Influence of reaction parameters on oxalic acid crystallization using conventional and ultrasonication: Doehlert matrix

Abstract

The present work aims to optimize the yield of crystallization using conventional and ultrasonic irradiation by using surface response methodology. The experiments were designed with the help of a Doehlert matrix which has not been previously reported. Initially, the solubility curve, induction time estimation and the metastable zone width have been thoroughly investigated. Later, using surface response obtained from statistics software, the effects of initial concentration and saturation temperature, stirring speed and initial concentration, and cooling temperature and stirring speed on yield of crystallization were compared using the conventional method and ultrasound- assisted crystallization. When compared to conventional methods, ultrasound-assisted crystallization has been shown to minimize the maximum reduction of MSZW and induction time. In ultrasound-assisted crystallization, the initial concentration, saturation temperature and stirring speed have been found to have a significant effect on the yield of crystallization than cooling temperature. The maximum yield of crystallization was 96.8% using ultrasound and 75.0% using conventional methods, respectively at an optimal condition of 1200 rpm, 15 °C cooling temperature, 80 °C saturation temperature and initial concentration of oxalic acid 75 g/50 mL of water. In comparison to the ultrasound method, the conventional method produced twice the average crystal size and irregular shape. Overall, the work has clearly established that ultrasound- assisted crystallization gives significant results as compared to the conventional method in terms of yield, metastable zone width, induction time and crystal characteristics.