SYNTHESIS OF ALCOHOLS FROM CARBON OXIDES AND HYDROGEN .20. AN INVESTIGATION OF THE THERMODYNAMIC CONSTRAINTS IN HIGHER ALCOHOL SYNTHESIS OVER CS-PROMOTED ZNCR-OXIDE CATALYST

A thermodynamic analysis of the oxygenate products of the higher alcohol synthesis (HAS) over an alkali promoted high-temperature methanol synthesis catalyst is performed for a wide range of operating conditions. By comparing actual fugacity ratios with equilibrium constants it is found that a number of reactions approach chemical equilibrium under typical synthesis conditions, namely: (a) formation of methanol; (b) water-gas shift reaction; (c) formation of methyl formate and possibly of higher methyl esters; (d) hydrogenation of aldehydes to primary alcohols; (e) hydrogenation of ketones to secondary alcohols; (f) ketonization reactions. The prevailing thermodynamic constraints determine the relative amounts of primary and secondary alcohols, aldehydes, ketones, esters, and acids. They also explain the experimental effects of temperature, pressure, and feed composition on the same products, as well as some of the differences in product composition observed between the HAS over modified high-temperature and low-temperature methanol catalysts. The observed departures from equilibrium provide insight into the reaction network and information on the mechanism of the synthesis. It is also found that the reactions under thermodynamic control are related to some of the major catalytic functions of ZnCr-oxide systems identified by an independent temperature-programmed surface reaction investigation. © 1990.