(32c) Steam Methane Reforming in a Membrane Reactor for Hydrogen Production

Economical generation of pure hydrogen represents a critical technology component for power generation by PEM fuel cells in a variety of mobile and stationary power applications. Hydrogen is conventionally produced by steam reforming of hydrocarbon fuels followed by a two-step water gas shift (WGS) reaction and hydrogen separation and purification by pressure swing adsorption (PSA). Combining the WGS reactor and hydrogen purification steps into a single membrane reactor, has the potential to significantly reduce the capital and operating costs of producing hydrogen, and consequently, reduce the price of hydrogen to the consumer. Due to simultaneous reaction and product separation, it is possible to increase the efficiency of the overall process by shifting the equilibrium and thereby producing more hydrogen than would be possible using the conventional approach, providing additional benefit to the consumer. High performance, high-temperature hydrogen separation membranes thus represent a key enabling technology for efficient hydrogen production using synthesis gas derived from a variety of feedstocks.

Palladium-alloy foils and extruded tubes are known to be completely selective for hydrogen separation, however, they are a relatively expensive option for large scale industrial applications. These product formats exhibit low hydrogen flux rates due to the thickness necessary for structural stability. By depositing thin palladium-alloy film on a porous substrate, hydrogen flux and structural stability of the composite Pd-alloy membrane is increased while reducing the membrane costs. Both the thin metal film deposition process and the porous substrate characteristics influence development of successful composite membranes for hydrogen separation application. Pall Corporation has successfully developed high flux and selectivity hydrogen separation membranes by depositing thin Pd-alloy films on tubular ceramic/porous stainless steel composite (AccuSep® Inorganic media) substrates. These composite membranes have demonstrated performance approaching U.S. DOE's year 2010 hydrogen flux target with structural stability against thermal cycling necessary for their commercial application.

Utilization of the Pd-alloy composite membranes in a membrane reactor configuration for conducting steam methane reforming (SMR) reaction allows operation at temperatures much lower than conventional SMR temperatures with simultaneous hydrogen separation for producing high purity hydrogen. This paper will present current status of Pd-alloy membrane technology at Pall Corporation. Results of model simulations to determine the effect of various operating conditions of steam to carbon ratio, space velocity, membrane temperature, and feed pressure on the potential benefits of conducting the SMR reaction in a membrane reactor configuration are discussed.

The composite membrane technology will reduce the capital cost of equipment required for hydrogen production by combining the hydrogen generation and purification steps. The U.S. DOE has set year 2010 targets of 250 scfh/ft2 for hydrogen flux and $1000/ft2 for membrane module cost. Combining these goals into a single goal of $4/scfh of hydrogen capacity sets a relevant, challenging goal for commercialization. This paper will also present the techno-economic evaluation of the membrane reactor process for hydrogen production and approaches for meeting the hydrogen production cost target.