Ionic liquids are room-temperature molten salts, composed mostly of organic ions that may undergo almost unlimited structural variations. This review covers the newest aspects of ionic liquids in applications where their ion conductivity is exploited; as electrochemical solvents for metal/semiconductor electrodeposition, and as batteries and fuel cells where conventional media, organic solvents (in batteries) or water (in polymer-electrolyte-membrane fuel cells), fail. Biology and biomimetic processes in ionic liquids are also discussed. In these decidedly different materials, some enzymes show activity that is not exhibited in more traditional systems, creating huge potential for bioinspired catalysis and biofuel cells. Our goal in this review is to survey the recent key developments and issues within ionic-liquid research in these areas. As well as informing materials scientists, we hope to generate interest in the wider community and encourage others to make use of ionic liquids in tackling scientific challenges.

Ionic-liquid materials for the electrochemical challenges of the future.

This review gives a survey on the latest most representative developments and progress concerning ionic liquids, from their fundamental properties to their applications in catalytic processes. It also highlights their emerging use for biomass treatment and transformation.

Ionic liquids and catalysis: Recent progress from knowledge to applications

https://pubs.rsc.org/en/Content/ArticlePDF/2013/GC/C2GC36364J

Deconstruction of lignocellulosic biomass with ionic liquids

Sustainability, industrial ecology, eco-efficiency, and green chemistry are directing the development of the next generation of materials, products, and processes. Biodegradable plastics and biocompatible composites generated from renewable biomass feedstock are regarded as promising materials that could replace synthetic polymers and reduce global dependence on fossil fuel sources.1 It is estimated that the world is currently consuming petroleum at a rate 100 000 times faster than nature can replace it.2 The growing global environmental awareness and societal concern, high rate of depletion of petroleum resources, concepts of sustainability, and new environmental regulations have triggered the search for new products and processes that are more compatible with the environment. The most abundant natural polymer in our environment is cellulose. It has an estimated annual biosphere production of 90 × 109 metric tons and, consequently, represents the most obvious renewable resource for producing biocomposites.3 Its highly ordered structure is responsible for its desirable mechanical properties but makes it a challenge to find suitable solvents for its dissolution.4 The first attempts to dissolve cellulose date back to the early 1920s.5 Several aqueous and nonaqueous cellulose solvents have been discovered since then, but all of these solvents suffer either from high environmental toxicity or from insufficient solvation power.6 In general, the traditional cellulose dissolution processes require relatively harsh conditions and the use of expensive and uncommon solvents, which usually cannot be recovered after the process.6-10 However, a new class of solvents was opened to the cellulose research community, when in 2002 Swatloski et al. reported the use of an ionic liquid as solvent for cellulose both for the regeneration of cellulose and for the chemical modification of the polysaccharide.7 In 1934, Graenacher had discovered a solvent system with the ability to dissolve cellulose, but this was thought to be of little practical value at the time.11,12 Ionic liquids are a group of salts that exist as liquids at relatively low temperatures (<100 °C). They have many attractive properties, including chemical and thermal stability, nonflammability, and immeasurably low vapor pressure.12 First discovered in 1914 by Walden, their huge potential in industry and research was only realized within the last few decades.13,14 This review aims to provide a summary of our current state of knowledge on the structural features of wood * To whom correspondence should be addressed. E-mail: ken.marsh@ canterbury.ac.nz. Tel.: +64 3364 2140. Fax: +64 3364 2063. † Department of Chemical and Process Engineering. ‡ Department of Mechanical Engineering. Andre Pinkert was born in Schwabach, Germany, in 1981. He studied Chemistry at the University of Erlangen-Nurnberg, Germany, and received his prediploma and diploma degrees in 2004 and 2008, respectively. During 2005, he joined the Marine Natural Products Group, lead by Murray H. Munro and John W. Blunt, at the University of Canterbury (UoC), New Zealand, working on the isolation and characterization of bioactive metabolites. In early 2006, he returned to Germany and resumed his studies at the University of Erlangen-Nurnberg, finishing his degree under the supervision of Rudi van Eldik. Associated with his studies, during 2007, he worked for AREVA NP on radio-nuclear chemistry and computer modeling. Since 2008, he is studying towards a Ph.D. degree at UoC under the supervision of Shusheng Pang, Ken Marsh, and Mark Staiger. His research focuses on biocomposites from natural fibers, processed via ionic liquids. Chem. Rev. 2009, 109, 6712–6728 6712

Ionic Liquids and Their Interaction with Cellulose

Utilization of natural polymers has attracted increasing attention because of the consumption and over-exploitation of non-renewable resources, such as coal and oil. The development of green processing of cellulose, the most abundant biorenewable material on Earth, is urgent from the viewpoints of both sustainability and environmental protection. The discovery of the dissolution of cellulose in ionic liquids (ILs, salts which melt below 100 °C) provides new opportunities for the processing of this biopolymer, however, many fundamental and practical questions need to be answered in order to determine if this will ultimately be a green or sustainable strategy. In this critical review, the open fundamental questions regarding the interactions of cellulose with both the IL cations and anions in the dissolution process are discussed. Investigations have shown that the interactions between the anion and cellulose play an important role in the solvation of cellulose, however, opinions on the role of the cation are conflicting. Some researchers have concluded that the cations are hydrogen bonding to this biopolymer, while others suggest they are not. Our review of the available data has led us to urge the use of more chemical units of solubility, such as ‘g cellulose per mole of IL’ or ‘mol IL per mol hydroxyl in cellulose’ to provide more consistency in data reporting and more insight into the dissolution mechanism. This review will also assess the greenness and sustainability of IL processing of biomass, where it would seem that the choices of cation and anion are critical not only to the science of the dissolution, but to the ultimate ‘greenness’ of any process (142 references).

Ionic liquid processing of cellulose

The dissolution of cellulose in different ionic liquids will be described as a very recent subject for a direct dissolving process, which was used to prepare regenerated cellulose fibres. The preparation of the dopes was arranged starting from slurry of cellulose in the aqueous ionic liquid by removing the water at elevated temperature, vacuum and high shearing rates. As ionic liquids, the 1-N-Butyl-3-methylimidazolium chloride, the 1-Ethyl-3-methylimidazolium chloride, the 1-N-Butyl-2,3-dimethylimidazolium chloride, the 1-N-Butyl-3-methylimidazolium acetate and the 1-Ethyl-3-methylimidazolium acetate were investigated. The cellulose solutions in ionic liquids were characterised by means of light microscopy, cone-plate rheometry and particle analysis. In addition these results were compared with cellulose solutions in N-methyl-morpholine-N-oxide monohydrate. Finally the cellulose dopes were shaped by a dry-wet spinning process to manufacture cellulose fibres. The properties of the resulted fibre had been determined and will be discussed.

Dissolution and forming of cellulose with ionic liquids

Ionic liquids (IL) are new direct dissolving systems for cellulose characterized by unique dissolving properties and simple technical handling. Selected IL-systems are non toxic and chemically as well as physically neutral which represents an advantage as compared to the commonly used direct solvent N-methylmorpholine-N-oxide (NMMO). Fibres can easily be prepared by coagulation in water. The BASF company as a leading producer of ionic liquids investigates the technical conversion of the preparation of cellulosic fibres using ionic liquids in cooperation with the Institut fur Textilchemie und Chemiefasern (ITCF), Denkendorf and the Thuringisches Institut fur Textil- und Kunststoff-Forschung (TITK), Rudolstadt. The major targets of this project are the selection of appropriate IL-systems, the IL recycling, rheology of spinning dopes and the charcterization of resulting fibre profiles. Essential results of this work and the potential for establishing a technical-scale process are summarized.

New Developments in Dissolving and Processing of Cellulose in Ionic Liquids

Some general comments about ionic liquids (ILs) and carbohydrates are given. The main scope of the review is to discuss the present state of the art of chemical modification of cellulose applying IL as reaction media considering own research results. ILs, namely i-butyl-3-methylimidazolium chloride (BMIMCl), 1-ethyl-3-methylimidazolium chloride (EMIMCI), 1-butyl-2,3-dimethylimidazolium chloride (BDMIMCI), 1-allyl-2,3-dimethylimidazolium bromide (ADMIMBr) and 1-ethyl-3-methylimidazolium acetate (EMIMAc) are solvents for cellulose (even for high molecular bacterial synthesized cellulose) and can easily be applied as reaction media for cellulose modification. We investigated the homogeneous acylation, carbanilation and silylation of the biopolymer cellulose. Under mild conditions and within short reaction time at low temperature (65 C to 80 °C) and low excess of reagent, various cellulose esters and carbanilates, dendronized cellulose and trimethylsilyl cellulose were obtained. The DS of the cellulose derivatives can be controlled by varying the reaction time, reaction temperature and the IL used as reaction medium.

Interactions of Ionic Liquids with Polysaccharides -2: Cellulose

The homogeneous conversion of cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate with 2-furoyl chloride, p-toluenesulfonyl chloride, and triphenylmethyl chloride yields surprisingly pure cellulose acetate samples in any case. From NMR spectroscopic studies, it may be concluded that during the homogeneous functionalization reactive intermediates including furane-2-carboxylic acid/acetic acid anhydride and acetic acid triphenylmethyl ester are formed leading to the cellulose acetates with DS values in the range from 0.55 to 1.86.

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Frank Meister

Papers

Dissolution and forming of cellulose with ionic liquids

New Developments in Dissolving and Processing of Cellulose in Ionic Liquids

Interactions of Ionic Liquids with Polysaccharides -2: Cellulose

Interactions of Ionic Liquids with Polysaccharides 1. Unexpected Acetylation of Cellulose with 1‐Ethyl‐3‐methylimidazolium Acetate

Thermostability of imidazolium ionic liquids as direct solvents for cellulose