Catalytic effect of calcium on reaction of phenol using reactive molecular dynamics simulation
【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) is studied using ReaxFF molecular dynamics simulations. The results show that calcium promotes the reaction rate of phenol, and promotes the conversion of phenol to gaseous, heavy tar and coke products. At low temperatures, very little amount of gas-Ca is observed. Ca is mainly involved in a repeated bond-breaking and bond-forming process between tar and coke. Ca species only promotes the polymerization of phenol at the low temperatures. While at high temperatures, a large amount of Ca is released in the form of gas-Ca, promoting the cracking of phenol. Ca promotes the production of H2, but has little effect on the production of CO. The activation energy for the polymerization and cracking of phenol are determined to be 52.96 kcal/mol and 16.08 kcal/mol respectively in the absence of Ca, compared to 37.33 kcal/mol and 13.34 kcal/mol respectively 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.
【Keywords】 pyrolysis; phenol; catalytic; ReaxFF; kinetics;
 Guan J, He D M, Zhang Q M. The technology of improving lignite quality through pyrolysis and the concept of poly-generation [J]. Coal Chemical Industry, 2011, 39 (6): 1–4 (in Chinese).
 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 (in Chinese).
 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.
 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 (in Chinese).
 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 (in Chinese).
 Liu 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 (in Chinese).
 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 (in Chinese).
 Lin S Y, Harada M, Suzuki Y, et al. Comparison of pyrolysis products between coal, coal/CaO, and coal/Ca(OH)2 materials [J]. Energy Fuels, 2003, 17 (3): 602–607.
 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.
 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.
 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 (in Chinese).
 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.
 Zhang J, Weng X, Han Y, et al. The effect of supercritical water on coal pyrolysis and hydrogen production: a combined ReaxFF and DFT study [J]. Fuel, 2013, 108 (11): 682–690.
 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.
 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.
 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.
 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.
 Zheng M, Li X, Nie F, et al. Investigation of overall pyrolysis stages for Liulin bituminous coal by large-scale ReaxFF molecular dynamics [J]. Energy & Fuels, 2017, 31 (4): 3675–3683.
 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 (in Chinese).
 Hong D K, Guo X. Molecular dynamics simulations of Zhundong coal pyrolysis using reactive force field [J]. Fuel, 2017, 210 (12): 58–66.
 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.
 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 (in Chinese).
 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.
 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.
 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.
 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.
 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.
 Ashraf C, van Duin Adri C T. Extension of the ReaxFF combustion force field toward syngas combustion and initial oxidation kinetics [J]. Journal of Physical Chemistry A, 2017, 121 (5): 1051.
 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.
 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.
 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.