Determination of Transesterification Reaction ... - ScienceDirect

Available online at www.sciencedirect.com

ScienceDirect Procedia - Social and Behavioral Sciences 195 (2015) 2492 – 2500

World Conference on Technology, Innovation and Entrepreneurship

Determination of transesterification reaction parameters giving the lowest viscosity waste cooking oil biodiesel Atilla Bilgina, Mert Gülümb*, İhsan Koyuncuogluc, Elif Nacd, Abdülvahap Cakmake a, b ,c, d ,e Karadeniz Technical University, Faculty of Engineering, Department of Mechanical Engineering, Trabzon 61080, Turkey

Abstract This study aims determination of transesterification reaction parameters to produce the lowest kinematic viscosity waste cooking oil biodiesel by using sodium hydroxide (NaOH) as catalyst and ethanol (C 2H5OH) as alcohol. For this purpose, the individual effects of main reaction parameters such as catalyst concentration (0.50-1.75 ), reaction temperature (60-90 ), reaction time (60-150 min.) and alcohol/oil molar ratio (6:1-15:1) on the kinematic viscosities of produced biodiesels were were investigated, respectively. According to results, reaction parameters giving the lowest kinematic viscosity of 4.387 reaction temperature, 120 minutes reaction time and 12:1 alcohol/oil molar determined as 1.25 catalyst concentration, 70 ratio. © Published by by Elsevier Ltd. Ltd. This is an open access article under the CC BY-NC-ND license © 2015 2015The TheAuthors. Authors. Published Elsevier (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Istanbul University. Peer-review under responsibility of Istanbul Univeristy. Keywords: Waste cooking oil biodiesel, transesterification, viscosity, ethanol, sodium hydroxide

1. Introduction Increasing prices and diminishing known supplies of fossil fuels, and global warming have lead to international interest in developing alternative fuel for engines (Salvi and Panwar, 2012; Alberici et al., 2012). Biodiesel, which is a substitute fuel made up of mono-alkyl esters of long-chain fatty acids prepared from renewable vegetable oils or animal fats as per the American Society for Testing and Materials (ASTM), has fascinated considerable interest as a renewable alternative fuel for diesel engines (Shah et al., 2013). Biodiesel has the following general advantages: *Corresponding author. Tel.: +90 462 377 41 30; fax: +90 462 377 33 36. E-mail address: [email protected]

1877-0428 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of Istanbul Univeristy. doi:10.1016/j.sbspro.2015.06.318

Atilla Bilgin et al. / Procedia - Social and Behavioral Sciences 195 (2015) 2492 – 2500

2493

(1) It is an oxygenated fuel which contains about 10-12 oxygen by weight in molecular structure, and has higher cetane number than petro-diesel fuel (here after referred as diesel fuel). These facts lead to better ignition quality and complete combustion. Thus the use of biodiesel instead of the diesel fuel significantly reduces the exhaust emissions such as carbon dioxide (CO), unburned hydrocarbons (HC) and smoke. Also, being a free-sulfur fuel, biodiesel leads to zero sulfur oxide (SOx) emissions (Salvi and Panwar, 2012; Alberici et al., 2012; Basha and Gopal, 2012; Borges and Diaz, 2013). (2) It is clean, biodegradable and non-toxic fuel, being beneficial for reservoirs, lakes, marine life and other environmentally sensitive places (Vicente et al., 2008). (3) It displays lubricating properties superior to diesel fuel, reducing premature wearing of fuel pumps (Alberici et al., 2012; Joshi and Pegg, 2007). (4) It has the potential to relieve the country’s dependence on foreign energy sources since it can be produced renewable and domestic feedstock (Yuan et al., 2003). (5) The flash point temperature of biodiesel is higher than that of diesel fuel which makes it safer regarding to the storage and transport (Alptekin and Canakci, 2008). (6) Biodiesel-diesel fuel blends or even pure biodiesel can be used in diesel engines with small modifications. Taking these advantages into consideration, it can be said that biodiesel is ideal fuel for diesel engines. However, biodiesel has some disadvantages such as poor low-temperature flow properties, higher viscosity and nitrogen-oxides (NOx) emissions and lower energy content (Yusuf et al., 2011). Also, the biodiesel produced from oils, no matter if it is neat vegetable oil or animal fat, is usually more expensive than diesel fuel from 10 to 50 . Therefore, the high cost of biodiesel is the major obstacle for its commercialization (Leung and Guo, 2006). Homogeneous catalyzed transesterification reaction has been commonly used to produce biodiesel. Sodium (NaOH) and potassium hydroxide (KOH) are generally preferred for this reaction in literature. Some studies in this type are summarized as following. In the study performed by Encinar and his colleagues (2002), production of biodiesel from Cynara cardunculus L was carried out by using ethanol as alcohol and different catalysts (sodium and potassium hydroxide). The operation variables for reaction temperature, catalyst concentration and ethanol/oil molar ratio were ranged as 25-75 , 0.251.50 wt and 3:1-15:1, respectively. The optimum parameters giving maximum biodiesel yield were found as ethanol/oil molar ratio 12:1, sodium hydroxide as catalyst (1.00 wt ) and 75 temperature. Zhang and his colleagues (2008) investigated the optimum conditions of two stage biodiesel production from Zanthoxylum bungeanum seed oil having high free fatty acids. The acid value of the oil was reduced from 45.51 mg KOH/g to 1.16 mg KOH/g by first stage acid catalyzed esterification reaction, performed with methyl alcohol/oil molar ratio of 24:1, sulfuric acid/oil weight ratio of 2.00 , reaction temperature of 60 and reaction time of 80 min. In the second stage, the pretreated oil was used for alkali-catalyzed transesterification and then the biodiesel having yield of higher than 98 was produced at the end of the reaction. El-Sabagh and his colleagues (2011) determined the optimum conditions of biodiesel production from waste frying oil. The transesterification process was carried out by using four types alcohol (methanol, ethanol, 1-propanol and 1-butanol). According to experimental results, when methanol/oil molar ratio of 6:1 and sodium hydroxide/oil weight ratio of 0.40 were used, maximum ester yield was obtained as 87 wt . Also, the researchers blended the produced optimum biodiesel and diesel fuel at different volume ratios (10, 15 and 20 ) to improve fuel properties of the biodiesel. Gülüm and Bilgin (2014) determined the production parameters for the producible lowest viscosity corn oil biodiesel by using sodium hydroxide (NaOH) as catalyst and methanol (CH3OH) as alcohol. The effects of main production parameters that influence the transesterification reaction such as catalyst amount, reaction temperature, reaction time, alcohol/oil molar ratio on the dynamic and kinematic viscosity of produced corn oil biodiesel was investigated. From the results obtained, production parameters that give the lowest viscosity was determined as 0.90 catalyst amount, 50 reaction temperature, 60 minute reaction time and 9:1 alcohol/oil molar ratio. Gülüm and Bilgin (2015) investigated densities of commercially available petro-diesel fuel and its blends with corn oil biodiesel. The corn oil biodiesel was produced according to previously determined optimum parameters such as 0.90 0 catalyst concentration, 9:1 methyl alcohol/oil molar ratio, 50 reaction temperature and 60 minute reaction time. The effects of temperature ( ) and biodiesel percentage in blend ( ) on the densities of blends were examined. The blends (B5, B10, B15, B20, B50 and B75) were prepared on a volume basis and their densities were measured by following ISO test method at temperatures of 10, 15, 20, 30 and 40 . New one- and two-dimensional equations were fitted to the measurements for identifying of variations of densities with respect to and ; and these equations were compared with other equations published in literature.

2494


The objective of the present work is to (1) investigate the individual effects of main transesterification reaction parameters such as catalyst concentration, reaction temperature, reaction time and alcohol/oil molar ratio on the kinematic viscosities of produced waste cooking oil biodiesels, (2) determine the values giving minimum kinematic viscosities for each reaction parameters. 2. Materials and Methods x

Materials

To produce biodiesel by basic catalyzed transesterification, waste cooking oil was provided from the university canteen. Ethanol of 99.8 purity and sodium hydroxide of pure grade were of Merck. x

Production parameters and biodiesel production

Physical and chemical properties of produced biodiesel are significantly affected by various reaction parameters. In this study, the effects of the following parameters on the kinematic viscosities of produced waste cooking oil biodiesels were investigated. . Catalyst concentrations, (mass of NaOH/mass of waste cooking oil): 0.50, 0.75, 1.00, 1.25, 1.50, 1.75 . Reaction temperatures, : 60, 70, 80, 90 . Reaction times, minute: 60, 90, 120, 150 . Alcohol/oil molar ratios: 6:1, 9:1, 12:1, 15:1 The above parameter values were selected as including the ranges in the literature (Karonis et al., 2009; Ginting et al., 2012; Barbosa et al., 2010; Issariyakul et al., 2008; Meneghetti et al., 2006). The transesterification reaction was carried out in a 1 L flat-bottomed flask, equipped with a magnetic stirrer heater, thermometer and spiral reflux condenser. Haake Falling Ball Viscometer, Isolab pycnometer, top loading balance with an accuracy of 0.01 , Haake Water Bath and stopwatch with an accuracy of 0.01 were used to measure dynamic viscosity and density. Before starting the reaction, a certain amount of sodium hydroxide (NaOH) according to chosen catalyst concentration was dissolved in a certain amount of ethyl alcohol (C2H5OH) depending on alcohol/oil molar ratio in a narrow-neck flask to make alcoholic solution of catalyst. In the flat bottomed flask, this alcoholic solution was added to the 200 waste cooking oil that was formerly warmed to about 80 in a beaker. Until a certain time, these reactants were mixed at a certain reaction temperature with stirring speed of 500 rpm by means of the magnetic stirrer heater. Transesterification reaction was carried out with the spiral reflux condenser for avoiding loss of alcohol. Also, reaction temperature was controlled by using the thermometer to remain at a constant temperature during the reaction. At the end of reaction, the resulting product mixture was transferred to a separating funnel. After a day, two phases occurred in the separating funnel. The upper phase consists of ethyl esters (biodiesel) while the lower one consists of glycerol, excess ethanol and the remaining catalyst together with soap. After separation of the two layers by gravity with gliserol, the upper layer (biodiesel) was washed with warm distilled water. Washed biodiesel was heated up to about 100 to remove ethyl alcohol and water residuals. x

Density measurement

The density of the produced biodiesel was determined by means of Eq. (1) and measurements in accordance with ISO 4787 standard:

m total biodiesel

mpycnometer pycnomete ycnometer m water

water

(1)


2495

where is density of biodiesel at intended temperature, is mass of the pycnometer filled with biodiesel, is mass of the empty pycnometer, is mass of water (empty pycnometer mass subtracted), is density of distilled water at intended temperature. and were experimentally determined as 43.00 and 50.02 , respectively. In order to minimize measurement errors, all the measurements were conducted three times for each sample and the results were averaged. Also uncertainty analysis was carried out depending on the sensitivities of measurement devices. x

Dynamic and kinematic viscosity measurement

The dynamic viscosity at 40 was determined in accordance with DIN 53015 standard by using Eq. (2) and making measurements by means of the Haake Falling Ball Viscometer, Haake Water Bath and stopwatch: biodiesel

Kball bal (

ball

biodiesel

)t

(2)

where is dynamic viscosity of produced biodiesel, is coefficient of the viscometer ball, and is falling time of the ball moving between two horizontal line marked on viscometer tube at limit velocity. and are 0.057 and 2.2 , respectively. The viscosity measurements were also conducted three times for each sample and the results were averaged. The kinematic viscosity was determined from Eq. (3) by dividing dynamic viscosity to density at same temperature: biodiesel

biodiesel

and

In Eq. (3), if

(3)

biodiesel

are in the unit of

and

, respectively, then

is obtained in

.

unit of x

/

Uncertainty analysis

The results obtained from experimental studies are generally calculated from measured physical quantities. These quantities have some uncertainties due to uncertainties of measuring tools and measurement systems. Therefore, uncertainty analysis should be applied for proving reliability of the calculated results. In this study, uncertainties of the measured and calculated physical quantities such as dynamic and kinematic viscosities and densities were determined by the method proposed by (Kline and McClintock, 2012 ). According to this method, if the result is a given function of the independent variables , , , and are the uncertainties of each independent variables, then the uncertainty of the result is calculated by using the equation:

wR

R w1 x1

2

R w2 x2

2

...

R wn xn

2

(4)

By using the method (4), the highest uncertainty was determined as 0.0946 , which show that the results have fairly high reliability. 3. Results and Discussion Parametric study was started by varying catalyst concentration. After determination of the optimum catalyst concentration, the effects of reaction temperature, reaction time and ethyl alcohol/oil molar ratio on kinematic

2496


viscosities of produced biodiesels were investigated, respectively. 3.1. Effects of catalyst concentration In order to research the effect of catalyst concentration on kinematic viscosity of biodiesel, . the alcohol/oil molar ratio: 9:1 . reaction temperature: 70 . reaction time: 90 minutes were kept constant throughout this set of the experiments and catalyst concentration was changed as 0.50, 0.75, 1.00, 1.25, 1.50 and 1.75 . The change of kinematic viscosity of produced biodiesel with respect to catalyst concentration is shown in Fig. 1. In this figure, as catalyst concentration is increased, kinematic viscosity of produced biodiesel gradually decreases until the catalyst concentration of 1.25 . At this point, the kinematic viscosity takes a minimum value of 4.441 . Then, when the catalyst concentration is continued to increase, the viscosity gradually increases. This variation can be attributed to the yield of the transesterification reaction. It is known that the viscosity of the produced biodiesel decreases with increasing reaction yield (Ghanei et al., 2011; Moradi et al., 2012). Because there is not enough amount of catalyst in reaction medium for low catalyst concentrations (e.g., 0.50 of sodium hydroxide), much of the triglycerides in the oil cannot be converted sufficiently to ethyl esters throughout the reaction period (90 minutes). This situation reduces yield of the transesterification reaction and increases kinematic viscosity of produced biodiesel. If higher catalyst concentration is used, the yield of the transesterification reaction improves and thus the viscosity of the produced biodiesel decreases. But, when excess catalyst concentration is used, the yield of the transesterification reaction decreases (Uzun et al., 2012; Encinar et al., 2005) and the viscosity of the produced biodiesel increases on account of formation of fatty acid salts (soap), decrease in activity of catalyst and difficulty in separation of glycerol. In the next stage of the study, catalyst concentration of 1.25 giving the lowest viscosity was kept constant and the other parameters were changed.

Fig. 1. Change of kinematic viscosity with respect to catalyst concentration.

3.2. Effects of reaction temperature To determine the effect of reaction temperature on kinematic viscosity of produced biodiesel, . catalyst concentration: 1.25


2497

. the alcohol/oil molar ratio: 9:1 . reaction time: 90 minutes were kept constant throughout this set of the experiments and reaction temperature was changed as 60, 70, 80 and 90 . Fig. 2 shows the changes of kinematic viscosity versus reaction temperature. In this figure, when reaction temperature is increased, the kinematic viscosity of produced biodiesel gradually decreases until the reaction temperature of 70 . At this point, the viscosity takes a minimum value of 4.441 . Then, as the reaction temperature is continued to increase, the viscosity gradually increases. Kinematic viscosity of biodiesel produced at low reaction temperatures (e.g., 60 ) is higher since transesterification reaction cannot be effectively completed. As the reaction temperature is increased, the yield of the transesterification reaction improves due to higher energy input (Uzun et al., 2012), and the viscosity of produced biodiesel decreases. In case of increasing reaction temperature higher than the boiling point of ethyl alcohol, viscosity of produced biodiesel increases due to diminishing of alcohol concentration by evaporating from reaction medium. Moreover, the saponification and decomposition of esters in biodiesel at higher temperatures may also be contributed to increase in viscosity of produced biodiesel. According to results, reaction temperature of 70 giving the lowest viscosity was regarded to be optimal value.

Fig. 2. Change of kinematic viscosity with respect to reaction temperature.

3.3. Effects of reaction time In order to investigate the effect of reaction time on kinematic viscosity of biodiesel, . catalyst concentration: 1.25 . reaction temperature: 70 . alcohol/oil molar ratio: 9:1 were kept constant throughout this set of the experiments and reaction time was changed as 60, 90, 120 and 150 minutes. Fig. 3 represents the changes of kinematic viscosity of biodiesel with respect to reaction time. Kinematic viscosity of produced biodiesel gradually decreases until the reaction time of 120 minutes when reaction time is increased. At this point, kinematic viscosity takes a minimum value of 4.387 . Then, as the reaction time is continued to increase, the viscosity gradually increases. The yield of transesterification reaction decreases in short reaction periods because of insufficient time for the reaction and thus viscosity of biodiesel becomes higher. With increasing in reaction time (Encinar et al., 2005), viscosity of biodiesel decreases due to the increase in yield of transesterification reaction and makes a minimum value at about 120 minutes. When reaction time is continued to

2498


increase, the transesterification reaction may shift towards reactants and thus causes to increase in viscosity of biodiesel. In the next stage of the study, based on these results, reaction time of 120 minutes giving the lowest viscosity was considered to be an optimum condition.

Fig. 3. Change of kinematic viscosity with respect to reaction time.

3.4. Effects of alcohol/oil molar ratio To analyze the effect of ethyl alcohol/oil molar ratio on kinematic viscosity of biodiesel, . catalyst concentration: 1.25 . reaction temperature: 70 . reaction time: 120 minutes were kept constant throughout this set of the experiments and molar ratio was changed as 6:1, 9:1, 12:1 and 15:1. Fig. 4 shows the change of kinematic viscosity of biodiesel versus molar ratio. Kinematic viscosity of produced biodiesel decreases until a value between 9:1 and 12:1 when molar ratio is increased. Considering the measurement values, the kinematic viscosity takes a minimum value as 4.347 cSt at 12:1 molar ratio. Then, as the molar ratio is continued to increase, the viscosity tends gradually to increase. According to the experimental results, the biodiesel has the maximum viscosity with 4.559 by using molar ratio of 6:1. When more alcohol/oil molar ratio is used (e.g., 9:1 or 12:1), because the transesterification reaction shifts toward products (El-Sabagh et al., 2011), the yield of the transesterification reaction increases and viscosity of biodiesel declines. Molar ratio of 15:1 gives higher the viscosity than 12:1 and 9:1 molar ratios because use of excess alcohol could be attributed to deactivation of the catalyst and increase in the solubility of the glycerol in the ethyl ester phase. Alcohol/oil molar ratio of 12:1 giving the lowest viscosity was taken to be optimal value.


2499

Fig. 4. Change of kinematic viscosity with respect to alcohol/oil molar ratio.

4. Conclusion In this study, the individual effects of catalyst concentration, reaction temperature, reaction time and ethyl alcohol/oil molar ratio on kinematic viscosity of produced biodiesel were investigated parametrically to produce the lowest viscosity waste cooking oil biodiesel by using NaOH as catalyst. It was determined that: . 1.25 catalyst concentration . 70 reaction temperature . 120 minutes reaction time . 12:1 ethyl alcohol/oil molar ratio give the lowest kinematic viscosity of 4.347

.

Acknowledgments The authors express their gratitude to Karadeniz Technical University Scientific Research Projects Fund for financial support received (Project No: 9745). References Salvi, B. L., Panwar, N. L., (2012). Biodiesel resources and production technologies – A review. Renewable and Sustainable Energy Reviews, 16, 3680-3689. Alberici, R. M., De Souza, V., De Sá, G. F., Morelli, R., Eberlin, M. N., & Daroda, R. J. (2012). Used frying oil: a proper feedstock for biodiesel production? Bioenerg. Res., 5, 1002-1008. Shah, S. N., Iha, O. K., Alves, F. C. S. C., Sharma, B. K., Erhan, S. Z., & Suarez, P. A. Z. (2013). Potential application of turnip oil (raphanus sativus L.) for biodiesel production: physical-chemical properties of neat oil, biofuels and their blends with ultra-low sulphur diesel (ULSD). Bioenerg. Res., 6, 841-850. Basha, S. A., & Gopal, K. R. (2012). A review of the effects of catalyst and additive on biodiesel production, performance, combustion and emission characteristics. Renewable and Sustainable Energy Reviews, 16, 711-717. Borges, M. E., & Díaz, L. (2013). Catalytic packed-bed reactor configuration for diesel production using waste oil as feedstock. Bioenerg. Res., 6, 222-228. Vicente, G., Martínez, M., & Aracil, J. (2008). Integrated biodiesel production: a comparison of different homogenous catalysts systems. Fuel, 87, 2355-2373. Joshi, R. M., & Pegg, M. J. (2007). Flow properties of biodiesel fuel blends at low temperatures. Fuel, 86, 143-151. Yuan, W., Hansen, A. C., & Zhang, Q. (2003). Predicting the physical properties of biodiesel for combustion modeling. ASAE, 46, 1487-1493.

2500


Alptekin, E., & Canakci, M. (2008). Determination of the density and the viscosities of biodiesel-diesel fuel blends. Renewable Energy 33, 26232630. Yusuf, N. N. A. N., Kamarudin, S.K., & Yaakub, Z. (2011). Overview on the current trends in biodiesel production. Energy Conversion and Management, 52, 2741-2751. Leung, D. Y. C., & Guo, Y. (2006). Transesterification of neat and used frying oil: Optimization for biodiesel production. Fuel Processing Technology, 87, 883-890. Encinar, J. M., González, J. F., Rodríguez, J. J., & Tejedor, A. (2002). Biodiesel fuels from vegetable oils: transesterification of cynaracardunculus l. oils with ethanol. Energy & Fuels, 16, 443-450. Zhang, J., & Jiang, L. (2008). Acid-catalyzed esterification of zanthoxylum bungeanum seed oil with high free fatty acids for biodiesel production. Bioresource Technology, 99, 8995-8998. El-Sabagh, S. M., Keera, S. T., & Taman, A. R. (2011). The characterization of biodiesel fuel from waste frying oil. Energy Sources, 33, 401-409. Gülüm, M., Bilgin, A. (2014). The effects of various production parameters on the some fuel properties of produced biodiesel from corn oil by using NaOH, 7th Automotive Technologies Congress. Bursa, Turkey, paper #B223. Gülüm, M., Bilgin, A. (2015). Density, flash point and heating value variations of corn oil biodiesel–diesel fuel blends. Fuel Processing Technology, 134, 456-464. Karonis, D., Anastopoulos, G., Zannikos, F., Stournas, S., & Lois, E. (2009). Determination of physicochemical properties of fatty acid ethyl esters (FAEE)-diesel fuel blends. SAE, 2009-01-1788. Ginting, M. S. A., Azizan, M. T., & Yusup, S. (2012). Alkaline in situ ethanolysis of Jatropha cursas. Fuel, 93, 82-85. Barbosa, D. D. Costa., Serra, T. M., Meneghetti, S. M. P., & Meneghetti, M. R. (2010). Biodiesel production by ethanolysis of mixed castor and soybean oils. Fuel, 89, 3791-3794. Issariyakul, T., Kulkarni, M. G., Meher, L. C., Dalai, A. K., & Bakhshi, N. N. (2008). Biodiesel production from mixtures of canola oil and used cooking oil. Chemical Engineering Journal, 140, 77-85. Meneghetti, S. M. P., Meneghetti, M. R., Wolf, C. R., Silva, E. C., Lima, G. E. S., Silva, L. D. L., Serra, T. M., Cauduro, F., & De Oliveira L. G. (2006). Biodiesel from castor oil: a comparison of ethanolysis versus methanolysis. Energy & Fuels, 20, 2262-2265. Holman, J. P. (2012). Experimental methods for engineers (8th ed.). New York: McGraw-Hill. Ghanei, R., Moradi, G., Taherpourkalantari, R., & Armandzadeh, E. (2011). Variation of physical properties during transesterification of sunflower oil to biodiesel as an approach to predict reaction progress. Fuel Processing Technology, 92, 1593-1598. Moradi, G. R., Dehghani, S., & Ghanei, R. (2012). Measurements of physical properties during transesterification of soybean oil to biodiesel for prediction of reaction progress. Energy Conversion and Management, 61, 67-70. Uzun, B. B., Kılıc, M., Ozbay, N., Putun, A. E., & Putun, E. (2012). Biodiesel production from waste frying oils: optimization of reaction parameters and determination of fuel properties. Energy, 44, 347-351. Encinar, J. M., González, J. F., & Rodríguez. R. A. (2005). Biodiesel from used frying oil, variables affecting the yields and characteristics of the biodiesel. Ind. Eng. Chem. Res., 44, 5491-5499.