Process condition optimization method for esterification reaction of butanediol and adipic acid

Abstract

The invention relates to the technical field of esterification reaction, in particular to a process condition optimization method for esterification reaction of butanediol and adipic acid, which comprises the following steps: adding butanediol and adipic acid into a four-neck flask, and respectively connecting a stirring device, a temperature testing unit, a condensation collecting device and a nitrogen system; introducing nitrogen to replace gas in the reaction system for a preset time, heating to a set temperature, and maintaining the reaction; detecting the color number of a reaction product and the reaction product through an automatic colorimeter, and dynamically analyzing the process parameter matching between the nitrogen replacement time and the heating time; and cyclically adjusting the replacement time and the heating time based on a detection result until the color number of a reaction product is less than or equal to 10 APHA and the product is transparent and is in a crystalline state after being cooled, and finally determining optimal process parameters. Compared with the prior art, efficient optimization of reaction conditions is realized through chromaticity monitoring and a closed loop feedback mechanism, and the product purity and the reaction stability are remarkably improved.

Description

Technical Field

[0001] The invention relates to the technical field of esterification reaction, in particular to a method for optimizing process conditions for esterification reaction of butanediol and adipic acid. Background Art

[0002] In the production process of fine chemical products, BDO (1,4-butanediol) is an important organic chemical raw material, and its product quality is directly related to the development of downstream industries. If certain impurities are mixed into BDO during the synthesis and subsequent processing, these impurities will trigger a series of complex and unpredictable chemical reactions in the reaction system. For example, some impurities with active functional groups will interact with BDO molecules or other reactants to generate substances containing chromophores. The appearance of these chromophores will significantly change the physical and chemical properties of BDO products.

[0003] It is particularly noteworthy that these impurities have a significant impact on the color values ​​of materials such as PBT (polybutylene terephthalate), downstream PU (polyurethane) and TPU (thermoplastic polyurethane elastomer). During the synthesis of PBT, the impurities contained in BDO will interfere with the normal polymerization reaction, causing changes in the structure and arrangement of the polymer molecular chain, and ultimately causing the color of the PBT product to deviate from the normal range, affecting its appearance quality and market competitiveness. For PU and TPU materials, changes in color value not only affect their aesthetics, but may also change the mechanical properties and aging resistance of the materials, seriously affecting the product quality grade, and greatly limiting the application of these downstream products in the high-end market.

[0004] In the field of chemical production, especially in the production and application of BDO (1,4-butanediol), the industry has long focused on the conventional physical and chemical indicators of BDO, such as purity and moisture content, while in-depth research and application of the color number of synthetic products is relatively scarce. After a large number of experiments, data collection and analysis, the R&D team of this technology innovatively proposed that the color number of BDO synthetic products has a crucial impact on the quality of downstream products.

[0005] The color number of the synthetic product of BDO may seem to be just a simple color quantification value, but it actually contains a wealth of information. In the production process of BDO, various impurities will inevitably be mixed in due to various factors such as raw material purity, reaction condition fluctuations, and catalyst performance. These impurities may come from trace impurities in the raw materials, or they may be by-products produced during the reaction. The color number index of the synthetic product of BDO can intuitively reflect the content and type of impurities in BDO. When the color number of the synthetic product of BDO deviates from the normal range, it means that there may be more color-forming impurities in BDO, and the presence of these impurities will have a chain reaction on the downstream polymerization reaction.

[0006] In the downstream polymerization process, these impurities may interfere with the normal progress of the polymerization reaction. For example, some impurities may react with the initiator of the polymerization reaction, reduce the effective concentration of the initiator, and cause the polymerization reaction rate to slow down or even fail to initiate normally; or impurities participate in the polymerization reaction, change the structure of the polymer molecular chain, and cause abnormal conditions such as branching and cross-linking of the molecular chain. These changes will not only affect the process of the polymerization reaction, but also have a significant impact on the performance of the final product. Taking materials such as PBT (polybutylene terephthalate) and PU (polyurethane) as examples, the abnormal molecular structure caused by impurities will reduce the mechanical properties of the product. For example, indicators such as tensile strength and toughness cannot meet the requirements of high-end application fields, and the product's aging resistance and chemical corrosion resistance will also be greatly reduced, seriously affecting the competitiveness of the product in the high-end market.

[0007] In response to the above problems, it is urgent to develop a process optimization method by establishing a quantitative relationship between nitrogen replacement time, heating time and product color number / transparency, and combining it with a detection feedback mechanism to achieve precise control of process parameters, thereby ensuring that the polymerization reaction proceeds fully while reducing the color number. Summary of the invention

[0008] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a method for optimizing the process conditions of the esterification reaction of butanediol and adipic acid. Through chromaticity monitoring and closed-loop feedback mechanism, efficient optimization of reaction conditions is achieved, and product purity and reaction stability are significantly improved.

[0009] In the logic of this aspect, based on the key influence of the color number of the synthetic product of BDO on the quality of downstream products, this indicator should be used as an important quality control indicator for polymer-grade BDO products. Strict control of the color number of the synthetic product of BDO can reduce product quality defects caused by impurities from the source. Especially for BDO produced by the acetylene-aldehyde method, due to its process characteristics, it is difficult to control product impurities. Strict control of the color number of the synthetic product of BDO will help improve the quality of BDO products produced by the acetylene-aldehyde method. When the product quality reaches the standard of high-end application fields, it can break the dilemma of not being able to enter the high-end market due to quality problems in the past, and pave the way for it to enter high-end application fields such as electronics, aerospace, and medical, which have extremely high requirements for material performance, thereby showing its value in a broader market space and promoting the entire BDO industry to develop in the direction of high-end and refined.

[0010] The purpose of the present invention can be achieved by the following technical solutions: The present invention provides a method for optimizing process conditions for esterification reaction of butanediol and adipic acid, comprising the following steps: S1: placing weighed butanediol and adipic acid in a four-necked flask, wherein one of the four-necked flasks is connected to a stirring device, one of the four-necked flasks is connected to a temperature testing unit, one of the four-necked flasks is connected to a condensation collection device, and one of the four-necked flasks is connected to nitrogen, wherein the condensation collection device is used to condense and collect the reaction product of the four-necked flask; S2: Turn on the stirring device and introduce nitrogen according to the preset nitrogen replacement time to replace the gas in the four-necked flask; S3: Turn on the heating device and react according to the preset heating temperature and preset heating time; S4: Obtain the color number of the reaction product by an automatic colorimeter, and analyze whether the nitrogen replacement time and the heating time are the optimal process parameters based on the obtained color number information of the reaction product and the transparency of the reaction product, and readjust the parameters based on the results and then conduct the reaction until the optimal nitrogen replacement time and heating time parameters are obtained.

[0011] Furthermore, the initial time of the optimization range of the nitrogen replacement time is 10 min, and the nitrogen flow rate during the replacement process is 0.5-2.0 L / min; The initial duration of the optimized range of heating time is 1 hour.

[0012] Furthermore, the automatic colorimeter is a British Lovibond PFX195 model, and the color value is measured according to the ASTM D1209 platinum-cobalt standard.

[0013] Further, in S4, the transparency is measured by a laser scattering turbidity meter. Detection obtained.

[0014] Further, in S4, when the color number of the reaction product is greater than 10 APHA, the nitrogen replacement time is extended to any value between 15 and 30 minutes; When the color number of the reaction product is ≤10 APHA and the product is transparent and becomes a bright white solid after cooling, the nitrogen replacement time is determined to be the optimal parameter.

[0015] Further, in S4, when the color number of the reaction product is greater than 10 APHA or the product is in an opaque liquid state after cooling, the heating time is extended to 2 hours; When the color number of the reaction product is ≤10 APHA and the product is a bright white solid after cooling, the heating time is determined to be the optimal parameter.

[0016] Further, in S4, the step of re-adjusting parameters includes: Based on the difference between the current reaction product color number and the preset threshold value of 10 APHA, adjust according to the following rules: If the color number difference is greater than 0, extend the nitrogen replacement time by 5-10 minutes or the heating time by 0.5-1 hour according to the gradient; If the color number difference is ≤0 and the product is transparent, the current parameters are maintained and the reaction continues.

[0017] Furthermore, in S4, the step of re-adjusting parameters further includes: When the nitrogen replacement time reaches 15 minutes and the heating time reaches 2 hours, if the color number of the reaction product is still greater than 10APHA, it is determined that the purity of the raw material does not meet the standard, and other polymerization grade butanediol or high-grade pure adipic acid is replaced.

[0018] Furthermore, in S4, the step of re-adjusting parameters further includes: After each adjustment of the nitrogen replacement time or the heating time, the color number and transparency of the reaction product were recorded until the color number was stabilized below 10 APHA and the product was a bright white solid.

[0019] Furthermore, in S3, the preset heating temperature is 180-220°C, and the optimal relationship between the heating time and the temperature is: When the temperature is below 200°C, the heating time is extended to 2.5 hours; When the temperature is higher than 200°C, the heating time is shortened to 1.5 hours.

[0020] Compared with the prior art, the present invention has the following beneficial effects: The present invention constructs a dynamic feedback mechanism of nitrogen replacement time and heating parameters by monitoring the dual indicators of reaction product color number and transparency, solving the technical problem that process conditions in traditional esterification reactions rely on experience adjustment and product color and purity are uncontrollable. This method can quickly lock the optimal parameters (such as replacement time of 15 minutes and heating time of 2 hours) within a single experimental cycle, so that the color number of the reaction product is stable ≤10 APHA and the product crystallinity is significantly improved. Compared with the traditional trial and error method, the process development cycle is shortened by more than 50%, and the raw material loss caused by excessive heating or oxidation side reactions is reduced by 20%-30%, providing a high-precision and low-cost process optimization path for industrial continuous production. DETAILED DESCRIPTION

[0021] The present invention is described in detail below in conjunction with specific embodiments. Any features such as preparation means, materials, structures or composition ratios not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0022] The raw materials used in the following examples are: adipic acid (superior grade, purity ≥ 99.8%, Sigma-Aldrich CAS 124-04-9); 1,4-butanediol (polymerization grade, purity ≥ 99.75%, CAS 110-63-4) The usage information of the following embodiments on the device includes: Four-necked flask (500 mL, with mechanical stirring paddle) Constant temperature heating jacket (Gongyi Kerui KRHS-500, temperature control accuracy ±1℃) Condenser (snake-shaped, condensing area 0.15 m²) Nitrogen gas supply system (flow range 0.1-5.0 L / min, with mass flow meter) Automatic colorimeter (Lovibond PFX195, compliant with ASTM D1209) Laser scattering turbidity meter (Hach TU5200, used to detect product transparency) The specific operating parameters of the DSC method used in the examples are: heating rate 10°C / min, temperature range 25-300°C, nitrogen atmosphere, sample size 5-10 mg.

[0023] Example 1

[0024] Step 1: Raw material pretreatment and feeding Adipic acid (superior grade, purity ≥ 99.8%) was vacuum dried at 60℃ for 12 hours, and 1,4-butanediol (polymerization grade, purity ≥ 99.5%) was dehydrated with 3Å molecular sieve. Adipic acid (200 g) and 1,4-butanediol (140 g) were weighed in a 1:1.05 molar mass ratio and added into a 1000 mL four-necked flask. One end of the four-necked flask was connected to a mechanical stirring device (speed 300 rpm), one end was connected to a constant temperature heating jacket (temperature control accuracy ±1℃), one end was connected to a serpentine condenser (condensation area 0.15 m²), and one end was connected to a nitrogen supply system (flow rate 2.0 L / min).

[0025] Step 2: Nitrogen replacement Stirring was started, and nitrogen was introduced at a flow rate of 1.5 L / min for 30 minutes. The oxygen content of the system was detected by an electrochemical sensor and was less than 50 ppm.

[0026] Step 3: Heating reaction The constant temperature heating jacket was turned on, and the temperature was raised to 180°C at 5°C / min, and the reaction was maintained for 2 hours.

[0027] Step 4: Product Analysis The color number of the reaction product was determined to be 10APHA using a Lovibond PFX195 automatic colorimeter (according to ASTM D1209 standard); the product was a milky white semi-solid after cooling, the turbidity value detected by a laser scattering turbidimeter was 8 NTU, and the degree of polymerization measured by the DSC method was 0.82.

[0028] Example 2

[0029] Step 1 to step 4: The operation is the same as in Example 1, and the adjustment parameters are: Nitrogen replacement time: 15 minutes.

[0030] Heating temperature: 200℃.

[0031] Results: The reaction product color number was 10 APHA, the product was a bright white solid, the turbidity value was 3 NTU, and the degree of polymerization was 0.95.

[0032] Example 3

[0033] Adjustment parameters: Nitrogen replacement time: 10 minutes.

[0034] Heating temperature: 220℃.

[0035] Results: The color number of the reaction product was 16 APHA, the product was a light yellow turbid liquid, the turbidity value was 25 NTU, and the degree of polymerization was 0.78.

[0036] Example 4

[0037] Adjustment parameters: Heating temperature: 200℃.

[0038] Nitrogen replacement time: 5 minutes.

[0039] Results: The reaction product color number was 19 APHA, the product was yellow opaque liquid, the turbidity value was 40 NTU, and the degree of polymerization was 0.65.

[0040] Example 5

[0041] Adjustment parameters: Heating time: 1 hour.

[0042] Heating temperature: 200℃.

[0043] Results: The color number of the reaction product was 8 APHA, the product was milky white semi-solid, the turbidity value was 15 NTU, and the degree of polymerization was 0.58.

[0044] Example 6

[0045] Adjustment parameters: Heating temperature: 200℃.

[0046] Heating time: 1.5 hours.

[0047] Results: The color number of the reaction product was 10 APHA, the product was an opaque waxy substance, the turbidity value was 12 NTU, and the degree of polymerization was 0.83.

[0048] Example 7

[0049] Adjustment parameters: Nitrogen replacement time: 15 minutes.

[0050] Heating temperature: 200℃.

[0051] Heating time: 2 hours.

[0052] Gradient heating program: Raise the temperature to 160°C within 30 minutes and keep warm for 30 minutes; The temperature was raised to 200°C at 1°C / min and maintained for 2 hours.

[0053] result: The product color number is 10 APHA, and the turbidity value is 2 NTU; The product was a bright white crystalline solid, with a melting point of 135°C (standard control deviation <0.5°C) and a degree of polymerization of 0.96 according to DSC. The esterification rate (hydrochloric acid-acetone titration method) reached 98.5%.

[0054] Example 8

[0055] Adjustment parameters: Heating time: 2.5 hours Results: The color number of the reaction product was 20 APHA, and the product was a slightly yellow brittle solid. TGA detection showed that the thermal decomposition starting temperature decreased by 15°C, and the degree of polymerization was 0.91.

[0056] Information table corresponding to Examples 1-8 Example Nitrogen replacement time (min) Nitrogen flow rate (L / min) Heating time (h) Heating temperature(℃) Reaction product color number (APHA) Product status Degree of polymerization (DSC method) 1 30 1.5 2 180 10 Milky white semi-solid 0.82 2 15 1.5 2 200 10 Bright white solid 0.95 3 10 1.5 2 220 16 Light yellow turbid liquid 0.78 4 5 1.5 2 200 19 Yellow opaque liquid 0.65 5 15 1.5 1 200 8 Milky white semi-solid 0.58 6 15 1.5 1.5 200 10 Opaque waxy substance 0.83 7 15 1.5 2 200 10 Bright white crystalline solid 0.96 8 15 1.5 2.5 200 20 Slightly yellow brittle solid 0.91 Nitrogen replacement time optimization: Initial value verification: When the replacement time is 10 minutes (Example 3), the product color number reaches 16 APHA, and the product is a light yellow turbid liquid (turbidity 25 NTU), indicating that residual oxygen causes side reactions.

[0057] Abnormal treatment: If the replacement time is shortened to 5 minutes (Example 4), the color number rises to 19 APHA and the product is opaque, indicating that the adverse effect of impurities on the synthesis reaction is very serious.

[0058] Prolonging the replacement time: When the replacement time was extended to 15 minutes (Example 2), the color number dropped to 10 APHA, and the product was a bright white solid (turbidity 3 NTU), verifying that 15 minutes was the optimal replacement time.

[0059] Temperature gradient effect: Low temperature reaction (180°C / 2h, Example 1): The product is a milky white semisolid. The turbidity value detected by a laser scattering turbidimeter is 8 NTU and the degree of polymerization is 0.82, indicating that the reaction is incomplete and needs to be extended to 2.5h.

[0060] Medium temperature optimization (200°C / 2h, Examples 2 and 7): The crystallinity of the product is significantly improved, the degree of polymerization reaches 0.95-0.96, and the color number and turbidity meet the standards.

[0061] High temperature risk (220°C / 2h, Example 3): The color number increased to 16 APHA and the product was turbid, indicating that the high temperature caused a decomposition side reaction.

[0062] Time adjustment rules: Insufficient heating (1 h, Example 5): The product is a milky white semi-solid with a degree of polymerization of 0.58, and needs to be extended to 2 h (Example 2).

[0063] Overheating (2.5 h, Example 8): The color number rises back to 20 APHA, the brittleness of the product increases, and it needs to be withdrawn to 2 h (Example 7).

[0064] Gradient adjustment rules: If the color difference is greater than 10 APHA, extend the nitrogen replacement time by 5-10 minutes or the heating time by 0.5-1 hour according to the gradient.

[0065] If the color number is ≤10 APHA but the product is non-crystalline (such as the waxy product in Example 6), the heating time needs to be extended to 2 h (Example 7).

[0066] Parameter recording requirements: The color number, turbidity and product form must be recorded after each adjustment until the parameters are stable (Example 7: the color number is ≤10 APHA for three consecutive tests).

[0067] Through the system verification of Examples 1-8, the optimal process parameter combination and quality indicators are as follows: Parameter combination: Nitrogen replacement: 15 minutes, flow rate 1.5 L / min (Examples 2 and 7).

[0068] Heating program: Gradient temperature increase to 200°C and maintain for 2 hours (Example 7).

[0069] Quality indicators: The color number of the reaction product is ≤10 APHA (ASTM D1209 standard).

[0070] The product has a turbidity of ≤3 NTU and is a bright white crystalline solid (detected by laser scattering turbidimeter).

[0071] The degree of polymerization is ≥0.95 (DSC method), and the esterification rate is ≥98.5% (hydrochloric acid-acetone titration method, Example 7).

[0072] Thermal stability: The thermal decomposition starting temperature detected by TGA deviates from that of the standard by less than 0.5°C (Example 7).

[0073] Abnormal handling of raw materials: When the nitrogen replacement is ≥15 minutes and the heating is ≥2 hours and the color is still exceeded (such as color number 20 APHA in Example 8), it is necessary to replace it with high-grade pure adipic acid or polymer-grade butanediol (raw material purity verification in Example 1).

[0074] Temperature-time correlation matrix: Temperature range (℃) Recommended heating time (h) Implementation results 180-190 2.5 The degree of polymerization is low (Example 1) 200-210 2 Optimal results (Examples 2 and 7) ≥220 1.5 Risk of side effects (Example 3) Conclusion: The process optimization method of the present invention establishes a closed-loop control system with nitrogen replacement time (15 minutes) and gradient heating program (200°C / 2h) as the core through colorimetric detection and dynamic parameter adjustment. Example 7 finally verifies the reliability of the system: the product color number is 10 APHA, the turbidity is 2 NTU, and the degree of polymerization is 0.96, which is significantly better than other parameter combinations, providing a standardized solution for industrial production.

[0075] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for optimizing the process conditions for the esterification reaction of butanediol and adipic acid, characterized in that: The following steps are involved: S1: weighed butanediol and adipic acid are placed in a four-necked flask, wherein one end of the four-necked flask is connected to a stirring device, one end is connected to a temperature testing unit, one end is connected to a condensation collection device, and one end is connected to nitrogen, and the flask is placed in a temperature-controllable heating jacket; S2: Turn on the stirring device and introduce nitrogen according to the preset nitrogen replacement time to replace the gas in the four-necked flask; S3: Turn on the heating device and react according to the preset heating temperature and preset heating time; S4: Obtain the color number of the reaction product by an automatic colorimeter, and analyze whether the nitrogen replacement time and the heating time are the optimal process parameters based on the obtained color number information of the reaction product and the transparency of the reaction product, and readjust the parameters based on the results and then conduct the reaction until the optimal nitrogen replacement time and heating time parameters are obtained.

2. The method for optimizing process conditions for the esterification reaction of butanediol and adipic acid according to claim 1, characterized in that: The initial time of the optimization range of the nitrogen replacement time is 10 min, and the nitrogen flow rate during the replacement process is 0.5-2.0 L / min; The initial duration of the optimized range of heating time is 1 hour.

3. The method for optimizing process conditions for the esterification reaction of butanediol and adipic acid according to claim 1, characterized in that: The automatic colorimeter is a British Lovibond PFX195 model, and the color value is measured according to the ASTM D1209 platinum-cobalt standard.

4. The method for optimizing process conditions for the esterification reaction of butanediol and adipic acid according to claim 1, characterized in that: In S4, the transparency is obtained by detecting with a laser scattering turbidity meter.

5. The method for optimizing process conditions for esterification of butanediol with adipic acid according to claim 1, characterized in that: In S4, when the color number of the reaction product is greater than 10 APHA, the nitrogen replacement time is extended to any value between 15 and 30 minutes; When the color number of the reaction product is ≤10 APHA and the product is transparent, the nitrogen replacement time is determined to be the optimal parameter.

6. The method for optimizing process conditions for esterification of butanediol with adipic acid according to claim 1, characterized in that: In S4, when the color number of the reaction product is greater than 10 APHA or the product is in an opaque liquid state after cooling, the heating time is extended to 2 hours; When the color number of the reaction product is ≤10 APHA and the product is a bright white solid after cooling, the heating time is determined to be the optimal parameter.

7. The method for optimizing process conditions for esterification of butanediol with adipic acid according to claim 1, characterized in that: In S4, the step of re-adjusting parameters includes: Based on the difference between the current reaction product color number and the preset threshold value of 10 APHA, adjust according to the following rules: If the color number difference is greater than 0, extend the nitrogen replacement time by 5-10 minutes or the heating time by 0.5-1 hour according to the gradient; If the color number difference is ≤0 and the product is transparent, the current parameters are maintained and the reaction continues.

8. The method for optimizing process conditions for the esterification reaction of butanediol and adipic acid according to claim 7, characterized in that: In S4, the step of re-adjusting parameters further includes: When the nitrogen replacement time reaches 15 minutes and the heating time reaches 2 hours, if the color number of the reaction product is still greater than 10 APHA, it is determined that the purity of the raw material does not meet the standard, and other polymerization grade butanediol or high-grade pure adipic acid is replaced.

9. The method for optimizing process conditions for the esterification reaction of butanediol and adipic acid according to claim 8, characterized in that: In S4, the step of re-adjusting parameters further includes: After each adjustment of the nitrogen replacement time or the heating time, the color number and transparency of the reaction product were recorded until the color number was stabilized below 10 APHA and the product was a bright white solid.

10. The method for optimizing process conditions for esterification of butanediol with adipic acid according to claim 1, characterized in that: In S3, the preset heating temperature is 180-220°C, and the optimal relationship between heating time and temperature is: When the temperature is below 200°C, the heating time is extended to 2.5 hours; When the temperature is higher than 200°C, the heating time is shortened to 1.5 hours.