ELSEVlER Fuel Processing Technology 49 (1996) 197-205 FUEL PROCESSING TECHNOLOGY Effects of hydrogen pressure and temperature on free radicals produced in coal-tire coprocessing Manjula M. Ibrahim, Mohindar S. Seehra * Physics Department, West Virginia University, P.O. Box 6315, Morgantown, WV26506-6315, USA Received 19 September 1995; accepted 17 April 1996 Abstract In-situ ESR (Electron spin resonance) spectroscopy of free radicals is used to investigate the coprocessing of Blind Canyon coal with Michelin tire rubber for temperatures up to 480°C and under H, and argon pressures up to 1000 psig. Comparing the free radical intensities of the coal and the tire alone with those obtained for the 1:l coal-tire mixtures, determined under 500 and 1000 psig of H, and under 1000 psig of intrt argon, the following observations are made. First, a strong synergism between the coal and the tire polymer is indicated, as the intensity of the ESR-active free radicals in the coal-tire mixture under H, pressure are enhanced severalfold beginning at = 200°C and peaking near 350°C. Second, increasing the H, pressure from 500 to 1000 psig reduces the free radical intensity, most likely because of enhanced hydrogenation. Third, the tire polymer gives a weak ESR-active signal whose characteristics change dramatically between 140°C and 2OO”C, indicating a phase change in the tire material. The synergistic effect observed here is consistent with the reported improved yields in direct liquefaction experiments using coal-tire mixtures. Keywords: Coal-tire coprocessing; Electron spin resonance; Free radical; Hydrogen pressure zyxwvutsrqponmlkjihgfedcbaZ 1. Introduction Most experiments in direct coal liquefaction (DCL) are carried out at elevated temperatures (= 400°C) and under high pressures (1000-2500 psig) of H,. In this paper, we present our recent results on the free radical in-situ ESR (electron spin resonance) spectroscopy of coal and of coal-tire mixtures carried out at temperatures up to 480°C and hydrogen pressures up to 1000 psig. This work was motivated by several * Corresponding author. 0378-3820/%/$15.00 Copyright 0 1996 Elsevier Science B.V. All rights reserved. PI/ SO378-3820(96)01038-7