RU2066235C1 - Method of sodium alkaline water solution production - Google Patents

Abstract

FIELD: alkaline regeneration, method to produce sodium alkaline water solutions from industrial alkaline sewage in caprolactam production in particular. SUBSTANCE: method is realized by electrodialysis of caprolactam production water solutions of alkaline sewage in three chamber electrolyzer with two cation-exchanging membranes. In the case before electrodialysis initial solution of caprolactam production alkaline sewage is introduced with 0.05 - 0.30 mass % of nonionogenic surface active substance of general formula R-O-(CH₂CH₂O)_nH, with R - alkyl of general formula C_pH_2p+1 or aryl of general formula

with n = 2 - 30, p = 4 - 22, m = 4 - 5. Method allows to produce water solution of sodium alkaline with concentration of NaOH up to 23 mass %, concentration of Na₂CO₃ of no more than 2 mass % and concentration of organic substances (according to chemical absorption of oxygen) of no more than 3000 mg O₂/ l. EFFECT: method allows to produce water solutions of sodium alkaline. 1 dwg

Description

 The invention relates to the field of industrial waste recovery, in particular to an improved method for producing aqueous solutions of sodium alkali from alkaline effluents from the production of caprolactam, and can be used in enterprises producing caprolactam by the benzene method. Such enterprises have a large amount of wastewater that is formed at the initial stages of the technological chain, namely, in the process of washing with a solution of caustic soda a reaction organic mixture coming from the cyclohexane oxidation shop with oxygen.

 The closest in technical essence and the achieved result to the claimed one is a method for producing an aqueous solution of sodium alkali from alkaline effluents produced by caprolactam (SCHPC), described in [2] In the known method, the preparation of a solution of sodium alkali is carried out by electrodialysis of the initial SCHPC in the current ranges of 2-8 A and voltages of 10-20 V and reach 70-82.5% of the extraction of sodium alkali, depending on the conditions of electrodialysis at a time of extraction from 145 to 490 minutes

Moreover, the resulting solution is contaminated with organic substances, determined by the chemical absorption of oxygen (COD) at the level of 6000-10,000 mg O ₂ per liter, the mass fraction of caustic soda is 10-12.6 wt. mass fraction of sodium carbonate is 4.0-5.0 wt.

Thus, the resulting aqueous alkali does not meet the requirements of the relevant GOST [2]
The technical result is a significant increase in the quality of the obtained aqueous alkali.

при n=2-30; p=4-22; m=4-9.The result is achieved by the claimed method for the preparation of aqueous solutions of sodium alkali from industrial alkali polystyrene by electrodialysis of aqueous solutions of alkali hydrogen sulfide, the distinguishing feature of which is that 0.05-0.3 wt. nonionic surfactant of the General formula (1):
RO- (CH ₂ CH ₂ O) _n H,
where R is alkyl of the general formula (2):
C _p H _{2p + 1} or aryl of the general formula (3):

when n = 2-30; p = 4-22; m = 4-9.

Compliance with the stated conditions allows you to bring the degree of extraction of sodium alkali from the initial solution SchSPK up to 90-95% to obtain an aqueous solution of sodium alkali with a content of Na ₂ CO _{3 of} 1.5-2.0 wt. COD at the level of 1500-3000 mg O ₂ per liter and bring the alkali concentration to 20 wt. This in aggregate is quite applicable for technological needs, which allows us to direct the resulting solution into recycling.

 The method is illustrated by the following examples.

 Example 1

The method is carried out in accordance with the prototype. The electrodialysis process is carried out in a laboratory setup, shown in the drawing. Laboratory electrodialyzer (pos. 5) consists of:
1) three chambers (I, II, III);
2) cation exchange membranes, MK-40;
3) two electrodes of the cathode (K) and the anode (A).

Through the chambers I, II, III in the process of electrodialysis pumped, respectively:
0.1 N sulfuric acid solution;
recyclable alkali hydrogen sulfide complex (before the start of the experiment, an appropriate amount of nonionic surfactant is added to the alkali green alcohol solution). The initial alkali hydrogen chloride solution contains 0.50 g-eq / l NaOH and 3.11 g-eq / l sodium carboxylic acids, only 3.61 g-eq / l sodium );
caustic soda solution with a concentration of 0.12 g-eq / L.

 The flow rates of these fluids are established using NP-1M brand peristaltic pumps. Before each experiment, 100 ml of processed solutions are loaded into containers (items 1, 2, 3, Fig. 1).

 All the mentioned solutions circulate in a closed circuit: capacity (pos. 1, 2, 3) peristaltic pump (pos. 4) electrodialyzer (pos. 5) - capacity.

The volume of each chamber of the electrodialyzer is 18 cm ³ the surface area is 30 cm ² .

 To regulate the current and voltage supplied to the electrodialyzer electrodes, the unit is equipped with an electronic unit. For the safe conduct of the electrodialysis process, the cathode of the installation is made of titanium and platinum, and the anode of lead.

где C $\genfrac{}{}{0ex}{}{\text{o}}{\text{с}}$ и C $\genfrac{}{}{0ex}{}{\text{о}}{\text{из}}$ концентрации соответственно солей карбоновых кислот и свободной щелочи перед началом процесса электродиализа в исходном ЩСПК, экв/л;
C $\genfrac{}{}{0ex}{}{\text{rjytxy}}{\text{с}}$ и C $\genfrac{}{}{0ex}{}{\text{rjytxy}}{\text{из}}$ концентрации в диализуемых ЩСПК к концу опыта.The concentration of alkali, sodium salts of carboxylic acids, sulfuric acid contained in solutions circulating through chambers I, II, III and subjected to electrolysis, was determined using standard methods. In addition, the content of Na ₂ CO ₃ and organic substances (COD) was determined in the prepared samples. The degree of extraction of alkali was determined by the formula:

where c $\genfrac{}{}{0ex}{}{\text{o}}{\text{from}}$ and C $\genfrac{}{}{0ex}{}{\text{about}}{\text{of}}$ the concentration, respectively, of the salts of carboxylic acids and free alkali before the start of the electrodialysis process in the initial alkali sulfate complex, equivalent / liter;
C $\genfrac{}{}{0ex}{}{\text{rjytxy}}{\text{from}}$ and C $\genfrac{}{}{0ex}{}{\text{rjytxy}}{\text{of}}$ Concentrations in dialyzable alkaliphosphonic acid complexes towards the end of the experiment

So, in experiment 1, at the initial total Na concentration of 3.61 geq / L, at the end of the experiment (after 260 min), 0.18 geq / L of sodium salts of carboxylic acids remained in the initial solution of SCHPC (95% recovery) . In this case, in chamber III, 100 ml of a NaOH solution with a sodium concentration of 3.55 g-eq / L with a total Na ₂ CO _{3 of} only 1.5 wt. (which, minus the concentration of the alkali initially present in this chamber, gives the same yield of 95%).

 The table below shows the results of experiments on the extraction of sodium alkali from alkali alcohol complex.

 As follows from the table, compliance with the stated conditions allows us to solve the problem.

Claims (1)

A method of producing aqueous solutions of sodium alkali from industrial alkaline effluents of caprolactam production by electrodialysis in a three-chamber electrodialyzer with two cation exchange membranes, characterized in that 0.05 0.30 wt. Is added to the initial solution of alkaline effluents of caprolactam production before electrodialysis. a nonionic surfactant of the general formula
RO- (CH ₂ CH ₂ O) _n H,
where R is an alkyl of the general formula C _p H _{2p + 1} or an aryl of the general formula

at n 2 30;
p 4 22;
m 4 9.

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