Method for preparing a dry cationic hydrogel polymer product, polymer product and its use

Abstract

The invention relates to a method for preparing a dry cationic hydrogel polymer product. The method comprises polymerisation of a reaction mixture comprising ethylenically unsaturated monomers in presence of water and initiator(s) by radical polymerisation and obtaining a hydrogel polymer. The hydrogel polymer is comminuted by chopping or shredding, and dried, whereby a dry hydrogel polymer product in powder form is obtained. At least one cationic reverse phase emulsion polymer is added to the hydro polymer at the comminuting step. The invention relates also to a dry cationic hydrogel polymer composition prepared by the method and its use.

Claims

1. Method for preparing a dry cationic hydrogel polymer product, the method comprising polymerising a reaction mixture comprising ethylenically unsaturated monomers in presence of water and initiator(s) by radical polymerisation and obtaining a hydrogel polymer, comminuting the hydrogel polymer by chopping or shredding, and drying the hydrogel polymer, whereby a dry hydrogel polymer product in powder form is obtained, wherein adding at least one cationic reverse phase emulsion polymer is added to the hydro polymer at the comminuting step.

2. Method according to claim 1, wherein the cationic reverse phase emulsion polymer is added in an amount of >5 weight %, preferably >10 weight %, more preferably >15 weight %, calculated from the weight of dry hydrogel polymer.

3. Method according to claim 1, wherein the cationic reverse phase emulsion polymer is cationic polyacrylamide having a charge density of 10-80 mol %, preferably 40-80 mol %, more preferably 60-80 mol %.

4. Method according to claim 1, wherein the reverse phase emulsion polymer is cationic branched and/or cross-linked polyacrylamide, where the amount of cross-linker agent is <500 ppm, preferably <250 ppm, more preferably <100 ppm, calculated from the total weight of the used monomers.

5. Method according to claim 1, characterised in that wherein the reverse phase emulsion polymer has a ratio of bulk viscosity to standard viscosity, i.e. BV/SV ratio, in the range from 125 to 550, preferably from 150 to 500.

6. Method according to claim 1, wherein the reverse phase emulsion polymer is added at comminuting step without addition of a lubricant.

7. Method according to claim 1, wherein the ethylenically unsaturated monomer is selected from acrylamide and its derivatives; methacrylamides; N-alkylacrylamides, such as N-methylacrylamide; and N,N-dialkylacrylamides, such as N,N-dimethylacrylamide.

8. Method according to claim 1, wherein the reaction mixture comprises cationic monomers.

9. Method according to claim 8, wherein the cationic monomers are selected from diallyldimethylammonium chloride (DADMAC); methacryloyloxyethyltrimethylammonium chloride; acryloyloxyethyltrimethylammonium chloride; methacrylamidopropyltrimethylammonium chloride; acrylamidopropyltrimethyl-ammonium chloride; diallyldimethylammonium chloride; dimethylaminoethyl acrylate; dimethylaminoethyl methacrylate; dimethylaminopropylacrylamide; dimethylamino-propylmethacrylamide; or a similar monomer.

10. Dry cationic hydrogel polymer composition prepared by a method according to claim 1.

11. Use of a dry cationic hydrogel polymer product prepared according to claim 1 for sludge dewatering, for treating municipal sludge, for treating mining sludges and/or waters, or as a treatment chemical in industrial water treatment processes or in pulp and paper manufacturing.

Description

Reference Example 1

Production of Reference Polymer 1

[0044] Cationic polyacrylamide gel was made by adiabatic redox polymerisation. The resulting polymer gel was dried and used as a reference. The charge density of Polymer 1 is 49 mol %, and the standard viscosity is 3.9 mPas.

Example 2

Production of Dry Cationic Hydrogel Polymer product

[0045] Dry cationic hydrogel polymer product comprising Polymer 1 and Polymer 2 was prepared. Polymer 1 is the same as in Example 1 and Polymer 2 is a cationic reverse phase emulsion polymer having charge density of 55 mol % and high branching degree, defined by BV/SV ratio of 330. The ratio of Polymer 1 to Polymer 2 was 90:10 w/w.

[0046] The production process was as follows: a portion of the undried hydrogel polymer prepared according to Example 1 is chopped and ground in a grinder (LM-10/P, Koneteollisuus Oy, Finland). Polymer 2 is added to the ground gel, and the mixture is mixed with an overhead stirrer for 1 minute at mixing speed of 300 rpm. The resulting product is dried in 60 ° C. oven. The dry product is milled with a Retsch mill and sieved to obtain consistent particle size fractions. The fraction with the particle size of 0.5-1 mm is used in performance trials.

Example 3

Production of Dry Cationic Hydrogel Polymer Product

[0047] Dry cationic hydrogel polymer product comprising of Polymer 1 and Polymer 2 in ratio 80:20 w/w is prepared in a similar manner as described in Example 2.

Example 4

Production of Dry Cationic Hydrogel Polymer Product

[0048] Dry cationic hydrogel polymer product comprising of Polymer 1 and Polymer 2 in ratio 70:30 w/w is prepared in a similar manner as described in Example 2.

Example 5

Performance Trial

[0049] The dry polymer product of Example 3 was tested using a general procedure with Free Drainage Test measurement as follows: 2 g of a dry polymer product is dissolved in 998 g of deionized water with 1 hour of gentle mixing to make a 0.2 weight % test solution, which was used in the experiment within the same day.

[0050] The Free Drainage test experiment was conducted using digested municipal sludge from waste water treatment plants WWTP1 (RWZI Kralingseveer, Rotterdam, Netherlands) and WWTP2 (RWZI Harnaschpolder, Den Haag, Netherlands). The dry solids concentration (DS) of the sludge was measured by drying 5 g of the sludge at 105° C. in an air circulatory oven for overnight and it was 3.8 weight % for WWTP1 sludge, and 3.7 weight % for WWTP2 sludge.

[0051] The polymer product dose in the experiment is defined as “kg/t”, where the “kg” refers to the mass of dry polymer product in kilograms, dosed as 0.2% solution and the “(t)” to the mass of 10.sup.3 kg of dry sludge solids. A single measurement point of the Free Drainage test experiment, presented in Tables 1 and 2, was collected in a following way: A volume of the 0.2 weight % polymer product solution was dosed into a 200 ml still sludge sample. The sample was mixed with an overhead stirrer for 10 seconds at 1000 rpm after which the mixed sample was poured to the free drainage funnel. The flocculation and dewatering power of a composition is evaluated in comparison of the Free Drainage volume after 5 s drainage time. Dried Polymer 1 from Example 1 and SD-2081 (Kemira Oyj, degree of branching—low, charge density—high, molecular weight—high) are used as references.

TABLE-US-00001 TABLE 1 Measurement results of Free Drainage Test experiments for dry polymer product of Example 3 with WWTP1 sludge. Optimum performance of the products. Optimum dosage Free drainage Product (kg/tDS) volume after 10 s Example 3 19 134 Polymer 1 13 93 (reference) SD-2081 18 127

TABLE-US-00002 TABLE 2 Measurement results of Free Drainage Test experiments for dry polymer product of Example 3 with WWTP2 sludge. Optimum performance of the products. Optimum dosage Free drainage Product (kg/tDS) volume after 5 s Example 3 12 110 Polymer 1, ref 13 86

[0052] Even if the invention was described with reference to what at present seems to be the most practical and preferred embodiments, it is appreciated that the invention shall not be limited to the embodiments described above, but the invention is intended to cover also different modifications and equivalent technical solutions within the scope of the enclosed claims.