GB679173A - Improvements in or relating to the separation of wax from hydrocarbon mixtures - Google Patents

Abstract

A process for the separation of a desired wax in solid form, from a hydrocarbon mixture containing the desired wax and also undesired waxy and/or oily constituents, comprises diluting the hydrocarbon mixture, when at such a temperature that the whole of the desired wax is in solid form, with a solvent for components of the mixture other than the desired wax, increasing the temperature of the dilute mixture by an amount such that form 2 to 30 per cent of the desired wax is dissolved in the solvent, thereafter again reducing the temperature of the mixture to the solidification temperature of the desired wax and separating the desired solidified wax from the solution. The process is applicable to the solvent dewaxing of mineral oils, particularly lubricating oil stocks, to the deoiling of wax, e.g. slack wax from dewaxing operations and to the separation of various grades of wax by solvent fractionation or fractional crystallization of petroleum mixtures comprising wax. If desired, the solvent employed may comprise a mixture of an oil solvent and a wax anti-solvent. Oil solvents mentioned are aromatic hydrocarbons such as benzol or toluol, low boiling aliphatic ethers such as isopropyl ether, halogenated aliphatic hydrocarbons such as propylene dichloride, and chlorinated aromatic hydrocarbons such as chlorobenzene. Wax anti-solvents mentioned are aliphatic ketones such as acetone or methyl ethyl ketone, sulphur dioxide, furfural, phenol, benzaldehyde, formates and acetates. The solvent may be added to the hydrocarbon mixture either in a single addition or by successive additions. Apparatus is described whereby the process of the invention is applied to the dewaxing of mineral oil to produce an oil fraction suitable for use as a lubricating oil and separation of the wax into various waxes having different physical properties. In the examples, wax cakes obtained by the solvent dewaxing of mineral oil are deoiled according to the process of the invention using a mixture of methyl ethyl ketone and toluene or a mixture of methyl ethyl ketone, tuloene and benzene as the solvent. Specification 534,462 is referred to.