Aromatics, Fischer-Tropsch process

Synfuels derived from natural gas (and coal) via syngas in the Fischer-Tropsch process have an inherent high quality (being, for example, sulphur- and aromatics-... 

The fact that Fischer-Tropsch fuels contain neither sulfur nor aromatics may become a strong selling point for the process. Less sulfur in the fuel has, of course, a direct effect on the sulfur oxides in the emissions, and the newly developed exhaust purification systems for lean burning engines that can be introduced means that all emissions, including GO2 and NOx, will diminish. Aromatics promote particulate formation in the combustion of diesel fuels and are therefore undesirable. We discuss this further in Ghapter 10. 

In addition to the Fischer-Tropsch-derived material, coal-derived liquids were also recovered from low-temperature coal gasification (not shown in Figures 18.3 and 18.4). These products were processed separately to produce chemicals, such as phenols, cresols, and ammonia, as well as an aromatic motor gasoline blending stock.34 The latter was mixed with the Fischer-Tropsch-derived motor gasoline. 

Dyotropic Rearrangements and Related o--cr Exchange Processes, 16, 33 Electronic Effects in Metallocenes and Certain Related Systems, 10, 79 Electronic Structure of Alkali Metal Adducts of Aromatic Hydrocarbons, 2, 115 Fast Exchange Reactions of Group I, II, and III Organometallic Compounds, 8, 167 Fischer-Tropsch Reaction, 17, 61 Flurocarbon Derivatives of Metals, 1, 143... 

Fischer-Tropsch A process for converting synthesis gas (a mixture of carbon monoxide and hydrogen) to liquid fuels. Modified versions were known as the Synol and Synthol processes. The process is operated under pressure at 200 to 350°C, over a catalyst. Several different catalyst systems have been used at different periods, notably iron-zinc oxide, nickel-thoria on kieselgtihr, cobalt-thoria on kieselgiihr, and cemented iron oxide. The main products are C5-Cn aliphatic hydrocarbons the aromatics content can be varied by varying the process conditions. The basic reaction was discovered in 1923 by F. Fischer and... 

The Fischer-Tropsch (FT) catalytic conversion process can be used to synthesize diesel fuels from a variety of feedstocks, including coal, natural gas and biomass. Synthetic diesel fuels can have excellent autoigitition characteristics. The Fischer-Tropsch diesel is composed of only straight-chain hydrocarbons and has no aromatics or sulfur. The synthetic Fischer-Tropsch diesel fuel can provide benefits in terms of both PM and NO, emissions. 

A mixture of CO + H2 is used in the Fischer-Tropsch reaction to make hydrocarbons in high yields. The reaction requires a catalyst, usually Fe or Ni supported on silica, a temperatue of 200-400°C and a short contact time. Depending on the conditions, aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, and acids can be produced. If NH3 is added to the CO + H2, then amino acids, purines, and pyrimidines can be formed.23 The intermediates in these reactions are not known, but it is likely that HCN is involved together with some of the intermediates postulated for the electric discharge processes. 

The energy consumption in our country is tilted heavily towards the middle distillate (kerosene/ATF and diesel oil). The demand of diesel oil alone is more than 37% [1]. The recoverable reserve of petroleum crude in India is 763 MMT against 193 billion tons of coal [2]. On the other hand, Fischer-Tropsch Synthesis (FTS) produces superior quality diesel oil since the feedstock does not contain sulphur and nitrogen compounds or aromatics. The only drawback is that the process produces a wide spectrum of products from C1-C340+ hydrocarbons [3]. Hence the present global effort is towards search for a particular product selective catalysts. 

ZSM-5 based catalysts are widely used commercially, either in their unpromoted acidic form, or as metal promoted catalysts. The aromatisation of light paraffins is an example of a refining process where ZSM-5 catalysts are often encountered. With the global shift towards higher octane unleaded petrol, aromatisation is one of the processes that can be used to produce high octane blending stock. In a Fischer-Tropsch environment, where the unrefined Fischer-Tropsch product contains very little aromatics, this is an especially attractive option. However, Fischer-Tropsch derived material does not only contain paraffins, but also contains olefins and oxygenates. 

The Synol and isosynthesis processes, as well as the Oxyl and iron nitride variations of the Fischer-Tropsch synthesis, were developed to produce special products from synthesis gas. All but the isosynthesis are designed to produce high yields of oxygenated materials. The isosynthesis yields highly branched aliphatic hydrocarbons and aromatics. While none of these processes has been used commercially, they could be of interest at some future time. 

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