Refractive index method for measuring hydrogen content in methyl hydrogen-containing silicone oil

Abstract

The invention discloses a refractive index method for measuring hydrogen content in methyl hydrogen silicone oil. The method comprises the following steps: measuring the refractive index of a methyl hydrogen-containing silicone oil standard sample with the known hydrogen content by using a digital display refractometer and taking octamethylcyclotetrasiloxane as a diluent, establishing a correction curve of the refractive index and the hydrogen content, and calculating the hydrogen content by measuring the refractive index of silicone oil to be measured. The method has the advantages of simplicity in operation, high analysis speed, good accuracy and the like.

Description

Technical Field

[0001] The invention relates to a method for determining the hydrogen content in methyl hydrogen-containing silicone oil, belonging to the technical field of chemical analysis and testing. Background Art

[0002] Methyl hydrogen silicone oil is a common organic silicon product. Its Si-H bond can be efficiently added to vinyl under Pt catalysis, so it is widely used in silicone rubber, textile and other fields. As a core indicator, hydrogen content affects the performance of vulcanized silicone rubber, such as vulcanization rate, hardness, etc., and is crucial to quality improvement and market satisfaction. Accurate analysis of hydrogen content is the key to ensuring product quality, promoting technological innovation and sustainable development of the industry.

[0003] At present, the main methods for measuring the hydrogen content in methyl hydrogen silicone oil are mid-infrared spectroscopy, near-infrared spectroscopy, gas spectroscopy, 1 H-NMR method and chemical titration method, etc. Mid-infrared and near-infrared spectroscopy have the advantages of being simple and rapid, but mid-infrared spectroscopy is greatly interfered by groups such as cyano and alkynyl, while the background interference in near-infrared spectroscopy is more serious, and the sensitivity of detection still needs to be improved. The gas measurement method measures hydrogen content, which is based on the conversion of H2 release of methyl hydrogen silicone oil in alkaline solution, but it is greatly affected by ambient temperature, device airtightness and operation. 1 The H-NMR method uses 1,4-dioxane or trioxymethylene as an internal standard to measure the hydrogen content, but the nuclear magnetic resonance instrument is expensive and has high maintenance costs, which limits its widespread application in industry. The chemical titration method is based on the substitution reaction between the Br2 / CH3COOH mixture and the Si-H bond, and then the remaining Br2 is consumed by KI. The generated I2 is titrated with Na2S2O3 solution to achieve quantitative analysis of silicon-hydrogen bonds. However, this method has high requirements for experimental equipment, and Br2 is highly toxic and harmful to personnel. Therefore, the development of a simple, rapid and safe method for detecting hydrogen content is of great significance for the production of methyl hydrogen silicone oil. Summary of the invention

[0004] The object of the present invention is to provide a refractive index method for determining the hydrogen content in methyl hydrogen silicone oil, which is simple to operate, has a fast analysis speed and high accuracy. The refractive index is one of the important indicators of silicone oil products. Related studies have shown that the type and content of groups on the polysiloxane molecular chain have a significant effect on the refractive index. Therefore, the relationship between the refractive index and the hydrogen content of methyl hydrogen silicone oil is explored, and a method for quickly detecting the hydrogen content in methyl hydrogen silicone oil is proposed. The specific steps are as follows: (1) After the digital refractometer is turned on and preheated, the refractive index of air and deionized water is calibrated in turn, and the mirror is cleaned with ethanol.

[0005] (2) A series of methyl hydrogen silicone oils with known hydrogen content are mixed evenly with diluents in proportion, and the corresponding refractive index is measured (n D ).

[0006] (3) n D With hydrogen content as the vertical axis and hydrogen content as the horizontal axis, a calibration curve is drawn.

[0007] (4) Measure the methyl hydrogen silicone oil to be tested according to step (2). n D , and calculate the hydrogen content.

[0008] Preferably, in step (1), the temperature during refractometer measurement is 25±0.1°C.

[0009] Preferably, in step (1), the accuracy of the refractometer is 0.00002. n D Keep to six decimal places.

[0010] Preferably, in step (2), the hydrogen content of the methyl hydrogenated silicone oil is in the range of 0.083 wt% to 1.24 wt%.

[0011] Preferably, in step (2), the diluent is octamethylcyclotetrasiloxane (D4) for the following reasons: First, D4 has good compatibility with methyl hydrogen silicone oil and no stratification phenomenon.

[0012] Second, the use of commercial chromatographically pure D4 has low impurity content, which can reduce the impact of solvent purity on n D Interference with detection.

[0013] Third, the kinematic viscosity of D4 is lower than 3.5 mm² / s, which makes it easier to disperse methyl hydrogen silicone oil than polydimethylsiloxane (5~350 mm² / s) to improve the repeatability of the test. Although the 2 mm² / s polydimethylsiloxane has a lower viscosity, its purity is not as good as the former, and n D It is greatly affected by the synthesis process of different manufacturers.

[0014] Fourth, methyl hydrogen silicone oil n D Higher than D4 ( =1.394), and the difference is obvious, while the When D4 is used as solvent, the change of unit hydrogen content of methyl hydrogen silicone oil leads to significant change of refractive index, which improves the test sensitivity. n D Siloxanes lower than D4, such as hexamethyldisiloxane and octamethyltrisiloxane, but they have lower flash points and are more flammable, requiring higher fire safety measures during use and storage.

[0015] Preferably, in step (2), methyl hydrogen silicone oil is added to D4 and treated with vortex vibration (50 Hz, 3 min) and ultrasound (60 W, 5 min) to achieve uniform mixing.

[0016] Preferably, in step (2), the volume ratio of methyl hydrogen silicone oil to D4 is 1:2.

[0017] Preferably, the correlation coefficient (R) of the calibration curve in step (3) 2 ) should be greater than 0.99.

[0018] The present invention is applicable to the following situations: (1) At present, the preparation methods of methyl hydrogenated silicone oil mainly include the co-hydrolysis condensation method based on dimethyl hydrogenated chlorosilane, the catalytic equilibrium method and the hydrolysis equilibrium method. Although the quality standards of silicone oil products produced by different synthesis processes are unified, there are still large differences in product stability, impurity types and contents, which still have a certain impact on the detection of hydrogen content of the product by refractometry. Therefore, the method proposed in the present invention is suitable for the rapid and simple determination of hydrogen content in methyl hydrogenated silicone oil with a fixed production route.

[0019] (2) The high viscosity of methyl hydrogen silicone oil may make it difficult to clean the refractometer mirror, which may have an adverse effect on subsequent detection. Therefore, the present invention recommends that the silicone oil be appropriately diluted before detection, and the kinematic viscosity of the diluted solution should not exceed 20 mm 2 / s.

[0020] Compared with the prior art, the advantages and positive effects of the present invention are: (1) Fast analysis speed, detection time is only 3 minutes.

[0021] (2) The relative standard deviations of the multiple measurement results of the same sample and the measurement results after one week of storage were no higher than 0.02%, indicating that the reproducibility and stability of the detection method were satisfactory.

[0022] (3) This method is simple to operate and the diluent (D4) used is of low toxicity, posing little health hazard to analysts and testers. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is the calibration curve of the refractive index and hydrogen content of the methyl hydrogen silicone oil standard (D4 is the diluent).

[0024] Figure 2 The calibration curve of the refractive index and hydrogen content of the methyl hydrogen silicone oil standard (2 mm 2 / s dimethyl silicone oil as diluent).

[0025] Figure 3 The calibration curve of the refractive index and hydrogen content of the methyl hydrogen silicone oil standard (5 mm 2 / s dimethyl silicone oil as diluent).

[0026] Figure 4 The calibration curve of the refractive index and hydrogen content of the methyl hydrogen silicone oil standard (10 mm 2 / s dimethyl silicone oil as diluent).

[0027] Figure 5 The calibration curve of the refractive index and hydrogen content of the methyl hydrogen silicone oil standard (350 mm 2 / s dimethyl silicone oil as diluent).

[0028] Figure 6 The mid-infrared spectrum of the methyl hydrogenated silicone oil standard is at 2160 cm -1 Calibration curve of the integrated area of ​​the characteristic peak and hydrogen content. DETAILED DESCRIPTION

[0029] The present invention is further described below in conjunction with the accompanying drawings and specific implementation modes, but the protection scope of the present invention is not limited to the following implementation modes.

[0030] Drawing of standard curve: (1) Turn on the Mettler-Toledo multirefractometer and set the detection temperature to 25 °C. After preheating for 5 min, calibrate the refractive index of air and water in turn. Clean the mirror with ethanol and wipe it clean with lens cleaning paper.

[0031] (2) Take 1 mL of methyl hydrogen silicone oil (purchased from Zhejiang Organic Silicone New Materials Co., Ltd., prepared by co-hydrolysis) into 5 mL centrifuge tubes, with hydrogen contents of 0.083wt%, 0.12wt%, 0.18wt%, 0.36wt%, 0.55wt%, 0.75wt%, 0.77wt%, 0.79wt%, 1.2wt% and 1.24wt%, and then add 2 mL of D4. After the mixed solution was vortexed (50 Hz, 1 min) and ultrasonicated (60 W, 2 min), the corresponding refractive index ( ), and the results are shown in Table 1.

[0032] (3) Methyl hydrogen silicone oil As the ordinate (y), the hydrogen content as the abscissa (x), draw a calibration curve ( Figure 1 ), the linear regression equation is y=-0.00156x+1.39731, and the correlation coefficient (R 2 ) is 0.99796.

[0033] Table 1 shows the refractive index of the methyl hydrogen silicone oil standard sample and the-1 The integrated area of ​​the characteristic peak at Hydrogen content (wt%) Refractive index <![CDATA[2160 cm -1 The integrated area at]]> 0.083 1.397210 0.388 0.12 1.397120 0.494 0.18 1.396980 0.615 0.36 1.396750 0.867 0.55 1.396390 1.484 0.75 1.396200 1.854 0.77 1.396170 2.031 0.79 1.396050 2.047 1.20 1.395430 2.910 1.24 1.395340 3.104 Embodiment 1: This example provides the refractometry test results of three different methyl hydrogen silicone oil samples (all purchased from Zhejiang Organic Silicone New Materials Co., Ltd., prepared by co-hydrolysis and condensation method), and the specific steps are as follows: Take the methyl hydrogen silicone oil samples 1, 2 and 3 to be tested, treat them according to step (2), and measure their n D is 1.396470, and when substituted into the equation y=-0.00156x+1.39731, the hydrogen contents are calculated to be 0.54wt%, 1.18wt% and 0.28wt% respectively.

[0034] Embodiment 2: This embodiment provides a 2 mm 2 / s dimethyl silicone oil (provided by Hubei Xingrui Silicon Materials Co., Ltd.) was used as the diluent, and the results of the 1, 2 and 3 methyl hydrogen silicone oil samples were tested by refractometry. The specific steps are as follows: The standard curve is drawn by dividing by 2 mm 2 / s dimethyl silicone oil instead of D4, the rest is the same as in Example 1, and the corresponding linear equation is y=-0.00127x+1.4002, R 2 =0.98755( Figure 2 The three samples were all 2 mm 2 / s dimethyl silicone oil was diluted three times and its n D They are 1.399540, 1.398740 and 1.399800 respectively. Substituting them into the equation, the hydrogen contents are calculated to be 0.52wt%, 1.15wt% and 0.31wt% respectively.

[0035] Embodiment 3: This embodiment provides a 5 mm 2 / s dimethyl silicone oil (provided by Hubei Xingrui Silicon Materials Co., Ltd.) was used as the diluent, and the results of the 1, 2 and 3 methyl hydrogen silicone oil samples were tested by refractometry. The specific steps are as follows: The steps for drawing the standard curve are as follows: 2 / s dimethyl silicone oil instead of D4, the rest is the same as in Example 1, and the corresponding linear equation is y=-0.00136x+1.39492, R 2 =0.98331( Figure 3 The three samples were all 5 mm 2 / s dimethyl silicone oil was diluted three times and its n DThey are 1.394220, 1.393380 and 1.394560 respectively. Substituting them into the equation, the hydrogen contents are calculated to be 0.51wt%, 1.13wt% and 0.26wt% respectively.

[0036] Embodiment 4: This embodiment provides a 10 mm 2 / s dimethyl silicone oil is used as the diluent, and the results of the refractometry test of No. 1, 2 and 3 methyl hydrogen silicone oil samples are as follows: The steps for drawing the standard curve are as follows: 2 / s dimethyl silicone oil instead of D4, the rest is the same as in Example 1, and the corresponding linear equation is y=-0.00121x+1.29866, R 2 =0.98735( Figure 4 ). All three samples were 10 mm 2 / s dimethyl silicone oil was diluted three times and its n D They are 1.297960, 1.297160 and 1.298280 respectively. Substituting them into the equation, the hydrogen contents are calculated to be 0.58wt%, 1.24wt% and 0.32wt% respectively.

[0037] Embodiment 5: This embodiment provides a 350 mm 2 / s dimethyl silicone oil (provided by Hubei Xingrui Silicon Materials Co., Ltd.) was used as the diluent, and the results of the 1, 2 and 3 methyl hydrogen silicone oil samples were tested by refractometry. The specific steps are as follows: The steps for drawing the standard curve are as follows: 2 / s dimethyl silicone oil instead of D4, the rest is the same as in Example 1, and the corresponding linear equation is y=-0.00112x+1.40315, R 2 =0.98564( Figure 5 ). All three samples were 350mm 2 / s dimethyl silicone oil was diluted three times and its n D They are 1.402500, 1.401760 and 1.402780 respectively. Substituting them into the equation, the hydrogen contents are calculated to be 0.58wt%, 1.23wt% and 0.33wt% respectively.

[0038] Embodiment 6: This example provides the refractometry test results of a methyl hydrogenated silicone oil sample (purchased from Jiangxi Xinjiayi New Materials Co., Ltd.) prepared by the hydrolysis equilibrium method. The specific steps are as follows: Take the methyl hydrogen silicone oil sample 4 to be tested, treat it according to the above step (2), and measure its nD The value is 1.395980, which is substituted into the linear equation y=-0.00156x+1.39731, and the hydrogen content of sample 4 is calculated to be 0.85wt%.

[0039] Embodiment 7: This example provides the refractometry test results of a methyl hydrogenated silicone oil sample prepared by a catalytic equilibrium method, and the specific steps are as follows: The preparation of methyl hydrogen silicone oil sample 5 refers to patent CN110938207B, using D4 as monomer and 1,1,3,3-tetramethyldihydrodisiloxane as end-capping agent, and reacting at 80 °C for 10 h under the action of modified white clay catalyst. After the purified sample 5 was treated according to the above step (2), its n D is 1.395840, and when substituted into the linear equation y=-0.00156x+1.39731, the hydrogen content of sample 5 is calculated to be 0.94wt%.

[0040] Verification example: To verify the accuracy of the test results in the above implementation case, the methyl hydrogenated silicone oil standard was first tested using a Bruker Fourier transform mid-infrared spectrometer. The parameters were set as follows: number of scans, 32 times; scanning range, 4000~500 cm -1 ; Resolution, 3 cm -1 . With silicone oil at 2160 cm -1 The integral area of ​​the characteristic peak at is taken as the ordinate (y), and the hydrogen content is taken as the abscissa (x). Draw the calibration curve ( Figure 6 ), the linear regression equation is y=2.2988x+0.2071, R 2 It is 0.99818.

[0041] The silicone oil sample to be tested in the implementation case was also measured by a mid-infrared spectrometer and recorded at 2160 cm -1 The integral area of ​​the characteristic peak at is substituted into the equation y=2.2988x+0.2071 to calculate the hydrogen content. The results are shown in Table 2. When D4 is used as a diluent (Example 1), the measured values ​​of the refractometry and mid-infrared methods are close, and the deviation is less than 0.02wt%. When dimethyl silicone oils of different kinematic viscosities are used as diluents (Examples 2 to 5), the deviations of the detection results of the refractometry and mid-infrared methods increase significantly, which shows that when D4 is used as a diluent, the accuracy of the refractometry detection of hydrogen content can be effectively improved. The results of Examples 6 and 7 show that the hydrogen content analysis method proposed in the present invention is more suitable for methyl hydrogen-containing silicone oils synthesized by the same process, while the quantitative results of methyl hydrogen-containing silicone oils prepared by other synthesis methods (hydrolysis equilibrium method, catalytic equilibrium method) are not accurate enough.

[0042] In summary, the refractometer method can achieve rapid and accurate measurement of hydrogen content in the methyl hydrogenated silicone oil production line within the enterprise, and the test results are stable. In addition, the price and maintenance cost of the refractometer are low, and the operation is simple, which is conducive to reducing the testing costs of small and medium-sized enterprises.

[0043] Table 2 is a comparison of the results of detecting the hydrogen content of methyl hydrogenated silicone oil samples by refractometry and mid-infrared method.

[0044]

[0045] The above is only a preferred embodiment of the present invention, and does not limit the present invention in other forms. The technical contents disclosed above can be applied to other fields by modification or modification. Any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the technical solution of the present invention still belongs to the protection scope of the technical solution of the present invention.

Claims

1. A refractive index method for determining the hydrogen content in methyl hydrogen silicone oil, characterized in that: The specific steps are as follows: (1) After the digital refractometer is turned on and preheated, calibrate the refractive index of air and deionized water in turn, and clean the mirror with ethanol; (2) Mix a series of methyl hydrogen silicone oils with known hydrogen content with diluent and measure the corresponding refractive index. n D ; (3) n D As the ordinate, the hydrogen content as the abscissa, draw a calibration curve; (4) Measure the methyl hydrogen silicone oil to be tested according to step (2). n D , and calculate the hydrogen content.

2. A refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: In step (1), the temperature during refractometer measurement is 25±0.1 °C.

3. The refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: In step (1), the accuracy of the refractometer is 0.00002, and the refractive index value is retained to six decimal places.

4. The refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: In step (2), the hydrogen content of the methyl hydrogenated silicone oil is 0.083 wt% to 1.24 wt%.

5. A refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: In step (2), the diluent is octamethylcyclotetrasiloxane, and the kinematic viscosity is 2 mm 2 / s, 5 mm 2 / s, 10 mm 2 / s and 350mm 2 / s one of the polydimethylsiloxanes.

6. The refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: In step (2), the volume ratio of methyl hydrogen silicone oil to diluent is 1:2-3.

7. The refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: In step (2), methyl hydrogen silicone oil is added to the diluent and subjected to vortex vibration and / or ultrasonic treatment to achieve uniform mixing.

8. The refractive index method for determining the hydrogen content in methyl hydrogen silicone oil according to claim 1, characterized in that: Correlation coefficient R of the calibration curve in step (3) 2 Greater than 0.99.

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