Transesterification Mechanism Research Articles

Polysulfone with Different Degrees of Sulfonation: Simple Method with Acetyl Sulfate

In this work, the authors present as an innovation, the homogeneous sulfonation of Udel® polysulfone (PSU) with acetylsulfate (ACS) under reflux at 45°C in dichloromethane and inert N2 atmosphere (g) for 1.5 h. Different proportions of ACS were used, obtaining sulfonated products with varying degrees of sulfonation (DS). Confirmation of sulfonated polysulfone (PSU-S), denominated as PSU-SA (high degree of sulfonation) and PSU-SB (low degree of sulfonation), was carried out by FTIR and 1H NMR. Determination of DS was carried out through thermogravimetric analysis (TGA/DSC), varying indexes between 0.883 and 3.022, which correspond to a sulfonated polymer with ion exchange capacity (IEC) from 1.720 to 4.400 meq/g. The evolution of DS related to methods used was monitored and confirmed by 1H NRM. Sulfonation is undertaken to enhance the suitability of this polymer for future applications in the production of biofuels, targeting its utilization in catalytic processes for esterification and transesterification mechanisms of oils and fats.

Preparation of biodiesel by transesterification of castor oil catalyzed by flaky halloysite supported ZnO/SnO2 heterojunction photocatalyst

Biodiesel belongs to renewable energy and is a potential substitute for petrochemical diesel. In this study, ZnO/SnO2@halloysite heterojunction photocatalyst was prepared by loading semiconductor zinc oxide and tin dioxide on layered kaolin by the improved wet calcination method, which was used to photocatalytic the transesterification of castor oil and ethanol to produce biodiesel. TG-DTG, BET, XRD, UV–vis and SEM-EDS were used to characterize the composition, specific surface area, light absorption characteristics and photocatalytic performance of the samples. The reaction conditions were optimized by the Taguchi method. The optimum reaction conditions were as follows: catalyst dosage 4 wt%, molar ratio of ethanol to oil 12:1, reaction temperature 75 °C. After 2 h, the yield of biodiesel was 96.75 %. In the study of catalyst reusability, the yield of biodiesel is still above 85 % after being reused for 5 times. The kinetics of photocatalytic transesterification was studied, and the results accorded with quasi-first-order kinetics. The activation energy was 75.02 kJ/mol. Lastly, an eight-step reaction mechanism of photocatalytic transesterification was proposed. The prepared castor oil biodiesel can be prepared into B20 biodiesel through additives or mixing to meet ASTM D6751 and EN 14214 standards.

Ring-ring equilibration (RRE) of cyclic poly(L-lactide)s by means of cyclic tin catalysts

With 2,2-dibutyl-2-stanna-1,3-dithiolane (DSTL) and 2-stanna-1,3-dioxa-4,5,6,7-dibenzoxepane (SnBiPh) as catalysts ring-expansion polymerizations (REP) were performed either in 2 M solution using three different solvents and two different temperatures or in bulk at 140 and 120 °C. A kinetically controlled rapid REP up to weight average molecular masses (Mẃs) above 300 000 was followed by a slower degradation of the molecular masses at 140 °C, but not at 120 °C Furthermore, a low molecular mass cyclic poly(L-lactide) (cPLA) with a Mn around 16 000 was prepared by polymerization in dilute solution and used as starting material for ring-ring equilibration at 140 °C in 2 M solutions. Again, a decrease of the molecular mass was detectable, suggesting that the equilibrium Mn is below 5 000. The degradation of the molecular masses via RRE was surprisingly more effective in solid cyclic PLA than in solution, and a specific transesterification mechanism involving loops on the surface of crystallites is proposed. This degradation favored the formation of extended-ring crystallites, which were detectable by a “saw-tooth pattern” in their MALDI mass spectra.

Readily available, biocompatible sodium citrate catalyst for efficient glycerol carbonate production through transesterification of glycerol and ethylene carbonate

As a by-product in the biodiesel industry, surplus glycerol (Gly) has attracted considerable concern. The transesterification of Gly is one of the most promising reaction pathways to convert Gly to a value-added chemical such as glycerol carbonate (GC). Currently, development of catalysts for the transesterification with high activity is underway. Herein, a readily available biocompatible sodium citrate (Na3-citrate) catalyst was applied for efficient production of GC through transesterification of Gly and ethylene carbonate (EC). The effects of reaction parameters such as reaction time, EC to Gly molar ratio, reaction temperature, and catalyst loading on the reaction were investigated. Under optimal conditions, 0.01 wt% of Na3-citrate showed high catalytic activities with a Gly conversion of > 99 %, a GC yield of > 99 %, and a high turnover frequency of 16,925 gGC⋅g−1Cat⋅h−1. Furthermore, the reaction kinetic model for transesterification was established, and the activation energy of the Na3-citrate catalyzed transesterification was calculated as 51.3 kJ·mol−1. In addition, density functional theory calculations were used to unveil mechanism of the Na3-citrate catalyzed transesterification. It revealed that citrate anion of Na3-citrate could activate hydroxy of Gly via strong hydrogen bond interaction, thereby efficiently promoting transesterification by reducing energy barrier of rate-determining step.

Unveiling the complementary mechanism in the one-pot synthesis of glycerol carbonate from CO2 and glycerol

The chemical conversion of inert carbon dioxide (CO2) into high value-added chemicals is a continuing challenge. In this work, an experimental and theoretical mechanism study is presented for one-pot synthesis of glycerol carbonate (GC) from CO2, glycerol (Gly), and propylene epoxide (PO) catalyzed by 1,8-diazabicyclo[5.4.0]undec-7-enenium iodide (HDBUI) ionic liquid. 92% GC yield was obtained in the one-pot reaction through cycloaddition of CO2 with PO to produce propylene carbonate (PC), followed by transesterification of Gly with PC to yield targeted products. Density functional theory (DFT) calculations were used to unveil the HDBUI-mediated catalytic mechanism and key catalytic species. It was revealed that the HDBUI-catalyzed cycloaddition was assisted by the hydrogen bond donor Gly, the transesterification reactant, by promoting the ring-opening of PO and the insertion of CO2. By activating Gly hydroxyl group, alkaline HDBUI-bonded propan-1-ylium-2-yl carbonate, an intermediate in cycloaddition, catalyzed transesterification. The complementary mechanism of cycloaddition and transesterification in the one-pot provides a feasible method for utilizing inert CO2.

Catalytic Characterization of Synthetic K+ and Na+ Sodalite Phases by Low Temperature Alkali Fusion of Kaolinite during the Transesterification of Spent Cooking Oil: Kinetic and Thermodynamic Properties

The mineral raw Egyptian kaolinite was used as a precursor in the synthesis of two sodalite phases (sodium sodalite (Na.SD) and potassium sodalite (K.SD)) according to the low alkali fusion technique. The synthesized Na.SD phase demonstrates enhanced total basicity (6.3 mmol OH/g), surface area (232.4 m2/g), and ion exchange capacity (126.4 meq/100 g) compared to the K.SD phase (217.6 m2/g (surface area), 96.8 meq/100 g (ion exchange capacity), 5.4 mmol OH/g (total basicity). The catalytic performance of the two sodalite phases validates the higher activity of the sodium phase (Na.SD) than the potassium phase (K.SD). The application of Na.SD resulted in biodiesel yields of 97.3% and 96.4% after 90 min and 60 min, respectively, while the maximum yield using K.SD (95.7%) was detected after 75 min. Robust base-catalyzed reactions using Na.SD and K.SD as catalysts were suggested as part of an operated transesterification mechanism. Moreover, these reactions exhibit pseudo-first order kinetics, and the rate constant values were estimated with consideration of the change in temperature. The estimated activation energies of Na.SD (27.9 kJ.mol−1) and K.SD (28.27 kJ.mol−1) reflected the suitability of these catalysts to be applied effectively under mild conditions. The essential thermodynamic functions, such as Gibb’s free energy (65.16 kJ.mol−1 (Na.SD) and 65.26 kJ.mol−1 (K.SD)), enthalpy (25.23 kJ.mol−1 (Na.SD) and 25.55 kJ.mol−1 (K.SD)), and entropy (−197.7 J.K−1.mol−1 (Na.SD) and −197.8 J.K−1.mol−1 (K.SD)), display the endothermic and spontaneous nature of the two transesterification systems.

Effect of ionic radius and valence state of alkali and alkaline earth metals on promoting the catalytic performance of La2O3 catalysts for glycerol carbonate production

Alkali metals and alkaline earth metals have been used to promote the catalytic performance of metal oxides in transesterification of glycerol and dimethyl carbonate, however, the promotional roles of the dopants in influencing the catalytic performance of the metal oxides have not been fully investigated which hinder the development of low-cost and high-efficiency catalysts in transesterification of glycerol and dimethyl carbonate. This paper, for the first time, systematically studied the influence of ionic radius and valence state of dopants, surface concentration of dopants and the basicity of the catalysts on the catalytic performance of La2O3 in transesterification of glycerol and dimethyl carbonate. Our results suggest that the ionic radius and valence state of the dopants are the determining factors, while the basic site density is not a crucial factor, although the basicity of catalyst surface is important in activating glycerol and dimethyl carbonate. Among alkali and alkaline earth metals, 25 mol% Na/La2O3 catalyst achieved the highest glycerol conversion (85 %) and glycerol carbonate yield (60 %) in the 70 °C and 2-hour reaction. After the detailed investigation, a plausible mechanism of glycerol and dimethyl carbonate transesterification on Na/La2O3 catalyst has been proposed. This research could help understand the promotional role of alkali metals and alkaline earth metals and the results may guide future design of metal oxide catalysts.

Kinetic, Thermodynamic, and Mechanistic Studies on the Effect of the Preparation Method on the Catalytic Activity of Synthetic Zeolite-A during the Transesterification of Waste Cooking Oil

Egyptian kaolinite was applied in the synthesis of zeolite-A by conventional hydrothermal and alkali fusion methods, resulting in two forms of zeolite-A: the hydrated phase (H.ZA) and the dehydrated phase (DH.ZA). The DH.ZA phase exhibits an enhanced surface area (488 m2/g), total basicity (7.73 mmol OH/g), high sodium content (20.2%), and a narrow particle size distribution (5 to 25 µm) as compared to the H.ZA phase (423 m2/g surface area, 5.88 mmol OH/g total basicity, 13.3% sodium content, and 10 to 45 µm particle size distribution). DH.ZA exhibits enhanced catalytic activity, achieving a biodiesel yield of 96.8% after 60 min at 60 °C, while the application of H.ZA resulted in a 95.8% yield after 120 min at 80 °C. The controlled transesterification mechanism in the presence of H.ZA and DH.ZA involved robust base-catalyzed reactions. The reactions follow the pseudo-first-order kinetics, and the rate constants (Kc) were determined at three different temperature values (40, 50 and 60 °C). The activation energies using H.ZA (35.9 kJ·mol−1) and DH.ZA (32.714 kJ·mol−1) demonstrates their efficiencies in mild conditions. The thermodynamic parameters of enthalpy (33.23 kJ·mol−1 (H.ZA) and 30.03 kJ·mol−1 (DH.ZA)), Gibb’s free energy (65.164 kJ·mol−1 (H.ZA) and 65.268 kJ·mol−1 (DH.ZA)), and entropy (−195.59 J·K−1·mol−1 (H.ZA) and −195.91 J·K−1·mol−1 (DH.ZA)) demonstrate the spontaneous and endothermic behaviours of these reactions. The obtained biodiesel matches the physical properties of the international standards, and the recyclability properties of the two zeolite phases demonstrate their suitability for commercial-scale applications.

Mechanism and kinetics of melt transesterification with siloxane diol

Chemical reactivity will have new traits in system combining organic and silicon compounds. In this paper, the kinetics of melt transesterification of dimethyl terephthalate (DMT) with a siloxane diol of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane (HP-TMDS) was fitted on the premise of the reaction mechanism obtained by quantum-chemistry calculation. This work reveals that the siloxane diol changes the reaction process and gives the classical transesterification its peculiarity, including more obvious advantage in kinetics for cyclic dimer and limited compatibility between reactant and catalyst. A solution is proposed to solve the problem resulting from the limited compatibility, which can be reference to any similar systems. The obvious advantage in kinetics for cyclic dimer brings a distinct feature in the product composition, which will provide more flexible and effective way to prepare silicon-containing polyesters.

Immobilization of Candida Rugosa lipase on Ca/Kit-6 used as bifunctional biocatalysts for the transesterification of coconut oil to biodiesel

Immobilization of Candida Rugosa lipase (CRL) on Ca doped Kit-6 solid was investigated via the adsorption method. Effects of the experimental parameters, such as pH value, temperature, time, and Ca content on the adsorption of CRL on Ca/Kit-6 were studied. In the Ca doped Ca/Kit-6 materials, Ca2+ coexisted in two environments: Ca2+ in CaO nanoparticles and in Ca-O-Si in the framework of Kit-6. There existed three kind of oxygen species: (1) lattice oxygen in CaO and SiO2; (2) Oxygen in structural defects; and (3) non-stoichiometric surface oxygen in OH form. The 0.5Ca/Kit-6 showed the most CRL immobilization capacity and stability under the optimal adsorption condition, which was correlated with its greater amount of basicity resulting from its more non-stoichiometric surface oxygen and oxygen in structural defects as well as more Ca2+ incorporation in the Kit-6 framework. In the production of biodiesel via transesterification of coconut oil, the catalysts showed better catalytic performance under weak basic than acidic condition. Under the optimal reaction conditions (40 °C, pH 7.5, 200 rpm, oil to methanol ratio 1:3 with stepwise addition of methanol, and 0.1 g of CRL/0.5Ca/Kit-6), the coconut oil conversion and biodiesel yield catalyzed with CRL/0.5Ca/Kit-6 was 95 and 98%, respectively. 10wt% water in the reaction mixture promoted the coconut oil transesterification to biodiesel. The CRL/0.5Ca/Kit-6 catalyst possessed bifunctional roles of the enzymatic catalysis role from immobilized CRL and the basic catalysis role from CaO doping. The CRL adsorption modes, water influence and the reaction mechanism of coconut oil transesterification were discussed.

Study on Kinetics and Reaction Parameters of Biodiesel Production from Sunflower Oil and Methanol Using Zinc Oxide Supported Calcium Oxide

This study investigated the effect of reaction parameter, reaction kinetics and mechanism of transesterification of sunflower oil with methanol by using CaO/ZnO heterogeneous catalyst. The influence of reaction time, molar ratio and catalyst amount and reaction temperature on fatty acid methyl esters (FAME) yield was investigated. The catalysts were prepared by incipient wetness impregnation and characterized by using X-ray diffraction (XRD) and Hammett indicator method. The FAME contents were analyzed by gas chromatography using the EN 14103 standard method. The highest FAME yield of 82% was obtained at 9/1 methanol/oil molar ratio, 3 wt.% catalyst amount and 3 hours of reaction time at 65 °C of reaction temperature by using 20% CaO/ZnO catalyst. The reaction could be considered pseudo first order with respect to triglyceride (TG). The reaction model based on Eley-Rideal mechanism was proposed where adsorbed methanol reacted with TG before desorption of glycerin. The results showed that experimental reaction rates exhibited good agreement with calculated reaction rates.

Investigation of the Initiating and Catalytic Behavior of Tri-n-butyltin(IV) n-Butoxide in Ring-Opening Polymerization of ε-Caprolactone and Transesterification of Poly(L-lactic acid)

T ri-n-butyltin(IV) n-butoxide (nBu3SnOnBu) was successfully synthesized and utilized as a stable and homogeneous initiator for the small-scale synthesis of biodegradable polymers in our laboratory. From our previous works, the initiating performance of nBu3SnOnBu in the ring-opening polymerization (ROP) of cyclic ester monomers was completely investigated by differential scanning calorimetry (DSC). It was found that nBu3SnOnBu acted as the slow initiator in the ROP of ε-caprolactone (ε-CL) due to its high steric hindrance around the active center. Moreover, it could be used in the stereoselective ROP of racemic-lactide (rac-LA). The synthesized nBu3SnOnBu showed higher stereoselectivity than the conventional tin(II) octoate (Sn(Oct)2) system. In this present work, the effectiveness of nBu3SnOnBu in scaled-up (250 g) of the synthesis of poly(ε-caprolactone) (PCL) was further investigated comparing to small-scale polymerization (4 g). Furthermore, the catalytic performance of this nBu3SnOnBu in the transesterification of high molecular weight poly(L-lactic acid) (PLA) was also investigated for the first time. The transesterification of PLA with 0.05 M and 0.10 M of soluble nBu3SnOnBu catalyst in CHCl3 was successfully investigated by the gel permeation chromatography (GPC) technique. It was found that the molecular weight of PLA dramatically decreased with increasing time and nBu3SnOnBu concentration. From the kinetics study, nBu3SnOnBu acted as a highly active transesterification catalyst for PLA. From a mechanistic study, the transesterification mechanism of PLA with nBu3SnOnBu catalyst was proposed through intramolecular transesterification.

Experimental and theoretical analysis revealing the underlying chemistry accounting for the heterogeneous transesterification reaction in Na2SiO3 and Li2SiO3 catalysts

The influence of sodium and lithium content in the metasilicate crystal structure (SiO32−) is herein analyzed concerning the heterogeneous transesterification reaction for biodiesel production. Na2SiO3 and Li2SiO3 were characterized structurally and microstructurally. The catalyst content was evaluated between 1 and 5 wt %, where the maximum conversions to FAME (∼99%) were obtained using 3 wt % of Na2SiO3 during 1 h at 65 °C. After some cyclic experiments, it was determined that Na2SiO3 possesses a better stability and consequently reutilization capacity than Li2SiO3 in terms of its triglycerides conversion to FAME. DFT calculations were then used to analyze these experimental differences, revealing significant differences between these two catalysts in terms of energy, geometrical configuration, and electronic structure. It was found that three active sites are required on both catalytic surfaces to overcome the methanol deprotonation, which is herein suggested as the rate-controlling step of the entire transesterification mechanism. In one site, the oxygen atom of methanol approaches, while Lewis acid and Brønsted base sites are needed for the methoxide anion stabilization and proton stabilization, respectively.

Evidence of Chemical Reaction in Binary Blends of Polycarbonate and a Semi-Flexible Liquid Crystal Polymer

In this study, we provide the experimental results of the binary blends of a semi-flexible nematic liquid crystal polymer (LCP1) and polycarbonate (PC) within their phase diagram. The LCP1/PC blends were investigated by Differential Scanning Calorimetry (DSC), Optical Microscopy (OM), Wide-angle X-Ray Diffraction (WXRD), Fourier Transfer Infrared (FTIR), Gel Permeation Chromatography (GPC), and Nuclear Magnetic Resonance (NMR) techniques and observed the evidence of chemical reaction between LCP1 and PC in their heat-treated blends possibly by transesterification mechanism.

Determination of active sites on Na2SiO3 and Li2SiO3 catalysts for methanol dissociation and methoxide stabilization concerning biodiesel production

Surfaces of sodium and lithium silicates are theoretically investigated to account for the role of dissimilar atoms, towards the methanol adsorption/dissociation within the transesterification reaction producing biodiesel in heterogeneous processes. The definition of active site is elucidated on these materials on the basis of the following calculations: electronic density, electrostatic potential, charges, geometrical parameters and density of states (total and projected) computed with periodic Density Functional Theory (DFT). The structural requirements of a catalytic surface for biodiesel production are analyzed relying on different atomic configurations of the highest intensity peaks, according to experimental X-ray analysis. This information reveals that the alkaline metals (Na, Li) on the surface participate in the methanol adsorption, subsequently; Si acts as Lewis acid site to stabilize the methoxide anion, while the oxygen atoms perform as Brönsted basic sites to abstract the proton from methanol. This constitutes the early stages of the transesterification mechanism, and possibly the rate-controlling step (RCS) of the biodiesel generation. In the sodium silicate, the alkaline metal possesses the ability to stabilize the methoxide anion through electrostatic interactions unlike the lithium silicate. This behavior could establish the difference in catalytic activity on these silicate surfaces, presumably defining the best performance for Na2SiO3, as experimentally observed

Investigating the Effects of Ultrasonic Frequency and Membrane Technology on Biodiesel Production from Chicken Waste

In this study, the experiments were carried out under different operating conditions to evaluate the effect of ultrasound waves on biodiesel production from chicken feet oil. A two-step esterification–transesterification mechanism was employed to improve the biodiesel quality. The continuous (methanol-to-oil molar ratio and KOH catalyst amount) and discrete (frequencies, 25 and 45 kHz) variables were investigated using the experimental design method. The five-level three-factor response surface method (RSM) was assisted to optimize the biodiesel synthesis variables. Applying RSM based on the central composite design (CCD), a polynomial equation was fitted to the experimental data with the aid of Design-Expert software. The model accuracy was checked by analysis of variance (ANOVA). The results showed the highest yield of 89.74% could be achieved by using an M/O molar ratio of 12, a KOH concentration of 1 wt%, and an ultrasound frequency of 45 kHz. Finally, a mathematical model of biodiesel production in a membrane system was developed. The reaction rate constant was calculated as a function of ultrasonic frequency. Compared with the conventional method, the membrane system has significantly improved chicken feet biodiesel production’s reaction rate. The membrane is more effective at higher frequencies than at lower ones.

Molecular Carbonyl Insertion as the Homogeneous Catalysis Mechanism for Transesterification of Dimethyl Terephthalate with Ethylene Glycol

Carbonyl insertion is identified and computationally quantified as a mechanism for homogeneous organotin catalysis of transesterification. Organotin species are widely used catalysts for reactions ...

Transesterification in Vitrimer Polymers Using Bifunctional Catalysts: Modeled with Solution-Phase Experimental Rates and Theoretical Analysis of Efficiency and Mechanisms.

Recently, thermoset vitrimer polymers have shown significant promise for structural applications because of their ability to be reshaped and remolded due to their covalent adaptive network (CAN). In these vitrimers, the transesterification reaction is responsible for the CAN, where the efficiency of the reaction is controlled either by organic or by organometallic catalysts. Understanding the mechanism of the transesterification reaction in the bulk phase using direct experimental techniques is extremely difficult due to the highly cross-linked complex structure of thermosetting vitrimers. Therefore, we use solution-phase experiments to investigate the catalytic efficiency and to guide density functional theory (DFT) simulations of the transesterification reaction mechanism with catalysts triazabicyclodecene (TBD), zinc acetate (Zn(OAc)2), 1-methylimidazole (1-MI), and dibutyltin oxide (DBTO). The estimated catalytic efficiency from the detailed DFT reaction path calculations follows the order TBD ≳ DBTO ≳ Zn(OAc)2 > 1-MI, which agrees with the experimental results. In addition to reaction path modeling, the mechanism and the relative rates of the transesterification reaction are analyzed with the assistance of Fukui indices as a measure of electrophilicity and nucleophilicity of atomic sites and with partial charges. It was found that the sum of the nucleophilicity index of the base and the electrophilicity index of the acid of the bifunctional catalysts correlates with the SN2 transition state and tetrahedral intermediate energies, which are related to the barrier of the rate-limiting step. This correlation provides a hypothesis for computational prescreening of potentially better catalysts that have an index in a range of values. These results provide a basis for understanding an important part of the mechanism of transesterification in vitrimer systems and may assist with designing new catalysts.

Synthesis of <i>Capsicum chinense</i> Citric Acid Esters-Its Methanol Trans-esterification Investigations with hplc Analysis and Its valorization as Gels-Crystals Ca-Salts

The esterification between citric acid molecules and raw material-<i>Capsicum chinense</i> organic molecules in excess was carried out at 137°C-410.15°K. The kinetics of the reaction showed that this reaction was second order compared with citric acid and the calculated initial and global speed constant were respectively 1.43×10^-1[L²×mol^-2×s^-1] and 3.84×10^-2 [L²×mol^-2×s^-1]. The synthesized raw material’s-<i>Capsicum chinense</i>’s citric acid esters solutions colors was from light yellow-1.5[mn] to highly orange yellow-60[mn] confirming the esterification between citric acid molecules and the main bioactive molecules constituting the Capsicum chinense including capsaïcine, quercetin and luteolin whose densities were superior to one and explained the high densities of the Capsicum chinense citric acid esters solutions between 0.9825[g/ml] to 1.0636[g/ml]. Then, the alkene concentrations in esters solutions recorded an increase initially and at the middle of the time reaction respectively due to citric acid dehydration and alkenes from the raw material’s-<i>Capsicum chinense</i>’s bioactive molecules. But, the diminution of these alkene concentrations recorded from 900[s] time reaction confirmed their etherification with carboxylic acid and/or alcohol organic functions catalyzed by citric acid’s protonic acid-H⁺. Second, the trans-esterification mechanisms of the raw materials’ citric acid esters solutions with methanol was explored, inventoried and carried out in order to extract its bioactive molecules and their derivatives synthesized during this trans-esterification reaction where citric acid’s protonic acid-H⁺ sites functioned as catalyst. Thus, a trans-esterification using reflux-assembly followed by an extraction procedures were established in this manuscript. Indeed, the hplc analysis of the dichloromethane extracts allowed to identify the <i>Capsicum chinense</i>’s bioactive molecules and these derivatives. Third, procedures to synthesize crystals and gel calcium salts of raw material’s citric acid esters solutions was established. An inventory of these gel-crystals structure was done in this manuscript and it was deduced that the first step of these procedures was the esters solution titration with NaOH-0.05N in order to determine the optimum quantities of calcium hydroxide for the synthesis using reflux assembly at 137°C followed by evaporations procedures. Then, once synthesized gel was suffered under thermic treatment until having solid crystals well-structured, both could be characterized by an established EDTA-0.01N and alkene procedures titrations established in this manuscript. Finally, an established titration procedure with NaOH-0.05N allowed to determine their equivalent citric acid molecules concentrations. It was noticed that their citric acid and calcium weight concentration ratio was respectively 4.354/1.67 (≈2/1) which confirmed the well-structured of the product regarding to the exploration salts synthesis-mechanisms figures done in this manuscript.

Fly ash as a new versatile acid-base catalyst for biodiesel production

The production of fatty acid methyl esters (FAME) from waste frying oil (WFO) was studied using fly ash as received as a heterogeneous catalyst. The fly ash used in this research had a high content of both CaO and SO3, two compounds that have been previously proposed as catalysts in FAME production. The study was carried out on the basis of a response surface methodology (RSM). The model generated by RSM predicted as optimal conditions to obtain a 100% FAME yield at a methanol-to-oil molar ratio of 3.1:1, 11.2 (wt.% based on oil weight) fly ash and a temperature of 59 °C with agitation at 245 rpm and 6 h of reaction time. Additional experiments comparing anhydrous with aqueous medium showed that fly ash presented a high catalytic capacity to transform free fatty acids (FFA) into FAME through consecutive hydrolysis and esterification processes (hydroesterification) compared with that associated with the transesterification mechanism. According to the results, the fly ash used in this study would act as a multipurpose or “versatile” catalyst due to its chemical composition with constituents that act as acidic and basic catalysts, therefore, catalyzing the transesterification and hydroesterification reactions simultaneously and increasing the conversion yields of FAME.