While research in the area of catalysis of biomass in ionic liquids has been the subject of significant work in recent years, there is still much to do. The potential of these biomass/IL systems has been proven at the laboratory scale, but the use of ILs in biomass processing has not reached its potential as an industrially viable tech­nology yet. One of the main inhibitors of industrial adoption is the cost of ILs. While increased adoption of IL technology will increase production and thus drive costs down, improved IL synthesis and processing methods would be beneficial to any process that relies on ILs.

Separation and recovery of ILs is one of the most important aspects of any biomass processing scheme due to the high cost of ILs and the potential for detrimental effects from ILs remaining in later processing steps. Separation of soluble products such as sugars from ILs and separation of ILs from aqueous solutions have received some attention, although there is still room for significant advances in this area [83—85]. Simply evaporating water from ILs is too energy intensive to be useful in most processes. Until satisfactory separation techniques are developed for recovery of both ILs and biomass products, the use of ILs will not gain wider use in the industrial world.

There are some areas that have been the subject of initial investigation that could use further research. As has been discussed in this chapter, metals and metal salts have been shown to be effective in a number of different catalytic systems. Since ILs provide a unique environment for metal complexes [143], there may still be better catalysts that take advantage of ILs for the catalysis of biomass. Supported metal catalysts could also use further study in the catalysis of biomass as long as the catalysts remain truly heterogeneous throughout the reaction processes. Addition­ally, the use of microwave irradiation to enhance rates and yields of reactions in ILs has received some attention from a limited number of researchers and could use further research.

Enzymatic catalysis of biomass in ionic liquids also has room to expand. Some work has already been done in making lipase-compatible ILs that also dissolve biomass [71], but more work could be done to expand on this idea. Cellulase — compatible ILs would allow biomass to be pretreated and saccharified in a one-pot process without the use of harsh acids or metal catalysts. Cellulase that is tolerant of ILs is already the subject of some research [144]. Because many ILs tend to inhibit enzymatic and microbial activity, there is significant room to develop ways to make ILs and bio-processes compatible.

8.2 Conclusions

ILs present a unique set of challenges as well as a unique set of advantages as solvents for processing biomass. ILs provide lignocellulose solvation, enhanced catalyst activity, recyclability and, in some cases simple separations making them a promising avenue of research and potential candidate as a technology in the next generation of biorefineries. In addition to the basic research needed to find the optimize the IL/catalyst/substrate combination, overcoming the unique challenges of ILs must be thoroughly investigated [145]. When applying the work done with compounds such as monosaccharides and lignin model compounds to lignocellu — lose, care must be taken to select ILs that will work for the process and accommo­date the realities of a more difficult lignocellulosic substrate. Processes designed with ILs will need to take these challenges into account, along with possible health effects and corrosion caused by highly ionic media [146].

Even with the remaining challenges of developing new industrial processes, the promise of homogenous conversion of biomass into fuels, commodity chemicals, and polymers is a strong motivator. While ILs have worked their way into some pilot scale and industrial processes [147], the technology for IL use in biomass processing on an industrial scale may still be somewhat immature. More research aimed at optimizing recent discoveries, developing separations and recycling processes, and discovering new uses for IL/biomass systems has the potential to make IL systems practicable for industrial biomass processing.