Method for screening solvents for dissolving azo initiators

Abstract

The application discloses a solvent screening method for dissolving azo initiators, which can screen a solvent for dissolving azo initiators to replace toluene, initiate a polymerization reaction to synthesize special-purpose polyvinyl chloride resin, and reduce the harm to operators in the production process. The solvent performance is scientifically and comprehensively evaluated from four aspects of solvent performance preliminary screening, performance evaluation of an initiating system suspension solution, polymerization reaction process monitoring and performance analysis of finished products, so that the correctness of the solvent screening is remarkably improved, the analysis difficulty is low, and the applicability and generalizability are high.

Description

Technical Field

[0001] This invention relates to the field of polyvinyl chloride (PVC) special resin production technology, and in particular to a solvent screening method for dissolving azo initiators. Background Technology

[0002] The production of polyvinyl chloride (PVC) resin generally employs emulsion polymerization and micro-suspension polymerization. Micro-suspension polymerization, with its simple operation and high latex solids content, is widely used and promoted. In micro-suspension polymerization, azo compounds are typically used as initiators. These compounds decompose free radicals at suitable reaction temperatures, initiating the free radical polymerization of vinyl chloride. These substances are convenient to use, exhibit minimal sticking to the reactor, and provide stable control of the polymerization reaction; however, toluene is required as a solvent to dissolve the solid initiator.

[0003] Toluene, one of the "three benzenes" in industry, can cause neurasthenia syndrome, hepatomegaly, and other diseases in operators with prolonged exposure, leading to specific injuries and even chemical-induced sudden death. Furthermore, it can remain in PVC products, affecting their performance and export prospects. Therefore, there is an urgent need to develop an environmentally friendly solvent to replace toluene for dissolving azo initiators, eliminating the hazards of toluene to operators and achieving the non-toxic and harmless production of PVC-specific resin additives.

[0004] In micro-suspension polymerization, monomers, water, emulsifiers, co-emulsifiers, and initiators are dispersed into submicron droplets under the action of homogenization equipment. These droplets utilize micelle competition to capture initiator free radicals, initiating PVC chain polymerization. This process requires that each latex particle contains exactly one free radical, which places high demands on the dispersibility and stability of the solvent-prepared initiation system. During chain growth, the solvent must not be sensitive to the free radicals generated by the initiator, and must not undergo side reactions such as chain transfer, thus not affecting the chain initiation rate. Simultaneously, the solvent must not participate in the polymerization reaction or attach to the ends of long PVC chains, affecting product quality and processing performance. Therefore, the selection of environmentally friendly solvents should comprehensively consider factors such as solvent solubility, the dispersion stability of the initiation system, the impact of the polymerization process, and changes in the performance of the finished product. Currently, there is no clear method for selecting solvents that dissolve azo initiators, and relying solely on differences in solvent solubility to select solvents for azo compounds cannot meet the requirements of the complex control process of polymerization reactions. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a solvent screening method for dissolving azo initiators. Based on the intrinsic mechanism of the polymerization reaction of polyvinyl chloride-specific resin, four key steps for solvent screening are proposed, and key indicators for each step are considered. This is a scientific and reliable method that can solve the safety and environmental protection issues of using toluene as a solvent.

[0006] To achieve this technical objective, the present invention adopts the following solution:

[0007] A solvent screening method for dissolving azo initiators includes the following steps:

[0008] S1. Initial screening of solvent properties: Determine the solvent's evaporation rate, boiling point, polarity, toxicity, and saturated solubility for azo initiators; the solvent's evaporation rate should be 0 to 3 times that of butyl acetate, its boiling point should be below 140℃, it should be polar, non-toxic or low-toxic, and its saturated solubility for azo initiators at 25℃ should be greater than 35g. Solvents that meet the above requirements will proceed to the next screening step, while solvents that do not meet the requirements will be excluded.

[0009] S2. Performance evaluation of the initiation system suspension: Dissolve the solid azo initiator in the solvent selected in step S1, stir thoroughly until completely dissolved, add to an appropriate amount of emulsion, and stir to form a suspension; test the solution viscosity, surface tension, emulsion stability, and storage stability of the suspension. Compare the test results with the corresponding indicators of the suspension formed by toluene as a solvent. The deviation of each test result of the suspension should be within ±10%. Solvents that meet the requirements will proceed to the next screening step, and solvents that do not meet the requirements will be excluded.

[0010] S3. Monitoring of the polymerization reaction process: The solvents selected in step S2 are used for vinyl chloride micro-suspension polymerization. The polymerization reaction time, temperature, pressure, conversion rate, circulating cooling water volume, and reaction heat release are monitored using a DCS control system. The monitoring results of each indicator are compared with the corresponding indicators in the polymerization process when toluene is used as a solvent. Based on the comparison results, each monitoring indicator is scored. The polymerization reaction time, temperature, pressure, and conversion rate are each worth 20 points, and the circulating cooling water volume and reaction heat release are each worth 10 points. The smaller the deviation between each monitoring indicator and the corresponding indicator in the reaction process when toluene is used as a solvent, the higher the score. Solvents with a score of 90 or above meet the requirements and proceed to the next screening step. Solvents with a score below 90 are excluded.

[0011] S4. Performance Analysis of Finished Product: The performance of the PVC-specific resin obtained in step S3 is analyzed, including the latex properties, rheological properties of the plasticized paste, transparency, mechanical properties, and thermal stability of the PVC-specific resin. The test results of each property are compared with the corresponding indicators of the PVC-specific resin produced using toluene as a solvent. If the deviation is within ±10%, it meets the requirements. Solvent screening is completed, and solvents that do not meet the requirements are eliminated.

[0012] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0013] 1. This invention comprehensively considers solvent performance and the intrinsic mechanism of polymerization reaction, proposes four key steps for initiator solvent screening, and considers the key indicators of each step, providing a scientific and reliable method for solvent screening of azo initiators, which significantly improves the accuracy of solvent screening and has strong practicality and scalability.

[0014] 2. This invention proposes a performance evaluation method for initiation system suspensions. This method can directly characterize the composite characteristics of suspensions, such as dispersibility and stability, of different initiation systems. It does not require polymerization reactions, is simple to operate, safe and reliable, and greatly simplifies the difficulty and workload of solvent screening, thereby improving solvent screening efficiency.

[0015] 3. This invention uses a scoring method to scientifically and intuitively evaluate the effects of different solvents on key parameters such as reaction time, temperature, pressure, conversion rate, circulating cooling water volume, and exothermic reaction during the polymerization process. It provides an intuitive view of the vinyl chloride polymerization process, making solvent selection more scientific and precise.

[0016] Furthermore, in step S2, the concentration of the azo initiator is 0.1~1wt%, and the emulsion is an aqueous solution of sodium dodecyl sulfate or sodium dodecylbenzene sulfonate.

[0017] Furthermore, in step S2, the solution viscosity test temperature is 25~35℃, and the shear rate is 50~500s. -1 The surface tension of the solution is tested at a temperature of 25~35℃, and the solution needs to stand for 10~20 minutes before the test.

[0018] Furthermore, the method for testing the emulsion stability and storage stability in step S2 is to let the suspension stand at 25~35℃ for 0~48h, irradiate it with strong light, and observe the phase separation of the solution. Attached Figure Description

[0019] Figure 1 This is a flowchart of the solvent screening method for dissolving azo initiators according to the present invention; Detailed Implementation

[0020] To fully understand the purpose, features and effects of the present invention, the present invention will be described in detail through the following specific embodiments, but the present invention is not limited thereto. Example 1

[0021] Xylene was selected as the solvent to be screened. Xylene has a boiling point of 135℃, an evaporation rate 0.68 times that of butyl acetate, an oral dose of 4000 mg / kg in rats, and irritation to the eyes and upper respiratory tract. It does not meet the relevant requirements of the "initial screening of solvent performance" and is therefore excluded. Example 2

[0022] Ethanol was selected as the solvent to be screened. Ethanol has an evaporation rate 2.4 times that of butyl acetate, a boiling point of 78.3℃, and is a polar molecule. At 25℃, its saturated solubility in azo compounds is 40g. It meets the relevant indicators for "initial screening of solvent performance" and will proceed to the next screening step.

[0023] Solid azobisisobutyronitrile was dissolved in ethanol and stirred thoroughly until completely dissolved. This solution was then added to an appropriate amount of sodium dodecylbenzenesulfonate aqueous solution, with an initiator solute concentration of 1 wt%. After stirring for 1 hour, a suspension was prepared. The viscosity and surface tension of this suspension at 30°C were tested. The results showed a viscosity of 35 mPa·s and a surface tension of 29.38 N / m, with deviations within 10% compared to the suspension prepared using toluene as a solvent. Further evaluation of emulsion stability revealed that the suspension prepared using ethanol as a solvent exhibited significant phase separation after standing for 1 hour, indicating poor emulsion stability. This did not meet the relevant requirements for the "Performance Evaluation of Initiation System Suspension," and was therefore excluded. Example 3

[0024] Butyl acetate was selected as the solvent to be screened. Butyl acetate has an evaporation rate of 1, a boiling point of 126℃, is a polar molecule, has an oral rat value of 10768 mg / kg, and has a saturated solubility of about 40% for azo compounds at 25℃. It meets the relevant indicators for "initial screening of solvent performance" and will proceed to the next screening step.

[0025] Solid azobisisobutyronitrile was dissolved in butyl acetate and stirred thoroughly until completely dissolved. The solution was then added to an appropriate amount of sodium dodecylbenzenesulfonate aqueous solution with an initiator solute concentration of 1 wt%. After stirring for 1 hour, a suspension was prepared. The viscosity and surface tension of this suspension at 30°C were tested. The results showed a viscosity of 33.9 mPa·s and a surface tension of 30.21 N / m, with deviations within 10%. Further evaluation of the emulsion stability and storage stability of the suspension was conducted. No phase separation was observed during the tests, and according to the emulsion stability assessment method, all results were classified as Grade 1. Butyl acetate was then selected for the next screening step.

[0026] After dissolving the azo initiator with butyl acetate, vinyl chloride was subjected to micro-suspension polymerization. The polymerization reaction time, temperature, pressure, conversion rate, circulating cooling water volume, and reaction exothermic changes were monitored using a DCS control system. The monitoring results of each indicator were compared with the corresponding indicators when toluene was used as a solvent. Based on the comparison results, each monitoring indicator was scored as follows: reaction time 20 points, temperature 18 points, pressure 18 points, conversion rate 17 points, circulating cooling water volume 8 points, and reaction exothermic change 9 points, for a total of 90 points. This met the requirements and proceeded to the next screening step.

[0027] The performance of the PVC-specific resin produced by polymerization using butyl acetate in the previous step was analyzed. The various indicators of the latex and the PVC finished product after spray drying and pulverization met the enterprise standard requirements. The results of the rheological properties analysis of PVC plasticizer and the tests of transparency, mechanical properties and thermal stability of PVC products were all within ±10% of the performance of PVC plasticizer produced by dissolving initiators with toluene, which met the requirements. The solvent screening was completed, and it was determined that butyl acetate can replace toluene as a solvent for dissolving azo initiators.

[0028] Finally, it should be noted that the above-listed embodiments are merely preferred embodiments of the present invention. Of course, those skilled in the art can make modifications and variations to the present invention. If such modifications and variations fall within the scope of the claims of the present invention and their equivalents, they should be considered as being within the protection scope of the present invention.

Claims

1. A method for screening solvents for dissolving azo-based initiators, characterized by, Comprise the following steps: S1, solvent performance preliminary screening: judge the evaporation rate, boiling point, polarity, toxicity and the saturated solubility of azo initiator of solvent; S2, the suspension solution performance evaluation of initiation system: the solid azo initiator is dissolved in the solvent screened in step S1, fully stirred until completely dissolved, added to a suitable amount of emulsion, stirred to form a suspension solution; The suspension solution is tested for solution viscosity, surface tension, emulsion stability and storage stability, and the test results are compared with the corresponding indicators of the suspension solution formed by toluene as the solvent; S3, the monitoring of polymerization process: the solvent screened in step S2 is used for micro-suspension polymerization of vinyl chloride, and the DCS control system is used to monitor the polymerization reaction time, temperature, pressure, conversion rate, circulating cold water volume and reaction heat release, and the monitoring results of each index are compared with the corresponding indexes in the polymerization process with toluene as the solvent; S4, performance analysis of finished product: the performance of the polyvinyl chloride special resin obtained in step S3 is analyzed, including the latex performance, plastic paste rheological property, transparency, mechanical property and thermal stability of the polyvinyl chloride special resin, and the performance test results are compared with the corresponding indexes of the polyvinyl chloride special resin produced by toluene as the solvent, the deviation is within ±10%, which meets the requirements, the screening of solvent is completed, and the solvent that does not meet the requirements is excluded; The preliminary screening standard of solvent in step S1: the solvent is polar, non-toxic or low toxicity, the evaporation rate of the solvent is 0~3 times of the evaporation rate of butyl acetate, the boiling point is lower than 140℃, and the saturated solubility of the solvent to azo initiator at 25℃ is greater than 35g; the solvent meeting the conditions enters the next step of screening, and the solvent not meeting the conditions is excluded; In step S2, the test results of the suspension solution are compared with the corresponding indexes of the suspension solution formed by toluene as the solvent, the solvent with a deviation within ±10% enters the next step of screening, and the solvent not meeting the conditions is excluded; In step S3, each monitoring index is scored according to the comparison results, wherein the polymerization reaction time, temperature, pressure and conversion rate are full marks of 20 points each, the circulating cold water volume and reaction heat release are full marks of 10 points each, the smaller the deviation of each monitoring index from the corresponding index in the polymerization process with toluene as the solvent, the higher the score, the solvent with a score of 90 points or more meets the requirements and enters the next step of screening, and the solvent with a score of less than 90 points is excluded.

2. The solvent screening method for dissolving azo-based initiators according to claim 1, characterized by, In step S2, the concentration of azo initiator is 0.1~1wt%, and the emulsion is sodium dodecyl sulfate aqueous solution or sodium dodecyl benzene sulfonate aqueous solution.

3. The solvent screening method for dissolving azo-based initiators according to claim 1, characterized by, The solution viscosity test temperature in step S2 is 25-35 °C, and the shear rate is 50-500 s -1 The solution surface tension test temperature is 25-35 °C, and the solution is allowed to stand for 10-20 min before testing.

4. The solvent screening method for dissolving azo-based initiators according to claim 1, characterized by, In step S2, the test method of emulsion stability and storage stability is that the suspension solution is placed at 25~35℃ for 0~48h, irradiated with strong light, and the phase separation of the solution is observed.

Images