Biomass-inorganic-organic ternary composite flocculant as well as preparation method and application thereof

Abstract

The invention discloses a biomass-inorganic-organic ternary composite flocculant and a preparation method and application thereof, and belongs to the field of coking wastewater treatment.The preparation method comprises the steps that chitosan serves as a substrate material, glutaraldehyde serves as a cross-linking agent, and polyferric sulfate (PFS) and chitosan are subjected to chemical cross-linking to generate an intermediate product PFS and chitosan composite particles; then potassium persulfate is used as an initiator, graft copolymerization of acrylamide and methacryloyloxyethyl trimethyl ammonium chloride is initiated through hydroxyl on the surface of PFS-chitosan, a cationic branched chain is introduced, and a final product is obtained. Through multi-component cooperation and structural design, the defects that a traditional flocculating agent is not thorough in demulsification, large in sludge amount, unstable in floc combination and the like in coking wastewater treatment are overcome, and the flocculating agent is particularly suitable for treating oil pollutants in coking wastewater.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of coking wastewater treatment, and particularly relates to a biomass-inorganic-organic ternary composite flocculant as well as a preparation method and application thereof. BACKGROUND

[0002] With the continuous development of the coking industry in China, the treatment of coking wastewater has gradually become an important challenge for the environmental protection industry. Coking wastewater is mainly wastewater generated in the high-temperature coking process of coal. This type of wastewater is complex in composition and contains a large amount of harmful substances such as phenol, cyanide, ammonia nitrogen, oil, suspended solids, etc. In order to ensure the effective performance of subsequent biochemical and advanced treatment, it is usually necessary to pretreat the coking wastewater, mainly to remove oil from the wastewater by demulsification. The oil pollutants in the coking wastewater are mainly tar, emulsified oil and dissolved oil, and the concentration can reach 50-1000 mg / L.

[0003] At present, the treatment methods for oil pollutants mainly include the comprehensive application of physical, chemical and biological treatment technologies. Common treatment technologies include filtration, adsorption, membrane separation technology, chemical oxidation, biological degradation and advanced oxidation method, etc. However, these common methods also have their limitations. For example, the filtration method has poor effect on dissolved pollutants (such as additives and emulsified oil); the membrane treatment technology has good effect, but has high technical cost, is easy to block and needs frequent maintenance; the chemical oxidation method may introduce secondary pollution (such as chloride ions); the biological degradation method may inhibit the microbial activity of high-concentration coking wastewater and needs pretreatment; the advanced oxidation method has high cost of catalyst and complex reaction condition control. Therefore, it is an important research direction for the treatment of coking wastewater with complex composition to develop an oil removal technology with low cost and simple operation.

[0004] Currently, the development and use of flocculants is an important direction in the field of coking wastewater oil pollutant treatment. Flocculants are chemical agents that can promote the aggregation of small suspended particles or colloidal substances in water to form larger flocculation (alum flowers), thereby facilitating sedimentation or filtration separation. In coking wastewater treatment, flocculants can be used for demulsification, oil removal, and removal of suspended solids. Adding appropriate flocculants to coking wastewater can effectively remove suspended particles, oil substances, and certain metal ions in coking wastewater, thereby reducing the color, turbidity, and pollution load of the wastewater. The mechanism of action of flocculants includes charge neutralization, adsorption bridging, and net capture sweeping, etc. Charge neutralization refers to the fact that oil droplets and particles in wastewater are usually negatively charged (such as emulsions), and flocculants (such as cationic) can reduce the repulsive force between oil droplets through electrostatic neutralization, causing them to aggregate. Adsorption bridging refers to the fact that long-chain molecules of high molecular weight flocculants (such as PAM) can adsorb multiple oil droplets or particles, forming a "bridge" structure, increasing the volume of the flocculation, and accelerating the sedimentation. Net capture sweeping refers to the fact that the hydroxide precipitate generated by the hydrolysis of metal salt flocculants (such as PAC) can wrap oil droplets, forming large flocculation, which is easy to separate. Compared with other treatment technologies, flocculants have lower cost, simple operation, strong adaptability, and are suitable for large-scale industrial wastewater treatment. At the same time, flocculants are also easy to use with other processes (such as air flotation, filtration, etc.), which can improve the treatment efficiency.

[0005] Currently, the commonly used flocculant in coking wastewater treatment is PAC, which is also widely used in other industrial wastewater treatment processes. PAC has excellent flocculation performance and can quickly remove suspended particles in water, break emulsion and remove colloidal substances and some metal ions. In addition, PAC has low cost and is suitable for a variety of water quality, so it has been widely used. However, PAC also has its shortcomings, that is, it is easily affected by pH (the best pH is 6-8), and the treatment effect of dissolved organic matter is poor. In addition, excessive PAC will introduce excessive aluminum ions into the water body, causing secondary pollution problems. In summary, PAC as a flocculant has significant advantages, but the treatment effect still needs to be further improved.

[0006] Although PAC has a wide range of applications, the high-molecular flocculants such as polyacrylamide are generally better in effect among flocculants. However, the hydrophilicity of general polyacrylamide is relatively high, and the adsorption effect on oil substances is poor. At present, the hydrophobicity of polyacrylamide is enhanced by introducing hydrophobic monomers. For example, both the patent CN107501443A and the patent CN103319652A introduce hydrophobic functional groups by reacting acrylamide with hydrophobic lipophilic monomers, thereby improving the adsorption capacity of polyacrylamide on oil substances. However, when dealing with coking wastewater which is a complex oil-containing wastewater, the single modified high-molecular flocculant is easily interfered by high salt and heavy metals in the coking wastewater, and the effect is reduced. In addition, the potential of these flocculants is relatively single, and the charge neutralization effect on small particles of oil droplets with different potentials is not stable. SUMMARY

[0007] The present application provides a biomass-inorganic-organic ternary composite flocculant and a preparation method and application thereof. Through multi-component cooperation and structure design, the prepared flocculant has obvious advantages in treating coking wastewater, can effectively improve the treatment efficiency, and reduce secondary pollution.

[0008] To achieve the above object, the following technical scheme is adopted in the present application. A biomass-inorganic-organic ternary composite flocculant, which provides a rigid core with PFS@chitosan, and a network structure on the surface with PAM-CO-DMC long chain. The composite flocculant is PFS and chitosan chemically cross-linked to generate PFS@chitosan composite particles. Acrylamide and methacryloyloxyethyl trimethyl ammonium chloride are grafted and copolymerized with the composite particles through the hydroxyl groups on the surface of the composite particles to introduce cationic branches, thereby obtaining the ternary composite flocculant.

[0009] A preparation method of a biomass-inorganic-organic ternary composite flocculant, comprising the following steps: S1: dissolving chitosan in an acetic acid solution to prepare a chitosan solution; S2: adding PFS (polyferric sulfate) stock solution to the chitosan solution, stirring at 40℃ for 1h, then adding crosslinking agent pentanediol, adjusting the pH to 5.0, and reacting at 50℃ for 2h, and then centrifuging, washing with water and drying to obtain PFS@chitosan powder; S3: dissolving acrylamide (AM) and methacryloyloxyethyl trimethyl ammonium chloride (DMC) in deionized water to obtain a monomer solution, dispersing the PFS@chitosan powder in the monomer solution at a ratio of 0.5g:50mL, removing oxygen after purging with nitrogen, adding potassium persulfate solution as an initiator, reacting at 60℃ for 4h, then adding hydroquinone to terminate the reaction, and then dialyzing and drying to obtain the ternary composite flocculant.

[0010] In the steps described above, the acetic acid solution is a 1% (v / v) acetic acid solution, and the Fe in the PFS stock solution... 3+ The concentration was 1.2 mol / L, and the mass ratio of PFS stock solution to chitosan was 1:1.

[0011] The potassium persulfate concentration is 1 wt%; the molar ratio of AM to DMC is (4~5):(1~2), preferably 4:1.

[0012] The biomass-inorganic-organic ternary composite flocculant prepared above is suitable for treating coking wastewater with complex components.

[0013] Beneficial effects: This invention provides a biomass-inorganic-organic ternary composite flocculant, its preparation method, and its application, which have the following advantages compared with the prior art: (1) Highly efficient demulsification and flocculation capabilities: This invention utilizes multi-component synergy (inorganic demulsification, bioadsorption, organic bridging) and structural design (core-shell targeting) to effectively demulsify and aggregate oil pollutants in coking wastewater. The cross-linked PFS on the chitosan surface utilizes Fe... 3+ Hydrolysis produces polynuclear hydroxyl complexes (such as [Fe3(OH)4)). 5+ ), with a charge density higher than Al 3+ (PAC) has a stronger demulsification ability; the chitosan center passes through -NH3 + It adsorbs small oil droplets through hydrophobic interactions; the PAM-CO-DMC side chains enhance charge neutralization and aggregate flocculent oil droplets through quaternary ammonium groups and bridging effects.

[0014] (2) High floc density: The composite flocculant of this invention uses PFS@chitosan as a rigid core and PAM-CO-DMC long chains to form a network structure. After rapid demulsification of PFS, chitosan and PAM-CO-DMC are adsorbed in succession, avoiding the problem of "over-demulsification and re-emulsification" of traditional flocculants, and forming dense flocs after capturing oil droplets. In addition, the hydrophobic groups of chitosan adsorb oil droplets, and the hydrophilic chains of PAM promote the separation of the aqueous phase, achieving a hydrophobic-hydrophilic balance. For the above reasons, the sludge produced by the flocculant is less likely to have the problems of loose and high water content of traditional flocculant sludge.

[0015] (3) Strong resistance to interference: Coking wastewater contains many interfering factors that affect the flocculant's effectiveness, such as high COD, high-salt surfactants, phenolic polycyclic aromatic hydrocarbons, and heavy metals. These interfering factors can adversely affect the treatment effect of traditional flocculants, usually requiring additional operations or the addition of extra reagents as countermeasures, thus increasing treatment costs. In this invention, the flocculant, under high-salt conditions, Fe... 3+ The charge neutralization ability remains stable (conventional Al). 3+The cationic branched quaternary ammonium group is positively charged in a high salt environment, reducing the interference of salt effect, enhancing the charge stability of the flocculant, and being more resistant to salt interference. In addition, chitosan has a spectrum of adsorption capacity, and hydrophobic adsorption has good affinity for oil and polycyclic aromatic hydrocarbons. π-π stacking makes it easy to adsorb aromatic compounds such as phenol. For heavy metal ions, the -NH2 and -OH groups on the surface of chitosan can form stable complexes with Hg 2+ , Cu 2+ , Cd 2+ , etc. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 is a reaction mechanism diagram of the preparation method of the present application; Figure 2 is a comparison diagram of COD and oil pollutant removal effects of examples 1-3 of the present application and PAC. DETAILED DESCRIPTION

[0017] The present application will be described in detail below in conjunction with the drawings and specific examples: Example 1

[0018] A biomass-inorganic-organic ternary composite oil removal flocculant preparation method comprises the following steps: In mole fraction, 4 parts of AM are dissolved in 50 ml of deionized water, then 1 part of DMC is added, stirred at 400 rpm at 60°C for 1-2 hours to obtain a monomer solution; 1 g of chitosan is dissolved in 100 mL of 1% acetic acid solution, and after stirring to transparency, 10 mL of PFS stock solution (Fe 3+ concentration 1.2 g / mol) is added dropwise to the chitosan solution (mass ratio 1:1), stirred at 40°C for 1 h, 0.5 mL of 25% glutaraldehyde is added, the pH is adjusted to 5.0 with acetic acid, and the reaction is carried out at 50°C for 2 h. Centrifugal water washing and drying give PFS@chitosan powder; 0.5 g of PFS@chitosan powder is dispersed in the monomer solution, deoxygenated by nitrogen for 15 min, 1 wt% of APS solution is added dropwise, and the reaction is carried out at 60°C for 4 h; then 0.05 g of hydroquinone is added, deionized water dialysis is carried out for 48 h, and low-temperature drying gives a new type of ternary composite flocculant. Example 2

[0019] A biomass-inorganic-organic ternary composite oil removal flocculant preparation method comprises the following steps: In mole fraction, 4 parts of AM are dissolved in 50 ml of deionized water, then 1 part of DMC is added, stirred at 400 rpm at 60°C for 1-2 hours to obtain a monomer solution; 1 g of chitosan is dissolved in 100 mL of 1% acetic acid solution, and after stirring to transparency, 10 mL of PFS stock solution (Fe3+ A concentration of 1.2 g / mol was added dropwise to a chitosan solution (mass ratio 1:1), stirred at 40℃ for 1 h, 0.5 mL of 25% glutaraldehyde was added, the pH was adjusted to 5.0 with acetic acid, and the reaction was carried out at 50℃ for 2 h. After centrifugation, washing with water and drying, PFS@chitosan powder was obtained. 0.5 g of PFS@chitosan powder was dispersed in a monomer solution, nitrogen gas was purged for 15 min to remove oxygen, 1 wt% APS solution was added dropwise, and the reaction was carried out at 60℃ for 4 h. Subsequently, 0.05 g of hydroquinone was added, and the mixture was dialyzed with deionized water for 48 h and dried at low temperature to obtain a novel ternary composite flocculant. Example 3

[0020] A method for preparing a biomass-inorganic-organic ternary composite oil-removing flocculant includes the following steps: In molar amounts, dissolve 4 parts of AM in 50 ml of deionized water, then add 2 parts of DMC, and stir at 400 rpm for 1-2 hours at 60°C to obtain a monomer solution; dissolve 1 g of chitosan in 100 mL of 1% acetic acid solution, stir until transparent, and then take 10 mL of PFS stock solution (Fe 3+ A concentration of 1.2 g / mol was added dropwise to a chitosan solution (mass ratio 1:1), stirred at 40℃ for 1 h, 0.5 mL of 25% glutaraldehyde was added, the pH was adjusted to 5.0 with acetic acid, and the reaction was carried out at 50℃ for 2 h. After centrifugation, washing with water and drying, PFS@chitosan powder was obtained. 0.5 g of PFS@chitosan powder was dispersed in a monomer solution, nitrogen gas was purged for 15 min to remove oxygen, 1 wt% APS solution was added dropwise, and the reaction was carried out at 60℃ for 4 h. Then, 0.05 g of hydroquinone was added to terminate the reaction, dialyzed with deionized water for 48 h, and dried at low temperature to obtain a novel ternary composite flocculant.

[0021] The composite flocculant prepared in the above embodiments, along with traditional PAC and PFS, were used for coking wastewater treatment. The mass ratio of the raw agent solution to the raw sludge was 50,000 ppm. The initial COD of the coking wastewater was 5561 mg / L, and the initial oil pollutant concentration was 654 mg / L.

[0022] Taking Example 1 as an example, under optimal reaction conditions, the effluent COD and oil pollutant concentrations were 1946 and 111 mg / L, respectively. The flocculation time was 45 min, the dosage was 400 mg / L, and the pH was 7.5. Therefore, Examples 1, 2, and 3 were compared with traditional PAC and PFS under optimal operating conditions. The comparison results are shown in Table 1.

[0023] Table 1. Comparison of results for coking wastewater treatment in Examples 1, 2, and 3, and with traditional PAC and PFS (unit: mg / L) Sample name Effluent COD Effluent oil Example 1 1780 111 Example 2 2114 132 Example 3 1894 124 PAC 2891 197 PFS 2558 164 It can be found from Table 1 that the removal rates of each index of the prepared new ternary composite flocculant, i.e., Examples 1, 2 and 3, and the conventional PAC and PFS flocculants are as shown in Table 2 and Table 3. Figure 2

[0024] Table 2 Removal rates of each index of Examples 1, 2 and 3 and the conventional PAC and PFS flocculants Sample name COD removal Oil removal Example 1 67.99% 83.03% Example 2 61.99% 79.82% Example 3 65.94% 81.04% PAC 48.01% 69.88% PFS 54.00% 74.92% It can be found from the comparison results in Table 2 that the treatment effect of the new composite flocculants prepared in Examples 1, 2 and 3 on the coking wastewater has obvious advantages compared with the conventional PAC and PFS, because of the multi-component synergistic effect of the present application, the PFS as the core performs strong demulsification to solve the problem of difficult-to-treat emulsified oil, the chitosan performs broad-spectrum adsorption to capture and enrich the oil droplets and other organic matters after demulsification, and the PAM-CO-DMC as the peripheral branched chain performs adsorption bridging to construct the enriched microparticles into stable and easily-separated large flocs.

[0025] Meanwhile, the flocculant prepared in Example 1 has better effect than that in Examples 2 and 3, for example, when the proportion of DMC is too low in Example 2, the cationic degree of the copolymer branched chain connected is too low, which causes insufficient electric neutralization capacity and poor demulsification effect, and insufficient electric charge also causes the decline of anti-interference performance. When the proportion of DMC is too high in Example 3, the cationic degree of the copolymer branched chain connected is too high, the high electric charge can make the electric neutralization capacity strong and the adsorption speed fast, but the high positive electric charge on the branched chain repels each other, which causes the polymer molecular chain to stretch in water, the bridging and netting capacity to decline, and the cost to increase because the price of DMC is higher than that of AM.

[0026] The above are only preferred embodiments of the present application, which will help the person skilled in the art to further understand the present application, but do not limit the present application in any form. It should be noted that for those skilled in the art, several modifications and improvements made without departing from the concept of the present application all belong to the protection of the present application.​

Claims

1. A method for preparing a biomass-inorganic-organic ternary composite flocculant, characterized in that, Includes the following steps: Prepare chitosan solution; PFS stock solution was added to the chitosan solution, mixed evenly, and then a crosslinking agent was added to react and obtain PFS@chitosan powder. Acrylamide and methacryloyloxyethyltrimethylammonium chloride were dissolved in deionized water to obtain a monomer solution. PFS@chitosan powder was dispersed in the monomer solution, and after deoxygenation, an initiator was added to react and obtain a ternary composite flocculant.

2. The preparation method of the biomass-inorganic-organic ternary composite flocculant according to claim 1, characterized in that, The chitosan solution is prepared by dissolving chitosan in acetic acid solution.

3. The preparation method of the biomass-inorganic-organic ternary composite flocculant according to claim 1, characterized in that, Fe in PFS stock solution 3+ The concentration is 1.2 mol / L.

4. The preparation method of the biomass-inorganic-organic ternary composite flocculant according to claim 1 or 3, characterized in that, The mass ratio of the PFS stock solution to chitosan is (1~2):(1~2).

5. The preparation method of the biomass-inorganic-organic ternary composite flocculant according to claim 1, characterized in that, After adding the crosslinking agent, the pH was adjusted to 5.0, the temperature was increased to 50℃ and the reaction was carried out for 2 hours. After centrifugation, washing with water and drying, PFS@chitosan powder was obtained.

6. The preparation method of the biomass-inorganic-organic ternary composite flocculant according to claim 1, characterized in that, After adding the initiator, the reaction was carried out at a constant temperature of 60°C for 4 hours. Hydroquinone was added to terminate the reaction, and the mixture was then dialyzed and dried to obtain the ternary composite flocculant.

7. The preparation method of the biomass-inorganic-organic ternary composite flocculant according to claim 1 or 6, characterized in that, The molar ratio of AM to DMC is (4~5):(1~2).

8. The biomass-inorganic-organic ternary composite flocculant prepared by the method according to any one of claims 1-7, characterized in that, It uses PFS@chitosan as a rigid core and has a network structure formed by long chains of PAM-CO-DMC on the surface.

9. The biomass-inorganic-organic ternary composite flocculant according to claim 8, characterized in that, In the composite flocculant, PFS is chemically cross-linked with chitosan to form PFS@chitosan composite particles, and acrylamide and methacryloyloxyethyltrimethylammonium chloride are grafted and copolymerized with the composite particles through the hydroxyl groups on the surface of the composite particles, introducing cationic side chains.

10. The application of the biomass-inorganic-organic ternary composite flocculant according to any one of claims 8-9, characterized in that, The composite flocculant is used to treat coking wastewater. During application, the PFS cross-linked on the chitosan surface is activated by Fe... 3+ Hydrolysis produces polynuclear hydroxy complexes, with the chitosan center via -NH3 + It adsorbs small oil droplets through hydrophobic interactions; the PAM-CO-DMC side chains enhance charge neutralization and aggregate flocculent oil droplets through quaternary ammonium groups and bridging effects.

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