Influence of temperature, catalysts and partial pressure of hydrogen on the co-processing of spanish lignites

Abstract

Studies on coal-oil co-processing are one aspect of the research carried out in the field of coal liquefaction. The oil used in the process is likely to be a heavy petroleum residue due, in part, to the economic constraints of the process and, moreover, to the expected chemical compatibility. This project studies the influence of the kind of coal, vacuum residue, catalyst and temperature on the co-processing conversion and the quality of liquid products. The influence of partial pressure of hydrogen is studied. Two different Spanish lignites were co-processed with a typical commercial vacuum residue and in the presence or absence of solid catalysts. Two supported catalysts, one with 25% Fe, as oxide, and a second with 25% Fe plus 10% Mo, as oxides, were prepared. Prior to their utilization, the catalysts were sulphided. The range of temperatures studied was 350–470°C. Experimental results show that the temperature and the partial pressure of hydrogen are the most important variables. A maximum conversion and proportion of valuable liquid oil fraction was obtained between 375 and 425°C. Temperatures exceeding this range produce a negative value of conversion because of the retrograde recombination reactions of radicals and, consequently, a great increment in the gases formed. The comparison of the two lignites used, Berguedà and Utrillas, confirms the relation between the structural composition and the level of maximum conversion attained. The results obtained with catalysts suggest that their effect overlaps or competes with the compounds present in the ashes when the level of ashes is high. The only general conclusion about the use of Fe and Fe-Mo catalysts is that the amount of sulphur present in the oil fraction is lower than that obtained without catalyst. With respect to the effects of hydrogen partial pressure, the main conclusion refers to the comparison between the normal loading of solid reagents and 3/4 of this loading. A wide screening of temperatures was carried out with normal and with 3/4 loadings, and with the other loading only one temperature was checked. The lowest loading (highest H2 content) produced an increment in the conversions attained and a displacement of the region of maximum conversion toward lower temperatures.