C, e.g. at an air temperature of 115°C its zone diameter was reduced from 100% to 45%. Selected enzymes, viz. dextran sucrase and invertase, were also dried and their residual activities determined by High Performance Liquid Chromatography. The residual activity of dextran sucrase was rapidly reduced at temperatures above 65°C, and the residual activity of invertase reduced rapidly at temperatures above 65°C; but drying with short residence times will retain most of its activity. The performance of various skin-forming encapsulants, viz. rice and wheat starch, dextrin, coffee, skim milk, fructose, gelatine 60 and 150 Bloom, and gum arabic, was evaluated to determine their capabilities for retention of ethanol as a model volatile, under different operating conditions. The effects of initial solids concentration, air velocity and temperature were monitored for each material tested. Ethanol content was analysed by Gas Liquid Chromatography and in some cases dried crusts were removed for examination. Volatiles retention was concluded to depend in all cases upon the rate and nature of the skin formation and selective diffusion phenomena. The results provided further insight into the inter-relationship between temperature, residence time and thermal degradation of heat-sensitive materials. They should also assist in selection of the preferred dryer for such materials, and of the operating parameter to enable maximum retention of the required physico-chemical characteristics in the dried materials.

Kinetic studies of the metathesis of 1-hexene using Re2O7/γ-Al2O3 and the synthesis and metathesis of oxazolines

The kinetics of the metathesis of 1-hexene using Re2O7/-Al_2O_3 as the catalyst were investigated under a variety of conditions. The experiments were carried out under high vacuum conditions. The product solutions were characterised by gas liquid chromatography and mass spectroscopy. The initial kinetics of the metathesis of 1-hexene showed that the reaction was first order in the weight of the catalyst and second order in the concentration of 1-hexene. A kinetic scheme which correlated the experimental data with the metallocarbene chain mechanism postulated by Herisson and Chauvin and the kinetics of the reaction was explained using a model based on the Langmuir-Hinshelwood theory. The low conversion of 1-hexene to its products is due to termination reactions which most likely occur by the decomposition of the metallocyclobutane intermediate to produce a cyclopropane derivative and an inactive centre. The optimum temperature for the metathesis of 1-hexene over Re_2O_7/-Al2O3 is 45oC and above this temperature, the rate of metathesis decreases rapidly. Co-catalysts alter the active sites for metathesis so that the catalyst is more selective to the metathesis of 1-hexene. However, the regeneration of metathesis activity is much worse for promoted catalysts than for the unpromoted. The synthesis and metathesis of 4,4-dimethyl-2-allowbreak (9-decenyl)-1,3-oxazoline and 4,4-dimethyl-2-allowbreak (3-pentenyl)-1,3-oxazoline was attempted and the products were analysed by thin layer chromatography, infra-red, 13C and 1H nmr and mass spectroscopy. Obtaining the oxazolines in a good yield with high purity was difficult and consequently metathesis of the impure products did not occur.

Characterisation and modification of hydrogel polymers

The work described in this thesis can be broadly divided into two sections. The first being the characterisation of hydrogel polymers in both their hydrated and dehydrated states and the second some aspects of the structural modification of polymers. The characterisation of hydrogel polymers in their dehydrated state (xerogels) involves such techniques as elemental analysis, pyrolysis gas liquid chromatography, infra-red spectroscopy, density determination and surface characterisation by contact angle measurements. The characterisation of some commercially available hydrogel materials was undertaken using such techniques and the results obtained were compared to laboratory synthesised systems in an attempt to assess the value of the combination of techniques employed. In the characterisation of hydrated polymers the amoumt and nature of water present is the single most important factor. The most convenient method of characterising this water involves the use of differential scanning calorimetry (DSC), coupled with total equilibrium water content measurements. DSC distinguishes between non-freezing and freezing water but in addition provides some information on the continuum of states in the freezing water fraction. Two aspects of the structural modification of hydrogel polymers were studied. The first involved the incorporation of acrylamide and substituted acryamide monomers into a copolymer system and an examination of the effect of this on the amino acid interaction of the polymers. The second was the attempted synthesis of cell surface analogues by the attachment of sugar type molecules to the polymer using a variety of reaction methods.

Surfactant coated aerosol powders and their properties

The hygroscopic growth of aerosols is an important factor effecting particle size. The consequence of the hygroscopic growth of pharrnaceutical aerosols is a change in their deposition characteristics, such that there is an increase in the total amount deposited in the lung. In this study the hygroscopic growth of disodium fluorescein (DF) aerosol powders was investigated by coating the powders with lauric and capric acids. The coating procedure was carried out in dichloromethane and chloroform, which acted as cosolvents for the fatty acids. An assessment of the extent and the nature of the coating was carried out. The qualitative assessment of the coating was achieved by infra-red spectroscopy, electronscanning chemical analysis and scanning electron microscopy. The quantitative analysis was carried out by differential refractometry, ultra-violet spectroscopy and gas liquid chromatography. These powders were generated under conditions approaching those in the lung, of 97 % relative humidity and 37"C. Coated and uncoated DF aerosol powders were introduced into a controlled temperature and relative humidity apparatus, designed and constructed for the investigation of hygroscopic growth in these studies. A vertical spinning disc device was used to generate the powders. Under conditions of controlled temperature and relative humidity mentioned, the growth ratio of disodium fluorescein alone was 1.45 compared with 1.68, for a nominal coating of DF with lauric acid of 0.12 gg-1, 1.0 for a nominal lauric acid coating of 0.2 gg-1, and 1.02 for a nominal capric acid coating of 0.18 gg-1. The range of control of hygroscopic growth of these aerosols has implications for the deposition of these preparations in the respiratory tract. These implications are discussed in the light of the current knowledge of the effects of hygroscopic growth on the deposition of pharmaceutical and environmental aerosols. A series of experiments in which pulmonary ventilation using a simple radioaerosol generator and delivery system are reported showing that particle size determination may be used to aid the design of diagnostic aerosol generators.

Influence of impact angles on penetration rates of CRAs exposed to a high velocity multiphase flow

A combined flow loop - jet impingement pilot plant has been used to determine mass loss rates in a mixed gas - saltwater - sand multiphase flow at impact velocities up to 70 m/s. Artificial brine with a salt content of 27 g/1 was used as liquid phase. Sand content, with grain size below 150 µ, was 2.7 g/l brine. CO at a pressure of 15 bar was used as gas phase. The impact angle between jet stream (nozzle) and sample surface was varied between 30 and 90°. Rectangular stainless steel disc samples with a size of 20 × 15 × 5 mm were used. They were mechanically ground and polished prior to testing. Damaged surfaces of specimens exposed to the high velocity multiphase flow were investigated by stereo microscopy, scanning electron microscopy (SEM) and an optical device for 3D surface measurements. Furthermore, samples were investigated by applying atomic force microscopy (AFM), magnetic force microscopy (MFM) and nanoindentation. Influence of impact velocity and impact angle on penetration rates (mass loss rates) of two CRAs (UNS S30400 and N08028) are presented. Moreover effects of chemical composition and mechanical properties are critically discussed. © 2008 by NACE International.

Modelling and simulation of biomass gasification in a circulating fluidized bed reactor

Computational Fluid Dynamics (CFD) has found great acceptance among the engineering community as a tool for research and design of processes that are practically difficult or expensive to study experimentally. One of these processes is the biomass gasification in a Circulating Fluidized Bed (CFB). Biomass gasification is the thermo-chemical conversion of biomass at a high temperature and a controlled oxygen amount into fuel gas, also sometime referred to as syngas. Circulating fluidized bed is a type of reactor in which it is possible to maintain a stable and continuous circulation of solids in a gas-solid system. The main objectives of this thesis are four folds: (i) Develop a three-dimensional predictive model of biomass gasification in a CFB riser using advanced Computational Fluid Dynamic (CFD) (ii) Experimentally validate the developed hydrodynamic model using conventional and advanced measuring techniques (iii) Study the complex hydrodynamics, heat transfer and reaction kinetics through modelling and simulation (iv) Study the CFB gasifier performance through parametric analysis and identify the optimum operating condition to maximize the product gas quality. Two different and complimentary experimental techniques were used to validate the hydrodynamic model, namely pressure measurement and particle tracking. The pressure measurement is a very common and widely used technique in fluidized bed studies, while, particle tracking using PEPT, which was originally developed for medical imaging, is a relatively new technique in the engineering field. It is relatively expensive and only available at few research centres around the world. This study started with a simple poly-dispersed single solid phase then moved to binary solid phases. The single solid phase was used for primary validations and eliminating unnecessary options and steps in building the hydrodynamic model. Then the outcomes from the primary validations were applied to the secondary validations of the binary mixture to avoid time consuming computations. Studies on binary solid mixture hydrodynamics is rarely reported in the literature. In this study the binary solid mixture was modelled and validated using experimental data from the both techniques mentioned above. Good agreement was achieved with the both techniques. According to the general gasification steps the developed model has been separated into three main gasification stages; drying, devolatilization and tar cracking, and partial combustion and gasification. The drying was modelled as a mass transfer from the solid phase to the gas phase. The devolatilization and tar cracking model consist of two steps; the devolatilization of the biomass which is used as a single reaction to generate the biomass gases from the volatile materials and tar cracking. The latter is also modelled as one reaction to generate gases with fixed mass fractions. The first reaction was classified as a heterogeneous reaction while the second reaction was classified as homogenous reaction. The partial combustion and gasification model consisted of carbon combustion reactions and carbon and gas phase reactions. The partial combustion considered was for C, CO, H2 and CH4. The carbon gasification reactions used in this study is the Boudouard reaction with CO2, the reaction with H2O and Methanation (Methane forming reaction) reaction to generate methane. The other gas phase reactions considered in this study are the water gas shift reaction, which is modelled as a reversible reaction and the methane steam reforming reaction. The developed gasification model was validated using different experimental data from the literature and for a wide range of operating conditions. Good agreement was observed, thus confirming the capability of the model in predicting biomass gasification in a CFB to a great accuracy. The developed model has been successfully used to carry out sensitivity and parametric analysis. The sensitivity analysis included: study of the effect of inclusion of various combustion reaction; and the effect of radiation in the gasification reaction. The developed model was also used to carry out parametric analysis by changing the following gasifier operating conditions: fuel/air ratio; biomass flow rates; sand (heat carrier) temperatures; sand flow rates; sand and biomass particle sizes; gasifying agent (pure air or pure steam); pyrolysis models used; steam/biomass ratio. Finally, based on these parametric and sensitivity analysis a final model was recommended for the simulation of biomass gasification in a CFB riser.

Synthesis of hydrazine by the fixation process

A critical review of the literature concerning organic derivatives of hydrazine, the ammonia-chlorine reaction and the electrolytic formation of hydrazine has been carried out. Apparatus was constructed to study the electrolysis of liquid ammonia, the formation of chloramine and the fixation of chloramine with a ketone to form an isohydrazone. In the latter case the reaction was carried out in a 3" diameter stirred tank and also in a 1" diameter, 2' high column reactor where the liquid phase was continuously recirculated. Two methods of analysis of azines and isohydrazones in a ketone solution have been developed. One is a colorimetric technique using p-dimethylaminobenzaldehyde and the other involves the hydrolysis of the organic derivative to hydrazine sulphate. Hydrazine was detected in low concentration in some of the electrolytic experiments carried out but it was concluded that this method did not show sufficient promise to warrant further investigation. The gas phase formation of chloramine and acetone isohydrazone has also been studied but in this system difficulties were encountered with the chlorine jet blocking with ammonium chloride. The formation of isohydrazones in a stirred tank reactor has been investigated in some detail and the effect of several parameters was determined. The yield was found to be extremely sensitive to chlorine concentration and in order to obtain yields of more than 90 per cent, the molar concentration of chlorine in the gas phase had to be of the order of 5 per cent. An optimum temperature in the region of 0°C was also detected. These results disagree with those quoted in previous studies but extensive experimental work has confirmed the information presented in this thesis. It has also been shown that at high yields the chloramine formation reaction took place in the gas phase.