Francis J. Derbyshire, George A. Odoerfer and D. Duayne Whitehurst
Mobil Oil Corporation, Mobil Research and Development Corporation, Central Research Division, Princeton, NJ 08540, USA
Abstract
Model compound studies have shown that 1,2,3,4-tetrahydroquinoline is an exceptionally good coal solvent. In the pure compound, subbituminous coal conversion to THF-soluble products approaches 100% under relatively mild reaction conditions. The effectiveness of tetrahydroquinoline for coal conversion appears to be related to its concentration relative to coal. The unique behaviour of tetrahydroquinoline is ascribed to its being a highly active H-donor; the fact that it is regenerable under reaction conditions by the reaction of hydrogen and quinoline; and that its polarity allows penetration of the coal structure and aids in dispersion of the dissolved coal. It has been found that, during reaction with coal, tetrahydroquinoline and other nitrogen compounds undergo extensive condensation reactions which result in an increase in the nitrogen content of the high boiling and non-distillable liquefaction products."
First of all, note this patent is owned by Mobil, who, as part of Exxon-Mobil, own the "MTG" - methanol-to-gasoline - process, wherein the methanol can be derived from coal and then converted into gasoline.
Second, tetralin can be easily regenerated under process conditions. It is not a totally consumed or wasted substance that will add great expense to the process.
Third, tetralin actually has the property of being able to penetrate coal particles, perhaps helping thereby to reduce the costs of mechanically preparing, grinding, the coal feed.
Finally, tetralin is not just a solvent, but a Hydrogen donor. It actually helps to make coal's solid carbon a liquid "hydro"carbon.