RU2203850C2 - Method of catalytic decomposition of hypochlorite - Google Patents

Abstract

FIELD: chemical technology; method of decontamination of aqueous solution of hypochlorite formed in the course of cleaning process gases from chlorine. SUBSTANCE: proposed method of catalytic decomposition of hypochlorite includes bringing flow of liquid containing hypochlorite-ions in contact with catalyst in form of particles which decomposes hypochlorite-ions giving off gaseous oxygen in counter flow of liquid containing hypochlorite-ions at temperature of 20-90 C. Used as catalyst is nickel oxide dispersed on aluminum oxide; flow of liquid after contact with catalyst is additionally brought in contact with grain filter containing fragments of catalyst particles formed in the course of contact of starting flow of liquid with said catalyst. Used as grain filter is river sand at size of grains of 0.2-2 mm. Used as catalyst are industrial catalysts of two types indicated in Specification. EFFECT: reduced losses of catalyst; enhanced efficiency. 4 cl, 3 ex

Description

 The invention relates to chemical technology, and in particular to methods of neutralizing an aqueous solution of hypochlorite formed in the process of purification of process gases from chlorine.

 There are a large number of ways to neutralize an aqueous solution of hypochlorite using all kinds of reducing agents, for example, technical lignosulfonate [RF patent 2073637, cl. From 01 to 11/06, publ. 02/20/97]. Such options for the neutralization of the hypochlorite solution require a significant consumption of reducing agents, and are associated with secondary pollution of wastewater with oxidation and chlorination products of reducing agents. In the case of using technical lignosulfonate, which is a waste from the production of cellulose, the formation of xenobiotics such as dioxin is not ruled out.

Very promising methods of catalytic neutralization of an aqueous solution of hypochlorite. Thus, a known method of neutralizing a solution of hypochlorite by decomposition of hypochlorite in the presence of a catalyst. The solution with the catalyst is heated to a temperature of 80 ÷ 100 ^o C and passed through a layer of bulk material, such as silica sand, containing 1 ÷ 5 g / l of Nickel hydroxide or cobalt [ed. St. USSR 311867, class From 01 to 11/06, publ. 08/19/71]. The method requires periodic regeneration of the contact mass. For this, the filter material is treated with hydrochloric acid, and nickel or cobalt hydroxides are precipitated from the resulting solution, which are returned to the process. The method is very time-consuming when designing a continuous process.

Another known method of neutralizing and disposing of a hypochlorite solution is based on the decomposition of hypochlorite when heated to 90 ^o C in the presence as a catalyst of a solution of heavy metal chlorides (iron and nickel), taken in volume ratio to a hypochlorite solution of 1: 500 ÷ 1: 1000 [RF patent 2091327, class C 02 F 1/72, C 01 F 11/24, publ. 09/27/97].

 This method solves the problem of organizing the decomposition of hypochlorite in a continuous form, but is complicated by the need for subsequent cleaning of the pulp from the resulting heavy metal hydroxides.

The closest set of essential features to the proposed is a known method of catalytic decomposition of hypochlorite according to the patent of the Russian Federation 2091296, class. C 01 B 11/06, C 02 F 1/70, publ. 09/27/97. This method involves contacting a fluid stream containing hypochlorite ions with a particulate catalyst layer that decomposes hypochlorite ions with the release of gaseous oxygen, the process being conducted in at least two series-connected catalyst layers that are arranged in a cascade with risers free from the catalyst, between successive layers, and a stream of liquid containing hypochlorite ions flows down through at least the first two of the series-connected layers in countercurrent to gaseous oxygen released during the decomposition of hypochlorite ions, and up through the risers between successive catalyst beds. The concentration of hypochlorite ions in the fluid stream in terms of sodium hypochlorite is at least 20 g / l. The fluid flow by a known method flows through the catalyst bed in the form of particles with a bulk velocity of 0.1 ÷ 10 h ^-1 at a temperature of 10 ÷ 90 ^o C. In the above example, the concentration of sodium hypochlorite in solution is reduced from 97.42 to 0.146 g / l ( the degree of purification is 99.85%), in another experiment, from 69.03 to 0.088 g / l (the degree of purification is 99.87%).

 In the known method used a special catalyst "Extrudate A" publ. EP 0397342 A with particles with a diameter of about 3 mm. The use of a domestic nickel-containing catalyst of the GIAP-3-6N brand is accompanied by a gradual destruction of the catalyst grains with the formation of a finely dispersed insoluble precipitate of aluminum and nickel hydroxides in an amount of 9 to 24 g per 1 liter of purified solution. The destruction and entrainment of hydroxides during the decomposition of an aqueous solution of hypochlorite leads to a significant consumption of catalyst (9-24 g per liter of purified solution).

 An object of the present invention is to reduce the loss of a catalyst with a solution to be purified during the decomposition of hypochlorite in aqueous solutions.

The problem is solved in that in a method for the catalytic decomposition of hypochlorite, comprising contacting a fluid stream containing hypochlorite ions with a particulate catalyst that decomposes hypochlorite ions with the release of gaseous oxygen, in countercurrent to a liquid stream containing hypochlorite ions, to a gaseous oxygen released by the decomposition of the hypochlorite ions at a temperature of 20-90 ^o C, according to the invention is used as catalyst nickel oxide dispersed on alumina, wherein at approx liquid after contacting with the catalyst is further contacted with a particulate filter comprising fragments of catalyst particles formed in the process of contacting a starting fluid stream to said catalyst.

 As a granular filter can use river sand with a grain size of 0.5-2 mm.

 As the catalyst can use industrial catalysts GIAP-3-6N or GIAP-8.

 The method was tested in laboratory conditions.

Example 1
A water-alkaline solution containing 90 g / l sodium hypochlorite is sent to a glass reactor equipped with an external electric heating. River sand with a grain size of 0.5 ÷ 2 mm in an amount of 100 cm ³ (bottom layer) and GIAP-3-6N industrial nickel-containing catalyst (top layer), which is nickel oxide dispersed on alumina, in an amount 50 cm ³ . The decomposition of hypochlorite is carried out at a temperature of 80 ^o With in countercurrent flow of the solution to the flow of oxygen released during the decomposition of hypochlorite. The sodium hypochlorite solution is fed into the reactor from above at a rate of 180 ml / h. This solution is sequentially contacted with the GIAP-3-6N catalyst and with a granular filter containing fragments of the catalyst, which are particles consisting of nickel and aluminum hydroxides. The concentration of sodium hypochlorite in the solution at the outlet of the reactor is 0.01 g / l, the concentration of nickel cations in this solution is 2.8 mg / l. The degree of decomposition of hypochlorite is 99.99%. The duration of the experiment was 16 hours. During this time, 2.9 L of the solution was purified. At the end of the experiment, the lower layer from the reactor (a layer of sand with fragments of catalyst particles) is treated with a solution of hydrochloric acid followed by acid analysis to determine the content of the catalyst in this layer. Found 2.3 g of Nickel cations, i.e. the concentration of Nickel in the material of the granular filter is 23 g / DM ³ .

Example 2
A water-alkaline solution containing 102 g / l sodium hypochlorite is sent from above to a reactor filled with layer sand of river sand with a grain size of 2 ÷ 3 mm in an amount of 180 cm ³ (lower layer) with a GIAP-8 nickel-containing industrial catalyst (upper layer) containing 6 wt.% Nickel oxide on alumina, granulation 2 ÷ 3 mm in an amount of 180 cm ³ . The decomposition of sodium hypochlorite is carried out at a temperature of 80 ^o C and a solution is supplied at a rate of 90 ml / h in countercurrent to the flow of oxygen released during the decomposition of hypochlorite. The concentration of hypochlorite in the solution at the outlet of the reactor is 0.07 g / l, which corresponds to a degree of decomposition of hypochlorite of 99.93%; the concentration of nickel cations in solution is 2.8 mg / L.

 Example 3 (control).

A water-alkaline solution containing 70 g / l sodium hypochlorite is decomposed in a catalyst bed of the GIAP-3-6N grade with a grain size of 1 ÷ 3 mm. The amount of catalyst is 100 cm ³ . The decomposition is carried out at a temperature of 80 ^o In countercurrent flow of a solution of sodium hypochlorite to the flow of oxygen. The feed rate of the solution is 120 ml / h. The concentration of sodium hypochlorite after contact with the catalyst is 0.14 g / l, which corresponds to a purity of 99.8%. The solution exiting the reactor contains a suspension of nickel and aluminum hydroxides; the total sediment content in the solution after purification from hypochlorite is 9.4 g / l.

 From examples 1 and 2 it is seen that the additional contacting of the solution to be purified with the catalyst in finely divided form, distributed on the granular material, significantly increases the degree of purification. This can be explained by the fact that the oxygen released does not linger on the fine particles of the catalyst and does not interfere with the contact of the solution with the catalyst, which is essential for a low residual concentration of hypochlorite in the solution. Granular material is a suitable carrier for such particles, moreover, a material with a grain size of 0.5 ÷ 2 mm is more effective (see example 1). Loss of catalyst does not exceed 2.8 mg per 1 liter of solution.

 Thus, the additional contacting of the hypochlorite solution with a layer of river sand in which fragments of a nickel-containing catalyst are dispersed improves the efficiency of decomposition of hypochlorite, reduces catalyst losses and eliminates the need for additional filtration of the solution from the precipitate resulting from the destruction of the catalyst.

Claims (4)

1. The method of catalytic decomposition of hypochlorite, comprising contacting a fluid stream containing hypochlorite ions with a particulate catalyst that decomposes hypochlorite ions with the release of gaseous oxygen, in countercurrent flow of a liquid containing hypochlorite ions to gaseous oxygen released during decomposition hypochlorite ions, at a temperature of 20-90 ^o C, characterized in that the catalyst used is nickel oxide dispersed on alumina, while the fluid flow after contacting with the catalyst is additionally contacted with a granular filter containing fragments of catalyst particles generated during the contacting of the initial liquid stream with said catalyst.  2. The method according to p. 1, characterized in that as a granular filter use river sand with a grain size of 0.2-2 mm  3. The method according to p. 1 or 2, characterized in that the catalyst used is an industrial catalyst GIAP-3-6H.  4. The method according to p. 1 or 2, characterized in that the industrial catalyst GIAP-8 is used as a catalyst.