Article pubs.acs.org/IECR
A Density Functional Theory Study on Pyrolysis Mechanism of Lignin in Hydrogen Plasma Xiaoyuan Huang,† Dang-guo Cheng,*,† Fengqiu Chen,‡ and Xiaoli Zhan† †
Department of Chemical and Biological Engineering, and ‡Key Laboratory of Biomass Chemical Engineering of Ministry of Education, Department of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China S Supporting Information *
ABSTRACT: The reaction mechanism of lignin pyrolysis in hydrogen plasma has been studied by using phenethyl phenyl ether as the model compound. Density functional theory was employed here. Many possible reactions were proposed. All calculations were performed in the Gaussian 09 program, and the reaction enthalpies and activation energies of these reactions were determined at the B3LYP/6-31G (d,p) level. Calculation results indicate that syngas and acetylene are the main products of lignin pyrolysis in hydrogen plasma. The aldehyde group is the main source of CO. The dehydrogenation process is responsible for the production of hydrogen, and active hydrogen atoms in plasma can make it more favorable. Acetylene mainly comes from the benzene ring and its branch. A subsequent discussion on biomass pyrolysis in plasma found that biomass composition has important effects on product distribution. Syngas can come from both cellulose and lignin, while only lignin is the main source of acetylene formation. It is necessary to first understand the pyrolysis kinetics of biomass to undertand its increasing attention in energy utilization. Biomass is mainly composed of cellulose, hemicellulose, and lignin, and these three components all affect the pyrolysis kinetics of biomass. Cellulose is the most abundant component in biomass (about 50 wt %), and the pyrolysis mechanism of cellulose can explain the pyrolysis behavior of biomass to a great extent, which has been studied extensively.12 Lignin constitutes 15−30 wt % of biomass, and it is a byproduct from the paper industry and bioethanol production. Lignin has a very different chemical structure from cellulose, so their contributions to the formation of pyrolysis products are also different.13 Studying the pyrolysis kinetics of lignin will not only help us get a full understanding of biomass pyrolysis, but also provide guidance for the utilization of byproduct lignin from other industries. There have been much experimental research on the pyrolysis kinetics of lignin, which gained different kinetic models under different conditions,14−23 but none of this research can tell us the detailed reaction pathways. Lignin is a complex polymer, and its structure and pyrolysis behavior varies with biomass types.24 To get a better insight into the pyrolysis behavior of lignin, phenethyl phenyl ether (PPE) has been suggested to be the model compound of lignin by Klein and Virk25 for the first time and in later researches.26−29 In this work, to figure out the pyrolysis mechanism of lignin in hydrogen plasma, the reaction pathways of PPE pyrolysis were studied using density functional theory (DFT). We have investigated the reaction pathways of cellulose pyrolysis in hydrogen plasma in our previous work.30 β-D-Glucopyranose
1. INTRODUCTION Biomass has drawn much attention as a renewable and clean energy source recently, due to the global energy shortage and environmental pollution caused by fossil fuels. Thermal pyrolysis is an effective way to convert biomass into various products such as bio-oil,1 syngas,2 and even high-value chemicals.3 As compared to conventional thermal pyrolysis, thermal plasma pyrolysis can provide several advantages in biomass conversion such as high conversion rate, low tar content in gaseous products, and a wide range of feedstock due to its unique properties of superhigh temperature and high density of energy and active species.4 So thermal plasma pyrolysis has become a new way for biomass utilization, and many researches have been carried out on this new technology.5−11 Pyrogas is quenched as soon as possible after biomass pyrolysis in plasma, and syngas is the main product. There are some light hydrocarbons (mainly methane, ethane, and acetylene) produced simultaneously, but barely no liquid products. Tang et al.6 did a preliminary economic analysis on biomass pyrolysis in thermal plasma based on their experiments, and the results indicate that the cost of syngas is $350/ ton with a capacity of 1500ton/year. They believe that cheaper feedstock from agricultural residues and more valuable products can compensate the cost of electric power consumed by the plasma generator, and make this process economically feasible. Besides, low CO2 concentration in products and low nitrogen and sulfur content in biomass would make it environmentally friendly. Shie et al.11 proposed to lower the electric energy cost by using a power supply generated from the syngas in products because the syngas in products contains more energy than that plasma generator consumes. They also considered that biomass feedstock is cheaper, and the investment costs of plants and equipment are lower. In short, plasma-assisted pyrolysis is a very promising technology for biomass utilization. © 2013 American Chemical Society
Received: Revised: Accepted: Published: 14107
June 23, 2013 September 3, 2013 September 5, 2013 September 5, 2013 dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
Figure 1. The reaction pathways of the initiation of PPE pyrolysis.
3.2. Initiation of PPE Pyrolysis. It has been summarized by Huang et al.29 on the basis of the literature that there are six routes for the initiation reactions of PPE pyrolysis, two molecular channels and four free-radical reaction pathways. Figure 1 presents the reaction pathways of the initiation step and the potential energy profiles along the reaction pathways. As shown in Figure 1, one of the molecular decomposition reactions has an intermediate IM1 in the reaction pathway, yet both of them lead to the formation of styrene and phenol at the end. In the four free-radical reaction pathways, four different bonds between two benzene rings of PPE are broken, and produce corresponding radicals. According to the energies needed for these six pathways, it is evident that two molecular decomposition reactions are more favorable, and styrene and phenol are the main products of the initiation step. Experimental results also prove that styrene and phenol account for more than 80% of all products of PPE fast pyrolysis.26,28 However, four free-radical reaction pathways cannot be completely ruled out. Because two of these four pathways require only a little higher energy than molecular reaction channels, and thermal plasma is totally qualified to provide the energy needed for the other two strongly endothermic reactions. To check the accuracy of our calculations, experimental results36−38 (inside the bracket) and calculated results29 (inside the parentheses) reported by other researchers are also included in the figure for comparison. The optimized geometries and important structure parameters of species (reactants, intermediates, transition states, and products) can be found in the Table S1 of the Supporting Information. This initiation step can be seen as the primary pyrolysis of PPE, and all the products from primary pyrolysis will go through further decomposition reactions which can be seen as the secondary pyrolysis. On the basis of the reported literature, we proposed the reaction pathways of secondary pyrolysis with some extra reasonable assumptions. For example, we not only consider the C−H bond direct-breaking processes reported in the literature, but also consider the corresponding hydrogen abstraction reactions because of an existing H· in reaction system. We choose to ignore those possible but not-reported reactions to make our work more efficient.
was chosen as the model compound, and syngas was the main product with a few light hydrocarbons produced simultaneously. PPE has benzene rings and lower oxygen content in its chemical structure than β-D-glucopyranose, and it is predicted that PPE will give higher hydrocarbons yield and lower carbon monoxide yield. The present work will verify this predication and promote the full understanding of biomass pyrolysis in thermal plasma.
2. METHOD OF CALCULATION Gaussian 09 suit of programs is used to carry out all the DFT calculations.31 Geometries of various reactants, products, and transition states (TSs) were optimized using the Hybrid density functional B3LYP32,33 method with the 6-31G(d,p) basic set. Then at the B3LYP/6-31G(d,p) level of theory, vibrational frequencies of all species were computed to obtain zero-point energy (ZPE) corrections. The QST2 and TS methods were used to find transition states. The transition state has only one imaginary frequency, and it was confirmed by inspection of the imaginary frequency in Gaussian view and performance of the intrinsic reaction coordinate (IRC) calculation. The activation energy for the reaction was defined as the relative energies between the TS and the reactant with ZPE included. 3. RESULTS AND DISCUSSION 3.1. The Generation of Hydrogen Plasma. Hydrogen plasma was used for this work. It is generated by the electric arc between the cathode and the anode in a plasma generator. When hydrogen gas passes through the electric arc, hydrogen molecules are decomposed into active hydrogen atoms via this reaction: H2 → 2H·. The generated hydrogen then enters the reaction zone where pyrolysis occurs. Our calculation indicates that the decomposition of a hydrogen molecule requires a high energy of 103.4 kcal/mol,34 and it has been reported that experimental and calculated results of the reaction enthalpy for this process is 104.2 kcal/mol and 104.0 kcal/mol, respectively.35 Obviously, such high energy needed for plasma generation is supplied by electric arc, because it can heat the hydrogen gas to a temperature as high as 2000−3500 °C. Thus the energy of electric power enters into the active hydrogen atoms in the thermal plasma. 14108
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
3.3. Decomposition of Styrene. It has been proved that at high temperature styrene can decompose into benzene and acetylene,28,39 and the C−C bond between benzene ring and branch can be broken too. As shown in Figure 2, the activation
Figure 3. The reaction pathways of phenol decomposition.
Figure 2. The reaction pathways of styrene decomposition.
energy for the direct decomposition of styrene has been calculated to be 105.3 kcal/mol, and the dissociation of C−C bond requires a high energy of 110.4 kcal/mol. 3.4. Decomposition of Phenol. Horn et al.40 carried out the high temperature pyrolysis of phenol in a shock-tube, and the experimental results show that the pyrolysis starts with the O−H bond dissociation of the hydroxyl group. They also mentioned that the OH· concentration in the reaction was quite low so that the reaction of the C−O bond cleavage producing OH· was negligible. The O−H bond dissociation energy has been estimated to be 85.8 ± 1.9 kcal/mol in the experiments of Angel et al.,41 and calculated to be 86.4 kcal/ mol by Mulder et al.42 Experiments41 and our calculations both indicate that an active hydrogen atom can lower the energy needed for the breaking of O−H bond, and the hydrogen molecule is produced. This kind of reaction is called hydrogen abstraction reaction. The C−O bond direct cleavage producing OH· is not favorable because of its high reaction enthalpy (107.9 kcal/mol in this work), just as Horn et al. suggested.40 However, OH· formation will be much easier with the participation of an active hydrogen atom, which requires an activation energy of 28.9 kcal/mol. So in this work C−O bond breaking reactions are also taken into consideration. As shown in Figure 3, two reaction pathways with an active hydrogen atom (marked by red lines) are more favorable, and they are the main reaction routes of the phenol decomposition. Further pyrolysis of phenoxy and phenyl radicals will be discussed later. 3.5. Decomposition of C6H5O−CH2−CH2. As shown in Figure 4, breaking can happen in the C−C bond and C−O bond on the branch of C6H5O−CH2−CH2·, producing smaller radicals.29 The C−C bond cleavage here needs a high energy of 93.2 kcal/mol. The C−O bond breaking process leads to the formation of ethylene and phenoxy radical via TS7 with a low activation energy of 13.3 kcal/mol, and it is slightly endothermic. No doubt that C−O bond breaking is more favorable here, and it is the main conversion path of C6H5O− CH2−CH2.
Figure 4. The reaction pathways of C6H5O−CH2−CH2· decomposition.
3.6. Decomposition of C6H5−CH2−CH2−O·. It has been reported that C6H5−CH2−CH2−O· can decompose into C6H5−CH2· and HCHO through C−C bond rupture, or C6H5−CH2−CHO through losing a H atom.29 As shown in Figure 5, energies required for these two processes are quite low, and dehydrogenation proceeds much more easily in the presence of active hydrogen atom. C6H5−CH2−CHO can further decompose into C6H5−CH3 and CO through a decarbonylate reaction,29 which has an activation energy of 74.9 kcal/mol. It has been demonstrated that the pyrolysis of toluene starts with C−H breaking on a methyl group, and C−C bond scission occurs between the benzene ring and methyl group as a parallel reaction.43 The active hydrogen atom makes the C−H breaking process easily occur, and it is easy to see from Figure 6 that the most favorable reaction route for C6H5−CH2−CHO should be the following: C6H5CH 2 − CHO → C6H5CH3 + CO 14109
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
Figure 5. The reaction pathways of C6H5−CH2−CH2−O· decomposition.
Figure 6. The reaction pathways of C6H5−CH2−CHO decomposition.
Figure 7. The reaction pathways of C6H5−CH2−CH2· decomposition.
14110
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
Figure 8. The reaction pathways of C6H5O−CH2· decomposition.
Figure 9. The reaction pathways of C6H5−CH2−O· decomposition.
C6H5CH3 + H· → C6H5CH 2 ·+H 2
C6H5−CH2· (comes from the initiation step and the decomposition of C6H5−CH2−CH2·) can decompose into C6H5· and CH2· through C−C bond scission just like toluene: C6H5−CH2· → C6H5· + CH2·. This reaction is endothermic by 121.4 kcal/mol. 3.8. Decomposition of C6H5O−CH2·. As shown in Figure 8, there are two reaction pathways for the decomposition of phenoxymethyl radical (C6H5O−CH2·): (1) C−O bond rupture producing phenyl radical and formaldehyde; (2) isomerization into benzyloxy radical (C6H5−CH2−O·) by a 1,2-phenyl shift via an intermediate IM2.29 The benzyloxy radical continues to decompose through two pathways: (1) C−C bond scission, producing the phenyl radical and formaldehyde; (2) dehydrogenation, producing benzaldehyde.29 As shown in Figure 9, these three reactions are all thermodynamically favorable, and the main products of the benzyloxy radical decomposition are phenyl radical, benzaldehyde, formaldehyde, and hydrogen.
The fate of C6H5−CH2· will be discussed in the next section. 3.7. Decomposition of C6H5−CH2−CH2· and C6H5− CH2·. Two C−C bonds on the branch of C6H5−CH2−CH2· can be broken and lead to the formation of C6H5−CH2·+CH2· or C6H5·+C2H4.29 The first route requires a high reaction enthalpy of 82.2 kcal/mol, while the energy needed for the second one is much lower even though there is a transition state in the reaction pathway. Besides C−C bond scission, C− H bond breaking is another way of the decomposition of C6H5−CH2−CH2·. The participation of an active hydrogen atom makes the dehydrogenation process strongly exothermic with a very low energy barrier. According to Figure 7, there are two possible reaction pathways for C6H5−CH2−CH2· decomposition: C6H5CH 2CH 2 · → C6H5·+C2H4 C6H5CH 2CH 2 · + H· → Styrene + H 2 14111
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
Figure 10. The reaction pathways of C6H5O· decomposition.
Benzaldehyde can further decompose into phenyl and formyl radicals through C−C bond breaking: C6H5−CHO → C6H5· + CHO·, and this process requires a high energy of 95.5 kcal/mol. 3.9. Decomposition of C6H5O·. It has been detected that c-C5H5· and CO are produced during the decomposition of C6H5O·,28,44 and then c-C5H5· can turn into C3H3· and C2H2 via ring-opening.28,45 These two reaction pathways and their potential energies are shown in Figure 10. 3.10. Decomposition of C6H6, C6H5·, HCHO, CHO·, C3H3·, CH2CH·, and C2H4. The further decomposition of these seven species in hydrogen plasma has been discussed in our previous work.30,34,46 The decomposition of C6H6, C6H5·, C3H3·, CH2CH·, and C2H4 produce mainly C2H2 and H2,34,46 and the main products of HCHO and CHO· are CO and H2.30 3.11. Termination. When considering a complete reaction chain of PPE decomposition, PPE should be turned into a small species at the end. As we have discussed before, there are many small radicals in the reaction system, mainly CH3· and CH2·, and they can turn into smaller radicals, as shown in Table 1.
Table 2. Reaction Enthalpies of Termination Step ΔH (kcal/mol)
a
reaction → CH2· + H· + H· → CH2· + H2 → CH· + H· + H· → CH· + H2
Ea (kcal/mol) 10.1 17.0
this work
ref
CH3· + H· → CH4 CH3· + CH3· → C2H6 CH2· + CH2· → C2H4 CH· + CH· → C2H2 OH· + H· → H2O
−103.9 −86.3 −169.7 −263.1 −111.7
−104.8, −104.948 −87.5,a49 −88.550 −173.7,50 −171.0a51 −265.651 −117.6,a52 −117.652 a47
Experimental results.
thermal plasma for its high temperature. Moreover, our calculation shows that the participation of active H· atoms can lower the energies needed for reactions. So the pyrolysis of PPE will be easier in hydrogen plasma. According to our previous analysis and discussion, we obtained the possible reaction pathways of PPE, as shown in Figure 11. It can be seen that the main products of lignin pyrolysis in hydrogen plasma are syngas (CO + H2) and acetylene with some light hydrocarbons (such as CH4, C2H4, and C2H6) as byproducts. This prediction is in accordance with the experiment results of Graef et al..53 They studied the pyrolysis of pure lignin extracted from wood in Ar + He + H2 plasma, and syngas and acetylene were the main products (the working gas of the plasma generator had been precluded). Syngas takes up over 80 vol % in the pyrogas, and acetylene concentration reaches 14 vol %. Calculations indicate that CO mainly comes from the decomposition of the aldehyde group, which comes from the transformation of −CH2−CH2−O−. The active H· atoms can participate in the C−H bond breaking process and remarkably lower the energies needed for dehydrogenation reactions, which makes the main contribution to the formation of hydrogen gas. Acetylene mainly comes from the decomposition of a benzene ring and its branch (−CH2−CH2−). Other light hydrocarbons are mainly produced during the quenching process via the combination of small radicals. It is easy to see that there is a difference between the product distributions of lignin and cellulose pyrolysis in hydrogen plasma. According to our previous work,30 the main product of cellulose pyrolysis is syngas, and few hydrocarbons are produced. This difference is caused by the different chemical structures of lignin and cellulose. Cellulose is a polymer of β-D-
Table 1. The Reaction Pathways and Energies of the Decomposition of CH3· and CH2· CH3· CH3· CH2· CH2·
reaction
ΔH (kcal/mol) 110.9 7.5 121.8 16.7
The product gases must be quenched due to the superhigh reaction temperature in the plasma reactor. No doubt that when pyrogas is quenched, these radicals can combine with H· (in the plasma or from the C−H bond breaking process, which is the most abundant radical in the reaction system) or themselves, and produce corresponding stable molecules. Then pyrolysis reactions will stop. The reaction enthalpies of these combination reactions and results (calculated and experimental) reported by other researchers47−52 are presented in Table 2. 3.12. General Discussion. Some reaction routes of PPE pyrolysis require high energy, but they will become feasible in 14112
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
Figure 11. The reaction pathways of the pyrolysis of PPE in hydrogen plasma.
glucopyranose, so there are many hydroxyl groups in cellulose. These hydroxyl groups turn into aldehydes during pyrolysis and lead to the formation of CO and H2 finally, while there are many benzene ring structures in lignin and the oxygen content is lower. Thus more acetylene and hydrocarbons can be produced. In short, a high oxygen content and no aromatic structure in cellulose result in the reduction of hydrocarbons (especially acetylene) during the pyrolysis of cellulose. As we have discussed above, it is predictable that when biomass is pyrolyzed in hydrogen plasma, the main products would be syngas and acetylene. Cellulose and lignin both contribute to the formation of syngas, while lignin is mainly responsible for the production of acetylene. When biomass contains more lignin, more acetylene and less carbon dioxide will be produced. This prediction is proven by the research of Zhao et al.8 Different biomass feedstocks were pyrolyzed in Ar + H2 plasma. Syngas and acetylene are the main products, and the acetylene concentration in the products increases with lignin content in biomass (see more details in Table S2 and Table S3 of Supporting Information). This prediction will give some primary guidance on biomass utilization. Choosing appropriate biomass feedstock is important for the formation of desired products. Besides changing the biomass source, adding other feedstock also can change the feedstock composition. Biomass copyrolysis with other feedstock such as waste tire, plastic, and medical waste is totally feasible because thermal plasma can handle a wide range of feedstock. It
not only can adjust product distribution, but also will help solve the environmental problems caused by these solid wastes.
4. CONCLUSIONS In this work, the pyrolysis mechanism of lignin in hydrogen plasma has been investigated and a subsequent discussion on biomass pyrolysis has been made. PPE is chosen as the model compound of lignin, and its decomposition is studied using the DFT method. According to our calculation results, the main products of PPE pyrolysis in hydrogen plasma would be syngas and acetylene. CO mainly comes from the decomposition of the aldehyde group, while H2 mainly comes from the dehydrogenation process. The benzene ring and its branch are the main source of acetylene. Our calculations imply that dehydrogenation reactions become favorable both thermodynamically and kinetically, due to the presence of the hydrogen atoms in plasma. Biomass composition turns out to have important effects on product distribution during biomass pyrolysis in plasma. Cellulose and lignin are both the sources of syngas, while lignin makes the main contribution to the formation of acetylene.
■
ASSOCIATED CONTENT
* Supporting Information S
More details of geometries of species (including reactants, products, and transition states) and experimental results of Zhao et al.8 (which can validate our calculations). This material is available free of charge via the Internet at http://pubs.acs.org. 14113
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
■
Article
(23) Zhang, M.; Resende, F. L. P.; Moutsoglou, A.; Raynie, D. E. Pyrolysis of lignin from prairie cordgrass, aspen, and Kraft lignin by Py-GC/MS and TGA/FTIR. J. Anal. Appl. Pyrol. 2012, 98, 65. (24) Wang, S.; Wang, K.; Liu, Q.; Gu, Y.; Luo, Z.; Cen, K.; Franssom, T. Comparison of the pyrolysis behavior of lignins from different tree species. Biotechnol. Adv. 2009, 27, 562. (25) Klein, M. T.; Virk, P. S. Model pathways in lignin thermolysis. 1. Phenethyl phenyl ether. Ind. Eng. Chem. Fundam. 1983, 22, 35. (26) Britt, P. F.; Buchanan, A. C., , III; Cooney, M. J.; Martineau, D. R. Flash vacuum pyrolysis of methoxy-substituted lignin model compounds. J. Org. Chem. 2000, 65, 1376. (27) Beste, A.; Buchanan, A. C., , III. Computational study of bond dissociation enthalpies for lignin model compounds. Substituent effects in phenethyl phenyl ethers. J. Org. Chem. 2009, 74, 2837. (28) Jarvis, M. W.; Daily, J. W.; Carstensen, H.; Dean, A. M.; Sharma, S.; Dayton, D. C.; Robichaud, D. J.; Nimlos, M. R. Direct detection of products from the pyrolysis of 2-phenethyl phenyl ether. J. Phys. Chem. A 2011, 115, 428. (29) Huang, X.; Liu, C.; Huang, J.; Li, H. Theory studies on pyrolysis mechanism of phenethyl phenyl ether. Comput. Theor. Chem. 2011, 976, 51. (30) Huang, X.; Cheng, D. G.; Chen, F.; Zhan, X. Reaction pathways of β-D-glucopyranose pyrolysis to syngas in hydrogen plasma: A density functional theory study. Bioresour. Technol. 2013, 143, 447. (31) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; et al. Gaussian 09, revision A.02; Gaussian Inc.: Wallingford, CT, 2009. (32) Becke, A. D. The original three parameters hybrid. J. Chem. Phys. 1993, 98, 5648. (33) Lee, C.; Yang, W.; Parr, R. G. Development of the Colle− Salvetti correlation-energy formula into a functional of the electron density. Phys. Rev. B 1998, 37, 785. (34) Huang, X.; Cheng, D. G.; Chen, F.; Zhan, X. The decomposition of aromatic hydrocarbons during coal pyrolysis in hydrogen plasma: A density functional theory study. Int. J. Hydrogen Energy 2012, 37, 18040. (35) Huggins, M. L. Bond energies and polarities. J. Am. Chem. Soc. 1953, 75, 4123. (36) Gilbert, K. E.; Gajewski, J. J. Coal liquefaction model studies: Free radical chain decomposition of diphenylpropane, dibenzyl ether, and phenyl ether via β-scission reactions. J. Org. Chem. 1982, 47, 4899. (37) Colussi, A. J.; Zabel, F.; Benson, S. W. The very low-pressure pyrolysis of phenyl ethyl ether, phenyl allyl ether, and benzyl methyl ether and enthalpy of formation of the phenoxy radical. Int. J. Chem. Kinet. 1977, 9, 161. (38) Britt, P. F.; Buchanan, A. C., , III.; Malcolm, E. A. Thermolysis of phenethyl phenyl ether: A model for ether linkages in lignin and low rank coal. J. Org. Chem. 1995, 60, 6523. (39) Muller-Markgraf, W.; Troe, J. Thermal decomposition of ethylbenzene, styrene, and bromophenylethane: UV absorption study in shock waves. J. Phys. Chem. 1988, 92, 4914. (40) Horn, C.; Roy, K.; Frank, P.; Just, T. Shock-tube study on the high-temperature pyrolysis of phenol. Proc. Combust. Inst. 1998, 27, 321. (41) Angel, L. A.; Ervin, K. M. Competitive threshold collisioninduced dissociation: gas-phase acidity and O-H bond dissociation enthalpy of phenol. J. Phys. Chem. A 2004, 108, 8346. (42) Mulder, P.; Korth, H.; Pratt, D. A.; DiLabio, G. A.; Valgimigli, L.; Pedulli, G. F.; Ingold, K. U. Critical re-evaluation of the O-H bond dissociation enthalpy in phenol. J. Phys. Chem. A 2005, 109, 2647. (43) Pamidimukkala, K. M.; Kern, R. D.; Patel, M. R.; Wei, H. C.; Kiefer, J. H. High-temperature pyrolysis of toluene. J. Phys. Chem. 1987, 91, 2148. (44) Lin, C. Y.; Lin, M. C. Thermal decomposition of methyl phenyl ether in shock waves: The kinetics of phenoxy radical reactions. J. Phys. Chem. 1986, 90, 425. (45) Moskaleva, L. V.; Lin, M. C. Unimolecular isomerization/ decomposition of cyclopentadienyl and related bimolecular reverse
AUTHOR INFORMATION
Corresponding Author
*Tel.: +86-571 87953382. E-mail:
[email protected]. Notes
The authors declare no competing financial interest.
■
REFERENCES
(1) Isahak, W. N. R. W.; Hisham, M. W. M.; Mohd Ambar Yarmo, M. A.; Hin, T. Y. A review on bio-oil production from biomass by using pyrolysis method. Renew. Sust. Energy Rev. 2012, 16, 5910. (2) Ruiz, J A.; Juarez, M. C.; Morales, M. P.; Munoz, P.; Mendivil, M. A. Biomass gasification for electricity generation: Review of current technology barriers. Renew. Sust. Energ. Rev. 2013, 18, 174. (3) Azadi, P.; Inderwildi, O. R.; Farnood, R.; King, D. A. Liquid fuels, hydrogen and chemicals from lignin: A critical review. Renew. Sust. Energ. Rev. 2013, 18, 506. (4) Venkatramani, N. Industrial plasma torches and applications. Curr. Sci. 2002, 83, 254. (5) Tang, L.; Huang, H. Biomass gasification using capacitively coupled RF plasma technology. Fuel 2005, 84, 2055. (6) Tang, L.; Huang, H. Plasma pyrolysis of biomass for production of syngas and carbon adsorbent. Energy Fuels 2005, 19, 1174. (7) van Oost, G.; Hrabovsky, M.; Kopercky, V.; Konrad, M.; Hlina, M.; Kavka, T. Pyrolysis/gasification of biomass for synthetic fuel production using a hybrid gas−water stabilized plasma torch. Vacuum 2008, 83, 209. (8) Zhao, Z.; Huang, H.; Wu, C.; Li, H.; Chen, Y. Biomass pyrolysis in an argon/hydrogen plasma reactor. Eng. Life Sci. 2001, 1, 197. (9) Bao, W.; Cao, Q.; Lv, Y.; Chang, L. Acetylene from the copyrolysis of biomass and waste tires or coal in the H2/Ar plasma. Energy Sources, Part A 2008, 30, 734. (10) Grigaitiene, V.; Snapkauskiene, V.; Valatkevicius, P.; Tamosiunas, A.; Valincius, V. Water vapor plasma technology for biomass conversion to synthetic gas. Catal. Today 2011, 167, 135. (11) Shie, J. L.; Tsou, F. J.; Lin, K. L.; Chang, C. Y. Bioenergy and products from thermal pyrolysis of rice straw using plasma torch. Bioresour. Technol. 2010, 101, 761. (12) Lédé, J. Cellulose pyrolysis kinetics: An historical review on the existence and role of intermediate active cellulose. J. Anal. Appl. Pyrol. 2012, 94, 17. (13) Yang, H.; Yan, R.; Chen, H.; Lee, D. H.; Zheng, C. Characteristics of hemicellulose, cellulose and lignin pyrolysis. Fuel 2007, 86, 1781. (14) Jegers, H. E.; Klein, M. T. Primary and secondary lignin pyrolysis reaction pathways. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 173. (15) T R Nunn, T. R.; Howard, J. B.; Longwell, J. P.; Peters, W A. Product compositions and kinetics in the rapid pyrolysis of milled wood lignin. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 844. (16) Caballero, J. A.; Font, R.; Marcilla, A. Pyrolysis of Kraft lignin: Yields and correlations. J. Anal. Appl. Pyrol. 1997, 39, 161. (17) Ferdous, D.; Dalai, A. K.; Bej, S. K.; Thring, R. W. Pyrolysis of lignins: Experimental and kinetics studies. Energy Fuels 2002, 16, 1405. (18) Liu, Q.; Wang, S.; Zheng, Y.; Luo, Z.; Cen, K. Mechanism study of wood lignin pyrolysis by using TG-FTIR analysis. J. Anal. Appl. Pyrol. 2008, 82, 170. (19) Hosoya, T.; Kawamoto, H.; Saka, S. Secondary reactions of lignin-derived primary tar components. J. Anal. Appl. Pyrol. 2008, 83, 78. (20) Shen, D K.; Gu, S.; Luo, K. H.; Wang, S. R.; Fang, M. X. The pyrolytic degradation of wood-derived lignin from pulping process. Bioresour. Technol. 2010, 101, 6136. (21) Jiang, G.; Nowakowski, D. J.; Bridgwater, A. V. Effect of the temperature on the composition of lignin pyrolysis products. Energy Fuels 2010, 24, 4470. (22) Huang, Y.; Wei, Z.; Qiu, Z.; Yin, X.; Wu, C. Study on structure and pyrolysis behavior of lignin derived from corncob acid hydrolysis residue. J. Anal. Appl. Pyrol. 2012, 93, 153. 14114
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
Industrial & Engineering Chemistry Research
Article
process: ab initio MO/statistical theory study. J. Comput. Chem. 2000, 21, 415. (46) Huang, X.; Gu, J.; Cheng, D. G.; Chen, F.; Zhan, X. Pathways of liquefied petroleum gas in hydrogen plasma: A density functional theory study. J. Energy Chem. 2013, 22, 484. (47) Dean, A. M. Predictions of pressure and temperature effects upon radical addition and recombination reactions. J. Phys. Chem. 1985, 89, 4600. (48) Sun, W.; Saeys, M. Construction of an ab initio model for industrial ethane pyrolysis. AIChE J. 2011, 57, 2458. (49) Towfighi, J.; Niaei, A.; Karimzadeh, R.; Saedi, G. Systematics and modelling representations of LPG thermal cracking for olefin production. Korean J. Chem. Eng. 2006, 23, 8. (50) Wang, J. G.; Liu, C. J.; Eliassion, B. Density functional theory study of synthesis of oxygenates and higher hydrocarbons form methane and carbon dioxide using cold plasmas. Energy Fuels 2004, 18, 148. (51) Wu, C. J.; Carter, E A. Ab initio bond strengths in ethylene and acetylene. J. Am. Chem. Soc. 1990, 112, 5893. (52) Ruscic, B.; Feller, D.; Dixon, D. A.; Peterson, K. A.; Harding, L. B.; Asher, R. L.; Wagner, A. F. Evidence for a lower enthalpy of formation hydroxyl radical and a lower gas-phase bond dissociation energy of water. J. Phys. Chem. A 2001, 105, 1. (53) Graef, M.; Allan, G. G.; Krieger, B. B. Rapid pyrolysis of biomass/lignin for production of acetylene. Prepr. Am. Chem. Soc., Div. Pet. Chem. 1979, 24, 432.
14115
dx.doi.org/10.1021/ie401974j | Ind. Eng. Chem. Res. 2013, 52, 14107−14115
