A Dual Reactor for Isothermal Thermochemical Cycles of H2O/CO2 Co-Splitting Using La0.3Sr0.7Co0.7Fe0.3O3 as an Oxygen Carrier

Tatiya Khamhangdatepon,Unalome Wetwatana Hartley,Navadol Laosiripojana,Nuchanart Siri-Nguan,Thana Sornchamni

doi:10.3390/pr9061018

Abstract

Catalytic performance of La0.3Sr0.7Co0.7Fe0.3O3 (LSCF3773 or LSCF) catalyst for syngas production via two step thermochemical cycles of H2O and CO2 co-splitting was investigated. Oxygen storage capacity (OSC) was found to depend on reduction temperature, rather than the oxidation temperature. The highest oxygen vacancy (Δδ) was achieved when the reduction and oxidation temperature were both fixed at 900 °C with the feed ratio (H2O to CO2) of 3 to 1, with an increasing amount of CO2 in the feed mixture. CO productivity reached its plateau at high ratios of H2O to CO2 (1:1, 1:2, and 1:2.5), while the total productivities were reduced with the same ratios. This indicated the existence of a CO2 blockage, which was the result of either high Ea of CO2 dissociation or high Ea of CO desorption, resulting in the loss in active species. From the results, it can be concluded that H2O and CO2 splitting reactions were competitive reactions. Ea of H2O and CO2 splitting was estimated at 31.01 kJ/mol and 48.05 kJ/mol, respectively, which agreed with the results obtained from the experimentation of the effect of the oxidation temperature. A dual-reactors system was applied to provide a continuous product stream, where the operation mode was switched between the reduction and oxidation step. The isothermal thermochemical cycles process, where the reduction and oxidation were performed at the same temperature, was also carried out in order to increase the overall efficiency of the process. The optimal time for the reduction and oxidation step was found to be 30 min for each step, giving total productivity of the syngas mixture at 28,000 μmol/g, approximately.

Highlights

The continuous increase in anthropogenic, atmospheric CO2 concentrations, and rapid expansion in the widespread use of fossil fuels, such as coal, oil, and natural gas, have resulted in the serious, worldwide greenhouse effect [1,2]
The results indicate that at different ranges of reduction temperatures or oxidation The results indicate that at different rangeswere of reduction temperatures oxidation temperatures, different initial rates of reaction measured as shown inorFigure temperatures, different initial rates of reaction were measured as shown in Higher reduction temperatures render higher amounts of oxygen vacancies; the3
The oxygen storage capacity (OSC) was found to depend on the reducwork investigated thethe synthesis of gas productionThe via highest thermochemical cycles tionThis temperature rather than oxidation temperature

Summary

Introduction

The continuous increase in anthropogenic, atmospheric CO2 concentrations, and rapid expansion in the widespread use of fossil fuels, such as coal, oil, and natural gas, have resulted in the serious, worldwide greenhouse effect [1,2]. In comparison to the direct thermal decomposition of CO2 and H2 O at high temperatures, thermochemical methods of CO2 and H2 O decomposition are driven at proper lower temperatures by joining high temperature endothermic chemical reactions and low temperature exothermic chemical reactions. As such, they present a smart method for fuel generation at high rates and efficiencies without noble metal catalysts [3], which, via redox chemical reactions, go around the CO–H2 –O2 separation problem [4]

Methods

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Discussion

Conclusion