超临界CO₂（ScCO₂）萃取可以减弱煤中有机物的分子间作用力，破坏非共价键，使小分子化合物从煤的大分子结构中脱离。因此，将ScCO₂萃取作为一种预处理手段来提高煤的生物可利用度，具有增产生物煤层气的潜能。以褐煤为研究对象，开展不同温压下ScCO₂萃取及生物降解产甲烷实验，明确萃余煤与萃取物的产甲烷效果、ScCO₂对褐煤的萃取能力及萃取物组成；通过与非超临界CO₂处理比较，结合萃余煤的二氯甲烷（DCM）二次萃取、低温液氮吸附实验，分析ScCO₂萃取增产生物煤层气的机理。结果显示，不同温压条件下的萃余煤生物甲烷产量均高于原煤，最佳产气的萃取条件为40  ℃-10 MPa，每克煤的最大甲烷产量为245.46 μmol，高出原煤84.68%。萃取物含有微生物可利用有机物，厌氧降解实验证实了萃取物具有产甲烷能力。因此，ScCO₂萃取能够促进褐煤的微生物降解、提高生物甲烷产量。此外，非超临界CO₂处理后的残煤甲烷产量显著低于ScCO₂萃余煤，说明温压并不是刺激生物甲烷产生的主要因素，而ScCO₂对有机物的萃取作用是其关键。然而，ScCO₂的萃取率较低且DCM二次萃取后仍检测到丰富的生物可利用的有机物，表明有机成分经ScCO₂作用后仍大量残留于煤体。低温液氮吸附结果显示，萃余煤的总孔容和比表面积降低，孔隙结构分布发生变化，说明萃取物经ScCO₂携带发生运移、吸附，导致大部分有机物残留于煤中。以上研究结果表明，ScCO₂萃取作用于煤中有机组分，导致部分有机物与煤体分离；而大量生物可利用有机物在煤体中发生运移、重排，提高了残煤的生物有效性，从而提高生物甲烷产量。

Supercritical CO₂ (ScCO₂) extraction can weaken the intermolecular forces and break the non covalent bonds of organics in coal, resulting in the separation of low molecular weight organics from its macromolecular structure. Therefore, the ScCO₂ extraction can be used as a pretreatment method to improve the bioavailability of coal, which have the potential to increase biogenic coalbed methane (CBM) production. The experiments of the ScCO₂ extraction at different temperatures and pressures, and the biodegradation of lignite were carried out to determine the biomethane production from extracted coal and extractions, the ScCO₂ extraction yield of lignite, and the composition of extractions.The methane production from non supercritical CO₂ treated coal, the secondary extraction of ScCO₂ extracted coal with dichloromethane (DCM), and low temperature liquid nitrogen adsorptiontesting were performed to further analyze the mechanism of ScCO₂ extraction toincrease biogenic CBM production.The results showed that the biomethaneproductions of extracted coal at different temperatures and pressureswereall higher than that of raw coal. The maximum methane production of 245.46 μmol/g coal was observed after ScCO₂ extractionat 40 ℃-10 MPa,which was 84.68%higher than that from raw coal.The extractions contained various bioavailable organics which could be utilized to produce methane by anaerobic microflora as revealed by anaerobic degradation experiments.Therefore, the ScCO₂ extraction could promote the microbial degradation of lignite to increase biomethane production.In addition, the methane productions of residual coal treatedby subcritical CO₂ were significantly lower than that of ScCO₂ extracted coal, indicating that the ScCO₂ extraction of organics was crucial tostimulatebiomethane production, not temperature and pressure. However, the extraction yields of ScCO₂ were low and abundant bioavailable organics were detected after the secondary extraction with DCM, indicating that a large number of organics still remained in the coal after ScCO₂ action.Theresults of low temperature liquid nitrogen adsorption test showed that the total pore volume and specific surface area of the ScCO₂ extracted coal decreased, and the pore structure distribution was changed after ScCO₂ extraction, indicating that the extract was transported and adsorbed by ScCO₂, resulting in most of the organic matter remaining in the coal.These results revealed that part of the organics in coal was separated from coal matrix by ScCO₂ extraction,while a large number of bioavailable organics was migrated andremoldedin coal during ScCO₂ extraction, which improved the bioavailability of residual coal, resulting in the increment of biomethane production.

1 实验部分

   1.1 煤样与菌群

   1.2 ScCO₂萃取实验

   1.3 生物降解产气实验

   1.4 非超临界CO₂处理实验

   1.5 有机溶剂萃取实验

   1.6 有机物成分测定

   1.7 孔隙参数测定

2 结果与分析

   2.1 萃余煤产气分析

   2.2 非超临界CO₂处理残煤产气分析

   2.3 萃取物产气能力分析

   2.4 萃余煤中生物可利用有机物分析

   2.5 ScCO₂萃取对孔隙结构的影响

3 结论