Effects of Milling and UV Pretreatment on the Pyrolytic Behavior and Thermal Stability of Softwood and Hardwood

Marco Mattonai,Luca Zaccaroni,Erika Ribechini,Federica Nardella

doi:10.1021/acs.energyfuels.1c01048

Marco Mattonai, Luca Zaccaroni + Show 2 more

Open Access

https://doi.org/10.1021/acs.energyfuels.1c01048

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Journal: Energy & Fuels	Publication Date: Jul 1, 2021
Citations: 8	License type: CC BY 4.0

Affiliation: University of Pisa

Abstract

UV/visible light is a promising radiation source for biomass pretreatment, but very little knowledge is available on the effect of UV on the thermal behavior of lignocellulose in comparison with more classical, physical pretreatment methods. In this paper, we investigate the effects of ball-milling and UV irradiation on two species of softwood and two species of hardwood, using X-ray diffractometry (XRD), evolved gas analysis-mass spectrometry (EGA-MS), and pyrolysis-gas chromatography coupled to mass spectrometry (Py-GC/MS). The XRD data showed that the crystalline fraction of cellulose was destroyed by milling, but not by irradiation. The EGA-MS data and isoconversional kinetic analysis showed that both milling and irradiation can reduce the thermal stability of wood up to a limit value. The Py-GC/MS data showed that irradiation caused the most significant changes in the pyrolytic behavior of the wood species, increasing the ratio of holocellulose to lignin pyrolysis products and the reactivity of cellulose toward the derivatizing agent. Softwoods were more affected by irradiation than hardwoods. This paper shows that UV irradiation can decrease the recalcitrance of biomass toward pyrolysis, but its efficiency is highly dependent on the type of lignocellulosic substrate.

Highlights

One of the main challenges that must be faced in these conversion processes is the recalcitrance of biomass, which is due to a combination of the entanglement of the holocellulose and lignin fractions, the crystalline domains of cellulose, and the presence of lignin−carbohydrate complexes (LCCs).[6−9] Several pretreatment techniques have been investigated to improve the overall pyrolytic yield of biomass and direct the mechanism toward the formation of specific, desirable products.[10,11]
The X-ray diffractometry (XRD) spectra obtained for all samples are available in the Supporting Information
Milling led to a complete cleavage of the crystalline phase of all wood samples, while irradiation had no significant effect on cellulose crystallinity

Summary

Introduction

Biomass conversion strategies through thermochemical methods have been widely investigated in the last century with the aim of improving the performances of the resulting biofuels[1−3] or the yield of specific valuable chemicals.[4,5] One of the main challenges that must be faced in these conversion processes is the recalcitrance of biomass, which is due to a combination of the entanglement of the holocellulose and lignin fractions, the crystalline domains of cellulose, and the presence of lignin−carbohydrate complexes (LCCs).[6−9] Several pretreatment techniques have been investigated to improve the overall pyrolytic yield of biomass and direct the mechanism toward the formation of specific, desirable products.[10,11] The most traditional pretreatments are based on wet chemistry, using acid, alkaline, or oxidating agents to cleave the chemical bonds in lignocellulose.[12]. Wang and co-workers observed a decrease in the thermal stability of cellulose from cedar and beech after ballmilling.[17] In a previous study by us,[6] we observed that isoconversional methods can be used to track the decrease in thermal stability of cellulose after ball-milling. The application of this strategy to whole lignocellulose could be interesting, but has not been explored yet in the literature

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Results

Conclusion