Study On Extraction Of Coal Using Supercritical Carbon Dioxide Mixed Solvent And Gasification Reactivity Of Residue Coals

Extraction of coal using supercritical carbon dioxide(SCCO2) with co-solvent was studied. Interaction between supercritical carbon dioxide and co-solvent was explored. Physical and chemical properties of extracted coal residues were characterized and their gasification reactivity was investigated. The main contents and results were summarized as follows:(1) Different co-solvent were used in the SCCO2extraction of coals. The role of supercritical carbon dioxide and co-solvent was studied. Co-solvent with high extraction yield was chosen and effects of extraction condition and coal type on extraction yield in mixed solvent were investigated. Result shows that with the addition of supercritical carbon dioxide, the one-time extraction yield of N-methyl-2-pyrrolidinone (NMP) decreased, however, the three-time extraction yield increased. The pressure affects little on extraction yield of mixed solvent. While with the increase of temperature, the extraction yield increased but it was found that the increase was not correlated to the changes of supercritical carbon dioxide.The extraction of lignite and bituminous coals increase with carbon content of coal.(2) Functional group and crystallite size of extracts was analyzed. Result shows that mixed solvent have strong selectivity for hydroxy rich matter and oxygen-containing substance. With the addition of SCCO2, the extraction of hydroxy rich matter was enhanced while the aliphatic matter in extracts decreased, crystallite structure in extracts was found similar with raw coals, but their graphitization degree were lower.(3) Physical and chemical properties of residue coals were characterized and their gasification reactivities were investigated. It was found that the surface of coal particles were damaged by the mixed solvent and the pore structure changed. Average stacking height of coal crystallite was reduced after extraction. Gasification rate was enhanced for all extracted coals and the gasification rate tends to increase with increasing extraction yield.