A comparison of various lignin-extraction methods to enhance the accessibility and ease of enzymatic hydrolysis of the cellulosic component of steam-pretreated poplar

Abstract

BackgroundCurrent single-stage delignification-pretreatment technologies to overcome lignocellulosic biomass recalcitrance are usually achieved at the expense of compromising the recovery of the polysaccharide components, particularly the hemicellulose fraction. One way to enhance overall sugar recovery is to tailor an efficient two-stage pretreatment that can pre-extract the more labile hemicellulose component before subjecting the cellulose-rich residual material to a second-stage delignification process. Previous work had shown that a mild steam pretreatment could recover >65% of the hemicellulose from poplar while limiting the acid-catalysed condensation of lignin. This potentially allowed for subsequent lignin extraction using various lignin solvents to produce a more accessible cellulosic substrate.ResultsA two-stage approach using steam and/or solvent pretreatment was assessed for its ability to separate hemicellulose and lignin from poplar wood chips while providing a cellulose-rich fraction that could be readily hydrolysed by cellulase enzymes. An initial steam-pretreatment stage was performed over a range of temperatures (160–200 °C) using an equivalent severity factor of 3.6. A higher steam temperature of 190 °C applied over a shorter residence time of 10 min effectively solubilized and recovered 75% of the hemicellulose while enhancing the ability of various solvents [deep eutectic solvent (DES), ethanol organosolv, soda/anthraquinone (soda/AQ) or a hydrotrope] to extract lignin in a second stage. When the second-stage treatments were compared, the mild DES treatment (lactic acid and betaine) at 130 °C, removed comparable amounts of lignin with higher selectivity than did the soda/AQ and organosolv pretreatments at 170 °C. However, the cellulose-rich substrates obtained after the second-stage organosolv and soda/AQ pretreatments showed the highest cellulose accessibility, as measured by the Simon’s staining technique. They were also the most susceptible to subsequent enzymatic hydrolysis.ConclusionsThe second-stage pretreatments varied in their ability to solubilize and extract the lignin component of steam-pretreated poplar while enhancing the enzymatic hydrolysis of the resulting cellulose-rich residual fractions. Although DES extraction was more selective in extracting lignin from the steam-pretreated substrates, the organosolv and soda/AQ post treatments disrupted the cellulose structure to a greater extent while enhancing the ease of enzymatic hydrolysis. Graphical abstractEffective hemicellulose removal via steam pretreatment followed by subsequent lignin extraction under acidic, alkaline or solvolytic conditions results in a highly accessible, more readily hydrolysed cellulose fraction.

Oxygen radical based on non-thermal atmospheric pressure plasma alleviates lignin-derived phenolic toxicity in yeast

“…Various biological, chemical, and physical pretreatment methods have been developed [8][9][10][11][12]. For economic reasons, alkaline hydrolysis is commonly used to prepare lignocelluloses for enzymatic saccharification and fermentation [58]; however, vanillin is generated as a toxic byproduct during this process [13,14].…”

“…Bioethanol production from lignocellulose generally involves three steps: (1) pretreatment to break down complex lignocellulose structures, (2) enzymatic hydrolysis of polysaccharides (i.e., cellulose and hemicellulose) into fermentable sugars, and (3) fermentation to convert sugars into ethanol [5]. Pretreatment is required to alter the biomass by changing its chemical or physical properties and to allow increased enzyme accessibility to cellulose [6,7], with various biological, chemical, and physical pretreatment methods having been developed [8][9][10][11][12]. Vanillin is generally generated as a byproduct during the process of fermentable-sugar production from lignocellulosic biomass, regardless of being herbage, softwood, or hardwood [13,14].…”

The Effect of Plant Source on the Properties of Lignin-Based Polyurethanes

“…The organosolv process is a sulfur free pulping process that uses a mixture of solvents such as methanol, ethanol, acetic acid, formic acid, and peroxy-organic acids to cook the wood and separate lignin from the other wood constituents (Xu et al, 2006, Tian et al, 2017. During the organosolv process, lignin becomes solubilized by solvent or solvents used through acidolytic or alkaline cleavage of aryl ether linkages resulting in an increased number of phenolic functionalities.…”

Nanometrology of Biomass for Bioenergy: The Role of Atomic Force Microscopy and Spectroscopy in Plant Cell Characterization

“…Controlling this process requires the understanding of the relationship between the chemical composition, the structural aspect, the biological infrastructure, and the mechanical properties of the PCW. The many delignification strategies have been based on various approaches (Singh et al, 2014) such as (1) physical treatments including mechanical (Cadoche and Lopez, 1989), pyrolysis , and steam processes (Tian et al, 2017), (2) chemical using organosolv (Erdocia et al, 2014), acid and alkaline hydrolysis (Singh et al, 2015;Carlos Martinez-Patino et al, 2017), or saccharification and fermentation (Healey et al, 2015), and (3) biological (Asina et al, 2016) and enzymatic (Al-Zuhair et al, 2015;Tian et al, 2017) treatments. To illustrate the complexity of delignification, an example based on a multistep chemical protocol, is given in Figure 1, resulting in a set of samples to be investigated using AFM techniques (Farahi et al, 2017).…”