CS217263B1 - Process for the production of perexuleucines, in particular hydrogen perexide, by cathodic oxygen reduction - Google Patents

Abstract

The invention relates to the field of inorganic technology and provides a method for producing peroxide compounds, in particular hydrogen peroxide, by cathodic reduction of oxygen on gas porous electrodes. The essence of the invention lies in the fact that alkali silicates are added to the electrolyte entering the electrolyzer or directly to the electrolyzer in an amount ensuring a silicate to alkali ratio of 0.1:1 to 5:1.

Description

The present invention relates to a process for the production of peroxy compounds, in particular hydrogen peroxide, by cathodic reduction of oxygen on gas porous electrodes.

Alkaline hydrogen peroxide solutions can advantageously be produced by cathodic oxygen reduction.

In this process, the alkali or oxygen-containing gas is introduced into the porous electrode or into a trickle bed where the reaction proceeds:

0 ₂ + H ₂ 0 + 2 o -? H0 ₂ + OH ”

On the anode, oxygen is excreted when using hydroxide solutions:

OH ”-> 0 ₂ + 2 H ₂ 0 + 4 ·

The electrolyte (KOH or NaOH) is usually introduced into the anode compartment of the electrolyzer, passes through the diaphragm into the cathode compartment, where it is enriched for the formation of peroxide, and further flows from the electrolyzer.

The resulting process taking place in the electrolyzer can be expressed by the equation 1/2 0 ₂ + OH - ^ H0 _ř

Thus, perhydroxyl ions are formed at the expense of hydroxyl ions.

Due to the low voltage on the electrolyzer, the power consumption of the electrolyzer is three to four times less than that of conventional peroxide production prior to perexedisulphates. A certain limitation of this process is that in good technical-ecenemic parameters it only takes place in alkaline environment from which concentrated pure peroxide solutions can only be obtained by means of several-stage production processes. However, in some areas of the industry, dilute alkaline hydrogen peroxide solutions can be directly used, for example, for bleaching pulp in the paper and pulp industry, in the textile industry, in wastewater treatment, etc. In this case, the costs of distillation of dilute peroxide solutions increase.

For bleaching, solutions are generally used in which the molar ratio of peroxide to caustic is about one, a ratio which cannot be achieved in the electrolytic preparation of alkaline hydrogen peroxide solutions by reducing oxygen in alkaline hydroxide solutions. Indeed, laboratory investigations have shown that although alkaline solutions containing up to 10% by weight of peroxide can be obtained, a molar ratio of peroxide to weight higher than 0.6 to 0.7 cannot be achieved.

For industrial applications, this implies that in the production of bleach liquors by cathodic oxygen reduction, it would be necessary either to add a solution of pure hydrogen peroxide to the electrolyte flowing from the electrolyzer or to neutralize some of the hydroxide in the electrolyte with acid. However, both processes are disadvantageous, since either the addition of the more expensive pure peroxide or the need for acid and, moreover, the loss of part of the hydroxide.

This difficulty is solved by a process for producing peroxy compounds, in particular hydrogen peroxide, by cathodic reduction of oxygen on gas porous electrodes, which consists in adding alkali silicates to the electrolyte entering the electrolyzer or directly de electrolyzer in an amount corresponding to the molar ratio of silicate to lye. , 1: 1 to 5: 1.

An advantage of the invention is that silicate is a common component of peroxide bleach baths to which it is added to retard peroxide decomposition, its addition to the electrolyte prior to entering the electrolyzer or directly into the electrolyzer does not involve any additional investment.

The effect of silicates on the electrolysis process can be explained on the basis of the following analysis of the conditions in the electrolyser.

In the cathode space of the electrolyzer increases with the degree of conversion of hydroxyl ions to perhydroxyl portion of perhydroxyl ions, which are migrated and diffused from the cathode space before the diaphragm to the anode space, resulting in a decrease in peroxide current yields. At conversion rates close to one, the proportion of hydroxyl ions in the catholyte decreases to zero and the peroxide current yields fall below the carrying limit. In an alkali silicate-containing electrolyte in an amount comparable to the initial hydroxide concentration, part of the current is fed through cations and anions of silicate, so that the proportion of the current fed by perhydroxyl ions and hence the loss of peroxide by migration is considerably less.

With the increasing degree of conversion, which indicates the ratio of total peroxide content to the concentration of the feed liquor, there is another unfavorable phenomenon - the increase in voltage losses in the electrolyzer, caused in the catholyte by the replacement of highly mobile hydrosyl ions. Both the low-mobility perhydroxyl ions and the anolyte by decreasing the concentration of hydroxyl-extinguishing agent in the diaphragm then both effects are applied simultaneously. In the presence of an alkali silicate, the conductivity of both the catholyte and the anolyte increases, both by the contribution caused by the mobility of cations and silicates, and by the mobility caused by the hydroxyl ion mobility, which is caused by hydrolysis of the silicate when the alkalinity has decreased:

sieve ₃ + & ₂ o Si ^ O ^ + 2 OH '

This can also explain the other beneficial effect of alkaline silicates, which is to increase the stability of the nickel anode. Indeed, as observed, is the nickel anode on which oxygen deposition occurs is sufficiently corrosion resistant only at hydroxyl ion concentrations in the anolyte of greater than 0.3 - 0.5 mol / sod? Pr © v ^! If electrolysis is carried out in dilute alkaline peroxide solutions (e.g. 1 to-KOH), at higher conversion stages, the hydroxyl ion concentration in the pcd anolyte decreases, and the anode corrodes very rapidly. The present alkali silicate acts in this system jax® buffer, which delivers hydroxyl ions and thus prevents the decrease in alkalinity.

The following are examples of embodiments of the method of use of the invention.

Example 1

The peroxide-containing electrolyser contained a porous carbon cathode with a contour area of 8 cm @ 2 with pure oxygen, a nickel anode, oxygen below, and a porous PVC PVCphragm filtering. The electrolyte was fed through the de-anode space, passed through a filtering diaPragme and, after enrichment with perhydroxyl ions in the cathode space, exited the electrolyzer. The electrolyzer was first introduced with 1 to-KOH. By decreasing the electrolyte flow rate at a constant pre-external load (0.3 A), the perexide concentration initially increased, but the growth slowed progressively and approached a limit hedge of 0.81 mel / day. at the effluent (ο ^ θ ^), the perevide yields (and the electrolyzer clamp voltage (E)).

Table 1

• in ^Target 2 ° 2 1 / H ₂ o ₂ £ (cm ^ / h) (mol / drn ^) (%) (IN) 8.5 0.53 89.0 1.39 6.7 0.66 87.5 1.42 5.2 0.81 75.6 2.6 3.54 0.81 51.4 5.2 2.1 0 ₊ 81 30.5 9

When introducing a 1? -KOH + 1.64? -K? SiO 2 solution in the electrelyser, a significantly higher perexide concentration could be achieved and at all flow rates the higher perexide current yield and electrolyzer voltage were lower (see Table II).

Table II

• in ° ^Η 2 ^θ 2, From h ₂ o _? E (cm ^ / h) (mel / dnr) (%) (IN) 8.7 0.54 94.0 1.34 8.3 0.56 92.0 1.35 4.85 0.97 89.8 1.44 4.22 1.16 84.3 1.64 3.49 1.36 84.0 1.68 2.1 2,0 71.3 2.12

Example 2

Further measurements were carried out in 1 M-KOH, in 3 µ-KOH and in mixed solutions of 1 M-KOH + + 0.64 L-K 2 SiO 2 and 1 M-KOH + 1.64 M-K 2 SiO 2. The experimental conditions were the same as those in Example 1. The equilibrium hedge yields of the perexide yield and the electrelyser voltage were obtained depending on the degree of conversion shown in Table III.

The life of the nickel aneda was 1 hi-ΚΟΓ. at a kenver degree of 0.63-0.75 only 200 to 600 h, but at an outlet of 1 ift-KOH + 1.64 MK ^ 10, the anode pe of 500 h was transferred at a kenver degree of 0.6-1, completely untouched and only for an additional 100 hours of transfer at a conversion rate of 1.6-2.0, the anode is disrupted 1a. In the 1 ift-KOH + 0.64 ift-K-SiO ^ residue, the anode pe 340 h of transport at the 0.9-1 kenver stage was unaffected, and only for longer than 500 h at the 0.7-1.2 inversion stage * started visibly keredovat.

Claims (1)

Process for the production of peroxy compounds, in particular hydrogen peroxide, by cathodic reduction of oxygen on gas porous electrodes, characterized in that alkali silicates are added to the electrolyte entering the electrolyzer or directly into the electrolyzer in an amount corresponding to a molar ratio of silicate to caustic of 0.1: 1 to 5 : 1.