The Path Ahead for Ionic Liquids

Microwave-Assisted Conversion of Carbohydrates

Catalytic conversion of carbohydrates into value-added products and platform chemicals became a trend in recent years. Microwave activation used in the processes of carbohydrate conversion coupled with the proper choice of catalysts makes it possible to enhance dramatically the efficiency and sometimes the selectivity of catalysts. This mini-review presents a brief literature survey related to state-of-the-art methods developed recently by the world research community to solve the problem of rational conversion of carbohydrates, mostly produced from natural resources and wastes (forestry and agriculture wastes) including production of hydrogen, synthesis gas, furanics, and alcohols. The focus is made on microwave technologies used for processing carbohydrates. Of particular interest is the use of heterogeneous catalysts and hybrid materials in processing carbohydrates.

Ionic liquids and deep eutectic solvents for the recovery of phenolic compounds: effect of ionic liquids structure and process parameters

Water pollution is a severe and challenging issue threatening the sustainable development of human civilization. Besides other pollutants, waste fluid streams contain phenolic compounds. These have an adverse effect on the human health and marine ecosystem due to their toxic, mutagenic, and carcinogenic nature. Therefore, it is necessary to remove such phenolic pollutants from waste stream fluids prior to discharging to the environment. Different methods have been proposed to remove phenolic compounds from wastewater, including extraction using ionic liquids (ILs) and deep eutectic solvent (DES), a class of organic salts having melting point below 100 °C and tunable physicochemical properties. The purpose of this review is to present the progress in utilizing ILs and DES for phenolic compound extraction from waste fluid streams. The effects of IL structural characteristics, such as anion type, cation type, alkyl chain length, and functional groups will be discussed. In addition, the impact of key process parameters such as pH, phenol concentration, phase ratio, and temperature will be also described. More importantly, several ideas for addressing the limitations of the treatment process and improving its efficiency and industrial viability will be presented. These ideas may form the basis for future studies on developing more effective IL-based processes for treating wastewaters contaminated with phenolic pollutants, to address a growing worldwide environmental problem.

Interactions of Biodegradable Ionic Liquids with a Model Naphthenic Acid

Density functional theory models are used to examine five biodegradable ionic liquids (ILs) each one consisting of a substitutional group (-OH, -NH2, -COOH, -COOCH3, and -OCH3) incorporated into the cation of 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). The results reveal that hydrogen atoms in -NH2, -COOH, and -COOCH3 form intramolecular hydrogen bonds with fluorine atoms in [BF4]-, whereas hydrogen atoms in -OH and -OCH3 do not form hydrogen bonds with [BF4]-. Further analysis of electron density at bond critical points and noncovalent interactions suggest that [BMIM][BF4] with -COOH has stronger intramolecular hydrogen bonds than other ILs. The extraction mechanism for a model naphthenic acid is hydrogen bonding, with F···H being the strongest hydrogen bond and O···H ranking second. More intermolecular hydrogen bonds occur when model naphthenic acid is adsorbed by [BMIM][BF4] with -COOH and -COOCH3. The interaction energy between model naphthenic acid and ILs with -COOH and -COOCH3 is higher than that with -OH, -NH2, and -OCH3.

An overview of key pretreatment processes for biological conversion of lignocellulosic biomass to bioethanol

Second-generation bioethanol can be produced from various lignocellulosic biomasses such as wood, agricultural or forest residues. Lignocellulosic biomass is inexpensive, renewable and abundant source for bioethanol production. The conversion of lignocellulosic biomass to bioethanol could be a promising technology though the process has several challenges and limitations such as biomass transport and handling, and efficient pretreatment methods for total delignification of lignocellulosics. Proper pretreatment methods can increase concentrations of fermentable sugars after enzymatic saccharification, thereby improving the efficiency of the whole process. Conversion of glucose as well as xylose to bioethanol needs some new fermentation technologies to make the whole process inexpensive. The main goal of pretreatment is to increase the digestibility of maximum available sugars. Each pretreatment process has a specific effect on the cellulose, hemicellulose and lignin fraction; thus, different pretreatment methods and conditions should be chosen according to the process configuration selected for the subsequent hydrolysis and fermentation steps. The cost of ethanol production from lignocellulosic biomass in current technologies is relatively high. Additionally, low yield still remains as one of the main challenges. This paper reviews the various technologies for maximum conversion of cellulose and hemicelluloses fraction to ethanol, and it point outs several key properties that should be targeted for low cost and maximum yield.

Ionic liquids and deep eutectic mixtures: sustainable solvents for extraction processes

In recent years, ionic liquids and deep eutectic mixtures have demonstrated great potential in extraction processes relevant to several scientific and technological activities. This review focuses on the applicability of these sustainable solvents in a variety of extraction techniques, including but not limited to liquid- and solid-phase (micro) extraction, microwave-assisted extraction, ultrasound-assisted extraction and pressurized liquid extraction. Selected applications of ionic liquids and deep eutectic mixtures on analytical method development, removal of environmental pollutants, selective isolation, and recovery of target compounds, purification of fuels, and azeotrope breaking are described and discussed.

Recycling of polymers: a review

Plastics are inexpensive, easy to mold, and lightweight. These and many other advantages make them very promising candidates for commercial applications. In many areas, they have substantially suppressed traditional materials. However, the problem of recycling still is a major challenge. There are both technological and economic issues that restrain the progress in this field. Herein, a state-of-art overview of recycling is provided together with an outlook for the future by using popular polymers such as polyolefins, poly(vinyl chloride), polyurethane, and poly(ethylene terephthalate) as examples. Different types of recycling, primary, secondary, tertiary, quaternary, and biological recycling, are discussed together with related issues, such as compatibilization and cross-linking. There are various projects in the European Union on research and application of these recycling approaches; selected examples are provided in this article. Their progress is mirrored by granted patents, most of which have a very limited scope and narrowly cover certain technologies. Global introduction of waste utilization techniques to the polymer market is currently not fully developed, but has an enormous potential.

Efficient Synthesis of 1-Acetylpyrene Using [Bmim]Cl–FeCl3 Ionic Liquid as Dual Catalyst and Solvent

Friedel–Crafts acylation of pyrene with acetic anhydride to 1-acetylpyrene catalyzed by three metal chloride and three Lewis acidic ionic liquids (ILs) containing 1-butyl-3-methylimidazolium chloride ([Bmim]Cl) and different metal chloride was investigated. ILs were prepared and tested for the acylation to explore the effects of Lewis acidity of ILs on the synthesis of 1-acetylpyrene. [Bmim]Cl–FeCl3 was found to be the most suitable catalyst, and the possible pathway for the acylation of pyrene with acetic anhydride catalyzed by [Bmim]Cl–FeCl3-IL was discussed. Pure 1-acetylpyrene was obtained and its structure was identified by gas chromatography–mass spectrometer, Fourier transform infrared and 1H NMR spectra.

A comparison of the effects of prenatal exposure of CD-1 mice to three imidazolium-based ionic liquids

BACKGROUND

Ionic liquids (ILs; salts with melting points below 100 degrees C) exhibit wide liquid ranges, non-flammability, and thermal stability among other properties. These unique salts are best known as "green" alternatives to traditional volatile organic solvents, which are utilized in both academia and industry. Our current study compares the developmental toxicity potential of three representative ionic liquids, with various chain lengths: 1-ethyl-3-methylimidazolium chloride ([C(2)mim]Cl), 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl), and 1-decyl-3methylimidazolium chloride ([C(10)mim]Cl).

METHODS

From gestation days (GD) 6-16, mated CD-1 mice were orally dosed with one of the following: 1,000, 2,000, or 3,000 mg/kg/day [C(2)mim]Cl; 113, 169, or 225 mg/kg/day [C(4)mim]Cl; 50, 75, or 100 mg/kg/day [C(10)mim]Cl; or the vehicle only. Dams were sacrificed on GD 17, and their litters were examined for adverse effects.

RESULTS

Fetal weight was significantly decreased in the two highest dosage groups exposed to [C(4)mim]Cl and [C(10)mim]Cl in comparison with their controls, but the [C(2)mim]Cl treated groups were not affected. An apparent teratogenic effect was associated with both [C(4)mim]Cl and [C(10)mim]Cl, as the offspring exhibited certain uncommon morphological defects. However, the incidences of malformations were low and no correlation between incidence and dosage could be made. No morphological defects were observed in any of the [C(2)mim]Cl-treated groups, despite maternal morbidity at the highest dosage level.

CONCLUSIONS

This study indicates that [C(4)mim]Cl and [C(10)mim]Cl may have adverse effects on development at high maternal exposures and strongly supports the supposition that the toxicity of imidazolium-based ILs is influenced by alkyl chain length.

High-throughput screening for ionic liquids dissolving (ligno-)cellulose

The recalcitrance of lignocellulosic biomass poses a major challenge for its sustainable and cost-effective utilization. Therefore, an efficient pretreatment is decisive for processes based on lignocellulose. A green and energy-efficient pretreatment could be the dissolution of lignocellulose in ionic liquids. Several ionic liquids were identified earlier which are capable to dissolve (ligno-)cellulose. However, due to their multitude and high costs, a high-throughput screening on small scale is essential for the determination of the most efficient ionic liquid. In this contribution two high-throughput systems are presented based on extinction or scattered light measurements. Quasi-continuous dissolution profiles allow a direct comparison of up to 96 ionic liquids per experiment in terms of their dissolution kinetics. The screening results indicate that among the ionic liquids tested EMIM Ac is the most efficient for dissolving cellulose. Moreover, it was observed that AMIM Cl is the most effective ionic liquid for dissolving wood chips.