WO1996018656A1

WO1996018656A1 - Method for preventing reactor fouling in the synthesis of water soluble polymers

Info

Publication number: WO1996018656A1
Application number: PCT/FR1995/001620
Authority: WO
Inventors: Christian Collette; Catherine Garnier; Dominique Guenez; Denis Tembou Nzudie
Original assignee: Elf Atochem S.A.
Priority date: 1994-12-15
Filing date: 1995-12-07
Publication date: 1996-06-20
Also published as: FR2728273B1; FR2728273A1

Abstract

The method of the invention comprises treating the reactor and its impellers by spraying thereon a terpolymer dispersion, of which one comonomer is a fluorocarbon comonomer of general formula (I), wherein R1, R2, B and Rf have the meanings given in the disclosure. Compared to conventional methods comprising special coating steps, the method of the invention is advantageously efficient, extremely simple and of very low cost.

Description

METHOD FOR AVOIDING FOULING OF SYNTHESIS REACTORS

WATER-SOLUBLE POLYMERS

DESCRIPTION

TECHNICAL AREA

The invention relates to equipment for the production of hydrophilic polymers and more specifically superabsorbent polymers for water and aqueous solutions. This is to avoid sizing and encrusting of reactors and synthesis tools.

These drawbacks, which considerably affect the productivity and quality of the final products, are due to the formation of a highly adhesive hydrated gel during the polymerization of the acrylic type monomers from their aqueous solutions. Deposits are formed, both on the walls of the reactors and on the agitation and homogenization bodies of the reaction media, which affects the general yield of the operation, considerably hinders the recovery of the hydrophilic polymer, and requires cleaning. of the work tool.

PRIOR ART

It was thought that the tackiness of the gel could be reduced by very precise control of the concentration of the monomer in its aqueous solution (JP 02-153906). We also thought of working in materials made of electropolished steel (JP 54-10,387) which proved to be quite ineffective in themselves. Attempts have been made to improve its behavior, without much success it seems, by various measures, in particular by keeping the reactor envelope at low temperature (JP 03-041104 - EP 0343 919). We then used materials coated with a fluorinated resin (US 4,625,001 or JP 57-63,305) on which the quantity of polymer retained is low and its adhesion low, which allows cleaning with low pressure guns. The drawbacks of this process are numerous, however. The coatings are to be renewed on average every three months, and they require the complete disassembly of the reactor and its dispatch to an equipped subcontractor. The loss of production (about 12 days per year) is very significant and the cost of the operation high. This is done in ovens of limited size, which consequently limits the size of the reactors capable of such treatment. Another drawback lies in the significant thickness (a few hundred micrometers) of the coating, which reduces the heat exchange efficiency of the wall of the reactor. STATEMENT OF THE INVENTION

We have now found that the spraying of an anti-dust agent judiciously chosen from partially fluorinated terpolymers on the surface of an electropolished reactor, the degree of roughness of which is less than 4 μm, and on its stirring device makes it possible to combine the advantages of the two systems without retaining the disadvantages. The invention consists in spraying an aqueous solution or suspension containing the fluorinated anti-scouring agent onto the surfaces of an electropolished reactor and of its agitating members which are called to be successively in contact with the reverse suspension of aqueous hydrophilic monomers and of the polymer gel suspension. After drying, a thin film (from 1 to 10 nM) of low surface energy is formed which is both hydrophobic and oleophobic and has a low adhesion tension. The lifespan of such a treatment is limited to durations of the order of a week and a new application of the product should be carried out as soon as there is an increase in the size or encrusting. These are only minor drawbacks with regard to the ease of implementation of the method and its insignificant cost.

The choice of anti-dust agent is paramount. According to the invention, a terpolymer resulting from the copolymerization of three monomers X, Y and Z defined as follows is used. X is a fluorocarbon monomer of formula:

R ₂ 0

R ₁ - CH = CC- 0 -B -Rf where R-] and R2 are together or independently H or CH3, where B is a bivalent sequence:

- (CH2-CH2) j- with i taking values from 1 to 6, preferably 1 to 3, or also a group -C2H4-SO2-NR-C2H4- in which R is either CH3 or C ₂ H ₅ , and where Rf is a perfluorinated residue -C _n F2n + l - with 6 <n <10,

Y a monomer of formula:

R ₂ O

R, - CH = CC - O - CH ¹ m 2m + 1

in which Ri and R2 have the same meaning as above, and where C _m H2 _m + ι is an aliphatic or cycloaliphatic residue in which m can take all the values from 1 to 22, preferably from 12 to 22. Y can be for example and without limitation, ethyl-2-hexyl methacrylate, stearyl acrylate or methacrylate, behenyl acrylate or methacrylate.

Z is a monomer having an ethylenic bond and at least one reactive group making it capable of reacting with another monomer, another compound or on the substrate itself to establish chemical crosslinking or a very strong chemical or physico-chemical interaction. These reactive groups are attributed a chemical or physical adhesion function of the thin deposit on electropolished steel. These groups are well known, they are polar or functional groups such as:

-OH, -NH ₂ , -NH-alkyl, -N- alkyl-iXalky ^), -COOH, CH - CH ₂

-SO3H, -CN, -CHO, -CH ₂ OH, -CH ₂ CI, 0

As such, there may be mentioned N-methylolacrylamide, N-methylol-methacrylamide, 2-hydroxy-3-chloropropyl acrylate or methacrylate, hydroxy- (C2-C4) -alkyl acrylate or methacrylate , maleic anhydride, chloro-2-ethyl acrylate or methacrylate, polyethylene glycol monoacrylate (degree of polymerization from 2 to 40), polyethylene glycol monomethacrylate (degree of polymerization from 2 to 40), acrylate or dicyclopentenyloxethyl methacrylate, glycidyl acrylate or methacrylate, ethoxy- or methoxyethyl acrylate or methacrylate, acrylic acid, t.butylaminoethyl methacrylate, N- (isobutoxymethyl) acrylamide, methyl ether methylacrylamidoglycolate ...

In the terpolymer of the invention, X enters for 10 to 80% by weight, Y for 0.1 to 50% and Z for the complement to 100%. These products are known for their tendency to be fixed on porous materials and it is by penetrating within their pores and by acting on the capillary penetration forces that they cause the reduction of their wetting by polar or non-polar liquids. They have therefore been recommended - US 3,896,035 (3M), US 3,462,296 (Dupont), JP 60-40182 (Asahi Glass) - for the treatment by impregnation of textiles, leather, paper and materials used in the building in order to make them hydrophobic and oleophobic. It was far from obvious that the application of the treatment to a stainless steel reactor which is absolutely not porous leads to the result of the invention. They are obtained by polymerization methods known per se. We can for example refer to this for the method of production indicated in French Patent No. 2,175,332. They are used according to the invention in the form of aqueous suspensions. These fluorocarbon polymers or copolymers useful for the invention give stainless steel a critical surface tension according to Zisman (see: Zisman

W.A. "Contact Angle, Wettability, and Adhesion" Adv. Chem., Ser. 43, 1 -51, 1964) at most 23 mN / m, preferably less than 20 nM / m. This characteristic

5 is supplemented by full-scale tests such as those which are set out below.

WAY OF CARRYING OUT THE INVENTION Test procedure:

- Installation of an electropolished tank. Size doesn't matter. The current I O sizes are between 1 and 50 rτ.3. The examples refer to a

13 rτv3

- Spraying on the hot walls of the reactor (60 to 100 ° C) of a dilute solution or suspension (at 0.5-5% in dry extract) at a rate of 0.5 to 50 mg / m2, and maintaining the walls in temperature for a time necessary for drying and

15 adhesion of the sprayed product (commonly 10 to 60 minutes).

- Coming of polymerization according to a reverse suspension process. In the examples, the arrival is 3t of product.

- At the end of the cycle, cleaning the reactor using a high pressure water gun.

The time and useful cleaning pressure are determined, and the amount of product adhered to the surfaces of the reactor is estimated by weighing.

EXAMPLES

Example 1 (reference in the absence of treatment)

In the absence of any treatment of the stainless steel of the reactor, the washing must be carried out with a rotating washing head, under an extremely high pressure (250 bars), for at least 20 minutes. The loss of polymer is 20 to 30 kg.

Example 1a

30 The entire reactor was coated with a fluorinated resin on the market, the Aflon

COP from Asahi Glass Co, Ltd which is an ethylene / tetrafluoroethylene copolymer. The operation is carried out in special ovens; the thickness of the coating is approximately 400 μm.

Washing can be carried out with a spray gun at a pressure of 40-50 bars. Her

The duration is approximately 10 minutes. The loss of polymer is estimated at 10 kg. This result would in itself be satisfactory, if it were not, as we said above, that it requires a heavy and costly treatment, which can only benefit small reactors, and that experience shows that be renewed every three months. Example 2 (counterexample)

The test procedure is that of the previous examples, but the reactor received 2 mg / m2 of a salt of alternating polystyrene / maleic anhydride copolymer with the following structure:

0 0 0 0

- H4 NH4

the polymer having been sprayed in the form of a concentrated aqueous solution at 1%.

The results are substantially those of Example 1, that is to say bad. The critical tension of the treated stainless steel is 35 mN / m.

The copolymer used here is industrially used in the surface treatment of paper to increase its hydrophobicity. The counterexample provides proof that it is not enough for an agent to be hydrophobic and to adhere to the metal to be effective within the meaning of the present invention. 15 Example 3 (counterexample)

Example 2 is reproduced, but the treatment agent is a 1% aqueous dispersion of a copolymer of 60% by weight of fluorinated alcohol methacrylate

CH2 = C (CH3) -CO-O-C2H4-C8F- | 7 of 25% by weight of ethyl-2-hexyl methacrylate and 15% by weight of butyl methacrylate, the quantity of polymer deposited being 0 of 1 mg / m2. It is a polymer which does not contain a type Z comonomer.

The pressure required for cleaning is now 100 bars, the cleaning time is 10 minutes and the loss of product is comparable to that which is observed on a new Aflon coating, and three times lower than that of the bare stainless steel reactor. The cycle time is 1 hour less than the cycle time in the Aflon-coated reactor.

The critical tension of the treated stainless steel is initially 17 mN / m. But the effect of the treatment disappears after one day.

Example 4 (counterexample)

Example 2 is reproduced, but the treatment agent is a 1% aqueous dispersion of a solution in N-methylpyrrolidone of a copolymer of fluorinated alcohol methacrylate, dimethylaminoethyl methacrylate and vinyl acetate, the amount of polymer deposited being 1 mg / m2.

The pressure necessary for cleaning is now 100 bars, the cleaning time 10 minutes and the loss of product is comparable to that which is observed on a new Aflon coating, and three times lower than that of the bare stainless steel reactor. The cycle time is 1 hour less than the cycle time in the Aflon-coated reactor.

The critical tension of the treated stainless steel is initially 19 mN / m. But the effect of the treatment disappears after two days. Example 5

Example 2 is reproduced, but the treatment agent is a 2% aqueous dispersion of a copolymer according to the invention of 60% by weight of the fluorinated alcohol methacrylate of Example 1, of 29% of methacrylate stearyl and 1% chloro-3-hydroxy-2-propyl methacrylate, the amount of polymer deposited being 1 mg / m2.

The critical tension of the treated stainless steel is initially 14 mN / m. Here, the effect of the treatment is still felt favorably after a week.

Claims

1. In a process for the production of superabsorbent polymers for water and aqueous solutions by reverse suspension polymerization of

5 acrylic monomers, during which the reactor made, as well as its stirring members, made of electropolished stainless steel is successively in contact with the reverse suspension of aqueous hydrophilic monomers, then with the polymer gel suspension, an improvement characterized by that the reactor and its stirring members are treated by application of an aqueous solution or dispersion of a fluorocarbon copolymer IO resulting from the copolymerization: from 10 to 80% by weight of fluorinated monomer of general formula

R ₂ 0

R ₁ - CH = C - C -0 - B - Rf

In which R1 and R2 are together or independently H or CH3, where B is a bivalent sequence

- (CH2-CH2) j- with i taking values from 1 to 6, preferably 1 to 3, or also a group -C2H4-SO2-NR-C2H4- in which R is either CH3 or C2H5, 20 and where Rf is a perfluorinated residue -C _n F2 _n + l, with 6 <n <10, and Rf is a perfluorinated residue -C _n F2n + l - with 6 <n <10, from 0.1 to 50% by weight of monomer of alkyl acrylate type of general formula

R ₂ o

R "C H ^ C - C - O - C H

^ ₅ ¹ m _{2m +} ι

in which R- | and R2 have the same meaning as above, and where C _m H2 _m + ι is an aliphatic or cycloaliphatic residue in which m can take all the values from 1 to 22, preferably from 12 to 22, and 30 from the complement to 100 % by weight of an ethylenic monomer comprising at least one reactive group capable of a very strong chemical or physico-chemical interaction with a metal substrate.

2. Treatment of an electropolished stainless steel reactor according to claim 1, characterized in that it comprises

35 - spraying the hot walls of the reactor with a dilute solution or suspension of the fluorocarbon copolymer, - keeping the walls at temperature for a time necessary for drying and for the adhesion of the sprayed product

3 Treatment according to either of Claims 1 or 2, characterized in that the amount of fluorocarbon copolymer deposited is between 0.5 to 50 mg / m2

4 Treatment according to either of Claims 1 to 3, characterized in that the fluorocarbon copolymer is a copolymer of fluorinated alcohol methacrylate

stearyl methacrylate and chloro-3-hyd roxy-2-propy methacrylate.