February 14, 2011
Here is a catalyst for converting acetic acid to ethanol in high yield. Ethanol has become important as an oxygenated gasoline additive and as a key intermediate for making ethylene and its derivatives. Conventional routes for making ethanol include ethylene hydration and sugar or starch fermentation.
The feedstocks for ethylene production are typically natural gas liquids or petroleum distillates such as naphtha and gas oil. The costs of these hydrocarbon-based feedstocks are rising as crude oil prices soar again. The costs of fermentation feedstocks such as sugarcane and corn are also rising.
V. J. Johnson and colleagues at Celanese make the case that alternative routes to ethanol would be beneficial, and they developed catalysts capable of carrying out the direct hydrogenolysis of acetic acid to ethanol in very high yields. Previous catalysts for this reaction had low activity or selectivity.
One of the new catalysts consists of 1 wt% platinum and 1 wt% tin on calcium silicate. In one example, this catalyst was loaded into a tubular reactor through which a gaseous stream containing ~4.4–13.8 mol% AcOH and ~14–77 mol% hydrogen was passed at a gaseous hourly space velocity of 2,500 h–1, a temperature of 250 °C, and a pressure of 22 bar. AcOH conversion was >70%, and EtOH selectivity was 99%.
The experiment was repeated with a catalyst that did not contain platinum. AcOH conversion was <10%, and EtOH selectivity was <1%. (Celanese International Corporation [Dallas]. US Patent 7,863,489, Jan. 4, 2011; Jeffrey S. Plotkin)