Production of high concentrated cellulosic ethanol by acetone/water oxidized pretreated beech wood

Constantinos Katsimpouras,Evangelos Topakas,Angelos A Lappas,Konstantinos G Kalogiannis,Aggeliki Kalogianni

doi:10.1186/s13068-017-0737-9

Abstract

BackgroundLignocellulosic biomass is an abundant and inexpensive resource for biofuel production. Alongside its biotechnological conversion, pretreatment is essential to enable efficient enzymatic hydrolysis by making cellulose susceptible to cellulases. Wet oxidation of biomass, such as acetone/water oxidation, that employs hot acetone, water, and oxygen, has been found to be an attractive pretreatment method for removing lignin while producing less degradation products. The remaining enriched cellulose fraction has the potential to be utilized under high gravity enzymatic saccharification and fermentation processes for the cost-competing production of bioethanol.ResultsBeech wood residual biomass was pretreated following an acetone/water oxidation process aiming at the production of high concentration of cellulosic ethanol. The effect of pressure, reaction time, temperature, and acetone-to-water ratio on the final composition of the pretreated samples was studied for the efficient utilization of the lignocellulosic feedstock. The optimal conditions were acetone/water ratio 1:1, 40 atm initial pressure of 40 vol% O2 gas, and 64 atm at reaction temperature of 175 °C for 2 h incubation. The pretreated beech wood underwent an optimization step studying the effect of enzyme loading and solids content on the enzymatic liquefaction/saccharification prior to fermentation. In a custom designed free-fall mixer at 50 °C for either 6 or 12 h of prehydrolysis using an enzyme loading of 9 mg/g dry matter at 20 wt% initial solids content, high ethanol concentration of 75.9 g/L was obtained.ConclusionThe optimization of the pretreatment process allowed the efficient utilization of beech wood residual biomass for the production of high concentrations of cellulosic ethanol, while obtaining lignin that can be upgraded towards high-added-value chemicals. The threshold of 4 wt% ethanol concentration that is required for the sustainable bioethanol production was surpassed almost twofold, underpinning the efficient conversion of biomass to ethanol and bio-based chemicals on behalf of the biorefinery concept.

Highlights

Lignocellulosic biomass is an abundant and inexpensive resource for biofuel production
Effect of different acetone/water oxidation (AWO) conditions on the final composition of the pretreated samples Biomass pretreatment with acetone/water mixtures The experimental conditions of each run are presented in Table 1, while Table 2 presents the lignin, cellulose, and hemicellulose contents of the final pulp along with recoveries in the solid product for each constituent
The results suggested that a 6-h liquefaction/saccharification step seems to be adequate for the subsequent fermentation process as the glucose release (g/L) exceeded 80 g/L, which theoretically is the minimum to achieve the ethanol concentration for a low-cost distillation [13]

Summary

Introduction

Lignocellulosic biomass is an abundant and inexpensive resource for biofuel production. Pretreatment is essential to enable efficient enzymatic hydrolysis by making cellulose susceptible to cellulases. Lignocellulosic biomass feedstocks have garnered a lot of interest, as they constitute a profuse resource for production of biofuels and other high-added-value. The pretreatment of lignocellulosic biomass is the costliest part of the process for the production of biofuels. Lignin surrounds cellulose and hemicellulose, Katsimpouras et al Biotechnol Biofuels (2017) 10:54 essentially making biomass highly recalcitrant to pathogens, microorganisms, and enzymes [2]. The main aim is to hydrolyze and remove hemicellulose, so as to enhance the fermentability of the biomass and efficiency of the enzymatic processes. Removing them along with the lignin that enhances the recalcitrance of biomass towards enzymes can greatly benefit the fermentation of the resulting substrates

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Results

Conclusion