A method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride

Abstract

The present invention relates to a method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride, comprising the following steps: (1) adding a certain amount of sodium fluoride and other sodium salt powders to waste acid containing hydrofluoric acid to carry out a fluorination reaction; (2) filtering after the fluorination reaction, drying the sodium hydrogen fluoride filter cake to remove surface water and then introducing it into a sodium hydrogen fluoride decomposition furnace for decomposition; (3) part of the sodium hydrogen fluoride filtrate is used to prepare sodium fluoride slurry, and part is neutralized; (4) the hydrogen fluoride gas generated by the decomposition of sodium hydrogen fluoride is refined through condensation and refining processes to obtain anhydrous hydrogen fluoride products. The treatment method of the present invention is simple, low in cost, and high in recovery efficiency, and is suitable for industrial promotion and application; the present invention converts fluorine-containing waste acid into fluorine products with high added value and market demand, which not only solves the problem of warehouse expansion in enterprises, but also realizes the recycling of fluorine resources.

Description

Technical Field

[0001] The invention relates to a method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride, belonging to the technical field of waste acid liquid recovery and utilization. Background Art

[0002] Low-concentration waste hydrofluoric acid is a byproduct waste acid produced by the fluorination process using anhydrous hydrogen fluoride, such as R22 production waste acid (HF content 10-18%). In recent years, various process technologies have been used to transform fluorine-containing wastewater or waste liquid of fluorosilicic acid into high value-added products, which can not only achieve the maximum utilization of resources and effectively curb fluorine pollution, but also help protect fluorite resources, and play an important role in promoting the development of my country's fluorine chemical industry.

[0003] At present, the general method of treating low-concentration waste hydrofluoric acid is to make other low-value-added fluoride salts (such as potassium fluoride, cryolite, etc.), or to prepare pickling liquid for cleaning metal surfaces. On the one hand, the treatment of this waste acid is subject to the market restrictions of fluoride salts and pickling liquids, and the phenomenon of warehouse expansion often occurs, causing the R22 production line to stop, affecting the normal production of the enterprise; on the other hand, the process is complicated and the treatment cost is high, which is not conducive to large-scale promotion. Summary of the invention

[0004] The invention provides a method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride, which solves the problems of small scale, high cost and complex process of existing low-concentration waste hydrofluoric acid treatment process.

[0005] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0006] A method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride comprises the following steps:

[0007] (1) adding a certain amount of sodium fluoride and other sodium salt powders to waste acid containing hydrofluoric acid to carry out a fluorination reaction;

[0008] (2) filtering after the fluorination reaction, drying the sodium bifluoride filter cake to remove surface water, and then introducing it into a sodium bifluoride decomposition furnace for decomposition to obtain hydrogen fluoride gas and sodium fluoride powder, and returning the sodium fluoride powder to the fluorination reaction kettle for reaction;

[0009] (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water;

[0010] (4) The hydrogen fluoride gas produced by the decomposition of sodium hydrogen fluoride is refined through condensation and refining processes to obtain anhydrous hydrogen fluoride product.

[0011] In some embodiments: based on weight ratio, the dosage of sodium fluoride is 2.1-2.5 times the amount of HF in the waste acid.

[0012] In some embodiments: the other sodium salt powder is a mixture of one or more of sodium chloride, sodium sulfate and sodium nitrate, which is specifically determined according to the type of impurity acid in the low-concentration hydrofluoric acid.

[0013] In some embodiments: based on the weight ratio, the dosage of the other sodium salt powder is 0.3-2.5 times the amount of HF in the waste acid.

[0014] In some embodiments: the drying temperature of sodium bifluoride is controlled below 80°C, and the decomposition temperature of sodium bifluoride is controlled between 160 and 250°C.

[0015] In some embodiments: the drying temperature of the sodium bifluoride is 2-5h, and the decomposition time of the sodium bifluoride is 8-20h.

[0016] In some embodiments: the fluorination reaction time is 1-3 hours.

[0017] Beneficial effects of the present invention:

[0018] Compared with the prior art, the present invention has the following beneficial effects:

[0019] (1) The treatment method of the present invention is simple, low in cost, and high in recovery efficiency, and is suitable for industrial promotion and application.

[0020] (2) The present invention converts fluorine-containing waste acid into fluorine products with high added value and market demand, which not only solves the problem of overstocking in enterprises, but also realizes the recycling of fluorine resources.

[0021] (3) The present invention recovers waste acid containing hydrofluoric acid, wherein the yield of hydrofluoric acid can reach more than 98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0024] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] like Figure 1 As shown, a method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride comprises the following steps:

[0026] (1) adding a certain amount of sodium fluoride and other sodium salt powders to waste acid containing hydrofluoric acid to carry out a fluorination reaction;

[0027] (2) filtering after the fluorination reaction, drying the sodium bifluoride filter cake to remove surface water, and then introducing it into a sodium bifluoride decomposition furnace for decomposition to obtain hydrogen fluoride gas and sodium fluoride powder, and returning the sodium fluoride powder to the fluorination reaction kettle for reaction;

[0028] (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water;

[0029] (4) The hydrogen fluoride gas produced by the decomposition of sodium bifluoride is refined through condensation and refining processes to obtain anhydrous hydrogen fluoride product. The composition of the waste acid containing hydrofluoric acid in the following examples is: HF-18.0%, HCl-2.8%, H2O-balance. According to the composition of the acid solution, the other sodium salt powder added is sodium chloride powder. If the waste acid contains sulfuric acid, sodium sulfate powder is added, and if it contains nitric acid, sodium nitrate is added. If it is a mixed acid, mixed sodium salt powder is added.

[0030] Example 1

[0031] A method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride comprises the following steps:

[0032] (1) 4000 g of waste acid containing hydrofluoric acid was added to a reaction kettle, and 1950 g of sodium fluoride and 4600 g of sodium chloride powder were added under stirring to carry out a fluorination reaction for 2 hours;

[0033] (2) After the fluorination reaction, the filter cake was filtered to control the moisture content of the wet filter cake to less than 0.5%, and 2940 g of the wet filter cake was produced. The sodium bifluoride filter cake was dried at 80° C. for 2 h to remove surface water, and then introduced into a sodium bifluoride decomposition furnace at 200° C. for decomposition for 12 h to obtain hydrogen fluoride gas and sodium fluoride powder. The sodium fluoride powder was returned to the fluorination reaction kettle for reaction;

[0034] (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water;

[0035] (4) The hydrogen fluoride gas generated by the decomposition of sodium bifluoride is condensed to obtain 650.1 g of hydrofluoric acid. The condensed hydrofluoric acid has an HF content of 99.25% and an H2O content of 0.75%. The HF recovery rate is calculated to be 89.6%;

[0036] Example 2

[0037] A method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride comprises the following steps:

[0038] (1) 4000 g of waste acid containing hydrofluoric acid was added to a reaction kettle, and 830 g of sodium chloride powder, 1980 g of the decomposition material in Example 1 (sodium fluoride powder and crystals) and 14720 g of the sodium bifluoride filtrate in Example 1 were added under stirring to carry out a fluorination reaction for 3 hours;

[0039] (2) After the fluorination reaction, the filter cake was filtered to control the moisture content of the wet filter cake to less than 0.5%, and 2945 g of the wet filter cake was produced. The sodium bifluoride filter cake was dried at 80° C. for 5 h to remove surface water, and then introduced into a sodium bifluoride decomposition furnace at 220° C. for decomposition for 8 h;

[0040] (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water;

[0041] (4) The hydrogen fluoride gas produced by the decomposition of sodium bifluoride was condensed to obtain 714.0 g of hydrofluoric acid, with an HF content of 99.35% and an H2O content of 0.65%. The HF recovery rate was measured to be 98.4%.

[0042] Example 3

[0043] A method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride comprises the following steps:

[0044] (1) 4000 g of waste acid containing hydrofluoric acid was added to a reaction kettle, and 830 g of sodium chloride powder, 1965 g of the decomposition material in Example 2 (sodium fluoride powder and crystals) and 14720 g of the sodium bifluoride filtrate in Example 2 were added under stirring to carry out a fluorination reaction for 2 hours;

[0045] (2) After the fluorination reaction, the filter cake was filtered to control the moisture content of the wet filter cake to less than 0.5%, and 2945 g of the wet filter cake was produced. The sodium bifluoride filter cake was dried at 80° C. for 5 h to remove surface water, and then introduced into a sodium bifluoride decomposition furnace at 220° C. for decomposition for 8 h;

[0046] (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water;

[0047] (4) The hydrogen fluoride gas produced by the decomposition of sodium bifluoride was condensed to obtain 714.2 g of hydrofluoric acid, with an HF content of 99.25% and a H2O content of 0.75%. The HF recovery rate was measured to be 98.4%.

[0048] Example 4

[0049] A method for recovering low-concentration hydrofluoric acid to prepare anhydrous hydrogen fluoride comprises the following steps:

[0050] (1) 4000 g of waste acid containing hydrofluoric acid was added to a reaction kettle, and 350 g of sodium chloride powder, 1910 g of the decomposition material in Example 3 (sodium fluoride powder and crystals) and 9000 g of the sodium bifluoride filtrate in Example 3 were added under stirring to carry out a fluorination reaction for 3 hours;

[0051] (2) After the fluorination reaction, the filter cake was filtered to control the moisture content of the wet filter cake to less than 0.5%, and 2910 g of the wet filter cake was produced. The sodium bifluoride filter cake was dried at 80° C. for 3 h to remove surface water, and then introduced into a sodium bifluoride decomposition furnace at 210° C. for decomposition for 12 h;

[0052] (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water;

[0053] (4) The hydrogen fluoride gas produced by the decomposition of sodium bifluoride was condensed to obtain 706.2 g of hydrofluoric acid, with an HF content of 99.55% and a H2O content of 0.45%. The HF recovery rate was measured to be 97.4%.

[0054] Although the embodiments of the present invention have been described above, it will be apparent to those skilled in the art that modifications and substitutions made without departing from the principles and spirit of the present invention are intended to fall within the scope of protection claimed by the present invention.

Claims

1. A method for recovering low-concentration hydrofluoric acid to produce anhydrous hydrogen fluoride, characterized in that: The following steps are involved: (1) adding a certain amount of sodium fluoride and other sodium salt powders to waste acid containing hydrofluoric acid to carry out a fluorination reaction; the other sodium salt powders are one or a mixture of sodium chloride, sodium sulfate and sodium nitrate; the amount of sodium fluoride added is 2.1-2.5 times the amount of HF in the waste acid according to the weight ratio; the amount of other sodium salt powders added is 0.3-2.5 times the amount of HF in the waste acid according to the weight ratio; the fluorination reaction time is 1-3 hours; (2) filtering after the fluorination reaction, drying the sodium bifluoride filter cake to remove surface water, and then introducing it into a sodium bifluoride decomposition furnace for decomposition to obtain hydrogen fluoride gas and sodium fluoride powder, and returning the sodium fluoride powder to the fluorination reaction kettle for reaction; (3) Part of the sodium bifluoride filtrate is used to prepare sodium fluoride slurry, and part of it is used for neutralization; the filtrate used for preparing the slurry is controlled to have a solid content of 18-22% by weight; when used for neutralization, the pH value of the neutralized liquid is controlled to be greater than 7.5, and after neutralization, it is sent to a multiple-effect evaporation system for concentration and dehydration, and the crystals separated by the multiple-effect evaporation are returned to the fluorination reactor for reaction, and the condensate produced by the multiple-effect evaporator can be reused as clean water; (4) The hydrogen fluoride gas produced by the decomposition of sodium hydrogen fluoride is refined through condensation and refining processes to obtain anhydrous hydrogen fluoride product.

2. The method for preparing anhydrous hydrogen fluoride by recovering low-concentration hydrofluoric acid according to claim 1, characterized in that: The drying temperature of the sodium bifluoride is controlled below 80°C, and the decomposition temperature of the sodium bifluoride is controlled between 160 and 250°C.

3. The method for preparing anhydrous hydrogen fluoride by recovering low-concentration hydrofluoric acid according to claim 2, characterized in that: The drying temperature of the sodium bifluoride is 2-5h, and the decomposition time of the sodium bifluoride is 8-20h.

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