EP2027062A2

EP2027062A2 - Method for producing chlorine by gas phase oxidation

Info

Publication number: EP2027062A2
Application number: EP07725053A
Authority: EP
Inventors: Aurel Wolf; Jürgen KINTRUP; Oliver Felix-Karl SCHLÜTER; Leslaw Mleczko
Original assignee: Bayer MaterialScience AG
Current assignee: Covestro Deutschland AG
Priority date: 2006-05-23
Filing date: 2007-05-10
Publication date: 2009-02-25
Also published as: WO2007134721A3; TW200808655A; RU2008150595A; US20070292336A1; WO2007134721A2; DE102006024543A1; KR20090020635A; JP2009537446A; CN101448735A; BRPI0711895A2

Abstract

The invention relates to a method for producing chlorine by the catalytic gas phase oxidation of hydrogen chloride using oxygen, wherein the catalyst comprises tin dioxide and at least one ruthenium compound containing oxygen.

Description

Process for producing chlorine by gas phase oxidation

The present invention relates to a process for producing chlorine by catalytic gas-phase oxidation of hydrogen chloride with oxygen, wherein the catalyst comprises tin dioxide and at least one oxygen-containing ruthenium compound.

The process of catalytic hydrogen chloride oxidation with oxygen in an exothermic equilibrium reaction, developed by Deacon in 1868, was at the beginning of technical chlorine chemistry:

4 HCl + O ₂ => 2 Cl ₂ + 2 H ₂ O.

The chloroalkali electrolysis, however, pushed the Deacon process far into the background. Nearly all chlorine production was achieved by electrolysis of aqueous saline solutions [Ullmann Encyclopedia of industrial chemistry, seventh release, 2006]. However, the attractiveness of the Deacon process has increased again recently as the demand for chlorine worldwide grows faster than the demand for caustic soda. This development is countered by the process for the production of chlorine by oxidation of hydrogen chloride, which is decoupled from the sodium hydroxide production. In addition, hydrogen chloride precipitates in large quantities, for example in phosgenation reactions, such as in isocyanate production, as by-product.

The oxidation of hydrogen chloride to chlorine is an equilibrium reaction. The position of the equilibrium shifts with increasing temperature to the detriment of the desired end product. It is therefore advantageous to use catalysts with the highest possible activity, which allow the reaction to proceed at low temperature.

The first catalysts for the hydrogen chloride oxidation contained as active component copper chloride or oxide and were already described in 1868 by Deacon. However, these showed low activity at low temperature (<400 ⁰ C). Although the activity could be increased by increasing the reaction temperature, it was disadvantageous that the volatility of the active components at high temperatures led to a rapid decrease in the catalyst activity.

EP 0 184 413 describes the oxidation of hydrogen chloride with catalysts based on chromium oxides. However, the process realized thereby had insufficient activity and high reaction temperatures. First catalysts for the hydrogen chloride oxidation with the catalytically active component

Ruthenium was already described in 1965 in DE 1 567 788. In this case, starting from RuCU, for example, supported on silica and alumina. However, the activity of these RuCySiO ₂ catalysts was very low. Further Ru-based catalysts with the active material ruthenium oxide or ruthenium mixed oxide and as carrier material various oxides, such as, for example, titanium dioxide, zirconium dioxide, etc., have been claimed in DE-A 197 48 299. The content of ruthenium oxide is 0.1% by weight to 20% by weight and the average particle diameter of ruthenium oxide is 1.0 nm to 10.0 nm. Further Ru catalysts supported on titanium dioxide or zirconium dioxide are known from DE-A 197 34 412 known. For the preparation of the ruthenium chloride and ruthenium oxide catalysts described therein, which comprise at least one compound titanium dioxide and zirconium dioxide, a number of Ru starting compounds have been indicated, such as, for example, ruthenium-carbonyl complexes, ruthenium salts of inorganic acids, ruthenium-nitrosyl complexes, ruthenium Amine complexes, ruthenium complexes of organic amines or ruthenium-acetylacetonate complexes. In a preferred embodiment, TiO _{2 was} used as a carrier in the form of rutile. The ruthenium oxide catalysts have a rather high activity, but their preparation is complex and requires a series of operations such as precipitation, impregnation followed by precipitation, etc., whose scale-up is technically difficult. In addition, Ru oxide catalysts also tend to sinter at high temperatures and thus to deactivate.

EP 0 936 184 A2 describes a process for catalytic hydrogen chloride oxidation wherein the catalyst is selected from an extensive list of possible catalysts. Among the catalysts is the variant designated by number (6), which consists of the active component (A) and a component (B). The component (B) is a compound component having a certain thermal conductivity. As an example, mention is made, among other things, of tin dioxide. In addition, the component (A) can be mounted on a support. However, possible carriers do not include tin dioxide. There is not a single example in which tin dioxide was used.

The previously developed catalysts for the Deacon process have a number of shortcomings. At low temperatures their activity is insufficient. Although the activity could be increased by increasing the reaction temperature, this led to sintering / deactivation or loss of the catalytic component.

The object of the present invention was to provide a catalytic system which accomplishes the oxidation of hydrogen chloride at low temperatures and with high activities. The task is solved by the development of a very specific combination of catalytically active components and a specific carrier material. Surprisingly, it has been rounded that by the targeted support of tin dioxide with a

Oxygen-containing ruthenium compound, due to a special interaction between catalytically active component and carrier, new highly active catalysts are provided, which have a high catalytic activity especially at temperatures of <350 ⁰ C in the hydrogen chloride oxidation. A further advantage of the catalyst system according to the invention is the simple and easily scalable application of the catalytically active component to the support.

The present invention thus provides a process for producing chlorine by catalytic gas-phase oxidation of hydrogen chloride with oxygen, wherein the catalyst comprises tin dioxide and at least one oxygen-containing ruthenium compound. The invention also provides a catalyst for gas phase oxidation based on tin dioxide as a carrier material and an oxygen-containing ruthenium compound

In a preferred embodiment, tin (IV) oxide is used as a carrier of the catalytically active component, particularly preferably tin dioxide in rutile structure.

According to the invention, the catalytically active component used is an oxygen-containing ruthenium compound. It is a compound in which oxygen ionic to polarized is covalently bonded to a ruthenium atom.

The catalytically active preferred ruthenium oxyhalide compound in the context of the invention is preferably obtainable by a process which first comprises applying an aqueous solution or suspension of at least one halide, eg. B. chloride containing ruthenium compound on tin dioxide and the subsequent precipitation and optionally the calcination of the precipitated product.

The precipitation may be carried out alkaline with direct formation of the oxygen-containing ruthenium compound. It may also be reductive with primary formation of metallic ruthenium, which is then calcined with oxygen supply to form the oxygen-containing ruthenium compound.

Alternatively, the oxygen-containing ruthenium compound may also be prepared by applying metallic ruthenium to tin dioxide and then oxidizing the ruthenium metal in an oxygen-containing gas or, in particular, exposing the metal ruthenium to tin dioxide to a gas composition of the reactant gases for a Deacon reaction, ie, at least HCl and oxygen-containing gases, to be obtained. For example, ruthenium is deposited as metal on the tin dioxide by CVD or MOCVD. A particularly preferred method includes applying an aqueous solution of

Ruthenium chloride on the tin dioxide.

The application particularly includes soaking the optionally freshly precipitated tin dioxide with the solution of the halide-containing ruthenium compound.

After application of the halide-containing ruthenium compound is generally carried out a precipitation and a drying or calcination step, which is conveniently carried out in the presence of oxygen or air at temperatures up to 650 ⁰ C.

Usually, the loading of the catalytically active component, i. the oxygen-containing ruthenium compound, in the range from 0.1 to 80% by weight, preferably in the range from 1 to 50% by weight, particularly preferably in the range from 1 to 20% by weight, based on the total weight of the catalyst ( Catalyst component and carrier).

Most preferably, the catalytic component, i. For example, the oxygen-containing ruthenium compound can be applied to the support by wet and wet impregnation of a support with suitable starting or starting compounds in liquid or colloidal form, up and co-deposition methods, as well as ion exchange and gas phase coating (CVD, PVD).

Suitable promoters are basic metals (for example alkali, alkaline earth and rare earth metals), preference is given to alkali metals, in particular Na and Cs, and alkaline earth metals, particular preference to alkaline earth metals, in particular Sr and Ba.

The promoters may, but are not limited to, be applied to the catalyst by impregnation and CVD methods, preferably an impregnation, particularly preferably after application of the main catalytic component.

For stabilizing the dispersion of the main catalytic component on the support, for example, but not limited to, various dispersion stabilizers such as scandium oxides, manganese oxides and lanthanum oxides, etc. can be used. The stabilizers are preferably applied together with the main catalytic component by impregnation and / or precipitation.

The tin dioxide used in the present invention is commercially available (e.g., from Chempur, Alfa Aesar) or obtainable, for example, by alkaline precipitation of stannic chloride and subsequent drying. It has in particular BET surface areas of about 1 to 300 m2 / g.

The tin dioxide used as the support according to the invention can undergo a reduction of the specific surface under thermal stress (such as at temperatures of more than 250 ^° C.), which may be accompanied by a reduction in catalyst activity. The above mentioned

Dispersion stabilizers can also serve to stabilize the surface of the tin dioxide at high temperatures.

The catalysts can be dried under normal pressure or preferably at reduced pressure, preferably at 40 to 200 ^° C. The drying time is preferably 10 minutes to 6 hours.

The novel catalyst is preferably used as described above in the catalytic process known as the Deacon process. 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 ⁰ 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. For example, a two- to four-fold excess of oxygen is customary. 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.

In addition to a ruthenium compound, suitable catalysts may also contain compounds of other noble metals, for example gold, palladium, platinum, osmium, iridium, silver, copper or rhenium. Suitable catalysts may further contain chromium (III) oxide.

The catalytic hydrogen chloride oxidation can be adiabatic or preferably isothermal or approximately isothermal, batchwise, but preferably continuously or as a fixed bed process, preferably as a fixed bed process, particularly preferably in tube bundle reactors to heterogeneous catalysts at a reactor temperature of 180 to 500 ⁰ C, preferably 200 to 400 ^0th 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 ,

Typical reactors in which the catalytic hydrogen chloride oxidation is carried out are fixed bed or fluidized bed reactors. The catalytic hydrogen chloride oxidation can preferably also be carried out in several stages.

In the case of the adiabatic, isothermal or approximately isothermal mode of operation, it is also possible to use a plurality of reactors with intermediate cooling, that is to say 2 to 10, preferably 2 to 6, particularly preferably 2 to 5, in particular 2 to 3, connected in series. The oxygen can be either completely together with the hydrogen chloride before the first reactor or over the be added distributed to different reactors. This series connection of individual reactors can also be combined in one apparatus.

A further preferred embodiment of a device suitable for the method consists in using a structured catalyst bed in which the catalyst activity increases in the flow direction. Such structuring of the catalyst bed can be achieved by different impregnation of 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 balls of titanium dioxide, zirconium dioxide or mixtures thereof,

Alumina, steatite, ceramic, glass, graphite or stainless steel can be used. In the preferred use of shaped catalyst bodies, the inert material should preferably have similar external dimensions.

As Katalysatorformkörpεr are Foπnkörper with any shapes, preferably are tablets, rings, cylinders, stars, wagon wheels or balls, particularly preferred are rings, cylinders or star strands as a form.

Suitable support materials which can be combined with tin dioxide are, for example, silicon dioxide, graphite, rutile or anatase titanium dioxide, zirconium dioxide, aluminum oxide or mixtures thereof, preferably titanium dioxide, zirconium dioxide, aluminum oxide or mixtures thereof, particularly preferably γ- or δ- Alumina or mixtures thereof.

For doping the catalysts are suitable as promoters alkali metals such as lithium, sodium, potassium, rubidium and cesium, preferably lithium, sodium and potassium, more preferably potassium, alkaline earth metals such as magnesium, calcium, strontium and barium, preferably magnesium and calcium, particularly 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 mixtures thereof.

The moldings can then be dried at a temperature of 100 to 400 ⁰ C, preferably 100 to 300 ⁰ C, for example, under a nitrogen, argon or air atmosphere and optionally calcined. Preferably, the moldings are first dried at 100 to 150 ⁰ C and then calcined at 200 to 400 ⁰ C.

The conversion of hydrogen chloride in a single pass may preferably be limited to 15 to 90%, preferably 40 to 85%, particularly preferably 50 to 70%. Unreacted

Hydrogen chloride can be partially or completely separated into the catalytic after separation

Hydrogen chloride oxidation can be attributed. The volume ratio of hydrogen chloride to oxygen at the reactor inlet is preferably 1: 1 to 20: 1, preferably 2: 1 to 8: 1, more preferably 2: 1 to 5: 1.

The heat of reaction of the catalytic hydrogen chloride oxidation can be used advantageously for the production of high-pressure steam. This can be used to operate a phosgenation reactor and / or distillation columns, in particular of isocyanate distillation columns.

In a further step, the chlorine formed is separated off. The separation step usually comprises several stages, namely the separation and optionally recycling of unreacted hydrogen chloride from the product gas stream of the catalytic hydrogen chloride oxidation, the drying of the obtained, substantially chlorine and oxygen-containing stream and the separation of chlorine from the dried stream.

The separation of unreacted hydrogen chloride and water vapor formed can be carried out by condensation of aqueous hydrochloric acid from the product gas stream of hydrogen chloride oxidation by cooling. Hydrogen chloride can also be absorbed in dilute hydrochloric acid or water.

The catalysts according to the invention for the hydrogen chloride oxidation are characterized by a high activity at low temperatures.

The following examples illustrate the present invention.

Examples

Example 1: Support of ruthenium oxide on Zinπ (IV) oxide

In a round bottom flask with dropping funnel and reflux condenser, 20 g of commercially available tin (IV) oxide were suspended in a solution of commercially available 2.35 g of ruthenium chloride n-hydrate in 50 ml of water and stirred for 30 minutes. Then, within a period of 30 minutes, 24 g of 10% sodium hydroxide solution were added dropwise and the mixture was stirred for 30 minutes. Further 12 g of 10% sodium hydroxide solution were added dropwise within 15 minutes and the reaction mixture was heated to 65 ° C. and kept at this temperature for 1 h. After cooling, the suspension was filtered off and the solid was washed 5 times with 50 ml of water. The damp solid was dried h and then calcined at 120 ⁰ C in a vacuum oven 4 at 300 ⁰ C in the air flow, whereby a ruthenium oxide catalyst supported was obtained in the tin (rV) oxide. The calculated amount of ruthenium was Ru / (RuO 2 + SnO 2) = 4.7% by weight.

Example 2: Carrying Ruthenium Oxide on Titanium (IV) Oxide (Comparative)

In a round bottom flask with dropping funnel and reflux condenser, 20 g of commercially available titanium (IV) oxide were suspended in a solution of commercially available 2.35 g of ruthenium chloride n-hydrate in 50 ml of water and stirred for 30 minutes. Then, within a period of 30 minutes, 24 g of 10% sodium hydroxide solution were added dropwise and the mixture was stirred for 30 minutes. Further 12 g of 10% sodium hydroxide solution were added dropwise within 15 minutes and the reaction mixture was heated to 65 ° C. and kept at this temperature for 1 h. After cooling, the suspension was filtered off and the solid was washed 5 times with 50 ml of water. The moist solid was dried at 120 ° C in a vacuum oven for 4 h and then calcined at 300 ⁰ C in a stream of air, whereby a ruthenium oxide catalyst supported on titanium (IV) oxide was obtained. The calculated amount of ruthenium was Ru / (RuO 2 + TiO 2) = 4.7% by weight.

Example 3 (reference): Blank test with tin dioxide

As a blank, tin dioxide was used instead of a catalyst and tested as described below. The small amount of chlorine produced is due to the gas phase reaction. Catalyst tests

Use of the catalysts in HCl oxidation

The catalysts from the example, the comparative example and the reference example were in a solid bed in a quartz reaction tube (diameter 10 mm) at 300 ⁰ C with a gas mixture of 80 ml / min (STP) of hydrogen chloride and 80 ml / min (STP) oxygen flowed through. The quartz reaction tube was heated by an electrically heated sand fluid bed. After 30 minutes, the product gas stream was passed into 16% potassium iodide solution for 10 minutes. The resulting iodine was then back titrated with 0.1 N thiosulfate standard solution to determine the amount of chlorine introduced. Table 1 shows the results.

Table 1: Activity in HCl oxidation

Example composition Chlorination Chlorine formation

mmol / min. g mmol / min.g

(Cat) (Ru)

1 RuO2 / SnO2 (4.7% 0.48 10.3

Ru)

2 (VgI) RuO2 / TiO2 (4.7% 0.38 8.1

Ru)

3 (Ref.) SnO2 (0.08)

Claims

claims:

A process for producing chlorine by catalytic gas-phase oxidation of hydrogen chloride with oxygen, wherein the catalyst comprises tin dioxide and at least one oxygen-containing ruthenium compound.

2. A process according to claim 1, wherein the catalyst is obtainable by a process comprising applying an aqueous solution or suspension of at least one halide-containing ruthenium compounds to tin dioxide and alkaline precipitating the oxygen-containing ruthenium compound.

The process of claim 2, wherein an aqueous solution of RuC13 is used.

4. The method according to any one of claims 1 to 3, wherein the reaction temperature in the catalytic gas phase oxidation is up to 450 ° C.

5. The method according to any one of claims 1 to 4, wherein the tin dioxide is in the rutile form.

6. Catalyst for gas phase oxidations based on tin dioxide as support material and an oxygen-containing ruthenium compound.