Effect of torrefaction on the pyrolysis behavior, kinetics, and phenolic products of lignin
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ORIGINAL ARTICLE
Effect of torrefaction on the pyrolysis behavior, kinetics, and phenolic products of lignin Xiaobing Cao 1 & Fan Chen 1 & Kehui Cen 1 & Jie Zhang 1 & Dengyu Chen 1
&
Yanjun Li 1
Received: 13 August 2020 / Revised: 25 October 2020 / Accepted: 6 November 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Torrefaction is a process of mild pyrolysis at 200–300 °C under nitrogen atmosphere and has been considered to be an effective way to improve the properties of biomass. In this study, lignin was subjected to torrefaction at 200 °C, 230 °C, 260 °C, and 290 °C. Thermogravimetric analysis of lignin samples was performed at a temperature ramp of 25 to 550 °C with the heating rates of 10, 20, 30, or 40 °C min−1. A distributed activation energy model was used to analyze the pyrolysis kinetics of lignin. Then, the lignin samples were subjected to pyrolysis at 600 °C for 10 s. The results showed that torrefaction had a significant effect on the physicochemical properties and pyrolysis characteristics of lignin. Among the torrefied samples, the sample treated at 290 °C exhibited the lowest mass yield (86.07%), lowest energy yield (93.25%), highest content of carbon (63.76%), highest higher heating value (25.18 MJ kg−1), and lowest content of oxygen (30.25%). The activation energy of torrefied lignin samples slightly changed in comparison with those of the raw samples. Torrefaction has a significant effect on pyrolysis products. The peak area % of S-type (41.4%) and P-type (5.4%) phenols in the bio-oil obtained by pyrolysis of LN-200 was the highest. Keywords Bio-oil . Fuel quality . Lignin . Pyrolysis behavior . Torrefaction
1 Introduction Lignocellulosic biomass is an environmentally friendly and renewable energy source. Biomass can be converted into bio-oil via rapid pyrolysis [1, 2]. However, biomass has many disadvantages, such as a high oxygen content and low energy density [3, 4]. Thus, pretreatment is required prior to pyrolysis utilization of biomass [5–7]. As an effective pretreatment method, torrefaction is conducted at low temperature and under nitrogen atmosphere [8, 9]. Lignin is one of the main components of biomass, and it is composed of three main units, namely, P, G, and S units. These units lead to an extremely complex structure of lignin. In recent years, the pyrolysis of lignin has received increased attention [10–12]. Ma et al. studied the relationship of thermal
* Dengyu Chen [email protected] * Yanjun Li [email protected] 1
College of Materials Science and Engineering, Nanjing Forestry University, Nanjing 210037, Jiangsu, China
degradation behavior and chemical structure of lignin and found that higher pyrolysis temperature promoted the formation of aromatics [10]. Ferdous et al. reported that the activation energies of Kraft and Alcell lignins varied from 129 to 361 kJ mol−1 based on the DAEM [13]. Müller-Hagedorn et al. found that typically, pine lignin exhibited more thermal stability than larch lignin [14]. Torrefaction pretreatment can be performed
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