A chain growth scheme for the higher alcohols synthesis

A chain growth scheme for the synthesis of alcohols from carbon monoxide and hydrogen is proposed. The scheme describes the alcohol product distribution, assuming one or two carbon addition at the α- or β-carbon atom of the growing alcohol. Estimates of the distribution parameters were obtained from selectivities measured for a range of operating conditions on a Cu ZnO catalyst promoted with 0.5% K2CO3. The α-addition is a slow step with a large activation energy (140 kJ/mol) while β-addition is faster and has a smaller activation energy (66 kJ/mol). Large methanol selectivities result from the slow initial α-addition, and large 2-methyl-1-propanol selectivities from α-addition being the only growth step of the 2-methyl-1-propanol intermediate. The rate of chain growth is approximately proportional to the CO partial pressure and the rate of chain termination proportional to the H2 partial pressure. Addition of alcohols to the synthesis gas resulted in significant increases in the yields of some of the alcohols, consistent with the chain growth scheme.