Determination of optimum parameters for esterification in high free fatty acid olive oil and ultrasound-assisted biodiesel production

In this study, biodiesel was produced from high free fatty acid (FFA) oil obtained from waste olives, whose food quality deteriorated by falling from the tree to the ground. The FFA value of the oil obtained from waste olives was determined as 23% by titration method. In order to produce biodiesel with high conversion efficiency, esterification process was carried out to reach at least 1% FFA value in the first stage of the study. Acid esterification experiments were designed according to Taguchi's L-16 (4(2) 2(1)) orthogonal array. The amount of sulfuric acid catalyst, methanol ratio, and mixing speed were taken as the test variables for the esterification process. For the lowest FFA value, optimum test parameters were determined using the signal-to-noise (S/N) ratio. In the biodiesel production stage, ultrasound-assisted transesterification method was preferred in terms of high conversion efficiency and short reaction duration. According to the results, it was determined that the optimum reaction conditions in the esterification process were 25% by weight acid catalyst (according to the weight of the FFA in the oil), 22:1 methanol molar ratio in terms of fatty acids, and 400 rpm mixing speed. At these reaction conditions, the FFA of the oil was reduced from 23 to 0.608% in a single step. In the ultrasound-assisted process, Waste olive oil methyl ester (WOOME) conversion yield of 98.7% was achieved in a reaction time of 10 min. The fuel properties of WOOME (also called biodiesel) were determined to be within the EN 14214 standard. As a result, optimization was made to minimize the use of alcohol and catalyst in the acid esterification process. Also, time and energy savings were achieved in biodiesel production with ultrasound-assisted.

Automated summary

In this study, biodiesel was produced from waste olives with high FFA content. Esterification and ultrasound-assisted transesterification processes were used to achieve high conversion efficiency and minimize the FFA content in the oil, resulting in a 98.7% conversion yield of WOOME within 10 minutes.