PURIFICATION OF ALKYL METHACRYLATES

1,235,208. Purification of alkyl methacrylates. EASTMAN KODAK CO. 20 Dec., 1968 [26 Dec., 1967], No. 60666/68. Heading C2C. Alkyl methacrylates which are contaminated with impurities having melting points below - 50‹ C. are purified by cooling a liquid mixture of said methacrylate and impurities so as to form a slurry of crystals of said methacrylate in a liquid medium richer in said impurities and causing said crystals to flow in a stream counter to a stream of liquid alkyl methacrylate, which liquid has been formed by melting previously formed crystals of alkyl methacrylate and which is at a temperature such that the crystals in said counter flowing stream partially melt and some of the liquid crystallizes and separating the liquid containing the remaining unmelted crystals of purified alkyl methacrylate. In the above process a portion of said unmelted crystals may be melted and the liquid recycled to said stream of liquid alkyl methacrylate; a portion of said counter-flowing stream, after said crystals have passed in counter-current therethrough, may be mixed with fresh contaminated alkyl methacrylate and the mixture cooled to form the slurry. The slurry preferably contains from 50-65% by wt. of solids and the crystals in said slurry suitably flow downwards in a vertical tower up which said stream of liquid alkyl methacrylate flows, the temperature of the stream at the bottom of the tower being 20-30‹ C. higher than the temperature at the top of the tower. Examples are given in which the alkyl methacrylate is methyl methacrylate (which may be obtained by the oxidative dehydrogenation of methyl isobutyrate) and the main impurity is methyl butyrate. Suitable flow diagrams for carrying out the above process are described.