Title page for ETD etd-11142007-101423


Type of Document Dissertation
Author Hacarlioglu, Pelin
Author's Email Address phacarli@vt.edu
URN etd-11142007-101423
Title Experimental and Modeling Studies of the Methane Steam Reforming Reaction at High Pressure in a Ceramic Membrane Reactor
Degree PhD
Department Chemical Engineering
Advisory Committee
Advisor Name Title
Oyama, Shigeo Ted Committee Chair
Cox, David F. Committee Member
Gibbs, Gerard V. Committee Member
Marand, Eva Committee Member
Keywords
  • steam reforming of methane
  • one-dimensional model
  • two-dimensional model
  • silica-alumina membrane
  • hydrogen
Date of Defense 2007-11-12
Availability unrestricted
Abstract
This dissertation describes the preparation of a novel inorganic membrane for hydrogen permeation and its application in a membrane reactor for the study of the methane steam reforming reaction. The investigations include both experimental studies of the membrane permeation mechanism and theoretical modeling of mass transfer through the membrane and simulation of the membrane reactor with 1-D and 2-D models.

A hydrothermally stable and hydrogen selective membrane composed of silica and alumina was successfully prepared on a macroporous alumina support by chemical vapor deposition in an inert atmosphere at high temperature. Before the deposition of the silica-alumina composite, multiple graded layers of alumina were coated on the alumina support with a mean pore size of 100 nm by the sequential application of three boehmite sols with gradually decreasing sol particle sizes of 630, 200 and 40 nm, respectively. The resulting supported composite alumina-silica membrane had high permeability for hydrogen in the order of 10-7 mol m-2 s-1 Pa-1 at 873 K with a H2 /CH4 selectivity of 940 and exhibited much higher stability to water vapor at the high temperature of 873 K. In addition, the same unusual permeance order of He>H2>Ne previously observed for the pure silica membrane was also observed for the alumina-silica membrane, indicating that the silica structure did not change much after introduction of the alumina. The permeation of hydrogen and helium through vitreous glass and silica membranes was modeled using ab initio density functional calculations. Comparison of the calculated activation energies to those reported for vitreous glass (20–40 kJ mol -1) indicated the presence of 5- and 6-membered siloxane rings, consistent with the accepted structure of glass as a disordered form of cristobalite.

The experimental studies of the steam reforming of methane were examined at various temperatures (773-923 K) and pressures (1-20 atm) with a commercial Ni/MgAl2O4 catalyst in a hydrogen selective silica-alumina membrane reactor and compared with a packed bed reactor. One-dimensional and two-dimensional modeling of the membrane rector and the packed bed reactor were performed at the same conditions and their performances were compared with the values obtained in the experimental study. Improved methane conversions and hydrogen yields were obtained in the membrane reactor compared to the packed bed reactor at all temperatures and pressures. From the two modeling studies, it was also found out that the two-dimensional model performed better in the membrane reactor case especially at higher pressures.

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