RU2328339C2 - Bubble kettle for liquid-phase ethylene chlorination with dispensed reagent supply - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: kettle contains the internal circular tube and perforated plates in the upper kettle part. In the kettle, the sequentially alternating dispensers of chlorine and ethylene are installed. The first and the last dispensers are those dispensing ethylene, and the distance between the adjacent dispensers is 1.2 - 1.5 m.

EFFECT: selectivity of process is increased while by-product output is reduced.

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Description

The technical field to which the invention relates.

The invention relates to organic synthesis technology and relates to a reactor for producing 1,2-dichloroethane by liquid-phase chlorination of ethylene with removal of the heat of reaction due to evaporation of the working medium. 1,2-Dichloroethane is an intermediate in the production of polyvinyl chloride and other polymeric materials.

The level of technology.

Close analogues to the proposed reactor for producing 1,2-dichloroethane are low-temperature and high-temperature reactors for liquid-phase chlorination of ethylene [1].

The low-temperature process reactor (Fig. 1) is a bubble column (1) connected in the upper and lower parts to a remote shell-and-tube heat exchanger (4). The working medium in the reactor is the reaction product - 1,2-dichloroethane in a liquid state with an admixture of by-products. Chlorine is introduced into the bottom of the column through a distributor (2). Above, ethylene is introduced into the resulting chlorine solution through a 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 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 the large consumption 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.

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 (5) (Fig. 2). 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 ethylene gas 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, fluid circulation occurs. Perforated plates (6) are installed in the upper part of the reactor, designed to intensify mixing. The upper part of the circulation pipe is in the form of a diffuser. The speed of the gas-liquid mixture in the diffuser is lower than the speed of free rise of gas bubbles, which contributes to the effective separation of gas from the liquid and prevents gas from entering the circulation pipe. This allows you to provide maximum driving force of the circulation process in the reactor. 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.

In a high-temperature chlorination reactor, chlorine and ethylene are fed into a liquid working medium, as a result of which liquid circulation occurs in the reactor [2, 3]. The flow rate of circulating 1,2-dichloroethane is 800 m ³ / h with an ethylene flow rate of 3000 m ³ / h and a chlorine flow rate of 3000 m ³ / h [2, 3]. The solubility of ethylene in 1,2-dichloroethane is 1.38 g per 1 kg of 1,2-dichloroethane [4]. In order for the entire ethylene flow rate of 3000 m ³ / h to dissolve in a stream of 1,2-dichloroethane 800 m ³ / h, the consumption of 1,2-dichloroethane 2400 m ³ / h is required [4]. Thus, in the available flow rate of circulating 1,2-dichloroethane, chlorine and ethylene do not completely dissolve. Insoluble chlorine and ethylene react in the gas phase with each other. According to [5], the interaction of chlorine and ethylene in the gas phase leads to an increase in the rate of side reactions and a decrease in the selectivity of the process. This is explained by the fact that in the gas phase, reactions proceed more rapidly than in liquids by a radical chain mechanism. Also in the gas phase there is no nonvolatile direct reaction catalyst [6], which is in a solution of 1,2-dichloroethane. This also leads to a decrease in the selectivity of the process. Thus, it is required to exclude the interaction of chlorine and ethylene in the gas phase.

Analogs of the bubbler reactor of liquid-phase chlorination of ethylene with a distributed input of reagents are also the inventions described in patents RU 2153394 C1, RU 2075344 C1, RU 2240861 C1. In these analogues, the interaction of chlorine and ethylene in the gas phase is also not excluded.

Of the analogues, the closest prototype for the proposed reactor is a high-temperature chlorination reactor (figure 2).

Disclosure of the invention.

The objective of the invention is to increase the selectivity of the process and reduce the yield of by-products while maintaining the advantages of the high-temperature process.

The proposed reactor is a gas lift column with distribution devices for introducing chlorine and ethylene. To improve the circulation of the working medium, a circulation pipe is installed inside the reactor. At the top of the reactor there are perforated plates designed to intensify mixing.

The task of the invention is solved due to the fact that, in contrast to the prototype, several chlorine and ethylene distributors alternating with each other in height are installed in the reactor, and the source ethylene is fed into the first and last distributors (Fig. 3). The results of operation of industrial reactors and laboratory experiments [7] (Fig. 4) show that the distance between adjacent chlorine and ethylene distributors should be 1.2-1.5 m. In this case, gaseous chlorine and ethylene have time to dissolve in the liquid.

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

1. Increasing the selectivity of the process and reducing the yield of by-products;

2. Reducing the required diameter of the reactor.

These technical results are achieved due to the fact that in the inventive bubbling reactor of liquid-phase chlorination of ethylene due to the installation of several switchgears with alternating supply of ethylene and chlorine from bottom to top along the height of the reactor (with ethylene being supplied to the first and last distributors), the initial chlorine and ethylene are dissolved more completely and uniformly without contact of chlorine and ethylene in the gas phase. In this case, the ethylene flow rate through one distributor is selected so as to ensure complete dissolution of ethylene in the given 1,2-dichloroethane flow rate. For example, based on data on the solubility of ethylene [4] at a flow rate of circulating 1,2-dichloroethane of 800 m ³ / h, the consumption of ethylene should be no more than 2400 m ³ / h.

This avoids the occurrence of the chlorination process in the gas phase, which leads to a decrease in the yield of by-products and an increase in the selectivity of the process as a whole [5].

A brief description of the drawings.

The design of the analogs of the reactor are presented in figure 1. and figure 2. Figure 1 schematically shows a General view of a low-temperature chlorination reactor, and Fig.2 - high-temperature.

Figure 1. The low-temperature ethylene chlorination bubble reactor consists of a column (1), gas distributors of chlorine (2) and ethylene (3), and a refrigerator (4).

Figure 2. The bubble gas-lift reactor of high-temperature liquid-phase chlorination of ethylene consists of a column (1), gas distributors of chlorine (2) and ethylene (3), a circulation pipe (5) and perforated plates (6).

Figure 3 shows the design of the proposed reactor with a distributed input of regents.

Figure 3. The bubbled reactor with distributed reagent inlet consists of a column (1), chlorine gas distributors (2) and (3), a circulation pipe (5) and perforated plates (6).

Figure 4. An experimental setup to study the dissolution of ethylene and chlorine bubbles. The installation consists of a glass tube (7), a gas cylinder (8), a connecting tube (9), lower and upper caps (10) and (12), a ruler (11), a pressure gauge (13), gaskets (14), and valve (15).

The implementation of the invention.

A bubble reactor of liquid-phase chlorination of ethylene with a distributed input of reagents operates as follows. The reactor is filled with liquid 1,2-dichloroethane to a working level. The flow of ethylene through the distributors (3) is turned on. The flow of chlorine gas (2) is turned on. The ethylene flow rate through a separate distributor is selected so as to ensure complete dissolution of ethylene in a given 1,2-dichloroethane flow rate. For example, based on data on the solubility of ethylene [4] at a flow rate of circulating 1,2-dichloroethane of 800 m ³ / h, the consumption of ethylene should be no more than 2400 m ³ / h. The introduction of the starting reagents through several distribution devices allows you to completely dissolve them in the liquid and exclude the interaction of chlorine and ethylene in the gas phase, which increases the selectivity of the process [5]. It also increases the uniformity of the distribution of the reactants along the height of the reactor.

As a result of the reaction, a large amount of heat is generated, due to which the reaction mixture boils. Due to the difference in density of the media in the circulation pipe and in the annular space, fluid circulation occurs. The resulting 1,2-dichloroethane in the form of vapors is removed from the top of the reactor, which makes it possible to remove together with the product the heat that is released during the chlorination reaction.

The distance between the distributors and their order depend on the rate of dissolution of gases in the working medium and was determined on the basis of experimental data [7]. Experimentally investigated the dissolution rate of chlorine bubbles and ethylene in 1,2-dichloroethane in a laboratory setting (figure 4). The dissolution rate was judged by the change in bubble volume over time. It was found that ethylene bubbles dissolve in 1,2-dichloroethane faster than chlorine bubbles. The mass transfer coefficient in a liquid upon dissolution of ethylene bubbles is 0.0006 m / s [7].

Chlorine dissolves in pure 1,2-dichloroethane more slowly than ethylene. The low dissolution rate of chlorine is due to the surface resistance of the solution. The mass transfer coefficient in a liquid during the dissolution of chlorine was 0.5 · 10 ^-6 m / s [7].

Due to the fact that ethylene dissolves in pure 1,2-dichloroethane faster than chlorine, it is proposed to install an ethylene distributor as the first distributor. This allows, by the time chlorine is introduced, to completely dissolve ethylene in 1,2-dichloroethane and to avoid the reaction in the gas phase, which will lead to an increase in the selectivity of the process [5]. The ethylene flow rate through one distributor is selected so as to ensure complete dissolution of ethylene in a given 1,2-dichloroethane flow rate.

Also, in the experimental setup (Fig. 4), it was determined that the ethylene bubble almost completely dissolves at a distance of 1.2 m. Under real industrial conditions, due to fluctuations in gas flow and liquid flow, the dissolution height may be greater. Therefore, it is proposed to establish a maximum height margin of 25%. That is, the distance between the ethylene and chlorine distributor must be taken from the range of 1.2-1.5 m, depending on the selected stock.

Chlorine is supplied to a separate distributor in the amount necessary to extract ethylene from the solution. In accordance with the laws of chemisorption [8], the absorption of chlorine bubbles by an ethylene solution will occur faster than the absorption of chlorine by pure 1,2-dichloroethane. Therefore, chlorine distributors are installed above ethylene distributors.

During chemisorption, chlorine, during the chlorination reaction, reduces the concentration of starting ethylene in solution to zero. Therefore, above the chlorine distributor, at a distance sufficient for the dissolution of chlorine and the reaction to complete the interaction of ethylene, another ethylene distributor is installed. Then there is a repetition of the ethylene dissolution process and the process of ethylene extraction from the solution with chlorine.

The number of valves depends on the total chlorine and ethylene load of the reactor. Due to the fact that several alternating chlorine and ethylene distributors are located in the reactor in height, the gas flow rate for each distributor is reduced in comparison with the total load on the reactor in proportion to the number of distributors. For example, if three chlorine distributors are installed, then with a total chlorine reactor load of 3000 m ³ / h, the flow of chlorine through one distributor will be 1000 m ³ / h.

The load on each distributor, namely the ethylene and chlorine costs for a separate switchgear, is determined from the considerations that the gas reagents should completely dissolve before the next overhead switchgear, preventing the reactants from reacting in the gas phase. For example, at a flow rate of 1,2-dichloroethane circulating in the reactor of 800 m ³ / h, the ethylene flow rate through the distributor can be taken equal to 1000 m ³ / h [7].

In order to avoid chlorine leakage from the reactor, ethylene is fed into the last switchgear, so that ethylene extracts chlorine residues from the 1,2-dichloroethane solution.

The required diameter of the reactor depends on the volumetric flow rate of chlorine and ethylene [9]. Since the volumetric flow rate of chlorine and ethylene per one distributor is reduced, this will reduce the diameter of the reactor. So, for example, in a known reactor with a chlorine load of 3000 nm ³ / h, the diameter of the reactor is 3600 mm [2, 3], when three chlorine distributors are installed, the load on one distributor will decrease three times, therefore, the cross-sectional area will decrease three times reactor and 1.73 times the diameter of the reactor will decrease.

Bibliography

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

2. Shishkin Z.A., Samsonov V.V., Kuznetsov A.M. et al. Research and modernization of a reactor for high-temperature liquid-phase chlorination of ethylene. // Collection of scientific papers of JSC IrkutskNIIkhimmash, Irkutsk, 1999, p. 308-312.

3. 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.

4. Podoplelov EV, Balchugov AV, Ulyanov B.A. et al. Experimental determination of the solubility of ethylene in 1,2-dichloroethane. // Collection of scientific papers of the AGTA, Angarsk, 2005, p.10-15.

5. Rozlovsky A.I. Kinetics of ethylene chlorination. // Chemical industry, 1991, No. 6, S. 323-330.

6. Avetyan M.G., Sonin E.V., Zaydman O.A. et al. Industrial development of a direct ethylene chlorination reactor combined with a distillation column. // Chemical industry, 1991, No. 6, p. 323-326.

7. Podoplelov EV, Balchugov AV, Ulyanov B.A. and others. Capillary convection during mass transfer between gas and liquid in the process of obtaining 1,2-dichloroethane. // Collection of scientific papers of the AGTA, Angarsk, 2006, p.20-24.

8. Ramm V.M. Gas absorption. M.: Higher School, 1975 - 560 p.

9. Balchugov A.V., Kuznetsov A.M., Ulyanov B.A., et al. Model of a gas lift bubbler reactor for producing 1,2-dichloroethane. // Collection of scientific papers of JSC IrkutskNIIkhimmash, Irkutsk, 1999, p. 317-325.

Claims (1)

A reactor for producing 1,2-dichloroethane by liquid-phase chlorination of ethylene with the removal of the heat of reaction due to evaporation of the working medium, with bubbling of reactants, with an internal circulation pipe and perforated plates in the upper part of the reactor, characterized in that the reactor has several series alternating with each other along the height of the ethylene and chlorine distributors, moreover, ethylene distributors are installed as the first and last distributors, and the distance between the adjacent distributors is accepted about equal 1.2-1.5 m.

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