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Cold Flow Properties of Fatty Esters
COLD FLOW PROPERTIES OF FATTY ESTERS A. Kleinova´1, J. Paligova´1, M. Vrbova´2, J. Mikulec2 and J. Cvengrosˇ1, 1
Faculty of Chemical and Food Technology STU, Bratislava, Slovak Republic. ´ RUP, a.s., Vlcˇie hrdlo, Bratislava, Slovak Republic. Slovnaft VU
2
Abstract: This article is devoted to the study of cold flow properties of neat esters of branched chain alcohols with fatty acids and blends of these esters with fossil diesel fuel. According to determined CFPP values the influence of alcohol branching on the fuel filterability is negligible. Fossil fuel blending with fatty esters of branched alcohols up to 10 vol % does not substantially change the cold flow properties of fossil fuel. The low-temperature properties of fossil diesel and fatty acid methyl/ethyl ester (FAME/FAEE) blends with low ester content (up to 10 vol %), prepared mainly from oils/fats with higher share of saturated fatty acids namely palm oil, tallow and lard, were also measured. The obtained results show that studied esters do not change lowtemperature properties of fossil fuel in the blends with the low esters content of 3–5 vol %, although their own CFPP is over the value permissible by the standard EN 14 214. However, current standard EN 590 specifies to meet all parameters of the standard EN 14 214 also for FAME assigned for blended fuels entirely. The proposal to repeal the CFPP limit for esters assigned for blending is fully justified, without any negative effects on fuel quality. Keywords: methyl esters; ethyl esters; blended fuels; cold flow properties; cold filter plugging point; branched alcohols.
INTRODUCTION
Correspondence to: Dr J. Cvengrosˇ, Faculty of Chemical and Food Technology STU, Radlinske´ho 9, 812 37, Bratislava, Slovak Republic. E-mail: jan.cvengros@ stuba.sk
DOI: 10.1205/psep07009 0957–5820/07/ $30.00 þ 0.00 Process Safety and Environmental Protection Trans IChemE, Part B, September 2007 # 2007 Institution of Chemical Engineers
our geographical latitudes can be seriously limited by seasonal drop of external temperatures, especially in winter period. If the temperature drop is large enough to achieve the saturation temperature of any of the FAME/ FAEE components, these precipitate in the liquid mixture in the form of microscopic crystals, invisible by the naked eye. At further decrease of temperature the submicrometer crystals grow further; as soon as they achieve the size of about 0.5 mm, they become visible. This temperature is then denoted as the cloud point. With further decrease of temperature the saturation temperatures of other components are achieved, the crystals gradually grow until they achieve the dimensions of about 0.5–1 mm, and they start to coalesce into sizeable agglomerates. Gradually the whole system ceases to be liquid, which is referred to as the pour point. Agglomeration of crystals occluded by the liquid phase hinders the flow of fuel through the fuel pipe and blocks the fuel filter. Except of CP and PP, also other parameters are used in order to evaluate the low temperature properties of fuels, e.g., LTFT (Low Temperature Flow Test ASTM D4539) in the North America and CFPP (Cold Filter Plugging Point EN 116) in Europe. These values are more relevant than CP and PP regarding the applicability of fuels at lower temperatures. Some correlation between CP and CFPP was found (Dunn and Bagby, 1995). The filterability
Alkyl esters of higher fatty acids, especially methyl esters (FAME) and ethyl esters (FAEE) are at present considered as real alternative fuels for diesel engines. They are produced by transesterification of natural triacylglycerols—vegetable oils, but also animal fats—with methanol in the presence of alkali catalysts. The main advantage of this alternative fuel is that its properties are similar to those of fossil diesel fuel (DF). They are miscible with DF in any ratio, and they can be used in standard diesel engines without adjustment of the engine. The most pronounced advantages include favourable emission profile in comparison with standard fuel, the fact they originate from domestic renewable sources, they do not increase the amount of CO2 in the atmosphere, and so on. There are, however, also disadvantages in comparison with standard fossil fuels, especially limited resources for their production, three to five times higher production price and less favourable low temperature properties. The behaviour at low temperatures is one of the few research problems of FAME/ FAEE. Unlike DF, the esters have relatively high cloud point CP, and the pour point PP as well. While the CP and PP of diesel fuel are around 2158C and 2278C respectively, the respective values for FAME are about 15 –258C higher. The use of alkyl esters in
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COLD FLOW PROPERTIES OF FATTY ESTERS CFPP defines the lowest temperature at which at least 20 ml of fuel passes through a 45 mm mesh sieve filter with the diameter of 15 mm under defined conditions (time 1 min, vacuum 200 mm H2O). CFPP is defined by melting points of individual components of blended FAME/FAEE. The melting points are influenced by lengths of acyl chains, by the number of double bonds, by isomeric state of unsaturated groups, and by the location of double bonds. The melting point increases with increasing length of the acyl, and decreases with the number of double bonds at the same number of carbon atoms. Conjugated double bonds increase the melting point. Cis-isomers have lower melting points than the trans-isomers. Generally, the double bond represents a defect in the structure of tightly ordered layers, and therefore decreases the melting point. In order to overcome the problems with fatty esters at low temperatures, five solutions have been proposed: (1) (2) (3) (4) (5)
blending of FAME/FAEE with conventional DF; use of additives—flow improvers; preparation of fatty esters with branched chains; preparation of esters with bulky substituents in the chain; winterization.
Blending of FAME with fossil DF is at present the preferred and most widely used method of improvement of low temperature properties of FAME. Fossil fuel in blended fuels acts at low temperatures as a solvent of precipitated crystals, which is reflected in improved low temperature characteristics of the fuel. Published data (Dunn and Bagby, 1995) indicate that blended fuels do not exhibit significantly inferior low temperature properties in comparison with neat fossil fuel up to the content of FAME 20 vol%. The attention is paid especially to CP and CFPP. The usual blending rates FAME : DF in the North America are 20 : 80, and in Europe were 30 : 70, respectively. At the ratio of 30 : 70, a significant reduction of emission in the faultlessly operating engine was achieved, accompanied by slight increase of consumption (2–5%) in comparison with neat DF. The advantage is preparation of the mixture by simple blending of the components. According to (Purcell et al., 1996) the properties of soybean oil-based FAME were as follows: cetane number (CN) 54.7, viscosity at 408C 3.05 mm2 s21, and CP 2 28C. The CN of DF was 43.2, the viscosity at 408C was 2.37 mm2 s21, and CP 2178C. The blend FAME : DF 30 : 70 had CN 49.1, viscosity at 408C was 2.84 mm2 s21. However, parameters of blended fuel can vary significantly according to the parameters of actual used DF which naturally are not constant. The output power of the blend was by about 4% lower than that of DF, while the output power of the neat ester was by about 9% lower. The emissions of CO and of polycondensed aromatic compounds (PAH) were significantly lower in comparison with DF, the NOx emissions were comparable. According to our measurements of low temperature properties of blended fuels containing 30% FAME from rapeseed oil, and 70% of diesel fuel of the class F (Slovnaft Bratislava), the CP, and CFPP of neat FAME were both 288C, while the CP and CFPP of fossil fuel were 2118C, and 2108C, respectively. The CP of the blended fuel was 298C, CFPP 2108C (Cvengrosˇ, 2000). The addition of biogenic component did not improve the low temperature properties, but it did not impair them either. A range of additives has been synthesised, which decrease CP, but especially PP. The choice includes the
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viscosity modifying polymers, e.g., inter-polymers containing carboxyls, copolymers styrene-malein anhydride, polymetacrylates, polyacrylates, copolymers ethylene-vinylacetate, polyoxyalkene compounds, and so on. These additives influence especially PP, CP in smaller extent. However, from the point of view of cold flow properties of the fuel, especially CP is important. Some additives improving the low temperature flow properties (PP-depressants) developed for fossil fuel are effective also for FAME-based alternative fuels. They are applied at low concentrations between 0.05 and 0.2 wt%. The flow improvers influence the saturation temperature at low temperature at which the nucleation of the respective component takes place neither in fossil fuel nor in FAME, but they influence the size and morphology of crystals, and the rate of their growth. The CP value is therefore altered only slightly, but the PP decreases significantly. These additives crystallise together with that component of the fuel, which is first to nucleate. The molecules of additives contain function groups, which prevent the crystal growth and agglomeration. This leads to formation of a large number of small compact needle-like particles, which form a porous filtration cake on the filter, and do not hinder the passage of the liquid phase through the filter (Dunn et al., 1996). In the case of blended fuels with flow improvers our measurements yielded interesting results. The CP of fossil fuel was 2118C, CFPP 2108C; the addition of 0.05% of the flow improver DF-4598 from the company LUBRIZOL decreased the CFPP to 2298C while the CP value did not change. The addition of the flow improver to FAME produced from rapeseed oil and with the CP and CFPP values of 288C, and 288C, respectively, resulted in no change. The addition of 0.05% of the additive LUBRIZOL DF-4598 to the blend of 30% of FAME and 70 vol% DF with the CP, and CFPP values of 2108C, and 2118C, respectively resulted in decrease of the CP and CFPP values of 2108C and 21278C, respectively (Cvengrosˇ, 2000). In another set of measurements (Bı´rova´ et al., 2003) with flow improvers of the company LUBOCONS Stupava, SR, the CFPP value of studied FAME from used fritting oils was þ18C. The CFPP of diesel fuel was 258C, and the CFPP of the blend of 31.8 vol% FAME, 67.5% DF, and 0.7% of LUBOFLOW 3101 was 2168C. The addition of 0.3% of LUBOFLOW 3111, the flow improver developed specially for the use with FAME from rapeseed oil, decreased the CFPP from the original value 2108C down to 2218C (Cvengrosˇ et al., 2004). Another possibility of influencing the low temperature properties of fatty esters is the synthesis, which builds a bulky substituent into the chain, on a double bond of an acyl, for example. A hypothesis exists that the bulky substituent disrupts the harmony during the solid phase formation, and the orientation in one direction. Similar effect is observed also with the use of secondary isopropyl- and isobutyl alcohols for the preparation of esters. According to Lee et al. (1995) the esters based on these alcohols and soybean oil-based FFA exhibit the onset temperatures from DSC (differential scanning calorimetry) measurements by 7–118C and 12–148C lower for isopropyland 2-butyl esters, respectively. Simultaneously, decreased values of CP and PP were recorded. However, due to economic reasons (higher price of isoalcohols), the possibilities in this respect are rather limited. Winterization removes by filtration the solid fraction formed by cooling of esters, and the liquid fraction of predominantly
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unsaturated compounds then exhibits lower CP and PP. Winterization removes especially saturated fatty esters with higher CN, and the CN of the residual blend decreases. The onset temperature of FAME made of soybean oil has been decreased this way from þ3.78C to 27.18C, but the yield was low (26%) (Lee et al., 1996). The used solvent has a marked influence on the process. The process is energetically demanding (cooling). However, in our geographical latitudes the natural cold in winter season can be utilized, the tanks with fuel can be stored outside, and the solid fraction can be used as the fuel in summer. The problem is low yield, around 33%, due to large occlusion of crystals with the liquid. Treatment of FAME with PP-depressants before winterisation decreases occlusion of crystals with the liquid phase, and thus the yield is increased. Our tests of FAME from used frying oils without modifications showed CFPP value of þ2 to 228C, and 268C after addition of 0.7% LUBOFLOW 3115F to the original FAME. The CFPP value equal to 288C was achieved after winterization of the original FAME at 258C with the recovery rate of 88%. The CFPP value after winterization and addition of LUBOFLOW 3115F was 2148C (Cvengrosˇ et al., 2004). The aim of the presented study is to evaluate the influence of the presence of branched chains of isoalcohols on flow properties of fatty esters at low temperatures. Both pure esters and esters blended with fossil fuel have been studied. Another aim of submitted paper is to obtain further information related to low-temperature properties of blended fuels with low content of FAME/FAEE to 10 vol% prepared from broad selection of natural triacylglycerols, especially from oils and fats with higher share of saturated fatty acids (stearic and palmitic acid).
MATERIALS AND METHODS For the measurements of cold flow properties of esters with branched alcohols we used ethyl esters of sunflower oil with increased amount of oleic acid, ethyl- and methyl esters of castor oil, and isopropyl esters, 2-butyl esters and 2-ethyl hexyl esters of technical-grade oleic acid. The share of acyls (acid profiles) of the respective sources of fatty acids are shown in the Table 1. The castor oil is characterized by dominant share (about 90%) of ricinoleic acid (12-hydroxy9-octadecenoic acid C18 : 1, OH). Esters of the technical oleic acid have been prepared in the standard way by acid catalysed esterification of the acid using a suitable alcohol. The esters based on sunflower and castor oil were prepared by alkali catalysed transesterification of the oil using methanol or ethanol (Cvengrosˇ and Povazˇanec, 1996). Raw esters were finally treated by
Table 1. Acid profile of used fatty acid sources for esters with branched alcohols (GLC, area %). Fatty acid sources
C14 C16 C18 : 0 C18 : 1 C18 : 2 C18 : 3 C20 : 0
High-oleic — sunflower oil Castor oil 1.0 Industrial oleic — acid
9.9 9.4 9.8
1.6 — 2.9
78.9
89.1 61.2
12-hydroxy-9-octadecenoic acid C18 : 1, OH.
15.6
0
—
— 23.0
— 2.2
0.5 1.0
Table 2. The fatty acid profile of studied vegetable oils and animal fats with higher acyl saturation (GLC, area %). Oil/fat
C14
C16
C18 : 0
C18 : 1
C18 : 2
Lard Beef tallow Palm oil Rapeseed oil Sunflower oil
1.5 5.7 1.0 0.1 0.1
31.2 37.4 44.8 5.4 7.1
16.5 13.2 4.4 1.5 4.2
42.0 39.5 38.9 63.4 25.4
6.6 3.9 10.6 21.5 63.1
C18 : 3
7.7
molecular distillation on a short-path evaporator (Cvengrosˇ, 1990). The transient diesel fuel without additives from Slovnaft Inc. Bratislava was used as the standard diesel fuel with the CFPP parameter of 288C. Parameters of used DF are also in Table 3. For the measurements of cold flow properties of esters with higher acyl saturation, we used FAME and FAEE prepared from sunflower, rapeseed and palm oil, from lard and beef tallow. The fatty acid profiles of used oils/fats are in Table 2. The esters were prepared by alkali-catalysed transesterification of relevant oils/fats with methanol or ethanol (Cvengrosˇ and Povazˇanec, 1996). The raw esters were then finally treated by molecular distillation. As standard diesel fuel was used transient diesel fuel without additives from Slovnaft a.s., Bratislava with CFPP 268C. Parameters of used DF are in Table 3. The fatty acid profile was determined by the GLC method. GLC analyses were carried out on a Hewlett-Packard 5890 series II chromatograph equipped with FID and glass column 1.4 m 3 mm I.D. packed with 10% diethylene glycol adipate on Chromatone NAW DMCS 0.125 – 0.16 mm. Nitrogen was used as the carrier gas at the flow rate of 30 ml min21. The oven temperature was held isothermally at 2008C, the injector and detector temperature was 230 and 2508C, respectively. The filterability CFPP was determined according to STN EN 116 on the equipment Walter Herzog MC 840 and Linetronic Oil-Lab 200.
RESULTS AND DISCUSSION Esters of Branched Alcohols The filterability values CFPP of neat esters and of their blends (5 and 10 vol%) with diesel fuel are shown in the Table 4. Table 4 shows also the CFPP value of the used reference fossil diesel fuel. The data shown in the Table 4 indicate that branching of the alcohol chain does not influence the filtration ability of pure esters significantly. For comparison, the CFPP values of FAME from rapeseed oil range between 29 and 2128C. The only exception are the 2-ethyl hexyl esters from the technical oleic acid, where notably low value of CFPP was achieved. Ethyl esters from sunflower oil have, in spite of high content of unsaturated oleic acid, relatively high CFPP. According to literature FAME from the classical sunflower oil have the CFPP value even higher, 228C (Peterson et al., 1987). The data on filterability of methyl- and ethyl esters of castor oil have not been published yet. Utilization of this natural product for fuel applications is the aim of focused effort in Brazil.
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COLD FLOW PROPERTIES OF FATTY ESTERS Table 3. Parameters of used DF.
Parameter Density at 158C, kg m23 Viscosity at 408C, mm2 s21 Sulphur content, mg kg21 Flash point, 8C Water content, mg kg21 Ash content, % m m21 Carbon residue, % m m21 Total contamination, mg kg21 Copper strip corrosion Oxidation stability, g m23 Cloud point, 8C CFPP, 8C Lubricity (wsd 1.4), mm Cetane number Distillation, 8C Initial boiling point (IBP) 10 % V/V 30 % V/V 50 % V/V 70 % V/V 90 % V/V 95 % V/V Final boiling point (FBP) Recovered at FBP, % V/V Total aromatics content, % m m21 monocyclic aromatics, % m m21 dicyclic aromatics, % m m21 tri- & more cyclic aromat., % m m21 Sum of PAH, % m m21
DF for the study of esters with higher acyl saturation
DF for the branched esters study
840.6 2.693 6.5 76 34.1 ,0.001 ,0.01 0.84
840.5 2.681 6.2 75 36.7 ,0.001 ,0.01 0.82
1a 0.5 26 26 596 49.9
1a 0.5 28 28 596 49.9
188.5 212.3 242.5 266.3 293.0 329.4 346.1 358.8 98.2
198.8 222.6 242.5 266.3 293.0 329.4 346.1 358.8 98.2 31.50
24.90
24.90
Esters with Higher Acyl Saturation
5.90
5.90
0.7
0.7
6.6
6.6
The values of filterability CFPP for pure esters and their blends with diesel fuel are shown in the Table 5. The CFPP value of the used reference diesel fuel is 268C. The CFPP values of neat esters in Table 5 evidently show dominant influence of the increased presence of saturated acyls on low-temperature properties of FAME and FAEE. Relatively high value of CFPP 228C for FAME from sunflower oil is, despite of its high degree un-saturation, in accordance with the literature (Peterson et al., 1987). In comparison with FAME, FAEE have higher CFPP, which is markedly higher for lipids with higher content of palmitic acid C16 : 0 (palm oil, beef tallow and lard) as well. Another part of the Table 5 summarizes the CFPP values for the blends of FAME and FAEE with the fossil diesel fuel (DF) for various content of esters in DF up to 10 vol%. In case of FAME and FAEE based on traditional vegetable oils like sunflower and rapeseed oil a slight depressant effect of addition of an ester up to the measured content of 10 vol% is observed for the CFPP of the blended fuel. For esters of the palm oil the concentration range is narrower,
Table 4. CFPP values of prepared fatty esters of branched alcohols. CFPP, 8C
Isopropyl esters of industrial oleic acid 2-butyl esters of industrial oleic acid 2-ethyl hexyl esters of industrial oleic acid Ethyl esters of high-oleic sunflower oil Methyl esters of castor oil Ethyl esters of castor oil Transient diesel fuel
esters can be their blending with conventional diesel fuel. The CFPP values of neat castor oil-based FAME/FAEE are relatively high. The presented data indicate that the attempts to decrease CFPP, and thus to improve low-temperature flow properties of fatty esters with the use of branched alcohols are not effective. Despite some optimistic data in literature (Foglia et al., 1997), both the presented results and the unpublished results of our previous measurements show that no significant decrease of the CFPP value of esters with branched alcohols could be achieved in comparison with FAME. Moreover, the economic reasons are also important: lower isoalcohols are notably more expensive than methanol. In the second part of the Table 4 the CFPP values of the blends of 5 and 10% of appropriate fatty esters with standard DF are shown. It is interesting that the addition of 10% of fatty esters practically does not influence the CFPP value of the blended fuel regardless to the origin and structure of the acyl or the alcohol chain. Tendency to utilize blended fuels with low ratio of biogenic component up to 5% (e.g., in Austria obligatory addition to the fossil fuel is 3% FAME) is supported also by the legislation; the presence of components up to 5% does not require further comments. At such low ratio FAME/ FAEEs their low-temperature properties practically do not influence the parameters of blended fuel. This way FAME/ FAEE from animal fats and from used frying oils with higher CFPP could be used.
31.50
Some of the properties of castor oil-based FAME/FAEE are not favourable The density of castor oil FAME (924.4 kg m23) and that of FAEE (914.3 kg m23) are higher than the limit of 900 kg m23 at 158C defined by the standard EN 14 214. The viscosity of castor oil FAME (13.34 mm2 s21) and that of FAEE (13.87 mm2 s21) at 408C are more than twice as high as the limit value of 5.00 mm2 s21. The possible solution to the problem of the high viscosity and density of the
Fatty esters
393
Neat esters
Esters þ DF 5 : 95
Esters þ DF 10 : 90
210
28
28
29
28
29
223
29
29
24
28
28
21 21 28
28 29 —
28 28 —
Table 5. Filterability CFPP for neat esters and their blends with diesel fuels CFPP of reference diesel fuel: 268C. Ester content, vol% FAME—sunflower oil FAEE—sunflower oil FAME—rapeseed oil FAEE—rapeseed oil FAME—beef tallow FAEE—beef tallow FAME—lard FAME—palm oil
Trans IChemE, Part B, Process Safety and Environmental Protection, 2007, 85(B5): 390 –395
100%
1%
3%
5%
10%
22 — 27 — þ12 þ14 þ12 þ14
26 27 27 27 210 27 29 27
27 27 28 27 26 þ1 29 26
27 27 29 28 þ3 þ7 27 27
27 28 28 28 þ9 þ13 — þ10
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KLEINOVA´ et al.
up to 5 vol% for FAME, and only up to 1 vol% for FAEE, apparently due to extremely high CFPP of pure palm oilbased esters. In case of animal fat-based esters the situation is from the point of view of CFPP more convenient for FAME, where the addition of FAME from lard decreases CFPP of the fossil DF up to the concentration of 5 vol%, and FAME from beef tallow does not aggravate CFPP of the basic fuel up to the content of 3 vol%. In case FAEE of these animal fats, the addition of esters increases CFPP of blended fuels even at low concentrations. The blend of FAEE from vegetable and animal sources, respectively, as a component of blended fuel with DF shows low-temperature characteristic as follows: The blend of 3 vol% of FAEE from beef tallow and 2% of FAEE from sunflower oil in DF has CFPP of 238C. The effect analogous to those known from phase equilibria of condensed systems is observed—the formation of eutectics, where the blended fuel has lower CFPP than its single components. For higher contents, which are not shown in the Table 5 and measured for FAME and FAEE from sunflower oil and for FAME from beef tallow up to 30 vol%, the CFPP values do not differ markedly from the values determined for 10 vol%. For esters, which show the tendency to increase CFPP already at low concentration in blended fuel, the measurement of CFPP at higher concentrations has no practical meaning. Of importance is also the selection of appropriate flow improvers at low temperatures, suitable for fossil fuel with small addition of FAME/FAEE. From the point of CFPP, FAME appear to be acceptable components of blended fuels with DF up to the content of 3–5 vol%, which even slightly improve the flow properties at low temperatures regardless of the origin of the initial triacylglycerols (TAG), i.e., regardless of the acyl profile and their saturation or un-saturation. We obtained similar result from the study of low-temperature properties of the DF blended fuels with esters based on isoalcohols (isopropyl-, 2-butyl-, 2-etylhexylalcohol), as mentioned above. Addition of fatty esters up to 10 vol% practically did not influence CFPP of the fossil component regardless of the structure of acyl and alkyl chain. This observation could provoke the activities focused on revision of the standard and related to evaluation of significance of the CFPP parameter for neat FAME, which are intended for use in blended fuels with fossil fuel. Considering this fact, CFPP of neat FAME themselves is not interesting, if the required CFPP can be achieved in the final blended fuel, especially with the use of appropriate flow improvers. However, the existing standard EN 590 requires all parameters defined in the standard EN 14 214 to be met also for FAME intended for blended fuels. But the experience has shown that FAME in such low concentration practically do not influence the low temperature properties of blended fuels. This way also FAME from animal fats, palm oil and from used deep-frying oils with high CFPP could find their use, although nowadays are, unfortunately, out of game. Both palm oil and animal fats represent great potential in the field of sources of natural TAG. It would be therefore useful to omit the obligatory parameter of CFPP in the standard EN 14 214 for FAME/FAEE intended for the use in blended fuels, with the addition that the parameter CFPP for blended diesel fuel according to EN 590 must be achieved. This important measure without negative effects on the quality of fuel would release renewable natural
sources of TAG with considerable capacity, which are at present inaccessible, decrease the dependence from fossil resources, enable to achieve more favourable ecologic impacts from the operation of engines (equilibrated CO2 balance, rapid decrease of PAH and solid particle emissions), ensure sufficient lubrication ability of fossil fuels and achieve many other positive effects (new jobs, utilization of set-aside land, and so on). Otherwise there will not be enough biocomponents, which meet all requirements of the standard, to achieve 5.75% ratio of liquid biofuels on the market in 2010 as one of the goals of EU. To achieve the required low-temperature parameters also for single components of blended fuels is the condition valid only in EU, in other parts of the world the standard is binding only for the resulting blended fuel. There exist other reasons for increased interest in blended fuels with low content of FAME/FAEE in DF. First of all, according to the valid standard, there exists no obligation to declare the presence of additive components in engine fuels up to the content of 5%. Also, it reflects the real situation with respect to availability and limitation of resources for production of FAME/FAEE. At least in the near future the biocomponent ratios in the blended fuels shall be not high from the capacity reasons. Finally the results (Walther, 2006; Ullmann et al., 2006) show lowered oxidation stabilities of the blends B20 (20 vol% FAME in DF), despite the fact, that the used FAME meet the standard EN 14 214 in all parameters. Blends of DF and 5% of FAME (B5) do not posses higher risk for deposit formation than DF alone, and coking of fuel injector nozzles does not occur.
CONCLUSIONS The influence of alcohol branching on the fuel filterability is negligible and was detected only in the case of 2-ethyl hexanol. Fossil fuel blending with fatty esters up to 10 vol% does not substantially change the cold flow properties of fossil fuel. FAME and with some limitation also FAEE, prepared on a basis of natural TAG with higher content of saturated fatty acids, at low contents up to 3–5 vol% in the blend with fossil fuels practically do not change low-temperature properties of the fossil fuel, despite the fact that they themselves have CFPP parameters over the limit defined by standard EN 14 214. The requirement of omission of the parameter CFPP for FAME/FAEE intended for the blended fuels and the requirement to meet only the standard EN 590 in the blended fuel is fully justified, and would bring a series of economic and ecologic advantages without negative effects on the quality of fuel.
REFERENCES Bı´rova´, A., Radovanovic´, D., Sˇimon, P. and Cvengrosˇ, J., 2003, Comparison of methyl esters low-temperature measurements with CFPP method, in Proc 41st Int Petroleum Conference, 6 –8 October, Bratislava, 10 pp. Cvengrosˇ, J., 1990, Laboratory molecular evaporators (in Slovak), Chem Prum, 40: 135–140. Cvengrosˇ, J., 2000, Low temperature properties of fuels based on fatty acid methyl esters (in Slovak), in Proc Conf “Demands to quality of motor fuel based on methyl esters of rapeseed oil”, TECHAGRO 2000, 5.4.2000, Brno, Czech Republic, 6 pp. Cvengrosˇ, J. and Povazˇanec, F., 1996, Production and treatment of rapeseed oil methyl esters as alternative fuels for diesel engines, Biores Technol, 55: 145–152.
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COLD FLOW PROPERTIES OF FATTY ESTERS Cvengrosˇ, J., Radovanovic´, D. and Mikulec, J., 2004, Oxidation stability and low-temperature properties of methyl esters based on used edible oils and fats, in Proc XII International Scientific Conference “Progress in Technology of Vegetable Fats”, 31 May–2 June, Piesˇˇtany, Slovak Republic, 7 pp. ISBN 83-9090617-1. Dunn, R.O. and Bagby, M.O., 1995, Low-temperature properties of triglyceride-based diesel fuels: transesterified methyl esters and petroleum middle distillate/ester blends, J Amer Oil Chem Soc, 72: 895–904. Dunn, R.O., Shockley, M.W. and Bagby, M.O., 1996, Improving the low-temperature properties of alternative diesel fuels: vegetable oil-derived methyl esters, J Am Oil Chem Soc, 73: 1719–1728. Foglia, T.A., Nelson, L.A., Dunn, R.O. and Marmer, W.N., 1997, Lowtemperature properties of alkyl esters of tallow and grease, J Amer Oil Chem Soc, 74: 951 –955. Lee, I., Johnson, L.A. and Hammond, E.G., 1995, Use of branchedchain esters to reduce the crystallization temperature of biodiesel, J Am Oil Chem Soc, 72: 1155– 1160. Lee, I., Johnson, L.A. and Hammond, E.G., 1996, Reducing the crystallization temperature of biodiesel by winterizing methyl soyate, J Am Oil Chem Soc, 73: 631– 636. Peterson, C.L., Korus, R.A., Mora, P.G. and Madsen, J.P., 1987, Fumigation with, propane and transesterification effects on injector coking with vegetable oils, Trans ASAE, 30: 28–35.
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Purcell, D.L., McClure, B.T., McDonald, J. and Basu, H.N., 1996, Transient testing of soy methyl ester fuels in an indirect injection, compression ignition engine, J Am Oil Chem Soc, 73: 381– 388. Ullmann, J., Dittus, B., Streeb, M. and Winter, J., 2006, Assessment of deposit formation by B5 at injection nozzles (in German), Proc Int Congress BBE/UFOP, 27–28 November, Berlin, Germany, 20 pp. Walther, D., 2006, Properties of the blends of FAME and diesel fuel— results (in German), Proc Int Congress BBE/UFOP, 27– 28 November, Berlin, Germany, 9 pp.
ACKNOWLEDGEMENT This work was supported by the Slovak Research and Development Agency under the contract No. APVV-20-037105. The manuscript was received 25 January 2007 and accepted for publication after revision 4 April 2007.
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Faculty of Chemical and Food Technology STU, Bratislava, Slovak Republic. ´ RUP, a.s., Vlcˇie hrdlo, Bratislava, Slovak Republic. Slovnaft VU
2
Abstract: This article is devoted to the study of cold flow properties of neat esters of branched chain alcohols with fatty acids and blends of these esters with fossil diesel fuel. According to determined CFPP values the influence of alcohol branching on the fuel filterability is negligible. Fossil fuel blending with fatty esters of branched alcohols up to 10 vol % does not substantially change the cold flow properties of fossil fuel. The low-temperature properties of fossil diesel and fatty acid methyl/ethyl ester (FAME/FAEE) blends with low ester content (up to 10 vol %), prepared mainly from oils/fats with higher share of saturated fatty acids namely palm oil, tallow and lard, were also measured. The obtained results show that studied esters do not change lowtemperature properties of fossil fuel in the blends with the low esters content of 3–5 vol %, although their own CFPP is over the value permissible by the standard EN 14 214. However, current standard EN 590 specifies to meet all parameters of the standard EN 14 214 also for FAME assigned for blended fuels entirely. The proposal to repeal the CFPP limit for esters assigned for blending is fully justified, without any negative effects on fuel quality. Keywords: methyl esters; ethyl esters; blended fuels; cold flow properties; cold filter plugging point; branched alcohols.
INTRODUCTION
Correspondence to: Dr J. Cvengrosˇ, Faculty of Chemical and Food Technology STU, Radlinske´ho 9, 812 37, Bratislava, Slovak Republic. E-mail: jan.cvengros@ stuba.sk
DOI: 10.1205/psep07009 0957–5820/07/ $30.00 þ 0.00 Process Safety and Environmental Protection Trans IChemE, Part B, September 2007 # 2007 Institution of Chemical Engineers
our geographical latitudes can be seriously limited by seasonal drop of external temperatures, especially in winter period. If the temperature drop is large enough to achieve the saturation temperature of any of the FAME/ FAEE components, these precipitate in the liquid mixture in the form of microscopic crystals, invisible by the naked eye. At further decrease of temperature the submicrometer crystals grow further; as soon as they achieve the size of about 0.5 mm, they become visible. This temperature is then denoted as the cloud point. With further decrease of temperature the saturation temperatures of other components are achieved, the crystals gradually grow until they achieve the dimensions of about 0.5–1 mm, and they start to coalesce into sizeable agglomerates. Gradually the whole system ceases to be liquid, which is referred to as the pour point. Agglomeration of crystals occluded by the liquid phase hinders the flow of fuel through the fuel pipe and blocks the fuel filter. Except of CP and PP, also other parameters are used in order to evaluate the low temperature properties of fuels, e.g., LTFT (Low Temperature Flow Test ASTM D4539) in the North America and CFPP (Cold Filter Plugging Point EN 116) in Europe. These values are more relevant than CP and PP regarding the applicability of fuels at lower temperatures. Some correlation between CP and CFPP was found (Dunn and Bagby, 1995). The filterability
Alkyl esters of higher fatty acids, especially methyl esters (FAME) and ethyl esters (FAEE) are at present considered as real alternative fuels for diesel engines. They are produced by transesterification of natural triacylglycerols—vegetable oils, but also animal fats—with methanol in the presence of alkali catalysts. The main advantage of this alternative fuel is that its properties are similar to those of fossil diesel fuel (DF). They are miscible with DF in any ratio, and they can be used in standard diesel engines without adjustment of the engine. The most pronounced advantages include favourable emission profile in comparison with standard fuel, the fact they originate from domestic renewable sources, they do not increase the amount of CO2 in the atmosphere, and so on. There are, however, also disadvantages in comparison with standard fossil fuels, especially limited resources for their production, three to five times higher production price and less favourable low temperature properties. The behaviour at low temperatures is one of the few research problems of FAME/ FAEE. Unlike DF, the esters have relatively high cloud point CP, and the pour point PP as well. While the CP and PP of diesel fuel are around 2158C and 2278C respectively, the respective values for FAME are about 15 –258C higher. The use of alkyl esters in
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COLD FLOW PROPERTIES OF FATTY ESTERS CFPP defines the lowest temperature at which at least 20 ml of fuel passes through a 45 mm mesh sieve filter with the diameter of 15 mm under defined conditions (time 1 min, vacuum 200 mm H2O). CFPP is defined by melting points of individual components of blended FAME/FAEE. The melting points are influenced by lengths of acyl chains, by the number of double bonds, by isomeric state of unsaturated groups, and by the location of double bonds. The melting point increases with increasing length of the acyl, and decreases with the number of double bonds at the same number of carbon atoms. Conjugated double bonds increase the melting point. Cis-isomers have lower melting points than the trans-isomers. Generally, the double bond represents a defect in the structure of tightly ordered layers, and therefore decreases the melting point. In order to overcome the problems with fatty esters at low temperatures, five solutions have been proposed: (1) (2) (3) (4) (5)
blending of FAME/FAEE with conventional DF; use of additives—flow improvers; preparation of fatty esters with branched chains; preparation of esters with bulky substituents in the chain; winterization.
Blending of FAME with fossil DF is at present the preferred and most widely used method of improvement of low temperature properties of FAME. Fossil fuel in blended fuels acts at low temperatures as a solvent of precipitated crystals, which is reflected in improved low temperature characteristics of the fuel. Published data (Dunn and Bagby, 1995) indicate that blended fuels do not exhibit significantly inferior low temperature properties in comparison with neat fossil fuel up to the content of FAME 20 vol%. The attention is paid especially to CP and CFPP. The usual blending rates FAME : DF in the North America are 20 : 80, and in Europe were 30 : 70, respectively. At the ratio of 30 : 70, a significant reduction of emission in the faultlessly operating engine was achieved, accompanied by slight increase of consumption (2–5%) in comparison with neat DF. The advantage is preparation of the mixture by simple blending of the components. According to (Purcell et al., 1996) the properties of soybean oil-based FAME were as follows: cetane number (CN) 54.7, viscosity at 408C 3.05 mm2 s21, and CP 2 28C. The CN of DF was 43.2, the viscosity at 408C was 2.37 mm2 s21, and CP 2178C. The blend FAME : DF 30 : 70 had CN 49.1, viscosity at 408C was 2.84 mm2 s21. However, parameters of blended fuel can vary significantly according to the parameters of actual used DF which naturally are not constant. The output power of the blend was by about 4% lower than that of DF, while the output power of the neat ester was by about 9% lower. The emissions of CO and of polycondensed aromatic compounds (PAH) were significantly lower in comparison with DF, the NOx emissions were comparable. According to our measurements of low temperature properties of blended fuels containing 30% FAME from rapeseed oil, and 70% of diesel fuel of the class F (Slovnaft Bratislava), the CP, and CFPP of neat FAME were both 288C, while the CP and CFPP of fossil fuel were 2118C, and 2108C, respectively. The CP of the blended fuel was 298C, CFPP 2108C (Cvengrosˇ, 2000). The addition of biogenic component did not improve the low temperature properties, but it did not impair them either. A range of additives has been synthesised, which decrease CP, but especially PP. The choice includes the
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viscosity modifying polymers, e.g., inter-polymers containing carboxyls, copolymers styrene-malein anhydride, polymetacrylates, polyacrylates, copolymers ethylene-vinylacetate, polyoxyalkene compounds, and so on. These additives influence especially PP, CP in smaller extent. However, from the point of view of cold flow properties of the fuel, especially CP is important. Some additives improving the low temperature flow properties (PP-depressants) developed for fossil fuel are effective also for FAME-based alternative fuels. They are applied at low concentrations between 0.05 and 0.2 wt%. The flow improvers influence the saturation temperature at low temperature at which the nucleation of the respective component takes place neither in fossil fuel nor in FAME, but they influence the size and morphology of crystals, and the rate of their growth. The CP value is therefore altered only slightly, but the PP decreases significantly. These additives crystallise together with that component of the fuel, which is first to nucleate. The molecules of additives contain function groups, which prevent the crystal growth and agglomeration. This leads to formation of a large number of small compact needle-like particles, which form a porous filtration cake on the filter, and do not hinder the passage of the liquid phase through the filter (Dunn et al., 1996). In the case of blended fuels with flow improvers our measurements yielded interesting results. The CP of fossil fuel was 2118C, CFPP 2108C; the addition of 0.05% of the flow improver DF-4598 from the company LUBRIZOL decreased the CFPP to 2298C while the CP value did not change. The addition of the flow improver to FAME produced from rapeseed oil and with the CP and CFPP values of 288C, and 288C, respectively, resulted in no change. The addition of 0.05% of the additive LUBRIZOL DF-4598 to the blend of 30% of FAME and 70 vol% DF with the CP, and CFPP values of 2108C, and 2118C, respectively resulted in decrease of the CP and CFPP values of 2108C and 21278C, respectively (Cvengrosˇ, 2000). In another set of measurements (Bı´rova´ et al., 2003) with flow improvers of the company LUBOCONS Stupava, SR, the CFPP value of studied FAME from used fritting oils was þ18C. The CFPP of diesel fuel was 258C, and the CFPP of the blend of 31.8 vol% FAME, 67.5% DF, and 0.7% of LUBOFLOW 3101 was 2168C. The addition of 0.3% of LUBOFLOW 3111, the flow improver developed specially for the use with FAME from rapeseed oil, decreased the CFPP from the original value 2108C down to 2218C (Cvengrosˇ et al., 2004). Another possibility of influencing the low temperature properties of fatty esters is the synthesis, which builds a bulky substituent into the chain, on a double bond of an acyl, for example. A hypothesis exists that the bulky substituent disrupts the harmony during the solid phase formation, and the orientation in one direction. Similar effect is observed also with the use of secondary isopropyl- and isobutyl alcohols for the preparation of esters. According to Lee et al. (1995) the esters based on these alcohols and soybean oil-based FFA exhibit the onset temperatures from DSC (differential scanning calorimetry) measurements by 7–118C and 12–148C lower for isopropyland 2-butyl esters, respectively. Simultaneously, decreased values of CP and PP were recorded. However, due to economic reasons (higher price of isoalcohols), the possibilities in this respect are rather limited. Winterization removes by filtration the solid fraction formed by cooling of esters, and the liquid fraction of predominantly
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unsaturated compounds then exhibits lower CP and PP. Winterization removes especially saturated fatty esters with higher CN, and the CN of the residual blend decreases. The onset temperature of FAME made of soybean oil has been decreased this way from þ3.78C to 27.18C, but the yield was low (26%) (Lee et al., 1996). The used solvent has a marked influence on the process. The process is energetically demanding (cooling). However, in our geographical latitudes the natural cold in winter season can be utilized, the tanks with fuel can be stored outside, and the solid fraction can be used as the fuel in summer. The problem is low yield, around 33%, due to large occlusion of crystals with the liquid. Treatment of FAME with PP-depressants before winterisation decreases occlusion of crystals with the liquid phase, and thus the yield is increased. Our tests of FAME from used frying oils without modifications showed CFPP value of þ2 to 228C, and 268C after addition of 0.7% LUBOFLOW 3115F to the original FAME. The CFPP value equal to 288C was achieved after winterization of the original FAME at 258C with the recovery rate of 88%. The CFPP value after winterization and addition of LUBOFLOW 3115F was 2148C (Cvengrosˇ et al., 2004). The aim of the presented study is to evaluate the influence of the presence of branched chains of isoalcohols on flow properties of fatty esters at low temperatures. Both pure esters and esters blended with fossil fuel have been studied. Another aim of submitted paper is to obtain further information related to low-temperature properties of blended fuels with low content of FAME/FAEE to 10 vol% prepared from broad selection of natural triacylglycerols, especially from oils and fats with higher share of saturated fatty acids (stearic and palmitic acid).
MATERIALS AND METHODS For the measurements of cold flow properties of esters with branched alcohols we used ethyl esters of sunflower oil with increased amount of oleic acid, ethyl- and methyl esters of castor oil, and isopropyl esters, 2-butyl esters and 2-ethyl hexyl esters of technical-grade oleic acid. The share of acyls (acid profiles) of the respective sources of fatty acids are shown in the Table 1. The castor oil is characterized by dominant share (about 90%) of ricinoleic acid (12-hydroxy9-octadecenoic acid C18 : 1, OH). Esters of the technical oleic acid have been prepared in the standard way by acid catalysed esterification of the acid using a suitable alcohol. The esters based on sunflower and castor oil were prepared by alkali catalysed transesterification of the oil using methanol or ethanol (Cvengrosˇ and Povazˇanec, 1996). Raw esters were finally treated by
Table 1. Acid profile of used fatty acid sources for esters with branched alcohols (GLC, area %). Fatty acid sources
C14 C16 C18 : 0 C18 : 1 C18 : 2 C18 : 3 C20 : 0
High-oleic — sunflower oil Castor oil 1.0 Industrial oleic — acid
9.9 9.4 9.8
1.6 — 2.9
78.9
89.1 61.2
12-hydroxy-9-octadecenoic acid C18 : 1, OH.
15.6
0
—
— 23.0
— 2.2
0.5 1.0
Table 2. The fatty acid profile of studied vegetable oils and animal fats with higher acyl saturation (GLC, area %). Oil/fat
C14
C16
C18 : 0
C18 : 1
C18 : 2
Lard Beef tallow Palm oil Rapeseed oil Sunflower oil
1.5 5.7 1.0 0.1 0.1
31.2 37.4 44.8 5.4 7.1
16.5 13.2 4.4 1.5 4.2
42.0 39.5 38.9 63.4 25.4
6.6 3.9 10.6 21.5 63.1
C18 : 3
7.7
molecular distillation on a short-path evaporator (Cvengrosˇ, 1990). The transient diesel fuel without additives from Slovnaft Inc. Bratislava was used as the standard diesel fuel with the CFPP parameter of 288C. Parameters of used DF are also in Table 3. For the measurements of cold flow properties of esters with higher acyl saturation, we used FAME and FAEE prepared from sunflower, rapeseed and palm oil, from lard and beef tallow. The fatty acid profiles of used oils/fats are in Table 2. The esters were prepared by alkali-catalysed transesterification of relevant oils/fats with methanol or ethanol (Cvengrosˇ and Povazˇanec, 1996). The raw esters were then finally treated by molecular distillation. As standard diesel fuel was used transient diesel fuel without additives from Slovnaft a.s., Bratislava with CFPP 268C. Parameters of used DF are in Table 3. The fatty acid profile was determined by the GLC method. GLC analyses were carried out on a Hewlett-Packard 5890 series II chromatograph equipped with FID and glass column 1.4 m 3 mm I.D. packed with 10% diethylene glycol adipate on Chromatone NAW DMCS 0.125 – 0.16 mm. Nitrogen was used as the carrier gas at the flow rate of 30 ml min21. The oven temperature was held isothermally at 2008C, the injector and detector temperature was 230 and 2508C, respectively. The filterability CFPP was determined according to STN EN 116 on the equipment Walter Herzog MC 840 and Linetronic Oil-Lab 200.
RESULTS AND DISCUSSION Esters of Branched Alcohols The filterability values CFPP of neat esters and of their blends (5 and 10 vol%) with diesel fuel are shown in the Table 4. Table 4 shows also the CFPP value of the used reference fossil diesel fuel. The data shown in the Table 4 indicate that branching of the alcohol chain does not influence the filtration ability of pure esters significantly. For comparison, the CFPP values of FAME from rapeseed oil range between 29 and 2128C. The only exception are the 2-ethyl hexyl esters from the technical oleic acid, where notably low value of CFPP was achieved. Ethyl esters from sunflower oil have, in spite of high content of unsaturated oleic acid, relatively high CFPP. According to literature FAME from the classical sunflower oil have the CFPP value even higher, 228C (Peterson et al., 1987). The data on filterability of methyl- and ethyl esters of castor oil have not been published yet. Utilization of this natural product for fuel applications is the aim of focused effort in Brazil.
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COLD FLOW PROPERTIES OF FATTY ESTERS Table 3. Parameters of used DF.
Parameter Density at 158C, kg m23 Viscosity at 408C, mm2 s21 Sulphur content, mg kg21 Flash point, 8C Water content, mg kg21 Ash content, % m m21 Carbon residue, % m m21 Total contamination, mg kg21 Copper strip corrosion Oxidation stability, g m23 Cloud point, 8C CFPP, 8C Lubricity (wsd 1.4), mm Cetane number Distillation, 8C Initial boiling point (IBP) 10 % V/V 30 % V/V 50 % V/V 70 % V/V 90 % V/V 95 % V/V Final boiling point (FBP) Recovered at FBP, % V/V Total aromatics content, % m m21 monocyclic aromatics, % m m21 dicyclic aromatics, % m m21 tri- & more cyclic aromat., % m m21 Sum of PAH, % m m21
DF for the study of esters with higher acyl saturation
DF for the branched esters study
840.6 2.693 6.5 76 34.1 ,0.001 ,0.01 0.84
840.5 2.681 6.2 75 36.7 ,0.001 ,0.01 0.82
1a 0.5 26 26 596 49.9
1a 0.5 28 28 596 49.9
188.5 212.3 242.5 266.3 293.0 329.4 346.1 358.8 98.2
198.8 222.6 242.5 266.3 293.0 329.4 346.1 358.8 98.2 31.50
24.90
24.90
Esters with Higher Acyl Saturation
5.90
5.90
0.7
0.7
6.6
6.6
The values of filterability CFPP for pure esters and their blends with diesel fuel are shown in the Table 5. The CFPP value of the used reference diesel fuel is 268C. The CFPP values of neat esters in Table 5 evidently show dominant influence of the increased presence of saturated acyls on low-temperature properties of FAME and FAEE. Relatively high value of CFPP 228C for FAME from sunflower oil is, despite of its high degree un-saturation, in accordance with the literature (Peterson et al., 1987). In comparison with FAME, FAEE have higher CFPP, which is markedly higher for lipids with higher content of palmitic acid C16 : 0 (palm oil, beef tallow and lard) as well. Another part of the Table 5 summarizes the CFPP values for the blends of FAME and FAEE with the fossil diesel fuel (DF) for various content of esters in DF up to 10 vol%. In case of FAME and FAEE based on traditional vegetable oils like sunflower and rapeseed oil a slight depressant effect of addition of an ester up to the measured content of 10 vol% is observed for the CFPP of the blended fuel. For esters of the palm oil the concentration range is narrower,
Table 4. CFPP values of prepared fatty esters of branched alcohols. CFPP, 8C
Isopropyl esters of industrial oleic acid 2-butyl esters of industrial oleic acid 2-ethyl hexyl esters of industrial oleic acid Ethyl esters of high-oleic sunflower oil Methyl esters of castor oil Ethyl esters of castor oil Transient diesel fuel
esters can be their blending with conventional diesel fuel. The CFPP values of neat castor oil-based FAME/FAEE are relatively high. The presented data indicate that the attempts to decrease CFPP, and thus to improve low-temperature flow properties of fatty esters with the use of branched alcohols are not effective. Despite some optimistic data in literature (Foglia et al., 1997), both the presented results and the unpublished results of our previous measurements show that no significant decrease of the CFPP value of esters with branched alcohols could be achieved in comparison with FAME. Moreover, the economic reasons are also important: lower isoalcohols are notably more expensive than methanol. In the second part of the Table 4 the CFPP values of the blends of 5 and 10% of appropriate fatty esters with standard DF are shown. It is interesting that the addition of 10% of fatty esters practically does not influence the CFPP value of the blended fuel regardless to the origin and structure of the acyl or the alcohol chain. Tendency to utilize blended fuels with low ratio of biogenic component up to 5% (e.g., in Austria obligatory addition to the fossil fuel is 3% FAME) is supported also by the legislation; the presence of components up to 5% does not require further comments. At such low ratio FAME/ FAEEs their low-temperature properties practically do not influence the parameters of blended fuel. This way FAME/ FAEE from animal fats and from used frying oils with higher CFPP could be used.
31.50
Some of the properties of castor oil-based FAME/FAEE are not favourable The density of castor oil FAME (924.4 kg m23) and that of FAEE (914.3 kg m23) are higher than the limit of 900 kg m23 at 158C defined by the standard EN 14 214. The viscosity of castor oil FAME (13.34 mm2 s21) and that of FAEE (13.87 mm2 s21) at 408C are more than twice as high as the limit value of 5.00 mm2 s21. The possible solution to the problem of the high viscosity and density of the
Fatty esters
393
Neat esters
Esters þ DF 5 : 95
Esters þ DF 10 : 90
210
28
28
29
28
29
223
29
29
24
28
28
21 21 28
28 29 —
28 28 —
Table 5. Filterability CFPP for neat esters and their blends with diesel fuels CFPP of reference diesel fuel: 268C. Ester content, vol% FAME—sunflower oil FAEE—sunflower oil FAME—rapeseed oil FAEE—rapeseed oil FAME—beef tallow FAEE—beef tallow FAME—lard FAME—palm oil
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100%
1%
3%
5%
10%
22 — 27 — þ12 þ14 þ12 þ14
26 27 27 27 210 27 29 27
27 27 28 27 26 þ1 29 26
27 27 29 28 þ3 þ7 27 27
27 28 28 28 þ9 þ13 — þ10
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KLEINOVA´ et al.
up to 5 vol% for FAME, and only up to 1 vol% for FAEE, apparently due to extremely high CFPP of pure palm oilbased esters. In case of animal fat-based esters the situation is from the point of view of CFPP more convenient for FAME, where the addition of FAME from lard decreases CFPP of the fossil DF up to the concentration of 5 vol%, and FAME from beef tallow does not aggravate CFPP of the basic fuel up to the content of 3 vol%. In case FAEE of these animal fats, the addition of esters increases CFPP of blended fuels even at low concentrations. The blend of FAEE from vegetable and animal sources, respectively, as a component of blended fuel with DF shows low-temperature characteristic as follows: The blend of 3 vol% of FAEE from beef tallow and 2% of FAEE from sunflower oil in DF has CFPP of 238C. The effect analogous to those known from phase equilibria of condensed systems is observed—the formation of eutectics, where the blended fuel has lower CFPP than its single components. For higher contents, which are not shown in the Table 5 and measured for FAME and FAEE from sunflower oil and for FAME from beef tallow up to 30 vol%, the CFPP values do not differ markedly from the values determined for 10 vol%. For esters, which show the tendency to increase CFPP already at low concentration in blended fuel, the measurement of CFPP at higher concentrations has no practical meaning. Of importance is also the selection of appropriate flow improvers at low temperatures, suitable for fossil fuel with small addition of FAME/FAEE. From the point of CFPP, FAME appear to be acceptable components of blended fuels with DF up to the content of 3–5 vol%, which even slightly improve the flow properties at low temperatures regardless of the origin of the initial triacylglycerols (TAG), i.e., regardless of the acyl profile and their saturation or un-saturation. We obtained similar result from the study of low-temperature properties of the DF blended fuels with esters based on isoalcohols (isopropyl-, 2-butyl-, 2-etylhexylalcohol), as mentioned above. Addition of fatty esters up to 10 vol% practically did not influence CFPP of the fossil component regardless of the structure of acyl and alkyl chain. This observation could provoke the activities focused on revision of the standard and related to evaluation of significance of the CFPP parameter for neat FAME, which are intended for use in blended fuels with fossil fuel. Considering this fact, CFPP of neat FAME themselves is not interesting, if the required CFPP can be achieved in the final blended fuel, especially with the use of appropriate flow improvers. However, the existing standard EN 590 requires all parameters defined in the standard EN 14 214 to be met also for FAME intended for blended fuels. But the experience has shown that FAME in such low concentration practically do not influence the low temperature properties of blended fuels. This way also FAME from animal fats, palm oil and from used deep-frying oils with high CFPP could find their use, although nowadays are, unfortunately, out of game. Both palm oil and animal fats represent great potential in the field of sources of natural TAG. It would be therefore useful to omit the obligatory parameter of CFPP in the standard EN 14 214 for FAME/FAEE intended for the use in blended fuels, with the addition that the parameter CFPP for blended diesel fuel according to EN 590 must be achieved. This important measure without negative effects on the quality of fuel would release renewable natural
sources of TAG with considerable capacity, which are at present inaccessible, decrease the dependence from fossil resources, enable to achieve more favourable ecologic impacts from the operation of engines (equilibrated CO2 balance, rapid decrease of PAH and solid particle emissions), ensure sufficient lubrication ability of fossil fuels and achieve many other positive effects (new jobs, utilization of set-aside land, and so on). Otherwise there will not be enough biocomponents, which meet all requirements of the standard, to achieve 5.75% ratio of liquid biofuels on the market in 2010 as one of the goals of EU. To achieve the required low-temperature parameters also for single components of blended fuels is the condition valid only in EU, in other parts of the world the standard is binding only for the resulting blended fuel. There exist other reasons for increased interest in blended fuels with low content of FAME/FAEE in DF. First of all, according to the valid standard, there exists no obligation to declare the presence of additive components in engine fuels up to the content of 5%. Also, it reflects the real situation with respect to availability and limitation of resources for production of FAME/FAEE. At least in the near future the biocomponent ratios in the blended fuels shall be not high from the capacity reasons. Finally the results (Walther, 2006; Ullmann et al., 2006) show lowered oxidation stabilities of the blends B20 (20 vol% FAME in DF), despite the fact, that the used FAME meet the standard EN 14 214 in all parameters. Blends of DF and 5% of FAME (B5) do not posses higher risk for deposit formation than DF alone, and coking of fuel injector nozzles does not occur.
CONCLUSIONS The influence of alcohol branching on the fuel filterability is negligible and was detected only in the case of 2-ethyl hexanol. Fossil fuel blending with fatty esters up to 10 vol% does not substantially change the cold flow properties of fossil fuel. FAME and with some limitation also FAEE, prepared on a basis of natural TAG with higher content of saturated fatty acids, at low contents up to 3–5 vol% in the blend with fossil fuels practically do not change low-temperature properties of the fossil fuel, despite the fact that they themselves have CFPP parameters over the limit defined by standard EN 14 214. The requirement of omission of the parameter CFPP for FAME/FAEE intended for the blended fuels and the requirement to meet only the standard EN 590 in the blended fuel is fully justified, and would bring a series of economic and ecologic advantages without negative effects on the quality of fuel.
REFERENCES Bı´rova´, A., Radovanovic´, D., Sˇimon, P. and Cvengrosˇ, J., 2003, Comparison of methyl esters low-temperature measurements with CFPP method, in Proc 41st Int Petroleum Conference, 6 –8 October, Bratislava, 10 pp. Cvengrosˇ, J., 1990, Laboratory molecular evaporators (in Slovak), Chem Prum, 40: 135–140. Cvengrosˇ, J., 2000, Low temperature properties of fuels based on fatty acid methyl esters (in Slovak), in Proc Conf “Demands to quality of motor fuel based on methyl esters of rapeseed oil”, TECHAGRO 2000, 5.4.2000, Brno, Czech Republic, 6 pp. Cvengrosˇ, J. and Povazˇanec, F., 1996, Production and treatment of rapeseed oil methyl esters as alternative fuels for diesel engines, Biores Technol, 55: 145–152.
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COLD FLOW PROPERTIES OF FATTY ESTERS Cvengrosˇ, J., Radovanovic´, D. and Mikulec, J., 2004, Oxidation stability and low-temperature properties of methyl esters based on used edible oils and fats, in Proc XII International Scientific Conference “Progress in Technology of Vegetable Fats”, 31 May–2 June, Piesˇˇtany, Slovak Republic, 7 pp. ISBN 83-9090617-1. Dunn, R.O. and Bagby, M.O., 1995, Low-temperature properties of triglyceride-based diesel fuels: transesterified methyl esters and petroleum middle distillate/ester blends, J Amer Oil Chem Soc, 72: 895–904. Dunn, R.O., Shockley, M.W. and Bagby, M.O., 1996, Improving the low-temperature properties of alternative diesel fuels: vegetable oil-derived methyl esters, J Am Oil Chem Soc, 73: 1719–1728. Foglia, T.A., Nelson, L.A., Dunn, R.O. and Marmer, W.N., 1997, Lowtemperature properties of alkyl esters of tallow and grease, J Amer Oil Chem Soc, 74: 951 –955. Lee, I., Johnson, L.A. and Hammond, E.G., 1995, Use of branchedchain esters to reduce the crystallization temperature of biodiesel, J Am Oil Chem Soc, 72: 1155– 1160. Lee, I., Johnson, L.A. and Hammond, E.G., 1996, Reducing the crystallization temperature of biodiesel by winterizing methyl soyate, J Am Oil Chem Soc, 73: 631– 636. Peterson, C.L., Korus, R.A., Mora, P.G. and Madsen, J.P., 1987, Fumigation with, propane and transesterification effects on injector coking with vegetable oils, Trans ASAE, 30: 28–35.
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Purcell, D.L., McClure, B.T., McDonald, J. and Basu, H.N., 1996, Transient testing of soy methyl ester fuels in an indirect injection, compression ignition engine, J Am Oil Chem Soc, 73: 381– 388. Ullmann, J., Dittus, B., Streeb, M. and Winter, J., 2006, Assessment of deposit formation by B5 at injection nozzles (in German), Proc Int Congress BBE/UFOP, 27–28 November, Berlin, Germany, 20 pp. Walther, D., 2006, Properties of the blends of FAME and diesel fuel— results (in German), Proc Int Congress BBE/UFOP, 27– 28 November, Berlin, Germany, 9 pp.
ACKNOWLEDGEMENT This work was supported by the Slovak Research and Development Agency under the contract No. APVV-20-037105. The manuscript was received 25 January 2007 and accepted for publication after revision 4 April 2007.
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