Patent GB-830932-A (GB)
Title: Improved method of making methyl mercaptan
Filed: 1956-06-21
Abstract: Catalytic apparatus for use in the production of methyl mercaptan by the vapour phase reaction under specified conditions of methanol with hydrogen sulphide in the presence of an activated alumina catalyst having an adsorptive surface area with respect to nitrogen of 10 to 150 sq. metres per gram (see Group IV (b)) comprises a number of small diameter vertical tubes in which the catalyst is mounted, the tubes being surrounded with a liquid which boils at the desired reaction temperature.  A suitable liquid is the entectic mixture of phenyl ether and diphenyl which may be circulated round the tubes while controlling the pressure in the vaporizing liquid to give desired boiling and reaction temperatures.  The catalyst at the inlet end of the tubes may be diluted with an inert material such as silica or fused alumina to facilitate temperature control.ALSO:Methyl mercaptan is prepared by a process comprising contacting in a reaction zone in the vapour phase hydrogen sulphide and methanol and, if desired, minor amounts of dimethyl ether, in a molar ration of H2S to total methanol greater than 2.5:1 with a catalyst comprising activated alumina having an adsorptive surface area (with respect to nitrogen) not greater than 150 square metres per gram but not lower than 10 square metres per gram and effecting the contact at a temperature in the range of 530 DEG  to 670 DEG  F., under superatmospheric pressure, with a space velocity in the range of about 0.2 to 4 lb. of total hydrogen sulphide plus total methanol per hour per pound of catalyst while maintaining a substantially uniform instantaneous temperature throughout the reaction zone, wherein the temperatures in all parts of the reaction zone are within 20 DEG  F. of a predetermined conversion temperature in the range of 530 DEG  to 670 DEG  F., and recovering methyl mercaptan from the effluent from the reaction zone.  Any dimethyl ether present in the feed to the reaction zone is regarded as being a source of methanol equivalent to twice its molecular proportion of methanol in determining the feed proportions of H2S: total methanol. The reaction is preferably effected at pressures of about 250 to 350 p.s.i.g. and under conditions such that a conversion of methanol of at least p  about 90 but less than 98% is achieved.  The mercaptan recovery is suitably effected by cooling the effluent vapours, separating from the condensate the methyl mercaptan phase, stripping therefrom the H2S and low boiling materials preferably under a pressure greater than the reactor pressure, and fractionating the residue from higher boiling materials such as higher mercaptans and dimethyl sulphide to isolate the methyl mercaptan and recycling the H2S to the reaction zone.  The fractionation of the methyl mercaptan may be facilitated by adding steam to the upper part of the column whereby any unchanged methanol present may be condensed out in a separate phase.  The methyl mercaptan recovered may be dried by calcium chloride treatment.  Suitable apparatus is described comprising two reactors, operatable in series or parallel, wherein a number of tubes filled with catalyst are surrounded by a boiling heat-transfer liquid the pressure on which is adjusted to give control to a desired reaction temperature.  In the lower portions of the tubes, the catalyst is diluted with inert material.  The catalyst is obtained by conventional methods and if too active is conditioned, for example, by use in the mercaptan synthesis until the desired activity is established.  A fluidized form of catalyst may be used.  An example is given using by-product H2S from petrol refinery and methanol containing about 7% dimethylether.