基于分子动力学模拟的胺溶剂碳捕集过程自扩散系数

doi:10.16085/j.issn.1000-6613.2025-0068

摘要/Abstract

摘要：

化学吸收法是当前广泛应用的CO₂捕集方法之一，而采用胺溶剂进行化学吸收的技术较为成熟。胺溶剂碳捕集过程是典型具备“三传一反”特性的化工过程。在这一过程中，扩散系数是评估其传质过程的重要参数，同时影响着胺溶剂吸收CO₂过程中的动力学性能评价和反应性能评价。由于传统的实验方法测量胺溶剂扩散系数较为烦琐，本文采用分子动力学模拟的方法进行研究。首先，研究发现通用小分子力场模型（PCFF）在胺溶剂水溶液体系下的模拟精度较低，为确保模拟的准确性，需要针对分子力场模型进行修正。结果表明，修正后的力场模型能准确描述甲基二乙醇胺（MDEA）溶剂中的分子间相互作用和自扩散系数，预测误差小于3%。随后，基于修正模型，本文计算了多种单胺溶剂的自扩散系数，并推导了自扩散系数与温度之间的定量关系。为探明胺溶剂动力学性质受反应进度变化产生的离子的影响，研究构建了不同反应进度下的模拟体系。基于结果，研究发现自扩散系数在反应过程中逐渐减小，且与反应进度呈线性关系。此外，对不同比例混合胺溶剂（如单乙醇胺与甲基二乙醇胺）的模拟显示，自扩散系数与MEA的质量分数近似呈线性关系。通过对分子间相互作用能和径向分布函数的进一步分析，本文阐明了胺溶剂自扩散系数的变化规律及其微观机制。综上，本文针对通用小分子力场模型进行了修正，并为优化胺溶剂的CO₂捕集性能提供了重要的理论支持和模拟工具。

关键词: 二氧化碳捕集, 胺溶剂, 分子动力学, 动力学性质, 传质, 分子模拟, 反应进度

Abstract:

Chemical absorption is one of the most widely used CO₂ capture methods, and amine solvent chemical absorption technology is more mature. The amine solvent carbon capture process is a typical chemical process with the characteristics of “three transfers and one inversion”. In this process, the diffusion coefficient is an important parameter for evaluating the mass transfer process, and it also affects the kinetic performance evaluation and the reaction performance evaluation of CO₂ absorption by amine solvents. In this study, the simulation accuracy of the traditional solvent molecular force field model was found to be low. To ensure the accuracy of the simulation, the solvent force-field model was first modified, and the results showed that the modified force-field model could accurately describe the intermolecular interactions and self-diffusion coefficients in the solvent of N-Methyldiethanolamine (MDEA), and the prediction error was less than 3%. Then, based on this model, the self-diffusion coefficients of other monoamine solvents [monoethanolamine (MEA), diethanolamine (DEA), etc.] were calculated, and the quantitative relationship between the self-diffusion coefficients and temperature was deduced. On the other hand, in order to explore the influence of ions generated during the reaction process on the kinetic properties of amine solvent, the simulation systems under different reaction progress were constructed. The findings of the study indicated a gradual decrease of the self-diffusion coefficient during the reaction process, with a concomitant linear relationship between the coefficient and the reaction progress. Furthermore, the simulation of mixed amine solvents (e.g. MEA and MDEA) at varying proportions demonstrated that the self-diffusion coefficient exhibited a linear relationship with the mass fraction of MEA. Through further analysis of the intermolecular interaction energy and radial distribution function, the variation rule of the amine solvent self-diffusion coefficient and its microscopic mechanism were explained. In conclusion, this study modified the force field model and provided important theoretical support and simulation tools for optimizing the CO₂ capture performance of amine solvents.

Key words: CO₂ capture, amine solvent, molecular dynamics, dynamic properties, mass transfer, molecular simulation, reaction progress

中图分类号:

TQ413.26

黄可儿, 刘佳豪, 李昊明, 周天航, 高金森, 蓝兴英. 基于分子动力学模拟的胺溶剂碳捕集过程自扩散系数[J]. 化工进展, 2025, 44(8): 4352-4364.

HUANG Ke’er, LIU Jiahao, LI Haoming, ZHOU Tianhang, GAO Jinsen, LAN Xingying. Self-diffusion coefficients in the process of carbon capture by amine solvents based on molecular dynamics simulation[J]. Chemical Industry and Engineering Progress, 2025, 44(8): 4352-4364.

图/表 20

图1 研究概述

表1 无水MEA在288K、298K和308K下模拟计算的自扩散系数和实验值

项目	288K	298K	308K
未修正力场结果/10^-10m²·s^-1	11.55	12.84	14.75
修正力场结果/10^-10m²·s^-1	0.41	0.64	1.15
阿伦尼乌斯方程拟合结果/10^-10m²·s^-1	0.41	0.61	0.89
实验结果/10^-10m²·s^-1	0.4	0.55	0.93

表2 修正后的PCFF下反应物、H2O、CO2和生成物的力场参数

分子	原子	ϵ/kcal·mol^-1	σ/Å
反应物	N	0.325（修正值）	4.070
	H（—CH₂—、—NH₂）	0.013	1.098
	C	0.054	4.010
	O	1.200（修正值）	3.535
	H（—OH）	0.020	2.955
H₂O	H	0.013	1.098
H₂O	O	0.9864（修正值）	3.608
CO₂	C	0.064	4.010
CO₂	O	0.060	3.535
生成物	N	0.325（修正值）	3.262
	H	0.013	1.098
	C	0.120	3.908
	O（—NHCOO—中第一个O）	0.167	3.596
	O（—NHCOO—中第二个O）	1.200（修正值）	3.535

图2 无水MEA的自扩散系数的计算模型及计算结果

图3 30% MDEA溶剂模型粉色和灰色球—分别代表MDEA和H2O分子

表3 30% MDEA溶剂在303K、313K和323K下模拟计算的自扩散系数和实验值[27]

结果	303K	313K	323K
模拟值/10^-10m²·s^-1	4.76	5.81	7.12
实验值/10^-10m²·s^-1	4.49	5.76	7.27

表4 单胺分子信息

英文缩写	中文名称	分子式	结构式	分子量
MEA	单乙醇胺	C₂H₇NO	NH₂CH₂CH₂OH	61.083
DEA	二乙醇胺	C₄H₁₁NO₂	NH(CH₂CH₂OH)₂	105.136
AEEA	羟乙基乙二胺	C₄H₁₂N₂O	NH₂CH₂CH₂NHCH₂CH₂OH	104.15
MDEA	甲基二乙醇胺	C₅H₁₃NO₂	CH₃N(CH₂CH₂OH)₂	119.16
EDEA	N-乙基二乙醇胺	C₆H₁₅NO₂	CH₃CH₂N(CH₂CH₂OH)₂	133.1888
DEA-1,2-PD	3-二乙氨基-1,2-丙二醇	C₇H₁₇NO₂	(CH₃CH₂)₂NCH₂(CHOH)CH₂OH	147.215

图4 不同30%单胺溶剂的自扩散系数

表5 30%不同单胺溶剂自扩散系数与温度之间的定量关系

不同单胺溶剂	自扩散系数公式
MEA	$2.06 × 10 - 7 e - 13848 R T$
DEA	$5.31 × 10 - 7 e - 17772 R T$
MDEA	$4.6 × 10 - 7 e - 17367 R T$
AEEA	$1.5 × 10 - 7 e - 13850 R T$
EDEA	$2.83 × 10 - 7 e - 16046 R T$
DEA-1,2-PD	$2.53 × 10 - 7 e - 15750 R T$

表5 30%不同单胺溶剂自扩散系数与温度之间的定量关系

不同单胺溶剂	自扩散系数公式
MEA	$2.06 × 10 - 7 e - 13848 R T$
DEA	$5.31 × 10 - 7 e - 17772 R T$
MDEA	$4.6 × 10 - 7 e - 17367 R T$
AEEA	$1.5 × 10 - 7 e - 13850 R T$
EDEA	$2.83 × 10 - 7 e - 16046 R T$
DEA-1,2-PD	$2.53 × 10 - 7 e - 15750 R T$

图5 313K下单胺溶剂中胺与水的RDF及胺分子与水分子的相互作用能

表6 30%单胺溶剂不同反应进度的分子个数

反应进度/%	分子个数
反应进度/%	MEA	DEA	MDEA	MEAH⁺MEACOO^-	DEAH⁺DEACOO^-	MDEAH⁺HCO $3 -$
0	253	147	130	0	0	0
10	227	133	117	13	7	13
20	203	117	104	25	15	26
30	177	103	91	38	22	39
40	151	89	78	51	29	52
50	127	73	65	63	37	65
60	101	59	52	76	44	78
70	77	45	39	88	51	91
80	51	29	26	101	59	104
90	25	15	13	114	66	117
100	0	0	0	126	74	130

表6 30%单胺溶剂不同反应进度的分子个数

反应进度/%	分子个数
反应进度/%	MEA	DEA	MDEA	MEAH⁺MEACOO^-	DEAH⁺DEACOO^-	MDEAH⁺HCO $3 -$
0	253	147	130	0	0	0
10	227	133	117	13	7	13
20	203	117	104	25	15	26
30	177	103	91	38	22	39
40	151	89	78	51	29	52
50	127	73	65	63	37	65
60	101	59	52	76	44	78
70	77	45	39	88	51	91
80	51	29	26	101	59	104
90	25	15	13	114	66	117
100	0	0	0	126	74	130

图6 30% MEA溶剂不同反应进度下的模型蓝色、灰色、黄色和粉色球—分别代表MEA、H2O、CO2和MEAH+MEACOO-

图7 30% MEA、DEA和MDEA溶剂与CO2反应不同反应进度的自扩散系数

图8 不同反应进度下反应物与水之间的RDF

图9 不同反应进度下生成物与水之间的RDF

图10 不同反应进度下分子之间的相互作用能

表7 混合胺溶剂中胺分子个数

质量分数	分子个数
质量分数	MEA	DEA	MDEA	DEA-1,2-PD
0.06	50	29	26	21
0.08	67	39	35	28
0.10	84	49	43	35
0.12	101	59	52	42
0.14	118	69	60	49
0.16	135	78	69	56
0.18	152	88	78	63
0.20	169	98	86	70
0.22	185	108	95	77
0.24	202	117	104	84

图11 不同比例混合胺溶剂的自扩散系数

图12 不同比例混合胺分子之间的RDF

图13 不同比例混合胺中胺分子与水分子的相互作用能

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