Process for purifying volatile organic liquids

摘要

Volatile impurities are removed from organic liquids, particularly polymerizable liquids such as acrylic compounds, by subjecting the liquid to distillation in a fractionating column in such a manner that the overhead vapours include the impurities. The vapours are condensed and scrubbed with an immiscible liquid which will retain a proportion of the impurities; the condensate is then separated from the scrubbing liquid and returned to the top of the column. The vapours may either be condensed by direct contact with the scrubbing liquid, or condensed by indirect cooling first and then contacted with the scrubbing liquid. One or more additional components may be added to the impure liquid in the still pot, either with the object of facilitating the distillation of the liquid or to sweep out the impurity at a lower temperature than that at which the liquid distils. In an example, acrylonitrile containing 0.882 per cent HCH (700 parts) and glacial acetic acid (150 parts) were charged to the still pot 1 and distilled up fractionating column 1a. The overhead vapours were condensed in condenser 13 and the condensate led to the bottom of packed tower 14 where it was scrubbed with 5 per cent sodium carbonate solution, saturated with acrylonitrile, introduced into the tower, through pipe 15, at a rate equal to that of condensate formation. The scrubbed liquid collected as a separate phase at the top of the scrubber and was returned to the column through line 18. Spent scrubbing liquid was withdrawn through overflow 17. The process was continued for 2 hours when analysis of a sample, withdrawn through outlet 21, showed that the overhead acrylonitrile contained less than 0.0017 per cent HCN. Valve 22 was then closed and the purified acrylonitrile distilled-off and collected through outlet 21. In another example, acrylonitrile containing 1.018 per cent HCN (700 parts) and methylene chloride (100 parts) were placed in still 1 and heated to a temperature between 42 DEG and 78 DEG C. Methylene chloride vapours passed from the top of the column, were condensed in condenser 13, and scrubbed with water, to remove HCN, in scrubber 14; the purified ester being returned to the column. After operating for 1.2 hours, the methylene chloride was removed from the still by rectification. The acrylonitrile remaining in the still was found to have an HCN content of less than 0.002 per cent. The purification of hydrocarbons, methyl acetate, and acetoacetic ester is also referred to. Specifications 431,398 and 586,489 are referred to.