A method for purifying octamethylcyclotetrasiloxane

Abstract

The invention relates to the technical field of octamethylcyclotetrasiloxane purification, and discloses a method for purifying octamethylcyclotetrasiloxane, comprising dissolving octamethylcyclotetrasiloxane to be purified and a metal ion complexing agent in a polar organic solvent to obtain a mixed liquid; cooling and solidifying to separate the octamethylcyclotetrasiloxane, washing the octamethylcyclotetrasiloxane solid with a polar organic solvent, then removing the residual polar organic solvent on the surface of the octamethylcyclotetrasiloxane, converting the octamethylcyclotetrasiloxane into a liquid state, and rectifying to obtain purified octamethylcyclotetrasiloxane; the amount of the metal ion complexing agent added is 0.01% to 1% of the mass of the polar organic solvent; and the mass ratio of octamethylcyclotetrasiloxane to the polar organic solvent is 1:0.1 to 10. The invention greatly reduces the amount of solvent to be removed in the rectification process, and the metal ion content in the octamethylcyclotetrasiloxane can reach the ppb level, meeting the application requirements for electronic grade octamethylcyclotetrasiloxane.

Description

Technical Field

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

[0002] Octamethylcyclotetrasiloxane (D4), as an important intermediate in the silicone industry, is widely used in electronics, automobiles, aerospace, textiles, daily chemicals, medical, machinery and agriculture. With the development of 5G and the semiconductor industry, D4 has gained increasing attention in industries such as integrated circuits and optical fibers due to its ring structure and excellent performance. However, these fields have very high requirements for the impurity content in D4, especially the metal impurity content must be controlled at the ppb level. At present, the purity of industrial-grade octamethylcyclotetrasiloxane is 98-99%, which contains metal ions, solid particles and other organic impurities, which cannot meet the application requirements. Therefore, the development of efficient and economical methods to remove impurities such as metal ions is the development direction of high-purity D4.

[0003] In order to meet the higher use requirements of industries such as integrated circuits, reports on reducing the content of metal ions and other impurities in D4 have appeared in the prior art. For example, the Chinese patent "A method for purifying electronic grade octamethylcyclotetrasiloxane" with the announcement number CN103788124B discloses that after the introduction of the complex tetramethoxyphenylphosphine, vacuum distillation can be performed to obtain D4 with a metal impurity content of less than 5ppb and a purity of 99.99%. This method is more convenient and the product quality is good, but the price of the complex used is too high and it is not suitable for mass production. Another example is the Chinese patent application "Octamethylcyclotetrasiloxane purification method" with the publication number CN113583038A. After D4 is treated with anion exchange resin and cation exchange resin, it is subjected to membrane filtration treatment, which can effectively remove metal ions and non-metallic impurities in D4 and reduce moisture, but this method is difficult to reach the electronic grade level.

[0004] The Chinese patent "Method for Removing Metal Impurities from Organic Silicon Compounds" with announcement number CN103788124B mixes octamethylcyclotetrasiloxane with polar organic solvent and metal adsorbent, and then separates octamethylcyclotetrasiloxane and organic solvent by distillation, which can reduce the metal ion content to ppb level, and the purity of octamethylcyclotetrasiloxane reaches 99.95%, which not only reaches the electronic grade level, but also is suitable for industrial production. However, in this method, the polar organic solvent and D4 need to be completely separated by distillation process, which has high energy consumption and complicated operation, which brings inconvenience to use. Summary of the invention

[0005] In view of the inconvenience caused by the complete distillation separation of octamethylcyclotetrasiloxane and a polar organic solvent, the present invention aims to provide a method for purifying octamethylcyclotetrasiloxane, wherein the octamethylcyclotetrasiloxane and the polar organic solvent are separated by coagulation to simplify the distillation process, and at the same time, the metal ion level in the purified and separated octamethylcyclotetrasiloxane can reach the ppb level, meeting the requirements of electronic grade applications.

[0006] The present invention provides the following technical solutions:

[0007] A method for purifying octamethylcyclotetrasiloxane comprises the following steps:

[0008] (1) dissolving octamethylcyclotetrasiloxane to be purified and a metal ion complexing agent in a polar organic solvent to obtain a mixed liquid;

[0009] (2) cooling the mixed liquid to solidify and separate octamethylcyclotetrasiloxane from the polar solvent, with the solidification temperature being ≤10°C;

[0010] (3) washing the octamethylcyclotetrasiloxane solid with a polar organic solvent at a temperature of ≤10° C., and then removing the residual polar organic solvent on the surface of the octamethylcyclotetrasiloxane;

[0011] (4) heating to convert the octamethylcyclotetrasiloxane into a liquid state, and rectifying the octamethylcyclotetrasiloxane to obtain purified octamethylcyclotetrasiloxane;

[0012] The amount of metal ion complexing agent added is 0.01% to 1% of the mass of the polar organic solvent;

[0013] The mass ratio of octamethylcyclotetrasiloxane to the polar organic solvent is 1:0.1-10.

[0014] Different from the prior art in which polar organic solvent and octamethylcyclotetrasiloxane are completely separated by distillation, the present invention separates industrial-grade octamethylcyclotetrasiloxane (with a purity of 98-99%) from the polar organic solvent by cooling and solidifying, and separates the remaining very small amount of polar organic solvent by distillation, thereby greatly reducing the workload of distillation separation. Specifically, the inventors, through research, selected a metal ion complexing agent soluble in a polar organic solvent to replace the metal adsorbent, mixed octamethylcyclotetrasiloxane, the metal ion complexing agent, and the polar organic solvent to form a homogeneous solution, the purity of the polar organic solvent used is superior purity or higher purity, such as electronic grade, the metal ions are removed by dissolving the polar organic solvent and the action of the metal ion complexing agent, the amount of the metal ion complexing agent added is controlled to be 0.01% to 1% of the mass of the polar organic solvent, more preferably 0.25 to 0.5%, the mass ratio of octamethylcyclotetrasiloxane to the polar organic solvent is 1:0.1 to 10, more preferably 1:1 to 2, and the solidification temperature is ≤10°C, more preferably ≤0°C, so that octamethylcyclotetrasiloxane can be solidified and separated from the polar organic solvent, and appropriate low-speed stirring can be maintained during the cooling and solidification separation process, the stirring speed is 20 to 50 rpm, and the cooling process is placed in a temperature-controlled environment, and the cooling rate is 1 to 5 min / °C. The octamethylcyclotetrasiloxane solid is washed and then converted into liquid distillation. Since only a very small amount of polar organic solvent remains, the separation work during the distillation operation is greatly reduced, while ensuring that the octamethylcyclotetrasiloxane after distillation can reach the ppb level.

[0015] As a preferred embodiment of the method of the present invention, the metal ion complexing agent is a crown ether or a crown ether derivative soluble in the polar organic solvent used. The crown ether or the crown ether derivative has good metal ion complexing ability and good solubility in polar organic solvents. The crown ether or its derivative used is such as 15-crown ether-5, 18-crown ether-6, cyclohexyl-containing crown ether, etc.

[0016] As a preferred embodiment of the method of the present invention, the metal ion complexing agent is 15-crown ether-5 or 18-crown ether-6, and more preferably 18-crown ether-6.

[0017] As a preferred embodiment of the method of the present invention, the mass ratio of octamethylcyclotetrasiloxane to the polar organic solvent is 1:1 to 2. The octamethylcyclotetrasiloxane maintains a relatively high concentration and is easily solidified and separated from the polar organic solvent, while the polar organic solvent maintains an appropriate dosage to achieve sufficient separation of metal ions.

[0018] As a preferred embodiment of the method of the present invention, the polar organic solvent is one of methanol, ethanol, isopropanol and acetone. The above reagents have good solubility and a boiling point below 100°C, which facilitates the distillation separation of the residual solvent at a lower temperature.

[0019] As a preferred embodiment of the method of the present invention,

[0020] The polar organic solvent contains at least ethanol and isopropanol;

[0021] Taking the volume of the two as 100%, isopropanol accounts for 60-70%. In further research, it was found that the mixed system of ethanol and isopropanol can further reduce the metal ion content in octamethylcyclotetrasiloxane, which may be due to the fact that ethanol and isopropanol have more similar polarity and different solubility for different metal ions.

[0022] As a preferred method of the present invention, the solidification temperature is -20 to 10° C. A lower solidification temperature requires greater energy consumption and reduces the economic degree, and a more preferred solidification temperature is -20 to 0° C.

[0023] As a preferred embodiment of the method of the present invention,

[0024] The solidification process of step (2) is:

[0025] First cool down to 0-10℃ to solidify, then cool down to -10--20℃ to solidify at a rate of 3-5min / ℃, until octamethylcyclotetrasiloxane is completely solidified and separated. First partially solidify at a slightly higher temperature, preferably 0-2℃, and then, if there are partially solidified crystals, place the solidification process in a dynamic slow cooling process, and then place it at a lower temperature to fully solidify, accurately control the solidification process, refine the crystal particle size, improve the solidification separation effect, avoid the inclusion of impurities such as metal ions during the solidification process, and further remove metal ions. When combined with a dual solvent system of ethanol and isopropanol, the concentration of some metal ions even reaches 0.1ppb level.

[0026] As the preferred embodiment of the method of the present invention, the distillation process is as follows:

[0027] 1) transferring liquid octamethylcyclotetrasiloxane to a lightness removal tower for negative pressure distillation to remove low-boiling impurities from the top of the tower;

[0028] 2) The octamethylcyclotetrasiloxane after light removal is transferred to a de-weighting tower for negative pressure distillation, and the fraction at 98-112° C. is collected at the top of the tower to obtain purified octamethylcyclotetrasiloxane.

[0029] Since only a very small amount of polar organic solvent remains in octamethylcyclotetrasiloxane after solidification and separation, the distillation process is greatly shortened, and no fraction flows out at 80-92°C at the top of the light removal tower, thereby removing polar solvents, hexamethylcyclotrisiloxane and other low-boiling substances. D4 is sent to the de-heavy tower for de-heavy removal, and the fraction at 98-112°C at the top of the de-heavy tower is collected to obtain purified octamethylcyclotetrasiloxane.

[0030] As a preferred embodiment of the method of the present invention,

[0031] The vacuum degree of step 1) is 0.097-0.098 MPa;

[0032] The vacuum degree of step 2) is 0.099 to 0.0995 MPa.

[0033] The beneficial effects of the present invention are as follows:

[0034] Compared with the prior art of separating organic solvents and octamethylcyclotetrasiloxane by distillation, the present invention optimizes the composition of the mixed system of polar organic solvents and octamethylcyclotetrasiloxane, separates octamethylcyclotetrasiloxane by cooling and solidification at a suitable temperature, greatly reduces the amount of polar organic solvent to be removed during the distillation process, and then performs distillation separation. The metal ion content in the octamethylcyclotetrasiloxane can reach the ppb level, meeting the application requirements for electronic-grade octamethylcyclotetrasiloxane. DETAILED DESCRIPTION

[0035] The specific implementation modes of the present invention are further described below.

[0036] Unless otherwise specified, the raw materials used in the present invention can be purchased from the market or are commonly used in the art. Unless otherwise specified, the methods in the following embodiments are all conventional methods in the art.

[0037] The metal ion concentrations of the octamethylcyclotetrasiloxane raw material in the following examples and comparative examples are shown in Table 1 below.

[0038] Table 1 Concentration of metal ions in octamethylcyclotetrasiloxane raw materials

[0039] ion Fe Ca Al Mn Ni Sn Cu Mg Sb Concentration / ppm 1.602 0.875 0.65 0.226 0.280 0.474 0.735 0.338 0.601

[0040] The total concentration of metal ions in the raw materials is 6.054 ppm.

[0041] Example 1 (ethanol / crown ether, 0°C, 100 parts / 200 parts)

[0042] A method for purifying octamethylcyclotetrasiloxane, comprising the following steps:

[0043] (1) Dissolve 100 parts by weight of industrial grade octamethylcyclotetrasiloxane and 0.5 parts of 18-crown ether-6 in 200 parts of electronic grade ethanol, stir evenly to obtain a mixed liquid, and let stand for 24 hours;

[0044] (2) Cooling the mixed liquid from room temperature to 0°C within 40 minutes and maintaining it under low-speed stirring at 20 rpm until the octamethylcyclotetrasiloxane is completely solidified and separated from the ethanol, then taking out the solidified solid and crushing it, vacuum filtering to remove the solvent and collecting the solid; (3) Rinse twice with 0°C electronic grade ethanol, and then vacuum filtering to remove the solvent;

[0045] (4) Heating octamethylcyclotetrasiloxane to 40° C. to convert it into a liquid state, and then distilling it in a light-removing tower with a vacuum degree of 0.098 MPa until no fraction flows out within 90° C. at the top of the tower. Then, the octamethylcyclotetrasiloxane after light-removal flows from the bottom of the tower into a heavy-removal tower, and distilling it under a vacuum degree of 0.0995 MPa. The fraction at 110° C. is collected at the top of the tower to obtain high-purity octamethylcyclotetrasiloxane with a low metal impurity content of more than 99.99%.

[0046] Example 2 (ethanol / crown ether, 0° C., 100 parts / 100 parts)

[0047] A method for purifying octamethylcyclotetrasiloxane, comprising the following steps:

[0048] (1) Dissolve 100 parts by weight of industrial grade octamethylcyclotetrasiloxane and 0.5 parts of 18-crown ether-6 in 100 parts of electronic grade ethanol, stir evenly to obtain a mixed liquid, and let stand for 24 hours;

[0049] (2) cooling the mixed liquid from room temperature to 0° C. within 40 minutes and stirring at a low speed of 50 rpm until the octamethylcyclotetrasiloxane is completely solidified and separated from the ethanol, then taking out the solidified solid and crushing it, and collecting the solid after vacuum filtration;

[0050] (3) Rinse twice with 0°C electronic grade ethanol, and then remove the solvent by vacuum filtration;

[0051] (4) Heating octamethylcyclotetrasiloxane to 40° C. to convert it into a liquid state, and then distilling it in a light-removing tower with a vacuum degree of 0.097 MPa until no fraction flows out within the range of 92° C. at the top of the tower. Then, the octamethylcyclotetrasiloxane after light-removal flows from the bottom of the tower into a heavy-removal tower, and distilling it under a vacuum degree of 0.0995 MPa. The fraction of 112° C. is collected at the top of the tower to obtain high-purity octamethylcyclotetrasiloxane with a low metal impurity content of more than 99.99%.

[0052] Example 3 (electronic grade isopropanol)

[0053] The difference from Example 1 is that electronic grade isopropanol is used instead of ethanol.

[0054] Example 4 (electronic grade methanol)

[0055] The difference from Example 1 is that electronic grade methanol is used instead of ethanol.

[0056] Example 5 (ethanol + isopropanol)

[0057] The difference from Example 1 is that 120 parts of electronic grade isopropanol and 80 parts of electronic grade ethanol are used instead of 200 parts of ethanol.

[0058] Example 6 (ethanol + isopropanol)

[0059] The difference from Example 1 is that 140 parts of electronic grade isopropanol and 60 parts of electronic grade ethanol are used instead of 200 parts of ethanol.

[0060] Example 7 (ethanol + isopropanol)

[0061] The difference from Example 1 is that 120 parts of electronic grade isopropanol and 80 parts of electronic grade ethanol are used instead of 200 parts of ethanol, and the cooling and solidification temperature is -20°C.

[0062] Comparative Example 1 (Methanol and Isopropanol)

[0063] The difference from Example 1 is that 120 parts of electronic isopropanol and 80 parts of electronic grade methanol are used instead of 200 parts of ethanol.

[0064] Comparative Example 2 (Isopropyl alcohol accounts for 90%)

[0065] The difference from Example 1 is that 180 parts of electronic grade isopropanol and 20 parts of electronic grade ethanol are used instead of 200 parts of ethanol.

[0066] Example 8 (Mixed Solvent / Dynamic Slow Cooling Solidification)

[0067] A method for purifying octamethylcyclotetrasiloxane, comprising the following steps:

[0068] (1) dissolving 100 parts by weight of industrial-grade octamethylcyclotetrasiloxane to be purified and 0.5 parts of 18-crown ether-6 in 120 parts of electronic-grade isopropanol and 80 parts of ethanol and stirring to obtain a mixed liquid;

[0069] (2) cooling the mixed liquid from room temperature to 0°C within 40 minutes and maintaining it for 5 minutes, stirring it at a low speed of 20 rpm, and then cooling it to -20°C within 60 minutes while stirring until the octamethylcyclotetrasiloxane is completely solidified and separated from the ethanol, and then taking out the solid and crushing it, and collecting the solid after vacuum filtration;

[0070] (3) Rinse the collected solid twice with 0°C electronic grade ethanol, and then remove the solvent by vacuum filtration;

[0071] (4) The octamethylcyclotetrasiloxane is heated to 40° C. and converted into a liquid state, and first sent to a light-removal tower and distilled at a vacuum degree of 0.098 MPa until no fraction flows out at 90° C. at the top of the tower, and then the octamethylcyclotetrasiloxane after light-removal is flowed from the bottom of the tower into a heavy-removal tower, and distilled at a vacuum degree of 0.0995 MPa, and a fraction at 110° C. is collected at the top of the tower to obtain high-purity octamethylcyclotetrasiloxane with a low metal impurity content of more than 99.99%.

[0072] Comparative Example 3 (Rapid Cooling)

[0073] The difference from Example 8 is that the temperature is lowered from 0°C to -20°C within 30 minutes under stirring.

[0074] Example 9 (Isopropanol / dynamic slow cooling solidification)

[0075] The difference from Example 8 is that 200 parts of electronic grade isopropanol are used instead of 120 parts of electronic grade isopropanol and 80 parts of methanol.

[0076] The octamethylcyclotetrasiloxane finally collected in the above examples and comparative examples was subjected to ICP-MS metal ion detection. The results are shown in Table 2.

[0077] Table 1 Metal ion concentration in octamethylcyclotetrasiloxane

[0078] Ions / ppb Fe / ppb Ca / ppb Al / ppb Mn / ppb Ni / ppb Sn / ppb Cu / ppb Mg / ppb Sb / ppb Raw material D4 1602 875 650 226 280 474 735 338 601 Example 1 42.1 28.0 18.4 3.1 3.0 3.3 1.2 2.0 1.1 Example 2 33.4 16.2 9.9 2.4 2.1 2.7 0.8 1.3 0.9 Example 3 25.3 10.1 7.8 1.6 1.5 1.9 0.6 0.8 0.5 Example 4 19.0 8.3 6.5 1.1 1.7 1.2 0.5 0.6 0.4 Example 5 12.4 8.7 7.2 1.2 1.3 1.4 0.3 0.3 0.4 Example 6 10.8 8.1 6.5 1.1 1.4 1.2 0.4 0.3 0.2 Example 7 9.6 7.5 6.3 0.8 1.2 1.0 0.3 0.2 0.3 Comparative Example 1 22.3 9.1 7.2 1.3 1.5 1.4 0.5 0.7 0.4 Comparative Example 2 27.1 12.3 9.4 2.2 2.3 2.5 0.8 1.4 0.7 Example 8 2.8 1.1 0.5 0.1 0.1 0.1 0.1 0.1 0.1 Comparative Example 3 9.4 7.6 6.5 0.8 1.3 1.2 0.2 0.3 0.2 Example 9 23.4 9.0 5.2 1.5 1.3 2.1 0.5 0.7 0.4

[0079] It can be seen from Table 2 that the present application scheme can effectively remove metal ion impurities in the octamethylcyclotetrasiloxane raw material.

[0080] Specific:

[0081] As shown in Examples 1 to 4, under optimized octamethylcyclotetrasiloxane, complexing agent, organic solvent dosage and cooling temperature, the total content of metal ions in the purified octamethylcyclotetrasiloxane does not exceed 100ppb, reaching the ppb level, which can meet the requirements of electronic grade applications. As shown in Examples 5 to 7 compared with Comparative Examples 1 and 2, ethanol and isopropanol are mixed and used, and the appropriate amount ratio is controlled to further reduce the concentration of metal ions. When the optimized ethanol and isopropanol mixed solvent is used, and combined with a suitable and controllable dynamic cooling and coagulation process, as shown in Example 8, the removal effect of metal ions can be improved, and the concentration of most metal ions can reach 0.1ppb level. While Example 7 is equivalent to Comparative Example 3, Example 9 is slightly improved relative to Example 3.

Claims

1. A method for purifying octamethylcyclotetrasiloxane, characterized in that: The following steps are involved: (1) dissolving octamethylcyclotetrasiloxane to be purified and a metal ion complexing agent in a polar organic solvent to obtain a mixed liquid; (2) cooling the mixed liquid to solidify and separate octamethylcyclotetrasiloxane from the polar solvent, with the solidification temperature being ≤10°C; (3) washing the octamethylcyclotetrasiloxane solid with a polar organic solvent at a temperature of ≤10° C., and then removing the residual polar organic solvent on the surface of the octamethylcyclotetrasiloxane; (4) heating to convert the octamethylcyclotetrasiloxane into a liquid state, and rectifying the octamethylcyclotetrasiloxane to obtain purified octamethylcyclotetrasiloxane; The amount of metal ion complexing agent added is 0.01% to 1% of the mass of the polar organic solvent; The mass ratio of octamethylcyclotetrasiloxane to the polar organic solvent is 1:0.1-10; The polar organic solvents are ethanol and isopropanol; taking the sum of the volumes of the two as 100%, isopropanol accounts for 60-70%.

2. The method for purifying octamethylcyclotetrasiloxane according to claim 1, characterized in that: The metal ion complexing agent is a crown ether soluble in the polar organic solvent used.

3. The method for purifying octamethylcyclotetrasiloxane according to claim 1 or 2, characterized in that: The metal ion complexing agent is 15-crown-5 or 18-crown-6.

4. The method for purifying octamethylcyclotetrasiloxane according to claim 1, characterized in that: The mass ratio of octamethylcyclotetrasiloxane to the polar organic solvent is 1:1-2.

5. The method for purifying octamethylcyclotetrasiloxane according to claim 1, characterized in that: The solidification temperature is -20 to 10°C.

6. The method for purifying octamethylcyclotetrasiloxane according to claim 1, characterized in that: The solidification process of step (2) is: First cool down to 0-10°C for solidification, then cool down to -10--20°C at a rate of 3-5 min / °C for solidification until octamethylcyclotetrasiloxane is completely solidified and separated.

7. The method for purifying octamethylcyclotetrasiloxane according to claim 1, characterized in that: The distillation process is as follows: 1) transferring liquid octamethylcyclotetrasiloxane to a lightness removal tower for negative pressure distillation to remove low-boiling impurities from the top of the tower; 2) The octamethylcyclotetrasiloxane after light removal is transferred to a de-weighting tower for negative pressure distillation, and the fraction at 98-112° C. is collected at the top of the tower to obtain purified octamethylcyclotetrasiloxane.

8. The purification method according to claim 7, characterized in that The vacuum degree of step 1) is 0.097-0.098 MPa; The vacuum degree of step 2) is 0.099 to 0.0995 MPa.