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Nanofiltration used for desalination and concentration in dye production
DESALINATION ELSEVIER
Desalination 140 (2001) 9%100 www.elsevier.com/locate/desal
Nanofiltration used for desalination and concentration in dye production Sanchuan Yu a*, Congjie Gao a, Hexiang Su b, Meihong Liu c aDevelopment Center of Water Treatment Technology, State Oceanic Administration, No. 148 Wenyi Road, Hangzhou, China Tel. +86 (570 886-6168; Fax +86 (571) 891-2021; email: [email protected] bShanghai Dyestuffs Chemical Plant No. 8, No. 1 Yong Deng Roaa~ Shanghai, China CCollege of Materials and Textiles, Zhefiang Institute of Science and Technology, No. 88 Wenyi Road, Hangzhou, China
Received 20 November 2000; accepted 19 January 2001
Abstract
A dye-producingplant using nanofiltrationmembrane technology for the desalting and concentratingof aqueous dye was designed and built in China in 1993. The design features, operating experience and typical results such as membrane selection, element style, flow diagram, operating pressure, salt passage through membrane and change of permeate flux are described in detail. The membrane system can produce aqueous dye with more than 25% dye and about less than 1% salt content. The improved process using nanofiltration membrane technology is continuous and automatic in operation. It is not very labor intensive, and produces dye products with high purity and consistent quality. Keywords: Nanofiltration; Desalination; Concentration; Dye
1. Introduction
Dyes are produced by chemical synthesis. However, the synthesis process produces salt (NaCI) and small molecular weight intermediates and residual compounds which reduce the purity of the dyes. Hence, the salt and impurities need to be removed before the dyes are dried for sale as powder. *Corresponding author.
Conventionally, dye is precipitated from an aqueous solution using salt (Fig. 1). The slurry is passed through a filter press. The filter retains the dye, and the filtrate containing salt and small molecular-weight residual products from chemical reactions is discarded. The retained dye is collected in trays and dried in ovens. The dried dye is then pulverized to produce a saleable powder. The purity of the final dye product as a powder from the conventional process is low
0011-9164/01/$- See front matter © 2001 Elsevier Science B.V. All rights reserved PII: S O 0 1 1 - 9 1 6 4 ( 0 1 ) 0 0 3 5 8 - 7
98
S. Yu et al. / Desalination 140 (2001) 97-100
C.onveatlanal Proum
ImprovedPmeen
I ChemlcelSynthesis J
ChemicalSynthm 1
IPrecipitationof Dye
Con~utrationusing NanofllU'ation ITrayDrytnli
Fig. 1. Conventional and improved process for dye production. about 30% salt content; further, the conventional process is carried out in various baths which makes the entire process very labor intensive and causes inconsistency in the production quality. A new process has been developed using nanofiltration membrane separation technology that is continuous in operation, is not very labor intensive, and produces a high-purity product of consistent quality (Fig. 1).
2. Improved process using nanofiltration Nanofiltration (NF) is a pressure-driven membrane process that falls between reverse osmosis (RO) and ultrafiltration (UF) in its separation characteristics, which permits the separation of certain species in a fluid by a combination of a sieving and sorption diffusion mechanism. The rejection is low for salts with monovalent anion and non-ionized organics with a molecular weight below 150, but is high for salts with diand multi-valent anions and organics with a molecular weight above 300. Thus, NF can be used for the simultaneous removal of sodium chloride (salt) and the concentration of aqueous dye solutions [1-3].
The improved NF process can be subdivided into diafiltration and concentration [4,5]. Diafiltration refers to the process of adding water to the feed dye solution that then permeates through the NF membrane under a certain operating pressure, carrying with it salts and impurities smaller than the molecular-weight cutoff of the NF membrane used. The process then is used to purifying the dye to wash away the salts and small molecular weight residual byproducts of chemical synthesis. The amount of water added depends on the desired purity level of the final product. The higher the level in the final product, the more water needs to be added to the system. The concentrating part of the process removes water from the dye solution under pressure and thus the dye content can be concentrated to about 30%. The concentration of the dye results in significant savings in energy consumption during the drying process since membrane processes are highly efficient compared to spray drying.
3. Description of the nanofiltration process A NF plant designed and built by the Development Center of Water Treatment Technology, SOA, Hangzhou, with 12 NF elements (style 4040) was installed at the Shanghai Dyestuffs Chemical Plant No. 8 in 1993 for the desalting and concentration of dye solution in dye production. The plant is the earliest and most successful NF industrial plant in China. The plant works well and smoothly, the performance is stable, and the purity and the consistency of the produced dye have improved. In the past 6 years, the NF membrane elements were replaced only once; the service life of the NF membrane is more than 3 years, and the economic and social benefits of the NF process are very remarkable. 3.1. Flow diagram o f the nanofiltration process
The flow diagram of the NF process (Fig. 2) shows the characteristics of a high feed flow rate
S. Yu et al. / Desalination 140 (2001) 97-100 Aqueom dye
Conc~trate (abom 3 5n~/h)
1ooi i
m ~
7e
~ Membr me
-I~.,mt
99
Membrane Element!
f
90
7O
1-
80
High p m s u r e pump P~aeate (0.5-1.Om~/h)
Fig. 2. Flow diagram of the NF process.
40 -qo o
1
2
3
4
6
6
Salt Commt ( ~ )
and short flow distance. The NF membrane elements used in the plant are spiral wound with cellulose acetate (the rejection of NaCl is about 50% for 2000mg/l aqueous sodium chloride at 1.0MPa), produced by the Development Center of Water Treatment Technology, SOA, Hangzhou. The pump used in the plant is an Osmonics multi-stage centrifuge high-pressure pump with a performance of 5.7 m3/h at 2.0 MPa. The operating pressure of the plant can be regulated in the range of 2.0--3.0 MPa.
Fig. 3. Salt passage ratio through membrane.
Table 1 Dye rejectionof the membrane Dye (molecularweight)
Rejection, %
Yellow Orange Red Blue Brown
= 100 = 100 99.10 99.80 = 100
(876) (747) (943) (725) (818)
3.2. Performance o f the nanofiltration process
Different kinds o f dyes with different molecular weights and structures were produced through the NF process. The rejection of dyes and the salt passage ratio of the membrane are shown in Table 1 and Fig. 3, respectively. The membrane rejects dyes with high efficiency, while the salt passage ratio through the membrane depends on the salt content of the feed dye solution, and will decrease as the salt is washed away from the dye solution during the NF process. The typical results obtained while desalting and concentrating the aqueous dye through the NF system are given in Table 2. The membrane system produced aqueous dye having more than 25% dye and less than 1% salt content. The typical change of permeate flux of the plant during the desalting and concentration process is
Table 2 Typical results obtained while desalting and concentrating dye using nanofiltration
Dye content, % NaCI content, %
Feed aqueous dye
Concentrated aqueous dye
9.88 4.16
25.6 0.64
shown in Fig. 4. The permeate flux will change with the removal of salt from the system and the increment of dye content. During the entire NF process, wash water is added at different times, as sometimes pre-concentrating before diafiltration is necessary. The system can be optimized for maximum salt passage, a minimum amount of wash water and the shortest time-consumption by
I00
S. Yu et al. / Desalination 140 (2001) 97-100
0.8
0.0
I
,
i
t
I
,
l
*
I
*
I
6
Ji
o
$
10
Opm
18
20
28
z TUne (h)
Fig. 4. Typical change of permeate flux during desalting and concentration.
controlling the conductivity of the permeate and concentrate. For diafiltration, the conductivity of the permeate is controlled so that it is larger than that of the concentrate, while for concentrating part, the conductivity of the permeate is controlled to be nearly equal to that of the concentrate.
membrane process followed by spray drying provided a continuous process, operating automatically and producing dye of high purity and consistency. Since the operation is automatic, the costs of labor have been drastically reduced.
References 4. C o n c l u s i o n s
The NF membrane separation technology was successfully used for desalting and concentration in dye production. The membrane system produced dye solution having more than 25% dye and about less than 1o~ salt content. The aqueous dye desalted and concentrated by NF was continuously dried by a spray dryer. Thus the NF
[1] P.K.Eriksson,Environ.Progr., 7(1) (1988) 58. [2] R. Rautenbach and A. Groschl, Desalination, 77 (1990) 77. [3] L.P.Raman,M. Cheryanand N. Rajagopalan,Chem. EngineeringProgr.,4 (1994) 68. [4] J. Cadotte, R. Forester, M. Kim, R. Peterson and T. Stocker, Desalination,70 (1988) 77. [5] C. Gao, Technol.Wat. TreaUnent,22(3) (1996) 147 [in Chinese].
Desalination 140 (2001) 9%100 www.elsevier.com/locate/desal
Nanofiltration used for desalination and concentration in dye production Sanchuan Yu a*, Congjie Gao a, Hexiang Su b, Meihong Liu c aDevelopment Center of Water Treatment Technology, State Oceanic Administration, No. 148 Wenyi Road, Hangzhou, China Tel. +86 (570 886-6168; Fax +86 (571) 891-2021; email: [email protected] bShanghai Dyestuffs Chemical Plant No. 8, No. 1 Yong Deng Roaa~ Shanghai, China CCollege of Materials and Textiles, Zhefiang Institute of Science and Technology, No. 88 Wenyi Road, Hangzhou, China
Received 20 November 2000; accepted 19 January 2001
Abstract
A dye-producingplant using nanofiltrationmembrane technology for the desalting and concentratingof aqueous dye was designed and built in China in 1993. The design features, operating experience and typical results such as membrane selection, element style, flow diagram, operating pressure, salt passage through membrane and change of permeate flux are described in detail. The membrane system can produce aqueous dye with more than 25% dye and about less than 1% salt content. The improved process using nanofiltration membrane technology is continuous and automatic in operation. It is not very labor intensive, and produces dye products with high purity and consistent quality. Keywords: Nanofiltration; Desalination; Concentration; Dye
1. Introduction
Dyes are produced by chemical synthesis. However, the synthesis process produces salt (NaCI) and small molecular weight intermediates and residual compounds which reduce the purity of the dyes. Hence, the salt and impurities need to be removed before the dyes are dried for sale as powder. *Corresponding author.
Conventionally, dye is precipitated from an aqueous solution using salt (Fig. 1). The slurry is passed through a filter press. The filter retains the dye, and the filtrate containing salt and small molecular-weight residual products from chemical reactions is discarded. The retained dye is collected in trays and dried in ovens. The dried dye is then pulverized to produce a saleable powder. The purity of the final dye product as a powder from the conventional process is low
0011-9164/01/$- See front matter © 2001 Elsevier Science B.V. All rights reserved PII: S O 0 1 1 - 9 1 6 4 ( 0 1 ) 0 0 3 5 8 - 7
98
S. Yu et al. / Desalination 140 (2001) 97-100
C.onveatlanal Proum
ImprovedPmeen
I ChemlcelSynthesis J
ChemicalSynthm 1
IPrecipitationof Dye
Con~utrationusing NanofllU'ation ITrayDrytnli
Fig. 1. Conventional and improved process for dye production. about 30% salt content; further, the conventional process is carried out in various baths which makes the entire process very labor intensive and causes inconsistency in the production quality. A new process has been developed using nanofiltration membrane separation technology that is continuous in operation, is not very labor intensive, and produces a high-purity product of consistent quality (Fig. 1).
2. Improved process using nanofiltration Nanofiltration (NF) is a pressure-driven membrane process that falls between reverse osmosis (RO) and ultrafiltration (UF) in its separation characteristics, which permits the separation of certain species in a fluid by a combination of a sieving and sorption diffusion mechanism. The rejection is low for salts with monovalent anion and non-ionized organics with a molecular weight below 150, but is high for salts with diand multi-valent anions and organics with a molecular weight above 300. Thus, NF can be used for the simultaneous removal of sodium chloride (salt) and the concentration of aqueous dye solutions [1-3].
The improved NF process can be subdivided into diafiltration and concentration [4,5]. Diafiltration refers to the process of adding water to the feed dye solution that then permeates through the NF membrane under a certain operating pressure, carrying with it salts and impurities smaller than the molecular-weight cutoff of the NF membrane used. The process then is used to purifying the dye to wash away the salts and small molecular weight residual byproducts of chemical synthesis. The amount of water added depends on the desired purity level of the final product. The higher the level in the final product, the more water needs to be added to the system. The concentrating part of the process removes water from the dye solution under pressure and thus the dye content can be concentrated to about 30%. The concentration of the dye results in significant savings in energy consumption during the drying process since membrane processes are highly efficient compared to spray drying.
3. Description of the nanofiltration process A NF plant designed and built by the Development Center of Water Treatment Technology, SOA, Hangzhou, with 12 NF elements (style 4040) was installed at the Shanghai Dyestuffs Chemical Plant No. 8 in 1993 for the desalting and concentration of dye solution in dye production. The plant is the earliest and most successful NF industrial plant in China. The plant works well and smoothly, the performance is stable, and the purity and the consistency of the produced dye have improved. In the past 6 years, the NF membrane elements were replaced only once; the service life of the NF membrane is more than 3 years, and the economic and social benefits of the NF process are very remarkable. 3.1. Flow diagram o f the nanofiltration process
The flow diagram of the NF process (Fig. 2) shows the characteristics of a high feed flow rate
S. Yu et al. / Desalination 140 (2001) 97-100 Aqueom dye
Conc~trate (abom 3 5n~/h)
1ooi i
m ~
7e
~ Membr me
-I~.,mt
99
Membrane Element!
f
90
7O
1-
80
High p m s u r e pump P~aeate (0.5-1.Om~/h)
Fig. 2. Flow diagram of the NF process.
40 -qo o
1
2
3
4
6
6
Salt Commt ( ~ )
and short flow distance. The NF membrane elements used in the plant are spiral wound with cellulose acetate (the rejection of NaCl is about 50% for 2000mg/l aqueous sodium chloride at 1.0MPa), produced by the Development Center of Water Treatment Technology, SOA, Hangzhou. The pump used in the plant is an Osmonics multi-stage centrifuge high-pressure pump with a performance of 5.7 m3/h at 2.0 MPa. The operating pressure of the plant can be regulated in the range of 2.0--3.0 MPa.
Fig. 3. Salt passage ratio through membrane.
Table 1 Dye rejectionof the membrane Dye (molecularweight)
Rejection, %
Yellow Orange Red Blue Brown
= 100 = 100 99.10 99.80 = 100
(876) (747) (943) (725) (818)
3.2. Performance o f the nanofiltration process
Different kinds o f dyes with different molecular weights and structures were produced through the NF process. The rejection of dyes and the salt passage ratio of the membrane are shown in Table 1 and Fig. 3, respectively. The membrane rejects dyes with high efficiency, while the salt passage ratio through the membrane depends on the salt content of the feed dye solution, and will decrease as the salt is washed away from the dye solution during the NF process. The typical results obtained while desalting and concentrating the aqueous dye through the NF system are given in Table 2. The membrane system produced aqueous dye having more than 25% dye and less than 1% salt content. The typical change of permeate flux of the plant during the desalting and concentration process is
Table 2 Typical results obtained while desalting and concentrating dye using nanofiltration
Dye content, % NaCI content, %
Feed aqueous dye
Concentrated aqueous dye
9.88 4.16
25.6 0.64
shown in Fig. 4. The permeate flux will change with the removal of salt from the system and the increment of dye content. During the entire NF process, wash water is added at different times, as sometimes pre-concentrating before diafiltration is necessary. The system can be optimized for maximum salt passage, a minimum amount of wash water and the shortest time-consumption by
I00
S. Yu et al. / Desalination 140 (2001) 97-100
0.8
0.0
I
,
i
t
I
,
l
*
I
*
I
6
Ji
o
$
10
Opm
18
20
28
z TUne (h)
Fig. 4. Typical change of permeate flux during desalting and concentration.
controlling the conductivity of the permeate and concentrate. For diafiltration, the conductivity of the permeate is controlled so that it is larger than that of the concentrate, while for concentrating part, the conductivity of the permeate is controlled to be nearly equal to that of the concentrate.
membrane process followed by spray drying provided a continuous process, operating automatically and producing dye of high purity and consistency. Since the operation is automatic, the costs of labor have been drastically reduced.
References 4. C o n c l u s i o n s
The NF membrane separation technology was successfully used for desalting and concentration in dye production. The membrane system produced dye solution having more than 25% dye and about less than 1o~ salt content. The aqueous dye desalted and concentrated by NF was continuously dried by a spray dryer. Thus the NF
[1] P.K.Eriksson,Environ.Progr., 7(1) (1988) 58. [2] R. Rautenbach and A. Groschl, Desalination, 77 (1990) 77. [3] L.P.Raman,M. Cheryanand N. Rajagopalan,Chem. EngineeringProgr.,4 (1994) 68. [4] J. Cadotte, R. Forester, M. Kim, R. Peterson and T. Stocker, Desalination,70 (1988) 77. [5] C. Gao, Technol.Wat. TreaUnent,22(3) (1996) 147 [in Chinese].