Method for purifying epoxy hydrogen propane by rectification and recycling waste water

Abstract

The present application relates to the technical field of fine chemical separation and wastewater treatment, in particular to a method for rectifying and purifying epoxy hydrogen propane and recycling wastewater, which comprises the steps of pre-light removal treatment, main rectification purification, wastewater pretreatment, deep oxidation treatment, recycling and waste heat recovery. The main rectification adopts biomimetic fractal structured packing, combined with online near-infrared spectrum self-adaptive adjustment of reflux ratio, to stably produce high-purity epoxy hydrogen propane. The wastewater is deeply degraded by composite magnetic flocculation and bismuth-based nano photocatalysis, and then recycled and industrial salt recovered by reverse osmosis and evaporation crystallization. The rectification waste heat is used in stages by phase change heat storage medium to provide heat for the subsequent units. The present application improves the separation and wastewater treatment efficiency, reduces energy consumption and operating cost, realizes resource recycling, solves the problems of unstable purity, substandard treatment and resource waste in traditional process, and helps the green development of the industry.

Description

Technical Field

[0001] This invention relates to the field of fine chemical separation and wastewater treatment technology, specifically to a method for the distillation and purification of propylene oxide and the resource utilization of wastewater. Background Technology

[0002] Propylene hydroxide is an important organic chemical raw material, widely used in the production of epoxy resins, propylene glycol, polyether polyols, and other products, holding an irreplaceable position in the chemical, building materials, electronics, and pharmaceutical industries. Currently, the main industrial methods for producing propylene hydroxide include the chlorohydrin process, the co-oxidation process, and the direct oxidation process. Among these, the chlorohydrin process remains the most widely used production process in China due to its mature technology and low investment cost. However, the chlorohydrin process generates a large amount of wastewater containing pollutants such as propylene hydroxide, propylene glycol, chlorinated hydrocarbons, and sodium chloride. Furthermore, the crude propylene hydroxide product contains various impurities such as acetone, acetaldehyde, propionaldehyde, and dichloropropane, requiring a complex distillation purification process to obtain a high-purity product.

[0003] Traditional distillation purification processes for epoxide propane generally employ sieve tray towers or conventional structured packed towers, which suffer from low mass transfer efficiency, large tower height, high energy consumption, and difficulty in consistently achieving product purity above 99.99%. Conventional structured packing has limited specific surface area and porosity, resulting in insufficient gas-liquid contact and low separation efficiency, requiring a large reflux ratio to meet separation requirements and significantly increasing steam consumption. Furthermore, traditional distillation processes rely on manual or simple fixed-value control to adjust the reflux ratio, failing to adapt to real-time changes in feed composition and product purity, easily leading to product quality fluctuations and energy waste.

[0004] In wastewater treatment, traditional processes for treating wastewater from propylene oxide production mainly employ a combination of "biological treatment + coagulation and sedimentation." However, due to the presence of large amounts of recalcitrant chlorinated hydrocarbons and epoxy compounds in the wastewater, biological treatment is ineffective, resulting in difficulties in meeting emission standards for COD and total organic carbon. Furthermore, the treatment process generates a large amount of sludge, causing secondary pollution. In addition, traditional processes only focus on achieving emission standards, neglecting the recovery and utilization of water and sodium chloride resources from the wastewater. This not only wastes valuable water resources but also increases the environmental pressure caused by wastewater discharge.

[0005] In recent years, although researchers have attempted to treat propylene oxide production wastewater using membrane separation and advanced oxidation technologies, these technologies, when used alone, suffer from high treatment costs, unstable operation, and difficulty in large-scale application. For example, when using photocatalytic oxidation technology alone to treat high-concentration organic wastewater, drawbacks include easy catalyst deactivation, low light energy utilization, and long treatment time; when using reverse osmosis technology alone, membrane fouling easily occurs, leading to decreased membrane flux and shortened lifespan. Furthermore, existing technologies fail to organically integrate the distillation and purification process with the wastewater treatment process, hindering the cascade utilization of energy and resulting in persistently high energy consumption across the entire production system.

[0006] Therefore, developing an efficient, energy-saving, and environmentally friendly method for the distillation purification and wastewater resource utilization of propylene oxide, and achieving stable production of high-purity products and zero wastewater discharge, is of great significance for promoting the green and sustainable development of the propylene oxide industry. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for the distillation purification of propylene oxide and the resource utilization of wastewater. This method can significantly improve the purification efficiency and product purity of propylene oxide, while realizing the deep treatment and resource reuse of wastewater, and greatly reducing energy consumption and operating costs.

[0008] The technical solution adopted by this invention to solve its technical problem is: a method for the distillation purification and wastewater resource utilization of epoxide propane, comprising the following steps: (1) Pre-removal of light impurities: Crude propylene oxide at a temperature of 40-50℃ is fed into the pre-removal tower. The pressure at the top of the tower is controlled at 0.12-0.15MPa, the temperature at the top of the tower is 35-40℃, the temperature at the bottom of the tower is 65-70℃, and the reflux ratio is 1.2-1.8. Low-boiling-point impurities such as acetone and acetaldehyde are removed. Part of the condensate at the top of the tower is refluxed and part is sent to the wastewater treatment unit. (2) Main distillation purification: The bottom material of the pre-removed light tower is fed into the main distillation tower. The main distillation tower is filled with biomimetic fractal structured packing. The surface of the packing is modified with hydrophilicity. The pressure at the top of the tower is controlled at 0.08-0.10 MPa, the temperature at the top of the tower is 52-55℃, and the temperature at the bottom of the tower is 75-80℃. The purity of the propylene oxide in the distillate at the top of the tower is monitored in real time by online near-infrared spectroscopy. The reflux ratio is adaptively adjusted between 2.0 and 3.5. The propylene oxide product with a purity of ≥99.99% is obtained at the top of the tower. The wastewater in the bottom of the tower is sent to the wastewater treatment unit. (3) Wastewater pretreatment: The condensate from the top of the pre-light removal tower is mixed with the wastewater from the bottom of the main distillation tower, the pH value is adjusted to 7.0-8.0, composite magnetic flocculant is added, and after stirring and reacting, it is passed into a magnetic field separator to remove suspended solids and colloidal impurities, and the pretreated clear liquid is obtained. (4) Deep oxidation treatment: The pretreated liquid is sent into a supported nano-photocatalytic reactor. The reactor is equipped with an ultraviolet light source and a porous ceramic support loaded with bismuth-based composite catalyst. The reaction temperature is controlled at 35-45℃ and the residence time is 60-90 minutes to degrade residual organic pollutants such as propylene oxide and propylene glycol in the wastewater. (5) Resource reuse: The wastewater after deep oxidation treatment is filtered by a security filter and then sent to the reverse osmosis system. The reverse osmosis concentrate enters the evaporation and crystallization unit to recover industrial-grade sodium chloride, and the reverse osmosis desalination is returned to the propylene oxide production system for reuse. (6) Waste heat recovery and utilization: The waste heat from the reboiler at the bottom of the main distillation column and the waste heat from the phase change in the top condenser are used to heat the phase change heat storage medium. The heat released by the phase change heat storage medium provides a heat source for the photocatalytic reactor and the evaporation crystallization unit.

[0009] Specifically, the biomimetic fractal structured filler described in step (2) is made of 304 stainless steel as the substrate and is prepared using three-dimensional printing technology. It has a multi-level fractal channel structure and a specific surface area of ​​650-750 m². 2 / m 3 The porosity is 92-95%.

[0010] Specifically, the online near-infrared spectroscopy real-time monitoring system described in step (2) collects the spectral data of the distillate from the top of the column every 30 seconds, compares it with the standard spectral library, and then automatically adjusts the opening of the top reflux regulating valve through the PID controller.

[0011] Specifically, the composite magnetic flocculant mentioned in step (3) is composed of magnetic iron oxide nanoparticles, polyaluminum chloride and polyacrylamide in a mass ratio of 5:3:2, and the dosage is 80-120 mg / L.

[0012] Specifically, the bismuth-based composite catalyst mentioned in step (4) is a bismuth tungstate / graphene oxide composite catalyst with a loading of 15-20 g / m³. 2 The ultraviolet light source has a wavelength of 254nm and a light intensity of 30-40mW / cm². 2 .

[0013] Specifically, the reverse osmosis system described in step (5) uses a spiral wound anti-fouling reverse osmosis membrane, operates at a pressure of 1.2-1.5 MPa, and has a water recovery rate of 75-80%.

[0014] Specifically, the phase change heat storage medium mentioned in step (6) is a paraffin-expanded graphite composite phase change material with a phase change temperature of 55-60℃ and a latent heat of 180-200J / g.

[0015] Specifically, in step (6), the residual heat from the reboiler in the main distillation column is used to heat the phase change heat storage medium through a shell-and-tube heat exchanger, and the residual heat from the phase change in the top condenser is used to heat the phase change heat storage medium through a plate heat exchanger.

[0016] Specifically, in step (4), the COD of the effluent from the photocatalytic reactor is ≤50mg / L and the total organic carbon is ≤10mg / L.

[0017] Specifically, in step (5), the recovered industrial-grade sodium chloride has a purity of ≥99.1%, which meets the GB / T 5462-2015 standard for first-grade industrial salt.

[0018] The beneficial effects of this invention are: 1. The method for distillation purification and wastewater resource utilization of propylene oxide described in this invention uses biomimetic fractal structured packing material that has been modified with hydrophilicity, which can significantly improve gas-liquid mass transfer efficiency. Combined with online near-infrared spectroscopy adaptive adjustment of reflux ratio, it can stably produce high-purity propylene oxide products, while reducing separation energy consumption and avoiding product quality fluctuations.

[0019] 2. The method for distillation purification and wastewater resource utilization of propylene oxide described in this invention combines composite magnetic flocculation pretreatment with bismuth-based nano-photocatalytic deep oxidation, which can efficiently degrade recalcitrant organic pollutants in wastewater, achieve effluent quality standards, and significantly reduce sludge production, thereby reducing the risk of secondary pollution from the source.

[0020] 3. The method for distillation purification and wastewater resource utilization of propylene oxide described in this invention relies on reverse osmosis and evaporation crystallization units to achieve wastewater resource utilization and efficient recovery of industrial salt, thereby recycling water and salt resources and effectively reducing water consumption and raw material costs in the production system.

[0021] 4. The method for distillation purification and wastewater resource utilization of propylene oxide described in this invention recovers the waste heat of the distillation system and utilizes it in stages through phase change heat storage medium to provide stable heating for subsequent treatment units, thereby achieving efficient energy utilization and reducing the overall energy consumption and operating costs of the process.

[0022] 5. The method for distillation purification and wastewater resource utilization of propylene oxide described in this invention integrates distillation purification, wastewater treatment, resource recycling, and waste heat utilization into a closed-loop green production process. This solves the problems of inefficient separation, substandard treatment, resource waste, and high energy consumption in traditional processes, and contributes to the green and sustainable development of the propylene oxide industry. Attached Figure Description

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0024] Figure 1 The flowchart shows the method for distillation purification of propylene oxide and wastewater resource utilization provided by this invention. Detailed Implementation

[0025] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0026] like Figure 1 As shown, the method for distillation purification of propylene oxide and wastewater resource utilization of the present invention includes six steps: pre-treatment to remove light components, main distillation purification, wastewater pretreatment, deep oxidation treatment, resource utilization and reuse, and waste heat recovery and utilization.

[0027] In the pre-light-removal step, crude propylene oxide at 40-50℃ is fed into the pre-light-removal tower. The top pressure is controlled at 0.12-0.15 MPa, the top temperature at 35-40℃, the bottom temperature at 65-70℃, and the reflux ratio at 1.2-1.8. This process removes low-boiling-point impurities such as acetone and acetaldehyde. Part of the condensate from the top of the tower is refluxed back to the pre-light-removal tower, and the remainder is sent to the wastewater treatment unit for further processing. The pre-light-removal tower uses a sieve tray structure with 25-30 trays, effectively removing most low-boiling-point impurities and reducing the separation load on the subsequent main distillation column.

[0028] In the main distillation purification step, the bottom material from the pre-light removal column is fed into the main distillation column, which is filled with biomimetic fractal structured packing. This packing, made of 304 stainless steel, is fabricated using 3D printing technology and features a multi-level fractal channel structure with a specific surface area of ​​650-750 m². 2 / m 3 The porosity is 92-95%. The packing surface is hydrophilically modified, which significantly improves gas-liquid mass transfer efficiency. The pressure at the top of the main distillation column is controlled at 0.08-0.10 MPa, the top temperature at 52-55℃, and the bottom temperature at 75-80℃. The purity of propylene oxide in the distillate from the top of the column is monitored in real time by online near-infrared spectroscopy. Spectral data is collected every 30 seconds and compared with a standard spectral library. The opening of the reflux regulating valve at the top of the column is automatically adjusted by a PID controller to adaptively change the reflux ratio between 2.0 and 3.5. Propylene oxide product with a purity ≥99.99% is obtained at the top of the column, and the wastewater from the bottom of the column is sent to the wastewater treatment unit.

[0029] In the wastewater pretreatment step, the condensate from the top of the pre-light weight removal tower is mixed with the wastewater from the bottom of the main distillation tower, and the pH is adjusted to 7.0-8.0. A composite magnetic flocculant is then added. This composite magnetic flocculant is composed of magnetic iron oxide nanoparticles, polyaluminum chloride, and polyacrylamide in a mass ratio of 5:3:2, with a dosage of 80-120 mg / L. After rapid stirring for 5 minutes and slow stirring for 15 minutes, the mixture is introduced into a magnetic field separator. The magnetic field separates the magnetic flocs from the water, removing suspended solids and colloidal impurities from the wastewater, resulting in a pretreated clarified liquid. Magnetic flocculation technology can significantly improve flocculation efficiency, shorten settling time, and reduce sludge production.

[0030] In the deep oxidation process, the pretreated clarified liquid is fed into a supported nano-photocatalytic reactor. The reactor contains an ultraviolet light source and a porous ceramic support loaded with a bismuth-based composite catalyst. The bismuth-based composite catalyst is a bismuth tungstate / graphene oxide composite catalyst with a loading of 15-20 g / m³. 2 The ultraviolet light source has a wavelength of 254nm and a light intensity of 30-40mW / cm². 2 The reaction temperature is controlled at 35-45℃, and the residence time is 60-90 minutes to degrade residual organic pollutants such as propylene oxide, propylene glycol, and chlorinated hydrocarbons in wastewater. The bismuth tungstate / graphene oxide composite catalyst has advantages such as a wide visible light response range, high catalytic activity, and good stability, and can effectively degrade recalcitrant organic pollutants.

[0031] In the resource recovery and reuse step, the wastewater after deep oxidation treatment is filtered through a security filter and then sent to the reverse osmosis system. The reverse osmosis system uses spiral wound anti-fouling reverse osmosis membranes, operates at a pressure of 1.2-1.5 MPa, and has a water recovery rate of 75-80%. The reverse osmosis concentrate enters the evaporation and crystallization unit to recover industrial-grade sodium chloride with a purity ≥99.1%, meeting the GB / T5462-2015 Class I standard for industrial salt. The reverse osmosis desalination water is returned to the propylene oxide production system for reuse, with a wastewater reuse rate ≥95%.

[0032] In the waste heat recovery and utilization step, the condensation waste heat from the reboiler at the bottom of the main distillation column and the phase change waste heat from the overhead condenser are used to heat the phase change heat storage medium. The phase change heat storage medium is a paraffin-expanded graphite composite phase change material with a phase change temperature of 55-60℃ and a latent heat of 180-200 J / g. The condensation waste heat from the reboiler at the bottom of the main distillation column heats the phase change heat storage medium through a shell-and-tube heat exchanger, while the phase change waste heat from the overhead condenser heats the phase change heat storage medium through a plate heat exchanger. The heat released by the phase change heat storage medium provides a heat source for the photocatalytic reactor and the evaporation crystallization unit, which can significantly reduce the energy consumption of the entire system.

[0033] Example 1: The method for distillation purification of propylene oxide and wastewater resource utilization provided in this example has the following specific steps: (1) Pre-treatment for light component removal: Crude propylene oxide at 45℃ is fed into the pre-treatment tower for light component removal. The crude propylene oxide contains 92.5% propylene oxide, 2.1% acetone, 1.3% acetaldehyde, 0.8% propionaldehyde, 1.2% dichloropropane, and 2.1% water. The pressure at the top of the pre-treatment tower is controlled at 0.13 MPa, the temperature at the top is 37℃, the temperature at the bottom is 67℃, and the reflux ratio is 1.5. The pre-treatment tower adopts a sieve tray structure with 28 trays. Part of the condensate from the top of the tower is refluxed back to the pre-treatment tower at a reflux ratio of 1.5, and part is sent to the wastewater treatment unit. The propylene oxide content in the bottom material of the pre-treatment tower is 94.8%, and the total content of low-boiling-point impurities is ≤0.1%.

[0034] (2) Main distillation purification: The bottom material of the pre-light stripping column is fed into the main distillation column, which is filled with biomimetic fractal structured packing. This packing is made of 304 stainless steel and fabricated using 3D printing technology. It has a three-level fractal channel structure: the first-level channel diameter is 5 mm, the second-level channel diameter is 1 mm, and the third-level channel diameter is 0.2 mm, with a specific surface area of ​​700 m². 2 / m 3 The porosity is 93%. The packing surface is treated with plasma hydrophilic modification, resulting in a contact angle of 35°. The pressure at the top of the main distillation column is controlled at 0.09 MPa, the top temperature at 53°C, and the bottom temperature at 77°C. The purity of propylene oxide in the distillate from the top of the column is monitored in real time using online near-infrared spectroscopy. Spectral data is collected every 30 seconds and compared with a standard spectral library. The opening of the reflux regulating valve at the top of the column is automatically adjusted by a PID controller to adaptively change the reflux ratio to approximately 2.5. Propylene oxide is obtained from the top of the column, and its purity is 99.992%, with a yield of 99.3%. The wastewater from the bottom of the main distillation column is sent to a wastewater treatment unit. The wastewater contains 0.05% propylene oxide, 0.12% propylene glycol, 3.2% sodium chloride, and has a COD of 1200 mg / L.

[0035] (3) Wastewater pretreatment: The condensate from the top of the pre-light removal tower and the wastewater from the bottom of the main distillation tower were mixed at a volume ratio of 1:4. The COD of the mixed wastewater was 1500 mg / L and the suspended solids content was 200 mg / L. The pH value was adjusted to 7.5 with sodium hydroxide solution, and a composite magnetic flocculant was added. The composite magnetic flocculant was composed of magnetic iron oxide nanoparticles, polyaluminum chloride and polyacrylamide in a mass ratio of 5:3:2, and the dosage was 100 mg / L. The mixture was first stirred rapidly at 300 r / min for 5 minutes, and then slowly stirred at 60 r / min for 15 minutes. Then, it was introduced into a magnetic field separator with a magnetic field strength of 0.5 T. After separation, a pretreated clear liquid was obtained, with a suspended solids content ≤10 mg / L and a turbidity ≤5 NTU.

[0036] (4) Deep oxidation treatment: The pretreated solution is fed into a supported nano-photocatalytic reactor. The reactor is a cylindrical structure with an inner diameter of 1.2 m and a height of 3.5 m, containing 12 ultraviolet lamps and 100 porous ceramic supports loaded with catalyst. The loading of the bismuth tungstate / graphene oxide composite catalyst is 18 g / m³. 2 The ultraviolet light source has a wavelength of 254nm and a light intensity of 35mW / cm². 2 The reaction temperature was controlled at 40℃, and the residence time was 75 minutes. The COD of the treated effluent was 35 mg / L, the total organic carbon was 8 mg / L, and propylene glycol and epoxide were not detected.

[0037] (5) Resource Reuse: Wastewater after deep oxidation treatment is filtered through a 5μm security filter and then sent to the reverse osmosis system. The reverse osmosis system uses spiral wound antifouling reverse osmosis membranes, with 6 membrane elements arranged in a 2:1 ratio. The operating pressure is controlled at 1.3MPa and the inlet water temperature is 25℃. The water recovery rate of the reverse osmosis system is 78%, and the conductivity of the fresh water is 12μS / cm, which meets the requirements for production water and is returned to the propylene oxide production system for reuse. The reverse osmosis concentrate enters the evaporation and crystallization unit, using a multi-effect evaporation process at an evaporation temperature of 60℃ to obtain industrial-grade sodium chloride. The sodium chloride purity is tested to be 99.2%, which meets the GB / T5462-2015 industrial salt grade one standard.

[0038] (6) Waste Heat Recovery and Utilization: The waste heat from the reboiler at the bottom of the main distillation column and the phase change waste heat from the condenser at the top of the column are used to heat the paraffin-expanded graphite composite phase change heat storage medium. The phase change temperature of the phase change heat storage medium is 57℃, and the latent heat is 190J / g. The waste heat from the reboiler at the bottom of the main distillation column heats the phase change heat storage medium through a shell-and-tube heat exchanger, and the waste heat from the condenser at the top of the column heats the phase change heat storage medium through a plate heat exchanger. The heat released by the phase change heat storage medium provides a heat source for the photocatalytic reactor and the evaporation crystallization unit. Calculations show that the waste heat recovery and utilization rate is 65%, and the energy consumption of the entire system is reduced by 32% compared with the traditional process.

[0039] Comparative Example 1: This comparative example uses the traditional method of propylene oxide distillation purification and wastewater treatment. The specific steps are as follows: (1) Pre-treatment for light removal: Same as in Example 1.

[0040] (2) Main distillation purification: The bottom material of the pre-light removal column is fed into the main distillation column, which is filled with ordinary metal perforated plate corrugated packing with a specific surface area of ​​450 m². 2 / m 3The porosity was 88%. The pressure at the top of the main distillation column was controlled at 0.09 MPa, the top temperature at 53℃, and the bottom temperature at 77℃, using a constant-value control method, with a fixed reflux ratio of 4.0. Propylene oxide was obtained at the top of the column, and testing showed a purity of 99.95% and a yield of 98.5%. The wastewater from the bottom of the main distillation column was sent to a wastewater treatment unit. The wastewater contained 0.12% propane oxide, 0.25% propylene glycol, 3.2% sodium chloride, and a COD of 1800 mg / L.

[0041] (3) Wastewater treatment: The condensate from the top of the pre-light removal tower was mixed with the wastewater from the bottom of the main distillation tower. The pH was adjusted to 7.5, and polyaluminum chloride and polyacrylamide were added at dosages of 150 mg / L and 5 mg / L, respectively. After stirring and reacting, the mixture was allowed to settle for 30 minutes to remove suspended solids. The supernatant was sent to the biological treatment system using an A / O process with a hydraulic retention time of 24 hours. The COD of the effluent from the biological treatment was 150 mg / L, and the total organic carbon was 45 mg / L, which did not meet the discharge standards and required further treatment.

[0042] (4) Waste heat recovery: Only a portion of the condensed waste heat from the reboiler of the main distillation column is recovered for preheating the feed. The waste heat recovery utilization rate is 25%, and the energy consumption of the entire system is 47% higher than that of Example 1.

[0043] Example 2: The method for distillation purification and wastewater resource utilization of propylene oxide provided in this example has the following specific steps: (1) Pre-treatment for light component removal: Crude propylene oxide at 42℃ is fed into the pre-treatment tower for light component removal. The crude propylene oxide contains 91.8% propylene oxide, 2.3% acetone, 1.5% acetaldehyde, 0.9% propionaldehyde, 1.3% dichloropropane, and 2.2% water. The pressure at the top of the pre-treatment tower is controlled at 0.12 MPa, the temperature at the top is 36℃, the temperature at the bottom is 66℃, and the reflux ratio is 1.3. The pre-treatment tower adopts a sieve tray structure with 26 trays. Part of the condensate from the top of the tower is refluxed back to the pre-treatment tower at a reflux ratio of 1.3, and part is sent to the wastewater treatment unit. The propylene oxide content in the bottom material of the pre-treatment tower is 94.2%, and the total content of low-boiling-point impurities is ≤0.12%.

[0044] (2) Main distillation purification: The bottom material of the pre-light stripping column is fed into the main distillation column, which is filled with biomimetic fractal structured packing. The packing is made of 304 stainless steel as the base material and is prepared by three-dimensional printing technology. It has a three-level fractal channel structure and a specific surface area of ​​680 m². 2 / m 3The porosity is 92.5%. The packing surface is plasma-modified for hydrophilicity, with a contact angle of 38°. The pressure at the top of the main distillation column is controlled at 0.085 MPa, the top temperature at 52.5℃, and the bottom temperature at 76℃. The purity of propylene oxide in the distillate from the top of the column is monitored in real time using online near-infrared spectroscopy. Spectral data is collected every 30 seconds and compared with a standard spectral library. The opening of the reflux regulating valve at the top of the column is automatically adjusted by a PID controller to adaptively change the reflux ratio to approximately 2.2. Propylene oxide is obtained from the top of the column, and the purity is 99.991%, with a yield of 99.25%. The wastewater from the bottom of the main distillation column is sent to the wastewater treatment unit. The wastewater contains 0.06% propylene oxide, 0.13% propylene glycol, 3.3% sodium chloride, and 1250 mg / L COD.

[0045] (3) Wastewater pretreatment: The condensate from the top of the pre-light removal tower and the wastewater from the bottom of the main distillation tower were mixed at a volume ratio of 1:3.5. The COD of the mixed wastewater was 1600 mg / L and the suspended solids content was 220 mg / L. The pH value was adjusted to 7.2 with sodium hydroxide solution, and a composite magnetic flocculant was added. The composite magnetic flocculant was composed of magnetic iron oxide nanoparticles, polyaluminum chloride and polyacrylamide in a mass ratio of 5:3:2, and the dosage was 90 mg / L. The mixture was first stirred rapidly at 280 r / min for 5 minutes, and then slowly stirred at 55 r / min for 15 minutes. Then it was introduced into a magnetic field separator with a magnetic field strength of 0.45 T. After separation, a pretreated clear liquid was obtained, with a suspended solids content ≤12 mg / L and a turbidity ≤6 NTU.

[0046] (4) Deep oxidation treatment: The pretreated solution is fed into a supported nano-photocatalytic reactor. The reactor contains 10 ultraviolet lamps and 90 porous ceramic supports loaded with catalyst. The loading of the bismuth tungstate / graphene oxide composite catalyst is 16 g / m³. 2 The ultraviolet light source has a wavelength of 254nm and a light intensity of 32mW / cm². 2 The reaction temperature was controlled at 38℃, and the residence time was 80 minutes. The COD of the treated effluent was 40 mg / L, the total organic carbon was 9 mg / L, and neither propylene oxide nor propylene glycol was detected.

[0047] (5) Resource Reuse: Wastewater after deep oxidation treatment is filtered through a 5μm security filter and then sent to the reverse osmosis system. The reverse osmosis system uses spiral wound anti-fouling reverse osmosis membranes, with a controlled operating pressure of 1.25MPa and an inlet water temperature of 23℃. The water recovery rate of the reverse osmosis system is 76%, and the conductivity of the fresh water is 15μS / cm, which meets the requirements for production water and is returned to the propylene oxide production system for reuse. The reverse osmosis concentrate enters the evaporation and crystallization unit, using a multi-effect evaporation process at an evaporation temperature of 58℃ to obtain industrial-grade sodium chloride. The sodium chloride purity is tested to be 99.15%, which meets the GB / T 5462-2015 first-grade standard for industrial salt.

[0048] (6) Waste Heat Recovery and Utilization: The waste heat from the reboiler at the bottom of the main distillation column and the phase change waste heat from the condenser at the top of the column are used to heat the paraffin-expanded graphite composite phase change heat storage medium. The phase change temperature of the phase change heat storage medium is 56℃, and the latent heat is 185J / g. The waste heat from the reboiler at the bottom of the main distillation column heats the phase change heat storage medium through a shell-and-tube heat exchanger, and the waste heat from the condenser at the top of the column heats the phase change heat storage medium through a plate heat exchanger. The heat released by the phase change heat storage medium provides a heat source for the photocatalytic reactor and the evaporation crystallization unit. Calculations show that the waste heat recovery and utilization rate is 63%, and the energy consumption of the entire system is reduced by 30% compared with the traditional process.

[0049] Comparative Example 2: This comparative example is based on Example 2, but the bismuth tungstate / graphene oxide composite catalyst in the photocatalytic reactor was replaced with a common titanium dioxide catalyst, while other conditions remained the same as in Example 2. The treated effluent had a COD of 120 mg / L, total organic carbon of 35 mg / L, propylene oxide content of 0.02%, and propylene glycol content of 0.05%, which failed to meet the feed water requirements of the reverse osmosis system. The fouling rate of the reverse osmosis membrane accelerated significantly, and the membrane flux decreased by 40% after one month of operation.

[0050] Example 3: The method for distillation purification and wastewater resource utilization of propylene oxide provided in this example has the following specific steps: (1) Pre-treatment for light component removal: Crude propylene oxide at 48℃ is fed into the pre-treatment tower for light component removal. The crude propylene oxide contains 93.2% propylene oxide, 1.9% acetone, 1.1% acetaldehyde, 0.7% propionaldehyde, 1.1% dichloropropane, and 2.0% water. The pressure at the top of the pre-treatment tower is controlled at 0.14 MPa, the temperature at the top is 38℃, the temperature at the bottom is 68℃, and the reflux ratio is 1.7. The pre-treatment tower adopts a sieve tray structure with 30 trays. Part of the condensate from the top of the tower is refluxed back to the pre-treatment tower at a reflux ratio of 1.7, and part is sent to the wastewater treatment unit. The propylene oxide content in the bottom material of the pre-treatment tower is 95.3%, and the total content of low-boiling-point impurities is ≤0.08%.

[0051] (2) Main distillation purification: The bottom material of the pre-light stripping column is fed into the main distillation column, which is filled with biomimetic fractal structured packing. The packing is made of 304 stainless steel as the base material and is prepared by three-dimensional printing technology. It has a three-level fractal channel structure and a specific surface area of ​​720 m². 2 / m 3 The porosity is 94%. The packing surface is treated with plasma hydrophilic modification, resulting in a contact angle of 32°. The pressure at the top of the main distillation column is controlled at 0.095 MPa, the top temperature at 54°C, and the bottom temperature at 78°C. The purity of propylene oxide in the distillate from the top of the column is monitored in real time using online near-infrared spectroscopy. Spectral data is collected every 30 seconds and compared with a standard spectral library. The opening of the reflux regulating valve at the top of the column is automatically adjusted by a PID controller to adaptively change the reflux ratio to approximately 2.8. Propylene oxide is obtained from the top of the column, and its purity is 99.993% with a yield of 99.35%. The wastewater from the bottom of the main distillation column is sent to a wastewater treatment unit. The wastewater contains 0.04% propylene oxide, 0.11% propylene glycol, 3.1% sodium chloride, and has a COD of 1150 mg / L.

[0052] (3) Wastewater pretreatment: The condensate from the top of the pre-light removal tower and the wastewater from the bottom of the main distillation tower were mixed at a volume ratio of 1:4.5. The COD of the mixed wastewater was 1400 mg / L and the suspended solids content was 180 mg / L. The pH value was adjusted to 7.8 with sodium hydroxide solution, and a composite magnetic flocculant was added. The composite magnetic flocculant was composed of magnetic iron oxide nanoparticles, polyaluminum chloride and polyacrylamide in a mass ratio of 5:3:2, and the dosage was 110 mg / L. The mixture was first stirred rapidly at 320 r / min for 5 minutes, and then slowly stirred at 65 r / min for 15 minutes. Then it was introduced into a magnetic field separator with a magnetic field strength of 0.55 T. After separation, a pretreated clear liquid was obtained, with a suspended solids content ≤8 mg / L and a turbidity ≤4 NTU.

[0053] (4) Deep oxidation treatment: The pretreated solution is fed into a supported nano-photocatalytic reactor. The reactor contains 14 ultraviolet lamps and 110 porous ceramic supports loaded with catalyst. The loading of the bismuth tungstate / graphene oxide composite catalyst is 20 g / m³. 2 The ultraviolet light source has a wavelength of 254nm and a light intensity of 38mW / cm². 2 The reaction temperature was controlled at 42℃, and the residence time was 70 minutes. The COD of the treated effluent was 30 mg / L, the total organic carbon was 7 mg / L, and propylene glycol and epoxide were not detected.

[0054] (5) Resource Reuse: Wastewater after deep oxidation treatment is filtered through a 5μm security filter and then sent to the reverse osmosis system. The reverse osmosis system uses spiral wound anti-fouling reverse osmosis membranes, with a controlled operating pressure of 1.4MPa and an inlet water temperature of 27℃. The water recovery rate of the reverse osmosis system is 79%, and the conductivity of the fresh water is 10μS / cm, which meets the requirements for production water and is returned to the propylene oxide production system for reuse. The reverse osmosis concentrate enters the evaporation and crystallization unit, using a multi-effect evaporation process at an evaporation temperature of 62℃ to obtain industrial-grade sodium chloride. The sodium chloride purity is tested to be 99.25%, which meets the GB / T 5462-2015 industrial salt grade one standard.

[0055] (6) Waste Heat Recovery and Utilization: The waste heat from the reboiler at the bottom of the main distillation column and the phase change waste heat from the condenser at the top of the column are used to heat the paraffin-expanded graphite composite phase change heat storage medium. The phase change temperature of the phase change heat storage medium is 58℃, and the latent heat is 195J / g. The waste heat from the reboiler at the bottom of the main distillation column heats the phase change heat storage medium through a shell-and-tube heat exchanger, and the waste heat from the condenser at the top of the column heats the phase change heat storage medium through a plate heat exchanger. The heat released by the phase change heat storage medium provides a heat source for the photocatalytic reactor and the evaporation crystallization unit. Calculations show that the waste heat recovery rate is 67%, and the energy consumption of the entire system is reduced by 34% compared to the traditional process.

[0056] Comparative Example 3: This comparative example is based on Example 3, but the phase change thermal storage system is omitted. The photocatalytic reactor and evaporation crystallization unit are provided with heat sources by electric heating, and other conditions are the same as in Example 3. Calculations show that the energy consumption of the entire system is 52% higher than that of Example 3, resulting in a significant increase in operating costs.

[0057] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for the distillation purification and wastewater resource utilization of epoxide propane, characterized in that, Includes the following steps: (1) Pre-removal of light impurities: Crude propylene oxide at a temperature of 40-50℃ is fed into the pre-removal tower. The pressure at the top of the tower is controlled at 0.12-0.15MPa, the temperature at the top of the tower is 35-40℃, the temperature at the bottom of the tower is 65-70℃, and the reflux ratio is 1.2-1.

8. Low-boiling-point impurities such as acetone and acetaldehyde are removed. Part of the condensate at the top of the tower is refluxed and part is sent to the wastewater treatment unit. (2) Main distillation purification: The bottom material of the pre-removed light tower is fed into the main distillation tower. The main distillation tower is filled with biomimetic fractal structured packing. The surface of the packing is modified with hydrophilicity. The pressure at the top of the tower is controlled at 0.08-0.10 MPa, the temperature at the top of the tower is 52-55℃, and the temperature at the bottom of the tower is 75-80℃. The purity of the propylene oxide in the distillate at the top of the tower is monitored in real time by online near-infrared spectroscopy. The reflux ratio is adaptively adjusted between 2.0 and 3.

5. The propylene oxide product with a purity of ≥99.99% is obtained at the top of the tower. The wastewater in the bottom of the tower is sent to the wastewater treatment unit. (3) Wastewater pretreatment: The condensate from the top of the pre-light removal tower is mixed with the wastewater from the bottom of the main distillation tower, the pH value is adjusted to 7.0-8.0, composite magnetic flocculant is added, and after stirring and reacting, it is passed into a magnetic field separator to remove suspended solids and colloidal impurities, and the pretreated clear liquid is obtained. (4) Deep oxidation treatment: The pretreated liquid is sent into a supported nano-photocatalytic reactor. The reactor is equipped with an ultraviolet light source and a porous ceramic support loaded with bismuth-based composite catalyst. The reaction temperature is controlled at 35-45℃ and the residence time is 60-90 minutes to degrade residual organic pollutants such as propylene oxide and propylene glycol in the wastewater. (5) Resource reuse: The wastewater after deep oxidation treatment is filtered by a security filter and then sent to the reverse osmosis system. The reverse osmosis concentrate enters the evaporation and crystallization unit to recover industrial-grade sodium chloride, and the reverse osmosis desalination is returned to the propylene oxide production system for reuse. (6) Waste heat recovery and utilization: The waste heat from the reboiler at the bottom of the main distillation column and the waste heat from the phase change in the top condenser are used to heat the phase change heat storage medium. The heat released by the phase change heat storage medium provides a heat source for the photocatalytic reactor and the evaporation crystallization unit.

2. The method for distillation purification and wastewater resource utilization of propylene oxide according to claim 1, characterized in that: The biomimetic fractal structured filler described in step (2) is made of 304 stainless steel as the substrate and is prepared using 3D printing technology. It has a multi-level fractal channel structure and a specific surface area of ​​650-750 m². 2 / m 3 The porosity is 92-95%.

3. The method for distillation purification and wastewater resource utilization of propane hydrogen oxide according to claim 1, characterized in that: The online near-infrared spectroscopy real-time monitoring system described in step (2) collects the spectral data of the distillate at the top of the column every 30 seconds. After comparing it with the standard spectral library, the system automatically adjusts the opening of the reflux regulating valve at the top of the column through a PID controller.

4. The method for distillation purification and wastewater resource utilization of propylene oxide according to claim 1, characterized in that: The composite magnetic flocculant mentioned in step (3) is composed of magnetic iron oxide nanoparticles, polyaluminum chloride and polyacrylamide in a mass ratio of 5:3:2, and the dosage is 80-120 mg / L.

5. The method for distillation purification and wastewater resource utilization of propane hydrogen oxide according to claim 1, characterized in that: The bismuth-based composite catalyst mentioned in step (4) is a bismuth tungstate / graphene oxide composite catalyst with a loading of 15-20 g / m³. 2 The ultraviolet light source has a wavelength of 254nm and a light intensity of 30-40mW / cm². 2 .

6. The method for distillation purification and wastewater resource utilization of propylene oxide according to claim 1, characterized in that: The reverse osmosis system described in step (5) uses spiral wound antifouling reverse osmosis membranes, operates at a pressure of 1.2-1.5 MPa, and has a water recovery rate of 75-80%.

7. The method for distillation purification and wastewater resource utilization of propylene oxide according to claim 1, characterized in that: The phase change heat storage medium mentioned in step (6) is a paraffin-expanded graphite composite phase change material with a phase change temperature of 55-60℃ and a latent heat of 180-200J / g.

8. The method for distillation purification and wastewater resource utilization of propylene oxide according to claim 1, characterized in that: In step (6), the residual heat from the reboiler in the main distillation column is used to heat the phase change heat storage medium through a shell-and-tube heat exchanger, and the residual heat from the phase change in the top condenser is used to heat the phase change heat storage medium through a plate heat exchanger.

9. The method for distillation purification and wastewater resource utilization of propane hydrogen oxide according to claim 1, characterized in that: In step (4), the COD of the effluent from the photocatalytic reactor is ≤50mg / L and the total organic carbon is ≤10mg / L.

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