WO1991019675A1 - Method and device for purifying water - Google Patents

Abstract

An absorbent material which is a cloth or fabric at least part of which is cellulosic is provided herein for removing heavy metal ions and negatively-charged materials from water. The material comprises such cloth or fabric which had been pretreated with an alkali. Such alkali-treated cloth is then preferably heated mildly until it was dry. The dried cloth is then washed and a high molecular weight polyethyleneimine is adsorbed therein and then fixed thereon with a cross-linking agent. Examples of such suitable cross-linking agents include bifunctional or multifunctional epoxy cross-linking agents, e.g., glutaraldehyde, epichlorohydrin, 1,4-butandioldiglycidyl ether, 1,2-ethanedioldiglycidyl ether, 1,3-diglycidylglycerol, triglycidylglycerol, and pentaerythritol, tetraglycidyl ether. Such absorbent material is useful for removing heavy metal ions and negatively charged materials from water.

Description

Title of Invention

Method and Device for Purifying Water.

Technical Field to Which the Invention Relates

This invention relates to an adsorbent material for adsorbing heavy metal ions and negatively-charged materials from aqueous solutions; to a process for preparing such an adsorbent material; and to a method for removing heavy metal ions and negatively-charged material from water by contacting the water with such adsorbent material. Relevant Background Art

Pollution of water by heavy metal ions has become a more serious concern because of the toxicity to aquatic lives and, most importantly, to humans who consume the water. Heavy metal ions are generally not metabolized and are not eliminated from the body, and hence they bioaccumulate and eventually interfere with normal physiological functions by combining with reactive groups. Toxic metal ions (e.g. barium, cadmium, chromium, cobalt, copper, lead, mercury, nickel, tin and zinc) are commonly found in effluents from the chemical, metal and mining industries. Iron ions, though nontoxic, support growth of iron bacteria, and iron and manganese ions impart foul taste and colour to water.

Increasing knowledge that even trace contamination of heavy metal ions seriously endangers public health has led to demands for more stringent legislation on the qualities of waste and potable waters.

Precipitation treatment is a widely used method for removing heavy metal ions from water. Most metal ions are precipitated in water as hydroxides. However, since such precipitation depends on the solubility of the metal hydroxide, the concentration of the metal ion remaining in the effluent is, in general, rela tively high. The effectiveness of this process is also affected by the nature and concentration of precipitation chemical and coagulant aids, and the pH. Furthermore, it is not particularly effective or sufficient for the removal of mercury, whose zero discharge is now demanded.

Ion exchange processes are very effective in removing heavy metal ions; metal ion concentrations in the effluent can be reduced to about 0.1 to about 0.01 mg/l. The processes are easily applicable even to the cases where waste water volumes and/or metal ion concentrations frequently fluctuate. Ion exchange resins are usually regenerated for repeated use, and metal ions are removed in a small volume of elution which can be treated by precipitation or other metal recovery processes. However, ion exchange by the resin is relatively-unspecific. Thus, if heavy metals exist in a high concentration solution along with other dissolved common ions (e.g., Na⁺, Ca⁺²), the resin will not selectively-remove the heavy metal ions desired and its exchange capacity will be rapidly reduced.

Heavy metal ion removal by chelating resins is far more effective as the process can achieve a reduction to about 0.01 to about 0.0005 mg/1 of heavy metal ions concentrations in treated water. Selectivety of the resins for the removal of specific ions is very high. However, some of the metal ions specifically-adsorbed on the resin are not readily eluted, which accordingly requires a large volume of elutant; otherwise they are not desorbed at all. Hence the chelating resins are being used for the purification of water of low metal ion concentration, or at a final stage of water purification. These resins, especially chelating resins are thus suitable for high purification of water, but their costs are still high. Many municipal water plants do not perform special treatment for removing heavy metal ions except for the use of the precipitation process, and many people still rely on untreated ground water and surface water which could be contaminated with heavy metals. Many commercialized water purification devices for domestic use are composed of activated charcoal which is effective for the capture of toxic organic chemicals but is not suitable for the removal of heavy metals.

Another serious concern with respect to potable water is pollution by pathogenic bacteria, viruses and parasites. In many parts of the world, water-borne diseases still remain a major menace to public health. According to some estimates, diarrhea, which may be caused by bacterial, viral or parasitic infects, is responsible for six million deaths per year in the world. It is clear that the pollution of water with human wastes is a major potential source of serious diseases. This problem is not limited to the countries which have not yet established systems for the sanitary disposal of wastes. People in developed countries are also threatened by such hazards. Increasing demands on the water resources necessitate re-use of surface waters. Untreated or partiallytreated waste waters containing feces of an infected population are discharged into potential water supplies. Runoff from urban and agricultural areas into surface waters also introduce pathogens into water supplies. Commonly, one municipality takes water for the water supply system from a water source immediately down stream from another municipality which drains its waste water into that water source.

Among the pathogenic organisms, the importance of viruses as agents of disease is well known. Medical treatments, e.g., using antibiotics, have been developed for the cure of diseases caused by bacteria, but no proper therapeutic treatment other than admin istration of vaccines is available against the diseases caused by viruses. Chlorine and other related chemicals are widely-applied for water disinfection, but this process is not always adequate against viruses. Enteroviruses, reoviruses and adenoviruses are very resistant to chlorine. Furthermore, treatment of water with halogen has been known to form trihalomethanes and some carcinogens.

Procedures and devices have been proposed in the patent and other literature to attempt to solve such problems.

Cellulose fiber and its derivatives are used as solid supports for purification and immobilization of biomaterials. However, fiber forms are readilycompressible so that a column packed with these materials cannot be operated with a fast flow rate. In contrast, cloth forms of the fiber are already compressed into such regular, compact and open structure that provide fast flow characters. Various types of ion exchangers and hydrophobic derivatives of cotton cloth have been proposed which can adsorb enzymes in active forms. Among them, polyethyleneimine-coated cloth has also been prepared through soaking cotton cloth in a diluted polyethyleneimine solution. Although this cloth can be used for immobilization of enzymes, its capacities for heavy metal uptakes are too low to use it for water treatment.

Conventional polyethyleneimine is a highly-branched water-soluble cationic polymer, containing about 30% primary, about 40% secondary and about 30% tertiary amine groups. The polyethleneimine molecule, which takes a compact spherical form in water with a high density of primary amine on its surface, is strongly attracted to negatively-charged colloids and solid surfaces, and hence one of the major technical applications of polyethlyeneimine is as a flocculant for waste water treatment. Since high molecular polyethyleneimine is safe and has been approved by the U.S. Environmental Protection Agency, it is also used for clarification of municipal drinking water. Furthermore, because amine groups numerously-contained in the polyethyleneimine act as electron donors to heavy metals, polyethyleneimine is an effective chelating polymer, as well as a weak anion exchanger. Thus, insolubilized polyethyleneimine in water should function as an adsorbent for materials containing negative charges (proteins, bacteria, viruses, humidic acids and colloids, e.g., clay), and heavy metals.

Water-insolubilization of polyethleneimine to prepare anion exchange and/or chelating resins has been proposed heretofore using the method of crosslinking with various bifunctional reagents, e.g., epichlorohydrin, allyl chloride, ethylene dibromide, glutaraldehyde, toluene diisocyanate, etc. However, these gels are, in general, mechanically-weak for a practical column process. On the other hand, mechanicallystrong anion exchange and/or chelating resins containing polyamine groups have been developed and commercialized. One of them is, for example, a styrene-divinylbenzene copolymer modified with low molecular polyethylene-polyamine after chloromethylation. Their preparations are complicated and thus costly.

Background Documents

Canadian Patent Number 1,085,388, issued September 9, 1980 to E.J. Haase, et al, related to a process for purifying industrial effluents by bringing such effluents into contact with certain specifically-defined, cationically-modified cellulose materials.

Canadian Patent Number 1,169,735, issued June 26, 1984 to S.E. Jorgensen, provided a process for the production of an anion exchanger e.g. a particular cellulose or a cellulose derivative, which was par ticularly suitable for the treatment of waste water. Canadian Patent Number 1,211,338, issued September 16, 1986 to I.W. Devoe, et al, provided a method of removing one or more defined metals from solution by contacting the solution with particularly-defined insoluble composition.

United States Patent Number 3,979,285, patented September 7, 1976 to H. Wegmuller, et al; United States Patent Number 4,025,428, patented May 24, 1977 to H. Wegmuller, et al; United States Patent Number 4,097,376, patented June 27, 1978 by H. Wegmuller, et al; and United States Patent Number 4,178,438, patented December 11, 1979 to J. Haase, et al; each provided a process for the purification of industrial effluents, by contacting the effluents with a specifically-defined, cationically-modified, cellulose-containing absorbent material.

United States Patent Number 4,577,013, patented March 18, 1986 by J. Merz, et al, provided a specifically-defined ionically-modified cellulose material for separating mixtures of ionically-charged components by chromatography.

Assessment of the Background Art

The background art does not provide an adsorbent which has high capability for chelating heavy metals and for adsorbing negatively-charged materials from water; does not provide a process for preparing an adsorbent which has high capability for chelating heavy metals and for adsorbing negatively-charged materials from water; does not provide a method for removing heavy metals and negatively-charged ions from water; does not provide technologies for improving the qualities of waste and rotable water; does not provide inexpensive ion exchange or chelating materials; does not provide for high capacity for heavy metal uptake in water-treatment procedures; and does not provide an inexpensive procedure for preparing such materials.

Consequently, inexpensive (and thus disposable) chelating support systems are desirable for a heavy metal removal device for domestic use, because regeneration procedure cannot be readily practised at home. In addition, the physical removal of bacteria and viruses by adsorption to solid surfaces is considered to be a desirable alternative method. Inexpensive and safely disposable adsorbents for pathogenic agents in water should be useful in the places where adequate disinfection systems are not available, and should be desirable for domestic use. Disclosure of Invention As Claimed

The invention, as claimed, is intended to provide a solution to such problems. It provides an adsorbent which has been pretreated with an alkali, then washed with water, and then having high molecular weight polyethyleneimine adsorbed and fixed thereon with a cross-linking agent.

The invention also provides a process for preparing such adsorbed material which includes the following steps, in sequence: a) pretreating the cloth or fabric substrate with an alkali; b) washing the pretreated substrate with water; c) adsorbing high molecular weight polyethyleneimine therein; and d) cross-linking the polyethyleneimine on the substrate with a crosslinking agent.

It also provides a method for removing heavy metals by the use of the above-described adsorbent material.

Advantageous Effects of the Invention

The present invention provides a new method for fixing a large amount of high molecular weight polyethyleneimine on non-woven cloth. The polyethyleneimine-fixed cloth is, as a result, stable in pro cedures involving repeated regeneration and storage in water, and it exhibits high adsorption capacities of heavy metal ions, proteins and bacterial and viruses.

By the present invention, simple and economic processes for the preparation of polyethyleneiminecoated cloths have been provided, the cloths having higher capabilities for chelating heavy metal ions as well as for adsorbing negatively-charged material, e.g., proteins and bacteria.

Description of Further Embodiments of the Invention

In the adsorbent material of this invention, the cloth or fabric upon which such high molecular weight polyethyleneimine has been adsorbed is preferably heated mildly until it is dry prior to having the polyethyleneimine adsorbed and fixed thereon with the cross-linking agent.

In another feature of this invention, the cloth or fabric preferably comprises a woven or a non-woven rayon fabric, or a woven or a non-woven rayon/polyester fabric or a woven or a non-woven wood pulp/polyester fabric, or a woven or non-woven cotton/ polyester cloth or cellulosic paper. The cloth or fabric is either in its open-apertured style or in its highly-absorbent, open-apertured style.

The cross-linking agent preferably comprises glutaraldehyde, epichlorohydrin, 1,4-butandioldiglycidyl ether, 1,2-ethanedioldiglycidyl ether, 1,3- diglycidylglycerol, triglycidylglycerol, pentaerythritol, tetraglycidyl ether, etc.

The process of this invention preferably includes the step of heating the cloth or fabric which has been adsorbed at a low temperature, mildly to a low temperature until it is dry prior to having the polyethyleneimine adsorbed and fixed thereon with the cross-linking agent. One feature of the process of this invention of treating the substrate preferably comprises: pretreating a cloth or fabric substrate at least part of which is cellulosic with an alkali; washing the pretreated substrate with water; adsorbing high molecular weight polyethyleneimine therein; and cross-linking the polyethyleneimine on the substrate with a cross- linking agent.

In another feature of the process of this invention, the alkaline solutions that penetrate and swell the cellulose fiber include inorganic bases, e.g., LiOH, NaOH and KOH, and organic bases, e.g., alkyl-ammonium bases. However, NaOH solutions of about 10% by weight to about 40% by weight NaOH known as "mercerization" solutions are generally used, for alkali-cellulose preparation. Accordingly, while the above-noted alkalis are applicable for the present invention, NaOH is preferable.

Wide ranges of NaOH concentrations (e.g., about 5% to about 40% by weight) can be applied according to circumstances. For certain preferred substrates, soaking in about 6% to about 12% by weight aqueous NaOH solution at room temperature for about 10 minutes, is recommendable. Thus, the alkaline solution preferably comprises an aqueous solution of NaOH, e.g., having a concentration of about 10% ± 5% by weight.

The water washing is preferably carried out until the substrate has a pH of about 7.

The amount of polyethyleneimine preferably adsorbed in the substrate is up to the maximum stoichiometric permissible amount. The process of absorbing the high molecular weight polyethyleneimine is carried out until a maximum of .the stoichiometric amount of the polyyethyleneimine is adsorbed thereon. Preferably, the polyethyleneimine has a molecular weight of about 60,000 + 20,000. The temperature of the heating preferably ranges from about 40°C to about 60°C, and the preferable heating time is longer than about 8 hours.

The cross-linking agent within the ambit of those previously-described preferably comprises glutaraldehyde, epichlorohydrin or 1,4-butanedioldiglycidyl ether.

In the method of this invention, the contacting of the water with the adsorbent material is preferably achieved by passing the water through a column packed with the adsorbent material.

Although polyethyleneimine has been shown to bind strongly to cellulose, the mechanism of such stable binding has not yet been elucidated. It has been speculated that the carboxyl group in cellulose may contribute to the ionic interaction between these macromolecules. However, it is believed that the introduction of carboxyl groups by carboxymethylation of the cellulose hydroxyl groups does not greatly increase stable binding of polyethyleneimine to cellulose. It is not desired to be bound by any specific theoretical mechanism for such binding. However, there may be other possible mechanisms, e.g., hydrogen bonding interaction, which may be effective for interaction between cellulose and polyethyleneimine. Since cellulose is rich in hydroxyl groups and polyethyleneimine is rich in amino groups, it is possible that hydrogen bonding may play a part in the interaction between them. The crystalline structure of cellulose is stabilized by extensive interchain hydrogen bondings which can only partly be disrupted by strong alkali. In contrast, rayon is regenerated cellulose whose hydrogen bondings could be more readily-disrupted by the alkali than native cellulose (e.g., cotton). Alkali treatment should then increase the capacity of rayon to form hydrogen bonding with polyethyleneimine. It is also believed that the hydrogen bonding between cellulose and polyethleneimine would increase as activity of water which hydrates the macromolecules is reduced by drying.

It has been found that alkali pre-treatment followed by washing with water allowed cloths, at least part of which were cellulosic, e.g., rayon cloth, to adsorb a large amount of high molecular weight polyethyleneimine from its concentrated solution. Following this, the cloth was dried to strengthen the holding of the polyethyleneimine thereto.

Although such cloth exhibited the significant capabilities of binding proteins and chelating heavy metal ions, the unfixed polyethyleneimine which is on the cloth is gradually released in water, especially in the aqueous solutions of chelatable metals. In order to fix the polyethyleneimine stably on the cloth, the process of this invention includes crosslinking adsorbed polyethyleneimine molecules with e.g., glutaraldehyde, epichlorohydrin or 1,4-butandioldiglycidyl ether. These regents are inexpensive and relatively safe and can be easily handled.

The substrate at least part of which is cellulosic, may be a non-woven fabric, i.e., a non-woven rayon fabric, a non-woven rayon/polyester fabric, or a non-woven wood pulp/polyester blend. Such fabric may be either in its open-apertured flat-type form, or in its highly-absorbent, open-apertured form.

It has been found that such fabrics, e.g., rayon/polyester non-woven fabric blends produce suitable substrates for the adsorbent material of the present invention. Such fabrics are commercially-available, under the Trade Mark SONTARA. SONTARA is the registered Trade Mark of DuPont for its spin-laced fabrics. SONTARA is a bulky, soft, strong, conformable, lightweight sheet made of hydraulically-interlaced fibers with no chemical orthermal bonding. These substrates are free of chemical additives (e.g., resins), binder and finish (which would interfere with modification); are soft, pliable and low-linting; and have non-ravelling edges and good absorbency.

Some typical properties of SONTARA are shown in the table shown on the following page:

Description of At Least One Way of Carrying Out The

Invention

Before describing in detail at least one way of carrying out the invention, a brief description of the drawings is given, in which:

Figure 1 is a graph showing the effect of repeated use on Cu uptake by polyethyleneimine-coated SONTARA

8423 (uncross-linked), with Cu⁺² uptake (in mg/g cloth) as ordinate and number of adsorption cycles as abscissa;

Figure 2 is a graph showing repeated Cu⁺² adsorption by glutaraldehyde-cross-linked polyethyleneimineSONTARA 8423 with Cu⁺² uptake (in mg/g cloth) as ordinate and number of adsorption cycles as abscissa;

Figure 3 is a graph showing the effect of time of contact with Cu⁺² solution on Cu⁺² uptake by glutaraldehyde-cross-linked polyethyleneimine-SONTARA 8423, with Cu⁺² uptake (in mg/g cloth) as ordinate time and time (in hours) as abscissa;

Figure 4 is a graph of the Cu⁺² uptake by epichlorohydrin-cross-linked polyethyleneimine-SONTARA 8423 with Cu⁺² uptake (in mg/g cloth) as ordinate and number of adsorption cycles as abscissa;

Figure 5 is a graph of the Cu⁺² uptake by polyethyleneimine-SONTARA 8423 cross-linked with 1,4-butandioldiglycidyl ether with Cu⁺² uptake (in mg/g cloth) as ordinate and number of adsorption cycles as abscissa;

Figure 6 is a graph of the effect of higher 1,4-butandioldiglycidyl ether concentration and higher temperature on Cu⁺² uptake by polyethyleneimine-SONTARA

8423 with Cu⁺² uptake (in mg/g cloth) as ordinate and number of adsorption cycles as abscissa;

Figure 7 is a graph of the kinetics of Cu⁺² uptakes by polyethyleneimine-SONTARA 8423 cross-linked with 1,4-butandioldiglycidyl ether with Cu⁺² uptake (in mg/g cloth) as ordinate and time (in hours) as abscissa;

Figure 8 is a graph showing the effect of NaOH concentration used in the pre-treatment of rayon cloth on the capacity of polyethyleneimine-treated cloth to adsorb bovine serum albumin with bovine serum albumin adsorption (in mg bovine serum albumin/g cloth) as ordinate and NaOH concentration (in % by weight) as abscissa;

Figure 9 is a graph showing the bovine serum albumin adsorption to polyethyleneimine-treated with bovine serum albumin adsorption (in mg bovine serum albumin/g cloth) as ordinate and heating period (in hours) as abscissa;

Figure 10 is a graph showing the bovine serum albumin adsorption to polyethyleneimine-coated SONTARA 8423 (uncross-linked), with bovine serum albumin adsorption (in mg bovine serum albumin/g cloth) as ordinate and number of cycles as abscissa;

Figure 11 is a graph of the bovine serum albumin adsorption to polyethyleneimine-SONTARA 8423 cross- linked in various concentrations of glutaraldehyde, with bovine serum albumin adsorption (in mg bovine serum albumin/g cloth) as ordinate and concentration of glutaraldehyde (in % by weight) as abscissa; and

Figure 12 is a graph of the removal of E. coli from water by a fixed bed of polyethyleneimine-SONTARA 8423 cross-linked with 1% 1,4-butandioldiglycidyl ether at room temperature, with optical density of effluent as ordinate and quantity of effluent (in ml) as abscissa.

The following are examples of various embodiments of this invention.

1. Preparation of Polyethyleneimine-Coated Rayon

Cloth

1-1. Adsorption of High Molecular Polyethylenei mine onto Rayon/Polyester Cloth

A 2 × 2 cm square of non-woven rayon-polyester blended cloth (SONTARA 8407 rayon/polyester; 70/30, DuPont, 50 g/m², apertured type or SONTARA 8423, 80 g/m², flat-type), was soaked in 10% by weight NaOH at room temperature for 10 minutes, thoroughly washed with water, filtered on a glass-sintered filter and blotted with paper. Polyethyleneimine (CORCAT P-600_TM, average molecular weight of approximately 60,000, Virginia Chemicals) was diluted to 11% by weight with water. 0.2 ml of this solution was added to the cloth segment placed in a glass vial which was then heated at 50°C overnight on a block heater. The dried segment was washed with water extensively and filtered. If not further modified, it was rinsed with 0.5 N HCl and 0.5 N NaOH for 30 minutes each, and washed with water thoroughly on a glass filter.

1-2 Cross-linking of Polyethyleneimine on Cloth

One segment (2×2 cm) of cloth treated with polyethyleneimine was soaked in 2 ml of aqueous 0.05%-0.4% by weight glutaraldehyde solution at room temperature for 2 hours with occasional shaking, and then washed with water thoroughly.

For cross-linking with epoxy reagents, a polyethyleneimine-adsorbed cloth segment was placed in methanol for 10 minutes, filtered and soaked in 2 ml of 0.5%-3% by weight epichlorohydrin or 1,4-butandioldiglycidyl ether in methanol at room temperature or 50°C for 3 hours with occassional shaking. The segment was washed with methanol and water extensively.

All segments prepared above were soaked in 0.5 N HCl and 0.5 N NaOH for at least 30 minutes each, and then washed with water.

2-1 Metal Ion Uptakes by Polyethyleneimine-Cloth On piece of 2×2 cm segment was shaken in 5 or 10 ml of 0.005-0.015 M CuSO₄ solutions at room temperature.

The solutions were used without pH adjustment unless otherwise stated. After a predetermined length of time, in hours, the supernatant was analyzed for unabsorbed metal ion. Cu⁺² adsorption was calculated by subtracting the unabsorbed amount from the original amount.

When the cloth segment was repeatedly-used to adsorb

Cu⁺², it was regenerated with 0.5 N HCl and 0.5 N NaOH and washed with water before readsorption of Cu⁺².

For uptakes of other metal ions, one segment of sample cloth was shaken in 10 ml of 0.01 M metal ion in 0.1 M acetate buffer (pH 5.5) at room temperature. The concentration of metal ion was determined by the method of chelatometric titration using 0.01 M ethylenediamine tetraacetic acid and pyridylzonaphthol as a metal indicator for Cu⁺², Ni⁺², Co⁺², Pb⁺², Zn⁺², and Cd⁺²; 0.05 M Mg-ethylenediamine tetraacetic acid and Erio Black T for Hg⁺², and Ca⁺²; and 0.01 M ethylenediamine tetraacetic acid and Erio Black T for Mn⁺² and Mg⁺².

Figure 1 is a graph of the effect of repeated use on Cu⁺² uptake by polyethyleneimine-coated SONTARA 8423 (uncross-linked). In every cycle, a 2×2 cm square segment of the polyethyleneimine-cloth was washed with 0.5 N HCl, 0.5 N NaOH and water, and contacted with 5 ml of 0.005 or 0.015 M CuSO₄ at room temperature overnight to adsorb Cu ion. Figure 2 shows that Cu⁺² adsorption to the polyethyleneimine-cloth graduallydecreased with repeated adsorption cycles. Since Cu⁺² adsorbed on the cloth was thoroughly-desorbed with 0.5 N HCl, which was judged from the disappearance of the blue colour from the chelating complex, the possibility of Cu⁺² accumulation on the cloth must be excluded. Consequently, the observed decrease of Cu⁺² uptake indicated gradual release of polyethyleneimine from the cloth into water.

2-2 Stability of Cross-Linked Polyethyleneimine To examine further the stability of cross-linked polyethyleneimine, the cloth was repeatedly used for Cu⁺² adsorption. The adsorption rate of Cu⁺² was also determined, since this will determine the flow rate at which the cloth can be used in a column operation.

The polyethyleneimine-coated rayon cloths were treated with 0.05%-0.4% by weight glutaraldehyde at room temperature for 2 hours, and repeatedly used for adsorption of Cu⁺². After each use, they were regenerated with 0.5 N HCl and 0.5 N NaOH, heated in water at 90°C for 3 hours and then contacted with 5 ml of 0.005 M CuSO₄ overnight.

Figure 2 is a graph which shows that the cloths treated with higher than 0.3% by weight glutaraldehyde exhibited stable Cu⁺² adsorption for 6 cycles of repeated use and regeneration.

Figure 3 is a graph of the effect of time of contact with Cu⁺² solution on Cu⁺² uptake by glutaraldehydecross-linked polyethyleneimine-SONTARA 8423. One 2×2 cm square segment of polyethyleneimine-cloth crosslinked with 0.4% by weight glutaraldehyde was contacted with 10 ml of 0.002 or 0.01 M CuSO₄ for various periods of time at room temperature. Figure 3 shows that the Cu⁺² uptakes reached a maximum within 2 - 3 hours at 0.01M CuSO₄, and 3 - 5 hours at 0.002M CuSO₄. On the other hand, it is known that resin of polyethyleneimine cross-linked with toluene diisocyanate requires more than 24 hours equilibration periods for metal ion adsorption. It is also known that macroreticular chelating resins containing amine groups also take more than 24 hours to reach to maximum Cu⁺² uptake in 0.01 M Cu solution. Thus, Cu⁺² adsorption to polyethyleneimine-cloth observed is a very rapid process. The polyethyleneimine fixed on the cloth may be exposed to a solution, and metal ions may be easily able to access to chelating groups despite the net work formation of polyethyleneimine through cross- linking.

Cu⁺² adsoprtion capacity of polyethyleneimine-rayon cloth cross-linked with 0.4% glutaraldeyde was 61 mg per g of cloth (0.96 mmol/g) in 0.01 M CuSO₄.

On the other hand, it is known that Cu⁺² uptakes by the resin of polyethyleneimine cross-linked with toluene diisocyanate is 90 mg Cu⁺² per g of polymer in 0.01 M cupric acetate. It is also known that the poloystyrene resins containing polyamino groups adsorb 1.5 mmol of Cu⁺² per 9 of resin (95 mg/g) in 0.01 M Cu solution at pH 6.

Figure 4 is a graph of the Cu⁺² uptake by epichlorohydrin cross-linked polyethyleneimine-SONTARA 8423. A 2×2 cm square segment of polyethyleneimine-cloth cross-linked with 0.5, 1 and 3% by weight epichlorohydrin at room temperature for 3 hours was repeatedlyregenerated with 0.5 N HCl and 0.5 N NaOH, heated with water at 90°C for 3 - 4 hours, and contacted with 5 ml of 0.005 MCuSO₄ at room temperature overnight. Figure 4 shows that Cu⁺² uptakes by polyethyleneimine-cloths with 0.5% or 1% by weight epichlorohydrine gradually decrease after 3 or 4 adsorption trials, respectively. Accordingly, the polyethyleneimine-cloth was cross- linked with 3% by weight epichlorohydrine, and the resulting cloth consequently exhibited steady Cu⁺² uptakes for at least 9 adsorption cycles.

Figure 5 is a graph of the Cu⁺² uptake by polyethyleneimine-SONTARA 8423 cross-linked with 1,4-butandioldiglycidyl ether. A 2×2 cm square polyethyleneimine-cloth segment cross-linked at room temperature in 0.5% or 1% 1,4-butandioldiglycidyl ether was repeatedly regenerated with 0.5 N HCl and 0.5 N NaOH, and soaked in 5 ml of 0.005 or 0.01 CuSO₄ at room temperature overnight for repeated Cu⁺² uptakes. Figure 5 shows the Cu uptakes by 1,4-butandioldiglycidyl ether-treated polyethyleneimine-cloths. Unlike epichlorohydrine-treated cloths, polyethyleneimine-cloth cross-linked with 0.5% and 1.0% 1,4-butandioldiglycidyl ether at room temperature constantly adsorbed Cu⁺² in 0.005 M Cu⁺² solution at least for 6 cycles. However, Cu⁺² uptake in 0.01 M Cu⁺² solution exhibited slight and gradual decrease during repeated uses. Therefore, the effect of cross-linking at higher concentrations of 1,4-butandioldiglycidyl ether and higher temperature was studied. The polyethyleneimine-rayon cloth segment was cross-linked with 3% 1,4-butandioldiglycidyl ether at room temperature or with 1% by weight 1,4-butandioldiglycidyl ether at 50°C, and repeatedly measured Cu⁺² adsorption capacity in 10 ml of 0.01 M CuSO₄.

Figure 6 is a graph of the effect of higher 1,4-butandioldiglycidyl ether concentrations and higher temperatures on Cu⁺² uptake by polyethyleneimineSONTARA 8423. A 2×2 cm square segment of polyethyleneimine cloth, cross-linked in 1% 1,4-butandioldiglycidyl ether at room temperature or 50°C, or in 3% by weight 1,4-butantioldiglycidyl ether at room temperature, was repeatedly-regenerated with 0.5 N HCl and 0.5 N NaOH and contacted with 10 ml of 0.01M CuSO₄ for 3 hours for repeated Cu⁺² uptakes. Figure 6 shows that while the cloth cross-linked with 1% by weight 1,4-butandioldiglycidyl ether at room temperature exhibited gradual decrease in its Cu⁺² adsorption, Cu⁺² uptakes by the polyethyleneimine-cloth cross-linked with 1% by weight 1,4-butandioldiglycidyl ether at 50°C or 3% 1,4-butandioldiglycidyl ether at room temperature were unchanged during 6 adsorption cycles, indicating that polyethyleneimine was more extensively cross-linked under these conditions.

Cu⁺² adsorption capacities of these cloths were 80 mg Cu⁺² per g of cloth (1.3 mmol/g), which is comparable to other chelating resins mentioned.

The rates of Cu⁺² adsorption to the 1,4-butandioldiglycidyl ether-cross-linked cloths were also examined.

Figure 7 is a graph of the kinetics of Cu⁺² uptakes by polyethyleneimine-SONTARA 8423 cross-linked with 1,4-butandioldiglycidyl ether. On 2×2 cm square segment of polyethyleimine-cloth, cross-linked in 1% by weight 1,4-butandioldiglycidyl ether at room temperature or 50°C, or in 3% by weight 1,4-butandioldiglycidyl ether at room temperature was soaked in 10 ml of 0.1M CuSO₄ for a various period and Cu⁺² uptake was measured. Figure 7 shows that Cu⁺² uptakes by these cloths reached maximum (80 mg Cu⁺²/g cloth) within 2 hours and hence their adsorption rates appeared to be much faster than those of chelating resins previously-described. It is known that after 3 hour-contact with 0.01 M Cu⁺² solution at pH 6, macroreticular polystyrene resin containing polyamino groups adsorbed 58 mg Cu⁺² per g of resin. On the other hand, the 1,4-butandioldiglycidyl ether-cross- linked polyethyleneimine-cloths of this invention adsorbed 68 - 76 mg Cu⁺² per g of cloth only in 1 hour contact time. This characteristic of polyethyleneimine-rayon cloths likely results from the open structure and hydrophilicity of the cloth on which the polyethyleneimine was immobilized. As mentioned above, unlike polystyrene resins, SONTARA 8423 and SONTARA 8407 rayon cloths, exhibit affinity to water. Such rapid adsorption of metal ions would be desirable for column operation, because water treatment needs to be performed with a fast flow rate. The high adsorption capacities and rapid adsorption rates would permit treatment of large volume of water per unit volume of column per unit of time.

The advantage of this rapid adsorption of Cu⁺² was examined in column studies. When a Cu solution of 22 mg/l was passed through a 1 mm stack of the fixed bed, which was formed of 10 circles (i.d. 1.6 cm) of polyethyleneimine-cloth cross-linked in 1% by weight 1,4-butandioldiglycidyl ether at room temperature, no Cu⁺² was detected for 215 or 205 bed volumes of effluent at the space velocity of 66 or 105, respectively. It is known that a column of macroreticular chelating resin is able to treat 200 - 250 bed volumes of Cu⁺² solution of 21 mg/l at space velocities of 30 - 15. Thus, the polyethyleneimine-cloth provides faster flow rate in a column operation. In addition to Cu⁺², polyethyleneimine forms chelates with various heavy metals. Uptakes of various metal ions by the polyethyleneimine-cloth treated with 1,4-butandioldiglycidyl ether were examined in 0.01 M metal solution at pH 5.5 - 6.0.

The results are shown in Table 1.

TABLE 1. Adsorption of metal ions on polyethyleneimine-SONTARA 8423 cross-linked with 1,4-butandioldiglycidyl ether(a).

PH adsorption capacity metal salt before after (mg/g) (m mol/g)

Hg HgCl₂ 5.4 5.6 428 2.13

Cu Cu(CH₃CO₂)₂ 5.5 5.6 74.9 1.18

Ni NiCl₂ 5.5 5.6 47.8 0.81

Co CoCl₂ 5.5 5.7 34.3 0.58

Cd Cd(CH₃CO₂) 5.6 5.8 64.1 0.57

Zn ZnSO₄ 5.5 5.6 37.5 0.57

Pb Pb(CH₃CO₂) 5.5 5.9 46.7 0.23

Mn MnSO₄ 5.6 6.1 1.8 0.03

(a) Polyethyleneimine-cloth was cross-linked in 3% by weight 1,4-butandioldiglycidyl ether at room temperature for 3 hours.

Table 1 shows that the cloth adsorbed various heavy metal ions in the order (on molar base) : Hg⁺²>Cu^+2>Ni+2>Co⁺²>Cd^+2"Zn⁺²>Pb⁺²>Mn⁺². This order is almost similar to those known for the aminated chelating resins and resins of cross-linked polyethyleneimine. Like Cu⁺², these heavy metal ions, except Hg were readily desorbed from cloth with 0.5-1 N HCl. It is known that Hg⁺² adsorbed on aminated chelating resin may be eluted with 6 N HNO₃ or 10 N HCl.

Potable water commonly contains Ca⁺² and Mg⁺². These ions are safe to health but lower the ion exchange capacities of cation-exchangers used in the treatment of water. In contrast, the polyethyleneimine-cloth adsorbed neither Ca⁺² nor Mg⁺², and thus its heavy metal ions adsorption capacities are little effected by the presence of these ions in water.

It has been found that polyethyleneimine was fixed on the alkali pre-treated cloth with a certain stability but gradually released in aqueous Cu⁺² solution. Cross-linking between amino groups of polyethyleneimine molecules would stabilize binding of polyethyleneimine to the cloth.

Although various cross-linking reagents could be used, two types of the cross-linker were selected; glutaraldehyde and epoxy reagents (epichlorohydrin and 1,4-butandioldiglycidyl ether), because they are inexpensive, relatively low in toxicity and easy to handle to carry out cross-linking reactions. Furthermore, glutaraldehyde is water-soluble so that the reaction can be carried out in water, and epoxy reagents form very stable bondings with amino groups.

The following polyethyleneimine (known by the Trade

Mark CORCAT) was applied to the rayon cloth:

av.mol.wt. of

Polyethyleneimine

CORCAT P-12 1200

CORCAT P-18 1800

CORCAT P-150 15000

CORCAT P-600 60000

The cloth treated with CORCAT P-12 and CORCAT P-18 hardly adsorbed Cu⁺² ions. The cloth treated with CORCAT P-150 adsorbed only 10% - 20% of the Cu⁺² ions captured by the cloth treated with CORCAT P-600. Hence, the preferable molecular weight of polyethyleneimine to be used in this invention may be higher than 60,000 ± 20,000. 4. Adsorption of Bovine Serum Albumin and Hemoglobin on Polyethyleneimine-Cloth

One ml of 5% bovine serum albumin or bovine hemoglobin was added to a 2×2 cm square segment of polyethyleneimine-treated cloth of this invention prepared as above-described at room temperature for 1 hour, followed by washing with water on a filter. To desorb ionically-bound proteins, the cloth segment was placed in 5 ml of 1 M NaCl solution at room temperature for 1 hour with occasional vortexing, and the extract was assayed for bovine serum albumin or bovine hemoglobin. Since some bovine hemoglobin still remained bound to the cloth after extraction with 1 M NaCl, the segment was further washed with water and soaked in 1% sodium lauryl sulfate at 95°C for 1 hour. The desorbed, non-ionically-bound bovine hemoglobin was also measured by the same method.

When the bovine serum albumin binding trial was repeated, the segment was regenerated with 0.5 N HCl and 0.5 N NaOH and washed with water before readsorption of bovine serum albumin.

The bovine serum albumin adsorption capacity of polyethyleneimine-treated cloth of this invention prepared as above-described was used as a measure of amount of polyethyleneimine binding to the rayon cloth.

Segments of non-woven rayon cloth, SONTARA 8423, were soaked in water or 10% by weight NaOH for 10 minutes, washed with water and treated with 1% by weight or 11% by weight polyethyleneimine solution, and their bovine serum albumin adsorption were measured after washing with 0.5 N HCl, 0.5 N NaOH and water.

The results are shown below in Table 2. TABLE 2. Effects of Alkali and Polyethyleneimine Treatments on Bovine Serum Albumin Adsorption to SONTARA 8423.

Pretreatment Concentration PolyethyBovine (a) of Polyethyleneimine Serum

leneimine (%) TreatAlbumin ment (b) (mg BSA/G cloth) water 1.0 short soaking 12 water 11.0 short soaking 23

10% NaOH 1.0 short soaking 86

10% NaOH 1.0 heating & drying 84

10% NaOH 11.0 heating & drying 261

10% NaOH 11.0 heating & drying 538

(a) For pre-treatment of cloth, a 2×2 cm square cloth segment was soaked in water or 10% NaOH at room temperature for 10 minutes and washed with water.

(b) After pre-treatment, the segment was soaked in 3 ml of polyethyleneimine solution at room temperature for about 1 hour (short soaking); or 0.2 ml of polyethyleneimine solution was added and heated at 50°C for overnight until dryness (heating & drying); or 0.5 ml of polyethyleneimine solution was added and heated at 50°C overnight in a capped vial (heating without dryness). All polyethyleneimine-treated segments were rinsed with 0.5 N HCl and 0.5 N NaOH and washed with water before bovine serum albumin adsorption procedure.

Table 2 shows that, without alkali pre-treatment, the cloth segments exhibited poor adsorption of bovine serum albumin whether they were applied with 1% by weight or 11% by weight polyethyleneimine. However, when segments were soaked in 10% NaOH and then treated with 1% by weight, polyethyleneimine, their bovine serum albumin adsorption greatly-improved but, at this concentration of polyethyleneimine, seemed not to be effected by heating and drying during polyethylene imine treatment. When alkali-pretreated cloth was treated with 11% by weight polyethyleneimine solution and heated in a capped vial at 50°C for overnight (but not dried), further increase in bovine serum albumin adsorption was observed. When the cloth was heated in 11% by weight polyethyleneimine at 50°C until dryness, bovine serum albumin adsorption was even greater.

These results indicate that alkali pre-treatment, higher polyethyleneimine concentration, and heating and drying greatly increased polyethyleneimine binding to the rayon cloth, which binding was stable against rinsing with diluted acid and alkali.

Since alkali pre-treatment was found to be an important factor for polyethyleneimine binding to SONTARA 8423, the effect of NaOH concentration was examined to determine optimal NaOH concentration. SONTARA 8407 was used to confirm the alkali effect in this rayon. The cloth segments (2×2 cm square) were pre-treated with various concentrations of NaOH for 10 minutes at room temperature and washed with water. Removal of NaOH by washing was found to be necessary for polyethyleneimone binding. The segments were then treated with 11% by weight polyethyleneimine (0.2 ml/ segment) and dried at 50°C for overnight. After washing with 0.5 N HCl, 0.5 N NaOH and water, the cloth was assayed for bovine serum albumin adsorption as described hereinbefore.

Figure 8 is a graph which shows that bovine serum albumin adsorption to the polyethyleneimine-cloths greatly-increased when the cloth was pre-treated with higher than 6% by weight NaOH solution, and that the optimum concentration was 10% for 10 minute soaking at room temperature. Higher than 10% by weight NaOH and/or longer treatment time destabilized the cloth structure, and also reduced bovine serum albumin adsorption capability. To determine the optimum amount of polyethyleneimine added to the cloth, the alkali-treated rayon cloths were treated with various concentrations of polyethyleneimine solutions and the bovine serum albumin adsorption capacities of the resulting polyethyleneimine cloths were measured. 0.2 ml of polyethyleneimine solution added to a 2×2 cm square of cloth segment was just enough to saturate both types of rayon cloths, SONTARA 8423 and SONTARA 8407.

The results are shown in Table 3.

TABLE 3. Bovine Serum Albumin Adsorption Capacities of SONTARA 8407 and 8423 Treated with Various Amounts of Polyethyleneimine (a).

Polyethyleneimine Solutions Added to 2 cm Square Cloth

Segment

cloth volume concentration, %

ml 3.3 5.5 6.6 11 16.5 33 Bovine Serum Albumin Adsorption, mg/g of cloth

SONTARA

8407 0.2 487 512 824 776 712

8423 0.1 335 461 522

0.2 455 554 513

(a) The cloth segments were pre-treated with 10% NaOH, polyethyleneimine solution was added and heated in an open vial at 50°C to dryness overnight. The resulting polyethyleneimine-cloth segment was rinsed with 0.5 N HCl and 0.5 N NaOH, washed with water and assayed for bovine serum albumin adsorption.

Table 3 shows that SONTARA 8407 treated with 0.2 ml Of 11% by weight polyethyleneimine exhibited the highest bovine serum albumin adsorption capacity. Similar results were also observed for SONTARA 8423 as a 2x2 cm square segment which was added 0.2 ml of 11% by weight polyethyleneimine and then dried showed largest adsorption of bovine serum albumin among the cloth segments examined. Administering higher than about 11% by weight polyethyleneimine or more than 0.2 ml of polyethyleneimine or more than 0.2 ml of polyethylene solution to the cloth did not improve bovine serum albumin adsorption capacity. It gave the cloth a rather sticky surface and it was difficult to remove excess polyethyleneimine from cloth.

Thus, it has been found possible to apply about 1% to about 33% polyethyleneimine solution just to saturate the cloth; 11+5% is preferable for SONTARA 8407 and SONTARA 8423, which corresponds to 0.6+0.3 g of polyethyleneimine per g of cloth, applied to these cloths.

To examine the effect of heating time and dryness, after NaOH pre-treatment, to 2×2 cm square segments of SONTARA 8423 were added 0.2 ml of 11% by weight polyethyleneimine, heated at 50°C for various periods and then their bovine serum albumin adsorption capacities were determined.

Figure 9 is a graph which shows that the protein adsorption increased linearly with the heating time until the cloth was completely dried after 8 hours.

To confirm this observation in SONTARA 8407, the alkali-treated segments of this cloth were similarly-treated with added polyethyleneimine solution, and were heated in various ways.

The results are shown in Table 4.

TABLE 4. Effect of Heating Condition for Polyethyleneimine Treatment on the Bovine Serum Albumin Adsorption Capacity of Resulting PolyethyleneimineSONTARA 8407 (a). heating heating state of cloth bovine serum albumin

temperature time after heating adsorption

(°C) (hr) (mg/g)

50 2 wet (b) 136

50 4 wet (b) 435

50 16 wet (c) 649

50 16 dry (b) 824

80 16 dry (b) 776

100 2 dry (b) 656

(a) The 2×2 cm square segments were soaked in 10% NaOH for 10 minutes, washed with water, 0.2 ml of 11% by weight polyethyleneimine was added and then heated under various conditions. The resulting polyethyleneimine-cloth segment was rinsed with 0.5 N HCl and 0.5 N NaOH, washed with water and assayed for bovine serum albumin adsorption.

(b) The segment was heated in an open vial.

(c) The segment was heated in a capped vial.

Table 4 shows that polyethyleimine-SONTARA 8407 also adsorbed more bovine serum albumin with longer heating at about 50°C for polyethyleneimine treatment. However, the cloth heated overnight in a capped vial showed poorer bovine serum albumin adsorption capability than the cloth heated in an open vial (thus dried), and hence complete drying was necessary to obtain greater bovine serum albumin adsorption by the polyethyleneimine-cloth. However, if drying temperature was too high, e.g., about 80°C to about 100°C, so that the polyethyleneimine-cloth was dried up too fast, less bovine serum albumin adsorption was observed.

Accordingly, heating at mild temperatures, e.g., 50°C, until dryness for more than 8 hours, was appropriate for preparation of the polyethyleneimine-coated non-woven rayon cloth exhibiting a sufficient protein adsorption. The long mild heating may be necessary for polyethyleneimine molecules to maximize interaction with the rayon cloth.

As described above, it has been found that the non-woven rayon/polyester cloth, previously-soaked in about 10% by weight NaOH and then washed with water, was able to load a large amount of polyethyleneimine from about 11% by weight polyethyleneimine solution, and that the following heating at about 50°C until dryness confirmed the stable polyethyleneimine holding against washing with diluted acid and alkali.

The same treatments with polyethyleneimine were ca rried out on other cellulose materials, as well as on a 100% polyester cloth as a control, and their bovine serum albumin adsorption capabilities were compared.

The results are shown in Table 5. TABLE 5. Bovine Serum Albumin Adsorption to Fabrics and Fiber Treated with Polyethyleneimine (a). fabrics and fiber bovine serum albumin

adsorption (mg/g)

SONTARA

8407 rayon/polyester;70/30 842

SONTARA

8423 rayon/polyester;70/30 538 commercial rayon fiber 614

SONTARA

8801 wood pulp/polyester;55/45 141 commercial cotton cloth (woven) 111 Whatman No. 1 filter paper 338

SONTARA

8122 100% polyester 10 (a) All 2×2 cm square cloth segments and 33 mg of rayon fiber were treated as described hereinabove.

Table 5 shows that rayon produced the polyethyleneimine-material possessing good bovine serum albumin adsorption capacities which are equivalent to or greater than those of commercial diethylaminoethylamine cellulose ion exchangers. Polyethyleneiminetreated SONTARA 8423 and SONTARA 8407 adsorbed 538 and 842 mg bovine serum albumin/g, respectively, while diethylaminoethylamine-Cellulose DE-23 and DE-52 (WHATMAN_TM) were reported to adsorb 425 and 750 mg bovine serum albumin/g, respectively.

Compared with rayon, polyethyleneimine holding on wooden cellulose and cotton was less, reflecting the high density of alkali-resistant crystalline structure in these native celluloses; it still was considerable.

Polyethyleneimine-treatment described herein as an essential feature of this invention can thus be widely-applied to cellulose cloths in the same manner as rayon cloths.

Little binding of polyethyleneimine to polyester was also observed, suggesting that polyethyleneimine holding on rayon/polyester cloth was entirely due to polyethyleneimine binding to its rayon component.

Thus, it has been found that cellulosic materials (fabric, cloth, paper) can be used according to aspects of this invention. Rayon, (re-generated cellulose), is preferred to natural cellulose because of its increased adsorption of polyethyleneimine. Non-woven cloth is preferable rather than woven cloth because of its superior character as a filter material. Accordingly, the following substrates may preferably be used acording to this invention: non-woven rayon cloth; non-woven rayon/polyester cloth, e.g., SONTARA 8407, or SONTARA 8423; non-woven wood-pulp/ polyester cloth, e.g., SONTARA 8801; (cellulosic) paper, e.g., various filter papers; woven rayon cloth; woven rayon/polyester cloth; woven cotton cloth; and woven cotton/polyester cloth.

To examine the stability of polyethyleneimine fixed on the rayon cloth, its bovine serum albumin and Cu⁺² adsorption capabilities were repeatedly determined. After each adsorption assay, the polyethyeleneiminecloth was regenerated with 0.5 N HCl and 0.5 N NaOH.

Figure 10 is a graph which shows the bovine serum albumin adsorption to polyethyleneimine-coated SONTARA 8423 (uncross-linked). The cloth segment was repeatedly regenerated with 0.5 N HCl and 0.5 N NaOH before each adsorption trial. Figure 10 shows that bovine serum albumin adsorption to the polyethyleneimine-coated rayon cloth remained unchanged during at least 6 adsorption cycles. This strongly suggests the possibility that the cloth may be used for enzyme immobilization.

The effect of glutaraldehyde cross-linking on protein adsorption to polyethyleneimine-cloth was also examined.

Figure 11 is a graph which shows the effect of adsorption to polyethyleneimine-SONTARA 8423 cross- linked in various concentrations of glutaraldehyde. Figure 11 shows that bovine serum albumin adsorption capability decreased with higher concentration of glutaraldehyde, as cross-linking reduced the number of amino groups available for proein binding. However, the polyethyleneimine-cloths cross-linked with 0.3% or 0.4% by weight glutaraldehyde still had considerable adsorption capacities of 200-250 mg bovine serum albumin/g. Polyethyleneimine-rayon cloths were cross-linked with about 0.5% to about 3% epichlorohydrine or 1,4-butandioldiglycidyl ether in methanol at room temperature for about 3 hours. To examine the stability of polyethyleneimine fixed on the cloths, 2x2 cm square segments of the resulting cloths were repeatedly-used for adsorption of Cu⁺² in 5 ml of 0.005 M or 0.01 M CuSO₄ at room temperature overnight. After each adsorption trial, segments of cloths were re-generated with 0.5 N HCl and 0.5 N NaOH, and heated in water at 90°C for about 3 to about 4 hours.

Water may be contaminated with undesirable proteineous materials of different isoelectric points (pI). Polyethyleneimine-rayon cloths cross-linked with epichlorohydrin or 1,4-butandioldiglycidyl ether were assayed for adsorption of bovine serum albumin (pI ca. 5.0) and hemoglobin (pI6.8) in water. The cloth segment was soaked in 5% by weight protein solution for 1 hour, adsorbed protein was desorbed with 1 M NaCl and measured. Although all adsorbed bovine serum albumin was extracted, the cloth segment to which bovine hemoglobin adsorbed still retained some homoglobin colour after this NaCl extraction, indicating some hemoglobin non-ionically bound to the cloth. The cloth was treated with 1% sodium lauryl sulfate at 95°C and the eluted bovine hemoglobin was measured. The results are shown below in Table 6.

TABLE 6. Adsorption of Bovine Serum Albumin and Bovine Hemoglobin to Polyethyleneimin-SONTARA 8423 Cross-linked with Epichlorohydrin or 1,4-Butandioldiglycidyl Ether (a).

Crosslinking Bovine Serum Bovine Hemoglobin

Condition Albumin AdsorpAdsorption (mg/g)

tion (mg/g)

NaCl(b) total NaCl(b) Sodium

Lauryl

Sulfate(c) epichlorohydrin

0.5 %, r.t. 353 264 (211) (53)

1 %, r.t. 296 212 (161) (51)

3 %, r.t. 304 146 (104) (42)

1, 4-butandioldiglycidyl ether

0.5 %, r.t. 383 221 (171) (50)

1 %, r.t. 342 188 (142) (46)

3 %, r.t. 224 89 ( 53) (36)

1 %, 50 C 67

without cross-linking 538 277 (226) (51)

(a) Polyethyleneimine-cloth was cross-linked for 3 hours at room temperature or 50°C in 0.5%-3% by weight cross-linking agents.

(b) Bovine serum albumin or bovine hemoglobin desorbed in 1 M NaCl at room temperature.

(c) Bovine hemoglibin desorbed in 1% sodium lauryl sulfate at 95°C after extraction with 1 M NaCl.

Table 6 shows that bovine serum albumin adsorption capacities of polyethyleneimine-rayon cloths decreased with higher concentrations of epichlorohydrin and 1,4-butandioldiglycidyl ether used as cross- linking agents, as observed for glutaraldehyde cross- linking. However, cross-linked polyethyleneiminecloths still exhibited the considerable capabilities of bovine serum albumin adsorption, when cross-linking was performed at room temperature. Since bovine hemoglobin has a higher pI and thus less negative charges in water than bovine serum albumin, adsorption of bovine hemoglobin to the polyethyleneimine-cloth was less than that of bovine serum albumin, but was still considerable. Furthermore, some bovine hemoglobin exhibited non-ionic binding to the cloth, since they were not desorbed in 1 M NaCl but were desorbed in 1% sodium lauryl sulfate. Thus, the bovine hemoglobin adsorption may also involve hydrophobic interaction. The ethylenecontaining backbone of polyethyleneimine is likely responsible for hydrophobic interaction.

The results indicate that the polyethyleneiminecloth will adsorb negatively-charged proteins through ionic interaction, as well as hydrophobic interaction. This ability of the polyethyleneimine-cloth to adsorb various proteins is useful in removing undesirable proteinous impurities, e.g., proteins in the effluents from food industries, or various viruses which have protein coats.

5. Adsorption of E. Coli Cells

E. coli Crooks strain was grown in M63 medium containing 0.5% by weight glucose and 1 mM MgSO₄, collected, washed twice with water or 0.9% NaCl and suspended in water or 0.9% NaCl. One 2×2 cm polyethyleneimine-cloth segment was gently shaken in 3 ml of the suspension at room temperature. Optical density at 500 nm was measured to determine the amount of bacteria in the initial suspension and in the supernatant after 1 hour contact. The difference gave the amount of E. coli adsorbed onto the cloth.

For adsorption on a column, 10 or 30 pieces of polyethyleneimine-cloth segments cut into circles to a height of 0.5 or 1.5 cm, respectively. E. coli suspensions of 0.6-1.1×10⁸ cells/ml were passed with a space velocity of 22-23 bed volumes per hour. Optical density of every 5 ml of effluent was examined and cell adsorption capacity of cloth was calculated from breakthrough bed volume.

Polyethyleneimine, as a cationic polymer, is believed to be able to adsorb bacteria, most of which are negatively charged in water. As a model, the adsorption of E. coli to polyethyleneimine-fixed rayon cloth was examined. A 2 cm square polyethyleneimine-cloth (uncross-linked or crosslinked with 1,4-butandioldiglycidyl ether) was soaked in 3 ml of E. coli suspension at room temperature for 1 hour.

The results are shown in Table 7.

TABLE 7. Adsorption of E. coli to Polyethyleneimine-SONTARA 8423 from 1 Hour Contact (a). initial concentration of cell Polyethyleneimine- SONTARA 8423 0.5×10⁸ 1.0×10⁸ 2.2×10⁸ cells adsorbed per g of cloth uncross-linked 3×10⁹(67)

cross-linked

in 1% 1,4-butandioldiglycidyl ether

at r.t. 7.1×10⁹(61)

in 1% 1,4-butandioldiglycidyl ether

at r.t. 5.1×10⁹(28) (b)

in 1% 1,4-butandioldiglycidyl ether

at 50°C 3 .3×10⁹ (49) 6.2×10⁹(45) 8.8×10⁹(23) in 3% 1,4-butandioldiglycidyl ether

at 50°C 5.8×10⁹(40)

(a) One 2 cm square of cloth was contacted with 3 ml of cell suspension in water for 1 hour at room temperature. The number of bacteria in the original suspension and the supernatant was determined from optical density at 500 nm.

(b) The cloth segment was contacted with cell suspension in 0.9% NaCl.

The number in the parentheses shows the removal coefficient.

Table 7 shows that uncross-linked polyethyleneiminecloth removed 84% of E. coli from 3 ml of suspension (1.0 × 10⁸ cells/ml) in water in 1 hour and that 1,4-butandioldiglycidyl ether-crosslinked polyethyleneimine-cloths also captured 82-67% of the bacteria. Cross-linking with 1,4-butandioldiglycidyl ether appeared to cause only a small reduction of bacteria adsorption. The polyethyleneimine-cloth also efficiently adsorbed E. coli from the bacterial suspension in 0.9% by weight NaCl: the polyethyleneimine cloth cross-linked with 1% by weight 1,4-butandioldiglycidyl ether at room temperature removed 60% of bacteria in 1 hour contact time.

Table 7 also shows the removal coefficients which are related with the initial rate constant of bacteria removal process as

(removal coefficient) = (V/Wt).log(N₀/N_t) where V is volume of cell suspension, W is weight of adsorbent, t is contact time, N₀ is initial cell number and N_t is cell number at contact time t. The removal coefficients for 1,4-butandioldiglycidyl ether-treated polyethyleneimine-cloth were 60-40 in water, and 28 in 0.9% by weight NaCl (the cloth treated with 1% by weight 1,4-butandioldiglycidyl ether at room temperature). It is known that crosslinked poly(N-benzyl-4-vinylpyridinium bromide) effectively removes bacteria in physiological saline at 37°C with a removal coefficient of 4.4. Although the conditions of bacteria adsorption are not identi cal, the polyethyleneimine-cloths appear to remove E. coli more rapidly than poly(vinylpyridinium).

To examine the adsorption of E . coli to the polyethyleneimine-cloth in column operations, an E. coli suspension in water was passed through a column packed with butanedioldiglycidyl-ether-cross-linked polyethyleneimine-cloth segments and the optical density of effluent was plotted against effluent volumes. Figure 12 is a graph which shows an example of the experiment. Figure 12 shows the removal of E. coli from water by a fixed bed of polyethyleneimine-SONTARA 8423 cross-linked with 1% 1,4-butandioldiglycidyl ether at room temperature. The volume of the bed formed of 30 circles (i.e., 1.6 cm) of cloth was 3 ml with 1.5 cm height. E. coli suspension of 1.1 × 10⁸ cells per ml was passed through with space velocity of 22, and a breakthrough was observed at 13 bed volumes (40 ml) of effluent.

Further results are shown in Tables 8A and 8B.

TABLE 8A. Removal of E. Coli from Water by Columns Packed with 1,4-Butandioldiglycidyl ether-Crosslinked Polyethyleneimine-SONTARA 8423.

Pieces

condition of of space

cross-linking cloth velocity

0.5% 1,4-butandioldiglycidyl ether, 50°C 10 23

1% 1,4-butandioldiglycidyl ether, r.t. 10 23

1% 1,4-butandioldiglycidyl ether, 50°C 30 22

1% 1, 4-butandioldiglycidyl ether, 50°C 30 22 TABLE 8B . cells in breakadsorbed condition of influent through cells per cross-linking (cells/ml) (bed vol.) g of cloth

0.5% 1,4-butandioldiglycidyl

ether, 50°C 1. 1×10 ⁸ 20 1.2×10 ¹⁰ 1% 1, 4-butandioldiglycidyl

ether, r.t. 1.1×10⁸ 35 2.1×10 ¹⁰

1% 1,4-butandioldiglycidyl

ether, 50°C 1.1×10 8 13 8.1×10⁹

1% 1,4-butandioldiglycidyl

ether, 50°C 5.9×10⁷ 20 6.4×10⁹ E. coli adsorption capacities of 1,4-butandioldiglycidyl ether-treated polyethyleneimine-cloth in the column, judged from breakthrough capacities, were 10¹⁰ cells/g at a space velocity of 22-23. In contrast, poly(vinylpyridinium) also exhibited similar capacities but the space velocity of effluent was 10 times less than the procedure of the present invention. These results suggest that polyethyleneiminecloth column could effectively remove bacterial from water with a rapid flow rate.

Cross-linked polyethyleneimine-cloths were examined for their capacity to adsorb bovine serum albumin and hemoglobin, metal ions and Escherichi coli bacteria.

6. Comparison of Invention with the Background Art The present invention provides a non-obvious improvement over previously referred-to Canadian Patent No. 1,169,735. Canadian Patent No. 1,169,735 is based on ionic adsorption of polyethyleneimine, unlike hydrogen bonding which is the theoretical basis of the present invention.

Canadian Patent No. 1,169,735 necessitates the adjustment of pH of the polyethyleneimine to 4 to 5 so that polyethyleneimine (-NH-,-NH₂) becomes, polyethyleneimine (-NH₂ ⁺-,-NH₃ ⁺) which can ionically adsorb to the SO₃- group in NaOH-washed, H₂SO₄-washed, sulfonate lignocellulose (sulfonated lignin rather than cellulose) or unidentified acid groups in washed pine bark.

The present invention necessitates the disruption of H⁺ bondings in rayon, so that hydroxyl groups in rayon can form H-bondings with the N atoms of polyethyleneimine. Thus, there is no need to adjust the pH of polyethyleneimine in the process of an aspect of this invention.

Canadian Patent No. 1,169,735 provides adsorbents in a particulate form, requiring a separation mechanism, e.g., decantation, filtration or centrifugation, whereas the use of a cloth form as in the present invention provides easy separation.

Since in the process of Canadian Patent No. 1,169,735 the polyethyleneimine is ionically adsorbed, NaCl seems to strip polyethyleneimine, necessitating polyethyleneimine reloading. On the other hand, in this invention, polyethyleneimine is chemically crosslinked, and thus is stable during regeneration.

It is believed that the product produced by the process of Canadian Patent No. 1,169,735 may be satisfactory for the treatment of industrial effluents, but it is believed that it could not be used for treatment of drinking water.

Comparative experiments were carried out in the process and utility of the adsorbent cloth of the present invention and the product of Canadian Patent 1,169,735. Since the alkali and acid washings taught in Canadian Patent No. 1,169,735 are too strong for the rayon cloths which are preferred embodiments of this invention, much milder washings were employed. The following experiments were carried to examine the effect of acid treatment on the adsorption of polyethyleneimine to the substrate.

The test procedure was as follows:

A 2 cm square of SONTARA 8423 was soaked in 10% by weight NaOH at room temperature for 10 min, washed with water, soaked in 0-60% by weight H₂SO₄ at room temperature for 2 or 4 hours, and then washed with water. After 0.2 ml 11% polyethyleneimine (without pH adjustment) or 7% by weight polyethyleneimine (pH 4.5 with HCl) was added, it was then heated at 50°C overnight, and washed with water, 0.5N NaOH and water.

The bovine serum albumin adsorption capacity as a measure of polyethyleneimine holding on cloth was then determined, with the following results, shown below in Table 9.

TABLE 9.

Acid Treatment Polyethyleneimine Bovine Serum

Albumin Adsorption

(mg per 2 cm square of cloth)

0% H₂SO₄, 2 h 11% 14.6

20% H₂SO₄ , 2 h 11% 14.4

40% H₂SO₄ , 2 h 11% 14.6

60% H₂SO₄ 2 h 11% 13.0 TABLE 9.

Acid Treatment Polyethyleneimine Bovine Serum

Albumin Adsorption

(mg per 2 cm square of cloth)

0% H₂SO₄, 4 h 7% , pH 4. 5 14 . 0

20% H₂SO₄, 4 h 7% , pH 4. 5 12 .5

40% H₂SO₄ 4 h 7% , pH 4 .5 12 .5

60% H₂SO₄ 4 h 7% , pH 4 . 5 8 . 4

As a result of these tests it can be seen that treatment with 60% by weight H₂SO₄ for 4 hours harmed the cloth. Acid treatment applied to rayon cloth did not improve the polyethyleneimine retaining on the cloth. Application of polyethyleneimine solution whose pH was adjusted to acidic (e.g., 4.5) also did not improve the polyethyleneimine retaining on the cloth.

There appears to be no advantage of acid treatment. The purpose of NaOH and acid treatments in Canadian Patent No. 1,169,735 were not described. However, it appears that they merely remove alkali and acidsoluble impurities from the bark.

Industrial Utility of the Invention

The process according to the invention can be carried out discontinuously, semi-continuously or continuously. In principle, the following embodiments are suitable:

a) the so-called stirring process in which the water to be purified is stirred with the polyethyleneiminecloth in a vessel or a series of vessels and then separated off; b) the so-called fixed bed process in which the liquor to be purified is fed through cellulose material arranged in a filter-like manner.

The polyethyleneimine-cloth adsorbed these substances at much faster rate than the previously developed chelating resins. A column packed with the polyethyleneimine-cloth could be operated for the removal of heavy metal ions and bacteria at rapid flow rates.

The flow rate depends upon the volume and size of column and the metal ion concentration in water. The ability of the column can be estimated from the capacity of treated water under the required flow rate.

The polyethyleneimine-cloth of an aspect of this invention, adsorbs metal ions under static condition faster than a chelating resin of the prior art. A column study carried out with the polyethyleneiminecloth of this invention, also exhibited the comparable results. These suggest that the faster flow rate (linear flow rate: M2/cm²/hr) may be available to the polyethyleneimine-cloth column so that the column with smaller diameter can be used for purifying a certain volume of water.

All materials used to prepare the polyethyleneiminecloths are relatively safe and inexpensive, and the preparation is simple. Accordingly, these economical and highly effective polyethyleneimine-cloths should be useful for recovering metal ions from water, final treatment of industrial waste water and purification of drinking water, especially for domestic use since the cloths are disposable.

Claims

We Claim:

1. An adsorbent material for adsorbing heavy metals and negatively charged materials comprising a cloth or fabric substrate, at least part of which is cellulosic, characterized in that it has been pretreated with an alkali, and further characterized in that it has been washed with water, and still further characterized in that high molecular weight polyethyleneimine has been adsorbed and fixed thereon with a cross-linking agent.

2. The adsorbent material of claim 1 characterized in that said fabric upon which said high molecular weight polyethyleneimine has been adsorbed is heated mildly until it is dry prior to having said polyethyleneimine adsorbed and fixed thereon with said cross-linking agent.

3. The adsorbent material of claims 1 or 2 characterized in that said cloth or fabric comprises a woven or a non-woven rayon fabric, or a woven or a non-woven rayon/polyester fabric or a woven or a non-woven woodpulp/polyester fabric, or a woven or non-woven cotton cloth or a woven or non-woven cotton/polyester cloth or cellulosic paper; and wherein the fabric is either in its open-apertured style or in its highly absorbent, open-apertured style.

4. The adsorbent material of any one of claims 1 to 3 inclusive characterized in that said cross-linking agent comprises glutaraldehyde, epichlorohydrin, 1,4- butandioldiglycidyl ether, 1,2-ethanedioldiglycidyl ether, 1,3-diglycidylglycerol, triglycidylglycerol, pentaerythritol, or tetraglycidyl ether.

5. A process for preparing an adsorbent material for adsorbing heavy metals and negatively charged materials, at least part of said cloth or fabric being cellulosic, characterized by the following steps, in sequence:

a) pretreating said cloth or fabric substrate with an alkali;

b) washing said pretreated substrate with water; c) adsorbing high molecular weight polyethyleneimine therein; and

d) cross-linking said polyethyleneimine on said substrate with a cross-linking agent.

6. The process of claim 5 characterized in that it includes the preliminary step of: heating said fabric heated mildly until it is dry prior to having said polyethyleneimine adsorbed and fixed thereon with said cross-linking agent.

7. The process of claims 5 or 6 further characterized in that said alkali is an inorganic base or an organic base.

8. The process of claim 7 characterized in that said inorganic base is selected from the group consisting of LiOH, NaOH and KOH.

9. The process of claim 8 characterized in that said organic base is an alkyl ammonium base.

10. The process of claim 8 characterized in that said inorganic base is an aqueous solution of the NaOH containing about 10% to about 40% by weight NaOH.

11. The process of claims 5 to 22 characterized in that said aqueous solution of NaOH has a concentration of about 10% ± 5% by weight.

12. The process of any one of claims 5 to 11 characterized in that said cross-linking agent comprises glutaraldehyde, epichlorohydrin 1,4-butandioldiglycidyl ether, 1,2-ethanedioldglycidyl ether, 1,3-diglycidylglycerol, triglycidylglycerol, pentaerythritol, or tetraglycidyl ether.

13. The process of any one of claims 5 to 12 characterized in that said water washing is carried out until the substrate has a pH of about 7.

14. The process of any one of claims 5 to 13 characterized in that said adsorbing of said high molecular weight polyethyleneimine is carried out and until a maximum of the stoichiometric amount of said polyethyleneimine is adsorbed thereon.

15. The process of claim 14 characterized in that said polyethyleneimine has a molecular weight of about

60,000 ± 20,000.

16. A method for removing heavy metal ions and negatively charged materials from water by contacting said water with an adsorbent material, part of which is cellulosic, characterized in that said adsorbent material is the adsorbent material as claimed in claims 1 to 4.

17. The method of claim 16 characterized in that said contacting is achieved by passing said water through a column packed with said adsorbent cloth.