Supercritical carbon dioxide is known to change the pore structure of coals and thus affect their carbon dioxide sequestration capacity. In this study, supercritical carbon dioxide dependence of pore morphology of coals was reviewed. Results indicated that the micropore surface area and volume of dry coals varied between –20% and 20% after exposure to supercritical carbon dioxide. Changes in the micropore size distribution of dry coals after supercritical carbon dioxide exposure were not found to be significant; however, the change in meso- and macropores with diameter of 2–8 nm was observed to be significant. Supercritical carbon dioxide and H2O exposure mainly influenced pores with diameters of 0.4–0.7, 0.7–0.9 and 2–8 nm. The variation in the pore fractal dimensions of the coals ranged from –0.5% to 0.5% after supercritical carbon dioxide exposure. Furthermore, the dependence of supercritical carbon dioxide on the pore structure of coals relies on the coal rank. The change in the pore structure of the coals after supercritical carbon dioxide exposure was observed to be related to the following aspects. First, supercritical carbon dioxide induced swelling in coal matrix, thus reducing the pore surface area and volume of the coal matrix and compressing the cleat system. Next, the extraction of supercritical carbon dioxide mobilised the small organic molecules dispersed in the coal matrix; this increased the pore volume, particularly of micropores. Finally, the mineral dissolution/precipitation also changed the pore structure of the coals. To further examine supercritical carbon dioxide dependence of coal pore morphology, the following studies should be performed. The characterisation of the chemical and pore structure of coals should be combined with existing coal structure models to account for the mechanism of supercritical carbon dioxide changing the pore structure of coals. Combination of physical experiments and numerical simulations is recommended to predict the changes in porosity and permeability of coals due to long-term carbon dioxide sequestration.

中文翻译：

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超临界二氧化碳流体对不同等级煤孔隙形态的影响：综述

众所周知，超临界二氧化碳会改变煤的孔隙结构，从而影响它们的二氧化碳封存能力。本研究综述了煤的孔隙形态对超临界二氧化碳的依赖性。结果表明，暴露于超临界二氧化碳后，干煤的微孔表面积和体积在 –20% 到 20% 之间变化。超临界二氧化碳暴露后干煤的微孔尺寸分布变化不显着；然而，观察到直径为 2-8 nm 的中孔和大孔的变化是显着的。超临界二氧化碳和 H2O 暴露主要影响直径为 0.4-0.7、0.7-0.9 和 2-8 nm 的孔隙。煤的孔隙分形维数的变化范围为 –0.5% 到 0。超临界二氧化碳暴露后 5%。此外，超临界二氧化碳对煤孔隙结构的依赖性取决于煤的等级。观察到超临界二氧化碳暴露后煤的孔隙结构变化与以下几个方面有关。首先，超临界二氧化碳引起煤基质膨胀，从而减少煤基质的孔隙表面积和体积，压缩割理系统。接下来，超临界二氧化碳的萃取使分散在煤基质中的有机小分子动起来；这增加了孔体积，尤其是微孔。最后，矿物溶解/沉淀也改变了煤的孔隙结构。为了进一步研究煤孔隙形态对超临界二氧化碳的依赖性，应进行以下研究。煤的化学和孔隙结构的表征应与现有的煤结构模型相结合，以解释超临界二氧化碳改变煤孔隙结构的机制。建议结合物理实验和数值模拟来预测由于长期封存二氧化碳而导致的煤孔隙度和渗透率的变化。