Thesis (M. Phil.)--University of Hong Kong, 1991.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

No description available.

M.Sc. (Chemistry) / Catalyst deactivation is a process that plays an important role in many catalytic processes. The forming of coke is in this respect the most common cause for deactivation. The research that has been done here has tried to give some insight into the mechanism of cokeforming with the help of Fourier Transform Infrared Spectroscopy (F)'IR). For this purpose a cobalt catalyst on an alumina carrier was used. The influence of the reaction time, the carbon monoxide to hydrogen ratio and the temperature on the rate and amount of coke formed was determined. A cell was developed that could be heated up to 500°C and could simultaneously be used in FTIR-spectroscopy in situ research. This enabled the determination of spectra at certain time intervals. In this way the development of the characteristic bands could be followed. Two other methods were used to support the transmission spectra : Diffuse Reflectance Spectroscopy and the burning of the coke from the catalyst. The latter was done to determine the amount of coke that had formed on the catalyst surface during the run. The amount of coke decreased with an increase of the hydrogen to carbonmonoxide ratio in the feed. Temperature also had a marked influence on coke formation: It decreased at higher temperatures. As expected the amount of coke increased with reaction time. In general the coke contained only a small hydrogen content. In conclusion it may be mentioned that the results obtained can contribute to the characterization of coke formed on Fischer-Tropsch catalysts.

Bibliography : pages 244-253. / The objective of this study was to determine the effect that the type of catalyst and reaction would have on the rate of deactivation, properties of coke and transport properties of the catalyst. HY and HM were chosen because of their different pore structures and acid site distributions. Hexane cracking at 1 atmosphere and high pressure propene oligomerisation provided two different reaction types. The transport properties of the catalysts were compared by measuring adsorption and diffusion using the GC technique with ancillary information obtained from ammonia TPD, mercury porosimetry and BET surface area measurements. It was confirmed that a knowledge of the crystallite size distribution was necessary to predict the adsorption and diffusion of light hydrocarbons in HY and HM. The adsorption constants and heats of sorption were found to,be much greater in HM than in HY, in agreement with the presence of a greater number of strong acid sites detected in HM by ammonia TPD. The diffusivities of the Tight hydrocarbons were too large to measure in HY. In HM only methane diffusion was too fast to measure. Diffusivities decreased and adsorption constant increased with increasing molecular size. HY had greater activity and slower deactivation than HM towards hexane cracking. The reaction as well as coking took place in the micro-pores. The graphitic coke content of HY was much greater than in HM. The introduction of the macro-pore adsorption term was necessary to predict diffusion in coked samples, emphasizing the severity of the diffusional resistance. While hydrocarbon diffusivities decreased after cracking, adsorption constants were found to increase in the presence of graphitic coke in J-IY. In HM the deactivation took place primarily by pore blockage, with strong acid sites being preferentially removed. Both diffusivities and adsorption constants decreased in the presence of coke in HM. In HY and HM deactivated by oligomerisation, macro-pore adsorption had to be taken into account, again emphasizing the severe diffusional resistance. Reaction as well as graphitic coke occurred predominantly in the micro-pores in HY. High boiling point hydrocarbons were able to migrate into the mesopores where they closed the mouths of the micro-pores in HY. Strongly adsorbed high boiling point hydrocarbons which deactivated the catalyst presented far less diffusional resistance in HY than the equivalent mass of graphitic coke. These high boiling point hydrocarbons also markedly lowered the adsorption constants. Graphitic coke was responsible for the modification of the catalyst selectivity. Temperature runaway in HY caused severe coking and hence deactivation. The inactivity of HM below 200°C was caused by strong adsorption and high diffusional resistance of reactant and product. Pore blockage was the dominant deactivation mechanism in HM, while in HY it was partial pore blockage by graphitic coke and pore mouth closure by high boiling point hydrocarbons. It was possible to restore the activity of HY for oligomerisation by flushing the high boiling point hydrocarbons in flowing nitrogen.

Thesis (M.Sc.)--University of the Witwatersrand, Faculty of Science (Chemistry), 1990 / Deactivation studies; making use of fixed bed reactors, wet chemical analysis, surface area, pore volume determinations and X-ray diffraction—, scanning electron microscope— and secondary ion mass spectrometry techniques; were performed on a low temperature iron Fischer—Tropsch catalyst. It was revealed that this catalyst is mainly deactivated by sulphur poisoning, oxidation of the catalytic reactive phases, sintering of the iron crystallites and to a lesser extent deactivation through fouling of the catalytic surface by carbonaceous deposits. It was found that the top entry section of the catalyst bed deactivated relatively fast, the bottom exit section also deactivated, but not as fast as the top section The central portion of the catalyst bed was least affected. Sulphur contaminants in the feed gas, even though present in only minute quantities, results in a loss of catalyst performance of the top section of the catalyst bed, while water, produced as a product from the Fischer—Tropsch reaction, oxidized and sintered the catalyst over the bottom section of the catalyst bed.

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 72-74). Also available on the Internet.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 232-249).

Thesis (M.S.)--University of Missouri-Columbia, 2004. / Typescript. Includes bibliographical references (leaves 72-74). Also available on the Internet.

A dissertation submitted to the Faculty of Science, University of the Wtlwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science / This dissertation focusses on the deactivation of SAP0-34 and modified SAPOs during methanol conversion under various conditions, in comparison to H-ZSM-5. SAPO-34 was found to deactivate rapidly during methanol conversdon. This was shown by the decrease in activity, surface area and pore volume of the catalyst. The deposited "coke" was analysed by in situ diffuse reflectance infra-red Fourier Transform spectroscopy,solid-state magic angle spinning nuclear magnetic resonance, gas chromatography mass spectroscopy (GCMS) of the HF- and dichloromethane-extracted to "coke"; and GCMS of the organic specfes released during regeneration of the catalyst and trapped in resin capillary inlet tubes.The "coke" consisted of alkylated aromatics and naphthalenes which probably formed on the surface or in the large cavities of SAPO-34. The amount of "coke" deposited during methanol conversion increased with reaction temperature, decreased with dilution of the methanol with water or nitrogen. and decreased with increased pressure, Incorporation of Ni into the SAPO framework did not decrease the rate of deactivation, but the "coke" that Has deposited was less bulky than that deposited in SAPO-34. Modification of the SAPO-34 with trlmethyl silylchloride decreased the rate at deactivation of the catalyst. / AC 2018