Modeling of Lignin Thermolysis

Abstract

Lignin thermolysis at temperatures from 300 to 600 °C and holding times from 101 to 104 s was simulated by a mathematical model. Modeling entailed a statistical interpretation of lignin structure and thermolysis, which was combined with experimental pyrolysis pathways and kinetics derived from model substrates that mimicked the chemical moieties within lignin. The model simulated the temporal evolution of lignin thermolysis products in each of four categories: namely, (i) gas, comprising methane and carbon monoxide; (ii) aqueous liquid, consisting of water and methanol; (iii) tar, containing single-ring aromatic liquids, the majority related to guaiacol, catechol, and phenol; and (iv) a carbonaceous residue, of multiple-ring aromatic products. Quantitative comparisons were effected between the simulated product yields and experimental product yields reported in the extensive literature on lignin thermolysis. Simulated gas yields and the variation of CO/CH4 within them were in good agreement with experiments. Simulated aqueous liquid yields compared poorly to experiments, being an order of magnitude smaller than reported. Simulated tar yields were of the same magnitude as reported in the literature; the model also predicted the appearance of all of some 30 phenolic compounds that have been detected in lignin tars. Simulated residue yields at long times accorded well with final “char” yields reported in the literature. Finally, simulated weight loss kinetics compared favorably to both the shapes and magnitudes of experimental observations reported as a function of time.

Assessment of the thermal behavior of lignins from softwood and hardwood species

“…Tejado et al (2007) found T g values of 100ºC and 144ºC for lignins from organosolv and kraft isolation methods. The higher T g from Klason lignin is probably due to its higher condensed structure (Klein andVirk 2008, Jiang et al 2010) when compared with lignin obtained from others separation methods. Figure 2 shows the TGA and DTG curves of the lignins studied.…”

“…Understand the pyrolysis kinetics of lignin and its correlation with physical and chemical properties of wood is important to better understand wood thermal degradation and provide useful information for rational design and scaling-up of pyrolysis reactors (Klein andVirk 2008, Jiang et al 2010). In order to better understand the thermal degradation and pyrolysis kinetics of lignin and its correlation with their properties, this study investigates the differences in thermal behavior and degradation kinetics of two Klason lignins obtained from different tree species.…”

Preparation and Characteristics of Biomass Char

“…Since biomass contains large amounts of volatiles, a porous structure is formed inside and on the surface of pyrolyzed biomass (Yan et al 2010;. Compared to those of biomass, the volatiles and oxygen content in biomass char are much smaller and the fixed carbon composition is larger (Chaudhari et al 2003;Klein et al 2008). Biomass char has high reactivity with lower nitrogen and sulfur levels than coal, resulting in less pollution than coal char and making it a good-quality gasification material.…”

Materials produced from plant biomass: part III: degradation kinetics and hydrogen bonding in lignin

“…On the other hand, fast pyrolysis is one of the lignin conversion processes that will potentially lead to more valuable phenol and phenolic compounds 4,9 . So, understanding the kinetics of pyrolysis of lignin and its correlation with physical and chemical properties of lignin is important to better understand the underlying processes and provide useful information for rational design and scaling-up of pyrolysis reactors 4,9 .…”

“…So, understanding the kinetics of pyrolysis of lignin and its correlation with physical and chemical properties of lignin is important to better understand the underlying processes and provide useful information for rational design and scaling-up of pyrolysis reactors 4,9 . However, one of the most uncertain parameter during lignin degradation is the order of reaction, since many authors assume a first order reaction and then obtain the activation energy and frequency factor.…”