Liquefaction behavior and product distribution for two Indiana coals and their macerals

Abstract

Vitrinite and exinite macerals were liquefied to gain a better understanding of their role in the liquefaction of whole coals. A minireactor was developed for liquefying small amounts (approximately 1 g) of coal samples; a modified liquid extraction column was also developed for product analysis. Vitrinite-rich whole coals and the vitrinites investigated had comparable liquefaction behavior but the kinetics of exinite liquefaction was substantially slower. At higher temperatures (425 "C), maltene production increased but was accompanied by a decrease in conversion. This suggests that repolymerization of the heavier fractions may occur. write addiiion to exinite samples increased conversions and increased maltene production in the liquid products. Comparison of the conversions of pure macerals and maceral mixtures indicated that there are synergistic effects between the macerals. Other variables investigated include choice of donor solvent, solvent-to-coal ratio, and reactor agitation.In recent years, numerous investigations have been made of the chemical and physical properties of coal and of coal liquefaction products. Much information has been collected describing the petrographic composition of coal (Stach et al., 1975); however, relatively limited information has been reported regarding the liquefaction behavior of pure or relatively pure macerals. Fisher et al. (1942) performed one of the first studies correlating liquefaction behavior with the chemical composition of coal. Vitrinite-rich samples produce high oil content coal liquids. Given et al., (1975a and 1975b) indicated the importance of petrographic composition on liquefaction behavior. Later work (Abdel-Baset et al., 1978) correlated the conversion of 68 whole coals with the concentration of reactive macerals (defined as vitrinite, pseudovitrinite, and sporinite). Considerable evidence exists (Mukherjee and Chowdhury 1965; Guin et ai., 1979a; Lee et al., 1977; Granoff and Thomas, 1977;Guin et al., 1979b), indicating that naturally occurring minerals in the coal can act as liquefaction catalysts. The complex structure and heterogeneity of coal has been a major problem in understanding the coal liquefaction process.Procuring pure maceral samples would be most helpful in studying the effect of petrological composition on coal liquefaction behavior. Sink-float procedures (Dormans et al., 1957;Ergun et al., 1959; Kroger, 1956) have been used in the past to separate macerals from whole coals. In these procedures, the macer& are separated by differences in their densities when the finely ground coal is suspended in a liquid medium such as carbon tetrachloride/toluene. This technique has three disadvantages: (1) it does not account for association or coexistence of individual macerals, maceral groups, or mineral matter in the coal matrix (such associations may affect liquefaction behavior); (2) exposing coal surfaces to liquids results in physical or chemical changes in the macerals; and (3) extensive grinding such as is necessary with these separation t...