Experimental Study on a Compact Methanol Steam Reformer with Pd/Ag Membrane

Abstract

The performance of high purity hydrogen production from methanol for a compact steam reformer with a hydrogen purification membrane was investigated experimentally. A 77 wt.% Pd/23 wt.% Ag membrane with 25µm thickness and CuO/ZnO/ Al 2 O 3 catalyst were used. Heating was performed by a Bunsen type burner using City Gas 13A. The methanol reforming and purification of H 2 were investigated at different reference catalyst zone temperatures (589-689K), pressures at the retentate side (0.2-0.5MPa), steam to methanol(S/C) ratios (0.8-1.6) and reactant flow rates (1.7 ×10 -4 to 4.4 ×10-4 mol/s). The results show that at high reference temperature, high pressure and certain points of the reactant flow rate, the maximum hydrogen permeation rate is obtained when the S/C ratio is around 1. The modified Sieverts' equation which considers the decrease in H 2 concentration at the membrane surface, was proposed. The experimental result was lower than the permeation rate estimated by the modified Sieverts' equation, which is probably caused by the adsorption of non-H 2 species during permeation. It is further demonstrated that the modified Sieverts' equation is able to estimate a more reasonable hydrogen permeation rate in comparison to the estimation by the ordinary Sieverts' equation. In addition, it is shown that the compact methanol steam reformer with a Pd/Ag membrane is able to produce high purity hydrogen with very low CO concentration, which fulfills the Polymer Electrolyte Fuel Cell (PEFC) requirement (<10ppm).

Effect of Feed Flow Rate of Hydrogen Mixture on Hydrogen Permeation for Flat Sheet Pd/Ag Membrane with Stagnating Flow

“…The estimation by the equation for the case of hydrogen mixture is quantitatively reconsidered by taking into account the hydrogen concentration decrease at the membrane surface of the upstream side due to permeation. This is a continuation of previous study (22) , which just described the equation predicted the trend of H 2 permeation flux qualitatively. The proposed estimation method is supposed to be practically useful for the permeation system with similar geometry, in which the similar geometry has been implemented for many applications (22)- (25) .…”

“…In this experiment, the gas mixture of hydrogen and nitrogen with a constant hydrogen mole fraction of 0.75 was used for all conditions. This mole fraction was selected based on the overall methanol steam reforming reaction model, as demonstrated in our previous study (22) .…”

“…Different from other researchers who used supported membrane (14), (20) , our study used the unsupported membrane with stagnating flow at the upstream side of the membrane surface, to study the effect of feed flow rate fundamentally without considering any possible influence from metal support (21) . In addition, the experimental results are discussed using an equation (22) that takes into account the effect of H 2 permeation itself, in which this equation demonstrates the relation for multiple variables (20) that depend on each other. The estimation by the equation for the case of hydrogen mixture is quantitatively reconsidered by taking into account the hydrogen concentration decrease at the membrane surface of the upstream side due to permeation.…”

Initial Study on Hydrogen Permeation with Flat Sheet Pd/Ag Membrane for Mixture of Hydrogen and Carbon Dioxide

“…In this experiment, the gas mixture of hydrogen and carbon dioxide with constant inlet H 2 mole fraction of 0.75 was used. This fraction was selected based on the overall methanol steam reforming reaction model, as mentioned in our previous study [10]. A flat sheet, dense 77wt.% Pd/23wt.% Ag purification membrane with a thickness of 25µm and diameter of 0.02m was set inside the test module.…”

Experimental study on a methanol auto-thermal reforming for compact reformer

“…Besides the CO remover using the chemical reaction, a methanol steam reformer with Pd/Ag membrane was proposed as a method of hydrogen purification. Faizal et al(2012) elucidated the importance of transport phenomena near the membrane for relatively low flow rate of reformed gas and proposed a quantitative estimation method of H 2 purification flow rate from reformed gas. It showed that the Pd/Ag membrane is useful for compact reformer to produce high purity hydrogen with very low CO concentration, which fulfills the PEFC requirement.…”