The effect of ultrasound on lipase-catalyzed hydrolysis of soy oil in solvent-free system

Comparative studies of lipase-catalyzed hydrolysis of soy oil in solvent-free system were carried out in shaking bath and in ultrasonic bath. A suitable ultrasonic power of 1.64 W cm(-2) was determined to guarantee satisfactory hydrolysis extent and lipase activity. The influence of temperature, pH, enzyme concentration and water/oil ratio was investigated subsequently. Compared with that in shaking bath, optimum temperature and inactivation temperature of lipase in ultrasonic bath were about 5-10 degrees C higher, while pH effect in ultrasonic bath was similar; ultrasound also led to a smooth increase of reaction rate at relatively higher enzyme loading and less use of water to saturate hydrolysis substrate. In optimum conditions, the overall hydrolysis reaction rate in the ultrasonic bath process was above 2-fold than that in the shaking bath process.     

Ultrasound assisted enzymatic conversion of non edible oil to methyl esters

Conventional and ultrasound-assisted hydrolysis and subsequent esterification of Nagchampa oil under mild operating conditions have been investigated with an objective of intensification of methyl esters production using a sustainable approach. The effect of ratio of reactants, temperature, enzyme loading, pretreatment of enzyme (using ultrasonic irradiations) on the hydrolysis and esterification reaction has been studied. Optimum conditions for hydrolysis were observed to be 1:1 weight ratio of oil: water for Lip Z and 1:3 for Lip 2 enzymes, enzyme loading of 400 units for Lip Z and 800 mg for Lip 2 enzymes and reaction time of 6 h. In the case of esterification reaction, optimum conditions obtained were oil to methanol molar ratio of 1:2, enzyme loading of 1000 mg and reaction time of 20 h. Use of pretreated enzyme (using ultrasonic irradiations) was found to increase the extent of esterification reaction from 75% to 92.5%. It was observed that use of ultrasound in the reaction significantly intensified the esterification reaction with time requirement reducing from 20 h for conventional stirring based approach to only about 7.5 h in the presence of ultrasound. The extent of esterification obtained with sonicated enzyme also increased to 96% from 75% with unsonicated enzyme.     

Ultrasound irradiation promoted efficient solvent-free lipase-catalyzed production of mono- and diacylglycerols from olive oil

This work reports the enzymatic production of mono- and diacylglycerols under the influence of ultrasound irradiation, in a solvent-free system, with and without the presence of surfactants at a constant temperature of 65°C, glycerol to oil molar ratio of 2:1 and a commercial immobilized lipase (Novozym 435) as catalyst. For this purpose, two operation modes were adopted: the use of a sonotrode (ultrasonic probe), without agitation, varying reaction time, irradiation amplitude (25-45% of the total power) and type of surfactant, and a mechanically stirred reactor (600 rpm) under ultrasound irradiation in a water bath, testing different surfactants. Results show that very satisfactory MAG and DAG yields, above 50 wt.%, can be obtained without the use of surfactant, at mild irradiation power supply (～130 W), with no important enzyme activity losses verified, in a relatively short reaction time (2h), and low enzyme content (7.5 wt.%). Also, reaction kinetic results show that contents of MAG+DAG as high as ～65 wt.% can be achieved at longer times (6h), indicating a promising route for producing MAG and DAG using ultrasound irradiation.     

Ultrasound assisted synthesis of isopropyl esters from palm fatty acid distillate

Esterification is one of the most preferred synthesis routes for organic esters which are most frequently used as plasticizers, solvents and perfumery and flavour chemicals. The present work deals with acid catalyzed synthesis of isopropyl esters from palm fatty acid distillate (PFAD) in the presence of ultrasonic irradiations operating at 25kHz frequency and 1kW of supplied power. Effect of different operating parameters such as molar ratio of reactants, catalyst quantity and operating temperature has been studied with an aim of optimization. It has been observed that ultrasound enhances the rate of reaction and the extent of equilibrium conversion. The optimum parameters for this process have been found to be 1:5 molar ratio of PFAD to isopropanol, catalyst concentration of 5% of PFAD and 60 degrees C reaction temperature. Maximum conversion levels of about 80% have been obtained in 6h of reaction time under these optimized conditions. Analysis of the kinetic data indicates that the reaction follows first order reversible path.     

Enzymatic synthesis of ascorbyl palmitate in ultrasound-assisted system: process optimization and kinetic evaluation

This work is focused on the optimization of reaction parameters for the synthesis of ascorbyl palmitate catalyzed by Candida antarctica lipase in different organic solvents under ultrasound irradiation. The sequential strategy of experimental design proved to be useful in determining the optimal conditions for reaction conversion in tert-butanol system using Novozym 435 as catalyst. The optimum production was achieved at 70°C, ascorbic acid to palmitic acid molar ratio of 1:9, enzyme concentration of 5 wt% at 3h of reaction, resulting in an ascorbyl palmitate conversion of about 27%. Reaction kinetics for ascorbyl palmitate production in ultrasound device showed that satisfactory reaction conversions (～26%) could be achieved in short reaction times (2h). The empirical kinetic model proposed is able to satisfactorily represent and predict the experimental data.     

An investigation of lipase catalysed sonochemical synthesis: A review

Ultrasonic irradiation has recently gained attention of researchers for its process intensification in numerous reactions. Earlier ultrasound was known for its application either to deactivate enzyme activity or to disrupt the cell. However, in recent years, practice of ultrasonic irradiation began to emerge as a tool for the activation of the enzymes under mild frequency conditions. The incorporation of ultrasound in any of enzymatic reactions not only increases yield but also accelerates the rate of reaction in the presence of mild conditions with better yield and less side-products. To attain maximum yield, it is crucial to understand the mechanism and effect of sonication on reaction especially for the lipase enzyme. Thus, the influence of ultrasound irradiation on reaction yield for different parameters including temperature, enzyme concentration, mole ratio of substrates, solvents ultrasonic frequency and power was reviewed and discussed. The physical effect of cavitation determined by bubble dynamics and rate of reaction through kinetic modelling also needs to be assessed for complete investigation and scale up of synthesis. Thus, prudish utilisation of ultrasound for enzymatic synthesis can serve better future for sustainable and green chemistry.     

Ultrasound assisted enzyme catalyzed synthesis of glycerol carbonate from glycerol and dimethyl carbonate

The present work illustrates the transesterification of glycerol to glycerol carbonate (GlyC) from dimethyl carbonate (DMC) using commercial immobilized lipase (Novozym 435) under ultrasonic irradiation. The experiments were performed in a batch reactor placed in an ultrasonic water bath using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound power on the conversion of glycerol to GlyC. It has been found that ultrasound-assisted lipase-catalyzed transesterification of glycerol would be a potential alternative to conventional alkali-catalyzed method, as high conversion (99.75%) was obtained at mild operating conditions: molar ratio of DMC to glycerol 3:1, catalyst amount of 13% (w/w), lower power input (100 W), duty cycle 50% and temperature (60 °C) in a relatively short reaction time (4 h) using Novozym 435 as catalyst. Ultrasound reduces the reaction time up to 4 h as compared to conventional stirring method (14 h) catalyzed by Novozym 435. The repeated use of the catalyst under the optimum experimental condition resulted in decay in both enzyme activity and product conversion.     

Using low intensity ultrasound to improve the efficiency of biological phosphorus removal

Low intensity ultrasound can produce various effects on biological materials, such as stimulating enzyme activity, cell growth, biosynthesis, etc., which may improve the efficiency of enhanced biological phosphorus removal (EBPR). We adopt total phosphorus (TP) and dehydrogenase activity (DHA) as indicators to confirm the feasibility of applying low intensity ultrasound in EBPR. Single-factor experiments and orthogonal test were conducted in batch anaerobic/oxic (A/O) process simulation to study the influence of ultrasonic intensity and exposure time in the EBPR process. The results showed that the optimal ultrasonic parameters were 0.2 W/cm² and 10 min under which condition the TP concentration in the effluent was 35–50% lower than that of the control (without ultrasonic irradiation). Changes of sludge activities after ultrasonic irradiation were examined. The improvement of sludge activity by ultrasound took 4 h after irradiation to reach the peak level, when an increase above 50% of DHA has been achieved by ultrasonic irradiation, and the enhancing effects induced by ultrasound disappeared in 16 h after irradiation. A tentative mechanism of biological phosphorus removal enhancement stimulated by ultrasound was discussed based on these phenomena.     

Ultrasound assisted enzyme catalyzed hydrolysis of waste cooking oil under solvent free condition

The present work demonstrates the hydrolysis of waste cooking oil (WCO) under solvent free condition using commercial available immobilized lipase (Novozyme 435) under the influence of ultrasound irradiation. The process parameters were optimized using a sequence of experimental protocol to evaluate the effects of temperature, molar ratios of substrates, enzyme loading, duty cycle and ultrasound intensity. It has been observed that ultrasound-assisted lipase-catalyzed hydrolysis of WCO would be a promising alternative for conventional methods. A maximum conversion of 75.19% was obtained at mild operating parameters: molar ratio of oil to water (buffer pH 7) 3:1, catalyst loading of 1.25% (w/w), lower ultrasound power 100 W (ultrasound intensity – 7356.68 W m⁻²), duty cycle 50% and temperature (50 °C) in a relatively short reaction time (2 h). The activation energy and thermodynamic study shows that the hydrolysis reaction is more feasible when ultrasound is combined with mechanical agitation as compared with the ultrasound alone and simple conventional stirring technique. Application of ultrasound considerably reduced the reaction time as compared to conventional reaction. The successive use of the catalyst for repetitive cycles under the optimum experimental conditions resulted in a loss of enzymatic activity and also minimized the product conversion.     

Ultrasound accelerated esterification of bile acids

In this study power ultrasound accelerated esterification reactions of some model substances and bile acids were done. In the model reactions the best result was 19-fold increase in the reaction rate when using ultrasound and the temperature was allowed to rise during the irradiation. In the case of bile acid methyl esters a clear increase in the reaction rates was also observed by ultrasonic irradiations.     

Rapid esterification of fatty acid using dicationic acidic ionic liquid catalyst via ultrasonic-assisted method

Biodiesel production via esterification/transesterification reactions can be catalyzed by homogenous or heterogeneous catalysts. Development of heterogeneous catalysts for biodiesel production is highly advantageous due to the ease of product purification and of catalyst recyclability. In this current work, a novel acidic [DABCODBS][CF₃SO₃]₂ dicationic ionic liquid (DIL) was used as heterogeneous catalyst to produce biodiesel using oleic acid as model oil. The esterification was conducted under ultrasonic irradiation (20 kHz) using a 14 mm ultrasonic horn transducer operated at various duty cycles. It was observed that the duty cycle, amplitude, methanol to oil molar ratio, catalyst amount and reaction temperature were the major factors that greatly impact the necessary reaction time to lead to a high yield of biodiesel. The reaction conditions were optimized with the aid of Response Surface Methodology (RSM) designed according to the Quadratic model of the Box Behnken method. The optimum conditions were found to be at catalyst amount of 0.64 mol%, methanol to oil ratio of 14.3:1, temperature of 59 °C, reaction time of 83 min and amplitude of 60% in continuous mode. The results showed that the oleic acid was successfully converted into esters with conversion value of 93.20% together with significant reduction of reaction time from 7 h (using mechanical stirring) to 83 min (using ultrasonication). The results also showed that the acidic DIL catalyst we designed purposely was efficient to catalyze the ultrasonic-assisted esterification yielding high conversion of oleic acid to methyl oleate on short times. The DIL was also recycled and reused for at least five times without significant reduction in performance. Overall, the procedure offers advantages including short reaction time, good yield, operational simplicity and environmentally benign characteristics.     

Ultrasound-assisted synthesis of NiFe- layered double hydroxides as efficient electrode materials in supercapacitors

Under ultrasound irradiation, NiFe-layered double hydroxide (NiFe-LDH) nanostructures with three molar ratios and three dissimilar reaction times were prepared. The powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and Fourier transform infrared spectroscopy (FT-IR) were employed to characterize the synthesized nanomaterials. Using a sonochemichal route, various morphologies of the NiFe-LDH nanostructures without any impurity and variations in the structure were produced. During the optimization process, it was found that sonication time and reagent concentration in a fixed irradiation frequency can affect the size and the morphology of the produced nanostructures. Under ultrasound irradiation, non-aggregated particles with uniform, spherical morphology were obtained with molar ratios of 4:1 (Ni:Fe) with 45 W at 180 min. The NiFe-LDH samples were observed to be supercapacitor under a 6 M KOH solution. When morphologically-controlled NiFe-LDH samples were used, the pseudo-capacitive behavior of the nanostructures was tuned. After 3 h of ultrasonic irradiation, the optimized sample (NiFe-LDH spherical nanostructures with 4:1 M ratio) had a high value of specific capacitance (168F g⁻¹).     

Ultrasound-assisted lipase-catalyzed transesterification of soybean oil in organic solvent system

This work reports the transesterification of soybean oil with ethanol using two commercial immobilized lipases under the influence of ultrasound irradiation. The experiments were performed in an ultrasonic water bath, following a sequence of experimental designs to assess the effects of temperature, enzyme and water concentrations, oil to ethanol molar ratio and output irradiation power on the reaction yield. Results show that ultrasound-assisted lipase-catalyzed transesterification of soybean oil with ethanol might be a potential alternative route to conventional alkali-catalyzed method, as high reaction yields (∼90 wt.%) were obtained at mild irradiation power supply (∼100 W), and temperature (60 °C) in a relatively short reaction time, 4 h, using Lipozyme RM IM as catalyst. The repeated use of the catalyst under the optimum experimental condition resulted in a decay in both enzyme activity and product conversion after two cycles. The use of Novozym 435 led to lower conversions (about 57%) but the enzyme activity was stable after eight cycles of use, showing, however, a reduction in product conversion after the forth cycle.     

Quantification of ultrasonic intensity based on the decomposition reaction of porphyrin

A simple method is proposed for quantification of the effective ultrasonic intensity in the reaction vessel based on the decomposition reaction of 5,10,15,20-tetrakis(4-sulfotophenyl) porphyrin (H₂TPPS⁴⁻). The change of concentration of porphyrin in solution irradiated by the ultrasound wave depends on the irradiation time and the output power of ultrasound generator. The decomposition ratio of porphyrin is defined as the ratio of the concentration of porphyrin after ultrasonic irradiation to that before ultrasonic irradiation. A linear relationship between the decomposition ratio of porphyrin and the concentration Fe³⁺ in the Fricke solution under sonication was obtained. The decomposition ratio was related to the absorption dose in radiation chemistry.     

Ultrasound-assisted butyl acetate synthesis catalyzed by Novozym 435: Enhanced activity and operational stability

The influence of low-frequency ultrasound (40 kHz) in the esterification reaction between acetic acid and butanol for flavor ester synthesis catalyzed by the commercial immobilized lipase B from Candida antarctica (Novozym 435) was evaluated. A central composite design and the response surface methodology were used to analyze the effects of the reaction parameters (temperature, substrate molar ratio, enzyme content and added water) and their response (yields of conversion in 2.5 h of reaction). The reaction was carried out using n-hexane as solvent. The optimal conditions for ultrasound-assisted butyl acetate synthesis were found to be: temperature of 46 °C; substrate molar ratio of 3.6:1 butanol:acetic acid; enzyme content of 7%; added water of 0.25%, conditions that are slightly different from those found using mechanical mixing. Over 94% of conversion was obtained in 2.5 h under these conditions. The optimal acid concentration for the reaction was determined to be 2.0 M, compared to 0.3 M without ultrasound treatment. Enzyme productivity was significantly improved to around 7.5-fold for each batch when comparing ultrasound and standard mechanical agitation. The biocatalyst could be directly reused for 14 reactions cycles keeping around 70% of its original activity, while activity was virtually zeroed in the third cycle using the standard mixing system. Thus, compared to the traditional mechanical agitation, ultrasound technology not only improves the process productivity, but also enhances enzyme recycling and stability in the presence of acetic acid, being a powerful tool to improve biocatalyst performance in this type of reaction.     

Ultrasound irradiation promoted enzymatic alcoholysis for synthesis of monoglyceryl phenolic acids in a solvent-free system

Monoglyceryl phenolic acids (MPAs) were known as the natural hydrophilic antioxidants which could be used in different fields such as food, pharmaceutical, cosmetic etc. A novel enzymatic route of MPAs synthesis by the alcoholysis of phenolic acid ethyl esters with glycerol under ultrasound irradiation in solvent free system was developed. Optimization of reaction parameters shows that a high conversion of above 97.4% can be obtained under the following conditions: phenolic acid ethyl esters to glycerol molar ratio of 1:10, with 6% catalyst (Novozym 435), at 60 °C and 200 rpm, with ultrasound input of 250 W, at 20 kHz frequency. Compared to the conventional stirring method, the activation energy for phenolic acid ethyl esters conversion was decreased from 65.0 kJ/mol to 32.1 kJ/mol under ultrasound promotion; the apparent kinetic constant (V_m/K_m) increased above 1.2-folds; the lipase amount decreased to 50%; the time required for the maximum conversion reduced up to 3-folds without damaging the lipase activity, which is the fastest report for enzymatic synthesis of MPAs.     

Ultrasound assisted intensification of biodiesel production using enzymatic interesterification

Ultrasound assisted intensification of synthesis of biodiesel from waste cooking oil using methyl acetate and immobilized lipase obtained from Thermomyces lanuginosus (Lipozyme TLIM) as a catalyst has been investigated in the present work. The reaction has also been investigated using the conventional approach based on stirring so as to establish the beneficial effects obtained due to the use of ultrasound. Effect of operating conditions such as reactant molar ratio (oil and methyl acetate), temperature and enzyme loading on the yield of biodiesel has been investigated. Optimum conditions for the conventional approach (without ultrasound) were established as reactant molar ratio of 1:12 (oil:methyl acetate), enzyme loading of 6% (w/v), temperature of 40 °C and reaction time of 24 h and under these conditions, 90.1% biodiesel yield was obtained. The optimum conditions for the ultrasound assisted approach were oil to methyl acetate molar ratio of 1:9, enzyme loading of 3% (w/v), and reaction time of 3 h and the biodiesel yield obtained under these conditions was 96.1%. Use of ultrasound resulted in significant reduction in the reaction time with higher yields and lower requirement of the enzyme loading. The obtained results have clearly established that ultrasound assisted interesterification was a fast and efficient approach for biodiesel production giving significant benefits, which can help in reducing the costs of production. Reusability studies for the enzyme were also performed but it was observed that reuse of the catalyst under the optimum experimental condition resulted in reduced enzyme activity and biodiesel yield.     

Kinetics of ultrasound-assisted lipase-catalyzed glycerolysis of olive oil in solvent-free system

This work reports experimental kinetic data of solvent-free glycerolysis of olive oil using a commercial immobilized lipase (Novozym 435) under the influence of ultrasound irradiation. The experiments were performed in a mechanically stirred reactor under ultrasound irradiation, evaluating the effects of temperature (50-70 °C), enzyme concentration (2.5-10 wt%) and glycerol to oil molar ratio (0.8:1-3:1). Results show that ultrasound-assisted lipase-catalyzed glycerolysis might be a potential alternative route to conventional methods, as high contents of reaction products, especially monoglycerides, were achieved at mild irradiation power supply (∼130 W) and temperature, in a relatively short reaction time (2 h) and low enzyme content (7.5 wt%). To completeness, two simplified kinetic modeling approaches, based on the ordered-sequential bi bi mechanism and reaction stoichiometry, were employed to represent the experimental data, thus allowing a better understanding of the reaction kinetics.     

Ultrasound assisted enzyme catalyzed transesterification of waste cooking oil with dimethyl carbonate

This work reports the production of biodiesel with waste cooking oil and dimethyl carbonate in solvent free system through transesterification by immobilized enzyme (Novozym 435) under the influence of ultrasound irradiation. The experiments were conducted in an ultrasonic water bath under three different conditions i.e. ultrasonic irradiation (UI) without stirring, UI coupled with stirring and only stirring to compare their overall effects on fatty acid methyl esters (FAME) conversion. As compared with the conventional stirring method, where FAME conversion was 38.69% at 4 h, the UI without stirring significantly enhanced the conversion of enzymatic transesterification to 57.68% for the same reaction time. However the reaction rate was further increased under the condition of ultrasonication coupled with stirring and resulted into higher conversion of 86.61% for the same reaction time. Effects of reaction parameters, such as temperature, ratio of DMC/oil, speed of agitation and enzyme loading on the conversion were investigated. Furthermore, repeated use of Novozym 435 showed gradual decline in both conversion as well as enzyme activity.     

Improved synthesis of sucrose fatty acid monoesters under ultrasonic irradiation

Sucrose fatty acid esters were synthesized by the transesterification of sucrose with aliphatic esters under ultrasound irradiation in good yield (?73%). The optimum reaction conditions for the transesterification reaction include a molar ratio of sucrose to fatty acid ethyl ester of 2:1 and the use of a 13% mol anhydrous K₂CO₃ catalyst. The optimum reaction temperature was set at 70 °C, the optimum reaction time was 2 h, and the optimum reaction pressure was 11 kPa. The reaction had excellent monoester selectivity. The proportion of monoester (6-monoester + 6′-monoester) in the purified products was up to 92–95% via flash column chromatography over silica gel, the ratios of 6-monoester/6′-monoester are 2.1–2.7, and the sucrose monoesters were identified by HPLC–MS, NMR and IR.