Sasol process

Another current development in the use of F-T chemistry in a three-phase slurry reactor is Exxon s Advanced Gas Conversion or AGC-21 technology (Eidt et al., 1994 Everett et al., 1995). The slurry reactor is the second stage of a three-step process to convert natural gas into a highly paraffinic water-clear hydrocarbon liquid. The AGC-21 technology, as in the Sasol process, is being developed to utilize the large reserves of natural gas that are too remote for economical transportation via pipelines. The converted liquid from the three-step process, which is free of sulfur, nitrogen, nickel, vanadium, asphaltenes, polycyclic aromatics, and salt, can be shipped in conventional oil tankers and utilized by most refineries or petrochemical facilities. 

A generalized scheme of the Sasol process is illustrated in Figure 1. The basic raw materials are coal, water and air. The plant is a complex operation consisting of many interlinked processes. This complexity is, however, not an important factor in the economics when it is borne in mind that the main cost is the production of synthesis gas, which accounts for over 50 % of the total. 

In its commercial plants Sasol has to date used only iron based catalysts. (The preparation and properties of these catalysts have been reviewed elsewhere (2).) Not only is iron by far the cheapest of the metals (see Table I) but iron catalysts also produce large amounts of low molecular weight olefins which are important in the Sasol process. (These olefins are oligomerized to either gasoline or diesel fuel and this allows the production of these two liquid fuels to match the market requirement.) A major drawback of iron is that at high temperatures carbon deposition occurs which results in catalyst disintegration. 

The Sasol process was in competition with MTG. Although our process offered sizable economic advantages in New Zealand over the Sasol process, ours was unproven commercially, while the Sasol technology had been commercialized. We were asking the New Zealand Government to take our word that we could scale up from four barrels to 14,000 barrels per day. They did, and the commercial process has performed as well as predicted, and in a number of cases even better. 

SELECTIVITY (CARBON ATOM BASIS) OF SASOL PROCESSES... 

If petroleum is cheap and readily available, the FT process is not commercially viable and in the 1960s, many industrial plants were closed. In South Africa, the Sasol process continues to use H2 and CO as feedstocks. Changes in the availability of oil reserves affect the views of industry as regards its feedstocks, and research interest in the FT reaction continues to be high. 

The Mobil methanol-to- oline (MTG) process is one of two current commercial technologies for producing synthetic fluid fuels from synthesis Until 1985, the sole "synfuel" process in commercial practice was the Sasol Process (in South Africa), which is based on classic Fischer-Tropsch chemistry and utilizes coal-derived synthesis The Sasol process produces a wide range of aliphatic hydrocarbon... 

Fluid bed operation proved to be difficult in the original trials held by Standard Oil and Hydrocarbon Research Incorporated in the United States. The main problems were obtaining a uniform density throughout the bed and proper gas mixing. The circulating fluid bed used by Kellogg and developed at Sasol eventually operated very well. Operating conditions for both Sasol processes are smnmarized below " ... 

The Sasol processes are of interest now that the conversion of synthesis gas-to-liquid products is being developed by a number of companies. The gas-to-liquid (GTL) process is of particular interest in the production of sulfur-free distillates. 

Since the end of the 1990s several companies have been developing processes to supply liquid hydrocarbons. Synthesis gas is produced and treated in variations of the Fischer-Tropsch process. High-boiling C10-C40 liquid and wax products can be converted to suUur-free, low-boiling products in the C10-C20 range by hydrocracking. Since 1955 only the Sasol processes have been tested extensively. 

In 1942, about 32 million gallons of aviation fuel were made from coal in Germany. In South Africa, the Sasol process for coal liquefaction has been a major source of gasoline and a variety of other petroleum products and chemicals for more than 50 years. 

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