Han Yanna, Yan Zhuangzhuang, Jin Lijun, Liao Junjie, Feng Guorui
College of Mining Engineering, Taiyuan University of Technology Taiyuan 030024 China
State Key Laboratory of Fine Chemicals, Institute of Coal Chemical Engineering, School of Chemical Engineering, Dalian University of Technology Dalian 116024 China.
RSC Adv. 2020 Apr 30;10(29):16949-16958. doi: 10.1039/d0ra01905d. eCollection 2020 Apr 29.
The interactions between O-H groups in kaolinite and re-adsorption water is an important aspect that should be considered in the hydraulic fracturing method for the production of shale gas, because the external water adsorbed by kaolinite in shale would significantly affect the desorption of methane. In this study, the interactions were investigated changing the amount of O-H groups and re-adsorption water in kaolinite by heating treatment and water re-adsorption. To overcome the overlap of IR vibration bands of the O-H functional groups in HO and those in parent kaolinite, kaolinite samples with DO re-adsorption were prepared by drying the HO from raw kaolinite and soaking the dried kaolinite in DO. The interactions between O-H groups in kaolinite and DO molecules were investigated by DRIFT and TG-MS. The results demonstrated that the vibration at 3670 ± 4 cm in the DRIFT spectra could be due to the outer O-H groups of the octahedral sheet on the upper surface of the kaolinite microcrystal structure, rather than a type of inner-surface O-H group. All types of O-H groups, including the inner O-H groups in kaolinite, could be transformed into O-D groups after DO re-adsorption at room temperature. The inner-surface O-H groups in kaolinite are the most preferred sites for DO re-adsorption; thus, they would be the key factor for studying the effect of re-adsorption water on methane desorption. When the temperature increased from 100 °C to 300 °C, two layers of kaolinite slipped away from each other, resulting in the transformation of inner-surface O-H groups into outer O-H groups. Thus, the temperature range of 100 to 300 °C was suggested for the heat treatment of kaolinite to decrease the content of inner-surface O-H groups; thereby, the amount of re-adsorption water was reduced. However, to thoroughly remove the re-adsorption water, a temperature higher than 650 °C should be used.
高岭石中O-H基团与再吸附水之间的相互作用是页岩气水力压裂开采方法中应考虑的一个重要方面，因为页岩中高岭石吸附的外部水会显著影响甲烷的解吸。在本研究中，通过热处理和水再吸附改变高岭石中O-H基团和再吸附水的量来研究这种相互作用。为了克服HO中O-H官能团与原始高岭石中O-H官能团的红外振动带重叠，通过将原始高岭石中的HO干燥并将干燥后的高岭石浸泡在DO中来制备具有DO再吸附的高岭石样品。通过漫反射红外傅里叶变换光谱（DRIFT）和热重-质谱联用（TG-MS）研究了高岭石中O-H基团与DO分子之间的相互作用。结果表明，DRIFT光谱中3670±4 cm处的振动可能归因于高岭石微晶结构上表面八面体片的外层O-H基团，而不是一种内表面O-H基团。包括高岭石内表面O-H基团在内的所有类型的O-H基团在室温下DO再吸附后都可以转化为O-D基团。高岭石内表面的O-H基团是DO再吸附的最优先位点；因此，它们将是研究再吸附水对甲烷解吸影响的关键因素。当温度从100℃升高到300℃时，两层高岭石相互滑动，导致内表面O-H基团转化为外表面O-H基团。因此，建议在100至300℃的温度范围内对高岭石进行热处理，以降低内表面O-H基团的含量；从而减少再吸附水的量。然而，为了彻底去除再吸附水，应使用高于650℃的温度。
