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Biodiesel is an alternative green fuel commonly used worldwide. The biodiesel production process consists mainly of production and purification steps. In the production step, there are two main reactions, transesterification and esterification, that require novel catalysts to achieve high yield in a short processing time; however, the immiscibility of the reactants limits the mass transfer and consequently the reaction rate. This article reviews the development of various catalysts: acid, base, and bifunctional catalysts, for transesterification and esterification. In addition, some interesting multifunctional reactors to improve biodiesel production are briefly discussed. A functionalized acid/base catalyst on a metal oxide support is a potential catalyst for transesterification/esterification. Moreover, an ultrasound-assisted reactor is a promising multifunctional reactor to be used in batch or continuous operation for biodiesel production with both homogeneous and heterogeneous catalysts. [ABSTRACT FROM AUTHOR]

A commercial household fruit blender is proposed as a simple, less time-consuming, and effective biodiesel production technique in this research work. Biodiesel was successfully produced in a 1200 W commercial household fruit blender. Due to the synergistic effect derived from the very high rotational speed of the blender blades integrated with micro-mixing level from cavitation phenomena, heat and mass transfer became greatly enhanced. The vigorous stirring inherently increased the temperature of the methanol-oil mixture to greater than 60 °C in less than 3 min, thus, a provision of external heating was not required. With a methanol to fresh refined palm oil molar ratio of 6:1 and 1 wt% sodium hydroxide catalyst, the FAME yield of 94.5% can be achieved in less than 3 min with the yield efficiency of 33.8 × 10−4 g/J for 500 mL of reaction volume. For 1000 mL of reaction volume at 1 min of reaction time, the FAME yield of 79.9% can be achieved with the yield efficiency of 122.3 × 10−4 g/J. Properties of the produced FAME comply with the EN 14214 and ASTM D 6751 standards. In conclusion, these results indicate that a high-power commercial household fruit blender can be utilized to produce biodiesel economically and effectively. Image 1 • Biodiesel was successfully produced in 1200 W commercial household fruit blender. • 94.5% FAME yield in <3 min with yield efficiency 33.8 × 10−4 g/J for 500 mL. • For 1 L at 1 min, 79.9% FAME yield achieved with yield efficiency 122.3 × 10−4 g/J. [ABSTRACT FROM AUTHOR]

• The RCR reduced the transesterification time while keeping a high FAME yield. • The grooved surface cone improved the rate of transesterification. • The RCR had high yield efficiency and productivity at a short residence time. The work developed a rotating cone reactor (RCR) as a promising multifunctional reactor for continuous biodiesel production from refined palm oil (RPO) homogeneously catalysed by NaOH. The effects of rotating cone geometry, rotational speed, catalyst amount, and reactant feed flow rate on FAME yield were investigated. Response surface methodology (RSM) and the Design Expert software were used to optimize the operating variables. The grooved cone surface was found to play an important role in increasing FAME yield. The model predicted a maximum FAME yield of 96.9 % at the process conditions of NaOH loading of 0.602 wt.% of oil, a feed flow rate of 298 mL/min, and a rotational speed of 751 rpm. It provided a high yield efficiency of 1.324 × 10−3 g/J and a high productivity of 0.715 mol/min at a very short residence time of 2 – 3 s. This resulted in a significant reduction in transesterification time, suggesting that the RCR is a promising multifunctional reactor for economical continuous biodiesel production. [Display omitted] [ABSTRACT FROM AUTHOR]

• Novel FAME hydrogenation using microwave plasma without catalyst. • Plasma system equipped with negative high voltage to accelerate ionized H. • Oxidation stability improved from 12.5 to 21.6 h. • Cold flow properties within the standards. • No trans C18:1 formation detected. Partially hydrogenated biodiesel or partially hydrogenated fatty acid methyl ester (H-FAME) derived from palm oil has been successfully synthesized using a microwave plasma system equipped with negative high voltage at low temperature without the use of a catalyst. The impact of the process parameters such as hydrogen gas feed flow rate, microwave power, reaction temperature, negative high voltage and reaction time on FAME composition and product properties were studied. It was found that the optimal condition for the highest conversion of polyunsaturated FAMEs was 8.5 L/min hydrogen flow rate, 500 W microwave power, 30 °C reaction temperature, 60 kV negative high voltage and 3 h of reaction time. The oxidation stability increased from 12.5 to 21.6 h and no trans C18:1 formation was detected. Further we found that the microwave plasma system equipped with negative high voltage can also be applied to effectively hydrogenate other chemicals at low temperatures without using a catalyst. [ABSTRACT FROM AUTHOR]

Biodiesel is a widely-used, renewable and environmentally-friendly fuel. The 700 W commercial household hand blender was proposed as simple and effective continuous FAME production technique using a homogeneous catalyst based on fresh refined palm oil, waste cooking oil (WCO), and various vegetable oils as feedstocks. The continuous system was designed and the effects of reaction volume, oil and methanol flow rate, reaction temperature and sodium hydroxide catalyst loading on FAME yield and yield efficiency were explored. The steady-state FAME yield of higher than 96.5% can be achieved from both fresh refined palm oil and WCO with the energy efficiency of 18.0 × 10-4 g/J (fresh refined palm oil) and 19.0 × 10-4 g/J (WCO) (6:1 methanol to oil molar ratio, reaction volume of 200 mL, total flow rate 12 mL/min, 60 °C, 0.8 wt% sodium hydroxide for palm oil and 1.5 wt% sodium hydroxide for WCO, highest stirring speed (10,640 rpm) at 220 V, no insulation), indicating that WCO shows good potential as a feedstock of biodiesel production. All properties of the synthesized FAMEs satisfy the EN 14214 and ASTM D 6751 standards. FAME produced from palm oil showed the highest FAME content, followed by sunflower oil and corn oil. The simple and low-cost kitchen hand blender is an alternative process intensification device to efficiently produce good quality FAME for household users, which is a convenient and environmentally-friendly method. WCO can also be recycled to produce a product with high economic value. [Display omitted] • Successful continuous FAME production using 700 W household hand blender. • Low residence time of 16.7 min can produce biodiesel of 0.6 kg/h. • This process intensification required low energy consumption. • Outstanding energy efficiency of 18.0 × 10−4 g/J for fresh palm oil. • Produced biodiesel complied with EN 14214 and ASTM D 6751 standards. [ABSTRACT FROM AUTHOR]

Waste cooking oil (WCO) as feedstocks for biodiesel production contains high free fatty acid and water, causing negative impacts on the biodiesel yield and its purity. In this work, three alternative methods for handling water content in WCO feedstocks using the earlier hybridization of esterification and transesterification in a single reactive distillation column (hybridized RD) were investigated. Our simulation results revealed that using two heat exchangers combined with the hybridized RD is a simple method to remove water from WCO. However, it requires the highest energy as well as biodiesel production cost (1.63 USD/kg biodiesel). The extended spacing stage modification of the hybridized RD was proposed to remove water content. It requires a new hybridized RD construction by spacing stages addition which can handle WCO with 10 wt% of water content and require less energy, resulting in lower biodiesel production cost (1.07 USD/kg biodiesel). The integration of pervaporation unit was found to be the best option. It offers the highest performance in terms of water removal and methanol recovery, resulting in the lowest biodiesel production cost (1.04 USD/kg biodiesel). This study shows that using pervaporation or extended spacing stages with hybridized RD are promising methods for biodiesel production from WCO. Image 1 • Improvement of biodiesel production process for feedstocks with high water content. • Comparison of different water removal methods for hybridized reactive distillation (RD). • Extended spacing stage of hybridized reactive distillation provides the lowest capital cost. • Hybridized RD with pervaporation membrane exhibits highest methanol recovery rate. [ABSTRACT FROM AUTHOR]

The enhancement in the catalytic activity by using metal loading on CaO/Al 2 O 3 pellet catalysts (M-CaO/Al 2 O 3) for transesterification of palm oil with a 12:1 methanol-to-oil molar ratio and 10 wt% of catalyst loading and stirring speed of 600 rpm at a reaction temperature of 65 °C was revealed. FAME yields at 6 h reaction time using K-CaO/Al 2 O 3 , Sr-CaO/Al 2 O 3 , Fe-CaO/Al 2 O 3 , Li-CaO/Al 2 O 3 , and CaO/Al 2 O 3 pellet catalysts were 88.8, 85.2, 67.0, 84.0, and 78.7%, respectively. M-CaO/Al 2 O 3 pellet catalysts can promote the initial rate, initial TOF, and FAME yield since the metal loading on the CaO/Al 2 O 3 pellet catalyst changes the environment of surface oxygen to increase lattice oxygen (O2−) as Lewis basic site. This work highlighted the role of O2− in the basicity and initial TOF with a linear correlation for metal oxide pellet catalyst. Although the K-CaO/Al 2 O 3 pellet catalyst gave the highest FAME yield, the highest leaching of the active species was observed. Therefore, the high catalytic activity and stability of the Sr-CaO/Al 2 O 3 pellet catalyst confirmed that there is more potential to drive toward continuous biodiesel production in the industry. [ABSTRACT FROM AUTHOR]

Abstract This study compares performance of different cavitation reactors for biodiesel production from palm oil using homogeneous and heterogeneous reaction systems. In addition, the effect of reaction volume of each reactor type was also investigated. For the smallest reaction volume of 165 mL, homogenizer and 20 kHz ultrasonic reactors offered the highest fatty acid methyl ester yield for both sodium hydroxide and calcium oxide catalysts. When the reaction volume was increased from 165 to 500 and 1000 mL with constant power input (80 W), homogenizer reactor did not significantly alter the rate of fatty acid methyl ester formation, unlike the other reactors which showed the decrease in the reaction rate. The reactor performance was evaluated in term of yield efficiency which was based on the amount of fatty acid methyl ester production, power consumption and reaction time. The increase of the reaction volume increased the yield efficiency of both the cavitation reactors and the mechanical stirred reactor. The highest yield efficiencies of 169.46 × 10−4 and 8.27 × 10−4 g/J were obtained from homogenizer reactor using sodium hydroxide and calcium oxide catalysts, respectively, using the reaction volume of 1000 mL. The homogenizer reactor also shows high flexibility of reaction volume usage with high biodiesel production performance in a batch system. Graphical abstract Image 1 Highlights • Different cavitation reactors were tested for fatty acid methyl ester production. • Reactors include mechanical stirrer (MS), ultrasonic (US) and homogenizer (HZ). • Yield efficiency increases with increasing reaction volume. • HZ offers the highest yield efficiency for both homo/heterogeneous reaction systems. [ABSTRACT FROM AUTHOR]

• High-efficiency biodiesel production using mixed solvent in ultrasonic reactor. • In-situ synergistic effect from mixed solvent addition for CaO catalyzed transesterification. • In-situ generation of calcium glyceroxide occurred during combination of ultrasonic and acetone. • Ultrasonic combined with mixed solvent achieves high biodiesel yield (97.3%) and yield efficiency. This work focuses on the improvement of biodiesel production with the addition of solvents (acetone, THF, and methyl myristate) in CaO catalyzed transesterification of palm oil and methanol in an ultrasonic reactor using a methanol to oil molar ratio of 9:1, reaction temperature of 60 °C, and CaO loading of 5 and 10 wt%. The addition of acetone and THF in the presence of ultrasonic irradiation expressed the synergistic effect which can accelerate the initial transesterification rate by increasing the solubility and in-situ generations of microbubble droplets and calcium glyceroxide as a new active species. The addition of methyl myristate enhanced the biodiesel yield by acting as an emulsifier of the reaction mixture and producing microemulsion droplets with the help of ultrasonic irradiation. Moreover, the mixed acetone and methyl myristate with existing ultrasonic irradiation can promote CaO catalyzed transesterification by accelerating the initial rate and achieving a high biodiesel yield (97.3%). The quality of the synthesized biodiesel in terms of physical properties is proven to meet the biodiesel standard. [ABSTRACT FROM AUTHOR]

• Highest surface area and basicity from extruded CaO-Al 2 O 3 compared to kaolin and diatomite binder. • CaO: Al 2 O 3 (A) mass ratio of 3.5: 1 calcined at 800 °C gave the highest FAME yield. • CaO-A pellet encourage to produce continuous biodiesel due to its high activity without leaching. In recent years, the use of heterogeneous catalysts has gained increasing attention for biodiesel production. Among metal oxide catalysts, CaO powder is widely explored and considered to be a promising catalyst. However, the powder catalyst is inappropriate for continuous biodiesel production. Therefore, the catalyst pellet fabrication parameters related to its properties and biodiesel yield were investigated. Key results included the observation that catalysts produced using an Al 2 O 3 binder possessed the highest catalytic activity compared to kaolin and diatomite supported catalysts, for calcination temperatures of 800 °C, possessing a comparable catalytic activity to the CaO powder. The CaO to Al 2 O 3 mass ratio exhibited a significant effect on the surface area and total basicity. The highest biodiesel yield was obtained using the CaO-A(800)-3.5:1 catalyst due to the presence of several active crystal phases including CaO, Ca(OH) 2 and CaSiO 3 phases to accelerate the transesterification rate. These fabricated CaO catalyst pellets can be utilized as a catalyst for the continuous biodiesel production process. [ABSTRACT FROM AUTHOR]

[Display omitted] Transesterification is a preferred reaction in biodiesel production using oil and alcohol as feedstocks. The major limitation of biodiesel production is the immiscibility of reactants resulting in the slow reaction rate. The development of an intensification reactor is the main purpose to eliminate the limitation and to increase the production capacity. The present research explored the state of the art for the hydrodynamic regime inside the rotating tube reactor (RTR) to enhance the biodiesel production rate using alkali-catalyzed transesterification based on the design specification. The influence of operating conditions in terms of methanol-to-oil molar ratio, NaOH loading, total flowrate, rotational speed using two dimensionless numbers, i.e. rotating Reynolds number (R e r) and Taylor number (T a) , as well as torque, were originally proposed to determine the optimal operating condition for biodiesel production in this RTR. This was interesting to report that the modulated wavy vortex flow is required to promote biodiesel yield in the RTR. The increment values of R e r , T a and torque associated with the turbulent Taylor vortex flow regime allowed the high reaction temperature which can generate excessive heat raising the methanol vaporization rate, leading to reduced biodiesel yield. Therefore, the optimal operating condition of this RTR was found to be 6:1 methanol-to-oil molar ratio, total flowrate of 30 mL/min, rotational speed of 1000 rpm at room temperature giving the highest yield of 97.5% with yield efficiency of 3.75 × 10 − 3 g/J and the quality of biodiesel met the ASTM specification. • High yield efficiency of 3.75 × 10 − 3 g/J obtained in rotating tube reactor (RTR). • Originate biodiesel yield-hydrodynamic regime correlation using T a , R e r and torque. • High biodiesel yield achieved in modulated wavy vortex flow regime of RTR. [ABSTRACT FROM AUTHOR]