Preparation of Pt-loaded hydrogen selective membranes for methanol reforming

Abstract

We prepared Pt-included microporous silica membranes (SiO 2/γ-Al 2O 3/Pt–SiO 2/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 °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 (γ-Al 2O 3/Pt–SiO 2/SUS) showed a remarkable H 2/CO separation factor of 5.22–7.03, exceeding the Knudsen-dominated transport characteristics expected from a mesoporous γ-Al 2O 3 layer. After coating a microporous silica skin layer on the Pt-included γ-Al 2O 3 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 °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 CH 3OH/H 2O 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.