- Email: [email protected]
Cleaner production of rubber seed oil methyl ester using a hydrodynamic cavitation: optimisation and parametric study
Accepted Manuscript Cleaner Production of Rubber Seed Oil Methyl Ester using a Hydrodynamic Cavitation: Optimisation and Parametric Study Awais Bokhari, Lai Fatt Chuah, Suzana Yusup, Jiří Jaromír Klemeš, Majid Majeed Akbar, Ruzaimah Nik M. Kamil PII:
S0959-6526(16)30367-5
DOI:
10.1016/j.jclepro.2016.04.091
Reference:
JCLP 7115
To appear in:
Journal of Cleaner Production
Received Date: 26 February 2016 Revised Date:
8 April 2016
Accepted Date: 21 April 2016
Please cite this article as: Bokhari A, Chuah LF, Yusup S, Klemeš JJ, Akbar MM, Kamil RNM, Cleaner Production of Rubber Seed Oil Methyl Ester using a Hydrodynamic Cavitation: Optimisation and Parametric Study, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.04.091. 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.
ACCEPTED MANUSCRIPT Total word count including tables and figures: 6885
Highlights About 6.5 fold higher energy efficiency using HC than mechanical stirring.
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About 5 fold less reaction time using HC than mechanical stirring.
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About 4.9 fold higher rate constant using HC compared to mechanical stirring.
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About 3.5 fold higher frequency factor using HC than mechanical stirring.
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List of abbreviations
RSO = Rubber seed oil RSOME = Rubber seed oil methyl ester
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TG = Triglyceride HC = Hydrodynamic cavitation MS = Mechanical stirring
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FFA = Free fatty acid x = Methyl ester conversion
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RSM = Response surface methodology CCD = Central composite design
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KOH = Potassium hydroxide
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Cleaner Production of Rubber Seed Oil Methyl Ester using a Hydrodynamic Cavitation: Optimisation and Parametric Study Awais Bokharia, Lai Fatt Chuaha,b*, Suzana Yusupa, Jiří Jaromír Klemešc, Majid Majeed Akbard, Ruzaimah Nik M. Kamile Chemical Engineering Department, Biomass Processing Laboratory, Center of Biofuel and Biochemical Research (CBBR),
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a
Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Seri Iskandar, Perak, Malaysia b
Pázmány Péter Catholic University, Faculty of Information Technology and Bionics, Práter u. 50/a, 1083 Budapest, Hungary d
e
Institute of Chemical Engineering and Technology, University of the Punjab, Lahore, Pakistan
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c
Marine Department Malaysia Northern Region, 11700 Gelugor, Penang, Malaysia
Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Seri Iskandar,
*
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Perak, Malaysia
Corresponding Author Email: [email protected]
ABSTRACT — Producing sustainable biodiesel using non-edible feedstock via transesterification reaction assisted hydrodynamic cavitation technology is a viable way to offset fossil diesel usage. This technology has
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affirmative environmental impacts with lower energy consumption and the reaction time and offers a cleaner possibility. Methyl ester conversion has been observed at a different inlet pressure of 1-3.5 bar on different plate geometries in 50 L pilot hydrodynamic cavitation reactor. Orifice plate with 21 holes of 1mm and inlet
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pressure of 3 bar found to be the optimal arrangement. Parametric optimisation used response surface methodology and found as alcohol to oil ratio of 6:1, catalyst loading of 1 wt. %, reaction time of 18 min and
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reaction temperature of 55 °C. About 5 fold shorter reaction time, 6.5 fold higher energy efficiency and 4.9 fold higher reaction rate constant using hydrodynamic cavitation compared to mechanical stirring. Hydrodynamic cavitation is concluded to be time saving and energy efficient process compared to mechanical stirring. This makes the process more environmental friendly using hydrodynamic cavitation. Most of the properties in rubber seed oil methyl ester were met the EN 14214 and ASTM D 6751 standards. Keywords— Cleaner production of biodiesel; optimisation; rubber seed oil methyl ester; mass transfer; fuel properties 3
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1.
Introduction
Sustainable development in industrialisation and motorisation has significantly increased the utilisation of fossil fuel (Harris et al., 2016). This phenomenon results in high greenhouse gas emissions to the environment
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(Tu and McDonnell., 2016). Environmental concerns are the key factor to inspire researchers to search renewable and sustainable fuel (Piemonte et al., 2016). Hydropower, tidal, solar, biodiesel, the wind, waves and geothermal were renewable energies to replace fossil fuel (Dwivedi et al., 2013). Biodiesel has become an attractive renewable fuel due to carbon footprint reduction (Chuah et al., 2015a). Biodiesel can be directly
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utilised in the diesel engine without any modifications due to its similarity properties with diesel fuel, such as
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heating value and viscosity (Chuah et al., 2015b). Greenhouse gas footprint is minimised (Čuček et al., 2014) when the local available non-edible feedstock is utilised for cleaner biodiesel production rather than to export it to other regions (Chuah et al., 2016).
Biodiesel production can be derived from manifold feedstock, such as edible oil (Permpool et al., 2015),
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non-edible oil (Chuah et al., 2015c), animal fat and algae (Medeiros et al., 2015). About 95 % of world biodiesel production is from the edible oil, which is obviously not the best solution creating foot-energy competition (Chuah et al., 2015d). Utilising edible oil in biodiesel production causes the price about 1.5-2 fold
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higher than diesel fuel (Maddikeri et al., 2012). Another consequence brought by the excessive consumption of
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edible oil is food crisis (Bokhari et al., 2015). By utilising non-edible for biodiesel production provides the best solution to prevent food crisis (Gimbun et al., 2013). Malaysia is one of the rubber producers in the worldwide (Yusup et al., 2015). Rubber tree known as Hevea brasiliensis, belongs to the family of euphorbiaceous provides 40 to 50 wt. % of oil yield (Abedin et al., 2014). Malaysia has sufficient production of rubber approximately 1,022,700 ha (hectare) with the capacity of 300 kg/ha annually. Consequently, rubber seed oil (RSO) is a promising non-edible feedstock oil for biodiesel production.
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The acid-catalysed reaction has been used to treat the untolerate free fatty acid (FFA) in feedstock and reduce its FFA until less than 2 % via esterification reaction in order to avoid the formation of emulsion and soap during transesterification reaction. This treated feedstock oil can be used to produce biodiesel in the presence
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of alkali catalyst via transesterification reaction. The direct conversion of triglyceride (TG) to methyl ester via transesterification reaction has been hindered by higher FFA concentration in RSO. FFA can react with alkali catalyst and results in saponification reaction (Morshed et al., 2011). To reduce FFA content in RSO, acid esterification is the chosen method to convert one mole of FFA into one mole of water and alkyl ester in the
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presence of alcohol. (Issariyakul et al., 2014).
Microwave, ultrasonic cavitation, supercritical condition, static mixer and hydrodynamic cavitation (HC) are the potential intensification technologies to get rid the mass transfer resistance between immiscible reactants (oil and alcohol). HC is the most efficient in terms of scalable, energy consumption and reaction time. Cavities in HC process are produced by destructive force, which causes the bubbles expansion and compression.
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Implosion and high interfacial area of cavities could eliminate the mass transfer between oil and alcohol (Gogate, 2008). HC has been intensively investigated in the shipping and wastewater treatment industries since twenty’s century. HC for biodiesel synthesis has been explored a decade ago by pioneering work of
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Ji et al. (2006) in 2006. However, there are not too many works related to biodiesel until now. Most of the
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studies were just at laboratory scale. Ghayal et al. (2013) have studied the HC process on the synthesis of frying oil at laboratory level with 10 L capacity. They investigated the orifice plate geometrical effects with variable upstream pressure, but no detailed information with regards to hole spacing and distribution pattern. In 2015, Chuah et al. (2016) have studied the HC process at 50 L capacity pilot plant for waste cooking oil methyl ester synthesis with detailed information of four orifice plates designed, hole spacing and distribution pattern. Bokhari et al. (2016) have successfully reduced the FFA of RSO to an acceptable level in just 30 min using optimised orifice plate and operating conditions. This study is a continuous work from Bokhari et al. (2016),
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which utilise treated RSO (2.64 mg KOH/g) for cleaner rubber seed oil methyl ester (RSOME) production in a pilot scale HC reactor. To best of our knowledge, this is the first work on newly designed four orifice plates, which utilise treated RSO for biodiesel production via transesterification reaction in a pilot scale HC reactor of
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50 L capacity. The effects of inlet pressure (1-3.5 bar) and geometrical parameters (total hole perimeter, α, β and β̥) on the RSOME conversion and yield efficiency were investigated. Response surface methodology (RSM) was used for the optimisation of transesterification conversion from treated RSO via HC. Biodiesel synthesis via mechanical stirring (MS) and HC in the same reactor has also investigated for comparison purpose in terms
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of conversion, reaction time, yield efficiency and kinetic parameters. Both standards of ASTM D 6751 and
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EN 14214 were being referred to the properties of produced RSOME in pilot HC reactor.
Materials
Treated RSO was obtained from the previous work of Bokhari et al. (2016). The properties of treated RSO are listed in Table 1. A standard mixture of 37 fatty acid methyl ester was obtained from Sigma Aldrich, Malaysia
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(Chuah et al., 2016). The chemicals used for this experiment were anhydrous methanol, potassium hydroxide pellets, sulphuric acid, anhydrous sodium sulphate, toluene, 2propanol, phenolphthalein, Wijs solution, acetic acid (glacial), cyclohexane, potassium iodide, sodium
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thiosulphate pentahydrate, starch, chloroform, acetone, hydrochloric acid and ethanol. All chemicals were
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analytical grade and have been purchased from Merck, Malaysia (Chuah et al., 2016). GC-FID - Agilent Technologies, 7890A GC System and capillary column - methylpolysiloxane (DB-23) (60 m x 0.25 mm x 0.25 µm) were used to determine the quantitative of methyl ester conversion by following EN 14103 standard method. The temperature programme started at 100 °C, holding for 2 min, heated at 10 °C/min until 200 °C, at 5 °C/min until 240 °C and finally holding for 7 min. Helium was used as a carrier gas at the flow rate of 4 mL/min. The hydrogen and air were used at the flow rate of 50 mL/min and 400 mL/min for the flame production (Bokhari et al., 2016). All experiments were repeated three times and the
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reported values were averages of the individual runs. The properties of the produced biodiesel were analysed according to ASTM D 6751 and EN 14214 standards.
Experimental setup
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3.
HC reactor with a 50 L capacity was made up by a double jacketed glass. HC reactor was connected to the diaphragm pump in a closed loop called batch reactor. Compressed air was used to operate the double diaphragm pump, which acted as a device to dissipate the energy in HC. The outlet of the pump was manifold
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into two lines. The inlet pressure and inlet flow rate to the orifice plate were regulated by two valves, which
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were the main line valve and bypass line valve. Figure 1 demonstrates the process flow configuration of HC reactor. At an inlet pressure of 3 bar, the mass flow of the main and bypass lines were 25.8 L/min and 15.1 L/min. The pressure gauges of P1 and P2 were used to determine the upstream and downstream pressures of the pipelines. The heat was supplied to the HC reactor by circulating liquid heating oil through the jacket surrounding the reactor in order to balance the dissipation of heat energy due to the cavitation events. The
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operating temperature of the reactor has been maintained at the desired level by controller temperature. The details of newly designed four orifice plates have been presented in the previous paper (Chuah et al., 2016). The values for diameter, hole number, total flow area and total hole perimeter of the four orifice plates were plate 1
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– 4.58 mm, 1, 16.5 mm2 and 14.39 mm, plate 2 – 1.00 mm, 21, 16.5 mm2 and 65.98 mm, plate 3 – 2.00 mm, 9,
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28.3 mm2 and 56.56 mm and plate 4–3.00 mm, 5, 35.3 mm2 and 47.13 mm. Optimisaton of orifice plate and inlet pressure via transesterification reaction were conducted under optimised operating conditions (alcohol to oil ratio of 6:1 and catalyst concentration of 1 wt. % at 55 oC), which found in our previous research work on a laboratory scale (Ahmad et al., 2014). The mixture passes through the four newly designed orifice plates at inlet pressures of 1, 2, 3 and 3.5 bar in order to create the constructive conditions with different orifice plate geometries. The upstream flow rate of reaction mixture and hole area of plate were used to calculate the velocity through the orifice. A 50 mL sample was collected with the regular interval of time. The collected
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samples were allowed to settle down under gravity by using a separating funnel for 4 h. The catalyst and byproduct were discharged through the opening of the funnel An ionised warm water at 40 °C was used to wash and remove the impurities in the product. Remaining alcohol and water in the product were evaporated under
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vacuum condition by using a rotary evaporator. In favour of ensuring water completely remove, a 10 g of anhydrous sodium sulphate was added to the product and then filtered by using filter paper (541 Whatman). All
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the experiments were conducted for three replicates to ensure reproducibility of the results.
Yield efficiency calculation
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Yield efficiency or called energy efficiency is defined to quantify the required pumping energy for dissociation the specific amount of oil in terms of efficiency parameter. Yield efficiency is calculated using the following Eq. (1).
(1)
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Yield efficiency = Amount of product produced (g) Pumping energy (J)
5.
Results and discussion
5.1
Effect of inlet pressure on methyl ester conversion
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Figure 2 illustrates the effect of inlet pressure or upstream pressure within the range of 1-3.5 bar at the reaction temperature of 55 °C on methyl ester conversion in four different orifice plate geometries. The results revealed
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that all orifice plate geometries have the increment on transesterification reaction rate when inlet pressure increased from 1 to 3 bar. There was no significant difference of reaction rate between 3 and 3.5 bar. It could be attributed to large cavities formed on the downstream area of an orifice plate, causing cavitation chocking due to coalescence of a large number of cavities (Ghayal et al., 2013). Many researchers reported that inlet pressure reached to certain value resulted in lower reaction rate (Chuah et al., 2016). Bagal and Gogate (2014) also reported the degradation rate decreased when inlet pressure at 4 bar. Vichare et al. (2000) also proved that decomposition reaction rate decreased at 3.8 bar. Therefore, the optimised inlet pressure of 3 bar has been 8
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selected for the remaining experiments. Required time to obtain methyl ester conversion ≥ 96.5 wt. % was 100 min for plate 1, 20 min for plate 2, 40 min for plate 3 and 60 min for plate 4.
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As cavitation number decreases, the conversion rate increases. The maximum benefits in methyl ester were being shown when cavitation number was reduced to 0.301. Lower cavitation number gave an exposure of the mixture to cavitational zone for a longer period and hence greater conversion. Ghayal et al. (2013) reported that the inlet pressure increased with an increase collapse intensity of cavities. Mass transfer resistance between two
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immiscible reactants was decreased by high collapsed cavities in the system. The high rate of transport process
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can be achieved by a sudden collapse of cavities, which generates high turbulence intensity in the fluid. An increase of liquid flow rate decreased the cavitation number (Vichare et al., 2000). The optimised plate 2 has been chosen for the remaining experiments due to ≥ 96.5 wt. % conversion obtained in just 20 min reaction time compared to other plates at optimised inlet pressure of 3 bar.
Effect of inlet pressure on yield efficiency
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5.2
The definition of yield efficiency is the amount of product per unit energy needed for the reaction. The total production expenses of biodiesel are relied on the total energy consumed and the cost of raw materials.
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Selection of plate geometries was based on the yield efficiency performance. The performance of yield
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efficiency on each orifice plate is shown in Figure 3. Yield efficiency of RSOME was increased by increasing the pressure up to 3 bar. At 3.5 bar, the effect on yield efficiency was marginal. Yield efficiency in relation to the plates at 3 bar of inlet pressure followed the order: plate 2 (0.91 mg/J) > plate 3 (0.80 mg/J) > plate 4 (0.79 mg/J) > plate 1 (0.60 mg/J).
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5.3
Effect of the orifice plate geometries on methyl ester conversion
This section briefly explains about each parameter with respect to alkali-catalysed via transesterification reaction. Plate 2 has achieved more than 96.5 wt. % conversion in a shorter reaction time of 20 min compared
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to other orifice plate geometries. For this reason, 20 min reaction time was chosen to study the effect of the total hole perimeter on the methyl ester conversion for all orifice plate geometries. Figure 4(a) shows the effect of the total hole perimeter on the methyl ester conversion at different inlet pressure. The total hole perimeter of all four orifice plates was in the range of 14.39-65.98 mm. A number of the hole could affect the cavitational event
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as reported by Senthil Kumar et al. (2000). Figure 4(a) revealed that the methyl ester conversion increased with
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an increase in the total hole perimeter at 1 to 3 bar of inlet pressure.
The α parameter is designated as the ratio of the total hole perimeter to the flow area of reaction mixture passing through the orifice plate (Ghayal et al., 2013). Figure 4(b) shows the relationship between α and methyl ester conversion at constant reaction time and inlet pressure of 20 min and 3 bar. The larger the α value in
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which the larger number of holes with smaller hole size, the better the methyl ester conversion achieved. In the present work, α parameter of the orifice plate geometries was varied from 0.87 to 4 mm-1. The α parameter affect on methyl ester conversion in relation to the plates at 3 bar of inlet pressue followed the order: plate 2
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(97.1 wt. %) > plate 3 (85.4 wt. %) > plate 4 (84.4 wt. %) > plate 1 (64.3 wt. %). It was found that about 13.7 %
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increased of methyl ester conversion in plate 2 compared to plates 3 and 4. The values of the total flow area of orifice plates were plate 1 - 16.5mm2, plate 2 - 16.5mm2, plate 3 - 28.3 mm2 and plate 4 - 35.3 mm2. The same total flow area of plates 1 and 2 were observed and it showed that plate 2 with 21 small hole diameter of 1 mm tend to give a better conversion compared to plate 1 with the only single hole diameter of 4.58 mm. This could be attributed to the number of holes increase, the cavity generating sports viz. shear layer area, frequency of turbulence and collapse pressure are also increased, which result to a larger amount of cavities
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(Basiri Parsa and Zonouzian, 2013). Cavitation helps to improve the mass transfer due to the better degree of emulsification generated, which lead to a better conversion.
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A dimensionless geometrical parameter ß is the ratio of hole diameter to the pipe diameter (Ghayal et al., 2013). Figure 4(c) portrays the relationship between ß and methyl ester conversion within 20 min of reaction time at an inlet pressure of 3 bar. The ß values of all orifice plates are plate 1- 0.31, plate 2 - 0.07, plate 3-0.13 and plate 40.20. It was found that the conversion increases with decreases of ß value, i.e. the plate 2 with the lowest ß
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values result in the highest methyl ester conversion of 97.10 wt. %. This is due to the fact that the smaller hole
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diameter in the orifice plate triggers a higher number of small bubbles, resulting in an increase of cavitational events and better emulsification, thus leads to a larger mass transfer. Vichare et al. (2000) claims that the intensity of turbulence increases as ß value decreases. The increase in turbulence makes the collapse of cavities more intense and generates large magnitude pressure pulses.
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A dimensionless parameter ߺ is the ratio of the total flow area to the cross sectional area of the pipe (Ghayal et al., 2013). Figure 4(d) illustrates the relationship between ߺ and the conversion for 20 min reaction time at 3 bar inlet pressure. In the present study, the ߺ parameter of the orifice plates was varied from 0.09 to
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0.20. It was shown that as the ߺ value decreases, the conversion increases, i.e. the rate of reaction was higher at
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smaller ߺ value. The same value of ߺ for plates 1 and 2 was compared. It was observed that the plate with a smaller and higher number of holes results in a better methyl ester conversion compared to plate 1 with only a single large hole size. This could be due to the lower ߺ value resulted in hgher cavitation intensity and turbulence frequency. A higher number of smaller holes in the plate resulted the mixture evenly distributed across the cross section of the pipe and hence larger probability for the cavity to experience the shear zone and collapse intensely (Ghayal et al., 2013). The smallest holes in plate 2 gave the maximum turbulence and larger
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shear layer area, which contributed to the greater collapse pressure and better conversion in a short reaction time.
Statistical analysis
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5.4
Parametric analysis for biodiesel production from RSO was obtained and analysed by using RSM provided by Design Expert 8.0 software. Central Composite Design (CCD) was applied as a standard RSM design tool to study the base catalysed transesterification reaction variables. These studies help in analysing the effect of each
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independent factor and the interactive effects of the parameters on the dependent response variable. RSM was
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used to study the parametric effect of four independent variables, such as A: alcohol to oil molar ratio, B: catalyst amount (wt. %), C: reaction time (min) and D: reaction temperature (oC). The chosen response was methyl ester conversion, which procured from the transesterification reaction in HC reactor at 3 bar of inlet pressure on orifice plate 2. Table 2 shows the ranges and levels of four independent variables with coded values of each parameter. The independent variables were coded to two levels namely: low (-1) and high (+1), -2 and
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+2 are coded as the axial points. A complete CCD design matrix in terms of real and coded independent variables are illustrated and the results are presented in Table 3. A mathematical model based on a second-order
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polynomial equation, which includes all interaction terms is shown in Eq. (2).
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Methyl ester conversion (wt. %) = 84.93 – 4.18A – 4.85B + 4.64C + 3.64D + 3.81AB + 2.06AC – 0.29AD – 3.16BC – 1.13BD + 1.65CD – 2.91A2 – 3.53B2 – 6.73C2 – 1.37 D2
(2)
The experimental data are observed using Design Expert programme and the coefficients are analysed using Ftest as shown in Table 4. The F-test gives the reliability of the fitted model with output response of methyl ester conversion. The highest F-value of catalyst amount and then followed by reaction time is the most influential effects on response. The p-values least significant behavior confirmed the significance of experimental data
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with modelled equation. The R2 value of 0.90 confirms that 90 % experimental point give reasonable precision with the predicted output.
Parametric effects of transesterification process
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5.5
Figure 5(a-f) portrays the 3-D plots of two parametric interaction on methyl ester conversion while other parameters remained constant. Figure 5(a) shows that at constant catalyst amount of 1 wt. % and 6:1 alcohol to oil molar ratio resulted in a higher conversion of RSOME. Alcohol to oil molar ratio is one of the important
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variables affect the methyl ester conversion. In order to produce three moles of fatty acid methyl ester and one
reversible
nature
of
this
reaction
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mole of glycerol, three moles of alcohol reacts with one mole of TG via transesterification reaction. The towards
product
when
a
higher
molar
ratio
is
used
(Issariyakul and Dalai, 2014). In HC reactor, the effect of alcohol to oil molar ratio on methyl ester conversion at a constant reaction temperature of 55°C, 1wt% of KOH catalyst and reaction time of 20 min were studied. Results revealed that the conversion experienced a decrement above 6:1 molar ratio of alcohol to oil could be
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due to the excess amount of alcohol causing the dilution of the oil with the alcohol (Chuah et al., 2015d). It was observed that the separation of glycerol layer become harder due to emulsification occurs at molar ratio of oil to alcohol beyond 6:1 (Eevera et al., 2009). Therefore, an optimum molar ratio of alcohol to oil was 6:1. Figure
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5(a) depicts the effect effect of catalyst amount on methyl ester conversion at the constant reaction temperature
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of 55°C, 6:1 of alcohol to oil molar ratio and reaction time of 20 min was investigated. Catalyst amount is one the most influential parameter that effects the methyl ester conversion. This variable is very important to avoid the generation of wastewater during washing step. FFA will direct react with the high concentration of KOH, which causes saponification and hence lowering the yield production (Tamilarasan and Sahadevan, 2014). Catalyst concentration from 0.5 to 1 wt. % at 20 min of reaction time, the methyl ester conversion increased from 44.8 to 97.10 wt. %. It has been proven that the reaction rate increased due to the presence of the catalyst.
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However, when the catalyst concentration is beyond 1wt. %, the decremented in methyl ester conversion was observed. For this reason, 1 wt. % of KOH catalyst was chosen for further study.
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Figure 5(f) shows the effect of reaction temperature and time on methyl ester conversion. The reaction temperature is another important variable, which affects methyl ester conversion in the transesterification reaction. The effect of reaction temperature ranges 32.5-62.5°C was investigated under fixed operation conditions of the molar ratio of oil to alcohol (6:1) and catalyst amount (1 wt. %) at 20 min reaction time. It was
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observed that when the reaction temperature increased from 40 to 55 oC, methyl ester conversion increased
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from 44.8 to 97.10 wt. %. This could be due to quick dispersion of alcohol in treated RSO and viscosity reduction in RSO when reaction temperature increases. This phenomenon is favourable to increase the solubility of TG in alcohol and improve the contact between oil and alcohol molecules (Dubey et al., 2015). Reaction rate and mass transfer are improved with high reaction temperature. Sufficient reaction time was needed to give a residential period for cavitational phenomena to occur. Methyl ester conversion increased with
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an increase of reaction time. The reaction time of 20 min in HC was ample to overcome the mass transfer
5.6
Reaction kinetics
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between oil and alcohol. After 20 min, the only marginal increase in conversion was observed.
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The homogenous catalytic reaction is the proposed mechanism. This reaction process obeys pseudo-first order kinetics, which acts as a function of the concentration of TG. Alcohol is not classified as a limiting reactant due to the high concentration of alcohol (two fold excess). Due to the reversible nature of the reaction during transesterification process, excess alcohol drives the reaction to move forward to the desired products- fatty acid methyl ester.
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Figure 6 presents the plot of –ln (1-x) versus time at different operating temperature by using HC and MS system and the obtained rate constants from these plots have been given in Table 5. In average, the rate constant by HC is 4.8 fold higher than MS with an increment in the operating temperature from 50 to 60 o C. A resemble
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result in terms of pseudo-first order kinetic fitting has been reported by Sivakumar et al. (2013) for transesterification of Ceiba Pentranda oil under MS system at different operating temperature.
Due to the high intensity of micro level turbulence generated by oscillating cavities, the reaction rate of methyl
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ester synthesis was increased. The high interfacial area in the HC reactor is very efficient in eliminating the
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mass transfer resistance between the TG and alcohol during the transesterification reaction. The cavities expand and compress intensely in a few µs, which results in high local pressure and temperature, hence favours the forward reaction. The sudden collapse of cavities due to its intensive expansion and compression generates high turbulence intensity of fluid flow that can enhance the rate of transport process and thus, lead to a better
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conversion.
The obtained rate constant values of each reaction temperature (50-60 o C) were used to calculate the activation
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energy for HC and MS. Figure 7 shows a plot of ln k versus 1/T. Based on present work, the resulting Arrhenius expression for methyl ester production using HC and MS are given by k = 5.084 E + 05 e
5.7
.
and
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k = 1.439 E + 05 e
-44.1 kJ/mol RT
-43.1 kJ/mol RT
Comparison between hydrodynamic cavitation and mechanical stirring optimum conditions and fuel properties
The numerical optimisation tool in RSM gives the optimised operating conditions for
catalyst amount
(1 wt. %), alcohol to oil molar ratio (6:1), reaction temperature (55 °C) and reaction time (18 min). These optimised parameters were verified and compared to MS under the similar operating conditions. The optimum 15
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conditions for methyl ester production from RSO through HC and MS are summarised in Table 6. It can be observed that both HC and MS system resulted in ≥ 96.5 wt. % of methyl ester conversion in 20 and 90 min reaction time. This could be caused by the high intensity of micro level turbulence generated by oscillating
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cavities with the high interfacial area in HC system. HC technology is very effective in eliminating the mass transfer resistance during the reaction and results in conversion. The alcohol-oil interface was only dependent on the stirrer bar (MS), which produced poor mass transfer between the immiscible reactants and resulted in slow conversion rate. Reaction rate constant using HC is 4.8 fold higher than MS. Majority of the properties in
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RSOME were complied ASTM D 6751 and EN 14214 standards. Only oxidation stability of RSOME found to
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be 3.2 h, which cannot meet the EN 14214 standard (6 h). However, this poor oxidation stability of biodiesel could be solved by adding antioxidant or blending with diesel fuel (Agarwal et al., 2015).
6.
Conclusions
Transesterification reaction of RSO producing methyl ester in a pilot scale HC reactor with four newly designed
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orifice plates has been successfully conducted. Orifice plate with 21 holes of 1mm diameter was demonstrated and found that methyl ester conversion ≥ 96.5 wt. % could be easily obtained in just 20 min of reaction time with maximum yield efficiency of 9.1E-04 g/J. RSM was employed to carried out parametric analysis and
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optimisation. The optimum conditions have been found to be alcohol to oil ratio of 6:1 molar ratio, the reaction
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time of 18 min and catalyst amount of 1 wt. % at 55 oC. Compared to MS, HC is more effective in providing excellent interfacial of oil-alcohol to eliminate the mass transfer resistance and significantly enhanced the conversion rate. About 5 fold shorter reaction time, 6.5 fold higher energy efficiency and 4.9 fold higher reaction rate constant using HC compared to MS. HC is concluded to have lower carbon footprint in terms of time saving and energy efficient process compared to MS. This make the process more environmental friendly using HC. The majority of the RSOME properties have been conformed both EN 14214 and ASTM D 6751 standards.
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Acknowledgments This research was conducted under MyRA Grant (No. 0153AB-J19) and PRGS Grant (No. 0153AB-K19). The authors would like to thank Universiti Teknologi PETRONAS, Public Service Department of Malaysia, Marine
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Department Malaysia, Ong Shying Weei, Timmy Chuah Tim Mie, Kar Mun Lee and Farhaini Jailani for their supports.
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Tamilarasan, S., Sahadevan, R., 2014. Ultrasonic assisted acid base transesterification of algal oil from marine
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macroalgae Caulerpa peltata: optimization and characterization studies. Fuel 128, 347-355. Tu, E., McDonnell, B.E., 2016. Monte Carlo analysis of life cycle energy consumption and greenhouse gas (GHG) emission for biodiesel production from trap grease. Journal of Cleaner Production 112, 2674-2683. Vichare, N.P., Gogate, P.R., Pandit, A.B., 2000. Optimization of hydrodynamic cavitation using a model reaction. Chemical Engineering Technology 23(8), 683-690.
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Yusup, S., Bokhari, A., Chuah, L.F., Ahamd, J., 2015. Pre-blended methyl esters production from crude palm
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and rubber seed oil via hydrodynamic cavitation reactor Chemical Engineering Transactions 43, 517-522.
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ACCEPTED MANUSCRIPT List of Table Captions Table 1
Properties of rubber seed oil
Table 2
Experiment
design
by
central
composite
design
for
transesterification process Detailed experimental results for transesterification process
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Table 3
with orifice plate 2 at inlet pressure of 3 bar
Analysis of variance for transesterification process
Table 5
Comparison of reaction rate constants and yield efficiency
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Table 4
between hydrodynamic cavitation and mechanical stirring Comparison of optimum conditions and fuel properties between
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Table 6
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ACCEPTED MANUSCRIPT Table 1. Properties of treated rubber seed oil This study mean ± standard deviation (n=3) Rubber seed oil 2.64 ± 0.04
Analysis Acid value (mg KOH/g) Density (g/cm3) Saponification value (mg KOH/g) FFA (%) Higher heating value (MJ/kg)
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0.87 ± 0.03 200 ± 1.10 1.3 ± 0.03 37.1 ± 0.06 95 ± 0.07 36 ± 0.06 0.04 ± 0.00 201 ± 1 40.75
at 20 °C at 40 °C
Kinematic viscosity (mm2/s)
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Moisture content (wt. %) Flash point (°C) Methyl ester content (wt. %)
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-1 6 1 10 40
0 8 1.5 15 47.5
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Note: Inlet pressure = 3 bar and plate 2 = 21 holes with 1mm diameter
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+2 12 2.5 25 62.5
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Process Parameters Alcohol to oil ratio (molar ratio) Catalyst amount (wt. %) Reaction time (min) Reaction temperature (°C)
ACCEPTED MANUSCRIPT Table 3. Detailed experimental results for transesterification process with orifice plate 2 at inlet pressure of 3 bar. Type
Alcohol to oil ratio
Catalyst amount (wt. %)
Reaction time (min)
Reaction temperature (oC)
1
Axial
8.0
1.5
15.0
62.5
Methyl ester conversion (wt. %) 90.8
2
Factorial
10.0
2.0
20.0
40.0
61.5
3
Factorial
6.0
2.0
10.0
4
Factorial
10.0
1.0
20.0
5
Factorial
10.0
1.0
10.0
6
Factorial
10.0
2.0
10.0
7
Factorial
6.0
1.0
10.0
8
Axial
8.0
1.5
5.0
9
Factorial
6.0
2.0
10.0
10
Center
8.0
1.5
15.0
11
Factorial
6.0
1.0
10.0
12
Factorial
10.0
1.0
13
Factorial
6.0
2.0
14
Factorial
6.0
1.0
15
Axial
8.0
1.5
16
Center
8.0
1.5
17
Center
8.0
1.5
18
Factorial
10.0
1.0
19
Factorial
10.0
20
Center
8.0
21
Axial
8.0
22
Axial
12.0
23
Axial
8.0
24
Factorial
6.0
25
Center
26
Axial
27
Factorial
29 30
66.6
55.0
79.8
55.0
61.6
55.0
57.1
40.0
78.6
47.5
44.8
55.0
70.1
47.5
86.2
55.0
82.1
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40.0
40.0
73.1
55.0
66.1
20.0
55.0
97.1
15.0
32.5
65.7
15.0
47.5
86.5
15.0
47.5
87.1
10.0
40.0
56.1
2.0
20.0
55.0
72.6
1.5
15.0
47.5
75.1
1.5
25.0
47.5
68.9
1.5
15.0
47.5
68.0
0.5
15.0
47.5
75.9
2.0
20.0
40.0
64.1
8.0
1.5
15.0
47.5
88.5
4.0
1.5
15.0
47.5
76.2
10.0
2.0
10.0
40.0
64.2
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20.0
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Run no.
Axial
8.0
2.5
15.0
47.5
63.3
Center
8.0
1.5
15.0
47.5
86.2
Factorial
6.0
1.0
20.0
40.0
85.2
ACCEPTED MANUSCRIPT Sum of squares
df
Mean square
F-value
p-value Prob > F
Model
3844.88
14.00
274.63
10.47
< 0.0001
A-Alcohol to oil ratio (molar ratio)
419.00
1.00
419.00
15.97
0.0012
B-Catalyst amount (wt. %)
565.32
1.00
565.32
21.55
0.0003
C-Reaction time (min)
517.27
1.00
517.27
19.72
0.0005
D-Reaction temperature (°C)
317.41
1.00
317.41
12.10
0.0034
AB
231.65
1.00
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Table 4. Analysis of variance for transesterification process
231.65
8.83
0.0095
Source
AC
67.57
1.00
67.57
2.58
0.1293
AD
1.37
1.00
1.37
0.05
0.8224
BC
159.52
1.00
159.52
6.08
0.0262
BD
20.43
1.00
20.43
0.78
0.3914
43.30
43.30
1.00
A2
232.04
1.00
2
342.47
1.00
2
1241.32
1.00
B C
0.2184
8.85
0.0095
342.47
13.06
0.0026
1241.32
47.32
< 0.0001
1.97
0.1813
1.14
0.4692
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2
1.65
232.04
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CD
51.56
1.00
51.56
Residual
393.47
15.00
26.23
Lack of Fit
273.69
10.00
27.37
Pure Error
119.77
5.00
23.95
4238.35
29.00
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Cor Total
Adj R-squared = 0.82 Mean = 73.30
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R- squared = 0.90 Std. dev. = 5.12
Adeq precision = 12.96 C.V% = 6.99
ACCEPTED MANUSCRIPT Table 5. Comparison of reaction rate constants and yield efficiency between hydrodynamic cavitation and mechanical stirring
50
Temperature (°C) 55
Rate constant for transesterification processing, min-1 (10-2) 17.68 3.62
0.60 0.13
0.91 0.14
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21.03 4.42 1.25 0.17
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12.99 2.70
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HC MS Yield efficiency, mg/J HC MS
60
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Method
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Optimum conditions Oil to methanol ratio Catalyst loading (wt. %) Temperature (°C) RPM Inlet pressure (bar) Time (min) Yield efficiency (mg/J) Reaction rate constant (min-1) Biodiesel properties
HC
MS
1:6 1 55 3 bar 18 0.91 0.177
1:6 1 55 600 90 0.14 0.036
0.87
Kinematic viscosity, (40 °C, mm2/s) Flash point (°C) Acid value (mg KOH/g oil) Ester conversion (wt. %)
3.80 151 0.30 97
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ASTM D 6751
0.87
EN 14214 0.86-0.90
3.82 152 0.42 97
3.5-5.0 ≥120 ≤0.5 ≥96.5
1.9-6.0 ≥130 ≤0.8
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Density (15 °C, g/cm3)
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Parameters
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Table 6. Comparison of optimum conditions and fuel properties between hydrodynamic cavitation and mechanical stirring
ACCEPTED MANUSCRIPT List of Figure Captions Schematic diagram of cavitation reactor system
Figure 2
Effect of inlet pressure on RSOME conversion
Figure 3
Effect of inlet pressure on yield efficiency
Figure 4
Effect of the plate geometries on RSOME conversion
Figure 5
Reaction parametric effects on RSOME conversion
Figure 6
Kinetic studies for establishing the rate constants
Figure 7
Arrhenius plot for estimation on activation energy
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Figure 1
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V4: Sampling valve
P2
Pressure gauge at down stream
Flow meter F HC reactor 50 L
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V3: Drain valve
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Figure 1
40 0
20
100
c. Plate 3
80
60
40 0
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40 60 Reaction time (min) 2 bar 3 bar
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40
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Methyl ester conversion (wt. %)
1 bar
40 60 Reaction time (min) 2 bar 3 bar
b. Plate 2
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Methyl ester conversion (wt. %)
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Methyl ester conversion (wt. %)
100
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100
20 1 bar
40 60 Reaction time (min) 2 bar 3 bar
80
40 60 Reaction time (min) 2 bar 3 bar
80
100 3.5 bar
d. Plate 4
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0
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Figure 2
100 3.5 bar
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2.5 2.0 1.5 1.0 0.5 0.0 0
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80
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1 bar
20
40 60 Reaction time (min) 2 bar 3 bar
80
40 60 Reaction time (min) 2 bar 3 bar
80
100 3.5 bar
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Yield efficiency (mg/J)
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Yield efficiency (mg/J)
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40 60 Reaction time (min) 2 bar 3 bar
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Figure 3
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ACCEPTED MANUSCRIPT a. Hydrodynamic cavitation 4.0
y = 0.2103x R² = 0.9574
3.5
y = 0.1768x R² = 0.9988
2.5
y = 0.1299x R² = 0.9878
2.0 1.5 1.0 0.5 0.0 10
15 Time (min) 55 °C
50 °C
4.0 3.5
y = 0.0362x R² = 0.9086
y = 0.0442x R² = 0.9072
3.0 2.5 2.0 1.5 1.0 0.5 0.0 5
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Figure 6
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ACCEPTED MANUSCRIPT 2.98E-03 3.00E-03 3.02E-03 3.04E-03 0.0
3.06E-03 3.08E-03 3.10E-03
3.12E-03
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S0959-6526(16)30367-5
DOI:
10.1016/j.jclepro.2016.04.091
Reference:
JCLP 7115
To appear in:
Journal of Cleaner Production
Received Date: 26 February 2016 Revised Date:
8 April 2016
Accepted Date: 21 April 2016
Please cite this article as: Bokhari A, Chuah LF, Yusup S, Klemeš JJ, Akbar MM, Kamil RNM, Cleaner Production of Rubber Seed Oil Methyl Ester using a Hydrodynamic Cavitation: Optimisation and Parametric Study, Journal of Cleaner Production (2016), doi: 10.1016/j.jclepro.2016.04.091. 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.
ACCEPTED MANUSCRIPT Total word count including tables and figures: 6885
Highlights About 6.5 fold higher energy efficiency using HC than mechanical stirring.
•
About 5 fold less reaction time using HC than mechanical stirring.
•
About 4.9 fold higher rate constant using HC compared to mechanical stirring.
•
About 3.5 fold higher frequency factor using HC than mechanical stirring.
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•
1
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List of abbreviations
RSO = Rubber seed oil RSOME = Rubber seed oil methyl ester
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TG = Triglyceride HC = Hydrodynamic cavitation MS = Mechanical stirring
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FFA = Free fatty acid x = Methyl ester conversion
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RSM = Response surface methodology CCD = Central composite design
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KOH = Potassium hydroxide
2
ACCEPTED MANUSCRIPT Total word count including tables and figures: 6885
Cleaner Production of Rubber Seed Oil Methyl Ester using a Hydrodynamic Cavitation: Optimisation and Parametric Study Awais Bokharia, Lai Fatt Chuaha,b*, Suzana Yusupa, Jiří Jaromír Klemešc, Majid Majeed Akbard, Ruzaimah Nik M. Kamile Chemical Engineering Department, Biomass Processing Laboratory, Center of Biofuel and Biochemical Research (CBBR),
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a
Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Seri Iskandar, Perak, Malaysia b
Pázmány Péter Catholic University, Faculty of Information Technology and Bionics, Práter u. 50/a, 1083 Budapest, Hungary d
e
Institute of Chemical Engineering and Technology, University of the Punjab, Lahore, Pakistan
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c
Marine Department Malaysia Northern Region, 11700 Gelugor, Penang, Malaysia
Fundamental and Applied Sciences Department, Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 32610 Seri Iskandar,
*
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Perak, Malaysia
Corresponding Author Email: [email protected]
ABSTRACT — Producing sustainable biodiesel using non-edible feedstock via transesterification reaction assisted hydrodynamic cavitation technology is a viable way to offset fossil diesel usage. This technology has
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affirmative environmental impacts with lower energy consumption and the reaction time and offers a cleaner possibility. Methyl ester conversion has been observed at a different inlet pressure of 1-3.5 bar on different plate geometries in 50 L pilot hydrodynamic cavitation reactor. Orifice plate with 21 holes of 1mm and inlet
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pressure of 3 bar found to be the optimal arrangement. Parametric optimisation used response surface methodology and found as alcohol to oil ratio of 6:1, catalyst loading of 1 wt. %, reaction time of 18 min and
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reaction temperature of 55 °C. About 5 fold shorter reaction time, 6.5 fold higher energy efficiency and 4.9 fold higher reaction rate constant using hydrodynamic cavitation compared to mechanical stirring. Hydrodynamic cavitation is concluded to be time saving and energy efficient process compared to mechanical stirring. This makes the process more environmental friendly using hydrodynamic cavitation. Most of the properties in rubber seed oil methyl ester were met the EN 14214 and ASTM D 6751 standards. Keywords— Cleaner production of biodiesel; optimisation; rubber seed oil methyl ester; mass transfer; fuel properties 3
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1.
Introduction
Sustainable development in industrialisation and motorisation has significantly increased the utilisation of fossil fuel (Harris et al., 2016). This phenomenon results in high greenhouse gas emissions to the environment
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(Tu and McDonnell., 2016). Environmental concerns are the key factor to inspire researchers to search renewable and sustainable fuel (Piemonte et al., 2016). Hydropower, tidal, solar, biodiesel, the wind, waves and geothermal were renewable energies to replace fossil fuel (Dwivedi et al., 2013). Biodiesel has become an attractive renewable fuel due to carbon footprint reduction (Chuah et al., 2015a). Biodiesel can be directly
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utilised in the diesel engine without any modifications due to its similarity properties with diesel fuel, such as
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heating value and viscosity (Chuah et al., 2015b). Greenhouse gas footprint is minimised (Čuček et al., 2014) when the local available non-edible feedstock is utilised for cleaner biodiesel production rather than to export it to other regions (Chuah et al., 2016).
Biodiesel production can be derived from manifold feedstock, such as edible oil (Permpool et al., 2015),
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non-edible oil (Chuah et al., 2015c), animal fat and algae (Medeiros et al., 2015). About 95 % of world biodiesel production is from the edible oil, which is obviously not the best solution creating foot-energy competition (Chuah et al., 2015d). Utilising edible oil in biodiesel production causes the price about 1.5-2 fold
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higher than diesel fuel (Maddikeri et al., 2012). Another consequence brought by the excessive consumption of
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edible oil is food crisis (Bokhari et al., 2015). By utilising non-edible for biodiesel production provides the best solution to prevent food crisis (Gimbun et al., 2013). Malaysia is one of the rubber producers in the worldwide (Yusup et al., 2015). Rubber tree known as Hevea brasiliensis, belongs to the family of euphorbiaceous provides 40 to 50 wt. % of oil yield (Abedin et al., 2014). Malaysia has sufficient production of rubber approximately 1,022,700 ha (hectare) with the capacity of 300 kg/ha annually. Consequently, rubber seed oil (RSO) is a promising non-edible feedstock oil for biodiesel production.
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The acid-catalysed reaction has been used to treat the untolerate free fatty acid (FFA) in feedstock and reduce its FFA until less than 2 % via esterification reaction in order to avoid the formation of emulsion and soap during transesterification reaction. This treated feedstock oil can be used to produce biodiesel in the presence
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of alkali catalyst via transesterification reaction. The direct conversion of triglyceride (TG) to methyl ester via transesterification reaction has been hindered by higher FFA concentration in RSO. FFA can react with alkali catalyst and results in saponification reaction (Morshed et al., 2011). To reduce FFA content in RSO, acid esterification is the chosen method to convert one mole of FFA into one mole of water and alkyl ester in the
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presence of alcohol. (Issariyakul et al., 2014).
Microwave, ultrasonic cavitation, supercritical condition, static mixer and hydrodynamic cavitation (HC) are the potential intensification technologies to get rid the mass transfer resistance between immiscible reactants (oil and alcohol). HC is the most efficient in terms of scalable, energy consumption and reaction time. Cavities in HC process are produced by destructive force, which causes the bubbles expansion and compression.
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Implosion and high interfacial area of cavities could eliminate the mass transfer between oil and alcohol (Gogate, 2008). HC has been intensively investigated in the shipping and wastewater treatment industries since twenty’s century. HC for biodiesel synthesis has been explored a decade ago by pioneering work of
EP
Ji et al. (2006) in 2006. However, there are not too many works related to biodiesel until now. Most of the
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studies were just at laboratory scale. Ghayal et al. (2013) have studied the HC process on the synthesis of frying oil at laboratory level with 10 L capacity. They investigated the orifice plate geometrical effects with variable upstream pressure, but no detailed information with regards to hole spacing and distribution pattern. In 2015, Chuah et al. (2016) have studied the HC process at 50 L capacity pilot plant for waste cooking oil methyl ester synthesis with detailed information of four orifice plates designed, hole spacing and distribution pattern. Bokhari et al. (2016) have successfully reduced the FFA of RSO to an acceptable level in just 30 min using optimised orifice plate and operating conditions. This study is a continuous work from Bokhari et al. (2016),
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which utilise treated RSO (2.64 mg KOH/g) for cleaner rubber seed oil methyl ester (RSOME) production in a pilot scale HC reactor. To best of our knowledge, this is the first work on newly designed four orifice plates, which utilise treated RSO for biodiesel production via transesterification reaction in a pilot scale HC reactor of
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50 L capacity. The effects of inlet pressure (1-3.5 bar) and geometrical parameters (total hole perimeter, α, β and β̥) on the RSOME conversion and yield efficiency were investigated. Response surface methodology (RSM) was used for the optimisation of transesterification conversion from treated RSO via HC. Biodiesel synthesis via mechanical stirring (MS) and HC in the same reactor has also investigated for comparison purpose in terms
SC
of conversion, reaction time, yield efficiency and kinetic parameters. Both standards of ASTM D 6751 and
2.
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EN 14214 were being referred to the properties of produced RSOME in pilot HC reactor.
Materials
Treated RSO was obtained from the previous work of Bokhari et al. (2016). The properties of treated RSO are listed in Table 1. A standard mixture of 37 fatty acid methyl ester was obtained from Sigma Aldrich, Malaysia
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thiosulphate pentahydrate, starch, chloroform, acetone, hydrochloric acid and ethanol. All chemicals were
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analytical grade and have been purchased from Merck, Malaysia
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reported values were averages of the individual runs. The properties of the produced biodiesel were analysed according to ASTM D 6751 and EN 14214 standards.
Experimental setup
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3.
HC reactor with a 50 L capacity was made up by a double jacketed glass. HC reactor was connected to the diaphragm pump in a closed loop called batch reactor. Compressed air was used to operate the double diaphragm pump, which acted as a device to dissipate the energy in HC. The outlet of the pump was manifold
SC
into two lines. The inlet pressure and inlet flow rate to the orifice plate were regulated by two valves, which
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were the main line valve and bypass line valve. Figure 1 demonstrates the process flow configuration of HC reactor. At an inlet pressure of 3 bar, the mass flow of the main and bypass lines were 25.8 L/min and 15.1 L/min. The pressure gauges of P1 and P2 were used to determine the upstream and downstream pressures of the pipelines. The heat was supplied to the HC reactor by circulating liquid heating oil through the jacket surrounding the reactor in order to balance the dissipation of heat energy due to the cavitation events. The
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operating temperature of the reactor has been maintained at the desired level by controller temperature. The details of newly designed four orifice plates have been presented in the previous paper (Chuah et al., 2016). The values for diameter, hole number, total flow area and total hole perimeter of the four orifice plates were plate 1
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– 4.58 mm, 1, 16.5 mm2 and 14.39 mm, plate 2 – 1.00 mm, 21, 16.5 mm2 and 65.98 mm, plate 3 – 2.00 mm, 9,
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28.3 mm2 and 56.56 mm and plate 4–3.00 mm, 5, 35.3 mm2 and 47.13 mm. Optimisaton of orifice plate and inlet pressure via transesterification reaction were conducted under optimised operating conditions (alcohol to oil ratio of 6:1 and catalyst concentration of 1 wt. % at 55 oC), which found in our previous research work on a laboratory scale (Ahmad et al., 2014). The mixture passes through the four newly designed orifice plates at inlet pressures of 1, 2, 3 and 3.5 bar in order to create the constructive conditions with different orifice plate geometries. The upstream flow rate of reaction mixture and hole area of plate were used to calculate the velocity through the orifice. A 50 mL sample was collected with the regular interval of time. The collected
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samples were allowed to settle down under gravity by using a separating funnel for 4 h. The catalyst and byproduct were discharged through the opening of the funnel An ionised warm water at 40 °C was used to wash and remove the impurities in the product. Remaining alcohol and water in the product were evaporated under
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vacuum condition by using a rotary evaporator. In favour of ensuring water completely remove, a 10 g of anhydrous sodium sulphate was added to the product and then filtered by using filter paper (541 Whatman). All
4.
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the experiments were conducted for three replicates to ensure reproducibility of the results.
Yield efficiency calculation
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Yield efficiency or called energy efficiency is defined to quantify the required pumping energy for dissociation the specific amount of oil in terms of efficiency parameter. Yield efficiency is calculated using the following Eq. (1).
(1)
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Yield efficiency = Amount of product produced (g) Pumping energy (J)
5.
Results and discussion
5.1
Effect of inlet pressure on methyl ester conversion
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Figure 2 illustrates the effect of inlet pressure or upstream pressure within the range of 1-3.5 bar at the reaction temperature of 55 °C on methyl ester conversion in four different orifice plate geometries. The results revealed
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that all orifice plate geometries have the increment on transesterification reaction rate when inlet pressure increased from 1 to 3 bar. There was no significant difference of reaction rate between 3 and 3.5 bar. It could be attributed to large cavities formed on the downstream area of an orifice plate, causing cavitation chocking due to coalescence of a large number of cavities (Ghayal et al., 2013). Many researchers reported that inlet pressure reached to certain value resulted in lower reaction rate (Chuah et al., 2016). Bagal and Gogate (2014) also reported the degradation rate decreased when inlet pressure at 4 bar. Vichare et al. (2000) also proved that decomposition reaction rate decreased at 3.8 bar. Therefore, the optimised inlet pressure of 3 bar has been 8
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selected for the remaining experiments. Required time to obtain methyl ester conversion ≥ 96.5 wt. % was 100 min for plate 1, 20 min for plate 2, 40 min for plate 3 and 60 min for plate 4.
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As cavitation number decreases, the conversion rate increases. The maximum benefits in methyl ester were being shown when cavitation number was reduced to 0.301. Lower cavitation number gave an exposure of the mixture to cavitational zone for a longer period and hence greater conversion. Ghayal et al. (2013) reported that the inlet pressure increased with an increase collapse intensity of cavities. Mass transfer resistance between two
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immiscible reactants was decreased by high collapsed cavities in the system. The high rate of transport process
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can be achieved by a sudden collapse of cavities, which generates high turbulence intensity in the fluid. An increase of liquid flow rate decreased the cavitation number (Vichare et al., 2000). The optimised plate 2 has been chosen for the remaining experiments due to ≥ 96.5 wt. % conversion obtained in just 20 min reaction time compared to other plates at optimised inlet pressure of 3 bar.
Effect of inlet pressure on yield efficiency
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5.2
The definition of yield efficiency is the amount of product per unit energy needed for the reaction. The total production expenses of biodiesel are relied on the total energy consumed and the cost of raw materials.
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Selection of plate geometries was based on the yield efficiency performance. The performance of yield
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efficiency on each orifice plate is shown in Figure 3. Yield efficiency of RSOME was increased by increasing the pressure up to 3 bar. At 3.5 bar, the effect on yield efficiency was marginal. Yield efficiency in relation to the plates at 3 bar of inlet pressure followed the order: plate 2 (0.91 mg/J) > plate 3 (0.80 mg/J) > plate 4 (0.79 mg/J) > plate 1 (0.60 mg/J).
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5.3
Effect of the orifice plate geometries on methyl ester conversion
This section briefly explains about each parameter with respect to alkali-catalysed via transesterification reaction. Plate 2 has achieved more than 96.5 wt. % conversion in a shorter reaction time of 20 min compared
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to other orifice plate geometries. For this reason, 20 min reaction time was chosen to study the effect of the total hole perimeter on the methyl ester conversion for all orifice plate geometries. Figure 4(a) shows the effect of the total hole perimeter on the methyl ester conversion at different inlet pressure. The total hole perimeter of all four orifice plates was in the range of 14.39-65.98 mm. A number of the hole could affect the cavitational event
SC
as reported by Senthil Kumar et al. (2000). Figure 4(a) revealed that the methyl ester conversion increased with
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an increase in the total hole perimeter at 1 to 3 bar of inlet pressure.
The α parameter is designated as the ratio of the total hole perimeter to the flow area of reaction mixture passing through the orifice plate (Ghayal et al., 2013). Figure 4(b) shows the relationship between α and methyl ester conversion at constant reaction time and inlet pressure of 20 min and 3 bar. The larger the α value in
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which the larger number of holes with smaller hole size, the better the methyl ester conversion achieved. In the present work, α parameter of the orifice plate geometries was varied from 0.87 to 4 mm-1. The α parameter affect on methyl ester conversion in relation to the plates at 3 bar of inlet pressue followed the order: plate 2
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(97.1 wt. %) > plate 3 (85.4 wt. %) > plate 4 (84.4 wt. %) > plate 1 (64.3 wt. %). It was found that about 13.7 %
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increased of methyl ester conversion in plate 2 compared to plates 3 and 4. The values of the total flow area of orifice plates were plate 1 - 16.5mm2, plate 2 - 16.5mm2, plate 3 - 28.3 mm2 and plate 4 - 35.3 mm2. The same total flow area of plates 1 and 2 were observed and it showed that plate 2 with 21 small hole diameter of 1 mm tend to give a better conversion compared to plate 1 with the only single hole diameter of 4.58 mm. This could be attributed to the number of holes increase, the cavity generating sports viz. shear layer area, frequency of turbulence and collapse pressure are also increased, which result to a larger amount of cavities
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(Basiri Parsa and Zonouzian, 2013). Cavitation helps to improve the mass transfer due to the better degree of emulsification generated, which lead to a better conversion.
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A dimensionless geometrical parameter ß is the ratio of hole diameter to the pipe diameter (Ghayal et al., 2013). Figure 4(c) portrays the relationship between ß and methyl ester conversion within 20 min of reaction time at an inlet pressure of 3 bar. The ß values of all orifice plates are plate 1- 0.31, plate 2 - 0.07, plate 3-0.13 and plate 40.20. It was found that the conversion increases with decreases of ß value, i.e. the plate 2 with the lowest ß
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values result in the highest methyl ester conversion of 97.10 wt. %. This is due to the fact that the smaller hole
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diameter in the orifice plate triggers a higher number of small bubbles, resulting in an increase of cavitational events and better emulsification, thus leads to a larger mass transfer. Vichare et al. (2000) claims that the intensity of turbulence increases as ß value decreases. The increase in turbulence makes the collapse of cavities more intense and generates large magnitude pressure pulses.
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A dimensionless parameter ߺ is the ratio of the total flow area to the cross sectional area of the pipe (Ghayal et al., 2013). Figure 4(d) illustrates the relationship between ߺ and the conversion for 20 min reaction time at 3 bar inlet pressure. In the present study, the ߺ parameter of the orifice plates was varied from 0.09 to
EP
0.20. It was shown that as the ߺ value decreases, the conversion increases, i.e. the rate of reaction was higher at
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smaller ߺ value. The same value of ߺ for plates 1 and 2 was compared. It was observed that the plate with a smaller and higher number of holes results in a better methyl ester conversion compared to plate 1 with only a single large hole size. This could be due to the lower ߺ value resulted in hgher cavitation intensity and turbulence frequency. A higher number of smaller holes in the plate resulted the mixture evenly distributed across the cross section of the pipe and hence larger probability for the cavity to experience the shear zone and collapse intensely (Ghayal et al., 2013). The smallest holes in plate 2 gave the maximum turbulence and larger
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shear layer area, which contributed to the greater collapse pressure and better conversion in a short reaction time.
Statistical analysis
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5.4
Parametric analysis for biodiesel production from RSO was obtained and analysed by using RSM provided by Design Expert 8.0 software. Central Composite Design (CCD) was applied as a standard RSM design tool to study the base catalysed transesterification reaction variables. These studies help in analysing the effect of each
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independent factor and the interactive effects of the parameters on the dependent response variable. RSM was
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used to study the parametric effect of four independent variables, such as A: alcohol to oil molar ratio, B: catalyst amount (wt. %), C: reaction time (min) and D: reaction temperature (oC). The chosen response was methyl ester conversion, which procured from the transesterification reaction in HC reactor at 3 bar of inlet pressure on orifice plate 2. Table 2 shows the ranges and levels of four independent variables with coded values of each parameter. The independent variables were coded to two levels namely: low (-1) and high (+1), -2 and
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+2 are coded as the axial points. A complete CCD design matrix in terms of real and coded independent variables are illustrated and the results are presented in Table 3. A mathematical model based on a second-order
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polynomial equation, which includes all interaction terms is shown in Eq. (2).
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Methyl ester conversion (wt. %) = 84.93 – 4.18A – 4.85B + 4.64C + 3.64D + 3.81AB + 2.06AC – 0.29AD – 3.16BC – 1.13BD + 1.65CD – 2.91A2 – 3.53B2 – 6.73C2 – 1.37 D2
(2)
The experimental data are observed using Design Expert programme and the coefficients are analysed using Ftest as shown in Table 4. The F-test gives the reliability of the fitted model with output response of methyl ester conversion. The highest F-value of catalyst amount and then followed by reaction time is the most influential effects on response. The p-values least significant behavior confirmed the significance of experimental data
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with modelled equation. The R2 value of 0.90 confirms that 90 % experimental point give reasonable precision with the predicted output.
Parametric effects of transesterification process
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5.5
Figure 5(a-f) portrays the 3-D plots of two parametric interaction on methyl ester conversion while other parameters remained constant. Figure 5(a) shows that at constant catalyst amount of 1 wt. % and 6:1 alcohol to oil molar ratio resulted in a higher conversion of RSOME. Alcohol to oil molar ratio is one of the important
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variables affect the methyl ester conversion. In order to produce three moles of fatty acid methyl ester and one
reversible
nature
of
this
reaction
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mole of glycerol, three moles of alcohol reacts with one mole of TG via transesterification reaction. The towards
product
when
a
higher
molar
ratio
is
used
(Issariyakul and Dalai, 2014). In HC reactor, the effect of alcohol to oil molar ratio on methyl ester conversion at a constant reaction temperature of 55°C, 1wt% of KOH catalyst and reaction time of 20 min were studied. Results revealed that the conversion experienced a decrement above 6:1 molar ratio of alcohol to oil could be
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due to the excess amount of alcohol causing the dilution of the oil with the alcohol (Chuah et al., 2015d). It was observed that the separation of glycerol layer become harder due to emulsification occurs at molar ratio of oil to alcohol beyond 6:1 (Eevera et al., 2009). Therefore, an optimum molar ratio of alcohol to oil was 6:1. Figure
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5(a) depicts the effect effect of catalyst amount on methyl ester conversion at the constant reaction temperature
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of 55°C, 6:1 of alcohol to oil molar ratio and reaction time of 20 min was investigated. Catalyst amount is one the most influential parameter that effects the methyl ester conversion. This variable is very important to avoid the generation of wastewater during washing step. FFA will direct react with the high concentration of KOH, which causes saponification and hence lowering the yield production (Tamilarasan and Sahadevan, 2014). Catalyst concentration from 0.5 to 1 wt. % at 20 min of reaction time, the methyl ester conversion increased from 44.8 to 97.10 wt. %. It has been proven that the reaction rate increased due to the presence of the catalyst.
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However, when the catalyst concentration is beyond 1wt. %, the decremented in methyl ester conversion was observed. For this reason, 1 wt. % of KOH catalyst was chosen for further study.
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Figure 5(f) shows the effect of reaction temperature and time on methyl ester conversion. The reaction temperature is another important variable, which affects methyl ester conversion in the transesterification reaction. The effect of reaction temperature ranges 32.5-62.5°C was investigated under fixed operation conditions of the molar ratio of oil to alcohol (6:1) and catalyst amount (1 wt. %) at 20 min reaction time. It was
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observed that when the reaction temperature increased from 40 to 55 oC, methyl ester conversion increased
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from 44.8 to 97.10 wt. %. This could be due to quick dispersion of alcohol in treated RSO and viscosity reduction in RSO when reaction temperature increases. This phenomenon is favourable to increase the solubility of TG in alcohol and improve the contact between oil and alcohol molecules (Dubey et al., 2015). Reaction rate and mass transfer are improved with high reaction temperature. Sufficient reaction time was needed to give a residential period for cavitational phenomena to occur. Methyl ester conversion increased with
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an increase of reaction time. The reaction time of 20 min in HC was ample to overcome the mass transfer
5.6
Reaction kinetics
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between oil and alcohol. After 20 min, the only marginal increase in conversion was observed.
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The homogenous catalytic reaction is the proposed mechanism. This reaction process obeys pseudo-first order kinetics, which acts as a function of the concentration of TG. Alcohol is not classified as a limiting reactant due to the high concentration of alcohol (two fold excess). Due to the reversible nature of the reaction during transesterification process, excess alcohol drives the reaction to move forward to the desired products- fatty acid methyl ester.
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Figure 6 presents the plot of –ln (1-x) versus time at different operating temperature by using HC and MS system and the obtained rate constants from these plots have been given in Table 5. In average, the rate constant by HC is 4.8 fold higher than MS with an increment in the operating temperature from 50 to 60 o C. A resemble
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result in terms of pseudo-first order kinetic fitting has been reported by Sivakumar et al. (2013) for transesterification of Ceiba Pentranda oil under MS system at different operating temperature.
Due to the high intensity of micro level turbulence generated by oscillating cavities, the reaction rate of methyl
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ester synthesis was increased. The high interfacial area in the HC reactor is very efficient in eliminating the
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mass transfer resistance between the TG and alcohol during the transesterification reaction. The cavities expand and compress intensely in a few µs, which results in high local pressure and temperature, hence favours the forward reaction. The sudden collapse of cavities due to its intensive expansion and compression generates high turbulence intensity of fluid flow that can enhance the rate of transport process and thus, lead to a better
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conversion.
The obtained rate constant values of each reaction temperature (50-60 o C) were used to calculate the activation
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energy for HC and MS. Figure 7 shows a plot of ln k versus 1/T. Based on present work, the resulting Arrhenius expression for methyl ester production using HC and MS are given by k = 5.084 E + 05 e
5.7
.
and
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k = 1.439 E + 05 e
-44.1 kJ/mol RT
-43.1 kJ/mol RT
Comparison between hydrodynamic cavitation and mechanical stirring optimum conditions and fuel properties
The numerical optimisation tool in RSM gives the optimised operating conditions for
catalyst amount
(1 wt. %), alcohol to oil molar ratio (6:1), reaction temperature (55 °C) and reaction time (18 min). These optimised parameters were verified and compared to MS under the similar operating conditions. The optimum 15
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conditions for methyl ester production from RSO through HC and MS are summarised in Table 6. It can be observed that both HC and MS system resulted in ≥ 96.5 wt. % of methyl ester conversion in 20 and 90 min reaction time. This could be caused by the high intensity of micro level turbulence generated by oscillating
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cavities with the high interfacial area in HC system. HC technology is very effective in eliminating the mass transfer resistance during the reaction and results in conversion. The alcohol-oil interface was only dependent on the stirrer bar (MS), which produced poor mass transfer between the immiscible reactants and resulted in slow conversion rate. Reaction rate constant using HC is 4.8 fold higher than MS. Majority of the properties in
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RSOME were complied ASTM D 6751 and EN 14214 standards. Only oxidation stability of RSOME found to
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be 3.2 h, which cannot meet the EN 14214 standard (6 h). However, this poor oxidation stability of biodiesel could be solved by adding antioxidant or blending with diesel fuel (Agarwal et al., 2015).
6.
Conclusions
Transesterification reaction of RSO producing methyl ester in a pilot scale HC reactor with four newly designed
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orifice plates has been successfully conducted. Orifice plate with 21 holes of 1mm diameter was demonstrated and found that methyl ester conversion ≥ 96.5 wt. % could be easily obtained in just 20 min of reaction time with maximum yield efficiency of 9.1E-04 g/J. RSM was employed to carried out parametric analysis and
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optimisation. The optimum conditions have been found to be alcohol to oil ratio of 6:1 molar ratio, the reaction
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time of 18 min and catalyst amount of 1 wt. % at 55 oC. Compared to MS, HC is more effective in providing excellent interfacial of oil-alcohol to eliminate the mass transfer resistance and significantly enhanced the conversion rate. About 5 fold shorter reaction time, 6.5 fold higher energy efficiency and 4.9 fold higher reaction rate constant using HC compared to MS. HC is concluded to have lower carbon footprint in terms of time saving and energy efficient process compared to MS. This make the process more environmental friendly using HC. The majority of the RSOME properties have been conformed both EN 14214 and ASTM D 6751 standards.
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Acknowledgments This research was conducted under MyRA Grant (No. 0153AB-J19) and PRGS Grant (No. 0153AB-K19). The authors would like to thank Universiti Teknologi PETRONAS, Public Service Department of Malaysia, Marine
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Department Malaysia, Ong Shying Weei, Timmy Chuah Tim Mie, Kar Mun Lee and Farhaini Jailani for their supports.
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Medeiros, D.L., Sales, E.A., Kiperstok, A., 2015. Energy production from microalgae biomass: carbon footprint
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and energy balance. Journal of Cleaner Production 96, 493-500. Morshed, M., Ferdous, K., Khan, M.R., Mazumder, M.S.I., Islam, M.A., Uddin, M.T., 2011. Rubber seed oil as a potential source for biodiesel production in Bangladesh. Fuel 90, 2981-2986. Piemonte, V., Paola, L.D., Iaquaniello, G., Prisciandaro, M., 2016. Biodiesel production from microalgae: ionic liquid process simulation. Journal of Cleaner Production 111, 62-68.
19
ACCEPTED MANUSCRIPT Total word count including tables and figures: 6885
Permpool, N., Bonnet, S., Gheewala, S.H., 2015. Greenhouse gas emissions from land use change due to oil palm expansion in Thailand for biodiesel production. Journal of Cleaner Production, 1-7. doi: 10.1016/j.jclepro.2015.05.048.
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Senthil Kumar, P., Siva Kumar, M., Pandit, A.B., 2000. Experimental quantification of chemical effects of hydrodynamic cavitation. Chemical Engineering Science 55, 1633-1639.
Sivakumar, P., Sindhanaiselvan, S., Gandhi, N.N., Devi, S.S., Renganathan, S., 2013. Optimization and kinetic studies on biodiesel production from underutilized Ceiba Pentandra oil. Fuel 103, 693-698.
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Tamilarasan, S., Sahadevan, R., 2014. Ultrasonic assisted acid base transesterification of algal oil from marine
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macroalgae Caulerpa peltata: optimization and characterization studies. Fuel 128, 347-355. Tu, E., McDonnell, B.E., 2016. Monte Carlo analysis of life cycle energy consumption and greenhouse gas (GHG) emission for biodiesel production from trap grease. Journal of Cleaner Production 112, 2674-2683. Vichare, N.P., Gogate, P.R., Pandit, A.B., 2000. Optimization of hydrodynamic cavitation using a model reaction. Chemical Engineering Technology 23(8), 683-690.
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Yusup, S., Bokhari, A., Chuah, L.F., Ahamd, J., 2015. Pre-blended methyl esters production from crude palm
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and rubber seed oil via hydrodynamic cavitation reactor Chemical Engineering Transactions 43, 517-522.
20
ACCEPTED MANUSCRIPT List of Table Captions Table 1
Properties of rubber seed oil
Table 2
Experiment
design
by
central
composite
design
for
transesterification process Detailed experimental results for transesterification process
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Table 3
with orifice plate 2 at inlet pressure of 3 bar
Analysis of variance for transesterification process
Table 5
Comparison of reaction rate constants and yield efficiency
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Table 4
between hydrodynamic cavitation and mechanical stirring Comparison of optimum conditions and fuel properties between
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Table 6
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hydrodynamic cavitation and mechanical stirring
ACCEPTED MANUSCRIPT Table 1. Properties of treated rubber seed oil This study mean ± standard deviation (n=3) Rubber seed oil 2.64 ± 0.04
Analysis Acid value (mg KOH/g) Density (g/cm3) Saponification value (mg KOH/g) FFA (%) Higher heating value (MJ/kg)
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0.87 ± 0.03 200 ± 1.10 1.3 ± 0.03 37.1 ± 0.06 95 ± 0.07 36 ± 0.06 0.04 ± 0.00 201 ± 1 40.75
at 20 °C at 40 °C
Kinematic viscosity (mm2/s)
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Moisture content (wt. %) Flash point (°C) Methyl ester content (wt. %)
ACCEPTED MANUSCRIPT Table 2. Experiment design by central composite design for transesterification process -2 4 0.5 5 32.5
-1 6 1 10 40
0 8 1.5 15 47.5
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Note: Inlet pressure = 3 bar and plate 2 = 21 holes with 1mm diameter
+1 10 2 20 55
+2 12 2.5 25 62.5
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Process Parameters Alcohol to oil ratio (molar ratio) Catalyst amount (wt. %) Reaction time (min) Reaction temperature (°C)
ACCEPTED MANUSCRIPT Table 3. Detailed experimental results for transesterification process with orifice plate 2 at inlet pressure of 3 bar. Type
Alcohol to oil ratio
Catalyst amount (wt. %)
Reaction time (min)
Reaction temperature (oC)
1
Axial
8.0
1.5
15.0
62.5
Methyl ester conversion (wt. %) 90.8
2
Factorial
10.0
2.0
20.0
40.0
61.5
3
Factorial
6.0
2.0
10.0
4
Factorial
10.0
1.0
20.0
5
Factorial
10.0
1.0
10.0
6
Factorial
10.0
2.0
10.0
7
Factorial
6.0
1.0
10.0
8
Axial
8.0
1.5
5.0
9
Factorial
6.0
2.0
10.0
10
Center
8.0
1.5
15.0
11
Factorial
6.0
1.0
10.0
12
Factorial
10.0
1.0
13
Factorial
6.0
2.0
14
Factorial
6.0
1.0
15
Axial
8.0
1.5
16
Center
8.0
1.5
17
Center
8.0
1.5
18
Factorial
10.0
1.0
19
Factorial
10.0
20
Center
8.0
21
Axial
8.0
22
Axial
12.0
23
Axial
8.0
24
Factorial
6.0
25
Center
26
Axial
27
Factorial
29 30
66.6
55.0
79.8
55.0
61.6
55.0
57.1
40.0
78.6
47.5
44.8
55.0
70.1
47.5
86.2
55.0
82.1
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40.0
40.0
73.1
55.0
66.1
20.0
55.0
97.1
15.0
32.5
65.7
15.0
47.5
86.5
15.0
47.5
87.1
10.0
40.0
56.1
2.0
20.0
55.0
72.6
1.5
15.0
47.5
75.1
1.5
25.0
47.5
68.9
1.5
15.0
47.5
68.0
0.5
15.0
47.5
75.9
2.0
20.0
40.0
64.1
8.0
1.5
15.0
47.5
88.5
4.0
1.5
15.0
47.5
76.2
10.0
2.0
10.0
40.0
64.2
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20.0
20.0
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Run no.
Axial
8.0
2.5
15.0
47.5
63.3
Center
8.0
1.5
15.0
47.5
86.2
Factorial
6.0
1.0
20.0
40.0
85.2
ACCEPTED MANUSCRIPT Sum of squares
df
Mean square
F-value
p-value Prob > F
Model
3844.88
14.00
274.63
10.47
< 0.0001
A-Alcohol to oil ratio (molar ratio)
419.00
1.00
419.00
15.97
0.0012
B-Catalyst amount (wt. %)
565.32
1.00
565.32
21.55
0.0003
C-Reaction time (min)
517.27
1.00
517.27
19.72
0.0005
D-Reaction temperature (°C)
317.41
1.00
317.41
12.10
0.0034
AB
231.65
1.00
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Table 4. Analysis of variance for transesterification process
231.65
8.83
0.0095
Source
AC
67.57
1.00
67.57
2.58
0.1293
AD
1.37
1.00
1.37
0.05
0.8224
BC
159.52
1.00
159.52
6.08
0.0262
BD
20.43
1.00
20.43
0.78
0.3914
43.30
43.30
1.00
A2
232.04
1.00
2
342.47
1.00
2
1241.32
1.00
B C
0.2184
8.85
0.0095
342.47
13.06
0.0026
1241.32
47.32
< 0.0001
1.97
0.1813
1.14
0.4692
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2
1.65
232.04
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CD
51.56
1.00
51.56
Residual
393.47
15.00
26.23
Lack of Fit
273.69
10.00
27.37
Pure Error
119.77
5.00
23.95
4238.35
29.00
D
Cor Total
Adj R-squared = 0.82 Mean = 73.30
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R- squared = 0.90 Std. dev. = 5.12
Adeq precision = 12.96 C.V% = 6.99
ACCEPTED MANUSCRIPT Table 5. Comparison of reaction rate constants and yield efficiency between hydrodynamic cavitation and mechanical stirring
50
Temperature (°C) 55
Rate constant for transesterification processing, min-1 (10-2) 17.68 3.62
0.60 0.13
0.91 0.14
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21.03 4.42 1.25 0.17
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12.99 2.70
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HC MS Yield efficiency, mg/J HC MS
60
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Method
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Optimum conditions Oil to methanol ratio Catalyst loading (wt. %) Temperature (°C) RPM Inlet pressure (bar) Time (min) Yield efficiency (mg/J) Reaction rate constant (min-1) Biodiesel properties
HC
MS
1:6 1 55 3 bar 18 0.91 0.177
1:6 1 55 600 90 0.14 0.036
0.87
Kinematic viscosity, (40 °C, mm2/s) Flash point (°C) Acid value (mg KOH/g oil) Ester conversion (wt. %)
3.80 151 0.30 97
TE D EP AC C
ASTM D 6751
0.87
EN 14214 0.86-0.90
3.82 152 0.42 97
3.5-5.0 ≥120 ≤0.5 ≥96.5
1.9-6.0 ≥130 ≤0.8
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Density (15 °C, g/cm3)
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Parameters
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Table 6. Comparison of optimum conditions and fuel properties between hydrodynamic cavitation and mechanical stirring
ACCEPTED MANUSCRIPT List of Figure Captions Schematic diagram of cavitation reactor system
Figure 2
Effect of inlet pressure on RSOME conversion
Figure 3
Effect of inlet pressure on yield efficiency
Figure 4
Effect of the plate geometries on RSOME conversion
Figure 5
Reaction parametric effects on RSOME conversion
Figure 6
Kinetic studies for establishing the rate constants
Figure 7
Arrhenius plot for estimation on activation energy
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Figure 1
ACCEPTED MANUSCRIPT
V4: Sampling valve
P2
Pressure gauge at down stream
Flow meter F HC reactor 50 L
P1
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Orifice plate
Pressure gauge at up stream
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V2: Bypass valve
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V1: Adjustable pressure valve
Double diaphragm pump
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V3: Drain valve
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Figure 1
40 0
20
100
c. Plate 3
80
60
40 0
20 1 bar
40 60 Reaction time (min) 2 bar 3 bar
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80
60
40
0
3.5 bar
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100
80
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Methyl ester conversion (wt. %)
1 bar
40 60 Reaction time (min) 2 bar 3 bar
b. Plate 2
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60
100
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80
Methyl ester conversion (wt. %)
a. Plate 1
80
100
Methyl ester conversion (wt. %)
100
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Methyl ester conversion (wt. %)
ACCEPTED MANUSCRIPT
100
20 1 bar
40 60 Reaction time (min) 2 bar 3 bar
80
40 60 Reaction time (min) 2 bar 3 bar
80
100 3.5 bar
d. Plate 4
80
60
40
3.5 bar
0
20 1 bar
Figure 2
100 3.5 bar
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a. Plate 1
2.0 1.5 1.0 0.5 0.0 20
b. Plate 2
2.5 2.0 1.5 1.0 0.5 0.0 0
20
c. Plate 3
2.5
100
3.5 bar
40 60 Reaction time (min) 2 bar 3 bar
80
100 3.5 bar
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2.0 1.5 1.0 0.5 0.0 0
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Yield efficiency (mg/J)
1 bar
20
40 60 Reaction time (min) 2 bar 3 bar
80
40 60 Reaction time (min) 2 bar 3 bar
80
100 3.5 bar
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1 bar
Yield efficiency (mg/J)
80
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Yield efficiency (mg/J)
1 bar
40 60 Reaction time (min) 2 bar 3 bar
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0
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Yield efficiency (mg/J)
2.5
d. Plate 4
2.5 2.0 1.5 1.0 0.5 0.0
0
20 1 bar
Figure 3
100 3.5 bar
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a.
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b.
d.
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Figure 4
ACCEPTED MANUSCRIPT (b)
(d)
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(c)
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(a)
(oC)
(f)
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(e)
(oC)
(oC)
Figure 5
ACCEPTED MANUSCRIPT a. Hydrodynamic cavitation 4.0
y = 0.2103x R² = 0.9574
3.5
y = 0.1768x R² = 0.9988
2.5
y = 0.1299x R² = 0.9878
2.0 1.5 1.0 0.5 0.0 10
15 Time (min) 55 °C
50 °C
4.0 3.5
y = 0.0362x R² = 0.9086
y = 0.0442x R² = 0.9072
3.0 2.5 2.0 1.5 1.0 0.5 0.0 5
15
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-ln (1-x)
60 °C
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b. Mechanical stirring
20
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5
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-ln (1-x)
3.0
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50 °C
25
35
45 Time (min) 55 °C
Figure 6
y = 0.027x R² = 0.7484 55
65 60 °C
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ACCEPTED MANUSCRIPT 2.98E-03 3.00E-03 3.02E-03 3.04E-03 0.0
3.06E-03 3.08E-03 3.10E-03
3.12E-03
-0.5 -1.0 y = -5188.8x + 14.044 R² = 0.9773
-1.5
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-2.5
y = -5306.2x + 12.83 R² = 0.99
-3.0 -3.5 -4.0 -4.5 -5.0 Mechanical Stirring
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1/Kelvin (1/T)
Hydrodynamic cavitation
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Figure 7
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ln (k)
-2.0