Pyrolysis of simple coal model compounds containing aromatic carboxylic acids: Does decarboxylation lead to cross-linking?
- Oak Ridge National Lab., TN (United States)
In recent years, it has been proposed that oxygen functional groups, prevalent in low rank coals, are major actors in retrograde reactions which inhibit their efficient thermochemical processing. In the pyrolysis and liquefaction of low-rank coals, low temperature cross-linking reactions have been correlated with the loss of carboxyl groups and the evolution of CO{sub 2} and H{sub 2}O. Pretreatments such as methylation, demineralization, or ion-exchange of the inorganic cations reduce cross-linking and CO{sub 2} evolution in pyrolysis, while the exchange of Na{sup +}, K{sup +}, Ca{sup ++}, and Ba{sup ++} into demineralized coal increases cross-linking and CO{sub 2} evolution in pyrolysis and liquefaction. These results suggest, in part, that decarboxylation pathways in coal may play an important role in the cross-linking of the coal polymer. However, the reaction pathways associated with the decarboxylation and cross-linking events in low rank coal are currently unknown. Furthermore, it is not known whether the reaction pathway that leads to decarboxylation also leads to cross-linking. Radical recombination or addition reactions have been suggested as being involved in retrograde reactions. However, the involvement of radical pathways in thermal decarboxylation reactions has recently been brought into question by the observation that decarboxylation of benzoic acid derivatives under coal liquefaction conditions yielded only small amounts of aryl-aryl coupling products. Therefore, to gain a better understanding of the role decarboxylation plays in cross-linking reactions in low rank coals, we have studied the pyrolysis of several bibenzyls containing aromatic carboxylic acids. The structures currently under investigation are 1,2-(3,3`-dicarboxyphenyl)ethane (1) and 1,2-(4,4`-dicarboxyphenyl)ethane(2). These compounds are capable of forming reactive free-radical intermediates at ca. 400{degrees}C through homolysis of the weak bibenzylic bonds.
- DOE Contract Number:
- AC05-84OR21400
- OSTI ID:
- 430318
- Report Number(s):
- CONF-960376-; ISSN 0569-3772; TRN: 97:000004-0046
- Journal Information:
- Preprints of Papers, American Chemical Society, Division of Fuel Chemistry, Vol. 41, Issue 2; Conference: Spring national meeting of the American Chemical Society (ACS), New Orleans, LA (United States), 24-28 Mar 1996; Other Information: PBD: 1996
- Country of Publication:
- United States
- Language:
- English
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