Ketalization of glycerol to solketal in supercritical acetone

In the last few years, the increasing production of biodiesel has led to an overproduction of glycerol, the main byproduct of this industry. This paper reports on the ketalization of glycerol in supercritical acetone to give solketal (4-hydroxymethyl-2,2-dimethyl-1,3-dioxolane), an oxygenated compound useful as chemical and fuel additive for gasoline, diesel and biodiesel. The application of supercritical fluids (SCFs) in the chemical synthesis was explored to carry out reactions to obtain the above cyclic ketal. The experimental results reveal a drastic change in the reaction behavior when the critical condition of acetone is reached (T = 508 K). Below 508 K the reaction rate of solketal production is very low, but above this temperature a rapid increase in the reaction rate is observed. Finally, the reaction rate is stabilized at 533 K and higher temperatures due to the conversion of glycerol to acrolein and polymeric products as side reactions.