Vacuum pressure application in biodiesel production from refined bleached deodorized palm olein

Abstract

Many developments in biodiesel production have been carried out to streamline costs and energy required. Studying biodiesel production at vacuum pressure aims to save energy by operating at lower temperatures than non-vacuum methods. This research aims to produce biodiesel from Refined Bleached Deodorized Palm Olein (RBDPO) under vacuum pressure conditions. In this research, RBDPO was methanolyzed using KOH as a catalyst. The process consists of several stages, namely making a methoxy solution, conducting the transesterification process, and purifying the methyl ester. This research is conducted using a sequential experimental design, following a one factor at a time approach. The first phase involves varying the operating pressure (650 mbar, 750 mbar, 850 mbar, and 950 mbar) while keeping the molar ratio of methanol to raw materials at 10:1, the reaction time at 60 min, the catalyst amount at 1%, and the reaction temperature at 50 °C. After identifying the highest conversion based on operating pressure, the second phase explores variations in the amount of catalyst (1%, 2%, 3%, and 4%). The third phase focuses on the molar ratio of methanol to raw materials (10:1, 12:1, 14:1, and 16:1). The fourth phase involves varying the reaction time (60, 70, 80, and 90 min). Finally, the reaction temperature is varied in the fifth phase (45 °C, 50 °C, 55 °C, and 60 °C). In this study, the highest biodiesel conversion obtained is 97.86% at a pressure of 750 mbar, reaction time of 60 min, catalyst amount of 1%, mole ratio of 14:1, and reaction temperature of 55 °C. The results of gas chromatography analysis show that C₁₆ and C₁₈ esters are the most common components in the raw materials and biodiesel produced. The results of the physical properties of biodiesel obtained are ester content of 97.53%, density (40 °C) of 879 kg/m³, kinematic viscosity (40 °C) of 3.920 cSt, flash point of 150 °C, and water content of 0 mg/kg, which meet ASTM D-6751, EN 14214, and Indonesian National Standard 7182:2015. This study demonstrates that applying vacuum conditions during transesterification not only enhances biodiesel conversion but has lower process energy.