Solvent Extraction Of Naomaohu Coal Under Supercritical Co₂

In this work,NMH coal was extracted by organic solvent under supercritical CO₂ to obtain small molecules.The structure and composition of extraction products were analyzed with multiple analytical technologies.The main research work and results are as follows:Cyclohexanone,THF and methanol were used to extract NMH coal under supercritical CO₂,and the effects of atmosphere and temperature,time,the ratio of solvent to coal?solvent:coal=m L:g?on the extract yield were investigated.The results show that supercritical CO₂ obviously affects the extract yield,and the extract yield under supercritical CO₂ is two times of that under N₂.Under supercritical CO₂,the optimum extract yield of NMH coal by cyclohexanone,THF and methanol is 9.5%,5.8%and 4.8%,respectively,when the condition is 150 ^oC,5 h and 10:1?the ratio of solvent to coal?.The structure and composition of organic solvent extraction products were analyzed with multiple analytical technologies.The results showed that the main component in extract is long-chain aliphatic substances.CYC-E and THF-E are richer in C=C substances in comparison with MeOH-E.THF-E has higher content of C=O substances and the content of carboxylic acid substances in MeOH-E is high.The molecular weight of CYC-E,THF-E and MeOH-E is about 574 amu,469 amu and 444 amu,respectively,and the average number of rings in each aromatic cluster of these extracts are 2 to 3,2 and 1 to 2 rings,respectively.The crystallite of aromatic layer of extract is slightly higher than that of raw coal,but the number of the crystallite layers is less than that of raw coal.XPS and solid-state ¹³C-NMR were applied to study the structural difference between NMH coal and its residue.The results indicated that the contents of C-H and C=O decrease with THF extraction,but the contents of N and S have not significant change.The aromatic cluster of NMH coal is two rings with about 4 substituent groups and the average chain length of the substituents is 3.18.The residue has less substituent groups and shorter branch than NMH coal.The content of aliphatic carbon in the extract is much higher than that of NMH coal and residue.THF-E were sequentially eluted with 30 m L n-hexane,20 mL n-hexane/dichloromethane?V:V=1:2?,10 mL ethanol/10 m L chloroform,and chloroform,affording fractions F₁ to F₄.The composition of each component was investigated by FT-IR,synchronous fluorescence spectroscopy and ¹H-NMR.The results show that F₁ mainly contains mono-aromatic with longer aliphatic chain.F₂ contains bicy-and tricy-aromatic substances with lower degree of substitution and shorter aliphatic chain.F₃ and F₄ mainly contains long-chain alkyl-substituted mono-and bicy-aromatic substances,but F₃ contains a large number of ester,hydroxyl and phenoxy groups and F₄ contains more long-chain alkyl than F₃.