# Evaluation of alkyl esters from Camelina sativa oil as biodiesel and as blend components in ultra low-sulfur diesel fuel q



## Bryan R. Moser * 

## , Steven F. Vaughn

United States Department of Agriculture, Agricultural Research Service, National Center for Agricultural Utilization Research, 1815 N. University St., Peoria, IL 61604, USA



### article info

Article history: Received 15 December 2008 Received in revised form 10 August 2009 Accepted 12 August 2009 Available online 8 September 2009

Keywords: Biodiesel Camelina sativa Diesel Fuel properties Methyl esters 

### abstract

Methyl and ethyl esters were prepared from camelina [ Camelina sativa (L.) Crantz] oil by homogenousbase-catalyzed transesterification for evaluation as biodiesel fuels. Camelina oil contained high percentages of linolenic (32.6 wt.%), linoleic (19.6 wt.%), and oleic (18.6 wt.%) acids. Consequently, camelina oilmethyl and ethyl esters (CSME and CSEE) exhibited poor oxidative stabilities and high iodine values versus methyl esters prepared from canola, palm, and soybean oils (CME, PME, and SME). Other fuel properties of CSME and CSEE were similar to CME, PME, and SME, such as low temperature operability, acid value, cetane number, kinematic viscosity, lubricity, sulfur and phosphorous contents, as well as surfacetension. As blend components in ultra low-sulfur diesel fuel, CSME and CSEE were essentially indistinguishable from SME and soybean oil ethyl ester blends with regard to low temperature operability, kinematic viscosity, lubricity, and surface tension. Published by Elsevier Ltd.

1. Introduction

Biodiesel, defined as an alternative fuel composed of mono-alkyl esters of long-chain fatty acids prepared from vegetable oils or animal fats, has attracted considerable interest as a substituteor blend component for conventional petroleum diesel fuel (petrodiesel). Biodiesel possesses significant technical advantages overpetrodiesel, such as derivation from renewable feedstocks, displacement of imported petroleum, inherent lubricity, essentiallyno sulfur content, superior flash point and biodegradability, reduced toxicity, as well as a reduction in most exhaust emissions. Important disadvantages of biodiesel include inferior oxidative and storage stability, lower volumetric energy content, inferior low temperature operability, and higher NOx exhaust emissions (Mittelbach and Remschmidt, 2004; Knothe et al., 2005; McCormick et al., 2006; Moser, 2009a). Additionally, the high cost of commodity vegetable oils, such as soybean oil in the United States, represents a serious threat to the economic viability of the biodiesel industry ( Paulson and Ginder, 2007; Retka-Schill, 2008a). Presently, feedstock acquisition accounts for up to 85% of biodiesel production costs ( Paulson and Ginder, 2007; Retka-Schill, 2008a). Feedstocks for biodiesel production vary considerably with location according to climate and availability. Generally, the mostabundant lipid in a particular region is the most common feedstock. Thus, rapeseed oil is predominantly used in Europe, palm oil predominates in tropical countries, and soybean oil and animalfats are primarily used in the United States (Mittelbach and Remschmidt, 2004; Knothe et al., 2005; Moser, 2009a). However, many of these oils are prohibitively expensive and have competing food-related uses. Consequently, the development of alternativefeedstocks for biodiesel production that meet all or most of the following criteria has attracted considerable research attention: highoil content, low agricultural inputs, favorable fatty acid composition, compatibility with existing farm equipment and infrastructure, production in a sustainable fashion in off-season or in agriculturally undesirable lands, definable growth seasons, anduniform seed maturation rates. Selected recent examples of biodiesel produced from feedstock oils that meet at least a majority of the above criteria include moringa ( Rashid et al., 2008 ), jatropha ( Tiwari et al., 2007 ), field pennycress ( Moser et al., 2009a ), and wild mustard (Jham et al., 2009 ). Camelina [ Camelina sativa (L.) Crantz], also known as false flax or gold-of-pleasure, is a spring annual broadleaf oilseed herb of the Brassicaceae family that grows well in temperate climates.Camelina has several positive agronomic attributes: low agricultural inputs, cold-weather tolerance, short growing season (85–100 days), compatibility with existing farm equipment, and grows well in semiarid regions and in low-fertility or saline soils. These qualities are unusual for an oilseed crop (Putnam et al., 1993; Retka-Schill, 2008b; Sawyer, 2008). Other more common

0960-8524/$ - see front matter Published by Elsevier Ltd. doi: 10.1016/j.biortech.2009.08.054

q 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.

* Corresponding author. Tel.: +1 309 681 6511; fax: +1 309 681 6340.

E-mail address: Bryan.Moser@ars.usda.gov (B.R. Moser). Bioresource Technology 101 (2010) 646–653

Contents lists available at ScienceDirect 

# Bioresource Technology

journal homepage: www.elsevier .com/locate/biortechoilseed crops, such as canola, soybean, rapeseed, and sunflower, have higher water, pesticide, and fertilizer requirements ( Budin et al., 1995; Sawyer, 2008 ). Moreover, camelina, unlike soybean, thrives in cool, arid climates and is nicely adapted to the more northerly regions of North America, Europe, and Asia. As such, itmay serve as a rotational crop for winter wheat, which would facilitate disrupting undesirable weed and pest cycles ( Retka-Schill, 2008b ). Camelina yields an average of 420–640 L/ha and the protein and fiber content in its meal byproduct is comparable to that of soybean meal ( Retka-Schill, 2008b; Sawyer, 2008). The seeds of camelina contain 28–40 wt.% of vegetable oil ( Putnam et al., 1993; Budin et al., 1995 ), which is far superior to that typically found in soybeans (18–22 wt.%). Camelina has traditionally been used for relatively high value products such as culinary oil, cosmetics, and animal feed ( Sawyer, 2008 ). Examples of camelina oil appearing in the scientific literature include its direct use as a fuel for diesel transport engines ( Bernardo et al., 2003 ) and as a chemical feedstock in the enzymatic production of long-chain esters ( Steinke et al., 2000a,b, 2001 ). Camelina oil may also serve as an industrial source of 

### a

linolenic acid (9Z,12Z,15Z-octadecatrienoic acid), as it generally contains 30–45 wt.% of this constituent ( Leonard, 1998; Ni Eidhin et al., 2003; Krist et al., 2006; Sawyer, 2008 ). Moreover, camelina oil was examined as a feedstock for biodiesel production ( Frohlich and Rice, 2005 ). We follow up in the current study with a more thorough examination of the fuel properties of methyl and ethyl esters prepared from alcoholysis of camelina oil, along with their evaluation as blend components in ultra low-sulfur diesel fuel (ULSD, <15 ppm S). A comparison with canola and palm oil methyl esters (CME and PME, respectively), along with soybean oil methyl and ethyl esters (SME and SEE, respectively), was also of interest. Important fuel properties elucidated of the alkyl esters, both neatand blended with ULSD, included low temperature operability, oxidative stability, cetane number, acid value, sulfur and phosphorous contents, lubricity, iodine value, surface tension, and kinematic viscosity. Although biodiesel can be used in modern unmodified diesel engines in the neat form, it is more commonly encountered as ablend component in petrodiesel, such as B20 (20% biodiesel by volume in petrodiesel). Currently, blends of up to B5 are allowed in ASTM D975 ( ASTM, 2008a ) ( Table 1 ), the US diesel fuel standard. In addition, ASTM D7467 ( ASTM, 2008b ) ( Table 1 ) was recently adopted for blends from B6 to B20 in petrodiesel. Biodiesel must be certified as acceptable according to ASTM D6751 ( ASTM, 2008c ) ( Table 1 ), the B100 standard, before its use as a fuel or blend component. Moreover, EN 14214 ( Committee for Standardization, 2003 ) ( Table 1 ) and EN 590 ( Committee for Standardization, 2004 ) are the European Union standards for biodiesel and petrodiesel (up to B5), respectively.

2. Experimental section

2.1. Materials

Camelina seeds were purchased from Marx Foods (Atlantic Highlands, NJ). ULSD, described as fungible by the manufacturer,was donated by a major petrochemical company that wished to remain anonymous. Conductivity and corrosion inhibitor additives were added by the manufacturer, but no drag reducing, lubricity,low temperature, or antioxidant additives were added. The commercial adsorbent Magnesol was purchased from The Dallas Group of America, Inc. (Whitehouse, NJ). Refined, bleached, and deodorized canola, palm, and soybean oils were purchased from KIC Chemicals, Inc (New Platz, NY). Fatty acid methyl (FAME) andethyl ester standards were purchased from Nu-Chek Prep, Inc. (Elysian, MN). All other chemicals and reagents were obtained from Sigma–Aldrich Corp (St. Louis, MO).

2.2. Camelina oil extraction

Camelina seeds (1000 g) were ground in a coffee grinder and oil was extracted with hexane for 24 h in a Soxhlet apparatus. Hexane was removed by rotary evaporation under reduced pressure (10 mbar; 30 C). For determination of total oil content, 10.0 g triplicates of ground seed were extracted (Soxhlet) for 24 h, and after hexane was removed by rotary evaporation (10 mbar; 30  C) the weight of the residual oil was calculated. The percentage of oil recovered from the samples was 30.5 wt.% ( 

### rM ± 0.4%).

2.3. Methanolysis of camelina oil

Methanolysis of camelina oil was conducted in a 500 mL threenecked round bottom flask connected to a reflux condenser and a mechanical magnetic stirrer set at 1200 rpm. Initially, camelina oil (180 g, 200 mL, 0.202 mol) and methanol (49 mL, 1.21 mol) were added to the flask and heated to 60 C (internal reaction temperature monitored by digital temperature probe), followed by addition of 1.0 wt.% NaOCH 3 (25 wt.% in CH 3 OH). After 1.5 h of reaction the mixture was equilibrated to room temperature and transferred to a separatory funnel. The lower glycerol phase wasremoved by gravity separation (>2 h settling time) followed by removal of methanol from the upper crude methyl ester phase by reduced pressure (10 mbar; 30 C) rotary evaporation. The crude methyl esters were treated with 2.5 wt.% Magnesol at 65  C for 25 min with continuous stirring (500 rpm), followed by filtration to remove the adsorbent to provide C. sativa oil methyl esters (CSME, 160 g, 89 wt.% yield based on original mass of camelina oil). Canola, palm, and soybean oil methyl esters were prepared in a similar fashion in essentially quantitative (>98 wt.%) yield. Free and total glycerol contents of CSME, CME, PME, and SME were determined according to ASTM D6584.

2.4. Ethanolysis of camelina oil

Ethanolysis of camelina oil was accomplished largely as described in Section 2.3 . Initially, camelina oil (180 g, 200 mL,0.202 mol) and ethanol (110 mL, 1.82 mol) were added to the reaction flask and heated to 70 C (internal reaction temperature monitored by digital temperature probe), followed by addition of Table 1 Selected specifications from biodiesel and ULSD fuel standards.

Biodiesel ULSD

ASTM D6751 EN 14214 ASTM D975 ASTM D7467
vol.% BD 100 100 0–5 6–20 CP (  C) Report – Not specified a Not specified a PP ( C) – – Not specified a Not specified a CFPP (  C) – Variableb Not specified a Not specified a OSI, 110  C (h) 3 min 6 min – 6 min

t , 40 C (mm 2 /s) 1.9–6.0 3.5–5.0 1.9–4.1 1.9–4.1 Lub, 60  C ( lm) –

– 520 max 520 max AV (mg KOH/g) 0.50 max 0.50 max – 0.30 max IV (g I 2 /100 g) – 120 max –

– CN 47 min 51 min 40 min 40 min S (ppm) 15 max 10 max 15 max 15 max P (mass%) 0.001 max 0.001 max –

–

a There are no requirements for low temperature operability in ASTM D975 or D7467, only guidance.

b Variable by location and time of year. B.R. Moser, S.F. Vaughn / Bioresource Technology 101 (2010) 646–653 6471.0 wt.% KOH (1.8 g). After 1.5 of reaction the mixture was cooledto room temperature and ethanol was removed by rotary evaporation (10 mbar; 35  C) followed by removal of glycerol by gravity separation (>2 h settling time). The crude ethyl esters were treated with 2.5 wt.% Magnesol as described in Section 2.3 to afford purified C. sativa oil ethyl esters (CSEE, 151 g, 84 wt.% yield). Soybean oil ethyl esters were prepared in a similar fashion in high yield (94 wt.%). Free and total glycerol contents of CSEE and SEE were determined according to ASTM D6584.

2.5. Fatty acid profile by GC

Fatty acid methyl esters (FAME) of camelina, canola, palm, and soybean oils were separated (triplicates, means reported) using a Varian (Walnut Creek, CA) 8400 GC equipped with an FID detector and a SP2380 (Supelco, Bellefonte, PA) column (30 m 0.25 mm i.d., 0.20 

### lm film thickness). Carrier gas was He at 1 mL/min. The oven temperature was initially held at 150  C for 15 min, then increased to 210  C at 2  C/min, followed by an increase to 220  C at 50  C/min, which was then held for 10 min. The injector and detector temperatures were set to 240 C and 270 C, respectively. FAME peaks were identified by comparison to the retention times of reference standards.

2.6. Fuel properties of alkyl esters and blends with ULSD

Cloud and pour point (CP and PP, respectively) determinations (triplicates, means reported) were made according to ASTM D5773 and ASTM D5949, respectively, using a model PSA-70S Phase Technology Analyzer (Richmond, B.C., Canada). Cloud and pour points were rounded to the nearest whole degree ( C). For a greater degree of accuracy, PP measurements were done with a resolution of 1  C instead of the specified 3  C increment. Cold filter plugging point (CFPP) was measured (triplicates, means reported) in accordance with ASTM D6371 utilizing a model FPP-5Gs ISL Automatic CFPP Analyzer (Houston, TX). Kinematic viscosity ( 

### t, mm2/s) was determined (triplicates,means reported) with Cannon–Fenske viscometers (Cannon Instrument Co., State College, PA) at 40 C in accordance with ASTM D445. Lubricity (Lub, 

### lm) determinations (duplicates, means reported) were performed at 60  C (±1 C) according to ASTM D6079 using a high-frequency reciprocating rig (HFRR) lubricity tester (PCS Instruments, London, England) from Lazar Scientific (Granger, IN). Reported wear scar ( 

### lm) values were the result of measuring the maximum lengths of the x- and y-axes of each wear scar with a Prior Scientific (Rockland, Massachusetts, USA) Epimat model M4000 microscope, followed by calculating the average of these maximum values.Oil stability index (OSI, h) was measured (triplicates, means reported) following EN 14112 with a Metrohm USA, Inc. (Riverview, FL) model 743 Rancimat instrument. For biodiesel (B100) samples, the flow rate of air through 3 ± 0.01 g of sample was 10 L/h with a block temperature of 110 C and a correction factor ( 

### DT) of 1.5 C. The glass conductivity measuring vessel contained 50 ± 0.1 mL of deionized water. For biodiesel samples blended with ULSD, the flow rate of air through 7.5 ± 0.1 g of sample was 10 L/h with a block temperature of 110  C ( 

### DT = 1.5  C). The conductivity measuring vessel contained 60 ± 0.1 mL of deionized water. Longer reaction vessels and gas inlet tubes were used for the blends to reduce ULSD evaporation. OSI was determined as the inflection point of a computer-generated plot of conductivity ( 

### lS/cm) of deionized water versus time (h). Experiments were terminated at 24 h.Acid value (AV, mg KOH/g) titrations (triplicates, means reported) were performed as described in American Oil Chemists’ Society (AOCS) official method Cd 3d-63 using a Metrohm 836 Titrando (Westbury, NY) autotitrator equipped with a model 801 stirrer and a Metrohm 6.0229.100 Solvotrode. However, the official method was modified for scale to use 2 g of sample and 0.02 M KOH. The titration endpoint was automatically determined bythe instrument and visually verified using a phenolphthalein indicator. Iodine value (IV) was calculated from the fatty acid profile according to AOCS Cd 1c-85. Surface tension ( 

### c , mN/m) was determined (quintuplets, means reported) at 24 ± 1 C and 40 ± 1 C with a Sita t60 bubble pressuretensiometer (Dresden, Germany). Dilutions and temperature control were handled by a Cat Ingenieurbüro M. Zipperer GmbH (Staufen, Germany) M26 stir plate and a model 

### l 10MC burette. A bubble lifetime of at least 4 s was used so that dynamic effects were not a factor in the measurements. The instrument was calibrated using pure water. Additionally, the surface tensions of several organic solutions were measured, and found to agree with literature values. Sulfur (S, ppm) and phosphorous (P, mass%) were measured by Magellan Midstream Partners, L.P. (Kansas City, KS) according to ASTM standards D5453 and D4951, respectively. Derived cetane number (DCN) was determined by Southwest Research Institute (San Antonio, TX) utilizing an Ignition Quality Tester TM (IQT) following ASTM D6890.

3. Results and discussion

3.1. Composition and physical properties of camelina oil

The oil content of camelina seeds was 30.5 wt.%, which was in agreement with the range reported in previous studies ( Budin et al., 1995; Leonard, 1998; Sawyer, 2008 ). The primary fatty acid identified in camelina oil was linolenic acid (C18:3; Table 2 ) at 32.6 wt.%, with other unsaturated fatty acids such as linoleic (C18:2; 19.6 wt.%), oleic (C18:1; 18.6 wt.%), and eicosenoic (C20:1; 12.4 wt.%) acids also detected in significant quantities. The majority of the remaining fatty acids aside from erucic acid (C22:1; 2.3 wt.%) were saturated species such as palmitic (C16:0; 6.8 wt.%), stearic (C18:0; 2.7 wt.%), and arachidic (C20:0;1.5 wt.%) acids. These results are in close agreement with prior reports on the fatty acid profile of camelina oil ( Budin et al., 1995; Frohlich and Rice, 2005; Krist et al., 2006 ). The relatively high polyunsaturated (88.7 wt.%) and trienoic (33.4 wt.%) acid contents of

Table 2 Fatty acid composition (wt.%) of camelina oil (CSO), with canola (CO), palm (PO), and soybean (SBO) oils shown for comparison.

Fatty acid a CSO CO PO SBO

C12:0 Trace 0.3 C14:0 0.1 1.1 C16:0 6.8 4.6 41.9 10.5 C18:0 2.7 2.1 4.6 4.1 C20:0 1.5 0.7 0.3 Trace C22:0 0.2 0.3 Trace C16:1 9 Trace 0.2 0.2 C18:1 9 18.6 64.3 41.2 22.5 C18:1 11 1.1 1.6 C18:2 9, 12 19.6 20.2 10.3 53.6 C18:3 9, 12, 15 32.6 7.6 0.1 7.7 C20:1 11 12.4 Trace Trace C20:2 11, 14 1.3 Trace C20:3 11, 14, 17 0.8 C22:1 13 2.3 C24:1 15 Trace

a For example, C18:1 9 signifies an 18 carbon fatty acid chain with one double bond located at carbon 9 (methyl 9Z-octadecenoate; methyl oleate). All double bonds are cis

. 648 B.R. Moser, S.F. Vaughn / Bioresource Technology 101 (2010) 646–653camelina oil resulted in an IV (151) that was substantially higher than the other oils listed in Table 3

. The AV of crude camelina oil was 2.06 mg KOH/g ( Table 3 ). Refined, bleached and deodorized (RBD) canola, palm, and soybean oils exhibited very low AV (<0.16 mg KOH/g, Table 3 ). The oil stability index (OSI) of camelina oil, determined at 110  C according to the Rancimat method (EN 14112) was lowest among the oils listed in Table 3 with a value of 2.2 h and was consistent with its high polyunsaturated fatty acid content. The CP and PP of camelina oil

were

 10  C and

 17 C, respectively. With the exception of palm oil, these values did not vary significantly from the other oils listed in Table 3 . The kinematic viscosity (40  C) of camelina oil (28.28 mm2/s) was noticeably lower than the values obtained for palm, canola, and soybean oils (41.69, 36.28, and 31.49 mm2 /s, respectively, Table 3 ). The wear scar generated by camelina oil according to ASTM D6079 (60  C) was 128 

### lm (shorter wear scars indicate better lubricity), which with the exception of palm oil (148 

### lm) did not vary significantly from the other oils in Table 3

. The surface tension at 24 C and 40 C of camelina oil (32.3 and30.7 nN/m, respectively) was similar to the values obtained for canola, palm, and soybean oils ( Table 3 ). 3.2. Preparation and quality of alkyl esters from camelina oil

Camelina oil was subjected to homogenous base-catalyzedtransesterification employing classic conditions described previously (Freedman et al., 1984; Moser, 2009a) to afford camelina oil methyl (CSME) and ethyl (CSEE) esters. The yields of CSME (89 wt.%) and CSEE (84 wt.%) were not quantitative. Under ideal conditions, base-catalyzed transesterifications normally proceed to completion ( Tiwari et al., 2007 ). The culprit was most likely the free fatty acid content of camelina oil, as measured by AV. Free fatty acids react with homogenous base catalysts such as sodium hydroxide and methoxide to form soap (sodium salt of fatty acid) and water (or methanol in the case of sodium methoxide), thus irreversibly quenching the catalyst and reducing product yield ( Lotero et al., 2005 ). The AVs of CSME and CSEE were 0.31 and 0.41 mg KOH/g, respectively ( Table 4 ). Although these values were higher thanthose obtained from methanolysis of RBD canola, palm, and soybean oils ( Table 4 ), they were below the maximum prescribed limits in ASTM D6751 and EN 14214 (<0.50 g KOH/g; Table 1 ). The AV of SEE was 0.37 mg KOH/g ( Table 4 ), which was comparable to CSME and CSEE. Additionally, the free and total glycerol contents of alkyl esters from camelina, canola, palm, and soybean oils were below the maximum allowable limits specified in ASTM D6751 and EN 14214.

3.3. Physical properties of camelina oil alkyl esters

The low temperature operability of CSME and CSEE was measured through CP, PP, and CFPP determination. As seen in Table 4, CSME provided CP, PP, and CFPP values of 3,

 4, and

 3  C,respectively, which were indistinguishable from CSEE. Methyl esters prepared from canola oil yielded superior low temperatureproperties, as indicated by lower CP, PP, and CFPP. The values obtained for SME and SEE were similar to CSME and CSEE. As expected, PME exhibited noticeably diminished low temperature operability in comparison to CSME and CSEE ( Moser et al., 2008; Moser, 2008a ). Strategies to improve the low temperature operability of CSME and CSEE may include the use of additives, blendingwith biodiesel produced from other feedstocks, crystallization fractionation, transesterification with long- or branched-chain alcohols, and/or blending with petrodiesel (Knothe et al., 2005; Moser, 2008a, 2009a; Moser et al., 2008). The OSI values of CSME and CSEE were 2.5 and 2.9 h ( Table 4 ), respectively. Methyl esters from canola (6.4 h), palm (10.3 h) and Table 3 Fatty acid trends and physical properties of camelina, canola, palm, and soybean oils.

CSO CO PO SBO

R saturates a 11.3 7.7 48.2 14.6 R unsaturates b 88.7 92.3 51.8 85.4 R polyunsaturates c 54.3 27.8 10.4 61.3 R C20+ d 16.5 Trace Trace R trienes e 33.4 7.6 0.1 7.7 CP (  C)

 10 (1) f

 9 (1) 11 (1)

 7 (1) PP ( C)

 17 (1)

 21 (1) 8 (1)

 9 (1) OSI, 110  C (h) 2.2 (0.2) 10.3 (0.2) 24.7 (0.2) 8.3 (0.1)

t , 40 C (mm2 /s) 28.28 (0.05) 36.28 (0.05) 41.69 (0.02) 31.49 (0.02) Lub, 60  C ( lm) 128 (2) 137 (3) 148 (4) 124 (1) AV (mg KOH/g) 2.06 (0.04) 0.04 (0.03) 0.15 (0.03) 0.03 (0.02) IV (g I 2 /100 g) 151 110 54 134 c, 24  C (mN/m) 32.3 (0.1) 34.2 (0.1) 33.8 (0.1) 34.2 (0.1) c, 40 C (mN/m) 30.7 (0.1) 32.2 (0.1) 32.0 (0.1) 32.2 (0.1)

a R saturates (wt.%) = C12:0 + C14:0 + C16:0 + C18:0 + C20:0 + C22:0.
b R unsaturates (wt.%) = C16:1 + C18:1 + C18:2 + C18:3 + C20:1 + C20:2 + C20:3 + C22:1 + C24:1.

c R polyunsaturates (wt.%) = C18:2 + C18:3 + C20:2 + C20:3.
d R C20+ (wt.%) = C20:0 + C22:0 + C20:1 + C20:2 + C20:3 + C22:1 + C24:1.

e R trienes (wt.%) = C18:3 + C20:3.
f Values in parentheses are standard deviations from the reported means.

Table 4 Fuel properties of camelina, canola, palm, and soybean oil alkyl esters, along with ultra low-sulfur diesel fuel a

.
CSME CSEE CME PME SME SEE ULSD CP (  C) 3 (1) b 2 (1) 0 (1) 17 (1) 0 (1) 0 (1)

 18 (1) PP ( C)

 4 (1)

 4 (1)

 9 (1) 15 (1)

 3 (1)

 4 (1)

 23 (1) CFPP (  C)

 3 (1)

 3 (1)

 7 (1) 12 (1)

 4 (1)

 5 (1)

 17 (1) OSI, 110  C (h) 2.5 (0.1) 2.9 (0.1) 6.4 (0.1) 10.3 (0.1) 5.0 (0.1) 6.0 (0.1) >24

t , 40 C (mm2 /s) 4.15 (0.01) 4.48 (0.01) 4.42 (0.23) 4.58 (0.01) 4.12 (0.01) 4.41 (0.02) 2.30 (0.01) Lub, 60  C ( lm) 122 (3) 145 (5) 169 (1) 172 (1) 135 (1) 137 (3) 571 (5) AV (mg KOH/g) 0.31 (0.01) 0.41 (0.02) 0.01 (0.01) 0.01 (0.01) 0.01 (0.01) 0.37 (0.01) 0 IV (g I 2 /100 g) 151 144 110 54 134 127 Nd c S (ppm) 3 3 2 2 1 1 8 P (mass%) 0 0 0 0 0 0 nd CN 52.8 nd nd nd nd nd 41.4 c, 24  C (mN/m) 31.0 (0.1) 30.8 (0.1) 30.9 (0.1) 30.5 (0.1) 31.0 (0.1) 30.4 (0.1) 27.3 (0.1) c, 40 C (mN/m) 29.5 (0.1) 29.3 (0.1) 29.4 (0.1) 29.0 (0.1) 29.5 (0.1) 29.1 (0.1) 25.9 (0.1)

a CSME: camelina oil methyl esters; CSEE: camelina oil ethyl esters; CME: canola oil methyl esters; PME: palm oil methyl esters; SME: soybean oil methyl esters; SEE: soybean oil ethyl esters, ULSD: ultra low-sulfur diesel fuel.

b Values in parentheses are standard deviations from the reported means.

c nd = not determined. B.R. Moser, S.F. Vaughn / Bioresource Technology 101 (2010) 646–653 649soybean (5.0 h) oils were more stable to oxidation than CSME and CSEE as a result of the high trienoic fatty acid content of camelina oil (33.4 wt.%; Table 3 ). The rate of autoxidation is dependant on the number and location of methylene-interrupted double bonds contained within fatty acid alkyl esters that comprise biodiesel. Polyunsaturated materials, especially trienoic constituents, areparticularly vulnerable to autoxidation, as evidenced by the relative rates of oxidation of the unsaturates: 1 for ethyl oleate, 41 for ethyl linoleate, and 98 for ethyl linolenate ( Holman and Elmer, 1947 ). In addition, the OSI values of methyl esters of oleic, linoleic, and linolenic acids were reported as 2.5, 1.0, and 0.2 h, respectively ( Moser, 2009b ). The combined trienoic fatty acid contents of canola, palm, and soybean oils were 7.6, 0.1, and 7.7 wt.%, respectively ( Table 3 ). Palm oil methyl esters were especially resistant to oxidation as a result of their high saturated (48.2 wt.%) and low polyunsaturated (10.4 wt.%) fatty ester composition. Both CSME and CSEE were unsatisfactory according to oxidative stability specifications ( Table 1 ) contained within ASTM D6751 (OSI >3 h) and EN 14214 (OSI > 6 h). Accordingly, addition of antioxidant additives ( Moser, 2008b ) or blending with more oxidatively stable feedstocks ( Moser, 2008a ) would be necessary to yield satisfactory oxidative stability from esters of camelina oil. The relatively high polyunsaturated fatty acid content of CSME and CSEE resulted in IVs of 151 and 144, respectively ( Table 4 ). Although ASTM D6751 does not contain an IV specification, EN 14214 limits IV to a maximum value of 120 ( Table 1 ). Consequently, CSME and CSEE, along with SME (IV 134) and SEE (IV127) were unsatisfactory according to EN 14214. In order for camelina oil to be acceptable as a feedstock with regard to IV in locations where the EN 14214 standard is applied, blending with feedstocks that contain a greater percentage of saturated fatty acids would be necessary ( Moser, 2008a ). The kinematic viscosities (40 C) of CSME and CSEE were 4.15 and 4.48 mm2 /s ( Table 4 ), which were satisfactory according to ASTM D6751 (1.9–6.0 mm2 /s; Table 1 ) and EN 14214 (3.5– 5.0 mm2 /s; Table 1 ). Among the methyl esters, an inverse relationship was elucidated between kinematic viscosity and polyunsaturated FAME content: PME (most viscous; lowest polyunsaturatedester content) > CME > CSME > SME (least viscous; highest polyunsaturated content). This was expected, as it is known that increasing levels of unsaturation result in lower kinematic viscosities. For example, the reported kinematic viscosities (40 C) of methyl esters of stearic, oleic, linoleic, and linolenic acids were 5.85, 4.51, 3.65, and 3.14 mm2/s, respectively (Knothe and Steidley, 2005a). As anticipated, the kinematic viscosities of the ethyl esters (CSEE and SEE) were higher than the corresponding methyl esters (CSME and SME). The DCN of CSME was above the minimum limits of 47 and 51 specified in ASTM D6751 and EN 14214, respectively, with a value of 52.8 ( Table 4 ). For comparison, a previous study reported the DCN of SME as 54.0 ( Knothe et al., 2006 ). Results generated by ASTM D6890 (DCN) generally correlate with CN determination byATSM D613. The ASTM D6890 method is approved as an alternative to the more traditional CN method (ASTM D613) specified in ASTM D6751. The sulfur contents of CSME and CSEEE were 3 ppm ( Table 4 ), which were satisfactory according to the specified maximum allowable limits in ASTM D6751 and EN 14214 of 15 and 10 ppm, respectively. SME was essentially free of sulfur (1 ppm),along with CME (2 ppm) and PME (2 ppm). In addition, phosphorous content is limited in ASTM D6751 and EN 14214 to a maximum value of 0.001 mass%. None of the methyl esters contained phosphorous ( Table 4 ). The lubricities (60  C) of CSME and CSEE were essentially indistinguishable from esters prepared from other oils ( Table 4 ). Although lubricity is not specified in ASTM D6751 or EN 14214, it is nonetheless an important fuel property. Fuels with poorlubricity can cause failure of diesel engine parts that rely on lubrication from fuels, such as fuel pumps and injectors ( Knothe et al., 2005; Knothe and Steidley, 2005b ). As such, lubricity specifications are included in petrodiesel standards in the United States (ASTM D975; <520 

### lm by ASTM D6079; Table 1 ) and Europe (EN 590; <460 

### lm). As expected, all alkyl esters were considerably below these maximum allowable limits, which was in agreement with previous studies that indicated biodiesel possessed inherently good lubricity ( Knothe and Steidley, 2005b; Moser et al., 2008; Jham et al., 2009; Moser et al., 2009a ). The wear scar generated by CSME (122 

### lm; Table 4 ) was significantly shorter than the corresponding scars for CME (169 

### lm), PME (172 

### lm), SME (135 

### lm), and SEE (137 

### lm), which was not surprising since increasing levels of unsaturation result in superior lubricity (shorter wear scars). For example, the reported wear scars produced by methyl esters of stearic, oleic, linoleic, and linolenic acids were 322, 290, 236, and 183 

### lm, respectively ( Knothe and Steidley, 2005b ). As previously stated, CSME and CSEE contained high percentages of in trienoic methyl esters (C18:3 and C20:3). Although surface tension is not specified in either ASTM D6751or EN 14214, it is nevertheless an important fuel property that affects atomization in combustion chambers in compression–ignition (diesel) engines ( Ejim et al., 2007 ). The surface tensions at 24  C and 40 C of CSME (31.0 and 29.5 mN/m) and CSEE (30.8 and 29.3 mN/m) were similar to SME and slightly higher than CME and PME ( Table 4 ). Both CSME/EE and SME/EE contained higher polyunsaturated fatty ester content (see Table 3 ) than CME and PME. Increasing levels of unsaturation were reported to increase surface tension ( Doll et al., 2007 ). Additionally, longer chainlengths among otherwise similar molecules are reported to increase surface tension ( Allen et al., 1999 ), which further explained why CSME and CSEE had higher surface tensions than CME and PME. Although CSME/EE had slightly higher surface tensions than CME, SME/EE, and PME, it is expected that the differences are not significant enough to negatively influence fuel atomization.

3.4. Evaluation of camelina oil alkyl esters as blend components in ULSD

Because biodiesel is completely miscible with ULSD, it can be used as a blend component in any proportion in ULSD. However, ASTM D975 and D7467 allow up to 5 and 20 vol.% biodiesel ( Table 1 ), respectively. The European petrodiesel standard, EN 590, allows for up to 5 vol.% biodiesel as well. Biodiesel and ULSD are not chemically similar: biodiesel is composed of long-chain fatty acid alkyl esters whereas ULSD is a complex mixture of aliphatic and aromatic hydrocarbons (12 or more carbons) that distill from crude petroleum oil in a similar temperature range (250–350  C). Fuel properties determined in the current study that were affected by blending included lubricity, oxidative stability, low temperatureoperability, kinematic viscosity, and surface tension. Other properties influenced by blending include exhaust emissions, flash point, sulfur content, and cetane number. As seen in Table 4, neat ULSD exhibited a DCN of 41.4, which was satisfactory according to ASTMD975 but significantly below the value obtained for CSME. The sulfur content of ULSD was acceptable with regard to ASTM D975 with a value of 8 ppm. Blending CSME with ULSD resulted in a small reduction in sulfur content, as evidenced by values of 8, 8, 7, and 7 ppm for the B2, B5, B10, and B20 blends. The results for DCN and sulfur content of ULSD were in agreement with a previous study ( Moser et al., 2009b ). Flash point and exhaust emissions were not measured because biodiesel is reported to be superior to petrodiesel with regard to these properties (Mittelbach andRemschmidt, 2004; Knothe et al., 2005). Furthermore, most regulated exhaust emissions (except for NOx ) of petrodiesel are 650 B.R. Moser, S.F. Vaughn / Bioresource Technology 101 (2010) 646–653reduced upon blending with biodiesel ( McCormick et al., 2006; Moser et al., 2009b ). Biodiesel was considerably less stable to oxidation than ULSD, as evidenced by an OSI value of greater than 24 h for ULSD ( Table 5 ). Consequently, blends of CSME, CSEE, SME, and SEE exhibited progressively lower OSI values as the percentage of biodiesel was increased from 0 to 20 vol.% ( Table 5 ). Comparison at the B20 level revealed that the CSME/EE blends were less stable to oxidationthan the SME/EE blends, which was consistent with the results obtained for neat methyl and ethyl esters discussed in Section 3.3

. The petrodiesel–biodiesel blend standard, ASTM D7467 ( Table 1 ), which covers B6 to B20 blends, specifies a minimum OSI value of 6.0 h. As seen in Table 5 , the B20 blend of CSEE failed to meet thisrequirement (5.8 h). Accordingly, employment of antioxidant additives would be required in the case of B20 CSEE-petrodiesel blends. The petrodiesel standard, ASTM D975 ( Table 1 ) does not contain an oxidative stability specification. As indicated in Table 5 , all B2 and B5 blends of CSME/EE and SME/EE, with the exception of B5 CSEE, exhibited OSI values greater than 24 h.Biodiesel is generally inferior to ULSD with regard to low temperature operability (Moser et al., 2008, 2009b). Illustrative of this is a comparison of neat ULSD (CP

 18  C; PP

 23  C; CFPP

 18 C; Table 5 ) to the neat biodiesel fuels listed in Table 4. Consequently,blends of CSME, CSEE, SME, and SEE in ULSD displayed progressively higher CP, PP, and CFPP values as the percentage of biodiesel was increased from 0 to 20 vol.% ( Table 5 ). Taking into consideration standard deviation, the behavior at each blend level among CSME, CSEE, SME, and SEE blends did not vary significantly. For example, the CFPP of B5 blends with CSME, CSEE, SME, and SEE

were

 15,

 16,

 17, and

 16 C, respectively. Neither ASTMD975 nor D7467 specify limits on low temperature operability. Instead, only guidance is provided. Petrodiesel is less viscous than biodiesel, as evidenced by the kinematic viscosity (40 C) of ULSD (2.30 mm2/s; Table 5 ) versus the biodiesel fuels ( Table 4 ). As a result, blends of CSME, CSEE,SME, and SEE in ULSD afforded progressively higher kinematic viscosities as the percentage of biodiesel was increased from 0 to 20 vol.% ( Table 5 ). This result was in agreement with previous reports that examined the kinematic viscosities of SME and PME blends in ULSD (Moser et al., 2008) and SME blends in low-sulfur diesel fuel (<500 ppm S) ( Doll et al., 2008 ). The behavior at each blend level among the CSME, CSEE, SME, and SEE blends did notvary significantly with regard to viscosity. For example, the kinematic viscosities of the B5 blends of CSME, CSEE, SME, and SEE were 2.38, 2.38, 2.37, and 2.38 mm2/s, respectively. All of the blends exhibited kinematic viscosities that were satisfactoryaccording to the petrodiesel (ASTM D975) and petrodiesel–biodiesel blend (ASTM D7467) standards, which both specify a range from 1.9–4.1 mm2 /s ( Table 1 ).As previously stated, petrodiesel (untreated with lubricityenhancing additives) was inferior to biodiesel with regard to lubricity. In fact, the wear scar generated by ULSD (571 

### lm; Table 5 ) was significantly longer than biodiesel (<173 

### lm; Table 4 ) and in excess of the maximum allowable wear scar lengths specified in ASTM D6751 and D7467 ( Table 1 ; <520 

### lm) and EN 590 (<460 

### lm). Accordingly, blends of CSME, CSEE, SME, and SEE in ULSD exhibited progressively better lubricities (shorter wear scars) as the percentage of biodiesel was increased from 0 to 20 vol.% ( Table 5 ). In fact, even at the B2 blend level, CSME/EE and SME/EEblends were satisfactory according to the aforementioned petrodiesel standard (ASTM D975), providing wear scars below 275 

### lm in all cases. Blends equal to or greater than the B5 blend level afforded wear scars below 200 

### lm ( Table 5 ). These results were in agreement with a previous report that examined the lubricity behavior of SME and PME blends in ULSD from 0.1 to 20 vol.% (Moser et al., 2008). Taking into consideration standard deviation, the lubricity behavior at each blend level among the CSME, CSEE, SME, and SEE blends did not vary significantly. For example, the wear scars generated by the B10 blends of CSME, CSEE, SME, and SEE were 142, 169, 154, and 159 

### lm, respectively. The surface tension of ULSD at 24 and 40 C (27.3 and 25.9 mN/
m; Table 5 ) was superior (lower value) to biodiesel (>29 mN/m; Table 4 ). Accordingly, blends of CSME, CSEE, SME, and SEE in ULSD exhibited progressively higher surface tensions as the percentage of biodiesel was increased from 0 to 20 vol.% ( Table 5 ), which was in agreement with a previous study ( Doll et al., 2008 ). However, as the percentage of CSME, for example, in ULSD was increased from B2 (27.4 mN/m at 24 C) to B20 (27.8 mN/m at

Table 5 Oxidative stability (OSI, h), low temperature operability (CP, PP, CFPP,  C), kinematic viscosity (mm2 /s, 40  C), lubricity (Lub, 60  C), and surface tension ( c, mN/m, 24  C and 40 C) of camelina and soybean oil methyl and ethyl esters blended with ultra low-sulfur diesel fuel.

Vol.% OSI(h) CP(  C) PP(  C) CFPP(  C) t(mm2 /s) Lub( lm) c, 24  C(mN/m) c, 40  C(mN/m)

0 >24

 18 (1) a

 23 (1)

 17 (1) 2.30 (0.01) 571 (5) 27.3 (0.1) 25.9 (0.1) Camelina oil methyl esters 2 >24

 16 (1)

 23 (1)

 17 (1) 2.33 (0.01) 248 (8) 27.4 (0.1) 26.1 (0.1) 5 >24

 14 (1)

 23 (1)

 15 (1) 2.38 (0.01) 147 (5) 27.5 (0.1) 26.0 (0.1) 10 16.6 (0.1)

 13 (1)

 22 (1)

 15 (1) 2.42 (0.01) 142 (7) 27.6 (0.1) 26.2 (0.1) 20 8.9 (0.1)

 11 (1)

 20 (1)

 14 (1) 2.58 (0.01) 136 (6) 27.8 (0.1) 26.5 (0.1) Camelina oil ethyl esters 2 >24

 15 (1)

 23 (1)

 17 (1) 2.33 (0.01) 260 (6) 27.4 (0.1) 26.0 (0.1) 5 17.8 (1.1)

 14 (1)

 23 (1)

 16 (1) 2.38 (0.01) 182 (3) 27.4 (0.1) 26.1 (0.1) 10 9.1 (0.3)

 13 (1)

 22 (1)

 15 (1) 2.48 (0.01) 169 (8) 27.5 (0.1) 26.2 (0.1) 20 5.8 (0.3)

 11 (1)

 20 (1)

 14 (1) 2.69 (0.02) 154 (5) 27.8 (0.1) 26.4 (0.1) Soybean oil methyl esters 2 >24

 18 (1)

 22 (1)

 17 (1) 2.31 (0.01) 271 (7) 27.4 (0.1) 26.0 (0.1) 5 >24

 16 (1)

 22 (1)

 17 (1) 2.37 (0.01) 198 (4) 27.4 (0.1) 26.0 (0.1) 10 >24

 14 (1)

 21 (1)

 17 (1) 2.41 (0.01) 154 (3) 27.6 (0.1) 26.1 (0.1) 20 17.1 (0.2)

 12 (1)

 17 (1)

 16 (1) 2.54 (0.01) 143 (4) 27.8 (0.1) 26.4 (0.1) Soybean oil ethyl esters 2 >24

 15 (1)

 22 (1)

 16 (1) 2.31 (0.01) 262 (6) 26.0 (0.1) 25.9 (0.1) 5 >24

 15 (1)

 22 (1)

 16 (1) 2.38 (0.01) 191 (5) 27.4 (0.1) 26.1 (0.1) 10 19.5 (0.4)

 14 (1)

 22 (1)

 13 (1) 2.47 (0.01) 159 (4) 27.5 (0.1) 26.2 (0.1) 20 13.1 (0.2)

 13 (1)

 17 (1)

 11 (1) 2.61 (0.01) 149 (5) 27.7 (0.1) 26.4 (0.1)

a Values in parentheses are standard deviations from the reported means. B.R. Moser, S.F. Vaughn / Bioresource Technology 101 (2010) 646–653 65124  C), a minimal increase in surface tension was noticed. Taking into consideration standard deviation, the surface tension behavior at each blend level among CSME, CSEE, SME, and SEE blends did not vary significantly. For example, the surface tensions (24 C) of the B10 blends with CSME, CSEE, SME, and SEE were 27.6, 27.5, 27.6,and 27.5 mN/m, respectively. The minimal increase in surface tension among the blends in comparison to neat ULSD was not considered substantial enough to negatively impact fuel atomization.

4. Conclusions

Camelina oil, which was obtained in 30.5 wt.% from dried seeds, contained a high percentage of polyunsaturated fatty acids (54.3 wt.%), as indicated by its linolenic (32.6 wt.%) and linoleic (19.6 wt.%) acid contents. Other fatty acids identified in camelina oil included oleic (18.6 wt.%), gondoic (12.4 wt.%), palmitic (6.8 wt.%), stearic (2.7 wt.%), and erucic (2.3 wt.%) acids, with lesser amounts of other constituents also detected. Methyl and ethyl esters were prepared in moderately highyields (89 and 84 wt.%, respectively) from camelina oil by homogenous base-catalyzed transesterification. The AV of crude camelina oil (2.06 mg KOH/g) was attributed to non-quantitative alkyl ester yields. The oxidative stability of biodiesel prepared from camelina oil was unsatisfactory according to ASTM D6751 and EN 14214 as a result of its high polyunsaturated fatty acid content. The high IVs of CSME and CSEE were also in excess of the limit contained in EN 14214. The low temperature operability of CSME and CSEE was similar to biodiesel prepared from canola and soybean oils, and superior to PME. The kinematic viscosity, AV, DCN, lubricity, sulfur and phosphorous contents, as well as the surface tensions of CSME and CSEE were satisfactory according to ASTM D6751 and EN 14214, where applicable.Evaluation of CSME and CSEE as blend components in ULSD revealed that blends at the B20 level were not satisfactory with regard to the oxidative stability specification contained withinASTM D7467. Otherwise, camelina-ULSD blends were indistinguishable from soybean-ULSD blends with regard to low temperature performance, kinematic viscosity, lubricity, and surface tension. Camelina oil alkyl esters, like soybean oil alkyl esters, may be used as lubricity-enhancing additives in petrodiesel. In summary, CSME and CSEE are acceptable as biodiesel fuels provided that antioxidant additives are employed. Overall, the properties of camelina oil alkyl esters, both neat and blended with petrodiesel, were similar to other commonly encountered biodiesel fuels, such as soybean, canola, and palm oil methyl esters.

Acknowledgements

The authors acknowledge Benetria N. Banks, Ray K. Holloway, Erin L. Walter, and Jennifer R. Koch for excellent technical assistance.

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