Influence of soybean biodiesel content on basic properties of biodiesel–diesel blends
R.A. Candeia
a,*, M.C.D. Silva
b, J.R. Carvalho Filho
a, M.G.A. Brasilino
a, T.C. Bicudo
a, I.M.G. Santos
a,
A.G. Souza
a aLaboratório de Combustíveis e Materiais, Departamento de Química, Centro de Ciências Exatas e da Natureza, Universidade Federal da Paraíba, Campus I, 58038-640 João Pessoa, PB, Brazil
b
Centro de Formação de Professores, Universidade Federal de Campina Grande, Campus de Cajazeiras, Cajazeiras, PB, Brazil
a r t i c l e
i n f o
Article history: Received 31 July 2007
Received in revised form 24 September 2008
Accepted 7 October 2008 Available online 6 November 2008 Keywords:
Soybean biodiesel Blends
Absolute viscosity
a b s t r a c t
The world tendency in last years is to restrict the use of fossil fuels and replace them partially or totally by renewable fuels. Accordingly, biodiesel is being studied as one of the main alternatives and the produc-tion and consumpproduc-tion of this pure biofuel and its binary blends with fossil diesel have been markedly grown. Thus, the present work evaluated the influence of biodiesel concentration on such blends when mixed to diesel in 5, 15, 25 and 50 volume percentages. For each blend, both methanol and ethanol bio-diesels were investigated. The biodiesel samples were physicochemically characterized. Their rheological behavior was analyzed. It was observed that the biodiesel enrichment leads to an acceptable increase in the viscosity and to a decrease in the volatilization of the binary blends. The viscosity was also shown to be temperature-dependent, as well as the fatty acids chain length and unsaturation.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
The scientific community has been investigating new types of renewable energy sources, mainly due to the greenhouse effect brought about by the growing usage of fossil energies. Alternatives to petroleum-derived fuels, such as biodiesel and ethanol, have the potential to satisfy the increasing energy demand, without
ad-versely affecting the environment[1,2]. In particular, biodiesel is
currently the most widely accepted alternative fuel for diesel en-gines, due to its technical, environmental and strategic advantages. Compared to fossil diesel, it has improved lubricity, lower toxicity,
higher flash point, and biodegradability[3].
Moreover, since biodiesel is oxygenated its combustion is more complete and produces fewer harmful emissions and pollutants. It
significantly reduces emissions such as CO2, particulate matter, CO,
SOx, volatile organic compounds, and unburned hydrocarbons, in
addition to its enhanced biodegradability, reduced toxicity and im-proved lubricity in comparison to conventional diesel fuel.
How-ever, biodiesel has portended to increase nitrogen oxides (NOx)
emissions[4,5]. Besides, the biodiesel produced from any vegetable
oil or animal fat generally has higher density, viscosity, cloud point and cetane number, and lower volatility and heating value
com-pared to diesel[4].
As biodiesel is completely miscible with diesel, the blending of both fuels in any proportion is possible and recommended in order to improve its qualities. However, the differences in chemical
nat-ure of biodiesel and diesel may cause differences in the physico-chemical properties, affecting engine performance and pollutant
emissions[4,5]. So, the quality control of biodiesel blends should
be monitored in several aspects.
Biodiesel–diesel blends have been widely studied and there are
several papers on this issue[3–9]. In a recent work, thermal and
rheological behaviors of diesel and methanol biodiesel blends were evaluated and the blends were shown to present similar stability to
that of pure diesel[6]. From the basic properties (density, heating
value, distillation curve, cloud point, cetane index, viscosity) of several palm oil biodiesel–diesel blends experimentally measured,
Benjumea et al. [4] evaluated mixing rules for predicting these
properties, as a function of biodiesel concentration in the blend,
and demonstrated their suitability[4].
Joshi and Pegg[8]investigated the flow properties of ethanol
fish biodiesel/diesel fuel blends (B80, B60, B40 and B20) at low
temperatures[8]. Their results were in accordance with the values
obtained for cloud and pour points, and also with the predicted vis-cosities obtained by Arrhenius equation as a function of tempera-ture and they developed an empirical equation for calculating the dynamic viscosities of these blends as a function of both tempera-ture and biodiesel content. Fuel properties and precipitate forma-tion in biodiesel blends at low temperature were also analyzed
by Tang et al.[3]. They demonstrated that the formation of
precip-itate during cold temperature storage depended on the feedstock
and blend concentration[3].
A relevant advantage of the blends is the minimization of nox-ious effects on the operation of injection systems caused by the rel-atively high biodiesel viscosity. The viscosity depends on the fatty 0016-2361/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.fuel.2008.10.015
*Corresponding author. Tel./fax: +55 83 3216 7441. E-mail address:[email protected](R.A. Candeia).
Contents lists available atScienceDirect
Fuel
acid composition of the parent oil, as well as on the extent of oxi-dation and polymerization of the biodiesel, what enables kinematic viscosity for the monitoring of the fuel quality during storage. Vis-cosity usually increases with the increasing chain length and de-creases with the increasing unsaturation. Moreover, viscosity quickly increases as the temperature decreases, and biodiesel and its blends demonstrate a temperature-dependent behavior similar
to diesel, despite the fact that the viscosity is higher[10,11].
In the literature, there are methods for predicting the biodiesel
viscosities[8,10,12]. It was identified that the viscosity, which is
the most significant property to affect the biodiesel as a fuel, re-duces with the increase in unsaturation and it is also affected by small amounts of glycerides. Moreover, the viscosities of saturated
ethyl esters (C8–C18) were slightly higher than those for the
corre-spondent methyl esters[10].
Therefore, the quality control of biodiesel is greatly important to the successful commercialization of this fuel and its blends. At this point, it is worth to note that the type (chemical functions, de-gree of unsaturation and chain length) and concentration of fatty acid esters as well as the structure of the ester moiety derived from the alcohol have an outstanding effect on the biodiesel properties, which will also influence the storage and oxidation. In this context, it is important to know the basic properties of biodiesel–diesel blends in order to verify if the fuel meets the standard specifica-tions. Thus, this work aimed at investigating the effect of the bio-diesel concentration of binary blends (B5, B15, B25, and B50) of methanol and ethanol soybean biodiesel with diesel fuel on the physicochemical and rheological properties.
2. Methods
2.1. Sample preparation
The biodiesel samples were obtained by alkali-catalyzed (KOH) transesterification of soybean oil, using the methanol (FAME - fatty acid methyl ester) and ethanol (FAEE – fatty acid ethyl ester) routes
[13,14]. The blends were prepared in the following proportions: 5% (B5), 15% (B15), 25% (B25) and 50% (B50) (v/v). The methyl and ethyl esters compositions were determined by gas chromatogra-phy with FID detector (GC-FID).
2.2. Physicochemical characterization
The physicochemical analyses were carried out according to the standards, as follows: kinematic viscosity at 40 °C (ASTM D445), distillation (ASTM D86), sulfur content (ASTM D4294), specific mass at 20 °C (ASTM D4052), cetane index (ASTM D4737) and flash point (ASTM D93).
2.3. Rheology
The rheological behavior was tested by means of the absolute viscosity determined in a Brookfield rheometer LV-DVII model, at 25 °C using a spindle 18 and coupled to a temperature controller. The measurements were taken at different shear rates.
3. Results and discussion
3.1. Physicochemical characterization
The composition of soybean biodiesel was determined and
re-vealed an elevated content of unsaturated fatty acids (Table 1).
The high degree of triacylglycerides conversion into methyl and ethyl esters through the transesterification process was evaluated by gas chromatography and revealed that soybean biodiesel
is mainly constituted by oleic (25%) and linoleic (53%) fatty acids.
The physicochemical characteristics of soybean FAME and FAEE
are compared inTable 2, where it is observed that the properties of
biodiesel (mainly the ethanol biodiesel) are relatively close to that of fossil diesel. The acid numbers of both samples meet the stan-dard limit, indicating that the free fatty acid content will not cause operational problems, such as corrosion and pump plugging, caused by corrosion and deposit formation. The cold filter plugging point (CFPP) of FAME and FAEE are drastically different, with the latter higher than the former, but still within the limits. CFPP of FAME ( 5 °C) is close to that of diesel ( 6 °C) and to that reported
in the literature for soybean methanol biodiesel ( 3 °C) [3], and
indicates that this biofuel can be used in any climate without flow problems at low temperature. Nevertheless, the usage of FAEE as a neat fuel or in rich biodiesel blends in cold climates or in the win-ter season has to be careful. The performance of soybean biodiesel at low temperatures is better than that of palm and cotton seed
methanol biofuels[3,4].
The amount of total sulfur in motor fuels was determined by ASTM D4294. The sulfur contents in B100 FAME and FAEE were ob-served to be smaller than the standard specification, what is one of the major advantages of biodiesel. Low sulfur has advantages both for the environment and the engine life. As expected, the sulfur
content of FAME and FAEE blends (Table 3) decreased as the
bio-diesel concentration in the blend increased from B5 to B50. The distillation results indicated that the boiling points of the ethyl esters were higher than those for the corresponding methyl esters, as the ethyl esters display higher molecular weights. Increasing the biodiesel concentration in the blends, the difference between the final and the initial boiling point (IBP) is reduced. Such tendency is more pronounced for FAEE-diesel blends. According to
Benjumea et al.[4]biodiesel is denser and slightly more viscous
than diesel, also presenting a narrower boiling interval, what indi-cates that the fatty acids have similar boiling points, as compared to the wide variety of hydrocarbons composing the diesel, with
dif-ferent volatilities [4,15]. In contrast, the final boiling point (FBP)
was lower in the biodiesel than in diesel, probably because the double bond of unsaturated esters could be polymerized at high temperatures, leading to the formation of gums and carbon residue
[15].
Fig. 1shows the distillation curves for pure (B100) and B5, B15, B25 and B50 blends. As can be seen, all curves tend to intercept at a point, corresponding to approximately 80% of distilled percentage. Before the interception point, distillation temperature increases strongly with distilled percentage, while after this point the trend is slighter. It is observed that the behavior of distillation tempera-tures of FAME blends are closer to that of diesel, meanwhile for FAEE blends the temperatures tend to the B100 behavior. Similar
results are found in literature for palm oil biodiesel [4]. Boiling
points much higher than the limits can be caused by free glycerin from incomplete separation of the ester and glycerol products after Table 1
Fatty acid chromatographic profile from ethanol and methanol soybean biodiesel.
FA FAME (%) FAEE (%) C 14:0 0.08 0.09 C 16:0 13.32 16.08 C 18:0 4.81 5.82 C 20:0 0.42 0.52 C 22:0 0.52 0.67 C 16:1 (9) 0.07 0.10 C 18:1 (9) 24.54 25.46 C 18:2 (9,12) 55.40 50.10 C 18:3 (9,12,15) 0.12 0.18 Others 0.74 0.99
the transesterification reaction[3]. So, the present results can be used to suggest the successful triacylglyceride conversion of the biodiesel samples.
The flash point of biodiesel is the temperature at which the fuel becomes a mixture that will ignite when exposed to a spark or flame, and it is related to the amount of methanol. Flash point is one of the main properties that could be associated with biodiesel composition. This parameter is then related to the amount of
unconverted triacylglycerides or a low content of mono-alkyl es-ters. It is known that high flash point ensures more safety in the handling and storage and ASTM D93 establishes a minimum of 130 °C for B100. Flash point values from soybean FAME (168 °C)
and FAEE (170 °C) were higher than that of diesel (53 °C) (Table
2). Since biodiesel has higher flash point than diesel, it is a safer
fuel than fossil diesel. As expected, the higher the proportion of
biodiesel in the blend, the higher is the flash point (Fig. 2a) and this
Table 2
Physicochemical properties of methyl and ethyl esters.
Parameter FAME FAEE Diesel ASTM limits
Acid number (mg KOH g 1
) 0.45 0.50 – 0.50 max Kinematic viscosity at 40 °C (mm2 s 1 ) 5.75 5.83 3.06 1.9–6.0 Specific mass at 20 °C (kg m3) 882.8 878.4 843.6 – Distillation (°C)
Initial boiling point 327 335 185.3 360 °C max
50% Fuel recovery 334 341 288.7
85% Fuel recovery 340 348 355.2
Final boiling point 352 362 374.2
Flash point (°C) 168 170 53 130 °C min
Total sulfur (%) 0.00 0.00 50.9 0.05% max (w/w)
Cetane index 56 60 0.274 47 min
Cold filter plugging point (°C) 5 10 6* 19
*For diesel fuel no. 2.
Table 3
Physicochemical characterization of FAME/diesel and FAEE/diesel blends.
Parameter Diesel B5 B15 B25 B50 FAME Kinematic viscosity at 40 °C (mm2 s 1 ) 3.06 4.45 4.50 4.64 4.75 Specific mass at 20 °C (kg m3) 843.6 845 849.5 853.6 862.9 Distillation (°C)
Initial boiling point 185.3 181.6 182.6 188.7 190
50% Fuel recovery 288.7 291.1 299 307 319
85% Fuel recovery 355.2 353.3 350.6 348.5 343
Final boiling point 374.2 357.9 361.8 366.1 368
Flash point (°C) 53 57 59 61 73 Cetane index 50.9 51.5 52.2 52.3 52.9 Total sulfur (%) 0.274 0.220 0.175 0.111 0.035 FAEE Kinematic viscosity at 40 °C (mm2 s 1 ) 3.06 4.51 4.65 4.75 5.13 Specific mass at 20 °C (kg/m3 ) 843.6 845.3 848.6 852.0 860.6 Distillation (°C)
Initial boiling point 185.3 215.9 222.1 227.3 233
50% Fuel recovery 288.7 295.3 306.2 315.4 339 85% Fuel recovery 355.2 352.7 351.6 349.7 347 End point 374.2 364.4 360.7 356.6 352 Flash point (°C) 53 57 59 61 73 Cetane index 50.9 53.5 54.1 54.3 54.7 Total sulfur (%) 0.274 0.199 0.176 0.117 0.093 0 20 40 60 80 100 150 200 250 300 350 400
T (
oC)
Distilled percentage
Diesel B5 B15 B25 B50 B100 0 20 40 60 80 100 150 200 250 300 350 400T (
oC)
Distilled percentage
Diesel B5 B15 B25 B50 B100is in agreement with the tendency of increasing the initial boiling point with the biodiesel concentration, which is also more evident for FAME. It may be noticed that the presence of fossil diesel
dras-tically decreases the flash point of the blends (Table 3), up to B50
[10].
The flash point and IBP are parameters of practical importance, once the higher the flash point, for instance, the higher is the safety during handling, transportation, and storage. Residual alcohol in the biodiesel causes a diminution in the flash point and then its va-lue can be used to monitor the purity of the biofuel. The IBP, for its time, can also indicate the purity of the biodiesel sample, since the presence of compounds such as glycerin (resulting from incom-plete separation of the ester and glycerol products after the transe-sterification reaction) and/or solvents (coming from possible adulterations) may alter the IBP and even the boiling point range. Glycerides have much higher boiling point than biodiesel or con-ventional diesel fuel and can lead to carbon deposits in the engine and durability problems.
The cetane index is a basic property of diesel and biodiesel, determined by the standard ASTM D613, and defined as a measure-ment of the ignition performance of a fuel. This parameter is influ-enced by structural features of fatty acid alkyl esters, such as chain length, degree of unsaturation and branching of the chain. It should be emphasized that the higher the cetane index, the better will be the combustion, improving the engine motor efficiency. Usually, the cetane number increases, with the increasing chain length and decreases with the increasing unsaturation. Residual methanol in biodiesel is responsible for a decrease in the cetane number decreasing of the fuel. For biodiesel, the cetane number displays
a minimum value of 47. FromTable 2, the cetane indices of FAME
and FAEE (56 and 60, respectively) are both higher than that of the diesel sample (50.9), indicating higher ignition than the fossil die-sel. Data from the literature showed a variation from 48 to 56 of cetane number for soybean FAME, values close to that reported
for a canola methanol biodiesel[16].
An increase in the cetane index was observed with the biodiesel
enrichment in the blends (Table 3). The results showed that from
B5 to B50, the cetane index slightly increased with the biodiesel concentration, and that FAEE samples displayed higher indices
than the FAME samples (Fig. 2b), possibly explained by the
addi-tional CH2moiety of the ethanol biodiesel. According to the
litera-ture[17], the average biodiesel cetane index is about 60, whereas
for the fossil diesel it is around 42. It should be emphasized that the higher the cetane index, the better will be the combustion, improving the engine motor efficiency. Biodiesel contains 10–11% oxygen by weight, what can lead to a more complete combustion than hydrocarbon-based diesel in an engine and high cetane num-ber reduces ignition delay of the fuel.
Viscosity is an important property of any fuel as it is an indica-tion of the ability of a material to flow. This parameter is also use-ful for evaluating the methyl and ethyl ester contents of biodiesel samples, since there is a correlation between the content of esters and the viscosity: the higher the viscosity, the lower the ester
con-tent[10]. ASTM D445 provides a method for obtaining the
kine-matic viscosity, which for biodiesel should be between 1.9 and
6.0 mm2s 1at 40 °C. The conversion from oil to biodiesel reduces
its molecular weight to about one-third that of the initial
triacyl-glycerides and the viscosity by a factor of about eight[17].
Biodie-sel has higher viscosity (about 5.0 mm2s 1, for both soybean FAME
and FAEE) than that of fossil diesel (about 3.0 mm2s 1). Biodiesel–
diesel blends constitute an alternative to improve this parameter of the biofuel. Besides, biodiesel viscosity is also a function of its fatty acid profile and, then, blends of biodiesel from different sources is able to reduce viscosity to the meet the required values.
Knothe[17]reported a viscosity of soybean FAME of about 4.0–
4.3 mm2s 1 at 40 °C, slightly lower than our results. The same
studies showed that sunflower and rapeseed FAME’s have similar
viscosities (4.39 and 4.53 mm2s 1, respectively)[17].
FromFig. 2c it can be observed that all the blends met the vis-cosity requirements. FAEE visvis-cosity is slightly higher than FAME
10 20 30 40 50 60 80 100 120 140
Flash P
o
int (
oC)
Biodiesel Blend (%)
FAME FAEE DIESEL ASTM 10 20 30 40 50 46 48 50 52 54 56Cetane n
umber
Biodiesel blend (%)
FAME FAEE DIESEL ASTM 10 20 30 40 50 1 2 3 4 5 6 7Kinematic viscosity (mm
2/s)
Biodiesel blend (%)
FAME FAEE DIESEL ASTMa
b
c
due to the additional CH2moiety at the alcoholic portion of the es-ter chain. Transeses-terification of vegetable oil produces eses-ters with a viscosity of approximately twice that of diesel. The higher viscos-ity of biodiesel, as compared to diesel, is due to the higher molec-ular mass and larger chemical structure of the biodiesel. Besides, the unsaturation of the main constituents of soybean biodiesel (oleic and linoleic acids) also leads to higher viscosities, what are detrimental to the operation of Diesel engines and may hamper the utilization of high percentages of biodiesel in the blends.
Comparing the results of the blends, the differences observed at the same mixtures were normally within the accuracy of the test. The higher viscosities observed for FAEE, as compared with FAME, agree with the fact that the molecular mass of the ethanol biodiesel is slightly higher than that of methanol biodiesel.
3.2. Rheological study
The rheological properties of the blends were investigated at different temperatures. A fluid is Newtonian when the
viscos-ity is constant, does not depend on the shear rate, at a deter-mined temperature. Conversely, a fluid is said to be non-Newtonian when the viscosity is not constant. In the case that the viscosity depends on time, the fluids are said to be thixotro-pic or rheopectic. When the viscosity does not depend on time, the fluids are called pseudoplastic, dilatant, plastic and Bingham
plastic[6,18,19].
Fig. 3presents the plots of shear stress versus shear rate for the FAME and FAEE blends, at 25 °C. All the samples displayed a typical
Newtonian behavior for higher shear rates (above about 80 s 1)
and a slight pseudoplastic behavior for lower shear rates, as the viscosities increased with the shear rate. Both behaviors can be
better visualized inFig. 4, which depicts the viscosities as a
func-tion of the shear rate. These results ratify the same rheological behavior previously described. It can also be noticed that the blend viscosities for both FAME and FAEE samples decreased from B50 to B5, influenced by interconnected parameters such as molecular
mass, intermolecular forces, and polarity[9]. These viscosity
mea-surements are in agreement with literature data[8,9,20], which
re-0 50 100 150 200 250 300 0.0 0.2 0.4 0.6 0.8 1.0 1.2
Shear stress (Pa)
Shear rate (s
-1)
B5 B15 B25 B50a
b
0 50 100 150 200 250 300 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4Shear stress (Pa)
Shear rate (s
-1)
B5 B15 B25 B50
Fig. 3. Shear stress versus shear rate plots of biodiesel/fossil diesel blends: (a) FAME and (b) FAEE.
0 50 100 150 200 250 4.0 4.5 5.0 5.5 6.0 6.5
Viscosity (mP
a.s)
Shear rate (s
-1)
B5 B15 B25 B50a
0 50 100 150 200 250 4.0 4.5 5.0 5.5 6.0 6.5Viscosity (mP
a.s)
Shear rate (s
-1)
B5 B15 B25 B50b
Fig. 4. Viscosity versus shear rate of biodiesel/fossil diesel blends: (a) FAME and (b) FAEE.
0 100 200 300 0 100 200 300 0.0 0.5 1.0 1.5 2.0 2.5
Shear Stress (Pa)
Shear Rate (s
-1)
Shear Rate (s
-1)
10 ºC 25 ºC 40 ºC
a
0.0 0.5 1.0 1.5 2.0 2.5Shear Stress (Pa)
10 ºC 25 ºC 40 ºC
b
ports that biodiesel displays a viscosity higher than fossil diesel,
due to the size of their fatty acid alkyl esters chains[21].
In order to investigate the effect of temperature on the rheol-ogy, B25 was randomly chosen to be studied at 10 °C, 25 °C and
40 °C (Figs. 5 and 6). As expected, the viscosity decreased with
the temperature. As previously reported, it can be noted a slight
pseudoplasticity up to a shear rate of 80 s 1, followed by a
Newto-nian behavior at higher shear rates. Nevertheless, it is worth to point out that the extent of pseudoplasticity decreases with the temperature.
4. Conclusions
Physicochemical parameters of soybean biodiesel–diesel blends were measured according to ASTM standards. The biodiesel con-centration in the blends as well as the size of the alcoholic moiety of the ester chain can influence the properties of the blends. For the analyzed samples, the properties were similar in some cases and diverge in others, but they do not significantly affect the fuel prop-erties. As expected, the higher the proportion of biodiesel in the
blend, the lower are the sulfur content and the emissions of CO2
and SOx, what are better characteristics on the environmental
point of view. In addition, cetane index and flash point are also higher in the biodiesel-richer blends. The variation of distillation temperature with distilled percentage for the blends was not uni-form throughout the boiling interval. Conversely, the biodiesel enrichment caused an increase in viscosity, besides reducing the volatility of the blends. Therefore, the usage of higher biodiesel lev-els in diesel cycle engines has to be more carefully studied, in order to assure a proper engine operation. According to the presented re-sults, it can be considered that biodiesel–diesel blends are a feasi-ble alternative and can be applied as diesel-replacement fuels, corroborating with the literature data.
Acknowledgements
The authors acknowledge CAPES Brazilian Agency for the finan-cial support.
References
[1] Corrêa SM, Arbilla G. Mercaptans emissions in diesel and biodiesel exhaust. Atmos Environ 2008. doi:10.1016/j.atmosenv.2008.05.036.
[2] Demirbas AH, Demirbas I. Importance of rural bioenergy for developing countries. Energy Convers Manage 2007;48:2386–98.
[3] Tang H, Salley SO, Simon Ng KY. Fuel properties and precipitate formation at low temperature in soy-, cottonseed-, and poultry fat-based biodiesel blends. Fuel 2008;87:3006–17.
[4] Benjumea P, Agudelo J, Agudelo A. Basic properties of palm oil biodiesel–diesel blends. Fuel 2008;87:2069–75.
[5] Jha SK, Fernando S, Filip To SD. Flame temperature analysis of biodiesel blends and components. Fuel 2008;87:1982–8.
[6] Candeia RA, Freitas JCO, Souza MAF, Conceição MM, Santos IMG, Soledade LEB, et al. Thermal and rheological behavior of diesel and methanol biodiesel blends. J Therm Anal Calorim 2007;87:653–6.
[7] Dzida M, Prusakiewicz P. The effect of temperature and pressure on the physicochemical properties of petroleum diesel oil and biodiesel fuel. Fuel 2008;87:1941–8.
[8] Joshi RM, Pegg MJ. Flow properties of biodiesel fuel blends at low temperatures. Fuel 2007;86:143–51.
[9] Goodrum JW, Geller DP, Adams TT. Rheological characterization of animal fats and their mixtures with #2 fuel oil. Biomass Bioenergy 2003;24:249–56. [10] Ma F, Hanna MA. Biodiesel production: a review. Bioresource Technol
1999;70:1–15.
[11] Monteiro MR, Ambrozin ARP, Lião LM, Ferreira AG. Critical review on analytical methods for biodiesel characterization. Talanta 2007. doi:10.1016/ j.talanta.2008.07.001.
[12] Pinto AC, Guarieiro LN, Rezende MJC, Ribeiro NM, Torres EA, Lopes WA, et al. Biodiesel: an overview. J Brazil Chem Soc 2005;16(6B):1313–30.
[13] Shu Q, Yang B, Yang J, Qing S. Predicting the viscosity of biodiesel fuels based on the mixture topological index method. Fuel 2007;86:1849–54.
[14] Meher LC, Vidya-Sagar D, Naik SN. Technical aspects of biodiesel production by transesterification – a review. Renew Sust Energ Rev 2006;10:248–68. [15] Phan AN, Phan TM. Biodiesel production from waste cooking oils. Fuel 2008.
doi:10.1016/j.fuel.2008.07.008.
[16] Fernando S, Karra P, Hernandez R, Jha SK. Effect of incompletely converted soybean oil on biodiesel quality. Energy 2007;32:844–51.
[17] Knothe G. Designer biodiesel: optimizing fatty ester composition to improve fuel properties. Energy Fuel 2008;22:1358–64.
[18] Knothe G, Gerpen JV, Krahl J. The biodiesel handbook. Champaign, Illinois: AOCS Press; 2005.
[19] Conceição MM, Candeia RA, Dantas HJ, Soledade LEB, Fernandes Jr VJ, Souza AG. Rheological behavior of castor oil biodiesel. Energy Fuel 2005;19:2185–8. [20] Tat ME, Gerpen JHV. The kinematic viscosity of biodiesel and its blends with
diesel fuel. J Am Oil Chem Soc 1998;76:1511–3.
[21] Rodrigues Jr JA, Cardoso FP, Lacheter R, Estevão LRM, Lima E, Nascimento RSV. Correlating chemical structure and physical properties of vegetable oil esters. J Am Oil Chem Soc 2006;83:353–7.
0 50 100 150 200 250 2 4 6 8 10 12
