Electrolysis: processes – compositions used therein – and methods – Electrolytic synthesis – Preparing inorganic compound
Patent
1998-05-18
1999-10-05
Gorgos, Kathryn
Electrolysis: processes, compositions used therein, and methods
Electrolytic synthesis
Preparing inorganic compound
C25B 124
Patent
active
059618132
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a process for the electrochemical conversion of hydrogen chloride to phosgene. According to the hitherto conventional processes, phosgene has been produced catalytically from free chlorine. The chlorine is either produced generically from NaCl electrolysis, wherein the HCl gas originating, for example, from isocyanate production, is further processed in the form of hydrochloric acid or is recovered as recycled chlorine from the electrolysis of aqueous hydrochloric acid.
U.S. Pat. No. 5,411,641 describes an electrochemical process for the production of chlorine in which dry direct oxidation of HCl to chlorine and protons proceeds in the electrochemical cell. Even with an aqueous electrolyte on the cathode side in conjunction with hydrogen production, the process operates at distinctly more favourable operating voltages than the conventional electrolysis of aqueous hydrochloric acid.
The object of the invention is directly to produce phosgene by electrochemical methods starting from gaseous hydrogen chloride.
This object is achieved according to the invention by HCl gas and dry CO gas being supplied as the educts to the anode of an electrochemical cell equipped with a proton-conducting membrane and the chlorine radicals formed from the anodic oxidation of HCl gas directly reacting with the CO gas to yield phosgene, while the simultaneously formed protons migrate through the membrane to the cathode and in the event of operation with aqueous HCl, are there reduced to hydrogen or, in the presence of oxygen, to water.
In this process, the chlorine radicals are typically anodically oxidised at the anode with CO gas to yield phosgene in accordance with the following reaction equations ##EQU1##
The reaction is preferably performed in such a manner that, in addition to the electrochemical anodic oxidation, an exothermic catalytic reaction of molecular chlorine with CO gas to yield phosgene proceeds in the support material containing carbon of the activated diffusion anode in accordance with the reaction equation
Due to the phosgene radicals arising in this reaction, the anodic overvoltage may be reduced by 0.2 V-0.6 V.
The process is advantageously performed in such a manner that, in order to reduce the operating voltage of the electrochemical cell, the oxygen is reduced on the cathode (3) and is consumed by reaction with the protons diffusing through the membrane to yield water.
Alternatively, the process may, however, be performed in such a manner that the cathode (3) is operated in aqueous hydrochloric acid, wherein hydrogen is produced as the secondary product.
In order to establish its proton conductivity, the membrane is additionally moistened with moist oxygen, which is supplied to the cathode with the educt gas.
According to a preferred embodiment, the electrochemical reactions at the cathode and anode are performed at a pressure of 2 bar to 6 bar.
A further development of the process according to the invention consists in cooling and liquefying the stream of phosgene drawn off from the anode side under the operating pressure in a recuperator and depressurising and vaporising the liquefied phosgene on the secondary side of the recuperator, wherein the refrigeration capacity required for liquefaction is created and any HCl and CO educt gas present in the phosgene liquefied on the primary side is simultaneously removed. Any such educt gas may then be returned to the electrochemical cell.
The electrochemical cell is here advantageously operated in a closed system, which also includes the recuperator, at a pressure of 2 bar to 10 bar, preferably of 2 bar to 6 bar, in such a manner that the pressure differential between the closed system and the electrochemical cell is virtually zero, such that even when relatively high pressures are used the electrochemical cell may be operated almost without pressure.
In comparison with conventional phosgene production processes, the following advantages are achieved: chloride may be directly electrochemically reacted in the gas phase to yield phosgene
REFERENCES:
patent: 5411641 (1995-05-01), Trainham, III et al.
Chemical Abstract, vol. 90, 1979, Ref. 159157m. No Month Available.
JP 4-6290 A. In. Patents Abstracts of Japan, C-928, Apr. 13,1992, vol. 16, No. 148.
Dobbers Jurgen
Gestermann Fritz
Rindfleisch Hans-Nicolaus
Bayer Aktiengesellschaft
Gil Joseph C.
Gorgos Kathryn
Whalen Lyndanne M.
Wong Edna
LandOfFree
Process for direct electrochemical gaseous phase phosgene synthe does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for direct electrochemical gaseous phase phosgene synthe, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for direct electrochemical gaseous phase phosgene synthe will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-1167168