Ionic liquids as a tool for lignocellulosic biomass fractionation

Co-densification of rice straw and cow dung in different food-to-microorganism ratios for biogas production

Agricultural residues such as rice straw (RS) are desirable raw materials for biogas generation. However, the recalcitrant nature of RS hinders biogas production, and its low bulk density increases storage space requirements, transportation needs, and overall costs. These challenges could be resolved by pretreatment and pelletization. In this study, various thermal pretreatments were performed, and the best conditions (temperature and time) were identified. Also, rice straw and cow dung pellets (RCP) at different food-to-microorganism (F/M) ratios (0.5-2.5) were prepared. Parameters such as bulk density, moisture absorption, and drop shatter tests were conducted to evaluate the physical properties. Finally, the biochemical methane potential (BMP) study of the best RCP with varying total solids (TS: 4-12%) content was investigated. The results indicate that hot air oven pretreatment (for 60 min at 120 °C) resulted in maximum solubilization. In physical characteristics, RCP with an F/M ratio of 2.5 pellets was ideal. The bulk density of RCP 2.5 was found to be around 25 times that of the raw. Also, the TS 8% yielded maximum biomethane (279 mL/g-VSconsumed) as compared to other TS contents. Overall, this study will propel the growth of bioenergy while simultaneously tackling the pressing issues related to RS management.

Fractionation of Arctic Brown Algae (Fucus vesiculosus) Biomass Using 1-Butyl-3-methylimidazolium-Based Ionic Liquids

Arctic brown algae are considered a promising industrial-scale source of bioactive sub-stances as polysaccharides, polyphenols, and low-molecular secondary metabolites. Conventional technologies for their processing are focused mainly on the isolation of polysaccharides and involve the use of hazardous solvents. In the present study a "green" approach to the fractionation of brown algae biomass based on the dissolution in ionic liquids (ILs) with 1-butil-3-methylimidazolium (bmim) cation with further sequential precipitation of polysaccharides and polyphenols with acetone and water, respectively, is proposed. The effects of IL cation nature, temperature, and treatment duration on the dissolution of bladderwrack (Fucus vesiculosus), yields of the fractions, and their chemical composition were studied involving FTIR and NMR spectroscopy, as well as size-exclusion chromatography and monosaccharide analysis. It was shown that the use of bmim acetate ensures almost complete dissolution of plant material after 24 h treatment at 150 °C and separate isolation of the polysaccharide mixture (alginates, cellulose, and fucoidan) and polyphenols (phlorotannins) with the yields of ~40 and ~10%, respectively. The near-quantitative extraction of polyphenolic fraction with the weight-average molecular mass of 10-20 kDa can be achieved even under mild conditions (80-100 °C). Efficient isolation of polysaccharides requires harsh conditions. Higher temperatures contribute to an increase in fucoidan content in the polysaccharide fraction.

Application of machine learning techniques to the modeling of solubility of sugar alcohols in ionic liquids

The current trend of chemical industries demands green processing, in particular with employing natural substances such as sugar-derived compounds. This matter has encouraged academic and industrial sections to seek new alternatives for extracting these materials. Ionic liquids (ILs) are currently paving the way for efficient extraction processes. To this end, accurate estimation of solubility data is of great importance. This study relies on machine learning methods for modeling the solubility data of sugar alcohols (SAs) in ILs. An initial relevancy analysis approved that the SA-IL equilibrium governs by the temperature, density and molecular weight of ILs, as well as the molecular weight, fusion temperature, and fusion enthalpy of SAs. Also, temperature and fusion temperature have the strongest influence on the SAs solubility in ILs. The performance of artificial neural networks (ANNs), least-squares support vector regression (LSSVR), and adaptive neuro-fuzzy inference systems (ANFIS) to predict SA solubility in ILs were compared utilizing a large databank (647 data points of 19 SAs and 21 ILs). Among the investigated models, ANFIS offered the best accuracy with an average absolute relative deviation (AARD%) of 7.43% and a coefficient of determination (R²) of 0.98359. The best performance of the ANFIS model was obtained with a cluster center radius of 0.435 when trained with 85% of the databank. Further analyses of the ANFIS model based on the leverage method revealed that this model is reliable enough due to its high level of coverage and wide range of applicability. Accordingly, this model can be effectively utilized in modeling the solubilities of SAs in ILs.

Preparation and characterization of cellulose nanocrystals from corncob via ionic liquid [Bmim][HSO4] hydrolysis: effects of major process conditions on dimensions of the product

In this study, cellulose nanocrystals were prepared via the hydrolysis of corncob (CC) biomass using Brønsted acid ionic liquid 1-butyl-3-methylimidazolium hydrogen sulfate [Bmim][HSO₄]. The corncob was subjected to alkaline pretreatment, and was then hydrolysed by [Bmim][HSO₄], which acted as both solvent and catalyst. The effects of process conditions, including mass percent of CC (1.0-10.0%), reaction temperature (46-110 °C), and reaction time (1.2-2.8 h) on the size of cellulose nanocrystals (IL-CCCNC) were investigated by response surface methodology-central composite design. The obtained IL-CCCNC was characterized by Fourier transforms infrared spectroscopy, zeta sizer, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and thermogravimetry. The results showed that the dimensions of the nanocellulose products were affected by the mass percent of CC and the reaction temperature, but were not significantly influenced by the reaction time under the studied conditions. The optimal conditions, estimated by the developed model, were a mass percent of 2.49%, reaction temperature of 100 °C, and reaction time of 1.5 h. The process successfully produced IL-CCCNC with a yield of 40.13%, average size of 166 nm, and crystallinity index (CrI) of 62.5%. The morphology, chemical fingerprints, and thermal properties of the obtained IL-CCCNC were comparable to those extracted by alkaline and acid hydrolysis. After the reaction, [Bmim][HSO₄] could be recovered with a yield of 88.32%, making it a viable green catalyst for the hydrolysis of CC cellulose. The findings are of direct industrial relevance as optimal processes can be developed to produce nanocellulose crystals with desirable size and physicochemical characteristics.

Ionic Liquid-Assisted Selective Extraction and Partitioning of Biomolecules from Macroalgae

Macroalgae are a promising feedstock for several industries due to their large content of proteins and carbohydrates and the high biomass productivities. A novel extraction and fractionation concept based on ionic liquids (ILs) using Ulva lactuca as model organism is presented. Biomolecules are first extracted by means of IL-assisted mechanical shear, followed by two-phase partitioning or ultrafiltration in order to fractionate proteins and carbohydrates and to recover the IL. Ethyl methyl imidazolium dibutyl phosphate ([Emim][DBP]) is strongly selective to proteins, leading to extraction yields up to 80.4% for proteins and 30.7% for carbohydrates. The complete process, including extraction and ultrafiltration, allowed protein recovery of up to 64.6 and 15.4% of the carbohydrates in the retentate phase, while a maximum of 85.7% of the IL was recovered in the permeate phase. The native structure of the extracted proteins was preserved during extraction and fractionation as shown by gel electrophoresis. Selective extraction of proteins from macroalgae under non-denaturing conditions using ILs followed by the recovery of IL using ultrafiltration is for the first time reported. The proposed extraction-fractionation approach is simple and can be potentially applied for the biorefinery of macroalgae at the commercial scale.

Closing the Nutrient Loop-The New Approaches to Recovering Biomass Minerals during the Biorefinery Processes

The recovery of plant mineral nutrients from the bio-based value chains is essential for a sustainable, circular bioeconomy, wherein resources are (re)used sustainably. The widest used approach is to recover plant nutrients on the last stage of biomass utilization processes-e.g., from ash, wastewater, or anaerobic digestate. The best approach is to recover mineral nutrients from the initial stages of biomass biorefinery, especially during biomass pre-treatments. Our paper aims to evaluate the nutrient recovery solutions from a trans-sectorial perspective, including biomass processing and the agricultural use of recovered nutrients. Several solutions integrated with the biomass pre-treatment stage, such as leaching/bioleaching, recovery from pre-treatment neoteric solvents, ionic liquids (ILs), and deep eutectic solvents (DESs) or integrated with hydrothermal treatments are discussed. Reducing mineral contents on silicon, phosphorus, and nitrogen biomass before the core biorefinery processes improves processability and yield and reduces corrosion and fouling effects. The recovered minerals are used as bio-based fertilizers or as silica-based plant biostimulants, with economic and environmental benefits.

Effect of autohydrolysis and ionosolv treatments on eucalyptus fractionation and recovered lignin properties†

Wood fractionation is key for the integral valorization of its three main components. In this sense, recovering the hemicellulosic fraction after the ionosolv treatment of lignocellulosic materials is one of the main drawbacks of this process. Thus, the incorporation of a previous autohydrolyisis step to recover the hemicellulosic sugars before the ionosolv treatment is an interesting approach. The influence of both treatments, autohydrolysis and ionosolv, on the biomass fractions recovery yields was studied by a central composite design of experiments, varying the autohydrolysis temperature in a 175–195 °C range and ionosolv time between 1–5 h. Lignin recovery and cellulose purity were maximized at 184 °C and 3.5 h of autohydrolysis temperature and ionosolv time, respectively. In addition, lignin properties were incorporated to the statistical model, revealing lignin recondensation at severe conditions and a higher influence of the ionosolv treatment on lignin characteristics. These results remarked the importance of studying the effect of both treatments in the whole fractionation process and not each process separately and enhanced the understanding of the treatments combination in a complete fractionation biorefinery approach.

This work enhances the understanding of the effect of autohydrolysis and ionosolv treatments combination on fractionation yields and lignin properties.

Processing of Biomass Prior to Hydrogen Fermentation and Post-Fermentative Broth Management

Using bioconversion and simultaneous value-added product generation requires purification of the gaseous and the liquid streams before, during, and after the bioconversion process. The effect of diversified process parameters on the efficiency of biohydrogen generation via biological processes is a broad object of research. Biomass-based raw materials are often applied in investigations regarding biohydrogen generation using dark fermentation and photo fermentation microorganisms. The literature lacks information regarding model mixtures of lignocellulose and starch-based biomass, while the research is carried out based on a single type of raw material. The utilization of lignocellulosic and starch biomasses as the substrates for bioconversion processes requires the decomposition of lignocellulosic polymers into hexoses and pentoses. Among the components of lignocelluloses, mainly lignin is responsible for biomass recalcitrance. The natural carbohydrate-lignin shields must be disrupted to enable lignin removal before biomass hydrolysis and fermentation. The matrix of chemical compounds resulting from this kind of pretreatment may significantly affect the efficiency of biotransformation processes. Therefore, the actual state of knowledge on the factors affecting the culture of dark fermentation and photo fermentation microorganisms and their adaptation to fermentation of hydrolysates obtained from biomass requires to be monitored and a state of the art regarding this topic shall become a contribution to the field of bioconversion processes and the management of liquid streams after fermentation. The future research direction should be recognized as striving to simplification of the procedure, applying the assumptions of the circular economy and the responsible generation of liquid and gas streams that can be used and purified without large energy expenditure. The optimization of pre-treatment steps is crucial for the latter stages of the procedure.

Rice straw structure changes following green pretreatment with petha wastewater for economically viable bioethanol production

Energy efficient and environment friendly pretreatment processes for the production of biofuel have remained elusive and the research is further compounded by the high cost of processing lignocellulosic biomass-an essential factor for producing sustainable biofuels. In the last few decades, a number of pretreatment methods have been proposed, specifically chemical pretreatments but are either expensive or harmful to the environment. To address this urgent need, we propose a green pretreatment method that utilises the highly alkaline by-product, petha wastewater to pretreat the lignocellulosic waste rice straw (RS). The effectiveness of the pretreatment was analysed by monitoring both enhanced cellulose content and reducing sugar yield along with removal of hemicellulose and lignin. We found that PWW pretreatment yielded five times more reducing sugar than native RS with 10.12% increment in cellulose content. SEM and EDX studies further revealed that our process enhanced surface roughness and carbon content (from 32.19% increased to 41.59% and 41.66% for A and D, respectively) along with reduction in silica content (from 8.68% in RS to 4.30% and 7.72% for A and D, respectively). XRD and FTIR analyses indicate crystallinity index (CI) and alteration in lignocellulosic structure of RS, respectively. Decrease in CI was about 43.4% in A whereas only 4.5% in D as compared to native RS (CI 54.55%). Thereby we found PWW to be better substitute of an alkali for pretreatment of RS with negligible environmental impacts.

Upcycling agro-industrial blueberry waste into platform chemicals and structured materials for application in marine environments

Blueberry pruning waste (BPw), sourced as residues from agroforestry operations in Chile, was used to produce added-value products, including platform chemicals and materials. BPw fractionation was implemented using biobased solvents (γ-valerolactone, GVL) and pyrolysis (500 °C), yielding solid fractions that are rich in phenols and antioxidants. The liquid fraction was found to be enriched in sugars, acids, and amides. Alongside, filaments and 3D-printed meshes were produced via wet spinning and Direct-Ink-Writing (DIW), respectively. For the latter purpose, BPw was dissolved in an ionic liquid, 1-ethyl-3-methylimidazolium acetate ([emim][OAc]), and regenerated into lignocellulose filaments with highly aligned nanofibrils (wide-angle X-ray scattering) that simultaneously showed extensibility (wet strain as high as 39%). BPw-derived lignocellulose filaments showed a tenacity (up to 2.3 cN dtex^-1) that is comparable to that of rayon fibers and showed low light reflectance (R _ES factor <3%). Meanwhile, DIW of the respective gels led to meshes with up to 60% wet stretchability. The LCF and meshes were demonstrated to have reliable performance in marine environments. As a demonstration, we show the prospects of replacing plastic cords and other materials used to restore coral reefs on the coast of Mexico.

Green mechano-chemical processing of lignocellulosic biomass for lignin recovery

Lignin extraction from biomass is heavily dependent on chemical processes that are harmful to the environment and the quality of the recovered lignin. Ionic liquid solvents are some of the latest solutions in green processing; however, their implementation for lignin recovery is limited by their high cost, typically high loadings requirements, and long processing times. To overcome these issues, in this study, high loadings of mixed hardwood flour (MHF) were processed with 1-butyl-3-methylimidazolium chloride (BmimCl) in a batch mixer. The rheological behaviour of the biomass and ionic liquid mixture was studied. The mixture had a high complex viscosity (approx. 10⁷ Pa s) at low shear rates and displayed pronounced shear thinning behavior at 50 wt% MHF loading. A 2² factorial design was also implemented to study the effects of MHF solid loading amount and residence time on lignin extraction yield. A maximum yield of 36.6% was obtained at the maximum solid loading amount and residence time (50 wt% and 45 min, respectively). The extracted lignin samples were also characterized in comparison with commercial Kraft lignin and lignosulfonate. The novelty of this study is the successful lignin extraction at high solid loadings and shorter residence times compared to previous biomass pre-treatments with ionic liquids that employs low solid loading and long processing times.

Ethanolysis of selected catalysis by functionalized acidic ionic liquids: an unexpected effect of ILs structural functionalization on selectivity phenomena

Functionalization of acidic imidazolium ILs (addition of OH groups, deactivation of C2–H proton) changes the selectivity of the carbohydrate ethanolysis reaction.

Organosolv and ionosolv processes for autohydrolyzed poplar fractionation: Lignin recovery and characterization

Biomass fractionation plays a major role in the search for competitive biorefineries, where the isolation and recovery of the three woody fractions is key. In this sense, we have used autohydrolyzed hemicellulose-free poplar as feedstock to compare two fractionation processes, organosolv and ionosolv, oriented to lignin recovery. The recovered lignins were then characterize by different techniques (NMR, GPC, TGA). Both treatments were tested at different temperatures to analyze temperature influence on lignin recovery and properties. The highest lignin recovery was obtained with the ionosolv process at 135 °C, reaching a solid yield of ~70%. Lignin characterization showed differences between both treatments. Lignins enriched in C-O linkages and G units were recovered with the organosolv process, where increasing temperature led to highly depolymerized lignins. However, lignins with higher C-C linkages and S units contents were obtained with the ionosolv process, producing more thermically stable lignins. In addition, increasing temperature caused lignin repolymerization when employing ionic liquids as solvents. Therefore, this work outlines the most important differences between ionosolv and organosolv processes for biomass fractionation, focusing on lignin recovery and its properties, which is the first step in order to valorize all biomass fractions.

Bioinspired Cellulase-Mimetic Solid Acid Catalysts for Cellulose Hydrolysis

Glucose produced by catalytic hydrolysis of cellulose is an important platform molecule for producing a variety of potential biobased fuels and chemicals. Catalysts such as mineral acids and enzymes have been intensively studied for cellulose hydrolysis. However, mineral acids show serious limitations concerning equipment corrosion, wastewater treatment and recyclability while enzymes have the issues such as high cost and thermal stability. Alternatively, solid acid catalysts are receiving increasing attention due to their high potential to overcome the limitations caused by conventional mineral acid catalysts but the slow mass transfer between the solid acid catalysts and cellulose as well as the absence of ideal binding sites on the surface of the solid acid catalysts are the key barriers to efficient cellulose hydrolysis. To bridge the gap, bio-inspired or bio-mimetic solid acid catalysts bearing both catalytic and binding sites are considered futuristic materials that possess added advantages over conventional solid catalysts, given their better substrate adsorption, high-temperature stability and easy recyclability. In this review, cellulase-mimetic solid acid catalysts featuring intrinsic structural characteristics such as binding and catalytic domains of cellulase are reviewed. The mechanism of cellulase-catalyzed cellulose hydrolysis, design of cellulase-mimetic catalysts, and the issues related to these cellulase-mimetic catalysts are critically discussed. Some potential research directions for designing more efficient catalysts for cellulose hydrolysis are proposed. We expect that this review can provide insights into the design and preparation of efficient bioinspired cellulase-mimetic catalysts for cellulose hydrolysis.

Integrated strategies for enzyme assisted extraction of bioactive molecules: A review

Conventional methods of extracting bioactive molecules are gradually losing pace due to their numerous disadvantages, such as product degradation, lower efficiency, and toxicity. Thus, in light of the rising demand for these bioactive, enzymes have garnered much attention for their efficiency in extraction. However, enzyme-assisted extraction is also plagued with a high capital cost that cannot justify the extraction yields obtained. In order to mitigate these problems, enzyme-assisted extraction can be consorted with non-conventional methods. This review includes current progress concerning the combined approaches while converging the recent advancements in the field that outperformed conventional extraction processes. It also highlights the design of biocatalyst and key parameters involved in the effective extraction of bioactive molecules. An integrated approach for efficiently extracting polyphenols, essential oils, pigments, and vitamins has been comprehensively reviewed. Furthermore, the different immobilization strategies have been discussed for large-scale implementation of enzymes for extraction. The integration of advanced non-conventional methods with enzyme-assisted extraction will open new avenues to enhance the overall extraction efficiency.

Biomass delignification with green solvents towards lignin valorisation: ionic liquids vs deep eutectic solvents

The use of renewable resources as feedstocks to ensure the production of goods and commodities for society has been explored in the last decades to switch off the overexploited and pollutant fossil-based economy. Today there is a strong movement to set bioeconomy as priority, but there are still challenges and technical limitations that must be overcome in the first place, particularly on biomass fractionation. For biomass to be an appellative raw material, an efficient and sustainable separation of its major components must be achieved. On the other hand, the technology development for biomass valorisation must follow green chemistry practices towards eco-friendly processes, otherwise no environmental leverage over traditional petrochemical technologies will be acquired. In this context, the application of green solvents, such as ionic liquids (ILs) and deep eutectic solvents (DES), in biomass fractionation is envisaged as promising technology that encompasses not only efficiency and environmental benefits, but also selectivity, which is a crucial demand to undertake cascade processes at biorefinery level. In particular, this article briefly discusses the disruptive achievements upon the application of ILs and DES in biomass delignification step towards an effective and selective separation of lignin from polysaccharides. The different physicochemical properties of these solvents, their interactions with lignin and their delignification capacity will be scrutinized, while some highlights will be given to the important characteristics of isolated lignin fractions for further valorisation. The advantages and disadvantages between ILs and DES in biomass delignification will be contrasted as well along the article.

The Dual Effect of Ionic Liquid Pretreatment on the Eucalyptus Kraft Pulp during Oxygen Delignification Process

Oxygen delignification presents high efficiency but causes damage to cellulose, therefore leading to an undesired loss in pulp strength. The effect of ionic liquid pretreatment of [BMIM][HSO₄] and [TEA][HSO₄] on oxygen delignification of the eucalyptus kraft pulp was investigated at 10% IL loading and 10% pulp consistency, after which composition analysis, pulp and fiber characterizations, and the mechanism of lignin degradation were carried out. A possible dual effect of enhancing delignification and protecting fibers from oxidation damage occurred simultaneously. The proposed [TEA][HSO₄] pretreatment facilitated lignin removal in oxygen delignification and provided fibers with improved DP, fiber length and width, and curl index, resulting in the enhanced physical strength of pulp. Particularly, its folding endurance improved by 110%. An unusual brightness reduction was identified, followed by detailed characterization on the pulps and extracted lignin with FTIR, UV, XPS, and HSQC. It was proposed that [TEA][HSO₄] catalyzed the cleavage of β-O-4 bonds in lignin during the oxygen delignification, with the formation of Hibbert’s ketones and quinonoid compounds. The decomposed lignin dissolved and migrated to the fiber surface, where they facilitated the access of the oxidation agent and protected the fiber framework from oxidation damage. Therefore, it was concluded that ionic liquid pretreatment has a dual effect on oxygen delignification.

Ionic liquids in the pretreatment of lignocellulosic biomass

The pretreatment is a key step in the processing of lignocellulosic biomass for its transformation into chemicals and materials of biorenewable origin. Ionic liquids, with their characteristic set of unique properties, have the potential to be the basis of novel pretreatment processes with higher effectiveness and improved sustainability as compared to the current state-of-the-art processes. In this opinion paper, the author provides a perspective on possible processing strategies for this pretreatment with ionic liquids, identifying different advantages as well as challenges to be overcome.

The Role of Ionic Liquids in the Lignin Separation from Lignocellulosic Biomass

Lignin is a natural polymer, one that has an abundant and renewable resource in biomass. Due to a tendency towards the use of biochemicals, the efficient utilization of lignin has gained wide attention. The delignification of lignocellulosic biomass makes its fractions (cellulose, hemicellulose, and lignin) susceptible to easier transformation to many different commodities like energy, chemicals, and materials that could be produced using the biorefinery concept. This review gives an overview of the field of lignin separation from lignocellulosic biomass and changes that occur in the biomass during this process, as well as taking a detailed look at the influence of parameters that lead the process of dissolution. According to recent studies, a number of ionic liquids (ILs) have shown a level of potential for industrial scale production in terms of the pretreatment of biomass. ILs are perspective green solvents for pretreatment of lignocellulosic biomass. These properties in ILs enable one to disrupt the complex structure of lignocellulose. In addition, the physicochemical properties of aprotic and protic ionic liquids (PILs) are summarized, with those properties making them suitable solvents for lignocellulose pretreatment which, especially, target lignin. The aim of the paper is to focus on the separation of lignin from lignocellulosic biomass, by keeping all components susceptible for biorefinery processes. The discussion includes interaction mechanisms between lignocellulosic biomass subcomponents and ILs to increase the lignin yield. According to our research, certain PILs have potential for the cost reduction of LC biomass pretreatment on the feasible separation of lignin.

A review of sustainable lignocellulose biorefining applying (natural) deep eutectic solvents (DESs) for separations, catalysis and enzymatic biotransformation processes

Conventional biorefinery processes are complex, engineered and energy-intensive, where biomass fractionation, a key functional step for the production of biomass-derived chemical substances, demands industrial organic solvents and harsh, environmentally harmful reaction conditions. There is a timely, clear and unmet economic need for a systematic, robust and affordable conversion method technology to become greener, sustainable and cost-effective. In this perspective, deep eutectic solvents (DESs) have been envisaged as the most advanced novel polar liquids that are entirely made of natural, molecular compounds that are capable of an association via hydrogen bonding interactions. DES has quickly emerged in various application functions thanks to a formulations’ simple preparation. These molecules themselves are biobased, renewable, biodegradable and eco-friendly. The present experimental review is providing the state of the art topical overview of trends regarding the employment of DESs in investigated biorefinery-related techniques. This review covers DESs for lignocellulosic component isolation, applications as (co)catalysts and their functionality range in biocatalysis. Furthermore, a special section of the DESs recyclability is included. For DESs to unlock numerous new (reactive) possibilities in future biorefineries, the critical estimation of its complexity in the reaction, separation, or fractionation medium should be addressed more in future studies.

Use of Ionic Liquids and Deep Eutectic Solvents in Polysaccharides Dissolution and Extraction Processes towards Sustainable Biomass Valorization

A shift to a bioeconomy development model has been evolving, conducting the scientific community to investigate new ways of producing chemicals, materials and fuels from renewable resources, i.e., biomass. Specifically, technologies that provide high performance and maximal use of biomass feedstocks into commodities with reduced environmental impact have been highly pursued. A key example comprises the extraction and/or dissolution of polysaccharides, one of the most abundant fractions of biomass, which still need to be improved regarding these processes' efficiency and selectivity parameters. In this context, the use of alternative solvents and the application of less energy-intensive processes in the extraction of polysaccharides might play an important role to reach higher efficiency and sustainability in biomass valorization. This review debates the latest achievements in sustainable processes for the extraction of polysaccharides from a myriad of biomass resources, including lignocellulosic materials and food residues. Particularly, the ability of ionic liquids (ILs) and deep eutectic solvents (DESs) to dissolve and extract the most abundant polysaccharides from natural sources, namely cellulose, chitin, starch, hemicelluloses and pectins, is scrutinized and the efficiencies between solvents are compared. The interaction mechanisms between solvent and polysaccharide are described, paving the way for the design of selective extraction processes. A detailed discussion of the work developed for each polysaccharide as well as the innovation degree and the development stage of dissolution and extraction technologies is presented. Their advantages and disadvantages are also identified, and possible synergies by integrating microwave- and ultrasound-assisted extraction (MAE and UAE) or a combination of both (UMAE) are briefly described. Overall, this review provides key information towards the design of more efficient, selective and sustainable extraction and dissolution processes of polysaccharides from biomass.

On the Effect of Hot-Water Pretreatment in Sulfur-Free Pulping of Aspen and Wheat Straw

In modern biorefineries, low value lignin and hemicellulose fractions are produced as side streams. New extraction methods for their purification are needed in order to utilize the whole biomass more efficiently and to produce special target products. In several new applications using plant-based biomaterials, the native-type chemical and polymeric properties are desired. Especially, production of high-quality native-type lignin enables valorization of biomass entirely, thus making novel processes sustainable and economically viable. To investigate sulfur-free possibilities for so-called "lignin first" technologies, we compared alkaline organosolv, formic acid organosolv, and ionic liquid processes to simple soda "cooking" using wheat straw and aspen as raw materials. All experiments were carried out using microwave-assisted pulping approach to enable rapid heat transfer and convenient control of temperature and pressure. The main target was to evaluate the advantage of a brief hot water extraction as a pretreatment for the pulping process. Most of these novel pulping methods resulted in high-quality lignin, which may be valorized more diversely than kraft lignin. Lignin fractions were thoroughly analyzed with NMR (¹³C and HSQC) and gel permeation chromatography to study the quality of the collected lignin. The cellulose fractions were analyzed by determining their lignin contents and carbohydrate profiles for further utilization in cellulose-based products or biofuels.

Wheat Bran Pretreatment by Room Temperature Ionic Liquid-Water Mixture: Optimization of Process Conditions by PLS-Surface Response Design

Room Temperature Ionic Liquids (RTILs) pretreatment are well-recognized to improve the enzymatic production of platform molecules such as sugar monomers from lignocellulosic biomass (LCB). The conditions for implementing this key step requires henceforth optimization to reach a satisfactory compromise between energy saving, required RTIL amount and hydrolysis yields. Wheat bran (WB) and destarched wheat bran (DWB), which constitute relevant sugar-rich feedstocks were selected for this present study. Pretreatments of these two distinct biomasses with various 1-ethyl-3-methylimidazolium acetate ([C2mim][OAc])-water mixtures prior to hydrolysis catalyzed by hemicellulolytic cocktail (Cellic CTec2) were finely investigated. The main operating conditions such as pretreatment temperature (25–150°C), time (40–180 min), WB and DWB loading (2–5% w/v) and concentration of [C2mim][OAc] in water [10–100% (v/v)] were screened through glucose and xylose yields and then optimized through a Partial Least Square (PLS)—Second Order Design. In an innovative way, the PLS results showed that the four factors and their interactions could be well-fitted by a second-order model (p < 0.05). The quadratic PLS models were used to predict optimal pretreatment conditions. Thus, maximum glucose (83%) and xylose (95%) yields were obtained from enzymatic hydrolysis of WB pretreated at 150°C for 40 min with 10% of [C2mim][OAc] in water and 5% of WB loading. For DWB, maximum glucose (100%) and xylose (57%) yields were achieved for pretreatment temperatures of 150°C and 25°C, respectively. The required duration was still 40 min, with 20% of [C2mim][OAc] in water and a 5% DWB loading. Then, Multiple Response Optimization (MRO) performed by Nelder-Mead Simplex Method displayed sugar yields similar to those obtained by individual PLS optimization. This complete statistical study confirmed that the established models were appropriate to predict the sugar yields achieved after different pretreatment conditions from WB and DWB biomasses. Finally, Scanning Electron microscopy (SEM) studies allowed us to establish clearer link between structural changes induced by pretreatment and the best enzymatic performances obtained.

Dissolution and Hydrolysis of Bleached Kraft Pulp Using Ionic Liquids

Forestry industries in Chile are facing an important challenge-diversifying their products using green technologies. In this study, the potential use of Ionic Liquids (ILs) to dissolve and hydrolyze eucalyptus wood (mix of Eucalyptus nitens and Eucalyptus globulus) kraft pulp was studied. The Bleached Hardwood Kraft Pulp (BHKP) from a Chilean pulp mill was used together with five different ILs: 1-butyl-3-methylimidazolium chloride [bmim][Cl], 1-butyl-3-methylimidazolium acetate [bmim][Ac], 1-butyl-3-methylimidazolium hydrogen sulfate [bmim][HSO4], 1-ethyl-3-methylimidazolium chloride [emim][Cl], 1-ethyl-3-methylimidazolium acetate [emim][Ac]. Experimentally, one vacuum reactor was designed to study the dissolution/hydrolysis process for each ILs; particularly, the cellulose dissolution process using [bmim][Cl] was studied proposing one molecular dynamic model. Experimental characterization using Atomic Force Microscopy, conductometric titration, among other techniques suggest that all ILs are capable of cellulose dissolution at different levels; in some cases, the dissolution evolved to partial hydrolysis appearing cellulose nanocrystals (CNC) in the form of spherical aggregates with a diameter of 40-120 nm. Molecular dynamics simulations showed that the [bmim][Cl] anions tend to interact actively with cellulose sites and water molecules in the dissolution process. The results showed the potential of some ILs to dissolve/hydrolyze the cellulose from Chilean Eucalyptus, maintaining reactive forms.

Synthesis of novel functional ionic liquids and their application in biomass

A series of dicationic ionic liquids (ILs) including [PF₆][(PYR)C₄(MIM)][Cl], [PF₆][(PYR)C₄(PYR)][Cl], [PF₆][(PYR)C₅(MIM)][Cl], and [PF₆][(PYR)C₅(PYR)][Cl], and monocationic ILs including [(PYR)C₄Cl][PF₆], [(PYR)C₅Cl][PF₆], [(MIM)C₂COOH][PF₆] and [(PYR)C₂COOH][PF₆] were synthesized. Their thermal stability and melting points were determined. Their solubility with organic solvents and the miscibility with water were investigated. These functional ILs are hydrophilic at high temperatures and they are hydrophobic at low temperatures, which enable the effective isolation of the resulting reducing sugar. High yields of reducing sugar were obtained for corn stalk after 8 h (20.73%) and potato starch after 6 h (72.50%) by the treatment with the mixture of [PF₆][(PYR)C₄(PYR)][Cl] and [(PYR)C₂COOH][PF₆]. The reuse of dicationic and monocationic ILs was successfully performed and no significant reduction in yields of reducing sugar was observed. These functional ILs have important implications in the design of homogeneous and heterogeneous systems with water and organic solvents, which could be used to satisfy some specific applications.

A series of dicationic and monocationic ionic liquids (ILs) were synthesized and investigated and it was found that these functional ILs have important implications in the design of homogeneous and heterogeneous systems.

Conversion of Symphytum officinale and Panicum virgatum plant extracts to 5-hydroxymethylfurfural catalysed by metal chlorides in ionic liquids

The present work examined the potential for two plants grown on Canadian soil, Symphytum officinale L. (common comfrey) and Panicum virgatum L. (switchgrass), to produce 5-hydroxymethylfurfural using metal chloride catalysis in two ionic liquids, 1-butyl-3-methylimidazolium chloride or 1-ethyl-3-methylimidazolium chloride. Furthermore, two pre-treatments, namely the dilute sulfuric acid treatment and the methanol extraction, were studied as a way to improve sugar availability and increase 5-hydroxymethylfurfural yields compared with untreated biomass. The 0.5 mol/L H2SO4 hydrolysis under autoclave conditions produced sugar-rich extracts containing 230 ± 23 mg of sugars per gram of hydrolysed biomass for comfrey and 425 ± 13 mg of sugars per gram of hydrolysed biomass for switchgrass. The methanol extraction produced extracts high in simple sugars with concentration of 300 ± 60 mg of sugars per gram of dry extract for comfrey and 202 ± 16 mg of sugars per gram of dry extract for switchgrass. The yield of 5-hydroxymethylfurfural was improved from less than 1% using untreated biomass to 6.04% and 18.0% using dry methanol extracts of comfrey and switchgrass, respectively. These yields, although small, are important, as they show for the first time that a methanol extract could enhance the metal chloride catalysis in ionic liquids for 5-hydroxymethylfurfural production from biomass.

Microwave-assisted ionic liquid-mediated rapid catalytic conversion of non-edible lignocellulosic Sunn hemp fibres to biofuels

Sunn hemp fibre - a cellulose-rich crystalline non-food energy crop, containing 75.6% cellulose, 10.05% hemicellulose, 10.32% lignin, with high crystallinity (80.17%) and degree of polymerization (650) - is identified as a new non-food substrate for lignocellulosic biofuel production. Microwave irradiation is employed to rapidly rupture the cellulose's glycosidic bonds and enhance glucose yield to 78.7% at 160 °C in only 46 min. The reactants - long-chain cellulose, ionic liquid, transition metal catalyst, and water - form a polar supramolecular complex that rotates under the microwave's alternating polarity and rapidly dissipates the electromagnetic energy through molecular collisions, thus accelerating glycosidic bond breakage. In 46 min, 1 kg of Sunn hemp fibres containing 756 g of cellulose produces 595 g of glucose at 160 °C, and 203 g of hydroxymethyl furfural (furanic biofuel precursor) at 180 °C. Yeast mediated glucose fermentation produces 75.6% bioethanol yield at 30 °C, and the ionic liquid is recycled for cost-effectiveness.

Deep Eutectic Solvent Aqueous Solutions as Efficient Media for the Solubilization of Hardwood Xylans

This work contributes to the development of integrated lignocellulosic-based biorefineries by the pioneering exploitation of hardwood xylans by solubilization and extraction in deep eutectic solvents (DES). DES formed by choline chloride and urea or acetic acid were initially evaluated as solvents for commercial xylan as a model compound. The effects of temperature, molar ratio, and concentration of the DES aqueous solutions were evaluated and optimized by using a response surface methodology. The results obtained demonstrated the potential of these solvents, with 328.23 g L^-1 of xylan solubilization using 66.7 wt % DES in water at 80 °C. Furthermore, xylans could be recovered by precipitation from the DES aqueous media in yields above 90 %. The detailed characterization of the xylans recovered after solubilization in aqueous DES demonstrated that 4-O-methyl groups were eliminated from the 4-O-methylglucuronic acids moieties and uronic acids (15 %) were cleaved from the xylan backbone during this process. The similar M_w values of both pristine and recovered xylans confirmed the success of the reported procedure. DES recovery in four additional extraction cycles was also demonstrated. Finally, the successful extraction of xylans from Eucalyptus globulus wood by using aqueous solutions of DES was demonstrated.

Synthesis, characterization and cellulose dissolution capabilities of ammonium-based room temperature ionic liquids (RTILs)

Green synthesis of room temperature ionic liquids (RTILs), are presented as friendly and challenging solvents for the effective dissolution of oil palm-lignocellulosic biomass. A series of Bronsted acidic-ionic liquids were prepared by the direct neutralization of diethyl dimethyl ammonium hydroxide with several (economical and environmental friendly) Bronsted acids as RTILs. The structural and physicochemical characterization was performed by applying various techniques as Fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), zeta-nanosizer and dynamic light scattering (DLS) respectively, to state the effect of anion on the extended cellulose dissolution capabilities of the synthesized RTILs under mild conditions. As a polysaccharide solvent, diethyl dimethyl ammonium phosphate (A1P) showed the extreme capability to extract 65 % of cellulose from biomass without any pretreatment for 30 min. The present study could be a significant step toward the synthesis of efficient RTILs and generating upgraded cellulose for Hi-tech engineered composites and energy concerns.

Cooking with Active Oxygen and Solid Alkali: A Promising Alternative Approach for Lignocellulosic Biorefineries

Lignocellulosic biomass, a matrix of biopolymers including cellulose, hemicellulose, and lignin, has gathered increasing attention in recent years for the production of chemicals, fuels, and materials through biorefinery processes owing to its renewability and availability. The fractionation of lignocellulose is considered to be the fundamental step to establish an economical and sustainable lignocellulosic biorefinery. In this Minireview, we summarize a newly developed oxygen delignification for lignocellulose fractionation called cooking with active oxygen and solid alkali (CAOSA), which can fractionate lignocellulose into its constituents and maintain its processable form. In the CAOSA approach, environmentally friendly chemicals are applied instead of undesirable chemicals such as strong alkalis and sulfides. Notably, the alkali recovery for this process promises to be relatively simple and does not require causticizing or sintering. These features make the CAOSA process an alternative for both lignocellulose fractionation and biomass pretreatment. The advantages and challenges of CAOSA are also discussed to provide a comprehensive perspective with respect to existing strategies.

Parametric study for the optimization of ionic liquid pretreatment of corn stover

A parametric study of the efficacy of the ionic liquid (IL) pretreatment (PT) of corn stover (CS) using 1-ethyl-3-methylimidazolium acetate ([C₂C₁Im][OAc]) and cholinium lysinate ([Ch][Lys]) was conducted. The impact of 50% and 15% biomass loading for milled and non-milled CS on IL-PT was evaluated, as well the impact of 20 and 5mg enzyme/g glucan on saccharification efficiency. The glucose and xylose released were generated from 32 conditions - 2 ionic liquids (ILs), 2 temperatures, 2 particle sizes (S), 2 solid loadings, and 2 enzyme loadings. Statistical analysis indicates that sugar yields were correlated with lignin and xylan removal and depends on the factors, where S did not explain variation in sugar yields. Both ILs were effective in pretreating large particle sized CS, without compromising sugar yields. The knowledge from material and energy balances is an essential step in directing optimization of sugar recovery at desirable process conditions.

Pretreatment of Lignocellulosic Biomass with Ionic Liquids and Ionic Liquid-Based Solvent Systems

Pretreatment is very important for the efficient production of value-added products from lignocellulosic biomass. However, traditional pretreatment methods have several disadvantages, including low efficiency and high pollution. This article gives an overview on the applications of ionic liquids (ILs) and IL-based solvent systems in the pretreatment of lignocellulosic biomass. It is divided into three parts: the first deals with the dissolution of biomass in ILs and IL-based solvent systems; the second focuses on the fractionation of biomass using ILs and IL-based solvent systems as solvents; the third emphasizes the enzymatic saccharification of biomass after pretreatment with ILs and IL-based solvent systems.

An ionic liquid treatment and fractionation of cellulose, hemicellulose and lignin from oil palm empty fruit bunch

This work reports on a complete isolation and characterization of lignocellulosic compounds from oil palm empty fruit bunch (OPEFB) by ionic liquid (IL) treatment and alkaline treatment processes. The fractionated lignocellulosic compounds were confirmed by FTIR and CP/MAS ¹³CNMR analyses. The yield of the cellulose, hemicellulose and lignin fractions was 52.72±1.50% wt., 27.17±1.68% wt. and 16.82±1.15% wt. with molecular weight of 1869g/mol, 1736g/mol and 2695g/mol, and degradation temperature of 325.65°C, 236.25°C, and 201.40°C, respectively. The SEM image illustrates the bundle-like fiber of cellulose fraction and smaller particle size of hemicellulose and lignin fractions with inconsistent shape. The XRD patterns depict the crystalline cellulose, amorphous lignin and partially amorphous hemicellulose fractions property. The IL could be recovered and reused with an overall recovery of 48% wt. after the fourth cycle.

The distribution and role of nanoclay in lignocellulose–polymer blends

We report nanoclay's role as a sealant for hygroscopic wood particles in hindering water penetration. This sealing attribute of nanoclay is different from its well-established role as a diffusion impeder by torturous paths for the penetrant.