Tverdov Ilya, Khafizov Nail R, Madzhidov Timur I, Varfolomeev Mikhail A, Yuan Chengdong, Kadkin Oleg N
Alexander Butlerov Institute of Chemistry, Kazan Federal University, ul. Lobachevskogo 1/29, Kazan 420008, Russia.
Department of Petroleum Engineering, Institute of Geology and Petroleum Technologies, Kazan Federal University, ul. Kremlevskaya 4/5, Kazan 420008, Russia.
ACS Omega. 2020 Aug 3;5(31):19589-19597. doi: 10.1021/acsomega.0c02069. eCollection 2020 Aug 11.
Steam injection is the most widely used technique for effectively reducing the viscosity of heavy oil in heavy oil production, in which in situ upgrading of heavy oil by aquathermolysis plays an important role. Earlier, transition-metal catalysts have been used for improving the efficiency of steam injection by catalytic aquathermolysis and achieving a higher degree of in situ oil upgrading. However, the unclear mechanism of aquathermolysis makes it difficult to choose efficient catalysts for different types of heavy oil. This theoretical study is aimed at deeply understanding the mechanism of in situ upgrading of sulfur-containing heavy oil and its catalysis. For this purpose, cyclohexyl phenyl sulfide (CPS) is selected as a model compound of sulfur-containing oil components, and, for the first time, a catalytic effect of transition metals on the thermochemistry and kinetics of its aquathermolysis is investigated by the density functional theory (DFT) methods with the use of the Becke three-parameter Lee-Yang-Parr (B3LYP), ωB97X-D, and M06-2X functionals. Calculation results show that the hydrolysis of CPS is characterized by fairly high energy barriers in comparison with other possible reaction routes leading to the cleavage of C-S bonds, while the heterolysis of C-S bonds in the presence of protons has a substantially lower kinetic barrier. According to the theoretical analysis, transition-metal ions significantly reduce the kinetic barrier of heterolysis. The Cu ion outperforms the other investigated metal ions and the hydrogen ion in the calculated rate constant by 5-6 (depending on the metal) and 7 orders of magnitude, respectively. The catalytic activity of the investigated transition-metal ions is arranged in the following sequence, depending on the used DFT functional: Cu ≫ Co ≈ Ni > Fe. It is theoretically confirmed that transition-metal ions, especially Cu, can serve as effective catalysts in aquathermolysis reactions. The proposed quantum-chemical approach for studying the catalytic aquathermolysis provides a new supplementary theoretical tool that can be used in the development of catalysts for different chemical transformations of heavy oil components in reservoirs due to hydrothermal treatment.
注蒸汽是稠油开采中有效降低稠油粘度应用最为广泛的技术，其中通过水热裂解实现稠油的原位改质发挥着重要作用。此前，过渡金属催化剂已被用于通过催化水热裂解提高注蒸汽效率并实现更高程度的原位原油改质。然而，水热裂解机理不明使得难以针对不同类型的稠油选择高效催化剂。本理论研究旨在深入理解含硫稠油原位改质及其催化作用的机理。为此，选择环己基苯硫醚（CPS）作为含硫油组分的模型化合物，首次运用密度泛函理论（DFT）方法，采用Becke三参数Lee - Yang - Parr（B3LYP）、ωB97X - D和M06 - 2X泛函，研究过渡金属对其水热裂解热化学和动力学的催化作用。计算结果表明，与导致C - S键断裂的其他可能反应路径相比，CPS的水解具有相当高的能垒，而在质子存在下C - S键的异裂具有显著更低的动力学能垒。根据理论分析，过渡金属离子显著降低了异裂的动力学能垒。在所计算的速率常数方面，Cu离子分别比其他研究的金属离子和氢离子高出5 - 6倍（取决于金属）和7个数量级。根据所使用的DFT泛函，所研究的过渡金属离子的催化活性按以下顺序排列：Cu ≫ Co ≈ Ni > Fe。从理论上证实，过渡金属离子，尤其是Cu，可作为水热裂解反应的有效催化剂。所提出的用于研究催化水热裂解的量子化学方法提供了一种新的补充理论工具，可用于开发因储层内热液处理而实现稠油组分不同化学转化的催化剂。
