Horn ultrasonic-assisted bleaching of vegetable oils with various viscosities as a green process: Computational fluid dynamics simulation of process

Abstract

Achieving a resource-protecting and environment friendly provide chain whereas following economic development has consistently been the target of countries across the world. Bleaching of soybean, canola, olive, sunflower and palm oils by ultrasonic horn reactor as a green process was simulated by computational fluid dynamics (CFD) to determine the effect of viscosity, amplitude (180 and 360 W), frequency (25 and 40 kHz) and temperature (35 and 65 °C). Multiphase, unsteady and axisymmetric modeling of the process examined led to the determination of shear rates. In addition, the viscosity power law model was applied to predict the vegetable oils’ viscosity with high accuracy. Besides that, the fatty acid composition of vegetable oils was measured by gas chromatography. ΣPUFA/(ΣMUFA + ΣSFA) content was highest for soybean (1.39) and lowest for palm oil (0.07). A positive relation was found between the color of bleached oil and ultrasound frequency and viscosity. It was found that the flow shear rate reduced with increasing the temperature and power of sonication. The creation of regions with a high velocity gradient and, consequently, elevated shear rates (especially near the horn tips or at the corners) affected oil viscosity. Sunflower oil behaved as a shear thinning fluid, except at moderate shear rates where Newtonian properties were observed. Rheological characteristics of palm oil were similar to those of olive oil as a shear thinning fluid. Semi-empirical correlations are proposed to determine the viscosity of oil as a function of its shear rate for this green process.