Study On The Solvent Extraction Of Two Low-rank Coals Under Mild Conditions

In this paper, thermal dissolution-depolymerization and extraction experiments wereconducted on two low-rank coals named Neimeng lignite and Shenhua bituminous coal undermild conditions. Four different types of organic solvents were used as thermal dissolutionsolvents in this study. After discussing the results of the experiments, suitable solvents andmethods have been found to separate the soluble component in coal efficiently. The effects oftreating temperature, treating time, additives, mass ratio of solvent to coal and the moisturecontent on the extraction yield were also investigated.It is shown that cyclohexanone was a suitable thermal dissolution solvent. Under thethermal treating temperature of275℃, the mass ratio of solvent to coal of4.5, the thermaldissolution time of2h, the yields of toluene soluble (TS) and tetrahydrofuran soluble (THFS)of Neimeng lignite were34.99%and13.18%after thermal dissolution-extraction. Under thethermal treating temperature of300℃, the mass ratio of solvent to coal of4.5, the thermaldissolution time of2h, the yields of TS and THFS of Shenhua bituminous coal were29.99%and9.16%after thermal dissolution-extraction. It is shown that some additives could increasethe yields of TS and THFS and could improve thermal dissolution-extraction of the twolow-rank coals. After adding2%additives, the yields of TS and THFS of Neimeng lignitewere raised to50.87%and23.56%, while the yields of TS and THFS of Shenhua bituminouscoal were raised to35.32%and38.08%.FTIR was carried out to analysis the functional groups of the raw coal and residual coal.The resulting products were analyzed with GC/MS. The characteristics of crosslinking insoluble molecule of low-rank coal and the rule of thermal dissolution-depolymerization underdifferent conditions were studied in this work. We found that the organic ingredients in coalcan be effectively separated through thermal dissolution-depolymerization process. The mainconclusions of this work were showed as follows:(1) Thermal dissolution-depolymerizationprocess mainly caused the broken of non-covalent bond and the weakened of structure in coal.With the extraction of soluble components, the re-establishment of a non-covalent bond in macromolecular structure of residual coal was accelerated. So, the macromolecular network incoal could not change under the thermal dissolution-depolymerization process.(2) The resultsof GC/MS analysis showed that, the main contents of THFS were oxy-compounds, aromatichydrocarbons and aliphatics in the order of content from large to small. It can be concludedthat the main contents of thermal dissolution extract were low-carbon components, which canbe used as high value-added low-carbon fuels and chemical raw materials after separation andpurification. These results were of great use to the study of the components, properties andutilization of the two low-rank coals.