Intensification of industrial processes: auto-tandem and molecular weight enlarged catalysis
Fenton, Lewis Michael
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The chemical industry is an essential part of modern society and therefore has a responsibility to develop solutions for the problems facing it. A major problem is continuing to match the material demands of a growing global population whilst simultaneously decreasing the consumption of finite natural resources and limiting the emissions of greenhouse gasses. An optimised catalytic system that shortens, or intensifies, the process chain for the production of chemicals can be an effective solution to this challenge. Auto-tandem catalysis is where a single metal-ligand complex facilitates two or more sequential transformations. For example: alkenes are hydroformylated into aldehydes which are then hydrogenated into alcohols. The alcohols have use as plasticisers or surfactants for metal extraction. A previously reported auto-tandem catalysis system was shown to be capable of sequential hydroformylation-hydrogenation of 1-octene to nonanol. It consisted of the neutral rhodium precursor [Rh(acac)(CO)2] and the bidentate ligand xantphos in 10% iPrOH/H2O co-solvent at temperatures of 160°C. Investigations, reported in this thesis, revealed that xantphos type ligands, with their large bite-angle, and high temperatures are required to generate the hydrogenation activity. However, in contrast to the previous system, water is not necessary; with the same results produced in toluene:iPrOH solutions and water:iPrOH solutions. It is proposed that the iPrOH or H2O has a direct influence in the catalytic cycle, either as a hydrogen-shuttle or generates a cationic rhodium species, known to be active in hydrogenation. High temperature NMR studies show the standard resting state of the hydroformylation catalyst is still predominant at high temperatures therefore the proposed catalytic cycle starts from this step. A recurring problem in the industrial process chain is the separation of the catalyst from the final products. Combing a TiO2 ceramic membrane with a POSS (polyhedral oligomeric silsesquioxane) modified tin catalyst and phosphonium iodide co-catalyst, for the coupling of epoxides and CO2 to make cyclic carbonates, was investigated. The catalyst system showed good substrate compatibility for a range of epoxides. In a prototype membrane set-up the system demonstrated a long catalyst life time, however significant leaching was also observed.