Process and apparatus for the synthesis of 1,2-dichloroethane

Abstract

Process for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst under conditions in which the synthesized 1,2-dichloroethane condenses out, but the ethylene and the chlorine are gaseous, in a reactor (3), wherein in the reactor (3) the stoichiometric ratio of ethylene to chlorine is adjusted such that ethylene is present in excess, characterized in that - a liquid 1,2-dichloroethane stream (5) is withdrawn from the reactor (3) and partially evaporated in an evaporation device (110); and - the evaporation device (110) is heated by means of the condensation heat of the vapor of a distillation column (114) and / or by means of the reaction heat of a plant for the high-temperature direct chlorination (214) of ethylene.

Description

Technical field of the invention

[0001] The present invention relates to a process according to the preamble of claim 1 and an apparatus according to the preamble of claim 17 for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst. State of the art

[0002] Such processes for the synthesis of 1,2-dichloroethane (also known as ethylene dichloride or EDC or DCE for short) are typically used in the production of vinyl chloride (also VC or VCM). Vinyl chloride is an intermediate in the production of polyvinyl chloride (PVC). The synthesis of 1,2-dichloroethane is usually carried out from ethylene and chlorine via the so-called direct chlorination of ethylene. The resulting 1,2-dichloroethane can then be converted to vinyl chloride by pyrolysis with elimination of hydrogen chloride (HCl). In this context, reference can be made to the publications JP 2006 335 665 A, KR 10 2012 0 067 400 A, RU 2 051 891 C1, US 2 099 231 A1, and EP 2 196 446 A1.

[0003] In commercially applied processes for the direct chlorination of ethylene, the reaction product EDC is typically also used as the reaction medium. The reactants, chlorine and ethylene, are introduced into liquid EDC in gaseous form, where they dissolve and then react with each other. The reaction medium is circulated in natural or forced circulation, with the reactants being added to the circulating EDC stream. In natural circulation reactors, the reactants are typically added in the reactor's riser tube.

[0004] A Lewis acid is typically used as the catalyst. For cost reasons, this is often iron(III) chloride (FeCl3). More complex catalyst systems contain an alkali halide, usually sodium chloride (NaCl), in addition to the Lewis acid. Such catalyst systems can suppress undesirable side reactions such as the further chlorination of EDC to 1,1,2-trichloroethane, even at higher temperatures, and therefore offer an economic advantage over the use of iron(III) chloride. One such catalyst system is described, for example, in DE 43 18 609.

[0005] The processes known from the prior art differ in terms of the reaction temperature and reaction control. In so-called low-temperature direct chlorination (LTDC or Low Temperature Direct Chlorination), the reactor is operated below the boiling point of the reaction medium EDC, which is 84°C (at atmospheric pressure). The product is withdrawn from the reactor in liquid form. Such processes are operated with an excess of chlorine, whereby the catalyst ferric chloride can form through the reaction of chlorine with iron from the reactor wall or from designated internals such as packing, etc. Since the liquid reaction product still contains dissolved chlorine and catalyst, it must first be treated in one or more washing steps with water and / or sodium hydroxide solution. This creates a wastewater stream, which in turn must be treated.Furthermore, an additional distillation step is necessary to remove dissolved water when processing the product by distillation.

[0006] High-temperature direct chlorination (HTDC) operates above the boiling point of the reaction medium. This allows the reaction product to be removed from the reactor in vapor form, while the catalyst remains in the reactor. This allows for the use of advanced catalyst systems and also allows the catalyst concentration to be adjusted to an optimal value.

[0007] In the direct chlorination plants described above, using the low-temperature direct chlorination process, it is necessary to remove excess chlorine or chlorine-containing byproducts from the 1,2-dichloroethane. Furthermore, the excess chlorine leads to increased corrosion in the reactor, which reduces the reactor's service life. Disclosure of the invention

[0008] The object of the present invention is to provide a process and an apparatus for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene, wherein the effort for purifying the synthesized 1,2-dichloroethane is reduced and the service life of the reactor is increased.

[0009] The object is achieved by a process for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst under conditions in which the synthesized 1,2-dichloroethane condenses, while the ethylene and chlorine are gaseous, in a reactor, wherein the stoichiometric ratio of ethylene to chlorine in the reactor is adjusted such that ethylene is present in excess. This process is further defined in patent claim 1.

[0010] The object is further achieved by a device for synthesizing 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst under conditions in which the synthesized 1,2-dichloroethane condenses, while the ethylene and chlorine are gaseous, in a reactor, wherein the stoichiometric ratio of ethylene to chlorine in the reactor can be adjusted such that ethylene is present in excess. This device is further defined in claim 17.

[0011] In the process and device, the reaction in the reactor is operated with an excess of ethylene, so that the chlorine introduced into the reactor is essentially consumed for the synthesis of 1,2-dichloroethane. The formation of highly chlorinated by-products in addition to the 1,2-dichloroethane is reduced. Therefore, it is not necessary to remove chlorine from the synthesized 1,2-dichloroethane, and the effort required to purify the 1,2-dichloroethane of highly chlorinated by-products is also reduced. Furthermore, the reduced chlorine content compared to the prior art leads to reduced corrosion in the reactor, thus significantly increasing the reactor's service life.

[0012] The process according to the invention can be used both for the construction of new low-temperature direct chlorination devices and for the conversion of existing low-temperature direct chlorination devices.

[0013] The conditions in the reactor are selected such that the synthesized 1,2-dichloroethane condenses, while the ethylene and chlorine remain gaseous. The temperature in the reactor is preferably set below the boiling point of 1,2-dichloroethane, in particular below 84°C.

[0014] An advantageous embodiment of the process provides that the stoichiometric ratio of ethylene to chlorine is at least 1.01:1. Preferably, the stoichiometric ratio of ethylene to chlorine is at least 1.05:1, particularly preferably at least 1.10:1.

[0015] It is advantageous if the stoichiometric ratio of ethylene to chlorine in the reactor is monitored and the supply of ethylene and chlorine to the reactor is regulated such that ethylene is present in excess. Monitoring can be carried out continuously or at discrete times. Preferably, the reactor has a detection device for detecting the stoichiometric ratio. The reactor can be controlled via a control device connected to the detection device, via which the flow of ethylene and / or chlorine into the reactor is adjusted.

[0016] The inventive embodiment of the process has proven advantageous, in which a liquid 1,2-dichloroethane stream is withdrawn from the reactor and partially evaporated in an evaporation device, as defined in patent claims 1 and 17. The 1,2-dichloroethane withdrawn from the reactor is partially converted by the evaporation device into gaseous 1,2-dichloroethane, which has a high degree of purity. This has the advantage that the 1,2-dichloroethane stream withdrawn from the reactor can be purified of the catalyst. A single-stage evaporation device is preferably used, so that the complexity is reduced compared to a multi-stage evaporation process.

[0017] It is particularly advantageous if less than 50% of the 1,2-dichloroethane stream withdrawn from the reactor is evaporated in the evaporation device. Preferably, the proportion of the 1,2-dichloroethane stream withdrawn from the reactor evaporated in the evaporation device corresponds to the amount of 1,2-dichloroethane produced in the reactor.

[0018] A preferred embodiment provides for the evaporation device to be designed as a falling-film evaporator. The 1,2-dichloroethane stream is preferably fed to the falling-film evaporator from above. The 1,2-dichloroethane can flow downward in the falling-film evaporator and partially evaporate by heating in the falling-film evaporator. The unevaporated portion of the 1,2-dichloroethane stream withdrawn from the reactor can collect in the lower region.

[0019] Preferably, the non-evaporated portion of the 1,2-dichloroethane stream withdrawn from the reactor is recycled to the reactor so that the catalyst contained in the non-evaporated 1,2-dichloroethane stream can be reused in the reactor.

[0020] It has also proven advantageous if the evaporation device is heated by means of the condensation heat of the vapor from a distillation column and / or by means of the reaction heat of a plant for the high-temperature direct chlorination of ethylene, as defined in patent claims 1 and 17. This has the advantage that the heat required for evaporation is provided by heat recovery measures, so that the supply of additional energy is not necessary. The distillation column is preferably a distillation column for separating higher-boiling components from 1,2-dichloroethane. The distillation column is preferably operated at a head temperature in the range from 120°C to 150°C, particularly preferably in the range from 127°C to 135°C.Heating using the condensation heat of the distillation column vapor is preferred when upgrading an existing LTDC plant does not involve a capacity increase. To heat the evaporator using the reaction heat of a plant for the high-temperature direct chlorination of ethylene, a vaporous 1,2-dichloroethane stream can be condensed and / or a liquid 1,2-dichloroethane stream can be cooled.

[0021] It is further advantageous if the 1,2-dichloroethane stream withdrawn from the reactor is preheated by means of a preferably warm 1,2-dichloroethane stream withdrawn from the evaporation device and / or by means of a, in particular liquid, preferably warm, 1,2-dichloroethane stream from a plant for the high-temperature direct chlorination of ethylene before being fed to the evaporation device. This allows the 1,2-dichloroethane stream withdrawn from the evaporation device to be cooled, and the energy released in the process to be recovered. It is particularly advantageous if the heat exchange between the streams withdrawn from the evaporation device and the reactor takes place in crossflow. Alternatively, a flash evaporation device can be used to cool the 1,2-dichloroethane stream withdrawn from the evaporation device.

[0022] An advantageous embodiment provides that the vaporous 1,2-dichloroethane stream emerging from the evaporation device is fed into a distillation column. The distillation column preferably separates compounds that have a higher boiling point than 1,2-dichloroethane. This embodiment is preferably used when, at the same time as upgrading an existing LTDC plant, the production capacity is to be increased by adding a new HTDC plant.

[0023] The catalyst used in the process according to the invention preferably comprises iron(III) chloride (FeCl3) and / or sodium chloride (NaCl).

[0024] It is advantageous if an ethylene-containing offgas from a high-temperature direct chlorination reactor is fed to the reactor, so that this offgas can be used for low-temperature direct chlorination, with the ethylene content being utilized to produce 1,2-dichloroethane. The ethylene-containing offgas is preferably compressed in a gas jet compressor, which is operated in particular with a gaseous ethylene stream.

[0025] The advantageous features described above in connection with the method according to the invention can also be used alone or in combination in the device according to the invention.

[0026] Further details, features, and advantages of the invention will become apparent from the drawings and the following description of preferred embodiments with reference to the drawings. The drawings merely illustrate exemplary embodiments of the invention, which do not limit the scope of the invention. Short description of the characters The Fig. Figure 1 shows a schematic representation of an apparatus for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene according to the prior art. The Fig. Figure 2 shows a first embodiment of an apparatus according to the invention for the synthesis of 1,2-dichloroethane from ethylene and chlorine in a schematic representation. The Fig. 3 shows a second embodiment of an apparatus according to the invention for the synthesis of 1,2-dichloroethane from ethylene and chlorine in a schematic representation. Embodiments of the invention

[0027] In the various figures, identical parts are always provided with the same reference symbols and are therefore usually named or mentioned only once.

[0028] In the Fig. Figure 1 shows a device for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene (LTDC plant), as is known in the art.

[0029] Ethylene 1 and chlorine 2 are fed into an LTDC reactor 3 in the presence of excess chlorine, where they dissolve in EDC and react with each other to form EDC. The reactor offgas 4 can be removed at the top of the reactor. The reaction proceeds at a temperature below the boiling point of EDC. The produced catalyst-containing EDC 5 is removed from the reactor in liquid form and subjected to washing with water 7 and sodium hydroxide solution 8, during which the catalyst passes into the aqueous phase and any remaining chlorine is converted into sodium hypochlorite by reaction with sodium hydroxide solution, which also dissolves in the aqueous phase. The wastewater stream 10 must be subjected to further treatment.

[0030] The now moist EDC 11 is fed to a dewatering column 12, in which, in conjunction with a plant for the production of VCM, moist EDC 18 from an oxychlorination plant can also be processed and at the top of which water and low boilers 16 are separated.

[0031] The dried EDC 9 is fed into a high-boiler column 13, at the top of which the purified EDC product 17 is withdrawn. At the bottom of the high-boiler column, a concentrated solution of high-boiler components in EDC 20 is withdrawn and fed into a vacuum column 15. In this column, high-boiler components 22 are separated at the bottom, and the EDC 21 obtained at the top is returned to the high-boiler column 13. If a complete plant complex for the production of VCM is implemented, a return stream 19 of EDC from a plant for the thermal cracking of EDC is also processed in the high-boiler column.

[0032] The representation of the three-stage distillative processing of EDC using columns 12, 13, and 15 is exemplary—this type of processing is known to those skilled in the art and is not part of the invention. To clarify the classification within a plant complex for the production of vinyl chloride, reference is made to EDC streams from an oxychlorination plant 18 and from a plant for the thermal decomposition of EDC 19. These relationships are also known to those skilled in the art.

[0033] In the Fig. Figure 2 shows a first embodiment of an apparatus for synthesizing 1,2-dichloroethane according to the invention. In this embodiment, heating in the evaporation device is carried out using vapor from a distillation column.

[0034] Fig. 2 shows an LTDC plant whose reaction product is evaporated in a single-stage evaporation step, with the heat required for evaporation being supplied as latent heat of the vapor stream to a high-boiler column. No additional heating steam is consumed. Ethylene 1 and chlorine 2 are fed into an LTDC reactor 3, where they react to form EDC. The reactor offgas stream 4 can be withdrawn at the top of the reactor. A liquid, catalyst-containing EDC stream 5 is withdrawn from the LTDC reactor and fed into a receiver 111. In a preferred embodiment, the EDC stream 5 is greater than the amount of EDC produced in the reactor.By means of a pump 106, the EDC stream is passed through one or more heat exchangers 107, 108, which serve for preheating and are preheated with the bottom stream 104 of the evaporator 110 and / or with the vaporous product EDC 120 from the evaporator 110. After preheating, the EDC stream enters the evaporator 110, where an amount of EDC corresponding to the amount of EDC produced in the LTDC reactor 3 is evaporated. The evaporated EDC stream 120 is cooled in the preheater 108 and in another heat exchanger 109, collected in the product receiver 112, and pumped to the plant boundary or to a downstream plant section in the VCM production network. The non-evaporated, catalyst-containing EDC portion 104 from the evaporator 110 is pumped back into the receiver 111, having previously been cooled by heat exchange in the preheater 107.From the receiver 111, an EDC stream corresponding to the non-vaporized EDC portion is pumped back into the LTDC reactor.

[0035] The evaporator 110 serves as the top condenser of the distillation column designed as a high-boiler column 114, in which other streams from the VCM production plant network, such as recycled EDC from thermal EDC cracking 116 or EDC dried in a dewatering column from oxychlorination 117, can also be processed. The condensed EDC 121 is collected in the reflux tank 113 of the high-boiler column 114 and pumped as reflux to column 114 or as product to the plant boundary.

[0036] The method described in the first embodiment is particularly suitable for upgrading existing LTDC plants if the upgrading is not intended to be accompanied by a capacity increase.

[0037] In the Fig. Figure 3 shows a second embodiment of an apparatus for synthesizing 1,2-dichloroethane according to the invention. In this embodiment, the evaporation step is heated using reaction heat extracted from an HTDC system.

[0038] The Fig. The HTDC plant shown as an example in Figure 3 has already been described in EP 1 161 406. However, other HTDC processes are also suitable for heating the evaporation step according to the invention.

[0039] Ethylene 1 and chlorine 2 are fed into an LTDC reactor 3, where they react to form EDC. The reactor offgas stream 4 can be withdrawn at the top of the reactor 3. A liquid, catalyst-containing EDC stream 5 is withdrawn from the LTDC reactor 3 and fed into a receiver 111. In a preferred embodiment, the EDC stream 5 is greater than the amount of EDC produced in the LTDC reactor 3. An EDC stream 122 is withdrawn from the receiver 111 by means of a pump 106, which, in a preferred embodiment of the invention, is greater than the amount of EDC produced in the LTDC reactor 3. The EDC stream 122 is passed through one or more heat exchangers 107, 108, which serve to preheat the stream and are heated with the EDC stream 104 from the bottom of the evaporator 110 and / or with a liquid, hot EDC stream 220 from the HTDC plant.After preheating, the EDC stream 122 enters the evaporator 110, where an amount of EDC corresponding to the amount of EDC produced in the LTDC reactor 3 is evaporated. The evaporated LTDC product stream 215 can, for example, be fed in vapor form into a distillation column or, in another preferred (not shown) embodiment of the invention, be used under condensation to preheat the liquid EDC from the LTDC reactor 3.

[0040] The non-evaporated portion of the EDC from the evaporator 110 is cooled by heat exchange with stream 122 from the receiver 111 and pumped back to the receiver 111. The EDC partially condensed in the evaporator 110 is collected in the HTDC product receiver 212 and pumped as product 213 to the plant boundary or as return stream 223 back to the HTDC reactor 214. Downstream of the product receiver 212 is an off-gas condensation section 221, which may also contain a freezer (not shown). The off-gas from the HTDC reactor 214, which contains ethylene in addition to other non-condensable components, is compressed in a gas jet gas compressor 216 using the ethylene feed stream 1 to the LTDC reactor 3 and fed into the LTDC reactor 3.

[0041] The method described in the second embodiment is particularly suitable for upgrading existing LTDC plants if, at the same time as upgrading the LTDC plant, a capacity increase is to be achieved by installing an additional HTDC plant.

[0042] In the above-described devices and methods for synthesizing 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst in a reactor 3 under conditions in which the synthesized 1,2-dichloroethane condenses, while the ethylene and chlorine are gaseous, the stoichiometric ratio of ethylene to chlorine in the reactor 3 is adjusted such that ethylene is present in excess. This reduces the effort required to purify the synthesized 1,2-dichloroethane and significantly increases the service life of the reactor 3. List of reference symbols 1 Ethylen 2 Chlor 3 LTDC reactor 4 LTDC reactor exhaust 5 Product EDC from reactor 6 EDC laundry 7 Washing water 8 Sodium hydroxide solution 9 EDC, dry 10 Wastewater stream 11 Product EDC, water-containing 12 Dewatering column 13 High boiler column 14 EDC product stream, purified 15 Vacuum column 16 Water and low-boiling substances 17 Product EDC, purified 18 EDC, wet, from oxychlorination 19 Reverse EDC from EDC cleavage 20 EDC + high boilers 21 Return EDC from vacuum column 22 high boilers 23 Column exhaust gas 104 EDC return flow to the circulation template 106 Circulation pump 107 preheaters 108 preheaters 109 Product capacitor 110 falling film evaporators 111 Circular template 112 Product template 113 Return tank 114 High boiler column 115 vapor stream 116 Reverse EDC from EDC cleavage 117 Dried EDC from oxychlorination 118 EDC return flow to the LTDC reactor 119 LTDC reactor exhaust 120 EDC from vaporizer 121 Condensed EDC from evaporator 122 EDC to the vaporizer 212 HTDC product template 213 HTDC product 214 HTDC reactor 215 LTDC product stream 216 Gas jet gas compressor 217 HTDC reactor exhaust 220 EDC circulating current, HTDC 221 HTDC post-condenser 223 EDC to the HTDC reactor

Claims

[1] Process for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst under conditions in which the synthesized 1,2-dichloroethane condenses out, but the ethylene and chlorine are gaseous, in a reactor (3), wherein in the reactor (3) the stoichiometric ratio of ethylene to chlorine is adjusted such that ethylene is present in excess, characterized by , that - a liquid 1,2-dichloroethane stream (5) is withdrawn from the reactor (3) and partially evaporated in an evaporation device (110); and - the evaporation device (110) is heated by means of the condensation heat of the vapor of a distillation column (114) and / or by means of the reaction heat of a plant for the high-temperature direct chlorination (214) of ethylene. [2] Method according to claim 1, characterized bythat the stoichiometric ratio of ethylene to chlorine is at least 1.01:

1. [3] Method according to one of the preceding claims, characterized by that the stoichiometric ratio of ethylene to chlorine in the reactor (3) is monitored and the supply of ethylene and chlorine to the reactor (3) is controlled such that ethylene is present in excess. [4] Method according to claim 1, characterized by that the evaporation device (110) is single-stage. [5] Method according to claim 1 or 4, characterized by that less than 50% of the 1,2-dichloroethane stream (5) withdrawn from the reactor (3) is evaporated in the evaporation device (110). [6] Method according to one of claims 1, 4 or 5, characterized by that the portion of the 1,2-dichloroethane stream (5) withdrawn from the reactor (3) evaporated in the evaporation device (110) corresponds to the amount of 1,2-dichloroethane produced in the reactor (3). [7] Method according to one of claims 1 or 4 to 6, characterized by that the evaporation device (110) is designed as a falling film evaporator. [8] Method according to one of claims 1 or 4 to 7, characterized by that the non-evaporated portion of the 1,2-dichloroethane stream (5) withdrawn from the reactor is returned to the reactor (3). [9] Method according to one of claims 1 or 4 to 8, characterized by that the vaporous 1,2-dichloroethane stream (121) emerging from the evaporation device (110) is fed into a distillation column (114). [10] Method according to claim 1 or 9, characterized by that by means of the distillation column (114) those compounds are separated which have a higher boiling point than 1,2-dichloroethane. [11] Method according to claim 1 or 10, characterized by that the distillation column (114) is operated at a head temperature in the range of 120°C to 150°C. [12] Method according to claim 11, characterized by that the distillation column (114) is operated at a head temperature in the range of 127°C to 135°C. [13] Method according to one of claims 1 or 4 to 12, characterized by that the 1,2-dichloroethane stream (5) withdrawn from the reactor (3) is preheated by means of a 1,2-dichloroethane stream (104, 120) withdrawn from the evaporation device (110) and / or by means of a 1,2-dichloroethane stream (220) from a plant for the high-temperature direct chlorination of ethylene before it is fed to the evaporation device (110). [14] Method according to claim 13, characterized by that the 1,2-dichloroethane stream (220) is liquid. [15] Method according to one of the preceding claims, characterized by that the catalyst contains FeCl3 and / or NaCl. [16] Method according to one of the preceding claims, characterized bythat an ethylene-containing exhaust gas (217) of a high-temperature direct chlorination reactor (214) is fed to the reactor (3). [17] Apparatus for the synthesis of 1,2-dichloroethane from ethylene and chlorine by low-temperature direct chlorination of ethylene in the presence of a catalyst under conditions in which the synthesized 1,2-dichloroethane condenses out, but the ethylene and chlorine are gaseous, in a reactor (3), wherein in the reactor (3) the stoichiometric ratio of ethylene to chlorine can be adjusted such that ethylene is present in excess, characterized by , that - a liquid 1,2-dichloroethane stream (5) is withdrawn from the reactor (3) and partially evaporated in an evaporation device (110); and - the evaporation device (110) is heated by means of the condensation heat of the vapor of a distillation column (114) and / or by means of the reaction heat of a plant for the high-temperature direct chlorination (214) of ethylene.

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