Fischer alkanes/alcohols

The Fischer-Tropsch synthesis, which may be broadly defined as the reductive polymerization of carbon monoxide, can be schematically represented as shown in Eq. (1). The CHO products in Eq. (1) are any organic molecules containing carbon, hydrogen, and oxygen which are stable under the reaction conditions employed in the synthesis. With most heterogeneous catalysts the primary products of the reaction are straight-chain alkanes, while the secondary products include branched-chain hydrocarbons, alkenes, alcohols, aldehydes, and carboxylic acids. The distribution of the various products depends on both the type of catalyst and the reaction conditions employed (4). 

It is now superflous to point out the renewed interest for the Fischer-Tropsch (F-T) synthesis (j) i. . the conversion of CO+H2 mixtures into a broad range of products including alkanes, alkenes, alcohols. Recent reviews (292.9k ) emphasized the central problem in F-T synthesis1 selectivity or more precisely chain-length control. 

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. 

Group II The activity drops more than the Ni surface concentration (Fig. 13), i.e., at least about 20 times. However, for several reactions this drop is two or more orders of magnitude. The reactions included in this group are methanation and Fischer-Tropsch synthesis, isomerization, de-hydrocyclization or hydrogenolysis of alkanes, ether formation from alcohols, metathesis of alkylamines, and possibly other reactions. 

The synthesis of fatty acids by a Fischer-Tropsch-type process as described in this chapter required the use of a catalyst (meteoritic iron) and a promoter. Potassium carbonate and rubidium carbonate were the only compounds evaluated which unambiguously facilitated the production of fatty acids. These catalytic combinations (meteoritic iron and potassium carbonate or rubidium carbonate) also produced substantial amounts of n-alkenes (in excess of n-alkanes) and aromatic hydrocarbons. A comprehensive study of the nonacidic oxygenated compounds produced in Fischer-Tropsch reactions (20,21) was not made. However, in the products analyzed (all promoted by potassium carbonate), long-chain alcohols and aldehydes were detected. 

The CO/H2 gas (also called water-gas) - depending on the CO H2 ratio - can also be converted (using the Fischer-Tropsch synthesis) to alkanes, alkenes and alcohols. Preferably, substances should be generated for application in known technical systems such as liquefied petroleum gas or low pressure gas (LPG) and gasoline as well as natural gas. The production of solar substitutes for diesels and oils (C > 8), that is petrol products from the fractional distillation of crude oil between 200 °C and 350 °C, is also possible, but offers no advantages in the solar fuel cycle and its stepwise replacement by gases and gasoline should be foreseen. 

Fischer Tropsch from synthesis gas to make alkanes or alcohols, G, catalyst, series of fixed beds, for alkanes, [-165 MJ/kmol] 350 °C, 40 s (1 species, 4 data), negligible temperature effect for alcohols [-245 MJ/kmol] 250 °C, 20 s (1 species, 4 data), negligible temperature effect. 

Because of decomposition problems of Rh catalysts during the separation of high-boiling products, most commercial plants for long-chain aldehydes (>Cjo) operate with Co catalysts. These approaches are based on unmodified catalysts under rather severe conditions (30 MPa, 200 C) [59]. Besides alcohols, alkanes are also formed. Through modification of the Co catalyst with phosphines, the pressure can be lowered (<10MPa) and, as a result, selectivity toward the formation of the linear alcohols is enhanced [60]. A suitable feedstock of higher olefins (up to C20) can be derived from Fischer-Tropsch feed (Sasol), or it is produced by SHOP. Products are commonly used for the production of surfactant alcohols. 

Most organic chemicals are currently made commercially iixim ethylene, a product of oil lehning. It is possible that in the next several decades we may have to shift toward other carbon sources for these chemicals as depletion of our oil reserves continues. Either coal or natural gas (methane) can be converted into CO/Hz mixtures with mr and steam (Eq. 12.18), and it is possible to convert such mixtures, variously called water-gas or synthesis gas to methanol (Eq. 12.18) and to allume fuels with various heterogeneous catadysts. In particular, the Fischer-Tropsch reaction (Eq. 12.19) converts synthesis gas to a mixture of long-chain alkanes and alcohols using heterogeneous catalysts. 

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 11.9, 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. 

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 ... 

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