基于试验和分子动力学模拟的海藻多糖热解机理
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摘要
该文选取海藻内2种主要的多糖分子:条浒苔硫酸多糖和羊栖菜褐藻糖胶,采用Py-GC/MS、TG-MS宏观试验和微观分子动力学模拟的方法研究海藻多糖热解过程及其热解主要产物的形成机理,Py-GC/MS试验表明条浒苔多糖的热解产物以呋喃类物质为主,典型产物为5-甲基-糠醛,而羊栖菜多糖的热解产物以酸酯类物质为主。对海藻多糖模型化合物的热解过程进行分子动力学模拟发现热解过程主要发生在中温阶段,温度升高到420 K时,开始有羟基断裂;温度升高到500 K时,糖苷键开始断裂,环状单体内部化学键相继分解成各种分子碎片,由于其成分差异,热解产物也不尽相同,模拟分析的热解规律与试验结果基本一致。该文还结合TG-MS试验结果推导其热解过程中主要气体产物H2O、CO2、SO2的形成机理。
In order to understand the thermal decomposition mechanism of seaweed polysaccharide and the formation mechanism of main products from the micro perspective, two main seaweed polysaccharides molecules, enteromorpha clathrate sulfated polysaccharides and sargassum fusiforme fucoidan were selected. Through Py-GC/MS and TG-MS experiments, the formation mechanism of products was analyzed. Py-GC/MS results showed that enteromorpha clathrate polysaccharides pyrolysis forms furans mainly, with 5-methyl-furfural as the typical product; while the products of sargassum fusiforme pyrolysis are mainly polysaccharide acid esters. The polymers builder of hyperchem and the semi-empirical method were used to build and optimize the molecular model of sulfated polysaccharides and fusiforme fucoidan. Then the characteristic parameters of molecules were obtained. Based on amber force field, the pyrolysis processes of the seaweed polysaccharide model compounds were simulated with the molecular dynamic method at 297-1200 K and periodic boundary conditions. The simulation results showed that the pyrolysis of lignin model compound can be divided into three stages: the low temperature stage(below 500 K), the intermediate temperature stage(500-800 K) and the high temperature decompositionstage(above 800 K). It was found that the reaction stage concentrated mainly in the intermediate temperature stage. The simulation results showed that hydroxide radical was produced at about 400 K. And when the temperature was increased to about 500 K, polysaccharides molecular monomers were formed with the break of glucoside bond. At the same time, pyranoid ring was also opened with the formation of various kinds of molecular fragments. The experimental results were basically in agreement with those of pyrolysis simulation. Besides, the formation mechanisms of H2 O, CO_2, and SO_2 during the pyrolysis of seaweed polysaccharides were analyzed combined with TG-MS gas release mass spectrometry. The GC-MS were adopted to analyze the composition of bio-oil which was obtained through fast pyrolysis. By comparing the experimental and simulational value, the influence of those pyrolysis gases content on the distribution of pyrolysis product and the reaction pathways was also analyzed. The results of TG-MS verify that the release of H2 O from seaweed polysaccharide occurs in the temperature range of 250-350 ℃. CO_2 mass spectrometry shows that there are two major precipitation peaks in the pyrolysis process, one at low temperature(200 ℃), and the other at high temperature(800℃). SO_2 mass spectra shows that there are two precipitation peaks in the range of 280-350 and 650-800 ℃. In the process of the seaweed polysaccharide pyrolysis, the maximum precipitation peaks of pyrolysis gases correspond to the DTG peaks under fixed heating rate. The three main light gases(H_2O, CO_2 and SO_2) show a bimodal characteristic. The precipitation of H2 O is mainly caused by the alkyl and carboxyl group fracturation. The main reason of the CO_2 generation is related to the decarboxylation reaction occurs in pyrolysis process. CO_2 precipitation is mainly due to the C-O-C fractured in low temperature range, and the main reason of the CO_2 generation is the biaryl ether decomposition in high temperature range. SO_2 precipitation is mainly due to the reaction of elimination of sulphate in low temperature range, and the main reason of the SO_2 generation is the sulphate decomposition in high temperature range.
In order to understand the thermal decomposition mechanism of seaweed polysaccharide and the formation mechanism of main products from the micro perspective, two main seaweed polysaccharides molecules, enteromorpha clathrate sulfated polysaccharides and sargassum fusiforme fucoidan were selected. Through Py-GC/MS and TG-MS experiments, the formation mechanism of products was analyzed. Py-GC/MS results showed that enteromorpha clathrate polysaccharides pyrolysis forms furans mainly, with 5-methyl-furfural as the typical product; while the products of sargassum fusiforme pyrolysis are mainly polysaccharide acid esters. The polymers builder of hyperchem and the semi-empirical method were used to build and optimize the molecular model of sulfated polysaccharides and fusiforme fucoidan. Then the characteristic parameters of molecules were obtained. Based on amber force field, the pyrolysis processes of the seaweed polysaccharide model compounds were simulated with the molecular dynamic method at 297-1200 K and periodic boundary conditions. The simulation results showed that the pyrolysis of lignin model compound can be divided into three stages: the low temperature stage(below 500 K), the intermediate temperature stage(500-800 K) and the high temperature decompositionstage(above 800 K). It was found that the reaction stage concentrated mainly in the intermediate temperature stage. The simulation results showed that hydroxide radical was produced at about 400 K. And when the temperature was increased to about 500 K, polysaccharides molecular monomers were formed with the break of glucoside bond. At the same time, pyranoid ring was also opened with the formation of various kinds of molecular fragments. The experimental results were basically in agreement with those of pyrolysis simulation. Besides, the formation mechanisms of H2 O, CO_2, and SO_2 during the pyrolysis of seaweed polysaccharides were analyzed combined with TG-MS gas release mass spectrometry. The GC-MS were adopted to analyze the composition of bio-oil which was obtained through fast pyrolysis. By comparing the experimental and simulational value, the influence of those pyrolysis gases content on the distribution of pyrolysis product and the reaction pathways was also analyzed. The results of TG-MS verify that the release of H2 O from seaweed polysaccharide occurs in the temperature range of 250-350 ℃. CO_2 mass spectrometry shows that there are two major precipitation peaks in the pyrolysis process, one at low temperature(200 ℃), and the other at high temperature(800℃). SO_2 mass spectra shows that there are two precipitation peaks in the range of 280-350 and 650-800 ℃. In the process of the seaweed polysaccharide pyrolysis, the maximum precipitation peaks of pyrolysis gases correspond to the DTG peaks under fixed heating rate. The three main light gases(H_2O, CO_2 and SO_2) show a bimodal characteristic. The precipitation of H2 O is mainly caused by the alkyl and carboxyl group fracturation. The main reason of the CO_2 generation is related to the decarboxylation reaction occurs in pyrolysis process. CO_2 precipitation is mainly due to the C-O-C fractured in low temperature range, and the main reason of the CO_2 generation is the biaryl ether decomposition in high temperature range. SO_2 precipitation is mainly due to the reaction of elimination of sulphate in low temperature range, and the main reason of the SO_2 generation is the sulphate decomposition in high temperature range.
引文
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[28]沈海军,史友进.碰撞C20-C20富勒烯分子的聚合与分裂[J].计算机与应用化学,2005,2(2):133-137.Shen Haijun,Shi Youjin.Polymerization and splitting of C20-C20 fullerene molecules in the collision[J].Computer and Applied Chemistry,2005,2(2):133-137.(in Chinese with English abstract)
[29]江德正,刘朝,魏顺安,等.纤维素热解过程的分子动力学模拟[J].工程热物理学,2009,30(12):1986-1990.Jiang Dezheng,Liu Zhao,Wei Shun’an,et al.Molecular dynamics simulation of pyrolysis process of cellulose[J].Journal of Engineering Thermo physics,2009,30(12):1986-1990.(in Chinese with English abstract)
[2]王爽,王宁,于立军,等.海藻的热解特性分析[J].中国电机工程学报,2007,27(14):102-106.Wang Shuang,Wang Ning,Yu Lijun,et al.Analysis on pyrolysis characteristics of seaweed[J].Proceedings of the CSEE,2007,27(14):102-106.(in Chinese with English abstract)
[3]郭晓兰,王君,陈明功,等.海藻热解特性及动力学分析[J].生物质化学工程,2007,41(3):1-5.Guo Xiaolan,Wang Jun,Chen Minggong,et al.Pyrolysis characteristics and kinetic analysis of marine algae[J].Biomass Chemical Engineering,2007,41(3):1-5.(in Chinese with English abstract)
[4]Wang S,Wang Q,Hu Y M,et al.Study on the synergistic co-pyrolysis behaviors of mixed rice husk and two types of seaweed by a combined TG-FTIR technique[J].Journal of Analytical and Applied Pyrolysis,2015,114(1):109-118.
[5]Saber M,Nakhshiniev B,Yoshikawa K.A review of production and upgrading of algal bio-oil[J].Renewable and Sustainable Energy Reviews,2016,58:918-930.
[6]Yusuf R,Halvorsen B,Melaaen M C.An experimental and computational study of wall to bed heat transfer in a bubbling gas-solid fluidized bed[J].International Journal of Multiphase Flow,2012,42:9-23.
[7]Smith A M,Ross A B.Production of bio-coal,bio-methane and fertilizer from seaweed via hydrothermal carbonisation[J].Algal Research,2016,16:1-11.
[8]Zhang L,Liu R,Yin R,et al.Upgrading of bio-oil from biomass fast pyrolysis in China:A review[J].Renewable and Sustainable Energy Reviews,2013,24:66-72.
[9]da Cunha M E,Schneider J K,Brasil M C,et al.Analysis of fractions and bio-oil of sugar cane straw by one-dimensional and two-dimensional gas chromatography with quadrupole mass spectrometry(GC×GC/qM S)[J].Microchemical Journal,2013,110:113-119.
[10]Liu Y,Li Z,Wang J,et al.Thermal degradation and pyrolysis behavior of aluminum alginate investigated by TG-FTIR-MSand Py-GC-MS[J].Polymer Degradation and Stability,2015,118:59-68.
[11]纪明侯.海藻化学[M].北京:科学出版社,1997:280-373.
[12]Wang S,Jiang X M,Wang Q,et al.Experiment and grey relational analysis of seaweed particle combustion in a fluidized bed[J].Energy Conversion and Management,2013,66:115-120.
[13]Cao L,Yuan X,Jiang L,et al.Thermogravimetric characteristics and kinetics analysis of oil cake and torrefied biomass blends[J].Fuel,2016,175(1):129-136.
[14]蒋定文,沈先荣,贾福星,等.羊栖菜多糖的提取及纯化[J].食品科学,2007,28(12):136-138.Jiang Dingwen,Shen Xianrong,Jia Fuxing,et al.Extraction and purification of polysaccharides from sargassum fusiforme[J].Food Science,2007,28(12):136-138.(in Chinese with English abstract)
[15]徐大伦,黄晓春,欧昌荣,等.浒苔水溶性多糖提取的工艺研究[J].浙江海洋学院学报:自然科学版,2005,24(1):67-69.Xu Dalun,Huang Xiaochun,Ou Changrong.The enteromorpha water soluble polysaccharide extraction process[J].Journal of Zhejiang Ocean University:Natural Science Edition,2005,24(1):67-69.(in Chinese with English abstract)
[16]齐晓辉,李红燕,郭守东,等.4种不同来源浒苔中多糖的提取分离及理化性质[J].中国海洋大学学报:自然科学版,2010(5):15-18.Qi Xiaohui,Li Hongyan,Guo Shoudong,et al.Four different sources in Enteromorpha prolifera polysaccharide extraction and separation of physicochemical properties[J].China Ocean University Journal:Natural Science Edition,2010(5):15-18.(in Chinese with English abstract)
[17]Xu J,Jiang J,Dai W,et al.Liquefaction of sawdust in hot compressed ethanol for the production of bio-oils[J].Process Safety and Environmental Protection,2012,90(4):333-338.
[18]Moraes M S A,Georges F,Almeida S R,et al.Analysis of products from pyrolysis of Brazilian sugar cane straw[J].Fuel Processing Technology,2012,101:35-43.
[19]王爽.海藻生物质热解与燃烧的试验与机理研究[D].上海:上海交通大学,2010.Wang Shuang.Experimental and Mechanism Study on Pyrolysis and Combustion of Seaweed Biomass[D].Shanghai:Shanghai Jiao Tong University,2010.(in Chinese with English abstract)
[20]Shafizaden F,Lai Y Z.Thermal degradation of 1,6-anhydrobeta-D-glucopyranose[J].The Journal of Organic Chemistry,1972,37(2):278-284.
[21]Dayton D C,Jenkins B M,Tum S Q,et al.Release of inorganic constituents from leached biomass during thermal conversion[J].Energy&Fuels,1999,13(4):860-870.
[22]Murillo J D,Ware E A,Biernacki J J.Characterization of milling effects on the physical and chemical nature of herbaceous biomass with comparison of fast pyrolysis product distributions using Py-GC/MS[J].Journal of Analytical and Applied Pyrolysis,2014,108:234-247.
[23]黄金保,童红,李伟民,等.基于分子动力学模拟的半纤维素热解机理研究[J].热力发电,2013,42(3):25-30.Huang Jinbao,Tong Hong,Li Weimin,et al.Study on the pyrolysis mechanism of semi cellulose based on molecular dynamics simulation[J].Thermal Power Generation,2013,42(3):25-30.(in Chinese with English abstract)
[24]Greaves A J,Churchley J H,Hutchings M G,et al.Achemometric approach to understanding the bioelimination of anionic,water-soluble dyes by a biomass using empirical and semi-empirical molecular descriptors[J].Water Research,2001,35(5):1225-1239.
[25]郭秀娟.生物质选择性热裂解机理研究[D].杭州:浙江大学,2011.Guo Xiujuan.Study on the Mechanism of Selective Pyrolysis of Biomass[D].Hangzhou:Zhejiang University,2011.(in Chinese with English abstract)
[26]Brebu M,Ucar S,Vasile C,et al.Co-pyrolysis of pine cone with synthetic polymers[J].Fuel,2010,89(8):1911-1918.
[27]黄金保,童红,李伟民,等.木质素热解机理的分子动力学模拟研究[J].材料导报,2012,26(20):138-142.Huang Jinbao,Tong Hong,Li Weimin,et al.Lignin pyrolysis mechanism of molecular dynamics simulation material[J].Herald,2012,26(20):138-142.(in Chinese with English abstract)
[28]沈海军,史友进.碰撞C20-C20富勒烯分子的聚合与分裂[J].计算机与应用化学,2005,2(2):133-137.Shen Haijun,Shi Youjin.Polymerization and splitting of C20-C20 fullerene molecules in the collision[J].Computer and Applied Chemistry,2005,2(2):133-137.(in Chinese with English abstract)
[29]江德正,刘朝,魏顺安,等.纤维素热解过程的分子动力学模拟[J].工程热物理学,2009,30(12):1986-1990.Jiang Dezheng,Liu Zhao,Wei Shun’an,et al.Molecular dynamics simulation of pyrolysis process of cellulose[J].Journal of Engineering Thermo physics,2009,30(12):1986-1990.(in Chinese with English abstract)