Experimental evaluation of simultaneous variations in biodiesel yield and color using choline hydroxide catalyst in an ultrasonic reactor

Abstract

Different color pigments in the vegetable oils can remain as impurities in the final biodiesel product and can cause negative impacts on its oxidation stability. Therefore, simultaneous optimization of the biodiesel color parameters and its production reaction yield can effectively diminish the costs of subsequent purification process. The current research study focuses on investigating color variations of waste cooking oil based methyl ester catalyzed by choline hydroxide (ChOH) in a lab-scale ultrasonic reactor. To intensify the reaction and enhance the biodiesel yield and color quality, the reaction time (A), catalyst amount (B), and ultrasonic amplitude (C) were optimized utilizing the response surface methodological (RSM) approach based on the Box-Behnken (BBD) experimental design. Under ChOH catalyzed conditions, the optimum values of A, B, and C were determined to be 4 min, 3 wt%, and 90%, respectively. The model predicted the biodiesel yield to be 95.89% and its color parameter values including lightness, redness and yellowness to be 56.49, 1.72, and 65.09, respectively. Data analysis showed that increasing the catalyst amount to 3 wt% increased the yield as well as lightness, redness and yellowness of the biodiesel color but decreased its redness. Moreover, by increasing the catalyst amount and ultrasonic amplitude, various pigments (including red) were significantly reduced. Also, a direct correlation observed between the yield and yellowness of the biodiesel. The application of an ultrasonic reactor in this research resulted in reduced reaction time, consumption of catalyst, and methanol compared to previous studies that used various other reactors and ChOH as catalyst.