Effect of pressure on copper/copper-oxide system functioning as an oxygen carrier in chemical looping combustion

Chemical Looping Combustion (CLC) is a promising technology that will utilize more efficient harvesting of energy along with decreased CO2 emissions into the atmosphere. In CLC system the emissions are composed of CO2 and H2O allowing the CO2 to be captured and disposed of in an environmentally more acceptable manner. CLC uses two basic reactions in this process; an oxidation step, and a reduction step as shown in Figure 1. The oxygen may come from air, or a purified oxygen supply. The oxygen is combined in the oxidation step with a metal to form a metal oxide. Typically the metal is either Ni or Cu, however there are a number of other metals that are being explored. Once the metal oxide is formed it is transferred to the fuel reactor where a hydrocarbon based fuel consumes the oxygen from the metal oxide and returns it back to a metallic state where the metal can be recycled and oxidized again. This step generates ample heat that is used to generate steam for the steam generation of electricity. Figure 1, (Chemical Looping Combustion) Copper is a very promising metal for CLC. The advantages of copper lie in it's two oxidation states. The first oxide that forms is copper(I) oxide, Cu2O, the next oxide formed is copper(II) oxide, CuO. Once the CuO is formed, the exposure to a non-oxidizing environment between our observed experimental range 850°C and 985°C in air, the copper oxide will spontaneously decompose into a different copper oxide, Cu2O. This trait makes copper a preferred oxygen carrier, because faster switching times can be implemented. This step from pure copper to the full CuO state is a difficult transition that requires a lot of work to explain. The step from Cu Cu(I) is explained by a stepwise oxidation. The kinetics and nature of the stepwise oxidation from Cu Cu(II) is analyzed as follows: Overall oxidation 2 Cu(s) + O2(g)↔ 2 CuO(s) Cu → Cu(I) 4Cu(s) + O2(g)↔ 2Cu2O(s) Cu(I)→ Cu(II) 2Cu2O(s) + O2(g)↔ 4 CuO(s) Based on the pseudo first-order in copper kinetics and half order in oxygen pressure applicable for each step in the oxidation reaction, increasing the pressure during the oxidation step should increase the rate of oxidation by the square root of the pressure in atmospheres. For example, if the reaction was conducted under the pressure condition 25 atm the rate of oxidation, i.e. reaction rate, should increase by 5 times. In this work, we will test these reaction kinetics using high pressure thermogravimetic analysis.