DE102008038032A1 - Catalytic oxidation of hydrogen chloride with oxygen in non-thermal plasma - Google Patents

Abstract

A process for the production of chlorine by catalytic oxidation of gaseous hydrogen chloride under the action of a non-thermal plasma is described.

Description

The The invention relates to a process for the production of chlorine by catalytic oxidation of gaseous hydrogen chloride under the influence of a non-thermal plasma. The combined effect of catalyst and plasma leads to higher levels of HCl conversion as each of the two activation methods taken individually. By lowering the reaction temperature in the plasma reactor in comparison the catalyzed Deacon reaction are very high HCl conversion levels without significant thermodynamic limitation possible.

The recycling of hydrogen chloride (HCl) to chlorine (Cl ₂ ) plays an essential role in the chlorine-processing chemical industry (cf. Ullmann Encyclopedia of technical chemistry. Verlag Chemie, Weinheim, 4th edition 1975, Vol. 9, p. 357 et seq. or Winnacker-Kuchler: Chemical Technology, Processes and Products. Wiley-VCH Verlag, 5th edition 2005, Vol. 3, p. 512 ff. ). A distinction is made between gaseous HCl and its aqueous solution, hydrochloric acid. HCl recycling processes according to the prior art are the electrolysis of hydrochloric acid and the oxidation of hydrogen chloride with oxygen (Deacon reaction) according to the reaction equation: 4 HCl + O ₂ <-> 2 Cl ₂ + 2 H ₂ O

The Deacon reaction can be carried out purely thermally at high temperatures (> 700 ° C) or catalyzed at lower temperatures (300 to 500 ° C). Suitable catalysts are for example in the DE 1 567 788 A1 described. Older processes usually use doped copper chloride as the catalytically active component (eg Shell chlorination process, Dow-Hercules process), while more modern processes use precious metals or their oxides and chlorides.

The Deacon reaction is with a standard reaction enthalpy of -57 kJ / mol of chlorine exothermic. It is reversible. For thermodynamic reasons are low reaction temperatures and excess oxygen desired to balance as possible move far towards product creation. That is the desire for the highest possible, technically usable reaction rates compared to the known catalysts temperatures above 300 ° C. At these temperatures is the Deacon balance is no longer completely on the product side. From the known thermodynamic data of the Deacon reaction can it is calculated that at 350 ° C reaction temperature, 0.1 MPa Gas pressure and a stoichiometric Eduktverhältnis of four parts of HCl to one part of oxygen, a maximum degree of HCl conversion of 85% is achievable. This value can be adjusted by a Increase oxygen excess. Indeed then increases the product processing supplied gas flow. Accordingly, the effort increases for the separation of chlorine. Could you mind lower the reaction temperature to 100 ° C, would be at stoichiometric Eduktverhältnis an equilibrium conversion 99% possible.

One Disadvantage of the catalyzed HCl oxidation, in particular with noble metal catalysts is that the catalyst used for the reaction is sensitive to contaminants in the feedstock. These can lead to significant loss of activity and thus lead to a reduction in total plant capacity.

In order to lower the reaction temperatures to the thermodynamically favorable range (<300 ° C), so-called. investigated non-thermal excitation sources. Such process principles are for example in Stiller ( W. Stiller: Non-thermally activated chemistry. Birkhäuser Verlag, Basel, Boston, 1987, pp. 33-34, pp. 45-49, pp. 122-124, pp. 138-145 .). Non-thermal activation HCl oxidation processes are in the literature JP 5 907 3405 . RU A 2253 607 . DD 88 309 . SU A 180 1943 , Cooper et al. ( WW Cooper, HS Mickley, RF Baddour: Oxidation of hydrogen chloride in a microwave discharge. Ind. Eng. Chem. Fundam. 7 (3), 400-409 (1968) ), van Drumpt ( JD van Drumpt: Oxidation of Hydrogen Chloride with Molecular Oxygen in a Silent Electrical Discharge. Ind. Eng. Chem. Fundam. 22 (4), 594-595 (1972) ) and DE 10 2006 022 761 A1 described. They are based predominantly on the photochemical activation of one of the two reaction partners, HCl or O ₂ .

Initiation of the Deacon reaction in cold plasma is mentioned only in a few documents:
SU A 1 801 943 describes a process for HCl oxidation with air in an electrical pulse discharge (10 to 40 kV peak voltage) at 20 to 30 ° C. With a residence time of up to 140 s in the discharge zone, HCl conversion rates up to 74% are achieved. The patent does not contain information on the discharge arrangement used and the specific energy consumption. The inventors emphasize the absence of a catalyst as an essential feature of their process. From the embodiments of the invention it appears that the dew point of the water of reaction in the product mixture is exceeded. This inevitably leads to the formation of water films on the reactor walls, which ultimately lead to an unstable discharge behavior (sparkover). How the condensation of the water of reaction in the discharge reactor at 20 to 30 ° C can be avoided is not described.

van Drumpt et al. (1972) describe the HCl oxidation in a modified Siemens tube at atmospheric pressure. It was possible to convert up to 6% of hydrogen chloride into chlorine. These are by far too low degrees of implementation for a sensible technical application.

From Cooper et al. (1968) the HCl oxidation in a high-energy microwave plasma is described. Low gas pressures of 13 to 27 mbar were used and temperatures of 500 to 700 ° C occurred. However, these temperatures far exceed the thermodynamically favored range by far. Furthermore, the low operating pressures of the microwave plasma are not very attractive for technical implementation.

The font DE 10 2006 022 761 A1 describes an integrated process for the preparation of isocyanates from phosgene and at least one amine and oxidation of the resulting hydrogen chloride with oxygen to chlorine, wherein the chlorine is recycled to produce the phosgene. In particular, it is assumed that processes for the production of chlorine by non-thermally activated reaction of hydrogen chloride with oxygen, in which from the resulting gas mixture in the reaction consisting at least of the target products of chlorine and water, unreacted hydrogen chloride and oxygen and optionally other minor components such as carbon dioxide and Nitrogen chlorine is removed and recycled into the phosgene production.

main disadvantage the few plasma-enhanced, non-thermal HCl oxidation processes described so far is an unsatisfactory energy efficiency. In no case very high HCl conversion rates (> 90%) been achieved, as for a technical application are desirable with simple gas workup.

task It is therefore the object of the present invention to provide a process for recycling from hydrogen chloride to chlorine, which can be operated easily, safely and energy-efficiently. In particular, very high hydrogen chloride conversion levels to be achieved so as to simplify the workup of the reaction products.

These Tasks are inventively heterogeneous catalyzed oxidation of hydrogen chloride in combination with a dissolved non-thermal plasma.

object The invention relates to a process for heterogeneously catalyzed oxidation of hydrogen chloride by means of oxygen-containing gases, thereby characterized in that a gas mixture consisting at least of hydrogen chloride and oxygen flows through a suitable solid catalyst and simultaneously exposed to the action of a non-thermal plasma becomes.

Prefers a method is used in which the non-thermal plasma is generated by silent electrical discharge.

In a particularly preferred embodiment of the new method is the silent electric discharge in a barrier reactor with one or more current-limiting dielectric barriers.

A Another particularly preferred embodiment is based on a tube bundle reactor. The individual reactor tubes are For example, as a plasma reactors with a cylindrical Discharge gap designed similar to those used for ozone generation Siemens tubes. The discharge gap is with a suitable Catalyst filled in the form of a fixed bed and is from Reaction mixture (hydrogen chloride, oxygen, chlorine, water vapor) continuously flows through. Any number of these reactors can be connected in parallel to ensure adequate plant capacity to create. After igniting the nonthermal plasma in the discharge tubes by applying a high voltage the hydrogen chloride by synergistic interaction of catalyst and oxidized plasma to chlorine. The reaction temperature can be be varied in a wide range. You should preferably above the dew point of the product mixture at the reactor outlet (about 100 ° C) be kept to prevent condensation in the reactor.

A Another preferred embodiment of the new method Therefore, characterized in that the plasma-assisted HCl oxidation in a reactor with a tube with inner and outer electrodes Such a reactor is also called a plasma reactor in particular, with respect to the electrodes the process gases are protected against corrosion are.

Especially preferred is a variant of the method in which the catalyst as a packed bed in the discharge gap of a barrier reactor is introduced. A barrier reactor is a plasma reactor in which the plasma is generated by a barrier discharge.

A Another variant of the new method is characterized characterized in that the plasma-assisted HCl oxidation in several parallel reactors in a tube bundle arrangement or parallel plate reactors is performed.

The Plasma-assisted HCl oxidation is especially at elevated Pressure, preferably at a pressure of up to 25 bar, more preferably 5 to 25 bar performed.

The Reaction temperature in the plasma-activated HCl oxidation can be set below about 300 ° C. In this Case, the HCl conversion by the plasma-chemical activation of the Reactants and their synergistic reaction on the catalyst determined. At the same time it provides homogeneous plasma-activated HCl oxidation in the gas space of the catalyst bed, a contribution to total sales. The total conversion in the presence of the catalyst is always higher as that in the empty discharge tube under the same outer Discharge conditions, d. H. same applied high voltage.

Prefers is therefore an alternative embodiment of the new method, which is characterized in that the reaction temperature of HCl oxidation in the range of the plasma in a range up to 300 ° C, preferably from 120 to 250 ° C, preferably 130 to 200 ° C. is set.

A Alternatively, the operation of the plasma reactor is at a catalyst temperature above 300 ° C. In this case, the catalysed overlap and the plasma-activated HCl oxidation. Also under these reaction conditions leads the combination according to the invention under certain conditions to higher overall HCl sales considered individually as each of the two forms of activation. Indeed is the maximum achievable HCl conversion by the thermodynamic Limited boundary conditions. The catalyst present catalyses Back and forth reaction in Deacon equilibrium.

It Therefore, a method is preferred in which the plasma-assisted HCl oxidation with a catalyzed HCl reaction is combined and carried out in a reaction space.

In a particularly preferred embodiment of the new method which is the reaction temperature of the combined plasma-assisted and catalyzed HCl oxidation in a range of at least 300 ° C, preferably from 320 to 450 ° C, preferably 350 to 400 ° C. set.

An overcoming the specified in the catalyzed process thermodynamic turnover limits succeeds by successively connected reactors, which after different Activation principles work. First, in one catalyzed process at high temperatures (eg 380 ° C) a certain HCl conversion> 50% reached. The product mixture leaving the process is heated to temperatures cooled below 300 ° C and through a plasma reactor directed. In this reaction by connecting in series from different reactors was surprisingly found that even at low HCl contents and high chlorine contents in the influx the plasma reactor no chlorine destruction, but always a significant increase in the chlorine content (HCl conversion) occurred. Very high total HCl conversion rates can be achieved in the manner described be achieved, with the catalyzed activation the main part contributes to the HCl turnover, while the plasma activation the desired, very high total sales to close to 100% causes.

In Another variant of the new method is the plasma-assisted HCl oxidation combined with a catalyzed HCl oxidation reaction and is carried out in separate reaction spaces, wherein the plasma-assisted HCl oxidation of the catalyzed HCl oxidation reaction is downstream.

A particularly preferred variant of the aforementioned method is characterized characterized in that first the major portion of the HCl oxidation in particular up to an HCl conversion of at least 70%, preferably at least 80% is achieved in the catalyzed oxidation process, followed by the plasma-assisted HCl oxidation.

For the generation of the non-thermal plasma, various discharge arrangements are possible. In a preferred embodiment, a tubular reactor used with cylindrically symmetrical inner and outer electrode. Between both there is at least one barrier (eg made of ceramic) Material), which is a direct breakdown of electrical discharge prevented. There may also be several barriers, z. B. before each electrode can be used. Between both electrodes arises a discharge gap (dielectric, plasma chamber) with a typical Thickness of a few millimeters, in which the catalyst in an optimal grain size is arranged as a loose bed. To generate the plasma becomes an alternating voltage between the two electrodes (eg 5 to 50 kV). This high voltage can be sinusoidal Voltage at low frequency (eg 50 Hz) or as pulsed Voltage with short pulse duration (eg in the micro or nanosecond range) and higher frequency (eg in the kHz or MHz range) become. The bulk bed between the high voltage electrodes Not only is it catalytically active, it can go beyond that by its dielectric properties and the discharge characteristics significantly affect (plasma physical effect).

• – die angelegte Hochspannung, in einem Bereich von 5 bis 50 kV, bevorzugt 20 bis 30 kV
• – die Wirkleistungsdichte, in einem Bereich von 50 bis 5000 J/l, bevorzugt im Bereich 200 bis 1000 J/l
• – die Art der angelegten Wechselspannung, entweder in Sinusform mit einer Frequenz von 50 oder 60 Hz oder als gepulste Hochspannung mit einer Pulsfrequenz im Bereich von 50 Hz bis 50 kHz, bevorzugt 1 bis 5 kHz, und einer Pulsanstiegszeit von 5 bis 5000 ns, bevorzugt von 100 bis 1000 ns
• – die reduzierte Feldstärke (gemessen in Townsend [Td]) sollte in einem Bereich von 200 bis 600 Td, bevorzugt 350 bis 500 Td adjustiert werden.

As electrical control variables for generating optimal plasma discharges, the following Pa parameters are used:

• - The applied high voltage, in a range of 5 to 50 kV, preferably 20 to 30 kV
• - The active power density, in a range of 50 to 5000 J / l, preferably in the range 200 to 1000 J / l
• - The type of applied AC voltage, either in sinusoidal form with a frequency of 50 or 60 Hz or as a pulsed high voltage with a pulse frequency in the range of 50 Hz to 50 kHz, preferably 1 to 5 kHz, and a pulse rise time of 5 to 5000 ns, preferably from 100 to 1000 ns
• The reduced field strength (measured in Townsend [Td]) should be adjusted in a range of 200 to 600 Td, preferably 350 to 500 Td.

Of the Discharge gap should have a thickness of 1 to 50 mm, preferably 3 to 10 mm.

It are discharge arrangements with both one-sided and double Barrier possible.

When Barrier material is ceramic materials and glasses apply. Barrier materials with high dielectric constants, z. As ferroelectric ceramics, the generation of particularly high Field strengths.

The Thickness of the barriers is in the range of about 0.1 to 5 mm, preferably in the range between 0.5 and 2 mm.

A particular embodiment uses solids having ferroelectric properties (eg barium titanate) as constituents of the packed bed or as catalyst supports. As a result, increasingly high-energy species are generated in the plasma, which can contribute to increased conversions in the plasma zone. Further suitable ferroelectrics are further ion crystals with perovskite structure such as lead zirconate titanate Pb (Zr _x Ti _1-x ) O ₃ and the following substances: strontium bismuth tantalate SrBi ₂ Ta ₂ O ₉ , bismuth titanate Bi ₄ Ti ₃ O ₁₂ , Bismuth lanthanum titanate Bi _4-x La _x Ti ₃ O ₁₂ , bismuth titanate niobate Bi ₃ TiNbO ₉ , strontium titanate SrTiO ₃ , barium strontium titanate Ba _x Sr _1-x TiO ₃ , sodium nitrite NaNO ₂ , hexagonal manganate RMnO3 with R = Y, Sc, In, Ho, Er, Tm, Yb, Lu.

In a further advantageous embodiment of a plasma reactor becomes the electrical barrier or the electrical barriers used simultaneously as a catalyst carrier. Therefore becomes a porous or rough barrier material with the catalytically active Coated components. A particular advantage of this embodiment lies in the fact that compared to the perfused Catalyst bed cm lower flow resistance ensteht. This allows smaller gap widths and thus higher electric field strengths in the plasma zone.

In another embodiment of the new method the silent electric discharge in a barrier reactor with a or multiple current-limiting dielectric barriers, its barrier or barriers simultaneously as a carrier serve for the catalyst.

Especially preferred is such a method when the silent electric Discharge in a barrier reactor with a ferroelectric barrier material, is carried out in particular based on barium titanate. However, other ferroelectrics can also be used.

When heterogeneous catalysts for the plasma-assisted Deacon reaction, a variety of solids have been effective proved. Depending on the temperature range used, they are preferred Oxides, oxide chlorides or chlorides of the metals of the 1st, 7th and 8th Subgroup of the periodic table, which in finely divided form on porous support materials, for. For example, titanium dioxide, are applied. Another effective catalyst consists of these catalytically active compounds on ferroelectric support materials, causing several mechanisms of action - chemical catalysis and a plasma physical effect (the amplification of the Plasma intensity) - can be advantageously combined can.

Of the Catalyst, which is preferably used in the new method, has as catalytic active components metals of the 1st, 7th or 8th subgroup of Periodic table of elements or oxides, oxide chlorides or chlorides the metals of the 1st, 7th or 8th subgroup, or mixtures of these Metals or metal compounds.

Especially the catalyst is preferably selected from the series: Ruthenium oxide, ruthenium chloride, ruthenium oxychloride or others Ruthenium compounds on silica, alumina, titania, Tin dioxide or zirconium dioxide as carrier.

The novel plasma-assisted HCl oxidation is particularly preferably used in combination with the catalyzed HCl oxidation with molecular oxygen which is also known as the Deacon process and which is operated in an upstream step or simultaneously. Here, hydrogen chloride is oxidized with oxygen in an exothermic equilibrium reaction to chlorine, whereby water vapor is obtained. The reaction temperature is usually 150 to 500 ° C, the usual reaction pressure is 1 to 25 bar. Since it is an equilibrium reaction, it is expedient to work at the lowest possible temperatures at which the catalyst still has sufficient activity. Furthermore, it is expedient to use oxygen in excess of stoichiometric amounts of hydrogen chloride. The usual is at For example, a two- to fourfold oxygen excess. Since no loss of selectivity is to be feared, it may be economically advantageous to work at relatively high pressure and, accordingly, longer residence time than normal pressure.

suitable contain preferred catalysts for the Deacon process Ruthenium oxide, ruthenium chloride, ruthenium oxychloride or others Ruthenium compounds on silica, alumina, titania, Tin dioxide or zirconium dioxide as carrier. Suitable catalysts For example, by applying ruthenium chloride on the support followed by drying or drying and calcining. Suitable catalysts can in addition to or instead of a ruthenium compound also Compounds of other precious metals, such as gold, palladium, platinum, Osmium, iridium, silver, copper or rhenium. suitable Catalysts may also contain chromium (III) oxide Catalyzed hydrogen chloride oxidation can be either adiabatic or isothermal or near isothermal, discontinuous, preferred but continuously as flow or fixed bed process, preferably as a fixed bed process, particularly preferably in tube bundle reactors on heterogeneous catalysts at a reactor temperature of 180 to 500 ° C, preferably 200 to 400 ° C, more preferably 220 to 350 ° C and a pressure of 1 to 25 bar (1000 to 25000 hPa), preferably 1.2 to 20 bar, more preferably 1.5 to 17 bar and in particular 2.0 to 15 bar are performed.

usual Reaction apparatus in which the catalyzed hydrogen chloride oxidation are carried out, are fixed bed or fluidized bed reactors. The catalyzed hydrogen chloride oxidation may also be preferred be carried out in several stages.

at The adiabatic driving style can also be several, in particular 2 to 10, preferably 4 to 8, more preferably 5 to 7 in series switched reactors are used with intermediate cooling. In isothermal or almost isothermal driving can also several, ie 2 to 10, preferably 2 to 6, particularly preferably 2 to 5, in particular 2 to 3, connected in series Reactors with additional intermediate cooling used become. The hydrogen chloride can be either complete along with the oxygen before the first reactor or over the different reactors are distributed. This arrangement individual reactors can also be combined in one apparatus.

A Another preferred embodiment of the one for Method suitable device is that one is a structured Catalyst bed begins, in which the catalyst activity increases in the flow direction. Such structuring the catalyst bed can by different impregnation the catalyst support with active material or by different Dilution of the catalyst with an inert material. As an inert material, for example, rings, cylinders or Spheres of titanium dioxide, tin dioxide, zirconium dioxide or mixtures thereof, Alumina, steatite, ceramic, glass, graphite or stainless steel used become. In the preferred use of shaped catalyst bodies the inert material should preferably have similar outer Have dimensions.

When Catalyst moldings are suitable moldings with any shapes, preferably tablets, rings, cylinders, stars, Cartwheels or balls, particularly preferred are rings, Cylinder or star strands as a shape.

When Heterogeneous catalysts are particularly suitable ruthenium compounds or copper compounds on substrates, which also doped ruthenium catalysts are preferred. Suitable carrier materials are, for example, silicon dioxide, Graphite, rutile or anatase titanium dioxide, tin dioxide, zirconium dioxide, Alumina or mixtures thereof, preferably titanium dioxide, tin dioxide, Zirconium dioxide, aluminum oxide or mixtures thereof, particularly preferably γ- or δ-alumina or mixtures thereof.

The copper or ruthenium-supported catalysts can be obtained, for example, by impregnation of the support material with aqueous solutions of CuCl ₂ or RuCl ₃ and optionally a promoter for doping, preferably in the form of their chlorides. The shaping of the catalyst can take place after or preferably before the impregnation of the support material.

to Doping of the catalysts are suitable as promoters alkali metals such as lithium, sodium, potassium, rubidium and cesium, are preferred Lithium, sodium and potassium, more preferably potassium, alkaline earth metals such as magnesium, calcium, strontium and barium, preferably magnesium and calcium, more preferably magnesium, rare earth metals such as scandium, Yttrium, lanthanum, cerium, praseodymium and neodymium, preferably scandium, Yttrium, lanthanum and cerium, more preferably lanthanum and cerium, or their mixtures.

The Shaped bodies can then be used in a Temperature of 100 to 400 ° C, preferably 100 to 300 ° C. for example, under a nitrogen, argon or air atmosphere dried and optionally calcined. To be favoured the moldings initially at 100 to 150 ° C. dried and then at 200 to 400 ° C. calcined.

The above for the Deacon process known catalyst systems can also be used for the plasma-assisted HCl oxidation.

Of the Hydrogen chloride conversion in single pass may be preferred to 15 to 90%, preferably 40 to 85%, more preferably 50 to 70% are limited. Unreacted minor hydrogen chloride residues may after partial or partial separation attributed to the catalyzed hydrogen chloride oxidation become. The volume ratio of hydrogen chloride to oxygen at the reactor inlet is preferably 1: 1 to 20: 1, preferably 1: 1 to 8: 1, more preferably 1: 1 to 5: 1.

In In a last step, the chlorine formed is separated off. The separation step usually includes several stages, namely the separation and optionally recycling of small residues of unreacted hydrogen chloride from the product gas stream the hydrogen chloride oxidation, the drying of the obtained, im essential chlorine and oxygen-containing stream and the Separation of chlorine from the dried stream.

The Chlorine produced by the new process is used in production processes used for the production of polymers such as polyurethanes and PVC, the by-product of the hydrogen chloride for the new Provide oxidation process.

Another The invention relates to a barrier reactor with one or a plurality of current-limiting dielectric barriers, in particular for Oxidation of hydrogen chloride by means of oxygen-containing gases, characterized in that in the discharge gap of the barrier reactor Catalyst is introduced as a fixed bed.

Prefers is a barrier reactor, characterized in that the reactor as tube reactor with a tube with inner and outer electrode is executed, in particular the electrodes opposite Process gases are executed protected against corrosion.

Prefers is also a barrier reactor in which the reactor is in the form of a tube bundle arrangement or executed several parallel plate reactors is.

The Invention is hereinafter exemplified by the examples which, however, are not Restricting the invention represent, explained in more detail.

Examples

example 1

The experimental apparatus consisted of a tube reactor made of glass (d _{outer tube} × d _{inner tube} × length = 15 × 10 × 300 mm ³ ) as well as measuring and metering devices. This tubular reactor consisted of a heatable outer tube and an inner tube. The wall thickness of outer and inner tube was about 1 mm. The outer tube was steamed with a metal mirror. The inner tube was cohesively filled by a copper tube. The metal sheath functioning as an outer electrode was connected to the ground potential of a high voltage generator. The copper inner tube was connected to the high voltage output of the generator. Between both electrodes a pulsed high voltage with variable amplitude and pulse frequency was applied. Typically, AC pulses were applied with a peak voltage of 30 kV, a frequency of 600 Hz and a pulse duration of approximately 10 μs. The gap between outer and inner glass tube (gap width 3 mm) was filled with rod-shaped catalyst (about 10 cm ³ , L × d (the rods) ≈ 2 × 1 mm ² , 1 wt .-% RuO ₂ on TiO ₂ ). The reactor temperature was set at 150 ° C. At the reactor exit was a cooled condensate separator.

Of the Catalyst filled annular gap was 50 ml / min a gas stream consisting of equal amounts of hydrogen chloride and Oxygen existed, flows through it. At the exit of the reactor Gas samples were taken and photometrically their chlorine content (absorption at 330 nm). With switched off high voltage could no significant chlorine content (<0.2 Vol .-%) are measured in the product gas. After switching on the high voltage and stabilization of the plasma was 20% by volume of chlorine in the product gas measured. This concentration corresponds to a degree of HCl conversion of 63%.

To Removing the catalyst filling were the same experimental conditions set again. Due to lack of the solid lengthened the residence time of the gas flow in the annular gap from about 4 s to 8 s. The chlorine content in the product stream after switching on the plasma was 5.5% by volume. This value corresponds to a HCl conversion of only 20%.

The Example shows that under the applied experimental conditions already a homogeneous plasma leads to significant HCl oxidation. The introduction of a catalyst enhances this effect considerably. The catalyst without plasma is among those used Reaction conditions (150 ° C) not active.

Example 2

The experimental conditions described in Example 1 were changed so that the plasma reactor was operated at a temperature of 350 ° C. Under these conditions, the ka enabled process already activated. When the plasma voltage was switched off, a chlorine concentration of 28.5% by volume was measured in the cooled product gas. This value corresponds to 80% HCl conversion. After switching on and stabilizing the plasma, the chlorine concentration increased to 34% by volume, which corresponds to an HCl conversion rate of about 90%.

The Example shows that under the conditions of a catalyzed HCl oxidation a significant increase in the chlorine yield by connecting the Plasmas is possible.

Example 3

The Experimental Example described in Example 1 was connected in series expanded by two identical reactors in their design. The first Reactor under the experimental conditions described in Example 2 (350 ° C, without condensate separator) without plasma support operated. The second reactor was under those described in Example 1 Conditions (150 ° C) with the product gas from reactor 1 as Input gas operated. Both reactors were heated to 120 ° C heated PTFE hose connected together. At first was Reactor 2 operated without plasma. In the product gas was a chlorine concentration measured at 28.5% by volume (corresponds to 80% HCl conversion). After switching on of the plasma, the chlorine concentration increased to 38 vol .-%, which is a HCl conversion rate of about 97% corresponds.

The Example shows that by cascading catalyzed and plasma-activated oxidation achievable very high HCl conversion levels are.

Example 4

The experimental setup described in Example 1 was modified such that the discharge gap, instead of rod-shaped catalyst (about 1% by weight of RuO ₂ on TiO ₂ ), with a fine-grained mixture of this catalyst having dielectric properties and barium titanate particles ferroelectric material which is catalytically inactive for the HCl oxidation was filled. Both components were mixed as sieved grain fraction (0.5 to 1 mm) in a mass ratio of 1: 1 and filled in the annular gap. Under the experimental conditions described in Example, 26% by volume of chlorine in the cooled reaction gas was measured. This corresponds to a degree of HCl conversion of 75%.

The Example shows that a mixture of catalytically active dielectric and catalytically inactive ferroelectric particles have a positive overall effect on the plasma-activated oxidation of HCl.

Example 5

The The experiment described in Example 4 was modified to that the annular gap of the reactor alone with ferroelectric material was filled, which as a carrier for a catalytically active component was used. For this purpose was Barium titanate (grain fraction 0.5 to 1 mm) by wet impregnation coated with ruthenium acetate (about 0.5% by weight of Ru) at 400 ° C calcined in the air stream and then as a packed bed in the Reactor installed. Under the experimental conditions described in Example 1 13.5% by volume of chlorine were measured in the product stream, the degree of HCl conversion of about 45%.

The Example shows that the special plasma physical properties of ferroelectric materials for the plasma-activated HCl oxidation can be exploited.

Example 6

The inner electrode of the reactor described in Example 1 was modified in the following manner: The smooth glass tube functioning as an inner barrier was replaced by a tube of porous, ceramic material with an outer diameter of 12 mm and a wall thickness of 2 mm. The free gap width thereby reduced to about 1 mm. The outer wall of the ceramic tube was wet-impregnated with ruthenium acetate (about 0.3 mg Ru per cm ^{2 of} the geometric surface). After calcination of the catalyst layer at 400 ° C in an air stream, the barrier tube were installed in the reactor and set the experimental conditions described in Example 1. Without active plasma, no significant chlorine concentrations (<0.2% by volume) were measured in the product gas. After switching on and stabilizing the plasma, 11.8% by volume of chlorine was measured. This value corresponds to an HCl conversion rate of around 40%.

The Example shows that a significant plasma effect also with a Catalyst layer reached on porous barrier material can be.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 1567788 A1 [0003]
• - JP 59073405 [0006]
• - RU 2253607 A [0006]
• - DD 88309 [0006]
• - SU 1801943 A [0006, 0007]
• DE 102006022761 A1 [0006, 0010]

Cited non-patent literature

• - Ullmann Encyclopedia of Technical Chemistry. Verlag Chemie, Weinheim, 4th edition 1975, Vol. 9, p. 357 et seq. [0002]
• - Winnacker-Kuchler: Chemical Technology, Processes and Products. Wiley-VCH Verlag, 5th edition 2005, Vol. 3, pp. 512 ff. [0002]
• - W. Stiller: Non-thermally activated chemistry. Birkhäuser Verlag, Basel, Boston, 1987, pp. 33-34, pp. 45-49, pp. 122-124, pp. 138-145. [0006]
• - WW Cooper, HS Mickley, RF Baddour: Oxidation of hydrogen chloride in a microwave discharge. Ind. Eng. Chem. Fundam. 7 (3), 400-409 (1968) [0006]
• - JD van Drumpt: Oxidation of Hydrogen Chloride with Molecular Oxygen in a Silent Electrical Discharge. Ind. Eng. Chem. Fundam. 22 (4), 594-595 (1972) [0006]
• - Drumpt et al. (1972) [0008]
• - Cooper et al. (1968) [0009]

Claims (19)

Process for the heterogeneously catalyzed oxidation of hydrogen chloride by means of oxygen-containing gases, characterized in that a gas mixture comprising at least hydrogen chloride and oxygen flows through a suitable solid catalyst and is simultaneously exposed to the action of a non-thermal plasma. Method according to claim 1, characterized in that that the catalyst as catalytic active components metals of 1st, 7th or 8th subgroup of the Periodic Table of the Elements or Oxides, oxide chlorides or chlorides of the metals of the 1st, 7th or 8th Subgroup, or mixtures of these metals or metal compounds having. Method according to claim 1 or 2, characterized the catalyst is selected from the series: ruthenium oxide, Ruthenium chloride, ruthenium oxychloride or other ruthenium compounds on silica, alumina, titania, tin dioxide or Zirconia as a carrier. Method according to one of claims 1 to 3, characterized in that the non-thermal plasma by silent electrical discharge is generated. Method according to one of claims 1 to 4, characterized in that the silent electric discharge in a barrier reactor with one or more current-limiting ones dielectric barriers is performed. Method according to one of claims 1 to 5, characterized in that the plasma-assisted HCl oxidation in a reactor with a tube with inner and outer electrodes is performed, the electrodes in particular against the process gases are protected against corrosion are. Method according to one of claims 1 to 6, characterized in that the catalyst as a packed bed is introduced into the discharge gap of a barrier reactor. Method according to one of claims 1 to 7, characterized in that the plasma-assisted HCl oxidation in several parallel reactors in a tube bundle arrangement or parallel plate reactors is performed. Method according to one of claims 1 to 8, characterized in that the plasma-assisted HCl oxidation at elevated pressure, in particular a pressure of up to 25 bar, preferably 5 to 25 bar is performed. Method according to one of claims 1 to 9, characterized in that the reaction temperature of the HCl oxidation in the range of the plasma in a range up to 300 ° C, preferably from 120 to 250 ° C, preferably 130 to 200 ° C set becomes. Method according to one of claims 1 to 9, characterized in that the plasma-assisted HCl oxidation is combined with a catalyzed HCl oxidation reaction and is carried out in a reaction space. Method according to claim 11, characterized in that that the the reaction temperature of the combined plasma-based and catalyzed HCl oxidation in a range of at least 300 ° C, preferably from 320 to 450 ° C, preferably 350 to 400 ° C. is set. Method according to one of claims 1 to 10, characterized in that the plasma-assisted HCl oxidation is combined with a catalyzed HCl oxidation reaction and is carried out in separate reaction spaces, the plasma enhanced HCl oxidation of the catalyzed HCl oxidation reaction is downstream. Method according to one of claims 1 to 13, characterized in that first the main part of HCl oxidation, in particular up to a HCl conversion of at least 70%, preferably at least 80% achieved in the catalyzed oxidation process is followed by the plasma-assisted HCl oxidation downstream is. Method according to one of claims 5 to 14, characterized in that the silent electric discharge in a barrier reactor with one or more current limiting dielectric barrier is performed, its barrier or barriers as a carrier for the same time Catalyst serve. Method according to one of claims 5 to 14, characterized in that the silent electric discharge in a barrier reactor with a ferroelectric barrier material, is carried out in particular based on barium titanate. Barrier reactor with one or more current-limiting dielectric barriers, in particular for the oxidation of hydrogen chloride by means of oxygen-containing gases, characterized in that in the discharge gap of the barrier reactor catalyst as a fixed bed is introduced. Barrier reactor according to claim 17, characterized in that the reactor is designed as a tubular reactor with a tube with inner and outer electrodes, wherein in particular the electrodes ge compared with process gases are executed protected against corrosion. Barrier reactor according to one of Claims 17 or 18, characterized in that the reactor in the form of a Tube bundle arrangement or several parallel connected Plate reactors is executed.