基于分子动力学模拟的轮胎橡胶气相热解产物反应机理

doi:10.16085/j.issn.1000-6613.2020-1421

摘要/Abstract

摘要：

运用分子动力学的方法，对轮胎橡胶的热解过程进行了模拟，并结合模拟结果和密度泛函数对其气相产物的反应路径进行推测计算。模拟结果表明，热解过程主要分为两个阶段，低温热解阶段发生的主要反应是橡胶长链断裂形成单体，主要产物为异戊二烯、苯乙烯和1,3-丁二烯；高温热解阶段发生的主要反应是单体进一步生成小分子气体，产物中CH₄、H₂、C₂H₄占大部分，还有少量C₂H₆、C₃H₆。其中CH₃·攻击异戊二烯和苯乙烯单体夺取特定位置的H·是生成CH₄的最优路径，H·攻击苯乙烯单体夺取特定位置的H·是生成H₂的最优路径，CH₂CH·攻击1,3-丁二烯单体夺取特定位置的H·是生成CH₂CH₂的最优路径。本文还将热解产物分别跟天然橡胶单独热解和天然橡胶与丁苯橡胶共热解的热解产物做对比，为废旧轮胎橡胶热解得到特定的气相产物和催化热解提供理论依据。

关键词: 轮胎橡胶, 分子动力学, 热解, 废物处理

Abstract:

In order to further understand the pyrolysis mechanism of tire rubber, the molecular dynamics method was used to simulate the pyrolysis process of tire rubber, and the reaction paths of gas-phase products were speculated by combining the simulation results and density function. The simulation results showed that the pyrolysis process was mainly divided into two stages: the low temperature pyrolysis stage where the main reaction was the long chain fracture of rubber to form monomers and the main products were isoprene, styrene and 1,3-butadiene, and the high temperature pyrolysis stage where the main reaction was that the monomers further generated small molecular gas in which CH₄, H₂ and C₂H₄ accounted for the majority with a small amount of C₂H₆ and C₃H₆. Among them, CH₃· attacking isoprene and styrene monomer to capture the H· at a specific position was the optimal path to generate CH₄, H· attacking styrene monomer to capture the H· at a specific position was the optimal path to generate H₂ and CH₂CH· attacking 1,3-butadiene monomer to capture the H· at a specific position was the optimal path to generate CH₂CH₂. The pyrolysis products were compared with those of natural rubber alone and natural rubber/butadiene styrene rubber co-pyrolysis. This would provide a theoretical basis for pyrolysis of waste tire rubber to obtain specific gaseous products and catalytic pyrolysis.

Key words: tyre rubber, molecular dynamics, pyrolysis, waste treatment

中图分类号:

TQ33

于双鹏, 杨启容, 陶礼, 刘亭, 杜威, 姚尔人. 基于分子动力学模拟的轮胎橡胶气相热解产物反应机理[J]. 化工进展, 2021, 40(6): 3119-3131.

YU Shuangpeng, YANG Qirong, TAO Li, LIU Ting, DU Wei, YAO Erren. Gas phase pyrolysis products of tire rubber based on molecular dynamics simulation[J]. Chemical Industry and Engineering Progress, 2021, 40(6): 3119-3131.

图/表 26

表1 客车和卡车轮胎的典型组成及其质量分数 (%)

成分	客车轮胎	卡车轮胎	说明
橡胶	47	45	使用了许多不同的天然橡胶和合成橡胶，例如，天然橡胶（聚异戊二烯）、丁苯橡胶、丁腈橡胶、氯丁橡胶、聚丁二烯橡胶
炭黑	21.5	22	用于增强橡胶的耐磨性
金属	16.5	21.5	用于增加轮胎强度
纺织材料	5.5	—	用于加固
氧化锌	1	2	与硬脂酸一起用于控制硫化过程并增强橡胶的物理性能
硫黄	1	1	用于交联橡胶内的聚合物链，增加硬度，防止在高温下过度变形
添加剂	7.5	5	用于部分替代炭黑的黏土或二氧化硅

表2 各橡胶的主要成分

橡胶类型

主要成分

天然橡胶

顺-1，4-聚异戊二烯［（C₅H₈）_n］

丁苯橡胶

1，3-丁二烯［（CH₂ $? ????$ CH—CH $? ????$ CH₂）_n］

苯乙烯［（C₆H₅—CH $? ????$ CH₂）］

顺丁橡胶

顺-1，4-聚丁二烯［（C₄H₆）_n］

表2 各橡胶的主要成分

橡胶类型

主要成分

天然橡胶

顺-1，4-聚异戊二烯［（C₅H₈）_n］

丁苯橡胶

1，3-丁二烯［（CH₂ $? ????$ CH—CH $? ????$ CH₂）_n］

苯乙烯［（C₆H₅—CH $? ????$ CH₂）］

顺丁橡胶

顺-1，4-聚丁二烯［（C₄H₆）_n］

图1 三种橡胶的单体和长链模型

图2 天然橡胶分子式

表3 天然橡胶单体的键长

键序号	键长/nm	键序号	键长/nm
①	1.140	⑤	1.439
②	1.439	⑥	1.139
③	1.141	⑦	1.521
④	1.539	⑧	1.141

图3 丁苯橡胶分子式

表4 丁苯橡胶单体的键长

键序号	键长/nm	键序号	键长/nm
⑨	1.072	?	1.029
⑩	1.547	?	1.540
?	1.047		1.14
?	1.621		1.539
?	1.078		1.141
?	1.517		1.14
?	1.106		1.14
?	1.371		1.54
?	1.523		1.14
?	1.424		1.54

图4 顺丁橡胶分子式

表5 文献中丁苯橡胶和天然橡胶单体的键长[20-21]

键序号	键长/nm	键序号	键长/nm
①	1.094	?	1.047
②	1.347	?	1.620
③	1.100	?	1.078
④	1.473	?	1.516
⑤	1.347	?	1.106
⑥	1.094	?	1.371
⑦	1.507	?	1.521
⑧	1.104	?	1.424
⑨	1.074	?	1.029
⑩	1.547

图5 优化后轮胎橡胶模型

图6 800K下轮胎橡胶模型

图7 1200K下轮胎橡胶模型

图8 1200K下的热解产物分布

图9 2600K下轮胎橡胶模型

图10 2600K下的热解产物分布

图11 C4H6·的反应路径

图12 异戊二烯产生自由基的反应路径

图13 苯乙烯产生自由基的反应路径

图14 1,3-丁二烯产生自由基的反应路径

图15 自由基生成过程的各反应吉布斯自由能变随温度的变化

图16 CH3·攻击3种橡胶单体的反应路径

图17 CH3·攻击3种橡胶单体的各反应吉布斯自由能变随温度的变化

图18 H·攻击3种橡胶单体的反应路径

图19 H·攻击3种橡胶单体的各反应吉布斯自由能变随温度的变化

图20 CH2?????CH·攻击3种橡胶单体的反应路径

图21 CH2?????CH·攻击3种橡胶单体的各反应吉布斯自由能变随温度的变化

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