Process for preparing 1,4-butanediol from maleic anhydride

A process for preparing 1,4-butanediol from maleic anhydride (MA) by esterification of the MA and catalytic hydrogenation of the ester formed in the liquid phase, wherein

• a) the MA is esterified using 1,4-butanediol in a molar ratio of 1,4-butanediol:MA=1.1-2:1,
• b) the esterification is carried out while distilling off the eliminated water, batchwise or continuously in 1-4 esterification stages in the temperature range of 100.degree.-130.degree. C. and in the pressure range of 1500-100 mbar,
• c) the oligoester formed in step b) is treated with excess hydrogen in a first hydrogenation step in the temperature range of 60.degree.-130.degree. C. over a support-free catalyst of compacted metal powder of Ni, Fe, Co or mixtures thereof, and
• d) the hydrogenation is completed in a second hydrogenation step in the temperature range of 190.degree.-230.degree. C. over a reduced, support-free catalyst of compacted powders of copper oxides, ZnO and Al.sub.2 O.sub.3 containing proportions of oxides of Ni, Fe, Co or mixtures of a plurality of these, with the temperature difference between the steps c) and d) being 60.degree.-130.degree. C., a 20 to 100-fold molar H.sub.2 excess being used and the steps c) and d) being carried out at the same or different pressure in the range of 100-400 bar.