超临界CO_(2)萃取提高褐煤生物甲烷产气模拟实验

Promoted microbial degradation of lignite by supercritical CO_(2) extraction to enhance coalbed methane production

超临界CO_(2)(ScCO_(2))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ScCO_(2)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ScCO_(2)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、ScCO_(2)对褐煤的萃取能力及萃取物组成;通过与非超临界CO_(2)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ScCO_(2)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245.46μmol,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,ScCO_(2)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CO_(2)处理后的残煤甲烷产量显著低于ScCO_(2)萃余煤,说明温压并不是刺激生物甲烷产生的主要因素,而ScCO_(2)对有机物的萃取作用是其关键。然而,ScCO_(2)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ScCO_(2)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ScCO_(2)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,ScCO_(2)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 CO_(2)(ScCO_(2))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 ScCO_(2) 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 ScCO_(2) 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 ScCO_(2) extraction yield of lignite,and the composition of extractions.The methane production from non-supercritical CO_(2) treated coal,the secondary extraction of ScCO_(2) extracted coal with dichloromethane(DCM),and low-temperature liquid nitrogen adsorptiontesting were performed to further analyze the mechanism of ScCO_(2) 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 245.46μmol/g coal was observed after ScCO_(2) 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 ScCO_(2) extraction could promote the microbial degradation of lignite to increase biomethane production.In addition,the methane productions of residual coal treatedby subcritical CO_(2) were significantly lower than that of ScCO_(2) extracted coal,indicating that the ScCO_(2) extraction of organics was crucial tostimulatebiomethane production,not temperature and pressure.However,the extraction yields of ScCO_(2) 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 ScCO_(2) action.Theresults of low-temperature liquid nitrogen adsorption test showed that the total pore volume and specific surface area of the ScCO_(2) extracted coal decreased,and the pore structure distribution was changed after ScCO_(2) extraction,indicating that the extract was transported and adsorbed by ScCO_(2),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 ScCO_(2) extraction,while a large number of bioavailable organics was migrated andremoldedin coal during ScCO_(2) extraction,which improved the bioavailability of residual coal,resulting in the increment of biomethane production.