Production method for continuous crystallization of high-purity pyromellitic dianhydride

Abstract

The invention relates to the technical field of pyromellitic dianhydride crystallization, in particular to a high-purity pyromellitic dianhydride continuous crystallization production method which comprises the following steps: introducing durene gas and oxygen-enriched gas into an oxidation reactor at the same time to output pyromellitic dianhydride gas; trapping pyromellitic dianhydride crude product particles; preparing a pyromellitic dianhydride test solution; the comprehensiveness of pyromellitic dianhydride gas trapping is judged; determining a comprehensive adjustment mode according to the comprehensive judgment result, namely adjusting the pressure difference in the oxidation reactor, or determining a crystallization mode of continuous crystallization, namely determining the single feeding amount in the crystallization process, or adjusting the reset frequency of the feeding position change in the crystallization process; and continuously crystallizing the pyromellitic dianhydride solution to separate out a pyromellitic dianhydride crystal finished product. According to the invention, the crystallization efficiency is improved, and the uniformity of crystallized crystals is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of pyromellitic dianhydride crystallization, and particularly relates to a production method for continuous crystallization of high-purity pyromellitic dianhydride. Background Art

[0002] In the prior art, compared with the traditional batch process, the continuous crystallization process can significantly improve production efficiency. By continuously inputting materials and outputting products, the waiting time and operation complexity in the production process are reduced, thereby increasing the overall production rate. The continuous crystallization technology helps to obtain high-quality pyromellitic dianhydride products.

[0003] Chinese Patent Publication No.: CN114853775A discloses a method for refining pyromellitic dianhydride, which is characterized by including the following steps: (1) Dissolution: Acetone and acetonitrile are mixed and stirred evenly in a dissolution kettle, and then crude anhydride containing pyromellitic dianhydride is added to the dissolution kettle, and the temperature is further raised and heated under reflux until the crude anhydride is dissolved, and the reflux temperature is 60-70°C; wherein, the purity of pyromellitic dianhydride in the crude anhydride raw material is 92-98%, acetone and acetonitrile are formulated into a mixed solvent with a weight ratio of (2-4):1, and the weight ratio of the crude anhydride to the mixed solvent is 1:(4-12); (2) Filtration: Insoluble impurities are removed by filtration in a hot state; (3) Oxidation: Air containing ozone is introduced into the filtrate for oxidation; (4) Distillation: Part of the solvent is removed by distillation; (5) Crystallization: The remaining mother liquor is cooled and crystallized while controlling the stirring rate until crystals precipitate; (6) Filtration-drying: The crystallized material is obtained as a qualified refined anhydride product through a filter dryer. It can be seen that the method for refining pyromellitic dianhydride has the problems that the pyromellitic dianhydride gas condenses prematurely due to the influence of low temperature when entering the condensation tower, and the air pressure at the reaction position increases due to the exothermic effect of the oxidation reaction, thereby squeezing the subsequent introduced raw materials, resulting in different intermolecular interaction potential energies, and further leading to a decrease in the crystallization efficiency during the crystallization process. Summary of the Invention

[0004] Therefore, the present invention provides a production method for continuous crystallization of high-purity pyromellitic dianhydride to overcome the problems in the prior art that the pyromellitic dianhydride gas condenses prematurely due to the influence of low temperature when entering the condensation tower, and the air pressure at the reaction position increases due to the exothermic effect of the oxidation reaction, thereby squeezing the subsequent introduced raw materials, resulting in different intermolecular interaction potential energies, and further leading to a decrease in the crystallization efficiency during the crystallization process.

[0005] To achieve the above object, the present invention provides a production method for continuous crystallization of high-purity pyromellitic dianhydride, including:

[0006] Simultaneously introducing mesitylene gas and oxygen-rich gas into an oxidation reactor for an oxidation reaction to output pyromellitic dianhydride gas;

[0007] Pass the pyromellitic dianhydride gas into a sublimation tower to sublime the pyromellitic dianhydride gas, and collect the crude pyromellitic dianhydride particles output from the sublimation tower;

[0008] Dissolve the crude pyromellitic dianhydride particles in a test solvent to prepare a pyromellitic dianhydride test solution;

[0009] Determine the comprehensiveness of the capture of the pyromellitic dianhydride gas according to the concentration of the pyromellitic dianhydride gas at the oxygen-rich gas inlet position of the oxidation reactor;

[0010] Determine the comprehensiveness adjustment method according to the determination result of the comprehensiveness, including adjusting the pressure difference in the oxidation reactor,

[0011] Alternatively, determine the crystallization method of continuous crystallization according to the average change rate of the distribution area of the crude pyromellitic dianhydride particles in the sublimation tower, including determining the single feed amount in the crystallization process according to the flow rate of the pyromellitic dianhydride gas entering the sublimation tower,

[0012] Alternatively, adjust the reset frequency of the change of the feed position in the crystallization process according to the maximum stacking thickness of the crude pyromellitic dianhydride particles;

[0013] Dissolve the crude pyromellitic dianhydride particles in a crystallization solvent according to the comprehensiveness adjustment method to generate a pyromellitic dianhydride standard solution, and perform continuous crystallization on the pyromellitic dianhydride solution to precipitate finished pyromellitic dianhydride crystals.

[0014] Further, determining the comprehensiveness of the capture of the pyromellitic dianhydride gas according to the concentration of the pyromellitic dianhydride gas at the oxygen-rich gas inlet position of the oxidation reactor includes:

[0015] Obtain the concentration of the pyromellitic dianhydride gas;

[0016] Compare the concentration of the pyromellitic dianhydride gas with a preset gas concentration;

[0017] If the concentration of the pyromellitic dianhydride gas is greater than the preset gas concentration, it is determined that the capture of the pyromellitic dianhydride gas is not comprehensive, and the pressure difference in the oxidation reactor is increased;

[0018] If the concentration of the pyromellitic dianhydride gas is less than the preset gas concentration, it is determined that the capture of the pyromellitic dianhydride gas is comprehensive.

[0019] Further, the pressure difference is the difference between the compressed gas pressure of the sublimation tower and the intake pressure of the oxygen-rich gas of the oxidation reactor.

[0020] Furthermore, the pressure difference is positively correlated with the concentration of the pyromellitic dianhydride gas.

[0021] Furthermore, determining the single feed amount in the crystallization process includes:

[0022] When the trapping of the pyromellitic dianhydride gas is complete, obtain the distribution area of the sublimed crude pyromellitic dianhydride particles on the lower surface of the sublimation tower and the duration for the complete sublimation of the pyromellitic dianhydride gas;

[0023] Calculate the average change rate of the distribution area of the crude pyromellitic dianhydride particles based on the distribution area of the sublimed crude pyromellitic dianhydride particles on the lower surface of the sublimation tower and the duration for the complete sublimation of the pyromellitic dianhydride gas;

[0024] Compare the average change rate with a preset average change rate;

[0025] If the average change rate is greater than the preset average change rate, determine that the type of the crude pyromellitic dianhydride particles is the dispersed type, and increase the single feed amount according to the distribution area of the crude pyromellitic dianhydride particles.

[0026] Furthermore, the increasing of the single feed amount according to the distribution area of the crude pyromellitic dianhydride particles includes:

[0027] When the crude pyromellitic dianhydride particles are of the dispersed type, obtain the flow rate of the pyromellitic dianhydride gas entering the sublimation tower;

[0028] If the flow rate is greater than the preset flow rate, determine that the sublimation dispersion condition does not meet the requirements, reduce the dispersion area of the crude pyromellitic dianhydride particles, and obtain the corrected dispersion area after reduction and the standard dispersion area that meets the adjustment conditions;

[0029] Calculate the area difference between the corrected dispersion area and the standard dispersion area, and increase the single feed amount according to the area difference.

[0030] Furthermore, the adjustment condition is that the average change rate is equal to the preset average change rate.

[0031] Furthermore, the corrected dispersion area is negatively correlated with the preset flow rate; the single feed amount is positively correlated with the area difference.

[0032] Furthermore, the adjusting of the reset frequency of the feed position change during the crystallization process according to the maximum stacking thickness of the crude pyromellitic dianhydride particles includes:

[0033] When the trapping of pyromellitic dianhydride gas is complete, obtain the average rate of change;

[0034] If the average rate of change is less than the preset average rate of change, determine that the type of the crude pyromellitic dianhydride particles is the stacked type, and obtain the standard maximum stacking thickness that meets the adjustment conditions;

[0035] Calculate the thickness difference between the maximum stacking thickness and the standard maximum stacking thickness, and increase the reset frequency of the change in the feeding position during the crystallization process according to the thickness difference,

[0036] Wherein, the reset frequency is the ratio of the number of times the feeding position completes the position change and resets to the unit time.

[0037] Further, the reset frequency is positively correlated with the thickness difference.

[0038] Compared with the prior art, the beneficial effect of the present invention is that the method of the present invention determines the position of the product in the oxidation reactor. Since heat is released at the reaction position during the oxidation reaction, the air pressure around the reaction increases, which in turn causes the pyromellitic dianhydride gas to diffuse irregularly under the action of the pressure difference. It will also squeeze the subsequent introduced oxygen-rich gas, making the distribution of pyromellitic dianhydride gas in the sublimation tower uneven, thereby affecting the crystallization efficiency of pyromellitic dianhydride. By adjusting the pressure difference in the oxidation reactor, it is possible to prevent the diffused pyromellitic dianhydride gas from sublimating prematurely due to temperature at the inlet position of the sublimation tower, avoiding local accumulation and premature sublimation of pyromellitic dianhydride gas at the inlet of the sublimation tower; due to the heat release effect of the oxidation reaction, the air pressure at the reaction position increases, which in turn squeezes the subsequent introduced raw materials, resulting in different intermolecular interaction potential energies. After sublimation, the particles show the phenomenon of dispersion due to large potential energy or stacking due to small potential energy due to the influence of the potential energy inside the molecules. The dispersed particles are prone to mutual extrusion during the crystallization process, resulting in incomplete crystallization, while the stacked particles are prone to form overly large aggregates, affecting the final purity and particle size distribution of pyromellitic dianhydride. By adjusting the crystallization conditions according to the type of the crude pyromellitic dianhydride particles, the improvement of the sufficiency of crystallization and the improvement of the crystal uniformity are realized, and thus the improvement of the crystallization efficiency is realized.

[0039] Furthermore, in the method of the present invention, by determining whether the comprehensiveness of the product capture meets the requirements, due to the pressure fluctuations formed during the reaction in the oxidation reactor, the pyromellitic dianhydride gas cannot be completely introduced into the sublimation tower for comprehensive capture, resulting in the escape of unreacted gas. This not only wastes raw materials but also may cause environmental pollution, or due to aggregation at the inlet position of the sublimation tower and being cooled and sublimated, sublimation particles accumulate at the inlet position of the sublimation tower, leading to a decrease in the capture efficiency. By measuring the concentration of the pyromellitic dianhydride gas and comparing it with a preset value, instant feedback and precise control of the capture effect are achieved.

[0040] Furthermore, in the method of the present invention, by increasing the pressure difference in the oxidation reactor, the air flow effect in the oxidation reactor is increased, thereby accelerating the entry of the pyromellitic dianhydride gas into the sublimation tower, reducing the accumulation of the pyromellitic dianhydride gas at the inlet position of the sublimation tower, and increasing the regularity of the movement trajectory of the pyromellitic dianhydride gas in the oxidation reactor, avoiding the reduction of the capture efficiency caused by the local accumulation of the pyromellitic dianhydride gas in the sublimation tower, and achieving an increase in the comprehensiveness of the capture of the crude pyromellitic dianhydride particles.

[0041] Furthermore, in the method of the present invention, by determining the type of the crude pyromellitic dianhydride particles, since the intermolecular potential energy is different when generating the pyromellitic dianhydride gas, the dispersion states during sublimation in the sublimation tower are different. For the particles of the dispersion type and the stacking type, there are significant differences in the crystallization efficiency and crystal quality during the crystallization process. By accurately judging the type of the crude pyromellitic dianhydride particles and adjusting the crystallization conditions accordingly, the improvement of the crystallization efficiency is achieved.

[0042] Furthermore, in the method of the present invention, by correcting the dispersion area of the crude pyromellitic dianhydride particles of the dispersion type, the accuracy of the adjustment parameters is improved. Since there is a strong cohesive force between the particles of the stacking type, their resistance to the external air flow is strong and they are not easily dispersed. Since the intermolecular interaction force of the products of the dispersion type is large and the degree of the external force affected by the flow rate is large, the upper-layer particles after condensation into particles are easily dispersed by the flowing gas, resulting in an error in the dispersion area affected by the external force after the sublimation ends, and further leading to inaccurate adjustment of the parameters in the subsequent adjustment. By correcting the dispersion area, the improvement of the stability and accuracy of the crystallization is achieved.

[0043] Furthermore, by increasing the single feed amount in the crystallization process of the dispersion type, the present invention reduces the problem that the crystallization efficiency of the dispersed pyromellitic dianhydride decreases due to the large internal potential energy during the crystallization process. Since the particles of pyromellitic dianhydride of the dispersion type have high activity during the crystallization process, their movement speed during crystallization is relatively fast, thus affecting the stability and efficiency of crystallization. By increasing the single feed amount, the particle concentration in the crystallizer can be increased and the space in the crystallizer can be reduced, so that the efficiency of crystal nucleus generation during crystallization is increased, and the stability and efficiency of crystallization are improved.

[0044] Furthermore, by increasing the reset frequency of the change in the feed position in the crystallization process of the stacked type, the present invention increases the laminar flow effect in the solution, which in turn drives the movement of pyromellitic dianhydride in the solution, avoiding the decrease in crystallization purity caused by its agglomeration. By increasing the reset frequency, the stacked structure can be broken, making the particles more dispersed, which is beneficial to obtaining pyromellitic dianhydride crystals with high purity and uniform particle size, and the crystallization effect is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 It is the overall flowchart of the production method for continuous crystallization of high-purity pyromellitic dianhydride according to an embodiment of the present invention;

[0046] Figure 2 It is the comprehensive flowchart for determining the gas capture of pyromellitic dianhydride in the production method for continuous crystallization of high-purity pyromellitic dianhydride according to an embodiment of the present invention;

[0047] Figure 3 It is the flowchart for determining the single feed amount in the crystallization process of the production method for continuous crystallization of high-purity pyromellitic dianhydride according to an embodiment of the present invention;

[0048] Figure 4 It is the partial structural schematic diagram of the crystallizer used in the production method for continuous crystallization of high-purity pyromellitic dianhydride according to an embodiment of the present invention;

[0049] Explanation of the reference numerals in the drawings: 1 - feed slide rail, 2 - feed slider, 3 - feed hose, 4 - feed valve. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] In order to make the objectives and advantages of the present invention clearer, the present invention will be further described below in conjunction with embodiments; it should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0051] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. Those skilled in the art should understand that these embodiments are only used to explain the technical principles of the present invention and do not limit the protection scope of the present invention.

[0052] It should be noted that in the description of the present invention, the terms indicating the direction or positional relationship such as "upper", "lower", "left", "right", "inner", "outer", etc. are based on the direction or positional relationship shown in the drawings. This is only for the convenience of description and does not indicate or imply that the device or element must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation to the present invention.

[0053] In addition, it should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "installation", "connection", and "coupling" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0054] Please refer to Figure 1 、 Figure 2 、 Figure 3 and Figure 4 as shown, which are respectively the overall flowchart of the production method for continuous crystallization of high-purity pyromellitic dianhydride in the embodiments of the present invention, the comprehensive flowchart for determining the comprehensiveness of pyromellitic dianhydride gas capture, the flowchart for determining the single feed amount in the crystallization process, and the partial structural schematic diagram of the crystallizer used in the production method for continuous crystallization of high-purity pyromellitic dianhydride. A production method for continuous crystallization of high-purity pyromellitic dianhydride in an embodiment of the present invention includes:

[0055] Step S1, simultaneously introducing mesitylene gas and oxygen-rich gas into an oxidation reactor for an oxidation reaction to output pyromellitic dianhydride gas;

[0056] Step S2, introducing the pyromellitic dianhydride gas into a sublimation tower to sublime the pyromellitic dianhydride gas, and capturing the crude pyromellitic dianhydride particles output from the sublimation tower;

[0057] Step S3, dissolving the crude pyromellitic dianhydride particles in a test solvent to prepare a pyromellitic dianhydride test solution;

[0058] Step S4, determining the comprehensiveness of pyromellitic dianhydride gas capture according to the concentration of the pyromellitic dianhydride gas at the oxygen-rich gas inlet position of the oxidation reactor;

[0059] Step S5, determining the comprehensive adjustment method according to the determination result of the comprehensiveness, including adjusting the pressure difference inside the oxidation reactor,

[0060] Alternatively, determine the crystallization mode of continuous crystallization according to the average change rate of the distribution area of the crude pyromellitic dianhydride particles in the sublimation tower, including determining the single feed amount in the crystallization process according to the flow rate of the pyromellitic dianhydride gas entering the sublimation tower.

[0061] Or, adjust the reset frequency of the change of the feed position in the crystallization process according to the maximum stacking thickness of the crude pyromellitic dianhydride particles.

[0062] In step S6, dissolve the crude pyromellitic dianhydride particles into the crystallization solvent according to the comprehensive adjustment method to generate a standard pyromellitic dianhydride solution, and perform continuous crystallization on the pyromellitic dianhydride solution to precipitate the finished pyromellitic dianhydride crystals.

[0063] Specifically, in step S1, the reactants participating in the oxidation reaction include durene gas used as the reaction raw material and oxygen-rich gas, and the active component used as the catalyst is a surface-coated catalyst of V2O5—TiO2.

[0064] Optionally, the oxygen-rich gas can be one or more of ozone and a nitrogen-oxygen mixed gas with an oxygen volume content of 21%-50%. A preferred embodiment of the oxygen-rich gas is a nitrogen-oxygen mixed gas with an oxygen volume content of 21%-50%.

[0065] Optionally, the general value range of the molar ratio of durene to the oxygen-rich gas is [(1:118), (1:131)], and a preferred embodiment of the molar ratio of durene to air is 1:124.

[0066] In practice, the catalyst can be selected from one of V2O5-P2O5 catalyst, V2O5-P2O5-Al2O3 catalyst, and V2O5-MoO3-P2O5 catalyst.

[0067] Specifically, in step S2, the method of sublimating the pyromellitic dianhydride gas is to introduce the sublimated gas of dry ice into the sublimation tower.

[0068] In step S2, a compressor is arranged inside the sublimation tower to compress the gas in the compressed sublimation tower so that the pyromellitic dianhydride gas enters the sublimation tower from the oxidation reactor.

[0069] A gas flow pipeline is connected between the oxidation reactor and the sublimation tower.

[0070] Specifically, in step S6, continuous crystallization of the pyromellitic dianhydride solution is achieved in the crystallizer.

[0071] Specifically, examples of the test solvent and the crystallization solvent include N-methyl-2-pyrrolidone, dimethyl sulfoxide, and dimethylformamide. Among them, the general value range of the mass concentration of the crude pyromellitic dianhydride particles in the above solution is [5%, 16%], and a preferred example of the mass concentration of the crude pyromellitic dianhydride particles in the above solution is 12%.

[0072] In the implementation, the method of the present invention determines the position of the product in the oxidation reactor. Since heat is released at the reaction position during the oxidation reaction, the air pressure around the reaction increases, which in turn causes the irregular diffusion of the pyromellitic dianhydride gas under the action of the pressure difference. It will also squeeze the subsequent oxygen-rich gas, making the distribution of the pyromellitic dianhydride gas in the sublimation tower uneven, thereby affecting the crystallization efficiency of the pyromellitic dianhydride. By adjusting the pressure difference in the oxidation reactor, the diffused pyromellitic dianhydride gas is prevented from sublimating prematurely due to temperature at the entrance of the sublimation tower, avoiding local accumulation and premature sublimation of the pyromellitic dianhydride gas at the entrance of the sublimation tower; due to the heat release of the oxidation reaction, the air pressure at the reaction position increases, which in turn squeezes the subsequent raw materials, resulting in different intermolecular interaction potential energies. The sublimated particles show the phenomenon of dispersion due to large potential energy or lamination due to small potential energy due to the influence of the intramolecular potential energy. The dispersed particles are prone to mutual extrusion during the crystallization process, resulting in incomplete crystallization, while the laminated particles are prone to form too large aggregates, affecting the purity and particle size distribution of the final pyromellitic dianhydride. By adjusting the crystallization conditions according to the type of the crude pyromellitic dianhydride particles, the improvement of the crystallization sufficiency and the improvement of the crystal uniformity are achieved, and thus the improvement of the crystallization efficiency is realized.

[0073] Specifically, the comprehensiveness of the pyromellitic dianhydride gas capture is determined according to the concentration of the pyromellitic dianhydride gas at the oxygen-rich gas inlet position of the oxidation reactor, including:

[0074] Obtain the concentration of the pyromellitic dianhydride gas;

[0075] Compare the concentration of the pyromellitic dianhydride gas with a preset gas concentration;

[0076] If the concentration of the pyromellitic dianhydride gas is greater than the preset gas concentration, it is determined that the pyromellitic dianhydride gas capture is not comprehensive, and the pressure difference in the oxidation reactor is increased;

[0077] If the concentration of the pyromellitic dianhydride gas is less than the preset gas concentration, it is determined that the pyromellitic dianhydride gas capture is comprehensive.

[0078] Specifically, a gas detector for detecting the volume concentration of the pyromellitic dianhydride gas is provided on the inner wall at the oxygen-rich gas inlet position of the oxidation reactor.

[0079] Specifically, a pressure regulating valve for regulating the pressure of the oxygen-rich gas is provided at the oxygen-rich gas inlet position of the oxidation reactor.

[0080] Specifically, the general value range of the preset gas concentration is [15% Vol, 26% Vol], and a preferred embodiment of the preset gas concentration is 20% Vol.

[0081] In implementation, in the method of the present invention, by determining whether the comprehensiveness of the product capture meets the requirements, due to the pressure fluctuation formed by the reaction in the oxidation reactor, the pyromellitic dianhydride gas cannot be completely introduced into the sublimation tower for comprehensive capture, resulting in the escape of unreacted gas, which not only wastes raw materials but also may cause environmental pollution, or due to aggregation at the inlet position of the sublimation tower and being cooled and sublimated, the sublimation particles accumulate at the inlet position of the sublimation tower, resulting in a decrease in the capture efficiency. By measuring the concentration of the pyromellitic dianhydride gas and comparing it with the preset value, the instant feedback and precise control of the capture effect are realized.

[0082] Specifically, the pressure difference is the difference between the compressed gas pressure of the sublimation tower and the intake pressure of the oxygen-rich gas in the oxidation reactor.

[0083] Specifically, the pressure difference is positively correlated with the concentration of the pyromellitic dianhydride gas.

[0084] In implementation, when the difference between the concentration of the pyromellitic dianhydride gas and the preset gas concentration is within 1% Vol, the pressure difference increases by 50 Pa. When the difference between the concentration of the pyromellitic dianhydride gas and the preset gas concentration exceeds 1% Vol, for each additional 1% Vol, the pressure difference increases by 60 Pa. For example, if the concentration of the pyromellitic dianhydride gas is 22% Vol and the current pressure difference is 600 Pa, then the pressure difference increases to 600 Pa + 50 Pa + 60 Pa = 710 Pa.

[0085] In implementation, in the method of the present invention, by increasing the pressure difference in the oxidation reactor, the air flow effect in the oxidation reactor is increased, thereby accelerating the entry of the pyromellitic dianhydride gas into the sublimation tower, reducing the accumulation of the pyromellitic dianhydride gas at the inlet position of the sublimation tower, and increasing the regularity of the movement trajectory of the pyromellitic dianhydride gas in the oxidation reactor, avoiding the reduction of the capture efficiency caused by the local accumulation of the pyromellitic dianhydride gas in the sublimation tower, and realizing the increase in the comprehensiveness of the capture of the crude pyromellitic dianhydride particles.

[0086] Specifically, determining the single feed amount in the crystallization process includes,

[0087] When the capture of pyromellitic dianhydride gas is complete, obtain the distribution area of the sublimated crude pyromellitic dianhydride particles on the lower surface of the sublimation tower and the duration for the complete sublimation of pyromellitic dianhydride gas.

[0088] Calculate the average change rate of the distribution area of the crude pyromellitic dianhydride particles based on the distribution area of the sublimated crude pyromellitic dianhydride particles on the lower surface of the sublimation tower and the duration for the complete sublimation of pyromellitic dianhydride gas.

[0089] Compare the average change rate with a preset average change rate.

[0090] If the average change rate is greater than the preset average change rate, determine that the type of the crude pyromellitic dianhydride particles is a dispersed type, and increase the single feed amount according to the distribution area of the crude pyromellitic dianhydride particles.

[0091] Specifically, the increase of the single feed amount according to the distribution area of the crude pyromellitic dianhydride particles includes:

[0092] When the crude pyromellitic dianhydride particles are of the dispersed type, obtain the flow rate of the pyromellitic dianhydride gas entering the sublimation tower.

[0093] If the flow rate is greater than a preset flow rate, determine that the sublimation dispersion condition does not meet the requirements, reduce the dispersion area of the crude pyromellitic dianhydride particles, and obtain the corrected dispersion area after reduction and the standard dispersion area that meets the adjustment condition.

[0094] Calculate the area difference between the corrected dispersion area and the standard dispersion area, and increase the single feed amount according to the area difference.

[0095] Specifically, the adjustment condition is that the average change rate is equal to the preset average change rate.

[0096] Specifically, the corrected dispersion area is negatively correlated with the preset flow rate; the single feed amount is positively correlated with the area difference.

[0097] Specifically, a camera is provided above the capture position in the sublimation tower to detect the distribution area of the crude pyromellitic dianhydride particles, and the detection method is to perform edge detection on the crude pyromellitic dianhydride particles and calculate the area.

[0098] Specifically, the general value range of the preset average change rate is [0.004㎡ / s, 0.007㎡ / s], and the preferred embodiment of the preset average change rate is 0.006㎡ / s.

[0099] In implementation, the method of the present invention determines the type of pyromellitic dianhydride crude product particles. Since the intermolecular potential energy is different when generating pyromellitic dianhydride gas, the dispersion state during sublimation in the sublimation tower is different. There are significant differences in the crystallization efficiency and crystal quality of dispersed-type and stacked-type particles during the crystallization process. By accurately judging the type of pyromellitic dianhydride crude product particles and adjusting the crystallization conditions accordingly, the improvement of crystallization efficiency is achieved.

[0100] Specifically, the general value range of the preset flow rate is [2.2 m / s, 2.5 m / s], and the preferred embodiment of the preset flow rate is 2.4 m / s.

[0101] Specifically, the corrected dispersion area is the product of the nth power of the flow rate and the empirical constant k, where n is the sensitivity index, and k and n are determined through experiments.

[0102] Specifically, the general value range of the sensitivity index is [0.88, 0.96], and the general value range of the empirical constant is [0.94, 0.99].

[0103] Preferably, the preferred embodiment of the sensitivity index is 0.9, and the preferred embodiment of the empirical constant is 0.96.

[0104] In implementation, the method of the present invention corrects the dispersion area of the dispersed-type pyromellitic dianhydride crude product particles to improve the accuracy of the adjustment parameters. Since there is a strong cohesive force between the stacked-type particles, their resistance to the external air flow is strong and they are not easily dispersed. Since the intermolecular interaction force of the dispersed-type product is large and the degree of external force affected by the flow rate is large, the upper-layer particles after condensation into particles are easily dispersed by the flowing gas, resulting in an error in the dispersion area affected by the external force after sublimation ends, and further leading to inaccurate adjustment of the parameters in the subsequent adjustment. By correcting the dispersion area, the improvement of the stability and accuracy of crystallization is achieved.

[0105] Specifically, the single feed rate is adjusted by the feed valve in the crystallizer.

[0106] In implementation, when the area difference between the corrected dispersion area and the standard dispersion area is within 0.0001 ㎡, the single feed rate is increased by 50 ml. When the area difference between the corrected dispersion area and the standard dispersion area exceeds 0.0001 ㎡, for every 0.0001 ㎡ exceeded, the single feed rate is increased by 65 ml. For example, if the area difference between the corrected dispersion area and the standard dispersion area is 0.0003 ㎡ and the current single feed rate is 600 ml, then the single feed rate is increased to 600 ml + 50 ml + 65 ml + 65 ml = 780 ml.

[0107] In implementation, the method of the present invention increases the single feed amount in the crystallization process of the dispersed type, reducing the problem that the crystallization efficiency of the dispersed pyromellitic dianhydride decreases due to the large internal potential energy during the crystallization process. Since the pyromellitic dianhydride particles of the dispersed type have high activity during the crystallization process, their movement speed during crystallization is relatively fast, thus affecting the stability and efficiency of crystallization. By increasing the single feed amount, the particle concentration in the crystallizer can be increased and the space in the crystallizer can be reduced, so that the efficiency of crystal nucleus generation during crystallization is increased, achieving an improvement in the stability and efficiency of crystallization.

[0108] Specifically, adjusting the reset frequency of the feed position change during the crystallization process according to the maximum stacking thickness of the crude pyromellitic dianhydride particles includes:

[0109] When the gas capture of pyromellitic dianhydride is complete, obtain the average change rate;

[0110] If the average change rate is less than the preset average change rate, determine that the type of the crude pyromellitic dianhydride particles is the stacking type, and obtain the standard maximum stacking thickness that meets the adjustment conditions;

[0111] Calculate the thickness difference between the maximum stacking thickness and the standard maximum stacking thickness, and increase the reset frequency of the feed position change during the crystallization process according to the thickness difference.

[0112] Wherein, the reset frequency is the ratio of the number of times the feed position completes the position change and resets to the unit time.

[0113] Specifically, the reset frequency is positively correlated with the thickness difference.

[0114] Specifically, a feed hose connected to the feed valve for feeding is provided in the crystallizer. The end of the feed hose is connected to a feed slider for adjusting the position of the feed hose, and a feed slide rail for restricting the position of the feed slider in the crystallizer is provided on the inner wall of the crystallizer.

[0115] Specifically, an infrared sensor is provided above the capture position in the sublimation tower for detecting the maximum stacking thickness. The detection method is that the infrared sensor emits infrared rays perpendicular to the plane where the pyromellitic dianhydride particles are located, and obtains the stacking thickness of the pyromellitic dianhydride particles at each position and takes the maximum value.

[0116] Specifically, the general value range of the number of feed positions within the position change cycle completed by the feed position per unit time is [4, 8], and the preferred embodiment of the number of feed positions within the position change cycle completed by the feed position per unit time is 6.

[0117] In implementation, when the thickness difference between the maximum stacking thickness and the standard maximum stacking thickness is within 0.001 m, the reset frequency increases by 0.08 times / minute. When the thickness difference between the maximum stacking thickness and the standard maximum stacking thickness exceeds 0.0001 ㎡, for every 0.001 m exceeded, the reset frequency increases by 0.05 times / minute. For example, if the thickness difference between the maximum stacking thickness and the standard maximum stacking thickness is 0.002 m and the reset frequency is 0.2 times / minute, then the reset frequency increases to 0.2 times / minute + 0.08 times / minute + 0.05 times / minute = 0.33 times / minute.

[0118] Specifically, the standard dispersion area and the standard maximum stacking thickness are respectively positively correlated with the concentration of pyromellitic dianhydride gas.

[0119] In implementation, the method of the present invention increases the reset frequency of the feed position change in the crystallization process of the stacking type, increasing the laminar flow effect in the solution and thus driving the movement of pyromellitic dianhydride in the solution, avoiding the decrease in crystallization purity caused by its agglomeration. By increasing the reset frequency, the stacking structure can be broken, making the particles more dispersed, which is conducive to obtaining pyromellitic dianhydride crystals with high purity and uniform particle size, achieving an increase in the crystallization effect.

[0120] So far, the technical solution of the present invention has been described in conjunction with the preferred embodiments shown in the drawings. However, it is easy for those skilled in the art to understand that the protection scope of the present invention is obviously not limited to these specific embodiments. Without departing from the principle of the present invention, those skilled in the art can make equivalent changes or substitutions to the relevant technical features, and the technical solutions after these changes or substitutions will all fall within the protection scope of the present invention.

Claims

1. A method for producing high-purity pyromellitic dianhydride by continuous crystallization, characterized in that: include: The durene gas and the oxygen-rich gas are simultaneously introduced into the oxidation reactor for oxidation reaction to output pyromellitic dianhydride gas; Passing the pyromellitic anhydride gas into a desublimation tower to desublimate the pyromellitic anhydride gas, and capturing crude pyromellitic anhydride particles output from the desublimation tower; Dissolving the crude pyromellitic anhydride particles into a test solvent to prepare a pyromellitic anhydride test solution; Determining the comprehensiveness of pyromellitic anhydride gas capture based on the concentration of the pyromellitic anhydride gas at the oxygen-rich gas inlet position of the oxidation reactor; Determining a comprehensive adjustment method based on the comprehensive determination result, including adjusting the pressure difference in the oxidation reactor, or, determining the continuous crystallization mode according to the average change rate of the distribution area of ​​the crude pyromellitic anhydride particles in the desublimation tower, including determining the single feed amount of the crystallization process according to the flow rate of the pyromellitic anhydride gas entering the desublimation tower, Or, adjusting the resetting frequency of the feed position change during the crystallization process according to the maximum stacking thickness of the crude pyromellitic dianhydride particles; According to the comprehensive adjustment method, the crude granules of pyromellitic anhydride are dissolved in a crystallization solvent to generate a pyromellitic anhydride standard solution, and the pyromellitic anhydride solution is continuously crystallized to precipitate pyromellitic anhydride crystal products.

2. The production method of continuous crystallization of high-purity pyromellitic dianhydride according to claim 1, characterized in that: The comprehensiveness of capturing the pyromellitic anhydride gas is determined based on the concentration of the pyromellitic anhydride gas at the oxygen-rich gas inlet position of the oxidation reactor, including: Obtaining the concentration of the pyromellitic anhydride gas; Comparing the concentration of the pyromellitic anhydride gas with a preset gas concentration; If the concentration of the pyromellitic anhydride gas is greater than the preset gas concentration, it is determined that the pyromellitic anhydride gas is not fully captured, and the pressure difference in the oxidation reactor is increased; If the concentration of the pyromellitic anhydride gas is less than the preset gas concentration, it is determined that the pyromellitic anhydride gas is fully captured.

3. The production method of continuous crystallization of high-purity pyromellitic dianhydride according to claim 2, characterized in that: The pressure difference is the difference between the compressed gas pressure of the desublimation tower and the inlet pressure of the oxygen-rich gas of the oxidation reactor.

4. The production method of continuous crystallization of high-purity pyromellitic dianhydride according to claim 3, characterized in that: The pressure difference is positively correlated with the concentration of the pyromellitic anhydride gas.

5. The production method of continuous crystallization of high-purity pyromellitic dianhydride according to claim 4, characterized in that: Determine the single feed amount for the crystallization process, including, When the pyromellitic anhydride gas is fully captured, the distribution area of ​​the crude pyromellitic anhydride particles on the lower surface of the desublimation tower after desublimation and the time taken for the pyromellitic anhydride gas to be completely desublimated are obtained; Calculating the average rate of change of the distribution area of ​​the crude pyromellitic dianhydride particles according to the distribution area of ​​the crude pyromellitic dianhydride particles on the lower surface of the desublimation tower after desublimation and the time it takes for the pyromellitic dianhydride gas to completely desublimate; comparing the average rate of change with a preset average rate of change; If the average change rate is greater than the preset average change rate, the type of the crude pyromellitic anhydride particles is determined to be a dispersed type, and the single feed amount is increased according to the distribution area of ​​the crude pyromellitic anhydride particles.

6. The production method of continuous crystallization of high-purity pyromellitic dianhydride according to claim 5, characterized in that: The method of increasing the single feed amount according to the distribution area of ​​the crude pyromellitic anhydride particles comprises: When the crude pyromellitic anhydride particles are of dispersed type, the flow rate of the pyromellitic anhydride gas entering the desublimation tower is obtained; If the flow rate is greater than the preset flow rate, it is determined that the desublimation dispersion condition does not meet the requirements, and the dispersion area of ​​the crude pyromellitic anhydride particles is reduced, and the reduced corrected dispersion area and the standard dispersion area that meets the adjustment conditions are obtained; The area difference between the corrected dispersion area and the standard dispersion area is calculated, and the single feed amount is increased according to the area difference.

7. The production method of continuous crystallization of high-purity pyromellitic dianhydride according to claim 6, characterized in that: The adjustment condition is that the average change rate is equal to the preset average change rate.

8. The method for producing high-purity pyromellitic dianhydride continuous crystallization according to claim 7, characterized in that: The corrected dispersion area is negatively correlated with the preset flow rate; the single feed volume is positively correlated with the area difference.

9. The method for producing high-purity pyromellitic dianhydride continuous crystallization according to claim 8, characterized in that: The method of adjusting the resetting frequency of the feed position change during the crystallization process according to the maximum stacking thickness of the crude pyromellitic dianhydride particles comprises: When the pyromellitic anhydride gas is fully captured, obtaining the average change rate; If the average change rate is less than the preset average change rate, the type of the crude pyromellitic anhydride particles is determined to be a stacking type, and a standard maximum stacking thickness that meets the adjustment conditions is obtained; calculating the thickness difference between the maximum stacking thickness and the standard maximum stacking thickness, and increasing the resetting frequency of the feed position change during the crystallization process according to the thickness difference, The reset frequency is the ratio of the number of times the feeding position completes position change and resets to the unit time.

10. The method for producing high-purity pyromellitic dianhydride continuous crystallization according to claim 9, characterized in that: The resetting frequency is positively correlated with the thickness difference.

Images