CA1148419A - Reverse osmosis membrane - Google Patents
Reverse osmosis membraneInfo
- Publication number
- CA1148419A CA1148419A CA000405032A CA405032A CA1148419A CA 1148419 A CA1148419 A CA 1148419A CA 000405032 A CA000405032 A CA 000405032A CA 405032 A CA405032 A CA 405032A CA 1148419 A CA1148419 A CA 1148419A
- Authority
- CA
- Canada
- Prior art keywords
- reverse osmosis
- chloride
- membrane
- halide
- osmosis membrane
- 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
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A20/00—Water conservation; Efficient water supply; Efficient water use
- Y02A20/124—Water desalination
- Y02A20/131—Reverse-osmosis
Abstract
A B S T R A C T
A composite permselective membrane is prepared by reaction of a film or layer containing cycloaliphatic polyfunctional secondary amines with a triacyl halide or its mixture with a diacyl halide. The membrane is useful in separating components of fluid mixtures or solutions, such as the removal of salts from aqueous solutions by reverse osmosis.
A composite permselective membrane is prepared by reaction of a film or layer containing cycloaliphatic polyfunctional secondary amines with a triacyl halide or its mixture with a diacyl halide. The membrane is useful in separating components of fluid mixtures or solutions, such as the removal of salts from aqueous solutions by reverse osmosis.
Description
4 1 ~
2 --This application is a division of co-pending application Serial No. 343,311, entitled "Reverse Osmosis Membrane".
Tecllnical ~ield This invcntion relates to pel~selective barri~rs in the form of thin film composite membranes for the selective separation of fluid mixtures and solutions. An aspect of this invention relates to polyamiaes (preferably ultrathin polyamides on porous supports) suitable for reverse osm~sis desalination of aqueous solutions containing dissolved solutes, to the process for preparing these mem~rane compositions, and to the process for using such membranes.
Back~ro nd o~ the Prior Art Reverse osmosis membranes have been prepared ~Lom a wide variety of ~no~n or preformed polymeric materials. In preparation of such membr2nes the polymer is typically dissolvea in a suitable solvent, cast in the form of films or fibers, and auenched in water to form asymmetric membranes. These membranes include numerous polyamide and polyimide~
type membranes that show utility in reve~se osmosis desalination processes~ In the book Reverse Osmosis and Synthetic Membranes, National Research Council of Canada, 1977, by S. Sourirajan, Chapter 9 by P. Blais presen~s an extensive list of polyamide ~5 membranes, includin~ their fabrication and propertieS.
These polyamide membranes are additionally described ` in U.S. Patent Nos. 3,567,632, 3,600,350, 3,687,~2,
Tecllnical ~ield This invcntion relates to pel~selective barri~rs in the form of thin film composite membranes for the selective separation of fluid mixtures and solutions. An aspect of this invention relates to polyamiaes (preferably ultrathin polyamides on porous supports) suitable for reverse osm~sis desalination of aqueous solutions containing dissolved solutes, to the process for preparing these mem~rane compositions, and to the process for using such membranes.
Back~ro nd o~ the Prior Art Reverse osmosis membranes have been prepared ~Lom a wide variety of ~no~n or preformed polymeric materials. In preparation of such membr2nes the polymer is typically dissolvea in a suitable solvent, cast in the form of films or fibers, and auenched in water to form asymmetric membranes. These membranes include numerous polyamide and polyimide~
type membranes that show utility in reve~se osmosis desalination processes~ In the book Reverse Osmosis and Synthetic Membranes, National Research Council of Canada, 1977, by S. Sourirajan, Chapter 9 by P. Blais presen~s an extensive list of polyamide ~5 membranes, includin~ their fabrication and propertieS.
These polyamide membranes are additionally described ` in U.S. Patent Nos. 3,567,632, 3,600,350, 3,687,~2,
3,696,031, 3,878,109, 3,90~,519, 3,9~,823, 3,951,789, and 3,993,625. These polyamide me~ran2s are presently understood to be substantially linear polymers synthesized in a prior operation, then cast or extruded into permselective membranes -~y solvent processes. Polyamide membr2nes made in this manner appear to exhibit rather low fluxes to water in reverse osmosis desalination processes, as lis-ted in Table 2 of the abovc-cited hook, such that these , ; ` ~
polyamide membrclnes have found practical use only in the form of hollow fine fibcrs as accordincJ to i the description in U.S. Patent ~o. 3,567,632.
In addi-tion, polyamide composite membranes, suitable for use in reverse osmosis dcsalination processes, have been prepared by condensation reactions in situ on a preformed support film. Examplcs of such membranes, and their preparation" are described in U.S. Patent Nos. 3,74~,642, 3,951 ~15, 4,005,012, and ~,039,440. For an example of an acid-catalyzed, in sit~ polymerization on the support, see U.S.
Patent No. 3,926,798. For an example of the crosslinXing of a preformed semi-permeable poly-benzimidazole membrane, see U.S. Patent No. 4,020,142.
Permselective membranes made by this thin film composite approach have, in some cases, exhibited ~reatly improved fluxes relative to preformed polyamides subsequently cast or extruded into membrane form by solvent processes. The aforemen-tioned U.S. Patent No. 3,7~,642 contains a detailed description of desalination membranes prepared by interfacial condensation reactions.
~ lowever, the membranes of the prior art, whether prepa~-ed from preformed polymers or by in situ 2S reaetions, have oftentimes exhibited one or more othe~r deficiencies such as low salt rejection, low d~l~abilit~ or resistance to compression, sensitivity to extremes of pH or temperature, and lack of resistance to microbial at-tack or oxidation by ch~orine in the feed water. Lack of resistance to chlorine in the feed water is a particularly note~orthy de-Ficiency in permselective polyamide membranes. According to U. S. Patent No. 3,951,815, th~ site of attack by chlorine on polyamicle mclnbranes is the amiclic hydroycn atom presel-t in the -~O--NT-I-"
group. In compositions such as the polypiperazine-amides described in U.S. Patent Nos. 3,687,842, 3,696,031, and 3,951,815, resistance to chlorine in feed waters appears to have been adequately demonstrated; however, such resistance to attack by chlorine is believed to be atypical.
It would appear that permselective polyamide mem-branes could be obtained by condensation polymerization of diacyl halides with secondary diamines. Theoretically, the resulting polymeric products would be devoid of amidic hydrogen and would therefore be expected to be insensitive to chlorine in the feed water. Representative polyamides such as this have been prepared from piperazine and its derivatives as described in U.S. Patent Nos. 3,687,842 and 3,696,031 and NTIS Rept. No. PB253 193/7GA.
These compositions exhibited permeate fluxes of 2.4 to 650 liters per square meter per day (1/m2-day) at a pressure of 80 atmospheres toward saline feed solutions containing 5,000 to 10,000 ppm sodium chloride. These fluxes are generally uneconomical for use in reverse osmosis desalin-ation processes (except in the form of hollow fine fibers).
Currently, process economics indicate a need for membrane fluxes of 600 to 800 1/m2-day at pressures of 55 to 70 atmospheres for seawater feed (35,000 to 42,000 ppm total dissolved salts). For brackish waters containing 3,000 to 10,000 ppm salts, economically attractive membranes must provide permeate fluxes of 600 to 800 l/m ~day at pressures of only 25 to 40 atmospheres. While specific reverse osmosis applications for permselective membranes may deviate from these requirements, such membranes will no-t achieve broad commercial applicability ~ _ n.. _.. ___.
polyamide membrclnes have found practical use only in the form of hollow fine fibcrs as accordincJ to i the description in U.S. Patent ~o. 3,567,632.
In addi-tion, polyamide composite membranes, suitable for use in reverse osmosis dcsalination processes, have been prepared by condensation reactions in situ on a preformed support film. Examplcs of such membranes, and their preparation" are described in U.S. Patent Nos. 3,74~,642, 3,951 ~15, 4,005,012, and ~,039,440. For an example of an acid-catalyzed, in sit~ polymerization on the support, see U.S.
Patent No. 3,926,798. For an example of the crosslinXing of a preformed semi-permeable poly-benzimidazole membrane, see U.S. Patent No. 4,020,142.
Permselective membranes made by this thin film composite approach have, in some cases, exhibited ~reatly improved fluxes relative to preformed polyamides subsequently cast or extruded into membrane form by solvent processes. The aforemen-tioned U.S. Patent No. 3,7~,642 contains a detailed description of desalination membranes prepared by interfacial condensation reactions.
~ lowever, the membranes of the prior art, whether prepa~-ed from preformed polymers or by in situ 2S reaetions, have oftentimes exhibited one or more othe~r deficiencies such as low salt rejection, low d~l~abilit~ or resistance to compression, sensitivity to extremes of pH or temperature, and lack of resistance to microbial at-tack or oxidation by ch~orine in the feed water. Lack of resistance to chlorine in the feed water is a particularly note~orthy de-Ficiency in permselective polyamide membranes. According to U. S. Patent No. 3,951,815, th~ site of attack by chlorine on polyamicle mclnbranes is the amiclic hydroycn atom presel-t in the -~O--NT-I-"
group. In compositions such as the polypiperazine-amides described in U.S. Patent Nos. 3,687,842, 3,696,031, and 3,951,815, resistance to chlorine in feed waters appears to have been adequately demonstrated; however, such resistance to attack by chlorine is believed to be atypical.
It would appear that permselective polyamide mem-branes could be obtained by condensation polymerization of diacyl halides with secondary diamines. Theoretically, the resulting polymeric products would be devoid of amidic hydrogen and would therefore be expected to be insensitive to chlorine in the feed water. Representative polyamides such as this have been prepared from piperazine and its derivatives as described in U.S. Patent Nos. 3,687,842 and 3,696,031 and NTIS Rept. No. PB253 193/7GA.
These compositions exhibited permeate fluxes of 2.4 to 650 liters per square meter per day (1/m2-day) at a pressure of 80 atmospheres toward saline feed solutions containing 5,000 to 10,000 ppm sodium chloride. These fluxes are generally uneconomical for use in reverse osmosis desalin-ation processes (except in the form of hollow fine fibers).
Currently, process economics indicate a need for membrane fluxes of 600 to 800 1/m2-day at pressures of 55 to 70 atmospheres for seawater feed (35,000 to 42,000 ppm total dissolved salts). For brackish waters containing 3,000 to 10,000 ppm salts, economically attractive membranes must provide permeate fluxes of 600 to 800 l/m ~day at pressures of only 25 to 40 atmospheres. While specific reverse osmosis applications for permselective membranes may deviate from these requirements, such membranes will no-t achieve broad commercial applicability ~ _ n.. _.. ___.
4~
unless they meet thcse criteria. A need ther~.~ore remains ~or p2rmse~1ective polyamide mer~rane..t7ilich combine the properties of chlorille resistar!ce a~d high flux as ~ell as the other properties mentioned above.
L~r~ t~
It has no~7 been discovered tha~ excellent permselective membranes combining high flu~es with chlorine resistance and lo~ salt passage can be prepared b~ the interfacial condensa-~ion of poly-unctional secondary amines ~7ith pol~functional acid halides having an acid halide functionality ~reater than 2. It has fur~her been found that mixtures of triacyl halides with diacyl halides may provide syner~istic, unexplained flux-enhancing effects on the permselective membranes in this invention. It has also been discovered that superior salt rejection properties can be achieved in the permselective memkranes of this invention by forming 'amide prepolymers of the polyfunctional secondary amines, subsequently employing these prepol~ers in the interfacial preparation of the membrane barrier `la~er.
In a preferred ernbodiment of this invention, .5 the permselective or reverse osmosis membrane is a composite comprising a microporous substrate and ~n "ultrathin" film having semipermeable properties ~eposited on one surface of said microporous substrate, the ultrathin film being formed by contacting an a~ueous solution of a chemical or chemicals contain-.ing a m~ltiplicity of secondary amine functional groups with vapors or a solution of an aromatic trifunctional (or higher) acid halide alone or in combination ~ith diacyl halidcs.
-Particularly good results are obtained with a thin film composite permselective membrane which comprises a micro-porous substrate (e.g. a conventional polysulfone support) and a thin film having semi-permeable properties deposited on one surface of the support, the thin film having been formed by contacting an aqueous solution of aliphatic heteroeyelie polyfunctional secondary amine (e.g. piperazine or substituted piperazine) with a relatively nonpolar solution of an aromatie triearboxylic acid halide alone or mixed with an aromatic diearboxylie aeid halide, the solution of polyfunctional acyl halides being capable of reacting with the poly~unctional secondary amine to deposit the resulting thin film on the support or substrate.
The invention is directed to a process for preparation of a composite reverse osmosis membrane comprising the steps of:
(a) coating a porous support with a layer com-prising an aqueous solution containing, dissolved therein, an essentially monomeric, polyfunctional, essentially water-soluble secondary amine;
(b) contacting the layer with an essentially water-insoluble, essentially monomeric, volatilizable poly-functional acid halide component having an average acid halide funetionality greater than 2.05, for a time suf-fieient to effeet in-situ chain extension and crosslinking reaetions between the seeondary amine and the polyfunctional acid halide; and (e) drying the produet of step (b) to form the eomposite reverse osmosis membrane.
The porous support may comprise a polysulfone film.
The secondary amine may be selected from the group con-sisting of piperazine and substituted piperazine. The acyl halide may eo~rise trimesoyl chloride or a mixture of trime-soyl chloride and isophthaloyl chloride. The polyfunctional halide of step (b) may comprise isophthaloyl chloride.
The invention is also directed to a composite reverse osmosis membrane prepared by the above process.
The invention is further directed to the improvement comprising using the membrane as the reverse osmosis membrane, in a process for desalination of saline water by reverse osmosis comprising contacting the saline water under pressure with a reverse osmosis membrane. The saline water may eontain at least about 3,000 parts per million by weight of an alkaline earth metal salt or a sulfate salt.
Definitions Throughout this specification, the following terms have the indicated meanings.
"Essentially monomeric" refers to a chemical compound eapable of chain extension and/or cross-linking and/or other polymerization reactions, which compound is relatively low in molecular weight, is typically readily soluble in one or more common liquid solvents, and is generally free of repeating units linked by polyamide (-CO-NH-) linkages.
However, provided that the solubility in liquid alkane (including halogenated alkane) solvents is not reduced below a fraction of a pereent by weight, a very small number of repeating polyamide units (e.g. two or three) can be present and the compound ean still have some "essentially monomeric" character.
For example, in the case of a polyfunctional acid halide monomer, the functionality can be increased by linking two triacid halides with a difunctional chain extender (diamine, diol, etc.) to form a tetraacid halide (or three triacid halides to form a pentaacid halide, etc.).
~ "Essentially soluble" (e.g. "essentially water soluble") denotes a measurable solubility in the solvent whieh exceeds a desired level (e.g. greater than .01 wt.-%
or, more typically, greater than 1.0 wt.-%) under ordinary eonditions of temperature and pressure (e.g. 20-25C. and ~S 1.0 atmosphere).
"Chain extension" refers to a type of chemical reaction, preferably intermolecular in nature, which causes the formation of a linear chain of repeating monomeric uni-ts or increases the size of a polymeric, oligomeric, or prepoly-meric molecular chain in an essentially linear fashion (i.e.
without necessarily increasing the crosslink density of the ` polymer, oligomer, or prepolymer).
- 7a -"Nonpolar solvent" refers to solvents having a polarity or dipole moment which is no greater - ~ -than the polarity or dipol~ moment of th~ low mole-cular t~eight, liquid, halogenat~cl hydrocarbon solven-ts (e.g~ d:ichloro.nethane). Accordingly, "nonpolar solvents" are considerably less polar than the typical polar`solvents such as wa-ter, Cl-C3 21}~anols, ammonia, etc. and tend to be less than about 5 ~t.-~- soluble in water at 20 C. Typi~cal "nonpolar solvents"
include the Cl-C12 aliphatic (incl~ing halo~enated aliphatic) solvents such as the al};ane (includin~
halogenated al~ane) solvents having a relting point bQlow 20 C. Non-aliphatic (e.g. aromatic) hydrocarbon solvents are l~ss preferred. The most conveniently used solvents are the Cl-C3 halogena~ed aliphatics, the C5-C8 alkanes, C5 and C6 cycloaliphatics, etc.
"Secondary amine/acid halide ratio" refers to the ratio of (a) equivalen-ts of secondary amine to (b) equivalents of acid halide (i.e. the halide obtain~d when one or more -OH functions of an acid such as a carboxylic acid, cyanuric acid, or an inorganic acid such as orthophosphoric acid are replaced with halogen) in a reaction mixture. For exa~ple, in a mixture o two moles of trimesoyl chloride (the acid chloride of trimesic acid, 1,3,5-benzenetricarboxylic acid) and three moles of piperazine, the secondary ?.5 amine~acid halide ratio would be 1:1 or stoichiometric, while in an equimolar mixture of these t~io compo~1nds, th~ sccondary amine/acid halide ratio ~o~ld be only 2:3 or 0.67:1 or l:l.S. A secondary amine/acid halide ~ . N~H/COCl) ratio of 1:1 (as in an e~uimolar mixture of isophthaloyl chloride or terephthaloyl chloxide and piperazine) tends to favor polyamide-` forming chain extension, ~hile an N~/COC1 ratio great~r than, say, 1.2:1 (e.g. 1.3:1 to 4:1), i.e.
an excess over stoichiometry of the ~ ~ component, tends to favor the formation of secon~ary amine-terminated polyamide prepolymers or oligomers having .
_ 9 _ relatively fe~l repeatinq units lin~cd b~ polyaride t-NlI-CO-) linkages and having a molecular ~eigrl~ in the hundreds or low thousands (i.e. well belo;~
100,000). An NRH/COCl ratio in the neic~hborhood of 1:1 (e.g. 0.8:1 up to 1.5:1) tends to favor both chain extension ancl crosslinkiny when the average functionality of one of the components ~pref2rably the -COCl component) is greater than 2.0 (e.g.
. > 2.05) and preferably about 2.1 to 3Ø The :` 10 resulting molecular weight of the condensation product (the polyamide~ is typically well above 100,000 and has a crosslink density in excess oE
one per 100,000. ~In prepolymer formation, it is also preferred to make use of an averac3e acid haiide functionality above 2.05, e.g. up to 3 or 4.~
The term "ultrathin" is defined in U.S. Patent-No. 3,551,'44 (Forrester), issued December 29, 1970 as referring to films, membranes, or layers having a thickness in the range of 0.05 to 5 microns (~ M).
For purposes o this invention, a 5-micron thickness would be atypical, and thicknesses belo~ 1 micron (1,000 m ~ M or 10,000 Angstroms) and even belo~ 0.5 micron (500 m~M) can provide good flux and good salt rejection. Thic~nesses below 0.05 microns are ~` 25 dirficult to achieve in practice and hence not ordinarily contemplated for ultrathin membrane technology, but, theoretically, thicknesses do~;n to perhaps 0.01 micron deposited on a suitable porous support could impart salt rejection properties to the membrane/support composite. Optimum flux and salt rejection properties appear ~o be obta~ned in the range of 0.05-0.3 micron (50-300 m~r~).
- Tne terms "polyamide prepolymer" and "polyamide oligomer" are used more or less interchangeably to denote relatively lo~J molecular ~eigllt polyamides .
' .
:
' ' . , : . ,. ::
:
.
Ls'3 (e.g. as low as about 200 or 300 and typlcally not more than a few thousand) having very few repeating units and/or very few amide (-NH-CO-) linkages, e.g. as low as three amide linkages per polyamide prepolymer molecule. The "polyamide prepolymers" preferred for use in this invention are secondary amine terminated, i.e., the number of terminal secondary amine residues would be generally equal to the functionality of the acid halide coreactant. For example, polyamide prepolymer derived from piperazine and trimesoyl chloride would typically have essentially three terminal piperazine residues. The number of repeating units and the molecular weight of the amine-terminated polyamide prepolymer is preferably kept low enough to insure à reasonable level of water solubility.
"Volatilizable" indicates a solid or liquid compound which can be boiled (preferably at normal atmospheric or modestly reduced pressures such as 100 mm Hg) without substan-tial chemical decomposition at temperatures below 1000 C., preferably below 500 C. Thus, isophthaloyl chloride, phos-phorus oxychloride, trimesoyl chloride, etc. are "volatilizable".
~0 Detailed Description The detailed description which follows is directed ; not only to the invention claimed in the present divisional ` application, but also to the invention claimed in co-pending Canadian patent application Serial No. 343,311, of which the present application is a division.
It has been found, in accordance with the present invention, that composite membranes characterized by high flux, high rejection, particularly of divalent salts, and good resistance to attack by chlorine can be prepared by interfacial polymerization reaction of a layer or film of a solution of the secondary amine on a porous support with, ~`~
~ .
- ]Oa -for example, a triacyl halide or its mixture with diacyl halides, particularly as exemplified by trimesoyl chloride, i.e. 1,3,5-benzenetricarboxylic acid chloride, or `` '~ .
4 il~
a mi~:ture of trimesoy] chloride alld isop'l~th~loyl chloride. In the conduct of this interEacial reac~ion, the acyl halide ~roups reac-t ~ith secondary amine ~roups to produce amide lin~ayes devoid Oc amidic hydroyen. Reaction is instantaneous at the interface because of the eY~ceptionally high reaction ra~e o~
acyl chlorides for amines. The three-pronge~
functionality of the triacyl halides leads to the generation of a highly crosslinked, three-aimensional polymeric network in the membrane. The membrane material is thus a polymer approaching infinite molecular weight ~e.g. well above 100,000 molecular weight) which further is generally insoluble in virtually any solvent that does not first seriously degrade its molecular structure. Hot~ever, not all of the acyl halide functional groups become bound into amide linkages. A substantial proportion of the acyl halide func-'ional groups are hydrolyzed by water present in the amine reagent, generatiny carboxylic acid ~roups or carboxylate salts. These carboxyl ~roups have been aiscovered to eYert surprising ! e-fects on the performance of the interfacial membrane, in that they enhance flux and profoundly effect the membrane's rejection of aqueous dissolved solutes.
Because of the highly crosslinked nature of these compositions, resulting in their ultrahigh molecular wei~ht and lack of solubility, these compositions are not well suited for processing into membranes by any conventional polymer processiny techniques such as film castin~ from solvents or melt forming.
It h~s been found that this invention can be prepared in the form of thin film composite membranes simply and efficiently by a series o steps comprising (1) application of the amine solution to th~ porous 3~ support, and preferably saturation of the support with t~e solution, preEerably follo~ed by pressing ~ .
of the support to remove ~cess aminc solution, ~2) reaction tJith the acid halide, and (3) drying ~e.~.
air drying) The porous support may be any of the types conventionally used in reverse osmosis processes.
The prefe-r~d supports, however, are those prepared from organic polymeric materials such as polysu'fone, cnlorinated polyvinyl chloride, p~lyvinyl butyral, polystyrene, cellulose esters, etc. Polysulfone film has been found to be a particularly effective suppor-t material for the membranes of the invention.
Preparation of such films is described in the above-men-tioned U.S. Patent Nos. 3,926,79~ and 4,039,~40, the disclasures of which are incorporated herein by reference The molecular formula o~ this invention can be represented therefore by the following:
X~
where A = secondary diamine dicarboxamide, ~0 B ~ trifunctional organic moiety, X = carboxylic acid or carboxylate salt, and C = difunctional organic moiety derived from a diacyl halide.
In the above structure, 1 + m must reside in the 25 r~nge of 2 to 100 percent o~ the polymer units, and n may vary from O to 98~ of the polymer units.
In some cases, m may approach zero.
A typical embodime~t of the foregoing structural formula can be prepared through interfacial reaction of the monomeric amines with triacyl halides or ~` mixtures of diacyl and triacyl halides. Alternatively, the same chemical composition can be prepared by - ' :, reaction of the amines with a tr:iacyl halide to form an essentially water solu~le, amine-terminated polyamide prepolyrner or oligomer, which then is further polymerized by interfacial reaction with diacyl or triacyl halides. As will subse~uently be shown in the exemplilication of pre~errea embodimen-ts-of the invention, the properties of the membranes o~
this invention can be widely varied depending upon the choice of routes to the final polymer composition and the ratios of acyl halides em~loyed.
The amine component in this invention may represent any polyfunctional secondary amine of aliphatic or cycloaliphatic origin to achieve chlorine resistance.
However, to achieve high membrane 1uY., selection of piperazine (including piperazine derivatives) is !' preferred in this invention as exemplified by piperazine, 2-methylpiperazine, 2,5-dimethylpipera~ine.
The N,N'-dial~yl-substituted alkylene diamines and linear polyethyleneimine are less preferred secondary amines and are considered to be less effective than the aforementioned piperazines. Use o~ mixtures of secondary amines may be`prac-ticed under this invention, including substantial amounts of mor.ofunctional secondary arnines such as morphollne or dimethylarnine, ` 25 so long as the average ~unctionality o~ the secondary amine mixture and the ratio of amine equivalents to acid halide equivalents in the prepolyrner orming-or polymer-forming reaction rnixture is in the desired ran~e, whereby the final membrane composition consists ~` 30 of a high molecular weight, crosslinked, insoluble polymer.
The higher-functionality acid halide ~e.g. the triacid halide) should either be volatilizable or essentially`soluble in nonpolar solvents such as the aliphatic type ~including halogenated aliphatics and cycloaliphatics). The acyl halides need not be ~ases or liquids at roorn te.-nperature (20-25 C.), particularly if they can be melted or dissolved readily or boiled wit-hout deconposition under ~. .
. . .
conveniently provided volatilization conditions r since the vapor of compounds such as the polyfunc-tional aromatic carboxylic acid chlorides, phosphorus oxychloride, and cyanuric chloride (2,4,6-trichloro-1,3,5-tria~ine~ is highly reac~ive ~ith secondary amine solutions when such solutions are brought into contact with the acid chloride vapor. CCyanuric chloride can be considered to be the acid chloride o~ cyanuric acid, C3N3[OH]3.) Finite, measurable solubility in readily available solvents such as the C5~C8 alkanes and the Cl-C3 halogenated,aliphatics is particularly desirable, thoucJh the solutions can be very dilute (down to 0.1% or even 0. 01o by ; weight) and total miscibility or even high'solubility is not required. The acid halide should be selected so that the acid halide functional groups ~e.g. -COCl) will react'rapidly with secondary amines at temperatures below 100 C., preferably below 30 C.
or even 25 C., the amide-forming reaction going substantially to completion in a very short time (e.g. less than a minute) under these conditions.
It is also pre~erred that the acid halide dissolved in nonpolar solvent react readily at concentrations `' of 0.01 to 10 wt.-%, particularly when the concentration of the secondary amine in the aqueous medium of the interfacial reaction system is in a similar range.
Thus, the acid halide should be selected ~Jith a v:iew toward these solubility criteria and for suitability in interfacial reaction systems, wherein the secondary amine is in the aqueous phase and the acid halide is in the nonpolar phase or a vapor phase.
Mixtures of triacyl halides may be used. Aromatic ~' acyl halides may be mononuclear or polynuclear ,` ~e.g. up to three aromatic rings), but mononuclear ' 35 compounds are prefe~red. Higher acyl halide . .
`
functionality may be achieved by synthesizing partial adducts of triacyl halides with difunctional reactants such as ethylene glycol. Such adducts would fall within the scope of this invention so long as they meet the aforementioned criteria.
The diacid halide which may be used in conjunction with the triacyl halide may be taken from a list of compounds including but not limited to oxyalyl chloride, succinoyl chloride, glutaryl chloride, adipoyl chloride, fumaryl chloride, itaconyl chloride, 1,2-cyclobutanedicarboxylic acid chloride, orthophthaloyl chloride, meta-phthaloyl chloride, terephthaloyl chloride, 2,6-pyridinedicarbonyl chloride, p,p'-biphenyl dicarboxylic acid chloride, naphthalene-1,4-dicarboxylic acid chloride, naphthalene-2,6-dicarboxylic acid chloride.
In virtually all cases, it is desirable that the diacid halide meet the same criteria as the triacid halides described pre-viously. Preferred diacyl halides in this invention are mononuclear aromatic halides, particularly as exemplified by meta-phthaloyl chloride and terephthaloyl chloride.
In one specific preferred embodiment of this invention, ; ~0 piperazine is employed in the form of an aqueous solution, " with the concentration of piperazine being about 0.0 to 10%
~ by weight, preferably about 0.5 to 3%. Although the piperazine i is, of course, itself an acid acceptor, the solution may also contain additional acid acceptors, such as sodium hydroxide, ~5 trisodium phosphate, N,N'-dimethylpiperazine or the like to facilitate the polymerization reaction. The presence ~```
of amounts of these is, however, generally not critical.
Application of the piperazine solution to the porous support is readily accomplished by any conventional means such as casting the solution on the support, dipping or immersing .',` ' .
X
the support in the solution, or spraying the solution on the sup~ort Generally, application of the piperazine solution to the support is most conveniently and efficiently accomplished by simply placing the support in the solution for a time sufficient to permit complete saturation of the support with the piperazine solution. Removal of excess piperazine solution is readily accomplished by conventional means such as rolling or pressing at pressures sufficient to remove excess solution ~Jithout damaging the support.
Reaction with the acid chloride, e.g. trimesoyl chloride or a combination of trimesoyl chloride and isophthaloyl chloride, is conducted under conventional conditions ~or interfacial reaction between the piperazine and the acid chloride. The acid chloride is preferably employed in the nonpolar solvent, the vapor phase contacting approach being ordinarily less preferred. Concentration of the acid chloride in the solvent will generally be in the range of 20 about 0.01 to 10% by weight, preferably about Q.l to
unless they meet thcse criteria. A need ther~.~ore remains ~or p2rmse~1ective polyamide mer~rane..t7ilich combine the properties of chlorille resistar!ce a~d high flux as ~ell as the other properties mentioned above.
L~r~ t~
It has no~7 been discovered tha~ excellent permselective membranes combining high flu~es with chlorine resistance and lo~ salt passage can be prepared b~ the interfacial condensa-~ion of poly-unctional secondary amines ~7ith pol~functional acid halides having an acid halide functionality ~reater than 2. It has fur~her been found that mixtures of triacyl halides with diacyl halides may provide syner~istic, unexplained flux-enhancing effects on the permselective membranes in this invention. It has also been discovered that superior salt rejection properties can be achieved in the permselective memkranes of this invention by forming 'amide prepolymers of the polyfunctional secondary amines, subsequently employing these prepol~ers in the interfacial preparation of the membrane barrier `la~er.
In a preferred ernbodiment of this invention, .5 the permselective or reverse osmosis membrane is a composite comprising a microporous substrate and ~n "ultrathin" film having semipermeable properties ~eposited on one surface of said microporous substrate, the ultrathin film being formed by contacting an a~ueous solution of a chemical or chemicals contain-.ing a m~ltiplicity of secondary amine functional groups with vapors or a solution of an aromatic trifunctional (or higher) acid halide alone or in combination ~ith diacyl halidcs.
-Particularly good results are obtained with a thin film composite permselective membrane which comprises a micro-porous substrate (e.g. a conventional polysulfone support) and a thin film having semi-permeable properties deposited on one surface of the support, the thin film having been formed by contacting an aqueous solution of aliphatic heteroeyelie polyfunctional secondary amine (e.g. piperazine or substituted piperazine) with a relatively nonpolar solution of an aromatie triearboxylic acid halide alone or mixed with an aromatic diearboxylie aeid halide, the solution of polyfunctional acyl halides being capable of reacting with the poly~unctional secondary amine to deposit the resulting thin film on the support or substrate.
The invention is directed to a process for preparation of a composite reverse osmosis membrane comprising the steps of:
(a) coating a porous support with a layer com-prising an aqueous solution containing, dissolved therein, an essentially monomeric, polyfunctional, essentially water-soluble secondary amine;
(b) contacting the layer with an essentially water-insoluble, essentially monomeric, volatilizable poly-functional acid halide component having an average acid halide funetionality greater than 2.05, for a time suf-fieient to effeet in-situ chain extension and crosslinking reaetions between the seeondary amine and the polyfunctional acid halide; and (e) drying the produet of step (b) to form the eomposite reverse osmosis membrane.
The porous support may comprise a polysulfone film.
The secondary amine may be selected from the group con-sisting of piperazine and substituted piperazine. The acyl halide may eo~rise trimesoyl chloride or a mixture of trime-soyl chloride and isophthaloyl chloride. The polyfunctional halide of step (b) may comprise isophthaloyl chloride.
The invention is also directed to a composite reverse osmosis membrane prepared by the above process.
The invention is further directed to the improvement comprising using the membrane as the reverse osmosis membrane, in a process for desalination of saline water by reverse osmosis comprising contacting the saline water under pressure with a reverse osmosis membrane. The saline water may eontain at least about 3,000 parts per million by weight of an alkaline earth metal salt or a sulfate salt.
Definitions Throughout this specification, the following terms have the indicated meanings.
"Essentially monomeric" refers to a chemical compound eapable of chain extension and/or cross-linking and/or other polymerization reactions, which compound is relatively low in molecular weight, is typically readily soluble in one or more common liquid solvents, and is generally free of repeating units linked by polyamide (-CO-NH-) linkages.
However, provided that the solubility in liquid alkane (including halogenated alkane) solvents is not reduced below a fraction of a pereent by weight, a very small number of repeating polyamide units (e.g. two or three) can be present and the compound ean still have some "essentially monomeric" character.
For example, in the case of a polyfunctional acid halide monomer, the functionality can be increased by linking two triacid halides with a difunctional chain extender (diamine, diol, etc.) to form a tetraacid halide (or three triacid halides to form a pentaacid halide, etc.).
~ "Essentially soluble" (e.g. "essentially water soluble") denotes a measurable solubility in the solvent whieh exceeds a desired level (e.g. greater than .01 wt.-%
or, more typically, greater than 1.0 wt.-%) under ordinary eonditions of temperature and pressure (e.g. 20-25C. and ~S 1.0 atmosphere).
"Chain extension" refers to a type of chemical reaction, preferably intermolecular in nature, which causes the formation of a linear chain of repeating monomeric uni-ts or increases the size of a polymeric, oligomeric, or prepoly-meric molecular chain in an essentially linear fashion (i.e.
without necessarily increasing the crosslink density of the ` polymer, oligomer, or prepolymer).
- 7a -"Nonpolar solvent" refers to solvents having a polarity or dipole moment which is no greater - ~ -than the polarity or dipol~ moment of th~ low mole-cular t~eight, liquid, halogenat~cl hydrocarbon solven-ts (e.g~ d:ichloro.nethane). Accordingly, "nonpolar solvents" are considerably less polar than the typical polar`solvents such as wa-ter, Cl-C3 21}~anols, ammonia, etc. and tend to be less than about 5 ~t.-~- soluble in water at 20 C. Typi~cal "nonpolar solvents"
include the Cl-C12 aliphatic (incl~ing halo~enated aliphatic) solvents such as the al};ane (includin~
halogenated al~ane) solvents having a relting point bQlow 20 C. Non-aliphatic (e.g. aromatic) hydrocarbon solvents are l~ss preferred. The most conveniently used solvents are the Cl-C3 halogena~ed aliphatics, the C5-C8 alkanes, C5 and C6 cycloaliphatics, etc.
"Secondary amine/acid halide ratio" refers to the ratio of (a) equivalen-ts of secondary amine to (b) equivalents of acid halide (i.e. the halide obtain~d when one or more -OH functions of an acid such as a carboxylic acid, cyanuric acid, or an inorganic acid such as orthophosphoric acid are replaced with halogen) in a reaction mixture. For exa~ple, in a mixture o two moles of trimesoyl chloride (the acid chloride of trimesic acid, 1,3,5-benzenetricarboxylic acid) and three moles of piperazine, the secondary ?.5 amine~acid halide ratio would be 1:1 or stoichiometric, while in an equimolar mixture of these t~io compo~1nds, th~ sccondary amine/acid halide ratio ~o~ld be only 2:3 or 0.67:1 or l:l.S. A secondary amine/acid halide ~ . N~H/COCl) ratio of 1:1 (as in an e~uimolar mixture of isophthaloyl chloride or terephthaloyl chloxide and piperazine) tends to favor polyamide-` forming chain extension, ~hile an N~/COC1 ratio great~r than, say, 1.2:1 (e.g. 1.3:1 to 4:1), i.e.
an excess over stoichiometry of the ~ ~ component, tends to favor the formation of secon~ary amine-terminated polyamide prepolymers or oligomers having .
_ 9 _ relatively fe~l repeatinq units lin~cd b~ polyaride t-NlI-CO-) linkages and having a molecular ~eigrl~ in the hundreds or low thousands (i.e. well belo;~
100,000). An NRH/COCl ratio in the neic~hborhood of 1:1 (e.g. 0.8:1 up to 1.5:1) tends to favor both chain extension ancl crosslinkiny when the average functionality of one of the components ~pref2rably the -COCl component) is greater than 2.0 (e.g.
. > 2.05) and preferably about 2.1 to 3Ø The :` 10 resulting molecular weight of the condensation product (the polyamide~ is typically well above 100,000 and has a crosslink density in excess oE
one per 100,000. ~In prepolymer formation, it is also preferred to make use of an averac3e acid haiide functionality above 2.05, e.g. up to 3 or 4.~
The term "ultrathin" is defined in U.S. Patent-No. 3,551,'44 (Forrester), issued December 29, 1970 as referring to films, membranes, or layers having a thickness in the range of 0.05 to 5 microns (~ M).
For purposes o this invention, a 5-micron thickness would be atypical, and thicknesses belo~ 1 micron (1,000 m ~ M or 10,000 Angstroms) and even belo~ 0.5 micron (500 m~M) can provide good flux and good salt rejection. Thic~nesses below 0.05 microns are ~` 25 dirficult to achieve in practice and hence not ordinarily contemplated for ultrathin membrane technology, but, theoretically, thicknesses do~;n to perhaps 0.01 micron deposited on a suitable porous support could impart salt rejection properties to the membrane/support composite. Optimum flux and salt rejection properties appear ~o be obta~ned in the range of 0.05-0.3 micron (50-300 m~r~).
- Tne terms "polyamide prepolymer" and "polyamide oligomer" are used more or less interchangeably to denote relatively lo~J molecular ~eigllt polyamides .
' .
:
' ' . , : . ,. ::
:
.
Ls'3 (e.g. as low as about 200 or 300 and typlcally not more than a few thousand) having very few repeating units and/or very few amide (-NH-CO-) linkages, e.g. as low as three amide linkages per polyamide prepolymer molecule. The "polyamide prepolymers" preferred for use in this invention are secondary amine terminated, i.e., the number of terminal secondary amine residues would be generally equal to the functionality of the acid halide coreactant. For example, polyamide prepolymer derived from piperazine and trimesoyl chloride would typically have essentially three terminal piperazine residues. The number of repeating units and the molecular weight of the amine-terminated polyamide prepolymer is preferably kept low enough to insure à reasonable level of water solubility.
"Volatilizable" indicates a solid or liquid compound which can be boiled (preferably at normal atmospheric or modestly reduced pressures such as 100 mm Hg) without substan-tial chemical decomposition at temperatures below 1000 C., preferably below 500 C. Thus, isophthaloyl chloride, phos-phorus oxychloride, trimesoyl chloride, etc. are "volatilizable".
~0 Detailed Description The detailed description which follows is directed ; not only to the invention claimed in the present divisional ` application, but also to the invention claimed in co-pending Canadian patent application Serial No. 343,311, of which the present application is a division.
It has been found, in accordance with the present invention, that composite membranes characterized by high flux, high rejection, particularly of divalent salts, and good resistance to attack by chlorine can be prepared by interfacial polymerization reaction of a layer or film of a solution of the secondary amine on a porous support with, ~`~
~ .
- ]Oa -for example, a triacyl halide or its mixture with diacyl halides, particularly as exemplified by trimesoyl chloride, i.e. 1,3,5-benzenetricarboxylic acid chloride, or `` '~ .
4 il~
a mi~:ture of trimesoy] chloride alld isop'l~th~loyl chloride. In the conduct of this interEacial reac~ion, the acyl halide ~roups reac-t ~ith secondary amine ~roups to produce amide lin~ayes devoid Oc amidic hydroyen. Reaction is instantaneous at the interface because of the eY~ceptionally high reaction ra~e o~
acyl chlorides for amines. The three-pronge~
functionality of the triacyl halides leads to the generation of a highly crosslinked, three-aimensional polymeric network in the membrane. The membrane material is thus a polymer approaching infinite molecular weight ~e.g. well above 100,000 molecular weight) which further is generally insoluble in virtually any solvent that does not first seriously degrade its molecular structure. Hot~ever, not all of the acyl halide functional groups become bound into amide linkages. A substantial proportion of the acyl halide func-'ional groups are hydrolyzed by water present in the amine reagent, generatiny carboxylic acid ~roups or carboxylate salts. These carboxyl ~roups have been aiscovered to eYert surprising ! e-fects on the performance of the interfacial membrane, in that they enhance flux and profoundly effect the membrane's rejection of aqueous dissolved solutes.
Because of the highly crosslinked nature of these compositions, resulting in their ultrahigh molecular wei~ht and lack of solubility, these compositions are not well suited for processing into membranes by any conventional polymer processiny techniques such as film castin~ from solvents or melt forming.
It h~s been found that this invention can be prepared in the form of thin film composite membranes simply and efficiently by a series o steps comprising (1) application of the amine solution to th~ porous 3~ support, and preferably saturation of the support with t~e solution, preEerably follo~ed by pressing ~ .
of the support to remove ~cess aminc solution, ~2) reaction tJith the acid halide, and (3) drying ~e.~.
air drying) The porous support may be any of the types conventionally used in reverse osmosis processes.
The prefe-r~d supports, however, are those prepared from organic polymeric materials such as polysu'fone, cnlorinated polyvinyl chloride, p~lyvinyl butyral, polystyrene, cellulose esters, etc. Polysulfone film has been found to be a particularly effective suppor-t material for the membranes of the invention.
Preparation of such films is described in the above-men-tioned U.S. Patent Nos. 3,926,79~ and 4,039,~40, the disclasures of which are incorporated herein by reference The molecular formula o~ this invention can be represented therefore by the following:
X~
where A = secondary diamine dicarboxamide, ~0 B ~ trifunctional organic moiety, X = carboxylic acid or carboxylate salt, and C = difunctional organic moiety derived from a diacyl halide.
In the above structure, 1 + m must reside in the 25 r~nge of 2 to 100 percent o~ the polymer units, and n may vary from O to 98~ of the polymer units.
In some cases, m may approach zero.
A typical embodime~t of the foregoing structural formula can be prepared through interfacial reaction of the monomeric amines with triacyl halides or ~` mixtures of diacyl and triacyl halides. Alternatively, the same chemical composition can be prepared by - ' :, reaction of the amines with a tr:iacyl halide to form an essentially water solu~le, amine-terminated polyamide prepolyrner or oligomer, which then is further polymerized by interfacial reaction with diacyl or triacyl halides. As will subse~uently be shown in the exemplilication of pre~errea embodimen-ts-of the invention, the properties of the membranes o~
this invention can be widely varied depending upon the choice of routes to the final polymer composition and the ratios of acyl halides em~loyed.
The amine component in this invention may represent any polyfunctional secondary amine of aliphatic or cycloaliphatic origin to achieve chlorine resistance.
However, to achieve high membrane 1uY., selection of piperazine (including piperazine derivatives) is !' preferred in this invention as exemplified by piperazine, 2-methylpiperazine, 2,5-dimethylpipera~ine.
The N,N'-dial~yl-substituted alkylene diamines and linear polyethyleneimine are less preferred secondary amines and are considered to be less effective than the aforementioned piperazines. Use o~ mixtures of secondary amines may be`prac-ticed under this invention, including substantial amounts of mor.ofunctional secondary arnines such as morphollne or dimethylarnine, ` 25 so long as the average ~unctionality o~ the secondary amine mixture and the ratio of amine equivalents to acid halide equivalents in the prepolyrner orming-or polymer-forming reaction rnixture is in the desired ran~e, whereby the final membrane composition consists ~` 30 of a high molecular weight, crosslinked, insoluble polymer.
The higher-functionality acid halide ~e.g. the triacid halide) should either be volatilizable or essentially`soluble in nonpolar solvents such as the aliphatic type ~including halogenated aliphatics and cycloaliphatics). The acyl halides need not be ~ases or liquids at roorn te.-nperature (20-25 C.), particularly if they can be melted or dissolved readily or boiled wit-hout deconposition under ~. .
. . .
conveniently provided volatilization conditions r since the vapor of compounds such as the polyfunc-tional aromatic carboxylic acid chlorides, phosphorus oxychloride, and cyanuric chloride (2,4,6-trichloro-1,3,5-tria~ine~ is highly reac~ive ~ith secondary amine solutions when such solutions are brought into contact with the acid chloride vapor. CCyanuric chloride can be considered to be the acid chloride o~ cyanuric acid, C3N3[OH]3.) Finite, measurable solubility in readily available solvents such as the C5~C8 alkanes and the Cl-C3 halogenated,aliphatics is particularly desirable, thoucJh the solutions can be very dilute (down to 0.1% or even 0. 01o by ; weight) and total miscibility or even high'solubility is not required. The acid halide should be selected so that the acid halide functional groups ~e.g. -COCl) will react'rapidly with secondary amines at temperatures below 100 C., preferably below 30 C.
or even 25 C., the amide-forming reaction going substantially to completion in a very short time (e.g. less than a minute) under these conditions.
It is also pre~erred that the acid halide dissolved in nonpolar solvent react readily at concentrations `' of 0.01 to 10 wt.-%, particularly when the concentration of the secondary amine in the aqueous medium of the interfacial reaction system is in a similar range.
Thus, the acid halide should be selected ~Jith a v:iew toward these solubility criteria and for suitability in interfacial reaction systems, wherein the secondary amine is in the aqueous phase and the acid halide is in the nonpolar phase or a vapor phase.
Mixtures of triacyl halides may be used. Aromatic ~' acyl halides may be mononuclear or polynuclear ,` ~e.g. up to three aromatic rings), but mononuclear ' 35 compounds are prefe~red. Higher acyl halide . .
`
functionality may be achieved by synthesizing partial adducts of triacyl halides with difunctional reactants such as ethylene glycol. Such adducts would fall within the scope of this invention so long as they meet the aforementioned criteria.
The diacid halide which may be used in conjunction with the triacyl halide may be taken from a list of compounds including but not limited to oxyalyl chloride, succinoyl chloride, glutaryl chloride, adipoyl chloride, fumaryl chloride, itaconyl chloride, 1,2-cyclobutanedicarboxylic acid chloride, orthophthaloyl chloride, meta-phthaloyl chloride, terephthaloyl chloride, 2,6-pyridinedicarbonyl chloride, p,p'-biphenyl dicarboxylic acid chloride, naphthalene-1,4-dicarboxylic acid chloride, naphthalene-2,6-dicarboxylic acid chloride.
In virtually all cases, it is desirable that the diacid halide meet the same criteria as the triacid halides described pre-viously. Preferred diacyl halides in this invention are mononuclear aromatic halides, particularly as exemplified by meta-phthaloyl chloride and terephthaloyl chloride.
In one specific preferred embodiment of this invention, ; ~0 piperazine is employed in the form of an aqueous solution, " with the concentration of piperazine being about 0.0 to 10%
~ by weight, preferably about 0.5 to 3%. Although the piperazine i is, of course, itself an acid acceptor, the solution may also contain additional acid acceptors, such as sodium hydroxide, ~5 trisodium phosphate, N,N'-dimethylpiperazine or the like to facilitate the polymerization reaction. The presence ~```
of amounts of these is, however, generally not critical.
Application of the piperazine solution to the porous support is readily accomplished by any conventional means such as casting the solution on the support, dipping or immersing .',` ' .
X
the support in the solution, or spraying the solution on the sup~ort Generally, application of the piperazine solution to the support is most conveniently and efficiently accomplished by simply placing the support in the solution for a time sufficient to permit complete saturation of the support with the piperazine solution. Removal of excess piperazine solution is readily accomplished by conventional means such as rolling or pressing at pressures sufficient to remove excess solution ~Jithout damaging the support.
Reaction with the acid chloride, e.g. trimesoyl chloride or a combination of trimesoyl chloride and isophthaloyl chloride, is conducted under conventional conditions ~or interfacial reaction between the piperazine and the acid chloride. The acid chloride is preferably employed in the nonpolar solvent, the vapor phase contacting approach being ordinarily less preferred. Concentration of the acid chloride in the solvent will generally be in the range of 20 about 0.01 to 10% by weight, preferably about Q.l to
5%, with the wei~ht ratio of acid chloride-to piperazine suitably being about 1:10 to 10~ enerally, ~` `room temperature is satisfactory for the reaction, with temperatures of about 10 to 30 C. usuall~
giving good results.
Reaction with the acid;chloride is generally ~` most conveniently and efficiently accomplished by simply i~mersing the porous support coated ~ith ` aqueous piperazine into the solvent solution of the acid ehloride for a time sufficient to form a thin coating of the resultiny poly(piperazineamide) on the surface of the porous support. Generally, a reaction time of about 1 second to 60 seconds is .~ sufficient to form a thin coating or film of the polymer possessing the desircd salt barrier characteristics. The resulting composite, consisting ` - . ~ ' ` ' . .
of the porous support having a thin coating or film of the poly(piperazineamide) on the surface thereof, is then air dried, preferably at a temperature of about 20 to 130 C.
for a period of about 1 to 30 minutes, to form the composite membrane of the invention. This membrane has been found to exhibit high rejection for divalent salts, particularly for magnesium sulfate, as well as high flux. Consequently, the membranes are particularly useful for applications such as brackish water desalting, whey concentration, electroplating chemical recovery, softening of hard water for municipal or home use, or for boiler feed water treatment.
` Where trimesoyl chloride alone is employed as the acid chloride, the polymerization reaction is believed to proceed primarily as follows:
1~ COCl _ _ _ + ~ ~ N wate ~ ~ ~ C-N~_~N _ _ ~C
COCl COCl f ~~' Im ~
. . . .
~a When isophthaloyl chloride is used as a co-reactant, the polymerization reaction is believed to proceed essentially ; to the following:
f ~ c~L~ ~
Where a combination of the two acid chlorides is employed, the mole ratio of isophthaloyl chloride to trimesoyl chloride may ran~e up to about ~9 to 1, with a ratio of abou-t 2 to 1 generally giving optimum results for maximurn ~ater fl~x, ana a ratio of 9 to 1 generally ~iving an optimum combi~ation of salt rejection and flux.
l~hen a co~bination of diacyl halide with a triacyl halide is used, a large increase in the flux of the resulting membranes is noted ~7hich would not be expected based on the performance of membranes made wi~h either the triacyl halide alone or the diac~l h~lide alone. Permeate fluxes are observed with these mixed acyl halide membranes which exceed all published values for other membranes that exhibit comparable salt rejection properties to~ards a salt such as maynesium sulfate dissolved in the aqueous feed. The m~mbranes of this invention also display ion selectivity, in that rejection of multivalent anions is uniforrnl~ very effecti~e, ~hile rejection of monovàlent anions is dependent upon operating conditions, the ionic strength of the feed water, and the ratio of the diacyl and triacyl halides used in the preparation of the membranes.
The invention ~ill be rnore specifically illustrated by the following ~xamples, the first of these Examples being a Control. Parts and percentages are hy ~Jeight unless otherwise indicated.
Example l_ (Control) This "Control" E~ample illustrates the performance of a poly(piperazine isophthalamide) membrane, described in U.S. Patent No. 3,696,031, but prepared àccording to the art of thin film composite membranes.
This Exa~ple is used for comparison purposes.
A composite mernbrane ~as prepared by saturating a polysulfone support film ~Jith a 1 wt.-~ aqueous solution of piperar~ine (N ~ ~12), which contained 1% NaO~I as an acid acceptor E~:cess solution ~Jas removed by pressing the film with a soft rubber roller. The saturated support ~^7as i~mersed in a 1 wt.-% solution of isophthaloyl chloride in hexane, at room temperature, for a period of 10 seconds. The drying and testing procedures for the resulting composite membrane were the same as tho5e of EYamples 2-6, and the flux and salt rejection data are repor-ted hereinafter in Table 1.
Examples 2-6 Example 2 illustrates the greatly improved m~mbrane flux performance achieved throu~h employment of trimesoyl chloride and piperazine. ~xamples 3-6 demons.rate the unexpected, synergistic effect of combinina the triacyl halide with a diacyl halide in the preparation of the membranes of this invention.
;' ` A series of composite membranes were prepared by the procedure described in Example 1 ~the Control).
In each case a polysulfone support film was saturated with a 1 ~t.-% a~ueous solution of piperazine, which also contained an additional acld acceptor as shown in Table 1. Excess solution was removed by pressing the film with a soft rubber roller.
The sa-turated support was then im~ersed in a hexane solution of the acid chloride, the type and concentrations of the acid chloride, in ~-~eight percent, being ~iven in Table 1, at room temperature for a ! 30 pex-iod of 10 seconds. The support was then removed from the reactant solution, drained and dried in air at a temperature of 25~ C. for a period of 30 minu-tes.
The resultin~ composite membrane was tested in a reverse osmosis cell for 24 ho~rs, using 0.5Oo 35- ~1gSO4 feed solution at 13.6 atmospheres and 25~ C.
.
P~esults are given in Table 1. It ~7ill be seen that the me~brane p~epared from isophthaloyl chloride alone tE~ample 1) sho~ed good salt rejection bu-t very low flux, while the membrane pre~ared from tri~nesoyl chloride alone ~Ex~mple 2) showed yood salt rejQction and much improved flux. As is apparent from the data of the Table, however, best results were obtained from a combination oE isophthaloyl chloride and trimesoyl chloride in suitable proportions (E~amples 3, 4, and 5), resulting in excellen~
salt rejection as well as greatly improved flux.
Table 1 Magnesium Ratio of Acyl Halides* Sulfate Trimesoyl Isophthal~ lux Salt Rejection E~ample Chloride Chloride _ l/m2d) (Percent) 1 0 1 155 9g.2 2 1 0 1060 9~.3 -3 1.5 0,5 1260 99.9 ~ 0.33 0.67 3140 99.6 0.2 0.8 2360 99.9
giving good results.
Reaction with the acid;chloride is generally ~` most conveniently and efficiently accomplished by simply i~mersing the porous support coated ~ith ` aqueous piperazine into the solvent solution of the acid ehloride for a time sufficient to form a thin coating of the resultiny poly(piperazineamide) on the surface of the porous support. Generally, a reaction time of about 1 second to 60 seconds is .~ sufficient to form a thin coating or film of the polymer possessing the desircd salt barrier characteristics. The resulting composite, consisting ` - . ~ ' ` ' . .
of the porous support having a thin coating or film of the poly(piperazineamide) on the surface thereof, is then air dried, preferably at a temperature of about 20 to 130 C.
for a period of about 1 to 30 minutes, to form the composite membrane of the invention. This membrane has been found to exhibit high rejection for divalent salts, particularly for magnesium sulfate, as well as high flux. Consequently, the membranes are particularly useful for applications such as brackish water desalting, whey concentration, electroplating chemical recovery, softening of hard water for municipal or home use, or for boiler feed water treatment.
` Where trimesoyl chloride alone is employed as the acid chloride, the polymerization reaction is believed to proceed primarily as follows:
1~ COCl _ _ _ + ~ ~ N wate ~ ~ ~ C-N~_~N _ _ ~C
COCl COCl f ~~' Im ~
. . . .
~a When isophthaloyl chloride is used as a co-reactant, the polymerization reaction is believed to proceed essentially ; to the following:
f ~ c~L~ ~
Where a combination of the two acid chlorides is employed, the mole ratio of isophthaloyl chloride to trimesoyl chloride may ran~e up to about ~9 to 1, with a ratio of abou-t 2 to 1 generally giving optimum results for maximurn ~ater fl~x, ana a ratio of 9 to 1 generally ~iving an optimum combi~ation of salt rejection and flux.
l~hen a co~bination of diacyl halide with a triacyl halide is used, a large increase in the flux of the resulting membranes is noted ~7hich would not be expected based on the performance of membranes made wi~h either the triacyl halide alone or the diac~l h~lide alone. Permeate fluxes are observed with these mixed acyl halide membranes which exceed all published values for other membranes that exhibit comparable salt rejection properties to~ards a salt such as maynesium sulfate dissolved in the aqueous feed. The m~mbranes of this invention also display ion selectivity, in that rejection of multivalent anions is uniforrnl~ very effecti~e, ~hile rejection of monovàlent anions is dependent upon operating conditions, the ionic strength of the feed water, and the ratio of the diacyl and triacyl halides used in the preparation of the membranes.
The invention ~ill be rnore specifically illustrated by the following ~xamples, the first of these Examples being a Control. Parts and percentages are hy ~Jeight unless otherwise indicated.
Example l_ (Control) This "Control" E~ample illustrates the performance of a poly(piperazine isophthalamide) membrane, described in U.S. Patent No. 3,696,031, but prepared àccording to the art of thin film composite membranes.
This Exa~ple is used for comparison purposes.
A composite mernbrane ~as prepared by saturating a polysulfone support film ~Jith a 1 wt.-~ aqueous solution of piperar~ine (N ~ ~12), which contained 1% NaO~I as an acid acceptor E~:cess solution ~Jas removed by pressing the film with a soft rubber roller. The saturated support ~^7as i~mersed in a 1 wt.-% solution of isophthaloyl chloride in hexane, at room temperature, for a period of 10 seconds. The drying and testing procedures for the resulting composite membrane were the same as tho5e of EYamples 2-6, and the flux and salt rejection data are repor-ted hereinafter in Table 1.
Examples 2-6 Example 2 illustrates the greatly improved m~mbrane flux performance achieved throu~h employment of trimesoyl chloride and piperazine. ~xamples 3-6 demons.rate the unexpected, synergistic effect of combinina the triacyl halide with a diacyl halide in the preparation of the membranes of this invention.
;' ` A series of composite membranes were prepared by the procedure described in Example 1 ~the Control).
In each case a polysulfone support film was saturated with a 1 ~t.-% a~ueous solution of piperazine, which also contained an additional acld acceptor as shown in Table 1. Excess solution was removed by pressing the film with a soft rubber roller.
The sa-turated support was then im~ersed in a hexane solution of the acid chloride, the type and concentrations of the acid chloride, in ~-~eight percent, being ~iven in Table 1, at room temperature for a ! 30 pex-iod of 10 seconds. The support was then removed from the reactant solution, drained and dried in air at a temperature of 25~ C. for a period of 30 minu-tes.
The resultin~ composite membrane was tested in a reverse osmosis cell for 24 ho~rs, using 0.5Oo 35- ~1gSO4 feed solution at 13.6 atmospheres and 25~ C.
.
P~esults are given in Table 1. It ~7ill be seen that the me~brane p~epared from isophthaloyl chloride alone tE~ample 1) sho~ed good salt rejection bu-t very low flux, while the membrane pre~ared from tri~nesoyl chloride alone ~Ex~mple 2) showed yood salt rejQction and much improved flux. As is apparent from the data of the Table, however, best results were obtained from a combination oE isophthaloyl chloride and trimesoyl chloride in suitable proportions (E~amples 3, 4, and 5), resulting in excellen~
salt rejection as well as greatly improved flux.
Table 1 Magnesium Ratio of Acyl Halides* Sulfate Trimesoyl Isophthal~ lux Salt Rejection E~ample Chloride Chloride _ l/m2d) (Percent) 1 0 1 155 9g.2 2 1 0 1060 9~.3 -3 1.5 0,5 1260 99.9 ~ 0.33 0.67 3140 99.6 0.2 0.8 2360 99.9
6 0.1 0.9 733 .99.0 *The presence of added acid acceptors varied depending upon acid chlorides used: for example 1, 1% NaOH;
for Example 2, 1% N,N-dimethylpiperazine plus 0.2~
NaOH; for Examples 3 to 6, 2% Na3PO412H2O plus 0 5~ sodium - dodecyl sul~ate.
Example 7 This Example illus-trates -the ion-selective properties of composite membranes of this inven-tion.
A membrane was prepared according to Example 2.
~his membrane was mounted in a reverse osmosis test cell and e~posed sequentially -to a series of a~ueous salt solutions for a period of 20 to 24 hours per aqueous test solution. Operating conditions ~ere 13.6 atmospheres pressure and 25 C. The flux and salt rejection data for this membrane to-~ard the various solutiolls, ~hich exhibits selectivity in 41~
the rejection o~ salts containiny divalent anions, ' arç shown in Table 2.
Table ~
Reverse Osmosls Test Data 5 Solutions Used in ~lu~ Salt Rejection Reverse Osmosis Test (l/rn2d) (Perc~n-t) . 0.1% ~IgSO~ 1430 98.0 0.5% NaCl 1710 50 0.5~ Na2SO4 1670 - 97.8 0.5~ MyC12 1300 46 0.5~ MySO~ 1300 97.9 ,~ E~amples 8-11 .
These Examples illustra-te the utility of this membrane invention in the treatment of various ~ater ` 15 sources.
.` Example 8: A membrane was prepared according : to Example 6, and was mounted in a reverse osmosis , test cell. Tests were run with a 3.5% synthetic sea~later feed ,(made with a s~nthetic sea salt from `I,ake Products Co., St. Louis, Missouri) and with a synthetic brackish feed of the following composition:
CaC12-2~I2O 5.3 g/l gSO4-7H2o 8.6 g/l NaCl 10.4 g/l 25Na2S4 10.0 g/l :.~ Na~CO3 0.2 g/l .
total dissolved solids 0.288~.
This membrane exhibited 9~.5% salt rejection and 1030 1/m2d at 68 atmospheres when tested toward synthetic seawater at 25 C. Toward synthetic brac~ish water at 40.8 atmospheres and 25 C., this membrane exhibited 94.6~ salt rejection and 1340 ` l/m2d flux.
E~:ample 9: A membrane prepared according to E~am~le 2.was tested for water so~teniny application .
.
using a tap water charac-teristic of "hard" ~ia~-~r containing magn~sium and ca~cium salts, said t,at2r ; having a conductivity of 0.53 x 10 mho. Th_ membrane produced 900 1/m2d and g~Q conducti~rit~r rejection at 13.6 atmosphel^es and 25~ C., produc~ng a "soft" water suitable for household use.
Example 10: A membrane was pr~pared acco-ding to Example 4 and was tested for ~ater sof~ening applications using a "hard" tap water as described in Example 9. ~his membrane exhibited 2360 1/m2d and 95.0% conductivity rejection at 13.6 atmos~heres and 25 C., producing a "soft" water suitable for household use.
~ ample 11: A membrane was prepared according to Example 2. This membrane when tested under reverse -~ osmosis conditions with 0.1~ magnesium sulfate at 13.6 a-tmospheres and 25 C. exhibited 1300 1/m2d ;- flux at 98% salt rejection. This membrane was immersed in 100 ppm aqueous chlorine as sodium hypochlorite for 72 hours and then was retested to aet~rmine its stability toward chlorine attack.
It exhibited a flux of 1380 1/m2d at 97.4~ salt rejection under the same conditions as before. This E~ample illustrates the chlorine resistance of this ~5 type of membrane.
Examples 12-15 Use of Amine-Terminated Polyamide -Prepolymer ~ntermedia es E~ample 12: An amine-terminated prepolymer of 3~ piperazine ~ith trimesoyl chloride ~Jas prepared 2S
follows. A solution of 2 grams (23 mllliequivalents) of trimesoyl chloride in 100 milliliters of 1,2-aichloroethane was added over a 5 minute period wi`th rapid stirring to a solution of 2 grams of piperazine t~7 meq) and 2 grams triethylamine, present as acid accc-~lor for n~utrali~ation, in 100 ml dichloroethane. (The NR~I/COCl ratio was 2. o~
The prepolymer precipitated from the dichloroethane ~` during the reaetion. The prepolymer ~JaS filtered 5 off, washed with dichloroethane, and air dried to yield appro~imately 4 grams ol product The prepolymer ~ was mixed ~ th 100 milliliters of water and stirre~
;~ for one hour at 60n C This solution was filterea to remove insolu~le and gelatinous res~dues from the prepolymer. Two grams of sodi~m hydroxide were added to the clear filtrate. A microporous polysulfone support was coated wi-th this solution, pressea with a rubber roller ~o xemove excess solution, then exposed to a 0.1% solution of isophthaloyl chloride in hexane for 10 seconds, and finally air dried at room temperature. This membrane when testea against 3.5% synthetic seawater at 6~ a~lospheres and ~5~ C.
~xhihited 430 1/m2d at 99.0~ salt rejection. Althou~h higher flux (e.g. 600 1/m2d) would be greatly preferred, ~0 flu~ was ~rea.ly superior to some prior art membranes, and a salt rejection capability above 9~rO is considered a significant achievement in this art.
E~ample 13: A solution of 2 grams (23 meq) of trimesoyl chloride in dichloroethane was added over ~5 lS minutes with rapid s-tirring to a solution of 1.5 grams (35 meq) piperazine and 0.5 grams ~6 meq) morpholine in 150 milliliters of dichloroethane.
t-N~I/COCl ratio = 1.78:1, including -NRH ~ontributed by morpholine.) The resulting suspension of prepolymer in dichloroethane was stirred for 30 minu~es, followed by filtrations, washing, and air drying of the prepolymer to yield approximately 4 grams of product.
The prepolymer ~as dissolved in 100 milliliters of water and filtered to remove a small amount of gelatinous ma,erial. T-~o grams of l~ dimethylpiperazine , .
- 2~ -acid acceptor ~as add~d to the solution. A microporous polysulf~ne substrate was coated ~.~ith the solution, pressed with a rubber roller to remove excess solutionl exposed to a 0.1% solution of isophthaloyl chloride in he~ane for lO seconds, then dried a~
130 C. in a circulating air oven for 15 minutes.
Tested against synthetic seawater at 6~ atmospheres and 25 C., this membrane exhibited 1750 l/m d at 93.5% salt rejection.
Example 14: A dichloroethane solution of 2.0 ~rams (33 meq) cyanuric chloride was added with rapid stirring to a solution of 2.8 grams (65 meq) piperazine. The prepolymer was filtered, ~ashed, and dried. (-NP~/COCl ratio = 1.97~ hen mixed ~ith lS water this prepolymer con-tained much water insoluble material which was filtered off. The clear filirate was neutralized with sodium hydroxide, followed by addition of 0.5 gram more sodium hydroxide. The solution was again filtered, providing 50 ml of clear filtrate. A membrane was prepared by interfacial rcaction of the ~mine prepolymer with isophthaloyl chloride as described in Example 13, then dried at 130~ C. in an oven. The resulting membrane exhibited 570 l/m d at 99.2% salt rejection ~hen tested à~ainst 2~ synthetic seawater at 68 a~mospheres and 25 C.
Exa_~le 15: A solution of 2.0 grams (39 meq~
}~hospllorus o~ychloride in lO0 milliliters of dichloroethane was added to a solution of 2.2 grams (rl meq) o~ piperazine in lO0 milliliters of dichloroethane with rapid stirring. (-NRH/acid halide rc~tio = 1.31:1.) The prepolymer precipitate ~as recovered and air dried. This prepolymer was conpletely c.oluble ~7hen dissolved in lO0 milliliters of water containing l.0 gram of sodium hydroxide. An interfacial membrane was formed on microporous polys~llfone , as described in Example 13, then air drie~ hen tested against synth~tic sea~ra~er at 6~ ~trnosp~e~es and 25 C., this membrane e~hibited lS30 1/m2d at 93.9% salt rejection.
Exarnple 16 A membrane was prepared accoraing to Example 4 except that 2,6-pyridinedicarboxyIic acid chloride was used in place of isophthaloyl chloride. When -~ tested against 0.5% aqueous magnesium sulfate solution at 13.6 atmospheres and 25 C., this membrane e~nibited 1210 l/m d at 95~ salt rejection.
Example 17 A wet polysulEone substrate was saturated ~Jith an aqueous solution containing 2% piperazine and 2~
morpholine by weight. This coated support was pressed with a rubber roller, exposed to a solution of 1~
trimesoyl chloride in hexane for 10 seconds, then dried at 130 C. When tested against synthetic seawater at 68 atmospheres, this membrane demonstrated 860 1/m2d at S6% salt rejection.
Example_18 According to the method of Exarnple 17, but using an aqueous solution of 1% piperazine and 5% diethanolamine, a membrane was prepared which exhibited 1550 1/m2d at 70~ salt rejec-tion toward synthetic seawater at 6S atl-nospheres~
for Example 2, 1% N,N-dimethylpiperazine plus 0.2~
NaOH; for Examples 3 to 6, 2% Na3PO412H2O plus 0 5~ sodium - dodecyl sul~ate.
Example 7 This Example illus-trates -the ion-selective properties of composite membranes of this inven-tion.
A membrane was prepared according to Example 2.
~his membrane was mounted in a reverse osmosis test cell and e~posed sequentially -to a series of a~ueous salt solutions for a period of 20 to 24 hours per aqueous test solution. Operating conditions ~ere 13.6 atmospheres pressure and 25 C. The flux and salt rejection data for this membrane to-~ard the various solutiolls, ~hich exhibits selectivity in 41~
the rejection o~ salts containiny divalent anions, ' arç shown in Table 2.
Table ~
Reverse Osmosls Test Data 5 Solutions Used in ~lu~ Salt Rejection Reverse Osmosis Test (l/rn2d) (Perc~n-t) . 0.1% ~IgSO~ 1430 98.0 0.5% NaCl 1710 50 0.5~ Na2SO4 1670 - 97.8 0.5~ MyC12 1300 46 0.5~ MySO~ 1300 97.9 ,~ E~amples 8-11 .
These Examples illustra-te the utility of this membrane invention in the treatment of various ~ater ` 15 sources.
.` Example 8: A membrane was prepared according : to Example 6, and was mounted in a reverse osmosis , test cell. Tests were run with a 3.5% synthetic sea~later feed ,(made with a s~nthetic sea salt from `I,ake Products Co., St. Louis, Missouri) and with a synthetic brackish feed of the following composition:
CaC12-2~I2O 5.3 g/l gSO4-7H2o 8.6 g/l NaCl 10.4 g/l 25Na2S4 10.0 g/l :.~ Na~CO3 0.2 g/l .
total dissolved solids 0.288~.
This membrane exhibited 9~.5% salt rejection and 1030 1/m2d at 68 atmospheres when tested toward synthetic seawater at 25 C. Toward synthetic brac~ish water at 40.8 atmospheres and 25 C., this membrane exhibited 94.6~ salt rejection and 1340 ` l/m2d flux.
E~:ample 9: A membrane prepared according to E~am~le 2.was tested for water so~teniny application .
.
using a tap water charac-teristic of "hard" ~ia~-~r containing magn~sium and ca~cium salts, said t,at2r ; having a conductivity of 0.53 x 10 mho. Th_ membrane produced 900 1/m2d and g~Q conducti~rit~r rejection at 13.6 atmosphel^es and 25~ C., produc~ng a "soft" water suitable for household use.
Example 10: A membrane was pr~pared acco-ding to Example 4 and was tested for ~ater sof~ening applications using a "hard" tap water as described in Example 9. ~his membrane exhibited 2360 1/m2d and 95.0% conductivity rejection at 13.6 atmos~heres and 25 C., producing a "soft" water suitable for household use.
~ ample 11: A membrane was prepared according to Example 2. This membrane when tested under reverse -~ osmosis conditions with 0.1~ magnesium sulfate at 13.6 a-tmospheres and 25 C. exhibited 1300 1/m2d ;- flux at 98% salt rejection. This membrane was immersed in 100 ppm aqueous chlorine as sodium hypochlorite for 72 hours and then was retested to aet~rmine its stability toward chlorine attack.
It exhibited a flux of 1380 1/m2d at 97.4~ salt rejection under the same conditions as before. This E~ample illustrates the chlorine resistance of this ~5 type of membrane.
Examples 12-15 Use of Amine-Terminated Polyamide -Prepolymer ~ntermedia es E~ample 12: An amine-terminated prepolymer of 3~ piperazine ~ith trimesoyl chloride ~Jas prepared 2S
follows. A solution of 2 grams (23 mllliequivalents) of trimesoyl chloride in 100 milliliters of 1,2-aichloroethane was added over a 5 minute period wi`th rapid stirring to a solution of 2 grams of piperazine t~7 meq) and 2 grams triethylamine, present as acid accc-~lor for n~utrali~ation, in 100 ml dichloroethane. (The NR~I/COCl ratio was 2. o~
The prepolymer precipitated from the dichloroethane ~` during the reaetion. The prepolymer ~JaS filtered 5 off, washed with dichloroethane, and air dried to yield appro~imately 4 grams ol product The prepolymer ~ was mixed ~ th 100 milliliters of water and stirre~
;~ for one hour at 60n C This solution was filterea to remove insolu~le and gelatinous res~dues from the prepolymer. Two grams of sodi~m hydroxide were added to the clear filtrate. A microporous polysulfone support was coated wi-th this solution, pressea with a rubber roller ~o xemove excess solution, then exposed to a 0.1% solution of isophthaloyl chloride in hexane for 10 seconds, and finally air dried at room temperature. This membrane when testea against 3.5% synthetic seawater at 6~ a~lospheres and ~5~ C.
~xhihited 430 1/m2d at 99.0~ salt rejection. Althou~h higher flux (e.g. 600 1/m2d) would be greatly preferred, ~0 flu~ was ~rea.ly superior to some prior art membranes, and a salt rejection capability above 9~rO is considered a significant achievement in this art.
E~ample 13: A solution of 2 grams (23 meq) of trimesoyl chloride in dichloroethane was added over ~5 lS minutes with rapid s-tirring to a solution of 1.5 grams (35 meq) piperazine and 0.5 grams ~6 meq) morpholine in 150 milliliters of dichloroethane.
t-N~I/COCl ratio = 1.78:1, including -NRH ~ontributed by morpholine.) The resulting suspension of prepolymer in dichloroethane was stirred for 30 minu~es, followed by filtrations, washing, and air drying of the prepolymer to yield approximately 4 grams of product.
The prepolymer ~as dissolved in 100 milliliters of water and filtered to remove a small amount of gelatinous ma,erial. T-~o grams of l~ dimethylpiperazine , .
- 2~ -acid acceptor ~as add~d to the solution. A microporous polysulf~ne substrate was coated ~.~ith the solution, pressed with a rubber roller to remove excess solutionl exposed to a 0.1% solution of isophthaloyl chloride in he~ane for lO seconds, then dried a~
130 C. in a circulating air oven for 15 minutes.
Tested against synthetic seawater at 6~ atmospheres and 25 C., this membrane exhibited 1750 l/m d at 93.5% salt rejection.
Example 14: A dichloroethane solution of 2.0 ~rams (33 meq) cyanuric chloride was added with rapid stirring to a solution of 2.8 grams (65 meq) piperazine. The prepolymer was filtered, ~ashed, and dried. (-NP~/COCl ratio = 1.97~ hen mixed ~ith lS water this prepolymer con-tained much water insoluble material which was filtered off. The clear filirate was neutralized with sodium hydroxide, followed by addition of 0.5 gram more sodium hydroxide. The solution was again filtered, providing 50 ml of clear filtrate. A membrane was prepared by interfacial rcaction of the ~mine prepolymer with isophthaloyl chloride as described in Example 13, then dried at 130~ C. in an oven. The resulting membrane exhibited 570 l/m d at 99.2% salt rejection ~hen tested à~ainst 2~ synthetic seawater at 68 a~mospheres and 25 C.
Exa_~le 15: A solution of 2.0 grams (39 meq~
}~hospllorus o~ychloride in lO0 milliliters of dichloroethane was added to a solution of 2.2 grams (rl meq) o~ piperazine in lO0 milliliters of dichloroethane with rapid stirring. (-NRH/acid halide rc~tio = 1.31:1.) The prepolymer precipitate ~as recovered and air dried. This prepolymer was conpletely c.oluble ~7hen dissolved in lO0 milliliters of water containing l.0 gram of sodium hydroxide. An interfacial membrane was formed on microporous polys~llfone , as described in Example 13, then air drie~ hen tested against synth~tic sea~ra~er at 6~ ~trnosp~e~es and 25 C., this membrane e~hibited lS30 1/m2d at 93.9% salt rejection.
Exarnple 16 A membrane was prepared accoraing to Example 4 except that 2,6-pyridinedicarboxyIic acid chloride was used in place of isophthaloyl chloride. When -~ tested against 0.5% aqueous magnesium sulfate solution at 13.6 atmospheres and 25 C., this membrane e~nibited 1210 l/m d at 95~ salt rejection.
Example 17 A wet polysulEone substrate was saturated ~Jith an aqueous solution containing 2% piperazine and 2~
morpholine by weight. This coated support was pressed with a rubber roller, exposed to a solution of 1~
trimesoyl chloride in hexane for 10 seconds, then dried at 130 C. When tested against synthetic seawater at 68 atmospheres, this membrane demonstrated 860 1/m2d at S6% salt rejection.
Example_18 According to the method of Exarnple 17, but using an aqueous solution of 1% piperazine and 5% diethanolamine, a membrane was prepared which exhibited 1550 1/m2d at 70~ salt rejec-tion toward synthetic seawater at 6S atl-nospheres~
Claims (9)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A process for preparation of a composite reverse osmosis membrane comprising the steps of:
(a) coating a porous support with a layer comprising an aqueous solution containing, dissolved therein, an essentially monomeric, polyfunctional, essentially water-soluble secondary amine;
(b) contacting the said layer with an essentially water-insoluble, essentially monomeric, volatilizable polyfunctional acid halide component having an average acid halide functionality greater than 2.05, for a time sufficient to effect in-situ chain extension and crosslinking reactions between the secondary amine and the polyfunctional acid halide; and (c) drying the product of step (b) to form the composite reverse osmosis membrane.
(a) coating a porous support with a layer comprising an aqueous solution containing, dissolved therein, an essentially monomeric, polyfunctional, essentially water-soluble secondary amine;
(b) contacting the said layer with an essentially water-insoluble, essentially monomeric, volatilizable polyfunctional acid halide component having an average acid halide functionality greater than 2.05, for a time sufficient to effect in-situ chain extension and crosslinking reactions between the secondary amine and the polyfunctional acid halide; and (c) drying the product of step (b) to form the composite reverse osmosis membrane.
2. The process of claim 1 in which the porous support comprises a polysulfone film.
3. The process of claim 1 in which said secondary amine is selected from the group consisting of piperazine and substituted piperazine.
4. The process of claim 1 in which the acyl halide comprises trimesoyl chloride.
5. The process of claim 1 in which the acyl halide comprises a mixture of trimesoyl chloride and isophthaloyl chloride.
6. A composite reverse osmosis membrane prepared by the process of claim 1.
7. The process of claim 1 in which the polyfunc-tional halide of step (b) comprises isophthaloyl chloride.
8. In a process for desalination of saline water by reverse osmosis comprising contacting the saline water under pressure with a reverse osmosis membrane, the improvement comprising using the membrane of claim 6 as the reverse osmosis membrane.
9. The process of claim 8 wherein the saline water contains at least about 3,000 parts per million by weight of an alkaline earth metal salt or a sulfate salt.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000405032A CA1148419A (en) | 1980-01-09 | 1982-06-11 | Reverse osmosis membrane |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000343311A CA1144433A (en) | 1979-01-10 | 1980-01-09 | Reverse osmosis membrane |
| CA000405032A CA1148419A (en) | 1980-01-09 | 1982-06-11 | Reverse osmosis membrane |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1148419A true CA1148419A (en) | 1983-06-21 |
Family
ID=25669026
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000405032A Expired CA1148419A (en) | 1980-01-09 | 1982-06-11 | Reverse osmosis membrane |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1148419A (en) |
-
1982
- 1982-06-11 CA CA000405032A patent/CA1148419A/en not_active Expired
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