CH_(4)在PVDF中的渗透特性及机理

Permeation Characteristic and Mechanism of CH_(4) in Polyvinylidene Fluoride

气体组分在热塑性塑料中的渗透导致起泡失效,给油气集输用热塑性塑料内衬复合管的安全运行带来极大隐患。为了解气体介质在热塑性塑料中的渗透特性并明确其渗透机理,从根本上提出了控制气体渗透的有效措施,研究了典型气体CH4在聚偏氟乙烯(PVDF)中的渗透特性,检测并分析了渗透样品结构成分和耐热性能,并基于蒙特卡洛法(GCMC)和分子动力学模拟了30℃、0.1 MPa下,CH_(4)在PVDF中的吸附扩散行为,研究了CH_(4)在PVDF中的吸附及扩散机理。研究结果表明,CH_(4)在PVDF中的渗透系数随温度升高而逐渐提高,渗透样品的结构成分及耐热性能未发生明显变化,气体渗透主要为物理渗透过程,不存在化学侵蚀破坏。模拟计算得到的渗透系数与实验结果一致,在30℃、0.1 MPa下,CH_(4)有选择性地聚集吸附在PVDF晶胞中,在其扩散过程中,CH4分子均在PVDF空穴内振动,并未出现空穴间的跃迁。

Permeation of gases in thermoplastics made the liner at the risk of blister,which brought a hidden danger for safety of thermoplastic lined composite pipes used for oil and gas gathering and transportation.In order to understand the permeation behavior and mechanism of gases in thermoplastics and to present effective methods to prevent permeation,permeation behavior of a typical gas CH_(4) in Polyvinylidene Fluoride(PVDF)was studied and composition and thermal resistance of the penetrated samples were analyzed.The permeation process including sorption and diffusion process of CH_(4) in PVDF at 30℃,0.1 MPa were simulated by molecular simulation to clarify the permeation mechanism.The results showed that permeation coefficient of CH4 in PVDF was increased with the increasing temperature.It was reveal that the mode of gas permeation is mainly physical process rather than chemical attack,because composition and thermal resistance of the samples were not change obviously after the gas permeation.The simulated results showed that the adsorption of CH_(4) molecule in PVDF was selective aggregation and adsorption.The CH_(4) molecules jump in a small space where the cavity was,but not exceed this area,exhibiting a movement in the cavity at this condition.