Method for producing 1,2-dichloroethane

 

(57) Abstract:

Describes a method for producing 1,2-dichloroethane by oxidative chlorination of ethylene in a fluidized bed of powdered catalyst, comprising feeding to the reaction zone hydrogen chloride, ethylene and process air or oxygen when the temperature control of the reaction gases, the outlet from the reaction zone is obtained dichloroethane and the heat of reaction with the refrigerant circulating in the cooling system, characterized in that the reaction zone set and maintain the setpoint temperature of the reaction gases by maintaining optimal value given the speed of the reaction gases in the reaction zone to use when raising or lowering it relative to the optimal value given the speed of the reaction gases, respectively increase or decrease the pressure of the reaction gases to recover the optimal value given the speed of the reaction gases with subsequent restoration of the setpoint temperature of the reaction gases by reducing the pressure of the refrigerant in the cooling system in the case of increasing the temperature of the reaction gases and correspondingly increasing pressure at low ke for operating reactors, allow customers to increase their productivity by 20-30%. 4 Il.

The present invention relates to chemical technology and can be used for the production of 1,2-dichloroethane (hereinafter - dichloroethane) by oxidative chlorination of ethylene in the gas phase in the presence of powdered catalyst which is in a state of fluidization.

A method of obtaining dichloroethane (see Technology of organic synthesis, ed. C. D. Capkin, G. A. Savinetskaya, V. I. The Chapurin. M.: Chemistry, 1987, pp. 254-255), which is implemented in the reactor column type having a cooling system consisting of a set in the reaction zone multi-tubular heat exchanger, which during operation of the reactor is completely within the layer of fluidized powdered catalyst. The known method involves feeding into the reaction zone gaseous source components - hydrogen chloride, ethylene, and process air in an excessive amount (about 3-5%), the removal from the reaction zone vapor synthesized dichloroethane, water vapor, oxides and carbon dioxide, vapor harmful side products and nitrogen. The reaction of ethylene oxychlorination process is accompanied by heat and is conducted at the rate the evaporation of the refrigerant water is forced under pressure is conducted through a tubular heat exchanger.

The disadvantage of this method is the inability to maintain the reaction temperature within the specified limits when its increase or decrease is due to the raising or lowering process load in the reaction zone, that is, when the increase or decrease of specific consumption of the starting components of the reaction and, for example, due to the lower selectivity is loaded in the reaction zone of the catalyst compared to its specified nominal indices of selectivity. The reason the above disadvantage is the limited capacity of the cooling system, which is designed to work in narrow limits of temperature in the reaction zone. Therefore, in practice, when the heat load in the reaction zone is greatly increased, and the cooling system may not provide adequate removal of heat, the temperature in the reaction zone may rise above the permissible limit. In this case, increasing the intensity of the adverse reactions, and this in turn leads to a further increase in the heat generation, as, for example, heat of reaction of the product such adverse reactions as carbon dioxide 6-fold increases those who increases the output side, including harmful products.

Also known is a method of obtaining dichloroethane oxidative chlorination of ethylene in a fluidized bed of powdered catalyst by feeding into the reaction zone hydrogen chloride, ethylene process air or oxygen when the temperature control of the reaction gases (see U.S. Pat. 3816554 A1, 11.06.74).

The method includes the removal from the reaction zone is obtained dichloroethane and the heat of reaction with the refrigerant circulating in the cooling system. Temperature control of the reaction gases is carried out by a corresponding change in pressure of water vapor at the outlet section of the heat exchanger of the cooling system. The pressure in the reaction zone does not change.

Thus, in the known method of producing dichloroethane is not taken into account the impact of changes in the speed of the reaction gases to the process of heat removal, and therefore it is not possible to increase the performance of the process of oxychlorination process on the yield of the target product, and also causes the reduction of the lifetime of the heat exchanger due to accelerated erosion wear of its leaf at high and at low heat loads on the reactor.

The task comprises imov heat transfer and expansion in the upper side of the acceptable range of heat loads that do not result in premature wear of the heat exchanger, i.e. ensuring that improve the performance of the proposed method for 20-30% of the maximum in comparison with the known method.

The technical result of the proposed method is expressed in providing work of system of cooling of the reaction gases in the conditions of lower thermal resistance at high and low heat loads, i.e. in the regime of smaller magnitude reductions in the pressure of the refrigerant at the outlet from the cooling system, allowing you to maintain a liquid film on the inner pipe wall of the heat exchanger along its entire length and to prevent the rapid destruction of the end rolls of the heat exchanger. This result is achieved by maintaining the optimal value given the speed of the reaction gases, washing the walls of the heat exchanger, which allows you to save the maximum value of heat transfer coefficient and to minimize the difference (gradient) of the surface temperature of heat transfer between a fluidized bed of powdered catalyst and the pipe wall of the heat exchanger system ohlazhdeniya ethylene in a fluidized bed of powdered catalyst, including the feed into the reaction zone gaseous source components - hydrogen chloride, ethylene and process air or oxygen, the removal from it of the synthesized dichloroethane, the heat of reaction with the refrigerant, such as water circulating in the cooling system, maintaining a setpoint temperature of the reaction gases in the reaction zone by adjusting the pressure of the refrigerant and its equilibrium boiling point in the cooling system, according to the invention maintain the setpoint temperature of the reaction gases in the reaction zone is as follows: set the optimal value of a given velocity of the reaction gases in the reaction zone and maintain it namely, when the increase or decrease the above speed of the reaction gases relative to that given its optimal value, the pressure of the reaction gases in the reaction zone respectively reduce or increase to repair the specified optimal value given the speed of the reaction gases, and then restore the setpoint temperature of the reaction gases, i.e. at elevated temperatures, the pressure of the refrigerant in the cooling system accordingly reduced, and if penitenciaria illustrated by drawings, where in Fig. 1 shows a schematic diagram of an industrial reactor, implements the method of Fig. 2 - site mixing of the starting components of Fig. 3 - profile (and gradients) temperature in the reaction zone and in the cooling system for the known and declared methods with increasing heat dissipation in comparison with the initial temperature profile of Fig.4 is a plot of heat transfer coefficient from changes given the speed of the reaction gases.

In the lower part of the housing 1 vertical reactor column type posted by the distribution of the false bottom 2 with directional down-mixing nozzles 3 having in its lower part an orifice 4 to enter the process air into the housing 1 and its distribution over the cross section of the column. In the wall of the shell 1 of the reactor welded nozzle 5 for supplying process air under the false bottom 2. Over the false bottom 2 in the housing 1 is entered switchgear tubular type, consisting of a nozzle 7 for supplying a mixture of ethylene with hydrogen chloride, the collector 8, the transverse distribution pipe 9 having a vertical distribution pipes 10, the output (lower) ends with the formation of the annular gap is introduced in the mixing patlasov, consisting of several sections of a vertical tubular heat exchanger 11. Each section of the heat exchanger 11 has an input 12 and an output 13 fittings for connection to an external reservoir (not shown). The socket 12 is connected to the collector supply of the refrigerant (water), and the socket 13 is connected to the collector output of the refrigerant (water mixture) on the capacitor. Annulus of the heat exchanger 11 is located above the false bottom 2, covered with a layer of fine powder of catalyst so that during operation of the reactor, when the solid catalyst particles pseudogiants flows of the reaction gases, the upper level of the layer of fluidized catalyst was located slightly above the sections of the heat exchanger 11 and to the tubes of the heat exchanger 11 entirely under the layer of fluidized catalyst. The inner space of the housing 1 located above the fluidized bed of catalyst represents a separation zone, which serves for the separation and deposition of the catalyst particles, which are removed from the reaction zone by the flow of the reaction gases. In the upper part of the separation zone has three cyclone 14, 15 and 16, each of which has a standpipe estrus 17, 18 and 19, kotowaza from the housing 1 of the final reaction products - of dichloroethane vapor, water vapor, vapour, side reaction products, impurities and inert gases. The upper ends and the lower ends of heat exchanger tubes 11 are interconnected by a curved tubular elements - rolls 21 and 22.

The method of producing dichloroethane in this reactor is carried out as follows. According to the technological regulations, calculate and set the optimal value of a given velocity of the reaction gases, which provides a maximum value of heat transfer coefficient. Through the nozzle 7, the collector 8, pipe 9 and then through the distribution pipes 10 into the reactor with a certain volumetric rate serves heated mixture of ethylene and hydrogen chloride. At the same time through the nozzle 5 under the false bottom 2 with a certain volumetric rate serves heated process air or oxygen through the holes 4 is fed into the mixing nozzle 3 where it is mixed with a mixture of ethylene and hydrogen chloride entering the counter flow in the mixing pipe 3 through distribution pipes 10. The resulting reaction gas mixture enters the reaction zone through the annular clearances between the walls of the mixing nozzle 3 and the walls Raspredelitelnaya flows of the reaction gases, passing through the layer of powder catalyst, bring him in suspended fluidized condition to ensure good interaction between the reaction gases and catalyst particles. When this occurs the reaction of synthesis of 1,2-dichloroethane, and the temperature in the reaction zone is increased due to a significant exothermic effect of the interaction of ethylene with hydrogen chloride. As the catalyst used chlorine copper, which is imbued with the media - microspherical powder of aluminum oxide. The pressure of the reaction gas in the reactor may vary within the maximum allowable range of 4.3 to 10.0 kgf/cm2and their temperature - in the range of 205 - 250oC. For any particular catalyst specify the optimal size working temperature of the reaction gases, for example - 224oC, which is supported throughout the entire process of synthesis of dichloroethane. The maintenance of the given initial value of the temperature of the reaction gases in the reaction zone at a constant heat load on the reactor (at a constant volumetric flow of the original components and their chemical composition, as well as at constant activity and selective ability of the catalyst) is produced through heat exchanger 11 system Klee pressure for the given temperature of the reaction gases and corresponding to this pressure equilibrium boiling point, providing efficient heat removal from the reaction zone at the maximum value of the coefficient of heat transfer from the layer of fluidized catalyst to the pipe wall of the heat exchanger 11 (see Fig.3).

In the case of increasing the heat load on the reactor, for example by increasing the volumetric flow of the original components of the reaction, and also by increasing the intensity of adverse reactions due to lower activity and selective ability of the catalyst while increasing the flow of the original components or with a constant flow rate, maintaining the setpoint temperature of the reaction gases in the reaction zone is as follows. With increasing heat load on the reactor to increase the temperature of the reaction gases in the reaction zone and the rate of the reaction gases in the reaction zone with respect to their set of optimal values. Due to the extreme nature of the dependence of heat transfer coefficient from changes given the speed of the reaction gases w (see Fig. 4), in this case with increasing reduced velocity of the reaction gases to w2the heat transfer coefficient is reduced to values2that has a smaller size in comparison with maximilianallee setpoint temperature of the reaction gases provide heat transfer coefficient increase up to its maximum value, that is, reduce the resistance teplootbora from the reaction zone. This reduces the flow area of the output fitting 20 by means of a gate valve (not shown) and thus increase the pressure of the reaction gases in the reaction zone by a certain amount corresponding to the amount of reduction given the speed of the reaction gases to restore its specified optimum values of wopt(see Fig.4). After recovery, given the optimal speed of the reaction gases in the reaction zone is restored to the maximum value of heat transfer coefficient tomaxand resistance to teplootbora from the reaction zone is reduced, resulting in a partial reduction of the temperature of the reaction gases. In order to reduce it to the given value, to produce the reduced pressure steam-water mixture in the tubes of the heat exchanger 11 by increasing the bore of the output socket 13 with a pressure regulator (not shown) by a certain amount, ensure a corresponding reduction in the equilibrium boiling point of water in the heat exchanger tubes 11. Due to this the temperature of the reaction gases in the reaction zone is reduced and restored to specify the flax increasing the heat load on the reactor (10-20% of valid). This provides and efficient operation of the heat exchanger 11 of the cooling system that is not experiencing congestion, because it works continuously at the maximum value of heat transfer coefficient. The operation of the heat exchanger 11 at the maximum value of heat transfer coefficient allows to minimize the temperature gradient at the boundary of the heat removal between the reaction zone and the pipe wall of the heat exchanger 11 (see Fig.3) in comparison with the known method, it has provided the necessary increase of the specific heat removal due to the smaller temperature gradient. A smaller temperature gradient in comparison with the known method requires a smaller quantity of pressure reduction of the refrigerant in the cooling system. This avoids increasing the speed of steam-water mixture in the tubes of the heat exchanger 11 to a critical value and ensures that the annular liquid layer on their inner walls, prevents the possibility of their rapid erosive wear, and wear and fracture limit of the rolls 21 and 22 in the sections of the heat exchanger 11.

The heat load on the reactor can be increased and reduced in comparison with the nominal cost of the initial components, for example, in the case of deterioration of quality and the health of its normative parameters. In this case, the temperature rise of the reaction gases in the reaction zone compared to its specified value is due to the relatively greater activation of the synthesis of side reaction products such as carbon dioxide, heat of reaction which is almost 6 times greater than the heat of fusion reaction of dichloroethane. In this case the speed of the reaction gases although increases due to the increase of their temperature, but may not reach its specified optimum value, that is, it can have a smaller value, for example, component a value of w1, which corresponds to a sharply reduced the value of the coefficient of heat transfer 1(see Fig.4). In order to increase the heat transfer coefficient to its predetermined optimum values, increase the flow area of the output nozzle 20 through the valve and thereby reduce the pressure in the reaction zone by a certain amount. By decreasing pressure in the reaction zone is increased given the speed of the reaction gases, and its specified optimum value is restored, so that the heat transfer coefficient increases to its maximum value. At the maximum heat transfer coefficient is moved by a certain amount. Further reduction of the temperature to restore it to its set value in the reaction zone is produced by reducing the pressure of the refrigerant in the cooling system at the exit of the nozzle 13.

In case of a significant reduction of the heat load on the reactor when the reduced flow of the original components of the reaction and decreases accordingly given the speed of the reaction gases, for example to a value of w1, and is significantly below its predetermined optimum values, the heat transfer coefficient also sharply reduced, for example to the value of1(see Fig.4), and, consequently, dramatically increases the resistance teplootbora from the reaction zone. For this reason, in the reaction zone, a sudden increase of the temperature of the reaction gases and it can rise significantly above its specified initial values because of the increased intensity of side effects, which causes an additional increase of the temperature. Given the speed of the reaction gases may slightly increase because of this raise the temperature of the gas mixture in the reaction zone, however, its value remains below its predetermined optimum values. For recovery, lowering the temperature of the reaction Gasum increase the flow area of the output nozzle 20 through the valve. Due to the reduced pressure in the reactor, the velocity of the reaction gases in the reaction zone increases and is restored to its predetermined optimal values of wopt(see Fig.4), in which the heat transfer coefficient takes its maximum value of max. Thanks to its increase, decreases thermal resistance to heat flow from the reaction zone to the walls of the heat exchanger 11 and, consequently, the temperature of the reaction gases is partially reduced by a certain amount, but does not reach the specified value. In order to additionally reduce it to the given value, actuates the pressure regulator on the output socket 13 of the heat exchanger 11, which increase by a certain amount the flow area at the outlet of the refrigerant, causing the pressure in the cooling system is reduced, and with it decreases and the equilibrium temperature of the refrigerant (see Fig.3), which leads to a slight increase of vaporization in the heat exchanger tubes 11 and to increase the intensity heat-extraction from the reaction zone. As a result, the temperature of the reaction gases in the reaction zone is reduced to the value of its preset value (see Fig. 3). The process oxy is to as by providing the maximum value of heat transfer coefficient, Teplodar from the reaction zone occurs with minimal thermal resistance.

In the process of ethylene oxychlorination process possible case, when thermal load decreases slightly due to a small decrease in the flow of the original components. Thus there is a relatively small reduction in the present rate of the reaction gases, for example, to a value of w3(see Fig.4) at which the heat transfer coefficient decreases slightly, for example, to the value of2that can lead to a small decrease in the temperature of the reaction gases in the reaction zone compared to its target value due to a small increase in thermal resistance between the reaction zone and the pipe wall of the heat exchanger 11. To raise the temperature of the reaction gases in the reaction zone increases given the speed of these gases prior to its optimal value by reducing the pressure in the reaction zone, i.e. through the valve increases the flow area of the nozzle 20. The result shows the speed of the reaction gases is increased to the optimum values of woptthe heat transfer coefficient increases to a maximum value ofmaxand although thermal resistance teplootbora, reduces energy is than its set value. Further, by increasing the refrigerant pressure in the cooling system increases its equilibrium boiling point, resulting in the intensity of the heat-extraction decreases and the temperature of the reaction gases in the reaction zone rises to its preset value.

Rising above the fluidized bed of catalyst, unreacted mixture of gases containing a significant amount of the catalyst undergoes a separation space of the reactor, where the selection of the principal amount of entrained gases to the catalyst. The selected catalyst is returned to the reaction zone. After that, the mixture of gases is fed to further purification in the cyclones 14, 15 and 16. Caught in the cyclone catalyst through the standpipe heat 17, 18 and 19 is returned to the reaction zone, and peeled a couple of dichloroethane and gases discharged from the reactor through the nozzle 20 and fed to the cooling and washing.

Thus, the proposed method in comparison with the known allows you to expand in the upper side of the allowable range with respect to thermal load on the reactor that does not lead to premature wear of the heat exchanger of the cooling system, i.e. to provide improved performance on target product by 20-30% from the second reactor model oxychlorination process in laboratory conditions. In addition, the proposed method creates the possibility of designing a new generation of reactors with high performance settings.

Method for producing 1,2-dichloroethane by oxidative chlorination of ethylene in a fluidized bed of powdered catalyst, comprising feeding to the reaction zone hydrogen chloride, ethylene and process air or oxygen, while controlling the temperature of the reaction gases, the outlet from the reaction zone is obtained dichloroethane and the heat of reaction with the refrigerant circulating in the cooling system, characterized in that the reaction zone set and maintain the setpoint temperature of the reaction gases by maintaining optimal value given the speed of the reaction gases in the reaction zone to use when raising or lowering it relative to the optimal value given the speed of the reaction gases, respectively increase or decrease the pressure of the reaction gases to recover the optimal value given the speed of the reaction gases with subsequent restoration of the setpoint temperature of the reaction gases by reducing the pressure of the refrigerant in the cooling system in the case of increasing the value of t is

 

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2 cl, 1 tbl, 4 ex

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