Transesterification of rapeseed oil for synthesizing biodiesel by K/KOH/γ-Al2O3 as heterogeneous base catalyst

The heterogeneous base catalyst, gamma-Al2O3 loaded with KOH and K (K/KOH/gamma-Al2O3) was first prepared and used in the transesterification of rapeseed oil with methanol to produce biodiesel. The prepared catalyst was characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller method, infrared spectroscopy and X-ray photoelectron spectroscopy. It was found that when gamma-Al2O3 is loaded with KOH and K, the Al-O-K species is produced, resulting in an increase in the catalytic activity. The impacts of catalyst preparation conditions on the catalytic activities of K/KOH/gamma-Al2O3 were investigated. The results demonstrate that the catalyst K/KOH/gamma-Al2O3 has high catalytic activity when the added amounts of KOH and K are 20 and 7.5 wt% respectively. The transesterification of rapeseed oil to biodiesel with the prepared heterogeneous base catalyst was optimized. It was found that the yield of biodiesel can reach as high as 84.52% after 1 h reaction at 60 degrees C, with a 9:1 molar ratio of methanol to oil, a catalyst amount of 4 wt%, and a stirring rate of 270 g.