Low-temperature, solvent-free dehydration of cineoles with heterogeneous acid catalysts for the production of high-density biofuels

BACKGROUND: Oxygenated terpenoids such as 1,4-cineole and1,8-cineole canbemajor components of turpentine andessential oils. These terpenoids can also be produced from sugars via a biosynthetic approach. Catalytic deoxygenation of these substrates has the potential to efficiently generate commercially important chemicals and highdensity fuels for turbine or diesel propulsion. RESULTS: The low-temperature deoxygenation reactions of 1,4-cineole and 1,8-cineole over the heterogeneous acid catalysts Amberlyst-15, Nafion SAC-13, and Montmorillonite K10 have been studied. 1,4-cineole was found to isomerize to terpinene-1-ol followed by dehydration to a mixture primarily composed of alpha- and gamma-terpinene. In a similar manner, 1,8-cineole was found to isomerize to alpha-terpineol followed by dehydration to primarily terpinolene and alpha-terpinene. Amberlyst-15 was the most active catalyst on a mass basis and gave 100% conversion of 1,4-cineole in 24 h at 85 degrees C. Longer reaction times or higher reaction temperatures led to significant conversion of the dehydrated monoterpenes to diterpenes. Similar trends were observed for Nafion SAC-13 and Montmorillonite K10. CONCLUSION: This work provides important mechanistic information regarding the dehydration chemistry of cineoles and shows the potential of heterogeneous acid catalysts to effectively convert oxygenated terpenoids to high density hydrocarbon mixtures with potential uses as renewable diesel fuels. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.