Kinematic viscosity of fatty acid methyl esters: Prediction, calculated viscosity contribution of esters with unavailable data, and carbon–oxygen equivalents

Many properties of biodiesel, the mono-alkyl esters of vegetable oils, animal fats or other triacylglycerol-containing feedstocks, are largely determined by its major components, the fatty acid alkyl esters. Therefore, information on the properties of individual components and their interaction is essential to understanding and predicting the properties of biodiesel fuels. Viscosity, which affects flow and combustion of a fuel, is such a property. In previous literature, the effect of the structure of fatty esters on viscosity was discussed. However, these data are largely confined to esters with an even number of carbon atoms in the chain and that are liquid at 40 °C. To gain a better understanding of kinematic viscosity, this work additionally reports data on esters with an odd number of carbons in the fatty acid chain and some unsaturated fatty esters. Furthermore, the kinematic viscosity of some biodiesel fuels is affected by components that are solids at 40 °C. A method based on polynomial regression for determining the calculated viscosity contribution (CVC) of esters that are solid at 40 °C (saturated esters in the C₂₀–C₂₄ range) or esters that are liquids but not available in pure form is presented as these values are essential for predicting the kinematic viscosity of mixtures containing such esters. The kinematic viscosity data of esters are compared to those of aliphatic hydrocarbons in the C₆–C₁₈ range and those of dimethyl diesters. The increase of kinematic viscosity with increasing number of CH₂ groups in the chain is non-linear and depends on the terminal functional groups, chain length and double bonds. To illustrate this effect, carbon–oxygen equivalents (COE) are used in which the numbers of carbon and oxygen atoms are added. A straightforward equation, taking into account only the amounts and kinematic viscosity values of the individual neat components, suffices to predict the viscosity of mixtures of fatty esters (biodiesel) at a given temperature.     

脂肪酸酯的技术与市场发展动向

论述了脂肪酸一元醇酯,多元醇酯的特性、合成及用途,并介绍了由脂肪酸酯开发“绿色”表面活性剂的最新技术动向。     

Enzymatic synthesis of monosaccharide fatty acid esters and their comparison with conventional products

5-O-Acyl-1,2-O-isopropylidene-D-xylofuranose and 6-O-acyl1,2∶3,4-di-O-isopropylidene-D-galactopyranose were enzymatically prepared from the corresponding monosaccharide acetals and commercial (crude) fatty acid mixtures. Subsequent acid-catalyzed hydrolysis of the isopropylidene group(s) gave monosaccharide esters with overall yields of 59–88%, where the monoester content was at least 80% (galactose oleate) and typically 90% for the other preparations. In contrast to sugar fatty acid esters prepared by conventional, high-temperature (trans)esterification, the enzymatically obtained monosaccharide esters contained no appreciable quantities of undersirable side products, and the only contaminants were monosaccharides and fatty acids.     

Kinematic viscosity of biodiesel components (fatty acid alkyl esters) and related compounds at low temperatures

Biodiesel, defined as the mono-alkyl esters of vegetable oils and animal fats is, has undergone rapid development and acceptance as an alternative diesel fuel. Kinematic viscosity is one of the fuel properties specified in biodiesel standards, with 40 °C being the temperature at which this property is to be determined and ranges of acceptable kinematic viscosity given. While data on kinematic viscosity of biodiesel and related materials at higher temperatures are available in the literature, this work reports on the kinematic viscosity of biodiesel and a variety of fatty acid alkyl esters at temperatures from 40 °C down to −10 °C in increments of 5 °C using the appropriately modified standard reference method ASTM D445. Investigating the low-temperature properties of biodiesel, including viscosity, of biodiesel and its components is important because of the problems associated with the use of biodiesel under these conditions. Such data may aid in developing biodiesel fuels optimized for fatty ester composition. An index termed here the low-temperature viscosity ratio (LTVR) using data at 0 °C and 40 °C (divide viscosity value at 0 °C by viscosity value at 40 °C) was used to evaluate individual compounds but also mixtures by their low-temperature viscosity behavior. Compounds tested included a variety of saturated, monounsaturated, diunsaturated and triunsaturated fatty esters, methyl ricinoleate, in which the OH group leads to a significant increase in viscosity as well as triolein, as well as some fatty alcohols and alkanes. Esters of oleic acid have the highest viscosity of all biodiesel components that are liquids at low temperatures. The behavior of blends of biodiesel and some fatty esters with a low-sulfur diesel fuel was also investigated.     

Chemo-enzymatic synthesis of disaccharide fatty acid esters

A novel enzymatic method for the synthesis of disaccharide fatty acid esters was developed with immobilizedMucor miehei lipase (Lipozyme IM-60; Novo Nordisk, Bagsvaerd, Denmark) as a catalyst. A range of lactose and maltose monoesters was prepared in overall yields of 48–77% from the corresponding sugar acetals and fatty acids.     

柠檬酸甘油单,二酸酯合成过程中沉淀物的分析

对柠檬酸和单甘酯酯化反应制取柠檬酸甘油单、二酸酯过程中产生的沉淀进行了红外光谱分析,并对沉淀产物的原因提出了合理的解析。     

Enzymatic synthesis of acetylated glucose fatty acid esters in organic solvent

Two immobilized lipases fromCandida antarctica (SP 382) andC. cylindraceae, nowrugosa (2001), catalyzed the synthesis of novel acetylated glucose fatty acid esters with glucose pentaacetate (GP) and Trisun 80 (80% oleic) vegetable oil or methyl oleate as substrates in organic solvents. The relative yield was between 6.4–52%, and the incorporation of oleic acid onto the glucose was between 31–100%. In addition, these enzymes were able to catalyze the synthesis of glucose fatty acid esters with free glucose as the sugar substrate. The highest oleic acid incorporation (100%) was obtained in benzene with SP 382 lipase and Trisun 80 as the acyl donor. With methyl oleate as the acyl donor, greater incorporation was obtained in benzene (90.5%) compared to 75% in isooctane. The 2001 lipase was better in benzene/pyridine (2∶1 vol/vol) 74%) and chloroform (61%) compared to benzene and isooctane. However, with free glucose and Trisun 80 as substrates, both enzymes gave acceptable levels of oleic acid incorporation (82–100%) in benzene, benzene/pyridine and pyridine. The best conditions for the ester interchange reaction reported are: lipase (10% by weight of substrate); incubation time 48 h; molar ratio of Trisun/GP 1∶2; 3 mL solvent and 3% added water. These glucose esters have potential applications as emulsifiers in food, cosmetics and pharmaceutical formulations.     

Hydrogenation of fatty acid methyl esters to fatty alcohols at supercritical conditions

Extremely rapid hydrogenation of fatty acid methyl esters (FAME) to fatty alcohols (FOH) occurs when the reaction is conducted in a substantially homogeneous supercritical phase, using propane as a solvent, over a solid catalyst. At these conditions, the limitations of hydrogen transport are eliminated. At temperatures above 240°C, complete conversion of the starting material was reached at residence times of 2 to 3 s, which is several orders of magnitude shorter than reported in the literature. Furthermore, formation of by-products, i.e., hydrocarbons, could be prevented by choosing the right process settings. Hydrogen concentration turned out to be the key parameter for achieving the above two goals. As a result of the supercritical conditions, we could control the hydrogen concentration at the catalyst surface independently of the other process parameters. When methylated rapeseed oil was used as a substrate, the hydrogenation catalyst was deactivated rapidly. However, by using methylated sunflower oil, a catalyst life similar to that obtained in industrial processes was achieved. Our results showed that the hydrogenation of FAME to FOH at supercritical conditions is a much more efficient method than any other published process.     

Separation of fatty acid esters from cholesterol in esterified natural and synthetic mixtures by supercritical carbon dioxide

The solubility of cholesterol in supercritical carbon dioxide was determined by a continuous flow method. The solubility of cholesterol increased with increasing pressure and exhibited retrograde behavior. The Chrastil equation was used to describe the relationship between solubility and the density of carbon dioxide. A model mixture was made by adding cholesterol and fatty acid esters together. Squid visceral oil was esterified as the feed material. Both the model mixture and esterified squid visceral oil were extracted by supercritical carbon dioxide. The experimental results showed that cholesterol could be removed from a model mixture and from esterified squid visceral oil at low pressure (1500 psig) and high temperature (328.2°K). Under these conditions, cholesterol content in the extract was reduced from 2867 mg/100 g to 14.1 mg/100 g.     

Preparation of fatty acid methyl esters for gas-chromatographic analysis of lipids in biological materials

Theoretically, preparation of fatty acid methyl esters (FAMEs) deals with reversible chemical reactions in a complex system. Methodologically, there are numerous ways, generally characterized by the type of catalysts used and steps involved. Although there are more than a half dozen common catalysts, the majority fall into either acidic (HCl, H₂SO₄ and BF₃) or alkaline types (NaOCH₃, KOH and NaOH), with each having its own catalytic capability and application limitations. In terms of steps, many conventional methods, including those officially recognized, consist of drying, digestion, extraction, purification, alkaline hydrolysis, transmethylation/methylation and postreaction work-up. Although these methods are capable of providing reliable estimates if some precautions are taken, they are cumbersome, time-consuming and cost-inefficient. A new approach has been to transmethylate lipidsin situ. Due to its simplicity, high sensitivity, comparable reliability and capability to determine total fatty acids, the method of direct transmethylation is finding a unique place in lipid determination. Regardless of which method is used, quantitative methylation requires chemists to take precautions at every step involved, particularly during FAME formation and subsequent recovery steps. Evidently, there is an urgent need for more systematic studies, guided by the chemical principle of reactions involved and physicochemical properties of regents and end products, into factors affecting these steps. Hopefully, this will lead to an improved method, which measures lipid composition in biological materials not only with high accuracy but also with high efficiency and minimum costs.     

A bulky phosphite-modified rhodium catalyst for the hydroformylation of unsaturated fatty acid esters

A series of hydroformylation experiments was performed with a high-grade and a technical-grade-derived methyl oleate (MO) and a rhodium catalyst modified by the bulky tris(2-tert-butyl-4-methylphenyl)phosphite. In the hydroformylation of pure methyl oleate, relatively high turnover numbers were obtained (400–500 mol/mol/h) under mild conditions (molar ratio MO/Rh=910, 80–100°C and 20 bar; CO/H₂=1:1, solvent toluene), leading to about 95% conversion in 3 h. Fast isomerization occurs under these conditions to produce the trans oleate. Trans oleate reacts more slowly than cis oleate. At temperatures below 50°C, isomerization does not occur. The use of technical-grade methyl oleate, containing 14% 9,12 diene, methyl linoleate (ML), results in lower reaction rates because dienes form stable π-allylic intermediates, which slowly undergo hydroformylation. More severe conditions were applied to obtain higher rates. The rate varied from 50 to 400 mol/mol/h, depending on conditions (molar ratio MO/Rh=910, T=50–120°C, P = 50–80 bar; CO/H₂=1:1–1:6, solvent, toluene). Several isomers of ML were formed during the reaction. Subsequent hydroformylation of these isomers results in a complicated mixture of products. The product mixture consists predominantly of methyl formylstearate, methyl formyloleate, methyl diformylstearate, and some yet unidentified side products. A comparison of the classic triphenylphosphine-modified catalyst and the bulky phosphite-modified catalyst has shown that the latter is several times more active.     

An improved reversed-phase thin-layer chromatography method for separation of fatty acid methyl esters

Resolution of fatty acid methyl esters (FAME) by thin-layer chromatography often is complicated by co-migration of certain acyl-isomers in heterogeneous mixtures. However, a novel reversed-phase thin-layer chromatography method which employs 10% (wt/vol) silver nitrate in a mobile phase containing acetonitrile/1,4-dioxane/acetic acid (80:20:1, vol/vol/vol) allows one-dimensional resolution of a wide range of acyl-methyl esters. This innovation enables improved separation of saturated FAME ranging from C₁₂ to C₂₂, and geometric isomers of C₁₄ to C₂₂ unsaturated FAME by thin-layer chromatography.     

Effects of epoxidation on the thermal oxidative stabilities of fatty acid esters derived from palm olein

A variety of esters from the reactions of monoalcohols with palm olein were prepared, epoxidized byin situ peroxyacid techniques, and some of their physical properties were compared. The thermal oxidative stabilities of these esters andbis(2-ethylhexyl) phthalate were studied. The esters were placed in an oven maintained at 120°C, and the loss of mass and acid, iodine, percent oxirane, hydroxyl, and peroxide values were monitored periodically. The epoxidized esters had higher densities and lower volatilities, and were more resistant toward oxidation than their unepoxidized counterparts. The stability of the oxirane was related to the initial acid value of the sample. Higher initial acid value resulted in a greater decrease in the oxirane content, indicating acid-catalyzed cleavage of the oxirane ring.     

聚甘油脂肪酸酯的表面性能研究

利用甘油聚合得到聚甘油,与一系列高级脂肪酸酯化合成聚甘油脂肪酸酯。分别测试和比较了合成产品的HLB值、表面张力、乳化性能、泡沫性能及钙皂分散性能,并讨论了合成影响因素,为研究聚甘油酯类产品应用性能提供了理论基础。     

Enzymatic synthesis of wax esters from rapeseed fatty acid methyl esters and a fatty alcohol

Wax esters were transesterified from fatty acid methyl esters of rapeseed and a fatty alcohol (1-hexadecanol, 16:0). The amounts of both the substrates were fixed to 0.1 mmol and an immobilized enzyme, Lipozyme, was used as catalyst. The experiment was performed following a statistic central composite design with five variables. The enzyme/lipid ratio was varied between 0.3–0.9 of the substrate weight and the enzyme was equilibrated to different water activities varying from 0.11 to 0.44. A temperature range of 50–80°C was investigated and the reaction time lasted up to 40 min. A solvent, isooctane, constituted 0–30% of the substrate weight. The first experimental series was performed in small closed test tubes. In the second series the caps of the test tubes were off to evaporate the methanol produced during the reaction. The highest initial reaction rate was 9.6 g_{wax esters}/g_enzyme · h. It appeared when: the enzyme/lipid ratio was low, 0.3, the temperature was high, 80°C; no isooctane was present; and the water activity was below 0.11. The initial reaction rate was independent of the caps on the test tubes. With the large amount of enzyme the yield of wax esters was above 70% after 10 min in both experimental series. In the reaction with caps, the reaction reached equilibrium at 83% after 20 min at 80°C. However, without caps the continuous evaporation of methanol increased the equilibrium constantly, and after 40 min at 80°C a yield of 90% was reached.     

A study of fatty acid methyl esters with epoxy or alkyne functionalities

Described are the physical and chemical properties of the methyl esters of two uncommon fatty acids: vernolic acid, containing an epoxy group, and crepenynic acid, containing a triple bond. The incorporation of an epoxy or alkyne group into the fatty acid structure is shown to greatly affect the properties compared to conventional unsaturated fatty acids. The methyl esters have been characterized and compared with ordinary fatty acid methyl esters (i.e., methyl oleate and linoleate) with respect to spectroscopic characterization [¹H nuclear magnetic resonance (NMR)], ¹³C NMR, and Fourier transform infrared), rheological properties, and oxidative reactivity (using chemiluminescence). Both methyl vernoleate and methyl crepenynate could successfully be produced by transesterification under basic conditions without reaction of the epoxy or alkyne groups. Rheological measurements showed that the methyl esters had a significantly lower viscosity compared to their triglyceride analogs. Smaller differences were seen when comparing the different methyl esters where methyl vernoleate had the highest viscosity due to the presence of the more polar oxirane group. Very large differences were found with respect to the oxidation rate of the different methyl esters. Methyl crepenynate was shown to oxidize extremely rapidly, whereas methyl vernoleate was very stable toward oxidation.     

从废弃油脂生物柴油中分离不饱和脂肪酸甲酯

以废弃油脂制生物柴油为原料,以95%醇为溶剂,采用尿素包合法提取不饱和脂肪酸甲酯,为生物柴油联产具有高附加值化工产品打下基础.重点考察了尿素用量、溶剂用量、包合时间和包合温度对不饱和脂肪酸甲酯分离效果的影响.结果表明,尿素包合法从生物柴油中分离不饱和脂肪酸甲酯的适宜工艺条件为:尿素,生物柴油质量比为1.4～1.7,溶剂/生物柴油质量比为4.6～6.0,包合温度为10℃,包合时间为18 h.在适宜条件下,不饱和脂肪酸甲酯含量可达93.5%,收率可达55.8%.     

α-sulfonated fatty acid esters: II. Solution behavior of α-sulfonated fatty acid polyethylene glycol esters

Sodium α-sulfonated, fatty acid polyethylene glycol monoesters [C _m H_2m+1CH(SO₃Na)COO(C₂H₄O) _n H] and diesters [C _m H_2m+1CH(SO₃Na)COO(C₂H₄O) _n COCH(SO₃Na)C _m H_2m+1], wherem=10–16 andn=1–35, were prepared by esterification of α-sulfonated, fatty acids with polyethylene glycols, followed by neutralization with NaOH. Crude products were purified by reversed-phase column chromatography on an octadecyl-modified silica gel. Characteristic solution behavior of these α-sulfonated fatty acid esters was, examined, and the following features were observed. All monoesters prepared in this work had Krafft points below 0°C and also possessed good calcium stabilities. Critical micelle concentrations of the monoesters increased monotonously, as a rule, with an increase in the number of oxyethylene units. These results suggest that the polyethylene glycol residue of the monoester behaves as a hydrophile. On the other hand, diesters possessed high water solubility, low foamability, and critical micelle concentrations that were lower by a factor of ten compared to those of the monoesters.     

Intensified and safe ozonolysis of fatty acid methyl esters in liquid CO2 in a continuous reactor

We demonstrate a continuous reactor for performing the ozonolysis of fatty acid methyl esters (FAMEs) using liquid CO₂ as solvent. The fast reaction kinetics allows the use of small‐volume reactors to completely convert the FAMEs, forming secondary ozonides as the primary products. The short residence times also help maximize the yields of the secondary ozonides by minimizing over‐oxidation and the formation of oligomeric products. The liquid CO₂ medium promotes safe reactor operation by providing an essential fraction of overall reactor cooling and by diluting the vapor phase organics. We also demonstrate a continuous stirred reactor for the safe thermal decomposition of the secondary ozonides to their corresponding acids and aldehydes. Using a lumped kinetic model for the thermal decomposition of the ozonolysis products, we estimate activation energy values of 108.6 ± 0.6 kJ mol^?1 for the decomposition of secondary ozonides and 122 ± 3 kJ mol^?1 for the decomposition of the undesired oligomeric species. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2819–2826, 2017     

Synthesis of alkyl glycoside fatty acid esters in non-aqueous media byCandida sp. lipase

Alkyl glycoside fatty acid esters were successfully synthesized by lipase-catalyzed transesterification of methyl glucoside, methyl glucoside, methyl galactoside and octyl glucoside with methyl oleate. The experiments were carried out in organic media with lipase enzymes fromCandida sp. as biocatalysts. Time course and the effects of temperature, solvent type, substrate concentration, added water and of immobilizedvs. nonimmobilized enzyme were studied. The optimal conditions for the enzymatic synthesis of alkyl glycoside fatty acid esters were: a molar ratio of alkyl glycoside and methyl oleate of 1:4, an immobilized lipase, SP382 fromCandida sp.; benzene/pyridine (2:1, vol/vol) with no added water; temperature, 55°C; reaction time, 48 h; and shaking at 200 rpm. Acceptable levels of oleic acid incorporation (58.6–100 mol%) onto the alkyl glycosides were achieved.