为研究不同煤阶CH₄吸附/解吸特征差异及解吸滞后效应,采集低、中、高煤阶样品,进行显微组分测定、液氮吸附、等温吸附/解吸等实验,系统分析不同煤阶样品物质成分、孔隙结构、吸附/解吸特征差异及解吸滞后效应,结合甲烷吸附热计算结果,从能量角度探讨煤层气解吸滞后机理。结果表明：①煤样的镜质组反射率R_o,max分别为0.43 %、1.26 %、3.27 %,低阶煤样品镜质组含量低、惰质组含量高、挥发分高和固定碳高,中、高阶样品则反之;煤变质程度增高,孔隙度、BET比表面积、BJH总孔容、分形维数D₂呈“V”型变化,D₁呈倒“V”型变化;②温度相同时,煤阶越高,残余吸附量越大,解吸难度增加。温度升高,残余吸附量呈先上升后下降的趋势,以40 ℃为拐点,温度对气体分子活化程度和煤的孔隙结构均有影响;③压力相同,煤阶越高,甲烷吸附速率越快,低压阶段（p<4 MPa）,吸附量增加快,高压阶段（p>4 MPa）,吸附量增加不明显;④DFS4 ^#、SGZ11 ^#、SH3 ^#三个煤样解吸过程中等量吸附热均大于吸附过程中的等量吸附热,表明解吸过程需要持续从体系外吸收热量,而处于吸附态的甲烷由于解吸需要的等量吸附热大于吸附时的等量吸附热需要从外界环境吸取能量,吸附和解吸过程的能量差异会导致解吸滞后;处于游离态的甲烷,由于高压作用下进入微小孔,致使煤基质膨胀变形,孔隙结构改变,导致甲烷解吸受限,造成解吸滞后。

In order to study the difference in adsorption/desorption characteristics and the desorption hysteresis of CH₄ in different coal ranks, low, medium, and high coal rank samples are collected for the experiments of micro-component determination, liquid nitrogen adsorption, and isothermal adsorption/desorption to systematically analyze the composition, pore structure, differences in adsorption/desorption characteristics and desorption hysteresis effects of different coal rank sample materials. Combined with the calculation results of methane adsorption heat, the mechanism of coalbed methane desorption hysteresis from the energy perspective is discussed. The results show that: ①The reflectance R_o,max of the vitrinite group of coal samples are 0.43 %, 1.26 %, and 3.27 %, respectively. Low-rank coal samples have low vitrinite group content, high inert matter group content, high volatile content and fixed carbon. Medium-rank and high-rank samples are reversed. The degree of coal metamorphism increases. Porosity, BET specific surface area, BJH total pore volume, and fractal dimension D₂ change in a “V” shape, and D₁ changes in an inverted “V” shape. ②Under isothermal condition, the residual adsorption amount becomes larger as the coal rank rises, and the desorption becomes more difficult. As the temperature rises, the residual adsorption capacity increases first and then decreases. With 40 ℃ as the inflection point, the temperature influences both the degree of activation of gas molecules and the pore structure of coal. ③When the pressure is the same, the higher the coal rank, the faster the methane adsorption rate at the low-pressure stage（p<4 MPa）, the adsorption capacity increases rapidly at the high-pressure stage（p>4 MPa）, and the adsorption capacity does not increase significantly. ④For the three coal samples, DFS4 ^#, SGZ11 ^#, and SH3 ^#, in the desorption process, their isosteric heat of adsorption are all greater than that in the adsorption process, indicating that the desorption process needs to continuously absorb heat from outside. Therefore, the methane in the adsorption state needs to absorb energy from the external environment, and the energy difference between the adsorption and desorption processes will cause desorption hysteresis. The methane in the free state enters into the micropores due to high pressure, resulting in the expansion and deformation of coal matrix, changes in pore structure, limit of methane desorption, and finally a desorption hysteresis effect.