Method for separating and purifying acidic nitro-aromatic hydrocarbon

Abstract

The invention relates to a separation and purification method in chemical production, and provides an energy-saving and efficient nitro-aromatic hydrocarbon separation and purification method. Gravity settling, alkali washing, cooling and filtering are combined, a liquid-liquid micro-mixer and cooling and filtering are used for replacing traditional tedious multi-stage neutralizing and water washing operation of a multi-kettle series connection or static mixer, impurities such as residual acid, phenols, sodium salt and water in the acidic nitro-aromatic hydrocarbon are efficiently removed, the emulsification phenomenon is avoided, and the quality of the acidic nitro-aromatic hydrocarbon is improved. And the treated material can ensure long-term stable operation of a subsequent rectification system. The method does not need a two-stage washing process in the prior art, and is low in material consumption, energy consumption and wastewater amount; the liquid-liquid mixer is used for the alkali washing process, and the alkali washing effect is remarkably improved; water and salts in the crude nitro-aromatic hydrocarbon are removed in one step in a fiber filter element cooling and filtering mode, and the separation efficiency is high; the whole set of separation and purification device is a totally-closed system device, is small in occupied area and simple to operate, and the purification effect is remarkably improved compared with a conventional process.

Description

Technical Field

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

[0002] Aromatic hydrocarbons and mixed acid nitration products contain residual acid and nitrophenol byproducts. After neutralization, sodium sulfate, sodium nitrate and other substances are produced, which are easy to aggregate and scale in the subsequent distillation system, thus affecting the continuous operation of the device. Phenols are converted into phenol salts after neutralization. These salts are self-oxidizing and highly explosive, so they need to be removed in the pre-distillation process.

[0003] At present, most nitroaromatic benzene manufacturers use neutralization and water washing to remove acid and salt substances, while traditional kettle-type series washing or tubular static mixers have the disadvantages of high energy consumption, large amount of wastewater, large floor space, uneven mixing, easy emulsification of materials, poor washing effect, etc., resulting in high moisture and salt content in crude nitrobenzene, increasing energy consumption and safety risks in subsequent processes. Therefore, in order to prevent safety accidents such as explosions, the distillation system needs to boil the tower and clean the pipeline regularly to prevent phenol salt accumulation and sodium salt scaling, thereby affecting the continuous operation of the device.

[0004] CN103664629B and CN102675118A both involve adding a coalescing separator on the basis of neutralization and water washing to reduce the sodium salt and phenol salt in crude nitrobenzene. However, the material is severely emulsified and has a high moisture content after washing. Moreover, after long-term operation, it is found that the coalescing separator is prone to clogging, affecting the continuous operation of the device.

[0005] CN1757630A realizes pipeline washing process of nitrobenzene. The specific operation is to directly install crude nitrobenzene tubular scrubber between nitration separator and washing wastewater separator to complete the neutralization and dephenolization process. This invention mainly solves the shortcomings of multiple kettles in series, such as large floor space, high energy consumption and complicated operation, but the washing effect is not significantly improved. In actual production, the pH of the discharge is often unstable due to poor mixing effect, and the alkali consumption far exceeds the theoretical value. Summary of the invention

[0006] The purpose of the present invention is to provide an energy-saving and efficient method for separating and purifying nitroaromatics.

[0007] The main technical scheme of the present invention is: a method for separating and purifying acidic nitroaromatics, which adopts gravity sedimentation, alkali washing, cooling and filtration to achieve efficient separation and purification of acidic nitroaromatics (materials after nitration of aromatics and mixed acid): the nitration product enters the nitration separator, the upper organic phase and alkali solution enter the alkali washing scrubber, the material at the outlet of the alkali washing scrubber enters the alkali washing separator, the lower organic phase enters the cooling tower, and then enters the filter. After treatment, the material is clear and transparent, the moisture content is less than 0.5%, and the sodium salt and phenol salt content is less than 5 mg / L.

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

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

[0010] The above-mentioned alkaline washing scrubber is a liquid-liquid micro-mixer, which adopts one or a combination of fluid rotation, segmentation, shearing, swirl injection and the like to enhance the mixing effect, and preferably a combination of multiple shearing and swirl injection to enhance the washing effect.

[0011] The nitroaromatics and alkali solution are transported to a liquid-liquid micro mixer by a pump in proportion, the alkali washing temperature is controlled to be 5-60° C., the residence time is 5-120 s, preferably 15-60 s, and the discharge enters a neutralization separator.

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

[0013] The above-mentioned alkali washing temperature is 5-60°C, preferably 10-30°C.

[0014] The filter adopts a hydrophobic dense fiber filter element, the filtration temperature is 0-45°C, the pressure is normal pressure, and the preferred filtration temperature is 5-20°C.

[0015] After filtration, solid impurities can be removed, and extremely small emulsified water droplets can be aggregated into larger water droplets, thereby separating and removing them from the organic phase. After the above separation and purification, the material is clear, transparent and neutral, with a water content of less than 0.5%, and sodium salt and phenol salt content of less than 5 mg / L.

[0016] The method of the present invention has the following advantages: 1. The two-stage water washing process in the existing process is eliminated, the material consumption, energy consumption and wastewater volume are significantly reduced, and the efficiency per ton of product can be increased by about 20%. 2. A liquid-liquid mixer is used to enhance the mixing effect, with low energy consumption, and the material is not easy to emulsify. The alkali washing effect is significantly improved, and the alkali consumption is reduced by more than 5%; 3. A special fiber filter element is used for cooling and filtration to remove water and salts from crude nitroaromatics in one step, with high separation efficiency. 4. The entire set of separation and purification equipment is a fully closed system, which is not prone to leakage, blockage and the like. The equipment occupies a small area and is simple to operate. The purification effect is significantly improved compared with conventional processes. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a schematic flow chart of a method for separating and purifying acidic nitroaromatics according to an embodiment of the present invention.

[0018] Figure 2 Schematic diagram of the process of separating and purifying acidic nitroaromatics in comparative example. Implementation

[0019] The present invention is described in detail below in conjunction with embodiments and drawings. Example

[0020] A method for separating and purifying acidic nitroaromatics, mainly comprising a nitrification separator, an alkali washing scrubber, an alkali washing separator, a cooling tower, a filter, a delivery pump and associated pipelines, the flow chart of which is shown in the attached Figure 1 . The specific operation is that the acidic nitration product enters the nitration separator, the material is left to stand for 10min-30min, the lower waste acid is concentrated and reused, the upper organic phase and alkali solution enter the liquid-liquid micro mixer (alkali washing scrubber) through the delivery pump respectively, the material residence time is 5-120s, the ratio of organic phase to alkali solution is 8:1-20:1, and the temperature is controlled at 5-60℃. The material at the mixer outlet enters the alkali washing separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to promote the precipitation of emulsified water and salt substances, and then enters the hydrophobic dense fiber filter through the delivery pump. The filtration temperature is 0-45℃ and the pressure is normal pressure. After treatment, the material is clear and transparent, the pH is neutral, the water and salt content are significantly reduced, and the subsequent distillation system can be operated stably for a long time.

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

[0022] Example 1: The product after nitration of benzene and mixed acid enters the nitration separator, the material is left to stand for 20 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the alkali wash liquid-liquid micro mixer by a delivery pump at a volume ratio of 20:1, the mixer adopts a combination of multiple shearing and swirl injection, the material residence time is 5s, the alkali wash temperature is controlled to be 60°C, and then enters the alkali wash separator to stand and stratify, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 45°C (this temperature is the subsequent filtration temperature, and the filtration pressure is normal pressure) and then enters the hydrophobic dense fiber filter through the delivery pump to obtain clear and transparent crude nitrobenzene, pH=7.0, and the moisture and salt content are reduced to 0.11% and 1.2mg / L respectively. According to the statistics of the device operation data, the energy consumption and wastewater volume of the process are significantly reduced, the alkali consumption is reduced by 7%, and the economic benefits of tons of products are improved by about 18%.

[0023] Example 2: The product after nitration of benzene and mixed acid enters the nitration separator, the material is left to stand for 10 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the alkali wash liquid-liquid micro mixer by a delivery pump at a volume ratio of 10:1, the mixer adopts a combination of multiple shearing and swirl injection, the material residence time is 120s, and the alkali washing temperature is controlled to be 5°C. The material at the mixer outlet enters the alkali wash separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 0°C, which promotes the precipitation of emulsified water and salt substances, and then enters the hydrophobic dense fiber filter through the delivery pump for filtration. After treatment, the material is clear and transparent, pH=7.1, and the moisture and salt content are reduced to 0.09% and 0.8mg / L respectively. According to the statistics of the device operation data, the energy consumption and wastewater volume of the process are significantly reduced, the alkali consumption is reduced by 11%, and the economic benefits per ton of product are increased by 21%.

[0024] Example 3: The product after nitration of toluene and mixed acid enters the nitration separator, the material is left to stand for 15 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the cyclone jet alkali washing liquid-liquid micro mixer through the delivery pump at a volume ratio of 10:1, the material residence time is 15s, and the alkali washing temperature is controlled to be 30°C. The material at the mixer outlet enters the alkali washing separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 20°C, which promotes the precipitation of emulsified water and salt substances, and then passes through the hydrophobic dense fiber filter through the delivery pump. After treatment, the material is clear and transparent, pH=7.1, and the moisture and salt content are reduced to 0.12% and 2.7mg / L respectively. According to the statistics of the device operation data, the process energy consumption and wastewater volume are reduced, the alkali consumption is reduced by 11%, and the economic benefits per ton of product are improved by about 19%.

[0025] Example 4: The product after nitration of toluene and mixed acid enters the nitration separator, the material is left to stand for 30 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the cyclone jet liquid-liquid micro mixer by a delivery pump at a volume ratio of 8:1, the material residence time is 60s, and the alkali washing temperature is controlled to be 10°C. The material at the mixer outlet enters the alkali washing separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 15°C, which promotes the precipitation of emulsified water and salt substances, and then passes through the hydrophobic dense fiber filter through the delivery pump. After treatment, the material is clear and transparent, pH=7.0, and the moisture and salt content are reduced to 0.17% and 2.1mg / L respectively. According to the statistics of the device operation data, the energy consumption and wastewater volume of the process are significantly reduced, the alkali consumption is reduced by 12%, and the economic benefits per ton of product are increased by about 20%.

[0026] Example 5: The product after nitration of benzene and mixed acid enters the nitration separator, the material is left to stand for 25 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the alkali wash liquid-liquid micro mixer through the delivery pump at a volume ratio of 15:1, the mixer adopts a combination of multiple shearing and swirl injection, the material residence time is 45s, and the alkali wash temperature is controlled to be 20°C. The material at the mixer outlet enters the alkali wash separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 5°C, which promotes the precipitation of emulsified water and salt substances, and then passes through the hydrophobic dense fiber filter through the delivery pump. After treatment, the material is clear and transparent, pH=6.9, and the moisture and salt content are reduced to 0.29% and 0.8mg / L respectively.

[0027] Example 6: The product after nitration of toluene and mixed acid enters the nitration separator, the material is left to stand for 30 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the alkali wash liquid-liquid micro mixer by a delivery pump at a volume ratio of 10:1, the mixer adopts a combination of multiple shearing and swirl injection, the material residence time is 30s, and the alkali wash temperature is controlled to be 30°C. The material at the mixer outlet enters the alkali wash separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 10°C, which promotes the precipitation of emulsified water and salt substances, and then passes through the hydrophobic dense fiber filter through the delivery pump. After treatment, the material is clear and transparent, pH=7.0, and the moisture and salt content are reduced to 0.11% and 1.9mg / L respectively. According to the statistics of the device operation data, the energy consumption and wastewater volume of the process are significantly reduced, the alkali consumption is reduced by 10%, and the economic benefits per ton of product are increased by 19%.

[0028] Example 7: The product after nitration of benzene and mixed acid enters the nitration separator, the material is left to stand for 25 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the alkali wash liquid-liquid micro mixer by a delivery pump at a volume ratio of 8:1, and the mixer adopts a combination of multiple shearing and swirl injection. The material residence time is 45s, and the alkali washing temperature is controlled to be 25°C. The material at the mixer outlet enters the alkali wash separator, the upper outlet enters the wastewater treatment system, and the lower organic phase enters the cooling tower to cool to 9°C, which promotes the precipitation of emulsified water and salt substances, and then passes through the hydrophobic dense fiber filter through the delivery pump. After treatment, the material is clear and transparent, pH=7.1, and the moisture and salt content are reduced to 0.09% and 3.6mg / L respectively. According to the statistics of the device operation data, the energy consumption and wastewater volume of the process are significantly reduced, the alkali consumption is reduced by 12%, and the economic benefits per ton of product are increased by about 21%.

[0029] Comparative Example 1: Separation device as attached Figure 2 , the product after nitration of benzene and mixed acid enters the nitration separator, the material is left to stand for 60 minutes, the lower waste acid goes to the concentration device, the upper organic phase and alkali solution enter the alkali washing scrubber and water washing scrubber respectively through the delivery pump at a volume ratio of 12:1, the scrubbers are all kettle-type series structures, the material stays in the scrubber for 15 minutes, and the washing temperature is controlled at 45°C. The material at the outlet of the scrubber enters the alkali washing and water washing separators respectively, and the standing time is about 45 minutes. The lower organic phase is the crude nitrobenzene entering the distillation system. The material is a white emulsion with severe emulsification, pH=7.4, and the water and salt contents are 1.91% and 8.3mg / L respectively.

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

Claims

1. A method for separating and purifying acidic nitroaromatics, characterized in that A combination of gravity sedimentation, alkali washing, cooling and filtration is used to efficiently separate and purify acidic nitroaromatics: the materials after nitration of aromatics and mixed acid enter the nitration separator, the upper organic phase and alkali solution enter the alkali washing scrubber, the materials at the outlet of the alkali washing scrubber enter the alkali washing separator, the lower organic phase enters the cooling tower and then enters the filter. After treatment, the materials are clear and transparent, with a moisture content of less than 0.5%, and the sodium salt and phenol salt content of less than 5 mg / L.

2. The method according to claim 1, characterized in that Nitroaromatic hydrocarbons include nitrobenzene and nitrotoluene.

3. The method according to claim 1, characterized in that The nitrification separator and alkali washing separator are gravity sedimentation separators with plate-type fillers installed inside; the nitrification separator and alkali washing separator are set up vertically or horizontally, and the material residence time is 10min-30min.

4. The method according to claim 1, characterized in that The alkaline washing scrubber is a liquid-liquid micro mixer, and the material stays in the liquid-liquid micro mixer for 5-120s.

5. The method according to claim 4, characterized in that The material stays in the liquid-liquid micro mixer for 15-60 seconds.

6. The method according to claim 4, characterized in that The liquid-liquid micro mixer adopts one or a combination of fluid rotation, segmentation, shearing and swirl injection.

7. The method according to claim 6, characterized in that The liquid-liquid micro mixer adopts a combination of multiple shearing and swirl injection.

8. The method according to claim 1 or 4, characterized in that The alkali washing temperature is 5-60°C, preferably 10-30°C.

9. The method according to claim 1, characterized in that The filter uses hydrophobic dense fibers.

10. The method according to claim 1 or 9, characterized in that The filtration temperature is 0-45°C, the pressure is normal pressure, and the preferred filtration temperature is 5-20°C.

11. The method according to claim 1, characterized in that The ratio of organic phase to alkali solution is 8:1-20:1.

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