Displacement and Diffusion of Methane and Carbon Dioxide in SBA-15 Studied by NMR

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• 作者：Yuanli Hu ; Xiulian Pan ; Xiuwen Han ; Xinhe Bao
• 刊名：Journal of Physical Chemistry C
• 出版年：2017
• 出版时间：February 2, 2017
• 年：2017
• 卷：121
• 期：4
• 页码：2481-2486
• 全文大小：394K
• ISSN：1932-7455

文摘

With increasing concern about the environmental impact of shale gas exploitation, nonaqueous fracturing with carbon dioxide has emerged as a promising alternative to increase gas production and, at the same time, to store large amounts of CO<sub>2sub>. The key process of CH<sub>4sub> displacement by CO<sub>2sub> is worth a systematic investigation from aspects of both experiment and simulation. In this work, the CH<sub>4sub> and CO<sub>2sub> displacement was studied with in situ <sup>13sup>C NMR in the pores of silica (SBA-15), which were functionalized with organic groups such as phenyl and cyclohexyl, in order to model the organic matter in shale with different aromaticity. Due to the stronger adsorption strength and higher capacity of CO<sub>2sub> in SBA-15, CH<sub>4sub> can be easily stripped out of the pores by CO<sub>2sub>, while the reverse process to displace CO<sub>2sub> with CH<sub>4sub> is not effective. Even though the displacement effect in the pores of SBA-15 with a higher aromaticity is relatively better at room temperature, the superiority is eliminated by high temperature. Furthermore, the results of pulse field gradient (PFG) NMR demonstrate that the self-diffusion coefficient of CO<sub>2sub> is an order of magnitude smaller than that of CH<sub>4sub>, and the existence of CO<sub>2sub> slows down the diffusion of CH<sub>4sub> slightly. The gas diffusion in both scenarios follows the trend: SBA-15 > SBA-phenyl > SBA-cyclohexyl.