A low boiling diluent recovery system and special process

Abstract

The present invention provides a low-boiling diluent recovery system and a special process, which can be applied to the recovery of low-boiling diluent waste liquids of different properties, has low cost, and does not generate secondary pollution during the recovery process. The system comprises a crude steam kettle and a distillation tower, wherein the top of the crude steam kettle is provided with two feed ports and one discharge port, and the bottom is provided with a discharge port, the top discharge port of the crude steam kettle is connected to the first distillation tower through a first condenser, the top discharge port of the first distillation tower is connected to a water separation tank and the first feed port of the second distillation tower through a second condenser, the bottom discharge port of the first distillation tower is connected to the second feed port of the second distillation tower and a wastewater station, the side discharge port of the water separation tank is connected to the first distillation tower, the top discharge port of the second distillation tower is connected to a low-boiling diluent finished product tank through a third condenser, an extract feed port is provided above the first feed port of the second distillation tower, and the bottom discharge port of the second distillation tower is connected to a top feed port of the crude steam kettle and the third distillation tower.

Description

Technical Field

[0001] The invention relates to the field of organic wastewater recovery, in particular to a recovery system and a special process for a low-boiling diluent. Background Art

[0002] Low-boiling diluent is a basic material for removing unnecessary photoresist from the edge of the substrate or the nozzle in the semiconductor manufacturing process to ensure the normal operation of the process. In recent years, the semiconductor industry has developed rapidly, and the amount of low-boiling diluent waste liquid generated has increased year by year. The main components of these low-boiling diluent waste liquids are organic matter (including tetrahydrofuran, methanol, ethanol, isopropanol, acetone, toluene, xylene, n-butanol, ethyl acetate, butyl acetate), water and a small amount of acid. If these waste liquids are discharged directly, it will not only bring great pressure to the ecological environment, but also cause huge waste of resources. Therefore, how to recycle these waste liquids has become an urgent problem to be solved.

[0003] At present, the main industrial methods for recovering low-boiling diluents are distillation, adsorption, membrane separation and solvent extraction. The distillation method refers to placing the low-boiling diluent in a distillation kettle, separating the liquid and residue after heating and condensing with a condenser. This method can recover most of the low-boiling diluents, but it consumes a lot of energy. The adsorption method refers to using adsorbents such as activated carbon and silica gel to adsorb impurities in the low-boiling diluent, and then recovering the adsorbed solvent. This method is only suitable for low-boiling diluents with low impurity content. The membrane separation method refers to using the osmotic effect of the membrane to separate the water and impurities in the low-boiling diluent, so as to achieve the purpose of recovering the low-boiling diluent. This method has simple equipment and convenient operation, but the life and performance of the membrane need to be regularly inspected and maintained. The solvent extraction method refers to using the solubility and mutual solubility of different solvents to extract impurities from the low-boiling diluent, and then recovering the solvent. This method can be applied to low-boiling diluents with high impurity content.

[0004] Patent CN208898766U discloses a system for recovering toluene, an active diluent of epoxy resin, comprising a distillation kettle connected to the outlet of the water washing oil phase of the water washing kettle, a distillation packing tower arranged above the distillation kettle, a first material reflux port arranged at the bottom of the distillation packing tower, a first condenser connected to the top gas outlet of the distillation packing tower, a first phase separator connected to the outlet of the first condenser, an oil-water separator connected to the bottom of the first phase separator, and a second material reflux port arranged at the bottom of the first phase separator; a water receiving tank connected to the water receiving tank, a vacuum water receiving tank and a water metering tank connected to the water receiving tank; a toluene settling tank connected to the oil phase outlet of the water separator. This patent can effectively solve the problems of high toluene content in the product, long vacuum distillation time, and high energy consumption in the existing system for recovering toluene, an active diluent of epoxy resin. However, this system can only recover organic matter with poor water solubility, and will be helpless when encountering organic matter with good water solubility in ethanol or isopropanol.

[0005] Patent CN115006860A discloses a method and device for recovering tetrahydrofuran from liquid polycarbosilane waste liquid, which includes a supergravity rotating bed distillation unit, an extractive distillation unit and a membrane separation unit in sequence according to the process flow, wherein the output end of the supergravity rotating bed distillation unit is connected to the input end of the extractive distillation unit, and the output end of the extractive distillation unit is connected to the input end of the membrane separation unit; the invention uses a combination of three separation methods, namely, supergravity rotary distillation, extractive distillation and membrane separation technology, to recover tetrahydrofuran from liquid polycarbosilane waste liquid, and has the advantages of easy operation, strong selectivity and stable operating performance. However, this system also has the disadvantages of high equipment maintenance cost and strict requirements for applicable waste liquid. Summary of the invention

[0006] In view of the shortcomings of the existing process for treating low-boiling diluent waste liquid, such as strict requirements on applicable waste liquid and high cost, the present invention provides a low-boiling diluent recovery system and process, which can be applied to the recovery of low-boiling diluent waste liquid of different properties, has low cost, and does not generate secondary pollution during the recovery process.

[0007] A low-boiling diluent recovery system comprises a rough distillation kettle and a distillation tower, characterized in that: the top of the rough distillation kettle is provided with two feed ports and one discharge port, and the bottom is provided with a discharge port, the top discharge port of the rough distillation kettle is connected to the first distillation tower through a first condenser, the top discharge port of the first distillation tower is connected to a water separation tank and the first feed port of the second distillation tower through a second condenser, the bottom discharge port of the first distillation tower is connected to the second feed port of the second distillation tower and a wastewater station, the bottom discharge port of the water separation tank is connected to the wastewater station, the side discharge port of the water separation tank is connected to the first distillation tower, the top discharge port of the second distillation tower is connected to a low-boiling diluent finished product tank through a third condenser, an extract feed port is provided above the first feed port of the second distillation tower, the bottom discharge port of the second distillation tower is connected to a top feed port of the rough distillation kettle and the third distillation tower, the top discharge port of the third distillation tower is connected to the wastewater station through a fourth condenser, and an extractant discharge port is provided at the bottom of the third distillation tower.

[0008] It is further characterized by:

[0009] A temperature sensor is provided at the top of the first distillation tower;

[0010] A density meter is arranged at the bottom of the water separation tank, and a perspective mirror is arranged at the side.

[0011] The present invention also provides a special process for recovering low-boiling diluent based on the above-mentioned low-boiling diluent recovery system, characterized in that it includes two process routes:

[0012] Process route 1 is for low-boiling diluents that produce azeotropy with water but have low mutual solubility or do not produce azeotropy with water, such as toluene, xylene, n-butanol, ethyl acetate, butyl acetate, etc.;

[0013] Process route 1 includes the following steps:

[0014] Step 1: low-boiling diluent waste liquid and alkali solution are input into a crude steam kettle through a pipeline to adjust the pH value of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature in the crude steam kettle is 120-140° C. and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser, it is pumped into the first distillation tower. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the discharge port at the bottom of the crude steam kettle.

[0015] Step 2: The temperature in the first distillation tower is 100-120°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled, and the top discharge is an azeotrope of low-boiling diluent and water. After the water content is detected to be lower than 0.1%, it is condensed in the second condenser and pumped into the water separation tank;

[0016] Step 3: The organic phase and water in the low-boiling diluent in the water separation tank are separated into layers, the water density is greater than that of the organic phase, the organic phase is in the upper layer, and the water is in the lower layer. After the water is discharged from the discharge port at the bottom of the water separation tank, the organic phase is returned to the first distillation tower;

[0017] Step 4: The returned organic phase is further purified in the first distillation tower, and the bottom discharge is a low-boiling diluent, which is pumped into the second distillation tower after the moisture content is tested to be up to standard;

[0018] Step 5: The temperature in the second distillation tower is 120-140°C, and the pressure is normal pressure. The low-boiling diluent is distilled, and the top discharge is the low-boiling diluent finished product. After the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser. The bottom discharge is the heavy component impurities, which are pumped back to the crude distillation kettle for regular bottom discharge;

[0019] Process route 2 is for low-boiling diluents that produce azeotropy with water and have high mutual solubility, such as tetrahydrofuran, methanol, ethanol, isopropanol, acetone, etc.;

[0020] Process route 2 includes the following steps:

[0021] Step 1: low-boiling diluent waste liquid and alkali solution are input into a crude steam kettle through a pipeline to adjust the pH of the mixed solution to neutral, the crude steam kettle is heated by a jacket, the temperature inside the crude steam kettle is 100-120°C, the pressure is normal pressure, the low-boiling diluent waste liquid is distilled into a mixture of low-boiling diluent and water, which is condensed in a first condenser and pumped into a first distillation tower, and the high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle;

[0022] Step 2: The temperature in the first distillation tower is 70-90°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled. The top discharge is the azeotrope of low-boiling diluent and water. After condensation in the second condenser, it is pumped into the second distillation tower. The bottom discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment.

[0023] Step 3: The temperature in the second distillation tower is 70-90°C, the pressure is normal pressure, the extractant is fed into the extractant feed port, the low-boiling diluent after extraction is distilled, the top discharge is the low-boiling diluent finished product, after the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser, and the bottom discharge is a mixture of the extractant and water, which is pumped into the third distillation tower after the content is tested;

[0024] Step 4: The temperature in the third distillation tower is 40-60°C and the pressure is -0.095-0.08MPa. The mixed liquid of the extractant and water is distilled, and the top discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment through the fourth condenser. The bottom discharge is the extractant. After the organic matter content and water content are tested to be up to standard, it is returned to the second distillation tower for recycling.

[0025] It is further characterized by:

[0026] In step 3 of process route 1, a density meter is used to monitor whether the lower water phase in the water separation tank is completely discharged;

[0027] In step 2 of process route 1 and step 2 of process route 2, a temperature sensor is used to determine whether the azeotrope of the low-boiling diluent and water in the first distillation tower is completely evaporated according to the tower top temperature;

[0028] In step 3 of process route 2, the extractant is one of ethylene glycol, diethylene glycol or ethylene glycol methyl ether.

[0029] The beneficial effect of the present invention is that the present invention provides a low-boiling diluent recovery system, which can process low-boiling diluents of different properties, including low-boiling diluents that produce azeotropy with water but have low miscibility with water, low-boiling diluents that produce azeotropy with water and have high miscibility with water, and low-boiling diluents that do not produce azeotropy with water, thereby realizing the recovery of low-boiling diluent waste liquids of different properties; the present invention combines two different process routes into the same process system, saving a lot of equipment costs; the present invention not only efficiently recovers valuable organic components in the low-boiling diluent, but also recycles the extract used in the process, and the impurities and wastewater are also collected centrally, and no secondary pollution is generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the system structure of the present invention;

[0031] Figure 2 It is a schematic diagram of the process route 1 of the present invention;

[0032] Figure 3 It is a schematic diagram of the process route 2 of the present invention. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with specific embodiments:

[0034] A low-boiling diluent recovery system comprises a crude distillation kettle 1 and a distillation tower. The crude distillation kettle 1 is provided with two feed ports and one discharge port at the top and one discharge port at the bottom. The top discharge port of the crude distillation kettle 1 is connected to a first distillation tower 3 through a first condenser 2. The top discharge port of the first distillation tower 3 is connected to a water separation tank 5 and a first feed port 61 of a second distillation tower 6 through a second condenser 4. The bottom discharge port of the first distillation tower 3 is connected to a second feed port 62 of the second distillation tower 6 and a wastewater station 7. The bottom discharge port of the water separation tank 5 is connected to a second feed port 63 of the second distillation tower 6 and a wastewater station 7. The side discharge port of the water separation tank 5 is connected to the first distillation tower 3, the top discharge port of the second distillation tower 6 is connected to the low-boiling diluent finished product tank 9 through the third condenser 8, an extractant feed port 63 is provided above the first feed port of the second distillation tower 6, the bottom discharge port of the second distillation tower 6 is connected to another top feed port of the rough distillation kettle 1 and the third distillation tower 10, the top discharge port of the third distillation tower 10 is connected to the wastewater station 7 through the fourth condenser 11, and an extractant discharge port 101 is provided at the bottom of the third distillation tower 10.

[0035] A temperature sensor (not shown) is provided at the top of the first distillation tower 3 for judging whether the azeotrope of the low-boiling diluent and water has been completely evaporated according to the tower top temperature.

[0036] A density meter (not shown) is provided at the bottom of the water separation tank 5 to monitor whether the lower water phase is completely drained; a perspective mirror (not shown) is provided on the side to ensure that the production line can still operate normally when the density meter fails.

[0037] The present invention also provides a special process for recovering low-boiling diluent based on the above-mentioned low-boiling diluent recovery system, which includes two process routes.

[0038] Embodiment 1

[0039] Process route 1 is for low-boiling diluents that produce azeotropy with water but have low mutual solubility or do not produce azeotropy with water, such as toluene, xylene, n-butanol, ethyl acetate, butyl acetate, etc.;

[0040] Process route 1 includes the following steps:

[0041] Step 1: low-boiling diluent waste liquid and alkali solution are input into the crude steam kettle through a pipeline to adjust the pH value of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature in the crude steam kettle 1 is 120°C and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser 2, it is pumped into the first distillation tower 3. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle 1;

[0042] Step 2: The temperature in the first distillation tower 3 is 110°C and the pressure is normal pressure. The mixture of the low-boiling diluent and water is distilled. The top discharge is the azeotrope of the low-boiling diluent and water. After the moisture content is detected to be lower than 0.1%, it is condensed by the second condenser 4 and pumped into the water separation tank 5. The temperature sensor is used to judge whether the azeotrope of the low-boiling diluent and water in the first distillation tower 3 is completely evaporated according to the tower top temperature;

[0043] Step 3: The organic phase and water in the low-boiling diluent in the water separation tank 5 are separated into layers. The water density is greater than that of the organic phase. The organic phase is in the upper layer and the water is in the lower layer. A density meter is used to monitor whether the lower water phase in the water separation tank 5 is completely discharged. After the water is discharged from the discharge port at the bottom of the water separation tank 5, the organic phase is returned to the first distillation tower 3.

[0044] Step 4: The returned organic phase is further purified in the first distillation tower 3, and the bottom discharge is a low-boiling diluent, which is pumped into the second distillation tower 6 after the moisture content is tested to be up to standard;

[0045] Step 5: The temperature in the second distillation tower 6 is 140°C and the pressure is normal pressure. The low-boiling diluent is distilled, and the top discharge is the low-boiling diluent finished product. After the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser 8. The bottom discharge is the heavy component impurities, which are pumped back to the rough distillation kettle 1 for regular bottom discharge;

[0046] Process route 2 is for low-boiling diluents that produce azeotropy with water and have high mutual solubility, such as tetrahydrofuran, methanol, ethanol, isopropanol, acetone, etc.;

[0047] Process route 2 includes the following steps:

[0048] Step 1: low-boiling diluent waste liquid and alkali solution are input into the crude steam kettle through a pipeline to adjust the pH of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature inside the crude steam kettle 1 is 100°C and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser 2, it is pumped into the first distillation tower 3. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle 1;

[0049] Step 2: The temperature in the first distillation tower 3 is 80°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled. The top discharge is the azeotrope of low-boiling diluent and water, which is condensed by the second condenser 4 and pumped into the second distillation tower 6. The bottom discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment. The temperature sensor is used to judge whether the azeotrope of low-boiling diluent and water in the first distillation tower 3 is completely evaporated according to the tower top temperature;

[0050] Step 3: The temperature in the second distillation tower 6 is 90° C., the pressure is normal pressure, the extractant is fed into the extractant feed port, the extractant is one of ethylene glycol, diethylene glycol or ethylene glycol methyl ether, the low-boiling diluent after extraction is distilled, the top discharge is the low-boiling diluent finished product, after the organic matter content and the water content are tested to be up to standard, it is pumped into the low-boiling diluent finished product tank through the third condenser 8, and the bottom discharge is a mixture of the extractant and water, which is pumped into the third distillation tower 10 after the content is tested;

[0051] The extractant feed port is located above the feed ports of the low-boiling diluent and the water azeotrope because the extractant can be fully mixed and dispersed in the raw material when flowing above the raw material, which can ensure that the contact time between the extractant and the raw material is longer, thereby improving the extraction efficiency;

[0052] Step 4: The temperature in the third distillation tower 10 is 50°C and the pressure is -0.095MPa. The mixed liquid of the extractant and water is distilled, and the top discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment through the fourth condenser 11. The bottom discharge is the extractant. After the organic matter content and water content are tested to be up to standard, it is returned to the second distillation tower 6 for recycling.

[0053] Embodiment 2

[0054] Process route 1 is for low-boiling diluents that produce azeotropy with water but have low mutual solubility or do not produce azeotropy with water, such as toluene, xylene, n-butanol, ethyl acetate, butyl acetate, etc.;

[0055] Process route 1 includes the following steps:

[0056] Step 1: low-boiling diluent waste liquid and alkali solution are input into the crude steam kettle through a pipeline to adjust the pH value of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature in the crude steam kettle 1 is 130° C. and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser 2, it is pumped into the first distillation tower 3. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle 1;

[0057] Step 2: The temperature in the first distillation tower 3 is 100°C and the pressure is normal pressure. The mixture of the low-boiling diluent and water is distilled. The top discharge is the azeotrope of the low-boiling diluent and water. After the moisture content is detected to be lower than 0.1%, it is condensed by the second condenser 4 and pumped into the water separation tank 5. The temperature sensor is used to judge whether the azeotrope of the low-boiling diluent and water in the first distillation tower 3 is completely evaporated according to the tower top temperature;

[0058] Step 3: The organic phase and water in the low-boiling diluent in the water separation tank 5 are separated into layers. The water density is greater than that of the organic phase. The organic phase is in the upper layer and the water is in the lower layer. A density meter is used to monitor whether the lower water phase in the water separation tank 5 is completely discharged. After the water is discharged from the discharge port at the bottom of the water separation tank 5, the organic phase is returned to the first distillation tower 3.

[0059] Step 4: The returned organic phase is further purified in the first distillation tower 3, and the bottom discharge is a low-boiling diluent, which is pumped into the second distillation tower 6 after the moisture content is tested to be up to standard;

[0060] Step 5: The temperature in the second distillation tower 6 is 120°C and the pressure is normal pressure. The low-boiling diluent is distilled, and the top discharge is the low-boiling diluent finished product. After the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser 8. The bottom discharge is the heavy component impurities, which are pumped back to the rough distillation kettle 1 for regular bottom discharge;

[0061] Process route 2 is for low-boiling diluents that produce azeotropy with water and have high mutual solubility, such as tetrahydrofuran, methanol, ethanol, isopropanol, acetone, etc.;

[0062] Process route 2 includes the following steps:

[0063] Step 1: low-boiling diluent waste liquid and alkali solution are input into the crude steam kettle through a pipeline to adjust the pH of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature inside the crude steam kettle 1 is 110°C and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser 2, it is pumped into the first distillation tower 3. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle 1;

[0064] Step 2: The temperature in the first distillation tower 3 is 70°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled. The top discharge is the azeotrope of low-boiling diluent and water, which is condensed by the second condenser 4 and pumped into the second distillation tower 6. The bottom discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment. The temperature sensor is used to judge whether the azeotrope of low-boiling diluent and water in the first distillation tower 3 is completely evaporated according to the tower top temperature;

[0065] Step 3: The temperature in the second distillation tower 6 is 70° C., the pressure is normal pressure, the extractant is fed into the extractant feed port, the extractant is one of ethylene glycol, diethylene glycol or ethylene glycol methyl ether, the low-boiling diluent after extraction is distilled, the top discharge is the low-boiling diluent finished product, after the organic matter content and the water content are tested to be up to standard, it is pumped into the low-boiling diluent finished product tank through the third condenser 8, and the bottom discharge is a mixture of the extractant and water, which is pumped into the third distillation tower 10 after the content is tested;

[0066] The extractant feed port is located above the feed ports of the low-boiling diluent and the water azeotrope because the extractant can be fully mixed and dispersed in the raw material when flowing above the raw material, which can ensure that the contact time between the extractant and the raw material is longer, thereby improving the extraction efficiency;

[0067] Step 4: The temperature in the third distillation tower 10 is 40°C and the pressure is -0.09MPa. The mixed liquid of the extractant and water is distilled, and the top discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment through the fourth condenser 11. The bottom discharge is the extractant. After the organic matter content and water content are tested to be up to standard, it is returned to the second distillation tower 6 for recycling.

[0068] Embodiment 3

[0069] Process route 1 is for low-boiling diluents that produce azeotropy with water but have low mutual solubility or do not produce azeotropy with water, such as toluene, xylene, n-butanol, ethyl acetate, butyl acetate, etc.;

[0070] Process route 1 includes the following steps:

[0071] Step 1: low-boiling diluent waste liquid and alkali solution are input into the crude steam kettle through a pipeline to adjust the pH of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature in the crude steam kettle 1 is 140°C and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser 2, it is pumped into the first distillation tower 3. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle 1;

[0072] Step 2: The temperature in the first distillation tower 3 is 100°C and the pressure is normal pressure. The mixture of the low-boiling diluent and water is distilled. The top discharge is the azeotrope of the low-boiling diluent and water. After the moisture content is detected to be lower than 0.1%, it is condensed by the second condenser 4 and pumped into the water separation tank 5. The temperature sensor is used to judge whether the azeotrope of the low-boiling diluent and water in the first distillation tower 3 is completely evaporated according to the tower top temperature;

[0073] Step 3: The organic phase and water in the low-boiling diluent in the water separation tank 5 are separated into layers. The water density is greater than that of the organic phase. The organic phase is in the upper layer and the water is in the lower layer. A density meter is used to monitor whether the lower water phase in the water separation tank 5 is completely discharged. After the water is discharged from the discharge port at the bottom of the water separation tank 5, the organic phase is returned to the first distillation tower 3.

[0074] Step 4: The returned organic phase is further purified in the first distillation tower 3, and the bottom discharge is a low-boiling diluent, which is pumped into the second distillation tower 6 after the moisture content is tested to be up to standard;

[0075] Step 5: The temperature in the second distillation tower 6 is 130°C and the pressure is normal pressure. The low-boiling diluent is distilled, and the top discharge is the low-boiling diluent finished product. After the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser 8. The bottom discharge is the heavy component impurities, which are pumped back to the rough distillation kettle 1 for regular bottom discharge;

[0076] Process route 2 is for low-boiling diluents that produce azeotropy with water and have high mutual solubility, such as tetrahydrofuran, methanol, ethanol, isopropanol, acetone, etc.;

[0077] Process route 2 includes the following steps:

[0078] Step 1: low-boiling diluent waste liquid and alkali solution are input into the crude steam kettle through a pipeline to adjust the pH of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature inside the crude steam kettle 1 is 120°C and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser 2, it is pumped into the first distillation tower 3. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle 1;

[0079] Step 2: The temperature in the first distillation tower 3 is 90°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled. The top discharge is the azeotrope of low-boiling diluent and water. After condensation in the second condenser 4, it is pumped into the second distillation tower 6. The bottom discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment. The temperature sensor is used to judge whether the azeotrope of low-boiling diluent and water in the first distillation tower 3 is completely evaporated according to the tower top temperature;

[0080] Step 3: The temperature in the second distillation tower 6 is 80° C., the pressure is normal pressure, the extractant is fed into the extractant feed port, the extractant is one of ethylene glycol, diethylene glycol or ethylene glycol methyl ether, the low-boiling diluent after extraction is distilled, the top discharge is the low-boiling diluent finished product, after the organic matter content and the water content are tested to be up to standard, it is pumped into the low-boiling diluent finished product tank through the third condenser 8, and the bottom discharge is a mixture of the extractant and water, which is pumped into the third distillation tower 10 after the content is tested;

[0081] The extractant feed port is located above the feed ports of the low-boiling diluent and the water azeotrope because the extractant can be fully mixed and dispersed in the raw material when flowing above the raw material, which can ensure that the contact time between the extractant and the raw material is longer, thereby improving the extraction efficiency;

[0082] Step 4: The temperature in the third distillation tower 10 is 60°C and the pressure is -0.08MPa. The mixed liquid of the extractant and water is distilled, and the top discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment through the fourth condenser 11. The bottom discharge is the extractant. After the organic matter content and water content are tested to be up to standard, it is returned to the second distillation tower 6 for recycling.

Claims

1. A special process for recovering a low-boiling diluent, characterized in that: A recovery system using a low-boiling diluent, comprising a crude distillation kettle and a distillation tower, wherein the crude distillation kettle is provided with two feed ports and one discharge port at the top and a discharge port at the bottom, the top discharge port of the crude distillation kettle is connected to the first distillation tower through a first condenser, the top discharge port of the first distillation tower is connected to a water separation tank and the first feed port of the second distillation tower through a second condenser, the bottom discharge port of the first distillation tower is connected to the second feed port of the second distillation tower and a wastewater station, the bottom discharge port of the water separation tank is connected to the wastewater station, the side discharge port of the water separation tank is connected to the first distillation tower, the top discharge port of the second distillation tower is connected to a low-boiling diluent finished product tank through a third condenser, an extract feed port is provided above the first feed port of the second distillation tower, the bottom discharge port of the second distillation tower is connected to a top feed port of the crude distillation kettle and the third distillation tower, the top discharge port of the third distillation tower is connected to the wastewater station through a fourth condenser, and an extractant discharge port is provided at the bottom of the third distillation tower; It includes two process routes; merging two different process routes into the same process system; Process route 1 is for low-boiling diluents that produce azeotropy with water but have low mutual solubility or do not produce azeotropy with water, such as toluene, xylene, n-butanol, ethyl acetate, and butyl acetate; Process route 1 includes the following steps: Step 1: low-boiling diluent waste liquid and alkali solution are input into a crude steam kettle through a pipeline to adjust the pH value of the mixed solution to neutral. The crude steam kettle is heated by a jacket. The temperature in the crude steam kettle is 120-140° C. and the pressure is normal pressure. The distillation discharge of the low-boiling diluent waste liquid is a mixture of low-boiling diluent and water. After condensation in the first condenser, it is pumped into the first distillation tower. The high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the discharge port at the bottom of the crude steam kettle. Step 2: The temperature in the first distillation tower is 100-120°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled, and the top discharge is an azeotrope of low-boiling diluent and water. After the water content is detected to be lower than 0.1%, it is condensed in the second condenser and pumped into the water separation tank; Step 3: The organic phase and water in the low-boiling diluent in the water separation tank are separated into layers, the water density is greater than that of the organic phase, the organic phase is in the upper layer, and the water is in the lower layer. After the water is discharged from the discharge port at the bottom of the water separation tank, the organic phase is returned to the first distillation tower; Step 4: The returned organic phase is further purified in the first distillation tower, and the bottom discharge is a low-boiling diluent, which is pumped into the second distillation tower after the moisture content is tested to be up to standard; Step 5: The temperature in the second distillation tower is 120-140°C, and the pressure is normal pressure. The low-boiling diluent is distilled, and the top discharge is the low-boiling diluent finished product. After the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser. The bottom discharge is the heavy component impurities, which are pumped back to the crude distillation kettle for regular bottom discharge; Process route 2 is for low-boiling diluents that produce azeotropy with water and have high mutual solubility, such as tetrahydrofuran, methanol, ethanol, isopropanol, and acetone; Process route 2 includes the following steps: Step 1: low-boiling diluent waste liquid and alkali solution are input into a crude steam kettle through a pipeline to adjust the pH of the mixed solution to neutral, the crude steam kettle is heated by a jacket, the temperature in the crude steam kettle is 100-120°C, the pressure is normal pressure, the low-boiling diluent waste liquid is distilled into a mixture of low-boiling diluent and water, which is condensed in a first condenser and pumped into a first distillation tower, and the high-boiling impurities generated during the distillation process are accumulated and discharged regularly from the bottom discharge port of the crude steam kettle; Step 2: The temperature in the first distillation tower is 70-90°C and the pressure is normal pressure. The mixture of low-boiling diluent and water is distilled. The top discharge is the azeotrope of low-boiling diluent and water. After condensation in the second condenser, it is pumped into the second distillation tower. The bottom discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment. Step 3: The temperature in the second distillation tower is 70-90°C, the pressure is normal pressure, the extractant is fed into the extractant feed port, the low-boiling diluent after extraction is distilled, the top discharge is the low-boiling diluent finished product, after the organic matter content and the water content are tested to be up to standard, they are pumped into the low-boiling diluent finished product tank through the third condenser, and the bottom discharge is a mixture of the extractant and water, which is pumped into the third distillation tower after the content is tested; Step 4: The temperature in the third distillation tower is 40-60°C and the pressure is -0.095-0.08MPa. The mixed liquid of the extractant and water is distilled, and the top discharge is water. After the COD is tested to be up to standard, it is pumped into the wastewater station for treatment through the fourth condenser. The bottom discharge is the extractant. After the organic matter content and water content are tested to be up to standard, it is returned to the second distillation tower for recycling.

2. The special process for recovering a low-boiling diluent according to claim 1, characterized in that: A temperature sensor is provided on the top of the first distillation tower.

3. The special process for recovering a low-boiling diluent according to claim 1, characterized in that: A density meter is arranged at the bottom of the water separation tank, and a perspective mirror is arranged at the side.

4. The special process for recovering a low-boiling diluent according to claim 1, characterized in that: In step 3 of process route 1, a density meter is used to monitor whether the lower water phase in the water separation tank has been completely discharged.

5. The special process for recovering a low-boiling diluent according to claim 1, characterized in that: In step 2 of process route 1, a temperature sensor is used to determine whether the azeotrope of the low-boiling diluent and water in the first distillation tower has been completely evaporated based on the tower top temperature.

6. The special process for recovering a low-boiling diluent according to claim 1, characterized in that: In step 3 of process route 2, the extractant is one of ethylene glycol, diethylene glycol or ethylene glycol methyl ether.

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