HIGHER-ALCOHOL SYNTHESIS REACTION STUDY V - EFFECT OF EXCESS ZNO ON CATALYST PERFORMANCE

A nonpromoted, K-promoted, and Cs-promoted 1:1 Zn/Cr spinel as well as K-and Cs-promoted Zn/Cr spinel catalysts containing excess ZnO were t ested for higher alcohol synthesis (HAS) using a syngas feedstream (1: 1 CO:Hz) Two reactor operating pressures, 1000 and 1500 psig, and two reactor bed temperatures, 400 and 440 degrees C, were used in order to determine the influence of these operating parameters, and the effect s of promotor concentrations and excess ZnO on the product stream comp osition. Of the catalysts tested, the 3 wt% Cs/Zn/Cr catalyst with exc ess ZnO yields the highest isobutanol production rate of 171 g/kg h at 440 degrees C and 1500 psig. Although lower methanol-to-isobutanol mo le ratios were attained, this catalyst yields a ratio of 1.4 which is nearly ideal for downstream synthesis of methyl tertiary-butyl ether ( MTBE). Superior performance is achieved using Cs as the promotor on th e Zn/Cr spinels in comparison to the K promotor. Lower hydrocarbon pro duction rates and corresponding increased selectivities to total alcoh ols, however, are obtained using K as the promotor of the 1:1 Zn/Cr sp inel catalysts while Cs is more effective in reducing the hydrocarbon production in the presence of excess ZnO. The addition of excess ZnO t o the Cs-promoted catalyst enhances not only the isobutanol rate but a lso results in increased selectivity, lower hydrocarbon production rat es and lower methanol-to-isobutanol mole ratios at the higher Cs readi ngs. Higher isobutanol production rates are also obtained over the K-p romoted Zn/Cr spinels containing excess ZnO in comparison to the K-sup ported 1:1 Zn/Cr spinels if 3 wt% or greater K addition is employed, b ut higher hydrocarbon production rates result in lower selectivities t o the desired alcohol products. (C) 1998 Elsevier Science B.V.