either in the liquid phase or in the gas phase the catalyst can be present in the form of beds of pellets as powder suspended in the liquid sulphur as coating on packing elements monoliths or knitteds the catalyst can be located at one or more places in the reaction vessel the catalyst is preferably located in the internals acting as gas collection regions to ensure complete conversion of hydrogen a catalyst bed is in a further embodiment of the invention installed above the liquid sulphur and all gas capture structures a catalyst bed enclosed by the liquid sulphur is also possible instead of pure hydrogen it is also possible to pass impure hydrogen through the liquid sulphur the impurities can be for example carbon dioxide hydrogen sulphide water methanol methane ethane propane or other volatile hydrocarbons preference is given to using hydrogen having a purity of from gt 65 by volume to 100 by volume and from gt 98 to 100 by volume of the hydrogen used being converted into hydrogen sulphide the impurities in the hydrogen or their reaction products are preferably not separated off before the synthesis of methyl mercaptan but left in the starting mixture the sulphur used can also contain various impurities overall the invention can firstly make more economical operation of production plants for hydrogen sulphide possible especially at pressures of gt 5 bar since the reaction vessel requires little maintenance and repairs and does not have to be partly or completely replaced even after prolonged operation over a number of years or decades as a result.