(515c) Using CaxLa1-xMn1-yXyO3 As Oxygen Carriers for Chemical-Looping Combustion

A new group of oxygen carrier (OC) materials based on the calcium manganate perovskite CaMnO_3-d have been investigated for use in chemical-looping combustion.   CaMnO_3-d  is an ABO₃-type of perovskite which is endowed with interesting properties by virtue of oxygen non-stoichiometry which creates mobile charge carriers by way of doping at the A- and B-sites in the parent compound. In this project compounds of the formula Ca_xLa_1-xMn_1-yX_yO_3+d (CLMX) were investigated as oxygen carrier materials.  A matrix of potential substituted Ca_xLa_1-xMn_1-yX_yO₃ (X = Fe, Ti, Cu, Mg) (CLMX) perovskites were synthesized using mechanical homogenization of primary solids in a rotary evaporator followed by drying and calcination at 1300°C. The resulting powders were subjected to net-shaping and particle fabrication via extrusion followed by crushing and sieving.  The oxygen release properties and the reactivity with methane and syngas were investigated using a batch fluidized batch reactor made of quartz.  A sample of 15 g of particles and a fuel flow of 450 Nml/min was used for all reactivity experiments. All of the materials showed high rates of oxygen release to the gas phase at 950°C, or so called uncoupling properties.  In addition the reactivity with methane was high, approaching 100% conversion for some of the materials at 950°C.  The oxygen carrier doped with Cu showed defluidization during the reducing period, which could explain the somewhat lower reactivity of this material.  The syngas conversion to CO₂ and H₂O was complete for all investigated materials.  The oxidized and reduced samples were also analyzed using x-ray powder diffraction.  Although the mechanical strength of the samples were somewhat low for use in a industrial CLC unit, the reactivity and very good uncoupling properties certainly make this low-cost system very interesting for CLC with different types of fuel.