JPS5824447B2 - Manufacturing method of reverse osmosis membrane - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Reverse osmosis is of considerable interest in the field of brine purification and desalination.

In reverse osmosis, a pressure greater than the osmotic pressure of the aqueous feed salt solution is applied to the side of the feed solution that is separated from the purified water by a semipermeable membrane.

This forces pure water to diffuse through the membrane, while salt molecules and other impurities remain blocked by the membrane.

The efficiency of reverse osmosis depends to a large extent on the properties of the membrane, and numerous membrane types and methods of their manufacture have been described in the prior art.

These membranes are typically cast from a solution of membrane material and solvent with or without the addition of other ingredients such as water, swelling agents, and the like.

This membrane is used in reverse osmosis as a film deposited on a porous support material.

However, these prior art membranes generally have deficiencies, such as having a too short useful life due to shrinkage or chemical or biological degradation, and operating inefficiently due to flow rates or salt repelling forces that are too low. become a target.

According to the present invention, a reverse osmosis membrane with excellent flow rate and salt rejection properties and without shrinkage or deterioration is produced by combining a polyethyleneimine film and a crosslinking agent having a functional group that reacts with the amine groups of the polyethyleneimine. It has now been discovered that a wax can be prepared by the reaction of

Polyethyleneimine (hereinafter abbreviated as PEI) is produced by polymerizing ethyleneimine, and has traditionally been used in a wide range of industrial applications such as adhesives, flocculants, ion exchange resins, complexing agents, and absorbents.

This means that the ratio of 1st class: 2nd class: 3rd class is approximately 1:2:1.
It is a highly branched polyamine with several amino nitrogens.

It is available in a wide range of molecular weights, from about 600 to 100,000, all of which are water soluble and produce solutions with a slightly cloudy appearance.

The molecular weight of the PEI is not a critical factor in the present invention, but its optimum value will depend on various factors such as the type of support, the nature of the brine feed, the desired salt rejection and the magnitude of the flow rate.

Generally, molecular weights of about 600 to ioooooo are suitable, with about 12,000 to 1ooooo usually preferred.

A film of PEI is prepared from an aqueous solution of this polymer.

This solution is usually easiest to prepare by gradually diluting the dried EI with water until the desired concentration is obtained.

Preferably, mixing is continued until a uniform, cloudy-looking solution is obtained, and then the solution is sipped.

The optimum concentration of PEI in an aqueous solution varies depending on the molecular weight of PEI.

The concentration of PEI is preferably 0.033 to 2.7% by weight.
A concentration of 0.33 to 1.0% by weight is usually preferred.

PEI films can be prepared by conventional methods, such as casting an aqueous PEI solution onto a support or immersing the support in the solution.

However, it is generally most convenient and effective to form the film by simply immersing the support in the PEI solution for a time sufficient to adsorb a thin film of the solution onto the support.

In general, the immersion contact time is not a critical factor (any time from a few seconds to 24 hours has been found to produce good films.

The support may be of a type commonly used in reverse osmosis.

These include porous glasses, sintered metals, ceramics, as well as organic polymeric materials (eg, cellulose esters, styrene, vinyl butyral, polysulfone, etc.).

Polysulfone film has been found to be a particularly effective support material for the membranes of the invention.

For the production of this support film,
of 5aline Water Re5earch
andDevelopment Progress R
eport (Salt water research inter-bureau progress report) A359, (1
(October 968).

This production method uses polysulfone dimethylformamide (D
MF) solution is poured onto a glass plate to form it, and then immersed in a 2% by weight DMF aqueous solution to gel the film.

Be qualitative.

The side of the polysulfone film exposed to air during casting is referred to as the "front face 11" and has fine pores, most of which are less than 100 Å in diameter.

The back surface of the film that is in contact with the glass plate has very large pores.

To obtain effective results in reverse osmosis desalination, the PEI coating must be applied toward the front side of the polysulfone support film.

The reverse osmosis membrane of the present invention is then prepared by reacting the PEI film with a crosslinking agent.

The cross-linking agent consists of a di- or tri-functional organic compound, ie a compound containing two or three functional groups capable of reacting with the amine groups in PEI.

Chloride and incyanate functional groups have been found to be particularly effective in crosslinking PEI.

However, other conventional crosslinking functional groups such as acid anhydrides, epoxies and olefins activated with polar substituents are also suitable.

Preferably, the crosslinking agent is an aromatic or heterocyclic compound.

This is because such compounds have been found to provide excellent reverse osmosis properties, particularly resistance to shrinkage.

Although the exact explanation for the superiority of such cross-linking agents is not known, it is believed that the cyclic cross-linking groups that connect the PEI structures contribute to the stiffness of the membrane and exhibit good resistance to compression. it is conceivable that.

The superiority of chloride and isocyanate functional groups and aromatic and heterocyclic linking groups is illustrated in the Examples below.

As shown in the data of the examples, four compounds,
That is, tolylene-2,4-diisocyanate, cyanuric chloride, terephthaloyl chloride and hisiphenyl ether disulfonyl chloride were found to be very effective in reverse osmosis.

Reaction of these compounds with PEI produces PEI structural aqueous amide and polyurea bonds.

Other suitable crosslinking agents include isophthaloyl dichloride, anhydrotrimellitic acid chloride and metabenzenedisulfonyl chloride.

The reaction between the PEI film and the crosslinking agent is conveniently carried out by immersing the film in a solution of the crosslinking agent.

The solvent used to dissolve the crosslinker must not dissolve either the PEI or the support material.

Hydrocarbon solvents such as n-hexane, heptane, octane or cyclohexane are generally the most practical.

The optimal concentration of crosslinking agent in the solvent varies considerably depending on the crosslinking agent, solvent, support, etc., and is best determined experimentally.

but. Concentrations of about 0.1 to 5.0% by weight are generally good.

about 90°C to 130°C, preferably about 110-115
High temperatures of 0.degree. C. are usually required to complete the crosslinking reaction.

The reaction can also be carried out to completion in the abovementioned solvent solution (one-step reaction), in which case this solvent solution and heating to the required temperature are performed.

Alternatively, the PEI film may be heated for about 10 seconds to 1 hour, for example.
After a short period of 0 minutes, it may be taken out and placed in a heater at the required temperature to complete the reaction (two-step reaction).

The optimal reaction time may also change depending on the above variables, but
A time of about 5 to 30 minutes is usually good.

If the crosslinking agent is easily hydrolyzed by water, it is necessary to dry the PEI film to remove free water before reaction with the crosslinking agent.

Air drying is usually sufficient, but application of heat, such as by a radiant gas heater or an infrared lamp, may also be used to accelerate drying.

However, if the crosslinking agent is of a type that is not easily hydrolyzed with water, drying can be omitted.

For example, low molecular weight P on a polysulfone support film
When reacting EI (molecular weight 12,000) with tolylene diisocyanate, very good results (see Examples) were obtained without the use of a drying step.

When drying a PEI-coated polysulfone support, heat is applied from the back side of the polysulfone film so that water vapor escapes through the large pores on the back side of the film and does not disturb the PEI layer on the front side of the film.

Optimal results, both from the standpoint of convenience and the reverse osmosis properties of the membrane product, are usually obtained by forming the membrane in situ on the support.

When this method is used, the support is coated with P as described above.
The PEI film is first adsorbed onto the support material by contacting with an aqueous solution of EI.

PEI is a cationic polyelectrolyte that is easily adsorbed onto porous materials and is therefore particularly suitable for in situ formation of membranes on porous support materials.

The adsorbed PEI is then reacted with a crosslinking agent as described above, resulting in in situ formation of a membrane on the support.

Here too, PEI exhibits a unique effect in its high degree of reactivity with crosslinking agents as well as its pronounced absorbability.

The membranes of the present invention, having a thickness in the range of about 1000 to 10000 membranes, resulting from the reaction of PEI's amine groups with a crosslinking agent, are insoluble in water or solvents and, if formed in situ, can be mechanically peeled from the support. It is normal that you cannot.

Polysulfone support films of the above type have been found to be particularly effective for the in-situ formation of the membranes of the present invention because of their high compressive resistance, small pore size (on the front side of the polysulfone film) and resistance to drying effects. did.

The following examples will serve to further explain the invention.

Examples 1-6 In this example, the support was a polysulfone film prepared as described above, with a thickness of 0.038 to 0.051 mm (1.5 to 2.0 mil) and a molecular weight of Made of 20,000 to 40,000 polysulfone.

The PE■ coating was applied to the front side of the polysulfone film by the following three steps.

(H) 0.33 to 1% by weight PEI (molecular weight 1
(2000) solutions were prepared by gradually diluting PEI with water until the desired concentration was obtained.

Mixing was continued until a uniform, cloudy-looking solution was obtained, and then the solution was passed through the mouth.

(ii) While the polysulfone support film was still wet, it was placed face down on the surface of the PEI solution for 1 minute.

(1**) Pull the support film out of the PEI solution, hold it vertically with clamps, and remove the moisture to about 0.
．． Air dried for approximately 10 minutes to reduce to 2%.

The PEI-coated polysulfone support film thus obtained was immersed in a solution of the crosslinker in n-hebutane maintained at a temperature of 90°C.

The reaction continued for 10 minutes.

The resulting membrane-support complex was then removed from the reaction medium, washed with heptane, and air-dried for 30 minutes at 25°C.

This was then tested in a reverse osmosis test tank under the test conditions described below.

Pressure 500 psig Flow rate: 11/min Feedstock: 3.5% NaCl Temperature: 25°C Test time: 20-24 hours PEI concentration in aqueous solution, crosslinker used, and The concentrations of crosslinking agents are shown in Table 1.

The results, i.e., the flow rate in gallons of water passed per square foot per day (gfd) or liters of water per square centimeter per day (the flow rate of water product through the membrane), as well as the flow rate in the feedstock. The salt rejection rate, expressed as % of the salt remaining unable to pass through the membrane relative to the total salt of the sample, is also shown in Table 1.

Examples 7-11 In this example, the reaction with the crosslinking agent was carried out without drying the support beforehand.

The support is the polysulfone film used in Examples 1-6.

The support film is made of PEI with a molecular weight of 12,000 and 0.66
wt% aqueous solution.

The film was removed and molded vertically for about 1 minute to remove excess PEI.

The wet film was placed in a flat vat and covered with a hexane solution of TDI for 3 minutes at room temperature.

The film was then removed, drained and cured in a heater for 10 minutes at a temperature of about 115°C.

The thickness of the finished PEI coating on the front side of the support film was 6000λ.

This was then tested in a reverse osmosis test tank under the following conditions.

Pressure: Crab 103 atm (1500 psig) Flow rate:
1.51/min Feedstock: 3.5% NaCl Temperature: 25°C Test time: 20-24 hours TDI concentrations and results are shown in Table 2.

When various membranes prepared by the method of the present invention were further subjected to reverse osmosis tests, no decrease in flow rate was observed during 200 hours of operation.

This shows that the compression resistance is high.

Claims (1)

[Claims] 1 Forming a layer of polyethyleneimine on a support made of a porous polymer film, and then crosslinking by reacting the amine groups of this polyethyleneimine with a polyfunctional crosslinking agent having chloride or isocyanate functional groups. A method for manufacturing a reverse osmosis membrane.