RU2243158C2 - Lithium hydroxide chlorination method - Google Patents

Abstract

FIELD: industrial inorganic synthesis.

SUBSTANCE: method of chlorination lithium hydroxide solution with chlorine/air mixture comprises four-step contacting of chlorine/air mixture with lithium hydroxide solution in presence of iron-nickel catalyst. Chlorination of lithium hydroxide solution is accomplished in the first two contacting steps (first and second absorbers) to achieve acid medium (pH ≤5.5) and thereby lithium carbonate precipitate formed upon chlorination is converted into soluble lithium chloride. Alkaline medium in third and fourth contacting steps (3^rd and 4^th absorbers) provide required chlorine trapping degree. Periodically, without stopping gas treatment process, direction of feeding of solution and chlorine/air mixture is changed. Thereafter, lithium hydroxide solution is chlorinated in 3rd and 4th absorbers to acid medium (pH ≤5.5).

EFFECT: achieved complete chlorination of lithium hydroxide, omitted clogging of pipelines and equipment with lithium carbonate and avoided use of aqueous hydrochloric acid in chlorination steps.

2 dwg

Description

The invention relates to the field of chemical industry, and in particular to methods of chlorination of alkaline reagents and can be used, for example, in the chlorination of lithium carbonate pulp.

In the production of lithium chloride by the method of chlorination of lithium hydroxide, a countercurrent solution of lithium alkali and a chlorine-air mixture is used through cyclone-foam apparatuses. In addition to obtaining the target product (lithium chloride solution), gas is purged from chlorine from the electrolysis baths.

In this regard, methods that make it possible to efficiently use an alkaline reagent for purification of waste gases from chlorine, prevent clogging of process pipelines and equipment with the resulting precipitation of lithium carbonate, and increase the operation life of the installation are very relevant.

The technology for producing a lithium chloride solution includes chlorination in the presence of an iron-nickel catalyst of lithium hydroxide or lithium carbonate with a chlorine-air mixture leaving the electrolysis baths, chemical cleaning of the obtained lithium chloride solution, its filtration and evaporation.

A known method of obtaining a solution of lithium chloride by chlorination of lithium hydroxide. (Lithium, its chemistry and technology. Ostroushko Yu.I. et al. - M.: Atomizdat, 1960, p. 59). The reaction of lithium hydroxide with chlorine occurs

2LiOH + Cl ₂ → LiClO + LiCl + Н ₂ О

The closest to the proposed method by technical nature and the achieved result is the prototype, patent 2186729, MKI C 01 D 15/04, 08/10/02 is a method for producing lithium chloride by the interaction of lithium hydroxide with a chlorine-air mixture in the presence of a reducing agent based on amine or amide groups by a two-stage countercurrent contact at a temperature of 50-60 ° C in the foam layer of the chlorine-air mixture. The output of lithium chloride is carried out from the first contact stage in the form of a stream of its aqueous solution of 150-200 kg / m ³ containing a residual amount of alkaline reagent providing the required degree of chlorine capture, and fresh alkaline reagent is fed by supplying it to the second contact stage ( figure 1)

The disadvantages of this method include the fact that when alkali is chlorinated to ensure the required degree of chlorine capture, the lithium chloride solution contains at the outlet of the first stage a residual amount of alkali (~ 0.4N LiOH), which in technology has to be neutralized with hydrochloric acid. In addition, the chlorine-air mixture leaving the electrolysis baths contains carbon dioxide (the content of carbon dioxide in the air is 0.02-0.04%), which reacts with lithium hydroxide to form lithium carbonate

The precipitation of lithium carbonate leads to clogging of the process pipelines and the ball nozzle of the absorbers, therefore, it is periodically necessary to switch to backup absorbers and wash the absorbers that were in use with a hydrochloric acid solution. When washing the absorbers, the reaction proceeds:

Li ₂ CO ₃ + 2CHl → 2LiCl + CO ₂ ↑ + H ₂ O

Thus, the disadvantages of the method include: chlorination of lithium alkali is not carried out completely (residual alkalinity - 0.4 N), which leads to an additional consumption of hydrochloric acid; carbonization of lithium alkali leads to clogging of the technological pipelines and the ball nozzle of the absorbers, which leads to their shutdown and forced washing with a solution of hydrochloric acid; The use of hydrochloric acid in lithium hydroxide chlorination technology leads to corrosion of titanium pipelines and titanium equipment.

The objective of the invention is the complete chlorination of lithium hydroxide, the exclusion of clogging lithium carbonate technological pipelines and equipment and the cessation of the use of hydrochloric acid in the technology of chlorination of lithium hydroxide.

The solution to this problem is achieved by the fact that the chlorination of lithium hydroxide, including alkaline absorption of chlorine from a chlorine-air mixture with a solution of lithium hydroxide at a temperature of 50-60 ° C in the foam layer of a chlorine-air mixture with an alkaline reagent, according to the claims, the chlorination of a lithium hydroxide solution is carried out in the presence of iron nickel catalyst by four-stage countercurrent contact, and the chlorination of lithium hydroxide in the first and second contact steps to remove carbonate deposits of lithium they are acidified (pH ≤ 5.5), and in the third and fourth stages the alkaline medium provides the required degree of chlorine capture, periodically, without stopping the gas cleaning process, change the flow direction of the solution and the chlorine-air mixture and wash the third and fourth stages from the precipitation formed lithium carbonate, and the required degree of chlorine capture provide the first and second stages of gas treatment.

The specified set of features is new and has an inventive step, since the complete chlorination of lithium hydroxide to pH ≤ 5.5 makes it possible to dispense with hydrochloric acid in the technology necessary to neutralize the residual alkalinity in the lithium chloride solution. At pH 5.5, the lithium bicarbonate in solution is converted to lithium chloride by the reaction

Li ₂ CO ₃ + Hcl = LiHCO ₃ + LiCl

LiHCO ₃ + Hcl = LiCl + CO ₂ ↑ + H ₂ O

The presence of an iron-nickel catalyst allows the formation of lithium hypochlorite to be destroyed to lithium chloride

2LiOH + Cl ₂ = LiCl + LiClO + H ₂ O

LiClO ^{catalyst Fe-Ni} LiCl + O

Four-stage cleaning of chlorine from the air leaving the electrolysis baths provides the required degree of chlorine capture, and the reverse supply of both the chlorine-air mixture and the lithium hydroxide solution eliminates the possibility of clogging with lithium carbonate precipitate of technological pipelines and equipment, the need to stop the equipment and rinse it with hydrochloric solution acids.

The method is as follows (see Figure 2):

The operating mode of the installation is continuous circulation-countercurrent. The chloro-air mixture is fed sequentially to the absorbers No. 1, No. 2, No. 3 and No. 4. In this case, the fans No. 11 and No. 10, the gate No. 5, No. 13, No. 15 and No. 8 are open, and the gate No. 7, No. 12, No. 6 and No. 14 are closed. The supply of a solution of lithium hydroxide is carried out sequentially through absorbers No. 4, No. 3, No. 2 and No. 1 countercurrent chlorine-air mixture. At the same time, valves No. 17 and No. 18 are open, and valves No. 16 and No. 19 are closed. Chlorination of lithium alkali in absorbers No. 1 and No. 2 lead to an acidic environment (pH ≤ 5.5). In them, the formed precipitate of lithium carbonate is converted to highly soluble chloride and lithium hypochlorite according to the reactions

Cl ₂ + H ₂ O → НСl + НСlO

Li ₂ СО ₃ + НСl + НСlO → LiCl + LiClO + СО ₂ ↑ + Н ₂ O

Absorbers No. 3 and No. 4 have an alkaline environment and provide sanitary cleaning from chlorine. Gradually, the technological pipelines and the ball nozzle of absorbers No. 3 and No. 4 become clogged with precipitation of lithium carbonate. Since acid absorbers are maintained in absorbers No. 1 and No. 2 (pH ≤ 5.5), the process pipelines and ball nozzle of absorbers No. 1 and No. 2 are clean. Periodically, without stopping the gas purification process, the direction of supply of the lithium hydroxide solution and the chlorine-air mixture is changed. In this case, the chloro-air mixture is supplied sequentially to the absorbers No. 3, No. 4, No. 1 and No. 2. At the same time, fans No. 11 and No. 9, gate No. 6, No. 14, No. 12 and No. 7 are open, and gate No. 15, No. 8, No. 13 and No. 5 are closed. The supply of lithium hydroxide solution is carried out sequentially through absorbers No. 2, No. 1, No. 4 and No. 3 countercurrent chlorine-air mixture. At the same time, valves No. 19 and No. 16 are open, and valves No. 18 and No. 17 are closed. Chlorination of lithium alkali in absorbers No. 3 and No. 4 leads to an acidic medium (pH ≤ 5.5), while pipelines and ball nozzles are washed from precipitation of lithium carbonate. Absorbers No. 1 and No. 2 have an alkaline environment and provide sanitary cleaning from chlorine. When lithium carbonate is clogged with precipitators of absorbers No. 1 and No. 2, the feed direction of the chlorine-air mixture and lithium hydroxide solution are again changed.

Claims (1)

A method of chlorinating lithium hydroxide, including alkaline absorption of chlorine from a chlorine-air mixture with a solution of lithium hydroxide at a temperature of 50-60 ° C in a foam layer of a chlorine-air mixture with an alkaline reagent, characterized in that the chlorination of a lithium hydroxide solution is carried out in the presence of an iron-nickel catalyst by a four-stage countercurrent contact, wherein Chlorination of lithium hydroxide in the first and second contact stages to remove lithium carbonate deposits is carried out to an acidic medium pH≤5.5, and in the third and the fourth stage for chlorine capture create an alkaline environment, periodically, without stopping the gas purification process, change the direction of the solution and chlorine-air mixture and wash the third and fourth stages from the formed lithium carbonate precipitates, and the first and second gas purification stages provide the required degree of chlorine capture.

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