Liquid purification or separation – Filter – Material
Reexamination Certificate
2000-09-12
2002-06-18
Fortuna, Ana (Department: 1723)
Liquid purification or separation
Filter
Material
C210S500370, C264S041000, C427S244000, C427S245000
Reexamination Certificate
active
06406626
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a high-performance composite semipermeable membrane for selectively transmitting and separating the components of liquid mixtures, a method for the production thereof and a method of removing harmful substances using same. With the composite semipermeable membrane obtained by means of the present invention it is possible, in particular, to recover drinking water at a high rate by permitting passage of silica and preventing deposition thereof at the membrane surface while selectively separating/removing the pollutants and trace quantities of harmful substances and their precursors, etc, contained in the raw water of water treatment plants.
TECHNICAL BACKGROUND
In relation to the separation of mixtures, there are various techniques for removing materials (for example salts) dissolved in solvents (for example water) but, in recent years, membrane separation methods have come to be used as energy-saving and resource-efficient processes. The membranes in membrane separation methods are microfiltration membranes, ultrafiltration membranes and reverse osmosis membranes. Furthermore, recently, membranes positioned between reverse osmosis membranes and ultrafiltration membranes (loose RO membranes or NF membranes: nanofiltration membranes) have appeared and have come to be used. This technology makes it possible to obtain drinking water from, for example, sea water, salt/brackish water and water containing harmful substances and, moreover, the technology has also been employed for the production of ultra-pure water for industrial use, for waste water treatment and for the recovery of valuable materials, etc.
The majority of the composite semipermeable membranes currently marketed are of two kinds, namely those having a gel layer and an active layer of crosslinked polymer on top of a microporous support membrane and those having an active layer of polycondensed monomer on top of a microporous support membrane. Of these, composite semipermeable membranes formed by coating a microporous support membrane with an ultra-thin membrane layer of crosslinked polyamide obtained by a polycondensation reaction between a polyfunctional amine and a polyfunctional acid halide are widely employed as reverse osmosis membranes of high permeability and selective separation characteristics.
However, the demand for practical semipermeable membranes for reverse osmosis is increasing year by year and, from the point of view of energy-saving, there is desired a semipermeable membrane with high water permeability where lower pressure operation is possible while still maintaining high solute removal properties. For example, from JP-A-64-56108 there is known a composite semipermeable membrane having good desalting properties and high water permeability in ultra-low pressure operation at 7.5 kg/cm
2
(0.75 MPa), based on the presence of 4-chloroformylphthalic anhydride. However, even with this method the desalting properties and the water permeability are unsatisfactory in the case of super ultra-low pressure operation at around 0.3 MPa. Now, operation at a high recovery rate is also desirable, but with membranes where the percentage silica removal is high the silica concentration on the concentrate side increases rapidly, and deposition occurs at the membrane surface, so that a lowering of membrane performance results and stable operation and enhanced water quality cannot be expected.
In recent years, in water treatment plants using river water, and lake and swamp water, or the like, as the raw water, the formation of carcinogenic halogen-containing organic materials (trihalomethanes) has become a serious problem owing to the fact that in the water treatment plant there is carried out the chlorine sterilization treatment of the soluble organic matter (trihalomethane precursors) flowing-in from peat bogs and regions between mountains, etc. The most important of the trihalomethane precursors is humic acid, which comprises soluble organic matter of molecular weight ranging from several thousands to several tens of thousands. In the case of the ozone/active carbon treatment methods, the introduction of which is currently being investigated in water treatment plants, while the percentage removal at the time of the start of operation is high, when long-term operation is carried out the percentage removal falls rapidly. For this reason, frequent replacement of the active carbon is necessary. Furthermore, with contact oxidation methods, biological membrane methods and other such biological treatment methods, since soluble organic matter is formed at the end of the biological metabolism, there is the problem that sufficient removal cannot be carried out. In membrane separation methods, the microfiltration membrane and ultrafiltration membrane pore diameters are large and satisfactory removal of humic acid cannot be achieved. Furthermore, with reverse osmosis membranes, while the pore diameter is small and the percentage humic acid removal is high, the percentage silica removal is also high and consequently high-recovery operation using reverse osmosis membranes is difficult.
In order to resolve problems of the kind described above, the objective of the present invention lies in offering a composite semipermeable membrane having high solute removal properties and high water permeability, where high-recovery operation is possible.
DISCLOSURE OF THE INVENTION
In order to realize the aforesaid objective, the present invention relates to a composite semipermeable membrane which is characterized in that it is a composite semipermeable membrane in which there is formed by polycondensation, on a microporous support membrane, a crosslinked polyamide ultra-thin membrane layer from a polyfunctional amine, a polyfunctional acid halide and a polyfunctional acid anhydride halide, and the flow of water permeate at an operating pressure of 0.3 MPa, a temperature of 25° C. and a pH of 6.5 lies in the range from 0.8 to 4.0 m
3
/m
2
.day and, furthermore, the percentage humic acid removal is at least 98% and, preferably, a composite semipermeable membrane characterized in that the carboxyl group concentration in the ultra-thin membrane layer analyzed using X-ray photoelectron spectroscopy (ESCA) is at least 0.02 but less than 0.06: a method for the production thereof; and a method of water purification using same.
Optimum Form for Practising the Invention
The polyfunctional amine in the present invention is a mixed amine of aliphatic polyfunctional amine and aromatic polyfunctional amine, where the aliphatic polyfunctional amine is preferably a piperazine type amine or derivative thereof as represented by [Formula 1], examples being piperazine, 2,5-dimethylpiperazine, 2-methylpiperazine, 2,6-dimethylpiperazine, 2,3,5-trimethylpiperazine, 2,5-diethylpiperazine, 2,3,5-triethylpiperazine, 2-n-propylpiperazine, 2,5-di-n-butylpiperazine and the like, with in particular piperazine and 2,5-dimethylpiperazine being preferred.
R
1
to R
8
are each selected from H, OH, COOH, SO
3
H, NH
2
and C
1
to C
4
straight chain and cyclic, saturated and unsaturated, aliphatic groups.
Furthermore, the aromatic polyfunctional amine is not particularly restricted providing it has no less than two amino groups per molecule, and examples include m-phenylenediamine, p-phenylenediamine and 1,3,5-triaminobenzene, plus the N-alkyl derivatives thereof such as N,N-dimethyl-m-phenylenediamine, N,N-diethyl-m-phenylenediamine, N,N-dimethyl-p-phenylenediamine, N,N-diethyl-p-phenylenediamine and the like, with m-phenylenediamine and 1,3,5-triaminobenzene being particularly preferred.
The molar ratio of the aliphatic polyfunctional amine to the aromatic polyfunctional amine used in the present invention lies in the range from 40/60 to 95/5, more preferably from 70/30 to 90/10. If the aliphatic polyfunctional amine is less than 40 mol %, the flow of water permeate declines, while if it is greater than 95 mol % good selective separation characteristics are not obtained.
The polyfunctional acid halide is an acid hali
Fusaoka Yoshinari
Murakami Mutsuo
Tateishi Yasushi
Fortuna Ana
Morrison & Foerster / LLP
Toray Industries Inc.
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