HK1080068B

HK1080068B - Method for producing unsaturated halogenic hydrocarbons and device suitable for use with said method

Info

Publication number: HK1080068B
Application number: HK06100121.6A
Authority: HK
Inventors: M．本耶; H.埃特尔; I．米尔克; T.维尔德; P．卡默霍费尔; P．施瓦茨迈尔
Original assignee: 犹德有限公司
Priority date: 2002-05-02
Filing date: 2003-04-30
Publication date: 2008-03-28

Description

Process for producing unsaturated halocarbons and apparatus suitable for use in the process

The present invention relates to a process for producing unsaturated halocarbons from saturated halocarbons and to equipment particularly suitable for carrying out the process. A preferred process involves the production of vinyl chloride (hereinafter also referred to as "VC") from 1, 2-dichloroethane (hereinafter also referred to as "DCE").

The incomplete thermal cracking of DCE for the production of VC has been operated on an industrial scale for many years. Here, a cracking furnace is used in which DCE is partially cracked into VC and hydrogen chloride at a furnace inlet pressure of 0.8-4MPa and a temperature of 450-550 ℃. Typical cracking conversion is about 55 mol% of the DCE used.

This process requires considerable amounts of energy for the various process steps, such as heating the DCE up to the cracking temperature, the reaction itself and the subsequent refining of the product mixture. One set of measures to improve process economics is directed to energy recovery, as proposed, for example, in the following documents: EP-B-276775, EP-A-264065 and DE-A-3630162.

Further improvements in process economics can also be achieved by striving for as high a conversion as possible in the cleavage reaction. For this purpose, so-called cracking promoters (also referred to below as "pyrolysis promoters") have also been added to the feed gas. These cracking promoters are compounds which decompose into free radicals under the conditions prevailing in the reactor and participate in chain reactions which lead to the formation of the desired product. The use of such compounds is known, for example, from US-A-4590318 or DE-A-3328691.

Further processes in which cleavage promoters are used in the pyrolysis of DCE are known from WO-A-96/35653, US-A-4584420, US-A-3860595, DE-A-1952770 and DE-A-1953240. Common to all these processes is the addition of these cracking promoters to the gas mixture to be cracked and the generation of free radicals therefrom by thermal decomposition. The free radical generation step prior to the addition of the cleavage promoter is not disclosed in the prior art.

Earlier, non-prepublished WO-A-02/94743 describes A method and apparatus for carrying out A free radical gas phase reaction. Here, a gas is introduced into the reactor, which gas contains the radicals generated by the thermal decomposition of the cleavage promoter in a previous step outside the reactor.

It is also known from WO-A-00/29359 that the operating life of the catalyst can be extended by the presence of hydrogen. In which case hydrogen is mixed into the feed gas.

It has also been proposed that the feed gas containing DCE can be mixed with hot particles and/or a gas stream or a hot gas stream and the heat transferred from the latter can be used for the pyrolysis of EDCs. In the process described in US-A-5488190, the pyrolysis of the feed gas in the cracking furnace is replaced by so-called superpyrolysis, in which the hot particles or gases transfer their energy to the feed gas as quickly as possible, and in which the pyrolysis must be carried out in less than A quarter of A second. This document also proposes adding a cracking promoter to the hot particles or gas. In this case, the reaction heat of the DCE cracking reaction is completely introduced into the reaction zone by the injected heat medium.

Furthermore, it has been proposed that DCE is cleaved to free radicals by laser and that these free radicals are used for radical chain reactions, such as for the preparation of vinyl chloride. Examples of this are given in SPIE, volume 458, Applications of Lasers to Industrial Chemistry (1984), pages 82-88, Umschau 1984, No. 16, page 482, and DE-A-2938353, DE-C-3008848 and EP-A-27554. However, this technology has not entered industrial production until now. The reason for this may be that the reactors proposed to date are not suitable for long-term operation.

The present invention provides a process which allows for an extended period of continuous operation of the cracking furnace compared to conventional processes.

According to the invention and in contrast to the known processes, initiator radicals are generated from the cleavage accelerator by non-thermal or thermal decomposition, in one or more spatially restricted zones, inside or outside the reactor, but separately from the actual cleavage reaction, which radicals, in a subsequent step, are introduced into the gas stream moving through the reactor. The provision of a high concentration of initiator radicals in a confined region within the interior space of the reactor promotes subsequent thermal cracking of the feedstock. In addition, the conditions used to generate the initiator radicals minimize coke formation.

It is an object of the present invention to provide a process for the pyrolysis of halogen-containing aliphatic hydrocarbons, by means of which a higher conversion is possible than in conventional processes at otherwise the same operating temperature, or by means of which the operating temperature can be reduced compared to conventional processes at otherwise the same conversion.

It has now been found that an increase in the yield of products in continuous pyrolysis can be achieved by introducing small amounts of initiator radical-containing gases into the reactor, without having to add large amounts of these gases.

In one embodiment (hereinafter referred to as "modification I"), the present invention provides a process for producing an ethylenically unsaturated halogenoaliphatic hydrocarbon by thermal cracking of a saturated halogenoaliphatic hydrocarbon, the process comprising the steps of:

a) introducing into a reactor a feed gas stream comprising a heated gaseous halogen-containing aliphatic hydrocarbon, passing into the interior of the reactor at least one gas feed line,

b) introducing a heated gas containing free radicals produced by thermal or non-thermal decomposition of the cracking promoter through at least one feed line to the reactor, wherein the temperature of the heated gas corresponds at least to the temperature of the reaction mixture prevailing in the reactor at the feed line opening in the case of free radicals produced by thermal decomposition and at least to the dew point temperature of the reaction mixture in the reactor at the feed line opening in the case of free radicals produced by non-thermal decomposition, and

c) the pressure and temperature inside the reactor are adjusted so that hydrogen halide and an ethylenically unsaturated halogenoaliphatic hydrocarbon are formed by thermal cracking of the halogenoaliphatic hydrocarbon,

provided that, in the case of the generation of radicals by thermal decomposition, this is carried out in the following manner: heating the gas comprising the cracking promoter diluted with an inert gas, or directing the gas comprising the cracking promoter through a heat source whose surface is flushed with an inert gas.

In another embodiment (hereinafter referred to as "modification II"), the present invention relates to a process for producing an ethylenically unsaturated halogenoaliphatic hydrocarbon by thermal cracking of a saturated halogenoaliphatic hydrocarbon, the process comprising the steps of:

a) introducing a feed gas stream comprising a heated gaseous halogen-containing aliphatic hydrocarbon into a reactor, passing inside the reactor at least one feed line for heated gas comprising a cracking promoter,

d) by means of suitable equipment for this purpose, free radicals are generated from the cleavage promoter thermally or non-thermally in a predetermined volume inside the reactor,

e) introducing a heated gas comprising a cracking promoter through a feed line into a predetermined volume, wherein the temperature of the heated gas corresponds at least to the temperature of the reaction mixture prevailing in the reactor at the feed line inlet in the case of free radical generation by thermal decomposition and at least to the dew point temperature of the reaction mixture in the reactor at the feed line inlet in the case of free radical generation by non-thermal decomposition, and

c) the pressure and temperature inside the reactor are adjusted so that hydrogen halide and an olefinic, halogen-containing aliphatic hydrocarbon are formed by thermal cracking of the halogen-containing aliphatic hydrocarbon.

The method of the invention is described for example in the system DCE/VC. It is also suitable for the preparation of other halogen-containing unsaturated hydrocarbons from halogen-containing saturated hydrocarbons. All these reactions have in common that the cleavage is a free-radical chain reaction in which, in addition to the desired product, undesired by-products are formed which lead to coking of the apparatus in long-term operation.

Preferably vinyl chloride is prepared from 1, 2-dichloroethane.

As the heated gas introduced into the feed gas stream through the feed line, any gas comprising free radicals derived from the cracking promoter may be used.

In variant I of the process according to the invention, the formation of free radicals from the cleavage promoter is carried out in the feed line to the reactor, preferably just before the feed line passes into the reactor. The feed line may lead to the reactor wall or, preferably, to the interior of the reactor to avoid reaction of the free radicals produced on the wall. In this variant, the apparatus for generating free radicals is therefore located in the feed line or preferably at its reactor-side end and supplies the formed free radicals into the reactor via the feed line.

According to variant II of the process of the invention, a gas comprising a cleavage promoter is supplied to the predetermined volume inside the reactor via the feed line and the cleavage promoter is cleaved there into free radicals by the action of the apparatus for generating free radicals. Also here, the feed line can lead to the reactor wall or preferably to the reactor interior in order to prevent recombination of the radicals generated at the reactor wall. In this variant, the feed line and the means for generating radicals are therefore separate from one another and the radicals are formed inside the reactor by the action of the means for generating radicals.

For both variants of the process according to the invention, it can also be provided that a further feed line is installed in the vicinity of the entry of the feed line for the gas comprising radicals or cleavage promoter, via which further feed line a heated inert gas can be introduced into the reactor zone into which the radicals are introduced or from which the radicals are generated from the cleavage promoter. This inert gas is used to dilute the reactive components and to prevent the formation of coke deposits.

Examples of cleavage promoters are known per se. These substances are generally halogen-containing, preferably chlorine-containing compounds, or molecular oxygen. Examples of this may be found in US-A-4590318 and DE-A-3328691 already mentioned above. Under the specific conditions of the process of the invention, DCE, for example, is also considered as a promoter of the pyrolysis reaction, since it decomposes, for example at the high temperatures regulated for thermally generating radicals, into radicals which promote the further course of the pyrolysis reaction. These radicals can also be generated by non-thermal decomposition of DCE, such as by electrical discharge or photolytic means.

Preferred cleavage promoters are molecular chlorine, nitrosyl chloride, trichloroacetyl chloride, chloral, hexachloroacetone, trichlorotoluene, monochloromethane, dichloromethane, trichloromethane, tetrachloromethane or hydrogen chloride.

The gas to be introduced and containing the cleavage promoter or the radical generated therefrom may further contain, in addition, an inert gas and/or a gas which is a component of the reaction system.

Examples of inert gases are gases which are inert under the reaction conditions prevailing in the reactor, for example nitrogen, noble gases, such as argon, or carbon dioxide.

Examples of gases which are components of the reaction system are hydrogen chloride and dichloroethane.

Since the introduction of the gas containing free radicals should not reduce the temperature in the reactor, it is suitable that the temperature of the gas containing non-thermally generated free radicals is at least chosen so high that it corresponds to the temperature of the gas stream at the inlet of the feed line to the reactor, whereas the temperature of the gas containing thermally generated free radicals is generally significantly higher than the temperature of the gas stream at the inlet of the feed line to the reactor.

When the free radicals are generated by non-thermal decomposition, it is also possible that the temperature of the heated gas to be introduced into the reactor, which contains the free radicals or cleavage promoter, is lower than the temperature of the reaction mixture at the inlet of the feed line to the reactor. However, the temperature of the heated gas to be introduced into the reactor, which contains free radicals or cleavage promoters, must be at least equal to the dew point temperature of the reaction mixture in the reactor at the inlet of the feed line.

It is preferred that the gas to be introduced is heated just prior to introduction or injection into the feed gas stream. Typical temperatures of the gases to be introduced vary within the range of 250-1500 deg.C, preferably 300-1500 deg.C, more preferably 500-1500 deg.C, especially preferably 500-1000 deg.C.

Typical temperatures of the feed gas stream vary within the range of 250 ℃ to 500 ℃.

The effect produced by the introduced gas depends, in addition to the selected temperature, on the nature of the gas and on its quantity. In general, not more than 10% by weight, preferably not more than 5% by weight, particularly preferably from 0.0005 to 5% by weight, based on the total feed stream in the reactor, is added in total.

Typically more than 90%, preferably more than 95%, of the required heat of reaction is provided by heating of the reactor walls, whereas the heat introduced by the hot, radical-containing gas in the case of thermally generated radicals is primarily used for the prior decomposition of the promoter substance. In the case of non-thermal generation of radicals, the heat introduced by the hot radical-containing gas serves to maintain its temperature above the dew point temperature of the reaction mixture at the point of introduction.

It is believed that the introduction of the free radical containing heated gas promotes free radical chain reactions in the feed gas, which ultimately results in increased concentration of free radicals and increased conversion in the cleavage reaction.

As feed line for the heated gas containing radicals, it is possible to use all apparatuses known to the person skilled in the art for this purpose. Examples of this are lines leading to the reactor and lines preferably comprising nozzles at their reactor-side end. Preferably immediately before their reactor-side end, a feed line for a heating device containing a heated gas.

The opening of the feed line can be located in the reactor wall. The feed line preferably opens into the interior of the reactor, in particular into the middle of the gas flow in the reactor, so that the heated gas does not come into contact with the reactor walls as far as possible.

The generation of free radicals from the cracking promoter may be carried out in the feed line of the reactor. However, the apparatus for generating radicals can also be installed at the end of the feed line for the gas comprising the cleavage promoter, or the apparatus for generating radicals is installed inside the reactor and generates an increased concentration of radicals in a predetermined volume, and the feed line to the reactor opens into this predetermined volume and allows the introduction of heated gases, such as inert gases and/or gases comprising the cleavage promoter.

The generation of free radicals from the cleavage promoter can be carried out by thermal or non-thermal methods. Examples of non-thermal methods are photolytic cleavage by electromagnetic or particle radiation or generation of non-thermal plasma by electrical discharge.

In variant I of the process according to the invention, in the case of the generation of free radicals by thermal decomposition, use is made of a gas which is diluted with an inert gas and comprises a cleavage promoter or of a heat source whose surface is flushed with an inert gas by conducting the gas comprising the cleavage promoter through it. These measures are clearly beneficial in reducing the tendency to coke formation.

In a preferred embodiment, the gas to be introduced, diluted with inert gas, comprising the free radicals in the feed line is electrically heated directly before introduction into the reactor.

In a further preferred embodiment, the gas to be introduced, preferably diluted with inert gas, comprising the cleavage promoter is introduced through the device for generating free radicals, in particular through the discharge zone, directly before introduction into the reactor at the end of the feed line.

Another preferred variant of the process according to the invention comprises generating a thermal plasma from an inert gas, cooling the thermal plasma to the desired temperature by the introduction of the inert gas so that a gas is obtained which has a temperature which is sufficiently high to be able to generate free radicals from the cleavage promoter, mixing this gas with the cleavage promoter, and introducing this mixture comprising free radicals into the reactor.

Another preferred variant of the process according to the invention relates to the use of a gas which is derived from a cracking promoter and in which free radicals are generated by an electric discharge, preferably a spark, potential barrier or corona discharge.

Another preferred variant of the process according to the invention relates to the use of a gas which is derived from a cracking promoter and in which free radicals are generated by means of a microwave discharge or a high-frequency discharge.

Another preferred variant of the process according to the invention relates to the use of a gas which is derived from a cracking promoter and in which heat and free radicals are simultaneously generated by a chemical reaction. Examples of this are the combustion or catalytic reaction of excess chlorine with hydrogen in or just upstream of the opening of the feed line into the reactor. For example, a chlorine detonation gas flame may be used in which chlorine gas is used in excess and an inert gas is preferably added thereto. Very particular preference is given to the reaction of excess chlorine with hydrogen on a catalytically active surface, such as platinum, in the presence of an inert gas.

Another preferred variant of the process according to the invention relates to the use of a gas which is derived from a cracking promoter and in which free radicals are generated by photochemical reactions in a feed line to the reactor or in a predetermined volume inside the reactor. An example of this is the use of a radiation source suitable for generating free radicals, which is installed in the feed line to the reactor, such as an excimer lamp, mercury gas lamp, laser, and which irradiates electromagnetic radiation or particle radiation suitable for generating free radicals, such as alpha or beta particles, into the feed line to the reactor or into the reactor.

In another preferred embodiment of the process according to the invention, a reactor is used which contains at least one catalytically active metal which is located inside the reactor and on a gas-permeable support.

As catalytically active metal, any metal may be used, including metal alloys, which is stable, e.g. does not melt, under the reaction conditions prevailing in the reactor. It is believed that the metal surface and/or the metal halide formed in the cleavage reaction reduces the activation energy of one or more steps of the free radical chain reaction and thus further facilitates the reaction.

Metals or metal alloys of transition group 8 of the periodic table of the elements, in particular iron, cobalt, nickel, rhodium, ruthenium, palladium or platinum, and alloys of these metals with gold, are preferably used as catalytically active metals.

Very particular preference is given to rhodium, ruthenium, palladium and platinum.

As gas-permeable support, it is possible to use all supports known to the person skilled in the art, which can be applied to selected regions of the inner wall of the reactor and/or to the interior of the reactor and which are provided with feed lines for flushing gas. The support can be a cage, which is formed, for example, by a wire mesh or a perforated metal sheet, which can accommodate the catalyst bed and through which a flushing gas can flow, for example by means of centrally located introduction by means of perforated pipes.

Furthermore, the gas-permeable support can be a gas-permeable plate made of catalytically active metal surrounded by a planar structure, for example a wire mesh.

The gas permeable support is preferably a porous body. This may consist of a catalytically active metal. It is preferably a porous ceramic, which is in particular coated with a catalytically active metal; or it is a porous ceramic doped with a catalytically active metal.

The catalytically active metal may be applied in any form in or on the gas-permeable support. Such arrangements are known to those skilled in the art.

For example, catalytically active metals having as large a surface area as possible may be employed: the volume ratio of the formed form exists. The catalytically active metal is preferably applied as a coating and/or as a dopant on or in a gas-permeable support.

To maintain the longest possible operating cycle, the catalytic activity of the metal must be maintained as long as possible and/or be able to be prepared or regenerated again during the continued operation of the reactor.

It has been found that this can be achieved by flushing the catalytic surface with a gaseous reducing agent.

As gaseous reducing agent it is possible to use reducing agents for coking products, all of which are gaseous at the temperatures prevailing in the reactor. Examples of this are hydrogen or a mixture of hydrogen and inert gases.

A gaseous reducing agent is introduced through a gas permeable support and a catalytically active metal is introduced through this support.

The gaseous reducing agent may be introduced continuously or at predetermined time intervals.

The gaseous reducing agent can be introduced in undiluted form or together with inert gases such as nitrogen and/or noble gases.

The temperature of the gaseous reducing agent introduced via the gas-permeable support is purposefully adapted to the temperature prevailing inside the reactor at the gas-permeable support.

The continuous or intermittent injection of hot gases into the reaction mixture enables an increase in the conversion rate and an increase in the product yield in the pyrolysis reaction; the parallel flushing with inert gas and/or reducing agent makes it possible to effectively prevent or retard coking on the surface of the catalytically active metal, which is optionally applied inside the reactor, and thus to prolong the operating cycle of the cracking furnace and to increase the conversion of the cracking reaction again. The operation of the reactor was not interrupted during the flushing process.

Instead of or together with the gaseous reducing agent, the cracking promoter can be supplied to the catalytically active metal in the reactor via a gas-permeable support. Examples of this have been mentioned above.

Preferably at least one feed line for the hot gas comprising the cracking promoter is introduced near the inlet of the feed gas stream into the reactor.

In this way, heated gas containing free radicals formed from the cracking promoter can be introduced into the reactor at this point, where a high concentration of free radicals is already present at the time the feed gas enters the reactor, which contributes to the efficient performance of the chain reaction.

In a preferred variant of the process according to the invention, the heated gas comprising the radicals formed from the cracking promoter is introduced into the feed gas stream via a plurality of feed lines while flowing through the reactor.

More particularly preferably, the number of feed lines in the first third of the reactor is greater than the number of feed lines in the second third and/or third.

The process of the invention can be carried out using the usual pressures and/or temperatures per se. The usual operating pressure is 0.8-4MPa (furnace inlet); typical operating temperatures are 450-. The endothermic cracking reaction requires continuous introduction of energy, which is carried out during the passage of the gas to be cracked through the reactor.

The process according to the invention makes it possible to reduce the usual operating temperatures. Thereby achieving a more economical process. Instead of lowering the operating temperature, an increase in yield can be obtained.

Another embodiment of the process according to the invention relates to the thermal cracking of the product gas in an adiabatic post-reactor installed downstream of the reactor, which process comprises the following measures:

f) introducing a product gas stream comprising a heated halogenous aliphatic hydrocarbon, a hydrogen halide and an ethylenically unsaturated halogenous aliphatic hydrocarbon from the reactor into an adiabatic after-reactor, in which the reaction is continued with cooling of the product gas by means of the heat supplied by the product gas stream and optionally through its inner space at least one feed line for a heated gas which comprises free radicals and is formed from a cracking promoter, and

g) optionally, introducing a heated gas containing radicals generated by thermal or non-thermal decomposition of the cracking promoter through a feed line to the adiabatic post-reactor, wherein in the case of radicals generated by thermal decomposition the temperature of the heated gas is at least the temperature of the reaction mixture prevailing at the feed line, and in the case of radicals generated by non-thermal decomposition the temperature of the heated gas is at least the temperature corresponding to the dew point of the reaction mixture at the feed line to the inlet of the adiabatic post-reactor,

The process according to the invention can here comprise only the measures f) and g) in an adiabatic after-reactor without the use of an upstream reactor, the inner space of which is passed through at least one feed line for heated gas.

However, it is preferred that the process according to the invention employing the measures f) and g) in an adiabatic after-reactor is combined with the use of an upstream reactor, the inner space of which is passed through at least one feed line for heated gas.

The invention also relates to a reactor for carrying out the process defined above, comprising the following components:

i) a feed line for a feed gas stream to the reactor, the feed gas stream comprising a saturated halogen-containing aliphatic hydrocarbon,

ii) at least one heated gas feed line to the interior of the reactor,

iii) a cracking promoter source connected to the feed line,

iv) a device installed in the feed line for generating free radicals from the cleavage promoter,

v) optionally, heating means for heating the gas in the feed line,

vi) heating means for heating and/or maintaining the temperature of the gas stream in the reactor, and

vii) a discharge line for a thermally cracked product gas stream withdrawn from the reactor, which product gas stream comprises an ethylenically unsaturated halogenoaliphatic hydrocarbon.

In another preferred embodiment, the invention also relates to a reactor for carrying out the process defined above, comprising the following components:

ii) at least one feed line for heated gas to the interior of the reactor,

iii) a cracking promoter source connected to the feed line,

viii) a device for generating free radicals from the cleavage promoter installed at the end of the feed line,

v) optionally, heating means for heating the gas in the feed line,

In a likewise preferred embodiment, the invention relates to a reactor for carrying out the process defined above, which reactor comprises the following components:

ix) a device, installed inside the reactor, which generates free radicals from the cleavage promoter within a predetermined volume inside the reactor,

x) at least one feed line to a heated gas comprising a cracking promoter in a predetermined volume inside the reactor,

iii) a cracking promoter source connected to the feed line,

v) heating means for heating the gas in the feed line,

As reactor, it is possible to use all types known to the person skilled in the art for such reactions. Preferably a tubular reactor.

An adiabatic post-reactor, preferably comprising components ii), iii) and iv), or ii), iii) and viii), or ix), x), iii) and v) as defined above, may be located downstream of the reactor according to the invention. In adiabatic post-reactors, the required heat of reaction is provided by the heat of the incoming product gas stream, which is thereby cooled.

Instead of combining the reactor according to the invention with an adiabatic post-reactor comprising components ii), iii) and iv), or ii), iii) and viii), or ix), x), iii) and v), such an adiabatic post-reactor may also be connected to a reactor known per se which does not contain components ii), iii) and iv), or ii), iii) and viii), or ix), x), iii) and v).

The feed line for the heated gas preferably consists of a metal line which opens into the reactor wall or preferably into the reactor interior and which contains nozzles at their reactor-side end and which preferably contains an electrical heating device for the heated gas immediately before its reactor-side end. In a preferred variant, the heating device consists entirely of ceramic.

Another preferred embodiment of the reactor according to the invention comprises a generator of thermal plasma, for example a high-frequency plasma generator, which is connected to the reactor with a gas feed line containing radicals, wherein the high-frequency plasma generator is connected, if appropriate, to a feed line of a further cracking promoter and optionally to a feed line of a further inert gas.

Preferably, a high-frequency plasma generator is mounted on the outer wall of the reactor in the vicinity of the opening of the feed line into the reactor.

Another preferred embodiment of the reactor according to the invention comprises a device for generating an electric discharge, preferably a spark, barrier or corona discharge, which is connected to the feed line of the reactor. This is likewise preferably arranged on the outer wall of the reactor in the vicinity of the opening of the feed line into the reactor.

Another preferred embodiment of the reactor according to the invention comprises means for generating a microwave discharge or a high-frequency discharge, which are connected to the feed line of the reactor. This is likewise preferably arranged on the outer wall of the reactor in the vicinity of the opening of the feed line into the reactor.

Another preferred embodiment of the reactor according to the invention comprises an apparatus in which heat and free radicals are simultaneously generated by a chemical reaction and which comprises at least two feed lines for the reactants and comprises a burner which leads directly to the reactor.

Another preferred embodiment of the reactor according to the invention comprises a radiation source which is installed in the feed line to the reactor or whose radiation is directed into the feed line to the reactor. This is likewise preferably carried out in the vicinity of the opening of the feed line into the reactor, on the outer wall of the reactor.

In a very preferred embodiment of the reactor according to the invention, there is at least one porous ceramic in the form of a spark plug (Kerze) in the interior of the reactor, the surface of which is coated with the catalytically active metal and/or which is doped with the catalytically active metal, and which is provided with a feed line for the gaseous reducing agent and/or the cracking promoter for supplying the catalytically active metal.

Further particularly preferred embodiments of the process and reactor according to the invention are described below with the aid of FIGS. 1 to 9.

In the context of the figures, it is,

FIG. 1 shows, in longitudinal section, a preferred apparatus for heating and introducing heated gas into a cracking reactor, the heated gas containing free radicals and formed from a cracking promoter,

figure 2 shows in longitudinal section the installation of the apparatus of figure 1 in a reaction tube,

FIG. 3 shows in longitudinal section a tubular reactor comprising the apparatus shown in FIG. 1,

figure 4 shows in longitudinal section a preferably used apparatus for generating radicals by means of a non-thermal plasma and for introducing a heated gas into a cleavage reactor, the heated gas containing radicals and being formed from a cleavage promoter,

figure 5 shows in longitudinal section another preferably used apparatus for the generation of radicals by a non-thermal plasma and for the introduction of heated gas into a cleavage reactor, which contains radicals and is formed from a cleavage promoter,

figure 6 shows in longitudinal section the installation of the apparatus of figure 4 or 5 in a reaction tube,

FIG. 7 shows, in longitudinal section, another preferably used apparatus for generating radicals from a cracking promoter by radiation and for introducing a gas into a cracking reactor, which gas contains radicals and is formed from the cracking promoter,

figure 8 shows a modified form of the device of figure 7 in longitudinal section,

fig. 9 shows a further development of the device of fig. 7 in longitudinal section.

In a particularly preferred variant of the process according to the invention, the feed gas stream is contacted with a gas comprising free radicals which are generated in one or more heating devices of the type depicted in FIG. 1 while flowing through the reactor.

The heating device is an electrically operated heating cartridge 1, which heating cartridge 1 preferably has a ceramic cladding and is preferably mounted in a housing 2 containing one or more concentric annular gaps 3.

The housing 2 may be composed of ceramic and/or metal. The housing preferably has a cylindrical shape.

The cartridge heater 1 is fixed in the housing 2 by means of gas-tight, pressure-resistant and heat-resistant leads 4. The lead wire 4 is preferably a lead wire provided with a screw thread into which the heating cartridge can be screwed and fixed.

The housing 2 has a gas inlet 5 through which a gas stream can be introduced, which gas stream contains the cracking promoter and is optionally diluted with an inert gas. The gas inlet 5 is preferably located in the outer wall of the housing 2.

Preferably, a plurality of concentric annular gaps 3 are formed in the housing through which the gas containing the cracking promoter flows. These annular gaps 3 contain at least two openings through which the gas containing the cracking promoter flows into and out of the annular gap. These openings are preferably arranged at the level of the front and rear ends of the heating device. As a result, the gas flow flows through each annular gap along the entire length of the heating device and the flow direction of the gas flow in each annular gap is turned around. In the embodiment shown, the gas stream moves from the outside of the housing 2 through the annular gap 3, repeatedly turns around in the annular gap 3, finally flows along the internally mounted heating cartridge 1 and then flows into the reaction space through the gas outlet 6, which is preferably configured in the form of a nozzle.

However, the housing 2 may also contain only one annular gap. In this case, the gas immediately flows along the heating cartridge 1 into the reaction space through the gas outlet 6.

The embodiment shown in fig. 1, which contains a plurality of annular gaps, offers the following advantages: the outer wall of the heating device is not heated above or significantly above the temperature prevailing in the reaction space by the intense heating of the gas containing the cracking promoter on the heating cartridge 1. This prevents the formation of increased coke deposits on the outer wall.

In another embodiment, the outer wall of the heating device, in particular the part of the heating device protruding into the reaction space, may be coated with an inert material, such as a metal oxide, a ceramic, boron nitride or silicon nitride.

The inner wall of the heating device opposite the heating cartridge 1 may also be coated with such a material.

In another embodiment, the apparatus contains at least two separate gas feed lines, one for the inert gas and the other for the promoter material. The feed line for the promoter substance is preferably arranged so that mixing with the inert gas takes place just before entry into the reaction space.

The heating device shown in fig. 1 is provided with a cone 8 on its outer wall, on the outside of which cone 8 there is a thread 7. The cone 8 and the part of the heating device forming the sealing edge of the pipeline seal consist of the following materials: the materials have approximately the same thermal expansion and in particular consist of the same material.

A possible arrangement of the heating device on the reaction tube is shown in fig. 2. A fixture 10 comprising a thread 11 and a shoulder 12 is welded to the reaction tube 9, which shoulder 12 forms a circumferential sealing edge.

If the heating device described in fig. 1 is screwed into the holder 10, the shoulder 12 is tangential to the cone 8 and thus forms a reliable seal.

This sealing principle is described in DE-A-4420368. Additional sealing (not shown in fig. 2) may be provided by the gland packing, also as already described in 4420368.

The heating apparatus shown in FIG. 1 can be installed in a conventional tubular reactor for producing ethylenically unsaturated halogenoaliphatic hydrocarbons from the thermal cracking of saturated halogenoaliphatic hydrocarbons.

Such an installation is schematically shown in fig. 3.

The tubular reactor comprises a furnace and a reaction tube.

In general, such furnaces fired with a primary energy carrier, such as oil or gas, are divided into a so-called radiant zone 16 and a convection zone 17.

In the radiant zone 16, the heat required for pyrolysis is transferred to the reaction tubes primarily by radiation of the furnace walls heated by the burners.

In the convection zone 17, the energy content of the hot flue gas leaving the radiant zone is utilized by convective heat transfer. For example, the feedstock for the pyrolysis reaction, such as EDC, may be preheated, evaporated, or superheated. It is also possible to generate steam and/or to preheat the combustion air.

In ｃA typical arrangement such as that shown in EP- ｃA-264065, liquid EDC is first preheated in the convection zone of the cracking furnace and then evaporated in ｃA specific evaporator outside the cracking furnace. The vaporous EDC may be passed into the convection zone again and superheated there, wherein the pyrolysis reaction may have already started. After the superheating is complete, the EDC enters the radiation zone, where the conversion to vinyl chloride and hydrogen chloride takes place.

Due to the high temperatures prevailing in the radiation zone and at the entrance to the convection zone, it is advantageous that the apparatus depicted in fig. 1 is not placed directly in these zones, since otherwise, for example, it is not possible or only possible with difficulty to set a defined temperature of the heated gas or gas mixture containing the radicals, which is introduced to promote the cracking reaction.

An arrangement as illustrated in figure 3 is therefore preferred.

The reactor comprises a furnace and reaction tubes extending in an annular manner in the furnace, wherein the furnace contains a radiation zone 16, a convection zone 17 and at least two unheated compartments 18, the loop of the reaction tubes passing from the radiation or convection zone 16, 17 into the unheated compartments 18 or from the unheated compartments into the radiation or convection zone 16, 17, wherein at least one device viii) or ix) is located in at least one compartment 18 and the compartments are equipped with reaction tubes such that the feed gas stream can be contacted at these locations with a heated gas comprising radicals.

Here, the cracking furnace is widened by at least two further unheated compartments 18, which compartments 18 may be insulated. The loop of the reaction tubes is then led from the actual radiation or convection zone 16, 17 through these compartments 18. In these loops, heating means 19 for introducing the heated gas containing radicals shown in fig. 1 are then installed, i.e. the reaction tubes are fitted, preferably at the loop bends and open to the straight long sides of these loops, so that the feed gas stream can be brought into contact with the heated gas containing radicals at these locations.

The loop of reactor tubes leading from the radiant or convection zones 16, 17 to the unheated compartment 18 is preferably provided with insulation.

In a further particularly preferred variant of the process according to the invention, the feed gas stream is contacted, while flowing through the reactor, with a non-thermal plasma comprising free radicals, which plasma is generated in one or more apparatuses of the type depicted in fig. 4 and 5.

Fig. 4 and 5 show a device known per se for generating radicals upstream from a vaporous cleavage promoter or a mixture of a cleavage promoter and an inert gas by means of a non-thermal plasma and for supplying the plasma to the reactor according to the invention.

In this case, free radicals are generated from the gaseous cracking promoter by an electrical discharge in a volume separate from the reaction space of the cracking reaction. The cracking promoter may be used undiluted or may be diluted with an inert gas such as nitrogen or a noble gas. The discharge is preferably a barrier or corona discharge. The free radicals produced in this way are then fed into the actual reaction space of the reactor according to the invention.

The apparatus shown in FIGS. 4 and 5, which is preferably used in the reactor according to the invention, is known from DE-A-19648999. Previously known devices are used for treating surfaces by high pressure plasma.

The device for generating a non-thermal plasma is advantageously combined with a sealing system, as is known from DE-a-4420368, which has been used for introducing measuring probes into cracking furnaces for vinyl chloride production.

In contrast to the embodiment described in DE-A-19648999, the plasma-generating apparatus is operated according to the invention at a significantly higher pressure of at least 5 bar, preferably 12 to 26 bar.

In contrast to the operation at normal pressure known from DE-a-19648999, a significantly higher voltage is necessary for the generation of, for example, barrier discharges.

The apparatus for plasma generation preferably used according to the invention comprises a gas inlet 43, a plasma generation zone 32 containing at least two electrodes 33, 34, and a gas outlet 28 leading to a reaction space 46, wherein the reaction space 46 and the plasma generation zone 32 are spatially separated from each other.

An example of a device for a reactor according to the invention and described in DE-A-19648999 is described in more detail below with reference to FIG. 4, which shows a longitudinal section.

The device has a substantially cylindrical housing 20, the housing 20 having a rear end 21 and a front end 22. Along its outer side 23, the housing 20 has a taper 24 and a thread 25. The housing 20 is composed of an electrically conductive material, such as a metal, preferably steel, or another metal that is stable under the conditions prevailing in the reactor.

In the region of its front end 22, the cylindrical housing 20 tapers and in the region of its cylindrical axis 26 contains an opening serving as a gas outlet 28. This opening may be formed by a nipple. In the region of its rear end 21, the housing 20 is provided with a flange 29 which contains the channels and inlets described further below.

In the interior of the housing 20, a ceramic tube 30 closed at one end in the region of the gas outlet 27 is mounted axially symmetrically to the shaft 26. The outer diameter of this ceramic tube 30 is chosen such that an annular gap, hereinafter referred to as plasma-generating region 32, is formed between the ceramic tube 30 and the inner side 31 of the housing 20. The inner side of the ceramic tube 30 is conductively coated by means of a metal coating, for example a conductive silver coating, and forms one electrode 33 of the plasma-generating device. The other electrode 34 is formed by the conductive housing 20 itself. The ceramic tube 30 and the annular gap-shaped plasma-generating region 32 are thus present between an electrode 33 formed as an internal coating and an electrode 34 formed by the housing 20.

A further tube 35 is present inside the ceramic tube 30, which is likewise mounted axisymmetrically to the cylindrical shaft 26, but is open at both ends. This further tube 35 is fixed inside the ceramic tube 30 in the region of the front end 22 of the housing 20 at a spacing by means of a spring 37 supported against the closed end 36 of the ceramic tube 30, so that an annular gap 38 also exists between the outside of the further tube 35 and the conductively coated inside of the ceramic tube 30. The spring 37 is formed, for example, by three or four wings and in each case allows unimpeded passage of gas from the interior space of the other tube 35 to the annular gap 38.

The spring 37 also connects a high-voltage lead 39, which is located symmetrically inside the other tube 35, with a conductive coating forming one of the electrodes 33, whereby the latter can be supplied with alternating current. In contrast, the housing 20 forming the other electrode 34 is grounded so that it can be touched without danger.

The flange 29 at the rear end 21 of the cylindrical housing 20 is basically used for supplying gas and high voltage and for grounding and guiding the gas flow through the various gaps inside the housing 20. The cylindrical flange 29 is fixed to the cylindrical housing 20 by means of a thread 40, which thread 40 fits into the outer region of the cylindrical housing 20. In its middle, the flange 29 contains an insulating, gas-tight and pressure-resistant bushing 41, through which bushing 41 the high-voltage lead 39 is passed axially into the housing 20. The flange 29 furthermore has a gas inlet 43, the gas inlet 43 leading from the outer connecting section through the channel 42 into the inner region of the further tube 35, the rear end of the further tube 35 being sealed by a sealing web 44 of the flange 29.

Furthermore, the flange 29 comprises, on its side facing the housing 20, an annular groove 45, the diameter of which is dimensioned such that it connects the annular gap 38 between the further tube 35 and the ceramic tube 30 in a gastight manner with the annular gap of the plasma-generating region 32, which plasma-generating region 32 is between the ceramic tube 30 and the inner side 31 of the housing.

To operate the apparatus, a selected gas or gas mixture is supplied to the gas inlet 43 and a high frequency, high voltage is connected between the high voltage lead 39 and the housing 20. The voltage and frequency to be selected depend on the type of gas, the geometry of the assembly, and the type of surface treatment and further factors, and can be freely selected by the person skilled in the art.

The gas enters the interior of the further tube 35 from the gas inlet 43, flows through this further tube 35 as far as the spring 37, enters the region between the spring 37 and the closed end of the ceramic tube 30 and again enters downwards into the annular gap 38 between the ceramic tube 30 and the further tube 35. The gas then reaches the flange 29 again into its annular groove 45 and is deflected again, this time upwardly, into the annular gap between the outside of the ceramic tube 30 and the inside of the housing 20, which annular gap forms the plasma-generating region 32. After flowing through this plasma generation region, the gas reaches the region of the gas outlet 28 and leaves the apparatus there and enters the reaction space 46, where the reaction to be initiated takes place.

Since the conductive coating of the ceramic tube 30 is at the same potential as the high voltage lead 39, the gas is not electrically affected both inside the further tube 35 and inside the annular gap 38. The bypassing of the gas through the further tube 35 and the annular gap 38 is carried out substantially for the purpose of cooling the interior of the apparatus. The working gas thus serves simultaneously as cooling gas, whereby additional internal cooling can be dispensed with.

Only in the plasma-generating region 32, the gas is present between the electrode 33 formed by the electrically conductive coating of the ceramic tube 30 and the electrode 34 formed by the envelope 20 and is partly ionized by the switched-on high-frequency high voltage, i.e. in the plasma state required for the generation of radicals. In the operation of this apparatus, the selected flow velocity should be high enough to maintain the plasma state even after the plasma gas exits through the gas outlet 28.

In another embodiment, the outer wall of the apparatus used according to the invention, in particular that part of the apparatus which protrudes into the reaction space, may be coated with an inert material, such as a metal oxide, ceramic, boron nitride or silicon nitride, to retard or prevent coke deposition.

In another embodiment shown in fig. 5, the apparatus contains one or more bore holes 47 in the housing 20 at the gas outlet 28, through which bore holes 47 the gas containing radicals can be removed into the reaction space 46.

The device used according to the invention preferably has a taper 24 and a thread 25 on its outer wall.

In fig. 6 a preferred way of mounting the apparatus of fig. 4 and 5 on a reaction tube is shown.

A fixture 49 containing threads 50 and a shoulder 51 is welded to the reaction tube 48, the shoulder 51 forming a circumferential sealing edge. If the device described in fig. 4 or fig. 5 is screwed into a fixture, the sealing edge 51 is tangential to the cone 46 and forms a reliable metal seal.

This sealing principle is known from DE-A-4420368. As also described therein, additional sealing (not shown in the figures) may be performed by the gland packing.

The entire apparatus can be installed on the reactor in the same manner as shown in fig. 3.

In a further particularly preferred variant of the process according to the invention, the feed gas stream is contacted, while flowing through the reactor, with a gas comprising free radicals, which gas is generated in one or more apparatuses of the type depicted in FIGS. 7, 8 and 9. In which reactor there is provided as means viii) or ix) at least one means for generating and introducing a gas comprising free radicals, which means comprises a compartment which is separate from the actual reaction space but connected thereto by at least one opening, which contains means for introducing a gas comprising a cleavage promoter, and means for irradiating this gas so that free radicals are photolytically generated in the compartment, which free radicals flow out into the reaction space through the at least one opening.

In this device, the radicals are generated by photolysis of a promoter substance, wherein the gaseous promoter substance can be present in pure form or in a mixture with an inert gas and/or with a gaseous reducing agent.

Photolysis takes place here in a compartment which is separated from the actual reaction space and is flowed through by the respective gas (mixture) and is broken down photolytically into radicals. The gas (mixture) containing the radicals then enters the actual reaction space through an opening, which may be configured in the form of a nozzle.

During the flow-through, but not necessarily also after exiting from the nozzle, the promoter substance is photolyzed by interaction with light from a suitable light source. Free radicals are formed here, which then promote the reaction taking place in the actual reaction space. This embodiment has the advantage that only small amounts of promoter substances are required.

The direct introduction of the promoter substance into the reaction space, as is known from the literature, leads, at the temperature level of the reaction to be influenced, for example in the range from 450 ℃ to 550 ℃, to the generation of free radicals by thermal decomposition of the promoter or by heterogeneous decomposition (wall reactions). In this case, the accelerators must be added in the following amounts: this amount has a significant impact on the reaction system and, in addition to the desired increase in conversion, results in increased formation of by-products, i.e., a decrease in selectivity, and an increase in the rate of formation of coke deposits.

These disadvantages are offset by the economic advantages obtained by increasing the conversion and lead to the use of promoter substances which cannot be carried out in industrial practice at present.

The embodiments described herein overcome this disadvantage by purposefully and efficiently decomposing the promoter species into free radicals in a compartment separate from the actual reaction, and thus only requiring the addition of small amounts of promoter species.

The promoter substance in the preparation of the halogen-containing ethylenically unsaturated hydrocarbon is generally a substance which forms chlorine radicals under the reaction conditions of the process. These may be chlorine gas itself or chlorine compounds such as CCl4 or other chlorinated hydrocarbons. In the process described herein, the promoter material may also be DCE, which is then preferably diluted with an inert gas.

In order to carry out the method variant, light from a light source suitable for the purpose is fed into the compartment separated from the actual reaction space by means of a light guide or a light-transmitting window, preferably a quartz window, and is transmitted through the compartment itself and preferably also through a part of the adjoining reaction space, i.e. a radiation device is provided which makes it possible to radiate the entire compartment and its adjoining reaction space. Thus in a preferred embodiment of the invention, device viii) or ix) contains an optical window and/or another optical conductor leading into the compartment.

In the compartment, the promoter gas (which may consist of the pure promoter substance or a mixture of the promoter substance and an inert gas) forms a gas cushion layer which chemically largely separates the photoconductor or the light window from the reaction space. The purpose of this measure is explained in detail below for the example of EDC cleavage.

An undesirable side reaction in EDC cracking is the deposition of coke on the reactor walls. The process of coke deposition proceeds more slowly on non-metallic materials, such as quartz, than on metallic materials. This fact has recently been exploited to retard the formation of coke in the reactor tubes by coating the inner wall of the tubes with a non-metallic coating. Despite this fact, coke can also be deposited on the optical window if the latter is directly exposed to the reaction mixture, i.e. mounted directly in the reactor wall, for example.

These problems have been described in DE-A-3008848. It is proposed here that the cleavage reaction is photochemically initiated by direct irradiation of light into the reaction space, both in the case of metal vapor lamps and when lasers are used as light sources. Also described therein are the following observations: when a continuously operating light source, such as a metal vapor lamp, is used, the window is quickly covered by the byproducts, while it remains uncovered when a laser is used.

As a remedy, it is proposed to use high flow speed operation in the region of the optical window, whereby the by-products formed are formed only in significant quantities downstream of the window.

However, this embodiment has the disadvantage that the "self-cleaning" of the window may be limited to the use of a pulsed laser, since in this case a short local heating of the gas in and around the coke particles generates a pressure shock which then severs the coke particles or the coke layer from the window. Although the use of a pulsed laser is not explicitly mentioned in DE-A-3008848, it is mentioned in DE-A-2938353 and DE-A-2938353 is explicitly incorporated by reference in DE-A-3008848.

The tests on which DE-A-3008848 and DE-A-2938353 are based were carried out in quartz reactors. However, in industrial reactors composed of metal, coke can form in the inlet region of the reactor and therefore "upstream" of the optical window which may be installed. A possible reason for this is that, on the one hand, the precursors of coke are formed by reaction on the walls in the inlet region of the reactor, and, on the other hand, even when the starting material DCE is refined by careful distillation in an industrial process, small amounts of coke precursors are introduced into the reactor together with the starting material. There is therefore a need for a further process which can be carried out easily in industrial practice and in which the formation of coke can be effectively avoided.

These disadvantages are overcome by the present invention, which provides a process or reactor in which light can be input to a reactor operating under VC production conditions or under similar conditions. For this purpose, the promoter substance is first photolytically cleaved in a compartment separate from the actual reaction space and then introduced into the reaction space.

Fig. 7 shows an apparatus for photolytic generation of radicals from a cleavage promoter, preferably for use in the reactor of the present invention. A clamp containing threads 52 and a circumferential sealing edge 53 on the inside is welded on the bend of the reaction tube. Into this clamp a conical shell 54 can be screwed, the front end of which conical shell 54 can be formed in the form of a nozzle and which can contain, for example, an internal hexagonal rim 55 for a better screwing. If the conical shell 54 is threaded into the clamp 56, it forms a reliable seal with the sealing edge 53 of the clamp under reaction conditions. The sealing principle proven to be effective is described in DE-A-4420368.

Using the same sealing principle, a further housing 57 containing a light-transmitting window 58, for example a quartz window, which may be coated with a translucent metal layer 59, wherein the metal is preferably a hydrogenation catalyst and very particularly preferably platinum, may be screwed into the holder 56. In a preferred embodiment of the invention, the transparent end of the light window and/or the further light conductor is thus coated with an optically translucent layer consisting of a metal which is suitable as a hydrogenation catalyst.

The optical window is clamped between clamps 60, 61 which on their side facing the window comprise circumferential grooves 62 which each can accommodate a seal 63, 64, preferably a metal seal and very particularly preferably a gold seal.

The window 58 is pressed against the clamp 61 by the clamp 60. This can be achieved by: the clamp 60 is screwed in by means of an annular or block bearing 65 having, for example, a blind hole 66.

The clamps 60 and 61, the groove 62 and the thicker seal are dimensioned such that when the assembly is screwed on, a determined face pressure is applied to the seal without damaging the light window.

In a preferred embodiment of the invention, the device viii) or ix) comprises two conical shells 54, 57, which conical shells 54, 57 are mounted such that an intermediate space 67 with at least one gas feed line is formed between the shells 54 and 57 and a compartment is formed which is separated from the reaction space 68 and from the outer space 69, and the shell 57 mounted remote from the reactor contains an optically transparent window 58 and/or another light conductor.

The intermediate space 67 between shells 54 and 57 has one or more gas feed lines and forms a compartment separated from the reaction space 68 and the outer space 69.

For example, pyrolysis of DCE to VC occurs in the reaction space 68. The whole assembly is installed at the reaction tube bend that protrudes from and is thermally insulated from the real radiant section of the furnace.

An inert gas, such as nitrogen or a noble gas, or a mixture of an inert gas and a promoter substance or a gaseous promoter substance, flows into compartment 67 through gas inlet 70. The gas leaves the compartment and flows into the reaction space through the opening 71.

Due to the permanent flushing of the compartment, the light window is separated from the reaction space 68 by a gas cushion layer. Coke precursors, such as acetylene, benzene or chloroprene, may therefore not reach the window and form coke deposits there.

In a preferred embodiment, the light window is coated with an optically translucent metal layer, wherein the metal is a hydrogenation catalyst, such as palladium.

If a small amount of hydrogen is now mixed into the promoter gas, coke precursors are reduced on its surface, which precursors reach the light window despite the flushing. As a result, no coke deposits are formed on the window surface.

Light from the light source transmits the light window and transfers energy to the molecules of the promoter substance, as a result of which the promoter substance decomposes (photolyzes) into free radicals which then promote the reaction taking place in the actual reaction space 68. The generation of free radicals and their subsequent transport to the reaction space is often difficult due to the rapid recombination of free radicals under the prevailing pressure conditions (typically 9-25 bar).

However, in the arrangement according to the invention, the entire compartment and preferably also the reaction space are transmitted. This results in the desired radicals also being formed from the promoter substance in the opening 71 and in the region of the reaction space adjacent to this opening and thus being able to reliably participate in the reaction. High flow velocities of initiator or flushing gas are therefore not required in order to rapidly transport, for example, radicals generated in the compartments into the reaction space.

This also means that initiation can be carried out using very small amounts of promoter gas, with the result that the reaction system is influenced only to a small extent and the formation of undesirable by-products is greatly suppressed.

In another preferred embodiment shown in fig. 8, the compartment 67 contains a further gas inlet 72, which gas inlet 72 extends as far as the surface of the light window 58. This allows the window and its immediate surrounding portion to be flushed with an inert gas or a mixture of inert gas and hydrogen while introducing the promoter substance or a mixture of promoter substance and inert gas through the gas inlet 70. This arrangement allows even better protection of the light window from coke deposits. That is, in a preferred embodiment of the invention, the intermediate space 67 contains a further gas inlet 72 which extends into the compartment up to close to the surface of the light window and/or the further light conductor and which enables the light window and/or the further light conductor and its surroundings to be flushed with an inert gas or with an inert gas together with hydrogen.

Another preferred embodiment shown in fig. 9 is similar to the embodiment shown in fig. 8. However, a further gas inlet 72 is in this case introduced in the direction of the opening 71 and serves for the supply of the promoter substance. The gas inlet 70 is used only for the supply of inert gas or flushing gas. In this way, radicals are generated from the promoter species near the reaction space 68 and away from the optical window 58. Thereby potentially providing further protection of the optical window 58 from coke deposits.

As the light source, any light source whose light is suitable for photolysis of the accelerator substance used may be used. This may be a UV lamp (e.g. a metal vapor lamp) or a laser. When using lasers, it is not of significance for the arrangement proposed here whether pulsed lasers or continuous-radiation lasers are used. Excimer lamps can also be used as light sources.

The radiation used can be input in different ways. For example, light may be input through a fiber optic bundle (as shown in FIG. 8). Furthermore, the light source (e.g. when a metal vapour lamp or excimer lamp is used) may be mounted directly in the housing 57 behind the light window. In this case, it is preferable to provide appropriate cooling. Light may also be input into the housing 57 through additional windows and deflected by mirrors onto the window 58.

In a particular embodiment, a device similar to that described in DE-A-19845512 or DE-Gbm-20003712 is used for the input of light. Previously known devices are used for observing processes in the combustion chamber of an internal combustion engine in operation, for example in the form of so-called spark plug adapters. Apart from their real purpose of use, i.e. optical observation of the combustion process, such devices are, due to their pressure and heat resistance, equally suitable for inputting light into chemical reactors in which the pressure and temperature conditions are similar to those in running internal combustion engines.

If such a device is used, the optical window shown in fig. 7, 8 and 9 with the sealing system described may be omitted. The optical lead wires may then be threaded into a dividing wall located in the shell 55 in the form of an adapter similar to one or more so-called spark plug adapters.

The installation of the device for photolytic generation of radicals from a cleavage promoter on a reactor according to the invention can be carried out in the same way as shown in fig. 3.

Claims

1. A process for preparing an ethylenically unsaturated halogenoaliphatic hydrocarbon by thermal cracking of a saturated halogenoaliphatic hydrocarbon, which comprises the following measures:

b) introducing a heated gas containing free radicals produced by thermal or non-thermal decomposition of the cleavage promoter through at least one feed line to the reactor, wherein the temperature of the heated gas corresponds at least to the temperature of the reaction mixture prevailing in the reactor at the feed line opening in the case of free radicals produced by thermal decomposition and at least to the dew point temperature of the reaction mixture at the feed line opening into the reactor interior in the case of free radicals produced by non-thermal decomposition, and

2. A process for preparing an ethylenically unsaturated halogenoaliphatic hydrocarbon by thermal cracking of a saturated halogenoaliphatic hydrocarbon, which comprises the following measures:

d) by means of a device for thermally or non-thermally generating free radicals from the cracking promoter in a predetermined volume inside the reactor,

e) introducing a heated gas comprising a cracking promoter through a feed line into a predetermined volume, wherein the temperature of the heated gas corresponds at least to the temperature of the reaction mixture prevailing in the reactor at the feed line opening in the case of free radical generation by thermal decomposition and at least to the dew point temperature of the reaction mixture at the feed line opening into the reactor interior in the case of free radical generation by non-thermal decomposition, and

c) the pressure and temperature inside the reactor are adjusted so that hydrogen halide and ethylenically unsaturated halogenoaliphatic hydrocarbon are formed by thermal cracking of the halogenoaliphatic hydrocarbon.

3. A process according to claim 1 or 2, characterized in that the saturated, halogen-containing, aliphatic hydrocarbon used is 1, 2-dichloroethane from which vinyl chloride is produced by thermal cracking.

4. A method according to claim 1 or 2, characterized in that the heated gas is produced from a cracking promoter, which is a chlorine-containing compound.

5. A process according to claim 4, characterized in that the cleavage promoter is molecular chlorine, nitrosyl chloride, trichloroacetyl chloride, chloral, hexachloroacetone, trichlorotoluene, monochloromethane, dichloromethane, trichloromethane, tetrachloromethane or hydrogen chloride.

6. The method according to claim 1 or 2, characterized in that the temperature of the heated gas is 500-1500 ℃.

7. The process of claim 1 or 2, characterized in that the total amount of heated gas fed to the reactor is not more than 10% by weight, based on the total feed stream in the reactor.

8. The process according to claim 1, characterized in that the process for generating free radicals from the cracking promoter is carried out by means of a free radical generating device which is installed at the end of the feed line for the gas comprising the cracking promoter.

9. A method according to claim 1 or 2, characterized in that the radicals are generated from the cleavage accelerator by means of a spark, potential barrier or corona discharge.

10. A method according to claim 1 or 2, characterized in that the radicals are generated from the cleavage promoter by means of a microwave discharge or a high-frequency discharge.

11. A process according to claim 1 or 2, characterized in that a feed line for heated gas leads to the reactor at least in the vicinity of the inlet of the feed gas stream into the reactor.

12. The process as claimed in claim 11, characterized in that the feed gas stream is contacted with a plurality of feed lines for the heated gas which lead to the reactor during the passage through the reactor.

13. Process according to claim 12, characterized in that the number of feed lines leading to the first third of the reactor is greater than the number of feed lines in the second third and/or third.

14. The process according to claim 1 or 2 for the thermal cracking of product gas in an adiabatic post-reactor installed downstream of the reactor, which process comprises the following measures:

f) introducing a product gas stream comprising a heated halogenous aliphatic hydrocarbon, a hydrogen halide and an ethylenically unsaturated halogenous aliphatic hydrocarbon from a reactor into an adiabatic after-reactor, continuing the reaction in the after-reactor with cooling of the product gas by means of heat provided by the product gas stream, and optionally passing inside the after-reactor at least one feed line for a heated gas which comprises free radicals and is formed from a cracking promoter, and

g) optionally, introducing a heated gas containing free radicals produced by thermal or non-thermal decomposition of the cracking promoter through a feed line to the adiabatic post-reactor, or thermally or non-thermally producing free radicals from the cracking promoter in a predetermined volume inside the adiabatic post-reactor through an apparatus, wherein in the case of free radicals produced by thermal decomposition the temperature of the heated gas is at least the temperature prevailing in the reaction mixture at the inlet of the feed line to the adiabatic post-reactor and in the case of free radicals produced by non-thermal decomposition the temperature thereof is at least the temperature corresponding to the dew point of the reaction mixture at the inlet of the feed line to the adiabatic post-reactor,

15. A process for preparing an ethylenically unsaturated halogenoaliphatic hydrocarbon by thermal cracking of a saturated halogenoaliphatic hydrocarbon, which comprises the following measures:

a) introducing a feed gas stream comprising a heated gaseous halogen-containing aliphatic hydrocarbon into a reactor,

f) introducing a product gas stream comprising a heated halogenous aliphatic hydrocarbon, a hydrogen halide and an ethylenically unsaturated halogenous aliphatic hydrocarbon from a reactor into an adiabatic after-reactor which is located downstream of the reactor and in which the reaction is continued with cooling of the product gas by means of heat supplied by the product gas stream and inside which there is at least one feed line for the heated gas, and

g) introducing a heated gas comprising free radicals produced by thermal or non-thermal decomposition of the cracking promoter through a feed line leading to the adiabatic post-reactor, or thermally or non-thermally producing free radicals from the cracking promoter in a predetermined volume inside the adiabatic post-reactor through an apparatus, wherein in the case of free radical production by thermal decomposition the temperature of the heated gas is at least the temperature prevailing in the reaction mixture at the feed line opening to the adiabatic post-reactor and in the case of free radical production by non-thermal decomposition the temperature thereof corresponds at least to the temperature of the dew point of the reaction mixture at the feed line opening to the adiabatic post-reactor,

16. A reactor for carrying out the process of claim 1, the reactor comprising the following components:

ii) at least one feed line for heated gas to the interior of the reactor,

iii) a cracking promoter source connected to the feed line,

iv) a device installed in the feed line for generating free radicals from the cleavage promoter in a non-thermal manner,

v) optionally, heating means for heating the gas in the feed line,

17. A reactor for carrying out the process of claim 1, the reactor comprising the following components:

ii) at least one feed line for heated gas to the interior of the reactor,

iii) a cracking promoter source connected to the feed line,

viii) a device for generating free radicals from the cleavage promoter installed at the reactor-side end of the feed line,

v) optionally, heating means for heating the gas in the feed line,

18. A reactor for carrying out the process of claim 2, the reactor comprising the following components:

i) a feed line to the reactor for a feed gas stream comprising a saturated halogen-containing aliphatic hydrocarbon,

iii) a cracking promoter source connected to the feed line,

v) heating means for heating the gas in the feed line,

19. A reactor according to any of claims 16, 17 and 18, characterized in that the reactor is a tubular reactor.

20. Reactor according to any one of claims 16, 17 and 18, characterized in that it comprises a generator of thermal plasma, which is connected to a feed line of the reactor, wherein the feed line is connected to a further feed line for inert gas and to a further feed line for a cracking promoter.

21. Reactor according to any of claims 16, 17 and 18, characterized in that it comprises means for generating an electric discharge, which means are connected to the feed line of the reactor.

22. The reactor of claim 21, wherein the discharge is a spark, barrier or corona discharge.

23. Reactor according to any of claims 16, 17 and 18, characterized in that it comprises means for generating a microwave or high-frequency discharge, which means are connected to the feed line of the reactor.

24. Reactor according to any of claims 16, 17 and 18, characterized in that it comprises a radiation source arranged in the feed line of the reactor or the radiation of which is directed into the feed line of the reactor.

25. A reactor as claimed in claim 17 or 18, characterized in that at least one device for generating and introducing a non-thermal plasma comprising radicals is provided as device viii) or ix), which device comprises a gas inlet (43), a plasma-generating zone (32) comprising at least two electrodes (33, 34), and a gas outlet (28) to a reaction space (46), wherein the reaction space (46) and the plasma-generating zone (32) are spatially separated from each other.

26. Reactor according to claim 25, characterized in that the device viii) or ix) comprises a cylindrical housing (20), which housing (20) has a rear end (21) and a front end (22), and which housing (20) is provided along at least a part of its outer side (23) with a taper (24) and a thread (25) consisting of an electrically conductive material which is stable under the conditions prevailing in the reactor.

27. Reactor according to claim 25, characterized in that it comprises a reaction tube (48) to which a clamp (49) comprising a thread (50) and a shoulder (51) is welded, in which clamp a device viii) or ix) is screwed.

28. Reactor according to claim 25, characterized in that it comprises a furnace and reaction tubes extending in an annular manner in the furnace, wherein the furnace contains a radiant zone (16), a convection zone (17) and at least two unheated compartments (18), the loop of the reaction tubes passing from the radiant or convection zone (16, 17) to the unheated compartments (18) or from the unheated compartments to the radiant or convection zone (16, 17), wherein at least one device viii) or ix) is located in at least one compartment (18), and the compartment is equipped with reaction tubes such that the feed gas stream can be contacted at these locations with a heated gas comprising free radicals.

29. Reactor according to any of claims 16, 17 and 18, characterized in that it is followed downstream by an adiabatic after-reactor comprising at least one device viii) or ix) according to claim 25.

30. A reactor according to any of claims 17 or 18, characterized in that at least one device for generating and introducing a gas comprising free radicals is provided as device viii) or ix), which device comprises a compartment, which is separate from the actual reaction space but connected thereto by at least one opening, which contains a device for introducing a gas comprising a cleavage promoter, and a device for irradiating this gas, such that free radicals are photolytically generated in the compartment, which free radicals flow out into the reaction space through the at least one opening.

31. A reactor according to claim 30, characterized in that the means viii) or ix) comprise an optical window leading into the compartment and/or another optical conductor.

32. Reactor according to claim 31, characterized in that the transparent end of the light window and/or the further light conductor is coated with an optically translucent layer consisting of a metal which is suitable as a hydrogenation catalyst.

33. Reactor according to claim 30, characterized in that the device viii) or ix) comprises two conical shells (54, 57), which conical shells (54, 57) are mounted such that an intermediate space (67) with at least one gas feed line is formed between the shells (54) and (57) and a compartment is formed which is separated from the reaction space (68) and from the outer space (69), and that the shell (57) mounted remote from the reactor contains an optically transparent window (58) and/or another light conductor.

34. Reactor according to claim 30, characterized in that a radiation device is provided which enables the irradiation of the entire compartment and its adjoining reaction space.

35. A reactor as claimed in claim 33, characterized in that the intermediate space (67) contains a further gas inlet (72) which extends into the compartment up to near the surface of the light window and/or the further light conductor and which enables the light window and/or the further light conductor and its surroundings to be flushed with inert gas or with inert gas together with hydrogen.

36. Reactor according to claim 30, characterized in that it comprises a reaction tube to which a fixture (53) comprising a thread (52) and a shoulder is welded, to which fixture the access device viii) or ix) is screwed.

37. Reactor according to claim 30, characterized in that it comprises a furnace and reaction tubes extending in an annular manner in the furnace, wherein the furnace contains a radiant zone (16), a convection zone (17) and at least one unheated compartment (18), the loop of the reaction tubes being passed from the radiant or convection zone (16, 17) into the unheated compartment (18) or from the unheated compartment (18) into the radiant or convection zone (16, 17), wherein at least one device viii) or ix) is located in at least one compartment (18), and the reaction tubes are installed in the compartment such that the feed gas stream can be contacted at these locations with a heated gas comprising radicals.

38. Reactor according to any of claims 16, 17 and 18, characterized in that downstream thereof is connected an adiabatic after-reactor comprising at least one device viii) or ix) according to claim 30.