Hydropyrolysis: a versatile technique for solid fuel liquefaction, sulphur speciation and biomarker release

Abstract High oil yields (ca. 60% both daf and carbon basis) with relatively low hydrocarbon gas yields can be achieved for coals and oil shales in fixed-bed pyrolysis at high hydrogen pressure (hydropyrolysis, 15 MPa) with relatively fast heating and a suitable dispersed catalyst, such as sulphided Mo or Fe. This article reviews the application of hydropyrolysis to biomass and its adaptation as an analytical technique to specify organic sulphur forms and to release covalently-bound biomarker hydrocarbons for coals and petroleum source rocks. Results for cellulose, eucalyptus wood and sugar cane bagasse demonstrate the potential of hydropyrolysis for producing bio-oils with much lower oxygen contents than by traditional pyrolysis processes. The inherent drawbacks with temperature programmed reduction (TPR) for specifying the organic sulphur forms in sedimentary organic matter in that (i) thiophenic sulphur has largely been undectable and (ii) sulphides interconvert readily into thiophenes have been overcome by the use of the well-swept fixed-bed hydropyrolysis reactor operating at 15 MPa. The application of high pressure TPR to pyrite-free bituminous coal and a type-IIS kerogen is described. To illustrate the ability of hydropyrolysis to release covalently-bound biomarker hydrocarbons from sedimentary organic matter, the yields and conformations of the hopanes and steranes released from a type I kerogen are presented.