Experimental Study on Storage and Oxidation Stability of Bitter

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An Experimental Study on Storage and Oxidation Stability of Bitter Apricot Kernel oil Biodiesel Virender Singh Gurau, Mudit Shankar Agarwal, Amit Sarin, and Sarbjot Singh Sandhu Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.6b01676 • Publication Date (Web): 09 Sep 2016 Downloaded from http://pubs.acs.org on September 10, 2016

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An Experimental Study on Storage and Oxidation Stability of Bitter Apricot Kernel oil Biodiesel Virender Singh Gurau1, Mudit Shankar Agarwal1, Amit Sarin2 and Sarbjot Singh Sandhu*3 1

Research Scholar, Department of Mechanical Engineering, Dr. B R Ambedkar NIT Jalandhar, Punjab, India

2

Professor, Department of Applied Sciences, Amritsar College of Engineering and Technology, Amritsar, Punjab, India

3

Assistant Professor, Department of Mechanical Engineering, Dr. B R Ambedkar NIT Jalandhar, Punjab, India Email: [email protected]

Abstract Worldwide biodiesel is accepted as a substitute for mineral diesel for its almost similar physical and chemical properties. As biodiesel is produced from vegetable oil, animal fat or waste frying oil and is composed of combination of saturated and unsaturated fatty acid, this makes it prone to oxidation with time. As a result of the oxidation, insoluble gums and deposits are formed which adversely affect the characteristics of the biodiesel and results in corrosion of engine components like injectors, piston rings, piston liners etc. during engine running. In this present study, storage and oxidation stability of biodiesel produced from bitter apricot kernel oil was investigated for six months under dark and sunlight storage condition without being exposed to air. Five antioxidants in small quantity viz. tert-Butylhydroquinone (TBHQ), Butylated Hydroxytoluene (BHT), Butylated Hydroxyanisole (BHA), Pyrogallol (PY) and Propyl Gallate (PG), one per sample was used to enhance the induction period. The result shows that by the dosage of antioxidants, biodiesel storage and oxidation stability can be maintained for six months in both storage conditions. Keywords: Apricot; Prunus armeniaca L.; oxidation; oxidation stability; storage stability; antioxidants; induction period

1. Introduction Biodiesel can be produced from vegetable oils, animal fat or waste frying oil by transesterification reaction. Biodiesel is a fuel composed of mono alkyl esters of long chain fatty

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acids. These fatty acid chains are the combination of saturated and unsaturated fatty acids. The amount of unsaturated fatty acids present in the biodiesel defines its oxidation stability. More the amount of unsaturated fatty acids in biodiesel, more it is prone to oxidation. The most common unsaturated fatty acids present in biodiesel are oleic (C18:1), linoleic (C18:2) and linolenic (C18:3). A previous study shows the relative oxidation rate for oleic, linoleic and linolenic acid as 1: 12: 25.1 Although degradation of biodiesel as a result of oxidation instability is undesirable, however it is advantageous from environmental point of view as it makes biodiesel relatively more biodegradable as compared to mineral diesel.

Oxidation of biodiesel is an auto oxidation

2

reaction which involves three steps: initiation, propagation and termination. The complete process is shown in figure 1. As a result of the oxidation, insoluble gums and deposits are produced which affect the properties and characteristics of the biodiesel and its engine application.

Figure 1: Auto oxidation reaction

As per ASTM D 6751 and EN 14214 standards, the biodiesel must have a minimum 3 and 6 hours of oxidation stability respectively at 110°C and thus it has become an important fuel quality parameter. During biodiesel production, some natural antioxidants get removed during water washing and subsequent moisture removal process and thus biodiesel becomes more prone


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to oxidation. Although it is not possible to avoid the oxidation of biodiesel, it can be delayed by using synthetic antioxidants. Previous studies3-14 found that the oxidation of biodiesel during storage results in increase in acid number, density and kinematic viscosity whereas induction period decreases. Sarin et al.3 carried out oxidation stability study of Jatropha biodiesel using five antioxidants: α-tocopherol (α-T), BHT, tert- Butylated phenol derivative (TBP), Octylated butylated diphenyl amine (OBPA) and TBHQ. The research concluded that in order to maintain the induction period of 6 hours; the order of efficiency of antioxidants is TBHQ > BHT > TBP > OBPA > α-T. Kivevele et al.5 studied the oxidation stability of Croton Megalocarpus biodiesel using three antioxidants; PY, PG and BHA. The effectiveness of antioxidants was found to be PY > PG > BHA. In another study by Jain et al.6 on six months storage stability of Jatropha biodiesel using PY antioxidants, it was found that the viscosity, peroxide value and acid number of biodiesel increases with storage time and 200 ppm of PY was sufficient to make the Jatropha biodiesel stable for six months. Shahabuddin et al.8 carried out experiments on three months storage stability of fuels viz. Jatropha biodiesel and its blends, palm oil biodiesel and its blend and coconut oil biodiesel without using any antioxidants. The study concluded that density, viscosity and acid value of fuels increases while flash point decreases with the storage time. It was also found that out of these properties, acid value is most critical as it goes out of specified value for all fuels in three months. Obadiah et al.9 conducted experiments on storage stability of Pongamia pinnata (L.) Pierre biodiesel using five antioxidants, viz. BHT, BHA, PY, Gallic Acid (GA) and TBHQ. The study revealed that the acid value and kinematic viscosity increases with storage period and out of five antioxidants, PY is the most effective. Likewise in another study on the effect of antioxidants BHT, PY, TBHQ, BHA and PG on fuel properties of Karanja biodiesel under different storage conditions, viz. in sunlight/dark exposure, with/without air exposure, with/without metal exposure, the advantageous effects on retarding the degradation of fuel sample due to oxidation were reported. 11 Previous studies reveal that limited work has been done on long term storage and oxidation stability of biodiesel under different storage conditions using antioxidants and their effect on biodiesel properties like acid value, kinematic viscosity, density and induction period. Further, no article is available on the oxidation and storage stability of a non-edible Bitter Apricot seed oil biodiesel. In the present study, the oxidation and storage stability of biodiesel produced from


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Indian originated Bitter Apricot kernel seed oil15 has been investigated over a storage period of six months under two different storage conditions: 1. closed to air in dark; and 2. closed to air and exposed to sunlight. The conditions selected are important from storage viewpoint. The biodiesel after production is kept in airtight containers and transported to distributors or filling stations. The biodiesel containers are exposed to sunlight or dark conditions during this transportation and storage in distributor sites and filling stations.

Considering these storage

situations, dark and sunlight storage conditions without exposing it to air were selected for the study. Five antioxidants viz. TBHQ, BHA, BHT, PY and PG have been used in the study. During storage, samples were taken out on monthly basis and different fuel quality parameters such as acid number, kinematic viscosity and induction period were monitored. Acid number and Kinematic viscosity of biodiesel were selected as monitoring parameters as these fuel properties dominantly affect engine application.

2. Materials and methods: The bitter Apricot kernel oil used in this work was purchased from Kullu, Himachal Pradesh, India. Biodiesel was produced from this oil by direct transesterification reaction as the oil has low free fatty acid (FFA) content. To obtain a yield of 98%, the reaction parameters were: temperature- 65°C, Molar ratio of oil: methanol- 1:6, catalyst concentration (KOH)- 1.5% and reaction time- 1 hour. Five antioxidants TBHQ, BHT, BHA, PY and PG, one per sample with purity grade > 98% were used in the concentration of 100, 200 and 300 ppm. Antioxidants in all concentrations were completely dissolved in biodiesel samples. The biodiesel samples were prepared and stored in the conditions: 1. closed to air in dark; and 2. closed to air and exposed to sunlight. Samples were monitored for their acid number, kinematic viscosity and induction period every month. The fatty acid composition of Bitter Apricot kernel oil biodiesel was analyzed by Gas Chromatography. During this analysis, 1 µl of sample was injected into the column. Initially the column oven temperature was kept at 40°C with a hold time of 1 minute and then heated up to 380°C with a ramp rate of 5°C/ min and held at this temperature for 5 minutes. Helium as a carrier gas was made to flow continuously at a constant rate of 1.5 ml/min throughout the analysis. The percentage of fatty acid composition was obtained by electronic integrated measurement using Flame Ionization detection (FID).


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Oxidation stability of biodiesel samples with varying antioxidant dosage was studied according to EN 14112 standard using Rancimat instrument. Figure 2 shows the measurement principle of Rancimat instrument. In oxidation stability testing, the biodiesel samples of 3g each are maintained at a steady temperature of 110°C and air is allowed to pass through each sample at a constant flow rate of 10 l/h. Each measuring vessel is filled with 50 ml deionized water. The oxidation products are shifted into the measuring vessel along with the air through the deionized water. Electrodes are used for continuous monitoring of conductivity of the deionized water. Sudden increase in the conductivity of deionized water represents the oxidation of biodiesel.12

Figure 2: Measurement principle of Rancimat Instrument

3. Results and Discussion: 3.1. Properties of Bitter Apricot Kernel oil Biodiesel: Table 1 shows the important physico-chemical properties of fuels viz. mineral diesel, Bitter Apricot kernel oil and its biodiesel. The properties of Bitter Apricot kernel oil biodiesel are in conformance with the ASTM D6751, EN 14214 and IS 15607 standards.


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Table 1: Physico- chemical properties of fuels Property

ASTM

EN 14214

IS 15607

Diesel

Raw oil

Biodiesel

0.5 (max.)

0.5 (max.)

-

2.29

0.46

860- 900

860- 900

830

917

881

3.5 – 5

2.5- 6

2.8

35.56

5.13

44.5

37.82

39.42

65.5

235.5

115.5

D6751 Acid

Value

(mg 0.5 (max.)

KOH/g) Density

@

15°C -

(kg/m3) Kinematic Viscosity 1.9 - 6 @ 40°C (cSt) Calorific

Value -

-

(MJ/kg) Flash Point (°C)

93 (min.)

> 101

120 (min.)

Fatty acid composition of bitter apricot biodiesel given in Table 2 shows that bitter apricot kernel seed oil biodiesel mainly consists of oleic acid (72%) and linoleic acid (20%).

Table 2: Fatty acid composition of Bitter Apricot kernel seed oil biodiesel Fatty Acid

Structure

Composition (%)

Palmitic

C16:0

3.30

Palmitoleic

C16:1

0.98

Stearic

C 18:0

1.62

Oleic

C18:1

71.76

Linoleic

C18:2

20.19

Linolenic

C18:3

0.13

Other

-

2.02

Table 3 shows the oxidation stability of various feed stocks with different fatty acid alkyl ester composition. Here, it can be observed that feedstock with high amount of saturated alkyl esters (C 14:0, C 16:0, C 18:0) have high oxidation stability, whereas feedstock with high amount of polyunsaturated alkyl esters (C 18:2, C 18:3) have low oxidation stability. As Bitter apricot kernel biodiesel has comparatively high monounsaturated alkyl esters (C 16:1, C 18:1), its


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oxidative stability is in the medium range which is in conformance with ASTM D 6751 and EN 14214 standards of 3 hours and 6 hours respectively. The order of increase in oxidation and storage stability for different alkyl esters has been given as polyunsaturated alkyl esters < monounsaturated alkyl esters < saturated alkyl esters in number of studies.2, 4,7,12 Table 3: Oxidation stability of various feedstock’s with different fatty acid alkyl ester composition Feedstock

Saturated alkyl

Monounsaturated

Polyunsaturated

Induction

esters (%)

alkyl esters (%)

alkyl esters (%)

period (hrs)

6.94

72.74

20.32

8.22

21.1

44.5

34.4

3.95

46.5

46

7.5

13.37

91

6.5

2.5

28.94

18.8

42.8

38.4

1.7

Bitter Apricot kernel Biodiesel Jatropha Biodiesel3 Palm oil Biodiesel8 Coconut oil Biodiesel8 Rice Bran oil Biodiesel10

3.2. Evaluation of storage stability 3.2.1. Acid Number The effect of antioxidants on acid number of biodiesel during storage period under dark and sunlight storage condition is summarized in figure 3 and 4. The acid number of biodiesel samples was found to increase with the increase in storage time. The possible reasons are the formation of hydro peroxides by auto oxidation mechanism2 and hydrolysis of methyl esters to fatty acids which are responsible for increase in acid number. Similar results were obtained by other researchers on storage stability testing of various biodiesels.6,8,9,11 The results show that acid number of biodiesel increased by 16.8% and 26.7% during six months in dark and sunlight storage conditions respectively without using any antioxidants. The degradation of biodiesel is more in sunlight storage conditions as compared to storage in dark. The probable reason is the triggering of photo oxidation16 under sunlight along with auto oxidation process which enhances the biodiesel degradation. The results obtained are in conformity with those obtained by Jose et al.17 under sunlight storage condition.


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Usage of antioxidants has resulted in reduction of biodiesel degradation. Addition of 300 ppm of antioxidants TBHQ, BHT, BHA, PY and PG prevent acid number degradation by 3.3%, 2.8%, 2.2%, 5.2% and 4.3% in dark storage condition and 7.9%, 7.2%, 7.9%, 10.7% and 10.3% in sunlight storage conditions respectively. Out of the antioxidants used, PY and PG seem to be more effective in preventing biodiesel degradation. The probable reason for being more effective may be due to two OH groups linked to the aromatic ring. Thus based on their electronegativities, they offer more sites for the formation of a complex between free radical and antioxidant radical for the stabilization of the ester chain.9 3.2.2. Kinematic Viscosity Figure 5 and 6 shows the effect of antioxidants on kinematic viscosity of biodiesel during storage period under dark and sunlight storage condition. Kinematic Viscosity of biodiesel samples was found to increase with increase in duration of storage. Likely reasons are formation of insoluble sediments as a result of oxidation process and combination of smaller molecules to higher weight molecules by a hydrolysis reaction which increases the viscosity of the biodiesel samples. Similar studies on storage stability test of various biodiesels also show increase in kinematic viscosity.6,8,9,11 The results obtained in this study show that viscosity of biodiesel increased by 12.9% and 14.4% during six months in dark and sunlight storage conditions respectively without using any antioxidants. The degradation of viscosity is more in sunlight storage condition because of absorption of ultra-violet (UV) radiation which would result in commencement of photo oxidation process. Jose et al.17 also concluded faster degradation of Karanja biodiesel under sunlight storage condition. Doping of 300 ppm concentration of antioxidants TBHQ, BHT, BHA, PY and PG prevent viscosity degradation by 2.9%, 2.9%, 2.1%, 4.5% and 4.5% in dark storage condition and 1.1%, 2.4%, 2.1%, 4.3% and 4.3% in sunlight storage conditions respectively. Of the five antioxidants, PY and PG seem to be more effective to prevent biodiesel degradation because of the two OH groups linked with aromatic ring which facilitate the stabilization of ester chain.9 3.2.3. Induction Period The effect of antioxidants on Induction period of biodiesel during storage time under dark and sunlight storage condition is shown in figure 7 and 8. Induction period of biodiesel sample was found to decrease with storage period. Induction period is an indication of biodiesel oxidation.


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The decrease in induction period shows that the biodiesel samples are oxidized with storage period. The variation in induction period is in line with other studies reported by Jain et al.6 and Agarwal et al.11. The results obtained show that the Induction period of biodiesel decreased by 57.3% and 71.6% during six months in dark and sunlight storage conditions respectively without using antioxidants. As already mentioned, the oxidation of biodiesel is predominant when exposed to sunlight due to addition of photo oxidation to auto oxidation process. Addition of 300 ppm concentration of antioxidants TBHQ, BHT, BHA, PY and PG elongate induction period by 104%, 173.5%, 181.2%, 497% and 502% in dark storage condition and 182%, 208%, 259.2%, 615% and 348.5% in sunlight storage condition respectively. Of the five antioxidants used, PY and PG appear to be more effective to prevent biodiesel degradation because of the two OH groups linked with aromatic ring which makes the ester chain more stable during oxidation.9


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Figure 3: Variation in Acid Number of biodiesel with different antioxidants in dark storage condition (a) TBHQ (b) BHT (c) BHA (d) PY (e) PG (f) comparative 300 PPM


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Figure 4: Variation in Acid Number of biodiesel with different antioxidants in sunlight storage condition (a) TBHQ (b) BHT (c) BHA (d) PY (e) PG (f) comparative 300 PPM


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Figure 5: Variation in Kinematic Viscosity of biodiesel with different antioxidants in dark storage condition (a) TBHQ (b) BHT (c) BHA (d) PY (e) PG (f) comparative 300 PPM


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Figure 6: Variation in Kinematic Viscosity of biodiesel with different antioxidants in sunlight storage condition (a) TBHQ (b) BHT (c) BHA (d) PY (e) PG (f) comparative 300 PPM


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Figure 7: Variation in Induction Period of biodiesel with different antioxidants in dark storage condition (a) TBHQ (b) BHT (c) BHA (d) PY (e) PG (f) comparative 300 PPM


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Figure 8: Variation in Induction period of biodiesel with different antioxidants in sunlight storage condition (a) TBHQ (b) BHT (c) BHA (d) PY (e) PG (f) comparative 300 PPM 4. Conclusions: The conclusions drawn from the present study are: It is feasible to convert Bitter Apricot kernel oil into biodiesel.


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The physico-chemical properties of produced biodiesel conform to ASTM D6751, IS 15607 and EN 14214 standards. The storage stability test shows that acid number and kinematic viscosity of biodiesel increases while induction period decreases with storage period. Even with addition of antioxidant, no biodiesel sample could meet the acid number specification after 6 months of storage. Without the addition of antioxidant, the neat biodiesel sample was able to meet the kinematic viscosity specification even after 6 months of storage in dark and sunlight storage conditions. Sunlight storage condition has more adverse effect on biodiesel properties as compared to dark storage condition. Without antioxidants, biodiesel fails to maintain the minimum induction period of 6 hour within 4th and 3rd month for dark and sunlight storage condition respectively. 100 ppm of BHT, BHA, PY and PG antioxidants maintain the Induction period of biodiesel up to six months in both dark and sunlight storage condition. Considering all the results, increasing order of effectiveness of antioxidants has been found to be PY> PG > BHA > BHT> TBHQ.


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Experimental Study on Storage and Oxidation Stability of Bitter

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