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Oxidative coupling of methane (OCM) is a compelling strategy for the direct conversion of methane to C2+ hydrocarbons in order to produce fuels and value-added chemicals. Nevertheless, it remains c...

As one of the possible alternatives to the Haber–Bosch process, electrochemical ammonia synthesis has been attracting considerable interest in recent years. However, most electrocatalysts are confr...

The global market size for acetic acid is expected to increase at a high compounded annual growth rate over the next few years due to an increased demand from the end-users such as the automobile, ...

The transformation of CO2 to chemicals and fuels offers a means of CO2 utilization while mitigating the global carbon footprint. An attractive strategy involves the CO2 reforming of methane with ox...

To meet the globally growing energy demands, it is essential to develop schemes with higher fuel conversion efficiency at temperatures

Production of various value-added chemicals through natural gas conversion with syngas as an intermediate is becoming increasingly popular because of the abundance of natural gas and maturation of ...

Syngas production is highly critical to the manufacturing of many value-added products, and its economic prospects can be increased through the enhancement of fuel conversion and the syngas yield. ...

Chemical looping is an advanced material and energy conversion technology that can achieve both high-level process intensification and efficiency. To analyze chemical looping processes, it is essential to include process conditions that are realistic and comparable to those that are expected in industrial systems. Relevant variations in these conditions as occurred in bench versus industrial-scale systems include isothermal versus adiabatic operation of the reactors and local versus global process heat integration. Naturally, the types of reactors employed dictate how the reactor operation is to be conducted from the heat integration viewpoint in the overall process arrangement. As an example, in industrial applications, a fluidized bed reactor is operated near uniform temperature conditions. A fixed bed or a moving bed reactor, on the other hand, is typically operated adiabatically, and thus under the autothermal operation, the nonisothermal condition prevails, leading to different strategies for process simulations and heat integration requirements. This study presents the chemical looping process simulation based on a moving bed reactor used as a reducer for two H₂ generation process configurations under autothermal operating conditions. The two process configurations are represented by the two-reactor (reducer–combustor followed by the water–gas shift reaction) and the three-reactor (reducer–oxidizer–combustor with water splitting for H₂ generation in the oxidizer) chemical looping systems with each configuration producing H₂ in a different operating scheme. The simulation results are compared with the conventional steam methane reforming (SMR) system as a baseline case to underscore the attractiveness of the chemical looping configurations. Specifically, for each configuration, the parametric study under the adiabatic conditions is used to optimize the operating conditions that can satisfy the heat balance requirements and can achieve a maximum H₂ yield. The exergy analysis indicates that the two-reactor chemical looping and three-reactor chemical looping systems can achieve, respectively, a 4.0 and 11.4% increase in relative percentage in the overall process exergy efficiency over the conventional steam methane reforming system.

The methane-to-syngas (MTS) chemical looping process is an advanced methane reforming technology for the production of high purity syngas. The developed MTS process utilizes metal oxide oxygen carr...

Oxygen chemistry plays a pivotal role in numerous chemical reactions. In particular, selective cleavage of C-H bonds by metal oxo species is highly desirable in dehydrogenation of light alkanes. However, high selectivity of alkene is usually hampered through consecutive oxygenation reactions in a conventional oxidative dehydrogenation (ODH) scheme. Herein, we show that dual-functional Mo-V-O mixed oxides selectively convert propane to propylene via an alternative chemical looping oxidative dehydrogenation (CL-ODH) approach. At 500 °C, we obtain 89% propylene selectivity at 36% propane conversion over 100 dehydrogenation-regeneration cycles. We attribute such high propylene yield-which exceeds that of previously reported ODH catalysts-to the involvement and precise modulation of bulk lattice oxygen via atomic-scale doping of Mo and show that increasing the binding energy of V-O bonds is critical to enhance the selectivity of propylene. This work provides the fundamental understanding of metal-oxygen chemistry and a promising strategy for alkane dehydrogenation.

Syngas is a valuable chemical intermediate for producing commodity chemicals, such as olefins, methanol, liquid fuels, etc. The chemical looping route for syngas production presents an attractive a...

In chemical looping technology when applied to gasification, reforming, and chemical syntheses, the operating pressure is an important factor that dictates the reactant conversion and product forma...

Reforming technologies produce syngas that serves as an important intermediate in the production of fuels and chemicals in the chemical and petrochemical industry. Only recently has reforming technology based on the chemical looping concept been attempted. Most chemical looping studies have been performed under ambient pressure conditions, but most processes that use syngas operate at an elevated pressure. Understanding the effect that pressure has on syngas generation in a chemical looping reactor is essential to the design of the overall system. This study characterizes and compares the effect of pressures on syngas yields under various chemical looping reforming operating conditions. Specifically, in this study, an iron-based oxygen carrier is used for the chemical looping partial oxidation reaction of methane to form syngas. The equilibrium simulation is of direct relevance to process applications, as demonstrated by the methane and metal oxide co-current reactor system, where in previous studies, exp...

Chemical looping oxidative coupling of methane (CLOCM) is a promising process for direct methane conversion to C2 products. Under the chemical looping approach, the oxygen carrier that provides lattice oxygen, in place of molecular oxygen, is used for methane oxidation. This study performs redox experiments that probe the C2 selectivity enhancement properties of a Mg–Mn composite oxygen carrier through the use of a low concentration of Li dopant. It was found that the C2 selectivity of the Li-doped oxygen carrier in CLOCM is universally higher than that of the undoped Mg6MnO8 oxygen carrier with a maximum improvement in selectivity of ∼50%. Density functional theory simulation reveals that the Li dopant has a short-range effect on the formation of oxygen vacancies. The Li-doping-induced oxygen vacancy reduces the adsorption energy of methyl radicals and increases the C–H activation barrier. These findings provide a catalytic dopant screening strategy for CLOCM, which will substantially enhance the C2 sele...

A three-dimensional ECVT sensing technique is applied to imaging complex slugging phenomena of a gas–solid fluidized bed under ambient and elevated temperature conditions. The study indicates that the time interval between rising slugs decreases with an increase in the gas velocity, reaching a nearly steady time interval value of about 1 s between two slugs when the gas velocity is ∼1.7 m/s above the minimum fluidization velocity. The fluidized bed behaves as a bubbling fluidized bed at low gas velocities. In slugging regime, the slug rise velocity increases with the gas velocity. A mechanistic analysis of forces around the dense phase solid particles suggests that the relationship between the slug rise velocity and the gas velocity for the square-nosed slugging bed is not strictly linear and is highly related to the interparticle forces, internal friction of particles, and gas velocity in addition to the wall stress.

A novel design of a coal gasifier using the chemical looping concept is introduced in the present study for high purity, H2-rich syngas generation using coal and methane as cofeeds. In this work, an iron–titanium composite metal oxide (ITCMO), capable of cracking the heavy hydrocarbons produced in coal pyrolysis as well as regulating the product syngas purity, is used as the oxygen carrier. The cocurrent moving bed avoids back-mixing of solid and gas reactants, allowing both phases to interact, reaching thermodynamic equilibrium conditions at the reactor gas outlet. This paper focuses on demonstrating the cocurrent moving bed reducer with the ITCMO oxygen carrier. A sensitivity analysis is performed to determine the optimal operating conditions for converting Powder River Basin coal using ASPEN Plus modeling. The tar-cracking capability is ascertained by the gas chromatography–mass spectrometry analysis. The bench scale moving bed reducer substantiated its capability of achieving near-full conversion of t...

This study quantifies the advantages of a chemical looping reducer reactor modularization strategy that leverages two or more reducer reactors operating in parallel to enhance syngas production beyond what is achievable by a single reducer reactor or conventional processes. The modularized system incorporates CO2 capture and utilization as a feedstock in an iron–titanium composite metal oxide based chemical looping system to enhance coal based chemical production. Simulations conducted in ASPEN Plus software suggest that adopting a cocurrent moving bed reducer reactor based modularization strategy can improve syngas yield by greater than 11% over a single chemical looping reducer reactor. Experiments conducted on a bench scale reducer reactor confirm the findings of the simulations. The modularization simulation was scaled up and incorporated into commercial sized methanol and acetic acid production plants. Chemical looping modularization demonstrates the ability to reduce coal consumption by 25% over a b...

The cyclic redox reactivity of metal oxides plays an important role in many energy fields such as fuel cells, photocatalysis, and chemical looping. In chemical looping systems, oxygen carriers are required to have high reactivity, recyclability, and high oxygen carrying capacity. We utilize catalytic lanthanum dopants to dramatically change the reactivity with carbonaceous fuels while maintaining or even improving the recyclability of iron-based oxygen carriers. A low concentration of La dopant is applied to maintain the high oxygen carrying capacity. These results are substantiated by ab initio DFT+U and thermochemistry analysis and will have a significant impact on future chemical looping oxygen carrier design.

Directly upgrading natural gas is limited by the stability of its primary component, methane, and process economics. Since the 1980s, oxidative coupling of methane (OCM) has shown potential to produce ethylene and ethane (C2s). The typical OCM approach catalytically converts methane to C2 products using molecular oxygen, reducing process efficiency. To overcome this, chemical looping OCM converts methane to hydrocarbons via intermediate oxygen carriers rather than gaseous cofed oxidants. The chemical looping approach for OCM has been studied mechanistically for the first time with a Mn–Mg-based catalytic oxygen carrier (COC). The COC delivered stable performance in a fixed bed for 100 cycles for more than 50 h with a 63.2% C2 selectivity and 23.2% yield. These experimental results and original process simulations of an OCM chemical looping system for C2 or liquid fuel production with electricity cogeneration present a direct method for methane utilization.

Redox reactions between fine solid fuels, such as pulverized coal powder, and coarse oxygen carrier particles can be carried out in a fixed/moving bed reactor chemical looping system. The migration pattern of the solid fuel powder and its contact time with coarse particles can significantly affect the reaction rate and the product yield. A number of challenges exist in transporting/mixing of fuel powder and in removing noncombustible waste (e.g., coal ash) from the reactor vessel in the chemical looping operation. Thus, it is important to understand the hydrodynamic behaviors of fine particles in such situations. This study describes an experimental approach that examines migration characteristics of fine particles (Geldart A/B), in both spatial and temporal aspects, in a packed bed of coarse particles (Geldart D). The experimental variables include the particle size distribution of the fine powder, the fine to coarse mass ratio, and flow conditions. At a given upward aeration flow within the range that i...

For gas to liquid (GTL)-type applications, partial oxidation of methane (CH4) is a viable route for conversion of natural gas to valuable chemicals. The oxygen for this partial oxidation process can be supplied using solid oxygen carriers, which can be single or mixed metal oxides. A particular partial oxidation scheme for CH4 conversion consists of two reactors, using Fe-based oxygen carrier particles, which circulate within the two units and undergo cyclic reduction–oxidation (redox) reactions. The solid carriers, therefore, serve as a vehicle for oxygen between the units, enabling clean conversion of the fossil fuel with high-purity product streams generated. Unlike the conventional combustion and/or gasification, the gaseous products of the two reactors are inherently separated. This allows for minimization of downstream processing and gas separation, making it a highly efficient energy conversion process. For applications involving high-pressure downstream processing (such as producing syngas as an i...

The L-valve, as a solids flow control device, has been used extensively in fluidized beds and circulating fluidized beds for controlling the solids circulation rate. Knowledge on L-valves, however,...

This study reports on the hydration characteristics in the three-step carbonation–calcination reaction (CCR) process with intermediate steam hydration. Specifically, experimental results of sorbent reactivation in a fluidized bed steam hydration reactor are presented along with the effect of the operating gas velocity (Ug) and different calcination conditions on the hydration reaction. The enhancing effect of increasing Ug on the hydration rate is evident but limited with a threshold at 0.3 m/s, above which the bulk phase mass transfer effects are less significant. The highest hydration conversion of 83% is achieved in 30 min at the highest Ug of 0.5 m/s. However, increasing Ug also yields lower steam utilization during hydration; thus an optimal operating condition with respect to both the solid and steam conversions shall be determined via an overall process analysis. In addition, the parametric effect of different calcination conditions, specifically, the calcination temperature, time, and reactor type...

This work evaluates the environmental impact of conventional and calcium looping processes implemented with CO2 separation to gain broad insight and identify opportunities for future improvement. These systems are assessed at multiple scales: equipment, value chain and economy, and emissions of CO2, water use, land use, and energy return on investment are estimated. The difference in the energy quality of hydrogen and electricity products is considered in developing aggregate metrics. Calcium looping is found to be superior due to its smaller life cycle impacts. However, this process has a smaller energy return on investment due to the higher energy and resource requirements in the calcination and air separation steps. Future efforts for reducing the energy intensity of these steps by developing new technologies and optimizing existing methods are recommended.

This work reports a novel low-cost and environmental-friendly preparation strategy for core-shell structured composite microparticles and discusses its formation mechanism. Different from most conventional strategies, which involve coating or coating-like processes, this reported strategy uses irreversible solid-phase ionic diffusion in a gas-solid reaction cycle (e.g., reduction and oxidation of Fe) to gradually move the shell material from a core-and-shell material mixture microparticle to the surface. Without the need for solvent as do many conventional processes, this novel process only involves gas-solid reactions, which reduces environmental impact. To substantiate this conceived strategy, a micrometer-sized microparticle made up of a mixture of Fe2O3 and Al2O3 powders is first reduced by H2 and then oxidized by O2 over 50 cycles at 900 °C. These reactions are known to proceed mainly through the diffusion of solid-phase Fe cations. SEM and EDX analyses verify the formation of an Al2O3 core-Fe2O3 shell structure at the end of the 50 reaction cycles. If the cyclic reactions of a microparticle proceed mainly through the diffusion of gaseous-reactant-derived O anions such as the mixture of Fe2O3 and TiO2 instead of solid-phase Fe cation diffusion, no formation of the core-shell structure is observed in the resulting microparticle. These two opposing results underscore the dominating role of solid-phase ionic diffusion in the formation of the core-shell structure. A 2-D continuum diffusion model is applied to account for the inter-Fe-particle bridging and directional product layer growth phenomena during an oxidation reaction. The simulation further verifies the conceived core-shell formation strategy.

In recent years, chemical looping has evolved into a promising technique for carbonaceous fuel conversion. The chemical looping technology using biomass material as feedstock could provide a process that is environmentally attractive and sustainable. The focus of this study is to examine the kinetics of biomass decomposition and to evaluate the feasibility of using biomass as a renewable source for chemical looping processes. A series of thermogravimetric experiments were carried out under inert and reactive gas environments to investigate the kinetics of the devolatilization and gasification stages of biomass decomposition. Since tar derived from biomass pyrolysis is a major concern for many biomass conversion techniques, the cracking of biomass derived light tar using iron oxide-based composites was also investigated in a fixed bed reactor. Furthermore, a bench scale moving bed reactor was used to study the feasibility of biomass chemical looping in both cocurrent and countercurrent gas–solid contact modes.

Eggshell waste, which contains 95% calcium carbonate (CaCO3), presents itself as an inexpensive calcium-based sorbent for removal of carbon dioxide (CO2) in combustion streams used to generate electricity. The utilization of eggshell waste in CO2 capture via cyclic carbonation-calcination reactions (CCR) was investigated in this work. Using thermogravimetric analysis, the CO2 capture capacity for multiple acetic acid pretreated eggshell samples was studied. This pretreatement generates a mesoporous structure, allowing the eggshell-derived sorbent to reach higher conversions over more CCR cycles while also removing the eggshell’s protein-rich membrane. Six acetic acid treatments were also explored for regeneration of spent sorbents after multiple cycles. The regeneration of spent sorbents with acetic acid provided a 38% improvement in CaO conversion over untreated shells after ten cycles. The eggshell membrane contained highly valuable Type X collagen, which can be recovered through the course of shell pre...

The syngas chemical looping (SCL) process has been demonstrated at The Ohio State University for the conversion of gaseous fuels, such as natural gas and syngas, to sequestration-ready carbon dioxi...

The coal direct chemical looping (CDCL) combustion process using an iron-based oxygen carrier has been developed and demonstrated in a 25-kWth subpilot unit. The CDCL subpilot unit is the first chemical looping demonstration unit with a circulating moving bed for the solid fuel conversions. To date, the CDCL subpilot unit at OSU has been operated for more than 550 h. The feasibility of the subpilot unit with various types of solid fuels including sub-bituminous coal and lignite coal has been tested. This article discusses the operational experience of a successful 200-h integrated, continuous demonstration with sub-bituminous coal and lignite coal. Throughout the 200-h continuous operation, the CDCL subpilot unit showed steady behavior in terms of solid circulation, coal handling, and oxygen carrier reactivity and recyclability. Tests with both coals confirmed more than 90% coal conversion with 99.5 vol % purity of CO2 achieved in the reducer. The sound design of the reducer allowed for nearly full coal c...

The decreasing CO2 capture capacity of calcium sorbents over multiple reaction cycles poses a significant challenge to the large-scale cyclic carbonation-calcination process. Several approaches, including intermediate hydration, have been suggested to overcome this limitation. Until this study, most hydration studies have been performed at laboratory-scale using thermogravimetric techniques at conditions that may not be feasible for process scale-up. Moreover, data on the design of a steam hydrator suitable for the calcium looping process is not available. For the first time, this study reports the design of a bench-scale high-temperature steam hydrator for calcium sorbent reactivation. The hydrator, consisting of a fluidized-bed reactor with additional internals, was evaluated using cold-flow tests following which several reaction parameters were investigated in the hot unit. The results obtained from these high-temperature steam hydration tests (300–500 °C) are discussed here. Specifically, at an averag...

Electrical capacitance volume tomography (ECVT) is a newly developed imaging technique that can quantify three-dimensional (3D) multiphase flows in a complex, geometric flow field. In this study, the 3D phase distribution images inside a gas–solid circulating fluidized bed (CFB) are obtained using ECVT. Specifically, measurements are made at a riser section and a 90° bend-shape riser exit section of the CFB. Inside the vertical riser, a symmetric core–annulus structure with a low solids holdup in the riser center along with a high solids holdup near the riser wall is observed. The average volume solids holdup and the thickness of the annulus decrease with the superficial gas velocity. A core–annulus flow structure is formed both in the vertical and horizontal parts of the bend. The annulus structure is noncentro-symmetric in the horizontal part of the bend. The solids holdup in the annulus near the top wall area in the bend is higher than that in other locations of the annulus. At a higher superficial gas...

The present work explores the fundamental mechanism behind the increased surface area and pore volume of CaO after hydration. First, a widely believed mechanism, the “physical attrition theory”, is...

The CaO–CaCO3 cycle offers a promising high-temperature CO2 capture technology, but the decay in CO2 absorption capacity of CaO over multiple cycles poses a challenge that needs to be overcome to m...

A novel process scheme for hydrogen production from coal with in situ CO2 capture, known as the coal-direct chemical looping (CDCL) gasification process, is discussed in this article. The CDCL process utilizes an iron oxide based oxygen carrier as a chemical looping medium to indirectly gasify coal into separate streams of H2 and CO2. ASPEN Plus reactor simulation models based on both thermodynamic equilibrium limitations and kinetic limitations are developed to analyze individual CDCL reactors. Process simulations are subsequently performed to estimate the performance of the CDCL process under various mass and energy management schemes. Reactor modeling results indicate that a moving bed reducer can effectively convert coal while reducing the oxygen carrier. The reduced oxygen carrier can in turn be oxidized by steam to produce hydrogen in a moving bed oxidizer. The fates of pollutants as well as the effects of various process operating parameters such as carbon and iron oxide conversions are also evalua...

The calcium looping process (CLP), which is being developed at The Ohio State University (OSU), is a clean coal technology for the production of hydrogen (H2) and electricity from coal-derived syng...

The syngas chemical looping (SCL) process employing the gas–solid counter-current flow pattern demonstrates an innovative approach to generate hydrogen and/or electricity from syngas accompanied with in situ carbon capture. Iron-based oxygen carriers donate oxygen for complete syngas conversion in the reducer. The reduced oxygen carriers are then oxidized by steam and/or air to generate hydrogen and/or heat in the oxidizer and/or the combustor, respectively. Previous studies have reported the performance of the iron-based oxygen carriers, the advantages of a moving bed reducer and oxidizer, and simulation of various parametric effects on the reactor design of the reducer, oxidizer, and combustor for a continuous system. In this study, a 25 kWth subpilot SCL unit was designed based on the simulated criteria and constructed to demonstrate the feasibility of generating high purity hydrogen with in situ carbon capture. Two test runs were presented using 4.5 mm × 2.5–4.5 mm cylindrical oxygen carriers comprisi...

Carbon dioxide (CO2) capture using calcium-based sorbents for post- and pre-combustion applications has the potential to become a viable technology. When applied to a pre-combustion system, the presence of calcium sorbents facilitates process intensification by combining the CO2 removal step with the reactions generating the fuel gas [syngas, hydrogen (H2), etc.] in a single step. Such a process is also capable of producing a high-purity sequestration-ready CO2 stream. The enhanced steam methane reforming (SMR) using the Calcium Looping Process (CLP) has been investigated in this work. The CLP comprises three reactors: the carbonation reactor or carbonator where the thermodynamic constraint of the reforming and water gas shift (WGS) reaction is overcome by the incessant removal of the CO2 product resulting in the production of high-purity H2, the calciner where the calcium sorbent is regenerated and a sequestration-ready CO2 stream is produced, and the hydrator where the regenerated sorbent is reactivated...

In this study, the high-pressure carbonation kinetics of calcium oxide (CaO) derived from three calcium-based sorbents, namely, limestone (CaCO3), calcium hydroxide [Ca(OH)2], and precipitated calcium carbonate (PCC), used in the calcium looping process (CLP) system were studied using a magnetic suspension balance (MSB) analyzer. Different total pressures (1000–15000 torr) and concentrations of CO2 (10–30%) were tested to determine their effects on the carbonation reaction rate at a specific operating temperature of the CLP system, namely, 700 °C. The carbonation reaction rate was found to increase with increasing concentration of CO2 (10–30%) at a constant total pressure of 5000 torr and to exhibit first-order kinetics. However, the total pressure has an effect on the carbonation reaction rate only at lower total pressures. With a 20% CO2 stream, the reaction rate was observed to increase until the total pressure reached 4000 torr, beyond which a further increase in total pressure had a negative effect o...

The chemical looping process (CLP) using calcium-based sorbents to capture CO2 through cyclic carbonation–calcination reaction (CCR) before, during, or after the conversion of carbonaceous fuel occurs, is a viable CO2 control technology. With extensive past and current research efforts, the basic process concept has been found to be attractive at larger scales. Additionally, process simulations based on experimental results indicate that the parasitic energy consumption for this high temperature process is relatively low compared to low temperature processes such as the amine-based process. The ability of the calcium-based sorbents to maintain stable reactivity and physical integrity in cyclic reaction under severe operating conditions is one of the most important criteria for the success of the calcium looping technology. Despite being abundant and cheap, calcium-based sorbents derived from naturally occurring precursors, such as limestone and dolomite, suffer from rapid reactivity deterioration after hi...

Experimental study of dry HCl removal from synthesis gas or flue gas using CaO sorbents, in the context of CaO-based chemical looping processes, is reported. The study was first conducted in a TGA and a fixed-bed reactor to test the effects of chloridation temperature, sorbent particle size, HCl concentration, and space velocity on the HCl capture capacity. The chloridation reactivity deterioration of CaO sorbents with multicyclic carbonation−calcination reaction (CCR) and/or at high calcination temperatures, which are of notable relevance to the CaO-based chemical looping processes, was also investigated. In addition, precipitation (activation) and hydration (reactivation) were used to enhance initial sorbent reactivity and to reactivate the deactivated sorbents, respectively. The effects of deactivation, activation, and reactivation were explained by the morphological property change of the sorbents. To further elucidate the solid phase reaction mechanism of CaO and HCl, ionic transfer behavior during c...

Much of the fundamental research reported in the literature on gas−solid fluidization properties has been performed with large gas−solid fluidized beds. However, little is known regarding gas−solid...

Enhancement in the production of high purity hydrogen (H2) from fuel gas, obtained from coal gasification, is limited by thermodynamics of the water gas shift reaction. However, this constraint can...

The concept of chemical looping reactions has been widely applied in chemical industries, for example, the production of hydrogen peroxide (H2O2) from hydrogen and oxygen using 9,10-anthraquinone as the looping intermediate. Fundamental research on chemical looping reactions has also been applied to energy systems, for example, the splitting of water (H2O) to produce oxygen and hydrogen using ZnO as the looping intermediate. Fossil fuel chemical looping applications had been used commercially with the steam-iron process for coal from the 1900s to the 1940s and had been demonstrated at a pilot scale with the carbon dioxide acceptor process in the 1960s and 1970s. There are presently no chemical looping processes using fossil fuels in commercial operation. A key factor that hampered the continued use of these earlier processes for fossil energy operation was the inadequacy of the reactivity and recyclability of the looping particles. This factor led to higher costs for product generation using the chemical ...

The techno-economic performances of various coal-based hydrogen and electricity cogeneration processes are examined under a carbon-constrained scenario. The baseline coal gasification process and the novel membrane and syngas chemical-looping processes are evaluated. Aspen Plus simulation is first performed to analyze the process efficiencies on the basis of a common set of assumptions. This is followed by economic analysis using the cost analysis principles suggested by the U.S. Department of Energy [Cost and Performance Baseline for Fossil Energy Plants, 2007]. The results indicate that the novel membrane and syngas chemical-looping strategies have the potential to notably reduce the energy and cost penalties for CO2 capture in coal conversion processes.

The calcium looping process (CLP) is one of the clean coal technologies being developed for the production of hydrogen (H2) and electricity from coal-derived syngas. It integrates the water−gas shift reaction with in situ carbon dioxide (CO2), sulfur, and halide removal in a single-stage reactor. In the CLP, a regenerable calcium-based sorbent is used to react with and remove CO2, sulfur, and halide impurities from the synthesis gas during the production of H2. The removal of CO2 creates a favorable equilibrium and drives the water−gas shift reaction forward per Le Chatelier’s principle enabling the production of high-purity H2. In this investigation, the feasibility and optimum process conditions for the production of H2 in the absence of a water−gas shift catalyst have been described. Calcium oxide (CaO) sorbent has been found to enhance H2 yield to a large extent even in the absence of a water−gas shift catalyst. Specifically, at high pressures, high carbon monoxide (CO) conversion and H2 purity (>99%)...

Clean-coal technologies that include carbon dioxide and sulfur capture during the production of electric power, liquid fuels, and hydrogen represent a major thrust area. The calcium looping process...