Abstract An in-depth understanding of the carbon dioxide (CO2) sorption behavior on coal is critical for CO2 sequestration in coal seams and enhanced coalbed methane recovery. However, CO2 induces the deformation of coal through physical and/or chemical reactions during the CO2 injection process, which has a significant effect on the gas flow and stability of the coal seams. This study investigates the isotherms and kinetics of CO2 sorption and hence deformation of a bituminous coal sample during isotherm tests at three different temperatures. The isotherms and kinetics curves of sorption and deformation can be described by the Langmuir and the pseudo-second-order (PSO) models, respectively. The experiment results and PSO model parameters indicate that a pore-filling effect at low pressure results in an overestimated amount of excess sorption, leading to a mismatched phenomenon between the sorption and swelling, that is the maximum amount of sorption fails to induce corresponding maximum swelling. The CO2-induced deformation is anisotropic and heterogeneous during the whole sorption process, which can be attributed to the bedding structure of coal and heterogeneous maceral distribution in coal. Because of the difference in the sorption characteristic between different macerals, the clay + inertinite-rich regions first rapidly swell and then suffer from compression through the later swelling of the vitrinite + liptinite -rich regions in coal, showing an “overshoot” behavior. The dissolution of CO2 induces a structural rearrangement of coal, leading to strains in different directions maintain changes without further CO2 intake. This phenomenon is observed in the first few sorption steps until the structure of coal reaches a stable state. The kinetic relationships between sorption and deformation in individual pressure steps are nearly linear or are linear up to a certain point but slopes of these curves are different, resulting in a simple quadratic polynomial relationship between sorption and deformation isothermals during the whole sorption process.

中文翻译：

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二氧化碳封存过程中煤变形的等温线和动力学及其与吸附的关系

摘要 深入了解煤对二氧化碳 (CO2) 的吸附行为对于煤层中的 CO2 封存和提高煤层气回收率至关重要。然而，CO2在CO2注入过程中通过物理和/或化学反应引起煤的变形，这对煤层的气流和稳定性具有显着影响。本研究调查了 CO2 吸附的等温线和动力学，从而研究了在三种不同温度下的等温线测试过程中烟煤样品的变形。吸附和变形的等温线和动力学曲线可以分别由 Langmuir 和伪二阶 (PSO) 模型描述。实验结果和 PSO 模型参数表明，低压下的孔隙填充效应导致过高估计的过量吸附量，导致吸附与溶胀不匹配的现象，即最大吸附量未能引起相应的最大溶胀。在整个吸附过程中，CO2 引起的变形是各向异性和非均质的，这与煤的层理结构和煤中的非均质成分分布有关。由于不同物质吸附特性的不同，煤中粘土+惰性富集区先快速膨胀，然后通过后期富镜质+锂铁矿区的膨胀受到压缩，表现出“超调”行为。CO2 的溶解引起煤的结构重排，导致不同方向的应变保持变化而不会进一步吸入 CO2。在最初的几个吸附步骤中观察到这种现象，直到煤的结构达到稳定状态。在单个压力步骤中吸附和变形之间的动力学关系接近线性或线性到某一点，但这些曲线的斜率不同，导致在整个吸附过程中吸附和变形等温线之间存在简单的二次多项式关系。