A method for liquid-phase adsorption separation and purification of 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene
By simulating the moving bed adsorption separation method, and using modified USY molecular sieve and biomass polysaccharide sphere-forming molecular sieve adsorbent, the problem of separating and purifying dichloronitrobenzene isomers was solved, realizing the continuous production of high-purity dichloronitrobenzene, reducing costs and improving efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA CATALYST HLDG CO LTD
- Filing Date
- 2023-12-25
- Publication Date
- 2026-06-30
AI Technical Summary
Existing technologies are insufficient for efficiently and cost-effectively separating and obtaining high-purity 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene. Conventional methods suffer from high energy consumption, complex processes, low yields, and low resource utilization.
A simulated moving bed adsorption separation method was adopted, using modified USY molecular sieve and biomass polysaccharide sphere-formed molecular sieve adsorbent, and adsorption-desorption were carried out through a countercurrent simulated moving bed to achieve the separation and purification of dichloronitrobenzene isomers.
The continuous production of high-purity 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene has been achieved, reducing production costs, improving production efficiency, and solving the tailing problem existing in conventional methods.
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Figure CN117820123B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a method for adsorption separation and purification of a mixture of dichloronitrobenzene isomers, specifically involving the adsorption separation and purification of two isomers, 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene. The method includes using a molecular sieve adsorbent for adsorption-desorption to obtain a high-purity single dichloronitrobenzene product, which belongs to the field of chemical separation applications. Background Technology
[0002] 3,4-DCNB is an intermediate in the synthesis of chlorofluoroaniline and dichlorofluorobenzene, and also a raw material for the preparation of quinolone, and is widely used in my country's pharmaceutical industry. 2,3-DCNB is an important intermediate and raw material for the preparation of plant protectants and the production of the "third-generation" fluoroquinolone drugs ofloxacin and lomefloxacin. In the process of nitrifying o-dichlorobenzene to prepare 3,4-dichloronitrobenzene (3,4-DCNB), 10-15% of 2,3-dichloronitrobenzene (2,3-DCNB) is produced as a byproduct. These two dichloronitrobenzene isomers have boiling points that differ by less than 2°C, making them difficult to separate using conventional vacuum distillation methods. Although the melting point difference is about 20°C, separation requires multi-stage crystallization, which has limitations such as high energy consumption, complex processes, low yield, and low purity. Industrially, after obtaining 3,4-DCNB with a purity of over 99% through melt crystallization, the remaining crystallization mother liquor (commonly known as "low-oil") contains approximately a 70:30 mass ratio of 3,4-DCNB to 2,3-DCNB. This "low-oil" is then hydrogenated to dichloroaniline, followed by separation via vacuum distillation. This method suffers from high hydrogenation reduction costs, increased low-oil consumption due to dechlorination and tar production during reduction, and limitations in the application of the resulting 2,3-DCA.
[0003] Patent CN112661651A discloses a purification method for 3,4-DCNB, which involves melting the nitration product of o-dichlorobenzene, cooling and crystallizing it to obtain a primary crystalline product, and then melting and evaporating it again to obtain 3,4-DCNB crystals. This method not only suffers from low yield, long process flow, difficulty in filtering the crystals, and high investment, but also cannot effectively recover and utilize the byproduct 2,3-DCNB, resulting in resource waste. Patent CN111714921B discloses a solvent crystallization separation system for 3,4-DCNB and 2,3-DCNB, which includes five sequential steps: material mixing, cooling crystallization, solid-liquid separation, solution evaporation, and condensation recovery. This method has a lengthy process flow, the melting and crystallization separation effect is limited by the composition of the eutectic, the standard product yield is low, and it also has disadvantages such as high cost and low resource utilization. Patent CN102875384A reports a method for extractive distillation to separate 3,4-DCNB. Although this method can obtain products deviating from the eutectic composition, it still requires a theoretical grade of over 60, and the purity of the obtained 3,4-DCNB is only 90%. Patent JP63002956A mentions using H-ZSM-5 type zeolite molecular sieve adsorption separation to separate low-oil content 2,3-DCNB with a purity of over 99%. However, the drawbacks are that this zeolite adsorbent has low adsorption capacity, small processing capacity, and cannot be used for continuous production. It requires frequent regeneration, and the process is cumbersome and inefficient, failing to meet industrial requirements.
[0004] Industrially, 3,4-dichloronitrobenzene is often prepared by nitration of o-dichlorobenzene under mixed acid conditions. However, this inevitably produces an ortho-impurity, 2,3-dichloronitrobenzene. These two isomers have similar boiling points. To date, developing a highly efficient, low-consumption, widely applicable separation system capable of simultaneously yielding high-purity 3,4-dichloronitrobenzene and 2,3-dichloronitrobenzene remains a challenging yet significant research endeavor. Summary of the Invention
[0005] This invention addresses the problems of high theoretical plate count, low efficiency, high energy consumption, and inability to simultaneously obtain high-purity 2,3-DCNB / 3,4-DCNB products by methods such as vacuum distillation and extractive distillation. It employs a simulated moving bed adsorption separation method for purification, which not only has low energy consumption and high efficiency, but also enables continuous production of two high-purity dichloronitrobenzene products.
[0006] This invention uses a "low-oil" component as part of the adsorption separation raw material and controls an appropriate process to purify 2,3-dichloronitrobenzene with a purity ≥99% from the extract of a simulated moving bed, and simultaneously purify 3,4-dichloronitrobenzene with a purity ≥99% from the residual liquid of the simulated moving bed.
[0007] This invention provides a method for the simultaneous purification of 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene through liquid-phase adsorption separation. The method involves separating and purifying a mixture of 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene isomers in a countercurrent simulated moving bed packed with a molecular sieve adsorbent. The molecular sieve adsorbent is obtained by spheroidizing USY molecular sieve with a first auxiliary agent and a second auxiliary agent. The first auxiliary agent is illite modified with a silicon coupling agent; the second auxiliary agent is biomass polysaccharide. The weight ratio of the USY molecular sieve to the first and second auxiliary agents is 1:(0.0516~0.176):(0.001~0.018).
[0008] Furthermore, in this invention, the countercurrent simulated moving bed comprises 4 to 30 adsorption columns or adsorption beds connected in series, from which 3,4-dichloronitrobenzene product is obtained by desorption from the adsorbate of the simulated moving bed, and 2,3-dichloronitrobenzene product is obtained by desorption from the extract.
[0009] Furthermore, in this invention, the silicon coupling agent is selected from at least one of KH550 (γ-aminopropyltriethoxysilane), KH560 (γ-glycidoxypropyltrimethoxysilane), and KH570 (γ-methacryloyloxypropyltrimethoxysilane).
[0010] Furthermore, in this invention, the biomass polysaccharide is selected from at least one of hydroxyethyl starch, carboxymethyl starch, chitosan, sodium alginate, and mannan.
[0011] Furthermore, in this invention, the method for separating and purifying dichloronitrobenzene involves an adsorption-desorption temperature of 100–200°C for the dichloronitrobenzene isomer mixture, a feed volume hourly space velocity (VHSV) of 0.1–0.5 h⁻¹ for the adsorbent relative to the adsorbent, and a pressure of 5–20 kg / cm² during the adsorption and desorption processes. 2 .
[0012] Furthermore, in the method for separating and purifying dichloronitrobenzene described in this invention, the particle size of the molecular sieve adsorbent is 0.2~2.5mm, preferably 0.3~0.8mm.
[0013] Furthermore, in this invention, the desorbent used in the method for separating and purifying dichloronitrobenzene is any one or more of toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, chlorobenzene, p-chlorotoluene, m-chlorotoluene, p-dichlorobenzene, and m-dichlorobenzene.
[0014] Furthermore, in this invention, the method for separating and purifying dichloronitrobenzene, wherein the preparation process of the molecular sieve adsorbent is as follows: USY molecular sieve with an average particle size ≤30μm, illite with an average particle size ≤50μm, and biomass polysaccharide are mixed and placed in a spheroidizing device. Deionized water is added under rotation to maintain the dry basis of the mixture at 70-80%, and the spheroid diameter is controlled to <1mm. Small spheres with φ0.3-0.8mm are sieved out. The small spheres are dehydrated and activated under negative pressure in a programmed temperature range of 80-600℃ to remove the additives. Then, they are cooled to 80-120℃ in an isolated water vapor environment and sealed and packaged to obtain the molecular sieve adsorbent.
[0015] Furthermore, in this invention, the molecular sieve adsorbent is used for performance evaluation and analysis of single-column pulse feeding of dichloronitrobenzene, wherein the selectivity coefficient β of 2,3-dichloronitrobenzene to 3,4-dichloronitrobenzene is >2.0, and the resolution R of 2,3-dichloronitrobenzene to 3,4-dichloronitrobenzene is >1.5.
[0016] The adsorption separation method employed in this invention can effectively solve the problem of separating and purifying dichloronitrobenzene isomers with similar boiling points. Based on the differences in adsorption strength of dichloronitrobenzene isomers on the adsorbent, a continuous method for obtaining high-purity target products is utilized using chromatographic separation principles. Typically, 3,4-dichloronitrobenzene is obtained through the nitration of o-dichlorobenzene, and the nitration product inevitably includes 2,3-dichloronitrobenzene. In reality, only by purifying 3,4-dichloronitrobenzene to >99% can it have industrial practical value, and obtaining 2,3-dichloronitrobenzene with a purity >99% can also bring significant economic benefits.
[0017] The beneficial effects of this invention are as follows: This invention addresses the difficulty of separating 2,3-dichloronitrobenzene / 3,4-dichloronitrobenzene isomers with similar boiling points using conventional distillation methods, and also the challenge of obtaining high-purity 2,3-dichloronitrobenzene. By preparing a molecular sieve adsorbent that specifically adsorbs 2,3-dichloronitrobenzene, high-purity 2,3-dichloronitrobenzene can be obtained while simultaneously solving the severe tailing problem present in other adsorbents. Furthermore, by modifying the process parameters of the simulated moving bed equipment in the adsorption separation process, high-purity 3,4-dichloronitrobenzene and high-purity 2,3-dichloronitrobenzene products can be obtained simultaneously. This not only solves the problem of not being able to obtain high-purity 2,3-dichloronitrobenzene using crystallization alone, but also achieves continuous production, reduces production costs, and improves production efficiency. Attached Figure Description
[0018] The present invention will be further described below with reference to the accompanying drawings and embodiments:
[0019] Appendix Figure 1 Data Envelopment Diagram of Single-Column Pulse Adsorption-Desorption Evaluation Using Example 1;
[0020] Appendix Figure 2 Data envelopment diagram of single-column pulse adsorption-desorption evaluation of adsorbent prepared in Example 2;
[0021] Appendix Figure 3 Data envelopment diagram for evaluating single-column pulse adsorption-desorption of adsorbent prepared in Example 3;
[0022] Appendix Figure 4 Data envelopment diagram of single-column pulse adsorption-desorption evaluation of adsorbent prepared in Example 4;
[0023] Appendix Figure 5 Data envelopment diagram for evaluating single-column pulse adsorption-desorption of adsorbent prepared in Example 5;
[0024] Appendix Figure 6 A simplified flow chart of a moving bed adsorption separation process simulating a pneumatic valve assembly or rotary valve. Detailed Implementation
[0025] The embodiments and comparative examples further illustrate the implementation methods and effects of the present invention, but the scope of protection of the present invention is not limited to the contents listed in the embodiments.
[0026] This invention can use a single-column pulse adsorption-desorption evaluation test process to measure the relative separation effect of the raw material mixture components by dynamically testing the separation coefficient β and resolution R of the purified components on the adsorbent based on the principle of chromatographic separation.
[0027] Single-column pulse adsorption-desorption experimental method: 95-99 wt% dry molecular sieve adsorbent beads are packed into the adsorption column. The column is purged with nitrogen to remove air, then desorbent is pumped in to remove nitrogen from the adsorbent voids, and the temperature is raised to 140°C. After the adsorption column is stabilized at 140°C, 2 ml of 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene feedstock (3,4-dichloronitrobenzene concentration approximately 68 wt%, 2,3-dichloronitrobenzene concentration approximately 32 wt%) is pulsed into the syringe via a six-way switching valve at the column inlet. Then, the six-way valve is switched to pump in the eluent at a flow rate of 1-2 ml / min. When the eluent outflow reaches 10-20 ml, an automatic fraction collector is used to collect 3-5 drops of liquid sample every 2 minutes. 40-60 samples are collected continuously for gas chromatography quantitative analysis of composition.
[0028] Example A
[0029] Preparation of illite modified with silicon coupling agent:
[0030] Illite was dried in a vacuum drying oven at 80℃ for 2 hours. 1000g of the dried illite was weighed and added to deionized water at a mass ratio of 1:5, followed by ultrasonic dispersion for 30 minutes. 10g of silane coupling agent KH570 was mixed with ethanol at a mass ratio of 1:10 and poured into a three-necked flask. The mixture was hydrolyzed at 60℃ for 30 minutes. The ultrasonically dispersed illite and the hydrolyzed KH570 were then mixed thoroughly in the three-necked flask, and wet modification was performed at 60℃ using a constant-temperature magnetic stirrer. After wet modification, the prepared product was washed and filtered multiple times, and then vacuum dried to constant weight to obtain illite modified with silane coupling agent KH570. Example 1
[0031] 1) Mix 100 kg of USY molecular sieve (nSiO2 / nAl2O3 = 6.14) with silicon coupling agent-modified illite and hydroxyethyl starch at a weight ratio of 1:0.0949:0.0162 until homogeneous. Take 30.0 kg of the mixed powder and roll it into small spheres of 0.1~0.2 mm in a sugar coating pan for later use. Then weigh 10 kg of the above small spheres and place them in the sugar coating pan. Start mixing them into large spheres at a frequency of 35 Hz. Then add 300 g of mixed powder every 5 minutes to gradually increase the diameter of the adsorbent spheres to more than 0.3 mm. Let the freshly rolled spheres air dry at room temperature for 24 hours. Sift the spheres with a size range of 0.3~0.8 mm and dry them at 120℃ for 24 hours. Then calcine the sphere samples at 550℃ for 6 hours to improve the strength of the spheres.
[0032] 2) The microsphere adsorbent prepared in step 1) was saturated with water in air at 25°C and 65% humidity, resulting in a water content of 25.5 wt%. It was then packed into a 4L exchange column. Deionized water was pumped into 10L of column at a flow hourly velocity (WHSV) of 1.5 h⁻¹ to ensure complete saturation. An alkali treatment solution (SiO₂: 0.9 g / L, NaOH: 60 g / L) was prepared by mixing water glass and NaOH. This solution was circulated internally through an alkali heat exchanger to raise the temperature of the alkali solution in the tank to 95°C. The solution was then pumped into the exchange column at a WHSV of 1.5 h⁻¹. -1 After 4 hours of treatment, stop adding alkali solution and replace with 85℃ hot purified water for 1.5 hours. -1 The adsorbent pellets were washed with water using volume hourly space velocity until the pH of the washing solution was below 10.0. After that, the adsorbent pellets were discharged and drained.
[0033] 3) The small ball adsorbent obtained in 2) is dried in a fluidized bed at 120℃ until the dry basis reaches 85.5%. After discharge, it is directly fed into the furnace and kiln for heating, dehydration and activation in a total of 6 temperature ranges: 150℃-250℃-400℃-500℃-550℃-250℃. The final dry basis is controlled at 97.64%. It is then packaged as the final adsorbent product and designated as XFJ-1. Example 2
[0034] 1) Mix 100 kg of USY molecular sieve (nSiO2 / nAl2O3 = 8.22) with silicon coupling agent-modified illite and carboxymethyl starch at a weight ratio of 1:0.0549:0.0016 until homogeneous. Take 30.0 kg of the mixed powder and roll it into small spheres of 0.1~0.2 mm in a sugar coating pan for later use. Then weigh 10 kg of the above small spheres and place them in the sugar coating pan. Start mixing them into large spheres at a frequency of 35 Hz. Then add 300 g of mixed powder every 5 minutes to gradually increase the diameter of the adsorbent spheres to more than 0.3 mm. Let the freshly rolled spheres air dry at room temperature for 24 hours. Sift the spheres with a size range of 0.3~0.8 mm and dry them at 120℃ for 24 hours. Then calcine the sphere samples at 550℃ for 6 hours to improve the strength of the spheres.
[0035] 2) The microspheres of adsorbent prepared in 1) were saturated with water in air at 25°C and 65% humidity, with a water content of 26.4 wt%. They were then packed into a 4L exchange column. Deionized water was pumped into 10L of column at a flow hourly space (WHSV) of 1.5 h⁻¹ to ensure complete saturation. An alkaline treatment solution (SiO₂: 0.9 g / L, NaOH: 60 g / L) was prepared by mixing water glass and NaOH. This solution was circulated internally through an alkaline heat exchanger to raise the temperature of the alkaline solution in the tank to 95°C. The alkaline treatment solution was then pumped into the exchange column at a WHSV of 1.5 h⁻¹ for 4 hours. After the alkaline treatment, the alkaline solution was stopped, and the microspheres were washed with 85°C hot purified water at a WHSV of 1.5 h⁻¹ until the pH of the washing solution was below 10.0. The adsorbent microspheres were then removed and drained.
[0036] 3) The small ball adsorbent obtained in 2) is dried in a fluidized bed at 120℃ until the dry basis reaches 84.7%. After discharge, it is directly fed into the furnace and kiln for heating, dehydration and activation in a total of 6 temperature ranges: 150℃-250℃-400℃-500℃-550℃-250℃. The final dry basis is controlled at 96.52%. It is then packaged as the final adsorbent product and designated as XFJ-2. Example 3
[0037] 1) Mix 100 kg of USY molecular sieve (nSiO2 / nAl2O3 = 12.20) with silicon coupling agent modified illite and sodium alginate at a weight ratio of 1:0.1056:0.0015 until homogeneous. Take 30.0 kg of the mixed powder and roll it into small spheres of 0.1~0.2 mm in a sugar coating pan for later use. Then weigh 10 kg of the above small spheres and place them in the sugar coating pan. Start mixing them into large spheres at a frequency of 35 Hz. Then add 300 g of mixed powder every 5 minutes to gradually increase the diameter of the adsorbent spheres to more than 0.3 mm. Let the freshly rolled spheres air dry at room temperature for 24 hours. Sieve the spheres with a size range of 0.3~0.8 mm and dry them at 120℃ for 24 hours. Then calcine the sphere samples at 550℃ for 6 hours to improve the strength of the spheres.
[0038] 2) The adsorbent pellets prepared in step 1) were saturated with water in air at 25°C and 65% humidity, resulting in a water content of 24.8 wt%. They were then loaded into a 4L exchange column. Deionized water was pumped into the column at a flow hourly velocity (WHV) of 1.5 h⁻¹ to ensure complete saturation. An alkaline treatment solution (SiO₂: 0.9 g / L, NaOH: 60 g / L) was prepared by mixing water glass and NaOH. This solution was circulated internally through an alkaline heat exchanger to raise the temperature of the alkaline solution in the tank to 95°C. The solution was then pumped into the exchange column at a WHV of 1.5 h⁻¹ for 4 hours. After the alkaline treatment, the alkaline solution was stopped, and the pellets were washed with 85°C hot purified water at a WHV of 1.5 h⁻¹ until the pH of the washing solution was below 10.0. The adsorbent pellets were then removed and drained.
[0039] 3) The small ball adsorbent obtained in 2) is dried in a fluidized bed at 120℃ until the dry basis reaches 86.3%. After discharge, it is directly fed into the furnace and kiln for heating, dehydration and activation in a total of 6 temperature ranges: 150℃-250℃-400℃-500℃-550℃-250℃. The final dry basis is controlled to 98.2%. It is then packaged as the final adsorbent product, denoted as XFJ-3. Example 4
[0040] 1) Mix 100 kg of USY molecular sieve (nSiO2 / nAl2O3 = 15.66) with illite modified by silicon coupling agent and chitosan at a weight ratio of 1:0.1659:0.0018 until homogeneous. Take 30.0 kg of the mixed powder and roll it into small spheres of 0.1~0.2 mm in a sugar coating pan for later use. Then weigh 10 kg of the above small spheres and place them in the sugar coating pan. Start mixing them into large spheres at a frequency of 35 Hz. Then add 300 g of mixed powder every 5 minutes to gradually increase the diameter of the adsorbent spheres to more than 0.3 mm. Let the freshly rolled spheres air dry at room temperature for 24 hours. Sieve the spheres with a size range of 0.3~0.8 mm and dry them at 120℃ for 24 hours. Then calcine the sphere samples at 550℃ for 6 hours to improve the strength of the spheres.
[0041] 2) The adsorbent pellets prepared in step 1) were saturated with water in air at 25°C and 65% humidity, resulting in a water content of 24.8 wt%. They were then loaded into a 4L exchange column. Deionized water was pumped into the column at a flow hourly velocity (WHV) of 1.5 h⁻¹ to ensure complete saturation. An alkaline treatment solution (SiO₂: 0.9 g / L, NaOH: 60 g / L) was prepared by mixing water glass and NaOH. This solution was circulated internally through an alkaline heat exchanger to raise the temperature of the alkaline solution in the tank to 95°C. The solution was then pumped into the exchange column at a WHV of 1.5 h⁻¹ for 4 hours. After the alkaline treatment, the alkaline solution was stopped, and the pellets were washed with 85°C hot purified water at a WHV of 1.5 h⁻¹ until the pH of the washing solution was below 10.0. The adsorbent pellets were then removed and drained.
[0042] 3) The small ball adsorbent obtained in 2) is dried in a fluidized bed at 120℃ until the dry basis reaches 83.8%. After discharge, it is directly fed into the furnace and kiln for heating, dehydration and activation in a total of 6 temperature ranges: 150℃-250℃-400℃-500℃-550℃-250℃. The final dry basis is controlled to 99.1%. It is then packaged as the final adsorbent product, denoted as XFJ-4. Example 5
[0043] 1) Mix 100 kg of USY molecular sieve (nSiO2 / nAl2O3 = 7.64) with silica-modified illite and mannan at a weight ratio of 1:0.1356:0.0018 until homogeneous. Take 30.0 kg of the mixed powder and roll it into small spheres of 0.1~0.2 mm in a sugar coating pan for later use. Then weigh 10 kg of the above small spheres and place them in the sugar coating pan. Start mixing them into large spheres at a frequency of 35 Hz. Then add 300 g of mixed powder every 5 minutes to gradually increase the diameter of the adsorbent spheres to more than 0.3 mm. Let the freshly rolled spheres air dry at room temperature for 24 hours. Sift the spheres with a size range of 0.3~0.8 mm and dry them at 120℃ for 24 hours. Then calcine the sphere samples at 550℃ for 6 hours to improve the strength of the spheres.
[0044] 2) The adsorbent pellets prepared in step 1) were saturated with water in air at 25°C and 65% humidity, resulting in a water content of 25.2 wt%. They were then packed into a 4L exchange column. Deionized water was pumped into the column at a flow hourly velocity (WHV) of 1.5 h⁻¹ to ensure complete saturation. An alkaline treatment solution (SiO₂: 0.9 g / L, NaOH: 60 g / L) was prepared by mixing water glass and NaOH. This solution was circulated internally through an alkaline heat exchanger to raise the temperature of the alkaline solution in the tank to 95°C. The solution was then pumped into the exchange column at a WHV of 1.5 h⁻¹ for 4 hours. After the alkaline treatment, the alkaline solution was stopped, and the pellets were washed with 85°C hot purified water at a WHV of 1.5 h⁻¹ until the pH of the washing solution was below 10.0. The adsorbent pellets were then removed and drained.
[0045] 3) The small ball adsorbent obtained in 2) is dried in a fluidized bed at 120℃ until the dry basis reaches 86.3%. After discharge, it is directly fed into the furnace and kiln for heating, dehydration and activation in a total of 6 temperature ranges: 150℃-250℃-400℃-500℃-550℃-250℃. The final dry basis is controlled at 95.9%. It is then packaged as the final adsorbent product, denoted as XFJ-5.
[0046] Examples 6-10
[0047] Dichloronitrobenzene feedstock (3,4-dichloronitrobenzene concentration approximately 68 wt%, 2,3-dichloronitrobenzene concentration approximately 32 wt%) was mixed with n-heptane in a 7:3 ratio as the pulse feedstock component. Toluene was used as the desorbent, and a single-column pulse adsorption-desorption evaluation method was employed.
[0048] Plot the envelopes of the above components with the volume of the desorbent for desorption on the x-axis and the concentrations of each component in the pulsed feed solution on the y-axis. Plot the volume of the desorbent for desorption on the x-axis and the concentrations of n-heptane, 2,3-dichloronitrobenzene, and 3,4-dichloronitrobenzene on the y-axis. n-Heptane, as a non-delayed inert compound, is not adsorbed and can be used as a tracer to obtain the dead volume of the adsorption system. Using the midpoint of the tracer's half-peak width (WHM) as the zero point, measure the net retention volume from the midpoint of the WHM of each component to the zero point. The net retention volume of any component is proportional to the partition coefficient at adsorption equilibrium, reflecting the interaction force between each component and the adsorbent material. The ratio of the net retention volumes of the two components is the selectivity coefficient β. The ratio of the net retention volume of 2,3-dichloronitrobenzene to that of 3,4-dichloronitrobenzene is the ratio of the adsorption performance of the adsorbent material for 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene, which is the adsorption selectivity of 2,3- / 3,4-DCNB, denoted as β(2,3- / 3,4-DCNB).
[0049] V 2,3 Defined as the 2,3-DCNB retention volume, it is calculated by subtracting the volume of desorbent consumed during n-heptane elution from the volume of desorbent consumed during 2,3-DCNB elution; similarly, V 3,4 Defined as the net retention volume of 3,4-DCNB, it is calculated by subtracting the volume of desorbent consumed in the n-heptane elution from the volume of desorbent consumed in the 3,4-DCNB elution; W F2,3 The full width at half maximum (FWHM) of the 2,3-DCNB envelope peak, W F3,4 The half-width (FWHM) of the 2,3-DCNB envelope peak is given by β, where β is the ratio of the net retention volumes of the two separated components. Resolution (R) is used to evaluate the degree of separation between the analyte and the separated substances and is a key indicator of the separation efficiency of a chromatographic system. The exchange rate of the desorbent to 3,4-DCNB is specified by the half-width of the 3,4-DCNB peak distribution; the narrower the peak width, the higher the desorption rate. The formula for calculating resolution (R) is:
[0050]
[0051] Table 1. Evaluation results of single-column pulse adsorption-desorption of adsorbents prepared in Examples 1-5
[0052]
[0053] By comparing Table 1 and Figures 1-5The pulse envelope results show that the adsorbent obtained using the embodiments of the present invention exhibits a clear characteristic of preferentially adsorbing 2,3-DCNB. The selectivity coefficient β of 2,3-DCNB for 3,4-DCNB is ≥2.1, and the resolution R of 2,3-DCNB for 3,4-DCNB is >1.6. The single-column pulse desorption envelope of the adsorbent prepared by the present invention does not show severe tailing of the 3,4-DCNB component, and the envelope peak shape has good symmetry and a small half-width, which is beneficial for the production of high-purity and high-yield 2,3-DCNB. The results clearly demonstrate the advantages of using the adsorbent according to the present invention to separate the 2,3-DCNB / 3,4-DCNB isomers. The desorption rate is significantly reduced, resulting in satisfactory separation results, while the delayed component 2,3-DCNB does not show obvious tailing.
[0054] Examples 11-15
[0055] The simulated moving bed device comprises 24 adsorption beds, each 300 mm high and 30 mm in diameter, with a total adsorbent loading of 5086.8 ml. Two circulating pumps connect the two ends of each adsorption bed to form a closed loop. The device has four feed streams entering and exiting the adsorption columns at different locations, with the feed positions periodically changing. Four feed lines extend from the connecting pipelines of adjacent adsorption columns for feeding or removing material from the adsorption columns, as shown in the attached diagram. Figure 6 As shown.
[0056] The four basic materials are: desorbent D, feed F, extract E, and adsorbate R. The 24 columns connected in series are divided into four sections: the adsorption zone consists of seven adsorption beds between the feed and adsorbate; the purification zone consists of nine adsorption beds between the extract and feed; the desorption zone consists of five adsorption beds between the desorbent and extract; and the isolation zone consists of three adsorption beds between the adsorbate and desorbent. The temperature of the entire adsorption system is controlled at 140℃, and the pressure at 8 bar. The step time is set to 90 seconds. At the end of the step time, all four materials simultaneously move one adsorption bed in the same direction as the liquid flow. This stepping process continues until the 24-column cycle is completed, with a cycle time of 2160 seconds.
[0057] A mixture of 2,3- / 3,4-dichloronitrobenzene (DCNB) (3,4-DCNB concentration approximately 68.3 wt%, 2,3-DCNB concentration approximately 31.7 wt%) was used as the feedstock for a simulated moving bed. The liquid flow temperature was 140°C, toluene was used as the desorbent, and the adsorption column pressure was maintained at approximately 8 bar. In Example 11, the purity of 2,3-DCNB in the extract after removing toluene was 99.44%, with a yield of 97.12%; the purity of 3,4-DCNB in the residual liquid after removing toluene was 99.57%, with a yield of 94.33%. The data results for Examples 12 to 15 are shown in Table 2.
[0058] Table 2. Parameters and separation results of 2,3- / 3,4-dichloronitrobenzene isomers on a continuous countercurrent simulated moving bed.
[0059]
[0060] Analysis of the data in Table 2 shows that when the small spherical adsorbent prepared in this invention is packed into a 24-bed simulated moving bed, the purity of 2,3-DCNB is >99.1% and the yield is >96.8%; the purity of 3,4-DCNB is >99.2% and the yield is >95.8%. This indicates that the adsorbent and process method of this invention can simultaneously produce high-purity 2,3-DCNB and 3,4-DCNB monoisomeric products.
[0061] The above-described embodiments are merely illustrative of the technical concept and features of the present invention, intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly, and should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.
Claims
1. A method for the simultaneous purification of 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene by liquid-phase adsorption separation, characterized in that: A mixture of 2,3-dichloronitrobenzene and 3,4-dichloronitrobenzene isomers was separated and purified in a countercurrent simulated moving bed packed with a molecular sieve adsorbent. The molecular sieve adsorbent was obtained by spherical molding of USY molecular sieve with a first auxiliary agent and a second auxiliary agent. The first auxiliary agent was illite modified with a silicon coupling agent. The second auxiliary agent was biomass polysaccharide. The weight ratio of the USY molecular sieve to the first and second auxiliary agents is 1:(0.0516~0.176):(0.001~0.018); The biomass polysaccharide is selected from at least one of hydroxyethyl starch, carboxymethyl starch, chitosan, sodium alginate, and mannan; The desorbent is any one or more of toluene, ethylbenzene, p-xylene, m-xylene, o-xylene, chlorobenzene, p-chlorotoluene, m-chlorotoluene, p-dichlorobenzene, and m-dichlorobenzene.
2. The method according to claim 1, wherein the countercurrent simulated moving bed comprises 4 to 30 adsorption columns or adsorption beds connected in series, and 3,4-dichloronitrobenzene product is obtained by desorption from the adsorbate of the simulated moving bed, and 2,3-dichloronitrobenzene product is obtained by desorption from the extract.
3. The method according to claim 1, wherein the silicon coupling agent is selected from at least one of γ-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane.
4. The method according to any one of claims 1-3, characterized in that: The adsorption-desorption temperature of the dichloronitrobenzene isomer mixture is 100–200℃, and the feed volume hourly space velocity (VHSV) of the adsorbent relative to the adsorbent is 0.1–0.5 h⁻¹. -1 The pressure during adsorption and desorption is 5~20 kg / cm³. 2 .
5. The method according to any one of claims 1-3, characterized in that: The particle size of the molecular sieve adsorbent is 0.2~2.5mm.
6. The method according to claim 5, characterized in that: The particle size of the molecular sieve adsorbent is 0.3~0.8 mm.
7. The method according to any one of claims 1-3, characterized in that: The preparation process of the molecular sieve adsorbent is as follows: USY molecular sieve with an average particle size ≤30μm, illite modified with a silicon coupling agent with an average particle size ≤50μm, and biomass polysaccharide are mixed and placed in a spheroidizing device. Deionized water is added under rotation to maintain the dry basis of the mixture at 70~80%, and the spheroid diameter is controlled to <1mm. Small spheres with φ0.3~0.8mm are sieved out. The small spheres are dehydrated and activated by programmed heating in the range of 80~600℃ to remove the additives. Then, they are cooled to 80~120℃ in an isolated water vapor environment and sealed and packaged to obtain the molecular sieve adsorbent.