Esterification Of Free Fatty Acids Research Articles

Esterification of a waste cooking oil using metal-hybrid catalysts for chemoenzymatic reactions

Waste cooking oil (WCO) serve as a cheap feedstocks for biodiesel production. However, the high acidity of this oil disqualifies it from using alkaline transesterification as the synthesis reaction for biodiesel production. Thus, the integration of enzymatic and chemical catalysts to form a hybrid catalyst for reducing oil acidity is a new option in the biodiesel industry. In the present study, five types of metal oxides and Candida rugosa lipase (CRL) were sequentially co-immobilized on the Alumina (Al2O3) for esterification of free fatty acid (FFA) to fatty acid methyl esters (FAMEs).The lowest FFA content achieved was 1.10% using CRL-CaO-Al2O3 for 24 h esterification reaction, correspond to a conversion rates of 66.94%. The FAMEs conversion of the treated WCO indicates that the hybrid catalyst also can perform transesterification of triglycerides in the oil. Among all the hybrid catalysts, CRL-MgO-Al2O3 shows the highest FAME conversion of 69.10%. The best immobilization time was recorded at 7 h which successfully reduced the FFA content until 1.39%. The application of heterogeneous enzyme-metal hybrid catalysts promise a better insight in the biodiesel industry in terms of its simplicity and catalyst recovery.

Sustainable biodiesel production from low-quantity oils utilizing H6PV3MoW8O40 supported on magnetic Fe3O4/ZIF-8 composites

The development of efficient and reusable catalysts is desired to improve biodiesel production process. For this purpose, the magnetic Fe3O4/ZIF-8 composites were first prepared by incorporating ZIF-8 MOF into Fe3O4 nanoparticles through in-situ approach, and then a vanadium-substituted heteropolyacid (HPA), H6PV3MoW8O40, was encapsulated in the support to afford the solid catalyst. The so-prepared catalysts were characterized by using XRD, FT-IR, TEM, SEM, TG, VSM, and nitrogen porosimetry measurement. Results revealed that the Fe3O4/ZIF-8 support was really formed, and the HPAs had been loaded on the magnetic composite. The catalytic performances of the developed catalysts were evaluated for the heterogeneous biodiesel production from the low-quantity oils. This catalyst had good magnetic responsiveness, and could catalyze the transesterification of soybean oil and esterification of free fatty acids (FFAs) simultaneously, thus achieving one-step transformation of triglycerides and FFAs to biodiesel in a heterogeneous manner. The transesterification conversion obtained was 92.6% with 30:1 methanol/oil molar ratio at a catalyst loading of 6 wt% and reaction temperature of 160 °C for 10 h. Moreover, the solid catalyst could be recycled by an external magnet, and displayed a good reusability with a minimal mass loss and a slight decrease in the activity after reuse for five runs. This protocol showed great potential for sustainable biodiesel production from the low-quantity oils due to the pronounced activity and good reusability of the solid catalyst.

Highly active organosulfonic aryl-silica nanoparticles as efficient catalysts for biomass derived biodiesel and fuel additives

Post-grafting methodologies were used to prepare aryl-organosulfonic acid functionalized silica nanoparticles (SO3H-aryl-SiO2NPs) as highly active heterogeneous acid catalysts for catalytic esterification of free fatty acids (FFA) and levulinic acid (LA), and aldol condensation of furfural with 3-methylfuran, well known renewable feedstocks for biodiesel and fuel additives production. The chemical and structural characterization of the SO3H-aryl-SiO2NPs confirmed the success of the functionalization. Complete conversion for all FFA was observed using SO3H-aryl-SiO2NPs after 2 h of reaction. SiO2NPs_CSPTMS showed to be the most active and stable catalyst with no significant loss of activity in the first 5 cycles. In the LA esterification in the presence of an alcohol, complete conversion and selectivity and high reusability were observed (e.g., 83.2% yield after 10 cycles in the presence of 1-propanol, SiO2NPs10_CSPTMS, at 120 °C and 2h reaction). Finally, aldol condensation of furfural and 3-methylfuran had been performed using SiO2NPs_CSPTMS catalysts with almost 100% yield after 10 min at 65 °C, high stability and reusability for 7 catalytic cycles.In general, the prepared SO3H-aryl-SiO2NPs have demonstrated promising catalytic performance for transformation of biomass-derived feedstocks into biodiesel and fuel additives.

Process optimization of biodiesel production from waste cooking oil by esterification of free fatty acids using La3+/ZnO-TiO2 photocatalyst

In this study, a highly active and reusable La3+/ZnO-TiO2 photocatalyst was prepared by sol–gel method. The production of biodiesel from waste cooking oil by a two-step method. In the first step, under the UV irradiation, La3+/ZnO-TiO2 photocatalytic esterification of ethanol with free fatty acids (FFA) in waste cooking oil (WCO) was studied. In the second step, NaOH catalyzed the transesterification of triglycerides with ethanol. La3+/ZnO-TiO2 photocatalysts were characterized by TG, XRD, SEM-EDS, HRTEM, BET, UV–vis spectroscopy and Raman spectra. The optimum conditions were obtained by orthogonal design. At 35 °C, the ethanol/oil molar ratio is 12:1, the catalyst dosage is 4 wt%, the UV irradiation time is 3 h, the reaction time is 3 h, and the conversion of FFA reaches 96.14%. After 5 cycles of experiments, the conversion rate of FFA is more than 87%, which indicates that the catalyst has stable activity and simple recovery. The reaction mechanism of photocatalytic esterification was proposed and the kinetics of esterification was studied. Through the analysis of the characteristics of biodiesel, it is proved that the biodiesel by the method mentioned in this study conforms to GB 25199-2017 and EN 14214 standards. Therefore, La3+/ZnO-TiO2 as a new photocatalyst opens up a new way for biodiesel production.

Simultaneous esterification and transesterification of waste phoenix seed oil with a high free fatty acid content using a free lipase catalyst to prepare biodiesel

Biodiesel is a typical renewable and green energy, that is usually produced by the transesterification of edible vegetable oils. However, the cost of edible vegetable oils as feedstock accounts for 60%–80% of the total cost of biodiesel production. To overcome these issues, in this work, a low-cost feedstock, waste phoenix seed oil (PSO) with a high free fatty acid (FFA) content (30.1 ± 0.6%), consisting of the main fatty acid, linoleic acid (30.2%), oleic acid (22.2%), and palmitic acid (17.4%), was developed as a new feedstock to prepare biodiesel. A novel one-step method including simultaneous esterification of FFAs and transesterification of the PSO to prepare biodiesel was developed. Free lipase was used as catalyst. The influences of the reaction parameters were explored and optimized by response surface methodology. The results showed that the free lipase Lipozyme TL100L from Thermomyces lanuginosus can simultaneously catalyze esterification and transesterification. Under the optimum conditions (enzyme load 9.7%, reaction time 6.9 h, reaction temperature 31 °C and substrate ratio (methanol/PSO) 4.3: 1 (mol/mol)), the maximum biodiesel yield (93.8 ± 0.5%) was achieved. The activation energy from biodiesel preparation using PSO with a high FFA content was 39.7 kJ/mol. Furthermore, the kinetic values for K'm and Vmax were 0.18 mol/L and 0.043 mol/(L·min), respectively. The reaction mechanism of the simultaneous esterification and transesterification was also proposed. These results indicate that PSO with a high FFA content can be used as a potential feedstock for biodiesel production.

Transcriptomic analysis suggested the involvement of impaired lipid droplet biogenesis in graphene oxide-induced cytotoxicity in human umbilical vein endothelial cells

Previous studies revealed that direct contact with graphene oxide (GO) induced cytotoxic effects, but the importance of involvement of metabolic pathways, in particular lipid metabolism pathways, might be overlooked. In this study, human umbilical vein endothelial cells (HUVECs) were exposed to GO with large size (denoted as GO-L) or small size (denoted as GO-S), and transcriptomics were used to understand the mechanisms of cytotoxicity of GO at systemic levels. It was shown that GO-L more significantly induced cytotoxicity compared with GO-S. Transcriptomic analysis revealed that compared with GO-S, GO-L had larger impact on gene ontology terms related with mitochondrial function as well as Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways related with cell death and growth. But GO-S showed greater influence on KEGG pathways related with lipid metabolism. Both types of GO showed minimal impact on oxidative stress but increased de novo lipogenesis protein fatty acid synthase (FASN). However, only GO-S significantly promoted acyl-CoA synthetase 3 (ACSL3), a key enzyme responsible for esterification of free fatty acids and lipid droplet biogenesis. Not surprisingly, GO-L but not GO-S impaired lipid droplet biogenesis, and increasing lipid levels by oleic acid or α-linolenic acid reduced the cytotoxicity of GO-L to HUVECs. Combined, the results from this study suggested that impaired lipid droplet biogenesis was involved in GO-induced cytotoxicity in HUVECs, and inducing lipid droplet biogenesis could prevent the cytotoxicity of GO.

Highly ordered mesoporous functionalized pyridinium protic ionic liquids framework as efficient system in esterification reactions for biofuels production

Polysiloxane acidic ionic liquids containing pyridinium trifluoroacetate salts (PMO-Py-IL) were synthesized from pyridine containing organosilane precursors. Characterization by SEM, XRD, TGA, and nitrogen porosimetry confirmed that both pyridinium cation and trifluoroacetate anion were successfully incorporated within the organosilica network. The resulting organic-inorganic hybrid nanomaterial (PMO-Py-IL) was studied as nanocatalyst in free fatty acids esterification into biodiesel-like compounds. Remarkably, the synergistic hydrophilic/hydrophobic effect of pyridinium and trifluoroacetate ionic liquid in the well-ordered channels of PMO-Py-IL nanomaterial enhanced the activity toward sustainable biodiesel-like esters production. More importantly, PMO-Py-IL nanocatalyst also exhibited an exceptional activity and stability. The catalyst could be easily separated to reuse at least in ten reactions runs preserving almost intact its catalytic activity under otherwise identical conditions to those employed for the fresh catalysts.

Synthesizing Precursors for Functional Food Structured Lipids from Soybean Oil Deodorized Distillates

A “green” scheme of synthesizing diglycerides as a means of valorizing an oil processing by-product, specifically soybean oil deodorized distillate (SODD), was established. Different glycerol dosing strategies were implemented in the solvent-free lipase catalyzed esterification of free fatty acids with glycerol within molar ratios of 2–4 and temperatures of 40–60 °C. The process responses were compared with non-dosed systems in this study and other similar processes reported in literature. Better 1,3-diglyceride selectivity at comparable yields were observed with glycerol dosed-systems over non-dosed systems. The presence of molecular sieves negatively affected 1,3-diglyceride selectivity, total diglyceride selectivity and yield. Selectivity of 0.91 ± 0.01 g diglycerides/g (mono + triglycerides), free fatty acid conversion of 57.87 ± 3.46%, and yield of 30.59 ± 1.26 g diglyceride/100 g raw material is obtained with SODD at 40 °C, overall free fatty acid to glycerol molar ratio of 2, 4 wt% Novozyme 435 and 48 h. The process scaled better than most solvent-based ones supported with hygroscopic sorbents in terms of reaction mass efficiency.

Biodiesel Production from Low-Quality Oils Using Heterogeneous Cesium Salts of Vanadium-Substituted Polyoxometalate Acid Catalyst

This research aims at developing an efficient and reusable catalyst to improve biodiesel production processes. To achieve this, a vanadium-substituted polyoxometalate (POM) acid, namely H6PV3MoW8O40, was firstly prepared, and then the heterogenzation of the homogeneous Keggin-type heteropoly acids was performed by the partial proton substitution by monovalent large cesium cations with the formation of solid Cs2H4PV3MoW8O40 catalysts. Several techniques, such as X-ray diffractometer, Fourier transform infrared, coupled plasma–atomic emission spectrometry, Diffuse reflectance ultraviolet–visible spectrum, thermal gravimetric analysis and N2 adsorption–desorption techniques, were employed to characterize the as-prepared solid catalyst. The solid acid catalyst had the capacity to catalyze both the transesterification of soybean oil and esterification of free fatty acids (FFAs) simultaneously, providing an efficient production process for the production of biodiesel from low-quality oils. Under the operational conditions of a methanol/oil molar ratio of 30:1, a catalyst dosage of 5 wt.%, a reaction temperature of 140 °C, and a reaction duration of 8 h, an oil conversion of 92.2% was attained with the total FFA transformation to biodiesel. Furthermore, the catalyst could be reutilized for several cycles with no significant drop in its activity, thus having great potential for application with a bright perspective in the production of biodiesel, especially from low-quality oil feedstocks.

Reusable and efficient heterogeneous catalysts for biodiesel production from free fatty acids and oils: Self-solidifying hybrid ionic liquids

A series of self-solidifying hybrid ionic liquids (SHILs) were synthesised via a mild nucleophilic substitution reaction between (3-aminopropyl)trimethoxysilane and 1,3-propanesultone followed by a facile sol-gel reaction, during which not any acid, catalyst or support was introduced. Part of the grafted –SO3H groups would make SHILs become solid nature by forming the zwitterion, while the rest of –SO3H groups could endue SHILs with acidic catalytic sites. Besides, –Si–O–Si– networks formed by the sol-gel reaction would further impart the water-tolerance and heterogeneity to SHILs, conducive to the easy separation and good reusability. For the oleic acid esterification catalysed by P-APTMS-PS-5 SHIL, 96.55% conversion was achieved under appropriate conditions (optimised by response surface methodology), and the catalytic activity well remained after 7 cycles. More importantly, SHILs exhibited excellent catalytic activity and satisfactory generality in the esterification of various free fatty acids, as well as in the transesterification of different oils, signifying the great potential for biodiesel production.

Grafting copolymerization of dual acidic ionic liquid on core-shell structured magnetic silica: A magnetically recyclable Brönsted acid catalyst for biodiesel production by one-pot transformation of low-quality oils

The objective of the current research is to prepare an efficient and magnetically separable Brönsted acid catalyst for one-pot transformation of low-quality oils to biodiesel. In this premise, the core–shell structured magnetic composites were firstly prepared by coating of silica shells on magnetic Fe3O4 nanoparticles. Thereafter, the grafting copolymerization of dual acidic ionic liquids (ILs, 1-vinyl-3-(3-sulfopropyl)imidazolium hydrogen sulfate as an monomer and 1.4-butanediyl-3,3′-bis-1-vinylimidazoliu hydrogen sulfate as a cross-linker agent) on the magnetic silica composite was conducted to impart the richer Brönsted acidic functionality on the support. The detailed catalyst characterization results showed that the magnetic silica support was really formed, and moreover the polymeric acidic ILs were successfully grafted on the magnetic support. The so-prepared solid catalyst had a large surface acidity (3.93 meq H+/g) and strong magnetism (27.5 emu/g). Benefiting from the synergism between the polymeric ILs and magnetic porous support, this developed catalyst displayed good catalytic activities toward both the transesterification of soybean oil and esterification of free fatty acids (FFAs), which endowed it to be a robust solid acid catalyst for one-pot biodiesel production from low-quality acidic oils. The solid catalyst could be simply recovered by an external magnet with minor loss of catalytic activity within five cycles, and further showed insensitivities to moisture and FFAs present in the feedstocks, possessing both economic and environmental advantages for the application in biodiesel production especially from the low-quality oils.

Comparison of Photo‐Esterification Capability of Bismuth Vanadate with Reduced Graphene Oxide Bismuth Vanadate (RGO/BiVO4) Composite for Biodiesel Production from High Free Fatty Acid Containing Non‐Edible Oil

AbstractBiodiesel has gained much more attention as an alternative and renewable energy source due to the continuous exhaustion of petroleum reserves and their inauspicious environmental effects. Non‐edible feedstocks are economically viable for the production of biodiesel but the presence of higher amount of free fatty acids (FFAs) in these oils is a main hurdle for getting good quality biodiesel. This issue can be addressed through esterification prior to transesterification of oil. This work was designed to evaluate soapnut oil as a source for biodiesel production. Moreover, the catalytic activity of two sunlight active photocatalysts; BiVO4 and RGO/BiVO4 was also compared for the esterification of higher FFA content present in soapnut oil. BiVO4 and RGO/BiVO4 were characterized through SEM, XRD and FT‐IR. Experimental results revealed that RGO/BiVO4 exhibited higher catalytic activity as compare to BiVO4 for the esterification of FFA under sunlight irradiation. Different process variables were optimized and maximum conversion of FFA (88 %) was obtained at 3 : 1 methanol to oil ratio, 5 % catalyst dose, 300 rpm stirring speed and 3 h of reaction time. Esterified oil was then transesterified by using MgO‐KOH heterogeneous catalyst and maximum yield (94 %) of soapnut methyl esters (SNMEs) was obtained at 9 : 1 methanol to oil ratio, 3 % catalyst dose, 2 h reaction time, 80 °C temperature and at 300 rpm stirring speed. The physic‐chemical analysis of synthesized biodiesel revealed that it meets ASTM standards.

Glycerolysis of free fatty acid in vegetable oil deodorizer distillate catalyzed by phosphonium-based deep eutectic solvent

Abstract Esterification of free fatty acids in a low-grade oil with glycerol, the by-product of transesterification, has been proposed as one possible method to reduce the cost of raw materials for biodiesel production. The glycerolysis reaction recycles the byproduct glycerol to create a much more efficient and cost-effective process. However, the glycerolysis reaction involves challenges, including its requirement of high temperature. This study is the first to apply the deep eutectic solvent (DES) as a catalyst for glycerolysis reaction to convert free fatty acid (FFA) in vegetable oil deodorizer distillate (VODD) being a waste product from the oil refining process into glycerides. The effects of temperature, catalyst dosage, and time on the esterification efficiency of fatty acid conversion were explored. The reaction progress and product solubility were studied by FT-IR and GC. The results revealed that the reaction reached equilibrium at an approximate free fatty acid (FFA) conversion of 90%. The reaction was a second-order reversible reaction, using 8 wt% catalyst loading lowered activation energy to 58.80 J/mol. The optimum condition was determined as 160 °C, 5 wt% DES loading, and 10 min reaction time.

Recent Progress in Microwave-assisted Modification of Vegetable Oils or Their Derivatives

Vegetable oils have been widely used in food, surfactants, lubricants, biodiesel, coatings, and other fields due to their advantages such as renewable, abundant, suitable for further processing, and biodegradable. On the other hand, microwave technology has attracted extensive attention in organic and polymeric chemistry because the technology can greatly shorten the reaction time, improve the yield of products, reduce side reactions, etc. This paper summarized recent advances on the microwave-assisted modification of vegetable oils or their derivatives, such as esterification of free fatty acids, transesterification of triglycerides, epoxidation, and polymerization.

Synthesis and IR Characterization of Activated Carbon Acid Catalysts from Cassava Peels and their Use in Esterification of Free Fatty Acid in Palm Kernel oil

The present study reports the preparation of four solid acids (CS, CPS, CAS and CPAS) from cassava peels and investigates their catalytic activities in the esterification of free fatty acid (FFA) in palm Kernel oil (PKO). The activated carbon obtained from carbonization was directly sulfonated with sulfuric acid (CS) or treated first with phosphoric acid before sulfonation (CPS). Another part of activated carbon was pyrolyzed at 800°C and treated as in the two previous cases (CAS and CPAS). The FTIR spectra of CS, CPS, CAS and CPAS showed characteristic absorption peaks of functional groups such as O=S=O (1031 cm-1), OH (3849 and 3405 cm-1), C=C (1555-1574 cm-1), S=O (1042,1031 cm-1) and P=O (754 cm-1), which confirm the presence of sulfonic, carboxylic and phosphoric groups on the surface of the activated carbon acids prepared. The total acid densities of the catalysts range from 2.26 to 3.49 mmol/g whereas the -SO3H densities were from 0.92 to 2.20 mmol/g. Amongthe four catalysts prepared, their effectiveness in the esterification of free fatty acid in palm kernel oil with a conversion rate from 70 to 90%, depended mostly on the sulfonic acid density on the catalyst, CPS showed the highest total and –SO3H acid densities with 3.49 and 2.2 mmol/g respectively and a highest free acid fatty conversion rate of 90%. Thus, CPS was more efficient than CS, CPAS and CAS. All the catalysts prepared could be reused in the esterification reaction with a mild decrease in the conversion rate.

Synthesis of CoO–NiO promoted sulfated ZrO2 super-acid oleophilic catalyst via co-precipitation impregnation route for biodiesel production

Abstract This study focuses on the synthesis of a novel heterogeneous CoO–NiO promoted sulfated ZrO2 (CN/SZ) catalyst and investigating its catalytic efficiency as a transesterification reagent. Catalytic performance has also been compared with two reference catalysts viz., sulfated ZrO2 (SZ) and pure ZrO2 (Z). Prepared materials were characterized using X-ray diffraction (XRD) technique, N2- adsorption/desorption study, scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDAX), Raman, Fourier Transformed Infrared (FTIR), and X-ray photoelectron (XP) spectroscopy techniques. Surface acidity and basicity were assessed by NH3 and CO2 temperature-programmed desorption (TPD) respectively that established high surface acidity and basicity of CN/SZ nanocatalyst. The reagent has shown supreme catalytic performance as only 0.2 wt% catalyst loading amount has provided 98.8% of biodiesel yield with 3:1 MeOH:Oil molar ratio at 65 °C for 2 h. Also, the reusability study has proved the efficacy of CN/SZ nanocatalyst that it can successfully be reused in five consecutive reaction cycles displaying promising results and the reactivated catalyst provided remarkably high biodiesel yield of 96.8%. Further, the mechanistic pathway of the simultaneous catalytic esterification of free fatty acid and transesterification of triglyceride occurring on catalyst surface has also been explored.

Use of hydrodynamic cavitation for esterification of free fatty acids in waste cooking oil

Esterification followed by transesterification process is widely applied for biodiesel production from oil with high free fatty acids (FFA) content to remove the FFA and increase the yield of biodiesel. The aim of this research was to study the esterification of waste cooking oil using the hydrodynamic cavitation apparatus. Waste cooking oil with initial FFA content 4.33% was esterified with methanol using sulfuric acid 1%-w/w as the catalyst. The reaction condition was kept constant for 120 minutes of total reaction time. At the best operating condition i.e. molar ratio of waste cooking oil to methanol 1:10 and reaction temperature 50 °C, the initial FFA of waste cooking oil 4.33% reduced to 0.76%. The experimental results also showed that the hydrodynamic cavitation had better performance than the conventional process using mechanical stirring.

Bifunctional Heterogeneous Catalyst for Biodiesel Production from Waste Vegetable Oil

Bifunctional solid catalysts facilitate the esterification of free fatty acids (FFA) into alkyl esters alongside the transesterification reaction, which allows for the use of waste vegetable oils with high water and FFA contents for biodiesel production. This makes the process economically viable and greener, as the waste fats and oils are readily available. The concurrent esterification and transesterification of waste palm oil (WPO) and waste sunflower oil (WSO) with methanol was investigated in the presence of calcium oxide on alumina catalyst in a conventional batch process. The catalyst characterization showed the existence of calcium oxide aluminates (calcined at 750 °C), which exhibited crystalline phases with porous/spongy-like particles. The high concentration of CaO in CaO/Al2O3 was a favorable support material in the heterogeneously-catalyzed transesterification reactions. The optimum catalyst parameters for the production of fatty acid methyl esters (FAMEs) were observed at 65 °C for 4 h with a methanol-to-oil ratio of 9:1, 60% (waste palm oil, or WPO) and 80% (waste sunflower oil, or WSO), CaO/Al2O3 (% wt/wt) catalyst ratio as well as 4% CaO/Al2O3 concentration (% wt.) for WSO and WPO. The simultaneous esterification/transesterification reactions at optimum conditions on WPO and WSO led to high yield of FAMEs of 89, 61 and 55% for WPO and 54, 75 and 98% for WSO at catalyst ratios (wt %) of 60, 70 and 80% respectively. The use of bifunctional heterogeneous catalyst (CaO/Al2O3) with waste vegetable oil can result in high performance and the upscaling of biodiesel production.

New Task-Specific and Reusable ZIF-like Grafted H6P2W18O62 Catalyst for the Effective Esterification of Free Fatty Acids.

The catalytic esterification of free fatty acids is an important reaction pathway for chemical synthesis and biodiesel production, wherein efficient heterogeneous catalysts are sought to replace mineral acids. Herein, the esterification of oleic acid together with some familiar fatty acids is demonstrated with methanol over a heterogeneous heteropolyacid-functionalized zeolite imidazolate framework [H6–nP2W18O62n–/ZIF(HnHis.)+n]. This new heterogeneous catalyst (named as HPA/ZIF(His.) throughout the text) with an average particle size of 80 nm was prepared via condensation of histamine with zinc chloride and characterized by means of Fourier transform infrared (FT-IR), X-ray diffraction (XRD), UV–vis, energy-dispersive X-ray spectrometry, Brunauer–Emmett–Teller, thermogravimetric analysis (TGA), inductively coupled plasma - optical emission spectrometry (ICP-OES), and scanning electron microscopy. According to the performed characterizations, an HPA loading of 40.5 wt % is obtained for HPA/ZIF(His.) from ICP-OES analysis. Moreover, a typical type-IV isotherm with similar adsorption–desorption properties as seen for ZIF-8 is attained. In addition, TGA measurement confirms less stability of HPA/ZIF(His.) compared to that of pure ZIF(His.). The catalytic performance of the nanomaterial is evaluated with respect to temperature, catalyst loading, and methanol/oleic acid ratio and leads to a high yield of methyl ester (>90%) under reflux for 4 h. The preliminary kinetic studies confirm a pseudo-first-order kinetic model for the esterification of oleic acid. To explore the scope of the HPA/ZIF(His.) catalyst in methyl ester production, other free fatty acids with various chain lengths are also successfully tested. Although the nanocatalyst loses a part of its activity during reuse, however, it is stable over at least four recycles as confirmed by XRD and FT-IR. Eventually, the response surface methodology (RSM) is used as a statistical modeling approach to get the best-optimized reaction conditions compared to the performed single-variable benchmarking experiments. Therefore, the central composite design (CCD) and RSM attained a platform to determine the relationship among the reaction time, acid/methanol molar ratio, and catalyst dosage.

Synthesis of heterogenized polyoxometalate-based ionic liquids with Brönsted-Lewis acid sites: A magnetically recyclable catalyst for biodiesel production from low-quality oils

The aim of this study is to develop a magnetically recyclable acid catalyst for biodiesel production from low-quality acidic oils. To achieve this, polyoxometalate (POM)-based sulfonated ionic liquids (ILs) bearing Brönsted-Lewis acid sites, namely (Py-Ps)PMo, were firstly prepared by reaction of pyridine with 1,3-propanesultone, followed by anion exchange with phosphomolybdic acid (HPMo). Thereafter, the so-prepared ILs were loaded on the amino-functionalized metal–organic framework (CoFe2O4/MIL-88B(Fe)-NH2) to synthesize the recoverable solid catalyst. The obtained CoFe2O4/MIL-88B(Fe)-NH2/(Py-Ps)PMo catalyst was characterized by several techniques, which provided an evidence that the acidic ILs were loaded on the magnetic support by strong charge interaction effect. This catalyst showed highly catalytic activities toward the transesterification of soybean oil and esterification of free fatty acids (FFAs), making it to be applicable for one-pot production of biodiesel from low-quality acidic oils. The catalytic performance was originated from the combination of the characteristics of Brönsted-Lewis acid sites and porous structure of the support. Moreover, the catalyst could be simply recovered by a permanent magnet and reutilized for several times with no remarkable attenuation of catalytic activity. Thus, the IL based solid catalyst possessed the potential of efficient and environmentally benign production of biodiesel practically from the low-quality oils.