How Can Ionic Liquids be Recycled

Imidazolium cations can be deprotonated by bases to form neutral carbenes. These carbenes are surprisingly stable and can be distilled. The ionic hquid can be recycled by further reaction of the carbene with an acid. 

The controlled decomposition reaction allows for a recycling or purification process of the ionic liquid [29]. In this case the ionic liquid is thermally cleaved. The neutral imidazole and alkylating agent are distilled, collected and re-reacted. 

However, in some cases it is even possible to distill the entire ionic liquid without decomposition. [HMIM]C1, for example, can be distilled at 150 °C at 0.5 mbar [30]. This has recently been demonstrated to be true also for fully alkylated cations [31]. These materials require higher temperatures of about 300 °C at 6 mbar. 

Ionic liquids are frequently reported as being non-flammable. This is only true up to the temperatures at which decomposition takes place. Some ionic liquids already start to decompose at 120 °C, others are stable up to nearly 400 °C. Upon decomposition neutral and volatile molecules are formed which of course can burn. This explains why ionic liquids do indeed have flash points, even if they are usually much higher than 100 °C. However, ionic liquids can easily be disposed of by 

---

BASF (2011), Frequently Asked Questions How can Ionic Liquids be recycled Available from http / / www.basionics.com/ en/ ionic-hquids/ faq.htm 2a... 

---