RU2560773C2 - Method of recycling chlororganic wastes - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to field of recycling chlorine-containing wastes of chemical industry productions. Method of recycling chlororganic wastes includes stages of their catalytic oxychlorination with mixture of oxygen-containing gas and hydrogen chloride and rectification of mixture of chlorohydrocarbons with release of tetrachloroethylene and trichloroethylene. Chlorohydrocarbons with boiling temperature in the range from temperature of trichloroethylene boiling to temperature of tetrachloroethylene boiling and highly boiling chlorohydrocarbons with boiling temperature higher than temperature of tetrachloroethylene boiling, obtained after rectification, are supplied for burning, products of burning are supplied to water trapping of gaseous hydrogen chloride and obtained hydrochloric acid is used at the stage of oxychlorination.

EFFECT: method is economical and environmentally friendly and makes it possible to obtain tetrachloroethylene and trichloroethylene with reduced hydrogen chloride consumption.

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Description

The invention relates to the field of processing of chlorine-containing waste from the chemical industry.

A number of methods for processing organochlorine wastes are known.

So, the known method [US Pat. RF 2288406, IPC F23G 7/04, C21B 5/02, publ. November 27, 2006] the destruction of organochlorine waste, which consists in the fact that the waste is injected into the blast furnace. The disadvantage of this method is that the waste productivity is limited by the productivity of the furnace itself and the products are metal chlorides in the slag, which itself is waste.

A known method of processing liquid chlorine-containing waste production of vinyl chloride [US Pat. RF 2159734, IPC С01В 7/01, op. November 27, 2000], in which the process is carried out in the presence of an aerosol catalyst.

A known method of producing hydrogen chloride HCl [US Pat. RF 2313514, IPC S07C 21/12, op. 12/27/07] from organochlorine wastes, including C ₁ -C ₂ hydrocarbons, through which they are subjected to exhaustive chlorination with chlorine in the presence of methane or lower chloromethanes, while the reaction is thermally thermally chlorinated. In this process, tetrachlorethylene is obtained as a commercial product. The disadvantages of this method are the formation in large quantities of solid carbon particles, and a high yield of carbon tetrachloride. In addition, carbon tetrachloride is difficult to further chlorine to produce tetrachlorethylene, and carbon tetrachloride production as a commercial product is limited to the Montreal Protocol.

A method for the disposal of organochlorine waste, [US Pat. RF 2431598, IPC С01В 7/01, op. October 20, 2011], in which they are subjected to thermal oxidation using oxygen, oxygen, nitric tetraoxide or nitric acid as an oxidizing agent. As a final product, a solution of hydrogen chloride in water is formed - hydrochloric acid. The disadvantage of these methods is that hydrochloric acid is not a highly profitable product, and the demand for it is currently fully satisfied.

In addition, a common drawback of all methods is the impossibility of obtaining from the waste marketable chemical products in demand on the market.

Closest to the claimed method is a method [Flid M.R., Treger Yu.A. Vinyl chloride: chemistry and technology. In 2 kn. Prince 2. - M .: publishing house Kalvis, 2008. - p. 158-160] the processing of organochlorine wastes from the production of chloromoronomers and chloropolymers, including wastes from the production of vinyl chloride, into commercial products — trichlorethylene and tetrachlorethylene using catalytic oxychlorination. The method is as follows: organochlorine waste, hydrogen chloride, hydrochloric acid and air are fed through an evaporator-superheater to an oxychlorination reactor filled with a copper chloride catalyst with the addition of alkali metal chlorides. Oxychlorination products are removed from the reactor and fed through a quenching nozzle and a quenching column irrigated with circulating diluted hydrochloric acid, while excess hydrochloric acid is constantly sent for disposal. Then organochlorine products are sent to a distillation unit for the separation of commercial products - perchlorethylene and trichlorethylene. Blow-offs formed at the stage of quenching and rectification are sent for sanitary cleaning. Organochlorine by-products formed in the oxychlorination step and separated from the commercial products in distillation columns are returned through an evaporator to the oxychlorination reactor.

Copper (II) chloride supported on an inert carrier is used as a catalyst for the oxychlorination process. With a high degree of resinification of the catalyst, it can be regenerated by supplying oxygen at a temperature of 450 ° C. However, this increases the ablation from the surface of the catalyst of copper chloride, which reduces the total resource of the catalyst.

Significant disadvantages of this method is that it requires hydrogen chloride in an amount of at least 0.8 kg per 1 kg of organochlorine waste, in addition, a secondary waste is formed in the process - a dilute solution of hydrochloric acid with a concentration of 2-5 wt.%, Contaminated with an admixture of organochlorine waste in an amount of at least 0.5 kg. Organochlorine compounds recirculating during the process with a boiling point above 121 ° C, especially completely chlorinated paraffins and arenas, are difficult to process in the oxychlorination reactor into the target products, which subsequently leads to accelerated resinification of the catalyst. These shortcomings cause a decrease in reactor efficiency and an increase in the cost of products.

The challenge facing the authors is to develop a method for processing organochlorine wastes with the production of tetrachlorethylene and trichlorethylene with reduced consumption of hydrogen chloride, economical and more environmentally friendly.

The essence of the proposed solution lies in the fact that the proposed method for processing organochlorine wastes, including the stages of their catalytic oxychlorination with a mixture of oxygen-containing gas and hydrogen chloride, distillation of a mixture of chlorohydrocarbons with the release of tetrachlorethylene and trichlorethylene, characterized in that chlorohydrocarbons with a boiling temperature lying in the range of three of boiling to the boiling point of tetrachlorethylene, and high-boiling chlorohydrocarbons with a boiling point above the temperature of ki eniya tetrachlorethylene obtained after rectification, is directed to incineration, products of combustion are directed to the water trapping of hydrogen chloride gas, hydrochloric acid and the resultant was used in the oxychlorination step.

Thus, the side high-boiling organochlorine compounds formed during the catalytic oxychlorination of organochlorine waste are sent to combustion to hydrogen chloride, followed by aqueous absorption of HCl and obtaining a concentrated hydrochloric acid solution, and at the oxychlorination stage this solution is used as a starting reagent, thereby replacing it with the earlier amount of hydrogen chloride.

This allows:

- to avoid the accumulation of high-boiling organochlorine compounds, thereby increasing the life of the catalyst;

- use hydrochloric acid generated in the process instead of expensive hydrogen chloride as a raw material;

- to avoid the formation of a large amount of liquid waste due to the recycling of hydrochloric acid, which was previously discarded as waste;

- the amount of secondary solid waste does not exceed 3% of the amount of recyclable waste.

During the catalytic oxychlorination of organochlorine wastes in the reactor, in addition to the target tetrachlorethylene and trichlorethylene, a mixture of organochlorine compounds is formed.

According to boiling points, this mixture can conditionally be divided into three groups:

- low boiling point with a boiling point not higher than the boiling point of trichlorethylene, i.e. 87.2 ° C

- intermediate compounds with a boiling point ranging from the boiling point of trichlorethylene (87.2 ° C) to the boiling point of tetrachlorethylene (121 ° C),

- high-boiling, with a boiling point above 121 ° C.

Low boiling compounds are recycled to the reactor for re-oxychlorination. Intermediate and high boiling compounds are sent to combustion to produce flue gases containing hydrogen chloride. Hydrogen chloride from flue gases is captured by dilute hydrochloric acid formed at the stage of quenching of oxychlorination products, strengthening the acid to a concentration of 15-25 wt.%.

The implementation of the proposed method allows to solve immediately all of the above disadvantages of the prototype: to ensure the recirculation of hydrochloric acid, which reduces the consumption of hydrogen chloride and, in addition, prevents the accumulation in the apparatus of high boiling compounds with a high molecular weight, which practically do not undergo oxychlorination, and polymerize, which causes resinification of the catalyst .

The scheme of a pilot plant for the processing of organochlorine wastes to produce trichlorethylene and tetrachlorethylene is shown in the Figure.

Installation includes (see. Figure):

evaporator 1,

oxychlorination reactor 2,

quenching nozzle 3, quenching column 4,

distillation columns 5, 6, 7, 8

combustion reactor 9,

mixing refrigerator 10,

scrubber 11.

The proposed method of processing chlorine-containing waste is as follows.

Liquid organochlorine wastes and a hydrochloric acid solution are metered into evaporator 1, where they co-evaporate and overheat to a temperature of 300-400 ° C, then their superheated vapors are mixed with a stream of air or oxygen, or their mixture and the resulting mixture is sent to reactor 2. In it, the process of oxychlorination occurs with the formation of a wide range of organochlorine compounds, while the total proportion of tetrachlorethylene and trichlorethylene in them is at least 50%, carbon dioxide and water. The gas-vapor mixture from the reactor 2 is fed to the quenching in the nozzle 3, irrigated with circulating hydrochloric acid with a concentration of 2-6%. Partially condensed reaction products are sent to a quenching column 4, to which 2-6% hydrochloric acid is also fed. Non-condensable gases from the column, mainly containing nitrogen, unreacted oxygen, water vapor, carbon dioxide, a small amount of organochlorine compound vapors are sent for sanitary cleaning.

Florentine is located in the lower part of the quenching column for density separation of two liquids: a diluted solution of hydrochloric acid with a concentration of 2-6% and a mixture of condensed organochlorine compounds.

Hydrochloric acid is directed to irrigate the mixing refrigerator 10, scrubber 11, quenching nozzle 3 and quenching column 4, while the excess part of hydrochloric acid, controlling the flow rate, is brought out to neutralize.

Organochlorine compounds are sent for distillation into four successive distillation columns. On the column 5, low-boiling products are separated, which are returned to the evaporator 1. On the column 6, a marketable product is isolated - trichlorethylene with a purity of not less than 99.5%, the bottom residue from this column is sent for separation to the column 7, which is intended for separation from the mixture of intermediate organochlorine compounds . Column 8 emit the second commercial product - tetrachlorethylene with a purity of at least 99.5%. The bottoms from this column are combined with intermediate compounds from the column 7, they are sent to the combustion reactor 9, which also serves air, or enriched air and propane-butane mixture to maintain combustion and achieve the desired flame temperature. The flue gases from the combustion reactor for cooling and quenching are fed to the mixing refrigerator 10 and then to the scrubber 11, in which almost complete removal of hydrogen chloride from the flue gases, their cooling. Hydrochloric acid hardens to a concentration of 15-25%.

Thus, the consumption of components is selected in such a way that exclusively solid waste is generated in the method, the amount of which does not exceed 3% by weight, of the amount of organochlorine waste received for processing.

The following are examples of specific process implementations.

Example 1

Typical organochlorine wastes from vinyl chloride production, consisting of 74.1 wt.% Dichloroethane, 10.5 wt.% Trichloromethane, 7.3 wt.% Tetrachlorethylene, 1.4 wt.% Tetrachloromethane, 6.7 wt.% Dichloroethylene, are fed into evaporator 1 with a flow rate of 1.25 kg / h. A solution of hydrochloric acid with a concentration of 20 wt.% From a scrubber 11 with a flow rate of 2, 3 kg / h is sent here.

At the outlet of the evaporator, a temperature of 350 ° C. is maintained. To compensate for the lack of chlorine in organochlorine wastes, anhydrous hydrogen chloride is also fed to the evaporator at a rate of 0.06 kg / h. Vapors from evaporator 1 are mixed with oxygen and air before flowing into the reactor at flow rates of 0.17 m ³ / h and 0.52 m ³ / h, respectively.

The oxychlorination process is carried out in a reactor at a temperature of 379 ° C and a pressure of 0.06 MPa. An oxychlorination reactor 2 exits a stream of reaction products at a rate of 4.35 kg / h.

Their composition: 11.8 wt.% Tetrachlorethylene, 11.8 wt.% Trichlorethylene, 0.4 wt.% Tetrachloromethane, 1.9 wt.% Dichloroethylene, 1.3 wt.% Trichloroethane, 3.8 wt.% Tetrachlorethane , 5.3 wt.% Pentachloroethane, hexachloroethane and other products, high-boiling compounds, 0.5 wt.% Carbon dioxide, 50 wt.% Water vapor, 1.3 wt.% Hydrogen chloride, 0.8 wt.% Oxygen, 11 , 1 wt.% Nitrogen. The products of oxychlorination from reactor 2 are fed into the quenching nozzle 3, which also contains a solution of hydrochloric acid with a concentration of 3 wt.% With a flow rate of 59 kg / h. The vapor-liquid mixture from the nozzle 3 enters the quenching column 4. A solution of hydrochloric acid with a concentration of 3% at a flow rate of 59 kg / h is supplied to the upper part of the column. Using a refrigerator of hydrochloric acid (not shown in the figure), a temperature of 30 ° C. is maintained in the quenching column.

In the Florentine of column 4, the liquid is separated into an organic layer of organochlorine compounds and a hydrochloric acid solution. Organochlorine compounds are removed by gravity from the lower outlet of the cube of quench column 4 with a flow rate of 1.58 kg / h, directed to rectification to column 5. From the middle outlet of the cube of quench column, hydrochloric acid is discharged to irrigate the quench nozzle and column with a total flow rate of 118 kg / h. The upper outlet of the column cube is designed to withdraw water additionally generated in the reactor with hydrogen chloride dissolved in it with a total flow rate of 2.14 kg / h, while the flow is divided into two parts: with a flow rate of 1.69 kg / h is fed to the scrubber 11 for strengthening , and with a flow rate of 0.46 kg / h is displayed for neutralization with a solution of sodium hydroxide.

Organochlorine compounds are fed to the column 5, on which there is a separation from a mixture of substances having a boiling point of not more than 87.2 ° C. In this case, the distillate with a flow rate of 0.1 kg / h mainly consists of chloroform, carbon tetrachloride, dichloroethylene and other compounds with a boiling point less than 87.2 ° C. The distillate is mixed with the original organochlorine waste and enters the evaporator 1. The bottoms of column 5 with a flow rate of 3.6 kg / h are sent to column 6, designed to isolate a commercial product - trichlorethylene with a purity of 99.5 wt.% In the form of distillate. The consumption of distillate is 0.52 kg / h.

The bottom residue of column 6 is sent to a distillation column 7, designed to separate the intermediate organochlorine compounds from the mixture. A distillate with a flow rate of 0.06 kg / h, consisting mainly of trichloroethane, is combined with high-boiling compounds and fed to a reactor 9. The bottom residue from this column is fed to a column 8, which is used to isolate tetrachlorethylene, which leaves as a distillate, with a purity of 99.5 wt.% with a flow rate of 0.52 kg / h. The bottom residue from this column, consisting of high-boiling compounds, with a flow rate of 0.38 kg / h is sent to the reactor 9 for combustion.

Organochlorine compounds with a total flow rate of 0.58 kg / h, air with a flow rate of 1.5 m ³ / h and a propane-butane mixture with a flow rate of 0.2 kg / h are fed into combustion reactor 9, while maintaining a temperature of 1200 ° C in the furnace. The flue gases from the reactor with a flow rate of 2.28 kg / h are sent to a mixing refrigerator 10, where hydrochloric acid with a concentration of 20 wt.% Is supplied with a flow rate of 80 kg / h. From the heat exchanger 10, the partially condensed mixture is sent to a scrubber, where the final capture of hydrogen chloride with a 3% hydrochloric acid solution is fed to the column at a rate of 1.69 kg / h. Non-condensable gases in the amount of 1.67 kg / h are sent for sanitary cleaning. Hardened hydrochloric acid with a flow rate of 2.3 kg / h and a concentration of 20 wt.% Sent to the evaporator 1 for oxychlorination.

Thus, the problem facing the developers of the proposed technical solution has been solved: a method has been created for processing organochlorine wastes to produce tetrachlorethylene and trichlorethylene with reduced consumption of hydrogen chloride, which is economical and more environmentally friendly.

Claims (1)

 A method of processing organochlorine wastes, including the stages of their catalytic oxychlorination with a mixture of oxygen-containing gas and hydrogen chloride, rectification of a mixture of chlorohydrocarbons with the release of tetrachlorethylene and trichlorethylene, characterized in that chlorohydrocarbons with a boiling point lying in the range from the boiling point of trichlorethylene to the boiling point of hydrogen chloride and tetrachloride boiling point higher than the boiling point of tetrachlorethylene obtained after distillation, e.g. vlyayut for combustion, the combustion products are directed to the water trapping of hydrogen chloride gas and the resulting hydrochloric acid is used in the oxychlorination step.

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