Method for purifying chlorination process titanium dioxide and byproduct hydrochloric acid by using sulfuric acid solution

Abstract

The method comprises the following steps: (a) adding a concentrated sulfuric acid solution and the byproduct hydrochloric acid into a reaction device, controlling the temperature in the reaction device to be 60-95 DEG C and the pressure to be 0.8-1.5 MPa, so that moisture in the byproduct hydrochloric acid is absorbed by concentrated sulfuric acid, and hydrochloric acid in the byproduct hydrochloric acid is separated out in a gaseous form; (b) condensing the hydrochloric acid gas separated out in the step (a) to obtain concentrated hydrochloric acid; and (c) controlling the temperature in the reaction device to be 100-140 DEG C and the pressure to be 0.8-1.2 MPa, and evaporating water in the concentrated sulfuric acid solution after water absorption in the reaction device to obtain the concentrated sulfuric acid solution. The method is simple and short in process, the purification efficiency of hydrochloric acid is higher than 85%, and meanwhile it is guaranteed that the concentration of hydrochloric acid is higher than 17.5%; and water in the sulfuric acid solution can be recycled in an evaporation manner, so that the sulfuric acid solution is recycled, and the energy consumption and the cost are greatly reduced.

Description

Technical Field

[0001] The invention relates to the technical field of by-product hydrochloric acid treatment, in particular to a method for purifying by-product hydrochloric acid produced by chlorination titanium dioxide by utilizing sulfuric acid solution. Background Art

[0002] The chemical name of titanium dioxide is titanium dioxide. It has high refractive index, ideal particle size distribution, excellent whiteness, gloss, dispersibility, wettability, hiding power, tinting power, weather resistance (light) and low oil absorption. It is a white pigment with excellent performance and is widely used in coatings, rubber, plastics, papermaking, printing inks, daily chemicals, electronics industry, micro-electromechanical and environmental protection industries. The chloride process for producing titanium dioxide is currently the main method for producing titanium dioxide in the world.

[0003] The chlorination method for producing titanium dioxide mainly involves mixing titanium-rich raw materials with petroleum coke, and then carrying out a chlorination reaction in a chlorination furnace to generate a mixture containing titanium tetrachloride. The mixture coming out of the top of the chlorination furnace is separated from slag and dust by a cyclone dust collector to obtain crude titanium tetrachloride; the VOCl contained in the crude titanium tetrachloride 3 Impurities such as vanadium are removed by reacting with mineral oil, etc., and refined titanium tetrachloride is obtained after distillation; refined titanium tetrachloride reacts with oxygen at high temperature to form titanium dioxide base material, and then high-grade rutile titanium dioxide is obtained after post-treatment. The principle of chlorination reaction is as follows:

[0004] TiO 2 +2C+2Cl 2 →TiCl 4 +2CO

[0005] TiO 2 +C+2Cl 2 →TiCl 4 +CO 2

[0006] Titanium tetrachloride will react with water to produce titanium dioxide during the subsequent distillation and hydrolysis process. The reaction equation is as follows:

[0007] TiCl 4 +2H 2 O→TiO 2 +4HCl

[0008] A large amount of by-product hydrochloric acid is produced during its production process. Since titanium concentrate is the main raw material for the production of titanium dioxide by the chloride process, its quality directly affects the impurities in the by-product hydrochloric acid. Common impurities in titanium concentrate include iron, silicon, aluminum, phosphorus, etc. These impurities will be converted into corresponding chlorides during the production process. The by-product hydrochloric acid contains impurities such as iron ions, heavy metal ions, chlorides, etc. Taking a hydrochloric acid test of the company as an example, the impurity concentration is Ti=23256mg / L, V=486mg / L, Fe=92.4mg / L, Si=74.9 / L, Al=56.3mg / L, Mg=34.3mg / L, CR=6.98mg / L, Mn=5.54mg / L, Ca=38.9mg / L. These impurities will affect the quality of hydrochloric acid and prevent it from being directly used in other production links. Therefore, it is very important to purify the by-product hydrochloric acid. The purified by-product hydrochloric acid can be used in chemical production, pharmaceutical production, food production, and other fields. Traditional purification methods have high energy consumption and low efficiency, and may cause the decomposition of hydrochloric acid during the heating process, affecting its quality. At present, the methods for recovering by-product hydrochloric acid include concentrated distillation, extraction, electrolysis, etc. These recovery and purification methods often consume a lot of energy and materials, resulting in high costs and a greater impact on the environment. A Chinese patent with publication number CN102515105A discloses a process for continuous extraction and distillation of concentrated hydrochloric acid. The method uses concentrated sulfuric acid as an extractant, and continuously adds dilute hydrochloric acid and concentrated sulfuric acid to a boiling distillation tower kettle at the same time. The strong water absorption of concentrated sulfuric acid is used to destroy HCl+H 2 O constant boiling point, increase HCl and H 2 The relative volatility of O, the HCl and H that are evaporated in the tower kettle exceed the azeotropic composition. 2 O is further separated in a distillation tower, and the top distillate is condensed to obtain concentrated hydrochloric acid, the top temperature is 107-108°C, the mass fraction of concentrated hydrochloric acid is 25-31%, the mass fraction of sulfuric acid in the bottom of the tower is 48-58%, and the temperature is 121-138°C. The diluted sulfuric acid is concentrated in vacuum and recycled. This method requires the distillation tower to be kept at boiling temperature, which consumes a lot of energy and may cause the decomposition of hydrochloric acid during the heating process, affecting its quality. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution, which can improve the purification efficiency of by-product hydrochloric acid and reduce energy consumption and cost.

[0010] The technical solution adopted by the present invention to solve the technical problem is: a method for purifying hydrochloric acid produced as a by-product of titanium dioxide produced by the chloride process by using a sulfuric acid solution, comprising the following steps:

[0011] (a) adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 60-95° C. and the pressure to 0.8-1.5 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid and the hydrochloric acid in the by-product hydrochloric acid is precipitated in a gaseous form;

[0012] (b) condensing the hydrochloric acid gas separated out in step (a) to obtain concentrated hydrochloric acid;

[0013] (c) controlling the temperature in the reaction device to 100-120° C. and the pressure to 0.8-1.0 MPa to evaporate the water in the concentrated sulfuric acid solution after absorbing water in the reaction device to obtain a concentrated sulfuric acid solution.

[0014] Furthermore, the concentrated sulfuric acid solution in step (c) is returned to step (a) for recycling.

[0015] Furthermore, the concentration of the concentrated sulfuric acid solution in step (a) is 75 to 99.5%.

[0016] Furthermore, the concentration of the by-product hydrochloric acid in step (a) is 15-30%.

[0017] Furthermore, in step (a), the volume ratio of the concentrated sulfuric acid solution to the by-product hydrochloric acid is 0.3 to 5:1.

[0018] Furthermore, the water vapor evaporated in step (c) is further processed or directly discharged into the atmosphere.

[0019] Further, when no bubbles are generated in step (c), the reaction is complete.

[0020] Furthermore, the reaction is completed when there are no bubbles or only low-frequency bubbles in step (a), wherein the low frequency is a bubble that is visible to the naked eye and is generated every ≥ 10 seconds.

[0021] The beneficial effects of the present invention are as follows: the method of the present invention is simple and has a short process; the purification efficiency of hydrochloric acid is greater than 85%; and the concentration of hydrochloric acid is ensured to be greater than 17.5%; water in the sulfuric acid solution can be recovered by evaporation, thereby realizing the reuse of the sulfuric acid solution and greatly reducing energy consumption and cost. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with embodiments.

[0023] Embodiment 1:

[0024] Take 100 mL of 98% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0025] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and HCl in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated HCl gas to obtain concentrated hydrochloric acid;

[0026] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0027] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 18.0%, and the hydrochloric acid purification efficiency (recovery rate) was 90%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 95%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 5g, and the sulfuric acid evaporation amount was 5mL.

[0028] Embodiment 2:

[0029] Take 100 mL of 85% sulfuric acid solution and 50 mL of 30% by-product hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0030] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.5 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0031] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0032] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 17.7%, and the hydrochloric acid purification efficiency was 86%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 83%, and the concentration of concentrated sulfuric acid solution after evaporation was 85%; the water vapor emission was 5g, and the sulfuric acid evaporation amount was 5mL.

[0033] Embodiment 3:

[0034] Take 100 mL of 98% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0035] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 70° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated HCl gas to obtain concentrated hydrochloric acid;

[0036] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0037] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 17.5%, and the hydrochloric acid purification efficiency was 85%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 96%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 4.6g, and the sulfuric acid evaporation amount was 5mL.

[0038] Embodiment 4:

[0039] Take 100 mL of 98% sulfuric acid solution and 50 mL of 15% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0040] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.0 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0041] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0042] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 17.6%, and the hydrochloric acid purification efficiency was 85%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 96%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 4.7g, and the sulfuric acid evaporation amount was 5mL.

[0043] Embodiment 5:

[0044] Take 100 mL of 98% sulfuric acid solution and 50 mL of 25% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0045] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0046] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0047] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 17.8%, and the hydrochloric acid purification efficiency was 87%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 96.3%, and the concentration of concentrated sulfuric acid solution after evaporation was 98.0%; the water vapor emission was 4.8g, and the sulfuric acid evaporation amount was 4mL.

[0048] Embodiment 6:

[0049] Take 100 mL of 90% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0050] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0051] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0052] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 17.6%, and the hydrochloric acid purification efficiency was 87%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 88%, and the concentration of concentrated sulfuric acid solution after evaporation was 90%; the water vapor emission was 4.7g, and the sulfuric acid evaporation amount was 4mL.

[0053] Embodiment 7:

[0054] Take 250 mL of 98% sulfuric acid solution and 50 mL of 20% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0055] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.5 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0056] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0057] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 18.4%, and the hydrochloric acid purification efficiency was 94%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 97%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 5.3g, and the sulfuric acid evaporation amount was 5.2mL.

[0058] Embodiment 8:

[0059] Take 100 mL of 98% sulfuric acid solution and 300 mL of 20% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0060] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0061] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 20° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0062] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 17.9%, and the hydrochloric acid purification efficiency was 84%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 93%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 10g, and the sulfuric acid evaporation amount was 5mL.

[0063] Comparative Example 1:

[0064] Take 100 mL of 70% sulfuric acid solution and 50 mL of 30% by-product hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0065] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0066] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0067] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 3%, and the hydrochloric acid purification efficiency was 13%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 69%, and the concentration of concentrated sulfuric acid solution after evaporation was 70%; the water vapor emission was 8g, and the sulfuric acid evaporation amount was 3mL.

[0068] Comparative Example 2:

[0069] Take 100 mL of 98% sulfuric acid solution and 50 mL of 10% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0070] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0071] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0072] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 8%, and the hydrochloric acid purification efficiency was 23%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 96%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 5.3g, and the sulfuric acid evaporation amount was 5mL.

[0073] Comparative Example 3:

[0074] Take 10 mL of 98% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0075] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0076] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0077] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 12.7%, and the hydrochloric acid purification efficiency was 48%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 92%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 8.8g, and the sulfuric acid evaporation amount was 6mL.

[0078] Comparative Example 4:

[0079] Take 100 mL of 98% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0080] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 40° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0081] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0082] The mass fraction of the hydrochloric acid obtained by condensation was measured to be 14.6%, and the hydrochloric acid purification efficiency was 54%; the concentration of the concentrated sulfuric acid solution after reaction with the by-product hydrochloric acid was 90%, and the concentration of the concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 20g, and the sulfuric acid evaporation amount was 3mL.

[0083] Comparative Example 5:

[0084] Take 100 mL of 98% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0085] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 95° C. and the pressure to 0.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and the hydrochloric acid in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated hydrochloric acid gas to obtain concentrated hydrochloric acid;

[0086] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0087] The mass fraction of the hydrochloric acid obtained by condensation was measured to be 14%, and the hydrochloric acid purification efficiency was 50%; the concentration of the concentrated sulfuric acid solution after reaction with the by-product hydrochloric acid was 92%, and the concentration of the concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 17g, and the sulfuric acid evaporation amount was 2mL.

[0088] Comparative Example 6:

[0089] Take 100 mL of 98% sulfuric acid solution and 50 mL of 30% byproduct hydrochloric acid for later use, and use a corrosion-resistant three-necked flask as a reaction device;

[0090] Adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 105° C. and the pressure to 1.2 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid, and HCl in the by-product hydrochloric acid is precipitated in gaseous form, and condensing the precipitated HCl gas to obtain concentrated hydrochloric acid;

[0091] When there are no bubbles in the reaction device, evaporation is performed, and the temperature in the reaction device is controlled to be 120° C. and the pressure is controlled to be 1.0 MPa, so that the water in the concentrated sulfuric acid solution after absorbing water in the reaction device is evaporated to obtain a concentrated sulfuric acid solution. The experiment is terminated when no bubbles are generated in the reaction device.

[0092] The mass fraction of concentrated hydrochloric acid obtained by condensation was measured to be 18.1%, and the hydrochloric acid purification efficiency (recovery rate) was 82%; the concentration of concentrated sulfuric acid solution after reaction with by-product hydrochloric acid was 97%, and the concentration of concentrated sulfuric acid solution after evaporation was 98%; the water vapor emission was 2g, and the sulfuric acid evaporation amount was 2mL.

[0093] Table 1 Parameters after reaction of Examples and Comparative Examples

[0094]

[0095] It can be seen from Table 1 that the purification efficiency of hydrochloric acid in the embodiment of the present invention is greater than 85%, while ensuring that the concentration of hydrochloric acid is greater than 17.5%.

Claims

1. A method for purifying hydrochloric acid produced as a by-product of titanium dioxide produced by the chloride process using a sulfuric acid solution, characterized in that: The following steps are involved: (a) adding concentrated sulfuric acid solution and by-product hydrochloric acid into a reaction device, controlling the temperature in the reaction device to 60-95° C. and the pressure to 0.8-1.5 MPa so that the water in the by-product hydrochloric acid is absorbed by the concentrated sulfuric acid and the hydrochloric acid in the by-product hydrochloric acid is precipitated in a gaseous form; (b) condensing the hydrochloric acid gas precipitated in step (a) to obtain concentrated hydrochloric acid; (c) controlling the temperature in the reaction device to 100-140° C. and the pressure to 0.8-1.2 MPa to evaporate the water in the concentrated sulfuric acid solution after absorbing water in the reaction device to obtain a concentrated sulfuric acid solution.

2. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 1, characterized in that: The concentrated sulfuric acid solution in step (c) is returned to step (a) for recycling.

3. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 1, characterized in that: The concentration of the concentrated sulfuric acid solution in step (a) is 75-99.5%.

4. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 1, characterized in that: The concentration of the by-product hydrochloric acid in step (a) is 15-30%.

5. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 1, characterized in that: In step (a), the volume ratio of concentrated sulfuric acid solution to by-product hydrochloric acid is 0.3 to 5:

1.

6. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 2, characterized in that: The water vapor evaporated in step (c) is further processed or discharged directly into the atmosphere.

7. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 1, characterized in that: When no bubbles are generated in step (c), the reaction is complete.

8. The method for purifying hydrochloric acid produced as a by-product of chloride process titanium dioxide by using sulfuric acid solution according to claim 1, characterized in that: When there are no bubbles or only low-frequency bubbles in step (a), the reaction is complete.

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