Preparation and Oxygen Permeation of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) Perovskite-Type Membranes: Experimental Study and Mathematical Modeling Amir Atabak Asadi, † Amir Behrouzifar, † Mona Iravaninia, † Toraj Mohammadi,* ,† and Afshin Pak ‡ † Research Centre for Membrane Separation Processes, Chemical Engineering Department, Iran University of Science and Technology (IUST), Narmak, Tehran, Iran ‡ Engineering Department of Oil & Gas Special Projects, Iranian Centeral Oil Field Company, Tehran, Iran ABSTRACT: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ nanopowder, synthesized via an autocombustion technique, was pressed into disk-shaped membranes. Results of permeation experiments revealed that oxygen permeation flux increases as temperature, feed side oxygen partial pressure, and feed and sweep gas flow rates increase, while it decreases with membrane thickness and permeate side oxygen partial pressure. A Nernst-Planck based mathematical model, including surface exchange kinetics and bulk diffusion, was developed to predict oxygen permeation flux. Considering nonelementary surface reactions and introducing system hydrodynamics into the model resulted in an excellent agreement (RMSD = 0.0344, AAD = 0.0274 and R 2 = 0.9960) between predicted and measured fluxes. Feed side surface exchange reactions, bulk diffusion, and permeate side surface exchange reaction resistances are in the range of R ex ′ =7 × 10 3 to 9 × 10 6 , R diff =1 × 10 5 to 2 × 10 7 , and R ex ″ =1 × 10 4 to 2 × 10 7 (s/m), respectively. The permeation rate-limiting step was determined using the membrane dimensionless characteristic thickness. 1. INTRODUCTION Oxygen production from the air is of great importance in a variety of industries. Ultrapure oxygen can be produced by mixed ionic and electronic conducting (MIEC) ceramic membranes at low cost and high efficiency. 1 Among MIEC materials, perov- skite type materials such as La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) have become of great interest due to their high oxygen permeation fluxes and excellent stabilities. 2 Oxygen permeation flux through perovskite membranes is mainly affected by perovskite composition, 3-5 powder preparation route, 6 and also membrane shaping and sintering conditions, 7-12 including sintering temperature and dwell time, heating and cooling rates, and even the furnace atmosphere. 13 Not only do operating conditions such as temperature, upstream oxygen concen- tration, feed and permeate side pressures, feed and sweep gases and their flow rates, and feed impurities even at very low concentrations influence oxygen permeability of the mem- brane, 14-16 but features such as thickness and age also affect the oxygen permeation rate through the membrane. 17-19 Developing a mathematical model based on experiments is worthwhile, not only to avoid wasting money and time for more data gathering but also to predict oxygen permeability through the membrane under specified conditions. Therefore, many researchers attempted to model oxygen permeation through perovskite membranes. 20-25 The main weakness of these models is assuming the surface reactions of oxygen as an elementary oxidation and reduction reaction, besides neglecting the effects of flow rates, which both lead to a diversion from accurate oxygen permeability evaluation. In this paper, oxygen permeability of the La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ membranes was studied experimentally. The influence of temperature, feed side oxygen partial pressure, and feed and sweep gas flow rates on oxygen permeation through four mem- branes with different thicknesses was investigated. After that, a mathematical model, which relates oxygen permeation flux to temperature, oxygen partial pressure upstream and down- stream, membrane thickness, and feed and sweep gas flow rates, was developed. Finally, to sum up the results and evaluate the proposed model, experimental data were compared with the values predicted by the model. With the aid of improvements, the mathematical model predictions showed excellent agree- ment with the experimental data. Moreover, the characteristic thickness of the membranes and the contribution of different resistances to oxygen permeation were calculated, and the effects of all operating parameters were discussed briefly. 2. EXPERIMENTAL SECTION 2.1. Materials. Required materials for the synthesis of La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) powder include metallic nitrates (La(NO 3 ) 3 ·6H 2 O, Sr(NO 3 ) 2 , Co(NO 3 ) 2 ·6H 2 O, and Fe(NO 3 ) 3 ·9H 2 O); ammonia solution; EDTA acid; citric acid; and ammonium nitrate, which were supplied by Merck Co. with a purity of higher than 99.9%. 2.2. Preparation of LSCF Powder. The La 0.6 Sr 0.4 Co 0.2 - Fe 0.8 O 3-δ membranes were prepared via an autocombustion method, based on the results obtained in our previous work. 26 First, the required amount of EDTA acid is dissolved in an ammonium solution. Second, the stoichiometric amounts of metal nitrates are dissolved into deionized water separately, and after that, these solutions are mixed to obtain a solution of metal nitrates. Citric acid is then introduced into this solution. The molar ratio of EDTA acid to citric acid to total metallic Received: October 23, 2011 Revised: January 14, 2012 Accepted: January 19, 2012 Published: January 19, 2012 Article pubs.acs.org/IECR © 2012 American Chemical Society 3069 dx.doi.org/10.1021/ie202434k | Ind. Eng. Chem. Res. 2012, 51, 3069-3080