Adsorption 3, 27-32 (1996) (~ 1996 Kluwer Academic Publishers. Manufacturedin The Netherlands. Zeolites Modified by CuCI for Separating CO from Gas Mixtures Containing C02 YOUCHANG XIE, JIAPING ZHANG, JIANGUO QIU, XIANZHONG TONG, JINPING FU, GE YANG, HAOJIE YAN AND YOUQI TANG Department of ChemistD,, Peking University, Beijing 100871, China 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 CuC1. When zeolite NaY or 13X is mixed with CuC1 and heated, high CO adsorption selectivity and capacity can be obtained. Isothermsshow the adsorbents have CO capacity much higher than CO2. This is because CuCI has dispersed onto the surface of the zeolites to form a monolayer after the heat treatment and the monolayer dispersed CuC1 can provide tremendous Cu(I) to selective adsorb CO and inhibit the CO2 adsorption. The monolayer dispersion of CuC1 is confirmed by XRD and EXAFS studies. The loading of CuC1 on the zeolites has a threshold below which the CuCI forms monolayer after heating and crystalline phase of CuCI can not be detected by XRD. An adsorbent of CuCI/NaY with CuC1 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~ and 0.4 MPa to 0.013 MPa, can obtain CO product with purity >99.5% and yield >85%. Keywords: CO adsorbent, CO2 adsorption, zeolite modification, monolayer dispersion Introduction Carbon monoxide is a valuable raw material for the syntheses of variety of chemicals such as phosgene for polyurethanes and polycarbonate, acetic acid, fomic acid, propionic acid, dimethyl formamide, oxylates, acrylic acid and metal carbonyls etc. Separation and recovery of carbon monoxide from gas mixtures by ad- sorption is of great interest in recent years. There are many large scale CO sources such as off-gases from steel plants and other metallurgical plants, synthesis gas from steam reforming, CO2 conversion and par- tial oxidation of hydrocarbon and coal gasification. In general, these gases contain CO together with CO2, N2, H2, CH4 and H20 as impurities. For the recovery of CO from the gas mixtures, a two-stage adsorption pro- cess, consisting of a first PSA stage to remove CO2 and moisture, and a second PSA stage to separate CO from the other gases, has been used (Beysel et al., 1988). This kind of process needs two adsorbents, which are a CO2 adsorbent to remove CO2 and H20 at first and a CO adsorbent to recover CO from the other gases. If an adsorbent with CO selectivity and capacity not only much higher than N2, H2 and CH4 but also than CO2 is available, a single-stage PSA process might use it to recover CO from the gas mixtures. Some studies have been reported in literature (Golden et al., 1991; Nishide et al., 1986; Tsuji et al., 1987). According to our long term study on CO adsorbents, we find that some zeolites modified by CuC1 are better adsorbents for the application. It was found (Xie and Youqi, 1990; Xie et al., 1984) in our laboratory that salts or oxides can disperse spon- taneously onto the surface and pores of zeolites or other supports to form a monolayer or submonolayer, we call it solid/solid adsorption. This phenomenon is quite widespread and has been confirmed by many tech- niques such as XRD, XPS, ISS, EXAFS, NMR and Raman spectra, etc. For example, heating a mixture of CuCI and a Na-zeolite at a suitable temperature (lower