<![CDATA[ABSTRACT. The washing stage is a critical step in biodiesel purification because it determines the total glycerol and water contents, which directly affect final fuel quality. This study aims to optimize the washing conditions of biodiesel produced from palm oil transesterification using sodium glyceroxide catalyst and to compare its characteristics with biodiesel produced using NaOH catalyst. Optimization was carried out using the Response Surface Methodology (RSM) with a Central Composite Design (CCD), in which the washing water to biodiesel ratio and washing temperature were used as independent variables, while total glycerol content and biodiesel water content were used as response variables. ANOVA analysis indicated that the quadratic model was statistically significant for both responses (p < 0.05), with the washing water to biodiesel ratio being the most dominant factor. The surface and contour plots revealed non-linear behavior at each optimization point. The optimum washing conditions were achieved at a water to biodiesel ratio of 1:1.9 and a washing temperature of 59 oC. The washing results demonstrated that biodiesel produced using sodium glyceroxide catalyst had lower total glycerol content and water content compared to biodiesel using NaOH catalyst, with reductions of 14.28% and 16.30%, respectively. These findings indicate that the use of sodium glyceroxide catalyst produces biodiesel that is easier to purify through the washing process and has better overall quality compared to biodiesel produced with NaOH catalyst. Keywords:Biodiesel, CCD, RSM, Sodium glyceroxide, Washing]]>
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