Reverse osmosis membrane having excellent anti-fouling...

Details Reverse osmosis membrane having excellent anti-fouling... Reverse osmosis membrane having excellent anti-fouling...

2001-08-02

2003-04-22

Fortuna, Ana (Department: 1723)

Plastic and nonmetallic article shaping or treating: processes

Pore forming in situ

Composite article making

C264S041000, C210S490000, C210S500380, C210S500250, C210S500260, C210S088000, C210S523000, C210S524000

Reexamination Certificate

active

06551536

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the invention
The present invention relates to a reverse osmosis membrane having excellent anti-fouling property, and, more specifically, to a nano structure type reverse osmosis membrane, in which TiO
2
, a representative photocatalyst having not only decomposition activity against various organic contaminants, but also antimicrobial activity against microorganisms, is incorporated to the membrane surface, and a method for preparing the same.
2. Description of the Related Art
In general, a reverse osmosis membrane has been applied to various fields, such as desalination of sea water, wastewater treatment, production of ultra pure water, treatment of purified water for households, and the like. With a view of increasing water permeability of the membrane or improving removal of salt, research for such reverse osmosis has been carried out. In this regard, U.S. Pat. No. 4,872,984 to Tomashke and U.S. Pat. No. 4,983,291 to Chau disclose a novel polyamide reverse osmosis membrane, capable of increasing water permeability and improving the removal of salt.
Meanwhile, water treatment processes using the reverse osmosis membrane suffer from fouling. Fouling is the deposition of material, referred to as foulant, on the membrane surface or in its pores, leading to a change in membrane behavior or even complete plugging of the membrane. These phenomena manifest themselves over time by increased operating pressure whereby water permeability properties, such as water permeability or removal of salt, are decreased. Hence, most of operation cost of water treatment facilities is used to repair damage caused by such fouling and in prevention of the fouling. There is thus a widely recognized need for fundamental preventive measures.
Examples of the foulant classified by form include inorganic crystalloids, organic contaminants, particulate matters and colloids, and microorganisms. In the case of the polyamide reverse osmosis membrane, the fouling attributed to microorganisms, in which microorganisms present in water are absorbed into the surface of the membrane and thus a thin bio-film is formed, is known to be the most serious one.
In order to decrease the fouling, pretreatment of water, modification of electrical properties of the membrane surface, modification of module process condition, and periodical cleaning are widely utilized. In particular, it is reported that the fouling by microorganisms, which is seriously generated in the reverse osmosis membrane, is drastically decreased by treatment with sterilizing agents, such as chlorine. However, chlorine creates carcinogenic by-products. So, when chlorine is applied as is to the process of producing potable water, it is known to cause many problems. Recently, research to produce membranes with antifouling properties is focused on change of electrical charge characteristics of the membrane surface. But, the fact is that a novel membrane, capable of drastically decreasing the fouling, is not developed yet.
Meanwhile, TiO
2
which is a highly effective photocatalyst, kills microorganisms under ultraviolet or solar radiation and decomposes organic contaminants. By use of such antimicrobial properties, many cases applied to packaging films, storing boxes, wall paper, seats, interior materials of automobiles, lamps, eye shields, air conditioners, electronic ranges, bottom materials, refrigerators and so on, are described in patents and papers.
In addition, techniques for decomposing organic contaminants and killing microorganisms by directly dispersing TiO
2
powder into water, in water treatment process, are known. Conventional water treatment processes using TiO
2
can decompose organic contaminants and kill microorganisms present in water, without harmful by-products, so that much research into applicability for water treatment processes has been continuously performed. However, the water treatment process for photodecomposition by adding TiO
2
particles to water suffers from the disadvantages of requiring a secondary process for recovering TiO
2
particles and difficultly in recycling the particles. Therefore, such process cannot be completely applied for water treatment.
BRIEF SUMMARY OF THE INVENTION
Therefore, it is an object of the present invention to overcome the above problems encountered in the prior arts and to provide a novel reverse osmosis membrane having excellent antifouling property, by incorporating TiO
2
particles of nano scale with photocatalytic properties to the membrane in a fixed form in order to fundamentally prevent fouling generated during the membrane use.
It is another object of the present invention to provide a method for manufacturing the reverse osmosis membrane having excellent antifouling property.
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, TiO
2
particles of nano scale are obtained by adding a titanium compound, such as Ti[OCH(CH
3
)
2
]
4
, TiCl
4
, TiOSO
4
, or TiOCl
2
, to an acidic aqueous solution, to perform hydrolysis. As such, use of aqueous solution of strong acid with a pH range of 0.5-3 results in favorable generation of nano particles. Soon after, a pH range of thusly obtained aqueous titanic acid solution is regulated to 1-6 or 9-13, thereby yielding a stable TiO
2
dispersed solution. However, it is more preferable that, because of concern about adulteration caused by impurities in said condition, TiO
2
particles are separated from the aqueous titanic acid solution obtained by hydrolyzing the titanium compound, and dried, to yield TiO
2
as a white powder, which is then dispersed into an acidic solution of pH 1-6 or an alkaline aqueous solution of pH 9-13, thereby obtaining a stable TiO
2
dispersed solution. In the case of using the aqueous solution less than 1 or exceeding 13 in pH, the membrane may be degraded by strong acid or strong alkali. On the other hand, if the pH of the aqueous solution exceeds 6 and is less than 9, TiO
2
particles of nano scale are aggregated and thus precipitated. Hence, stability of dispersed solution becomes poor.
The methods for separating TiO
2
particles from aqueous titanic acid solution and for drying the TiO
2
particles are not limited in the present invention, and all separation and drying methods can be utilized. In this regard, the aqueous solution can be directly evaporated and thus dried.
Meanwhile, upon production of TiO
2
through hydrolysis of titanium compound, various metal oxides are added in the amount of 0.1-1.0 wt % to the aqueous solution, thereby obtaining TiO
2
particles of nano scale doped with the metal ions. When such particles are used for preparation of stable TiO
2
dispersed solution, TiO
2
photocatalytic effect can be increased. As such, the usable metal oxides comprise LiOH, Mg(ClO
4
)
2
, AlCl
3
, VCl
3
, VOSO
4
.3H
2
O, VOCl
3
, Cr(NO
3
)
3
, MnF
3
, F
2
(NO
3
)
3
.9H
2
O, CoF
3
, NiCl
2
, Zn(ClO
4
)
2
, Ga(NO
3
)
3
, Zr[OCH(CH
3
)
2
]
4
, NbCl
5
, MoCl
3
, RUCl
3
, Rh(NO
3
)
3
.2H
2
O, SnCl
4
, SbCl
3
, TaCl
5
, ReCl
5
, OsCl
3
, SbCl
5
and so on. Such metal oxide is.preferably added in the amount of about 0.1-1.0 wt %, based on the weight of the aqueous solution.
In the present invention, the reverse osmosis membrane incorporated with TiO
2
particles of nano scale is prepared by immersing the reverse osmosis membrane into stable TiO
2
dispersed solution. The immersing period of time varies with pH of the solution, but is not specifically limited, as long as TiO
2
particles are sufficiently incorporated to the membrane. The mechanism of incorporation of TiO
2
into the membrane is believed to be such that TiO
2
is self-assembled to functional groups present on the surface of the membrane by coordination bonds and thus fixed. In addition, as the reverse osmosis membrane of the present invention, use can be made of all kinds of membranes including a polyamide type reverse osmosis membrane.
In the present invention, TiO
2
having excellent photocatalytic effect is used and thus the reverse osmosis membrane with superior anti-fouling prope

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