PDF Publication Title:
Text from PDF Page: 003
34 FIG. 3: Process flow sheet for the DuPont Anhydrous HCl Process. ment and commercialization program. To meet the milestones set, a diverse work group along with dedicated laboratory and plant resources were provided. The “proof of concept” for the DuPont anhydrous HCl process was first demonstrated at UC Berkeley in a 1.0 cm2 fuel cell type electrolyzer.10 In the summer of 1994, a 300 cm2 single cell was built and operated at the DuPont experimental station. In April of 1995, this electrolyzer setup was further scaled by a factor of 30 and a 0.9 m2 single cell was built and operated at a current density of 13 kA/m2 at a potential of 2.0 V. On November 9, 1995, almost two years after the demonstration of the concept, a three cell bipolar stack with a combined active area of approximately 2.0 m2 along with the necessary infrastructure were built and operated.8 Each cell in the stack was operated at a steady current den- sity of 10 kA/m2 and potential of 2.0 V. The 3-cell electrolyzer with an active area of 2.0 m2 is shown in FIG. 1. Also, during this period, significant improvements in the electrolyzer design were acheived by the engineering design team at DuPont and DeNora of Milan, Italy. This resulted in an improved electrolyzer, different in design and in some of the materials for key components. The second generation 3-cell electrolyzer is shown in FIG. 2. Improvements in the electrochemical per- formance were also acheived by using catalyst- coated Nafion® membranes. Recent experiments have demonstrated that by using a catalyst-coated Nafion membrane, the electrolyzer could be operated steadily at current densities as high as 12 kA/m2 at potentials as low as 1.7 V. The measured current efficiencies under these conditions were greater than 99%. Process Description The basic flow sheet for the DuPont anhydrous HCl process is shown in FIG. 3.9 The design of the electrolyzer stack is based on PEMFC technology and was developed by DuPont and DeNora of Milan, Italy. The anode and cathode can be bonded to the Nafion membrane to form a catalyst-coated membrane. A variation of the electrodes is to use E-Tek ELAT electrodes, which are essentially gas diffusion backings impregnated with catalyst. The electrolyzer is usually operated at a pressure and temperature ranging from 450-550 kPa and 70-90 °C, respectively. Byproduct HCl vapor from a chemical reaction is fed to the anode side of the electrolyzer. The HCl vapor reacts at the anode, producing Cl2 gas and protons. The protons that are produced along with the chlorine are transported across the Nafion membrane to the cathode side where two protons recombine to form hydrogen gas. The typical molar conversion per pass achieved in the electrolyzer is on the order of 70-85%. Dilute hydrochloric acid (1-5 wt%) is fed to the cathode to maintain the Nafion membrane hydration and also to control the electrolyzer temperature. The anode exit stream containing traces of water, unreacted HCl and chlorine are fed to a concen- trated sulfuric acid drying tower. The sulfuric acid concentration in the tower is maintained at 93%. This drying operation reduces the water concentra- tion of the product gases from approximately 300 parts per million (ppm) to less than 20 ppm. The gases from the drier are then condensed. This is accomplished by compressing the gas mixture to 850 kPa followed by chilling with brine maintained at -25 °C. The liquefied gas mixture is then fed into a distillation column operating at 2400 kPa. Here HCl and inerts are removed from the top of the column and dry Cl2 is removed from the bottom. This separation is rather simple due to the large span in the difference in the boiling points of HCl, inerts (e.g., N2, H2, etc.) and chlorine. The recovered HCl FIG. 4. An experimental polarization curve depicting the relationship between the applied current density and the energy requirements per ton of chlorine. The Electrochemical Society Interface • Fall 1998PDF Image | RECYCLING CHLORINE FROM HYDROGEN CHLORIDE
PDF Search Title:
RECYCLING CHLORINE FROM HYDROGEN CHLORIDEOriginal File Name Searched:
IF8-98-Pages32-36.pdfDIY PDF Search: Google It | Yahoo | Bing
Salgenx Redox Flow Battery Technology: Power up your energy storage game with Salgenx Salt Water Battery. With its advanced technology, the flow battery provides reliable, scalable, and sustainable energy storage for utility-scale projects. Upgrade to a Salgenx flow battery today and take control of your energy future.
| CONTACT TEL: 608-238-6001 Email: greg@salgenx.com | RSS | AMP |