阅读说明：本技术 用于通过溶气浮选处理水性进料的方法 (Method for treating aqueous feed by dissolved air flotation ) 是由 马蒂·希耶塔涅米 于里·瓦伊梅基 约纳斯·利坎德 罗萨·卡塞列尔 于 2018-12-14 设计创作，主要内容包括：本发明涉及用于通过溶气浮选,特别是通过溶解空气浮选(DAF)来处理水性进料的方法,该水性进料源自纤维素来源的纤维材料的工业加工,例如纸浆、纸、纸板、再生纤维纸浆等的制造,其中水性进料包含水相和悬浮在水相中的固体颗粒材料。该方法包括使絮凝剂与水性进料接触,并通过絮凝剂和悬浮的固体颗粒材料的相互作用将悬浮的固体颗粒材料絮凝为絮凝物,使形成的絮凝物与气泡接触,并在浮选池中诱导它们的漂浮。用于絮凝悬浮的固体颗粒材料的絮凝剂包含电荷密度为至多1.7meq/g干,优选地至多1.5meq/g干,更优选地至多1.1meq/g干的聚合物组合物,并且聚合物组合物包含阳离子合成第一聚合物,其在pH 2.8下的电荷密度为至少1.0meq/g干,和至少一种第二聚合物,其是通过(甲基)丙烯酰胺的聚合得到的聚合物,第二聚合物在阳离子第一聚合物的存在下聚合,其中第一聚合物具有比第二聚合物更高的电荷密度。(The present invention relates to a process for treating an aqueous feed originating from industrial processing of cellulosic derived fibrous material, such as the manufacture of pulp, paper, cardboard, recycled fibre pulp and the like, by dissolved air flotation, in particular by Dissolved Air Flotation (DAF), wherein the aqueous feed comprises an aqueous phase and solid particulate material suspended in the aqueous phase. The method comprises contacting a flocculant with an aqueous feed and flocculating suspended solid particulate material into floes by interaction of the flocculant and the suspended solid particulate material, contacting the formed floes with gas bubbles and inducing their flotation in a flotation cell. A flocculant for flocculating a suspended solid particulate material comprises a polymer composition having a charge density of at most 1.7meq/g dry, preferably at most 1.5meq/g dry, more preferably at most 1.1meq/g dry and the polymer composition comprises a cationic synthetic first polymer having a charge density of at least 1.0meq/g dry at pH 2.8 and at least one second polymer which is a polymer obtained by polymerisation of (meth) acrylamide, the second polymer being polymerised in the presence of the cationic first polymer, wherein the first polymer has a higher charge density than the second polymer.)

1. Method for treating an aqueous feed originating from industrial processing of cellulosic derived fibrous material, such as the manufacture of pulp, paper, cardboard, recycled fibre pulp and the like, by dissolved air flotation, in particular by Dissolved Air Flotation (DAF), wherein the aqueous feed comprises an aqueous phase and solid particulate material suspended in the aqueous phase, wherein the method comprises

-contacting a flocculant with the aqueous feed and flocculating the suspended solid particulate material into floes by interaction of the flocculant and the suspended solid particulate material,

-contacting the formed flocs with gas bubbles and inducing them to float in a flotation cell,

It is characterized in that

The flocculant for flocculating suspended solid particulate material comprises a polymer composition having a charge density of at most 1.7meq/g dry, preferably at most 1.5meq/g dry, more preferably at most 1.1meq/g dry, comprising

-a cationic synthetic first polymer having a charge density of at least 1.0meq/g dry at pH 2.8,

At least one second polymer, which is a polymer obtained by polymerization of (meth) acrylamide, said second polymer being polymerized in the presence of a cationic first polymer,

Wherein the first polymer has a higher charge density than the second polymer.

2. The method according to claim 1, wherein the second polymer is obtained by polymerization of (meth) acrylamide and at least one second monomer in an amount of 0.2-19 wt-%, calculated from the total dry polymer material weight of the polymer composition.

3. The method according to claim 1 or 2, characterized in that the cationic synthetic first polymer has a charge density in the range of 1-12meq/g dry, preferably 1-8meq/g dry, more preferably 1.3-8meq/g dry, even more preferably 5-7meq/g dry at pH 2.8.

4. The method of claim 1, 2 or 3, wherein the cationic synthetic first polymer is selected from polyamines; a homopolymer of a cationic first monomer obtained by free radical polymerization; a copolymer of acrylamide and a cationic first monomer obtained by free radical polymerization; or any combination of the others.

5. The method according to claim 4, characterized in that the cationic synthetic first polymer is a polyamine selected from the group consisting of copolymers of epichlorohydrin and dimethylamine, copolymers of epichlorohydrin, dimethylamine and ethylenediamine, and linear or crosslinked polyamidoamines.

6. The method of claim 4 or 5, wherein the cationic synthetic first polymer is a homopolymer of a cationic first monomer selected from the group consisting of: 2- (dimethylamino) ethyl acrylate (ADAM), [2- (acryloyloxy) ethyl ] trimethyl ammonium chloride (ADAM-Cl), 2- (dimethylamino) ethyl acrylate benzyl chloride, 2- (dimethylamino) ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy) ethyl ] trimethyl ammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3- (acryloylamino) propyl ] trimethyl ammonium chloride (APTAC), [3- (methacryloylamino) propyl ] trimethyl ammonium chloride (MAPTAC), and diallyldimethyl ammonium chloride (DADMAC).

7. The method according to any of the preceding claims 1-6, characterized in that the polymer composition comprises the cationic synthetic first polymer in an amount of 0.5-35 wt-%, preferably 1-15 wt-%, more preferably 2-9 wt-%, calculated from the weight of the dry polymer material of the polymer composition.

8. The method according to any of claims 1 to 7, characterized in that the weight average molecular weight MW of the cationic first polymer is < 500000 g/mol, preferably < 100000 g/mol, more preferably < 50000 g/mol, even more preferably <20000 g/mol.

9. The method of any one of claims 1-8, wherein the second polymer is cationic and the second monomer is selected from the group consisting of: 2- (dimethylamino) ethyl acrylate (ADAM), [2- (acryloyloxy) ethyl ] trimethyl ammonium chloride (ADAM-Cl), 2- (dimethylamino) ethyl acrylate benzyl chloride, 2- (dimethylamino) ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy) ethyl ] trimethyl ammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3- (acryloylamino) propyl ] trimethyl ammonium chloride (APTAC), [3- (methacryloylamino) propyl ] trimethyl ammonium chloride (MAPTAC), and diallyldimethyl ammonium chloride (DADMAC).

10. The method according to any of claims 1 to 9, wherein the second polymer is obtained by using adiabatic gel polymerization, preferably at an acidic pH < 6.

11. Method according to any one of claims 1-10, characterised in that the standard viscosity of the polymer composition is in the range of 3-6mPas, preferably 3.6-5.0 mPas.

12. The process according to any one of claims 1 to 11, characterized in that the intrinsic viscosity of the polymer composition is in the range of 4 to 20dl/g, preferably 7 to 15 dl/g.

13. Method according to any one of claims 1 to 12, characterised in that the aqueous feed comprises suspended solid particulate material in a total amount of less than 6000mg/l, 50-5000mg/l, preferably 150-4000 mg/l.

14. The method according to any of claims 1-13, characterized in that the conductivity of the aqueous feed is in the range of 0.2-10mS/cm, preferably 0.5-5.0mS/cm, more preferably 1.0-4.0 mS/cm.

15. The process according to any of claims 1-14, characterized in that the cationic demand of the aqueous feed is in the range of 20-3000 μ eq/l, preferably 200-3000 μ eq/l, more preferably 100-2000 μ eq/l, even more preferably 400-1500 μ eq/l, such as 500-1500 μ eq/l.

16. The method according to any one of claims 1-15, characterised in that the pH of the aqueous feed is in the range of 4-9.5, preferably 4-8.

17. The method according to any one of claims 1-16, wherein the suspended solid particulate material comprises inorganic mineral particles and cellulose fibres and/or fibrils.

18. A method according to any one of claims 1-17, characterised in that the flocculant comprising the polymer composition is used in an amount of 0.1-10mg/l, preferably 0.2-3mg/l, more preferably 0.2-1.0mg/l, given as dry polymer composition/aqueous feed volume.

19. The method according to any one of claims 1-18, characterized in that a coagulant is introduced into the aqueous feed before contacting the aqueous feed with the flocculant.

Technical Field

The present invention relates to a method for treating an aqueous feed from the manufacture of pulp, paper, cardboard, recycled fibre pulp and the like by dissolved air flotation, in particular Dissolved Air Flotation (DAF), according to the preambles of the appended independent claims.

Background

Dissolved air flotation is used to purify various aqueous feeds from pulp, paper and board manufacturing processes. A flocculant may be added to the aqueous feed to be treated to flocculate suspended solid particulate material present in the feed prior to introducing the feed into the flotation cell. In a typical dissolved air flotation process, dispersed water containing dissolved gases is introduced into a flotation cell along with an aqueous feed. When the dispersion water enters the flotation cell, the dissolved gas is released in the form of small bubbles. The flocs are in contact with small bubbles, so that the bubbles attach to the formed flocs. The bubbles float the flocs on the surface where a floating layer or island of surface sludge is formed, which can be removed from the surface, for example with a scraper or through an overflow outlet. Purified water is typically removed from the lower portion of the basin. Generally, after the gas is dissolved therein, a part of the purified water is separated and used as dispersion water.

Conventionally, high molecular weight polyacrylamide flocculants are used to flocculate suspended solid particulate material in the feed before it enters the flotation cell. Due to increased awareness of environmental concerns and regulations, industrial processes such as pulp and paper processes are becoming more and more closed, which means that they use less fresh water. This results in an increase in conductivity or total ionic strength (i.e., salt concentration) in the process water. At the same time, the use of recycled fibers as a fiber source in papermaking has increased, which provides the process water with a large amount of dissolved and colloidal substances, so-called anionic trash. Both the increased conductivity and the increased loading of dissolved and colloidal materials tend to interfere with the performance of conventional flocculant polymers. Therefore, there is a need for a new and efficient method for removing suspended solid material in a Dissolved Air Flotation (DAF) process.

Disclosure of Invention

It is an object of the present invention to minimize or even eliminate the disadvantages of the prior art.

It is also an object to provide a method which is also effective in treating aqueous feed from industrial processing of cellulosic derived fibrous material, such as the manufacture of pulp, paper, paperboard, recycled fibre pulp and the like, wherein the aqueous feed has an increased conductivity and/or an increased cationic demand, which reflects the amount of dissolved and colloidal substances in the aqueous feed.

It is a further object of the invention to provide a method for providing a stable, durable floc.

It is a further object of the present invention to provide a method of providing purified water having a low concentration of suspended solid particulate matter and a low turbidity.

These objects are achieved by the present invention having the features presented below in the characterizing part of the independent claims. Some preferred embodiments are disclosed in the dependent claims.

Where applicable, embodiments mentioned herein relate to all aspects of the invention, even if this is not always individually mentioned.

In a typical process according to the invention for treating an aqueous feed by dissolved air flotation, in particular by Dissolved Air Flotation (DAF), the aqueous feed originates from industrial processing of cellulosic derived fibrous material, such as the manufacture of pulp, paper, cardboard, recycled fibre pulp and the like, wherein the aqueous feed comprises an aqueous phase and solid particulate material suspended in the aqueous phase, and the process comprises

-contacting a flocculant with the aqueous feed and flocculating the suspended solid particulate material into flocs by interaction of the flocculant and the suspended solid particulate material,

-contacting the formed flocs with gas bubbles and inducing their flotation in a flotation cell,

Wherein the flocculating agent for flocculating the suspended solid particulate material comprises a polymer composition having a charge density of at most 1.7meq/g dry, preferably at most 1.5meq/g dry, more preferably at most 1.1meq/g dry, comprising

-a cationic synthetic first polymer having a charge density of at least 1.0meq/g dry at pH 2.8.

At least one second polymer, which is a polymer obtained by polymerization of (meth) acrylamide, the second polymer being polymerized in the presence of the cationic first polymer,

Wherein the first polymer has a higher charge density than the second polymer.

It has now been unexpectedly found that unexpected improvements can be obtained in the treatment of aqueous feeds in dissolved air flotation when flocculants comprising specific polymer compositions are used for flocculation of suspended solid particulate materials. Flocculants comprising particular polymer compositions successfully interact and flocculate suspended solid particulate materials, including possibly at least a portion of anionic colloidal particles, and produce structurally stable and long-lived flocs. Without wishing to be bound by theory, it is hypothesized that the first polymer of the polymer composition having a higher charge density than the second polymer interacts with the anionic colloidal particles and/or the anionic dissolved species, thereby anchoring the polymer composition comprising physically entangled polymer chains of the first and second polymers with these species. The increased conductivity and/or increased cationic demand of the aqueous feed will generally exert compressive forces on the cationically charged polymer chains, but since the cationic charge of the polymer composition (and in particular of its second polymer) is only moderate, the physically entangled polymer chains are less compressed and they remain more extended. This may effectively flocculate the suspended solid particulate material with the second polymer of the polymer composition. In this way, the flocculation capability of the polymer composition, including the extension of the entangled polymer chains and the ability of individual polymers to form ionic bonds and participate in electrostatic interactions, is not depleted by increased cation demand and/or conductivity, but rather retains the solid particulate material for suspension and is able to form strong flocs.

According to the present invention, the use of a flocculant comprising a particular polymer composition may provide enhanced floc size, floc stability, and/or sludge cake density. In particular, improved floc stability is an advantageous feature of dissolved air flotation, in which case it may take several minutes to transport the formed flocs through the flotation cell to the surface. Once the floes reach the surface, they form a surface sludge that should not dissolve or disintegrate back into the water phase of the flotation cell. A higher surface sludge density, i.e. a lower water content in the surface sludge, may improve the scraping result of the surface sludge.

In the present context, the term "solid particulate material" includes different organic and inorganic solid particles present in the aqueous feed. The aqueous feed may comprise, for example, fibrous material, such as long and/or short fibrous material, and/or inorganic mineral particles. The fibrous material is a cellulosic fibrous material derived from wood or non-wood sources, preferably from wood sources. Long fiber material represents the portion of the fibers remaining on the 100 mesh wire, and short fiber material or fiber fragments represents the portion of the fibers passing through the 100 mesh wire. Although the long fiber material is more likely to flocculate, a high proportion of long fiber material is not required. Effective flocculation can be obtained by a specific polymer composition even when the aqueous feed comprises less than 20 wt-%, even less than 10 wt-%, calculated from the suspended solids content of the aqueous feed, of long fiber material. Furthermore, the aqueous feed may comprise inorganic mineral particles and it may have an ash content value in the range of 20-90%, preferably 20-85%, calculated from solids. The ash content value is determined by using the standard ISO 1762, temperature 525 ℃. The inorganic mineral particles in the aqueous feed as well as in the surface sludge are usually derived from fillers and coating materials used in paper and board manufacturing. The solid particulate material may further comprise colloidal particles having at least one dimension of 1nm to 1 μm, and microflocs obtained by interaction between the dissolved material and the coagulant(s). In some embodiments, the solids content of the aqueous feed may be in the range of 50 to 5000mg/l, preferably 150 to 4000 mg/l.

In this context, the term "floc stability" refers to maintaining floc size and/or inhibiting floc size reduction as a function of time. For example, the floc size may change by less than 20% 1 minute to 5 minutes after addition of the flocculant. Floc size can be measured, for example, by Focused Beam Reflectance Measurement (FBRM) at 500rpm using a DDJ type mixer. As noted, floc stability is particularly advantageous in dissolved air flotation, where the passage/retention time of the flocs can be several minutes, sometimes up to 6 minutes or more. The formed floes preferably retain their size as they progress through the flotation cell to its surface. Maintaining proper floe size throughout the flotation process enhances flotation, thereby promoting increased feed capacity and shortened transit time. The flocs formed are preferably also subjected to mechanical forces, for example during removal of the floating layer or floc islands. The use of the described polymer compositions provides unexpected improvements, especially floc stability.

The increase in floc density (which can be measured by the thickness of the surface sludge after the flocs rise to the surface) can provide a high surface sludge consistency.

in the present context, the term "anionic trash" is to be understood as anionic dissolved or colloidal material present in the aqueous phase of the aqueous feed, the anionic trash may contain various fats and resinates, hemicellulose and oxidation by-products thereof, lignin derivatives and/or anionic additives from shredded or recycled paper, such as dispersants and/or anionic latex particles, the cationic demand of the aqueous feed, as measured by the multek titration, reflects the amount of anionic dissolved and colloidal material, i.e. anionic trash, in the aqueous feed, the present invention is particularly applicable to aqueous feeds with an increased cationic demand, the aqueous feed may have a cationic demand value as measured by multek in the range of 20-3000 mueq/l, preferably 200-3000 mueq/l, more preferably 100-2000 mueq/l, even more preferably 400-1500 mueq/l, sometimes even more preferably 500-1500 mueq/l.

The aqueous feed may be obtained from any industrial process in which cellulosic derived fibrous material, such as fibers, is treated or processed. Typical examples of such processes are the manufacture of pulp, paper, board or tissue, or various processes in which recycled fibre material is treated, such as pulping or deinking. The aqueous feed treated by the process of the present invention may comprise process water from such an industrial process or effluent, i.e. wastewater, from such an industrial process. The aqueous feed from industrial processing of cellulosic derived fibrous material may comprise suspended solid particulate material, preferably comprising inorganic mineral particles, cellulose fibres and/or fibrils and optionally anionic trash suspended in an aqueous phase. The aqueous feed to the flotation cell may contain suspended solid particulate material in a total amount of less than 6000mg/l, preferably 50 to 5000mg/l, more preferably 150 to 4000 mg/l.

According to one embodiment, dissolved air flotation comprises at least the following steps:

(a) The dispersion water is obtained by dissolving a compressed gas in the dispersion water,

(b) An aqueous feed is obtained from industrial processing of cellulosic derived fibrous material, wherein the aqueous feed comprises an aqueous phase and solid particulate material, such as fibres and/or fibre fragments suspended in the aqueous phase,

(c) Introducing a flocculant into the aqueous feed and/or dispersion water,

(d) Flocculating the suspended solid particulate material into floes by interaction of the flocculating agent and the suspended solid particulate material,

(e) Introducing an aqueous feed and dispersion water into a flotation cell and reducing the pressure of dissolved gas in the dispersion water, thereby releasing the gas in the form of bubbles,

(f) Allowing the bubbles to interact with the flocs and cause them to float, thereby forming a surface sludge on the surface or top of the purified water,

(g) Separating at least a portion of the formed surface sludge from the purified water by at least partially removing the surface sludge from the basin, and

(h) The purified water is drained from the basin and preferably a portion of the purified water is used to obtain the dispersion water in step (a).

In dissolved air flotation, dispersed water can be obtained by dissolving compressed gas, preferably air, in water. When the dispersion water is introduced into the flotation cell, the pressure of the dissolved gas in the dispersion water is abruptly reduced, so that the dissolved gas is released from the dispersion water in the form of bubbles, and the dispersion water may be fed into the flotation cell, for example, by a pressure-drop device such as a pressure-drop nozzle. According to one embodiment the flow rate of dispersion water is about 5-10 vol% of the total feed to the flotation cell of dissolved air flotation.

The aqueous feed may be introduced into the flotation cell simultaneously, simultaneously or separately with the dispersing water or simultaneously as a feed. In the former case the flotation cell has separate feed connections for the aqueous feed and for the dispersion water, and in the latter case the aqueous feed and the dispersion water preferably meet immediately before the flotation cell and are introduced as one feed into the flotation cell through a single feed connection.

According to one embodiment of the invention, the gas is dissolved in the aqueous feed, so that it also serves as dispersing water. In this embodiment, the flocculant is preferably introduced into the aqueous feed prior to the dissolution of the gas.

A flocculant comprising a polymer composition as defined above and elsewhere herein may be introduced into the aqueous feed before the feed enters the flotation cell through the feed connection. Alternatively, the flocculant is introduced into the dispersion water before it enters the flotation tank or into both the aqueous feed and the dispersion water. When the flocculant is introduced into the aqueous feed, it may be introduced or added to the aqueous feed 0 seconds to 10 minutes, preferably 1 second to 10 minutes, more preferably 1 to 60 seconds before it enters the flotation cell, thereby forming floes in the aqueous feed. Alternatively, when a flocculant is added to the dispersion water, flocs are mainly formed when the dispersion water and the aqueous feed are in contact with each other, e.g. immediately before or after they enter the flotation cell.

The flocculant may be added continuously or periodically to the aqueous feed and/or dispersion water. Where the flocculant is added to both the aqueous feed and dispersion water, the flocculant may be added continuously in one stream and periodically to the other stream.

Typically, the flocculant comprising the polymer composition flocculates suspended solid material present in the aqueous feed, such as fibres, fibrils, inorganic particles and/or anionic trash, and provides optimal floc size and stability for flotation. Thus, the floes show a good rate of rise in the flotation cell and are not easily broken down even under shear or mechanical stress (e.g., vigorous mixing) or during the removal of surface sludge.

The polymer composition used as a flocculant is typically diluted or dissolved in water before being introduced into the aqueous feed and/or dispersion water.

In the flotation basin, the bubbles are made to interact with and induce flotation of the formed flocs, thereby forming surface sludge on the surface or on top of the purified water. The bubbles can attach to the formed flocs and cause them to float, i.e. they rise to the surface of the aqueous phase present in the flotation cell. While the aqueous phase is purified. The floating floes form surface sludge, which may be in the form of floating continuous or discontinuous sludge blanket, or it may be in the form of separate floating sludge islands. Surface sludge may be removed or disposed of from the upper part of the flotation tank, i.e. from the surface of the aqueous liquid phase being purified in the tank. A purified water stream, i.e. purified filtrate, can be discharged from the lower part of the flotation cell. Preferably, a part of the purified water is used to obtain dispersed water. This means that a part of the purified water is separated from the purified water stream discharged from the flotation cell; the compressed gas is dissolved in the separated part of the purified water and recycled as dispersion water to the flotation cell.

Flocculants comprising polymer compositions provide good stability and flotation capacity for flocs, which improves the quality of purified water. According to a preferred embodiment, the purified water has a lower consistency of solid particulate material than the untreated aqueous feed to the flotation cell > 70%, preferably > 80%, more preferably > 90%. Additionally or alternatively, the purified water may have turbidity values of up to 2000NTU, preferably < 200NTU, more preferably < 50NTU, e.g. 1-30NTU, which values reflect the effectiveness of the polymer composition in reducing the colloidal material content.

The conductivity of the aqueous feed to the flotation cell may be in the range of from 0.2 to 10mS/cm, preferably from 0.5 to 5.0mS/cm, more preferably from 1.0 to 4.0 mS/cm. The pH of the aqueous feed may be in the range of 4 to 9.5, preferably 4 to 8. The pH of the aqueous phase in the flotation cell may be in the range of 4 to 9.5, preferably 6.0 to 8.5, more preferably 7 to 8.5, even more preferably 7 to 8. The dissolved air flotation process can be enhanced at acidic to neutral pH, but flocculant consumption generally increases when the pH of the aqueous feed exceeds 8, and even further increases are generally noted when the pH rises above 9. However, the polymer compositions used as flocculants in the present invention are not susceptible to elevated pH and/or elevated conductivity. It has been observed that their increased consumption is modest at elevated pH and/or conductivity levels compared to conventional flocculants. Thus, the use of the flocculants of the present invention with specific polymer compositions enables the formation of stable flocs even if the aqueous feed shows elevated cation demand and/or conductivity levels.

A polymer composition suitable for use as or as part of a flocculating agent in the present process comprises a cationic synthetic first polymer and a second polymer which is a copolymer of (meth) acrylamide, the second polymer being polymerised in the presence of the cationic synthetic first polymer. Preferably, polymerization of the second polymer in the presence of the first polymer results in physical three-dimensional entanglement of the polymer chains of the first and second polymers. The first and second polymers become inseparable from each other without breaking the polymer chains. It has been observed that using such polymer compositions improves floc formation and stability. The polymer composition also provides flocs of optimal size, meaning that they are large enough to be easily removed as surface sludge, yet small enough to efficiently rise through flotation cells on the surface by means of attached bubbles. Without wishing to be bound by theory, it is hypothesized that the entanglement of the polymer chains of the first and second polymers improves the structure of the polymers, especially in environments with high electrical conductivity. The second polymer is able to remain stretched and form floes of the desired size.

The cationic synthetic first polymer may be obtained by radical polymerization or polycondensation. It may be a linear or branched polymer.

Cationic synthesis the first polymer may be prepared by polymerizing suitable monomers in a polymerization reactor. After the polymerization reaction is complete, the first cationically synthesized first polymer preferably does not contain a reactive polymerizable group, such as a carbon-carbon double bond, in its structure. In a preferred embodiment, when polymerized in the presence of the first polymer, the monomers of the second polymer react with each other and do not form covalent bonds with the first polymer present as polymerization medium. Covalent bonds between the first polymer and the second polymer are not necessary to provide a three-dimensional structure to the polymer composition because the first polymer and the second polymer are physically entangled and their polymer chains are inseparably intertwined or interlaced with each other.

The cationic synthetic first polymer is water soluble and preferably has a structure free of hydrophobic groups.

The cationic synthetic first polymer may have a weight average molecular weight in the range of 1000 to 500000 g/mol. Preferably, the cationic synthetic first polymer may have a weight average molecular weight MW < 500000 g/mol, preferably < 100000g/mol, more preferably < 50000 g/mol, even more preferably < 20000 g/mol. According to one embodiment of the invention, the weight average molecular weight MW of the cationically synthesised first polymer may be in the range of 1000-250000 g/mol, preferably 1500-100000 g/mol, more preferably 1500-50000 g/mol, even more preferably 2000-20000 g/mol. It has been observed that cationic synthesis of the first polymer is more effective in, for example, interaction with anionic trash when the weight average molecular weight of the first polymer is low. It is believed that when the first polymer has a low molecular weight, it is less affected by compressive forces caused by increased conductivity and/or cationic demand, even when it has a high cationic charge. The weight average molecular weight is determined by using Size Exclusion Chromatography (SEC), such as gel permeation chromatography, using methods well known to the skilled artisan and based on polyethylene oxide standards.

The cationic synthetic first polymer may generally have a charge density of at least 1.0meq/g dry, measured at pH 2.8. According to a preferred embodiment, the cationic synthetic first polymer may have a charge density measured at pH 2.8 in the range of 1-12meq/g dry, preferably 1-8meq/g dry, more preferably 1.3-8meq/g dry, even more preferably 5-7meq/g dry, sometimes even 7-8meq/g dry. In some embodiments, the charge density may be 1.5 to 6.5meq/g dry. When the amount of cationically charged building blocks in the polymerization is known, the charge density of the cationically synthesized first polymer can theoretically be calculated.

It was unexpectedly observed that the low weight average molecular weight and preferably the moderate to high charge density of the cationic synthetic first polymer enhances its interaction with interfering anionic species present in the aqueous feed to the flotation cell. Without being bound by theory, it is hypothesized that the first cationically synthesized polymer interacts with small anionic particulate materials, such as anionic trash, while the second polymer is more active in floc formation.

According to one embodiment of the invention, the cationic synthetic first polymer is selected from polyamines; a homopolymer of a cationic first monomer obtained by free radical polymerization; a copolymer of acrylamide and a cationic first monomer obtained by free radical polymerization; or any combination thereof.

According to one embodiment, the polymer composition may comprise the cationic synthetic first polymer in an amount of 0.5-35 wt-%, preferably 1-15 wt-%, more preferably 2-9 wt-%, even more preferably 3-8 wt-%, calculated from the total dry polymer material weight of the polymer composition.

The cationic synthetic first polymer may be a polyamine selected from the group consisting of copolymers of epichlorohydrin and dimethylamine, copolymers of epichlorohydrin, dimethylamine and ethylenediamine, and linear or crosslinked polyamidoamines. Such polymers may be obtained by polycondensation. The polyamine may have a weight average molecular weight of 1000 to 300000 g/mol, preferably 1000 to 120000 g/mol, preferably 2000 to 20000 g/mol. Polyamines can have a high cationic charge.

According to one embodiment, the cationic synthetic first polymer may be obtained by free radical polymerization and is a homopolymer of the cationic first monomer. The cationic first monomer may be selected from the group consisting of: 2- (dimethylamino) ethyl acrylate (ADAM), [2- (acryloyloxy) ethyl ] trimethyl ammonium chloride (ADAM-Cl), 2- (dimethylamino) ethyl acrylate benzyl chloride, 2- (dimethylamino) ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy) ethyl ] trimethyl ammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3- (acryloylamino) propyl ] trimethyl ammonium chloride (APTAC), [3- (methacryloylamino) propyl ] trimethyl ammonium chloride (MAPTAC), and diallyldimethyl ammonium chloride (DADMAC). For those listed monomers that contain quaternary nitrogen in their structure, the cationicity is not pH dependent, which is a preferred feature. More preferably, the cationic synthetic first monomer for the homopolymer is [3- (acrylamido) propyl ] trimethyl ammonium chloride (APTAC), [3- (methacrylamido) propyl ] trimethyl ammonium chloride (MAPTAC), or diallyldimethyl ammonium chloride (DADMAC) because these monomers provide a pH-independent cationic charge. They also have hydrolytic stability so that charge loss over time due to hydrolysis can be minimized. Even more preferably, the cationic synthetic first monomer is diallyldimethylammonium chloride (DADMAC) because it is very stable with respect to hydrolysis. Preferably, the polymer composition may comprise a homopolymer in one of the amounts disclosed above.

According to another embodiment, the cationic synthetic first polymer may be obtained by radical polymerization and may be a copolymer of acrylamide and a cationic first monomer according to the above list, or it may be an at least partially hydrolyzed poly (N-vinylformamide). Preferably, the cationic synthetic first polymer may be a copolymer of acrylamide and a cationic first monomer which is diallyldimethylammonium chloride (DADMAC). Preferably, the polymer composition may comprise the copolymer in one of the amounts disclosed above.

According to a preferred embodiment of the present invention, the cationic synthetic first polymer is selected from polyamines, preferably from copolymers of epichlorohydrin and dimethylamine, and copolymers of epichlorohydrin, dimethylamine and ethylenediamine; a homopolymer of a cationic first monomer obtained by free-radical polymerization, preferably diallyldimethylammonium chloride (DADMAC); and copolymers of acrylamide and a cationic first monomer, preferably diallyldimethylammonium chloride (DADMAC), obtained by free-radical polymerization.

According to a preferred embodiment of the invention, the cationic synthetic first polymer is a linear polymer. When the cationically synthesized polymer is a linear polymer, the solubility of the polymer composition may be improved.

According to one embodiment of the invention, the second polymer is obtained by polymerization of (meth) acrylamide and at least one second monomer in an amount of 0.2-19 wt-%, preferably 0.5-12 wt-%, more preferably 1-6 wt-%, calculated from the total dry polymer material weight of the polymer composition. According to another embodiment, the second polymer is a copolymer of (meth) acrylamide and at least one second monomer in an amount of 0.1 to 10 mol%, preferably 0.3 to 6 mol%, more preferably 0.5 to 3 mol%, calculated from the total amount of monomers of the polymer composition.

Preferably, the second polymer is a cationic polymer, which means that the second monomer is cationic.

When the second polymer is cationic, the cationic second monomer may be selected from the group comprising: 2- (dimethylamino) ethyl acrylate (ADAM), [2- (acryloyloxy) ethyl ] trimethyl ammonium chloride (ADAM-Cl), 2- (dimethylamino) ethyl acrylate benzyl chloride, 2- (dimethylamino) ethyl acrylate dimethyl sulfate, 2-dimethylaminoethyl methacrylate (MADAM), [2- (methacryloyloxy) ethyl ] trimethyl ammonium chloride (MADAM-Cl), 2-dimethylaminoethyl methacrylate dimethyl sulfate, [3- (acryloylamino) propyl ] trimethyl ammonium chloride (APTAC), [3- (methacryloylamino) propyl ] trimethyl ammonium chloride (MAPTAC), and diallyldimethyl ammonium chloride (DADMAC). For some of the listed monomers, the cationicity varies as a function of pH, for example, they are more cationic at acidic pH and less cationic at neutral pH. Monomers containing quaternary nitrogen in their structure provide cationic charge independent of pH and are therefore preferred.

According to a preferred embodiment of the present invention, the second polymer is a copolymer of acrylamide and [2- (acryloyloxy) ethyl ] trimethyl ammonium chloride (ADAM-Cl), [3- (acrylamido) propyl ] trimethyl ammonium chloride (APTAC), [3- (methacryloylamino) propyl ] trimethyl ammonium chloride (MAPTAC), combinations thereof. These monomers can be polymerized into high molecular weight polymers, which is advantageous for the flocculation efficiency of the polymer composition. In addition, they provide a cationic charge that is independent of pH. The amount of ADAM-Cl, APTAC and/or MAPTAC may be 0.1 to 10 mol-%, preferably 0.3 to 6 mol-%, more preferably 0.5 to 3 mol-%, calculated from the total amount of monomers of the polymer composition.

According to a preferred embodiment of the present invention, the second polymer is polymerized without adding a multifunctional crosslinking agent, such as methylene bisacrylamide, to the monomer mixture. In this way the extension and/or extent of the polymer chains of the second polymer may be improved.

The second polymer is preferably polymerized in the presence of the first polymer as a polyamine.

Cationic synthesis the first polymer has a higher charge density than the second polymer. Cationic Synthesis the difference in cationicity of the first polymer and the second polymer is at least 1meq/g dry, preferably at least 2meq/g dry, more preferably at least 3meq/g dry, even more preferably at least 4meq/g dry, and sometimes even at least 5meq/g dry. It is believed that the greater the difference in cationicity, the more pronounced the interaction between the first polymer and the anionic species and the extension of the polymer chain extension of the second polymer, even at elevated cation demand and/or conductivity. The highest difference in cationic degree can be obtained by selecting a polyamine and/or a cationic homopolymer as the first polymer, and a second polymer comprising only acrylamide or a small amount of cationic monomer.

In one embodiment of the invention, the cationically synthesized first polymer is a homopolymer and the difference in cationicity between the cationically synthesized first polymer and the second polymer is at least 30 mol-%, preferably at least 90 mol-%, more preferably at least 94 mol-%. This can enhance both flocculation and fixation, especially for sludges with a cation demand of at least 800 μ eq/l.

Preferably, the monomers used for the polymerization of the cationic synthesis of the first polymer and the second polymer are different from each other.

the polymer composition may have an overall charge density of at most 1.7meq/g dry, preferably at most 1.5meq/g dry according to one embodiment of the invention, the overall charge density of the polymer composition may be in the range of 0.1 to 1.7meq/g dry, preferably 0.1 to 1.5meq/g dry, more preferably 0.7 to 2.0meq/g dry the overall charge density value may be measured at pH 7.0 by using Mutek the overall charge density includes that it has been observed that when the overall charge density of the polymer composition is < 1.7meq/g dry it provides excellent performance in floc formation and gives a high quality clarified filtrate.

According to one embodiment of the invention, the polymer composition comprises 0.5-25 wt-%, preferably 2-10 wt-%, more preferably 3-8 wt-% of the first polymer and 75-99.5 wt-%, preferably 90-98 wt-%, more preferably 92-97 wt-% of the second polymer. The weight percentages are calculated from the polymer content of the polymer composition (dry/dry).

The polymer composition may preferably be in the form of a dry powder or a particulate material or a particulate product, and is dissolved in water and diluted to the desired appropriate feed concentration before its use. The resulting polymer composition may be dried and optionally ground to a suitable particle size. According to one embodiment, the dry polymer composition in the form of a particulate product or a particulate material or a powder may have a solids content of at least 80 wt-%, preferably at least 85 wt-%, more preferably at least 90 wt-%. The dry particulate polymer composition is easy and cost-effective to transport and store, can remain stable for long periods of time, and is resistant to microbial degradation.

According to one embodiment, the polymer content in the polymer composition is at least 25 wt-%, preferably at least 60 wt-%, more preferably at least 80 wt-%. For example, polymer compositions having a lower polymer content, obtained by dispersion or emulsion polymerization, have the advantage of being easily dissolved. In view of product logistics issues, for example, a polymer product with a higher polymer content obtained by gel polymerization is more cost-effective. High polymer content has the additional benefit of improving microbial stability.

According to a preferred embodiment, the first polymer may be obtained by solution polymerization, for example by non-radical solution polymerization. The second polymer may be obtained by gel polymerization, e.g. by adiabatic gel polymerization, preferably at an acidic pH <6, preferably in the pH range of 2.5-5.5, more preferably 3-4. The acidic pH is particularly advantageous when hydrolytically unstable cationic monomers are used in the first and/or second polymer, thereby reducing hydrolysis of the cationic groups.

according to one embodiment of the invention, the polymer composition may have a standard viscosity in the range of 3-6mPas, preferably 3.6-5.0mPas, measured at a solids content of 0.1 wt-% in aqueous NaCl (1M) at 25 ℃ using a Brookfield DVII T viscometer with an U L adapter.

According to one embodiment of the invention, the polymer composition may have an intrinsic viscosity in the range of 4 to 20dl/g, preferably 7 to 15 dl/g. Intrinsic viscosity values were determined by testing at 25 ℃ for NaNO ₃A series of dilutions of different polymer contents in aqueous solution (0.1M) was obtained in a known manner by measuring the mean flow time with a Ubbelohde capillary viscometer (0C), calculated from the corrected mean flow time Specific viscosity, the specific viscosity divided by the concentration to obtain the reduced viscosity of each dilution, the reduced viscosity plotted as a function of concentration, and the Y-axis intercept read to give the intrinsic viscosity. It has been observed that a specific intrinsic viscosity range provides the best performance for the polymer composition. If the intrinsic viscosity is lower, flocculation performance may be reduced and higher intrinsic viscosity values may result in a decrease in dissolution time and/or an increase in the amount of insoluble particles in the dried polymer composition.

According to a preferred embodiment of the invention, the flocculant comprising the polymer composition is used or added to the aqueous feed in an amount of 0.1-10mg/l, preferably 0.2-3mg/l, more preferably 0.2-1.0mg/l, given as dry polymer composition/volume of aqueous feed. In another embodiment, the polymer composition may be added to the aqueous feed in an amount of 1 to 5mg/l, given as dry polymer composition/volume of aqueous feed. The amount of flocculant comprising the polymer composition required is equal to or preferably less than the dosage of conventional polymer flocculants.

According to one embodiment of the invention, a coagulant may be introduced into the aqueous feed and/or dispersion water. The coagulant is preferably introduced before the aqueous feed is contacted with the flocculant, i.e. before the flocculant is introduced. Suitable coagulants may be selected from bentonite, silica sol, polyaluminium chloride, alum, ferric sulphate, ferric chlorite. According to a preferred embodiment, the flocculant is added immediately after the coagulant is added, for example within about 1 minute of the coagulant addition. The coagulant interacts with the dissolved substance (optionally also with other substances, such as colloidal particles) and forms microflocs. These microflocs can then be flocculated by a flocculating agent.

Detailed Description

Experiment of

Some embodiments of the invention are described in the following non-limiting examples.