AU2006232824B2

AU2006232824B2 - Method and device for producing concentrated polymer solutions

Info

Publication number: AU2006232824B2
Application number: AU2006232824A
Authority: AU
Inventors: Thorsten Buddenberg; Werner Fischer; Hartmut Pawel
Original assignee: Solenis Technologies Cayman LP
Current assignee: Solenis Technologies Cayman LP
Priority date: 2005-04-08
Filing date: 2006-04-05
Publication date: 2011-11-10
Anticipated expiration: 2026-04-05
Also published as: EP1882004B1; RU2007141413A; AP2007004177A0; CN101193952B; JP2008534757A; PT1882004E; BRPI0610690A2; DK1882004T3; RU2387679C2; CA2602039A1; AU2006232824A1; EP1882004A1; MX2007012455A; DE102005016401A1; CN101193952A; ES2544242T3; WO2006105942A1; MA29436B1; KR20080007574A; NO20075544L

Abstract

The invention relates to a method for producing concentrated polymer solutions from polymer granules, during which the granules are dispersed with water in a first stage, and are redispersed in a second stage with a lower mixing or dispersing efficiency/m. The invention also relates to a device for carrying out the method.

Description

- 1 Process and apparatus for the production of concentrated polymer solutions The present invention relates to a process for the production of solutions of water-soluble polymers from granulated polymers, particularly high molecular synthetic polymers and to an 5 apparatus for carrying out said process. Water-soluble polymers frequently have poor dissolution behavior, especially when they have a high molecular weight. Polyacrylamides, for example, represent a large group of water-soluble polymers. Acrylamide polymers are used predominantly in the form of their io high-molecular (mean molecular weight >105), anionic, cationic, or amphoteric copolymers in many areas of solid-liquid separation. Besides municipal wastewater treatment plants and the paper industry, the mining industry is another important user of flocculating agents. The polymers are used as an aqueous solution, the concentration of the polymer being about 15 0.5 wt%. When preparing the aqueous solutions, the required quantity of polymer is added to water with stirring and dispersed in the solution. Dispersal of the solid acrylamide polymers in water is hampered by their tendency to form lumps, i.e., to agglomerate, on contacting water. The lumps of solid polymer are formed directly after the introduction of the polymer powder into the water through encapsulation of undissolved solids in an outer coating of the water 20 wet polymer, which delays further penetration of water into the solid particles. These agglomerations are caused, in particular, by the fine fractions of the polymer powder below 200 pm. A ripening time of from 1 to 2 hours is necessary for complete dissolution of the polymer with 25 continued moderate stirring. In order to prepare the solution of active substance, a twin-tank system comprising a ripening tank and a storage tank, each having a capacity between 3 m 3 and 10 M 3 , is known, depending on the manufacturer or the desired capacity. After ripening, the prepared polymer solution is returned to the storage tank, where it is likewise continuously stirred and continuously removed therefrom till empty. Polymer solution freshly 30 prepared in the meantime in the ripening tank is then pumped into the empty storage tank. The polymer solution sometimes remains in the tank for several days before use because of the high filling volumes and long ripening, waiting, refilling, and evacuation times. Because of this, the effectiveness of the polymer solution may decrease due to biological and shear-induced degradation processes. In order to guarantee a semi-continuous supply of polymer solution, so-called three-chamber dissolving systems are used. In a three-chamber dissolving system, the granules wetted by -2 a tangential stream of water pass into the first chamber and are homogenized and dissolved by an agitator system. The rising liquid level in the first chamber causes the latter to overflow, and the solution thus passes into the second chamber, where an agitator is likewise present to effect homogenization and dissolution. When the liquid in the second chamber reaches 5 the overflow mark, the solution flows into the third chamber where homogenization and dissolution thereof is again effected by an agitator. A level gage having a minimum contact (start wetting process chamber 1) and a maximum contact (stop wetting process chamber 1) is present in the third chamber and starts or stops the wetting process in the first chamber according to the level of the liquid. The granules dissolved in this way can be used for the 10 production process after a ripening time of about 30-60 min. In addition, after the ripening time there are still portions of gel in the aqueous polymer solutions which contain undissolved polymer. The gel content not only causes a loss of action of the polymer solution but also leads to technical problems due to plugged screens 15 or, in the case of paper production, to irregular paper surfaces. Solutions up to a concentration of about 0.5 wt% can still be pumped so gently that no noticeable shearing degradation occurs during pumping. Forced conveyance of highly concentrated solutions is perfectly possible but will always result in part of the polymer being 20 degraded. Limitation to polymer solutions of low concentration on an industrial scale necessitates setting up large, unwieldy, and costly dissolving stations. To obtain polymer solutions as free from gel as possible, various shearing systems are known in the prior art which, however, in addition to reducing the amount of gel, cause 25 undesirable lowering of the viscosity of the polymer solution. The drop in viscosity is due to a reduction of the molecular weight of the polymers and causes reduced effectiveness. Thus, in WO 95/20 431 a process is described in which an aqueous gel containing polymer solution is passed under pressure through in-line filters of decreasing mesh width. 30 In EP 0 050 312 Al, an apparatus and a process are described for dispersing a polymer powder and subsequently dissolving it in a turbulent flow of solvent. In this case, great dependence on the grain size of the polymer powder is found. Dispersal takes place in an apparatus consisting substantially of a funnel with a filling opening for the polymer powder 35 and a tangential liquid feed, a drain pipe with an annular nozzle and a jet pump. In this case effect losses clearly appear due to undissolved swollen bodies at polymer powder grain sizes > 800 micrometers. Finely divided polymer powder contents lead to excessive solution -3 viscosity and to plugging of the apparatus. In EP 0 051 264 Al, a process is described for dissolving granules of polyacrylamide gels in turbulent streams. In this case, the dissolving stage is preceded by treatment of the polymer 5 granules with a solution of polyvalent salts over a period of up to 20 minutes. The swollen polymer bodies thus formed are recirculated through a flow-type apparatus consisting of the dissolving tank and a pipe system until the swollen bodies have been destroyed. The flow apparatus is described in DE-OS-28 07 709. Because of the added salts, the polymer solutions produced by this process display reduced effectiveness as flocculating agents. 10 DE-OS 26 27 367 describes a process and apparatus for mixing polymer polyelectrolyte powders with water, in which the powder is air-forced into a pipe and sprayed with liquid therein and subsequently liquid-entrained into a dissolving tank equipped with agitating means. It is recommended that the powder-transporting conduits be manufactured from 15 transparent plastics material to make it possible to locate plugs caused by agglomerated polymer powder. GB 2 067 908 discloses an apparatus and a process, in which a powder is air-forced into a vertical cylindrical column and is moistened for the purpose of forming a homogeneous 20 solution. The column has nozzles through which the solvent is fed. However, this process cannot prevent the formation of very small and extremely small gel particles. DE 102 10 511 Al discloses a dissolving apparatus in which a mixing tank is supplied via a vortex cup with liquid or powdered polymer and water. By means of mixing baffles in the 25 mixing tank two-zone recirculating mixing is created by circulation or turbulent flow intended to cause dissolution of the polymer powder. The ready-to-use polymer solution is withdrawn at the bottom of the dissolving apparatus. Polymer degradation results from the strong turbulence involved and impairs the effectiveness of the polymer solution. In practice, the dissolution of the powdered polymer presents problems due to the fact that unwanted gel 30 contents are not completely avoided. Batch polymer concentrations clearly exceeding 1 wt% cannot be produced with this apparatus. DE 32 43 671 describes an apparatus for continuous mixing of pulverulent materials with liquids in which the pulverulent solids are drawn through a central feed pipe into an annular 35 mixing chamber equipped with a rotary pump and impeller wheel with interspersed gear rings. A stream of liquid is introduced into the mixing chamber tangentially. The entrained powder is centrifuged with the liquid phase into the rotor-stator gear ring labyrinth and -4 colloidally dissolved or dispersed during this forced transport. This dispersion is then withdrawn through a stationary screen. DE 35 17 879 Al describes a development of this dissolving system modified by permanent 5 built-in multidisk rings. Despite the relatively elaborate mixing technique, this system is not suitable for the production of a totally gel-free solution of polyelectrolyte powders. Moreover, in the case of products sensitive to shearing such as high-molecular water-soluble flocculant polymers, a molecular weight decrease and therefore a loss of efficiency are caused. 10 DE 197 17 161 describes an apparatus for continuous breaking up a poorly wettable pulverulent material with a liquid, consisting of a tubular feed device for the pulverulent material and a dispersing device downstream thereof, a liquid being injected under pressure between the feed and dispersing units in order to prevent adhesions to areas in contact with the powder. In the case of highly viscous media, the dispersing device must have a pump 15 installed downstream thereof in order to assure reliable transportation of the liquid away from the dispersing device. EP 729 780 A2 describes an installation for dispersing a predefined quantity of liquid with a predefined quantity of pulverulent solids, in which the predefined quantity of liquid is 20 recirculated from its vigorously stirred supply tank a number of times through the mixing device and is thus enriched with additional solid each time. The problems of dissolving soluble solid powders are not discussed. DE 196 22 191 Al describes a process and apparatus for contamination-free metering and 25 conveying of solid powders from a powder supply container into a dispersing or dissolving tank in which said powders are to be dispersed or dissolved. The powder is metered, free of dust, into a funnel and drawn into a liquid jet pump at its bottom outlet, dispersed and dissolved and then conveyed to the dissolving tank. The process enables dust-free conveyance of the powder, but the dissolved polymers are not free of gel contents. 30 WO 92/21 436 discloses an apparatus for dispersing, suspending, or emulsifying gases, liquids and/or flowable solids, which has a disk-shaped rotor in a dispersing chamber with two material inlets and one product outlet. The streams of material are physically combined in the marginal region of the rotor disk equipped with teeth or vanes. Optionally, the 35 dispersing unit is operated with an additional stator exerting an additional dispersing and shearing action with its radial openings. Because of the intense shearing action occurring during dispersal and dissolution of granules of water-soluble polymers, efficiency losses are -5 incurred by molecular degradation. It would be advantageous to provide a process for dissolving water-soluble, pulverulent and, in particular, high molecular weight polymers, by means of which a substantially gel-free polymer solution is produced, thereby 5 dispensing with the cost of subsequent removal of the gel content. There should be no, or only slight, impairment of the effectiveness of the polymers caused by the process of the invention, i.e., in the dissolution process, the polymer molecules must be dissolved without significant destruction. It would be advantageous if the process can be carried out either batchwise for 10 short periods or continuously and enable the production of solution concentrations of> wt%. Accordingly the process of the invention should also offer the possibility of dissolving polymer powders with high contents of fine polymer particles below 250 im and, in particular, below 100 gm, which are usually difficult to dissolve, 15 without incurring disadvantages relating to the properties of the solution. There is provided a process for the production of an aqueous polymer solution from solid particles of a water-soluble polymer, by physically combining the water and polymer particles in a dispersing unit, characterized in that - dispersal of the particles in the water is conducted by applying a first power level 20 per cubic meter, - the water/particle mixture, after leaving the dispersing unit, is transferred to an agitated tank and substantially dissolved therein with stirring, - the aqueous polymer solution is, after its residence time in the agitated tank, subjected to a second dispersing operation in the dispersing using a lower power 25 level per cubic meter than in the first dispersal. In an embodiment of the invention there is provided a process for the production of an aqueous polymer dispersion from solid particles of a water-soluble polymer, by physically combining water and the polymer particles in a dispersing unit, wherein - 5a - a first dispersal of said particles in water is carried out while applying a first power level per cubic meter, - the water/particle mixture, after leaving said dispersing unit, is passed to an agitation tank, where the particles are substantially dissolved with stirring, 5 - the substantially dissolved water/particle mixture, following the residence time in the agitation tank, is subjected to a second dispersal in a dispersing unit at a lower power level per cubic meter than that used during the first dispersal. It has been found, surprisingly, that the production of aqueous, gel-free solutions of water-soluble polymers is possible while largely avoiding a decrease in the molecular 10 weight by means of double dispersal in which the second dispersal is conducted at a lower mixing or dispersing power level per cubic meter.

- U In a preferred embodiment for the first dispersal of the water/polymer powder mixture, the power level is limited to 550-1600 Wh/m 3 and more preferably to 100-1000 Wh/m 3 . If the mixing energy is too low, the dispersing effect is not optimal, resulting in a prolonged 5 residence time in the downstream agitator vessel. If the mixing energy is too high, partial destruction of the molecular structure of the polymers occurs, i.e., there is a substantial decrease in the molecular weight and a concomitant reduction of the effectiveness of the polymer as flocculant. 10 In the process of the invention a dispersing unit is preferably used such as is described in WO 92/21436. This document is incorporated herein by reference. The dispersing unit consists of a disk-shaped rotor in a dispersing chamber and is provided with two inlets for polymer powder and water respectively and one product outlet. The two material streams are physically combined in the marginal region of the rotor disk, preferably in the axial direction, 15 at which point the dispersing process takes place. The product outlet is located at the outer edge of the dispersing chamber. On its outer edge, the rotor has a rotor rim with teeth or radial openings. Optionally a stator provided with radial openings for dispersing the polymer powder may be provided in the dispersing apparatus for cooperation with the rotor. 20 After the first dispersing stage, the polymer/water mixture, in which the finer particles are already partially dissolved and the coarser polymer particles dispersed, is transferred to an agitated tank and stirred therein by slowly rotating agitators. This agitation ensures that substantially all of the polymer particles are wetted and subjected to incipient dissolution, and sedimentation during the remaining dissolving process is prevented, while shearing 25 degradation due to agitation does not occur with this arrangement. Suitable agitators that may be used in the process of the invention are, for example, straight-arm paddle agitators, vane agitators, and anchor agitators. The use of slowly rotating blade agitators at rotary speeds of up to 300 rpm have proven effective in the realization of the process. Other suitable agitators are known to the person skilled in the art. 30 The residence time of the polymer/water mixture in the agitated tank is preferably from 1 to 15 minutes, more preferably from 2 to 10 minutes and most preferably from 3 to 6 minutes. In the case of a continuous process in which the agitated tank is constantly charged with fresh polymer/water mixture, the above-mentioned residence times are applicable as average 35 residence times. Depending on the kind of polymer being dispersed, the residence time may fluctuate, e.g., cationic polymers often require a shorter residence time than anionic polymers.

-7 After leaving the agitated tank, the aqueous polymer solution, which still contains partially undissolved gel fractions, is subjected to a second dispersing process, during which the gel content is gently converted to the dissolved state while avoiding polymer degradation. In a 5 preferred embodiment, a mixing and dispersing power level of from 200 to 500 Wh/m 3 and more preferably from 250 to 400 Wh/m 3 is maintained. If the mixing energy is too low, the gel fractions cannot be completely dissolved, and if it is too high, the polymer undergoes shearing degradation. 10 The process of the invention enables the production of solutions of water-soluble polymers over a broad range of concentrations. This concentration range may fluctuate, depending on the molecular weight of the polymer. Whereas in the case of high molecular weight synthetic polymers, a solution stronger than 1% must be considered as concentrated because of the strong viscosity development, in the case of low molecular weight polymers distinctly higher 15 concentrations are possible. High molecular weight water-soluble polymers are preferably produced according to the invention in a concentration range greater than 1 wt%, more preferably greater than 2 wt% and most preferably greater than 2.5 wt%. Water-soluble polymers that are advantageously dissolved by the process of the invention 20 include both synthetic and natural types. Of the natural polymers, for example, mention may be made of the water-soluble polysaccharides derived from cellulose, starch, galactomannan, chitosan, and xanthan and particularly their water-soluble derivatives. The derivatization can be accomplished by 25 physical processes and/or chemical processes such as the use of etherifying and esterifying agents and leads to neutral, anionic, nonionic, and cationic products. Suitable chemical derivatives are primarily those of the type carboxyl, carboxyalkyl, hydroxyalkyl, and mixtures thereof. As examples thereof mention may be made of the compounds carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, carboxymethyl starch, oxidized starch, 30 gelatinized starch, and cationic starch ethers. The process of the invention is especially suited for dissolving synthetic water-soluble polymers, such as those used as flocculants, whose average molecular weight is usually greater than 105 and preferably greater than 10 . The polymers are usually in the form of 35 powder, the particles of commercial powder usually covering the range of from 250 pm to 1250 pm obtained by screening in the production process.

Synthetic water-soluble polymers for the purposes of this invention are formed from water soluble ethylenically unsaturated monomers by free-radical polymerization. Depending on the monomeric composition, nonionic, cationic, anionic, or amphoteric polymers may be formed. 5 Polyacrylamides represent a preferred group among the synthetic water-soluble polymers that may be used according to the invention. For the purposes of this patent, the term "polyacrylamide" refers to a water-soluble homopolymer or copolymer containing acrylamide as a monomeric component. 10 Examples of suitable anionic comonomers for polyacrylamides for example, are (meth)acrylic acid, vinylsulfonic acid, acrylamidomethylpropanesulfonic acid, (meth)allylsulfonic acid, maleic acid, fumaric acid, and itaconic acid. All of the acids listed may be polymerized as free acids, as salts, or a mixture thereof. The monomers may be neutralized with alkali metal 15 hydroxides, alkaline earth metal hydroxides, amines, amino alcohols and/or ammonia. Besides these, any other bases may be used which form a water-soluble salt with the acid, and mixed neutralization using different bases is also possible. Preferred anionic comonomers are acrylic acid, vinylsulfonic acid, and acrylamidomethylpropanesulfonic acid and/or salts thereof. 20 Suitable nonionic comonomers for the polyacrylamides are completely or partially water soluble monomers, for example methacrylonitrile, N,N-dimethylacrylamide, vinyl pyridine, vinyl acetate, methacrylamide, hydroxy group-containing esters of polymerizable acids, the hydroxyethyl and hydroxypropyl esters of acrylic and methacrylic acids, also amino group 25 containing esters and amines of polymerizable acids such as dialkylamino esters, e.g., dimethylamino and diethylamino esters of acrylic and methacrylic acids, e.g., dimethylaminoethyl acrylate or, for example, the corresponding amines such as dimethylaminopropylacrylamide. Partially water-soluble monomers are used only to the extent that they do not impair the water-solubility of the resulting copolymer. 30 Suitable comonomers for cationic polyacrylamides are, for example, cationized esters of (meth)acrylic acid, such as dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, diethylaminopropyl (meth)acrylate, dimethylaminopropyl (meth)acrylate, diethylaminopropyl (meth)acrylate, dimethylaminobutyl (methacrylate), diethylaminobutyl 35 (meth)acrylate, cationized amides of (meth)acrylic acid such as dimethylaminoethyl (meth)acrylamide, diethylaminoethyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, dimethylaminopropyl (meth)acrylamide, diethylaminopropyl (meth)acrylamide, dimethylaminobutyl (meth)acrylamide, diethylaminobutyl (meth)acrylamide, cationized N-alkyl mono- and diamides with alkyl radicals containing from 1 to 6 carbons, such as N-methyl (meth)acrylamide, N,N-dimethylacrylamide, N-ethyl (meth)acrylamide, N-propyl (meth)acrylamide, tert.-butyl (meth)acrylamide, cationized N-vinylimidazoles as well as 5 substituted N-vinylimidazoles, such as N-vinyl-2-methylimidazole, N-vinyl-4-methylimidazole, N-vinyl-5-methylimidazole, N-vinyl-2-ethylimidazole and cationized N-vinylimidazolines, such as vinylimidazoline, N-vinyl-2-methylimidazoline, and N-vinyl-2-ethylimidazoline. The basic monomers are used in a form neutralized or quaternized with mineral acids or io organic acids, the quaternization preferably being undertaken with dimethyl sulfate, diethyl sulfate, methyl chloride, ethyl chloride, or benzyl chloride. In a preferred embodiment, the monomers quaternized with methyl chloride or benzyl chloride are used. Preferred comonomers for cationic polyacrylamides are the cationized esters and amides of 15 (meth)acrylic acid, in each case containing one quaternized N atom, and quaternized dimethylaminopropyl-acrylamide and quaternized dimethylaminoethyl acrylate are very preferably used. Another advantage of the process of the invention is that it is not sensitive to the particle size 20 distribution of the polymer granules used. In practice, these polymer powders are produced with the smallest possible fractions below 250 pm in order, on one hand, to prevent the generation of dust, and on the other, to avoid agglomeration of these fines when they are introduced into the dissolving water. Due to the process of the invention, it is possible to leave these finely divided components in the product since they can be dissolved without 25 problem. In an advantageous embodiment of the process of the invention, the polymer solution is produced exclusively using finely divided polymer powder having a particle size below 200 pm and preferably below 150 pm. As regards the upper limit of the size of the polymer powder particles, powders having particle sizes of 1250 pm and larger can be dissolved without problem. 30 Another object of the invention is to provide an apparatus for carrying out the process of the invention in the batch mode according to claim 11 and a device for continuous operation according to claim 12. 35 Figure 1 shows a device with which the process of the invention can be carried out in the form of batchwise production of the solution. The polymer granules are conveyed by a pneumatic conveyor (HOO01) from a polymer granules storage container, for example, a big bag or a sack, to the charging hopper of the metering unit (H0002). The metering unit (H0002) meters the required quantity of granules (depending on the required concentration) into a powder supply tank (B0001). 5 Alternatively, the granules may be conveyed by a flexible conveyor screw directly from the polymer granules storage container to the tank B0001. The tank (80004) serves as the water supply and contains the quantity of water necessary for a solution batch. 10 The batch dispersing unit (UO001) is started, part of the supplied water is drawn out of the tank (80004), and the agitator (ROO01) in container (B0002) is also started. The valve (H0003) opens as soon as the valve (H0004) has reached its end position. The 15 granules are drawn in by the vacuum generated by the dispersing unit (UO001). The granules are wetted by the water and subsequently pumped into the tank (B0002). The dispersing unit (UO001) consists of a disk-shaped rotor and can be operated with an additional stator in an optional embodiment. 20 When the granules container (B0001) is completely empty, the valve (H0003) is closed. The container (80002) is filled with the residual water still remaining in the tank (80004) via the dispersing unit until the level gage (L00001) switches off the dispersing unit (UO001) and closes the water valve (H0004). 25 The contents of the tank (80002) are homogenized with the aid of an agitator (ROO01) for about 1 to 15 minutes. On conclusion of the stirring time, the solution is removed from the tank (80002) with the aid 30 of the unit (UO001) and conveyed into the stock solution tank (80003). The dispersing unit (U 0001) serves as a refilling pump and dispersing unit and is adapted to shear, and thus dissolve, the gel still present. The unit is driven at a lower mixing and dispersing power level per cubic meter than in the case of the initial dispersing operation. The level gage (L00001) terminates the filling process, and the procedure can now be restarted. 35 Figure 2 shows a device with which the process of the invention can be carried out in the form of continuous production of the solution.

- I I The polymer granules are conveyed by a pneumatic conveyor (HOO01) from a polymer granules storage container, e.g., a big bag or a sack, to the charging hopper of the metering unit (H0002). 5 The granules are supplied with the aid of a metering unit (H0002) (with a pre-fixed conveying power). Alternatively, the units H0001 and H0002 may be replaced by a flexible screw conveyor. 10 The required water is made available online without fluctuations in pressure and feed rate. Production of the solution is begun by starting the water supply, after which the granules valve (H0003) of the dispersing unit (UO001) is opened and the metering unit (H0002) started. Now the granules are drawn in by the vacuum generated by the dispersing unit 15 (UO001). The granules are wetted by the water and conveyed into a tank (B0002). The dispersing unit (UO001) consists of a disk-shaped rotor and in an optional embodiment can be operated with an additional stator. The contents of the tank (80002) are homogenized by an agitator (ROO01) and prevented 20 from settling. The average residence time in the tank is 1 to 15 minutes. The solution departing from the tank is conveyed by an additional dispersing unit (U0002) into a stock solution tank. The unit (UO001) is adapted to shear, and thus dissolve, the gel still present. The unit (U0002) operates at a lower mixing and dispersing power level per cubic meter than the unit (UO001). 25 Description of the individual components B0001 Granules supplier 30 The granules supplier is required only for batchwise operation of the dispersing unit so that the required quantity of granules can be provided proportionately to the amount of water and the required concentration. B0002 tank 35 The tank serves to receive the polymer granules dispersed in water. It is equipped with a level monitor and an agitator. The agitator has the task of homogenizing the water/polymer granules mixture as the granules dissolve and of preventing settling of the dispersed polymer granules; a shearing effect on the dispersed granules is to be avoided as far as possible. Accordingly, slowly rotating agitators will preferably be used at this stage. Straight-arm paddle agitators, vane agitators, and anchor agitators are examples of agitators that may be 5 used. When operating in continuous mode, it may be of advantage if two or more agitated tanks are connected in series or so-called continuous flow chamber systems (so-called multi chamber installations) are used. 10 B0003 Tank This tank serves for storage of gel-free, highly concentrated flocculant solution. The stock solution or service solution, depending on the required concentration, is made available to 15 the user from this tank. H0001 suction conveyor The suction conveyor serves to convey the granules and is always positioned above the 20 metering screw. For example, if the granules are sucked out of a big bag, the sucked granules then drop into the supply hopper of the metering screw. H0002 metering screw 25 The metering screw meters the granules at the required rate. The conveying power can be adjusted by varying the rotary speed of the screw drive. The metered quantity specified is weighed in advance and adjusted to the specific requirements. In the operating state, the screw conveys the required quantity into a powder-receiving vessel (batchwise operation) or proportionately to the flow of water (continuous operation). The supply hopper of the 30 metering screw is filled as required by the suction conveyor. The hopper is additionally monitored by means of a capacitive proximity switch which sends an alarm as soon as the value drops below the minimum and may be used to switch off the downstream systems. H0003 granules valve 35 The valve is installed between the metering screw and the dispersing unit and opens as soon as the wetting process is started.

R0001 agitator system The agitator promotes the homogenization and dissolution of the mixture of incipiently 5 dissolved polymer powder and wetted polymer powder particles accumulating in the dispersing unit and prevents sedimentation of the granules not yet fully dissolved. U0001 and U0002 dispersing units 10 This dispersing unit is an in-line dispersing machine comprising a variable disk-shaped rotor system. Because of this design, the liquid flowing in the dispersing units builds up a high vacuum capable of drawing in powders/granules without losses and without producing dust. The in-line dispersing machine is preferably equipped with a motor suitable for frequency 15 transformation. Separation between the motor shaft and the separately mounted machine shaft is afforded by a clutch. A two-part rotor is installed in the mixing chamber (rotor hub and rotor vane carrier) with two, preferably highly polished rotor hubs and two strippers to prevent adhesions. The liquid inflow and outflow take place through flanges, and the powder is admitted through an intake fixture mounted eccentrically on the mixing chamber. 20 The dispersing unit consists of a disk-shaped rotor in a dispersing chamber and is provided with two material inlets for the polymer powder and water and one product outlet. The two material streams are physically combined at the periphery of the rotor disk, preferably in the axial direction, at which time the dispersing process takes place. The product outlet is 25 located at the outer edge of the wetting chamber. At its periphery, the rotor has a rotor rim with teeth or radial openings. Optionally, a stator provided with radial openings for dispersing the polymer powder may be installed in the dispersing unit for cooperation with the rotor. 30 The invention may be used to advantage in all fields in which - the flocculants are metered as service solution having a concentration greater than or equal to 1%, 35 - a gel-free flocculant solution is required, - I-!r - a large quantity of flocculant is required in a short time, and sufficient space is unavailable for large dissolving installations, - the production of highly concentrated stock solutions is required. 5 The highly concentrated polymer solutions that are produced by the process of the invention are particularly well suited for clarification of slurries and the removal of water from sludges such as accumulate in, say, wastewater treatment plants, in silt dredging or in mining, especially when these slurries accumulate continuously in large volumes. The polymer 10 solutions are also particularly suitable for use as flocculants in papermaking processes and as surge polymers in tertiary petroleum conveying. Examples 15 Example 1 For dewatering municipal sewage sludge on chamber filter presses, solutions of a cationic polyacrylamide, type Praestoff*658BC-S" were used as flocculants in a concentration of 2 wt%, the solutions being prepared according to the process of the invention in an apparatus 20 as shown in Fig. 1. In the first dispersing stage, a dispersing power level of 900 Wh/m 3 was applied, and in the second dispersing stage, it was 300 Wh/m'. The agitated tank B0002 was equipped with a slowly rotating blade-agitator (250 rpm). For comparison, the sewage sludge was treated with a conventionally prepared 0.2% strength solution of the same cationic polyacrylamide. A total of 49 test batches was run, each with 1 m 3 of flocculant solution. The 25 flocculant solutions according to the process of the invention were free from gel bodies and had an outstanding flocculating effect. In order to achieve a solids content of about 40 wt% in the filter cake when the 0.2% strength solution was used, about 4.5 kg of flocculant were required per ton of dry substance, while only 3.7 kg of the solution produced according to the invention were required. 30 #:Praestol* 658 BC-S is a cationic polyacrylamide supplied by Stockhausen GmbH having a molecular weight greater than 106 and a degree of cationogenicity of 8% and a 10% content of granules < 315 pm of and a lower than 5% content of granules < 100 pm. 35 Example 2 Using the equipment and settings of Example 1, a 1% strength polymer solution was - 13 prepared from a cationic polymer powder consisting predominantly of fine fractions. According to the sieve analysis, the polymer had the following composition: >1250 pm 0.1% 5 >1000 pm 0.7% > 800 pm 5.7% 1o > 500 pm 7.8% > 315 pm 3.4% > 100 pm 44.7% 15 > 63 pm 29.4% < 63 pm 8.2% 20 After passing through the first dispersing stage at 900 Wh/m 3 , stirring was continued in the dispersing tank for 5 minutes, after which the water/particle mixture had essentially become a solution, i.e. the particles were dissolved or at least wetted by, and incipiently dissolved in, the water. Following passage through the agitated vessel, the second dispersing step was performed at 300 Wh/m 3 . 25 Despite the high content of fines, the polymer solution could be produced without problems and had only insignificant gel contents of less than 5 ml/L. [The gel content is determined by diluting 1000 ml of polymer solution to a strength of 0.1 wt% and pouring it through a standard sieve having a mesh width of 0.315 mm and collecting the gel bodies and 30 subsequently determining their volume in a measuring cylinder.] The viscosity of the 1% strength solution was 1500 mPa-s after production and was unchanged after 1 h. The test results clearly demonstrated the advantages of the polymer solutions produced by the process of the invention. The polymer solutions, which were highly concentrated 35 compared with the normal operating procedure, caused a reduction in the volume of the flocculant solution and in the service water costs by approximately 90% and a reduction in the quantity of flocculant about 15%. In addition, a reduction in power supply costs by 80% -16 resulted from savings on agitation and metering. Another advantage of the process of the invention is the possibility of producing polymer solutions from finely divided polymer powders, which cannot be used for conventional dissolution due to their strong tendency to agglomerate. 5 Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group 10 of integers or steps. The reference to any prior art in this specification is not, and should not be taken as, an acknowledgment or any form of suggestion that the prior art forms part of the common general knowledge. 15 10/10/1 l.ck I6830speci.16

Claims

1. A process for the production of an aqueous polymer dispersion from solid 5 particles of a water-soluble polymer, by physically combining water and the polymer particles in a dispersing unit, wherein - a first dispersal of said particles in water is carried out while applying a first power level per cubic meter, - the water/particle mixture, after leaving said dispersing unit, is passed to an 10 agitation tank, where the particles are substantially dissolved with stirring, - the substantially dissolved water/particle mixture, following the residence time in the agitation tank, is subjected to a second dispersal in a dispersing unit at a lower power level per cubic meter than that used during the first dispersal. 15

2. The process according to claim 1, wherein in the first dispersal a mixing or dispersing power level of from 550 to 1600 Wh/m 3 is applied.

3. The process according to claim I or claim 2, wherein the second dispersal a 20 mixing or dispersing power of from 200 to 500 Wh/m 3 is applied.

4. The process as defined in any one of claims 1 to 3, wherein the dispersed polymer particles have a residence time in said agitation tank of from 1 to 15 min. 25

5. The process as defined in any one of claims 1 to 4, wherein said polymer particles are prevented from settling in said agitation tank by a slowly rotating agitator.

6. The process as defined in any one of claims 1 to 5, wherein the first and 30 second dispersals are carried out in a dispersing unit comprising a dispersing chamber containing a disk-shaped rotor, in the marginal region of which there is present a rotor rim having teeth or radial openings. 17/10/1 Ick16830claims,17 - 18

7. The process as defined in any one of claims 1 to 6, wherein the water-soluble polymers used are synthetic anionic, cationic, or amphoteric polymers.

8. The process as defined in any one of claims I to 7, wherein said polymer 5 solution has a concentration greater than 1 wt%.

9. The use of the aqueous polymer dispersion produced according to the process defined in any one of claims 1 to 8 as a flocculant.

10 10. The use of the aqueous polymer dispersion produced according to the process defined in any one of claims 1 to 8 as a flocculant in the clarification of slurries and the dewatering of sludges obtained from wastewater treatment plants, from mining wastes and from silt transportation plants or in flocculation processes involved in papermaking. 15

11. The use of the aqueous polymer solution produced according to the process defined in any one of claims I to 8 as an auxiliary in tertiary petroleum production. 17/10/IIckl6830claiins,18