Lignin forms an important part of lignocellulosic biomass and is an abundantly available residue. It is a potential renewable source of phenol. Liquefaction of enzymatic hydrolysis lignin as well as catalytical hydrodeoxygenation of the main intermediates in the degradation of lignin, that is, catechol and guaiacol, was studied. The cleavage of the ether bonds, which are abundant in the molecular structure of lignin, can be realised in near-critical water (573 to 673？K, 20 to 30？MPa). Hydrothermal treatment in this context provides high selectivity in respect to hydroxybenzenes, especially catechol. RANEY Nickel was found to be an adequate catalyst for hydrodeoxygenation. Although it does not influence the cleavage of ether bonds, RANEY Nickel favours the production of phenol from both lignin and catechol. The main product from hydrodeoxygenation of guaiacol with RANEY Nickel was cyclohexanol. Reaction mechanism and kinetics of the degradation of guaiacol were explored. 1. Introduction Earth？s resources of crude oil are limited [1]. An important challenge for scientists and engineers is to develop technologies that are largely independent from fossil crude oils. Biomass, especially organic waste material, has a high potential to replace crude oil as a basic input material for the production of many organic chemicals. Lignocellulosic biomass is one of the most abundant renewable organic materials in the world. Lignin, a major component of lignocellulosic biomass, is mostly available as waste material. The paper industry produces more than 50 million tons of dry lignin every year worldwide [2]. It is mainly burned to recover its energetic value. Lignin has a structure similar to brown coal, being an aromatic heteropolymer. The three basic building blocks, p-coumaryl alcohol, coniferyl alcohol, and sinapyl alcohol. are interlinked by C–C or ether bonds. The latter is the weaker one of the two bonds mentioned and thus of high interest for lignin degradation. As lignin is relatively resistant to chemical or enzymatic degradation, harsh reaction conditions are required to break down this polymer [3]. By cleavage of the ether bonds, aromatic monomers are formed. Thus lignin provides high potential to serve as a renewable source for phenol or benzene [4]. Phenol is extremely interesting as building block for synthetic polymers, resins, and epoxy- or polyurethane [3]. It is however a challenge to gain a high-value product from a chemically complicated and inhomogeneous component as lignin. In order to do so, char formation is to be avoided. Char formation can be
References
[1]
S. J. Okullo and F. Reynès, “Can reserve additions in mature crude oil provinces attenuate peak oil?” Energy, vol. 36, no. 9, pp. 5755–5764, 2011.
[2]
J. Puls, “Lignin—Verfügbarkeit, Markt und Verwendung: perspektiven für schwefelfreie Lignine,” Gülzower Fachgespr？che, vol. 31, pp. 18–41, 2009.
[3]
M. Kleinert and T. Barth, “Phenols from lignin,” Chemical Engineering and Technology, vol. 31, no. 5, pp. 736–745, 2008.
[4]
T. Hirth, “Lignin als Aromatenquelle.,” Gülzower Fachgespr？che, vol. 31, pp. 197–222, 2009.
[5]
E. Dorrestijn, L. J. J. Laarhoven, I. W. C. E. Arends, and P. Mulder, “Occurrence and reactivity of phenoxyl linkages in lignin and low rank coal,” Journal of Analytical and Applied Pyrolysis, vol. 54, no. 1, pp. 153–192, 2000.
[6]
D. F. McMillen, R. Malhotra, S. J. Chang, S. E. Nigenda, and G. A. St. John G.A., “Coupling pathways for dihydroxy aromatics during coal pyrolysis and liquefaction,” Fuel, vol. 83, no. 11-12, pp. 1455–1467, 2004.
[7]
D. J. Nowakowski, A. V. Bridgwater, D. C. Elliott, D. Meier, and P. de Wild, “Lignin fast pyrolysis: results from an international collaboration,” Journal of Analytical and Applied Pyrolysis, vol. 88, no. 1, pp. 53–72, 2010.
[8]
M. Kleinert, J. R. Gasson, and T. Barth, “Optimizing solvolysis conditions for integrated depolymerisation and hydrodeoxygenation of lignin to produce liquid biofuel,” Journal of Analytical and Applied Pyrolysis, vol. 85, no. 1-2, pp. 108–117, 2009.
[9]
Z. Liu and F. S. Zhang, “Effects of various solvents on the liquefaction of biomass to produce fuels and chemical feedstocks,” Energy Conversion and Management, vol. 49, no. 12, pp. 3498–3504, 2008.
[10]
Wahyudiono, M. Sasaki, and M. Goto, “Recovery of phenolic compounds through the decomposition of lignin in near and supercritical water,” Chemical Engineering and Processing, vol. 47, no. 9-10, pp. 1609–1619, 2008.
[11]
S. S. Toor, L. Rosendahl, and A. Rudolf, “Hydrothermal liquefaction of biomass: a review of subcritical water technologies,” Energy, vol. 36, no. 5, pp. 2328–2342, 2011.
[12]
C. Yokoyama, K. Nishi, A. Nakajima, and K. Seino, “Thermolysis of organosolv lignin in supercritical water and supercritical methanol,” Sekiyu Gakkaishi, vol. 41, no. 4, p. 250, 1998.
[13]
M. Saisu, T. Sato, M. Watanabe, T. Adschiri, and K. Arai, “Conversion of lignin with supercritical water-phenol mixtures,” Energy and Fuels, vol. 17, no. 4, pp. 922–928, 2003.
[14]
B. Zhang, H. J. Huang, and S. Ramaswamy, “Reaction kinetics of the hydrothermal treatment of lignin,” Applied Biochemistry and Biotechnology, vol. 147, no. 1–3, pp. 119–131, 2008.
[15]
Wahyudiono, M. Sasaki, and M. Goto, “Thermal decomposition of guaiacol in sub- and supercritical water and its kinetic analysis,” Journal of Material Cycles and Waste Management, vol. 13, no. 1, pp. 68–79, 2011.
[16]
H. Y. Zhao, D. Li, P. Bui, and S. T. Oyama, “Hydrodeoxygenation of guaiacol as model compound for pyrolysis oil on transition metal phosphide hydroprocessing catalysts,” Applied Catalysis A, vol. 391, no. 1-2, pp. 305–310, 2011.
[17]
A. Gutierrez, R. K. Kaila, M. L. Honkela, R. Slioor, and A. O. I. Krause, “Hydrodeoxygenation of guaiacol on noble metal catalysts,” Catalysis Today, vol. 147, no. 3-4, pp. 239–246, 2009.
[18]
A. Kruse, D. Meier, P. Rimbrecht, and M. Schacht, “Gasification of pyrocatechol in supercritical water in the presence of potassium hydroxide,” Industrial and Engineering Chemistry Research, vol. 39, no. 12, pp. 4842–4848, 2000.
[19]
A. Sina？, A. Kruse, and J. Rathert, “Influence of the heating rate and the type of catalyst on the formation of key intermediates and on the generation of gases during hydropyrolysis of glucose in supercritical water in a batch reactor,” Industrial and Engineering Chemistry Research, vol. 43, no. 2, pp. 502–508, 2004.
[20]
J. Yanik, S. Ebale, A. Kruse, M. Saglam, and M. Yüksel, “Biomass gasification in supercritical water: II. Effect of catalyst,” International Journal of Hydrogen Energy, vol. 33, no. 17, pp. 4520–4526, 2008.
[21]
H. Habazaki, M. Yamasaki, B. P. Zhang et al., “Co-methanation of carbon monoxide and carbon dioxide on supported nickel and cobalt catalysts prepared from amorphous alloys,” Applied Catalysis A, vol. 172, no. 1, pp. 131–140, 1998.
[22]
Wahyudiono, M. Sasaki, and M. Goto, “Kinetic study for liquefaction of tar in sub- and supercritical water,” Polymer Degradation and Stability, vol. 93, no. 6, pp. 1194–1204, 2008.
[23]
H. E. Jegers and M. T. Klein, “Primary and secondary lignin pyrolysis reaction pathways,” Industrial and Engineering Chemistry Process Design and Development, vol. 24, no. 1, pp. 173–183, 1985.
[24]
T. Nimmanwudipong, R. C. Runnebaum, D. E. Block, and B. C. Gates, “Catalytic conversion of guaiacol catalyzed by platinum supported on alumina: reaction network including hydrodeoxygenation reactions,” Energy and Fuels, vol. 25, no. 8, pp. 3417–3427, 2011.
[25]
E. Dorrestijn and P. Mulder, “The radical-induced decomposition of 2-methoxyphenol,” Journal of the Chemical Society. Perkin Transactions 2, no. 4, pp. 777–780, 1999.
[26]
A. Vuori, “Pyrolysis studies of some simple coal related aromatic methyl ethers,” Fuel, vol. 65, no. 11, pp. 1575–1583, 1986.
[27]
J. C. Mackie, K. R. Doolan, and P. F. Nelson, “Kinetics of the thermal decomposition of methoxybenzene (anisole),” Journal of Physical Chemistry, vol. 93, no. 2, pp. 664–670, 1989.
[28]
W. Bühler, E. Dinjus, H. J. Ederer, A. Kruse, and C. Mas, “Ionic reactions and pyrolysis of glycerol as competing reaction pathways in near- and supercritical water,” Journal of Supercritical Fluids, vol. 22, no. 1, pp. 37–53, 2002.
