IL25457A - Process for brominating water and aqueous solutions - Google Patents

Description

C O H E N Z E D E & S P I S B A C H R EG D . PATE N T A TT O R N EY S 24, LEVONTIN STR., P. O. B. 1169 T E U - A V I V P A T E N T S & D E S I G N S O R D I N A N C E 15221/66 SPECIFICATION PRQCBSS FOR BROMIK TING WATER AMD AQUEOUS SOLUTIONS We, THE DOW CHEMICAL COMPANY, a corporation organised and existing under the laws of the State of Delaware, of 929 East Main Street, Midland, Michigan, U.S.A., and JACK FERRER MILLS, a citizen of the U.S.A., of 5 Andre, Midland, County of Midland, State of Michigan, U.S.A., ROBERT DUARE GOOD ENOUGH, a citizen of the U.S.A., of 3612 Dartmouth, Midland, County of Midland, State of Michigan, U.S.A., WILLIAM FREDERICK NEK ER VIS, a citizen of the U.S.A., of 4615 Hampshire Court, Midland, County of Midland, State of Michigan, U.S .A · , DO HEREBY DECLARE ihe nature of this invention and in what manner Ihe same is to be performed to be particularly described and ascertained in and by the following statement: This invention relates to a process for treating water and aqueous solutions with bromine to control the microorganisms therein.

The use of chlorine and bromine in the disinfection and sterilization of water supplies for many diverse purposes is well known. Chlorination of municipal water supplies has been a standard practice in the United States and abroad for many years. It is now generally recognized that on an equimolar basis, bromine is several times as effective as chlorine for the control of bacteria, algae, slime, and other microorganisms in water supplies. In fact, excellent control of many bacteria in water can be effected using as little as 0.1 ppm bromine.

With badly contaminated water, a heavy initial shock treatment with from 3 to 30 ppm bromine may be desirable to kill the contaminating microorganisms after which a residual bromine concentration of 0.1 to 1.0 ppm is generally effective in maintaining sanitary water. The level of the shock treatment is, of course, dependent on the nature of the contaminating microorganisms. For treatment of water for human consumption, shock treat-ment with 3 to 5 ppm bromine generally suffices to kill the un-desired bacteria. However, heavy contamination with slime and algae, as may be encountered in water used in industrial cooling towers, often requires shock treatment with 10 to 30 ppm of bromine. For example, while treatment with 2 ppm bromine notice-ably inhibits the growth of Chlorella, a common strain of algae, 10 ppm bromine are required for pronounced inhibition and between 10-20 ppm for complete kill.

In addition to its effectiveness as an antimicrobial, there are further advantages to the use of bromine in sanitizing water supplies. Because of its lower volatility, maintaining a desired residual level of halogen in the treated water is easier with bromine than chlorine, particularly under conditions of turbulent flow and agitation. Furthermore, bromine imparts little or no undesirable taste or odor to the treated water.

Indeed, since bromine acts to destroy suspended or dissolved organic matter which often causes undesirable color and odor, it is particularly suited for use as a sanitizing agent for swimming pools where sparkling clear, colorless and odorless water is highly desirable.

Thus , treating water with bromine is advantageous in providing large volumes of water suitable as potable municipal supplies and for many other commercial, industrial and residential purposes. In particular, bromine is extremely desirable for use as a sanitizing agent for swimming pools, industrial cooling towers, and similar recirculating water systems since a very low concentration of bromine is effective both in destroying the bacteria initially present and in maintaining hygienic conditions in spite of repeated recontamination.

However, because of the highly corrosive nature of elemental bromine, a serious hazard is involved in its use. The danger in handling liquid bromine has discouraged its use as a sanitizing agent, particularly in smaller systems where elaborate equipment for handling liquid bromine is not feasible. In some localities use of liquid bromine has been restricted by ordinance.

Thus, there exists a need for a safe and practical process whereby bromine can be stored, handled, and added to water by unskilled personnel. Such a process requires a form of bromine which is easily and safely prepared, which is stable during storage and shipment, which does not cause serious burns in case of accidental skin contact, and yet which releases elemental bromine as required for sanitizing treatment.

It has now been discovered and the discovery forms the basis for the present invention that a brominated anion exchange resin containing polybromide anions slowly give up bromine to water and aqueous solutions with which it comes into contact.

Thus, the brominated anion exchange resin provides an extremely convenient, effective and safe means for handling elemental bro-for use in treating water and aqueous solutions to control microorganisms. In accordance with the present invention water or aqueous solutions may be readily brominated by bringing at least a portion thereof into contact with a brominated anion exchange resin and intimately mixing the so brominated solution with the remaining unbrominated portion. The brominated resin employed contains polybromide ions in association with the ion exchange sites of the resin. Preferably the anion exchange resin employed is comprised of a water-insoluble polymer to which quaternary ammonium groups are chemically bonded.

The brominated anion exchange resin of the invention serves essentially as a reservoir from which elemental bromine can be removed as required to establish or to maintain control of bacteria, algae, slime, and other microorganisms in a body of water. Not only do such resins possess highly useful and desired properties in respect to both bromine loading and elution characteristics, but also are chemically stable for prolonged periods under normal storage conditions and can be prepared, stored, and shipped safely without degradation in quality. Although definitely not recommended, momentary accidental contact of the polybromide resin even with wet skin will not cause burns. Furthermore, the aqueous solution obtained by contact of the polybromide resin with water is sufficiently dilute so that burns will not result from brief skin contact.

Thus, the invention described herein concerns an improved process for treating water with bromine. In a more preferred embodiment of the invention, this improved process comprises: (1) contacting an anion exchange resin in polybromide form with water whereby bromine is removed from the polybromide resin to give an aqueous solution containing from 10 to 10,000 ppm bromine and (2) mixing a sufficient amount of said aqueous bromine solution with the water to be treated to establish therein a concentration in the range from about 0.02 to 30.0 ppm bromine.

The adsorption of elemental bromine by an anion exchange resin was reported in Chem. and Ind. , 1238 (1957) by Aveston and Everest who found that when an anion exchange resin was treated with an aqueous solution containing elemental bromine, the polybromide anion, Brn— wherein n is 3, 5 or 7, became the predomi-nant anionic species in the resin phase. With a quaternary ammonium resin and excess bromine, the resin was converted to Br.-, form by adsorption of 3 moles of bromine per equivalent of resin.

In the practice of the present invention, commercial anion exchange resins prepared by the reaction of a chloromethyl-ated styrene-divinylbenzene resin with an appropriate organic amine are suitable as bromine carriers.

Since the operating characteristics of the polybromide anion exchange resin column are similar to those of conventional ion exchange resin columns, commercial resins and conventional operating techniques are generally satisfactory in terms of such factors as degree of resin cross-linking, mesh size, and flow rates .

A particularly effective method for the preparation of a suitable polybromide resin is to pass an essentially saturated solution of bromine in aqueous sodium bromide slowly through a bed of the anion exchange resin. In this manner a commercial resin having a dry weight capacity of 3.50 meq./g. (milli equivalents per gram), Cl~ form, rapidly adsorbed 3 moles of bromine per equivalent of chloride originally on the resin. The result-ing polybromide resin in wet form contained about 48.6 weight percent bromine. This adsorbed bromine was quantitatively removed by treatment with a sodium bisulfite solution. An attempt to load the resin further under more forcing conditions resulted in bromination of the resin matrix, the elutable bromine content remaining at about 3 moles per equivalent of resin.

If the polybromide resin is dried or exposed to large volumes of air, some of the adsorbed bromine may be lost. However, if stored in a sealed container of bromine-resistant material such as polyvinyl chloride, the resin is stable for prolonged periods.

With conventional flow rates of from 1 to 10 gpm./ft.^ (4 to 41 ml/cm^ per minute) of resin bed cross-sectional area, elution of bromine with water is essentially independent of the exact method of contact. An equilibrium is rapidly established between the bromine adsorbed by the anion exchange resin and that present in the aqueous phase. At room temperature the aqueous phase in contact with a quaternary ammonium resin in a fully loaded Brη~ form contained about 7,000 ppm bromine. Elution studies with acolumn of this resin indicated that the bro-mine concentration in the eluent dropped to about 1,300 ppm after 100 bed volumes of water passed through the column. After passage of 1,400 bed volumes, the bromine concentration in the eluent dropped to about 50 ppm and about 95 percent of the adsorbed bromine had been removed. Further elution reduced the residual bromine content of the resin still lower and the eluent bromine concentration then dropped to 10 ppm and less.

Temperature does have a marked effect on the equilibrium of bromine between the resin and aqueous phases. For example, water in contact with an approximately equivalent amount of polybromide resin containing 2.14 moles of bromine per equivalent of resin had an equilibrium concentration of about 13,800 ppm bromine at 55°C. and 4,270 ppm at 27°C.

Regeneration of the exhausted or partially exhausted polybromide resin is readily achieved by treatment with a bromine solution as previously described whenever desired.

A higher eluent concentration of bromine is needed for a shock treatment requiring 10-30 ppm bromine in the treated water than is needed for maintaining a residual of 0.02-1.0 ppm bromine. The frequency of regeneration will depend on the requirements of the particular system.

The bromine-containing eluent solution can be metered and added to another body of water as required to establish or to maintain a desired bromine concentration in the treated water. Conventional analytical techniques can be employed to determine bromine concentrations and to control the treatment process. If desired, automatic equipment can be used to monitor continually the bromine concentration in the treated water and to add the more concentrated bromine eluate as required to maintain the bromine concentration within desired limits. Such control is particularly suitable with a recirculating system such as common-ly employed in residential swimming pools where a portion of the water circulating through the system can be diverted by suitable means to pass through and to eluate bromine from a polybromide resin column.

Example 1 - Polybromide Resins A. A portion of a commercial quaternary ammonium styrene- 8% divinylbenzene anion exchange resin comprised of spheroidal particles ranging in average diameters from 0.9 to 0.3 mm and having a dry weight capacity of 3.5 meq./g. Cl— form was placed in a 1"/ (2.54 cm.) i.d. glass column and loaded with bromine by slowly passing an excess of an aqueous solution containing about 35 wt. % bromine and 17 wt. % sodium bromide up through the column. After complete loading, the excess bromine solution was drained from the column and the polybromide resin rinsed with a small amount of water. A sample of the resulting wet polybromide resin rinsed with a small amount of water. A sample of the resulting wet polybromide resin was found to contain 48.6 wt. 7a bromine. The adsorbed bromine was quantitatively removed from a portion of the treated resin by treatment with a sodium sulfite solution. The bromine thus eluted as bromide corresponded to a theoretical capacity of 3 moles of bromine/equivalent of resin anion exchange capacity.

B. In an attempt to load the resin further, the concentrated aqueous bromine solution was warmed to 50° C. and recycled through the resin bed for several hours. The resin was then allowed to stand at room temperature for several days in contact with the bromine solution. The resulting wet resin was found to contain 64.9 wt„ % total bromine. However, after treating this resin with excess sodium sulfite solution, it retained 16.4 wt. % bromine indicating bromination of the resin matrix. The elutable bromine was equivalent to about 3 moles of bromine per equivalent of initial resin capacity.

C. In a similar manner the polybromide forms of other styrene-divinylbenzene resin containing from 1 to 16% divinylben-zene were prepared. Also, a quaternary poly (vin lpyridine) resin as described by Greer in United States Patent 2,801,223 and a commercial quaternized polyethoxypolyamine resin were converted to similar polybromide forms. Although the bromine capacities of these resinswere similar in proportion to their initial anion exchange capacity, the latter two resins were less stable than the preferred quaternary ammonium styrene-divinylbenzene resins. Example 2 - Elution Characteristics Using a 1" (2.54 cm.) i.d. column filled with the polybromide form of resin as described in Example 1A, a series of elution runs was made at room temperature. No appreciable variation in elution characteristics was found using flow rates of 5 and 10 gpm./ft.^ (20 to 41 ml/cm^ per minute), a bed depth of 18 and 36 inches, (40.7 and 91.4 cm), and upflow and downflow feed. Table I presents data from a typical elution run using a wet resin containing initially 48.5 wt. % bromine.

Table I Elution Characteristics Bed Volumes of Eluent 10 50 100 300 600 1400 Br2 in eluent, ppm 7000 3000 1300 350 150 50 Total Br2 eluted 9.9% 30.0% 55.2% 74.8% 85.5% 95.4% Exam le 3 - Swimming Pool Unit A small resin column, 4" (10 cm.) in diameter and 18" (40.7 cm.) high, loaded with 0.13 ft.3 (3.7 1) of the resin of Example 1 in the polybromide form and containing about 5.2 lbs. (2.35 kg.) of bromine, was installed in the recycle line of a 20,000 gallon (75.7 m3) outdoor residential pool. By means of appropriate valves, a portion of the recycle water could be diverted after the filter unit to pass through the resin column, thereby eluting a portion of the adsorbed bromine for addition to the main recycle stream.

Initially flow of recycle water through the resin column was controlled manually to maintain a bromine concentration in the main body of the pool between about 0.70 and 1.20 ppm. Subsequently an automatic instrument was installed to measure the residual bromine in the recycle stream and to control a solenoid valve on the line to the polybromide column thereby diverting a portion of the recycle stream through the polybromide resin column intermittently as required to maintain a desired bromine concentration. For example, in a warm mid-afternoon period, the resin column was used with a cycle of about 10 minutes on-stream followed by about 20 minutes off- stream. After each on-stream period, the bromine concentration in the pool continued to rise for a few minutes because of the pool mixing characteristics before dropping slowly as the bromine was consumed. Nonetheless the bromine concentration in the pool was easily maintained between about 0.80 to 1.05 ppm. During the night, bromine consumption was essentially nil.

During an extended test period with the polybromide resin column, the swimming pool showed no signs of algae growth and maintained an essentially sterile condition with a bacterial plate count of less than 0.1 per cc.

Claims (6)

HAVING NOW particularly described end ascertained she nature of our said invention and in what manner the same is to be performed, we declare that what we claim Is:

1. A process for brominating water or aqueous solutions to inhibit the growth of microorganisms in which process at least a portion of the water or solution is brought into contact with a brominated anion exchange resin and the so brominated solution intimately mixed with the remaining unbrominated water or solution.

2. A process as claimed in Claim 1 wherein the brominated anion exchange resin employed contains polybromide anions in association with ion exchange sites of the resin.

3. A process as claimed in Claims 1 or 2 wherein the anion exchange resin employed is comprised of a water insoluble polymer to which quaternary ammonium groups are chemically bonded.

4. A process for brominating aqueous solutions substantially as hereinbefore described with reference to the specific examples .

5. Aqueous solutions whenever brominated by the process of any of Claims 1-4. DATED THIS 18th day of March, 1

6. COHFN &K K & SFISBACH P.O.BOX 1169, TEL-AVIV Attorneys for Applicants