Preparation of Pt-loaded hydrogen selective membranes for methanol reforming

Abstract

We prepared Pt-included microporous silica membranes (SiO2/gamma-AI(2)O(3)/Pt-SiO2/porous stainless steel (SUS)) to improve CO removal efficiency in a methanol reforming membrane reactor. The permeation test of an H-2 (99%)/CO(1%) mixture between 25 and 200 degrees C was conducted to observe the effect of the Pt intermediate layer included in the membrane on CO removal efficiency. A mesoporous membrane with the Pt intermediate layer (gamma-Al2O3/Pt-SiO2/SUS) showed a remarkable H-2/CO separation factor of 5.22-7.03, exceeding the Knudsen-dominated transport characteristics expected from a mesoporous gamma-Al2O3 layer. After coating a microporous silica skin layer on the Pt-included gamma-Al2O3 membrane, CO was not detected in the permeate side of the membrane by the corona ionization detector (CID). When the Pt-included microporous silica membrane was used in the methanol reforming membrane reactor, methanol conversion at 200 degrees C (methanol/water feed flow rate = 0.004 ml/min) was improved from 73.2% to 93.2% in comparison with the case of a conventional reactor, and CO in the produced gas mixture was efficiently rejected through the Pt-included silica composite membrane. The introduction of the Pt catalyst into the intermediate layer of the composite membrane contributed to the improvement in CO removal efficiency. The dilution of CH3OH/H2O feed led to an increase in the extent of methanol conversion improvement (a difference of methanol conversion between a membrane reactor and a conventional reactor) due to an increase in the hydrogen recovery. (c) 2006 Elsevier B.V. All rights reserved.