Bioresource Technology 112 (2012) 355–358

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Bioresource Technology

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Short Communication

Biodiesel from Siberian apricot (Prunus sibirica L.) seed kernel oil

Libing Wang a,b, Haiyan Yu a,⇑a Research Institute of Forestry, Chinese Academy Forestry, Beijing 100091, Chinab Research Institute of Forestry New Technology, Chinese Academy Forestry, Beijing 100091, China

a r t i c l e i n f o

Article history:Received 26 December 2011Received in revised form 24 February 2012Accepted 24 February 2012Available online 4 March 2012

Keywords:BiodieselSiberian apricot seed kernel oilPrunus sibirica L.Fatty acid compositionFuel properties

0960-8524/$ - see front matter � 2012 Elsevier Ltd. Adoi:10.1016/j.biortech.2012.02.120

⇑ Corresponding author. Tel.: +86 010 62889649; faE-mail address: 13520914079@163.com (H. Yu).

a b s t r a c t

In this paper, Siberian apricot (Prunus sibirica L.) seed kernel oil was investigated for the first time as apromising non-conventional feedstock for preparation of biodiesel. Siberian apricot seed kernel has highoil content (50.18 ± 3.92%), and the oil has low acid value (0.46 mg g�1) and low water content (0.17%).The fatty acid composition of the Siberian apricot seed kernel oil includes a high percentage of oleic acid(65.23 ± 4.97%) and linoleic acid (28.92 ± 4.62%). The measured fuel properties of the Siberian apricot bio-diesel, except cetane number and oxidative stability, were conformed to EN 14214-08, ASTM D6751-10and GB/T 20828-07 standards, especially the cold flow properties were excellent (Cold filter pluggingpoint �14 �C). The addition of 500 ppm tert-butylhydroquinone (TBHQ) resulted in a higher inductionperiod (7.7 h) compliant with all the three biodiesel standards.

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1. Introduction apricot are fewer than what is normally needed for typical cultivated

Biodiesel, which consists of mono alkyl esters of long chain fattyacids, is biodegradable and environmentally benign fuel used indiesel engines (Karmakar et al., 2010). However, the biodiesel pre-sents a significant challenge because of high-cost feedstock andincreasingly aggravating tension between energy crisis and foodsecurity (Wang et al., 2012). The use of low cost feedstocks suchas waste cooking oils and non-conventional seed oils can reducebiodiesel production cost and increase supply while avoiding thefood versus fuel problem (Rashid et al., 2011). Therefore, it is nec-essary to search for non-conventional feedstocks for biodiesel pro-duction. Some recent studies of biodiesel from non-conventionalfeedstocks include Mahua (Ghadge and Raheman, 2005), Milo(Rashid et al., 2011), Moringa oleifera (Rashid et al., 2008), Prunusdulcis (Atapour and Kariminia, 2011), Prunus armeniaca (Gumusand Kasifoglu, 2010; Ullah et al., 2009), Croton megalocarpus (Aliyuet al., 2010), Camelina (Moser and Vaughn, 2010), and others.

Siberian apricot (Prunus sibirica L.), a member of the family Rosa-ceae and the genus Prunus, is a deciduous shrub native to the tem-perate, continental, mountainous region, which includes EasternSiberia regions, Maritime Territory of Russia, eastern and southeast-ern regions of Mongolia, northern and north-eastern regions of Chi-na. Siberian apricot is widely distributed with a total area of about1,700,000 ha, and the annual seeds production is above 192,500 tonsin China (Wang, 2011; Zhang, 2003). It grows in temperate climatesand thrives with abundant solar radiation, low temperature, strongwind, low rainfall and poor soil. The agricultural inputs for Siberian

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plants. The Siberian apricot blossoms and bears fruit at 4th year, en-ters into the full bearing period at the 8th year. After 20 years, theyield decreases. It grows old after 40 years until stopping fruit-bear-ing (Zhang, 2003). The traditional use of Siberian apricot focuses onits ecological benefits, such as water and soil conservation, wind-break, sand fixation, environment protection and greening (Zhanget al., 2006). The seed kernel oil of the Siberian apricot can be usedfor edible oils, lubricants, cosmetics, surfactants, and in the preven-tion of cardiovascular diseases and lowering of plasma cholesterollevels (Kris et al., 2001). However, the seed kernel of Siberian apricotcontains amygdalin that can decompose into glucose, benzaldehydeand hydrocyanic acid by the b-glucosidase enzyme. In small quanti-ties, hydrogen cyanide has shown the effects to stimulate respirationand improve digestion as well as be good for the treatment of cancer.In quantity, however, it can cause respiratory failure and even death(Chang et al., 2006).

The objective of the present study was to explore the utility ofSiberian apricot methyl esters as a potential source of biodiesel. Anexperiment was carried out to determine the oil content and fattyacid composition of the Siberian apricot seed kernel oil. The fuelproperties of biodiesel made with apricot seed kernel oil wereevaluated and compared with the specifications in the ASTMD6751-10, EN 14214-08 and GB/T 20828-07 biodiesel standards.

2. Methods

2.1. Materials

The fully matured Siberian apricot (P. sibirica L.) fruits werepicked from shrubs in July 2010 in the Balinyou National Tractor

Table 1Oil contents and oil properties of Siberian apricot seed kernel.

Parameter Siberian apricot

Oil contents (wt.%) 50.18 ± 3.92a

Acid value (mg KOH g�1) 0.46Water content (wt.%) 0.17

Fatty acid composition (wt.%)C14:0 (Myristic acid) 0.03 ± 0.09a

C16:0 (Palmitic acid) 3.79 ± 0.78a

C16:1 (Palmitoleic acid) 0.67 ± 0.25a

C18:0 (Stearic acid) 1.01 ± 0.31a

C18:1 (Oleic acid) 65.23 ± 4.97a

C18:2 (Linoleic acid) 28.92 ± 4.62a

C18:3 (a-Linolenic acid) 0.14 ± 0.05a

C20:0 (Arachidic acid) 0.09 ± 0.04a

C20:1 (Cis-11-eicosenoic acid) 0.11 ± 0.02a

a Values are mean ± S.D of triplicate determination.

356 L. Wang, H. Yu / Bioresource Technology 112 (2012) 355–358

Ploughing Forest Farm, Chifeng City, Inner Mongolia AutonomousRegion, China (geographical coordinates approximately 43�440 N,118�440 E). Seeds were obtained from removed fleshes by hand-processing. The fresh seeds were stored at room temperature for1 week to dry before they were transferred to the laboratory inpolypropylene bags under cool conditions. Kernels were obtainedfrom hulls and stored.

Pure fatty acid methyl esters were purchased from SigmaChemical Co. (USA). Methanol, potassium hydroxide and all otherregents (AR) were from Sinopharm Chemical Reagent Co., Ltd.,Beijing.

2.2. Extraction of seed kernel oil

The kernels of Siberian apricot seeds were dried and crushedusing a domestic grinder giving a mean particle size of the milledkernels of 0.8 mm. Fat components were extracted with petroleumether using a Soxhlet apparatus at 45–50 �C for 6–8 h until theextraction was completed. The oil content was determined as thedifference in weight of the dried kernel sample before and afterthe extraction. The determination was performed in triplicate,and the data reported as mean ± standard deviation.

The acid value and water content of Siberian apricot seeds ker-nel oil were measured by AOCS Official Method Cd 3d-63 and ENISO 8534.

2.3. Trans-esterification experiments

A 2 L three-necked round-bottomed reactor, equipped withthermostat, sampling outlet, a reflux condenser and a mechanicaloverhead stirrer (set at 600 rpm stirring rate) was used for transe-sterification of Siberian apricot oil. 1000 g of Siberian apricot oilwas transferred to the reactor, which was pre-heated to desiredtemperatures before starting the reaction. A 10 g alcoholic KOH(1 mass% with respect to oil) was added to a predetermined200 g anhydrous methanol (approximately 5.5:1 mol ratio ofmethanol/oil), and the mixture was stirred until KOH dissolvedcompletely. The methanol-KOH solution was added to the pre-heated Siberian apricot oil and stirred at 60–65 �C for 1 h. Afterthe transesterification reaction, the mixture was allowed to cooldown and equilibrate for overnight. The reaction product will beseparated to two layers with the upper layer being methyl esterand the lower layer being glycerin. This was followed by conven-tional work-up consisting of separation of phases, washing theresulting methyl esters with water until the water was neutraland drying with magnesium sulfate. The upper layer will be furtheranalyzed by gas chromatography to determine the fatty acid com-position and biodiesel yield.

2.4. Methyl ester analysis and biodiesel yield

The Siberian apricot seed kernel oil methyl ester fatty acid com-position was identified by gas chromatography–mass spectrometry(GC–MS). The hexane (1 ll) extract was injected into a highly polarHP Innowax capillary column of 30 m length (inner diameter0.32 m, film thickness 0.5 mm, split 1:20). An Agilent 6890 (Califor-nia, USA) equipped with flame ionization detector (FID) was used.The injector and detector temperatures were 250 and 280 �C,respectively. Oven temperature was programmed from 190 �C hold-ing at 3 min to 240 �C at the rate of 15 �C/min for 17 min. The carriergas was high-purity hydrogen. Peaks of fatty acid methyl esterswere identified by comparing their retention time with that of theknown standards, run under similar separation conditions. Peakintegration was performed by applying HP3398A software.

In this research, the yield of biodiesel was calculated using thefollowing equation:

Biodiesel yieldðwt%Þ ¼ Amount of FAMEðgÞAmount of oil usedðgÞ � 100% ð1Þ

2.5. Fuel properties of the methyl ester

Fuel properties of the methyl ester were determined according toASTM and EN standard methods: density (ASTM D5002), kinematicviscosity at 40 �C (ASTM D445), flash point (ASTM D93), cold filterplugging point (ASTM D6371), sulfur content (ASTM D5453), watercontent (EN ISO 12937), copper strip corrosion (ASTM D130), cetanenumber (ASTM D6890), oxidative stability (EN 14112), acid value(ASTM D664), free glycerin (ASTM D6584) and total glycerin (ASTMD6584) were determined following standard procedures asspecified.

3. Results and discussion

3.1. Oil properties and biodiesel yield

Siberian apricot seed kernels were found to contain after extrac-tion 50.18 ± 3.92% (w/w) oil (Table 1), which is in agreement withprevious literature (Zhang, 2003; Luo and Liu, 2007). As the woodyenergy plant, the oil content of Siberian apricot seed kernels wasmuch higher than that of traditional oil plants such as Jatrophacurcas L. (38.09%), Sapium sebiferum L. (12–29%) and Vernicia mon-tana Lour. (21–41%) in China (Karmakar et al., 2010; Wang, 2011).

The very low acid value (0.46 mg g�1) and water content (0.17%)of the Siberian apricot seed kernels oil enabled direct base-catalyzedtransesterification for biodiesel production without acid pretreat-ment (Table 1), and the yield of biodiesel was obtained at 88.7%.

3.2. Fatty acid composition

The fatty acids composition in the seed kernels of the Siberianapricot analyzed were determined as myristic acid (C14:0), pal-mitic acid (C16:0), palmitoleic acid (C16:1), stearic acid (C18:0),oleic acid (C18:1), linoleic acid (C18:2), a-linolenic acid (C18:3),arachidic acid (C20:0) and Cis-11-eicosenoic acid (C20:1) (Table1). The percentage of fatty acid composition from the present studywas generally agreed with previously reported study (Sun et al.,1994). Of the nine fatty acids, oleic acid is the most prevalent withthe value of 65.23 ± 4.97%, and linoleic acid (28.92 ± 4.62%) was thepredominant saturated fatty acid.

L. Wang, H. Yu / Bioresource Technology 112 (2012) 355–358 357

3.3. Fuel properties

3.3.1. 1Cold filter plugging pointThe important parameter for low temperature applications of a

fuel is the cold filter plugging point (CFPP). The EN 14214 standarddoes not mention a low-temperature parameter in its list of spec-ifications. However, each country using UNE-EN 14214 can specifycertain temperature limits for different times of year depending onclimate conditions. A low CFPP implies better cold flow properties.As shown in Table 2, the Siberian apricot biodiesel presented a sat-isfactory CFPP (�14 �C). This value was excellent because the Sibe-rian apricot seed kernel oil fatty acids composition has a highpercentage (95.08%) of monounsaturated fatty acids and polyun-saturated acids (Table 1).

3.3.2. Cetane numberThe cetane number (CN) is one of the important parameters,

which is considered during the selection of methyl esters for usingas biodiesel. Table 2 shows that the cetane number for Siberianapricot biodiesel was 48.8, which complies with quality standardsthat prescribe a minimum of 47 (ASTM D6751-10), and wasslightly lower than the standard (EN 14214-08 and GB/T 20828-07) limits (Table 2). Therefore, the Siberian apricot biodiesel agreedwith the standard of EN 14214-08 and GB/T 20828-07 must bemodified the cetane number by use of additives before being usedin an industrial application. This value for the cetane number isreasonable due to the fatty acid composition of the Siberian apricotseed kernel oil, which is mostly consisted of 28.92 ± 4.62% linoleicacid (Table 1) and the cetane numbers of methyl linoleate is 38.2(Knothe et al., 2003).

3.3.3. Oxidative stabilityOxidative stability was one of the important technical issues

that affects the quality of biodiesel. The oxidation stability ofSiberian apricot biodiesel was determined by measuring the induc-tion time using a Rancimat method (EN 14112), giving an induc-tion period of 2.7 h. This value of Siberian apricot biodiesel

Table 2Fuel properties of Siberian apricot seed kernels oil methyl esters with comparison tobiodiesel standards.

Fuel properties Siberianapricot

ASTMD6751-10

EN14214-08

GB/T20828-2007

Density (kgm�3; 15 �C) 878.2 –a 860–900

820–900

Kinematic viscosity(mm2 s�1; 40 �C)

4.341 1.9–6.0 3.50–5.00

1.9–6.0

Flash point (�C) 173 130 min 101 min 130 minCold filter plugging

point (�C)�14 –a –b Report

Sulfur content (mg kg�1) 4.7 15 (S15)max500 (S500)max

10.0max

50 (S50)max500 (S500)max

Water content(mg kg�1)

270 –a 500 max 500 max

Copper strip corrosion(50 �C; 3 h)

1a No. 3 max No. 1max

No. 1 max

Cetane number 48.8 47 min 51 min 49 minAcid number (mg KOH/

g)0.25 0.50 max 0.50

max0.80 max

Oxidative stability (h;110 �C)

2.7 3.0 min 6.0 min 6.0 min

Free glycerin (% mass) 0.013 0.02 max 0.02max

0.02 max

Total glycerin (% mass) 0.12 0.24 max 0.25max

0.24 max

a No specified limit.b Not specified Variable by location and time of year.

oxidative stability did not complies with the minimum prescribedin the EN 14214-08(6 h), ASTM D6751-10(3 h) and GB/T 20828-07(6 h) standard. The poor oxidative stability of Siberian apricotbiodiesel can be attributed to the relatively high methyl linoleatecontent (28.92 ± 4.62%) of the fatty acid composition of the Sibe-rian apricot seed kernel oil (Table 1). The oxidative stability ofmethyl linoleate was found to be 0.94 h (Knothe, 2008). However,the addition of the common synthetic antioxidant tert-butylhydro-quinone (TBHQ) improved the resistance to oxidation of Siberianapricot biodiesel, as evidenced by induction periods (IPs) of 5.6(250 ppm TBHQ) and 7.7 (500 ppm TBHQ) h. A comparison to thebiodiesel standards revealed that, at the higher treatment level(500 ppm TBHQ), Siberian apricot biodiesel afforded an IP compli-ant with the specifications ASTM D6751-10, EN 14214-08 and GB/T20828-07 standards.

3.3.4. Flash pointThe biodiesel fuel flash point, the temperature at which it will

ignite when exposed to a flame or spark, is higher than the petro-diesel standards of transportation safety. The flash point of the bio-diesel sample produced in this study was 173 �C (Table 2). It wasabove the minimum values prescribed in the specifications ASTMD6751-10, EN 14214-08 and GB/T 20828-07 standards.

3.3.5. Other fuel propertiesOther fuel properties of Siberian apricot biodiesel such as den-

sity, kinematic viscosity, sulfur content, water content, copper stripcorrosion, acid value, free glycerin and total glycerin were alsodetermined (Table 2). As expected, all other aforementioned prop-erties of Siberian apricot biodiesel satisfied EN 14214-08, ASTMD6751-10 and GB/T 20828-07 standards.

Besides these fuel properties, the concentration of linolenic acidand acids containing four double bonds in fatty acid methyl estersshould not exceed the limit of 12% and 1% respectively in accor-dance with EN 14214-08. The a-linolenic acid of the Siberian apri-cot seed kernel oil (0.14 ± 0.05%) is much lower than 12% (Table 1)and the fatty acid methyl esters do not contain fatty acids with fourdouble bonds.

4. Conclusions

Siberian apricot has high oil content, low acid value and watercontent. The most results of fuel properties compared well withEN 14214-08, ASTM D6751-10 and GB/T 20828-07 standards,especially the cold flow properties were excellent (CFPP �14 �C).The cetane number and oxidative stability would require the useof additives and antioxidants to meet specifications in biodieselstandards. Siberian apricot has plenty of wild resources and fewerhusbandry management practices required in China. Overall, Sibe-rian apricot is low cost, high oil-producing and low acid value spe-cies for biodiesel feedstock in China.

Acknowledgements

The author acknowledges the financial support of Special Fundfor Forest scientific Research in the Public Interest (201004001)and National Key Technology Research and Development Programof China during the 12th Five-Year Plan (2011BAD22B08) for thisresearch.

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