Patent GB-798394-A (GB)
Title: Preparation of dichlorbutenes
Inventor: TURCK KARL HEINRICH WALTER
IPC: C07C17/02
Filed: 1956-05-15
Abstract: The process of the parent Specification for producing dichlorbutenes is modified by chlorinating butadiene-1:3, which has been derived from n-butane and/or n-butene.  The monochlorbutenes and/or dichlorbutanes from the chlorination product are separated, subjected to pyrolysis to produce butadiene, which is then introduced to the chlorination stage and the dichlorbutenes recovered from the chlorination product. Suitable starting materials may comprise n-butane, n-butene-1, n-butene-2, mixtures of any of these compounds, and mixtures of any of these compounds with butadiene-1:3, and may be obtained from a crude C4 stream from the distillation of cracked petroleum.  The conditions of chlorination are the same as in the parent Specification.  Any mono-chlorbutenes, dichlorbutanes, and monochlorbutanes formed during the chlorination are separated from the remainder of the reaction product before being submitted to pyrolysis, either as a single fraction or the monochlorbutenes and dichlorbutanes may be separated and pyrolysed separately.  Any monochlorbutanes present are generally separated with the monochlorbutenes.  Suitable temperatures for the pyrolysis reaction are from 450-750 DEG  C.  The pyrolysis is preferably carried out in a non-catalytic manner, preferably in an unpacked reaction tube, although packings of carbon chips, glass wool or pumice may be used. It is preferable to pyrolyse the mono-chlorbutenes and the dichlorbutanes separately in order to keep large quantities of vinyl chlorides which may be formed on the pyrolysis of dichlorbutanes out of the main system.  Part of the reaction product from the main pyrolysis reactor preferably after the separation of butadiene and hydrogen chloride therefrom, is preferably passed into a subsidiary dichlorbutane pyrolysis reactor.  The product from this reactor may be fractionated to recover: (a) butadiene which is fed to the chlorination reactor with or without the hydrogen chloride; (b) mono-chlorbutenes and unreacted dichlorbutanes which are recycled to the subsidiary pyrolysis, and (c) the vinyl-type chlorides which can be pyrolysed to butadiene under extreme catalytic conditions.  Any butadiene-1:2 formed may be converted to butadiene-1:3 by contacting it, e.g. with fuller's earth, at an elevated temperature.  It is preferable however to pass the butadiene/hydrogen chloride fraction directly to the co-chlorination stage.  Alternatively a fraction containing both monochlorbutenes and dichlorbutanes is separated from the chlorination product and submitted to pyrolysis in a primary reactor.  The pyrolysis product is then fractionated to recover butadiene which is fed to the chlorination reactor with or without the hydrogen chloride, and the unpyrolysed residue is recycled to the pyrolysis.  Part of the pyrolysis product, preferably after separation of butadiene and hydrogen chloride is continuously removed and passed to a secondary pyrolysis reactor with more severe conditions.  The butadiene so formed is then separated and passed with or without the hydrogen chloride to the chlorination.  The butadiene so formed may be separated, preferably together with hydrogen chloride from the pyrolysis products and fed into the chlorinator, preferably after being adjusted to a temperature near that at which the chlorination is carried out, while unreacted monochlorbutenes are recycled to the pyrolysis reactor. Alternatively the whole effluent from the pyrolysis reactor or the butadiene and hydrogen chloride fraction alone may be mixed with the effluent from the chlorination reactor.  Any butene present in the pyrolysis reaction product may also be separated and introduced into the chlorination stage with the butadiene.  When butene-1 is used as a feed it is preferable to isomerize the 3:4-dichlorbutene-1 formed to 1 :4-dichlorbutene-2 in order to separate it easily from the 1 : 2-dichlorbutane, formed.  Alternatively the formation of dichlorbutanes may be reduced by controlling the reaction temperature.  The reaction products may be worked up as described in the parent Specification.  In starting up the process of the invention butene together with butadiene may be fed into the chlorination reactor and the amount of externally added butadiene slowly reduced as this compound formed from the pyrolysis of the monochlorbutenes, builds up in the system.  Alternatively the initial feed may be butene alone.  Examples are given of the preparation of dichlorbutenes using mixtures of butene-2 and butadiene, as starting material, and flow diagrams are also given.