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Monday, May 3, 2010
Long Beach Convention Center
Among the numerous thermochemical cycles for hydrogen production, the copper-chlorine (Cu-Cl) cycle is one of the most promising as it requires heat input at a relatively low temperature (550°C). Prior proof-of-concept experimental work has shown that the chemistry is viable while preliminary modeling has shown that the efficiency and cost of hydrogen production have the potential to meet DOE’s targets. One of the most challenging steps in the Cu-Cl cycle is the hydrolysis of CuCl2 into Cu2OCl2 and HCl while avoiding the need for excess water and the undesired thermolysis reaction, which gives CuCl and Cl2. Indeed, the mechanisms of CuCl2 hydrolysis, an important step in the Cu-Cl cycle, are not fully understood. Although the stoichiometry of the hydrolysis reaction, 2CuCl2 + H2O ⇔Cu2OCl2 + 2HCl, indicates a necessary steam-to-CuCl2 molar ratio of 0.5, a ratio as high as 23 has been typically required to obtain near 100% conversion of the CuCl2 to the desired products at atmospheric pressure.
Argonne National Laboratory has designed a spray reactor where an aqueous solution of CuCl2 is atomized into a heated zone, into which steam/Ar are injected in co- or counter-current flow. Both a pneumatic and an ultrasonic nebulizer were tested. Water was vaporized rapidly from the droplets to form CuCl2 particles, which subsequently reacted with steam. Solid products of the reaction were analyzed for their phase composition, and particle sizes. Analyses of gaseous products from the hydrolysis reactions were conducted at the Commissariat à L’Energie Atomique using UV-spectrometry and conductivity.
In the experiments, the operating parameters were varied to determine the conditions that provide high Cu2OCl2 yields (i.e., promote hydrolysis and inhibit thermolysis of CuCl2) while minimizing the steam-to-CuCl2 molar ratio.
With a pneumatic nebulizer, the counter-current flow design gave high yields of Cu2OCl2 compared to the co-current flow design, but some CuCl2 remained unreacted in both designs. With an ultrasonic nozzle, over 95% yields of Cu2OCl2 were obtained at a steam-to-CuCl2 molar ratio around 20–23 at 1 atm pressure.
Some CuCl was present in the products with both types of atomizers but this is believed to be due to decomposition of Cu2OCl2 rather than CuCl2, as confirmed by the presence of HCl and the absence of Cl2 at the reaction temperature studied.
It is highly desirable to conduct this reaction with less excess steam to improve the process efficiency. According to the available equilibrium-based model, the needed amount of steam can be decreased by conducting the hydrolysis reaction at a reduced pressure. The experiments at 0.4 atm and 0.7 atm showed that it is possible to lower the steam-to-CuCl2 molar ratio to 15, while still obtaining good yields of the desired products. An important effect of running the hydrolysis reaction at reduced pressure is the significant decrease of CuCl concentration in the solid products, which effect was not predicted by prior modeling.
Argonne National Laboratory has designed a spray reactor where an aqueous solution of CuCl2 is atomized into a heated zone, into which steam/Ar are injected in co- or counter-current flow. Both a pneumatic and an ultrasonic nebulizer were tested. Water was vaporized rapidly from the droplets to form CuCl2 particles, which subsequently reacted with steam. Solid products of the reaction were analyzed for their phase composition, and particle sizes. Analyses of gaseous products from the hydrolysis reactions were conducted at the Commissariat à L’Energie Atomique using UV-spectrometry and conductivity.
In the experiments, the operating parameters were varied to determine the conditions that provide high Cu2OCl2 yields (i.e., promote hydrolysis and inhibit thermolysis of CuCl2) while minimizing the steam-to-CuCl2 molar ratio.
With a pneumatic nebulizer, the counter-current flow design gave high yields of Cu2OCl2 compared to the co-current flow design, but some CuCl2 remained unreacted in both designs. With an ultrasonic nozzle, over 95% yields of Cu2OCl2 were obtained at a steam-to-CuCl2 molar ratio around 20–23 at 1 atm pressure.
Some CuCl was present in the products with both types of atomizers but this is believed to be due to decomposition of Cu2OCl2 rather than CuCl2, as confirmed by the presence of HCl and the absence of Cl2 at the reaction temperature studied.
It is highly desirable to conduct this reaction with less excess steam to improve the process efficiency. According to the available equilibrium-based model, the needed amount of steam can be decreased by conducting the hydrolysis reaction at a reduced pressure. The experiments at 0.4 atm and 0.7 atm showed that it is possible to lower the steam-to-CuCl2 molar ratio to 15, while still obtaining good yields of the desired products. An important effect of running the hydrolysis reaction at reduced pressure is the significant decrease of CuCl concentration in the solid products, which effect was not predicted by prior modeling.
The effects of the operating parameters studied will be presented and possible explanations based on kinetics and residence times will be suggested.