Cellulose ionic liquid biomass

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

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. 

The application of ionic liquid to biomass separation recently started to attract a great deal of attention. Cellulose is poorly soluble in conventional solvents due to its many intermolecular hydrogen bonds. Ionic liquid was believed to be capable of disrupting such hydrogen bonds between different polysaccharide chains, thus decreasing the compactness of cellulose and... 

Figure 7.2 Examples of commonly used ionic liquid for cellulose dissolution and biomass separation.

Swatloski et al. showed previously that [C4mim]Cl is an excellent solvent in which to solubilise cellulose [47], and recently, it has been demonstrated that ionic liquids based on ethanoate and formate anions are also efficient solvents for this purpose [48, 49]. In particular, [C2mim][02CCH3] has been shown to be a potential solvent for a new commercial process for the preparation of cellulose fibres. Neutron diffraction and complementary MD simulations have been performed on both the [Cimim]Cl and [C2mim][02CCH3]/glucose system in order to increase our understanding of ionic liquid properties relevant to the biomass dissolution... 

In spite of the possibilities that are opened up by using ionic liquids in biomass chemistry, both their recovery and reuse for continuous processes remain a formidable challenge for the industrialization of new technologies. Ionic liquids are relatively expensive compared to traditional solvents and the high cost of utilizing ionic liquids must be offset this is mandatory for the development of commercially viable processes. In addition, the technology available now shows that ionic liquids can only dissolve about 10-15 wt % cellulose to give very thick and viscous solutions at these low concentrations. 

Very recently [126] the above described catalytic activity of [C2CiIm][OAc] in the benzoin condensation has been reported to provide a novel route for biomass processing. 5-Hydroxymethylfurfural - that can be produced effectively from plant biomass resources such as glucose or cellulose [127] - can undergo a facile benzoin condensation (see Fig. 12) in [C2Cilm][OAc], catalyzed by the solvent itself under very mild conditions (60-80°C) with excellent yields (up to 98% within 1 h). The product of the reaction, 5,5 -di(hydroxymethyl)furoin has been suggested for use as a possible C12 kerosene/jet fuel [126]. Later, also a redox esterification reactirai has been reported in this ionic liquid [174]. 

Xia, S., Baker, G. A., Li, H., Ravula, S., Zhao, H. Aqueous ionic liquids and deep eutectic solvents for cellulosic biomass pretreatment and saccharification. RSC Advances 2014, 4,10586-10596. 

Cheng C, Varanasi P, Li CL, Liu HB, Menichenko YB, Simmons BA, Kent MS, Singh S (2011) Transition of cellulose crystalline structure and surface morphology of biomass as a function of ionic liquid pretreatment and its relation to enzymatic hydrolysis. Biomacromolecules 12(4) 933-941. doi 10.1021/bml01240z... 

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