(307a) Hydrogen Production In a Large Scale Water Gas Shift Pd Based Membrane Reactor

Palladium and palladium based membranes represent an appealing technology option  to increase the CO conversion and the H₂ recovery on the Water Gas Shift reactor due to the continuous removal of hydrogen over the course of the reaction. Even though many studies have been performed in this area their outcome typically represents a proof of concept involving small membrane area reactors. The objective of the present study  is therefore to demonstrate the possibility of scaling up the system to produce up to 2 lb day^-1 of pure hydrogen from syngas feed. To attain high hydrogen production rates large surface area composite Pd membranes (1”OD, 10” length) were prepared and tested under pure hydrogen and water gas shift reaction conditions. In particular, composite Pd membranes were prepared by the electroless plating method on porous metal substrates (Stainless Steel 316L). The oxidation step at 400-500°C and the grading step with alumina particles of different sizes were performed to achieve thin (< 15 microns) and defect free membranes. Furthermore composite Pd membranes were tested using a large scale Water Gas Shift Catalytic Membrane Reactor (WGS-CMR) testing rig consisting of a tube-and-shell reactor, filled with high temperature Iron-chrome oxide shift catalyst (HIFUEL, Alfa Aesar). The desired mixed gas composition and feed flow rates were adjusted with mass flow controllers (H₂, CO, CO₂ and N₂) and a high pressure water pump for steam generation. Gases were mixed in a ballast volume (4 L) and further mixed with steam in a preheater, filled with raschig rings, ensuring a minimum temperature of 300°C before entering the WGS-CMR to avoid condensation. Permeate and retentate flows were measured with mass flow meters while retentate (reactor pressure) and permeate pressures were regulated with two back pressure regulators. A micro GC, Agilent 490, equipped with two capillary columns and two TCD detectors has been used to determine the retentate, permeate as well as the feed compositions. The retentate flow was chilled and dried (zeolite 5A) before the flow measurement to avoid instrument damaging and then further treated with Agilent moisture traps before the GC analysis. Syngas similar to the real gasifier reacting mixture (H₂/CO/CO₂ in ratios approximately of 1/1/0.5 on a dry basis and H₂O/CO ratios having values over 2) was fed in the WGS-CMR with a total flow up to 40 NL min^-1, 25 bar maximum pressure and temperature ranging between 400-450°C. The composite Pd membranes used in the reaction showed permeances as high as 35 m³ m^-2 h^-1 bar^-0.5 and stable H₂/He selectivities at 450°C. Results of the above experimental studies of large scale composite Pd membranes will be presented under WGS reaction conditions along with slipstreams tests conducted at an operating gasifier during the presentation.