Microwave-assisted Esterification Research Articles

Kinetic modeling of microwave-assisted esterification for biofuel additive production: conversion of levulinic acid with pentanol using Dowex® 50WX8 catalyst

This study explores the esterification of levulinic acid with 1-pentanol, employing Dowex® 50WX8 as a catalyst under microwave irradiation. Key parameters such as the pentanol/acid molar ratio, temperature, and catalyst loading were evaluated and utilized for kinetic modeling. The kinetic behavior of the reaction was investigated using a dual-model approach: a pseudo-homogeneous model to account for the microwave effect and catalytic contributions modeled through LHHW and Eley–Rideal mechanisms. The best model was chosen based on statistical results obtained from Markov Chain Monte Carlo (MCMC) analysis, which involved an LHHW model with the surface reaction as the limiting step, resulting in an activation energy of 50.6 kJ mol−1 for the catalytic synthesis of pentyl levulinate. The role of the alcohol in the esterification route was explained, and catalytic stability was confirmed, with the catalyst maintaining activity over multiple cycles. The absence of mass transfer limitations was proved using the Weisz–Prater criterion. A plausible reaction pathway was proposed for the levulinic acid esterification over the 50WX8 catalyst.Graphical abstract

Microwave-assisted esterification and electro-enhanced solid-phase microextraction of omega-3 polyunsaturated fatty acids in eggs

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs), a type of fatty acid that has many health benefits, are of increasing concern. Herein, we developed a method for the rapid esterification and enrichment of ω-3 PUFAs in eggs, which includes microwave-assisted esterification (MAE) and electrically enhanced solid-phase microextraction (EE-SPME). Combined with gas chromatographic, efficient detection of ω-3 PUFAs was achieved in eggs. Under microwave radiation, the esterification efficiency exhibited a significant increase ranging from 5.06 to 10.65 times. The EE-SPME method reduced extraction time from 50 to 15 min. In addition, improvements in extractive fiber coating materials were explored, which ensured efficient extraction of ω-3 PUFAs. Under the optimal conditions, the method displayed a low detection limit (1.01–1.54 μg L−1), good recoveries (85.82%–106.01%), and wide linear range (7.5–1000 μg L−1), which was successfully applied to determine ω-3 PUFAs in real egg samples.

Microwave-Assisted, Solid-State Procedure to Covalently Conjugate Hyaluronic Acid to Curcumin: Validation of a Green Synthetic Protocol.

A microwave-assisted esterification reaction to prepare hyaluronan-curcumin derivatives by employing a solvent-free process was developed. In particular, a solid-state strategy to react two molecules characterized by totally different solubility profiles was developed. Hyaluronic acid, a highly hydrosoluble polysaccharide, was reacted with hydrophobic and even water-unstable curcumin. Microwave (MW) irradiation was employed to activate the reaction between the two solid compounds through the direct interaction with them and to preserve the integrity of the sensitive curcumin species. This new protocol can be considered efficient, fast, and also eco-friendly, avoiding the employment of toxic organic bases and solvents. A cytotoxicity test suggested that the developed hyaluronan-curcumin conjugate (HA-CUR) could be considered a candidate for its implementation as a new material. In addition, preliminary studies revealed promising anti-inflammatory activity and open future perspectives of further investigation.

Graphene oxide-catalyzed microwave-assisted esterification of oleic acid to biodiesel

The combination of graphene oxide (GO) catalyst and microwave (MW) heating was applied for the esterification of oleic acid with methanol to synthesize methyl oleate. GO was synthesized using the modified Hummers method from graphite powder and characterized by various instrumental methods. To optimize the reaction parameters, reaction temperature, reaction time, methanol-oleic acid molar ratio, and catalyst amount were investigated. An oleic acid conversion of 96.2% was achieved in a reaction time of 1 h at a reaction temperature of 100 °C, using a methanol-oleic acid molar ratio of 9:1 and 5 wt% of GO. In addition, to compare MW heating and conventional heating on the efficiency of esterification, the esterification reaction was carried out with conventional heating under optimized conditions. Finally, the catalytic effect of GO in the conversion of waste cooking oil (WCO) into biodiesel was investigated.

Microwave synthesis of novel chenodeoxycholic acid esters and comparative study of chromatographic behavior and lipophilicity

In this study, eco-friendly microwave-assisted esterification reactions of chenodeoxycholic acid with medium-chain diols (1,2-ethanediol, 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, and 1,10-decanediol) or tetraethylene glycol were accomplished. The synthesized bile acid esters were obtained with high yields (up to 81 %) and purity in a short reaction time (15 min). It is shown that the microwave technique is a suitable method for the preparation of chenodeoxycholic acid esters. In order to obtain detailed insight into the lipophilic behavior of the studied chenodeoxycholic acid esters, a comparative study of chromatographic behavior and lipophilicity was performed. Also, the present study deals with the estimation of pH – logD profiles in order to get an overview of the changes in lipophilicity related to the pH value changes. The obtained results indicate that studied compounds have logD values in the range acceptable for potential drug candidates. Chromatographic lipophilicity of synthesized chenodeoxycholic acid esters successfully correlate with in silico lipophilicity descriptors.

Improved dispersibility of nanofibrillated cellulose via simple microwave-assisted esterification

Nanofibrillated cellulose (NFC) has been successfully esterified by lactic acid (LA) in the presence of HCl catalyst in an aqueous medium using a simple microwave heating process. The degree of substitution (DS) of ester groups on modified NFC (mNFC) was quantified through a systematic characterization consisting of titration, NMR, and XPS, revealing a consistent trend in the levels of DS in mNFC. The reaction parameters of the microwave heating process including the ratio between NFC and LA (1:10), amount of catalyst (5 wt%), energy input and time, have been optimized, achieving a DS of 0.66 in mNFC with a typical power of 800 Watts in 1 min only. The TEM and XRD results confirmed that the structure and characteristics of the nanofibrillated fibers were preserved following the process. Finally, the improved dispersibility of mNFC with high DS in low polarity solvents and polylactic acid (PLA) matrix was validated.

Removal of cationic dyes by a novel carboxylate sugar beet pulp with maleic anhydride assisted by microwave

A novel biosorbent (MSBP) was synthesized in this paper by microwave-assisted esterification with maleic anhydride (MA) using sugar beet pulp (SBP) as raw material. Characterization of prepared MSBP was done by measuring TG/DTG, BET surface area analysis, XRD and FT-IR analysis. Then MSBP was used for the adsorption of methylene blue (MB), and the experimental parameters such as microwave time, microwave power and mixing ratio were optimized. The water retention capacity and antibacterial activity of MSBP were determined. The results showed that the optimum modification conditions were a microwave time of 2 min, a microwave power of 1000 W, and a mixing ratio of 15:3 between MA and SBP, under which the cation adsorption capacity of MSBP was 343.35 mg/g. In addition, the esterification reaction allowed MSBP to form a tightly cross-linked structure, resulting in lower water retention capacity. At the same time, the modified MSBP also showed antibacterial activity against E. coli and S. aureus. In summary, a simple and efficient monofunctional modification method was used in this study, and a green sugar beet pulp-based biosorbent was successfully prepared.

Microwave-assisted biodiesel production using –SO3H functionalized heterogeneous catalyst derived from a lignin-rich biomass

The synthesis of biodiesel from renewable resources has immense potential as a sustainable and cost-effective energy alternative. In this work, a reusable –SO3H functionalized heterogeneous catalyst that has a total acid density of 2.06 mmol/g was prepared from walnut (Juglans regia) shell powder by low-temperature hydrothermal carbonization (WNS-SO3H). Walnut shell (WNS) contains more lignin (50.3%), which shows great resistance toward moisture. The prepared catalyst was employed for the effective conversion of oleic acid to methyl oleate by a microwave-assisted esterification reaction. The EDS analysis revealed the significant presence of sulfur (4.76 wt%), oxygen (51.24 wt%), and carbon (44 wt%) content. The results of the XPS analysis confirm the bonding of C–S, C–C, C=C, C–O, and C=O. Meanwhile, the presence of –SO3H (the responsible factor for the esterification of oleic acid) was confirmed by FTIR analysis. Under the optimized conditions (9 wt% catalyst loading, 1:16 oleic acid to methanol molar ratio, 60 min reaction time, and 85 °C temperature), the conversion of oleic acid to biodiesel was found to be 99.01 ± 0.3%. The obtained methyl oleate was characterized by employing 13C and 1H nuclear magnetic spectroscopy. The conversion yield and chemical composition of methyl oleate were confirmed by gas chromatography analysis. In conclusion, it can be a sustainable catalyst because the catalyst preparation controls the agro-waste, a great conversion is achieved due to the high lignin content, and the catalyst was reusable for five effective reaction cycles.

Use of Bioprinted Lipases in Microwave-Assisted Esterification Reactions

In this study, a comparative evaluation was performed in batch esterification reactions under conventional heating (CH) and assisted by microwave irradiation (MW) using bioprinted lipases. Microwave-irradiation-assisted reactions generally provide higher productivities and improve synthesis performance in terms of increased rate and reduced reaction times, resulting in higher interest yields in less time. Productivity was calculated with the enzymes: Burkholderia cepacia lipase (BCL), Candida rugosa lipase (CRL), and porcine pancreas lipase (PPL) using different fatty acids (lauric acid (12:0), myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), and oleic acid (18:1)) and alcohols at a molar ratio of 1:8. The microwave reactor was operated at a temperature of 45 °C, and power varied between 50 W and 200 W. Bioprinted BCL (bBCL) showed the highest productivity among the tested lipases. In the reaction with the best result, bBCL with lauric acid under MW, the reaction time decreased from 24 h (CH) to 25 min (MW) and the productivity increased 33 times compared with the reactions under CH. The increase in productivity demonstrates its activation that occurred as a result of conformational changes of the enzyme in the bioprinting process, confirmed by Fourier transform infrared (FTIR) spectrometric analysis, which reduces the content of bBCL α-helix with lauric acid. The biocatalyst showed high operational stability over eight cycles, while losing only 19% of its initial activity with half-life times of 12.8 batches. The storage time was five weeks, maintaining ≈80% activity. The results demonstrate the prospect of a new enzymatic route to obtain hyperactive catalysts, with the use of bioprinted lipases in esterification reactions under microwave irradiation, for the synthesis of esters with a view to large-scale industrial application.

Microwave-assisted esterification of bleached and unbleached cellulose nanofibers

Microwave-assisted esterification of bleached and unbleached cellulose nanofibers

Optimization of microwave-assisted esterification of succinic acid using Box-Behnken design approach.

Esters of butanedioic acid (succinic acid) are appealing renewable esters as fuel additives and solvents. In the present study, we have investigated reaction routes for the esterification of succinic acid (SA) with alcohols like methanol (MeOH), ethanol (EtOH), and 2-propanol (2-PrOH) using heterogeneous catalyst D-Hβ (moderate Bronsted acidity) in a microwave (MW)-irradiated reactor to increase yield and minimize waste generation. Using the Box-Behnken design (BBD) approach, operating parameters such as reaction time, microwave power, and catalyst dosing were optimized for SA esterification with MeOH. At optimum conditions using D-Hβ catalyst, 99% maximum conversion was achieved with 98% selectivity of dimethyl succinate (DMS). At optimum conditions, the esterification of SA with EtOH and 2-PrOH was also performed. The use of D-Hβ is economically more advantageous as it can be reused directly without any prior washing and also showed significant activity.

P-Chloride-Free Synthesis of Phosphoric Esters: Microwave-Assisted Esterification of Alkyl- and Dialkyl Phosphoric Ester-Acids Obtained from Phosphorus Pentoxide

AbstractIt is a reasonable endeavour to replace P-chloride starting materials (e.g., POCl3) with greener and cheaper reagents. Our purpose was to start from phosphorus pentoxide, i.e. to utilize its reaction with alcohols in the preparation of (HO)2P(O)(OR) and HOP(O)(OR)2, and to convert the mixtures of the corresponding monoester and diester, so obtained, into the target trialkyl esters. Separate experiments showed that the monobutylphosphate undergo microwave (MW)-assisted esterification with butanol in the presence of [bmim][BF4] catalyst at 200 °C to afford dibutylphosphate in a selective manner (ca. 95%) that, in turn, may be converted into tributylphosphate by alkylation under MW irradiation. In this way, the mixtures of (HO)2P(O)(OR) and HOP(O)(OR)2 obtained by the practical reaction of phosphorus pentoxide and alcohol (ROH) could also be converted in two additional steps into the corresponding trialkyl esters. The three-step synthesis of trialkylphosphates starting from phosphorus pentoxide was also transformed in a one-pot (step 1: preparation of the monoester diester mixture, step 2: diesterification) and telescoping (step 3: triesterification) variation, avoiding the isolation and purification of the intermediates, and affording the triesters­ in 86–93% yields. The three- and two-step P-chloride-free methods developed are ‘green’ and of more general value.

Artificial neural network method modeling of microwave-assisted esterification of PFAD over mesoporous TiO2‒ZnO catalyst

An artificial neural network (ANN) was employed to predict biodiesel yield through microwave-assisted esterification of palm fatty acid distillate (PFAD) oil over TiO2‒ZnO mesostructured catalyst. The experimental data of biodiesel content (%) was carried out via changing three input factors (i.e. methanol:PFAD molar ratio, catalyst concentration, and reaction time). The results indicated that ANN is an appropriate approach for modeling and optimizing fatty acid methyl ester (FAME) yield performed over the microwave-assisted esterification process. The network was trained by five different algorithms (i.e. batch backpropagation (BBP), incremental backpropagation (IBP), Levenberg‒Marquardt (LM), genetic algorithm (GA), and quick propagation (QP)). The evaluation disclosed that the QP algorithm gave the least root mean squared error (RMSE), absolute average deviation (AAD), and the highest determination coefficient (R2) for both training and testing data groups. The confirmation test results of the ANN-based on QP-3-10-1 revealed that the RMSE, AAD, and the highest R2 were 0.741, 0.776, and 0.997, correspondingly. All in all, QP‒3‒10‒1 model offered the best possible mathematical qualities amongst all algorithms. Over this method, the FAME yield was determined at 97.45% (relating to the actual FAME yield of 97.33%) which was attained over 3 wt% mesoporous TiO2‒ZnO catalyst, methanol:PFAD molar ratio of 9:1 within 25 min of operating time. The esterification reaction conditions predicted by ANN showed to be potential for modeling and predicting FAME yield with an extremely well precision of 97.06%.

Influence of Radial Dimension and Electric Field on a Microwave-Assisted Esterification

Enzymatic synthesis of ethyl hexanoate from hexanoic acid and ethanol in a solvent-free system, carried out at optimum conditions, has been modeled. The process follows a Ping-Pong Bi-Bi reaction rate and it is endothermic, so microwave heating is provided to prevent its shutdown. The mathematical model has been numerically solved with the FEM method. Results show that microwave heating can be successfully used to carry out this kind of reaction.

Microwave-Assisted Synthesis of Lactose Acetates with Antimicrobial, Cytotoxic, and Antiviral Properties

The task of this study was to perform the "green" synthesis of lactose octaacetate through microwave irradiation and to establish their biological activities. Lactose ester was prepared after microwave-assisted esterification of lactose with acetic anhydride (yield 85-90 %). Lactose octaacetate was characterized by a high degree of acetylation (DS 3.2-3.7). The lactose esters' structure was elucidated by infrared spectroscopy and nuclear magnetic resonance spectroscopy. Lactose octaacetate showed better antifungal activities than antibacterial activities. It possessed slight to moderate antifungal activities against Aspergillus niger ATCC 1015, Penicillium sp., Rhizopus sp., Fusarium moniliforme ATCC 38932. Lactose acetates demonstrated low cytotoxicity against three cell lines: Madin-Darby bovine kidney (MDBK) cells, human epithelial type 2 (HEp-2), and Madin-Darby canine kidney (MDCK) cells. This is the first report for antiviral activity of lactose acetates against herpes simplex virus type 1 (HSV-1), influenza virus A/Panama/2007/99/H3N2 - (IAV/H3N2), PV-1 and Coxsackievirus B1. It was found that this compound showed activity with SI = 2.4 only against PV-1, but against HSV-1, IAV/H3N2, and Coxsackievirus B1 was inactive. The current study demonstrated the applications of lactose acetates as antimicrobial and antiviral substances in food, pharmaceutical, agricultural and cosmetic preparations.

Microwave-assisted esterification of P-acids

The possibilities for the preparation of dialky phenylphosphonates were evaluated. On the one hand, the oxidation of phenyl-H-phosphinates gave the corresponding phenylphosphonic acid monoesters. On the other hand, phenylphosphonates may be prepared by MW-assisted direct esterification of phenylphosphonic acid. The reaction with alcohols was performed under MW irradiation in the presence of an ionic liquid as the catalyst. The second ester function was established by alkylating esterification carried out with alkyl halides in the presence of triethylamine under MW conditions.

Feasibility Study of Microwave‐Assisted Biodiesel Production from Vegetable Oil Refinery Waste

AbstractVegetable oil refinery waste containing acid oil is used as an inexpensive feedstock for producing biodiesel by microwave‐assisted esterification (MAE) method. Effects of some main variables such as free fatty acid:methanol molar ratio (1:1, 1:5, and 1:10), reaction time (5, 30, and 60 min), and catalyst concentration (1%, 2%, and 3%) on physicochemical properties of produced biodiesel are investigated. Optimum reaction conditions of MAE are free fatty acid:methanol molar ratio of 1:10, reaction time of 60 min, and a catalyst concentration of 3%, while having 95.79% conversion yield. By increasing the conversion yield of the biodiesel, density and color brightness increase, while viscosity and refractive index decrease. There are no significant differences between physicochemical and heating properties of biodiesel produced by MAE and magnetic stirrer esterification (MSE) methods. Meanwhile, energy consumption of MAE method is almost four times lower than that of MSE. MAE as a promising alternative to the conventional esterification method can be considered as an energy‐efficient method for producing biodiesel from inexpensive vegetable oil refinery waste.Practical applications: Acid oil is an inexpensive by‐product of alkali refining in vegetable oil plants that would pollute the environment if not rendered safely. In this study, MAE is used to convert acid oil to biodiesel as a practical process for bringing alkali refining waste into production cycle. Acid oil can provide a reduction in the cost of biodiesel production. In addition, application of energy‐efficient MAE method can facilitate the economical production of biodiesel.

Parametric, kinetic, and thermodynamic studies of microwave-assisted esterification of Kusum oil

In this research, non-edible Kusum oil was used to convert the free fatty acid into its methyl esters using a silicotungstic acid catalyst. The microwave as a heat source was used to fasten the rate of esterification of Kusum oil. The parametric study of the effect of methanol to oil molar ratio, catalyst amount, temperature, and time was carried out to obtain the reasonable conversion of free fatty acid. The study revealed that 9:1 molar ratio, 65 °C, 3.6 wt% catalyst, and 13 min of reaction time gave 92% free fatty acid (FFA) conversion. Further, the present study also estimates the kinetic and thermodynamic parameters of Kusum oil esterification. The kinetic study was performed at four temperatures with a pre-optimized 9:1 molar ratio of methanol to oil, 3.6 wt.% Silicotungstic acid for different time intervals. The kinetic study revealed that microwave-assisted acid-catalyzed esterification reaction is pseudo-first-order having activation energy 38.82 kJ.mol−1 and pre-exponential factor 219,037 min−1, respectively. The higher value of pre-exponential factor and lower activation energy in the kinetic study indicates the non-thermal effect associated with microwave heating. The rate constant and Gibbs’ free energy change at 65 °C was 0.224 min−1 and 98.89 kJ.mol−1. The values of Enthalpy and Entropy changes were 36.06 kJ.mol−1 and −0.185 kJ.mol−1.K − 1. It shows the reaction is non-spontaneous and endergonic by nature.

Co-modification of lignocellulosic biomass by maleic anhydride and ferric hydroxide for the highly efficient biosorption of methylene blue

Ferric hydroxide and microwave-assisted solvent-free esterification was applied in the modification of SBP to synthesize an efficient cationic dye adsorbent.

Artificial Neural Network Method for Modeling of Microwave-Assisted Esterification of PFAD Over Mesoporous TiO <sub>2</sub>‒ZnO Catalyst

Artificial Neural Network Method for Modeling of Microwave-Assisted Esterification of PFAD Over Mesoporous TiO <sub>2</sub>‒ZnO Catalyst