CA2162641A1 - Process for the oxidation of hydrogen chloride - Google Patents
Process for the oxidation of hydrogen chlorideInfo
- Publication number
- CA2162641A1 CA2162641A1 CA002162641A CA2162641A CA2162641A1 CA 2162641 A1 CA2162641 A1 CA 2162641A1 CA 002162641 A CA002162641 A CA 002162641A CA 2162641 A CA2162641 A CA 2162641A CA 2162641 A1 CA2162641 A1 CA 2162641A1
- Authority
- CA
- Canada
- Prior art keywords
- hydrogen chloride
- oxygen
- salt melt
- chloride
- chlorine
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B7/00—Halogens; Halogen acids
- C01B7/01—Chlorine; Hydrogen chloride
- C01B7/03—Preparation from chlorides
- C01B7/04—Preparation of chlorine from hydrogen chloride
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/06—Halogens; Compounds thereof
- B01J27/08—Halides
- B01J27/10—Chlorides
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J27/00—Catalysts comprising the elements or compounds of halogens, sulfur, selenium, tellurium, phosphorus or nitrogen; Catalysts comprising carbon compounds
- B01J27/06—Halogens; Compounds thereof
- B01J27/08—Halides
- B01J27/122—Halides of copper
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P20/00—Technologies relating to chemical industry
- Y02P20/50—Improvements relating to the production of bulk chemicals
- Y02P20/582—Recycling of unreacted starting or intermediate materials
Abstract
In a particularly advantageous manner, hydrogen chloride is oxidized to chlorinewith oxygen in the presence of a salt melt, if a salt melt which contains metal salts, salt depressing the melting point and if appropriate promoters is used, temperatures between 300 and 600°C are employed, the salt melt is dispersed in the gas containing hydrogen chloride and oxygen in such a way that contact timesof 0.01 to 100 seconds result, the reaction gases are cooled and hydrogen chloride and water are separated out of the reaction mixture, the reaction gases substantially freed from most of the water and some of the hydrogen chloride arefreed from residual water using sulphuric acid, and the gas mixture then essentially containing chlorine, hydrogen chloride and oxygen is compressed to 2to 10 bar, the chlorine is liquefied by cooling and the remaining, essentially oxygen-containing gas is recycled in whole or in part to the reaction zone.
Description
Le A 30 707-US/ Gai/klu/S-P 2 1 6 2 6 4 1 I
Process for the oxidation of hydro~en chloride The present invention relates to an improved process for the preparation of chlorine from hydrogen chloride.
In the industrial use of chlorine for the preparation of organic compounds, large amounts of hydrogen chloride form. Thus, for example, in the production of isocyanates which serve as raw materials for plastic foams and paints, between 0.58 and 1.4 t of hydrogen chloride form per ton of isocyanate. The chlorinationof hydrocarbons, e.g. of benzene and toluene, likewise results in large amounts of hydrogen chloride. Thus, in the preparation of chlorobenzene, 0.32 t of hydrogenchloride forms per ton of chlorobenzene.
Various processes are known for disposing of hydrogen chloride. Thus, for example, the hydrogen chloride arising can be split electrolytically into chlorine and hydrogen after conversion into aqueous hydrochloric acid. This process has the disadvantage of the high requirement for electrical energy. About 1600 KWh are required per ton of hydrogen chloride to be electrolysed. A further disadvantage is the high capital costs of providing the electrical energy, of transforming and rectifying the electric current and especially of the electrolysis cells.
For this reason, attempts have already been made to carry out the oxidation of hydrogen chloride chemically using oxygen and in the presence of catalysts. Thisprocess is termed the "Deacon process" in textbooks of inorganic chemistry (see,e.g., Lehrbuch der anorganischen Chemie, [Textbook of inorganic chemistry], Hollemann-Wiberg, 40th-46th edition 1958, pp.81 and 455). The advantage of this Deacon process is that no energy needs to be supplied from outside for the reaction. However, a disadvantage in this process is that the reaction can only be carried out to an equilibrium position. Therefore, after the Deacon process has been carried out, it is always necessary to fractionate a mixture which still contains hydrogen chloride and oxygen.
Attempts have already also been made to remedy this fundamental disadvantage of the Deacon process by a procedure in two stages. The use e.g. of catalyst systems is described, for example Cu(I) salts (see US-A 4 119 705, 2 418 931, 2 418 930 Le A 30 707-US 2 t 62 6 ~ ~
and 2 447 323) or vanadium oxides (see US-A-4 107 280) which are able to absorb oxygen and hydrogen chloride and, under other experimental conditions, e.g. at higher temperature, to elimin~te chlorine again with reformation of the original catalyst. The advantage of such a concept is that the reaction water formed in the reaction of hydrogen chloride with the oxygen-containing catalyst can be separated off in the 1st stage, and highly enriched chlorine is formed in the 2nd stage. A disadvantage in this concept is that the catalyst system must be heated and cooled between the two reaction stages and, if appropriate, must be transported from one reaction zone to the other. In combination with the relatively low ability of the catalysts used to release oxygen - e.g. 1 t of vanadium oxidemelt can release only about 10 kg of oxygen - this means considerable technical complexity which consumes a large part of the advantages of the Deacon process.
The concepts existing to date for the industrial implementation of the Deacon process in a single-stage reaction are unsatisfactory. The proposal made by Deacon in the 19th century, to use a fixed-bed reactor having a copper-containing catalyst using air as oxidizing agent, provides only highly dilute, impure chlorine, which can at the most be used for the preparation of chlorine bleaching liquor (see Chem. Eng. Progr. 44, 657 (1948)).
An improved technique was developed with the socalled "Oppauer-process" (see DE 857 633). This uses, for example, a mixture of iron(III) chloride and potassium chloride which, as a melt at temperatures of approximately 450C, serves as reaction medium and catalyst. The reactor used is a tower, lined with ceramic material, having a centrally incorporated inner pipe, so that passing in the feedstock gases hydrogen chloride and oxygen effects a circulation of the molten salts.
However, an exceptional disadvantage in this concept is the very low space-time yield (about 15 g of chlorine per litre of melt and per hour). For this reason, the Oppauer process is not advantageous in comparison with electrolysis of hydrogen chloride.
The poor space-time yield is accompanied by a large number of further disadvantages, such as large standing volumes of molten salts, large apparatus LeA30707-US 2~ 6~641 volumes with correspondingly high capital costs and cost-intensive maintenance.
Furthermore, thermal management of such large melt volumes can only be performed very poorly with respect to temperature maintenance, heating up and during shutdown of the plant, which is further reinforced by the thermal inertia of the large reactors.
In order to avoid these disadvantages, it has been proposed to carry out the reaction at a lower temperature, e.g. below 400C. However, at these temperatures there is the possibility of solids separating out of the copper salt melt. The salt melt has therefore been applied to a particulate inert support, e.g. silica or aluminium oxide, and the reaction has been carried out in a fluidized bed (see GB-B 908 022). A new proposal recommends chromium-containing catalysts on inert supports, a temperature below 400C likewise being chosen (see EP-A 184 413).
In all of these proposals to solve the problems of the Deacon process using the fluidized-bed technique, the unsatisfactory stability of the catalysts and their highly complex disposal after deactivation is highly disadvantageous. In addition, the fine dust which is unavoidable in the fluidized-bed technique poses problems in its removal from the reaction mixtures. Moreover, the fluidized reaction zone which requires a hard catalyst leads to increased erosion which, in combination with the corrosion caused by the reaction mixture, produces considerable technical problems and impairs the availability of an industrial plant.
A further disadvantage of the procedure using molten salts on inert supports, i.e. at temperatures of above 400C, is that a satisfactory reaction rate and, consequently, a good space-time yield is possible only if a relatively high oxygen excess is employed. However, this requires work-up of the reaction mixture using a solvent, e.g. CCl4 or S2Cl2 (see DE-A 1 467 142).
The object was therefore to find a process which permits the oxidation of hydrogen chloride with oxygen in the simplest manner possible and with a high space-time yield and which uses the technique of employing a system of molten salts as catalyst which is advantageous per se in comparison with the fluidized-bed 30 technique for the Deacon process and avoids the disadvantages of the previousvariants, e.g. the two-stage salt melt process or the single-stage Oppauer process.
Le A 30 707-US
` ~ 216264~
It would, moreover, be advantageous in this context if a smaller oxygen excess in comparison with stoichiometric conditions could be employed.
A process has now been found for the oxidation of hydrogen chloride with oxygen in the presence of a salt melt, which is characterized in that 5 - a salt melt which contains metal salts, salts depressing the melting point and if appropriate promoters is employed, - temperatures between 300 and 600C are employed, - the salt melt is dispersed in the gas containing hydrogen chloride and oxygen in such a way that contact times of 0.01 to 100 seconds result, 10 - the reaction gases are cooled and hydrogen chloride and water are separated out of the reaction mixture, i~
- the reaction gases freed from most of the water and some of the hydrogen chloride are freed from residual water using sulphuric acid and - the gas mixture then essentially containing chlorine, hydrogen chloride and oxygen is compressed to 2 to 10 bar, the chlorine is liquefied by cooling and, if appropriate after further purification, is separated off, and - the remaining, essentially oxygen-containing gas is recycled in whole or in part to the reaction zone.
In principle, hydrogen chloride of any origin can be fed to the process according 20 to the invention, e.g any hydrogen-chloride-containing gas mixtures. Preference is given to hydrogen-chloride-containing gas mixtures as arise in chlorinations andphosgenations. Such hydrogen-chloride-containing gas streams can be fed into theprocess according to the invention in the gaseous state or as aqueous hydrochloric acid absorbed in water. The gas streams containing hydrogen chloride may, 25 depending on their origin, possibly contain organic impurities, e.g. carbon monoxide, carbonyl sulphide, phosgene and chlorinated and nonchlorinated LeA30 707-US 21 62641 organics, for instance various chlorobenzenes. It is generally expedient to keep the content of organic impurities in the hydrogen chloride to be used as low as possible in order to minimize formation of undesirable, frequently toxic chlorinated organics. This can be performed in a manner known per se, e.g. by 5 absorption with water and/or by adsorption onto an adsorbent, e.g. activated carbon.
The oxygen required can be used as such or in a mixture with preferably inert gases. Preference is given to gases having oxygen contents above 90/0 by volume.
Salt melts without promoters can be e.g. mixtures of metal salts and salts 10 depressing the melting point. Metal salts can be salts which are either catalytically inactive or catalytically active for the oxidation of hydrogen chloride with oxygen.
Metal salts which can be used are, e.g., salts of metals of main groups I to V and subgroups I to VIII of the Periodic Table of the Elements. Preference is given to salts of aluminium, lanthanum, titanium, zirconium, vanadium, niobium, 15 chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper and zinc. Particular preference is given to salts of vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc. Very particular preference is given to copper salts.
Salt depressing the melting point can be e.g. salts of metals of main groups and20 subgroups I to III and main groups IV to V of the Periodic Table of the Elements, for example salts of lithium, sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, aluminium, gallium, indium, thallium, germanium, tin, lead, antimony, bismuth, zinc and silver. Preference is given to salts of lithium, sodium, potassium, aluminium and zinc. Particular preference is given to salts of 25 potassium.
Salt melts without promoters are e.g. mixtures of the following type:
LiCI/KCI, ZnCI2/KCl, KCI/NaCI/LiCI, MgCI2/KCI, AICI3/KCI, AlCI3/NaCI, V205/K2SO4/K2S207, CrCI3/NaCI/KCI, MnCI2/NaCI, MnCI2/KCI, MnCI2/KCI/NaCI, MnCI2/AlCI3, MnCI2/GaCI3, MnCI2/SnCI2, MnCI2/PbCI2, - ~162~41 Le A 30 707-US
-MnCI2/ZnCI2, FeCI3/LiCI, FeCI3/NaCI7 FeCI3/KCI, FeCI3/CsCI, FeCI3/KCI, FeCl3/AlCl3, FeCl3/GaCI~, FeCI3/SnCI4, FeCI3/PbCI2, FeCI3/BiCI3, FeCI3/TiCI4, FeCI3/MoCls, FeCI3/ZnCI2, FeCI3/NaCI/ZrCI4, FeCI3/KCI/ZrCI4, FeCI3/NaCI/WCI4, CoCI2/NaCI, CoCI2/KCI, CoCI2/GaCI3, CoCI2/SnCI2, 5 CoCI2/PbCI2, CoCI2/ZnCI2, CuCI/NaCI, CuCI/KCI, CuCI/RbCI, CuCI/CsCI, CuCI/AlCI3, CuCl/GaCl3, CuGl/InCI3, CuCI/TlCI, CuCI/SnCI2, CuCI/PbCI2, CuCI/BiCI3, CuCI/FeCI3, CuCI/AgCI, CuCI/ZnCI2, LaCI3/FeCI2/SnCl2, NaCI/SnCI2, FeCI2/SnCI2 and NaCI/CaCI2. Preference is given to mixtures of the type V2O5/K2SO4/K2S2O7, CrCI3/NaCI/KCI, MnCI2/KCI, FeCI3/KCI and 10 CuCl/KCI. Particular preference is given to mixtures of the type V205/K2SO4/K2S207, FeCI3/KCI and CuCI/KCI. Very particular preference is given to a mixture of KCI and CuCI.
If metal oxides, e.g. V2O5, are used, these are converted into salts when the process according to the invention is carried out.
¢ 15 The promoters to be added, if appropriate, to the salt melts can be, e.g., metal salts of subgroups I to VIII of the Periodic Table of the Elements and/or of therare earths, for instance salts of scandium, yttrium, lanthanum, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, m~ng~nese, rhenium, iron, ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum7 copper, silver, gold and salts of the rare earths, for instance salts of, for example, cerium, praseodymium, neodymium, samarium, europium, gadolinium, and of thorium and uranium. Preference is given to salts of lanthanum, titanium,zirconium, vanadium, chromium, molybdenum, tungsten, manganese, rhenium, iron, ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, cerium, praseodymium, neodymium and thorium. Particular preference is given to salts of lanthanum, vanadium, chromium, manganese, iron, cobalt, nickel, copper,cerium, praseodymium and neodymium. Very particular preference is given to salts of iron and copper.
Mixtures containing promoters are e.g. mixtures of the following type:
LiCl/KCl/FeCI3, LiCl/KCl/NdCI3/PrCI3, KCl/NaCI/LiCl/FeCl3, KCl/NaCl/LiCI/NdCI3/PrCl3, MgCI2/KCI/FeCI37 MgCI2/KCI/NdCI3/PrCI37 MgCI2/KCl/LaCI37 MgCI2/KCI/CeCI37 AlCl3/KCI/FeCI37 AlCI3/KCI/NdCl3, Le A 30 707-US 2 1 6 2 6 4 1 AlCl3/KCl/PrCl3, AlCl3/KCl/NdCl3/PrCl3, AlCl3/KCl/LaCI3, AlCI3/KCI/CeCl3, AlCI3/NaCl/FeCI3, AlCI3/NaCI/NdCI3, AlCI3/NaCI/PrCI3, AlCI3/NaCI/NdCI3/PrCI3, Alcl3/NaCI/LaCI3, Alcl3lNacllcecl3~ V25/K2S4/K2S27/FeCl3' V25/K2S4/K2S207/CuCl, V2O5/K2SO4/K2s2o7lLacl3 V2OslK2So4lK2s2o7lcecl3, V2oslK2so4lK2s2o7lNdcl3 V205/K2SO4/K2S207/NdCI3/PrCl3, CrCl3/NaCl/KCl/FeCl3, MnCI2/KCl/FeCI3, MnCI2/KCI/LaCl3, MnCl2/KCl/CeCI3, MnCI2/KCI/NdCl3/PrCI3, MnCI2/AlCI3/FeCI3, MnCI2/KCI/NaCI/FeCI3, MnCI2/SnCI2/FeCI3, MnCl2/SnCl2/LaCl3, MnCl2/SnCl2/CeCl3, MnCl2/SnCl2/NdCl3, MnCl2/SnCl2/PrCl3, MnCl2/SnCl2/NdCI3/PrCI3, FeCI3/KCl/NdCl3/PrCl3, FeCl3/LiCl/CuCI, FeCl3/NaCl/CuCI, FeCI3/KCl/CuCI, FeCI3/ZnCl2/CuCl, FeCl3/NaCl/ZrCl4, CoCl2/SnCl2/FeCl3, CuCI/KCI/FeCI3, CuCI/AlCI3/FeCI3, CuCI/BiCI3/FeCI3, CuCl/CsCI/FeCI3, CuCI/FeCI3, CuCl/SnCl2/FeCl3, CuCl/ZnCI2/FeCI3, CuCI/TlCl/FeCl3, CuCl/KCl/NdCl3, CuCl/KCI/PrCI3, CuCI/KCl/LaCI3, CuCI/KCl/CeCl3, CuCl/KC1/NdCl3/PrCl3, ZnCI2/KCI/FeCI3, ZnCI2/KCl/NdCl3/PrCl3. Preference is given to mixtures of the type:
V205/K2SO4/K2S207/FeCl3, FeCl3/KCl/NdCl3/PrCl3, CuCl/KCl/FeCl3, CuCl/AlCl3/FeCl3, CuCl/BiCl3/FeCl3, CuCl/CsCl/FeCl3, CuCl/FeCl3, CuCl/SnCl2/FeCl3, CuCl/ZnCl2/FeCl3, CuCl/KCl/NdCl3, CuCl/KCl/PrCl3, CuCl/KCl/LaCl3, CuCl/KCl/CeCl3, CuCI/KCI/NdCl3/PrCl3, CeCI3/NaCI/SnCI2, CeCl3/FeCl2/SnCl2 and NdCl3/NaCl/CaCI2. Particular preference is given to CuCl/KCI/FeCl3, CuCl/KCl/NdCl3, CuCl/KCl/PrCl3 and CuCl/KCl/NdCl3/PrCl3 mixtures. Very particular preference is given to a mixture of CuCl, KCl and FeCl3.
The salt melts to be used can if appropriate simultaneously also contain a plurality of components from the group consisting of the metal salts, the salts depressingthe melting point and/or the promoters.
If a promoter also complies with the definition given for the salts depressing the melting point, in this case the separate addition of a salt depressing the melting point is not absolutely necessary; the promoter then assumes both functions.
However, it is preferable to employ salt melts which contain at least 3 different components, where at least one component complies with the definition given for metal salts, at least one component complies with the definition given for the salts Le A 30 707-US 21 6 2 6 41 depressing the melting point and at least one component complies with the definition given for promoters.
If the metal component of the salt melt constituents described can assume a plurality of oxidation states, for example iron, copper or vanadium, this metal S component can be used in any oxidation state or in any mixtures of differentoxidation states. While the process according to the invention is being carried out the oxidation state can change.
The amount of the salts depressing the melting point employed in the process according to the invention, based on the entire melt, can be between 0 and 99%
by weight, preferably between 10 and 90% by weight and corresponds, very particularly preferably, roughly to the composition of the eutectic mixture of the components used.
The concentration of promoters in the salt melt can be, e.g., 0 to 100 mol %, preferably 0.1 to 50 mol%, and particularly preferably 0.1 to 10 mol%, in each case based on the entire salt melt.
The metal salts, salts depressing the melting point and, if appropriate, promoters can be used e.g. directly as salts, e.g. as halides, nitrates, sulphates or pyrosulphates. Precursors of metal salts can also be used, e.g. metal oxides or metal hydroxides or elemental metals which are transformed into metal salts whenthe process according to the invention is carried out. Preferably, chlorides areused.
The ratio of hydrogen chloride to oxygen can be varied within wide limits. For example, the molar ratio of hydrogen chloride to oxygen can vary between 40:1 and 1:2.5. Preferably, this ratio is between 20:1 and 1:125, particularly preferably between 8:1 and 1:0.5, very particularly preferably between 5:1 and 1:0.3.
The gas containing hydrogen chloride and oxygen is conducted as a continuous phase into a reaction zone and the salt melt is dispersed therein. Preferably, the continuous phase and the salt melt are conducted in counter-current to one another, contact times between 0.1 and 4 seconds are implemented and the Le A 30 707-US 2 1 6 2 6 4 1 procedure is carried out at 350 to 550C. Suitable reactors for this are e.g. packed reactors and jet reactors, trickling film columns and spray towers.
The gases coming from the reaction can contain, for example, 40 to 50% by weight of chlorine, 30 to 40% by weight of hydrogen chloride, 0.5 to 10% by 5 weight of oxygen, 10 to 20% by weight of water (steam) and possibly entrained inert gases, e.g. nitrogen, and possibly small amounts of organics.
Before the gases coming from the reaction are cooled and hydrogen chloride and water are separated out therefrom, it is advantageous first to remove entrained and/or volatilized portions of the salt melt therefrom. For this purpose, this gas 10 can be scrubbed, for example with one or more condensed phases from the overall process, and the scrubbing liquid can be recycled to the reaction zone.
The reaction gases, if appropriate freed of entrained and/or volatilized salt melt portions, are preferably rapidly cooled to a temperature below 300C, preferablybelow 200C, and in particular to 120 to 180C. This cooling can be performed, 15 for example, in a spray cooler. Alternatively, or additionally, the reaction gases can be cooled in an absorption tower filled with previously condensed, aqueous hydrochloric acid, if appropriate with addition of fresh water, and hydrogen chloride and water can be condensed together.
The concentration of the resulting aqueous hydrochloric acid can be varied within 20 wide limits, which poses no difficulty to those skilled in the art. It is preferably aimed to obtain 35 to 37% by weight strength aqueous hydrochloric acid (socalledconcentrated hydrochloric acid). This can then be used for any desired purposes for which concentrated aqueous hydrochloric acid is known to be used. Before thefurther use, a purification known per se can be carried out, for example by 25 blowing through inert gas (e.g. air) and/or by absorption of impurities (e.g. onto activated carbon). In this manner, e.g. residual chlorine and/or in the organicspresent can be removed. In this manner, it is possible to obtain, e.g., 5 to 15% by weight of the hydrogen chloride fed to the process according to the invention aspure, preferably concentrated, aqueous hydrochloric acid.
Le A 30 707-US 2 1 6 2 6 4 1 The aqueous hydrochloric acid separated off can also be used in another manner.
Thus, for example, concentrated sulphuric acid can be added to the aqueous hydrochloric acid initially separated off and thus free it of water. The resulting, preferably unpurified, hydrogen chloride gas can then be recycled to the reaction 5 zone of the process according to the invention. The reaction water in this case results as more or less dilute sulphuric acid. This can be used in a known manner or concentrated and thus the reaction water can be obtained as such.
The gas stream remaining after the cooling and separation out of hydrogen chloride and water essentially contains the chlorine formed in the reaction zone, 10 unreacted oxygen, residual portions of hydrogen chloride and steam, and possibly inert gases and/or possibly small amounts of organics.
Before chlorine is separated off from this gas stream, residual steam is first removed. This is achieved by the addition of concentrated sulphuric acid. The resulting, generally only slightly diluted sulphuric acid can, if appropriate after 15 concentration, be further used at a different point in the process according to the invention or in another (known) manner, e.g. for the production of fertilizers.
The gas stream freed of residual steam to a very great extent contains, for example, 60 to 97% by weight of chlorine and is now compressed to 2 to 10 bar.
This compression can be carried out in a single stage or multiple stages.
20 Preferably, two stages are employed. Compression apparatuses which are suitable are, e.g., piston compressors, rotary compressors and screw compressors. After the compression the gas mixture is cooled until the chlorine liquefies. Suitable temperatures are e.g. at a pressure of 10 bar those below 34C, and at a pressure of 2 bar those below -20C. At other pressures, suitable temperatures can be 25 determined by extrapolation from these values. Chlorine is obtained in this manner in li~uid form which can be used, if appropriate after further purif1cation, in liquid form or, after vaporization, like chlorine originating from the electrolysis of sodium chloride. Preferably, the chlorine is used for chlorinations and phosgenations of organic compounds. If the chlorine separated off is further used 30 in gaseous form, the cold stored in the chlorine separated off in liquid form can be utilized for any cooling purposes.
. ~ ~
Le A 30 707-US 21 6 2 6 41 -The gas remaining after the chlorine separation off generally contains essentially oxygen, and in addition small traces of chlorine and hydrogen chloride, possiblyinert gases and/or possibly small amounts of organics, usually chlorinated organics. This gas is wholly or partially recycled to the reaction zone of the 5 process according to the invention. It is advantageous, in particular when theprocess according to the invention is carried out for a relatively long time, torecycle only some of this gas and to eject the rest. In this manner accumulation of inert gas and organics in the reaction system is avoided. Environmentally polluting constituents, e.g. chlorine, hydrogen chloride and, possibly, organic impurities, in 10 particular chlorinated organic impurities, can be separated from the ejected part of the gas by absorption and/or adsorption. The absorption can be carried out e.g using water or aqueous alkalis, and the adsorption can be carried out e.g. usingsilica gel, aluminium oxides and/or activated carbon. Preferably, regenerable activated carbon is used.
15 The process according to the invention has a number of surprising advantages.Thus, the reaction can be carried out in a continuously uniformly active reaction zone, a salt melt surface which is constantly being renewed is available for thereaction, a substantial freedom of choice of conditions for the melt and of the gas streams is available, high conversion rates and high space-time yields may be 20 achieved and only relatively small amounts of salt melt and relatively small apparatuses are required. It is further advantageous that the reaction can be carried out without supply of energy from outside, under continuous reaction conditions,without problems with respect to long-term stability of the reactors, with the reaction water being separated off in the form of a concentrated aqueous 25 hydrochloric acid, with a high concentration of chlorine in the reaction gas and with the chlorine being separated off by compression and liquefaction without external solvent.
Le A 30 707-US 21 6 2 6 4 l -Examples Example 1 In an apparatus to be operated continuously, a gas mixture comprising 3900 g of hydrogen chloride, 854 g of oxygen, 211 g of chlorine and 192 g of nitrogen was reacted per hour in a trickling film reactor at 370C in the presence of a salt melt.
The salt melt comprised 9000 g of the eutectic mixture of potassium chloride andcopper(I) dichloride. For the reaction, the salt melt was pneumatically transported at intervals by the feedstock gas stream into a storage vessel situated above the packing bed and continuously metered onto the packing bed. The diameter of the packing bed was 40 mm. The feedstock gas mixture preheated to 370C was passed through the packing bed from bottom to top. The hot product gas mixture leaving the reactor comprised 780 g of hydrogen chloride, 160 g of oxygen, 3245 g of chlorine, 780 g of water and 192 g of nitrogen. It was cooled to 150Cin a spray cooler with 408 g of 34% by weight strength aqueous hydrochloric acid, and in a downstream absorption tower already filled with 3526 g of 34% by weight strength aqueous hydrochloric acid the reaction water formed and unreacted hydrogen chloride were separated off in the form of 34% strength by weight aqueous hydrochloric acid. In this manner, 397 g of hydrogen chloride, 769 g of water and 9 g of chlorine were separated off. The remaining reaction gas (per hour 383 g of hydrogen chloride, 160 g of oxygen, 3236 g of chlorine and 192 g of nitrogen) was dried with concentrated sulphuric acid in a drying tower, then compressed to 6 bar and cooled to -10C. This resulted in 2308 g of chlorine in liquid form which additionally contained 91 g of hydrogen chloride in dissolved form. The non-condensed portions of the gas were conducted into a second condensation stage operated at -25C, where a further 576 g of chlorine and a further 41 g of hydrogen chloride in liquid form were separated off From the non-condensed residual gas, a part-stream comprising 100 g of hydrogen chloride, 63 g of oxygen, 141 g of chlorine and 75 g of nitrogen was ejected. The remaining gas stream (per hour 150 g of hydrogen chloride, 94 g of oxygen, 211 gof chlorine and 112 g of nitrogen) was recycled to the reactor.
Le A 30 707-US
Example 2 In continuously operated trickling film reactor, a gas mixture preheated to 480C, comprising 5967 g of hydrogen chloride, 888 g of oxygen, 248 g of chlorine 124 g of steam and 154 g of nitrogen was reacted per hour at 480C in the presence of a salt melt as described in Example 1. The hot product gas mixture leaving the reactor comprised, per hour, 2586 g of hydrogen chloride, 137 g of oxygen, 3536 g of chlorine, 970 g of water and 154 g of nitrogen. It was cooled to 150C in a spray cooler using 29% strength by weight aqueous hydrochloric acid, and in a downstream absorption tower the reaction water formed and unreacted hydrogen chloride were separated off in the form of 29% strength by weight hydrochloric acid. The amounts separated off were 334 g of hydrogen chloride and 830 g of water. The procedure was further carried out as described in Example 1. A total of 3284 g of liquid chlorine which contained 31 g of hydrogenchloride and 8 g of oxygen resulted. From the non-condensed gas, a part stream which, per hour, comprised 1 g of hydrogen chloride, 64 g of oxygen, 87 g of chlorine and 72 g of nitrogen was ejected. The residual gas was recycled to the reactor.
Example 3 In a continuously operated trickling film reactor, a gas mixture preheated to 480C, comprising 326 g of hydrogen chloride and 71 g of oxygen, was reacted per hour as described in Example 1 at 480C in the presence of a salt melt. The salt melt comprised a mixture of 1174 g of potassium chloride, 1001 g of copper(I) chloride, 2255 g of copper(II) chloride and 600 g of neodymium chloride hydrate. Per hour, 25 1 of melt were metered through a column (d = 50 mm; h =
70 mm) packed with Raschig rings and were reacted in counter-current with the feedstock gases The product gas mixture leaving the reactor comprised, per hour,218 g of hydrogen chloride, 47.2 g of oxygen, 104 g of chlorine and 26 5 g of steam. As described in Example 1, the product gases were cooled to 150C in a spray cooler using aqueous hydrochloric acid, the reaction water was separated off in an absorption tower as aqueous hydrochloric acid, the product gases were dried with concentrated sulphuric acid, and chlorine was taken off in liquid form by compression to 6 bar and cooling to -10C
Le A 30 707-US
~ 2 1 6264 1 Example 4 In a continuously operated trickling film reactor, a gas mixture preheated to 480C7 comprising 81.5 g of hydrogen chloride and 17.8 g of oxygen, was reacted per hour as described in Example 1 at 480C in the presence of a salt melt. The salt melt comprised a mixture of 1174 g of potassium chloride, 1001 g of copper(I) chloride, 2255 g of copper(II) chloride and 600 g of neodymium chloride hydrate. Per hour, 25 1 of melt were metered through a column (d = 50 mm; h =
70 mm) packed with Raschig rings and were reacted in counter-current with the feedstock gases. The product gas mixture leaving the reactor comprised, per hour, 27.3 g of hydrogen chloride, 5.9 g of oxygen, 52.6 g of chlorine and 13.3 g of steam. As described in Example 1, the product gases were cooled to l50C in a spray cooler using aqueous hydrochloric acid, the reaction water was separated off in an absorption tower as aqueous hydrochloric acid, the product gases were dried with concentrated sulphuric acid, and chlorine was taken off in liquid form by compression to 6 bar and cooling to -10C.
Example 5 In a continuously operated trickling film reactor, a gas mixture preheated to 480C, comprising 407.5 g of hydrogen chloride and 85.2 g of oxygen, was reacted per hour as described in Example 1 at 450C in the presence of a salt melt. The salt melt comprised a mixture of 1174 g of potassium chloride, 1001 g of copper(I) chloride and 2255 g of copper(II) chloride. Per hour, 20.6 l of melt were metered through a column (d = 50 mm; h = 70 mm) packed with Raschig rings and were reacted in counter-current with the feedstock gases. The product gas mixture leaving the reactor comprised, per hour, 361.7 g of hydrogen chloride, 75.6 g of oxygen, 44.3 g of chlorine and 11.2 g of steam. As described in Example 1, the product gases were cooled to 1 50C in a spray cooler using aqueous hydrochloric acid, the reaction water was separated off in an absorptiontower as aqueous hydrochloric acid, the product gases were dried with concentrated sulphuric acid, and chlorine was taken off in liquid form by compression to 6 bar and cooling to -10C.
Process for the oxidation of hydro~en chloride The present invention relates to an improved process for the preparation of chlorine from hydrogen chloride.
In the industrial use of chlorine for the preparation of organic compounds, large amounts of hydrogen chloride form. Thus, for example, in the production of isocyanates which serve as raw materials for plastic foams and paints, between 0.58 and 1.4 t of hydrogen chloride form per ton of isocyanate. The chlorinationof hydrocarbons, e.g. of benzene and toluene, likewise results in large amounts of hydrogen chloride. Thus, in the preparation of chlorobenzene, 0.32 t of hydrogenchloride forms per ton of chlorobenzene.
Various processes are known for disposing of hydrogen chloride. Thus, for example, the hydrogen chloride arising can be split electrolytically into chlorine and hydrogen after conversion into aqueous hydrochloric acid. This process has the disadvantage of the high requirement for electrical energy. About 1600 KWh are required per ton of hydrogen chloride to be electrolysed. A further disadvantage is the high capital costs of providing the electrical energy, of transforming and rectifying the electric current and especially of the electrolysis cells.
For this reason, attempts have already been made to carry out the oxidation of hydrogen chloride chemically using oxygen and in the presence of catalysts. Thisprocess is termed the "Deacon process" in textbooks of inorganic chemistry (see,e.g., Lehrbuch der anorganischen Chemie, [Textbook of inorganic chemistry], Hollemann-Wiberg, 40th-46th edition 1958, pp.81 and 455). The advantage of this Deacon process is that no energy needs to be supplied from outside for the reaction. However, a disadvantage in this process is that the reaction can only be carried out to an equilibrium position. Therefore, after the Deacon process has been carried out, it is always necessary to fractionate a mixture which still contains hydrogen chloride and oxygen.
Attempts have already also been made to remedy this fundamental disadvantage of the Deacon process by a procedure in two stages. The use e.g. of catalyst systems is described, for example Cu(I) salts (see US-A 4 119 705, 2 418 931, 2 418 930 Le A 30 707-US 2 t 62 6 ~ ~
and 2 447 323) or vanadium oxides (see US-A-4 107 280) which are able to absorb oxygen and hydrogen chloride and, under other experimental conditions, e.g. at higher temperature, to elimin~te chlorine again with reformation of the original catalyst. The advantage of such a concept is that the reaction water formed in the reaction of hydrogen chloride with the oxygen-containing catalyst can be separated off in the 1st stage, and highly enriched chlorine is formed in the 2nd stage. A disadvantage in this concept is that the catalyst system must be heated and cooled between the two reaction stages and, if appropriate, must be transported from one reaction zone to the other. In combination with the relatively low ability of the catalysts used to release oxygen - e.g. 1 t of vanadium oxidemelt can release only about 10 kg of oxygen - this means considerable technical complexity which consumes a large part of the advantages of the Deacon process.
The concepts existing to date for the industrial implementation of the Deacon process in a single-stage reaction are unsatisfactory. The proposal made by Deacon in the 19th century, to use a fixed-bed reactor having a copper-containing catalyst using air as oxidizing agent, provides only highly dilute, impure chlorine, which can at the most be used for the preparation of chlorine bleaching liquor (see Chem. Eng. Progr. 44, 657 (1948)).
An improved technique was developed with the socalled "Oppauer-process" (see DE 857 633). This uses, for example, a mixture of iron(III) chloride and potassium chloride which, as a melt at temperatures of approximately 450C, serves as reaction medium and catalyst. The reactor used is a tower, lined with ceramic material, having a centrally incorporated inner pipe, so that passing in the feedstock gases hydrogen chloride and oxygen effects a circulation of the molten salts.
However, an exceptional disadvantage in this concept is the very low space-time yield (about 15 g of chlorine per litre of melt and per hour). For this reason, the Oppauer process is not advantageous in comparison with electrolysis of hydrogen chloride.
The poor space-time yield is accompanied by a large number of further disadvantages, such as large standing volumes of molten salts, large apparatus LeA30707-US 2~ 6~641 volumes with correspondingly high capital costs and cost-intensive maintenance.
Furthermore, thermal management of such large melt volumes can only be performed very poorly with respect to temperature maintenance, heating up and during shutdown of the plant, which is further reinforced by the thermal inertia of the large reactors.
In order to avoid these disadvantages, it has been proposed to carry out the reaction at a lower temperature, e.g. below 400C. However, at these temperatures there is the possibility of solids separating out of the copper salt melt. The salt melt has therefore been applied to a particulate inert support, e.g. silica or aluminium oxide, and the reaction has been carried out in a fluidized bed (see GB-B 908 022). A new proposal recommends chromium-containing catalysts on inert supports, a temperature below 400C likewise being chosen (see EP-A 184 413).
In all of these proposals to solve the problems of the Deacon process using the fluidized-bed technique, the unsatisfactory stability of the catalysts and their highly complex disposal after deactivation is highly disadvantageous. In addition, the fine dust which is unavoidable in the fluidized-bed technique poses problems in its removal from the reaction mixtures. Moreover, the fluidized reaction zone which requires a hard catalyst leads to increased erosion which, in combination with the corrosion caused by the reaction mixture, produces considerable technical problems and impairs the availability of an industrial plant.
A further disadvantage of the procedure using molten salts on inert supports, i.e. at temperatures of above 400C, is that a satisfactory reaction rate and, consequently, a good space-time yield is possible only if a relatively high oxygen excess is employed. However, this requires work-up of the reaction mixture using a solvent, e.g. CCl4 or S2Cl2 (see DE-A 1 467 142).
The object was therefore to find a process which permits the oxidation of hydrogen chloride with oxygen in the simplest manner possible and with a high space-time yield and which uses the technique of employing a system of molten salts as catalyst which is advantageous per se in comparison with the fluidized-bed 30 technique for the Deacon process and avoids the disadvantages of the previousvariants, e.g. the two-stage salt melt process or the single-stage Oppauer process.
Le A 30 707-US
` ~ 216264~
It would, moreover, be advantageous in this context if a smaller oxygen excess in comparison with stoichiometric conditions could be employed.
A process has now been found for the oxidation of hydrogen chloride with oxygen in the presence of a salt melt, which is characterized in that 5 - a salt melt which contains metal salts, salts depressing the melting point and if appropriate promoters is employed, - temperatures between 300 and 600C are employed, - the salt melt is dispersed in the gas containing hydrogen chloride and oxygen in such a way that contact times of 0.01 to 100 seconds result, 10 - the reaction gases are cooled and hydrogen chloride and water are separated out of the reaction mixture, i~
- the reaction gases freed from most of the water and some of the hydrogen chloride are freed from residual water using sulphuric acid and - the gas mixture then essentially containing chlorine, hydrogen chloride and oxygen is compressed to 2 to 10 bar, the chlorine is liquefied by cooling and, if appropriate after further purification, is separated off, and - the remaining, essentially oxygen-containing gas is recycled in whole or in part to the reaction zone.
In principle, hydrogen chloride of any origin can be fed to the process according 20 to the invention, e.g any hydrogen-chloride-containing gas mixtures. Preference is given to hydrogen-chloride-containing gas mixtures as arise in chlorinations andphosgenations. Such hydrogen-chloride-containing gas streams can be fed into theprocess according to the invention in the gaseous state or as aqueous hydrochloric acid absorbed in water. The gas streams containing hydrogen chloride may, 25 depending on their origin, possibly contain organic impurities, e.g. carbon monoxide, carbonyl sulphide, phosgene and chlorinated and nonchlorinated LeA30 707-US 21 62641 organics, for instance various chlorobenzenes. It is generally expedient to keep the content of organic impurities in the hydrogen chloride to be used as low as possible in order to minimize formation of undesirable, frequently toxic chlorinated organics. This can be performed in a manner known per se, e.g. by 5 absorption with water and/or by adsorption onto an adsorbent, e.g. activated carbon.
The oxygen required can be used as such or in a mixture with preferably inert gases. Preference is given to gases having oxygen contents above 90/0 by volume.
Salt melts without promoters can be e.g. mixtures of metal salts and salts 10 depressing the melting point. Metal salts can be salts which are either catalytically inactive or catalytically active for the oxidation of hydrogen chloride with oxygen.
Metal salts which can be used are, e.g., salts of metals of main groups I to V and subgroups I to VIII of the Periodic Table of the Elements. Preference is given to salts of aluminium, lanthanum, titanium, zirconium, vanadium, niobium, 15 chromium, molybdenum, tungsten, manganese, iron, cobalt, nickel, copper and zinc. Particular preference is given to salts of vanadium, chromium, manganese, iron, cobalt, nickel, copper and zinc. Very particular preference is given to copper salts.
Salt depressing the melting point can be e.g. salts of metals of main groups and20 subgroups I to III and main groups IV to V of the Periodic Table of the Elements, for example salts of lithium, sodium, potassium, rubidium, caesium, magnesium, calcium, strontium, barium, aluminium, gallium, indium, thallium, germanium, tin, lead, antimony, bismuth, zinc and silver. Preference is given to salts of lithium, sodium, potassium, aluminium and zinc. Particular preference is given to salts of 25 potassium.
Salt melts without promoters are e.g. mixtures of the following type:
LiCI/KCI, ZnCI2/KCl, KCI/NaCI/LiCI, MgCI2/KCI, AICI3/KCI, AlCI3/NaCI, V205/K2SO4/K2S207, CrCI3/NaCI/KCI, MnCI2/NaCI, MnCI2/KCI, MnCI2/KCI/NaCI, MnCI2/AlCI3, MnCI2/GaCI3, MnCI2/SnCI2, MnCI2/PbCI2, - ~162~41 Le A 30 707-US
-MnCI2/ZnCI2, FeCI3/LiCI, FeCI3/NaCI7 FeCI3/KCI, FeCI3/CsCI, FeCI3/KCI, FeCl3/AlCl3, FeCl3/GaCI~, FeCI3/SnCI4, FeCI3/PbCI2, FeCI3/BiCI3, FeCI3/TiCI4, FeCI3/MoCls, FeCI3/ZnCI2, FeCI3/NaCI/ZrCI4, FeCI3/KCI/ZrCI4, FeCI3/NaCI/WCI4, CoCI2/NaCI, CoCI2/KCI, CoCI2/GaCI3, CoCI2/SnCI2, 5 CoCI2/PbCI2, CoCI2/ZnCI2, CuCI/NaCI, CuCI/KCI, CuCI/RbCI, CuCI/CsCI, CuCI/AlCI3, CuCl/GaCl3, CuGl/InCI3, CuCI/TlCI, CuCI/SnCI2, CuCI/PbCI2, CuCI/BiCI3, CuCI/FeCI3, CuCI/AgCI, CuCI/ZnCI2, LaCI3/FeCI2/SnCl2, NaCI/SnCI2, FeCI2/SnCI2 and NaCI/CaCI2. Preference is given to mixtures of the type V2O5/K2SO4/K2S2O7, CrCI3/NaCI/KCI, MnCI2/KCI, FeCI3/KCI and 10 CuCl/KCI. Particular preference is given to mixtures of the type V205/K2SO4/K2S207, FeCI3/KCI and CuCI/KCI. Very particular preference is given to a mixture of KCI and CuCI.
If metal oxides, e.g. V2O5, are used, these are converted into salts when the process according to the invention is carried out.
¢ 15 The promoters to be added, if appropriate, to the salt melts can be, e.g., metal salts of subgroups I to VIII of the Periodic Table of the Elements and/or of therare earths, for instance salts of scandium, yttrium, lanthanum, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, m~ng~nese, rhenium, iron, ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum7 copper, silver, gold and salts of the rare earths, for instance salts of, for example, cerium, praseodymium, neodymium, samarium, europium, gadolinium, and of thorium and uranium. Preference is given to salts of lanthanum, titanium,zirconium, vanadium, chromium, molybdenum, tungsten, manganese, rhenium, iron, ruthenium, cobalt, rhodium, iridium, nickel, palladium, platinum, copper, cerium, praseodymium, neodymium and thorium. Particular preference is given to salts of lanthanum, vanadium, chromium, manganese, iron, cobalt, nickel, copper,cerium, praseodymium and neodymium. Very particular preference is given to salts of iron and copper.
Mixtures containing promoters are e.g. mixtures of the following type:
LiCl/KCl/FeCI3, LiCl/KCl/NdCI3/PrCI3, KCl/NaCI/LiCl/FeCl3, KCl/NaCl/LiCI/NdCI3/PrCl3, MgCI2/KCI/FeCI37 MgCI2/KCI/NdCI3/PrCI37 MgCI2/KCl/LaCI37 MgCI2/KCI/CeCI37 AlCl3/KCI/FeCI37 AlCI3/KCI/NdCl3, Le A 30 707-US 2 1 6 2 6 4 1 AlCl3/KCl/PrCl3, AlCl3/KCl/NdCl3/PrCl3, AlCl3/KCl/LaCI3, AlCI3/KCI/CeCl3, AlCI3/NaCl/FeCI3, AlCI3/NaCI/NdCI3, AlCI3/NaCI/PrCI3, AlCI3/NaCI/NdCI3/PrCI3, Alcl3/NaCI/LaCI3, Alcl3lNacllcecl3~ V25/K2S4/K2S27/FeCl3' V25/K2S4/K2S207/CuCl, V2O5/K2SO4/K2s2o7lLacl3 V2OslK2So4lK2s2o7lcecl3, V2oslK2so4lK2s2o7lNdcl3 V205/K2SO4/K2S207/NdCI3/PrCl3, CrCl3/NaCl/KCl/FeCl3, MnCI2/KCl/FeCI3, MnCI2/KCI/LaCl3, MnCl2/KCl/CeCI3, MnCI2/KCI/NdCl3/PrCI3, MnCI2/AlCI3/FeCI3, MnCI2/KCI/NaCI/FeCI3, MnCI2/SnCI2/FeCI3, MnCl2/SnCl2/LaCl3, MnCl2/SnCl2/CeCl3, MnCl2/SnCl2/NdCl3, MnCl2/SnCl2/PrCl3, MnCl2/SnCl2/NdCI3/PrCI3, FeCI3/KCl/NdCl3/PrCl3, FeCl3/LiCl/CuCI, FeCl3/NaCl/CuCI, FeCI3/KCl/CuCI, FeCI3/ZnCl2/CuCl, FeCl3/NaCl/ZrCl4, CoCl2/SnCl2/FeCl3, CuCI/KCI/FeCI3, CuCI/AlCI3/FeCI3, CuCI/BiCI3/FeCI3, CuCl/CsCI/FeCI3, CuCI/FeCI3, CuCl/SnCl2/FeCl3, CuCl/ZnCI2/FeCI3, CuCI/TlCl/FeCl3, CuCl/KCl/NdCl3, CuCl/KCI/PrCI3, CuCI/KCl/LaCI3, CuCI/KCl/CeCl3, CuCl/KC1/NdCl3/PrCl3, ZnCI2/KCI/FeCI3, ZnCI2/KCl/NdCl3/PrCl3. Preference is given to mixtures of the type:
V205/K2SO4/K2S207/FeCl3, FeCl3/KCl/NdCl3/PrCl3, CuCl/KCl/FeCl3, CuCl/AlCl3/FeCl3, CuCl/BiCl3/FeCl3, CuCl/CsCl/FeCl3, CuCl/FeCl3, CuCl/SnCl2/FeCl3, CuCl/ZnCl2/FeCl3, CuCl/KCl/NdCl3, CuCl/KCl/PrCl3, CuCl/KCl/LaCl3, CuCl/KCl/CeCl3, CuCI/KCI/NdCl3/PrCl3, CeCI3/NaCI/SnCI2, CeCl3/FeCl2/SnCl2 and NdCl3/NaCl/CaCI2. Particular preference is given to CuCl/KCI/FeCl3, CuCl/KCl/NdCl3, CuCl/KCl/PrCl3 and CuCl/KCl/NdCl3/PrCl3 mixtures. Very particular preference is given to a mixture of CuCl, KCl and FeCl3.
The salt melts to be used can if appropriate simultaneously also contain a plurality of components from the group consisting of the metal salts, the salts depressingthe melting point and/or the promoters.
If a promoter also complies with the definition given for the salts depressing the melting point, in this case the separate addition of a salt depressing the melting point is not absolutely necessary; the promoter then assumes both functions.
However, it is preferable to employ salt melts which contain at least 3 different components, where at least one component complies with the definition given for metal salts, at least one component complies with the definition given for the salts Le A 30 707-US 21 6 2 6 41 depressing the melting point and at least one component complies with the definition given for promoters.
If the metal component of the salt melt constituents described can assume a plurality of oxidation states, for example iron, copper or vanadium, this metal S component can be used in any oxidation state or in any mixtures of differentoxidation states. While the process according to the invention is being carried out the oxidation state can change.
The amount of the salts depressing the melting point employed in the process according to the invention, based on the entire melt, can be between 0 and 99%
by weight, preferably between 10 and 90% by weight and corresponds, very particularly preferably, roughly to the composition of the eutectic mixture of the components used.
The concentration of promoters in the salt melt can be, e.g., 0 to 100 mol %, preferably 0.1 to 50 mol%, and particularly preferably 0.1 to 10 mol%, in each case based on the entire salt melt.
The metal salts, salts depressing the melting point and, if appropriate, promoters can be used e.g. directly as salts, e.g. as halides, nitrates, sulphates or pyrosulphates. Precursors of metal salts can also be used, e.g. metal oxides or metal hydroxides or elemental metals which are transformed into metal salts whenthe process according to the invention is carried out. Preferably, chlorides areused.
The ratio of hydrogen chloride to oxygen can be varied within wide limits. For example, the molar ratio of hydrogen chloride to oxygen can vary between 40:1 and 1:2.5. Preferably, this ratio is between 20:1 and 1:125, particularly preferably between 8:1 and 1:0.5, very particularly preferably between 5:1 and 1:0.3.
The gas containing hydrogen chloride and oxygen is conducted as a continuous phase into a reaction zone and the salt melt is dispersed therein. Preferably, the continuous phase and the salt melt are conducted in counter-current to one another, contact times between 0.1 and 4 seconds are implemented and the Le A 30 707-US 2 1 6 2 6 4 1 procedure is carried out at 350 to 550C. Suitable reactors for this are e.g. packed reactors and jet reactors, trickling film columns and spray towers.
The gases coming from the reaction can contain, for example, 40 to 50% by weight of chlorine, 30 to 40% by weight of hydrogen chloride, 0.5 to 10% by 5 weight of oxygen, 10 to 20% by weight of water (steam) and possibly entrained inert gases, e.g. nitrogen, and possibly small amounts of organics.
Before the gases coming from the reaction are cooled and hydrogen chloride and water are separated out therefrom, it is advantageous first to remove entrained and/or volatilized portions of the salt melt therefrom. For this purpose, this gas 10 can be scrubbed, for example with one or more condensed phases from the overall process, and the scrubbing liquid can be recycled to the reaction zone.
The reaction gases, if appropriate freed of entrained and/or volatilized salt melt portions, are preferably rapidly cooled to a temperature below 300C, preferablybelow 200C, and in particular to 120 to 180C. This cooling can be performed, 15 for example, in a spray cooler. Alternatively, or additionally, the reaction gases can be cooled in an absorption tower filled with previously condensed, aqueous hydrochloric acid, if appropriate with addition of fresh water, and hydrogen chloride and water can be condensed together.
The concentration of the resulting aqueous hydrochloric acid can be varied within 20 wide limits, which poses no difficulty to those skilled in the art. It is preferably aimed to obtain 35 to 37% by weight strength aqueous hydrochloric acid (socalledconcentrated hydrochloric acid). This can then be used for any desired purposes for which concentrated aqueous hydrochloric acid is known to be used. Before thefurther use, a purification known per se can be carried out, for example by 25 blowing through inert gas (e.g. air) and/or by absorption of impurities (e.g. onto activated carbon). In this manner, e.g. residual chlorine and/or in the organicspresent can be removed. In this manner, it is possible to obtain, e.g., 5 to 15% by weight of the hydrogen chloride fed to the process according to the invention aspure, preferably concentrated, aqueous hydrochloric acid.
Le A 30 707-US 2 1 6 2 6 4 1 The aqueous hydrochloric acid separated off can also be used in another manner.
Thus, for example, concentrated sulphuric acid can be added to the aqueous hydrochloric acid initially separated off and thus free it of water. The resulting, preferably unpurified, hydrogen chloride gas can then be recycled to the reaction 5 zone of the process according to the invention. The reaction water in this case results as more or less dilute sulphuric acid. This can be used in a known manner or concentrated and thus the reaction water can be obtained as such.
The gas stream remaining after the cooling and separation out of hydrogen chloride and water essentially contains the chlorine formed in the reaction zone, 10 unreacted oxygen, residual portions of hydrogen chloride and steam, and possibly inert gases and/or possibly small amounts of organics.
Before chlorine is separated off from this gas stream, residual steam is first removed. This is achieved by the addition of concentrated sulphuric acid. The resulting, generally only slightly diluted sulphuric acid can, if appropriate after 15 concentration, be further used at a different point in the process according to the invention or in another (known) manner, e.g. for the production of fertilizers.
The gas stream freed of residual steam to a very great extent contains, for example, 60 to 97% by weight of chlorine and is now compressed to 2 to 10 bar.
This compression can be carried out in a single stage or multiple stages.
20 Preferably, two stages are employed. Compression apparatuses which are suitable are, e.g., piston compressors, rotary compressors and screw compressors. After the compression the gas mixture is cooled until the chlorine liquefies. Suitable temperatures are e.g. at a pressure of 10 bar those below 34C, and at a pressure of 2 bar those below -20C. At other pressures, suitable temperatures can be 25 determined by extrapolation from these values. Chlorine is obtained in this manner in li~uid form which can be used, if appropriate after further purif1cation, in liquid form or, after vaporization, like chlorine originating from the electrolysis of sodium chloride. Preferably, the chlorine is used for chlorinations and phosgenations of organic compounds. If the chlorine separated off is further used 30 in gaseous form, the cold stored in the chlorine separated off in liquid form can be utilized for any cooling purposes.
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Le A 30 707-US 21 6 2 6 41 -The gas remaining after the chlorine separation off generally contains essentially oxygen, and in addition small traces of chlorine and hydrogen chloride, possiblyinert gases and/or possibly small amounts of organics, usually chlorinated organics. This gas is wholly or partially recycled to the reaction zone of the 5 process according to the invention. It is advantageous, in particular when theprocess according to the invention is carried out for a relatively long time, torecycle only some of this gas and to eject the rest. In this manner accumulation of inert gas and organics in the reaction system is avoided. Environmentally polluting constituents, e.g. chlorine, hydrogen chloride and, possibly, organic impurities, in 10 particular chlorinated organic impurities, can be separated from the ejected part of the gas by absorption and/or adsorption. The absorption can be carried out e.g using water or aqueous alkalis, and the adsorption can be carried out e.g. usingsilica gel, aluminium oxides and/or activated carbon. Preferably, regenerable activated carbon is used.
15 The process according to the invention has a number of surprising advantages.Thus, the reaction can be carried out in a continuously uniformly active reaction zone, a salt melt surface which is constantly being renewed is available for thereaction, a substantial freedom of choice of conditions for the melt and of the gas streams is available, high conversion rates and high space-time yields may be 20 achieved and only relatively small amounts of salt melt and relatively small apparatuses are required. It is further advantageous that the reaction can be carried out without supply of energy from outside, under continuous reaction conditions,without problems with respect to long-term stability of the reactors, with the reaction water being separated off in the form of a concentrated aqueous 25 hydrochloric acid, with a high concentration of chlorine in the reaction gas and with the chlorine being separated off by compression and liquefaction without external solvent.
Le A 30 707-US 21 6 2 6 4 l -Examples Example 1 In an apparatus to be operated continuously, a gas mixture comprising 3900 g of hydrogen chloride, 854 g of oxygen, 211 g of chlorine and 192 g of nitrogen was reacted per hour in a trickling film reactor at 370C in the presence of a salt melt.
The salt melt comprised 9000 g of the eutectic mixture of potassium chloride andcopper(I) dichloride. For the reaction, the salt melt was pneumatically transported at intervals by the feedstock gas stream into a storage vessel situated above the packing bed and continuously metered onto the packing bed. The diameter of the packing bed was 40 mm. The feedstock gas mixture preheated to 370C was passed through the packing bed from bottom to top. The hot product gas mixture leaving the reactor comprised 780 g of hydrogen chloride, 160 g of oxygen, 3245 g of chlorine, 780 g of water and 192 g of nitrogen. It was cooled to 150Cin a spray cooler with 408 g of 34% by weight strength aqueous hydrochloric acid, and in a downstream absorption tower already filled with 3526 g of 34% by weight strength aqueous hydrochloric acid the reaction water formed and unreacted hydrogen chloride were separated off in the form of 34% strength by weight aqueous hydrochloric acid. In this manner, 397 g of hydrogen chloride, 769 g of water and 9 g of chlorine were separated off. The remaining reaction gas (per hour 383 g of hydrogen chloride, 160 g of oxygen, 3236 g of chlorine and 192 g of nitrogen) was dried with concentrated sulphuric acid in a drying tower, then compressed to 6 bar and cooled to -10C. This resulted in 2308 g of chlorine in liquid form which additionally contained 91 g of hydrogen chloride in dissolved form. The non-condensed portions of the gas were conducted into a second condensation stage operated at -25C, where a further 576 g of chlorine and a further 41 g of hydrogen chloride in liquid form were separated off From the non-condensed residual gas, a part-stream comprising 100 g of hydrogen chloride, 63 g of oxygen, 141 g of chlorine and 75 g of nitrogen was ejected. The remaining gas stream (per hour 150 g of hydrogen chloride, 94 g of oxygen, 211 gof chlorine and 112 g of nitrogen) was recycled to the reactor.
Le A 30 707-US
Example 2 In continuously operated trickling film reactor, a gas mixture preheated to 480C, comprising 5967 g of hydrogen chloride, 888 g of oxygen, 248 g of chlorine 124 g of steam and 154 g of nitrogen was reacted per hour at 480C in the presence of a salt melt as described in Example 1. The hot product gas mixture leaving the reactor comprised, per hour, 2586 g of hydrogen chloride, 137 g of oxygen, 3536 g of chlorine, 970 g of water and 154 g of nitrogen. It was cooled to 150C in a spray cooler using 29% strength by weight aqueous hydrochloric acid, and in a downstream absorption tower the reaction water formed and unreacted hydrogen chloride were separated off in the form of 29% strength by weight hydrochloric acid. The amounts separated off were 334 g of hydrogen chloride and 830 g of water. The procedure was further carried out as described in Example 1. A total of 3284 g of liquid chlorine which contained 31 g of hydrogenchloride and 8 g of oxygen resulted. From the non-condensed gas, a part stream which, per hour, comprised 1 g of hydrogen chloride, 64 g of oxygen, 87 g of chlorine and 72 g of nitrogen was ejected. The residual gas was recycled to the reactor.
Example 3 In a continuously operated trickling film reactor, a gas mixture preheated to 480C, comprising 326 g of hydrogen chloride and 71 g of oxygen, was reacted per hour as described in Example 1 at 480C in the presence of a salt melt. The salt melt comprised a mixture of 1174 g of potassium chloride, 1001 g of copper(I) chloride, 2255 g of copper(II) chloride and 600 g of neodymium chloride hydrate. Per hour, 25 1 of melt were metered through a column (d = 50 mm; h =
70 mm) packed with Raschig rings and were reacted in counter-current with the feedstock gases The product gas mixture leaving the reactor comprised, per hour,218 g of hydrogen chloride, 47.2 g of oxygen, 104 g of chlorine and 26 5 g of steam. As described in Example 1, the product gases were cooled to 150C in a spray cooler using aqueous hydrochloric acid, the reaction water was separated off in an absorption tower as aqueous hydrochloric acid, the product gases were dried with concentrated sulphuric acid, and chlorine was taken off in liquid form by compression to 6 bar and cooling to -10C
Le A 30 707-US
~ 2 1 6264 1 Example 4 In a continuously operated trickling film reactor, a gas mixture preheated to 480C7 comprising 81.5 g of hydrogen chloride and 17.8 g of oxygen, was reacted per hour as described in Example 1 at 480C in the presence of a salt melt. The salt melt comprised a mixture of 1174 g of potassium chloride, 1001 g of copper(I) chloride, 2255 g of copper(II) chloride and 600 g of neodymium chloride hydrate. Per hour, 25 1 of melt were metered through a column (d = 50 mm; h =
70 mm) packed with Raschig rings and were reacted in counter-current with the feedstock gases. The product gas mixture leaving the reactor comprised, per hour, 27.3 g of hydrogen chloride, 5.9 g of oxygen, 52.6 g of chlorine and 13.3 g of steam. As described in Example 1, the product gases were cooled to l50C in a spray cooler using aqueous hydrochloric acid, the reaction water was separated off in an absorption tower as aqueous hydrochloric acid, the product gases were dried with concentrated sulphuric acid, and chlorine was taken off in liquid form by compression to 6 bar and cooling to -10C.
Example 5 In a continuously operated trickling film reactor, a gas mixture preheated to 480C, comprising 407.5 g of hydrogen chloride and 85.2 g of oxygen, was reacted per hour as described in Example 1 at 450C in the presence of a salt melt. The salt melt comprised a mixture of 1174 g of potassium chloride, 1001 g of copper(I) chloride and 2255 g of copper(II) chloride. Per hour, 20.6 l of melt were metered through a column (d = 50 mm; h = 70 mm) packed with Raschig rings and were reacted in counter-current with the feedstock gases. The product gas mixture leaving the reactor comprised, per hour, 361.7 g of hydrogen chloride, 75.6 g of oxygen, 44.3 g of chlorine and 11.2 g of steam. As described in Example 1, the product gases were cooled to 1 50C in a spray cooler using aqueous hydrochloric acid, the reaction water was separated off in an absorptiontower as aqueous hydrochloric acid, the product gases were dried with concentrated sulphuric acid, and chlorine was taken off in liquid form by compression to 6 bar and cooling to -10C.
Claims (11)
1. A process for the oxidation of hydrogen chloride with oxygen in contact with a salt melt, in which the salt melt contains a metal salt and a salt to depress the melting point, the oxidation is effected at a temperature between 300 and 600°C, the salt melt is dispersed in the gas containing hydrogen chloride and oxygen in such a way that the contact time is from 0.01 to 100 seconds, the reaction gases are cooled and hydrogen chloride and water are separated from the reaction mixture, the reaction gases freed from most of the water and some of the hydrogen chloride are contacted with sulphuric acid to remove residual water and the gas mixture then essentially containing chlorine, hydrogen chloride and oxygen is compressed to 2 to 10 bar, the chlorine is liquefied by cooling and is separated off, and the remaining, essentially oxygen-containing gas is recycled to the reaction zone.
2. The process of claim 1, in which the oxygen-containing gas present after chlorine has been separated off is only partially recycled to the reaction zone and, from the rest of the gas, the non-condensed portions of chlorine, hydrogen chloride and, where present, organic impurities are separated off by absorption or adsorption.
3. The process according to claim 1, in which a salt melt which comprises a mixture of potassium chloride and copper(I) chloride is used, the oxidation is carried out at 350 to 550°C and the reaction gases are cooled to a temperature below 300°C to separate off hydrogen chloride and water.
4. The process of claim 1, in which a salt melt which contains potassium chloride, copper(I) chloride and iron(III) chlorid is used.
5. The process of claim 1, in which a salt melt which contains potassium chloride, copper(I) chloride and neodymium trichloride is used.
6. The process of claim 1, in which the salt melt is reacted with hydrogen chloride and oxygen in a trickling film reactor.
7. The process of claim 1, in which the salt melt is reacted with hydrogen chloride and oxygen in a jet reactor.
8. The process of claim 1, in which the salt melt is reacted with hydrogen chloride and oxygen in a spray tower.
9. The process of claim 1, in which the salt melt additionally contains a promoter.
10. The process of claim 1, in which the liquefied chlorine is purified before it is separated off.
11. The process of claim 1, in which a salt melt is used which contains potassium chloride, copper(I) chloride, neodymium trichloride and praseodymium trichloride.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4440642.8 | 1994-11-14 | ||
| DE4440642A DE4440642A1 (en) | 1994-11-14 | 1994-11-14 | Process for the oxidation of hydrogen chloride |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2162641A1 true CA2162641A1 (en) | 1996-05-15 |
Family
ID=6533283
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002162641A Abandoned CA2162641A1 (en) | 1994-11-14 | 1995-11-10 | Process for the oxidation of hydrogen chloride |
Country Status (8)
| Country | Link |
|---|---|
| EP (1) | EP0711728B1 (en) |
| JP (1) | JPH08225304A (en) |
| KR (1) | KR960017502A (en) |
| CN (1) | CN1129192A (en) |
| AT (1) | ATE181038T1 (en) |
| BR (1) | BR9505150A (en) |
| CA (1) | CA2162641A1 (en) |
| DE (2) | DE4440642A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6387345B1 (en) | 1995-09-26 | 2002-05-14 | Bayer Aktiengesellschaft | Process for working up reaction gases during the oxidation HCI to chlorine |
| US20100202959A1 (en) * | 2007-07-13 | 2010-08-12 | Bayer Technology Services Gmbh | Catalyst and process for preparing chlorine by gas phase oxidation of hydrogen chloride |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| KR101516812B1 (en) | 1998-02-16 | 2015-04-30 | 스미또모 가가꾸 가부시끼가이샤 | Process for producing chlorine |
| JP4182608B2 (en) * | 1999-11-10 | 2008-11-19 | 住友化学株式会社 | Separation and recovery of hydrogen chloride and water |
| JP2005306712A (en) * | 2004-10-15 | 2005-11-04 | Sumitomo Chemical Co Ltd | Method for manufacturing chlorine and hydrochloric acid |
| JP5041769B2 (en) * | 2006-09-06 | 2012-10-03 | 住友化学株式会社 | Startup method |
| DE102008050976A1 (en) * | 2008-10-09 | 2010-04-15 | Bayer Technology Services Gmbh | Process for the production of chlorine from process gases |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4107280A (en) * | 1977-08-01 | 1978-08-15 | Battelle Memorial Institute | Oxidation of hydrogen halides to elemental halogens with catalytic molten salt mixtures |
| US4537835A (en) * | 1977-02-18 | 1985-08-27 | Battelle Memorial Institute | Oxidation of hydrogen halides to elemental halogens |
| US4329525A (en) * | 1978-02-21 | 1982-05-11 | The Lummus Company | Production of chlorinated compounds by use of molten salts |
| US5084264A (en) * | 1989-12-12 | 1992-01-28 | Battelle Memorial Institute | Process for oxidation of hydrogen halides to elemental halogens |
-
1994
- 1994-11-14 DE DE4440642A patent/DE4440642A1/en not_active Withdrawn
-
1995
- 1995-11-02 DE DE59506153T patent/DE59506153D1/en not_active Expired - Fee Related
- 1995-11-02 EP EP95117253A patent/EP0711728B1/en not_active Expired - Lifetime
- 1995-11-02 AT AT95117253T patent/ATE181038T1/en not_active IP Right Cessation
- 1995-11-08 JP JP7314664A patent/JPH08225304A/en active Pending
- 1995-11-10 CA CA002162641A patent/CA2162641A1/en not_active Abandoned
- 1995-11-13 BR BR9505150A patent/BR9505150A/en not_active Application Discontinuation
- 1995-11-13 KR KR1019950040968A patent/KR960017502A/en not_active Application Discontinuation
- 1995-11-14 CN CN95119831A patent/CN1129192A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US6387345B1 (en) | 1995-09-26 | 2002-05-14 | Bayer Aktiengesellschaft | Process for working up reaction gases during the oxidation HCI to chlorine |
| US20100202959A1 (en) * | 2007-07-13 | 2010-08-12 | Bayer Technology Services Gmbh | Catalyst and process for preparing chlorine by gas phase oxidation of hydrogen chloride |
Also Published As
| Publication number | Publication date |
|---|---|
| KR960017502A (en) | 1996-06-17 |
| CN1129192A (en) | 1996-08-21 |
| DE59506153D1 (en) | 1999-07-15 |
| JPH08225304A (en) | 1996-09-03 |
| DE4440642A1 (en) | 1996-05-15 |
| BR9505150A (en) | 1997-10-21 |
| EP0711728B1 (en) | 1999-06-09 |
| EP0711728A1 (en) | 1996-05-15 |
| ATE181038T1 (en) | 1999-06-15 |
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