The depletion of fossil resources, the volatility of the oil price market and the urgency to mitigate the effects of climate change have pushed the development in chemical industry for sustainable, energy efficient and economic processes for fine chemical production. Selective oxidation of alcohols using noble metal catalysts is a key catalytic conversion for the production of carbonylic and carboxylic compounds for the chemical, pharmaceutical, automobile or consumer goods industry. Gold based catalysts, in particular, have demonstrated superior performance over commonly employed catalysts or stoichiometric oxidants. Challenges, however, remain to develop not only active and selective catalysts but with a long lifetime for industrial application. This thesis is based on the study and development of gold based catalyst systems for the selective oxidation of alcohols under mild conditions. The main model compound studied is the selective oxidation of salicyl alcohol to salicyl aldehyde and salicylic acid. Salicyl aldehyde is a very important chemical compound for the production of a range of fine chemicals and chelating compounds with an estimated market capacity of 4000-6000 tonnes/year. Reactions were carried out in a semi-batch stirred glass reactor under atmospheric pressure using air as oxidant and water as solvent. The setup successfully enabled the direct study of the kinetics and mechanism without influences of mass transport. Studies demonstrated the reaction followed sequential mechanism of first order with the consecutive oxidation of salicyl aldehyde to salicylic acid. The main catalyst system used was gold on powdered activated carbon, prepared by sol-immobilisation using Tetrakis(hydroxymethyl)phosphonium chloride (THPC) as stabiliser. 1wt% Au/C achieved maximum turnover frequency numbers (TOF) of 342 h-1 and selectivities of 79% towards salicyl aldehyde at 100% conversion. The increase in gold loading to 3wt% resulted in a decrease in activity caused by an increased gold particle size. The addition of Pd as second active metal showed the formation of an alloy and a decrease in activity with the increase in Pd amount. The application of the Au/C catalyst system for continuous processing was investigated using gold on granular carbon in a trickle bed reactor. Base-free selective oxidation of salicyl alcohol was studied via synthesis of MgO dispersed on oxides, in particular hydrotalcites. The basicity, measured by CO2 adsorption capacity, increased with increased loading of MgO. The catalysts showed potential activity, achieving 59% conversion with 90% selectivity towards salicyl aldehyde.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:616817 |
| Date | January 2013 |
| Creators | Chaturvedula, Sumana |
| Contributors | Chadwick, David |
| Publisher | Imperial College London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/10044/1/14614 |
Page generated in 0.002 seconds