Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B1/00—Electrolytic production of inorganic compounds or non-metals
  • C25B1/01—Products
  • C25B1/24—Halogens or compounds thereof
  • C25B1/26—Chlorine; Compounds thereof
• • 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
• • 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
  • Y02P20/20—Improvements relating to chlorine production

Definitions

• a low temperature plasma e.g. generated by electrical discharge
• reaction cooled so far that the reaction water and hydrogen chloride condense out in the form of concentrated hydrochloric acid.
• the resulting hydrochloric acid is separated and the remaining gaseous reaction mixture is freed from residual water by washing with sulfuric acid or other methods such as drying with zeolites.
• the liberated from residual water chlorine-containing reaction gas mixture is then compressed, with oxygen and other gas components remain in the gas phase and can be separated from the liquefied chlorine.
• Such processes for the production of pure chlorine from gas mixtures are described, for example, in the published specifications DE 195 35 716 A1 and DE 102 35 476 A1.
• the now purified chlorine is then fed to use, for example in the production of isocyanates.
• the resulting aqueous solution of hydrogen chloride (hydrochloric acid) is separated from the gas mixture, characterized in that d) the separated hydrochloric acid is at least partially supplied to an electrochemical oxidation in which at least a portion of the aqueous hydrochloric acid is oxidized to chlorine,
• the process is preferably carried out continuously, since an equally possible batch or semibatch operation is somewhat more technically complicated than the continuous process.
• the hydrogen chloride obtained in the reaction of phosgene with an organic amine generally contains organic minor components which can interfere with both the thermal catalyzed or non-thermal activated HCl oxidation and the electrochemical oxidation of an aqueous hydrogen chloride solution according to step (c).
• organic constituents include, for example, the solvents used in the preparation of isocyanates, such as chlorobenzene, o-dichlorobenzene or p-dichlorobenzene. If a gas diffusion electrode is used as the cathode during the electrolysis, the catalyst of the gas diffusion electrode can also be deactivated by the organic impurities.
• the phosgene may be washed out of the gas stream in one or more stages with a cold solvent or solvent-phosgene mixture.
• Suitable solvents for this purpose for example, the solvents used in the phosgenation chlorobenzene and o-dichlorobenzene are.
• the temperature of the solvent or of the solvent-phosgene mixture for this purpose is in the range from -15 to -46 ° C.
• the separated from the gaseous product stream phosgene can be fed back to the phosgenation.
• the hydrogen chloride obtained after separation of the phosgene and a portion of the solvent residue may contain, in addition to the inert gases such as nitrogen and carbon monoxide, 0.1 to 1% by weight of solvent and 0.1 to 2% by weight of phosgene.
• a distillation of the chlorine hydrogen can be provided for the optionally provided purification of the hydrogen chloride from the phosgenation. This takes place after condensation of the gaseous hydrogen chloride from the phosgenation.
• the purified hydrogen chloride is removed as the top product of the distillation, wherein the distillation under known to those skilled, for such a distillation customary conditions of pressure, temperature u.a. he follows.
• the hydrogen chloride separated off and optionally purified according to the above-described process can then be supplied to the HCl oxidation with oxygen.
• This HCl oxidation is carried out as described preferably by the Deacon process.
• 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 done by different impregnation of the catalyst support with active material or by different dilution of the catalyst with an inert material.
• 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.
• the inert material should preferably have similar external dimensions.
• Ruthenium compounds or copper compounds on support materials are particularly suitable as heterogeneous catalysts, preference being given to optionally doped ruthenium catalysts.
• suitable carrier materials are 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 ⁇ - or ⁇ -aluminum oxide or mixtures thereof.
• the copper or ruthenium-supported catalysts can be obtained, for example, by impregnating the support material with aqueous solutions of CuCl 2 or R ⁇ 1Cl 3 and optionally a promoter for doping, preferably in the form of their chlorides.
• the shaping of the catalyst can take place after or preferably before the impregnation of the support material.
• 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.
• 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, yt
• 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%. After conversion, unreacted hydrogen chloride can be partly or completely recycled to the catalytic hydrogen chloride oxidation.
• 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.
• Fig. 1 an example of the use of the method as a supplement and part of an isocyanate production is shown.
• isocyanate e.g., toluene diisocyanate, TDI
• Oxidation process 5 reacted with oxygen, here in a Deacon process by means of catalyst.
• reaction mixture 19 from stage 5 is cooled (step 6).
• the resulting gas mixture 20 consisting at least of chlorine, oxygen and minor constituents such as nitrogen, carbon dioxide, etc. and is treated with conc. Sulfuric acid 21 (96%) dried (step 7).
• the electrolysis stage is an ODC electrolysis in which oxygen is used as a reactant on the cathode side.
• the chlorine gas obtained from the purification stage 8 can be used again directly in the phosgene synthesis 1.
• the oxygen-containing stream 23 obtained in this step is used in step 5 (HCl oxidation) and step 9 (electrolysis cell).
• the concentration of hydrochloric acid 27 fed to the electrolytic cell 9 is 14 to 15% by weight of HCl, and the hydrochloric acid 28 leaving the electrolysis 9 is 11 to 13% by weight of HCl.
• the hydrochloric acid stream 28 is mixed with concentrated hydrochloric acid 26 from the separation stage 6 and fed back to the cell 9.
• the oxygen consumed at step 5 and step 9 is replaced by oxygen from an external source 24.
• the oxygen 25 not consumed in the cathode compartment of the electrolysis cell is circulated and mixed with fresh oxygen from an external source 24.
• the also in the cathode compartment accumulating about 2 wt.% Hydrochloric acid 29 is fed to the hydrochloric acid separation 6 where it serves as an absorbent for excess gaseous hydrogen chloride.
• the combined gas stream 30, 20 is cooled in one or more stages by means of a refrigeration unit, e.g. a tube heat exchanger, cooled and dried. Drying 7 can be carried out, for example, with the aid of a suitable drying agent in an absorption column equipped with mass transfer elements.
• a suitable desiccant may be used, e.g. in DE 10 235 476 A, in addition to molecular sieves or hygroscopic adsorbents, e.g. Be sulfuric acid.
• the drying can be done in one or more stages.
• the drying is preferably carried out in two stages by bringing the chlorine to be dried in a first stage with a sulfuric acid of lower concentration, preferably 70 to 80%, particularly preferably 75 to 80%, in contact.
• the residual moisture is removed from the chlorine by means of a more highly concentrated sulfuric acid of preferably 88 to 96%, more preferably 92-96%.
• the chlorine (22) which has been dried in this way and has a residual moisture content of preferably not more than 100 ppm, more preferably not more than 20 ppm, can be passed through a droplet separator in order to remove any sulfuric acid droplets still contained therein.
• a stream of 35.9 t / h of purified hydrogen chloride from an isocyanate plant is split into two streams.
• 29.5 t / h are subjected to HCl oxidation and 6.4 t / h to HCl absorption.
• 29.5 t / h of HCl are fed with 12.9 t / h of oxygen (content greater than 99%) of a catalytic HCl oxidation.
• the oxidation takes place at 333 0 C and 3.4 bar.
• the HCl conversion in the reactor is 85%.
• the gas mixture leaving the reactor is cooled to 100 0 C, the condensed HCl with the water of reaction in an HCl absorption.
• the cooled process gas stream (4.4 t / h HCl, 7.4 t / h oxygen, 24.4 t / h chlorine, 6.18 t / h water) is mixed with 6.4 t / h of purified hydrogen chloride in the HCl Absorption passed. In this HCl absorption unit, a 30 wt.
• the electrolysis is operated at a current density of 5 kA / m 2 at 55 ° C and a voltage of 1.39 V.
• the anode and cathode material used is a palladium-stabilized titanium.
• Anode and cathode half-shell are separated by an ion exchange membrane from DUPONT, type Nafion 324.
• the cathode used is an oxygen-consuming cathode from ETEK, which contains a rhodium sulphide-supported catalyst. Oxygen is supplied to the cathode half-element at 100% excess, ie, 9.17 t / h.
• a purified HCl gas stream of 35.9 t / h is fed to the HCl oxidation with 100% oxygen excess, ie, 15.7 t / h of oxygen.
• the conversion is 85%, leaving the reactor 5.4 t / h of HCl, 9.0 t / h of oxygen, 7.5 t / h of water and 29.7 t / h of chlorine.
• This process gas 19 is fed to an HCl absorption, which is operated with a first partial flow of 177.8 t / h from NaCl-depleted NaCl-containing solution (18.3% by weight NaCl) originating from NaCl electrolysis.
• the water and the hydrogen chloride of the process gas 19 is absorbed.
• the current leaving the absorption is composed as follows: 152.8 t / h of water, 32.5 t / h of NaCl, 5.4 t / h of hydrogen chloride.
• this stream is combined with the second substream of the NaCl-containing solution of 118.2 t / h, mixed with 26.4 t / h of solid NaCl and returned to the NaCl electrolysis.
• the NaCl electrolysis consists of 1475 bipolar electrolysis elements per 2.71m 2 membrane area. NaCl electrolysis is operated with titanium anode shells bearing a noble metal oxide coated titanium anode.

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• 2006
  • 2006-05-18 DE DE102006023261A patent/DE102006023261A1/de not_active Withdrawn
• 2007
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  • 2007-05-10 CN CNA2007800180695A patent/CN101448732A/zh active Pending
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  • 2007-05-10 WO PCT/EP2007/004147 patent/WO2007134726A2/de not_active Ceased
  • 2007-05-10 ES ES07725069T patent/ES2744378T3/es active Active
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