A method for separating and purifying acidic nitroaromatics

Abstract

The present application relates to a kind of separation and purification methods in chemical production, provide a kind of energy-saving, efficient nitro aromatic hydrocarbon separation, purification method.Adopt gravity sedimentation, alkali washing, cooling, filter combination, utilize liquid-liquid micro-mixer and cooling filter replace traditional multistage neutralization water washing operation of complicated multistage, high-efficiency removal acid, phenolic, sodium salt and water and other impurities in acidic nitro aromatic hydrocarbon, avoid emulsification phenomenon, after processing material can ensure the long-term stable operation of subsequent rectification system.The present application does not need two-stage water washing process in existing process, material consumption energy consumption and waste water volume are low;Liquid-liquid mixer is used in alkali washing process, and alkali washing effect is significantly improved;Water and salt in crude nitro aromatic hydrocarbon are removed by the way of fiber filter core cooling filtration, and the separation efficiency is high;The whole separation and purification device is fully enclosed system equipment, and the land area is small, and the operation is simple, and the purification effect is significantly improved compared with conventional process.

Description

Technical Field

[0001] This invention relates to a separation and purification method in chemical production, specifically a technical solution for deacidification, demulsification, desalination, and dehydration of materials after aromatic hydrocarbon nitration. Background Technology

[0002] The nitration products of aromatics and mixed acids contain residual acids and nitrophenolic byproducts. After neutralization, substances such as sodium sulfate and sodium nitrate are produced, which easily accumulate and scale in the subsequent distillation system, thus affecting the continuous operation of the unit. Phenolic substances are converted into phenol salts after neutralization. These salts have the potential for self-oxidation and high explosiveness, so they must be removed in the subsequent stage before distillation.

[0003] Currently, most nitrobenzene manufacturers use neutralization and water washing to remove acids and salts. However, traditional batch scrubbers or tubular static mixers have drawbacks such as high energy consumption, large wastewater volume, large footprint, uneven mixing, easy emulsification of materials, and poor washing effect. This results in high moisture and salt content in crude nitrobenzene, increasing energy consumption and safety risks in subsequent processes. Therefore, to prevent safety accidents such as explosions, the distillation system needs to be boiled regularly and the pipelines cleaned to prevent phenolic salt accumulation and sodium salt scaling, which could affect the continuous operation of the unit.

[0004] CN103664629B and CN102675118A both involve adding a coalescing separator to the neutralization and washing process to reduce sodium and phenolate in crude nitrobenzene. However, the material is severely emulsified and has a high moisture content after washing. Furthermore, after long-term operation, it was found that the coalescing separator is prone to clogging, affecting the continuous operation of the unit.

[0005] CN1757630A implements a pipelined washing process for nitrobenzene. Specifically, a crude nitrobenzene tubular scrubber is directly installed between the nitration separator and the washing wastewater separator to complete the neutralization and phenol removal processes. This invention primarily addresses the drawbacks of multi-tank series washing, such as large footprint, high energy consumption, and cumbersome operation; however, it does not significantly improve the washing effect. In actual production, poor mixing often leads to unstable pH in the discharge, resulting in alkali consumption far exceeding theoretical values. Summary of the Invention

[0006] The purpose of this invention is to provide an energy-saving and efficient method for separating and purifying nitroaromatic hydrocarbons.

[0007] The main technical solution of this invention is as follows: a method for separating and purifying acidic nitroaromatic hydrocarbons, which combines gravity sedimentation, alkaline washing, cooling, and filtration to achieve efficient separation and purification of acidic nitroaromatic hydrocarbons (aromatic hydrocarbons and mixed acid nitrated materials): the nitration product enters the nitration separator, the upper organic phase and alkaline solution enter the alkaline washing scrubber, the material from the alkaline washing scrubber enters the alkaline washing separator, the lower organic phase enters the cooling tower, and then enters the filter. The processed material is clear and transparent, with a moisture content of less than 0.5% and a sodium salt and phenolate content of less than 5 mg / L.

[0008] Generally, the nitroaromatic hydrocarbons described in the method of the present invention are nitrobenzene and nitrotoluene.

[0009] The above-mentioned nitration separator and alkali washing separator are gravity sedimentation separators, which are filled with plate packing. The separator can be set up vertically or horizontally, and the material residence time is 10min-30min.

[0010] The aforementioned alkaline washing machine is a liquid-liquid micro-mixer that uses one or more of the following methods to enhance the mixing effect: fluid rotation, division, shearing, and swirling jet. The combination of multiple shearing and swirling jet is preferred to enhance the washing effect.

[0011] The above-mentioned nitroaromatic hydrocarbons and alkaline solution are pumped to a liquid-liquid micro-mixer in proportion, the alkaline washing temperature is controlled at 5-60℃, the residence time is 5-120s, preferably 15-60s, and the material is discharged into a neutralization separator.

[0012] The ratio of the organic phase to the alkaline solution is 8:1 to 20:1.

[0013] The alkaline washing temperature mentioned above is 5-60℃, preferably 10-30℃.

[0014] The above-mentioned filter uses a hydrophobic dense fiber filter element, with a filtration temperature of 0-45℃ and a pressure of normal pressure, preferably a filtration temperature of 5-20℃.

[0015] After filtration, solid impurities can be removed, and tiny emulsified water droplets can be agglomerated into larger water droplets, thereby achieving separation and removal from the organic phase. After the above separation and purification, the material is clear, transparent and neutral, with a moisture content of less than 0.5% and sodium salt and phenolate content of less than 5 mg / L.

[0016] The method of this invention has the following advantages: 1. It eliminates the two-stage water washing process in existing processes, significantly reducing material consumption, energy consumption, and wastewater volume, and increasing efficiency by approximately 20% per ton of product. 2. It uses a liquid-liquid mixer to enhance mixing, resulting in low energy consumption, reduced material emulsification, and significantly improved alkali washing effect, reducing alkali consumption by more than 5%. 3. It uses a special fiber filter element for cooling filtration to remove water and salts from crude nitroaromatics in one step, achieving high separation efficiency. 4. The entire separation and purification device is a fully enclosed system, less prone to leakage and blockage, with a small footprint, simple operation, and significantly improved purification effect compared to conventional processes. Attached Figure Description

[0017] Figure 1 This is a schematic flowchart of the method for separating and purifying acidic nitroaromatic hydrocarbons according to an embodiment of the present invention.

[0018] Figure 2 This is a schematic diagram of a comparative method for separating and purifying acidic nitroaromatic hydrocarbons. Implementation

[0019] The present invention will now be described in detail with reference to the embodiments and accompanying drawings. Example

[0020] A method for separating and purifying acidic nitroaromatic hydrocarbons mainly includes a nitration separator, an alkaline washing scrubber, an alkaline washing separator, a cooling tower, a filter, a transfer pump, and auxiliary pipelines. A flow chart is attached. Figure 1 The specific operation involves the acidic nitration product entering a nitration separator, where it is allowed to stand for 10-30 minutes. The lower layer of waste acid is concentrated and reused. The upper organic phase and alkaline solution are pumped separately into a liquid-liquid micro-mixer (alkaline washer), with a residence time of 5-120 seconds. The ratio of organic phase to alkaline solution is 8:1-20:1, and the temperature is controlled at 5-60℃. The material from the mixer outlet enters the alkaline wash separator. The upper outlet enters the wastewater treatment system, while the lower organic phase enters a cooling tower to promote the precipitation of emulsion water and salts. The material is then pumped into a hydrophobic dense fiber filter at a temperature of 0-45℃ and an atmospheric pressure. The treated material is clear and transparent, with a neutral pH and significantly reduced moisture and salt content, enabling long-term stable operation of the subsequent distillation system.

[0021] The nitroaromatic hydrocarbons in the examples are nitrobenzene and nitrotoluene.

[0022] Example 1: The nitration product of benzene and mixed acid enters a nitration separator. After standing for 20 minutes, the lower waste acid is sent to a concentration unit. The upper organic phase and alkali solution are pumped separately into an alkali washing liquid-liquid micro-mixer at a volume ratio of 20:1. The mixer uses a combination of multiple shearing and cyclone jetting. The material residence time is 5 seconds, and the alkali washing temperature is controlled at 60°C. The mixture then enters the alkali washing separator for further stratification. The upper outlet enters the wastewater treatment system, while the lower organic phase is cooled to 45°C in a cooling tower (this temperature is the subsequent filtration temperature; the filtration pressure is atmospheric pressure). It is then pumped into a hydrophobic dense fiber filter to obtain clear, transparent crude nitrobenzene with a pH of 7.0 and reduced moisture and salt content to 0.11% and 1.2 mg / L, respectively. According to the equipment operation data, this process significantly reduces material and energy consumption and wastewater volume, reduces alkali consumption by 7%, and increases the economic benefit per ton of product by approximately 18%.

[0023] Example 2: The nitration product of benzene and mixed acid enters a nitration separator. After standing for 10 minutes, the lower waste acid is sent to a concentration unit. The upper organic phase and alkali solution are pumped into an alkali washing liquid-liquid micro-mixer at a volume ratio of 10:1. The mixer uses a combination of multiple shearing and cyclone jetting. The material residence time is 120 seconds, and the alkali washing temperature is controlled at 5°C. The material from the mixer outlet enters the alkali washing separator. The upper outlet enters the wastewater treatment system, while the lower organic phase enters a cooling tower to cool to 0°C, causing the emulsion water and salts to precipitate. The treated material is then pumped into a hydrophobic dense fiber filter for filtration. The treated material is clear and transparent, with a pH of 7.1, and the moisture and salt content reduced to 0.09% and 0.8 mg / L, respectively. Statistical analysis of the unit's operating data shows that this process significantly reduces material and energy consumption and wastewater volume, reduces alkali consumption by 11%, and increases economic benefits per ton of product by 21%.

[0024] Example 3: The nitration product of toluene and mixed acid enters a nitration separator. The material is allowed to stand for 15 minutes. The lower layer of waste acid goes to a concentration unit, while the upper organic phase and alkali solution are pumped separately into a cyclone jet-type alkali washing liquid-liquid micro-mixer at a volume ratio of 10:1. The material residence time is 15 seconds, and the alkali washing temperature is controlled at 30°C. The material from the mixer outlet enters the alkali washing separator. The upper outlet enters the wastewater treatment system, while the lower organic phase enters a cooling tower to cool to 20°C, promoting the precipitation of emulsified water and salts. It is then pumped through a hydrophobic dense fiber filter. The treated material is clear and transparent, with a pH of 7.1, and the moisture and salt content reduced to 0.12% and 2.7 mg / L, respectively. According to the equipment operation data, this process reduces material and energy consumption and wastewater volume, reduces alkali consumption by 11%, and increases the economic benefit per ton of product by approximately 19%.

[0025] Example 4: The nitration products of toluene and mixed acid enter a nitration separator. The material is allowed to stand for 30 minutes. The lower layer of waste acid goes to a concentration unit, while the upper organic phase and alkali solution are pumped into a cyclone jet liquid-liquid micro-mixer at a volume ratio of 8:1. The material residence time is 60 seconds, and the alkali washing temperature is controlled at 10°C. The material from the mixer outlet enters an alkali washing separator. The upper outlet enters a wastewater treatment system, while the lower organic phase enters a cooling tower to cool to 15°C, promoting the precipitation of emulsified water and salts. The treated material is then pumped through a hydrophobic dense fiber filter. The treated material is clear and transparent, with a pH of 7.0, and the moisture and salt content reduced to 0.17% and 2.1 mg / L, respectively. Statistical analysis of the unit's operating data shows that this process significantly reduces material and energy consumption and wastewater volume, reduces alkali consumption by 12%, and increases economic benefits per ton of product by approximately 20%.

[0026] Example 5: The nitration products of benzene and mixed acid enter a nitration separator. The material is allowed to stand for 25 minutes. The lower waste acid is sent to a concentration unit, while the upper organic phase and alkaline solution are pumped into an alkaline washing liquid-liquid micro-mixer at a volume ratio of 15:1. The mixer uses a combination of multiple shearing and swirling jet methods, with a material residence time of 45 seconds and an alkaline washing temperature controlled at 20°C. The material from the mixer outlet enters the alkaline washing separator. The upper outlet enters the wastewater treatment system, while the lower organic phase enters a cooling tower to cool to 5°C, promoting the precipitation of emulsified water and salts. The material is then pumped through a hydrophobic dense fiber filter. After treatment, the material is clear and transparent, with a pH of 6.9 and moisture and salt content reduced to 0.29% and 0.8 mg / L, respectively.

[0027] Example 6: The nitration product of toluene and mixed acid enters a nitration separator. The material is allowed to stand for 30 minutes. The lower layer of waste acid goes to a concentration unit, while the upper organic phase and alkali solution are pumped separately into an alkali washing liquid-liquid micro-mixer at a 10:1 volume ratio. The mixer employs a combination of multiple shearing and swirling jet methods, with a material residence time of 30 seconds and an alkali washing temperature controlled at 30°C. The material from the mixer outlet enters the alkali washing separator. The upper outlet enters the wastewater treatment system, while the lower organic phase enters a cooling tower to cool to 10°C, promoting the precipitation of emulsified water and salts. It is then pumped through a hydrophobic dense fiber filter. The treated material is clear and transparent, with a pH of 7.0, and moisture and salt content reduced to 0.11% and 1.9 mg / L, respectively. Statistical analysis of the unit's operating data shows that this process significantly reduces material and energy consumption and wastewater volume, reduces alkali consumption by 10%, and increases economic benefits per ton of product by 19%.

[0028] Example 7: The nitration product of benzene and mixed acid enters the nitration separator. The material is allowed to stand for 25 minutes. The lower waste acid is sent to the concentration unit, while the upper organic phase and alkali solution are pumped into the alkali washing liquid-liquid micro-mixer at a volume ratio of 8:1. The mixer uses a combination of multiple shearing and cyclone jetting. The material residence time is 45 seconds, and the alkali washing temperature is controlled at 25°C. The material from the mixer outlet enters the alkali washing separator. The upper outlet enters the wastewater treatment system, while the lower organic phase enters the cooling tower to cool to 9°C, promoting the precipitation of emulsion water and salts. It is then pumped through a hydrophobic dense fiber filter. The treated material is clear and transparent, with a pH of 7.1, and the moisture and salt content reduced to 0.09% and 3.6 mg / L, respectively. According to the equipment operation data, this process significantly reduces material and energy consumption and wastewater volume, reduces alkali consumption by 12%, and increases the economic benefit per ton of product by approximately 21%.

[0029] Comparative Example 1: Separation device as shown in the attached diagram Figure 2 The nitration products of benzene and mixed acid are fed into a nitration separator. The material is allowed to stand for 60 minutes. The lower layer of waste acid is sent to a concentration unit. The upper organic phase and alkaline solution are pumped at a volume ratio of 12:1 into an alkaline washing scrubber and a water washing scrubber, respectively. Both scrubbers are series-connected, batch-type structures. The material resides in the scrubber for 15 minutes, and the washing temperature is controlled at 45℃. The material from the scrubber outlet is fed into the alkaline washing and water washing separators, respectively, and allowed to stand for approximately 45 minutes. The lower organic phase is the crude nitrobenzene that enters the distillation system. The material is a white emulsion, heavily emulsified, with a pH of 7.4, and moisture and salt contents of 1.91% and 8.3 mg / L, respectively.

[0030] Comparative Example 2: The scrubber was a tubular static mixer, and other operating conditions were basically the same as in Comparative Example 1. The resulting crude nitrobenzene was a white emulsion with severe emulsification, pH=7.3, and water and salt contents of 2.26% and 7.9 mg / L, respectively.

Claims

1. A method for separating and purifying acidic nitroaromatic hydrocarbons, characterized in that: A combination of gravity sedimentation, alkaline washing, cooling, and filtration is used for the efficient separation and purification of acidic nitroaromatic hydrocarbons: the aromatic hydrocarbons and the nitrated material from the mixed acid enter the nitration separator; the upper organic phase and alkaline solution enter the alkaline washing scrubber; the material from the alkaline washing scrubber outlet enters the alkaline washing separator; the lower organic phase enters the cooling tower, and then enters the filter. The treated material is clear and transparent, with a moisture content of less than 0.5% and sodium and phenolate content of less than 5 mg / L; the alkaline washing scrubber is a liquid-liquid micro-mixer, which employs one or more of the following methods: fluid rotation, division, shearing, and swirling jet; the filter uses hydrophobic dense fiber.

2. The method as described in claim 1, characterized in that... Nitroaromatic hydrocarbons include nitrobenzene and nitrobenzene.

3. The method as described in claim 1, characterized in that... The nitration separator and the alkaline washing separator are gravity sedimentation separators, with plate packing inside; the nitration separator and the alkaline washing separator are installed vertically or horizontally, and the material residence time is 10min-30min.

4. The method as described in claim 1, characterized in that... The residence time of the material in the liquid-liquid micro mixer is 5-120s.

5. The method as described in claim 4, characterized in that... The residence time of the material in the liquid-liquid micro mixer is 15-60 seconds.

6. The method as described in claim 1, characterized in that... The liquid-liquid micro-mixer employs a combination of multiple shearing and swirling jetting techniques.

7. The method as described in claim 1, characterized in that... The alkaline washing temperature is 5-60℃.

8. The method as described in claim 1, characterized in that... The filtration temperature is 0-45℃, and the pressure is normal pressure.

9. The method as described in claim 1, characterized in that... The ratio of organic phase to alkaline solution is 8:1 to 20:1.

Images