GB2253841A

GB2253841A - Biocide for aqueous based systems

Info

Publication number: GB2253841A
Application number: GB9100170A
Authority: GB
Inventors: Karen Rimmer; S T Pippard
Original assignee: WR Grace and Co Conn; WR Grace and Co
Current assignee: WR Grace and Co Conn; WR Grace and Co
Priority date: 1991-01-04
Filing date: 1991-01-04
Publication date: 1992-09-23
Anticipated expiration: 2011-01-04
Also published as: ZA9232B; GB2253841B; GB9100170D0; CA2058688A1

Abstract

A method for treating an aqueous system is described which comprises incorporating therein a dithiolan having the general formula: <IMAGE> wherein each X and Y, which may be the same or different, represents fluorine, chlorine or bromine, and a benzoazole having the general formula: <IMAGE> where Z represents oxygen or sulphur, A represents hydrogen, alkyl of 1 to 8 carbon atoms, alkoxy, hydroxyl, sulphonate, carboxylate, cyano, halo, nitro or optionally substituted amino, n is from 1 to 4 and m is 1 or 2 such that when m is 2 each A may be the same or different.

Description

BIOCIDE The invention relates to the use of biocides in aqueous systems.

Bloc ides are commonly used in various aqueous systems in order to control the formation of slime and other microorganisms which can cause fouling of the systems and also harbour materials which can give rise to corrosion of the system. Fouling not only reduces water flow but it also reduces heat transfer. Thus it is common practice to add biocides to, in particular, cooling water systems such as those involving cooling towers and also to the aqueous systems used in pulp and paper mill systems.

A wide variety of materials has been employed to act as biocides in such systems. One material which has recently been found to be an effective biocide is 5-oxo-3,4-dichloro1,2-dithiolan (commonly referred to as "2-dithiolan").

It has now surprisingly been found that if dithiolan is used in combination with 2-(thiocyanomethylthio) benzothiazole (TCMTB) broad spectrum activity can be obtained and, indeed, the combination is synergistic.

Accordingly, the present invention provides a composition suitable for addition to an aqueous system which comprises a dithiolan having the general formula given below and benzoazole having the general formula given below.

The dithiolans which can be used in the present invention have the general formula:

wherein each of X and Y, which may be the same or different, represents fluorine, chlorine or bromine, especially chlorine.

The benzoazoles which may be used in the present invention have the general formula:

where Z represents oxygen or sulphur, A represents hydrogen, alkyl of 1 to 8 carbon atoms, alkoxy, hydroxyl, sulphonate, carboxylate, cyano, halo, nitro or optionally substituted amino, n is from 1 to 4 and m is 1 or 2 such that when m is 2 each A may be the same or different. Preferably Z is sulphur, A is hydrogen and n is 1.

While the ratios of the dithiolan to the TCMTB can vary over a wide range it has been found that a weight ratio from 3:1 to 1:3 is generally particularly effective.

The compositions of the present invention typically comprise one or more solvents. Dithiolan is available commercially as a methyl carbitol solution. Other solvents which can be used include butyldiglycol as well as N-methyl pyrrolidone and tripropylene glycol n-butyl ether (TPnB).

Typical solvents for the benzoazole include, dimethylformamide, diethylene glycol monoethylether and Nmethyl pyrrolidone (NMP). While NMP is a good solvent for both products it is not in general, therefore, a mixture of solvents is employed to ensure a homogeneous and stable solution. Typical combinations of solvents include N-methyl pyrrolidone and either butyldiglycol or diethylene glycol.

TCMTB is available commercially as an 80% solution.

The compositions of the present invention will generally contain from 0.1 to 10%, especially from 0.25 to 3%, by weight of each of the dithiolan and the benzoazole.

Other ingredients conventionally employed in biocidal compositions for water treatment can be included if desired.

In particular biodispersants can be incorporated especially phenol ethoxylates of the formula:

where x is 2 to 40, especially 4. Typically biodispersants are present in an amount from 1 to 10, especially about 5, % weight.

While it will generally be more convenient to add the two active ingredients together they can be added separately if desired. Accordingly, the present invention also provides a method for treating an aqueous system which comprises incorporating therein a dithiolan as defined above and a benzoazole as defined above.

Typically the active ingredients are present in an amount from 1 to 500, preferably 1 to 100, and especially 1 to 25, ppm (active).

The following Examples further illustrate the present invention: EXAMPLE 1 Pseudomonas fluorescens previously isolated from an industrial cooling system water sample was grown on nutrient agar. Dilutions were prepared in Ringers solution, using standard microbiological techniques, to obtain bacterial counts of between 105 - 106 organisms per ml when incubated at 22 C for 3 days on nutrient agar.This bacterial suspension was then exposed for 1, 2 and 4 hours to various concentrations of 2-(thiocyanomethylthio)benzothiazole and 5oxo-3,4-dichloro-1,2-dithiolan both alone and in combination at different ratios, namely: Formula 1 TCMTB 2.5 (80% active) N - Methyl Pyrrolidone 10.0 Butyl Diglycol 87.5 Formula 2 TCMTB 1.75 (80% active) N - Methyl Pyrrolidone 10.0 Dithiolan 5.0 (10% active) Butyl Diglycol 83.25 Formula 3 TCMTB 1.25 (80% active) N - Methyl Pyrrolidone 2.0 Dithiolan 10.0 (10% active) Diethylene Glycol 86.75 Formula 4 TCMTB 0.625 (80% active) N - Methyl Pyrrolidone 2.0 Dithiolan 15.0 (10% active) Diethylene Glycol 82.375 Formula 5 Dithiolan 20.0 (10% active) N-Methyl Pyrrolidone 10.0 Butyl Diglycol 70.0.

At the various contact periods samples were taken and incubated at 2200 for 3 days on nutrient agar and surviving bacteria counted.

For each contact period and ration of biocides studied, graphs were constructed of per cent bacteria surviving as a function of biocide concentration.

The result obtained can be seen in Table 1.

EXAMPLE 2 A Penicillium sp previously isolated from an industrial water system was grown on Rose Bengal Chloramphenicol agar base. Serial dilutions were prepared in Ringers solution using standard microbiological techniques to obtain fungal counts of between 104 - 105 colony forming units per ml when incubated at 300C for 3 days on Rose Bengal Chloramphenicol agar base. This fungal suspension was then exposed for the same contact periods and to the same concentrations of 2 (thiocyanomethylthio) benzothiazole and 5-oxo-3,4-dichloro1,2-dithiolan as for EXAMPLE 1.

At the stated contact periods, samples were taken and incubated at 300C for 3 days on Rose Bengal Chloramphenicol agar base and#surviving fungi counted, for each contact period and ratio of biocide concentration.

The results obtained can be seen in Table 2.

Figures 1 and 2 clearly show that the combination tested displayed synergy because much less than the theoretical amounts were needed to achieve 100% kill.

TABLE 1 Pseudomonas fluorescens

CONTACT PERIOD CONCENTRATION % KILL (HOURS) (ppm) RATIO OF TCMTB:DITHIOLE 2:0 1.5:0.5 1:1 0.5:1.5 0:2 FORMULA 1 FORMULA 2 FORMULA 3 FORMULA 4 FORMULA 5 1. O 100 0 0 100 86.30 0 200 0 0 100 | 98.32 97.3 400 0 0 100 100 ' 97. 31 600 0 0 100 100 . 100 800 0 0 100 100 | 100 2.0 100 0 0 100 93.93 96.9 200 0 0 100 99.92 99.8 400 0 0 100 100 99.98 600 0 0 100 100 100 800 0 0 100 100 100 4.0 100 0 0 100 99.98 99.98 200 0 98.7 100 100 100 400 0 100 100 100 100 600 90.55 100 100 100 100 800 100 100 100 TABLE 2 Penicillium sp

CONTACT PERIOD CONCENTRATION % KILL (HOURS) (ppm) RATIO OF TCMTB:DITHIOLE 2:0 1.5:0.5 1:1 0.5:1.5 0:2 FORMULA 1 FORMULA 2 FORMULA 3 FORMULA 4 FORMULA 5 1.0 100 3.27 82.65 100 | 100 100 100 200 33.14 100 100 100 100 400 42.96 100 100 100 100 600 44.38 100 100 100 100 1 800 55.48 100 | 100 100 100 2.0 | 100 41.68 100 | 100 100 1100 200 53.06 | 100 ssj 100 ,' 100 | 100 400 56.19 | 100 100 100 100 600 93.53 | 100 100 100 100 800 93.83 1 100 2 100 | 100 1 100 4.0 100 47.79 2 100 ~ 100 | 100 100 200 64.72 i 100 | 100 ~ 100 100 400 90.26 i, 100 1 100 1 100 100 600 96.17 | 100 | 100 | 100 100 800 100 | 100 | 100 1 100 100

Claims

1. A method for treating aqueous systems which comprises incorporating therein a dithiolan having the general formula:

wherein each of X and Y, which may be the same or different, represents fluorine, chlorine or bromine, especially chlorine, and a benzoazole having the general formula:

2. A method according to claim 1 in which X and Y both represent chlorine.

3. A method according to claim 1 or 2 in which Z represents sulphur, A represents hydrogen and n is 1.

4. A method according to any one of claims 1 to 3 in which the weight ratio of dithiolan to benzoazole is from 3:1 to 1:3.

5. A method according to any one of the preceding claims in which the dithiolan and benzoazole are each present in an amount from 1 to 500 ppm.

6. A method according to claim 5 in which the dithiolan and benzoazole are each present in an amount from 1 to 25 ppm.

7. A composition suitable for addition to an aqueous system which comprises at least one dithiolan as defined in claim 1 or 2 and at least one benzoazole as defined in claim 1 or 3.

8. A composition according to claim 7 in which the weight ratio of dithiolan to benzoazole is from 3:1 to 1:3.

9. A composition according to claim 7 or 8 which comprises 0.1 to 10% by weight of each of the dithiolan and benzoazole.

10. A composition according to claim 9 which comprises 0.25 to 3% by weight of each of the dithiolan and benzoazole.

11. A composition according to any one of claims 7 to 10 which comprises one or more solvents.

12. A composition according to claim 11 which comprises methyl carbitol, butyldiglycol, Nmethylpyrrolidone, tripropylene glycol n-butyl ether, dimethylformamide or diethylene glycol monoethyl ether.

13. A composition according to any one of claims 7 to 12 which comprises 1 to 10% by weight of a biodispersant.

14. A composition according to any one of claims 7 to 13 in which the biodispersant is a phenol ethoxylate.

15. A composition according to claim 7 substantially as described in the Example.

16. A method according to any one of claims 1 to 6 which comprises adding a composition as claimed in any one of claims 7 to 15.

17. A method according to claim 1 substantially as described in the Example.