Flocculating agent for improving anti-shearing performance and application

Abstract

The invention belongs to the field of polymers, and discloses a flocculating agent for improving anti-shearing performance, the flocculating agent is composed of a first flocculating agent and a second flocculating agent; the first flocculating agent and the second flocculating agent are both polyacrylamide polymers; a monomer for synthesizing the first flocculating agent contains an acrylamide cross-linking agent; monomers for synthesizing the second flocculating agent do not contain an acrylamide cross-linking agent; both the monomer for synthesizing the first flocculating agent and the monomer for synthesizing the second flocculating agent contain cationic monomers. The flocculant is formed by compounding two flocculants, the flocculant with a small dosage is micro-crosslinking polyacrylamide with small cation density, the flocculant with a large dosage is non-crosslinking acrylamide with high cation density, the latter is easy to flocculate papermaking filler, and the former reinforces flocculated bodies and improves the shear resistance.

Description

Technical Field

[0001] This invention belongs to the field of polymers, and specifically relates to a flocculant for improving shear resistance and its application. Background Technology

[0002] Polyacrylamide is a water-soluble polymer, a general term for homopolymers or copolymers obtained by free radical polymerization of acrylamide and its derivatives. It can be classified into anionic, cationic, nonionic, and amphoteric types. Polyacrylamide possesses flocculating, thickening, water-absorbing, and drag-reducing properties, and is widely used in crude oil extraction, papermaking, and wastewater treatment.

[0003] Cationic polyacrylamide is the most commonly used filler pretreatment agent in the papermaking industry. On the one hand, it needs to agglomerate small-sized filler particles into large flocs to ensure that the filler can be better retained during the paper forming process. On the other hand, it also needs to ensure the shear resistance of these flocs, because the flocs will be subjected to shear force after being added to the wet end of papermaking. If the shear resistance of the flocs is not good, the flocs will be broken down into small-sized particles when subjected to shear force, resulting in a decrease in the filler retention rate.

[0004] The technical problem to be solved in this case is: how to maintain a stable flocculated particle size of papermaking fillers after shear force is applied during the flocculation process. Summary of the Invention

[0005] Based on this, the first objective of the present invention is to provide a flocculant for improving shear resistance, wherein the flocculant is composed of two flocculants, wherein the flocculant used in a smaller amount is micro-crosslinked polyacrylamide with low cationic density, and the flocculant used in a larger amount is non-crosslinked acrylamide with high cationic density. The latter is easy to flocculate paper fillers, while the former is used to reinforce the already flocculent body and improve shear resistance.

[0006] In addition, the present invention also discloses the application of the above-mentioned flocculant.

[0007] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0008] A flocculant for improving shear resistance, the flocculant comprising a first flocculant and a second flocculant; both the first flocculant and the second flocculant are polyacrylamide polymers;

[0009] The monomers used to synthesize the first flocculant contain acrylamide crosslinking agents; the monomers used to synthesize the second flocculant do not contain acrylamide crosslinking agents; both the monomers used to synthesize the first flocculant and the monomers used to synthesize the second flocculant contain cationic monomers; the molar percentage content of cationic monomers in the first flocculant is x, and the molar percentage content of cationic monomers in the second flocculant is y;

[0010] x ≥ 5% and y ≤ 50%; x:y = 1:2~8;

[0011] The amount of acrylamide crosslinking agent in the first flocculant is equivalent to 500~1000 ppm of the total molar amount of monomers in the first flocculant.

[0012] In the above-mentioned flocculants for improving shear resistance, the first flocculant is a structural unit composed of the following monomers: acrylamide, cationic monomer, and acrylamide crosslinking agent; the cationic monomer accounts for 5 to 15% of the total molar amount of all structural units constituting the first flocculant.

[0013] In the above-mentioned flocculant for improving shear resistance, the second flocculant includes the following structural units: acrylamide and cationic monomer; the cationic monomer accounts for 30-50% of the total molar amount of all structural units constituting the first flocculant.

[0014] In the above-mentioned flocculant for improving shear resistance, the second flocculant further includes a water-soluble monomer; the water-soluble monomer is one or more combinations of acrylic acid, acrylate, and (meth)acrylate hydroxyalkyl ester.

[0015] In the above-mentioned flocculants for improving shear resistance, the water-soluble monomer accounts for 0 to 5% of the total molar amount of all structural units constituting the second flocculant.

[0016] In the above-mentioned flocculants for improving shear resistance, both the first flocculant and the second flocculant are obtained by free radical solution polymerization;

[0017] The cationic monomer is one or more combinations of dimethylaminoethyl acrylate methyl chloride quaternary salt, acryloamidopropyltrimethylammonium chloride, and acrylooxyethyltrimethylammonium chloride.

[0018] The acrylamide crosslinking agent is N,N-methylenebisacrylamide.

[0019] In the above-mentioned flocculants for improving shear resistance, the free radical solution polymerization uses water as a solvent and employs a water-soluble initiator to initiate the reaction to obtain the first flocculant and the second flocculant.

[0020] In the above-mentioned flocculants for improving shear resistance, the weight ratio of the first flocculant to the second flocculant is 1:5~10.

[0021] In the above-mentioned flocculants for improving shear resistance, the total solids content of the flocculant is 10~20wt%.

[0022] Meanwhile, the present invention also discloses the use of additives for preparing fillers in flocculation papermaking processes using any of the flocculants described above.

[0023] The beneficial effects of this invention are as follows:

[0024] This invention uses a combination of two flocculants. The flocculant used in smaller quantities is micro-crosslinked polyacrylamide with low cationic density, while the flocculant used in larger quantities is non-crosslinked acrylamide with high cationic density. The latter is easy to flocculate paper fillers, while the former is used to reinforce the already flocculent body and improve its shear resistance. Detailed Implementation

[0025] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0026] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0027] Preparation of the first flocculant

[0028] The preparation method of the first flocculant is as follows:

[0029] Acrylamide, cationic monomer, N,N-methylenebisacrylamide, and water were added to the reaction vessel. Nitrogen gas was introduced while stirring to maintain an inert gas atmosphere in the system. After deoxygenation, the system was heated to 60°C, and an initiator was added dropwise to the reaction system. The initiator was azobisisobutyramidine hydrochloride, and its amount was equivalent to 0.5 wt% of the total monomer. The dropwise addition time was 2 h. After the dropwise addition was completed, the system was kept at the temperature for 3 h. Then, the initiator was added to eliminate unreacted monomers, and a viscous liquid was obtained.

[0030] In the above preparation process, the amount of water used is 85 wt% of the total weight of the monomer and water.

[0031] The formulation of the first flocculant can be found in Table 1;

[0032] Table 1. Formulation Table (Unit: Moles)

[0033] Preparation of the second flocculant

[0034] The preparation method of the second flocculant is as follows:

[0035] Acrylamide, cationic monomer, optional water-soluble monomer, and water are added to the reaction vessel. Nitrogen gas is introduced while stirring to maintain an inert gas atmosphere in the system. After deoxygenation, the system is heated to 60°C, and an initiator is added dropwise to the reaction system. The initiator is potassium persulfate, and its amount is equivalent to 0.5 wt% of the total monomer. The dropwise addition time is 2 h. After the dropwise addition is completed, the temperature is maintained for 3 h. Then, the initiator is added to eliminate unreacted monomers to obtain a viscous liquid.

[0036] In the above preparation process, the amount of water used is 80 wt% of the total weight of the monomer and water.

[0037] The formulation of the second flocculant can be found in Table 2;

[0038] Table 2 Formulation Table (Unit: Moles)

[0039] Preparation of flocculants

[0040] The flocculant is made by mixing the first flocculant and the second flocculant mentioned above. This mixing method can be pre-mixing or adding it on-site during the papermaking process. If it is added on-site during the papermaking process, the second flocculant should be added first, followed by the first flocculant.

[0041] The relevant formulation of the flocculant prepared in this invention can be found in Table 3;

[0042] Table 3 Flocculant Formulation Table

[0043] First flocculant serial number Second flocculant serial number weight ratio Flocculant 1 1 3 1:5 Flocculant 2 2 2 1:7 Flocculant 3 3 1 1:10 Flocculant 4 1 4 1:5 Flocculant 5 1 5 1:5 Flocculant 6 1 6 1:5 Flocculant 7 2 4 1:5 Flocculant 8 3 5 1:5 Comparison Flocculant 1 4 1 1:5 Comparison Flocculant 2 5 1 1:5 Comparison of flocculants 3 1 / / Comparison Flocculant 4 / 1 / Comparison of flocculants 5 1 1 1:3 Comparison of flocculants 6 1 1 1:12

[0044] Flocculation performance test of calcium carbonate

[0045] The experimental procedure was as follows: A calcium carbonate aqueous dispersion suspension with a fineness of 2-5 μm was diluted to a solid content of approximately 20 wt%. Then, 200 g of the diluted calcium carbonate sample was taken, and flocculant was added at a stirring speed of 800 rpm at a rate of 1.8 kg / t of calcium carbonate. Samples were taken every 2 minutes and the D50 particle size was measured using a Malvern laser particle size analyzer. After 8 minutes, the stirring speed was increased to 2000 rpm, and samples were taken every 2 minutes and the D50 particle size was measured using a Malvern laser particle size analyzer.

[0046] Table 4. Flocculant effect on filler flocculation and shear resistance test

[0047] 0min 2min 4min 6min 8min 10min 12min 14min Blank group 2.23 2.22 2.19 2.05 2.18 2.15 2.17 2.16 Flocculant 1 136.22 133.36 120.41 119.47 109.78 74.23 62.18 56.22 Flocculant 2 105.94 96.51 98.56 93.78 96.71 67.02 53.72 45.64 Flocculant 3 99.77 95.83 91.00 84.97 84.26 56.25 46.48 40.09 Flocculant 4 124.06 123.33 124.75 118.68 113.70 80.95 69.24 64.37 Flocculant 5 111.74 104.75 102.02 98.89 98.60 67.94 58.27 52.79 Flocculant 6 105.96 96.54 96.62 93.81 96.75 67.02 57.77 52.22 Flocculant 7 112.63 114.69 115.94 114.11 109.65 70.68 64.71 58.43 Flocculant 8 135.03 142.68 132.84 126.08 120.55 86.17 75.58 69.12 Comparison Flocculant 1 26.47 24.24 22.78 20.56 20.05 18.64 17.45 15.51 Comparison Flocculant 2 24.402 20.745 20.005 18.52 18.64 12.68 10.79 9.67 Comparison of flocculants 3 167.2 169.0 196.6 181.6 174.2 111.8 96.1 90.9 Comparison Flocculant 4 13.92 13.65 13.39 13.42 13.24 9.79 8.58 8.08 Comparison of flocculants 5 136.08 155.30 137.78 138.79 132.64 98.86 87.95 81.58 Comparison of flocculants 6 46.92 47.60 46.17 42.20 45.80 26.52 21.70 18.57

[0048] Results Analysis: Table 4 shows that when only the first flocculant is used, the filler flocs treated with the flocculant have good shear resistance, but the median particle size is relatively large (paper manufacturers require 30-60 μm). When only the second flocculant is used, the median particle size of the filler flocs treated with the flocculant is relatively small and not shear resistant. When the weight ratio of the first flocculant to the second flocculant varies from 1:5 to 10, the median particle size of the filler flocs treated with the flocculant increases with the increase of the amount of the first flocculant, and the shear resistance is also improved. When the amount of acrylamide crosslinking agent in the first flocculant varies from 500 to 1000 ppm to the total molar amount of the monomers of the first flocculant, the shear resistance of the filler flocs treated with the flocculant is stronger and the median particle size is larger with the increase of the amount of acrylamide crosslinking agent.

[0049] The embodiments presented herein are merely selected implementations based on combinations of all possible embodiments. The appended claims should not be limited to the embodiments described herein. Some numerical ranges used in the claims include sub-ranges within them, and variations within these ranges should also be covered by the appended claims.

Claims

1. A flocculant for improving shear resistance, characterized in that, The flocculant is composed of a first flocculant and a second flocculant; both the first flocculant and the second flocculant are polyacrylamide polymers. The monomers used to synthesize the first flocculant contain acrylamide crosslinking agents; the monomers used to synthesize the second flocculant do not contain acrylamide crosslinking agents; both the monomers used to synthesize the first flocculant and the monomers used to synthesize the second flocculant contain cationic monomers; the molar percentage content of cationic monomers in the first flocculant is x, and the molar percentage content of cationic monomers in the second flocculant is y; x ≥ 5% and y ≤ 50%; x:y = 1:2~8; The amount of acrylamide crosslinking agent in the first flocculant is equivalent to 500~1000 ppm of the total molar amount of monomers in the first flocculant.

2. The flocculant for improving shear resistance according to claim 1, characterized in that, The first flocculant is a structural unit composed of the following monomers: acrylamide, cationic monomer, and acrylamide crosslinking agent; the cationic monomer accounts for 5 to 15% of the total molar amount of all structural units constituting the first flocculant.

3. The flocculant for improving shear resistance according to claim 1, characterized in that, The second flocculant comprises the following structural units: acrylamide and cationic monomer; the cationic monomer accounts for 30-50% of the total molar amount of all structural units constituting the first flocculant.

4. The flocculant for improving shear resistance according to claim 3, characterized in that, The second flocculant also includes a water-soluble monomer; the water-soluble monomer is one or more of acrylic acid, acrylate, and (meth)acrylate hydroxyalkyl ester.

5. The flocculant for improving shear resistance according to claim 4, characterized in that, The water-soluble monomer accounts for 0 to 5% of the total molar amount of all structural units constituting the second flocculant.

6. The flocculant for improving shear resistance according to claim 1, characterized in that, Both the first flocculant and the second flocculant were obtained by free radical solution polymerization; The cationic monomer is one or more combinations of dimethylaminoethyl acrylate methyl chloride quaternary salt, acryloamidopropyltrimethylammonium chloride, and acrylooxyethyltrimethylammonium chloride. The acrylamide crosslinking agent is N,N-methylenebisacrylamide.

7. The flocculant for improving shear resistance according to claim 6, characterized in that, The free radical solution polymerization uses water as a solvent and employs a water-soluble initiator to initiate the reaction, thereby producing the first flocculant and the second flocculant.

8. The flocculant for improving shear resistance according to claim 1, characterized in that, The weight ratio of the first flocculant to the second flocculant is 1:5~10.

9. The flocculant for improving shear resistance according to claim 1, characterized in that, The total solids content of the flocculant is 10-20 wt%.

10. Use of an additive for preparing fillers in a flocculation papermaking process using a flocculant as described in any one of claims 1 to 9.

Images