Sasol plants in South Africa

Imperial Chemical Industries (ICI) operated a coal hydrogenation plant at a pressure of 20 MPa (2900 psi) and a temperature of 400—500°C to produce Hquid hydrocarbon fuel from 1935 to the outbreak of World War II. As many as 12 such plants operated in Germany during World War II to make the country less dependent on petroleum from natural sources but the process was discontinued when hostihties ceased (see Coal conversion PROCESSES,liquefaction). Currentiy the Fisher-Tropsch process is being used at the Sasol plants in South Africa to convert synthesis gas into largely ahphatic hydrocarbons at 10—20 MPa and about 400°C to supply 70% of the fuel needed for transportation. 

Conventional Transportation Fuels. Synthesis gas produced from coal gasification or from natural gas by partial oxidation or steam reforming can be converted into a variety of transportation fuels, such as gasoline, aviation turbine fuel (see Aviation and other gas turbine fuels), and diesel fuel. A widely known process used for this appHcation is the Eischer-Tropsch process which converts synthesis gas into largely aHphatic hydrocarbons over an iron or cobalt catalyst. The process was operated successfully in Germany during World War II and is being used commercially at the Sasol plants in South Africa. 

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. 

Both the ARGE and Kellogg processes were commercialized in 1955 at the Sasol plant in South Africa with a capacity of 240000 t/a hydrocarbons. While the fixed-bed process proved reliable from the beginning, numerous modifications had to be made to the Kellogg process. The major difficulties encountered were concerned with the fluidization of the catalyst. This led to the development of the Sasol Synthol process which is now a highly reliable large-scale industrial operation [15]. 

The Sasol plants in South Africa have been a fundamental element in the development of the LTFT synthetic fuels industry. 

To date, the Fischer-Tropsch is the only commercially operating method for the indirect production of liquids from coal the Sasol plant in South Africa (Figure 19.22) has been in operation since 1956 (Hoogendorn and Salomon, 1957 Bodle and Vygas, 1974 Singh, 1981 Swart et al., 1981 Dry and Erasmus, 1987 Chadeesingh, 2011). 

This mixture is then refined to make various grades of fuels and chemicals. At present, only the Sasol plant in South Africa uses this Fischer-Tropsch process commercially. 

Operation at very low temperatures with very sharp separations results in relatively complex flow schemes. This, combined with the need for low level refrigeration, leads to high plant costs. As a result, most applications of the Rectisol process represent relatively difficult gas treating conditions where other gas treating processes are not suitable for one reason or another. Typical applications are the purification of gas streams in the heavy oil partial oxidation processes of Shell and Texaco and the Lurgi coal gasification process, as used at the Sasol plants in South Africa. 

L. Seglin Why has Lurgi selected the hot gas recycle process for methanation rather than the isothermal reactor (ARGE) design which they used for the Fischer-Tropsch plant in SASOL s plant in South Africa ... 

Figure 1 Picture of a Sasol Fischer-Tropsch plant in South-Africa...

A sizeable amount of work expended in Fischer-Tropsch in both catalyst research as well as pilot plant studies and design. Much of the design work in the SASOL I indirect liquefaction plant in South Africa and the pilot plant in Louisiana, Missouri, was obtained from the bank of information that was generated at PETC. 

Prewar (1938) German production of F-T fuel was around 660 kt/a a trial plant built in Brownsville Texas in the 1950s produced 360 kt/a, and Sasol production in South Africa is currently (2005) around 7 Mt/a. Shell has a plant in Malaysia with a capacity of 500 kt/a to make waxes (long chain alkanes) by F-T from syngas using a hydrogenating Co catalyst. 

The detailed isomer distribution data of Pichler, Schulz, and Kiihne (16,17) for hydrogenated hydrocarbons from a fixed-bed synthesis on a precipitated cobalt catalyst at atmospheric pressure (Co.-ThOgikieselguhr = 100 18 100) at 190°C and the entrained reactors of Sasol commercial plant in South Africa, using a reduced fused iron catalyst at 22 atm and about 320°C, were used for testing the nine chain-growth schemes in Table I in the range Co-Cg, Before the analyses, the hydrocarbons were hydrogenated under conditions that should only saturate olefins. The... 

Sasol is planning a new 3.3 Mt per year GTL plant in South Africa. Sasol, as well as Shell, is, in collaboration with China, investigating the construction of GTL plants in China, which has large reserves of coal (10). 

Sasol has built and operated several FT plants in South Africa. The product usually follows the Anderson-Schulz-Flory distribution and typically consists of linear paraffins and waxes in the range of C5-C40. It is emphasized that A/f° values depend on the number of C atoms in the resulting -paraffln. Thus, for = 1,2,3, and 4, A77° values are -206.1, -347.3, -497.5, and -649.9 kJ/mol, respectively. In fact, it can be inferred from these examples that A/7° -148.2 x — 54.8... 

The basic reaction was discovered in 1923 by F. Fischer and H. Tropsch, working at the Kaiser Wilhelm Institute for Coal Research in Miilheim, Germany. In 1984, Mako and Samuel wrote, The quantity of patents and literature that has appeared on the subject in the past 60 years makes it virtually impossible to retrace stepwise the developments of the Fischer-Tropsch synthesis. The first full-scale plant was built by Ruhrchemie at Holten, from 1934 to 1936 by 1939, eight more plants had been built in Germany. All of these plants were disabled by air attacks in 1944. Used in the SASOL coal gasification plant in South Africa. The first modern Fischer-Tropsch plant outside Africa was built by Shell in Malaysia in 1993, based on natural gas. 

SASOL. SASOL, South Africa, has constmcted a plant to recover 50,000 tons each of 1-pentene and 1-hexene by extractive distillation from Fischer-Tropsch hydrocarbons produced from coal-based synthesis gas. The company is marketing both products primarily as comonomers for LLDPE and HDPE (see Olefin polymers). Although there is still no developed market for 1-pentene in the mid-1990s, the 1-hexene market is well estabhshed. The Fischer-Tropsch technology produces a geometric carbon-number distribution of various odd and even, linear, branched, and alpha and internal olefins however, with additional investment, other odd and even carbon numbers can also be recovered. The Fischer-Tropsch plants were originally constmcted to produce gasoline and other hydrocarbon fuels to fill the lack of petroleum resources in South Africa. 

The first commercial operation of the Lurgi process was in Germany in 1936 using brown coal. The reactor was modified to stir the coal bed to permit utilization of bituminous coal. One plant was built at the Dorsten Works of Steinkohlengas AG, and the Sasol plants were built in South Africa to provide synthesis gas for Hquid fuels. 

SASOLII a.ndIII. Two additional plants weie built and aie in operation in South Africa near Secunda. The combined annual coal consumption for SASOL II, commissioned in 1980, and SASOL III, in 1983, is 25 x 10 t, and these plants together produce approximately 1.3 x lO" m (80,000 barrels) per day of transportation fuels. A block flow diagram for these processes is shown in Figure 15. The product distribution for SASOL II and III is much narrower in comparison to SASOL I. The later plants use only fluid-bed reactor technology, and extensive use of secondary catalytic processing of intermediates (alkylation, polymerisation, etc) is practiced to maximise the production of transportation fuels. 

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