Biogasification potential of medium- to high-rank coals and its controlling mechanisms at a molecular structural level

Authors

BAO Yuan, College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China; Shaanxi Provincial Key Laboratory of Geological Support for Coal Green Exploitation, Geological Research Institute for Coal Green Mining, Xi’an University of Science and Technology, Xi’an 710054, ChinaFollow
LI Jiajun, College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China
LI Dan, College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China
CHEN Xueru, College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China
WANG Xiaojing, College of Geology and Environment, Xi’an University of Science and Technology, Xi’an 710054, China

Abstract

Objective Coals with varying metamorphic grades differ significantly in the potential for methane generation through microbial degradation. Medium- to high-rank coals can generate a substantial volume of methane through microbial degradation. However, key factors governing their biogasification potential remain poorly understood. This study aims to identify the dominant factors controlling the potential of medium- to high-rank coals for methane generation through microbial degradation, as well as relevant controlling mechanisms, from the perspective of molecular structures.Methods The Carboniferous-Permian medium- to high-rank coals along the eastern margin of the Ordos Basin were investigated in this study. Using experiments on the hydrocarbon generation of the coals through the degradation of indigenous microorganisms and the analysis of hydrocarbon generation kinetics, combined with gas chromatography (GC) and Fourier transform infrared spectroscopy (FTIR), this study revealed the biogasification potential of coal samples from different coal seams, along with the laws of changes in the structures of functional groups on the sample surfaces. Furthermore, based on Pearson correlation analysis, the intrinsic relationships between the molecular structural parameters and hydrocarbon generation potential of coals were explored.Results The microbial degradation-induced methane generation of medium- to high-rank coal samples can be divided into three stages: an initial lag phase (0‒28 d), an exponential growth phase (28‒42 d), and a plateau and attenuation phase (after 42 d). Fitting parameter analysis of the Modified Gompertz, SGompertz, and Logistic models reveals that the Modified Gompertz model exhibited the optimal fitting performance. This model yielded an estimated maximum methane production of 8.94‒14.65 m³/t and a peak methane generation rate reaching up to 2.18 m³/t/d. FTIR analysis indicates that, following microbial degradation, the coal samples showed decreases of 14.3% and 26.8%, respectively, in the absorbance peak intensities of oxygen-containing functional groups and aliphatic structures. Coal samples from different coal seams showed pronounced differences in aliphatic structure, aromatic structure, and the characteristics of oxygen-containing functional groups. Pearson correlation analysis reveals that the maximum methane yield (A₀) exhibited strong positive correlations with both the ratio of aliphatic chain length to aromatic C=C bond abundance (quantified as $I_{{\mathrm{H}}_1} $) and the ratio of aliphatic to aromatic structures (A_al/A_ar). Specifically, coal samples enriched in long-chain aliphatic structures exhibited greater methane generation potential, and a positive correlation was observed between the aliphatic methylene content and the gas production capacity. Conclusions Compared to low-rank coals, medium- to high-rank coals exhibit a prolonged initial lag phase but an elevated methane production rate in the exponential growth phase. Aliphatic and aromatic structures emerge as key factors influencing the potential of medium- to high-rank coals for methane generation through microbial degradation, with $I_{{\mathrm{H}}_1} $ and A_al/A_ar serving as effective indicators for evaluating the biogasification potential of the coals. The results of this study provide an important theoretical basis for assessing the biogasification potential of coal seams with medium to high metamorphic grades.

Keywords

medium- and high-rank coal, biogasification, methane generation potential, functional group structure, Ordos basin

DOI

10.12363/issn.1001-1986.25.08.0632

Recommended Citation

BAO Yuan, LI Jiajun, LI Dan, et al. (2026) "Biogasification potential of medium- to high-rank coals and its controlling mechanisms at a molecular structural level," Coal Geology & Exploration: Vol. 54: Iss. 3, Article 5.
DOI: 10.12363/issn.1001-1986.25.08.0632
Available at: https://cge.researchcommons.org/journal/vol54/iss3/5

Reference

[1] 中华人民共和国自然资源部. 中国矿产资源报告2024[R]. 北京：地质出版社，2024.

[2] 王双明,师庆民,孙强,等. 富油煤原位热解技术战略价值与科学探索[J]. 煤田地质与勘探,2024,52(7):1−13

WANG Shuangming,SHI Qingmin,SUN Qiang,et al. Strategic value and scientific exploration of in– situ pyrolysis of tar–rich coals[J]. Coal Geology & Exploration,2024,52(7):1−13

[3] 于海洋,许永彬,陈智明,等. 双碳目标下煤炭深部流态化开采及前景[J]. 洁净煤技术,2023,29(1):15−32

YU Haiyang,XU Yongbin,CHEN Zhiming,et al. Deep fluidized coal mining and its prospect under the target of carbon peak and carbon neutralization[J]. Clean Coal Technology,2023,29(1):15−32

[4] 王爱宽,秦勇,兰凤娟. 基于本源菌的褐煤生物气生成过程与可能途径[J]. 高校地质学报,2012,18(3):485−489

WANG Aikuan,QIN Yong,LAN Fengjuan. Processes and possible pathways of biogenic coalbed methane generation from lignites based on parent methanogen[J]. Geological Journal of China Universities,2012,18(3):485−489

[5] 鲍园,李争岩,安超,等. 多手段表征富油煤微生物厌氧发酵孔隙结构变化特征及机制[J]. 煤炭学报,2023,48(2):891−899

BAO Yuan,LI Zhengyan,AN Chao,et al. Multi–method characterization of pore structure evolution characteristics and mechanism of tar–rich coal by anaerobic fermentation[J]. Journal of China Coal Society,2023,48(2):891−899

[6] BAO Yuan,LI Zhengyan,MENG Jiahao,et al. Reformation of coal reservoirs by microorganisms and its significance in CBM exploitation[J]. Fuel,2024,360:130642.

[7] 苏现波,吴昱,夏大平,等. 温度对低煤阶煤生物甲烷生成的影响[J]. 煤田地质与勘探,2012,40(5):24−26

SU Xianbo,WU Yu,XIA Daping,et al. Effect of temperature on biological methane generation of low rank coal[J]. Coal Geology & Exploration,2012,40(5):24−26

[8] 苏现波,徐影,吴昱,等. 盐度、pH对低煤阶煤层生物甲烷生成的影响[J]. 煤炭学报,2011,36(8):1302−1306

SU Xianbo,XU Ying,WU Yu,et al. Effect of salinity and pH on biogenic methane production of low–rank coal[J]. Journal of China Coal Society,2011,36(8):1302−1306

[9] 夏大平,陈鑫,苏现波,等. 氧化还原电位对低煤阶煤生物甲烷生成的影响[J]. 天然气工业,2012,32(11):107−110

XIA Daping,CHEN Xin,SU Xianbo,et al. Impact of oxidation–reduction potential on the generation of biogenic methane in low–rank coals[J]. Natural Gas Industry,2012,32(11):107−110

[10] 夏大平,兰建义,陈曦,等. 微量元素在煤层生物甲烷形成时激励与阻滞体系研究[J]. 煤炭学报,2017,42(5):1230−1235

XIA Daping,LAN Jianyi,CHEN Xi,et al. Study on the excitation and blocking system of trace elements in coals on the production of biogenic methane[J]. Journal of China Coal Society,2017,42(5):1230−1235

[11] 李啸宇,何环,张倩,等. 黄铁矿对煤生物产气和微生物群落结构的影响[J]. 微生物学报,2023,63(6):2185−2203

LI Xiaoyu,HE Huan,ZHANG Qian,et al. Influence of pyrite on biogenic coal bed methane production and microbial community structure[J]. Acta Microbiologica Sinica,2023,63(6):2185−2203

[12] 何环,黄新颖,黄再兴,等. 高岭土对煤生物产气的影响及微生物群落响应[J]. 煤田地质与勘探,2022,50(6):1−10

HE Huan,HUANG Xinying,HUANG Zaixing,et al. Effect of kaolin on biogenic coalbed methane production and the response of microbial community[J]. Coal Geology & Exploration,2022,50(6):1−10

[13] SMITH H J,SCHWEITZER H D,BARNHART E P,et al. Effect of an algal amendment on the microbial conversion of coal to methane at different sulfate concentrations from the Powder River Basin,USA[J]. International Journal of Coal Geology,2021,248:103860.

[14] 侯彪,王子升,周艺璇,等. 不同煤阶煤制生物甲烷的代谢功能差异性研究[J]. 煤炭科学技术,2021,49(12):119−126

HOU Biao,WANG Zisheng,ZHOU Yixuan,et al. Difference of metabolic functions in biomethane produced from different rank coals[J]. Coal Science and Technology,2021,49(12):119−126

[15] 杨甫,贺丹,马东民,等. 低阶煤储层微观孔隙结构多尺度联合表征[J]. 岩性油气藏,2020,32(3):14−23

YANG Fu,HE Dan,MA Dongmin,et al. Multi–scale joint characterization of micro–pore structure of low–rank coal reservoir[J]. Lithologic Reservoirs,2020,32(3):14−23

[16] CAI Yuliang,ZHAI Cheng,YU Xu,et al. Quantitative characterization of water transport and wetting patterns in coal using LF–NMR and FTIR techniques[J]. Fuel,2023,350:128790.

[17] 赵云刚,李美芬,曾凡桂,等. 伊敏褐煤不同化学组分结构特征的红外光谱研究[J]. 煤炭学报,2018,43(2):546−554

ZHAO Yungang,LI Meifen,ZENG Fangui,et al. FTIR study of structural characteristics of different chemical components from Yimin lignite[J]. Journal of China Coal Society,2018,43(2):546−554

[18] 郭智栋,王玉斌,鲍园,等. 韩城地区煤层气成因类型及微生物开发潜力[J]. 西安科技大学学报,2023,43(3):539−548

GUO Zhidong,WANG Yubin,BAO Yuan,et al. Coalbed methane generation and microbial–development potential in Hancheng Block[J]. Journal of Xi’an University of Science and Technology,2023,43(3):539−548

[19] BAO Yuan,JU Yiwen,HUANG Haiping,et al. Potential and constraints of biogenic methane generation from coals and mudstones from Huaibei coalfield,Eastern China[J]. Energy & Fuels,2019,33(1):287−295.

[20] BAO Yuan,WANG Wenbo,MA Dongmin,et al. Gas origin and constraint of δ¹³C (CH₄) distribution in the Dafosi mine field in the southern margin of the Ordos Basin,China[J]. Energy & Fuels,2020,34(11):14065−14073.

[21] 苏现波,夏大平,赵伟仲,等. 煤层气生物工程研究进展[J]. 煤炭科学技术,2020,48(6):1−30

SU Xianbo,XIA Daping,ZHAO Weizhong,et al. Research advances of coalbed gas bioengineering[J]. Coal Science and Technology,2020,48(6):1−30

[22] SUSILAWATI R,EVANS P N,ESTERLE J S,et al. Temporal changes in microbial community composition during culture enrichment experiments with Indonesian coals[J]. International Journal of Coal Geology,2015,137:66−76.

[23] EMEBU S,PECHA J,JANÁČOVÁ D. Review on anaerobic digestion models:Model classification & elaboration of process phenomena[J]. Renewable and Sustainable Energy Reviews,2022,160:112288.

[24] LI Dan,BAO Yuan,LIU Xiangrong,et al. Constraints and dynamic assessment of biomethane generation from cyclically nutrients stimulation[J]. Journal of Cleaner Production,2024,451:141728.

[25] SHAN Tuo,BAO Yuan,LIU Xiangrong,et al. Evolution characteristics and molecular constraints of microbial communities during coal biogasification[J]. Bioprocess and Biosystems Engineering,2024,47(12):2075−2089.

[26] KUMAR V,RAWAT J,PATIL R C,et al. Exploring the functional significance of novel cellulolytic bacteria for the anaerobic digestion of rice straw[J]. Renewable Energy,2021,169:485−497.

[27] GUAN Ruolin,GU Junyu,WACHEMO A C,et al. Novel insights into anaerobic digestion of rice straw using combined pretreatment with CaO and the liquid fraction of digestate:Anaerobic digestion performance and kinetic analysis[J]. Energy & Fuels,2020,34(2):1119−1130.

[28] 李丹,鲍园,徐凤银,等. 厌氧微生物降解下镜煤与暗煤化学结构差异特征及其演化规律[J]. 煤炭科学技术,2025,53(3):174−186

LI Dan,BAO Yuan,XU Fengyin,et al. Characteristics and evolution of chemical structural differences between vitrain and durain during anaerobic microbial degradation[J]. Coal Science and Technology,2025,53(3):174−186

[29] 郭胜利. 水浸煤氧化活性增强机理及其抑制研究[D]. 淮南：安徽理工大学，2022.

GUO Shengli. Study on the mechanism of oxidation activity enhancement of water–soaked coal and its inhibition[D]. Huainan：Anhui University of Science and Technology，2022.

[30] 聂志强,杨秀清,韩作颖. 不同煤阶生物成因煤层气微生物群落的功能及多样性研究进展[J]. 微生物学通报,2019,46(5):1127−1135

NIE Zhiqiang,YANG Xiuqing,HAN Zuoying. Function and diversity of microbial community in biogenic coal–bed methane with different coal ranks:A review[J]. Microbiology China,2019,46(5):1127−1135

[31] 宋金星,郭红玉,陈山来,等. 煤中显微组分对生物甲烷代谢的控制效应[J]. 天然气工业,2016,36(5):25−30

SONG Jinxing,GUO Hongyu,CHEN Shanlai,et al. Control effects of coal maceral composition on the metabolism of biogenic methane[J]. Natural Gas Industry,2016,36(5):25−30

[32] HU Yiliang,BAO Yuan,MENG Jiahao,et al. Biogasification efficiency and molecular constraints of tar–rich coal after microwave radiation[J]. Korean Journal of Chemical Engineering,2025,42(5):1085−1098.

[33] ZHOU Zhuo,ZHANG Cuijing,LIU Pengfei,et al. Non–syntrophic methanogenic hydrocarbon degradation by an archaeal species[J]. Nature,2022,601(7892):257−262.

[34] CHENG Lei,SHI Shengbao,YANG Lu,et al. Preferential degradation of long–chain alkyl substituted hydrocarbons in heavy oil under methanogenic conditions[J]. Organic Geochemistry,2019,138:103927.

[35] 周天尧,柳炳俊,薛生,等. 多手段表征生物降解煤基质分子结构变化特征及机制[J]. 煤炭学报,2025,50(增刊1):394−406

ZHOU Tianyao,LIU Bingjun,XUE Sheng,et al. Multi–method characterization of molecular structure changes and mechanisms of biodegradation of coal with different degrees of metamorphism[J]. Journal of China Coal Society,2025,50(Sup.1):394−406

[36] QI Mengjiao,SU Xianbo,ZHAO Weizhong,et al. Metabolic mechanisms of carbon and nitrogen interactions during anaerobic digestion of coal[J]. Renewable Energy,2024,237:121653.