Thermal stability of fatty acids in subcritical water

In this work, hydrolytic reaction conditions of various temperatures (300-370 degrees C) and times (0-30 min) at a constant pressure of 20 MPa were applied to the thermal decomposition of three kinds of fatty acids (FAs), stearic acid, oleic acid, and linoleic acid, in subcritical water. The degradation characteristics were investigated from the derived data, and the thermal stability of FAs in subcritical water was estimated. The primary reactions we observed were isomerization and pyrolysis of FAs. The main pathway of degradation was deduced by analyzing the contents of pyrolyzed products. We found that more saturated FAs have greater thermal stability in subcritical water. All FAs remained stable at 300 degrees C or below. Based on these results, we recommend that hydrolysis of vegetable oils and fats using subcritical water should be carried out below 300 degrees C (at 20 MPa) and for less than 30 min to obtain high-yield FA production. (C) 2012 Elsevier B.V. All rights reserved.