Pickering emulsifier silica nanonet and preparation method and application thereof

Abstract

The application relates to the technical field of catalysts, in particular to a Pickering emulsifier silica nanonet and a preparation method and application thereof. The preparation method comprises the following steps: dissolving cetyltrimethylammonium chloride in water, uniformly mixing, and adjusting the pH to 10; placing the cetyltrimethylammonium chloride solution in a water bath, adding an ethyl silicate n-decane solution, carrying out reaction after homogenization emulsification, and cooling, suction filtering, washing, drying, crushing to obtain the Pickering emulsifier silica nanonet. The Pickering emulsifier silica nanonet preparation method is simple and can be mass-produced. The degradation efficiency of polyester is high, and a high alcoholysis efficiency can be achieved at a lower reaction temperature and in a very short reaction time.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a Pickering emulsifier silicon dioxide nanonet and a preparation method and application thereof. BACKGROUND

[0002] Polyethylene terephthalate (PET) is a widely used thermoplastic polymer resin with excellent mechanical properties, creep resistance, electrical insulation, transparency and safety, and is used in synthetic fibers, insulation materials, plastic films, packaging bottles and food packaging and many other fields. However, in the past half century, the consumption and processing of PET have soared, causing great waste of resources and posing a great threat to environmental safety. Achieving efficient degradation of waste PET has important practical significance for alleviating environmental pollution and energy crisis and achieving a carbon-neutral society (MacArthur E., Science 2017, 358(6365), 843-843).

[0003] Currently, the main methods for treating PET are physical and chemical methods. The physical method is a commonly used method for treating PET in industry, which is low in cost and easy to operate. However, it is a downcycling process, and the recycled PET has poor performance and can only be used to produce low-grade products (Sardon H., Science 2018, 360, 380-381). The chemical method is to depolymerize waste PET into monomers by chemical reaction and then polymerize them into new PET. This method is an ideal method for PET recycling and is the main direction of current research (Hong M., Green Chemistry 2017, 19, 3692-3706). Currently, the main methods for chemical depolymerization of PET are hydrolysis, pyrolysis, alcoholysis and ammonolysis, among which the ethylene glycol alcoholysis method has gradually attracted attention due to its advantages of not being volatile and being able to produce continuously (Ignatyev I.A., ChemSusChem 2014, 7, 1579-1593). Researchers have developed various catalytic technologies around the ethylene glycol alcoholysis method, such as supercritical method, microwave-assisted method and homogeneous reaction method, to improve its reaction efficiency.

[0004] However, in the current PET ethylene glycol alcoholysis method, there are some reaction conditions that are extremely harsh or the use of additives is difficult to separate from ethylene glycol. In addition, the current PET ethylene glycol alcoholysis method usually needs to be operated at a high temperature of nearly 200℃, which has high energy consumption, and the yield of the product, ethylene glycol terephthalate (BHET), is generally not high, which hinders the further development of the PET ethylene glycol alcoholysis method.

[0005] Pickering emulsion catalysis has proven to be a highly efficient reaction system. This system overcomes the solubility and incompatibility issues of hydrophilic and hydrophobic reactants in traditional heterogeneous catalysis. Furthermore, its large interfacial area increases the contact opportunities between reactants, effectively improving heat and mass transfer between reactants and products at the reaction interface, significantly increasing the reaction rate (Ming Z., Nature Communications 2022, 13, 475). In addition, compared to emulsion systems stable with molecular surfactants, Pickering emulsion systems offer advantages such as low particulate emulsifier dosage, low cost, high stability, good recyclability, and non-toxicity (Wu J., Small 2016, 12, 4633-4648). However, as reaction temperatures increase, medium pressure is often required to maintain the stability of Pickering emulsions; therefore, research on medium- and high-temperature Pickering emulsion catalysis systems is extremely limited. Developing a Pickering emulsion catalytic system to improve the reaction rate of PET ethylene glycol alcoholysis under mild reaction conditions has extremely significant research and practical value. Currently, there are no research reports internationally on using the Pickering emulsion system for medium- and high-temperature catalytic reactions under normal pressure. Summary of the Invention

[0006] The purpose of this invention is to provide a Pickering emulsifier silica nanonet, its preparation method, and its application. It can achieve high alcoholysis efficiency at relatively mild reaction temperatures and in extremely short reaction times.

[0007] A Pickering emulsifier silica nanonet, the preparation method includes the following steps:

[0008] 1) Dissolve hexadecyltrimethylammonium chloride in water, mix well, and adjust the pH to 10;

[0009] 2) Place a hexadecyltrimethylammonium chloride solution in a water bath, add a decane solution of tetraethyl orthosilicate, homogenize and emulsify, then react, cool, filter, wash, dry, and pulverize to obtain Pickering emulsifier silica nanonet.

[0010] In the aforementioned Pickering emulsifier silica nanonet, step 1) involves adjusting the pH to 10 using 25% concentrated ammonia.

[0011] In the above-mentioned Pickering emulsifier silica nanonet, in step 2), the water bath temperature is 50°C.

[0012] In the above-mentioned Pickering emulsifier silica nanonet, in step 2), the homogenization speed of the homogenization emulsification is 10000 rpm and the time is 10 min.

[0013] The Pickering emulsifier silica nanonet of the above, in step 2), the reaction is constant temperature reaction at 60 DEG C for 18h.

[0014] The use of the Pickering emulsifier silica nanonet of the above in degrading polyester.

[0015] The use of the above, the polyester is polyethylene terephthalate.

[0016] The use of the above, the method is as follows:

[0017] 1) polyethylene terephthalate is crushed, sieved and dried to constant weight;

[0018] 2) the Pickering emulsifier silica nanonet of claim 1 and the catalyst are dispersed into ethylene glycol by ultrasonic wave, and heated to a certain temperature;

[0019] 3) polyethylene terephthalate is added to the oil phase, heated to the temperature in step 2), and polyethylene terephthalate is dissolved;

[0020] 4) the ethylene glycol phase obtained in step 2) and the oil phase obtained in step 3) are mixed, and the emulsion is formed by rapid stirring, and the emulsion is reacted at the temperature in step 3) for a period of time;

[0021] 5) the emulsion obtained in step 4) is filtered, the filtrate is poured into water, concentrated by rotary evaporation, and a large amount of white needle-shaped crystals is precipitated overnight at low temperature, the crystals are filtered and dried to constant weight to obtain the product bis-hydroxyethyl terephthalate.

[0022] The use of the above, in step 3), the catalyst can be one or more of zinc acetate, zinc nitrate, zinc sulfate, manganese acetate, cobalt acetate, sodium carbonate, urea, phosphotungstic acid hydrate, nitrogen-doped graphene, cobalt quantum dots, zinc acetate ionic liquid, and zinc acetate choline.

[0023] The use of the above, in step 2), the certain temperature is 150 DEG C to 190 DEG C.

[0024] The use of the above, in step 3), the oil phase includes at least one of aromatic hydrocarbon and aliphatic hydrocarbon.

[0025] The use of the above, in step 4), the stirring is emulsified by a homogenizer or a homogenizer, and the homogenization or homogenization speed can be 1000 rpm to 50000 rpm.

[0026] The use of the above, in step 4), the reaction time can be 1 min to 60 min.

[0027] The use of the above, in step 5), the temperature is 0 DEG C to 10 DEG C.

[0028] The present application has the following beneficial effects:

[0029] The present application provides a Pickering emulsifier silica nanonet, the composition of the Pickering emulsion catalytic system is flexible and extensive, the preparation and separation method is simple, and batch production can be realized. The Pickering emulsion catalytic system has high degradation efficiency on polyester, and can achieve high alcoholysis efficiency in a short reaction time at a low reaction temperature. By recycling and degrading polyester into raw monomers through the Pickering emulsion catalytic system, the catalytic reaction efficiency can be greatly improved, the reaction energy consumption can be reduced, the cost can be saved, environmental pollution and energy crisis can be effectively alleviated, and the social goal of carbon neutralization can be achieved. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 It is a scanning electron microscope photo of the Pickering emulsifier silica nanonet of the present application embodiment 1.

[0031] Figure 2 It is a microscope photo of the Pickering emulsion catalytic system of the present application embodiment 2.

[0032] Figure 3 It is an infrared spectrum of the product of the present application embodiment 3.

[0033] Figure 4 It is a nuclear magnetic resonance spectrum of the product of the present application embodiment 3.

[0034] Figure 5 It is a mass spectrum of the product of the present application embodiment 3.

[0035] Figure 6 It is the product yield of the present application embodiment 4.

[0036] Figure 7 It is the reactant conversion rate and product yield of the present application embodiment 5.

[0037] Figure 8 It is the reactant conversion rate and product yield of the present application embodiment 6. DETAILED DESCRIPTION

[0038] The present application will be further described below in conjunction with specific embodiments, but the present application is not limited to the following embodiments. In the following examples, the experimental methods used are conventional methods unless otherwise specified. In the following examples, the materials, reagents, etc. used are commercially available unless otherwise specified.

[0039] Preparation of Pickering emulsifier silica nanonet in example 1

[0040] Dissolve 0.5 g, 1.0 g, 1.5 g, 2.0 g, 2.5 g, 3.0 g of cetyltrimethylammonium chloride into 100 mL of water respectively and mix well. Adjust the pH of the above solution to 10 with 25% ammonia water and place the solution in a 50°C water bath. Add a mixed solution of 20 g of n-decane with 4.0 g of tetraethyl orthosilicate into the above aqueous solution, homogenize and emulsify at a speed of 10,000 rpm for 10 min at 60°C and react for 18 h at a constant temperature. Cool the reaction system to room temperature, filter, wash, dry and crush to obtain the Pickering emulsifier silica nanonet. As shown in the scanning electron micrograph of Figure 1 The Pickering emulsifier silica nanonet has a typical two-dimensional network structure. When the amount of cetyltrimethylammonium chloride added is 0.5 g, 1.0 g, 1.5 g, 2.0 g, 2.5 g, 3.0 g, the average diameter of the mesh of the Pickering emulsifier silica nanonet is 7 nm, 10 nm, 16 nm, 22 nm, 26 nm and 24 nm. When the average diameter of the mesh is 26 nm, the silica nanonet has the largest specific surface area, which is conducive to the formation of stable Pickering emulsion.

[0041] Example 2 Pickering emulsifier silica nanonet catalytic degradation of polyethylene terephthalate

[0042] Wash the waste PET bottle, crush it with a crusher for 5 min, then pass it through a 100-mesh sieve and dry the powder to constant weight to obtain the reaction raw material PET; disperse 30 mg of Pickering emulsifier silica nanonet (average mesh diameter 26 nm) and 1.5 g of phosphotungstic acid hydrate in ethylene glycol with ultrasonic waves and heat to 190°C; add 1.5 g of the reaction raw material PET to 30 g of naphthalene and heat to 190°C to dissolve the PET; mix the above ethylene glycol phase and naphthalene phase, homogenize and emulsify at a speed of 50,000 rpm for 5 min and start the emulsion to react at 190°C for 60 min; Figure 2 The micrograph of the Pickering emulsion catalytic system; filter the reacted emulsion, pour the filtrate into water, concentrate by rotary evaporation and precipitate a large amount of white needle-like crystals at 10°C overnight, filter the crystals and dry to constant weight to obtain the product BHET. The conversion rate of PET is 100% and the yield of BHET is 90%. Higher reaction temperature is conducive to the alcoholysis reaction of PET in the Pickering emulsion catalytic system.

[0043] Example 3 Pickering emulsifier silica nanonet catalytic degradation of polyethylene terephthalate

[0044] The waste PET bottle is washed, crushed by a crusher for 5 minutes, and then sieved through a 100-mesh sieve. The powder is dried to constant weight to obtain the reaction raw material PET. 30 mg of Pickering emulsifier silica nanonet (average mesh diameter 26 nm) and 2.5 g of sodium carbonate are dispersed into ethylene glycol by ultrasonic waves and heated to 180°C. 1.5 g of the reaction raw material PET is added into 30 g of biphenyl and heated to 180°C to dissolve the PET. The above ethylene glycol phase and biphenyl phase are mixed and homogenously emulsified at a homogenization speed of 40,000 rpm for 5 minutes. The emulsion is started to react at 180°C for 30 minutes. The reacted emulsion is filtered, and the filtrate is poured into water. After being concentrated by rotary evaporation, a large amount of white needle-shaped crystals is precipitated at 8°C overnight. The crystals are filtered and dried to constant weight to obtain the product BHET. Figure 3 The infrared spectrum of the product BHET is shown in Figure 1, Figure 4 The nuclear magnetic spectrum of the product BHET is shown in Figure 2, Figure 5 The mass spectrum of the product BHET is shown in Figure 3; the conversion rate of PET is 100%, and the yield of BHET is 85%. The reaction temperature has a great influence on the PET alcoholysis reaction in the Pickering emulsion catalytic system. High reaction temperature is beneficial to the alcoholysis reaction of PET.

[0045] Example 4 Pickering Emulsifier Silica Nanonet Catalytic Degradation of Polyethylene Terephthalate

[0046] The waste PET bottle is washed, crushed by a crusher for 5 minutes, and then sieved through a 100-mesh sieve. The powder is dried to constant weight to obtain the reaction raw material PET. 30 mg of Pickering emulsifier silica nanonet (average mesh diameter 26 nm) and 2.5 g of urea are dispersed into ethylene glycol by ultrasonic waves and heated to 160°C. 1.5 g of the reaction raw material PET is added into 30 g of naphthalene and heated to 160°C to dissolve the PET. The above ethylene glycol phase and naphthalene phase are mixed and homogenously emulsified at a homogenization speed of 30,000 rpm for 5 minutes. The emulsion is started to react at 170°C for 20 minutes. The reacted emulsion is filtered, and the filtrate is poured into water. After being concentrated by rotary evaporation, a large amount of white needle-shaped crystals is precipitated at 5°C overnight. The crystals are filtered and dried to constant weight to obtain the product BHET. Figure 6 The yield of the product BHET, the conversion rate of PET is 98%, and the yield of BHET is 79%.

[0047] Example 5 Pickering Emulsifier Silica Nanonet Catalytic Degradation of Polyethylene Terephthalate

[0048] The waste PET bottle was washed and crushed for 5 minutes by a crusher, then sieved through a 100-mesh screen, and the powder was dried to constant weight to obtain the reaction raw material PET; 70 mg of Pickering emulsifier silica nanonet (average mesh diameter 26 nm) and 2.0 g of cobalt acetate were dispersed into ethylene glycol by ultrasonic waves, and heated to 170°C; 1.5 g of the reaction raw material PET was added into 30 g of naphthalene, and heated to 170°C to dissolve the PET; the above-mentioned ethylene glycol phase and naphthalene phase were mixed and homogenously emulsified, the homogenization speed was 20,000 rpm, the emulsification time was 5 minutes, and the emulsion was started to react at 170°C for 80 minutes; the reacted emulsion was filtered, the filtrate was poured into water, concentrated by rotary evaporation, and left overnight at 3°C to precipitate a large amount of white needle-shaped crystals, which were filtered and dried to constant weight to obtain the product BHET. Figure 7 The conversion rate of PET was 100%, and the yield of BHET was 91%. The addition amount of the Pickering emulsifier silica nanonet had a great influence on the PET alcoholysis reaction in the Pickering emulsion catalytic system, and a high nanonet addition amount was beneficial to the alcoholysis reaction of PET.

[0049] Example 6 Pickering Emulsifier Silica Nanonet Catalytic Degradation of Polyethylene Terephthalate

[0050] The waste PET bottle was washed and crushed for 5 minutes by a crusher, then sieved through a 100-mesh screen, and the powder was dried to constant weight to obtain the reaction raw material PET; 70 mg of Pickering emulsifier silica nanonet (average mesh diameter 26 nm) and 2.0 g of cobalt acetate were dispersed into ethylene glycol by ultrasonic waves, and heated to 170°C; 1.5 g of the reaction raw material PET was added into 30 g of naphthalene, and heated to 170°C to dissolve the PET; the above-mentioned ethylene glycol phase and naphthalene phase were mixed and homogenously emulsified, the homogenization speed was 20,000 rpm, the emulsification time was 5 minutes, and the emulsion was started to react at 170°C for 80 minutes; the reacted emulsion was filtered, the filtrate was poured into water, concentrated by rotary evaporation, and left overnight at 3°C to precipitate a large amount of white needle-shaped crystals, which were filtered and dried to constant weight to obtain the product BHET. Figure 8 The conversion rate of PET was 100%, and the yield of BHET was 91%. The addition amount of the Pickering emulsifier silica nanonet had a great influence on the PET alcoholysis reaction in the Pickering emulsion catalytic system, and a high nanonet addition amount was beneficial to the alcoholysis reaction of PET.

[0051] Example 6 Pickering Emulsifier Silica Nanonet Catalytic Degradation of Polyethylene Terephthalate

[0052] The waste PET bottle was washed and crushed for 5 minutes by a crusher, then sieved through a 100-mesh screen, and the powder was dried to constant weight to obtain the reaction raw material PET; 70 mg of Pickering emulsifier silica nanonet (average mesh diameter 26 nm) and 1.5 g of zinc acetate were dispersed in ethylene glycol by ultrasonic waves, and heated to 170°C; 1.5 g of the reaction raw material PET was added to 30 g of naphthalene, and heated to 170°C to dissolve the PET; the above-mentioned ethylene glycol phase and naphthalene phase were mixed and homogenously emulsified, the homogenization speed was 5000 rpm, the emulsification time was 5 min, and the emulsion was started to react at 170°C for 10 min; the reacted emulsion was filtered, the filtrate was poured into water, concentrated by rotary evaporation, and left overnight at 2°C to precipitate a large amount of white needle-shaped crystals; the crystals were filtered and dried to constant weight to obtain the product BHET. The conversion rate of PET was 100%, and the yield of BHET was 91%. The reaction time has limited effect on the PET alcoholysis reaction in the Pickering emulsion catalytic system, and the reaction time of 5 min to 10 min is beneficial to the alcoholysis reaction of PET.

Claims

1. The application of a Pickering emulsifier silica nanomesh in the degradation of polyethylene terephthalate, characterized in that, The method for degrading polyethylene terephthalate using Pickering emulsifier and silica nanonet is as follows: (1) Pulverize, sieve, and dry polyethylene terephthalate to constant weight; (2) The Pickering emulsifier silica nanonet and catalyst were dispersed in ethylene glycol by ultrasonication and heated to 150 ℃ ~ 190 ℃; (3) Add polyethylene terephthalate to the oil phase and heat to the temperature described in step (2) to dissolve the polyethylene terephthalate; (4) Mix the ethylene glycol phase obtained in step (2) and the oil phase obtained in step (3), and stir rapidly to form an emulsion. The emulsion is reacted at the same temperature as described in step (3) for a period of time. (5) Filter the emulsion obtained in step (4), pour the filtrate into water, concentrate by rotary evaporation, and then leave it at low temperature overnight to precipitate a large amount of white needle-like crystals. Filter the crystals and dry them to constant weight to obtain the product diethyl terephthalate. The method for preparing the Pickering emulsifier silica nanonet includes the following steps: ① Dissolve hexadecyltrimethylammonium chloride in water, mix well, and adjust the pH to 10; ② Place a hexadecyltrimethylammonium chloride solution in a water bath, add a decane solution of tetraethyl orthosilicate, homogenize and emulsify, and then react. The reaction is carried out at a constant temperature of 60 °C for 18 h. After cooling, filtration, washing, drying, and pulverizing, Pickering emulsifier silica nanonets are obtained.

2. The application according to claim 1, characterized in that, In step ① of the method for preparing silica nanonets with Pickering emulsifier, adjusting the pH to 10 is done using 25% concentrated ammonia.

3. The application according to claim 1, characterized in that, In step ② of the method for preparing the Pickering emulsifier silica nanonet, the water bath temperature is 50 ℃.

4. The application according to claim 1, characterized in that, In step ② of the method for preparing the silica nanonet using Pickering emulsifier, the homogenization speed of the homogenization emulsification is 10,000 rpm and the time is 10 min.

5. The application according to claim 1, characterized in that, In step (2) of the method for degrading polyethylene terephthalate using Pickering emulsifier silica nanonet, the catalyst is one or more of zinc acetate, zinc nitrate, zinc sulfate, manganese acetate, cobalt acetate, sodium carbonate, urea, phosphotungstic acid hydrate, cobalt quantum dots, zinc acetate ionic liquid, and zinc acetate choline.

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