Fractionation of spent liquor from organosolv-pretreatment using lignin-incompatible extraction
Introduction
Awareness of environmental issues and economic pressures is leading to increased demand for renewable fuels and products. Bio-refinery is now an emerging technique to produce renewable carbon for fuels and chemicals. In recent years, attention has been paid to bio-products as substitutes for fuels or petroleum (Garcia et al., 2009). One of the world’s most abundant forms of biomass is lignocellulosic materials, including sawdust, forestry and garden wastes. It has been estimated that approximately 6.5 Mt of woody waste is generated each year by the Australian forestry and timber industries (McIntosh et al., 2012), of which around 1.7 Mt are landfilled or combusted, which is wasteful and contributes to the ongoing problem of greenhouse gas emissions (Taylor and Warnken, 2008).
Recently, researchers have begun focusing on organosolv pretreatment as a more effective way of refining lignocellulosic materials. This process is believed to fractionate value-added products like lignin, cellulose and hemicellulose with almost no change in their structure (Chen et al., 2017). Pretreatment using GVL at 160 °C to 220 °C has proven to produce a high level of cellulose (70%–90%) and large amounts of lignin being removed, in the presence of sulfuric acid (Luterbacher et al., 2014). Liquor is the liquid flow that remains after the organosolv pretreatment, and it contains GVL as solvent, dissolved lignin and monosaccharides degraded from cellulose or hemicellulose. These high-value products can be utilised for further chemical production like sugar fermentation (Luterbacher et al., 2015) or lignin depolymerisation (Dier et al., 2017).
The removal and recycling of GVL are the critical stages before utilising liquor, as GVL has an inhibiting effect on microbial growth in biological processes (Luterbacher et al., 2014). In addition, GVL is relatively expensive and it is important to recycle it from the solvent system as economically as possible (Han et al., 2015). Many methods have been proposed to separate GVL from liquors, and the idea common to all of them is to enrich GVL in a water-insoluble phase. Li et al. (2017) managed to create biphasic liquor by adding NaCl to form a saturated salt solution using ultrasound at 35 kHz. NaCl and monosaccharides remained in the aqueous fraction, while GVL was enriched in the organic fraction. However, NaCl is not an ideal separating reagent as high saline concentration in aqueous solution has side effects on micro-organisms and stops their growth during the fermentation of monosaccharides. Luterbacher et al. (2014) devised a method to recover GVL from liquor using phenolic compounds, but remaining phenol compounds were also regarded as an inhibitor to micro-organisms (Guo et al., 2013). Han et al. (2015) reported a method using CO2-based extraction and separation units to recycle GVL at 296 K and 68 bars. After five gas-phase extractions, 99.6% of GVL, 95.1% of furfural and 95.1% of HMF were recovered using liquid CO2, and the monosaccharide recovery was 85.5%. Despite the high level of recovery, the total capital cost for this method is exorbitant, especially in the extraction and separation units. Motagamwala et al. (2016) proposed a co-solvent method to recycle GVL at 300 psi in an inert atmosphere. GVL retained in the aqueous phase was removed to below 2 wt% with 4 extractions using benzene, minimising potential inhibition to micro-organisms. Using this method, they also recovered 94.3% of monosaccharides and 75% of total lignin. As estimated in their research (Motagamwala et al., 2016), the capital cost for extraction and co-solvent separation (6.8 MM$) is much lower than that of CO2-based extraction (47.8 MM$). The lower capital cost indicated the recycling of GVL under mild temperature and pressure conditions is more economical. Therefore, extraction, especially liquid-liquid extraction, has the potential for the recovery of GVL at ambient temperature and pressure.
In addition to GVL, lignin is a valuable by-product dissolved in liquor. Lignin is a heterogeneous, aromatic co-polymer and usually bonded with hemicellulose and cellulose by ester and hydrogen bonds. Lignin-based products can be used as dispersants, carbon fibres, bioactive agents, etc. (Matsushita, 2015). A variety of methods are proposed to separate lignin from liquor, including acid precipitation (Le et al., 2016, Li et al., 2017), membrane filtration (Aminzadeh et al., 2018) and adsorption (Ohman et al., 2007). Membrane filtration is one of the traditional methods employed in the papermaking industry for separating lignin from black liquor. Ceramic membranes can remove lignin directly without pH modification, whereas the performance of membranes declines over time, causing relatively high operating costs to prevail (Aminzadeh et al., 2018).
Acid precipitation is another method commonly used to separate lignin from liquor after organosolv pretreatment (Kumar et al., 2016, Li et al., 2017, Zhao et al., 2009), and this method is to add excess incompatible solvent (also known as anti-solvent or precipitating solvent) (Lora and Glasser, 2002), like diluted acid or water, into liquor to precipitate dissolved lignin, while it causes significant monosaccharide and GVL loss during dilution. Another acid precipitation strategy is using separating reagents, for instance nonylphenol (Han et al., 2015) or mineral salt, e.g. NaCl (Li et al., 2017). Separating reagents enrich lignin and GVL in organic fraction, followed by acid dilution of the organic fraction to precipitate lignin, leaving monosaccharides unchanged in the aqueous fraction. Both approaches focus on lignin precipitation other than GVL recovery, as the addition of acid dilutes GVL makes it harder to recover. Therefore, adding solvent that is incompatible with lignin can be a simple and easy way to separate lignin from liquor.
Many researchers have reported GVL extraction or lignin precipitation using different kinds of reagents, although there is little literature on fractionating them simultaneously. Therefore the emphasis of this research is to develop a method which combines the liquid-liquid extraction of GVL and organic solvent precipitation of lignin. To differentiate this method from conventional liquid-liquid extraction and organic solvent precipitation, the method developed in this research is referred to as lignin-incompatible extraction. Lignin-incompatible extraction is believed to separate GVL, lignin and monosaccharide from liquor simultaneously at ambient temperature and pressure, which can be simple and economical.
Section snippets
Materials
All chemicals, including GVL, alkali lignin, xylose, glucose, toluene, diethyl ether, dichloromethane (DCM), n-butyl acetate and ethyl acetate were reagent grade or higher and purchased from Sigma Chemical Co. (St. Louis, MO). Eucalyptus obliqua sawdust harvested from south-eastern Australia was kindly provided by Smartwood Moulding (Bacchus Marsh, Victoria) in November 2014. The sawdust was ground using an A11 basic bladed analytical mill (IKA USA), sieved to <1 mm utilising a No. 18 (ASTM)
Selection of solvent for extraction
The organosolv pretreatment of lignocellulosic materials using GVL results in two products. The solid product has high cellulose content, while the liquid product, which is referred as liquor, contains GVL, lignin and monosaccharides. The recycling of GVL will only be possible if it can be extracted from liquor. The solvents PhMe, Et2O, DCM, BuAc and EtAc were all investigated. Artificial liquors were used to assess the solvent single-extraction efficiency and lignin-incompatibility and
Conclusions
Using lignin-incompatible extraction, lignin and GVL were simultaneously recovered from liquors generated from GVL fractionation of Eucalyptus oblique. Toluene revealed high potential as a lignin-incompatible solvent at pH 5.0, where 89.5% of lignin precipitated and 93.9% of xylose remained in the aqueous fraction. GVL recovery of 87.6% was achieved and the rGVL elicited a similar pretreatment performance compared to pure GVL. Lignin precipitated using this method had a weaker hydrogen-bonding
References (28)
- et al.
Membrane filtration of kraft lignin: structural characteristics and antioxidant activity of the low-molecular-weight fraction
Ind. Crops Prod.
(2018) - et al.
Solvent fractionation of renewable woody feedstocks: organosolv generation of biorefinery process streams for the production of biobased chemicals
Biomass Bioenergy
(2011) - et al.
A review on the pretreatment of lignocellulose for high-value chemicals
Fuel Process. Technol.
(2017) - et al.
Characterization of lignins obtained by selective precipitation
Sep. Purif. Technol.
(2009) - et al.
Butanol production from hemicellulosic hydrolysate of corn fiber by a Clostridium beijerinckii mutant with high inhibitor-tolerance
Bioresour. Technol.
(2013) - et al.
A lignocellulosic ethanol strategy via nonenzymatic sugar production: process synthesis and analysis
Bioresour. Technol.
(2015) - et al.
Alkaline polyol pulping and enzymatic hydrolysis of softwood: effect of pulping severity and pulp properties on cellulase activity and overall sugar yield
Bioresour. Technol.
(2013) - et al.
Valorization of bamboo by gamma-valerolactone/acid/water to produce digestible cellulose, degraded sugars and lignin
Bioresour. Technol.
(2017) - et al.
Ethanol production from Eucalyptus plantation thinnings
Bioresour. Technol.
(2012) - et al.
Biorefining of wheat straw using an acetic and formic acid based organosolv fractionation process
Bioresour. Technol.
(2014)
Bioethanol potential of Eucalyptus obliqua sawdust using gamma-valerolactone fractionation
Bioresour. Technol.
Chemical, structural, and thermal characterizations of alkali-soluble lignins and hemicelluloses, and cellulose from maize stems, rye straw, and rice straw
Polym. Degrad. Stab.
Improvement of acetone, butanol, and ethanol production from woody biomass using organosolv pretreatment
Bioprocess Biosyst. Eng.
Sustainable electrochemical depolymerization of lignin in reusable ionic liquids
Sci. Rep.
Cited by (24)
Integrated laccase delignification with improved lignocellulose recalcitrance for enhancing enzymatic saccharification of ensiled rice straw
2023, Industrial Crops and ProductsApplications of biomass-derived solvents in biomass pretreatment – Strategies, challenges, and prospects
2023, Bioresource TechnologyCitation Excerpt :Such a biphasic nature at room temperature caused the selective carbohydrate partition into the aqueous phase, thereby avoiding the need for an expensive post-reaction separation process (Fig. 3). Sun et al. developed a lignin-incompatible extraction technique using calcium carbonate and toluene to simultaneously precipitate lignin and recover GLV and monosaccharides from the GVL pretreated liquor (Sun et al., 2018). GVL/H2O system also offers a promising platform for producing cellulose pulp for industrial applications (Yang et al., 2020).
Ionic Liquid Assisted Pretreatment to Improve Cellulose Fractionation of Lignocellulosic Biomass
2021, Ionic Liquid-Based Technologies for Environmental SustainabilityEffect of inorganic additives and optimisation of the electro-assisted organosolv pretreatment of biomass
2021, Journal of Environmental Chemical EngineeringCitation Excerpt :The columns were maintained at 85 °C with a flow of 0.4 mL/min of degassed Milli-Q water, as the column manufacturer suggested. We have previously shown that the spent [Bmim]OAc/GVL can be regenerated by using a lignin-incompatible extraction [16]. Specifically, spent [Bmim]OAc/GVL was thoroughly mixed with water (of equal volume to spent liquor) and dichloromethane (DCM, of equal volume to spent liquor).
Ionic liquid assisted pretreatment to improve cellulose fractionation of lignocellulosic biomass
2021, Ionic Liquid-Based Technologies for Environmental Sustainability