Acidity improvement of refined-bleached used vegetable oils as dielectric liquid using two-level factorial design

Abstract

Recent studies have shown that modifying the chemical structure of used vegetable oils (UVOs) as an alternative dielectric liquid for oil-immersed transformers has improved these oils' physical, electrical and chemical properties. However, previous researchers have implemented the one-factor-at-a-time method as their experimental design approach. Therefore, they overlooked the possibility that combining mixing process parameters at optimum ratios will yield a better result. Hence, in this study, the two-level (2^k) factorial design is applied to achieve the lowest acidity level of UVOs through chemical refining process namely as refined-bleached used vegetable oils (RBUVOs). The involved process parameters are oil temperature, mixing speed and mixing time. Based on the results of 2³ factorial design, it is found that oil temperature has the most significant effect on acidity, with a percentage contribution of 35.76%. The result also shows that the best mixing process parameters of RBUVOs were: oil temperature (60 °C), mixing speed (1,000 rpm) and mixing time (30 min). Note that these mixing process parameters produced better RBUVOs with an acidity value of 0.0221 mg KOH/g. A regression model is also developed to predict the acidity of RBUVOs as a function of oil temperature, mixing speed and mixing time.