Synthesis of short chain alcohols over a Cs-promoted Cu/ZnO/Cr2O3 catalyst Original Research Article

An investigation on the effects of the operating conditions on the higher alcohol synthesis (HAS) from syngas over a Cs-doped CuZnCr oxide catalyst has been performed. The effect of temperature, CO/H2 ratio, space velocity and oxygenates, and water addition to the feed stream has been studied in order to maximize the short-chain alcohols productivity. It has been found that: (i) the reaction temperature is a key-parameter to control the alcohol productivity, and temperatures in the range 560–585 K are adequate for obtaining high production of C2single bondC3 alcohols. Also, in this temperature range the formation of undesired side-products (hydrocarbons) is minimized, (ii) the gradual enrichment of hydrogen in the reactant mixture (in the range H2/CO = 0.8−1.65) causes a progressive increase in the formation of methanol and a decrease in the amounts of C2+ oxygenates, (iii) the product distribution is rather unaffected by space velocity in the range 9040–15300 Ncc/(h gcat), (iv) the addition of methanol to the CO/H2 feed stream does not leads to significant variations in the product distribution, (v) the addition of ethanol to the feed stream significantly increases the overall C2+ oxygenate productivity, (vi) the results obtained upon ester injection to the CO/H2 feed stream are parallel to those obtained upon injection of the corresponding alcohols, i.e. methyl formate and methyl acetate behave as methanol and ethanol, respectively, (vii) water addition does not significantly affect the methanol synthesis reaction, whereas exerts a dramatic inhibitory effect on the formation of the C2+ linear and branched alcohols. The observed effect of the operating conditions on the HAS have been discussed in the light of the thermodynamic and kinetic characteristics of the synthesis.