SEPARATION OF FISCHER-TROPSCH CATALYST WAX MIXTURES USING DENSE-GAS AND LIQUID EXTRACTION/

This paper describes a catalyst/wax separation technique based on dens e-gas and/or liquid extraction of the soluble hydrocarbon components f rom the insoluble inorganic catalyst particles. The separation by extr action can also be performed in conjunction with magnetic separation o f iron catalyst particles. Extractions of 4.91 wt % catalyst in wax we re performed with n-butane, n-pentane, and n-hexane. Up to 91 wt % of the catalyst/wax feed mixture to the extractor could be recovered as a catalyst-free wax (combined yield of the second- and third-stage sepa rators). High-temperature gel permeation chromatography was used to me asure the average molecular weight of the extraction fractions. The ex traction process separates the wax according to molecular weight. The lower molecular weight wax components are extracted from the catalyst/ wax mixture and accumulate in the second-stage separator, while the hi gher molecular weight wax components remain in the first-stage separat or. The low molecular weight wax fraction can be remixed with the cata lyst and pumped back into the slurry reactor, reducing the average mol ecular weight, reducing the viscosity, and improving the transport pro perties of the reaction media while minimizing the chances of reactor gelation due to buildup of high molecular weight waxes.