Aspects of donor solvent coal dissolution reactions: Effects of organosulphur compounds on hydrogen transfer, decomposition of 1,3-diphenylpropane and liquefaction of Illinois coals

Abstract

The effects of organic sulphur compounds on the hydrogen atom exchange reactions between tetralin- d 12 and diphenylmethane, the thermal decomposition of 1,3-diphenylpropane in tetralin and the thermal dissolution of three coals from the Illinois Basin in tetralin were investigated at 300–500 °C. All three reactions are promoted significantly by disulphides, thiols and certain thioethers, whereas thiophens are ineffective. The pattern of reactivity for the exchange reaction is diphenyl disulphide[(phenyl- methyl)thio]benzene benzenethiol hydrogen sulphide l,l'-thiobisbenzene. The naphthalenethiols promote the exchange more effectively than benzenethiol, whereas butanethiol is less reactive. These results can be accounted for on the basis of enhanced rates of the initiation and propagation reactions. Thermochemical analyses support this interpretation. The rate of decomposition of 1,3-diphenylpropane in tetralin to give principally toluene and ethylbenzene is also accelerated. In this instance, the thiyl radicals formed from the organosulphur compounds accelerate the abstraction of benzylic hydrogen atoms from the diphenylpropane and thereby provide a greater steady-state concentration of the unstable l(1,3- diphenyl)propyl radical. Thiols, thioethers and disulphides accelerate the thermal dissolution reactions of three coals from the Illinois Basin. These organosulphur compounds are more effective reagents, on a molar basis, than hydrogen sulphide, pyrite or pyrrhotite. Illinois No. 6 coal, for example, is rendered 70% soluble in pyridine after 5 min reaction at 350 °C in the presence of benzenethiol. The role of organic and inorganic sulphur-containing compounds on the dissolution reaction is discussed.