GB2250737A

GB2250737A - Biocide

Info

Publication number: GB2250737A
Application number: GB9026965A
Authority: GB
Inventors: Karen Rimmer; Andrew Stephen Jamieson
Original assignee: WR Grace and Co Conn; WR Grace and Co
Current assignee: WR Grace and Co Conn; WR Grace and Co
Priority date: 1990-12-12
Filing date: 1990-12-12
Publication date: 1992-06-17
Also published as: GB9026965D0

Abstract

A composition suitable for addition to an aqueous system comprises a dithiolan having the formula: <IMAGE> wherein each x and y, which maybe the same or different represents flourine, chlorine or bromine, and an alkylthioalkyamine of the formula CH3-(CH2)x-S-(CH2) y-NH2 where x is an integer from 7 to 11 and y is 2 or 3.

Description

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

Biocides 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-dichloro-l,2-dithiolan (commonly referred to as "dithiolan"). While this is, in general, an effective biocide for aqueous systems it is, unfortunately, not satisfactory when the system has a high pH. Indeed very few biocides are effective against bacteria, algae and fungi over a broad pH range. Under such circumstances it is frequently the case that a mixture of biocides is employed such that the combination possesses wide biocidal activity.

It has been found that biocides which are generally effective at high pH include alkylthioalkylamines and, in particular, that known as "DTEA" which is 2-(decylthio) ethanamine hydrochloride. We, therefore, concluded that a mixture of DTEA and dithiolan might be an effective biocidal composition. Unfortunately it is not possible to obtain a stable homogeneous composition simply by mixing the ingredients. Until now it has been impossible to formulate dithiolan with aqueous active ingredients because of incompatible problems. Unfortunately DTEA is only available commercially as an aqueous propylene glycol solution which does not form a storage stable formulation with dithiolan.It has now been found, according to the present invention, that by using special solvents it is possible to obtain a storage stable mixture of the dithiolan and the 2 (decylthio)ethanamine, or a salt thereof, (referred to simply as "DTEA") and thereby a biocidal composition which is effective over a wide range of conditions.

According to the present invention there is provided a composition suitable for addition to an aqueous system which comprises a dithiolan having the formula set out below, a solvent for the dithiolan, an alkylthioalkylamine of the formula: CH3-(CH2),-S-(CH2)y NHZ in which x is an integer of 7 to 11 and y is 2 or 3, an acid addition salt thereof, and also a solvent which is less hydrophobic than the solvent for the dithiolan which has the effect of stabilising the solution of dithiolan and the solution of alkylthioalkylamine. It has been found that such compositions are stable over several days with no separating out of components.Suitable acid addition salts for the thioalkylamine include those of mineral acids such as HC1, HBr, H3P04, HNO3 and H2S04, and organic acids such as carboxylic acids e.g. acetic, propionic, butyric and glycolic acids. The preferred salt is the hydrochloride. - Preferably x is 9 and y is 2 i.e. DTEA and the following discussion will refer, for convenience, to DTEA but it is to be understood that it applies equally to the other thioalkylamines and their salts.

The way of preparing the compositions has an important bearing on their stability. For this purpose it is desirable to protect the dithiolan from the aqueous DTEA solution by first adding the solvent for it, for example tripropylene glycol n-butyl ether (TPnB) and then propylene glycol or other solvent which acts as the stabilising solvent, to the dithiolan and finally adding the DTEA, typically as an aqueous propylene glycol solution, preferably after thorough mixing.

Alternatively the solvents can be added to the DTEA and the dithiolan added to the resulting mixture. That this is effective is surprising because DTEA is not stable in propylene glycol by itself. Also mixtures of DTEA with the dithiolan solution or with the dithiolan solvent are not compatible. The reason for using propylene glycol is because this relatively polar solvent allows the DTEA to solubilise in the relatively non polar environment of the dithiolan and solvent therefor.

The dithiolan is relatively expensive but the concentration needed is low. However, what this means is that in order that it can be dispersed satisfactorily in a system relatively large amounts of solvent has to be used. The commercially available solution of DTEA is only somewhat more expensive than the solvent. Accordingly, by means of the present invention it is possible to replace some of the dithiolan solvent by the DTEA solution without adding significantly to expense while at the same time making the formulation biocidally significantly more effective.

Although TPnB is the preferred solvent for dithiolan other effective solvents can be employed such as N-methyl pyrrolidone and butyl diglycol.

As the DTEA is available as an aqueous propylene glycol solution it will be appreciated that it is advantageous to also use propylene glycol as well as the stabilising solvent, since this ensures compatibility but other solvents can be used for this purpose, especially other glycol solvents such as diethylene glycol, or butyl diglycol which is less preferred.

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 relative concentrations of the various ingredients in the composition are suitably as follows (by weight): Stabilising solvent: 25 to 50%, preferably 30 to 40%, especially about 33%; Dithiolan solvent: 25 to 60%, preferably 30 to 50% especially about 50%; DTEA: 0.5 to 10%, preferably 0.5 to 5% especially about 1% and Dithiolan: 0.25 to 3%, preferably 0.5 to 1.5%, especially about 1%.

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

If the composition contains about 1% by weight active of each of the two biocides then typical amounts of the composition to be added to the aqueous system will be from 10 to 500 ppm, especially from 25 to 200 ppm. The composition can be added to the aqueous system in a conventional manner.

The following Example further illustrates the present invention.

EXAMPLE The following formulation was prepared by the method described above: DTEA 6.67 % (by weight) (15 % active concentration in aqueous propylene glycol) Dithiolan 10.00 % (10 t active concentration in propylene glycol) TPnB 50.00 % Propylene glycol 33.30 % This, referred to as A, was added to a typical industrial cooling water sample at concentrations of 25, 50, 100 and 200 ppm. A commercial product, namely Kathon WT (a mixture of isothiazolones), referred to as B, was similarly evaluated. The results obtained are tabulated below. They are expressed in terms of surviving bacteria per ml following exposure to the biocide for 1, 2 and 4 hours.

BIOCIDE CONCENTRATION BIOCIDE CONTACT BIOCIDE j 25 1 50 PERIOD (Hours) | PPM | PPM 0.5 A t'4.05 x 105 | 2.22 x 105 B 1.0 x 106 i 1.0 x 106 1100 200 0.5 A 14.9 x 104 | 1.48 x 104 B 17.65 x 105 4.61 x 105 Control Result + 1.0 x 106 orgs/ml

BIOCIDE CONTACT PERIOD (Hours) PPM PPM 2.0 1 A 5.3 x 104 4.8 x 104 B 6.9 x 104 7.4 x 104 ------------------------ 100 200 2.0 A | 3.06 x 104 5.49 x 103 B | 9,50 x 104 3.90 x 104 Control Result + 3.98 x 105 orgs/ml It can be seen that the composition of this invention is more effective than the commercially available product.

Claims

1. A composition suitable for addition to an aqueous system which comprises a dithiolan having the formula:

wherein each of X and Y, which may be the same or different, represents fluorine, chlorine or bromine, a solvent for the dithiolan, an alkylthioalkylamine of the formula: CH3-(CH2)X- S-(CH2)y-NH2 in which x is an integer from 7 to 11 and y is 2 or 3, or an acid addition salt thereof, and a solvent which is less hydrophobic than the solvent for the dithiolan which has the effect of stabilising the solution of dithiolan and the solution of the 2-(decylthio) ethanamine.

2. A composition according to claim 1 in which X is chlorine.

3. A composition according to claim 1 or 2 in which the solvent for the dithiolan is tripropylene glycol nbutyl ether, N-methylpyrolidone or butyl diglycol.

4. A composition according to any one of claims 1 to 3 in which the thioalkylamine is used in the form of its hydrochloride.

5. A composition according to any one of claims 1 to 4 in which the thioalkylamine is 2-(decylthio)ethanamine.

6. A composition according to any one of the preceding claims in which the less hydrophobic solvent is propylene glycol or diethylene glycol.

7. A composition according to any one of the preceding claims which comprises 0.25 to 3% by weight of the dithiolan, 0.5 to 10% by weight of the thioalkylamine, 25 to 60% by weight of the solvent for the dithiolan and 25 to 50% by weight of the less hydrophobic solvent.

8. A composition according to claim 7 which contains 0.5 to 1.5% by weight of the dithiolan, 0.5 to 5% by weight of the thioalkylamine, 30 to 50% by weight of the solvent for the dithiolan and 30 to 40% by weight of the less hydrophobic solvent.

9. A composition according to any one of the preceding claims which also comprises a biodispersant.

10. A composition according to claim 9 in which the biodispersant is a phenol ethoxylate.

11. A composition according to claim 1 substantially as described in the Example.

12. A process for preparing a composition as claimed in any one of the preceding claims which comprises adding the solvent for the dithiolan and the less hydrophobic solvent to the dithiolan and then adding the alkylthioalkylamine to the resulting mixture.

13. A process according to claim 12 in which the alkylthioalkylamine is added as an aqueous propylene glycol solution.

14. A method of treating an aqueous system which comprises adding thereto a composition as claimed in any one of claims 1 to 11 or one obtained by a process as claimed in claim 12 or 13.

15. A method according to claim 14 which comprises adding 10 to 500 ppm of the composition.

16. A method according to claim 15 which comprises adding from 25 to 200 ppm of the composition.