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Bull. Chem. Soc. Ethiop. 2020, 34(2), 249-258. ISSN 1011-3924
2020 Chemical Society of Ethiopia and The Authors Printed in Ethiopia
DOI: https://dx.doi.org/10.4314/bcse.v34i2.4
__________
*Corresponding author. E-mail: ahmed.hussen29@aau.edu.et
This work is licensed under the Creative Commons Attribution 4.0 International License
PRODUCTION AND CHARACTERIZATION OF BIODIESEL AND GLYCERINE
PELLET FROM MACROALGAE STRAIN: CLADOPHORA GLOMERATA
Dawit Firemichael
1,2
, Ahmed Hussen
2*
and Wendawek Abebe
3
1
Department of Chemistry, School of Graduate Studies, Dilla University, P.O. Box 419, Dilla,
Ethiopia
2
Center for Environmental Sciences, College of Natural and Computational Sciences, Addis
Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia
3
Department of Biology, College of Natural and Computational Sciences, Hawasa University,
P.O. Box 5, Hawasa, Ethiopia
(Received September 1, 2019; Revised August 8, 2020; Accepted August 19, 2020)
ABSTRACT. Biodiesel was prepared by extracting oil from Cladophora glomerata green algae followed by
transesterification of the oil using NaOH as a catalyst. The algae Oil extraction was carried out using two different
techniques (Soxhlet and refluxing) and similar oil yield was obtained (23-24%). The resulting biodiesel s howed
desirable physical and chemical properties. Specific gravity, acid value, iodine value, ash content and calorific
value of the algae biodiesel were within the specification of American Society for Testing and Materials (ASTM)
and European Standards (EN). The analysis of fatty acid methyl ester composition revealed, 63, 27 and 10% for 9-
octadecodenoic, hexadeconic and octadeconoic acid methyl ester, respectively. From the production line, two
waste streams (glycerol and residual biomass) were combined to form a glycerine pellet. The measured energy
content of the glycerine pellet was found to be comparable with firewood. Therefore, C. glomerata could
potentially be utilized for the production of both biodiesel and glycerine pellet with no net waste in the
transesterification process.
KEY WORDS: Algae oil, Biodiesel, Transesterification, Glycerine pellet, Macroalgae, Cladophora glomerata
INTRODUCTION
Conventional sources of energy like natural gas, oil and coal have caused immense damage to
the environment by increasing the carbon in the atmosphere causing various global climatic
events, such as acidic rain and global warming [1]. Currently, bio-fuels are being explored as an
alternative source of energy. Among the bio-fuels, biodiesel seems to be at the forefront because
of its environmental credentials such as renewability, biodegradability and clean combustion
behaviour [2]. The production of biodiesel from oil crops [3, 4], waste oil [5], plant seed oil [6]
and fruit and vegetable wastes [7] had been reported in the literature. These feedstocks are
mainly known to be the first and second generation sources of biofuel [8].
Algae are the third generation fuel, which are considered as the most promising alternative
and renewable feedstock sources for producing biodiesel [9]. Like other vegetable oils or lipids,
the algae oils are composed of triglycerides (fatty acid ester of glycerol), which can be
converted into methyl esters (biodiesel) and glycerol via transesterification process. Algae have
several advantages over conventional crops. Because of their simple cellular structure, algae
have higher rates of biomass and oil production, faster growth rate than other conventional crops
[10]. The per unit area yield of oil from algae is estimated to be from 20,000 to 80,000 L per
acre, per year; this is 7–31 times greater than the next best crop, palm oil [11]. In contrast to the
first and second generation, algae can be grown in water bodies (which account two thirds of the
earth surface) by avoiding the use of land [12, 13].
Dawit Firemichael et al.
Bull. Chem. Soc. Ethiop. 2020, 34(2)
250
Based on cellular complexity algae could be classified in to two as microalgea and
macroalgae. Microalgae are unicellular, plant like organisms which range from 1–50 μm in size
[14] and can be seen only using a microscope. On the other hand, macroalgae are multicellular,
macroscopic, and can grow up to 60 m in length [15]. Different research findings reported that
both macroalgae and microalgae are important sources of biofuel. Deriving biodiesel from
microalgae, however, presents some significant challenges. There are high costs attached to
cultivation and harvesting of microalgae, rendering them economically infeasible with current
technologies and processes. In addition, the vulnerability of microalgae to contaminants and
elements necessitates the use of sophisticated systems such as bioreactors which increase the
cost and complexity of operations. Nevertheless, because of their high oil yield, microalgae are
widely studied [16-18] as biodiesel feedstock.
Macroalgea present significant advantages in their ease of cultivation and harvesting, and
subsequently low costs for both [19]. Besides, macro-algae are effective in nutrients uptake (N,
P) from sewage and industrial waste water without being affected [20]. Irrespective of these
advantageous of macroalgae over microalgae, there are few studies on macroalgae as biodiesel
feedstock [21, 22]. In Ethiopia there are several species of green algae. However, research
activities made to utilize them as feedstock for bio-fuel production is scant and at its infancy
stage. Therefore, in the present study, one of a macroalgae named Cladophora glomerata,
collected from lake Hawasa, was studied for its potential of biodiesel production. The oil was
extracted, transesterified and characterized using standard methods. Furthermore, the residual
biomass of the transesterification process was mixed with glycerol to produce a glycerine pellet
which could be used as refuse derived fuels (RDF). The glycerine pellet energy content was
estimated and compared with firewood.
EXPERIMENTAL
Chemicals, apparatus and instruments
Methanol, chloroform, and n-hexane (99.7% purity) was purchased from Merck (Darmstadt,
Germany), while the sodium hydroxide was from LobaChemie (GmbH, Switzerland). Glycerol
standard (99.5% purity) was obtained from VWR International. Trichloethylene (98% purity)
was purchased from Thomas Scientific and used after further purification. Apparatus used were:
Soxhlet extractor, thermo-regulator heater equipped with stirrer (MGW-LAUDA, D6970,
Germany), specific gravity bottle, pH meter (Hanna model No. 02895), rotary evaporator, oven
(BTOV 1423), Ferranti portable viscometer model VL, Abbe refractometer, and Hewlett
adiabatic bomb calorimeter (model 1242). GC-MS (Little Falls, CA, USA), flame photometry
(JENWAY PFP7, Germany) and UV-Visible spectrophotometer (Thermo Scientific, USA) were
the instruments used in the biodiesel characterization.
Sample collection and preparation
Samples of C. glomerata were collected from Lake Hawassa; Ethiopia from May to July in
2012. The identification of the algae to species level was undertaken on the site by using algae
identification field guide. The samples were washed with lake water in situ to remove trapped
mud, sand, epiphytes and attached particles and then put into clean polyethylene bags. The open
air dried algae biomasses were ground with mortar and pestle. The ground algae biomasses were
further dried for 20 min at 80 °C to remove moisture.
Oil extraction
Two extraction methods (Soxhlet and refluxing) were employed for the extraction of algae oil.
In Soxhlet, 30 g dried algae biomass was placed in a thimble made from filter paper and loaded
Production and characterization of biodiesel and glycerine pellet from macroalgae strain
Bull. Chem. Soc. Ethiop. 2020, 34(2)
251
to Soxhlet apparatus. Trichloethylene (300 mL) was added in the ratio of 1:10 g/mL and
extracted for 18 h and rotator evaporated to remove the solvent. Refluxing was carried for 3 h by
mixing 30 g algae biomass and 300 mL Trichloethylene in a distillation flask. The extract was
separated by using Buchner funnel under weak vacuum and the solvent was removed using
rotator evaporator.
Algae biodiesel production
Transesterification reaction procedure reported by Refaat et al. [23] and Muthukumar [24] has
been used with modification for the production of biodiesel. In the first step, the amount of the
NaOH catalyst required was determined by titration which was found to be 6.3 g NaOH/L oil.
Accordingly, 0.63 g of NaOH was taken for 100 mL of algae oil. This amount of NaOH was
dissolved in 20 mL of methanol and the mixture was heated to 60 ºC before mixing it with the
oil. The methanol-NaOH solution was added to algae oil at 60 ºC with a volumetric ratio of 1:5.
The mixture was then blended by using magnetic stirrer for 1½ h and allowed to settle for 24 h
at room temperature to separate glycerol from crude biodiesel. The crude biodiesel was then
washed by adding 30% (v/v) of warm water at 50 ºC followed by rocking for 5 min. The
washing process was repeated four times to make sure that all the soap residuals have been
removed. The washed biodiesel was then placed in an oven at 100 ºC for 6 h to evaporate any
water that might be left during washing. Finally; the volume and weight of the biodiesel were
measured, and the sample was stored for characterization.
Determination of physico-chemical properties of algae biodiesel
Both preliminary biodiesel quality tests (soot, 3/27, water solubility and refractive index test)
and critical biodiesel tests (density, specific gravity, iodine value, kinematic viscosity, pour
point, cloud point, carbon residue, ash content, acid value and calorific value) were determined
at petroleum quality test laboratory in accordance with ASTM standard test methods [25].
Fatty acids methyl ester composition of the algae biodiesel was determined using GC-MS.
The GC-MS was equipped with an inert XL Mass detector (Agilent-Technologies 5975), auto
injector (Agilent-Technologies7683B series) and HP-5MS 5% phenyl methyl silox capillary
column (27 m x 250 μm with film thickness x 0.24 μm). The sample for injection was prepared
by diluting 1 μL of the algal biodiesel with 99 μL of n-hexane. And from this solution 1.0 μL of
the sample was injected into the GC-MS in the split less mode. Helium was used as a carrier gas
with a flow rate of 1 mL/min. The temperature of column oven was programmed, it started at 40
°C for 0 min hold and ramped to 100 °C at 4 °C/min and retained for one minute at 100 °C. It
was increased from 100 to 310 °C at 10 °C/min where it was finally held for 16 min. The
temperature of the injector and MS transfer line was set at 250 and 280 °C, respectively. An
electron ionization system (with ionization energy, i.e. 70 eV) was used for GC-MS detection
while scanning mass ranged from 33–500 m/z. The fatty acid methyl ester compositions were
determined as relative percentage of the total peak area.
The amount of free glycerol in the biodiesel was measured with a UV-Visible
spectrophotometer based on the method developed by Keppy et al. [26]. The sample was first
treated with sodium periodate which reacts with free glycerol in the sample to generate
formaldehyde. Then reaction between this formaldehyde and acetyl acetone produced the yellow
complex, 3,5-diacetyl-1,4-dihydrolutidine. This yellow compound exhibited a maximum
absorbance peak at 410 nm, where its concentration in the sample was measured. The
concentration of the complex was proportional to the amount of free glycerol in the sample. For
the calibration graph, stock standard solution of glycerol (1000 mg/kg) was prepared by diluting
1 g of glycerol solution into a 1 L solvent (1:1 ratio of deionized water and ethanol) and series
of six glycerol reference standards were prepared in the range of 0 (blank) to 18.75 mg/kg from
Dawit Firemichael et al.
Bull. Chem. Soc. Ethiop. 2020, 34(2)
252
the stock solution by serial dilution. Working standards and the samples were treated with 1.2
mL of a 10 mM sodium periodate solution and shaken for 0.5 min. Each solution was then
treated with 1.2 mL of a 0.2 M acetylacetone solution, placed in a water bath at 70 °C for 1 min
and stirred manually. The solutions were immediately placed in cold water to stop the reaction.
Finally, the absorbance of the complex formed was plotted against the concentration of the
glycerol standard solutions. The calibration curve showed very good correlation coefficient
value (0.997). Based on this calibration curve the free glycerol content in algal biodiesel sample
was determined.
Flash point was calculated based on Eq. (1), which relates calorific value (heat of
combustion), viscosity, density and flash point [27]. Except flash point all other variables can be
obtained experimentally.
= 0.4527 − 0.0008ρ − 0.0003 + 40.3667 (1)
where, heat of combustion (MJ/kg), ν is viscosity (mm
2
/s), ρ is density (g/L), and FP is flash
point (°C).
The metals (sodium, potassium, magnesium and calcium) content were determined using a
flame photometer. The sample (5 g) was taken in a silica crucible and heated on a hot plate and
the residue was further burned to ash in a muffle furnace at 525 °C. After dissolving the ash in a
concentrated sulphuric and nitric acids, the metal content was analyzed using a flame
photometer. The flame photometer was first calibrated by aspirating series of standard solutions
and then the sample solutions were aspirated and quantified.
Glycerine pellet preparation
Glycerine pellet formation is fairly straight forward. The raw materials (waste glycerine and
waste biomass) were mixed by weight ratio and blended by hand in a large mixing bowl. The
ratios of glycerine (30 g) to waste biomass (50 g) were then mixed to produce a crude
unfinished material. This raw pellet is transferred into the mold, a short length of PVC with one
end sealed. The diameter of the PVC pipe is 12.5 mm, and its length is101.6 mm. The mold
helps the pellet retain its cylindrical shape. Then a short PVC rod, slightly smaller than the PVC
internal diameter, was inserted into the open end of the mold to compress the pellet. Pressure
was applied by hand for 2 min. This pressure not only reduced the pellet size, but also facilitates
the glycerine to permeate the materials and form a single firm unit as shown in Figure 1. Finally,
the calorific value or energy content of the sun-dried glycerine pellet was determined by bomb
calorimeter.
Figure 1. Glycerine pellet produced from waste glycerine and biomass.
Production and characterization of biodiesel and glycerine
Algae oil yield
The amounts
of algae oil extracted by Soxhlet and refluxing were 24.2 and 23.4%, respectively.
Statistical analysis (t-
test at probability 5%) showed no significant difference in the amount of
oil obtained using the two methods. Nevertheless, in terms of time, reflux
Soxhlet. Because 7.26 g of oil was extracted after 18 h of Soxhlet extraction while 7.01 g is
obtained within 3 h of refluxing time.
The amount of oil obtained from
other m
acroalgae species reported before. For example,
yield from E. Compressa
macroalgae
[28] obtained 1.56-
4.14% oil yiel
Chlorophyceae and
Phaeophyceae
Biodiesel yield
The biodiesel prepared using 100 g algae oil, 20 g methanol, 0.7 g NaOH at 60 °C and 1½ h
reaction time
yielded 96.8 g biodiesel and 22 g glycerol
might be attributed to some un
the washing stage of the transesterification process. Conversion
production test parameter b
conversion yield obtained in this work (96.8 ± 0.4%)
indicates that the oil from C.
G
Figure 2.
Biodiesel and glycerol percentage yield from algae oil
The biodiesel yield obtained from this study is much higher than those reported by other
researchers; Muthukumar
et al.
respectively,
from two different algae strain.
Preliminary quality test
Methanol and biodiesel were mixed in the ratio of 27:3, agitated and settled for 30 min. As a
result, no formation of layer, turbidity and cloud was observed which indicates a positive result
for 3/27 test. Similarly, in water solubility test clear layers
biodiesel also passes this preliminary test.
The amount of CO
2
released from combustion is an indication of the efficiency of the
combustion reaction. Table 1 shows that the time required for color change in gasoline and
biod
iesel is less compared to kerosene; the more CO
Production and characterization of biodiesel and glycerine
pellet from macroalgae strain
Bull. Chem. Soc. Ethiop. 2020, 34(2)
RESULTS AND DISCUSSION
of algae oil extracted by Soxhlet and refluxing were 24.2 and 23.4%, respectively.
test at probability 5%) showed no significant difference in the amount of
oil obtained using the two methods. Nevertheless, in terms of time, reflux
ing is much better than
Soxhlet. Because 7.26 g of oil was extracted after 18 h of Soxhlet extraction while 7.01 g is
obtained within 3 h of refluxing time.
The amount of oil obtained from
C. glomerate
was found to be higher than the oil content of
acroalgae species reported before. For example,
Suganya et al. [21]
reported 11.14% oil
macroalgae
by Soxhlet extraction. Similarly, El Maghraby and Fakhry
4.14% oil yiel
d from three different macroalgae specious (
Rhodophyceae
Phaeophyceae
).
The biodiesel prepared using 100 g algae oil, 20 g methanol, 0.7 g NaOH at 60 °C and 1½ h
yielded 96.8 g biodiesel and 22 g glycerol
as shown in Figure 2. The loss of 1.2 g
might be attributed to some un
-reacted
alcohol, residual catalyst and emulsion removed during
the washing stage of the transesterification process. Conversion
yield is set as one biodiesel
production test parameter b
y EN (EN14103), which ranges between 96-100%.
So, the
conversion yield obtained in this work (96.8 ± 0.4%)
falls within the EN specification. This
G
lomerata is a potential candidate for biodiesel feedstock.
Biodiesel and glycerol percentage yield from algae oil
.
The biodiesel yield obtained from this study is much higher than those reported by other
et al.
[24] and Mondal et al. [29]
reported 60 and 80% biodiesel yield,
from two different algae strain.
Methanol and biodiesel were mixed in the ratio of 27:3, agitated and settled for 30 min. As a
result, no formation of layer, turbidity and cloud was observed which indicates a positive result
for 3/27 test. Similarly, in water solubility test clear layers
were formed implying that the
biodiesel also passes this preliminary test.
released from combustion is an indication of the efficiency of the
combustion reaction. Table 1 shows that the time required for color change in gasoline and
iesel is less compared to kerosene; the more CO
2
is available the faster the color change
pellet from macroalgae strain
253
of algae oil extracted by Soxhlet and refluxing were 24.2 and 23.4%, respectively.
test at probability 5%) showed no significant difference in the amount of
ing is much better than
Soxhlet. Because 7.26 g of oil was extracted after 18 h of Soxhlet extraction while 7.01 g is
was found to be higher than the oil content of
reported 11.14% oil
by Soxhlet extraction. Similarly, El Maghraby and Fakhry
Rhodophyceae
,
The biodiesel prepared using 100 g algae oil, 20 g methanol, 0.7 g NaOH at 60 °C and 1½ h
as shown in Figure 2. The loss of 1.2 g
alcohol, residual catalyst and emulsion removed during
yield is set as one biodiesel
So, the
falls within the EN specification. This
The biodiesel yield obtained from this study is much higher than those reported by other
reported 60 and 80% biodiesel yield,
Methanol and biodiesel were mixed in the ratio of 27:3, agitated and settled for 30 min. As a
result, no formation of layer, turbidity and cloud was observed which indicates a positive result
were formed implying that the
released from combustion is an indication of the efficiency of the
combustion reaction. Table 1 shows that the time required for color change in gasoline and
is available the faster the color change
Dawit Firemichael et al.
Bull. Chem. Soc. Ethiop. 2020, 34(2)
254
takes place. When gasoline and biodiesel is burning more CO
2
is released than it is in kerosene
burning. Hence less time is required to cause color change in the universal indicator. This
indicates that the combustion efficiency of biodiesel is comparable with gasoline but better than
kerosene. Soot occurs when a combustion reaction is not complete. The more soot, the less
efficient the combustion process. As it can be seen in Table 1, the biodiesel forms less soot
compared to gasoline and kerosene. This is because algal biodiesel contains oxygen which
increases efficiency of combustion. In addition, it contains less of heavy oil residues that are
normally found in diesel fuel.
Table 1. Soot testing efficiency of biodiesel.
Fuel type
Time of color
change (min)
Initial color of
universal indicator
Soot observations at
glass funnel
Final color of
universal indicator
No Fuel (control)
- - - -
Diesel (gasoline)
5.7 Violet Medium soot Red
Biodiesel 6.0 Violet
Less soot Red
Kerosene 7.2 Violet
More soot Red
Refractive index is the other preliminary parameter that can be quickly evaluated. As can be
seen in Table 2, the biodiesel derived from C. glomerata has a refractive index of 1.437 which is
within the acceptable range. This implies that heavier molecules are converted into lighter one’s
during transesterification process. In general, the preliminary biodiesel quality test results
suggest that there is high probability that the biodiesel prepared would also meet the critical
quality test specifications.
Critical parameters quality test
From Table 2 it can be seen that most of the critical chemical and physical quality control
parameters are in good agreement with ASTM and EN test specifications.
Table 2. Biodiesel quality test result.
Properties ASTM and EN standard values Result of the p
resent
study
Method
Limits
Units
Methyl ester EN14103 96.5 % W 96.8
free glycerol D6584 0.02 Maximum Mass % 0.000247
Flash point Calculated 92 Minimum °C 103.0667
Refractive index ( 30°C) - 1.38 -1.49
1.437
Acid number D 974 0.50 Maximum mg KOH/g 0.197
Iodine value EN1411 120 Maximum g I/100g 101.4973
Kinematic viscosity ( 40 °C) D445 1.9 - 6.5 mm
2
/s 6.794
Cloud point D2500 Not given °C -3
Pour point D97 Not given °C
-7
Density (15 °C) EN14214 860-900 Kg/m
3
889
Specific gravity (15.56 °C) D1298 870 –900 Kg/m
3
891
Calorific value - - MJ/kg 39.37
Na + K content EN 14538 5 Maximum ppm 0.67
Ca +
Mg content
EN 14538
1 Max
imum
ppm
0.62
The properties of the fatty acid component and their structural features determine the fuel
properties of biodiesel. Important fuel properties influenced by the fatty acid profile include
density, specific gravity, acid value, pour and cloud point, viscosity and heat of combustion [30,
31]. The major fatty acid methyl ester composition of C. Glomerata was found to be
hexadeconic acid methyl ester (C16:0) (27%), 9-octadecenoic acid methyl ester (C18:1) (63%)
and octadecenoic acid methyl ester (C18:0) (10%). The mass spectra of these three fatty acid
methyl esters showed 99% spectral similarity with NIST-05 mass spectral library.
Production and characterization of biodiesel and glycerine pellet from macroalgae strain
Bull. Chem. Soc. Ethiop. 2020, 34(2)
255
The total content of unsaturated fatty acid methyl ester (63%) was found to be higher than
the total saturated fatty acid methyl esters (37%) in the biodiesel. This is further evidenced by
the higher iodine value (103.1 g I/100 g) which indicates the presence of more unsaturated fatty
acid methyl ester. The iodine value was also within the limit of EN standard (≤ 120 g I/100 g).
Free glycerol is an undesirable by product in the transesterification reactions. It is known to
cause clogging in fuel filters, injectors and deposit in the bottom of fuel storage tanks [25]. To
prevent these operational problems, ASTM and EN limits free glycerol to 0.02 weight percent
maximum. In the present work, free glycerol content of the biodiesel was determined to be 2.47
mg/ kg or 0.000247 weight percent, which is well below the ASTM and EN limit set.
Specific gravity has been described as one of the most basic and most important properties
of fuel because some important performance indicators such as cetane number and heating
values are associated with it [31]. From 10 to 60 °C, specific gravity values of palm oil biodiesel
have been reported to be 1.033413 to1.035419 times that of fossil diesel [32]. Similarly, the
specific gravity of the biodiesel from this study was found to be 1.0433255 times that of
petroleum diesel (at the reference temperature 15.56 °C). The specific gravity obtained (891
kg/m
3
) fall well within the limit specified for biodiesel fuels (870–900 kg/m
3
) by the ASTM
Standard. This value is also comparable with previous reports on palm kernel biodiesel (883
kg/m
3
), and soy bean biodiesel (880 kg/m
3
) [31, 32]. Density of the biodiesel (889 kg/m
3
) also
falls within EN (EN14214: 860-900) tolerable limit. It is also comparable with previous studies;
Eruca sativa (881 kg/m
3
), rapeseed (875 kg/m
3
), and spent frying oil (873 kg/m
3
) and frying oil
biodiesel (873 kg/m
3
) [33, 34].
The acid value indicates the degree of fuel ageing during storage, as it gradually increases
due to hydrolytic cleavage of ester bonds. High fuel acidity has been discussed in the context of
corrosion and the formation of deposits within the engine [30]. To mitigate these negative
effects, the EN and ASTM Standards allows a maximum acid value of 0.5 mg of KOH/g. The
acid value of the algae biodiesel gave 0.197 KOH/g which is in agreement with the specified
limit, implying that the algae biodiesel will not pose problem on the long-term performance of
the engine.
Cold flow properties of biodiesel are expressed in terms of cloud point (CP) and pour point
(PP). CP is the temperature at which a liquid fatty material becomes cloudy due to formation of
crystals while PP is the lowest temperature at which it will still flow [30]. The cloud and Pour
point of algae biodiesel was -3 and -7 °C, respectively. The CP and PP values of the algae
biodiesel in the present study, is much better than the CP and PP values of biodiesels derived
from other feed stocks (olive oil: -2 and -3 °C; rapeseed oil: -2 and-9 °C; soybean oil: 0 and -2
°C; sunflower oil: 2 and -1 °C; tallow: 17 and 15 °C) [30]. The saturated fatty acids have
significantly higher melting point than unsaturated fatty acids. For example, due to its high
content of saturated compounds, tallow and palm oil methyl esters have CP of 17 and 13 °C,
respectively. In contrast, feed stocks with relatively low concentrations of saturated long-chain
fatty acids generally yield biodiesel with much lower CP and PP [30, 35]. Thus, the lower CP
and PP value observed in the present study is attributable to the higher proportion of the
unsaturated methyl ester (C18:1) and less proportion of the saturated methyl esters (C18:0 and
C16:0) found in the algal biodiesel.
The kinematic viscosity (6.71 mm
2
/s) of the algae biodiesel was slightly higher than ASTM
(1.9-6.0 mm
2
/s) standard value. The nature of dominant fatty acids, carbon chain length, and
degree of saturation are important factors that determine viscosity [30, 35, 36]. For instance,
viscosity increases with the number of CH
2
moieties in the fatty ester chain and decreases with
an increasing unsaturation [37]. This implies that presence of multiple bonds imparted low
viscosity to biodiesel. Therefore, in the present study, the dominant monounsaturated oleic acid
(63%) is responsible for the slight increment of kinematic viscosity of the produced algae
biodiesel. Compared with the literature value, the viscosity of the algae biodiesel in the present
work (6.71 mm
2
/s) is much lower than castor oil biodiesel (10.43 mm
2
/s) [38].
Dawit Firemichael et al.
Bull. Chem. Soc. Ethiop. 2020, 34(2)
256
Heating of combustion (calorific value) of a fuel is the thermal energy released per unit
quantity of fuel when the fuel is burned completely, and the products of combustion are cooled
back to the initial temperature of the combustible mixtures. It measures the energy content in the
fuel. The calorific value of algae biodiesel reported in this study (39.37 MJ/kg) was found to be
comparable with previous studies on soybean (39.48 MJ/kg), rapeseed (39.46 MJ/kg), and
jatropha (39.45 MJ/kg) [39]. The calculated value of flash point for algae biodiesel was found to
be 103.0667 °C which is within ASTM (≥ 92 °C) recommended limit. Other parameters such as
alkaline (Na and K) and alkaline earth metal (Ca and Mg) content also meet the requirement
specified by ASTM (Table 2). It is well known that the content of these metals (Na, K, Ca and
Mg) in biodiesel is mainly determined by the efficiency of the washing step. The results indicate
that the washing procedure used was efficient in removal of these metals from the produced
algae biodiesel.
Glycerine pellet evaluation
A key element of this part of the study is energy estimation of glycerine pellet which is
produced in our laboratory. The bomb calorimeter result revealed that the glycerine pellet has
13.65 MJ/kg of energy. As it can be seen in Table 3, the energy content of glycerine pellet from
this study is comparable with other competing energy sources implying that it could be used as
an additional refuse derived fuel (RDF).The glycerine pellet burns cleaner than the coal
currently used as fuel in many industries. Additionally, since two pre-existing waste streams are
used to make the pellets, it doesn't require new raw materials. Also, the energy required for
making it is substantially less than the energy required to produce coal. Most importantly, the
glycerine pellet is nearly carbon-neutral fuel.
Table 3. Energy content of different RDF and glycerine pellet (Brady et al. [40]).
Fuel source Energy (MJ/kg)
Coal 11-24
Dry wood 14.7-17.4
Waste plastic 29-40
Household waste (RDF) 12-16
Household (RDF) 13-16
Paper sludge (RDF) 12.5-22
Waste wood 15-17
Glycerin pellet (from this study) 13.65
FAO [41] report indicates that 1 kg of fuel wood gives 13.8 MJ and one cubic meter of fuel
wood equals to 750 kg [42]. Based on this data, one cubic meter of fuel wood is equal to 758 kg
of glycerine pellet. Consequently, 1 kg glycerine pellet replaces 0.0013 cubic meter of fuel
wood. In general, the cost of raw material is often the biggest obstacle to large scale
commercialization of biodiesel. It is estimated to cost 70-85% of biodiesel production cost [43].
Therefore, utilization of biodiesel residuals to generate commercially important by products (i.e.
glycerine pellet) is a recommended approach to decrease the cost of biodiesel.
CONCLUSION
The green algae Cladophera glomerata oil was extracted and chemically converted via alkaline
transesterification reaction to biodiesel (fatty acid methyl ester). The oil yield obtained from C.
glomerta in this study is much better than most of the macroalgae strain reported from previous
studies. The biodiesel produced mainly composed of monounsaturated (63%) and saturated
(37%) fattyacids. All the determined parameters of algae biodiesel were found to comply with
ASTM and EN standard values implying its suitability as diesel fuel substitute. Furthermore, the
Production and characterization of biodiesel and glycerine pellet from macroalgae strain
Bull. Chem. Soc. Ethiop. 2020, 34(2)
257
glycerine pellet prepared, could also be used as an important source of fuel, replacing firewood
particularly in the developing nations like Ethiopia. However, large scale production for
commercial purposes requires optimization of different parameters such as glycerol to biomass
ratio, pellet size, a pilot scale operation and holistic economic evaluation of the production
process.
ACKNOWLEDGEMENTS
The authors acknowledge financial support by Giz-Ethiopia (Energy Coordination Office).
Furthermore, the following organization in Ethiopia: Minister of Water and Energy, Minister of
Agriculture, Health and Nutrition Research Institute and Petroleum Supply Enterprise are
gratefully acknowledged for providing laboratory facility.
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