Fischer-Tropsch processes, alkane

Fischer-Tropsch Process. The Hterature on the hydrogenation of carbon monoxide dates back to 1902 when the synthesis of methane from synthesis gas over a nickel catalyst was reported (17). In 1923, F. Fischer and H. Tropsch reported the formation of a mixture of organic compounds they called synthol by reaction of synthesis gas over alkalized iron turnings at 10—15 MPa (99—150 atm) and 400—450°C (18). This mixture contained mostly oxygenated compounds, but also contained a small amount of alkanes and alkenes. Further study of the reaction at 0.7 MPa (6.9 atm) revealed that low pressure favored olefinic and paraffinic hydrocarbons and minimized oxygenates, but at this pressure the reaction rate was very low. Because of their pioneering work on catalytic hydrocarbon synthesis, this class of reactions became known as the Fischer-Tropsch (FT) synthesis. 

The Fischer-Tropsch process produces alkanes and alkenes ... 

The steps in the hydroformylation reaction are closely related to those that occur in the Fischer-Tropsch process, which is the reductive conversion of carbon monoxide to alkanes and occurs by a repetitive series of carbonylation, migration, and reduction... 

Moreover, alkanes can also be produced from the reaction of reforming products, H2 and CO/CO2, via methanation and Fischer-Tropsch processes. 

Good evidence has been obtained that heterogeneous iron, ruthenium, cobalt, and nickel catalysts which convert synthesis gas to methane or higher alkanes (Fischer-Tropsch process) effect the initial dissociation of CO to a catalyst-bound carbide (8-13). The carbide is subsequently reduced by H2to a catalyst-bound methylidene, which under reaction conditions is either polymerized or further hydrogenated 13). This is essentially identical to the hydrocarbon synthesis mechanism advanced by Fischer and Tropsch in 1926 14). For these reactions, formyl intermediates seem all but excluded. 

The history of the oxo reaction is also noteworthy. It was developed originally in Germany in the years following World War 1. At that time, the German chemical industry was faced with inadequate supplies of petroleum. Many German chemists therefore turned to research on ways by which hydrocarbons could be synthesized from smaller building blocks, particularly carbon monoxide and hydrogen derived from coal. The success achieved was remarkable and led to alkane and alkene syntheses known as the Fischer-Tropsch process ... 

The resulting Fischer-Tropsch process led to both alkanes and alkenes from the reduction of carbon monoxide (CO) by hydrogen (H2) over a cobalt catalyst (which is a mixture of dicobalt octacarbonyl [Co2(CO)8] and cobalt tetracarbonyl hydride [HCo(CO)4] and which is used at temperatures over 120°C and pressures above 200 atm), that is,... 

Formation of methane and longer chain alkanes catalyzed by traces of iron, cobalt, and nickel or by acidic impurities (see Fischer-Tropsch process. Section 6.11.1) (Liu, 2003 Twigg, 2001) ... 

Except for cobalt systems, other metals also demonstrate activity in the Fischer-Tropsch process. Mo/HZSM-5 turned out to be active in FT synthesis [98], The catalysts were tested at a low H /CO molar ratio 1.0, this composition being typical for biomass gasification. Liquid hydrocarbons obtained on Mo/HZSM-5 at 573 K were presented by alkylaromatics and lower branched and cyclic alkanes. The formation of aliphatic hydrocarbons was close to zero. The gas products included Cj-C alkanes. Higher alcohols and carboxylic acids (C,-Cg) were observed in the aqueous phase. The formation of hydrocarbons on Mo/zeolite is accounted for by the bifunctional zeolite acidity and molybdenum metal activities via alcohols as intermediates. The zeolite Y was also found to be a good support for Mo in the FT reaction. 

From Figure 11.8, it can be seen that Alkane, is produced from biomass in the conversion pathway sequence of pyrolysis and Fischer-Tropsch processes 1 and 2 followed by fractional distillation of alkanes, which are all thermochemical pathways. It is worth pointing out that specific separation processes that suit the identified product can be chosen and included in the integrated biorefinery to refine and separate the final product from by-products. Hence, separation processes for alkanes are chosen based on the results of the product design identified in stage 1 of the methodology. The performance of the separation processes is then taken into consideration in identifying the product yield and economic potential of the overall conversion pathway. 

From Figure 11.9, it can be seen that alcohols are produced from biomass in the conversion pathway sequence of ammonia explosion, organosolv separation, dehydration of sugars, hydrogenation of furfural and hydrogenation of TUFA 1. Alkane,- is produced from fractional distillation of alkanes, which are produced from pyrolysis of biomass, followed by Fischer-Tropsch process 2 together with dehydration of alcohols 2. The selected conversion pathways consist of both biochemical and thermochemical pathways. The comparison of the results generated for scenario 1 and 2 is summarised in Table 11.13. 

Generally, the Fischer—Tropsch process is operated in the temperature range of 150—300°C to avoid high methane byproduct formation. Increased pressure leads to higher conversion rates and also favors formation of desired long-chain alkanes. Typical pressures are in the range of one to several tens of atmospheres. The FT hydrogenation reaction is catalyzed mainly by Fe and Co catalysts, while the size and... 

Once the syngas is produced, the Fischer-Tropsch process can be used to produce primarily alkanes, through what is essentially a polymerization reaction... 

Synthesis gas is a mixture of carbon monoxide and hydrogen. In the Fischer-Tropsch process, the formation of alkane, alkene, alcohol of large chain-length occurs, depending on the catalyst used, as follows ... 

All meteorite analyses are made more difficult because of the problem of contamination. Thus one group (Kvenholden, 1970) reported the presence of polycyclic aliphatic compounds, while a second (Studier, 1972) found straight-chain alkanes to be the dominant species. The latter result was often cited and taken as evidence that processes similar to the Fischer-Tropsch synthesis must have occurred in nebula regions of the cosmos. 

Considerable attention has been paid to the application of CNTs as the catalyst support for Fischer Tropsch synthesis (FTS), mainly driven by utilization of the confinement effect (Section 15.2.3). In general, this process is a potential alternative to synthesize fuel (alkanes) or basic chemicals like alkenes or alcohols from syngas, which can be derived from coal or biomass. The broad product spectrum, which can be controlled only to a limited extent by the catalyst, prohibited its industrial realization so far, however, it is considered an important building block for future energy and chemical resource management based on renewables. 

Notably, once the oxygenated hydrocarbons have been converted into synthesis gas, it is then possible to carry out the subsequent conversion of synthesis gas into a variety of liquid products by well-established catalytic processes, such as the production of long-chain alkanes by Fischer-Tropsch synthesis and/or the production of methanol. 

Possible inter relationships of natural substances are important. Similarities of the low molecular weight alkane isomers from crude oil and Fischer-Tropsch synthesis product have been reported. A similar composition for high temperature coal carbonization has been found. The C4 to C7 alkane isomers from these sources can be calculated quantitatively with equations developed for Fischer-Tropsch products. A reversal of the concentrations of the monomethyl isomers from CG (2 Me > 3 Me) to C7 (3 Me > 2 Me) occurs in all three products comparisons at higher carbon numbers indicate some dissimilarities. Naphthene isomers for crude oil and high temperature coal carbonization also have similar compositions. Aliphatic hydrocarbons from low temperature coal processes are considerably different. The C1 isotopic composition of pure compounds from the various sources are being compared in order to provide information on their origin. 

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