Chemical Looping Air Separation Using a Perovskite-Based Oxygen Sorbent: System Design and Process Analysis

Abstract

Oxygen is a critical industrial gas whose global market is projected to reach $48 billion/year within this decade. However, oxygen production is highly energy-intensive because of the limited efficiency of the commercial cryogenic air separation technology. The present study systematically investigated a chemical looping air separation (CLAS) approach as an alternative to cryogenic distillation. In particular, a Sr0.8Ca0.2Fe0.4Co0.6O3−δ (SCFC) oxygen sorbent was used as the basis for both experimental and simulation studies. To demonstrate the sorbent robustness, experimental studies were carried out over 10,000 redox cycles in a bench-scale testbed. Excellent sorbent stability and >90% oxygen purity were achieved using steam as the purge gas. Oxygen purity can be further increased to >95% by optimizing the operating conditions and pressure swing absorption cycle structure. Based on the experimental results, a CLAS system design and a process model were established. The process model estimates a base case CLAS energy consumption of 0.66 MJ/kg O2. This represents a 15% decrease compared to cryogenic air separation (0.78 MJ/kg O2). It is noted that most of the thermal energy consumed by CLAS is at relatively low temperatures (∼120 °C). When accounting for the quality of this low-grade heat, an energy consumption as low as 0.40 MJ/kg O2 can be anticipated for a practical system. Sensitivity analysis was also performed on the various CLAS operational and design parameters such as reactor sizes, pressure drop, thermodynamic driving forces, oxygen uptake and release rates, heat loss, and the energy consumption for steam generation. It was determined that CLAS has excellent potential to be an efficient oxygen production technology. This study also highlights the importance of developing advanced sorbents with suitable redox thermodynamics and fast redox kinetics for improved efficiency and smaller reactor sizes.

Oxygen Storage Capacity of Co-Doped SrTiO3 with High Redox Performance

“…Oxygen storage materials (OSMs) have been used in various technologies such as solid oxide fuel cells, , oxygen separation, − and oxygen sensors − and have also been applied to unique chemical reactions such as those in the purification of automotive exhaust gases − and chemical looping processes. − This is because OSMs are able to reversibly release and store oxide ions inside their crystal structures depending on the reaction conditions, which include temperature and oxygen partial pressure. ,,, To improve OSM properties, these materials are designed to maintain their original framework, even after releasing oxide ions from the crystal lattice. Structural transitions based on crystallographic relationships during the oxygen-release process are generally referred to as topotactic transformations.…”

Mixed oxides as multi-functional reaction media for chemical looping catalysis

“…In addition to the limited catalytic selectivity and stability, the key obstacles hindering the development of ODH technologies resides in the safety concerns over co-feeding oxygen with hydrocarbon feedstocks, and the high cost and energy consumptions for oxygen generation. In fact, state-ofthe-art cryogenic air separation technology itself only achieves a 25% second law efficiency, or B0.78 GJ per tonne O 2 in terms of actual energy consumption, 11,12 making it a highly energy and emission intensive industrial process.…”

Precursor engineering of hydrotalcite-derived redox sorbents for reversible and stable thermochemical oxygen storage

“…1a) 2 . This concept has been extended to a variety of chemical processes, including chemical looping combustion (CLC) 4,5 , methane reforming and partial oxidation 6-8 , CO 2 conversion 9-11 , hydrogen production 12,13 , air separation [14][15][16][17] , and redox catalytic processes for chemical…”