Ionic liquids:Green Solvents

"Ionic liquids (ILs)" are the liquids composed entirely of ions that are fluid around or below 100°C.

In 2005, one of my former colleagues synthesized chemicals in the lab using ionic liquids, which represents the trends of green chemistry because many of the solvents of yesterday’s industry are now recognized and regulated as harmful.

In 2006, another of my former colleagues have done a research on ionic liquids.delignification biomass. Recently we can quite a lot of research activities and reports have been focusing on the treatment of lignocellulosic biomass in the ionic liquids for biorefinery. And a patent has been issued to such a technology.

Yesterday, our VP asked us to evaluate the commercialization of ionic liquid pretreatment of lignocellulosic biomass.

I am surprised at the fast pace of the "green wave" of ionic liquid toward us!

Why are ionic liquids attracting so much attention? Because they

• have low or near zero vapor pressure because they are salts and can reduce volatile organic compounds emission. Yes, ionic liquids are the candidate to replace volatile organic solvent replacement!
• have the ability to design specific physical and chemical properties (Tunable properties) and allow to designer solvents. This is the most useful property of ILs. The range of physical and chemical properties available with ILs is considerably wider than those of commonly used organic solvents. Thus, an appropriate “Task Specific Ionic Liquid (TSIL)” can be designed with the precise physical and chemical properties desired by the end user.
• have low melting point, enabling them to be liquids at or below room temperature. e.g.
  1-ethyl, 3-methyl imidazolium benzoate for example has a melting point of -61°C.
• have different water miscibility.Some are water miscible and some are not. This property can be switched ON and OFF according to the process requirements by modifying the cation structure of a ionic liquid or by changing its anion. The anion chosen plays a prominent role in IL water miscibility. [PF6]-, [(CF3SO2)2N]- for example are generally water immiscible anions, and [CH3COO]-, [CF3COO]-, [NO3]-, Br-, I-, and Cl- are generally water miscible anions.
• have large liquid range and thermal stability, which makes them useful for reactions that need to be maintained at either low-high or both low and high temperatures. For example, 1- ethyl, 3-methyl imidazolium bis(trifloromethylsulfonyl) imide has a liquid range of 471 degrees, with a melting point -15°C and a decomposition temperature a 455°C. This property makes ILs useful for reactions that need to be maintained at either low-high or both low and high temperatures.
• have high air and water stability
• have high ionic conductivity and a large electrochemical window
• are recyclable

So, ILs CAN DO WHAT TRADITIONAL SOLVENTS CAN NOT DO!

It has been known that pretreatment of lignocellulosic materials using ionic liquids is more environment-friendly than conventional pretreatment methods because the ionic liquids can be recovered and reused. Moreover, by fractionating lignocellulose with ionic liquids it is possible to extract cellulose cleanly.

Unfortunately there is probably still a long way about its commercialization as green solvents, specifically as a media for biomass pretreatment because of the high price of ionic liquids, the cost IL recovery process, and the understanding of physico-chemical mechanisms during biomass pretreatment.

Cost, cost, a "energy barrier" for technology commercilization!