Catalytic effect of calcium on reaction of phenol using reactive molecular dynamics simulation

doi:10.11949/j.issn.0438-1157.20181058

Abstract

Abstract:

The process of calcium-catalyzed secondary reaction of coal pyrolysis tar is complicated, and it is difficult to deeply explore its mechanism through experimental research methods. The effect of calcium on the reaction of phenol (tar model compound) was studied using ReaxFF molecular dynamics simulations. The results showed that calcium promoted the reaction rate of phenol, and promoted the conversion of phenol to gaseous, heavy tar and coke products. At low temperatures, very little amounts of gas-Ca were observed. Ca was mainly involved in a repeated bond-breaking and bond-forming process between tar and coke. Ca species only promoted the polymerization of phenol at the low temperatures. While at high temperatures, a large amount of Ca was released in the form of gas-Ca, promoting the cracking of phenol. Ca promoted the production of H₂, but had little effect on the production of CO. The activation energies for the polymerization and cracking of phenol are determined to be 52.96 kcal/mol and 16.08 kcal/mol in the absence of Ca, compared to 37.33 kcal/mol and 13.34 kcal/mol in the presence of Ca. This means that the role of Ca in reducing the activation energy for phenol polymerization is much more significant than that for phenol cracking reactions.

Key words: pyrolysis, phenol, catalytic, ReaxFF, kinetics

摘要：

钙催化煤热解焦油二次反应的过程较为复杂，通过实验研究手段难以深入探究其机理。采用基于反应力场的分子动力学模拟方法研究了钙对焦油模型化合物苯酚反应的影响。结果表明，钙提高了苯酚的反应速率，促进了苯酚向气体产物、重质焦油和焦炭产物转化。在较低温度下，没有发现与气体产物键结的钙，钙主要迁移转化到重质焦油和焦炭产物中，促进了苯酚的缩聚反应。在较高温度下，有大量的钙与气体产物键结，促进了苯酚的裂解反应，提高了H₂的生成量，但对CO的生成几乎没有影响。根据一级反应动力学模型，钙对苯酚裂解反应的活化能影响较小，但显著降低了苯酚缩聚反应的活化能。

关键词: 热解, 苯酚, 催化, ReaxFF, 动力学

CLC Number:

TQ 530.2

Dikun HONG, Zheng CAO, Changmin YANG, Liang LIU, Xin GUO. Catalytic effect of calcium on reaction of phenol using reactive molecular dynamics simulation[J]. CIESC Journal, 2019, 70(5): 1788-1794.

洪迪昆, 操政, 杨昌敏, 刘亮, 郭欣. 钙催化苯酚反应的分子动力学模拟[J]. 化工学报, 2019, 70(5): 1788-1794.

Figures/Tables 7

Fig.1 Simulation system of phenol reaction

Fig.2 Time evolution of number of phenol molecular at different temperatures (solid symbol: Ca-form system; hollow symbol: Ca-free system)

Fig.3 Distributions of C0—4, C5—11 and C12+ products at different temperatures (solid: Ca-form system; hollow: Ca-free system)

Fig.4 Time evolution of number of H2, CO and H2O at 3000 K

Fig.5 Distributions of Ca species during phenol reaction at 2000 K and 3000 K

Fig.6 Time evolution of C0－4 and C12+ yields at different temperatures

Fig.7 Determination of activation energies for cracking and polymerization of phenol

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