One-pot synthesis of levulinic acid from cellulose in ionic liquids

Enhanced dissolution of galactomannan and highly efficient selenium functionalization using ionic liquids with dual roles as solvents and catalysts

Galactomannan stands as a promising heteropolysaccharide, yet its randomly distributed non-linear structures and high molecular mass remain a huge challenge in solubilization and wide range of chemical modifications. This work develops a task specific approach for efficient dissolve of galactomannan in ionic liquids (ILs) by destructing and reconstructing intermolecular/intramolecular hydrogen bonds of galactomannan. Combining density functional theory calculations and experimental results, a reasonable mechanism of polysaccharide dissolution is proposed that the hydrogen bond networks of polysaccharide are broken, thus the hydroxyl groups are fully exposed and activated to facilitate functionalization. In view of the enhanced solubilization, an excellent effect in selenylation of galactomannan is notably improved by employing ILs with dual roles as solvents and catalysts. Typically, the introduction of -SO3H in ILs (SFILs) effectively enhances the protonation ability of selenium donor and thus further improves the functionalization efficiency. Furthermore, a surprising finding is observed that selenium content and average molecular mass of functionalized polysaccharide can be manipulated by the anions-cations synergistic effect which is highly dependent on SFILs acidity strength. This work proposed an integrated and promising strategy for improving the solubilization and functionalization manipulating by ILs, showing a great referential value for the widespread application in polysaccharide-rich resources.

Orientated inhibition of humin formation in efficient production of levulinic acid from cellulose with high substrate loading: Synergistic role of additives

The main bottleneck in the direct conversion of cellulose to levulinic acid (LA), a promising bio-based platform chemical, lies in the severe formation of humins, especially at high substrate loading (>10 wt%). Herein, we report an efficient catalytic system consisting of a 2-methyltetrahydrofuran/water (MTHF/H₂O) biphasic solvent with NaCl and cetyltrimethylammonium bromide (CTAB) as additives for converting cellulose (15 wt%) to LA in the presence of a benzenesulfonic acid catalyst. We show that both NaCl and CTAB accelerated the depolymerization of cellulose and formation of LA. However, NaCl favored the humin formation via degradative condensations, whereas CTAB inhibited humin formation by restraining the routes of both degradative and dehydrated condensations. A synergistic role of NaCl and CTAB on suppressing humin formations is illustrated. The combined use of NaCl and CTAB led to an increased LA yield (60.8 mol%) from microcrystalline cellulose in MTHF/H₂O (V_MTHF/V_H2O = 2/1) at 453 K for 2 h. Moreover, it was efficient for converting cellulose fractioned from several kinds of lignocellulosic biomass, wherein a high LA yield of 81.0 mol% was achieved from wheat straw cellulose. This work presents a new strategy for advancing LA biorefinery by synergistically promoting cellulose depolymerization with orientated inhibition of undesired humin formation.

Conversion of cellulose into valuable chemicals using sulfonated amorphous carbon in 1-ethyl-3-methylimidazolium chloride

In this study, three carbon-based solid acid catalysts were prepared via the one-step hydrothermal procedure using glucose and Brønsted acid, including sulfuric acid, p-toluenesulfonic acid, or hydrochloric acid. The as-synthesized catalysts were tested for their ability to convert cellulose into valuable chemicals. The effects of Brønsted acidic catalyst, catalyst loading, solvent, temperature, time, and reactor on the reaction were investigated. The as-synthesized C-H₂SO₄ catalyst containing Brønsted acid sites (-SO₃H, -OH, and -COOH functional groups) demonstrated high activity in the transformation of cellulose into valuable chemicals with the yield of total products of 88.17% including 49.79% LA in 1-ethyl-3-methylimidazolium chloride ([EMIM]Cl) solvent at 120 °C in 24 h. The recyclability and stability of C-H₂SO₄ were also observed. A proposed mechanism of cellulose conversion into valuable chemicals in the presence of C-H₂SO₄ was presented. The current method could provide a feasible approach for the conversion of cellulose into valuable chemicals.

MoWa: A Disinfectant for Hospital Surfaces Contaminated With Methicillin-Resistant Staphylococcus aureus (MRSA) and Other Nosocomial Pathogens

Introduction

Staphylococcus aureus strains, including methicillin-resistant S. aureus (MRSA) and methicillin-sensitive S. aureus (MSSA), are a main cause of nosocomial infection in the world. The majority of nosocomial S. aureus-infection are traced back to a source of contaminated surfaces including surgery tables. We assessed the efficacy of a mixture of levulinic acid (LA) and sodium dodecyl sulfate (SDS), hereafter called MoWa, to eradicate nosocomial pathogens from contaminated surfaces.

Methods and Results

A dose response study demonstrated that MoWa killed 24 h planktonic cultures of S. aureus strains starting at a concentration of (LA) 8.2/(SDS) 0.3 mM while 24 h preformed biofilms were eradicated with 32/1.3 mM. A time course study further showed that attached MRSA bacteria were eradicated within 4 h of incubation with 65/2 mM MoWa. Staphylococci were killed as confirmed by bacterial counts, and fluorescence micrographs that were stained with the live/dead bacterial assay. We then simulated contamination of hospital surfaces by inoculating bacteria on a surface prone to contamination. Once dried, contaminated surfaces were sprayed with MoWa or mock-treated, and treated contaminated surfaces were swabbed and bacteria counted. While bacteria in the mock-treated samples grew at a density of ~10⁴ cfu/cm², those treated for ~1 min with MoWa (1.0/0.04 M) had been eradicated below limit of detection. A similar eradication efficacy was obtained when surfaces were contaminated with other nosocomial pathogens, such as Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, or Staphylococcus epidermidis.

Conclusions

MoWa kills planktonic and biofilms made by MRSA and MSSA strains and showed great efficacy to disinfect MRSA-, and MSSA-contaminated, surfaces and surfaces contaminated with other important nosocomial pathogens.

High-efficiency recovery, regeneration and recycling of 1-ethyl-3-methylimidazolium hydrogen sulfate for levulinic acid production from sugarcane bagasse with membrane-based techniques

Ionic liquids have been proven efficient and environmental medium for producing platform chemical levulinic acid. Lack of high-efficiency, stable and low-cost recovery strategy with complex electrolyte form restricts the further scale-up of ionic liquids for platform chemicals production. Membrane-based techniques including ultrafiltration (UF) and bipolar membrane electrodialysis (BMED) were employed for the high-efficiency recovery, regeneration and recycling of 1-ethyl-3-methylimidazolium hydrogen sulfate [Emim][HSO₄] for levulinic acid production from sugarcane bagasse. UF-BMED treatment works based on the interception of macromolecule biomass degradation products by UF treatment with regional recovery of Emim⁺ and SO₄^2- by BMED treatment. Effect of major parameters on [Emim][HSO₄] recovery performance was determined. Recovery ratio for Emim⁺ and SO₄^2- approached 95.4% and 95.9%. Energy consumption of specific [Emim][HSO₄] recovery was closed to 5.8 kWh/kg. Insight gained from this study suggests a high-efficiency and economical strategy for platform chemicals production with green solvent ionic liquids.

Catalytic Conversion of Glucose into Levulinic Acid Using 2-Phenyl-2-Imidazoline Based Ionic Liquid Catalyst

Levulinic acid (LA) is an industrially important product that can be catalytically valorized into important value-added chemicals. In this study, hydrothermal conversion of glucose into levulinic acid was attempted using Brønsted acidic ionic liquid catalyst synthesized using 2-phenyl-2-imidazoline, and 2-phenyl-2-imidazoline-based ionic liquid catalyst used in this study was synthesized in the laboratory using different anions (NO₃, H₂PO₄, and Cl) and characterized using ¹H NMR, TGA, and FT-IR spectroscopic techniques. The activity trend of the Brønsted acidic ionic liquid catalysts synthesized in the laboratory was found in the following order: [C₄SO₃HPhim][Cl] > [C₄SO₃HPhim][NO₃] > [C₄SO₃HPhim][H₂PO₄]. A maximum 63% yield of the levulinic acid was obtained with 98% glucose conversion at 180 °C and 3 h reaction time using [C₄SO₃HPhim][Cl] ionic liquid catalyst. The effect of different reaction conditions such as reaction time, temperature, ionic liquid catalyst structures, catalyst amount, and solvents on the LA yield were investigated. Reusability of [C₄SO₃HPhim][Cl] catalyst up to four cycles was observed. This study demonstrates the potential of the 2-phenyl-2-imidazoline-based ionic liquid for the conversion of glucose into the important platform chemical levulinic acid.

A Study of the Ionic Liquid-Based Ultrasonic-Assisted Extraction of Isoliquiritigenin from Glycyrrhiza uralensis

We successfully extracted isoliquiritigenin from Glycyrrhiza uralensis through the utilization of an ionic liquid-based ultrasonic-assisted extraction (ILUAE) approach. Briefly, we utilized the solution of 1-butyl-3-methylimidazolium bromide ([BMIM]Br) as solvent and optimized key ILUAE parameters such as solid-liquid ratios, concentrations of ionic liquids, and the times of ultrasonication. Based on a single-factor experiment, we utilized the response surface method (RSM) approach to optimize the extraction procedure. The approach revealed that the optimal energy consumption time was 120 min, with the ultrasonic extraction temperature of 60°C. Using these optimized parameters together with the solid-liquid ratio (dried G. uralensis powder: [BMIM]Br of 0.3 mol/L) of 1 : 16.163 and the [BMIM]Br of 0.3 mol/L, we achieved a 0.665 mg/g extraction yield. Overall, these findings thus indicate that we were able to effectively use ILUAE as an efficient approach to reliably extract isoliquiritigenin in a reproducible and environmentally friendly manner.

Softened Wood Treated by Deep Eutectic Solvents

Due to its good physical properties, softened wood (SW) has been widely used in the fields of home furnishing, interior decoration, and construction, such as decorative panels, softened wood flooring, wooden bricks, and softened wood furniture. However, traditional methods of wood softening often fail to meet the requirements of enterprises for softening wood. Here, inspired by the research related to wood softening, we propose a method for directly preparing softened wood (SW) using a new type of "ionic liquid" eutectic solvent (DES) owing to its low cost, environmental friendliness, recyclability, and other advantages. To improve the adaptability of the study, a total of five types of DESs were designed and prepared, and by the microwave-assisted DES treatment of natural wood (NW), the purpose of softening wood was achieved. Then, we conducted a series of comparative analyses and performance tests on NW and SW, including microscopic images, chemical composition, color difference, and mechanical properties. The results show that the wood softened by DES has become a highly porous network structure, and partial lignin, hemicellulose, and cellulose have been removed. At the same time, different degrees of color change, lower hardness, excellent mechanical flexibility, and a compression rebound rate of up to about 90% are obtained. The above-mentioned various properties of SW provide great potential for its application in wood products.

Production of Levulinic Acid from Cellulose and Cellulosic Biomass in Different Catalytic Systems

The reasonable and effective use of lignocellulosic biomass is an important way to solve the current energy crisis. Cellulose is abundant in nature and can be hydrolyzed to a variety of important energy substances and platform compounds—for instance, glucose, 5-hydroxymethylfurfural (HMF), levulinic acid (LA), etc. As a chemical linker between biomass and petroleum processing, LA has become an ideal feedstock for the formation of liquid fuels. At present, some problems such as low yield, high equipment requirements, difficult separation, and serious environmental pollution in the production of LA from cellulose have still not been solved. Thus, a more efficient and green catalytic system of this process for industrial production is highly desired. Herein, we focus on the reaction mechanism, pretreatment, and catalytic systems of LA from cellulose and cellulosic biomass, and a series of existing technologies for producing LA are reviewed. On the other hand, the industrial production of LA is discussed in depth to improve the yield of LA and make the process economical and energy efficient. Additionally, practical suggestions for the enhancement of the stability and efficiency of the catalysts are also proposed. The use of cellulose to produce LA is consistent with the concept of sustainable development, and the dependence on fossil resources will be greatly reduced through the realization of this process route.

Performance of 1-(3-Sulfopropyl)-3-Methylimidazolium Hydrogen Sulfate as a Catalyst for Hardwood Upgrading into Bio-Based Platform Chemicals

The acidic ionic liquid 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate ([C3SO3Hmim]HSO4) was employed as a catalyst for manufacturing polysaccharide-derived products (soluble hemicellulose-derived saccharides, furans, and/or organic acids) from Eucalyptus globulus wood. Operation was performed in aqueous media supplemented with [C3SO3Hmim]HSO4 and methyl isobutyl ketone, following two different processing schemes: one-pot reaction or the solubilization of hemicelluloses by hydrothermal processing followed by the separate manufacture of the target compounds from both hemicellulose-derived saccharides and cellulose. Depending on the operational conditions, the one-pot reaction could be directed to the formation of furfural (at molar conversions up to 92.6%), levulinic acid (at molar conversions up to 45.8%), or mixtures of furfural and levulinic acid (at molar conversions up to 81.3% and 44.8%, respectively). In comparison, after hydrothermal processing, the liquid phase (containing hemicellulose-derived saccharides) yielded furfural at molar conversions near 78%, whereas levulinic acid was produced from the cellulose-enriched, solid phase at molar conversions up to 49.5%.

Manufacture of Platform Chemicals from Pine Wood Polysaccharides in Media Containing Acidic Ionic Liquids

Pinus pinaster wood samples were subjected to chemical processing for manufacturing furans and organic acids from the polysaccharide fractions (cellulose and hemicellulose). The operation was performed in a single reaction stage at 180 or 190 °C, using a microwave reactor. The reaction media contained wood, water, methyl isobutyl ketone, and an acidic ionic liquid, which acted as a catalyst. In media catalyzed with 1-butyl-3-methylimidazolium hydrogen sulfate, up to 60.5% pentosan conversion into furfural was achieved, but the conversions of cellulose and (galacto) glucomannan in levulinic acid were low. Improved results were achieved when AILs bearing a sulfonated alkyl chain were employed as catalysts. In media containing 1-(3-sulfopropyl)-3-methylimidazolium hydrogen sulfate as a catalyst, near quantitative conversion of pentosans into furfural was achieved at a short reaction time (7.5 min), together with 32.8% conversion of hexosans into levulinic acid. Longer reaction times improved the production of organic acids, but resulted in some furfural consumption. A similar reaction pattern was observed in experiments using 1-(3-sulfobutyl)-3-methylimidazolium hydrogen sulfate as a catalyst.

Acid-Catalysed Conversion of Carbohydrates into Furan-Type Molecules in Zinc Chloride Hydrate

Acid-catalysed conversion of biomass, specifically cellulose, holds promise to create value-added, renewable replacements for many petrochemical products. We investigated an unusual acid-catalysed transformation of cellulose and cellobiose in the biphasic solvent system zinc chloride hydrate (ionic liquid)/anisole. Here, furyl hydroxymethyl ketone and furfural are obtained as major products, which are valuable but less commonly formed in high yields in transformations of cellulosic substrates. We explored this chemistry in small-scale model reactions and applied the optimised methods to the conversion of cellulose in bench-scale processes. The optimum reaction system and preferred reaction conditions are defined to select for highly desirable furanoid products in the highest known yields (up to 46 %) directly from cellulose or cellobiose. The method avoids the use of added catalysts: the ionic solvent zinc chloride hydrate possesses the intrinsic acidity required for the hydrolysis and chemical transformation steps. The process involves inexpensive media for the catalytic conversion of cellulose into high-value products under mild processing conditions.

Sugar dehydration to 5-hydroxymethylfurfural in mixtures of water/[Bmim]Cl catalyzed by iron sulfate

Stabilization effect of [Bmim]Cl on HMF is demonstrated, which can suppress the rehydration and polymerization side-reactions and enhance HMF yield.

Production of xylose, levulinic acid, and lignin from spent aromatic biomass with a recyclable Brønsted acid synthesized from d-limonene as renewable feedstock from citrus waste

This work aimed to develop a green protocol for chemical processing of spent aromatic biomass to obtain xylose, levulinic acid, and lignin in good yields via treatment with p-cymene-2-sulphonic acid (p-CSA), a Brønsted acid synthesised from d-limonene as a renewable feedstock from citrus waste. Chemical processing of palmarosa biomass with p-CSA under heating in an autoclave resulted in hydrolysate containing xylose (~16% yield). Further processing of pre-treated biomass with p-CSA in presence of aq. HCl under refluxing caused a selective degradation of cellulose to levulinic acid (~22% yield with respect to biomass). The residual biomass was used to afford lignin in good yields.

Catalytic preparation of levulinic acid from cellobiose via Brønsted-Lewis acidic ionic liquids functional catalysts

Brønsted-Lewis acidic ionic liquids (ILs) were applied to catalyze cellobiose to prepare levulinic acid (LA) in one pot under hydrothermal conditions. Under the optimum conditions, the highest LA yield of 67.51% was obtained when low [HO₃S-(CH₂)₃-mim]Cl-FeCl₃ (molar fraction of FeCl₃ x = 0.60) was used. This indicated the Brønsted-Lewis acidic ILs played an active role in the conversion of cellobiose to LA. The catalytic mechanism of ILs had been established, disclosing that the Brønsted-Lewis acidic ILs had the catalytic synergistic effect originating from its double acid sites. During the reaction process, the Lewis acid sites improved the isomerization of glucose to fructose, then the Brønsted and Lewis acid sites simultaneously enhanced the dehydration of fructose to produce hydroxymethylfurfural (HMF), which was propitious to the synthesize LA with high yield. In addition, LA could be easily extracted by methyl isobutyl ketone (MIBK), and the ILs could retain its basic activity after 5 cycles. The solid residues were characterized using SEM, FT-IR and TG-DTG spectroscopy. It was the conclusion that a large amount of humins were produced during the cellobiose conversion process. In this reaction, the ILs not only overcomes the problems of the conventional catalyst, but also completes the reaction-separation integration and the recycling of the catalyst. This paper provided an important theoretical basis for the application of ILs in the field of biomass.

Catalytic conversion of duckweed to methyl levulinate in the presence of acidic ionic liquids

In this study, an efficient strategy is proposed for selective methyl levulinate production from duckweed, a typical fast-growing aquatic microalgae in warm and humid regions, in the presence of acidic ionic liquids (ILs). The results show that IL structure has a significant effect on its acidic strength, which finally determines the process efficiency for levulinate methyl generation. With the optimized catalyst of [C₃H₆SO₃HPy]HSO₄, 88.0% duckweed is consumed, resulting in a comparable methyl levulinate yield of 73.7% and a process efficiency of 81.8% at 170 °C for 5 h. Furthermore, this process is substantially influenced by the reaction condition, particularly, it is significantly temperature-dependent. In addition, solvent has a remarkable intensified effect on the process efficiency, which dramatically decreases from 81.8 to 53.7% when methanol is replaced by water.

Chemocatalytic Conversion of Cellulose into Key Platform Chemicals

Chemocatalytic transformation of lignocellulosic biomass to value-added chemicals has attracted global interest in order to build up sustainable societies. Cellulose, the first most abundant constituent of lignocellulosic biomass, has received extensive attention for its comprehensive utilization of resource, such as its catalytic conversion into high value-added chemicals and fuels (e.g., HMF, DMF, and isosorbide). However, the low reactivity of cellulose has prevented its use in chemical industry due to stable chemical structure and poor solubility in common solvents over the cellulose. Recently, homogeneous or heterogeneous catalysis for the conversion of cellulose has been expected to overcome this issue, because various types of pretreatment and homogeneous or heterogeneous catalysts can be designed and applied in a wide range of reaction conditions. In this review, we show the present situation and perspective of homogeneous or heterogeneous catalysis for the direct conversion of cellulose into useful platform chemicals.

Exploring and exploiting different catalytic systems for the direct conversion of cellulose into levulinic acid

The single step conversion of cellulose into levulinic acid has been studied under hydrothermal conditions with several catalytic systems.

Hydrothermal conversion of glucose to levulinic acid using multifunctional ionic liquids: effects of metal ion co-catalysts on the product yield

An efficient catalytic system comprising Bronsted acidic ionic liquids and Lewis acidic metal salts for hydrothermal glucose conversion to platform chemicals.

Catalytic Conversion of Carbohydrates to Levulinate Ester over Heteropolyanion-Based Ionic Liquids

An efficient one-pot approach for the production of levulinate ester from renewable carbohydrates is demonstrated over heteropolyanion-based ionic liquid (IL-POM) catalysts with alcohols as the promoters and solvents. The relationships between the structure, acidic strength, and solubility of the IL-POM in methanol and the catalytic performance were studied intensively. A cellulose conversion of 100 % could be achieved with a 71.4 % yield of methyl levulinate over the catalyst [PyPS]₃ PW₁₂ O₄₀ [PyPS=1-(3-sulfopropyl)pyridinium] at 150 °C for 5 h. This high efficiency is ascribed to the reasonably high activity of the ionic liquid (IL) catalyst and reaction coupling with rapid in situ esterification of the generated levulinic acid with the alcohol promoter, which allows the insolubility of cellulose encountered in biomass conversion to be overcome. Furthermore, the present process exhibits high feedstock adaptability for typical carbohydrates and handy catalyst recovery by a simple self-separation procedure through temperature control.

Biosorbents based on agricultural wastes for ionic liquid removal: An approach to agricultural wastes management

Modified biochars produced from different agricultural wastes were used as low-cost biosorbents to remove hydrophilic ionic liquid, 1-butyl-3-methyl-imidazolium chloride ([BMIM][Cl]). Herein, the biosorbents based on peanut shell, corn stalk and wheat straw (denoted as PB-K-N, CB-K-N and WB-K-N) all exhibited higher [BMIM][Cl] removal than many other carbonaceous adsorbents and the adsorption capacities were as the following: PB-K-N > CB-K-N > WB-K-N. The characterizations of biosorbents indicated that they had great deal of similarity in morphological, textural and surface chemical properties such as possessing simultaneously accessible microporous structure and abundant oxygen-containing functional groups. Additionally, adsorption of [BMIM][Cl] onto PB-K-N, CB-K-N and WB-K-N prepared from the modified process, which was better described by pseudo-second order kinetic and Freundlich isotherm models. Therefore, the viable approach could also be applied in other biomass materials treatment for the efficient removal of ILs from aqueous solutions, as well as recycling agricultural wastes to ease their disposal pressure.

Catalytic Transformation of Lignocellulose into Chemicals and Fuel Products in Ionic Liquids

Innovative valorization of naturally abundant and renewable lignocellulosic biomass is of great importance in the pursuit of a sustainable future and biobased economy. Ionic liquids (ILs) as an important kind of green solvents and functional fluids have attracted significant attention for the catalytic transformation of lignocellulosic feedstocks into a diverse range of products. Taking advantage of some unique properties of ILs with different functions, the catalytic transformation processes can be carried out more efficiently and potentially with lower environmental impacts. Also, a new product portfolio may be derived from catalytic systems with ILs as media. This review focuses on the catalytic chemical conversion of lignocellulose and its primary ingredients (i.e., cellulose, hemicellulose, and lignin) into value-added chemicals and fuel products using ILs as the reaction media. An outlook is provided at the end of this review to highlight the challenges and opportunities associated with this interesting and important area.

Advances in the conversion of glucose and cellulose to 5-hydroxymethylfurfural over heterogeneous catalysts

This review provides a holistic overview of the developed heterogeneous catalysts for HMF production from dehydration of glucose and cellulose in various solvent systems.