Butadiene: Ethanol over Copper, then over Tantalum-Promoted Silica Gel

Butadiene is the 'B' in ABS. Toussaint and Dunn of Carbide and Carbon (US 2,421,361, 1947) made it straight from ethanol in two converters: a copper catalyst first turns part of the alcohol into acetaldehyde and hydrogen, then silica gel with a little tantalum oxide joins alcohol and aldehyde into butadiene. Their 20-hour run made 296 g of butadiene from 2,206 g of ethanol. The off-gas is nearly all hydrogen: no flames, good ventilation. The picture: our diagram.