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Hanping Chen - One of the best experts on this subject based on the ideXlab platform.
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Hemicellulose Pyrolysis Mechanism based on functional group evolutions by two-dimensional perturbation correlation infrared spectroscopy
Fuel, 2020Co-Authors: Haiping Yang, Yingquan Chen, Biao Liu, Jianjun Xiao, Zhiguo Dong, Meng Gong, Hanping ChenAbstract:Abstract To gain an improved understanding of the hemicellulose Pyrolysis Mechanism, two-dimensional correlation infrared spectroscopy (2D-PCIS) was employed to analyze the functional group evolution in xylan chars between 200 and 600 °C, and through combination with the obtained volatiles releasing properties. Simultaneously, the pathway of xylan decomposition was deduced to illustrate the Pyrolysis Mechanism. The depolymerization and ring-opening reactions of xylan started at 200℃. After that, it was mainly xylan matrix degradation reaction to form char structure which mainly consisted of phenyl rings and oxygen-containing cyclic compounds with aliphatic chains. With temperature increasing (300–450 ℃), the decarbonylation reaction, removal of C C and fatty chains reactions were intensified and the molecular structures of xylan char reconstructed to form fused-ring compounds on the order of 1 × 2 and 2 × 2 through condensation. Dehydrogenation and polycondensation reaction of xylan increased at higher temperature (450–600 °C). The char structure was composed of high-order fused-ring compounds, and the production of H2 and CH4 increased greatly.
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Algae pyrolytic poly-generation: Influence of component difference and temperature on products characteristics
Energy, 2017Co-Authors: Wei Chen, Zixu Yang, Mingwei Xia, Xianhua Wang, Haiping Yang, Yingquan Chen, Hanping ChenAbstract:Pyrolytic poly-generation of three algae (Enteromorpha prolifera (EP), Spirulina platensis (SP) and Nannochloropsis sp. (NS)) was carried out in a fixed bed reactor and Pyrolysis Mechanism was explored in detail. Influences of Pyrolysis temperature (400–800 °C) and biochemical components (carbohydrates, proteins and lipids) of algae on pyrolytic behavior and products characteristics were investigated. EP showed higher char yield, while SP and NS showed high bio-oil yields. At lower temperature (400–500 °C), CO2 was the main gas product, while H2, CH4 and CO evolved out quickly with temperature increasing. EP cracking could release more CO, while SP and NS cracking could release more H2, CH4 and C2. While for bio-oil, it was variant with algae composition and temperature, as EP showed higher furans, SP yielded large amounts of N-containing chemicals, while aliphatics and carboxylic acids were the dominated components for NS. However, aromatics gradually became the major compounds for all bio-oil at 700–800 °C. For char, C-O/C-O-C/C=N, C=O/C-N and COO- groups cracking gradually with temperature increasing and resulted in more aromatic C=C. The optimum operating temperature is 500–600 °C for algae pyrolytic poly-generation to achieve higher value of char, bio-oil and gas products together.
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biomass based pyrolytic polygeneration system for bamboo industry waste evolution of the char structure and the Pyrolysis Mechanism
Energy & Fuels, 2016Co-Authors: Haiping Yang, Baojun Huan, Jian Li, Yingquan Chen, Hanping ChenAbstract:Biomass-based pyrolytic polygeneration system can commercialize all products (liquids, gases, and solids) generated during Pyrolysis, while fast Pyrolysis, gasification and carbonization, can only singly commercialize liquids, gases, and solids, respectively. To determine the optimum operational parameters for biomass pyrolytic polygeneration while using bamboo waste as the feedstock, the product characteristics were investigated over a temperature range of 250 to 950 °C. Meanwhile, details of the evolution of the char structure were analyzed to reveal the Pyrolysis Mechanism. Results showed that to increase the yield of char, the operational temperature should be at 350 °C; however, at this temperature, no inner pores were formed and a low quality char product was produced. Thus, the optimum operating temperature recommended for biomass pyrolytic polygeneration of bamboo waste was set to 550 °C. At the optimum temperature, the surface area of the char was 200 m2/g, the calorific value of gas was 14 MJ/m3...
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Biomass-Based Pyrolytic Polygeneration System for Bamboo Industry Waste: Evolution of the Char Structure and the Pyrolysis Mechanism
2016Co-Authors: Haiping Yang, Baojun Huan, Yingquan Chen, Ying Gao, Hanping ChenAbstract:Biomass-based pyrolytic polygeneration system can commercialize all products (liquids, gases, and solids) generated during Pyrolysis, while fast Pyrolysis, gasification and carbonization, can only singly commercialize liquids, gases, and solids, respectively. To determine the optimum operational parameters for biomass pyrolytic polygeneration while using bamboo waste as the feedstock, the product characteristics were investigated over a temperature range of 250 to 950 °C. Meanwhile, details of the evolution of the char structure were analyzed to reveal the Pyrolysis Mechanism. Results showed that to increase the yield of char, the operational temperature should be at 350 °C; however, at this temperature, no inner pores were formed and a low quality char product was produced. Thus, the optimum operating temperature recommended for biomass pyrolytic polygeneration of bamboo waste was set to 550 °C. At the optimum temperature, the surface area of the char was 200 m2/g, the calorific value of gas was 14 MJ/m3, and the concentration of phenols in liquid reached the maximum level. A Pyrolysis Mechanism based on the evolution of the char structure was proposed. First, the ordered organic macrostructure in raw biomass was converted to a network-like structure consisting of a “3D network of benzene rings” during the “initial decomposition stage (550°C)”. The results of this study are expected to be beneficial for the comprehensive utilization of bamboo waste and provide new insight into the Pyrolysis Mechanism
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Pyrolysis Mechanism of βo4 type lignin model dimer
Journal of Analytical and Applied Pyrolysis, 2015Co-Authors: Lei Chen, Xianhua Wang, Feixian Luo, Jingai Shao, Yang Fang, Hanping ChenAbstract:A βO4 type lignin dimer compound was synthesized, namely 1-(4-methoxyphenyl)-2-(2-methoxyphenoxy) ethanol. To elucidate its Pyrolysis Mechanism, analytical Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) experiments were performed to reveal the distribution of the pyrolytic products under different temperatures. Concurrently, density functional theory (DFT) calculations were conducted to analyze and verify the thermal decomposition Mechanisms of the lignin dimer and the product formation pathways. The results show that the lignin dimer will undergo the CβO bond homolysis to produce 4-methoxystyrene and guaiacol at low Pyrolysis temperatures. Whereas at medium Pyrolysis temperatures, besides the CβO homolysis, CβO concerted decomposition will also take place to form carbonyl-containing phenolics. At high Pyrolysis temperatures, the primary pyrolytic products will undergo secondary decomposition reactions to form a complex variety of products. With the combination of the experimental results and theoretical calculations, the Pyrolysis Mechanism of the lignin dimer model compound is clearly interpreted in this study.
Haiping Yang - One of the best experts on this subject based on the ideXlab platform.
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Hemicellulose Pyrolysis Mechanism based on functional group evolutions by two-dimensional perturbation correlation infrared spectroscopy
Fuel, 2020Co-Authors: Haiping Yang, Yingquan Chen, Biao Liu, Jianjun Xiao, Zhiguo Dong, Meng Gong, Hanping ChenAbstract:Abstract To gain an improved understanding of the hemicellulose Pyrolysis Mechanism, two-dimensional correlation infrared spectroscopy (2D-PCIS) was employed to analyze the functional group evolution in xylan chars between 200 and 600 °C, and through combination with the obtained volatiles releasing properties. Simultaneously, the pathway of xylan decomposition was deduced to illustrate the Pyrolysis Mechanism. The depolymerization and ring-opening reactions of xylan started at 200℃. After that, it was mainly xylan matrix degradation reaction to form char structure which mainly consisted of phenyl rings and oxygen-containing cyclic compounds with aliphatic chains. With temperature increasing (300–450 ℃), the decarbonylation reaction, removal of C C and fatty chains reactions were intensified and the molecular structures of xylan char reconstructed to form fused-ring compounds on the order of 1 × 2 and 2 × 2 through condensation. Dehydrogenation and polycondensation reaction of xylan increased at higher temperature (450–600 °C). The char structure was composed of high-order fused-ring compounds, and the production of H2 and CH4 increased greatly.
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lignocellulosic biomass Pyrolysis Mechanism a state of the art review
Progress in Energy and Combustion Science, 2017Co-Authors: Shurong Wang, Haiping YangAbstract:Abstract The past decades have seen increasing interest in developing Pyrolysis pathways to produce biofuels and bio-based chemicals from lignocellulosic biomass. Pyrolysis is a key stage in other thermochemical conversion processes, such as combustion and gasification. Understanding the reaction Mechanisms of biomass Pyrolysis will facilitate the process optimization and reactor design of commercial-scale biorefineries. However, the multiscale complexity of the biomass structures and reactions involved in Pyrolysis make it challenging to elucidate the Mechanism. This article provides a broad review of the state-of-art biomass Pyrolysis research. Considering the complexity of the biomass structure, the Pyrolysis characteristics of its three major individual components (cellulose, hemicellulose and lignin) are discussed in detail. Recently developed experimental technologies, such as Py-GC–MS/FID, TG-MS/TG-FTIR, in situ spectroscopy, 2D-PCIS, isotopic labeling method, in situ EPR and PIMS have been employed for biomass Pyrolysis research, including online monitoring of the evolution of key intermediate products and the qualitative and quantitative measurement of the Pyrolysis products. Based on experimental results, many macroscopic kinetic modeling methods with comprehensive Mechanism schemes, such as the distributed activation energy model (DAEM), isoconversional method, detailed lumped kinetic model, kinetic Monte Carlo model, have been developed to simulate the mass loss behavior during biomass Pyrolysis and to predict the resulting product distribution. Combined with molecular simulations of the elemental reaction routes, an in-depth understanding of the biomass Pyrolysis Mechanism may be obtained. Aiming to further improve the quality of Pyrolysis products, the effects of various catalytic methods and feedstock pretreatment technologies on the Pyrolysis behavior are also reviewed. At last, a brief conclusion for the challenge and perspectives of biomass Pyrolysis is provided.
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Algae pyrolytic poly-generation: Influence of component difference and temperature on products characteristics
Energy, 2017Co-Authors: Wei Chen, Zixu Yang, Mingwei Xia, Xianhua Wang, Haiping Yang, Yingquan Chen, Hanping ChenAbstract:Pyrolytic poly-generation of three algae (Enteromorpha prolifera (EP), Spirulina platensis (SP) and Nannochloropsis sp. (NS)) was carried out in a fixed bed reactor and Pyrolysis Mechanism was explored in detail. Influences of Pyrolysis temperature (400–800 °C) and biochemical components (carbohydrates, proteins and lipids) of algae on pyrolytic behavior and products characteristics were investigated. EP showed higher char yield, while SP and NS showed high bio-oil yields. At lower temperature (400–500 °C), CO2 was the main gas product, while H2, CH4 and CO evolved out quickly with temperature increasing. EP cracking could release more CO, while SP and NS cracking could release more H2, CH4 and C2. While for bio-oil, it was variant with algae composition and temperature, as EP showed higher furans, SP yielded large amounts of N-containing chemicals, while aliphatics and carboxylic acids were the dominated components for NS. However, aromatics gradually became the major compounds for all bio-oil at 700–800 °C. For char, C-O/C-O-C/C=N, C=O/C-N and COO- groups cracking gradually with temperature increasing and resulted in more aromatic C=C. The optimum operating temperature is 500–600 °C for algae pyrolytic poly-generation to achieve higher value of char, bio-oil and gas products together.
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biomass based pyrolytic polygeneration system for bamboo industry waste evolution of the char structure and the Pyrolysis Mechanism
Energy & Fuels, 2016Co-Authors: Haiping Yang, Baojun Huan, Jian Li, Yingquan Chen, Hanping ChenAbstract:Biomass-based pyrolytic polygeneration system can commercialize all products (liquids, gases, and solids) generated during Pyrolysis, while fast Pyrolysis, gasification and carbonization, can only singly commercialize liquids, gases, and solids, respectively. To determine the optimum operational parameters for biomass pyrolytic polygeneration while using bamboo waste as the feedstock, the product characteristics were investigated over a temperature range of 250 to 950 °C. Meanwhile, details of the evolution of the char structure were analyzed to reveal the Pyrolysis Mechanism. Results showed that to increase the yield of char, the operational temperature should be at 350 °C; however, at this temperature, no inner pores were formed and a low quality char product was produced. Thus, the optimum operating temperature recommended for biomass pyrolytic polygeneration of bamboo waste was set to 550 °C. At the optimum temperature, the surface area of the char was 200 m2/g, the calorific value of gas was 14 MJ/m3...
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Biomass-Based Pyrolytic Polygeneration System for Bamboo Industry Waste: Evolution of the Char Structure and the Pyrolysis Mechanism
2016Co-Authors: Haiping Yang, Baojun Huan, Yingquan Chen, Ying Gao, Hanping ChenAbstract:Biomass-based pyrolytic polygeneration system can commercialize all products (liquids, gases, and solids) generated during Pyrolysis, while fast Pyrolysis, gasification and carbonization, can only singly commercialize liquids, gases, and solids, respectively. To determine the optimum operational parameters for biomass pyrolytic polygeneration while using bamboo waste as the feedstock, the product characteristics were investigated over a temperature range of 250 to 950 °C. Meanwhile, details of the evolution of the char structure were analyzed to reveal the Pyrolysis Mechanism. Results showed that to increase the yield of char, the operational temperature should be at 350 °C; however, at this temperature, no inner pores were formed and a low quality char product was produced. Thus, the optimum operating temperature recommended for biomass pyrolytic polygeneration of bamboo waste was set to 550 °C. At the optimum temperature, the surface area of the char was 200 m2/g, the calorific value of gas was 14 MJ/m3, and the concentration of phenols in liquid reached the maximum level. A Pyrolysis Mechanism based on the evolution of the char structure was proposed. First, the ordered organic macrostructure in raw biomass was converted to a network-like structure consisting of a “3D network of benzene rings” during the “initial decomposition stage (550°C)”. The results of this study are expected to be beneficial for the comprehensive utilization of bamboo waste and provide new insight into the Pyrolysis Mechanism
Shurong Wang - One of the best experts on this subject based on the ideXlab platform.
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initial Pyrolysis Mechanism of cellulose revealed by in situ drift analysis and theoretical calculation
Combustion and Flame, 2019Co-Authors: Gongxin Dai, Kaige Wang, Guanyu Wang, Shurong WangAbstract:Abstract Cellulose is one of the major components of biomass. The study on its Pyrolysis process will be beneficial to the in-depth understanding of biomass Pyrolysis Mechanism. In this work, in-situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFT) combined with two-dimensional perturbation correlation infrared spectroscopy (2D-PCIS) was first used to characterize the evolution process of the functional groups in cellulose during Pyrolysis. The results showed that the degradation of carbon skeleton was prior to the dehydration of free hydroxyls after the destruction of hydrogen bond networks during Pyrolysis. The thermal stability of C O in cellulose followed by the order of glycosidic bond O in glucopyranose ring O between glucopyranose ring and hydroxyl. Followingly, micro Pyrolysis experiment was performed to analyze the Pyrolysis products of cellulose at various temperatures. It was found that the rupture of glucopyranose rings to form 2C and 4C products was more difficult than the dissociation of C6 hydroxymethyls, and required higher Pyrolysis temperature. Quantum chemistry calculation was further carried out to study the key reaction pathways including dehydration, cleavage of glycosidic bond, ring opening and fragmentation in the initial stage of cellulose Pyrolysis. The result showed that the concerted cleavage of glycosidic bond to form LG-end short chain was the most favored with the lowest activation energy. The ring opening of the glucose unit in the chain occurred via the cleavage of C1-O. The formed ring opening product was more likely to degrade via the dissociation of C6 hydroxymethyl compared with the breakage of C2–C3 to form 2C and 4C products. Besides, the dehydration of hydroxyls in glucose units required high energy barriers and was difficult to occur.
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Mechanism study on the Pyrolysis of the typical ether linkages in biomass
Fuel, 2019Co-Authors: Gongxin Dai, Yanan Zhu, Yang Pan, Jiuzhong Yang, Guanyu Wang, Prasert Reubroycharoen, Shurong WangAbstract:Abstract The in-depth study of the cleavage behaviors of linkages in biomass is important for the better understanding of biomass Pyrolysis Mechanism. This study aimed to clarify the Pyrolysis Mechanism of the typical ether linkages in biomass including β-1,4-glycosidic bond, α-O-4 bond and methoxyl using cellobiose, benzylphenyl ether and guaiacol as the model compounds. Combining the detection of the key intermediates, especially radicals by SVUV-PIMS and the evaluation of the reaction pathways by density functional theory (DFT) quantum chemical calculations, it was found that the concerted cleavage of β-1,4-glycosidic bond was more kinetically favorable than homolytic cleavage and heterolytic cleavage, and the ring opening of cellobiose via the breakage of C1′-O was likely to occur before the cleavage of glycosidic bond. The α-O-4 bond in benzylphenyl ether was mainly cleaved by Cα-O homolysis, and it was easy for the formed radicals to recombine with each other to yield phenolic dimers. In the initial evolution process of methoxyl in guaiacol, homolytic demethylation was the most important unimolecular reaction, while demethoxylation and radical-induced rearrangement reactions were difficult to occur due to their high energy barriers. In the presence of the formed methyl radicals from homolytic demethylation reaction, these two reactions would occur since their energy barriers were significantly reduced at this condition.
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lignocellulosic biomass Pyrolysis Mechanism a state of the art review
Progress in Energy and Combustion Science, 2017Co-Authors: Shurong Wang, Haiping YangAbstract:Abstract The past decades have seen increasing interest in developing Pyrolysis pathways to produce biofuels and bio-based chemicals from lignocellulosic biomass. Pyrolysis is a key stage in other thermochemical conversion processes, such as combustion and gasification. Understanding the reaction Mechanisms of biomass Pyrolysis will facilitate the process optimization and reactor design of commercial-scale biorefineries. However, the multiscale complexity of the biomass structures and reactions involved in Pyrolysis make it challenging to elucidate the Mechanism. This article provides a broad review of the state-of-art biomass Pyrolysis research. Considering the complexity of the biomass structure, the Pyrolysis characteristics of its three major individual components (cellulose, hemicellulose and lignin) are discussed in detail. Recently developed experimental technologies, such as Py-GC–MS/FID, TG-MS/TG-FTIR, in situ spectroscopy, 2D-PCIS, isotopic labeling method, in situ EPR and PIMS have been employed for biomass Pyrolysis research, including online monitoring of the evolution of key intermediate products and the qualitative and quantitative measurement of the Pyrolysis products. Based on experimental results, many macroscopic kinetic modeling methods with comprehensive Mechanism schemes, such as the distributed activation energy model (DAEM), isoconversional method, detailed lumped kinetic model, kinetic Monte Carlo model, have been developed to simulate the mass loss behavior during biomass Pyrolysis and to predict the resulting product distribution. Combined with molecular simulations of the elemental reaction routes, an in-depth understanding of the biomass Pyrolysis Mechanism may be obtained. Aiming to further improve the quality of Pyrolysis products, the effects of various catalytic methods and feedstock pretreatment technologies on the Pyrolysis behavior are also reviewed. At last, a brief conclusion for the challenge and perspectives of biomass Pyrolysis is provided.
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Mechanism study on the Pyrolysis of a synthetic β o 4 dimer as lignin model compound
Proceedings of the Combustion Institute, 2017Co-Authors: Shurong Wang, Jinsong Zhou, Gongxin Dai, Zhongyang Luo, Zhangjie Shi, Kefa CenAbstract:Abstract In this study, a β-O-4 dimer with abundant oxygen substituents was successfully synthesized, and was used as the model compound for lignin to study the Pyrolysis Mechanism. Py-GC/MS (micro pyrolyzer coupled with gas chromatography/mass spectrometry) was employed to identify the distribution of pyrolytic products under temperatures of 150–850 °C. It was found that the yields of methoxylated monoaromatics underwent tendencies of first increase and then decrease at high temperature. Polyaromatics and benzofuran were only detected at high temperature. Based on experimental analysis, a detailed Pyrolysis kinetic model was developed by combining the density functional theory (DFT) and the transition state theory (TST). The homolysis of C β -O was the most favorable route for the initial depolymerization of dimer rather than the concerted retro-ene fragmentation. For the evolution of intermediate products, the breakage of ether bond and the keto-enol tautomerization of enols were the most favorable routes, while intramolecular cyclization and group dissociation exhibited high energy barriers and low reaction rates. The methoxyl in guaiacol preferred to undergo demethylation leading to the formation of catechol.
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Pyrolysis Mechanism study of minimally damaged hemicellulose polymers isolated from agricultural waste straw samples
Bioresource Technology, 2015Co-Authors: Shurong Wang, Bin Ru, Jinsong ZhouAbstract:Abstract The Pyrolysis Mechanism of hemicellulose has been investigated using two minimally damaged hemicellulose polymers isolated from two agricultural straw samples. The obtained hemicelluloses have been characterized by multiple methods, and the results showed that they were mainly composed of l -arabino-4-O-methyl- d -glucurono- d -xylan. Their O-acetyl groups and high degrees of polymerization and branching were well preserved. Their pyrolyses were subsequently investigated by TG-FTIR and Py-GC/MS. The evolutions of four typical volatile components and the distributions of eight product species were scrutinized. A DG-DAEM kinetic model was applied to quantify the contributions of two major pyrolytic routes for devolatilization during hemicellulose Pyrolysis. A mean activation energy of 150 kJ/mol for the formation of volatiles was derived. The thermal stability of each bond in four typical fragments of hemicellulose was assessed by DFT study, and the deduced decomposition pathways were in agreement with experimental analysis.
Chao Liu - One of the best experts on this subject based on the ideXlab platform.
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comprehensive understanding the chemical structure evolution and crucial intermediate radical in situ observation in enzymatic hydrolysis mild acidolysis lignin Pyrolysis
Journal of Analytical and Applied Pyrolysis, 2019Co-Authors: Ming Lei, Jiajin Liang, Chao LiuAbstract:Abstract The in-depth understanding of free radical involved in lignin Pyrolysis, is the most important technical barrier for Pyrolysis Mechanism research. Herein, we report an in situ project by using EPR high temperature cavity for the observation of generated radical in lignin Pyrolysis, along with the other state-of-the-art techniques such as two-dimensional heteronuclear single-quantum coherence nuclear magnetic resonance (2D HSQC-NMR) and Py-GCMS combined with high temperature oven. The result showed that the originate lignin structure had significant influence on the pyrolytic products and the radical process. Compared with hardwood and non-wood lignin, softwood lignin tented to produce more amount of radical, due to the higher content of guaiacyl type subunits and phenylcoumaran structure. Corresponding with the two mainly pyrolytic reaction stage according the activation energy, the radical reaction of lignin Pyrolysis was divided into three stages: radical inducing stage, the main reacting stage and the quenching stage.
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a reaxff based molecular dynamics study of the Pyrolysis Mechanism of hfo 1336mzz z
International Journal of Refrigeration-revue Internationale Du Froid, 2017Co-Authors: Erguang Huo, Chao Liu, Chaobin DangAbstract:Abstract A series of ReaxFF molecular dynamics simulations are performed to investigate the Pyrolysis Mechanisms of HFO-1336mzz(Z). Five initiation reaction pathways are observed in the process of Pyrolysis. By comparing the activation energy of the reactions, the ground state CF3CH=CHCF3 exciting into the triplet state CF3CH-CHCF3 is the main initial reaction pathway with the activation energy of 238.553 kJ mol−1. HF and C2F2 are the dominant products and other final products including CF4, CHF3 and C2F4 are detected in the process of Pyrolysis as well. The intra-molecular elimination (1, 2-elimination), radical attacking Mechanism and radical combination reaction are three formation Mechanisms of HF. The formation Mechanism of C2F2 is slightly different from HF, including fluorine transfer reaction, radical combination reaction and defluorination. By the kinetic analysis of HFO-1336mzz(Z) Pyrolysis, the pre-exponential factor and activation energy are obtained from ReaxFF simulations.
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Study on the Pyrolysis Mechanism of three guaiacyl-type lignin monomeric model compounds
Journal of Analytical and Applied Pyrolysis, 2016Co-Authors: Chao Liu, Yubin Deng, Hongyan Mou, Jiajin Liang, Ming LeiAbstract:In this work, vanillin, vanillic acid and vanillyl alcohol were selected as guaiacyl-type monomeric model compounds to study the secondary Pyrolysis Mechanism of lignin. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was used to characterize products derived from the Pyrolysis of lignin model compounds. Based on the free-radical theory, it was speculated that the Pyrolysis of lignin model compounds concerned two processes: common degradation and specific degradation. By applying the density functional theory (DFT) method to study the detailed reaction pathways and energy changes, it revealed that the potential energy of the synergy process was lower than that of the radical-induced process during the functional group removal. Thereby CO, CO2, and HCHO were preferentially released along the synergy route. The enthalpy changes and experimental yields of products from the further degradation of guaiacol were basically consistent. Furthermore, the distinction of the potential energy between common degradation and specific degradation of each lignin model compound under various temperatures contributed to the different priority of the two degradation processes, as well as the different yields and species of pyrolytic products.
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density functional theory studies on Pyrolysis Mechanism of β o 4 type lignin dimer model compound
Journal of Analytical and Applied Pyrolysis, 2014Co-Authors: Jinbao Huang, Chao Liu, Hong Tong, Lirong RenAbstract:Abstract Lignin is the main component of biomass with a complex, heterogeneous, three-dimensional polymeric structure of three main monolignols ( p -coumaryl, coniferyl, and sinapyl alcohol). In order to understand the Pyrolysis Mechanism of lignin and identify the chemical pathways for the formations of key products during Pyrolysis, the Pyrolysis processes of β -O-4 type lignin dimer model compound 1 (1-phenyl-2-phenoxy-1,3-propanediol) were theoretically investigated by employing density functional theory (DFT) methods at the B3LYP/6-31G(d,p) level. Based on related experimental and calculation results of bond dissociation energies of β -O-4 type lignin dimer, three possible pyrolytic pathways (the homolytic cleavage of C β O bond, the homolytic cleavage of C α C β bond and the concerted reactions) were proposed, the activation energies of each reaction step were calculated, and the temperature effect on Pyrolysis processes was analyzed. The calculation results indicate that the homolytic cleavage reaction of C β O bond and concerted reaction pathways (3) could be the major reaction channels, and the homolytic cleavage reaction of C α C β bond and concerted reaction pathways (1) and (2) could be the competitive reaction channels in Pyrolysis processes. The concerted reactions would dominate over free-radical homolytic reactions at lower temperatures, while at high temperatures the free-radical reaction (C O homolysis) would dominate over the concerted reactions.
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study of guaiacol Pyrolysis Mechanism based on density function theory
Fuel Processing Technology, 2014Co-Authors: Chao Liu, Yayun Zhang, Xiaolu HuangAbstract:Abstract Five possible pyrolytic pathways of guaiacol were proposed with an emphasis on the reactivity of the methoxy group. Pathway 1 is about the homolysis of O CH 3 . Pathways 2–4 focus on the demethoxylation of guaiacol. Pathway 5 concerns the O CH 3 rearrangement. Standard thermodynamic and kinetic parameters of each reaction pathway were calculated at different temperatures based on density functional theory methods by using Gaussian 03 package at B3LYP/6–31G++(d,p) level. According to the calculation results, the five reaction pathways were ranked as Path 3, Path 1, Path 4, Path 2 and Path 5, in descending order of reactivity. Kinetic analyses results of the three demethoxylation reaction pathways (Path 2, Path 3 and Path 4) indicate that coupling a hydrogen radical to the carbon atom to which the methoxyl group bond can effectively lower the reaction energy barrier that existed in the process of demethoxylation. Pathway 5 demonstrates the possible formation Mechanism of o-quinonemethide which is the key polymerization intermediate during lignin Pyrolysis process.
Heming Xiao - One of the best experts on this subject based on the ideXlab platform.
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A theoretical investigation on the structures, densities, detonation properties and Pyrolysis Mechanism of the nitro derivatives of toluenes.
Journal of Hazardous Materials, 2009Co-Authors: Guixiang Wang, Xuedong Gong, Yan Liu, Heming XiaoAbstract:Abstract The nitro derivatives of toluenes are optimized to obtain their molecular geometries and electronic structures at the DFT-B3LYP/6-31G* level. Detonation properties are evaluated using the modified Kamlet–Jacobs equations based on the calculated densities and heats of formation. It is found that there are good linear relationships between density, detonation velocity, detonation pressure and the number of nitro and methyl groups. Thermal stability and the Pyrolysis Mechanism of the title compounds are investigated by calculating the bond dissociation energies at the unrestricted B3LYP/6-31G* level. The activation energies of H-transfer reaction are smaller than the BDEs of all bonds and this illustrates that the Pyrolysis of the title compounds may be started from the isomerization reaction of H transfer. According to the quantitative standard of energetics and stability as an HEDC (high energy density compound), pentanitrotoluene essentially satisfies this requirement. In addition, we have discussed the effect of the nitro and methyl groups on the static electronic structural parameters and the kinetic parameter.
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theoretical studies on the structures thermodynamic properties detonation properties and Pyrolysis Mechanisms of spiro nitramines
Journal of Physical Chemistry A, 2006Co-Authors: Ling Qiu, Heming Xiao, Xuedong Gong, Weihua ZhuAbstract:Density function theory (DFT) has been employed to study the geometric and electronic structures of a series of spiro nitramines at the B3LYP/6-31G** level. The calculated results agree reasonably with available experimental data. Thermodynamic properties derived from the infrared spectra on the basis of statistical thermodynamic principles are linearly correlated with the number of nitramine groups as well as the temperature. Detonation performances were evaluated by the Kamlet-Jacobs equations based on the calculated densities and heats of formation. It is found that some compounds with the predicted densities of ca. 1.9 g/cm3, detonation velocities over 9 km/s, and detonation pressures of about 39 GPa (some even over 40 GPa) may be novel potential candidates of high energy density materials (HEDMs). Thermal stability and the Pyrolysis Mechanism of the title compounds were investigated by calculating the bond dissociation energies (BDE) at the B3LYP/6-31G** level and the activation energies (Ea) with th...
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computational studies on the infrared vibrational spectra thermodynamic properties detonation properties and Pyrolysis Mechanism of octanitrocubane
Journal of Chemical Physics, 2002Co-Authors: Ji Zhang, Heming XiaoAbstract:The molecular geometries, infrared vibrational spectra, and thermodynamic properties of octanitrocubane (ONC) are calculated using the density functional theory (DFT) method at the B3LYP/6-31G* level. The IR frequency scaling factor 0.9501 suitable for polynitrocubanes is obtained at the B3LYP/6-31G* level, and the calculated IR frequencies of ONC are scaled. The accurate heat of formation 726.47 kJ/mol of ONC in gas phase is obtained via designed isodesmic reaction in which the cubane cage skeleton has been kept. The sublimation enthalpy, density, and heat of formation for ONC crystal are also calculated, and they are 220.63 kJ/mol, 2.189 g/cm3, and 505.84 kJ/mol, respectively. In addition, the estimated detonation velocity and detonation pressure of ONC are 10.26 mm/ms and 520.86 kbar, respectively. Finally, the Pyrolysis Mechanism of ONC is studied using various theoretical methods, i.e., MP2, DFT, and selected MINDO/3 semiempirical MO, based on the unrestricted Hartree–Fock model. The calculated results show that the Pyrolysis initiation reaction of ONC, i.e., rate-controlling step, is to form a diradical by the single C–C bond breaking in the cube. The second C–C bond breaking is easily followed to form a nitrocyclooctatetraene. The calculated activation energy for the Pyrolysis initiation reaction of ONC, obtained from B3LYP/6-31G* method, is 155.30 kJ/mol, which this rather large activation energy indicates that ONC is a new type of energetic material with less sensitivity and better thermal stability, and has highly exploitable values.
