The process of separating hydrocarbons which solidify readily (waxes) from petroleum fractions. Removal of wax is usually necessary to produce lubricating oil which will remain fluid down to the lowest temperature of use. The wax removed may be purified further to produce commercial paraffin or microcrystalline waxes.
Most commercial dewaxing processes utilize solvent dilution, chilling to crystallize the wax, and filtration. Wax crystals are formed by chilling through the walls of scraped surface chillers, and wax is separated from the resultant wax-oil-solvent slurry by using fully enclosed rotary vacuum filters. In a process modification, most of the chilling is accomplished by multistage injection of very cold solvent into the waxy oil with vigorous agitation, resulting in more uniform and compact wax crystals which filter faster.
Complex dewaxing requires no refrigeration, but depends upon the formation of a solid urea-n-paraffin complex which is separated by filtration and then decomposed. The catalytic dewaxing process is based on selective hydrocracking of the normal paraffins; it uses a molecular sieve-based catalyst in which the active hydrocracking sites are accessible only to the paraffin molecules. See also Wax, petroleum.
