Hybrid Copper Chloride Cycle for Hydrogen Production

In view of the upcoming hydrogen economy, Argonne researchers are studying thermochemical cycles to determine their potential to produce hydrogen effectively with respect to energy usage and cost. Most emphasis has been placed on baseline sulfur cycles, though a small effort is currently ongoing for alternative cycles, one of which is the copper chloride (Cu-Cl) cycle. The chemistry of this cycle is illustrated in the figure below. Heat/electricity and water are the only inputs, while oxygen and hydrogen are the only products. All of the chemicals are recycled.

The Copper Chloride Cycle

Researcher Magali Ferrandon sets up the syringe pump, which provides the feed to the hydrolysis reactor. The syringe pump feeds CuCl2 solution (blue) to the hydrolysis reactor in very small, measured amounts.

The Cu-Cl cycle consists of three major reactions. In the electrochemical reaction, cuprous chloride (CuCl) is converted to cupric chloride (CuCl₂) at the anode and hydrogen ion is converted to H2 at the cathode at ~100ºC and 24 bars. The CuCl₂ is transferred to the hydrolysis reactor where it contacts excess steam at ~375ºC and 1 bar to form copper oxychloride (Cu2OCl₂). The copper oxychloride is then decomposed in the oxychloride decomposition reactor to give molten CuCl and oxygen at 550ºC and 1 bar.

Experimental Results

All of the reactions have been demonstrated in proof-of-concept experiments. The two thermal reactions, the hydrolysis of CuCl₂, and the decomposition of Cu₂OCl₂, have been proven at Argonne. The electrolytic reaction was demonstrated at Atomic Energy of Canada Limited (AECL) recently and at the Gas Technology Institute. The advantages of this cycle are the relatively low maximum temperature (550°C compared to the 850°C required for the sulfur cycles), high yields without catalysts in the thermal reactions, reasonable kinetics, relatively easy gas-solid or gas-liquid separations, unit operations that are commercially practiced, and international support. The efficiency of the hydrogen production process has been calculated for the current conceptual process design using a mass and energy balanced flowsheet as about 40% low heating value (LHV). The cost of hydrogen production has been estimated as $4.38 for 2015 technology and $3.01 for 2025 technology using the H2A cost analysis methodology.

May 2008