Rapid hydropyrolysis of coals for production of liquid hydrocarbons

Abstract

Production of fuels and chemicals from coal is becoming attractive due to potential high cost and uncertain supply of crude petroleum oil. Conventional techniques of coal liquefaction, though technically feasible, have been expensive due to hydrogen requirements, high pressure equipment, and high cost of commercial supported catalysts. In this study, a novel technique for rapid hydropyrolysis of bituminous, subbituminous, and lignite coals has been investigated. Rapid hydropyrolysis is the process of heating at a fast rate to high temperature in a hydrogen environment. A coal sample in hydrogen atmosphere is targeted, in the absence of a catalyst, with a high intensity xenon light beam. A shuttering mechanism is incorporated to expose the coal sample only for a few seconds at a time. This technique provides the best of several processes: high heating rate of the coal sample to achieve a high carbon conversion, and control of secondary reactions via low ambient hydrogen gas temperature to potentially achieve high yields of liquid hydrocarbons. This technique also provides an effective economic alternative to the use of expensive commercial catalysts for the conventional coal liquefaction process. The operating parameters studied were exposure time, peak temperature, particle size, gaseous atmosphere, and coal rank. The most suitable conditions for the rapid hydropyrolysis of coals were found to be 30 seconds exposure time, 900\sp\circC peak temperature, 63 to 74 micrometer particle size, and in hydrogen atmosphere (1 atm). The total amount of coal converted to liquid and gaseous products for bituminous coal was found to be 38.5% and decreased to 33.6% for subbituminous coal and to 32.2% for lignite. The amount of liquid hydrocarbons produced were 16.3%, 8.8%, and 3.5% for bituminous, subbituminous, and lignite coal, respectively. In this process, a radiative heat source is used. The rapid hydropyrolysis method used in this study has several advantages over the coal liquefaction processes. It is conducted at atmospheric pressure, at a relatively shorter exposure time (less than one minute), and in the absence of a catalyst