Treatment and characterization of biomass of soybean and rice hulls using ionic liquids for the liberation of fermentable sugars.

Jairton Dupont,Marco Antônio Z Ayub,Tania M.H Costa,Fernanda Da Cunha-Pereira,Carla R Matte

doi:10.1590/0001-3765202020191258

Jairton Dupont, Marco Antônio Z Ayub + Show 3 more

Open Access

https://doi.org/10.1590/0001-3765202020191258

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Abstract

We investigated the changes in the physical structure of cellulose recovered from soybean and rice hulls treated with the ionic liquids 1-butyl-3-methylimidazolium chloride ([bmim][Cl]) and 1-butyl-3-methylimidazolium acetate ([bmim][Ac]). The characterization was carried out by a combination of thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Regenerated cellulose from soybean hull showed loss of crystallinity and high structural disruption caused by both ionic liquid treatments as compared to the untreated material. In contrast, rice hull presented only a small structural disruption when treated with [bmim][Ac] and was practically unaffected by [bmim][Cl], showing that this biomass residue is recalcitrance towards physico-chemical treatments, possibly as a consequence of its high composition content in silica. These results suggest the use of soybean hull as a substrate to be treated with ionic liquids in the preparation of lignocellulosic hydrolysates to be used in second-generation ethanol production, whereas other methods should be considered to treat rice hull biomass.

Highlights

Lignocellulosic biomass derived from agricultural wastes, grasses, and trees are abundant and renewable feedstock to produce biofuels and chemicals
We used thermogravimetric analysis (TGA and derivative thermograms (DTG)) to obtain information on the weight loss of samples as a function of temperature, defining the thermal decomposition profiles of untreated and regenerated cellulose. This analysis is important to determine whether the pretreatment of soybean and rice hulls using the ionic liquids (ILs) affected the thermal stability of the lignocellulosic materials
These results suggest that IL treatment of samples decreased the thermal stability of cellulose, which may be related to the decrease in crystallinity of the biomass, confirmed by results shown in X-RAY powder diffraction (XRD) (Figure 5), where the peak 16.6o was reduced

Summary

Introduction

Lignocellulosic biomass derived from agricultural wastes, grasses, and trees are abundant and renewable feedstock to produce biofuels and chemicals. Among several possible lignocellulosic residues used in industry, soybean hulls are of importance, representing up to 10 % of the seed weight (Ipharraguerre & Clark 2003), of the most cultivated oilseed worldwide, with its production reaching 350 million tons in 2018 (USDA 2018). Rice hulls represents 20 % (mass fraction) of the harvested rice, and it is one of the most abundant lignocellulosic by-products of cereal industries, accounting for more than 120 million tons generated per year (USDA 2018). These materials are formed by polymeric carbohydrates cellulose and hemicellulose, and by lignin (Zhang & Zhao 2010, Yoo et al 2017, Vasheghani Farahani et al 2016). Lignin, comprising 15 to 35 % of the lignocellulosic matrix (Ek et al 2009, Vasheghani Farahani et al 2016) is a complex aromatic polymer of phenylpropanoid units acting as

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