RU2282610C1 - Method for production of 1,2-dichloroethane with nitrogen addition - Google Patents

Abstract

FIELD: organic chemistry.

SUBSTANCE: 1,2-dichloroethane is obtained by liquid phase ethylene chlorination with discharging of reaction heat due to operation medium boiling. In claimed process nitrogen is added to chlorine and ethylene reagents. Ratio of chlorine volume consumption to nitrogen volume consumption is maintained as 1:1. Reaction is carried out at temperature lower than 1,2-dichloroethane boiling point, and discharging of reaction heat is carried out by evaporative cooling of operation medium in nitrogen.

EFFECT: process of increased selectivity; decreased yield of by-products.

1 tbl, 5 dwg

Description

The technical field to which the invention relates.

The invention relates to a method for producing 1,2-dichloroethane by high-temperature liquid-phase chlorination of ethylene with removal of the heat of reaction due to evaporation of the working medium during boiling.

The prior art.

The closest methods for producing 1,2-dichloroethane are high-temperature and low-temperature liquid-phase chlorination of ethylene [1].

The high-temperature process is carried out at a temperature equal to the boiling point of the working medium (83.5-110 ° C, depending on pressure). The high-temperature process reactor is a bubble gas lift column 1, equipped with an internal circulation pipe 4 (figure 1). The working medium is liquid 1,2-dichloroethane. The catalyst of the process is FeCl ₃ , which is in the reactor in dissolved form. To obtain a solution, gaseous chlorine through the distributor 2 is fed into the lower part of the annular space. The reaction is carried out upstream when gaseous ethylene is introduced into the reactor through a distributor 3. Due to the difference in density of the media in the circulation pipe and in the annular space, liquid circulation occurs. Perforated plates 6 are installed in the upper part of the reactor, designed to intensify mixing. The upper part of the reactor acts as a separator to separate liquid droplets from steam. The reaction products are discharged in the form of vapors to the rectification stage through a fitting in the reactor lid. Due to its low volatility, the catalyst remains in the reactor. To maintain the liquid level, 1,2-dichloroethane is introduced into the lower part of the reactor.

An important advantage of the high-temperature process in comparison with the low-temperature process is profitability: the heat generated is spent on evaporation and rectification of products, there is no waste water, and the consumption of catalyst is minimal.

The disadvantage of the high-temperature process is the low selectivity (98.0-98.7%), associated with an increase in the rate of adverse reactions with increasing temperature. By-products - trichloroethane, trichloethylene and other higher chlorine derivatives of ethane - are formed in the reactor as a result of substitution chlorination reactions. The rate of adverse reactions decreases with decreasing temperature [2]. When 1 mole of 1,2-dichloroethane is formed, a sufficient amount of heat is released to evaporate 6 moles of 1,2-dichloroethane.

The low-temperature process (figure 2) is carried out in a bubble column 1, connected in the upper and lower parts with a remote shell-and-tube heat exchanger 5. The working medium in the reactor is the reaction product - 1,2-dichloroethane in a liquid state. Chlorine is introduced into the bottom of the column through the distributor 2. Above, ethylene is introduced into the resulting chlorine solution through the distributor 3. Due to the difference in the densities of the media in the refrigerator and the column, the circulation of the working medium with an upward flow in the column occurs. The temperature in the reactor is 65 ° C. The synthesis product is removed by gravity through the overflow. The separation of the product from the catalyst is carried out at the stage of purification. The catalyst after the purification step cannot be regenerated. The products of the process from the purification stage go to rectification.

The advantage of the low-temperature process is its high selectivity (99.6%), which is explained by the slowdown of the side reactions of substitution chlorination with decreasing temperature. The disadvantages of the low-temperature process include a large flow of wastewater at the stage of purification of the product from the catalyst, a significant consumption of catalyst per unit of production, high energy costs for cooling the reaction mass, and irrational use of the heat of reaction.

Disclosure of the invention.

The objective of the invention is to develop a new method for the production of 1,2-dichloroethane by liquid-phase chlorination of ethylene with the addition of nitrogen in the reagents. It is proposed to carry out the process of liquid-phase chlorination of ethylene at a temperature below the boiling point of dichloroethane by adding nitrogen (ethylene and chlorine) to the feedstock to the reactor. Heat will not be removed during boiling, as in the high-temperature process, but due to the evaporation of 1,2-dichloroethane into nitrogen. At the outlet of the reactor, nitrogen is saturated with 1,2-dichloroethane vapors. The greater the nitrogen flow rate, the lower the temperature of the working medium (figure 3). The graph in (figure 3) is based on the material and thermal balances of the reactor. By reducing the temperature, the yield of by-products decreases. By reducing the yield of by-products, the selectivity of the process increases.

When implementing the invention, the following results can be obtained:

1. The addition of nitrogen to chlorine leads to a decrease in the concentration of chlorine in the gas phase. As a result of this, the equilibrium concentration of chlorine in the liquid decreases in accordance with Henry's law [3]:

where x ^* is the equilibrium concentration of gas in solution (mol. fractions); y _A is the concentration of chlorine in the gas (mol. fractions); m is the constant of phase equilibrium.

By reducing the concentration of chlorine in 1,2-dichloroethane, the rate of adverse reactions will decrease. This follows from the work [5], which shows that a decrease in the concentration of dissolved chlorine in a liquid leads to a decrease in the rate of formation of by-products in accordance with the equation:

where W is the rate of adverse reactions; k is the reaction rate constant; [C ₂ H ₄ ] is the concentration of ethylene in the liquid; [Cl ₂ ] is the concentration of chlorine in the liquid.

2. Gaseous nitrogen supplied additionally improves mixing of the working medium, eliminating stagnant zones. In [4], it was shown that the mixing coefficients in the apparatus with a bubble layer increase with increasing gas flow.

3. The temperature in the reactor is maintained below the boiling point, this leads to a decrease in the rate of adverse reactions. The dependence of the rate of adverse reactions on temperature is given in [6]:

where W is the rate of adverse reactions, c ^-1 ; R is the universal gas constant, J / (kmol · K); T is the temperature of the reaction mixture, K; [C ₂ H ₄ Cl ₂ ] is the concentration of 1,2-dichloroethane in the liquid. An increase in the rate of adverse reactions with increasing temperature is confirmed by [2].

Thus, when nitrogen is added to the reagents, more favorable conditions are created for the process.

A brief description of the drawings.

List of figures:

figure 1 - bubble gas lift reactor of high temperature liquid phase chlorination of ethylene;

figure 2 - bubble reactor low-temperature chlorination of ethylene;

figure 3 - dependence of the temperature of the working medium on the flow of nitrogen at a flow of chlorine of 3000 m ³ / h under normal conditions;

4 is a bubble gas lift reactor of a liquid phase chlorination of ethylene with the addition of nitrogen in the reactants;

Figure 5 - industrial bubble reactor.

1 and 2 describe analogues of the invention. In Fig. 3, a graph shows the dependence of the temperature of the working medium on the flow rate of nitrogen added to the reagents. Figure 4 describes a reactor in which the invention may be implemented. Figure 5 shows an industrial reactor, which tested a new method for producing 1,2-dichloroethane.

The implementation of the invention.

The invention is carried out in a bubble reactor of liquid-phase chlorination of ethylene. The temperature of the working medium in the reactor is maintained within 78-83 ° C at a pressure in the upper part of the reactor of 1 at. A bubble reactor for the production of 1,2-dichloroethane by liquid-phase chlorination of ethylene with the addition of nitrogen in the reactants (Fig. 4) works as follows. Gaseous chlorine with nitrogen through the distributor 2 is fed into the lower part of the annular space. The reaction is carried out upstream when gaseous ethylene with nitrogen is introduced into the reactor through a distributor 3. Due to the difference in density of the media in the circulation pipe and in the annular space, liquid circulation occurs. Perforated plates 6 are installed in the upper part of the reactor, designed to intensify mixing. The upper part of the reactor acts as a separator to separate liquid droplets from steam. In the gas-liquid separator 7, nitrogen is separated from the liquid product. Part of the condensed 1,2-dichloroethane to maintain the liquid level is pumped 9 to the lower part of the reactor, and the other part in the form of the finished product is discharged into collection tanks. Nitrogen from the gas-liquid separator 7 is fed by compressor 8 to the line of chlorine and ethylene.

The results of industrial tests of a method for producing 1,2-dichloroethane with the addition of nitrogen in reagents

The high selectivity of the new method for producing 1,2-dichloroethane was confirmed by tests at an industrial reactor (SayanskKhimplast JSC, Sayansk) with an estimated chlorine output of 300 m ³ / h. The reactor is a bubble gas lift column 1 with a diameter of 1.4 m, equipped with an internal circulation pipe 4 with an outer diameter of 219 mm and a height of 9600 mm (figure 5). Over the entire height of the column, five perforated plates are installed at a distance of 1000 mm from each other with a hole diameter of 12 mm.

The test procedure was as follows. The reactor was filled with 1,2-dichloroethane, after which chlorine together with nitrogen was supplied through switchgear 2, and ethylene through 3. Moreover, the ratio of the volumetric flow rate of chlorine to the volumetric flow rate of nitrogen was maintained 1: 1. Then, after the reactor was brought to a steady state, temperatures were measured in the upper and lower parts of the reactor, and the consumption of chlorine, ethylene, and nitrogen was monitored. The main operating parameters are given in table. one.

Table 1 The industrial test modes of the new method Mode number Chlorine consumption Ethylene consumption Nitrogen consumption T _Cf (in the upper part of the reactor), DCE, wt.% (At the exit of the capacitor) m ³ / h m ³ / h m ³ / h ° C one 240 250 240 77 99.94 2 204 210 210 76 99.93 3 235.2 245 240 77 99.94 four 230 245 240 77 99.96 5 243.6 245 250 77 99.92 6 235.2 240 240 76 99.92 7 239.4 240 240 76 99.95

The temperature of the working medium in the reactor was 76-77 ° C at a pressure in the top of the reactor of 1 atm, which is lower than the boiling point of 1,2-dichloroethane (83.5 ° C). Heat was removed through the evaporation of 1,2-dichloroethane into nitrogen. There was no boiling in the reactor.

In order to determine the selectivity of the process, samples of liquid 1,2-dichloroethane were analyzed at the outlet of the condenser 5, and the composition of the product was determined using gas-liquid chromatography. The results of the analyzes in table 1.

Tests showed that the selectivity of the process for producing 1,2-dichloroethane with the addition of nitrogen to the reagents was more than 99.9% (Table 1). For comparison, the selectivity of the process without the addition of nitrogen in the same reactor with a capacity of 300 m ³ / h was 98%. High selectivity was obtained with a ratio of chlorine to nitrogen consumption of 1: 1. Thus, a new method for producing 1,2-dichloroethane allows to increase the selectivity of the process from 98% to 99.90-99.97% compared with the high-temperature method, to reduce the yield of by-products.

Information sources

1. Lebedev N.N. Chemistry and technology of basic organic and petrochemical synthesis. Ed. 2nd, per. M .: Chemistry, 1975 - 736 p.

2. Avetyan M.G., Sonin E.V., Zaydman O.A. et al. Investigation of the process of direct chlorination of ethylene in an industrial environment. // Chemical industry, 1991, No. 12, S. 710-713.

3. Ramm V.M. Gas absorption. Ed. M .: Chemistry, 1966.

4. Dilman VV, Eisenbud M.B. On the coefficient of longitudinal mixing in flowing bubbler reactor columns. // Chemical industry, 1962, No. 8, p. 607.

5. Rozhkov V.I., Zaydman O.A., Sonin E.V., Krishtal N.F., Avetyan M.G., Treger Yu.A., Kharitonov V.I., Perevalov A.F., Mubarakov R.G. Patterns of liquid-phase chlorination of ethylene. // Chem. prom 1991. No. 7. P.398.

6. Rozhkov V.I., Zaydman O.A., Sonin E.V., Avetyan M.G., Krishtal N.F., Treger Yu.A., Kharitonov V.I. Liquid phase chlorination of 1,2-dichloroethane in the presence of ferric chloride. // Chem. prom 1991. No 5. P.261.

Claims (1)

A method of producing 1,2-dichloroethane by liquid-phase chlorination of ethylene with removal of the reaction heat due to boiling of the working medium, characterized in that nitrogen is added to the chlorine and ethylene reagents, and the ratio of the volumetric flow rate of chlorine to the volumetric flow rate of nitrogen is maintained 1: 1, while the process proceeds at a temperature below the boiling point of 1,2-dichloroethane, and the heat of reaction is removed by evaporative cooling of the working medium into nitrogen.

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