Method for recovering hydrogen chloride from epichlorohydrin waste acid

Abstract

The application discloses a method for recovering hydrogen chloride in epoxy chloropropane waste acid, and relates to the technical field of chemical waste acid recovery, and comprises the following steps: S1, pretreating the waste acid to remove impurities; S2, mixing the pretreated waste acid with an extractant solution to obtain a to-be-distilled mixed solution; S3, performing normal-pressure distillation on the to-be-distilled mixed solution in a distillation column, obtaining hydrogen chloride gas at the top of the distillation column, and discharging a dilute acid mother liquor at the bottom of the distillation column; and S4, performing vacuum flash evaporation concentration treatment on the dilute acid mother liquor to obtain a sodium chloride solution and a flash evaporation gas phase, and obtaining low-acid waste water by condensing the flash evaporation gas phase; the extractant comprises the sodium chloride solution obtained in S4. The method utilizes the salt effect of sodium chloride to break the constant-boiling balance of hydrochloric acid under normal pressure, realizes deep recovery of hydrogen chloride, completes regeneration and closed-loop circulation of the salt agent through vacuum flash evaporation, reduces hazardous waste output, can reduce steam energy consumption under the conditions of negative pressure and low temperature, relieves crystallization and fouling and equipment corrosion, and prolongs the stable operation period of the device.

Description

Technical Field

[0001] This application relates to the field of chemical waste acid recovery technology, and in particular to a method for recovering hydrogen chloride from epichlorohydrin waste acid. Background Technology

[0002] Epichlorohydrin is an important organic chemical raw material, widely used in the production of epoxy resins, synthetic glycerin, chlorohydrin rubber, and other products. The chlorohydrin process is one of the mainstream production processes for epichlorohydrin in China. This process generates a large amount of azeotropic dilute waste hydrochloric acid with a mass fraction of 20-25%. This waste acid has a complex composition, containing small amounts of organic impurities and suspended particulate matter, making it unsuitable for direct sale as a product.

[0003] Existing technologies employ a calcium chloride salt extraction distillation process, which works by utilizing the strong hydration of divalent calcium ions to bind water molecules in the liquid phase, thus disrupting the azeotropic equilibrium of hydrochloric acid and achieving hydrogen chloride separation. However, this process is problematic when applied to the treatment of epichlorohydrin waste acid from the chlorohydrin process. The solubility of calcium chloride varies greatly with temperature, and it is prone to crystallization at low temperatures, which continuously clogs the distillation packing, heat exchanger tube bundles and conveying pipelines, resulting in short continuous and stable operation cycles for the unit. Calcium chloride is an external extractant, and as the system circulates, calcium salts and impurities in the system continue to accumulate, requiring the periodic discharge of large amounts of calcium-containing waste salt solution. Existing processes mostly use atmospheric pressure evaporation to regenerate calcium chloride solution, which has high evaporation temperatures and large steam consumption. Summary of the Invention

[0004] In order to solve at least one of the above-mentioned technical problems and to develop a recovery process with high hydrogen chloride recovery rate, low operating energy consumption, low hazardous waste production, and long-term stable operation of the equipment, this application provides a method for recovering hydrogen chloride from epichlorohydrin waste acid.

[0005] On the one hand, this application provides a method for recovering hydrogen chloride from epichlorohydrin waste acid, comprising the following steps: S1. Pre-treat the waste acid to remove impurities; S2. Mix the pretreated waste acid with the extractant solution to obtain the mixture to be distilled; S3. The mixture to be distilled is subjected to atmospheric pressure distillation in a distillation column. Hydrogen chloride gas is obtained at the top of the distillation column and dilute acid mother liquor is discharged from the bottom of the distillation column. S4. The dilute acid mother liquor is concentrated by vacuum flash evaporation to obtain sodium chloride solution and flash vapor phase. The flash vapor phase is condensed to obtain low acid wastewater. The extractant includes the sodium chloride solution obtained in S4, wherein the mass concentration of sodium chloride in the sodium chloride solution is not less than 65 wt%.

[0006] By adopting the above technical solution, sodium chloride ionizes into Na in the liquid phase. +With Cl - Na + By binding free water molecules in the system through hydration and reducing the activity of water, Cl... - By suppressing the dissociation equilibrium of HCl through the common ion effect, the atmospheric pressure azeotropic limitation of hydrochloric acid is broken. The boiling point of the system water is lowered by vacuum flash evaporation, and the concentration and regeneration of sodium chloride solution are completed at low temperature, avoiding the problems of salt crystallization and scaling and accelerated equipment corrosion caused by atmospheric pressure high-temperature evaporation. At the same time, the concentrated sodium chloride solution is directly returned to the feed end for recycling, forming a closed-loop salt agent circulation system, which significantly reduces the amount of external salt agent added and the amount of waste salt solution discharged, reducing the amount of hazardous waste generated from the source. The process as a whole forms a synergistic closed loop of materials and energy, and the hydrogen chloride recovery rate is significantly improved compared with the traditional salt-free desorption process.

[0007] Optionally, the extractant also includes trimethylglycine hydrochloride, wherein sodium chloride accounts for 92-97 wt% and trimethylglycine hydrochloride accounts for 3-8 wt% of the solute in the extractant, based on 100 wt% of the solute in the extractant.

[0008] By adopting the above technical solution, trimethylglycine hydrochloride is a quaternary ammonium organic chloride, and its cation hydration capacity is much stronger than that of Na+. + A small amount of this compound enhances the salt effect in the system and increases the relative volatility of HCl. Simultaneously, its surface activity reduces gas-liquid interfacial tension, refines the mass transfer film within the distillation column, and improves gas-liquid mass transfer efficiency, significantly increasing the desorption depth of hydrogen chloride while maintaining a constant total salt concentration. The positively charged quaternary ammonium cation of trimethylglycine hydrochloride can adsorb onto the inner wall of metal equipment to form a hydrophobic protective film, creating a synergistic protective effect with corrosion inhibitors and reducing the pitting and crevice corrosion rates of the high-chlorine liquid phase.

[0009] Optionally, in S1, the waste acid is preheated, and the preheated dilute waste hydrochloric acid is filtered to remove impurities with a filtration accuracy of ≥5μm. The preheating process involves heat exchange between the waste acid and the dilute acid mother liquor obtained in S3, preheating to 60~80℃.

[0010] By adopting the above technical solution, the high-temperature dilute acid mother liquor discharged from the bottom of the distillation column is used as a heat source. The heat exchanger exchanges heat with the ambient temperature feed waste acid in a countercurrent manner. On the one hand, the feed temperature is increased, reducing the steam heating load of the reboiler at the bottom of the distillation column; on the other hand, the temperature of the mother liquor at the bottom of the column is reduced, reducing the evaporation load of the subsequent vacuum flash evaporation unit.

[0011] Optionally, in S2, the extractant solution has a mass concentration of 60-70%, and the waste acid and extractant solution are mixed at a mass ratio of 1:1.

[0012] By adopting the above technical solution, a 60-70 wt% sodium chloride concentration provides sufficient ionic strength to ensure effective salt-effect separation. Simultaneously, this concentration is lower than the saturation solubility at the corresponding temperature, preventing salt crystal precipitation that could clog pipes and packing materials, thus ensuring separation efficiency and operational stability. A 1:1 mass mixing ratio maintains appropriate salt and acid concentrations in the mixed system, ensuring both the depth of HCl desorption and preventing an increase in solution viscosity due to excessively high salt concentration, thus avoiding a decrease in mass transfer efficiency.

[0013] Optionally, in S3, the bottom temperature of the distillation column is 115~130℃, and the reflux ratio is 1~2; the vapor phase at the top of the distillation column is cooled to 10~18℃ by a condenser, and the resulting hydrogen chloride has a purity ≥99wt%. By adopting the above technical solution, the temperature is sufficient to ensure the complete volatilization and removal of HCl, while avoiding excessively high temperatures that lead to steam waste, accelerated equipment corrosion, and supersaturation and scaling of the brine solution; if the temperature is too low, the HCl desorption will be incomplete, and the residual acid at the bottom of the tower will increase. Cooling the gas phase at the top of the tower to 10~18℃ can fully condense the water vapor and hydrochloric acid droplets entrained in the gas phase, and remove moisture through gas-liquid separation, ensuring that the purity of the produced hydrogen chloride gas is ≥99wt%.

[0014] Optionally, in S4, the pressure of the vacuum flash concentration process is 0.01–0.08 MPa, and the temperature is 90–100 °C.

[0015] Optionally, an organophosphate compound corrosion inhibitor is added to the extractant, and the concentration of the corrosion inhibitor is 50~120 ppm based on the total mass of the extractant solution.

[0016] By adopting the above technical solution, the phosphonic acid groups of the organophosphate corrosion inhibitor form coordination bonds with iron atoms on the metal surface, and are directionally adsorbed on the inner wall of the equipment to form a dense and continuous hydrophobic protective film, blocking high concentrations of Cl. - H + Direct contact with the metal substrate effectively inhibits uniform corrosion, pitting corrosion, and crevice corrosion of stainless steel; the compound system is composed of various organophosphonates and synergists, with different molecular chain lengths complementing each other to form a film, resulting in a protective effect superior to a single corrosion inhibitor.

[0017] On the other hand, this application also provides a device for recovering hydrogen chloride from epichlorohydrin waste acid, for implementing the above-mentioned recovery method, including a pretreatment unit, a mixing unit, an extractive distillation unit, and a vacuum flash concentration unit. The pretreatment unit includes a heat exchanger and a filter; the mixing unit includes a dissolving tank and a static mixer; the extractive distillation unit includes an extractive distillation column, a bottom reboiler, and a top condenser; and the vacuum flash concentration unit includes a vacuum flash tank, a flash condenser, and a vacuum unit. Waste acid is introduced into the cold side inlet of the heat exchanger, the cold side outlet is connected to the feed inlet of the filter, the hot side inlet is connected to the bottom outlet of the extractive distillation column, and the hot side outlet of the heat exchanger is connected to the feed inlet of the vacuum flash tank; the outlet of the dissolving tank and the outlet of the filter are both connected to the feed inlet of the static mixer. The outlet of the static mixer is connected to the middle feed inlet of the extractive distillation column, the vapor outlet of the top condenser produces hydrogen chloride gas, and the bottom reboiler is connected to heating steam. The vapor phase outlet at the top of the vacuum flash tank is connected to the vapor phase inlet of the flash condenser. The condensate outlet of the flash condenser produces low-acid wastewater. The non-condensable gas outlet of the flash condenser is connected to the vacuum unit. The concentrated brine outlet at the bottom of the vacuum flash tank is connected to the dissolving tank.

[0018] Optionally, a graded anti-corrosion structure may also be included, wherein the graded anti-corrosion structure is configured in zones according to the type of contact medium: The medium flow side of the tower top condenser and flash condenser is made of graphite material; The heat exchanger, precision filter, dissolving tank, static mixer, extractive distillation column, vacuum flash tank, and bottom reboiler are made of 316L stainless steel with epoxy resin lining. Fluoroplastic lining of the flow-through components of the material conveying pump; The flange interfaces of the equipment and pipelines all use expanded PTFE seals.

[0019] In summary, this invention utilizes Na produced by the ionization of sodium chloride. + Hydration reduces the activity of water, simultaneously passing Cl- through the body. - The common ion effect inhibits HCl dissociation, and its dual effect breaks the azeotropic equilibrium of hydrochloric acid at atmospheric pressure. This eliminates the need for high-pressure operation and the addition of high-valence metal salts, achieving deep separation of hydrogen chloride and improving hydrogen chloride recovery rate under atmospheric pressure. Regeneration of the sodium chloride extractant is achieved through vacuum flash evaporation concentration. The regenerated brine is directly recycled back to the mixing process, forming a brine-extractant cycle and reducing the amount of extractant added. Furthermore, since the extractant is sodium chloride, there is no introduction of external high-valence metal ions, reducing the problem of large amounts of waste brine discharged due to continuous impurity accumulation, thus reducing hazardous waste generation and disposal costs. The vacuum flash evaporation method completes the brine concentration and regeneration. The negative pressure environment lowers the boiling point of water, allowing for dehydration and brine concentration at low temperatures, reducing heating steam consumption and operating energy consumption. Simultaneously, the low-temperature operation reduces the problems of salt supersaturation crystallization and scaling, and equipment corrosion, effectively extending the continuous and stable operation cycle of the unit. Attached Figure Description

[0020] Figure 1 This is a flowchart of the equipment process for the technical solution of this application. Detailed Implementation

[0021] The present application will be further described in detail below with reference to the embodiments and accompanying drawings.

[0022] Unless otherwise specified, the main components involved in the following embodiments of this application are all purchased from commercially available products.

[0023] The subject of this application is azeotropic dilute hydrochloric acid produced by the epichlorohydrin process, hereinafter referred to as waste acid. The waste acid contains 25 wt% HCl and small amounts of suspended impurities such as silt and iron oxides.

[0024] Sodium chloride: Industrial grade, ≥99wt%; Calcium chloride: Industrial grade, ≥94wt%; Trimethylglycine hydrochloride: Industrial grade, purity ≥98wt%; Organophosphate compound corrosion inhibitor: a general industrial corrosion inhibitor for perchloric acidic water systems, with one or more of aminotrimethylenephosphonic acid, hydroxyethylidene diphosphonic acid, and ethylenediaminetetramethylenephosphonic acid as the main active ingredients; in the following examples of this application, the active ingredients are composed of 40wt% aminotrimethylenephosphonic acid, 35wt% hydroxyethylidene diphosphonic acid, 10wt% zinc sulfate heptahydrate and 15wt% polyacrylic acid, and are prepared into an aqueous solution with a total active ingredient content of 50wt% for use.

[0025] Liquid alkali: Industrial grade, 32wt% sodium hydroxide aqueous solution. Specific Implementation

[0027] Example 1 like Figure 1 As shown, this embodiment provides a device for recovering hydrogen chloride from epichlorohydrin waste acid, including a pretreatment unit, a mixing unit, an extractive distillation unit, and a vacuum flash concentration unit.

[0028] The pretreatment unit includes a heat exchanger and a filter; the mixing unit includes a dissolving tank and a static mixer; the extractive distillation unit includes an extractive distillation column, a bottom reboiler, and a top condenser; and the vacuum flash concentration unit includes a vacuum flash tank, a flash condenser, and a vacuum unit.

[0029] Waste acid is introduced into the cold side inlet of the heat exchanger, the cold side outlet is connected to the feed inlet of the filter, the hot side inlet is connected to the bottom outlet of the extractive distillation column, and the hot side outlet of the heat exchanger is connected to the feed inlet of the vacuum flash tank; the outlet of the dissolving tank and the outlet of the filter are both connected to the feed inlet of the static mixer.

[0030] The outlet of the static mixer is connected to the middle feed inlet of the extractive distillation column, the vapor outlet of the top condenser produces hydrogen chloride gas, and the bottom reboiler is connected to heating steam.

[0031] The vapor phase outlet at the top of the vacuum flash tank is connected to the vapor phase inlet of the flash condenser. The condensate outlet of the flash condenser produces low-acid wastewater. The non-condensable gas outlet of the flash condenser is connected to the vacuum unit. The concentrated brine outlet at the bottom of the vacuum flash tank is connected to the dissolving tank.

[0032] The medium flow side of the tower top condenser and flash condenser is made of graphite.

[0033] The heat exchanger, precision filter, dissolving tank, static mixer, extractive distillation column, vacuum flash tank, and bottom reboiler are made of 316L stainless steel with epoxy resin lining.

[0034] Fluoroplastic lining is used for the flow-through components of the material conveying pump.

[0035] The flange interfaces of the equipment and pipelines all use expanded PTFE seals.

[0036] Example 2 This embodiment provides a method for recovering hydrogen chloride from epichlorohydrin waste acid, as detailed below.

[0037] S1. Pretreatment of epichlorohydrin waste acid: Take 25wt% HCl-containing epichlorohydrin waste acid from the chlorohydrin process and pass it into a heat exchanger with a feed rate of 10 L / h. Use the high-temperature dilute acid mother liquor discharged from the bottom of the extractive distillation column in S3 as a heat source for countercurrent heat exchange to preheat the waste acid to 70℃. After preheating, the waste acid is filtered to remove suspended impurities with a filtration accuracy of 5μm.

[0038] S2. Preparation of the distillation mixture: Prepare a sodium chloride extractant solution with a mass concentration of 65 wt%. Add an organophosphate compound corrosion inhibitor to the sodium chloride extractant solution. The concentration of the corrosion inhibitor is 100 ppm, based on the total mass of the extractant solution. The pretreated waste acid and the sodium chloride extractant solution containing the corrosion inhibitor are fed into a static mixer at a mass ratio of 1:1 and mixed thoroughly to obtain the distillation mixture.

[0039] S3. Atmospheric Distillation Separation: The mixture to be distilled is fed into the middle of the extractive distillation column. Atmospheric distillation with salt is carried out in the column. The reboiler at the bottom of the column is heated by low-pressure saturated steam at 0.8 MPa. The bottom temperature is controlled at 125℃ and the reflux ratio is 1.5. The vapor phase at the top of the distillation column is cooled to 14℃ by the top condenser. After gas-liquid separation, hydrogen chloride gas is obtained. The condensate is refluxed into the extractive distillation column. The dilute acid mother liquor containing sodium chloride is discharged from the bottom of the distillation column.

[0040] S4. Reduced-Pressure Flash Concentration Treatment: The dilute acid mother liquor from the bottom of the tower is first sent to a heat exchanger as a heat source to preheat the feed waste acid. After cooling, it is sent to a vacuum flash tank for reduced-pressure flash concentration treatment. The operating pressure is controlled at 0.04 MPa and the operating temperature at 95℃. The flash vapor generated by flash condensation is condensed by a flash condenser to obtain low-acid wastewater, which is sent to the plant's wastewater treatment system. The bottom of the flash tank is concentrated to obtain a 65wt% sodium chloride solution, which is cooled and returned to the dissolving tank for recycling as an extractant. A small amount of sodium chloride is added periodically to compensate for system losses.

[0041] Example 3 This embodiment provides a method for recovering hydrogen chloride from epichlorohydrin waste acid. Compared with Embodiment 2, the extractant used in this application is sodium chloride and trimethylglycine hydrochloride. For example, based on 100wt% of the solute in the extractant, sodium chloride accounts for 94wt% and trimethylglycine hydrochloride accounts for 6wt%, as detailed below.

[0042] S1. Pretreatment of epichlorohydrin waste acid: Take 25wt% HCl-containing epichlorohydrin waste acid from the chlorohydrin process and pass it into a heat exchanger at a feed rate of 10L / h. Use the high-temperature dilute acid mother liquor discharged from the bottom of the extractive distillation column in S3 as a heat source for countercurrent heat exchange to preheat the waste acid to 70℃. After preheating, the waste acid is filtered to remove suspended impurities with a filtration accuracy of 5μm.

[0043] S2. Preparation of the distillation mixture: Prepare a compound extractant solution with a total solute mass concentration of 65 wt%; add an organophosphate compound corrosion inhibitor to the compound extractant solution, with the concentration of the corrosion inhibitor being 70 ppm based on the total mass of the extractant solution; mix the pretreated waste acid and the compound extractant solution containing the corrosion inhibitor in a 1:1 mass ratio in a static mixer to obtain the distillation mixture.

[0044] S3. Atmospheric Distillation Separation: The mixture to be distilled is fed into the middle of the extractive distillation column. Atmospheric distillation with salt is carried out in the column. The reboiler at the bottom of the column is heated by low-pressure saturated steam at 0.8 MPa. The bottom temperature is controlled at 120°C and the reflux ratio is 1.5. The vapor phase at the top of the distillation column is cooled to 14°C by the top condenser. After gas-liquid separation, hydrogen chloride gas is obtained. The condensate is refluxed into the extractive distillation column. The bottom of the distillation column discharges a dilute acid mother liquor containing sodium chloride and trimethylglycine hydrochloride.

[0045] S4. Reduced-Pressure Flash Concentration Treatment: The dilute acid mother liquor from the bottom of the tower is first sent to a heat exchanger as a heat source to preheat the feed waste acid. After cooling, it is sent to a vacuum flash tank for reduced-pressure flash concentration treatment. The operating pressure is controlled at 0.04 MPa and the operating temperature at 95℃. The flash vapor generated by flash condensation is condensed by a flash condenser to obtain low-acid wastewater, which is sent to the plant's wastewater treatment system. The bottom of the flash tank is concentrated to obtain a compound sodium chloride solution with a total solute mass concentration of 65 wt%. After cooling, it is returned to the dissolving tank for recycling as an extractant. A small amount of sodium chloride and trimethylglycine hydrochloride are added periodically to compensate for system losses.

[0046] Comparative Example 1 This embodiment provides a method for recovering hydrogen chloride from epichlorohydrin waste acid, using calcium chloride as the extractant, as detailed below.

[0047] S1. Pretreatment of epichlorohydrin waste acid: Take 25wt% HCl from epichlorohydrin waste acid produced by the chlorohydrin process, filter to remove large particulate suspended impurities, and set the feed rate to 10L / h.

[0048] S2. Preparation of the distillation mixture: Prepare a calcium chloride extractant solution with a mass concentration of 50 wt%. Add an organic phosphate compound corrosion inhibitor to the calcium chloride extractant solution. The concentration of the corrosion inhibitor is 100 ppm, based on the total mass of the extractant solution. Mix the pretreated waste acid and the calcium chloride extractant solution uniformly at a mass ratio of 1:1 to obtain the distillation mixture.

[0049] S3. Atmospheric Distillation Separation: The mixture to be distilled is fed into the extractive distillation column for atmospheric distillation. Low-pressure saturated steam is introduced into the reboiler at the bottom of the column for heating. The bottom temperature is controlled at 128℃ and the reflux ratio is 1.5. The vapor phase at the top of the distillation column is cooled to 14℃ by the top condenser. After gas-liquid separation, hydrogen chloride gas is obtained. The condensate is refluxed back into the extractive distillation column. The dilute acid mother liquor containing calcium chloride is discharged from the bottom of the distillation column.

[0050] S4. Atmospheric pressure evaporation and salt agent regeneration: The dilute acid mother liquor at the bottom of the tower is sent to an atmospheric pressure evaporator for atmospheric pressure evaporation and concentration. The concentrated calcium chloride solution is returned to the dissolving tank for recycling as an extractant. The gas phase generated by evaporation is condensed to obtain acidic wastewater, which is sent to the plant's wastewater treatment system. During operation, the calcium salt waste liquid enriched with impurities is periodically discharged to replenish the calcium chloride extractant and make up for the loss.

[0051] Comparative Example 2 This embodiment provides a method for recovering hydrogen chloride from epichlorohydrin waste acid, as detailed below.

[0052] S1. Pretreatment of epichlorohydrin waste acid: Take 25wt% HCl-containing epichlorohydrin waste acid from the chlorohydrin process and pass it into a heat exchanger at a feed rate of 10L / h. Use the high-temperature dilute acid mother liquor discharged from the bottom of the extractive distillation column in S3 as a heat source for countercurrent heat exchange to preheat the waste acid to 70℃. After preheating, the waste acid is filtered to remove suspended impurities with a filtration accuracy of 5μm.

[0053] S2. Preparation of the distillation mixture: Prepare a sodium chloride extractant solution with a mass concentration of 65 wt%. Add an organophosphate compound corrosion inhibitor to the sodium chloride extractant solution. The concentration of the corrosion inhibitor is 100 ppm, based on the total mass of the extractant solution. The pretreated waste acid and the sodium chloride extractant solution containing the corrosion inhibitor are fed into a static mixer at a mass ratio of 1:1 and mixed thoroughly to obtain the distillation mixture.

[0054] S3. Distillation Separation: The mixture to be distilled is fed into a dual-tower pressure-swing distillation system for separation. The system consists of a high-pressure distillation tower and a low-pressure distillation tower connected in series. The mixture first enters the middle of the high-pressure distillation tower as feed, and low-pressure saturated steam is introduced into the reboiler at the bottom of the tower for heating. The operating pressure inside the tower is 0.3 MPa, and the bottom temperature is controlled at 150°C. The vapor phase at the top of the tower is condensed and partially refluxed, while part of it is sent to the low-pressure distillation tower. The operating pressure of the low-pressure distillation tower is 0.05 MPa. After the vapor phase at the top of the tower is condensed, hydrogen chloride gas is produced, and dilute acid mother liquor containing sodium chloride is discharged from the bottom of the tower.

[0055] S4. Reduced Pressure Flash Concentration Treatment: The dilute acid mother liquor discharged from the bottom of the low-pressure distillation column is first sent to a heat exchanger as a heat source to preheat the feed waste acid. After cooling, it is sent to a vacuum flash tank for reduced pressure flash concentration treatment. The operating pressure is controlled at 0.04 MPa and the operating temperature at 95℃. The flash vapor generated by flash condensation is condensed by a flash condenser to obtain low-acid wastewater, which is sent to the plant's wastewater treatment system. The bottom of the flash tank is concentrated to obtain a 65wt% sodium chloride solution, which is cooled and returned to the dissolving tank for recycling as an extractant. A small amount of sodium chloride is added periodically to make up for system losses.

[0056] The performance test data of Examples 2-3 and Comparative Examples 1-2 are shown in Table 1.

[0057] Table 1

[0058] Example 2 uses sodium chloride as the extractant, through Na + Hydration and Cl - The common ion effect synergistically breaks the azeotropic equilibrium at atmospheric pressure, and the energy utilization is achieved by preheating the feed with the residual heat of the mother liquor at the bottom of the tower. Combined with vacuum flash evaporation to lower the boiling point of water to achieve low-temperature salt agent regeneration, and combined with staged corrosion prevention and corrosion inhibitor film protection, the separation efficiency is increased compared with the traditional calcium salt process, while reducing crystallization blockage.

[0059] Example 3: Based on sodium chloride, trimethylglycine hydrochloride was added to form a compound system. The salt effect and gas-liquid mass transfer efficiency were further enhanced by the stronger hydration capacity and surface activity of quaternary ammonium cations. At the same time, the quaternary ammonium groups can synergistically adsorb and form films with organophosphorus corrosion inhibitors, thereby improving the separation depth and corrosion resistance without increasing the total salt concentration.

[0060] Comparative Example 1 relies on the strong hydration of divalent calcium chloride cations to break the azeotropic effect of hydrochloric acid. However, the solubility of calcium chloride fluctuates greatly with temperature and is prone to crystallization and blockage. Furthermore, the mass fraction of HCl in the dilute acid mother liquor at the bottom of the tower is higher than that of this application, and the purity is not as high as that of this application. The recycling rate of the extractant is also low.

[0061] Although Comparative Example 2 added sodium chloride extractant, its core separation logic relied on the shift in the azeotropic point of hydrochloric acid caused by the pressure swing of the two towers to achieve separation. The process is different from that of this application, and it failed to give full play to the enhancing effect of salt on atmospheric distillation. Moreover, the heat exchange and reflux energy consumption of the two-tower series process is higher and the separation depth is limited.

[0062] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A method for recovering hydrogen chloride from epichlorohydrin waste acid, characterized in that, Includes the following steps: S1. Pre-treat the waste acid to remove impurities; S2. Mix the pretreated waste acid with the extractant solution to obtain the mixture to be distilled; S3. The mixture to be distilled is subjected to atmospheric pressure distillation in a distillation column. Hydrogen chloride gas is obtained at the top of the distillation column and dilute acid mother liquor is discharged from the bottom of the distillation column. S4. The dilute acid mother liquor is concentrated by vacuum flash evaporation to obtain sodium chloride solution and flash vapor phase. The flash vapor phase is condensed to obtain low acid wastewater. The extractant includes the sodium chloride solution obtained in S4, wherein the mass concentration of sodium chloride in the sodium chloride solution is not less than 65 wt%.

2. The method for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 1, characterized in that, The extractant also includes trimethylglycine hydrochloride, which, based on 100wt% of the solute in the extractant, contains 92-97wt% sodium chloride and 3-8wt% trimethylglycine hydrochloride.

3. A method for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 1 or 2, characterized in that, In S1, the waste acid is preheated. After preheating, the waste acid is filtered to remove impurities with a filtration accuracy of ≥5μm. The preheating process involves heat exchange between the waste acid and the dilute acid mother liquor obtained in S3, preheating to 60~80℃.

4. A method for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 1 or 2, characterized in that, In S2, the extractant solution has a mass concentration of 60-70%, and the waste acid and extractant solution are mixed at a mass ratio of 1:

1.

5. A method for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 1 or 2, characterized in that, In S3, the bottom temperature of the distillation column is 115~130℃, and the reflux ratio is 1~2; the vapor phase at the top of the distillation column is cooled to 10~18℃ by a condenser, and the hydrogen chloride obtained has a purity ≥99wt%.

6. A method for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 1 or 2, characterized in that, In S4, the pressure of the vacuum flash concentration process is 0.01–0.08 MPa, and the temperature is 90–100 °C.

7. A method for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 1 or 2, characterized in that, The extractant is supplemented with an organic phosphate compound corrosion inhibitor, and the concentration of the corrosion inhibitor is 50~120 ppm based on the total mass of the extractant solution.

8. A device for recovering hydrogen chloride from epichlorohydrin waste acid, characterized in that, The method for implementing the recovery method according to any one of claims 1 to 7 includes a pretreatment unit, a mixing unit, an extractive distillation unit, and a vacuum flash concentration unit. The pretreatment unit includes a heat exchanger and a filter; the mixing unit includes a dissolving tank and a static mixer; the extractive distillation unit includes an extractive distillation column, a bottom reboiler, and a top condenser; and the vacuum flash concentration unit includes a vacuum flash tank, a flash condenser, and a vacuum unit. Waste acid is introduced into the cold side inlet of the heat exchanger, the cold side outlet is connected to the feed inlet of the filter, the hot side inlet is connected to the bottom outlet of the extractive distillation column, and the hot side outlet of the heat exchanger is connected to the feed inlet of the vacuum flash tank; the outlet of the dissolving tank and the outlet of the filter are both connected to the feed inlet of the static mixer. The outlet of the static mixer is connected to the middle feed inlet of the extractive distillation column, the vapor outlet of the top condenser produces hydrogen chloride gas, and the bottom reboiler is connected to heating steam. The vapor phase outlet at the top of the vacuum flash tank is connected to the vapor phase inlet of the flash condenser. The condensate outlet of the flash condenser produces low-acid wastewater. The non-condensable gas outlet of the flash condenser is connected to the vacuum unit. The concentrated brine outlet at the bottom of the vacuum flash tank is connected to the dissolving tank.

9. The device for recovering hydrogen chloride from epichlorohydrin waste acid according to claim 8, characterized in that, It also includes a graded anti-corrosion structure, which is set up in zones according to the type of contact medium: The medium flow side of the tower top condenser and flash condenser is made of graphite material; The heat exchanger, precision filter, dissolving tank, static mixer, extractive distillation column, vacuum flash tank, and bottom reboiler are made of 316L stainless steel with epoxy resin lining. Fluoroplastic lining of the flow-through components of the material conveying pump; The flange connections of the equipment and pipelines all use expanded PTFE seals.

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