KR100241085B1 - Oxychlorination of ethylene in two stage fixed-bed reactor - Google Patents

Abstract

In the method of chlorination of ethylene which produces 1,2-dichloroethane (EDC) by reacting ethylene with a chlorine source and an oxygen source in the presence of a catalyst in a fixed bed acidification reactor, a double reactor system is used, and the catalyst is It is a cupric chloride catalyst whose active profile is arranged such that the reactant stream is first contacted with the first high active catalyst layer and then with the second low active catalyst layer and finally with the third high active catalyst layer.

Description

Oxidation of Ethylene in a Two-Stage Fixed Bed Reactor

The present invention relates to oxychlorination of ethylene to produce chlorinated hydrocarbons, in particular 1,2-dichloroethane (EDC), in a fixed bed reaction system consisting of a single reactor.

Under high temperature and pressure, catalysts are known to react hydrocarbons such as ethylene with gases containing hydrogen chloride and elemental oxygen, in particular air or oxygen enriched air, to produce chlorinated hydrocarbons such as EDC. This reaction can be carried out with two different reaction techniques. One is a fluidized bed reactor technique in which a gaseous mixture of reactants is in contact with a flowable catalyst powder. The other is a fixed bed reactor technology in which gaseous reactants flow along a catalyst fixed inside the reactor.

Fluid bed reactors are characterized by poor adhesion of the catalyst powder, instability of operation, low selectivity due to solid back mixing of gas and catalyst in the reactor, and loss of heat transfer due to the impurity of the cooler bundle. Has many shortcomings, such as limiting the reaction rate to reduce the loss of catalyst when washing off.

Fixed bed reactor technology has been developed to solve this problem. (See US Pat. No. 3,892,816 and US Pat. No. 4,123,467)

Fixed bed reactors have overcome many of the problems associated with fluid bed reactors, but have encountered many new problems. An important problem in fixed bed reactors is that it is difficult to transfer the heat generated by the oxidative exothermic reaction away from the reactor to prevent overheating. For this reason, it is not possible to add all the necessary reactants in the correct stoichiometric ratio. First of all, it is not stable because of the flammability that the concentration of oxygen in the mixture is above 8%, so the reaction consists of two or more successive stages (usually three stages). That is, ethylene is introduced into the first reactor while hydrochloric acid and oxygen are split feed into the reactors. Unreacted ethylene and some inert gases circulate to the first reactor.

In many attempts to reduce such things as the occurrence of hot spots, it has been known to alter the activity profile of a catalyst to increase its activity in the flow direction in a fixed bed reactor. An example can be found in EP 0146925. In any case, the use of a multi-reactor system has been known in the prior art to use a profiled catalyst.

The three reactor systems of the prior art have many disadvantages. For example, the partial pressure of the reactants also decreases because the contact time from the first to third stages decreases. This means that the three reactors have to be operated at different temperatures, thus requiring individual cooling jackets. First of all, despite this precaution, the productivity of each reactor is different. This is especially noticeable in the third reactor, where the productivity is about 50% of the first reactor.

Moreover, the result of the pressure drop across the entire catalyst bed system in the three reactors requires considerable energy consumption to recycle the off-gas.

Above all, it is obvious that setting up and maintaining three reactor systems is more expensive than systems having one or two reactors.

The inventors have therefore developed a new process for the catalytic oxidation of ethylene using a twin reactor system. A special catalyst loading schem can maintain the same EDC productivity as three reactor systems. This means that in terms of the volume of catalyst used, the overall productivity is 50% greater than that obtained in three reactor systems.

In accordance with a first aspect of the present invention, the present inventors have described 1,2-dichloroethane (EDC) comprising reacting an ethylene, chlorine source and oxygen source in the presence of a catalyst in a fixed bed chlorination reactor. A method of oxychlorination of ethylene is produced, in which a bireactor system is used, wherein the catalyst is a cupric chloride catalyst whose active profile is in contact with the first highly active catalyst bed and is continuously And then contact with the second low active catalyst layer and finally contact with the third high active catalyst layer.

The third catalyst layer is a profiled catalyst and includes multiple catalyst layers arranged in order of increasing activity.

The loading of the catalyst according to the invention is preferably applied to both reactors in two reactor systems.

The loading of the catalyst according to the invention makes it possible to start the reaction as soon as the reactants are in contact with the first highly active catalyst bed. Before the temperature of the reactants exceeds 270 ° C. to 285 ° C., the reactants flow and come into contact with the low active catalyst layer, reducing the speed and consequently lowering the temperature of the reaction. Therefore, it is advantageous that the first high active catalyst layer is short. In any case, the ideal length of the catalyst bed is empirically determined by determining the maximum length of catalyst bed that can be used while the reaction does not exceed 285 ° C.

The second low activity catalyst layer is arranged such that the reaction started at high speed by the first catalyst layer does not exceed the hot point of 285 ° C.

The third high active catalyst layer is arranged to maximize the conversion of reactants without exceeding 285 ° C. The third catalyst layer is preferably a catalyst layer profiled to increase the activity in the flow direction of the reactants.

Suitable specific catalyst loading methods are selected depending on the throughput of the reactants as well as the maximum expected temperature of the hot spot and the length and internal diameter of the reactor used.

Various catalysts are known in the art for which activity has been found for use in the process of the invention. Preferred catalysts are supported catalysts having cupric chloride as an active ingredient and carrying alumina, silica gel or aluminosilicate as a support. The support may be spherical, cuboid, conical, hollow cylinder, cylindrical pellet, multilobate pellet, or the like.

The copper content of the catalyst is preferably different depending on the activity required. That is, it is preferable that the first active catalyst layer has a high copper content, the second low active catalyst layer has a low copper content, and the third high active catalyst layer has a high copper content. If the third catalyst is a profiled catalyst, the copper content of the catalyst may be similarly profiled.

In addition to the cupric chloride active ingredient, the catalyst may also contain such accelerators as chlorides of potassium, magnesium, cesium, lithium, sodium, calcium and cerium to increase the selectivity of the EDC.

The reactor type applied to the process of the invention is a tubular reactor. It consists of a number of tubes stacked together in one cooling jacket. The inner diameter of each tube is suitably 15-40 mm. Smaller diameters of less than 15 mm are not good because a large number of tubes must be used in an industrial reactor to obtain sufficient throughput. On the other hand, a diameter larger than 40 mm is not good because it requires a low specific throughput in order to keep the temperature low by causing an excessively high hot spot inside the catalyst bed. Preferable diameter is 20-30 mm.

The suitable length of the reactor is 3-9 m. If the length is shorter than 3 m, the residence time will be too short resulting in lower conversion of the reactants or lower specific throughput. To achieve high conversion of hydrochloric acid and oxygen and high specific throughput, lengths of more than 9 m are not required. Preferable length is 3.5-7 m.

It is preferable to add the entire amount of ethylene to the first reactor with 40 to 100% chlorine source. Preferred chlorine source is hydrochloric acid.

The oxygen source is preferably pure oxygen, and the volume of pure oxygen introduced into the first reactor is preferably 2-6% of the total volume of the product introduced into the first reactor, which corresponds to 40-60% of the total oxygen introduced into the reaction.

In the second reactor, the oxygen concentration can be increased to 7-10% without risk when other reaction mixtures with higher flash points are used. With respect to the chlorine source, the excess of oxygen due to stoichiometric needs will range from 0 to 15%.

The unreacted gas is preferably recycled back from the second reactor to the first reactor. The recovered gas composition, which contains some or all of the unreacted ethylene recovered after standard cooling and condensation, reaches equilibrium, which depends on the rate of combustion, the amount of inert gas in the feed and the rate of removal. Therefore, the concentration of ethylene can vary from 10% to almost 90%. As a result, the excess of ethylene in the reactor depends on the ethylene concentration in the off-gas to be recycled and the recycle flow rate.

If at least some of the released ethylene or other gases are not recycled, they can be used in other processes such as direct chlorination of them.

The recycle flow rate can be adjusted to control the hot spot by adjusting the oxygen concentration at the inlet of the first reactor.

The hot spot temperature itself depends on several parameters. Generally, the hot spot of 230-260 degreeC is preferable for the tubular reactor with an inner diameter of 27 mm, and the hot point of 250-275 degreeC is preferable for the tubular reactor with an inner diameter of 32 mm.

It is preferred to preheat the reaction to between 100 and 200 ° C. The pressure of the reaction can be raised to 20 barg, with a preferred pressure of 4-7 barg.

The performance of the two stage process is excellent. The conversion of hydrochloric acid is generally above 98% even with a very small amount of oxygen, and more than 99% conversion with a 10% oxygen excess can easily be obtained in the second stage. In addition, the selectivity of the reaction is high. The combustion rate is low, with less than 1% ethylene being converted to carbon monoxide and carbon dioxide. By-products such as methylene chloride are about 1500-3000 ppm in the resulting EDC.

The invention is described in detail by way of the following examples, for purposes of illustration only. 1 is a schematic representation of two reactor systems of the present invention.

Comparative Example 1

The reactors were 313 mm (1.25 inches) o.d. Three units of nickel tubes, 14 BWG, 14 feet long; On the inner and inner axes of each tube were 6 mm o.d. thermowells with four sliding thermocouples capable of recording the temperature profile of the reactor. The reactor is wrapped in an outer jacket where the temperature of the reaction is controlled using 210 ° C., 18 barg steam. The reaction pressure was controlled by an air valve in the outlet line.

The reaction was preheated in an exchanger warmed with 18 barg steam. Ethylene, chlorine and nitrogen were mixed together in a special mixer with a gas velocity greater than the ethylene flame propagation rate and oxygen was added to the mixture.

As a catalyst, a standard industrial catalyst for a three-stage fixed bed process consisting of hollow cylinders containing copper and potassium chloride composed as follows was used.

In the first reactor, 60% of the volume was charged with a catalyst bed containing 3.2% w / w Cu, 1.3% w / w K and 1.4% w / w Cs. The remaining 40% was filled with a catalyst bed containing 5.5% w / w Cu, 1.8% w / w K and 2.0% w / w Cs. In the second reactor, 60% of the volume is filled with a catalyst containing 3.7% w / w Cu and 1.4% w / w Cu, and 20% of the volume contains 6% w / w Cu and 1% w / w K. The catalyst was filled with the remaining 20% with a catalyst containing Cu 7% w / w, K 1% w / w. The third reactor was filled with one type of catalyst containing Cu 7% w / w, K 1% w / w.

The first reactor was charged with a mixture of 212 mol / h ethylene, 85.7 mol / h hydrochloric acid, 17.5 mol / h oxygen and 31 mol / h nitrogen. In the second reactor, 85.7 mol / h hydrochloric acid and 17.5 mol / h oxygen were added. In the third reactor, 8.75 mol / h of oxygen was added. The concentration of oxygen at the inlet of the first reactor was 5% (stoichiometric -18%); The concentration of oxygen at the inlet of the second reactor was 4.6% (stoichiometric -30%); The concentration of oxygen at the inlet of the third reactor was 3% (stoichiometrically + 9.6%); Overall oxygen excess was 2.1%. The inlet pressure of the first reactor was 6.3 bar and the outlet pressure of the third reactor was 4.25 bar. The temperature of the cooling jacket was maintained at 210 ° C.

Emission vapors, a mixture of ethylene, oxygen, hydrochloric acid, EDC, water, COx and by-products, were analyzed. The overall result is as follows:

Comparative Example 2

This example consists of only two reactors and the same catalyst loading design as reactors 1 and 2 of Comparative Example 1. A mixture of ethylene (212 mol / h), hydrochloric acid (85.7 mol / h), oxygen (20.5 mol / h) and 31 mol of nitrogen was added to the first reaction stage. In the second reaction step, 85.7 mol / h hydrochloric acid and 23.25 mol / h oxygen were added. The concentration of oxygen at the inlet of the first reactor was 5.9% (stoichiometrically -4.5%); The concentration of oxygen at the inlet of the second reactor was 6.05% (stoichiometric + 4.22%).

The result is as follows:

It can be seen that the temperature of the hot spot is too high.

Comparative Example 3

This example was carried out under the same conditions as in Comparative Example 2 except that the loading method was arranged to lower the hot point to 270 ° C. In this case the activity of the catalyst in the flow direction of the reactants was profiled to increase from top to bottom. The loading method was as follows:

First reactor: graphite 7%; 48% catalyst containing Cu 2.7% w / w, K 0.8% w / w, Cs 1% w / w; 23% catalyst containing Cu 3.3% w / w, K 1.1% w / w; And 22% catalyst containing Cu 7.8% w / w, K 0.8% w / w.

Second reactor: graphite 7%; 42% of a catalyst containing Cu 2.7% w / w, K 0.9% w / w; 30% of a catalyst containing Cu 5.5% w / w, K 0.6% w / w; And 21% catalyst containing 7.8% w / w Cu, 0.8% w / w K.

The concentration of oxygen at the reactor inlet was the same as in Comparative Example 2. The result is as follows:

In this case, the temperature of the hot spot was acceptable, but the conversion of oxygen and hydrochloric acid was too low.

This example was carried out in the same reactor and reactant amounts as in Comparative Example 2 except for the following catalyst design.

First reactor: loading mode: graphite 7%; 3% catalyst containing Cu 6.5% w / w, K 2.2% w / w; 40% of a catalyst containing Cu 2.7% w / w, K 0.8% w / w; 22% catalyst containing Cu 3.75% w / w, K 1.2% w / w; And 28% catalyst containing 7.8% w / w Cu, 0.8% w / w K.

Second reactor: loading: 3% catalyst containing Cu 6.5% w / w, K 2.2% w / w; 31% of a catalyst containing Cu 2.9% w / w, K 1.2% w / w; 18% catalyst containing Cu 3.9% w / w, K 1.3% w / w; And 48% catalyst containing Cu 7.8% w / w, K 0.8% w / w.

The result is as follows:

The conversion and hot point were good.

Example 5

This example was run with the same equipment and throughput as Comparative Example 3 except for the following catalyst design.

First reactor: graphite 7%; 3% catalyst containing Cu 6.5% w / w, K 2.2% w / w; 45% of a catalyst containing Cu 2.7% w / w, K 0.8% w / w; 28% catalyst containing Cu 3.75% w / w, K 1.2% w / w; And 22% catalyst containing Cu 7.8% w / w, K 0.8% w / w.

Second reactor: 3% catalyst containing Cu 6.5% w / w, K 2.2% w / w; 31% of a catalyst containing Cu 2.9% w / w, K 1.2% w / w; 20% of a catalyst containing Cu 3.9% w / w, K 1.3% w / w; And 46% catalyst containing 7.8% w / w Cu.

The result is as follows:

The conversion and hot point were good. Note the lower pressure drop using a two-stage system.

Claims (9)

In a method of oxidizing ethylene to produce 1,2-dichloroethane (EDC) comprising reacting ethylene with a chlorine source and an oxygen source in the presence of a catalyst in a fixed bed acidification reactor, using a twin reactor system and The catalyst is a copper chloride catalyst, the active profile of which is arranged to be in contact with the first high active catalyst layer first, and subsequently with the second low active catalyst layer, and finally with the third high active catalyst layer. Way. The method of claim 1 wherein the third catalyst bed comprises multiple catalyst beds having increased activity in the flow direction of the reactants. The process according to claim 1 or 2, wherein the activity of the catalyst is profiled in each of the two reactors. The process according to claim 1 or 2, wherein the reaction temperature does not exceed 285 ° C. The process according to claim 1 or 2, wherein the catalyst comprises an accelerator such as chlorides of potassium, magnesium, cesium, lithium, sodium, calcium and cerium. The process according to claim 1 or 2, wherein 40 to 60% of the total oxygen source introduced into the reaction is introduced into the first reactor. The process according to claim 1 or 2, wherein 40-100% of the total chlorine sources added to the reaction are introduced into the first reactor. The process of claim 1 or 2, wherein at least a portion of the exhaust gas exiting the second reactor is recycled to the first reactor. The process according to claim 1 or 2, wherein the reaction proceeds at a pressure of 4-7 barg.

Images