Study on biogas production of low and medium rank coals by ASE extraction

In order to study the increasing effect of organic solvent extraction on biogas of different coal rank,the medium rank coal and low rank coal were pretreated by accelerated solvent extraction (ASE). Biogenic gas formation experiments were carried out on raw coal,extracted residual coal,and extracted residue. By changing the condition parameters of ASE,the effects of different extraction temperature and extraction times on the extraction efficiency of coal were discussed. The production way and yield increasing effect of biomethane from raw coal,extracted residual coal and extract residue of different coal rank were analyzed. The analysis of raw coal,extracted residual coal and gas-formed residual coal was carried out by Fourier transform infrared spectroscopy (FTIR). The changes of chemical structure and functional groups in coals were studied. The results showed that the optimum conditions of ASE extraction were that the extraction temperature was 100 ℃ and the extraction times were 10 times. The extraction rate of medium rank coal was 1.06%,and that of low rank coal was 4.23%. In the methane production process of coal biomass,the methane produced in the first stage was mainly the reduction pathway of hydrocarbon dioxide,while the methane produced in the second stage was mainly dominated by acetic acid fermentation. After ASE extraction,the biomethane yield of extracted residual coal and extract residue of middle rank coal was 38% and 210% higher than that of raw coal,respectively. The biomethane yield of extracted residual coal and extract residue of low rank coal was 17% and 113% higher than that of raw coal,respectively. The methane yield of extracted residual coal and extracted residue of low rank coal extracted by ASE was higher than that of medium rank coal,which was increased by 33% and 4%,respectively. After the raw coal was extracted by ASE,some aromatic rings were opened,the contents of carbon-carbon double bonds and carboxyl groups are increased. After the extraction of extracted residual coal by microorganisms,the contents of carbon-carbon double bonds and carboxyl groups in coal decreased. The extraction of different rank coals could obviously improve the utilization efficiency of microorganisms and increase the production of biomethane. This method could provide a new way to study the synergism of coal biomethane.