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Simulation and analysis of pressure swing adsorption: ethanol drying process by the electrical analogue
Separation and Purification Technology 31 (2003) 31 /35 www.elsevier.com/locate/seppur
Simulation and analysis of pressure swing adsorption: ethanol drying process by the electrical analogue Jianyu Guan a,*, Xijun Hu b a
b
Research Institute of Chemical Engineering, South China University of Technology, Guangzhou 510640, China Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
Abstract One column pressure swing adsorption (PSA) for dehydration of mixture of ethanol 93.54% and water 6.46% (wt) was simulated numerically by the electrical analogue model at feed pressure 2.0 /5.0 bar, operating temperature 120 / 150 8C, and vacuum desorption. Increasing feed pressure may increase recovery and productivity. An anisotropic valve connecting the column entrance with the product tank may improve the operating results to obtain 99.9% ethanol at feed pressure 3.5 bar. Vacuum desorption may raise product purity and recovery to obtain 99.9 ethanol and 60% recovery at feed pressure 2.0 bar and blowdown to 0.4 bar. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Adsorption; Pressure swing adsorption; Ethanol; Water; Azeotrope
1. Introduction Anhydrous ethanol is widely used in industries, such as organic syntheses, painting, medicine, cosmetics, perfume, etc. Mixing anhydrous ethanol and petrol can form a steady mixture, called gasohol, used as motor car fuel. Anhydrous ethanol may be used as an important oxygenic additive in lead-free petrol [1]. However, 95.57 ethanol and 4.43% (wt) water will form an azeotrope at 78.15 8C and 1.013 bar. Traditional distillation to obtain anhydrous ethanol is a high energetic process. Azeotropic distillation, extractive distillation and salt rectification are the most
* Corresponding author. E-mail address: [email protected] (J. Guan).
important processes [1]. Adsorption as a low energy consumption process has been attracted more attention. The adsorption equilibrium and kinetics of ethanol/water mixture on molecular sieve, such as 3A, 4A, NaX, NaY, etc. have been studied both in liquid phase [2,3] and vapor phase ([4 /8]). Rao and Sircar [9] reported their concentration swing adsorption for production of motor fuel grade alcohol. But less paper involves pressure swing adsorption (PSA) for ethanol drying. PSA is widely used in separation and purification of gas mixtures, which is mainly because of easy and quick desorption of the adsorbent only by depressurization. In contrast, for the separation and purification of liquid phase, the adsorbent is desorbed usually by solvent rinse or heating. Solvent rinse requires a suitable solvent and further separation and recovery of the solvent
1383-5866/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 0 2 ) 0 0 1 5 1 - X
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J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
after the rinse. And the method of heating requires long operating period of heating for desorption and then cooling for adsorption, which lowers the productivity of the adsorbent beds. Heat energy is also required to evaporate the liquid remaining in the void of the beds and raise the temperature of the adsorbent and the beds. In the present article, PSA process for ethanol drying will be explored with the electrical analogue simulation. Many mathematical models for simulating PSA have been developed in last 30 years [10]. Most of the models are constructed by partial differential equations based on the assumption of continuity, and it is assumed ordinarily that pressure drop for fluid flowing through pipelines and the packed bed might be neglectable and the boundary conditions might be simplified. The electrical analogue model [11] looks particular, which decomposes packed beds, storage tanks, valves and pipelines to resistors, capacitors and inductors. Mass and momentum transfer processes are equivalent to electricity acting on its elements. A set of ordinary differential equations (ODE) is set up to describe a whole PSA system. The entrances of adsorbent column are connected with the relative electrical elements, in which BC needs not be paid any attention to. Momentum transfer, the power source of PSA, is emphasized, including gas flowing in the pipelines outside adsorbent columns. The factors affecting the operating results, such as fluid resistance of pipelines, mass transfer in adsorbent column, competitive adsorption, and temperature effect, etc. are represented by those three elementary elements. The model is well consistent to the experiments in rapid PSA [11,12] and pressurization and depressurization [13,14].
2. Theory Two basic equivalences are introduced as molar quantity equivalent (mol) to electrical charge and pressure P (N/m2) to electrical potential. Then we can derive molar flowrate Q (mol/s) as electrical current, fluid resistance or mass transfer resistance as a resistor R (Ns/m2 mol), a space for adsorption
or accumulation of gas as a capacitor C (mol m2/ N), and impedance to the change of flowrate as an inductor L (N s2/m2 mol) [11]. Usually the inductance is very small and does not influence the simulating results [13], but it is significant to numerical steadiness, specially at the instant of valves on or off. From the above definitions, the R /C /L network and its relative equations can be formed for an adsorbent column. Three objects R , C and L may be simulated by; RQDP
C
L
dP Q dt
dQ dt
RQ DP
where, t represents time (s). With the help of object oriented programming technique of C// computer language, a heterogenic node list with column, pipe, tank and other equipment is established and their respective states of pressure, flowrate and temperature are calculated by the virtual functions. Columns and tanks being connected with pipes are simulated by pointers. A discretionarily connected PSA flowsheet may be automatically converted to an electrical network, and the ODE may be automatically set up according to Kirchhoff’s law and solved. The concentration of water vapor in feed is low in the present study, and the pressure equalization step is less significant, and so one column PSA is adopted here as an instance. The flowsheet of one column PSA shown in Fig. 1 may be converted to the electrical chart shown in Fig. 2, where the subscript f, b, e and p represent the pipelines of feed, blowdown, column end and product, respectively. Pf, Pa and Pp are constant voltage sources, representing the pressure of feed, blowdown and product, respectively. We assumes the storage tank be large enough to keep the feed pressure constant. The switch K simulates solenoid valves A and B to undergo adsorption when touching A, delay when
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
33
bility factor Z at the state of feed, and it is assumed that Z be constant in the calculation. Z is calculated by the second virial coefficient [15]. Adsorption equilibrium data of water vapor on 3A molecular sieve at higher pressure can not be looked up in publications. The isotherm dependent on temperature adopted by the present calculation refers to [5], and is extended to the operating pressure, shown as in Fig. 3. It is reasonable, being compared with the isotherm of water vapour on NaX and KNaX zeolite [7]. Pore in 3A is too small for ethanol molecules to penetrate into [2], and so qethanol /0 is assumed. Isotherm of water vapour on 3A may be formulated by; q
10k(P=1:1085 104 T)1=n 1 k(P=1:1085 104 T)1=n
k 8:0107 e6014=T Fig. 1. Schematic diagram of one column PSA.
n 4:223(1050:7=T)
where, q is adsorption amount (mol/kg adsorbent), P is the pressure of water vapor (bar) and T represents temperature (K). The adsorbent column f16 mm /1.21 m was packed with 160.5 g 3A molecular sieve, with voidage of 0.40. Set feed composition of 6.46 water and 93.54%(wt) ethanol. Mass transfer resistances from external film mass transfer and macropore diffusion, and nonisothermal operation are assumed. The mass transfer resistance expression and heat transfer equations are shown as in [12]
Fig. 2. Electrical chart of one column PSA.
insulating, and blowdown when touching B. The set of ODE for this process may refer to [11,12].
3. Results and discussion The state equation P /V /T of water vapour and ethanol vapour is modified by the compressi-
Fig. 3. Isotherms of water vapour on 3A molecular sieve.
34
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
and [14]. Heat of adsorption of water vapour is 4200 J/g [4]. The other parameters for calculation may refer to [11,12]. The operating results may be represented by product purity, recovery and productivity. Product flowrate and its corresponding purity, recovery and productivity may be obtained by regulating Rp. The operating results at various feed pressures are shown as in Fig. 4. An upper limit of the purity is laid relative to the peed pressure. Purity may be up to 99.6% if feed pressure is 5 bar. Both recovery and productivity will be increased with the increase of feed pressure. Purity/recovery and purity/productivity curves have a sharp section in which purity almost keeps constant while recovery and productivity are from zero to a higher value. The purity above 99.5% recovery 55% and productivity 160 g products/kg adsorbent per h may be obtained for 5 bar feed pressure. The operation was simulated at feed pressure 3.5 bar and temperature 120, 135 and 150 8C, respectively. It was shown that the purity /recovery and purity/productivity curves at different temperature are almost the same or temperature less affects the operating results. Higher temperature will be unfavorable to adsorption but favorable to desorption.
Fig. 4. Effect of feed pressure on operating results. Operating time (s): adsorption 4.0, delay 5.0, blowdown 4.0; */ recovery; - - - productivity; Feed pressure bar: 1:2.0; 2:3.5; 3:5.0
As an example of fluid resistance of pipeline affecting the operating results, an anisotropic valve is mounted in the pipeline of the column entrance to product tank. The cocurrent (flowing from the column entrance to product tank) resistance coefficient equals to 104, and the countercurrent (flowing from product tank to column entrance) coefficient 104, 104, 105 and 106, respectively. The optimal value of anti-direction coefficient is 104 /105 (feed pressure 3.5 bar), at which the purity is up to 99.8% (wt). Two cases are shown as in Fig. 5. About 99.5% purity corresponds to 60% recovery and 110 g products/ kg adsorbent per h. In above simulation, constant voltage sources Pa and Pp are set to atmospheric pressure 1 bar. Letting Pa /0.4 bar causes the column to blowdown to the vacuum source and the adsorbent to desorb in vacuum. It is shown in Fig. 6 that the products with purity of 99.9% (wt) may be attained. Operating stages of adsorption for 15 s, delay for 0 s and blowdown for 20 s are optimal for the present PSA unit and operating conditions, in which the recovery reaches 73% for the purity of 99.5% (wt). The purity and recovery can be raised by desorption in vacuum, comparing with the purity /recovery curve in Fig. 4 at feed pressure
Fig. 5. Effect of the anisotropic valve on operating results. Operating time (s): adsorption 4.0, delay 5.0, blowdown 4.0; */ recovery; - - - productivity; feed pressure 3.5 bar; Cocurrent resistance resistance; 1:104; 2:104.
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
35
ethanol with recovery 75% and productivity 30 g/ kg adsorbent per h.
Acknowledgements The authors are grateful to the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKUST6114/97P) and to National Natural Science Foundation of China (Project No: 29876011) for financial support of proceeding the research.
Fig. 6. Operating results with vacuum desorption. Operating time (s): adsorption 15.0, delay 0.0, blowdown 20.0; */ recovery; - - - productivity; Feed pressure 2.0 bar; vacuum 0.4 bar.
of 2.0 bar. About 99.5% purity corresponds to 75% recovery and 30 g products/kg adsorbent per h.
4. Conclusion One column PSA for ethanol drying was simulated with the electrical analogue model. Operating temperature within 120/150 8C less affects the purity/recovery and purity /productivity curves. Raising feed pressure may increase product purity limit, recovery and productivity. Operating results may be improved by installing an anisotropic valve in the pipeline connecting column entrance with product tank, and 99.5% (wt) ethanol may be produced with recovery 60% and productivity 110 g/kg adsorbent per h at 3.5 bar feed pressure. Desorption in vacuum of 0.4 bar may produce 99.9% (wt) ethanol with recovery 60%, productivity 17 g/kg adsorbent per h, and 99.5% (wt)
References [1] K.T. Xu, Distillation Processes of Alcohol (in Chinese), China Light Industry Press, 1998. [2] W.K. Teo, D.M. Ruthven, Ind. Eng. Chem. Process Des. Dev. 25 (1986) 17. [3] M.J. Carmo, J.C. Gubulin, Brazilian J. Chem. Eng. 14 (1997) 217. [4] A. Carton, G. Gonzalez, A.I.D.L. Torre, J.L. Cabezas, J. Chem. Tech. Biotechnol. 39 (1987) 125. [5] B. Sowerby, B.D. Crittenden, Trans. Icheme 69 (part A) (1991) 3. [6] J. Weitkamp, S. Ernst, B. Gunzel, W.D. Deckwer, Zeolites 11 (1991) 314. [7] L. Czepirski, E.K. Czepirska (1992). In: M. Suzuki (Eds.), Fundamentals of Adsorption, Proceedings of IVth international conference on fundamentals of adsorption, Kyoto, pp. 121. [8] C. Colella, M. Pansini, F. Alfani, M. Cantarella, A. Gallifuoco, Microporous Mater. 3 (1994) 219. [9] M.B. Rao, S. Sircar, Sep. Sci. Technol. 27 (1992) 1875. [10] D.M. Ruthven, S. Farooq, K.S. Knaebel, Pressure Swing Adsorption, VCH, 1994. [11] J. Guan, Z. Ye, Chem. Eng. Sci. 45 (1990) 3063. [12] J. Guan, Z. Ye, Chem. Eng. Sci. 48 (1993) 2821. [13] B.D. Crittenden, J. Guan, W.N. Ng, W.J. Thomas, Chem. Eng. Sci. 49 (1994) 2657. [14] B.D. Crittenden, J. Guan, W.N. Ng, W.J. Thomas, Chem. Eng. Sci. 50 (1995) 1417. [15] R.H. Perry, Perry’s Chemical Engineer’s Handbook, sixth ed., McGraw-Hill, 1984.
Simulation and analysis of pressure swing adsorption: ethanol drying process by the electrical analogue Jianyu Guan a,*, Xijun Hu b a
b
Research Institute of Chemical Engineering, South China University of Technology, Guangzhou 510640, China Department of Chemical Engineering, Hong Kong University of Science and Technology, Clear Water Bay, Hong Kong
Abstract One column pressure swing adsorption (PSA) for dehydration of mixture of ethanol 93.54% and water 6.46% (wt) was simulated numerically by the electrical analogue model at feed pressure 2.0 /5.0 bar, operating temperature 120 / 150 8C, and vacuum desorption. Increasing feed pressure may increase recovery and productivity. An anisotropic valve connecting the column entrance with the product tank may improve the operating results to obtain 99.9% ethanol at feed pressure 3.5 bar. Vacuum desorption may raise product purity and recovery to obtain 99.9 ethanol and 60% recovery at feed pressure 2.0 bar and blowdown to 0.4 bar. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Adsorption; Pressure swing adsorption; Ethanol; Water; Azeotrope
1. Introduction Anhydrous ethanol is widely used in industries, such as organic syntheses, painting, medicine, cosmetics, perfume, etc. Mixing anhydrous ethanol and petrol can form a steady mixture, called gasohol, used as motor car fuel. Anhydrous ethanol may be used as an important oxygenic additive in lead-free petrol [1]. However, 95.57 ethanol and 4.43% (wt) water will form an azeotrope at 78.15 8C and 1.013 bar. Traditional distillation to obtain anhydrous ethanol is a high energetic process. Azeotropic distillation, extractive distillation and salt rectification are the most
* Corresponding author. E-mail address: [email protected] (J. Guan).
important processes [1]. Adsorption as a low energy consumption process has been attracted more attention. The adsorption equilibrium and kinetics of ethanol/water mixture on molecular sieve, such as 3A, 4A, NaX, NaY, etc. have been studied both in liquid phase [2,3] and vapor phase ([4 /8]). Rao and Sircar [9] reported their concentration swing adsorption for production of motor fuel grade alcohol. But less paper involves pressure swing adsorption (PSA) for ethanol drying. PSA is widely used in separation and purification of gas mixtures, which is mainly because of easy and quick desorption of the adsorbent only by depressurization. In contrast, for the separation and purification of liquid phase, the adsorbent is desorbed usually by solvent rinse or heating. Solvent rinse requires a suitable solvent and further separation and recovery of the solvent
1383-5866/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 1 3 8 3 - 5 8 6 6 ( 0 2 ) 0 0 1 5 1 - X
32
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
after the rinse. And the method of heating requires long operating period of heating for desorption and then cooling for adsorption, which lowers the productivity of the adsorbent beds. Heat energy is also required to evaporate the liquid remaining in the void of the beds and raise the temperature of the adsorbent and the beds. In the present article, PSA process for ethanol drying will be explored with the electrical analogue simulation. Many mathematical models for simulating PSA have been developed in last 30 years [10]. Most of the models are constructed by partial differential equations based on the assumption of continuity, and it is assumed ordinarily that pressure drop for fluid flowing through pipelines and the packed bed might be neglectable and the boundary conditions might be simplified. The electrical analogue model [11] looks particular, which decomposes packed beds, storage tanks, valves and pipelines to resistors, capacitors and inductors. Mass and momentum transfer processes are equivalent to electricity acting on its elements. A set of ordinary differential equations (ODE) is set up to describe a whole PSA system. The entrances of adsorbent column are connected with the relative electrical elements, in which BC needs not be paid any attention to. Momentum transfer, the power source of PSA, is emphasized, including gas flowing in the pipelines outside adsorbent columns. The factors affecting the operating results, such as fluid resistance of pipelines, mass transfer in adsorbent column, competitive adsorption, and temperature effect, etc. are represented by those three elementary elements. The model is well consistent to the experiments in rapid PSA [11,12] and pressurization and depressurization [13,14].
2. Theory Two basic equivalences are introduced as molar quantity equivalent (mol) to electrical charge and pressure P (N/m2) to electrical potential. Then we can derive molar flowrate Q (mol/s) as electrical current, fluid resistance or mass transfer resistance as a resistor R (Ns/m2 mol), a space for adsorption
or accumulation of gas as a capacitor C (mol m2/ N), and impedance to the change of flowrate as an inductor L (N s2/m2 mol) [11]. Usually the inductance is very small and does not influence the simulating results [13], but it is significant to numerical steadiness, specially at the instant of valves on or off. From the above definitions, the R /C /L network and its relative equations can be formed for an adsorbent column. Three objects R , C and L may be simulated by; RQDP
C
L
dP Q dt
dQ dt
RQ DP
where, t represents time (s). With the help of object oriented programming technique of C// computer language, a heterogenic node list with column, pipe, tank and other equipment is established and their respective states of pressure, flowrate and temperature are calculated by the virtual functions. Columns and tanks being connected with pipes are simulated by pointers. A discretionarily connected PSA flowsheet may be automatically converted to an electrical network, and the ODE may be automatically set up according to Kirchhoff’s law and solved. The concentration of water vapor in feed is low in the present study, and the pressure equalization step is less significant, and so one column PSA is adopted here as an instance. The flowsheet of one column PSA shown in Fig. 1 may be converted to the electrical chart shown in Fig. 2, where the subscript f, b, e and p represent the pipelines of feed, blowdown, column end and product, respectively. Pf, Pa and Pp are constant voltage sources, representing the pressure of feed, blowdown and product, respectively. We assumes the storage tank be large enough to keep the feed pressure constant. The switch K simulates solenoid valves A and B to undergo adsorption when touching A, delay when
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
33
bility factor Z at the state of feed, and it is assumed that Z be constant in the calculation. Z is calculated by the second virial coefficient [15]. Adsorption equilibrium data of water vapor on 3A molecular sieve at higher pressure can not be looked up in publications. The isotherm dependent on temperature adopted by the present calculation refers to [5], and is extended to the operating pressure, shown as in Fig. 3. It is reasonable, being compared with the isotherm of water vapour on NaX and KNaX zeolite [7]. Pore in 3A is too small for ethanol molecules to penetrate into [2], and so qethanol /0 is assumed. Isotherm of water vapour on 3A may be formulated by; q
10k(P=1:1085 104 T)1=n 1 k(P=1:1085 104 T)1=n
k 8:0107 e6014=T Fig. 1. Schematic diagram of one column PSA.
n 4:223(1050:7=T)
where, q is adsorption amount (mol/kg adsorbent), P is the pressure of water vapor (bar) and T represents temperature (K). The adsorbent column f16 mm /1.21 m was packed with 160.5 g 3A molecular sieve, with voidage of 0.40. Set feed composition of 6.46 water and 93.54%(wt) ethanol. Mass transfer resistances from external film mass transfer and macropore diffusion, and nonisothermal operation are assumed. The mass transfer resistance expression and heat transfer equations are shown as in [12]
Fig. 2. Electrical chart of one column PSA.
insulating, and blowdown when touching B. The set of ODE for this process may refer to [11,12].
3. Results and discussion The state equation P /V /T of water vapour and ethanol vapour is modified by the compressi-
Fig. 3. Isotherms of water vapour on 3A molecular sieve.
34
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
and [14]. Heat of adsorption of water vapour is 4200 J/g [4]. The other parameters for calculation may refer to [11,12]. The operating results may be represented by product purity, recovery and productivity. Product flowrate and its corresponding purity, recovery and productivity may be obtained by regulating Rp. The operating results at various feed pressures are shown as in Fig. 4. An upper limit of the purity is laid relative to the peed pressure. Purity may be up to 99.6% if feed pressure is 5 bar. Both recovery and productivity will be increased with the increase of feed pressure. Purity/recovery and purity/productivity curves have a sharp section in which purity almost keeps constant while recovery and productivity are from zero to a higher value. The purity above 99.5% recovery 55% and productivity 160 g products/kg adsorbent per h may be obtained for 5 bar feed pressure. The operation was simulated at feed pressure 3.5 bar and temperature 120, 135 and 150 8C, respectively. It was shown that the purity /recovery and purity/productivity curves at different temperature are almost the same or temperature less affects the operating results. Higher temperature will be unfavorable to adsorption but favorable to desorption.
Fig. 4. Effect of feed pressure on operating results. Operating time (s): adsorption 4.0, delay 5.0, blowdown 4.0; */ recovery; - - - productivity; Feed pressure bar: 1:2.0; 2:3.5; 3:5.0
As an example of fluid resistance of pipeline affecting the operating results, an anisotropic valve is mounted in the pipeline of the column entrance to product tank. The cocurrent (flowing from the column entrance to product tank) resistance coefficient equals to 104, and the countercurrent (flowing from product tank to column entrance) coefficient 104, 104, 105 and 106, respectively. The optimal value of anti-direction coefficient is 104 /105 (feed pressure 3.5 bar), at which the purity is up to 99.8% (wt). Two cases are shown as in Fig. 5. About 99.5% purity corresponds to 60% recovery and 110 g products/ kg adsorbent per h. In above simulation, constant voltage sources Pa and Pp are set to atmospheric pressure 1 bar. Letting Pa /0.4 bar causes the column to blowdown to the vacuum source and the adsorbent to desorb in vacuum. It is shown in Fig. 6 that the products with purity of 99.9% (wt) may be attained. Operating stages of adsorption for 15 s, delay for 0 s and blowdown for 20 s are optimal for the present PSA unit and operating conditions, in which the recovery reaches 73% for the purity of 99.5% (wt). The purity and recovery can be raised by desorption in vacuum, comparing with the purity /recovery curve in Fig. 4 at feed pressure
Fig. 5. Effect of the anisotropic valve on operating results. Operating time (s): adsorption 4.0, delay 5.0, blowdown 4.0; */ recovery; - - - productivity; feed pressure 3.5 bar; Cocurrent resistance resistance; 1:104; 2:104.
J. Guan, X. Hu / Separation and Purification Technology 31 (2003) 31 /35
35
ethanol with recovery 75% and productivity 30 g/ kg adsorbent per h.
Acknowledgements The authors are grateful to the Research Grants Council of the Hong Kong Special Administrative Region, China (Project No. HKUST6114/97P) and to National Natural Science Foundation of China (Project No: 29876011) for financial support of proceeding the research.
Fig. 6. Operating results with vacuum desorption. Operating time (s): adsorption 15.0, delay 0.0, blowdown 20.0; */ recovery; - - - productivity; Feed pressure 2.0 bar; vacuum 0.4 bar.
of 2.0 bar. About 99.5% purity corresponds to 75% recovery and 30 g products/kg adsorbent per h.
4. Conclusion One column PSA for ethanol drying was simulated with the electrical analogue model. Operating temperature within 120/150 8C less affects the purity/recovery and purity /productivity curves. Raising feed pressure may increase product purity limit, recovery and productivity. Operating results may be improved by installing an anisotropic valve in the pipeline connecting column entrance with product tank, and 99.5% (wt) ethanol may be produced with recovery 60% and productivity 110 g/kg adsorbent per h at 3.5 bar feed pressure. Desorption in vacuum of 0.4 bar may produce 99.9% (wt) ethanol with recovery 60%, productivity 17 g/kg adsorbent per h, and 99.5% (wt)
References [1] K.T. Xu, Distillation Processes of Alcohol (in Chinese), China Light Industry Press, 1998. [2] W.K. Teo, D.M. Ruthven, Ind. Eng. Chem. Process Des. Dev. 25 (1986) 17. [3] M.J. Carmo, J.C. Gubulin, Brazilian J. Chem. Eng. 14 (1997) 217. [4] A. Carton, G. Gonzalez, A.I.D.L. Torre, J.L. Cabezas, J. Chem. Tech. Biotechnol. 39 (1987) 125. [5] B. Sowerby, B.D. Crittenden, Trans. Icheme 69 (part A) (1991) 3. [6] J. Weitkamp, S. Ernst, B. Gunzel, W.D. Deckwer, Zeolites 11 (1991) 314. [7] L. Czepirski, E.K. Czepirska (1992). In: M. Suzuki (Eds.), Fundamentals of Adsorption, Proceedings of IVth international conference on fundamentals of adsorption, Kyoto, pp. 121. [8] C. Colella, M. Pansini, F. Alfani, M. Cantarella, A. Gallifuoco, Microporous Mater. 3 (1994) 219. [9] M.B. Rao, S. Sircar, Sep. Sci. Technol. 27 (1992) 1875. [10] D.M. Ruthven, S. Farooq, K.S. Knaebel, Pressure Swing Adsorption, VCH, 1994. [11] J. Guan, Z. Ye, Chem. Eng. Sci. 45 (1990) 3063. [12] J. Guan, Z. Ye, Chem. Eng. Sci. 48 (1993) 2821. [13] B.D. Crittenden, J. Guan, W.N. Ng, W.J. Thomas, Chem. Eng. Sci. 49 (1994) 2657. [14] B.D. Crittenden, J. Guan, W.N. Ng, W.J. Thomas, Chem. Eng. Sci. 50 (1995) 1417. [15] R.H. Perry, Perry’s Chemical Engineer’s Handbook, sixth ed., McGraw-Hill, 1984.