Robust Membrane Reactor for Hydrogen Production from Industrial Process Stream
DOE Phase I Contract No. DE-FG02-04ER83934
The goal of this Phase I program was to develop hydrogen transport membranes that are robust and durable under harsh industrial operating conditions, especially towards water-gas-shift (WGS) feed streams containing CO, steam, CO2, hydrogen and small amount of sulfur compounds (up to 200 ppmv). The proprietary composite membranes were tested with a sulfur-free simulated WGS feed stream, and showed excellent stability. Eight different palladium alloys were screened in dry sulfur-containing hydrogen feed streams (i.e., 2-200 ppmv H2S) in order to identify potential sulfur-tolerant alloys for the use of membrane surface catalysts.
Pure palladium and selected palladium alloy membranes were tested for separating hydrogen with a simulated sulfur-free WGS feed stream in the target temperature of 320-440 °C. The presence of CO, CO2, and steam in the feed did not pose any detrimental effect on the hydrogen permeation performance of these membranes. These metals and alloys are all inert towards CO, CO2, and steam under the membrane operating conditions.
In the interested WGS temperature range of 320-440 °C, the proprietary composite membrane, which employed pure palladium as the surface catalyst, was found could not resist as little as 1 ppmv of H2S, and quickly lost its activity. This activity loss was found associated with the transformation of palladium metal into bulk palladium sulfide, Pd4S, on the membrane surface. Several alloys were found to maintain good stability and sufficient catalytic activity with a feed containing 40% H2 and H2S as high as 200 ppmv.
Integration of WGS catalyst with Eltron’s composite membranes proved to be feasible and advantageous. Commercial low temperature WGS catalysts can be placed directly on top of the membranes, and the membranes maintained stable and good performance under WGS feed stream over four months at 340 °C.
Hydrogen is a highly desired product due to its economic value and strategic significance. Hydrogen purification membranes developed at Eltron Research are rapidly approaching commercial viability. Eltron hydrogen transport membranes will be used to separate hydrogen from reaction mixtures containing predominantly CO2, steam, residual CO, unreacted methane and hydrocarbons, and sulfur impurities. The sulfur tolerant catalysts identified in this Phase I program should be more than adequate to handle residual sulfur from feed streams derived from natural gas.