Sepiolite composite material, preparation method and application of sepiolite composite material in tanning soaking waste liquid

Abstract

The invention belongs to the technical field of water treatment agents, and discloses a sepiolite composite material, a preparation method and application of the sepiolite composite material in tanning soaking waste liquid. The sepiolite composite material comprises: a sepiolite carrier; the quaternary ammonium salt molecular layer is anchored on the surface of the sepiolite carrier in a gradient manner; the quaternary ammonium salt molecular layer comprises dodecyl trimethyl ammonium chloride and hexadecyl trimethyl ammonium chloride; the beta-cyclodextrin molecules are combined on the surface of the quaternary ammonium salt molecular layer through intermolecular force. According to the invention, a bifunctional interface with both a broad-spectrum hydrophobic adsorption domain (quaternary ammonium salt layer) and a specific molecular recognition domain (cyclodextrin layer) is successfully constructed on the surface of sepiolite. According to the design, the defect that a single modified material is limited in function is overcome, the synergistic effect of graded capturing and cooperative locking on grease pollutants is achieved, and the comprehensive adsorption performance and selectivity of the composite material in a complex system are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of water treatment agents, in particular to a sepiolite composite material, a preparation method and application thereof in tannery soaking waste liquid. BACKGROUND

[0002] With the increasingly stringent environmental protection requirements and the deepening of the resource concept, industrial wastewater treatment has developed from simple pollutant removal to component recovery and recycling. Tannery soaking waste liquid is complex in composition, containing a large amount of oil, surfactant, protein hydrolysate and inorganic salt, etc. Among them, oil is the key component causing subsequent treatment load and pollution, while surfactant and protein hydrolysate are beneficial components required in the soaking process and have recycling value. Therefore, developing a material capable of selectively separating oil and retaining beneficial components is a core challenge to realize the resource recycling of the waste liquid.

[0003] As a natural fibrous chain-layered silicate mineral, sepiolite is widely used as an adsorbent carrier due to its large specific surface area, abundant surface silicon hydroxyl groups and good chemical stability. To improve its affinity for organic pollutants, the existing technology usually uses cationic surfactants (such as hexadecyl trimethyl ammonium chloride, CTAC) for organic modification. The modified sepiolite can effectively adsorb oil, but its hydrophobic surface is uniform, lacks selectivity for oil molecules of different chain lengths and polarities, and will indiscriminately adsorb surfactants in the demulsified wastewater, resulting in loss of beneficial components and failure to achieve selective separation.

[0004] Cyclodextrin can form inclusion compounds with molecules of specific size due to its unique hydrophobic cavity structure, and is often used for molecular recognition and selective adsorption. However, direct loading of cyclodextrin on sepiolite usually has problems such as weak binding force, easy falling off and low utilization rate of inclusion sites. Although existing technologies use cross-linking agents for fixation, the cross-linking process may block the cyclodextrin cavity, affecting its inclusion ability and introducing secondary pollution risk.

[0005] In view of this, the present application is proposed. SUMMARY

[0006] The present application aims to at least solve one of the above technical problems, and provides a sepiolite composite material, a preparation method and application thereof in tannery soaking waste liquid.

[0007] To achieve the above-mentioned purpose, the first technical solution adopted by the present application is: A sepiolite composite material, comprising: a sepiolite carrier; a gradient-anchored quaternary ammonium salt molecular layer on the surface of the sepiolite carrier, the quaternary ammonium salt molecular layer comprising dodecyl trimethyl ammonium chloride and hexadecyl trimethyl ammonium chloride; Beta-cyclodextrin molecules are combined on the surface of the quaternary ammonium salt molecular layer by intermolecular forces.

[0008] Preferably, the dodecyl trimethyl ammonium chloride and the hexadecyl trimethyl ammonium chloride form a gradient distribution from the orifice to the inside of the pore in the pore channel of the sepiolite carrier.

[0009] Preferably, the mass percentage concentration of the hexadecyl trimethyl ammonium chloride is 0.5-0.8wt%, and the mass percentage concentration of the dodecyl trimethyl ammonium chloride is 2.0-2.2wt%.

[0010] Preferably, the mass ratio of the sepiolite to the quaternary ammonium salt is 10:1-15:1, and the mass ratio of the beta-cyclodextrin to the sepiolite is 1:8-1:12.

[0011] Preferably, the surface of the sepiolite composite material is further coated with a crosslinked polymer shell layer.

[0012] The second technical solution adopted by the present application is: The preparation method of the sepiolite composite material comprises the following steps: acidizing the sepiolite with a hydrochloric acid solution, washing and drying to obtain acidized sepiolite; The acidized sepiolite is first reacted with a hexadecyl trimethyl ammonium chloride solution at a first temperature to obtain a suspension; then dodecyl trimethyl ammonium chloride solution is added to the suspension, and a second reaction is carried out at a second temperature; after the reaction is completed, solid-liquid separation and drying are carried out to obtain gradient-modified sepiolite; The gradient-modified sepiolite is reacted with a beta-cyclodextrin solution for a third reaction, so that the cyclodextrin is combined on the surface thereof by intermolecular forces; solid-liquid separation and drying are carried out to obtain the sepiolite composite material.

[0013] Preferably, the first temperature is room temperature, and the second temperature is 60-65℃.

[0014] The third technical solution adopted by the present application is: The preparation method of the sepiolite composite material coated with a crosslinked polymer shell layer comprises the following steps: The sepiolite composite material is prepared by the method of the second technical solution; The sepiolite composite material, styrene, a crosslinking agent and an emulsifier are subjected to high-speed emulsification in an aqueous phase to form an emulsion; An initiator is added to the emulsion to carry out emulsion polymerization reaction, so as to form a crosslinked polymer shell layer on the surface of the sepiolite composite material; The product after the reaction is subjected to solid-liquid separation, washing and drying to obtain the sepiolite composite material coated with a crosslinked polymer shell layer.

[0015] Preferably, the crosslinking agent is N, N'-methylene bisacrylamide; and the emulsifier is a complex system of sodium dodecyl sulfate and polyvinyl alcohol.

[0016] The fourth technical solution adopted by the present application is: The application of sepiolite composite in selective separation of grease components in tannery immersion waste liquid, the sepiolite composite preferentially adsorbs grease, while retaining surfactants and protein hydrolysates in the waste liquid.

[0017] Preferably, the grease includes at least one of free fatty acids, monoglycerides, diglycerides and triglycerides.

[0018] The fifth technical solution adopted by the present application is: A resource recycling method of tannery immersion waste liquid, comprising the following steps: The sepiolite composite is added to the tannery immersion waste liquid, stirred and adsorbed to selectively remove grease; Solid-liquid separation to obtain regenerated sepiolite composite and purified waste liquid from which the grease is desorbed; The purified waste liquid is reused in the tannery immersion process.

[0019] Preferably, after obtaining the regenerated sepiolite composite and the purified waste liquid from which the grease is desorbed, the method further comprises a regeneration step of washing and drying the regenerated sepiolite composite, and the regenerated sepiolite composite is reused in the step of selectively removing grease.

[0020] Compared with the prior art, the present application has the following beneficial effects: 1. The present application successfully constructs a bifunctional interface on the surface of sepiolite, which has both a "broad-spectrum hydrophobic adsorption domain" (quaternary ammonium salt layer) and a "specific molecular recognition domain" (cyclodextrin layer). This design overcomes the limitations of single modified materials, realizes the synergistic effect of graded capture and locking of grease pollutants, and significantly improves the comprehensive adsorption performance and selectivity of the composite material in complex systems.

[0021] 2. The sepiolite composite provided by the present application can realize accurate differentiation of different components based on size matching, hydrophobicity difference and chemical affinity. The gradient hydrophobic microenvironment can effectively capture grease molecules of different chain lengths; and the cavity inclusion effect of cyclodextrin is specific to free fatty acids and small molecule glycerides. More importantly, it can effectively exclude surfactant micelles, protein hydrolysates and inorganic salt ions that are too large in size or hydrophilic, thereby efficiently removing grease while retaining beneficial components (surfactant retention rate > 90%) in the waste liquid that have reuse value, laying a foundation for direct reuse of the waste liquid.

[0022] 3. In the sepiolite composite provided by the present application, cyclodextrin is directly fixed to the interface modified by quaternary ammonium salt through intermolecular forces (such as hydrogen bonds), avoiding the use of chemical cross-linking agents, not only maintaining the integrity of the cyclodextrin cavity and high inclusion efficiency, but also ensuring the stability of the interface layer. The composite is easy to regenerate and can be reused after simple washing. The adsorption capacity attenuation rate is less than 7% after 10 times of continuous use, and the operation cost is low and environmentally friendly.

[0023] 4. The present application not only provides a high-performance composite material, but also creates a new process for resourceful treatment of tannery immersion waste liquid. Through the selective separation effect of the material, the purified waste liquid can be used for the immersion process, and the recovered oil can also be resourcefully utilized, truly realizing "waste into treasure", solving the problems of resource waste and high cost in traditional treatment methods, and having significant economic and environmental benefits. DETAILED DESCRIPTION

[0024] The technical solutions in the embodiments of the present application will be described below in conjunction with examples and comparative examples of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all the embodiments. Based on the examples in the present application, all other examples obtained by those skilled in the art without creative labor are within the scope of protection of the present application.

[0025] The first embodiment of the present application provides a sepiolite composite, comprising: a sepiolite carrier; a quaternary ammonium salt molecular layer gradient anchored on the surface of the sepiolite carrier, the quaternary ammonium salt molecular layer comprising dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride; β-cyclodextrin molecules combined on the surface of the quaternary ammonium salt molecular layer through intermolecular forces.

[0026] The sepiolite composite provided by the embodiment of the present application takes sepiolite fibrous chain layered silicate nanofiber as a core carrier, and rich silicon hydroxyl and aluminum hydroxyl on the surface of the sepiolite provide active sites for subsequent functionalization. By using the differences in the molecular size, diffusion rate and hydrophobicity of cetyltrimethylammonium chloride (CTAC, long chain) and dodecyltrimethylammonium chloride (DTAC, short chain), a gradient modification is performed through a step-by-step reaction strategy, and an ordered gradient distribution is formed in the sepiolite channel: the DTAC molecule is small and diffuses fast, and thus preferentially occupies the pore opening region; the CTAC molecule is large and has strong hydrophobicity, and thus is more likely to migrate to the deep channel, and finally forms a gradient microenvironment of "pore opening short chain hydrophobic - channel long chain hydrophobic". The short chain region (dominated by DTAC): it is rich in and preferentially adsorbs oil and fat molecules with relatively strong polarity and short molecular chains (such as short-chain fatty acids); the long chain region (dominated by CTAC): it strongly captures non-polar and long-chain oil and fat molecules (such as triglycerides) through strong hydrophobic interaction. This structure enables oil and fat molecules of different chain lengths and polarities to find the most suitable binding sites, thereby greatly improving the adsorption capacity and rate and realizing the "graded capture" of mixed oil and fat.

[0027] The β-cyclodextrin (β-CD) forms a dense hydrogen bond network with the remaining silicon hydroxyl sites on the sepiolite surface which has been modified into a quaternary ammonium salt through the hydroxyl groups on its outer rim, and is firmly "locked" on the interface. The hydrophobic cavity (inner diameter of about 0.6-0.8 nm) of the β-CD can specifically recognize and include matching hydrophobic molecules, and it can accurately include free fatty acids (FFA) and small molecule hydrophobic fragments such as monoglycerides (MAG) and diglycerides (DAG) produced after oil and fat hydrolysis to form stable inclusion compounds, thereby realizing "precise locking" and preventing desorption.

[0028] In general, the quaternary ammonium salt is gradient-anchored on the sepiolite surface to form a hydrophobic-hydrophilic microzone, preferentially adsorbs oil and fat, and at the same time repels proteins and water-soluble surfactants; the β-cyclodextrin is combined through intermolecular forces, the cavity structure is complete, and it can include oil and fat molecules; the β-cyclodextrin can dynamically adjust the conformation to adapt to different oil and fat molecules; at the same time, the intermolecular force combination is reversible, and can dissociate and recombine under specific conditions, which is beneficial to the adsorption-desorption cycle process. If the β-cyclodextrin is fixed on the sepiolite through a covalent bond, the cavity may be partially blocked or the orientation is limited, resulting in a decrease in the inclusion efficiency, and the chemical bond combination is basically irreversible and difficult to break once formed.

[0029] It should be noted that in the above gradient modification stage, CTAC and DTAC, which are cationic surfactants, are used in sequence for modification. This is because sepiolite has a natural pore structure (pore size of about 0.36 x 1.06 nm) and a negatively charged surface, which is suitable for cationic quaternary ammonium salts (such as CTAC and DTAC) to gradually enter the pores through ion exchange + hydrophobic interaction, forming a gradient distribution from the pore mouth to the pore. Anionic surfactants, such as sodium dodecyl sulfonate (SDS), etc., are difficult to enter the pores due to charge repulsion, tend to accumulate at the pore mouth, block the pores, destroy the gradient structure, and exhibit a significant decrease in specific surface area, pore volume, adsorption rate, equilibrium adsorption capacity, and lack of selectivity for oil removal.

[0030] Due to the special fibrous structure and microporous channel of sepiolite, sufficient quaternary ammonium salt molecules are needed to fill the pores and form a gradient distribution. Long-chain quaternary ammonium salts occupy the pore mouth first, and short-chain quaternary ammonium salts enter the pore later, forming a gradient from the outside to the inside. At the same time, CTAC has a longer carbon chain and greater steric hindrance than DTAC. Therefore, the amount and concentration of CTAC and DTAC should be appropriate to form a gradient, and the concentration of CTAC should be lower.

[0031] As some examples, the mass percentage concentration of cetyltrimethylammonium chloride is 0.5-0.8 wt%, and the mass percentage concentration of dodecyltrimethylammonium chloride is 2.0-2.2 wt%; the mass ratio of sepiolite to quaternary ammonium salt is 10:1-15:1; and the mass ratio of cetyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2:1-3:1.

[0032] For the amount and concentration of β-cyclodextrin, those skilled in the art can adjust based on the specific surface area and pore volume of sepiolite. The concentration of β-CD is generally controlled in the range of 0.5-2.0 g / L. A too low concentration will result in insufficient adsorption capacity for oil and decreased selectivity, while a too high concentration will cause β-CD to easily aggregate, reducing the actual available active sites. In some preferred embodiments, the mass ratio of β-cyclodextrin to sepiolite is 1:8-1:12.

[0033] In some preferred embodiments, the sepiolite composite material surface is further coated with a cross-linked polymer shell layer, the polymer shell layer has a polystyrene main chain skeleton, is cross-linked by N,N'-methylene bisacrylamide (MBA) to form a three-dimensional network structure, and β-cyclodextrin is distributed in the network as a functional side chain or grafting unit to provide selective adsorption sites. The cross-linked polymer shell is used to enhance the stability and service life, and finally forms a core-shell composite material with sepiolite as the core and polymer as the shell. The cross-linked polymer shell wraps the functionalized sepiolite core, preventing the internal quaternary ammonium salt and cyclodextrin from falling off and flowing away during mechanical stirring, hydraulic flushing or regeneration. The mechanical strength and chemical stability of the material are greatly improved, and it can withstand multiple adsorption-desorption cycles, which is the key to whether the material can be applied in practical engineering.

[0034] The second embodiment of the present application provides a preparation method of sepiolite composite material, comprising the following steps: acidizing sepiolite with a hydrochloric acid solution, washing and drying to obtain acidized sepiolite; The acidized sepiolite is first reacted with a cetyltrimethylammonium chloride solution at a first temperature to obtain a suspension; then a dodecyltrimethylammonium chloride solution is added to the suspension, and a second reaction is carried out at a second temperature. After the reaction is completed, solid-liquid separation and drying are carried out to obtain gradient-modified sepiolite; The gradient-modified sepiolite is reacted with a β-cyclodextrin solution for a third reaction, so that the cyclodextrin is combined on the surface thereof through intermolecular forces. After solid-liquid separation and drying, the sepiolite composite material is obtained.

[0035] In this embodiment, the specific surface area and pore structure of sepiolite are increased by acidizing pretreatment, and then CTAC and DTAC are used for gradient anchoring modification: DTAC molecules first occupy the pore openings due to their small size and fast diffusion, and CTAC molecules preferentially migrate to the deep part of the pore due to their large size and stronger hydrophobic interaction; by means of the size difference of the molecules, diffusion limitation and the negative potential gradient of the inner surface of the pore, an ordered gradient distribution of "short chains at the pore opening-long chains in the pore" is formed.

[0036] The specific preparation method of the acidized sepiolite is a common technical means in the art and does not need special limitation. In order to fully expose the buried active sites, ultrasonic treatment can also be carried out after acidizing.

[0037] In some preferred embodiments, the first temperature is room temperature, and the second temperature is 60-65℃.

[0038] As a specific embodiment, the preparation method of the sepiolite composite material is as follows: The sepiolite is acidized with hydrochloric acid to obtain pretreated sepiolite, the molar concentration of hydrochloric acid is 2-3 mol / L, the reaction temperature is 70-80℃, and the reaction time is 4-5 h; The pretreated sepiolite is dispersed in a hexadecyl trimethyl ammonium chloride solution and magnetically stirred at room temperature at a rotation speed of 200-300 rpm for 2-3 h to obtain a suspension; A dodecyl trimethyl ammonium chloride solution is added to the suspension, the temperature is raised to 60-65°C and stirring is performed for 6-7 h to obtain a mixture, the liquid is retained after centrifugation, and the gradient modified sepiolite (G-Sep) is obtained after washing, vacuum drying, etc. The G-Sep is dispersed in water, ultrasonic treatment is performed, and then mixed with a β-cyclodextrin solution, stirring is performed at 50-60°C for 4-5 h to obtain an inclusion compound, the inclusion compound is separated by centrifugation, and the sepiolite composite CD-G-Sep is obtained by freeze-drying.

[0039] The third embodiment of the present application provides a preparation method of a sepiolite composite material whose surface is further coated with a cross-linked polymer shell layer, comprising the following steps: The sepiolite composite material is prepared by the method of the second embodiment; The sepiolite composite material, styrene, a cross-linking agent and an emulsifier are subjected to high-speed emulsification in an aqueous phase to form an emulsion; An initiator is added to the emulsion, and emulsion polymerization is performed to form a cross-linked polymer shell layer on the surface of the sepiolite composite material; The product after the reaction is subjected to solid-liquid separation, washing and drying to obtain a sepiolite composite material coated with a cross-linked polymer shell layer.

[0040] In some preferred embodiments, the mass ratio of the sepiolite composite material to styrene is 1:1-1:3, the mass percentage of the cross-linking agent relative to styrene is 2-5 wt%, and the mass percentage of the emulsifier relative to styrene is 1-3 wt%.

[0041] In some preferred embodiments, the cross-linking agent is N,N'-methylenebisacrylamide, the emulsifier is a complex system of sodium dodecyl sulfate and polyvinyl alcohol, the mass ratio of sodium dodecyl sulfate to polyvinyl alcohol is preferably 1:2-1:4, and the initiator is potassium persulfate, and the mass percentage of potassium persulfate relative to styrene is 0.6-1.2 wt%.

[0042] In some preferred embodiments, the rotation speed of high-speed emulsification is 8000-15000 rpm, the time is 3-8 minutes, and the temperature is room temperature-30°C.

[0043] The fourth embodiment of the present application provides an application of a sepiolite composite material in selective separation of grease components in tannery immersion waste liquid, and the sepiolite composite material can preferentially adsorb grease while retaining surfactants and protein hydrolysates in the waste liquid.

[0044] In the application process, the quaternary ammonium salt layer of the sepiolite composite is responsible for quickly adsorbing a large amount of oil and fat, especially macromolecules (such as triglycerides) that cannot be accommodated in the β-CD cavity. The cyclodextrin layer is responsible for specifically including small molecular fragments. The two are spatially adjacent, and can realize the synergistic process of "adsorption-crushing-reinclusion" of oil and fat molecules, significantly improving the overall removal efficiency.

[0045] Understandably, the sepiolite composite provided by the present application can be applied not only to tanning immersion waste liquid, but also to other wastewater containing oil and fat, and the sepiolite composite can achieve selective adsorption of oil and fat components.

[0046] In the above application process, the sepiolite composite repels non-target components through multiple mechanisms: (1) size exclusion: the micelles formed by surfactants in water are much larger in size (usually > 10 nm) than the entrance of the β-CD cavity (~ 0.6 nm) and cannot be included. (2) Hydrophilic exclusion: protein hydrolysate (polypeptide, amino acid) is hydrophilic and lacks affinity with the hydrophobic quaternary ammonium salt alkyl chain and the β-CD cavity, and will not be adsorbed. (3) Charge repulsion: the positive charge head carried by the quaternary ammonium salt will repel inorganic cations (such as Na⁺) that also carry positive charges; the negative hydroxyl groups on the outer edge of the β-CD will also repel inorganic anions (such as Cl⁻). Therefore, the salt is perfectly preserved.

[0047] The embodiment of the present application can adsorb common oil and fat, including at least one of free fatty acid, monoglyceride, diglyceride and triglyceride.

[0048] The fifth embodiment of the present application provides a resource recycling method for tanning immersion waste liquid, comprising the following steps: The sepiolite composite is added to the tanning immersion waste liquid, stirred and adsorbed to selectively remove oil and fat; Solid-liquid separation to obtain regenerated sepiolite composite and purified waste liquid from which the oil and fat is desorbed; The purified waste liquid is reused in the tanning immersion process.

[0049] In some preferred embodiments, after obtaining the regenerated sepiolite composite and the purified waste liquid from which the oil and fat is desorbed, a regeneration step of washing and drying the regenerated sepiolite composite is further included, and the regenerated sepiolite composite is reused in the selective removal of oil and fat step.

[0050] In order to make the technical scheme of the present application clearer, the sepiolite composite, preparation and performance are described in detail through multiple specific embodiments.

[0051] Example 1 Preparation of sepiolite composite The sepiolite is added into 2.3 mol / L HCl solution, stirred in a 78℃ water bath for 4.5 h, filtered, washed, dried for 12-16 h, and ground and sieved to obtain acidified sepiolite; the acidified sepiolite is dispersed in an ethanol-water (1:1) solution, and ultrasonically treated at an ultrasonic power of 400-500 W for 30-40 min, centrifugally separated, and vacuum dried to obtain pretreated sepiolite; The pretreated sepiolite is dispersed in a 0.6 wt% hexadecyltrimethylammonium chloride solution, and magnetically stirred at room temperature at a rotation speed of 200-300 rpm for 3 h to obtain a suspension; 2.1 wt% dodecyltrimethylammonium chloride solution is slowly added to the suspension, then the temperature is raised to 63℃ and stirred for 6 h to obtain a mixture; the mixture is centrifugally separated, washed, and vacuum dried at 50-60℃ to obtain gradient-modified sepiolite (G-Sep); wherein the mass ratio of sepiolite to quaternary ammonium salt is 12:1, and the mass ratio of hexadecyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2.5:1; The G-Sep is dispersed in water and ultrasonically treated for 10-15 min, 2.3 g / L β-CD solution (the mass ratio of β-CD to sepiolite is 1:10) is slowly added, and stirred at 52℃ for 5 h; the centrifugal separation, freeze-drying to obtain sepiolite composite CD-G-Sep.

[0052] Example 2 Preparation of sepiolite composite A cross-linked polymer shell layer is prepared based on the sepiolite composite CD-G-Sep obtained in Example 1. The specific method is as follows: Styrene, β-cyclodextrin, and potassium persulfate are mixed, and then reacted at 78℃ for 4 h to obtain St-β-CD prepolymer; Sodium dodecyl sulfate is fully dissolved in deionized water, and polyvinyl alcohol is added; the mixture is heated and stirred at 75-85℃ for 30-40 min, and then cooled to room temperature; the pH is adjusted to 9 to obtain an emulsifier solution; The CD-G-Sep prepared in Example 1 is added to the emulsifier solution, and after intermittent ultrasonic dispersion at a power of 200-300 W for 20-25 min with an interval of 5 s working and 2 s stopping, St-β-CD prepolymer is added under nitrogen protection, high-speed emulsification is carried out for 3-5 min, N,N'-methylenebisacrylamide is added, and emulsification is continued for 1-2 min; the temperature is raised to 75-80℃, and potassium persulfate and sodium bisulfite solutions are added under nitrogen protection; then the mixture is reacted at 300-350 rpm for 4-5 h, and cooled to room temperature; centrifugal separation is carried out for 10 min, and the centrifuged solution is washed and vacuum dried to obtain sepiolite composite with a cross-linked polymer shell layer.

[0053] Example 3 Preparation of sepiolite composite Preparation method refers to Example 2, and the key parameters are as follows: Pretreatment of sepiolite: 2.0 mol / L HC1, 70°C water bath for 4h; Gradient modification: first treated with 0.5 wt% CTAC for 2h, then added 2.0 wt% DTAC, stirred at 60°C for 6h; wherein the mass ratio of sepiolite to quaternary ammonium salt is 10:1, and the mass ratio of cetyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2:1; Cyclodextrin anchoring: β-CD concentration 2.0 g / L, mass ratio of β-CD to sepiolite 1:8, stirred at 50°C for 4h; Prepolymer preparation: 75°C for 4h to obtain the final sepiolite composite material.

[0054] Example 4 Preparation of sepiolite composite material Preparation method refers to Example 2, and the key parameters are as follows: Pretreatment of sepiolite: 3.0 mol / L HC1, 80°C water bath for 5h; Gradient modification: first treated with 0.8 wt% CTAC for 3h, then added 2.2 wt% DTAC, stirred at 65°C for 7h; wherein the mass ratio of sepiolite to quaternary ammonium salt is 15:1, and the mass ratio of cetyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 3:1; Cyclodextrin anchoring: β-CD concentration 2.5 g / L, mass ratio of β-CD to sepiolite 1:12, stirred at 55°C for 5h; Prepolymer preparation: 80°C for 5h to obtain the final sepiolite composite material.

[0055] Example 5 Preparation of sepiolite composite material Preparation method refers to Example 2, and the key parameters are as follows: Pretreatment of sepiolite: 2.5 mol / L HC1, 75°C water bath for 4.5h; Gradient modification: first treated with 0.6 wt% CTAC (mass ratio of sepiolite to quaternary ammonium salt is 12.5:1) for 2.5h, then added 2.1 wt% DTAC, stirred at 65°C for 6.5h; wherein the mass ratio of sepiolite to quaternary ammonium salt is 12.5:1, and the mass ratio of cetyltrimethylammonium chloride to dodecyltrimethylammonium chloride is 2.5:1; Cyclodextrin anchoring: β-CD concentration 2.25 g / L, mass ratio of β-CD to sepiolite 1:10, stirred at 55°C for 4.5h; Prepolymer preparation: 80°C for 4.5h to obtain the final sepiolite composite material.

[0056] Comparative Example 1 Raw Sepiolite: Directly use commercial sepiolite, only basic cleaning and drying treatment.

[0057] Comparative Example 2 Compared with Example 1, the difference is that only gradient modified sepiolite G-Sep is prepared by carrying out the steps of cyclodextrin anchoring and emulsion polymerization.

[0058] Comparative Example 3 Compared with Example 1, the difference is only that modification is carried out only with CTAC, i.e. DTAC in Example 1 is also replaced with an equal amount of CTAC, modification is carried out with 2.7 wt% CTAC, and the remaining steps and parameters are the same as in Example 1.

[0059] Comparative Example 4 Compared with Example 1, the difference is only that modification is carried out only with DTAC, i.e. CTAC in Example 1 is also replaced with an equal amount of DTAC, modification is carried out with 2.7 wt% DTAC, and the remaining steps and parameters are the same as in Example 1.

[0060] Comparative Example 5 Compared with Example 1, the difference is only that modification is carried out with CTAB, i.e. DTAC, CTAC in Example 1 is replaced with an equal amount of CTAB, modification is carried out with 2.7 wt% CTAB, and the remaining steps and parameters are the same as in Example 1.

[0061] Comparative Example 6 Compared with Example 1, the difference is only that the pretreated sepiolite is directly complexed with β-CD without going through the steps of quaternary ammonium salt modification and emulsion polymerization.

[0062] Comparative Example 7 Traditional cross-linked β-cyclodextrin composite Preparation of cross-linked β-CD polymer: β-cyclodextrin was dissolved in 50 mL of deionized water, stirred well until completely dissolved, and the pH was adjusted to 11-12; under ice bath conditions, epoxy chloropropane was slowly added (molar ratio of β-CD: epoxy chloropropane = 1:10), after ice bath stirring for 2 hours, the temperature was increased to 60°C and reacted for 6 hours, neutralized to pH 7-8, dialysis was used to remove small molecular impurities (dialysis bag molecular weight cut-off 3500 Da, dialysis for 48 hours), and freeze-drying was used to obtain cross-linked β-CD polymer; Sepiolite pretreatment: 2.3 mol / L HCl, 78°C water bath for 4.5 hours, deionized water washing to neutral, 80°C drying for 12 hours; Preparation of composite material: Pretreated sepiolite (2 g) was dispersed in deionized water (100 mL), sonicated for 15 minutes, crosslinked β-CD polymer (calculated based on β-CD content of 2.3 g / L) was added, stirred at 52°C for 5 hours to allow the polymer to adsorb on the surface of sepiolite, centrifuged (8000 rpm, 10 minutes), washed 3 times with deionized water, and vacuum dried at 80°C for 12 hours to obtain the final composite material.

[0063] Comparative Example 8 Compared with Example 1, the only difference is that CTAC and DTAC are mixed and added to the modification at one time, while the other steps and parameters are the same as in Example 1.

[0064] Comparative Example 9 Compared with Example 1, the only difference is that the order of CTAC and DTAC modification is reversed, with DTAC modification performed first and then CTAC modification performed. All other steps and parameters are the same as in Example 1.

[0065] Comparative Example 10 Compared with Example 1, the only difference is that dodecyltrimethylammonium chloride is replaced with an equal amount of sodium dodecyl sulfonate; all other steps and parameters are the same as in Example 1. Comparative Example 11 Compared with Example 1, the only difference is that only sodium dodecyl sulfonate is used for modification. That is, the treatment of hexadecyltrimethylammonium chloride and dodecyltrimethylammonium chloride in Example 1 is replaced by a one-time treatment of 2.7 wt% sodium dodecyl sulfonate. All other steps and parameters are the same as in Example 1.

[0066] Comparative Example 12 Compared with Example 1, the only difference is that the order of β-cyclodextrin treatment and quaternary ammonium salt gradient modification is changed, that is, β-cyclodextrin is grafted first, followed by quaternary ammonium salt gradient modification. All other steps and parameters are the same as in Example 1.

[0067] Comparative Example 13 Compared with Example 1, the only difference is that quaternary ammonium salt gradient modification and β-cyclodextrin treatment are performed simultaneously, while the other steps and parameters are the same as in Example 1.

[0068] Test case The following experiments were conducted on the sepiolite materials prepared in the above embodiments and comparative examples: 1. Measurement of adsorption capacity of mixed oils The sepiolite material was dried in an oven at 105°C for 2 hours, cooled to room temperature, weighed and recorded the initial mass m0; 1.0 g of the dried sample was taken and placed in a 50 mL beaker, an excess of oil product (about 15-20 g) was added to ensure complete immersion of the sample; oscillated in a constant temperature water bath at 25°C for 2 hours at a speed of 150 rpm; allowed to stand for 30 min to fully adsorb; the excess oil on the surface was quickly filtered off with filter paper, and the oil-adsorbed sample was transferred to a pre-weighed beaker for weighing and recording the total mass after adsorption m1. The adsorption capacity calculation formula is: adsorption capacity = (m1 - m0) / m0 (g oil / g adsorbent). The results are shown in Table 1.

[0069] Table 1 Comparison of adsorption capacity of mixed oil and fat .

[0070] 2. Selective adsorption test of long-chain fatty acids A mixed fatty acid solution (n-hexane system) composed of C8, C10, C12, C14, C16, and C18 was used as the adsorbed object, and the specific method was as follows: each fatty acid was accurately weighed and prepared into a 100 mg / L n-hexane solution, 50 mg / L of internal standard heptadecanoic acid was added, the total volume was 500 mL, and it was preserved under nitrogen. 0.1 g of sepiolite sample was taken in a 25 mL conical flask with a stopper, 20 mL of mixed fatty acid solution was added, oscillated at 25°C for 2 h at 180 r / min, filtered with a 0.45 μm filter membrane, the filtrate was collected, and the concentration was determined by gas chromatograph. The removal rate calculation formula is: removal rate (%) = (C0 - C) / C0 × 100%, wherein C0 is the initial concentration, and C is the equilibrium concentration. The test results are shown in Table 2.

[0071] Table 2 Removal rate of each sample on long-chain fatty acids .

[0072] 3. Comparison of cyclic use performance First adsorption: 2.0 g of sepiolite sample was taken for soybean oil adsorption, and the initial adsorption capacity was recorded as 100% reference value; desorption and regeneration: the oil-adsorbed sample was eluted with n-hexane, the solid-liquid ratio was 1:10, and it was oscillated at room temperature for 30 min, and the elution was repeated for 3 times until the eluate was colorless, and it was dried in an oven at 105°C for 2 hours to constant weight; cyclic test: the adsorption-desorption process was repeated, and after the 3rd, 5th, 7th, 10th, and 15th cycles, the adsorption capacity was determined and the retention rate was calculated. The retention rate calculation formula is: retention rate (%) = adsorption capacity of the nth cycle / initial adsorption capacity × 100%. The results are shown in Table 3.

[0073] Table 3 Cyclic use performance of each sample .

[0074] 4. β-CD shedding rate determination The stability of β-cyclodextrin (β-CD) loaded on the surface of sepiolite composites during the recycling process was evaluated. The β-CD content in the regeneration eluent of the composites was quantitatively determined by high-performance liquid chromatography (HPLC), and the single shedding amount and cumulative shedding rate were calculated.

[0075] Eluent sample preparation: The sepiolite composites were subjected to adsorption-regeneration cycle experiments according to the method of "3. Recycling performance comparison" above. The eluent after each regeneration operation was collected, made up to 100 mL, and filtered with a 0.22 μm filter membrane for testing; HPLC analysis conditions: mobile phase: acetonitrile: water = 75:25 (v / v); Standard curve preparation: Accurately weigh the β-CD standard (purity ≥ 98%), and prepare a series of standard solutions with concentrations of 0.1, 0.5, 1.0, 2.0, 5.0, and 10.0 mg / L. Analyze the samples in order of low concentration to high concentration according to the above chromatographic conditions, record the peak area of each concentration standard, and draw the concentration-peak area standard curve; Analysis of the sample to be tested: After filtering the prepared eluent sample with a 0.22 μm filter membrane, directly analyze the sample, and record the chromatographic peak area consistent with the retention time of the standard; Result calculation: According to the peak area of the sample to be tested, substitute it into the standard curve to calculate the concentration of β-CD in the eluent. The cumulative shedding rate calculation formula is as follows: single shedding amount (mg) = eluent concentration (mg / L) x eluent volume (L); cumulative shedding rate (%) = Σ single shedding amount / initial β-CD loading amount x 100%. The results are shown in Table 4.

[0076] Table 4 β-CD shedding rate of each sample .

[0077] 5. Comparison of adsorption kinetics constants Prepare 12 identical 100 mL conical flasks, each containing 1.0 g of sepiolite sample and 20 mL of soybean oil. Constant temperature oscillation (25°C, oscillation speed 180 rpm), sample at preset time points (1, 3, 5, 10, 15, 30, 45, 60, 90, 120 min). After sampling, quickly filter the solid-liquid phases, weigh the mass change of the adsorbent, and calculate the instantaneous adsorption amount qt. Use the pseudo-second-order kinetics equation to fit, linear regression to obtain k2 (rate constant), qe (equilibrium adsorption amount) and R 2 (fitting degree), and calculate the half-adsorption time: t1 / 2= 1 / (k2qe 2) + t / qe. The results are shown in Table 5.

[0078] Table 5 Adsorption kinetics constants of various samples .

[0079] 6. Actual tannery effluent treatment effect Effluent source and composition: tannery effluent, COD: 25000 mg / L; oil: 5000 mg / L; surfactant: 500 mg / L; protein: 1000 mg / L; chloride ion: 18500 mg / L; pH: 7.8. The COD of the effluent needs to be removed to below 3000 mg / L to become purified liquid.

[0080] Each sepiolite sample was added to the effluent, 25°C, mechanical stirring 120 rpm, contact time 2 hours, standing for 30 minutes, 0.45 μm filter membrane filtration, and the treated liquid was collected. Each index after treatment was measured according to the corresponding method, and the removal rate and retention rate were calculated. Removal rate (%) = (Cinitial - Cafter treatment) / Cinitial x 100%; retention rate (%) = Cafter treatment / Cinitial x 100%. The results are shown in Table 6.

[0081] Table 6 Comparison of treatment effects of various samples .

[0082] The above examples are only used to illustrate the technical solutions of the present application, and not to limit them; although the present application has been described in detail with reference to the foregoing examples, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing examples, or make equivalent replacements for part of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A sepiolite composite material, characterized in that, include: Sepiolite carrier; a quaternary ammonium salt molecular layer gradient anchored on the surface of the sepiolite carrier, the quaternary ammonium salt molecular layer comprising dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride; β-cyclodextrin molecules bound to the surface of the quaternary ammonium salt molecular layer by intermolecular forces.

2. The sepiolite composite material as described in claim 1, characterized in that, The dodecyltrimethylammonium chloride and hexadecyltrimethylammonium chloride form a gradient distribution from the pore opening to the inside of the pore within the sepiolite carrier.

3. The sepiolite composite material as described in claim 1, characterized in that, The mass percentage concentration of hexadecyltrimethylammonium chloride is 0.5~0.8 wt%, and the mass percentage concentration of dodecyltrimethylammonium chloride is 2.0~2.2 wt%.

4. The sepiolite composite material as described in claim 1, characterized in that, The mass ratio of sepiolite to quaternary ammonium salt is 10:1 to 15:1, and the mass ratio of β-cyclodextrin to sepiolite is 1:8 to 1:

12.

5. The sepiolite composite material according to any one of claims 1 to 4, characterized in that, The surface of the sepiolite composite material is also coated with a cross-linked polymer shell.

6. The method for preparing the sepiolite composite material according to any one of claims 1 to 4, characterized in that, Includes the following steps: Sepiolite was acidified with hydrochloric acid solution, and then washed and dried to obtain acidified sepiolite. The acidified sepiolite was first reacted with a hexadecyltrimethylammonium chloride solution at a first temperature to obtain a suspension; then a dodecyltrimethylammonium chloride solution was added to the suspension, and a second reaction was carried out at a second temperature. After the reaction was completed, the mixture was separated into solid and liquid phases and dried to obtain gradient-modified sepiolite. The gradient-modified sepiolite was subjected to a third reaction with a β-cyclodextrin solution, which caused the cyclodextrin to bind to its surface through intermolecular forces. After solid-liquid separation and drying, the sepiolite composite material was obtained.

7. The method for preparing sepiolite composite material as described in claim 6, characterized in that, The first temperature is room temperature, and the second temperature is 60~65℃.

8. The method for preparing the sepiolite composite material as described in claim 5, characterized in that, Includes the following steps: The method described in claim 6 or 7 is used to prepare a sepiolite composite material; the sepiolite composite material, styrene, crosslinking agent and emulsifier are emulsified in an aqueous phase at high speed to form an emulsion; an initiator is added to the emulsion to carry out an emulsion polymerization reaction, forming a crosslinked polymer shell on the surface of the sepiolite composite material; the reaction product is subjected to solid-liquid separation, washing and drying to obtain a sepiolite composite material coated with a crosslinked polymer shell.

9. The application of the sepiolite composite material as described in any one of claims 1 to 5 in the selective separation of oil components in leather tanning soaking wastewater, characterized in that, The sepiolite composite material preferentially adsorbs oils while retaining surfactants and protein hydrolysates in the waste liquid.

10. A method for the resource recycling of waste liquid from leather tanning, characterized in that, The process includes the following steps: adding the sepiolite composite material according to any one of claims 1 to 5 to the tanning soaking waste liquid, stirring and adsorbing to selectively remove grease; separating the solid and liquid to obtain the regenerated sepiolite composite material and the purified waste liquid desorbed from the grease; and reusing the purified waste liquid in the tanning soaking process.