Effect of Cooking Conditions on Selected Properties of Biodiesel Produced from Palm-Based Waste Cooking Oils

Abstract

Cooking conditions affect oil properties and consequently, the quality of the derived biodiesel. Nevertheless, little information regarding the impact of the cooking process on biodiesel properties is currently available, especially for palm biodiesel. Therefore, this study examined the effect of cooking temperature, time of use, and length of reuse, on selected properties of biodiesel produced from palm-based waste cooking oils (WCO). Several WCO collected from restaurants belonging to four categories, namely fried chicken restaurants, fast food restaurants, snack producers, and typical restaurants, were subjected to base-catalyzed transesterification. The biodiesel yield was calculated, and the produced biodiesel was characterized as to its kinematic viscosity, calorific value, and cetane number. As a result, palm-based WCO performed better than other WCO in terms of biodiesel yield regardless of the conditions that they experienced, achieving almost 95% in some cases. The yield decreased as the cooking temperature and length of reuse moved upward, whereas the kinematic viscosity was sensitive only to the length of reuse, rising with increasing reuse. Non-compliance with biodiesel standards and technical requirements was observed in a few cases. The calorific value did not significantly change unless the cooking conditions were severe. The cetane number dropped as use and reuse decreased, remaining better compared to petrodiesel (70.2 ± 3.2 on average). Typical restaurants would generate the most suitable WCO to produce biodiesel, i.e., yield: 93.1 ± 0.2%; kinematic viscosity: 5.0 ± 0.3 mm2/s; calorific value: 39.9 ± 0.1 MJ/kg; density: 919 ± 9 kg/m3; and cetane number: 67.4 on average. This is consistent with the less severe cooking conditions employed at these restaurants.