Surface Characterization of Sulfated Iron Oxide and Its Synthesis of Biodiesel Under Microwave Radiation

The solid acid catalysts SO 4 2− /Fe 2 O 3 were prepared by impregnation technique, and the preparation conditions were different in calcination temperature, concentration of impregnation solution of H 2 SO 4 and impregnation time. The characterization was performed by using Fourier transform infrared spectrometer (FTIR), X-ray diffraction (XRD), Temperature programed desorption of NH 3 (NH 3 ‒TPD), N 2 ‒BET and microwave absorbing test. As shown by FTIR spectra, the S=O functional group existed in the sample, which was essential for the strong acidity of the SO 4 2‒ /M x O y type solid acids. The XRD results indicated that when the calcination temperature exceeded 400℃, iron in SO 4 2‒ /Fe 2 O 3 transformed from amorphous to crystalline phase. The results from NH 3 -TPD showed that the prepared sample possessed strong acid and superacid sites. As shown by N 2 -BET results, the BET surface area of the samples was up to 200m 2 /g, and their pore size distributions essentially belonged to mesoporous characteristic distribution. The SO 4 2− /Fe 2 O 3 solid acid catalysts were used for the transesterification of castor oil under microwave radiation to produce biodiesel. The amounts of FAME in the product were analyzed by high-performance liquid chromatography. The highest yield of product was 65.3 wt.% when the reaction temperature was 65 ℃, alcohol/oil molar ratio was 30/1, catalyst loading was 20 wt.%, the reaction time was 3 h and the power of microwave was 300 w. Furthermore, the reaction results showed that SO 4 2‒ /Fe 2 O 3 had better catalytic activity under microwave radiation than under conventional heating condition.