利用反应分子动力学ReaxFF方法模拟了聚乙烯热解碳沉积二氧化硅基底的微观过程,通过分析沉积过程中碳结构、体系产物数目及碳碳径向分布函数的变化来揭示聚乙烯碳化机理。结果表明:碳结构的形成主要是远离基底芳香环的沉积成片生长和靠近基底的小分子碳的渗入、析出,连接在沉积的碳结构上。其中远离基底的聚乙烯热解有两个方向,一是直接热解为小分子的碳氢化合物(C2H4、C3H6、C4H8等),继而小分子碳氢化合物继续反应脱氢,重组形成碳链和碳环;二是未完全断链的碳氢长链(C>5),与碳氢小分子进行反应。研究温度和保温时间对沉积的影响得知,升温可以加快反应速率,但不改变整体的反应趋势。温度为2500K,在保证碳源充足的情况下,会有更多的碳形成稳定的碳环结构,持续生长。从ReaxFF动力学角度研究高分子聚合物制备碳材料的机理,可以为相关实验研究提供理论支持。
The reaction molecular dynamics simulation ReaxFF method was used to simulate the micro-process of polyethylene pyrolysis carbon deposition on silicon dioxide substrate.The polyethylene carbonization mechanism was revealed by analyzing the changes of carbon structure,system product number,and carbon-carbon radial distribution function during the deposition process.The results showed that the formation of carbon structure was mainly the deposition of sheet growth away from the substrate aromatic ring and the infiltration and precipitation of small molecular carbon near the substrate,which were linked to the deposited carbon structure.The pyrolysis of polyethylene had two directions.One was the direct pyrolysis of polyethylene into small molecular hydrocarbons (C2H4,C3H6,C4H8,etc.),and then the small molecular hydrocarbons continued to react with dehydrogenation and recombine the carbon chain.The second was the incompletely broken long hydrocarbon chain (C>5),which reacted with small hydrocarbon molecules,dehydrogenation,recombination and cyclization.The influence of temperature and holding time on the deposition was studied.The results showed that raising the temperature could accelerate the reaction rate,but did not change the overall reaction trend.When the temperature was 2500 K and the carbon source was sufficient,more carbon formed a stable carbon ring structure and continued to grow.In this paper,the mechanism of pyrolysis of polymer to prepare carbon materials was studied from the perspective of ReaxFF kinetics,which could provide theoretical support for related experimental studies.
[1] Qureshi M S,Oasmaa A,Pihkola H,et al.Pyrolysis of plastic waste:opportunities and challenges[J].Journal of Analytical and Applied Pyrolysis,2020,152:104804.
[2] 顾菁,程磊磊,王亚琢,等.聚乙烯高压热解及其反应机理研究[J].燃料化学学报,2021,49(3):395-406.
[3] 贺兴处,陈德珍,梅振飞,等.CaO催化PE热解及H2O对催化过程影响的ReaxFF MD研究与机理分析[J].化工学报,2021,72(9):4665-4674.
[4] Gaca P,Drzewiecka M,Kaleta W,et al.Catalytic degradation of polyethylene over mesoporous molecular sieve MCM-41 modified with heteropoly compounds[J].Polish Journal of Environmental Studies,2008,17(1):25-31.
[5] Lopez G,Artetxe M,Amutio M,et al.Thermochemical routes for the valorization of waste polyolefinic plastics to produce fuels and chemicals:a review[J].Renewable and Sustainable Energy Reviews,2017,73:346-368.
[6] Kumar S,Panda A K,Singh R K.A review on tertiary recycling of high-density polyethylene to fuel[J].Resources,Conservation and Recycling,2011,55(11):893-910.
[7] Jha K K,Kannan T T M,Senthilvelan N.Optimization of catalytic pyrolysis process for change of plastic waste into fuel[J].Materials Today:Proceedings,2021,39:708-711.
[8] Al-Salem S M,Antelava A,Constantinou A,et al.A review on thermal and catalytic pyrolysis of plastic solid waste (PSW)[J].Journal of Environmental Management,2017,197:177-198.
[9] Marcilla A,Beltrán M I,Navarro R.Thermal and catalytic pyrolysis of polyethylene over HZSM5 and HUSY zeolites in a batch reactor under dynamic conditions[J].Applied Catalysis B:Environmental,2009,86(1):78-86.
[10] Onwudili J A,Insura N,Williams P T.Composition of products from the pyrolysis of polyethylene and polystyrene in a closed batch reactor:effects of temperature and residence time[J].Journal of Analytical and Applied Pyrolysis,2009,86(2):293-303.
[11] Takuma K,Uemichi Y,Ayame A.Product distribution from catalytic degradation of polyethylene over H-gallosilicate[J].Applied Catalysis A:General,2000,192(2):273-280.
[12] Williams P T,Williams E A.Fluidised bed pyrolysis of low density polyethylene to produce petrochemical feedstock[J].Journal of Analytical and Applied Pyrolysis,1999,51(1):107-126.
[13] Artetxe M,Lopez G,Amutio M,et al.Light olefins from HDPE cracking in a two-step thermal and catalytic process[J].Chemical Engineering Journal,2012,207-208:27-34.
[14] Artetxe M,Lopez G,Elordi G,et al.Production of light olefins from polyethylene in a two-step process:pyrolysis in a conical spouted bed and downstream high-temperature thermal cracking[J].Industrial & Engineering Chemistry Research,2012,51(43):13915-13923.
[15] Mastral F J,Esperanza E,Garcí A P,et al.Pyrolysis of high-density polyethylene in a fluidised bed reactor.influence of the temperature and residence time[J].Journal of Analytical and Applied Pyrolysis,2002,63(1):1-15.
[16] Wang Y,Li Y,Zhang C,et al.A study on co-pyrolysis mechanisms of biomass and polyethylene via ReaxFF molecular dynamic simulation and density functional theory[J].Process Safety and Environmental Protection,2021,150:22-35.
[17] Chen S,Liu Z,Jiang S,et al.Carbonization:a feasible route for reutilization of plastic wastes[J].Science of The Total Environment,2020,710:136250.
[18] Gong J,Chen X,Tang T.Recent progress in controlled carbonization of (waste) polymers[J].Progress in Polymer Science,2019,94:1-32.
[19] Kwiecińska B K,Pusz S.Pyrolytic carbon-definition,classification and occurrence[J].International Journal of Coal Geology,2016,163:1-7.
[20] Delhaes P.Chemical vapor deposition and infiltration processes of carbon materials[J].Carbon,2002,40(5):641-657.
[21] Gao X,Wang Y,Zhang Z,et al.Conductive nano-carbon coating on silica by pyrolysis of polyethylene[J].Materials Letters,2019,255:126567.
[22] Van Duin A C T,Dasgupta S,Lorant F,et al.ReaxFF:a reactive force field for hydrocarbons[J].The Journal of Physical Chemistry A,2001,105(41):9396-9409.
[23] Chenoweth K,Van Duin A C T,Goddard W A.ReaxFF reactive force field for molecular dynamics simulations of hydrocarbon oxidation[J].The Journal of Physical Chemistry A,2008,112(5):1040-1053.
[24] Zou C,Raman S,Van Duin A C T.Large-scale reactive molecular dynamics simulation and kinetic modeling of high-temperature pyrolysis of the gloeocapsomorphaprisca microfossils[J].The Journal of Physical Chemistry B,2014,118(23):6302-6315.
[25] Zhang W,Van Duin A C T.Atomistic-scale simulations of the graphene growth on a silicon carbide substrate using thermal decomposition and chemical vapor deposition[J].Chemistry of Materials,2020,32(19):8306-8317.
[26] Neyts E C,Ostrikov K,Han Z J,et al.Defect healing and enhanced nucleation of carbon nanotubes by low-energy ion bombardment[J].Physical Review Letters,2013,110(6):065501.
[27] 彭莉娟,姚倩,王静波,等.RDX及其衍生物高温热解的反应分子动力学模拟[J].物理化学学报,2017,33(4):745-754.
[28] Montgomery-Walsh R,Nimbalkar S,Bunnell J,et al.Molecular dynamics simulation of evolution of nanostructures and functional groups in glassy carbon under pyrolysis[J].Carbon,2021,184:627-640.
[29] Chen M,Zhu Y,Xia J,et al.Molecular insights into the initial formation of pyrolytic carbon upon carbon fiber surface[J].Carbon,2019,148:307-316.
[30] Saha B,Furmanchuk A O,Dzenis Y,et al.Multi-step mechanism of carbonization in templated polyacrylonitrile derived fibers:ReaxFF model uncovers origins of graphite alignment[J].Carbon,2015,94:694-704.
[31] Liu Q,Liu S,Lv Y,et al.Atomic-scale insight into the pyrolysis of polycarbonate by ReaxFF-based reactive molecular dynamics simulation[J].Fuel,2021,287:119484.
[32] Liu S,Van Duin A C T,Van Duin D M,et al.Atomistic insights into nucleation and formation of hexagonal boron nitride on nickel from first-principles-based reactive molecular dynamics simulations[J].ACS Nano,2017,11(4):3585-3596.
[33] Zhang C,Zhang C,Ma Y,et al.Imaging the C black formation by acetylene pyrolysis with molecular reactive force field simulations[J].Physical Chemistry Chemical Physics,2015,17(17):11469-11480.
[34] Liu X,Li X,Liu J,et al.Study of high density polyethylene (HDPE) pyrolysis with reactive molecular dynamics[J].Polymer Degradation and Stability,2014,104:62-70.
基金资助
国家自然科学基金面上项目(52073012)
PDF
