The influence of the CO inhibition effect on the estimation of the H 2 purification unit surface

Abstract

The CO inhibition effect on H 2 permeance through commercial Pd-based membranes was analysed by means of permeation measurements at different CO compositions (0–30% molar) and temperatures (593–723 K) with the aim to determine the increase of the membrane area in order to compensate the H 2 flux reduction owing to the CO inhibition effect. The permeance of H 2 fed with carbon monoxide was observed to decrease with respect to the case of pure hydrogen. At 647 K the H 2 permeance of a pure feed of 316 μmol m −2 s −1 Pa −0.5 reduces progressively until 275 μmol m −2 s −1 Pa −0.5 when 15% or more of CO is present in the system, until it reaches a plateau at 20%. The inhibition effect occurring when CO is present in the feed stream reduces with the progressive temperature increase; the reduction of the permeance decreases exponentially by 23% at 593 K and by 3% at 723 K with 10% of CO. The inhibition effect is seen to be reversible. An H 2 flux profile in a Sieverts' plot shows the effect produced by the increase of the CO composition along the Pd-based membrane length. The H 2 flux profile allows the area of a Pd-based membrane to be evaluated in order to have the same permeate flow rate of H 2 when it is fed with CO or as a pure stream. Moreover, a qualitative comparison between the H 2 flux profiles and a previously proposed model has been carried out. Although studies on the CO inhibition and dilution effects are present in the literature, however, an appropriate evaluation of the H 2 membrane purification unit surface using measurements of permeances of H 2 mixed with CO has until now never been proposed. This information proves important in the design of a hydrogen purification unit.