Process for the production of unsaturated aldehydes

摘要

An aldolisation-dehydration process is disclosed for converting an aldehyde, e.g. n-valeraldehyde, to a substituted acrolein, e.g. propyl butyl acrolein (2-propylhept-2-enal). Aldolisation and dehydration are effected in a stirred tank reactor (16;111) using an alkali catalyst, such as sodium hydroxide. A reaction product stream (23;113) containing both organic and aqueous phases is supplied to an intermediate section of a distillation zone (25;123) which further includes a higher temperature section below the intermediate section and a lower temperature distillation section. Decomposition aldols and "heaving" to regenerate aldehyde or aldehydes occurs in the higher temperature section of the distillation column so that aldehyde or aldehydes are recoverable from the top of the distillation section in a heterogeneous azeotrope containing water and aldehyde. On condensation and phase separation the lower water layer (34;150) can be discharged from the plant without the need for neutralisation. From the bottom of the distillation zone a mixture (36;157) of substituted acrolein and alkali catalyst solution is obtained. The substituted acrolein is recovered as product (45;173), while the catalyst solution (47;175) is recycled to the aldolisation reactor. Part (49;181) of the catalyst solution is purged to control the level of Cannizzaro reaction products.