Study on reaction force field simulation of pyrolysis interaction among components of oily sludge

doi:10.11949/0438-1157.20201206

Abstract

Abstract:

The composition of petroleum hydrocarbons in oily sludge is complex, and it is difficult to reveal the interaction between components in the pyrolysis process only by the macroscopic analysis results of products. Five compounds, namely n-dodecane, 1-dodecene, methylcyclohexane, p-xylene, and 1-methylnaphthalene, were represented as alkanes, alkenes, cyclanes, monocyclic aromatics and polycyclic aromatic hydrocarbons in oily sludge to construct model compounds of petroleum hydrocarbon in oily sludge. The molecular dynamics simulation method based on reaction field was used to study the distribution of products and the interactions among components during pyrolysis. The results showed that the pyrolysis products of model compounds were dominated by small molecular compounds H₂ and C_1—3, C₂H₄ and C₃H₆ in the early pyrolysis phase, and C₂H₂, C₃H₄ and H₂ in the late pyrolysis phase. Compared with the separate pyrolysis of each component in the model compound, the consumption rate of each component in the mixed pyrolysis process of petroleum hydrocarbon is obviously accelerated, and the number of pyrolysis product fragments also increases to a certain extent. According to the first-order reaction kinetic model, the apparent activation energy of petroleum hydrocarbon components in the mixed pyrolysis process decreased to different degrees, among which the apparent activation energy of alkanes, alkenes, and cycloalkanes decreased by 16.493 kJ/mol, 50.571 kJ/mol and 146.289 kJ/mol, respectively, which proved the synergistic effect of pyrolysis among petroleum hydrocarbon components of oily sludge from the level of molecular simulation.

Key words: oily sludge, pyrolysis, simulation, ReaxFF, kinetics

摘要：

含油污泥中石油烃组分复杂，仅靠产物的宏观分析结果难以揭示热解过程组分之间的相互作用。以正十二烷、1-十二烯、甲基环己烷、对二甲苯和1-甲基萘五种化合物分别代表含油污泥中石油烃的链烷烃、链烯烃、环烷烃、单环芳烃和多环芳烃五种组分，构建含油污泥石油烃的模型化合物。采用基于反应力场的分子动力学模拟方法，研究了热解过程中的产物分布及各组分之间的相互作用。结果表明，模型化合物热解产物以H₂和C_1~3的小分子化合物为主，热解前期主要为C₂H₄、C₃H₆，热解后期主要为C₂H₂、C₃H₄和H₂。相对于模型化合物中各组分单独热解，混合热解过程中石油烃各组分的消耗速率明显加快，且热解产物的片段数也有一定程度的增加。根据一级反应动力学模型，石油烃各组分在混合热解过程中的表观活化能有不同程度降低，其中链烷烃、链烯烃和环烷烃的表观活化能分别降低了16.493 kJ/mol、50.571 kJ/mol和146.289 kJ/mol，这从分子模拟层面证明了含油污泥石油烃各组分之间热解的协同作用。

关键词: 含油污泥, 热解, 模拟, 反应力场, 动力学

CLC Number:

TE 992.3

WEN Yanjun, JIANG Chi, LI Wenxuan, XIE Yingshen, WANG Gang, HOU Yingfei. Study on reaction force field simulation of pyrolysis interaction among components of oily sludge[J]. CIESC Journal, 2021, 72(2): 1100-1106.

温燕军, 蒋驰, 李文轩, 谢颖燊, 王刚, 侯影飞. 含油污泥各组分热解相互作用的反应力场模拟研究[J]. 化工学报, 2021, 72(2): 1100-1106.

Figures/Tables 12

Fig.1 GC-MS analysis diagram of oil extraction from oily sludge

Table 1 Petroleum hydrocarbon composition of oily sludge

组分	比例/%
链烷烃	32.53
链烯烃	29.34
环烷烃	28.18
单环芳烃	6.19
多环芳烃	3.76

Fig.2 Change of fragment number of pyrolysis products of oily sludge components at different temperatures

Fig.3 Change of fragment number of products with different carbon content with time

Fig.4 Distribution of main products in pyrolysis simulation of oily sludge

Table 2 Pyrolysis gas composition of oily sludge

产物名称	组成/%
CH₄	16.6
C₂H₂	3.1
C₂H₄	11.2
C₂H₆	10.9
C₃H₄	1.9
C₃H₆	4.7
C₃H₈	5.3
H₂	23.1

Fig.5 Change of reactants during pyrolysis of oily sludge

Fig.6 Change of pyrolysis products of oily sludge

Fig.7 Variation of molecular number of mixed pyrolysis alkanes at different temperatures

Fig.8 Fitting diagram of reaction rate constant k value

Fig.9 Fitting diagram of activation energy and pre-exponential factor

Table 3 Activation energy of main components of oily sludge

组分	活化能/(kJ/mol)
组分	混合热解	单独热解
链烷烃	203.792	220.285
链烯烃	202.337	252.908
环烷烃	172.829	319.118

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