Development and testing of a combined catalyst/sorbent core-in-shell material for the production of high concentration hydrogen

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2008-01-01
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Albrecht, Karl
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Brent H. Shanks
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Chemical and Biological Engineering

The function of the Department of Chemical and Biological Engineering has been to prepare students for the study and application of chemistry in industry. This focus has included preparation for employment in various industries as well as the development, design, and operation of equipment and processes within industry.Through the CBE Department, Iowa State University is nationally recognized for its initiatives in bioinformatics, biomaterials, bioproducts, metabolic/tissue engineering, multiphase computational fluid dynamics, advanced polymeric materials and nanostructured materials.

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The Department of Chemical Engineering was founded in 1913 under the Department of Physics and Illuminating Engineering. From 1915 to 1931 it was jointly administered by the Divisions of Industrial Science and Engineering, and from 1931 onward it has been under the Division/College of Engineering. In 1928 it merged with Mining Engineering, and from 1973–1979 it merged with Nuclear Engineering. It became Chemical and Biological Engineering in 2005.

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1913 - present

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  • Department of Chemical Engineering (1913–1928)
  • Department of Chemical and Mining Engineering (1928–1957)
  • Department of Chemical Engineering (1957–1973, 1979–2005)
    • Department of Chemical and Biological Engineering (2005–present)

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Abstract

A combined catalyst and sorbent for the production of hydrogen from CH4 or CO was developed and tested. The combined catalyst and sorbent was a spherical multi-layered material having a CaO-based sorbent core and an outer shell composed mainly of alumina. The CaO sorbent core was employed to absorb CO2, one of the reaction products. The alumina shell protected the friable CaO core and also supported a Ni catalyst. The development of the material focused separately on the development of the core and shell. First, since the CO2 absorption capacity of CaO-based sorbents diminishes as they are repeatedly used and regenerated, the development of a more stable CaO-based sorbent was investigated. Both the addition of MgO, which acted as a sintering inhibitor, and severe initial calcination conditions for the CaO precursor limestone produced a more stable CaO sorbent. Second, an alumina-based material with good physical strength and high surface area was developed to serve as the shell of the core-in-shell material. The addition of either fine particle limestone or lanthanum oxide to the alumina shell formulation produced a material with enhanced physical strength, which was most likely due to the formation of a binding aluminate phase.

Reaction testing of the core-in-shell pellets with a 3:1 molar ratio of H2O:CH4 in the feed produced a high concentration of H2 via simultaneous application of the steam-methane reforming reaction, the water-gas shift reaction and the reaction of CO2 with CaO. This testing was conducted with a tubular fixed bed reactor over a temperature range of 550-650yC and a pressure range of 1.0-10.0 atm. The rapid absorption of CO2 by CaO produced CH4 and CO conversions greater than would have been possible without a sorbent. Lifecycle testing determined that a high concentration of H2 could be produced over 10 cycles of H2 production and sorbent regeneration. However, the length of time that H2 was produced diminished with each cycle due to a loss of CO2 absorption capacity by the CaO sorbent. Physical characterization of the pellets after lifecycle testing also revealed that some pellets fractured during lifecycle testing and that the Ni catalyst sintered.

Core-in-shell pellets with alternate shell formulations were also tested in the fixed bed reactor for the production of high concentrations of H2 from a mixture of CO and steam via the water-gas shift reaction. Three alumina shell formulations were tested: a formulation with mostly alumina in the shell, a formulation with 10 wt% Fe2O3 added to the alumina shell formulation and a formulation with Ni impregnated onto the shell. The rapid absorption of CO2 by the sorbent allowed for a high concentration of H2 to be produced and a high CO conversion to be achieved between 550-600yC at 1.0 atm with any of these formulations. However, once the CaO sorbent became loaded, only the formulation with Ni present converted CO to reaction equilibrium levels. On the other hand, by absorbing CO2 the formulation with mainly alumina in the shell appeared to be an attractive material for the production of H2 from syngas. Furthermore, this formulation would be resistant to sulfurous gases that might be present.

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Tue Jan 01 00:00:00 UTC 2008