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Advanced simulation to choose a cheaper membrane process for salt removal from complex mixtures
Desalination 224 (2008) 191–194
Advanced simulation to choose a cheaper membrane process for salt removal from complex mixtures Nicolae Sdrula IPROCHIM S.A.,19-21 Mihai Eminescu Street, 010512 Bucharest 1, Romania Tel. +40 (21) 610-7985; Fax: +40 (21) 210-2701; email: [email protected] Received 28 November 2006; Accepted 9 February 2007
Abstract Most of chemical reactions have — as a final result — a large mixture of end products out of which the main one represents a small rate when compared with secondary products. One of these reactions results in a mixture of products that takes place in the process obtaining ethylene amines. The reaction occurring at elevated pressure and temperature, between dichloroethane and ammonia, conducts to amino-chlorohydrates intermediate products which are then neutralized by means of NaOH. Finally the amines and NaCl are formed. Then excess ammonia is removed resulting in a mixture of NaCl, water and amines. Currently a procedure separated the amines from the rest of the components by evaporation and centrifugation. Since this desalting method causes many problems regarding steam consumption, clogging, corrosion and erosion of the equipment, it was suggested in a previous paper, based on pilot scale calculations (100 l/h), to solve these problems by using membrane technology, i.e. ED or PV. The study pointed out that PV appeared to be more advantageous than ED. The new paper takes into account the same membrane processes as the previous study using advanced simulation for the variables involved in the process, including the sensitivity cost analysis as well. The scale of the current plant is an industrial one (5400–7200 kg/h) and therefore the results can be a more realistic support for a potential investor. Keywords: Electrodialysis; Pervaporation; Desalting; Cost analysis
1. Introduction Most chemical reactions usually applied in chemical plants have — as final results — a large mixture of end products, from which the main or desired products are in small quantities compared with secondary or by-products; and as a con-
sequence, it is difficult to be further separated. One of these reactions, resulting in a mixture of main products together with by-products, takes place in the process to obtain ethylene amines and derivatives. The reaction stage occurs at about 70 bars and 100E between dichloroethane and
Presented at the 11th Aachen Membrane Colloquium, 28–29 March, 2007, Aachen, Germany. 0011-9164/08/$– See front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.desal.2007.02.093
192
N. Sdrula / Desalination 224 (2008) 191–194
ammonia solution conducting to form aminochlorohydrates. These chlorohydrates are then neutralized in the presence of natrium hydroxide and amines (ethylene amines and derivates) and sodium chloride are formed. The mixture is then introduced in a double columns system in order to remove the excess of ammonia. The next step on which is focused the advanced simulation work is the removal of sodium chloride salt from the mixture, while the last steps are mainly classical separation columns. Since the removal of salt by concentration/ filtration causes many problems regarding crystal growth, high rate of steam consumption for water/amine evaporation, clogging, corrosion and erosion of the equipment, it was suggested in a previous experiment, based on preliminary calculations to solve the problems using membrane technology, i.e. ED or PV, in order to remove the salt from the mixture and to obtain a clear aqueous solution of amines. PV appeared to be more advantageous than ED [1]. The new paper presents, continuing the work, the results obtained by advanced simulation, taking into account almost all variables involved in the process for the considered membrane systems. This time the data involved in the simulation work have as a basis the figures of an industrial plant, so the results are of more interest for producers. 2. Process conditions The mixture of amines (mostly containing ethylenediamine, diethylenetriamine and trietyl-
lenetetramine), water and dissolved sodium chloride is obtained from the process at around 105ºC and atmospheric pressure. Instead of treating with a simple evaporation process that produced many problems, the mixture can be conducted in one of membrane process units. The total flow rate resulting from the industrial-scale plant is about 5400 kg/h. The mixture has the following average composition (% wt): C Water 69.40 C Sodium chloride 20.40 C Amines 10.20 3. Membrane systems As per a previous paper, the processes which can properly perform the separation of amines (in water solution) by sodium chloride (dissolved in water) are pervaporation or electrodialysis [2,3]. Before processing, in the case of electrodialysis, the mixture has to be diluted with water up to maximum of 200 g/l of NaCl while the temperature has to be cooled down to around 50ºC in order to protect the membranes. These measures conduct to around 7200 kg/h total amount of feed. 4. Process assumptions and data In order to simplify the systems some assumptions were taken in consideration as per data indicated in Table 1. The recovery of amines in the product was considered of 99% per each process. The input data are given in Table 2.
Table 1 Process assumptions Process
Assumptions
ED
No amine transport Through membrane Preferential amine transport
PV
Measures Polarization concentration neglected Polarization concentration neglected
1.2 to1.5 times dilution of feed High vacuum No dilution
Feed cooling at ca 50ºC Temperature-resistant membrane
N. Sdrula / Desalination 224 (2008) 191–194
193
Table 2 Engineering input data Process
a
b
c
d
ED
Average stream density: 0.4 kA/m2 Specific permeate flux: 0.8 kg/m2h
ED double cells in a unit of 1.0×1.0 mm Selectivity at least 20
Stream yield: 80%
Plate membrane
Efficiency: 99%
Spiral membrane
PV
Table 3 Engineering output data Process ED PV
Membrane surface, m2 157.7 1200
Cell number
Stream per cell, A
Permeate composition
Comments
220
285
—
—
0.25 g NaCl/l in amine solution Amine solution min. 60%
Downstream measure due to salt presence No salt in permeate
Table 4 Costs of treated mixture (in €) Process
ED PV
One time costs
Annual variable costs
Site and permitting
Equipmenta
Start-up
Labor Supplies
Utilities
Effluent disposal
Analytical service
Maintenance
20,000 20,000
2e+05 3e+05
20,000 15,000
6,0000 8,000 60,000 6,000
75,000 50,000
30,000 20,000
16,000 16,000
18,000 12,000
a
Estimated values.
Based on the feed flow quantity (as per item 2 and 3) and the engineering input figures, the data in Table 3 were obtained. 5. Economic analysis The period of plant life is considered to be 10 years. The unit costs of a treated mixture are given in Table 4. The resulting costs for the treatment of 1000 kg of complex mixture are: C For the ED process: €4.00 C For the PV process: €3.47
6. Conclusions The study had as its basis a practical existing case in one chemical plant and tried to stress the importance of hybrid processes for solving different problems of chemical engineering by combining the classical unitary processes with membrane ones. The replacing of some classical steps for separation purposes with membrane processes can be an important decision both for existing owners of the process and the producers of membrane units and/or equipment. The present paper is a new attempt at a higher
194
N. Sdrula / Desalination 224 (2008) 191–194
scale to demonstrate the reliability of such membrane processes making at the same time a cost comparison between two processes. The made assumptions help to simplify the computations but some other variables, including sensitive analysis can be taken in account. However, it is very clear for an investor that for any new mixture to be separated by a membrane process, pilot or labor tests have to be performed in order to obtain reliable data for industrial plant. Chemical branches offer wide opportunities of applications for membrane technologies and this attempt try to stress once again upon the impor-
tance of hybrid processes to be applied in the future.
References [1] N. Sdrula, Simulation for determination of optimal conditions for salt removal for aqueous amine solution, Desalination, 189 (2006) 138–140. [2] T. Melin, Membranverfahren Parts 1 and 2, RWTH Aachen, WS 1999/2000. [3] R. Dima and V. Plesu, Ingineria separarilor cu membrane, Bren, Bucuresti, 1999.
Advanced simulation to choose a cheaper membrane process for salt removal from complex mixtures Nicolae Sdrula IPROCHIM S.A.,19-21 Mihai Eminescu Street, 010512 Bucharest 1, Romania Tel. +40 (21) 610-7985; Fax: +40 (21) 210-2701; email: [email protected] Received 28 November 2006; Accepted 9 February 2007
Abstract Most of chemical reactions have — as a final result — a large mixture of end products out of which the main one represents a small rate when compared with secondary products. One of these reactions results in a mixture of products that takes place in the process obtaining ethylene amines. The reaction occurring at elevated pressure and temperature, between dichloroethane and ammonia, conducts to amino-chlorohydrates intermediate products which are then neutralized by means of NaOH. Finally the amines and NaCl are formed. Then excess ammonia is removed resulting in a mixture of NaCl, water and amines. Currently a procedure separated the amines from the rest of the components by evaporation and centrifugation. Since this desalting method causes many problems regarding steam consumption, clogging, corrosion and erosion of the equipment, it was suggested in a previous paper, based on pilot scale calculations (100 l/h), to solve these problems by using membrane technology, i.e. ED or PV. The study pointed out that PV appeared to be more advantageous than ED. The new paper takes into account the same membrane processes as the previous study using advanced simulation for the variables involved in the process, including the sensitivity cost analysis as well. The scale of the current plant is an industrial one (5400–7200 kg/h) and therefore the results can be a more realistic support for a potential investor. Keywords: Electrodialysis; Pervaporation; Desalting; Cost analysis
1. Introduction Most chemical reactions usually applied in chemical plants have — as final results — a large mixture of end products, from which the main or desired products are in small quantities compared with secondary or by-products; and as a con-
sequence, it is difficult to be further separated. One of these reactions, resulting in a mixture of main products together with by-products, takes place in the process to obtain ethylene amines and derivatives. The reaction stage occurs at about 70 bars and 100E between dichloroethane and
Presented at the 11th Aachen Membrane Colloquium, 28–29 March, 2007, Aachen, Germany. 0011-9164/08/$– See front matter © 2008 Published by Elsevier B.V. doi:10.1016/j.desal.2007.02.093
192
N. Sdrula / Desalination 224 (2008) 191–194
ammonia solution conducting to form aminochlorohydrates. These chlorohydrates are then neutralized in the presence of natrium hydroxide and amines (ethylene amines and derivates) and sodium chloride are formed. The mixture is then introduced in a double columns system in order to remove the excess of ammonia. The next step on which is focused the advanced simulation work is the removal of sodium chloride salt from the mixture, while the last steps are mainly classical separation columns. Since the removal of salt by concentration/ filtration causes many problems regarding crystal growth, high rate of steam consumption for water/amine evaporation, clogging, corrosion and erosion of the equipment, it was suggested in a previous experiment, based on preliminary calculations to solve the problems using membrane technology, i.e. ED or PV, in order to remove the salt from the mixture and to obtain a clear aqueous solution of amines. PV appeared to be more advantageous than ED [1]. The new paper presents, continuing the work, the results obtained by advanced simulation, taking into account almost all variables involved in the process for the considered membrane systems. This time the data involved in the simulation work have as a basis the figures of an industrial plant, so the results are of more interest for producers. 2. Process conditions The mixture of amines (mostly containing ethylenediamine, diethylenetriamine and trietyl-
lenetetramine), water and dissolved sodium chloride is obtained from the process at around 105ºC and atmospheric pressure. Instead of treating with a simple evaporation process that produced many problems, the mixture can be conducted in one of membrane process units. The total flow rate resulting from the industrial-scale plant is about 5400 kg/h. The mixture has the following average composition (% wt): C Water 69.40 C Sodium chloride 20.40 C Amines 10.20 3. Membrane systems As per a previous paper, the processes which can properly perform the separation of amines (in water solution) by sodium chloride (dissolved in water) are pervaporation or electrodialysis [2,3]. Before processing, in the case of electrodialysis, the mixture has to be diluted with water up to maximum of 200 g/l of NaCl while the temperature has to be cooled down to around 50ºC in order to protect the membranes. These measures conduct to around 7200 kg/h total amount of feed. 4. Process assumptions and data In order to simplify the systems some assumptions were taken in consideration as per data indicated in Table 1. The recovery of amines in the product was considered of 99% per each process. The input data are given in Table 2.
Table 1 Process assumptions Process
Assumptions
ED
No amine transport Through membrane Preferential amine transport
PV
Measures Polarization concentration neglected Polarization concentration neglected
1.2 to1.5 times dilution of feed High vacuum No dilution
Feed cooling at ca 50ºC Temperature-resistant membrane
N. Sdrula / Desalination 224 (2008) 191–194
193
Table 2 Engineering input data Process
a
b
c
d
ED
Average stream density: 0.4 kA/m2 Specific permeate flux: 0.8 kg/m2h
ED double cells in a unit of 1.0×1.0 mm Selectivity at least 20
Stream yield: 80%
Plate membrane
Efficiency: 99%
Spiral membrane
PV
Table 3 Engineering output data Process ED PV
Membrane surface, m2 157.7 1200
Cell number
Stream per cell, A
Permeate composition
Comments
220
285
—
—
0.25 g NaCl/l in amine solution Amine solution min. 60%
Downstream measure due to salt presence No salt in permeate
Table 4 Costs of treated mixture (in €) Process
ED PV
One time costs
Annual variable costs
Site and permitting
Equipmenta
Start-up
Labor Supplies
Utilities
Effluent disposal
Analytical service
Maintenance
20,000 20,000
2e+05 3e+05
20,000 15,000
6,0000 8,000 60,000 6,000
75,000 50,000
30,000 20,000
16,000 16,000
18,000 12,000
a
Estimated values.
Based on the feed flow quantity (as per item 2 and 3) and the engineering input figures, the data in Table 3 were obtained. 5. Economic analysis The period of plant life is considered to be 10 years. The unit costs of a treated mixture are given in Table 4. The resulting costs for the treatment of 1000 kg of complex mixture are: C For the ED process: €4.00 C For the PV process: €3.47
6. Conclusions The study had as its basis a practical existing case in one chemical plant and tried to stress the importance of hybrid processes for solving different problems of chemical engineering by combining the classical unitary processes with membrane ones. The replacing of some classical steps for separation purposes with membrane processes can be an important decision both for existing owners of the process and the producers of membrane units and/or equipment. The present paper is a new attempt at a higher
194
N. Sdrula / Desalination 224 (2008) 191–194
scale to demonstrate the reliability of such membrane processes making at the same time a cost comparison between two processes. The made assumptions help to simplify the computations but some other variables, including sensitive analysis can be taken in account. However, it is very clear for an investor that for any new mixture to be separated by a membrane process, pilot or labor tests have to be performed in order to obtain reliable data for industrial plant. Chemical branches offer wide opportunities of applications for membrane technologies and this attempt try to stress once again upon the impor-
tance of hybrid processes to be applied in the future.
References [1] N. Sdrula, Simulation for determination of optimal conditions for salt removal for aqueous amine solution, Desalination, 189 (2006) 138–140. [2] T. Melin, Membranverfahren Parts 1 and 2, RWTH Aachen, WS 1999/2000. [3] R. Dima and V. Plesu, Ingineria separarilor cu membrane, Bren, Bucuresti, 1999.