Scholarly article on topic 'Biodiesel production from microalgae S pirulina maxima  by two step process: Optimization of process variable'

Biodiesel production from microalgae S pirulina maxima by two step process: Optimization of process variable Academic research paper on "Chemical engineering"

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Abstract of research paper on Chemical engineering, author of scientific article — M.A. Rahman, M.A. Aziz, Rami Ali Al-khulaidi, Nazmus Sakib, Maidul Islam

Abstract Biodiesel from green energy source is gaining tremendous attention for ecofriendly and economically aspect. In this investigation, a two-step process was developed for the production of biodiesel from microalgae Spirulina maxima and determined best operating conditions for the steps. In the first stage, acid esterification was conducted to lessen acid value (AV) from 10.66 to 0.51 mgKOH/g of the feedstock and optimal conditions for maximum esterified oil yielding were found at molar ratio 12:1, temperature 60°C, 1% (wt%) H2SO4, and mixing intensity 400 rpm for a reaction time of 90 min. The second stage alkali transesterification was carried out for maximum biodiesel yielding (86.1%) and optimal conditions were found at molar ratio 9:1, temperature 65°C, mixing intensity 600 rpm, catalyst concentration 0.75% (wt%) KOH for a reaction time of 20 min. Biodiesel were analyzed according to ASTM standards and results were within standards limit. Results will helpful to produce third generation algal biodiesel from microalgae Spirulina maxima in an efficient manner.

Academic research paper on topic "Biodiesel production from microalgae S pirulina maxima by two step process: Optimization of process variable"

Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

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ELSEVIER

Journal of Radiation Research and Applied Sciences

journal homepage: http://www.elsevier.com/locate/jrras

Biodiesel production from microalgae Spirulina maxima by two step process: Optimization of process variable

M.A. Rahman a' *, M.A. Aziz b, Rami Ali Al-khulaidi b, Nazmus Sakib b, Maidul Islam c

a Department of Mechanical Engineering, Rajshahi University of Engineering and Technology, Rajshahi 6204, Bangladesh b Department of Mechatronics Engineering, International Islamic University Malaysia, Jalan Gombak, 53100 Kuala Lumpur, Selangor, Malaysia c Department of Mechanical Engineering, International Islamic University Malaysia, Jalan Gombak, 53100 Kuala Lumpur, Selangor, Malaysia

ARTICLE INFO

ABSTRACT

Article history: Received 17 October 2016 Received in revised form 22 February 2017 Accepted 28 February 2017 Available online xxx

Keywords:

Spirulina maxima

Esterification

Transesterification

Optimization

Biodiesel

Biodiesel from green energy source is gaining tremendous attention for ecofriendly and economically aspect. In this investigation, a two-step process was developed for the production of biodiesel from microalgae Spirulina maxima and determined best operating conditions for the steps. In the first stage, acid esterification was conducted to lessen acid value (AV) from 10.66 to 0.51 mgKOH/g of the feedstock and optimal conditions for maximum esterified oil yielding were found at molar ratio 12:1, temperature 60°C, 1% (wt%) H2SO4, and mixing intensity 400 rpm for a reaction time of 90 min. The second stage alkali transesterification was carried out for maximum biodiesel yielding (86.1%) and optimal conditions were found at molar ratio 9:1, temperature 65°C, mixing intensity 600 rpm, catalyst concentration 0.75% (wt%) KOH for a reaction time of 20 min. Biodiesel were analyzed according to ASTM standards and results were within standards limit. Results will helpful to produce third generation algal biodiesel from microalgae Spirulina maxima in an efficient manner.

© 2017 The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/

by-nc-nd/4.0/).

1. Introduction

Rapid depletion of fossil fuel demanded the alternative and sustainable fuel, which can replace the conventional fuel for the fulfillment of energy crisis with minimal environmental impact. Researchers are working overnight to discover renewable, sustainable and eco-friendly energy sources, which can replace or reduce the excess load on the conventional fuel. Thus, developing viable and renewable source of fuel is always burning issue over the world.

Now a days, biodiesel becomes an acceptable alternative options to researchers for supplementing conventional fuel. The properties of biodiesel are very close to diesel and it can be blended at any portion with diesel and can be used in existing engine without any modification. But at present biodiesel costs 1.5—3 times more than diesel due to the higher cost of raw feedstocks and unavailability of oil crops that serves as a source of biodiesel production (Chisti,

* Corresponding author. Tel.: +880 1738451050. E-mail address: atiq07ruet@gmail.com (M.A. Rahman).

Peer review under responsibility of The Egyptian Society of Radiation Sciences and Applications.

2007; Leung & Guo, 2006). Microalgae is one of the most prominent alternative source for the conventional feedstocks. The first and second generation biodiesel research are in saturated level but third generation i.e. biodiesel from algae research is in promising stage. Algae contain highly oil content than other feedstock. The yield (per acre) of oil from algae is over 200 times the yield from the best-performing plant/vegetable oils (Demirbas, 2009). Biodiesel from algae is renewable, biodegradable, nontoxic, and potential as a green alternative fuel for CI engine. It has satisfactory combustion and emission profile than petroleum fuel (Mata, Martins, & Caetano, 2010). In this experiment microalgae Spirulina maxima was selected for the investigation. It is a blue-green algae belonging to the family of oscillatoriaceae. It is large in size which grows everywhere in shallow ponds of high salinity and alkalinity.

Biodiesel production from vegetable oils has been extensively studied in recent literature reviews (Deng, Fang, & Liu, 2010; Ghadge & Raheman, 2005; Patil & Deng, 2009; Phan & Phan, 2008; Rashid & Anwar, 2008) whereas a limited number of investigation has been reported for the production of biodiesel from microalgae. Demirbas (2011) reported that biodiesel from micro-algae can be converted either biochemical or thermochemical conversion. Miao and Wu (2006) suggested a new process, which combined bioengineering and transesterification, and reported that

http://dx.doi.org/10.1016/j.jrras.2017.02.004

1687-8507/© 2017 The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

MA. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

this method is feasible and effective for the production of high quality biodiesel from C. protothecoides micro algal oil. Suganya, Gandhi, and Renganathan (2013) optimized two-step process (esterification followed by transesterification) parameters for gaining a maximum biodiesel yield from marine macroalgae E. compressa. Suganya and Renganathan (2012) optimized biodiesel extraction parameters from marine macroalgae Ulva lactuca. Chen, Liu, Zhang, Chen, and Wang (2012) produce biodiesel from algae Scenedesmus sp. by two-step catalytic conversion.

Though biodiesel production from algae has been recently investigated by some researchers but best operating conditions for esterification followed by transesterification are still inconsistent. So the main object of this investigation is to optimize algal biodiesel production parameters (molar ratio, temperature, catalyst concentration, reaction time, and mixing intensity) from micro algae Spirulina maxima. Many reseracher has applied either esterification or trasnesterification for the production of biodiesel from algae and faces problems of lower yield or longer reaction time. Since algal biodiesel contains high free fatty acid (FFA) thus using of base catalyst in transesterification, FFA leads to saponification, hydrolysis reaction, increase catalyst consumption, reduces catalyst effectiveness and decrease the amount of biodiesel yielding (El-Mashad, Zhang, & Avena-Bustillos, 2008). Moreover, separation of glycerin is very difficult due to the formation of soap which needs a large amount alkaline water for washing the soap (Wan Omar, Nordin, Mohamed, & Amin, 2009). Again when an acid catalyst is used to overcome this problem, it takes longer time to complete the reaction due to slower reaction rate than base catalyst (Ramadhas, Jayaraj, & Muraleedharan, 2005; Wang, Pengzhan Liu, & Zhang, 2007). Therefore, a two-stage combine process is developed for biodiesel production from algae. Algal oil is to be esterified by the acid catalyst in the first stage for reducing FFA or AV followed transesterification by the alkaline catalyst for maximizing biodiesel yield in the second stage (Berchmans & Hirata, 2008; Zhang, Dube, McLean, & Kates, 2003). In this investigation, sulfuric acid (H2SO4) was used as an acid catalyst and KOH was used as an alkali catalyst. Besides optimizing production parameters, biodiesel was characterized by GC-MS, FTIR and some physicochemical properties were analyzed according to ASTM standards.

2. Experiments

2.1. Materials

Spirulina maxima was collected from the local area at Dhaka, Bangladesh. Crude algal oil was extracted from dry biomass by soxhlet apparatus in Institute of Fuel research & Development (IFRD) center under Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh. The chemicals such as methanol (99.8%), ethanol (99%), potassium hydroxide (KOH) (99.6%), phenophtaline, hydrochloric acid (99%), sulfuric acid (96%), distill water were purchased from the local market at Dhaka, Bangladesh.

2.2. Esterification

A quantity of 1 L crude oil was poured into a flask and heated at 55° C for moisture removal. The flask was well equipped with a reflux condenser to avoid methanol loss. An appropriate volume of methanol and the sulfuric acid mixture was heated at 55°C in a separate flux and then poured into algal oil slowly. To observe the AV of the mixture and yield, methanol to oil ratio, catalyst concentration, reaction temperature, reaction time, stirring speed were varied at different conditions. Atypical acid catalyst esterification is shown in Fig. 1 (Huang, Chen, Wei, Zhang, & Chen, 2010). The time

of 2 h was taken for reaction and settle down for 1 h (Ghadge & Raheman, 2005; Patil & Deng, 2009). The reaction was routinely monitored and drawn at predetermine time for the measurement of AV and the yield. The optimum condition for next step was fixed up according to the lowest AV values of the yield. Then, the mixture was kept in a distinct funnel to settle into two layers. The upper layer which contains biodiesel was separated and washing by distill water for purification. Catalyst, alcohol, impurities etc. were removed from bottom layer esterified oil. The esterified oil had an AV less than 1 mgKOH/g was used for transesterification.

2.3. Transesterification

The esterified oil was poured into the glass reactor and heated at 55° C. In separate flasks, the catalyst KOH was dissolved in methanol at various concentration and molar ratio. Then methanoic KOH was heated to 55° C and mixed with the esterified oil. To observe biodiesel yield, molar ratio, catalyst concentration, temperature, reaction time, stirring speed were varied at different conditions. A typical base catalyst transesterification is shown in Fig. 2 (Huang et al., 2010). The mixture was allowed to 1 h for the reaction and settle down for 2 h in a different funnel to separate the glycerol and biodiesel layer. The upper phase contained biodiesel and lower phase was glycerol. The upper layer was collected and washing for purification while the lower layer of glycerin was discarded. A typical schematic block diagram for biodiesel production is shown in Fig. 3.

2.4. Measurements

2.4.1. Acid value (AV)

At first 2 (two) gram oil and 50 ml of ethanol was mixed in a beaker. Two-three drops of phenolphthalein were added to the blends as a pH pointer. The mixture was stirred for 30 min. Then 0.1N KOH was added drop by drop to the sample and was titrated until appearing a faint stable pink color. The titration was carry on for about 15 min to get end point. This whole procedure was repeated for three times and the average value was taken as result. In accord with the approved method of American Oil Chemists Society (AOCS) the following equation (Eq. (1)) was used to calculate AV of the biodiesel.

catalyst

xNx 56.1

(mgKOH/g)

where, Vcatalyst - Volume of catalyst used, N- Normality of catalyst (0.1N), Woii - Weight of oil sample (g).

2.4.2. Saponification value (SV)

Three grams of the oil was mixed with 25 ml of the ethanoic KOH in a beaker. The sample was well enclosed and sank in a water bath for 30 min. Two-three drops of phenolphthalein were added to the mixture as a pH pointer. 0.5 M HCl was added drop by drop to the sample and was titrated until the color change. A blank level test was also performed in parallel using all above procedures without the oil sample addition. This whole procedure was repeated for three times and the average value was taken as result.

HO-C-R + CH3OH <-► CH3-O-C-R + H20

Fatty Acid Methanol Biodiesel Water

Fig. 1. Esterification reaction with acid catalyst.

M.A. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1 —8

ch2coor'

ÇH2OH

CH3COOR1

CHCOOR + 3CH3O H <-CH2COOR3

—> CH-OH + CH3COOR

CH2OH CH3COOR3 Triglyceride + Methanol Glycerol + Biodiesel

Fig. 2. Transesterification reaction with base catalyst.

In accord with the approved method of AOCS the following equation (Eq. (2)) was used to calculate SV of the biodiesel.

„, 56.1 x V1 - N x V2 .

SV =-^-2 (mgKOH/g)

where, V1 -Volume of ethanoic KOH used in blank titration (ml), V2 -Volume of ethanoic KOH used in titration with the oil (ml), N-Normality of acid (0.5N), W-Weight of the oil sample (g).

2.5. Analytical calculation

Biodiesel yield (% w/w) was calculated for different conditions by using the following Eq. (3) (Leung & Guo, 2006)

Yield of biodiesel(%)

Weight of the biodiesel produced (g) Weight of the algal oil sample used (g) x 100%

2.6. Analysis

Biodiesel produced at optimum conditions was characterized by GC-MS analyzer (model- GC-MS-QP 2010, Shimadzu) to analyze free fatty acid (FFA) composition of the oil. A VF-5 MS capillary column (5% phenyl-95% methyl polysiloxane) coated with a 0.25 mm film of with length of 30 mm and internal diameter 0.25 mm was used. The GC was equipped with a split injector at 200° C with a split ratio of 1:10. Helium gas of 99.995% purity was used as carrier gas at flow rate of 1.51 ml/min. The oven initial

Fig. 3. Flow diagram for biodiesel production.

temperature of each run was started at 70° C for 2 min, then raised to 300° C and maintained for l0 min. All the compounds were identified by means of the NIST library. FTIR analysis was done to find out functional group presence in the derived biodiesel by an analyzer (Perkin Elmer FTIR 2000) producing infrared spectros-copy. The physicochemical analysis were carried out according to the standards, as follows: kinematic viscosity at 40°C (ASTM D445), cetane number (ASTM D613), acid value (ASTM D664), iodine value (EN14111), flash point (ASTM D93), Flash point (ASTM D93) and carbon residue (ASTM D524).

3. Results and discussion

3.1. Optimization of esterification parameters

3.1.1. Molar ratio

The most vital factors that affect the conversion efficiency is methanol to algal oil ratio. Stoichiometrically, to complete a transesterification reaction 3:1 methanol-oil ratio is required. But, in actual practice, molar ratio higher than 3:1 is required to completion the reaction quickly (Demirbas, 2009; Patil & Deng, 2009). In this experiment different molar ratios were varied (3:1, 6:1, 9:1, 12:1, and 15:1) for investigation. Initial conditions were fixed at 65°C, 1.5% sulfuric acid and 350 rpm for 2 h of reaction time. The effect of molar ratio on AV and yield is shown in Fig. 4(a). AV decreased with an increase in molar ratio whereas opposite trends was shown in esterified oil yield. The AV reduced from 8.2 to 3 mgKOH/g and esterified oil yield was increased to 22.2% with increase of molar ratio from 3:1 to 12:1. Further increased of molar ratio, there was no significant reduction in AV due to the effect of water production (Berchmans & Hirata, 2008). The maximum yield (22.2%) was attained at 12:1 M ratio. Deng et al. (2010) was reported same result on the acid esterification of J. curcas L. seed oil. The investigation was optimum methanol to algal oil ratio 9:1 for reducing the lowest AV from 10.45 to 1.21 mg KOH/g.

3.1.2. Catalyst concentration

The effect of catalyst concentration on yield is shown in Fig. 4(b). Catalyst concentration was varied from 0.50 to 2.5 wt% and initial conditions were set up at 65°C, molar ratio 12:1 and 350 rpm for 2 h. The AV was decreased sharply from 10.66 to the lowest value of 2.6 mgKOH/g with a maximum yield of 27.2% at 1% sulfuric acid. Further increased in concentration, AV rose again due to hydrolyze of triglyceride to convert FFAs and alcohols according to Eq. (4) (Deng et al., 2010).

Triglyceride + Water = FFA + low weight molecular alcohols (4)

Patil and Deng (2009) reported similar result on acid esterifi-cation of karanja oil for reducing the acid value to 0.72 mg KOH/g at an optimum acid concentration 1% of sulfuric acid.

3.1.3. Temperature

The reduction of AV was significantly depends on temperature. The temperature of the reaction was varied in the range of40—70°C but higher than 70° C was disregarded for the current investigation because of at higher temperature there is a possibility of methanol loss due to vaporization (Leung, Wu, & Leung, 2010), increase product cloudiness and production cost (Ramadhas et al., 2005). Initial conditions were fixed at methanol: oil- 12:1,1% of catalyst concentration and 350 rpm for 2 h. With an increased in temperature from 40° C to 60° C, a sharp decreased of AV from 7.4 to 1.5 mgKOH/g (Fig. 4(c)) with the maximum yielding of 35% was observed. This was due to increase of solvent solubility with increase diffusion rate (Suganya et al., 2013). Further increased

M.A. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

Acid value (mgKOH/g) Biodiesel yield (%)

10 15 20 25

Acid value (mgKOH/g) Biodiesel yield (%)

Acid value (mgKOH/g) Biodiesel yield (%)

Acid value (mgKOH/g) Biodiesel yield (%)

Acid value (mgKOH/g) Biodiesel yield (%)

Fig. 4. (a). Effect of molar ratio on reaction. (b). Effect of catalyst concentration on reaction. (c). Effect of temperature on reaction. (d). Effect of reaction time on reaction. (e). Effect of mixing intensity on reaction.

beyond this temperature, there was no significant change in AV. Ghadge and Raheman (2005), Patil and Deng (2009) was also reported the same result (60°C) on the acid esterification of karanja as well as for jatropha oil and crude mahua oil respectively.

3.1.4. Reaction time

The reaction time plays a significant role in biodiesel production. The experiment was carried out from 15 to 120 min with 15 min interval. Initial conditions were fixed at methanol: oil- 12:1,

M.A. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

20 30 40 50 60 Reaction Time (min.)

s—✓

20 30 40 50

Reaction Time (min.)

20 30 40 50

Reaction Time (min.)

20 30 40 50 Reaction Time (min.)

Fig. 5. (a). Influence of molar ratio. (b). Influence of catalyst concentration. (c). Influence of temperature. (d). Influence of mixing intensity.

1% sulfuric acid, temperature 60° C and 350 rpm mixing intensity. The reaction progressed quickly during the first 90 min, beyond 90 min there was no significant drop in the AV (see Fig. 4(d)) due to the generation of water which barred further reaction (Ghadge & Raheman, 2005). The AV of the oil reduced from 7 to 1.3 mgKOH/ g during first 90 min with the maximum yielding of 40.12%. Tiwari, Kumar, and Raheman (2007) was also examined almost same result (88 min) on the acid esterification of Jatropha curcas oil to decrease AV from 14 mgKOH/g to less than 1 mgKOH/g. Suganya et al. (2013)

Table 1

Components of biodiesel.

Components Structure % (w/w)

Myristic acid C14:0 0.34

Palmitic acid C16:0 40.20

Palmitoleic C16:1 9.18

Stearic C18:0 1.18

Oleic C 18:1 5.43

Linoleic C 18:2 17.87

Linolenic C 18:3 18.34

Others - 7.46

also reported optimum reaction time 90 min to reduce AV from 8.2 to 1.53 mg KOH/g of esterified oil from macro algae E. compressa.

3.1.5. Mixing intensity

In order to attain an absolute efficient reaction between the

Fig. 6. FTIR spectroscopy of diesel and biodiesel.

6 MA. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

Table 2

Frequency comparison table of Diesel and Biodiesel.

Diesel Biodiesel

Absorption peak (cm-1) Bond types Family Absorption peak (cm-1) Bond types Family

2923.9-2854.5 1745.3 1457.3 1377.1 723.3 vas s(C-H) stretching v (C=O) stretching v (C-H) bending v (C=O) = C-H bending Alkanes Aldehyde/ketone Alkanes Fluoride Alkanes 2922.1-2852.7 1770.8-1650 1465.2 1063-966.6 719.4 vas s (C-H) stretching v (C=O) stretching v (C-H) stretching v (C-O) stretching 5 (c-H) deform Alkanes Aldehyde/ketone Alkanes Alcohol benzene

v- Stretching, 5-deformation, subscript s-symmetric, as-asymmetric.

chemical components and the oil, it must be mixing well. The experiment was carried out with different stirring speed from 200 to 450 rpm with 50 rpm interval. Initial conditions were fixed at methanol: algal oil 12:1, 1% sulfuric acid, temperature 60°C for 90 min. At low stirring speed (200 rpm), biodiesel yield (20%) was lowest due to the improper mixing of reactant. The gradual increasing of mixing intensity from 200 to 400 rpm, AV was significantly decreased from 6.2 to 0.51 mgKOH/g with the maximum yield of 43% due to an increase of the homogenization of the reactants (see Fig. 4(e)). Further increased in rpm, there was no change in AV or biodiesel yield. At 450 rpm, the AV of the produced esterified oil was also 0.51 mgKOH/g. So the optimum condition for maximum biodiesel yielding was selected as 400 rpm. Suganya et al. (2013) also carried out optimum mixing intensity 400 rpm to decrease AV from 7.4 mg KOH/g to less than 1% in a range of 150—500 rpm. Zheng et al. (2006) also investigate same result (400 rpm) from waste frying oil.

3.2. Optimization of transesterification parameters

3.2.1. Molar ratio

The molar ratio is one of the significant parameters for biodiesel production. A molar ratio less than 6:1, reaction rate is unsatisfactory. Moreover, it creates soap and decreases biodiesel production (Cetinkaya & Karaosmanoglu, 2004), thus molar ratio less than 6:1 was disregarded. In this study various molar ratios in the range of 6:1 to12:1 were conducted with initial conditions of 1% KOH, 60°C at 500 rpm for 60 min. Yield of biodiesel was increased with increase in the molar ratio (see Fig. 5(a)). The maximum biodiesel yield (65%) was achieved at molar ratio of 9:1 for 30 min of reaction time. The reason behind that, excess methanol intensified solubility of algal oil due to the high viscosity (Suganya et al., 2013). Further increased in molar ratio above 9:1, biodiesel yield again decreased over whole of the reaction period due to emulsification. Excess amount methanol than required increase the solubility of glycerol which impede the separation of biodiesel and by-products layer. As a result, soluble glycerol existing in the methyl ester phase cause foam formation and therefore apparent loss of biodiesel (Phan &

Phan, 2008). Patil and Deng (2009) has done an experiment and obtained maximum yield for karanja (80%) and J. curcas (86%) oil at ratio- 9:1 with initial conditions 55°C, 1% KOH, and mixing intensity 1000 rpm for a reaction time of 60 min.

3.2.2. Catalyst concentration

To evaluate the effect of catalyst concentration on the reaction, KOH concentration was varied from 0.50 to 1.5 wt%. Initial operation conditions were fixed up at temperature 60°C, methanol: oil 9:1 and mixing intensity 500 rpm for 60 min. Fig. 5(b) shows the effect of catalyst concentration on transesterification reaction. The maximum biodiesel yield (75%) was obtained at catalyst concentration of 0.75 wt% after 20 min of reaction time. Concentration of 0.75% KOH was sufficient to complete the conversion triglycerides of algal oil into biodiesel. Further increased in KOH concentration from 1 to 1.5 wt%, reduced biodiesel yield. Biodiesel yield was 70% and 67% for the catalyst concentration of 1 and 1.5 wt% respectively. This was due to formation of large amount of soap when excess concentrated KOH was added and consequently this soap formation reduced biodiesel yield (Leung & Guo, 2006). Therefore, the optimum condition of catalyst concentration 0.75% KOH for maximum biodiesel yielding was used for the remaining experiments. Phan and Phan (2008) reported maximum biodiesel yield from waste cooking oils at methanol to oil 8:1, temperature 50° C, 0.75% KOH concentration for 80—90 min reaction time.

3.2.3. Temperature

The effect of temperature is one of the important factor for biodiesel production. To evaluate the maximum biodiesel yield, temperature was varied from 45°C to 65°C (see Fig. 5(c)). Initial operation conditions was fixed up at methanol: oil- 9:1,0.75% KOH, mixing intensity 500 rpm for 60 min. The temperature of reaction above the boiling point of methanol was neglected as at high temperature accelerates the formation of soap. The biodiesel yield from triglyceride increased with an increase in temperature. The reason could be proper combination of oil and methanol due to increase the solubility of molecules (Suganya et al., 2013). The maximum biodiesel yield (80.13%) was obtained for the

Table 3

. Physiochemical properties of biodiesel.

Properties Experimental results Crude oil Biodiesel Limits (ASTM D6751)

Density (kg/m3) at 15°C 0.945 0.864 0.86—0.89

Kinematic viscosity (mm2/s) at 40°C 38.3 4.47 1.9—6.0

Higher Calorific Value (MJ/kg) n.d. 38.43 n.a.

Cetane Number (CN) n.d. 48 n.a.

Acid value (mgKOH/g) 10.659 0.475 0.50 max.

Iodine value (IV) 82.2 n.d. n.a.

Saponification value (mgKOH/g) 191.9 n.d. n.a.

Flash point (°C) n.d. 178 130 max.

Carbon residue (wt%) n.d. 0.045 0.050 max.

n.a. - not available, n.d. - not determined.

M.A. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1 —8

temperature of 65° C at around 25 min of reaction time. Rashid and Anwar (2008) reported similar results for maximum biodiesel production (90.6%) from rapeseed oil at 65° C.

3.2.4. Mixing intensity

Another important factor is mixing intensity as it increases interact area between the catalyst and alcoholic oil. Due to the improper mixing, the reaction did interface of the two layer and therefore drops biodiesel yield (Rashid & Anwar, 2008). The effect of mixing intensity on the reaction was investigated with varying the intensity from 400 to 700 rpm (see Fig. 5(d)). Initial operation conditions were fixed up at temperature 65°C, methanol: oil 9:1 and 0.75% KOH concentration for 60 min. Biodiesel yield increased with an increase in mixing intensity due to an increase of the ho-mogenization of the reactants. At lower mixing speed (400 rpm), biodiesel yield was lowest due to the improper mixing of reactant. When stirring speed increased from 400 to 600 rpm, biodiesel yield increased from 65% to 86.1% after 20 min. Further increased in stirring speed there was no significant change in biodiesel yield. The maximum biodiesel yield (86.1%) was obtained for the string speed 600 rpm after 20 min of reaction time. Suganya et al. (2013) carried out similar result of optimum mixing intensity 600 rpm for maximum biodiesel yield (92.8%) at 1% NaOH, 55°C reaction temperature, and 9:1 molar ratio for reaction time of 90 min.

3.3. GC-MS

The fatty acid compositions of the produced biodiesel is shown in Table 1. The fatty acid profile consists of stearic acid, myristic acid, palmitic acid, palmitoleic acid, linoleic, oleic acid, linolenic acid etc. The major fatty acids were palmitic acid (40.2%), linoleic (17.87%), linolenic acids (18.34%). It was characterized by a high concentration of unsaturated fatty acid than saturated fatty acid. The low concentration of saturated fatty acid has lower oxidation resistance for biodiesel (Mostafa & El-Gendy, 2013).

3.4. FTIR

FTIR spectroscopy of biodiesel and diesel and their frequency distribution is shown in Fig. 6 and Table 2 respectively. FTIR results for diesel was taken from the paper (Nabi, Akhter, & Rahman, 2013). The main components both of diesel and biodiesel are aliphatic hydrocarbons. The chemical structures of diesel are similar to the long carbon chains of the main components of biodiesel. For diesel, the characteristic absorption bands for the vibrations of C—H, around 2923.9 & 2854.5 cm-1 corresponding to the asymmetric and symmetric vibration modes of methyl groups respectively indicate the presence of alkane and appearance is very strong. For biodiesel, the characteristic absorption bands for the vibrations of C—H, around 2922.1 & 2852.7 cm-1 corresponding to the asymmetric and symmetric vibration modes of methyl groups respectively indicate the presence of alkane and appearance is very strong. In the range (1800-1000 cm-1), biodiesel peaks 1770.8 and 1650 represents the C=O (Aldehyde/ketone) stretching whereas diesel absorption peak 1745.3 cm-1 represents also aldehyde/ke-tone. The peaks of biodiesel 1063 cm-1 and 966.64 cm-1 represent alcohol, a functional group of stretching carbohydrates and for diesel 1377.1 cm-1 present of fluoride. The absorbance peaks for biodiesel 1465.2 cm-1 and 719.4 cm-1 for the vibrations of C—H represent alkane. A strong signal was identified in between wave numbers 1750 cm-1 to 1000 cm-1 for biodiesel spectroscopy which confirmed the presence of biodiesel. In biodiesel spectra, the absence of a peak higher than 3000 cm-1 corresponding to —OH of carboxylic acid indicates complete transesterification (Mostafa & El-Gendy, 2013). Lastly, the major absorption peak both of the

diesel and biodiesel are alkanes and their bond type is very strong. Base on the analysis, hydrocarbon groups C-H indicates diesel and biodiesel are saturated hydrocarbon and prospective to be used as an alternative fuels for engine (Nabi et al., 2013).

3.5. Fuel properties

An alternative fuel is one whose properties match with international standard thus investigated results were compared to ASTM D6751 standard limits. Table 3 shows physiochemical properties of crude algal oil and biodiesel produced at optimum conditions of transesterification.

The kinematic viscosity and density of produced biodiesel was

0.864.kg/m3 and 4.47 mm2/s respectively. The AV of the crude algal oil was 10.66 mgKOH/g whereas produced biodiesel was 0.51 mgKOH/g which was within ASTM standard. This indicates the fuel has no any operational problems, such as corrosion, pump plugging (Candeia et al., 2009). The higher iodine value (IV) represents the lower oxidation stability of the fuel. The IV of biodiesel were within the EN 14214 biodiesel standard (max. 120). Saponification value of crude biodiesel was 191.9 mgKOH/g. Cetane number (CN) of biodiesel was 50. Flash point of produced biodiesel had a higher value 178° C, which implies less flammable and much safer in handling, storage, and transport. The higher calorific value of a fuel is the standard heat of reaction at a constant pressure where the fuel burns completely with oxygen and higher calorific value fuel gives higher heat output. HCV value of biodiesel was 38.43 MJ/kg.

4. Conclusion

In this investigation, a two-step process were employed for biodiesel production from microalgae Spirulina maxima. From the investigation, the following clues can be summarized-

1. First step esterification was accomplished to reduce the AV from 10.66 to 0.51 mgKOH/g and optimum conditions were found at methanol: oil 12:1, temperature 60°C, catalyst concentration 1 wt% sulfuric acid (H2SO4), time 90 min and mixing intensity 400 rpm.

2. Second step alkaline transesterification was performed for maximizing biodiesel yield (86.1%) and optimum conditions were found at methanol: oil ratio 9:1, temperature 65°C, mixing intensity 600 rpm, catalyst concentration 0.75 wt% KOH.

3. Determined fuel properties match with ASTM biodiesel requirement.

Acknowledgments

This experiment has been carried out in Rajshahi University of Engineering & Technology (RUET) and Institute of Fuel Research & Development (IFRD) center under Bangladesh Council of Scientific and Industrial Research (BCSIR), Dhaka, Bangladesh. Authors would like to thank Lab expert of BCSIR and RUET for the technical assistance.

References

Berchmans, H. J., & Hirata, S. (2008). Biodiesel production from crude Jatropha curcas L. seed oil with a high content of free fatty acids. Bioresource Technology, 99(6), 1716—1721.

Candeia, R. A., Silva, M. C. D., Carvalho Filho, J. R., Brasilino, M. G. A., Bicudo, T. C., Santos, I. M. G., et al. (2009). Influence of soybean biodiesel content on basic properties of biodiesel-diesel blends. Fuel, 88, 738—743. Cetinkaya, M., & Karaosmanoglu, F. (2004). Optimization of base-catalyzed trans-

esterification reaction of used cooking oil. Energy & Fuels, 18(6), 1888—1895. Chen, L., Liu, T., Zhang, W., Chen, X., & Wang, J. (2012). Biodiesel production from algae oil high in free fatty acids by two-step catalytic conversion. Bioresource

8 MA. Rahman et al. / Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

Technology, 111, 208-214.

Chisti, Y. (2o07). Biodiesel from microalgae. Biotechnology Advances, 25, 294-306.

Demirbas, A. (2009). Progress and recent trends in biodiesel fuels. Energy Conversion and Management, 50(1), 14-34.

Demirbas, M. F. (2011). Biofuels from algae for sustainable development. Applied Energy, 88(10), 3473-3480.

Deng, X., Fang, Z., & Liu, Y. H. (2010). Ultrasonic transesterification of Jatropha curcas L. oil to biodiesel by a two-step process. Energy Conversion and Management, 51(12), 2802-2807.

El-Mashad, H. M., Zhang, R., & Avena-Bustillos, R. J. (2008). A two-step process for biodiesel production from salmon oil. Biosystems Engineering, 99(2), 220-227.

Ghadge, S. V., & Raheman, H. (2005). Biodiesel production from mahua (Madhuca indica) oil having high free fatty acids. Biomass and Bioenergy, 28(6), 601-605.

Huang, G., Chen, F., Wei, D., Zhang, X., & Chen, G. (2010). Biodiesel production by microalgal biotechnology. Applied Energy, 87(1), 38-46.

Leung, D. Y. C., & Guo, Y. (2006). Transesterification of neat and used frying oil: Optimization for biodiesel production. Fuel Processing Technology, 87(10), 883-890.

Leung, D. Y. C., Wu, X., & Leung, M. K. H. (2010). A review on biodiesel production using catalyzed transesterification. Applied Energy, 87(4), 1083-1095.

Mata, T. M., Martins, A. A., & Caetano, N. S. (2010). Microalgae for biodiesel production and other applications: A review. Renewable and Sustainable Energy Reviews, 14(1), 217-232.

Miao, X., & Wu, Q. (2006). Biodiesel production from heterotrophic microalgal oil. Bioresource Technology, 97(6), 841 -846.

Mostafa, S. S. M., & El-Gendy, N. S. (2013). Evaluation of fuel properties for micro-algae Spirulina platensis bio-diesel and its blends with Egyptian petro-diesel. Arabian Journal of Chemistry. http://dx.doi.org/10.1016/j.arabjc.2013.07.034.

Nabi, M. N., Akhter, M. S., & Rahman, M. A. (2013). Waste transformer oil as an

alternative fuel for diesel engine. Procedia Engineering, 56, 401—406.

Patil, P. D., & Deng, S. (2009). Optimization of biodiesel production from edible and non-edible vegetable oils. Fuel, 88(7), 1302—1306.

Phan, A. N., & Phan, T. M. (2008). Biodiesel production from waste cooking oils. Fuel, 87, 3490—3496.

Ramadhas, A. S., Jayaraj, S., & Muraleedharan, C. (2005). Biodiesel production from high FFA rubber seed oil. Fuel, 84(4), 335—340.

Rashid, U., & Anwar, F. (2008). Production of biodiesel through optimized alkaline-catalyzed transesterification of rapeseed oil. Fuel, 87(3), 265—273.

Suganya, T., Gandhi, N. N., & Renganathan, S. (2013). Production of algal biodiesel from marine macroalgae Enteromorpha compressa by two step process: Optimization and kinetic study. Bioresource Technology, 128, 392—400.

Suganya, T., & Renganathan, S. (2012). Optimization and kinetic studies on algal oil extraction from marine macroalgae Ulva lactuca. Bioresource Technology, 107, 319—326.

Tiwari, A. K., Kumar, A., & Raheman, H. (2007). Biodiesel production from jatropha oil (Jatropha curcas) with high free fatty acids: An optimized process. Biomass and Bioenergy, 31(8), 569—575.

Wan Omar, W. N. N., Nordin, N., Mohamed, M., & Amin, N. A. S. (2009). A two-step biodiesel production from waste cooking oil: Optimization of pre treatment step. Journal of Applied Sciences, 9(17), 3098—3103.

Wang, Y., Pengzhan Liu, S. O., & Zhang, Z. (2007). Preparation of biodiesel from waste cooking oil via two-step catalyzed process. Energy Conversion and Management, 48(1), 184—188.

Zhang, Y., Dube, M. A., McLean, D. D., & Kates, M. (2003). Biodiesel production from waste cooking oil: 2. Economic assessment and sensitivity analysis. Bioresource Technology, 90(3), 229—240.

Zheng, S., Kates, M., Dubé, M. A., & McLean, D. D. (2006). Acid-catalyzed production of biodiesel from waste frying oil. Biomass and Bioenergy, 30(3), 267—272.