Comparison of Mist Circulation Biodiesel Water Washing with Traditional Methods

Transcription

1 Research article Comparison of Mist Circulation Biodiesel Water Washing with Traditional Methods Mahdi Feizollahnejad 1, Barat Ghobadian 1**, Ali Zenouzi 1, Ali Motevali 1 Department of Agriculture Machinery Engineering, Tarbiat Modares University, Tehran, Iran Corresponding Author Barat Ghobadian, ghobadib@modares.ac.ir, ali.motevali62@yahoo.com Tel: ; FAX: Abstract This paper describes the investigation on waterwashing methods of produced biodiesel for eliminating its impurities. Considering the merits and demerits of three typical biodiesel waterwashing methods i.e. mixing, water mist and bubble washing, with the aim of finding the suitable one, a new method was innovated which was named mist circulation. The new method of mist circulation possesses the benefits of both mist and bubble washing methods. It is both gentle and economical as far as water spray and consumption is concerned. Biodiesel waterwashing was carried out in three levels of 20, 40 and 60 C temperature for three methods of traditional water washing namely mixing, bubble washing, mist washing and also the new innovative mist circulation method. Several experiments were carried out in order to compare this new method with the three other ones experimentally. Test results of soap content showed that in similar conditions, minimum amount of soap was left in biodiesel for new method compared with other methods. It was found that the soap content in biodiesel after waterwashing with mist circulation method at 60 C was ppm, while for the same temperature it was 0.029, and ppm for water mist, bubble washing and mixing respectively. The average required time for mist circulation was 15%, 8% and 5% less than mixing, bubble washing and water mist respectively. The average elapsed time for mixing, bubble washing, water mist and mist circulation was 75, 70, 68 and 65 minutes respectively which shows the higher efficiency of mist circulation. This is due to gentleness and less emulsion formation for this method compared with other methods. The amount of consumed water in all methods except water mist was approximately the same. For purification of biodiesel at 60 C the amount of used water was 2.3, 2, 8, 2 liters per liter of produced biodiesel for mixing, bubble washing, water mist and mist circulation respectively. Copyright IJRETR, all rights reserved. Keywords: Water washing methods, Mixing, Bubble Washing, Water Mist, Mist Circulation. 249

2 1. Introduction Due to rapid increase in production of internal combustion engines and reduction in fossil fuel resources, there is a great desire to use renewable fuels. One of the renewable fuels which have drawn the people s attention a lot is biodiesel.the important characteristics of biodiesel such as reduction in exhaust pollution and being a renewable fuel distinguish it from other fuels [1]. Compared with bioethanol, biodiesel has three prominent characteristics which are as follow [1]: - Biodiesel has net useful efficient energy around 3-4 times that of bioethanol. - Using biodiesel in diesel engines always had a very efficient experience without any anxiety about probable problems for the engine. In return bioethanol has not been acceptable most of the time because of low useful energy. In addition, the energy content of biodiesel is 120,000 BTU per gallon while it is 80,000 BTU for bioethanol. - Every one even not very skilled with primary equipment can easily produce biodiesel. One of the cheep resources of biodiesel production is waste vegetable oil (WVO) or waste cooking oil. Conducted experiments show that the characteristics of produced biodiesel from WVO are according to biodiesel standards. The flash point and pour point of this fuel are 184 C and -3 C respectively. Also total sulfur content of biodiesel is 18 ppm while that of the diesel fuel which is used in transportation buses of Tehran city contains more than 500 ppm sulfur which is 18 times more than biodiesel. The average sulfur content of diesel fuel in Iran is 7000 ppm [3]. Test results of using different biodiesel and petrodiesel blends from B 0 D 100 to B 25 D 75 in MF-399 tractor engine has shown that the power and torque of this tractor engine increased using these blends. This could be attributed to good combustion quality of biodiesel blends due to the existence of oxygen molecule in biodiesel. Test results showed that the B 5 D 95 blend has the maximum increase in power and torque and the minimum increase in fuel consumption compared with other blends. If the strategy was to use a high amount of biodiesel, then the B 25 D 75 blend could be preferred due to low specific fuel consumption [4]. After the transesterification reaction, some amount of alcohol, potassium hydroxide and soap remain in biodiesel in the form of suspension [5]. Existence of alcohol in biodiesel can cause burning and explosion during engine operation which can damage the engine parts. Potassium hydroxide causes corrosion in some internal part of injection pump. Also the soap in biodiesel reduces the lubrication of injection pump and increases the abrasion of moving parts such as rotor and plungers [6]. Some of researches in produce biodiesel by water washing including: Liu et al. [7], Kusdiana and Saka [8], Du et al. [9], Hak et al. [10], Doradot al. [11], Karaosmanoglu et al. [12], Šiler-Marinkovic and Tomaševic [13], Predojevic [14] and etc. Biodiesel should be purified before using its use in internal combustion engines. After processing of biodiesel, some impurities such as excessive methanol, soap, glycerol and catalyst remain in it. Each of these impurities can cause several problems and may damage the engine. Therefore the purification of biodiesel is unavoidable. There are some scientific references which advise the use of impure biodiesel due to high cost and long time of purification process, and laborious operations. There is no standard test code for soap content of biodiesel. Also each purification method has its own merits and 250

3 demerits. Therefore, in this research work the focus is on comparison of traditional purification method and also introducing a new purification method which has more advantages than other traditional methods. Also the soap content and other brilliant characteristic of the new method are clarified. 2. Materials and Methods The produced biodiesel using transesterification reaction is usually used in internal combustion engines. After glycerol separation, the obtained biodiesel contains impurities which may cause reduction in engine life time and sometimes may even cause explosion. Impurities which exist in biodiesel include: methanol, soap, glycerol and catalyst. All of these impurities are soluble in water. Therefore in a research work leaded to this paper, the biodiesel was water washed. Three typical methods of waterwashing which exist in the literature today were used in these researches are as follow: - Mixing - Water mist - Bubble washing For carrying out the mixing method of water washing a mechanical mixer was designed, fabricated used to mix water and biodiesel. This method can be simply carried out which is the only its merit but due to high intensity and emulsion formation it is not recommended. The water mist method sprays water through the nozzles to the biodiesel surface and water settles at the bottom of vessel because of higher density than biodiesel. This method is gentle and the formation of emulsion is reduced. Therefore, the required time for separation of water from biodiesel is reduced too. This is the merit of water mist method. The demerit of this method is increasing in consumption of water which is at least 5 times of mixing method. The bubble washing was carried out by putting an air distributor at the bottom of washing vessel. The air was blown through this distributor by means a pneumatic pump. In this method the water ascends to the top through biodiesel by means of bubbles and washes the biodiesel like water mist. This method is also gentle but it uses less water than mist washing which makes it more efficient than this method. Because of these two advantages, the bubble washing method has been used most frequently in the world. Increasing in polymerization of biodiesel during engine operation has been reported as a disadvantage of this method. The bubble washing method clods and clogging of injectors by putting oxygen molecules between the unsaturated molecules of biodiesel and creation of long chain polymers causes the formation of polymer. Figure 1 shows the schematic of traditional biodiesel water washing methods. Figure 1: Traditional biodiesel water washing methods. 251

4 As far as the merits and demerits of different washing method is concerned, in this research work a new method which is the modified version of mist washing method, was innovated and named mist circulation (Figure 2). In this method, water was sprayed on the surface of biodiesel after settling at the bottom of washing tank circulated again to the mist nozzles by means of a hydraulic pump in order to repeat the washing process with the same water. This results in economized use of water. This task could be achieved by means of a hydraulic pump and nozzle without any extra cost. The only important point is that, the flow rate of pump should be low enough to let the water settling and separation from biodiesel. In the absence of water, the biodiesel will be pumped to nozzles which cause formation of emulsion that increases the time of separation. Figure 2 shows the working procedure of mist circulation method. Figure 2: new mist circulation method. To evaluate different washing methods, effective parameters that affect the quality of washing process were evaluated. Reduction in biodiesel impurities and improving biodiesel quality is the goal of washing process. Therefore, in the present case, the aim for evaluating different washing methods was to determine the method in which the biodiesel impurities could be minimum with high efficiency. Soap and catalyst are the two impurities in biodiesel. In a suitable waterwashing method, the least amount of soap and catalyst should be left in biodiesel. The soap test was used to determine he soap content. For conducting this test, first biodiesel was solved in a solvent like isopropanol alcohol. Also, 3 drops of bromophenol blue solution was added to the mixture as an indicator. Then titration was carried out using 0.01 N chloridric acids with an automated burette. While adding chloridric acid the mixture of biodiesel and isopropanol was mixed by means of magnetic stirrer so that the test could be performed accurately. At beginning, the color of mixture was dark green and the titration was continued till reaching the crystalline yellow. After finishing the titration, the quantity of consumed chloridric acid for titration was determined by mans of burette. Also the amount of soap and catalyst residue was calculated using the equations (1 and 2): 252

5 Quantity of consumed acid (cc) Soap (ppm) (1) Weight of biodiesel (gr) Quantity of consumed acid (cc) Catalyst (ppm) 561 (2) Weight of biodiesel (gr) To determine the effect of materials used in titration, the blank titration was used. In this case, the titration procedure was carried out, without biodiesel and the calculated quantity from blank titration was subtracted from main test value to show the real soap content in biodiesel. The amount of used water per each liter of biodiesel purification was another effective factor in evaluation of different washing methods. The lower water consumption means the suitable efficiency to be approached. Because the low water consumption reduces the cost of washing and therefore the cost of final biodiesel product could be reduced. One of the important factors while using biodiesel in CI engines is the water content of biodiesel after purification. According to ASTM-D6751 standard, the water content of biodiesel should be less than 0.05% by weight. After different stages of washing and separating by means of settling, a little amount of water remains in biodiesel in the form of emulsion which is more than standard limitation. Therefore, this amount of water is to be completely removed or at least reduced. In experimental and laboratory level, water absorbent materials (such as P 2 O 5 ) were used to dry biodiesel. After absorption of water, the biodiesel was filtered to separate the absorbent materials, though due to high cost of absorbent materials this method of drying in industrial level is not economically feasible. Therefore, in this research work, the heating method was used for drying. In this method, the biodiesel was kept at C in a drying tank for duration of 6 hours. Because of high temperature, the molecules of water bonded easier and faster to each other, formed big drops, and due to higher density than biodiesel settled easily and separated from biodiesel. After purification of biodiesel with different methods of washing, the water content of each sample from each method was determined using Carl Fisher 703 Ti stand. Another important factor in purification of biodiesel was the required time for purification. Because the purification process takes more time than other biodiesel production processes, therefore it was considered in this investigation presented in this paper. Temperature also affects biodiesel quality washing time. Three levels of temperature for evaluating the methods of biodiesel water washing were considered. Table 1 shows the matrix of experimentation for evaluation of mist circulation waterwashing and its comparison with other traditional methods. Table1: Matrix of experimentation. S.No. parameters Levels Washing method Mixing Bubble washing Water mist Mist circulation 2 Temperature( C) Used water After evaluation of different washing methods, a new mist circulation method was devised and mounted on semi continuous biodiesel processor to evaluate the practical results of this new method. 253

6 The semi continuous biodiesel processor consists of different containers (Fig. 3). Container one is for preparation of waste cooking oil. The methoxide tank is for mixing methanol and catalyst and preparing methoxide. Other containers are reaction tank, glycerol separation tank, washing tank and finally the drying tank. Using different tanks in this system is to increase the speed of production and improve quality of biodiesel. This arrangement has made the processor as a semi continuous processor. Different equipments of washing which were mentioned in this article were equipped with washing tank. Figure 3 shows the designed and fabricated biodiesel processor. Figure 3: Semi Continuous Biodiesel Processor plant. 3. Results and discussion Figures 5-8 show the relationship between washing methods and different parameters in biodiesel purification. Some of these parameters such as washing time (figure 5) and total amount of consumed water (figures 8) explain the economical effects and some other parameters such as soap and water content (figures 6 and 7) show the purity of final biodiesel product. Figure 4 shows the effect of washing method on waterwashing time at various temperatures. As it is seen in figure 4, among the four water washing methods, the mist-circulation requires the minimum time for waterwashing of biodiesel because this method is gentle and it results in reduction of emulsion formation and therefore the required time for breaking the emulsion and separation of water from biodiesel is minimized. Scrutinizing the merits and demerits of different washing methods, this new method (mist circulation) was innovated and tested in present research work. As literature review shows and also mentioned earlier, three typical conventional (traditional) waterwashing methods are mixing, water mist and bubble waterwashing. Among these methods although water mist is gentle and needs shorter time than the other ones, but it consumes too much water and is not economically feasible. The work carried out in this research was modification of water mist method to eliminate its disadvantages and introduction of a new method. This method which was named mist circulation dose not needs circulation of water till completely filling the washing tank. After filling the tank up to 254

7 soap residue (ppm) water washing time(min). International Journal of Renewable Energy Technology Research desired level, the inlet water value is shutting down and the settled water is circulated through nozzles by means of a water pump to mist the same amount of water without adding any extra fresh water and therefore the mist circulation name was selected for this procedure. As it is observed in figure 5, this method needs shorter time than the other methods. These results resemble those reported by Kusdiana and Saka [8] and Hak et al. [10] Temperature=60 C mixing bubble mist mist circulation water washing methods Figure 4: Effect of water washing method on required time for washing. Figure 5 shows the effect of washing method on soap content of biodiesel. Mist- circulation, water mist and bubble washing are more effective than mixing in eliminating soap from biodiesel. This is because these methods turn the water into drops and the contact area of biodiesel with water increases. Therefore, the drops solve the soap easily but in mixing method, the water is not turned into drops and the contact area of water with biodiesel is reduced. Therefore it has the least effect on eliminating soap from biodiesel. It is obvious from figure 5 that the soap residue in biodiesel final product is minimum in the case of mist circulation and comparable with water mist method Temperature=60 C mixing bubble mist mist circulation waterwashing methods Figure 5: Effect of water washing method on soap residue in biodiesel. Figure 6 shows the effect of waterwashing method on biodiesel water content. It is observed that the presence of water in biodiesel after mist circulation waterwashing is less than the other methods. As it was mentioned before, the presence of water in biodiesel after waterwashing is directly related with 255

8 Total water consumption(lit). Biodiesel water content (%). International Journal of Renewable Energy Technology Research emulsion formation and the emulsion itself depends on the waterwashing method. Therefore, every waterwashing method which is gentle produces less emulsion and the result is the low percentage of water in biodiesel. With regard to previous information, mist circulation and water mist are gentler than other methods and the bubble washing method stands in third the place from gentleness view point. These results resemble those reported by Ghobadian and Khatamifar [3], Zenouzi [4]. Temperature=60 C mixing bubble mist mist circulation water washing methods Figure 6: Effect of water washing method on biodiesel water content. Figure 7 shows the effect of waterwashing method on total water consumption for biodiesel purification. The minimum water consumption belongs to mist circulation method. It shows that this method has a better efficiency than the other methods in optimum use of water. The bubble washing stands in second place in this aspect but since it makes oxygen molecule available at the disposal of biodiesel, therefore it causes the oxidation and polymerization of biodiesel at high engine pressure and temperature. In mixing method, the water is not turned into drops and therefore the contact area of water and biodiesel is negligible. So, it has low efficiency in biodiesel purification. This is the reason that water consumption is not optimum in this method. In the similar manner, the water mist method is not economically feasible because of high water consumption. Eliminating the high water consumption, the mist circulation method would be the best option for biodiesel purification especially when large scale biodiesel production is concerned. These results resemble those reported by Ghobadian and Khatamifar [3], Zenouzi [4], Kusdiana and Saka [8] and Hak et al. [10] Temperature= 60 C mist mixing bubble mist circulation water washing methods Figure 7: Effect of water washing method on total water consumption. 256

9 4. Conclusions The conclusions drown from this research work are follow: 1- The three traditional methods of biodiesel water washing have been compared and a new method was devised. 2- Among the four water washing methods, the innovative mist circulation method requires minimum time for water washing. 3- The soap residue in biodiesel final product is minimum in case of mist circulation. 4- The presence of water in biodiesel after mist circulation is less than the other water washing methods. 5- The minimum water consumption for biodiesel purification belongs to mist circulation method. Acknowledgements The financial support of Iranian Fuel Conservation Organization (IFCO) of NIOC to carry out this research work is highly appreciated. References [1] N. Kuwahara, M.D. Berni, S. V. Bajay Renew Energ, 16 (1999) [2] Coltrain, Biodiesel and Svo Discussion Forums (2002). [3] B. Ghobadian, M. Khatamifar, Proceedings of the 4 th International Conference on Internal Combustion Engines. Nov (2005), Tehran. Iran. [4] A. Zenouzi, MSc Thesis, Tabiat Modares University. Tehran, Iran (2007). [5] M. Alovert, Bubble washing biodiesel and Emulsions. Available: (2005). [6] Anonymous, Biodiesel (B100). Available (2006). [7] X. Liu, H. He, Y. Wang, S. Zhu Fuel 87 (2008) [8] D. Kusdiana, S. Saka Bioresour Technol 91 (2004) [9] W. Du, Y.Y. Xu, D.H. Liu, J. Zhang J Mol Catal B 30 (2004) [10] J.K. Hak, S.K. Bo, J.K. Min, M.P. Young Catal Today 93 (2004) [11] M.P. Dorado, E. Ballesteros, F.J. Lopez, M. Mittelbach Energ Fuels 18 (2004) [12] F. Karaosmanoglu, K.B. Cigizoglu, M. Tuter, S. Ertekin Energ Fuel 10 (1996) [13] S.S. Šiler-Marinkovic, V.A. Tomaševic Fuel 77 (1998) [14] J. Zlatica Predojevic Fuel 87 (2008)