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AN OVERVIEW OF R&D ACTIVITIES FOR THE Cu-Cl CYCLE WITH EMPHASIS ON THE HYDROLYSIS REACTION
Figure 6: Measurement of oxygen evolution from Cu 2 OCl 2
as a function of temperature using mass spectrometry
2.50E-08
800
2.00E-08
Cu2OCl2 021709
50.7mg Homemade
Temp 021709
465ºC
700
600
MS signal for O 2
1.50E-08
1.00E-08
5.00E-09
402ºC
553ºC
500
400
300
200
Temperature (oC)
100
0.00E+00
0
50 60 70 80 90 100 110 120 130 140 150
Time (min)
partial validation of our conceptual design for a commercial hydrolysis reactor. Critical to obtaining
the high yields necessary for commercial operation is high mass and heat transfer. A spray reactor
has thus proposed in the conceptual process design. In order to achieve the mass and heat transfer
needed, the CuCl 2 slurry would be injected at 24 bar (obtained from a crystalliser unit) into a
hydrolysis reactor containing superheated steam. The pressure in the reactor is to be about 0.25 bar.
As the droplets enter the hot reactor, the pressure drop would cause the droplets/particles in the
slurry to be injected at supersonic speed. Under these conditions, the slurry would form a free jet.
As the CuCl 2 jet expands, it aspirates the superheated steam into the jet resulting in high mass and
heat transfer between the CuCl 2 droplets/particles and the steam. Thus, the need for an Ar carrier gas,
which was found to be critical in the laboratory, will be eliminated for commercial operation.
The test results with the ultrasonic nozzle were obtained with an estimated steam to copper
(S/Cu) ratio of 23 and the humidified Ar was injected co-currently with the CuCl 2 solution. Several
variables remain to be investigated, i.e. lower S/Cu ratios, counter-current instead of co-current
operation, and subatmospheric pressures. LeChatelier’s Principle predicts that reducing the pressure
in the hydrolysis reactor should reduce the S/Cu ratio. The effect of a reduced pressure was quantified
by the results of a sensitivity study using Aspen. Aspen predicts that a S/Cu ratio of 17 is needed for
essentially complete conversion at 375°C and atmospheric pressure while a S/Cu ratio of 13 is required
at 0.5 bar. The conceptual process design specifies that the hydrolysis reactor be run at 0.25 bar. The
pressure drop in the reactor is achieved by adding a low temperature steam ejector after the
condenser at the exit of the hydrolysis reactor in the conceptual design.
One of the most important characteristics of this cycle is the relatively low maximum process
temperature required, about 550°C. Early tests showed that a temperature of 530-550°C was required
for complete decomposition (Serban, 2004). The results of the decomposition studies with the Cu 2 OCl 2
produced with the ultrasonic nozzle also showed that the maximum temperature is near 550°C.
The results of the energy and mass balance from the current Aspen flow sheet/ heat exchanger
network optimised with pinch analysis gave an efficiency for the cycle of 39 to 41% (LHV), as shown in
Table 2. This result is based on assumptions regarding the performance of the electrolyser and the
crystalliser. In the electrolyser, 2H + is reduced to H 2 (g) and CuCl is oxidised to CuCl 2 . For the purposes
of the efficiency calculation, we have assumed cell operating parameters of 0.7 V and 500 mA/cm 2 for
2015. We have assumed technical improvements in membranes, electrocatalysts and electrode
materials will allow a reduction in cell emf to 0.63 V and 500 mA/cm 2 for 2025. This calculation assumes
a 40% factor for converting heat to electricity. In the crystalliser the spent anolyte is processed into a
CuCl 2 slurry suitable for the feed for the hydrolysis reactor.
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