Influence of Butanol/Ethanol Blend Ratios in Palm Oil/Diesel based Microemulsion Biofuels using Alcohol Ethoxylate Surfactant - Phase Behaviors and Fuel Characteristics U-Larak Peson a,b, Sutha Khaodhiar c,d, Ampira Charoensaeng* a,b a The Petroleum and Petrochemical College, Chulalongkorn University b Center of Excellence on Petrochemical and Materials Technology c Department of Environmental Engineering, Chulalongkorn University d Center of Excellence on Hazardous Substance Management, Chulalongkorn University Keywords : Reverse micellar microemulsion, Palm Oil, Alcohol exthoxylate surfactants, Ethanol, Butanol, Microemulsion biofuel ABSTRACT The vegetable oils based reverse micelle microemulsions, known as microemulsion biofuels, have been increased in attention for biofuel production. This work aims to formulate microemulsion biofuels containing palm oil/diesel blend as a nonpolar phase, and ethanol/butanol, as a polar phase. The nonionic alcohol ethoxylate surfactant containing polyethylene oxide group (EO1) was selected as a stabilizing agent. A pseudo-ternary phase diagram was conducted to determine an isotropic region in the phase behavior of microemulsion systems. The ability of butanol added for reducing the phase separation and amount of surfactant required to from the microemulsified fuels was explored. Togerther with, the effect of cosurfactant structure, straight chain (1-octanol) and branch chain alcohol (2-ethyl-1-hexanol) were investigated systematically through their phase behaviors. The fuel properties (i.e., kinematic viscosity, density, heating value) were examined and compared with neat biofuels. The results suggested that the percentage of surfactant used to stabilize the microemulsion decreased with increasing butanol fraction in the mixture of butanol/ethanol blend. The microemulsion with branching structure in cosurfactant required more surfactant to formulate the microemulsions. The addition of butanol to palm oil/diesel blended with ethanol affecting fuel properties was noted. *Ampira.c@chula.ac.th INTRODUCTION Vegetable oils are widely used as an alternative fuel for diesel engines because of their advantages; they are produced from a renewable resource and have lower exhaust gas emissions after combustion due to the oxygen in their chemical structures. Notwithstanding, the high viscosity of vegetable oils could lead to diesel engines in a poor atomization and operational problems (Nitchawan et al., 2014, Mofijur et al., 2016). There are several thermal and chemical methods to reduce the viscosity of vegetable oils, for instance, a direct blending of vegetable oil/diesel, pyrolysis, transesterification and microemulsification (Atmanli et al., 2016). The vegetable oil-based microemulsions can be formulated owing to the usability of surfactants to create the thermodynamically stable Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 1
mixture of immiscible fluids with different polarity, where the polar phase (e.g., water, ethanol) stabilized by the surfactant is solubilized as a dispersed phase in a nonpolar phase (e.g., palm oil, canola). In addition, the addition of dispersed droplets has been known to reduce the viscosity of the microemulsion biofuels. Butanol, a liquid fuel derived from renewable resources, has been considered as a polar phase in the microemulsified fuels due to its fuel properties (Fernando et al., 2005; Qureshi et al., 2008; Kibbey et al., 2014; Yilmaz et al., 2014). The addition of butanol in the polar phase was found to improve the overall biofuel property for engine operating parameters, by decreasing in overall emissions such as oxides of nitrogen, carbon monoxide and hydrocarbon (Yilmaz et al., 2014). In our previous study, the microemulsion biofuels were formed by palm oil/diesel blend as an oil phase, using sorbitan monooleate (Span 80) and fatty acid methyl ester (Biodiesel) as a surfactant a volume ratio of 1:1 the ethanol/butanol blend as an alcohol phase was introduced in the formulation. The results indicated that the addition of butanol increased with increasing the viscosity of microemulsion biofuels (Waritta, 2015). Thus, the purpose of this study is to formulate palm oil/diesel blend based microemulsion biofuels using nonionic surfactant systems, with stable microemulsion formation and comparable diesel properties. The effects of blending ratio of butanol/ethanol (BuOH/EtOH) and cosurfactant structures on isotropic or single microemulsion biofuels are examined. Moreover, the fuel properties, including kinematic viscosity, density, cloud point, sulfur content and heat of combustion are measured to evaluate the ability for utilizing the microemulsion biofuels. EXPERIMENTAL A. Materials The nonionic linear alkyl alcohol ethoxylate surfactant with one-polyethylene oxide group (EO1) (99% active) was obtained from Thai Ethoxylate Company, Ltd. (Thailand). The cosurfactants are 1-octanol (99% purity) and 2-ethyl-hexanol ( 99.6% purity), and were purchased from Acros Organic (Italmar, Thailand). A food-grade pure palm oil (Morakot industries Public Company, Thailand) was purchased from a local market (Bangkok, Thailand). The diesel fuel (The Shell Company Ltd., Thailand) was purchased from local gas station (Bangkok, Thailand). Ethanol and butanol, with 99.9% purity and 99.4% purity respectively, were purchased from Merck (Thailand). All chemical were used as received. The properties of surfactant and chemicals used in this study are tabulated in Table 1. Table1: Properties of the surfactants and the cosurfactant Materials Chemical structure Symbol Molecular Weight (g/mol) Density (g/ml) HLB Surfactants C 12,14 H 25,29 (EO) 1 OH EO1 244 0.837 3.60 Cosurfactant 1-Octanol Oct 130.23 0.825-2-ethyl-1-hexanol 2-ethyl 130.20 0.833 - Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 2
B. Microemulsion preparation 1.) The microemulsion fuels were prepared in a 15 ml glass vial by palm oil/diesel mixture at 1:1 by volume and surfactant/cosurfactant (S/C) at the molar ratio of 1:8, and the amount of ethanol added to each vial were varied. The sample was gently mixed by hand-shaken and then placed at room temperature (25 ± 2ºC) to observed the phase separation. The microemulsion phase behavior of each sample was observed for 30 days to ensure its stability. 2) The microemulsion fuel prepared at fixed 20% by volume of alcohol, in which the amount of butanol in butanol/ethanol mixture were varied from 10:90, 20:80, 30:70, 40:60 and 50:50. The prepared alcohol solution was added to the surfactant/cosurfactant mixture (1:8 by molar ratio), and palm oil/diesel blend (1:1 by volume ratio) to study the effect of alcohols in the microemulsion fuel formation. C. Pseudo-Ternary phase diagram A pseudo-ternary phase diagram was conducted to examine the phase behavior of the microemulsion biofuels. A miscibility curve of microemulsion was constructed through the stepwise addition of alcohols to concentrated stock solutions of the oil (i.e., palm oil/diesel) and surfactant with or without cosurfactant in different volume ratios (Bora et al., 2016). The upper vertex of the diagram represents the surfactant/cosurfactant system (S/C) while the two vertices at the bottom are the vegetable oil/diesel blend and the alcohol at the left side and right side, respectively. The point in the pseudo three-phase diagram can be used to calculated relation in volume percentage for each component. D. Viscosity measurement The kinematic viscosity of the microemulsion biofuels was measured by Cannon-Fenske Routine viscometer according to ASTM D 445. The flow rates, described in cst/sec unit, were calculated by counting time at 25ºC, 40ºC and 60ºC. Finally, the kinematic viscosity can be calculated by Equation (1) as follows: μ = Kt (1) Where μ is the kinematic viscosity (cst), K is viscosity constant, and t is time of sample flow in viscometer E. Density measurement The density of the sample was measured at 20 C by density meter (DMA 4500 M). F. Heat of combustion measurement The gross heat of combustion was measured by oxygen bomb calorimeter (Ac-500) according to ASTM D 240. The fuel was placed in a crucible inside calorimeter to measure the temperature and to collect carbon residuals. The heat of combustion was calculated by the measured temperature increase of the water bath surrounding the bomb. G. Cloud point measurement The cloud point was determined following ASTM D 2500, by cooling temperature controlled bath. The microemulsion fuel was visually observed for turbidity as the temperature was decreased by every 1 C. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 3
H. Sulfur content measurement The sulfur content in the microemulsion fuel samples was analyzed by sulfur analysis method complying with ASTM D2622, D7039 and ISO 20884 methods (the Sindie 2622 benchtop analyzer). RESULTS AND DISCUSSION A. Microemulsion phase behavior For microemulsion phase behaviors, the area above the miscibility curve of pseudo-ternary phase diagram exhibits the amount of each component in the minimum requirement that can form a single phase microemulsion. The separate phase where is the area under the curve that presents the less of surfactant fraction in the system as shown in Figure 1. (Bora et al., 2015).The minimum percentage of each component used to form the biofuel representing in the area just above the miscibility curve. This study, the microemulsion biofuels were prepared by palm oil/diesel blend at 50:50 by volume as an oil phase, a mixture of alcohol ethoxylate surfactant (EO1) and 1-octanol at a molar ratio of 1:8 (S/C), and various ethanol concentrations as a polar phase. The result demonstrated that the surfactant concentration used to form the single phase increased with an increase the percentage of ethanol until approximately 55% by volume and then, less surfactant was required to solubilize all liquid fuel components. This trend is consistent with the studies of Pengpreecha et al. (2014) and Arpornpong et al. (2014). Figure 1. Pseudo-ternary phase diagram of microemulsion biofuel systems using EO1 as a surfactant and 1-octanol as a cosurfactant at molar ratio of 1:8 (S/C) in palm oil/diesel blend ratio at 1:1 by volume, at room temperature (25 ± 2ºC) B. Effect of cosurfactants structure on the microemulsion phase behavior For the effect of cosurfactant structure, the microemulsion systems were formed by the palm oil/diesel blend at 50:50 by volume and ethanol at fixed 20% by volume. The surfactant systems were prepared by a mixture of surfactant and cosurfactant mixture at the molar ratio of 1:8 (S/C). The two selected cosurfactants deviated by their alkyl structure, 1- octanol or 2-ethyl-hexanol were investigated. From Table 2, the result of the microemulsion biofuel system with 2-ethyl-1-hexanol required more amount of the surfactant to form the single phase compared with 1-octanol. This result could be due to the Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 4
steric barrier of its branching structure affecting the formation of reverse micelle surfactant aggregates. It can be concluded that structure of the cosurfactant has an influence on the single phase microemulsion formation of the palm oil/diesel and ethanol systems. Table 2. The amount of required surfactant to formulate microemulsion biofuel systems using EO1 as a surfactant and 1-octanol and 2-ethyl-hexanol as a cosurfactants at a molar ratio of 1:8 (S/C), in palm oil/diesel blended ratio at 50:50 by volume at room temperature (25 ± 2ºC). Sample Percentage by volume (%) Surfactant Cosurfactant Palm oil/diesel(1:1) Ethanol EO1/1-octanol 1.69 8.31 72 20 EO1/2-ethyl-hexanol 2.23 10.77 67 20 C. The effect of BuOH/EtOH ratios on the minimum surfactant concentration required to formulate a single phase microemulsion biofuel The palm oil/diesel blend and EO1 and 1-octanol as a surfactant/cosurfactant system in a fixed volume of the alcohol phase at 20% were conducted in microemulsion systems. The percentages of butanol in the mixture of BuOH/EtOH blends on the amount of surfactant used were investigated as shown in Figure 2. It was found that the amount of surfactant to formulate the single phase decreased with the percentage of butanol in the BuOH/EtOH fraction increased. For butanol fraction in BuOH/EtOH blending ratio from 0 to 50 by volume, the minimum surfactant concentration required were decreased by 50% by volume. It is interesting to note that the amount of surfactant was less influent for the microemulsion system contained butanol fraction more than 20% by volume of alcohol. This could be because butanol has less hydrophilic property than ethanol. Therefore, the addition of butanol can facilitate the usability of surfactant to form a single phase microemulsion. EO1/octanol Figure 2. The amount of surfactant concentration required to formulate microemulsion biofuel systems with varying BuOH/EtOH blending ratios by volume, using linear alkyl alcohol ethoxylate surfactant (EO1) and 1-octanol as a cosurfactant at molar ratio of 1:8 (S/C), in palm oil/diesel blend at 1:1 by volume ratio, at room temperature (25 ± 2ºC). Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 5
D. Effect of temperature on kinematic viscosity microemulsion fuel property The kinematic viscosities at different temperatures of the microemulsion biofuel systems containing EO1 and 1-octanol at fixed molar of 1:8 (S/C), in palm oil/diesel blend at ratio of 1:1 by volume and with different BuOH/EtOH blending ratios in 20% volume of alcohol are shown in Figure 3. It was observed for all the microemulsion systems that the kinematic viscosities gradually decreased with increasing temperatures. These results are consistent with Kibbey et al. (2014) that the temperature has a significant impact on the viscosity of the system. In detail, at higher temperature 40 C and 60 C, it was observed that the amount of butanol in alcohol phase increased with slightly increasing the viscosity of the microemulsion system under room temperature (25 C). Although the presence of butanol in the alcohol phase can reduce the amount of surfactant usage to formulate the stable microemulsion fuels, the addition of butanol in the BuOH/EtOH also affects the overall viscosity of the microemulsion systems at which to the inappropriate zone above the diesel no.2 standard. Figure 3 The kinematic viscosity of the microemulsion fuels at various temperatures at 25 C, 40 C and 60 C using EO1 as a surfactant and 1-octanol as a cosurfactant, in a molar ratio of 1:8 (S/C) in the palm oil/diesel blended at 1:1 by volume ratio E. Fuel properties Table 2 shows the fuel properties of the microemulsion biofuels containing ethanol alone and 10:90 BuOH/EtOH (v/v %) at 20% by volume of alcohol. It can be noted that the microemulsion systems with butanol have higher viscosity and density than those of the ethanol alone systems. Since the density and kinematic viscosity of the microemulsion biofuels are affected by the dispersed system (surfactants, cosurfactants molecules, and alcohols). The microemulsion systems with butanol also had a higher heat of combustion than the system with ethanol alone. This could be because the heat of combustion of ethanol (26.8 MJ/Kg) is lower than butanol (33 MJ/Kg) (Evangelos et al., 2013). However, both of the microemulsion fuels with different butanol content had higher cloud points than regular diesel (7±0.1 C) due to the intrinsic property of vegetable oil. It is interesting to note that the microemulsion fuels had a lower sulfur content than that of the diesel. This leads to a benefit concerning lower SO x emissions after combustion. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 6
Table 2 : Properties of microemulsion biofuel Sample Formula(%vol) Properties of microemulsion biofuels (Surfactant:Oil: EtOH:BuOH) Kinematic viscosity at Density (g/ml) Heat of combustion Cloud point Sulphur Content (ppm) 40 C (cst) (MJ/kg) ( C) EO1/1-oct 10:70:20:0 4.76±0.02 0.8496 39.23±0.11 10±0.1 9.75±0.63 EO1(10:90)/1-oct 9:71:18:2 4.92±0.01 0.8500 39.28±0.82 10±0.1 12.54±0.17 Diesel - 2.34±0.01 0.8248 45.8 a 7±0.1 29.25 Biodiesel(B100) b - 6.0 0.8760 - - - a the data obtained from Arpornpong et al., 2014 b the data obtained from Bernat et al., 2012 CONCLUSIONS The results of this work suggest that the stable microemulsion biofuels containing palm oil/diesel blend, alcohol ethoxylate surfactant with EO1, cosurfactant, BuOH/EtOH blend were obtained. The structure of cosurfactant had an influence on the formation of reverse micellar surfactant aggregates. The surfactant concentrations can be maintained in the presence of butanol as an alcohol phase to formulate the microemulsion biofuels. However, the fuel properties, kinematic viscosity, density, heating value, and cloud point of the palm oil/diesel based microemulsion biofuels are inappropriate levels for regular diesel but can be comparable with the no. 2 diesel standard and neat biodiesel (B100). The palm oil/diesel blend with the alcohol ethoxylate surfactant exhibited a low sulfur content according to a fraction of vegetable oil, which results in lower toxic emission after combustion. ACKNOWLEDGEMENTS The scholarship and funding of the thesis work provided by the Petroleum and Petrochemical College; and the National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials, Thailand and the Thailand Research Fund. We would like to thanks the support from the Center of Excellence on Hazardous Substance Management (HSM), Chulalongkorn University. We would like extend our gratitude to thank Thai Ethoxylate Company, Ltd. (Bangkok, Thailand) for providing the surfactants. REFERENCES Anantarakitti, N, Arpornpong, N., Khaodhiar, S. and Charoensaeng, A. (2014). Effect of nonionic surfactant structure on fuel properties of microemulsion-based biofuel from palm oil. Fuel, 10-118. Arpornpong, N. (2013). Alternative renewable biofuel from palm oil-diesel based reverse micelle microemulsions. Arpornpong, N., Attaphong, C., Charoensaeng, A., Sabatini, D.A. and Khaodhiar, S. (2014). Ethanol-in-palm oil/diesel microemulsion-based biofuel: Phase behavior, viscosity, and droplet size. Fuel, 132, 101-106. Petrochemical and Materials Technology Tuesday May 23, 2017, Pathumwan Princess Hotel, Bangkok, Thailand Page 7
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