The optimization of the production of propylene glycol is based on direct entropy minimization subject to operational constraints. Entropy production model has been developed using mass, energy and entropy balances. By means of analytical derivatives it was found that a minimum of entropy production rate is reached when a particular relationship between the temperature of the inlet stream and the temperature of reaction is satisfied for a given residence time in the reactor. The results reveal the behavior and the new operating conditions, from which a higher conversion rate has been obtained when compared with the classical modus operandi. (C) 2008 Elsevier B.V. All rights reserved.