Date of Award
Doctor of Philosophy (PhD)
Professor R.B. Anderson
The synthesis of alcohols from carbon monoxide and hydrogen on a commercial Cu/ZnO catalyst, promoted with K₂CO₃ for the synthesis of higher alcohols, particularly 2-methyl-1-propanol, has been investigated.
Discrimination of rate equations for the methanol synthesis, derived from published proposals for the reaction mechanism, was achieved using sequential experimental design. The optimum equation assumed the hydrogenation of a CH₂O surface intermediate as the rate determining step, consistent with proposals from adsorption and isotope studies. Rate equations derived from mechanisms, assuming the hydrogenation of hydroxycarbene or methoxy intermediates as the rate determining step, failed to describe the measured kinetics. The temperature dependence of the parameters for the optimum equation was also determined.
The optimum promoter concentration for the Cu/ZnO catalyst was 0.5% K₂CO₃ by weight. The promotion effect was related to the CO and CO₂ chemisorption uptakes relative to the N₂ monolayer volume, the maximum effect occurring when these were equal. The intrinsic activity of the Cu/ZnO catalyst permitted less severe operating conditions than has previously been reported for the 2-methyl-1-propanol synthesis. The H₂/CO feed ratio was important in determining the higher alcohol selectivity; increasing CO and decreasing H₂ favoured higher alcohol production. At low H₂/CO ratios, the increased butanol selectivity with increased conversions were explained by a decreased hydrogenation of the methanol precursor and increased concentration of the higher alcohol precursors. The reaction temperature was limited by low butanol selectivities below 260°C and catalyst instability above 300°C.
A chain growth scheme which quantitatively described the observed alcohol distribution for a range of operating conditions, is also presented. Growth was assumed to occur at the α- or β- carbon atoms of the adsorbed precursor. The rate of growth varied as the CO partial pressure and the rate of termination as the H₂ partial pressure. The assumed growth rules are consistent with increased alcohol yields observed with the addition of alcohols to the feed gas. • .' " increased alcohols . growth ~ied as. the CO par~~~ of terminat~on as the H2 partial growth rules are consistent with II with the adAition of
Smith, Kevin James, "The Synthesis of Alcohols from Carbon Monoxide and Hydrogen" (1982). Open Access Dissertations and Theses. Paper 1506.