Preparation Of Supercritical Carbon Dioxide Thickener By Living Polymerization And Study On The Thickening Mechanism

Carbon dioxide flooding technology is the best way to achieve carbon dioxide emission reduction under the current economic and technical conditions.The CO₂transportation and oil displacement processes are mostly carried out under supercritical conditions.The viscosity of supercritical CO₂ is generally between 0.03～0.10 m Pa·s,which is much smaller than that of crude oil.This difference creates an unfavorable mobility ratio and viscous fingering of CO₂.The fingering phenomenon will lead to the early breakthrough of CO₂ and the low degree of oil recovery.Aiming at the problems of poor solubility,high cost and unenvironmental protection of the current tackifiers,research on new supercritical CO₂ tackifiers is carried out.A series of supercritical CO₂ thickeners were designed by GROMACS molecular dynamics program,and the molecular dynamics simulation of the thickener and CO₂system was carried out.The polymer-CO₂ interaction,radial distribution function,cohesive energy density,solubility parameter and viscosity of the system were analyzed,and the polymer with the best solubility and viscosity enhancement effect in supercritical CO₂ was selected.From the aspects of polymer structure-property,etc.,its dissolution and viscosity enhancement mechanism in supercritical CO₂ was explored.The following conclusions are drawn:（1）Vinyl acetate-maleic anhydride copolymer can increase the viscosity of supercritical CO₂ by 2.53 times under the conditions of25MPa and 313.15K.The increase of the linear alkyl group of the polymer increases the interaction between the polymer molecules,which helps the polymer to form a spatial network structure in CO₂,and effectively improves the viscosity increase effect.However,the longer the branched alkyl group is,the weaker the ability of the polymer to interact with CO₂,which is not conducive to the compatibility of the polymer with CO₂.（2）Vinyl acetate-maleic anhydride-styrene copolymer with a molar ratio of 2:4:1 can increase the viscosity of supercritical CO₂ by 3.02 times under the conditions of 25MPa and 313.15K.Although the solubility decreases with the introduction of styrene groups,its viscosity increases with it.Theπ-πstacking between styrene groups increases the polymer-polymer interaction and makes the polymer molecules more effective.Agglomeration is formed,thereby increasing the viscosity of the entire system.（3）The synthesis experiment was carried out on the preferred vinyl acetate-maleic anhydride-styrene copolymer tackifier,and the characterization was performed by means of infrared spectroscopy.The synthesized product is the target product.Finally,based on the results of molecular simulation analysis,the best supercritical CO₂ thickener was selected and synthesized and characterized.In this paper,only maleic anhydride and vinyl acetate are used as typical objects to design the molecular chain structure and the composition of the copolymerization system.In the follow-up,molecular simulations and experiments can be combined to select other CO₂-philic groups as monomers to design and synthesize more efficiently.Fluorine-free hydrocarbon supercritical CO₂ tackifier.