Method for recovering siloxane monomer from waste silicone rubber

Abstract

The invention provides a method for recovering a siloxane monomer from waste silicone rubber, the waste silicone rubber is subjected to a high-temperature reflux depolymerization reaction in a solvent under the action of a catalyst CaO / ZnFe2O4 to obtain the siloxane monomer, and the solvent comprises hexane, methanol and ethylenediamine. Through the combined action of the catalyst and the solvent, the recovery rate of the siloxane monomer in the waste silicone rubber can be obviously improved. According to the recovery method, recovery can be completed within 6 h, the recovery rate is high, the recovery rate of the siloxane monomers is 80% or above, and the recovery rate of the filler is 90% or above.

Description

Technical Field

[0001] The present application relates to the technical field of rubber recycling, and in particular to a method for recycling siloxane monomers from waste silicone rubber. Background Art

[0002] Composite insulators are widely used in the external insulation of power transmission lines due to their excellent anti-pollution flashover performance. The material of the silicone rubber composite insulator shed sheath is high temperature vulcanized silicone rubber, which is a dimethylsiloxane-based elastomer that is initiated by organic peroxide, mixed with reinforcing fillers and vulcanizers, and vulcanized under heat and pressure. Since the silicone rubber part of the insulator is directly exposed to the atmosphere, it is affected by environmental factors such as temperature, pollution, humidity, irradiation, microorganisms, and multi-factor interaction coupling effects of electrical phenomena such as partial discharge and high field strength during operation. After long-term use, main chain depolymerization and side chain oxidation occur; from a macroscopic point of view, it manifests as fading, cracking, powdering, hardening, and reduced hydrophobicity. So far, more than 4 million insulators have been in operation for more than 10 years and have entered the middle and late stages of their life cycle. Therefore, how to recycle waste silicone rubber will become an inevitable problem. Since silicone rubber is relatively stable and extremely difficult to decompose under natural conditions, it must be processed first if it is to be recycled. At present, there are three main methods for recycling waste high-temperature vulcanized silicone rubber: physical crushing, chemical depolymerization and fixed-value pyrolysis. The physical crushing method is to embrittle the block or granular waste rubber at ultra-low temperature or room temperature, and then mechanically crush it. Ultra-low temperature crushing can produce fine powder with a particle size of 75-355μm, but the production cost and operating cost are correspondingly high; the room temperature crushing method has a simple process and low energy consumption, but the particle size of the obtained powder is larger, between 150-830μm. The chemical depolymerization method is divided into acid catalysis and base catalysis. The acid catalysis method can depolymerize polydimethylsiloxane with a high degree of polymerization into slurry at room temperature. The commonly used catalyst is sulfuric acid, because sulfuric acid can dissolve siloxane and destroy the -Si-O-Si- bond at the same time. When sulfuric acid is used as a silicone rubber cracking catalyst, the catalytic activity decreases with the decrease of sulfuric acid concentration, but high concentration sulfuric acid will cause severe corrosion of the equipment and a high substitution rate. At the same time, the acid-catalyzed cracking method has a large amount of acidic waste liquid, which will lead to secondary pollution problems and increase the cost of comprehensive utilization. Alkali is a catalyst for the polymerization, rearrangement and equilibrium of organosiloxanes. The base-catalyzed cracking method has a high cracking efficiency and less equipment corrosion, but the catalyst consumption is large. It takes 700-750 kg of KOH to produce 1 ton of crude dimethyl carbonate. The fixed-value pyrolysis method is to convert waste silicone rubber into rubber compounds that can be reprocessed and vulcanized through moderate depolymerization reactions, or depolymerize into cyclic siloxane intermediates or even siloxane monomers. Siloxane has a repeated -Si-O- as the main chain of the molecular chain; because the bond energy of the Si-O bond is higher than that of the CC bond, silicone rubber has better high temperature resistance than other general-purpose rubbers. The pyrolysis process is complex and energy-intensive, and the effective recovery portion only accounts for about one-third of the total pyrolysis treatment, which greatly increases the cracking cost.

[0003] At present, the great difficulty in degrading retired silicone rubber into monomers and recycling it is how to remove the filler from the rubber. Since there is a strong interaction between the filler and the PDMS chain, which hinders the separation of the filler and the PDMS chain, it is not so easy to find an effective solvent that also promotes depolymerization. At the same time, there is no catalyst that can be a good catalyst to achieve efficient, pollution-free and low-energy monomer recovery; at the same time, the catalyst and the filler cannot be separated well.

[0004] In view of this, this application is filed. Summary of the invention

[0005] The purpose of the present application is to overcome the above-mentioned existing defects and provide a method for efficiently and quickly separating and recovering siloxane monomers from silicone rubber.

[0006] To achieve the above objectives, this application adopts the following technical solutions:

[0007] The present application provides a method for recovering siloxane monomers from waste silicone rubber, comprising the following steps:

[0008] S1: crushing the waste silicone rubber, dissolving it in a solvent until the waste silicone rubber is completely dissolved to obtain a suspension, and filtering to obtain a filtrate and a filter residue; the solvent includes hexane, methanol and ethylenediamine;

[0009] S2: Add the catalyst CaO / ZnFe to the filtrate obtained in step S1. 2 O 4 , then heating and distilling to carry out depolymerization reaction, condensing and collecting the depolymerization product to obtain siloxane monomer;

[0010] S3: The filter residue obtained in step S1 is washed and dried to obtain filler.

[0011] As an embodiment of the present application, the volume ratio of hexane, methanol and ethylenediamine in the solvent is 1:(2-3):(3-5).

[0012] As an implementation scheme of the present application, the ratio of the waste silicone rubber to the solvent is (100-150) g:100 mL.

[0013] As an embodiment of the present application, the catalyst CaO / ZnFe 2 O 4 The mass of CaO in the waste silicone rubber is 10-15% of the mass of the waste silicone rubber.

[0014] As an embodiment of the present application, the catalyst CaO / ZnFe 2 O 4 Among them, CaO and ZnFe 2 O 4The mass ratio is (0.3~0.5):1.

[0015] As an embodiment of the present application, the distillation temperature in step S2 is 170-200°C.

[0016] As an implementation scheme of the present application, the heating rate in step S2 is 5 to 10° C. / min.

[0017] As an embodiment of the present application, the depolymerization reaction time in step S2 is 2 to 6 hours.

[0018] As an implementation scheme of the present application, the cleaning in step S3 is to use ethanol and water alternately for cleaning.

[0019] As an embodiment of the present application, the drying temperature in step S3 is 40-60°C.

[0020] Compared with the prior art, the beneficial effects of this application are:

[0021] The present invention uses a specific mixed solvent (hexane, methanol and ethylenediamine) and a composite oxide solid base catalyst (CaO / ZnFe 2 O 4 ) to depolymerize waste silicone rubber and recover siloxane monomers and inorganic fillers. The depolymerization speed is fast, the solvent composition is simple, and the recovery rate is high, thus achieving high-value utilization of waste silicone rubber.

[0022] When the method of the present application is used to recycle waste silicone rubber, the recovery rate of siloxane monomers is above 80%, and the recovery rate of fillers is above 90%. DETAILED DESCRIPTION

[0023] To better illustrate the purpose, technical solutions and advantages of the present application, the present application will be further described below in conjunction with specific examples, but the examples do not limit the present application in any form. Unless otherwise specified, the reagents, methods and equipment used in the present application are conventional reagents, methods and equipment in the art. Unless otherwise specified, the reagents and materials used in the present application are commercially available.

[0024] In the present application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions containing the listed features.

[0025] In this application, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are deemed to be continuous and include the minimum and maximum values ​​of the range, as well as each value between such minimum and maximum values. Further, when a range refers to an integer, each integer between the minimum and maximum values ​​of the range is included. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be merged. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all subranges included therein.

[0026] The reagents or instruments used in this application without indicating the manufacturer are all conventional products that can be obtained through commercial purchase.

[0027] The present application provides a method for recovering siloxane monomers from waste silicone rubber, comprising the following steps:

[0028] S1: crushing the waste silicone rubber, dissolving it in a solvent until the waste silicone rubber is completely dissolved to obtain a suspension, and filtering to obtain a filtrate and a filter residue; the solvent includes hexane, methanol and ethylenediamine;

[0029] S2: Add the catalyst CaO / ZnFe to the filtrate obtained in step S1. 2 O 4 , then heating and distilling to carry out depolymerization reaction, condensing and collecting the depolymerization product to obtain siloxane monomer;

[0030] S3: The filter residue obtained in step S1 is washed and dried to obtain filler.

[0031] The present invention adopts a specific mixed solvent and a composite oxide solid base catalyst (CaO / ZnFe 2 O 4 ) to depolymerize waste silicone rubber and recover siloxane monomers and inorganic fillers. The depolymerization speed is fast, the solvent composition is simple, and the recovery rate is high, thus achieving high-value utilization of waste silicone rubber.

[0032] In some embodiments of the present application, the volume ratio of hexane, methanol and ethylenediamine in the solvent is 1:(2-3):(3-5). The usage ratio of hexane, methanol and ethylenediamine within this range can better promote catalyst activation and improve depolymerization efficiency and recovery rate.

[0033] In some embodiments of the present application, the ratio of the waste silicone rubber to the solvent is (100-150) g: 100 mL. When the amount of waste silicone rubber added is within this range, it can be dissolved and dispersed evenly in the solvent, thereby improving the depolymerization efficiency.

[0034] In some embodiments of the present application, the catalyst CaO / ZnFe 2 O 4The mass of CaO is 10-15% of the mass of waste silicone rubber.

[0035] In some embodiments of the present application, the catalyst CaO / ZnFe 2 O 4 Among them, CaO and ZnFe 2 O 4 The mass ratio is (0.3-0.5): 1. The catalyst belongs to a composite oxide solid base catalyst, CaO is the catalytic active component, ZnFe 2 O 4 As carrier, CaO and ZnFe 2 O 4 The mass ratio of CaO to ZnFe is within the above-mentioned suitable range. 2 O 4 The catalyst is evenly dispersed on the surface and more active sites are exposed, which can give full play to the catalytic activity and improve the degradation efficiency and the recovery rate of the monomer.

[0036] In some embodiments of the present application, the distillation temperature in step S2 is 170-200°C.

[0037] In some embodiments of the present application, the heating rate in step S2 is 5-10° C. / min.

[0038] In some embodiments of the present application, the depolymerization reaction time in step S2 is 2 to 6 hours.

[0039] In some embodiments of the present application, the cleaning in step S3 is washing using ethanol and water alternately.

[0040] In some embodiments of the present application, the drying temperature in step S3 is 40-60°C.

[0041] It should be noted that in this application, the catalyst CaO / ZnFe 2 O 4 It is prepared in-house by a method comprising the following steps:

[0042] S1: Raw material preparation

[0043] ZnFe 2 O 4 Calcinate in air atmosphere at 450-600°C for 4-6 hours; dissolve the CaO precursor in water to form an aqueous solution;

[0044] S2: ZnFe after calcination in step S1 2 O 4 Adding into the aqueous solution containing CaO precursor, dispersing for 12 to 15 hours to obtain a dispersion;

[0045] S3: The precipitate collected after centrifugation of the dispersion obtained in step S2 is washed and dried, and then calcined at 800-1000° C. for 24-48 hours in an air atmosphere to obtain the catalyst CaO / ZnFe 2 O 4 .

[0046] In some embodiments of the present application, in step S1, calcining ZnFe 2 O 4 The heating rate is 5-8℃ / min.

[0047] In some embodiments of the present application, the precursor of CaO is an organic calcium salt, which includes but is not limited to calcium ethoxide (chemical formula is Ca(CH 3 OH) 2 ).

[0048] In some embodiments of the present application, in the aqueous solution described in step S1, the concentration of the CaO precursor is 15-25 wt %.

[0049] In some embodiments of the present application, the dispersing operation in step S2 is stirring, and the stirring rate is 600-800 r / min.

[0050] In some embodiments of the present application, the heating rate of the calcination in step S3 is 5-8° C. / min.

[0051] In some embodiments of the present application, the cleaning step in step S3 is: washing with water and ethanol alternately at least 3 times.

[0052] In some embodiments of the present application, the drying in step S3 is drying at 60-80° C. to constant weight.

[0053] The following are specific embodiments of the present application.

[0054] In this application, the composition of the waste silicone rubber used is: 40wt% PDMS glue (polydimethylsiloxane), 9wt% SiO 2 , 51wt% alumina.

[0055] Example 1

[0056] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, comprising the following steps:

[0057] S1: 100 g of waste silicone rubber was crushed and added into 100 mL of solvent (hexane, methanol and ethylenediamine in a volume ratio of 1:2:3), and stirred until the waste silicone rubber was completely dissolved to obtain a suspension, and filtered to obtain a filtrate and a filter residue;

[0058] S2: Add the catalyst CaO / ZnFe to the filtrate obtained in step S1. 2 O 4 (CaO and ZnFe 2 O 4 The mass ratio of the catalyst is 0.36:1), the mass of CaO in the catalyst accounts for 10% of the mass of the waste silicone rubber; then the temperature is raised to 170°C at a rate of 5°C / min and distilled for 3h to obtain a depolymerization product, and the depolymerization product is condensed and collected to obtain a siloxane monomer;

[0059] S3: The filter residue obtained in step S1 is washed three times with ethanol and water alternately, and dried in a drying oven at 60° C. to obtain a filler;

[0060] In this embodiment, the catalyst CaO / ZnFe 2 O 4 For homemade, the preparation method includes the following steps:

[0061] (1) Weigh 30g of ZnFe 2 O 4 Place it in a magnetic boat and heat it to 500°C at a rate of 5°C / min in air atmosphere and keep it for 5h;

[0062] (2) Weigh 20 g of Ca(CH 3 OH) 2 Dissolve in 100 mL of deionized water and stir at a stirring rate of 800 rad / min for 120 min to fully dissolve;

[0063] (3) 10 g of calcined ZnFe 2 O 4 Addition of Ca(CH 3 OH) 2 The solution was stirred at 25 °C at a stirring rate of 800 rad / min for 12 h;

[0064] (4) centrifuging the solution and collecting the precipitate;

[0065] (5) After repeated washing with deionized water and ethanol for 3 times, it was dried at 80 °C for 8 h;

[0066] (6) The dried solid was placed in a magnetic boat and heated to 800 °C at a rate of 5 °C / min in air atmosphere and maintained for 24 h.

[0067] Example 2

[0068] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in the solvent, the volume ratio of hexane, methanol and ethylenediamine is 1:2:5.

[0069] Example 3

[0070] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in the solvent, the volume ratio of hexane, methanol and ethylenediamine is 1:3:4.

[0071] Example 4

[0072] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that in the solvent, the volume ratio of hexane, methanol and ethylenediamine is 1:1:1.

[0073] Example 5

[0074] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in step S1, the amount of waste silicone rubber added is 130 g.

[0075] Example 6

[0076] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in step S1, the amount of waste silicone rubber added is 150 g.

[0077] Example 7

[0078] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that the catalyst CaO / ZnFe 2 O 4 The mass of CaO in the waste silicone rubber is 13% of the mass of the waste silicone rubber.

[0079] Example 8

[0080] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that the catalyst CaO / ZnFe 2 O 4 The mass of CaO in the waste silicone rubber is 15% of the mass of the waste silicone rubber.

[0081] Example 9

[0082] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that the heating rate in step S2 is 7° C. / min.

[0083] Example 10

[0084] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that the heating rate in step S2 is 10° C. / min.

[0085] Embodiment 11

[0086] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Embodiment 1. The difference from Embodiment 1 is that in step S2, distillation is performed at 170°C for 6 hours.

[0087] Example 12

[0088] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Embodiment 1. The difference from Embodiment 1 is that in step S2, distillation is performed at 200°C for 3 hours.

[0089] Example 13

[0090] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that: CaO and ZnFe 2 O 4 The mass ratio is 0.5:1.

[0091] Embodiment 14

[0092] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that: CaO and ZnFe 2 O 4 The mass ratio is 0.3:1.

[0093] Embodiment 15

[0094] This embodiment provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that the catalyst CaO / ZnFe 2 O 4 In the preparation process of 3 OH) 2 Replaced by CaCO 3 At the same time, adaptive adjustment of CaCO 3 The dosage is to ensure that the CaO and ZnFe 2 O 4 The mass ratio remains unchanged.

[0095] Comparative Example 1

[0096] This comparative example provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that the catalyst is replaced with CaO / MgO. The preparation method of the catalyst includes the following steps:

[0097] (1) Weigh 30 g of MgO and place it in a magnetic boat. Raise the temperature to 500 °C at a rate of 5 °C / min in air and keep it for 5 h.

[0098] (2) Weigh 20 g of CaCO 3 Dissolve in 100 mL of deionized water and stir at a stirring rate of 800 rad / min for 120 min to fully dissolve;

[0099] (3) Add 10 g of calcined MgO to Ca(CH 3 OH) 2 The solution was stirred at room temperature at a stirring rate of 800 rad / min for 12 h;

[0100] (4) centrifuging the solution and collecting the precipitate;

[0101] (5) washing with deionized water and ethanol repeatedly for three times, and drying the obtained solid at 80 °C for 8 h;

[0102] (6) The dried solid was placed in a magnetic boat and heated to 800 °C at a rate of 5 °C / min in air atmosphere and maintained for 24 h.

[0103] Comparative Example 2

[0104] This comparative example provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out by referring to the steps of Example 1. The difference from Example 1 is that the catalyst is replaced by MgO / ZnFe 2 O 4 .

[0105] Comparative Example 3

[0106] This comparative example provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in the solvent described in step S1, the volume ratio of hexane to methanol is 1:2, that is, ethylenediamine is not added.

[0107] Comparative Example 4

[0108] This comparative example provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in the solvent described in step S1, the volume ratio of hexane to ethylenediamine is 1:3, that is, methanol is not added.

[0109] Comparative Example 5

[0110] This comparative example provides a method for recovering siloxane monomers from waste silicone rubber, which is carried out with reference to the steps of Example 1. The difference from Example 1 is that in the solvent described in step S1, the volume ratio of methanol to ethylenediamine is 2:3, that is, hexane is not added.

[0111] Performance Testing

[0112] The recycling performance of the waste silicone rubber of the above embodiments and comparative examples was tested:

[0113] 1. Recovery rate of siloxane monomer (%) = m1 / (m×40%)×100%, wherein m represents the amount of waste silicone rubber added in step S1, and m1 represents the mass of siloxane monomer collected in step S2, which is measured using a gas chromatograph;

[0114] Gas chromatography test steps: using commercially available cyclosiloxane D3 (hexamethylcyclotrisiloxane), D4 (octamethylcyclotetrasiloxane), D5 (decamethylcyclopentasiloxane), and D6 (dodecamethylcyclohexasiloxane) as standard products, gas chromatography analysis of monomer composition was performed on GC, and the chromatographic conditions were: solvent acetone; sample concentration: 0.05 g / mL; temperature programming: 50-320°C; heating rate: 10°C / min; injector and detector temperature: 320°C;

[0115] 2. Recovery rate of filler (%) = m2 / (m×60%)×100%, where m represents the amount of waste silicone rubber added in step S1, and m2 represents the mass of the filler obtained in step S3;

[0116] The specific test results are shown in Table 1.

[0117] Table 1

[0118]

[0119]

[0120] From the above results we can see that:

[0121] The method of the present application can be used to recycle waste silicone rubber, which can significantly improve the recycling efficiency. The recycling can be completed within 6 hours with a high recovery rate. The recovery rate of siloxane monomers is above 80%, and the recovery rate of fillers is above 90%.

[0122] The recovery results of the comparative example further prove that the recovery rate of siloxane monomers in waste silicone rubber can be significantly improved through the combined action of the catalyst and the solvent.

[0123] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present application rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to the preferred embodiments, ordinary technicians in this field should understand that the technical solution of the present application can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present application.

Claims

1. A method for recovering siloxane monomers from waste silicone rubber, characterized in that: The steps include: S1: crushing the waste silicone rubber, dissolving it in a solvent until the waste silicone rubber is completely dissolved to obtain a suspension, and filtering to obtain a filtrate and a filter residue; the solvent includes hexane, methanol and ethylenediamine; S2: adding a catalyst CaO / ZnFe2O4 to the filtrate obtained in step S1, then heating and distilling to carry out a depolymerization reaction, condensing and collecting the depolymerization product to obtain a siloxane monomer; S3: The filter residue obtained in step S1 is washed and dried to obtain filler.

2. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The volume ratio of hexane, methanol and ethylenediamine in the solvent is 1:(2-3):(3-5).

3. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The ratio of the waste silicone rubber to the solvent is (100-150) g:100 mL.

4. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The mass of CaO in the catalyst CaO / ZnFe2O4 is 10-15% of the mass of the waste silicone rubber.

5. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: In the catalyst CaO / ZnFe2O4, the mass ratio of CaO to ZnFe2O4 is (0.3-0.5):

1.

6. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The distillation temperature in step S2 is 170-200°C.

7. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The heating rate in step S2 is 5-10°C / min.

8. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The depolymerization reaction time in step S2 is 2 to 6 hours.

9. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The cleaning in step S3 is performed by alternately washing with ethanol and water.

10. The method for recovering siloxane monomers from waste silicone rubber according to claim 1, characterized in that: The drying temperature in step S3 is 40-60°C.

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