Concentrated aqueous bromine solutions and their preparation

Details Concentrated aqueous bromine solutions and their preparation Concentrated aqueous bromine solutions and their preparation

2000-09-18

2001-10-09

Pryor, Alton (Department: 1616)

Drug, bio-affecting and body treating compositions

Inorganic active ingredient containing

Elemental sulfur or compound thereof

C424S615000, C424S665000, C424S722000, C424S723000

Reexamination Certificate

active

06299909

ABSTRACT:

REFERENCE TO OTHER COMMONLY-OWNED COPENDING APPLICATIONS
Reference is also made to commonly-owned copending application Ser. Nos. 09/404,184, filed Sep. 24, 1999; Ser. No. 09/451,319, filed Nov. 30, 1999; Ser. No. 09/451,344, filed Nov. 30, 1999; Ser. No. 09/456,781, filed Dec. 8, 1999; Ser. No. 09/506,911, filed Feb. 18, 2000; and Ser. No. 09/663,788, filed Sep. 18, 2000. Reference is also made to commonly-owned copending application Ser. No. 09/296,499, filed Apr. 22, 1999.
BACKGROUND
Bromine-based biocides have proven biocidal advantages over chlorination-dechlorination for the microbiological control of cooling waters and disinfection of waste treatment systems. The water treatment industry recognizes these advantages to be cost-effective control at higher pH values, almost no loss in biocidal activity in the presence of ammonia, and effective control of bacteria, algae and mollusks.
A common way of introducing bromine based biocides into a water system is through the use of aqueous NaBr in conjunction with NaOCl bleach. The user feeds both materials to a common point whereupon the NaOCl oxidizes the bromide ion to HOBr/OBr
⊖
. This activated solution is then introduced directly into the water system to be treated. The feeding of the two liquids in this fashion is necessary because the HOBr/OBr
⊖
mixture is unstable and has to be generated on-site just prior to its introduction to the water. Furthermore, the feeding, and metering of two liquids is cumbersome, especially as the system has to be designed to allow time for the activation of bromide ion to occur. Consequently many biocide users have expressed the need for a single-feed, bromine-based biocide. Molecular bromine chloride is deemed to meet these demands. It is a liquid at room temperature and can be fed directly to the water system, where immediate hydrolysis occurs to yield HOBr.
BrCl+H
2
O→HOBr+HCl
Bromine chloride is a fuming, red liquid or gas, with a boiling point of 5°, and a vapor pressure of 1800 mm at 25° C. It corrodes most metals in the presence of water.
It can be seen that certain characteristics of bromine chloride—especially its corrosiveness, high vapor pressure and fuming tendencies—necessitate care and skill in its handling and use.
An economically acceptable way of stabilizing high concentrations of aqueous solutions of bromine chloride is described in U.S. Pat. No. 5,141,652 to Moore, et al. The solution is prepared from bromine chloride, water and a halide salt or hydrohalic acid. These solutions were found to decompose at a rate of less than 30% per year and in cases of high halide salt concentration, less than 5% per year. Moreover, solutions containing the equivalent of 15% elemental bromine could be prepared. Unfortunately, the relatively high acidity of these solutions and their tendency to be corrosive and fuming impose limitations on their commercial acceptance.
U.S. Pat. No. 6,068,861, referred to at the outset, describes, inter alia, a new process of forming concentrated aqueous solutions ofbiocidally active bromine and in so doing, provides novel and eminently useful concentrated aqueous biocidal solutions of bromine chloride. Such solutions are formed by a process which comprises mixing (a) bromine chloride with (b) an aqueous solution of alkali metal salt of sulfamic acid (preferably the sodium salt), the resulting solution having a pH of at least about 7, e.g., in the range of 7 to about 13.5. The amounts of (a) and (b) used are such that (i) the content of active bromine in the solution is at least 100,000 ppm (wt/wt) and (ii) the atom ratio of nitrogen to active bromine from (a) and (b) is greater than 0.93, and preferably is greater than 1.
SUMMARY OF THE INVENTION
One objective of this invention is to enable the process of U.S. Pat. No. 6,068,861 to be carried out not only in a commercially-feasible manner, but in addition, in an exceptionally efficient manner on a continuous basis. Other objectives may appear hereinafter.
In one of its embodiments this invention provides a process of producing a concentrated liquid biocide composition which process comprises continuously or intermittently feeding (i) bromine chloride into mixing apparatus where said bromine chloride contacts (ii) an aqueous solution of alkali metal salt of sulfamic acid, to produce an aqueous product having an active bromine content of at least 100,000 ppm (wt/wt), and an atom ratio of nitrogen to active bromine from (i) and (ii) greater than 0.93:1.
In a preferred embodiment, the aqueous solution of alkali metal salt of sulfamic acid is present in said mixing apparatus to which the bromine chloride is being fed. In another preferred embodiment, bromine chloride and aqueous solution of alkali metal salt of sulfamic acid are continuously being fed into said mixing apparatus, and product is withdrawn from said mixing apparatus at a rate sufficient to enable the continuous feeding to be maintained.
In other embodiments, the bromine chloride is continuously formed from bromine and chlorine, preferably in nearly equimolar amounts, and at least a portion of the bromine chloride being continuously produced is used as the feed of bromine chloride. Thus in plant facilities where bromine chloride is required or desired for use(s) in addition to that required to maintain the continuous feed of (i) above, the continuous production of the bromine chloride can be scaled up to serve all such uses.
A preferred embodiment includes, in addition to producing the concentrated liquid biocide composition as described above, the following concurrent operation, namely, continuously, but alternately, withdrawing from at least one and then from at least one other of at least two reaction vessels, an aqueous solution of alkali metal salt of sulfamic acid at a rate that maintains a stream of (ii), and during the time the solution is being withdrawn from said at least one of at least two reaction vessels, forming additional aqueous solution of alkali metal salt of sulfamic acid in said at least one other of at least two reaction vessels from which solution is not then being withdrawn. In this way, aqueous alkali metal sulfamate solution can be continuously withdrawn from one or more tanks (“Tank(s) I”) to serve as a continuous feed of (ii), while forming more of such solution in one or more other tanks (“Tank(s) II”), so that when Tank(s) I is/are depleted, the system is switched to Tank(s) II which then serve(s) as the supply for a continuous feed of (ii) until depleted, and by that time more of such solution has been formed in Tank(s) I. Thus by alternating the supply and the production from one tank (or group of tanks) to another tank (or group of tanks) and switching back and forth between the filled tanks as the supply, a continuous feed of the aqueous alkali metal sulfamate solution can be maintained without material interruption.
A particularly preferred embodiment of this invention is a process which comprises:
A) continuously feeding into mixing apparatus (i) a bromine chloride stream identified below in C), and (ii) a separate feed stream of an aqueous solution of alkali metal salt of sulfamic acid identified below in D), in proportions that produce an aqueous product having an active bromine content of at least 100,000 ppm (wt/wt), and an atom ratio of nitrogen to active bromine from (i) and (ii) greater than 0.93;
B) withdrawing the aqueous product from the mixing apparatus at a rate sufficient to enable the continuous feeding in A) to be maintained;
C) continuously contacting bromine and chlorine in a vessel in quantities such that bromine chloride is produced, and continuously withdrawing from this vessel a bromine chloride product stream at a rate that maintains the feed of (i) in A), at least a portion of this bromine chloride product stream constituting the bromine chloride stream (i) of A);
D) continuously, but alternately, withdrawing from at least one and then from at least one other of at least two reaction vessels, an aqueous solution of alkali metal salt of sulfamic acid at a rate th

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