GB2322128A - Part polymeric-part inorganic coagulant - Google Patents

Abstract

A coagulant is formed by the reaction of at least one inorganic coagulant with at least one polymer (preferably cationic) derived from one or more vinyl monomers. The inorganic coagulant may be an Al or Fe salt and the vinyl monomer may be selected from the group consisting of dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, polydadmac, epichlorhydrin and dimethylamine. Preferably the process for forming the coagulant comprises maintaining a solution of the inorganic coagulant at 25-80‹C, adding the polymer(s) to the solution, stirring the solution for at least 15 minutes, cooling it and then filtering it. The mixed coagulant (ie coagulant compound) produced by this process contains an organic-inorganic chain and is suitable for clarifying drinking water.

Description

Mixed Coagulants Raw water contains various contaminants which must be eliminated in order to obtain drinking water. The most usual contaminants are organic substances, such as humic acids, cations, for example Fe++, and anions, for example SO4-, and the like.

The usual method for clarifying influent water in drinking water treatment plants which contains said contaminants involves dosing with coagulants based on salts of aluminium and iron such as aluminium sulphate, ferric sulphate, ferric chloride, aluminium polyhydroxychloride or aluminium polyhydroxychlorosulphate.

This method gives rise to several problems: - excessive sensitivity of raw water to the pH because of the narrow pH range in which coagulation is effective; - coagulant dosing must be accurate because over-underdosing or a pH outside the effective range results in free Awl+++ and Fe+++ cations; - high dose requirements for coagulants, which cause cost, stocks and filter - maintenance problems.

The applicant has found a solution to the aforementioned problems by using as coagulants products having considerably greater chain lengths obtained by a synthesis of the aforementioned conventional coagulants with water-soluble cationic polymers derived from the polymerization or condensation of derivatives of vinyl monomers.

The novel coagulants, which may be described as mixed coagulants because they possess an organic-inorganic chain, have further advantages when used in water clarification: - the flocculates formed during decantation are more resistant, without breakdown, to the agitation and churning produced in water for pumping; - decantability is improved; - coagulation kinetics is improved, and the difference compared to that of conventional coagulants increases in proportion to decreasing water temperature; - water quality parameters, such as colour, turbidity and residual cations, such as Awl+++, are improved.

The novel coagulants are synthesized by a novel method which modifies those used heretofore for the preparation of traditional coagulants based on salts of iron and aluminium. The coagulants heretofore known are: aluminium sulphate Al2(SO4)3 ferric chloride FeCl3 aluminium polyhydroxychlorosulphate AlnC lx(OH)y(SO4)z ferric sulphate Fe2(SO4)3 to the structure of which salts are added, once they are produced or during their production process, organic chains of water-soluble cationic polymers obtained by condensation or polymerization of radicals of vinyl monomers, and preferably of one or more of the following monomers (or their derivatives, such as salts or quaternaries): Dimethylaminoethyl acrylate Dimethylaminoethyl methacrylate Diethylaminoethyl acrylate Diethylaminoethyl methacrylate Diallyldimethyl ammonium chloride Epichlorhydrin Dimethylamine the solution being stirred for at least 15 minutes, but preferably for more than 1 hour and at a temperature higher than room temperature, when it is then cooled and filtered.

The treatment of water with these mixed coagulants consists of dosing, upon completion of the usual preoxidation stages for this type of mixed coagulant instead of for the coagulants normally employed, either to achieve microflocculation over sand filters, pressure filtration, decantation or any other type of physicochemical process used in the treatment of drinking water that includes the use of traditional coagulants such as those described above.

In the following examples, some of the aforementioned monomers were used, although the use of their salts, for example, Na or quaternized derivatives, would remain within the scope of the invention.

Example 1.

After obtaining by known methods in a stirred reactor equipped with a heating jacket basic aluminium polyhydroxychlorosulphate (10% concentration, as A1203, 50% basicity and 2% sulphate content), Superfloc C 577 (a cationic polymer obtained by condensing epichlorhydrin with dimethylamine to a molecular weight of 75,000 g/mol and which is available commercially as a 50 % aqueous solution) was added to the reaction mass at 55"C in an amount such that the active polymer constituted 1% of the total weight of the final product. Stirring was maintained at a temperature in the range of 50-60"C for one hour, and the mixture was then cooled and filtered to produce a mixed coagulant.

Example Into a stirred reactor having a capacity of 1.5 litres and equipped with a heating jacket were placed 698 grams of demineralized water, 147 grams of 63% concentration hydrated alumina (as Al203) and 255 grams of 98% concentration V:F7 sulphuric acid.

The reactor was sealed and the mixture heated to 140"C with stirring for two hours. The temperature was lowered to 60"C, whereupon were added 22.0 grams of Superfloc C 577 (a cationic polymer obtained by condensing epichlorhydrin with dimethylamine to a molecular weight of 75,000 glmol and which is available commercially as a 50% aqueous solution). Stirring was maintained at a temperature in the range of 55-65"C for one hour, and the mixture was then cooled and filtered to produce a mixed coagulant.

Example After obtaining by known methods in a stirred reactor equipped with a heating jacket basic aluminium polyhydroxychlorosulphate (10% concentration, as A1203 50% basicity and 2 % sulphate content), a cationic polymer obtained by polymerizing radicals of diallyl dimethyl ammonium chloride to a molecular weight of 200,000 glmol and which is available commercially as a 20% aqueous solution, was added to the reaction mass at 48"C in an amount such that the active polymer constituted 0.5% of the total weight of the final product. Stirring was maintained at a temperature in the range of 45-50"C for one hour, and the mixture was then cooled and filtered to produce a mixed coagulant.

Example 4.

Into a stirred reactor having a capacity of 1.5 litres and equipped with a heating jacket were placed 698 grams of demineralized water, 147 grams of 63 % concentration hydrated alumina (as Awl203) and 255 grams of 98% concentration sulphuric acid. The reactor was sealed and the mixture heated to 140"C and stirred for two hours. The temperature was lowered to 60"C, whereupon were added 11.0 grams of a cationic polymer obtained by polymerizing radicals of diallyl dimethyl ammonium chloride to a molecular weight of 1,000,000 g/mol and which is available commercially as a granular solid. Stirring was maintained at a temperature in the range of 55-65"C for two hours, and the mixture was then cooled and filtered to produce a mixed coagulant.

The materials, dimensions, proportions and, in general, any other incidental or secondary details that do not alter, change or modify the essence of the proposed process can be varied.

The terms in which this report is drafted are a true and accurate reflection of the object described and should be interpreted in their widest sense and never in a limitative manner.

Claims (8)

1. A process for producing mixed coagulants for water clarification, characterized in that to a solution of an inorganic coagulant for water clarification, maintained at a temperature in the range of 25-80 C, is added at least one water-soluble cationic polymer derived from one or more vinyl monomers, in an amount that constitutes between 0.1 and 10% of the total weight of the final product, the solution being stirred for at least 15 minutes at a temperature higher than room temperature, whereupon the mixture is cooled and filtered.

2. A process for producing mixed coagulants for water clarification, according to the preceding claim, characterized in that the vinyl monomer or monomers are one or several of the following monomers: Dimethylaminoethyl acrylate D imethylaminoethyl methacrylate Diethylaminoethyl acrylate Diethylaminoethyl methacrylate Diallyldimethyl ammonium chloride Epichlorhydrin Dimethylamine

3. A process for producing mixed coagulants for water clarification, according to the preceding claims, characterized in that the stirring temperature of the solution is in the range of 30-80 and the duration of stirring is more than one hour.

4. A mixed coagulant for water clarification, characterized in that its structure comprises an inorganic portion derived from at least one coagulant salt of Al or Fe and an organic portion consisting of a polymer derived from a vinyl monomer.

5. A mixed coagulant for water clarification, according to claim 4, and obtained in accordance with the process claimed in claims 1 to 3.

6. A method for water clarification, characterized in that, upon completion of the preoxidation stage, a mixed coagulant according to those claimed in the preceding claims is dosed.

7. A process for producing mixed coagulants for water clarification as claimed in claim 1 and substantially as described herein.

8. A method as claimed in claim 7 and substantially as described herein.

8. A mixed coagulant for water clarification as claimed in claim 4 and substantially as described herein.