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Glycol dehydration
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sieves. Membrane systems can also be used, but can suffer from moisture loss during periods of depressurisation. This invention overcomes the problem by maintaining gas flow through the membrane cartridge by the simple expedient of providing a gas reservoir or auxiliary compressor. This gives a constant gas flow through the membrane cartridge even if the main compressor is out of action. Further protection against low temperatures and dewpoint attainment is given by a heating element wrapped round the membrane cartridge.
Patent number: US 4944776 Date: 31 July 1990 Inventors: L.A. Keyser, D.A. Nelson, D.C. Thornton Applicant: Andrew Corporation
Poly(phenylene oxide) asymmetric membrane The membrane is formed from a 5-50 wt % solution of poly (2,6dimethyl)phen.ylene oxide in a solvent mixture which is mainly an aprotic solvent. This solution is formed into a nascent membrane at between 50 and 200°C; the nascent membrane is then partially dried at 20-200°C for a period of anything between 0.3 seconds and 10 mins. Preferred values for the wide reaction conditions allowed by the patent are a solution concentration of 15-35 wt % and nascent membrane formation at 70-125°C, preferably for between 3 secs and 5 mins. The polymer solution can be cast or extruded to form the nascent membrane, which can be flat or a hollow fibre. The main components of the solvent nixture are Nmethylpyrrolidone and N,N-
14
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dimethylacetamide. The final product is the outcome of precipitating the nascent membrane in a coagulation bath at 0-80°C, preferably 10-30°C; the bath is miscible with the main component of the solvent mixture but is not a solvent for the poly(phenylane oxide) membrane. The final product is an integrally skinned membrane which is suitable for gas separation processes.
Patent number: US 4944775 Date: 31 July 1990 Inventor: D.A. Hayes Applicant: E I Du Pont de Nemours & Co.
Glycol dehydration Pervaporation is proposed as a better alternative to distillation when concentrating solutions of ethylene glycol. The selectivity of the membrane is important. This invention claims that glycol content in the permeate can be as low as 0.4% when this membrane is employed; less than 10% of the permeate glycol content of prior art membranes. Flux rates are typically three times greater than previously achieved in those circumstances. The selectivity is achieved by constructing a composite membrane on a polyester backing. The basic membrane support is a 50 micron-thick porous polysulphone layer, on which is positioned a 2 micron separating layer of cross-linked polyvinyl alcohol. The cross-linking agent is an aliphatic dialdehyde, preferably glutaraldehyde; the desirable mean molecular weight of the polyvinyl alcohol is 115,000.
Patent number: US 4941976 Date: 17 July 1990 Inventor: C.R. Bartels, J. Reale Jr. Applicant: Texaco Inc.
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I
Chlorinestable membrane compositions These materials can be employed both in reverse osmosis and in gas separation processes. Their resistance to attack by dissolved chlorine reduces the cost and complexity of water or effluent treatment processes upstream of the reverse osmosis unit. The selectively permeable film comprises a cross-linked vinyl addition polymer. This is made by manufacturing a hydroxyalkyl methacrylate film which has a vinylarylalkyl dialkylsulphonium salt as the main crosslinking agent. The chlorine resistance of the membrane is evidenced by the following table, which shows flux and NaC1 rejection characteristics in a test. The same membrane was used throughout the test, and the conditions were varied from time to time: the total duration of the test was 1099 hours. For the first 775 hours of the test, the water was at a pH of 4.5 and contained 2500 ppm NaC1 and 10 p p m chlorine.
Operating conditions After After After After After
Flux Rejection
7 hrs 100 hrs 300 hrs 500 hrs 775 hrs
Distilled water for 72 hrs
(GFD)
(%)
1.33 1.40 1.42 1.42 1.24
90.2 93.8 93.5 93.1 91.5
1.56
10 p p m CI~ at pH 4.5 After 18 hrs 1.20 After 96 hrs 1.33
87.8 92.1
10 p p m CI~ at pH 8.0 After 37 hrs 1.56 After 156 hrs 1.66
69.8 70.2
Membrane Technology
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sieves. Membrane systems can also be used, but can suffer from moisture loss during periods of depressurisation. This invention overcomes the problem by maintaining gas flow through the membrane cartridge by the simple expedient of providing a gas reservoir or auxiliary compressor. This gives a constant gas flow through the membrane cartridge even if the main compressor is out of action. Further protection against low temperatures and dewpoint attainment is given by a heating element wrapped round the membrane cartridge.
Patent number: US 4944776 Date: 31 July 1990 Inventors: L.A. Keyser, D.A. Nelson, D.C. Thornton Applicant: Andrew Corporation
Poly(phenylene oxide) asymmetric membrane The membrane is formed from a 5-50 wt % solution of poly (2,6dimethyl)phen.ylene oxide in a solvent mixture which is mainly an aprotic solvent. This solution is formed into a nascent membrane at between 50 and 200°C; the nascent membrane is then partially dried at 20-200°C for a period of anything between 0.3 seconds and 10 mins. Preferred values for the wide reaction conditions allowed by the patent are a solution concentration of 15-35 wt % and nascent membrane formation at 70-125°C, preferably for between 3 secs and 5 mins. The polymer solution can be cast or extruded to form the nascent membrane, which can be flat or a hollow fibre. The main components of the solvent nixture are Nmethylpyrrolidone and N,N-
14
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dimethylacetamide. The final product is the outcome of precipitating the nascent membrane in a coagulation bath at 0-80°C, preferably 10-30°C; the bath is miscible with the main component of the solvent mixture but is not a solvent for the poly(phenylane oxide) membrane. The final product is an integrally skinned membrane which is suitable for gas separation processes.
Patent number: US 4944775 Date: 31 July 1990 Inventor: D.A. Hayes Applicant: E I Du Pont de Nemours & Co.
Glycol dehydration Pervaporation is proposed as a better alternative to distillation when concentrating solutions of ethylene glycol. The selectivity of the membrane is important. This invention claims that glycol content in the permeate can be as low as 0.4% when this membrane is employed; less than 10% of the permeate glycol content of prior art membranes. Flux rates are typically three times greater than previously achieved in those circumstances. The selectivity is achieved by constructing a composite membrane on a polyester backing. The basic membrane support is a 50 micron-thick porous polysulphone layer, on which is positioned a 2 micron separating layer of cross-linked polyvinyl alcohol. The cross-linking agent is an aliphatic dialdehyde, preferably glutaraldehyde; the desirable mean molecular weight of the polyvinyl alcohol is 115,000.
Patent number: US 4941976 Date: 17 July 1990 Inventor: C.R. Bartels, J. Reale Jr. Applicant: Texaco Inc.
•
I
Chlorinestable membrane compositions These materials can be employed both in reverse osmosis and in gas separation processes. Their resistance to attack by dissolved chlorine reduces the cost and complexity of water or effluent treatment processes upstream of the reverse osmosis unit. The selectively permeable film comprises a cross-linked vinyl addition polymer. This is made by manufacturing a hydroxyalkyl methacrylate film which has a vinylarylalkyl dialkylsulphonium salt as the main crosslinking agent. The chlorine resistance of the membrane is evidenced by the following table, which shows flux and NaC1 rejection characteristics in a test. The same membrane was used throughout the test, and the conditions were varied from time to time: the total duration of the test was 1099 hours. For the first 775 hours of the test, the water was at a pH of 4.5 and contained 2500 ppm NaC1 and 10 p p m chlorine.
Operating conditions After After After After After
Flux Rejection
7 hrs 100 hrs 300 hrs 500 hrs 775 hrs
Distilled water for 72 hrs
(GFD)
(%)
1.33 1.40 1.42 1.42 1.24
90.2 93.8 93.5 93.1 91.5
1.56
10 p p m CI~ at pH 4.5 After 18 hrs 1.20 After 96 hrs 1.33
87.8 92.1
10 p p m CI~ at pH 8.0 After 37 hrs 1.56 After 156 hrs 1.66
69.8 70.2
Membrane Technology