Ca 2+ ion leaching and poor pore structure are obstacles of CaO for biodiesel production . To this end, a typical Zr–based metal organic framework, UiO–66(Zr) is adopted to support calcium acetate to prepare CaO/ZrO 2 catalyst. For comparison, catalyst precursor is activated in nitrogen (UCN) and air (UCA) atmosphere, respectively. Preparation factors including calcium acetate addition and activation temperature are evaluated. Moreover, effects of transesterification parameters on oil conversion are investigated and the optimized parameters are further used to examine catalyst reusability . Meanwhile, catalysts are characterized with TG, XRD, XPS , FTIR, Hammett indicator titration, N 2 adsorption and desorption. Results reveal UCN calcined at 650 °C (UCN650) and UCA calcined at 700 °C (UCA700) separately exhibits the best catalytic performance. The maximum conversion of 96.99% is achieved by UCN650 with catalyst amount of 6 wt% and molar ratio of methanol to oil of 9 at 65 °C for 60 min. Even after being used 3 cycles, conversion of 92.76% is still achieved by UCN650. By contrast, UCA700 shows lower conversion of 92.94% at the first cycle with catalyst amount of 8 wt% and molar ratio of methanol to oil of 9 at 65 °C for 60 min.
Yunfei Liu,Hewei Yu,Xiuxiu Chen,Zekai Sun,Lizeng Peng,Hongyu Si
This study focused on the optimized preparation of biodiesel over a ZrO 2 -modified CaO catalyst. CaO/ZrO 2 catalysts were synthesized by impregnation, co-precipitation, and sol-gel methods, and analyzed by various characterization methods, including N 2 adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermally programmed desorption of CO 2 (CO 2 -TPD), and scanning electron microscopy (SEM). The CaO/ZrO 2 catalyst synthesized by the impregnation method had a uniform microstructure, good crystallinity, a uniform spherical particle structure with large pores and slits, and a density of surface alkali sites of 1.898 mmol g - 1 . Using the impregnation method, the best synthesis conditions were determined as a calcination temperature of 700 °C and a Ca/Zr molar ratio of 3:2. Furthermore, the optimal reaction conditions were determined by single-factor experiments as a catalyst dosage of 8 wt%, a molar ratio of methanol to oil of 12, a reaction temperature of 64 °C, and a reaction time of 2 h. Under these reaction conditions, the yield of fatty acid methyl esters (FAME) reached 95.9 %, decreasing only marginally to 77.6 % after four reuses of the catalyst. It is hoped that this study may provide important research guidance for developing solid basic catalysts for preparing FAME by transesterification under mild conditions.
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