Coal liquefaction chemistry

Fundamental studies of coal liquefaction have shown that the structure of solvent molecules can determine the nature of liquid yields that result at any particular set of reaction conditions. One approach to understanding coal liquefaction chemistry is to use well-defined solvents or to study reactions of solvents with pure compounds which may represent bond-types that are likely present in coal [1,2]. It is postulated that one of the major routes in coal liquefaction is initiation by thermal activation to form free radicals which abstract hydrogen from any readily available source. The solvent may, therefore, function as a direct source of hydrogen (donor), indirect source of hydrogen (hydrogen-transfer agent), or may directly react with the coal (adduction). The actual role of solvent thus becomes a significant parameter. 

Retrograde Diels-Alder reactions are unlikely reactions in coal liquefaction chemistry due, again, to the lack of suitable molecular structures. Decomposition of cyclohexene to ethylene and 1,3-butadiene, for instance, is 40 kcal/mol endothermic and at 450°C proceeds at a rate such that the half-life of cyclohexene is 13 hours (11a). For tetralin to react by an analogous reaction, resonance stability would be lost, and the reaction would be many orders of magnitude slower than cyclohexene. 

R. P. Skowronski, J. J. Ratto and L. A. Heredy, "Deuterium Tracer Method for Investigating the Chemistry of Coal Liquefaction", Annual Report, 1977, Rockwell International,... 

Numerous implications on the fundamental chemistry of coal liquefaction can be drawn from the observed reaction of solvent isomerization and adduction. The literature indicates that... 

Makino, E. Coal liquefaction, in Ullmann s Encyclopedia of Industrial Chemistry, 7th ed., CRC Press, Boca Raton, Fla, 2005. 

Whitehurst, D. D. Mitchell, T. O. Faicasiu, M. Coal Liquefaction-The Chemistry and Technology ofThermal Processes (Academic Press 1980, N.Y.), pp. 207-272 and references cited therein. 

The chemistry of coal liquefaction is not very well understood, even after more than two decades of research into the kinetics and mechanism of the process. There have been a number of models for conversion proposed, most of them focused on the several liquefaction products, including preasphaltenes, asphaltenes, oils, and gases. A survey of some of the models has been presented (1 ), and a common feature among them is the multiplicity of paths connecting all of the components. 

We have our work divided into process engineering, process chemistry, catalysis, and support technology. As an example, one of the indirect liquefaction projects, tube wall reactor, deals with the design and operation of high thermal efficiency catalytic reactors for syn-gas conversion. Other activities are coal liquefaction properties of coal minerals, the role of catalysts, coal liquid product stability, and environmental impact—to name a few. 

Coal Liquefaction, The Chemistry and Technology of Thermal Processes Academic Press, New York, 1980, 178-189. 

A question of considerable interest in coal hydroliquefaction chemistry is the amount and nature of "organically bound metals in the coal. One reason for this interest is the observation that when supported metal direct conversion catalysts are used in liquefaction reactors, a primary mode of deactivation is metals deposition Q, 2). In particular, recent work at the Pittsburgh Energy Technology Center (PETC) (4,5) and elsewhere (3) has indicated very high levels of titanium deposition on supported Co Mo catalysts used in the fixed bed continuous reactor system. It has been suggested that the culprits in such deposition are soluble metal species (6 9) The analyses of a Western Kentucky (Homestead) hvBb feed coal and of material deposited between the catalyst pellets in the fixed bed reactor at PETC (4) are shown in Table I. 

Consequences of the Mass Spectrometric and Infrared Analysis of Oils and Asphaltenes for the Chemistry of Coal Liquefaction... 

Liquid clathrates represent an interesting area of supra-molecular chemistry. Over the years, the move from air-sensitive to air-stable liquid clathrate systems greatly simplified their handling procedures. Also, with the emergence of air-stable liquid clathrate systems, their possible applications broadened beyond early useful applications of coal liquefaction and hydrocarbon separations to include aqueous separations and catalytic systems. 

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