Gasification will likely be the cornerstone of future energy and chemical processes due to its flexibility to accommodate numerous feedstocks such as coal, biomass, and natural gas, and to produce a variety of products, including heat and specialty chemicals. Advanced integrated gasification combined cycle schemes require the production of clean hydrogen to fuel innovative combustion turbines and fuel cells.

This research will focus on development and assessment of membranes tailored for application in severe environments associated with syngas conversion. The overall objective is to make significant advances toward developing low-cost membrane materials and architectures that have high hydrogen selectivity, provide high hydrogen fluxes, and resist degradation by syngas-laden contaminants. The NETLRegional University Alliance (NETL-RUA) Hydrogen and Clean Fuels Project will focus on development of hydrogen separation technologies tailored for conditions consistent with post-warm gas cleaning and integration into water-gas shift technologies. Development and demonstration of syngas conversion technologies will facilitate the advancement of affordable fuels, intermediate chemicals, and power from coal-based feeds.

Proposed Fuels Research at NETL
Designing metallic alloys for hydrogen separation membranes applicable to the elevated temperatures in a syngas environment poses significant challenges. In terms of bulk structure, a membrane microstructure that demonstrates long-term stability at high operating temperatures is required. The structure needs to have high solubility and diffusivity for hydrogen atoms, allowing fluxes capable of meeting performance targets in real gas environments. Other

Simple schematic of a hydrogen separation palladium (Pd) membrane

significant challenges are related to the surface of the membrane alloys. The alloy surface is required to have catalytic activity for hydrogen dissociation and to maintain this activity for extended periods of time. However, at elevated temperatures, the syngas environment poses opportunities for various reactions to take place on the surface of metals. Syngas species containing oxygen, sulfur, and carbon have been shown to have deleterious effects on membrane surfaces. Therefore, the alloy surface has to be extremely resistant to these reactions to maintain high catalytic activity. Development of a more durable membrane that can withstand and function under real operating conditions may be more important than focusing on a flux goal.

Surface of a palladium-based membrane alloy showing the growth of sulfides that occurred during exposure in a gasifier

While membranes must still have desirable flux properties, thicker membranes that are more stable at higher temperatures may, relative to cost, be of greater value.

This research will focus on elevated temperature conditions where high efficiencies of separation are possible, and effects of sulfur species are minimized. The proposed three-year project is aimed at providing a design basis for a robust hydrogen separation module based on metal membrane technology. This NETL-RUA Hydrogen and Clean Fuels Project will incorporate an integrated approach, combining computational study, laboratory experimentation, and coupon/slip-stream exposure of membrane alloys for use in syngas environments. Specific research efforts will focus on understanding the following—

  • The influence of hydrogen sulfide on surface catalytic activity.

  • Surface stability within syngas environments.

  • Bulk stability and bulk transport, which includes any effect of surface products.

  • The knowledge-base’s application to design and optimization of a membrane module.

  • Opportunities for the integration of membrane technologies into other unit operations.

  • Novel membrane materials identified for use in syngas environments.

The successful execution of this research will result in an advanced understanding of bulk and surface chemical phenomena that influence membrane performance and the design of engineered materials tailored for operation in syngas environments.

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