New routes to CO based chemicals : catalyst development

Carbon monoxide is a versatile chemical feedstock and is likely to have an increasingly important role. Recent trends in global environment policies call for cleaner and more environmentally kind fuels and manufacturing processes. Depleting oil reserves has forced us to find alternative sources to replace petroleum as the main feedstock in the fuel and petrochemical industries. Carbon monoxide which may be produced from natural gas and coal has the potential to be used as a chemical resource of the future. Methanol as one of the industrially important chemicals which which may be produced from carbon monoxide can offer solutions to environmental problems associated with fuel production. In terms of petrochemical reactions involving carbon monoxide, for example, a better process which avoids the use of toxic chemicals, such as phosgene in the production of isocyanates, is always going to be more acceptable due to its reduced environmental impact. The work described in this thesis has focussed on alternative routes to the production of carbon monoxide-based chemicals namely methanol and phenyl isocyanate. A number of new heterogeneous catalyst systems have been developed, characterised and investigated for the synthesis of methanol and phenyl isocyanate. An approach to methanol synthesis involving methyformate intermediates has been employed in this work. Copper chromite catalysts promoted with alkali metals have been studied for methylformate hydrogenolysis, the rate determining step in the synthesis of methanol via methylformate. Alkali metals added as catalyst promoters have been found to alter the electronic properties of the catalysts resulting in a change in the strength of adsorption of carbon monoxide which can poison the hydrogenolysis catalysts. While reduced carbon monoxide adsorption on the catalysts might be beneficial, the extent of methyl formate adsorption also seems to be of great importance in determining the overall activity for methyl formate hydrogenolysis. Although the initial activities of the copper chromite catalysts for methyl formate hydrogenolysis increase with temperature, deactivation of the catalysts becomes more pronounced at high temperatures. This increased deactivation was attributed to the production of carbon dioxide, which has a more detrimental effect than carbon monoxide, from the water gas shift reaction. The promoted copper chromite catalysts showed good resistance to carbon monoxide poisoning when used in the concurrent synthesis of methanol via methyl formate from synthesis gas. The results suggest that more attention should be given to the development of better carbonylation catalysts. Complexes of copper and palladium have been prepared in-situ in the supercages of Y-zeolites by ligand exchanging metal ammine complexes with chelating ligands. The resulting complexes are larger than the channels connecting the supercages in the zeolite internal structure, thus creating ship-in-a-bottle catalysts. Temperature has been found to have a marked affect on the extent of the ligand exchange reaction. Stoichiometric replacement of ammonia was possible at high temperatures. The ship-in-a-bottle catalysts were characterised by XRD, ESCA, Raman Spectoscopy, Diffuse Reflectance Spectroscopy and Electron Microprobe techniques. The catalysts were investigated in methanol formation reactions. They were then used successfully in a new process for the production of isocyanates directly from the reductive carbonylation of nitre-aromatics. A ship-in-a-bottle catalyst system based on phenanthroline complexes of palladium seems particularly suitable for this reaction. It has excellent thermal stability and no leaching of the complexes into the solution was noted with this system which is very important in preserving the catalytic properties.