A method for optimizing the process conditions of the esterification reaction of butanediol and adipic acid

Abstract

The present invention relates to the technical field of esterification reactions, and specifically relates to a method for optimizing the process conditions of the esterification reaction of butanediol and adipic acid, comprising the following steps: adding butanediol and adipic acid into a four-necked flask, and respectively connecting a stirring device, a temperature testing unit, a condensation and collection device, and a nitrogen system; after introducing nitrogen to displace the gas in the reaction system for a preset time, heating to a set temperature and maintaining the reaction; detecting the color number of the reaction product through an automatic colorimeter, and dynamically analyzing the matching of the process parameters of the nitrogen displacement time and the heating time for the reaction product; cyclically adjusting the displacement time and the heating time based on the detection results until the color number of the reaction product ≤ 10 APHA and the product is transparent and crystalline after cooling, and finally determining the optimal process parameters. Compared with the prior art, the present invention realizes the efficient optimization of the reaction conditions through colorimetric monitoring and a closed-loop feedback mechanism, significantly improving the product purity and reaction stability.

Description

Technical Field

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

[0002] In the production process of fine chemical products, BDO (1,4 - butanediol), as an important organic chemical raw material, its product quality is directly related to the development of downstream industries. In the synthesis and subsequent processing of BDO, if certain impurities are mixed in, 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, and then generate substances containing chromogenic groups. The appearance of these chromogenic groups will significantly change the physical and chemical properties of BDO products.

[0003] Particularly noteworthy is 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). In the synthesis process of PBT, the impurities contained in BDO will interfere with the normal progress of the polymerization reaction, resulting in changes in the structure and arrangement of polymer molecular chains, and ultimately causing the color of PBT products to deviate from the normal range, affecting their appearance quality and market competitiveness. For PU and TPU materials, the change in color value not only affects 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), for a long time, the industry has mainly focused on the conventional physical and chemical indicators of BDO, such as purity, moisture content, etc., while the in - depth research and application of the color number index of synthetic products are relatively lacking. The R & D team of this technology, through a large number of experiments, data collection and analysis, innovatively proposed that the color number index of BDO synthetic products has a crucial impact on the quality of downstream products.

[0005] The color number of BDO synthetic products seems to be just a simple numerical quantification of color, but actually contains rich information. During the production of BDO, due to various factors such as raw material purity, reaction condition fluctuations, and catalyst performance, it is inevitable to mix in various impurities. These impurities may come from trace impurities in raw materials or may be by - products generated during the reaction process. The color number index of BDO synthetic products can directly reflect the content and types of impurities in BDO. When the color number of BDO synthetic products deviates from the normal range, it means that there may be more chromogenic impurities in BDO, and the existence of these impurities will have a chain reaction on downstream polymerization reactions.

[0006] During the downstream polymerization reaction process, these impurities may interfere with the normal progress of the polymerization reaction. For example, certain impurities may react with the initiator of the polymerization reaction, reducing the effective concentration of the initiator, resulting in a slowdown or even failure of the polymerization reaction to initiate normally; or the impurities participate in the polymerization reaction, changing the structure of the polymer molecular chain, causing abnormal situations such as branching and crosslinking 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 anti-aging performance and chemical corrosion resistance of the product will also be greatly reduced, seriously affecting the competitiveness of the product in the high-end market.

[0007] To address the above problems, it is urgent to develop a process optimization method. By establishing a quantitative relationship between the nitrogen replacement time, heating time and the product color number / transparency, and combining with a detection feedback mechanism, precise control of process parameters can be achieved, thereby reducing the color number while ensuring the full progress of the polymerization reaction. Summary of the Invention

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

[0009] In the logical concept of this aspect, based on the key impact of the color number index of the synthetic product of BDO on the quality of downstream products, this index should be an important quality control index for polymer-grade BDO products. Strict control of the color number of the synthetic product of BDO can reduce product quality defects caused by impurity problems from the source. Especially for BDO produced by the alkyne aldehyde method, due to the process characteristics, it is difficult to control product impurities. By strictly controlling the color number of the synthetic product of BDO, it helps to improve the quality of BDO products produced by the alkyne aldehyde method. When the product quality meets the standards of high-end application fields, it can break the previous dilemma of being unable to enter the high-end market due to quality problems, open up a way for it to enter high-end application fields such as electronics, aerospace, and medical, which are highly sophisticated and have extremely high requirements for material performance, and thus demonstrate its value in a broader market space, promoting the development of the entire BDO industry towards high-end and refined directions.

[0010] The purpose of the present invention can be achieved by the following technical solutions:

[0011] The present invention provides a method for optimizing the process conditions of the esterification reaction of butanediol and adipic acid, including the following steps:

[0012] S1: Place the weighed butanediol and adipic acid in a four-necked flask. One neck of the four-necked flask is connected to a stirring device, one is connected to a temperature testing unit, one is connected to a condensation and collection device, and one is connected to nitrogen. The condensation and collection device is used to condense and collect the reaction products of the four-necked flask.

[0013] 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.

[0014] S3: Turn on the heating device and carry out the reaction according to the preset heating temperature and preset heating time.

[0015] S4: Obtain the color number of the reaction product through an automatic colorimeter. Combine the obtained color number information of the reaction product and the transparency of the reaction product to analyze whether the nitrogen replacement time and heating time are the optimal process parameters. Based on the results, readjust the parameters and then carry out the reaction until the optimal nitrogen replacement time and heating time parameters are obtained.

[0016] Further, the initial time of the optimized 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;

[0017] The initial duration of the optimized range of the heating time is 1 h.

[0018] Further, the automatic colorimeter is the Lovibond PFX195 type from the UK, and the chromaticity value is determined according to the ASTM D1209 platinum-cobalt standard.

[0019] Further, in S4, the transparency is detected by a laser scattering turbidimeter

[0020] and obtained.

[0021] Further, in S4, when the color number of the reaction product > 10 APHA, extend the nitrogen replacement time to any value in the range of 15 - 30 min;

[0022] When the color number of the reaction product ≤ 10 APHA and the product is transparent and shows a bright white solid state after cooling, determine that the nitrogen replacement time is the optimal parameter.

[0023] Further, in S4, when the color number of the reaction product > 10 APHA or the product shows an opaque liquid state after cooling, extend the heating time to 2 hours;

[0024] When the color number of the reaction product ≤ 10 APHA and the product shows a bright white solid state after cooling, determine that the heating time is the optimal parameter.

[0025] Further, in S4, the steps of readjusting the parameters include:

[0026] Based on the difference between the current color number of the reaction product and the preset threshold of 10 APHA, adjust according to the following rules:

[0027] If the color number difference > 0, extend the nitrogen displacement time by 5 - 10 minutes in gradient or extend the heating time by 0.5 - 1 hour;

[0028] If the color number difference ≤ 0 and the product is transparent, continue the reaction with the current parameters.

[0029] Furthermore, in S4, the steps of readjusting the parameters further include:

[0030] When the nitrogen displacement time reaches 15 minutes and the heating time reaches 2 hours, if the color number of the reaction product is still > 10 APHA, it is determined that the raw material purity does not meet the standard, then replace with other polymer-grade butanediol or analytical reagent grade adipic acid.

[0031] Furthermore, in S4, the steps of readjusting the parameters further include:

[0032] After each adjustment of the nitrogen displacement time or the heating time, record the color number of the reaction product and the transparency of the product until the color number is stable below 10 APHA and the product is in the form of a bright white solid.

[0033] Furthermore, in S3, the preset heating temperature is 180 - 220 °C, and the optimized relationship between the heating time and the temperature is:

[0034] When the temperature is below 200 °C, extend the heating time to 2.5 hours;

[0035] When the temperature is above 200 °C, shorten the heating time to 1.5 hours.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] By combining the dual indicators of monitoring the color number and transparency of the reaction product, the present invention constructs a dynamic feedback mechanism for the nitrogen displacement time and the heating parameters, and solves the technical problems of process conditions depending on empirical adjustment and uncontrollable product chromaticity and purity in traditional esterification reactions. This method can quickly lock the optimal parameters (such as displacement time of 15 minutes and heating time of 2 hours) within a single experimental cycle, make the color number of the reaction product stable ≤ 10 APHA and significantly improve the product crystallinity, shorten the process development cycle by more than 50% compared with the traditional trial-and-error method, and at the same time reduce the raw material loss caused by overheating or oxidation side reactions by 20% - 30%, providing a high-precision and low-cost process optimization path for industrial continuous production. Specific embodiments

[0038] The present invention will be described in detail below in conjunction with specific embodiments. Features such as preparation means, materials, structures, or composition ratios that are not clearly described in this technical solution are regarded as common technical features disclosed in the prior art.

[0039] The usage information of raw materials in the following examples is as follows: adipic acid (guaranteed reagent, purity ≥ 99.8%, Sigma - Aldrich CAS 124 - 04 - 9); 1,4 - butanediol (polymerization grade, purity ≥ 99.75%, CAS 110 - 63 - 4)

[0040] The usage information of equipment in the following examples includes:

[0041] Four - necked flask (500 mL, with mechanical stirring paddle)

[0042] Constant - temperature heating mantle (Gongyi Kerei KRHS - 500, temperature control accuracy ±1°C)

[0043] Condenser (snake - shaped, condensation area 0.15 m²)

[0044] Nitrogen gas supply system (flow rate range 0.1 - 5.0 L / min, with mass flow meter)

[0045] Automatic colorimeter (Lovibond PFX195, compliant with ASTM D1209 standard)

[0046] Laser scattering turbidimeter (Hach TU5200, used to detect the transparency of the product)

[0047] The specific operating parameters of the DSC method adopted in the examples are: heating rate 10°C / min, temperature range 25 - 300°C, nitrogen atmosphere, sample amount 5 - 10 mg.

[0048] Example 1

[0049] Step 1: Pretreatment and feeding of raw materials

[0050] Adipic acid (guaranteed reagent, purity ≥ 99.8%) was vacuum - dried at 60°C for 12 hours, and 1,4 - butanediol (polymerization grade, purity ≥ 99.5%) was dehydrated by 3Å molecular sieve. Adipic acid (200 g) and 1,4 - butanediol (140 g) were weighed according to a molar mass ratio of 1:1.05 and added to a 1000 - mL four - necked flask. One opening of the four - necked flask was connected to a mechanical stirring device (rotation speed 300 rpm), one opening was connected to a constant - temperature heating mantle (temperature control accuracy ±1°C), one opening was connected to a snake - shaped condenser (condensation area 0.15 m²), and one opening was connected to a nitrogen gas supply system (flow rate 2.0 L / min).

[0051] Step 2: Nitrogen replacement

[0052] Start stirring and introduce nitrogen at a flow rate of 1.5 L / min for 30 minutes. Detect the oxygen content in the system with an electrochemical sensor and ensure it is <50 ppm.

[0053] Step 3: Heat the reaction

[0054] Turn on the constant temperature heating mantle and heat it up to 180°C at a rate of 5°C / min, and maintain the reaction for 2 hours.

[0055] Step 4: Product analysis

[0056] Use a Lovibond PFX195 automatic colorimeter (in accordance with ASTM D1209 standard) to measure the color number of the reaction product as 10 APHA; after the product cools, it is a milky white semi-solid, the turbidity value detected by a laser scattering turbidimeter is 8 NTU, and the degree of polymerization measured by DSC method is 0.82.

[0057] Example 2

[0058] Steps 1 to 4: The operations are the same as in Example 1, and the parameters are adjusted as follows:

[0059] Nitrogen replacement time: 15 minutes.

[0060] Heating temperature: 200°C.

[0061] Result: The color number of the reaction product is 10 APHA, the product is a bright white solid, the turbidity value is 3 NTU, and the degree of polymerization is 0.95.

[0062] Example 3

[0063] Adjust the parameters:

[0064] Nitrogen replacement time: 10 minutes.

[0065] Heating temperature: 220°C.

[0066] Result: The color number of the reaction product is 16 APHA, the product is a light yellow turbid liquid, the turbidity value is 25 NTU, and the degree of polymerization is 0.78.

[0067] Example 4

[0068] Adjust the parameters:

[0069] Heating temperature: 200°C.

[0070] Nitrogen replacement time: 5 minutes.

[0071] Result: The color number of the reaction product is 19 APHA, the product is a yellow opaque liquid, the turbidity value is 40 NTU, and the degree of polymerization is 0.65.

[0072] Example 5

[0073] Adjust the parameters:

[0074] Heating time: 1 hour.

[0075] Heating temperature: 200 °C.

[0076] Result: The color number of the reaction product is 8 APHA, the product is a milky white semi-solid, the turbidity value is 15 NTU, and the degree of polymerization is 0.58.

[0077] Example 6

[0078] Adjusted parameters:

[0079] Heating temperature: 200 °C.

[0080] Heating time: 1.5 hours.

[0081] Result: The color number of the reaction product is 10 APHA, the product is an opaque wax, the turbidity value is 12 NTU, and the degree of polymerization is 0.83.

[0082] Example 7

[0083] Adjusted parameters:

[0084] Nitrogen replacement time: 15 minutes.

[0085] Heating temperature: 200 °C.

[0086] Heating time: 2 hours.

[0087] Gradient heating program:

[0088] Heat up to 160 °C within 30 minutes and hold for 30 minutes;

[0089] Heat up to 200 °C at a rate of 1 °C / min and maintain for 2 hours.

[0090] Result:

[0091] The color number of the product is 10 APHA, and the turbidity value is 2 NTU;

[0092] The product is a bright white crystalline solid. DSC method shows that the melting point is 135 °C (deviation from the standard sample < 0.5 °C), and the degree of polymerization is 0.96;

[0093] The esterification rate (hydrochloric acid-acetone titration method) reaches 98.5%.

[0094] Example 8

[0095] Adjusted parameters:

[0096] Heating time: 2.5 hours

[0097] Results: The color number of the reaction product is 20 APHA. The product is a slightly yellowish brittle solid. TGA detection shows that the initial temperature of thermal decomposition decreases by 15 °C, and the degree of polymerization is 0.91.

[0098] Information table corresponding to Examples 1 - 8

[0099] Example Nitrogen replacement time (min) Nitrogen flow rate (L / min) Heating time (h) Heating temperature (°C) Color number of reaction product (APHA) Product state 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 wax 0.83 7 15 1.5 2 200 10 Bright white crystalline solid 0.96 8 15 1.5 2.5 200 20 Light yellow brittle solid 0.91

[0100] Optimization of nitrogen replacement time:

[0101] Initial value verification: When the replacement time is 10 minutes (Example 3), the color number of the product reaches 16 APHA, and the product is a light yellow turbid liquid (turbidity 25 NTU), indicating that oxygen residue causes side reactions.

[0102] Exception handling: 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.

[0103] Extend the replacement time: When the replacement time is extended to 15 minutes (Example 2), the color number drops to 10 APHA, and the product is a bright white solid (turbidity 3 NTU), verifying that 15 minutes is the optimal replacement time.

[0104] Influence of temperature gradient:

[0105] Low-temperature reaction (180 °C / 2 h, Example 1): The product is a milky semi-solid, and 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 2.5 h.

[0106] Medium-temperature optimization (200 °C / 2 h, 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.

[0107] High-temperature risk (220 °C / 2 h, Example 3): The color number rises to 16 APHA, and the product is turbid, indicating that high temperature causes decomposition side reactions.

[0108] Time adjustment rule:

[0109] Insufficient heating (1 h, Example 5): The product is a milky semi-solid, and the degree of polymerization is 0.58, and it needs to be extended to 2 h (Example 2).

[0110] Overheating (2.5 h, Example 8): The color number rises back to 20 APHA, and the brittleness of the product increases, and it needs to be reduced to 2 h (Example 7).

[0111] Gradient adjustment rule:

[0112] If the color number difference > 10 APHA, extend the nitrogen replacement time by 5 - 10 minutes in gradient or extend the heating time by 0.5 - 1 hour.

[0113] If the color number ≤ 10 APHA but the product is non - crystalline (such as the wax in Example 6), continue to extend the heating time to 2 h (Example 7).

[0114] Parameter recording requirements: After each adjustment, record the color number, turbidity, and product morphology until the parameters are stable (the color number ≤ 10 APHA in three consecutive detections in Example 7).

[0115] Through the system verification of Examples 1 - 8, the optimal process parameter combination and quality indicators are as follows:

[0116] Parameter combination:

[0117] Nitrogen replacement: 15 minutes, flow rate 1.5 L / min (Examples 2, 7).

[0118] Heating program: Gradually heat up to 200 °C and maintain for 2 hours (Example 7).

[0119] Quality indicators:

[0120] The color number of the reaction product ≤ 10 APHA (ASTM D1209 standard).

[0121] The turbidity of the product ≤ 3 NTU, showing a bright white crystalline solid (detected by a laser scattering turbidimeter).

[0122] Degree of polymerization ≥ 0.95 (DSC method), esterification rate ≥ 98.5% (hydrochloric acid - acetone titration method, Example 7).

[0123] Thermal stability: The deviation of the initial temperature of thermal decomposition detected by TGA from the standard sample < 0.5 °C (Example 7).

[0124] Abnormal treatment of raw materials:

[0125] When the nitrogen replacement ≥ 15 minutes and the heating ≥ 2 h still exceed the standard (such as the color number 20 APHA in Example 8), replace the adipic acid of guaranteed reagent grade or the butanediol of polymerization grade (verification of the raw material purity in Example 1).

[0126] Temperature - time correlation matrix:

[0127] Temperature range (°C) Recommended heating time (h) Verification result of example 180-190 2.5 Low degree of polymerization (Example 1) 200-210 2 Optimal result (Examples 2, 7) ≥220 1.5 Risk of side reaction (Example 3)

[0128] Conclusion: The process optimization method of the present invention establishes a closed-loop control system centered on the nitrogen replacement time (15 minutes) and the gradient heating program (200 °C / 2 h) through chromaticity detection and dynamic parameter adjustment. Example 7 finally verifies the reliability of the system: the product has a color number of 10 APHA, a turbidity of 2 NTU, and a degree of polymerization of 0.96, which is significantly better than other parameter combinations, providing a standardized solution for industrial production.

[0129] The above description of the embodiments is to enable those of ordinary skill in the art to understand and use the invention. 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 efforts. Therefore, the present invention is not limited to the above embodiments, and all improvements and modifications made by those skilled in the art without departing from the scope of the present invention according to the disclosure of the present invention should be within the protection scope 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 2, 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.