Alternative Lime Pretreatment of Corn Stover for Second-Generation Bioethanol Production

Iria Fírvida,Aloia Romaní,Gil Garrote,Patricia Gullón,Beatriz Gullón,Pablo G Del Río

doi:10.3390/agronomy11010155

Abstract

In this work, a delignification process, using lime (Ca(OH)2) as an alternative alkali, was evaluated to improve enzymatic saccharification of corn stover cellulose, with the final goal of obtaining second-generation bioethanol. For that, an experimental design was conducted in order to assay the effect of temperature, lime loading, and time on the corn stover fractionation and enzymatic susceptibility of cellulose. Under conditions evaluated, lime pretreatment was selective for the recovery of cellulose (average of 91%) and xylan (average of 75.3%) in the solid phase. In addition, operating in mild conditions, a delignification up to 40% was also attained. On the other hand, a maximal cellulose-to-glucose conversion (CGCMAX) of 89.5% was achieved using the solid, resulting from the treatment carried out at 90 °C for 5 h and lime loading of 0.4 g of Ca(OH)2/g of corn stover. Finally, under selected conditions of pretreatment, 28.7 g/L (or 3.6% v/v) of bioethanol was produced (corresponding to 72.4% of ethanol conversion) by simultaneous saccharification and fermentation. Hence, the process, based on an alternative alkali proposed in this work, allowed the successful production of biofuel from the important and abundant agro-industrial residue of corn stover.

Highlights

A sustainable future relies on an increased share of eco-friendly energy, in developing countries
In light of the resulting data obtained in this work, the suitable use of lime processing for the improvement of enzymatic saccharification of cellulose from corn stover using low temperatures, pressures, and low-cost chemicals is noteworthy
After 24 h, the ethanol conversion ranged from 33.2% of ECMAX up to 67.1% of ECMAX

Summary

Introduction

A sustainable future relies on an increased share of eco-friendly energy, in developing countries. The ethanol obtained from different food-related sources, such as sugarcane, sugar beet, or maize (sources of sucrose and starch, respectively) is commonly known as first-generation bioethanol [3,4,5]. The use of crops as feedstock may lead to some conflicts, augmenting the demand and price of foods [7,8,9]. In this way, the use of alternative, ubiquitous, and renewable sources is fundamental for the production of biofuels under a more profitable and sustainable point of view [10,11,12,13,14]. Lignocellulosic materials (LCMs) fulfill these characteristics, including attractive choices for the partial replacement of fossil fuels, like remarkable availability, ubiquity, enhancement of local economy resulting from cultivation, carbon neutrality, and appropriateness for the manufacture of LCM-derived ethanol [15,16]

Objectives

Methods

Results

Conclusion