A method for rapid dehydration and depolymerization of montmorillonite nanosheets

Abstract

The present invention relates to the technical field of clay dehydration, and specifically relates to a method for rapid dehydration and depolymerization of montmorillonite nanosheets. The steps are as follows: adding an aggregating agent to the montmorillonite nanosheet suspension, and obtaining a centrifuged product through mixing and centrifugal concentration; adding a depolymerizing agent to the centrifuged product, and obtaining re-dispersed montmorillonite nanosheets after mixing; wherein, the aggregating agent includes at least one or more functional groups capable of connecting with the hydroxyl groups on the end faces of the nanosheets through intermolecular forces. This method adds an aggregating agent to the montmorillonite nanosheet suspension, and its characteristic functional groups are connected to the hydroxyl groups on the end faces of the montmorillonite nanosheets through hydrogen bonds, enabling the nanosheets to be connected from small pieces into large pieces, increasing the particle size of the nanosheets, and improving the sedimentation dehydration rate of the nanosheets. By adding a depolymerizing agent, the hydrogen bonds between the nanosheets and the agent are broken, the nanosheets are re-dispersed, the performance of the montmorillonite nanosheets is restored, and montmorillonite nanosheets with high concentration and low viscosity are obtained.

Description

Technical Field

[0001] The present invention relates to the technical field of clay dehydration, and particularly relates to a method for rapid dehydration and depolymerization of montmorillonite nanosheets. Background Art

[0002] Montmorillonite, as a typical layered clay mineral, has excellent physical and chemical properties and can be exfoliated to obtain nanosheets with two-dimensional structural characteristics. Due to the excellent stability, flame retardancy and adsorption properties of montmorillonite nanosheets, they are widely used in many industrial fields. However, during the exfoliation process, in order to prevent gelation of the exfoliated nanosheets, a low-concentration montmorillonite suspension with a concentration of less than 3% is often used for exfoliation. However, in practical applications, low-concentration nanosheets have limitations. For example, when using montmorillonite nanosheets to prepare flame retardant materials, products prepared from high-concentration nanosheets have better performance. At the same time, when preparing clay-based multifunctional membranes, high-concentration and highly fluid nanosheets are the basis for preparing thin and dense functional membranes. Currently, the common method for concentrating montmorillonite nanosheets is evaporation concentration, but this method takes a long time and consumes a large amount of energy, making it difficult to meet the engineering requirements. Therefore, it is very urgent to develop an efficient and economical montmorillonite nanosheet concentration approach.

[0003] Centrifugation, as a promising clay concentration technology, has been applied at the industrial level, and efficient dehydration of clay can be achieved through centrifugation. In the published paper (C.V. Nguyen, A.V. Nguyen, A. Doi, E. Dinh, T.V. Nguyen, M. Ejtemaei, D. Osborne, Advanced solid-liquid separation for dewatering fine coal tailings by combining chemical reagents and solid bowl centrifugation. Sep. Purif. Technol. 259 (2021) 118172.), Nguyen et al. studied the centrifugal dehydration of montmorillonite-containing tailings. It was found that after adding metal cations and flocculants, the surface charge of the clay was neutralized, causing particle aggregation and the sedimentation rate could be increased to 98.6%. In the published paper (A. McFarlane, K. Bremmell, J. Addai-Mensah, Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization. J. Colloid Interface Sci. 293 (2006) 116-127.), McFarlane et al. studied the method to accelerate the dehydration of montmorillonite. By adding metal cations and flocculants, the sedimentation effect of montmorillonite was improved to a certain extent. After adding the flocculant polyacrylamide, montmorillonite aggregated together, thus increasing its solid content. However, compared with montmorillonite, montmorillonite nanosheets usually have a more negative surface charge, which increases their dispersion stability and slows down sedimentation. More importantly, water molecules are more likely to diffuse and adhere to the surface of montmorillonite nanosheets, hindering the effectiveness of the dehydration process. Although the dispersion stability of the nanosheets can be reduced to a certain extent by adding cations and flocculants to achieve the concentration effect, the highly concentrated montmorillonite nanosheets obtained after adding metal cations and flocculants tend to aggregate, losing the original fluidity of the nanosheets, severely limiting the practical application of the nanosheets. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for rapid dehydration and depolymerization of montmorillonite nanosheets, which is simple in technology, convenient to operate, and low in cost. The obtained re-dispersed montmorillonite nanosheet solution system has the advantages of high concentration, good fluidity, and being suitable for industrial applications.

[0005] The solution adopted by the present invention to achieve the purpose is as follows: A method for rapid dehydration and depolymerization of montmorillonite nanosheets, comprising the following steps:

[0006] (a) Adding an aggregating agent to the montmorillonite nanosheet suspension, and obtaining a centrifuged product through mixing and centrifugal concentration;

[0007] (b) Adding a depolymerizing agent to the centrifuged product obtained in step (a), and obtaining redispersed montmorillonite nanosheets after mixing;

[0008] Among them, in step (a), the aggregating agent includes at least one or more functional groups capable of connecting with the hydroxyl groups on the end faces of the nanosheets through intermolecular forces.

[0009] Preferably, the functional group is selected from amino group (-NH2), sulfonic acid group (-SO3H), carboxyl group (-COOH), hydrazino group (-NHNH2), etc.

[0010] Preferably, the aggregating agent includes at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyethylenepolyamine and its derivatives, methylsulfonic acid, ethylsulfonic acid, disodium disulfonate and its derivatives, formic acid, acetic acid, propionic acid and its derivatives, methylhydrazine, unsymmetrical dimethylhydrazine, benzylhydrazine and its derivatives.

[0011] The agents with amino functional groups include diethylenetriamine, triethylenetetramine, tetraethylenepentamine and polyethylenepolyamine and its derivatives, etc.; the agents with sulfonic acid functional groups include methylsulfonic acid, ethylsulfonic acid, disodium disulfonate and its derivatives, etc.; the agents with carboxyl functional groups include formic acid, acetic acid, propionic acid and its derivatives, etc.; the agents with hydrazino functional groups include methylhydrazine, unsymmetrical dimethylhydrazine, benzylhydrazine and its derivatives, etc. The added aggregating agent is any one of pure substances or a mixture evenly mixed in any proportion through any combination method.

[0012] Preferably, in step (a), the mass concentration of the montmorillonite nanosheet suspension is 0.1wt% - 5wt%.

[0013] Preferably, in step (a), the dosage of the aggregating agent is 0.1% - 10% of the solid mass of the montmorillonite nanosheets.

[0014] Preferably, in step (a), the centrifugal acceleration is 1000 - 16000g.

[0015] Preferably, in step (b), the depolymerizing agent is an alkaline solution, including at least one of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous lithium hydroxide solution, and ammonia water.

[0016] Preferably, in step (b), the concentration of the depolymerizing agent is 1 - 10mol / L.

[0017] Preferably, in the step (b), the volume ratio of the centrifuged product to the depolymerizing agent is 1000-3000:1.

[0018] The principle involved in the method of the present invention is as follows: Based on the surface and structural characteristics of montmorillonite nanosheets, on the one hand, an aggregating agent is used to connect small sheets into large sheets through hydrogen bonds with the hydroxyl groups on the end faces of montmorillonite nanosheets, increasing the particle size of the nanosheets and thus rapidly sedimenting, completing the efficient dehydration of the nanosheets; on the other hand, a depolymerizing agent is used to break the hydrogen bond between the nanosheets and the aggregating agent, depolymerizing the nanosheets, while satisfying the performance of montmorillonite itself without change, increasing the concentration of the nanosheets to meet the actual application scenarios.

[0019] The present invention has the following advantages and beneficial effects:

[0020] 1. By adding an aggregating agent to the montmorillonite nanosheet suspension, the characteristic functional groups of which are connected to the hydroxyl groups on the end faces of montmorillonite nanosheets through hydrogen bonds, the nanosheets are connected from small sheets into large sheets, increasing the particle size of the nanosheets and greatly improving the sedimentation dehydration rate of the nanosheets.

[0021] 2. After the aggregating agent causes the nanosheets to agglomerate and sediment, by adding a depolymerizing agent to the centrifuged nanosheets, the hydrogen bond between the nanosheets and the agent is broken, and the nanosheets are redispersed, restoring the performance of the montmorillonite nanosheets, obtaining a montmorillonite nanosheet solution system with high concentration and low viscosity, ensuring the practical application of the montmorillonite nanosheets.

[0022] 3. The present invention also has the advantages of simple technology, convenient operation, low cost, etc., ensuring the industrial application value of montmorillonite nanosheets. Description of the Drawings

[0023] Figure 1 It is a comparison chart of the yield (a) and solid content (b) of montmorillonite nanosheets after centrifugation in Example 1 and Comparative Example 1;

[0024] Figure 2 It is an infrared spectrogram of montmorillonite nanosheets and after adding an aggregating agent in Example 2;

[0025] Figure 3 It is a scanning electron micrograph of montmorillonite nanosheets after centrifugation in Example 2 before adding a depolymerizing agent (a) and after adding 100 μL of depolymerizing agent (b);

[0026] Figure 4 It is a graph showing the change in the viscosity of the montmorillonite nanosheet suspension with the addition amount of the depolymerizing agent and ultrapure water in Example 2 and Comparative Example 2;

[0027] Figure 5Schematic diagrams of the changes after adding 100 μL of depolymerizing agent and 100 μL of aqueous solution to the centrifuged montmorillonite nanosheets in Example 2 and Comparative Example 2, respectively. Detailed implementation manners

[0028] For a better understanding of the present invention, the following examples further illustrate the present invention, but the content of the present invention is not limited to the following examples only.

[0029] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the present invention will be further described below with reference to examples, but it is not intended to limit the present invention. The preparation steps of the two-dimensional montmorillonite nanosheets in the present invention refer to the patent with the publication number CN114890433A.

[0030] Example 1

[0031] A method for rapid dehydration and depolymerization of montmorillonite nanosheets: the concentration of the initial montmorillonite nanosheet suspension is 0.6 wt%, and the method for rapid dehydration and depolymerization of the nanosheets is as follows:

[0032] Add 10% tetraethylenepentamine to the montmorillonite nanosheet suspension, stir for 10 min under the condition of 500 r / min, and centrifuge for 1 min under the condition of 1000 g centrifugation. Then, 50 μL of 5 mol / L sodium hydroxide solution is dropped into 150 mL of the centrifuged product and stirred, and the montmorillonite nanosheets regain fluidity.

[0033] Example 2

[0034] A method for rapid dehydration and depolymerization of montmorillonite nanosheets: the concentration of the initial montmorillonite nanosheet suspension is 0.6 wt%, and the method for rapid dehydration and depolymerization of the nanosheets is as follows:

[0035] Add 5% tetraethylenepentamine to the montmorillonite nanosheet suspension, stir for 10 min under the condition of 500 r / min, and centrifuge for 20 min under the condition of 16000 g centrifugation. Then, 5 mol / L sodium hydroxide solution is dropped into 150 mL of the centrifuged product and stirred, and the viscosity changes of the system are tested at different volumes of sodium hydroxide, and the volumes of sodium hydroxide are 0, 25 μL, 50 μL, 75 μL, and 100 μL, respectively.

[0036] Example 3

[0037] A method for rapid dehydration and depolymerization of montmorillonite nanosheets: the concentration of the initial montmorillonite nanosheet suspension is 0.1 wt%, and the method for rapid dehydration and depolymerization is as follows:

[0038] Add 10% sodium dithionate to the montmorillonite nanosheet suspension, stir for 30 min under the condition of 1000 r / min, and centrifuge for 1 min under the condition of centrifugation at 16000 g. Then, 90 μL of 5 mol / L potassium hydroxide solution was dropped into 200 mL of the centrifuged product and stirred, and the montmorillonite nanosheets regained fluidity.

[0039] Example 4

[0040] A method for rapid dehydration and depolymerization of montmorillonite nanosheets: The concentration of the initial montmorillonite nanosheet suspension is 0.1 wt%, and the method for rapid dehydration and depolymerization of the nanosheets is as follows:

[0041] Add 0.1% tetraethylenepentamine to the montmorillonite nanosheet suspension, stir for 10 min under the condition of 200 r / min, and centrifuge for 10 min under the condition of centrifugation at 1000 g. Then, 50 μL of 1 mol / L lithium hydroxide solution was dropped into 100 mL of the centrifuged product and stirred, and the montmorillonite nanosheets regained fluidity.

[0042] Example 5

[0043] A method for rapid dehydration and depolymerization of montmorillonite nanosheets: The concentration of the initial montmorillonite nanosheet suspension is 5 wt%, and the method for rapid dehydration and depolymerization of the nanosheets is as follows:

[0044] Add 0.1% tetraethylenepentamine to the montmorillonite nanosheet suspension, stir for 10 min under the condition of 200 r / min, and centrifuge for 5 min under the condition of centrifugation at 5000 g. Then, 100 μL of 10 mol / L ammonia water was dropped into the centrifuged product and stirred, and the montmorillonite nanosheets regained fluidity.

[0045] Comparative Example 1

[0046] A method for directly centrifuging and dehydrating montmorillonite nanosheets: The concentration of the initial montmorillonite nanosheet suspension is 0.6 wt%, stir for 10 min under the condition of 500 r / min, and then centrifuge for 1 min under the condition of centrifugation at 1000 g.

[0047] The bar charts of the yield and solid content values of the nanosheets obtained by centrifugation in Example 1 and Comparative Example 1 are as Figure 1 shown.

[0048] Figure 1Results of the yield (a) and solid content (b) of montmorillonite nanosheets after centrifugation in Example 1 and Comparative Example 1. Under the condition of a low centrifugal acceleration of 1000 g, without using an aggregating agent, the nanosheets could hardly settle, and the recovery rate was only 2.07%, and the solid content was only 0.87%, failing to achieve the purpose of concentrating the nanosheets. After adding the aggregating agent, the montmorillonite nanosheets could completely precipitate within 1 min. Compared with not adding the aggregating agent, the recovery rate of the nanosheets increased by nearly 40 times, and the solid content increased by nearly 2 times, indicating that the dehydration performance of the montmorillonite nanosheets was greatly improved.

[0049] Figure 2 Infrared spectra of montmorillonite nanosheets and after adding an aggregating agent in Example 2. The infrared spectra of montmorillonite nanosheets before and after adding tetraethylenepentamine revealed the reaction between the aggregating agent and montmorillonite nanosheets. From the infrared spectrum of montmorillonite nanosheets, a series of peaks of montmorillonite were detected at 3628 cm -1 (vAl-OH), 1640 cm -1 (δH-O-H), 1038 cm -1 (vSi-O), 523 cm -1 (vSi-O-Al) and 467 cm -1 (vSi-O-Si). After adding the aggregating agent tetraethylenepentamine, new peaks such as N-H vibration and C-H symmetric stretching of tetraethylenepentamine appeared at 1463 cm -1 , 2859 cm -1 and 2957 cm -1 respectively, accompanied by weakened peaks of vAl-OH and δH-O-H, proving that tetraethylenepentamine and montmorillonite nanosheets were combined through the reaction of -OH and -NH, that is, through hydrogen bonding.

[0050] Comparative Example 2

[0051] Method for depolymerizing montmorillonite nanosheets: The concentration of the initial montmorillonite nanosheet suspension was 0.6 wt%. The method for concentrating and depolymerizing the nanosheets was as follows:

[0052] Add 5% tetraethylenepentamine to the montmorillonite nanosheet suspension, stir for 10 min under the condition of 500 r / min, centrifuge for 20 min under the condition of centrifugation at 16000 g, and then drop water with the same volume as the depolymerizing agent in Example 2, which were 0, 25 μL, 50 μL, 75 μL, 100 μL respectively, and stir.

[0053] Figure 3 Scanning electron micrographs of montmorillonite nanosheets after centrifugation in Example 2 before adding the depolymerizing agent (a) and after adding 100 μL of the depolymerizing agent (b). As Figure 3As shown in ab, during the addition of the deagglomerating agent, the network structure formed between the montmorillonite nanosheets and the agglomerating agent was destroyed and decomposed, becoming a randomly dispersed structure. This phenomenon indicates that the hydrogen bonds between the montmorillonite nanosheets and the agglomerating agent are broken, and the montmorillonite nanosheet solution system is redispersed.

[0054] The schematic diagrams of the change in viscosity and fluidity of the montmorillonite nanosheets in Example 2 and Comparative Example 2 are shown in FIG. Figure 4 and Figure 5 .from Figure 4 It can be seen that the montmorillonite nanosheet system with the addition of aggregating agent has high concentration and high viscosity. The montmorillonite nanosheets are gelled and have no fluidity. After adding a small amount of water to the nanosheet and aggregating agent system, its viscosity basically does not change, but as the deaggregating agent is added to the system, its viscosity gradually decreases. After adding 100 μL, it can be seen that the deaggregating agent has a significant improvement effect on the viscosity of the system and restores the fluidity of the nanosheets. Figure 5 The figure is a schematic diagram of the changes of the centrifuged montmorillonite nanosheets after adding 100μL of depolymerizing agent and aqueous solution. It can be seen intuitively from the figure that after adding the aqueous solution, the nanosheets are still in a gel state, and the nanosheet and aggregating agent system after adding the depolymerizing agent has restored fluidity. Therefore, the aggregating agent can not only combine with the montmorillonite nanosheets to promote the dehydration process, but also ensure the recovery of the performance of the nanosheets. After adding the depolymerizing agent, high-concentration, low-viscosity and fluid montmorillonite nanosheets can be obtained, thereby preparing high-performance clay-based multifunctional membranes.

[0055] The above is only a preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and changes can be made without departing from the principle of the present invention, and these improvements and changes are also regarded as the protection scope of the present invention.

Claims

1. A method for rapid dehydration and depolymerization of montmorillonite nanosheets, characterized in that It includes the following steps: (a) Adding an aggregating agent to the montmorillonite nanosheet suspension, and obtaining a centrifuged product through mixing and centrifugal concentration; (b) Adding a depolymerizing agent to the centrifuged product obtained in step (a), and obtaining redispersed montmorillonite nanosheets after mixing; Wherein, the aggregating agent in step (a) includes at least one or more functional groups capable of connecting with the hydroxyl groups on the end face of the nanosheets through intermolecular forces; The aggregating agent includes at least one of diethylenetriamine, triethylenetetramine, tetraethylenepentamine, polyethylenepolyamine and its derivatives, methylsulfonic acid, ethylsulfonic acid, disodium disulfonate and its derivatives, formic acid, acetic acid, propionic acid and its derivatives, methylhydrazine, unsymmetrical dimethylhydrazine, benzylhydrazine and its derivatives; In step (b), the depolymerizing agent is an alkaline solution, including at least one of aqueous sodium hydroxide solution, aqueous potassium hydroxide solution, aqueous lithium hydroxide solution, and ammonia water.

2. The method for rapid dehydration and depolymerization of montmorillonite nanosheets according to claim 1, wherein: The functional group is selected from at least one of amino group, sulfonic acid group, carboxyl group, and hydrazine group.

3. The method for rapid dehydration and depolymerization of montmorillonite nanosheets according to claim 1, wherein: In step (a), the mass concentration of the montmorillonite nanosheet suspension is 0.1 wt%-5 wt%.

4. The method for rapid dehydration and depolymerization of montmorillonite nanosheets according to claim 1, characterized in that: In step (a), the dosage of the aggregating agent is 0.1%-10% of the solid mass of the montmorillonite nanosheets.

5. The method for rapid dehydration and depolymerization of montmorillonite nanosheets according to claim 1, characterized in that: In step (a), the centrifugal acceleration is 1000-16000g.

6. The method for rapid dehydration and depolymerization of montmorillonite nanosheets according to claim 1, wherein: In step (b), the concentration of the depolymerizing agent is 1-10 mol / L.

7. The method for rapid dehydration and depolymerization of montmorillonite nanosheets according to claim 1, characterized in that: In step (b), the volume ratio of the centrifuged product to the depolymerizing agent is 1000-3000:1.

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