RU2476386C1 - Method of recycling still waste liquid of ammonium-soda production - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to field of still waste liquid recycling, which is formed in production of coda ash by ammonia method. Still waste liquid is processed with sodium hydroxide with mole ratio CaCl₂:NaOH, equal 1:2÷2,25 (mainly 1:2), calcium hydroxide precipitation, which is obtained in the process, is filtered, filtrate, consisting of sodium chloride, is subjected to electrochemical processing in two-chamber electrolyser with cathion-exchanging membrane at current density 350÷1400 A/m² with obtaining hydroxide of sodium and chlorine.

EFFECT: invention makes it possible to simplify method of still waste liquid recycling, reduce energy consumption on recycling and obtaining calcium hydroxide, hydroxide of sodium and chlorine as marketable products.

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Description

The present invention relates to the field of processing distillation liquid generated in the production of soda ash according to the ammonia method. Up to 9 m ^{3 of} distillation liquid containing about 100 g / l CaCl ₂ , about 50 g / l NaCl and other impurities are formed per 1 ton of soda ash after ammonia regeneration (D.A. Kuznetsov et al. General chemical technology. - M. , Higher School, 1970 .-- 344 p., P. 141).

A known method of producing anhydrous calcium peroxide, where distillation liquid is used as feedstock is a waste product of soda ash production, including 82.13 ÷ 142.07 g / l CaCl ₂ , 45.26 ÷ 68 g / l NaCl, 0.407 ÷ 1.78 g / l Ca (OH) ₂ , 0.46 ÷ 0.624 g / l CaCO ₃ , 0.784 ÷ 1.21 g / l Na ₂ SO ₄ , as well as ammonia solution and hydrogen peroxide (US Pat. 2341449, Russia, IPC С01В 15 / 043. Method for the production of anhydrous calcium peroxide / EI Bakhonina, I. Kh. Bikbulatov, A. Yu. Bakiev, PP Daminev, PP Nasyrov, FR Oparina (Russia). Ufa State Petroleum Technical University - No. 2007119247 / 15; claimed May 23, 2007 )

The disadvantages of this method include the need to use such reagents as hydrogen peroxide and ammonia solution. In addition, in the production of calcium peroxide by this method, a significant amount of wastewater containing ammonium and sodium chlorides is formed.

A known method of processing distiller liquid is to use it after preparation for injection into oil wells in order to maintain reservoir pressure. Preparation of distillation fluid includes the following operations:

- dilution of distiller liquid with water to remove supersaturation on gypsum;

- carbonization of the distiller liquid with a gas from a calcareous furnace in the presence of a reture sludge;

- sedimentation and transportation of carbonated distillation fluid for injection into the oil reservoir (I.D. Zaitsev, G.A. Tkach, N.D. Stoev. Production of soda. - M., Chemistry, 1986. - 312 p., p .98 -201).

The disadvantages of this method include the need for the location of the production of soda in the area of oil production.

Closest to the claimed, i.e. The prototype is a method for processing distillation liquid to produce calcium chloride. After carbonization and sludge, a seed of active anhydrite CaSO _{4 is} added to the distillation liquid to prevent the encrustation of the heat transfer surfaces of the evaporator battery. The clarified distilled liquid with a seed is fed into the first evaporation battery, where it is evaporated to a content of 18% CaCl ₂ . The partially distilled and clarified from the seed distillation liquid is sent to the second evaporation unit, where it is concentrated up to 38% in Cal ₂ . In this case, the bulk of NaCl is released. Suspension of NaCl in a 38% solution of CaCl ₂ after settling is centrifuged and solid NaCl is sent to consumers or returned to the production of soda. The clarified 38% CaCl ₂ solution is fed to a vacuum crystallization unit, where it is concentrated up to 40% CaCl ₂ , and an additional amount of NaCl is released into the solid phase. The clarified 40% solution of CaCl ₂ is fed to the evaporator, where it is evaporated to the state of melt (72% CaCl ₂ ). The melt CaCl ₂ after scaling, drying and calcination is a finished product. Consumption rates for 1 ton of calcium chloride (67% CaCl ₂ ) are:

distillation liquid, m ³ 7.3 gas of lime kilns, m ³ 96.6 circulating water, m ³ 162 steam, GJ 16,4 electricity, MJ 410

(G.A. Tkach, V.P. Shaporev, V.M. Titov. Production of soda using low-waste technology. - Kharkov, KHPU, 1998. - 429 p., Pp. 359-368).

The main disadvantages of the prototype include multi-stage production, sophisticated technological equipment, the use of gas from lime kilns and high energy costs. So, for the processing of 1 m ^{3 of} distillation liquid using this technology, 13.2 m ^{3 of} gas from lime kilns and 2.31 GJ of energy are needed.

The present invention solves the technical problem of simplifying the method of processing distiller liquid, reducing energy costs for processing and obtaining calcium hydroxide, sodium hydroxide and chlorine as commercial products.

The essence of the invention lies in the fact that the distillation liquid according to the invention is treated with sodium hydroxide at a molar ratio of CaCl ₂ : NaOH equal to 1: 2 ÷ 2.25 (mainly 1: 2), the resulting precipitate of calcium hydroxide is filtered off, and the filtrate consisting of sodium chloride is subjected to electrochemical processing in a two-chamber electrolyzer with a cation exchange membrane at a current density of 350 ÷ 1400 A / m ² to obtain sodium hydroxide and chlorine, and the filtrate is loaded into the anode chamber of the electrolyzer.

A method of processing a distiller liquid is as follows. The distillation liquid is treated with sodium hydroxide. In this case, calcium chloride passes into calcium hydroxide and precipitates

CaCl ₂ + 2NaOH → Ca (OH) ₂ + 2NaCl.

The filtrate obtained by separation of calcium hydroxide and containing sodium chloride is placed in the anode chamber of a two-chamber electrolyzer with a cation exchange membrane K (see Fig. 1). In the cathode chamber to create the initial electrical conductivity is placed 0.1 N. sodium hydroxide solution. In the electric field created in the electrolyzer, when voltage is applied to the electrodes, Na ⁺ cations are transferred from the anode chamber through the cation exchange membrane to the cathode chamber of the electrolyzer. In the cathode chamber, water decomposes with the release of gaseous hydrogen and the formation of OH ions ^-

2H ₂ O + 2e → H ₂ + 2OH ^- .

As a result of this, sodium hydroxide is concentrated in the cathode chamber in an amount greater than that necessary for the treatment of calcium chloride. Cl ^- ions decompose in the anode chamber

2Cl ^- -2e → Cl ₂

with the formation of gaseous chlorine. Thus, in the anode chamber of the electrolyzer is the extraction of sodium chloride from the filtrate.

As a result of processing 1 m ^{3 of} distillation liquid can be obtained in the form of marketable products:

calcium hydroxide, kg 66.7 sodium hydroxide, kg 34.2 chlorine kg 94.3

Example 1

Sodium hydroxide is added to 100 ml of distillation liquid obtained in the production of soda ash at Sterlitamak Soda OJSC and containing 105.6 g / l calcium chloride and 50.5 g / l sodium chloride, and the concentration of calcium chloride is determined after precipitation of calcium hydroxide clarified liquid.

The results of the experiments are presented in table 1.

Table 1 The molar ratio of CaCl ₂ : NaOH 1: 1.75 1: 2 1: 2.25 The concentration of CaCl ₂ , g / l 26,4 0.51 0.47

From the results shown in table 1, it is seen that when the distillation liquid is treated with sodium hydroxide, calcium in the form of hydroxide precipitates. The content of calcium chloride remaining in the solution depends on the amount of alkali added. Moreover, an increase in the molar ratio of CaCl ₂ : NaOH of more than 1: 2 does not lead to a noticeable decrease in the concentration of calcium chloride in the clarified part of the distiller liquid.

Example 2

A solution obtained from a distiller liquid is pumped through the anode chamber of a two-chamber electrolyzer with a MK-40 cation-exchange membrane brand after sodium hydroxide is added to it at a molar ratio of CaCl ₂ : NaOH equal to 1: 2 and calcium chloride is isolated from it in the form of hydroxide. Before the experiment, 0.1 N is poured into the cathode chamber. sodium hydroxide solution. The process of electrochemical processing is carried out at room temperature for 6 hours at various current loads.

The results of the experiments are presented in table 2.

table 2 Current density, A / m ² The concentration of NaOH, g / l Current output,% The cost of electricity, GJ / m ³ 357 492 63.3 1.42 714 490 65.1 1.65 1074 500 62,4 1.98 1429 510 64.5 2.00

From the data presented in table 2, it is seen that sodium hydroxide with a concentration of 490 ÷ 510 g / l is formed in the cathode chamber of the electrolyzer. The current output of sodium hydroxide ranges from 62.4 ÷ 65.1%, without detecting a dependence on the current density. The cost of electricity for processing 1 m ^{3 of} distiller liquid increases with increasing current load on the cell and varies from 1.42 to 2.00 GJ / m ³ . With an increase in current density above 1429 A / m ^2, there is a significant heating of solutions in the electrolyzer and a sharp increase in energy consumption, therefore, an increase in current density above 1429 A / m ^{2 is} undesirable.

Using the proposed method for processing distillation liquid of ammonia-soda production in comparison with the existing one has the following advantages:

a) reduction of energy consumption for the processing of distiller liquid;

b) obtaining calcium hydroxide, sodium hydroxide and chlorine in the form of marketable products;

c) obtaining water purified from calcium and sodium chlorides.

Claims (1)

A method of processing an ammonia-soda production distiller liquid, characterized in that the distiller liquid is treated with sodium hydroxide at a molar ratio of CaCl ₂ : NaOH of 1: 2 ÷ 2.25, the resulting calcium hydroxide precipitate is filtered off, and the filtrate consisting of sodium chloride are subjected to electrochemical processing in a two-chamber electrolyzer with a cation exchange membrane at a current density of 350 ÷ 1400 A / m ² to obtain sodium hydroxide and chlorine, and the filtrate is loaded into the anode chamber of the electrolyzer.

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