Hydropyrolysis: Fundamentals, Two-Stage Processing and PDU Operation

Abstract

Fundamental aspects of hydropyrolysis in terms of how both reaction conditions and reactor geometry affect product yields and compositions are reviewed, followed by a description of the pressurised fluidised-bed hydroretorting (PFH) process developed at the Institute of Gas Technology (IGT) as an example of an oil shale hydroretorting process that has been successfully operated on a PDU scale. The use of low temperatures and long solids residence times in well-swept fixed-and fluidised-bed reactors are essential to achieve high selectivity to liquid products in hydropyrolysis. For oil shales, hydrogen pressures of ca 5–10 MPa are generally sufficient to approach the maximum ecomomical oil yield compared to those of over 30 MPa for coals, unless suitable dispersed catalysts are used. Hydropyrolysis oils generally more aromatic with lower heteroatom contents with increasing hydrogen pressure. The PFH process developed at IGT has been scaled-up from a 100 g batch unit to a 100 kg hr^-1 semi-continous PDU. To assess the potential oil yields from PFH, a hydroretorting assay unit was used extensively . Compared to Western U.S. (Eocene, Type I kerogen) oil shales, which give high oil yields in conventional retorting processes, Eastern Devonian shales (Type II kerogens) have considerably lower atomic H/C ratios which severely restricts the attainable oil yields. In hydretorting at 538°C and 6.9 MPa, the oil yields from Eastern U.S. shales were substantially improved and usually doubled using the PFH process.