The invention relates to a four-effect rectification
system for synthesizing a leather
dimethyl formamide solution by a wet method, and a
recovery method. The four-effect rectification
system comprises decompressing concentration towers, a normal-pressure rectification
tower and a decompressing deacidification
tower, wherein one decompressing concentration
tower is added between two decompressing concentration towers in a three-effect rectification
recovery system; the normal-pressure rectification tower adopts a filler tower. The process comprises the steps of feeding and preheating. By the concentration towers, the processes of one-stage decompressing concentration, two-stage decompressing concentration, three-stage decompressing concentration, normal-pressure rectification and decompressing deacidification are adopted, wherein the one-stage decompressing concentration tower, the two-stage decompressing concentration tower, the three-stage decompressing concentration tower, the normal-pressure rectification tower and the decompressing deacidification tower all adopt filler towers. The
recovery technological procedure adopts a circulation process, and the generated
heat energy is circularly used between the procedures of
steaming at a tower top, heating by a tower kettle, feeding, preheating, condensing a finished product, preheating, rectifying and boiling again. Compared with a three-effect DMF recovery process which is widely applied at present, energy is at least saved by more than 20%; the purity of a recovered finished product DMF reaches 99.99%, the
water content is below 200ppm, the acidity is below 20ppm, and the
alkalinity is below 10ppm.