Aniline acetonitrile pretreatment process for reducing emission of volatile organic compounds

Abstract

The invention relates to the technical field of pretreatment of organic chemical raw materials, discloses an anilinoacetonitrile pretreatment process for reducing emission of volatile organic compounds, and aims to solve the problems that in the prior art, when solid anilinoacetonitrile is fed, the volatile organic compounds escape, and impurities are mixed into hydrolysate, so that the quality is reduced. The method comprises the following steps: conveying solid-state anilinoacetonitrile to a pretreatment container under a closed condition, carrying out segmented temperature control heating to completely convert the solid-state anilinoacetonitrile into a uniform liquid phase, standing in a closed and constant-temperature environment, and synchronously realizing condensation reflux of volatile organic compounds and gravity settling of polymorphic impurities, finally, supernatant liquid is conveyed to a downstream process through a closed heat preservation pipeline, bottom sedimentation impurities are discharged, emission of volatile organic compounds is reduced from the source, impurities such as catalyst residues and polymers in the raw materials are efficiently separated, the purity of anilinoacetonitrile is improved, and the production cost is reduced through the whole-process closed operation and function cooperation treatment steps. The yield and quality of downstream products are guaranteed, and meanwhile, the working environment is improved.

Description

Technical Field

[0001] This invention relates to the field of organic chemical raw material pretreatment technology, and in particular to an aniline acetonitrile pretreatment process for reducing volatile organic compound emissions. Background Technology

[0002] Aniline acetonitrile is a key intermediate in the field of organic synthesis and is widely used in the preparation of products such as indigo dyes and pharmaceutical compounds. In the existing technology, the industrial synthesis of aniline acetonitrile is mostly carried out by condensation reaction of aniline and hydroxyacetonitrile under the action of alkaline catalyst. For example, Chinese patent CN114716348A discloses a production method and system for aniline acetonitrile. After preheating the raw materials, they are fed into a combination system of microreactor and delayed reactor for reaction. The advantages of microreactor in precise temperature control and high mass and heat transfer efficiency are used to avoid polymerization side reactions caused by local overheating. Combined with phase separation and vacuum low-temperature evaporation dehydration process, high yield of aniline acetonitrile is prepared.

[0003] In the industrial production of aniline acetonitrile as a raw material to prepare aniline acetate via hydrolysis, there are two common technical challenges: First, existing processes typically involve directly feeding solid aniline acetonitrile into an open or semi-open hydrolysis reactor manually or mechanically. During the feeding process and initially after feeding, a large amount of volatile organic compounds (VOCs) in the raw material, mainly unreacted aniline, will escape into the workshop environment. Second, industrial-grade aniline acetonitrile usually contains various impurities, including incompletely reacted catalyst particles, polymer particles generated from side reactions, unreacted hydroxyacetonitrile, and trace amounts of aniline. If these solid raw materials containing complex impurities are directly fed into the hydrolysis reactor, the impurities will mix into the hydrolysis product aniline acetate, resulting in a reduction in its effective content and directly affecting the yield and quality of downstream indigo synthesis. Summary of the Invention

[0004] The technical problem to be solved by this invention is: how to provide a simple and effective pretreatment method for aniline acetonitrile hydrolysis, which enables the closed-loop internal circulation of volatile organic compounds and the preliminary separation of various forms of impurities to be achieved simultaneously in the same operating unit, thereby achieving the dual purpose of reducing emissions from the source and improving the purity of raw materials.

[0005] To achieve the above objectives, this application adopts the following technical solution: an aniline acetonitrile pretreatment process for reducing volatile organic compound emissions, comprising the following steps: S1: conveying solid aniline acetonitrile to a pretreatment container under closed conditions; S2: heating the solid aniline acetonitrile in the pretreatment container under closed conditions until it is completely melted into a liquid state; S3: allowing the liquid aniline acetonitrile to stand under closed conditions to simultaneously achieve condensation and reflux of volatile organic compounds and sedimentation and separation of impurities; S4: conveying the clear liquid formed after standing to the downstream process through a closed insulated pipeline and discharging the impurities settled at the bottom.

[0006] Preferably, the heating in S2 is segmented temperature-controlled heating, including a first stage of heating the material to 36-38℃ and holding it at that temperature for 70-90 minutes, and a second stage of continuing to heat it to 50-60℃.

[0007] Preferably, the settling temperature in step S3 is 50-60℃, and the settling time is 3.4-5.0h.

[0008] Preferably, the heating rate in the first stage is 0.8-1.2℃ / min, and the heating rate in the second stage is 1.0-2.0℃ / min.

[0009] Preferably, the settling process in S3 includes a first settling period, followed by low-speed stirring, and then a second settling period after the stirring is completed.

[0010] Preferably, the low-speed stirring speed is 30-40 r / min and the stirring time is 20-40 min.

[0011] Preferably, after the settling process in S3 is completed and the bottom sedimented impurities are discharged, a cooling and impurity separation step is included before the transfer of the upper clear liquid in S4.

[0012] Preferably, the cooling and precipitation process includes reducing the system temperature from the static temperature to 43-47°C at a rate of 0.3-0.5°C / min and holding the temperature for 50-70 minutes, after which the precipitate that has formed again is discharged.

[0013] Preferably, the heat tracing temperature of the sealed insulated pipe is 43-45℃.

[0014] Preferably, the solid aniline-based acetonitrile raw material contains at least one impurity selected from aniline, hydroxyacetonitrile, a benzene ring-containing organic polymer, and sodium carbonate or sodium hydroxide.

[0015] The technical effects and advantages of this invention are as follows: In this invention, the problems of volatile organic compound (VOC) emission and raw material impurities in aniline acetonitrile before hydrolysis are addressed by coupling closed-loop feeding, segmented temperature-controlled melting, and isothermal settling under specific conditions. This allows the single settling operation to simultaneously achieve dual functions. On the one hand, it forms a closed thermodynamic equilibrium system, utilizing the principle of temperature difference condensation to achieve efficient in-situ capture and internal circulation of VOCs. On the other hand, as a controlled sedimentation kinetic environment, it utilizes optimized fluid conditions and sufficient residence time to achieve deep gravity separation and coagulation removal of multi-scale and multi-form impurities in the raw materials. This reduces the fugitive emission of organic compounds such as aniline, removes catalyst residues, polymers, and other impurities from the raw materials, and increases the effective content of potassium aniline acetate, the downstream hydrolysis product. Attached Figure Description

[0016] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a trend graph showing the influence of the melting temperature of the present invention on product purity and emission concentration. Figure 2 This is a trend graph showing the effect of the settling time on product purity and emission concentration according to the present invention. Detailed Implementation

[0017] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0018] This invention provides an aniline-based acetonitrile pretreatment process for reducing volatile organic compound (VOC) emissions. Its core lies in a series of sequentially connected and synergistically functioning operational steps in a closed environment to simultaneously achieve source capture of VOCs and efficient separation of impurities from the raw materials before they enter the hydrolysis reactor. The main steps include: S1: Solid aniline acetonitrile is transported to a pretreatment container under closed conditions; S2: Heating it in stages with controlled temperature in a closed container until it is completely converted into a homogeneous liquid phase; S3: Allow sufficient time for standing under sealed conditions and at a specific temperature to simultaneously complete the condensation and reflux of volatile organic compounds and the gravity settling of impurities. S4: The upper refined liquid obtained after settling is transported to the downstream hydrolysis process through a sealed insulated pipeline, and the impurities settled at the bottom are discharged.

[0019] The following section elaborates on the specific technical problems solved, the technical means employed, and the technical effects produced by each of the above steps.

[0020] This invention employs a fully enclosed conveying method, in which solid aniline acetonitrile is introduced into a pretreatment container. The pretreatment container is connected to the downstream process via a closed pipeline, thereby preventing the release of volatile organic compounds due to dust and surface desorption during material transfer at the initial stage. This enclosed environment is the basis for effectively controlling emissions in all subsequent operations.

[0021] After feeding, while keeping the container sealed, the material is heated in stages with controlled temperature. Specifically, the material is first slowly and uniformly heated from room temperature to 36-38℃ at a rate of 0.8-1.2℃ / min, and then kept at that temperature for 70-90 minutes. The purpose of this stage is not to melt all the solids immediately, but to soften the surface of the solid particles so that the volatile components adsorbed in the internal micropores can be released slowly at a lower vapor pressure, such as aniline (C6H7N). Because the system is sealed, the released aniline vapor is confined to the space at the top of the container and begins to partially condense and reflux.

[0022] Next, the material is heated to 50-60℃ at a rate of 1.0-2.0℃ / min. At this temperature, all solid aniline acetonitrile is completely converted into the liquid phase, and the viscosity of the system decreases significantly to about 0.8-1.2 mPa·s.

[0023] The formation of the liquid phase is a prerequisite for subsequent separation based on density difference. The entire melting process takes place in a closed system, and the volatilized organic compounds such as aniline continue to accumulate in the gas phase.

[0024] After melting is complete, the system enters the critical heat preservation and settling stage, in which the liquid material is settling in a sealed container at a constant temperature to remove impurities. The settling time is preferably 3.4-5.0 hours.

[0025] It should be noted that the impurities contained in industrial aniline acetonitrile products mainly include: unreacted raw materials, by-reaction products generated during the alkaline catalytic synthesis process, and residual catalyst components. Unreacted raw materials include aniline (C6H7N) and hydroxyacetonitrile (C2H3NO); by-products generated during the base-catalyzed synthesis are mainly benzene-containing organic polymers with varying molecular weights; residual catalyst components generally include sodium carbonate (Na2CO3) or sodium hydroxide (NaOH). These inorganic salts may exist in the form of visible solid particles, micron-sized fine particles, or submicron-sized colloidal particles, and there may be a large or small density difference between them and the main component, aniline acetonitrile.

[0026] According to the principle of gas-liquid equilibrium, at a constant static temperature, aniline in the liquid phase will continue to volatilize until its partial pressure in the gas phase reaches the saturated vapor pressure at that temperature. Since the system is completely closed and the top space is limited, the concentration of aniline in the gas phase rapidly approaches saturation. The key point is that, due to heat exchange with the external environment, the inner surface temperature of the container wall and top cover is usually slightly lower than the temperature of the core liquid phase inside. This temperature difference causes the saturated aniline vapor to condense on the relatively low-temperature wall surface, forming droplets that flow back to the main liquid phase along the wall surface, reducing the partial pressure of aniline in the gas phase and promoting further volatilization of aniline in the liquid phase until its concentration in the liquid phase decreases.

[0027] Meanwhile, according to Stokes' law of settling, the settling velocity of particles is directly proportional to the density difference between the particles and the liquid and inversely proportional to the viscosity of the liquid. At a system temperature of 50-60℃, the liquid phase aniline acetonitrile maintains a low viscosity. For impurities with significant density differences, such as sodium carbonate particles, the settling velocity is relatively fast, and within a certain standing time, it is sufficient to completely settle to the bottom of the container, forming a dense bottom sediment.

[0028] For impurities with densities close to those of the bulk liquid, the settling velocity of individual microparticles will be very slow. During long-term isothermal settling, the extremely weak natural convection caused by micro-temperature inhomogeneity or Brownian motion within the system is insufficient to lift the already settled large particles, but it can promote frequent collisions of micron and submicron particles. For example, colloidal sodium carbonate undergoes heterogeneous aggregation after particle collision, agglomerating into larger flocs with higher effective density, thereby accelerating its settling velocity. The specific isothermal environment provides the necessary conditions for the stable growth and settling of the flocs.

[0029] After settling, the material naturally forms clear layers under gravity. The bottom layer is a thick slurry composed of catalyst residues and other materials with the highest density. The middle layer may contain a small amount of aggregated polymer flocs, while the top layer is a clear and bright refined aniline acetonitrile liquid.

[0030] First, the supernatant is transferred to the downstream hydrolysis reactor at a speed of less than 5L / min using a transfer pump. Then, the bottom impurities are discharged through the slag discharge valve at the bottom of the container. The entire separation and transfer process is completed under closed conditions. It is worth mentioning that the entire conveying pipeline is heat-traced and insulated, with the temperature maintained at 43-45℃, slightly higher than the melting point of aniline acetonitrile. This prevents the viscosity from increasing dramatically or local crystallization from occurring due to heat dissipation during transportation, ensuring smooth pipeline flow and material uniformity.

[0031] To verify the effect of the aniline acetonitrile pretreatment process provided by this invention on improving the purity of downstream hydrolysis products, a detailed explanation is provided below through test examples. The specific test scheme is as follows.

[0032] Test Example 1 This test case aims to verify the effect of the second-stage melting temperature on the pretreatment effect of aniline acetonitrile, and to determine the optimal temperature operating range that can minimize volatile organic compound emissions and improve the purity of the final product while ensuring that the raw materials are fully melted and impurities are settled.

[0033] Using a uniform batch of industrial-grade aniline acetonitrile as the initial product, the content of its main component was tested by high performance liquid chromatography (HPLC) and found to be 95.5 ± 0.2%, with a moisture content of 0.3%. The main impurities included aniline, hydroxyacetonitrile, sodium carbonate, and trace amounts of organic polymers.

[0034] This test consisted of 19 treatment groups, with 500g of solid aniline acetonitrile weighed out for each group and labeled T1-T19. T2-T19 groups underwent the complete pretreatment process described in this invention. Each treatment group was repeated three times in parallel to evaluate the reproducibility of the results, as detailed below: T1: Using existing operations, without pretreatment, solid aniline acetonitrile is directly added to the hydrolysis reactor; T2: The first stage preheating temperature is set to 36℃ and held for 80 minutes; the second stage preheating temperature is set to 45℃ and held for 4.2 hours. T3: The first stage preheating temperature is set to 36℃ and held for 80 minutes; the second stage preheating temperature is set to 46℃ and held for 4.2 hours. T4: The first stage preheating temperature is set at 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set at 47℃, and the standing time is 4.2 hours. T5: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 48℃, and the standing time is 4.2 hours. T6: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 49℃, and the standing time is 4.2 hours. T7: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 50℃, and the standing time is 4.2 hours. T8: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 51℃, and the standing time is 4.2 hours. T9: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 52℃, and the standing time is 4.2 hours. T10: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 53℃, and the standing time is 4.2 hours. T11: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 54℃, and the standing time is 4.2 hours. T12: The first stage preheating temperature is set to 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃, and the standing time is 4.2 hours. T13: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 56℃ and the holding time is 4.2 hours. T14: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 57℃ and the settling time is 4.2 hours. T15: The first stage preheating temperature is set at 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set at 58℃, and the standing time is 4.2 hours. T16: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 59℃ and the settling time is 4.2 hours. T17: The first stage preheating temperature is set to 36℃ and the holding time is 80min; the second stage preheating temperature is set to 60℃ and the settling time is 4.2h. T18: The first stage preheating temperature is set at 36℃, and the holding time is 80 minutes. The second stage preheating temperature is set at 61℃, and the standing time is 4.2 hours. T19: The first stage preheating temperature is set to 36℃ and held for 80 minutes. The second stage preheating temperature is set to 62℃ and held for 4.2 hours.

[0035] For T1, solid-phase aniline acetonitrile was added to a 5L hydrolysis vessel containing 90℃ hot water while stirring, and the mixture was stirred and melted while being added. For T2-T19, the content of the main component of the liquid-phase aniline acetonitrile was determined by HPLC using random sampling. The results are shown in Table 1. The liquid-phase aniline acetonitrile was then added to a 5L hydrolysis vessel. A 48% potassium hydroxide solution and deionized water were quantitatively added to each hydrolysis vessel to control the total concentration of the reaction system at 30%. The reaction was carried out at room temperature and stirred at 150 r / min for 4 hours to complete the hydrolysis. After the reaction was completed, the system was heated to 90°C and purged with nitrogen for 1 hour to remove the generated ammonia. The hydrolysate was then transferred to a rotary evaporator and concentrated at 80°C and -0.095 MPa until crystals precipitated. Subsequently, it was dried in an oven at 105°C to constant weight to obtain white to pale yellow potassium aniline acetate solid.

[0036] Potentiometric titration was performed. 0.5 g of dried potassium aniline sample was weighed and dissolved in 50 mL of deionized water. Potentiometric titration was then conducted using a 0.1 mol / L hydrochloric acid standard solution. The titration endpoint was the pH jump point. The content of aniline acetate was calculated based on the volume of hydrochloric acid consumed and converted to the effective content of potassium aniline acetate. The results are shown in Table 1 and [Table data would be inserted here]. Figure 1 As shown.

[0037] The concentration of aniline vapor in the exhaust port of the pretreatment container was directly read using a photoionization detector. Readings were taken after the container had stabilized during the settling phase, and data were recorded hourly. The average value was calculated. The results are shown in Table 1 and [Table data missing]. Figure 1 As shown.

[0038] The experimental data were averaged after three repetitions, and the results are summarized in Table 1 below: Table 1. Test results of product purity and emission concentration at different melting temperatures.

[0039] According to Table 1 and Figure 1 Data shows that the effective content of potassium salt, as a core quality indicator, first increases and then decreases with increasing melting temperature. When the temperature is in the range of 50-60℃, the effective content of potassium salt stabilizes at a high level of 96.0-96.4%, indicating that within this temperature range, the raw material melts completely and has good fluidity, which is conducive to the efficient sedimentation and separation of impurities during the subsequent settling process. When the temperature in the second stage is below 50℃, melting may be incomplete or the viscosity of the system may be too high, resulting in insufficient separation of impurities and a significant decrease in the effective content of potassium salt. When the temperature is above 60℃, excessive thermal stress may cause slight thermal decomposition or side reactions of aniline acetonitrile. At the same time, it may make it more difficult for some volatile impurities to condense and reflux, resulting in a decrease in product purity instead of an increase.

[0040] The concentration of aniline at the exhaust port is strongly correlated with temperature. Within the optimized range of 50-60℃, the emission concentration remains at a low level below 10ppm. When the temperature is below 50℃, due to insufficient melting and limited mass transfer, the release of VOCs is prolonged in the subsequent process, resulting in a slightly higher emission concentration. When the temperature is above 60℃, the saturated vapor pressure of substances such as aniline increases, exceeding the system's condensation and reflux capacity, leading to a sharp increase in emission concentration.

[0041] Controlling the melting temperature in the second stage at 50-60℃ is a key and non-obvious technical choice. It should be noted that this range is not a broad or arbitrary interval, but rather an optimal range achieved by considering multiple dimensions such as complete melting, raw material stability, and impurity separation efficiency.

[0042] Test Example 2 This test case aims to verify the effect of settling time on the degree of impurity sedimentation and the efficiency of volatile organic compound removal during the pretreatment of aniline acetonitrile, and to determine the settling time range that achieves the optimal balance between efficient separation, ensuring product quality and production efficiency.

[0043] The test raw material used was industrial-grade aniline acetonitrile from the same batch as that used in Test Example 1, with an initial main component content of 95.5 ± 0.2%.

[0044] This test consisted of 16 treatment groups, labeled S1-S16. 500g of solid aniline acetonitrile was weighed for each group, and all groups underwent the complete pretreatment process described in this invention. Each treatment group was repeated three times in parallel to evaluate the reproducibility of the results, as detailed below: S1: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the holding time is 3.0 hours. S2: The first stage preheating temperature is set to 36℃ and held for 80 minutes; the second stage preheating temperature is set to 55℃ and held for 3.2 hours. S3: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 3.4 hours. S4: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the holding time is 3.6 hours. S5: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the settling time is 3.8 hours. S6: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the settling time is 4.0 hours. S7: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the holding time is 4.2 hours. S8: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 4.4 hours. S9: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the settling time is 4.6 hours. S10: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes; the second stage preheating temperature is set to 55℃ and the standing time is 4.8 hours. S11: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 5.0 hours. S12: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 5.2 hours. S13: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 5.4 hours. S14: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 5.6 hours. S15: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the standing time is 5.8 hours. S16: The first stage preheating temperature is set to 36℃ and the holding time is 80 minutes. The second stage preheating temperature is set to 55℃ and the settling time is 6.0 hours.

[0045] The operating procedures were exactly the same as those for groups T2-T19 in Test Example 1, except that the settling time for each treatment group was strictly followed during the settling step. After settling, liquid aniline acetonitrile was collected, the content of the main component was determined, and VOCs emission data were recorded. The results are shown in Table 2 and... Figure 2 As shown.

[0046] The hydrolysis process for producing potassium aniline acetate was identical to that in Test Example 1. The collected liquid-phase aniline acetonitrile was used for hydrolysis, ammonia removal, concentration, and drying to obtain the final potassium aniline acetate product. The effective potassium salt content was tested, and the results are shown in Table 2. Figure 2 As shown.

[0047] The experimental data were averaged after three repetitions, and the results are summarized in Table 2 below: Table 2. Test results of product purity and emission concentration under different settling times.

[0048] According to Table 2 and Figure 2 Data shows that the effective potassium salt content changes in stages with increasing settling time. Within 3.2-3.4 hours, the purity increases rapidly as denser particles and rapidly agglomerated colloids settle sufficiently. When the settling time reaches 3.4 hours, the effective potassium salt content has increased to 96.1%. Within 4.2-5.0 hours, the purity enters a plateau period, indicating that the main settleable impurities have been basically removed. After 5.0 hours, the purity does not continue to increase and even shows a very slight downward trend. This phenomenon can be attributed to the fact that under long-term constant temperature settling, the aniline acetonitrile may undergo extremely slow thermally induced side reactions, such as trace amounts of dimerization or oxidation, generating new impurities. At the same time, the VOC emission concentration drops to and remains at the detection limit after the settling time exceeds 4.0 hours, indicating that extending the settling time does not provide additional benefit for VOC removal. Comparing S3 and S11, the purity of their final products differs by only 0.3%, and their VOC emission levels are comparable. However, extending the settling time means a decrease in equipment utilization and a relative increase in energy consumption. Therefore, from a techno-economic perspective, a longer settling time is not necessarily better. Limiting the settling time to 3.4-5.0 hours can ensure product purity and extremely low VOC emissions while maximizing production efficiency.

[0049] The aforementioned test examples established the effectiveness and optimal range of the core process steps of the present invention. Based on the core process, for impurities of different forms, especially colloidal and dissolved impurities, the present invention can further adopt physical auxiliary means for treatment without introducing external chemical substances, without changing the physical nature of the process, and the entire process is completed in a closed system.

[0050] It should be noted that the following embodiments should not be regarded as the entirety of the present invention or as a limitation or restriction on the technical solution of the present invention.

[0051] Example 1 This embodiment provides an aniline-based acetonitrile pretreatment process to reduce volatile organic compound emissions, addressing the problem in the aforementioned processes where colloidal impurities and fine polymer particles in the raw materials are difficult to remove effectively through simple settling: S31: After completing the segmented temperature-controlled melting step, that is, after the material is heated to 55°C, keep the system sealed and let it stand for 2.0 hours to allow most of the denser impurities to initially settle. S32: Start the stirring device in the pretreatment container and stir at a low speed of 30r / min for 30min to promote the collision and aggregation of residual micro particles and colloids, forming larger and easier-to-settle flocs; S33: After stirring, let the system stand at 55°C for 1.5 hours to allow the newly formed flocs to settle completely.

[0052] After settling, liquid aniline acetonitrile was collected, and the content of the main component was determined to be 96.9%. Compared with the control sample with the same total settling time but without low-speed stirring, the purity increased by about 0.2%. The effective content of potassium salt obtained from downstream hydrolysis reached 96.6%, proving that this auxiliary method can effectively enhance the removal of colloids and fine impurities.

[0053] Example 2 This embodiment provides a pretreatment process for aniline acetonitrile to reduce volatile organic compound emissions, addressing the problem in the aforementioned processes where dissolved impurities with densities close to aniline acetonitrile are difficult to effectively separate by gravity sedimentation: S41: After settling and removing bottom sediment, keep the system closed and uniformly reduce the system temperature from 55℃ to 47℃ at a rate of 0.3℃ / min to induce the precipitation of dissolved impurities by utilizing solubility differences. S42: Maintain a constant temperature of 47℃ for 50 minutes to allow the precipitated material to fully aggregate and grow; S43: After the heat preservation is completed, the upper clear liquid is transferred to the downstream hydrolysis reactor using a transfer pump, and the thin layer of precipitate formed in this process is discharged.

[0054] After separation, liquid aniline acetonitrile was collected and its main component content was determined to be 97.0%. The effective content of potassium salt obtained by downstream hydrolysis reached 96.6%, proving that effective separation of dissolved impurities can be achieved through precise temperature control.

[0055] Example 3 This embodiment provides an aniline-based acetonitrile pretreatment process to reduce volatile organic compound emissions, targeting scenarios where impurities in the raw materials have complex forms and require deep removal to obtain ultra-high purity raw materials: S31: After completing the segmented temperature-controlled melting step, that is, after the material is heated to 55°C, keep the system sealed and let it stand for 2.0 hours to allow most of the denser impurities to initially settle. S32: Start the stirring device in the pretreatment container and stir at a low speed of 40r / min for 30min to promote the collision and aggregation of residual micro particles and colloids, forming larger and easier-to-settle flocs; S33: After stirring, let the system stand at 55°C for 1.5 hours to allow the newly formed flocs to settle completely.

[0056] S41: After settling and removing bottom sediment, keep the system closed and uniformly reduce the system temperature from 55℃ to 43℃ at a rate of 0.5℃ / min to induce the precipitation of dissolved impurities by utilizing solubility differences. S42: Maintain a constant temperature of 43℃ for 70 minutes to allow the precipitated material to fully aggregate and grow; S43: After the heat preservation is completed, the upper clear liquid is transferred to the downstream hydrolysis reactor using a transfer pump, and the thin layer of precipitate formed in this process is discharged.

[0057] The liquid phase of aniline acetonitrile was collected, and its main component content was determined to be 97.2%. The effective content of potassium salt obtained from downstream hydrolysis was 96.8%.

[0058] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A pretreatment process for aniline-acetonitrile to reduce volatile organic compound emissions, characterized in that, Includes the following steps: S1: Solid aniline acetonitrile is transported to a pretreatment container under closed conditions; S2: In the pretreatment container, solid aniline acetonitrile is heated under sealed conditions until it is completely melted into a liquid state; S3: Liquid aniline acetonitrile is allowed to stand under closed conditions to simultaneously achieve condensation and reflux of volatile organic compounds and sedimentation and separation of impurities; S4: The clear liquid formed after settling is transported to the downstream process through a sealed insulated pipeline, and the impurities settled at the bottom are discharged.

2. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 1, characterized in that: The heating in S2 is a segmented temperature-controlled heating, which includes a first stage of heating the material to 36-38℃ and holding it at that temperature for 70-90 minutes, and a second stage of continuing to heat it to 50-60℃.

3. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 2, characterized in that: The settling temperature in S3 is 50-60℃, and the settling time is 3.4-5.0h.

4. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 2, characterized in that: The heating rate in the first stage is 0.8-1.2℃ / min, and the heating rate in the second stage is 1.0-2.0℃ / min.

5. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 3, characterized in that: The settling process in S3 includes a first settling period, followed by low-speed stirring, and then a second settling period after the stirring is completed.

6. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 5, characterized in that: The low-speed stirring speed is 30-40 r / min, and the stirring time is 20-40 min.

7. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 3, characterized in that: After the settling process in step S3 is completed and the bottom sedimented impurities are discharged, a cooling and impurity separation step is also included before the transfer of the upper clear liquid in step S4.

8. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 7, characterized in that: The cooling and precipitation process involves reducing the system temperature from the static temperature to 43-47°C at a rate of 0.3-0.5°C / min and holding the temperature for 50-70 minutes, after which the precipitate that has formed again is discharged.

9. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 1, characterized in that: The heat tracing temperature of the sealed insulated pipe is 43-45℃.

10. The aniline-acetonitrile pretreatment process for reducing volatile organic compound emissions according to claim 1, characterized in that: The solid aniline-based acetonitrile raw material contains aniline, hydroxyacetonitrile, a benzene ring-containing organic polymer, and at least one impurity from sodium carbonate or sodium hydroxide.

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