Catalytic liquefaction processes

The final category of direct liquefaction process employs the concept of catalytic liquefaction in which a suitable catalyst is used to add hydrogen to the coal. These processes usually require a liquid medium with the catalyst dispersed throughout or may even employ a fixed-bed reactor (see p. 394). On the other hand, the catalyst may also be dispersed within the coal whereupon the combined coal-catalyst system can be injected into the reactor. 

In order to achieve the direct hydrogenation of the coal, the catalyst and the coal must be in intimate contact, but if this is not the case, process inefficiency is the general rule. On the other hand, there has been the tendency of late to achieve coal-catalyst contact by the use of a hydrogen donor solvent. Alternatively, a catalyst with a sufficiently high vapor pressure may be employed so that catalyst deposition on the coal surface) is achieved under process conditions. 

Processes in which the coal and the catalyst are in intimate contact in the presence of hydrogen gas are often referred to as solid-gas catalytic hydrocarbonization or dry coal hydrogenation. The major features of these processes are (1) rapid heating to temperatures of the order of 450°C-600°C 

Bergius Bergius Plug flow Iron oxide 4 0 895 3000-10000 

University University of Utah Entrained flow Zinc chloride. 500-550 930-1020 1500-2500 

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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). 

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). ... 

The second, catalytic liquefaction process is similar to the first except that there is a catalyst in direct contact with the coal. ZnCl2 and other Friedel-Crafts catalysts, including AICI3, as well as BFj-phenol and other complexes catalyze the depolymerization-hydrogenation of coals, but usually forceful conditions (375 t25°C, 100-200 atm) are needed. Superacidic HF-BF3-induced liquefaction of coals8 involves depolymerization-ionic hydrogenation at relatively modest 150-170°C. 

Data for the kinetics of coal liquefaction have been published in the literature (1-11). A review of the reported studies has recently been given by Oblad (12). The reported data were mostly obtained in bench-scale reactors. Guin et al. (7) studied the mechanism of coal particle dissolution, whereas Neavel (7), Kang et al. (8), and Gleim (10) examined the role of solvent on coal liquefaction. Tarrer et al. (9) examined the effects of coal minerals on reaction rates during coal liquefaction, whereas Whitehurst and Mitchell (11) studied the short contact time coal liquefaction process. It is believed that hydrogen donor solvent plays an important role in the coal liquefaction process. The reaction paths in a donor solvent coal liquefaction process have been reviewed by Squires (6). The reported studies examined both thermal and catalytic liquefaction processes. So far, however, very little effort has been made to present a detailed kinetic model for the intrinsic kinetics of coal liquefaction. 

Catalytic liquefaction process allows a slurry of coal and oil to be hydrogenated over active catalysts in a fixed bed reactor, in an ebullating bed reactor or in a trickle bed reactor to produce a liqiiid hydrocarbon product ... 

The second section of this volume describes several potentially new liquefaction processes which may have higher efficiencies than today s developing technologies. The theme of the Storch Award Symposium, featured throughout these six chapters, was new process potentials through the use of short-contact-time thermal processes followed by catalytic upgrading. 

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. 

Stephens, H. P., and Chapman, R. N., The Kinetics of Catalytic Hydrogenation of Pyrene Implications for Direct Coal Liquefaction Processing. In Am. Chem. Soc. Div. Fuel Chem, 1983. Prepr. Pap. 28 pp. 161-168. 

Catalytic coal liquefaction processes do not specifically use hydrogen donor solvents although coal is introduced into the liquefaction reactor as a slurry in a recycle liquid stream. Catalyst is used as a powder or as granules such as pellets or extrudates. If powdered catalyst is used, it is mixed with the coal/liquid stream entering the reactor. Pelleted catalyst can be used in fixed bed reactors if precautions are taken to avoid plugging with solids or in fluidized bed reactors. In the latter case, the reacting system is actually a three phase fluidized bed, that is, catalyst particles and coal solids, as well as liquid, are fluidized by gas. 

After World War II, direct liquefaction of coal became uneconomical as the use of lower-cost petroleum products became more widespread. However, the German process of indirect coal liquefaction, the Fischer-Tropsch process, continued to hold some interest. The Fischer-Tropsch process first involved production of a carbon monoxide and hydrogen-rich synthesis gas by the controlled gasification of coal followed by a catalytic reaction process to yield a valuable mixture of hydrocarbon products. Simplified Fischer-Tropsch reactions are shown by the following equations ... 

A multistage liquefaction process consisting of deashing, hydrogen-transfer liquefaction, catalytic depolymerization with FeS2, catalytic hydro-... 

T he ash content and trace element distribution in oils produced from coal are of concern for two different reasons—they bear on possible environmental hazards from the use of the oil and they determine the suitability of the oil for firing in gas turbines. Some trace element analyses of oils produced by the catalytic liquefaction of three coals are reported, together with analyses of the solid residues from the process. The data are neither comprehensive nor particularly accurate and are offered at this time because, in the absence of better information from other laboratories, they seem to be of some interest. 

The SRC-II process is one of several coal liquefaction processes currently under development in programs funded by the Department of Energy (DOE). Product from this process is a distillate that is relatively attractive as a feed for conversion to transportation fuels. Essentially all of the nitrogen, sulfur, and oxygen can be removed in a single catalytic hydro-treating stage to yield a naphtha that is an excellent feed for a catalytic reformer and a middle distillate fraction that is a... 

The available information leads one to believe that the maximum production of liquids with no net hydrogen consumption and the low-temperature catalytic hydrocarbonization/gasification are alternatives which appear to have great merit. The former of these, when applied to western coals, appears to be technically ready for commercial application and economically competitive with alternative coal liquefaction processes. Advantages of the flash hydropyrolysis processes over the Coalcon process are difficult to perceive. 

What, then, does the future hold This author believes that the catalytic hydrocarbonization/gasification concept will ultimately achieve commercial success for the production of liquid and gaseous fuels from coal. In selected applications, the mild hydrocarbonization of western coal to produce liquid and gaseous fuels with power generation from the low-sulfur char may also be commercially attractive. Finally, further development of the flash hydropyrolysis technology, as exemplified by the Rocketdyne project, may eventually lead to a technically and economically attractive liquefaction process. But the most important questions still remain unanswered. Does private industry have sufficient interest to pursue the possibilities Where is the interest focused Will a private consortium build a hydrocarbonization/ cogeneration complex using western coal Will the phoenix arise from the ashes ... 

Several processes have been developed for coal liquefaction. Large-scale pilot plants have been in operation for the solvent-refining coal (SRC) process, and a pilot plant is being constructed for the H-Coal process, which is a direct catalytic process. Construction of demonstration plants is under consideration. The coal liquids produced from the current processes contain large amounts of residual fuels. They probably will be used initially as boiler fuels for stationary power plants. However, the nitrogen content of coal liquids is much higher than the petroleum residual fuels. The sulfur contents of coal liquids can vary considerably they depend on the type of coal and the liquefaction process used. Current coal liquefaction processes are capable of produc-... 

Although SRC-II was basically a thermal liquefaction process, it was most successful using bituminous coals with a high native pyrite content. Iron sulfides are well known to have catalytic properties for coal liquefaction. Recycling part of the ash-minerals-containing bottoms had two beneficial effects (1) it increased the pyrite concentration in the reactor feed, and (2) it increased the residence time for heavy components, thus giving them more time to hydrocrack to distillate products. A block flow diagram of the SRC-II process is shown in Fig. 19.19. 

CSF [Consol Synthetic Fuels] A two-stage coal liquefaction process. In the first stage, the coal is extracted with process-derived oil and the ash removed. In the second, the extract is catalytically hydrogenated. Piloted by the Consolidation Coal Company, Cresap, WV, from 1963 to 1972. See also H-Coal, SRC, Synthoil. 

IG-NUE A coal liquefaction process developed by Bergbau-Forschung in Germany during World War II. Catalytic metal salts were impregnated in, or precipitated on, the coal. A pilot plant was to have been built in Westphalia in 1977. 

LSE [Liquid Solvent Extraction] A coal liquefaction process, under development in 1990 by British Coal, at Point of Ayr, North Wales, now closed. The coal is dissolved in a coal-derived hydrocarbon solvent and then catalytically hydrocracked. 

Utilization of wood-biomass residues as well as waste polymers is the important direction of recent research activities. It is known that direct catalytic liquefaction of plant biomass can be used to produce liquid fuels and chemicals [1,2]. Co-pyrolysis and co-hydropyrolysis processes have the potential for the environmentally friendly transformation of lignocellulosic and plastic waste to valuable chemicals. 

Obtained data show that, the mixtures of the different types of the natural and synthetic organic polymers can be successfully converted with a high yield to light distillate fraction by pyrolysis under inert atmosphere and catalytic hydtopyrolysis in the autoclave conditions. The optimum tenqreiature of biomass / plastic mixtures conveision which coiresponds to the maximum yield of liquids is 390 - 400 C. In the CO liquefaction processes the interaction between products of natural and synthetic polymers thermal deconqwsition takes place. 

While many studies indicate that pyrrhotites are probably involved in the liquefaction process, the exact mechanism by which pyrrhotite catalyzes the conversion of coal to oil is not clear. Based on the works of Thomas et al. (1 ) and Derbyshire et al., (13) one can suggest that a possible role of pyrrhotite is as a hydrogenation catalyst. However, more work is necessary on the surface properties of the pyrrhotites and the interaction with model compounds before a definite catalytic mechanism can be proposed. 

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