原油精馏塔中铵盐吸湿特性及其腐蚀行为

doi:10.16085/j.issn.1000-6613.2022-1529

摘要/Abstract

摘要：

原油精馏塔顶部循环系统中由于铵盐沉积引发的腐蚀问题，是导致设备及管道局部失效泄漏的问题之一。为了认识铵盐腐蚀的机理，本文采用了从头算分子动力学（AIMD）的模拟方法以及原位电化学测试的实验方法分别探究了铵盐的吸湿潮解特性及其溶液在不同温度与浓度下对于20号碳钢的腐蚀演化规律。电化学阻抗谱与表面表征结果反映了腐蚀的界面过程是受腐蚀产物生长、成膜以及破损行为影响下的动态传质过程，结合线性极化电阻以及失重测试揭示了腐蚀速率的变化是由产物的传质效应与电极反应过程共同决定。AIMD模拟结果表明NH₄Cl在水分子的作用下会发生包括电离、水解、质子转移链等一系列反应使得溶液呈酸性，并导致体系中的电荷状态发生了改变，这可能是引发腐蚀的一个重要原因。

关键词: 腐蚀, 反应动力学, 分子模拟, 界面, 传质

Abstract:

The corrosion problem caused by ammonium salts deposition in the top circulation system of crude oil distillation column is one of the problems that lead to local failure and leakage of equipment and pipelines. To understand the mechanism of corrosion, the simulation method of Ab initio molecular dynamics (AIMD) and the experimental method of in situ electrochemical measurements were conducted to explore the hygroscopic properties of ammonium salts and the corrosion evolution for SAE 1020 carbon steel at different temperatures and concentrations. The results of electrochemical impedance spectroscopy and surface characterization reflected that the interfacial process of corrosion was a dynamic mass transfer process under the influence of corrosion product growth, film formation and damage behavior, combined with linear polarization resistance and weight loss tests, and the change of corrosion rate was determined by the mass transfer effect of the product and the electrode reaction process. The results of AIMD demonstrated that the charge state in the system under the action of water molecules was altered, including ionization, hydrolysis, proton transfer chain, etc., which may be an important cause of corrosion.

Key words: corrosion, reaction dynamics, molecular simulation, interface, mass transfer

中图分类号:

TE624

李瑞东, 黄辉, 同国虎, 王跃社. 原油精馏塔中铵盐吸湿特性及其腐蚀行为[J]. 化工进展, 2023, 42(6): 2809-2818.

LI Ruidong, HUANG Hui, TONG Guohu, WANG Yueshe. Hygroscopic properties and corrosion behavior of ammonium salt in a crude oil distillation column[J]. Chemical Industry and Engineering Progress, 2023, 42(6): 2809-2818.

图/表 11

表1 20号碳钢的元素组成及含量

元素	质量分数/%
C	0.17~0.23
Si	0.17~0.37
Mn	0.35~0.65
P	≤0.035
S	≤0.035
Ni	≤0.30
Cr	≤0.25
Cu	≤0.25
Fe	剩余

图1 用于AIMD计算的分子模型

图2 不同的模型在20ps模拟过程中的温度与势能变化

图3 单层NH4Cl与100 H2O分子的模型在不同时刻的构型变化及局部放大图

图4 AIMD轨迹的RDF曲线与其积分曲线

图5 NHO氢键数量分布变化

图6 不同温度与浓度条件下的动电位极化测试结果图

图7 电化学阻抗谱测试结果图

图8 LPR方法与失重实验方法得到的不同条件下腐蚀速率变化

图9 不同工况下腐蚀96h后的表面形貌

图10 不同工况下腐蚀96h后的横截面形貌

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