(137c) Stability Study of Dense Cermet Membranes for Hydrogen Separation

ABSTRACT

Argonne National
Laboratory is developing dense cermet (i.e. ceramic-metal composite) hydrogen
transport membranes (HTMs) for
separating hydrogen from mixed gases, particularly product streams generated
during coal gasification and/or methane reforming. Hydrogen separation with
these membranes is nongalvanic (i.e., it does not use electrodes or an external
power supply to drive the separation), and hydrogen separated from the feed
stream is of high purity, so post-separation steps are unnecessary.

These cermet membranes (60-70vol%
Pd with Y₂O₃-stabilized ZrO₂) with
thickness of 10-20 mm were prepared by conventional ink/paste
painting and co-sintering techniques on a porous substrate (alumina or
zirconia). Nongalvanic hydrogen permeation flux in the temperature range of 400°C-600°C were measured. The chemical stability of
membranes was tested in various gas mixtures that contained H₂, CO,
CO₂, and/or H₂S. The dense HTM demonstrated high
selectivity for H₂ over CO and CO₂. When tested in
a gas mixture that contained 30% CO₂ and 1% CO at 400-600 °C. HTM
cermet membrane showed continuous slow performance degradation; however, the
observed flux degradation can be fully reversed. Because
H₂S reacts with Pd-containing membranes to form palladium sulfide
(Pd₄S), which impedes hydrogen permeation through the membranes, the
Pd/Pd₄S phase boundary was determined in the temperature
range of 400-600°C using various feed gases with 10-50% H₂ and
≈5-100 ppm H₂S.  Tests
in H₂S-containing atmospheres showed that the membrane is stable at 500°C in gases that contain 10% H₂
and 15-20 ppm H₂S for 200 hrs and at 550°C in gases that contain 10% H₂
and 25-30 ppm H₂S for 100 hrs. These results suggest that
Pd-containing cermet membranes are promising candidate for hydrogen
separation/purification under coal gasification conditions. The present
status of HTM development at Argonne will be presented in this talk.

Work supported
by the U.S. Department of Energy, Office of Fossil Energy, National Energy
Technology Laboratory's Clean Fuels Program, under
Contract DE-AC02-06CH11357.