Sasol's Slurry Phase Reactor
In the early 1980s, Sasol began developing a slurry-phase reactor (SPR) for low-temperature Fischer–Tropsch (LTFT) synthesis, intended to convert coal-derived carbon monoxide into long-chain hydrocarbons in the diesel boiling-range. The reactor, comprising gas, liquid wax, and suspended solid catalyst, used a proprietary cobalt formulation. Previous fixed-bed and entrained fluidized-bed designs were hindered by wax buildup and loss of fluidization under the low-temperature, high-molecular-weight product conditions characteristic of heavy Fischer–Tropsch synthesis.
The SPR offers near-isothermal operation, which promotes steady and predictable product distributions while mitigating safety risks. Heat removal for the strongly exothermic reaction is provided by internal cooling tubes circulating water, with steam generated through absorption of the latent heat of vaporization. It also features very low pressure drop and can achieve carbon monoxide conversions of about 80%, compared with the 30–40% typically reported for fixed-bed LTFT reactors, while requiring lower catalyst inventory. Catalyst regeneration is performed continuously, improving uptime relative to fixed-bed systems.
Scale-up presented significant challenges: advancing from a 5-cm laboratory tube to a 1-m demonstration reactor required nearly a decade. Gas holdup emerged as a critical operating parameter, influencing both the axial pressure profile and the allowable catalyst loading. Sasol commissioned its first commercial-scale SPR in 1993; the reactor measured roughly 5 m in diameter and 22 m in height. Heat removal for the strongly exothermic reaction is provided by internal cooling tubes circulating water, with steam generated through absorption of the latent heat of vaporization.
Bibliography
Fox, J. M., Ogen, B. D., Chang, E., DeSate, F. F., & Summers, R. L. (1990, November 8). The slurry phase Fischer–Tropsch reactor: A comparison of slurry versus fixed-bed reactor designs for Fischer–Tropsch distillate production. Presented at the U.S. Department of Energy, Pittsburgh Energy Technology Center, Indirect Liquefaction Contractor’s Review Meeting. Bechtel Group, Inc.
Espinoza, R. L., Steynberg, A. P., Jager, B., & Vosloo, A. C. (1999). Low temperature Fischer–Tropsch synthesis from a Sasol perspective. Applied Catalysis A: General, 186, 13–26. https://doi.org/10.1016/S0926-860X(99)00161-1
