Transesterification of canola oil catalyzed by nanopowder calcium oxide

•We studied two nanopowder CaO catalyst for transesterification of canola oil.•Nanopowder CaOs possess high activity due to their larger BET surface areas.•High surface area nano-CaO reduced catalyst loading by a factor of 10.•Nanopowder CaOs could be used 10 times without significant deactivation.•Particle size did not have any effect on the amount of Ca leaching.

Two types of commercial nanopowder calcium oxides, a higher surface area (HSA nano-CaO) and moderate surface area (nano-CaO) were studied for the transesterification of canola oil. The effect of reaction temperature, catalyst/oil weight ratio, and methanol/oil molar ratio on the reaction performance was investigated. The results show that nanopowder CaOs possess high activity due to their larger BET surface areas. At 65 °C, 99.85% biodiesel yield was obtained at 2 h when 3 wt.% of the nano-CaO catalyst was used with 9:1 methanol/oil molar ratio. The required catalyst/oil weight ratio to achieve the same yield under the same conditions was 10 times less for the HSA-nano-CaO catalyst. In contrast, only 88.59% and 16.23% yield were obtained for calcium methoxide (Ca(OCH3)2) and laboratory-grade CaO, respectively. A Langmuir–Hinshelwood model-based reaction mechanism was proposed for nano-CaO catalyzed transesterification reaction. The reaction was assumed to be first order with respect to triglyceride. The apparent reaction constants, apparent activation energy and pre-exponential factors have been calculated based on experimental data. Nanopowder CaOs were capable of being used without significant deactivation for 10 cycles. A slight drop in activity was ascribed to a combination of surface area loss from particle aggregation, the formation of Ca(OCH3)2, CaCO3, a Ca-glycerin complex, and adsorbed CO2 on the catalyst surface. Particle size did not have any effect on the amount of Ca leaching but leaching did increase with longer reaction time especially at higher catalyst loadings. Increasing the methanol/oil molar ratio increased Ca leaching in the glycerol-rich phase and decreased Ca leaching in the biodiesel-rich phase.