Investigation of Biodiesel Stability under Vacuum Heating Process

Abstract

High water content is one of the most concerning issues when implementing biodiesel as a diesel fuel blend. Vacuum heating is one of several methods to reduce the water content of biodiesel, at certain conditions, it may damage the stability of biodiesel. This study aims to understand the stability of biodiesel including water content, total acid number, and oxidation stability under vacuum heating process. The three stability parameters were tested according to ASTM D6304, ASTM D664, and EN 15751, respectively. Biodiesel with high water content was heated under a vacuum pressure of -720 mmHg. The heating temperature and time were varied to determine the effect of both variables on the stability of biodiesel. The result shows that higher heating temperature produces lower water content and higher reduction of oxidation stability. Similar effects were also observed at a longer heating time. However, either temperature or time variations gave no noticeable effect on the acid number, while oxidation stability can be maintained above 22 hours. The results of this study can be used as a recommendation in determining the limits of acceptable operating conditions in the biodiesel vacuum heating process.