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

Fuel 86 (2007) 2560–2567 www.fuelfirst.com

Kinematic viscosity of biodiesel components (fatty acid alkyl esters) and related compounds at low temperatures Gerhard Knothe *, Kevin R. Steidley National Center for Agricultural Utilization Research, Agricultural Research Service, US Department of Agriculture, 1815 N. University St., Peoria, IL 61604, USA Received 27 September 2006; received in revised form 10 January 2007; accepted 7 February 2007 Available online 7 March 2007

Abstract Biodiesel, defined as the mono-alkyl esters of vegetable oils and animal fats is, has undergone rapid development and acceptance as an alternative diesel fuel. Kinematic viscosity is one of the fuel properties specified in biodiesel standards, with 40 °C being the temperature at which this property is to be determined and ranges of acceptable kinematic viscosity given. While data on kinematic viscosity of biodiesel and related materials at higher temperatures are available in the literature, this work reports on the kinematic viscosity of biodiesel and a variety of fatty acid alkyl esters at temperatures from 40 °C down to 10 °C in increments of 5 °C using the appropriately modified standard reference method ASTM D445. Investigating the low-temperature properties of biodiesel, including viscosity, of biodiesel and its components is important because of the problems associated with the use of biodiesel under these conditions. Such data may aid in developing biodiesel fuels optimized for fatty ester composition. An index termed here the low-temperature viscosity ratio (LTVR) using data at 0 °C and 40 °C (divide viscosity value at 0 °C by viscosity value at 40 °C) was used to evaluate individual compounds but also mixtures by their low-temperature viscosity behavior. Compounds tested included a variety of saturated, monounsaturated, diunsaturated and triunsaturated fatty esters, methyl ricinoleate, in which the OH group leads to a significant increase in viscosity as well as triolein, as well as some fatty alcohols and alkanes. Esters of oleic acid have the highest viscosity of all biodiesel components that are liquids at low temperatures. The behavior of blends of biodiesel and some fatty esters with a low-sulfur diesel fuel was also investigated. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Biodiesel; Diesel fuel; Fatty acid alkyl esters; Low-temperature properties; Kinematic viscosity

1. Introduction The depletion of the world’s fossil fuel reserves has sparked considerable and urgent interest in alternative energy sources, especially renewable fuels. Biodiesel [1,2] is such a renewable fuel. It is obtained by transesterifying vegetable oils or other materials largely comprised of triacylglycerols, such as animal fats or used frying oils, with monohydric alcohols to give the corresponding mono-alkyl esters. Biodiesel production and use have increased almost exponentially in many countries around the world recently. Compatibility with the existing fuel distribution infrastruc-

*

Corresponding author. Tel.: +1 309 681 6112; fax: +1 309 681 6340. E-mail address: [email protected] (G. Knothe).

0016-2361/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2007.02.006

ture, currently high petroleum prices as well as legislative and regulatory incentives are easing the path of biodiesel into the market. Technical challenges such as reducing NOx exhaust emissions in conjunction with the effect of new exhaust emission reduction technologies, improving oxidative stability and cold flow properties remain. Advantages of biodiesel compared to petrodiesel include reduction of most exhaust emissions, biodegradability, higher flash point, renewability and domestic origin. The high viscosity of vegetable oils or fats used as diesel fuels causes operational problems such as poor atomization upon injection into the combustion chamber and engine deposits. Transesterifying oils or fats to the corresponding alkyl esters reduces viscosity by almost an order of magnitude. Furthermore, too high viscosity at low temperatures can interfere with the transport of the fuel from the

G. Knothe, K.R. Steidley / Fuel 86 (2007) 2560–2567

2. Experimental All neat esters (methyl, ethyl, n-propyl, n-butyl) were purchased from NuChek-Prep, Inc. (Elysian, MN) and were of purity >99% as confirmed by random checks (nuclear magnetic resonance spectroscopy (NMR), Bruker (Billerica, MA) Avance 500 spectrometer operating at 500 MHz for 1H-NMR with CDCl3 as solvent, and/or

C17

2.4e+07

C18

C16

2.2e+07

C19

C15

2e+07

Abundance

tank to the engine, which can affect even the transesterified oil or fat, the biodiesel. Any biodiesel fuel, including those optimized for fatty acid composition, need to meet the kinematic viscosity specifications (determinations at 40 °C) in biodiesel standards which are 1.9–6.0 mm2/s in the American standard ASTM D6751 [3] and 3.5– 5.0 mm2/s in the European standard EN 14214 [4]. The kinematic viscosity specifications in petrodiesel standards are 1.9–4.1 mm2/s (No. 2 diesel fuel, to which biodiesel is usually compared; No. 1 diesel fuel is 1.3–2.4 mm2/s) in the American standard ASTM D975 [5] and 2.0– 4.5 mm2/s in the European standard EN 590 [6]. The viscosity of biodiesel is slightly greater than that of petrodiesel, which is reflected in the specifications in the standards. ASTM standards relating to viscosity include D341 [7], D445 [8], and D2270 [9] and D341 [9], which deal with viscosity–temperature charts, determination of kinematic viscosity, and calculating the viscosity index, respectively. Recently, we reported the influence of compound structure of biodiesel components, notably fatty acid alkyl esters, on its kinematic viscosity [10]. There is only scant or no information available on the kinematic viscosity of individual biodiesel components at lower temperatures. To the best of our knowledge, the only reports on the kinematic viscosity of biodiesel and some of its components are a study of the low-temperature viscosities of biodiesel/petrodiesel blends [11], a report on the low-temperature properties (3 to 15 °C) of soybean, used soybean, mustard, and used mustard oils [12], a report on two soy methyl esters, one of them genetically modified at 2–100 °C in steps of 20 °C [13], work on the viscosity of saturated fatty acid methyl esters at 25 °C (besides 40 and 50 °C) [14], viscosities of three biodiesel fuels (canola and soy methyl esters, ethyl esters of fish oil) using a Saybolt viscometer at temperatures from 20 °C to 300 °C [15]. There are also several reports in the literature on the kinematic or dynamic viscosity of neat fatty esters at various temperatures, the lowest being usually 20 °C [16–26, see also references in these papers]. Other literature deals with predicting the kinematic viscosity of mixtures [27,28]. The present work now focuses on systematically reporting the low-temperature kinematic viscosity of not only biodiesel but also its various fatty acid alkyl ester components in neat form. An index termed the low-temp viscosity ratio (LTVR) using data at 0 °C and 40 °C (divide viscosity value at 0 °C by viscosity value at 40 °C) is used to evaluate individual compounds but also some mixtures by their lowtemperature viscosity behavior.

2561

C14

1.8e+07 1.6e+07

C20

C1 3

1.4e+07

C21

C12

1.2e+07 C8 1e+07

C1 0 C9 C11

C22

8000000 6000000

C23

4000000

C24

2000000

C25

0 20

40

60

80 100

120 140

160 180

200

Time (min) Fig. 1. GC–MS profile (total ion chromatogram) of the low-sulfur diesel fuel used in this work. The labels C8–C25 indicate the peaks caused by the straight-chain alkanes with these carbon numbers.

gas chromatography–mass spectrometry (GC–MS), Agilent Technologies (Palo Alto, CA) 6890 gas chromatograph coupled to an Agilent Technologies 5973 mass selective detector at 70 eV, HP-5 capillary column) of some materials. Straight-chain alkanes (decane, dodecane, tetradecane; P99%, verified by GC–MS analyses) were purchased from Aldrich (Milwaukee, WI) and used as received. Biodiesel (methyl soyate; trade name SoyGold) was obtained from Ag Environmental Products, Lenexa, KS. The fatty acid composition of this biodiesel fuel was (GC determination) 10.79% palmitic acid, 4.21% stearic acid, 23.61% oleic acid, 0.80% vaccenic acid (D11), 53.37% linoleic acid and 7.21% linolenic acid. Low-sulfur petrodiesel fuel (30 ppm sulfur) was obtained from Chevron–Phillips (Pascagoula, MS). The GC–MS profile of this petrodiesel fuel is depicted in Fig. 1. The kinematic viscosity values of the biodiesel and petrodiesel fuels are given in Table 1.

Table 1 Low-temperature kinematic viscosity (mm2/s) data of the commercial petrodiesel and biodiesel fuels used in this work Temperature (°C)

40 35 30 25 20 15 10 5 0 5 10 LTVR a

Fuel Biodiesel

Petrodiesel

4.15 4.64 5.15 5.76 6.43 7.52 8.67 10.47 11.75 nda nd

2.90 3.25 3.64 4.08 4.55 5.31 6.21 7.23 8.58 10.81 nd

2.83

2.96

Not determined. Formation of solids at this temperature.

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Kinematic viscosity values were determined with Cannon–Fenske viscometers (Cannon Instrument Co., State College, PA) at temperatures ranging from 10 °C to 40 °C following the standard method ASTM D445 [7] modified for use at temperatures below 40 °C by employing a thermostat or a Cannon TE-1000 low-temperature bath. All viscosity data reported here are means of triplicate determinations. Reproducibility of the viscosity data was excellent, with standard deviations generally less than 0.025 for lower viscosity values (less than about 6–8 mm2/s) and increasing proportionally for higher viscosity values. 3. Results and discussion The results of the determinations of kinematic viscosity for the compounds and mixtures studied here are given in Tables 2–10, with Tables 2–5 giving data for neat compounds and Table 6 for blends of fatty esters and Tables 7–10 for blends of biodiesel or neat fatty esters with petrodiesel. Specifically, Table 2 gives kinematic viscosity data for common fatty acid methyl esters, methyl decanoate (C10:0), methyl laurate (C12:0), methyl myristoleate (C14:1), methyl palmitoleate (C16:1), methyl oleate (C18:1), methyl linoleate (C18:2), methyl linolenate (C18:3), methyl ricinoleate (C18:1, 12-OH) as well as, for comparison purposes, two alcohols (1-decanol and oleyl alcohol) as well as a triacylglycerol (triolein). Table 3 lists kinematic viscosity data for the ethyl, propyl and butyl esters of lauric, oleic and linoleic acids as well as ethyl linolenate. Table 4 provides kinematic viscosity data for positional and geometrical C18:1 isomers, methyl elaidate, methyl petroselinate and methyl petroselaidate. Table 5 presents kinematic viscosity data for three alkanes, decane,

dodecane and tetradecane commonly found in petrodiesel. Table 6 provides data on blends of methyl oleate with methyl linoleate (50:50) and methyl oleate with methyl palmitate and methyl stearate (95:5; 90:10 and 85:15) as well as methyl palmitoleate with methyl palmitate (both 95:5). Table 7 contains kinematic viscosity data for blends of biodiesel with petrodiesel (B10, B20, B30, B40, B50, B60, B70, B80, B90). Tables 8–10 give kinematic viscosity for the same blend levels of petrodiesel with methyl oleate, methyl linoleate and methyl ricinoleate, respectively. For purposes of visualization, some data from the aforementioned tables are depicted in Figs. 2 and 3. Fig. 2 plots the kinematic viscosity of biodiesel and five neat alkyl esters (methyl laurate, methyl oleate, butyl oleate, methyl linoleate and methyl linolenate). Fig. 3 shows data for biodiesel and methyl oleate in comparison to the petrodiesel fuel used here as well as B20 and B50 blends and the petrodiesel components decane and tetradecane. Effects of molecular structure on kinematic viscosity have been defined in the literature [10, and references therein]. Viscosity is reduced by shorter chain length. Introduction of cis double bonds also reduces viscosity while trans double bonds have less effect on viscosity compared to saturated compounds with an equal number of carbons. Branched esters display viscosity similar to their straightchain counterparts. An OH group in the chain, such as found in methyl ricinoleate, increases viscosity considerably. Overall, the effect of oxygenated moieties on kinematic viscosity is COOH  C–OH > COOCH3  C@O > C–O–C > no oxygen (with a reversal of COOH vs. OH at shorter chain lengths). Aliphatic hydrocarbons display a smaller viscosity range. Viscosity increases for hydrocarbons are smaller than for fatty acid alkyl esters when chain length increases.

Table 2 Low-temperature kinematic viscosity (mm2/s) data of saturated and unsaturated fatty compounds Temperature (°C)

Fatty acid methyl estera C10:0

C12:0

C14:1

C16:1

C18:1, D9c

C18:2

C18:3

C18:1, 12-OH

C10:0

C18:1

40 35 30 25 20 15 10 5 0 5 10

1.71 1.87 2.05 2.23 2.45 2.71 3.10 3.49 4.04 4.68 5.40

2.41 2.69 2.95 3.29 3.63 4.07 4.79 5.45 ndc – –

2.73 3.04 3.37 3.71 4.13 4.73 5.35 6.13 7.01 8.37 9.92

3.67 3.96 4.42 4.94 5.56 6.38 7.33 8.55 10.15 12.19 14.77

4.51 5.08 5.72 6.44 7.33 8.51 9.91 11.66 14.03 17.22 21.33

3.65 4.08 4.53 5.03 5.61 6.43 7.30 8.47 9.84 11.80 14.10

3.09 3.32 3.88 4.07 4.57 5.14 5.53 6.59 7.33 8.81 10.19

15.29 18.58 23.83 29.77 37.07 49.47 64.74 91.92 123.83 182.36 271.50

8.01 9.53 11.38 13.18 16.26 20.86 25.64 33.19 ndc – –

16.92 20.69 25.64 29.57 37.65 49.27 62.11 82.26 ndc – –

LTVR

2.37

–

2.57

2.76

3.11

2.70

2.37

8.10

–

–

a

Trioleinb

Alcohols

38.44 46.18 58.02 71.04 86.82 113.51 145.71 200.89 261.27 376.35 ndc 6.80

Systematic (trivial) names of fatty acid methyl esters in this table in the sequence of the columns from left to right: Methyl decanoate (caprate), methyl dodecanoate (laurate), methyl 9(Z)-tetradecenoate (myristoleate), methyl 9(Z)-hexadecenoate (palmitoleate) acid, methyl 9(Z)-octadecenoate (oleate), methyl 9(Z),12(Z)-octadecadienoate (linoleate), methyl 9(Z),12(Z),15(Z)-octadecatrienoate (linolenate) acid, methyl 12-hydroxy-9(Z)-octadecenoate (ricinoleate). b Triacylglycerol (triglyceride). c Not determined. Formation of crystals at this temperature.

G. Knothe, K.R. Steidley / Fuel 86 (2007) 2560–2567

2563

Table 3 Low-temperature kinematic viscosity (mm2/s) data of ethyl, propyl, and butyl esters of lauric, oleic, linoleic and linolenic acids Temperature (°C)

Fatty acid alkyl ester C 12:0

C18:1, D9c

C18:2

C18:3

Et

Pr

Bu

Et

Pr

Bu

Et

Pr

Bu

Et

40 35 30 25 20 15 10 5 0 5 10

2.58 2.86 3.17 3.45 3.87 4.43 5.13 5.93 6.78 nda –

3.04 3.38 3.74 4.09 4.66 5.35 6.26 7.25 8.48 10.18 nda

3.36 3.78 4.18 4.57 5.22 6.03 7.08 8.26 9.70 11.80 nda

4.73 5.30 6.01 6.73 7.68 8.83 10.29 12.15 14.49 18.04 22.18

5.40 6.10 6.90 7.84 8.96 10.39 12.21 14.83 17.42 22.05 27.34

5.63 6.36 7.19 8.22 9.42 10.89 12.76 15.46 18.26 23.07 28.91

4.10 4.49 4.94 5.45 6.32 7.12 8.25 9.59 11.59 13.85 16.81

4.50 5.04 5.67 6.33 7.21 8.27 9.44 11.13 13.17 16.37 20.13

4.94 5.53 6.14 6.86 8.13 9.38 10.69 12.59 14.62 18.06 22.16

3.45 3.69 4.03 4.38 4.93 5.48 6.22 7.09 8.66 9.95 11.80

LTVR

2.63

2.79

2.89

3.06

3.23

3.26

2.83

2.93

2.96

2.51

a

Not determined. Formation of crystals at this temperature.

Table 4 Low-temperature kinematic viscosity (mm2/s) data of C18:1 methyl estersa Temperature (°C)

Fatty acid methyl ester

40 35 30 25 20 15 10 5 0 5 10 LTVR

C18:1, D9 cisb

C18:1, D9 trans

C18:1, D6 cis

C18:1, D6 trans

4.51 5.08 5.72 6.44 7.33 8.51 9.91 11.66 14.03 17.22 21.33

5.20 5.93 6.75 7.64 8.87 10.37 12.26 nd – – –

4.60 5.17 5.93 6.54 7.59 8.73 10.05 12.07 14.34 18.00 nd

5.19 6.16 7.03 7.98 9.41 10.91 ndc – – – –

3.11

–

3.12

–

a

Systematic (trivial) names of the compounds in this table in the sequence of the columns from left to right: methyl 9(Z)-octadecenoate (oleate), methyl 9(E)-octadecenoate (elaidate), methyl 6(Z)-octadecenoate (petroselinate), methyl 6(E)-octadecenoate (petroselaidate). b Data from Table 2. c Not determined. Formation of crystals at this temperature.

Table 5 Low-temperature kinematic viscosity (mm2/s) data of three alkanes Temperature (°C)

Alkane Decane

Dodecane

Tetradecane

40 35 30 25 20 15 10 5 0 5 10

0.97 1.03 1.11 1.18 1.26 1.36 1.48 1.61 1.76 1.97 2.15

1.42 1.55 1.69 1.81 2.01 2.21 2.36 2.71 3.03 3.41 nd

2.07 2.25 2.50 2.71 3.06 3.39 3.82 nda – – –

LTVR

1.81

2.14

–

a

Not determined. Formation of crystals at this temperature.

3.1. Low-temperature viscosity ratio For purposes of the present discussion, an index termed the low-temperature viscosity ratio (LTVR) using data at 0 °C and 40 °C will be used. To determine this index, the kinematic viscosity value at 0 °C of a compound is divided by the kinematic viscosity value at 40 °C: LTVR ¼ g0 =g40

ð1Þ

There are numerous fatty compounds which are liquids at 40 °C but solids at 0 °C due to higher melting points. These compounds, mainly saturated esters such as palmitates and stearates, would not be assigned an LTVR according to the present definition, which is acceptable due to the observation that they do not significantly affect viscosity in the amounts they are usually present in or even

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G. Knothe, K.R. Steidley / Fuel 86 (2007) 2560–2567

Table 6 Low-temperature kinematic viscosity (mm2/s) data of a 50:50 blend of methyl oleate with methyl linoleate as well as 95:5, 90:10 and 85:15 blends of methyl oleate with methyl palmitate or methyl stearate and a 95:5 blend of methyl palmitoleate with methyl palmitate Temperature (°C)

40 35 30 25 20 15 10 5 0 5 10 LTVR a

C18:1/C18:2

C18:1/C16:0

50:50

95:5

90:10

85:15

C18:1/C18:0 95:5

90:10

85:15

C18:2/C16:0 95:5

90:10

85:15

C18:2/C18:0 95:5

90:10

85:15

95:5

C16:1/C16:0

4.28 4.83 5.40 6.02 6.90 7.92 9.14 11.10 13.05 15.87 19.50

4.55 5.08 5.67 6.46 7.31 8.51 9.80 11.79 14.40 nda –

4.39 5.05 5.63 6.32 7.24 8.25 9.87 11.58 nda – –

4.42 5.06 5.63 6.36 7.26 8.35 9.94 nda – – –

4.49 5.16 5.78 6.49 7.40 8.55 10.11 nda – – –

4.57 5.30 5.83 6.59 7.51 8.73 nda – – – –

4.65 5.34 5.96 6.69 7.75 nda – – – – –

3.78 4.19 4.70 5.11 5.81 6.76 7.66 9.04 nda – –

3.74 4.13 4.57 5.06 5.71 6.69 7.68 8.95 nda – –

3.76 4.20 4.62 5.16 5.85 6.74 7.78 nda – – –

3.74 4.23 4.64 5.07 5.72 6.63 7.69 nda – – –

3.92 4.41 4.78 5.19 5.98 6.78 nda – – – –

4.07 4.36 4.88 5.26 6.21 nda – – – – –

3.61 4.00 4.44 5.00 5.62 6.42 7.44 8.74 10.53 nd –

3.05

3.16

–

–

–

–

–

–

–

–

–

–

–

2.92

Not determined. Formation of solids at this temperature.

Table 7 Low-temperature kinematic viscosity (mm2/s) data of blends of commercial biodiesel, in low-sulfur petrodiesel Temperature (°C)

40 35 30 25 20 15 10 5 0 5 10 LTVR a

Commercial biodiesel (%) 10

20

30

40

50

60

70

80

90

2.95 3.35 3.74 4.15 4.68 5.37 6.23 7.47 8.63 10.77 nd

3.07 3.44 3.82 4.30 4.85 5.54 6.44 7.66 8.84 11.04 nd

3.15 3.53 3.94 4.39 4.92 5.69 6.61 7.78 9.15 11.23 nd

3.26 3.64 4.05 4.52 5.08 5.88 6.82 8.01 9.46 11.63 nd

3.38 3.77 4.22 4.76 5.24 6.11 7.00 8.33 9.67 12.04 nd

3.53 3.97 4.44 4.94 5.49 6.36 7.35 8.70 10.14 nda –

3.64 4.09 4.57 5.09 5.66 6.57 7.67 8.97 10.54 nd –

3.77 4.25 4.72 5.27 5.90 6.84 8.00 9.35 11.04 nd –

3.94 4.42 4.89 5.48 6.11 7.13 8.17 9.97 11.16 nd –

2.93

2.88

2.91

2.90

2.86

2.87

2.90

2.93

2.83

Not determined. Formation of solids at this temperature.

Table 8 Low-temperature kinematic viscosity (mm2/s) data of blends of methyl oleate in low-sulfur petrodiesel Temperature (°C)

40 35 30 25 20 15 10 5 0 5 10 LTVR a

Methyl oleate (%) 10

20

30

40

50

60

70

80

90

2.97 3.36 3.73 4.18 4.73 5.60 6.49 7.62 8.76 11.07 nda

3.08 3.50 3.89 4.38 4.93 5.82 6.73 8.01 9.14 11.56 nd

3.21 3.62 4.04 4.53 5.15 6.01 7.01 8.40 9.51 11.71 nd

3.37 3.80 4.22 4.76 5.37 6.29 7.49 8.60 9.97 12.25 nd

3.49 3.98 4.49 4.96 5.76 6.54 7.87 9.06 10.45 12.97 nd

3.67 4.15 4.63 5.21 5.84 6.87 8.19 9.69 11.74 14.39 17.21

3.83 4.35 4.90 5.47 6.16 7.23 8.58 10.18 12.31 15.21 18.75

4.02 4.56 5.09 5.75 6.47 7.65 9.01 10.63 12.94 15.96 19.98

4.22 4.79 5.36 6.03 6.79 8.10 9.55 11.28 13.78 16.91 21.14

2.95

2.97

2.96

2.96

2.99

3.20

3.21

3.22

3.27

Not determined. Formation of solids at this temperature.

somewhat above. This is shown in the discussion below of mixtures such as methyl oleate or methyl linoleate with methyl palmitate or methyl stearate.

The LTVR evaluates individual compounds and mixtures by their low-temperature viscosity behavior, specifically by their relative increase in kinematic viscosity to

G. Knothe, K.R. Steidley / Fuel 86 (2007) 2560–2567

2565

Table 9 Low-temperature kinematic viscosity (mm2/s) data of blends of methyl linoleate in low-sulfur petrodiesel Temperature (°C)

Methyl linoleate (%)

40 35 30 25 20 15 10 5 0 5 10 LTVR

10

20

30

40

50

60

70

80

90

2.97 3.39 3.70 4.16 4.59 5.36 6.28 7.36 8.73 10.64 13.30

3.02 3.42 3.79 4.22 4.70 5.45 6.34 7.46 8.81 10.76 13.51

3.08 3.50 3.85 4.32 4.77 5.60 6.44 7.68 8.92 11.15 13.67

3.18 3.60 4.02 4.52 4.93 5.80 6.67 7.94 9.21 11.47 14.09

3.30 3.72 4.10 4.59 5.06 6.02 6.89 8.24 9.59 11.96 14.70

3.39 3.82 4.23 4.73 5.26 6.11 7.17 8.48 9.72 12.11 14.72

3.50 3.95 4.39 4.87 5.42 6.30 7.35 8.84 10.07 12.49 15.09

3.70 4.17 4.62 5.18 5.75 6.75 7.82 9.28 10.89 13.33 16.37

3.79 4.26 4.71 5.27 5.87 6.87 7.98 9.36 11.01 13.41 16.37

2.94

2.92

2.90

2.90

2.91

2.87

2.88

2.94

2.91

Table 10 Low-temperature kinematic viscosity (mm2/s) data of blends of methyl ricinoleate in low-sulfur petrodiesel Temperature (°C)

Methyl ricinoleate (%)

40 35 30 25 20 15 10 5 0 5 10 LTVR a

10

20

30

40

50

60

70

80

90

3.24 3.41 4.07 4.63 5.13 6.07 7.22 7.95 10.38 13.28 nda

3.63 4.14 4.73 5.38 6.11 7.23 8.75 10.43 12.91 16.37 nd

4.20 4.85 5.61 6.49 7.39 8.97 11.01 13.36 16.75 21.83 nd

4.95 5.77 6.67 7.86 9.16 11.08 13.92 17.41 21.91 29.16 nd

5.85 6.99 8.13 9.57 11.11 13.85 17.70 22.35 28.65 38.80 nd

7.03 8.48 10.01 11.93 13.99 17.74 22.84 28.75 38.70 52.22 nd

8.47 10.27 12.24 14.66 17.44 22.47 29.52 37.88 51.69 71.01 nd

10.29 12.65 15.25 18.55 22.34 29.68 38.88 50.80 69.72 97.77 nd

12.48 15.57 18.92 23.18 28.07 38.02 50.51 67.01 94.23 133.27 nd

3.20

3.56

3.99

4.43

4.90

5.50

6.10

6.78

7.55

Not determined. Formation of solids at this temperature.

25

Kinematic Viscosity (mm2 / sec)

Kinematic Viscosity (mm2 / sec)

30

25

20

15

10

5

0

20

15

10

5

0 -10

0

10

20

30

40

Temperature (OC)

-10

0

10

20

30

40

Temperature (oC)

Fig. 2. Kinematic viscosity in the range from 40 °C to 10 °C for  methyl soyate (biodiesel), n methyl laurate, s methyl oleate, d butyl oleate, h methyl linoleate and j methyl linolenate. For exact data, see Tables 1–3.

Fig. 3. Kinematic viscosity in the range from 40 °C to 10 °C for  methyl soyate (biodiesel),  petrodiesel, s methyl oleate, h B20, j B50, . decane and m tetradecane. For data, see Tables 1, 2, 5 and 6.

one another at these lower temperatures. The LTVR can be seen as a simplified index of change of kinematic viscosity

with temperature compared to the viscosity index (VI) which is commonly determined by measuring the viscosity

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at 40 °C and 100 °C by means of an equation given in standards such as ASTM D2270 [9]. 3.2. Neat fatty compounds The effects of molecular structure of neat fatty esters discussed above are also visible at low temperatures (Tables 2–4; Fig. 2). As noted in other literature, the differences in kinematic viscosity increase with decreasing temperature both in absolute and relative values, the latter being reflected by the LTVR. For example, with increasing chain length, the LTVR of monounsaturated methyl esters increases from 2.57 for methyl myristoleate to 2.76 for methyl palmitoleate to 3.11 for methyl oleate. On the other hand, for constant chain length, the LTVR shows a significant decrease with increasing unsaturation, decreasing to 2.70 in methyl linoleate and 2.37 in methyl linolenate compared to methyl oleate. The effect of an additional double bond is thus slightly greater than reduction of chain length by two methylene moieties. The position of the double bond in the chain does not appear to affect the LTVR as shown by data for methyl oleate vs. methyl petroselinate (D6) (Table 4). The ethyl, propyl and butyl esters for which data are given in Table 3 possess, as previously reported [10, and references therein], greater viscosity than methyl esters. Interestingly, however, the increase in the LTVR of these higher esters compared to methyl esters is less than when the chain length of the fatty acid moiety increases. This indicates that higher esters of shorter chain acids possess advantageous low-temperature viscosity properties compared to methyl esters of longer-chain fatty acids for the same number of carbon atoms. Esters of oleic acid have the highest viscosity of all esters of fatty acids most commonly occurring in oils fats and that are liquid at low temperatures 60 °C. In comparison to the neat fatty compounds, straightchain alkanes (Table 5) display a lower LTVR, indeed one that is lower than that of petrodiesel. Therefore, the higher LTVR of petrodiesel vs. straight-chain alkanes is caused by components other than its major alkane components. Four compounds, two of them alcohols (1-decanol and oleyl alcohol) as well as methyl ricinoleate and triolein, with viscosity significantly exceeding that of the other materials studied here are included in Table 2. While the kinematic viscosity of methyl ricinoleate is significantly less than that of triolein, the LTVR of methyl ricinoleate is higher, showing that, when comparing two materials, greater viscosity at 40 °C does not necessarily imply a greater LTVR, an observation also made similarly for the viscosity index. 3.3. Influence of saturated compounds To study the influence of esters with high melting points on the viscosity of esters with low melting points, saturated

fatty acid methyl esters (methyl palmitate and methyl stearate) that are solids at ambient temperature were mixed with unsaturated fatty acid methyl esters with low melting points (methyl oleate and methyl linoleate). The concentration of the saturated esters was chosen in such a fashion to reflect the amounts present in common vegetable oils such as soybean or rapeseed (canola) oil. The data in Table 6 show that for concentrations of 5%, 10% or 15% of saturated esters in unsaturated esters, there is little influence on the kinematic viscosity of the unsaturated esters in vegetable oils by saturated fatty acid methyl esters that are solids below ambient temperature. The effect of methyl palmitate vs. methyl stearate is relatively minor (0.4– 0.5 mm2/s increase with methyl stearate) at these concentrations in terms of kinematic viscosity. However, there was significant influence on the crystallization temperature resulting from methyl palmitate vs. methyl stearate as the data in Table 6 shows, although a detailed study on crystallization temperature and related phenomena is beyond the scope of this work. 3.4. Blends Data for blends of commercial petrodiesel with commercial biodiesel, methyl oleate, methyl linoleate and methyl ricinoleate are given in Tables 7–10, respectively. Although blends with more than 50% biodiesel are unlikely to find commercial use, their data are included in these tables for sake of completeness. The results coincide with other work [11] in which the temperature-dependent viscosity behavior of biodiesel and its blends was reported to be similar to that of No. 1 and No. 2 diesel fuels with some measurements to 10 °C or lower for some blends. In that work [11], a blending equation to allow kinematic viscosity to be calculated as a function of the biodiesel fraction was given. The present data for 50:50 blends show that the viscosity of these blends follows more strongly that commercial petrodiesel, which has the lowest viscosity of these materials (see also Fig. 3). For example, at 40 °C the viscosity of 50:50 petrodiesel/biodiesel is 3.38 mm2/s, a value differing by 0.48 mm2/s from that of petrodiesel but differing by 0.77 mm2/s from that of the biodiesel fuel used (see also data in Table 1). At 0 °C, the differences are 1.09 and 2.08 mm2/s. Thus the viscosity of low-level blends of biodiesel with petrodiesel is only relatively insignificantly affected by biodiesel. Similar results hold for the blends of petrodiesel with methyl oleate and methyl linoleate, showing that enrichment of specific fatty acids in compositionally modified vegetable oils does not have any significant effect on biodiesel viscosity at low temperatures. Even low-level blends of methyl ricinoleate, the major fatty ester in castor oil-derived biodiesel, do not appear to display any major viscosity problem compared to blends of petrodiesel with the commercial biodiesel used here. The LTVR did not change significantly for all blends, even when using higher-viscosity methyl oleate in blends with petrodiesel, although there was an increase for petrodie-

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sel/methyl oleate blends when increasing methyl oleate from 50% to 60%. 4. Summary and conclusions The low-temperature viscosity behavior of biodiesel, its components, related fatty materials and blends of fatty compounds as well as blends with petrodiesel were investigated. A variety of fatty esters was studied neat and in blends with petrodiesel. The blends showed a behavior closer to that of petrodiesel than of biodiesel or its neat components. Esters with shorter fatty acid chains but longer alcohol moieties display somewhat lower viscosities than esters with longer fatty acid chains and shorter alcohol moieties. Saturated esters with high melting points have only little influence on kinematic viscosity at lower temperatures and at concentrations observed in many common vegetable oils. The present data can be used for assessing fatty esters in terms of enriching them in biodiesel for the sake of improving fuel properties. Furthermore, the data presented here can be used for predicting or verifying the viscosity of yet non-investigated compounds as well as of mixtures. Disclaimer Product names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by USDA implies no approval of the product to the exclusion of others that may also be suitable. References [1] Knothe G, Van Gerpen J, Krahl J, editors. The biodiesel handbook. Champaign (IL): AOCS Press; 2005. [2] Mittelbach M, Remschmidt C. Biodiesel – the comprehensive handbook publ. M Mittelbach, Graz, Austria, 2004. [3] ASTM standard D6751. Standard specification for biodiesel fuel (B100) blend stock for distillate fuels. ASTM, West Conshohocken, PA. [4] EN14214. Automotive fuels – fatty acid methyl esters (FAME) for diesel engines – requirements and test methods, Beuth-Verlag, Berlin, Germany. [5] ASTM standard D975. Standard specification for diesel fuel oils. ASTM, West Conshohocken, PA. [6] EN590. Automotive fuels – diesel – requirements and test methods, Beuth-Verlag, Berlin, Germany. [7] ASTM standard D341. Standard test method for viscosity–temperature charts for liquid petroleum products, ASTM, West Conshohocken, PA.

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[8] ASTM standard D445. Standard test method for kinematic viscosity of transparent and opaque liquids, ASTM, West Conshohocken, PA. [9] ASTM standard D2270. Standard practice for calculating viscosity index from kinematic viscosity at 40 and 100 °C, ASTM, West Conshohocken, PA. [10] Knothe G, Steidley KR. Kinematic viscosity of biodiesel fuel components and related compounds. Influence of compound structure and comparison to petrodiesel fuel components. Fuel 2005;84(9):1059–65. [11] Tat ME, Van Gerpen JH. The kinematic viscosity of biodiesel and its blends with diesel fuel. J Am Oil Chem Soc 1999;76(12):1511–3. [12] Srivastava A, Prasad R. Rheological behavior of fatty acid methyl esters. Indian J Chem Technol 2001;8(6):473–81. [13] Yuan W, Hansen AC, Zhang Q, Tan Z. Temperature-dependent kinematic viscosity of selected biodiesel fuels and blends with diesel fuel. J Am Oil Chem Soc 2005;82(3):195–9. [14] Krisnangkura K, Yimsuwan T, Pairintra R. An empirical approach in predicting biodiesel viscosity at various temperatures. Fuel 2006;85(1):107–13. [15] Tate RE, Watts KC, Allen CAW, Wilkie KI. The viscosities of three biodiesel fuels at temperatures up to 300 °C. Fuel 2006;85(7–8): 1010–5. [16] Kaufmann HP, Funke S. The field of fats. LIX. The viscometry of fats (Zur Viskometrie der Fette (Studien auf dem Fettgebiet, 59. Mitteilung)). Fette Seifen 1938;45(5):255–62. [17] Ravich GB. Viscosity of higher fatty acids and fats. Akad Nauk SSSR 1941;1:427–40. Chem Abstr 1946;40:6271. [18] Bonhorst CW, Althouse PM, Triebold HO. Esters of naturally occurring fatty acids. Ind Eng Chem 1948;40(12):2379–84. [19] Kern DQ, Van Nostrand W. Heat transfer characteristics of fatty acids. Ind Eng Chem 1949;41(10):2209–12. [20] Gros AT, Feuge RO. Surface and interfacial tensions, viscosities, and other physical properties of some n-aliphatic acids and their methyl and ethyl esters. J Am Oil Chem Soc 1952;29:313–7. [21] Shigley JW, Bonhorst CW, Liang CC, Althouse PM, Triebold HO. Physical characterization of (a) a series of ethyl esters and (b) a series of ethanoate esters. J Am Oil Chem Soc 1955;32(4):213–5. [22] Teeter HM, Cowan JC. Viscometric properties of higher fatty acids and their derivatives. J Am Oil Chem Soc 1956;33(4):163–9. [23] Gouw TH, Vlugter JC, Roelands CJA. Physical properties of fatty acid methyl esters. VI. Viscosity. J Am Oil Chem Soc 1966;43(7):433–4. [24] Fernandez-Martin F, Montes F. Viscosity of multicomponent systems of normal fatty acids: principle of congruence. J Am Oil Chem Soc 1976;53(4):130–1. [25] Noureddini H, Teoh BC, Clements LD. Viscosities of vegetable oils and fatty acids. J Am Oil Chem Soc 1992;69(12):1189–91. [26] Valeri D, Meirelles AJA. Viscosities of fatty acids, triglycerides, and their binary mixtures. J Am Oil Chem Soc 1997;74(10):1221–6. [27] Allen CAW, Watts KC, Ackman RG, Pegg MJ. Predicting the viscosity of biodiesel fuels from their fatty acid ester composition. Fuel 1999;78(11):1319–26. [28] Rabelo J, Batista E, Cavaleri FW, Meirelles AJA. Viscosity prediction for fatty systems. J Am Oil Chem Soc 2000;77(12):1255–61.