CA1096556A - Flexible microporous cellulosic membranes and methods of formation and use thereof - Google Patents
Flexible microporous cellulosic membranes and methods of formation and use thereofInfo
- Publication number
- CA1096556A CA1096556A CA316,347A CA316347A CA1096556A CA 1096556 A CA1096556 A CA 1096556A CA 316347 A CA316347 A CA 316347A CA 1096556 A CA1096556 A CA 1096556A
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- CA
- Canada
- Prior art keywords
- membrane
- membranes
- cellulose
- polymers
- formation
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000012528 membrane Substances 0.000 title claims abstract description 57
- 238000000034 method Methods 0.000 title claims description 15
- 230000015572 biosynthetic process Effects 0.000 title claims description 4
- 229920000642 polymer Polymers 0.000 claims abstract description 28
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 claims abstract description 18
- 239000000020 Nitrocellulose Substances 0.000 claims abstract description 17
- FJWGYAHXMCUOOM-QHOUIDNNSA-N [(2s,3r,4s,5r,6r)-2-[(2r,3r,4s,5r,6s)-4,5-dinitrooxy-2-(nitrooxymethyl)-6-[(2r,3r,4s,5r,6s)-4,5,6-trinitrooxy-2-(nitrooxymethyl)oxan-3-yl]oxyoxan-3-yl]oxy-3,5-dinitrooxy-6-(nitrooxymethyl)oxan-4-yl] nitrate Chemical compound O([C@@H]1O[C@@H]([C@H]([C@H](O[N+]([O-])=O)[C@H]1O[N+]([O-])=O)O[C@H]1[C@@H]([C@@H](O[N+]([O-])=O)[C@H](O[N+]([O-])=O)[C@@H](CO[N+]([O-])=O)O1)O[N+]([O-])=O)CO[N+](=O)[O-])[C@@H]1[C@@H](CO[N+]([O-])=O)O[C@@H](O[N+]([O-])=O)[C@H](O[N+]([O-])=O)[C@H]1O[N+]([O-])=O FJWGYAHXMCUOOM-QHOUIDNNSA-N 0.000 claims abstract description 17
- 229920001220 nitrocellulos Polymers 0.000 claims abstract description 17
- 239000000203 mixture Substances 0.000 claims abstract description 16
- 229920002301 cellulose acetate Polymers 0.000 claims abstract description 13
- 238000001471 micro-filtration Methods 0.000 claims abstract description 12
- 229920001282 polysaccharide Polymers 0.000 claims abstract description 10
- 239000005017 polysaccharide Substances 0.000 claims abstract description 10
- 150000004676 glycans Chemical class 0.000 claims abstract description 8
- 239000011148 porous material Substances 0.000 claims description 27
- 238000005266 casting Methods 0.000 claims description 11
- KXJGSNRAQWDDJT-UHFFFAOYSA-N 1-acetyl-5-bromo-2h-indol-3-one Chemical compound BrC1=CC=C2N(C(=O)C)CC(=O)C2=C1 KXJGSNRAQWDDJT-UHFFFAOYSA-N 0.000 claims description 10
- 238000001914 filtration Methods 0.000 claims description 6
- 239000002245 particle Substances 0.000 claims description 4
- 238000009826 distribution Methods 0.000 claims description 2
- 239000006194 liquid suspension Substances 0.000 claims 1
- 150000002148 esters Chemical class 0.000 abstract description 2
- 229920002678 cellulose Polymers 0.000 description 13
- 239000001913 cellulose Substances 0.000 description 13
- 239000002904 solvent Substances 0.000 description 9
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 6
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- CSCPPACGZOOCGX-UHFFFAOYSA-N Acetone Chemical compound CC(C)=O CSCPPACGZOOCGX-UHFFFAOYSA-N 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 235000019441 ethanol Nutrition 0.000 description 4
- 239000000463 material Substances 0.000 description 4
- 238000000108 ultra-filtration Methods 0.000 description 4
- WEVYAHXRMPXWCK-UHFFFAOYSA-N Acetonitrile Chemical compound CC#N WEVYAHXRMPXWCK-UHFFFAOYSA-N 0.000 description 3
- NLHHRLWOUZZQLW-UHFFFAOYSA-N Acrylonitrile Chemical compound C=CC#N NLHHRLWOUZZQLW-UHFFFAOYSA-N 0.000 description 3
- PEDCQBHIVMGVHV-UHFFFAOYSA-N Glycerine Chemical compound OCC(O)CO PEDCQBHIVMGVHV-UHFFFAOYSA-N 0.000 description 3
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 3
- 239000003795 chemical substances by application Substances 0.000 description 3
- -1 polysaccharide ethers Chemical class 0.000 description 3
- 238000001223 reverse osmosis Methods 0.000 description 3
- 230000001954 sterilising effect Effects 0.000 description 3
- 238000004659 sterilization and disinfection Methods 0.000 description 3
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 229920001661 Chitosan Polymers 0.000 description 2
- 229920000869 Homopolysaccharide Polymers 0.000 description 2
- 239000003570 air Substances 0.000 description 2
- 239000012620 biological material Substances 0.000 description 2
- 150000002170 ethers Chemical class 0.000 description 2
- 239000000706 filtrate Substances 0.000 description 2
- 238000002156 mixing Methods 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000012360 testing method Methods 0.000 description 2
- QTBSBXVTEAMEQO-UHFFFAOYSA-M Acetate Chemical compound CC([O-])=O QTBSBXVTEAMEQO-UHFFFAOYSA-M 0.000 description 1
- 229920000742 Cotton Polymers 0.000 description 1
- 239000001856 Ethyl cellulose Substances 0.000 description 1
- ZZSNKZQZMQGXPY-UHFFFAOYSA-N Ethyl cellulose Chemical compound CCOCC1OC(OC)C(OCC)C(OCC)C1OC1C(O)C(O)C(OC)C(CO)O1 ZZSNKZQZMQGXPY-UHFFFAOYSA-N 0.000 description 1
- 229920001131 Pulp (paper) Polymers 0.000 description 1
- 239000012080 ambient air Substances 0.000 description 1
- 238000009835 boiling Methods 0.000 description 1
- 239000012612 commercial material Substances 0.000 description 1
- 238000010960 commercial process Methods 0.000 description 1
- 238000007796 conventional method Methods 0.000 description 1
- 125000004093 cyano group Chemical group *C#N 0.000 description 1
- 238000004090 dissolution Methods 0.000 description 1
- 239000012153 distilled water Substances 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 229920001249 ethyl cellulose Polymers 0.000 description 1
- 235000019325 ethyl cellulose Nutrition 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 235000013305 food Nutrition 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- 125000002887 hydroxy group Chemical group [H]O* 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000006193 liquid solution Substances 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000005374 membrane filtration Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000000704 physical effect Effects 0.000 description 1
- 239000004014 plasticizer Substances 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 125000001436 propyl group Chemical group [H]C([*])([H])C([H])([H])C([H])([H])[H] 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000002002 slurry Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 239000002344 surface layer Substances 0.000 description 1
- 239000000725 suspension Substances 0.000 description 1
- 230000008961 swelling Effects 0.000 description 1
- 229920001059 synthetic polymer Polymers 0.000 description 1
- 239000003039 volatile agent Substances 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/08—Polysaccharides
- B01D71/12—Cellulose derivatives
- B01D71/22—Cellulose ethers
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/08—Polysaccharides
- B01D71/12—Cellulose derivatives
- B01D71/14—Esters of organic acids
- B01D71/16—Cellulose acetate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D71/00—Semi-permeable membranes for separation processes or apparatus characterised by the material; Manufacturing processes specially adapted therefor
- B01D71/06—Organic material
- B01D71/08—Polysaccharides
- B01D71/12—Cellulose derivatives
- B01D71/20—Esters of inorganic acids, e.g. cellulose nitrate
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D61/00—Processes of separation using semi-permeable membranes, e.g. dialysis, osmosis or ultrafiltration; Apparatus, accessories or auxiliary operations specially adapted therefor
- B01D61/14—Ultrafiltration; Microfiltration
- B01D61/147—Microfiltration
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Inorganic Chemistry (AREA)
- Separation Using Semi-Permeable Membranes (AREA)
Abstract
Abstract Microfiltration membranes are described comprising 10% to 50% cyanoethylated polysaccharide ether polymers blended with 50% to 90X polymers of cellulose nitrate, cellulose acetate or mixtures of the two. These membranes are flexible and strong and can be readily pleated for use in cartridge filters as well as used flat in con-ventional single- or multi-plate holders. They are also more thermally stable than conventional "mixed ester" (cellulose nitrate/cellulose acetate) membranes.
Description
Technical Field The invention herein relates to cellulosic membranes. More particularly, it relates to those membranes formed from cellulose derivatives and having pore sizes and configuratiorls suitable for use in microfiltration processes.
Background of Prior Art Cellulose and its derivatives are well known and have been described in numerous books and publications. See, e.g., Ott et al, eds., "Cellulose and Cellulose Derivatives", Hi~h Polymers, Vol. V, especially Section IX (Interscience, 1954) and Kirk-Othmer, Encyclo-pedia of Chemical Technolo~y, ~ol. 4, pages 593-683 (2d edn., 19~7).
Microporous membranes composed of cellulose derivatives, primarily cellulose nitrate and/or cellulose acetate are also well known and have been extensively described ancl studied; see Kesting, Synthetic Polymer c Membranes (McGraw-~lill, 1971), especially Chapters 1, 2 and 5. Such membranes find utility in a wide variety of laboratory and commercial processes involving microfiltration.
Micro-Filtration is a membrane filtration process intended to effect filtration of particles having a size in the range o-F about 0.1 to about 10 micrometers. Microfiltration is to be distinguished from two other types oF processes which also utilize semipermeable membranes for separation: ultrafiltrat;on and reverse osmosis. Ultra-filtration operates at a significantly lower particle size range than micro-f;ltration and is intended for Filtration of individual polyrner molecules. Reverse osmosis operates at yet lower particle size ranges and is used to Filter individual ions. Membranes intended for use in microfiltration have pores which are visible under normal light magni-fication, while those intended for use in reverse osmosis and ultra-filtration do not show visible pores. (In the past ultrafiltration and microf;ltration have sometimes been considered to be synonymous, but curren-t filtration practice and theory now clearly distinguish between the two, such that the membrane materials utilized for micro-filtra'cion are not considered to be equivalent to those used for ultrafiltration. See Kesting, op. cit.~ Chapter 1.
Although the cellulose derivative membranes such as the cellulose nitrate and cellulose acetate "mixed ester" membranes have been used widely for a number of years, they suffer from -two serious ' ~
~Q~, Ei5S~i
Background of Prior Art Cellulose and its derivatives are well known and have been described in numerous books and publications. See, e.g., Ott et al, eds., "Cellulose and Cellulose Derivatives", Hi~h Polymers, Vol. V, especially Section IX (Interscience, 1954) and Kirk-Othmer, Encyclo-pedia of Chemical Technolo~y, ~ol. 4, pages 593-683 (2d edn., 19~7).
Microporous membranes composed of cellulose derivatives, primarily cellulose nitrate and/or cellulose acetate are also well known and have been extensively described ancl studied; see Kesting, Synthetic Polymer c Membranes (McGraw-~lill, 1971), especially Chapters 1, 2 and 5. Such membranes find utility in a wide variety of laboratory and commercial processes involving microfiltration.
Micro-Filtration is a membrane filtration process intended to effect filtration of particles having a size in the range o-F about 0.1 to about 10 micrometers. Microfiltration is to be distinguished from two other types oF processes which also utilize semipermeable membranes for separation: ultrafiltrat;on and reverse osmosis. Ultra-filtration operates at a significantly lower particle size range than micro-f;ltration and is intended for Filtration of individual polyrner molecules. Reverse osmosis operates at yet lower particle size ranges and is used to Filter individual ions. Membranes intended for use in microfiltration have pores which are visible under normal light magni-fication, while those intended for use in reverse osmosis and ultra-filtration do not show visible pores. (In the past ultrafiltration and microf;ltration have sometimes been considered to be synonymous, but curren-t filtration practice and theory now clearly distinguish between the two, such that the membrane materials utilized for micro-filtra'cion are not considered to be equivalent to those used for ultrafiltration. See Kesting, op. cit.~ Chapter 1.
Although the cellulose derivative membranes such as the cellulose nitrate and cellulose acetate "mixed ester" membranes have been used widely for a number of years, they suffer from -two serious ' ~
~Q~, Ei5S~i
-2-deficiencies: they are very brittle and they have little thermal stability. They are therefore very susceptible to breaking during handling and must be handled with great caut;on. Sterilization through autoclaving is obtained only with some difficulty because of the brittleness and low thermal stability. Their brittleness also of course precludes their being folded and therefore they cannot be pleated to make them suitable for use in cartidge filtration units.
There have been attempts to alleviate the brittleness problem by incorporating plasticizers into the compositions but this technique has not met with marked success.
Ethylcellulose has been found to confer some ;ncrease in strength to cellulose nitrate membranes but such membranes are sus-ceptible to dissolution in alcohol which causes blockage of the pores.
It would therefore be highly desirable to have a membrane which would have pores of a size appropriate for use in microfiltraiton processes and yet be strong, flexible, unaffected by the chemical nature of common filtrates, and capable of being autoclaved for sterilization.
Brief Summary of Invention The invention herein is a novel membrane for microfiltration which comprises a combination of cyanoethylated polysaccharide ether polymers and polymers of cellulose nitrate, ce11ulose acetate, or mixtures of cellulose ace~a~e and cellulose nitrate polym~rs. In the present membrane the cyanoethylated polysaccharide ether polymers will 25 be present as from 10% to 50% by weight of the composition with the balance of the compos~tion being the cellulose nitrate and/or cellulose acetate polymers.
Detailed Description of Invention The ethers useful in the present invention are the cyano~
30 ethylated ethers of homopolysaccharides, notably cellulose and chitosan.
Preferred among these is cyanoethylcellulose. Cellulose, chi~in and the related homopolysaccharides having reactive hydroxyl groups are known to react in the presence of a base with acrylonitr;le to form cyanoethylated polysaccharide ethers. Reactions of this type have 35 been described in the Ott et al reference mentioned above, particularly r in Section IX-E-9. Consequently, cyanoethylcellulose may be formed by the reaction of acrylonitrile with cellulose in the presence of a base ~65~;6 such as dilute sodium hydroxide, while cyanoethylchitosan may be similarly formed.
The novel membranes of the present invention are formed by blending together the eyanoethylated polysaccharide ether polymers and the polymers of cellulose nitrate, cellulose acetate, or a mixture of cellulose acetate and cellulose nitrate. In the blend of this com-position the cyanoethylated polysaccharide ether polymers will be present as from about 10% to 50% by weight of the composition, while the cellulose nitrate and/or cellulose acetate polymers will be present 0 as the balance (90% to 50% by weight) of the composition. Whether cellulose nitrate, cellulose acetate, or a mixture of the two types of polymers will be preferred for blending with ~he ether polymers will be determined by the particular application for which the finished membrane is ultimately to be used, and will be readily determined by those skilled in the art. For most purposes, however, it will be found that the cellulose nitrate polymers will be preferred.
The membranes of the present invention are formed by phase inversion casting in either wet or dry systems in accordance wit'n conventional techniques of the prior art. In such techniques the membranes are cast from a slurry of the polymers and pore forming agents (nonsolvents) dispersed in suitable solvents. The phase inversion process is described in detai1 in Kesting, oP. cit., Section 5.1 and those details need not be repeated here. The phase inversion casting process may be carried out under "wet" or "dry" conditions.
These designations refer to the medium in which the fina1 sol~ent removal after phase inversion is carried out. In the com~only used "dry" process the ~lnal solvent removal is carried out in the presence of air or other gaseous medium which is chemically inert to the membrane. In a "wet" process the final solvent removal is carriPd out in a liquid solution which is also inert chemically to the membrane.
The phase inversion casting process may be carried out under any convenient conditions of the type described in the afsrementioned Kesting reference. The membrane is cast onto an appropriate substrate commonly in ambient air and at a temperature of approximately 20C to 25C. Membrane thickness is controlled by use of a doctor blade. The - particular pore size desired will be determined by control of the reaction conditions in a manner understood by those skilled in the ~LQc~
art. The Kesting reference (especially Sect;on 5.2) sets forth the effects of variations in the solubility, concentration, structural regularity, miscibility, volatility and other physical properties of the polymers, solvents and nonsolvents of the types useful herein.
For instance, ;t is known that the higher the solids concentration of the polymer, the smaller will be the pore size of the finished membrane.
Solids contents will normally be in the range of about 4.25% to 8.0 %
by weight~ commonly 4.25% to 6.5% and preferably 5.0% to 5.5%.
Similarly, the higher the concentration of non-solvents the larger will be the pore size, while the higher the boiling point of the nonsolvent the larger will be the final pore size for a given con-centration o~ nonsolvent. The effects of other variables are also well known. For instance, the higher the processing temperature the smaller will be the final pore size. In a dry process the flow of air or other inert gas should be low enough to prevent "skinning" of the surface of the membrane (i.e. formation of a surface layer with pores of a size less than the pore size required for microfiltration) while yet retaining high enough flow velocity to allow remGval of solvent volatiles.
The microfiltration membranes of the invention will have pore size distributions such that average pore sizes are in the range of 9.05 to 10.0 um, normally 0.1 to 5.0 um. While the pore sizes of each membrane are not all uniform, the pore sizeOdistribution is sufficiently small tha~ one can readily differentiate between membranes having average pore sizes of 0.22 um, 0.45 um7 0~65 um9 and so forth.
The preferred solvent or swelling agents for use in the pr~sent invention are acetone and acetonitrile~ although other materials having similar properties under a given set of reaction conditions in conjunotion with the materials of the present compositions can also be used. Similarly~ a variety of nonsolvents (pore producing agents) may be used, preferred among which are ethanol and the isomeric propyl and butyl alcohols. The proportions of solvents and nonsolvents may be varied over a wide range as described in Section 5.1 of the Kesting reference. Typically there will be on the order of 50% to 55% solvent and about 40% nonsolvent in the solution or suspension containing the polymers. These proportions may be Yaried considerably, however, to regulate the rapidity of phase inversion, to compensate for the various types of materials which may be present, and to effect the ~ormation of various sizes of pores.
The following examples will illustrate the novel membranes of the present invention and also their method of manufacture.
Example 1 Cellulose from cotton linters or wood pulp is reacted with an equal weight of 2% aqueous sodium hydroxide and acrylonitrile in the ratio of 15 parts by weight of acrylonitrile per part by weight of cellulose to produce cyanoethylcellulose having an 11.9 percent nitrogen content and a degree of substitution ~D.S.) of approximately 2.5. The resulting cyanoethylcellulose may be used as produced.
Example 2 Chitosan (hydrolyzed ch;tin) is cyanoethylated as in Example 1 to produce a cyanoethylchitosan which when incorporated into a cellulose nitrate membrane behaves as does the product of Example 1.
Example 3 A solution containing 4% cellulose nitrate, 1% cyanoethyl-cellulose, 54.2 % acetone, 23.7~ ethyl alcohol, 12.3% n-butyl alcohol,
There have been attempts to alleviate the brittleness problem by incorporating plasticizers into the compositions but this technique has not met with marked success.
Ethylcellulose has been found to confer some ;ncrease in strength to cellulose nitrate membranes but such membranes are sus-ceptible to dissolution in alcohol which causes blockage of the pores.
It would therefore be highly desirable to have a membrane which would have pores of a size appropriate for use in microfiltraiton processes and yet be strong, flexible, unaffected by the chemical nature of common filtrates, and capable of being autoclaved for sterilization.
Brief Summary of Invention The invention herein is a novel membrane for microfiltration which comprises a combination of cyanoethylated polysaccharide ether polymers and polymers of cellulose nitrate, ce11ulose acetate, or mixtures of cellulose ace~a~e and cellulose nitrate polym~rs. In the present membrane the cyanoethylated polysaccharide ether polymers will 25 be present as from 10% to 50% by weight of the composition with the balance of the compos~tion being the cellulose nitrate and/or cellulose acetate polymers.
Detailed Description of Invention The ethers useful in the present invention are the cyano~
30 ethylated ethers of homopolysaccharides, notably cellulose and chitosan.
Preferred among these is cyanoethylcellulose. Cellulose, chi~in and the related homopolysaccharides having reactive hydroxyl groups are known to react in the presence of a base with acrylonitr;le to form cyanoethylated polysaccharide ethers. Reactions of this type have 35 been described in the Ott et al reference mentioned above, particularly r in Section IX-E-9. Consequently, cyanoethylcellulose may be formed by the reaction of acrylonitrile with cellulose in the presence of a base ~65~;6 such as dilute sodium hydroxide, while cyanoethylchitosan may be similarly formed.
The novel membranes of the present invention are formed by blending together the eyanoethylated polysaccharide ether polymers and the polymers of cellulose nitrate, cellulose acetate, or a mixture of cellulose acetate and cellulose nitrate. In the blend of this com-position the cyanoethylated polysaccharide ether polymers will be present as from about 10% to 50% by weight of the composition, while the cellulose nitrate and/or cellulose acetate polymers will be present 0 as the balance (90% to 50% by weight) of the composition. Whether cellulose nitrate, cellulose acetate, or a mixture of the two types of polymers will be preferred for blending with ~he ether polymers will be determined by the particular application for which the finished membrane is ultimately to be used, and will be readily determined by those skilled in the art. For most purposes, however, it will be found that the cellulose nitrate polymers will be preferred.
The membranes of the present invention are formed by phase inversion casting in either wet or dry systems in accordance wit'n conventional techniques of the prior art. In such techniques the membranes are cast from a slurry of the polymers and pore forming agents (nonsolvents) dispersed in suitable solvents. The phase inversion process is described in detai1 in Kesting, oP. cit., Section 5.1 and those details need not be repeated here. The phase inversion casting process may be carried out under "wet" or "dry" conditions.
These designations refer to the medium in which the fina1 sol~ent removal after phase inversion is carried out. In the com~only used "dry" process the ~lnal solvent removal is carried out in the presence of air or other gaseous medium which is chemically inert to the membrane. In a "wet" process the final solvent removal is carriPd out in a liquid solution which is also inert chemically to the membrane.
The phase inversion casting process may be carried out under any convenient conditions of the type described in the afsrementioned Kesting reference. The membrane is cast onto an appropriate substrate commonly in ambient air and at a temperature of approximately 20C to 25C. Membrane thickness is controlled by use of a doctor blade. The - particular pore size desired will be determined by control of the reaction conditions in a manner understood by those skilled in the ~LQc~
art. The Kesting reference (especially Sect;on 5.2) sets forth the effects of variations in the solubility, concentration, structural regularity, miscibility, volatility and other physical properties of the polymers, solvents and nonsolvents of the types useful herein.
For instance, ;t is known that the higher the solids concentration of the polymer, the smaller will be the pore size of the finished membrane.
Solids contents will normally be in the range of about 4.25% to 8.0 %
by weight~ commonly 4.25% to 6.5% and preferably 5.0% to 5.5%.
Similarly, the higher the concentration of non-solvents the larger will be the pore size, while the higher the boiling point of the nonsolvent the larger will be the final pore size for a given con-centration o~ nonsolvent. The effects of other variables are also well known. For instance, the higher the processing temperature the smaller will be the final pore size. In a dry process the flow of air or other inert gas should be low enough to prevent "skinning" of the surface of the membrane (i.e. formation of a surface layer with pores of a size less than the pore size required for microfiltration) while yet retaining high enough flow velocity to allow remGval of solvent volatiles.
The microfiltration membranes of the invention will have pore size distributions such that average pore sizes are in the range of 9.05 to 10.0 um, normally 0.1 to 5.0 um. While the pore sizes of each membrane are not all uniform, the pore sizeOdistribution is sufficiently small tha~ one can readily differentiate between membranes having average pore sizes of 0.22 um, 0.45 um7 0~65 um9 and so forth.
The preferred solvent or swelling agents for use in the pr~sent invention are acetone and acetonitrile~ although other materials having similar properties under a given set of reaction conditions in conjunotion with the materials of the present compositions can also be used. Similarly~ a variety of nonsolvents (pore producing agents) may be used, preferred among which are ethanol and the isomeric propyl and butyl alcohols. The proportions of solvents and nonsolvents may be varied over a wide range as described in Section 5.1 of the Kesting reference. Typically there will be on the order of 50% to 55% solvent and about 40% nonsolvent in the solution or suspension containing the polymers. These proportions may be Yaried considerably, however, to regulate the rapidity of phase inversion, to compensate for the various types of materials which may be present, and to effect the ~ormation of various sizes of pores.
The following examples will illustrate the novel membranes of the present invention and also their method of manufacture.
Example 1 Cellulose from cotton linters or wood pulp is reacted with an equal weight of 2% aqueous sodium hydroxide and acrylonitrile in the ratio of 15 parts by weight of acrylonitrile per part by weight of cellulose to produce cyanoethylcellulose having an 11.9 percent nitrogen content and a degree of substitution ~D.S.) of approximately 2.5. The resulting cyanoethylcellulose may be used as produced.
Example 2 Chitosan (hydrolyzed ch;tin) is cyanoethylated as in Example 1 to produce a cyanoethylchitosan which when incorporated into a cellulose nitrate membrane behaves as does the product of Example 1.
Example 3 A solution containing 4% cellulose nitrate, 1% cyanoethyl-cellulose, 54.2 % acetone, 23.7~ ethyl alcohol, 12.3% n-butyl alcohol,
3.3% water and 1.5% glycerol is allowed to desolvate completely in a dry phase inversion casting process to produce flexible heat resistant membranes having pore sizes suitable for microfiltration. In various experiments using this solution reaction conditions were varied according to the guidelines discussed above to produce membranes having substantially uniform pore sizes in the range of from 0.05 to 5O0 um.
Example 4 A solution similar to that described in Example 3 but con-taining 1% cyanoethylchitosan instead of cyanoethyl-cellulose ls allowed to desolvate partially and then is immersed in water (wet phase inversion casting process) to produce microporous membranes equivalent to those formulated in accordance with Example 3.
Example 5 A solution similar to that described in Example 3 but con-taining 4% cellulose nitrate, 0.5% cellulose acetate, and 0.5% cyano-ethylcellulose is utilized in a dry phase inversion casting process toform membranes equivalent to those of Example 3.
~L~ i5 Example 6 A solution similar to that described in Example 3 but containing 4.5~ cellulose acetate and 0.~% cyanoethyl-cellulose is used in a dry phase inversion casting process to form membranes S equivalent to those of Example 3.
For comparison purposes, the properties of membranes formed in accordance with Example 3 above and having average pore sizes of 0 22 um were compared with commercial 0.22 um cellulose nitrate-cellulose acetate membranes of the prior art. The commercial materials were all found to be quite brittle such that just ordinary handling and flexing caused rupture of many samples. On the other hand, the membranes of the present invention were quite flexible, to the point where they could be readily bent into tight U-shapes and even creased without rupture of the membrane. In autoclave sterilization tests in which the membranes were placed unrestrained in an autoclave at 261F
(127C~ for one hour, the membranes of the prior art not containing any cyanoethylated polysaccharide ethers were found to shrink by approximately 12% to 14%, while the membranes of the present invention shrank only approximately 0.08%. It is thus evident ~rom these tests that the membrane compositions of the present invention are markedly superior to the membranes o~ the prior art. ~~
Statement of Industrial Apelication The invention herein provides membrane filters for use in a wide variety of industrial and related microfiltr~tion applications, including (but not limited to~ filtration of pharmaceuticals9 bio-logical materials, foods, aerospace fuels and distilled water used in electronics, pharmaceutical, and aerospace processes Generally, the filters are used in industrial applications where it is vital that all partlculate matter and/or biological material greater than the pore size of the filter must be removed from the filtrate.
~,
Example 4 A solution similar to that described in Example 3 but con-taining 1% cyanoethylchitosan instead of cyanoethyl-cellulose ls allowed to desolvate partially and then is immersed in water (wet phase inversion casting process) to produce microporous membranes equivalent to those formulated in accordance with Example 3.
Example 5 A solution similar to that described in Example 3 but con-taining 4% cellulose nitrate, 0.5% cellulose acetate, and 0.5% cyano-ethylcellulose is utilized in a dry phase inversion casting process toform membranes equivalent to those of Example 3.
~L~ i5 Example 6 A solution similar to that described in Example 3 but containing 4.5~ cellulose acetate and 0.~% cyanoethyl-cellulose is used in a dry phase inversion casting process to form membranes S equivalent to those of Example 3.
For comparison purposes, the properties of membranes formed in accordance with Example 3 above and having average pore sizes of 0 22 um were compared with commercial 0.22 um cellulose nitrate-cellulose acetate membranes of the prior art. The commercial materials were all found to be quite brittle such that just ordinary handling and flexing caused rupture of many samples. On the other hand, the membranes of the present invention were quite flexible, to the point where they could be readily bent into tight U-shapes and even creased without rupture of the membrane. In autoclave sterilization tests in which the membranes were placed unrestrained in an autoclave at 261F
(127C~ for one hour, the membranes of the prior art not containing any cyanoethylated polysaccharide ethers were found to shrink by approximately 12% to 14%, while the membranes of the present invention shrank only approximately 0.08%. It is thus evident ~rom these tests that the membrane compositions of the present invention are markedly superior to the membranes o~ the prior art. ~~
Statement of Industrial Apelication The invention herein provides membrane filters for use in a wide variety of industrial and related microfiltr~tion applications, including (but not limited to~ filtration of pharmaceuticals9 bio-logical materials, foods, aerospace fuels and distilled water used in electronics, pharmaceutical, and aerospace processes Generally, the filters are used in industrial applications where it is vital that all partlculate matter and/or biological material greater than the pore size of the filter must be removed from the filtrate.
~,
Claims (8)
1. A membrane for microfiltration which comprises a blend of 10% to 50% by weight of at least one cyanoethylated polysaccharide ether polymer and 50% to 90% by weight of at least one polymer selected from the group consisting of cellulose nitrate polymers, cellulose acetate polymers or mixtures thereof.
2. A membrane as in Claim 1 wherein said cyanoethylated polysaccharide ether polymer is a polymer of cyanoethylcellulose or cyanoethylchitosan.
3. A membrane as in Claim 2 wherein said cyanoethylated polysaccharide ether polymer is a polymer of cyanoethylcellulose.
4. A membrane as in Claims 1 or 3 having a pore size distribution with an average pore size in the range of 0.05 to 10.0 um.
5. A membrane as in Claim 4 wherein the average pore size is in the range of 0.1 to 5.0 um.
6. A method of formation of a membrane as in Claims 1 or 3 comprising casting said blend of polymers in a wet phase inversion casting process.
7. A method of formation of a membrane as in Claims 1 or 3 comprising casting said blend of polymers in a dry phase inversion casting process.
8. A microfiltration process comprising filtering a liquid suspension of particles having sizes in the range of 0.05 to 10.0 um through a membrane as in Claims 1 or 3.
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US85277677A | 1977-11-18 | 1977-11-18 | |
| US852,776 | 1977-11-18 | ||
| US953,377 | 1977-11-21 | ||
| US05/953,377 US4220477A (en) | 1978-10-23 | 1978-10-23 | Flexible microporous cellulosic membranes and methods of formation and use thereof |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1096556A true CA1096556A (en) | 1981-03-03 |
Family
ID=27127086
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA316,347A Expired CA1096556A (en) | 1977-11-18 | 1978-11-16 | Flexible microporous cellulosic membranes and methods of formation and use thereof |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS5490082A (en) |
| BR (1) | BR7807556A (en) |
| CA (1) | CA1096556A (en) |
| DE (1) | DE2849863C3 (en) |
| FR (1) | FR2409077A1 (en) |
| GB (1) | GB2009031B (en) |
| IE (1) | IE47585B1 (en) |
| IT (1) | IT7851950A0 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE19613484A1 (en) * | 1996-04-04 | 1997-10-09 | Buna Sow Leuna Olefinverb Gmbh | Biodegradable gas separation membrane with high selectivity for carbon di:oxide permeation |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE329117C (en) * | 1916-08-21 | 1920-11-15 | Richard Zsigmondy Dr | Membrane filters and processes for their manufacture |
| DE1017596B (en) * | 1956-07-04 | 1957-10-17 | Membranfiltergesellschaft Sart | Method and device for the continuous production of membrane filters |
| JPS5538366B2 (en) * | 1974-03-13 | 1980-10-03 | ||
| GB1430323A (en) * | 1974-03-20 | 1976-03-31 | Chem Systems | Process for the preparation of asymmetric reverse osmosis membranes |
-
1978
- 1978-11-09 GB GB7843859A patent/GB2009031B/en not_active Expired
- 1978-11-16 CA CA316,347A patent/CA1096556A/en not_active Expired
- 1978-11-17 JP JP14122278A patent/JPS5490082A/en active Granted
- 1978-11-17 FR FR7832489A patent/FR2409077A1/en active Granted
- 1978-11-17 DE DE2849863A patent/DE2849863C3/en not_active Expired
- 1978-11-17 IE IE2266/78A patent/IE47585B1/en unknown
- 1978-11-17 IT IT7851950A patent/IT7851950A0/en unknown
- 1978-11-17 BR BR7807556A patent/BR7807556A/en unknown
Also Published As
| Publication number | Publication date |
|---|---|
| BR7807556A (en) | 1979-07-24 |
| JPS5490082A (en) | 1979-07-17 |
| FR2409077B1 (en) | 1984-11-16 |
| IE782266L (en) | 1979-05-18 |
| DE2849863B2 (en) | 1981-03-12 |
| GB2009031B (en) | 1982-03-10 |
| DE2849863C3 (en) | 1982-06-24 |
| DE2849863A1 (en) | 1979-05-31 |
| IT7851950A0 (en) | 1978-11-17 |
| IE47585B1 (en) | 1984-05-02 |
| JPS5634132B2 (en) | 1981-08-08 |
| FR2409077A1 (en) | 1979-06-15 |
| GB2009031A (en) | 1979-06-13 |
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