This review highlights various aspects of current palladium membrane research and serves as a comprehensive bibliography covering palladium membrane preparation methods and applications. There are many promising uses for palladium membranes, although widespread use of the available technologies is constrained primarily by the high cost of palladium, lack of durability due to hydrogen embrittlement, and susceptibility to fouling. Various researchers in the field are tackling these problems and fabricating thinner palladium alloy composite membranes that better withstand contaminantion and thermal cycling. What has been accomplished to address these issues and the directions presently being explored are discussed.

Innovations in palladium membrane research

The permeability of hydrogen in bulk palladium at elevated temperatures and pressures

The high-temperature rate of reaction of the homogeneous, reverse water–gas shift reaction (rWGSR) has been evaluated in quartz reactors with rapid feed preheating under both low- and high-pressure conditions. The form of the power-law rate expression was consistent with the Bradford mechanism. The Arrhenius expressions for the reaction rate constant, corresponding to the empty reactor, were in very good agreement with the low-pressure results of Graven and Long, but yielded rate constants roughly four times greater than those obtained in our packed reactor and those reported by Kochubei and Moin and by Tingey. Reactor geometry was not responsible for these differences because computational fluid dynamics simulations revealed similar residence time distributions and comparable conversions when the same kinetic expression was used to model the rWGSR in each reactor. Most likely, the empty NETL reactor and the Graven and Long reactor did not attain an invariant value of the concentration of the chain carrier (H) at low reaction times, which led to an overestimation of the rate constant. Conversions attained in an Inconel® 600 reactor operating at comparable conditions were approximately two orders of magnitude greater than those realized in the quartz reactor. This dramatic increase in conversion suggests that the Inconel® 600 surfaces, which were depleted of nickel during the reaction, catalyzed the rWGSR. © 2004 American Institute of Chemical Engineers AIChE J, 50: 1028–1041, 2004

High-Temperature Kinetics of the Homogeneous Reverse Water-Gas Shift Reaction

The kinetics of the high-temperature (1070–1134 K), low- and high-pressure gas-phase forward water–gas shift reaction (fWGSR) were evaluated in an empty quartz reactor and a quartz reactor packed with quartz particles. The power-law expression for the reaction rate was consistent with the Bradford mechanism and was invariant with respect to pressure. The experimental rate constant was lower than that published by Graven and Long, and slightly higher than estimates obtained using the reaction rate expression derived from the Bradford mechanism in conjunction with values of reaction rate constants obtained from the GRI database. Similar experiments conducted using a reactor composed of Inconel® 600, a representative reactor shell material, exhibited substantially enhanced rates of reaction. A simple power-law rate expression was incorporated into a surface-catalyzed plug flow reactor (PFR) model to correlate the results between 600 and 900 K. Palladium and palladium–copper alloy surfaces, representative of hydrogen membranes, were also shown to enhance the fWGSR rate, but not as much as the Inconel® 600 surfaces. © 2005 American Institute of Chemical Engineers AIChE J, 2005

Uncatalyzed and wall‐catalyzed forward water–gas shift reaction kinetics

This chapter provides an up-to-date overview on the production of biomass-derived syngas by biomass gasification based technologies. Without being comprehensive, each section focused on relevant examples of processes that have been technically proven at pilot or demonstration scales together with some recent research work that put perspectives for the future. It starts by presenting some of the most promising gasification reactors considered for syngas production. It then addresses the secondary gas treatment covering the most critical gas cleaning up and gas conditioning stages. By the end of the chapter, recent trends toward process intensification in the whole process of syngas production are depicted. A full discussion on selected relevant process intensification strategies is included to show the critical role played by synergy between chemistry, catalysis, reaction and process engineering involving an interdisciplinary and multi-scale integrating approach.

Biomass Gasification to Produce Syngas

A novel configuration for hydrogen production from the water gas shift reaction is proposed, using high temperature to enhance the rate of reaction and employing a hydrogen separation membrane for the collection of the high purity hydrogen product. Experimental high-temperature, high-pressure flux measurements have been made on a material that shows promise for such an application. Mixed oxide and metal “cermet” ion-transport disk membranes, fabricated at Argonne National Laboratory, were evaluated for hydrogen permeability on a unique high-temperature, high-pressure test unit constructed at the National Energy Technology Laboratory. Hydrogen permeation was found to be proportional to ΔPH20.5. At 700°C, the membrane permeability was 9.62×10−3 [cm22/min][mol/lit]0.5, or 5.63×10−9 [mol/m s Pa0.5]. The membrane permeability increased to 3.31×10−2 [cm2/min][mol/lit]0.5, or 1.76×10−8 [mol/m s Pa0.5] at 900°C. The membrane material was also characterized for surface changes and structural integrity using scanning electron microscopy/X-ray microanalysis, and X-ray photoelectron spectroscopy as a function of temperature, pressure, and hydrogen exposure. Although the membrane performed well for the short periods of time employed in this study, long-term stability remains a concern. The feasibility of using this mixed-oxide ceramic membrane to remove hydrogen from the reaction mixture was modeled for the optimization of the water-gas shift reaction. This reversible reaction is characterized by a very low equilibrium constant at elevated temperatures (>800°C); consequently CO conversion at these temperatures is typically less than 50%. In the scenario modeled, CO conversion was increased from 35% in the absence of a membrane to 79% with a membrane present, with still higher values possible if hydrogen was actively removed from the permeate side of the membrane. In the model, the effectiveness of the configuration is limited by the buildup of hydrogen partial pressure on the permeate side of the membrane. The model provided estimates of the conversion of CO attained for a specified feed, reactor size and permeate pressure.

Evaluation and Modeling of a High-temperature, High-pressure, Hydrogen Separation Membrane for Enhanced Hydrogen Production from the Water-gas Shift Reaction

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Evaluation and Modeling of a High-temperature, High-pressure, Hydrogen Separation Membrane for Enhanced Hydrogen Production from the Water-gas Shift Reaction