Zeolites modified by CuCl for separating CO from gas mixtures containing CO₂

Abstract

Although zeolites such as NaY and 13X adsorb CO₂ much more than CO, the adsorption amount of CO₂ and CO can be reversed if the zeolites are modified with CuCl. When zeolite NaY or 13X is mixed with CuCl and heated, high CO adsorption selectivity and capacity can be obtained. Isotherms show the adsorbents have CO capacity much higher than CO₂. This is because CuCl has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuCl can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO₂ adsorption. The monolayer dispersion of CuCl is confirmed by XRD and EXAFS studies. The loading of CuCl on the zeolites has a threshold below which the CuCl forms monolayer after heating and crystalline phase of CuCl can not be detected by XRD. An adsorbent of CuCl/NaY with CuCl content closed to the monolayer capacity shows very high CO selective adsorbability for CO₂, N₂, H₂ and CH₄. At temperature higher than room temperature, the adsorbent has even better CO selectivity for CO₂. Using the adsorbent, a single-stage 4 beds PSA process, working at 70°C and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%.