Low-temperature properties of triglyceride-based diesel fuels: Transesterified methyl esters and petroleum middle distillate/ester blends

This work examines low-temperature properties of triglyceride-based alternate fuels for direct-injection compression-ignition engines. Methyl esters from transesterified soybean oil were studied as neat fuels and in blends with petroleum middle distillates (No. 1 or No. 2 diesel fuel). Admixed methyl esters composed of 5–30 vol% tallowate methyl esters in soyate methyl esters were also examined. Pour points, cloud points, and kinematic viscosities were measured; viscosities at cooler temperatures were studied to evaluate effects of sustained exposure. Low-temperature filterability studies were conducted in accordance with two standard methodologies. The North American standard was the low-temperature flow test (LTFT), and its European equivalent was the cold-filter plugging point (CFPP). With respect to cold-flow properties, blending methyl esters with middle distillates is limited to relatively low ester contents before the properties become preclusive. Under most conditions, cold-flow properties were not greatly affected by admixing the methyl esters with up to 30 vol% tallowate (before blending). Least squares analysis showed that both LTFT and CFPP of formulations containing at least 10 vol% methyl esters are linear functions of cloud point. In addition, statistical analysis of the LTFT data showed a strong 1:1 correlation between LTFT and CP. This result may prove crucial in efforts to improve low-temperature flow properties of alternate diesel fuels that contain methyl esters derived from triglycerides.     

Thermal analysis of alternative diesel fuels from vegetable oils

The relatively poor cold-flow properties of monoalkyl esters of vegetable oils and animal fats (biodiesel) present a major obstacle to their development as alternative fuels and extenders for combustion in direct injection compressionignition (diesel) engines. In this work, differential scanning calorimetry (DSC) heating and cooling curves of methyl soyate (SME), methyl tallowate (TME), SME/TME admixtures, and winterized SME were analyzed. Completion of melt, crystallization onset (Onset), and other temperatures corresponding to melting and freezing peaks were correlated to predict cloud point (CP), pour point (PP), cold filter plugging point (CFPP), and low-temperature flow test (LTFT) data. Effects of treating methyl esters with cold-flow improvers were examined. Low-temperature flow properties of biodiesel may be accurately inferred from subambient DSC analyses of high-melting or freezing (β-form) peaks. The temperature of maximal heat flow for freezing peaks gave the best accuracy for predicting CP, PP, and CFPP, while freezing point gave the best accuracy for predicting LTFT. Onset also gave good correlations with respect to predicting PP, CFPP, and LTFT. Cooling scan parameters were more reliable than heating scan parameters. Presented at the 88th American Oil Chemists’ Society’s Annual Meeting & Expo, Seattle, Washington, May 11–14, 1997.     

Low-temperature properties of alkyl esters of tallow and grease

The low-temperature properties of mono-alkyl esters derived from tallow and recycled greases were determined for neat esters and 20% ester blends in No. 2 low-sulfur diesel fuel. Properties studied included cloud point, pour point, cold filter plugging point, low-temperature flow test, crystallization onset temperature, and kinematic viscosity. Compositional properties of the alkyl esters determined included water, residual free fatty acids, and free glycerol content. In general, the secondary alkyl esters of tallow showed significantly improved cold-temperature properties over the normal tallow alkyl ester derivatives. The low-temperature flow test did not show a 1:1 correlation with cloud point as previously observed with methyl soyate and methyl tallowate. For the homologous series methyl to n-butyl tallowate, ethyl tallowate had the best broad-spectrum low-temperature properties, both neat and when blended in diesel fuel. For the greases studied, both the normal and branched alkyl ester derivatives showed improved properties over corresponding tallow esters, especially with neat esters.     

Low-temperature flow properties of vegetable oil/cosolvent blend diesel fuels

Vegetable oils are an attractive renewable source for alternative diesel fuels. However, the relatively high kinematic viscosity of vegetable oils must be reduced to make them more compatible with conventional compression-ignition engines and fuel systems. Cosolvent blending is a low-cost and easy-to-adapt technology that reduces viscosity by diluting the vegetable oil with a low-M.W. alcohol (methanol or ethanol). The cosolvent (A), which consists of one or more amphiphilic compounds, is added to solubilize the otherwise nearly immiscible oil-polar alcohol mixture. This work investigates cold flow properties and phase equilibrium behavior associated with blends consisting of soybean oil (SBO) and methanol where A=8∶1 (mol) n-butanol/oleyl alcohol; 6∶1 (mol) 2-octanol/triethylammonium linoleate; and 4∶1 (mol) 2-octanol/Unadol 40 (alcohols from SBO FA); and a blend of 2∶1 (vol/vol) No. 2 diesel fuel/SBO and 95% ethanol where A=n-butanol. Cloud point (CP), pour point, cold filter plugging point (CFPP), and low-temperature flow test (LTFT) results were compared with corresponding phase separation temperature (T _ϕ) data measured at equilibrium. Although CP data were measured under non-equilibrium experimental conditions, a nearly linear correlation was found between T _ϕ and CP. Statistical analysis showed that T _ϕ may also be correlated with CFPP and LTFT. Analysis of heating and cooling DSC curves indicated that peak temperatures may be employed to predict cold flow properties and T _ϕ behavior for SBO/cosolvent blends. Cooling curve parameters correlated more readily than heating curve parameters. Finally, relatively low quantities of heat evolved during freezing indicated that crystallization in the SBO/cosolvent blends studied in this work occurs easily during cooling.     

Temperature-dependent kinematic viscosity of selected biodiesel fuels and blends with diesel fuel

The kinematic viscosities of four biodiesel fuels—two natural soybean oil methyl esters, one genetically modified soybean oil methyl ester, and one yellow grease methyl ester—and their 75, 50, and 25% blends with No. 2 diesel fuel were measured in the temperature range from 20 to 100°C in steps of 20°C. The measurements indicated that all these fuels had viscosity-temperature relationships similar to No. 2 diesel fuel, which followed the Vogel equation as expected. A weighted semilog blending equation was developed in which the mass-based kinematic viscosity of the individual components was used to compute the mixture viscosity. A weight factor of 1.08 was applied to biodiesel fuel to account for its effect on the mixture viscosity. The average absolute deviation achieved with this method was 2.1%, which was better than the uncorrected mass average blending equation that had an average absolute deviation of 4.5%. The relationship between the viscosity and the specific gravity of biodiesel fuels was studied. A method that could estimate the viscosity from the specific gravity of biodiesel fuel was developed. The average absolute deviation for all the samples using this method was 2.7%. The accuracy of this method was comparable to the weighted mass-based semilog blending equation.     

Exhaust emissions and fuel properties of partially hydrogenated soybean oil methyl esters blended with ultra low sulfur diesel fuel

Important fuel properties and emission characteristics of blends (20 vol.%) of soybean oil methyl esters (SME) and partially hydrogenated SME (PHSME) in ultra low sulfur diesel fuel (ULSD) were determined and compared with neat ULSD. The following changes were observed for B20 blends of SME and PHSME versus neat ULSD: improved lubricity, higher kinematic viscosity and cetane number, lower sulfur content, and inferior low-temperature properties and oxidative stability. With respect to exhaust emissions, B20 blends of PHSME and SME exhibited lower PM and CO emissions in comparison to those of neat ULSD. The PHSME blend also showed a significant reduction in THC emissions. Both SME and PHSME B20 blends yielded small increases in NO_x emissions. The reduction in double bond content of PHSME did not result in a statistically significant difference in NO_x emissions versus SME at the B20 blend level. The test engine consumed a greater amount of fuel operating on the SME and PHSME blends than on neat ULSD, but the increase was smaller for the PHSME blend.     

Cold flow properties of fuel mixtures containing biodiesel derived from animal fatty waste

The aims of the present study were to evaluate the cold temperature behavior of methyl esters of vegetable and animal origin and of their mixtures with fossil diesel fuel, as well as to investigate the effectiveness of different depressants. Various blends of rapeseed oil methyl esters, linseed oil methyl esters, pork lard methyl esters and fossil diesel fuel were prepared, and both cloud point and cold filter plugging point (CFPP) were analyzed. It was found that mixtures with CFPP values of –5 °C and lower may contain up to 25% of pork lard methyl esters; whereas the ratio of summer fossil diesel fuel and rapeseed oil methyl esters may vary over a wide range, i.e. such mixtures can be used in a diesel engine in the summer. In the transitory periods it is possible to use up to 20% animal and vegetable ester blends (3 : 7) with winter fossil diesel, whereas only up to 5% of esters can be added to the fuel used in winter. In order to improve the cold properties of rapeseed oil, pork lard and linseed oil methyl ester mixtures, various additives were tested. Depressant Viscoplex 10–35 with an optimal dose of 5000 mg/kg was found to be the most effective.     

The kinematic viscosity of biodiesel and its blends with diesel fuel

As the use of biodiesel becomes more wide-spread, engine manufacturers have expressed concern about biodiesel’s higher viscosity. In particular, they are concerned that biodiesel may exhibit different viscosity-temperature characteristics that could result in higher fuel injection pressures at low engine operating temperatures. This study presents data for the kinematic viscosity of biodiesel and its blends with No. 1 and No. 2 diesel fuels at 75, 50, and 20% biodiesel, from close to their melting point to 100°C. The results indicate that while their viscosity is higher, biodiesel and its blends demonstrate temperature-dependent behavior similar to that of No. 1 and No. 2 diesel fuels. Equations of the same general form are shown to correlate viscosity data for both biodiesel and diesel fuel, and for their blends. A blending equation is presented that allows the kinematic viscosity to be calculated as a function of the biodiesel fraction.     

Low-temperature property and engine performance evaluation of ethyl and isopropyl esters of tallow and grease

Three monoalkyl fatty acid esters derived from tallow and grease were prepared by lipase-catalyzed transesterification and evaluated as prospective diesel engine fuels. The low-temperature properties of the esters, both neat and as 20% blends in No. 2 diesel fuel, were evaluated. Those properties included cloud point, pour point, cold filter plugging point, low-temperature flow test, and crystallization onset temperature. Other properties of the esters, such as kinematic viscosity, heating value, and calculated cetane number, also were determined. All three esters had acceptable physical and low-temperature properties, as well as acceptable fuel properties at the 20% level in diesel blends. Engine performance and emissions for the ester blends were determined in a direct-injection, matched two-cylinder diesel engine. Among the monoalkyl esters studied, ethyl greasate had better properties and engine performance characteristics than the two tallow esters. For the latter esters, isopropyl tallowate had better properties than ethyl tallowate. Presented in part at the 88th Annual Meeting of American Oil Chemists’ Society, Seattle, WA, May 1997.     

柴油降滤剂CDC-SO的合成表征与降滤性质研究

对柴油降滤剂进行了研究,以一缩二丙二醇、柠檬酸为原料,首次合成了以一缩二丙二醇为核心的多羟基多酸CDC小分子,再利用酯化反应依次与带有功能化基团的硬脂酸、十八醇接枝合成了新型的多元酯类CDC-SO大分子,并研究了单体配比、催化剂用量、溶剂用量和酯化反应时间对目的产物助滤效果的影响.将该添加剂以600 μg/g的加剂量添加于0#轻柴油中,柴油的冷滤点降低达6℃,其性能优于市场上普遍使用的T1804和T1805.     

Low-temperature property and engine performance evaluation of ethyl and isopropyl esters of tallow and grease

Three monoalkyl fatty acid esters derived from tallow and grease were prepared by lipase-catalyzed transesterification and evaluated as prospective diesel engine fuels. The low-temperature properties of the esters, both neat and as 20% blends in No. 2 diesel fuel, were evaluated. Those properties included cloud point, pour point, cold filter plugging point, low-temperature flow test, and crystallization onset temperature. Other properties of the esters, such as kinematic viscosity, heating value, and calculated cetane number, also were determined. All three esters had acceptable physical and low-temperature properties, as well as acceptable fuel properties at the 20% level in diesel blends. Engine performance and emissions for the ester blends were determined in a direct-injection, matched two-cylinder diesel engine. Among the monoalkyl esters studied, ethyl greasate had better properties and engine performance characteristics than the two tallow esters. For the latter esters, isopropyl tallowate had better properties than ethyl tallowate. Presented in part at the 88th Annual Meeting of American Oil Chemists’ Society, Seattle, WA, May 1997.     

Fuel properties and emissions of soybean oil esters as diesel fuel

The effects of using blends of methyl and isopropyl esters of soybean oil with No. 2 diesel fuel were studied at several steady-state operating conditions in a four-cylinder turbocharged diesel engine. Fuel blends that contained 20, 50, and 70% methyl soyate and 20 and 50% isopropyl soyate were tested. Fuel properties, such as cetane number, also were investigated. Both methyl and isopropyl esters provided significant reductions in particulate emissions compared with No. 2 diesel fuel. A blend of 50% methyl ester and 50% No. 2 diesel fuel provided a reduction of 37% in the carbon portion of the particulates and 25% in the total particulates. The 50% blend of isopropyl ester and 50% No. 2 diesel fuel gave a 55% reduction in carbon and a 28% reduction in total particulate emissions. Emissions of carbon monoxide and unburned hydrocarbons also were reduced significantly. Oxides of nitrogen increased by 12%.     

C5-MSV柴油降凝剂的研究

采用与马来酸酐接枝的方法对C5石油树脂进行改性,接枝物与苯乙烯、醋酸乙烯酯共聚,用高碳醇进行醇解,研制出一种新型柴油降凝剂。考察了C5石油树脂与马来酸酐的质量比、苯乙烯和醋酸乙烯酯的用量、引发剂用量以及反应时间、反应温度对降凝剂效果的影响。结果表明,最佳反应条件是:C5石油树脂∶马来酸酐=10∶1.2(质量比),过氧化苯甲酰0.1 g,苯乙烯1.30 g,醋酸乙烯酯1.60 g。此降凝剂用于抚顺石化0#柴油馏分,可降低其冷滤点5℃。     

C_5-MSV柴油降凝剂的研究

采用与马来酸酐接枝的方法对C5石油树脂进行改性,接枝物与苯乙烯、醋酸乙烯酯共聚,用高碳醇进行醇解,研制出一种新型柴油降凝剂。考察了C5石油树脂与马来酸酐的质量比、苯乙烯和醋酸乙烯酯的用量、引发剂用量以及反应时间、反应温度对降凝剂效果的影响。结果表明,最佳反应条件是：C5石油树脂∶马来酸酐=10∶1.2（质量比）,过氧化苯甲酰0.1 g,苯乙烯1.30 g,醋酸乙烯酯1.60 g。此降凝剂用于抚顺石化0#柴油馏分,可降低其冷滤点5℃。     

A continuous process for the conversion of vegetable oils into methyl esters of fatty acids

A continuous process for the transesterification of triglycerides to methyl esters was investigated in a pilot plant. The process was equipped with a motionless and a high-shear mixer. The experimental studies explored variations in the mixing intensity, stoichiometry, and catalyst concentration on the overall conversion. The combined as well as individual effect of mixers was examined. The developed process resulted in high conversions of vegetable oils into methyl esters. Conversion of triglycerides to methyl esters in excess of 98% was achieved. Larger excess amounts of alcohol favored higher conversions. The motionless and high-shear mixers each provided adequate mixing for the process. Higher catalyst concentrations resulted in higher conversions but increased the solubility of methyl esters in the glycerol layer. This reduced the amount of methyl esters separated by gravity settling. Presented in part at the Third Liquid Fuel Conference, Nashville, September 15–17, 1996.     

Determination of the mass fraction of methyl esters in mixed fuels

This paper presents the results of two methods employed to determine the methyl ester (ME) fraction in mixed fuels prepared from MEs of higher fatty acids and fossil Diesel fuel. The first method is based on determining the ester number of the mixed fuel. The second one utilises the measurement of the carbonyl band intensity in the mixed fuel by infrared (IR) spectroscopy. The ME fraction in the tested mixed fuels was always set to 30 wt‐%. Applying the first method the ester numbers of mixed fuels were determined and the ME fraction was defined using an averaged molar mass of ME. The differences between the values of the measured and real fraction of ME varied between −0.2 and +0.8 wt‐%. If the value of the average molar mass of ME was not known, the molar mass of methyl oleate was used as a reference. Thereby the differences in determining the ME fraction in mixed fuels ranged between −0.1 and +0.9 wt‐%. Employing the IR spectroscopy method the differences between the measured and the real fraction of ME varied between −1.0 and +0.5 wt‐%. Both methods are suitable to determine the ME fraction in mixed fuels.     

柴油低温流动改进剂的研究及工业应用

介绍了T系列柴油低温流动改进剂实验室和工业试验情况。实验室研究结果表明，T系列柴油低温流动改进剂具有较好的柴油感受性，降凝效果较好。工业应用结果表明，T系列柴油低温流动改进剂对大港柴油具有较好的感受性，加剂比在0.1%左右时能大幅度降低柴油的冷滤点，可将+5号及0号柴油分别调合成0号和－10号柴油。     

Reducing the crystallization temperature of biodiesel by winterizing methyl soyate

Methyl soyate, made from typical soybean varieties, has a crystallization onset temperature (T _co) of 3.7°C and, as a biodiesel fuel, is prone to crystallization of its high-melting saturated methyl esters at cold operating temperatures. Removal of saturated esters by winterization was assessed as a means of reducing theT _co of methyl soyate. Winterizing neat methyl esters of typical soybean oil produced aT _co of −7.1°C, but this was not an efficient way of removing saturated methyl esters because of the low yield (26%) of the separated liquid fraction. However, aT _co of −6.5°C with 86% yield was obtained by winterizing the neat methyl esters of a low-palmitate soybean oil; aT _co of −5.8°C with 77% yield was obtained by winterizing methyl esters of normal soybean oil diluted with hexane.     

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.     

间戊二烯C5石油树脂改性作为柴油降凝剂的研究

间戊二烯C5石油树脂在引发剂的作用下与马来酸酐发生接枝反应,再用直链烷烃醇进行酯化,制得梳状结构的柴油降凝剂。戊二烯C5石油树脂改性制备柴油降凝剂的最佳反应条件是:各物质质量比C5石油树脂∶马来酸酐∶引发剂∶混合醇∶溶剂(二甲苯)为100∶12∶1∶20∶8,混合醇用量比C12∶C16∶C18为0.4∶0.3∶0.3,反应温度80℃,反应时间4 h,所得到的改性石油树脂降凝剂与T 602C降凝剂复配(改性石油树脂降凝剂加入量为400μg/g,T 602C加入量为1 000μg/g)对柴油具有很好的降凝效果,可将抚顺石化公司生产的-10#柴油馏分的冷滤点降低7℃。