Published December 1997
Du Pont has developed a new membrane-cell technology for producing chlorine from gaseous anhydrous hydrogen chloride (HCl)—an inevitable and undesirable by-product of many organic chlorination processes. The new process uses an especially developed electrolytic cell to generate a nearly dry chlorine at anode from the HCl feed. Because of the anhydrous nature of the feedstream, the risk of oxidation of water at anode is eliminated and current densities up to 12 kA/m2 can be maintained. The cell has a proton-conducting membrane that is made of NAFION�—a proprietary copolymer product of Du Pont. Both the anode and cathode are either self-standing electrodes with ruthenium dioxide, or consist of a membrane electrode assembly in which the electrochemically active material is bonded to the membrane. The anode and cathode current distributors are fabricated from an electrically conductive composite material that is chemically inert. Lower cell voltage, higher current densities, and a drier chlorine product are all translated into substantial capital savings.
The technology was patented in 1995 and a pilot plant was built by Du Pont at its Corpus Christi site in Texas, where important operating parameters are being tested. Du Pont intends to put its technology to commercial use soon.
In this Review we present an evaluation of the Du Pont membrane-cell technology for production of chlorine from HCl obtained as a by-product in a toluene diisocyanate (TDI) plant. We also present a comparison of the process economics with those of other competing technologies like Kel-Chlor 1, MT-Chlor, Carrier Catalyst, and the Uhde electrolytic process.