Patent GB-806720-A (GB)
Title: Improvements in the production of chlorstyrenes
IPC: C08F14/02
Filed: 1957-08-20
Abstract: Nuclear chlorinated styrenes which have been prepared by treating ethylbenzene or a nuclear chlorinated ethylbenzene with chlorine at elevated temperatures in the gas phase in the presence of a chlorination catalyst containing a platinum metal or compound thereof or in the presence of activated carbon followed by dehydrogenating the resulting chlorinated product in the presence of a dehydrogenation catalyst at elevated temperatures in the gas phase may be purified by treating the mixture obtained from the dehydrogenation reaction under polymerizing conditions, separating off the non-polymeric fraction and depolymerizing the polymer into monomers.  The dehydrogenation product comprises a mixture of compounds which may include styrene, ethylchlorobenzene, ethyldichlorobenzene, chlorostyrene and dichlorostyrene and may be polymerized in the presence or absence of catalysts and at reduced, normal or elevated temperatures.  If the reaction is carried out between about 5 DEG  and 30 DEG  C. a redox system catalyst such as a per compound together with a soluble organic reducing agent such as sulphinic acids, formic acid, amines, organic hydrazine compounds, mercaptans, a -ketols or sugars may be used.  Compounds such as cobalt naphthenate, iron laurate, iron acetyl acetonate or nickel acetoacetic ester may also be used.  Between about 40 DEG  and 100 DEG  C. thermally unstable azo compounds and peroxides such as hydrogen peroxide, dialkyl, diaryl, diacyl and diaroyl peroxides, keto peroxides, peroxy acids and peroxy esters may be used.  Above 100 DEG  C. catalysts are not always necessary.  The polymerization may also be promoted by irradiation.  The dehydrogenation product is preferably dried prior to polymerization.  The non-dehydrogenated products may be distilled from the polymer at normal or preferably reduced pressures.  The depolymerization is generally carried out thermally, at a normal or reduced pressure, and preferably in an iron vessel since iron is found to have a catalytic effect and improve the yield of monomers.  Temperatures in the range 250-650 DEG  C., preferably 400-600 DEG  C., are found to be satisfactory.  It is found that working at reduced pressure considerably reduces the losses by cracking but produces a mixture of monomers, dimers and trimers so it is preferred to work in two steps, the first at reduced pressure and the second, after removal of the monomers by distillation, at atmospheric pressure to depolymerize the dimers and trimers.  In examples: (6) a dehydrogenation product is heated at 60-80 DEG  C. in the presence of methyl ethyl ketone peroxide and the polymer depolymerized in an iron vessel in two stages at 550 DEG  C.; (7) is similar to (6) using cumene peroxide and p-toluene sulphinic acid as polymerization catalyst.ALSO:Nuclear chlorinated styrenes are prepared by treating ethylbenzene or a partly nuclear chlorinated ethyl-benzene at elevated temperatures in the vapour phase with chlorine in the presence of a chlorination catalyst containing a platinum metal or a platinum metal compound, or in the presence of activated carbon, dehydrogenating the resulting chlorinated product at elevated temperatures in the gas phase in the presence of a dehydrogenation catalyst and separating the chlorostyrenes from the resulting mixture.  The chlorination may be carried out in the range 140-400 DEG  C., preferably 170-370 DEG  C., and the ethylbenzene and chlorine may be diluted with an inert gas, e.g. nitrogen.  Other inert organic solvents, e.g. carbon tetrachloride or low-boiling naphtha fractions may be introduced into the reaction vessel.  The ratio of chlorine to inert gas and to ethylbenzene may be varied according to the degree of chlorination desired and the exit gases may be treated for the removal of hydrogen chloride which is formed in the reaction.  The platinum metals, particularly palladium chloride, are found to be suitable catalysts and they may be used on carriers such as aluminium oxide, silica gel, pumice, activated carbon or fuller's earth.  The catalyst may be static or moving in the reaction vessel and a fluidized-bed system may also be used.  The dehydrogenation may be carried out by passing the ethylchlorobenzenes together with superheated steam over the catalyst which may be any of the conventional dehydrogenation catalysts, e.g. palladium, nickel or copper compounds, oxides of the 5th and 6th sub-groups of the Periodic Table or mixtures of these.  A mixed catalyst containing zinc oxide and small amounts of non-volatile alkali and alkaline-earth metal inorganic salts is also found to be suitable. The mixed catalysts may also contain oxides of aluminium, magnesium or thorium.  The products of the dehydrogenation which may include styrene, ethylchlorobenzene, ethyldichlorobenzene, chlorostyrene and dichlorostyrene may be separated by fractional distillation, or preferably by treating the mixture under polymerizing conditions, distilling off the non-polymerized components and recovering the monomers by depolymerization.  The polymerization may be carried out at any temperature but below 100 DEG  C. a conventional polymerization catalyst is used.  The depolymerization may be carried out thermally, preferably in an iron reaction vessel, in the temperature range 250-650 DEG  C.  A preferred method involves carrying out the depolymerization in two steps, the first at a reduced pressure when a mixture of monomers, dimers and trimers is obtained and the second, after the monomers have been removed, at normal pressure; in this way the loss by cracking is reduced.  In examples: (1), (2) ethylbenzene is chlorinated with a chlorine/nitrogen mixture over a palladium chloride/alumina catalyst and the product dehydrogenated over a zinc oxide catalyst; (3) as (1) using a fluidized bed chlorination catalyst, nine mixed catalysts are described; (4) as (1) using an alkaline zinc oxide dehydrogenation catalyst; (5) as (1) but varying the ratios so as to obtain primarily a dichloro product and dehydrogenating with a vanadium oxide/cadmium oxide catalyst; (6), (8) describe the polymerization of a dehydrogenation product using methyl ethyl ketone peroxide as catalyst and a two-step depolymerization in an iron vessel; (7) as (6) using cumene peroxide and p-toluene sulphinic acid as catalyst.