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Evaluation of the batch distillation process in the ethanol production
Ian David Lockhart Bogle and Michael Fairweather (Editors), Proceedings of the 22nd European Symposium on Computer Aided Process Engineering, 17 - 20 June 2012, London. © 2012 Elsevier B.V. All rights reserved.
Evaluation of the batch distillation process in the ethanol production a
Alvarez M.E.T., a Moraes E.B., a,b Rodrigues J.C., a Bonon A.J., a Wolf-Maciel M.R.
a
Separation Process Development Laboratory, School of Chemical Engineering, State University of Campinas-UNICAMP, Av. Albert Einsteins, 500 Campinas-SP 13083-852, Brazil b Federal University of ABC – UFABC, Av. dos Estados, 5001 – Santo André-SP 09210580, Brazil
Abstract Experimental data and simulations in Aspen Plus® for the batch distillation process were obtained from an ethanol/water mixture. The simulation was carried out in order to verify the effectiveness of the calculations for the batch distillation process for recovering ethanol, using a plate column. The experimental data were taken from a packed batch distillation column. The separation of ethanol/water mixture was studied at different reflux ratios. The ethanol was quantified through a gas chromatography analyses. The simulation and the experimental data were performed considering the ethanol concentration in the wine that comes from the sugarcane fermentation. It was verified that the higher ethanol concentration was obtained in one hour of distillation and the accumulate ethanol concentration was above to 80% (mole) when operated at constant reflux. So, it is possible to obtain high yields and concentrations of ethanol in a short time. Keywords: ethanol, distillation, experimental data, simulation.
1. Introduction In the 1970s, the Brazilian government started a program for ethanol production from sugarcane in order to effectively to replace gasoline in a large scale. For a time, this program was dropped, but due to the production instability of the world´s largest oil producers and energy concerns, the search for alternative sources of energy, preferentially from renewable sources, has again sparked interest in this subject (Dias, 2011; Junqueira et al., 2009). The fermentation processes employed in the Brazilian ethanol industry require low substract concentration and produce wine of low ethanol content (around 7.0 to 8.5 w/w).When the intention is to use ethanol as a fuel, ethanol concentration must be of at least 92.5 a 93.8 w/w. In the batch distillation column, the feed is loaded to the distillation flask at the beginning of the process. It is then heated to its boiling point, and the products are withdrawn sequentially from the column’s top, according to its boiling point. (Demicoli and Stichlmair, 2004). Batch distillation has been used to evaluate the effect of the recycling of foreshots and feints in the grappa distillation (Porto et al. 2010) and in the separation of a complex azeotropic mixture, comparing two methods of separation, showing that the columns hold-ups have influence on the component separation (Watson et al. 1995). On the other hand, the use of the Aspen Plus Commercial Simulator can simulate the batch distillation in order to perform the process as well as to know the operating conditions. In this work, a batch distillation column was used to obtain hydrated ethanol. The feed was composed of ethanol/water (around 7.0 w/w of ethanol). In simulations were considered a plate
Evaluation of the batch distillation process in the ethanol production
633
distillation column and in the experiments, a packed column was used. Finally, the results were compared, in order to evaluate the ethanol recovery.
2. Batch Distillation column 2.1. Details of the batch distillation column A batch distillation column, model Autodest 800AC of Fischer Technology with a capacity of 80 Lt was used and conditioned for ethanol distillation. The packed column is filled with Propak 316 and equipped with a silvered vacuum mantle. Distillation flask and the packed column have an external heat mantle and the temperature is controlled by a Pt 100. The vapour temperature at the top of the column is also verified by a Pt 100. In the main condenser, a cryostat was used with a capacity of 360 Kcal at 0°C. All system is controlled through Indusoft Web studioTM v6.2 supervisory installed in PC that allows data acquisition of the batch column distillation. The batch column distillation, Autodest 800AC, is equivalent to a column of 15 theoretical plates (ASTM D 2892). 2.2. Distillation In order to evaluate the ethanol recovery by batch distillation of wine coming from the fermentation of sugarcane, a binary mixture of ethanol/water was considered as the feed with approximately 7% (w/w) of ethanol concentration, produced in Brazilian alcohol refineries. The distillation was carried out at atmospheric pressure and operating temperatures have been adjusted after different experiments. The distillate flask and column temperatures were 170°C and 100°C, respectively. The temperature of the cryostat condenser was maintained at 0°C. When the condensation starts at the top of the column, the distillate was withdrawn after 15 minutes of stabilization of the system and the temperature of the initial vapor was 69°C. In each 5 minutes, samples were collected for the following reflux ratio (L/D): 0.75, 1.5, 2.5, 3.5 and 4.5. The ethanol content in the collected samples was subsequently quantified by gas chromatography method.
3. Experimental 3.1. Materials The reagents, n-propanol (99.1% - Fisher Scientific) HPLC grade, ethanol (99.9% Merck) analytical grade were used for analytical methods. 3.2. Analytical Techniques and Procedure Ethanol was determined by gas chromatography using an Agilent Technologies, 6850A model with BP-225 capillary column (SGE) (50% cianopropifenil –PDMS; 25.0m × 3.2×10-4m × 2.5×10-7m) and equipped with a flame ionization detector (FID). Hydrogen was used as carried gas and synthetic air to burn the flame. The flow rate of nitrogen was 1.6×10-3 L/min while the flow rate of synthetic air was 450.0×10-3 L/min and the column temperature was 40°C for 2.5 min. A calibration curve was made with five different points (5, 10, 15, 20 and 25% v/v of ethanol, with 5% n-propanol as internal standard), all analyses were carried out in duplicate. 1×10-6 L of samples were transferred to 10.0×10-3 L of volumetric flask, 0.3×10-3 L of n-propanol was added as internal standard, using ultrapure water as solvent. 1.0×10-6 L of samples was injected into a chromatograph and all measurements were made also in duplicate.
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Alvarez et al.
4. Simulations Aspen Plus® is one of the most used commercial simulator in the world, because its complete package of thermodynamics properties and estimative methods. So, Aspen Plus® was used to simulate the batch distillation process. Simulations in this work were made considering a plate column, equivalent to the packed column of the Fischer Technology, due the absence of the identical column in Aspen Plus database. Ethanol recovery was, then, evaluated using a batch distillation column, considering a plate column. The feed was composed of ethanol/water (7.02 %w/w of ethanol). The feed temperature was maintained at 170°C. The simulation was carried out at atmospheric pressure and the feed charged was 50 Kg. In setup of the block was considered 10 minutes as feed time in initial charge. The stop specification was defined as 3.4 hours of distillation. Obtained results were compared with experimental data obtained from a batch packed distillation column.
5. Results and discussion
Ethanol composition (% w/w)
Experimental data results for packed batch distillation at different reflux ratios are presented in Fig. 1. It was observed that the ethanol composition was between 82 to 92 % (w/w) in the first 80 minutes of distillation. After this time, there was a sharp decline in ethanol composition, reaching values close to 65 % (w/w). It was also verified that the reflux ratio did not influence when the purpose is to reach high ethanol composition, because the conposition profile follows the same tendency for all reflux ratios studied. 94 92 90 88 86 84 82 80 78 76 74 72 70 68 66 64 62
Reflux ratio 0.75 1.5 2.5 3.5 4.5
0
20
40
60
80
100
120
140
Distillation time (min) Figure 1. Variation of the ethanol composition in the Distillate vs time at different reflux ratios
A random value of reflux ratio was assumed for study and comparison of the performance between a packed column and a plate column. Experimental data were collected using a packed column at a constant reflux ratio of 2.5. The distillate fractions were collected every 18 minutes and, then, analyzed the ethanol composition in the mixture by gas chromatography. The results are shown in Fig.2. Simultaneously, considering the operating conditions of the experimental data, a simulation in Aspen Plus was performed. In this case, taking into account a column of 15 theoretical plates, equivalent to the packed column. Fig.2,
Evaluation of the batch distillation process in the ethanol production
635
the intention is to show the variation in ethanol composition as a function of time for the simulated data and experimental data from a plate column and from a packed column, respectively. Figure 2 shows the same ethanol composition profile in the distillate, ie, when time increases, the ethanol composition decreases. Moreover, it is possible to observe that in the first 40 minutes of operation, both columns have the same performance, ie, the ethanol composition remains the same in both cases. However, after this time it is verified that the ethanol composition in the distillate tends to decrease more rapidly in the case of packed column than if working with a plate column. 90
Ethanol composition (% mole)
85 80 75 70 65 60 55 50 45 40 35 0
20
40
60
80 100 120 140 160 180 200 220
Distillation time (min) Figure 2. Variation of the ethanol composition in the Distillate vs time (reflux = 2.5; ż – experimental data-packed column, Ƒ – simulation – plate column)
Table 1 shows the mass flow rate and the mixture composition of the steams in the batch distillation column. The simulation results show that at the end of 204 min of operation and at a reflux ratio of 2.5, ethanol is obtained at a concentration of 69.5% (mole), however, it is observed that only 7.18 kg were recovered. Table 1. Stream compositions and Flows of the component in a plate column destillation Component Mass Flow Rate Kg/hr Ethanol Water Mole Fraction Ethanol Water Mass Fraction Ethanol Water
Feed
Reboiler
Distillate
21.050 278.950
13.870 277.719
7.180 1.231
0.029 0.971
0.019 0.981
0.695 0.305
0.070 0.930
0.048 0.952
0.854 0.146
The results of accumulated composition and the percentage of ethanol recovery are presented in Table 2. It can be verified that in the first hour of operation, the
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Alvarez et al.
accumulated ethanol concentration is around 82% (mole), which can be concluded that at this time interval both columns have the same performance and purpose in a final ethanol concentration. On the other hand, in the simulation of the plate column, only 34.1% of ethanol is recovered at an accumulated concentration of 69.61% (mole), which can result in a higher energy consumption and operating costs in a given operation time if compared to a recovery of 51.81% (mole) in a packed column. Although the accumulated concentration in a packed column is a little smaller, the recovery is 51.81%, just over 50% recovered when compared with a plate column. Table 2. Ethanol composition and recovery in the distillation process Distillation Packed column 60 min 204 min Plate column 60 min 204 min
Acumulated ethanol (% mole)
Recovery (%)
82.33 58.63
51.81
82.59 69.61
34.10
6. Conclusions Experimental data and simulated data were obtained and compared in the batch distillation process using a packed column and a plate column, respectively. It was developed an analysis method by gas chromatography using an internal standard to quantify ethanol in the samples, while water was calculated by difference. The results showed that operating in a packed column, more than 50% of ethanol is recovered when compared with a plate column. Therefore, if the option is to operate a plate column, it can require more time to achieve a higher yield and, therefore, excessive energy consumption is required. The batch distillation with a packed column can be a good alternative when the interest is to get a greater ethanol recovery in a shorter time, regardless of accumulated ethanol concentration.
Acknowledgements The authors are grateful to CNPq and FAPESP for the financial support.
References American Society for Testing Material, ASTM D 2892, Standard test method for distillation of crude petroleum (15-theoretical plate column), West Conshohocken, (Pennsylvania): ASTM International, 2005. 32p. Demicoli, D., Stichlmair, J., 2004. Computers Chem. Engng. 28, 643. Dias, M.O.S., 2011. Desenvolvimento e otimização de processos de produção de etanol de primeira e segunda geração e eletricidade a partir da cana-de-açucar, D Sc. Thesis, FEQ/Unicamp, Campinas, (in portuguese). Junqueira, T.L., Dias, M.O.S., Maciel, M.R.W., Filho, R.M., Rosell, C.E.V., Atala, D.I.P. 2009. Computer Aided Chem. Engng. 26, 827. Porto, C., Natolino, A., Corti, D. 2010. Food Sci. Technol. 45, 271. Watson, S., Julia, J., Macchietto, S., 1995. Computers Chem. Engng. 19, S589.
Evaluation of the batch distillation process in the ethanol production a
Alvarez M.E.T., a Moraes E.B., a,b Rodrigues J.C., a Bonon A.J., a Wolf-Maciel M.R.
a
Separation Process Development Laboratory, School of Chemical Engineering, State University of Campinas-UNICAMP, Av. Albert Einsteins, 500 Campinas-SP 13083-852, Brazil b Federal University of ABC – UFABC, Av. dos Estados, 5001 – Santo André-SP 09210580, Brazil
Abstract Experimental data and simulations in Aspen Plus® for the batch distillation process were obtained from an ethanol/water mixture. The simulation was carried out in order to verify the effectiveness of the calculations for the batch distillation process for recovering ethanol, using a plate column. The experimental data were taken from a packed batch distillation column. The separation of ethanol/water mixture was studied at different reflux ratios. The ethanol was quantified through a gas chromatography analyses. The simulation and the experimental data were performed considering the ethanol concentration in the wine that comes from the sugarcane fermentation. It was verified that the higher ethanol concentration was obtained in one hour of distillation and the accumulate ethanol concentration was above to 80% (mole) when operated at constant reflux. So, it is possible to obtain high yields and concentrations of ethanol in a short time. Keywords: ethanol, distillation, experimental data, simulation.
1. Introduction In the 1970s, the Brazilian government started a program for ethanol production from sugarcane in order to effectively to replace gasoline in a large scale. For a time, this program was dropped, but due to the production instability of the world´s largest oil producers and energy concerns, the search for alternative sources of energy, preferentially from renewable sources, has again sparked interest in this subject (Dias, 2011; Junqueira et al., 2009). The fermentation processes employed in the Brazilian ethanol industry require low substract concentration and produce wine of low ethanol content (around 7.0 to 8.5 w/w).When the intention is to use ethanol as a fuel, ethanol concentration must be of at least 92.5 a 93.8 w/w. In the batch distillation column, the feed is loaded to the distillation flask at the beginning of the process. It is then heated to its boiling point, and the products are withdrawn sequentially from the column’s top, according to its boiling point. (Demicoli and Stichlmair, 2004). Batch distillation has been used to evaluate the effect of the recycling of foreshots and feints in the grappa distillation (Porto et al. 2010) and in the separation of a complex azeotropic mixture, comparing two methods of separation, showing that the columns hold-ups have influence on the component separation (Watson et al. 1995). On the other hand, the use of the Aspen Plus Commercial Simulator can simulate the batch distillation in order to perform the process as well as to know the operating conditions. In this work, a batch distillation column was used to obtain hydrated ethanol. The feed was composed of ethanol/water (around 7.0 w/w of ethanol). In simulations were considered a plate
Evaluation of the batch distillation process in the ethanol production
633
distillation column and in the experiments, a packed column was used. Finally, the results were compared, in order to evaluate the ethanol recovery.
2. Batch Distillation column 2.1. Details of the batch distillation column A batch distillation column, model Autodest 800AC of Fischer Technology with a capacity of 80 Lt was used and conditioned for ethanol distillation. The packed column is filled with Propak 316 and equipped with a silvered vacuum mantle. Distillation flask and the packed column have an external heat mantle and the temperature is controlled by a Pt 100. The vapour temperature at the top of the column is also verified by a Pt 100. In the main condenser, a cryostat was used with a capacity of 360 Kcal at 0°C. All system is controlled through Indusoft Web studioTM v6.2 supervisory installed in PC that allows data acquisition of the batch column distillation. The batch column distillation, Autodest 800AC, is equivalent to a column of 15 theoretical plates (ASTM D 2892). 2.2. Distillation In order to evaluate the ethanol recovery by batch distillation of wine coming from the fermentation of sugarcane, a binary mixture of ethanol/water was considered as the feed with approximately 7% (w/w) of ethanol concentration, produced in Brazilian alcohol refineries. The distillation was carried out at atmospheric pressure and operating temperatures have been adjusted after different experiments. The distillate flask and column temperatures were 170°C and 100°C, respectively. The temperature of the cryostat condenser was maintained at 0°C. When the condensation starts at the top of the column, the distillate was withdrawn after 15 minutes of stabilization of the system and the temperature of the initial vapor was 69°C. In each 5 minutes, samples were collected for the following reflux ratio (L/D): 0.75, 1.5, 2.5, 3.5 and 4.5. The ethanol content in the collected samples was subsequently quantified by gas chromatography method.
3. Experimental 3.1. Materials The reagents, n-propanol (99.1% - Fisher Scientific) HPLC grade, ethanol (99.9% Merck) analytical grade were used for analytical methods. 3.2. Analytical Techniques and Procedure Ethanol was determined by gas chromatography using an Agilent Technologies, 6850A model with BP-225 capillary column (SGE) (50% cianopropifenil –PDMS; 25.0m × 3.2×10-4m × 2.5×10-7m) and equipped with a flame ionization detector (FID). Hydrogen was used as carried gas and synthetic air to burn the flame. The flow rate of nitrogen was 1.6×10-3 L/min while the flow rate of synthetic air was 450.0×10-3 L/min and the column temperature was 40°C for 2.5 min. A calibration curve was made with five different points (5, 10, 15, 20 and 25% v/v of ethanol, with 5% n-propanol as internal standard), all analyses were carried out in duplicate. 1×10-6 L of samples were transferred to 10.0×10-3 L of volumetric flask, 0.3×10-3 L of n-propanol was added as internal standard, using ultrapure water as solvent. 1.0×10-6 L of samples was injected into a chromatograph and all measurements were made also in duplicate.
634
Alvarez et al.
4. Simulations Aspen Plus® is one of the most used commercial simulator in the world, because its complete package of thermodynamics properties and estimative methods. So, Aspen Plus® was used to simulate the batch distillation process. Simulations in this work were made considering a plate column, equivalent to the packed column of the Fischer Technology, due the absence of the identical column in Aspen Plus database. Ethanol recovery was, then, evaluated using a batch distillation column, considering a plate column. The feed was composed of ethanol/water (7.02 %w/w of ethanol). The feed temperature was maintained at 170°C. The simulation was carried out at atmospheric pressure and the feed charged was 50 Kg. In setup of the block was considered 10 minutes as feed time in initial charge. The stop specification was defined as 3.4 hours of distillation. Obtained results were compared with experimental data obtained from a batch packed distillation column.
5. Results and discussion
Ethanol composition (% w/w)
Experimental data results for packed batch distillation at different reflux ratios are presented in Fig. 1. It was observed that the ethanol composition was between 82 to 92 % (w/w) in the first 80 minutes of distillation. After this time, there was a sharp decline in ethanol composition, reaching values close to 65 % (w/w). It was also verified that the reflux ratio did not influence when the purpose is to reach high ethanol composition, because the conposition profile follows the same tendency for all reflux ratios studied. 94 92 90 88 86 84 82 80 78 76 74 72 70 68 66 64 62
Reflux ratio 0.75 1.5 2.5 3.5 4.5
0
20
40
60
80
100
120
140
Distillation time (min) Figure 1. Variation of the ethanol composition in the Distillate vs time at different reflux ratios
A random value of reflux ratio was assumed for study and comparison of the performance between a packed column and a plate column. Experimental data were collected using a packed column at a constant reflux ratio of 2.5. The distillate fractions were collected every 18 minutes and, then, analyzed the ethanol composition in the mixture by gas chromatography. The results are shown in Fig.2. Simultaneously, considering the operating conditions of the experimental data, a simulation in Aspen Plus was performed. In this case, taking into account a column of 15 theoretical plates, equivalent to the packed column. Fig.2,
Evaluation of the batch distillation process in the ethanol production
635
the intention is to show the variation in ethanol composition as a function of time for the simulated data and experimental data from a plate column and from a packed column, respectively. Figure 2 shows the same ethanol composition profile in the distillate, ie, when time increases, the ethanol composition decreases. Moreover, it is possible to observe that in the first 40 minutes of operation, both columns have the same performance, ie, the ethanol composition remains the same in both cases. However, after this time it is verified that the ethanol composition in the distillate tends to decrease more rapidly in the case of packed column than if working with a plate column. 90
Ethanol composition (% mole)
85 80 75 70 65 60 55 50 45 40 35 0
20
40
60
80 100 120 140 160 180 200 220
Distillation time (min) Figure 2. Variation of the ethanol composition in the Distillate vs time (reflux = 2.5; ż – experimental data-packed column, Ƒ – simulation – plate column)
Table 1 shows the mass flow rate and the mixture composition of the steams in the batch distillation column. The simulation results show that at the end of 204 min of operation and at a reflux ratio of 2.5, ethanol is obtained at a concentration of 69.5% (mole), however, it is observed that only 7.18 kg were recovered. Table 1. Stream compositions and Flows of the component in a plate column destillation Component Mass Flow Rate Kg/hr Ethanol Water Mole Fraction Ethanol Water Mass Fraction Ethanol Water
Feed
Reboiler
Distillate
21.050 278.950
13.870 277.719
7.180 1.231
0.029 0.971
0.019 0.981
0.695 0.305
0.070 0.930
0.048 0.952
0.854 0.146
The results of accumulated composition and the percentage of ethanol recovery are presented in Table 2. It can be verified that in the first hour of operation, the
636
Alvarez et al.
accumulated ethanol concentration is around 82% (mole), which can be concluded that at this time interval both columns have the same performance and purpose in a final ethanol concentration. On the other hand, in the simulation of the plate column, only 34.1% of ethanol is recovered at an accumulated concentration of 69.61% (mole), which can result in a higher energy consumption and operating costs in a given operation time if compared to a recovery of 51.81% (mole) in a packed column. Although the accumulated concentration in a packed column is a little smaller, the recovery is 51.81%, just over 50% recovered when compared with a plate column. Table 2. Ethanol composition and recovery in the distillation process Distillation Packed column 60 min 204 min Plate column 60 min 204 min
Acumulated ethanol (% mole)
Recovery (%)
82.33 58.63
51.81
82.59 69.61
34.10
6. Conclusions Experimental data and simulated data were obtained and compared in the batch distillation process using a packed column and a plate column, respectively. It was developed an analysis method by gas chromatography using an internal standard to quantify ethanol in the samples, while water was calculated by difference. The results showed that operating in a packed column, more than 50% of ethanol is recovered when compared with a plate column. Therefore, if the option is to operate a plate column, it can require more time to achieve a higher yield and, therefore, excessive energy consumption is required. The batch distillation with a packed column can be a good alternative when the interest is to get a greater ethanol recovery in a shorter time, regardless of accumulated ethanol concentration.
Acknowledgements The authors are grateful to CNPq and FAPESP for the financial support.
References American Society for Testing Material, ASTM D 2892, Standard test method for distillation of crude petroleum (15-theoretical plate column), West Conshohocken, (Pennsylvania): ASTM International, 2005. 32p. Demicoli, D., Stichlmair, J., 2004. Computers Chem. Engng. 28, 643. Dias, M.O.S., 2011. Desenvolvimento e otimização de processos de produção de etanol de primeira e segunda geração e eletricidade a partir da cana-de-açucar, D Sc. Thesis, FEQ/Unicamp, Campinas, (in portuguese). Junqueira, T.L., Dias, M.O.S., Maciel, M.R.W., Filho, R.M., Rosell, C.E.V., Atala, D.I.P. 2009. Computer Aided Chem. Engng. 26, 827. Porto, C., Natolino, A., Corti, D. 2010. Food Sci. Technol. 45, 271. Watson, S., Julia, J., Macchietto, S., 1995. Computers Chem. Engng. 19, S589.