Indian Journal of Chemical Technology
Vol. 15, September 2008, pp. 467-471
Investigation of acid oil as a source of biodiesel
B M Kulkarni, B G Pujar & S Shanmukhappa*
Chemistry Research Centre, Bapuji Institute of Engineering and Technology, Davangere 577 004, India
Email: [email protected]
Received 11 April 2007; revised 18 June 2008
Acid oil which is a byproduct of vegetable oil industry has been investigated for its suitability as a source of biodiesel, as
it is economic and readily available in considerable quantities at most of vegetable oil refinery sites. The biodiesel from acid
oil is produced by a new type of “ED3R” esterification process developed at the Institute. Fuel properties of biodiesel thus
produced are compared with standard biodiesel and diesel fuel. Blends of biodiesel and diesel fuel are prepared. Fuel
property variations of biodiesel blends produced are reported.
Keywords: Acid oil, Biodiesel, Biodiesel blend, Fuel property variation
High energy demand and increased environmental
pollution related problems due to rampant use of
fossil fuels have necessiated the development and
adaptation to renewable and ecofriendly fuels. Biodiesel is one such initiative which has been projected
as ecofriendly and renewable alternative to diesel
fuel. Its ecofriendly nature, reduced engine emission
profiles and direct usability at existing diesel engines1
have attracted the world attention to a large extent.
Biodiesel is a mixture of fatty acid methyl ester
(FAME) compounds derived from renewable feed
stocks like vegetable oils and animal fats2. Resulting
ester compounds mixture shows fuel properties quite
similar to diesel fuel3. Most of biodiesel at present is
produced from transesterification of vegetable oil
with methanol using potassium hydroxide as catalyst
and glycerol is obtained as a byproduct. Acid type
catalysts4, variety of lipases5 supercritical and noncatalytic6 types of methods have also been reported.
All these methods specify the use of refined vegetable
oils which increase the cost of biodiesel. Though use
of fried oils7, waste oils8, nonedible oils9 is reported to
be economic, collection and availability of required
quantities for such types of oils is still at its nascent
stage in the country. To make biodiesel as a viable
programme, alternate resources which are ecomomic,
sufficient and readily available are to be identified
and appropriate type of technology which can produce
biodiesel of acceptable quality is to be developed10.
Acid oil which is a byproduct of vegetable oil
refinery operations may prove a viable source, as it is
cheap and readily available in significant quantities as
unutilized byproduct. Chemical composition and fuel
properties of acid oil are determined. Acid oil
predominantly consists of long chain free fatty acid
mixture along with small amounts of mineral acids (12%), free moisture (5-8%), phospholipids and sterols
(8-10%) which all impart a characteristic pungent
odor and dark brown colour to the acid oil. Acid oil
because of its oxygenated nature and chain type of
configurational compounds present, has fuel properties which are different than diesel fuel. Heating
values are slightly lower while viscosity and ignition
values are higher than diesel fuel11. If viscosity of acid
oil is reduced and brought closer to diesel fuel, it can
also be used as alternative to diesel fuel. Viscosity of
acid oil is reduced by modified esterification process
using acid type of catalysts. As the conventional
transesterification process does not produce any
desired results, a new type of “ED3R” esterification
process developed at the Institute is employed.
The objective of the present study is (i) To produce
biodiesel from acid oil. (ii) To compare the fuel
properties of biodiesel thus produced with standard
specifications of biodiesel. (iii) Blending of biodiesel
sample with diesel fuel, and (iv) To study the
variations of fuel properties of such types of blends
produced.
Experimental Procedure
Acid oil sample used in the present study was
obtained from M/S Murugharajendra Oil Industries
Pvt. Ltd., Chitradurga, a nearby medium scale
vegetable oil refining complex. The unit processes
INDIAN J. CHEM. TECHNOL., SEPTEMBER 2008
468
about 15,000 metric tonnes of all variety of local and
imported edible vegetable oils and generates about
600 metric tonnes of acid oil per annum as a
byproduct.
Biodiesel sample required for the study was
prepared from acid oil by employing “ED3R”
esterification process. Study was carried out in a
closed type of reactor provided with adjustable
electrical heating unit, a continuous methanol
recirculation and methanol vapors escaping
arrangements. Reaction mixture was maintained at
70oC, methanol-water vapors were condensed, and
recycled back throughout the course of reaction.
Excess methanol used was recovered and reused in
subsequent batches. Resulting crude ester mixture was
washed thrice with equal amounts of water, allowed
to stand overnight. Water settled at bottom was
separated. Top ester layer produced was separated and
batch distilled. Escaping vapors were condensed and
collected as neat biodiesel. Reactor used had a
capacity to process ten liters of acid oil per batch.
About 75 to 80% of acid oil added was obtained as
neat biodiesel.
Diesel fuel used for the study was purchased from
a nearby Indian Oil Corporation (IOC) retail outlet.
Diesel fuel used was first tested for its fuel properties
to ensure its compliance to standard specifications and
later used.
Blends of biodiesel of required compositions were
prepared by flash mixing technique. Appropriate
quantities of neat biodiesel B (100) and diesel B (0)
fuels were used. Five liters of solution of required
compositions were prepared and later used for fuel
property determination studies.
Fuel properties were determined according to the
guidelines of American Society for Testing of
Materials (ASTM). Fuel properties like API gravity,
viscosity, higher heating value, cetane index, and pour
points were determined. All analytical instruments
used for the present studies were confirming to Indian
Petroleum Institute (IPI) specifications.
Results and Discussion
Acid oil
Chemical composition and fuel properties of acid
oil along with some vegetable oils are given in
Tables 1 and 2. As free fatty acids of acid oil are
derivatives of vegetable oils and account for nearly
98% of total size of vegetable oil, chemical and fuel
properties of acid oil are very close to those of
vegetable oils. Typical fatty acid distribution of acid
oil as obtained by gas chromatograph mass spectral
(GCMS) studies with fatty acid distribution of other
vegetable oils are given in Table 3. Spectral
observations clearly indicate that fatty acids of acid
oil are all long carbon chain compounds containing
number of saturated and unsaturated double bonds.
Due to presence of large number of hydrogen bonds
viscosity values of acid oil are about 12-15 folds
higher than ASTM specified upper limit of 4.1 cSt for
diesel fuel.
Typical viscosity temperature variations of acid oil
are compared with diesel fuel in Fig. 1 and Andrade
(Kelvin) plot obtained is shown in Fig. 2. Viscosity of
acid oil decreases sharply with temperature and
follows a Kelvin12 equation of type,
Table 1 — Composition of acid oil
Sl. No. Constituents
% by weight
1
Total fatty acids (TFA)
88.1
2
Mineral acids (MA)
1.1
3
Moisture content (M)
2.2
4
Unsaponifiable matter (USM)
8.6
Table 2 — Chemical and fuel properties of acid oil, diesel fuel and selected vegetable oils
Sl. No. Fuel Property
Acid oil
Diesel fuel
Rice bran oil
Sunflower oil
Jatroba oil
Cotton seed oil
1
Acid value
198
-
184
188
194
196
2
Iodine value
122
-
104
138
106
108
3
Specific gravity
0.914
0.842
0.918
0.921
0.919
0.916
4
Kinematic viscosity (cSt)
48.4
4.1
40.2
34.6
40.4
35.6
5
Heating value (MJ/kg)
36.6
42.2
38.6
39.6
39.7
39.4
6
Flash point (oC)
212
52
242
272
240
236
7
o
Pour point ( C)
+11
-16
+11
+14
+10
+15
8
Cetane value
39.5
45.1
41.6
36.8
51.0
42.3
KULKARNI et al.: INVESTIGATION OF ACID OIL AS A SOURCE OF BIODIESEL
469
Table 3 — Fatty acid distribution of acid oil and some vegetable oils
Sl. No. Oil name
1
Fatty acid distribution (%)
(Carbon chain: No. of double bonds)
Acid oil*
17
2
Cotton seed oil
3
Sunflower oil17
4
Rice bran oil
5
Jatroba oil
17
16:0
16:1
18:0
18:1
18:2
Others
20.3
2.0
1.2
22.4
55.8
0.1
28.7
-
0.9
13.0
57.4
0.3
6.4
0.1
2.9
17.7
72.9
-
14.8
0.3
1.9
45.2
34.2
0.2
4.2
14.2
6.9
43.1
34.3
1.4
*Experimentally determined by GCMS
ln η = A + (B/T)
…(1)
where η is kinematic viscosity of acid oil, A and B are
viscosity coefficients of acid oil, T is temperature in
o
Kelvin.
Fatty acids of acid oil are all of high molecular
weights, hence they are non volatile and vaporize only
at high temperatures. Since they are all of narrow
carbon chain (Z) distribution (14 ≤ Z ≤ 18) they start
distilling at high temperatures and most of them
readily escape once the mixture starts boiling. The
temperatures required to distill out 10% (T10), 50%
(T50) and 90% (T90) of acid oil are very close. Typical
distillation range curves obtained for acid oil and
diesel fuel are shown in Fig. 3. Because of higher
viscosity and distillation range temperatures, acid oil
has lower ignition quality (cetane index) than ASTM
recommended minimum of 40 for diesel fuel. As
viscosity and ignition quality of acid oil are not within
the permissible limits it cannot be directly used as
substitute for diesel fuel.
Fig. 1 — Variation of viscosity of acid oil with temperature
Biodiesel
Typical fuel properties of biodiesel sample
produced are compared with standard biodiesel and
diesel fuel in Table 4. Biodiesel produced from acid
oil closely meets the standard specifications.
Chemical and fuel properties of biodiesel are
distinctly different from those of diesel fuel, as the
types of compounds associated with biodiesel are
different. Biodiesel is a mixture of FAME compounds
which are all of narrow range and typical long carbon
chain types of saturated and unsaturated oxygenated
hydrocarbon structures, while diesel fuel is a mixture
of large range alkyl, substituted naphthene and
aromatic types of hydrocarbon compounds14.
Elemental composition and relative amounts of
compounds present in biodiesel and diesel fuel are
shown in Tables 5 and 6. Due to presence of
Fig. 2 — Andrade plot of acid oil
Fig. 3 — Distillation range curves of acid oil and diesel
fuel samples
INDIAN J. CHEM. TECHNOL., SEPTEMBER 2008
470
Table 4 — Fuel properties of biodiesel, diesel fuel samples and their respective standards
Sl. No. Fuel property
Biodiesel sample
Standard biodiesel*
Diesel sample
Standard diesel**
0.886
0.87-0.89
0.846
0.84-0.86
1
Density(kg/L)
2
Kinematic viscosity (cSt)
5.2
3.5-5.2
2.07
1.92-4.1
3
Higher heating value (MJ/kg)
40.6
Min.39.2
45.5
Min.45.2
4
Cetane index
54.4
Min.50
42.0
Min.40
5
Flash point (oC)
102
Min.100
54
Min.52
6
Pour point (oC)
7
Distillation range temperatures (oC)
*ASTM: D6751, **BIS: 1460-1974.
-8
Min.-5
-20
Min.-16
300-350
Max.360
180-326
Max.342
Table 5 — Elemental analysis of biodiesel and diesel fuels
Sl.No.
Elements
Composition (%)
Table 6 — Composition of biodiesel and diesel fuels
Sl.No.
Biodiesel
Diesel fuel
1
Carbon (C)
79.6
86.4
2
Hydrogen (H)
10.5
13.6
3
Oxygen (O)
8.6
-
4
Nitrogen (N)
1.3
-
5
C/H
7.6
6.5
Type of compounds
Biodiesel
Diesel fuel
1
n-Aliphatic
15.2
67.4
2
Olefinics
84.7
3.4
3
Aromatics
-
20.1
4
Naphthenes
-
9.1
electronegative element oxygen, biodiesel is slightly
more polar than diesel fuel as a result viscosity of
biodiesel is higher than diesel fuel. Presence of
elemental oxygen lowers the heating value of
biodiesel when compared to diesel fuel15.
Blend properties
Biodiesel blend contains both types of compounds
of biodiesel and diesel fuels; hence these blends
exhibit dual properties. Properties of blends vary with
the composition and properties of neat biodiesel and
diesel fuels used (Table 7). Typical viscosity
composition variations of blends obtained is shown in
Fig. 4. A mixture law equation16 of type (2) is found
out to be satisfactory for viscosity of blends.
ηB = η1m1 X η2m2
Fig. 4 — Viscosity of biodiesel blend
…(2)
where ηB is kinematic viscosity of blend, η1 and η2 are
kinematic viscosities of neat biodiesel and diesel fuel
samples used, m1 and m2 are their corresponding mass
fractions of biodiesel and diesel fuel in the blend. The
measured values shown in Fig. 5 are in agreement
with predicted values based on Eq. (2).
Conclusions
Based upon foregoing experimental results the
following conclusions are drawn
Fig. 5 — Measured and predicted kinematic viscosity of biodiesel
blend fuels
KULKARNI et al.: INVESTIGATION OF ACID OIL AS A SOURCE OF BIODIESEL
471
Table 7 — Fuel properties of biodiesel-diesel fuel blends
Sl. No.
Composition of blend
Fuel properties
Kinematic viscosity
(c.St.)
Heating value
(MJ/kg)
Density
kg/L
Pour point
(oC)
Cetane index
1
Neat biodiesel
5.2
39.6
0.890
-3
59.6
2
80% blend B (80)
4.1
40.1
0.884
-4.6
54.0
3
60% blend B (60)
3.8
40.6
0.876
-6.2
52.8
4
40% blend B (40)
3.6
41.5
0.866
-8.0
51.6
5
20% blend B (20)
3.0
42.2
0.855
-10.2
50.8
6
Neat diesel
2.1
45.5
0.840
-20
50.0
(i) Acid oil which is a byproduct of vegetable oil
refineries can be used for biodiesel
developmental activities. Since acid oil contains
free fatty acids and moisture levels much higher
than refined vegetable oils conventional
transesterification process does not produce any
desired results.
(ii) Biodiesel of acceptable quality can easily be
produced by ED3R Esterification process.
(iii) Blending of biodiesel with diesel fuel produces
a blend whose fuel properties vary with the
composition and properties of neat fuels used.
Carbon chain length (Z), number (n), location
(∆) of double bonds and relative amounts (m)
of compounds present all influence the fuel
properties of the blends.
(iv) Fuel properties of biodiesel fuel produced vary
with the source of feed stock used.
Acknowledgement
The authors are grateful to All India Council for
Technical Education (AICTE), New Delhi for their
financial assistance under research promotion scheme
(RPS). Authors also thank M/s Murugharajendra Oil
Industries Pvt. Ltd. Chitradurga, Management Bapuji
Educational Association (BEA) Davangere, Prof. B.T.
Achyutha, Principal, Bapuji Institute of Engineering
and Technology for their support and encouragement.
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