Transesterification Of Waste Frying Oil Research Articles

Walnut-shaped calcium oxide-cancrinite spheres for transesterification of waste frying oil

Producing biodiesel via transesterification of waste oils or fats with short-chain alcohol is one of the possible ways to alleviate global energy and environmental issues, and further reducing the cost of transesterification catalyst is the essential strategy to enhance the competitiveness of biodiesel, such as applying industrial solid wastes as the source of catalyst active species. Thus in this work, via one-step pyrolysis of the calcium-rich residue, a byproduct from the hydrothermal treating (140–180 °C for 2–4 h) of paper mill sludge (PMS), a novel walnut-shaped calcium oxide-cancrinite based catalyst was prepared and applied to the transesterification of waste frying oil. The hydrothermal condition (changed from 140 oC-2 h to 180 oC-4 h) of PMS slightly influenced the yield of fatty acid methyl ester (YFAME), which ranged from 98.87% to 96.95% due to the slight decrease of the total basicity of strong basic sites (TSBβ+γ) from 149.6 to 102.9 μmol g−1. On the contrary, the pyrolysis temperature had a much greater effect on the transesterification performance of obtained catalysts. The optimum pyrolysis temperature was 750 °C and when it was increased to 850 °C, the increased bonding tendency of Si with Ca passivated the activity of calcium species and reduced the basic intensity and basicity of PSC-850, thus lowering its transesterification activity. Besides, the key process parameters were optimized and at the conditions of 70 °C, 3 h, 6.0 wt% of catalyst dosage, 10:1 of molar ratio of methanol to oil, over 95% of YFAME can be reached. The work herein not only provided a feasible way to recycle the inorganic solid residue of PMS but further lowered the cost of preparing biodiesel.

Oxidation reaction mechanism of hydrothermal carbon microspheres with applications to transesterification after sulfonation

AbstractBackgroundAn efficient sulfonic acid‐type acid catalyst with high acid site density based on hydrothermal carbon microspheres (HCMs) has been developed. The reaction by which double bonds in the HCMs were oxidized to generate carboxyl groups was evaluated based on density functional theory calculations.ResultsSulfonic acid‐type HCMs (SHCMs) were prepared from HCMs through a three‐step process comprising oxidation, amidation and sulfonation. An analysis of the oxidation process indicated that the formation of carboxyl groups involved the activation of O2 molecules and CH bonds, the cleavage of CC bonds, the homolytic fission of peroxy acids and the coupling reactions of H• radicals. The formation of numerous carboxyl groups on the HCM surfaces was the key to obtaining SHCMs with a high acid density of 14.5 mmol g−1.ConclusionsThe SHCMs obtained exhibited good catalytic performance during the transesterification of waste frying oil with methanol. Reactions performed using a methanol/oil molar ratio of 9:1 at 90 °C for 5 h gave a fatty acid methyl ester yield of 85.56%. © 2022 Society of Chemical Industry (SCI).

Electrolytic transesterification of waste frying oil using Na+/zeolite–chitosan biocomposite for biodiesel production

Given the economic and environmental advantages of using Waste Fried Oil (WFO) as a starting material, this investigation explores the conversion of WFO to Fatty Acid Methyl Ester (FAME) via electrolysis for use in waste. In electrolysis, hydroxyl ions are generated from water in close proximity to the cathode. When hydroxyl ions react with methanol, they produce a species of nucleophilic methoxide which is the main actor in converting WFO into FAME. This study specifically investigates the effects of voltage, catalyst concentration, co solvent amount, rotation speed, and molar ratio of methanol to WFO in electrolytic transesterification converting WFO into FAME using graphite electrodes in the presence of a heterogeneous, catalytic zeolite–chitosan composite. With an alcohol to WFO molar ratio of 8:1, 1 wt% zeolite-chitosan composite concentration at 40 V in the presence of 2 wt% H2O of the whole solution at room temperature and stirrer rate of 400 rpm and reaction time of 30 min, a 96.5% yield of FAME was achieved. Characterization of physical and biodiesel fuel properties was performed using American Society for Testing and Materials (ASTM) methods. The biocomposite was characterized using Fourier Transform Infrared (FTIR), X–ray Diffraction (XRD), Transmission Electron Microscopy(TEM), Brunauer Emmett Teller(BET), Thermogravimetric analysis (TG), Scanning Electron Microscopy (SEM) and Energy Dispersive X–ray spectrometry (EDX). Finally, the physical properties of FAME produced under optimal conditions were studied using Gas Chromatography–Mass Spectrometry (GC–MS), FTIR, surface tension, and viscosity.

Preparation of a carbon microsphere–based solid acid application to waste frying oil transesterification

The present work designed a new strategy incorporating oxidation, amidation and sulfonation to prepare carbon microsphere–based solid acids having a high density of sulfonic acid group. The carboxyl group concentration of the microspheres was increased through an oxidation process to provide grafting sites for amidation. Subsequently, p–phenylenediamine was introduced via an amidation reaction to provide more active sites for sulfonation. Finally, a sulfonic acid–type solid acid with an amount of surface acidic site of 11.3 mmol/g was obtained using a sulfonation process. Analyses by X–ray photoelectron and Fourier transform infrared (FTIR) spectroscopy confirmed the introduction of amino groups followed by sulfonic acid groups. These results were in agreement with thermogravimetric data. This material exhibited good catalytic performance during the transesterification of waste frying oil (WFO) and gave a fatty acid methyl ester yield of 92.2% after 4 h at 140 °C. This synthetic strategy is expected to provide a new approach to the preparation of sulfonic acid solid acids.

Valorization of waste chicken egg shells towards synthesis of heterogeneous catalyst for biodiesel production: Optimization and statistical analysis

The present research elucidates the synthesis of Zn/CaO catalyst from waste chicken egg shells and its application towards synthesis of biodiesel using waste frying oil (WFO) as a feedstock. The study also emphasizes on significant factor analysis and parametric optimization using Taguchi approach. The waste egg shells were calcined at 900 °C to obtain CaO and further loaded with Zn via wet incipient impregnation method. The engineered solid catalyst was characterized by thermogravimetric analysis (TGA), scanning electron microscope (SEM), Fourier-transform infrared spectroscopy (FTIR), BET analyzer and X-ray diffraction (XRD). The Taguchi approach was employed to recognize factors affecting yield of biodiesel significantly. The variables considered for optimizing the transesterification process were reaction time, catalyst loading, methanol to oil ratio and reaction temperature. The produced biodiesel was examined experimentally for estimation of physicochemical properties. The observed optimum conditions were: reaction temperature 65 °C, catalyst loading 4 wt%, reaction time 150 min, and methanol to oil ratio 15:1 giving a maximum biodiesel yield of 93.27%. Taguchi method also revealed that contribution of catalyst concentration and reaction temperature has pronounced effect on biodiesel yield. Hence, the developed Zn/CaO catalyst from waste chicken egg shells could be considered as efficient and active catalyst for transesterification of waste frying oil towards biodiesel production.

Combination of biodiesel, glycerol, and methanol as liquid fuel

Waste frying oil is a harmful liquid to human body and environment. However, it can be utilized as fuel. Transesterification of waste frying oil with methanol is presence of potassium hydroxide as catalyst produces fatty acid methyl ester (FAME) known as biodiesel as main product with glycerol as byproduct. Previously, several researches have been carried out concerning about utilization of both substances as renewable liquid fuel. In this research, three materials biodiesel, glycerol, and methanol which involved in transesterification process are combined in order to determine another renewable liquid fuel. Combination with composition 1:1:1 to 1:1:4 (v/v) is burned in an external combustion engine. Viscosity of glycerol is the main problem to form fuel for the engine. The result shows that the higher percentage of the methanol, the easier is the combustion. Composition by volume 1:1:4 of biodiesel, glycerol, and methanol respectively is the best mixture of liquid fuel for boiler burner.

Titania-termite hill composite as a heterogeneous catalyst: preparation, characterization, and performance in transesterification of waste frying oil

AbstractTo reveal the catalytic potential of abandoned naturally occurring material, we synthesized titania-termite hill composite (Ti-THC) via an incipient wetness impregnation route, characterized by various techniques and tested as a catalyst for transesterification of waste frying oil (WFO). The reusability of the prepared catalyst was also studied to evaluate its stability. The effects of reaction process parameters, such as temperature, time, catalyst loading and methanol/WFO molar ratio on fatty acid methyl ester (FAME) yield, were investigated using a central composite design approach. SEM result revealed pores formation on the catalyst surface, while XRD and EDX analyses confirmed successful insertion of titania into the aluminosilicate layer of the termite hill. The maximum FAME yield of 90.78% was obtained at optimum experimental conditions of 71.16 °C reaction temperature, 2.12 h reaction time, 1.03 wt.% catalyst loading and 9.96:1 methanol/WFO molar ratio. The catalyst still maintained its better stability after being reused for three reaction cycles.

Preparation of a Sulfonic‐Acid‐Type Ordered Mesoporous Carbon Solid Acid via Hydrothermal Synthesis for the Transesterification of Waste Frying Oil

AbstractHydrothermal carbonisation was used to synthesise hydrothermally ordered mesoporous carbon (HOMC), employing sucrose as the carbon source, a P123 block copolymer as the surfactant and tetraethyl orthosilicate as the silicon source. A high‐density sulfonic‐acid‐based solid acid catalyst (HOMC‐SO3H) was subsequently prepared via low‐temperature sulfonation of the HOMC with concentrated sulfuric acid. Transmission electron microscopy and small‐angle X‐ray diffraction analyses showed that both the HOMC and HOMC‐SO3H exhibited an ordered mesoporous structure. The N2 Brunauer‐Emmett‐Teller surface areas of the HOMC and HOMC‐SO3H were determined to be 112 and 87 m2/g, respectively, and the average pore sizes were 11.0 and 15.1 nm, respectively. X‐ray photoelectron spectroscopy data confirmed that −SO3H groups were successfully introduced onto the HOMC surface by the sulfonation process, and a surface acid concentration of 5.9 mmol/g HOMC‐SO3H was determined by acid‐base titration. The HOMC‐SO3H was applied to the transesterification of waste frying oil with methanol and a fatty acid methyl ester yield of 95 % was obtained after a 5 h reaction at 180 °C.

Enzymatic Transesterification of Waste Frying Oil from Local Restaurants in East Colombia Using a Combined Lipase System

The search for innovation and biotechnological strategies in the biodiesel production chain have become a topic of interest for scientific community owing the importance of renewable energy sources. This work aimed to implement an enzymatic transesterification process to obtain biodiesel from waste frying oil (WFO). The transesterification was performed by varying reaction times (8 h, 12 h and 16 h), enzyme concentrations of lipase XX 25 split (14%, 16% and 18%), pH of reaction media (6, 7 and 8) and reaction temperature (35, 38 and 40 °C) with a fixed alcohol–oil molar ratio of 3:1. The optimum operating conditions were selected to quantify the amount of fatty acid methyl esters (FAMEs) generated. The highest biodiesel production was reached with an enzyme concentration of 14%, reaction time of 8 h, pH of 7 and temperature of 38 °C. It was estimated a FAMEs production of 42.86% for the selected experiment; however, best physicochemical characteristics of biodiesel were achieved with an enzyme concentration of 16% and reaction time of 8 h. Results suggested that enzymatic transesterification process was favorable because the amount of methyl esters obtained was similar to the content of fatty acids in the WFO.

Application of Artificial Neural Network to Predict Biodiesel Yield from Waste Frying Oil Transesterification

Used frying oil (UFO) has a great potential as feedstock for biodiesel production. This study aims to develop an artificial neural network (ANN) model to predict biodiesel yield produced from base-catalyzed transesterification of UFO. The experiment was performed with 100 mL of UFO at three different molar ratios (oil:methanol) (namely 1:4, 1:5, and 1:6), conducted with reaction temperatures of 30 to 55oC (raised by 5oC), and reaction time of 0.25, 0.5, 1, 2, 3, 6, 8, and 10 minutes. Prediction model was based on ANN model consisting of three layers with 27 combinations of three activation functions (tansig, logsig, purelin). All activation function architectures were trained using Levenberg- Marquardt train type with 126 data set (87.5%) and learning rate of 0.001. Model validation used 18 data set (12.5%) measured at reaction time of 8 min. Results showed that two ANN models with activation function of logsig-purelin-logsig and purelin-logsig-tansig be the best with RRMSE of 2.41% and 2.44% with R2 of 0.9355 and 0.9391, respectively. Predictions of biodiesel yield using ANN models are significantly better than those of first-order kinetics.

Glycerol from waste frying oil as sustainable fuel

In search of renewable and environmentally friendly fuel, transesterification of waste frying oil was an excellent method to produce biodiesel. Transesterification was not only producing biodiesel but also creating glycerol as by product. Unfortunately, transesterification of waste frying oil causes the colour of glycerol usually dark brown due to impurities, caramelization, and Millard reaction. In order to improve quality of glycerol, absorption using activated charcoal was applied. Glycerol was intended to replace diesel fuel for boiler burner. Due to high viscosity, glycerol was mixed with methanol. Mixture of glycerol and methanol in various compositions was applied on boiler burner. By analyzing the flame and flue gas, composition of 10% glycerol and 90% methanol was the best mixture.

Synthesis of fatty acid methyl ester via transesterification of waste frying oil by a zinc-modified pumice catalyst: Taguchi approach to parametric optimization

Methanolysis of waste frying oil (WFO) was conducted to synthesize fatty acid methyl esters (FAME) using zinc-modified pumice (ZMP) as a heterogeneous catalyst. The ZMP catalyst was prepared via incipient wetness impregnation method and characterized by various spectroscopic techniques such as Brunauer–Emmett–Teller (BET) surface area, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), X-ray fluorescence (XRF), Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). Taguchi design approach was employed to optimize the transesterification process variables, which include reaction temperature (50–70 °C), reaction time (1–3 h), methanol/WFO molar ratio (6:1–12:1) and catalyst loading (1–3 wt%). The transesterification reaction kinetic and impact of reaction temperature on the reaction rate were investigated. The kinetic data obtained at different temperatures were evaluated using zero-order and pseudo-first-order models. Among the process variables studied, FAME yield was mostly affected by the reaction temperature, methanol/WFO molar ratio, and catalyst loading. The maximum FAME yield of 91.05 wt% was attained at the optimum reaction temperature of 60 °C, 3 wt% catalyst loading, and 12:1 methanol/WFO molar ratio. The better activity exhibited by the ZMP catalyst in the transesterification reaction was attributed to the interaction among several metal oxides present in the catalyst as confirmed by the EDX, XRF and XRD analyses. The catalyst stability study showed that the ZMP could be reused up to four times. The pseudo-first-order model gave the best fit with the catalytic reaction data, and the activation energy was 50.61 kJ mol−1.

Concave carbon-microsphere-based solid acid catalysts for transesterification and epoxidation

In this study, concave carbon microspheres (CCMSs) were synthesized using glucose as the raw material in the presence of an anionic surfactant sodium dodecyl sulfate (SDS) by a hydrothermal method. Sulfonic acid groups (−SO3H) were attached on the CCMSs surfaces by sulfonation using concentrated sulfuric acid, affording a solid acid catalyst (CCMSs catalyst). Scanning electron microscopy (SEM) results revealed that the diameters of the microspheres are 1–3 μm, and the diameters of the concave are 1–2 μm; hence, micron or submicron reaction cells can be formed Furthermore, sulfonation did not change the morphology of the carbon microspheres. N2-BET measurement results revealed that at a hydrothermal temperature and time of 180 °C and 8 h, respectively, and an SDS dosage of 0.10 g, the Brunauer-Emmett-Teller (BET) surface area of CCMSs could reach up to 7.7 m2/g. X–ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) results confirmed that CCMSs are successfully modified by sulfonation. The surface acid amounts of CCMSs before and after sulfonation were 3.7 and 5.6 mmol H+/g, respectively. CCMSs catalyst was used to catalyze the transesterification of waste frying oil, affording fatty acid methyl ester in 93% yield. CCMSs catalyst was used to catalyze the epoxidation of waste frying oil, achieving a double-bond conversion of 79% and a relative epoxy yield of 57%.

Preparation of mesoporous double‐layer carbon microsphere‐based solid acid catalyst by hydrothermal method and its application in catalytic transesterification of waste frying oil

AbstractBACKGROUNDMesoporous double‐layer carbon microspheres (DCSs) were synthesized using hollow tin(IV) oxide (SnO2) microspheres as hard template and sucrose as carbon precursor via the hydrothermal method. Sulfonic acid groups (‐SO3H) were introduced onto the surfaces of DCS by sulfuric acid heating and sulfanilic acid diazonium coupling, respectively, to form two solid acids (DCS‐SS and DCS‐DS, respectively).RESULTSThe transmission electron microscopy images showed that the carbon microspheres possessed a hollow double‐layer structure with diameters of about 200 to 300 nm and shell thickness of about 30 to 50 nm. Furthermore, the sulfonate treatments caused no changes in the morphology of carbon microspheres. The nitrogen (N2)‐Brunauer–Emmett–Teller (BET) results indicate that DCS, DCS‐SS, and DCS‐DS featured mesopores with an average pore size of 4.5 to 4.8 nm and BET surface areas of 75 m2/g, 57 m2/g, and 53 m2/g, respectively. The X‐ray photoelectron spectroscopy and Fourier‐transform infrared results confirmed that the DCS‐SS and DCS‐DS contained a ‐SO3H group and their surface acid densities are 4.5 and 4.1 mmol/g, respectively.CONCLUSIONDCS‐SS and DCS‐DS were used to catalyze the transesterification of waste frying oil, and the highest yields of fatty acid methyl esters, that is, 85% and 80%, respectively, could be obtained. © 2019 Society of Chemical Industry

Purification of residual glycerol recovered from biodiesel production

Transesterification is the most widely used reaction in the production of biodiesel. It involves the breaking of the triglyceride structure and the exchange of alkyl groups with the hydroxide groups of the alcohol to obtain the new ester (biodiesel). In this process residual glycerol is also produced, but since it is of low purity few alternatives for its application have been identified. In this context, a methodology for the purification of the residual glycerol was developed with a view to adding value to this product and making the process more economically attractive. In this study, residual glycerol was obtained from the transesterification of waste frying oil and of virgin soybean oil in bench scale. The purification method was also applied to residual glycerol obtained from a similar process on industrial scale. The product obtained after each step was characterized to evaluate the contribution of each unit of the operation to the quality of the final product. The results obtained show an increase in the degree of the glycerol purity in each step. It can thus be concluded that the method presented herein can be used to increase the quality of residual glycerol obtained from the biodiesel production process resulting in its acceptable commercial value.

Biodiesel and Crude Glycerol from Waste Frying Oil: Production, Characterization and Evaluation of Biodiesel Oxidative Stability with Diesel Blends

Waste oils are becoming increasingly more important as feedstock for the production of fuels and glycerol as byproduc. Optimization of homogeneous transesterification of waste frying oil (WFO) to biodiesel over hydroxide potassium (KOH) catalyst have been investigated. In this respect, response surface methodology (RSM) was applied to determine the relationships between methanol and WFO molar ratio (3:1–12:1), KOH concentration (0.5%–2%) and temperature (25–65 °C) on the conversion yield. Transesterification of WFO produced 96.33% maximum methyl ester yield at the optimum methanol/WFO molar ratio 7.3:1, KOH loading 0.5 wt. % and the reaction temperature was 58.30 °C. The physicochemical properties of optimized biodiesel met the requirements of the European Norm 14214, such as kinematic viscosity at 40 °C 4.57 mm/s2, the sulfur content 0.005 wt. %, and the density at 15 °C 889.3 kg/m3. This study also examined the accelerated oxidation of biodiesel and biodiesel/diesel blends under combined temperature and air effect at different periods of time while measuring their acidity. Results have shown that total acid number increased proportionally to the biodiesel content of the biodiesel/diesel blends from 0.5 mgKOH/g for B7 (7% (v/v) biodiesel and 93% (v/v) diesel) up to 2.8 mg KOH/g for B100 (100% biodiesel). The synthesized trans-esterified oil can be a potential alternative to petrodiesel, hence its application at an industrial scale. This work also reports some properties of crude glycerol (CG) derived from biodiesel from WFO. The glycerol yield (%), pH, water content (wt. %), density at 15 °C (g/cm3), and kinematic viscosity at 40 °C (mm2/s) was analyzed according to standard test methods.

Preparation, characterization and application of ordered mesoporous sulfated zirconia

A series of ordered mesoporous sulfated zirconia (OMSZ) with different calcination temperatures (400–650 °C) have been synthesized by a self-assembly method using zirconium n-propoxide as raw material, P123 (EO20PO70EO20) as structure-directing agent and ammonium sulfate as sulfonating agent. The transmission electron microscopy results indicated that the OMSZ had the ordered mesoporous structure and the X-ray diffraction analysis further revealed that the OMSZ had hexagonal ordering structure. The N2–BET results showed that the OMSZ were mesoporous materials and, when the calcination temperature was 500 °C, the BET surface area could reach 183 m2/g. Temperature-programed desorption of NH3 (NH3–TPD) analysis confirmed that the OMSZ possessed a superacid when the calcination temperature was higher than 450 °C. FTIR-pyridine adsorption results indicated that the OMSZ surfaces were mainly the Lewis acid sites. The catalytic activity of OMSZ was observed for transesterification of waste frying oil, and 92% of yield could be obtained after 6 h at 200 °C.

Performance characteristics of a supercharged variable compression ratio diesel engine fueled by biodiesel blends

Massive pressure was recently exerted on the automotive industry to explore sustainable and eco-friendly fuels. Biodiesel has attracted many researchers over the last decades as an important source of alternative fuel. The redeeming feature of biodiesel is that it reduces the emission of exhaust harmful gases, however, this feature comes at engine performance penalty. Therefore, this study was carried out to investigate the effect of varying the air flow and compression ratios on the performance of biodiesel-diesel fuel engines. The biodiesel was sourced from the transesterification of waste frying oil and was used in selected blends with ratios, by volume ranging from a volume of 0–50% biodiesel-diesel blend. A four strokes naturally-aspirated direct injection diesel engine was investigated in this study. The engine was equipped with a supercharger to increase the density of air supplied to the engine, and with another device to change the compression ratios. The engine brake power, brake specific fuel consumption and brake thermal efficiency were the performance parameters of the present work. The engine was kept running over a speed range from 1000 to 2000 rpm at 250 rpm intervals and three compression ratios (14, 16 and 18) under full load mode of operation, and different intake air pressures. The result indicated that forced induction operation using the supercharger increased the performance of the dual fuel mode by 25% at the highest compression ratio (18) compared to that of natural aspiration. On the other hand, it was revealed that the higher the compression ratio of the engine, the higher the performance obtained from the blend. In fact, supercharging the engine along with the higher compression ratio improved the penetration of the forced air into the fuel charge despite the biodiesel higher viscosity. The appropriate penetration of the biodiesel warranted the higher temperature and pressure in the engine cylinder, which in turn improved the combustion and performance of the dual fuel engine.

Synthesis and characterization of anthill‐eggshell‐Ni‐Co mixed oxides composite catalyst for biodiesel production from waste frying oil

AbstractThis study was conducted to develop a new composite heterogeneous catalyst, anthill‐eggshell‐Ni‐Co mixed oxides (AENiCo), for biodiesel production via transesterification of waste frying oil. The catalyst was synthesized using a co‐precipitation method and was characterized by Brunauer‐Emmett‐Teller (BET) surface area analysis, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), X‐ray diffraction (XRD) and X‐ray fluorescence (XRF). The effects of parameters affecting the catalytic reaction, reaction temperature (40–80°C), reaction time (1–5 h), catalyst loading (1–9 wt%), and methanol‐to‐oil ratio (3:1–15:1) were investigated. The stability of the spent catalyst was also investigated during reuse. The data obtained showed that the maximum biodiesel yield of 90.23% could be obtained at a reaction temperature of 70°C, reaction time of 2 h, with a catalyst loading of 3 wt% and methanol‐to‐oil ratio of 12:1. The stability study showed that the AENiCo catalyst could be reused for up to four cycles. © 2018 Society of Chemical Industry and John Wiley & Sons, Ltd

Transesterification of Waste Frying Oil and Soybean Oil by Combi-lipases Under Ultrasound-Assisted Reactions.

This work describes the use of an ultrasound system for the enzymatic transesterification of oils using combi-lipases as biocatalyst. The reactions were carried out evaluating the individual use of waste oil and fresh soybean oil, and the immobilized lipases CALB, TLL, and RML were used as biocatalysts. It was performed in a mixture design of three factors to obtain the ideal mixture of lipases according to the composition of fatty acids present in each oil, and the main reaction variables were optimized. After 18h of reaction, ultrasound provided a biodiesel yield of about 90% when using soybean oil and 70% using the waste oil. The results showed that ultrasound technology, in combination with the application of enzyme mixtures, known as combi-lipases, and the use of waste oil, could be a promising route to reduce the overall process costs of enzymatic production of biodiesel.