High-efficiency clean production process of sodium p-nitrophenol

Abstract

This invention relates to the field of fine chemical production technology, and in particular to a highly efficient and clean production process for sodium p-nitrophenolate. Using p-nitrochlorobenzene and sodium hydroxide as raw materials, the invention employs core processes such as precise pretreatment with liquid alkali, pressurized hydrolysis reaction, staged recovery of tail gas, gradient cooling crystallization, and two-stage piston-push centrifugal separation. Combined with upgraded equipment including a large-scale hydrolysis reactor, a DCS distributed control system, and a horizontal siphon scraper self-unloading centrifuge, the invention achieves highly efficient and stable production of sodium p-nitrophenolate. The optimized process increases production capacity to 21 tons / day (a 40% increase), product yield to 95%–96%, product purity to 99.8%, significantly improves automation, reduces reliance on manual operation by over 80%, and saves over 200,000 yuan annually in wastewater treatment costs, demonstrating significant economic, environmental, and social benefits.

Description

Technical Field

[0001] This invention relates to the technical field of fine chemical production, and in particular to a highly efficient and clean production process for sodium p-nitrophenolate. Background Technology

[0002] Sodium p-nitrophenolate is an important fine chemical intermediate, widely used in the synthesis of downstream products such as 4,4′-dinitrodiphenyl ether (DNDPE). Its purity and yield directly affect the quality of the downstream products. Currently, the industrial production of sodium p-nitrophenolate mainly adopts the alkaline pressure hydrolysis process of p-nitrochlorobenzene, but the traditional process has the following prominent problems:

[0003] 1. Limited production capacity: Traditional processes use small-volume (approximately 10m³) hydrolysis reactors, which have limited single-batch processing capacity, with a capacity of approximately 15 tons / day. This results in low plant utilization and makes it difficult to meet market demand.

[0004] II. Inaccurate temperature and pressure control: Traditional processes rely on manual control of feed rate, reaction temperature and pressure, which leads to large operational errors, resulting in significant fluctuations in reaction temperature and pressure, incomplete conversion of raw materials, and a product yield of only about 92%.

[0005] 3. Insufficient crystallization purity: The crystallization process uses artificial temperature control, and the temperature gradient is not precise, which easily produces impurities, resulting in a product purity of about 99.5%, which cannot fully meet the strict requirements of downstream DNDPE synthesis for high-purity raw materials.

[0006] 4. Low level of automation: Each process relies heavily on manual operation, and operational errors lead to large fluctuations in product quality, low production efficiency, and high production management costs.

[0007] 5. Inefficient exhaust gas treatment: The original process lacked a graded treatment mechanism for exhaust gas, resulting in significant material losses, failure to meet emission standards for harmful components in the exhaust gas, and heavy environmental pressure.

[0008] VI. Low solid-liquid separation efficiency: The original process uses a vacuum filter tank for solid-liquid separation, which has a high permeability but results in a large loss of solid content in the product, reducing the yield and increasing the difficulty and cost of treating solids in wastewater.

[0009] In view of the above problems, there is an urgent need to develop a highly efficient and clean production process for sodium p-nitrophenolate that can significantly improve production capacity, yield, product purity and automation level, while reducing energy consumption and environmental costs. Summary of the Invention

[0010] The purpose of this invention is to provide an efficient and clean production process for sodium p-nitrophenolate, aiming to solve the problems of low capacity, low yield, insufficient product purity, large human operation error, and crude exhaust gas treatment in the traditional sodium p-nitrophenolate production process mentioned in the background art.

[0011] To achieve the above objectives, the present invention provides the following technical solution: a highly efficient and clean production process for sodium p-nitrophenolate, comprising the following steps:

[0012] S1. Liquid alkali pretreatment: A liquid alkali storage tank is set up to temporarily store the 32% concentrated alkali transported from the boundary area. After that, the condensate is accurately pumped into the liquid alkali tank through a metering pump to accurately dilute the liquid alkali to the concentration required for the reaction. This replaces the original manual proportioning method, eliminates the raw material concentration error from the source, and ensures that the hydrolysis reaction conditions are stable and controllable.

[0013] S2. Pressurized Hydrolysis Reaction: Diluted liquid alkali and p-nitrochlorobenzene are fed into the hydrolysis reactor via a metered feed pump. The molar ratio of raw materials is controlled at p-nitrochlorobenzene:sodium hydroxide = 1:2.0~2.50. After purging with nitrogen, the reactor is sealed and heated to 150~160℃ to initiate the reaction. A high-pressure cooling water pipeline system is used to stabilize the reaction temperature at 160~180℃ and the pressure at 0.6~0.9MPa. In large-scale hydrolysis reactors, the molar ratio of raw materials (p-nitrochlorobenzene:NaOH) is precisely controlled at 1:2.2, and the reactor is sealed after purging with 0.06~0.1MPa of nitrogen. Equipped with a high-pressure cooling water pipeline system, utilizing the exothermic characteristics of the reaction itself, the heating and cooling are automatically adjusted by a DCS system to stabilize the hydrolysis reaction temperature at 160~180℃ and the pressure at 0.6~0.9MPa, solving the core problems of large temperature and pressure fluctuations and incomplete raw material conversion in the original process.

[0014] S3. Tail Gas and Material Treatment: The hydrolyzed clinker is pumped into the crystallization kettle via a pressurized conveying pipeline; a new gas-liquid separator is added, and after the reaction is completed, the pressure is slowly reduced to 0.1MPa. The reaction tail gas and the crystallization kettle tail gas are then sent to the gas-liquid separator for gas-liquid separation; the gas phase is sent to the tail gas absorption tower for treatment, and the removal rate of harmful components is increased to more than 98%, meeting the latest environmental emission standards; the liquid phase is automatically recovered to the p-nitrochlorobenzene metering tank via a conveying pump, realizing the recycling of materials and reducing losses.

[0015] S4. Gradient Cooling Crystallization: The hydrolyzed clinker is pumped into the crystallization kettle via a pressurized pipeline. It is first naturally cooled to 60°C in the crystallization kettle, and then further cooled to 30-32°C by a newly added circulating water cooling unit, forming a two-stage gradient precision cooling crystallization process. Compared to the original single, non-precise cooling process, gradient crystallization results in more complete and uniform crystallization, less impurity precipitation, and an increase in product purity from 99.5% to 99.8%.

[0016] S5. Centrifugal Separation: After crystallization, the material is separated by a horizontal siphon scraper self-discharging centrifuge to obtain sodium p-nitrophenolate. The original solid-liquid separation method using a horizontal siphon scraper self-discharging centrifuge replaces the traditional vacuum filter tank, and is equipped with an automatic discharge program. The horizontal siphon scraper self-discharging centrifuge offers higher separation efficiency, lower product moisture content, and less solid content loss, effectively improving product yield, reducing solids concentration in wastewater, and saving over 200,000 yuan annually in water treatment costs. Simultaneously, automated discharge significantly reduces manual labor intensity.

[0017] Furthermore, in step S2, the hydrolysis reactor is a large-scale reactor with a volume of not less than 15m³; the original 10m³ hydrolysis reactor is upgraded to a 17m³ large-scale hydrolysis reactor, which increases the processing capacity of raw materials per batch, increasing the production capacity from 15 tons / day to 21 tons / day, an increase of 40%. The production capacity is increased on the basis of the existing plant, without the need for additional plant land, and the depreciation cost per unit product is reduced, indirectly saving about 15% of public energy consumption; the pressure of nitrogen gas introduced is 0.06~0.1MPa.

[0018] Furthermore, in step S2, the high-pressure cooling water pipeline system is linked with the heating system, and the reaction temperature and pressure are monitored and automatically adjusted in real time by the DCS distributed control system, with a temperature control accuracy of ±2℃ and a pressure control accuracy of ±0.02MPa.

[0019] Furthermore, in step S3, the gas-liquid separator simultaneously collects the tail gas from the crystallization vessel. After gas-liquid separation, the gas phase is uniformly sent to the tail gas absorption tower for treatment, and the removal rate of harmful components is not less than 98%.

[0020] Furthermore, in step S4, during the gradient cooling crystallization, the cooling rate during the natural cooling stage is no greater than 2℃ / min, the cooling rate during the cooling stage of the circulating water cooling unit is controlled at 0.5~1℃ / min, and the final crystallization temperature is 30~32℃.

[0021] Furthermore, in step S5, the horizontal siphon scraper self-discharging centrifuge is equipped with an automatic discharge program, replacing the traditional solid-liquid separation method of the suction filter tank, and the product moisture content is not higher than 25%.

[0022] Furthermore, the entire process is equipped with a DCS distributed automation control interlocking system, which monitors key parameters such as temperature, pressure, feed rate, and crystallization temperature in real time, accurately and automatically, reducing reliance on manual operation by more than 80% and reducing the risk of human error by 90%; the production cycle of a single batch is shortened by 10%, and the overall production efficiency is increased by 25%.

[0023] A sodium p-nitrophenolate production system for implementing any of the above-described processes, comprising, in sequence along the process flow direction:

[0024] Liquid alkali pretreatment unit: includes a liquid alkali storage tank and a metering pump, used to accurately dilute the liquid alkali to the concentration required for the reaction;

[0025] Hydrolysis reaction unit: including a large-scale hydrolysis reactor, a metering feed pump and a high-pressure cooling water pipeline system, used to complete the pressurized hydrolysis reaction of p-nitrochlorobenzene under precise temperature and pressure conditions;

[0026] Tail gas recovery unit: includes a gas-liquid separator and a tail gas absorption tower, used for graded treatment of reaction tail gas and material recovery;

[0027] Crystallization unit: includes crystallization kettle and circulating water cooling unit, used to achieve gradient precise cooling crystallization of clinker;

[0028] Separation unit: includes a horizontal siphon scraper self-discharging centrifuge for efficient solid-liquid separation to obtain sodium p-nitrophenolate product;

[0029] Control unit: including DCS distributed control system, which monitors and automatically adjusts key parameters of the entire process in real time.

[0030] Furthermore, the large-scale hydrolysis reactor has a volume of 20m³ and is equipped with a stirring device, temperature sensor, pressure sensor and high-pressure cooling water jacket. The reactor body is designed to withstand a pressure of not less than 1.5MPa.

[0031] Furthermore, the crystallization vessel and the circulating water cooling unit are controlled by temperature feedback linkage, and the temperature deviation at each stage of the crystallization process does not exceed ±1℃, ensuring that the product crystallization particle size is uniform and the purity is stable.

[0032] Preferably, for special requirements with higher purity (≥99.9%), the following optimizations are made to the above basic process: In the gradient cooling crystallization step, the circulating water cooling unit further reduces the final crystallization temperature to 28~30℃, while controlling the cooling rate at 0.3~0.5℃ / min, and extending the crystallization holding time to more than 2 hours to ensure that the product is fully crystallized and reduce impurity encapsulation; After the centrifugation separation step, a washing process is added, and the centrifuged product is washed with pure water at a solid-liquid ratio of 1:0.3 (mass ratio), and after centrifugation again, high-purity sodium p-nitrophenolate is obtained.

[0033] Compared with the prior art, the beneficial effects of the present invention are:

[0034] 1. Significantly increased production capacity: By replacing the 17m³ large-scale hydrolysis reactor, the production capacity increased from 15 tons / day to 21 tons / day, an increase of 40%, without the need for additional factory land, and the unit product production cost was significantly reduced;

[0035] 2. Improved product yield: Through precise molar ratio control, precise temperature and pressure control, and gradient crystallization process, the product yield has been increased from 92% to 95%-96%, the solid content of the product in water has been reduced by about 30%, the amount of water treatment chemicals has been reduced by 25%, and the annual water treatment cost has been reduced by more than 200,000 yuan.

[0036] 3. Improved product purity: The gradient cooling crystallization process increases the product purity from 99.5% to 99.8%, providing high-purity raw materials for downstream DNDPE synthesis and ensuring the quality of downstream products from the source;

[0037] 4. Significantly improved automation level: DCS full-process monitoring reduces reliance on manual operation by more than 80%, increases production efficiency by 25%, and lays the foundation for intelligent production;

[0038] 5. Improved environmental protection and safety performance: The exhaust gas is treated in stages, and the removal rate of harmful components is ≥98%, meeting the latest environmental protection standards; the material conveying pressurized pipeline reduces the risk of leakage; and the high-pressure cooling water is precisely controlled to eliminate the safety hazards of sudden temperature and pressure rises. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the overall process for the efficient and clean production of sodium nitrophenolate according to the present invention;

[0040] Figure 2 This is a schematic diagram of the temperature-time curve of the gradient cooling crystallization process of this invention;

[0041] Figure 3 This is a schematic diagram of the connection of the production system device of the present invention. Detailed Implementation

[0042] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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.

[0043] The supporting production system of this invention is assembled according to the structure described in claims 8-10, and is sequentially equipped with a liquid alkali storage tank, a metering pump, a quantitative feed pump, a 17m³ large-scale hydrolysis reactor, a high-pressure cooling water pipeline system, a gas-liquid separator, a tail gas absorption tower, a pressurized conveying pipeline, a crystallization reactor, a circulating water cooling unit, a horizontal siphon scraper self-unloading centrifuge, and a DCS distributed control system; wherein the large-scale hydrolysis reactor is designed to withstand a pressure of not less than 1.5MPa, and has a built-in stirring device, temperature sensor, pressure sensor and high-pressure cooling water jacket; the crystallization reactor and the circulating water cooling unit adopt a temperature feedback linkage control structure.

[0044] Example 1: Standard Production Batch Process Implementation

[0045] This embodiment describes conventional industrial-scale mass production according to the process parameters defined in claims 1-7. The raw materials are p-nitrochlorobenzene and 32% industrial liquid alkali by mass. The specific production steps are as follows:

[0046] S1. Liquid alkali pretreatment: 32% concentrated liquid alkali from the boundary area is temporarily stored in a liquid alkali storage tank. Cooling water is precisely and quantitatively injected through a metering pump. After thorough mixing, the liquid alkali is diluted to a NaOH mass fraction of about 20%. This method abandons the traditional manual proportioning and batching mode and avoids the problem of raw material concentration deviation from the source.

[0047] S2. Pressurized hydrolysis reaction: The diluted liquid alkali and p-nitrochlorobenzene are fed into a 17m³ large-scale hydrolysis reactor via a metered feed pump at a molar ratio of 1:2.15. The stirring device inside the reactor is turned on. After sealing the feed pipeline, 0.08MPa nitrogen gas is introduced into the reactor and the reactor body is sealed. The heating system is started, and the temperature rise is monitored in real time by the DCS distributed control system. The temperature rises to 155℃ to initiate an exothermic reaction. The high-pressure cooling water pipeline system is switched to link and control the heating system to stabilize the reaction temperature at 175℃±2℃ and the reaction pressure at 0.85MPa±0.02MPa. The constant temperature and pressure are maintained until the residual p-nitrochlorobenzene in the reactor reaches the standard, which is the endpoint of the reaction.

[0048] S3. Tail Gas and Material Treatment: After the reaction endpoint, the pressure relief valve is slowly opened to steadily reduce the internal pressure of the hydrolysis reactor to 0.1 MPa. The tail gas generated by the reaction, along with the tail gas generated by the crystallization reactor, is introduced into a gas-liquid separator to complete the gas-liquid separation operation. The gaseous medium after gas-liquid separation is sent to the tail gas absorption tower for alkaline absorption treatment before being discharged. The removal rate of harmful components in the tail gas is ≥98%. The liquid material obtained from gas-liquid separation is recycled to the p-nitrochlorobenzene metering tank by a transfer pump for recycling. The clinker after hydrolysis is transported to the crystallization reactor in a closed manner through a pressurized conveying pipeline.

[0049] S4. Gradient cooling crystallization: The clinker is first naturally cooled to 60℃ in the crystallization kettle, and the cooling rate is controlled at 1~2℃ / min during this stage. After the natural cooling is completed, the circulating water cooling unit is started to continue cooling the material at a cooling rate of 0.5~1℃ / min. Finally, the material is cooled to 32~35℃ to complete the crystallization. The temperature of the entire crystallization process is controlled by the DCS system, and the temperature deviation of each stage of crystallization does not exceed ±1℃.

[0050] S5. Centrifugal Separation: After crystallization, the material is fed into a horizontal siphon scraper self-discharging centrifuge. The equipment's built-in automatic discharge program is activated to implement solid-liquid separation. The moisture content of the solid product after separation is controlled within 25%. The obtained solid material is the conventional grade sodium p-nitrophenolate finished product. The mother liquor generated during separation is uniformly transported to the wastewater treatment system for disposal.

[0051] The industrial production indicators of this embodiment are compared with those of the original traditional process, as shown in the table below:

[0052]

[0053] Example 2: High-purity customized production

[0054] This embodiment optimizes the crystallization and post-processing steps based on the basic process framework of Example 1 to produce high-end customized sodium p-nitrophenolate with a purity ≥99.9%. The remaining pretreatment, hydrolysis, and tail gas treatment process parameters remain the same as in Example 1, with the following differentiated process adjustments:

[0055] Gradient cooling crystallization process adjustment: In step S4, the temperature of the circulating water cooling unit is adjusted to lower the crystallization endpoint temperature to 28~30℃, the cooling rate during the cooling stage is controlled at 0.3~0.5℃ / min, and the crystallization holding time is extended to more than 2 hours after the material reaches the endpoint temperature to reduce impurity crystal encapsulation and improve the crystallization purity of the product.

[0056] Add a finished product washing process: After the S5 centrifugal separation process, a pure water washing step is added. The solid product discharged from the centrifuge is washed with pure water at a solid-liquid mass ratio of 1:0.3. After washing, it is centrifuged again in a self-unloading centrifuge to dehydrate, and finally a high-purity sodium p-nitrophenolate product with a stable purity of 99.9% is obtained, which is suitable for the use of high-end DNDPE raw materials.

[0057] Example 3: Annual Continuous Production Stability Verification

[0058] Continuous industrial pilot production was carried out using the standard process parameters of Example 1, with a total of 180 production batches completed without interruption. The entire process relied on a DCS automated interlocking system to control the operating parameters of each process. The product testing and environmental monitoring data for each batch are summarized as follows:

[0059] (1) Product yield statistics: The average yield of the whole batch was 95.3%, and the standard deviation of the yield was 0.4%; the standard deviation of the yield of the traditional process under the same production conditions was about 1.8%, and the batch yield stability of this process was greatly improved;

[0060] (2) Product purity statistics: The average purity of the finished products in all batches was 99.82%, and no batch had a purity lower than 99.8%. The quality uniformity of the finished products was significantly better than that of traditional processes.

[0061] (3) Environmental emission indicators: All exhaust gas samples from the entire batch met the standards, with a compliance rate of 100%, which complies with the current environmental emission standards;

[0062] (4) Automated operation effect: During the full-process automated operation of DCS, the number of on-site manual intervention operations is reduced by more than 85% compared with traditional processes, and no safety production accidents caused by human operation errors occur in the entire production cycle.

[0063] 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 highly efficient and clean production process for sodium p-nitrophenolate, characterized in that, Includes the following steps: S1. Liquid alkali pretreatment: 32% liquid alkali is transported to the liquid alkali storage tank. Soft water is precisely injected into the liquid alkali tank through a metering pump to dilute the liquid alkali to the concentration required for the reaction. S2. Pressurized hydrolysis reaction: Diluted liquid alkali and p-nitrochlorobenzene are fed into the hydrolysis reactor via a metered feed pump. The molar ratio of raw materials is controlled at p-nitrochlorobenzene: sodium hydroxide = 1:2.0~2.

50. After nitrogen gas is introduced, the reactor is sealed and heated to 150~160℃ to initiate the reaction. The reaction temperature is stably controlled at 160~180℃ and the pressure is stably controlled at 0.6~0.9MPa using a high-pressure cooling water pipeline system. S3. Tail gas and material treatment: After the reaction is completed, the pressure is slowly reduced to 0.1MPa, and the tail gas is introduced into a gas-liquid separator for gas-liquid separation. The gas phase is sent to the tail gas absorption tower for treatment, and the liquid phase is automatically recovered to the p-nitrochlorobenzene metering tank by a transfer pump. The hydrolyzed clinker is pumped into the crystallization kettle through a pressurized conveying pipeline. S4. Gradient cooling crystallization: The clinker is first cooled naturally to 60°C in the crystallization kettle, and then cooled to 30~32°C by the circulating water cooling unit to achieve gradient precise crystallization; S5. Centrifugal separation: After crystallization, the material is continuously fed into a horizontal siphon scraper self-discharging centrifuge for separation. Under the interlocking control of specific parameters, a stable quality sodium p-nitrophenolate product is obtained.

2. The efficient and clean production process for sodium p-nitrophenolate according to claim 1, characterized in that, In step S2, the hydrolysis reactor is a large-scale reactor with a volume of not less than 15m³, and the nitrogen gas pressure is 0.06~0.1MPa.

3. The efficient and clean production process for sodium p-nitrophenolate according to claim 1, characterized in that, In step S2, the high-pressure cooling water pipeline system is linked with the heating system. The reaction temperature and pressure are monitored and automatically adjusted in real time by the DCS distributed control system, with a temperature control accuracy of ±2℃ and a pressure control accuracy of ±0.02MPa.

4. The efficient and clean production process for sodium p-nitrophenolate according to claim 1, characterized in that, In step S3, the gas-liquid separator simultaneously collects the tail gas from the crystallization vessel. After gas-liquid separation, the gas phase is uniformly sent to the tail gas absorption tower for treatment, and the removal rate of harmful components is not less than 98%.

5. The efficient and clean production process for sodium p-nitrophenolate according to claim 1, characterized in that, In step S4, during the gradient cooling crystallization, the cooling rate during the natural cooling stage is no more than 2℃ / min, the cooling rate during the cooling stage of the circulating water cooling unit is controlled at 0.5~1℃ / min, and the final crystallization temperature is 30~32℃.

6. The efficient and clean production process for sodium p-nitrophenolate according to claim 1, characterized in that, In step S5, the self-unloading centrifuge is equipped with an automatic discharge program, which replaces the traditional solid-liquid separation method of the vacuum filter tank, and the product moisture content is no higher than 25%.

7. The efficient and clean production process for sodium p-nitrophenolate according to any one of claims 1-6, characterized in that, The entire process is equipped with a DCS distributed automation control interlocking system, which monitors parameters such as temperature, pressure, feed rate, and crystallization temperature in real time, accurately and automatically. This reduces the reliance on manual operation by more than 80%, and shortens the production cycle of a single batch by more than 10% compared to the original process.

8. A sodium p-nitrophenolate production system implementing the process of any one of claims 1-7, characterized in that, Along the process flow direction, it includes, in sequence: Liquid alkali pretreatment unit: includes a liquid alkali storage tank and a metering pump, used to accurately dilute the liquid alkali to the concentration required for the reaction; Hydrolysis reaction unit: including a large-scale hydrolysis reactor, a metering feed pump and a high-pressure cooling water pipeline system, used to complete the pressurized hydrolysis reaction of p-nitrochlorobenzene under precise temperature and pressure conditions; Tail gas recovery unit: includes a gas-liquid separator and a tail gas absorption tower, used for graded treatment of reaction tail gas and material recovery; Crystallization unit: includes crystallization kettle and circulating water cooling unit, used to achieve gradient precise cooling crystallization of clinker; Separation unit: includes a horizontal siphon scraper self-discharging centrifuge, used for continuous feeding and efficient solid-liquid separation to obtain sodium p-nitrophenolate product; Control unit: including DCS distributed control system, which monitors and automatically adjusts key parameters of the entire process in real time.

9. The sodium p-nitrophenolate production system according to claim 8, characterized in that, The large-scale hydrolysis reactor has a volume of 20m³ and is equipped with a stirring device, temperature sensor, pressure sensor and high-pressure cooling water jacket. The reactor body is designed to withstand a pressure of not less than 1.5MPa.

10. The sodium p-nitrophenolate production system according to claim 8, characterized in that, The crystallization kettle and the circulating water cooling unit are linked and controlled by temperature feedback. The temperature deviation at each stage of the crystallization process does not exceed ±1℃, ensuring that the product crystallization particle size is uniform and the purity is stable.

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