(570k) Hydrogen Generation From Acetic Acid and Ammonia Using Pd-Based Membrane Reactors

Pd-based membrane reactors have been shown to be extremely efficient in generating and separating high purity hydrogen from various fuels. In the current study steam reforming of acetic acid and ammonia decomposition reactions were separately carried out in membrane reactors containing a Pd ?nanopore' [1] membrane.

Acetic acid is the main component of the aqueous stream obtained upon fast pyrolysis of algae. The hydrogen generated in the membrane reactor can be used in fuel cells. Alternately the hydrogen can subsequently be used for deoxygenation of pyrolysis oil (organic phase obtained from pyrolysis) so as to make it suitable for use as bio-fuel. The steam reforming of acetic acid was carried out in both a conventional packed bed reactor [PBR] and a packed bed membrane reactor [PBMR] containing a ?nanopre' Pd membrane. A Ni/Al2O3 catalyst was used and the study was carried out at different temperatures, pressures and flow rates. The talk will present a comparison of the results for the PBR and the PBMR. The focus will be on the conversions, hydrogen productivities, and utilizations that were obtained. The rate limiting steps will also be discussed along with techniques to overcome them and increase productivity.

In previous studies [2, 3, 4] both radial transport of hydrogen and permeation of hydrogen through the membrane have been shown to be the productivity limiting steps. One way to overcome these limitations is to deposit a catalyst layer on the surface of the Pd-based membrane. Some results related to depositing a Ni/Al2O3 layer on a Pd membrane will also be discussed. The catalytic membrane was initially used for carrying out NH3 decomposition, which has been shown to be severely affected by slow radial transport of hydrogen [3]. By depositing the catalyst as a layer on the Pd membrane the radial distance that the hydrogen has to travel has been drastically reduced. The comparison of NH3 decomposition in a catalytic membrane reactor with a PBMR will also be presented.

References

1. Nair, B., and Harold, M.P. ?Pd Encapsulated and Nanopore Hollow Fiber Membranes: Synthesis and Permeation Studies,? J. Membrane Sci., 290, 182-195 (2007) 2. Nair, B., and Harold, M.P. ?Experiments and Modeling of Transport in Composite Pd and Pd/Ag Coated Alumina Hollow Fibers,? J. Membrane Sci , 311, 53-67 (2008) 3. Israni, S.H., Nair, B., and Harold, M.P., ?Hydrogen Generation and Purification in a Composite Pd Hollow Fiber Membrane Reactor: Experiments and Modeling,? Catalysis Today,139, 299-311 (2008) 4. Israni, S.H., and Harold, M. P., ?Methanol steam reforming in Pd-Ag membrane reactors: Experiments and modeling of single-fiber packed bed membrane reactor', In preparation