Liquefaction catalysts

Solid liquefaction catalysts have been prepared by three procedures. 

Recoverable catalysts also offer a promising way to economize the cost of liquefaction catalysts (74, 75). Dow designed a process that utilized fine powders of MoS2 that were reported to be recoverable by hydroclone however, specific details have not been published (76). 

X. Lifetime, Recovery, and Regeneration of Liquefaction Catalyst in the Primary and Secondary Stages... 

Liquefaction catalysts, such as sulfides, lose their catalytic activity, especially hydrogenation activity when they are transformed into sulfate or oxide. Even reduction of the extent of sulfiding leads to a significant loss in catalyst activity. The crystalline form of the catalyst may also influence the catalytic activity. Thus, the level of sulfur during coal liquefaction is critical. This can be controlled by the addition of sulfur additives. 

The second approach depends heavily on obtaining very specific coals, which may exist in only limited supplies. Carbonates and chlorides have been found to be easily extracted by weak acids, such as acetic acid, without harming catalysts such as FeS or Ni-MoS, although regeneration and resulfiding may be necessary because some of the sulfur may be replaced by oxygen during liquefaction. Catalyst deactivation by minerals deposition will not be of concern for coals extracted in this way. 

In coal liquefaction, highly dispersed, disposable, catalysts are needed because maximal contact between coal and catalysts is essential. It is assumed that one of the roles of the coal liquefaction catalyst is to assist in the rehydrogenation of the donor solvent (e.g. tetralin) by facilitating the hydrogen transfer from the gas phase.36,37... 

Past efforts in developing coal liquefaction catalysts have focused on alumina-supported systems and, except for exploratory studies, little attention has been given to systematic development of novel formulations. A particularly promising approach to the development of new catalysts specifically designed lor coal liquefaction processes lies in the formulation of multicomponent systems that, in comparison to work on single or bimetallic systems, are essentially unexplored. Use of multimetallic systems offers the possibility of multifunctional catalysts that are needed to perform the many different reactions encountered in coal processing. Because of its versatility for the preparation of multimetallic catalysts, the HTO system is an excellent candidate for further development. 

Hydrous titanium metal oxide catalysts are extremely versatile materials that have promise as direct coal liquefaction catalysts. Previous studies have shown that they perform well in both batch and bench-scale coal liquefaction tests. 

DW Matson, JC Linehen, JG Darab, ME Buehler. Nanophase iron-based liquefaction catalysts synthesis, characterization, and model compound reactivity. Energy and Fuels 1994 8 10. 

Different types of other coal liquefaction processes have been also developed to convert coals to liqnid hydrocarbon fnels. These include high-temperature solvent extraction processes in which no catalyst is added. The solvent is usually a hydroaromatic hydrogen donor, whereas molecnlar hydrogen is added as a secondary source of hydrogen. Similar but catalytic liquefaction processes use zinc chloride and other catalysts, usually under forceful conditions (375-425°C, 100-200 atm). In our own research, superacidic HF-BFo-induced hydroliquefaction of coals, which involves depolymerization-ionic hydrogenation, was found to be highly effective at relatively modest temperatnres (150-170°C). 

Liquefaction. Liquefaction of coal to oil was first accompHshed in 1914. Hydrogen was placed with a paste of coal, heavy oil, and a small amount of iron oxide catalyst at 450° and 20 MPa (200 atm) in stirred autoclaves. This process was developed by the I. G. Earbenindustrie AG to give commercial quaUty gasoline as the principal product. Twelve hydrogenation plants were operated during World War II to make Hquid fuels (see CoAL... 

Background Indirect coal liquefaction differs fundamentally from direct coal hquefaction in that the coal is first converted to a synthesis gas (a mixture of H9 and CO) which is then converted over a catalyst to the final product. Figure 27-9 presents a simplified process flow diagram for a typical indirect coal hquefaction process. The synthesis gas is produced in a gasifier (see a description of coal gasifiers earlier in this section), where the coal is partially combusted at high temperature and moderate pressure with a mixture of oxygen and steam. In addition to H9 and CO, the raw synthesis gas contains other constituents (such as CO9, H9S, NH3, N9, and CHJ, as well as particulates. 

Liquefaction of coal involves the extraction of carbon by solvents at high pressures and at temperatures up to about 500 C, followed by separation of the extract, which is then hydrogenated in the presence of a catalyst to yield hydrocarbon oils. The corrosion conditions are not regarded as severe. 

In direct liquefaction, coal is heated in the presence of hydrogen and a catalyst such as cobalt-molybdenum or nickel-molybdenum on alumina to give a greater yield of high-quality hydrocarbons than that produced by pyrolysis. This hydrogenation process has been demonstrated in several 50- to 250-ton-per-day plants. 

The formation of these thermal fragments is necessary to catalytic liquefaction processes before the catalysts can become effective for hydrogen introduction, cracking and/or heteroatom removal (10). ... 

In catalytic coal liquefaction processes, reaction temperatures must be high in order to insure that thermal reactions disrupt the coal structure to the point that the catalyst can act on the products. 

To improve selectivity and conservation of hydrogen over present liquefaction technology in the conversion of coal to high quality liquids, we believe that thermal reactions should be kept as short as possible. Catalytic processes must be used for upgrading but should be used in a temperature regime which is optimal for such catalysts. 

Kinetics of Direct Liquefaction of Coal in the Presence of Molybdenum—Iron Catalyst... 

Many studies on direct liquefaction of coal have been carried out since the 1910 s, and the effects of kinds of coal, pasting oil and catalyst, moisture, ash, temperature, hydrogen pressure, stirring and heating-up rate of paste on coal conversion, asphaltene and oil yields have been also investigated by many workers. However, few kinetic studies on their effects to reaction rate have been reported. 

In this paper the effects of kinds of coal, pasting oil, catalyst and reaction temperature on coal liquefaction are illustrated, and a few kinetic models for catalytic liquefaction of five coals carried out in an autoclave reactor are proposed. 

Under the same reaction conditions, the reaction rate are depend on the mechanism of coal liquefaction and kinds coal and catalyst. The reaction rate is in the following order Morwell> Bukit... 

---