Optimization of Hydrothermal Pretreatment of Lignocellulosic Biomass in the Bioethanol Production Process

Abstract

The natural resistance to enzymatic deconstruction exhibited by lignocellulosic materials has designated pretreatment as a key step in the biological conversion of biomass to ethanol. Hydrothermal pretreatment in pure water represents a challenging approach because it is a method with low operational costs and does not involve the use of organic solvents, difficult to handle chemicals, and "external" liquid or solid catalysts. In the present work, a systematic study has been performed to optimize the hydrothermal treatment of lignocellulosic biomass (beech wood) with the aim of maximizing the enzymatic digestibility of cellulose in the treated solids and obtaining a liquid side product that could also be utilized for the production of ethanol or valuable chemicals. Hydrothermal treatment experiments were conducted in a batch-mode, high-pressure reactor under autogeneous pressure at varying temperature (130-220 °C) and time (15-180 min) regimes, and at a liquid-to-solid ratio (LSR) of 15. The intensification of the process was expressed by the severity factor, log R(o). The major changes induced in the solid biomass were the dissolution/removal of hemicellulose to the process liquid and the partial removal and relocation of lignin on the external surface of biomass particles in the form of recondensed droplets. The above structural changes led to a 2.5-fold increase in surface area and total pore volume of the pretreated biomass solids. The enzymatic hydrolysis of cellulose to glucose increased from less than 7 wt% for the parent biomass to as high as 70 wt% for the treated solids. Maximum xylan recovery (60 wt%) in the hydrothermal process liquid was observed at about 80 wt% hemicellulose removal; this was accomplished by moderate treatment severities (log R(o)=3.8-4.1). At higher severities (log R(o)=4.7), xylose degradation products, mainly furfural and formic acid, were the predominant chemicals formed.

Hydrothermal Treatment and Enzymatic Saccharification of Corncobs

“…Arabinan and acetyl groups were completely released at 200 °C and 220 °C, respectively. These observations were in good agreement with previous studies on the evaluation of the hydrothermal pretreatment to reduce biomass recalcitrance using different raw materials for enhanced enzymatic digestibility, such as beech (Nitsos et al 2013), hybrid polar (Kim et al 2009), soybean straw (Wan et al 2011), and wheat straw .…”

“…This restricts the efficiency of the enzymatic hydrolysis of the parent biomass. Thus, a pretreatment step is critical for the success of the overall biochemical conversion process (Nitsos et al 2013). The goals of pretreatment are to remove the recalcitrant barriers and increase the enzymatic digestibility of cellulose by altering the chemical compositions and physical structures of biomass feedstock (Zhao et al 2012).…”

Chemical, Energetic, and Structural Characteristics of Hydrothermal Carbonization Solid Products for Lawn Grass

“…An absorption peak located at 1515 cm -1 , which could be related to aromatic ring stretching vibration appeared. This could be attributed to the removal of the amorphous fraction (Nitsos et al 2013), as indicated in Fig. 7.…”

Enhanced Cellulase Production by a Novel Thermophilic Bacillus licheniformis 2D55: Characterization and Application in Lignocellulosic Saccharification

“…Pre-treatment is usually required to deconstruct the tough complex structures in lignocellulosic biomass prior to hydrolysis. Acid and alkali pre-treatment technologies have been used on lignocellulosic biomass (Krishnan et al 2010;Sindhu et al 2011); most thermal pre-treatment requires high temperatures above 100 °C (Nitsos et al 2013;Zheng and Rehmann 2014). However, fungal cellulases available for saccharification have optimum activities at 50 °C.…”