Liquid purification or separation – Processes – Liquid/liquid solvent or colloidal extraction or diffusing...
Reexamination Certificate
2001-05-25
2003-02-18
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Processes
Liquid/liquid solvent or colloidal extraction or diffusing...
C210S500280, C210S490000, C210S321600, C264S041000, C427S244000, C427S245000
Reexamination Certificate
active
06521130
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a composite semipermeable membrane which can be suitably employed in, for example, the desalination of seawater and brackish water, the production of ultra-pure water for use in semiconductor washing and the like, the purification of water supplies, the production of water for boilers, the re-utilization of waste water and sewage, the recovery of electrodeposition coating materials used as undercoats for motor vehicles and the like, the concentration of fruit juice and the production of wine; and a method for the production thereof; together with a water treatment method employing same.
TECHNICAL BACKGROUND
Aromatic polyamide semipermeable membranes are highly rigid due to the fact that they contain benzene rings, and they have the advantage that they can be readily produced by interfacial polycondensation between an aromatic polyfunctional amine and an aromatic polyfunctional acid chloride, so they are widely employed. As the aromatic polyfunctional amine there can be used, for example, m-phenylenediamine or triaminobenzene, and as the aromatic polyfunctional acid chloride there can be used, for example, the commercial monomer known as trimesoyl chloride, and membrane production is easy. In terms of the method of production, in general a polysulphone ultrafiltration membrane is formed on a polyester base material such as a nonwoven fabric, to produce a porous substrate, and this is coated with an aqueous solution of the polyfunctional amine such as m-phenylenediamine or triaminobenzene, after which coating is performed with a solution of for example trimesoyl chloride dissolved in a nonpolar solvent and, by a polycondensation reaction at the interface, there is formed a polyamide separating functional layer. A number of such aromatic polyamide semipermeable membranes have been reported hitherto (U.S. Pat. Nos. 3,744,642 and 3,926,798).
The aforesaid aromatic polyamide semipermeable membranes are characterized by outstanding pressure resistance and resistance to hydrolysis, but there are desired semipermeable membranes which can operate at still lower pressures than existing operating pressures and, furthermore, which have high water permeability.
Hence, in order to enhance the water permeability of the membrane, a number of methods have been investigated whereby additives such as polar solvents are added either to the amine solution or to the acid chloride solution, or to both, in the formation of the polyamide separating functional layer by interfacial polycondensation. For example, there are methods in which an ether such as diethyl ether, methyl t-butyl ether, tetrahydrofuran or dioxane, a ketone such as acetone, methyl isobutyl ketone or 2-butanone, or an ester such as methyl acetate, ethyl formate or ethyl acetate, is added to the acid chloride solution.
However, there has been the problem that, in the production of for example ultra-pure water for semiconductor washing in the semiconductor industry, as well as having higher water permeability a semipermeable membrane with an enhanced rejection capacity in terms of organic materials and the like is demanded, but the aforesaid methods are inadequate for this.
Against the background of the conventional problems described above, the objectives of the present invention lie in offering a method for the production of a composite semipermeable membrane which, while maintaining a high rejection rate, is also outstanding in its water permeability compared to hitherto; and the composite semipermeable membrane produced by this method.
DISCLOSURE OF THE INVENTION
In order to meet the aforesaid objectives, the present invention relates to a method of producing a composite semipermeable membrane which is characterized in that a separating functional layer containing crosslinked polyamide is formed in the presence of 1) carboxylic acid ester with a total of 8 or more carbons, or 2) carboxylic acid; to the composite semipermeable membrane produced in this way; and to a water treatment method employing same.
Optimum Form for Practising the Invention
The carboxylic acid ester with a total of 8 or more carbons is not particularly restricted in the structure of its main chain and ester region, and it may have any chemical structure such as linear, branched, cyclic, saturated or unsaturated. If the total number of carbons in the carboxylic acid ester is less than 8, there is a tendency for the separating functional layer water permeability enhancement effect to be reduced, while if the total number of carbons exceeds 20 then the boiling point is high, it is difficult to eliminate the ester from the composite semipermeable membrane and it becomes difficult to manifest high water permeability. Hence, the total number of carbons is preferably in the range 8 to 20, and more preferably 8 to 12. As examples of carboxylic acid esters where the main chain and ester moieties comprise straight chain alkyl groups, there are ethyl caproate, ethyl heptanoate, methyl caprylate, ethyl caprylate, methyl pelargonate, ethyl pelargonate, ethyl nonanoate, methyl decanoate, ethyl decanoate, methyl undecanoate, ethyl undecanoate, methyl dodecanoate, ethyl dodecanoate, methyl tridecanoate, ethyl tridecanoate and the like; as examples of cyclic unsaturated carboxylic acid esters, there are methyl benzoate, phenyl benzoate, phenyl acetate and the like; as examples of cyclic saturated carboxylic acid esters there are methyl cyclohexanecarboxylate, cyclohexyl acetate and the like; and as examples of branched saturated alkyl carboxylic acid esters, there are isoamyl caprylate, isobutyl isobutyrate, isobutyl isopentanoate, isopropyl t-butylacetate, ethyl 2-ethylheptanoate, methyl 3-methylnonanoate and the like. Furthermore, as examples of unsaturated alkyl carboxylic acid esters, there can be employed hexyl methacrylate, ethyl trans-3-hexenoate, ethyl cis-2-octenaote, ethyl trans-4-nonenoate and the like. In order to bring about the presence of such a carboxylic acid ester, the ester may be added to the polyfunctional amine solution or to the polyfunctional acid chloride solution, or it can be used to impregnate the porous substrate. In the case where it is added to the polyfunctional amine solution or to the polyfunctional acid chloride solution, the concentration is not particularly restricted but, if too much is added, it can be difficult to remove from the composite semipermeable membrane formed, while if too little is added it is difficult to show any effect. Hence, from 0.01 wt % to 50 wt % is preferred, with 0.1% to 10% being further preferred.
In the present invention, it is desirable that an acylation catalyst be jointly present along with the aforesaid carboxylic acid ester. An acylation catalyst refers to a catalyst which promotes hydrolysis reaction and increases the amount of carboxyl groups produced. Examples thereof are nitrogen-containing organic compounds such as pyridine, dimethyl formamide, N-methylpyrrolidone, 2-pyrrolidone, 2-piperidone, N,N-dimethylformamide, N,N-diethylformamide, N,N′-dimethylpropyleneurea, 1,1′-carbonyldipyrrolidine and hexamethylphosphoramide. Of these, compounds with the following structures have a higher effect in terms of enhancing the membrane properties and so are preferred.
(1) N-alkylamides or N,N-dialkylamides having an alkyl group with at least 3 carbons as a substituent group on the nitrogen atom.
(2) Cyclic alkylamides or N-alkyl cyclic alkylamides having a cyclic structure with 5 or more carbons.
(3) N,N,N′,N′-tetraalkylureas having alkyl groups as substituents on the nitrogen atoms.
(4) Alkylene ureas having a cyclic structure containing an alkylene chain with 3 or more carbons.
As compounds which fall into category (1), there can be used for example N-cyclohexylformamide, N,N-diisopropylformamide, N,N-diisopropylacetamide and N,N-dibutylformamide Furthermore, as compounds which fall into category (2), there can be used &dgr;-valerolactam, N-methyl-&dgr;-valerolactam, &egr;-caprolactam, N-methyl-&egr;-caprolactam, 2-azacyclooctanone and 2-azac
Fusaoka Yoshinari
Ito Akihiko
Kono Shunji
Fortuna Ana
Morrison & Foerster / LLP
Toray Industries Inc.
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