钙催化苯酚反应的分子动力学模拟
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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H_2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。
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 H_2, 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.
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 H_2, 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.
引文
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[2]冯冬冬,赵义军,唐文博,等.热解温度及AAEM元素对生物质快速热解焦油的影响[J].化工学报,2016,67(6):2558-2567.Feng D D,Zhao Y J,Tang W B,et al.Effect of temperature and AAEM species on fast pyrolysis of biomass tar[J].CIESC Journal,2016,67(6):2558-2567.
[3]Li X,Wu H,Hayashi J I,et al.Volatilisation and catalytic effects of alkali and alkaline earth metallic species during the pyrolysis and gasification of Victorian brown coal(Ⅵ):Further investigation into the effects of volatile-char interactions[J].Fuel,2004,83(10):1273-1279.
[4]樊文克,崔童敏,李宏俊,等.碱金属碱土金属对神府煤焦气化活性的影响[J].燃料化学学报,2016,44(8):897-903.Fan W K,Cui T M,Li H J,et al.Effect of AAEM on gasification reactivity of Shenfu char[J].Journal of Fuel Chemistry and Technology,2016,44(8):897-903.
[5]熊杰,周志杰,许慎启,等.碱金属对煤热解和气化反应速率的影响[J].化工学报,2011,62(1):192-198.Xiong J,Zhou Z J,Xu S Q,et al.Effect of alkali metal on rate of coal pyrolysis and gasification[J].CIESC Journal,2011,62(1):192-198.
[6]刘振宇,王仁醒,纪雷鸣,等.钙化合物在煤热解过程中的作用[J].北京化工大学学报(自然科学版),2015,42(4):1-9Liu Z Y,Wang R X,Ji L M,et al.Effect of calcium compounds on pyrolysis of coals[J].Journal of Beijing University of Chemical Technology(Natural Science Edition),2015,42(4):1-9
[7]黄小河,张守玉,杨靖宁,等.准东煤高温燃烧过程中含钙矿物质的转化规律[J].化工学报,2017,68(10):3906-3911.Huang X H,Zhang S Y,Yang J N,et al.Calcium transformation during Zhundong coal combustion process[J].CIESC Journal,2017,68(10):3906-3911.
[8]Lin S Y,Harada M,Suzuki Y,et al.Comparison of pyrolysis products between coal,coal/CaO,and coal/Ca(OH)2materials[J].Energy Fuels,2003,17(3):602-607.
[9]Zhu T,Zhang S,Huang J,et al.Effect of calcium oxide on pyrolysis of coal in a fluidized bed[J].Fuel Processing Technology,2000,64(1):271-284.
[10]Jia Y,Huang J,Wang Y.Effects of calcium oxide on the cracking of coal tar in the freeboard of a fluidized bed[J].Energy&Fuels,2004,18(6):1625-1632.
[11]杨靖宁,张守玉,姚云隆,等.高温热解过程中新疆高碱煤中钙的演变[J].煤炭学报,2016,41(10):2555-2559.Yang J N,Zhang S Y,Yao Y L,et al.Calcium transformation during the high-temperature pyrolysis process of high-alkali coal from Xinjiang[J].Journal of China Coal Society,2016,41(10):2555-2559.
[12]van Duin Adri C T,Dasgupta S,Lorant F,et al.ReaxFF:a reactive force field for hydrocarbons[J].Journal of Physical Chemistry A,2001,105(41):9396-9409.
[13]Zhang J,Weng X,Han Y,et al.The effect of supercritical water on coal pyrolysis and hydrogen production:a combined ReaxFFand DFT study[J].Fuel,2013,108(11):682-690.
[14]Zheng M,Li X,Liu J,et al.Initial chemical reaction simulation of coal pyrolysis via ReaxFF molecular dynamics[J].Energy&Fuels,2013,27(6):2942-2951.
[15]Zheng M,Li X,Liu J,et al.Pyrolysis of Liulin coal simulated by GPU-based ReaxFF MD with cheminformatics analysis[J].Energy&Fuels,2014,28(1):522-534.
[16]Bhoi S,Banerjee T,Mohanty K.Molecular dynamic simulation of spontaneous combustion and pyrolysis of brown coal using ReaxFF[J].Fuel,2014,136(6):326-333.
[17]Wang H,Feng Y,Zhang X,et al.Study of coal hydropyrolysis and desulfurization by ReaxFF molecular dynamics simulation[J].Fuel,2015,145(4):241-248.
[18]Zheng M,Li X,Nie F,et al.Investigation of overall pyrolysis stages for Liulin bituminous coal by large-scale ReaxFFmolecular dynamics[J].Energy&Fuels,2017,31(4):3675-3683.
[19]高宁,王一超,刘育红.丙炔基双酚A醚硼聚合物热解过程的ReaxFF分子动力学模拟[J].化工学报,2015,66(4):1557-1564.Gao N,Wang Y C,Liu Y H.Molecular dynamics simulations of thermal pyrolysis of novel dipropargyl ether of bisphenol A based boron-containing polymer[J].CIESC Journal,2015,66(4):1557-1564.
[20]Hong D K,Guo X.Molecular dynamics simulations of Zhundong coal pyrolysis using reactive force field[J].Fuel,2017,210(12):58-66.
[21]Bai Y,Yan L,Li G,et al.Effects of demineralization on phenols distribution and formation during coal pyrolysis[J].Fuel,2014,134(9):368-374.
[22]洪迪昆,刘亮,郭欣.温度对聚丙烯酰胺稀溶液黏度影响的分子动力学模拟[J].中国电机工程学报,2015,35(23):6099-6104.Hong D K,Liu L,Guo X.Molecular dynamics simulation of temperature impact on the viscosity of polyacrylamide dilute solution[J].Proceedings of the CSEE,2015,35(23):6099-6104.
[23]Qi X J,Guo X,Zheng C G.Density functional study the interaction of oxygen molecule with defect sites of grapheme[J].Applied Surface Science,2012,259(259):195-200.
[24]Thompson P A,Robbins M O.Shear flow near solids:epitaxial order and flow boundary conditions[J].Physical Review A,1990,41(12):6830-6837.
[25]Berendsen H,Postma J,Gunsteren W,et al.Molecular dynamics with coupling to an external bath[J].Journal of Chemical Physics,1984,81(8):3684-3690.
[26]Cheng X M,Wang Q D,Li J Q,et al.ReaxFF molecular dynamics simulations of oxidation of toluene at high temperatures[J].Journal of Physical Chemistry A,2012,116(40):9811.
[27]Lummen N.ReaxFF-molecular dynamics simulations of nonoxidative and non-catalyzed thermal decomposition of methane at high temperatures[J].Physical Chemistry Chemical Physics,2010,12(28):7883-7893.
[28]Ashraf C,van Duin Adri C T.Extension of the ReaxFFcombustion force field toward syngas combustion and initial oxidation kinetics[J].Journal of Physical Chemistry A,2017,121(5):1051.
[29]Mao Q,van Duin Adri C T,Luo K H.Investigation of methane oxidation by palladium-based catalyst via ReaxFF molecular dynamics simulation[J].Proceedings of the Combustion Institute,2016,36(3):4339-4346.
[30]Roets L,Bunt J R,Neomagus H,et al.The effect of added minerals on the pyrolysis products derived from a vitrinite-rich demineralised South African coal[J].Journal of Analytical&Applied Pyrolysis,2016,121(12):41-49.
[31]Castro-marcano F,van Duin Adri C T,Mathews J P,et al.Pyrolysis of a large-scale molecular model for Illinois no.6 coal using the ReaxFF reactive force field[J].Journal of Analytical&Applied Pyrolysis,2014,109(12):79-89.