Decomposition of a Lignin Model Compound under Hydrothermal Conditions

Abstract

Lignin, which is the second most abundant polymeric aromatic organic substance in wood biomass after cellulose, and contains many oxygen-based functional groups, has been proposed as an alternative source of chemical compounds. Guaiacol, a model compound for lignin, was reacted in supercritical water using a batch-type reactor at temperatures of 653-673 K and various pressures under an argon atmosphere. The effects of temperature and reaction time at the same pressure were combined into a single severity parameter that was used to monitor the decomposition of guaiacol to its derived compounds. The main products in aqueous solution were catechol, phenol, and o-cresol. The amounts present approached 40.73 wt %, 14.18 wt %, and 4.45 wt %, respectively. With an increase in the reaction time at the same conditions, the amount of guaiacol decreased and the quantity of derived compounds of guaiacol increased. Based on the experimental results, a reaction mechanism for the decomposition of guaiacol was proposed. The process investigated in this study may form the basis for an efficient method of wood biomass decomposition. IntroductionIn recent years, there has been an increasing focus on the utilization of biomass. A variety of conversion processes which would allow the use of biomass as an alternative source of energy and chemical compounds have been proposed. Wood biomass consists of 40-45 wt % cellulose, 25-35 wt % hemicellulose, 15-30 wt % lignin, and other compounds (up to 10 wt %) [1]. Much research has been conducted on cellulose utilization technology.The use of supercritical water (T c = 647.2 K and P c = 22.1 MPa) is a promising technology for the decomposition of wood biomass, because it can be applied at lower temperatures than are usual for biomass treatment 1) . In particular, supercritical water has many advantages when used as a solvent or reaction medium [2][3][4][5][6][7]. It is completely miscible with light gases, hydrocarbons, and aromatics. It has been found that supercritical water plays an important role as a thermally stable solvent in which various organic decomposition and formation reactions can proceed without a catalyst, including oxidation and hydrolysis, two major reactions for completely converting organic materials into carbon dioxide, water and nitrogen. It has been found that the main products of hydrolysis can be produced with a high yield from cellulose under these conditions [8][9][10][11][12][13][14].Antal et al.[2] carried out gasification of biomass with a carbon catalyst in supercritical water at > 923 K, and achieved almost complete gasification, with hydrogen, carbon dioxide, and methane as the major products. Sasaki et al. [11] carried out cellulose decomposition in supercritical water at 623-673 K under non-catalytic conditions and obtained a yield of hydrolysis products approaching 75 %. The effect of alkali salts as a catalyst on cellulose conversion has also been widely investigated [15,16]. Saisu et al. [17] reported the decomposition of lignin to chemical compounds i...

Supercritical Water Gasification of Biomass: A Literature and Technology Overview

“…As a lignin model component, guaiacol conversion in supercritical water has been examined by Wahyudiono et al [48,49] and Dileo et al [50]. In addition, Yong and Matsumura [34,35] investigated the lignin decomposition pathway through guaiacol.…”

Hydrothermal Liquefaction of Desert Shrub Salix psammophila to High Value-added Chemicals and Hydrochar with Recycled Processing Water

“…Table 2 shows the peak areas of 2-methoxyphenol (retention time (RT) = 6.26 min), 4-ethyl-2-methoxyphenol (RT = 7.78 min), and 2,6-dimethoxyphenol (RT = 8.3 min) increased with increased reaction temperatures. Interestingly, the study of Wahyudiono and colleagues showed that higher temperatures were conducive to conversion of the methoxyl aromatic products (Wahyudiono et al 2007). …”

Supercritical Water-induced Lignin Decomposition Reactions: A Structural and Quantitative Study

“…The substantial presence of 4-methylphenol and 4-ethylphenol in the XRL could also be caused by a higher probability for the formation and coupling of methyl-radicals and phenyl radicals from H-type units. Additionally, a lower level of G-type compounds formed from lignin ether-bond hydrolysis can easily lead to polyhydroxy phenol by dealkylation reactions, as shown in past work (Kanetake et al 2007;Toor et al 2011). Thus, catechol compounds can be obtained from guaiacol.…”