棉籽油间歇式酯交换反应动力学的研究

生物柴油(棉籽油甲酯)可以由棉籽油与甲醇在催化剂KOH存在下通过酯交换反应制得。故对棉籽油间歇式酯交换反应动力学进行了研究,并考察了反应温度和催化剂浓度对产物棉籽油甲酯浓度的影响。用液相色谱法分析棉籽油的组成;用气相色谱法分析产物中棉籽油甲酯的含量。由实验数据绘制的动力学曲线得到酯交换反应在开始阶段为准二级反应,以后紧接转为一级反应和零级反应,与文献报导的棕榈油酯交换反应动力学结果一致。由实验数据求出酯交换反应在开始阶段的动力学参数,35℃、45℃时的反应速率常数分别为0.9179Lmol-1min-1和1.049Lmol-1min-1,酯交换反应的活化能为10.88kJmol-1。根据实验结果得到棉籽油酯交换反应的最佳反应温度为45℃,最佳催化剂为1.1%KOH。     

强碱催化棉籽油酯交换制备生物柴油的动力学

脂肪酸甲酯（生物柴油）,通常是由植物油与甲醇在催化剂作用下通过酯交换反应而得到的．生物柴油作为潜在的柴油能源替代品,以其可生物降解、可再生、尾气排放中的有毒气体（SOx等）低等诸多优点,近年来得到越来越多的重视．目前,世界各国都在积极发展生物柴油的生产和开展相应研究．     

Effects of ultrasonification and mechanical stirring methods for the production of biodiesel from rapeseed oil

This study was conducted to compare the effects of ultrasonic energy and mechanical stirring methods in bio-diesel production from rapeseed oil under base catalysis conditions. With the transesterification of rapeseed oil, the molar ratio of methanol to vegetable oil was 6: 1, and the amount of catalysts added to the vegetable oil was 0.3, 0.5 and 1.0% (wt/wt). The main components of methyl esters from the transesterification of rapeseed oil were oleic acid (48.5%, C18:1) and linoleic acid (18.1%, C18:2). In addition, the optimum conditions to produce fatty acid methyl esters (96.6%) were 0.5% KOH after 25 min of ultrasonification at 40 °C as compared to mechanical stirring at 60 °C. The maximum conversion ratio was 75.6% with 1.0% NaOH after 40 min of ultrasonification at 40 °C. These results indicate that ultrasonic energy could be a valuable tool for transesterification of fatty acids from rapeseed oil in terms of the reaction time and temperature.     

Oxidation stability of methyl esters studied by differential thermal analysis and rancimat

The oxidation stability of methyl esters derived from fresh rapeseed oil and waste frying oil, used as alternative biodiesel fuels, both distilled and undistilled, unstabilized and stabilized by pyrogallol and BHT, was studied by differential thermal analysis (DTA) under nonisothermal conditions at various heating rates and by the Rancimat test under isothermal conditions at 110°C. The results obtained by both techniques are compared. Both techniques show that oxidation stability increases considerably with the addition of antioxidants and that pyrogallol is very efficient. Distillation of the methyl esters prepared from rapeseed oil decreases their oxidation stability, obviously owing to the removal of natural antioxidants. The stability of methyl esters prepared from the waste frying oil is determined mainly by the history of the oil. From the DTA measurements, the kinetic parameters of an Arrhenius-like equation describing the temperature dependence of the oxidation induction period were obtained. The parameters enable one to assess the protective factor of antioxidants for temperatures outside the measuring region, estimate the residual stability, and model the process of biodiesel oxidation under nonisothermal conditions.     

Preparation of rapeseed oil esters of lower aliphatic alcohols

Rapeseed oil esters with lower aliphatic alcohols (C₁−C₄) were prepared in simple batch mode using an alkali (KOH) or acid (H₂SO₄) catalyst. The transesterification reaction conditions were optimized in order to obtain high yields of esters of the quality defined by standards for biodiesel fuels and for a short reaction time. Under these conditions it was possible to prepare only the methyl and ethyl esters catalyzed by KOH. Propyl and butyl esters were obtained only under acid catalysis conditions. The reaction catalyzed by H₂SO₄ was successfully accelerated using slightly higher catalyst concentrations at the boiling points of the alcohols used. The branched-chain alcohols reacted more slowly than their linear homologs, while t-butanol did not react at all. It was also possible to transesterify rapeseed oil using a mixture of alcohols characteristic of the end products of some fermentation processes (e.g., the acetone-butanol fermentation). A simple calculation was made which showed that, because of the higher price of longer-chain alcohols and because of the more intensive energy input during production the esters of these alcohols, they are economically unfavorable as biodiesel fuels when compared with the methyl ester.     

Kinetics of Palm Oil Methanolysis

A kinetics study of palm oil methanolysis was conducted at three different temperatures and three different concentrations of catalyst, sodium hydroxide, keeping constant the molar ratio of methanol to oil and the rotational speed of the impeller (6:1 and 400 rpm). The maximum conversion of palm oil and productivity to methyl esters were obtained at 60 °C and 1 wt% of NaOH based on palm oil, and they were 100 and 97.6%, respectively. The statistical analysis of conversions of palm oil and productivities to methyl esters as functions of temperature and concentration of catalyst, after 80 min of reaction, allowed them to fit second order polynomial equations, which adequately describe the experimental behavior. The experimental data appear to be a good fit into a second order kinetic model for the three stepwise reactions, and the reaction rate constants and the activation energies were determined. In this article we present the kinetic constant and activation energies for the experiments with 0.2% wt of NaOH. The effect of molar ratio on the concentration of products was investigated, while the temperature (55 °C), the concentration of catalyst (0.60 wt% of NaOH), and the rotational speed (400 rpm), were held constant. The results showed that the conversion and the productivity increased due to methanol excess, and were higher for the reactions with a molar ratio of 6:1.     

A kinetic study of quicklime-catalyzed sunflower oil methanolysis

The quicklime-catalyzed sunflower oil methanolysis was studied at mild reaction conditions. Quicklime (calcined at 550 °C for 4 h) in amounts of 1.0, 2.5, 5.0 and 10.0% (based on the oil weight) and different molar ratios of methanol-to-oil (6:1, 12:1 and 18:1) were employed to investigate their influence on the methyl esters content and the kinetics of the methanolysis reaction. The optimal methanol-to-oil molar ratio and quicklime amount for achieving the highest fatty acid methyl esters content were established to be 12:1 and 5% (based on the oil weight), respectively. The sigmoidal kinetics of quicklime-catalyzed methanolysis reaction was described by a model which included the changing mechanism of the reaction and the triacylglycerols mass transfer limitation. The kinetic parameters were determined and correlated with the process variables. A good agreement between the kinetic model and the experimental data for all applied reaction conditions was observed.     

Liquid–Liquid Equilibrium for Systems Containing Epoxidized Oils,Formic Acid,and Water: Experimental and Modeling

Epoxidized oils are eco-friendly plasticizers, which are industrially produced through the epoxidation reaction in a formic acid-hydrogen peroxide autocatalyzed system. The fundamental knowledge to describe the phase equilibrium of systems after epoxidation reaction is lacking, which is crucial for the design of the purification facilities. This work reported experimental data for the liquid–liquid equilibrium of three systems, i.e., epoxidized fatty acid methyl esters + formic acid + water, epoxidized fatty acid 2-ethylhexyl esters + formic acid + water, and epoxidized soybean oil + formic acid + water, in the temperature range (303.15–348.15) K under atmospheric pressure. The results indicated that the liquid–liquid equilibrium constant of formic acid in the systems followed the order of epoxidized fatty acid 2-ethylhexyl esters > epoxidized fatty acid methyl esters > epoxidized soybean oil. Moreover, the obtained experimental data were correlated using nonrandom two liquid (NRTL) and universal quasi chemical (UNIQUAC) models. The maximum root mean square deviation (RMSD) values as low as 0.0052 and 0.0263 were estimated using the NRTL and UNIQUAC model, respectively. The NRTL model is more suitable than the UNIQUAC model to describe the liquid–liquid equilibrium behavior of these ternary systems.     

Reactive extraction of oilseeds with dialkyl carbonates

Using dialkyl carbonates as reagents for lipase‐catalyzed transesterification, the reaction is driven by the evolvement of carbon dioxide as the co‐product and thus no longer an equilibrium reaction. Therefore this transesterification method is faster and quantitative conversions can be obtained. Short‐chain dialkyl carbonates, like other short‐chain esters, are also suitable solvents for seed oil extraction. Thus, extraction and transesterification can be combined in a single reaction. This reaction, called reactive extraction, was carried out in a standard Soxhlet apparatus with rapeseed, linseed and calendula seed as the raw materials and with dimethyl and diethyl carbonate as extraction solvent and transesterification reagent at the same time. Fatty acid methyl esters and ethyl esters respectively were obtained with higher yields than those achieved by conventional two step extraction / transesterification. In the case of linseed fatty acid esters and especially calendula seed fatty acid esters, the iodine values of the products obtained by one‐pot‐two‐step reactive extraction were significantly higher.     

KINETIC STUDY OF S-ALKYLATION OF 2-MERCAPTOBENZIMIDAZOLE CATALYZED BY TETRABUTYLAMMONIUM BROMIDE

The S-alkylation of 2-mercaptobenzimidazole (MBI) by α-bromo-m-xylene (RBr) under phase transfer catalytic reaction condition was successfully carried out in an aqueous solution of KOH/organic solvent two-phase medium. No product was obtained from N-alkylation during or after the reaction period by using a limited quantity of α-bromo-m-xylene. The reaction is greatly enhanced by adding a small amount of tetrabutylammonium bromide (TBAB) and/or potassium hydroxide. Based on the experimental evidence, a rational reaction mechanism is proposed. A kinetic model is derived, from which a pseudo steady-state hypothesis (PSSH) is applied to the reaction system. The kinetic behaviors and the characteristics of the reaction are sufficiently described by the pseudo first-order rate law. The effects of the reaction conditions, including agitation speed, amount of TBAB catalyst, amount of KOH, quaternary ammonium salts, volume of water, volume of dichloromethane, amount of 2-mercaptobenzimidazole, amount of α-bromo-m-xylene, inorganic salts, organic solvents, and temperature on the conversion of the reactant and the apparent rate constants (k_app) were investigated in detailed. Rational explanations are provided for the observed phenomena from experimental results.     

Biodiesel from rapeseed oil,methanol and KOH. 3. Analysis of composition of actual reaction mixture

Detailed analysis is described of the samples taken after suitable reaction times from the actual reaction mixture during the production of biodiesel fuel using methanolysis of rapeseed oil catalyzed by KOH. Three methods for stoppage of reaction (neutralisation of catalyst, dilution by two suitable solvents) in the sample are used. The contents of mono‐, di‐ and triacylglycerols, methylesters of fatty acids (biodiesel) and potassium salts of fatty acids of rapeseed oil, glycerol (by HPLC method), basicity (by potentiometric titration) and water (by GC and Karl‐Fischer method) in the samples are determined. An example of these determinations is described.     

Kinetics of Alkaline Catalyzed Methanolysis of Sunflower Oil

The kinetics of methanolysis of sunflower oil with KOH as catalyst was investigated. The content of triglycerides, the resulting methyl esters as well as diglycerides and monoglycerides was analyzed at different times at molar ratios of methanol: sunflower oil = 3:1 and 3.3:1. At a molar ratio of 3:1 the kinetic order appears to be second order in the first minutes, but then the reaction rate decreases rapidly due to the formation of glycerine as a second phase, which leads to a loss of methanol and catalyst. The effect of temperature, amount of catalyst and type of vegetable oil on formation of methyl esters was examined.     

Analysis of hydroxylated fatty acids from plant oils

A novel process has been described recently for the preparation of hydroxylated fatty acids (HOFA) and HOFA methyl esters from plant oils. HOFA methyl esters prepared from conventional and alternative plant oils were characterized by various chromatographic methods (thin-layer chromatography, high-performance liquid chromatography, and gas chromatography) and gas chromatography-mass spectrometry as well as¹H and¹³C nuclear magnetic resonance spectroscopy. HOFA methyl esters obtained fromEuphorbia lathyris seed oil, low-erucic acid rapeseed oil, and sunflower oil contain as major constituents methylthreo-9,10-dihydroxy octadecanoate (derived from oleic acid) and methyl dihydroxy tetrahydrofuran octadecanoates, e.g., methyl 9,12-dihydroxy-10,13-epoxy octadecanoates and methyl 10,13-dihydroxy-9,12-epoxy octadecanoates (derived from linoleic acid). Other constituents detected in the products include methyl esters of saturated fatty acids (not epoxidized/derivatized) and traces of methyl esters of epoxy fatty acids (not hydrolyzed). The products that contain high levels of monomeric HOFA may find wide application in a variety of technical products.     

Biodiesel from rapeseed oil,methanol and KOH. 2. Composition of solution of KOH in methanol as reaction partner of oil

The composition of the solutions of solid KOH in methanol has been measured by means of determinating the content of water in the equilibrium mixture. The dependence of the equilibrium reaction extent ζ¹ and the concentration equilibrium constant Kc on the ratio of the initial amounts of methanol and KOH containing 0.164 and 16.27 wt‐% of water are determined and theoretically described. The concentration of CH₃O¯ ions can be calculated with these results. This value is very important for the course of the alkaline catalyzed methanolysis of rapeseed oil to biodiesel, because the methoxide ions are the true catalyst of such a transesterification.     

Isothermal Curing Kinetics of Epoxidized Fatty Acid Methyl Esters and Triacylglycerols

Plant oil triacylglycerols are attractive renewable resources for biobased epoxy resins. We investigated the curing kinetics of three model epoxidized fatty acid methyl esters and representative epoxidized triacylglycerols with varied epoxide functionalities and distributions in the presence of a latent cationic initiator. Isothermal differential scanning calorimetry (DSC) was used to analyze the curing kinetics of the epoxy systems, and kinetic parameters (i.e., rate constants, reaction orders) were determined. Both epoxidized fatty esters and triacylglycerols followed the autocatalytic curing mechanism, and the DSC data were analyzed according to the Kamal autocatalytic model. Epoxidized methyl linoleate (EMLO) had the highest maximum curing rate, followed by epoxidized methyl linolenate (EMLON), and epoxidized methyl oleate (EMO) had the lowest maximum curing rate. We conclude that EMLO with two epoxide groups has the highest reactivity in this curing system, while the EMO with one epoxide group has the lowest reactivity. For epoxidized triacylglycerols, epoxidized camelina oil had the highest curing reactivity at higher temperatures, followed by epoxidized linseed oil and soybean oil.     

Product sampling during transient continuous countercurrent hydrolysis of canola oil and development of a kinetic model

A chemical kinetic model has been developed for the transient stage of the continuous countercurrent hydrolysis of triglycerides to free fatty acids and glycerol. Departure functions and group contribution methods were applied to determine the equilibrium constants of the four reversible reactions in the kinetic model. Continuous countercurrent hydrolysis of canola oil in subcritical water was conducted experimentally in a lab-scale reactor over a range of temperatures and the concentrations of all neutral components were quantified. Several of the rate constants in the model were obtained by modeling this experimental data, with the remaining determined from calculated equilibrium constants. Some reactions not included in the present, or previous, hydrolysis modeling efforts were identified from glycerolysis kinetic studies and may explain the slight discrepancy between model and experiment. The rate constants determined in this paper indicate that diglycerides in the feedstock accelerate the transition from “emulsive hydrolysis” to “rapid hydrolysis”.     

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.     

Biodiesel fuel from rapeseed oil,methanol, and KOH. Analytical methods in research and production

The enumeration of the analytical methods used in the production of biodiesel from rapeseed oil and methanol catalyzed by KOH and published till 1997 is given. Some of our original methods for individual or simultaneous determination of the main components in the reaction mixture are described. All these methods can be also used to analyse the non-equilibrium complex and heterogeneous mixture.     

Optimization of the transesterification reaction in biodiesel production

In this paper response surface methodology (RSM) was used to study the transesterification reaction of rapeseed oil for biodiesel production. The three main factors that drive the conversion of triglycerides into fatty acid methyl esters (FAME) were studied according to a full factorial design at two levels. These factors were catalyst concentration (KOH), temperature and reaction time. The range investigated for each factor was selected taking into account the process of Fox Petroli S.p.A. Analysis of variance (ANOVA) was used to determine the significance of the factors and their interactions which primarily affect the first of the two transesterification stages. This analysis evidenced the best operating conditions of the first transesterification reaction performed at Fox’s plant: KOH concentration 0.6% w/w, temperature 50 °C and reaction time 90 min with a CH₃OH to KOH ratio equal to 60. Three empirical models were derived to correlate the experimental results, suitable to predict the behavior of triglyceride, diglyceride and monoglyceride concentration. These models showed a good agreement with the experimental results, demonstrating that this methodology may be useful for industrial process optimization.     

Production of alkenyl succinic anhydrides from low‐erucic and low‐linolenic rapeseed oil methyl esters

Fatty acid methyl esters from low‐erucic and low‐linolenic rapeseed oil were used to produce alkenyl succinic anhydrides. A second‐order Doehlert uniform network design was used to investigate the influence of the reaction temperature and the molar ratio between the maleic anhydride and the main unsaturated rapeseed oil methyl esters on the yield of alkenyl succinic anhydride from methyl oleate. Further subjects of investigation were the conversion of methyl oleate, the formation of side reaction products, the Gardner color of the product and its viscosity, and finally the content of maleic anhydride remaining in the medium after the reaction. Alkenyl succinic anhydride from methyl oleate was isolated by column chromatography and analyzed by IR, ¹H‐ and ¹³C‐NMR and MS. The optimal reaction conditions for obtaining the maximum yield of alkenyl succinic anhydride from methyl oleate in the experimental domain (80%) were 210‐220 °C and a maleic anhydride/rapeseed oil methyl ester molar ratio of 1.5. However, the products synthesized in these conditions showed a high degree of viscosity (0.45 kg m^?1 s^?1), a very dark color (18 Gardner color) and a high content of undesirable side products (6%), which could hinder their industrial use. A molar ratio of less than 1.5 led to a clearer and less viscous product, although with a lower alkenyl succinic anhydride content.