A method for preparing high-purity octamethylcyclotetrasiloxane

Abstract

The invention discloses a method for preparing high-purity octamethylcyclotetrasiloxane, and belongs to the technical field of octamethylcyclotetrasiloxane purification. The invention treats crude octamethylcyclotetrasiloxane by combining distillation-adsorption-re-distillation, thereby overcoming the problem that trace impurities are difficult to be removed by a single distillation method. The distillation-adsorption-re-distillation method is combined for operation, and the advantages of each method are brought into play, and impurities such as hexamethylcyclotrisiloxane and decamethylcyclopentasiloxane with similar boiling points are reduced, so that the octamethylcyclotetrasiloxane product reaches a very high purity. The invention adopts an adsorption treatment method to adsorb and separate phosphorus-containing and boron impurities and metal impurities in alkane residues in the octamethylcyclotetrasiloxane, thereby obtaining electronic-grade octamethylcyclotetrasiloxane, and the product purity can reach more than 99.99%.

Description

Technical Field

[0001] The invention relates to the technical field of octamethylcyclotetrasiloxane purification, and in particular to a method for preparing high-purity octamethylcyclotetrasiloxane. Background Art

[0002] Octamethylcyclotetrasiloxane (D4 for short) is an important organosilicon compound, widely used in cosmetics, personal care products, coatings, and industrial silicone rubber manufacturing. D4 has good chemical stability, thermal stability, and biocompatibility, and is an important intermediate for synthesizing more complex siloxane compounds. With the continuous expansion of downstream application fields, the requirements for D4 product quality and purity are also increasing. High-purity D4 can not only improve the performance of end products, but also reduce subsequent production costs.

[0003] Industrial octamethylcyclotetrasiloxane (D4) is mainly obtained by hydrolysis of dimethyldichlorosilane (Me2). At present, the organic silicon raw materials used in integrated circuit manufacturing must reach electronic grade, and the content of general commercial octamethylcyclotetrasiloxane after ordinary purification is only 99%. Industrial-grade octamethylcyclotetrasiloxane contains metals such as iron, magnesium, and aluminum and non-metallic ions such as boron and phosphorus. However, metals such as iron, magnesium, and aluminum and non-metallic ions such as boron and phosphorus cannot be removed by distillation, which will have a serious impact on the manufacture of integrated circuit materials. Therefore, it is necessary to provide a preparation method of high-purity octamethylcyclotetrasiloxane.

[0004] Chinese patent document CN103788124A provides a method for purifying electronic grade octamethylcyclotetrasiloxane. The patent uses a highly efficient special metal complexing ligand to complex a trace amount of heavy metal ions in a solution to generate non-volatile high-boiling point compounds, thereby fundamentally solving the problem of purifying heavy metal ions. However, the metal complexing ligand used in the patent is expensive, and the process is difficult to achieve mass production due to the high cost. Summary of the invention

[0005] The main purpose of the invention is to provide a method for preparing high-purity octamethylcyclotetrasiloxane.

[0006] To achieve the above object, the present invention provides a method for preparing high-purity octamethylcyclotetrasiloxane, comprising the following steps:

[0007] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane into the first distillation tower, perform distillation and light removal treatment to remove low boiling point impurities, and then draw out the light-removed product from the bottom of the tower;

[0008] Preferably, the temperature of the bottom of the first distillation tower is 180-185°C, the top temperature is 176-180°C, and the bottom pressure is 0.1MPa-0.2MPa; the theoretical plate number of the first distillation tower is 70-80; in this step, some low-boiling substances, such as hexamethylcyclotrisiloxane and unreacted dimethyldichlorosilane, can be removed by distillation and light removal treatment.

[0009] S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, and then the de-heavy product is drawn out from the top of the tower;

[0010] Preferably, the temperature of the bottom of the second distillation tower is 205-210°C, the top temperature is 185-190°C, the bottom pressure is 0.08MPa-0.1MPa, and the number of theoretical plates of the second distillation tower is 80-90. In this step, some high-boiling substances, such as decamethylcyclopentasiloxane and linear siloxane oligomers such as dimers and trimers generated during the reaction, can be removed by distillation and de-weighting treatment.

[0011] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent to adsorb impurities;

[0012] Preferably, the preparation method of the adsorbent is as follows:

[0013] (1) adding activated carbon to a potassium permanganate aqueous solution and soaking it, filtering it after the soaking is completed, collecting the solid, washing it until the filtrate is neutral, and drying it to obtain pretreated activated carbon;

[0014] (2) dispersing the pretreated activated carbon in anhydrous ethanol, adding epichlorohydrin and ethylenediamine, heating to react, filtering, collecting the solid, washing and drying, and then dispersing it in chloroform, adding triethylamine, and adding itaconyl chloride dropwise in an ice bath. After the addition is completed, heating to react, after the reaction is completed, filtering and collecting the solid, washing and drying the solid to obtain modified activated carbon;

[0015] (3) Dispersing the modified activated carbon in water, adding 1-vinyl-3-ethylimidazolium bromide, pyridine mercapto, and benzoyl peroxide, heating for reaction, filtering after the reaction is completed, collecting the solid, washing, and drying to obtain the adsorbent.

[0016] Further preferably, the concentration of the potassium permanganate aqueous solution in step (1) is 10-30 wt %, and the soaking time is 2-4 h.

[0017] Further preferably, in the step (2), the mass ratio of pretreated activated carbon, epichlorohydrin, ethylenediamine and itaconyl chloride is 15-25:10-15:5-8:30-50.

[0018] Further preferably, in the step (3), the mass ratio of modified activated carbon, 1-vinyl-3-ethylimidazolium bromide and pyridine mercapto is 5-10:1-2:1-1.5.

[0019] S4, distillation and de-lightening: adding the product after the adsorption to the third distillation tower for de-lightening, and performing distillation and de-lightening treatment. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0020] Preferably, the temperature of the bottom of the third distillation tower is 185-190°C, the top temperature is 180-185°C, and the bottom pressure is 0.1MPa-0.2MPa; the theoretical plate number of the third distillation tower is 50-60; in this step, the residual light components in the product can be further removed by distillation and then de-weighting treatment.

[0021] S5, distillation and re-heavy removal: the re-light-removed product is introduced into the fourth distillation tower for re-heavy removal, and the distillation and re-heavy removal product enters the finished product collection tank to obtain the high-purity octamethylcyclotetrasiloxane.

[0022] Preferably, the temperature of the bottom of the fourth distillation tower is 205-210°C, the top temperature is 185-190°C, and the bottom pressure is 0.08MPa-0.1MPa; the theoretical plate number of the fourth distillation tower is 60-70; in this step, the heavy components remaining in the product can be further removed by distillation and then de-heavy treatment, thereby ensuring the high purity of the product.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1) The method for preparing high-purity octamethylcyclotetrasiloxane provided by the present invention treats the crude octamethylcyclotetrasiloxane by combining distillation-adsorption-re-distillation, thereby overcoming the problem that trace impurities are difficult to remove by a single distillation method. The combined operation of distillation-adsorption-re-distillation method can give play to their respective advantages, reduce impurities such as hexamethylcyclotrisiloxane and decamethylcyclopentasiloxane with similar boiling points, and make the octamethylcyclotetrasiloxane product reach a very high purity. The present invention adopts an adsorption treatment method to adsorb and separate the phosphorus-containing, boron-containing impurities and metal impurities remaining in the alkane in the octamethylcyclotetrasiloxane, thereby obtaining electronic grade octamethylcyclotetrasiloxane, and the product purity can reach more than 99.99%;

[0025] 2) The adsorbent provided by the present invention uses activated carbon as an adsorption carrier. The activated carbon has a high specific surface area and porosity and is a low-cost adsorption material. However, its adsorption performance for non-metallic impurities such as phosphorus and boron and metal impurities is poor. The present invention first treats the activated carbon with potassium permanganate to increase the oxygen-containing functional groups on the surface of the activated carbon and improve its adsorption performance. Then, itaconyl chloride is grafted on its surface. Then, the ionic liquid, mercaptopyridine and the carbon-carbon double bond in the itaconyl chloride molecule undergo a reverse addition reaction to graft the ionic liquid and mercaptopyridine onto the activated carbon molecule. The pyridine group in mercaptopyridine and the imidazole group in the ionic liquid can coordinate with boron and phosphorus elements, thereby removing the boron and phosphorus elements in octamethylcyclotetrasiloxane well, thereby improving the removal effect of the activated carbon on boron and phosphorus elements. In addition, itaconyl chloride forms an amide bond with the amino activated carbon and can form a coordination bond with metal impurities, thereby improving the adsorption performance for metal ions. DETAILED DESCRIPTION

[0026] To avoid redundancy, the items used in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0027] The sources of some raw materials used in the present invention are as follows:

[0028] Activated carbon, 200 mesh, coconut shell powder charcoal, was purchased from Dongguan Huahai Carbon Industry Environmental Protection Co., Ltd.

[0029] Example 1

[0030] A method for preparing high-purity octamethylcyclotetrasiloxane comprises the following steps:

[0031] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane to the first distillation tower, carry out distillation and light removal treatment, the bottom temperature of the first distillation tower is 182°C, the top temperature is 178°C, the bottom pressure is 0.14MPa, the theoretical plate number is 75, remove low boiling point impurities and then draw out the light-removed product from the bottom of the tower;

[0032] S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, the temperature of the second distillation tower kettle is 208 ° C, the tower top temperature is 187 ° C, the tower kettle pressure is 0.09 MPa, the theoretical plate number is 86, the high boiling point impurities are removed and the de-heavy product is then drawn out from the tower top;

[0033] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent, and the temperature of the adsorption tank is 36° C., for impurity adsorption;

[0034] The preparation method of the adsorbent is as follows:

[0035] (1) 60 g of activated carbon was added to 200 mL of a 20 wt% potassium permanganate aqueous solution and soaked for 3 h. After the soaking was completed, the solid was filtered, washed until the filtrate was neutral, and dried to obtain pretreated activated carbon;

[0036] (2) Disperse 40 g of pretreated activated carbon in 200 mL of anhydrous ethanol, add 25.6 g of epichlorohydrin and 14.8 g of ethylenediamine, heat at 60 ° C for reaction for 5 h, filter, collect the solid, wash and dry, and then disperse in chloroform, add 32.5 g of triethylamine, and dropwise add 82 g of itaconyl chloride in an ice bath. After the dropwise addition is completed, heat to 35 ° C for reaction for 1 h. After the reaction is completed, filter and collect the solid, filter, collect the solid, wash and dry to obtain modified activated carbon;

[0037] (3) Dispersing 16.5 g of modified activated carbon in 200 mL of water, adding 3.2 g of 1-vinyl-3-ethylimidazolium bromide, 2.4 g of mercaptopyridine, and 0.4 g of benzoyl peroxide, heating at 60° C. for 6 h, filtering after the reaction is completed, collecting the solid, washing, and drying to obtain the adsorbent;

[0038] S4, distillation and de-lightening: the product after the adsorption is added to the third distillation tower for de-lightening, and distillation and de-lightening treatment is performed. The temperature of the bottom of the third distillation tower is 188°C, the temperature of the top of the tower is 183°C, the pressure of the bottom of the tower is 0.16MPa, and the theoretical plate number of the third distillation tower is 56. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0039] S5, distillation and re-heavy removal: the re-light product is introduced into the fourth distillation tower for re-heavy removal, and distillation and re-heavy removal treatment is performed. The temperature of the bottom of the fourth distillation tower is 208° C., the temperature of the top of the tower is 188° C., and the pressure of the bottom of the tower is 0.09 MPa; the theoretical plate number of the fourth distillation tower is 65; the product of distillation and re-heavy removal enters the finished product collection tank, and the high-purity octamethylcyclotetrasiloxane is obtained.

[0040] Example 2

[0041] A method for preparing high-purity octamethylcyclotetrasiloxane comprises the following steps:

[0042] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane to the first distillation tower, carry out distillation and light removal treatment, the bottom temperature of the first distillation tower is 180°C, the top temperature is 176°C, the bottom pressure is 0.1MPa, the theoretical plate number is 70, remove low boiling point impurities and then draw out the light-removed product from the bottom of the tower;

[0043] S2, distillation and de-heavy treatment: the product after de-heavy treatment is introduced into the second distillation tower for de-heavy treatment, the temperature of the second distillation tower kettle is 205 ° C, the tower top temperature is 185 ° C, the tower kettle pressure is 0.08 MPa, the theoretical plate number is 80, the high boiling point impurities are removed and the de-heavy product is then drawn out from the tower top;

[0044] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent, and the temperature of the adsorption tank is 36° C., for impurity adsorption;

[0045] The preparation method of the adsorbent is as follows:

[0046] (1) 60 g of activated carbon was added to 200 mL of a 10 wt% potassium permanganate aqueous solution and soaked for 2 h. After the soaking was completed, the mixture was filtered, the solid was collected, washed until the filtrate was neutral, and dried to obtain pretreated activated carbon;

[0047] (2) Disperse 30 g of pretreated activated carbon in 200 mL of anhydrous ethanol, add 20.5 g of epichlorohydrin and 10.3 g of ethylenediamine, heat at 60° C. for reaction for 5 h, filter, collect the solid, wash and dry, and then disperse in chloroform, add 30 g of triethylamine, and dropwise add 60.5 g of itaconyl chloride in an ice bath. After the dropwise addition is completed, heat to 35° C. for reaction for 1 h. After the reaction is completed, filter and collect the solid, filter, collect the solid, wash and dry to obtain modified activated carbon;

[0048] (3) Dispersing 12.4 g of modified activated carbon in 200 mL of water, adding 2.1 g of 1-vinyl-3-ethylimidazolium bromide, 2 g of mercaptopyridine, and 0.3 g of benzoyl peroxide, heating at 60° C. for 6 h, filtering after the reaction is completed, collecting the solid, washing, and drying to obtain the adsorbent;

[0049] S4, distillation and de-lightening: the product after the adsorption is added to the third distillation tower for de-lightening, and distillation and de-lightening treatment is performed. The temperature of the bottom of the third distillation tower is 185°C, the temperature of the top of the tower is 180°C, the pressure of the bottom of the tower is 0.1MPa, and the theoretical plate number of the third distillation tower is 50. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0050] S5, distillation and re-heavy removal: the re-light product is introduced into the fourth distillation tower for re-heavy removal, and distillation and re-heavy removal treatment is performed. The temperature of the bottom of the fourth distillation tower is 205° C., the temperature of the top of the tower is 185° C., and the pressure of the bottom of the tower is 0.08 MPa; the theoretical plate number of the fourth distillation tower is 60; the product of distillation and re-heavy removal enters the finished product collection tank, and the high-purity octamethylcyclotetrasiloxane is obtained.

[0051] Example 3

[0052] A method for preparing high-purity octamethylcyclotetrasiloxane comprises the following steps:

[0053] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane to the first distillation tower, carry out distillation and light removal treatment, the bottom temperature of the first distillation tower is 185°C, the top temperature is 180°C, the bottom pressure is 0.2MPa, the theoretical plate number is 80, remove low boiling point impurities and then draw out the light-removed product from the bottom of the tower;

[0054] S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, the temperature of the second distillation tower kettle is 210 ° C, the tower top temperature is 190 ° C, the tower kettle pressure is 0.1 MPa, the theoretical plate number is 90, the high boiling point impurities are removed and the de-heavy product is then drawn out from the top of the tower;

[0055] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent, and the temperature of the adsorption tank is 36° C., for impurity adsorption;

[0056] The preparation method of the adsorbent is as follows:

[0057] (1) 60 g of activated carbon was added to 200 mL of a 30 wt% potassium permanganate aqueous solution and soaked for 4 h. After the soaking was completed, the mixture was filtered, the solid was collected, washed until the filtrate was neutral, and dried to obtain pretreated activated carbon;

[0058] (2) Disperse 50 g of pretreated activated carbon in 200 mL of anhydrous ethanol, add 30 g of epichlorohydrin and 15.8 g of ethylenediamine, heat at 60 ° C for reaction for 5 h, filter, collect the solid, wash and dry, and then disperse in chloroform, add 41 g of triethylamine, and dropwise add 100 g of itaconyl chloride in an ice bath. After the dropwise addition is completed, heat to 35 ° C for reaction for 1 h. After the reaction is completed, filter and collect the solid, filter, collect the solid, wash and dry to obtain modified activated carbon;

[0059] (3) Dispersing 20 g of modified activated carbon in 200 mL of water, adding 4 g of 1-vinyl-3-ethylimidazolium bromide, 3 g of mercaptopyridine, and 0.5 g of benzoyl peroxide, heating at 60° C. for 6 h, filtering after the reaction is completed, collecting the solid, washing, and drying to obtain the adsorbent;

[0060] S4, distillation and de-lightening: the product after the adsorption is added to the third distillation tower for de-lightening, and distillation and de-lightening treatment is performed. The temperature of the bottom of the third distillation tower is 190°C, the temperature of the top of the tower is 185°C, the pressure of the bottom of the tower is 0.2MPa, and the theoretical plate number of the third distillation tower is 60. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0061] S5, distillation and re-heavy removal: the re-light product is introduced into the fourth distillation tower for re-heavy removal, and distillation and re-heavy removal treatment is performed. The temperature of the bottom of the fourth distillation tower is 210° C., the temperature of the top of the tower is 190° C., and the pressure of the bottom of the tower is 0.1 MPa; the theoretical plate number of the fourth distillation tower is 70; the product of distillation and re-heavy removal enters a finished product collection tank to obtain the high-purity octamethylcyclotetrasiloxane.

[0062] Comparative Example 1

[0063] A method for preparing high-purity octamethylcyclotetrasiloxane is similar to Example 1, except that mercaptopyridine is not added to the adsorbent, and specifically comprises the following steps:

[0064] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane to the first distillation tower, carry out distillation and light removal treatment, the bottom temperature of the first distillation tower is 182°C, the top temperature is 178°C, the bottom pressure is 0.14MPa, the theoretical plate number is 75, remove low boiling point impurities and then draw out the light-removed product from the bottom of the tower;

[0065] S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, the temperature of the second distillation tower kettle is 208 ° C, the tower top temperature is 187 ° C, the tower kettle pressure is 0.09 MPa, the theoretical plate number is 86, the high boiling point impurities are removed and the de-heavy product is then drawn out from the tower top;

[0066] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent, and the temperature of the adsorption tank is 36° C., for impurity adsorption;

[0067] The preparation method of the adsorbent is as follows:

[0068] (1) 60 g of activated carbon was added to 200 mL of a 20 wt% potassium permanganate aqueous solution and soaked for 3 h. After the soaking was completed, the solid was filtered, washed until the filtrate was neutral, and dried to obtain pretreated activated carbon;

[0069] (2) Disperse 40 g of pretreated activated carbon in 200 mL of anhydrous ethanol, add 25.6 g of epichlorohydrin and 14.8 g of ethylenediamine, heat at 60 ° C for reaction for 5 h, filter, collect the solid, wash and dry, and then disperse in chloroform, add 32.5 g of triethylamine, and dropwise add 82 g of itaconyl chloride in an ice bath. After the dropwise addition is completed, heat to 35 ° C for reaction for 1 h. After the reaction is completed, filter and collect the solid, filter, collect the solid, wash and dry to obtain modified activated carbon;

[0070] (3) Dispersing 16.5 g of modified activated carbon in 200 mL of water, adding 3.2 g of 1-vinyl-3-ethylimidazolium bromide and 0.4 g of benzoyl peroxide, heating at 60° C. for 6 h, filtering after the reaction is complete, collecting the solid, washing and drying to obtain the adsorbent;

[0071] S4, distillation and de-lightening: the product after the adsorption is added to the third distillation tower for de-lightening, and distillation and de-lightening treatment is performed. The temperature of the bottom of the third distillation tower is 188°C, the temperature of the top of the tower is 183°C, the pressure of the bottom of the tower is 0.16MPa, and the theoretical plate number of the third distillation tower is 56. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0072] S5, distillation and re-heavy removal: the re-light product is introduced into the fourth distillation tower for re-heavy removal, and distillation and re-heavy removal treatment is performed. The temperature of the bottom of the fourth distillation tower is 208° C., the temperature of the top of the tower is 188° C., and the pressure of the bottom of the tower is 0.09 MPa; the theoretical plate number of the fourth distillation tower is 65; the product of distillation and re-heavy removal enters the finished product collection tank, and the high-purity octamethylcyclotetrasiloxane is obtained.

[0073] Comparative Example 2

[0074] A method for preparing high-purity octamethylcyclotetrasiloxane is similar to Example 1, except that 1-vinyl-3-ethylimidazolium bromide is not added to the adsorbent, and specifically comprises the following steps:

[0075] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane to the first distillation tower, carry out distillation and light removal treatment, the bottom temperature of the first distillation tower is 182°C, the top temperature is 178°C, the bottom pressure is 0.14MPa, the theoretical plate number is 75, remove low boiling point impurities and then draw out the light-removed product from the bottom of the tower;

[0076] S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, the temperature of the second distillation tower kettle is 208 ° C, the tower top temperature is 187 ° C, the tower kettle pressure is 0.09 MPa, the theoretical plate number is 86, the high boiling point impurities are removed and the de-heavy product is then drawn out from the tower top;

[0077] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent, and the temperature of the adsorption tank is 36° C., for impurity adsorption;

[0078] The preparation method of the adsorbent is as follows:

[0079] (1) 60 g of activated carbon was added to 200 mL of a 20 wt% potassium permanganate aqueous solution and soaked for 3 h. After the soaking was completed, the solid was filtered, washed until the filtrate was neutral, and dried to obtain pretreated activated carbon;

[0080] (2) Disperse 40 g of pretreated activated carbon in 200 mL of anhydrous ethanol, add 25.6 g of epichlorohydrin and 14.8 g of ethylenediamine, heat at 60 ° C for reaction for 5 h, filter, collect the solid, wash and dry, and then disperse in chloroform, add 32.5 g of triethylamine, and dropwise add 82 g of itaconyl chloride in an ice bath. After the dropwise addition is completed, heat to 35 ° C for reaction for 1 h. After the reaction is completed, filter and collect the solid, filter, collect the solid, wash and dry to obtain modified activated carbon;

[0081] (3) 16.5 g of modified activated carbon was dispersed in 200 mL of water, 2.4 g of mercaptopyridine and 0.4 g of benzoyl peroxide were added, and the mixture was heated at 60° C. for 6 h. After the reaction was completed, the mixture was filtered, and the solid was collected, washed, and dried to obtain the adsorbent;

[0082] S4, distillation and de-lightening: the product after the adsorption is added to the third distillation tower for de-lightening, and distillation and de-lightening treatment is performed. The temperature of the bottom of the third distillation tower is 188°C, the temperature of the top of the tower is 183°C, the pressure of the bottom of the tower is 0.16MPa, and the theoretical plate number of the third distillation tower is 56. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0083] S5, distillation and re-heavy removal: the re-light product is introduced into the fourth distillation tower for re-heavy removal, and distillation and re-heavy removal treatment is performed. The temperature of the bottom of the fourth distillation tower is 208° C., the temperature of the top of the tower is 188° C., and the pressure of the bottom of the tower is 0.09 MPa; the theoretical plate number of the fourth distillation tower is 65; the product of distillation and re-heavy removal enters the finished product collection tank, and the high-purity octamethylcyclotetrasiloxane is obtained.

[0084] Comparative Example 3

[0085] A method for preparing high-purity octamethylcyclotetrasiloxane is similar to Example 1, except that itaconyl chloride is not added to the adsorbent, and specifically comprises the following steps:

[0086] S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane to the first distillation tower, carry out distillation and light removal treatment, the bottom temperature of the first distillation tower is 182°C, the top temperature is 178°C, the bottom pressure is 0.14MPa, the theoretical plate number is 75, remove low boiling point impurities and then draw out the light-removed product from the bottom of the tower;

[0087] S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, the temperature of the second distillation tower kettle is 208 ° C, the tower top temperature is 187 ° C, the tower kettle pressure is 0.09 MPa, the theoretical plate number is 86, the high boiling point impurities are removed and the de-heavy product is then drawn out from the tower top;

[0088] S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent, and the temperature of the adsorption tank is 36° C., for impurity adsorption;

[0089] The preparation method of the adsorbent is as follows:

[0090] (1) 60 g of activated carbon was added to 200 mL of a 20 wt% potassium permanganate aqueous solution and soaked for 3 h. After the soaking was completed, the solid was filtered, washed until the filtrate was neutral, and dried to obtain pretreated activated carbon;

[0091] (2) 40 g of pretreated activated carbon was dispersed in 200 mL of anhydrous ethanol, 25.6 g of epichlorohydrin and 14.8 g of ethylenediamine were added, and the mixture was heated at 60° C. for 5 h, filtered, the solid was collected, washed and dried, 16.5 g was dispersed in 200 mL of water, 3.2 g of 1-vinyl-3-ethylimidazolium bromide, 2.4 g of mercaptopyridine and 0.4 g of benzoyl peroxide were added, and the mixture was heated at 60° C. for 6 h, filtered after the reaction was completed, the solid was collected, washed and dried to obtain the adsorbent;

[0092] S4, distillation and de-lightening: the product after the adsorption is added to the third distillation tower for de-lightening, and distillation and de-lightening treatment is performed. The temperature of the bottom of the third distillation tower is 188°C, the temperature of the top of the tower is 183°C, the pressure of the bottom of the tower is 0.16MPa, and the theoretical plate number of the third distillation tower is 56. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower;

[0093] S5, distillation and re-heavy removal: the re-light product is introduced into the fourth distillation tower for re-heavy removal, and distillation and re-heavy removal treatment is performed. The temperature of the bottom of the fourth distillation tower is 208° C., the temperature of the top of the tower is 188° C., and the pressure of the bottom of the tower is 0.09 MPa; the theoretical plate number of the fourth distillation tower is 65; the product of distillation and re-heavy removal enters the finished product collection tank, and the high-purity octamethylcyclotetrasiloxane is obtained.

[0094] The octamethylcyclotetrasiloxane prepared in Examples 1-3 and Comparative Examples 1-3 was tested for purity, and the test results are shown in Table 1:

[0095] Table 1 Octamethylcyclotetrasiloxane purity test results

[0096]

[0097]

[0098] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A method for preparing high-purity octamethylcyclotetrasiloxane, characterized in that: The steps include: S1, distillation and light removal: add industrial grade octamethylcyclotetrasiloxane into the first distillation tower, perform distillation and light removal treatment to remove low boiling point impurities, and then draw out the light-removed product from the bottom of the tower; S2, distillation and de-heavy: the product after de-heavy is introduced into the second distillation tower for de-heavy treatment, and then the de-heavy product is drawn out from the top of the tower; S3, adsorption: introducing the deweighting product into an adsorption tank, wherein the adsorption tank is filled with an adsorbent to adsorb impurities; S4, distillation and de-lightening: adding the product after the adsorption to the third distillation tower for de-lightening, and performing distillation and de-lightening treatment. After the treatment is completed, the product after de-lightening is drawn out from the bottom of the tower; S5, distillation and re-heavy removal: the re-light-removed product is introduced into the fourth distillation tower for re-heavy removal, and the distillation and re-heavy removal product enters the finished product collection tank to obtain the high-purity octamethylcyclotetrasiloxane.

2. The preparation method according to claim 1, characterized in that: In the step S1, the temperature of the bottom of the first distillation tower is 180-185° C., the temperature of the top of the tower is 176-180° C., the pressure of the bottom of the tower is 0.1 MPa-0.2 MPa, and the number of theoretical plates of the first distillation tower is 70-80.

3. The preparation method according to claim 1, characterized in that: In the step S2, the temperature of the bottom of the second distillation tower is 205-210° C., the temperature of the top of the tower is 185-190° C., and the pressure of the bottom of the tower is 0.08 MPa-0.1 MPa; the number of theoretical plates of the second distillation tower is 80-90.

4. The preparation method according to claim 1, characterized in that: The preparation method of the adsorbent in step S3 is as follows: (1) adding activated carbon to a potassium permanganate aqueous solution and soaking it, filtering it after the soaking is completed, collecting the solid, washing it until the filtrate is neutral, and drying it to obtain pretreated activated carbon; (2) dispersing the pretreated activated carbon in anhydrous ethanol, adding epichlorohydrin and ethylenediamine, heating to react, filtering, collecting the solid, washing and drying, and then dispersing it in chloroform, adding triethylamine, and adding itaconyl chloride dropwise in an ice bath. After the addition is completed, heating to react, after the reaction is completed, filtering and collecting the solid, washing and drying the solid to obtain modified activated carbon; (3) Dispersing the modified activated carbon in water, adding 1-vinyl-3-ethylimidazolium bromide, pyridine mercapto, and benzoyl peroxide, heating for reaction, filtering after the reaction is completed, collecting the solid, washing, and drying to obtain the adsorbent.

5. The preparation method according to claim 4, characterized in that: In the step (1), the concentration of the potassium permanganate aqueous solution is 10-30 wt %, and the soaking time is 2-4 h.

6. The preparation method according to claim 4, characterized in that: In the step (2), the mass ratio of pretreated activated carbon, epichlorohydrin, ethylenediamine and itaconyl chloride is 15-25:10-15:5-8:30-50.

7. The preparation method according to claim 4, characterized in that: In the step (3), the mass ratio of modified activated carbon, 1-vinyl-3-ethylimidazolium bromide and mercaptopyridine is 5-10:1-2:1-1.

5.

8. The preparation method according to claim 1, characterized in that: The temperature of the bottom of the third distillation tower is 185-190° C., the temperature of the top of the tower is 180-185° C., and the pressure of the bottom of the tower is 0.1 MPa-0.2 MPa; the number of theoretical plates of the third distillation tower is 50-60.

9. The preparation method according to claim 1, characterized in that: The temperature of the bottom of the fourth distillation tower is 205-210°C, and the temperature of the top of the tower is 185-190°C.

10. The preparation method according to claim 9, characterized in that: The bottom pressure of the fourth distillation tower is 0.08MPa-0.1MPa; the theoretical plate number of the fourth distillation tower is 60-70.

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