Depolymerization, coal

Transalkylation involves the transfer of alkyl groups between aromatic nuclei, usually in the presence of strong Lewis acids. Heredy and Neuworth used this reaction to "depolymerize" coal. As a result of the reaction of coal with BF3 and phenol, the solubility of coal in phenol or pyridine increased substantially. Various modifications of this reaction have since been reported . Transall lation reactions in the presence of trifluoromethane sulfonic acid and aromatic hydrocarbons have recently been used by Benjamin et al. and Farcasiu et al. to identify structural features in coals and heavy petroleum ends, respectively. 

Lower-temperature liquefaction processes may be the targets of future research. As discussed previously, acidic catalysts can depolymerize coal at temperatures as low as 150°C. Thus so far, rather unconventional catalysts,... 

In a few cases, pure compounds have been isolated and identified though they comprise <1 percent of depolymerized coal substance. 

In all cases cited the depolymerized coal product contained phenol. Ouchi showed that as depolymerization progressed the intensity of infrared absorption attributed to phenolic hydroxyl increased regularly. 

Acid catalyzed depolymerization of coal with phenol affords a means for dissolution of coal under relatively mild conditions (185°C, ambient pressure). Once dissolved, separation of ash constituents and unreacted char is accomplished by filtration or centrifugation (also under mild conditions). Depolymerized coal recovered as a low ash product from excess phenol could be dissolved in a coal derived solvent and hydrogenated to stable liquids. It might be anticipated that access to hydrogen and contact with the catalyst would be more efficient in the case of the solubilized coal substance than for coal particle slurries. Hydrogenation might proceed more efficiently and with less... 

It was found that phenol not only depolymerizes coal to colloidal and molecular size, but it also disintegrates coarse coal producing a smaller screen size distribution. This last effect is believed to be similar to that reported by workers at Syracuse University Research Corporation. (11) As a result, the extent and rate of depolymerization were nearly independent of initial particle size. 

Procedures were used in this work which could be converted to industrial process steps. Coal was refluxed with a phenol-catalyst mixture at atmospheric pressure. The hot solution was filtered through a tared filter which had been precoated with filter aid. Contents of the filter were washed, first with hot phenol-methanol mixture (20/1, v/v) to remove adhering depolymerized coal, and finally, with methanol to remove phenol and catalyst. The filter cake was dried at 10 mm Hg pressure and 140-160 C and weighed. 

The residue on the filter contains ash constituents from the coal, unreacted coal, and possibly phenol combined with partially depolymerized coal of molecular size too large to be soluble. 

The determination of depolymerized coal in this filtrate was accomplished by diluting a weighed aliquot with 20-30 times its weight of water. Phenol and catalyst dissolve whereas the depolymerized coal product precipitates. The precipitate was filtered, water washed, and dried in a vacuum at 110 C. The weight of this precipitated product was designated as maf (moisture and ash free) depolymerized product. 

Equation (6) shows that the combined phenol is derived from the total increase in the weight of coal. No distinction is made between phenol trapped in the residue or combined with soluble depolymerized coal. The weight gain is a measure of the extent of reaction. Ouchi, a. also utilized this total weight increase as a measure of the extent of reaction. 

It is apparent that many of the solvents undergo reaction with coal, but the reaction may not depolymerize the coal to soluble fragments. Alternatively, the solvent may be a poor one in which to dissolve the depolymerized coal product. 

The decision to employ decal in as a solvent was made to circumvent difficulties in handling small quantities of coal and catalyst in a large autoclave and to facilitate separation of solvent and coal reaction products. In some respects this was an unfortunate choice. Some reaction with decal in occurred, so accurate measurement of Hp consumption by reaction with coal was not possible. Further, both coal and depolymerized coal were virtually insoluble in this solvent so the hoped for advantage of solvent solubility anticipated for depolymerized coal may have been lost. 

The ratio of aliphatic protons to aromatic protons for the heavy oil was 4.01/1 and of methylene to methyl 1/1.75. For the asphaltenes, the ratio of aliphatic protons to aromatic protons was 3.49/1 and of methylene to methyl 1/1.1. The asphaltenes were observed to melt at HG C. Molecular weights obtained by vapor phase osmometry (o-xylene solvent) were 407 for the heavy oil and 638 for the asphaltenes. There appears to be little difference in the relative yield of heavy oils and asphaltenes from depolymerized coal as compared with the "as received" coals. Acknowledgements... 

Figure 5. Extract yields from depolumerized coals (3) (PTSA (W) depolymerized coals, pyridine extracts (O) depolymerized coals, benzene-ethanol extracts BF3 (Aj depolymerized coals, phenol extracts)...

We have undertaken a thorough study of the Heredy-Neuworth procedure for solubilizing (depolymerizing) coals (24, 25, 26). The reaction is an acid-catalyzed transalkylation, which, when carried out on coals, renders them soluble. 

Acylation attempts to depolymerize coal by the introduction of acyl [RC(=0)-0-] groups have also... 

Since the 1970s, coal liquefaction has been extensively studied worldwide to produce petroleum substitutes (Speight, 2008). Major processes are operated under high or moderate hydrogen pressures with significant consumption of this element to depolymerize coal into a product similar to petroleum—it should be noted that the word depolymerize is used incorrectly since coal is not a... 

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