Lv Xiaofang, Bai Boyu, Liang Shangbin, Zeng Wenguang, Liu Yang, Ma Qianli, Zhang Haifeng, Wang Chuanshuo, Zhou Shidong
Jiangsu Key Laboratory of Oil and Gas Storage & Transportation Technology, Changzhou University Changzhou 213016 China
China Petroleum & Chemical Corporation Northwest Oilfield Branch, Petroleum Engineering Technology Research Institute Urumqi 830011 China.
RSC Adv. 2022 Aug 1;12(33):21203-21212. doi: 10.1039/d2ra03768h. eCollection 2022 Jul 21.
The hydrate formation rate is the key to the implementation of solid gas storage and transportation technology by the hydrate method. As a MOF material with strong hydrothermal stability, ZIF-8 has been proved to play a significant role in promoting the nucleation and growth of hydrate. However, the growth kinetics promotion mechanism and growth law of methane hydrate in the ZIF-8 promoter system have not been clarified at present. Therefore, the growth kinetics experiment of methane hydrate in the ZIF-8 promoter system was carried out in a high-pressure visualization reactor to systematically study the effects of the ZIF-8 concentration, undercooling degree, and pressure on the growth law of methane hydrate. The experimental results showed that: (1) the concentration of ZIF-8 had a significant shortening effect on the induction period of methane hydrate. With the increase in the ZIF-8 concentration, the induction time of methane hydrate was shortened from 5.85 h to 0.85 h. The methane gas consumption showed a gradually increasing trend at first, and then with the reaction going on, a dense hydrate film was formed at the gas-liquid interface, which increased the mass transfer resistance, resulting in the increase in the methane gas consumption gradually becoming stable. There were four stages in the growth process of hydrate, namely rapid formation, slow formation, secondary formation, and end formation and the optimal dosage of ZIF-8 promoter exists, and the optimal critical specific content was 0.02 mg mL. (2) With the increase of undercooling, the induction time of methane hydrate decreased significantly, and the increase in the methane consumption also showed an increasing trend at first and then decreased. (3) With the increase of the system pressure to 7 MPa, the induction time of methane hydrate decreased from 1.02 h at 6 MPa to 0.2 h at 7 MPa, and the decrease rate was 80.8%, which was mainly due to the presence of "OPEN GATE" in the ZIF-8 accelerator. With the increase of the system pressure, the pore opening of the ZIF-8 material increased, the adsorption of methane increased, and the nucleation and growth of methane hydrate were promoted.
水合物生成速率是水合物法实现固态气体储存与运输技术的关键。作为一种具有强水热稳定性的金属有机框架（MOF）材料，ZIF-8已被证明在促进水合物的成核与生长方面发挥着重要作用。然而，目前ZIF-8促进体系中甲烷水合物的生长动力学促进机制及生长规律尚未明确。因此，在高压可视化反应器中开展了ZIF-8促进体系中甲烷水合物的生长动力学实验，以系统研究ZIF-8浓度、过冷度和压力对甲烷水合物生长规律的影响。实验结果表明：（1）ZIF-8浓度对甲烷水合物的诱导期有显著的缩短作用。随着ZIF-8浓度的增加，甲烷水合物的诱导时间从5.85 h缩短至0.85 h。甲烷气体消耗起初呈逐渐增加趋势，随后随着反应进行，气液界面形成致密的水合物膜，传质阻力增大，导致甲烷气体消耗增加逐渐趋于稳定。水合物生长过程存在快速形成、缓慢形成、二次形成和终了形成四个阶段，且ZIF-8促进剂存在最佳用量，最佳临界比含量为0.02 mg/mL。（2）随着过冷度的增加，甲烷水合物的诱导时间显著降低，甲烷消耗增加同样起初呈上升趋势，随后下降。（3）随着体系压力升高至7 MPa，甲烷水合物的诱导时间从6 MPa时的1.02 h降至7 MPa时的0.2 h，下降率为80.8%，这主要是由于ZIF-8促进剂中存在“开放窗口”。随着体系压力增加，ZIF-8材料的孔径增大，甲烷吸附量增加，促进了甲烷水合物的成核与生长。
