Palm Oil Based Biofuels by Reverse Micelle Microemulsion: The Effects of Palm Oil Properties and Solid Fat Content Supitcha Insoma, Noulkamol Arpornpong b, Pomthong Malakul a, David A. Sabatinic, Ampira Charoensaeng*,a a

The Petroleum and Petrochemical College, Chulalongkorn University, Bangkok, Thailand Faculty of Agriculture, Natural Resources and Environment, Naresuan University, Phitsanulok, Thailand c School of Civil Engineering and Environmental Science, The University of Oklahoma, USA b

Keywords : Biofuel, Microemulsion, Reverse micelle, Nonionic surfactant, Solid fat ABSTRACT Palm oil is a superior resource for producing biofuels. It is a local agriculture product derived from renewable resource and environmentally safe fuel. One of the biofuel production technologies to reduce vegetable oil’s viscosity is reverse micellar microemulsification. This work aims to formulate microemulsion biofuels (ME) by palm oil/diesel blended with ethanol system using nonionic surfactants. The ME were prepared by refined bleached and deodorized palm oil (RBDPO) and diesel blended as an oil phase, and ethanol as a polar phase, then stabilized by two different surfactant system; an alcohol ethoxylate surfactant with EO groups: n = 1 and 5, and palm oil methyl ester (PME) mixed with 1-octanol as a surfactant/cosurfactant (S/C). The minimum surfactant concentrations with different molar ratios of S/C; 1:4, 1:8 and 1:16 were conducted and the appropriation formulation was selected. The results showed that the system at S/C molar ratio of 1:4 required less amount of surfactant than those of the systems at S/C molar ratio of 1:8 and 1:16 to formulate a single phase microemulsion. While the kinematic viscosity measurements of the AE-EO1, AE-EO5 and PME systems with different surfactant structures were no significantly different. The effect of palm oil based microemulsion formation on the solid fat precipitation were evaluated and discussed. *[email protected] INTRODUCTION Vegetable oils have been widely considered as such an alternative fuel source because of their non- toxicity and renewable natures. Among them, palm oils have been widely used in biofuel production (e.g. biodiesel) due to their reasonable price. However, high viscosity of vegetable oil limits their utilization as a diesel fuel; of which the direct use of vegetable oil can lead to long term engine failures. Therefore, several technologies of reducing vegetable oil viscosity have been widely developed. Vegetable-oil-based microemulsification have been raised great interests because of simple production process, less emissions and burnt more completely. Microemulsion biofuel (ME) is a direct combination of hydrophilic (i.e., ethanol) and hydrophobic (i.e., diesel fuel and vegetable oil) fuels stabilized by surfactant in order to form a single phase microemulsion or homogeneous liquid mixture under appropriate conditions. Ethanol has received increased interest in many research studies because ethanol is a renewable energy source from agricultural feedstocks such as sugar cane and corn. In fuel blending application, ethanol is used as a viscosity reducer for vegetable oil and/or diesel with ethanol blends. However, ethanol has limited solubility between ethanol and diesel blends in wide range of condition. Recently, vegetable oil based microemulsion

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technology has been developed. The mixture of diesel and vegetable oil with ethanol can be applied in diesel engines without engine modification through microemulsification process. In micellar microemulsion of water-in-oil system, ethanol is used in place of the polar phase in which the ethanol droplet dispersed in the oil phase can reduce total viscosity of vegetable oil and diesel mixture. Several types of surfactants have been used to form ME such as anionic carboxylate based extended surfactant, renewable based nonionic surfactant (Attaphong et al., 2013). Among these, nonionic surfactants exhibit better performance than those of the anionic surfactant system. The reasons are because the nonionic surfactant solubilizes more oils without salt addition and they does not form phase separation at low surfactant concentration. The aim of this research is to formulate microemulsion biofuels containing palm oil (refined bleached deodorized palm oil; RBDPO)/ diesel blended with ethanol using nonionic surfactant system. This research also focuses on the effects of surfactant/cosurfactant (S/C) ratio on phase behavior, kinematic viscosity and the effect of S/C ratio on the precipitated solid fats in the ME systems. EXPERIMENTAL METHOD A. Materials Table 1: Properties of nonionic surfactants and cosurfactant Molecular Materials

Chemical structure

Symbol

Weight (g/mol)

Density (g/mL)

HLB

Surfactants C12,14H25,29–(EO)1–OH

AE-EO1

244

0.837

3.60

C12,14H25,29–(EO)5–OH

AE-EO5

420

0.924

10.48

Palm oil Methyl Ester

PME

283.37

0.864

4.17

Oct

130.23

0.825

-

Cosurfactant 1-Octanol

The refined bleached deodorized palm oil (RBDPO) was supported by Bangchak Biofuel Co., Ltd while palm olein as commercial grade was obtained from local market. Alcohol ethoxylate surfactants (AE-EOn) and palm oil methyl ester (PME) were used as a non surfactant in this study. The AE-EOn surfactants were obtained from Thai Ethoxylate Company, Ltd as were used as recieved. The cosurfactant was 1-octanol (99% purity) and purchased from the Acros Organics chemical company. Ethanol (99% purity) was used as a polar liquid fuel and purchased from Merck Company. B. Oil Preparation

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In RBDPO preparation, the neat RBDPO was shaken before use, and then the neat RBDPO was heated at 80°C for 30 min to ensure that the oil is in a liquid state (De et al., 1989), and then the oil solution was mixed with diesel at a ratio of 1:1 (v/v). Synthetic RBDPO was used as a control sample and prepared by the mixture of palm stearin (solid part) and palm olein (liquid part) in the fraction of palm stearin to palm olein about 30 to 70 (vol.%) (Scholtz et al., 2004). The palm stearin was heated at 80°C for 30 min to ensure that the mixture is liquid (De et al., 1989) before mixed with palm olein, and then the palm oil mixture was mixed with diesel at a ratio of 1:1 (v/v). C. Microemulsion Preparation A ME mixture consists of vegetable oil/diesel blended at 1:1 by volume; the S/C at molar ratio of 1:8 was used to stabilize polar phase (ethanol) and oil phase (vegetable oil/diesel mixture) to be a single phase solution. Each ME sample was prepared in a 15 mL glass vial. Amounts (1, 2, 3, 4 and 5 mL) of ethanol with 5 mL of palm oil/diesel blend were added into surfactant and cosurfactant blends to determine microemulsion phase behavior for each formulation. In addition, the fixed amount of ethanol at 5 mL and varied palm oil/diesel blends in 1, 2, 3, 4 and 5 mL were conducted. Finally, all mixtures were hand-shaken gently and placed at 25±2ºC for 7 days to observe phase separation. The homogeneous and stable ME was determined by visual observation. D. Pseudo-Ternary Phase Diagram Pseudo-ternary phase diagram which is a triangle diagram that consists of three main components, typically used to determine phase behavior of ME. The upper vertex represents AE-EO1, AE-EO5 and 1-octanol mixture by fixed molar ratio of 1:8. The vertex at the bottom in the left hand side represents refined bleached deodorized palm oil (RBDPO) and diesel blend at 1:1 (v/v) ratio, and the right hand side represents ethanol. The ME systems were controlled at room temperature (25±2ºC). All data points in a pseudo-ternary phase diagram were calculated based on three components in a volume percent. E. Viscosity Measurement The kinematic viscosity was measured by Cannon-Fenske Routine viscometer following ASTM D 445. The kinematic viscosity can be calculated by Equation (1), µ = Kt Eq. (1) where µ is kinematic viscosity (cSt), K is viscosity constant (K=0.01606 cSt/s) and t is time of sample flow in the viscometer. In this study, the viscosities of the microemulsuion fuels were compared with the No.2 diesel fuel at 40°C. RESULTS AND DISCUSSION A. Effect of surfactant/cosurfactant ratios at 20 vol.% of ethanol For the phase behavior study, the minimum surfactant concentration that used to form a single phase microemulsion, distinguishing by three molar ratios of S/C 1:4, 1:8 and 1:16, and neat RBDPO and synthetic RBDPO as a control system were determined. The ME systems were prepared by AE-EO1, AE-EO5 and PME as a surfactant and 1octanol as a cosurfactant. Ethanol was fixed at 20 % by volume of the total biofuel mixture. Neat palm oil (RBDPO and olein) and diesel was blended at a ratio of 1:1(v/v) and used as an oil phase. The result demonstrated that the S/C ratios at the molar ratio of 1:4, 1:8 and 1:16 required the similar amounts of surfactant at minimum concentration to formulate a single phase microemulsion for both RBDPO and synthetic RBDPO, re249

spectively. In addition, the results obtained from the neat RBDPO did not deviated from the synthetic RBDPO, which was used as a control. For the effect of surfactant types, (AE-EO1, AE-EO5) and PME, the minimum total surfactant concentration to formulate a single phase microemulsion of the AE-EO1 system with different S/C ratios of 1:4, 1:8 and 1:16 were similar to those of the system with PME as the surfactant at 2 vol.% of surfactant. For the system with AE-EO5, the surfactant amount used for formulating a single phase microemulsion with 1-octanol at the mole ratio of 1:4 was about 3 vol.% while, those of the systems at the molar ratio of 1:8 and 1:16 were about 4 vol.%. The results are consistent with Attaphong and coworkers (2012) that at low percentage of alcohol (less than 30 vol.%), the S/C ratio does not affect the nonionic surfactant concentration used to form a single phase microemulsion. B. The effect of surfactant/cosurfactant ratios on solid fats formation This part demonstrated the height of precipitated solid fat versus amount of surfactant in different S/C ratios. Overall, it is clear that amount of the precipitates is influenced by amount of surfactant, surfactant’s structures, oil types and S/C ratios. Height of the precipitates (cm)

3.0 2.5 2.0 1.5 1.0 0.5 0.0

Neat RBDPO

2

3 4 5 Vol.% of surfactant concentration 1:4 (AE-EO1) 1:4 (AE-EO5) 1/4 (PME) 1:8 (AE-EO1)

Figure 1 Height of the precipitates versus surfactant concentration (vol.%) using AEEO1, AE-EO5 and PME as a surfactant and 1-octanol as a cosurfactant with S/C molar ratios of 1:4, 1:8, 1:16 and the neat RBDPO/diesel blended at the ratio of 1:1 (v/v) in 20 vol.% of ethanol. For effect of palm oil types on the solid fat precipitation using PME as the surfactant (see Figures 1 and 2), it is interesting to note that the amounts of precipitates in the synthetic RBDPO’s systems (as a control) were more than those of the neat RBDPO’s systems. The reason could be the fact that, some fatty acids or monoglycerols can act as a cosurfactant and help the surfactant solubilize the oil phase. In this case, palmitic acid which is the dominant constituent of the fatty acids of neat RBDPO is in the range of 42-47 % while 4.90-48.90 % of the palmitic acid contains in synthetic RBDPO. Effect of surfactant’s structures on the solid fat precipitation were observed for the ME systems using AE-EO1, AE-EO5 and PME as a surfactant (see Figure 2), the amount of precipitated solid fats formed in the system using AE-EO1 are higher than that of the systems using AE-EO5 and PME. It can be noted that the ester group and EO group in the alcohol ethoxylate surfactants play a significant role in influencing the crystallization of the precipitates.

250

Height of the precipitateds (cm)

3.0

Synthetic RBDPO

2.5 2.0 1.5 1.0 0.5 0.0 2

3

4

Vol.% of surfactant concentration 1:4 (AE-EO1) 1:4 (AE-EO5) 1/4 (PME) 1:8 (AE-EO1)

5

Figure 2 Height of the precipitates versus surfactant concentration (vol.%) using AEEO1, AE-EO5 and PME as a surfactant and 1-octanol as a cosurfactant with S/C molar ratios of 1:4, 1:8, 1:16 and the synthetic RBDPO/diesel blended at the ratio of 1:1 (v/v) in 20 vol.% of ethanol. Effects of surfactant/cosurfactant ratios on the precipitated semi-solid fat formation were observed for the ME systems using AE-EO1, AE-EO5 and PME at 4 vol.% as shown in Figure 2. It is worth noting that the phase behaviors of the microemulsion systems were not influenced by S/C ratios while the amount of precipitated solid fats of each surfactant system was attributed by the S/C ratios. The precipitates of the ME systems using PME were less than those of the ME systems using AE-EO1 and AE-EO5. Moreover, the amount of precipitates formed in the ME systems using AE-EO1 and AE-EO5 were different due to the steric effects of EO group in the alcohol ethoxylate. It is interesting to note that, the amounts of solid fats precipitated in the ME systems using PME were less than those of the AE-EOn systems for almost S/C ratios. In addition, the effect of S/C ratio on the solid fat precipitation in the ME systems using the neat RBDPO was similar to those of the ME systems using the synthetic RBDPO. C. Kinematic Viscosity Study Table 2: Kinematic viscosity of microemulsion biofuel system with different S/C ratios. Sample AE-EO1 AE-EO5 PME

Kinematic viscosity (cSt) with different S/C ratios 1:4 1:8 1:16 5.80±0.03 5.25±0.01 5.20±0.05 5.98±0.01 5.29±0.01 5.25±0.02 5.33±0.01 5.25±0.01 5.22±0.01

To study the effect of S/C ratios on viscosity of the ME at 40°C, AE-EO1, AE-EO5 and PME were selected as a surfactant and was mixed with 1-octanol at three different S/C ratios of 1:4, 1:8 and 1:16 (M:M) in neat RBDPO/diesel blended at the ratio of 1:1 (v/v) at 20 vol.% of ethanol. The viscosities of the ME systems distinguished by S/C ratio were shown in Table 2. It was found that the viscosity of the ME decreases with increasing of the amount of cosurfactant in surfactant and cosurfactant mixture. Due to the limitation of surfactant preparation at low surfactant concentration and cost-effective

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consideration, the S/C molar ratio of 1:8 can be used to maintain the viscosity of the ME at which their viscosities are comparable with No.2 diesel fuel (1.9-4.1 cSt) and biofuel standard (1.9-6.0 cSt) (Hoekman et al., 2012). The results are consistent with Anantarakitti and coworkers (2014) that the S/C ratio of 1:8 was the appropriate condition to formulate the biofuels at comparable viscosity. CONCLUSIONS Changing the S/C molar ratios does not affect the amount of surfactant used to form the single phase microemulsion. The amounts of precipitates from in the RBDPO/diesel blend systems are influenced by the surfactant concentration and structures, and S/C ratio. The neat RBDPO and synthetic RBDPO can be formulated a single phase microemulsion biofuels with comparable viscosity. Although, the use of neat RBDPO instead of palm olein has benefits in terms of economic and environmental aspects, the limitation of their usages in diesel engines such as wax precipitation needs to be considered. ACKNOWLEDGEMENTS This thesis work is partially funded by The Petroleum and Petrochemical College; The National Center of Excellence for Petroleum, Petrochemicals, and Advanced Materials, The Ratchadapisek Sompote Endowment Fund (2015), Chulalongkorn University (CU26-900-FC) and The Thailand Research Fund (TRG5780163 and IRG5780012). In addition, I extend our gratitude to thank Thai Ethoxylate Company, Ltd. and Bangchak Biofuel Co., Ltd., for provide linear alkyl alcohol ethoxylate and RBDPO, respectively. REFERENCES Abdul Hadi, N. (2013). Physico-chemical properties of palm stearin, soybean oil and their binary blends, Universiti Teknologi MARA. 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. 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. Attaphong, C. and Sabatini, D.A. (2013). Phase behaviors of vegetable oil-based microemulsion fuels: the effects of temperatures, surfactants, oils, and water in ethanol. Energy & Fuels 27(11), 6773-6780. De., M, L., D. M., J.M. and Blackman, B. (1989). Polymorphic behavior of some fully hydrogenated oils and their mixtures with liquid oil. 66(12), 1777-1780. Hoekman, S.K., Broch, A., Robbins, C., Ceniceros, E. and Natarajan, M. (2012). Review of biodiesel composition, properties, and specifications. Renewable and sustainable energy reviews 16(1), 143-169. Morad, M.D.N.A. and Aziz, M.M.K.A. (2006).Process design in degumming and bleaching of palm oil. Scholtz, S.C., Pieters, M., Oosthuizen, W., Jerling, J.C., Bosman, M.J. and Vorster, H.H. (2004). The effect of red palm olein and refined palm olein on lipids and haemostatic factors in hyperfibrinogenaemic subjects. Thrombosis research 113(1), 13-25.

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