The use of thermally modified koalin as a heterogeneous catalyst for producing biodiesel

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1 The use of thermally modified koalin as a heterogeneous catalyst for producing biodiesel Hilary Rutto Department of Chemical Engineering, Vanderbilpark Campus, Vaal University Of Technology, Private Bag X0, Vanderbilpark, South Africa, 900 Biodiesel was produced from used waste cooking oil (WCO) using thermally modified kaolin as a heterogeneous base catalyst. Response surface methodology based on a central composite design (CCD) was used to optimize the following four transesterification variables namely: temperature, (30-0 C), reaction time, (- 6hr), methanol to oil ratio, (0-50 wt %) and amount of catalyst, (-6 grams). Important fuel properties such as viscosity, density and flash point were measured and compared with American Society for Testing and Material (ASTM) standards for biodiesel. The catalyst was reused to determine its stability. The optimum conditions for biodiesel production were found as follows: temperature 9.3 C, amount of catalyst of.03 wt %, methanol to oil ratio 8.6 wt %, reaction time of.56 hr. The optimum yield of biodiesel yield was 95.06%. The results show that the important fuel properties of the biodiesel produced at optimum conditions met the biodiesel ASTM standard. It was also observed that thermally modified kaolin heterogeneous catalyst can be recycled up to three times. Keywords: Biodiesel; WCO; central composite design; transesterification; Thermally Modified Koalin;. Introduction The depletion of fossil fuels has caused the price of petroleum to rise remarkably and also air pollution caused by vehicles is of environmental concern, therefore there is a need to find alternative energy such as biodiesel which is biodegradable, non-toxic and renewable []. Research conducted in Turkey shows the consumption of diesel fuel have reached alarming rate and that production of fossil fuel in Turkey might Turkey might diminish by 038 [-3]. Therefore there is a need to search for alternative energy. Feed stocks for biodiesel production can be classified into into edible and non-edible oils. Biodiesel production can be produced from edible vegetable oils like soybean corn and canola, result show they be good as a diesel substitute []. The non-edible oils such as animal fats, Jatropha curcas, and waste oils such as yellow grease and soybean soapstock have been used in the production of biodiesel [5-7] There are basically two types of catalyst that are used in the production of biodiesel namely Homogenous and heterogeneous. The term homogeneous means the catalysts are in the same phase with its reactants, whereas heterogeneous means that the catalysts are in a different phase from its reactant. Further homogenous catalyst can be categorised into homogenous bases and acids. In biodiesel production Potassium hydroxide, sodium hydroxide, sodium methoxide are the commonly used basic catalysts production [8]. An example of commonly used homogenous acid catalyst is sulphuric acids, sulphuric acids is commonly used esterify excess free fatty acids when the free fatty acid content is high [9]. Homogenous and heterogeneous base catalyst and have different advantages and disadvantages, generally the advantages of heterogeneous catalyst is on its noncorrosive, environmental benign and can be recycled [0-]. However the disadvantages are they require high reaction temperature, pressure and more process time as they have low micro porosity and therefore low diffusion limitation. The advantages of heterogeneous acid catalyst are they can catalyse esterification and transesterification simultaneously. The surface response methodology is a powerful statistical method, usually it includes the application of design expert software that can be used to test multiple process variables because few experimental runs are needed compared to a one factor-at-a time method []. In addition, interactions between variables can be identified and quantified. Kaolin is cheap abundant clay found in many parts of Africa, and its suitability as a catalyst as it contains very small amounts of potassium oxide is important for this study. This research investigates the impregnation kaolin using postasium hydroxide as a homogenous catalyst so as to improve it catalytic properties. The effect of process variables such temperature, amount of catalyst, amount of methanol to oil ratio and reaction time on the yield of biodiesel from waste vegatable oil are investigated using surface response methodology. A mathematical model will be developed to determine the biodiesel yield. The important fuel properties of biodiesel produced at optimum conditions are also investigated if they are within the ASTM standard of biodiesel. FORMATEX

2 . Material and method. Material Waste vegetable and kaolin was supplied by the cafeteria and GW base materials respectively. Potassium hydroxide, methanol, phenolphthalein solution, isopropyl alcohol were obtained from a Chem Lab a local chemical supplier. The XRF analysis of the Kaolin shows the chemical composition of kaolin consists of following in wt %: SiO 65.9 %, Fe O 3 0.6%, CaO 0.%, Na O 0.5 %, AI O 3.6 %, TiO 0.8%, MgO 0.% and K O.8%.. Method.. Catalyst preparation This impregnation of potassium hydroxide into kaolin was performed at different mass ratio (Potassium hydroxide: Kaolin) ranging between :-:6, this was done using a reflux condenser, at 60 C for hours with continuous stirring. A muffle furnace was used to calcine the catalyst at a temperature of 00 C for 5 hours... Experimental design The experimental design chosen for this study was a Central Composite Design (CCD) that aids in investigating linear, quadratic, cubic and cross-product effects. The reaction parameters studied were the reaction temperature, reaction period, amount of catalyst and methanol to oil ratio. The latter independent parameters are illustrated in Table. This table lists the range and levels of the four independent variables studied. The CCD comprises of a two-levels of full factorial design ( = 6), eight axial points and six centre points. The value for this CCD is fixed at. The complete design matrix employed and results are given in Table. Table : Levels of transesterification process variables employed for this study Variable Coding Units levels Reaction temperature Reaction time Amount of catalyst Methanol in oil ratio x x x 3 x C hr grams wt % All the variables at zero level constitutes the centre points while the combination of each of the variables at either lowest (-) or highest (+) level with the other variables at zero level constitutes the axial points. Each response of the transesterification process was used to develop a mathematical model correlating the yield of biodiesel with the transesterification process variables studied through first order, second order, third order and interaction terms according to the following second order polynomial equation. O = i i, = i Y= β + β X + β X X + β X + β X X X + β X = ki k, i, = k where Y is the predicted biodiesel yield, X and X i represents the parameters, B o is the offset term, B is the linear effect, B i is the first order interaction effect, and B is the squared effect while B is the cubic effect. The Design Expert software was used for regression analysis of the experimental data to fit the third order polynomial equation and also for the evaluation of the statistical significance of the equation developed. i = 3 00 FORMATEX 03

3 Table : Experimental design matrix and biodiesel yield % Process variables Experimental Temperature ( C) Reaction time (min) Amount of catalyst (grams) Amount of methanol in oil (wt %) Biodiesel yield (wt %) E E E E E E E E E E E E E E E E E E E E E Biodiesel production The Waste vegetable oil (WVO) was filtered and heated at 00 C to remove solids and water respectively. The FFA was measured measure using the titration method and it was found that its value was less than %, therefore the two step alkali acid transesterification process was unnecessary: A sample was prepared at given amounts of catalysis, methanol to oil ratio, temperature and reaction shown the experimental design in Table. The catalyst was recycled three times under optimum conditions... Model fitting and statistical analysis Design expert (6.0.6) software was used as regression analysis tool to fit experimental data to the third order polynomial regression model. The evaluation of statistical significance of the model was developed...5 Characterization of fuel properties of biodiesel The biodiesel produced at optimal conditions was measured using the ASTM biodiesel standard. The following parameters were determined: Viscosity, density and flash point was determined using the ASTM D5, ASTM 98 and ASTM D93 respectively. 3. Results and discussion 3. Development of the regression model equation By using multiple regression analysis, the response obtained in Table was linked using the polynomial equation, evaluated using the Design expert software to give the above full regression model equation. The final model in terms of actual value after excluding the insignificant terms (identified using Fisher s Test) is FORMATEX 03 0

4 Y = x 9.7x 0.0x x 0.09x +.7x +.39x x x +.5x x 0.x 0.0x x 3 The negative sign in front of the terms specifies an antagonistic effect, while the positive sign indicates synergistic effect. The coefficient correlation (R ) can be used to evaluate the quality of the model. The R for Eq. ) is This suggests that 7.70 % of the total deviation in the biodiesel yield responses is clarified by the model. 8 B iodiesel yield ( mass % ) Biodiesel yield ( mass %) Methanol to oil ratio ( wt %) Time (hr) Time (hr) (a) (b) Figure : The effect of methanol to oil and reaction time on the biodiesel yield (a) response surface plot (b) two dimensional plot where methanol to oil ration is held at +.89 and wt %. 3. Effects of process variable Fig shows the effect of methanol to oil ratio and reaction times on the yield of biodiesel the amount of catalyst and reaction temperature is held constant at 3.5 g and at 75 C respectively. As seen in Fig. when high amount of methanol to oil ratio is used the biodiesel yield is low compared to when low amount of methanol to oil ratio is used. This is because there is a reverse reaction where glycerol and biodiesel are converted back to oil and methanol which causes the yield to decrease. As also depicted in Fig. 3, at long reaction period the biodiesel yield increases, this explains why heterogonous catalyst such kaolin require more time for conversion of triglyceride into fatty acid methyl esters [3]. 0 FORMATEX 03

5 (a) (b) Figure : The effect of the amount of catalyst and methanol to oil ratio on the biodiesel yield (a) response surface plot (b) two dimensional plot where methanol to oil ration is held at +.89 and wt % Biodiesel yield (mass %) Biodiesel yield ( mass %) Time (hr) Temperature ( C) Temperature ( C) (a) (b) Figure 3: The effect of reaction temperature and time on the biodiesel yield (a) response surface plot (b) two dimensional plot where the reaction time is held at and -.8 hr. Fig. shows the influence of the amount of methanol to oil ratio and the amount of catalyst on the yield of biodiesel, the reaction time and reaction temperature are held constant at hr and 75 C respectively. As seen from Fig more biodiesel is formed when less methanol is used and vice versa. When more amounts of catalysts is used the biodiesel yield decreases. High amounts of catalyst causes the formation of more soap, this reduces the yield of biodiesel. large amount of methanol to oil ratio causes a reverse transesterification reaction which leads to the formation of more oil and methanol. Fig.3 shows the variation of reaction time and temperature on the yield of biodiesel where the amount of catalyst and the amount of methanol to oil ratio area held constant at zero level. As it can be seen in Fig 3, more biodiesel is produced when the reaction period is increased. This is because at low reaction time beyond the optimum minimum FORMATEX 03 03

6 reaction time leads to incomplete reaction and cause less molecular reaction of triglyceride with methanol and thus reducing biodiesel yield. As the temperature increases the biodiesel yield decreases. This is because temperature is inversely proportional to viscosity therefore high temperature will increase biodiesel flow property but reduce reaction time between reactants. This can result in low biodiesel yield because a low mass transfer is subdominant at very high temperature [-5]. The influence of one parameter was evaluated and plotted against the yield while the other parameters where kept constant. As shown in Fig. the reaction time has a positive influence on the yield of biodiesel The reaction temperature, amount of catalyst, amount of methanol to oil ratio showed a negative influence in the following order reaction temperature, methanol in oil ratio, amount of catalyst.. It can generally be observed that the biodiesel yield increases as the reaction time increase and decreases as the reaction temperature, methanol to oil ratio and amount of catalyst is increases. This is in excellent agreement with the result in literature of biofuel. 95. Biodiesel yield (mass %) A D C B D B C A Dev iation f rom Ref erence Point Figure : Individual effect of process variables on the biodiesel yield A reaction temperature; B reaction time; C Amount of catalyst; D-methanol to oil ratio. 3.3 Fuel properties of Waste vegetable oil methyl ester compared to other oil methyl ester Important fuel properties of methyl esters produced from marula oil were determined and compared to that of atropha [5] and palm oil [6] methyl ester which is shown in Table 3. The fuel properties of bioidiesel synthesized from waste vegetable oil are within the ASTM standards of biodiesel. The density of WCO biodiesel is 8886kg/m 3 slightly higher than atropha (880 kg/m 3 ) and palm methyl ester (86. kg/m 3 ) ultimately all are within the specified limit of ( kg/m 3 ). The kinematic viscosity of WCO biodiesel (. mm s - ) at 0 C is slightly lower than atropha (. mm s - ) and palm oil (.5 mm s - ) but all meet the viscosity ASTM standard of biodiesel. The flash point of biodiesel from waste cooking oil (79 C), atropha (63 C) and palm (76 C) are within the ASTM standard. Table 3: Fuel properties of waste vegetable biodiesel compared to other biodiesel and ASTM standard Parameter WCO Jatropha Palm ASTM D675-0 ( ³ m Density at 5 ºC (kg ( ¹ s Kinematic viscosity 0 ºC (mm ² Flash point ( C) >30 0 FORMATEX 03

7 3. Reusability of kaolin heterogeneous catalyst Figure 5: An illustration of the reusability of kaolin heterogeneous catalyst Fig 5. Shows that the thermaly modified and heterogenous koalin catalyst can be recycled more than three times, this is exclleent grement with that advantages of using heterogenous catalyst in comparison to homogenenous catalyst.. Conclusion This study has shown that it was possible to heterogeous kaolin using potassium hydroxide. Results shows that it was feasible to produce biodiesel from waste cooking oil using a one step alakali catalyst transesterification process. The response surface technique was used to determine the optimal condition that can be used to produce biodiesel from waste cooking oil. The optimum conditions for producing biodiesel were: reaction temperature of 9.3 C, amount of catalyst at..08 g, reaction time at.56 hr, and amount of methanol in the oil at 8.6 wt %. The optimum yield of biodiesel was 95.06%. It was found out that that important fuel properties biodiesel produced at optimum condition met the biodiesel ASTM standard. Acknowledgement The support by KT Magongwa and MM Maloka is gratefully acknowledged in this work, together with the funds from the university lab fee. Reference [] Yi-Hsu Ju., and Shaik, R.V.. Rice bran as a potential resource for biodiesel. Journal of scientific and industrial research, 005;6: [] Edigera, V.S., Akar, SARIMA forecasting of primary energy demand by fuel in Turkey. Energy Policy.007;35: [3] Edigera, V.S., Akar, S., & Ugurlu, B., Forecasting production of fossil fuel sources in Turkey using a comparative regression and ARIMA model. Energy Policy 006; 3: [] Freedman B, Butterfield RO, Pryde EHTransesterification kinetics of soybean oil. Journal of American Oil Chemical Society.986;63: [5] Leung DYC, Guo Y. Transesterification of neat and used frying oil: optimization for biodiesel production. Fuel Process Technology,006; 87: FORMATEX 03 05

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