超临界CO2-水混相流体中缓蚀剂的吸附行为与作用机理研究

Supercritical CO2 widely exists in carbon capture and storage, oil–gas exploiting situation. Supercritical CO2–H2O miscible flooding is very corrosive to carbon steel. The corrosion inhibition efficiency of conventional CO2 corrosion inhibitors declined greatly when they were applied in supercritical CO2–H2O miscible flooding. Many key factors may be changed by supercritical CO2, such as the dissolution of inhibitors, construction of double layer, repairing process of the inhibition film, the interaction between inhibitor and metal, structure and constituents of corrosion/inhibition multiple film. The phase equilibrium of supercritical CO2–H2O miscible flooding and the solubility/partition coefficients of different inhibitors are calculated. High pressure electrochemical tests and surface micro-analysis techniques are applied in this study. The effect of some different inhibitors on the corrosion electrochemical behavior of carbon steel and the adsorption-desorption behavior of the inhibitors on carbon steel in supercritical CO2–H2O miscible flooding are studied. Quantum chemistry calculation is applied to reveal the adsorption of inhibitors and study the effect of functional group and molecule polarity on the dissolution and inhibition efficiency of inhibitors. It is anticipated that this research would reveal the inhibition mechanism of inhibitors in supercritical CO2–H2O miscible flooding and provide an essential insight into development of corrosion inhibitors in supercritical CO2–H2O miscible flooding.

超临界CO2广泛存在于碳捕捉与封存、油气开采等环境中。超临界CO2与水形成的混相流体对碳钢具有极强的腐蚀性。在超临界CO2-水混相流体中，常规CO2缓蚀剂的缓蚀性能急剧下降，甚至失效。超临界CO2可能对缓蚀剂在介质中的溶解、金属/溶液双电层构造、界面缓蚀剂的补充与修复、缓蚀剂分子与金属间的作用力、缓蚀/腐蚀复合膜结构与组成等产生影响。本项目分析、计算CO2-水混相流体的相平衡及不同类型缓蚀剂在混相介质中的溶解与分配；采用动态高压电化学测试技术，结合表面微观分析手段，研究在不同流速的超临界CO2-水混相流体中，缓蚀剂对碳钢腐蚀电化学行为的影响，探讨缓蚀剂在碳钢表面的吸脱附行为。同时结合量子化学计算，阐明缓蚀剂在金属表面的吸附状态及缓蚀剂的极性、官能团等对其溶解、分配、缓蚀性能的影响。从本质上揭示超临界CO2-水混相流体中缓蚀剂的作用机理，为超临界CO2-水混相流体中的缓蚀剂开发提供理论依据。

超临界CO2驱工艺能够大幅提高油气采收率，但是传统CO2缓蚀剂在超临界CO2驱环境下性能急剧下降、甚至失效。本项目旨在阐明传统二氧化碳缓蚀剂的失效原因并探明不同缓蚀剂在超临界CO2-水混相流体中的吸附行为与作用机理。首先，我们建立了超临界CO2-水混相流体中缓蚀剂评价的动态电化学测试系统，有效 消除了动态流体的干扰，能够获得噪声低、可靠性高的电化学数据；其次，结合微分电容曲线等手段，发现当CO2由非超临界状态转变为超临界状态时，碳钢表面由携带过剩负电荷转为携带过剩正电荷，而传统CO2缓蚀剂在CO2介质中呈阳离子状态，超临界CO2状态下碳钢表面正电荷的排斥作用，使得传统CO2缓蚀剂无法在碳钢表面紧密吸附，导致传统CO2缓蚀剂的缓蚀性能急剧下降；第三，采用视窗高压釜及取样器，探明当介质中CO2处于超临界状态时，由于超临界CO2的萃取效应，非离子型低极性缓蚀剂富集到超临界CO2中，能更有效地抑制腐蚀；第四，根据超临界CO2驱工艺中金属的腐蚀机制，基于量子化学计算，设计并筛选、制备出多种应用于超临界CO2-水混相流体的缓蚀剂，如2-巯基苯并噻唑、硫脲基咪唑啉等，这些缓蚀剂分子具有多吸附中心、阳离子化倾向低等特点，在CO2处于超临界状态时，具有很好的缓蚀性能；最后，项目首次将纳米材料引入到抑制CO2腐蚀，制备出官能化氧化石墨烯、碳量子点、MOFs等多种纳米尺度缓蚀剂，并阐明了它们在含CO2的腐蚀介质中的缓蚀机制。