Ca-Zr modified clinoptilolite catalyst as a novel bifunctional catalyst for biodiesel production from badly acidified feedstock oil and process optimization

In this research, a series of Ca-Zr/clinoptilolite catalysts, which are activated at the different calcination temperatures, are synthesized by the simple co-precipitation method and then applied in catalyzing transesterification of the high-acid-value feedstock oil with methanol to produce biodiesel. The acidic and basic sites in the catalyst originate from the synergistic effect of Zr and Ca. The excellent pore structure of the Ca-Zr/clinoptilolite catalyst is conducive to the rapid diffusion of reactant molecules such as triglycerides within the catalyst, thereby enhancing the transesterification efficiency. The Ca-Zr/clinoptilolite catalyst activated at 850 °C is preferred as the final catalyst due to the highest catalytic activity in transesterification. The response surface methodology (RSM) with the central composition designs (CCD) is employed to optimize the catalyzed transesterification parameters of the methanol to oil molar ratio, catalyst amount, and reaction temperature at the fixed reaction duration of 180 min. At the methanol to oil molar ratio of 16.9, catalyst amount of 7 wt%, and reaction temperature of 131 °C, the highest biodiesel yield of 97.43 % is achieved. On the whole, the Ca-Zr/clinoptilolite catalyst exhibits the great acid resistance capability and stability in catalyzing transesterification of the high-acid-value feedstock oil for biodiesel production.