Lignocellulosic biomass delignification using aqueous alcohol solutions with the catalysis of acidic ionic liquids: A comparison study of solvents

A review on the calculation and application of lignin Hansen solubility parameters

Hansen solubility parameters (HSPs) play a critical role in the majority of processes involving lignin depolymerization, separation, fractionation, and polymer blending, which are directly related to dissolution properties. However, the calculation of lignin HSPs is highly complicated due to the diversity of sources and the complexity of lignin structures. Despite their important role, lignin HSPs have been undervalued, attracting insufficient attention. This review summarizes the calculation methods for lignin HSPs and proposes a straightforward method based on lignin subunits. Furthermore, it highlights the crucial applications of lignin HSPs, such as identifying ideal solvents for lignin dissolution, selecting suitable solvents for lignin depolymerization and extraction, designing green solvents for lignin fractionation, and guiding the preparation of lignin-based composites. For instance, leveraging HSPs to design a series of solvents could potentially achieve sequential controllable lignin fractionation, addressing issues of low value-added applications of lignin resulting from poor homogeneity. Notably, HSPs serve as valuable tools for understanding the dissolution behavior of lignin. Consequently, we expect this review to be of great interest to researchers specializing in lignin and other macromolecules.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Bleaching-free, lignin-tolerant, high-yield production of nanocrystalline cellulose from lignocellulosic biomass

Nanocrystalline cellulose (NCC) preparation in an integrated fractionation manner is expected to solve the problems of low yield and environmental impact in the traditional process. An integrated fractionation strategy for NCC production from wood was developed through catalytic biomass fractionation, the partial dissolution of cellulose-rich materials (CRMs) in aqueous tetrabutylphosphonium hydroxide, and short-term ultrasonication. The presented process could tolerate a high CRM lignin content of 21.2 wt % and provide a high NCC yield of 76.6 wt % (34.3 wt % of the original biomass). The increase in the CRM lignin content decreased the NCC yield, facilitated the crystal transition of NCC from cellulose I to cellulose II, and showed no apparent effects on the NCC morphology. A partial/selective dissolution mechanism is proposed for the presented strategy. This study provided a promising efficient fractionation-based method toward comprehensive and high-value utilization of lignocellulosic biomass through effective delignification and high-yield NCC production.

Deep Eutectic Solvents: Alternative Solvents for Biomass-Based Waste Valorization

Innovative technologies can transform what are now considered “waste streams” into feedstocks for a range of products. Indeed, the use of biomass as a source of biopolymers and chemicals currently has a consolidated economic dimension, with well-developed and regulated markets, in which the evaluation of the manufacturing processes relies on specific criteria such as purity and yield, and respects defined regulatory parameters for the process safety. In this context, ionic liquids and deep eutectic solvents have been proposed as environmentally friendly solvents for applications related to biomass waste valorization. This mini-review draws attention to some recent advancements in the use of a series of new-solvent technologies, with an emphasis on deep eutectic solvents (DESs) as key players in the development of new processes for biomass waste valorization. This work aims to highlight the role and importance of DESs in the following three strategic areas: chitin recovery from biomass and isolation of valuable chemicals and biofuels from biomass waste streams.

An insight into the principles of lignocellulosic biomass-based zero-waste biorefineries: a green leap towards imperishable energy-based future

Lignocellulosic biomass (LCB) is an energy source that has a huge impact in today's world. The depletion of fossil fuels, increased pollution, climatic changes, etc. have led the public and private sectors to move towards sustainability i.e. using LCB for the production of biofuels and value-added compounds. A major bottleneck of the process is the recalcitrant nature of LCB. This can be overcome by using various pretreatment strategies like physical, chemical, biological, physicochemical, etc. Further, the pretreated biomass is made to undergo various steps like hydrolysis, saccharification, etc. for the conversion of value-added products and the remaining waste residues can be further utilized for the synthesis of secondary products thus favouring the zero-waste biorefinery concept. Currently, microorganisms are being explored for their use in biorefinery but the unavailability of commercial strains is a major limitation. Thus, the use of metagenomics can be used to overcome the limitation which is both cost-effective and environmentally friendly. The review deliberates the composition of LCBs, and their recalcitrance nature, followed by the structural changes caused by various pretreatment methods. The further steps in biorefineries, strategies for the development of zero-waste refineries, bottlenecks, and suggestions are also discussed. Special emphasis is given to the use of metagenomics for the discovery of microorganisms efficient for zero-waste biorefineries.

Integral valorization of Acacia dealbata wood in organic medium catalyzed by an acidic ionic liquid

In this work, a novel delignification process was proposed for the fractionation of invasive species such as Acacia dealbata wood. Organosolv process catalyzed with an acidic ionic liquid, 1-butyl-3-methylimidazolium hydrosulfate was evaluated to obtain cellulose-enriched solids and liquid fractions rich in hemicelluloses derived compounds and lignin. Under selected operating conditions (190 °C, 60% ethanol, 60 min of reaction time and 0.6 g 1-butyl-3-methylimidazolium hydrosulfate/g wood), high solubilization of lignin and hemicelluloses and cellulose recovery (87.5%, 88.7% and 88.3%, respectively), with a pulp yield of 43.1% were achieved. Moreover, 62.6 % of lignin was recovered by precipitation from the black liquor (composed mainly by 4.43 g xylose/L, 7.66 g furfural/L and 3.59 g acetic acid/L). In addition, enzymatic digestibility of delignified wood was also assayed. Overall, this work presents an alternative biorefinery scheme based in the use of environmentally friendly solvent and catalyst for selective fractionation of A. dealbata wood.

The Role of Ionic Liquids on Biomass Liquefaction—A Short Review of the Recent Advances

Biomass is recognised as one of the most attractive feedstocks among the alternative resources, having a high potential for the sustainable production of valuable chemicals and biofuels. Due to its abundance, convenience, carbon neutrality and eco-friendliness, biomass is believed to positively impact the current environmental crisis caused by the extensive use of petroleum resources. For this reason, the search for processes that can convert this feedstock, resolving some inherent drawbacks, is needed. Biomass liquefaction using ionic liquids (ILs) as catalysts has received appreciable attention in renewable fuels and chemicals production. With the potential for a substantial number of anion and cation pairings, ILs can be an attractive medium towards reusability and sustainability for these processes due to the unique and tunable combinations of their functional groups-and, therefore, their properties. In this review, several studies using ILs in biomass liquefaction are compared and discussed. With a particular emphasis on the last five years, advantages and disadvantages will be discussed using this class of liquids addressing essential issues such as yields, reusability and conversion, among others.

Effects of Heat Treatment on Interfacial Properties of Pinus Massoniana Wood

Understanding the interfacial changes of wood during heat treatment can facilitate the improvement of the bonding and coating processes of heat-treated wood. Steam was used as the medium to modify Pinusmassoniana wood through heat treatment at 160, 180, 200, and 220 °C. Changes to the surface characteristics after heat treatment were characterized by Fourier transform-infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron microscope (SEM) and contact angle measurement. The results showed that: (1) hemicelluloses were the first to experience degradation at 160 °C, and this degradation was the most intense at 200 °C. The cellulose started experiencing obvious degradation at 200 °C, while there was less degradation of lignin at this temperature. (2) Oxygen-containing groups like hydroxyl and carbonyl were gradually reduced as temperature increased with deepened color and passivated surface. (3) Cellulose crystallinity presented a variable trend of increasing–decreasing–increasing. (4) Surface porosity and roughness of Pinus massoniana wood both increased after heat treatment. (5) The Pinus massoniana wood interface turned from hydrophilic to hydrophobic, and 180 °C was a turning point for the wettability of the Pinus massoniana wood interface.

Quantitative recovery and regeneration of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate via industrial strategy for sustainable biomass processing

Quantitative recovery is necessary for scale-up application of acidic ionic liquids (AILs). Ultrafiltration and bipolar membrane electrodialysis (BMED) was employed for the recovery and regeneration of acidic ionic liquid 1-butyl-3-methylimidazolium hydrogen sulphate (Bmim[HSO₄]) after biomass pretreatment. Ultrafiltration was designed for the purification of BMED feed solution. During BMED treatment, Bmim⁺ retention with OH^- generation occurred in mixing section and SO₄^2- immigration with H⁺ generation occurred in aciding section. Resulting aqueous Bmim[OH] in mixing section and H₂SO₄ in aciding section could be utilized for quantitative synthesis of Bmim[HSO₄]. Influence of BMED operating mode and major parameters including BMED feed concentration and current density of BMED module were studied in detail. The highest recovery ratio for Bmim⁺ and SO₄^2- reached 96.2% and 96.0%. And the lowest energy consumption of specific Bmim[HSO₄] recovery approached 9.0 kw∙h/kg. Insight gained from this study suggested a sustainable biomass processing methodology using AILs.

Robust versatile nanocellulose/polyvinyl alcohol/carbon dot hydrogels for biomechanical sensing

A new type of nanocellulose/poly(vinyl alcohol)/carbon dot (NPC) multifunctional hydrogel was successfully fabricated by an one-step in-situ hydrothermal method. The one-pot strategy led to the formation of a complex hydrogen bonding/dynamic boric acid ester/nitrogen-doped carbon dots network, and endowed the hydrogel with multifunctionality. The hydrogel underwent self-healing at room temperature (25 °C) and exhibited double-emission fluorescence and high mechanical strength (tensile strength of up to 2.98 MPa). An NPC hydrogel-based capacitive sensor exhibited remarkable linear capacitance responsiveness toward pressure, strain, and glucose concentration, and enabled real-time synchronous quantitative pressure/glucose sensing with multiple linear correlations, which was a key performance criteria for biomechanical sensors. The versatility and multiple advantages of the as-prepared hydrogel demonstrate the potential of biological-mechanical sensing materials using natural cellulosic biomass.

Evaluating the potential of a novel hardwood biomass using a superbase ionic liquid

Lignocellulosic biomass, being ubiquitous and easily accessible, bears a huge potential for sustainable energy and other products.

Effects of sodium and calcium chloride ionic stresses on model yeast membranes revealed by molecular dynamics simulation

As efforts to move a renewable economy grow, it will be necessary to make use of microbial conversion strategies for the production of novel materials or the upgrading of waste to high-value products. One critical technical challenge currently limiting waste upgrading remains the difficulty in obtaining single-pot conversion techniques where physical, chemical, and biological conversion are performed in a single step. To overcome this challenge, a detailed understanding of how different stresses impact microbial membrane stability will be necessary. Using all-atom molecular dynamics simulations, we examine the impacts of moderate concentrations of NaCl and CaCl₂on a model yeast plasma membrane. Weak, though statistically significant, changes in membrane morphology and dynamics functions are observed that are consistent with swelling and stiffening. Additionally, an examination of the ion-lipid contacts and the behavior of water at the water-membrane interface suggests that the impacts of these common salts may, in part, be mediated through changes to water-membrane hydrogen-bonding and hydration water dynamics.

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.

Ionic liquid based pretreatment of lignocellulosic biomass for enhanced bioconversion

Lignocellulosic biomass is the most plentiful renewable biomolecule and an alternative bioresource for the production of biofuels and biochemicals in biorefineries. But biomass recalcitrance is a bottleneck in their usage, thus necessitating their pretreatment for hydrolysis. Most pretreatment technologies, result in toxic by-products or have lower yield. Ionic liquids (ILs) have successfully advanced as 'greener and recyclable' alternatives to volatile organic solvents for lignocellulosic biomass dissolution. This review covers recent developments made in usage of IL-based techniques with focus on biomass breakdown mechanism, process parameter design, impact of cation and anion groups, and the advantageous impact of ILs on the subsequent processing of the fractionated biomass. Progress and barriers for large-scale commercial usage of ILs in emerging biorefineries were critically evaluated using the principles of economies of scale and green chemistry in an environmentally sustainable way.

Sustainability metrics of pretreatment processes in a waste derived lignocellulosic biomass biorefinery

Excessive utilization of fossil fuels has resulted in serious concerns about climate change. Integrating biorefinery technology to convert waste-derived-lignocellulosic biomass into biofuels and biopolymers has become an emerging topic toward our sustainable future. Pretreatment to fractionate the building block chemicals from the biomass is a crucial unit operation to ease the downstream processes in biorefinery. However, application of solvents and chemicals in the process can create many operational and environmental challenges in sensitive areas like highly populated cities. To shed light on how to determine a green biorefinery, this study presents the sustainability metrics of various pretreatment techniques and their operational risks during urbanization. The proposed green indexes include fractionation outputs, chemical recyclability, operational profile, and safety factors. In line with the design principles of lignin valorization, the issue of urban biomass and water-and-energy nexus are addressed to support future development and application of urban biorefinery for municipal waste management.

Utilization of inorganic salts as adjuvants for ionic liquid-water pretreatment of lignocellulosic biomass: enzymatic hydrolysis and ionic liquid recycle

Pretreatment of lignocellulosic biomass with ionic liquids (ILs) for the large-scale biorefinery remains challenging due to its high price. This study focused on the utilization of inorganic salts as adjuvants for ionic liquid-water pretreatment to improve the tolerance to water and the reusability of the ILs. After the pretreatment of rice straw by the mixture of 40% 1-ethyl-3-methylimidazolium chloride ([C2mim]Cl) + 53% water + 7% K2CO3 at 110 °C for 1 h, the residues became highly susceptible to enzymatic hydrolysis; 93.70% of lignin was removed, and 92.07% sugar yield was achieved. [C2mim]Cl-K2CO3 aqueous biphasic system was formed at room temperature when K2CO3 concentration increased to more than 30%, and the [C2mim]Cl recovery of 94.32% was achieved. The results indicate that the addition of inorganic salts to IL aqueous solutions can significantly reduce the cost of IL pretreatment, while maintaining an efficient enzymatic hydrolysis of lignocellulosic biomass.