Niranjani Deshpande

Shale gas-to-syngas chemical looping process for stable shale gas conversion to high purity syngas with a H2 : CO ratio of 2 : 1

The shale gas-to-syngas (STS) chemical looping process was conceived by Fan and associates in 2013 for the production of high-purity syngas from shale gas. The STS process producing syngas does not require the use of molecular oxygen from air separation and steam. This paper describes the rationale for the process concept with experimental data that substantiates the process validity. Specifically, the STS process consists of a co-current gas (shale gas)–solid (metal oxides) moving bed contact mode reducer operation with metal oxides for shale gas conversion to syngas. The reduced metal oxides from the reducer operation are regenerated via an oxidation operation with air. Various active metal oxides or metal oxide composites can be utilized. However, it is through the combination of desired metal oxides and co-current moving bed reducer that high syngas purity and a desirable H2 : CO molar ratio of ∼2 : 1 can be achieved. In this study, active iron–titanium composite metal oxide (ITCMO) materials are used as the oxygen carrier for the demonstration of the STS process. The desirable thermodynamic property of ITCMO is a key factor for the generation of high quality syngas. The co-current moving bed provides a desirable gas–solid contacting pattern that minimizes carbon deposition and maximizes the syngas yield. The syngas produced by the STS process can achieve a H2 : CO molar ratio of ∼2 : 1 with little CO2, CH4 and steam, which is required for downstream processes to produce liquid fuels and chemicals. The experimental results for reaction kinetics including oxygen carrier recyclability and pressure effects are obtained by thermogravimetric analysis (TGA), and syngas generation using a fixed bed, a bench-scale moving bed, and a sub-pilot scale moving bed reactor demonstrations are achieved in this study. The bench and sub-pilot demonstrations confirm that the syngas produced by the STS process is close to thermodynamic equilibrium with the reduced ITCMO. Furthermore, simulation studies are conducted to compare the efficiency of the STS process with a conventional autothermal natural gas reforming process.

Nanostructure formation mechanism and ion diffusion in iron–titanium composite materials with chemical looping redox reactions

Iron oxide composites are enabling materials in energy conversion systems including chemical looping and photocatalysis. Extensive earlier experimental findings indicate that inert oxides such as titanium oxide can greatly improve the reactivity of iron oxide over multiple redox cycles. Knowledge on the evolution of the nanoscale morphology of the Fe–Ti materials during the oxidation and reduction is thus of considerable importance. It is also of interest to the fundamental understanding of the ion diffusion mechanism in the reaction processes. In this study, Fe–Ti composite microparticles undergoing cycles of oxidation and reduction are examined at the nano-scale, and the interfacial characteristics of the iron titanium oxides within the composites are probed. Nanobelts are observed to simultaneously form on the microparticle surface during the oxidation at 700 °C, while microblades are found at 900 °C. Additionally, unlike pure iron microparticles that become dense on surface due to sintering effect, Fe–Ti microparticles are transformed into porous particles after redox cycles. The atomistic thermodynamics methods and density functional theory calculations are carried out to investigate the ionic diffusion and vacancy formation during the oxidation and reduction process. A number of surface configurations are considered, and the Ti–Ti–O– terminated surface is computed to the most stable surface structure at experimental conditions. It was found that in oxidation processes, surface Ti atoms are more favorable for oxygen adsorption and dissociation than Fe atoms. The energy barrier of Fe ion diffusion towards the surface, on the other hand, is lower than Ti ion diffusion, which contributes to the Fe2O3-dominant nanobelt formation. The volume change due to high temperature associated with the solid state transformation at the Fe2O3/FeTiO3 interface produces compressive stresses, which stimulate Fe2O3 nanobelt growth to accompany the interface reaction. Also, as the vacancy formation energy of FeTiO3 is lower than Fe2O3 in the reduction process, it indicates that it is easier for a FeTiO3 surface to form vacancy defects, thereby enhancing the porous surface structure formation and O2 diffusivity. The good agreements between experiments and DFT calculations further substantiate nanostructure formation mechanism in redox reactions of iron titanium composite materials.

High Purity Hydrogen Production with In-Situ Carbon Dioxide and Sulfur Capture in a Single Stage Reactor

Enhancement in the production of high purity hydrogen (H{sub 2}) from fuel gas, obtained from coal gasification, is limited by thermodynamics of the water gas shift (WGS) reaction. However, this constraint can be overcome by conducting the WGS in the presence of a CO{sub 2}-acceptor. The continuous removal of CO{sub 2} from the reaction mixture helps to drive the equilibrium-limited WGS reaction forward. Since calcium oxide (CaO) exhibits high CO{sub 2} capture capacity as compared to other sorbents, it is an ideal candidate for such a technique. The Calcium Looping Process (CLP) developed at The Ohio State University (OSU) utilizes the above concept to enable high purity H{sub 2} production from synthesis gas (syngas) derived from coal gasification. The CLP integrates the WGS reaction with insitu CO{sub 2}, sulfur and halide removal at high temperatures while eliminating the need for a WGS catalyst, thus reducing the overall footprint of the hydrogen production process. The CLP comprises three reactors - the carbonator, where the thermodynamic constraint of the WGS reaction is overcome by the constant removal of CO{sub 2} product and high purity H{sub 2} is produced with contaminant removal; the calciner, where the calcium sorbent is regenerated and a sequestration-ready CO{sub 2} stream is produced; and the hydrator, where the calcined sorbent is reactivated to improve its recyclability. As a part of this project, the CLP was extensively investigated by performing experiments at lab-, bench- and subpilot-scale setups. A comprehensive techno-economic analysis was also conducted to determine the feasibility of the CLP at commercial scale. This report provides a detailed account of all the results obtained during the project period.