Surface charge enhanced titanium-based coagulant, preparation method and application

Abstract

The invention discloses a surface charge enhanced titanium-based coagulant as well as a preparation method and application thereof. The coagulant is prepared from a hydrolyzable titanium source precursor and a multifunctional cationization coordination agent simultaneously containing (a) an anchoring group, (b) a quaternary ammonium salt group and (c) C8-C22 alkyl through a sol-gel reaction in an anhydrous alcohol solvent in one step, the coordination agent is bonded with a titanium-oxygen skeleton through an anchoring group, and still keeps a potential greater than + 15 mVZeta in a high-pH water body. The flocculant is synthesized at room temperature, is simple in process, large in floc particle size and fast in sedimentation, shows an excellent removal effect on high-algae, low-temperature, low-turbidity, high-humic-acid and emulsified oil wastewater, and can be used as an anti-biological-pollution pretreatment agent before membrane filtration, and titanium residues after filtration are lower than the detection limit.

Description

Technical Field

[0001] This invention relates to a surface charge-enhanced titanium-based coagulant, its preparation method, and its application. Background Technology

[0002] Coagulation and sedimentation are the core components for removing colloids, algae, and organic pollutants. Aluminum salts (such as polyaluminum chloride) and iron salts (such as ferric chloride) coagulants exhibit good charge-carrying properties within the pH range of 6–7, but their fatal drawbacks lie in poor low-temperature adaptability, small floc size, slow settling, and high residual metal concentration: Al 3+ Residues pose a risk of biotoxicity, Fe 3+ Residue can easily cause excessive color in the effluent and corrode the pipe network.

[0003] Titanium-based coagulants have become a research hotspot due to their strong hydrolysis driving force, high biocompatibility, large floc size, and fast settling velocity. However, existing polytitanium chloride (PTC) or acetylacetone-modified titanium coagulants (TXC) still have the following drawbacks:

[0004] Insufficient surface positive charge – isoelectric point is only pH 4–5, carries a negative charge under alkaline conditions, resulting in low coagulation efficiency;

[0005] Limited functionality – lacks targeted capture of hydrophilic AOM and emulsified oils.

[0006] Based on this, the present invention provides a surface charge-enhanced titanium-based coagulant, its preparation method, and its application. Summary of the Invention

[0007] The present invention provides a surface charge-enhanced titanium-based coagulant, its preparation method, and its application in order to solve the problems existing in the prior art.

[0008] The technical solutions adopted in this invention are as follows:

[0009] A surface charge-enhanced titanium-based coagulant, wherein the coagulant is prepared by a sol-gel reaction of a hydrolyzable titanium source precursor and a multifunctional cationic ligand in an anhydrous alcohol solvent.

[0010] The multifunctional cationic ligand is a single compound containing the following (a), (b), and (c) groups simultaneously:

[0011] (a) An anchoring groups that can form chemical bonds with titanium atoms;

[0012] (b) A quaternary ammonium salt group that provides a pH-independent positive charge;

[0013] (c) C8–C22 straight-chain or branched alkyl groups that provide hydrophobic adsorption and bridging effects.

[0014] Furthermore, the hydrolyzable titanium source precursor is titanium tetrachloride or tetrabutyl titanate.

[0015] Furthermore, the anchoring group is an alkoxysilyl or carboxyl group.

[0016] Furthermore, the multifunctional cationic coordinating agent is a single compound conforming to the following general formula (A) or (B):

[0017] (A) Silane quaternary ammonium salts:

[0018] (R1O)3-Si–(CH2) m –N + (R2)(R3)–R4·X - ;

[0019] Wherein, R1 is methyl or ethyl; m is an integer from 1 to 6; R2 and R3 are methyl or ethyl; R4 is a C8–C22 saturated or unsaturated alkyl group; X - Halogen ions;

[0020] (B) Long-chain alkyl quaternary ammonium carboxylic acids:

[0021] R5–N + (R6)(R7)–(CH2) n –COO - ;

[0022] Wherein, R5 is a C8–C22 saturated or unsaturated alkyl group; R6 and R7 are methyl or ethyl; and n is an integer from 1 to 4.

[0023] Furthermore, the multifunctional cationic ligand is 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride or N-dodecyl-N,N-dimethylglycine.

[0024] Furthermore, the molar ratio of titanium element to multifunctional cationizing ligand in the titanium source precursor is 5:1 to 20:1.

[0025] This invention also discloses a method for preparing a surface charge-enhanced titanium-based coagulant, characterized by comprising the following steps:

[0026] (1) Dissolve the hydrolyzable titanium source precursor in an anhydrous alcohol solvent to obtain a titanium source solution;

[0027] (2) Add the multifunctional cationizing ligand to the titanium source solution and stir at room temperature for 0.5–2 h to form a modified precursor;

[0028] (3) Add water or alkaline solution to the modified precursor to make the molar ratio of water to titanium 2:1–10:1 and carry out hydrolysis-polymerization reaction;

[0029] (4) After the reaction is completed, the mixture is aged and dried to obtain the surface charge enhanced titanium-based coagulant.

[0030] Further, in step (3), a 0.01–0.1 mol / L NaOH dilute solution is used as the alkali solution, the molar ratio of alkali to titanium is 0.5–1.5, and the total amount of water added still satisfies the water to titanium molar ratio of 2:1–10:1.

[0031] The present invention also discloses the application of a surface charge-enhanced titanium-based coagulant in the treatment of algae-containing water bodies with a pH value higher than 8.

[0032] This invention also discloses the application of a surface charge-enhanced titanium-based coagulant in the purification of low-temperature water bodies with a water temperature ≤5℃ and turbidity ≤10NTU.

[0033] This invention also discloses the application of a surface charge-enhanced titanium-based coagulant as an anti-biofouling pretreatment agent before membrane filtration processes.

[0034] The present invention has the following beneficial effects:

[0035] (1) Under alkaline conditions of pH 7.5-9.5, the surface of the coagulant remains positively charged, with a Zeta potential of > +15mV, achieving an algal cell removal rate of ≥98% and a DOC removal rate of ≥60%, which significantly improves the problem of low efficiency caused by the high pH negative charge of traditional titanium-based coagulants.

[0036] (2) In the test of raw water with low temperature of 4℃ and low turbidity of 5NTU, the remaining turbidity was ≤0.5NTU and the turbidity removal rate was ≥90%, indicating that the low temperature and low turbidity environment still has a good purification effect.

[0037] (3) The average particle size of the flocs increased from 210 μm in traditional PTC to ≥700 μm, and the settling time T90 was shortened from 25 min to ≤6 min, which significantly accelerated the separation of mud and water.

[0038] (4) For high humic acid or oily emulsified wastewater, the removal performance of DOC and emulsified oil is better than that of unmodified titanium coagulant through simultaneous adsorption of hydrophobic long-chain alkyl groups.

[0039] (5) When used for pretreatment before membrane filtration, it can delay biofouling of membrane modules and reduce the frequency of chemical cleaning. The synthesis process is mainly carried out under mild conditions (room temperature to 60°C) and anhydrous ethanol solvent is used. The titanium residue after filtration is lower than the detection limit, which has the potential to be applied to drinking water treatment. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the invention.

[0041] Figure 2 This is a comparison chart of Zeta potentials. Detailed Implementation

[0042] The invention will now be further described with reference to the accompanying drawings.

[0043] To enable those skilled in the art to clearly and completely understand and implement the present invention, the present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are only for explaining the present invention and are not intended to limit the scope of protection of the present invention. Any equivalent substitutions or improvements based on the technical concept of the present invention without departing from the principles of the present invention should be considered to fall within the scope of protection of the present invention.

[0044] Example 1

[0045] Preparation of surface charge-enhanced titanium-based coagulant (STC-Q) based on silane quaternary ammonium salt coagulants:

[0046] (1) Add 40 mL of anhydrous ethanol to a three-necked flask protected by dry nitrogen and cool it to 0–5 °C in an ice bath;

[0047] (2) Slowly add 0.05 mol of titanium tetrachloride (TiCl4) dropwise, controlling the dropping rate to avoid violent exothermic reactions;

[0048] (3) After TiCl4 is completely dissolved, add 0.005 mol of 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride (DMOAP, CAS: 27668-52-6). This compound also contains:

[0049] (a) Trimethoxysilane anchoring group, (b) Quaternary ammonium salt positively charged group, (c) C 18 Straight-chain hydrophobic alkyl group.

[0050] (4) Remove the ice bath, raise the temperature to room temperature (25°C), stir the reaction for 1 hour to form a transparent modified precursor solution;

[0051] (5) Mix deionized water and anhydrous ethanol at a volume ratio of 1:1 to prepare an aqueous solution, and slowly add it dropwise to the above system at a molar ratio of H2O:Ti = 3:1; at the same time, add 0.025 mol NaOH (i.e., alkali:Ti = 0.5:1) to regulate the hydrolysis rate;

[0052] (6) Transfer the reaction solution to a 60°C constant temperature water bath and age for 2 hours to form a stable sol;

[0053] (7) The sol was dried in a vacuum drying oven at 80°C for 12 hours and then ground to obtain a light yellow powder, which is the surface charge enhanced titanium-based coagulant (denoted as STC-Q) of the present invention.

[0054] Example 2

[0055] Preparation of titanium-based coagulant (Ti-LB) based on long-chain betaine complexing agents:

[0056] (1) Dissolve 0.05 mol tetrabutyl titanate (TBT) in 50 mL of anhydrous ethanol to form a clear solution;

[0057] (2) Add 0.005 mol of N-dodecyl-N,N-dimethylglycine (lauryl betaine, CAS: 683-10-3), whose molecular structure includes:

[0058] (a) Carboxyl anchoring group, (b) Internal salt type quaternary ammonium positive charge (pH independent), (c) C 12 Hydrophobic alkyl groups;

[0059] (3) Stir the reaction at room temperature for 2 hours to form a homogeneous modified precursor;

[0060] (4) Add deionized water (H2O:Ti=4:1, molar ratio) and add 0.075mol NH3·H2O (calculated as NH3, its molar ratio with Ti is 1.5:1) to promote controlled hydrolysis;

[0061] (5) After aging at room temperature for 24 hours, a milky white stable emulsion is obtained, which is the coagulant described in this invention (denoted as Ti-LB). It can be added directly or spray-dried into powder.

[0062] Comparative Example 1: Conventional acetylacetone-modified titanium coagulant (TXC)

[0063] Except for replacing DMOAP in Example 1 with 0.005 mol acetylacetone, the remaining steps were exactly the same as in Example 1 to prepare TXC coagulant. This material does not contain quaternary ammonium salt positively charged groups or long-chain hydrophobic alkyl groups.

[0064] Comparative Example 2: Unmodified polytitanium chloride (PTC)

[0065] Except for the absence of any organic ligands, the remaining steps were the same as in Example 1 (only the TiCl4 + water / ethanol system) to prepare PTC coagulant.

[0066] Application performance testing:

[0067] Two typical types of difficult-to-treat raw water were selected for beaker coagulation experiments:

[0068] Test Scenario A: High pH algae-containing water body

[0069] Raw water: pH=8.5, Microcystis aeruginosa density 5×10⁻⁶ 5 cells / mL, dissolved organic carbon (DOC) = 6.5 mg / L;

[0070] Dosage: 4 mg / L (calculated as Ti);

[0071] Stir quickly for 2 minutes (200 rpm), then stir slowly for 15 minutes (40 rpm), and let stand for 30 minutes before taking the supernatant for analysis.

[0072] Test Scenario B: Low Temperature and Low Turbidity Water

[0073] Raw water: temperature 4℃, turbidity 5.0 NTU, pH=7.0;

[0074] Dosage: 3 mg / L (calculated as Ti);

[0075] The stirring and settling conditions are the same as above.

[0076] The test results are shown in the table below:

[0077] Table 1: Comparison of Treatment Effects of Various Coagulants

[0078]

[0079] In addition, STC-Q was added at 2 mg / L (based on Ti) to the raw water of simulated surface water and continuously treated for 30 days using a coagulation-ultrafiltration process. The results showed that the rate of increase of transmembrane pressure difference (TMP) decreased by 40%, indicating that it has a good anti-biofouling pretreatment effect.

[0080] According to ICP-MS analysis, the residual titanium concentration in the filtrate after treatment in each example was less than 0.001 mg / L (detection limit), which is far below the limit of aluminum (0.2 mg / L) in the "Standards for Drinking Water Quality" (GB5749-2022), and the sodium ion concentration was <5 mg / L, which does not affect water quality safety.

[0081] Figure 1 This is a schematic diagram illustrating the synthesis principle of the present invention.

[0082] Figure 2 This is a comparison chart of Zeta potentials, based on... Figure 2 The zeta potential of acetylacetone-modified titanium salt coagulants decreases significantly with increasing pH. They only exhibit a high charge under acidic conditions; under alkaline conditions (pH>7), their zeta potential is negative, indicating poor removal ability for negatively charged pollutants. In contrast, the surface charge-enhanced titanium-based coagulant STC-Q of this invention possesses a high zeta potential (>20mV) over a wide pH range, demonstrating that its pollutant removal performance is unaffected by pH and exhibits stable treatment effects.

[0083] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements without departing from the principle of the present invention, and these improvements should also be considered within the scope of protection of the present invention.

Claims

1. A surface charge-enhanced titanium-based coagulant, characterized in that: The coagulant is prepared by a sol-gel reaction of a hydrolyzable titanium source precursor and a multifunctional cationic ligand in an anhydrous alcohol solvent. The multifunctional cationic ligand is a single compound containing the following (a), (b), and (c) groups simultaneously: (a) An anchoring groups that can form chemical bonds with titanium atoms; (b) A quaternary ammonium salt group that provides a pH-independent positive charge; (c) C8–C22 straight-chain or branched alkyl groups that provide hydrophobic adsorption and bridging effects.

2. The surface charge-enhanced titanium-based coagulant as described in claim 1, characterized in that: The hydrolyzable titanium source precursor is titanium tetrachloride or tetrabutyl titanate.

3. The surface charge-enhanced titanium-based coagulant as described in claim 1, characterized in that: The anchoring group is an alkoxysilyl group or a carboxyl group.

4. The surface charge-enhanced titanium-based coagulant as described in claim 1, characterized in that: The multifunctional cationic coordinating agent is a single compound conforming to the following general formula (A) or (B): (A) Silane quaternary ammonium salts: (R1O)3-Si–(CH2) m –N + (R2)(R3)–R4·X - ; Wherein, R1 is methyl or ethyl; m is an integer from 1 to 6; R2 and R3 are methyl or ethyl; R4 is a C8–C22 saturated or unsaturated alkyl group; X - Halogen ions; (B) Long-chain alkyl quaternary ammonium carboxylic acids: R5–N + (R6)(R7)–(CH2) n –COO - ; Wherein, R5 is a C8–C22 saturated or unsaturated alkyl group; R6 and R7 are methyl or ethyl; and n is an integer from 1 to 4.

5. The surface charge-enhanced titanium-based coagulant as described in claim 1, characterized in that: The multifunctional cationic ligand is 3-(trimethoxysilyl)propyldimethyloctadecylammonium chloride or N-dodecyl-N,N-dimethylglycine.

6. The surface charge-enhanced titanium-based coagulant as described in claim 1, characterized in that: The molar ratio of titanium to multifunctional cationizing ligand in the titanium source precursor is 5:1 to 20:

1.

7. A method for preparing a surface charge-enhanced titanium-based coagulant as described in any one of claims 1-6, characterized in that: Includes the following steps: (1) Dissolve the hydrolyzable titanium source precursor in an anhydrous alcohol solvent to obtain a titanium source solution; (2) Add the multifunctional cationizing ligand to the titanium source solution and stir at room temperature for 0.5–2 h to form a modified precursor; (3) Add water or alkaline solution to the modified precursor to make the molar ratio of water to titanium 2:1–10:1 and carry out hydrolysis-polymerization reaction; (4) After the reaction is completed, the mixture is aged and dried to obtain the surface charge enhanced titanium-based coagulant.

8. The application of a surface charge-enhanced titanium-based coagulant as described in any one of claims 1-6 in the treatment of algae-containing water bodies with a pH value higher than 8.

9. The application of a surface charge-enhanced titanium-based coagulant as described in any one of claims 1-6 in the purification of low-temperature water bodies with a water temperature ≤5℃ and turbidity ≤10NTU.

10. The application of a surface charge-enhanced titanium-based coagulant as described in any one of claims 1-6 as an anti-biofouling pretreatment agent before membrane filtration processes.

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