摘要
煤变质作用过程存在多次阶跃点,并发生以热降解-热裂解作用为主形成烷烃气.为探究中阶煤结构演化特征,以西山煤田中阶煤为研究对象,采用傅里叶红外光谱测试分析方法对中阶煤化学结构演化特征及其与烷烃气碳同位素关系进行了研究.结果表明,煤层气碳同位素值位于-57.20‰～-31.41‰之间,乙烷与甲烷碳同位素值相比变化相对较弱.样品中羟基以自缔合氢键为主,芳香烃结构以苯环三取代为主,芳碳率在演化中变化较弱,芳环缩合度则出现增大—减小—增大的变化趋势,脂肪烃以亚甲基含量为主,支链化程度参数在演化中出现减小—急增—减小的阶段性变化.结合甲烷碳同位素特征分析认为,中阶煤阶段结构演化可划分为五个阶段,第一阶段(0.65%<Ro<1.10%)以热解作用为主导,δ13 C1 呈微弱减小的趋势;第二阶段(1.10%<Ro<1.30%)以热解与缩聚的叠合为主,δ13 C1 值开始变重;第三阶段(1.30%<Ro<1.50%)由煤的热解逐渐进入以缩聚作用为主,烷烃气大量生成,δ13 C1 值变重趋势减弱;第四阶段(1.50%<Ro<1.80%)以缩聚作用为主,第五阶段(1.80%<Ro<2.0%)则由芳环的缩聚为叠合阶段做准备,δ13 C1 值的减小或与纳米孔隙结构变化对甲烷吸附的差异有关.中阶煤化学结构演化和碳同位素变化关系的研究对指导煤层气勘探开发和煤炭资源清洁利用具有重要意义.
Abstract
Several coalification jump points exists in coal metamorphism,in which alkane gas formed through thermal degradation and pyrolysis.In order to study the chemical structure evolution characteristics of middle-rank coals,coal seams in Xishan coalfield were collected and the structural evolution was analyzed by Fourier infrared spectroscopy.The results show that carbon isotopes values range from-57.20‰ to-31.41‰,in which ethane isotopes ratio changes weakly than methane.The hydroxyl groups in samples are dominated by self-hoofed hydrogen bonds,and the aromatic hydrocarbon structures are dominated by tri-substituted benzene rings.The aromatic carbon ratio changes weakly while the aromatic ring condensation degree shows a trend of increasing-decreasing-increasing.Aliphatic hydrocarbons are dominated by methylene content,and the branching degree parameter has decreased-increased-decreased during the evolution.Coupling with the characterization of carbon isotopes of methane,structural evolution in middle rank coals included five stages.The first stage(0.65%<Ro<1.10%)was dominated by thermal degradation and decreasing of δ13C1 values.Thermal degradation and polycondensation were cooperated together in the second stage(1.10%<Ro<1.30%)and δ13C1 values became heavy.The third stage was characterized by the polycondensation and formation of many alkene gases.The congruence effect was prepared when the polycondensation ended in the fourth stage(1.50%<Ro<1.80%)and fifth stage(1.80%<Ro<2.0%),in which δ13C1 values were reducing since the adsorption effect of nanopores.The analysis of the structural evolution in middle-rank coals and carbon isotope changes are of great significance for guiding the exploration,development and clean utilization of coalbed methane.
基金项目
山西省基础研究计划自由探索类项目(202203021212475)
山西省基础研究计划自由探索类项目(202203021221230)
煤矿安全技术国家重点实验室开放课题基金(sklcmst106)
山西省高等学校教学改革创新项目(J20221257)
山西省高等学校教学改革创新项目(J2021807)
NETL
NSTL
万方数据