A method and system for treating process wastewater from 2,6-di-tert-butyl-p-cresol production

Abstract

The present application relates to a kind of 2,6-di-tert-butyl-p-cresol production process wastewater treatment method and system, comprising the following steps: 1 water treatment: using the process of intermittent rectification+evaporation concentration+slice, first rectification, open tower kettle heating steam and overhead cooler, after 1 hour in full reflux state stability, control tower top gas phase temperature 82~102 ℃, collect first fraction, second fraction, then adjust the reflux ratio to 0, i.e. change rectification into evaporation, collect and recycle water 1, remaining kettle material is cooled crystallization slice, obtain sodium p-toluenesulfonate;2 water treatment: using the process of intermittent rectification treatment to recover tertiary butyl alcohol in 2 water, open tower kettle heating steam and overhead cooler, after 1 hour in full reflux state stability, control tower top gas phase temperature 82~102 ℃, respectively collect first fraction, second fraction, remaining kettle liquid is transported to neutralization and alkali preparation post.The present application separates 1 water and 2 water and handles separately, saves energy consumption, and water is recycled.

Description

Technical Field

[0001] This invention relates to a method and system for treating wastewater from the production process of 2,6-di-tert-butyl-p-cresol, belonging to the technical field of chemical production wastewater treatment. Background Technology

[0002] The antioxidant 2,6-di-tert-butyl-p-cresol (BHT) is produced by the alkylation reaction of p-cresol with isobutylene under the action of acidic catalysts such as p-toluenesulfonic acid. After the reaction, the acidic catalyst needs to be neutralized with an alkaline solution. After neutralization, sedimentation and separation yield a neutralization mother liquor (referred to as primary water). The process wastewater after removing the primary water undergoes a first wash to obtain a wash water (referred to as secondary water). The neutralization mother liquor and wash water are combined and collectively referred to as BHT production process wastewater, which contains approximately 5% sodium p-toluenesulfonate and 1-2% tert-butanol. Tert-butanol is a hydration byproduct of isobutylene under the action of an acidic catalyst. The current treatment method is to evaporate and concentrate the wastewater to a water content of approximately 40% in the reactor liquid, then cool, crystallize, slice, and package the concentrated sodium p-toluenesulfonate solution as a byproduct for sale. See [link to relevant documentation]. Figure 1 The main problems are: First, the byproduct tert-butanol is not discharged from the system outlet and instead enters the evaporation and concentration recovery water. Because tert-butanol continuously accumulates, directly using the recovery water for neutralization alkali preparation or washing leads to unclear stratification during neutralization and washing. Furthermore, the tert-butanol wastewater has very poor biodegradability, with a BOD of almost zero. Direct discharge into wastewater treatment plants would significantly impact biological treatment units and affect the normal operation of the wastewater treatment plants. Second, combining the primary and secondary wastewater for evaporation and concentration is technically unreasonable, economically unfeasible, and energy-intensive. Therefore, the treatment of wastewater from BHT production processes has always been a difficult problem for related production enterprises. Summary of the Invention

[0003] To address the problems existing in current wastewater treatment methods, this invention discloses a method and system for treating wastewater from the production of 2,6-di-tert-butyl-p-cresol, the specific technical solution of which is as follows: A method for treating wastewater from the production process of 2,6-di-tert-butyl-p-cresol includes the following steps: Step 1: The process wastewater is first neutralized. After neutralization, the process wastewater after the first separation of water is washed. After washing, the process wastewater after the second separation of water is sent to the BHT crystallization station. Step 2: Primary water treatment: A batch distillation + evaporation concentration + slicing process is adopted. First, distillation is carried out. The heating steam in the column bottom is turned on and the column top cooler is turned on. After the total reflux state is stabilized for 1 hour, the column top vapor temperature is controlled at 82~102℃. The first water fraction and the second water fraction are collected. The reflux ratio of the first water fraction is 10±2 and the reflux ratio of the second water fraction is 6±2. Then the reflux ratio is adjusted to 0, that is, the distillation is changed to evaporation. The recovered water 1 is collected. The remaining material in the reactor is cooled, crystallized and sliced ​​to obtain sodium p-toluenesulfonate. Step 3: Secondary water treatment: The tert-butanol in the secondary water is recovered using an intermittent distillation process. The heating steam in the column bottom is turned on, and the column top cooler is turned on. After the total reflux state is stabilized for 1 hour, the column top vapor temperature is controlled at 82~102℃. The first fraction and the second fraction of the secondary water are collected separately. The reflux ratio of the first fraction of the secondary water is 10±2, and the reflux ratio of the second fraction of the secondary water is 6±2. The remaining liquid in the bottom is sent to the neutralization and alkali preparation station as recovered water 2.

[0004] Furthermore, in step 2, the mass content of tert-butanol in the primary water fraction is greater than 60%, and the extracted mass accounts for 2-3% of the total mass.

[0005] Furthermore, the first water distillation fraction in step 2 is used as a transition fraction, with a tert-butanol content of 20-30%, and the amount extracted accounts for 2-3% of the total amount, and is transported to the next batch of second water distillation.

[0006] Furthermore, the tert-butanol content of the recycled water 1 in step 2 is 0.05%~0.15%, the extraction rate is 75%~80%, and it is transported to the next batch of washing water.

[0007] Furthermore, in step 2, the reactor material used for cooling the crystallized slices accounts for 13% to 17% of the total mass.

[0008] Furthermore, in step 3, the tert-butanol content in the second water fraction is greater than 60%, and the extracted mass accounts for 2-3% of the total mass.

[0009] Furthermore, the secondary water distillate in step 3 is used as a transition fraction, with a tert-butanol content of 20-30%, and the extracted mass accounts for 2-3% of the total mass, and is transported to the next batch of secondary water distillation.

[0010] Furthermore, the remaining liquid in step 3 accounts for 93% to 97% of the total mass.

[0011] The system for implementing the above-mentioned wastewater treatment method for the 2,6-di-tert-butyl-p-cresol production process includes a primary water system and a secondary water system. The primary water system includes a neutralization vessel and a primary water distillation tower vessel connected in series via pipelines. The secondary water system includes a water washing tower and a secondary water distillation tower vessel connected in series via pipelines. The process wastewater is first neutralized with alkali and then sent to the neutralization vessel of the primary water system. After neutralization in the neutralization vessel, primary water is separated and sent to the bottom of the primary water distillation column. The remaining process wastewater is sent to the water washing tower of the secondary water system for further washing and separation. The bottom of the primary water distillation column outputs primary water fraction I, primary water fraction II, and recycled water 1 in sequence. Primary water fraction I is sent to the tert-butanol enrichment system, and primary water fraction II is sent to the bottom of the secondary water distillation column of the secondary water system. After collecting primary water fraction II, the reflux ratio of the primary water distillation column is adjusted to 0, and recycled water 1 is evaporated and sent to the water washing tower of the secondary water system as washing water. The remaining material after evaporation is sent to the cooling crystallization and slicing system. The secondary water system's washing tower is connected to the process wastewater from the neutralization vessel of the primary water system. Secondary water is separated through washing, and the remaining wastewater is sent to the BHT crystallization station. The secondary water is sent to the bottom of the secondary water distillation tower, where it is distilled to produce secondary water fraction I, secondary water fraction II, and recycled water 2. Secondary water fraction I is sent to the tert-butanol enrichment system, and secondary water fraction II is sent to the bottom of the secondary water distillation tower of the secondary water system. After collecting secondary water fraction II, the remaining bottom liquid is sent as recycled water 2 to the neutralization and alkali preparation station as water for neutralization and alkali preparation.

[0012] Furthermore, one-way valves are installed on the pipelines between the neutralization vessel and the reboiler of the primary water system, the pipelines between the water washing tower and the reboiler of the secondary water system, and the pipeline between the neutralization vessel and the water washing tower.

[0013] The beneficial effects of this invention are: This invention recovers and purifies over 60% of tert-butanol from BHT production wastewater, allowing it to be sold as a byproduct. This solves the problem of the old process's reclaimed water being neither reusable nor biochemically treatable. By separating the primary and secondary wastewater, the secondary wastewater only needs distillation to recover most of the tert-butanol, eliminating the need for further evaporation before being directly used for neutralization and alkali preparation, reducing evaporation by over 50% compared to the old process. The second fraction (transition fraction, excluding sodium p-toluenesulfonate) collected during the distillation of both primary and secondary wastewater is also reused in the next batch of secondary wastewater distillation, effectively minimizing total evaporation and significantly saving energy. Reclaimed water 1 contains no sodium p-toluenesulfonate and has a tert-butanol content of less than 0.1%, making it suitable for washing without affecting stratification. Reclaimed water 2 contains only about 0.2% sodium p-toluenesulfonate and about 0.1% tert-butanol, making it suitable for neutralization and alkali preparation without affecting post-neutralization stratification. This invention solves all the problems associated with the old process. Attached Figure Description

[0014] Figure 1 This is the wastewater treatment flow chart before the improvement. Figure 2This is a flow chart of the improved wastewater treatment process of this invention. Detailed Implementation

[0015] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that the following specific embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0016] The results of actual sampling monitoring and simulation calculations show that the tert-butanol content in the tert-butanol-water azeotrope is as high as 87%, which provides technical support for the recovery of tert-butanol aqueous solutions with a mass content greater than 60% as by-products using distillation. Secondly, analysis shows that the tert-butanol content in the primary and secondary waters is not significantly different, around 2% (mass content), while the sodium p-toluenesulfonate content differs greatly. The sodium p-toluenesulfonate mass content in the primary water is as high as 9-10%, while the mass content in the secondary water is only 0.1-0.3%. This means that the primary and secondary waters should be treated separately, which is more technically reasonable, economical, and has great potential for energy saving and consumption reduction. To achieve the above objectives, the primary and secondary waters will be treated separately. The detailed implementation plan is described below (see...). Figure 2 ): I. Primary Water Treatment: A batch distillation + evaporation concentration + slicing process is adopted. First, distillation is carried out to collect the first fraction of primary water (tert-butanol byproduct, tert-butanol content is greater than 60%, which can be sold as a byproduct, with a recovery rate of 2-3% and a reflux ratio of about 10) and the second fraction of primary water (transition fraction, tert-butanol content of 20-30%, with a recovery rate of 2-3% and a reflux ratio of about 6, which is reused for the second distillation of the next batch of water). Then, the reflux ratio is adjusted to 0, that is, the distillation is changed to evaporation, and the recovered water 1 is collected, with a tert-butanol content of about 0.1%, and a recovery rate of 75-80%, which can be reused for the washing water of the next batch. The remaining batch of material, which accounts for about 15% of the total, is cooled, crystallized and sliced ​​to obtain sodium p-toluenesulfonate byproduct.

[0017] II. Secondary Water Treatment: Due to the very low sodium p-toluenesulfonate content in the secondary water, only a batch distillation process is needed to recover the tert-butanol. The first fraction of the secondary water (tert-butanol byproduct, with a content greater than 60%, which can be sold as a byproduct, accounting for 2-3% of the output, with a reflux ratio of approximately 10) and the second fraction (transition fraction, with a tert-butanol content of 20-30%, accounting for 2-3% of the output, with a reflux ratio of approximately 6, to be reused in the next batch of secondary water distillation) are collected separately. The remaining still liquid accounts for approximately 95% of the total volume. Because the sodium p-toluenesulfonate content is very low, no evaporation treatment is required, and it can be directly used in the neutralization and alkali preparation stage.

[0018] The following are specific application examples of the present invention: Example

[0019] Example 1

[0020] Primary water treatment 8000 kg of water containing 2.46% tert-butanol and 8.91% sodium p-toluenesulfonate was pumped into the reboiler of the distillation column. The reboiler heating steam and the overhead cooler were turned on. After stabilizing under total reflux for one hour, the overhead vapor temperature was controlled at 82–102 °C, the reflux ratio at 8–12, and the reflux temperature at 40 °C. The first and second fractions of the water were collected separately. Once the tert-butanol content in the reboiler was deemed acceptable, the reflux was stopped, and the collection of recycled water (1) was switched on. The temperature of recycled water (1) was controlled at 70 °C for direct use in the washing process after neutralization. The heating steam was stopped when the reboiler temperature reached approximately 120 °C. After the solids content was deemed acceptable, the product was discharged to a rotary drum cooling crystallizer for slicing and packaging to obtain sodium p-toluenesulfonate as a byproduct. The measurement and analysis results of each fraction are summarized in Table 1.

[0021] Table 1

[0022] Example 2

[0023] Secondary water treatment 8000 kg of water containing 2.32% tert-butanol and 0.16% sodium p-toluenesulfonate was pumped into the reboiler of the distillation column. The reboiler heating steam and the overhead cooler were turned on. After stabilizing under total reflux for one hour, the overhead vapor temperature was controlled at 82–102 °C, the reflux ratio at 8–12, and the reflux temperature at 40 °C. The first and second fractions of the water were collected separately. Heating steam was stopped once the reboiler temperature reached 102 °C. After the tert-butanol content in the reboiler was found to be within acceptable limits, the product was discharged to the recovery water storage tank. The measurement and analysis results of each fraction are summarized in Table 2.

[0024] Table 2

[0025] Verification Example 1 Two sets of recycled water 350 kg of recycled water 2 from Example 2 was pumped into the neutralization vessel. 18 kg of sodium carbonate was added under stirring until completely dissolved. One batch of alkylating agent was slowly pumped into the neutralization vessel. After the pumping was completed, stirring was continued for half an hour. Stirring was stopped, and the mixture was allowed to stand and settle for 1 hour. The neutralization mother liquor (first-stage water) was separated from the bottom. Careful observation revealed a clear stratification interface, which was the same as the stratification effect of alkali solution prepared with tap water. This proves that recycled water 2 can be used for neutralization alkali preparation.

[0026] Verification Example 2 In Example 1, the alkylated liquid after the first separation of water (neutralization mother liquor) was added to 350 kg of the recycled water 1 from Example 1. After stirring for half an hour and letting it stand for 1 hour, the second separation of water (washing water) was achieved from the bottom. Careful observation revealed a clear stratification interface, which was the same as the stratification effect when washing with tap water, proving that recycled water 1 can be applied to the washing process.

[0027] Those skilled in the art will understand that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0028] Based on the above-described preferred embodiments of the present invention, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the inventive concept. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A method for treating wastewater from the production process of 2,6-di-tert-butyl-p-cresol, characterized in that, Includes the following steps: Step 1: The process wastewater is first neutralized. After neutralization, the process wastewater after the first separation of water is washed with water. After washing with water, the process wastewater after the second separation of water is sent to the BHT crystallization station. Step 2: Primary water treatment: A batch distillation + evaporation concentration + slicing process is adopted. First, distillation is carried out. The heating steam in the column bottom is turned on and the column top cooler is turned on. After the total reflux state is stabilized for 1 hour, the column top vapor temperature is controlled at 82~102℃. The first water fraction and the second water fraction are collected. The reflux ratio of the first water fraction is 10±2 and the reflux ratio of the second water fraction is 6±2. Then the reflux ratio is adjusted to 0, that is, the distillation is changed to evaporation. The recovered water 1 is collected. The remaining material in the reactor is cooled, crystallized and sliced ​​to obtain sodium p-toluenesulfonate. Step 3: Secondary water treatment: The tert-butanol in the secondary water is recovered using an intermittent distillation process. The heating steam in the column bottom is turned on, and the column top cooler is turned on. After the total reflux state is stabilized for 1 hour, the column top vapor temperature is controlled at 82~102℃. The first fraction and the second fraction of the secondary water are collected separately. The reflux ratio of the first fraction of the secondary water is 10±2, and the reflux ratio of the second fraction of the secondary water is 6±2. The remaining liquid in the bottom is sent to the neutralization and alkali preparation station as recovered water 2.

2. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, In step 2, the tert-butanol content in the primary water fraction is greater than 60%, and the extracted mass accounts for 2-3% of the total mass.

3. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The first water distillation fraction in step 2 is used as a transition fraction, with a tert-butanol content of 20-30%, and the amount extracted accounts for 2-3% of the total amount. It is then transported to the next batch of second water distillation.

4. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The tert-butanol content of the recycled water 1 in step 2 is 0.05%~0.15%, and the extracted amount accounts for 75%~80%, which is then transported to the next batch of washing water.

5. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, In step 2, the reactor material used for cooling the crystallized slices accounts for 13% to 17% of the total mass.

6. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, In step 3, the tert-butanol content in the secondary water fraction is greater than 60%, and the extracted mass accounts for 2-3% of the total mass.

7. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The secondary water distillate in step 3 is used as a transition fraction, with a tert-butanol content of 20-30%, and the extracted mass accounts for 2-3% of the total mass. It is then transported to the next batch of secondary water distillation.

8. The wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol according to claim 1, characterized in that, The remaining liquid in step 3 accounts for 93% to 97% of the total mass.

9. A system for implementing the wastewater treatment method for the production process of 2,6-di-tert-butyl-p-cresol as described in any one of claims 1-8, characterized in that, It includes a primary water system and a secondary water system. The primary water system includes a neutralization vessel and a primary water distillation tower vessel connected in series by pipelines. The secondary water system includes a water washing tower and a secondary water distillation tower vessel connected in series by pipelines. The process wastewater is first neutralized with alkali and then sent to the neutralization vessel of the primary water system. After neutralization in the neutralization vessel, primary water is separated and sent to the bottom of the primary water distillation column. The remaining process wastewater is sent to the water washing tower of the secondary water system for further washing and separation. The bottom of the primary water distillation column outputs primary water fraction I, primary water fraction II, and recycled water 1 in sequence. Primary water fraction I is sent to the tert-butanol enrichment system, and primary water fraction II is sent to the bottom of the secondary water distillation column of the secondary water system. After collecting primary water fraction II, the reflux ratio of the primary water distillation column is adjusted to 0, and recycled water 1 is evaporated and sent to the water washing tower of the secondary water system as washing water. The remaining material after evaporation is sent to the cooling crystallization and slicing system. The secondary water system's washing tower receives residual process wastewater from the neutralization vessel of the primary water system. Secondary water is separated through washing. The remaining wastewater is then transported to the BHT crystallization station. The secondary water is transported to the bottom of the secondary water distillation tower. The secondary water distillation tower distills secondary water fraction I, secondary water fraction II, and recycled water 2. Secondary water fraction I is transported to the tert-butanol enrichment system. Secondary water fraction II is transported to the bottom of the secondary water distillation tower in the secondary water system. After collecting secondary water fraction II, the remaining bottom liquid is transported as recycled water 2 to the neutralization and alkali preparation station as water for neutralization and alkali preparation.

10. The wastewater treatment system for the production process of 2,6-di-tert-butyl-p-cresol according to claim 9, characterized in that, One-way valves are installed on the pipelines between the neutralization vessel and the reboiler of the primary water system, the pipelines between the washing tower and the reboiler of the secondary water system, and the pipeline between the neutralization vessel and the washing tower.

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