Solvent–Coal–Mineral Interaction during Solvent Extraction of Coal

Abstract

Solvent extraction of coal is a coal-to-liquids conversion process whereby the organic matter in coal is dissolved in a solvent to produce a substantially mineral matter free product. The solvent extraction of Poplar lignite coal was studied with three model solvents (tetralin, quinoline, and 1-naphtol) and one industrial coal liquid derived solvent. Of interest was the fate of hydrogen, nitrogen, sulfur, and mineral constituents during physical dissolution at 200 °C and during reactive dissolution at 400 °C. The hydrogen redistribution in all solvents at 400 °C was within a narrow range, even though hydrogen-donor solvents resulted in higher extraction yield and in a higher H/C ratio of the residue. Quinoline strongly interacted with the coal, which masked its high physical extraction yield at 200 °C and enabled more mineral matter to be stabilized in solution. This behavior is typical of nitrogen bases in the coal, but was amplified by quinoline. Nitrogen redistribution took place with all solvents to nitrogen enrich the residue. Little or no sulfur redistribution took place during solvent extraction at 200 °C with any of the solvents, but at 400 °C, sulfur was redistributed. Evidence that sulfur is removed from the mineral matter during solvent extraction was provided by an observed decrease in S/Fe ratio, decrease in sulfur content of the ash, and increase in S/C ratio of extraction residues.

Effectivity of Phenol during Solvent Extraction of a South African Bituminous Coal under Mild Conditions

“…The temperature range of 300–360 °C was chosen to investigate the influence of temperature on yields obtained under mild conditions, for two reasons. First, there is a broad consensus in the literature that the main thermal decomposition of coal starts at temperatures of ∼350–375 °C. ,, The investigation focuses on temperatures below the main decomposition temperature of coal. Second, previous investigators have found this to be a useful temperature range for studying the extraction of South African coals with other solvents. , It was observed that the coal conversion (as defined earlier) increases as the temperature increases, i.e., a low coal conversion of 12% was observed at 300 °C, increasing to 50% at 360 °C (see Figure ).…”

“…The solvent extraction chemistry may be compared to that of pyrolytic conditions with no solvent present, as found in coking reactions, whereby an increase in conversion is related to hydrogen depletion of the coal residue to form coke . Carbonization of coals in closed systems, under inert gaseous conditions, generally results in an increase in coke and gas yields, with a decrease in tar yields.…”

Direct Coal Liquefaction: Low Temperature Dissolution Process

“…Clays, such as montmorillonite, strongly retains water and water associated with such clay minerals can only be removed at ∼200 °C. In previous work with Poplar lignite, it was reported that the mineral matter contained a high Al content, with an overall Al:Si ratio of 0.75:1 on a mass basis . This is suggestive of a high clay content in the mineral matter of Poplar lignite, which supports the explanation that clay may be retaining water strongly in the Poplar B sample.…”

Separative Refining of Coals through Solvolytic Extraction under Milder Conditions: A Review

“…Coal extractability is largely governed by how solvent interacts with coal and the coal–solvent interactions become greater than the coal–coal interactions. So it is important to study the role of solvent–coal–mineral interaction, and this has been reported by Hernandez et al The use of solvents like tetralin, quinoline, and naphthol and an industrial solvent HT-1006 were made to study the coal–mineral–solvent interaction. The hydrogen donor solvents such as tetralin and HT-1006 showed higher extraction yields at the appropriate solvent extraction temperature.…”