Patent GB-722252-A (GB)
Title: Improvements in or relating to the removal of sulphur compounds from oil fractions of mineral oil origin
IPC: C10G21/00
Filed: 1951-01-08
Abstract: Oil fractions of universal origin are desulphurized by mixing with at least one added hydrocarbon as defined below and, simultaneously or thereafter, subjecting the mixture to extractive distillation in the presence of a selective polar solvent so that a hydrocarbon fraction of reduced sulphur content is removed overhead, leaving a bottoms product comprising the selective solvent, the sulphur compounds removed from the feedstock and the added hydrocarbon.  The feedstock must be one which contains a major proportion of hydrocarbons which are members of the group consisting of paraffins, naphthenes, mono-olefins and poly-olefins and must be one which contains a minor proportion of aromatic hydrocarbons or is free thereof.  The added hydrocarbon must be of at least one chemical type which is higher in the order of susceptibility to extraction than any of the hydrocarbons constituting the major proportion, as mentioned above, of the feedstock.  The order of susceptibility to extraction is: (1) Aromatics; (2) poly-olefins; (3) mono-olefins; (4) naphthenes; (5) paraffins.  Thus the added hydrocarbons may be aromatic. Where the added hydrocarbons have boiling points within or approximate to the boiling range of the feedstock, the bottoms product may be fractionally distilled to take sulphur compounds and added hydrocarbons overhead, leaving the selective solvent for recycle. The overhead product thus obtained may be desulphurized, for example, by treatment with concentrated sulphuric acid or by catalytic vapourphase hydrogenation, and the desulphurized product recycled for use as the added hydrocarbons. According to an alternative procedure, the added hydrocarbons consist of an aromatic hydrocarbon mixture boiling, preferably by at least 20 DEG C., above the upper limit of the ASTM boiling range of the feedstock and boiling below the boiling point or boiling range of the selective solvent, preferably by at least 20 DEG C., and the bottoms product from the extractive distillation is distilled to take the sulphur compounds overhead. The mixture of aromatics and selective solvent remaining may be recycled to the extractive distillation or, alternatively, during the removal by distillation, of the sulphur compounds, the aromatics may be separated as an intermediate or tray cut, leaving only the selective solvent.  The aromatics and the selective solvent may then be recycled separately to the extractive distillation. According to another alternative procedure, the added hydrocarbons consist of an aromatic hydrocarbon fraction boiling, preferably by at least 20 DEG C., above the boiling point or upper limit of the boiling range of the selective solvent.  In this case, in the subsequent distillation to take the sulphur compounds overhead, it is the selective solvent which is separated as an intermediate or tray cut.  The feedstock may be an olefin-containing shale oil fraction or cracked petroleum fraction.  Where the olefins or diolefins present are C5 or lower, any aromatic hydrocarbon may be employed as the added hydrocarbon. Where hexenes are present, toluene or higher aromatics may be employed and, when heptenes are present, xylenes or higher aromatics may be employed. For a feedstock consisting of octenes, the C9 or higher aromatics may be employed.  Suitable selective solvents are phenol, cresols, furfural, aniline and acetone.  According to the Provisional Specification, the added hydrocarbons may belong to the chemical type of the hydrocarbons predominating in the feedstock, provided the added hydrocarbons are of a higher boiling range than that of the feedstock.