A method for removing trace impurities from high-concentration by-product hydrochloric acid

Abstract

The present invention discloses a method for removing trace impurities from highly concentrated by-product hydrochloric acid. The method involves filtering the by-product hydrochloric acid from the sulfur process to remove most of the sulfur particles. The sulfur particles are discharged through a slag discharge port at the lower end of the membrane filter and then introduced into a storage tank for the by-product hydrochloric acid from the acetic anhydride process. The free chlorine in the by-product hydrochloric acid from the acetic anhydride process is used to oxidize low-cost sulfur-containing impurities in the by-product hydrochloric acid from the sulfur process. The resulting disulfur dichloride is then hydrolyzed to produce elemental sulfur and sulfur dioxide. The sulfur dioxide reacts with water to produce sulfurous acid. The free chlorine reacts with sulfite to produce sulfurous acid, and the chlorine gas is intercepted by a redox reaction. After precise filtration and oxidation, the free chlorine in the by-product hydrochloric acid can be intercepted, improving the quality of the by-product hydrochloric acid from the sulfur process. The resulting sulfur particles are then dehydrated and dried and recycled into glyphosate production. The by-product hydrochloric acid is then reused in glyphosate production, without affecting the quality and yield of glyphosate and without generating any odor.

Description

Technical Field

[0001] The invention discloses a technology for removing trace impurities in high-concentration by-product hydrochloric acid, belongs to the field of chemical production technology, and particularly relates to intercepting impurities such as residual chlorine and sulfur in the by-product hydrochloric acid of chloroacetic acid so that the impurities can be reused in glyphosate production. Background Art

[0002] Currently, domestic chloroacetic acid manufacturers mostly use glacial acetic acid as the raw material and sulfur powder or acetic anhydride as the catalyst. A chlorination reaction is carried out by passing chlorine gas. The chlorinated solution is cooled, crystallized, and filtered to produce the chloroacetic acid crystal product. The production of chloroacetic acid using both different catalysts is accompanied by the generation of large amounts of off-gas. Hydrogen chloride is the primary component (approximately 80%). Industrial production of 1 ton of chloroacetic acid produces approximately 1.5 tons of hydrochloric acid with a concentration of approximately 30%. The off-gas from the sulfur-based chloroacetic acid production process contains not only hydrogen chloride but also various impurities and unreacted products from side reactions, including sulfur particles, SO₂, SO₃, Cl₂, and CH₃COOH. Patent application CN109231168B, entitled "Method for Reducing the Content of Sulfuric Acid in Hydrochloric Acid and Acetic Acid Byproducts in Chloroacetic Acid Production," discusses impurities in hydrochloric acid produced as a byproduct of the sulfur-based process. However, the off-gas from the acetic anhydride-based chloroacetic acid production process contains, in addition to hydrogen chloride, Cl₂ and CH₃COOH. The invention with publication number CN108100996A, entitled "System and method for treating by-product HCl in a continuous chloroacetic acid production process", provides relevant descriptions of impurities in hydrochloric acid produced as a by-product in the acetic anhydride process.

[0003] Currently, factories use falling-film absorbers to recover acetic acid and hydrochloric acid. However, the recovered hydrochloric acid still contains sulfur, SO₂, SO₃, Cl₂, etc., and can only be treated as waste acid. Excessive sulfur accumulation can clog pipelines, seriously affecting the company's economic benefits and resource utilization. Therefore, the present invention aims to remove low-cost sulfur-containing impurities from the by-product hydrochloric acid, allowing the waste acid to be reused for glyphosate dealcoholization. Simultaneously, the sulfur is recovered and recycled for use in chloroacetic acid production, thereby achieving the goals of protecting the environment, reducing costs, and maximizing the value of the waste acid and sulfur.

[0004] The invention, published with publication number CN108854490B and titled "A Process for Purifying Chloroacetic Acid Tail Gas and Desulfurizing Byproduct Hydrochloric Acid," primarily involves passing the tail gas from chloroacetic acid production through a first and second desulfurization and dechlorination tower, where it is sprayed and absorbed using an aqueous FeCl3·6H2O solution containing ferric chloride at a concentration of 0.1-0.5 mol / L. This process requires the addition of ferric chloride, introducing new impurities and increasing production costs. It also hinders the recycling of hydrochloric acid and poses a certain degree of environmental pollution.

[0005] The invention patent, publication number CN102249189A, entitled "A Method for Recovering Hydrochloric Acid in Chloroacetic Acid Production," primarily involves passing chloroacetic acid tail gas through a desulfurization tower, followed by water washing and absorption to produce first-grade hydrochloric acid. The operating pressure is 0.1-0.4 MPa, and the temperature for washing and absorbing the hydrochloric acid is 300-500°C. However, this method has disadvantages such as high energy consumption and large water consumption. Summary of the Invention

[0006] The present invention provides a technology for removing trace impurities from highly concentrated by-product hydrochloric acid. This process treats free chlorine and impurities such as SO₂, SO₃, and sulfur in the hydrochloric acid produced as a by-product of chloroacetic acid production, improving its quality and enabling its reuse in glyphosate production. Furthermore, sulfur particles are recovered for use in chloroacetic acid production. The process achieves high dechlorination and desulfurization rates, is highly operational, and transforms waste into a sustainable resource, thoroughly resolving environmental issues and maximizing the value of waste.

[0007] To implement the present invention, the following technical solution is adopted, comprising the following steps:

[0008] (1) The tail gas from chloroacetic acid synthesis is sequentially washed with acetic acid, desulfurized and dechlorinated, and then washed with hydrochloric acid to produce a hydrochloric acid solution as a by-product;

[0009] (2) The by-product hydrochloric acid solution is filtered through a membrane;

[0010] (3) The hydrochloric acid solution after membrane filtration is passed into the by-product hydrochloric acid of the acetic anhydride method for oxidation to obtain high-concentration by-product hydrochloric acid.

[0011] Acetic acid and hydrochloric acid scrubbing units were added to the existing sulfur-based chloroacetic acid production unit to reduce impurity levels in the exhaust gas at the source. The hydrochloric acid produced by the scrubbing units, used in glyphosate synthesis, produces a strong sulfur odor. Testing and analysis determined that this was due to the oxidation of residual sulfur and sulfide in the hydrochloric acid to sulfur dioxide, which then converted to sulfurous acid. Furthermore, the storage tanks leading to the by-product hydrochloric acid were frequently clogged with sulfur particles. Therefore, a membrane filtration unit was installed between the points where the by-product hydrochloric acid enters the hydrochloric acid storage tanks to filter the hydrochloric acid produced by the sulfur-based chloroacetic acid production process, intercepting solid impurities such as sulfur. This filtration removes most of the sulfur particles, reducing the turbidity from 10-100 NTU to below 2 NTU. Residual free chlorine in the by-product hydrochloric acid produced by the acetic anhydride process was used to oxidize the sulfite to sulfate. The resulting purified hydrochloric acid was then reused in the glyphosate dealcoholation experiment.

[0012] In the present invention, the chloroacetic acid synthesis tail gas is hydrochloric acid tail gas produced as a by-product of the sulfur process, and the by-product hydrochloric acid tail gas contains 30-35% hydrochloric acid, SO2, SO3, and sulfur. The composition of the by-product hydrochloric acid tail gas is described in detail in the invention with publication number CN108854490B, entitled "Process for Purifying Chloroacetic Acid Tail Gas and Desulfurizing By-product Hydrochloric Acid."

[0013] The three-stage acetic acid washing, two-stage desulfurization and dechlorination, and three-stage hydrochloric acid washing processes described in the present invention are described in detail in the invention with publication number CN108854490B, entitled "A process for purifying chloroacetic acid tail gas and desulfurizing by-product hydrochloric acid."

[0014] The precision filtration device is made of polyethylene tube, with a pressure difference of 0.01-0.1MPa (stable at about 0.08MPa). In the environment of high-concentration by-product hydrochloric acid, it can prevent membrane corrosion and is pressure-resistant and anti-deformation. The flow rate of by-product hydrochloric acid solution filtered by the precision filtration device is 0.5-2 m 3 The filtered sulfur is discharged from the slag outlet and then recycled for chloroacetic acid production after drying and other operations.

[0015] The physicochemical properties of the hydrochloric acid produced as a byproduct of the acetic anhydride process are characterized by a free chlorine content of 800-1000 ppm. However, the tail gas from chloroacetic acid produced by the acetic anhydride process contains, in addition to hydrogen chloride, Cl₂ and CH₃COOH. Patent application CN108100996A, entitled "System and Method for Treating Byproduct HCl in a Continuous Chloroacetic Acid Production Process," provides information on impurities in the hydrochloric acid produced as a byproduct of the acetic anhydride process.

[0016] The acetic anhydride method produces hydrochloric acid with a by-product of 3-6 m 3 / h (in some preferred cases the speed is 3-6m 3 / h, more preferably 5-6m 3 / h) is introduced into the hydrochloric acid solution after membrane filtration, and the oxidation rate is accelerated by stirring in the mixed hydrochloric acid storage tank (i.e., the newly added hydrochloric acid storage tank described in the embodiment) to achieve impurity removal.

[0017] In the present invention, the residual free chlorine in the hydrochloric acid by-product of the acetic anhydride process is used to oxidize the low-valent sulfur-containing impurities in the hydrochloric acid by-product of the sulfur process. The sulfur reacts with chlorine to undergo a redox reaction to remove the residual sulfur. The resulting disulfur dichloride is then hydrolyzed to produce elemental sulfur and sulfur dioxide. The sulfur dioxide reacts with water to produce sulfurous acid. The free chlorine reacts with sulfite to undergo a redox reaction to intercept the chlorine. This achieves two goals at once: intercepting chlorine and removing sulfur.

[0018] The chemical equation of the reaction is:

[0019] 2S + Cl2 = S2Cl2;

[0020] S2Cl2+ H2O= S + SO2;

[0021] SO2+ H2O = H2SO3;

[0022] SO32- + Cl2+ H2O = SO42- + 2H+ + 2Cl-.

[0023] The refined hydrochloric acid obtained in the present invention is used in a glyphosate dealcoholization test, where the methanol is removed by reacting the synthetic liquid after glyphosate synthesis and depolymerization with the refined hydrochloric acid. When the sulfite content is below 1500 ppm, there is no significant impact on the yield, quality, or odor of glyphosate synthesis, and the product can be used for glyphosate dealcoholization.

[0024] The present invention has the following characteristics:

[0025] (1) After adding acetic acid washing and hydrochloric acid washing devices, the content of acetic acid and hydrochloric acid in the exhaust gas was greatly reduced.

[0026] (2) It can effectively remove sulfide, sulfate ions and free chlorine in the by-product hydrochloric acid, and significantly improve the quality of the by-product hydrochloric acid.

[0027] (3) This process does not introduce new reagents, the equipment is simple and the operability is strong.

[0028] (4) The by-product hydrochloric acid can be fully used in the dealcoholization of glyphosate industry, reducing the pressure on hydrochloric acid storage in chloroacetic acid enterprises and turning waste into treasure. DETAILED DESCRIPTION

[0029] The technical features of the present invention are further described in detail below with reference to the embodiments:

[0030] Taking steps (1), (2), and (3) in the process for purifying chloroacetic acid tail gas and desulfurizing by-product hydrochloric acid in CN108854490B as the relevant steps in this case, the following test was conducted:

[0031] The tail gas of chloroacetic acid synthesis reactor is about 2000m 3 / h, and successively passes through acetic acid recovery tower 1 (gas pressure at tower outlet is about 0.1Mpa, temperature is about 25℃), acetic acid recovery tower 2 (gas pressure at tower outlet is about 0.1Mpa, temperature is about 28℃), acetic acid recovery tower 3 (gas pressure at tower outlet is about 0.09Mpa, temperature is about 29℃), acetic acid recovery tower 4, desulfurization and dechlorination tower 1, desulfurization and dechlorination tower 2, hydrochloric acid absorption tower 1 (gas pressure at tower outlet is about 0.065Mpa, temperature is about 42℃), hydrochloric acid absorption tower 2 (gas pressure at tower outlet is about 0.03Mpa, temperature is about 58℃), hydrochloric acid absorption tower 3, and by-product hydrochloric acid solution, which is then connected to the precision membrane filtration device through a pipeline with a pressure difference of 0.01-0.1MPa (stable at about 0.08Mpa) and a flow rate of 1m 3 / h, the filtered hydrochloric acid is introduced into the newly added hydrochloric acid storage tank, and at the same time, the hydrochloric acid is added into the newly added hydrochloric acid storage tank at a rate of 4m 3 The by-product hydrochloric acid of the acetic anhydride process (the tail gas mixture of Example 1 in CN 108100996A) was introduced at a rate of 100 ppm / h to remove trace impurities in the high-concentration by-product hydrochloric acid.

[0032] The comparison of the implementation effect after using the above process for membrane filtration and oxidation of the by-product hydrochloric acid produced by the acetic anhydride method on the by-product hydrochloric acid produced by the sulfur method is as follows:

[0033]

[0034] Note: Before membrane filtration refers to the hydrochloric acid produced as a by-product of the sulfur process that has not passed through a precision membrane filtration device.

[0035] After membrane filtration refers to the hydrochloric acid produced as a by-product of the sulfur process after it has passed through a precision membrane filtration device.

[0036] The newly added refers to the by-product hydrochloric acid produced by the acetic anhydride method after the by-product hydrochloric acid is oxidized by the by-product hydrochloric acid of the sulfur method.

[0037] From the above experimental data, it can be seen that when the by-product hydrochloric acid obtained by the sulfur process without membrane filtration is passed into the by-product hydrochloric acid of the acetic anhydride process, the SO32- concentration in the newly obtained hydrochloric acid drops from 14092ppm to 8560ppm; and after membrane filtration, the turbidity of the by-product hydrochloric acid of the sulfur process drops from 99NTU to 0.91NTU, preventing sulfur particles from entering the downstream, and the SO32- concentration in the newly obtained hydrochloric acid drops from 14092ppm to 734ppm, greatly reducing the sulfur-containing impurities in the by-product hydrochloric acid.

[0038] Examples 5-8

[0039] The method and steps are the same as in Example 1, except that the by-product hydrochloric acid produced by the sulfur process is introduced at a speed of 1 m 3 / h (low-cost sulfur-containing impurities in Example 1 of CN108854490B), Examples 5, 6, 7, and 8 were 1m 3 / h、3m3 / h、5m 3 / h、6m 3 The hydrochloric acid produced as a by-product of the acetic anhydride process (the tail gas mixture in Example 1 of CN 108100996 A) was introduced at a rate of / h. The experimental results are as follows:

[0040]

[0041] For the above Examples 5-8, the by-product highly concentrated hydrochloric acid was oxidized to remove low-valent sulfides as described above and then reused in glyphosate production. The results are as follows:

[0042]

[0043] From the above test data, it can be seen that the injection speed of hydrochloric acid produced as a by-product of the sulfur process is 1 m 3 / h, the introduction rate of hydrochloric acid produced as a by-product of the acetic anhydride process is 4m 3 / h, and when the sulfite content in the high-concentration by-product hydrochloric acid after oxidation treatment is below 800ppm, it has no impact on glyphosate production and can be recycled into glyphosate production.

Claims

1. A method for removing trace impurities from high-concentration by-product hydrochloric acid, characterized in that: The steps include: (1) The chloroacetic acid synthesis tail gas is sequentially subjected to acetic acid washing, desulfurization and dechlorination, and hydrochloric acid washing to obtain a by-product hydrochloric acid solution. The chloroacetic acid synthesis tail gas is a by-product hydrochloric acid tail gas produced by the sulfur process, and the by-product hydrochloric acid tail gas contains 30-35% hydrochloric acid, as well as SO2, SO3, and sulfur; (2) The by-product hydrochloric acid solution is filtered through a membrane; (3) The hydrochloric acid solution after membrane filtration is passed into the by-product hydrochloric acid of the acetic anhydride method for oxidation to obtain high-concentration by-product hydrochloric acid. The physical and chemical properties of the by-product hydrochloric acid of the acetic anhydride method are that the free chlorine content is 800-1000ppm, while the tail gas of the chloroacetic acid produced by the acetic anhydride method contains 90-96% hydrogen chloride, as well as Cl2 and CH3COOH.

2. The method for removing trace impurities from high-concentration by-product hydrochloric acid according to claim 1, characterized in that: The acetic acid washing, desulfurization and dechlorination, and hydrochloric acid washing processes in step (1) are as follows: (1) Chloroacetic acid synthesis tail gas is first recovered by acetic acid recovery one tower, acetic acid recovery two towers, and acetic acid recovery three towers to recycle the acetic acid in the tail gas, and the acetic acid recovered continues to return to the chloroacetic acid synthesis reactor for recycling; (2) The tail gas after recovering acetic acid in step (1) is then passed through a first desulfurization and dechlorination tower and a second desulfurization and dechlorination tower to intercept sulfur dioxide and excess chlorine in the tail gas. An oxidant is added to the first desulfurization and dechlorination tower and the second desulfurization and dechlorination tower. The oxidant is an aqueous solution of ferric chloride, and the molar concentration of iron ions is 0.5 mol / L. The gas pressure of the first desulfurization and dechlorination tower is 0.06-0.09 MPa and the temperature is 30-40°C; the gas pressure of the second desulfurization and dechlorination tower is 0.06-0.09 MPa and the temperature is 30-35°C. (3) The tail gas after intercepting the sulfur dioxide and excess chlorine in the tail gas is then passed through the hydrochloric acid absorption tower 1 and the hydrochloric acid absorption tower 2 to recover the hydrogen chloride gas, thereby obtaining the by-product hydrochloric acid solution.

3. The method for removing trace impurities in high-concentration by-product hydrochloric acid according to claim 1, characterized in that: The membrane filtration in step (2) is a precision filtration device, wherein the precision filtration device is made of polyethylene tubes with a pressure difference of 0.01-0.1 MPa. In an environment with high concentration of by-product hydrochloric acid, the membrane can be prevented from corrosion and is pressure-resistant and deformation-resistant. The flow rate of the by-product hydrochloric acid solution filtered by the precision filtration device is 0.5-2 m 3 / h, the filtered sulfur is released from the slag outlet, and then recycled for chloroacetic acid production after drying.

4. The method for removing trace impurities from high-concentration by-product hydrochloric acid according to claim 1, characterized in that: The by-product hydrochloric acid of acetic anhydride method is 3-6m 3 / h is introduced into the hydrochloric acid solution after membrane filtration, and the oxidation process is realized and impurities are removed through stirring in the mixed hydrochloric acid storage tank.

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