- Email: [email protected]
Increased bio-oil yield from Swietenia macrophylla seeds through microwave pretreatment and ultrasonic-assisted solvent extraction
Accepted Manuscript Increased bio-oil yield from Swietenia macrophylla seeds through microwave pretreatment and ultrasonic-assisted solvent extraction Rey P. Gumaling, Jay R.E. Agusan, Neil Ven Cent R. Ellacer, Gretel Mary T. Abi Abi, Jasmin Roxatte P. Pajaron, Jose Rey Q. Joyno, Cherry Q. Joyno, Alexander L. Ido, Renato O. Arazo PII:
S2468-2039(18)30103-1
DOI:
10.1016/j.serj.2018.06.003
Reference:
SERJ 136
To appear in:
Sustainable Environment Research
Received Date: 12 March 2018 Revised Date:
30 April 2018
Accepted Date: 15 June 2018
Please cite this article as: Gumaling RP, Agusan JRE, Cent R. Ellacer NV, Abi Abi GMT, Pajaron JRP, Joyno JRQ, Joyno CQ, Ido AL, Arazo RO, Increased bio-oil yield from Swietenia macrophylla seeds through microwave pretreatment and ultrasonic-assisted solvent extraction, Sustainable Environment Research (2018), doi: 10.1016/j.serj.2018.06.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Received 12 March 2018 Received in revised form 29 April 2018 Accepted 15 June 2018
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Increased bio-oil yield from Swietenia macrophylla seeds through microwave
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pretreatment and ultrasonic-assisted solvent extraction
a
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Rey P. Gumaling a, Jay R E. Agusan a, Neil Ven Cent R. Ellacer a, Gretel Mary T. Abi Abi a, Jasmin Roxatte P. Pajaron a, Jose Rey Q. Joyno a, Cherry Q. Joyno a, Alexander L. Ido a, Renato O. Arazo a,b*
College of Engineering and Technology, University of Science and Technology of Southern Philippines, Claveria 9004, Philippines Project Development Office, University of Science and Technology of Southern Philippines, Claveria 9004, Philippines
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b
*Corresponding author Email: [email protected] (Dr. Renato O. Arazo)
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Abstract Low recovery coupled with intensive energy requirement due to long processing time makes the potential of bio-oil production not seamlessly appreciated. In this study,
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the optimization of bio-oil yield from non-edible Swietenia macrophylla seeds through microwave pretreatment before ultrasonic-assisted solvent extraction was investigated. Central composite design of response surface methodology was employed to analyze the
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effects to the bio-oil yield of the irradiation time (4-8 min) and irradiation power (90-450 W) as pretreatment variables using a microwave oven at 2.45 GHz frequency. Results
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showed that microwave pretreatment significantly increased the bio-oil yield by 5% with optimum recovery of 43% at shortened pretreatment time of 7 min instead of 6 h in the conventional oven heating method. The bio-oil yield increased when the irradiation time was increased, while irradiation power showed no significant effect. Analysis of the
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produced bio-oil through Fourier Transform Infrared Radiation spectroscopy identified similar functional groups present both in the extracted bio-oils from the microwave and the conventional pretreated seeds indicating that the former pretreatment, like the latter,
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did not destruct the compounds present in the seeds. The study demonstrated that the seeds of S. macrophylla have strong potential for bio-oil production and poise huge
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implications to the future of liquid biofuel and chemical industries.
Keywords: Swietenia macrophylla; Microwave Pretreatment; Oil Extraction; Optimization; Response Surface Methodology
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1. Introduction The finite source of petroleum oil reserve would be exhausted in the next century due to the increasing consumption of crude oil products to feed engines [1]. The
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overdependence of this nonrenewable product, driven by economic growth and rapid industrialization in the developed and developing countries, contributes greatly to the increased greenhouse gases in the atmosphere which cause the global climate change [2].
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Hence, the twin crises of fossil fuel depletion and environmental degradation attract researchers to continually search for an alternative energy resource that is sustainably
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appropriate and environmentally benign.
Interest in biofuels, like liquid biodiesel with bio-oil feedstock, is becoming more attractive due to its renewable origin and environmental benefit of emitting less carbon dioxide, sulfur oxides and hydrocarbon [3]. More importantly, the bio-oil derived from
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second and third generation biomass like Swietenia macrophylla seeds [4], Hevea brasiliensis seeds [5], and microalgae [6] as feedstocks for biodiesel production were preferred over the first generation like corn, wheat, peanut, and coconut to avoid the
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possible competition in food production and food industries. Related literature shows that bio-oil from S. macrophylla seeds contain common
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unsaturated fatty acids such as oleic (26%), linoleic (33%), linolenic (12%) and saturated fatty acids, namely, palmitic (13%) and stearic (14%) suggesting its suitability for biodiesel production [7]. These fatty acids could be recovered through suitable extraction method that would maximize bio-oil yield. One of these is the ultrasonic-assisted solvent extraction (UASE) method that ruptures the membrane of the S. macrophylla seeds thereby promoting maximum bio-oil extraction [5].
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Aside from the extraction using organic solvents aided by ultrasonication, biomass pretreatment by means of microwave irradiation is also proven to increase biooil recovery [9]. Microwave irradiation applied to biomass as the pretreatment is
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advantageous not only because of increase bio-oil recovery but also in the reduction of processing time needed as compared to conventional pretreatment [8,10–13].
To date, there has been no study yet on the optimization of bio-oil yield from S.
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macrophylla seeds when subjected to microwave pretreatment (MWP). In this work, the seeds of S. macrophylla, an oil-rich second-generation biomass from an exotic Philippine
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species of the family Meliaceae, were used to produce bio-oil, a potential feedstock for biodiesel production [4,14]. It ultimately aims to give scientific information on the effects of MPV
to the bio-oil recovery from S. macrophylla seeds. Specifically, optimization of
the bio-oil yield was investigated considering the effects of irradiation time and
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irradiation power as operating variables through the central composite design (CCD) of response surface methodology. This is an appropriate statistical tool that does not only serve for the design of experiments but also capable of giving 3D plots to closely
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investigate the effects and determine the optimum values of chosen variables [15]. The functional groups present in the produced bio-oils were, likewise, identified through
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Fourier Transform Infrared Radiation (FTIR) spectroscopy analysis. 2. Materials and methods 2.1. S. macrophylla seeds preparation The S. macrophylla seeds used in this study were collected from Poblacion,
Claveria, Misamis Oriental, Philippines. The pods were broken to collect the seeds. The whole seeds were sundried, cleaned by airing, oven dried (Contherm Designer Series 4
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Oven, Model: CE Z011) at 100 ± 1 °C for 24 h, powdered and sieved at 10 mm mesh before pretreatment and extraction. Only those particles that passed the sieve were used
2.2 Parametric and optimization studies
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as biomass.
A parametric study in MWP was conducted using important parameters/variables
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according to the literature [10,11] such as irradiation time and irradiation power. The runs were based on the parametric study principle of taking one variable as constant while
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varying other variable, and a peak was known in a graph once plotted. The values of the observed peaks were used as center points (level 0) of the variables. Based on the parametric investigation of this work, the levels and range of values of the variables were known (Table 1) and were used in the design of experiment in the subsequent optimization study.
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In the optimization study, the CCD of response surface methodology was used in the design of experiment with the aid of Design Expert 7.0 software. The combinations of all runs, consisting irradiation time and power, were based on experimental design
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generated by the CCD. The experiment was conducted at room temperature (25 ± 1 °C).
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For each run, 15 g of oven dried powder of S. macrophylla seeds were placed in the plate of a microwave oven (JEI2340WPSL GE Model, China) with 2.45 GHz frequency and following the predetermined irradiation time and power. After which, the pretreated samples were cooled down inside the desiccator. Fig. 1 describes the pretreatment experimental set-up of powdered seeds.
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2.3 Ultrasonic-assisted n-hexane extraction Pretreated powdered seeds were subjected to UASE using n-hexane following the experimental procedures described in the study of Mabayo et al. [5]. The n-hexane (96%,
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GR grade, Duksan Pure Chemicals) used in the bio-oil extraction was purchased from Harnwell Chemical, Cagayan de Oro City, Philippines. The experiment was conducted at the Chemistry Laboratory of the University of Science and Technology of Southern
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Philippines with a room temperature of 25 ± 1 °C. Each UASE run, with variable irradiation time and power set according to the design of experiments, was done with 75
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mL hexane, 50 µm resonance amplitude, 60 ± 5 °C reaction temperature at 15 min sonication time, and 15 g powdered seeds. 2.4 Control set-up for MWP
To compare the results that were generated from the optimization study and to
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determine the efficiency of MWP, a conventional heating using the oven as control experiment was conducted. For the control experiment, powdered S. macrophylla seeds samples were dried in an oven (Contherm Designer Series, Model: CE Z011) at 60 ± 5 °C
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for 6 h [11].
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2.5 Bio-oil yield determination The percent bio-oil yield from S. macrophylla seeds was determined using digital
analytical balance. The percent yield was calculated using Eq. (1).
%
100
(1)
where %Y is the percent yield (wt%) of the bio-oil extracted from powdered seeds, m1 is 6
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the mass of produced bio-oil, and m2 is the mass of powdered seeds used in extraction. 2.6 Product analysis
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Proximate analyses of the powdered seeds in terms of moisture content and ash content from microwave heating and conventional oven heating were conducted and analyzed. The moisture content was determined using drying oven (Contherm Designer
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Series Oven, Model: CE Z011) at 100 ± 1 °C for 24 h. The LabTech LEF-304P-2 muffle furnace was used in ash content analysis at 600 ± 25 °C for 3 h.
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The bio-oils, both from microwave and conventionally pretreated seeds, were subjected to FTIR spectroscopy analysis to compare if there are differences in the functional groups. The FTIR spectroscopy analysis was conducted at the Pilipinas Kao, Incorporated at Jasaan, Misamis Oriental, Philippines using Shimadzu 8400S. 2.7 Statistical analysis and modelling
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Statistical analysis and modeling were done through CCD using Design Expert 7.0 software. Analysis of variance was the statistical tool used in the study that determined the most appropriate model equation that best fits the data gathered in the
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experimental runs. The percent yield of the experimental runs underwent graphical
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modeling and established the interactive effects of the chosen operating variables through the visual 3D plot.
3. Results and discussion
3.1 Seeds characterization Characteristics of Swietenia macrophylla seeds such as moisture and ash contents
and physical appearance were determined before these were utilized as feedstock. The S. macrophylla fruit pod was brown with oval seed (Fig. 2). Each winged pod weighed 0.2 7
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± 0.1 g while each seed weighed 0.5 ± 0.1 g. The seeds moisture content recorded 6.1 ± 0.2%, on wet basis, which is lower than the 10.6 ± 0.4% reported elsewhere [4]. Low moisture content is desirable considering the least possibility that water shall be elevated
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to the liquid product during bio-oil extraction. The recorded S. macrophylla seed’s ash content of 10.9±0.1% is just comparable to diverse bio-based fuel products [16]. As a supplementary data from other work, the ultimate analysis of S. macrophylla seeds
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showed that the carbon, hydrogen, nitrogen, sulfur, and oxygen percent contents were
3.2 MWP parametric analysis
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48.14, 6.40, 0.28, 0.03, and 45.15, respectively [17].
Fig. 3a shows the bio-oil yield from 15 g microwave pretreated S. macrophylla seeds produced at variable irradiation powers with 3 min irradiation time. The bio-oil yield peaks at 270 W irradiation power (42.4%). This result was used as the center point
1).
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(level 0) in making the level and range of MVP variable in this study (as shown in Table
At 270 W irradiation power as constant and variable irradiation times, the bio-oil
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yield peaks at 6 min with 43.5% yield (Fig. 3b). The design of experiment used the 6 min
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as the center value (level 0) of the irradiation time (as shown in Table 1). Therefore, the 270 W irradiation power and 6 min irradiation time were taken as
the center of the levels of variables in the design of experiment of independent variables using the CCD of the response surface methodology (Table 1).
3.3 Percent bio-oil yield of seeds subjected to MWP As seen in Table 2, the highest bio-oil yield of 46 wt% was achieved at 8 min irradiation time and 270 W irradiation power; while the lowest yield of 39 wt% was 8
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achieved at 5 min irradiation time and 180 W irradiation power. This means that the large increase in irradiation time and a small increase in irradiation power during pretreatment
3.4 Model fitting of bio-oil yield as subjected to MWP
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would result in higher bio-oil yield.
The CCD’s analysis particularly the fit summary revealed that response surface
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quadratic model best fitted in predicting the percentage of bio-oil yield from S. macrophylla seeds as affected by MWP variables. The ANOVA result of the response
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surface quadratic model for the percentage of bio-oil yield is shown in Table 3. The model p-value of 0.0001 indicates a highly significant quadratic model with high accuracy in predicting the bio-oil yield of microwave pretreated S. macrophylla seeds. The model p-value of 0.0001 means that there is only 0.01% chance that error could arise from the noise. The lack of fit F-value of 0.35 implies that the lack of fit is not
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significant relative to pure error and that there is 79.1% chance that the lack of fit F-value this large could arise through the noise. It is good to note that the lack of fit is not significant implying that the model is fit.
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The coefficient of variance and determination could also support that the
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quadratic model is robust. The coefficient of determination (R2) value of 0.96 is high which means that the regression model for the bio-oil yield was satisfactory and demonstrated a high degree of correlations between the actual data and predicted values. It also signifies that there is 96% certainty that the generated model can explain the variability of the data. Further, the adjusted coefficient of determination (Adj. R2) of 0.93 is also high which could support the suitability of generated model in presenting the correlation of actual and experimental values. The coefficient of variance percentage of 9
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1.15% was low enough to represent adequacy of data indicating that the model owns high precision and reliability for fitting experimental values. Eq. (2) shows the quadratic
and irradiation power (W), respectively.
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model equation in terms of actual factors where A and B represent irradiation time (min),
(2)
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37.71 − 1.76 + 0.03 − 0.01 + 0.44
The predicted values of bio-oil yield could be determined using the generated
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quadratic equation. This equation could also support how the terms affect the bio-oil yield. Unlike term B (irradiation power), term A (irradiation time) was found significant and has a negative numerical coefficient which means that increasing the irradiation time, when taken singly, may lead to a decrease in yield, but the square of it (A2) resulted
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otherwise. Hence, the model equation can be further investigated using a 3D plot to determine the overall effect of the two contrasting coefficients of A and A2 terms. The overall result showed that the effect of irradiation time (A and A2 combined) significantly
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increased the bio-oil yield (see Fig. 4).
Table 4 shows that the actual values were seen close to the predicted values which
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could further support the claim that the model fitness owns high degree of correlations between the actual and the predicted ones. Fig. 5 shows the diagnostic graph of the actual versus predicted responses of the experimental runs. The actual values according to data points on the graph are positioned close to the predicted values represented by the straight line signifying a high degree of correlations between the actual and predicted values (Fig. 5). This could mean that the model fitness is strong and reliable. This result supports the
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claim that response surface quadratic model is the most suitable model for predicting the bio-oil yield from microwave pretreated S. macrophylla seeds.
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3.6 Effects of the MWP’s operating variables to the bio-oil yield Fig. 4 illustrates that as the irradiation time increases, the bio-oil yield increases. A similar finding was observed by others [10,12,18,19]. This result clearly shows that increasing the exposure time could provide greater rupture of cell structure. Irradiation
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power, on the other hand, has no statistical basis to support its significant effect on the
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bio-oil yield. Nonetheless, the Fig. 4 illustrates that the increase of irradiation power at the shorter time resulted in little addition of the bio-oil yield. At longer irradiation time, the increase of irradiation power resulted in a small and insignificant increase of bio-oil product. This result implies that irradiation power effect is not significant when compared
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to irradiation time.
3.7 Optimization of the bio-oil yield via MWP Numerical optimization suggested two solutions that could result in optimum bio-
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oil yield from S. macrophylla seeds via MWP. The solution with the highest desirability was chosen and ran in triplicate following the suggested values of the operating variables.
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The validated or the actual bio-oil yield of 43.3 ± 0.3% is close to the theoretical yield of 43.8% with the percent error of 0.8–1.8% (7 min at 180 W). The percent error falls below the 5% acceptable error signifying that the model is valid and owns high degree of precision in predicting the bio-oil yield from S. macrophylla seeds. This outcome means
that the bio-oil yield of the microwave pretreated seeds can be determined using the equation generated by simply plugging in the values of irradiation time and power. Ping et al. [8] reported the bio-oil yield of 29.5 ± 1.6% from S. macrophylla seeds 11
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applying MWP followed by solvent extraction using the mixture of methanol and chloroform. The optimum condition in this study applying the same pretreatment technique followed by ultrasonic-aided hexane extraction was way higher than the
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reported yield in the study of Ping et al. [8]. This finding implies that the CCD of response surface methodology helped in making result way higher than the previously reported bio-oil yield as well as in establishing the optimum conditions. Further, the
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finding tells that the use of hexane as a solvent in the ultrasonication could significantly
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increase the bio-oil yield from S. macrophylla seeds.
3.7 Comparison of MWP with the conventional method
To identify the best pretreatment method, conventional oven treatment of the seeds was compared with MWP under the optimal conditions. MWP under 180 W power at 7 min time enabled to extract 43.3 ± 0.4%, which is apparently superior to that of
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conventional treatment with 37.9 ± 0.1% yield under 60 °C temperature and 6 h time. This result means that MWP could promote the UASE of bio-oil. The result is also true with the study of Ren et al. [11] wherein MWP could enhance bio-oil extraction from
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flaxseeds. The high extraction yield of microwave pretreated S. macrophylla seeds could
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be attributed to the modification of cellular membrane due to the pretreatment which further enhances the solvent extraction. 3.8 Product analysis
The moisture and ash contents of pretreated S. macrophylla seeds were analyzed.
Its powder’s moisture content on dry basis of 4.8 ± 0.1% could be reduced to 3.4 ± 0.1% through microwave treatment method. This result could be due to the quick and efficient release of moisture when the seeds were subjected to MWP. It was also observed in the 12
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study of Wang et al. [20] wherein the biomass became dehydrated after being subjected to microwave heating. Likewise, ash content could be reduced from 10.8 ± 0.02% to 9.1 ± 0.4% using MWP. This outcome could be due to the ability of microwave heating to
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modify the cellular structure causing lower organic compound content in the S. macrophylla seeds [20]. The less moisture and ash contents in S. macrophylla seeds are desirable because it can solve ignition and combustion problems when used as feed in
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engines [16]. Further, the low moisture and ash contents are good considering the less possibility that water and ash will be elevated to the products during extraction stage.
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The extracted bio-oil from microwave pretreated and conventionally treated seeds were subjected to FTIR analysis to determine whether they both possess the same functional group or not. The spectral features of bio-oil from S. macrophylla seeds are displayed in Fig. 6.
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The actual peaks of the extracted bio-oils were identified, and the corresponding functional groups were determined. The absorption peaks at 3008.0 cm-1[a] and 3001.2 cm-1[b] are due to C-H asymmetric stretch suggesting the presence of alkene. Peaks
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appearing at 2918.7 cm-1[a] and 2916.8 cm-1[b] are due to the C-H symmetric of alkyl compounds, while, 2847.3 cm-1[a] and 2840.6 cm-1[b] are due to C-H antisymmetric stretch
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alkyl group from lipids. The absorption peaks at 1743.7 cm-1[a] and 1733.3 cm-1[b] are due
to C=O stretch indicating the possible presence of ester carbonyl group. Peaks appearing at 1465.1 cm-1[a] and 1461.2 cm-1[b] are assigned to the C-H antisymmetric deformation
vibrations suggesting the presence of methyl esters while 1375.2 cm-1[a] and 1374.1 cm-1[b] peaks are assigned to the symmetric deformation vibrations, respectively. The bands at 1231.3 cm-1[a], 1227.2 cm-1[b], 1161.5 cm-1[a], and 1161.2 cm-1[b] correspond to the C-O
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stretching vibration suggesting the possible presence of the ester groups. The peaks at 722.1 cm-1[a] and 723.7 cm-1[b] are due to C-H bond from long-chain alkane. All identified compounds present in the S. macrophylla bio-oil are also reported by others [14,21–23].
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The results showed similar functional groups present in the extracted bio-oils from the conventional oven pretreated, and microwave pretreated seeds indicating that the compounds before extraction were not destructed to both MWP and conventional
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pretreated processes.
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4. Conclusions
In this study, the optimization of bio-oil yield from non-edible S. macrophylla seeds through MWP before UASE was investigated. MWP of S. macrophylla seeds before UASE proved to increase the bio-oil yield by 5% with optimum recovery of 43.3 ± 0.3 wt% at 180 W irradiation power and 7 min irradiation time. Increased in irradiation
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time, during the MWP of S. macrophylla seeds before extraction process, significantly increased the bio-oil yield; while irradiation power has no statistical basis to support its significant effect on the bio-oil yield. Characterization of the bio-oil product through
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FTIR spectroscopy showed similar functional groups both in the microwave and
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conventionally pretreated seeds suggesting the presence of alkanes, alkenes, esters, and other alkyl and carbonyl groups indicating the presence of desirable compounds for the production of biodiesel fuel and bringing into the center stage the huge implications of the future of biofuel industry worldwide.
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Acknowledgment
The authors would like to acknowledge the faculty and staff of the College of Engineering and Technology of the University of Science and Technology of Southern
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Philippines in Claveria, Philippines, for the support in the conduct of the study. References
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Table 1. Experimental range and levels of independent variables powder
Coded level
Variable
−1
0
1
2
Irradiation time (min)
4
5
6
7
8
Irradiation power (W)
90
180
270
360
450
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−2
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Table 2. Experimental result of bio-oil extraction subjected to MWP
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1 2 3 4 5 6 7 8 9 10 11 12 13
Irradiation power (W) 180 180 270 270 450 270 360 270 270 90 270 360 270
Yield (%) 39.0 43.8 40.7 42.0 42.5 41.3 40.9 40.9 45.8 41.9 40.5 43.3 39.8
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Irradiation time (min) 5 7 6 6 6 6 5 6 8 6 6 7 4
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Run
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UASE: 15 g powdered seeds, 15 min sonication time, 75 mL hexane, 50 µm resonance amplitude, 60 ± 5 °C temperature
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Table 3. ANOVA of the model for percentage bio-oil yield as influenced by MWP
df
F value
p-value Prob > F
7.50 30.4 0.58 1.58 4.35 1.73 0.23 0.11 0.32
32.4 131 2.48 6.80 18.8 7.46
0.0001a < 0.0001a 0.159 b 0.035a 0.003a 0.029a
0.35
0.791b
C.V.% = 1.15 Adeq. precision = 20.3
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Model 37.5 5 A− Time 30.4 1 0.58 1 B− Power AB 1.58 1 A2 4.35 1 2 B 1.73 1 Residual 1.62 7 Lack of fit 0.34 3 Pure error 1.28 4 Cor total 39.1 12 2 2 R = 0.96 Adj. R = 0.93 Std. dev. = 0.48 Mean = 41.7 a significant; b insignificant
Mean square
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Sum of squares
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Source
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Table 4. Actual vs. predicted bio-oil yield as influenced by MWP
Irradiation power (W) 180 180 270 270 450 270 360 270 270 90 270 360 270
Actual (%) 39.0 43.8 40.7 42.0 42.5 41.3 40.9 40.9 45.8 41.9 40.5 43.3 39.8
Predicted (%) 39.3 43.8 41.1 41.1 42.6 41.1 41.1 41.1 46.0 41.7 41.1 43.0 39.6
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Irradiation time (min) 5 7 6 6 6 6 5 6 8 6 6 7 4
Bio-oil yield
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1 2 3 4 5 6 7 8 9 10 11 12 13
Operating variable
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Run
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UASE: 15 g powdered seeds, 15 min sonication time, 75 mL hexane, 50 µm resonance amplitude, 60 ± 5 °C temperature
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LEGEND
1 – Microwave reactor 2 – Control panel 3 – Turntable plate 4 – S. macrophylla seeds powder in petri dish
5 – Support roller ring 6 – Turntable motor hub 7 – Microwave door
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Fig. 1. Experimental set-up in the microwave pretreatment of seeds.
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Whole seeds with pods
Whole seeds without pods
Seeds powder
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Fig. 2. The S. macrophylla seeds.
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(a)
42.4
42.5
R² = 0.96
42.3 41.8
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% Yield
42.0 41.5 41.1
40.9
41.0 40.5 4
5
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00 90 1801270 360 2450 540 3
6
(b)
44
42.5
42 41.4
43.1
42.6
40.8
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% Yield
R² = 0.98
43.5 43.2
43
41
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Irradiation power (W)
40.2
40 39
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0
2
4 6 Irradiation time (min)
8
10
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Fig. 3. Bio-oil yield of S. macrophylla seeds at variable (a) irradiation powers and (b) irradiation times.
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Fig. 4. Contour and 3D response surface plots showing the effects of irradiation time and irradiation power to bio-oil yield.
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Fig. 5. Diagnostic graph on the actual versus predicted bio-oil yield as influenced by MWP.
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Transmittance (%)
(a)
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Wavelength (cm-1)
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Transmittance (%)
(b)
Wavelength (cm-1)
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Fig. 6. FTIR spectra of the extracted bio-oil from (a) microwave and (b) oven pretreated seeds.
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S2468-2039(18)30103-1
DOI:
10.1016/j.serj.2018.06.003
Reference:
SERJ 136
To appear in:
Sustainable Environment Research
Received Date: 12 March 2018 Revised Date:
30 April 2018
Accepted Date: 15 June 2018
Please cite this article as: Gumaling RP, Agusan JRE, Cent R. Ellacer NV, Abi Abi GMT, Pajaron JRP, Joyno JRQ, Joyno CQ, Ido AL, Arazo RO, Increased bio-oil yield from Swietenia macrophylla seeds through microwave pretreatment and ultrasonic-assisted solvent extraction, Sustainable Environment Research (2018), doi: 10.1016/j.serj.2018.06.003. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Received 12 March 2018 Received in revised form 29 April 2018 Accepted 15 June 2018
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Increased bio-oil yield from Swietenia macrophylla seeds through microwave
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pretreatment and ultrasonic-assisted solvent extraction
a
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Rey P. Gumaling a, Jay R E. Agusan a, Neil Ven Cent R. Ellacer a, Gretel Mary T. Abi Abi a, Jasmin Roxatte P. Pajaron a, Jose Rey Q. Joyno a, Cherry Q. Joyno a, Alexander L. Ido a, Renato O. Arazo a,b*
College of Engineering and Technology, University of Science and Technology of Southern Philippines, Claveria 9004, Philippines Project Development Office, University of Science and Technology of Southern Philippines, Claveria 9004, Philippines
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b
*Corresponding author Email: [email protected] (Dr. Renato O. Arazo)
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Abstract Low recovery coupled with intensive energy requirement due to long processing time makes the potential of bio-oil production not seamlessly appreciated. In this study,
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the optimization of bio-oil yield from non-edible Swietenia macrophylla seeds through microwave pretreatment before ultrasonic-assisted solvent extraction was investigated. Central composite design of response surface methodology was employed to analyze the
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effects to the bio-oil yield of the irradiation time (4-8 min) and irradiation power (90-450 W) as pretreatment variables using a microwave oven at 2.45 GHz frequency. Results
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showed that microwave pretreatment significantly increased the bio-oil yield by 5% with optimum recovery of 43% at shortened pretreatment time of 7 min instead of 6 h in the conventional oven heating method. The bio-oil yield increased when the irradiation time was increased, while irradiation power showed no significant effect. Analysis of the
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produced bio-oil through Fourier Transform Infrared Radiation spectroscopy identified similar functional groups present both in the extracted bio-oils from the microwave and the conventional pretreated seeds indicating that the former pretreatment, like the latter,
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did not destruct the compounds present in the seeds. The study demonstrated that the seeds of S. macrophylla have strong potential for bio-oil production and poise huge
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implications to the future of liquid biofuel and chemical industries.
Keywords: Swietenia macrophylla; Microwave Pretreatment; Oil Extraction; Optimization; Response Surface Methodology
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1. Introduction The finite source of petroleum oil reserve would be exhausted in the next century due to the increasing consumption of crude oil products to feed engines [1]. The
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overdependence of this nonrenewable product, driven by economic growth and rapid industrialization in the developed and developing countries, contributes greatly to the increased greenhouse gases in the atmosphere which cause the global climate change [2].
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Hence, the twin crises of fossil fuel depletion and environmental degradation attract researchers to continually search for an alternative energy resource that is sustainably
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appropriate and environmentally benign.
Interest in biofuels, like liquid biodiesel with bio-oil feedstock, is becoming more attractive due to its renewable origin and environmental benefit of emitting less carbon dioxide, sulfur oxides and hydrocarbon [3]. More importantly, the bio-oil derived from
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second and third generation biomass like Swietenia macrophylla seeds [4], Hevea brasiliensis seeds [5], and microalgae [6] as feedstocks for biodiesel production were preferred over the first generation like corn, wheat, peanut, and coconut to avoid the
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possible competition in food production and food industries. Related literature shows that bio-oil from S. macrophylla seeds contain common
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unsaturated fatty acids such as oleic (26%), linoleic (33%), linolenic (12%) and saturated fatty acids, namely, palmitic (13%) and stearic (14%) suggesting its suitability for biodiesel production [7]. These fatty acids could be recovered through suitable extraction method that would maximize bio-oil yield. One of these is the ultrasonic-assisted solvent extraction (UASE) method that ruptures the membrane of the S. macrophylla seeds thereby promoting maximum bio-oil extraction [5].
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Aside from the extraction using organic solvents aided by ultrasonication, biomass pretreatment by means of microwave irradiation is also proven to increase biooil recovery [9]. Microwave irradiation applied to biomass as the pretreatment is
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advantageous not only because of increase bio-oil recovery but also in the reduction of processing time needed as compared to conventional pretreatment [8,10–13].
To date, there has been no study yet on the optimization of bio-oil yield from S.
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macrophylla seeds when subjected to microwave pretreatment (MWP). In this work, the seeds of S. macrophylla, an oil-rich second-generation biomass from an exotic Philippine
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species of the family Meliaceae, were used to produce bio-oil, a potential feedstock for biodiesel production [4,14]. It ultimately aims to give scientific information on the effects of MPV
to the bio-oil recovery from S. macrophylla seeds. Specifically, optimization of
the bio-oil yield was investigated considering the effects of irradiation time and
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irradiation power as operating variables through the central composite design (CCD) of response surface methodology. This is an appropriate statistical tool that does not only serve for the design of experiments but also capable of giving 3D plots to closely
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investigate the effects and determine the optimum values of chosen variables [15]. The functional groups present in the produced bio-oils were, likewise, identified through
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Fourier Transform Infrared Radiation (FTIR) spectroscopy analysis. 2. Materials and methods 2.1. S. macrophylla seeds preparation The S. macrophylla seeds used in this study were collected from Poblacion,
Claveria, Misamis Oriental, Philippines. The pods were broken to collect the seeds. The whole seeds were sundried, cleaned by airing, oven dried (Contherm Designer Series 4
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Oven, Model: CE Z011) at 100 ± 1 °C for 24 h, powdered and sieved at 10 mm mesh before pretreatment and extraction. Only those particles that passed the sieve were used
2.2 Parametric and optimization studies
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as biomass.
A parametric study in MWP was conducted using important parameters/variables
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according to the literature [10,11] such as irradiation time and irradiation power. The runs were based on the parametric study principle of taking one variable as constant while
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varying other variable, and a peak was known in a graph once plotted. The values of the observed peaks were used as center points (level 0) of the variables. Based on the parametric investigation of this work, the levels and range of values of the variables were known (Table 1) and were used in the design of experiment in the subsequent optimization study.
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In the optimization study, the CCD of response surface methodology was used in the design of experiment with the aid of Design Expert 7.0 software. The combinations of all runs, consisting irradiation time and power, were based on experimental design
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generated by the CCD. The experiment was conducted at room temperature (25 ± 1 °C).
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For each run, 15 g of oven dried powder of S. macrophylla seeds were placed in the plate of a microwave oven (JEI2340WPSL GE Model, China) with 2.45 GHz frequency and following the predetermined irradiation time and power. After which, the pretreated samples were cooled down inside the desiccator. Fig. 1 describes the pretreatment experimental set-up of powdered seeds.
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2.3 Ultrasonic-assisted n-hexane extraction Pretreated powdered seeds were subjected to UASE using n-hexane following the experimental procedures described in the study of Mabayo et al. [5]. The n-hexane (96%,
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GR grade, Duksan Pure Chemicals) used in the bio-oil extraction was purchased from Harnwell Chemical, Cagayan de Oro City, Philippines. The experiment was conducted at the Chemistry Laboratory of the University of Science and Technology of Southern
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Philippines with a room temperature of 25 ± 1 °C. Each UASE run, with variable irradiation time and power set according to the design of experiments, was done with 75
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mL hexane, 50 µm resonance amplitude, 60 ± 5 °C reaction temperature at 15 min sonication time, and 15 g powdered seeds. 2.4 Control set-up for MWP
To compare the results that were generated from the optimization study and to
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determine the efficiency of MWP, a conventional heating using the oven as control experiment was conducted. For the control experiment, powdered S. macrophylla seeds samples were dried in an oven (Contherm Designer Series, Model: CE Z011) at 60 ± 5 °C
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for 6 h [11].
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2.5 Bio-oil yield determination The percent bio-oil yield from S. macrophylla seeds was determined using digital
analytical balance. The percent yield was calculated using Eq. (1).
%
100
(1)
where %Y is the percent yield (wt%) of the bio-oil extracted from powdered seeds, m1 is 6
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the mass of produced bio-oil, and m2 is the mass of powdered seeds used in extraction. 2.6 Product analysis
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Proximate analyses of the powdered seeds in terms of moisture content and ash content from microwave heating and conventional oven heating were conducted and analyzed. The moisture content was determined using drying oven (Contherm Designer
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Series Oven, Model: CE Z011) at 100 ± 1 °C for 24 h. The LabTech LEF-304P-2 muffle furnace was used in ash content analysis at 600 ± 25 °C for 3 h.
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The bio-oils, both from microwave and conventionally pretreated seeds, were subjected to FTIR spectroscopy analysis to compare if there are differences in the functional groups. The FTIR spectroscopy analysis was conducted at the Pilipinas Kao, Incorporated at Jasaan, Misamis Oriental, Philippines using Shimadzu 8400S. 2.7 Statistical analysis and modelling
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Statistical analysis and modeling were done through CCD using Design Expert 7.0 software. Analysis of variance was the statistical tool used in the study that determined the most appropriate model equation that best fits the data gathered in the
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experimental runs. The percent yield of the experimental runs underwent graphical
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modeling and established the interactive effects of the chosen operating variables through the visual 3D plot.
3. Results and discussion
3.1 Seeds characterization Characteristics of Swietenia macrophylla seeds such as moisture and ash contents
and physical appearance were determined before these were utilized as feedstock. The S. macrophylla fruit pod was brown with oval seed (Fig. 2). Each winged pod weighed 0.2 7
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± 0.1 g while each seed weighed 0.5 ± 0.1 g. The seeds moisture content recorded 6.1 ± 0.2%, on wet basis, which is lower than the 10.6 ± 0.4% reported elsewhere [4]. Low moisture content is desirable considering the least possibility that water shall be elevated
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to the liquid product during bio-oil extraction. The recorded S. macrophylla seed’s ash content of 10.9±0.1% is just comparable to diverse bio-based fuel products [16]. As a supplementary data from other work, the ultimate analysis of S. macrophylla seeds
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showed that the carbon, hydrogen, nitrogen, sulfur, and oxygen percent contents were
3.2 MWP parametric analysis
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48.14, 6.40, 0.28, 0.03, and 45.15, respectively [17].
Fig. 3a shows the bio-oil yield from 15 g microwave pretreated S. macrophylla seeds produced at variable irradiation powers with 3 min irradiation time. The bio-oil yield peaks at 270 W irradiation power (42.4%). This result was used as the center point
1).
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(level 0) in making the level and range of MVP variable in this study (as shown in Table
At 270 W irradiation power as constant and variable irradiation times, the bio-oil
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yield peaks at 6 min with 43.5% yield (Fig. 3b). The design of experiment used the 6 min
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as the center value (level 0) of the irradiation time (as shown in Table 1). Therefore, the 270 W irradiation power and 6 min irradiation time were taken as
the center of the levels of variables in the design of experiment of independent variables using the CCD of the response surface methodology (Table 1).
3.3 Percent bio-oil yield of seeds subjected to MWP As seen in Table 2, the highest bio-oil yield of 46 wt% was achieved at 8 min irradiation time and 270 W irradiation power; while the lowest yield of 39 wt% was 8
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achieved at 5 min irradiation time and 180 W irradiation power. This means that the large increase in irradiation time and a small increase in irradiation power during pretreatment
3.4 Model fitting of bio-oil yield as subjected to MWP
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would result in higher bio-oil yield.
The CCD’s analysis particularly the fit summary revealed that response surface
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quadratic model best fitted in predicting the percentage of bio-oil yield from S. macrophylla seeds as affected by MWP variables. The ANOVA result of the response
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surface quadratic model for the percentage of bio-oil yield is shown in Table 3. The model p-value of 0.0001 indicates a highly significant quadratic model with high accuracy in predicting the bio-oil yield of microwave pretreated S. macrophylla seeds. The model p-value of 0.0001 means that there is only 0.01% chance that error could arise from the noise. The lack of fit F-value of 0.35 implies that the lack of fit is not
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significant relative to pure error and that there is 79.1% chance that the lack of fit F-value this large could arise through the noise. It is good to note that the lack of fit is not significant implying that the model is fit.
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The coefficient of variance and determination could also support that the
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quadratic model is robust. The coefficient of determination (R2) value of 0.96 is high which means that the regression model for the bio-oil yield was satisfactory and demonstrated a high degree of correlations between the actual data and predicted values. It also signifies that there is 96% certainty that the generated model can explain the variability of the data. Further, the adjusted coefficient of determination (Adj. R2) of 0.93 is also high which could support the suitability of generated model in presenting the correlation of actual and experimental values. The coefficient of variance percentage of 9
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1.15% was low enough to represent adequacy of data indicating that the model owns high precision and reliability for fitting experimental values. Eq. (2) shows the quadratic
and irradiation power (W), respectively.
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model equation in terms of actual factors where A and B represent irradiation time (min),
(2)
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37.71 − 1.76 + 0.03 − 0.01 + 0.44
The predicted values of bio-oil yield could be determined using the generated
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quadratic equation. This equation could also support how the terms affect the bio-oil yield. Unlike term B (irradiation power), term A (irradiation time) was found significant and has a negative numerical coefficient which means that increasing the irradiation time, when taken singly, may lead to a decrease in yield, but the square of it (A2) resulted
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otherwise. Hence, the model equation can be further investigated using a 3D plot to determine the overall effect of the two contrasting coefficients of A and A2 terms. The overall result showed that the effect of irradiation time (A and A2 combined) significantly
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increased the bio-oil yield (see Fig. 4).
Table 4 shows that the actual values were seen close to the predicted values which
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could further support the claim that the model fitness owns high degree of correlations between the actual and the predicted ones. Fig. 5 shows the diagnostic graph of the actual versus predicted responses of the experimental runs. The actual values according to data points on the graph are positioned close to the predicted values represented by the straight line signifying a high degree of correlations between the actual and predicted values (Fig. 5). This could mean that the model fitness is strong and reliable. This result supports the
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claim that response surface quadratic model is the most suitable model for predicting the bio-oil yield from microwave pretreated S. macrophylla seeds.
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3.6 Effects of the MWP’s operating variables to the bio-oil yield Fig. 4 illustrates that as the irradiation time increases, the bio-oil yield increases. A similar finding was observed by others [10,12,18,19]. This result clearly shows that increasing the exposure time could provide greater rupture of cell structure. Irradiation
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power, on the other hand, has no statistical basis to support its significant effect on the
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bio-oil yield. Nonetheless, the Fig. 4 illustrates that the increase of irradiation power at the shorter time resulted in little addition of the bio-oil yield. At longer irradiation time, the increase of irradiation power resulted in a small and insignificant increase of bio-oil product. This result implies that irradiation power effect is not significant when compared
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to irradiation time.
3.7 Optimization of the bio-oil yield via MWP Numerical optimization suggested two solutions that could result in optimum bio-
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oil yield from S. macrophylla seeds via MWP. The solution with the highest desirability was chosen and ran in triplicate following the suggested values of the operating variables.
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The validated or the actual bio-oil yield of 43.3 ± 0.3% is close to the theoretical yield of 43.8% with the percent error of 0.8–1.8% (7 min at 180 W). The percent error falls below the 5% acceptable error signifying that the model is valid and owns high degree of precision in predicting the bio-oil yield from S. macrophylla seeds. This outcome means
that the bio-oil yield of the microwave pretreated seeds can be determined using the equation generated by simply plugging in the values of irradiation time and power. Ping et al. [8] reported the bio-oil yield of 29.5 ± 1.6% from S. macrophylla seeds 11
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applying MWP followed by solvent extraction using the mixture of methanol and chloroform. The optimum condition in this study applying the same pretreatment technique followed by ultrasonic-aided hexane extraction was way higher than the
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reported yield in the study of Ping et al. [8]. This finding implies that the CCD of response surface methodology helped in making result way higher than the previously reported bio-oil yield as well as in establishing the optimum conditions. Further, the
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finding tells that the use of hexane as a solvent in the ultrasonication could significantly
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increase the bio-oil yield from S. macrophylla seeds.
3.7 Comparison of MWP with the conventional method
To identify the best pretreatment method, conventional oven treatment of the seeds was compared with MWP under the optimal conditions. MWP under 180 W power at 7 min time enabled to extract 43.3 ± 0.4%, which is apparently superior to that of
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conventional treatment with 37.9 ± 0.1% yield under 60 °C temperature and 6 h time. This result means that MWP could promote the UASE of bio-oil. The result is also true with the study of Ren et al. [11] wherein MWP could enhance bio-oil extraction from
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flaxseeds. The high extraction yield of microwave pretreated S. macrophylla seeds could
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be attributed to the modification of cellular membrane due to the pretreatment which further enhances the solvent extraction. 3.8 Product analysis
The moisture and ash contents of pretreated S. macrophylla seeds were analyzed.
Its powder’s moisture content on dry basis of 4.8 ± 0.1% could be reduced to 3.4 ± 0.1% through microwave treatment method. This result could be due to the quick and efficient release of moisture when the seeds were subjected to MWP. It was also observed in the 12
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study of Wang et al. [20] wherein the biomass became dehydrated after being subjected to microwave heating. Likewise, ash content could be reduced from 10.8 ± 0.02% to 9.1 ± 0.4% using MWP. This outcome could be due to the ability of microwave heating to
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modify the cellular structure causing lower organic compound content in the S. macrophylla seeds [20]. The less moisture and ash contents in S. macrophylla seeds are desirable because it can solve ignition and combustion problems when used as feed in
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engines [16]. Further, the low moisture and ash contents are good considering the less possibility that water and ash will be elevated to the products during extraction stage.
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The extracted bio-oil from microwave pretreated and conventionally treated seeds were subjected to FTIR analysis to determine whether they both possess the same functional group or not. The spectral features of bio-oil from S. macrophylla seeds are displayed in Fig. 6.
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The actual peaks of the extracted bio-oils were identified, and the corresponding functional groups were determined. The absorption peaks at 3008.0 cm-1[a] and 3001.2 cm-1[b] are due to C-H asymmetric stretch suggesting the presence of alkene. Peaks
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appearing at 2918.7 cm-1[a] and 2916.8 cm-1[b] are due to the C-H symmetric of alkyl compounds, while, 2847.3 cm-1[a] and 2840.6 cm-1[b] are due to C-H antisymmetric stretch
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alkyl group from lipids. The absorption peaks at 1743.7 cm-1[a] and 1733.3 cm-1[b] are due
to C=O stretch indicating the possible presence of ester carbonyl group. Peaks appearing at 1465.1 cm-1[a] and 1461.2 cm-1[b] are assigned to the C-H antisymmetric deformation
vibrations suggesting the presence of methyl esters while 1375.2 cm-1[a] and 1374.1 cm-1[b] peaks are assigned to the symmetric deformation vibrations, respectively. The bands at 1231.3 cm-1[a], 1227.2 cm-1[b], 1161.5 cm-1[a], and 1161.2 cm-1[b] correspond to the C-O
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stretching vibration suggesting the possible presence of the ester groups. The peaks at 722.1 cm-1[a] and 723.7 cm-1[b] are due to C-H bond from long-chain alkane. All identified compounds present in the S. macrophylla bio-oil are also reported by others [14,21–23].
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The results showed similar functional groups present in the extracted bio-oils from the conventional oven pretreated, and microwave pretreated seeds indicating that the compounds before extraction were not destructed to both MWP and conventional
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pretreated processes.
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4. Conclusions
In this study, the optimization of bio-oil yield from non-edible S. macrophylla seeds through MWP before UASE was investigated. MWP of S. macrophylla seeds before UASE proved to increase the bio-oil yield by 5% with optimum recovery of 43.3 ± 0.3 wt% at 180 W irradiation power and 7 min irradiation time. Increased in irradiation
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time, during the MWP of S. macrophylla seeds before extraction process, significantly increased the bio-oil yield; while irradiation power has no statistical basis to support its significant effect on the bio-oil yield. Characterization of the bio-oil product through
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FTIR spectroscopy showed similar functional groups both in the microwave and
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conventionally pretreated seeds suggesting the presence of alkanes, alkenes, esters, and other alkyl and carbonyl groups indicating the presence of desirable compounds for the production of biodiesel fuel and bringing into the center stage the huge implications of the future of biofuel industry worldwide.
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Acknowledgment
The authors would like to acknowledge the faculty and staff of the College of Engineering and Technology of the University of Science and Technology of Southern
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Philippines in Claveria, Philippines, for the support in the conduct of the study. References
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Optimization of microwave pretreatment variables for canola oil extraction. J Food
mechanical extraction yield and quality of vegetable oil from Chilean hazelnuts (Gevuina avellana Mol). Innov Food Sci Emerg 2008;9:495–500. [20]
Wang X, Chen H, Luo K, Shao J, Yang H. The influence of microwave drying on
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biomass pyrolysis. Energ Fuel 2007;22:67–74.
Coates J. Interpretation of infrared spectra: a practical approach. In: Meyers RA, editor. Encyclopedia of Analytical Chemistry. Newtown, CT: John Wiley & Sons;
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2000. p. 10815–37.
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spectroscopic analyses of biodiesel. Eur Int J Sci Technol 2013;2:137–46.
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Table 1. Experimental range and levels of independent variables powder
Coded level
Variable
−1
0
1
2
Irradiation time (min)
4
5
6
7
8
Irradiation power (W)
90
180
270
360
450
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−2
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Table 2. Experimental result of bio-oil extraction subjected to MWP
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1 2 3 4 5 6 7 8 9 10 11 12 13
Irradiation power (W) 180 180 270 270 450 270 360 270 270 90 270 360 270
Yield (%) 39.0 43.8 40.7 42.0 42.5 41.3 40.9 40.9 45.8 41.9 40.5 43.3 39.8
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Irradiation time (min) 5 7 6 6 6 6 5 6 8 6 6 7 4
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Run
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UASE: 15 g powdered seeds, 15 min sonication time, 75 mL hexane, 50 µm resonance amplitude, 60 ± 5 °C temperature
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Table 3. ANOVA of the model for percentage bio-oil yield as influenced by MWP
df
F value
p-value Prob > F
7.50 30.4 0.58 1.58 4.35 1.73 0.23 0.11 0.32
32.4 131 2.48 6.80 18.8 7.46
0.0001a < 0.0001a 0.159 b 0.035a 0.003a 0.029a
0.35
0.791b
C.V.% = 1.15 Adeq. precision = 20.3
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Model 37.5 5 A− Time 30.4 1 0.58 1 B− Power AB 1.58 1 A2 4.35 1 2 B 1.73 1 Residual 1.62 7 Lack of fit 0.34 3 Pure error 1.28 4 Cor total 39.1 12 2 2 R = 0.96 Adj. R = 0.93 Std. dev. = 0.48 Mean = 41.7 a significant; b insignificant
Mean square
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Sum of squares
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Table 4. Actual vs. predicted bio-oil yield as influenced by MWP
Irradiation power (W) 180 180 270 270 450 270 360 270 270 90 270 360 270
Actual (%) 39.0 43.8 40.7 42.0 42.5 41.3 40.9 40.9 45.8 41.9 40.5 43.3 39.8
Predicted (%) 39.3 43.8 41.1 41.1 42.6 41.1 41.1 41.1 46.0 41.7 41.1 43.0 39.6
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Irradiation time (min) 5 7 6 6 6 6 5 6 8 6 6 7 4
Bio-oil yield
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1 2 3 4 5 6 7 8 9 10 11 12 13
Operating variable
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UASE: 15 g powdered seeds, 15 min sonication time, 75 mL hexane, 50 µm resonance amplitude, 60 ± 5 °C temperature
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LEGEND
1 – Microwave reactor 2 – Control panel 3 – Turntable plate 4 – S. macrophylla seeds powder in petri dish
5 – Support roller ring 6 – Turntable motor hub 7 – Microwave door
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Fig. 1. Experimental set-up in the microwave pretreatment of seeds.
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Whole seeds with pods
Whole seeds without pods
Seeds powder
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Fig. 2. The S. macrophylla seeds.
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(a)
42.4
42.5
R² = 0.96
42.3 41.8
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% Yield
42.0 41.5 41.1
40.9
41.0 40.5 4
5
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(b)
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42.5
42 41.4
43.1
42.6
40.8
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% Yield
R² = 0.98
43.5 43.2
43
41
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Irradiation power (W)
40.2
40 39
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2
4 6 Irradiation time (min)
8
10
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Fig. 3. Bio-oil yield of S. macrophylla seeds at variable (a) irradiation powers and (b) irradiation times.
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Fig. 4. Contour and 3D response surface plots showing the effects of irradiation time and irradiation power to bio-oil yield.
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Fig. 5. Diagnostic graph on the actual versus predicted bio-oil yield as influenced by MWP.
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Transmittance (%)
(a)
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Wavelength (cm-1)
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Transmittance (%)
(b)
Wavelength (cm-1)
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Fig. 6. FTIR spectra of the extracted bio-oil from (a) microwave and (b) oven pretreated seeds.
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