EP2566820A1

EP2566820A1 - Process for treating waste water resulting from the synthesis of a halogenated vinyl polymer

Info

Publication number: EP2566820A1
Application number: EP11731016A
Authority: EP
Inventors: Pascal Dufour
Original assignee: Kem One SAS
Current assignee: Kem One SAS
Priority date: 2010-05-03
Filing date: 2011-04-18
Publication date: 2013-03-13
Also published as: FR2959503A1; FR2959503B1; WO2011138537A1

Abstract

The present invention relates to a process for treating waste water resulting from the synthesis of a halogenated vinyl polymer, having a pH of between 5 and 10 and preferably between 6 and 8, by flocculation of particles in suspension in said waste water, said process comprising a step of bringing said waste water into contact with at least one tannin and at least one cationic polymer.

Description

The present invention relates to a process for the treatment of a wastewater resulting from the synthesis of a halogenated vinyl polymer, such as PVC, including wastewater comprising at least one embodiment of the present invention. fine solid particles in suspension.

The polymerization processes of polyvinyl chloride, and more particularly the processes in suspension or in emulsion in water comprise the following steps:

the introduction into water of an initiator generating free radicals, generally a peroxide, solid or liquid additives, in the form of fine particles in suspension or in solution in water, of which mention may be made of protective colloids, dispersing agents or suspending agents (cellulose ethers, partially hydrolysed polyvinyl acetate, polyvinyl alcohol or "PVA", gelatin, etc.). , and

the addition with stirring monomers vinyl chloride, and

heating the reaction mixture obtained to obtain polyvinyl chloride.

The polyvinyl chloride obtained is in the form of an aqueous suspension comprising part of the solid additives introduced at the beginning of the process, in the form of fine particles suspended in water.

The polyvinyl chloride thus synthesized is solid and has a uniform particle size obtained by implementing precise amounts of additives. Polyvinyl chloride is then separated from the particles in suspension after its polymerization, usually by filtration, using for example a wringer. The water is often cooled to ambient temperature before being discharged by systems for recovering heat upstream of a physicochemical treatment station.

The water resulting from this filtration, hereinafter referred to as "wastewater" that is found in particular at the exit of the wringer is most often directed to a physicochemical or biological treatment station before subsequent rejection in a course of water for example.

In order to obtain an effective separation of the solids present in the aqueous suspension obtained at the end of the process for the synthesis of polyvinyl chloride, flocculating agents are used.

The flocculation systems used to date, most often implement salts of polyaluminium chloride in combination with organic flocculants. They do not allow total precipitation of the suspended particles, and the physicochemical treatments of water mentioned above are then supplemented by treatment in the biological station before discharge.

Ferric chloride is also used as a flocculating agent, but does not provide sufficient reduction in turbidity even at high dosage, for example 1000 mg / l of water.

It is also known from European Patent Application EP0509891 the use of tannins as flocculating agents intended to eliminate polyvinyl alcohol which may be present in wine, at acid pH, close to 2. The use of tannin as a flocculating agent under the conditions described in this patent application, that is to say at very acidic pH is not applicable to a wastewater treatment process resulting from the polymerization of halogenated vinyl monomers. Indeed, flocculation is well obtained at a pH of about 2 or 2.5 (example 1), but such a process is however not satisfactory since it makes it necessary to modify the pH of the wastewater by acid acidification. hydrochloric acid, which is not feasible industrially because the traces of chlorides cause very acidic pH pitting corrosion for stainless steel used in most reactors.

In addition, the use of tannins as flocculants to remove particles in suspension in waste water at a pH of about 6 or 7 does not give a satisfactory result (Example 1).

There is therefore a permanent need for a new wastewater treatment process resulting from the synthesis of a halogenated vinyl polymer, presenting an alternative to known processes, and whose effectiveness makes it possible to obtain sufficiently pure water at the end of the process. treatment so that it can be recycled, that is to say, within the meaning of the present invention, reused at the beginning of the vinyl chloride monomer polymerization process, which implements water.

In particular, there is a need for a new process for treating wastewater from the synthesis of a halogenated vinyl polymer which is effective on waste water whose pH is between 6 and 8. Such a process is particularly interesting industrially because it does not require prior acidification of the wastewater, which represents a cost important and a major disadvantage as recalled above.

The inventors have shown that tannins, for example ellagic, gallic or catechetical tannins, especially those extracted from natural raw materials, such as wood or walnut or other, combined with cationic polymers can precipitate colloids, especially PVA, to end up after decantation with a clear water free of particles in suspension and this without modification of the pH of the water.

The subject of the invention is therefore a process for treating a waste water resulting from the synthesis of a halogenated vinyl polymer having a pH of between 5 and 10 and preferably of between 6 and 8 by flocculation of particles in suspension in said wastewater, said process comprising a step of contacting said wastewater with at least one tannin and at least one cationic polymer.

For the purposes of the present invention, flocculation means the formation of flocks from particles initially suspended in water, which aggregate into flocs, destroying the stability of the initial suspension and causing sedimentation and / or migration of said particles to the surface of the water.

As a preamble, it will be noted that the expression "between" or "between" must be interpreted, in the present description, as including the bounds cited.

The halogenated vinyl polymer may in particular be a fluorinated and / or chlorinated homo- or copolymer. It is usually a thermoplastic polymer.

A preferred example of chlorinated polymer is polyvinyl chloride or PVC. Such a polymer is especially marketed by the company ARKEMA under the trade name Lacovyl. Other chlorinated polymers useful in this invention are vinyl chloride copolymers with monomers such as acrylonitrile, ethylene, propylene, vinyl acetate, and polyvinylidene chloride or derivatives thereof. acrylic. It is also possible that the chlorinated polymer according to the invention is a mixture including at least two of the chlorinated polymers or copolymers above. In the case of vinyl chloride copolymers, it is preferable that the proportion of vinyl chloride units is greater than 25% and advantageously not more than 99% of the total weight of the copolymer.

As fluorinated polymers, mention may be made especially of those comprising one or more monomers of formula (I):

CFX = CHX '(I) where X and X' independently denote a hydrogen or halogen atom, preferably fluorine or chlorine, or a preferably perfluorinated perhalogenated alkyl radical, preferably with X = F and X '= H.

Examples of fluoropolymers that may be mentioned include:

polyvinylidene fluoride (PVDF),

copolymers of vinylidene fluoride with, for example, hexafluoropropylene (HFP), chlorotrifluoroethylene (CTFE), hexafluoropropylene (HFP), trifluoroethylene (VF3) or tetrafluoroethylene (TFE),

homo- and copolymers of trifluoroethylene (VF3), the fluoroethylene / propylene copolymers (FEP),

copolymers of ethylene with fluoroethylene / propylene (FEP), tetrafluoroethylene (TFE), perfluoromethylvinyl ether (PFMVE), chlorotrifluoroethylene (CTFE) or hexafluoropropylene

(HFP), and

- their mixtures,

Some of these polymers are in particular marketed by ARKEMA under the trade name Kynar ^® .

PVDF and PVC are preferred for use in the present invention.

For the purposes of the present invention, the term "tannin" means water-soluble phenolic compounds having a molecular mass of between 500 and 3000 Dalton, which can be grouped into two categories, hydrolysable tannins and condensed tannins.

The hydrolyzable tannins comprise a diene residue and an organic compound having at least one carboxylic function and a phenolic hydroxyl. Among the hydrolyzable tannins, mention may be made, by way of example, of the products of the esterification of the hydroxyl functions of glucose by acids such as gallic acid, cinnamic acid and, more generally, polyphenolic acids. More particularly, mention may be made of monomeric hydrolysable tannins such as gall tannin, or pentagalloylglucose which may come from plants of the family of ericaceous fagaceae, geraniaceous, aceraceous, ellagic tannin resulting from the reaction of glucose with hexahydroxydiphenic acid, which may be derived from gall oak gall, tannin dihydroellagic resulting from the oxidation of ellagic tannin, hydrolyzable tannins oligomers formed of acid gallic acid, ellagic acid and 2000 to 5000 dares, for example the rugosin of the meadow-queen, and the hamamelitanin of the witch hazel.

Condensed tannins also known as catechin tannins or proanthocyanidols include polymers of flavones-3-ol and anthocyanidins. Condensed tannins are based on phenols, others are mixtures of esters, glucose or other sugars. By way of example, mention may be made of fruit procyanidols such as catechol, epicatechol, gallocatechol and epigallocatechol. Procyanidols type B: a single interflavanic bond (C4 and C8) procyanidols type A: flavanic double bond (in C4 and C8 and C2 and C1), derived from horse chestnut and cinnamon, the proanthocyanidols in particular anthocyanidins: delphinidol (from cypress) and cyanidol. Most condensed tannins are anthocyanidins or proanthocyanidols.

Preferably, 1 to 100 mg of tannin are used per liter of waste water, and preferably 5 to 20 mg of tannin per liter of waste water.

For the purposes of the present invention, the term "cationic polymer" means a polymer derived from the condensation of dimethylamine and epichlorohydrin, diallyldimethylammonium polychloride, copolymers of acrylamide and quaternary esters or amides of acrylic acid or methacrylic. Among these polymers, mention may be made more particularly of the following cationic polymers:

(1) homopolymers or copolymers derived from acrylic or methacrylic esters or amides and in particular copolymers of acrylamide and dimethylaminoethyl methacrylate quaternized with dimethyl sulfate or dimethyl halide, copolymers of acrylamide and methacryloyloxyethyltrimethylammonium chloride, copolymer of acrylamide and methacryloyloxyethyltrimethylammonium methosulfate, quaternized vinylpyrrolidone / acrylate or dialkylaminoalkylmethacrylate copolymers or no, the dimethylaminoethyl methacrylate / vinylcaprolactam / vinylpyrrolidone terpolymers, and the quaternized vinylpyrrolidone / dimethylaminopropyl methacrylamide copolymer.

(2) quaternized polysaccharides such as guar gums containing cationic trialkylammonium groups.

(3) Quaternary copolymers of vinylpyrrolidone and vinylimidazole,

(4) chitosans or their salts, especially chitosan acetate, lactate, glutamate, gluconate or pyrrolidonecarboxylate.

(5) Cationic cellulose derivatives such as cellulose copolymers or cellulose derivatives grafted with a water-soluble monomer comprising a quaternary ammonium group such as hydroxyalkylcelluloses, such as hydroxymethylhydroxyethyl or hydroxypropylcelluloses grafted in particular with a salt of methacryloyloxyethyltrimethylammonium, methacrylamidopropyltrimethylammonium or dimethyldiallylammonium.

Preferably, 1 to 100 mg of cationic polymer per liter of wastewater are used, and preferably 2 to 20 mg of cationic polymer per liter of waste water.

By "particles" is meant within the meaning of the present invention, solid particles having a diameter between 0.1 and 200 microns as measured by particle size by diffraction and scattering by using an apparatus MAS ERS I ZER2000 ^® from MALVERN, and / or micelles.

Preferably, the particles comprise a population of particles having a diameter of between 0.1 and 50 micrometers (μm), in particular comprising PVA and a population of particles with a diameter of between 1 and 200 μm, in particular comprising particles of PVC.

Preferably, the suspended particles comprise compounds selected from protective colloids, dispersing agents or suspending agents alone, in admixture or in combination with very small particles of halogenated vinyl polymer. By way of example, mention may be made of cellulose ethers, partially or completely hydrolysed polyvinyl acetate, polyvinyl alcohol or PVA, gelatin, cellulose polymers, preferably hydroxypropylmethylcellulose, and their mixtures.

For the purposes of the present invention, used water is understood to mean a water comprising the particles defined above, but also halogenated vinyl polymer in the form of fine particles, and dissolved organic solvents originating from solutions of organic peroxide solvents. The wastewater before treatment can be characterized as follows.

Suspended substances (MES): from 50 to 300 mg / 1

PVA content: 5 to 30 mg / l, COD 200 to 400 mg / 1, pH greater than or equal

and up to 10.

COD is the Chemical Oxygen Demand measured by oxidation to potassium dichromate according to the method described in the standard "Standart Methods for the Examination of Water and Waste Water" (15th edition). Said wastewater can be put in contact simultaneously with the polymer. cationic and tannin.

The method of the invention allows the treatment of waste water whose temperature is between 10 ° C and 95 ° C. It is therefore not necessary to cool the wastewater before treating it, which is a considerable advantage when it is intended to reuse the water in a new polymer synthesis cycle. This embodiment avoids the use of heat recovery systems or heat exchangers.

In a preferred embodiment, said waste water is contacted first with a cationic polymer and then with a tannin. This embodiment makes it possible to promote the formation of flocs. Preferably, the cationic polymer is added and then left in contact with the waste water for 30 seconds to 15 minutes, and preferably 1 minute to 5 minutes, then the tannin is added.

This embodiment is preferably implemented when the water to be treated has a temperature between 10 and 30 ° C.

Alternatively, when the water to be treated has a temperature between 30 ° and 95 ° C, and preferably between 35 and 75 ° C, said wastewater may be contacting simultaneously with the cationic polymer and with the tannin.

When the wastewater is in contact with both the cationic polymer and the tannin, the method of the invention may comprise a ripening step during which flocs form and grow. Thus, preferably, said waste water is contacted 1 to 60 minutes, preferably 5 to 30 minutes, and most preferably 15 minutes with at least one tannin and at least one cationic polymer.

It is possible to complete the sedimentation of the flocs formed by the tannin by adding an electrically neutral polymer, for example the solid polymer marketed by the company Nalco under the trade name Prosedim AS 34 for increasing the size of the flocs into a cluster of size up to 1 mm, 1 cm or more.

The method which is the subject of the invention allows a very efficient precipitation of the particles in suspension, and in particular of polyvinyl alcohol (examples 2 and 3).

However, the precipitation of polyvinyl alcohol is essential when it is desired to reuse the treated wastewater at the beginning of the polymerization process of the halogenated vinyl monomers. In fact, the presence of PVA in the water used at the beginning of the polymerization process would modify the quality of the halogenated vinyl polymer obtained in an unacceptable manner, by modifying the particle size of the particles of said polymer.

Thus, in a preferred embodiment of the invention, the wastewater resulting from the treatment by contacting said waste water with at least one tannin and at least one at least one cationic polymer is used during a halogenated vinyl polymer synthesis process.

This recycling can be directly integrated into the design of a halogenated vinyl polymer production unit.

In one embodiment of the invention, the treated water is further subjected to reverse osmosis treatment. Reverse osmosis is a tangential filtration, in which water supply flow moves parallel to the surface of a membrane. Significant pressure, greater than the osmotic pressure, is applied to the water, forcing it to cross the membrane in one direction. The membrane, permeable to liquids, separates the liquid into two distinct streams. On the one hand the permeate, which is purified water, ready to be recycled and on the other hand the retentate which contains all the salts and retained materials. By way of example, the water is treated by a spiral filtration module composed of a perforated central tube on which the membranes are fixed. Each membrane is equipped with a spacer that transports the permeate to the central tube. The spacers also provide equal distribution of the feed fluid over the entire surface of the membrane.

The invention is further illustrated by the following non-limiting examples.

In the following examples, the following commercial products were used:

"MK3810": strong cationic polymer sold by the company Servivap under the trade name MK3810. "AS 34": solid polymer marketed by Nalco under the trade name Prosedim AS 34.

"Tannin œnologique éllagique": tannin marketed by the company Laffort

Example 1 (comparative)

The pH of a wastewater taken from the spinning machines of a PVC production line is measured at 6.5 and then acidified with hydrochloric acid below 6.5 to 2. By flocculation with 10 mg of tannin per liter of water after pH adjustment, flocculation is ineffective above a pH of 2.5.

1

witness

no jar 2 3 4 5 6 without

AS34 pH 6.5 2 2.5 3 3.5 4 concentration of the tannin solution

10 10 10 10 10 10 mg / l

PVA supernatant assay after 2 h

7.51 3.49 3.49 5.10 5.96 6.42 decantation in mg / l

PVA determination supernatant after 72 h

5.02 2.64 2.47 2.73 3.49 4.43 decantation in mg / l

PVA supernatant assay after addition

of 1 ppm of AS34 and after 2 hours of 7.41 2.21 1.70 5.02 5.71 4.85 decantation in mg / l

Turbidity supernatant after addition of 1

ppm of AS34 and after 2 hours of 151 19 16 1 18 133 78 decantation in NTU

PVA supernatant assay after addition

of 3 ppm of AS34 and after 48 hours of 7.41 - - 4.26 5.71 4.94 decantation in mg / l Turbidity supernatant after addition of 3

ppm of AS34 and after 48 h of 1 17 - - 79 97 62 decantation in NTU

COD supernatant after adding 3

ppm of AS34 and after 72 hours of 158 140 136 150 146 170 decantation in mg / l

Turbidity supernatant after addition of 3

ppm of AS34 and after 72 hours of 65 - - 33 45 45 decantation in NTU

Turbidity supernatant after addition of 3

ppm of AS34 and after 10 days of 32 18 16 33 38 35 decantation in NTU

Example 2 (in accordance with the invention)

Process wastewater withdrawn from the spinners of a PVC production line was characterized as follows:

MES: 57 mg / l

Turbidity: 154 NTU

PVA content 7.5 mg / l

COD 160 mg / l

pH 6, 5

The unit NTU or "Nephelometric turbidy unit" is defined according to the method described in the reference book "Standart Methods for the Examination of Water and Waste Water (15th edition)"

A flocculation test is carried out with an increasing dose of strong cationic polymer MK3810 in the presence of oenological ellagic tannin (Laffort) at a dose of 10 mg / l. The cationic polymer is added before the selected tannin dose at 10 mg / l. The gallic tannins of the trademark GALLACOLL SP or gallic tannin marketed by Fluka are also suitable. The implementation conditions are as follows:

1) addition of Cationic polymer MK 3810: addition of 0.5 to 15 ppm in the wastewater and stirring for 1 minute at 200 rpm then 4 minutes at 40 rpm, then optionally stirring 15 minutes at 40 rpm,

2) addition of 10 ppm of the ellagic enological tannin marketed by Laffort, for 15 minutes at 40 revolutions per minute, then a magnification of the flocs is observed, then

3) addition of 0.5 ppm to 1 ppm of a flocculating agent AS 34, for 2 minutes at 40 revolutions per minute

The products are added in mg / 1 of commercial solution of MK3810 and in mg of dry solid for tannins and for the solid flocculant Prosedim AS 34.

The dry extract of commercial MK 3810, that is to say the solid residue after drying in an oven at 100 ° C. is 70% relative to the total weight of the residue.

The results after flocculation are as follows:

COD supernatant after addition

of 1 ppm of AS34 and after 2 hours 174 162 - 146 150 220 of decantation in mg / l

A ripening step of the flocculation with the tannin for about 15 minutes was performed. To accelerate the settling of the flocs, a polymer from the company Nalco brand Prosedim AS34 can be used at the end of floc formation.

At the optimal dosage of cationic polymer MK3810 and with 10 mg / l of gall tannin, the water has a low turbidity of 4 to 8 NTU and a low PVA content of 0.6 to 0.9 mg / l.

The insoluble compounds remaining in the treated water are less than 1 mg / l after passage of the decanted water supernatant membrane 0.22 ym.

Example 3 (in accordance with the invention) The process water of example 2, taken at 65 ° C. on a production unit in 20 liter cans, is used, a measurement such as that defined in example 2 is performed without waiting for a cooling of the water. The water at 65 ° C. (test 1) is found near 60 ° C. at the end of the test and that tested at 40 ° C. (test 2) is found at the end of the test at 35 ° C.

The two hot-water flocculation tests are carried out with the strong cationic polymer MK3810 at 5 mg / l in the presence of the enamel eutrophic tannin (Laffort) at a dose of 7 mg / l.

The conditions of implementation on hot water are simplified, by introduction of the polymer cationic, then with the other hand, at the same time, the previously predisposed tannin is introduced.

The reactor used for the test is equipped with a stirrer which is allowed to rotate for 1 minute at 200 rpm and then for 15 minutes at 40 rpm. 4 minutes before stopping the stirring helix, the prepared dose of AS34 is introduced to weigh down the flocks. After the next 20 minutes of settling without agitation, the turbidity of the surface water of the jar is measured with the turbidimeter.

The results on hot water after treatment are as follows:

These results demonstrate the advantage over hot water to immediately put the cationic flocculant and tannin.

Claims

A method of treating waste water from the synthesis of a halogenated vinyl polymer having a pH of from 5 to 10 and preferably from 6 to 8 by flocculation of particles suspended in said waste water, said process comprising a step of contacting said wastewater with at least one tannin and at least one cationic polymer.

Process according to claim 1, characterized in that the halogenated vinyl polymer is chosen from: polyvinyl chloride (PVC); copolymers of vinyl chloride with monomers selected from acrylonitrile, ethylene, propylene, or vinyl acetate; polyvinylidene chloride; and their mixtures.

Process according to Claim 1 or 2, characterized in that the halogenated vinyl polymer is chosen from fluorinated polymers comprising one or more monomers of formula (I):

CFX = CHX '(I) where X and X' independently denote a hydrogen or halogen atom, preferably fluorine or chlorine, or a preferably perfluorinated perhalogenated alkyl radical, preferably with X = F and

4. Method according to any one of claims 1 to 3, characterized in that the tannin is ellagic tannin or gallic tannin.

5. Method according to any one of claims 1 to 4, characterized in that the cationic polymer is chosen from homopolymers or copolymers derived from acrylic or methacrylic esters or amides, quaternized polysaccharides, quaternary copolymers of vinylpyrrolidone and vinylimidazole, chitosan or salts thereof, cellulose copolymers or cellulose derivatives grafted with a water-soluble monomer having a quaternary ammonium group and mixtures thereof.

6. Method according to any one of claims 1 to 5, characterized in that the particles in suspension are solid particles having a diameter of between 0.1 and 200 μm and / or micelles.

7. Process according to any one of claims 1 to 6, characterized in that the particles in suspension comprise compounds chosen from cellulose ethers, poly (vinyl acetate) partially or totally hydrolysed, polyvinyl alcohol. , gelatin, cellulosic polymers, preferably hydroxypropylmethylcellulose, and mixtures thereof.

8. Method according to any one of claims 1 to 7, characterized in that the water to be treated has a temperature between 10 ° and 30 ° C, and said waste water is contacted first with a cationic polymer then with a tannin.

Process according to any one of Claims 1 to 7, characterized in that the water to be treated has a temperature of between 30 ° and 95 ° C, and preferably between 35 and 75 ° C, and the said wastewater is brought into contact. simultaneously with the cationic polymer and with the tannin. 10. Process according to any one of the claims

1 to 7 and 9, characterized in that said waste water is brought into contact 1 to 60 minutes, preferably 5 to 30 minutes, and very preferably 15 minutes with at least one tannin and at least one cationic polymer.

Treatment process according to any one of Claims 1 to 10, characterized in that the wastewater resulting from the treatment by bringing said wastewater into contact with at least one tannin and at least one cationic polymer is implemented during of a process for synthesizing a halogenated vinyl polymer.