Liquefaction, coal, process conditions

A large program of work on coal liquefaction at the U.S. Bureau of Mines station at Bruceton, Pa., under the direction of H. H. Storch, was stimulated by the pre-war and wartime developments in Germany (49,50,51,52,53). The very extensive studies showed that, with some modification of processing conditions, most U.S. coals could be converted to liquid fuels in acceptable yields... 

An enormous amount of work both at bench scale and at pilot plant scale have been conducted to study the production of liquid and gaseous hydrocarbons from coal. Since most of the analytical methods are either very time consuming or very specialized, almost all the data available on the coal liquefaction process are based on distillation data or on the assumption that all products which are not insoluble solids are converted. It is known that products of liquefaction vary based on coal, reaction conditions, and media of reaction hence, conversion and yield may be based on very different products. 

Effect of Liquefaction Processing Conditions on Combustion Characteristics of Solvent-Refined Coal... 

At 450"C in the presence of the dispersed catalyst, results are remarkably similar with respect to distillate yields, coal conversions, and net hydrogen consumption. Use of a superior hydrogen donor solvent in the liquefaction experiments does lead to a consistently lower gas make and slightly higher coal conversion to heptane solubles than in the coprocessing runs under comparable processing conditions. 

Hydropyrolysis Process. Two hydropyrolysis reactors were used in this study. The Sunnyside and Asphalt Ridge bitumen were processed in a reactor consisting of a coiled stainless steel tube 3/16" i.d. x 236" long. This reactor has been previously described by Ramakrishnan (1). The TS-IIC oil was processed in a reactor originally developed for short residence time coal liquefaction. This reactor also consists of coiled stainless steel tubes 3/16" i.d. The length of this tube system can be varied from 20 to 120 feet, and has been previously described by Wood, et al. (10). The length of the reactor for runs reported in this paper was 100 feet. Average residence times were calculated from the volumetric flow rates and the reactor volume at process conditions. The reaction mixture, which is predominantly H, was assumed for purposes of this calculation to behave as an ideal gas. The reactors were pre-sulfided with H S to inhibit catalytic reactions from wall surfaces. 

Coal liquefaction under supercritical (or subcritical) water condition has some advantages over organic solvents. Supercritical water is miscible with H2, CO, aromatics, and oils, which provides a unique, homogeneous reaction medium for coal liquefaction. CTL process with supercritical water is more environment-friendly than SRC-II process and has higher conversion for low-rank coal [31,32]. 

The first process was studied by Berthelot in 1867 and was further developed in Germany by Bergius in 1910. The early Bergius process involved the reaction of H2 under atmospheric pressure with pulverized coal suspended in an oil heated to about 450°C in the presence of a catalyst such as stannous formate or Mo. The liquid oil product is separated from the solid residue and processed as ordinary crude oil. Modem developments in this coal liquefaction approach include (1) Exxon Donner Solvent (EDS) process, (2) the HRI H-Coal process, and (3) the Gulf Solvent Refined Coal SRC-II process. The major improvement of these processes over the Bergius process is in the catalyst used, allowing for milder reaction conditions. 

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). 

Carbonaceous solids appear as a result of retrogressive reactions, in which organic thermal fragments recombine to produce insoluble semi-cokes (59,65). Coke formation is observed during liquefaction of all coals and its extent can vary widely according to the coal, the reaction solvent, and reaction conditions. The predominant inorganic species produced during the process of coal... 

Since the earliest days of coal liquefaction processing and research, the need for correlations of coal properties with coal reactivity under direct hydroliquefaction conditions has been recognized by coal scientists. This article traces the history of reactivity correlations from the earliest work of Bergius through the classic work at the Bruceton Bureau of Mines during the 1940 s to the most recent advances in this subject. Particular emphasis in this review is placed on an examination of the contributions of Professor Peter Given and his co-workers. Reactivity methodologies and techniques for correlation are presented and critically evaluated for utility and applicability as predictive tools. 

Much of the recent research in direct coal liquefaction seeks to develop methods for dissolving coal at low reaction severity (defined as temperatures below 350 and pressures of 1000-1500psig). Most of these efforts have been prompted by several incentives that exist for converting coal at milder reaction conditions than those utilized in conventional processes, including ... 

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. 

Catalysts and donors do not always perform most efficiently under the same conditions. Hence, optimal application is achieved in consecutive steps, where the best conditions can be selected for each step separately. In such a two-step primary liquefaction process, expensive catalysts, such as Co-Mo and Ni-Mo, are not necessarily employed. These catalysts are more appropriately used when the coal has been depolymerized to soluble products and catalyst poisons are not present in the final upgrading stages. 

Also, it should be noted that shale oil is predominently in the middle distillate boiling range with low residue and naphtha content. The absence of resid in coal liquids results from the severe hydrogenation conditions imposed in the coal liquefaction processes and the use of the remaining residue for hydrogen production. For shale oil, the retorting process destroys most the residual materials leaving a syncrude that is mainly a distillate. 

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