Donald C. Cronauer

Dependence of coal liquefaction behaviour on coal characteristics. 2. Role of petrographic composition

Abstract The techniques used were the same as those used in Part 1 (p 34). Comparison of the liquefaction behaviour of two lithotypes from a Kentucky bituminous coal indicated that in this process pseudovitrinite is a reactive maceral. The hydrogenation of sets of maceral concentrates obtained from a New Mexico sub-bituminous and a Kentucky bituminous coal showed fair correlations between conversion and the total concentration of the presumed reactive macerals (vitrinite, pseudovitrinite and sporinite). Similar concentrates from a Montana lignite showed no such correlation; the one sample that showed a high conversion was a high-density fraction that had a high mineral-matter content and in which nearly all the pyrite in the coal had accumulated. Two samples that have boghead and cannel characteristics gave quite different results on hydrogenation. Both were highly aliphatic in structure and had unusually high hydrogen contents and volatile matter. One, which contained appreciable proportions of sporinite, alginite and resinite, gave essentially no conversion to oil. The other, predominantly vitrinitic but containing alginite as the second most abundant maceral, gave an excellent yield of an oil of low viscosity and aromaticity. It was concluded that although rank, petrographic composition and perhaps geological history are important factors determining liquefaction behaviour, there are other characteristics of coals that may at times override these basic parameters, and the composition of the inorganic matter may be the most significant of these other characteristics.

Dependence of coal liquefaction behaviour on coal characteristics. 1. Vitrinite-rich samples

Abstract The liquefaction behaviour of a number of vitrinite-rich coals has been determined in batch autoclaves at temperatures of 385–425 °C and pressures of about 8.6 MPa (85 atm) of hydrogen. In one set of experiments, impregnated ammonium molybdate was used as catalyst, with no added liquid as vehicle. In a second set, a proprietary catalyst was used and anthracene oil served as vehicle. Lignites, sub-bituminous, medium-volatile and low-volatile bituminous coals gave relatively poor conversions. However, a lignite sample that had been subjected to ion-exchange treatments gave high conversion, and the viscosity and structural parameters of the products varied with the nature of the treatment. In general the highest conversions were observed for coals in the high-volatile bituminous range, but within this broad range and for the comparatively small set of samples studied neither these data nor the structural characteristics of the products show any very evident correlation with rank parameters or with the geological history of the sample. Two geologically young bituminous coals from the Pacific Coal Province gave excellent conversions; both had very high mineral-matter contents, a fact that may be very relevant.

Hydrogen/deuterium transfer in coal liquefaction

Abstract Reactions have been made with deuterium-labelled solvent (d 4 - and d 12 -tetralin) and both Powhatan bituminous (Pittsburgh Seam) coal and model compounds under coal liquefaction conditions to study hydrogen transfer mechanisms. Powhatan coal liquefies quickly. Hydrogen transfer from the solvent to the reaction products continues throughout the heating period (up to 60 min). Significant hydrogen/deuterium exchange occurs and this strongly affects the distribution of deuterium in the products and also affects the extent of conversion as measured by the amount of THF-insoluble material. Increased deuteration of the solvent leads to decreased conversion. This exchange is enhanced by heavy aromatic species and by the presence of mineral matter and unconverted coal solids.

Structural aspects of sub-bituminous coal deduced from solvation studies. 2. Hydrophenanthrene solvents

Abstract In order better to delineate the contribution of coal molecules to liquefaction products, donor solvents of discrete structure and narrow molecular-weight range have been satisfactorily employed. Partially hydrogenated phenanthrenes are ideally suited for these studies. This ring system is 1. (a) prevalent in all coals 2. (b) thermally stable, and 3. (c) capable of functioning ideally in a redox environment. Coal depolymerization can take place in the absence of a catalyst and hydrogen, provided that the level of hydroaromatics, especially octahydrophenanthrene, is sufficiently high to ensure that the coal free-radicals can be quenched before they recombine. Solvation (liquefaction) levels reach a maximum (>98%) with octahydrophenanthrene, making the indirect study of coal possible with a minimum of solvent ‘background’. The role of catalyst, if used during solvation, appears to be that of maintaining the proper level of hydroaromatics and of upgrading the liquids produced. Sub-bituminous coal appears primarily to consist of two- and three-condensedring structures linked by heteroatoms, mainly oxygen.

Liquefaction of coal using supercritical fluid mixtures

Abstract Powhatan No. 5 and Bruceton coals were liquefied for 15–60 min at 653 K and 30 MPa in supercritical aqueous mixtures containing 10–20 wt% tetrahydroquinoline (THQ), quinoline or tetralin. The THQ-water mixtures produced the highest conversion to tetrahydrofuran (THF) soluble products (up to 74%). Tetralin-water, quinoline-water and pure water solvents gave increasingly lower yields of THF solubles. Addition of hydrogen to the quinoline-water solvent mixture increased yields slightly, but not to the level obtained using the THQ-water mixture. The yields of THF solubles in all instances depended upon the concentration of solvent in the mixture, with the 10 wt% THQ and 10 wt% tetralin (in water) giving higher yields than either 0 or 20 wt% concentrations. The nitrogen-containing solvents were chemically bonded to the THF-soluble product, as observed by g.p.c.

Structural aspects of sub-bituminous coal deduced from solvation studies. 1. Anthracene-oil solvents

Abstract In order to study coal structure indirectly and the role of hydrogen donors, an investigation of the major parameters involved in the solvation of a Wyoming sub-bituminous coal has been made. This study utilized the catalytic and non-catalytic hydrogenation of anthracene oil and coal-solvent slurries. Indirect evidence concerning major structural units in the coal was obtained and the net contribution of coal to liquefaction products was estimated. The significance of each parameter to the degradation of coal molecules was also estimated. Data support the concept that coal liquefaction follows a solid → asphaltene → resin → oil route. This stepwise dissociation of the solid is directly related to the breaking of Cue5f8O, Cue5f8N, and to a lesser degree Cue5f8C bonds, resulting in the formation of free radicals of relatively low molecular weight. These free radicals are stabilized by hydrogen transfer from hydroaromatic solvent molecules. A lack of significant quantities of high-molecular-weight hydrocarbons derived from coal solvation implies the prevalence of small molecular units in the coal structure.

Behavior of phenolics in coal liquefaction: adduction tendency and coal conversion capability

Abstract A series of coal liquefaction reactions has been carried out at 450°C to examine the adduction tendency and the coal liquefaction efficiency of 1-naphthol using a product extraction scheme which minimizes co-solvent effects. An additional set of experiments was conducted to provide information on the relative effectiveness of substituted phenols compared with the parent compound. The results indicate that 1-naphthol is a better solvent than phenanthrene, but a significantly poorer one than tetralin with regard to total conversion. Mixtures of this compound with tetralin do not promote conversion above that available from tetralin alone. In all cases, loss of naphthol by adduction to the coal liquids is a major problem. The three cresols effect higher degrees of coal conversion when used 1:1 with tetralin than does phenol, but the mixtures are not as effective as tetralin alone. The single-ring phenolic species were found to exhibit only a very moderate tendency for adduction.