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Due to the increasing demand for green and industrial biodiesel production, recyclable and stable catalysts need to be developed. Li/NaY zeolite catalysts with different molar ratios of Li2CO3 to NaY zeolite were synthesized from fly ash by hydrothermal and microemulsion-assisted co-precipitation method, and used to catalyze the transesterification of castor oil with ethanol. The structure, composition and morphology of Li/NaY zeolite catalysts were characterized by thermogravimetric (TG), X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) surface area and Fourier transform infrared (FT-IR) spectroscopy. Under the optimized conditions of molar ratio of Li2CO3 to NaY zeolite of 1:1, calcination temperature of 750 °C and calcination time of 4 h for catalyst preparation, the FAEE yield of 98.6% was obtained (catalyst amount with respect to oil of 3 wt%, ethanol/oil molar ratio of 18:1, reaction temperature of 75 °C and reaction time of 2 h). The results show that the catalyst has excellent stability (including air tolerance and reusability) and a certain regenerative capacity (the FAEE yield was increased by 17% after activation treatment), which are crucial for industrial applications. Pseudo-first-order reactions and pseudo-second-order kinetic models were compared to demonstrate the proposed reaction mechanism. The pseudo-first-order reactions kinetic model was fit with experimental data (R2 = 0.9906). Activation energy of 57.37 KJ/mol was required for transesterification of castor oil into biodiesel using Li/NaY zeolite catalyst.

In this study, PEG/MgO/ZSM-5@Fe3O4 magnetic catalyst was synthesized using polyethylene glycol (PEG) as a mediator, and was applied to the microwave-assisted in-situ transesterification of Spirulina platensis with ethanol. The effect of different proportion of mediator on catalyst performance was investigated. The composition, structure, morphology, specific surface area, magnetization and basicity of the catalysts were all characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET), vibrating sample magnetometer (VSM) and Hammett indicator. The catalytic performance evaluation results showed that the highest yield of biodiesel could reach 95.8% under the optimum reaction condition using 15PEG/MgO/Z@Fe3O4 catalyst. In addition, the catalyst can be reused for six times without leaching of active components, which still had a high conversion of biodiesel. Finally, the physicochemical properties of the biodiesel were also tested, which were in accordance with GB and EN standards.

In this study, a highly active and reusable La3+/ZnO-TiO2 photocatalyst was prepared by sol–gel method. The production of biodiesel from waste cooking oil by a two-step method. In the first step, under the UV irradiation, La3+/ZnO-TiO2 photocatalytic esterification of ethanol with free fatty acids (FFA) in waste cooking oil (WCO) was studied. In the second step, NaOH catalyzed the transesterification of triglycerides with ethanol. La3+/ZnO-TiO2 photocatalysts were characterized by TG, XRD, SEM-EDS, HRTEM, BET, UV–vis spectroscopy and Raman spectra. The optimum conditions were obtained by orthogonal design. At 35 °C, the ethanol/oil molar ratio is 12:1, the catalyst dosage is 4 wt%, the UV irradiation time is 3 h, the reaction time is 3 h, and the conversion of FFA reaches 96.14%. After 5 cycles of experiments, the conversion rate of FFA is more than 87%, which indicates that the catalyst has stable activity and simple recovery. The reaction mechanism of photocatalytic esterification was proposed and the kinetics of esterification was studied. Through the analysis of the characteristics of biodiesel, it is proved that the biodiesel by the method mentioned in this study conforms to GB 25199-2017 and EN 14214 standards. Therefore, La3+/ZnO-TiO2 as a new photocatalyst opens up a new way for biodiesel production.

With the further expansion of the fossil crisis and the increasing demand for biodiesel, it is imperative to develop highly reusable catalysts. Therefore, in this study, the completed synthesis of MgO/ZSM-5 catalysts via impregnation and ultrasonic dispersion methods were achieved to be applied in the clean production from Spirulina platensis-derived biodiesel. Physiochemical analyses including thermogravimetry (TG), temperature programmed desorption of CO2 (CO2-TPD), X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), Fourier transform infrared spectroscopy (FTIR) and Brunauer–Emmett–Teller surface area (BET) were used to define the basicity, structure, composition and morphology of synthesized catalysts. The optimum process conditions obtained by Taguchi method were as follows, the molar ratio of ethanol to oil was 15/1, the catalyst concentration was 3 wt%, and the yield of biodiesel reached 92.1% after 1 h reaction at 75 °C. The optimal catalyst had strong stability and catalytic activity in the repeated cycle test, even after five cycles, the yield of biodiesel was still above 85%. The transesterification of Spirulina oil catalyzed by MgO/ZSM-5 catalyst accorded with the pseudo-first-order kinetics, and the activation energy was 49.67 kJ/mol. Finally, the economic feasibility analysis of biodiesel illustrated that the new supported catalyst can effectively reduce the cost of production and provide favorable support for the future continuously industrial production.

The main purpose of this work was to develop a highly efficient and stable solid base catalyst for the preparation of biodiesel to meet the needs for green and clean production. To this end, a series of carbon-based magnesium oxide (MgO) solid base catalysts with high specific surface area were prepared by a sol-gel method and calcination for biodiesel production from castor oil. The effects of different organic additives and calcination temperatures on the physicochemical properties of catalysts were analyzed and evaluated by XRD, SEM, EDX, BET, FTIR and TGA. SEM and BET results indicated that the carbon-based MgO catalysts have a proper particle size distribution and a higher specific surface area. Meanwhile, EDX and TG analysis evidenced the presence of residual carbon in the MgO samples, which was confirmed to have a positive effect on the performance of the catalysts. The transesterification reaction was carried out in a batch reactor with condensed reflux to assess the performance of the catalysts. The MgO-UREA-800 catalyst exhibited impressive catalytic performance and an optimum biodiesel yield of 96.5% was obtained at the molar ratio of ethanol to oil of 12:1, catalyst loading of 6 wt%, reaction temperature of 75 °C and reaction time of 60 min. The catalyst durability tests showed that the catalysts could be reused in five cycles of operation without significant losses in activity.