Hydrogen-Transfer Reactions

Abstract

The hydrogen-transfer reactions that occur during coal liquefaction reactions are essential for the conversion of intractable coal molecules into liquids and soluble products. Virtually all the practical processes for coal liquefaction, such as the solvent-refined Coal II process,(1) the Exxon donor-solvent process,(2) the integrated two-stage liquefaction process, (3a,3b) and the Chevron coal liquefaction process,(4) use a portion of the liquid coal products as a solvent for the dissolution reaction. In the more recently developed Chevron coal liquefaction process,(4) the liquefaction reaction is carried out in two separate, but closely coupled, reactors as shown in Figure 1. A slurry of the coal in a portion of the coal liquid (recycle oil) is introduced into the first-stage reactor and the product of this phase of the reaction is then fed into the second-stage reactor. The large coal molecules are decomposed and, in part, dissolved in the first reactor and the initial product is refined catalytically in the second reactor to yield the coal liquefaction products which include a fraction suitable for use as the solvent for the reaction. The conversion reactions require not only the addition of hydrogen but also the redistribution of the hydrogen atoms already present in the coal molecules.