Patent ID: 7271299

Claim:
A process for preparing optionally alkyl-substituted 1,4-butanediol by two-stage catalytic hydrogenation in the gas phase of C 4 -dicarboxylic acids and/or of derivatives thereof having the following steps: a) introducing a gas stream of a C 4 -dicarboxylic acid or of a derivative thereof at from 200 to 300° C. and from 2 to 60 bar into a first reactor and catalytically hydrogenating it in the gas phase to a product which contains mainly optionally alkyl-substituted γ-butyrolactone; b) removing succinic anhydride from the product obtained in step a); c) introducing the product stream obtained in step b) into a second reactor at a temperature of from 150° C. to 240° C. and a pressure of from 15 to 100 bar and catalytically hydrogenating it in the gas phase to optionally alkyl-substituted 1,4-butanediol; d) removing the desired product from intermediates, by-products and any unconverted reactant; e) optionally recycling unconverted intermediates into one or both hydrogenation stages, said hydrogenation stages each using a catalyst which is free from chromium which comprises ≦95% by weight of CuO, and ≧5% by weight of an oxidic support, and said second reactor having a higher pressure than said first reactor, and wherein the catalyst space velocity of the first hydrogenation stage is in the range from 0.02 to 1 kg of reactant/1 catalyst•hour, and the catalyst space velocity of the second hydrogenation stage is in the range from 0.02 to 1.5 kg of reactant/1 of catalyst•hour.