Pyridine solubles liquefaction

In outline of what follows we will begin by brief reference to previous work on coal liquefaction. The present approach will then be motivated from considerations of coal structure and hydro-gen-donor activity. A theoretical section follows in the form of a pericyclic hypothesis for the coal liquefaction mechanism, with focus on the hydrogen transfer step. Experiments suggested by the theory are then discussed, with presentation of preliminary results for hydrogen transfer among model substrates as well as for the liquefaction of an Illinois No. 6 coal to hexane-, benzene-, and pyridine-solubles by selected hydrogen donors. 

Results showing the effectiveness of the A1- and A2-dialins in coal liquefaction relative to control solvents, naphthalene, Decalin, and fetralin, are presented in Tables 3.1 and 3.2. In both these tables, each row provides the conversion of the coal sample to each of hexane-, benzene-, and pyridine-solubles (plus gases) by the indicated solvent. Table 3.1 contains data derived at a temperature of 400 C and a reaction time of 0.5 hr. Among the control solvents, it can be seen that the naphthalene... 

The dialins were also found to be more effective donor solvents than Tetralin in the liquefaction of an Illinois No. 6 HVA bituminous coal. For example, at 400 C and 0.5 hr reaction time, A2-dialin yielded 16% more pyridine-solubles and 37% more hex-... 

Primary Conversions and Influence of Mobile Phase Yields for the various H-donor and non-donor solvent extractions of Linby coal at 400% are summarised in Table III the conversions for the THF-extracted coal include the extracted material. Surprisingly, pre-extraction with THF significantly increases primary conversions in the polynuclear aromatic compounds (PACs) investigated. These findings appear to be contrary to those of other liquefaction (16) and pyrolysis (17) studies where prior removal of chloroform-extractable material significantly reduced conversions. However, Rincon and Cruz (18) have reported recently that pre-swelling coals in THF increases conversions for both anthracene oil and tetralin. The fact that Point of Ayr (87% dmmf C) coal yielded over 80% pyridine-solubles in pyrene (C.E. Snape, unpublished data) without pre-extraction is consistent with the earlier results of Qarke et al (19) for anthracene oil extraction where UK coals... 

The lower yields of pyridine-solubles obtained with tetralin compared to 9,10-dihydrophenanthrene (Table ni) and even to naphthalene and pyrene for the THF-extracted coal (Table m. Figures 1 and 2) again are probably attributable to tetralin being largely vaporised at liquefaction temperatures. 

Summary of Experiments. Fifteen coal liquefaction experiments were done using two coals and two solvents supplied by Mobil Research and Development Corporation. Each coal-solvent combination was tried at conditions designed to give conversions to pyridine solubles of about 65 and 80 percent of MAF coal. 

MAF conversions to pyridine solubles from short contact time coal liquefaction are dependent on the coal type, solvent source, and reaction severity. As reaction severity increases conversions approach a maximum value with a hydrogen-enriched solvent but go through a maximum and decline with a hydrogen-depleted... 

The elemental composition for the initial coal [for Monterey coal (2)] and its short-contact-time liquefaction products (defined as pyridine soluble) are shown in Table II. 

When coal is heated in a slurrying vehicle, it is liquefied at 400°C-500°C (750°F-930°F). Though the reaction mechanism involving conversion of coal to oil is very complex, it appears that the interaction of coal with solvent at the initial stage of the reactions plays the vital role to determine the sequential conversion of coal substances—first to a pyridine-soluble solid and thereafter to benzene-soluble liquid hydrocarbons and low-boiling products. Thus the isolation and identification of the products of coal-solvent interactions to yield pyridine-soluble matter may provide information regarding the suitability of the coal for liquefaction. 

If the initial reactions of coal are purely thermal, one might expect that the H-donor level will be of minor importance if times are kept short. In fact, all coals contain a certain portion of material that is extractable by pyridine. On heating coals to liquefaction temperatures, some additional material also becomes soluble in even non-donor solvents. Thus, there is a portion of all coals which can be solubilized with little dependence on the nature of the solvent. 

Oele et al. (l2l) classified the solvents into five groM s with respect to their effect on coal. The three gro 5>s that are of interest in liquefaction practice are the specific solvents (e.g. pyridine), degrading solvents (e.g. anthracene), and reactive solvents (e.g. tetralin). Dryden (l22) suggested to Tise the square of the solubility parameter in correlating solvent effectiveness. The solubility parameter is a measure of the cohesive forces in a solution that has no excess entropy of mixing (l23). Silver and coworker, based on Kiebler s data (l ), found that solvents with a nonpolar solubility parameter of 9.5 (cal/c.c.) appeared to be most effective for coal dissolution (12 ). 

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