静止闭口系统中气体水合反应成核点的预测与验证

In the field of gas hydrate kinetics, uncertainties in nucleation process of gas hydrate challenge the efforts of researchers around the world. In this program, in stead of the traditional research way of only focusing on the hydrate formers, the studying object becomes the quiescent closed system with reaction cell and gas hydrate formers. A new potential model of gas hydrate driving force was proposed as a function of temperature, pressure, saturation, physical properties of gas hydrate formers, physical properties of reaction cell, the interfacial free energy between gas hydrate formers and the interfacial free energy between gas hydrate former and reaction cell. And a visualized high-pressure reaction cell was developed to study the nucleation processes of HCFC141b hydrate, CO2 hydrate and CH4 hydrate respectively. In the process of research, Fluent Software was used to simulate the temperature distribution, the pressure distribution, the concentration distribution and the potential function distribution of driving force and to demarcate the preferred region of nucleation in time-varying process of nucleation. Then, feasibility and stability of nucleation was analyzed and nucleating point was predicted by molecular dynamics simulation in the preferred region of nucleation. Finally, the predicted nucleating point was verified by the experimental one tested by the infrared camera and CCD cameral. It is of great significance of this program to explain the uncertainty of gas hydrate reaction and to cease the controversy on many problems including the driving force, induction time and growth rate, and to discover the heat and mass transfer in process of gas hydrate reaction and to industrialize the gas hydrate technologies.

针对气体水合物成核过程不确定性大这一国际难点和热点问题，本项目突破传统以水合反应物为研究对象的思路，以水合反应器和水合反应物组成的静止闭口系统为研究对象，首次建立包括温度、压力、饱和度、反应物物性、反应器物性、反应物与反应器间界面自由能、反应物之间的界面自由能等参数在内的气体水合物生成驱动力势函数模型；继而，对于可视化反应器中HCFC141b、CO2、CH4等气体水合物的成核过程，首先利用Flunent软件模拟时变过程中温度场、压力场、浓度分布、水合反应生成驱动力势函数场，标定水合物优先成核区域，然后结合分子动力学模拟分析区域内水合物成核的可行性和稳定性，预测水合反应成核点；最后利用红外热像仪测得的气体水合物成核点检验预测结果。项目研究结果对准确解释水合反应的不确定性，平息对生成驱动力、诱导时间、生长速率等问题的争论，准确揭示水合反应过程的传热传质机理及气体水合物技术工业化应用有重要意义。

气体水合物技术可广泛应用于天然气储运、水合物蓄冷、混合气体分离、海水淡化、水溶液浓缩等领域。然而，由于水合反应物通常不互溶，导致水合物结晶的诱导期长、过冷度大、生成速率小。本项目首先以水合反应器和水合反应物组成的静止闭口系统为研究对象，分别研究纯水、表面活性剂、多孔介质等不同体系中气体水合物的生成过程，确定不同的反应体系对气体水合物生成过程的诱导时间、生成速率等的定量影响。首先，通过实验分别研究了在纯水、1950ppm的十二烷基硫酸钠(SDS)和400ppm的十二烷基苯磺酸钠(SDBS)体系中C3H8水合物的生成过程，研究结果表明：纯水体系C3H8水合物生成过程的诱导时间较长；表面活性剂的加入，明显地缩短了水合物生成过程的诱导时间，且提高了其生成速率，十二烷基硫酸钠（SDS）和十二烷基苯磺酸钠（SDBS）体系中C3H8水合物的生成速率分别达到了0.0224和0.0222mm/h。其次，通过实验研究了压力扰动对气体水合物生成过程的影响，结果表明：与无扰动条件相比，压力扰动可以有效地促进C3H8水合物的生成过程；压力扰动条件下C3H8水合物的平均生长速率达到了0.0526mm/h。再次，通过实验研究了不同初始压力条件下C3H8水合物的生成过程，研究了不同初始压力对不同体系中C3H8水合物静态生成过程的定量影响。结果表明：不论是纯水体系还是表面活性剂体系，初始压力越高，气体水合物生成过程的诱导时间越短；初始压力越高，气体水合物的平均生成速率越大。最后，通过实验研究了多孔介质体系中气体水合物的生成与分解过程，研究结果表明：当多孔介质孔径为13.8nm至26.7nm之间时，多孔介质粒径越小，气体水合物生成过程的诱导时间越长；饱和水体系的多孔介质中，当多孔介质孔径为13.8nm至26.7nm之间时，多孔介质的孔径越小，多孔介质中气体水合物生成过程的平均生成速率就越大，多孔介质水合物的储气量就越大。项目研究结果对准确解释水合反应的不确定性、诱导时间、生成速率、生成驱动力等问题，以及准确解释水合反应过程的传热传质机理及气体水合物技术的工业化应用具有总要的意义。