枣泉煤分子模型构建及热解的分子模拟
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摘要
以宁东枣泉煤为研究对象,使用工业分析、元素分析、X射线光电子能谱、~(13)C固体核磁等表征手段和计算机辅助,构建获得枣泉煤大分子结构模型。经过分子动力学退火动力学模拟和几何结构全优化,与初始结构相比键长、键角发生明显改变,立体构型显著,芳香层片之间近似平行的排列方式明显。获得的傅里叶变换红外和~(13)C固体核磁的实验与计算谱图总体吻合较好,进一步证明了构建模型的合理性。使用反应分子动力学方法模拟枣泉煤的热解过程,考察不同热解终温和升温速率对热解行为的影响。结果发现,随着温度的升高,反应速率逐渐加快。不同升温速率对枣泉煤热解过程中气体的产生有显著影响。在动力学模拟中大多产生C_(15)以下的碎片,大分子的种类则并不多。随着升温速率的增加,气、液、固三相产物整体上都呈现下降的趋势。此外,还根据反应分子动力学模拟结果追踪了热解过程中CO_2的形成机理,获得了三种不同的CO_2形成路径。
This work studied the macromolecular structure model of Zaoquan coal from Ningdong, China by means of various characterizations such as industrial analysis, elemental analysis, X-ray photoelectron spectroscopy and ~(13)C nuclear magnetic resonance(NMR), combined with computer-aided techniques. After annealing dynamics simulation and fully geometric structural optimizations, the bond length, bond angle and the spatial configuration of coal molecular structure were changed significantly compared with the initial one. Also the arrangement mode of the aromatic layers became nearly parallel. The calculated spectra of Fourier transform infrared and ~(13)C NMR agreed well with those in experiments, which further confirmed the obtained coal molecular model. Based on the molecular model, the effects of final temperature and heating rate upon chemical behavior of coal pyrolysis were studied by using the reactive force field molecular dynamics simulations. It was shown that the reaction rate was gradually increased as temperature increased. The heating rate was rather significant for gas generation during coal pyrolysis.In simulations, most of the fragments produced were below C_(15), while the species of macromolecules were the minority. As heating rate increased, the gas, liquid and solids products were all decreased. In addition, according to the results of reaction molecular dynamics simulation, the formation mechanism of CO_2 in the pyrolysis process was traced, and three different CO_2 formation paths were obtained.
This work studied the macromolecular structure model of Zaoquan coal from Ningdong, China by means of various characterizations such as industrial analysis, elemental analysis, X-ray photoelectron spectroscopy and ~(13)C nuclear magnetic resonance(NMR), combined with computer-aided techniques. After annealing dynamics simulation and fully geometric structural optimizations, the bond length, bond angle and the spatial configuration of coal molecular structure were changed significantly compared with the initial one. Also the arrangement mode of the aromatic layers became nearly parallel. The calculated spectra of Fourier transform infrared and ~(13)C NMR agreed well with those in experiments, which further confirmed the obtained coal molecular model. Based on the molecular model, the effects of final temperature and heating rate upon chemical behavior of coal pyrolysis were studied by using the reactive force field molecular dynamics simulations. It was shown that the reaction rate was gradually increased as temperature increased. The heating rate was rather significant for gas generation during coal pyrolysis.In simulations, most of the fragments produced were below C_(15), while the species of macromolecules were the minority. As heating rate increased, the gas, liquid and solids products were all decreased. In addition, according to the results of reaction molecular dynamics simulation, the formation mechanism of CO_2 in the pyrolysis process was traced, and three different CO_2 formation paths were obtained.
引文
[1] Lei Z, Yang D, Zhang Y H, et al. Constructions of coal and char molecular models based on the molecular simulation technology[J]. Journal of Fuel Chemistry&Technology, 2017, 45(7):769-779.
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[7]相建华,曾凡桂,李彬,等.成庄无烟煤大分子结构模型及其分子模拟[J].燃料化学学报, 2013, 41(4):391-399.Xiang J H, Zeng F G, Li B, et al Construction of macromolecular structural model of anthracite from Chengzhuang coal mine and its molecular simulation[J]. Journal of Chemistry and Technology,2013, 41(4):391-399.
[8] Behar F, Hatcher P G. Artificial coalification of a fossil wood from brown coal by confined system pyrolysis[J]. Fuel&Energy Abstracts, 1996, 37(3):984-994.
[9] Salmon E, van Duin Act, Lorant F, et al. Early maturation processes in coal(2):Reactive dynamics simulations using the ReaxFF reactive force field on Morwell Brown coal structures[J].Organic Geochemistry, 2009, 40(12):1195-1209.
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[11] Mushtaq F, Mat R, Ani F N. A review on microwave assisted pyrolysis of coal and biomass for fuel production[J]. Renewable&Sustainable Energy Reviews, 2014, 39(6):555-574.
[12] Abdelsayed V, Shekhawat D, Smith M W, et al. Microwaveassisted pyrolysis of Mississippi coal:a comparative study with conventional pyrolysis[J]. Fuel, 2018, 217:656-667.
[13] Gao S, Zhai L, Qin Y, et al. Investigation into the cleavage of chemical bonds induced by CO2and its mechanism during the pressurized pyrolysis of coal[J]. Energy&Fuels, 2018, 32(3):3243-3253.
[14]陈兆辉,高士秋,许光文.煤热解过程分析与工艺调控方法[J].化工学报, 2017, 68(10):3693-3707.Chen Z H, Gao S Q, Xu G W. Analysis and control methods of coal pyrolysis process[J]. CIESC Journal, 2017, 68(10):3693-3707.
[15] van Duin Act, Dasgupta S, Lorant F, et al. ReaxFF:a reactive force field for hydrocarbons[J]. Journal of Physical Chemistry A,2001, 105(41):9396-9409.
[16] Salmon E, van Duin Act, Lorant F, et al. Thermal decomposition process in algaenan of Botryococcus braunii race L.(2):Molecular dynamics simulations using the ReaxFF reactive force field[J].Organic Geochemistry, 2009, 40(3):416-427.
[17] Wang H, Feng Y, Zhang X, et al. Study of coal hydropyrolysis and desulfurization by ReaxFF molecular dynamics simulation[J].Fuel, 2015, 145:241-248.
[18] Wang J P, Li G Y, Guo R, et al. Theoretical and experimental insight into coal structure:establishing a chemical model for Yuzhou lignite[J]. Energy&Fuels, 2016, 31(1):124-132.
[19] Zhan J H, Wu R, Liu X, et al. Preliminary understanding of initial reaction process for subbituminous coal pyrolysis with molecular dynamics simulation[J]. Fuel, 2014, 134(9):283-292.
[20] Hong D, Guo X. Molecular dynamics simulations of Zhundong coal pyrolysis using reactive force field[J]. Fuel, 2017, 210:58-66.
[21] Li W, Zhu Y, Chen S, et al. Research on the structural characteristics of vitrinite in different coal ranks[J]. Fuel, 2013,107(9):647-652.
[22]朱学栋,朱子彬,韩崇家,等.煤中含氧官能团的红外光谱定量分析[J].燃料化学学报, 1999,(4):335-339.Zhu X D, Zhu Z B, Han C J, et al. Quantitative determination of oxygen containing functional groups in coal by FTIR spectroscopy[J]. Journal of Fuel Chemistry and Technology, 1999,(4):335-339.
[23] Hayashi J, Takahashi H, Doi S, et al. Reactions in brown coal pyrolysis responsible for heating rate effect on tar yield[J]. Energy&Fuels, 2000, 14(2):400-408.
[24] Yan G C, Zhang Z Q, Yan K F. Reactive molecular dynamics simulations of the initial stage of brown coal oxidation at high temperatures[J]. Molecular Physics, 2012, 111(1):147-156.
[25] Chen B, Diao Z J, Zhao Y L, et al. A ReaxFF molecular dynamics(MD)simulation for the hydrogenation reaction with coal related model compounds[J]. Fuel, 2015, 154(5):114-122.
[26] 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.
[27] Zhou Z, Guo L, Chen L, et al. Study of pyrolysis of brown coal and gasification of coal-water slurry using the ReaxFF reactive force field[J]. International Journal of Energy Research, 2018, 42(7):2465-2480.
[28]刘振宇.煤化学的前沿与挑战:结构与反应[J].中国科学:化学, 2014, 44(9):1431-1438.Liu Z Y. Advancement in coal chemistry:structure and reactivity[J]. Scientia Sinica Chimica, 2014, 44(9):1431-1438.
[29]张小盟,李宁煜,高文青.宁夏煤炭利用效率的影响因素分析[J].煤炭加工与综合利用, 2017,(3):59-65.Zhang X M, Li N Y, Gao W Q. Analysis on the factors affecting the utilization efficiency of coal in Ningxia[J]. Coal Processing and Comprehensive Utilization, 2017,(3):59-65.
[30]李壮楣,王艳美,李平,等.宁东红石湾煤大分子模型构建及量子化学计算[J].化工学报, 2018, 69(5):2208-2216.Li Z M, Wang Y M, Li P, et al. Macromolecular model construction and quantum chemical calculation of Ningdong Hongshiwan coal[J]. CIESC Journal, 2018, 69(5):2208-2216.
[31] Zhao Y, Truhlar D G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics,noncovalent interactions, excited states, and transition elements:two new functionals and systematic testing of four M06-class functionals and 12 other functionals[J]. Theor. Chem. Acc., 2008,120:215-241.
[32] Weismiller M R, van Duin Act, Lee J, et al. ReaxFF reactive force field development and applications for molecular dynamics simulations of ammonia borane dehydrogenation and combustion[J]. Journal of Physical Chemistry A, 2010, 114:5485-5492.
[33] 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.
[34]张莉.五牧场11号煤结构模型构建及其超分子特征[D].太原:太原理工大学, 2013.Zhang L. Molecular structure model building and supermolecule characteristic of Wumuchang No. 11 coal[D]. Taiyuan:Taiyuan University of Technology, 2013.
[35]马伦,陆大荣,梁汉东,等.神华长焰煤大分子结构特征的研究[J].燃料化学学报, 2013, 41(5):513-522.Ma L, Lu D R, Liang H D, et al. Preliminary study on macromolecular structure characteristics of Shenhua long flame coal[J]. Journal of Fuel Chemistry&Technology, 2013, 41(5):513-522.
[36] 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.
[37] Li W, Zhu Y M, Wang G, et al. Molecular model and ReaxFF molecular dynamics simulation of coal vitrinite pyrolysis[J].Journal of Molecular Modeling, 2015, 21(8):188-200.
[2] Xie K C. Structure and Reactivity of Coal[M]. New York:Springer-Verlag Press, 2015:1-27.
[3] Mathews J P, Chaffee A L. The molecular representations of coal—a review[J]. Fuel, 2012, 96(7):1-14.
[4] Carlson G A. Computer simulation of the molecular structure of bituminous coal[J]. Energy&Fuels, 1992, 6(6):771-778.
[5] Zhang Z, Kang Q, Wei S, et al. Large scale molecular model construction of Xishan bituminous coal[J]. Energy&Fuels, 2017,31:1310-1317.
[6] Mathews J P, Sharma A. The structural alignment of coal and the analogous case of Argonne Upper Freeport coal[J]. Fuel, 2012, 95(1):19-24.
[7]相建华,曾凡桂,李彬,等.成庄无烟煤大分子结构模型及其分子模拟[J].燃料化学学报, 2013, 41(4):391-399.Xiang J H, Zeng F G, Li B, et al Construction of macromolecular structural model of anthracite from Chengzhuang coal mine and its molecular simulation[J]. Journal of Chemistry and Technology,2013, 41(4):391-399.
[8] Behar F, Hatcher P G. Artificial coalification of a fossil wood from brown coal by confined system pyrolysis[J]. Fuel&Energy Abstracts, 1996, 37(3):984-994.
[9] Salmon E, van Duin Act, Lorant F, et al. Early maturation processes in coal(2):Reactive dynamics simulations using the ReaxFF reactive force field on Morwell Brown coal structures[J].Organic Geochemistry, 2009, 40(12):1195-1209.
[10] Heek K H V, Hodek W. Structure and pyrolysis behaviour of different coals and relevant model substances[J]. Fuel, 1994, 73(6):886-896.
[11] Mushtaq F, Mat R, Ani F N. A review on microwave assisted pyrolysis of coal and biomass for fuel production[J]. Renewable&Sustainable Energy Reviews, 2014, 39(6):555-574.
[12] Abdelsayed V, Shekhawat D, Smith M W, et al. Microwaveassisted pyrolysis of Mississippi coal:a comparative study with conventional pyrolysis[J]. Fuel, 2018, 217:656-667.
[13] Gao S, Zhai L, Qin Y, et al. Investigation into the cleavage of chemical bonds induced by CO2and its mechanism during the pressurized pyrolysis of coal[J]. Energy&Fuels, 2018, 32(3):3243-3253.
[14]陈兆辉,高士秋,许光文.煤热解过程分析与工艺调控方法[J].化工学报, 2017, 68(10):3693-3707.Chen Z H, Gao S Q, Xu G W. Analysis and control methods of coal pyrolysis process[J]. CIESC Journal, 2017, 68(10):3693-3707.
[15] van Duin Act, Dasgupta S, Lorant F, et al. ReaxFF:a reactive force field for hydrocarbons[J]. Journal of Physical Chemistry A,2001, 105(41):9396-9409.
[16] Salmon E, van Duin Act, Lorant F, et al. Thermal decomposition process in algaenan of Botryococcus braunii race L.(2):Molecular dynamics simulations using the ReaxFF reactive force field[J].Organic Geochemistry, 2009, 40(3):416-427.
[17] Wang H, Feng Y, Zhang X, et al. Study of coal hydropyrolysis and desulfurization by ReaxFF molecular dynamics simulation[J].Fuel, 2015, 145:241-248.
[18] Wang J P, Li G Y, Guo R, et al. Theoretical and experimental insight into coal structure:establishing a chemical model for Yuzhou lignite[J]. Energy&Fuels, 2016, 31(1):124-132.
[19] Zhan J H, Wu R, Liu X, et al. Preliminary understanding of initial reaction process for subbituminous coal pyrolysis with molecular dynamics simulation[J]. Fuel, 2014, 134(9):283-292.
[20] Hong D, Guo X. Molecular dynamics simulations of Zhundong coal pyrolysis using reactive force field[J]. Fuel, 2017, 210:58-66.
[21] Li W, Zhu Y, Chen S, et al. Research on the structural characteristics of vitrinite in different coal ranks[J]. Fuel, 2013,107(9):647-652.
[22]朱学栋,朱子彬,韩崇家,等.煤中含氧官能团的红外光谱定量分析[J].燃料化学学报, 1999,(4):335-339.Zhu X D, Zhu Z B, Han C J, et al. Quantitative determination of oxygen containing functional groups in coal by FTIR spectroscopy[J]. Journal of Fuel Chemistry and Technology, 1999,(4):335-339.
[23] Hayashi J, Takahashi H, Doi S, et al. Reactions in brown coal pyrolysis responsible for heating rate effect on tar yield[J]. Energy&Fuels, 2000, 14(2):400-408.
[24] Yan G C, Zhang Z Q, Yan K F. Reactive molecular dynamics simulations of the initial stage of brown coal oxidation at high temperatures[J]. Molecular Physics, 2012, 111(1):147-156.
[25] Chen B, Diao Z J, Zhao Y L, et al. A ReaxFF molecular dynamics(MD)simulation for the hydrogenation reaction with coal related model compounds[J]. Fuel, 2015, 154(5):114-122.
[26] 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.
[27] Zhou Z, Guo L, Chen L, et al. Study of pyrolysis of brown coal and gasification of coal-water slurry using the ReaxFF reactive force field[J]. International Journal of Energy Research, 2018, 42(7):2465-2480.
[28]刘振宇.煤化学的前沿与挑战:结构与反应[J].中国科学:化学, 2014, 44(9):1431-1438.Liu Z Y. Advancement in coal chemistry:structure and reactivity[J]. Scientia Sinica Chimica, 2014, 44(9):1431-1438.
[29]张小盟,李宁煜,高文青.宁夏煤炭利用效率的影响因素分析[J].煤炭加工与综合利用, 2017,(3):59-65.Zhang X M, Li N Y, Gao W Q. Analysis on the factors affecting the utilization efficiency of coal in Ningxia[J]. Coal Processing and Comprehensive Utilization, 2017,(3):59-65.
[30]李壮楣,王艳美,李平,等.宁东红石湾煤大分子模型构建及量子化学计算[J].化工学报, 2018, 69(5):2208-2216.Li Z M, Wang Y M, Li P, et al. Macromolecular model construction and quantum chemical calculation of Ningdong Hongshiwan coal[J]. CIESC Journal, 2018, 69(5):2208-2216.
[31] Zhao Y, Truhlar D G. The M06 suite of density functionals for main group thermochemistry, thermochemical kinetics,noncovalent interactions, excited states, and transition elements:two new functionals and systematic testing of four M06-class functionals and 12 other functionals[J]. Theor. Chem. Acc., 2008,120:215-241.
[32] Weismiller M R, van Duin Act, Lee J, et al. ReaxFF reactive force field development and applications for molecular dynamics simulations of ammonia borane dehydrogenation and combustion[J]. Journal of Physical Chemistry A, 2010, 114:5485-5492.
[33] 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.
[34]张莉.五牧场11号煤结构模型构建及其超分子特征[D].太原:太原理工大学, 2013.Zhang L. Molecular structure model building and supermolecule characteristic of Wumuchang No. 11 coal[D]. Taiyuan:Taiyuan University of Technology, 2013.
[35]马伦,陆大荣,梁汉东,等.神华长焰煤大分子结构特征的研究[J].燃料化学学报, 2013, 41(5):513-522.Ma L, Lu D R, Liang H D, et al. Preliminary study on macromolecular structure characteristics of Shenhua long flame coal[J]. Journal of Fuel Chemistry&Technology, 2013, 41(5):513-522.
[36] 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.
[37] Li W, Zhu Y M, Wang G, et al. Molecular model and ReaxFF molecular dynamics simulation of coal vitrinite pyrolysis[J].Journal of Molecular Modeling, 2015, 21(8):188-200.