Process for the complete or partial removal of conjugated dienes from hydrocarbon mixtures and for the production of cyclic aldehydes

摘要

Conjugated dienes are removed from hydrocarbon mixtures containing such dienes and cyclic aldehydes are prepared, by subjecting the hydrocarbon mixture and an olefinically unsaturated aliphatic aldehyde to the Diels-Alder reaction for the condensation of the dienes and aldehyde with formation of cyclic aldehydes and fractionally distilling the product to recover cyclic aldehydes and purified hydrocarbon. Hydrocarbon mixtures boiling over a wide range, e.g. of 60 DEG C., may be fractionated to obtain two or more fractions each containing at least one conjugated diene and such fractions may be separately treated as above; in this connection, reference is made to the separation of a mixture of C4-6 hydrocarbons into conjugated-diene containing C4, C5 and C6 fractions. The Diels-Alder reaction may be carried out at 50-200 DEG C. under a pressure sufficient to maintain the reactants substantially in the liquid state. Preferably, a slight excess of aldehyde is used. Specified unsaturated aldehydes are acrolein, methacrolein, crotonaldehyde and ethyl propyl acrolein. In an example, a mixture of C4 hydrocarbons containing 60 mole. per cent butadiene is reacted with acrolein and the product fractionated, yielding fractions of tetrahydrobenzaldehyde, unreacted acrolein and C4 hydrocarbons containing 7.7 mole. per cent butadiene. A flow sheet (not shown) illustrates suitable apparatus. According to the Provisional Specification, the products are preferably recovered by fractional distillation and reference is made to the removal of isoprene and piperylene from C5 hydrocarbons.ALSO:Conjugated dienes are removed from mixtures of hydrocarbons containing such dienes by subjecting the hydrocarbon mixture and an olefinically unsaturated aliphatic aldehyde to the Diels-Alder reaction for the condensation of the dienes and aldehyde with formation of cyclic aldehydes and fractionally distilling the product to separate the cyclic aldehydes from the unreacted hydrocarbons. Hydrocarbon mixtures boiling over a wide range may be distilled to separate fractions of which two at least each contain one or more conjugated dienes and these fractions may be purified separately as above; thus a C4-6 mixture may be separated into C4, C5 and C6 fractions. The Diels-Alder reaction may be carried out at 50-200 DEG C, and under a pressure sufficient to maintain the reactants substantially in the liquid state. Specified aldehydes are acrolein, methacrolein, crotonaldehyde and ethyl propyl acrolein. In an example, a mixture of C4 hydrocarbons containing 60 mole per cent butadiene is reacted with acrolein and the product is fractionated yielding fractions of tetrahydrobenzaldehyde, unreacted acrolein and C4 hydrocarbons containing 7.7 mole per cent butadiene. A flow sheet (not shown), illustrates suitable apparatus. According to the Provisional Specification, the recovery of the purified hydrocarbons is preferably effected by distillation, and reference is made to removal of isoprene and piperylene from C5 hydrocarbons.