GB591358A - Process for the separation and purification of alkyl halides - Google Patents

Abstract

Alkyl halides, highly purified, are recovered from the polymer-free recycle materials in a low temperature olefinic catalytic polymerization reaction in which an alkyl halide having up to 4 carbon atoms has been employed as a solvent for a Friedel-Crafts catalyst, the recycle materials comprising the solvent, unreacted olefinic material and volatile impurities, by a process comprising drying the recycle materials, separating therefrom by fractiona <PICT:0591358/IV/1> tion a fraction consisting essentially of alkyl halide, scrubbing the fraction with 90-93 per cent w/w sulphuric acid at a temperature below 140 DEG F., preferably between 120 DEG and 140 DEG F., and distilling the acid treated alkyl halides. Desirably, a two-stage scrubbing is employed, first using 87-90 per cent sulphuric acid and then the 90-93 per cent acid. The purified alkyl halide is thereby freed of catalyst poisons and impurities including water, olefines and oxygenated and acidic compounds, and is suitable for re-use in the low temperature polymerization, for example, of iso-olefines with or without conjugated diolefines having 4 to 6 carbon atoms at temperatures below - 10 DEG C. Thus in an application, a mixture of an iso-olefine and diolefine from 1 is cooled and passed to polymerization zone 3 together with recycle materials from 6 and catalyst in methyl chloride from vessel 5. The reaction mixture is then led to a flashing zone 4 where unreacted materials and methyl chloride are volatilized off, leaving the polymer to be recovered at 7. The flashed material is cooled at 8 to separate water vapour, passed through a drier 11 and fed as a compressed vapour to distillation column 13. In this column, an amount of methyl chloride, containing less than 1 per cent olefinic material, sufficient to serve as catalyst solvent is removed overhead, the residue leaving as bottoms and being re-cycled to the polymerization zone through line 6. The methyl chloride is passed via heater 17 to primary tower 18 where it is scrubbed, preferably in vapour phase, with 87-90 per cent sulphuric acid and is then passed through line 24 to secondary scrubber 25 for scrubbing with the 90-93 per cent sulphuric acid. The scrubbed vapours are then led via line 26 through an acid-intrainment drum 29 and thence to a clean-up column 30 where heavy olefinic material, polymer and sulphur dioxide may be removed as bottoms. The sulphur dioxide may also be removed by means of solid caustic soda or lime. The purified alkyl halide which contains less than 100 parts, and preferably less than 10 parts per million of olefinic material is finally liquefied by cooler 33, and mixed with catalyst in vessel 5 and the solution fed to the polymerization zone. Australian Specification 112,875 is referred to.