Effect of solvent structure and amine addition on the depolymerization of a bituminous Venezuelan coal

Abstract

This research article describes the solvents composition and structure effects on the depolymerization/extraction yield of a bituminous coal from the Naricual coalfield, located in Eastern Venezuela. Benzene, chloroform, N,N-dimethylformamide (DMF), 3-methylphenol (m-cresol), hexahydropyridine (piperidine) and toluene have been used as solvents; dimethylamine and p-phenylenediamine were used as additives (coal: amine 10:1 ratio), testing possible changes in yield in a Soxhlet extraction system in a 12 h lapse. The extraction/depolymerization capabilities were increased as follow: benzene < toluene < chloroform < DMF < m-cresol < piperidine. Boiling temperature, Hildebrand solubility and empirical polarity parameter ET(30) do not explain the yield solvent’s behavior used in Naricual coals extraction. On the other hand, H-bonding ability and electron-donor availability in the solvent are critical factors in the coal extraction/depolymerization process. These results confirm the important role of specific interactions in determining the extraction/depolymerization behavior of this coal. When amines were added, the yield increased significantly, but in a different extent. Furthermore, added amine opens the coal structure for solvent penetration. Identity of the amine and the synergistic mixture of solvent and an amine are key factors affecting the depolymerization of the coal under study.