(395an) Synthesis and Evaluation of Stable Oxygen-Selective BaO Sorbent for Air Separation

Air separation unit is required for the production of pure oxygen for the oxy-fuel combustion. Cryogenic air separation is suitable for the large-scale air separation but requires high energy consumption. Nitrogen-selective adsorptive air separation is not appropriate for large-scale oxygen production and has poor selectivity. Oxygen-selective BaO/BaO₂ sorbent had been used for air separation as Brin process before cryogenic air distillation but it is known the BaO/BaO₂ sorbent has a poor stability at high temperature. In this study, to provide the multicylce operation capability, oxygen-selective BaO sorbent with uniformly mixed MgO which can stabilize BaO/BaO₂ particles at high temperature was prepared by precipitation of double carbonate and reduction to oxide. From thermogravimetric analysis, sorption isotherm interestingly showed an abrupt increase around the transition oxygen pressure. When the oxygen pressure was below 124 mmHg at 700^oC, sorption of O₂ hardly occured. However, sorption isotherm curve sharply increased when the pressure increased above 124 mmHg. As the temperature increased, the transition O₂ pressure increased because decomposition of BaO₂ to BaO was favored at high temperature. Sorption capacity at about 600 mmHg O₂ was about 2 mmol/g at 700^oC, which enables high productivity of O₂. The prepared sorbent exhibited a good stability during 10 times cyclic operations of sorption and desorption at 700^oC because MgO acts as a barrier against sintering of BaO/BaO₂. The time for 80% of sorption and desorption at 700^oC were around 1 to 2 min, meaning the uniformly mixed MgO/BaO sorbent has fast reaction kinetics.