As a promising approach for carbon dioxide capture, chemical looping combustion has been extensively investigated for more than two decades. However, the chemical looping strategy can be and has been extended well beyond carbon capture. In fact, significant impacts on emission reduction, energy conservation, and value-creation can be anticipated from chemical looping beyond combustion (CLBC). This article aims to demonstrate the versatility and transformational benefits of CLBC. Specifically, we focus on the use of oxygen carriers or redox catalysts for chemical production – a $4 trillion industry that consumes 40.9 quadrillion BTU of energy. Compared to state-of-the-art chemical production technologies, we illustrate that chemical looping offers significant opportunities for process intensification and exergy loss minimization. In many cases, an order of magnitude reduction in energy consumption and CO2 emission can be realized without the needs for carbon dioxide capture. In addition to providing various CLBC examples, this article elaborates on generalized design principles for CLBC, potential benefits and pitfalls, as well as redox catalyst selection, design, optimization, and redox reaction mechanism.

/pdf/chemical-looping-beyond-combustion-a-perspective-2ohy8fd521.pdf

Chemical looping beyond combustion – a perspective

Hydrogen is an attractive energy carrier due to its potentially high energy efficiency and low generation of pollutants, which can be used for transportation and stationary power generation. However, hydrogen is not readily available in sufficient quantities and the production cost is still high. Steam methane reforming (SMR) process is now the most widely used technology for H 2 production, but this process is complex and cannot get thorough carbon capture. Hydrogen production using chemical looping technology has received a great deal of attention in recent years because it can produce hydrogen with higher process efficiency and can capture carbon dioxide. Many researchers have carried out intensive research work on the hydrogen production processes using chemical looping technology. Based on the previous studies stated in the literature, the authors try to give an overview on the recent advances of two categories, chemical looping reforming (CLR) and chemical looping hydrogen production (CLH) processes. Besides, the characteristics of the processes are pointed out based on the comparison with the conventional SMR process. The existing technical problems and the aspects of future research of each approach are also summarized.

Review of hydrogen production using chemical-looping technology

The emergence of high-entropy materials (HEMs) with their excellent mechanical properties, stability at high temperatures, and high chemical stability is poised to yield new advancement in the performance of energy storage and conversion technologies. This review covers the recent developments in catalysis, water splitting, fuel cells, batteries, supercapacitors, and hydrogen storage enabled by HEMs covering metallic, oxide, and non-oxide alloys. Here, first, the primary rules for the proper selection of the elements and the formation of a favorable single solid solution phase in HEMs are defined. Furthermore, recent developments in different fields of energy conversion and storage achieved by HEMs are discussed. Higher electrocatalytic and catalytic activities with longer cycling stability and durability compared to conventional noble metal-based catalysts are reported for high-entropy materials. In electrochemical energy storage systems, high-entropy oxides and alloys have shown superior performance as anode and cathode materials with long cycling stability and high capacity retention. Also, when used as metal hydrides for hydrogen storage, remarkably high hydrogen storage capacity and structural stability are observed for HEMs. In the end, future directions and new energy-related technologies that can be enabled by the application of HEMs are outlined.

Recent progress of high-entropy materials for energy storage and conversion

Microwave-assisted pyrolysis of sewage sludge: A review

Chemical looping gasification of biomass with Fe2O3/CaO as the oxygen carrier for hydrogen-enriched syngas production

The high reaction temperature required for chemical looping in water splitting presents challenges in terms of producing stable oxygen carrier materials (OCMs). The currently available materials are generally prepared by a deposition method through which iron oxides and refractory supports are spatially separated, thus having low activity and stability. Here, we report CoFeAlOx as an OCM, in which the active phase of the CoFe alloy and the parent spinel support are homogeneously mixed into a solid solution. Using a variety of characterization techniques, we studied the exsolution and dissolution effects of the CoFe alloy on the spinel support in a chemical looping redox cycle and found that the exsolution process can be tailored by the reduction level, which determines the interface structure. When reduced by CO, the exsolved particles were similar to the deposited analogues, showing obvious sintering. However, for the sample reduced by CO and CO2, the exsolved CoFe alloy can be embedded into the support, with it re-emerging fresh and confined at each reduction period. After 20 cycles, it showed a high hydrogen production rate and outstanding stability, demonstrating that the controllable exsolution could significantly improve the high temperature redox performance. Based on these results, this study also provides a new dimension for designing improved redox materials for chemical looping, calcium looping, or solar-driven thermochemical applications.

Enhanced hydrogen production performance through controllable redox exsolution within CoFeAlOx spinel oxygen carrier materials

Chemical looping pyrolysis-gasification of biomass for high H2/CO syngas production

Chemical looping gasification (CLG) in a dual fluidized bed gasifier was proposed to increase the H2/CO ratio and to simplify the process in gasification. The gasifier offered two separate fluidized bed reactors, fuel reactor (FR) and steam reactor (SR), for biomass gasification and H2 production. Iron ore was used as the oxygen carrier (OC), providing lattice oxygen for gasification in the FR, transferring to the SR for reacting with steam to produce H2, and then achieving the circulation and reoxidation through the loop seal. The product gas from the FR and the SR could be controlled to make high H2/CO ratio syngas by this process. The experiment for the CLG of sawdust was conducted in a dual fluidized bed gasifier, regarding the influence of different FR temperatures, SR temperatures, steam/biomass (S/B) ratios, and steam preheating temperatures. The optimum operating condition was obtained by the analysis showed as follows: the FR temperature of 820 °C, the SR temperature of 910 °C, the S/B ratio of 1...

High H2/CO Ratio Syngas Production from Chemical Looping Gasification of Sawdust in a Dual Fluidized Bed Gasifier

The iron-based oxygen carrier with high oxygen transfer capacity has always been the key point in the chemical looping hydrogen generation (CLHG) process. In this study, CeO2-modified iron-based oxygen carriers with the porous reticular structure were prepared by the sol–gel method. Samples were tested in a thermogravimetric analyzer (TGA) and lab-scale fixed-bed reactor, respectively, to evaluate their capacities of hydrogen production and the resistance to carbon deposition or Fe3C formation. The effects of preparation conditions (CeO2 loading and [C6H8O7·H2O]/[PEG400] molar ratio) and experimental conditions (reducing atmosphere and temperature) on the physicochemical properties of CeO2-modified iron-based oxygen carriers were investigated. The initial screening test in TGA was done to select the samples with excellent reducibility and strong resistance to carbon deposition or Fe3C formation. Subsequent tests in the fixed-bed reactor were conducted to evaluate the redox characteristics and cyclic perfo...

Dewang Zeng

Papers

Enhanced hydrogen production performance through controllable redox exsolution within CoFeAlOx spinel oxygen carrier materials

Chemical looping pyrolysis-gasification of biomass for high H2/CO syngas production

High H2/CO Ratio Syngas Production from Chemical Looping Gasification of Sawdust in a Dual Fluidized Bed Gasifier

Performance of CeO2-Modified Iron-Based Oxygen Carrier in the Chemical Looping Hydrogen Generation Process

Continuous hydrogen production from non-aqueous phase bio-oil via chemical looping redox cycles