Patent GB-679175-A (GB)
Title: Improvements relating to the refining of petroleum hydrocarbons
Filed: 1948-08-26
Abstract: A petroleum fraction consisting of the naphtha and kerosine fractions is subjected to catalytic disulphurization in the vapour phase followed by separation of the hydrogen sulphide and hydrogen-rich gases formed, recycle of the hydrogen-rich gases and fractionation of the desulphurized products.  The catalyst over which the vapour of the petroleum fraction is passed is one which combines activity for the dehydrogenation of naphthenes to aromatics with activity for the conversion of organically combined sulphur to hydrogen sulphide and which is not poisoned as a catalyst by the presence of sulphur compounds.  The desulphurization is carried out under such conditions of temperature and pressure that the dehydrogenation of naphthenes contained in the petroleum fraction is effected to an extent not substantially in excess of that required to produce sufficient hydrogen to convert organically combined sulphur contained in the petroleum fraction into hydrogen sulphide and to maintain the pressure in the reaction zone.  The desulphurization reaction may be carried out at 650-800 DEG F and 25-500 lbs./sq. inch pressure with a space velocity up to 10 volume/volume/hr.  Suitable catalysts are metal sulphides and oxides, especially those of the 6th group, either alone or in admixture with other sulphides or oxides, or in chemical combination with other sulphides or oxides.  Thus chromium oxide, tungsten sulphide, cobalt molybdate, cobalt thiomolybdate or pellets consisting of two parts tungsten sulphide with one part nickel sulphide may be employed as the catalyst. The catalyst may be mixed with or deposited on a porous carrier such as natural or heat-treated bauxite, activated alumina or kieselguhr.  The preferred catalyst consists of cobalt molybdate supported on alumina.  The separation of the gases from the desulphurized product may be effected by cooling at the reaction pressure.  As the reaction proceeds, the proportion of hydrogen sulphide in the thus-separated gases builds up to constant value, the hydrogen sulphide thereafter remaining dissolved in the desulphurized product until it is depressurized.  The gases may be recycled with this constant proportion of hydrogen sulphide therein or alternatively the hydrogen sulphide may be removed before recycling.  In addition the gases, before recycling, may be submitted to treatment to increase the relative proportion of hydrogen therein. Thus they may be passed through an oil tower wherein light hydrocarbons are preferentially absorbed.  In an example, a fraction (sulphur content 0.15 per cent) taken from crude petroleum of Iranian origin and boiling within the range 95-235 DEG C is passed in the vapour phase at 780 DEG F and 100 lbs./sq. inch pressure and a space velocity of 3 volumes/volume/hr. over cobalt molybdate supported on alumina.  Hydrogen sulphide and a hydrogen rich gas mixture are separated from the treated fraction and the hydrogen-rich gas mixture is recycled at the rate of 2000 cu. ft./barrel.  The treated fraction is separated by distillation into a naphtha fraction having a boiling range of 95-190 DEG C and a kerosine fraction having a boiling range of 190-235 DEG C.  A procedure is described for the working up of desulphurized products of the invention in which the products are separated by distillation into gasoline, white spirit and kerosine fractions. Part of the white spirit is bulked with some or all of the kerosine and submitted to solvent extraction with sulphur dioxide. The raffinate is a finished kerosine while the extract is distilled to give an aromatic distillate boiling within the gasoline range, an aromatic distillate suitable for use as a blending agent for tractor vaporizing oils and a residue suitable for use as a fuel oil. Specifications 654,152, 663,038 and 669,536 are referred to.