RU2498937C1 - Method of extracting chlorine from chlorine and vinyl chloride production wastes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to a method of extracting chlorine from chlorine and vinyl chloride production wastes. The method involves burning organochlorine wastes and producing chlorine by electrolysis. Without additional removal of chlorine and other impurities, hydrochloric acid from the waste incineration apparatus is mixed in a reaction vessel with a stream or part of a stream of anolyte from the electrolysis apparatus, which contains an electrolysis waste - sodium chlorate in amount of 0.5-10 g/dm³, at temperature of 92-106°C, while keeping concentration of hydrochloric acid in the reaction mass at 10-20 g/dm³. The method enables to avoid formation of chlorine dioxide and cuts the duration of decomposing sodium chlorate to sodium chloride and molecular chlorine, which is returned to the production process to the step for synthesis of 1,2-dichloroethane, an intermediate product in production of vinyl chloride.

EFFECT: invention also increases efficiency of production due to rational use of raw materials.

2 cl, 2 tbl, 7 ex

Description

Vinyl chloride (VC) is a large-capacity intermediate product of organic synthesis. More than 95% of it is used for the production of polyvinyl chloride (PVC) and copolymers. PVC is one of the most important base polymers, along with polyethylene and polypropylene. World production and consumption of PVC is about 35 million tons per year.

In industrial practice, VC is obtained by a balanced method from chlorine and ethylene through the gas-phase, thermal dehydrochlorination step of intermediate 1,2-dichloroethane

$${\text{C}}_{\text{2}}{\text{H}}_{\text{four}}+{\text{Cl}}_{\text{2}}={\text{C}}_{\text{2}}{\text{H}}_{\text{four}}{\text{Cl}}_{\text{2}}\left(\text{one}\right)$$

$${\text{C}}_{\text{2}}{\text{H}}_{\text{four}}{\text{Cl}}_{\text{2}}={\text{C}}_{\text{2}}{\text{H}}_{\text{3}}\text{Cl}+\text{Hcl}\left(\text{2}\right)$$

$${\text{C}}_{\text{2}}{\text{H}}_{\text{four}}+\text{2HCl}+\text{0}{\text{.5O}}_{\text{2}}={\text{C}}_{\text{2}}{\text{H}}_{\text{four}}{\text{Cl}}_{\text{2}}+{\text{H}}_{\text{2}}\text{O}\left(\text{3}\right)$$

This method produces more than 90% of the total world VC volume (Bunten M.J. et.al. Encyclopedia of Polymer Science and Engineering. Vol.17 and Supplement - Jon Wiley & Sons Inc., 1989, p. 247 [1]).

Chlorine in the global chemical industry is obtained by electrolysis of aqueous solutions of alkali metal chlorides, in particular sodium chloride.

$$\text{NaCl}+{\text{H}}_{\text{2}}\text{O}=\text{0}{\text{.5Cl}}_{\text{2}}+\text{0}{\text{.5H}}_{\text{2}}+\text{NaOH}\text{(four)}$$

Organochlorine by-products, such as isomeric trichloroethanes, isomeric tetrachloroethanes, pentachloroethane, trichlorethylene, perchlorethylene, 1,1-dichloroethane, chloroform, etc. are formed at all stages of the balanced production method of VC (see equations 1-3). These by-products are concentrated in cubes and phlegm distillation columns and make up production waste. In modern installations for the production of BX, these wastes are generated in an amount of 20-30 kg. for each ton of BX and must be disposed of. The most economical method for the disposal of organochlorine wastes is burning in furnaces at temperatures of 950-1200 ° C, followed by extraction of hydrogen chloride from the flue gases. Hydrogen chloride is usually absorbed by water, forming 3-20% concentration of hydrochloric acid and contaminated with impurities of chlorine, iron compounds, etc. (Muganlinsky F.F., Treger Yu.A., Lyushin M.M. Chemistry and technology of organohalogen compounds. - M .: Chemistry, 1991, p.202-216 [2]). Due to the presence of impurities, primarily dissolved chlorine, the use of hydrochloric acid is difficult. It does not find sale and in some cases it is neutralized and discharged into chemical contaminated effluents, which are subject to special treatment. Or hydrochloric acid is purified on special plants to various depths, depending on the purpose of its further use. (Levinsky M.I., Mazanko A.F., Novikov I.N. Hydrogen chloride and hydrochloric acid. - M.: Chemistry, 1985, p.25-95 [3]). Modern integrated plants for the production of VC include an organochlorine waste incinerator, as well as a purification and preparation unit for hydrochloric acid and hydrogen chloride for further use.

In the electrolysis of aqueous solutions of sodium chloride (brines), along with chlorine, hydrogen and caustic, a by-product of sodium chlorate is formed. The latter pollutes the brine - anolyte cycle (RAC), increases the corrosion activity of brines. The sodium chlorate content in the RAC varies in the range of 0.5-15 g / dm ³ . Due to the increased corrosion activity of the RAC, there is a need to protect equipment and pipelines or to manufacture them from special materials resistant to corrosion.

The present invention relates to methods for the production of chlorine and BX. The purpose of the invention is to increase production efficiency due to the rational use of raw materials, simplifying the technological scheme of the integrated production of chlorine and BX, reducing operational and capital costs.

This goal is achieved in that a stream of hydrochloric acid with a concentration of 4-20% obtained from the installation for the combustion of organochlorine wastes produced by BX without additional purification from chlorine and other impurities is combined with the anolyte stream from the electrolysis unit (full or part of the stream) containing sodium chlorate in an amount 0.5-10 g / dm ³ in the mixer. From the mixer, the combined flows through a steam mixer enter a reactor operating at a temperature of 92-106 ° C and a pressure of 0.15-0.2 MPa, in which hydrochloric acid from an organochlorine waste incinerator is oxidized by sodium chlorate from anolyte to molecular chlorine, and sodium chlorate is converted to sodium chloride .

$${\text{NaClO}}_{\text{3}}+\text{6HCl}={\text{3Cl}}_{\text{2}}\uparrow +\text{NaCl}+{\text{3H}}_{\text{2}}\text{O}\left(\text{5}\right)$$

The resulting chlorine is removed from the reactor to the factory-wide wet chlorine collector, then goes through the drying stage and goes to the synthesis unit for 1,2-dichloroethane, an intermediate in the production of VC (see equations 1, 2). The liquid reaction mixture from the reactor, which is a brine in which sodium chlorate is converted to sodium chloride, enters the general stream of anolyte for vacuum dechlorination and further processing according to the existing technological scheme.

Thus, chlorine contained in organochlorine wastes produced by VC is extracted from them after combustion and conversion to hydrochloric acid due to oxidation by electrolysis waste, namely sodium chlorate. The extracted chlorine is returned to the production process at the highly selective stage of direct chlorination of ethylene to produce 1,2-dichloroethane (see equation 1) of the intermediate synthesis of VC. At the same time, sodium chlorate is removed from the RAC to concentrations sufficient to reduce the corrosive activity of the brine. This scheme defines the economic effect of the present invention.

EP 1149861 A1 [4] claims a method for recovering hydrogen chloride from an organochlorine waste incinerator for the production of VC to the ethylene oxychlorination step. In this method, hydrochloric acid is purified from dissolved chlorine and other impurities by reducing them with hydrazine or hydroxylamine hydrochloric acid or sodium thiosulfate. For purification in the environment, a redox potential is created in the range of 600-850 mV (not more than 900 mV). For further purification, the acid is distilled. Then, gaseous hydrogen chloride is extracted from it, dried, compressed and sent to the stream to the oxychlorination reactor of the BX production unit. This method in comparison with the claimed in the present invention has significant disadvantages due to the need for purification of hydrochloric acid with expensive and toxic reagents, distillation of the acid, extraction of dry hydrogen chloride and its compression. Hydrogen chloride is sent to the oxychlorination step, which is less selective for 1,2-dichloroethane than the direct chlorination step. It is well known from world practice in the production of VX that reaction (1) proceeds with a selectivity of more than 99.5%, and reaction (3) with a selectivity of 97.5-98.5%. In connection with this fact, in patent DE 10252859 A1 [5], a method for producing VC is described, in which it is proposed to exclude the stage of ethylene oxychlorination from the scheme and replace it with direct catalytic oxidation of hydrogen chloride with oxygen to chlorine (equation (6). Thus obtained chlorine, goes to the stage of direct chlorination of ethylene (equation (1)). As an oxidation catalyst, it is proposed to use ruthenium and / or gold compounds on a support of choice from silicon dioxide, aluminum oxide, titanium dioxide, zirconium dioxide or their cm here is.

$$\text{2HCl}+\text{0}{\text{.5O}}_{\text{2}}\leftrightarrow {\text{Cl}}_{\text{2}}+{\text{H}}_{\text{2}}\text{O}\left(\text{6}\right)$$

Other methods are known for the catalytic oxidation of hydrogen chloride using various heterogeneous catalysts (the so-called Deacon method). In the international application WO 2010/040462 A1 [6], process gases containing hydrogen chloride are proposed to be oxidized using uranium compounds as catalysts, in particular Na ₆ U ₇ O ₂₄ or Ba ₃ U ₇ O ₂₄ . The claimed method, where the oxidation of hydrogen chloride is carried out on copper oxide in a fluidized bed in three reaction zones (WO 96/15066 [7]). Other heterogeneous catalytic systems based on transition metal oxides with additions of alkali metal chlorides and trivalent rare-earth metal chlorides for the oxidation of hydrogen chloride to chlorine (equation 6) in complex multi-stage processes at temperatures above 300 ° C (WO 91/06505 [8]) are described. In patent RU 2373139 C1 [9] a vanadium catalyst for the oxidation of hydrogen chloride by oxygen at temperatures of 270-370 ° C is claimed. US Pat. No. 5,707,919 [10] claims a complex catalyst based on dichromium trioxide.

The catalytic methods for the oxidation of hydrogen chloride, compared with our proposed method, have a number of significant drawbacks, namely: the need to prepare special catalysts with a complex composition, high reaction temperatures, insufficient depth of the process due to the equilibrium of reaction 6 and thermodynamic limitations, the presence and necessity of oxygen preparation or oxygen-containing gas. For the process in a fluidized bed of catalyst requires complex equipment (see, for example, US patent No. 7736589 B2 [11]).

In our proposed method, hydrogen chloride in the form of hydrochloric acid from an organochlorine waste incinerator is oxidized in the liquid phase to molecular chlorine without additional preparation, in a simple reactor at a temperature of 92-106 ° С, sodium chlorate contained in the anolyte from electrolysis cells, without preliminary isolation of the oxidizing agent from anolyte.

Several processes have been patented based on the known hydrogen chloride oxidation reaction with a mixture of nitric and sulfuric acids (US Patent No. 3950501, International Application No. WO 01/49600 A1, EP Patent No. 1272425 A1 [12-14]). The process of oxidation of hydrogen chloride with nitric acid in the presence of concentrated sulfuric acid requires special hardware design from materials resistant to a mixture of aggressive acids, includes the stages of oxidation of nitrous acid to nitric oxygen after the main reaction and concentration of sulfuric acid by distillation. These are the main disadvantages of this method compared to the proposed one.

A known method of producing chlorine from gaseous hydrogen chloride (patent RU 2253607 C1 [15]) by oxidizing with air oxygen when the reaction mixture is irradiated with high-pressure mercury-quartz lamps with a radiation volume density (10-40) × 10 ⁴ W / cm ³ . To suppress the hydrolysis of chlorine with water, the mixture is cooled in a condenser to 2-3 ° C. This method is suitable for installations of low power, and requires special hardware design. Another known method for producing chlorine from hydrogen chloride is described in patent SU 1801943 A1 [16]. The oxidation process is proposed to be carried out in the zone of electric pulse discharges at a space velocity of 26-413 h ^-1 . The main disadvantage of the method is low chlorine yields - at the level of 40%.

Several patents describe methods for the destruction of sodium chlorate in sodium chloride brines with concentrated hydrochloric acid. US Pat. No. 4,169,773 [17] proposes to treat a portion of the anolyte from an electrolysis unit with hydrochloric acid in a stoichiometric or excess ratio in accordance with equation (5). The amount of excess in the patent is not specified. To remove explosive chlorine dioxide from the reaction mixture formed by reaction equation (7), it is irradiated with ultraviolet light.

$${\text{NaClO}}_{\text{3}}+\text{2HCl}={\text{Clo}}_{\text{2}}+\text{0}{\text{.5Cl}}_{\text{2}}+\text{NaCl}+{\text{H}}_{\text{2}}\text{O}\left(\text{7}\right)$$

Similar conditions for the destruction of sodium chlorate in brine are described in patents US 4481088 [18] and EP 0098500 Al [19]. Sodium chlorate is destroyed by concentrated hydrochloric acid (30-35%) in the brine obtained after the operation of additional saturation of depleted brine from electrolyzers. Acid is used in an amount of 6-10 mol per mol of sodium chlorate. The yield of chlorine dioxide is about 11% of the mass of chlorine formed.

We found that while maintaining the concentration of hydrogen chloride in the reaction mixtures in an amount of 10-20 g / dm ^{3 in} excess of stoichiometry (equation (5)), the formation of chlorine dioxide is almost completely suppressed, and the destruction time of sodium chlorate decreases. Maintaining an acid concentration of 10-20 g / dm ³ is of particular importance when removing small concentrations (less than 0.5 g / dm ³ ) of sodium chlorate from the RAC, which are difficult to destroy, probably due to a decrease in the reaction rate at low concentrations. This is confirmed by the fact that temperature has a great influence on the rate of destruction of sodium chlorate. Conclusions are made on the basis of laboratory experiments, the results are shown in table 1.

The presence of sodium chlorate in the anolyte at a level of 0.3 g / dm ³ increases the corrosiveness of the medium against carbon steel and steel D.

The content of chlorine dioxide was controlled by a photometric method based on the ability of chlorine dioxide (ClO ₂ ) in the presence of malonic acid to convert the colorless form of N, N-diethyl-para-phenylenediamine to a semi-oxidized colored form. When the concentration in the reaction mass of hydrogen chloride is more than 10 g / dm ^{3, the} formation of chlorine dioxide is not observed (the detection limit of the analytical method is 0.05 mg / dm ³ ).

Table 1 The effect of excess hydrogen chloride and temperature on the rate of destruction of sodium chlorate in the anolyte. The initial content of NaClO ₃ , mg / DM Test conditions The destruction time of NaClO ₃ in the given conditions, min The content of NaClO ₃ after testing, mg / DM ³ (conversion,%) Temperature ° C The content of HCl, g / DM ³ pH 380 90-92 18.6 0.29 10 210 (44.7) 380 90-92 18.6 0.29 twenty 130 (65.8) 380 90-92 18.6 0.29 thirty 35 (90.7) 380 90-92 fifteen 0.40 thirty 135 (64.5) 380 90-92 fifteen 0.40 40 50 (86.8) 380 106 18.6 0.29 5 19 (95.0) 380 106 18.6 0.29 10 5.4 (98.6) 380 106 14.9 0.38 5 25 (93.4) 380 106 14.9 0.38 10 5 (98.7) 400 106 11.16 0.51 5 140 (65.0) 400 106 11.16 0.51 10 74 (81.5) 400 106 11.16 0.51 twenty 3 (99.2) 400 106 7.44 0.68 10 320 (20.0) 400 106 7.44 0.68 fifteen 190 (52.5) 400 106 7.44 0.68 thirty 61 (84.7)

Sufficient time for the destruction of sodium chlorate in the anolyte with a sodium chloride concentration of more than 150 g / dm ³ to a residual chlorate concentration of about 0.1 g / dm ³ is 25-30 minutes. The higher the concentration of sodium chloride in the initial solution, the shorter the time required for the destruction of chlorate (see table 2). These data are consistent with those cited in the previously mentioned patents [18-19].

table 2 The dependence of the time of destruction of sodium chlorate on the concentration of sodium chloride in brine. The concentration of the component in the initial mixture Experience Parameters The concentration of the component in the mixture after the experiment. NaCl, g / dm ³ HCl, g / dm ³ NaClO ₃ g / dm ³ t, ° C Min time HCl, g / dm ³ NaClO ₃ g / dm ³ 150 17.5 1.18 103-104 10 15.9 0.40 twenty 15.4 0.18 25 15.3 0.15 thirty 15.3 0.12 35 15.1 0.05 165 17.5 1.18 103-104 10 15.8 0.37 fifteen 15.4 0.17 twenty 15.3 0.15 25 15.3 0.11 thirty 15.0 0.05 175 17.5 1.18 103-104 10 15.7 0.33 fifteen 15.4 0.17 twenty 15.2 0.09 25 15.0 0.05

The present invention is illustrated by the following examples:

Example 1

Part of the flow of anolyte from electrolysis cells in an amount of 20.1 m ³ / h is mixed with 11 m ³ / h of hydrochloric acid from a waste incinerator in a static mixer. Then the mixture from the static mixer through the steam mixer, where it is heated to 95-106 ° C, enters the reaction vessel. The temperature in the reaction zone is 102 ° C. The concentration of sodium chlorate in the anolyte is 1.2 g / dm ³ , the concentration of hydrogen chloride in hydrochloric acid from the waste incinerator is 5.5% of the mass. The residence time of the reaction mass in the reaction vessel is 30 minutes The released chlorine from the upper part of the reaction vessel enters the plant-wide wet chlorine collector and then is dried. Anolyte from a reaction vessel with a concentration of sodium chlorate 0.07 g / dm ³ and hydrogen chloride 14.8 g / dm ^{3 is} combined with the main stream of anolyte from electrolysis cells and fed to a vacuum dechlorination unit and then processed according to the existing technological scheme. The degree of destruction of sodium chlorate is 91.0%. Chlorine dioxide is not detected. The resulting chlorine, together with the main chlorine stream from the electrolysis after drying, goes to the installation for the synthesis of 1,2-dichloroethane intermediate product of the production of VC.

Example 2

20.4 m ³ / h of anolyte from electrolyzers with a sodium chlorate concentration of 1.26 g / dm ³ is mixed with 10 m ³ / h of hydrochloric acid at a concentration of 5% from the organic chlorine waste incinerator for the production of VC in a static mixer. Then the mixture enters the steam mixer, where 2 m ³ / hour of steam - 6 is supplied to heat the mixture and then to the reaction vessel. The residence time of the reaction mass in the vessel for 30 minutes at a temperature of 100 ° C. At the outlet of the reaction vessel, the concentration of sodium chlorate is 0.1 g / dm ³ , the degree of destruction of sodium chlorate 88.2%. Chlorine dioxide is not detected. The released chlorine from the upper part of the reaction vessel enters the plant-wide wet chlorine collector for drying and then for the synthesis of 1,2-dichloroethane. Anolyte after a reaction vessel with a concentration of hydrogen chloride of 15.3 g / dm ^{3 is} combined with the main stream of anolyte from electrolysis cells and is sent for further processing.

Examples 3-6.

A treatment of 18-21 m ³ / h of anolyte 10-11 m ³ / h of hydrochloric acid from the waste incinerator is carried out under similar conditions as described in examples 1-2. The degree of conversion of sodium chlorate in the anolyte was 89.0-92.2%.

Example 7

A mixture of 20 ml is quickly heated in a three-necked flask equipped with a reflux condenser, a thermometer, a dropping funnel and a system for trapping the released gases. (0.02 dm ³ ) 10% hydrochloric acid and 50 ml. (0.05 dm ³ ) brine containing 10.2 g / dm ³ sodium chlorate and 150 g / dm ³ sodium chloride. The mixture is aged at 100-103 ° C for 30 minutes. The released chlorine is captured in bottles filled with 10% potassium iodide solution. In this case, chlorine quantitatively displaces iodine from potassium iodide. The amount of iodine is determined by titration with a standard solution of sodium thiosulfate. Thus, the amount of chlorine formed is determined. The concentration of sodium chlorate in solution after the reaction was 0.143 g / dm ³ . The degree of conversion of sodium chlorate was 98.0%. Chlorine released 0.99 grams (99% of theory). The content of hydrogen chloride in the solution after the reaction of 15.3 g / DM ³ . Chlorine dioxide is not detected.

The invention can be used in the production of other organochlorine substances, for example, chloromethanes, allyl chloride, benzyl chloride, chlorobenzene, etc., i.e. where organochlorine wastes are generated and burned. In this case, the installation for the production of chlorine and caustic by the electrolysis method should be located from the combustion unit at a distance providing economic feasibility of organizing process flows as described in the present invention.

In addition, the invention can be used in the production of diisocyanates and polycarbonates, where there are significant amounts of by-product hydrogen chloride, and plants for the production of chlorine and caustic are included in a single production complex.

Claims (2)

1. A method of extracting chlorine from waste products of chlorine and vinyl chloride production, including the processes of burning organochlorine waste and producing chlorine by electrolysis, characterized in that hydrochloric acid from the waste incinerator without additional purification from chlorine and other impurities is mixed in the reaction vessel with a stream or part of a stream anolyte from an electrolysis unit containing electrolysis waste - sodium chlorate in an amount of 0.5-10 g / dm ³ , at a temperature of 92-106 ° C and maintaining the concentration of hydrochloric acid in the reaction mass 10-20 g / dm ³ , which eliminates the formation of chlorine dioxide and reduces the time of destruction of sodium chlorate with the formation of sodium chloride and molecular chlorine, which is returned to the production process at the stage of synthesis of 1,2-dichloroethane, an intermediate in the production of vinyl chloride. 2. The method according to claim 1, characterized in that the residence time of the reaction mass in the reaction vessel is 25-30 minutes