SU1213087A1 - Method of regenerating nitrating mixture - Google Patents

Description

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 This invention relates to the regeneration of sulfur-nitric acid nitrating mixtures, which are formed in the process of obtaining difficult-to-yield organic-nitro compounds.

The purpose of the invention is to simplify and intensify the process and improve working conditions.

The proposed method is carried out under laboratory conditions as follows.

For the electrochemical regeneration of the acid used, a diaphragm electrolytic cell of a circumferential structure with an anolyte working volume of 100 ml and a catolyte of 400 ml is used. A platinum plate 5 with a working surface area of 50 cm is used as an anode, as well as a cooled stainless steel coil, and anolyte and catholyte as the cathode are separated by a porous alund diaphragm. Sulfuric acid containing nitric acid and oxides of nitrogen is poured into the anode space of the cell, and nitric acid with a concentration of at least 50% is fed into the cathode. A constant electric current of 10–20 A (anode current density of 0.2–0.4 A / cm) is passed through the cell. Temperature 10-50 ° C. At temperatures below 10 ° C, the viscosity of the anolyte increases dramatically, and as a result, the resistance of the solution and energy consumption increase. Therefore, lowering the temperature is less desirable. The upper temperature limit () is limited by the summer-, honor of the mixture components, which at higher temperatures than becomes very significant.

As a result of electrolysis, the anolyte is dehydrated and a selective accumulation of nitric acid and a sharp decrease in the content of nitrogen oxides are observed.

The processes that occur in this case are as follows.

At the platinum anode, oxygen is released due to indirect electrolysis of water as follows:

502 -.- 2е 50з-И / 2 (SO - НгО HjSOi,

The formation and accumulation of nitric acid in the anolyte occurs as a result of the following processes.

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Nitrogen oxide dissociates in sulfuric acid by the leveling of HSO4 NO + HNOJ + HSO;

During electrolysis in an electric field, nitrosonium ions (NO) selectively migrate to the cathode space, while nitric acid molecules remain in the anolyte. Present in the waste

10 Acid impurities of nitro products (for example, trinitrotoluene, trinitrobenzene, etc.) in the amount of 1-2% are electrochemically oxidized at the anode to CO and HNO and do not interfere with the process.

In the cathode space of the electrolyzer, the electrochemical reduction of nitric acid to water occurs, N0 N07. The emitted oxides

Nitrogen is added to oxygenation of the air to the fullest possible conversion of nitric oxide to dioxide and then liquefied or absorbed by sulfuric acid (spent acid). The resulting mixture is used in the anolyte for electrochemical processing into a nitrating mixture. The concentration of nitric acid in the catholyte must not be lower than 50%, otherwise the formation of nitrogen compounds in a lower oxidation state (NjO, Hz, NHj, etc.) and hydrogen is possible, which leads, on the one hand, to the loss of bound nitrogen and on the other

On the other hand, it causes contamination of nitrogen oxides (N0 and M0g) with the use of extraneous gases.

Example 1. Used acid, which is 70% sulfuric acid, containing 2% of oxides of nitrogen and 2% of trinitrotoluene, is mixed with liquid nitrogen tetroxide in a mass ratio,:, (in terms of monohydrate) equal to 1: 4. Mass ratio

N, jOt,: HjO is equal to 1: 1.71. The resulting 70% sulfuric acid, containing 15.8% by weight of nitrogen tetroxide, in an amount of 100 ml (175 g) is poured into the anode space of the cell. 400 ml of 66% nitric acid is poured into the cathode one.

A constant current of 10–20 A is applied to the cell (the anode current density is 0.2–0.4 A / cm2). Temperature 20-40 s. After passing through the cell 105 AH of electricity in the anolyte

115 g of the nitrating mixture of the composition,%: HNOj 18 is formed; SO 17; , 6A, containing less than 1% of nitrogen oxides and less than 0.1% of organic nitroproducts.

Example 2. Sulfuric acid of various concentrations from 70% to 95% is mixed with nitrogen tetroxide in various proportions and the resulting mixtures are subjected to electrolysis in the anode space of the electrolytic cell to reduce the concentration of nitrogen oxides to less than 1%. The volume of anolyte is 100 ml. Catholyte - 66% - on nitric acid. Temperature and current density - as in the previous example.

The results of the experiments are presented in the table.

From the table it can be seen that the nitrating properties of the mixture can be obtained on the basis of spent sulfuric acid with a concentration of 70-95%. However, with a low content of nitrogen oxides in the initial mixture (Example 3) and, accordingly, with a low mass ratio, an insufficient amount of nitric acid is formed in the resulting mixture.

In addition, in this case (example 3)

an increase in anolyte overflow into the cathode space is also observed, leading to a loss of product, and an increase in resistance is observed at the terminals of the cell, which leads to an increase in power consumption. Consequently, the minimum amount of nitrogen oxides in the initial mixture should be at least 9% or a mass ratio of at least (1: 3) (examples 2 and 3). The maximum content of nitrogen oxides is limited by their solubility in sulfuric acid. At 70%. dissolves about 16% (mass ratio, is 1: 1.58) and in 95% HtSOi, about 40% (mass ratio N40ts: H, 0 equals 1: 0.075)

When using, for example, sulfuric acid with a concentration of less than 70% as a raw material, the proposed regeneration method fails to be ineffective or not workable at all. On the one hand, dilute sulfuric acid is a well-conducting fluid and

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The reduction of nitrogen oxides reduces the electrical conductivity of the solution, and on the other hand, in dilute sulfuric acid, the oxides of nitrogen undergo hydrolysis to form volatile nitric oxide, which leads to the loss of bound nitrogen from the solution. Only in solutions of sulfuric acid with a concentration of 70-95% are nitrogen oxides highly soluble and are in a tightly bound state, which ensures the efficiency of the process.

In the case of using a mixture of 70% sulfuric acid in concentrated nitric acid as an anolyte (an anolyte of composition Н ЗОц-НКОэ-НгО) during electrolysis, a rapid decrease in the content of nitric acid is observed as a result of its migration into the cathode space. It was also not possible to obtain a working acid mixture.

With the introduction of nitrogen trioxide or nitrosylsulfuric acid (system, - and NOHSO -HiSO (,) into 70% sulfuric acid, the oxidation process takes place at a low voltage, but no significant conversion of NOHSO (to nitric acid) is achieved.

For various reasons, did not give a positive result and other attempts.

Only by electrochemical oxidation of a solution of NjOi, in sulfuric acid in a diaphragm electrolyzer, was it possible to obtain a product — a working acid mixture of the composition,%: HNO3 10-30; H, SO 30-70; SO 10-50.

It follows from the table that there is a minimum limit for the amount of nitrogen tetroxide introduced into the spent acid mixture (ACS), which depends on the water content in the ACS. With a mass ratio of N.O J,: H jO of 1: 3.5 (example 3), it is not possible to obtain a mixture of the required composition (10-30% HN03, 30-70%, 10-50% SOj). The content of nitrogen tetroxide in the ACS should be such that the ratio NjO (,: HiO was more than 1: 3. The maximum content of four oxides is limited by the solubility in sulfuric acid.

As regards the composition of catholyte, a solution of a strong electro-solution must be used to carry out the method, which eliminates the harmful occurrence of osmosis. When used in kaJ

 As cathode nitric acid with a concentration of not less than 50%, such problems as reprocessing the spent catalite and providing the process with nitrogen oxides, i. the process becomes generally closed and waste-free. In addition, in the case of the use of nitric acid in the cathode space, the regenerative process proceeds somewhat more effectively due to the more favorable nature of ion migration, -.

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Editor N. Yatsola

Compiled by O. Zobnin

Tehred T. Dubinchak Proofreader M. Maksimishinets

Order 753/38 Circulation 615 Subscription VNIIPI USSR State Committee

for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab, 4/5

Branch PPP Patent, g. Uzhgorod, st. Project, 4

Thus, the proposed method allows to obtain a nitrating mixture for nitrating difficultly nitriding organic compounds in one stage of electrochemical oxidation of the spent acid in the anode space of a diaphragm electrolyzer for several hours, and low temperatures of the process and the possibility of electrochemical oxidation of impurities of nitroderivatives give the method also positive qualities. elimination of explosiveness and danger.

Claims (1)

METHOD FOR REGENERATING A NITRUS-MIXTURE MIXTURE containing an aqueous solution of sulfuric acid with a concentration of 70-95% mixed with nitrogen oxides and organic nitro products, characterized in that, in order to simplify and intensify the process and improve working conditions, nitric oxide is introduced into the initial mixture to a ratio of nitrogen tetroxide and water of at least 1: 3 and the resulting mixture is subjected to oxidation in the anode space of the diaphragm electrolyzer on platinum anodes, and a solution of a strong electrolyte is fed into the cathode space.