![Reaction mechanism of anthraquinone (AQ) in alkaline pretreatment. [Adapted, and reproduced, with permission, from ref 14. Copyright 2006, John Wiley and Sons, Weinheim, Germany.]](https://www.researchgate.net/profile/Bin-Li-185/publication/305684085/figure/fig6/AS:631605714493467@1527597945776/Reaction-mechanism-of-anthraquinone-AQ-in-alkaline-pretreatment-Adapted-and_Q320.jpg)
Content uploaded by Bin Li
Author content
All content in this area was uploaded by Bin Li on May 29, 2018
Content may be subject to copyright.
A preview of the PDF is not available
Review of Alkali-Based Pretreatment To Enhance Enzymatic Saccharification for Lignocellulosic Biomass Conversion
Abstract and Figures
Lignocelluloses have been the focus of much attention on their conversion into fermentable sugars for cellulosic ethanol production, both from the viewpoint of energy and the environment. Pretreatment plays a crucial rule in biomass conversion, to overcome the chemical and structural difficulties which have evolved in lignocelluloses, and to produce a cost effective fermentable sugar via enzymatic saccharification. Among the developed pretreatment approaches, alkali-based pretreatment technology, which can utilize the equipment and chemical recovery system in pulping industry, has been considered one of the most promising pretreatment methods, due mainly to its high efficiency in delignification and high final total sugar yields. This paper reviews the classification, mechanism, advantages, disadvantages, and the progress of alkali-based pretreatment technologies, in order to better understand the fundamental principles of alkali-based pretreatments. This is of vital importance for the process improvement and commercial production of alkali-based pretreatment for producing cellulosic ethanol.
Figures - uploaded by Bin Li
Author content
All figure content in this area was uploaded by Bin Li
Content may be subject to copyright.
... The hydrolysis step of these macromolecules is expected to be the rate-limiting step of BSG fermentation, similarly to most lignocellulosic complex organic feedstocks [14,24]. The low fermentability of lignocellulose can be explained by the limited accessibility of microbial enzymes to the structural polysaccharides due to the tight bonding between the hemicellulose, cellulose, and lignin constituents and the high crystallinity of cellulose [25][26][27]. ...
... Indeed, above these temperatures, alkaline solutions degrade carbohydrates leading to a reduction in fermentable sugars due to peeling and stopping reaction pathways. These processes result in the formation of isosaccharinic acids and metasaccharinic acids, respectively [27,32]. ...
The substitution of fossil resources with renewable carbon requires the development of cost-efficient treatments and conversion processes for biomass. Brewer’s spent grains (BSG) are low-cost organic residues from the agroindustry. The valorization of BSG has been investigated to produce carboxylates through acidogenic fermentation. However, the high lignocellulose content of BSG limits their fermentability. This study examines moderate-temperature dilute alkaline pretreatments of BSG to improve their fermentability and their conversion to short- and medium-chain carboxylates (SCC and MCC) using mixed microbial fermentation. Room temperature and 80 °C pretreatments for 40 or 120 min with a KOH concentration of 0.25 M or 0.5 M were tested. The KOH added for pretreatment was then successfully neutralized by sparging CO2 to adjust the pH to 6 prior the fermentation. The alkaline pretreatment increased the BSG to carboxylate conversion yield from 15 to 21%Total_COD. It increased the final metabolite production by 29 ± 9% as compared to raw BSG. Carboxylates accounted for 89 to 93% of the identified metabolites; SCC represented 85 to 99.5% of the carboxylates produced; and the remaining 0.5 to 15% were MCC. Increasing the pretreatment temperature is detrimental to the production of MCC. The highest MCC proportion was obtained from BSG pretreated at room temperature under 0.25 M KOH. Alkaline pretreatment of BSG enabled a considerable reduction in fermentation time, reaching in 4 days the metabolite production obtained in 14 days with raw BSG.
... However, it has been suggested that the selected pre-treatment method should aim to, 1) avoid the need for size reduction of biomass particles, 2) preserve the hemicellulose fraction for lignocellulosic biomass, 3) reduce/remove inhibitory components and minimise their formation, 4) improve accessibility to difficult components within the biomass, 5) minimise power consumption, 6) improve the properties of the biomass surface for improved microbial interactions, 7) improve the hydrolysis rate of lipids and proteins, and 8) utilise a low cost catalyst/method for recycling of the catalyst and regeneration of lignin for co-product production (for lignocellulose) (Kumar and Sharma, 2017;Parthiba Karthikeyan et al., 2018). The majority of pre-treatment methods aim to improve the biodegradability of agricultural residues (Table 3) due to the presence of lignin, which is a major barrier to the enzymatic saccharification (Xu et al., 2016), or to aid in the breakdown of polysaccharides for microbes which may not produce the required enzymes for saccharification. However, most of the available pretreatment methods are yet to be commercialised due to the high cost of biomass pre-treatment, and many do not meet the requirements for commercial application (Xu et al., 2016). ...
... The majority of pre-treatment methods aim to improve the biodegradability of agricultural residues (Table 3) due to the presence of lignin, which is a major barrier to the enzymatic saccharification (Xu et al., 2016), or to aid in the breakdown of polysaccharides for microbes which may not produce the required enzymes for saccharification. However, most of the available pretreatment methods are yet to be commercialised due to the high cost of biomass pre-treatment, and many do not meet the requirements for commercial application (Xu et al., 2016). ...
Food waste (FW) costs the global economy $1 trillion annually and is associated with 8% of anthropogenic greenhouse gas emissions. Anaerobic digestion (AD) is an effective technology for recycling organic waste, including FW, for energy and nutrient recovery. Current major revenue streams for AD include the sale of biogas/power, gate fees, and digestate (fertiliser). However, subsidies provided by governments are a major profit driver for commercial facilities and are generally required for profitability, limiting its widespread adoption. Lactic acid (LA) is a high value intermediate of the AD process and literature evidence has indicated the recovery of LA can significantly boost the revenue generated from FW-AD. Moreover, FW fermentation naturally tends towards LA accumulation, promotion of LA producing bacteria, and inhibition of alternate competing microbes, making LA attractive for commercial production from FW. The integration of LA production and recovery into FW-AD could improve its economic performance and reduce the need for subsidy support, providing a platform for global adoption of the AD technology. However, challenges, such as 1) the low LA yield on FW, 2) seasonality of the FW composition, 3) unknown influence of LA recovery on downstream AD, and 4) impact of standard operational procedures for AD on upstream LA production, still exist making this focus area for future research. Even so, literature has shown the benefits of the LA-AD biorefinery, detailing improved process economics, increased FW utilisation, and elimination of subsidy support. Therefore, this review focuses on exploring the integrating LA production into AD by examining the current status of AD, LA integration strategies, challenges associated with LA production from FW, and identifies key challenges and considerations associated with downstream AD of fermented waste.
... It exhibits remarkable lignin removal capabilities under non-pressurized conditions at low temperatures (< 100 °C) (Gandla et al. 2018). However, NaOH pretreatment faces two persistent challenges in alkaline pretreatment: the substantial water consumption required to wash alkali-treated lignocellulosic solid residue for subsequent enzymatic hydrolysis and fermentation (Xu et al. 2016), and the generation of considerable black liquor during the pretreatment process and waste washing water during the washing process . ...
A surface response design was employed to develop a sodium hydroxide (NaOH) pretreatment method for Quercus variabilis Blume using low NaOH concentration at low temperature. Nevertheless, the persistent issues associated with alkaline pretreatment of lignocellulose, namely high-water consumption and wastewater generation, remain prevalent in this pretreatment process. To address these challenges, this study aimed to conduct enzymatic hydrolysis of NaOH-treated Q. variabilis Blume without the intermediary washing steps. The results revealed that, following pretreatment and solid-liquid separation, NaOH-treated Q. variabilis Blume could be directly subjected to cellulase-mediated hydrolysis with pH adjustment, eliminating the need for washing steps. The maximum enzymatic hydrolysis efficiency reached 95.9% under specific conditions (1.2% NaOH, 8.9 °C, 32.1 h). This approach offers a promising avenue to enhance the enzyme hydrolysis rate of NaOH-treated lignocellulose. Notably, the low-temperature and low-concentration NaOH treatment effectively removed a substantial portion of lignin and hemicelluloses, resulting in a higher crystallinity index of the cellulose-rich residue compared to substrates treated solely with steam explosion. The integration of direct pretreatment and alkaline treatment emerges as an environmentally friendly and economically viable method for producing glucose and high-purity lignin. The obtained lignin can be further transformed into high-value products within the biorefinery framework.
... In pursuit of reducing the dependence on depleting fossil resources and meeting the rising energy requirements, it is an attractive but challenging opportunity to process inedible biomass into various biobased products and bioenergy in lignocellulosic biorefineris [1][2][3] . Given the structural features of lignocellulose components, achieving fermentable sugar release for biofuel production is a well-known and sought-after illustration for structural carbohydrate utilization (cellulose and hemicelluloses, accounting for 60-85 wt%) 4 . Valorizing lignin (accounting for 15-30 wt%) composed of phenylpropanoid units into useful chemicals is another key to amplifying the economic viability of future biorefineries 5 . ...
Thought-out utilization of entire lignocellulose is of great importance to achieving sustainable and cost-effective biorefineries. However, there is a trade-off between efficient carbohydrate utilization and lignin-to-chemical conversion yield. Here, we fractionate corn stover into a carbohydrate fraction with high enzymatic digestibility and reactive lignin with satisfactory catalytic depolymerization activity using a mild high-solid process with aqueous diethylamine (DEA). During the fractionation, in situ amination of lignin achieves extensive delignification, effective lignin stabilization, and dramatically reduced nonproductive adsorption of cellulase on the substrate. Furthermore, by designing a tandem fractionation-hydrogenolysis strategy, the dissolved lignin is depolymerized and aminated simultaneously to co-produce monophenolics and pyridine bases. The process represents the viable scheme of transforming real lignin into pyridine bases in high yield, resulting from the reactions between cleaved lignin side chains and amines. This work opens a promising approach to the efficient valorization of lignocellulose.
To enhance the sustainability of lignocellulosic biomass utilization process, a significant attention is given to a high-value lignin byproduct of this process. Herein, antimicrobial, antioxidant, and physicochemical properties of lignin in black liquor extracted from sugarcane leaf (SCL) for levulinic acid (LA) and hydrochar production were investigated. The lignin was extracted from SCL through an alkaline pretreatment process using 5–25 wt% of either NaOH or KOH at 120–160 °C. Disk diffusion susceptibility tests, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) revealed that the SCL lignin is effective against Gram-positive bacteria (S. aureus) rather than Gram-negative bacteria (E. coli and S. typhimurium). Different alkaline reagents marginally affected the antimicrobial and antioxidant activities of the lignin. Py-GC/MS analysis results determined that the SCL lignin contained mainly p-hydroxyphenyl (H) and guaiacyl (G) with a small amount of syringyl (S) lignin. Furthermore, the structural alterations and linkages of SCL lignin during alkaline pretreatment were examined using 2D-HSQC NMR, providing valuable insights into the transformation processes. The conversion of delignified SCL to LA through a catalytic hydrothermal process using various acid catalysts indicated that the alkaline pretreatment could enhance LA yield with a maximum yield of 33.4 wt%. Additionally, fuel property characterization of the hydrochar co-product from LA production determined that the hydrochar can be used as a coal substitute.
The recent interest in the production of biohydrogen (bio-H2) from biomass in laboratory scale has enhanced, while there is a need for subsequent technical advancements in the associated biological processes to make it economically viable. H2 is considered as one of the most competitive substitutes for fossil fuels where biological processes are reflected as the most eco-friendly alternatives for meeting future H2 demands. The bio-H2 from agricultural waste is especially advantageous since these biomass is readily available, biodegradable, inexpensive, and renewable. Such wastes are composed of complex lignocellulosic substrates that can be biologically degraded by the complex microbial consortia where dark fermentation coupled with other biological processes like photofermentation and microbial electrolysis cell under various operating conditions has been proved to be a key technology for H2 production from various agricultural wastes. This study emphasizes on different technological advancements in terms of pre-treatment of biomasses for lignin removal, reactor design optimization, and hybridization of different techniques for H2 production from agri-wastes with a special focus on the role of nanoparticles and biotechnological advancements for process stabilization and enhancement of H2 production. The study has revealed that despite the proven efficiency of the various approaches, a detailed and in-depth research is needed for understanding the cellulosic H2 generation process at a molecular level.
Lignocellulosic biomass pretreatment and cellulose dissolution are principal challenges for its conversion to high-
value chemicals, materials and fuels. This work focused on production of soluble cellooligosaccharides (COS)
from palm bunch for future use as nutraceutical supplement to enhance human’s immune and digestive systems. Deep eutectic solvents (DESs) have been found as eco-friendly, renewable and promising solvents selective for lignin and hemicellulose removal from biomass. Additionally, the investigation of most suitable DES for both cellulose dissolution and subsequently cleavage of cellulose to COS is crucial. In the study, palm empty fruit bunch (EFB) was pretreated in different DES for screening of most favorable cellulose inter- and intra-molecular structural dissolution in a combination with beta,1–4 glycosidic bond cleavage by elevated reaction temperature for COS production. ChCl/urea was found to be the most promising DES for dissolving 76.83% of EFB constituents. The highest COS production yield at 90.1%w/w based on treated EFB fraction (74.7% COS yield based on
cellulose in native EFB) was achieved in ChCl/urea DES from cellulose fraction extracted from EFB at 240 ◦C for 20 min. The study additionally provided insightful characterization and elucidation of COS molecular structure using 2D-HSQC and MALDI-TOF/MS techniques. MALDI-TOF/MS was a promising and rapid technique for simultaneously qualitative and quantitative analysis of COS at different degrees of polymerization in COS product.
For the thermomechanical pulping (TMP) process both wood chip quality and the refining process have important effects on the resulting pulp and paper quality. Properties of wood raw material give a framework for final pulp properties. During TMP refining the specific energy consumption and refining intensity strongly impact fibre and pulp qualities. Increasing specific energy consumption benefits the development of fibres and improves their properties. However, high intensity refining tends to shorten the fibres and produces more fines content when compared with low intensity refining. This review focuses on the influence of key variables of chip qualities and the refining process on TMP pulp and paper qualities.
Enzymatic saccharification/hydrolysis is one of the key steps for the bioconversion of lignocelluloses into sustainable biofuels. In this work, corn stover was pretreated with a novel modified alkali process (NaOH + anthraquinone (AQ) + sodium lignosulfonate (SLS)), and then enzymatically hydrolyzed with an enzyme cocktail (cellulase (Celluclast 1.5L), β-glucosidase (Novozyme 188) and xylanase (from thermomyceslanuginosus)) in the pH range of 4.0-6.5. It was found that the suitable pH for the enzymatic saccharification process to achieve a high glucan yield was between 4.2 and 5.7, while the appropriate pH to obtain a high xylan yield was in the range of 4.0-4.7. The best pH for the enzymatic saccharification process was found to be 4.4 in terms of the final total sugar yield, as xylanase worked most efficiently in the pH range of 4.0-4.7, under the conditions in the study. The addition of xylanase in the enzymatic saccharification process could hydrolyze xylan in the substrates and reduce the nonspecific binding of cellulase, thus improving the total sugar yields.
This monograph consists of the proceedings of the Fifth International Symposium on the Activation of Dioxygen and Homogeneous Catalytic Oxidation, held in College Station, Texas, March 14-19, 1993. It contains an introductory chapter authored by Professors D. H. R. Barton and D. T. Sawyer, and twenty-nine chapters describing presentations by the plenary lecturers and invited speakers. One of the invited speakers, who could not submit a manuscript for reasons beyond his control, is represented by an abstract of his lecture. Also included are abstracts of forty-seven posters contributed by participants in the symposium. Readers who may wish to know more about the subjects presented in abstract form are invited to communicate directly with the authors of the abstracts. This is the fifth international symposium that has been held on this subject. The first was hosted by the CNRS, May 21-29, 1979, in Bendor, France (on the Island of Bandol). The second meeting was organized as a NATO workshop in Padova, Italy, June 24-27, 1984. This was followed by a meeting in Tsukuba, Japan, July 12-16, 1987. The fourth symposium was held at Balatonfured, Hungary, September 10-14, 1990. The sixth meeting is scheduled to take place in Delft, The Netherlands (late Spring, 1996); the organizer and host will be Professor R. A. Sheldon.
In this two volume set, Dr. Herbert Sixta, head of the cellulose and viscose research department at Lenzing AG in Austria, has brought together a team of authors to produce the first comprehensive handbook on the market. Alongside the traditional aspects of pulping processes, pulp used in industry and paper pulps, this book describes all pulping processes used for paper and board manufacturing as well as waste liquor treatment, pulp bleaching and environmental aspects, while also covering pulp properties and applications. From the content: - Chemical Pulp - Mechanical Pulp - Recovered Paper and Recycled Fibers - Analytical Characterization of Pulps This handbook is essential reading for all chemists and engineers in the paper and pulp industry.
A novel stepwise pretreatment on corn stalk (CS) by alkali deacetylation combined with liquid hot water (LHW) was investigated to enhance enzymatic hydrolysis. After deacetylated treatment, strength of alkali deacetylation of CS was from 1.79% to 91.34% which was subsequently pretreated by LHW with severity from 3.27 to 4.27. It was found that higher strength of alkali deacetylation could reduce both the degradation of hemicellulose and inhibitors formation in liquid hot water pretreatment (LHWP). Enzymatic hydrolysis efficiency was confirmed to be affected by LHW pretreatment severity (PS) and strength of alkali treatment. This combined pretreatment of alkali deacetylation and LHW could not only increase glucose yield, but also enhance energy utilization efficiency. The maximum enzymatic hydrolysis of 87.55% ± 3.64 with the ratio of glucose yield to energy input at 50.39 g glucose kJ -1 was obtained when strength of alkali deacetylation at 84.96% with PS at 3.97 were used.
To understand the structural changes of lignin after soda-AQ and kraft pretreatment, milled straw lignin, black liquor lignin and residual lignin extracted from wheat straw were characterized by FT-IR, UV, GPC and NMR. The results showed that the main lignin linkages were β-aryl ether substructures (β-O-4'), followed by phenylcoumaran (β-5') and resinol (β-β') substructures, while minor content of spirodienone (β-1'), dibenzodioxocin (5-5') and α,β-diaryl ether linkages were detected as well. After pretreatment, most lignin inter-units and lignin-carbohydrate complex (LCC) linkages were degraded and dissolved in black liquor, with minor amount left in residual pretreated biomass. In addition, through quantitative (13)C and 2D-HSQC NMR spectral analysis, lignin and LCC were found to be more degraded after kraft pretreatment than soda-AQ pretreatment. Furthermore, the subsequent enzymatic hydrolysis results showed that more cellulose in wheat straw was converted to glucose after kraft pretreatment, indicating that LCC linkages were important in the enzymatic hydrolysis process.
A novel process improves conventional and modified kroft cooking by producing two or more white liquors of chemical concentrotions optimizied for the different phases of the cook. The process involves feeding the chips and hydrosulfide-rich liquor early in and hydrosulfide-rich liquor early in the cook followed by an alkli-rich liquor or liquors later in the cook. The author presents results of previous analytical and experimental work amied at verifying process benefits and describes the proposed liquormaking process in conceptual terms and parctical process options.
In this work, the effectiveness of hydrogen peroxide-assisted sodium carbonate (HSC) pretreatment of corn stover to produce fermentable sugars was investigated. It was found that the addition of H2O2 (a green oxidative agent) in Na2CO3 pretreatment could enhance the lignin removal and increase the hydrophilicity of the residual lignin, leading to the improved enzymatic digestibility and the yield of fermentable sugars. Also, results showed that lignin removal (in the range of 12-65%) was positively and linearly correlated with final total sugar yields. Post PFI refining could further improve the enzyme accessibility by increasing porosity of substrates. After HSC pretreatment (40 wt % Na2CO3 and 15 wt % H2O2, 120°C for 60 min) and enzymatic hydrolysis, the final total sugar yield could achieve 79%, which was about 10% higher in comparison with the conventional Na2CO3 pretreatment under the same conditions. HSC pretreatment will have less environmental impact and less barriers for large scale production.
The native form of lignocellulosic biomass is resistant to enzymatic breakdown. A well-designed pretreatment that can promote enzymatic hydrolysis of biomass with reasonable processing cost is therefore necessary. To this end, a number of different types of pretreatment technologies have been developed with a common goal of making biomass more susceptible to enzymatic saccharification. Among those, a pretreatment method using alkaline reagent has emerged as one of the most viable process options due primarily to its strong pretreatment effect and relatively simple process scheme. The main features of alkaline pretreatment are that it selectively removes lignin without degrading carbohydrates, and increases porosity and surface area, thereby enhancing enzymatic hydrolysis. In this review, the leading alkaline pretreatment technologies are described and their features and comparative performances are discussed from a process viewpoint. Attempts were also made to give insights into the chemical and physical changes of biomass brought about by pretreatment.
Copyright © 2015 Elsevier Ltd. All rights reserved.