Crystallization Behavior of Fatty Acid Methyl Esters

Biodiesel from most agricultural feedstocks has flow properties that are prone to startup and operability problems during cold weather. Biodiesel from soybean oil is generally a mixture of long-chain fatty acid alkyl esters composed of 0.15–0.20 mass fraction saturated esters (melting point [MP] ≫ 0 °C) mixed with unsaturated esters (MP < 0 °C). This work investigates the crystallization properties of two saturated fatty acid methyl esters (FAME) commonly found in biodiesel from soybean oil. Differential scanning calorimetry (DSC) heating and cooling scans of methyl palmitate (MeC16), methyl stearate (MeC18) and methyl oleate (MeC18:1) in pure form were analyzed. Crystallization behavior in ternary FAME mixtures was inferred by the application of thermodynamic models based on ideal solution and freezing-point depression theories. Activity coefficients for MeC16 and MeC18 in MeC18:1 solvent were determined by analyzing DSC cooling curves for binary FAME mixtures. Eutectic points were predicted by both models. Crystallization onset temperatures inferred from freezing point depression theory were more accurate than those for ideal solutions with respect to a direct DSC cooling curve analysis of corresponding ternary mixtures. This work shows that the crystallization onset temperature (cloud point) of biodiesel may be predicted by freezing-point depression theory if the activity coefficients of the component FAME are known. The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not constitute an official endorsement or approval by USDA or ARS of any product or service to the exclusion of others that may be suitable.     

Comparisons of Biodiesel Produced from Unrefined Oils of Different Peanut Cultivars

Biodiesels were prepared according to standard procedures from unrefined oils of eight commercially available peanut cultivars and compared for differences in physical properties important to fuel performance. Dynamic viscosity, kinematic viscosity and density were measured from 100 to 15 °C, and differences (p < 0.05) in these physical properties occurred more frequently at lower temperatures when comparing the different cultivars. Unlike data for the oil feedstocks, no meaningful correlations among biodiesel fatty acid profiles and either fuel viscosity or density were observed. Low temperature crystallization of the peanut biodiesels was measured via differential scanning calorimetry. Increased concentrations of long chain saturated fatty acid methyl esters (FAME) were associated with an increased propensity for low temperature crystallization, and the single FAME category most associated with low temperature crystallization was C:24. Tempering at 10 °C followed by analysis of the soluble fractions (winterization), improved crystallization properties and confirmed the importance that long chain saturated FAMEs play in the final functionality of peanut biodiesel. Peanut data is also compared to data for canola and soy biodiesels, as these feedstocks are more common worldwide for biodiesel production. Overall, this work suggests that minimizing the concentration of long chain saturated FAMEs within peanut biodiesel, either through processing and/or breeding efforts would improve the low temperature performance of peanut biodiesel.     

Solidification behavior of acylglycerols in fatty acid methyl esters and effects on the cold flow properties of biodiesel

The formation of precipitates in biodiesel (comprising fatty acid methyl esters [FAMEs] obtained from plant oils) can lead to the clogging of fuel filters. Such precipitates are often caused by the solidification of acylglycerols (monoacylglycerols [MAGs], diacylglycerols [DAGs], and triacylglycerols [TAGs]) that have higher melting points than FAMEs. Based on our prior study on the solidification behavior of MAG/FAME binary mixtures, the present work investigated the behavior of various DAGs and TAGs combined with FAMEs. Differential scanning calorimetry was used to clarify the effects of acylglycerols on the cold-flow properties of biodiesel. When DAGs and TAGs were added to FAMEs, the liquidus temperatures (above which the mixtures were completely liquid) increased steeply even at low concentrations. This same behavior was observed previously in trials with MAGs, indicating that all acylglycerols readily precipitate in combination with FAMEs. However, thermodynamic analyses established that the reasons for such precipitation were different for different compounds. MAGs precipitates because they contain two hydroxyl groups and therefore have a low affinity for FAMEs. In contrast, TAGs precipitates as a result of their high enthalpies of fusion (which in turn are caused by high molecular weights), while both factors affect the precipitation of DAGs. A non-solid-solution thermodynamic model that assumes a eutectic system was found to accurately predict the liquidus temperatures of binary and multicomponent mixtures containing various acylglycerols with FAMEs.     

Cooling rate and dilution affect the nanostructure and microstructure differently in model fats

The effects of cooling rate and solid mass fraction on the polymorphism, nano and microstructure, thermal and rheological properties of binary mixtures of fully hydrogenated canola oil and canola oil at 20°C have been studied. The β‐polymorph was observed in fully hydrogenated canola oil (FHCO) when crystallized at slow cooling rates (0.1C°/min), however crystallization at higher cooling rates (0.7 and 10°C/min) resulted in the formation of the α form. The β‐polymorph was detected in all the binary mixtures of FHCO/canola oil and was not affected by crystallization at different cooling rates. Melting thermograms obtained from 100% FHCO displayed three melting peaks, associated with the development of the β‐polymorph via α→ β′→ β‐polymorphic transition in the DSC pan. Some solubilization of solid FHCO into canola oil was observed and the solubility was proportionally higher with increasing liquid oil fraction. The strong influence of the matrix concentration on micro/nanoscale structure was demonstrated by characterization of crystal size using cryogenic transmission electron (Cryo‐TEM) and polarized light microscopy (PLM). Crystallization under higher cooling rates lead to formation of smaller nano and meso‐structural elements. Furthermore, oscillatory rheology showed the influence of structural elements' size and polymorphism on material strength. The shear storage modulus (G′) of the mixtures was higher when crystallized at fast cooling rates (10°C/min). In contrast, for pure FHCO, G′ increased by lowering the cooling rate and the highest storage modulus was observed after crystallization at 0.1°C/min.     

Branched‐Chain Fatty Acid Methyl Esters as Cold Flow Improvers for Biodiesel

Biodiesel is an alternative diesel fuel derived mainly from the transesterification of plant oils with methanol or ethanol. This fuel is generally made from commodity oils such as canola, palm or soybean and has a number of properties that make it compatible in compression‐ignition engines. Despite its many advantages, biodiesel has poor cold flow properties that may impact its deployment during cooler months in moderate temperature climates. This work is a study on the use of skeletally branched‐chain‐fatty acid methyl esters (BC‐FAME) as additives and diluents to decrease the cloud point (CP) and pour point (PP) of biodiesel. Two BC‐FAME, methyl iso‐oleate and methyl iso‐stearate isomers (Me iso‐C_18:1 and Me iso‐C_18:0), were tested in mixtures with fatty acid methyl esters (FAME) of canola, palm and soybean oil (CaME, PME and SME). Results showed that mixing linear FAME with up to 2 mass% BC‐FAME did not greatly affect CP, PP or kinematic viscosity (ν) relative to the unmixed biodiesel fuels. In contrast, higher concentrations of BC‐FAME, namely between 17 and 39 mass%, significantly improved CP and PP without raising ν in excess of limits in the biodiesel fuel standard specification ASTM D 6751. Furthermore, it is shown that biodiesel/Me iso‐C_18:0 mixtures matched or exceeded the performance of biodiesel/Me iso‐C_18:1 mixtures in terms of decreasing CP and PP under certain conditions. This was taken as evidence that additives or diluents with chemical structures based on long‐chain saturated chains may be more effective at reducing the cold flow properties of mixtures with biodiesel than structures based on long‐chain unsaturated chains.     

Energy Additivity Approaches to QSPR Modeling in Estimation of Dynamic Viscosity of Fatty Acid Methyl Ester and Biodiesel

Viscosity is an important physical property of fatty acid methyl esters (FAME) and biodiesel (mixture of FAMEs). In this work, quantitative structure–property relationship (QSPR) for estimation of dynamic viscosity of FAMEs and biodiesel is approached via the Gibbs energy additivity method. The Gibbs energy of dynamic viscous flow is simply derived from the sum of the Gibbs energy of kinematic viscous flow and Gibbs energy of volumetric expansion. The derived model can be used for estimation of dynamic viscosity of saturated and unsaturated FAMEs commonly found in nature. Also, the proposed model can be extended to a mixture of FAMEs or biodiesel as well as biodiesel blends. Thus, the dynamic viscosity of FAMEs as well as neat and blended biodiesels can be estimated by the same equation from the carbon number (z) and number of double bonds (n_d) at different temperature (T). The average absolute deviation (AAD) values for saturated, unsaturated FAMEs, biodiesels, and biodiesel blends (at 20–100 °C) are approximately the same as the original model for estimation of kinematic viscosity.     

Biodiesel Production from Rubber Seed Oil by Transesterification Using a Co‐solvent of Fatty Acid Methyl Esters

Rubber seed oil (RSO) is a high‐potential feedstock for the production of biodiesel fuel (BDF) in Asia. Transesterification using fatty acid methyl esters (FAMEs) as co‐solvents was developed for BDF production from RSO with high content of free fatty acids (FFAs). The homogeneous system (FAMEs/triglyceride/methanol) was attained when the FAME content was more than 30 wt %. After esterification of RSO, the crude RSO obtained was transesterified with FAMEs as a co‐solvent. The quality of BDF with high FAME content satisfied the criteria of the EN 14214/JIS K2390 standards. These results suggest that FAMEs converted from FFAs can be applied as a co‐solvent and, thus, reused for BDF production.     

Glycerolysis of Crude Methyl Esters with Crude Glycerol from Biodiesel Production

Glycerolysis of crude fatty acid methyl esters (FAME) with crude glycerol derived from biodiesel production was performed. The reaction was accomplished at temperatures ranging between 160 and 200 °C and molar ratios of FAME to glycerol ranging between 1.5 and 3.0. Increasing the temperature improved the formation rate of monoglycerides (MG) and diglycerides (DG). However, increasing both the temperature and the molar ratio of glycerol to FAME diminished the formation of MG. Best results (43 % MG and 26 % DG in 10 min) were obtained at 200 °C using the lowest concentration of glycerol. The effects of soap and NaOH present in crude glycerol were controlled by carrying out the reaction with pure glycerol. In comparison with NaOH-catalyzed reactions, soap-catalyzed reactions resulted in a slower formation rate of products. However, soap-catalyzed reactions were less prone to secondary reactions, affording maximum yields of MG and DG, which were higher than those obtained with NaOH-catalyzed reactions at 180 and 200 °C.     

Biodiesel potential of rendered fat from avian influenza infected poultry in a burial site

To test the feasibility of biodiesel production using rendered fat from avian influenza (AI) infected poultry in a burial site, we conducted a laboratory-scale transesterification. Each content of fatty acid methyl esters (FAME) was identified to estimate the characteristics of produced biodiesel. Analytical results of the whole FAME profile show that the rendered fat from AI carcass can be a useful source of biodiesel production. The results show 47% of total fat mass can be recovered as biodiesel. Although natural biodegradation in the burial site and soil impurities lowered the yield, the compositional properties of FAMEs confirm that the produced biodiesel presents adequate fuel characteristics, satisfying common biodiesel specifications. These findings provide evidence that our approach can be a viable option to recycle buried carcass sustainably while terminating burial sites.     

Production and characterization of biodiesel from trap grease

The feasibility of the production of biodiesel from trap grease containing 51.5% free fatty acids (FFAs) was investigated. The esterification of FFAs by an acid catalyst followed by the transesterification of triglycerides by an alkali catalyst was examined. The esterification of trap grease by sulfuric acid as a homogeneous catalyst or by Amberlyst-15 as a heterogeneous catalyst was optimized through a response surface methodology. After the two-step esterification of trap grease by sulfuric acid, the acid value decreased from 102.9 mg KOH/g to 2.75 mg KOH/g. Through the transesterification by potassium hydroxide, fatty acid methyl ester (FAME) content reached 92.4%. Following the esterification of trap grease by Amberlyst-15, the acid value decreased to 3.23 mg KOH/g. With the transesterification by potassium hydroxide, FAME content increased to 94.1%. After the distillation of the produced biodiesel, FAME content increased again, to 97.6%. The oxidation stability of the trap grease biodiesel was 0.17 h, and its cold filter plugging point was 4 °C. As the FAME content of the trap grease biodiesel satisfies the Korean Biodiesel Standard, the trap grease biodiesel seems to be applicable for use as an engine fuel after properties improvement.     

Rheology of vegetable oil analogs and triglycerides

The rheological properties of two complex mixtures of short-chain triglycerides were experimentally determined. Dynamic or absolute viscosities of the mixtures were measured for shear rates of 0.32 to 64.69 s⁻¹ at temperatures between 25 and 80°C. The compositions of the mixtures were based on the oil of the plant species Cuphea viscosissima VS-320, a natural source of short-chain triglycerides. The dynamic viscosities of these mixtures were compared to those of a traditional vegetable oil (peanut oil) and diesel fuel. The results of this comparison were used to make estimates of the performance of such triglyceride mixtures as diesel fuel substitutes, since viscosity can be a key indicator of fuel performance for possible substitute diesel fuels. The crystallization temperatures of these two mixtures were also determined experimentally, and the effects of crystallization on fuel performance were projected. Additionally, the dynamic viscosities of pure triglycerides from C6∶0 to C18∶0 at 75°C were plotted vs. chain length. These viscosities were measured at high shear rates (>6 s⁻¹) where dynamic viscosity is shear-independent. An obvious trend in the relationship between triglyceride chain length and viscosity was observed. A second-order regression was used to obtain an equation for this relationship. This equation was used as a model for composition dependence of viscosity. This model was applied to the viscosities of the triglyceride mixtures examined here. There was good agreement between the model and the actual, measured viscosity values determined in this study.     

Identification, FT-IR, NMR (H and C) and GC/MS studies of fatty acid methyl esters in biodiesel from rocket seed oil

Biodiesel was synthesized from rocket seed oil by base-catalyzed transesterification with methanol. The synthesis of biodiesel was confirmed by FT-IR and NMR (¹H and ¹³C) spectroscopy. Various fuel properties of the synthesized biodiesel were determined using ASTM methods and discussed accordingly. A total of eleven fatty acid methyl esters (FAMEs) were identified in rocket seed oil biodiesel (RSOB) by the retention time and the fragmentation pattern data of GC/MS analysis. The identified FAMEs were, methyl 9-hexadecenoate (C16:1), 14-methyl pentadecanoate (C16:0), methyl 9,12-octadecadienoate (C18:2), methyl 9-octadecenoate (C18:1), methyl octadecanoate (C18:0), methyl 11-eicosenoate (C20:1), methyl eicosanoate (C20:0), methyl 13-docosenoate (C22:1), methyl docosanoate (C22:0), methyl 15-tetracosenoate (24:1) and methyl tetracosanoate (C24:0). The percentage conversion of triglycerides to corresponding methyl esters determined by ¹H NMR was 88.49%.     

利用可再生油料资源发展生物炼油化工厂

石油、天然气、煤炭资源终将枯竭,利用可再生资源生产燃料和化工产品正在兴起.利用植物油与甲醇酯交换,可以制备脂肪酸甲酯.脂肪酸甲酯是一种优质清洁燃料,即生物柴油;同时,脂肪酸甲酯及其联产的甘油进一步精制和深加工可以生产许多化工产品.本文从生物柴油的国内外发展概况出发,结合国内的现状,对我国发展生物柴油的影响因素进行了分析,认为原料油的价格和供应量是关键;同样,也对生产化工产品作了相应的探讨,认为这是增加利润的关键.最后形成利用可再生油料资源发展炼油化工厂的设想.     

Use of branched-chain esters to reduce the crystallization temperature of biodiesel

To reduce the tendency of biodiesel to crystallize at low temperatures, branched-chain alcohols were used to esterify various fats and oils, and the crystallization properties of the branched esters were compared with those of methyl esters by using differential scanning calorimetry (DSC), cloud point, and pour point. Compared with the methyl esters that are commonly used in biodiesel, branched-chain esters greatly reduced the crystallization onset temperature (T_CO) of neat esters and their corresponding ester diesel fuel blends. Isopropyl and 2-butyl esters of normal (∼10 wt% palmitate) soybean oil (SBO) crystallized 7–11 and 12–14°C lower, respectively, than the corresponding methyl esters. The benefit of the branched-chain esters in lowering T_CO increased when the esters were blended with diesel fuel. Esters made from a low-palmitate (3.8%) SBO crystallized 5–6°C lower than those of normal SBO. Isopropyl esters of lard and tallow had T_CO values similar to that of methyl esters of SBO. DSC provided an accurate means of monitoring crystallization, and the DSC results correlated with cloud and pour point measurements.     

Separation of fatty acid methyl esters from tall oil by selective adsorption

Fatty acid methyl esters (FAME) and resin acids (RA) were separated from tall oil by selective adsorption. Commercial nonmodified molecular sieve 13X was used as adsorbent. The adsorption isotherms of fatty acids (FA), FAME, and RA on molecular sieve 13X at 25°C were determined using various solvents. The solvents were methanol, ethanol, isopropanol, acetone, benzene, hexane, isooctane, petroleum ether (40–60°C), and petroleum naphtha (80–180°C). With each solvent, FA and RA were adsorbed to a greater extent than FAME. Adsorption isotherms for RA and FAME in binary adsorption systems were also determined using petroleum ether, petroleum naphtha, benzene, and isopropanol. For each component in the binary adsorption, the equilibrium amounts are lower than the values for pure component adsorption. The adsorption of FAME decreased in the presence of RA markedly in petroleum ether and petroleum naphtha. This fact may be the indication of the phenomenon of selective adsorption. Separation was accomplished by adding a solution of esterified tall oil in solvents used in the binary adsorption systems, through a column packed with molecular sieve 13X. With petroleum naphtha, FAME and RA were recovered in yields of 93 and 94%, respectively, from esterified tall oil. Petroleum naphtha gave the best results. The effects of particle size of adsorbent and flow rate of solvent on the efficiency of the separation were also investigated in fixed-bed column studies. The particle size of adsorbent did not apparently alter the results. Changes in the particle size should not significantly change the number of available adsorption sites in a microporous molecular sieve.     

Investigation of the Parameters Affecting the Cetane Number of Biodiesel

The cetane number is the most significant property for measuring the ignition quality of fuels for compression ignition diesel engines. In this study, the derived cetane number (DCN) of several types of biodiesel, biodiesel components and ultra-low sulfur diesel (ULSD) was determined using an Ignition Quality Tester (IQT™). The chemical structure of FAME leads to a higher cetane number of biodiesel compared to ULSD. The contribution to DCN from minor components present in biodiesel is not significant. Oxidation of biodiesel samples results in higher DCN values while depending on the conditions of oxidation. A greater than 25% increase was observed when oxidation was carried out in a way to retain volatile oxidative products such as carboxylic acids and aldehydes. Accelerated oxidation of cotton seed oil (CSO) biodiesel at 110 °C and 10 L/min air flow rate after 210 min resulted in a loss of 14% of the FAME content, of which 10% can be attributed to the oxidation of methyl linoleate (C18:2), whereas oxidation of soy bean oil (SBO) biodiesel resulted in a loss of 21% total FAME after 210 min. A significant amount of methyl linolenate (C18:3) remained un-reacted after 210 min of oxidation. Ambient oxidation of distilled biodiesel samples resulted in a very high cetane number. Oxidative products such as aldehydes, hydroperoxides and oligomers of FAME are probably responsible for this higher DCN. This study enhances the understanding of the effect of composition on the cetane number of biodiesel as well as the effect of oxidative aging on both biodiesel composition and the resultant DCN.     

Degradation of fatty acid methyl esters in biodiesels exposed to sunlight and seawater

The degradation of fatty acid methyl esters (FAMEs) has been characterized in selected biodiesels exposed to sunlight and seawater, and markers are identified that can be used to match a weathered biodiesel spill to its source. Samples of one synthetic and three commercial biodiesels were subjected to a regime of controlled weathering for 71 days. Experiments were designed to promote photo-oxidation, biodegradation or a combination of both processes. The FAME compositions of the biodiesels were measured by GC-MS at various times. Unsaturated FAMEs were preferentially degraded by photo-oxidation. Saturated C16 and C18 FAMEs were the most persistent compounds. The diagnostic ratio C16:0/(C16:0 + C18:0), calculated from the peak area of the total ion chromatograms (TICs), varied by less than 2% (RSD) during 71 days of weathering and could be used to distinguish among the biodiesels studied.     

An empirical approach in predicting biodiesel viscosity at various temperatures

A thermodynamic model is proposed for the determination of kinematic viscosities of saturated fatty acid methyl esters (FAMEs) of various chain lengths at different temperatures. The linearity of the natural logarithm of viscosity-carbon number, plot is limited to a narrow carbon number range. The predicted viscosities of FAMEs of C_12:0-C_18:0, which are commonly found in vegetable oils and used as biodiesels, agree well with the experimental values. The highest difference is 0.354 cSt (5.60%), for methyl stearate at 40 °C. When the proposed method for viscosity calculation of saturated FAMEs are used in combination with the methods for viscosities of biodiesel the mixtures, the predicted viscosities agree well with the values reported in the literatures and the measured values. The differences between the predicted viscosities and those reported in the literatures (at 40 °C) are 1.08 to 8.56% (for eight different vegetable oil methyl esters). The differences between the predicted viscosities and the measured values for coconut methyl esters, at 25, 40 and 50 °C are 9.20, 5.53 and 5.57%, respectively. The differences are slightly higher than those of palm oil methyl esters (4.48, 2.06 and 2.48%, respectively).The proposed method can also be applied to predict the viscosities of free fatty acids and it is speculated it may be applied to other homologous series as well.     

癸酸甲酯、月桂酸甲酯和肉豆蔻酸甲酯的液相声速测量

癸酸甲酯、月桂酸甲酯和肉豆蔻酸甲酯3种脂肪酸甲酯是生物柴油的主要成分,其声速是喷油系统优化设计和等熵压缩因子计算中所必需的参数之一。针对癸酸甲酯、月桂酸甲脂和肉豆蔻酸甲脂3种物质声速实验数据缺乏的现状,利用布里渊光散射法,沿0.1、2.5、5.5和8.5 MPa 4条等压线,在288.15~498.15 K温度范围内,分别测量了癸酸甲酯、月桂酸甲酯和肉豆蔻酸甲酯的液相声速;分析了声速随温度、压力的变化规律;依据实验数据,给出了在本文p-T热力学区域内,3种物质液相声速与温度和压力的关联式;关联式计算值与实验数据的相对偏差绝对平均值分别为：0.17%（癸酸甲酯）、0.10%（月桂酸甲酯）和0.15%（肉豆蔻酸甲酯）,满足工程应用需求。     

Spherulitic crystallization in blends of poly(ethylene oxide) and poly(methyl methacrylate)

The crystallization kinetics of binary blends of poly(ethylene oxide) and poly(methyl methacrylate) were investigated. The isothermal spherulitic growth rates were measured by means of a polarized light microscope. The temperature and composition dependence on the growth rates have been analysed. The temperature range studied was from 44° to 58°C. The introduction of poly(methyl methacrylate) into poly(ethylene oxide) resulted in a reduction of the spherulitic growth rate as the proportion of poly(methyl methacrylate) was increased from zero to 40% by weight. Results have been analysed using the theoretical equations of Boon and Azcue for the growth rate of polymer-diluent mixtures. The experimental results are in good agreement with this equation. The temperature coefficient is negative as is the case in the crystallization of bulk homopolymers.