Separation of Fischer−Tropsch Catalyst/Wax Mixtures Using Dense-Gas and Liquid Extraction

Abstract

This paper describes a catalyst/wax separation technique based on dense-gas and/or liquid extraction of the soluble hydrocarbon components from the insoluble inorganic catalyst particles.The separation by extraction can also be performed in conjunction with magnetic separation of iron catalyst particles. Extractions of 4.91 wt % catalyst in wax were 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 separators). High-temperature gel permeation chromatography was used to measure the average molecular weight of the extraction fractions. The extraction 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 higher molecular weight wax components remain in the first-stage separator. The low molecular weight wax fraction can be remixed with the catalyst and pumped back into the slurry reactor, reducing the average molecular weight, reducing the viscosity, and improving the transport properties of the reaction media while minimizing the chances of reactor gelation due to buildup of high molecular weight waxes.

Separation of Fischer−Tropsch Wax from Catalyst Using Near-Critical Fluid Extraction: Analysis of Process Feasibility

“…Extraction temperatures varied between 515 and 530 K, 535 and 580 K, and 570 and 600 K for n -pentane, n -hexane, and n -heptane, respectively. These solvent/nonsolvent ratios are considerably lower than those used by White and co-workers, , and the present extraction pressures for n -pentane and n -hexane are lower while the extraction temperatures are 50 to 100 K higher. However, at least some of the extractions of White and co-workers appear to be at supercritical conditions, since essentially all of the hydrocarbon in the catalyst/wax slurry was extracted into the liquid phase.…”

“…Experimental studies have been carried out by White and co-workers , to determine whether a catalyst-free wax (<0.1 wt %) can be produced from a slurry of F−T catalyst using NCE or supercritical extraction. A semicontinuous apparatus was used to process a slurry containing 5 wt % of an iron-based catalyst obtained from the AFDU.…”

Vapor−Liquid Equilibria for the Hexane + Hexadecane and Hexane + 1-Hexadecanol Systems at Elevated Temperatures and Pressures

“…Supercritical fluid (SCF) extraction was first proposed by Roberts et al (1992) for the separation of the catalyst from the wax, followed by fractionation of the wax product itself. As has been demonstrated by White et al (1996), a wax that contains as little as 0.05 mass % catalyst can be recovered with supercritical hexane (T c ) 507.5 K, P c ) 30.1 bar). Furthermore, preliminary calculations by Biales et al (1997) indicate that product fractionation and recovery are most effective when SCF solvents with critical temperatures near the operating temperature of the SBC reactor (i.e., 473-573 K) are used.…”

Atual estágio de desenvolvimento da tecnologia GTL e perspectivas para o Brasil

“…Os principais processos de separação dos finos são: sedimentação, separação centrífuga (usando hidrociclone), filtração sob pressão, extração líquido-líquido convencional ou supercrítica, separação magnética de alta intensidade ou técnicas combinadas. 7,45,[59][60][61] VIABILIDADE TÉCNICA, ECONÔMICA E AMBIENTAL DA TECNOLOGIA GTL…”