The effect of ethylene-vinyl acetate copolymer on the formation process of wax crystals and hydrates  

作　　者：Limin Wang Jinrong Duan Bei Liu Zhi Li Guangjin Chen 

机构地区：[1]State Key Laboratory of Heavy Oil Processing,China University of Petroleum,Beijing 102249,China [2]State Key Laboratory of Heavy Oil Processing,China University of Petroleum-Beijing at Karamay,Karamay 834000,China

出　　处：《Chinese Journal of Chemical Engineering》2024年第9期109-119,共11页中国化学工程学报（英文版）

基　　金：financial support received from National Natural Science Foundation of China(22178378 and 22127812);"Tianchi Talent"Recruitment Program,Xinjiang Tianshan Innovation Team(2022TSYCTD0002);Xinjiang Uygur Region"One Case,One Policy"Strategic Talent Introduction Project(XQZX20240054)are gratefully acknowledged.

摘　　要：Ethylene-vinyl acetate copolymer(EVA) as a kind of effective polymeric pour point depressant has been extensively used in the pipeline transportation of crude oil to inhibit wax deposition and improve the low temperature fluidity of crude oil. In this work, molecular dynamics simulations were performed to investigate the effect of EVA on wax-hydrate coexistence system to evaluate the application potentiality of EVA to the flow assurance of deep-sea oil-gas-water multiphase flow system. Our simulation results reveal that wax molecules gradually stretched and stacked from random coiling to a directional and ordered crystalline state during the process of wax solidification. The strong affinity of polar vinyl acetate side chains of EVA to neighboring water molecules made the EVA molecule prefer being in a curly state,which disrupted the ordered crystallization of surrounding wax molecules and delayed the solidification rate of wax cluster. In addition, it is found that EVA cocrystallized with wax molecules to form eutectic when the wax was fully solidified. The simulation results of hydrate nucleation and growth show that the EVA molecule displayed a two-sided effect on gas adsorption of wax crystals, which was the key factor that affected the nucleation and growth of hydrates in the methane-water system. The nonpolar hydrocarbon backbone of EVA increased the diffusion rate of methane and water, allowing more methane to diffuse to the surface of wax crystals, reducing the methane concentration in aqueous solutions and inhibiting the hydrate formation. On the other hand, the nonpolar vinyl acetate chains had a repulsive effect on methane, which reduced the adsorption area of methane on the eutectic surface and decreased the adsorption threshold value of the wax crystal. The excluded methane molecules would continue dissociating in the aqueous phase and participating in the nucleation and growth process of hydrates.Therefore, the probability of hydrate formation would be increased. It was worth noting that the inhibit

关 键 词：Wax crystallization Hydrate formation Ethylene-vinyl acetate copolymer Molecular dynamics simulation 

分 类 号：TE832[石油与天然气工程—油气储运工程] TE39