Comparative Thermal Degradation Behaviors and Kinetic Mechanisms of Typical Hardwood and Softwood in Oxygenous Atmosphere

Xiaokang Xu,Ruiyu Chen,Renming Pan

doi:10.3390/pr9091598

Abstract

In order to utilize woody biomass effectively for bioenergy and chemical feedstocks, the comparative thermal degradation behaviors and kinetic mechanisms of typical hardwood (beech wood) and softwood (camphorwood) were studied at various heating rates in air. The Kissinger-Akahira-Sunose approach combined with the Coats-Redfern approach was employed to estimate the kinetic triplet. Softwood degradation began and ended at lower temperatures than hardwood. Compared with softwood, the maximal reaction rate of hardwood was greater and occurred in the higher temperature region. Two decomposition regions were determined by the variation of activation energy, and the dividing point was α = 0.6 and α = 0.65 for hardwood and softwood, respectively. Moreover, the average activation energy of hardwood was larger than that of softwood during the whole decomposition process. The thermal degradation process occurring in region 1 was dominated by the Avrami-Erofeev and 3D diffusion models for hardwood and softwood, respectively. Furthermore, the kinetic modeling results showed good consistency between the experimental and simulated curves under 5, 15, 20, and 40 K/min. It is noted that the thermogravimetric experimental profile under 20 K/min was not used for estimating the kinetic triplet. Besides, the combustion performance of hardwood is superior to softwood under the same external conditions (heating rate and atmosphere).

Highlights

The heating rates had an important influence on the locations and values of the peaks, but it did not change the patterns of the reaction rate curves
The peaks and shoulder moved towards the high-temperature regions for both hardwood and softwood with the elevated heating rate
The reaction rate value of the shoulder rarely varied with the heating rate, and the first peak value declined with the heating rate while the second peak value first increased and decreased with the heating rate

Summary

Introduction

The rapid development of industry is driven by the consumption of a large number of energy resources, mainly fossil energy. The large consumption of fossil energy will lead to energy shortages or even energy crisis, and cause serious air pollution and climate change [1,2,3]. The concentration of carbon dioxide in the atmosphere has increased by nearly 30% [4], which is widely considered to be the main cause of the greenhouse effect [5]. The biomass utilization for bioenergy can help to reduce the emission of greenhouse gases and other toxic and harmful gases [6,7], and reduce the dependence of social development on fossil energy [8,9]. As a representative renewable biomass, woody biomass is anticipated to take on an increasingly significant role in the production of bioenergy (such as biochar and biogas) and chemical feedstocks [10,11]

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Conclusion