CS251468B1 - Method of sodium,potassium or calcium hypochlorite's aqueous solutions or suspensions continuous preparation - Google Patents

Description

It is an object of the present invention to provide a continuous process for preparing aqueous solutions or suspensions. sodium, potassium or calcium hypochlorite.

Alkali metal, calcium, magnesium and aluminum hypochlorites are among the bleaching agents whose use is widespread mainly in the textile and paper industries. The bleaching and also bactericidal activity of hypochlorites is given by the oxidative ability of so-called. active chlorine, which thus constitutes the active ingredient of hypochlorites. The term "active chlorine" means, by oxidation equivalent, the amount of chlorine gas released from the substance by the action of hydrochloric acid. It follows that 1 kg of pure sodium hypochlorite contains 0.9524 kg, i. 95.24 wt. % active chlorine.

The bleaching efficacy of hypochlorite was probably first pointed out by BERTHOLLET, who in 1785 prepared the first bleaching hypochlorite liquor known as 'Eau de Javelle' by saturating an aqueous solution of KOH with chlorine. It was not until 1820 that LABARRAQUE replaced the expensive and limited available potassium hydroxide with sodium hydroxide or sodium hydroxide ('Eau de Labarraque').

In addition to this, considerable amounts of hypochlorite are currently used in a variety of chemical syntheses that utilize their oxidation or chlorination properties. Reactions of this type include, for example, the production of some phenoxy fatty acid derivatives, which are widely used herbicides and crop growth regulators, which are now widely used in industrial practice. Preparations of this type include, but are not limited to, 2,4-methyl-4-chlorophenoxyacetic acid, which has recently been used in aqueous sodium hypochlorite to chlorinate the reaction mixture after condensation of o-cresol with monochloroacetic acid.

Alkaline hypochlorites are also used, for example, in the manufacture of certain benzothiazole-based rubber accelerators. For example, in the production of N-cyclohexyl-2-benzothiazolesulfenamide, an aqueous solution of cooled sodium hypochlorite is used in the process stage of continuously guided oxidation condensation (in the oxidation reactor cascade).

The crystalline alkali metal hypochlorites are very volatile and expensive to prepare. Therefore, only their aqueous solutions with a different active chlorine content are produced for industrial use. However, the aqueous solutions of alkali metal hypochlorites are not complete at all. Mainly salts of heavy metals and themselves

metals (cobalt, nickel, manganese, iron, honey) catalyze the decomposition associated with the formation of C 2 -C 10 '---- ► 2 Cl- + 02 ΔΗ = —155.75 kJ. ·

Several hundred thousand tons of sodium hypochlorite solution are produced annually in the world, and these solutions are produced either at the point of consumption of NaClO or at the source of the chlorine source. Industrially, alkali metal hypochlorite solutions are produced essentially by the following two different methods:

By electrolysis of alkaline chloride solutions (usually NaClj in electrolysers, without diaphragm (A. and B. Schuckert; C. Kellner; F. Oettel - M. Haasov or some other type of electrolyser)),.

Chemical production is undoubtedly advantageous since it requires less operating costs and allows the manufacture of products with a higher concentration of active substance (140-150 grams of active chlorine / l against about 20 grams of active chlorine / l in the electrochemical production of CIO solutions').

In addition to various types of calcium hypochlorite conversions, for example in terms of reaction schemes:

CaOCl ₂ + NasCO 3 ----- NaOCl + + NaCl + CaCO 3

CaOCl ₂ + Na ₂ SO 4 ----> NaOCl + + NaCl + CaSO 3

CaOCl ₂ + 2 NaOH -----> NaOCl + + NaCl + Ca (OH) 2, the reaction of the respective diluted alkali metal solution with elemental chlorine is most commonly used in the industrial production of aqueous alkali hypochlorite solutions.

This is because all the halogenate ions are formed by dissolving halogen in the hydroxide according to the reaction:

X 2 + 2 OH '----> X- + XO ~ + H2O.

The reactions are rapid - the equilibrium constants of all these reactions are quite advantageous (7.5.1015 _for chlorine, 2.10 ⁸ for bromine and 30 for iodine),

However, the situation is complicated by the tendency of the halogen ions to disproportionate in the neutral and, in particular, the alkaline environment to form halogenate ions within the meaning of the reaction scheme:

OH

3XO ------> 2X- + XO 3 -.

For all halides are very competitive equilibrium constant - of the order of 10 ²⁷ decent chloride and oxygen under the scheme:

for CIO ^- , 1015 for BrO and 10 ²⁰ for JO. Therefore, the composition of the products obtained by dissolving the halogens in principle depends on the rates at which the primary halogenated ion ions undergo disproportionation, and these rates vary for all halogens in particular with temperature. Disproportionation of hypochlorites is only very slow at normal and low temperatures. Thus, when chlorine reacts with the corresponding "cold" alkali, practically pure solutions of hypochlorite and chloride can be obtained, virtually free of chlorate ions. The reaction can be expressed as follows:

Ch + 2 OH ----> Cl + ClO + H2O.

The reaction is markedly exothermic and 80.8 kj (272.2 kcal per kg of chlorine is released per 1 mol of chlorine). This amount of heat needs to be effectively removed from the reaction system by cooling to eliminate the unwanted side reaction associated with the hypochlorite decomposition and chlorate as well as the decomposition of hypochlorite into chloride and oxygen.

In order to achieve optimum results in the preparation of alkali metal hypochlorites, the following technological conditions must be met in particular:

- to maintain a temperature of 30 - 40 ° C during chlorination and to ensure that the temperature does not burn more than 50 to 55 ° C for a short period of time, - to ensure the best possible dispersion of the gaseous reactant, 1 mole of chlorine per 2 moles of alkali, - work with dilute aqueous alkali solutions, for example in the preparation of NaOCl, use a solution containing 215-220 g

NaOH per liter solution (approx. 18% aqueous NaOH solution), - exclude the presence of heavy metal salts as well as the metals themselves, such as cobalt, nickel, manganese, honey and iron.

To prepare 1 ton of active chlorine in sodium hypochlorite, for example:

1.01 t of chlorine,

1.19-1.2 t NaOH, about 44 m ^{3 of} water and about 42 kWh.

Several patents have been patented by the alkali metal hypochlorite and bleach lye technology based on the saturation of sodium and potassium hydroxides with chlorine, most notably GB 984 378, US 3 222 269, FR 1 349 076 (1963) and Fr. 1352 198 ( 1962).

At present, most alkali metal hypochlorite manufacturers are fed with chlorinated solutions of chlorine hydroxides, typically using tower chlorinators made of rubber sheet, in which 2 cooling earthenware snakes are supported coaxially carried by a centrally located hollow cooling pocket. Chlorine and air are metered through a pressure regulator that automatically maintains the correct ratio between the two gaseous components and the rotameter flow meter to the bottom of the chlorinator, where it is dispersed by means of a divider structure. Recently, titanium and nickel-chromium-molybdenum steels of the Mastelloy C type, Remanit HC and the like have been used as construction materials for the production of chlorates and heat exchangers.

It has now been found that all conditions intended to achieve optimum results in the preparation of aqueous alkaline hypochlorite solutions and aqueous calcium hypochlorite solutions or suspensions can advantageously be observed using a continuous method of preparing aqueous sodium hypochlorite, potassium or calcium hypochlorite solutions or suspensions by reacting a dilute aqueous hydroxide solution; and / or sodium or potassium carbonate or an aqueous suspension of calcium hydroxide with a mixture of chlorine and air, or by reaction with gaseous and / or liquid chlorine at a temperature of 10 to 55 ° C according to the invention. This method of continuous preparation consists in that an aqueous solution of sodium or potassium hydroxide and / or carbonate, or an aqueous suspension of calcium hydroxide and a mixture of chlorine and air, chlorine and gaseous inert, or gaseous and / or liquid chlorine are metered in one or more. A plurality of locations in the reaction medium, consisting of a mixture of reaction product and starting materials, are circulated at a rate of at least 7 and at most 485 times greater than the rate of feed of the aqueous solution or hydroxide or carbonate slurry into the reaction medium.

Furthermore, it has been found that by circulating the reaction medium, it is possible to achieve the effect of differences in specific gravity and hence hydrostatic pressure in the reaction medium and / or the change of kinetic energy into the reaction medium of the dosed components.

This novel process for the continuous preparation of aqueous chlorine solutions or suspensions6 has a number of advantages, including at least the following:

- allows to achieve high yields and purity of the product with minimum excess of reactants;

- ensures very perfect dispersion of chlorine in the liquid phase of the reaction mixture;

- allows high efficiency heat dissipation from the reaction mixture and virtually prevents the formation of concentrated or temperature gradients in the reaction mixture;

- it is more economical and simple in its simplicity in terms of technical manageability, which guarantees trouble-free operation and a high level of operational cleanliness;

- the simplicity of the technological solution makes it possible to realize the production of hypochlorite exclusively on the basis of common, standardized mechanical and technological equipment made of more accessible and economically accessible materials.

A plant assembly suitable for the preparation of aqueous hypochlorite solutions, especially alkali metals, is schematically shown in FIG. no. 1. The apparatus consisted of duplicated, water-cooled reaction tank 1, glass heat exchangers-coolers 2, a porcelain circulation pump 3 and a glass column mixer 4, and chlorine gas with air. Individual parts of the device were interconnected by glass piping.

Another all-glass assembly of a mechanical engineering apparatus suitable for carrying out a process for producing aqueous hypochlorite solutions according to the invention is shown in FIG. Second

The device consists of two vertical tubes which form the arms of the circulating reactor and are interconnected at the top and bottom. The ascending arm 1 is provided with an inlet of a mixture of chlorine and air 12 with a gas distributor 2 made of porous material. The inlet 11 of the aqueous solution or suspension of the alkali is located above the inlet 12 of the gas mixture. A set of heat exchangers - coolers is built into both arms of the circulation reactor. The reaction product flows continuously through the liquid cap-overflow 4 built into the top of the interconnection of the upstream 1 and downstream arms 3 of the circulation reactor.

They illustrate the novel process, but do not limit the examples below.

Example 1

In order to prepare an aqueous sodium hypochlorite solution according to the method of the invention, a mechanical-technological apparatus is shown schematically in FIG. 1. The apparatus consisted of duplicated and water-cooled reservoir 1, glass heat exchangers - coolers 2, a porcelain circulation pump 3 whose performance according to the manufacturer's data was equal to 400 liters / min and a glass column mixer of chlorine gas with air. sticks interconnected by a standardized glass pipe. A dilute aqueous solution of about 18% NaOH 11, temperature 23 ° C, was fed into the circulating reaction medium into the suction side of the circulation pump of reaction mixture 3 in an amount of 14.45 kg, i.e. about 12 L. min ^-1 . Chlorine gas / air mixture 12 prepared in mixer 4 by mixing chlorine gas 13 dosed in an amount of 2.3 kg Ch. min ^-1 with air 14, the amount of which was controlled by means of a pressure reducing valve, was fed into the circulating reaction medium through a glass inlet pipe, downstream of the circulation pump 3, into the discharge section of the pipeline forming the mixer 5. to a volumetric feed rate of an aqueous NaOH solution of 33.3.

The temperature of the circulating reaction mixture was maintained at 35 ° C on average in the heat exchangers 2 and in the container 1 duplicator.

Under these conditions, an average of 16.7 kg of an aqueous solution of sodium hypochlorite 15 containing 13.8 wt. % of active chlorine, the pH of the undiluted solution being 9.5 to 10.5. The product - aqueous hypochlorite solution was continuously discharged via an overflow on the container 1 through a liquid - siphon cap.

Example 2

In the preparation of the aqueous potassium hypochlorite solution according to the method of the invention, the machine-technology apparatus according to FIG. 2, the apparatus used consisted of two glass vertical tubes constituting the arms of the circulating reactor interconnected at the top and bottom. The ascending arm 1 was provided with a chlorine / air mixture 12 with a gas distributor made of porous material 2 with apertures of about 250 microns. The inlet of the 17.3% aqueous KOH 11 solution was placed at a small distance above the inlet of the gas mixture 12. A heat exchanger-cooler system was incorporated into both arms. The reaction product continuously flowed through the weir 4 at the top of the connection of the ascending 1 and descending arms 3.

In an all-glass apparatus of this construction, an average of 7.550 g of a 17.3% aqueous KOH solution and 808.3 grams of chlorine gas, into which compressed air was admixed, were metered in for an minute. Due to the differences in the specific gravity of the reaction mixture in the ascending 1 and descending arm 3 of the chlorination reactor, the reaction mixture was efficiently circulated while circulating through the heat exchangers-chillers maintaining the temperature of the reaction mixture below 40 ° C.

8,358.3 g of an aqueous hypochlorite solution containing 11.76% active chlorine were obtained in a minute, with an average pH of about 10.0. Chemical analysis revealed that the product contained an average of 0.3% free KOH.

Claims (2)

1. A process for the continuous preparation of aqueous solutions or suspensions of sodium, potassium or calcium hypochlorite by reacting a dilute aqueous solution of sodium and / or potassium carbonate or an aqueous suspension of calcium hydroxide with a mixture of chlorine and air, chlorine and gaseous iert; or liquid chlorine at a temperature of 10 to 55 ° C, characterized in that the aqueous solution of sodium or potassium hydroxide and / or carbonate or an aqueous suspension of calcium hydroxide and a mixture of chlorine and air, chlorine and gaseous inert or gaseous and / or liquid chlorine one or more sites into the reaction medium, consisting of a mixture of the reaction product and the starting materials, which circulates at a rate of at least 7 and at most 485 times greater than the rate of feed of the aqueous solution or hydroxide or carbonate slurry into the reaction medium The heat of reaction is removed from the system by cooling. 2. The process according to claim 1, wherein the circulation of the reaction medium is achieved by the effect of differences in specific gravity and hence the hydrostatic pressure in the reaction medium and / or by the change of kinetic energy into the reaction medium of the components. system bell.