Study On Coal Extraction With The Solvent Of Dimethylformamide Mixed With Supercritical Carbon Dioxide

This article is under the background of coal staged utilization. Luhuo coal and Shenfu coal are extracted with supercritical carbon dioxide (scCO2)/dimethylformamide (DMF) mixed solvent. Study is focused on extraction yield, extracts' types and contents, and residues' characters. The main contents are as follows:(1) Extraction yields of two coals with mixed solvent are studied. Results show that extraction yields of mixed solvent are higher than those of pure scCO2 and DMF solvent. Extraction yields increase with the increase of pressure, decrease at first and increase slightly later with the enhancement in temperature. The maximum values occur at the volume ratio of 1:1 of two solvents. The extraction yield of Luhuo coal soars after 200℃because of cracking.(2) Characters of extracts of two coals are studied. Results show that the main types of extracts of Luhuo coal and Shenfu coal are aromatic compounds and paraffins. Increases in temperature and pressure will enhance types and paraffins'ratio in Luhuo coal's extract. Pressure plays less important role in the types of Shenfu coals'extract, but enhancement in temperature will increase the ratio of paraffins. Among the main extracts of two coals, some valuable components are detected like retene, phthalates, antioxidant BHT, hydroxyl-Qi and paraffins, which have widespread application prospect and scientific research value.(3) Characters of residues of two coals are studied. Results show that the fixed carbon content of two coals will increase and the ash content will decrease with the increase of temperature. Pressure affects little on these. The content of oxygen in two coals will decrease while the content of carbon will increase with the increase of temperature. Study on residues show that solvent will erode the surface of coals, which will dissolve edges of pores in the coals, and thus cause the declines of BET surface area and the increase of pore size. FTIR results reveal that absorption peaks of aromatic are strengthen and that of methyl and methylene are weaken after extraction. But on the whole, little change happens, which means extraction doesn't affect the main structure of coals. Analysis of gasification shows that after extraction, the gasification activity of Shenfu coal declines but Luhuo coals' increase a little. Temperature and pressure have little effect on the character of residues both physically and chemically.