Hydrogen Production in a Large Scale Water–Gas Shift Pd-Based Catalytic Membrane Reactor

Abstract

Composite palladium and Pd-based membranes represent an appealing technology option to increase the CO conversion and the H2 recovery in the water–gas shift (WGS) reactor as a result of 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 reactors with small membrane area. The present study therefore addresses the scaling up of the process to obtain high hydrogen production rates through the use of large surface area, ∼0.02 m2, composite Pd membranes. Two thin, δ < 10 μm, defect-free composite membranes were prepared by the electroless plating method on porous stainless steel tubular supports and tested under pure gases and water–gas shift reaction conditions. Syngas similar to the actual gasifier reacting mixture (40% H2, 42.2% CO, and 17.8% CO2 and steam to carbon ratio varying between 2.5 and 3.5) was fed to the WGS catalytic membrane reactor (WGS-CMR) with a total flow rate up to 1.5 Nm3 h–1, 20 bar maximum pressure, and temperatures ranging 420–440 °C. In the presence of crushed catalyst, CO conversions higher than the equilibrium conversions were obtained within the entire gas hour space velocity (GHSV) range considered in the present study, for pressures between 7 and 20 bar. At a relatively low feed flow rate, GHSV = 1130 h–1, a maximum CO conversion of 98.1% was achieved, with a hydrogen recovery of 81.5% at 440 °C. On the other hand, at the highest GHSVs, the system appeared to be limited by the activity of the ferrochrome catalyst. At 20 bar of absolute pressure in the retentate side, 440 °C, and GHSV = 5650 h–1, the hydrogen production rate was found to be 5.6 Nm3 day–1. Remarkably high hydrogen purity, in excess of 99.97% and 99.2% for the two membranes, respectively, was achieved also in experiments performed with a retentate pressure of 20 bar.