Method for separating p-nitrochlorobenzene from o-nitrochlorobenzene and m-nitrochlorobenzene in chlorobenzene nitration product
By combining selective adsorbents and desorbents, the problem of separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products was solved, achieving a highly efficient and low-energy separation process, improving product purity, and reducing equipment requirements.
Patent Information
- Application Number
- CN202511396326.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-09-28
- Publication Date
- 2026-01-02
AI Technical Summary
In existing technologies, separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products is difficult. Traditional methods are energy-intensive, require large equipment investments, and are difficult to achieve the required purity.
Selective adsorbents such as surface-modified mesoporous molecular sieves (MCM-41 or SBA-15) are used to adsorb p-nitrochlorobenzene. After desorption with a desorbent, the adsorbent is subjected to vacuum distillation. Subsequently, p-nitrochlorobenzene and o-nitrochlorobenzene are separated by melt crystallization and distillation.
It achieves high-purity (greater than 99%) separation of p-nitrochlorobenzene and o-nitrochlorobenzene, significantly reducing energy consumption, simplifying the process, and reducing equipment investment.
Abstract
Description
Technical Field
[0001] This invention relates to the field of nitration product separation technology, specifically a method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products. Background Technology
[0002] The products of the nitration reaction of chlorobenzene are important intermediates in dyes, pesticides, and pharmaceuticals. The nitration reaction typically produces a mixture of three isomers: p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene. The para- and ortho-isomers are the main products, while the meta-isomer is present in small quantities but is difficult to separate. Traditional separation processes often combine crystallization with multiple distillations. First, the high melting point of p-nitrochlorobenzene is used for initial separation via melt crystallization. Then, multiple distillations are used to separate the ortho- and meta-isomers. However, this method has the following drawbacks:
[0003] First, the boiling points of o-nitrochlorobenzene and p-nitrochlorobenzene differ by only 4°C, and their relative volatility is close to 1, requiring distillation columns with a high theoretical plate number and a large reflux ratio, resulting in huge energy consumption. Second, the low content of m-nitrochlorobenzene makes separation difficult, and it is easy to contaminate both para- and ortho-products during the distillation process, making it difficult to meet purity standards. In addition, traditional processes require a combination of multiple crystallizations and multi-tower distillations, resulting in long processes, large equipment investments, low yields, and high energy consumption.
[0004] Therefore, there is an urgent need for an efficient and energy-saving method to separate the three nitrochlorobenzene isomers (p-, ortho-, and meta-), so as to obtain high-purity p-nitrochlorobenzene and ortho-nitrochlorobenzene, and to enrich and purify meta-nitrochlorobenzene. Summary of the Invention
[0005] (a) Technical problems to be solved
[0006] To address the shortcomings of existing technologies, this invention provides a method for separating p-nitrochlorobenzene from ortho-nitrochlorobenzene and meta-nitrochlorobenzene in chlorobenzene nitration products, thus solving the problems mentioned in the background art.
[0007] (II) Technical Solution
[0008] To achieve the above objectives, the present invention provides the following technical solution:
[0009] According to a first aspect of the present invention, a method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products is provided, comprising the following steps:
[0010] Step 1: Pass the chlorinated benzene nitration product into a moving bed containing an adsorbent to selectively adsorb m-nitrochlorobenzene, obtaining a raffinate phase free of the meta-isomer and an adsorbent phase rich in m-nitrochlorobenzene.
[0011] Step 2: Desorb the adsorbed phase with a desorbent, and then perform vacuum distillation on the desorbed liquid. Collect the m-nitrochlorobenzene product in the bottom of the column, and obtain the regenerated desorbent at the top of the column for recycling.
[0012] Step 3: Melt and crystallize the residual phase to separate the p-nitrochlorobenzene product and the crystallization mother liquor;
[0013] Step 4: Distill the crystallization mother liquor to obtain o-nitrochlorobenzene product from the bottom of the distillation column.
[0014] Preferably, in step 1, the adsorbent is selected from surface-modified mesoporous molecular sieves, the molecular sieve is selected from MCM-41 or SBA-15, and the surface-modifying functional groups of the mesoporous molecular sieve are amino or sulfonic acid groups.
[0015] Preferably, in step 1, before the chlorobenzene nitration product is introduced into a moving bed containing a fixed adsorbent for selective adsorption, the chlorobenzene nitration product needs to be preheated at a temperature of 80–100°C.
[0016] Preferably, in step 2, the desorbent is selected from toluene or xylene.
[0017] Preferably, in step 2, the parameters of the reduced pressure distillation are: pressure 10-50 kPa, top temperature 70-90°C, bottom temperature 180-190°C, reflux ratio 1-4:1, and theoretical plate number 15-30.
[0018] Preferably, in step 3, the melting and crystallization process is as follows: first, heat to 85-95℃ to melt and hold for 15-30 minutes, then cool to 45-55℃ at a cooling rate of 0.1-0.5℃ / h and grow crystals for 1-4 hours before discharging the mother liquor, then heat to 78-81℃ at a heating rate of 0.05-0.2℃ / h to induce sweating and flow out, and finally heat to 85-90℃ to melt and flow out.
[0019] Preferably, in step 4, the distillation parameters are: pressure 10-30 kPa, top temperature 178-183°C, bottom temperature 185-190°C, reflux ratio 1-4:1, and theoretical plate number 20-35.
[0020] Beneficial effects
[0021] This invention provides a method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products. It has the following beneficial effects:
[0022] (1) The present invention provides a method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products. By selecting an adsorbent with specific selective adsorption, m-nitrochlorobenzene is adsorbed and removed by a desorbent. High-purity m-nitrochlorobenzene is obtained by simple vacuum distillation. Then, p-nitrochlorobenzene and o-nitrochlorobenzene are separated by melt crystallization and distillation, with a purity greater than 99%.
[0023] (2) The method provided in this scheme for separating p-nitrochlorobenzene, o-nitrochlorobenzene and m-nitrochlorobenzene in chlorobenzene nitration products has significantly reduced energy consumption compared with the traditional multi-tower distillation process. At the same time, each reaction unit is mild, easy to control, and the separation process is simple. Detailed Implementation
[0024] To make the objectives, technical methods, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0025] Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.
[0026] The adsorbent in this invention is prepared by the following method:
[0027] Adsorbent I: Amino-modified MCM-41 was prepared by the following method:
[0028] a. Take 10g of material with a specific surface area > 1000m 2 / g, MCM-41 molecular sieve with pore size of 2-4nm was vacuum dried at 120℃ for 4h to remove adsorbed water from the surface of the molecular sieve.
[0029] b. Transfer the dried MCM-41 molecular sieve to a three-necked flask containing 200 mL of toluene and disperse it ultrasonically for 30 min under nitrogen protection.
[0030] c. Under a nitrogen atmosphere, 15 mL of 3-aminopropyltriethoxysilane was added dropwise to a three-necked flask at a rate of 1 mL / min. After the addition was complete, the temperature was raised to 110 °C and the mixture was refluxed for 24 h.
[0031] d. After the reaction is complete, cool to room temperature, filter and wash, and finally dry under vacuum at 80℃ for 6 hours to obtain amino-modified MCM-41.
[0032] Adsorbent II: Amino-modified SBA-15 was prepared by the following method:
[0033] a. Take 8g of material with a specific surface area > 800m2 / g, SBA-15 molecular sieve with pore size of 5-8nm was activated at 150℃ for 3h, and then the activated SBA-15 molecular sieve was dispersed in 150mL of toluene, while 0.5g of potassium carbonate was added as a catalyst.
[0034] b. Slowly add 12 mL of 3-aminopropyltriethoxysilane dropwise to the SBA-15 molecular sieve suspension, transfer it to a high-pressure reactor, and then react at 120 °C under the condition of 0.3-0.5 MPa for 12 h.
[0035] c. After the reaction is complete, cool to room temperature, filter, wash, and finally dry at 100℃ for 4 hours and then vacuum dry at 60℃ overnight to obtain amino-modified SBA-15.
[0036] Adsorbent III: Sulfonic acid-modified MCM-41 was prepared by the following method:
[0037] a. Disperse 10g of activated MCM-41 molecular sieve in 200mL of toluene, then add 20mL of 3-mercaptopropyltrimethoxysilane, and reflux at 110℃ for 18h under nitrogen protection to obtain mercapto-modified MCM-41.
[0038] b. Disperse the mercapto-modified MCM-41 in 100 mL of methanol, then add 50 mL of 30% hydrogen peroxide and 5 mL of glacial acetic acid, and stir the reaction at 60 °C for 8 h.
[0039] c. After the reaction is complete, wash with deionized water until neutral, then exchange solvent with ethanol, and finally dry under vacuum at 80℃ for 6 hours to obtain sulfonic acid modified MCM-41.
[0040] Adsorbent IV: SBA-15 modified with sulfonic acid groups was prepared by the following method:
[0041] a. Activate 8g of SBA-15 molecular sieve at 120℃, disperse it in 150mL of toluene, then add 15mL of 3-mercaptopropyltrimethoxysilane and 0.3g of hydroquinone, and reflux at 115℃ for 20h to obtain thiol-modified SBA-15.
[0042] b. Add the thiol-modified SBA-15 to the vortex formic acid solution and oxidize at 40℃ for 6 hours, then wash with water.
[0043] c. The residual acid was neutralized with 0.1 mol / L sodium bicarbonate, washed with ethanol, and dried under vacuum at 60 °C to obtain SBA-15 modified with sulfonic acid groups.
[0044] To better illustrate the content of this invention, the following description is provided in conjunction with specific embodiments.
[0045] Example 1
[0046] Step 1: First, preheat 1000 kg of chlorobenzene nitration product to 90°C, and then pass it into a moving bed with an amino-modified SBA-15 to selectively adsorb the m-nitrochlorobenzene in the chlorobenzene nitration product, and obtain the raffinate phase with the meta-isomer removed and the adsorbed phase rich in m-nitrochlorobenzene.
[0047] Step 2: Desorb the adsorbed phase with toluene to obtain the eluent. Then, set the pressure in the recovery column to 20 kPa, the top temperature to 78°C, the bottom temperature to 185°C, the reflux ratio to 2.5:1, and the theoretical plate number to 25. Perform vacuum distillation on the eluent and collect the m-nitrochlorobenzene product with a purity of 99.2% in the bottom of the column. The regenerated toluene obtained at the top of the column is recycled.
[0048] Step 3: Pump the residual phase into the melt crystallizer, heat the residual phase to 90°C and hold for 15 minutes, then cool it down to 50°C at a rate of 0.3°C / h to grow crystals for 2 hours and then discharge the mother liquor. Then heat it up to 80°C at a rate of 0.05°C / h to allow it to sweat out, and finally heat it up to 87°C to melt and flow out a p-nitrochlorobenzene product with a purity of 99.8%.
[0049] Step 4: Set the pressure in the distillation column to 20 kPa, the top temperature to 180℃, the bottom temperature to 188℃, the reflux ratio to 2:1, and the theoretical plate number to 28. Distill the mother liquor to obtain o-nitrochlorobenzene with a purity of 99.6% through the bottom of the column.
[0050] Example 2
[0051] Step 1: First, preheat 1000 kg of chlorobenzene nitration product to 90°C, and then pass it into a moving bed with an amino-modified MCM-41 built-in to selectively adsorb the m-nitrochlorobenzene in the chlorobenzene nitration product, and obtain the raffinate phase with the meta-isomer removed and the adsorbed phase rich in m-nitrochlorobenzene.
[0052] Step 2: Desorb the adsorbed phase with toluene to obtain the eluent. Then, set the pressure in the recovery column to 25 kPa, the top temperature to 80℃, the bottom temperature to 188℃, the reflux ratio to 2.5:1, and the theoretical plate number to 25. Perform vacuum distillation on the eluent and collect the m-nitrochlorobenzene product with a purity of 99.3% in the bottom of the column. The regenerated toluene obtained at the top of the column is recycled.
[0053] Step 3: Pump the residual phase into the melt crystallizer, heat the residual phase to 88°C and hold for 15 minutes. Then, cool it down to 50°C at a rate of 0.2°C / h to grow crystals for 2 hours and then discharge the mother liquor. Then, heat it up to 80°C at a rate of 0.1°C / h to allow it to sweat out. Finally, heat it up to 87°C to melt and flow out a p-nitrochlorobenzene product with a purity of 99.7%.
[0054] Step 4: Set the pressure in the distillation column to 20 kPa, the top temperature to 178°C, the bottom temperature to 185°C, the reflux ratio to 2:1, and the theoretical plate number to 28. Distill the mother liquor to obtain o-nitrochlorobenzene with a purity of 99.4% through the bottom of the column.
[0055] Example 3
[0056] Step 1: First, preheat 1000 kg of chlorobenzene nitration product to 90°C, and then pass it into a moving bed with built-in sulfonic acid group modified MCM-41 to selectively adsorb the m-nitrochlorobenzene in the chlorobenzene nitration product, and obtain the raffinate phase with the meta-isomer removed and the adsorbed phase rich in m-nitrochlorobenzene.
[0057] Step 2: Desorb the adsorbed phase with toluene to obtain the eluent. Then, set the pressure in the recovery column to 30 kPa, the top temperature to 90°C, the bottom temperature to 190°C, the reflux ratio to 3:1, and the theoretical plate number to 25. Perform vacuum distillation on the eluent and collect the 99.5% pure m-nitrochlorobenzene product in the bottom of the column. The regenerated toluene obtained at the top of the column is recycled.
[0058] Step 3: Pump the residual phase into the melt crystallizer, heat the residual phase to 95°C and hold for 15 minutes. Then, cool it down to 50°C at a rate of 0.1°C / h to grow crystals for 2 hours and then discharge the mother liquor. Then, heat it up to 81°C at a rate of 0.1°C / h to allow it to sweat out. Finally, heat it up to 90°C to melt and flow out a p-nitrochlorobenzene product with a purity of 99.8%.
[0059] Step 4: Set the pressure in the distillation column to 25 kPa, the top temperature to 183℃, the bottom temperature to 188℃, the reflux ratio to 2:1, and the theoretical plate number to 28. Distill the mother liquor to obtain o-nitrochlorobenzene with a purity of 99.5% through the bottom of the column.
[0060] Example 4
[0061] Step 1: First, preheat 1000 kg of chlorobenzene nitration product to 90°C, and then pass it into a moving bed with SBA-15 modified with sulfonic acid groups to selectively adsorb the m-nitrochlorobenzene in the chlorobenzene nitration product, and obtain the raffinate phase with the meta-isomer removed and the adsorbed phase rich in m-nitrochlorobenzene.
[0062] Step 2: Desorb the adsorbed phase with toluene to obtain the eluent. Then, set the pressure in the recovery column to 30 kPa, the top temperature to 90°C, the bottom temperature to 190°C, the reflux ratio to 3:1, and the theoretical plate number to 25. Perform vacuum distillation on the eluent and collect the 99.5% pure m-nitrochlorobenzene product in the bottom of the column. The regenerated toluene obtained at the top of the column is recycled.
[0063] Step 3: Pump the residual phase into the melt crystallizer, heat the residual phase to 95°C and hold for 15 minutes. Then, cool it down to 50°C at a rate of 0.1°C / h to grow crystals for 2 hours and then discharge the mother liquor. Then, heat it up to 81°C at a rate of 0.1°C / h to allow it to sweat out. Finally, heat it up to 90°C to melt and flow out a p-nitrochlorobenzene product with a purity of 99.8%.
[0064] Step 4: Set the pressure in the distillation column to 25 kPa, the top temperature to 183℃, the bottom temperature to 188℃, the reflux ratio to 2:1, and the theoretical plate number to 28. Distill the mother liquor to obtain o-nitrochlorobenzene with a purity of 99.5% through the bottom of the column.
[0065] Comparative Example 1
[0066] Step 1: First, 1000 kg of chlorobenzene nitration product is fed into a crystallization kettle and heated to 90°C to completely melt it into a liquid. Then, the temperature is lowered to 50°C at a rate of 0.5°C / h. The crude p-nitrochlorobenzene is separated from the mother liquor by centrifugation. Finally, the crude p-nitrochlorobenzene is heated to 80°C for evaporation to obtain a p-nitrochlorobenzene product with a purity of 99.1%.
[0067] Step 2: The mother liquor is fed into the pre-separation tower. Under the condition of -0.08MPa, the top temperature of the tower is set to 190℃, the bottom temperature of the tower is set to 210℃, the reflux ratio is 2:1, and the theoretical number of plates is 35 for preliminary separation. The top of the tower yields a mixture containing ortho- and meta-positions and a small amount of para-positions, while high-boiling-point impurities are discharged from the bottom of the tower.
[0068] Step 3: The mixture obtained from the top of the pre-separation tower is fed into the main separation tower. Under the conditions of -0.09 MPa, the top temperature of the tower is set to 185°C, the bottom temperature of the tower is set to 195°C, the reflux ratio is 12:1, and the theoretical plate number is 75. The mixture containing para and meta positions is discharged from the top of the tower, and the o-nitrochlorobenzene product with a purity of 98.9% is discharged from the bottom of the tower.
[0069] Step 4: Pass the mixture of para- and meta-positions of sweat that oozed out in Step 3 into the recovery tower. Set the pressure to -0.09 MPa, the top temperature to 175°C, the bottom temperature to 185°C, the reflux ratio to 18:1, and the theoretical number of plates to 65. At the top of the tower, meta-position oil rich in m-nitrochlorobenzene is obtained, and at the bottom of the tower, a mixture containing para-nitrochlorobenzene is obtained and sent back to the pretreatment tower.
[0070] Table 1 shows a comparison of the energy consumption of Embodiments 1-4 of the present invention with that of Comparative Example 1:
[0071] Table 1
[0072] Energy consumption indicators Examples 1-4 Comparative Example 1 Comparison results Steam consumption 850kg / ton 3800kg / ton ≈4.5 times Electricity consumption 120kWh / ton 180kWh / ton ≈1.5 times Cooling water consumption <![CDATA[120m 3 ]]> <![CDATA[450m 3 ]]> ≈3.8 times
[0073] The product purity obtained using the separation schemes in Examples 1 to 4 is significantly higher than that of the product separated in Comparative Example 1. Furthermore, as shown in Table 1, the technical solution provided by this invention significantly saves energy, with annual savings of 147,500 tons of steam, 3 million kWh of electricity, and 1.65 million m³ of cooling water. 3 Despite the increased investment in adsorption units per year, the overall economic benefits are significantly improved, demonstrating excellent market competitiveness.
[0074] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.
Claims
1. A method for separating p-nitrochlorobenzene from o-nitrochlorobenzene and m-nitrochlorobenzene in chlorobenzene nitration products, characterized in that: Includes the following steps: Step 1: Pass the chlorinated benzene nitration product into a moving bed containing an adsorbent to selectively adsorb m-nitrochlorobenzene, obtaining a raffinate phase free of the meta-isomer and an adsorbent phase rich in m-nitrochlorobenzene. Step 2: Desorb the adsorbed phase with a desorbent, and then perform vacuum distillation on the desorbed liquid. Collect the m-nitrochlorobenzene product in the bottom of the column, and obtain the regenerated desorbent at the top of the column for recycling. Step 3: Melt and crystallize the residual phase to separate the p-nitrochlorobenzene product and the crystallization mother liquor; Step 4: Distill the crystallization mother liquor to obtain o-nitrochlorobenzene product from the bottom of the distillation column.
2. The method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products according to claim 1, characterized in that: In step 1, the adsorbent is selected from surface-modified mesoporous molecular sieves, the molecular sieves are MCM-41 or SBA-15, and the surface-modified functional groups of the mesoporous molecular sieves are amino or sulfonic acid groups.
3. The method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products according to claim 1, characterized in that: In step 1, before the chlorobenzene nitration product is introduced into a moving bed containing a fixed adsorbent for selective adsorption, the chlorobenzene nitration product needs to be preheated at a temperature of 80–100°C.
4. The method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products according to claim 1, characterized in that: In step 2, the desorbent is selected from toluene or xylene.
5. The method for separating nitrochlorobenzene from o-nitrochlorobenzene and m-nitrochlorobenzene in chlorobenzene digestion products according to claim 4, characterized in that: In step 2, the parameters for vacuum distillation are: pressure 10-50 kPa, top temperature 70-90°C, bottom temperature 180-190°C, reflux ratio 1-4:1, and theoretical plate number 15-30.
6. The method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products according to claim 1, characterized in that: In step 3, the melting and crystallization process is as follows: first, heat to 85-95℃ and hold for 15-30 minutes, then cool to 45-55℃ at a cooling rate of 0.1-0.5℃ / h and grow crystals for 1-4 hours before draining the mother liquor, then heat to 78-81℃ at a heating rate of 0.05-0.2℃ / h for sweating and out, and finally heat to 85-90℃ to melt and flow out.
7. The method for separating p-nitrochlorobenzene, o-nitrochlorobenzene, and m-nitrochlorobenzene from chlorobenzene nitration products according to claim 1, characterized in that: In step 4, the parameters of the distillation are: pressure 10-30 kPa, top temperature 178-183℃, bottom temperature 185-190℃, reflux ratio 1-4:1, and theoretical plate number 20-35.