Pretreatment and mass transfer effects on the coal liquefaction process

Several coal pretreatments aimed at enhancing subsequent liquefaction yields have been investigated. The pretreatments were classified into two categories; Type I which are designed to reduce intraparticle mass transfer limitations between the coal and liquefaction media; and Type II which are designed to affect the liquefaction chemistry. Two Type I pretreatments were evaluated, solvent swelling and thermal presoaking, using Illinois No. 6 and Wyodak coal. In general little improvement ({dollar}<{dollar}6%) in liquefaction yields resulted from either swelling the coal in solvents such as methanol, pyridine, chloroform, acetone, and tetrahydrofuran, or by thermally presoaking the coal in the liquefaction solvent at 300{dollar}spcirc{dollar}C for 10-15 minutes prior to the liquefaction step. Particle size experiments were also performed to further assess the degree of intraparticle mass transfer limitations. Varying the initial particle size from 10 x 48 mesh to {dollar}-{dollar}230 mesh had also little ({dollar}<{dollar}8%) effect on liquefaction yields. The particle size-conversion data was also used to evaluate 3 reaction-diffusion models.; Hydrothermal (Type II) pretreatments were also investigated. Pretreatment of Illinois No. 6 coal using two different procedures at moderate temperatures, 100-300{dollar}spcirc{dollar}C, resulted in small (up to 8%) but consistent increases in subsequent donor solvent (tetralin) liquefaction. Significant increases in aqueous KOH/CO liquefaction yields, from 40 to 60%, were observed with a specific batch of PSOC-1098 coal. However, no effect of the hydrothermal pretreatment on aqueous liquefaction yields was observed for sources of Illinois No. 6 coal. It is hypothesized that long term weathering is responsible for the difference in response to the hydrothermal pretreatments.; Experiments were also performed to assess potential mixing limitations associated with the tubing bomb reactor used in this study. Liquefaction yields obtained in the tubing bomb reactor were compared to that of a stirred autoclave reactor for several different liquefaction systems. Thermal donor solvent liquefaction yields (at 400-425{dollar}spcirc{dollar}C for 20 minutes) in the tubing bomb reactor were comparable to those obtained in the stirred autoclave reactor. However, catalytic (Ammonium Tetrathiomolybdate) liquefaction yields were slightly lower (7%), and aqueous liquefaction yields (at 400{dollar}spcirc{dollar}C for 20 minutes) were considerably lower (20-30%) in the tubing bomb reactor than in the stirred autoclave. Based on the results, guidelines for using the tubing bomb reactor are proposed.