Molecular Simulation on Permeation Behavior of CH4/CO2/H2S Mixture Gas in PVDF at Service Conditions

Polymers

Jixing Meng¹  Huifang Chu²  Xuemin Zhang²  Xiong Gao³  Houbu Li⁴  Han Ding⁴  Guoquan Qi⁴ 

[1] Jiangsu Key Laboratory of Engineering Mechanics, Southeast University, Nanjing 210096, China;School of Materials Science and Engineering, Chang’an University, Xi’an 710064, China;Shaanxi Yanchang Petroleum Northwest Rubber LLC, Xianyang 712023, China;State Key Laboratory of Performance and Structural Safety for Petroleum Tubular Goods and Equipment Materials, CNPC Tubular Goods Research Institute, Xi’an 710077, China;

关键词: PVDF;    permeation;    sorption;    diffusion;    molecular simulation;    oil and gas gathering and transportation;   

DOI  :  10.3390/polym14030545

来源: DOAJ

【 摘 要 】

Reinforced thermoplastic composite pipes (RTPs) have been widely used for oil and gas gathering and transportation. Polyvinylidene fluoride (PVDF) has the greatest potential as a thermoplastic liner of RTPs due to its excellent thermal and mechanical properties. However, permeation of gases is inevitable in the thermoplastic liner, which may lead to blister failure of the liner and damage the safe operation of the RTPs. In order to clarify the permeation behavior and obtain the permeation mechanism of the mixture gas (CH₄/CO₂/H₂S) in PVDF at the normal service conditions, molecular simulations were carried out by combining the Grand Canonical Monte Carlo (GCMC) method and the Molecular Dynamics (MD) method. The simulated results showed that the solubility coefficients of gases increased with the decrease in temperature and the increase in pressure. The adsorption isotherms of all gases were consistent with the Langmuir model. The order of the adsorption concentration for different gases was H₂S > CO₂> CH₄. The isosteric heats of gases at all the actual service conditions were much less than 42 kJ/mol, which indicated that the adsorption for all the gases belonged to the physical adsorption. Both of the diffusion and permeation coefficients increased with the increase in temperature and pressure. The diffusion belonged to Einstein diffusion and the diffusion coefficients of each gas followed the order of CH₄ > CO₂ > H₂S. During the permeation process, the adsorption of gas molecules in PVDF exhibited selective aggregation, and most of them were adsorbed in the low potential energy region of PVDF cell. The mixed-gas molecules vibrated within the hole of PVDF at relatively low temperature and pressure. As the temperature and pressure increase, the gas molecules jumped into the neighboring holes occasionally and then dwelled in the holes, moving around their equilibrium positions.

【 授权许可】

Unknown