Effect of tert-butylhydroquinone on biodiesel properties during extreme oxidation conditions

Abstract

The use of alternative sources for fuel production has been gaining attention in the past years. Thus, the role of biodiesel seems to be crucial, as it can contribute to the sustainable economic growth of developing countries. The main raw materials for biodiesel production are vegetable oils, obtaining fatty acid methyl (or ethyl) esters through transesterification with methanol (or ethanol). The properties of these natural feedstocks can influence the quality of biodiesel. Specifically, its oxidative stability is usually low, not complying with the lower limit established by standards. As a consequence, some properties of biodiesel (especially viscosity and acid number) can vary during storage due to oxidation. In order to avoid these undesirable effects, antioxidant addition, as well as the selection of stable oils, is necessary. Among them, tert-butylhydroquinone (TBHQ) is one of the most popular additives. The aim of this work was to assess the evolution of some properties of biodiesel from different sources (cardoon, waste cooking, rapeseed and high-oleic safflower oil) during extreme oxidation conditions, evaluating the effectiveness of TBHQ addition on quality maintenance. As a result, the most unstable samples (cardoon and waste cooking biodiesel) required higher amounts of TBHQ (750 and 450 ppm, respectively) to comply with the standard (induction point = 8 h), whereas high-oleic safflower did not require any addition (induction point = 8.35 h). During extreme oxidation conditions, all the samples kept their viscosity and acid number values when the right amount of TBHQ was added, assuring their quality parameters during storage.