Process for producing unsaturated nitrile.

摘要

A process for producing an unsaturated nitrile comprising the steps of water-cooling, in a quenching column, a reaction mixture containing the unsaturated nitrile, a saturated nitrile and prussic acid, said reaction mixture being obtained by ammoxidation of an olefin, absorbing the reaction mixture with the absorption water in an absorption column, subjecting the resulting absorption solution to extractive distillation in a stripping column by using solvent water, taking out a distillate containing the crude unsaturated nitrile and prussic acid from the top of the stripping column, and then removing the prussic acid, water and the like from the distillate by distillation in distillation columns of a de-prussic acid column, a dehydration column and a product column to obtain the unsaturated nitrile, wherein the solvent water obtained from the lower part of the stripping column and being substantially free from the unsaturated nitrile and prussic acid contained in the feed to the stripping column is recycled as the absorption water in the absorption column or the solvent water effluent from the acetonitrile-stripping column obtained by feeding the solvent water withdrawn from the lower part of the said stripping column to remove acetonitrile substantially is recycled as the solvent water in the stripping column and/or the absorption water in the absorption column, characterized in that when the absorption solution effluent from the stripping column is preheated with the solvent water withdrawn from the lower part of the stripping column and/or the solvent water withdrawn from the lower part of the acetonitrile-stripping column and then fed to the stripping column, the absorption solution is preheated by previously passing the same through at least one column selected from the group consisting of the cooler for the circulating water in the quenching column, the condenser for the overhead vapor in the stripping column, the condenser for the overhead vapor in the dehydration column, and the condenser for the overhead vapor in the product column, and the solvent water is used, prior to pre-heating the above absorption solution, as a heat source of at least one column selected from the distillation columns in the de-prussic acid column, the dehydration column and the product column.