HIGH TEMPERATURE OXYGEN SORPTION PROCESS FOR AIR SEPARATION AND OXYGEN REMOVAL
Perovskite-type oxides have been extensively studied as memrbane material for oxygen perrmeation due to its infinitely large permselectivity and reasonably high permeation flux. However, major hurdles exist for commerization of membrane separation on this type of materials. A high temperature oxygen sorption process was proposed recently. This work is dedicated to study the fundamentals of this proposed novel oxygen sorption process, focusing on material selection, sorption equilibrium and kinetics and other sorption properties of perovskite-type sorbents. Two perovskite-type oxides, La 0.1 Sr 0.9 Co 0.5 Fe 0.5 O 3- ? (LSCF-1) and 0.1 Sr 0.9 Co0.9Fe 0.1 O 3- ? (LSCF-2) were selected as candidate materials for this study. These two materials exhibit large change of oxygen nonstoichiometry in the temperature and oxygen partial pressure ranges of the investigation. A simple cluster defect model was successfully employed to describe the dependence of oxygen nonstoichiometry on oxygen partial pressure. A semi-empirical equation was developed from the cluster model. Heat of sorption was estimated by three different approaches: isosteric method, heat of reaction in cluster defect model, and simultaneous DSC-TGA measurement. For LSCF-1, the heat of sorption determined by these three methods agree well with each other, and is in the range of 100~133 kJ/mol. Within the ranges of temperature and P O2 of this study, LSCF-1 showed good structural stability, while a phase transition between brownmillerite and perovskite was found on LSCF-2. For oxygen sorption on fine powder, surface reaction is believed to be the rate-limiting step. Generally, surface reaction rate increases with P O2 , which brings about fast sorption and relatively slow desorption processes. In the investigation of particle size effect, crystalline size, instead of aggregate size, was found to be the determining factor of surface reaction rate. Experimental study was conducted for air separation on this new type sorbent. Fast sorption process and relatively large sorption capacity were found in air separation at temperature equal to or higher than 400(C. Comparing to fast sorption process, desorption takes much longer time for full regeneration. This highly asymmetric sorption and desorption breakthrough behaviors result from slow desorption rate and highly favorable sorption isotherms of these two materials.
School:University of Cincinnati
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:perovskite oxygen sorption equilibrium kinetic air separation
Date of Publication:01/01/2002