Inorganic membrane reactor: case study : methane steam reforming

Sukamta

Abstract

Methods of preparation of an inorganic composite membrane and the performance of
the membranes obtained have been investigated in this work. The membranes
obtained were microporous silica coated y/alumina and dense palladium coated oc-
alumina membranes. The preparations of the membranes have been carried out by the
dip coating technique and electroless plating method respectively. Characterization of
the membranes obtained with single gas permeation measurements at high
temperature and various pressures were accomplished. The performance of both
membranes has been examined for methane steam reforming on a commercial
nickel/alumina catalyst (ICI 57-4). A simulation study on methane steam reforming
for both conventional and membrane reactor has been completed to examine the
performance of these membrane reactors.
For the dip coating method, a microporous silica/y-alumina membrane was obtained
and single gas permeations for hydrogen and nitrogen at high temperature have been
measured. At 700 K the H2/N2 selectivity was 4.63. From the correlation between
temperature and the permeation of nitrogen in the silica membrane it could be
concluded that the permeation occurs in the transition region, which is controlled by
both the Knudsen mechanism and some viscous flow. At a range of temperature
between 623- 743 K the pore diameter calculated by hydrogen permeation is 0.57 nm.
The effects of temperature on the permeation of the membrane and hydrothermal
stability have been investigated. A hydrothermal exposure at around 723 K for more
than 720 hours during methane steam reforming does not make any membrane
transformation that leads to pore changes. A dense palladium coated a-alumina membrane was prepared by the electroless
plating method. The single gas permeation for hydrogen and nitrogen at high
1 O
temperature has been measured. At 700 K the HI and N2 flux were 7.96 cm /cm .min
and 0.05 cm3/cm2.min respectively and the selectivity of H2/N2 was 175.03. The
pressure dependence of the tfe flux for the Pd membrane was found to be to the power
of 0.5, which is the theoretical value. The Fb diffusion through the metal membrane is
activated by temperature and can be described by an Arrhenius equation. The
activation energy (Ea) is 17.94 kJ/mol for the temperature range of 673-823 K.
Both membranes were studied for methane steam reforming by employing them as
membrane reactors. The steam reforming focused on the improvement effects of the
membrane on the conversion of methane. The effects of pressure, methane feed flow
rate and ratio of steam/methane, as well as sweep gas on reactions have been
investigated experimentally under conditions of no diffusion limitation.
The influence of the membrane with a hydrogen permeable wall on the conversion of
methane has also been simulated for methane steam reforming in a tubular catalytic
reactor. The effects of the main variables as applied in the experiments of the methane
steam reforming have been investigated in the simulation study either. The results of
the simulation have been compared to the results of the experimental works.
The general behavior is similar for both silica and palladium membrane reactors, i.e.:
by selectively removing one of the products from the reaction mixture, the methane
conversion can be improved to values higher than the thermodynamic equilibrium composition. From these results, it was concluded that in line with the permeation
studies, the performance of the palladium composite membrane was far superior to
that of the silica membrane for the steam reforming of methane.

Citation

Sukamta. Inorganic membrane reactor: case study : methane steam reforming. (Thesis). Salford : University of Salford

• Thesis Type: Thesis
• Deposit Date: Oct 3, 2012
• Award Date: Jan 1, 2004