RAPPORT. Jeg erklærer at arbeidet er utført selvstendig og i samsvar med NTNUs eksamensreglement. Dato og underskrifter:

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1 NTNU Norwegian University of Science and Technology Faculty of Natural Sciences and Technology Department of Chemical Engineering RAPPORT Felleslab, TKP 4105 og TKP 4110 Tittel: Biodiesel production in a batch reactor Sted: Trondheim Versjon: Forfattere: Anders Leirpoll & Kasper Linnestad Veileder: Marie D. Strømsheim Utført i tiden: Kl. 8:15-13:00 Antall sider: Hovedrapp: Bilag: Abstract The reaction rate, selectivity and conversion rate of the transesterification of soybean oil (SBO) by methanol was to be studied in a stirred batch reactor. Sodium hydroxide (NaOH) was used as a catalyst. Samples were collected in intervals, centrifuged and analyzed by gas chromatography. The reaction was determined to be of second order using the integral method. Jeg erklærer at arbeidet er utført selvstendig og i samsvar med NTNUs eksamensreglement. Dato og underskrifter: Address Location Tel Sem Sælands vei 4 NO-7491 Trondheim Fax Org. no. NO

2 i Table of Contents 1 Introduction Theory Reaction Mechanism Gas chromatography Experimental Reaction Analysis Results Discussion Conclusion... 7 References... 8 List of Symbols and Abbreviations... 9 Appendix A - Kinetics... A-1 Appendix B - Calculations... B-1 Appendix C - Data... C-1

3 1 1 Introduction This experiment was carried out as a part of the felleslab for the courses TKP4105 and TKP 4110 at NTNU during fall The understanding of reaction rate, selectivity and conversion rate is important to a chemical engineer, and testing of these in the lab, using different parameters is essential in fine-tuning of reactors. The purpose of this exercise is to study a catalysts effect on reaction parameters. 2 Theory 2.1 Reaction Mechanism The most common way to produce biodiesel is the transesterification reaction of vegetable oils with low molecular weight alcohols. In Figure 1 the total reaction is shown, where a glyceride reacts with methanol to make glycerin and alkyl esters. Figure 1: The total reaction As can be seen in Figure 1, three moles of methanol is consumed for each mole of soybean oil converted, considering the reversibility of each step in the reaction mechanism, methanol is employed in excess. In this experiment we will catalyze the reaction using the hydroxide ion. Hydroxide deprotonates the alcohol, producing an alkoxide, shown in (2.1): However, this reaction could also be carried out with an acid catalyst. With an acid catalyst anhydrous conditions are not required, but they require higher temperatures since the acid catalyzed reaction is slow [1]. Thus, a base catalyzed reaction is preferred due to time limitations and safety. In Figure 2 the catalyzed reaction is shown, where the protonated alcohol performs a nucleophilic attack at the carbonyl group, making a tetrahedral intermediate, releasing the alkyl (2.1)

4 2 ester and forming the anion of the diglyceride. The catalyst is then deprotonated by the anion, reforming the hydroxide, which can then start a new catalytic cycle. Figure 2: Reaction catalyzed by hydroxide. The total reaction for a triglyceride can be built up by three smaller reversible reactions. In each step the glyceride takes up one alcohol and releases an alkyl ester. This is shown in Figure 3 for a triglyceride, but diglycerides and monoglycerides are converted by the same mechanism into alkyl esters and glycerine.

5 Figure 3: The reaction mechanism from triglyceride, via diglyceride and monoglyceride, producing glycerin and alkyl esters. The reaction is catalyzed by the hydroxide anion. 3

6 4 Industrially speaking, alkaline-catalyzed transesterifications are preferred. This is because they are faster than their acid-catalyzed counterparts, and are less corrosive to industrial equipment [2]. 2.2 Gas chromatography Gas chromatography (GC) is used for separation and detection of gasses and volatile components in mainly organic solutions. This is an analytical solution used to test the purity of the sample or the relative amount of each component of the test sample. [3] In gas chromatography we have a moving phase, usually an inert gas, and a stationary phase consisting of a polymer or glass, called column. The sample will elute at different times on the column, called the retention time of the component. Using this, the weight fraction of each component can be calculated. [3] 3 Experimental 3.1 Reaction The experiment was performed in a batch reactor, as shown in script. Soy bean oil (279.2 ml) was brought into the dry reactor. Water bath temperature (70 ) and stirring speed ( 00 rpm) was set. Methanol (70.8 ml) was disposed in an Erlenmeyer flask (500 m ) along with weighed (0.62 g) pellets of sodium hydroxide. The flask was covered with parafilm and stirred with a magnetic plate until all pellets were dissolved. When the reactor reached set-point temperature, the solution was carefully added using a funnel, while the stopwatch was started. First sample was taken after 3 minutes, then 7 samples were taken per minute, then 3 every 3 minutes and finally 2 every 5 minutes. Every sample taken had a volume of 5 ml; temperature was noted for every sample. Samples were placed into numbered centrifuge tubes cooled in an ice bath, shook carefully, and then left to settle. Tubes were centrifuged at 4000 rpm for 10 minutes. Table 1: The amount of each reactant and catalyst used in the experiment, calculated as shown in B.1 Calculations of the amount of reactants and catalyst in Appendix B - are presented. Component Amount Methanol 70.8 ml Soy bean oil ml Sodium Hydroxide 0.62 g 3.2 Analysis Each sample was taken from the upper layer and weighed (250 mg) into vials (10 ml) using a Pasteur pipette. 5 ml of IS methyl heptadecanoate in heptane solution was added using the beaker. The syringe was washed ten times with the sample, before 1 was injected into the gas chromatograph (GC from here on). GC was run according to script. Data was noted for every sample.

7 X 5 4 Results Inverse concentration of onverted SBO,, was calculated and plotted against, time, shown in Figure 4. Regression was performed in Microsoft Excel. The calculations are presented in Appendix B - Calculations /C SBO [L/mol] y = x R² = t [min] Figure 4: Plot of inverse concentration of onverted SBO, in liters per mol versus time, in minutes. The data for the plot is given in Table 7 in Appendix C - Data. Conversion,, was calculated and plotted against, shown in Figure 5. An example calculation is shown in Appendix B - Calculations t [min] Figure 5: Conversion, Appendix C - Data., plotted against time, in minutes. The data for the plot is given in Table 8 in The selectivity for each component was calculated in Appendix B - Calculations. A plot of the selectivities against time is displayed in

8 Selectivity percentage 6 Figure % 50.00% 40.00% 30.00% 20.00% 10.00% C16:0 - Palmitic acid C18:0 - Stearic acid C18:1 - Oleic acid C18:2 - Linoleic acid C18:3 - Linolenic acid 0.00% t [min] Figure 6: Selectivity percentage plotted against time,, for each component. The data for the plot is given in Table 9 in Appendix C - Data. 5 Discussion From Figure 4 it can be seen that linear regression does not fit the 1 versus plot perfectly. With a coefficient of determination of 0.56 the linearity of the trend is rather weak. The coefficient of determination is a measure of how god a model, e.g. a regression, fits a sample set. If the coefficient of determination is close to one, the model is considered to be good. In this case, the coefficient of determination is considerably lower than one, subsequently the model is not a good fit to the samples collected [4]. This is most likely due to ertainties in the composition obtained from the GC. For instance, 1 is not a strict increasing ftion, which is a clear indication that there are large ertainties in the data set. However, the reaction is expected to be of second order because each step is an elementary reaction in which two molecules react with each other [5]. However, this does not account for the reversibility of the reactions, but due to the excess of methanol the reversibility of each step is negligible and the kinetics of the overall reaction coincide well with that of a second order [6]. From Figure 5 it can be seen that the conversion rate of SBO increased with time, with some deviations. The conversion is not a strict increasing ftion, for the same reasons as 1 is not. Although varying grades of conversion were calculated, the main trend was increasing, and then leveling off to some extent. This is expected, as more SBO will react to BIOD over time. The deviations from an increasing trend in conversion can also come from temperature variance or that the ertainties in the data, as discussed above. Reaction rates are heavily affected by temperature, which might explain the variance, and the temperature was observed to be changing slightly throughout the experiment.

9 7 The catalyst does not show any preference for any of the fatty acid methyl esters (FAME), the selectivity is constants for the duration of the experiment, as can be seen in Figure 6. Furthermore, the selectivity is the same as the original composition of the soybean oil [7], even when the differences in molecular weight has been accounted for as can be seen in Table 6, there are some slight deviations though, but they are smaller than the ertainties of the data. 6 Conclusion The reaction rate, selectivity and conversion rate of the transesterification of soybean oil (SBO) by methanol was to be studied in a stirred batch reactor. Sodium hydroxide (NaOH) was used as a catalyst. Samples were collected in intervals, centrifuged and analyzed by gas chromatography. The reaction order could not be precisely calculated due to large ertainties in the data set, but it was expected to be of second order.

10 8 References [1] Edgar Lotero et al., "Synthesis of Biodiesel via Acid Catalysis," Industrial & Engineering Chemistry Research, vol. XLIV, no. 14, pp , January [Online]. pdf [2] "Biodiesel production in a batch reactor script," Department of Chemical Engineering, Norwegian University of Technology and Science, Trondheim,. [3] Raymond P. W. Scott, "Chrom-Ed Book Series," in Gas Chromatography.: Library for Science, LLC, 2003, vol. II. [4] Ronald E. Walpole, Raymond H. Myers, Sharon L. Myers, and Keying Ye, Probability & Statistics for Engineers & Scientists, 9th ed., Diedre Lynch, Ed. Boston: Pearson Education, Inc., [5] Timothy Lawrence Turner, "Modeling and Simulation of Reaction Kinetics for Biodiesel Production," North Carolina State University, Raleigh, Master Thesis [Online]. [6] H. Noureddini and D. Zhu, "Kinetics of Transesterification of Soybean Oil," Journal of the American Oil Chemists' Society, vol. LXXIV, no. 11, pp , [Online]. [7] Earl G. Hammond, Lawrence A. Johnson, Caiping Su, Tong Wang, and Pamela J. White, ailey s Industrial Oil and Fat Products, 6th ed., Fereidoon Shahidi, Ed. Ames, Iowa: John Wiley & Sons, Inc., 2005, vol. VI. [8] H. Scott Fogler, Elements of Chemical Reaction Engineering, 4th ed. Westford, Massachusetts: Pearson Education Ltd., 2009.

11 9 List of Symbols and Abbreviations Symbol Unit Description BIOD Biodiesel mol Concentration of component mol Concentration of component mol Start concentration of component FAME Fatty acid methyl esters GC Gas chromatography IS Internal standard s Reaction rate constant mol Molecular weight of component Mass of component mol The number of moles of component Coefficient of determination rpm rounds/min Rounds per minute mol s Reaction rate of component SBO Soybean oil K Temperature s Time Volume of component Total volume g Total mass wt Weight percentage of component Conversion Mole fraction of component cm Density of component

12 A-1 Appendix A - Kinetics To determine the reaction rate constant, the following equation is used [8] (A.1) Where is concentration of component, is time and is the reaction rate of component. If the reaction is of second order Integrating from at 0, to at d d 1 d 1 1 d (A.2) (A.3) Plotting 1 as a ftion of time gives a linear curve with slope.

13 B-1 Appendix B - Calculations B.1 Calculations of the amount of reactants and catalyst Volume,, equals mass,, divided by density,, Mass can be substituted by the number of moles,, times molecular weight,, (B.1) (B.2) Then the total volume,, can be found. It is assumed that the volume of NaOH is negligible and that all excess volumes are zero. The total volume is then the sum of the volume of each component; here methanol (MeOH from here on) and soy bean oil (SBO from here on). Using this and (B.2) yields, e (B.3) The relationship between number of moles of MeOH, and number of moles of SBO, is, If the equation for total volume is rearranged for e, it can be written as, e This gives the number of moles of methanol, inserting this into (B.2) gives the volume of methanol needed for the reaction, e e tot (B.4) (B.5) (B.6) The volume of soy bean oil is then given by, The total mass of the solution By applying (B.1), (B.8) can be rewritten to,, if we neglect the mass of NaOH, is e (B.7) (B.8) e e (B.9) The mass of NaOH needed for the experiment is given as a weight percentage, and thus can be calculated via, a a (B.10) The results of these calculations are summarized in Table 1.

14 B-2 B.2 Calculation of the mass of onverted soybean oil, biodiesel and the internal standard in each sample The mass of the methyl heptadecanoate (internal standard IS) can be calculated from, (B.11) where is the mass of the internal standard; is the concentration of the internal standard in the solution and is the volume of the solution for each sample. The weight percentage of the methyl heptadecanoate internal standard in the sample injected in the gas chromatograph (GC) is then, wt (B.12) where is the mass of each sample extracted from the reactor. Inserting the values given in the script in (B.12) yields, wt 1 The GC analysis gives the mass percentage of each component; however the weight percentages of the internal standard do not coincide with the ones calculated from (B.12). To account for this a scaling factor, is introduced, with calculations shown for sample #1: wt wt wt 1 wt (B.13) Where wt is the weight percentage of the IS given by the GC, wt is the weight percentage of BIOD given by the GC. The weight percentages of the IS and BIOD from the GC is displayed in Table 2 together with. Table 2: The weight percentages of BIOD and IS from the GC analysis are displayed together with the scaling factor. Sample # wt wt % % % % % % % % % % % % % % % % % % % % % % % % 7.22 The real values for the weight percentages of the BIOD can then be calculated by rearranging (B.13): wt wt (B.14) Where wt is the weight percentage of the IS found by (B.12). The weight percentage of the onverted soybean oil ( ) can then be calculated, and an example is shown for sample #1:

15 B-3 wt 100 wt wt 100 wt 1 wt Table 3 lists the values for the weight percentages calculated by (B.12), (B.14) and (B.15) together with the sample mass. Table 3: The weight percentage of the internal standard in each sample, calculated utilizing (B.12), and the weight percentages of the biodiesel (BIOD) and the onverted soybean oil ( ). Sample # Sample mass wt wt wt % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % % (B.15) B.3 Calculation of the conversion The mass of and BIOD in each sample is given by: The number of moles of and BIOD in each sample is: The volume of the sample (without IS) can be calculated by wt sample (B.16) wt sample (B.17) sample The concentration of in each sample is, with an example shown for sample #1: (B.18) sample wt sample In a batch reactor with constant volume, the concentration of a reactant is given by [8]: 0 1 (B.19) (1 ) (B.20)

16 B-4 Where is the concentration of specie ; is the start concentration of specie and is the conversion. Rearranged with respect to the conversion, with an example shown for sample #1: (B.21) The concentration of onverted soybean oil and the conversion is presented in Table 4. Table 4: The time, concentration of onverted SBO, and conversion, are shown for each sample Sample # Time [min] [mol/l] X B.4 Calculation of the selectivity of each fatty acid methyl ester The weight percentage of each FAME is given by the GC analysis and then scaled with a scaling constant as in (B.14). The number of moles of each FAME can then be calculated via (B.17). The selectivity is then given as [2], with an example shown for sample #1 for C16:0: 11 1 (B.22) The selectivity of each FAME is listed in Table 5. Table 5: Selectivity of the different components is shown for each sample. Sample # Selectivity C16:0 Selectivity C:18:0 Selectivity C:18:1 Selectivity C:18:2 Selectivity C:18: % 6.45 % % % 7.08 % % 5.19 % % % 6.92 % % 4.07 % % % 7.30 % % 4.02 % % % 7.09 % % 4.17 % % % 6.89 % % 4.16 % % % 7.09 % % 3.86 % % % 6.94 % % 3.88 % % % 7.25 % % 4.17 % % % 7.05 % % 4.18 % % % 7.08 % % 4.19 % % % 6.89 %

17 B-5 Sample # Selectivity C16:0 Selectivity C:18:0 Selectivity C:18:1 Selectivity C:18:2 Selectivity C:18: % 4.19 % % % 7.04 % The molar percentages of each component in SBO are shown in Table 6. Table 6: Molar percentages of each component in SBO. Palmitic C16:0 Stearic C18:0 Oleic C18:1 Linoleic C18:2 Linolenic C18: Wt% % 4.09 % % % 7.23 % mol% % 4.03 % % % 7.27 %

18 C-1 Appendix C - Data The data for Figure 4 are given in Table 7, is the time and onverted soybean oil. is the concentration of Table 7: Data for Figure 4. min [ ] The data for Figure 5 is given in Table 8, is the time and is the conversion of soybean oil. Table 8: Data for Figure 5. min The data for Figure 6 is given in Table 9, is the time and is the selectivity of FAME. Table 9: Data for Figure min Palmitic Stearic Oleic Linoleic Linolenic % 6.45 % % % 7.08 %

19 C min Palmitic Stearic Oleic Linoleic Linolenic % 5.19 % % % 6.92 % % 4.07 % % % 7.30 % % 4.02 % % % 7.09 % % 4.17 % % % 6.89 % % 4.16 % % % 7.09 % % 3.86 % % % 6.94 % % 3.88 % % % 7.25 % % 4.17 % % % 7.05 % % 4.18 % % % 7.08 % % 4.19 % % % 6.89 % % 4.19 % % % 7.04 %