WO2019081324A1

WO2019081324A1 - A process and apparatus for producing aqueous polymer solutions

Info

Publication number: WO2019081324A1
Application number: PCT/EP2018/078499
Authority: WO
Inventors: Faissal-Ali El-Toufaili; Dennis Loesch; Dirk Meckelnburg; Markus OSTERMAYR
Original assignee: Basf Se
Priority date: 2017-10-25
Filing date: 2018-10-18
Publication date: 2019-05-02
Also published as: AR113374A1

Abstract

Process for producing an aqueous polymer solution comprising the steps of providing an aqueous polymer gel comprising a water-soluble polymer and comminuting and dissolving the aqueous polymergel in an aqueous liquid, thereby obtaining an aqueous polymer solution, wherein comminution is conducted by conveying the aqueous polymer gel through a comminution unit comprising at least a perforated sheet and moveable cutting means. Apparatus for conducting said process comprising a comminution unit comprising at least a perforated sheet and moveable cutting means.

Description

A process and apparatus for producing aqueous polymer solutions

The invention relates to a process for producing an aqueous polymer solution comprising the steps of providing an aqueous polymer gel comprising a water-soluble polymer and comminuting and dissolving the aqueous polymer gel in an aqueous liquid, thereby obtaining an aqueous polymer solution, wherein comminution is conducted by conveying the aqueous polymer gel through a comminution unit comprising at least a perforated sheet and moveable cutting means. The invention furthermore relates to an apparatus for conducting said process comprising a comminution unit comprising at least a perforated sheet and moveable cutting means.

Water-soluble, high molecular weight homo- and copolymers of water-soluble, monoethylenically unsaturated monomers such as for example acrylamide, acrylic acid, or ATBS are known in the art and may be used for various applications.

A common polymerization technology for manufacturing such high molecular weight polymers is the so called "gel polymerization". In gel polymerization, an aqueous monomer solution having a relatively high concentration of monomers, for example from 20 % by weight to 35 % by weight is polymerized by means of suitable

polymerization initiators under essentially adiabatic conditions in an unstirred reactor thereby forming a polymer gel.

Such polymer gels formed often are converted to polymer powders by comminuting the gel into smaller pieces by one or more size reduction steps, drying such gel pieces for example in a fluid bed dryer followed by sieving, grinding and packaging. The obtained polymer powders, for example polyacrylamide powders are packaged and shipped to customers for use, for example in mining and oilfield applications, water treatment, sewage treatment, papermaking, and agriculture. The polymer gel obtained from gel polymerization typically comprises from 65 % to 80 % of water. The residual amount of water in polyacrylamide powders typically is from about 4 to 12 % by weight. So, "drying" such polyacrylamide gels does not mean to remove only some residual moisture in course of drying but rather about 0.55 to 0.75 kg of water need to be removed per kg of polymer gel, or -with other words- per kg of polymer powder produced also 1.5 to 2.5 kg of water are "produced".

It goes without saying that removeable such a high amount of water from the polymer gels in course of drying is energy extensive and consequently the operational costs for drying are high. Furthermore, high-performance dryers are necessary as well as equipment for size reduction, sieving and grinding. Consequently, the capital expenditure for the entire post-processing equipment including size reduction, drying, sieving, grinding is significant in relation to the total capital expenditure for the entire plant. It has therefore been suggested not to dry aqueous polymer gels after manufacture but directly dissolving said aqueous polymer gels in water thereby obtaining diluted aqueous solutions of water-soluble polymers such as polyacrylamides without drying and re-dissolving the dry powder. Advantageously, dissolving aqueous polymer gels in water may be performed on-site, i.e. at the side at which the solutions of water soluble polymers are used.

Several technologies have been suggested for dissolving aqueous polymer gels in water.

DE 21 08 703 discloses a method of dissolving polymer gels by rubbing the gel against a rough surface in the presence of water.

GB 1 441 340 discloses a method of dissolving polymer gels by extruding the aqueous polymer gel through an orifice in an orifice sheet having an inside surface and an outside surface, periodically cutting the gel at the inside of the orifice sheet and continuing extruding, impinging solvent for the gel on the exiting segmented gel strand exiting from the outside of the orifice sheet, mixing the gel particles and solvent to dissolve the gel particles in the solvent.

US 3,255,142 discloses a method of dissolving polymer gels by extruding said polymer gels into a transversely flowing stream of liquid solvent.

US 4,1 13,688 discloses a method of dissolving polymer gels which comprises two size reduction steps. The method comprises extruding said polymer gels into flowing water through die holes in an extrusion die sheet, said holes having a diameter of ~ 0.15 mm to ~ 12.7 mm, forming polymer gel strands, and cutting such polymer gel strands to a length of less than ~ 19.05 mm, thereby obtaining a slurry of the cut gel particles in the flowing water. In the second size reduction step, the slurry of gel particles is subjected to high shear forces immediately after formation of such slurry, i.e. before any substantial dissolution of the polymer gel occurs, thereby reducing the average maximum dimension of the gel particles to less than 0.76 mm. In a final step, the resultant slurry of fine gel particles and additional water are mixed under low shear conditions thereby forming a dilute aqueous solution of the polymer.

US 4,845,192 discloses a method of rapidly dissolving particles of gels of water-soluble polymers comprising forming a suspension of such gel particles in water and subjecting said suspension to instantaneous and momentary conditions of high shearing effective to finely slice said particles.

US 4,605,689 discloses a method for on-site production of aqueous polyacrylamide solutions for enhanced oil recovery. In a first step an aqueous polyacrylamide gel is provided by polymerizing acrylamide and preferably acrylic acid as comonomer. The aqueous polyacrylamide gel obtained is conveyed together with a minor amount of aqueous solvent through at least one static cutting device thereby obtaining a slurry of small gel particles in water, the gel particles are dissolved in the aqueous solvent which forms a homogeneous solution concentrate which is then readily diluted with aqueous solvent thereby obtaining a diluted aqueous polyacrylamide solution.

Our older application WO 2017/186567 A1 relates to a process for producing an aqueous polymer solution comprising the steps of providing an aqueous polymer gel comprising at least 10 % by weight of active polymer, cutting the aqueous

polyacrylamide gel by means of a water-jet at a pressure of at least 150 bar to reduce the size of the aqueous polymer gel, and dissolving the aqueous polymer gel in an aqueous liquid.

Our older application WO 2017/186697 A1 relates to a method of preparing an aqueous polyacrylamide solution, comprising hydrolyzing acrylonitrile in water in presence of a biocatalyst thereby obtaining an acrylamide solution, directly

polymerizing the acrylamide solution thereby obtaining a polyacrylamide gel, and directly dissolving the polyacrylamide gel by addition of water, preferably by means of a static mixer, thereby obtaining an aqueous polyacrylamide solution. The method may be carried out on-site.

Our older application WO 2017/186685 A1 relates to a method of preparing an aqueous polyacrylamide solution, comprising hydrolyzing acrylonitrile in water in presence of a biocatalyst thereby obtaining an acrylamide solution, directly

polymerizing the acrylamide solution thereby obtaining a polyacrylamide gel, and directly dissolving the polyacrylamide gel by addition of water by means of a mixer comprising a rotatable impeller thereby obtaining an aqueous polyacrylamide solution. Such a mixer is also known in the art as Urschel-mixer and applies high shearing forces. The method may be carried out on-site.

Our older application WO 2017/186698 A1 relates to a method of preparing an aqueous polyacrylamide solution, comprising hydrolyzing acrylonitrile in water in presence of a biocatalyst thereby obtaining an acrylamide solution, directly

polymerizing the acrylamide solution thereby obtaining a polyacrylamide gel, and directly dissolving the polyacrylamide gel by addition of water by means of water jet cutting, thereby obtaining an aqueous polyacrylamide solution. The method may be carried out on-site.

The application of high shearing forces in course of dissolving high molecular weight polyacrylamides may cause polymer degradation. It was an object of the present invention to provide an improved process and apparatus for producing aqueous polymer solutions by dissolving aqueous polymer gels which avoids high shearing forces. Accordingly, in one embodiment of the present invention, a process for producing an aqueous polymer solution has been found, comprising the steps of

[1 ] providing an aqueous polymer gel comprising 5 % to 45 % by weight of a water-soluble polymer obtainable by polymerization of an aqueous solution comprising water-soluble, monoethylenically unsaturated monomers,

[2] comminuting and dissolving the aqueous polymer gel in an aqueous liquid, thereby obtaining an aqueous polymer solution,

wherein step [2] comprises

[2-1 ] conveying the aqueous polymer gel through a comminution unit

comprising at least

• a perforated sheet, and

• moveable cutting means,

and adding at least a portion of the aqueous liquid into the comminution unit,

wherein the relative velocity between the cutting means and the aqueous polymer gel does not exceed 3 m/s,

thereby obtaining an aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel, and

[2-2] adding the remainder of the aqueous liquid to the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel obtained in course of step [2-1 ] and dissolving the aqueous polymer gel pieces in the aqueous, liquid thereby obtaining said aqueous polymer solution.

Preferably, the movable cutting means are selected from the group of rotating knives, rotating water-jets or cutting rollers.

List of figures:

With regard to the invention, the following can be stated specifically:

By means of the process according to the present invention, it is possible to prepare aqueous solutions of polymers using an aqueous polymer gel as starting material, wherein the aqueous polymer gel is obtainable by polymerization of an aqueous solution comprising water-soluble, monoethylenically unsaturated monomers.

Such an aqueous polymer gel may be regarded as a polymer-water system in which there is a three-dimensional network structure composed of macromolecules or their associates and which is capable of retaining significant amounts of water. Such a system keeps its shape under the action of its own weight and differs in this feature from a polymer solution. Suitable definition of a polymer gel is given in the article by LZ Rogovina et al, Polymer Science, Ser. C, 2008, Vol. 50, No. 1 , pp. 85-92.

The aqueous polymer gel comprises 5 % by weight to 45% by weight of a water- soluble polymer, wherein the percentages relate to the total of all components of the aqueous polymer gel. Suitably the contents of water-soluble polymer in the aqueous polymer gel may be from 8 % to 45 % by weight, desirably from 8 % to 40 % by weight, preferably from 20 to 35 % by weight and for example from 20 to 25 % by weight. Aqueous polymer gel

The aqueous polymer gel to be used as starting material is obtainable by

polymerization of an aqueous solution comprising water-soluble, monoethylenically unsaturated monomers. Preferably, polymerization is conducted by radical

polymerization.

The term "water-soluble monomers" in the context of this invention means that the monomers are to be soluble in the aqueous monomer solution to be used for polymerization in the desired use concentration. It is thus not absolutely necessary that the monomers to be used are miscible with water without any gap; instead, it is sufficient if they meet the minimum requirement mentioned. It is to be noted that the presence of one monoethylenically unsaturated monomer in the monomer solution, for example acrylamide or acrylic acid, might enhance the solubility of other monomers as compared to water only. In general, the solubility of the water-soluble monomers in water at room temperature should be at least 50 g/l, preferably at least 100 g/l.

In a preferred embodiment of the invention the aqueous polymer gels are aqueous polyacrylamide gel. The term "polyacrylamide" as used herein means water-soluble polymers comprising at least 10 %, preferably at least 20 %, and more preferably at least 30 % by weight of acrylamide, wherein the amounts relate to the total amount of all monomers relating to the polymer. Polyacrylamides include homopolymers and copolymers of acrylamide and other monoethylenically unsaturated comonomers. Polyacrylamide copolymers are preferred. Basically, the kind and amount of water-soluble, monoethylenically unsaturated comonomers to be used is not limited and depends on the desired properties and the desired use of the aqueous solutions of polymers to be manufactured.

Neutral monomers

Examples of suitable monomers comprise uncharged water-soluble, monoethylenically unsaturated monomers. Examples comprise acrylamide, methacrylamide, N- methyl(meth)acrylamide, N,N'-dimethyl(meth)acrylamide, N-methylol(meth)acrylamide or N-vinylpyrrolidone. Further examples have been mentioned in WO 2015/158517 A1 page 7, lines 9 to 14. In one embodiment of the invention, at least one of the water- soluble, monoethylenically unsaturated monomers in the aqueous monomer solution is acrylamide. Anionic monomers

Further examples of suitable monomers comprise water-soluble, monoethylenically unsaturated monomers comprising at least one acid group, or salts thereof. The acidic groups are preferably selected from the group of -COOH, -SO3H and -PO3H2 or salts thereof. Preference is given to monomers comprising COOH groups and/or -SO3H groups or salts thereof. Suitable counterions include especially alkali metal ions such as Li⁺, Na⁺ or K⁺, and also ammonium ions such as Nh or ammonium ions having organic radicals. Examples of ammonium ions having organic radicals include

[NH(CH₃)₃]⁺, [NH₂(CH₃)₂]⁺, [NH₃(CH₃)]⁺, [NH(C₂H₅ )₃]⁺, [NH₂(C₂H₅ )2]⁺, [NH₃(C₂H₅ )]⁺, [NH₃(CH₂CH₂OH)]⁺, [H₃N-CH₂CH₂-NH₃]²⁺ or [H(H₃C)₂N-CH₂CH₂CH₂NH₃]²⁺.

Examples of monomers comprising -COOH groups include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaric acid or salts thereof.

Preference is given to acrylic acid or salts thereof.

Examples of monomers comprising -S0₃H groups or salts thereof include vinylsulfonic acid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid (ATBS), 2- methacrylamido-2-methylpropanesulfonic acid, 2-acrylamidobutanesulfonic acid, 3- acrylamido-3-methylbutanesulfonic acid or 2-acrylamido-2,4,4-trimethylpentanesulfonic acid. Preference is given to 2-acrylamido-2-methylpropanesulfonic acid (ATBS) or salts thereof.

Examples of monomers comprising -P0₃H₂ groups or salts thereof include

vinylphosphonic acid, allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids or (meth)acryloyloxyalkylphosphonic acids, preferably vinylphosphonic acid.

Preferred monomers comprising acidic groups comprise acrylic acid and/or ATBS or salts thereof.

Cationic monomers

Further examples of monomers comprise water-soluble, monoethylenically unsaturated monomers comprising cationic groups. Suitable cationic monomers include especially monomers having ammonium groups, especially ammonium derivatives of N-(co- aminoalkyl)(meth)acrylamides or co-aminoalkyl (meth)acrylates such as

2-trimethylammoniooethyl acrylate chloride H₂C=CH-CO-CH₂CH₂N⁺(CH₃)₃ CI- (DMA3Q). Further examples have been mentioned in WO 2015/158517 A1 page 8, lines 15 to 37. Preference is given to DMA3Q. Associative monomers

In one embodiment, the monomers comprise at least one associative monomer.

Associative monomers typically may only be used as comonomers besides other monoethylenically unsaturated monomers, in particular besides acrylamide.

Associative monomers impart hydrophobically associating properties to polymers, in particular to polyacrylamides. Associative monomers to be used in the context of this invention are water-soluble, monoethylenically unsaturated monomers having at least one hydrophilic group and at least one, preferably terminal, hydrophobic group.

Examples of associative monomers have been described for example in WO

2010/133527, WO 2012/069478, WO 2015/086468 or WO 2015/158517.

"Hydrophobically associating copolymers" are understood by a person skilled in the art to mean water-soluble copolymers which, as well as hydrophilic units (in a sufficient amount to assure water solubility), have hydrophobic groups in lateral or terminal positions. In aqueous solution, the hydrophobic groups can associate with one another. Because of this associative interaction, there is an increase in the viscosity of the aqueous polymer solution compared to a polymer of the same kind that merely does not have any associative groups.

Examples of suitable associative monomers comprise monomers having the general formula

(I) wherein R¹ is H or methyl, R² is a linking hydrophilic group and R³ is a terminal hydrophobic group. Further examples comprise having the general formula H₂C=C(R¹)-R²-R³-R⁴ (II) wherein R¹, R² and R³ are each as defined above, and R⁴ is a hydrophilic group.

The linking hydrophilic R² group may be a group comprising ethylene oxide units, for example a group comprising 5 to 80 ethylene oxide units, which is joined to the

H2C=C(R¹)- group in a suitable manner, for example by means of a single bond or of a suitable linking group. In another embodiment, the hydrophilic linking group R² may be a group comprising quaternary ammonium groups.

In one embodiment, the associative monomers are monomers of the general formula

wherein R¹ has the meaning defined above and k is a number from 10 to 80, for example, 20 to 40. R^3a is an aliphatic and/or aromatic, straight-chain or branched hydrocarbyl radical having 8 to 40 carbon atoms, preferably 12 to 32 carbon atoms.

Examples of such groups include n-octyl, n-decyl, n-dodecyl, n-tetradecyl, n-hexadecyl or n-octadecyl groups. In a further embodiment, the groups are aromatic groups, especially substituted phenyl radicals, especially distyrylphenyl groups and/or tristyryl phenyl groups. In another embodiment, the associative monomers are monomers of the general formula H2C=C(R¹)-0-(CH2)n-0-(CH2CH20)x-(CH2-CH(R⁵)0)y-(CH2CH₂0)zH (V), wherein R¹ is defined as above and the R⁵ radicals are each independently selected from hydrocarbyl radicals comprising at least 2 carbon atoms, preferably from ethyl or propyl groups. In formula (V) n is a natural number from 2 to 6, for example 4, x is a number from 10 to 50, preferably from 12 to 40, and for example, from 20 to 30 and y is a number from 5 to 30, preferably 8 to 25. In formula (V), z is a number from 0 to 5, for example 1 to 4, i.e. the terminal block of ethylene oxide units is thus merely optionally present. In an embodiment of the invention, it is possible to use at least two monomers (V), wherein the R¹ and R⁶ radicals and indices n, x and y are each the same, but in one of the monomers z = 0 while z > 0 in the other, preferably 1 to 4.

In another embodiment, the associative monomers are cationic monomers. Examples of cationic associative monomers have been disclosed in WO 2015/158517 A1 , page 1 1 , line 20 to page 12, lines 14 to 42. In one embodiment, the cationic monomers having the general formula H₂C=C(R¹)-C(=0)0-(CH2)k-N⁺(CH3)(CH₃)(R⁶) X^" (VI) or H₂C=C(R¹)-C(=0)N(R )-(CH2)k-N⁺(CH3)(CH₃)(R⁶) X^" (VII) may be used, wherein R has the meaning as defined above, k is 2 or 3, R⁶ is a hydrocarbyl group, preferably an aliphatic hydrocarbyl group, having 8 to 18 carbon atoms, and X^" is a negatively charged counterion, preferably Ch and/or Br.

Further monomers

Besides water-soluble monoethylenically unsaturated monomers, also water-soluble, ethylenically unsaturated monomers having more than one ethylenic group may be used. Monomers of this kind can be used in special cases in order to achieve easy crosslinking of the polymers. The amount thereof should generally not exceed 2% by weight, preferably 1 % by weight and especially 0.5% by weight, based on the sum total of all the monomers. More preferably, the monomers to be used in the present invention are only monoethylenically unsaturated monomers.

Composition of polymers

The specific composition of the polymers in the aqueous polymer solutions to be manufactured according the process of the present invention may be selected according to the desired use of the polymers.

Preferred polymers comprise, besides at least 10 % by weight of acrylamide, at least one further water-soluble, monoethylenically unsaturated monomer, preferably at least one further monomer selected from the group of acrylic acid or salts thereof, ATBS or salts thereof, associative monomers, in particular those of formula (V) or DMA3Q, more preferably at least further one monomer selected from acrylic acid or salts thereof, ATBS or salts thereof, associative monomers, in particular those of formula (V). In one embodiment, polyacrylamides comprise 20 % to 90 % by weight of acrylamide and 10 % to 80 % by weight of acrylic acid and/or salts thereof, wherein the amounts of the monomers relate to the total of all monomers in the polymer. In one embodiment, polyacrylamides comprise 20 % to 40 % by weight of acrylamide and 60 % to 80 % by weight of acrylic acid and/or salts thereof.

In one embodiment, polyacrylamides comprise 55 % to 75 % by weight of acrylamide and 25 % to 45 % by weight of acrylic acid and/or salts thereof.

In one embodiment, polyacrylamides comprise 45 % to 75 % by weight of acrylamide and 25 % to 55 % by weight of ATBS and/or salts thereof.

In one embodiment, polyacrylamides comprise 30 % to 80 % by weight of acrylamide, 10 % to 40 % by weight of acrylic acid and/or salts thereof, and 10 % to 40 % by weight of ATBS and/or salts thereof.

In one embodiment, polyacrylamides comprise 45 % to 75 % by weight of acrylamide, 0.1 to 5 %, preferably 0.1 to 2 % by weight of at least one associative monomer of the general formulas (I) or (II) mentioned above and 10 to 54.9 % by weight of acrylic acid and/or ATBS and/or salts thereof. Preferably, the associative monomer(s) have the general formula (V) including the preferred embodiments mentioned above.

In one embodiment, polyacrylamides comprise 60 % to 75 % by weight of acrylamide, 0.1 to 5 %, preferably 0.1 to 2 % by weight of at least one associative monomer of the general formula (V) mentioned above, including the preferred embodiments, and 20 to 39.9 % by weight of acrylic acid or salts thereof.

In one embodiment, polyacrylamides comprise 45 % to 55 % by weight of acrylamide, 0.1 to 5 %, preferably 0.1 to 2 % by weight of at least one associative monomer of the general formula (V) mentioned above, including the preferred embodiments, and 40 to 54.9 % by weight of acrylic acid or salts thereof.

In one embodiment, the polyacrylamides comprise 60 % to 99 % by weight of acrylamide and 1 % to 40 % by weight of DMA3Q.

In one embodiment, the polyacrylamides comprise 10 % to 50 % by weight of acrylamide and 50 % to 90 % by weight of DMA3Q. In one embodiment, the polyacrylamides comprise 90 to 99.5 % by weight of acrylamide, 0.5 to 2 % by weight of at least one associative monomer, and 0 % to 9.5 % by weight of and anionic monomer, for example ATBS or a cationic monomer, for example DM3AQ. Preferably, the associative monomer(s) have the general formula (V) including the preferred embodiments mentioned above.

In all embodiments mentioned above, the amount of the monomers relates to the total of all monomers in the polymers. Further water-soluble, monoethylenically unsaturated monomers may be present besides those specifically mentioned, however, the embodiments each include also one embodiment in which besides the monomers specifically mentioned no further monomers are present, i.e. the total amount of the monomers specifically mentioned is 100 % by weight.

The weight average molecular weight M_w of the polymers to be manufactured may be selected by the skilled artisan according to the intended use of the polymers.

Preferably, the weight average molecular weight M_w of the polymers to be

manufactured, in particular polyacrylamides to be manufactured usually ranges from 1 ^*10⁶ g/mol to 50^*10⁶ g/mol, preferably from 1.5^*10⁶ g/mol to 40^*10⁶ g/mol, more preferably from 2^*10⁶ g/mol to 30^*10⁶ g/mol, and for example from 5^*10⁶ g/mol to 25^*10⁶ g/mol.

Step [1 ] - Providing an aqueous polymer gel

In course of step [1], an aqueous polymer gel comprising 5 % to 45 % by weight of a water-soluble polymer is provided, wherein the aqueous polymer gel is obtainable by polymerization of an aqueous solution comprising water-soluble, monoethylenically unsaturated monomers.

The concentration of the monomers in the aqueous monomer solution more or less corresponds to the polymer concentration in the aqueous polymer gel. In particular, the concentration of the monomers in the aqueous monomer solution is from

5 % by weight to 45% by weight, wherein the percentages relate to the total of all components of all components of the aqueous monomer solution. Suitably the contents of monomer in the aqueous monomer solution may be from 8 % to 40 % by weight, desirably from 15 % to 40 % by weight, preferably from 20 to 35 % by weight and for example from 20 to 25 % by weight. "Providing an aqueous polymer gel" shall mean that the aqueous polymer gel is available at the site at which the process according to the present invention is conducted. In one embodiment of the invention, the polymerization of the aqueous solution comprising monoethylenically unsaturated monomers may be conducted at the same site. In another embodiment of the invention, the polymerization may be conducted at another site and the aqueous polymer gel transported to the site the process according to the present invention is conducted. Correspondingly, the term "means for providing an aqueous polymer gel" may be a polymerization unit for conducting the polymerization or a transport unit for transporting the aqueous polymer gel to the site of use. In yet another embodiment of the invention, it may be a transportable polymerization unit, i.e. a unit allowing polymerizing the aqueous solution comprising water-soluble, monoethylenically unsaturated monomers thereby obtaining an aqueous polymer gel and transporting the polymerization unit filled with the aqueous polymer gel to another site for further handling.

Preferably, the aqueous monomer solution is polymerized in the presence of suitable initiators for radical polymerization under adiabatic conditions. Such a polymerization technique is also briefly denominated by the skilled artisan as "adiabatic gel polymerization". Reactors for adiabatic gel polymerization are unstirred. Due to the relatively high monomer concentration the aqueous monomer solution used solidifies in course of polymerization thereby yielding an aqueous polymer gel. The term "polymer gel" has been defined for instance by L. Z. Rogovina et al., Polymer Science, Ser. C, 2008, Vol. 50, No. 1 , pp. 85-92.

"Adiabatic" is understood by the person skilled in the art to mean that there is no exchange of heat with the environment. This ideal is naturally difficult to achieve in practical chemical engineering. In the context of this invention, "adiabatic" shall consequently be understood to mean "essentially adiabatic", meaning that the reactor is not supplied with any heat from the outside during the polymerization, i.e. is not heated, and the reactor is not cooled during the polymerization. However, it will be clear to the person skilled in the art that - according to the internal temperature of the reactor and the ambient temperature - certain amounts of heat can be released or absorbed via the reactor wall because of temperature gradients, but this effect naturally plays an ever lesser role with increasing reactor size. The polymerization of the aqueous monomer solution generates polymerization heat. Due to the adiabatic reaction conditions the temperature of the polymerization mixture increases in course of polymerization. The polymerization of the aqueous monomer solution comprising monoethylenically unsaturated monomers is performed in the presence of suitable initiators for radical polymerization. Suitable initiators for radical polymerization, in particular adiabatic gel polymerization are known to the skilled artisan. Before polymerization the aqueous monomer solution should be inerted in basically known manner.

In a preferred embodiment, redox initiators are used for initiating. Redox initiators can initiate a free-radical polymerization even at temperatures of less than +5°C. Examples of redox initiators are known to the skilled artisan and include systems based on Fe²⁺/Fe³⁺ - H2O2, Fe²⁺/Fe³⁺ - alkyl hydroperoxides, alkyl hydroperoxides - sulfite, for example t-butyl hydroperoxide - sodium sulfite, peroxides - thiosulfate or alkyl hydroperoxides - sulfinates, for example alkyl hydroperoxides/ hydroxymethane- sulfinates, for example t-butyl hydroperoxide - sodium hydroxymethanesulfinate. Furthermore, water-soluble azo initiators may be used. The azo initiators are preferably fully water-soluble, but it is sufficient that they are soluble in the monomer solution in the desired amount. Examples of suitable azo initiators include 2,2'-azobis[2-(2- imidazolin-2-yl)propane] dihydrochloride, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, 2,2'-azobis[N-(2-carboxyethyl)-2-methylpropionamidine hydrate, 2,2'- azobis{2-[1 -(2-hydroxyethyl)-2-imidazolin-2-yl]propane} dihydrochloride, 2,2'-azobis(1 - imino-1 -pyrrolidino-2-ethylpropane) dihydrochloride or azobis(isobutyronitrile).

In one embodiment of the invention a combination of at least one redox initiator and at least one azo initiator is used. The redox initiator efficiently starts polymerization already at temperatures below +5°C. When the reaction mixture heats up, also the azo initiators decompose and start polymerization.

Besides monomers and initiators, also additives and auxiliaries may be added to the aqueous monomer solution.

Examples of such further additives and auxiliaries comprise bases or acids, complexing agents, defoamers, surfactants, or stabilizers. Radical polymerization starts after adding the initiator solutions to the aqueous monomer solution thereby forming an aqueous polyacrylamide gel. Due to the polymerization heat generated in course of polymerization and the adiabatic reaction conditions, the temperature in the polymerization unit increases. The temperature of the aqueous monomer solution before the onset of polymerization should not exceed 30°C and preferably may be from -5°C to +5°C. The temperature after polymerization may be in the range from 50°C to 95°C, for example from 55°C to 70°C. The polymerization may be performed in a polymerization unit having a volume of 1 m³ to 40 m³, preferably from 5 m³ to 40 m³, and for example 20 m³ to 30 m³. The polymerization unit may be a transportable polymerization unit which may be transported for instance by trucks or railcars. The polymerization unit may be of cylindrical or conical shape. One preferred embodiment is schematically shown in Figure 1 . The preferred polymerization unit (hereinafter denoted as "P1 ") comprises a cylindrical upper part (1 ) and a conical part (2) at its lower end. At the lower end, there is a bottom opening (3) which may be opened and closed. After polymerization, the polyacrylamide gel formed is removed through the opening (3). It furthermore comprises means (4) such as legs or similar elements allowing to deploy the transportable polymerization unit in a vertical manner. The diameter (D) of the polymerization unit in the cylindrical section may in particular be from 1 .5 to 2.5 m, preferably from 2 m to 2.5 m and the length (L) of the cylindrical section may be from 4 to 6 m, preferably 5 to 6 m. The conus angle a in the conical part (see also Figure 1 ) may be from 15° to 90°, preferably from 20° to 40°. The diameter of the bottom opening (3) may for example be from 0.2 to 0.8 m, in particular from 0.4 to 0.7 m, preferably from 0.5 to 0.7 m. The volume of the preferred

polymerization unit described herein may preferably be from 20 m³ to 30 m³. Besides the opening (3) the polymerization unit comprises one or more feeds for the aqueous monomer solution, initiator solutions, gases such as nitrogen or other additives. The inner wall of the transportable polymerization unit may be coated with an anti-adhesive coating. For polymerization and removal of the polymerization unit P1 is operated in a vertical position as depicted in Figure 1 . For transport, it may preferably be tilted to a horizontal position.

After polymerization, the aqueous polymer gel is removed from the polymerization unit. Basically, removeable the aqueous polymer gel may be performed by any kind of technology. The details depend on the specific design of the polymerization vessel and the connected equipment for comminuting and dissolving the aqueous polymer gel.

Preferably, the aqueous polymer gel may be removed by applying pressure onto the gel and pressing it through an opening in the polymerization unit. By the way of example, pressure may be generated by mechanical means such as a piston, by means of gases such as compressed air, nitrogen, argon or by means of aqueous fluids, in particular water.

For removeable the polymer gel from the preferred polymerization unit P1 described above the polymerization unit P1 is operated in vertical position. The aqueous polymer gel is removed through the opening (3) at the bottom which is opened for the purpose of removeable by applying pressure onto the gel from the top side of the reactor.

Pressure may be applied using gases and/or water. Examples of gases comprise pressurized air, nitrogen or argon. Basically, any kind of gas may be used, provided it does not react with the polymer gel. The pressure to be applied for removeable the gel may be selected by the skilled artisan. Factors relevant for the selection of the pressure include the viscosity of the polymer gel, the width of the bottom opening (3), the geometry of the polymerization unit or -if present- the kind of anti-adhesive layer. For example, pressures may range from 1 10,000 Pa to 1 ,000,000 Pa, in particular 150,000 Pa to 750,000 Pa, for example 200,000 Pa to 500,000 Pa (absolute pressures).

Removing the aqueous polyacrylamide gel may be supported by a thin water-film at the inner walls of the reactor, in particular on the walls of the conical part of the reactor. Such a thin water-film may be generated by injecting water or an aqueous fluid through fine holes in the wall of the reactor into the reactor, in particular holes in the conical part. Step [2] Comminution and dissolution of the aqueous polymer gel

In course of step [2] the aqueous polymer gel is comminuted and dissolved in an aqueous liquid, thereby obtaining an aqueous polymer solution.

Comminuting the aqueous polymer gel before dissolution in an aqueous liquid is helpful, because smaller gel particles dissolve more quickly in the aqueous liquid than larger gel particles. It should be kept in mind that already removing the aqueous polymer gel from the polymerization unit may cause some disintegration of the gel into smaller gel pieces.

Step [2] comprises at least the following two sub-steps, namely [2-1 ] conveying the aqueous polymer gel through a comminution unit comprising at least

• a perforated sheet, and

• moveable cutting means,

and adding at least a portion of the aqueous liquid into the comminution unit, wherein the relative velocity between the cutting means and the aqueous polymer gel does not exceed 3 m/s,

[2-2] adding the remainder of the aqueous liquid to the aqueous mixture

comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel obtained in course of step [2-1] and dissolving the aqueous polymer gel pieces in the aqueous liquid thereby obtaining said aqueous polymer solution.

The aqueous liquid used for dissolving the aqueous polymer gel comprises water. The term "water" includes any kind of water such as desalinated water, fresh water or water comprising salts, such as brines, sea water, formation water, or mixtures thereof.

Besides water, the aqueous liquid may comprise organic solvents miscible with water, however the amount of water relating to the total of all solvent should be at least 70 % by weight, preferably at least 90 % by weight, more preferably at least 95 % by weight. In one preferred embodiment, the aqueous liquid comprises only water as solvent. Furthermore, the aqueous liquid may optionally also comprise additives such as for example surfactants, complexing agents, bases, acids of the like. Kind and amount of such additives may be selected according to the intended use of the aqueous polymer solution. Of course, additives may also be added at a later stage, for example after complete dissolution of the aqueous polymer gel. Step [2-1 ] The comminution unit comprises at least a perforated sheet and moveable cutting means. It furthermore comprises means for adding aqueous liquid into the comminution unit.

The comminution unit comprises at least one inlet for feeding the comminution unit with the aqueous polymer gel and an outlet for removing the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel as already described above. Basically, the inlet and the outlet may be in any suitable orientation. In one embodiment, the comminution unit may be substantially upright with the inlet at the upper end and the outlet at the lower end. In another embodiment, the inlet may be at the upper end and the outlet may be at the side of the comminution unit. In yet another embodiment, the comminution unit may comprise a bent section between the inlet and the outlet. For example, the bent section may be bent by 90°C. In such a comminution unit, the inlet may be at the upper end while the outlet is side wards.

The passage of the aqueous polymer gel through the comminution unit may be by gravity alone, or may be fed into the comminution unit under pressure, for instance, by pumping, mechanically feeding, by gas pressure or by the action of a vacuum. In one embodiment, the aqueous polymer gel is fed into the comminution unit by means of pressure, in particular of gas or water pressure. Using external pressure may result in a more uniform and/or quicker passage of the aqueous polymer gel through the comminution unit, even in case the passage by gravity only basically is possible.

In another embodiment, the aqueous polymer gel may be fed into the comminution unit by means of screw conveyors.

In other embodiments, the aqueous polymer gel may be fed into the comminution unit by a pump. Such a pump may be helpful in achieving a constant feed rate and a constant pressure. Suitable are all pumps capable of transporting aqueous polymer gels, in particular positive displacement pumps such as a progressive cavity pump or a screw spindle pump.

According to the invention, at least a portion of the aqueous liquid to be used for dissolving the aqueous polymer gel is already added in course of step [2-1 ] and the remainder in course of step [2-2]. The term "at least" also includes that all aqueous liquid is already added in course of step [2-1 ] so that there is no remainder to be added in step [2-2]. In a preferred embodiment, the aqueous liquid is not completely added in course of step [2-1] and the remainder is added in course of step [2-2]. The portion of aqueous liquid to be added already into the comminution unit in course of step [2-1 ] may be from 1 % to 100 % by wt. relating to the total of aqueous liquid to be used for dissolving the aqueous polymer gel, preferably from 1 % by wt. to 80 % by wt., more preferably from 10 to 50 % by wt.. In course of step [2-1] already a part of the aqueous polymer gel dissolves in the aqueous liquid thereby yielding the abovementioned mixture of comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel. Basically, the portion of aqueous liquid to be added in course of comminution may be added at any point of the comminution unit. Preferred embodiments will follow below.

The perforated sheet extends across the entire cross section of the comminution unit so that the aqueous polymer gel is forced to pass through the hole perforated sheet when being conveyed through the comminution unit. In the context of the present invention, the term "perforated sheet" means any sheetlike device comprising flow paths for the aqueous polymer gel as well as areas which do not allow the gel to flow. When the aqueous polymer gel passes through a perforated sheet strings, cords or pieces of aqueous polymer gel may be formed. Basically, any kind of perforated sheets may be used in the context of the present invention. In one embodiment of the invention, perforated sheets are selected from hole perforated sheets, sieves or nettings.

Hole perforated sheets comprise holes. The shape of the holes is not specifically limited. Examples comprise circular holes, ellipsoidal holes, triangular holes, quadrangular holes such as quadratic, rectangular, or rhombic holes, pentagonal holes, hexagonal holes or star-like holes but also longitudinal holes such as slots. The holes may be cylindrical holes but they may also be conical. The dimensions of the holes are not specifically limited. However, preferably at least one dimension of the holes should be from 0.5 to 5 mm. In one embodiment of the invention, the hole perforated sheet comprises circular holes having a diameter from 0.5 to 5 mm, for example from 1 mm to 3 mm. The area of the holes in the hole perforated sheet may be from 10 % to 50 %, for example from 20 to 30 % of the total area of the hole perforated sheet. The distance between the holes should be selected such that the mechanical stability of the hole perforated sheet is ensured and that the strings (or cords) of aqueous polymer gel formed by conveying the aqueous polymer gel through the hole perforated sheet do not paste together after passage through the hole perforated sheet. In one embodiment, the closest distance between individual holes should not be less than 1 mm.

The hole perforated sheet preferably is made of metals, in particular steel. It may be just one, solid sheet but it may also be a compound of two or more individual sheets. The sheet may be self-supporting or it may comprise supports such as a supporting grid to provide mechanical stability. The total thickness of a self-supporting hole perforated sheet may be for example from 5 mm to 50 mm, preferably from 5 mm to 20 mm. Sheets comprising a support may be thinner, for example from 1 mm to 3 mm.

Nettings may be any kinds of nettings. The openings in the nettings may be for example square openings, rectangular or rhombical openings. The open area of nettings may be up to 70% of the total area of the netting.

The perforated sheet may be an even sheet. In other embodiments, it may have an uneven shape. For example, the sheet may be bent, folded or both. In one embodiment of the invention, the perforated sheet may be a half-pipe.

The comminution unit furthermore comprises at least one moveable cuttings means. The term "moveable" means that the cutting means are no static cutting means such as a static knife but move in course of cutting the aqueous polymer gel. The movement basically may be any kind of movement such as rotation, oszillation or a linear movement. In a preferred embodiment of the invention the moveable cutting means are rotatable cutting means.

In order to avoid high shearing forces which might damage the polymers, within the context of the present invention the relative velocity between the movable cutting means and the aqueous polymer gel should not exceed 3 m/s, preferably 2 m/s.

Depending on the nature and construction of the movable cutting means, the relative velocity may be constant for the entire cutting means or it may vary. The latter may specifically be the case for rotating cutting means. Naturally, the effective velocity of such a rotating cutting means increases from the rotation axis towards the end of the cutting means.

In one embodiment of the invention, moveable cutting means may be selected from moveable knives, cutting rollers and moveable water-jets having a pressure of at least 150^*10⁵ Pa, preferably from rotating knives, cutting rollers and rotating water-jets having a pressure of at least 150^*10⁵ Pa.

The comminution unit may comprise only one of such moveable cutting means, two or more of the same cutting means or a combination of at least two different of said cutting means. In one embodiment of the invention the comminution unit comprises at least one moveable knife. In another embodiment, the comminution unit comprises at least one moveable water-jet, preferably two or more than two water-jets. The cutting means may be arranged -in flow direction- before and/or after the perforated sheet. In case of a vertical comminution unit the cutting means may be arranged above and/or below the hole perforated sheet. According to the invention, the cutting means are arranged nearby the perforated sheet. Preferably, the distance between the cutting means and the perforated sheet is less than 10 cm, preferably less than 5 cm, for example less than 1 cm. Depending on the construction of the comminution unit, the distance between the cutting means and the perforated sheet may not be constant. Should this be the case, said distance relates to the shortest distance between the cutting means and the perforated sheet

By the way of example, a moveable knife may have a distance of 0 mm to 5 mm, for example from 0 mm to 1 mm. A distance of 0 mm means, that the knife is in contact with the perforated sheet. For water-jets, the distance between the center of the nozzles and the perforated sheet may be for example from 5 mm to 10 mm.

In another embodiment, a moveable knife may be integrated with a hole perforated sheet. Such an embodiment may be realized by using a stack of at least 3 hole perforated sheets wherein the middle one is movable.

A moveable water-jet used as cutting means has a pressure of at least 150^*10⁵ Pa. The pressure may be considerably higher than this, for instance, up to 10,000^*10⁵ Pa. However, it is not normally necessary for the pressure to be as high as this and lower pressures, for instance no higher than 7,500^*10⁵ Pa are usually adequate. In one embodiment of the invention, the pressure of the water jet is from 150^*10⁵ Pa to 5,000^*10⁵ Pa, preferably from 200^*10⁵ Pa to 2,000^*10⁵ Pa, more preferably from 250^*10⁵ Pa to 1000^*10⁵ Pa.

Typically, the water-jet would flow from a nozzle having a nozzle orifice of suitable diameter. By the term nozzle we mean a device which is designed to control the direction or the characteristics of a fluid flow, including to increase the velocity, as it exits. In general, the nozzle orifice diameter should be from 0.1 mm to 3.00 mm, for instance, from 0.25 mm to 2.00, or from 0.25 mm to 1 .00 mm, suitably from 0.30 mm to 0.90 mm, desirably from 0.40 mm 0.80 mm. In one embodiment of the invention, a multiplicity of nozzles is arranged on at least one head, each head containing from 2 to 10 nozzles, for example 2 to 4 nozzles.

The at least one nozzle may perform any kind of movement. Preferably, it may rotate or oscillate thereby generating a rotating or oscillating water-jet.

In one embodiment, the at least one nozzle oscillates. Such oscillation of the nozzle may produce a fan shaped water stream sweep pattern. Each oscillating nozzle may have a sweep of up to 180°. Typically, the sweep may be 30° to 180°, for instance from 35° to 75°. The exact range of the sweep will often depend on the exact number of nozzles employed. The oscillation frequency should for instance be up to 50 s^_1 (cycles per second), typically from 0.5 S^"1 to 50 s^_1. In another preferred embodiment of the invention, the at least one nozzle rotates and the stream of aqueous liquid generated forms a circular sweep pattern. The at least one nozzle may be a multiplicity of nozzles housed on at least one head. Such at least one rotating nozzle may be rotated by the action of a suitable motorized drive mechanism.

In one embodiment of the invention, the at least one rotating nozzle, or at least one head comprising two or more nozzles is mounted centrally and the aqueous liquid stream extends substantially perpendicular to the axis of the direction of the incoming aqueous polymer gel. In this embodiment, the aqueous liquid stream sweep pattern is disc shaped. In an adaptation of this preferred aspect the rotating nozzle or head, which is/are mounted centrally, may generate at least one stream of liquid which is not perpendicular to the direction of the incoming aqueous polymer gel, but instead is angled such that the at least one aqueous liquid stream sweep pattern is a cone shaped, for instance, an upright cone where the at least one aqueous liquid stream is angled downwards, or an inverted cone where the at least one aqueous liquid stream is angled upwards. Where the at least one aqueous liquid stream is angled either upwards or downwards it is preferred that the angle is no more than 50° up or down from the position which is perpendicular to the direction of the incoming aqueous polymer gel. Preferably this angle should be from 5° to 45°, more preferably from 10° to 35°, particularly from 15° to 25°.

In a further embodiment of the invention, the at least one rotating nozzle or rotating head is not mounted centrally but off center. For instance, the rotating nozzle may be located at or close to the wall of the surrounding wall section. Typically, the nozzle or head would be orientated such that it generates at least one eccentric aqueous stream sweep pattern.

The rotating nozzle or rotating head may rotate at a frequency of up to 3000 rpm (revolutions per minute (i.e. 50 s^_1 cycles per second)). The rotational frequency may be selected by the skilled artisan. A higher rotational frequency, for example a rotational frequency from 500 rpm to 3000 rpm) may by trend tear the aqueous polymer gel into smaller parts while a smaller rotational frequency, for example from 10 rpm to less than 500 ppm, preferably 20 rpm to 200 rpm more properly cuts the aqueous polymer gel.

Desirably, a curtain of aqueous liquid is provided on the inside of the surrounding wall section. "Aqueous liquid" shall have the meaning as defined above. This curtain of aqueous liquid may help prevent aqueous polymer gel from sticking to the wall of the surrounding wall section and reduce friction of the moveable polymer thereby reducing necessary static pressure or avoiding additional mechanical means to move the polymer towards the cutting area. Such curtain of aqueous liquid may be produced by providing a secondary water supply. Typically, the pressure of the water should be below 30 bar, for instance, from 3 bar to 20 bar, desirably from 5 bar to 10 bar. The water may be fed to a ring main, in the form of an annulus, and mounted on the inside of the surrounding wall section. In order to be most effective, the ring main or annulus should be mounted at or close to the top of the surrounding wall section to provide the maximum protection by the curtain of aqueous liquid. Desirably the aqueous liquid flows from the ring main or annulus down the inner surface of the wall of the surrounding wall section as a curtain.

In one embodiment, the comminution unit may comprise additionally a sieve tray. It is the aim of using a sieve tray to prevent oversized aqueous polymer gel pieces from passing into the dissolution stage. The sieve tray should have openings of a size corresponding to the maximum size of aqueous polymer gel pieces which should be allowed to pass to the next stage. A sieve tray would be mounted -in flow direction- after the perforated sheet and the cutting means. Suitably the sieve tray may be a mesh formed by a plurality of inter-meshing wires or bars. Alternatively, the sieve tray may be formed as a surface with a plurality of holes cut therein, for instance, analogous to a colander. Preferably, the sieve tray may be affixed to the surrounding wall section. It may also be desirable for additional streams of aqueous liquid to be directed at the surface of the sieve tray in order to facilitate the size reduction of the oversized aqueous polymer gel pieces captured by the tray.

Figure 2 illustrates schematically a comminution unit for the aqueous polymer gel comprising a combination of perforated sheet and rotating water-jets. The comminution unit comprises a surrounding wall section (10), in this case a tubular wall, surrounding a centrally mounted nozzle (1 1 ) which rotates and is driven by a motor (12) or propelled by the flowing water, which forms the stream. The nozzle is supported on a fixed mounting (13). A high-pressure stream of aqueous liquid (14) is ejected perpendicular to the axis of the device and rotates as the nozzle rotates. The stream of aqueous liquid forms a circular disc pattern as the nozzle rotates. The nozzle is fed from a feed line (15) supplied by a high-pressure source (16) for aqueous liquid. A perforated sheet (17) is located above the water-jets. A secondary supply (18) for aqueous liquid of low pressure is fed into a ring main (20), in the form of an annulus, located at the upper end of the tubular wall. Aqueous liquid flows out of the annulus to form a curtain (19) of aqueous liquid, which prevents aqueous polymer gel from sticking to the tubular wall. The aqueous polymer gel (21 ) enters the comminution unit from above and passes at first through the perforated sheet (17). The perforated sheet generates strings of aqueous polymer gel ("spaghetti") which are cut thereafter the water-jets to form aqueous polymer gel pieces and then mixture of aqueous liquid and the cut aqueous polymer gel pieces (22) exit from the bottom of the device. The comminution unit may comprise only one nozzle or only one head. Preferably, a head comprising 2 to 4 nozzles may be used. In other embodiments, two or more heads may be used, for example 2 to 4 heads which may be arranged in a suitable geometry below or above the perforated sheet.

The portion of aqueous liquid to be added into the comminution unit comprising at least a combination of water-jets and a perforated sheet may be low. Adding only 1 % by weight of aqueous liquid relating to the total amount of liquid to be used for dissolving the aqueous polymer gel may already significantly improve transport of the aqueous polymer gel through the comminution unit and its comminution. In certain

embodiments, the amount may be from 1 % to 10 % by weight.

In another embodiment, the comminution unit comprises a combination of at least a perforated sheet, preferably a hole perforation sheet and a moveable knife, preferably a rotating knife. The knife may be mounted -in flow direction- before or after the perforated sheet, preferably after the perforated sheet. It may be made of spring steel or pressed onto the perforated sheet by springs. The aqueous liquid is added into the cutting space and may be added through one or more than one inlets for aqueous liquid. If the aqueous liquid is added before the perforated sheet for example 5 % to 25 % of the total amount of aqueous liquid may be added. If the aqueous liquid is added after the perforated sheet for example up to 100 % of the total amount of aqueous liquid may be added, for example up to 50 % by weight, preferably 20 to 50 % by weight. Figure 3 illustrates schematically a comminution unit for the aqueous polymer gel comprising a combination of perforated sheet and a rotating knife. The comminution unit is similar to that illustrated in Figure 2, however instead of a water-jet the comminution unit comprises a rotating knife (23). In that embodiment, water is introduced through a water supply (24) into the space below the perforated sheet (17).

In another embodiment of the invention, the cutting means is a cutting roller. Such a cutting roller comprises a rotating roll which comprises one knife or more than one knives fixed to the roll. The perforated sheet is bent, for example a half-pipe having a radius adapted to the radius of the roller comprising knives and arranged above the roller in such a manner that the knives of the rotating roll cut the aqueous polymer gel passing through the perforated sheet. A portion of the aqueous liquid is introduced into the cutting space after the perforated sheet.

The particle size of the aqueous polymer gel pieces obtained in course of step [2-1 ] is not specifically limited. Factors relevant for the particle size include the diameter of the holes in the perforated sheet and the layout and arrangement of the moveable knives and/or moveable water-jets. In an embodiment of the invention, pieces of aqueous polymer gel should conveniently have a size such that at least two dimensions are no more than 5 mm. Preferably three dimensions of the aqueous polymer gel pieces should be no more than 0.5 cm. There is no lower limit necessary for the aqueous polymer gel pieces, since the smaller the pieces the easier it will be for the polymer to dissolve. Frequently, aqueous polymer gel pieces obtained in course of step [2-1] may have a size such that three dimensions are as low as 1 mm or smaller. Often the aqueous polymer gel pieces tend to have three dimensions each of from 1 mm to 5 mm. Basically, the aqueous polymer gel may be transferred by any means from a polymerization unit used for polymerization. For example, the aqueous polymer gel may be transferred into the comminution unit by screw conveyors or belt conveyors.

In one embodiment of the invention, the comminution unit may be connected directly with such a polymerization unit. For that purpose, an opening, preferably a bottom opening, in the polymerization unit may be connected with the comminution unit and the aqueous polymer gel may the transferred directly through the opening in the polymerization unit into the comminution unit. Preferably, the comminution unit according to the present invention is connected with the polymerization unit P1 described above. For connection, the bottom opening (3) of the polymerization unit is connected with the comminution unit. Preferably, the comminution unit is in vertical position and the comminution unit located directly under the bottom opening (3), so that the aqueous polymer gel which is pressed through the bottom opening (3) directly enters into the comminution unit. Preferably, the aqueous polymer gel is removed from the polymerization unit by pressing gas, such as nitrogen, argon or pressurized air and/or aqueous liquid, in particular water, onto the upper surface of the aqueous polymer gel and pressing the aqueous polymer gel plug flow like through the bottom opening (3).

Figures 4 to 8 schematically show several embodiments of comminution units according to the present invention connected with a polymerization unit having an upper cylindrical part and a lower conical part, in particular a polymerization unit P1. Figure 4 schematically shows a polymerization unit having an upper cylindrical part (30), a lower conical part (31 ) and a bottom opening (35) which may be opened and closed. The polymerization unit is connected with a comminution unit comprising a perforated sheet (32). One rotating head (33) for water-jets (34) is mounted below the perforated sheet. The aqueous polymer gel is removed from the polymerization unit (30) by opening the bottom opening (35) and applying pressure, in particular gas pressure, onto the upper surface of the aqueous polymer gel in the polymerization unit The gel is conveyed through the opened bottom opening (35) into the comminution unit. In the comminution unit is passes the perforated sheet thereby forming strings of aqueous polymer gel which are cut thereafter by the water-jets to form aqueous polymer gel pieces. The mixture of aqueous liquid and the cut aqueous polymer gel pieces (22) exit from the bottom of the device. Figure 5 shows a similar embodiment except that not one but two heads comprising nozzles are mounted below the perforated sheet. Of course, also more than two heads comprising nozzles may be used, for example 4 heads.

Figures 6 and 7 show similar embodiments in which the nozzle(s) for water-jets are mounted above and not below the perforated sheet.

Figure 8 schematically shows an alternative embodiment comprising a rotating knife mounted below the perforated sheet for cutting. Its function is the same a detailed above (figures 4 and 5), except that a mechanical knife and not water-jets are used for cutting the strings of polymer gel. In this embodiment, aqueous liquid (37) is added into the cutting space below the perforated sheet. The aqueous liquid may be added through one or more than one inlets for the aqueous liquid.

Comminuting aqueous polymer gels with the comminution unit may be a one-step process, i.e. the comminution unit comprises one perforated sheet and one of more cutting means. In other embodiments, it may comprise two or more perforated sheets with decreasing size of holes. Cutting may be performed at least at the last of the perforated sheets. The comminution unit may optionally comprise additional means for comminuting the aqueous polymer gels besides those disclosed above. However, if such additional means are present, they should not generate high shear forces in order to avoid damaging the polymers. For example, using Urschel-mixers as described in the state- of-the-art should be avoided. In one embodiment, in course of step [2-1 ] only the combination of a perforated sheet and movable cuttings means as described above is used.

Although the focus of step [2-1] is on comminuting the aqueous polymer gel, already a certain part of the aqueous polymer gel dissolves in the aqueous liquid added thereby yielding a mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel. The amount of aqueous polymer gel which already dissolves in the aqueous liquid may depend on the chosen comminution technology. If water-jets are used for comminution already a significant part of the aqueous polymer gel may already dissolve. This is an important difference to the method disclosed in US 4, 1 13,688 which excludes that significant amounts of aqueous polymer gels already dissolve in course of cutting the aqueous polymer gel. Step [2-2]

After comminuting the aqueous polymer gel in course of step [2-1 ], the obtained mixture is transferred comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel is transferred to a dissolution unit for carrying out step [2-2]. For example, the mixture may be transferred through a pipe connecting the comminution unit and the dissolution unit.

In course of step [2-2], the remainder of the aqueous liquid -if any- is added to the mixture of an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel obtained in course of step [2-1 ] and the aqueous polymer gel pieces are dissolved in the aqueous liquid, thereby obtaining an aqueous polymer solution. Additional aqueous liquid -if any- may be added into the dissolution unit and/or it may be added in course of transferring the mixture to the dissolution unit, for example by adding it into a pipe connecting the comminution unit with the dissolution unit. Of course, both possibilities may be combined, i.e. a part if the remainder is added in course of transfer and another part is added into the dissolution unit.

The dissolution of the aqueous polymer gel pieces in the aqueous liquid basically may be performed in any kind of dissolution unit. Examples of suitable dissolution units comprise stirred vessels. A dissolution unit may only comprise one vessel or it may comprise more than one vessel which may be operated in series or in parallel. Mixing may also be achieved by flowing the contents of the dissolution vessel out through a conduit and then recirculating back into the mixing vessel. Other examples comprise a combination of static mixers with unstirred vessels or in-line dispersing such as rotor- stator units. The concentration of the aqueous polymer solution is selected by the skilled artisan according to the intended use of the solution. Typically, the concentration of the aqueous polymer solution may be up to 2% by weight, for instance, from 0.01 to 2%, suitably from 0.05 to 1.5%, often, 0.1 % to 1 %. Further embodiments of the invention

In another embodiment, the present invention relates to a process for producing an aqueous polymer solution, comprising at least the steps of

[2] comminuting and dissolving the aqueous polymer gel in an aqueous liquid, thereby obtaining an aqueous polymer solution, wherein step [2] comprises

[2-1 ] conveying the aqueous polymer gel through a comminution unit

comprising at least

• a perforated sheet, and

• moveable water-jets having a pressure of at least 150^*10⁵ Pa for cutting the aqueous polymer gel,

and adding at least a portion of the aqueous liquid into the

comminution unit,

Details of the process including preferred embodiments, in particular including preferred embodiments of water-jet-cutting have already been disclosed above and refer to the corresponding passages of the specification.

Apparatus for producing an aqueous polymer solution

In a further embodiment, the present invention relates to an apparatus for producing an aqueous polymer solution, comprising at least

(a) means for providing an aqueous polymer gel comprising 5 % to 45 % by

weight of a water-soluble polymer obtainable by polymerization of an aqueous solution comprising monoethylenically unsaturated monomers,

(b) a comminution unit for comminuting the aqueous polymer gel in the presence of an aqueous liquid thereby obtaining an aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel, wherein the comminution unit comprises at least

• a perforated sheet,

• movable cutting means, and

· means for adding aqueous liquid into the comminution unit,

(c) means for transferring the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel to a dissolution unit, and (d) means for adding additional aqueous liquid to the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel, and

(e) a dissolution unit for dissolving the aqueous polymer gel pieces in the

aqueous liquid thereby obtaining said aqueous polymer solution.

Details of the apparatus including preferred embodiments have already been disclosed above and we refer to the corresponding passages of the specification.

Preferably, the movable cutting means are moveable water-jets having a pressure of at least 150^*10⁵ Pa. Preferred embodiments of such a water-jet cutting unit have also been disclosed above.

Use of the aqueous polymer solutions

The aqueous polymer solutions manufactured according to the present invention, preferably the aqueous polyacrylamide solutions, may be used for various purposes, for example for mining applications, oilfield applications, water treatment, waste water cleanup, paper making or agricultural applications.

For the application, the aqueous polymer solutions, preferably the aqueous

polyacrylamide solutions may be used as such or they may be formulated with further components. The specific composition of aqueous polymer solutions is selected by the skilled artisan according to the intended use of the polymer solution.

Advantages of the process according to the invention

The present invention provides an advantageous process for dissolving aqueous polymer gels in aqueous liquids. As compared to other technologies, there are only little shear forces which is important for dissolving aqueous polymer gels of high- molecular weight polymers without damaging the polymer. The apparatus may be constructed very compact. Furthermore, it is an easy construction principle (in contrast to the construction principle of an impact mill for example) thereby enabling the construction of a cheap apparatus. Finally, the apparatus comprises no dead space in which aqueous polymers gels may dry and stick the apparatus.

Claims

A process for producing an aqueous polymer solution comprising the steps of

[2-1 ] conveying the aqueous polymer gel through a comminution unit

comprising at least

• a perforated sheet, and

• moveable cutting means,

and adding at least a portion of the aqueous liquid into the comminution unit,

[2-2] adding the remainder of the aqueous liquid to the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel obtained in course of step [2-1 ] and dissolving the aqueous polymer gel pieces in the aqueous liquid thereby obtaining said aqueous polymer solution.

Process according to claim 1 , wherein the perforated sheet is selected from hole perforated sheets, sieves and nettings.

Process according to claim 2, wherein the hole perforated sheet comprises circular holes having a diameter from 0.5 to 5 mm.

Process according to any of claims 1 to 3, wherein the moveable cutting means are selected from the group of moveable knives, cutting rollers and moveable water-jets having a pressure of at least 150^*10⁵ Pa.

Process according to any of claims 1 to 3, wherein the moveable cutting means are moveable water-jets having a pressure of at least 150^*10⁵ Pa.

Process according to claim 5, wherein the moveable water-jet(s) are generated from at least one moveable nozzle.

7. Process according to claim 5, wherein the moveable water-jets are generated from at least one moveable head comprising a multiplicity of nozzles. 8. Process according to claim 5, wherein the movable cutting water-jets are rotating water-jets.

9. Process according to claim 8, wherein the rotating water-jet(s) are generated from at least one rotating nozzle or from at least one rotating head comprising a multiplicity of nozzles.

10. Process according to any of claims 1 to 3, wherein the moveable cutting means are moveable knives. 1 1 . Process according to claim 10, wherein the moveable knife is a rotating knife.

12. Process according to any of claims 1 to 1 1 , wherein the cutting means are

arranged -in flow direction- after the perforated sheet. 13. Process according to any of claims 1 to 12, wherein 1 to 80 % by weight of the aqueous liquid -relating to the total amount of aqueous liquid- are added in course of step [2-1] and the remainder in course of step [2-2].

Process according to any of claims 1 to 12, wherein 10 to 50 % by weight of the aqueous liquid -relating to the total amount of aqueous liquid- are added in course of step [2-1] and the remainder in course of step [2-2].

Process according to claim 1 , wherein the perforated sheet is even, the cutting means is a rotating knife, which is arranged -in flow direction- after the perforated sheet, and a portion of the aqueous liquid is introduced into the cutting space after the perforated sheet.

16. Process according to claim 15, wherein the amount of aqueous liquid to be added into the cutting space is up to 50 % by weight of the entire amount of water needed for dissolving the aqueous polymer gel.

17. Process according to claim 1 , wherein the perforated sheet is bent, the cutting means is a cutting roller, which is arranged -in flow direction- after the perforated sheet, and a portion of the aqueous liquid is introduced into the cutting space after the perforated sheet.

18. Process according to any of claims 1 to 17, wherein the comminution unit is connected with a polymerization unit for conducting step [1 ].

19. Process according claim 18, wherein the polymerization unit comprises a

cylindrical upper part, a conical part at its lower end, and a bottom opening which may be opened and closed, and wherein the bottom opening is connected with the inlet of the comminution unit.

20. Process according to claim 18 or 19, wherein the aqueous polymer gel is

conveyed from the polymerization unit unto the comminution unit by means of gas pressure.

21 . Process according to claim 18 or 19, wherein the aqueous polymer gel is

conveyed from the polymerization unit unto the comminution unit by means of a screw conveyor.

22. Process according to any of claims 1 to 21 , wherein step [2-2] is carried out in at least one stirred vessel. 23. A process for producing an aqueous polymer solution comprising the steps of

[2-1 ] conveying the aqueous polymer gel through a comminution unit

comprising at least

• a perforated sheet, and

and adding at least a portion of the aqueous liquid into the comminution unit,

[2-2] adding the remainder of the aqueous liquid to the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel obtained in course of step [2-1 ] and dissolving the aqueous polymer gel pieces in the aqueous liquid thereby obtaining said aqueous polymer solution. An apparatus for producing an aqueous polymer solution, comprising at least

(a) means for providing an aqueous polymer gel comprising 5 % to 45 % by

• a perforated sheet,

• movable cutting means, and

• means for adding aqueous liquid into the comminution unit,

(c) means for transferring the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel to a dissolution unit, and

(d) means for adding additional aqueous liquid to the aqueous mixture comprising an aqueous liquid comprising dissolved aqueous polymer and undissolved pieces of aqueous polymer gel, and

(e) a dissolution unit for dissolving the aqueous polymer gel pieces in the

aqueous liquid thereby obtaining said aqueous polymer solution.

An apparatus according to claim 24, wherein the perforated sheet is selected from hole perforated sheets, sieves and nettings.

26. An apparatus according to claim 25, wherein the hole perforated sheet comprises circular holes having a diameter from 0.5 to 5 mm.

27. An apparatus according to any of claims 24 to 26, wherein the cutting means are selected from the group of moveable knives, cutting rollers and moveable water- jets having a pressure of at least 150^*10⁵ Pa.

28. An apparatus according to any of claims 24 to 26, wherein the moveable cutting means are moveable water-jets having a pressure of at least 150^*10⁵ Pa.

29. An apparatus according to claim 28, wherein the moveable water-jet(s) are

generated from at least one moveable nozzle.

30. An apparatus according to claim 29, wherein the moveable water-jets are

generated from at least one moveable head comprising a multiplicity of nozzles.

31 . An apparatus according to any of claims 24 to 26, wherein the movable cutting means are rotating water-jets having a pressure of at least 150^*10⁵ Pa.

32. An apparatus according to claim 31 , wherein the rotating water-jet(s) are

generated from at least one rotating nozzle nozzles or from at least one rotating head comprising a multiplicity of nozzles.

33. An apparatus according to any of claims 24 to 26, wherein the moveable cutting means are moveable knives.

34. An apparatus according to claim 33, wherein the moveable knife is a rotating knife.

An apparatus according to any of claims 24 to 34, wherein the cutting means are arranged -in flow direction- after the perforated sheet.

An apparatus according to claim 24, wherein the perforated sheet is even, the cutting means is a rotating knife, which is arranged -in flow direction- after the perforated sheet, and a portion of the aqueous liquid is introduced into the cutting after the perforated sheet.

An apparatus according to claim 36, wherein the amount of aqueous liquid to be added into the cutting space is up to 50 % by weight of the entire amount of water needed for dissolving the aqueous polymer gel.

An apparatus according to claim 27, wherein the perforated sheet is bent, the cutting means is a cutting roller, which is arranged -in flow direction- after the perforated sheet, and a portion of the aqueous liquid is introduced into the cutting after the perforated sheet.