Review of Oxygen Carriers for Chemical Looping with Oxygen Uncoupling (CLOU): Thermodynamics, Material Development, and Synthesis

Abstract

Global warming and climate change are most likely linked to the increasing concentration of the greenhouse gas carbon dioxide (CO2) in the atmosphere. Additionally, the consumption of fossil fuels is predicted further to increase in the coming decades, particularly due to the rapid development of populous countries such as Brazil, India, and China. Therefore, it is imperative to develop and implement processes that avoid the emission of anthropogenic CO2. One possible midterm solution is carbon‐dioxide capture and storage (CCS). In this context, the so‐called chemical‐looping combustion (CLC) process, that is, an emerging 3rd‐generation CCS technology, is particularly attractive due to its very low predicted CO2‐capture costs compared to the currently available technology (i.e., amine scrubbing). In CLC, lattice oxygen from a solid‐state oxygen carrier is used to combust a hydrocarbon fuel, which yields, after the condensation of steam, a pure stream of CO2 suitable for sequestration. To allow the application of CLC to solid fuels, chemical looping with oxygen uncoupling (CLOU) has been proposed. Here molecular oxygen is provided by using the decomposition reaction of the oxygen carrier, thus, effectively the solid fuel is combusted in an oxyfuel mode. Importantly, a cornerstone of the CLOU process is the development of suitable oxygen carriers. In the first part of the review we discuss the thermodynamic properties of various CLOU materials. Subsequently, recent advances in the development of novel oxygen carriers are summarized. In particular, we focus on the physical and chemical properties of the new materials and the synthesis strategies employed. The review is concluded with an outlook on the CLOU process.

Use of natural ores as oxygen carriers in chemical looping combustion: A review

“…iG-CLC involves a direct feed and gasification of the solid fuel in the fuel reactor and fluidization through the addition of steam, CO 2 or a mixture of these gases. CLOU uses unique OCs that readily release gaseous oxygen and rather than gasifying with additional CO 2 or steam, gasification takes place in the FR using this released O 2 (Adanez et al, 2012;Imtiaz et al, 2013;Mattisson et al, 2014;Cormos, 2017). While each of these processes has strengths and weaknesses the real task in the CLC process is carried out by the oxygen carrier itself.…”

“…However many of these methods increase production costs for the OC and therefore decrease the economic feasibility of such systems (Porrazzo et al, 2016;Abad et al, 2007). The use of raw metal ores has been investigated by numerous groups as a method of providing a readily available and cheap oxygen carrier for the chemical looping process Wang et al, 2015a;Adanez et al, 2012;Imtiaz et al, 2013). The objective of this paper is to compile the latest work involving the use of natural ores as OCs in CLC processes.…”

Chemical and calcium looping reforming for hydrogen production and carbon dioxide capture

“…The release of gaseous oxygen is important for gasification of solid fuels, because in principle they must first be gasified by H 2 O or CO 2 before reaction with the oxygen carrier can take place, and this is an inherently slow step. Arguably, the most promising of these is CuO, which can release O 2 in the reaction (Eqn (16.15)), although the ability of Mn to perform in the presence of other metals such as iron makes it a potentially important candidate (Imtiaz, Hooseini, & M€ uller, 2013) and the area of doping less reactive systems such as the iron one to improve performance is receiving increasing attention, especially where coal combustion is considered (Fan & Siriwardane, 2014):…”

Reduction kinetics analysis of sol–gel-derived CuO/CuAl2O4 oxygen carrier for chemical looping with oxygen uncoupling

“…In principle, the capability of a certain material to release/uptake O 2 cyclically is first determined by its thermodynamic properties. Imtiaz et al [8] summarized the thermodynamics and experimental studies concerning the development of the materials that are commonly used as OCs for CLOU, i.e., CuO/Cu 2 O, Mn 2 O 3 /Mn 3 O 4 and Co 3 O 4 /CoO. Among the monometallic oxides, the CuO/Cu 2 O system has received considerable attention since it has some advantageous characteristics such as high oxygen transport capacity, stable recyclability of oxygen release and uptake, moderate price, being exothermic for fuel combustion in the FR, and being environmental friendly [9].…”