Supercritical Solvent Effects on Hydrocarbon Product Distributions from Fischer-Tropsch Synthesis over an Alumina-Supported Cobalt Catalyst

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• 作者：Xiwen Huang ; Nimir O. Elbashir ; and Christopher B. Roberts
• 刊名：Industrial & Engineering Chemistry Research
• 出版年：2004
• 出版时间：September 29, 2004
• 年：2004
• 卷：43
• 期：20
• 页码：6369 - 6381
• 全文大小：237K
• 年卷期：v.43,no.20(September 29, 2004)
• ISSN：1520-5045

文摘

This study is designed to examine the effects of supercritical fluid (SCF) solvents (pentane orhexane) on product distributions from Fischer-Tropsch synthesis (FTS) over an alumina-supported cobalt catalyst in a fixed-bed-reactor. The influence of reaction conditions (such astemperature, pressure, syngas feed ratio, contact time, and space velocity) on the FTShydrocarbon product distributions in the supercritical solvents was studied. Changing thedensity-dependent bulk thermophysical properties of the supercritical pentane medium, by tuningeither temperature (210-250 C) or pressure (45-65 bar), resulted in notable effects on the(C₆₊) hydrocarbon product distributions and selectivity. One particular set of experiments wasdesigned to directly compare hexane and pentane solvent effects at constant density (ca., =0.3 g/cm³) and temperature (240 C) where significantly higher pressure was required in pentaneto achieve this density. Interestingly, both pentane and hexane supercritical FTS performedalmost identically at the common density, in terms of hydrocarbon product distribution; however,higher CO conversion was obtained for the pentane phase reaction, because of the pressureeffects on the kinetics. Within the investigated range of conditions, the chain-growth probability(-value) increases as the pressure increases and the temperature decreases; however, theinfluence of reaction temperature on the chain growth probability was determined to be morepronounced than that of the effect of pressure. Through comparison of hydrocarbon distributionsin both SCF-phase and gas-phase FTS, we conclude that the enhanced -value in SCF-FTS isdue to the enhanced solubilities of heavy hydrocarbon products in the SCF medium, therebyimproving vacant-site accessibility for the readsorption of olefins and subsequent chain growth,as well as the elimination of the adsorption layer.