Fischer Tropsch process Sasol processes

Figure 2.4 Fischer-Tropsch process—Sasol II plant.

Secunda discharges no process water effluents. AU. water streams produced are cleaned and reused in the plant. The methane and light hydrocarbons in the product are reformed with steam to generate synthesis gas for recycle (14). Even at this large scale, the cost of producing fuels and chemicals by the Fischer-Tropsch process is dominated by the cost of synthesis gas production. Sasol has estimated that gas production accounts for 58% of total production costs (39). 

Sasol Fischer-Tropsch Process. 1-Propanol is one of the products from Sasol s Fischer-Tropsch process (7). Coal (qv) is gasified ia Lurgi reactors to produce synthesis gas (H2/CO). After separation from gas Hquids and purification, the synthesis gas is fed iato the Sasol Synthol plant where it is entrained with a powdered iron-based catalyst within the fluid-bed reactors. The exothermic Fischer-Tropsch reaction produces a mixture of hydrocarbons (qv) and oxygenates. The condensation products from the process consist of hydrocarbon Hquids and an aqueous stream that contains a mixture of ketones (qv) and alcohols. The ketones and alcohols are recovered and most of the alcohols are used for the blending of high octane gasoline. Some of the alcohol streams are further purified by distillation to yield pure 1-propanol and ethanol ia a multiunit plant, which has a total capacity of 25,000-30,000 t/yr (see Coal conversion processes, gasification). 

Development of SASOL. Over 70% of South Africa s needs for transportation fuels are being suppHed by iadirect Hquefaction of coal. The medium pressure Fischer-Tropsch process was put iato operation at Sasolburgh, South Africa ia 1955 (47). An overall flow schematic for SASOL I is shown ia Figure 12. The product slate from this faciUty is amazingly complex. Materials ranging from hydrocarbons through oxygenates, alcohols, and acids are all produced. 

Fig. 12. Flow scheme for the SASOL I Fischer-Tropsch process. To convert MPa to psig, multiply by 145.

FIG. 23-24 Reactors with moving catalysts, a) Transport fluidized type for the Sasol Fischer-Tropsch process, nonregenerating, (h) Esso type of stable fluidized bed reactor/regeuerator for cracldug petroleum oils, (c) UOP reformer with moving bed of platinum catalyst and continuous regeneration of a controlled quantity of catalyst, (d) Flow distribution in a fluidized bed the catalyst rains through the bubbles. 

Fluidized Catalyst Reactor. Two systems have been proposed, based on large scale operation of the Fischer-Tropsch process (to produce liquid hydrocarbons) at SASOL and at Carthage Hydrocol. The SASOL system was designed by M. W. Kellogg and has been operating for about 20 years (57, 58, 59, 60). 

Dry, M. E. 1982. Sasol s Fischer-Tropsch experience. Hydrocarb. Process. 61 121-24. 

Espinoza, R.L., Shingles, T., Duvenhage, D.J., and Langenhoven, P.L., Method of modifying and controlling catalyst selectivity in a Fischer-Tropsch process. U.S. patent 6,653,357, Sasol Technology, Nov. 25, 2003. 

Synthol A version of the Fischer-Tropsch process, for making liquid fuels and organic chemicals from syngas. Developed by Pullman Kellogg between 1940 and 1960. First operated at the SASOL plant in South Africa in 1955. The name was used also for the product from the original Fischer-Tropsch process, developed in the 1920s. See also Synol. Hydrocarbon Process., 1963, 42(11), 225. 

Another, highly selective oligomerisation reaction of ethene should be mentioned here, namely the trimerisation of ethene to give 1-hexene. Worldwide it is produced in a 0.5 Mt/y quantity and used as a comonomer for ethene polymerisation. The largest producer is BP with 40 % market share utilizing the Amoco process, formerly the Albemarle (Ethyl Corporation) process. About 25 % is made by Sasol in South Africa where it is distilled from the broad mixture of hydrocarbons obtained via the Fischer-Tropsch process, the conversion of syn-gas to fuel. The third important process has been developed by Phillips. 

In this article a general review of the Fischer-Tropsch process is given, but since Sasol operates the only proven commercial plants the emphasis will fall on the Sasol operations. 

The first Sasol plant (Sasol One) came on stream in 1955 and is still in production. The profitability of this operation initially was low because the price of crude oil remained depressed for many years due to the discovery and exploitation of the huge oil deposits in the Middle East. After 1973, however, the price of crude oil rose rapidly and consequently the profitability of the Fischer-Tropsch process in South Africa improved dramatically. This lead to the construction of two much bigger plants (Sasol Two and Sasol Three) which came on stream in 1980 and 1982 respectively. 

Transport fluidized bed reactor is used for the Sasol Fischer-Tropsch process (Fig. 19-23a). 

A transport reactor is also used in the Sasol Fischer-Tropsch process. The catalyst is promoted iron. It circulates through the 1.0-m (3.28-ft) ID riser at 72,600 kg/h (160,000 lbm/h) at 340°C (644°F) and 23 atm (338 psi) and has a life of about 50 days. Figure 19-23a shows an in-line heat exchanger in the Sasol unit. 

Slurry reactors find many applications in chemical industry. Most of these arc heterogeneous catalytic processes with hydrogenation of edible oils as the most classic example and SASOL s novel continuous Fischer Tropsch slurry synthesis process [1], the latest impressive new development in this area. Doraiswamy and Sharma [2] identified over 50 different slurry reactor applications, and an updated list would no doubt be longer still. 

SPD [Slurry Phase Distillate] A process for making diesel fuel, kerosene, and naphtha from natural gas. Developed by Sasol from the Fischer-Tropsch process, and first commercialized in South Africa in 1993. A joint venture with Haldor Topsoe for the further development and commercialization of the process was announced in 1996. Commercialization in Nigeria was announced in 1998. An agreement with Engelhard to provide the catalyst was announced in 2000. 

The Fischer-Tropsch process has several variants one of which (a high temperature process) produces significant volumes of olefins. This particular variant, known as the Synthol Process, is used to produce fuels from both coal and natural gas in South Africa. A recent development of this process (The Sasol High Temperature Process ) has replaced the original entrained-bed reactors with fluid-bed reactors. The product breakdown is shown in Table 11.3. 

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