Thermodynamic possibilities and constraints of pure hydrogen production by a chromium, nickel, and manganese-based chemical looping process at lower temperaturesReportar como inadecuado




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Chemical Papers

, Volume 61, Issue 2, pp 110–120

Received: 25 August 2006Revised: 03 October 2006Accepted: 02 November 2006

Abstract

The reduction of chromium, nickel, and manganese oxides by hydrogen, CO, CH4, and model syngas mixtures of CO + H2 or H2 + CO + CO2 and oxidation by water vapor has been studied from the thermodynamic and chemical equilibrium point of view. Attention was concentrated not only on the convenient conditions for reduction of the relevant oxides to metals or lower oxides at temperatures in the range 400–1000 K, but also on the possible formation of soot, carbides, and carbonates as precursors for the carbon monoxide and carbon dioxide formation in the steam oxidation step. Reduction of very stable Cr2O3 to metallic Cr by hydrogen or CO at temperatures of 400–1000 K is thermodynamically excluded. Reduction of nickel oxide NiO and manganese oxide Mn3O4 by hydrogen or CO at such temperatures is feasible. The oxidation of MnO and Ni by steam and simultaneous production of hydrogen at temperatures between 400 and 1000 K is a difficult step from the thermodynamics viewpoint. Assuming the Ni—NiO system, the formation of nickel aluminum spinel could be used to increase the equilibrium hydrogen yield, thus, enabling the hydrogen production via looping redox process. The equilibrium hydrogen yield under the conditions of steam oxidation of the Ni—NiO system is, however, substantially lower than that for the Fe—Fe3O4 system. The system comprising nickel ferrite seems to be unsuitable for cyclic redox processes. Under strongly reducing conditions, at high CO concentrations-partial pressures, formation of nickel carbide Ni3C is thermodynamically favored. Pressurized conditions during the reduction step with CO-CO2 containing gases enhance the formation of soot and carbon-containing compounds such as carbides and-or carbonates.

Keywordshydrogen chromium nickel manganese chemical looping thermodynamics  Download to read the full article text



Autor: K. Svoboda - A. Siewiorek - D. Baxter - J. Rogut - M. Punčochář

Fuente: https://link.springer.com/







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