Esterification Of Oleic Acid Research Articles

Corn Stover Lignin as a Solid Acid Catalyst for the Esterification of Oleic Acid

AbstractThe catastrophic ramifications of fossil fuels on the environment have prompted the search for renewable energy sources. Over the recent decades, biodiesel has garnered attention as a promising direct alternative to diesel fuel; however, reliance on homogeneous catalysts and the requirement for refined vegetable oil feedstocks present financial and sustainability concerns. Thus, there exists a need for the development of sustainable and cost‐effective catalytic solutions. Herein, the application of lignin, an abundant and renewable biomass, as an effective heterogeneous catalyst is reported for biodiesel production via the esterification of oleic acid. Lignin is extracted from corn straw using sulfuric acid, which endows sulfonic acid groups (0.85 mmol g−1) to its structure allowing it to act as an acid catalyst without additional post‐treatments. Conversion of oleic oil to biodiesel is achieved at 97% using a 1:3 oleic acid to methanol molar ratio with a 5 wt.% catalyst loading at 90 °C after only 30 min. Moreover, the catalyst exhibits a remarkable turnover frequency of 2.61 min−1 proving its efficiency. These findings demonstrate that heterogeneous catalysts can be prepared from biomass waste offering a significantly cheaper and less intensive synthesis process and allowing for a paradigm shift to non‐edible and waste cooking oils.

Impact of abiotic stressors on oleic acid accumulation in the leaves of young quinoa plants

Investigating the impact of not only individual stress factors but also their combined effect on plants becomes imperative in the context of natural and climatic fluctuations. 18-carbon unsaturated fatty acids such as oleic (18:1), linoleic (18:2) and α-linolenic (18:3) serve as vital non-enzymatic antioxidants, making significant contributions to plant defense. Moreover, they are indispensable in assessing the nutritional and biological value of plant lipids. Currently, Chenopodium quinoa L., a member of the Amaranth family, is increasingly recognized as a valuable source of antioxidant metabolites. Current study examined the fluctuation patterns in oleic acid ester content, serving as a non-enzymatic antioxidant, when plant exposed to varying intensities of osmotic, saline, and combined stress. A constant concentration of oleic acid esters was shown under different levels of saline stress. Osmotic stress did not affect the oleic acid content. Under salt stress, the oleic acid content increased compared to the control, varying at different NaCl concentrations. However, under combined stress, there was a significant increase in ester content, peaking at a stress level of 200NaCl/L+PEG, followed by a decrease as stress increased. It was noted that signs of stress for the photochemical quenching index of YII and ETR in photosystem II of young quinoa plants also occur with a combination of exposure to 300 mM/L NaCl + PEG. It was suggested that the level of combined stress at 200NaCl/P is transitional from eustress to distress. The results obtained could potentially become the basis for the targeted synthesis of valuable plant antioxidants for food and pharmaceutical purposes in the future.

Kinetic and Parametric Studies on Oleic Acid Esterification Catalyzed by Purolite CT151

Kinetic and Parametric Studies on Oleic Acid Esterification Catalyzed by Purolite CT151

Formulation of a carbon-based solid acid catalyst from groundnut husk for the esterification of oleic acid

In this research, a biochar was prepared from groundnut husk and sulphuric acid. The biochar wassulphonated with chlorosulphonic acid to give a carbon-based sulphonated solid acid catalyst (SAC). The catalyst was characterised by N2 adsorption and desorption at 77K after degassing overnight under vacuum at 250˚ C, scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, and total acid density measurement. The results of the acid density measurement showed that the sulphonated biochar has a relatively high acid density of 3.2 mmol/g, while that of the non-sulphonated counterpart is 0.56 mmol/g. Comparison of the percentage conversion of oleic acid by esterification with methanol and butanol was carried out under three different conditions, viz: without catalyst, with the non-sulphonated biochar and with the sulphonated biochar, under the same experimental conditions of 5% catalyst weight percent (based on weight of acid), acid-methanol mole ratio of 1:12, reaction temperature of 70 oC, and five hours reaction time. Up to 91.6% percentage conversion of oleic acid to methyl oleate and 86.4% for butyl oleate were achieved, proving the effectiveness of the sulphonated biochar in catalysing the esterification reaction of oleic acid with methanol and butanol. The results of this study are expected to provide insights into the development of sustainable and cost-effective solid acid catalysts for the synthesis of oleate esters and other value-added materials from renewable feedstocks.

Sustainable synthesis of 2-ethyl hexyl oleate via lipase-catalyzed esterification: A holistic simulation and cost analysis study

Lipase catalyzed synthesis of fatty acid esters has recently attracted much attention as it represents a cleaner production route compared to the conventional energy intensive chemical method. In this study, the technical and economic viability of 2-ethyl hexyl oleate (2-EHO) synthesis by the catalytic esterification of oleic acid (OA) and 2-ethyl hexyl alcohol (2-EHA) in a stirred tank reactor using Novozym 435 (Candida antarctica lipase B) was investigated. A conversion rate of 91% was obtained by adopting the subsequent optimized parameters: 4% enzyme amount, 2 h reaction time, 4:1 M ratio of alcohol to fatty acid, 150 rpm stirring speed, and 60 °C temperature. The lipase operational stability study showed that enzymes can be used for 30 successive cycles without significant lose in activity. The use of Aspen Plus simulator enabled the development of a detailed process flow diagram, which significantly improved the understanding of this clean production method and assessed the overall costs. A holistic cost analysis revealed a production cost of $2109 per ton of 2-EHO, thereby yielding an approximate 28% profit margin relative to prevailing market rates. Rigorous financial assessments corroborated the project's viability, substantiating a net present value (NPV) of $14.7 MM, a return on investment (ROI) of 583.91% (plant life time = 15 years), projected Payback Period stands at 6 years, and an internal rate of return (IRR) of 23%. These results confirm the technical and economic feasibility of lipase catalyzed production of 2-EHO, highlighting its potential as an environmentally and profitable approach in the synthesis of fatty acid esters.

Investigation on solvent-free esterification of oleic acid by hemp tea waste-immobilized Candida rugosa lipase

This study aimed at Candida rugosa lipase immobilization on a low-cost and readily available support. Among agro-industrial crops, hemp tea waste was chosen as the carrier because it provides higher immobilization performance than hemp flower and leaf wastes. Support characterization by ATR-FTIR, SEM and elemental analysis and the optimization of the adsorption immobilization process were performed. The lipase adsorption immobilization was obtained by soaking the support with hexane under mild agitation for 2 h and a successively incubating the enzyme for 1 h at room temperature without removing the solvent. The esterification of oleic acid with n-decanol was tested in a solvent-free system by studying some parameters that influence the reaction, such as the substrates molar ratio, the lipase activity/oleic acid ratio, reaction temperature and the presence/absence of molecular sieves. The biocatalyst showed the ability to bring the esterification reaction to equilibrium under 60 min and good reusability (maintaining 60 % of its original activity after three successive esterification reactions) but low conversion (21 %) at the optimized conditions (40 °C, 1:2 substrates molar ratio, 0.56 lipase/oleic acid ratio, without sieves). Comparing the results with those obtained by free lipase form at the same activity (1 U) and experimental conditions, slightly higher conversion (%) appeared for the free lipase. All this highlighted that probably the source of lipase for its carbohydrate-binding pocket and lid structure affected the esterification of oleic acid but certainly, the immobilization didn’t induce any lipase conformational change also allowing the reuse of the catalytic material.

Ionic Porous Aromatic Frameworks Embedding Polyoxometalates for Heterogeneous Catalysis.

Porous aromatic frameworks (PAFs) are highly promising functional porous solids known for their feasible amenability and extraordinary stability. When the framework was modified by ionic functional groups, these ionic PAFs (iPAFs) exhibited charged channels for adsorption, separation, and catalysis. However, the surface areas of ionic porous frameworks are usually lower than that of neutral frameworks, and their synthesis is limited by specific strategies and complex modification processes. To address these challenges, an intuitive route to construct ionic porous framework with high specific surface area was proposed. Herein, a multivariate ionic porous aromatic framework (MTV-iPAFs, named PAF-270) was synthesized using readily available building units with ionic functional groups through a multivariable synthesis strategy. PAF-270 exhibited hierarchical structure with the highest specific surface area among reported imidazolium-functionalized PAFs. Utilizing its physical and chemical properties, the availability for polyoxometalate loading and heterogeneous catalysis of PAF-270 were explored. PAF-270 exhibited a high adsorption capacity up to 50 % for both H3O40PW12 (HPW) and (NH4)5H6PV8Mo4O40 (V8). HPW@PAF-270 and V8@PAF-270 exhibited excellent catalytic abilities for oleic acid esterification and extractive oxidative desulfurization, respectively. Due to the stability of PAFs, these materials also showed remarkable resistance to temperature and pH changes. Overall, these results underscore the potential application of MTV-iPAFs as versatile functional porous materials.

Synthesis of Zr/La-BTC Bimetallic Metal-Organic Framework (MOF) for Oleic Acid Esterification

Biodiesel plays an essential role in renewable energy as an alternative fuel to tackle the challenges of global warming, environmental degradation, and alternative fossil fuels. Oleic acid can be converted into biodiesel by the esterification process, which employs heterogeneous catalysts such as metal-organic frameworks (MOF). In this study, Zr/La-BTC MOFs were used as different kinds of catalysts to change oleic acid into biodiesel. The characterization results of Zr-BTC, La-BTC, and Zr/La-BTC using FTIR and XRD show that the MOF has been successfully formed. The crystallite sizes for La-BTC, and Zr/La-BTC MOFs are 15.7407 nm and 39.0392 nm, respectively. The surface area of Zr-BTC, La-BTC, and Zr/La-BTC MOFs are 167.101 m2/g, 12.328 m2/g, and 4.764 m2/g. The morphology of Zr-BTC MOF using SEM is irregular, La-BTC is rod-shaped crystal, and Zr/La-BTC is like a knot bond with a narrow waist. The most optimal reaction was obtained at a 5% (w/w) catalyst dosage of total oleic acid and methanol (1:60 mol), 65 °C, and a reaction time of 4 hours, producing 78.11% oleic acid conversion. GC-MS analysis identified that the biodiesel contains oleic acid, palmitic acid, methyl oleate, and methyl palmitate.

Phytochemical Screening and Antidiabetic Efficacy of Balanites aegyptiaca Seed Extract and Their Silver Nanoparticles on Muscle and Pancreatic Cell Lines.

Balanites aegyptiaca (L.) Delile, a member of the Zygophyllaceae family, is commonly known as the desert date. This tree is famous for yielding edible fruits and is esteemed for its nutritional richness and diverse health advantages. The primary aim of this research was to assess the potential antidiabetic and cytotoxic effects of seed extracts from B. aegyptiaca and its AgNPs for the first time on C2C12 and MIN6 cells, focusing on glucose uptake and insulin secretion, respectively. Additionally, the seed extracts underwent column chromatography through different solvent systems, resulting in the isolation of five distinct fractions with a mixture of methanol and water as an eluting solvent in different ratios. Comprehensive characterization of the aqueous seed extract was carried out using GC-MS and UPLC-MS. The study determined that the aqueous seed extract exhibited no toxicity at any tested concentration (6.25-100 μg/mL) on both cell types. The calculated IC50 values were 206.00 and 140.44 μg/mL for C2C12 and MIN6 cells, respectively, for seeds of AgNPs. Additionally, the aqueous seed extract and their AgNPs significantly increased glucose uptake by 150.45% and 156.00% of the control in C2C12 cells at a concentration of 100 μg/mL. Insulin secretion was also notably enhanced by 3.47- and 3.92-fold of the control after administering seed extracts and AgNPs, respectively, at 100 μg/mL. GC-MS and UPLC-MS analyses identified various compounds across different categories. Notably, the F2 fraction (methanol and water in ratio of 80:20 as eluting solvent) exhibited the highest glucose uptake activity (156.81% of control), while the F3 fraction (methanol and water in ratio of 70:30 as eluting solvent) fraction demonstrated the highest insulin secretion activity (3.70 folds of the control) among all fractions at 100 μg/mL. GC-MS analysis was employed to characterize both fractions, aiming to identify the compounds contributing to their antidiabetic potential. The study's findings concluded that both seed extracts and their AgNPs possess significant antidiabetic properties, with elevated activity observed in the case of AgNPs in both assays. Various compounds, including diosgenin, oleic acid, linoleic acid and palmitic acid esters were detected in the seed extracts, known for their reported antidiabetic and hypoglycemic effects.

Optimization of Methyl Oleate Synthesis with Sulfonated Pyrrolidonium Ionic Liquids as Catalysts Using the Response Surface Methodology

In order to improve the efficiency of biodiesel production from esterification of free fatty acids, an alternative to sulfuric acid has been explored in this study. These catalysts including three pyrrolidonium ionic liquids (ILs), 1-methyl-2-pyrrolidonium hydrogen sulfate ([Hnmp]HSO4), 2-pyrrolidonium hydrogen sulfate ([Hnhp]HSO4), and 1-(3-sulfonic acid) propyl-2-pyrrolidonium hydrogen sulfate ([C3SO3Hnhp]HSO4), were applied as catalysts to produce biodiesel through the esterification reaction of oleic acid with methanol. The catalytic performances of the synthesized ILs for the esterification of oleic acid were evaluated, and [C3SO3Hnhp]HSO4 exhibited the best catalytic activity among all tested acidic ILs. Moreover, the esterification of oleic acid with methanol by the [C3SO3Hnhp]HSO4-catalyzed was systematically explored, and the reaction conditions were further optimized through a single-factor experiment, the Plackett-Burman design, and a response surface methodology. It was found that optimum response for oleic acid conversion was 97.4% under reaction condition of using catalyst dosage of 12.5%, methanol/oleic acid molar ratio of 9:1, reaction time at 4 h and reaction temperature at 70 °C. In addition, the catalytic activity of [C3SO3Hnhp]HSO4 still remained high level after 5 cycles. In a conclusion, the IL [C3SO3Hnhp]HSO4 has great potential as a catalyst for producing fatty acid methyl esters via the esterification reaction.

The chemical and biological characteristics of fatty acid esters of hydroxyl fatty acids.

With the continuous advancements in detection methods and the exploration of unknown substances, an increasing number of bioactive compounds are being discovered. Fatty acid esters of hydroxyl fatty acids (FAHFAs), a class of endogenous lipids found in 2014, exhibit various physiological activities, such as improving glucose tolerance and insulin sensitivity, stimulating insulin secretion, and demonstrating broad anti-inflammatory effects. Moreover, some FAHFAs are closely linked to intestinal health and can serve as potential biomarkers for gut health. Various FAHFAs have been observed in food, including palmitic acid esters of hydroxy stearic acids (PAHSA), oleic acid esters of hydroxy stearic acids (OAHSA), linoleic acid esters of hydroxy linoleic acid (LAHLA). As a type of lipid regularly consumed in the daily diet, it is highly important to ascertain the types and quantities of FAHFAs present in the diet. This article, based on existing research, provides a review of the analysis methods for FAHFAs, particularly focusing on the separation of chiral isomers. It also summarizes the sources and contents of dietary FAHFAs, emphasizing their bioavailability and impact on the gut. Understanding the beneficial effects of these lipids in the diet can serve as a valuable reference for the development of specific functional foods.

Surface‐modified NiFe2O4 nanoparticles for the production of biodiesel from fatty acids and microalgae lipids Dunaliella salina

Development of a new and sustainable catalyst is necessary to the society for providing economical technology. Surface modification of nanometal oxides is one of the rapidly growing methods for developing a sustainable catalyst with attractive properties than their parent oxide. In this work, surface‐modified nickel ferrites have been carried out using 4,4′‐biphenyldisulfonic acid (BPDSA) as the linker. Thus, obtained modified material has been characterized using different techniques such as DLS, FT‐IR, TGA, XRD, VSM, and XPS. This well‐characterized, stable, robust, recyclable material offers a good conversion in the fatty acid, that is, oleic acid esterification in the presence of methanol in a short period of time (3.0 h). Based on the kinetic study in the oleic acid esterification, it fits in the pseudo first‐order kinetics, and activation energy was found to be 60.0 kJ/mol. Further, the potentiality of our catalyst was also tested in the transesterification of various raw materials like mustard oil, olive oil, almond oil, and neem oil. In addition, it provides an excellent conversion with microalgae lipid extraction for the production of biodiesel. The kinematic viscosity of the methyl oleate (biodiesel) has been found to be 5.0426 mm2/s at 25°C whereas the dynamic viscosity is 6.0511 mPa, which is nearly the same as biodiesel obtained from Dunaliella salina, microalgae lipid.

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.

Epoxidized esters of succinic acid, oleic acid and propylene glycol as an effective bioplasticizer for PVC: A study of processing conditions on the physico‐chemical properties

AbstractThe present study evaluated the use of epoxidized esters of succinic acid, oleic acid, and propylene glycol as a bioplasticizer for poly(vinyl chloride) (PVC) and compared the results with the commercial phthalate plasticizer di(2‐ethylhexyl)phthalate. The chemical properties, structure, and biodegradation of the obtained bioplasticizer were analyzed. In order to analyze the influence of different PVC processing conditions on the properties of the obtained samples, the gelation process was carried out at 170, 180, 190, and 200°C at a time of 1.5–10.0 min. Mechanical properties, thermal characteristics, Fourier transform infrared spectroscopy analysis, plasticizer migration, and color change were determined for the resulting plasticized PVC samples. The performed studies allowed to confirm the obtaining of a biodegradable bioplasticizer (after 28 days, the decomposition rate in respirometry test was 72.7%). The optimal conditions for PVC processing were determined. For them the properties of the obtained material were superior. Processing PVC at 170°C for 7.5 min proved to be the most optimal conditions for the bioplasticizer synthesized in this study. Under these conditions, tensile strength of about 23 MPa and elongation at break of 200% were obtained, while plasticizer migration was very low (4.4% after 7 days and 6.8% after 28 days).

Microwave-driven oleic acid esterification over chlorosulfonic acid-treated hydroxyapatite: synergism for intensified biodiesel production.

Treating hydroxyapatite (HAP) with sulfonic acid without structural destruction remains challenging owing to the sensitivity of HAP to acidic pH. In this work, natural derived HAP was prepared using natural phosphate via a dissolution/precipitation process. Notwithstanding the challenge, the prepared HAP was treated with three concentrations of chlorosulfonic acid in dichloromethane to prepare HAP-S1, HAP-S2 and HAP-S3 depending on the acid content under carefully controlled conditions. The treatment of HAP with the lowest acid concentration led to the preservation of the apatite framework with surface modification of sulfonic acid groups. As the acid concentration increased, HAP, CaHPO4 and CaSO4 were obtained. A further increase in the acid concentration led to the formation of CaSO4 with the coexistence of Ca(H2PO4)2·H2O. Subsequently, the catalytic activity of HAP-S1 was evaluated in oleic acid esterification under microwave irradiation, resulting in a yield of up to 87% under optimized conditions of 10 wt% of catalyst to oleic acid weight, 10 : 1 methanol to oleic acid molar ratio, and 40 min reaction duration under microwave irradiation at 150 °C. The activity of HAP-S1 was attributed to the active S[double bond, length as m-dash]O and S-O-H functional groups, and a possible mechanism of acid-catalyzed esterification is proposed. The catalyst was also tested in the transesterification reaction of rapeseed oil, achieving a conversion of 40.2% after 60 min reaction duration under microwave irradiation. Furthermore, the catalyst was evaluated in a two-step esterification reaction to investigate its activity towards acidified feedstocks. Results showed that after two successive runs, acidity was reduced by 79.6% with a total FAME yield of 40.13%. The obtained results indicate that this catalyst, being an acid catalyst, is more suitable for direct esterification.

Comparison of the Catabolic Rates of Linoleic and Oleic Acid Hydroperoxides Using 13CO2 Expired from Mice.

Unsaturated fatty acids, such as oleic and linoleic acids, are easily oxidized by exposure to temperature and light in the presence of air to form unsaturated fatty acid hydroperoxides as primary oxidation products. However, the catabolic rates of unsaturated fatty acid hydroperoxides in the human body remain unknown. In this study, ethyl esters of 13C-labeled linoleic acid (*C18:2-EE) and oleic acid (*C18:1-EE) and their hydroperoxides (*C18:2-EE-OOH and *C18:1-EE-OOH, respectively) prepared by the photo-oxidation of *C18:2-EE and *C18:1-EE, respectively, were administered to mice and their catabolic rates were determined by measuring the expired 13CO2 levels. *C18:2-EE-OOH and *C18:1-EE-OOH were β-oxidized faster than *C18:2-EE and *C18:1-EE, respectively. Notably, rapid β-oxidation of *C18:2-EE-OOH and *C18:1-EE-OOH was similar to that of medium-chain fatty acids, such as octanoic acid. Then, degradation products of C18:2-EE-OOH and C18:1-EE-OOH were analyzed under gastric conditions by gas chromatography/mass spectrometry. Major decomposition products of C18:2-EE-OOH and C18:1-EE-OOH were medium-chain compounds, such as octanoic acid ethyl ester, 9-oxo-nonanoic acid ethyl ester, and 10-oxo-8-decenoic acid ethyl esters, indicating that C18:2-EE-OOH and C18:1-EE-OOH isomers formed during photo-oxidation were decomposed under acidic conditions. These findings support previous reports that dietary lipid hydroperoxides are not absorbed into the intestine as lipid hydroperoxides but as degradation products. This is the first study to suggest that dietary lipid hydroperoxides decompose during gastric digestion to form medium-chain compounds that are directly absorbed into the liver via the portal vein and rapidly catabolized via β-oxidation.

Sulfonated hierarchical ZSM-5 zeolite monoliths as solid acid catalyst for esterification of oleic acid.

Sulfonated hierarchical H-ZSM-5 monoliths were synthesized via ice-templating as solid acid catalysts for biodiesel production. Characterization confirmed successful -SO3 group grafting, increasing acid density. The catalysts achieved over 90% conversion of oleic acid in esterification, with easy recovery and reuse, and the relationship between porosity and acid density was explored.

Comparative catalytic efficacy of cost-effective MIL-101(Cr) based PET waste for biodiesel production

Polyethylene terephthalate (PET) use has increased, causing more PET trash and environmental and health issues. Disposal and burning alone cannot solve this problem. Thus, PET recovery methods with low byproducts are the priority. The recycling rate is still below 30%, so different cleaning methods are being investigated. Therefore, studies have focused on extracting terephthalic acid from PET bottles for MOF synthesis to reduce their cost of production. Herein, MIL-101(Cr) was synthesized from PET bottles and used as a solid catalyst for oleic acid esterification with methanol to produce methyl oleate (biodiesel), an alternative energy source to fossil fuels—the highest biodiesel yields at 1:39 molar ratio of oleic acid to MeOH, 6 wt% loading, 65 °C, and 4 h reactions time were attained at 86.9 and 80% for MIL-101(Cr) on a pristine and scrap basis, respectively. The kinetic study revealed that activation energies were 25.27 kJ/mol and 28.3 kJ/mol for original and waste-derived MIL-101(Cr). The waste-derived MIL-101(Cr) was reused three times while five-time cycles for the original MIL-101(Cr).

Taguchi method for optimizing the cation exchange resin catalyzed esterification of oleic acid with ethanol and adsorption kinetics study

In this study, solid acid catalysts (cation exchange resins) were used to catalyze the esterification reaction of acidified oil and ethanol for the preparation of biodiesel. The catalyst was characterized by SEM, BET, XRD, and FTIR. The esterification reaction was studied under various conditions using one-way analysis. Process optimization was performed by the Taguchi method, revealing that the optimal conditions for maximum oleic acid conversion (91.63%) were a catalyst dosage of 20 wt%, ethanol/oleic acid molar ratio of 9:1, reaction time of 5 h, and reaction temperature of 80 ℃. In addition, the adsorption behavior of cation exchange resin (S-CER) on oleic acid and ethanol during the esterification process was investigated. The Freundlich and Langmuir adsorption kinetic models of the resin were also established. This study focused on the dynamic equilibrium of oleic acid and ethanol adsorption on the S-CER catalyst surface. The adsorption process was found to align better with the Freundlich isotherm equation. According to this equation, oleic acid's maximum adsorption capacity was found to be 371.24 mg/g. Lastly, a pseudo-primary kinetic equation for the esterification reaction was formulated, and the calculated activation energy for the reaction was 35.59 kJ/mol.

Preparation of Brönsted-Lewis dual acidic catalyst Ce-HPW-F and its simultaneous catalytic esterification and transesterification of oleic acid and castor oil with methanol to synthesize biodiesel

A series of Brönsted-Lewis dual acidic catalyst Ce(x)-HPW-F(x = 1/3, 2/3, 1, 4/3, x is the molar ratio of Ce to HPW) were synthesized by introducing Ce3+ and F- into 12-tungstophosphoric acid (H3PW12O40, HPW) with Keggin structure. The structure, morphology, valence state, elemental composition, acid site density and type of Ce-HPW-F catalyst were analyzed by FT-IR, XRD, BET, SEM, XPS, NH3-TPD, and Py-IR. The catalytic activities and stabilities of the obtained catalysts were studied in the esterification and transesterification reactions of oleic acid and castor oil (Simulated acidified oil, SAO). The Ce(1/3)-HPW-F has presented optimum catalytic activity. A yield of fatty acid methyl esters (FAME) 93.0 % was obtained at the 18:1 methanol to SAO molar ratio, 4 wt% catalyst, 110°C reaction temperature and reaction time of 90 min. The high catalytic activity of Ce(1/3)-HPW-F could be attributed to the strong Brönsted and Lewis acidity. The Lewis acidity was generated from the partial exchange of Ce3+ with the proton (H+) in HPW and increased through the formation of Ce-F bond between the strongly electronegative F- and Ce3+. Meanwhile, in the highly polar medium (methanol), the binding force between O and H+ was reduced due to the negative charge dispersion of the outer oxygen in the phosphotungstic acid anion and the polarization of W=Od formed by the terminal O and W. This may lead to the stepwise dissociation of H+ in HPW that had not been exchanged by Ce3+. However, F- could form the hydrogen bond with H+ to avoid the occurrence of the above phenomenon. After reusing Ce(1/3)-HPW-F catalyst for four times, the total yield of FAME could still achieve more than 75 %.