Supercritical CO2, the Key Solvent for Sustainable Processes
In processes that transform matter, solvents are very frequently used. A solvent is a liquid that dissolves substances. This is very useful especially when these substances are in a solid state. Also, in the fi eld of chemistry, solvents are essential for carrying out reactions: they allow effective contact of the reactive molecules, adjustment of the viscosity of the reaction system, and may also act as a “thermal buffer” in exothermic reactions. Of course, the omnipresent solvent is liquid water, especially because most biochemical reactions occur in water based mixtures. However, although water is a very powerful solvent, many compounds are poorly soluble in water (lipids for instance) and also water exhibits hydrolytic properties that can be undesirable. In such cases, organic solvents are used and their great variety can provide a solution to almost any case. However, this convenience may result in disadvantages that are now unacceptable in our society: toxicity, often fl ammability and volatile organic compounds (VOC) emissions, etc. Of course, completely eliminating these solvents would be diffi cult but concepts of green chemistry give us strong incentives to systematically rethink their use. Among the alternative paths, supercritical fl uids and especially supercritical CO2, can bring about a solution. They can also be the source of new products. All of the interest in these media for proposing novel sustainable processes is elaborated below.