The kinetics of epoxidation of trimethylolpropane ester

Kinetics pertaining epoxidation reaction of a palm oil‐based synthetic lubricant trimethylolpropane (TMP) ester were investigated. The epoxidation reaction of TMP ester was carried out utilizing peracetic acid generated by an in situ technique. The analysis of the reaction kinetics was performed within the low temperature (30, 50, and 60°C) and high temperature (70, 80, and 90°C) regions, owing to the nature of the reactions. The maximum conversion of the unsaturated carbon to oxirane ring was achieved in 1 h at high temperature region, while epoxidation of TMP esters took more than 4 h to reach the maximum conversion at the low temperature region. From the experimental data, the kinetics of epoxidation of TMP esters fitted well with both the second‐order and pseudo first‐order models. The rate constants for pseudo first‐order model increased from 0.0009 to 0.0055 by increasing temperature at the low temperature region, and from 0.0129 to 0.0209 within the high temperature region. The values of activation energies at low temperature and high temperature regions were found to be 69.4 and 53.3 kJ/mol, respectively.     

Highly accurate photopyroelectric measurement of thermal diffusivity of vegetable oils

High‐accuracy photopyroelectric measurements, in the thermal‐wave‐resonator‐cavity configuration, were performed in order to measure the thermal diffusivity of some vegetable oils. The high resolution (relative error ±0.5%) of the above method allows for the detection of small changes in the values of this dynamic thermal parameter. The accuracy of the results is mainly due to the possibility to precisely control the variation (30‐nm step) of sample thickness, a proper selection of the range of the thickness scan (2 µ_m < L_m < 4 µ_m ? 5 µ_m), and an iterative procedure of data analysis. A correlation between thermal diffusivity and the fatty acid composition (obtained via gas chromatography) is suggested for some fresh (sunflower, hemp, flax, and soybean) oils and for hemp oil exposed to a microwave field: Thermal diffusivity appears to be determined by the overall content of polyunsaturated fatty acids.     

Catalytic conversion of vegetable oils in a continuous FCC pilot plant

In this paper the influence of admixtures of rapeseed, soybean and palm oil into VGO on FCC performance has been studied. The oils were mixed in steps of 20 wt.% and tested in a fully continuous operated FCC pilot plant. The experiments show that the product distribution changes slightly. Higher ratios of vegetable oils hardly affect the gasoline yields but cause a decrease in cracking gas. Oxygen contained in the vegetable oils is converted predominantly to water. It has been demonstrated that the obtained gasoline is oxygen free and shows improved properties for RON and MON. The cracking gas contains high amounts of propene and ethene, which can be used as base materials for the production of synthetic materials from renewable sources.     

Epoxidation of Canola Oil with Hydrogen Peroxide Catalyzed by Acidic Ion Exchange Resin

Canola oil with an iodine value of 112/100 g, and containing 60% oleic acid and 20% linoleic acid, was epoxidised using a peroxyacid generated in situ from hydrogen peroxide and a carboxylic acid (acetic or formic acid) in the presence of an acidic ion exchange resin (AIER), Amberlite IR 120H. Acetic acid was found to be a better oxygen carrier than formic acid, as it produced about 10% more conversion of ethylenic unsaturation to oxirane than that produced by formic acid under otherwise identical conditions. A detailed process developmental study was then performed with the acetic acid/AIER combination. The parameters optimised were temperature (65 °C), acetic acid to ethylenic unsaturation molar ratio (0.5), hydrogen peroxide to ethylenic unsaturation molar ratio (1.5), and AIER loading (22%). An iodine conversion of 88.4% and a relative conversion to oxirane of 90% were obtained at the optimum reaction conditions. The heterogeneous catalyst, AIER, was found to be reusable and exhibited a negligible loss in activity.     

Kinetics of epoxidation of jatropha oil with peroxyacetic and peroxyformic acid catalysed by acidic ion exchange resin

The kinetics of epoxidation of jatropha oil by peroxyacetic/peroxyformic acid, formed in situ by the reaction of aqueous hydrogen peroxide and acetic/formic acid, in the presence of an acidic ion exchange resin as catalyst in or without toluene, was studied. The presence of an inert solvent in the reaction mixture appeared to stabilise the epoxidation product and minimise the side reaction such as the opening of the oxirane ring. The effect of several reaction parameters such as stirring speed, hydrogen peroxide-to-ethylenic unsaturation molar ratio, acetic/formic acid-to-ethylenic unsaturation molar ratio, temperature, and catalyst loading on the epoxidation rate as well as on the oxirane ring stability and iodine value of the epoxidised jatropha oil were examined. The multiphase process consists of a consecutive reaction, acidic ion exchange resin catalysed peroxyacid formation followed by epoxidation. The catalytic reaction of peroxyacetic/peroxyformic acid formation was found to be characterised by adsorption of only acetic (or formic) acid and peroxyacetic/peroxyformic acid on the active catalyst sites, and the irreversible surface reaction was the overall rate determining step. The proposed kinetic model takes into consideration two side reactions, namely, epoxy ring opening involving the formation of hydroxy acetate and hydroxyl groups and the reaction of the peroxyacid and epoxy group. The kinetic and adsorption constants of the rate equations were estimated by the best fit using nonlinear regression method. Good agreement between experimental and predicted data validated the proposed kinetic model. From the estimated kinetic constants, the apparent activation energy for epoxidation reaction was found to be 53.6 kJ/mol. This value compares well with those reported by other investigators for the same reaction over similar catalysts.     

Chemoenzymatic epoxidation of unsaturated fatty acid esters and plant oils

In the presence of an immobilized lipase fromCandida antacrtica (Novozym 435^R) fatty acids are converted to peroxy acids by the reaction with hydrogen peroxide. In a similar reaction, fatty acid esters are perhydrolyzed to peroxy acids. Unsaturated fatty acid esters subsequently epoxidize themselves, and in this way epoxidized plant oils can be prepared with good yields (rapeseed oil 91%, sunflower oil 88%, linseed oil 80%). The hydrolysis of the plant oil to mono- and diglycerides can be suppressed by the addition of a small amount of free fatty acids. Rapeseed oil methyl ester can also be epoxidized; the conversion of C=C-bonds is 95%, and the composition of the epoxy fatty acid methyl esters corresponds to the composition of the unsaturated methyl esters in the substrate. Based partly on a lecture at the 86th AOCS Annual Meeting & Expo, San Antonio, Texas, May 7–11, 1995.     

Transesterification of vegetable oils over a phosphazenium hydroxide catalyst incorporated onto silica

The catalytic activity of a phosphazenium hydroxide (PzOH) catalyst incorporated onto silica (PzOH/SiO₂) was investigated in the transesterification of vegetable oils with methanol. The PzOH stably incorporated onto silica (SiO₂) maintained its basicity and converted methanol molecules to methoxide ions. The PzOH/SiO₂ catalyst exhibited high activity in the transesterification of palm, corn, grape seed, and soybean oils (S-oil) with methanol, achieving ~ 90% conversion at 75 °C with a catalyst loading of 0.2 g per 4.8 ml of S-oil. Although the accumulation of organic materials on PzOH/SiO₂ reduced its activity, this accumulation was effectively removed by washing with methanol. The high activity of PzOH/SiO₂ was responsible for its strong basicity and for the free mobility of the PzOH moiety.     

不同植物油脂在近临界水中水解反应动力学的比较

系统地测定了压力10 MPa、温度170℃～240℃范围内橄榄油、花生油、大豆油、红花油等植物油脂在近临界水中无催化水解反应动力学数据。实验结果表明,近临界水中油脂水解反应是一个典型的自催化反应,采用二级自催化反应动力学模型对动力学数据进行了拟合,得到了橄榄油、花生油、大豆油、红花油等四种植物油脂的水解反应活化能分别为41.8 kJ/mol、37.3 kJ/mol、37.7 kJ/mol、31.2 kJ/mol。油脂水解活化能与其碘价密切相关,随着油脂碘价的增加,水解活化能逐渐降低。     

Long storage stability of biodiesel from vegetable and used frying oils

Biodiesel is defined as the mono-alkyl esters of vegetable oils. Production of biodiesel has grown tremendously in European Union in the last years. Though the commercial prospects for biodiesel have also grown, there remains some concern with respect to its resistance to oxidative degradation during storage. Due to the chemical structure of biodiesel the presence of the double bond in the molecule produce a high level of reactivity with the oxygen, especially when it placed in contact with air. Consequently, storage of biodiesel over extended periods may lead to degradation of fuel properties that can compromise fuel quality.This study used samples of biodiesel prepared by the process of transesterification from different vegetable oils: high oleic sunflower oil (HOSO), high and low erucic Brassica carinata oil (HEBO and LEBO) respectively and used frying oil (UFO). These biodiesels, produced from different sources, were used to determine the effects of long storage under different conditions on oxidation stability. Samples were stored in white (exposed) and amber (not exposed) glass containers at room temperature.The study was conducted for a period of 30-months. At regular intervals, samples were taken to measure the following physicochemical quality parameters: acid value (AV), peroxide value (PV), viscosity (ν), iodine value (IV) and insoluble impurities (II). Results showed that AV, PV, ν and II increased, while IV decreased with increasing storage time of biodiesel samples. However, slight differences were found between biodiesel samples exposed and not exposed to daylight before a storage time of 12 months. But after this period the differences were significant.     

Effect of FA composition on epoxidation kinetics of TAG

The rate constants of epoxidation were determined by reacting formic acid with a number of oils, pure TAG, and pure FAME. These results showed that FA composition had a significant effect on the value of the rate constant. In TAG, the double bonds of oleic acid and linoleic acid were equally reactive, and the double bonds of linolenic acid were approximately three times more reactive than oleic and linoleic acids. For FAME, the rate constants of epoxidation increased as the level of unsaturation increased. Furthermore, the rate constants of epoxidation for the FAME were higher than their respective TAG. We conclude that steric and electronic effects caused FA with different levels of unsaturation to have different reactivities. These results were used to derive a model that predicts the epoxidation kinetics of oils from their FA composition. The predictions of the model closely match the experimentally determined rate constants.     

Quantification of free and esterified steryl glucosides in vegetable oils and biodiesel

Steryl glucosides (SG) are minor components that dramatically modify the low temperature performance of fatty acid methyl esters (FAME) used as biodiesel. SG are naturally present in vegetable oils but they may also be the result of the transesterification of esterified steryl glucosides (ESG). These are present in vegetable oils at a level of a few hundred milligrams per kilogram, depending on the nature of the feedstock. We developed an analytical method to quantify SG and ESG in vegetable oils and in FAME. The purification of SG and ESG was performed by liquid chromatography on silica gel, and the analysis of the trimethylsilyl derivatives was achieved by gas chromatography and flame ionization detection. The filterability of biodiesel is affected when the SG content is higher than 20 mg/kg. Therefore, the sensitivity of this new method is adapted for this purpose since the quantification limit is 10 mg/kg of SG and ESG. The recoveries are acceptable, between 75% and 90% depending on the species and content, and the reproducibility relative standard deviation, evaluated at 10%, is comparable to other studies.     

Density and viscosity of vegetable oils

A generalized method was developed to estimate the liquid density of vegetable oils and fatty acids. The correlation for vegetable oils was based on fatty acid critical properties and composition of the oil. The correlations predicted the density of vegetable oils and fatty acids with an average absolute deviation of 0.21 and 0.77%, respectively. The present method is slightly more accurate in predicting vegetable oil density and simpler than the method of Halvorsen et al. Also, a method is introduced that predicts viscosity from density data, thus relating two key properties of vegetable oils.     

Studies on the properties of polyesters and polyester blends of selected vegetable oils

Melon‐seed and rubber‐seed oils have been used in the synthesis of polyester resins. Results reveal that rubber‐seed oil can completely be substituted for linseed and soyabean oils in the synthesis of both long and medium‐oil–length polyester resins. Melon‐seed oil was found to be a substitute for 50% of linseed oil and 50% of soyabean oil in the synthesis of long‐oil–length polyester resins. It also substituted for 15% of linseed oil and 50% of soyabean oil in the synthesis of medium‐oil–length polyester resins. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 1441–1446, 2000     

Graphical method to select vegetable oils as potential feedstock for biodiesel production

Chemical compositions of 80 vegetable oils were collected from literature and the properties of the obtainable biodiesel (methyl esters) have been predicted by empirical relationships. The purpose has been to check the viability of predicting if a biodiesel could meet the EN 14214 standards knowing only the fatty acid profile (FAP) of the parent oil. Two parameters were used in this investigation: (i) average number of carbon atoms in the fatty acid chains, (ii) average number of double bonds (C?C) per molecule. Two new empirical relationships have been proposed to predict the viscosity and the cetane number of biodiesel from the two parameters. The range of values of the two parameters leading to biodiesel meeting the EN 14214 standard for viscosity, cetane number, iodine value, and cold filter plugging point have been graphically obtained by overlapping the corresponding level surfaces. Practical applications: This work provides biodiesel producers with indications of the quality of biodiesel without the need for analytical testing of the product (indeed, of the product itself). Only the fatty acid profile of the starting vegetable oil is required. The quality of biodiesel can be estimated by using a chart developed in this work, allowing to estimate, e.g. if the biodiesel meets the European standards. The work can be useful to rapidly screen oil seed crops in studies of genetic engineering that require high throughput.     

Studies on phytosterol oxides. II: Content in some vegetable oils and in French fries prepared in these oils

Hydrogenated rapeseed oil/palm oil blend, sunflower oil and high-oleic sunflower oil, and French fries fried in these oils were assessed for contents of sterol oxidation products. Different oxidation products of phytosterols (7α- and 7β-hydroxy-sito-and campesterol, 7-ketosito- and 7-ketocampesterol, 5α,6α-epoxy-sito- and campesterol, 5β,6β-epoxy-sito-and campesterol, dihydroxysitosterol and dihydroxycampesterol) were identified and quantiated by gas chromatography (GC) and GC-mass spectroscopy. Rapeseed oil/palm oil blend contained 41 ppm total sterol oxides before frying operations. After two days of frying, this level was increased to 60 ppm. Sunflower oil and high-oleic sunflower oil had 40 and 46 ppm sterol oxides, respectively, before frying operations. After two days of frying operations, these levels increased to 57 and 56 ppm, respectively. In addition to campesterol and sitosterol oxidation products, small amounts of 7α- and 7β-hydroxystigmasterol were detected in the oil samples. Total sterol oxides in the lipids of French fries fried at 200°C in rapeseed oil/palm oil blend, sunflower oil, and high-oleic sunflower oil were 32, 37, and 54 ppm, respectively. The levels of total oxidized sterols, calculated per g sample, ranged from 2.4 to 4.0 ppm. In addition to the content of phytosterol oxides, full scan mass spectra of several oxidation products of stigmasterol are reported for the first time. Part of these results were presented at the 86th Annual Meeting of the AOCS, May 7–11, 1995, San Antonio, TX.     

Kinetics of in situ epoxidation of soybean oil in bulk catalyzed by ion exchange resin

The kinetics of the epoxidation of soybean oil in bulk by peracetic acid formed in situ, in the presence of an ion exchange resin as the catalyst, was studied. The proposed kinetic model takes into consideration two side reactions of the epoxy ring opening involving the formation of hydroxy acetate and hydroxyl groups as well as the reactions of the formation of the peracid and epoxy groups. The catalytic reaction of the peracetic acid formation was characterized by adsorption of only acetic acid and peracetic acid on the active catalyst sites, and irreversible surface reaction was the overall rate-determining step. Kinetic parameters were estimated by fitting experimental data using the Marquardt method. Good agreement between the calculated and experimental data indicated that the proposed kinetic model was correct. The effect of different reaction variables on epoxidation was also discussed. The conditions for obtaining optimal epoxide yield (91% conversion, 5.99% epoxide content in product) were found to be: 0.5 mole of glacial acetic acid and 1.1 mole of hydrogen peroxide (30% aqueous solution) per mole of ethylenic unsaturation, in the presence of 5 wt% of the ion exchange resin at 75°C, over the reaction period of 8 h.