Process for production of halohydrins

摘要

Halohydrins are obtained by reaction of a normally liquid substantially water-insoluble olefinic type compound containing one or more halogen atoms per molecule with a hypohalous acid by carrying out the reaction in an aqueous reaction mixture in such manner that the organic phase present is maintained in a dispersed condition in the form of droplets of diameter less than 100 microns and preferably less than 50 microns. The olefinic compound may contain one or more olefinic double bonds in an aliphatic radical and those specified are allyl chloride, allyl bromide, methallyl chloride, chloroprene, 2-chloro-1-propene, bromo-butylenes, and chloro-butylenes. The process may be carried out batchwise or continuously and is particularly described with reference to the production of the dichlorohydrin isomers (1,2-dichloro-3-hydroxypropane and 1,3-dichloro-2-hydroxypropane) by adding allyl chloride and chlorine to an aqueous reaction mixture. In the non-recirculating system illustrated in Fig. 1, allyl chloride is continuously admitted through conduit 3 to a fresh-water inlet stream passing through conduit 4, the allyl chloride being finely dispersed in the water stream by passage through the centrifugal pump 5 and maintained in the dispersed condition as the stream passes the point at which chlorine is introduced through conduit 6. The residence time in that part of conduit 4 lying beyond the conduit 6 should be sufficient to permit the completion of the reaction before the product stream is withdrawn from the system. In the preferred method of continuous operation allyl chloride is fed to and rapidly dispersed in an aqueous reaction medium as the latter is continuously recycled through the apparatus. Such a system is shown in Fig. 2 in which an aqueous reaction stream is continuously recycled through conduit 7 while much smaller amounts of make-up water, allyl chloride and chlorine are continuously injected into the recycle stream at points A, B and C respectively and a correspondingly small product stream is withdrawn from the system. The allyl chloride and other organic phase components are finely dispersed as the stream passes the centrifugal pump 8 and the product stream can be withdrawn at any point after a sufficient time interval has elapsed. The reaction mixture is preferably circulated at the rate of at least 250 volumes per volume of allyl chloride added. The apparatus shown in Fig. 3 is adapted for continuous or batch operation and comprises a reactor 9 in which the aqueous reaction mixture is agitated by propellers 11, the interior walls of the reactor being provided with radial vanes 13 to assist in breaking up any vortices in the reaction mixture. When used in continuous operation the vessel 9 is provided with water, the propellers started, and the valves 14, 15, 16 and 17 opened to allow make-up water, allyl chloride and chlorine respectively to flow into the vessel and a product stream to be continuously withdrawn therefrom, the allyl chloride being broken up into the finely divided state on passing through a mixer 18. In batch operation the valve 17 is closed until all the water, allyl chloride and chlorine have been added to the agitated reaction mixture, the valve being opened when reaction is complete. The necessary degree of dispersion may be effected by other dispersion or mixing devices, e.g. by use of orifice plates or jets. The allyl chloride and chlorine are added to the aqueous reaction medium in substantially equimolar proportions and may be supplied in either the liquid or gaseous form. It is preferred to use from 10 to 50 volumes of water for each volume of allyl chloride. The reaction can be conducted under atmospheric, subatmospheric or superatmospheric pressure and temperatures of between 10 DEG and 90 DEG C. can generally be employed. Caustic alkali may be added to raise the pH of the reaction mixture to between 2.5 and 6. The dichlorohydrin can be recovered from the reaction mixture by distillation, but when the product is to be converted to glycerine no such separation is necessary since the entire dichlorohydrin solution can be subjected to hydrolysis directly. In examples (1) the arrangement shown in Fig. 2 is modified by having a mixer (comprising a centrifugal pump in which the impeller is replaced by a rod) inserted in the conduit 7 immediately downstream from the point of chlorine introduction in addition to the centrifugal pump 8 and the aqueous reaction medium (247 volumes) is circulated through the system at a rate of about 1300 volumes per minute, allyl chloride and make-up water being continuously fed to the recirculating mixture at about 4.37 and 113.6 volumes per minute respectively, whilst chlorine is added in substantially equimolar proportion based on the allyl chloride. All the non-aqueous phase components present in the stream leaving the pump are dispersed into particles of from 3 to 20 microns diameter and the product stream comprising the dichlorohydrin isomers is withdrawn at about 132.5 volumes per minute, the reaction zone comprising about 82 volumes of liquid in the section of the conduit immediately downstream of the chlorine addition point C; (2) as in 1 except that the reaction mixture is circulated at a rate of 5300 volumes per minute; (3) as in (1) except that the allyl chloride is supplied to the circulating mixture through an atomizing jet at a point just downstream from the centrifugal pump 8.