Ammonia, Fischer-Tropsch process

As a constituent of synthesis gas, hydrogen is a precursor for ammonia, methanol, Oxo alcohols, and hydrocarbons from Fischer Tropsch processes. The direct use of hydrogen as a clean fuel for automobiles and buses is currently being evaluated compared to fuel cell vehicles that use hydrocarbon fuels which are converted through on-board reformers to a hydrogen-rich gas. Direct use of H2 provides greater efficiency and environmental benefits. ... 

In general, TPR measurements are interpreted on a qualitative basis as in the example discussed above. Attempts to calculate activation energies of reduction by means of Expression (2-7) can only be undertaken if the TPR pattern represents a single, well-defined process. This requires, for example, that all catalyst particles are equivalent. In a supported catalyst, all particles should have the same morphology and all atoms of the supported phase should be affected by the support in the same way, otherwise the TPR pattern would represent a combination of different reduction reactions. Such strict conditions are seldom obeyed in supported catalysts but are more easily met in unsupported particles. As an example we discuss the TPR work by Wimmers et al. [8] on the reduction of unsupported Fe203 particles (diameter approximately 300 nm). Such research is of interest with regard to the synthesis of ammonia and the Fischer-Tropsch process, both of which are carried out over unsupported iron catalysts. 

Another important application of iron is as an industrial catalyst. It is used in catalyst compositions in the Haber process for synthesis of ammonia, and in Fischer-Tropsch process for producing synthetic gasoline. 

Iron catalysts have found only limited use in usual hydrogenations, although they play industrially important roles in the ammonia synthesis and Fischer-Tropsch process. Iron catalysts have been reported to be selective for the hydrogenation of alkynes to alkenes at elevated temperatures and pressures. Examples of the use of Raney Fe, Fe from Fe(CO)5, and Urushibara Fe are seen in eqs. 4.27,4.28, and 4.29, respectively. 

Chemicals—H2, CO, or both are used as chemical feedstock for the production of ammonia, oxo-chemicals, methanol, acetic acid, hydrogen, fertilizer, or synthetic hydrocarbon fnels (zero-snlfnr diesel and other transportation fnels) manufactnred nsing Fischer-Tropsch processing, and other chemicals. 

See ammonia, anhydrous Oxo process Haber, Fritz water gas gasification Fischer-Tropsch process. 

Iron surfaces have received far more interest than the other two elements in this group, mainly because of the extensive use of promoted iron catalysts in the synthesis of ammonia and in the Fischer-Tropsch process. Iron is distinct from ruthenium and osmium in that it normally... 

Water gas is used extensively in the industry for the manufacture of ammonia, methanol, hydrogen (for hydrotreating, hydrocracking of petroleum fractions and other hydrogenations in the petroleum refining and petrochemical industry), hydrocarbons (by the Fischer-Tropsch process) and metals (by the reduction of the oxide ore). 

Industrial production. Hydrogen can be produced commercially by several processes. Historically, it was first produced from coke oven gas, and in Germany by the Fischer-Tropsch process and to a lesser extent by the Messerschmidtt process. The hydrogen was separated from the coke oven gas (i.e., 56 vol.% H, 26 vol.% CH, 7 vol.% CO and others) by liquefaction and used afterwards in ammonia synthesis. The Fischer-Tropsch process... 

Synthesis gas is used as a feedstock for numerous petrochemical processes, including ammonia-based fertiliser, alkenes production (via the Fischer-Tropsch process) and methanol production. The general catalysed process is as follows ... 

Removal of carbon monoxide and carbon dioxide by methanation is required for the protection of certain hydrogenation and ammonia synthesis catalysts against rapid deactivation. It is also necessary when the hydrogen is used in hydroprocessing operations because CO2 and CO can lead to temperature excursions and catalyst damage in the reactors. Furthermore, methanation is an essential step in the reaction systems associated with the Fischer-Tropsch synthesis and with the production of synthetic natural gas from liquid hydrocarbons and coal. Grayson (1956) presented a detailed discussion of methanation in connection with the Fischer-Tropsch process. 

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. 

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. 

Iron has a rich surface coordination chemistry that forms the basis of its important catalytic properties. There are many catalytic applications in which metallic iron or its oxides play a vital part, and the best known are associated with the synthesis of ammonia from hydrogen and nitrogen at high pressure (Haber-Bosch Process), and in hydrocarbon synthesis from CO/C02/hydrogen mixtures (Fischer-Tropsch synthesis). The surface species present in the former includes hydrides and nitrides as well as NH, NH2, and coordinated NH3 itself. Many intermediates have been proposed for hydrogenation of carbon oxides during Fischer-Tropsch synthesis that include growing hydrocarbon chains. 

The methanation reaction is a highly exothermic process (AH = —49.2 kcal/ mol). The high reaction heat does not cause problems in the purification of hydrogen for ammonia synthesis since only low amounts of residual CO is involved. In methanation of synthesis gas, however, specially designed reactors, cooling systems and highly diluted reactants must be applied. In adiabatic operation less than 3% of CO is allowed in the feed.214 Temperature control is also important to prevent carbon deposition and catalyst sintering. The mechanism of methanation is believed to follow the same pathway as that of Fischer-Tropsch synthesis. 

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