Kinetics of palm oil transesterification in a batch reactor

Methyl esters were produced by transesterification of palm oil with methanol in the presence of a catalyst (KOH). The rate of transesterification in a batch reactor increased with temperature up to 60°C. Higher temperatures did not reduce the time to reach maximal conversion. The conversion of triglycerides (TG), diglycerides (DG), and monoglycerides (MG) appeared to be second order up to 30 min of reaction time. Reaction rate constants for TG, DG, and MG hydrolysis reactions were 0.018–0.191 (wt%·min)⁻¹, and were higher at higher temperatures and higher for the MG reaction than for TG hydrolysis. Activation energies were 14.7, 14.2, and 6.4 kcal/mol for the TG, DG, and MG hydrolysis reactions, respectively. The optimal catalyst concentration was 1% KOH.     

Kinetic study of the base-catalyzed transesterification of monoglycerides from <Emphasis Type="Italic">pongamia</Emphasis> oil

The kinetics of the transeterification of vegetable oil is known to follow a three-step reaction mechanism. The third step involves the transesterification of MG. In this study, the transesterification of MG obtained from crude Pongamia oil was achieved with methanol in the presence of KOH as the catalyst. A MG/methanol ratio of 1∶10 was used at different temperatures (30, 45, 55, and 60°C). ¹H NMR was used to monitor the progress of transesterification. The study revealed that the kinetics of this reaction followed a reversible second-order model, with a good fit obtained for all temperatures except 30°C. This result is explained as arising out of the importance of transport effects at low temperatures. The forward rate constant increased with an increase in temperature, whereas the reverse rate constant showed a decreasing trend, suggesting that the proposed reverse reaction was not an elementary step.     

A continuous process for the glycerolysis of soybean oil

A continuous process for the glycerolysis of soybean oil with pure and crude glycerol, the co-product from the transesterification of soybean oil, was investigated in a pilot plant. The process was equipped with a static and a high-shear mixer. The experimental studies explored the effects of variations in mixing intensity, temperature, reactant flow rates, and reactant stoichiometry on the formation of MG and DG. The developed process resulted in high conversion of TG to MG. The most favorable conditions were 230°C, 40 mL/min total flow, 25 min of reaction time, 2.5∶1 molar ratio of glycerol/soybean oil, and 3600 rpm for the reactions involving crude glycerol where the concentrations of MG and DG in the product were about 56 and 36 wt%, respectively. Under similar conditions, glycerolysis of pure glycerol resulted in 58% MG and 33% DG. In general, higher temperatures and mixing intensities favored the conversion of TG to MG and DG. Reaction temperature had a greater influence on the extent of the reaction than mixing. The formation of MG approached equilibrium for nearly all cases under investigation.     

Biodiesel from an alkaline transesterification reaction of soybean oil using ultrasonic mixing

The feasibility of using ultrasonic mixing to obtain biodiesel from soybean oil was established. The alkaline transesterification reaction was studied at three levels of temperature and four alcohol-to-oil ratios. Excellent yields were obtained for all conditions. For example, at 40°C with ultrasonic agitation and a molar ratio of 6∶1 methanol/oil, the conversion to FAME was greater than 99.4% after about 15 min. For a 6∶1 methanol/oil ratio and a 25 to 60°C temperature range, a pseudo second-order kinetic model was confirmed for the hydrolysis of DG and TG. Reaction rate constants were three to five times higher than those reported in the literature for, mechanical agitation. We suspect that the observed mass transfer and kinetic rate enhancements were due to the increase in interfacial area and activity of the microscopic and macroscopic bubbles formed when ultrasonic waves of 20 kHz were applied to a two-phase reaction system.     

The Effect of Water on the Transesterification Kinetics of Cotton Seed Oil with Ethanol

A kinetic model for the transesterification of a cotton seed oil with ethanol in the presence of water is proposed. The effect of water content in the reacting mixture on the transesterification reaction is studied. The dependence of the equilibrium constants and reaction rate constants on the water content is presented. Equilibrium was reached within less than 30 min reaction time in all cases. The increase of the water content results in decrease of the conversion level of the oil. By increasing the ethanol/oil ratio the conversion of triglyceride increases and the concentration of mono- and diglyceride in the product mixtures are reduced.     

Triglyceride specificity ofCandida cylindracea lipase: Effect of docosahexaenoic acid on resistance of triglyceride to lipase

Tuna oil was hydrolyzed withCandida cylindracea lipase. After 70% hydrolysis of the oil, the docosahexaenoic acid (DHA) content in the glyceride mixture [a mixture of TG (triglyceride), DG (diglyceride) and MG (monoglyceride)] was twice that of the original oil. DHA-rich TG and DG were observed, but DHA-rich MG was absent.C. cylin-dracea lipase seemed to have a “triglyceride specificity,” and it favors TG without DHA over TG containing DHA. In accordance with this hypothesis, TG containing a mixture of oleic acid (OA) and DHA was synthesized and then hydrolyzed withC. cylindracea lipase. TGs in the hydrolysis product were fractionated and analyzed quantitatively by high-performance liquid chromatography. Four kinds of TGs were obtained. TG with three molecules of OA was hydrolyzed most easily. Increasing the DHA content of TG resulted in less hydrolysis of TG. The results suggested thatC. cylindracea lipase had a TG specificity for the whole structure of TG in preference to the individual ester bonds; OA coexisting with DHA in TG was resistant toC. cylindracea lipase due to the TG structure.     

A comparison of attenuated total reflectance-FTIR spectroscopy and GPC for monitoring biodiesel production

Gel permeation chromatography (GPC) and attenuated total reflectance (ATR)-FTIR spectroscopy were used to monitor the products of transesterification of waste frying oil in methanol to FAME or biodiesel. To evaluate the reliability and reproducibility of each method, quantitative analyses of mixtures of standards (TG, DG, MG, FAME, and glycerol) as well as lipid products of transesterification were carried out. The reproducibility of each method was found to be within ±1–5%. The differences between the results of the two methods were less than ±2%. The GPC method showed good separation of the intermediate products MG and glycerol from the TG starting material and FAME, but DG were not completely separated from TG, GPC gave good quantitative results for MG and FAME, but the TG and DG analyses required correction, depending on the mole ratio of TG/DG. In contrast, ATR-FTIR spectroscopy could only give quantitative data for the sum of TG+DG+MG.     

Kinetics of methyl ester production from mixed crude palm oil by using acid-alkali catalyst

The production of biodiesel from high free fatty acid mixed crude palm oil using a two-stage process was investigated. The kinetics of the reactions was determined in a batch reactor at various reaction temperatures. It was found that the optimum conditions for reducing high free fatty acid (FFA) in MCPO (8-12 wt.%/wt oil) using esterification was a 10:1 molar ratio of methanol to FFA and using 10 wt.%/wt of sulfuric acid (based on FFA) as catalyst. The subsequent transesterification reaction to convert triglycerides to the methyl ester was found to be optimal using 6:1 molar ratio of methanol to the triglyceride (TG) in MCPO and using 0.6 wt.%/vol_TG sodium hydroxide as catalyst. Both reactions were carried out in a stirred batch reactor over a period of 20 min at 55, 60 and 65 °C. The concentration of compounds in each sample was analyzed by Thin Layer Chromatography/Flame Ionization Detector (TLC/FID), Karl Fischer, and titration techniques. The results were used for calculating the rate coefficients by using the curve-fitting tool of MATLAB. Optimal reaction rate coefficients for the forward and reverse esterification reactions of FFA were 1.340 and 0.682 l mol⁻¹ min⁻¹, respectively. The corresponding optimal transesterification, rate coefficients for the forward reactions of TG, diglyceride (DG), and monoglyceride (MG) of transesterification were 2.600, 1.186, and 2.303 l mol⁻¹ min⁻¹, and for the reverse reactions were 0.248, 0.227, and 0.022 l mol⁻¹ min⁻¹, respectively.     

Recovery of oil <Emphasis Type="Italic">via</Emphasis> acid-catalyzed transesterification

The process of preparing oil palm seed for planting generates vast quantities of waste pulp. The pulp (ca 80% oil), for which no use has been found, is indiscriminately dumped because either reprocessing it into a useful product or disposing of it properly is expensive. In situ transesterification of the pulp with methanol and ethanol using sulfuric acid as catalyst was carried out on a laboratory scale. Our aim was to develop a process to recover the largely hydrolytically degraded oil (PV, 25–26; FFA, 25–26%) from the pulp. Acid-catalyzed conversions of the oil into alkyl esters were 96–97% for both methanol and ethanol. The accompanying concentrations of FFA, TG, DG, and MG were low. The identities and proportions of FA ester in the alkyl esters reflected the FA content of the palm oil. The values for the esterified products of some fuel properties such as cloud point and viscosity were slightly below the general current specification. However, with optimization of the reaction conditions and simplification of some of the technical aspects, the waste pulp could be a good source of alkyl esters for both oleochemical and fuel applications.     

酯化-酯交换两步法制备生物柴油的动力学

以潲水油（WCO）为原料,探讨了酯化-酯交换两步法制备生物柴油的反应动力学。以活性炭负载硫酸铁［Fe₂(SO₄)₃/AC］为负载型催化剂,通过测定不同反应温度、不同甲醇/脂肪酸（FFA）摩尔比条件下WCO中游离脂肪酸的转化率,以此确定酯化反应的动力学控制步骤及动力学方程中的待定参数,从而建立了在实验温度范围内酯化反应的动力学方程,并根据碱催化酯交换反应机理,在简化的动力学模型基础上,推导出了WCO中甘油三酯（TG）与甲醇发生酯交换反应的宏观动力学方程。结果表明,酯化反应和酯交换反应的动力学方程在实验条件范围内都能较好地描述各自的反应过程。     

A simplified Horiuti-Polanyi scheme for the hydrogenation of triacylglycerols

A simplification of the Horiuti-Polanyi reaction scheme for the hydrogenation of triacylglycerols taking into account saturation andcis-trans isomerization of double bonds and neglecting their positional isomerization is presented. From the comparison of experimental and calculated kinetic runs, the rate constants of individual reaction steps are obtained and the effects of hydrogen flow, hydrogen dispersion, oil unsaturation and catalyst quality on the rate constants are examined. Criteria for comprehensive characterization of the processes occurring in the course of hydrogenation, i.e., saturation and isomerization indices, are proposed.     

Lipase-catalyzed glycerolysis of olive oil in organic solvent medium: Optimization using response surface methodology

Enzymatic glycerolysis of olive oil for mono- (MG) and diglycerides (DG) synthesis was investigated. Several pure organic solvents and co-solvent mixtures were screened in a batch reaction system. The yields of MG and DG in co-solvent mixtures exceeded those of the corresponding pure organic solvents. Batch reaction conditions of the glycerolysis reaction, the lipase amount, the glycerol to oil molar ratio, the reaction time, and temperature, were studied. In these systems, the high content of reaction products, especially MG (55.8 wt%) and DG (16.4wt%) was achieved at 40 °C temperature and 0.025 g of lipase with relatively low glycerol to oil molar ratio (2: 1) within 4 h of reaction time in isopropanol/tert-butanol (1: 3) solvent mixture. Glycerolysis reaction was optimized with the assistance of response surface methodology (RSM). Optimal condition for reaction conversion was recommended as lipase amount 0.025 g, glycerol to oil molar ratio 2: 1, reaction time 4 h and temperature 40 °C.     

Selective distribution of saturated fatty acids into the monoglyceride fraction during enzymatic glycerolysis

Four triglyceride fats and oils (beef tallow, lard, rapeseed oil and soybean oil) were reacted with glycerol while using lipase as the catalyst. For all fats examined, at reaction temperatures above the critical temperature (T_c), the fatty acid compositions of the monoglyceride (MG) and diglyceride (DG) fractions and of the original fat were similar. A relatively low yield of MG was obtained (20–30 wt%). When the reaction was carried out with beef tallow or lard at a temperature below the T_c (40°C), the concentration of saturated fatty acids in the MG fraction was 2 to 4 times greater than that in the DG fraction. Correspondingly, the concentration of unsaturated fatty acids in the DG fraction was more than two times greater than that in the MG fraction. At 5°C, a similar trend was observed for rapeseed oil and soybean oil. Direct analysis of partial glycerides during glycerolysis by high-temperature gas-liquid chromatography showed that below T_c the content of C16 MG increased relatively more than C18 MG. C36 DG and C54 TG were apparently resistant to glycerolysis. Preferential distribution of saturated fatty acids into the MG fraction was accompanied by a high yield of monoglyceride (45–70 wt%) and solidification of the reaction mixture. It is concluded that during glycerolysis below T_c, preferential crystallization occurs for MGs that contain a saturated fatty acid.     

Kinetics of Soybean Oil Hydrolysis on Niobium Catalysts

The catalytic hydrolysis of soybean oil was used as an alternative for the production of monoglycerides (MG) and diglycerides (DG). The reactions were conducted in a stainless-steel tubular reactor in the temperature range of 240–290 °C, on niobium phosphate (NBP) and niobium oxide (NBO) as catalysts. In the hydrolysis reactions at 270 °C, the maximum selectivities of the products of interest were obtained at 22 % MG and 48 % DG for the reaction with NBP, and 7 % MG and 33 % DG with NBO, for 59 % and 36 % of triglyceride conversion in 10 min, respectively. The proposed kinetic model presented a good fit of the theoretical model with the experimental data, showing that the previous hypotheses considered for the mechanism development are suitable for describing the kinetics of soybean oil hydrolysis.     

Supercritical production and fractionation of fatty acid esters and acylglycerols

The production of biodiesel or fatty acid esters (FAE) from lipids with supercritical methanol (scMeOH) has gained interest in the last decade because it allows the direct transesterification of crude oils and fats. The reaction should be carried out above 593 K in order to achieve complete conversion. When milder conditions are set, also monoglycerides (MG) and diglycerides (DG), together with glycerol, are obtained as byproducts of the transesterification process. Acylglycerols are common food emulsifiers and surface active agents in many industrial cleaning products.The main goal of this work is to study the fractionation of FAE and acylglycerols by using CO₂ as a green solvent. Mixtures of FAE, MG and DG were produced by partial transesterification of sunflower oil with scMeOH in a temperature range of 556–605 K and using different methanol to oil molar ratios (between 20 and 50). Then, experimental data on phase equilibria of reaction products + CO₂ were measured at 298 K and 313 K in a variable volume cell with windows. The measured data were used to test the predictive capability of the Group Contribution with Association Equation of State (GCA-EoS). The acylglycerols can be purified by near critical extraction of the FAE with CO₂. The simulation of the extraction process working with CO₂, in liquid or supercritical state, gives a concentration of acylglycerols higher than 99.8 wt.% in the raffinate phase with a concentration of FAE above 97 wt.% in the extract phase.     

Transesterification in poly(ethylene terephthalate) and poly(ethylene naphthalate 2,6-dicarboxylate) blends: model compounds study

Kinetics of transesterification reaction in poly(ethylene terephthalate)-poly(ethylene naphthalate 2,6-dicarboxylate), PET-PEN, blends resulting from melt processing was simulated using model compounds of ethylene dibenzoate (BEB) and ethylene dinaphthoate (NEN). The exchange reaction between BEB and NEN was followed by ¹H NMR spectroscopy using signals from the aliphatic protons of ethylene glycol moieties at 4.66 and 4.78 ppm, respectively. The first-order kinetics was established under pseudo-first-order conditions for both reactants. Thus, the overall transesterification reaction was second order reversible. The reversibility was confirmed experimentally by heating a mixed sequence of 1-benzoate 2-naphthoate ethylene (BEN) under similar conditions. Both forward reaction of the equimolar amounts of the reagents and reverse reaction came to equilibrium at the same molar ratio of the reactants and reaction products of roughly 0.25:0.50:0.25 for BEB, BEN, and NEN, respectively. The rate equation for the transesterification reaction in the model system was modified using half-concentration of BEN, which is the only effective in the intermolecular exchange. Direct ester-ester exchange was deduced as a prevailing mechanism for the transesterification reaction under the conditions studied, and the values of equilibrium and rate constants, as well as other basic thermodynamic and kinetic parameters were determined. The use of Zn(OAc)₂ as a catalyst resulted in a significant decrease in the activation enthalpy of transesterification, which might be due to the partial switch of the reaction mechanism from primarily pseudo-homolytic to more heterolytic where Zn^II acts as a Lewis base which binds to the ester carbonyl oxygen.     

Back Extraction of HCl from TOA Dissolved in N-Octanol by Aqueous Ammonia in a Microchannel Device

To recover the extractant in the preparation of KH₂PO₄ using the extraction method, studies for the back extraction of HCl by aqueous ammonia from TOA (trioctylamine) dissolved in n-octanol were conducted. First, the reaction of HCl back extraction from TOA in n-octanol with aqueous ammonia was examined in shaking flasks and the equilibrium of this reaction was validated. The equilibrium constant of the stripping reaction was determined in the temperature range of 297.7-318.2 K and the reaction enthalpy was found to be -17.8 kJ/mol indicating that the stripping reaction was exothermic. Then kinetic experiments were performed in a microchannel device with the elimination of mass transfer limitations, as demonstrated by the experimental results. A kinetic model was established to obtain the forward and backward interfacial reaction rate constants with the help of the obtained equilibrium constant of the stripping reaction. This model described the measured data well and predicted correctly the change of HCl concentration in the oil phase along with the residence time in our experiments. Furthermore, the activation energy for the forward (8.21 kJ/mol) and backward (26.0 kJ/mol) reaction was determined and subsequently the forward and backward interfacial reaction rate constants were determined in the temperature range of 298.7-313.2 K.     

Transesterification Kinetics of Soybean Oil for Production of Biodiesel in Supercritical Methanol

A kinetic study on soybean oil transesterification without a catalyst in subcritical and supercritical methanol was made at pressures between 8.7 and 36 MPa. It was found that the conversion of soybean oil into the corresponding methyl esters was enhanced considerably in the supercritical methanol. The apparent activation energies of the transesterification are different with the subcritical and the supercritical states of methanol, which are 11.2 and 56.0 kJ/mol (molar ratio of methanol to oil: 42, pressure: 28 MPa), respectively. The reaction pressure considerably influenced the yield of fatty acid methyl esters (FAME) in the pressure range from ambient pressure up to 25 MPa (280 °C, 42:1). The reaction activation volume of transesterification in supercritical methanol is approximately −206 cm³/mol. The PΔV ^≠ term accounts for nearly 10% of the apparent activation energy, and can not be ignored (280 °C, 42:1).     

Multi‐Step Controlled Kinetics of the Transesterification of Crude Soybean Oil with Methanol by Mg(OCH3)2

This work focuses on a kinetic model that can be expressed as three significant controlled regions, i.e., a mass transfer controlled region in the internal surface of a heterogeneous catalyst, an irreversible chemical reaction controlled region in the pseudo‐homogenous fluid body and a reversible equilibrium chemical reaction controlled region near to the transesterification equilibrium stage. With the help of MATLAB7.0 software, the apparent reaction rate constants, k₂, k₂⁺ and k₂^–, were calculated and the corresponding apparent activation energies were calculated to be 67.450, 60.680 and 58.279 kJ·mol^–1, respectively. According to the confirmation experiments, it is indicated that the results can be applied for predicting the FAME yield at other reaction temperatures.     

Comparison of bio- and autocatalytic esterification of oils using mono- and diglycerides

The purpose of this study was to investigate enzymatic and autocatalytic esterification of FFA in rice bran oil (RBO), palm oil (PO), and palm kernel oil (PKO), using MG and DG as esterifying agents. The reactions were carried out at low pressure (4–6 mm Hg) either in the absence of any added catalyst at high temperature (210–230°C) or in the presence of Mucor miehei lipase at low temperature (60°C). The reactions were carried out using different concentrations of MG, and the optimal FFA/MG ratio and time were 2∶1 (molar) and 6 h, respectively, in both auto- and enzyme-catalyzed processes. With DG as the esterifying agent in the autocatalytic process, the optimal temperature was 220°C, and the optimal FFA/DG ratio was 1∶1.25. For both MG and DG, the enzymatic process was more effective in reducing FFA and produced more favorable levels of unsaponifiable matter and color in the final product. The PV of the final products were also lower (1.8–2.9 mequiv/kg) by using the enzymatic process. To produce edible-grade oil, a single deodorization step would be required after enzymatic esterification; whereas, alkali refining, bleaching, and deodorization would be required after autocatalytic treatment.