EP2344432A1

EP2344432A1 - Method and device for producing ethylenically unsaturated halogenated hydrocarbons

Info

Publication number: EP2344432A1
Application number: EP09778304A
Authority: EP
Inventors: Michael Benje; Peter Kammerhofer; Klaus Krejci; Rainer Kampschulte; Helmut Grumann
Original assignee: Uhde GmbH; Vinnolit GmbH and Co KG
Current assignee: ThyssenKrupp Industrial Solutions AG; Westlake Vinnolit GmbH and Co KG
Priority date: 2008-09-26
Filing date: 2009-09-03
Publication date: 2011-07-20
Also published as: KR20110076967A; ZA201101613B; US20110230683A1; CN102177115A; DE102008049260A1; WO2010034397A1; TW201022185A; DE102008049260B4; RU2011116408A; BRPI0919043A2

Abstract

The invention relates to a method and a device for producing ethylenically unsaturated halogenated hydrocarbons, especially of vinyl chloride, by thermally cracking 1,2-dichloroethane, using physical or chemical measures initiating the cracking reaction. The method and the device according to the invention allow the output obtainable using the cracking reactors of a defined size to be considerably increased. According to the method, initiating measures are used to increase the flux density through the wall of the reactor tube and at the same to increase the reactant feed rate and the heating capacity of the reaction furnace to such an extent that the conversion percentage of the reaction is not considerably increased as compared to methods not using initiating measures. In order to be able to operate the method in an economical manner even when the reaction temperature is reduced, the process parameters have to be adjusted such that the evaporation of the quantity of feedstock used is brought about to at least 50% by means of the perceptible heat content of the reaction mixture leaving the reaction zone.

Description

description

Process and apparatus for the preparation of ethylenically unsaturated halogenated hydrocarbons

The present invention relates to a particularly economical process and a device suitable for the production of ethylenically unsaturated

Halogen compounds by thermal cleavage of halogenated aliphatic hydrocarbons, in particular the production of vinyl chloride by thermal cleavage of 1, 2-dichloroethane.

The invention is described below by way of example by the production of vinyl chloride (hereinafter referred to as VCM) by thermal cleavage of 1,2-dichloroethane (referred to hereinafter as EDC), but it can also be used for the preparation of other ethylenically unsaturated halogen compounds.

Today, VCM is mainly produced by thermal cleavage of EDC, with the implementation of the equation

C ₂ H ₄ Cl ₂ + 71 kJ> C ₂ H ₃ Cl + HCl

is technically carried out in a reaction tube, which in turn is arranged in a gas or oil fired furnace.

The reaction is usually allowed to proceed to a conversion of 55-65%, based on the EDC used (in the following Feed-EDC). The temperature of the furnace reaction mixture leaving (the furnace outlet temperature) is about 480 - 520 ⁰ C. The reaction is operated under pressure. Typical pressures at the inlet of the furnace amount to approx. 13-30 bar abs in today's processes. At higher conversions and consequent higher partial pressure of VCM in the reaction mixture, under the reaction conditions VCM is increasingly converted into secondary products such as acetylene and benzene, which in turn are precursors of coke deposits. The formation of coke deposits necessitates the shutdown and cleaning of the reactor at regular intervals. Against this background, a conversion of 55%, based on the EDC used, has proven to be particularly advantageous in practice.

Most of the methods used today work with cuboid ovens, in which the reaction tube is arranged centrally as a coil constructed of vertically stacked horizontal tubes, wherein the coil can be made one or two-speed. In the case of the catchy arrangement, the tubes can be arranged either in alignment or offset. The furnaces are heated by burners arranged in rows in the furnace walls. The heat transfer to the reaction tubes is predominantly by wall and gas radiation, but also convective by the resulting during heating by burner flue gas. Occasionally, the EDC cleavage is carried out in other furnace types, with different arrangement of the reaction tubes and the burner.

The invention is in principle applicable to all furnace types and burner arrangements as well as to other ways of heating the reaction.

A typical tube reactor used for EDC cleavage comprises a furnace and a reaction tube. In general, such a furnace fired with a primary energy source, such as oil or gas, is divided into a so-called radiation zone and a convection zone.

In the radiation zone, the heat required for the cleavage is transferred to the reaction tube mainly by radiation from the burner-heated furnace walls and the hot flue gas. In the convection zone, the energy content of the hot, emerging from the radiation zone flue gases, is used by convective heat transfer. Thus, the starting material of the cleavage reaction, for example EDC, can be preheated, evaporated or superheated. Likewise, the generation of water vapor and / or the preheating of combustion air is possible.

In a typical arrangement, e.g. is described in EP 264.065 A1, liquid EDC is first preheated in the convection zone of the cracking furnace and then evaporated in a special evaporator outside the cracking furnace. The vaporous EDC is then in turn fed to the convection zone and superheated there, preferably in the shock tubes, whereby the cleavage reaction can already begin. After overheating, the EDC enters the radiation zone, where the conversion to vinyl chloride and hydrogen chloride takes place.

The burners are usually arranged on the longitudinal and front sides of the furnace in superimposed rows, wherein the aim is to achieve the most uniform distribution of heat radiation along the circumference of the reaction tubes by the type and arrangement of the burner.

The part of the furnace in which the burners and the reaction tubes are arranged and in which the predominant conversion of the cleavage reaction takes place is called the radiation zone. Above the actual reaction tubes and in the flow direction of the reaction mixture seen in front of the radiation zone are still rows of tubes whose tubes are preferably arranged horizontally next to each other. These rows of tubes are typically unaffected, and shield overlying internals, such as finned heat exchanger tubes of the convection zone, from the direct combustion chamber radiation largely from. In addition, these tube rows increase the thermal efficiency of the reaction zone through structurally optimized convective heat transfer. The term "shock pipes" or "shock zone" is common in technical terminology for these pipes or rows of pipes. As a "reaction zone" in the context of the invention, the reaction tubes located in the flow direction of the reaction gas following the shock zone, which are preferably arranged vertically aligned or offset one above the other, to understand. Here, most of the EDC used is converted into VCM.

The actual cleavage reaction takes place in the gaseous state of matter. Before entering the reaction zone, the EDC is first preheated and then evaporated and possibly overheated. Finally, the vaporous EDC enters the reactor, where it is usually heated further in the shock pipes and finally enters the reaction zone, where at temperatures above about 400 ⁰ C, the thermal cracking reaction begins.

The evaporation of the EDC takes place in modern systems outside of the cracking furnace in a separate apparatus, the EDC evaporator instead. This is heated by steam in some processes. More economical is the heating with the sensible heat of the exiting the furnace reaction mixture. In older systems, liquid EDC is placed in the preheat zone of the furnace and then evaporates within the furnace.

The invention is directed to a process which comprises vaporizing the feed EDC outside the cracking furnace by means of a separate apparatus.

In the method according to the invention, the sensible heat content of the reaction mixture leaving the cracking furnace is utilized in order to evaporate the EDC used before entering the cracking furnace, ie. H. the EDC evaporator is heated with the hot reactor outlet stream, hereinafter "cracked gas", which is thereby cooled, but the partial or complete condensation of the cracked gas is avoided. Particularly advantageous for this, a device has been found, as they are e.g. in EP 276,775 A2.

Although most of the EDC used is reacted in the reaction zone, EDC is also converted into VCM in the pipeline from the outlet of the cracking furnace until it enters the EDC evaporator, the reaction adiabatically heating the cracking gas withdraws and the fission gas cools. This proportion of total sales, hereinafter "post-reaction", continues into the EDC evaporator, where the reaction finally stops when the temperature falls below a certain minimum temperature. The sum of the volumes of the pipe section from the exit from the cracking furnace to the entry into the EDC evaporator and the cracked gas side of the EDC

Evaporator itself to the outlet nozzle of the EDC evaporator is referred to as "post-reaction zone" in the context of the invention.

The heat of the hot zone leaving the radiation zone, hot flue gas is arranged in the adjoining the radiation zone and spatially above this

Convection zone used by convective heat transfer, for example, the following operations can be performed:

- preheating of liquid EDC - evaporation of preheated EDC

- Heating of heat transfer media

- preheating of boiler feed water

- Generation of water vapor

- Preheating of combustion air - Preheating other (even process-foreign) media.

The evaporation of EDC in the tubes located in the convection zone is dispensed with in modern plants, since in this procedure, the evaporator tubes cocaine quickly, which reduces the shortened cleaning intervals, the economics of the process.

The apparatus combination of radiation and convection zone with the associated flue gas chimney is called by the expert cracking furnace.

The use of the heat content of the flue gas, in particular for the preheating of the EDC, is of central importance for the economy of the process, as a As complete as possible utilization of the heat of combustion of the fuel must be sought.

The reaction mixture leaving the cracking furnace contains, in addition to the desired product VCM, also HCl (hydrogen chloride) and unreacted EDC. These are separated in subsequent process steps and returned to the process or further utilized. Furthermore, the reaction mixture contains by-products, which are also separated, worked up and further recycled or recycled back into the process. These relationships are known in the art.

For the process of particular importance, the by-products coke and tarry substances that arise over several reaction steps from low molecular weight by-products such as acetylene and benzene and settle in the coils of the cracking furnace (and in downstream equipment such as the EDC evaporator), where they a deterioration in the heat transfer, and, over the narrowing of the free cross-section, lead to an increase in the pressure loss.

As a result, the system must be shut down and cleaned at regular intervals. Because of the high cost of cleaning itself and the associated loss of production as long as possible time intervals between the purifications are sought.

After leaving the cracking furnace, the sensible heat of the cracked gas, as already described above, can be used to vaporize the feed EDC.

Devices for this purpose are z. As described in EP 264.065 A1, DE 103 26 248 A1 or in DE 36 30 162 A1. A device according to EP 264,065 A1 has proved particularly advantageous in which the feed EDC is vaporized outside the furnace by means of the sensible heat content of the cracking gas.

Directly after the use of heat by evaporation of feed EDC or cooling of the cracked gas (in processes in which the heat of the cracked gas is not recovered is, also directly after leaving the cracking furnace), the cracking gas is washed in a so-called quench column by direct contact with a cool, liquid recycle or circulating stream and further cooled. This has, above all, the purpose of washing out coke particles contained in the cracking gas or of condensing vapor-like tarry substances and likewise of washing them out, since both components would interfere in the subsequent work-up steps.

Finally, the cleavage gas is fed to a work-up by distillation in which the components hydrogen chloride (HCl), VCM and EDC are separated from one another.

As a rule, this work-up stage generally comprises at least one column which is operated under pressure and is recovered in pure HCl as the top product (hereinafter HCI column).

In recent years, the construction of VCM production facilities by thermal splitting of EDC tends to increase production capacities and thus ever-increasing plant sizes. The production height achievable with a cracking furnace is limited by various factors.

Thus, for example, the pressure loss over the shock pipes and the actual reactor tubes must not be too high, so that at the top of the HCI column sufficient pressure prevails in order to be able to condense the hydrogen chloride with an economically acceptable energy. The lower limit for this column head pressure is about 9 - 1 1 bar abs.

The volume-time yield relative to VCM in kg VCM / (m ³ h), based on the reactor volume, ie the total volume of the reaction tubes, depends essentially on the heat flux density (dimension W / m ² ), ie the amount of heat per unit area can be transferred through the pipe wall to the flowing reaction mixture, as well as the ratio of the surface to the volume of the reaction tube (dimension m ² / m ³ ). Since the ratio surface / volume of the tubes decreases with increasing tube diameter, the recoverable space-time yields become increasingly smaller with increasing diameter of the reactor tubes. One way of at least partially compensating for this effect would be to increase the heat flux density. However, this can not be increased above a certain limit in conventional processes, since otherwise high internal wall temperatures of the reactor tube lead to increased by-product formation and greatly accelerated coke deposition. Average heat flux densities of approx. 28 - 32 kW / m ² are usual in practice.

Due to these limitations, there is currently one for EDC cracking furnaces

Capacity cap of approx. 250,000 t / year VCM. Larger capacities must be achieved by connecting two or more ovens in parallel, ie. H. be realized by mehrstraßigen structure.

If it were possible to significantly increase the capacity of a cracking furnace, the capacity limit above which a multi-path structure of EDC splitting is required could be shifted up. By saving one or more ovens with the associated periphery (among others EDC evaporator, feed preheating, quench column), the realization of high plant capacities would result in a very significant economic advantage.

However, an economic advantage would also result in plant capacities below the limit, from which a multi-path construction is required. If it were possible to significantly increase the space-time yield of the EDC cleavage reaction, then one would manage with smaller reactor volumes. In concrete terms, this means for the cracking furnace that fewer reactor tubes or reactor tubes of a smaller diameter would have to be installed. Since these pipes are made of expensive high-temperature materials and constitute a significant cost component in the construction of a cracking furnace, it would be possible to build a cracking furnace for a certain investment capacity significantly cheaper than before. For a long time attempts have been made to increase the space-time yield of EDC cleavage by various means. These measures aim to increase the production volume achievable with a given reactor volume and can be divided into:

- Use of heterogeneous catalysts

- Use of chemical promoters

- other measures (for example, coupling of electromagnetic radiation).

It is generally believed that the previously proposed physical or chemical initiation measures contribute to the provision of chlorine radicals in the reaction space. The thermal EDC cleavage is a radical chain reaction whose first step is the cleavage of a chlorine radical from an EDC molecule:

C ₂ H ₄ Cl ₂ > C ₂ H ₄ Cl + Cl

The high activation energy of this first step compared to the downstream chain propagation steps is the reason why the cleavage reaction only noticeably starts above a temperature of about 420 ^° C.

The use of a heterogeneous catalyst allows the cleavage of a chlorine radical from the EDC molecule, for example by dissociative adsorption of the EDC molecule on the catalyst surface. With heterogeneous catalysts, very high EDC conversions can be achieved. However, due to high local partial pressures of VCM at and near the catalyst surface, decomposition of the VCM and thus coke formation on the catalyst surface occurs which leads to rapid deactivation of the catalyst. Due to the frequent regeneration required thereby, heterogeneous catalysts have hitherto not found entry into the large-scale production of VCM. Physical measures, such as exposure to short-wave light, provide the energy to split off the chlorine radical from an external source. Thus, the absorption of a short-wave light quantum by the EDC molecule provides the energy for the cleavage of the chlorine radical:

C ₂ H ₄ Cl ₂ + hv> C ₂ H ₄ Cl + Cl

When using chemical initiators, either a chlorine atom is cleaved from the EDC molecule by reaction of the EDC with the initiator, or the chlorine radicals are provided by decomposition of the initiator. Chemical initiators are, for example, elemental chlorine, bromine, iodine, elemental oxygen, chlorine compounds such as carbon tetrachloride (CCI ₄ ), or chlorine-oxygen compounds such as hexachloroacetone.

All measures initiating the reaction cause a significant reduction in the temperature level in the reactor or a constant increase in the conversion at the same conversion.

There is extensive literature on the use of thermal EDC cleavage catalysts. As an example, EP 002,021 A1 may be mentioned.

The use of catalysts in practice precludes their high coking tendency and the need for frequent regeneration intervening.

Even physical measures such as the coupling of electromagnetic radiation into the reaction tube (described for example in DE 30 08 848 A1 or DE 29 38 353 A1) have not found their way into industrial practice despite their basic suitability. The reasons for this are probably due to safety reasons, (since, for example, a pressure-resistant optical window is required for the coupling of light). Other physical measures described, such as the injection of a heated gas into the reaction mixture (WO 02 / 094,743 A2), have hitherto not been used on an industrial scale. DE 103 19811 A1 describes the electromagnetic and photolytic induction of radical reactions. In addition, this document describes a device for introducing this energy into a reactor. Although this document generally mentions the use of cleavage promoters. However, there are no details on the design and operation of the reactor used to find.

The use of chemical promoters is in principle technically the least expensive, because neither the reactor must be filled with catalyst (facilities for filling / emptying and regeneration are required), additional facilities for coupling electromagnetic radiation are required. The promoter can be added in a simple manner to the feed-EDC stream.

The increase in the conversion of the EDC cleavage by addition of halogens or halogen-releasing compounds has already been described by Barton et al. (US 2,378,859 A), wherein the basic experiments were carried out at atmospheric pressure in a Giasapparatur. Krekeler (DE Patent No. 857,957) described a process for thermal EDC cleavage under elevated pressure. The implementation at elevated pressure is fundamental for large-scale application, since only then an economic separation of the reaction mixture is possible. This relationship is known to the person skilled in the art. Krekeler also already recognized the problem of accelerated coking at high sales and called a reasonable upper limit of 66% on sales. Schmidt et al. in DE-AS-1, 210,800 described a method in which the driving at elevated pressure with the addition of a halogen is combined. At operating temperatures of 500 - 620 ⁰ C, conversions of approx. 90% are achieved. Schmidt et al. also already described that the conversion runs as a function of the addition amount of halogen in a saturation, ie that from a certain addition amount of halogen in relation to the feed EDC stream no significant increase in sales is more achieved.

The simultaneous addition of halogen or other chemical promoters to at least two sites of the reactor tube has been described by Sonin et al. in DE 1 953 240 A. described. 450 ⁰ C transactions between 65 and 80% is reached - here were carried out at reaction temperatures of from 250th

Scharein et al. DE 2 130 297 A describes a process for the thermal decomposition of EDC under pressure, in which chlorine is added at several points of the reactor tube. In this case, conversions of 75.6% (Example 1) or 70.5% (Example 2) are achieved at a reaction temperature of 350-425 ° C. In this publication, the importance of the ratio surface / volume of the reactor as well as the importance of Heizflächenbelastung (heat flux density) is pointed out.

The problem of rapid coking of the reactor at high cleavage reaction rates is addressed in one of Demaiziere et al. in US Pat. No. 5,705,720 A, by diluting the vaporous EDC entering the reactor with hydrogen chloride. In this case, hydrogen chloride is added to the EDC in a molar ratio of 0.1 to 1.8. At the same time, split promoters can also be added to the mixture of EDC and HCl by this process. Since the VCM partial pressure is kept low by dilution with large amounts of HCl, high conversions can be realized without coking the reactor. The disadvantage here, however, is the energy expenditure for heating and the subsequent separation of the HCl added for the dilution.

Longhini in US Pat. No. 4,590,318 A discloses a process in which a promoter is metered into the cleavage gas after leaving the cleavage furnace, i.e. into the post-reaction zone. In this case, the heat content of the fission gas is utilized in order to increase the total conversion of the EDC cleavage. However, this method is inferior measures to increase the space-time yield in the cracking furnace itself, since only after the exit from the cracking furnace in the gap gas stream still contained heat can be utilized and the usable amount of heat is limited when the heat of the cracked gas stream to evaporate the feed -EDC should be used.

Felix et al. (EP 0 133699 A1), Wiedrich et al. (US 4,584,420 A) and Mielke (DE 42 28 593 A1) teach the use of chlorinated organic compounds instead of chlorine as Dissociation promoters. In principle, the same effects on the EDC cleavage reaction can be achieved as with elemental halogens, such as chlorine or bromine. However, as these are substances that are often not available (such as chlorine) in the VCM production facility, they have to be introduced separately in the process, which in turn increases the cost of procuring and disposing of residues ,

DE 102 19 723 A1 relates to a process for the addition of cleavage promoters in the preparation of unsaturated halogen-containing hydrocarbons. This document does not disclose details of the thermal design of the reactor.

Although the effects of cleavage promoters on the thermal EDC cleavage reaction and its principal advantages have been known for some time, the use of cleavage promoters has not been found in the commercial production of VCM by thermal cleavage.

This is due to the fact that all previously disclosed methods aimed at increased conversions of the cleavage reaction (at least 65%), although it was recognized early (DE patent 857 957) that above this limit with significantly increased coking tendency of the reactor tubes and the post-reaction zone is to be expected , The increased coking tendency, which hitherto prevented the use of cleavage promoters in practice, is not due to the promoters themselves, but to the coincidence of higher VCM partial pressures in the reaction mixture (as they correspond to conversions above 65%) with high temperatures of the cleavage gas and the inner wall of the reactor tube. This assumption is particularly by the in the US

5,705,720 A, where high conversions with and without a cleavage promoter can be achieved by dilution of the reaction mixture with relatively large amounts of HCl without increased coking tendency occurring.

In conventional processes, the use of promoters has always been accompanied by an increase in sales and has hitherto led to the absence of splitting promoters Entrance into the large-scale production of VCM by thermal cleavage of EDC have found.

The problem is therefore to exploit the properties of cleavage promoters so that the space-time yield in the reaction zone of the cracking furnace is substantially increased, the required Abreinigungsintervalle are not shorter than in an installation of the same production capacity without the use of promoters and the heat content of the cracking gas is used to vaporize the feed used.

Object of the present invention is to provide a reactor with respect to conventional systems significantly increased capacity. This can realize the advantages described above.

Another object of the present invention is to provide a process for the thermal cleavage of halogenated aliphatic hydrocarbons, in which over conventional methods significantly increased space-time yields can be achieved and is characterized by a low coking tendency.

The invention relates to a process for the thermal cleavage of halogenated aliphatic hydrocarbons to ethylenically unsaturated halogenated hydrocarbons in a reactor which comprises reaction tubes with upstream shock pipes through a convection zone and through a downstream arranged in the flow direction of the reaction gas reaction tubes, wherein burners are provided in the radiation zone, in order to supply thermal energy to the shock and reaction tubes, and comprising a heating device for the halogenated aliphatic hydrocarbon ("feed") arranged outside the reactor, which is heated with the energy content of the reaction gases leaving the radiation zone, characterized in that a) the Reaction tubes a chemical promoter for the thermal cleavage is supplied and / or within the reactor at one or more locations a locally limited energy supply to promote the thermal cleavage in the reaction tubes, b) the amount of the chemical promoter and / or the intensity of the localized energy supply to form radicals in the reaction tubes is chosen so that with the energy content of emerging from the radiation zone Reactive gases at least 50%, preferably at least 70%, of the halogenated aliphatic hydrocarbon used can be evaporated without condensation of the exiting the radiation zone reaction gases occurs, c) the heat exchange surface in the radiation zone, defined as the sum of

Surface of the shock pipes and the surface of the reaction tubes, is dimensioned so that the average heat flux through the heat exchange surface of the radiation zone at least 35 kW / m ² , preferably at least 40 kW / m ² , and d) the conversion of the cleavage reaction, based on the used halogenated aliphatic hydrocarbon, between 50 and 65%.

The invention further relates to a device for the thermal cleavage of halogenated aliphatic hydrocarbons to ethylenically unsaturated halogenated hydrocarbons comprising a reactor, which comprises a convection zone and by a downstream arranged in the flow direction of the reaction gas reaction tubes with upstream shock pipes, wherein burners are provided in the radiation zone for supplying thermal energy to the shock and reaction tubes and comprising a halogenated aliphatic hydrocarbon ("feed") heating device located outside the reactor and heated with the energy content of the reaction gases leaving the radiation zone, comprising:

A) means for supplying chemical promoters for the thermal cracking into the reaction tubes and / or means for supplying locally limited energy for promoting thermal cracking at one or more points of the reaction tubes, B) means for selecting the amount of the chemical promoter and / or the intensity of the localized energy supply to form radicals in the reaction tubes in such a way that with the energy content of the reaction gases exiting from the radiation zone at least 50%, preferably at least 70%, of the used halogenated aliphatic

Hydrocarbon can be evaporated without condensation occurs exiting the reaction zone reaction gases, and

C) heat exchange surfaces in the radiation zone, defined as the sum of the surface of the shock tubes and the surface of the reaction tubes, which are dimensioned such that the average heat flux through the

Heat exchange surface of the radiation zone is at least 35 kW / m ² .

It has surprisingly been found that the production amount achievable with cleavage reactors of a given size can be increased considerably if the heat exchanger surfaces are dimensioned such that heat flow densities above 35 kW / m ^{2 are} established, and initiation measures are used to control the reaction temperature and the reaction temperature Lower the internal wall temperature of the reaction tube. At the same time, the educt feed stream and the heating power of the reaction furnace are increased in such a way that the conversion of the reaction does not increase significantly in comparison to processes without using initiating measures. In order to continue to be able to operate the process economically despite the lowering of the reaction temperature, the process parameters must be set so that the evaporation of the amount of feed used is at least 50% by means of the sensible heat content of the reaction mixture leaving the reaction zone.

In a preferred embodiment of the method according to the invention, as an additional measure, the flue gas is condensed in a heat exchanger and the waste heat of the flue gas is used for preheating the burner air or other media, for example liquid educt. In the process variant, the heat from the cooling of the flue gas below its dew point and the heat of condensation of the water vapor contained in the flue gas is used.

The heat exchange takes place in this measure preferably at the outlet of the flue gas from the convection zone.

This measure is used in particular for fuels with a low proportion of acid-forming components. However, it can also be used for fuels with a medium to high proportion of acid-forming components.

The device according to the invention comprises, in this process variant D), at least one heat exchanger which is suitable for obtaining waste heat from the condensation of the flue gas for the preheating of the combustion air or other media, e.g. of liquid educt, is used.

The consumption of fuel of a cracking furnace while maintaining the efficiency of the splitting process can also be significantly reduced by the measure of recovering the latent heat contained in the flue gas and the preheating of the combustion air.

The supply of chemical promoter for the thermal cleavage can take place anywhere. The promoter may be added to the feed, preferably to the gaseous feed. Preferably, the promoter is supplied to the shock or in particular the reaction tubes in the radiation zone.

The localized power supply to promote thermal cracking occurs within the reactor at one or more locations in the reaction tubes.

The method according to the invention is described by way of example on the system EDC / VC. It is also suitable for the production of other halogenated unsaturated carbon Hydrogens from halogen-containing saturated hydrocarbons. All these reactions have in common that the cleavage is a radical chain reaction, in addition to the desired product unwanted by-products are formed, which lead to a coking of plants in continuous operation. Preferably, the preparation of vinyl chloride from 1, 2-dichloroethane.

For the purposes of this description, "locally limited energy input for promoting the thermal cleavage into the reaction tubes" means those physical measures which are capable of initiating the cleavage reaction. It may be z. B. to the coupling of high-energy electromagnetic radiation, the local supply of thermal or non-thermal plasmas, such as hot inert gases.

In the context of this description, "average heat flux density through the heat exchange surface of the radiation zone" is to be understood as meaning the total amount of heat transferred through the heat exchange surface of the steeling zone divided by the heat exchange surface of the radiation zone. This is according to the invention at least 35 kW / m ² .

The term "without condensation entering the reaction gases emerging from the radiation zone" is to be understood in the context of the present description that neither partial condensation nor total condensation of the reaction gas occurs.

Means for supplying chemical promoters for thermal cleavage are known in the art. These are usually feed lines which allow the introduction of predetermined amounts of chemical promoters into the feed gas stream, or they are feed lines which allow the introduction of predetermined amounts of chemical promoters into the reaction tubes at the level of the radiation zone. These feed lines may have nozzles at the reactor end. Preferably, one or more of these leads open in

Direction of flow of the reaction gas seen in the first third of the radiation zone in the pipes. Means for supplying locally limited energy to promote thermal cracking in the reaction tubes at one or more locations of the radiation zone are also known to those skilled in the art. In this case, it may also be supply lines, which optionally have nozzles at the reactor end, is passed over the thermal or non-thermal plasma in the height of the radiation zone in the reaction tubes; or it may be windows, is coupled via the electromagnetic radiation or particle radiation in the height of the radiation zone in the reaction tubes. Preferably, one or more of these feed lines open in the direction of flow of the reaction gas in the first third of the radiation zone into the pipelines; or in the first third, the windows for coupling the radiation are attached.

Means for selecting the amount of the chemical promoter and / or the intensity of the localized energy supply to form radicals in the reaction tubes are also known in the art. These are generally control loops in which a leader is used to control the quantity or intensity. As guide variables, all process parameters can be used, with the help of which the energy content of the reaction gases emerging from the radiation zone can be concluded. Examples include the temperature of the exiting reaction gases, the content of cleavage products in the reaction gases or the wall temperature of the reaction tubes at selected locations.

The dimensioning of the heat exchange surfaces in the radiation zone can be determined by a person skilled in the art on the basis of routine experiments.

The above-described combination of measures or features, compared to conventional methods or devices, greatly increased space-time yields possible without the disadvantages known from the literature, such as increased formation of by-products and strong coking tendency occur. Electromagnetic radiation of a suitable wavelength or particle radiation is irradiated at one or more points of the shock tubes or the tubes in the reaction zone, or a chemical promoter is added or a combination of these measures takes place. In the case of the addition of a chemical promoter, the addition may also take place in the feed line of the gaseous feed, for example to the EDC from the EDC evaporator, for entry into the cracking furnace.

Preferably, the localized energy supply for the formation of radicals by electromagnetic radiation or by particle radiation is effected; This is particularly preferably ultraviolet laser light.

In the case of adding a chemical promoter, the use of elemental halogen, especially elemental chlorine, is preferred.

The chemical promoter may be diluted with a gas that is inert with respect to the cleavage reaction, with the use of hydrogen chloride being preferred. The amount of inert gas used as diluent should not exceed 5 mol% of the feed stream.

The intensity of the electromagnetic radiation or of the particle radiation or the amount of the chemical promoter is adjusted so that the molar conversion, based on the feed used, at the gap-side outlet of the feed evaporator is between 50 and 65%, preferably between 52 and 57%. ,

Particular preference is given to a molar conversion, based on the EDC used, at the gap-side outlet of the feed evaporator of 55%.

The temperature of the reactor leaving the reaction mixture is preferably between 400 ⁰ C and 470 ⁰ C.

The heat exchange surface, defined as the sum of the outer surfaces of the (un-filtered) shock pipes and the tubes in the reaction zone, is dimensioned the average heat flow density, defined as the quotient of the total heat transferred to the cracked gas in the radiation zone and the sum of the outer surface of the unaffected shock pipes and the tubes in the reaction zone, is at least 35 kW / m ² .

Preferably, a dimensioning of the heat exchange surface is such that the average heat flow density, defined as the quotient of the total, transferred in the radiation zone to the fission gas heat and the sum of the outer surface of the unaffected shock tubes and the tubes in the reaction zone between 40 kW / m ² and 80 kW / m ² , more preferably between 45 kW / m ² and 65 kW / m ² .

The inventive method is particularly preferably used for the thermal cleavage of 1, 2-dichloroethane to vinyl chloride.

With the method according to the invention high space-time yield can be achieved. These are preferably, based on the volume of the reaction tube, defined as the sum of the volumes of the shock tubes and the reaction tubes, from entry into the radiation zone of the reactor to the exit from the radiation zone of the reactor, at least 2000 kg, preferably 3000 to 6000 kg, of ethylenic unsaturated halogenated hydrocarbons, preferably vinyl chloride, per hour and cubic meter.

In addition to the thermal cleavage of halogenated, aliphatic hydrocarbons in the actual cracking furnace, the process according to the invention also includes, as a further process step, the evaporation of the liquid feed, for example the liquid EDC, before it enters the radiation zone of the cracking furnace. These measures must be considered for a determination of the efficiency of the cleavage process together with the actual thermal cleavage or with the operation of the cracking furnace.

A preferred embodiment of the invention is directed to a method in which the sensible heat of the cracking gas is utilized to produce liquid, preheated feed, For example, EDC to evaporate before entering the radiation zone, wherein preferably a heat exchanger is used, as has already been described in EP 276,775 A2. It is particularly important to ensure that on the one hand the fission gas is still hot enough when leaving the cracking furnace to evaporate with its sensible heat content, the total amount of the feed and that on the other hand, the temperature of the fission gas does not fall below a minimum value when entering this heat exchanger, to prevent the condensation of tarry substances in the heat exchanger tubes.

In a further preferred embodiment of the feed vaporization, which was also described in EP 276,775 A2, the temperature of the cracking gas at the outlet from the cracking furnace is so low that the heat content of the cracking gas is insufficient to completely vaporize the feed. In this embodiment of the invention, the missing portion of vaporous feed is produced by flash evaporation of liquid feed into a container, preferably in the Ausdampfgefäß a heat exchanger, as described in EP 276,775 A2. The preheating of the liquid feed takes place advantageously in the convection zone of the cracking furnace. In this embodiment of the invention, too, care must be taken that the temperature of the fission gas does not fall below a minimum value when entering this heat exchanger in order to prevent the condensation of tarry substances in the heat exchanger tubes.

The heat content of the fission gas is used to evaporate by means of indirect heat exchange at least 50% of the feed used, without the fission gas thereby partially or completely condensed.

As a heat exchanger, an apparatus is preferably used, as described for example in EP 264.065 A1. In this case, liquid halogenated aliphatic hydrocarbon with the hot, the ethylenically unsaturated halogenated hydrocarbon-containing product gas leaving the reactor, indirectly heated, evaporated and introduced the resulting gaseous educt gas into the reactor, the liquid halogenated aliphatic hydrocarbon in a first container with the Product gas is heated to boiling and transferred from there to a second container in which it is partially evaporated without further heating under lower pressure than in the first container, the vaporized educt gas fed into the reactor and the unvaporized halogenated aliphatic hydrocarbon in the first container is returned.

In a particularly preferred variant of this process, the halogenated aliphatic hydrocarbon is heated prior to feeding into the second vessel in the convection zone of the reactor with the flue gas which produces the burner heating the reactor.

Particularly preferred is a procedure in which the entire feed used is vaporized by indirect heat exchange with the cleavage gas, without the cleavage gas thereby partially or completely condensed.

If the evaporation of the feed is not completely by means of the heat content of the cracking gas, the residual amount of feed is preferably evaporated by flash evaporation in a container, wherein the feed is previously preheated in the liquid state in the convection zone of the cracking furnace. As a container for Ent- voltage evaporation while the Ausdampfgefäß a heat exchanger is preferably used, as it is for. As described in EP 264.065 A1.

In a further preferred variant of the method according to the invention, the temperature of the reaction gas entering into the heating device arranged outside the reactor is measured and serves as a reference variable for the regulation of the addition amount of the chemical promoter and / or for the intensity of the locally limited energy supply. Of course, other measured variables can be used as a reference variable, for example, the content of products of the cleavage reaction.

In a further preferred variant of the method, the molar conversion of the cleavage reaction downstream after the exit of the cleavage gas from the EDC evaporator or determined at the top of the quench column, for example with an online analyzer, preferably by means of an online gas chromatograph.

In a further preferred variant of the method according to the invention, the flue gas is sucked off after leaving the convection zone by a flue gas blower and transferred into one or more heat exchangers, where it is condensed. The waste heat is used to heat the burner air. The resulting condensate is optionally worked up and discharged from the process. The remaining gaseous constituents of the flue gas are optionally purified and discharged into the atmosphere.

Particular preference is given to a method in which the flue gas to be cooled below the dew point is introduced into the heat exchanger in the downward direction from above, leaves the heat exchanger in the upward direction after cooling, and the resulting condensate can drain freely from the heat exchanger downwards and thus completely is separated from the flue gas stream.

The amount of fuel can be distributed both in equal parts as well as unequal parts on the burner rows of the furnace.

Reactor tubes with a clear diameter of at least 200 mm, preferably from 250 to 350 mm, can be used. The clear diameter of the reactor tubes is not limited to these dimensions.

When using gap promoters and / or when using physical measures to initiate the feed cleavage reaction, the process according to the invention makes it possible to use high average heat flow densities and avoids the usually occurring disadvantages of high space-time yields in the thermic feed cleavage.

The advantage of the method lies in particular in the fact that when setting moderate sales, which correspond to those of "conventional" methods under Use of promoters comparatively very high heat flux densities can be set and thus high heat fluxes can be transferred to the cracking gas, without the formation rates of by-products or coke are increased. The reason for this is that the addition of promoters and / or the use of physical measures to initiate the cleavage reaction significantly reduce the overall temperature level in the reaction chamber and the inner wall temperature of the reactor tube, whereby the reaction mixture is exposed to gentle conditions despite high heat transfer rates.

Since the reactor volumes which are smaller in comparison to conventional methods (equivalent to smaller tube lengths in the radiation zone) cause lower flow pressure losses, reactors designed in accordance with the invention can be exposed to comparatively higher feed quantities without the minimum pressure required for economic separation of the reaction mixture on entry into the HCl mixture. Falls below the column.

Another advantage is that even reactor tube diameter can be realized, which are not accessible by conventional methods, otherwise due to their low surface area / volume ratio too high internal wall temperatures would occur.

The economy of the process is also influenced by the sum of the pressure losses of the cracking furnace (consisting of convection and radiation zone), the heat exchanger for the evaporation of the feed, and any quenching system ("quench column") which should be as small as possible in the distillative separation of cleavage products, they must be condensed at the top of a column, a chiller being used to cool the condenser, the greater the sum of the pressure losses over the entire "thermal cleavage" system, the lower the pressure at the top of the column and the separated cleavage product, for example HCl, must be condensed at a correspondingly lower temperature This leads to an increased specific energy consumption of the refrigeration machine, which in turn adversely affects the economy of the entire process. The invention will be explained below with reference to examples. A limitation is not intended thereby.

example 1

42500 kg / h of vaporous EDC were abs in a cracking furnace at a pressure of 21 bar. and an inlet temperature of 360 ⁰ C passed through a coil of 232 m in length and a clear diameter of 153.4 mm. At the reactor inlet, a mixture of 42.5 kg / h of chlorine (corresponding to 1000 ppm by weight) and 250 kg / h of hydrogen chloride were metered into the vaporous EDC. The reactor volume was 4.3 m ³ . The fired power was 10,000 kW. The temperature of the cracked gas on exit from the furnace was 418 ^C C; the turnover was 52.5%. The temperature of the flue gas at the outlet of the radiation zone Con t 897 ⁰ C. The absorbed thermal output of 5113 kW, the average heat flow density Con t 42 kW / m ^2. The reactor power was 3270 kg VCM / m ³ h.

Example 2

64000 kg / h of vapor EDC were in a cracking furnace at a pressure of 21 bar abs. and an inlet temperature of 360 ⁰ C passed through a coil of 232 m in length and a clear diameter of 153.4 mm. At the reactor inlet, a mixture of 64 kg / h of chlorine (corresponding to 1000 ppm by weight) and 250 kg / h of hydrogen chloride were added to the vaporous EDC. The reactor volume was 4.3 m ³ . The unterfeuerte power was 20000 kW. The temperature of the cracked gas on exit from the furnace was 440 ° C; the turnover was 52.8%. The temperature of the flue gas at the exit from the radiation zone was 1074 ^° C. The absorbed heat output was 8220 kW, the average heat flux density was 67 kW / m ² . The reactor power was 4960 kg VCM / m ³ h.

Example 3 36160 kg / h of vapor EDC were passed in a cracking furnace at a pressure of 21 bar abs, and an inlet temperature of 360 ⁰ C through a coil of 130 m in length and a clear diameter of 153.4 mm. At the reactor inlet, a mixture of 36.1 kg / h of chlorine (corresponding to 1000 ppm by weight) and 250 kg / h of hydrogen chloride were added to the vaporous EDC. The reactor volume was 2.4 m ³ . The fired power was 10,000 kW. The temperature of the cracked gas on exit from the oven was 433 ⁰ C; the turnover was 52.7%. The temperature of the flue gas at the exit from the radiation zone was 997 ^° C. The absorbed heat output was 4550 kW, the mean heat flux density was 72 kW / m ² . The reactor power was 5010 kg VCM / m ³ h.

Example 4 (comparative example, conventional method)

36160 kg / h of vapor EDC were in a cracking furnace at a pressure of 21 bar abs. and an inlet temperature of 360 ⁰ C passed through a coil of 403 m in length and a clear diameter of 153.4 mm. The reactor volume was 7.5 m ³ . The fired power was 10,000 kW. The temperature of the cracked gas on exit from the furnace was 490 ⁰ C; the turnover was 52.8%. The temperature of the flue gas on exit from the radiation zone was 866 ⁰ C. The absorbed thermal output of 5290 kW, the average heat flux was 25 kW / m ^2. The reactor power was 1606 kg VCM / m ³ h.

Claims

Claims 208ku04.wo

1. A process for the thermal cleavage of halogenated aliphatic hydrocarbons to ethylenically unsaturated halogenated hydrocarbons in a reactor, by a convection zone and by a flow direction of the

Reaction gas downstream radiation zone extending reaction tubes comprising upstream shock pipes, wherein in the radiation zone burners are provided to supply thermal energy to the shock and reaction tubes, and which comprises an outside of the reactor arranged heating device for the halogenated aliphatic hydrocarbon, which with the energy content of the radiation zone exiting reaction gases is heated, characterized in that a) the reaction tubes, a chemical promoter for the thermal cleavage is supplied and / or within the reactor at one or more locations a locally limited energy supply to promote the thermal

Cleavage into the reaction tubes b) the amount of the chemical promoter and / or the intensity of the localized energy supply to form radicals in the reaction tubes is chosen so that the energy content of the exiting the radiation zone reaction gases at least 50% of the halogenated aliphatic hydrocarbon used c) the heat exchange surface in the radiation zone, defined as the sum of the surface of the shock pipes and the surface of the reaction tubes, is dimensioned such that the average heat flux through the heat exchange surface of the radiation zone is at least 35 kW / m ² , and d) the conversion of the cleavage reaction, based on the halo genierten aliphatic hydrocarbon used is between 50 and 65%.

2. The method according to claim 1, characterized in that the locally limited energy supply for the formation of radicals by electromagnetic radiation or by particle radiation is effected.

3. The method according to claim 2, characterized in that it is the electromagnetic radiation is ultraviolet laser light.

4. The method according to claim 1, characterized in that elemental chlorine is used as the chemical promoter.

5. The method according to claim 4, characterized in that the elemental chlorine is diluted with hydrogen chloride, wherein the amount of hydrogen chloride used for dilution is at most 5 mol% of the halogenated aliphatic hydrocarbon stream used.

6. The method according to at least one of claims 1 to 5, characterized in that the temperature of the reactor leaving the reaction mixture is between 400 ⁰ C and 470 ⁰ C.

7. The method according to at least one of claims 1 to 6, characterized in that the average heat flux density in the radiation zone between 45 and 65 kW / m ² .

8. The method according to at least one of claims 1 to 7, characterized in that the conversion, based on the halogenated aliphatic used

Hydrocarbon, between 52% and 57%.

9. The method according to at least one of claims 1 to 8, characterized in that the halogenated aliphatic hydrocarbon is 1, 2-dichloroethane and the ethylenically unsaturated halogenated hydrocarbon is vinyl chloride.

10. The method according to at least one of claims 1 to 9, characterized in that the space-time yield, based on the volume of the reaction tube from entry into the radiation zone of the reactor to the exit from the radiation zone of the reactor, at least 2000 kg of vinyl chloride per Hour and cubic meter.

11. The method according to at least one of claims 1 to 10, characterized in that liquid halogenated aliphatic hydrocarbon with the hot, the ethylenically unsaturated halogenated hydrocarbon-containing product gas leaving the reactor, indirectly heated, evaporated and introduced the resulting gaseous starting material into the reactor is, wherein the liquid halogenated aliphatic hydrocarbon is heated to boiling in a first container with the product gas and transferred from there into a second container in which it is partially evaporated without further heating at a lower pressure than in the first container, wherein the vaporized Feedstock gas fed to the reactor and the unvaporized halogenated aliphatic

Hydrocarbon is returned to the first container.

12. The method according to claim 11, characterized in that the halogenated aliphatic hydrocarbon prior to feeding into the second container in the convection zone of the reactor with the flue gas, which heating the reactor

Produce burner, is heated.

13. The method according to at least one of claims 1 to 12, characterized in that the temperature of the reaction gas entering the outside of the reactor is measured and measured as

Reference variable for the control of the addition amount of the chemical promoter and / or for the intensity of the localized energy supply is used.

14. The method according to at least one of claims 1 to 13, characterized in that the conversion of the cleavage reaction downstream after leaving the

Fission gas from the heating device for the halogenated aliphatic hydrocarbon or at the top of the quench column is determined, preferably by means of an online analysis method, in particular mean of an online gas chromatograph.

15. The method according to at least one of claims 1 to 14, characterized in that the flue gas condenses in a heat exchanger and the

Waste heat of the flue gas is used to preheat the burner air or other media.

16. The method according to claim 15, characterized in that the heat exchange takes place at the outlet of the flue gas from the convection zone.

17. The method according to claim 16, characterized in that the flue gas is sucked off after leaving the convection zone by a flue gas fan and transferred into one or more heat exchangers, where it is condensed, that the waste heat is used to heat the burner air that the resulting

If necessary, condensate is worked up and discharged from the process, and the remaining gaseous constituents of the flue gas are optionally purified and released into the atmosphere.

18. The method according to any one of claims 15 to 17, characterized in that the below the dew point to be cooled flue gas is introduced into the heat exchanger held in the downward direction from above, after cooling leaves the heat exchanger in the upward direction, and the resulting condensate from the heat exchanger free can run down and thus completely separated from the flue gas stream.

19. An apparatus for the thermal cleavage of halogenated aliphatic hydrocarbons to ethylenically unsaturated halogenated hydrocarbons comprising a reactor comprising by a convection zone and by a downstream in the flow of the reaction gas radiant zone extending reaction tubes with upstream shock pipes, wherein in the radiation zone burners are provided to the Shock and reaction tubes thermal energy and comprising a halogenating aliphatic hydrocarbon heating device located outside the reactor, which is heated with the energy content of the reaction gases leaving the radiation zone, comprising: A) means for supplying chemical promoters for the thermal

Cleavage into the reaction tubes and / or means for supplying localized energy to promote thermal cracking at one or more locations of the reaction tubes,

B) means for selecting the amount of the chemical promoter and / or the intensity of the localized energy supply to form radicals in the reaction tubes in such a way that at least 50% of the halogenated aliphatic hydrocarbon used are evaporated with the energy content of the reaction gases leaving the radiation zone can occur without condensation of the exiting from the radiation zone reaction gases, and

C) Heat exchange surfaces in the radiation zone, defined as the sum of the surface of the shock tubes and the surface of the reaction tubes, which are dimensioned so that the average heat flux through the heat exchange surface of the radiation zone is at least 35 kW / m ² .

20. The device according to claim 19, characterized in that the means for supplying chemical promoters for the thermal cleavage in the reaction tubes are supply lines, which allow the introduction of predetermined amounts of chemical promoters in the feed gas stream.

21. The device according to claim 19, characterized in that the means for supplying chemical promoters for the thermal cleavage are leads, which allow the introduction of predetermined amounts of chemical promoters in the reaction tubes in the height of the radiation zone, preferably leads, at the reactor end Have nozzles, particularly preferred

Feed lines, which open in the direction of flow of the reaction gas in the first third of the radiation zone open into the pipes.

22. The device according to claim 19, characterized in that the means for supplying locally limited energy for promoting the cleavage reaction in the reaction tubes at one or more points of the radiation zone are supply lines, which preferably have nozzles at the reactor end, on the thermal or non- thermal plasma in the height of the radiation zone is passed into the reaction tubes or the windows are coupled via the electromagnetic radiation or particle radiation in the height of the radiation zone in the reaction tubes, particularly preferably leads or windows, seen in the flow direction of the reaction gas in the first third of

Radiation zone open or mounted in the pipes.

23. The device according to claim 19, characterized in that the means for selecting the amount of the chemical promoter and / or the intensity of the localized energy supply to form radicals in the reaction tubes

Are control loops in which a reference variable is used to control the amount of chemical promoter and / or the intensity of the localized energy input.

24. The device according to claim 19, characterized in that as a reference variable, the temperature of the exiting reaction gases, the content of fission products in the reaction gases or the wall temperature of the reaction tubes are used at selected locations.

25. The device according to at least one of claims 19 to 24, characterized in that the arranged outside the reactor heating device for the halogenated aliphatic hydrocarbon comprises a first container and a second container, wherein the liquid halogenated aliphatic hydrocarbon in the first container with the product gas until heated to boiling and transferred from there to the second container in which he without further

Heating under a lower pressure than in the first container is partially evaporated, wherein the vaporized educt gas fed to the reactor and not vaporized halogenated aliphatic hydrocarbon is recycled to the first vessel.

26. The device according to claim 25, characterized in that the halogenated aliphatic hydrocarbon before feeding into the second container in a

Piping is passed through the convection zone of the reactor, where it is heated with the flue gas, which produce the burner heating the reactor.

27. The device according to at least one of claims 19 to 26, characterized in that said D) comprises at least one heat exchanger, the

Recovery of waste heat from the condensation of the flue gas for preheating the combustion air or other media is used.