Method for recovering hydrochloric acid and metal catalyst from waste acid formed in Cl2 preparation

Abstract

The invention relates to a method for recovering hydrochloric acid and a metal catalyst from waste acid formed in Cl2 preparation. The method comprises the following steps: filtering metal catalyst-containing waste acid from the bottom of a waste acid washing absorption tower by using a filter; acid separation, purification and recovery: adsorbing hydrochloric acid in the waste acid by adopting acid-retardant short-bed composite resin, enabling metal salts not to be adsorbed and to flow out through the resin, and desorbing after the composite resin is saturated by adsorption to obtain a hydrochloric acid solution; metal salt separation, purification and recovery: concentrating the metal salt in the wastewater by adopting a sulfonic acid group and hydrochloric acid group dual-ionic liquid composite membrane, and recycling low-salt wastewater to a waste acid absorption system for cyclic utilization; adjusting alkali in an acid precipitation tank: concentrating the metal salt-containing wastewater into the acid precipitation tank, adding alkali, and controlling the pH value; feeding the wastewater into a stirring tank, adding a silicon dioxide modifier, taking supernatant liquid as a raw material for preparing chlorine by electrolysis, and centrifuging bottom turbid liquid to hydrotalcite; according to the scheme, efficient recycling of hydrochloric acid and the metal catalyst is achieved.

Description

Technical Field

[0001] The invention belongs to the technical field of wastewater treatment, and in particular relates to a method for recovering hydrochloric acid and a metal catalyst from waste acid formed in the production of Cl2. Background Art

[0002] Chlorine is a very important chemical product and raw material with a wide range of applications, mainly including new materials industries such as polyurethane, epoxy resin, chlorinated hydrocarbons, chlorinated polymers, chlorinated rubber, disinfectants, detergents, food additives, cosmetic additives and other fine chemical industries, chlorobenzene series, synthetic glycerol, chloroacetic acid, benzyl chloride and other pesticides, pharmaceutical industry, as well as new energy industries such as polysilicon manufacturing and papermaking, textile, metallurgy and petrochemical industries.

[0003] The main industrial methods for producing chlorine are electrolysis, direct oxidation and catalytic oxidation. When chlorine is produced by catalytic oxidation, HCl is converted into Cl2 mainly through Cu-based catalyst fluidized bed technology, achieving closed-loop recycling of chlorine resources and zero emission of the reaction. The waste hydrochloric acid produced by this production process is difficult to handle. The waste hydrochloric acid contains 1% catalyst and 0.5-1.5g / L metal ions. Direct wastewater treatment will cause catalyst loss and excessive metal content in wastewater, and it is difficult to treat it biochemically.

[0004] The HCl content in the waste acid is 21%-26%. In the original process route, the waste acid does not contain a catalyst, and the waste acid can be directly treated as waste water by neutralization with alkali solution. The metal catalyst in the waste acid of the new process route has a certain economic value (such as copper and nickel). Based on the concept of material recovery and circular economy, the recovery of valuable metal catalysts and water resource reuse technology from waste acid has gradually become the development trend of waste acid treatment in my country. Therefore, the recycling of metal catalysts in waste acid should be given priority, and a reasonable recovery process should be carried out according to the composition, acid amount, impurity composition and different process requirements. The metal recovery process in waste acid generally uses electroplating technology to reduce metal ions to a metallic state, but the metal recovery rate and the quality of the recovered metal will be affected by the reduction of the metal content in the waste acid during the process. Therefore, it is necessary to regularly detect the metal ion content in the waste acid to replenish the waste acid, which in turn causes the separation process to be cumbersome, requires a lot of manpower, and the electroplating operation cost is high. The recovery of acid liquid from waste acid generally adopts a heating distillation process to recover acid liquid with a lower boiling point, such as nitric acid with a lower boiling point than sulfuric acid. However, the recovery of sulfuric acid with a higher boiling point requires additional recovery and processing equipment, resulting in an increase in the primary recovery cost of the process.

[0005] At present, there are some shortcomings in the actual application of industrial waste acid treatment and recovery processes, such as easy to cause secondary pollution, complicated processes, low metal recovery rate, high recovery costs, etc. Therefore, exploring and developing new methods and devices for metal recovery and resource utilization in waste acid is of great significance to the green and clean production, energy conservation and emission reduction of my country's industrial enterprises. Summary of the invention

[0006] The present invention aims at the existing technical problems and provides a method for recovering hydrochloric acid and a metal catalyst from waste acid formed in the production of Cl2. The metal catalyst is extracted from the waste acid to prepare industrial-grade hydrotalcite, and the hydrochloric acid in the waste acid is recovered at the same time, which can become a raw material for electrolytic production of chlorine in a chlor-alkali device. The whole process realizes the cyclic and efficient utilization of various resources and solves the problems of secondary pollution caused by waste slag generated by the existing process technology, complicated process, low metal recovery rate, high recovery cost, etc.

[0007] In order to achieve the above object, the specific technical scheme of the present invention is as follows:

[0008] A method for recovering hydrochloric acid and a metal catalyst from waste acid formed in the production of Cl2, the method comprising the following steps:

[0009] S1: Using a filter to filter the metal catalyst-containing waste acid from the bottom of the waste acid washing absorption tower;

[0010] S2: Acid separation, purification and recovery: A low-bed acid-blocked composite resin is used to adsorb hydrochloric acid in the waste acid of S1. Metal salts are not adsorbed and flow out through the resin. After the composite resin is saturated with adsorption, it is desorbed to obtain a hydrochloric acid solution.

[0011] S3: Separation, purification and recovery of metal salts: Use sulfonic acid and hydrochloric acid diionic liquid composite membranes to concentrate metal salts in wastewater, and reuse low-salt wastewater in the waste acid absorption system for recycling;

[0012] S4: Alkali adjustment in acid precipitation tank: The concentrated metal salt-containing wastewater from S3 enters the acid precipitation tank, where alkali is added to control the pH value;

[0013] S5: The wastewater from S4 enters the mixing tank, where a silica modifier is added. The upper clear liquid is used as a raw material for electrolytic chlorine production, and the suspended liquid at the bottom is centrifuged to obtain hydrotalcite.

[0014] The present invention utilizes the specific selection and acid resistance of sulfonic acid and hydrochloric acid diionic liquid composite membranes for metals to treat metal salts in acidic wastewater, introduces sulfonic acid and hydrochloric acid functional groups with electrostatic repulsion and interception efficiency for metal salts into the ultra-thin functional layer for filtration, exerts the synergistic effect of membrane pore size screening and electrostatic repulsion and interception, and realizes that the prepared filter membrane has excellent metal salt interception performance and excellent permeability characteristics, and at the same time, the introduced hydrochloric acid group can effectively improve its flux performance and acid resistance, obtains high-metal salt-containing wastewater on the retentate side, and obtains metal ion selectivity and acid resistance. Conventional sulfonic acid composite membranes cannot be applied to the strong acid and high-salt wastewater system, and the application of sulfonic acid and hydrochloric acid diionic liquid composite membranes in this field overcomes the technical difficulties of strong acid corrosion, poor metal selectivity and low permeability.

[0015] In one embodiment of the present invention, S1 removes insoluble matter in wastewater, preferably removes catalyst fine powder and / or silicate; preferably, the filter is a precision ceramic membrane filter; preferably, the filter has an accuracy of 10-50 μm, preferably 20-30 μm.

[0016] In one embodiment of the present invention, the metal content in the wastewater discharged from S2 is 0.5 g / L-1.5 g / L, and the hydrochloric acid content is less than 0.5%. After the composite resin is saturated with adsorption, it is backwashed with pure water to desorb and obtain a hydrochloric acid solution.

[0017] In one embodiment of the present invention, S2 acid-retarded short bed composite resin is selected from acid-retarded resin, preferably commonly used resin Tulsimer A-853E and / or A-107CL. When the acid-retarded short bed composite resin is used for the first time, it needs to be activated with an acid solution at 50°C-70°C.

[0018] In one embodiment of the present invention, the membrane structure in S3 is one or more of a folded microporous membrane, a folded nanofiltration membrane, and a spiral ultrafiltration membrane. In the present invention, the primary permeate side of the membrane concentration system is low-salt wastewater, and the secondary permeate side wastewater can be returned to the waste acid absorption system for recycling.

[0019] In one embodiment of the present invention, the metal salt content in the wastewater after S3 concentration is 30-150 g / L, preferably 50-100 g / L.

[0020] In one embodiment of the present invention, S3 said membrane is prepared by a solution casting method; preferably, said method comprises the following steps: dissolving butyl 3-methylimidazolium trifluoromethanesulfonate and diethylmorpholine hydrochloride in dimethylacetamide, stirring, heating, concentrating, and degassing; casting the concentrated solution on a polymer support membrane, standing to solidify, drying, and heating to obtain butyl 3-methylimidazolium trifluoromethanesulfonate & diethylmorpholine hydrochloride-polymer ionic liquid membrane; preferably, said polymer support membrane is a PVC support membrane.

[0021] In one embodiment of the present invention, the amount of butyl 3-methylimidazolium trifluoromethanesulfonate added in S3 is 0.2-5 wt % of diethylmorpholine hydrochloride.

[0022] In one embodiment of the present invention, the reaction temperature of S3 raw material is 40-100°C.

[0023] In one embodiment of the present invention, the S3 solidification temperature is 20-70°C.

[0024] In one embodiment of the present invention, the acid precipitation tank described in S4 is composed of a coarse adjustment tank and a fine adjustment tank. In the art, high-metal salt wastewater can be subjected to two-stage alkali adjustment in the acid precipitation tank, and each part of the acid precipitation tank is alternately connected by undercurrent and overflow to enhance the mass transfer efficiency of the neutralization reaction, and a scraper is arranged at the orifice.

[0025] In one embodiment of the present invention, the S4 rough adjustment tank controls the pH value of the wastewater at 5-7, and the fine adjustment tank controls the pH value at 8-9.

[0026] In one embodiment of the present invention, the S5 temperature is 50°C-100°C.

[0027] In one embodiment of the present invention, the salt content of the supernatant liquid of S5 is greater than 5%. The salt content of the weakly alkaline high-salt wastewater is greater than 5%, and the impurity metal index meets the requirements, and it can be sent to a chlor-alkali plant. The chlorine produced by electrolysis can be used to synthesize phosgene as an isocyanate raw material, and the HCl produced can be used as a raw material for chlorine production by catalytic oxidation. The silica modifier forms a directional adsorption on the metal salt, forms a metal plate layer on the surface of the silica through the variable valence metal, and then attracts other metal ions to continuously overlap into a metal plate layer, and then adsorbs anions and water, and finally forms a suspended liquid layered compound hydrotalcite, which enters the centrifuge for centrifugation. After centrifugation, a dry cake-like hydrotalcite can be obtained, thereby realizing the recovery and utilization of metal ions.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) The catalyst and dissolved metal ions in the waste acid generated by the Cl2 production device are fully recovered and utilized, and the hydrochloric acid in the waste acid is recovered. The catalyst can be reused in the chlorine production unit. The hydrotalcite prepared from the metal ions can be used as an adsorbent or catalyst carrier. The recovered hydrochloric acid can be sent to the hydrochloric acid analysis device to produce HCl, and HCl can be used as a raw material for the Cl2 production device. The full utilization of the chlorine cycle and metal catalyst of the Cl2 production device is realized, the unit consumption and raw material cost are reduced, and it has economic benefits.

[0030] (2) The metal ions in the waste acid can be completely removed. The metal ions in the treated wastewater are less than 0.5 ppm. The brine produced in the mixing tank is used in the chlor-alkali industry. No waste brine is discharged during the entire process, thus achieving the recycling of sodium chloride and water.

[0031] (3) The provided method for efficiently recovering hydrochloric acid and metal catalyst from waste acid has a simple process flow, is easy to operate, has low industrial cost, saves energy, is environmentally friendly, and has economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 The invention is a process flow diagram of a method for efficiently recovering hydrochloric acid and a metal catalyst from waste acid; wherein (1) is a wastewater absorption tower, (2) is waste acid containing a metal catalyst, (3) is a ceramic membrane filter, (4) is a resin adsorption column, (5) is a membrane concentration system, (6) is an alkaline solution, (7) is a wastewater acid precipitation tank, (8) is a modifier, (9) is a stirring tank, (10) is brine, (11) is a centrifuge, and (12) is hydrotalcite. DETAILED DESCRIPTION

[0033] The following is further explained in conjunction with specific embodiments and drawings. The following embodiments are only used to more clearly illustrate the technical solution of this patent and are therefore only used as examples and cannot be used to limit the scope of protection of this patent.

[0034] Reagents:

[0035] Dimethylacetamide (Aladdin, 99%, AR), butyl 3-methylimidazolium trifluoromethanesulfonate (Shanghai Chengjie Chemical, 98%, AR), N-ethylmorpholine (Sigma, 99%, AR), 2-chloroethanol (Sigma, 99%, AR), acetonitrile (Aladdin, 99.5%, AR), ether (Aladdin, 99.5%, AR), acetone (Aladdin, 99.5%, AR), ethanol (Aladdin, 99.7%, AR), PVC support membrane is polyvinyl chloride (Sinopharm, K71-72, AR), polyethersulfone (BASF, Germany, degree of polymerization 400,000).

[0036] Synthesis method of N-ethylmorpholine hydrochloride: N-ethylmorpholine (0.2 mol) and 2-chloroethanol (0.24 mol) were added to a 100 mL three-necked flask, 30 mL of acetonitrile was added as solvent, and heated under magnetic stirring, and the reaction temperature was controlled at 85°C. After the reaction was completed, the solvent was evaporated with a rotary evaporator to obtain a crude product. The crude product was washed twice with ether and recrystallized with an acetone / ethanol mixed solvent to obtain the target compound, N-ethylmorpholine hydrochloride.

[0037] Instruments and equipment:

[0038] Thermogravimetric analyzer, Q-500, TA Instruments, USA;

[0039] Nuclear magnetic resonance spectrometer, Varian DLG400, Varian, USA;

[0040] Heat collecting constant temperature magnetic stirring bath, HWCL-1 Zhengzhou Great Wall Science and Technology Industry and Trade Co., Ltd.;

[0041] Fourier transform infrared spectrometer, NEXUS EURO, Thermo Nicolet, USA.

[0042] Chemical structure characterization:

[0043] (1) Nuclear magnetic resonance (NMR)

[0044] In the preparation process of ion membrane, the chemical structure of monomers and polymers is mainly characterized by nuclear magnetic resonance (NMR). The test instrument is BrukeradvanceⅢ500, produced by Bruker Company of Switzerland. The test conditions are 500MHz and the test temperature is 25℃. The solvent used is d8-THF, and the internal standard is tetramethylsilane (TMS) for testing.

[0045] Structural characterization data of diethylmorpholine hydrochloride: white solid, mp53~54℃; 1 H NMR (300MHz, DMSO) δ: 1.23 (t, J=7.06Hz, 3H, CH2CH3), 3.39~3.46 (m, 4H, CH2NCH2), 3.48~3.70 (m, 6H, CH2CH3, NCH2-CH2OH), 3.92 (s, 4H, CH2OCH2), 5.74 (s, 1H, OH); 13 C NMR (DMSO, 75MHz) δ: 7.45 (CH3), 46.89 (CH2), 55.31 (2C, NCH2), 58.23 (NCH2CH2OH), 60.15 (CH2OH), 62.03 (2C, OCH2).

[0046] (2) Infrared spectroscopy (FT-IR)

[0047] The experimental samples were characterized using an advanced Fourier transform infrared spectrometer. Test conditions: 32 scans with a resolution of 4 cm -1 , wave number range 400-4000cm -1 The samples in this experiment were tested by transmission method, and the ion membrane samples were fully dried before the test.

[0048] Unless otherwise specified in the present invention, the % and ppm are all mass ratios.

[0049] Preparation Example 1

[0050] Preparation of 0.2wt% [bmim][OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane.

[0051] Dimethylacetamide was dried with 5A molecular sieve for 12 hours. First, 2g of butyl 3-methylimidazolium trifluoromethanesulfonate ([bmim][OTF]) and 10g of nitrogen diethylmorpholine hydrochloride were dissolved in 20mL DMAc, and stirred with a magnetic stirrer in a conical flask with a lid at 40℃ for 4 hours to make the solution uniform. The solution was concentrated after heating at 40℃ for 3 hours in a beaker, and then allowed to stand at room temperature for 12 hours for degassing. The PVC microporous membrane was fixed on a smooth glass plate with adhesive tape for use. Then the concentrated solution was spread on a flat glass plate, and a film was cast on the PVC support film with a scraper, and then allowed to stand at 20℃ for 12 hours for solidification and drying, and then heated to 80℃ to obtain a 0.2wt% [bmim][OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane.

[0052] Preparation Example 2

[0053] Preparation of 5wt% [bmim][OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane.

[0054] Dimethylacetamide was dried with 5A molecular sieve for 12 hours. First, 25g of butyl 3-methylimidazolium trifluoromethanesulfonate ([bmim][OTF]) and 5g of nitrogen diethylmorpholine hydrochloride were dissolved in 150mL of DMAc, and stirred with a magnetic stirrer in a conical flask with a lid at 40°C for 3 hours to make the solution uniform. The solution was concentrated after being heated at 100°C for 3 hours in a beaker, and then allowed to stand at room temperature for 12 hours to degas. The PVC microporous membrane was fixed on a smooth glass plate with adhesive tape for use. Then the concentrated solution was spread on a flat glass plate, and a film was cast on the PVC support film with a scraper, and then allowed to stand at 70°C for 12 hours for solidification and drying, and then heated to 80°C to obtain a 5wt% [bmim][OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane.

[0055] Preparation Example 3

[0056] Preparation of 2.5wt% [bmim][OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane.

[0057] Dimethylacetamide was dried with 5A molecular sieves for 12 hours. First, 5g of butyl 3-methylimidazolium trifluoromethanesulfonate ([bmim][OTF]) and 2g of nitrogen diethylmorpholine hydrochloride were dissolved in 50mL of DMAc, and stirred with a magnetic stirrer in a conical flask with a lid at 60℃ for 5 hours to make the solution uniform. The solution was concentrated after heating at 60℃ for 3 hours in a beaker, and then allowed to stand at room temperature for 12 hours for degassing. The PVC microporous membrane was fixed on a smooth glass plate with adhesive tape for use. Then the concentrated solution was spread on a flat glass plate, and a film was cast on the PVC support film with a scraper, and then allowed to stand at 60℃ for 12 hours for solidification and drying, and then heated to 80℃ to obtain a 2.5wt% [bmim][OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane.

[0058] Example 1

[0059] The metal catalyst waste acid produced by the Cl2 production process at the bottom of Wanhua Chemical's acid washing absorption tower is filtered using a precision ceramic membrane filter with a filter accuracy of 10μm and a waste acid flow rate of 90m 3 / h, the filter pressure drop is 20KPa. The metal salt-containing waste acid after filtration enters the acid-blocked low-bed composite resin TulsimerA-853E adsorption column. The hydrochloric acid content in the waste acid is 22%. The resin column treats 10t / h of waste acid. The waste acid flows into and discharges the system from top to bottom. The metal content in the discharged wastewater is 0.5g / L and the hydrochloric acid content is 0.45%.

[0060] The metal salt-containing wastewater after adsorption enters the membrane concentration system and is separated by a two-stage 0.2wt% [bmim] [OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane. The metal salts in the wastewater are concentrated by using the sulfonic acid group and hydrochloric acid group double ionic liquid to selectively concentrate the metals. The wastewater inlet flow rate is 10t / h. 9t / h of low-metal salt wastewater is produced on the primary permeate side and recycled to the top of the wastewater absorption tower for capturing HCl to achieve wastewater recycling. The metal ion content in the wastewater is less than 1ppm. The wastewater on the primary retentate side enters the secondary membrane for concentration. The secondary retentate side is the concentrated metal salt wastewater. The metal salt content in the wastewater is 30g / L. The wastewater outlet flow rate is 0.1t / h, and the concentration multiple is 100 times.

[0061] High-metal salt wastewater is alkali-adjusted in the acid precipitation tank. A 5wt% sodium hydroxide solution is used to first adjust the pH value of the wastewater to 5 in the coarse adjustment tank, and then the pH is further reduced to 8 in the fine adjustment tank. An online pH meter is used to monitor the pH value changes of the wastewater in real time and change the alkali solution flow rate. After alkali adjustment, the wastewater enters three stirring tanks in sequence for hydrotalcite synthesis. A single stirring tank can process 0.8 tons of metal brine. The stirring tank is heated by hot water and the temperature is set at 50°C. After 7 hours, the feeding is completed. The configured 60wt% silica modifier is added from the top of the stirring tank at 3 kg, and the mixture is kept warm and stirred for 30 minutes. Then the stirring and insulation are stopped, and the mixture is naturally cooled for 6 hours. The overflow valve on the side of the stirring tank is opened to discharge the upper clear liquid in the stirring tank. The clear liquid volume is 0.5 tons. The main component of the clear liquid is NaCl, and the salt content is 6%. It is sent to the chlor-alkali device as a raw material for electrolytic chlorine production. Then the drain valve at the bottom of the stirring tank is opened to discharge the hydrotalcite suspension in the lower layer of the stirring tank into the centrifuge. The suspension volume is 0.3 tons. The centrifuge is started and the speed is set to 5000 rpm. After centrifugation for 2 minutes, dry cake-like hydrotalcite is obtained.

[0062] Table 1 Data analysis table of each component

[0063]

[0064] Example 2

[0065] The metal catalyst waste acid produced by the Cl2 production process at the bottom of Wanhua Chemical's acid washing absorption tower is filtered using a precision ceramic membrane filter with a filter accuracy of 25μm and a waste acid flow rate of 95m 3 / h, the filter pressure drop is 40KPa. The metal salt-containing waste acid after filtration enters the acid-blocked low-bed composite resin TulsimerA-107CL adsorption column. The hydrochloric acid content in the waste acid is 22%. The resin column treats 15t / h of waste acid. The waste acid flows into and discharges the system from top to bottom. The metal content in the discharged wastewater is 1g / L and the hydrochloric acid content is 0.4%.

[0066] The metal salt-containing wastewater after adsorption enters the membrane concentration system and is separated by a two-stage 5wt% [bmim][OTF]&nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane. The metal salts in the wastewater are concentrated by using the sulfonic acid group and hydrochloric acid group diionic liquid to selectively concentrate the metals. The wastewater inlet flow rate is 15t / h. 14t / h of low-metal salt wastewater is generated on the primary permeate side and recycled to the top of the wastewater absorption tower for capturing HCl to achieve wastewater recycling. The metal ion content in the wastewater is less than 1ppm. The wastewater on the primary retentate side enters the secondary membrane for concentration. The secondary retentate side is the concentrated metal salt wastewater. The metal salt content in the wastewater is 70g / L. The wastewater outlet flow rate is 0.15t / h, and the concentration multiple is 100 times.

[0067] The high-metal salt wastewater is alkali-adjusted in the acid precipitation tank. A 5wt% sodium hydroxide solution is used to first adjust the pH value of the wastewater to 6 in the coarse adjustment tank, and then the pH is further reduced to 8.5 in the fine adjustment tank. An online pH meter is used to monitor the pH value changes of the wastewater in real time and change the alkali solution flow rate. After alkali adjustment, the wastewater enters three stirring tanks in sequence for hydrotalcite synthesis. A single stirring tank can process 0.9 tons of metal brine. The stirring tank is heated by hot water and the temperature is set at 80°C. After 7.5 hours, the feeding is completed. The configured 60wt% silica modifier is added at 4 kg from the top of the stirring tank, and the mixture is kept warm and stirred for 30 minutes. Then the stirring and insulation are stopped, and the mixture is naturally cooled for 7 hours. The overflow valve on the side of the stirring tank is opened to discharge the upper clear liquid in the stirring tank. The clear liquid volume is 0.5 tons. The main component of the clear liquid is NaCl, and the salt content is 7%. It is sent to the chlor-alkali device as a raw material for electrolytic chlorine production. Then the drain valve at the bottom of the stirring tank is opened to discharge the hydrotalcite suspension in the lower layer of the stirring tank into the centrifuge. The suspension volume is 0.4 tons. The centrifuge is started and the speed is set to 5000 rpm. After centrifugation for 3 minutes, dry cake-like hydrotalcite is obtained.

[0068] Table 2 Data analysis table of each component

[0069]

[0070] Example 3

[0071] The metal catalyst waste acid produced by the Cl2 production process at the bottom of Wanhua Chemical's acid washing absorption tower is filtered using a precision ceramic membrane filter with a filter accuracy of 50μm and a waste acid flow rate of 100m 3 / h, the filter pressure drop is 60KPa. The metal salt-containing waste acid after filtration enters the acid-blocked low-bed composite resin TulsimerA-853E adsorption column. The hydrochloric acid content in the waste acid is 22%. The resin column treats 20t / h of waste acid. The waste acid flows into and discharges the system from top to bottom. The metal content in the discharged wastewater is 1.5g / L and the hydrochloric acid content is 0.3%.

[0072] The metal salt-containing wastewater after adsorption enters the membrane concentration system and is separated by a two-stage 2.5wt% [bmim] [OTF] & nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane. The metal salts in the wastewater are concentrated by using the sulfonic acid group and hydrochloric acid group double ionic liquid to selectively concentrate the metals. The wastewater inlet flow rate is 20t / h. 19t / h of low-metal salt wastewater is generated on the primary permeate side and recycled to the top of the wastewater absorption tower for capturing HCl to achieve wastewater recycling. The metal ion content in the wastewater is less than 1ppm. The wastewater on the primary retentate side enters the secondary membrane for concentration. The secondary retentate side is the concentrated metal salt wastewater. The metal salt content in the wastewater is 150g / L. The wastewater outlet flow rate is 0.2t / h, and the concentration multiple is 100 times.

[0073] High-metal salt wastewater is alkali-adjusted in the acid precipitation tank. A 5wt% sodium hydroxide solution is used to first adjust the pH value of the wastewater to 7 in the coarse adjustment tank, and then the pH is further reduced to 9 in the fine adjustment tank. An online pH meter is used to monitor the pH value changes of the wastewater in real time and change the alkali solution flow rate. After alkali adjustment, the wastewater enters three stirring tanks in sequence for hydrotalcite synthesis. A single stirring tank can process 1 t of metal brine. The stirring tank is heated by hot water and the temperature is set at 100°C. After 8 hours, the feeding is completed, and 5 kg of the configured 60wt% silica modifier is added from the top of the stirring tank. The mixture is kept warm and stirred for 30 minutes, and then the stirring and insulation are stopped. The mixture is naturally cooled for 8 hours. The overflow valve on the side of the stirring tank is opened to discharge the upper clear liquid in the stirring tank. The clear liquid volume is 0.5 t. The main component of the clear liquid is NaCl, and the salt content is 8%. It is sent to the chlor-alkali device as a raw material for electrolytic chlorine production. Then the drain valve at the bottom of the stirring tank is opened to discharge the hydrotalcite suspension in the lower layer of the stirring tank into the centrifuge. The suspension volume is 0.5 t. The centrifuge is started and the speed is set to 5000 rpm. After centrifugation for 5 minutes, dry cake-like hydrotalcite is obtained.

[0074] Table 3 Data analysis of each component

[0075]

[0076] Comparative Example 1

[0077] Compared with Example 1, the difference is that the [bmim][OTF]&nitrogen diethylmorpholine hydrochloride-PVC ionic liquid membrane is replaced by a polyethersulfone (PES) nanofiltration membrane.

[0078] The metal catalyst waste acid produced by the Cl2 production process at the bottom of Wanhua Chemical's acid washing absorption tower is filtered using a precision ceramic membrane filter with a filter accuracy of 10μm and a waste acid flow rate of 90m 3 / h, the filter pressure drop is 20KPa. The metal salt-containing waste acid after filtration enters the acid-blocked low-bed composite resin TulsimerA-853E adsorption column. The hydrochloric acid content in the waste acid is 22%. The resin column treats 10t / h of waste acid. The waste acid flows into and discharges the system from top to bottom. The metal content in the discharged wastewater is 0.5g / L and the hydrochloric acid content is 0.45%.

[0079] The metal salt-containing wastewater after adsorption enters the membrane concentration system and is separated by a two-stage polyethersulfone (PES) nanofiltration membrane. The wastewater inlet flow rate is 10 t / h. The first-stage permeate side produces 5 t / h of low-metal salt wastewater which is recycled to the top of the wastewater absorption tower to capture HCl and realize wastewater recycling. The metal ion content in the wastewater has not been significantly reduced. The wastewater on the first-stage retentate side enters the second-stage membrane for concentration. The second-stage retentate side is the concentrated metal salt wastewater. The wastewater effluent flow rate is 5 t / h, and the concentration multiple is 2 times.

[0080] High-metal salt wastewater is alkali-adjusted in the acid precipitation tank. A 5wt% sodium hydroxide solution is used to first adjust the pH value of the wastewater to 5 in the coarse adjustment tank, and then the pH is further reduced to 8 in the fine adjustment tank. An online pH meter is used to monitor the pH value changes of the wastewater in real time and change the alkali solution flow rate. After alkali adjustment, the wastewater enters three stirring tanks in sequence for hydrotalcite synthesis. A single stirring tank can process 0.8 tons of metal brine. The stirring tank is heated by hot water and the temperature is set at 50°C. After 7 hours, the feeding is completed, and 3 kg of the configured 60wt% modifier is added from the top of the stirring tank. The mixture is kept warm and stirred for 30 minutes, and then the stirring and insulation are stopped. The mixture is naturally cooled for 6 hours. The overflow valve on the side of the stirring tank is opened to discharge the upper clear liquid in the stirring tank. The clear liquid volume is 0.75 tons. The main component of the clear liquid is NaCl, and the salt content is 1%. It is sent to the chlor-alkali device as a raw material for electrolytic chlorine production. Then the drain valve at the bottom of the stirring tank is opened to discharge the hydrotalcite suspension in the lower layer of the stirring tank into the centrifuge. The suspension volume is 0.05 tons. The centrifuge is started and the speed is set to 5000rpm. After centrifugation for 2 minutes, dry cake-like hydrotalcite is obtained.

[0081] Table 4 Data analysis table of each component

[0082]

[0083] Comparative Example 2

[0084] Compared with Example 1, the difference is that the membrane filtration is replaced by ion exchange column filtration.

[0085] The specific process of differentiation is as follows: the metal salt-containing wastewater after adsorption enters the ion exchange column system filled with D751 resin, and a two-stage ion exchange column is used for ion exchange. The wastewater inlet flow rate is 10t / h, and the filtrate produces 9.95t / h of wastewater which is recycled to the top of the wastewater absorption tower to capture HCl and realize wastewater recycling. The metal ions in the wastewater are 500ppm, and the metal salt wastewater effluent flow rate after backwashing is 0.05t / h, and the metal salt content in the wastewater is 1g / L.

[0086] The rest is the same as in Example 1.

[0087] Table 5 Data analysis table of each component

[0088]

[0089] By comparing the above embodiments and comparative examples, it can be found that the scheme of the present invention can recover 97.7% of HCl in waste acid, reduce metal ions in waste water to 1 ppm, and reprocess the recovered metal ions into hydrotalcite, thereby solving the problem of secondary pollution of waste residues. The scheme has the advantages of simple and efficient process route, high metal recovery rate and low recovery cost.

Claims

1. A method for recovering hydrochloric acid and a metal catalyst from waste acid formed in the production of Cl2, characterized in that: The method comprises the following steps: S1: Using a filter to filter the metal catalyst-containing waste acid from the bottom of the waste acid washing absorption tower; S2: Acid separation, purification and recovery: A low-bed acid-blocked composite resin is used to adsorb hydrochloric acid in the waste acid of S1. Metal salts are not adsorbed and flow out through the resin. After the composite resin is saturated with adsorption, it is desorbed to obtain a hydrochloric acid solution. S3: Separation, purification and recovery of metal salts: Use sulfonic acid and hydrochloric acid diionic liquid composite membranes to concentrate metal salts in wastewater, and reuse low-salt wastewater in the waste acid absorption system for recycling; S4: Alkali adjustment in acid precipitation tank: The concentrated metal salt-containing wastewater from S3 enters the acid precipitation tank, where alkali is added to control the pH value; S5: The wastewater from S4 enters the mixing tank, where a silica modifier is added. The upper clear liquid is used as a raw material for electrolytic chlorine production, and the suspended liquid at the bottom is centrifuged to obtain hydrotalcite.

2. The method according to claim 1, characterized in that S1 removes insoluble matter from the wastewater, preferably removes catalyst fines and / or silicates; Preferably, the filter is a precision ceramic membrane filter; Preferably, the filter has a precision of 10-50 μm, preferably 20-30 μm.

3. The method according to claim 1 or 2, characterized in that: The metal content in the wastewater discharged from S2 is 0.5g / L-1.5g / L, and the hydrochloric acid content is less than 0.5%.

4. The method according to any one of claims 1 to 3, characterized in that S3 The membrane structure is one or more of a folded microporous membrane, a folded nanofiltration membrane, and a spiral ultrafiltration membrane; And / or, the metal salt content in the wastewater after S3 concentration is 30-150 g / L, preferably 50-100 g / L.

5. The method according to any one of claims 1 to 4, characterized in that S3 The membrane is prepared by solution casting; Preferably, the method comprises the following steps: dissolving butyl 3-methylimidazolium trifluoromethanesulfonate and diethylmorpholine hydrochloride in dimethylacetamide, stirring, heating, concentrating, and degassing; casting the concentrated solution on a polymer support membrane, standing to solidify, drying, and heating to obtain a butyl 3-methylimidazolium trifluoromethanesulfonate & diethylmorpholine hydrochloride-polymer ionic liquid membrane; Preferably, the polymer support film is a PVC support film.

6. The method according to claim 5, characterized in that S3 The amount of butyl 3-methylimidazolium trifluoromethanesulfonate added is 0.2-5wt% of diethylmorpholine hydrochloride; and / or, the reaction temperature of S3 raw material is 40-100°C; And / or, S3 solidification temperature is 20-70°C.

7. The method according to any one of claims 1 to 6, characterized in that S4 The acid precipitation tank is composed of a coarse adjustment tank and a fine adjustment tank; And / or, the S4 rough adjustment tank controls the pH value of the wastewater at 5-7, and the fine adjustment tank controls the pH value at 8-9.

8. The method according to any one of claims 1 to 7, characterized in that S5 temperature is 50℃-100℃; And / or, the salt content of the supernatant in S5 is greater than 5%.

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