EP1534416A1

EP1534416A1 - Reactor and process for the production and/or drying of water-soluble polymers (wsps) or their derivatives

Info

Publication number: EP1534416A1
Application number: EP03792089A
Authority: EP
Inventors: Sahbi Belkhiria
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-08-20
Filing date: 2003-08-20
Publication date: 2005-06-01
Also published as: AU2003249838A1; WO2004018087A1

Abstract

The invention relates to a method for the continuous or batch production of Water Soluble Polymers (WSP) in closed kneader reactors.

Description

Reactor and Process for the production and/or drying of Water- Soluble Polymers (WSPs) or their derivatives

This Invention relates to an improved batch or continuous process for the production or modification of Hydrosoluble Polymers, referred hereafter, as WSPs. More particularly, this invention relates to a continuous kneader reactor, having at least one shaft, for the production or modification of WSPs and a process in which such continuous closed reactor could be combined with a continuous moved bed and closed dryer, avoiding the needs of intermediate maturity tank(s) and allowing the condensing then recycling of solvents and/or unreacted components.

1. INTRODUCTION

Presently, It is difficult to imagine an aspect of our modern life not touched by WSPs or their derivatives. They are utilized in several applications that include water and sewage treatment, mining, oil well drilling, oil production, coatings, paints, adhesives, detergents, cosmetics, papermaking, ceramics, textiles, etc.

Polymerization

The (co)polymerization reaction to produce WSPs can be carried out either in aqueous and initially homogenous phase (bulk solutions polymerization, precipitation polymerization) or in water-in-oil and therefore heterogeneous phase (reverse emulsion or reverse suspension polymerizations). In this latter case, usually, the presence of at least one surfactant and/or other emulsion stabilizer(s) is necessary. 1. Bulk solution polymerization: An homogenous solution of the monomeric reactant(s) mixture is initially prepared. Generally, water is the only solvent present in the mixture. But the reaction can also be carried out in the presence of other solvents or a combination thereof. After reaction initiation, and as the polymerization is taking place, the reaction mixture becomes more and more viscous and a gelly WSP is progressively formed. In precipitation polymerization, the monomer(s) are reacted in a medium, which is a solvent for them but a non-solvent for the polymer. As the polymer forms, it precipitates from the monomer phase.

2. Reverse phase suspension or emulsion polymerizations (referred hereafter as Suspension Polymerization, for commodity): In these cases, two phases are present in the reaction mixture: An organic continuous phase and an aqueous discontinuous phase (droplets), in which the (co)monomers and other reactants and additives are dissolved.

Generally, at least one suspending agent such as surfactants is usually used to stabilize the heterogeneous mixture. Compared to solution polymerization, the suspension polymerization leads to less viscous reaction media and better heat transfer.

For the abovementioned two ways, the polymerization is generally carried out under inert condition, i.e. in the presence of inert gas.

WSPs are generally obtained by two ways:

WSPs are usually produced by (co)polymerization of at least one water-soluble monoethylenically unsaturated monomer and/or at least one water-insoluble monoethylenically unsaturated monomer that can be totally or partly transformed to a water-soluble one by chemical modification(s), in the presence of at least one initiator, and usually other additives such as surfactant(s). The obtained WSP is generally composed of a high molecular weight linear polymer chains. Linear poly(meth)acrylic acids and partially or totally neutralized poly(meth)acryIic acids, poly(meth)acrylamides and partial or total hydrolyzates of poly(meth)acrylamides, poly(meth)acrylonitriles and partial or total hydrolyzates of poly(meth)acrylonitriles, polyethylene or polypropylene glycols, polyvinyl alcohol or poly(allylamines) are some examples of WSPs.

Another way to prepare WSPs is to carry on at least one modification on one or more already available natural or synthetic polymer chains such as polysaccharides, poly(meth)acrylic acids, poly(meth)acrylate esters, poly(meth)acrylamides, poly(meth)acrylonitriles, polyanhydrides, etc. Examples of such modifications include thermal treatment, partial or total neutralization, hydrolysis, saponification, dehydration, addition or substitution of chemical ionic and/or non-ionic functional groups, etc.

Finishing

WSPs are generally sold either in a powder form or in "dried" emulsion form, depending on the process and finishing operations (finishing step). During the finishing step, one or more reactants or additives such as solvent(s), initiator(s), surfactant(s), or a combination thereof, are removed from (ex.: during drying) and/or added to (ex.: in reaction completion phase) the WSP gel.

During the finishing step, the process efficiency can be improved through, for example, increasing temperature, maximizing conversion, and/or recycling of solvents and unreacted components. The product properties (ex.: higher solubility rate in water) may also be improved during this step by, for example, additives addition.

The finishing step may be carried out in atmospheric, vacuum, or inert conditions and in the presence or absence of heating. Example of Reactants and Components for WSPs Production

Water-soluble monoethylenically unsaturated monomers

Any monomer, its salts, hydrolyzates, derivatives or a combination thereof that is partly or totally miscible with water and that yields, after (co)polymerization, WSPs or polymers that can be transformed by modification(s) of their functional groups into WSPs.

Example of water-soluble monoethylenically unsaturated monomers used for preparing WSPs include α, β- ethylenically unsaturated carboxylic acid such as (meth)acrylic acid, maleic acid, maleic anhydride, fumaric acid, crotonic acid, citraconic acid, their esters (ex. (meth)acrylates of Methyl, ethyl, N- butyl, 2- hydroxyethyl, etc.), their N-substituted (alkyl)amides (ex. (meth)acrylamide, Nimethyhlacrylamide, N-terbutyl-acrylamide, N,NI-dimethylacrylamide, etc.), or their alkali metal and/or ammonium salts (ex. sodium (meth)acrylate, potassium(meth)acrylate, ammonium (meth)acrylate, etc.)

Other examples of water-soluble monoethylenically unsaturated monomers used for preparing WSPs include monomers containing nitrile group (ex. (meth)acrylonitrile, etc.), sulfo group (vinyl sulfonic acid, etc.), esters obtained by reaction of organic oxides (ethylene oxide, propylene oxide, etc.) or carboxylic acids with alcohols and there derivates.

Other examples of water-soluble monoethylenically unsaturated monomers used for preparing WSPs include (meth)acroleine, vinyl acetate, vinyl propionate, N-vinylpirrolidone, N-vinylformamide, N-vinycaprolactame and their derivatives.

Other examples of water-soluble monoethylenically unsaturated monomers used for preparing WSPs include cationic monomers such as diallyldialkylammonium chloride, methacryloyloxyethyltrimethyl-ammonium chloride, methacryloyloxyethyltrimethyl-ammonium sulfate, 3-

(methacrylamido)propyltrimethyl-ammonium chloride, dialkylaminoethyl methacrylate, ...

A combination of two or more of the above-mention water-soluble monoethylenically unsaturated monomers and their derivatives can also be used.

Polymers used for production of WSPs

Any natural or synthetic polymer or a combination thereof that is water-soluble or becomes partly or totally water-soluble after neutralisation, hydrolysis, and/or other modification(s) of their functional groups. Examples of such polymers are polysaccharides, alginates, poly(meth)acrylic acids, poly(meth)acrylate esters, poly(meth)acrylamides, poly(meth)acrylonitriles, polyanhydrides, etc. Examples of such modifications include partial or total neutralization, hydrolysis, saponification, dehydration, addition of chemical ionic and/or non-ionic functional groups,, etc.

Initiators. Additives, and/or Surfactants: This includes any type of initiator(s),

Additive(s), Surfactant(s) or a combination thereof, that is usually and industrially employed for the production of WSPs or improve their properties.

WSPs Derivatives WSPs can be thermally and/or chemically modified by at least one modification of its functional group(s) yielding to an increase or a decrease of the hydrophilic property of the resulting polymer. Examples of such modifications include curing, compounding, esterification, amidation, partial or total neutralization, hydrolysis, saponification, dehydration. More generally, it consists mainly on the addition or substitution of chemical ionic and/or non-ionic functional groups. II. WSPs Production (Reaction and/or Drying)

A method for the continuous production of WSPs as described in part I, which method comprises the continuous production of the polymer in a kneader reactor having at least one shaft, the eventual (but not necessary) continuous mixing of additive(s) with that polymer, and/or its continuous drying, wherein said dryer is characterized by a moved product-bed. For the bulk solution polymerization, this method will allow higher monomer concentrations and, for example, replace the conventional moving belt reactors and dryers, wherein the product remains motionless on a moveable surface. For suspension polymerization, the method allows the use of higher monomer concentrations while controlling efficiently the reaction and mixing parameters and yielding a high product quality. Any kneader having at least one shaft and that can work continuously can be employed as a reactor to produce WSPs. Some Examples of such kneaders are those commercialized by List AG (ex. DTB, ORP, CRP or CKR) or SMS GmbH (ex. Reactotherm, Reasol, Reavisc, Reacom, or Reaflow). Due to their higher self-cleaning and mixing efficiency, twin-shaft kneader reactors are preferred. On the other hand, any continuous moved-bed dryer (e.g. rotary dryer, drum dryer, Discotherm dryer) that can work continuously, preferably under vacuum can be employed for drying WSPs according to the process. Examples of such dryers are those commercialized by List AG (ex. DT) or SMS GmbH (ex. Reactotherm, Rovactor).

However, it is also possible but not preferred that the polymeric mixture exiting the continuous kneader reactor having at least one shaft, be directly dried through any conventional continuous but not moved-bed dryer (ex. belt dryer) already employed in WSPs drying.

For lower production capacities, kneaders reactors having at least one shaft and working in a batch way can also be employed to produce WSPs or their derivatives. WSPs Production in Kneaders Reactors

The production and processing of WSPs, according to the description in paragraph I, can for example, be ideally and safely carried out in one of the continuous single or twin-shaft kneader reactors of the companies List AG (ex. DTB, ORP, CRP or CKR), SMS GmbH (ex. Reactotherm, Reasol, Reavisc, Reacom, or Reaflow), or other companies that manufacture analogous equipment.

For example, during the course of solution polymerization when a WSP is produced, the viscosity of the reaction mixture increases as a gel is formed. The intermeshing of the kneading elements assures a uniform mixture over time and cuts the gelly mass into small, uniform gel particles, which are discharged at a conversion up to 90% or even more. Orientation angle of the kneading elements assures the axial conveying of the pasty polymer. The shape of kneading elements is an additional parameter to adjust the compression or shear between the intermeshing zones. Due to its capacity to mix efficiently very viscous media, the kneader is also very suitable to produce WSPs by functional groups modification(s) of polymeric mixtures.

The reaction can be carried out at any pressure. Preferably, evaporative cooling can be used to remove the heat of reaction, especially when the autoacceleration of the reaction rate occurs (gel or Trommsdorff - Norrish effect). Depending on the degree of vacuum present into the reactor, approximately 0.1 % to 50% or more of the water and/or other solvent(s) is evaporated to remove the high reaction heat of the monomers (ex.:≡70KJ/mol for the acrylates monomers). The condensed phase may contain traces or low concentrations of monomer(s) additives and/or surfactants. The evaporated water or liquid mixture can be condensed, eventually separated, then totally (reflux) or partly recycled in the reaction mixture (evaporative cooling). Alternatively, it can also be totally removed to dry partially the produced WSP. Continuous Kneader Reactors

The Kneader Reactors are particularly very suitable to produce WSPs since they are designed to improve the radial/axial self-cleaning and axial conveying of viscous polymers, in addition to a good mixing during the reaction. Therefore, the system allows avoiding the complete filling/plugging of the reactor and the dead zones whilst working continuously. Torque is very important to the compression zones, especially with regard to solid or gel particles. Particularly, the twin-shaft kneaders are optimized in order to avoid compression zones between the barrel and the kneading elements, and the intermeshing zones of the kneading elements. At these conditions, no significant presence of squeezed or destroyed gels was observed, but a good and uniform quality of WSPs.

The above and other objects and advantages of novel features of the present invention will become apparent from the following detailed description of a preferred embodiment of the invention illustrated in the accompanying drawing, which shows a schema of the invention.

As illustrative example, the case of a bulk solution polymerization to produce WSPs in a twin-shaft kneading reactor is considered.

Polymerization Reaction:

Reactants and catalysts are continuously fed in a twin-shaft kneading reactor 1 by arrow A together with vapor and/or inert gas by arrow B.

The bulk solution polymerization, as described in paragraph I, is conducted in the twin-shaft kneading reactor 1 equipped with a vacuum and condensing systems and in which the axial conveying is optimal and the gel free flowing particles can be formed. If necessary, the gel particle size can be adjusted at the end of the twin-shaft kneading reactor 1 and after discharge means 3 with a twin-screw 4 by means of adjustable knives 5. The cutting of the gel should be done at this wet stage (in vapour environment) in order to keep the cut particles free flowing. The particle size at this stage of the continuous process is very important because of the drying efficiency, which is improved while processing small particles (diffusion controlled).

Another possibility is the side discharge of WSP gel particles. In that case, a weir is then installed to regulate the fill level in the reactor. This option eliminates the needs of the discharge twin-screw.

Vapor and/or inert gas may be removed from the discharge means 3 after the knives.

Drying:

The WSP particles coming out of the twin-shaft kneading reactor 1 are already free-flowing particles because of the humidity and eventually the presence of other component(s) or a combination thereof acting as lubricant(s) on the surface of the particles.

Trying to dry these hydrated gel particles directly in a continuous moved-bed dryer 2 (e.g. rotary dryer, drum dryer, Discotherm dryer) would generally result in a compacting of the hydrated gel particles.

However, the mixing shown through arrow C of one or more appropriate additives or a combination thereof with the flow of hydrated gel particles coming out of the twin-shaft kneading reactor within a rotary mixer-tube 6 avoids the stickiness of the hydrated gel particles between each other while being separated from the superficial liquid film. These additives act as a free-flowing agent in the continuous dryer 2 wherein the product-bed is moved. The additive(s) could be in a powder or a liquid form, preferably as a powder and more preferably the powder consisting on dried WSP fines D, which can be recycled at the end of the process and may be milled before being mixed as a free-flowing agent. However, any material or a combination of materials that are used in WSP finishing, as described in paragraph I, may also be employed as a free flowing agent while improving the polymer properties, i.e. improved polymer dissolution rate, reduced residual monomers, reduced dust, etc.

After the dryer 2, the dried WSP could be transferred to a not shown mill and sieve.

The foregoing pre-drying mixing process can be carried out at atmospheric pressure or in the presence of air, inert gas and/or vacuum. The presence of vacuum is preferred. Also for adjustment, the process may operate under vacuum by using any commercial periphery systems.

The new method of drying is innovative compared to the usual continuous belt convective dryer. Based on the dryer only, the financial impact is a considerable reduction of the drying investments when a moved-bed dryer is compared to a moving belt dryer wherein the product rests motionless on a movable surface. Moreover, by employing the moved-bed dryer 2, the use of maturity tanks to complete reaction can be avoided since this completion reaction can be carried out into the dryer.

Each of the kneading reactor 1 and the dryer 2 can be used independently or in combination with the other (cf. Fig.1). Combining of the two equipment to carry on the whole process is preferred, however.

Each of the reactor 1 and the dryer 2 can be equipped with a condensing system. The discharge 3 includes a discharge twin-screw 4 and adjustable knives system 5, and is inserted between the twin-shaft kneading reactor 1 and the dryer 2. If necessary, a pressure lock chamber 7 may also be inserted between the reactor and the dryer. The pressure lock chamber is particularly important when the reactor 1 and the dryer 2 are functioning at different pressures. Any pressure lock chamber present on the market can be used.

The process described above and consisting on using either the reactor 1 or the dryer 2 or the combination thereof has the advantages to be more efficient economically and environmentally and gives an improved product's quality since it has the benefits of being more compact (lower space occupation), controlling better the reaction and drying parameters, avoiding the use of maturity tank(s), and giving the possibility to condense the evaporated solvents, and/or unreacted components then recycle them with larger recycling rate, which allows less residuals and gas wastes to be treated.

List of Figure Positions:

Claims

1. A method for the continuous or batch production or modification of WSPs, in closed kneader reactors.

2. A method according to claim 1 , in which the closed kneader reactor (1 ) consists on an agitated vessel, which vessel has at least one agitating shaft, such shaft(s) being preferably heated additionally to the vessel to increase the heat transfer and reaction temperature control.

3. A method according to claims 1 and 2, in which the closed kneader reactor (1 ) is preferably a twin-shaft kneader.

4. A method according to claims 1 and 2, in which the WSPs are produced by bulk solution polymerization or by reverse suspension or emulsion polymerization.

5. A method according to claims 1 and 2, in which the WSPs may be produced by at least one modification of functional groups of one or more already available natural or synthetic polymers.

6. A method according to claims 1 and 2, in which the WSPs may be modified thermally and/or chemically by at least one modification of its functional group(s) yielding to a change of at least one of its properties, particularly, its hydrophilic property.

7. A method according to claims 1 and 2, in which the WSPs may be modified by mixing the WSPs with at least one additional material leading to a change in its thermal, mechanical and/or hydrophilic property. Examples of such additional materials include polymer(s), glass fiber, SiO₂, TiO₂, Kaolin, etc.

8. A method according to claims 1 and 2, in which the production of the WSP in the closed kneader reactor is carried out at any pressure, preferably under vacuum and/or in the .presence of gas, steam or a combination thereof.

9. A method according to claim 2, in which the closed kneader reactor is equipped with a condensing (8), reflux, and/or recycling system.

10. A method according to claim 1 , 2 and 9, in which the reaction heat production and the temperature of the reacting mixture into the closed kneader reactor (1) can be controlled by evaporative cooling.

11. A method according to claims 1 and 2, in which the closed kneader reactor is preferably a continuous kneader reactor, most preferably a continuous twin-shaft kneader reactor

12. A continuous process, according to claims 1 , 2 and 11 , for the production of dried or emulsified WSPs by carrying out the polymerization reaction, either in an initially homogenous aqueous monomer solution (bulk aqueous solution polymerization) or in a heterogeneous water-in-oil reactant mixture (reverse phase suspension or emulsion polymerization) in a continuous closed polymerization kneader-reactor (1 ), then drying of the resulting polymer gel into a continuous moved bed closed dryer (2), avoiding the needs of standard intermediate maturity tank(s).

13. A method according to claim 12, in which the moved bed closed dryer (2) is any continuous moved-bed dryer that can work continuously, preferably under vacuum and more preferably that has at least one agitating shaft, such shaft(s) being preferably heated additionally to the vessel to increase the heat transfer and drying efficiency.

14. A method according to claim 13, in which the drying of the polymeric product is carried out under vacuum or in the presence of heated air, inert gas, steam or a combination thereof, preferably under vacuum.

15. A method according to claim 12 and 13, in which the maturity of the polymer, i.e reaction reaching very high conversion, may be carried out into the first zone of the moved bed closed dryer (2).

16. A method according to claim 12, in which the mixing effect into either or both the closed continuous polymerization reactor (1) and the dryer (2) could be used to incorporate (C), to the produced gel mix, one or more additional (co)monomer(s), surfactants, initiator(s), additive(s) or solvent(s) or a combination thereof.

17. A method according to claim 12, in which the mixing effect into either or both the closed continuous polymerization reactor (1) and the dryer (2) could be used to incorporate, to the produced gel, the recycled dry WSP fines that may exit from the continuous discharge system (DS) and the siever.

18. A method according to claim 12, in which either or both the continuous polymerization reactor (1 ) and the dryer (2) could be equipped with condensing and recycling systems of residual reactant(s), solvent(s) and/or additives or a combination thereof.

19. A method according to claim 18, in which the condensing and recycling systems of the continuous polymerization reactor (1 ) and the dryer (2) could be operated in an independent or combined way.

20. A method according to claim 18, in which the residual reactant(s), solvent(s) and additives or a combination thereof could be totally or partly recycled, together or separately at one or more locations of the continuous production process of claim 12. 5

21. A method according to claim 12, in which a pressure lock chamber (7) or a gel cutting system (5) or a combination thereof could be inserted between the continuous polymerization reactor (1 ) and the dryer (2).

22. A method according to claim 21 , in which the type of the pressure lock chamber is of any type of commercially available pressure lock chambers, o preferably a rotary valve or a piston lock system.

23. A method according to claim 21 , in which the pressure lock chamber could also be used to incorporate, to the reaction mixture exiting the polymerization reactor, one or more additional (co)monomer(s), additive(s), initiator(s), and/or solvents or a combination thereof. It may also be used to 5 incorporate recycled dry WSP fines.

24. A method according to claim 21 , in which the type of the gel cutting system is of any type of commercially available cutting systems.

25. A method according to claim 21 , in which the gel cutting system could also be used to incorporate one or more additional (co)monomer(s), additive(s), 0 initiator(s) and solvents or a combination thereof to the reaction mixture exiting the polymerization reactor. The gel cutting system may also be used to incorporate recycled dry WSP fines.

26. A method according to claim 25, in which the gel particles of a required size could be continuously mixed with at least one additive improving free- flowing and eventually other properties in a mixing screw or in a rotary mixer-tube (6), which has a final portion with holes allowing the additive(s) to be recycled before entering the dryer (2).

27. A method according to claims 12 and 21 , in which the continuous polymerization reactor (1), the dryer (2) and any device between them can function at equal pressure or at different pressures.

28. A method according to claim 27, in which the continuous polymerization reactor (1), the dryer (2) and any device between them function preferably at different degrees of vacuum.

29. A method according to claims 28 and 21 , in which the degree of vacuum into the dryer (2) is lower, preferably much lower than that in the continuous polymerization reactor (1 ) and the other devices between them.

30. A method according to claim 29 and 12, in which when the hot polymeric mixture enters the dryer (2), which is under much higher temperature and degree of vacuum than the polymerization reactor (1) and intermediate devices, the polymer is readily flashed leading to intensive evaporation of solvent(s) and_. un-reacted components and hence to higher drying efficiency of the WSP, wherein the flash allows the WSP particles to be more porous and thus to have an increased dissolution rate.

31. A method according to claim 12, in which the continuous closed kneader reactor (1 ) and the moved bed closed dryer (2) may not be combined and may be used separately and independently to produce (respectively dry) 5 WSPs gels or emulsions.

32. A method according to claim 31 in which, it is also possible but not preferred that the WSPs mixture exiting the continuous kneader reactor having at least one shaft, be directly dried through any conventional continuous but not moved-bed dryer (ex. belt dryer) that are already o employed in WSPs industry.