Ionic liquid biomass separation

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. 

Separation of biomass components is the very important initial step for the upcoming efficient utilization of biomass sources. Several physical and chemical separation methods are currently employed to overcome the recalcitrance of lignocelluloses. These methods include acid hydrolysis, alkaline hydrolysis, ammonia fiber expansion, hot water, organic solvent, and ionic liquid separation technologies. In this section of the chapter, all of the above separation methods are discussed. 

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.

Figure 7.5 Biomass separation system and the recovery of used ionic liquid. ...

However, ionic liquid is expensive and it should be used effectively. So after reactions, efficient recovery and removal of residual biomass solutes from ionic liquid is an important step, which is necessary for recycling the ionic liquid and in an ionic liquid separation process. 

The recovery of the ionic liquid l-ethyl-3-methylimidazolium acetate (abbreviated as [C2mim][OAc]) with a solvent mixture containing acetone, 2-propanol, and a small amount of water was demonstrated. This formed a phase switchable solvent system, which could concentrate and separate oleophilic solutes, short chain carbohydrates, and lignin fragments from used ionic liquid in a two-stage extraction procedure. Figure 7.5 shows the whole process of ionic liquid recovery and biomass separation. The research was conducted by pre-treating 100 g of corn stover with 10 wt.% of ionic liquid. After the separation process, the recovered ionic liquid contained few residual solutes, so it could be reused for biomass dissolution and... 

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