WO2002096560A1

WO2002096560A1 - Anion exchangers and processes for preparing them

Info

Publication number: WO2002096560A1
Application number: PCT/JP2002/005062
Authority: WO
Inventors: Takanobu Sugo; Noriaki Seko; Kunio Fujiwara; Kazuyoshi Takeda; Makoto Komatsu; Eiichi Akiyama; Mari Katsumine
Original assignee: Ebara Corporation
Priority date: 2001-05-25
Filing date: 2002-05-24
Publication date: 2002-12-05
Also published as: JP2002346400A; TW555595B

Abstract

An object of the present invention is to provide an anion exchanger having a high ion exchange capacity by introducing larger amounts of anion exchange groups than in conventional ion exchange resins without causing the problem of the amine odor.Anion exchangers of the present invention comprise a graft polymer side chain derived from a styrene compound having a haloalkyl group on the benzene ring on a backbone of an organic polymer base characterized in that a functional group derived from a polyamine compound having one tertiary amino group and one or more primary, secondary or tertiary amino groups and/or quaternary ammonium groups has been introduced onto said graft polymer side chain.

Description

DESCRIPTION ANION EXCHANGERS AND PROCESSES FOR PREPARING THEM

FIELD OF THE INVENTION

The present invention relates to ion exchangers capable of adsorbing ionic components in the air or in water and processes for preparing them. Particularly, the present invention relates to novel anion exchangers and processes for preparing them.

PRIOR ART

Bead-like ion exchange resins commonly known as ion exchangers are mainly classified into a group of strongly acidic cation exchange resins having sulfoniσ or the like, a group of strongly basic anion exchange resins having quaternary ammonium or the like, a group of weakly acidic cation exchange resins having carboxyl or the like and a group of weakly basic anion exchange resins having tertiary amino or the like. The most widely used ion exchange resins among them are strongly acidic cation exchange resins and strongly basic anion exchange resins.

In the preparation of these ion exchange resins, a base resin in the form of beads of polystyrene σrosslinked with divinylbenzene is generally used. When a strongly acidic cation exchange resin having sulfone groups is to be prepared, for example, this base resin is sulfonated with a sulfonating agent such as sulfuric acid or chlorosulfonic acid to introduce sulfone groups into the base, whereby a strongly acidic cation exchange resin is obtained. When a strongly basic anion exchange resin having quaternary ammonium groups is to be prepared, for example, the base resin is chloromethylated and then quaternized by a reaction with a tertiary amine such as trimethylamine to give a strongly basic anion exchange resin.

Strongly basic anion exchange resins normally have a neutral salt splitting capacity of 1.2 meq/mL, which is lower than that of strongly acidic cation exchange resins , about 2.0 meq/mL. This led to the problem of increased costs when strongly basic anion exchange resins are used for desalting for water treatment because they are needed in larger amounts. Thus, attempts were made to introduce more anion exchange groups into the base for cost reduction, which invited the problem that the trimethylamine odor is intensified by the introduction of large amounts of quaternary ammonium groups into the base. This is attributed to the so-called Hofmann degradation, which means elimination of quaternary ammonium groups by heating or the like because of the low chemical stability of quaternary ammonium groups to heat . This problem of the amine odor was a major issue not only when large amounts of quaternary ammonium groups were introduced into the base but also generally in strongly basic anion exchangers having quaternary ammonium groups.

DISCLOSURE OF THE INVRNTTON

The present invention was achieved as a result of our careful studies to obtain a novel strongly basic anion exchanger having a high neutral salt splitting capacity by introducing large amounts of anion exchange groups into the base without causing the problem of the amine odor due to Hofmann degradation.

In order to solve the above problems , the present invention relates to an anion exchanger comprising a graft polymer side chain derived from a styrene compound having a haloalkyl group on the benzene ring on a backbone of an organic polymer base characterized in that a functional group derived from a polyamine compound having one tertiary amino group and one or more primary, secondary or tertiary amino groups and/or quaternary ammonium groups has been introduced onto said graft polymer side chain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing the gas removal performance test apparatus used in the examples of the present invention .

THE MOST PREFERRED EMBODIMENTS OF THE INVENTION

Various aspects of the present invention are explained in detail below. In the following description, the "styrene compound having a haloalkyl group on the benzene ring" is simply referred to as "haloalkyl- substituted styrene" .

Organic polymer bases for preparing anion exchangers of the present invention are preferably polyolefin-based organic polymer bases. Polyolefin-based organic polymer bases are suitable for the purpose of introducing a graft side chain by radiation-induced graft polymerization because they are not degradable by radiations. Specific examples of polyolefin-based polymer materials well suitable for use as organic polymer bases for preparing anion exchangers of the present invention include, but not limited to, polyolefins such as polyethylene and polypropylene; halogenated polyolefins such as PTFE and polyvinylchloride; and olefin-halogenated olefin copolymers such as ethylene-ethylene tetrafluoride copolymers and ethylene-vinyl alcohol copolymers (EVA) .

These organic polymer bases can be preferably in the form of a polymer elemental fiber or a woven or nonwoven fabric consisting of an assembly thereof, net, film, porous membrane or the like. In conventional bead-like ion exchange resins subjected to frequently recurring treatment-regeneration cycles, what was important lies in the ion exchange capacity per packed column and the regeneration efficiency because they were desired to increase the amount of treated liquid per cycle as much as possible with less amounts of regenerating agents. However, ion exchangers of the present invention are designed for one-way use because they are especially intended to be effective in applications other than previously such as adsorption of trace gaseous components in gases, elimination or transfer of trace metal ions and particles in liquids , or catalysis . From this viewpoint , polymer bases for anion exchangers of the present invention are preferably in the form of a fibrous material, net, film, porous membrane or the like because they can be easily handled during disposal and readily incinerated as compared with conventional resins. Moreover, polymers in these forms have a large surface area enough to increase the removal speed of metal ions or trace gaseous components and

I they are light and readily formable. Some woven/nonwoven fabric bases or porous membranes have a filter function or other functions by themselves so that a multifunctional material can be formed by introducing an anion exchange group into a base having such a function because it can remove not only metal ions or gaseous components but also fine particles or the like. Woven/nonwoven materials are preferred as organic polymer materials of the present invention used in the form of a filter because they can be suitably used as bases for radiation-induced graft polymerization and are light and easy to form into a filter. Anion exchangers of the present invention are characterized in that a graft polymer side chain derived from a haloalkyl-substituted styrene is formed on a backbone of an organic polymer base as described above and an anion exchange group is introduced onto the side chain. In the present invention, a preferred means for introducing a graft polymer side chain onto a backbone of an organic polymer base is radiation-induced graft polymerization. Radiation-induced graft polymerization is a method that allows a desired graft polymer side chain to be introduced into an organic polymer base by irradiating the base to produce a radical and reacting it with a graft monomer, and this method is most preferred for the purpose of the present invention because the number or length of graft chains can be relatively freely controlled and polymer side chains can be introduced into existing polymer materials in various shapes.

Radiations that can be used in radiation-induced graft polymerization well suitable for the purpose of the present invention include α-rays, β-rays, γ-rays, electron rays, UV ray, etc., among which γ-rays and electron rays are preferred for use in the present invention. Radiation- induced graft polymerization includes pre-irradiation graft polymerization involving preliminarily irradiating a graft base and then bringing it into contact with a polymerizable monomer (graft monomer) for reaction, and simultaneous irradiation graft polymerization involving simultaneously irradiating a base and a monomer, and either method can be used in the present invention. Radiation-induced graft polymerization includes various manners of contact between a monomer and a base, such as liquid phase graft polymerization performed with a base immersed in a monomer solution, gas phase graft polymerization performed with a base in contact with the vapor of a monomer, or immersion gas phase graft polymerization performed by immersing a base in a monomer solution and then removing it from the monomer solution for reaction in a gas phase, and any method can be used in the present invention. Fibers and woven/nonwoven fabrics consisting of a fiber assembly are the most preferred materials for use as organic polymer bases for preparing anion exchangers of the present invention, and are especially well suitable for use in the immersion gas phase graft polymerization because they tend to retain monomer solutions .

The graft polymer side chain introduced onto the polymer backbone of an organic polymer base in anion exchangers of the present invention is derived from a haloalkyl-substituted styrene. The polymer side chain is introduced by graft-polymerizing a haloalkyl-substituted styrene onto a backbone of an organic polymer base. An example of haloalkyl-substituted styrenes preferred for use in the present invention is an n-haloalkyl-substituted styrene represented by the formula:

Especially preferred are chloromethylstyrene represented by the formula:

and bromoethylstyrene represented by the formula:

Among them, chloromethylstyrene is especially preferred because it can increase the polyamination degree and it has high chemical durability. Most preferred for the purpose of the present invention is p- chloromethylstyrene having a vinyl group and a chloromethyl group at the para-position because it can be used to form an anion exchanger with excellent ion removal performance.

The graft polymer side chain introduced into an organic polymer base may also be a graft copolymer side chain of a haloalkyl-substituted styrene with another polymerizable monomer. For example, chloromethylstyrene and a hydrophilic polymerizable monomer such as acrylamide can be graft-σopolymerized onto an organic polymer base to confer an additional function on the base or increase the polyamination degree.

In anion exchangers of the present invention, a functional group derived from a polyamine compound having one tertiary amino group and one or more primary, secondary or tertiary amino groups and/or quaternary ammonium groups has been introduced onto the graft polymer side chain by reacting such a polyamine compound with the organic polymer base having the graft polymer side chain introduced as described above. Polyamine compounds that can be used in the present invention include straight or branched polyamines such as diethylenetriamine and triethylenetriamine; and cyclic or polyσycliσ polyamines such as triethylenediamine represented by the formula:

l,8-diazabicyclo[5,4,0]undec-7-ene (hereinafter referred to as "diazabicyσloundecene" by the common name) represented by the formula:

and hexamethylenetetramine represented by the formula:

Especially, polyamine compounds exemplified by the chemical formulae above have a loan pair called bridgehead so that they are highly reactive. Therefore, they are readily quaternized to greatly contribute to the increase of ion exchange capacity in combination with the very high reactivity of amino groups unused for bonding to the graft polymer side chain.

When a polyamine compound having at least one tertiary amino group and one or more primary, secondary or tertiary amino groups and/or quaternary ammonium groups is reacted to a graft polymer side chain derived from a haloalkylstyrene, the tertiary amino group(s) is (are) quaternized to cause linkage at that site. However, the other amino groups or ammonium groups contained in the polyamine compound remain unreacted. Namely, two or more amino groups or ammonium groups are introduced per one haloalkyl molecule, with the result that two-fold or more anion exchange groups can be introduced as compared with conventional ion exchange resins .

Polyamine compounds could also be introduced into conventional bead-like ion exchange resins, but the polyamination degree or the increase in ion exchange capacity was considerably lower as compared with anion exchangers of the present invention. This is probably because the crosslinked structure of the base of bead-like ion exchange resins hinders polyamine compounds from entering into the resins or causes polyamine compounds themselves to be crosslinked. In anion exchangers of the present invention, however, a polyamine compound has been introduced into graft polymer side chains of an organic polymer base so that the sites at which the polyamine compound has been introduced have higher electric charges and repulse each other to expand the distance between the graft polymer side chains, whereby the polyamine compound can readily enter. This has the effect of not only increasing the polyamination degree but also suppressing crosslinkage, with the result that an ion exchanger having a very high ion exchange capacity can be obtained. In contrast to conventional bead-like ion exchange resins in which polymer backbones are crosslinked to each other to compensate for the deterioration of physical strength of the matrix due to the introduction of ion exchange groups , anion exchangers of the present invention can confer a high anion exchange capacity on the organic polymer base while maintaining the physical strength of the polymer backbone by providing side chains in the form of polymer chains containing anion exchange groups on the polymer backbone of the base. In anion exchangers of the present invention, the backbone plays the role of maintaining the physical strength or keeping the shape.

ADVANTAGES OF THE INVENTION

In anion exchangers of the present invention, a high amination degree was attained by introducing a polyamine compound into a graft polymer side chain of an organic polymer base to solve the problem of conventional methods that the strength was inevitably lowered when more amines were to be introduced. The present invention also solves the problem of conventional methods that the amine odor increases with the amination degree. This is probably because the compounds having two or more amine groups in one molecule used in the present invention have a boiling point raising with the number of functional groups to lower the vapor pressure and thus suppress the emission of the amine odor. In addition, anion exchangers of the present invention are readily disposable by incineration or other means and lighter and less expensive as compared with conventional ion exchange resins.

Anion exchangers of the present invention can be used as materials for eliminating metal ions in water or adsorbing trace gaseous components in the air, etc.

The following examples illustrate various embodiments of the present invention without, however, limiting the invention thereto.

EXAMPLES Example I

A hea -fused nonwoven fabric having an areal density of 55 g/m² and a thickness of 0.35 mm made of a polyethylene (sheath) / polypropylene (core) composite fiber of about 17 μm in diameter was used as an organic polymer base. This nonwoven base was irradiated with electron rays at 150 kGy in a nitrogen atmosphere. Chloromethylstyrene (available from Seimi Chemical under trade name CMS-AM) was passed through a packed bed of activated alumina to remove polymerization inhibitors and then deoxidized by nitrogen blowing. The irradiated nonwoven base was immersed in this chloromethylstyrene solution and reacted at 50°C for 6 hours. The nonwoven fabric was removed from the solution and immersed in toluene for 3 hours to remove homopolymers . The grafting degree calculated from weight gain after drying was 161%. This grafted nonwoven fabric was immersed in a 10% aqueous triethylenediamine solution and reacted at 80°C for 3 hours. After reaction, the nonwoven base was washed with water and then regenerated by immersion in a 5% aqueous sodium hydroxide solution for 1 hour. This was thoroughly washed with pure water and dried in a vacuum drier at 50°C for 3 hours.

A strongly basic anion exchange nonwoven fabric having a neutral salt splitting capacity of 1.67 meq/g and a total exchange capacity of 3.43 meq/g was obtained.

Namely, it contained quaternary ammonium groups capable of splitting neutral salts at 1.67 meq/g and unreacted tertiary amino groups at 1.76 meq/g, which corresponds to the difference between the total exchange capacity and the neutral salt splitting capacity. Thus, the amounts of quaternary ammonium groups and tertiary amino groups are approximately equal, showing that triethylenediamine was introduced without being crosslinked. The polyamination degree of graf -polymerized chloromethylstyrene calculated from weight change was as high as 94%.

This nonwoven fabric was regenerated in a sodium hydroxide solution and dried, and then stored in a zippered plastic bag. When the bag was opened after one month, no amine odor was noted.

Comparative example 1

The chloromethylstyrene-grafted nonwoven fabric in Example 1 was quaternized by immersion in a 10% trimethylamine solution at 50°C for 3 hours. Regeneration treatment was performed in the same manner as in Example 1. A strongly basic anion exchange nonwoven fabric having a neutral salt splitting capacity of 2.2 meq/g was obtained. The neutral salt splitting capacity per unit weight was high and the polyamination degree per graft-polymerized chloromethylstyrene calculated from weight change was 96%, which was enough comparable to the value of Example 1. This nonwoven fabric was regenerated in a sodium hydroxide solution and dried, and then stored in a zippered plastic bag. When the bag was opened after one month, a heavy amine odor was noted. This was washed with water and stored in the same manner in a plastic bag, which was then opened with the same amine odor noted. On the basis of the fact that the strongly basic anion exchange nonwoven fabrics of Example 1 and Comparative example 1 have almost the same length and width, the ion exchange capacity per unit area of the strongly basic anion exchange nonwoven fabric of Example 1 was compared with that of Comparative example 1 to show that the neutral salt splitting capacity is almost comparable and the total exchange capacity is approximately twice higher. It was also suggested that the strongly basic anion exchange nonwoven fabric of Example 1 was not only regenerative, free of amine odor and easy to handle but also characterized by low gaseous emission in the air.

Example 2

A sample of the strongly basic anion exchange nonwoven fabric (regenerative) obtained in Example 1 was fitted in a polyvinylchloride column of 5 cm in diameter and subjected to a hydrogen chloride gas removal test in the gas removal performance test apparatus shown in Fig. 1. References in Fig. 1 represent the following elements: 1 : column, 2 : nonwoven fabric sample, 3 : sampling port for measuring inlet concentration, 4: sampling port for measuring outlet concentration, 5: pump, 6: permeator, 7: filter holder. The permeator was controlled to adjust the hydrogen chloride gas concentration at the inlet of the column to 1 ppm, and the column was ventilated at an air flow of 15 L/min. Initially, hydrogen chloride was not detected at the outlet , and the hydrogen chloride gas concentration at the outlet was kept below 0.1 ppm for 34.5 hours of ventilation.

Comparative example 2

The strongly basic anion exchange nonwoven fabric obtained in Comparative example 1 was subjected to a hydrogen chloride gas removal test in the same manner as in Example 2. Initially, hydrogen chloride was not detected at the outlet, and the hydrogen chloride gas concentration at the outlet was kept below 0.1 ppm for 18.1 hours of ventilation.

When Example 2 and Comparative example 2 were compared, the anion exchanger of the present invention had an ionic gas removal performance represented by a service life about twice longer than that of the anion exchanger of the comparative example. In both cases, the initial removal performance was 99% or more.

Example 3 The heat-fusible nonwoven fabric used in Example 1 was irradiated with γ-rays at 100 kGy with cooling on dry ice in a nitrogen atmosphere. Then, chloromethylstyrene was graft-polymerized in the same manner as in Example 1 to give a chloromethylstyrene-grafted nonwoven fabric having a grafting degree of 138%. This grafted nonwoven fabric was immersed in a 20% solution of diazabiσycloundecene in dimethylformamide at 80°C and reacted for 6 hours. The nonwoven fabric was regenerated with sodium hydroxide and then measured for ion exchange capacity. An anion exchange nonwoven fabric simultaneously having strongly basic anion exchange groups and weakly basic anion exchange bases was obtained at a neutral salt splitting capacity of 1.41 meq/g and a total exchange capacity of 2.65 meq/g. Namely, it contained quaternary ammonium groups capable of splitting neutral salts at 1.41 meq/g and unreacted tertiary amino groups at 1.24 meq/g, which corresponds to the difference between the total exchange capacity and the neutral salt splitting capacity. Thus, the amounts of quaternary . ammonium groups and tertiary amino groups are approximately equal, showing that diazabicycloundecene was introduced without being crosslinked.

Example 4 The anion exchange nonwoven fabric obtained in Example 3 was subjected to a hydrogen chloride gas removal test by the same procedure as in Example 2. Initially, hydrogen chloride was not detected at the outlet , and the hydrogen chloride concentration at the outlet was kept below 0.1 ppm for 31 hours of ventilation, showing the effect of using a polyamine compound.

Claims

1. An anion exchanger comprising a graft polymer side chain derived from a styrene compound having a haloalkyl group on the benzene ring on a backbone of an organic polymer base characterized in that a functional group derived from a polyamine compound having one tertiary amino group and one or more primary, secondary or tertiary amino groups and/or quaternary ammonium groups has been introduced onto said graft polymer side chain.

2. The anion "exchanger of Claim 1 wherein said graft polymer side chain has been introduced onto a backbone of the organic polymer base using radiation-induced graft polymerization.

3. The anion exchanger of Claim 1 or 2 wherein said polyamine compound is selected from triethylenediamine, diazabicycloundecene and hexamethylenetetramine .

4. A process for preparing the anion exchanger of any one of Claims 1 to 3 comprising graft-polymer!zing a styrene compound having a haloalkyl group on the benzene ring onto an organic polymer base to form a graft polymer side chain and then introducing a functional group derived from a polyamine compound having one tertiary amino group and one or more primary, secondary or tertiary amino groups and/or quaternary ammonium groups onto said graft polymer side chain by reacting said graft polymer side chain with said polyamine compound.

5. The process of Claim 4 wherein graft polymerization is carried out using radiation-induced graft polymerization.

Fig.1

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