Patent GB-639128-A (GB)
Title: A process for dewaxing mineral oils
IPC: C10G73/06
Filed: 1947-01-30
Abstract: Mineral oils are dewaxed by separating them by distillation into fractions of such narrow boiling range that in each fraction the melting point of the straight chain paraffin hydrocarbon having the lowest melting point is higher than that of the isoparaffin or cyclic paraffin in that fraction having the highest melting point.  Each fraction, after the addition of a solvent, is cooled to a temperature at which the solubility of the straight chain paraffins is very low, but the iso- and/or the cyclic paraffins still remain in solution. The straight-chain paraffins are then separated from the solution and the latter may be cooled to a temperature sufficiently low to cause such iso- and/or cyclic paraffins to come out of the solution as would impair the desired pour-point of the dewaxed oil. Alternatively the filtrate obtained from the separation of the straight paraffins may be cooled down to -50 DEG  C. and the solution in the solvent of the liquid oil substantially consisting of aromatic constituents may be removed.  Solvent is then added to the solid part, the temperature of the mixture adjusted to -10 DEG  C. to -15 DEG  C., and the mixture separated into solid iso- and/or cyclic paraffins and a solution of liquid iso-and/or cyclic paraffins.  The filtrates of various fractions may be combined after the separation of the straight-chain paraffins and the iso- and/or cyclic paraffins obtained from the combined filtrates.  Suitable solvents are methyl ethyl ketone, methyl isobutyl ketone, acetone, and esters such as ethyl acetate, either alone or mixed with benzene or other aromatic hydrocarbons or with a highly aromatic gasoline fraction.  In the example a 60 per cent residue obtained by the distillation of Taudjoeng crude petroleum is separated by fractional distillation under reduced pressure into six distillate p  fractions of about 9 per cent each (calculated on the original crude) and a residual fraction.  Each of the distillate fractions except the first is mixed with five times its weight of methyl isobutyl ketone, and the mixtures are cooled to -17 DEG , +3 DEG , +13 DEG , +22 DEG  and +32 DEG  C., respectively.  In each case the normal paraffin wax thus separated is filtered off and washed with the same solvent.  In the case of the last four distillate fractions the combined filtrate and washings from each of these fractions is evaporated down until the residue contains the original quantity of solvent.  The dewaxing is then repeated in each case at -23 DEG  C. and the solvent distilled off from the filtrate.  The correct first dewaxing temperature for each fraction is determined by dewaxing the fraction at some arbitrarily selected temperature and determining by means of refractive index and melting point measurements whether the wax fraction thus obtained consists solely of straight chain hydrocarbons.  If not, the test is repeated using a higher dewaxing temperature.  If, on the other hand, the wax obtained consists solely of straight chain hydrocarbons the test is repeated using a somewhat lower temperature until the separated wax is found just to contain a perceptible amount of iso- and/or cyclic paraffins.  If desired, each wax fraction may be analyzed by dissolving it in 15 parts by weight of the dewaxing solvent and obtaining successive crops of wax by cooling to progressively lower temperatures and filtering off the separated wax at each stage.  After removal of solvent the melting points and refractive indices of each fraction are determined. Specifications 356,172 and 566,413 are referred to.