Fischer product streams

This process can be tailored to maximize the hydrogen production while capturing C02, or the ratio between CO and H2 in the product stream can be adjusted for different applications. For example, the optimal ratio of H2 to CO is 2 for the Fischer-Tropsch synthesis. 

If the gasifier product stream is intended for downstream use as the feedstock for further upgrading such as methanation, methanol or Fischer Tropsch synthesis, very thorough desulphuri-sation is essential since the catalysts in these upgrading processes are highly sensitive to sulphur poisoning. The methanation catalysts normally cannot tolerate more than 0.05 ppm of sulphur in the feedstock. In addition to H2S sulphur values in the gasifier product it may contain COS, CS2, mercaptans and thiophenes. These are normally removed by activated carbon or zinc oxide filters ahead of the sensitive synthesis catalyst beds. 

The reactor operates either at low (200-240°C) or high (300-350°C) temperatures and between 1-4 MPa. The product mix changes from longer to shorter chain length molecules as the temperature increases. The product stream from a Fischer-Tropsch reactor is a mix of many components but by selecting the right operating conditions the mix can be adjusted so that the product stream has mostly diesel fuel properties. 

The Type IV concept can also be used in the field ofhigher alkenes, but in this instance the product phase is the apolar one and a polar catalyst has to be applied. In this field, technology developed by Union Carbide seems most advanced (see below). Recently, Sasol announced the commercialization in 2001 of a Rh-catalyzed hydroformylation ( low-pressure oxo ) technology, licensed from Kvaerner (previously Davy McKee), for conversion of Sasol s Fischer-Tropsch 1-alkenes to detergent alcohols, on 120 kt/a scale [56]. On the basis of the advanced status of Union Carbide s higher alkene technology, it seems probable that Sasol will apply the latter in South Africa. Sasol s Fischer-Tropsch streams consist of alkenes diluted in a soup of... 

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). 

The refinery design included the recovery of nonacid oxygenates in the Fischer-Tropsch aqueous product that are lighter boiling than water.30 The oxygenate chemicals recovered from the aqueous product included methanol (mainly from Fe-LTFT), ethanol (from Fe-HTFT, Fe-LTFT, and acetaldehyde hydrogenation), as well as mixed heavier alcohol and ketone streams. The carboxylic acids were not recovered and were processed with the wastewater. 

The Fischer-Tropsch aqueous product was not further refined and was treated as a wastewater stream. This was in line with the simplicity of the refinery design, poor economy of scale for oxygenate recovery, and inherently low water-soluble oxygenate production from Co-LTFT synthesis. 

Fig. 1.97.1. Schema of the Coulometer MeBzelle DL 36 for measurement of residual moisture content (RM) after Karl Fischer. In the titration cell (1) iodine is electrolytically produced (3) from an iodine-containing analyt (2). Water in the titration cell reacts with the iodine. When the water is used up, a small excess of iodine is produced, which is detected by special electrodes, which leads to iodine production being stopped. The amount of water in the cell can be calculated from the reading of the coulometer, and the amount of electrical charge needed. The solids are introduced into the cell either by a lock, or the water is desorbed in an oven and carried by a gas stream into the cell. 10 pg in a sample can be detected with an accuracy of reading of 0.1 pg (KF Coulometer DL36, Mettler-Toledo AG, CH-8603 Schwerzenbach, Switzerland).

Oxygenates from paraffin stream (Fischer Tropsch product) NaX, CaA [164]... 

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. 

At the Mellon Institute he applied l4C tracers to examine the behavior of intermediates in Fischer-Tropsch synthesis over iron catalysts. By adding small amounts of radioactively labeled compounds to the CO/H2 synthesis gas mixtures, he was able to prove that some of these compounds (e.g., small alcohols) are involved in the initiation step of the chain growth process that leads to larger hydrocarbon products. It was during this era that his associates first placed a catalytic reactor into the carrier gas stream of a gas chromatograph and developed the microcatalytic pulse reactor, which is now a standard piece of equipment for mechanistic studies with labeled molecules. While at Mellon Institute Emmett began editing his comprehensive set of seven volumes called Catalysis, which he continued at Hopkins. 

The production of gasoline from methanol is a parallel process to the Fischer-Tropsch synthesis of hydrocarbons from syngas (Section 4.7.2). A shape-selective zeolite (ZSM-5) was the catalyst of choice in the process put on stream in 1987 by Mobil in New Zealand however the plant was later closed. The zeolite was used at ca. 400°C in a fluid catalyst reactor, which allows prompt removal of the heat of reaction. 

The introduction of iron-zinc catalysts led to the low pressure nthesis of liquid and solid hydrocarbons from CO/Hj in 1925 [19. 20. However, it was found that these catalysts were deactivated rapidly and thus further investigations concentrated on nickel and cobalt catalysts. They led to the introduction of a standardized cobalt-based catalyst for llic normal-pressure synthesis of mainly saturated hydrocarbons at temperatures below 200 C. In 1936, the first four commercial plants went on stream. Until 1945 the Fischer-Tropscit synthesis was carried out in nine plants in Germany, one plant in France, four plants in Japan and one plant in Manchuria. The total capacity amounted to approximately one million tons of hydrocarbons per year in 1943. The catalysts used consisted of Co (1(X) parts), ThO (5 parts). MgO (8 parts), and kieselgur (200 parts) and were prepared by precipitation of the nitrates. These catalysts were used in fixed-bed reactors at normal or medium pressures (< 10 bar) and produced mainly saturated straightproduct obtained consisted of 46% gasoline. 23% diesel oil, 3% lubricating oil and 28% waxes (3.15). 

Meanwhile, Saso) II went on stream (1980) using the entrained-bed process with a capacity of approximately 2 million t/a and Sasol III with the same capacity is under construction and its production startHip is scheduled for 1982. By then, roughly 40% of the motor fuels consumed in South Africa will be produced by Fischer-Tropsch synthesis [2,12]. 

In summary, we have shown that by pyrolyzing waste polymers such as polyethylene, waxy products similar to those from Fischer-Tropsch processing can be made, which can then be converted to high-quality lubricant oils via wax hydroisomerization. While a detailed economic analysis has not yet been carried out, the much higher value of lube oil relative to transportation fuels suggests that this may be a more viable and profitable way of disposing of waste plastic, a growing waste stream problem. 

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