Ionic liquid biomass

The dehydration of fructose 40 or glucose into 5-hydroxymethylfurfural 41 is a process which has been exploited to convert biomass into higher value products. The reaction has been achieved using a chromium NHC complex, formed in situ from CrCl and the NHC 42 (Scheme 11.10) [16], The reaction is performed in the ionic liquid BMIM+Cl (l-butyl-3-methylimidazolium chloride). 

Various nonconventional reaction media have been intensively studied in recent years, including water [34], supercritical COj [35], Jluorous hiphasic [36], and ionic liquids [37] alone or in hquid-liquid biphasic combinations. The use of water and supercritical carbon dioxide as reaction media fits with the current trend toward the use of renewable, biomass-based raw materials, which are ultimately derived from carbon dioxide and water. 

Since late 2007, the Energy Biosciences Institute in Berkeley has been the center for cooperation between scientists from the University of California and the Agricultural Department of the University of Illinois for the production of fuels from so-called energy crops like switch grass. In this second-generation biofuel project that is financed over a 10-year period with 500 million by oil company BP, biomass is converted with the help of synthetic catalysts, for example, organometallic compounds, in a special solvent medium, better known as ionic liquids, into hydrocarbons with properties close to automotive fuels. 

Keywords Biomass, Cellulose, Hemicellulose, Ionic liquids, Lignin... 

For all of these reasons, there has been a rapid intensification of efforts in recent years to develop processes that will allow us to utilise a variety of plant materials, biomass, as a source of chemicals and liquid fuels. Ionic liquids have been widely investigated as solvents for these processes because of some of the unique properties that they possess. The goal of this overview therefore, is to survey and discuss recent developments in the use of ionic liquids in this extremely important field of biomass processing. 

Ionic Liquids in Biomass Conversion Processes 4.1 Ionic Liquids as Green Solvents... 

An important property of an ionic liquid in terms of its applications in biomass processing is its thermal stability, which is usually measured by thermogravimetric analysis. Nucleophilicity of the anion has been found to have an effect on the thermal stability of many ionic liquids due the role of the anion in the degradation of the cation [76], Quaternary ammonium, imidazolium, phosphonium and pyrrolidinium cations degrade at lower temperatures in the presence of highly nucleophilic anions such as halides due to Hoffman elimination and reverse Menschutkin reactions [76-79],... 

The challenges of using an ionic liquid in a biomass process are general to using an ionic liquid in any process, i.e. designing an effective ionic liquid with low toxicity,... 

A patent on biomass fractionation using ionic liquids describes extraction of cellulose from lignocellulose by dissolution in [C4mim CI, followed by addition of a caustic solution to precipitate cellulose while solubilising lignin and hemi-cellulose [191]. One of the main advantages of the process was the partial phase separation between the ionic liquid and the aqueous caustic phase, which enabled easier recycling of the ionic liquid. 

Ionic liquids have only just begun to be investigated for biomass related processes within the last 10 years, yet there are already many exciting examples of how they can be applied in this area. They have been used in cellulose functionalisation, thermochemical depolymerisation, enzymatic depolymerisation, extraction of biomass components, and biomass pretreatment processes. In a growing number of cases, ionic liquid processes have been patented, which suggests future commercial value. 

As one looks back over the last few decades it is possible to see trends emerging in the ionic liquids that are used and the main foci of interest. Early chloroaluminate systems with potential electrochemical applications gave way to ionic liquids with more air stable anions, with interest moving on to chemicals synthesis and catalysis. Then came new systems with specific properties to use as Task Specific Ionic Liquids (see Chapter 3), or for dissolving biomass polymers (Chapter 10), or as engineering fluids of various types. A small number of papers have now appeared on mixtures of ionic liquids. The exciting thing about ionic liquids is that as each development has occurred it has been in addition to the previous activities and not a replacement for these. 

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