In an effort to develop selective solid sorbents for acidic gas (CO 2 and H 2 S) removal from natural gas mixtures, we synthesized amine-surface-modified silica xerogel and MCM-48 materials. With large amounts of basic amine groups on the surface, the sorbents are able to selectively bind the acidic gases CO 2 and H 2 S. High adsorption capacities and adsorption rates were obtained for both gases. The adsorption-desorption isotherms of the gases and thermogravimetric analysis of the sorbents showed that these sorbents can be regenerated completely under mild conditions such as those used in pressure swing or temperature swing adsorption processes. We have also investigated the effect of moisture on the adsorption of CO 2 and H 2 S by TPD-MS and infrared spectroscopy. The results indicated that the presence of water vapor doubled the amount of CO 2 adsorbed and barely affected the H 2 S adsorption.

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Purification of normal α-olefins by removal of dienes has been demonstrated previously in our laboratories by π-complexation using Ag+ ion-exchanged zeolite (Ag−Y) or AgNO3/SiO2 sorbent. Although Ag−Y could purify 1-butene/1,3-butadiene effectively, the purification performance was degraded by H2 and/or H2S poisoning. A new sorbent for 1-butene/1,3-butadiene purification was developed in this study by ion-exchange of Cu2+ cations into Y-zeolite followed by reduction of Cu2+ to Cu+. The performance of the Cu+-zeolite, Cu(I)−Y or Cu−Y, was found to be superior to that of Ag−Y. Cu−Y exhibited higher diene/olefin separation factors than Ag−Y by approximately an order of magnitude. Furthermore, unlike Ag−Y, exposure to H2S/H2 at 120 °C had virtually no effect on 1,3-butadiene/1-butene adsorption, indicating the excellent poisoning resistance of Cu−Y. XPS and EPR analyses showed that half of the Cu2+ cations in Cu−Y underwent autoreduction to Cu+ either in vacuo or in He, resulting in the same purification capability with Cu−Y obtained by reduction with CO.

Clinoptilolites were tailored through controlled ion exchange with both indigenous cations, such as Na+ and Mg+, and other cations, such as Li+, Sr2+, and Ce3+. These partially exchanged clinoptilolites are characterized through neutron activation analysis, and the adsorption isotherms and diffusion rates of nitrogen and methane were measured. Partially exchanged Ce clinoptilolite showed reversal of equilibrium selectivity from nitrogen to methane as the extent of Ce3+ exchange increased, while mixed Na/Li (also referred to as partially exchanged Li+) clinoptilolites showed reversal of equilibrium selectivity as the extent of Li+ exchange decreased. High-pressure isotherms on mixed Mg/Na clinoptilolites and partially exchanged Ce clinoptilolites were measured through the differential adsorption bed technique. Pressure swing adsorption (PSA) simulations were performed on a two-stage PSA process operating on a five-step PSA cycle for the tailored clinoptilolite sorbents. The simulation results of tailored clinoptilolites were compared against those of the commercial sorbent ETS-4 and the purified clinoptilolite. The tailored clinoptilolites gave slightly less recovery than purified clinoptilolite and ETS-4 but showed 50% improvement in product throughput, making tailored clinoptilolites suitable for use in a PSA process for nitrogen/methane separation.

It was found earlier in our laboratories that Ag ion-exchanged zeolite was capable of purifying 1-butene by selective adsorbing trace amounts of 1,3-butadiene. The effect of Ag content in Ag ion-exchanged Y-zeolite (Ag-Y) on 1,3-butadiene/1-butene adsorption was investigated using Ag-Y with different Si/Al ratios and different degrees of Ag + /Na + exchange (AgNa-Y). AgNa-Y with a Ag content of 34 Ag/u.c. exhibited excellent adsorption performance in terms of both separation factor and uptake rate. The influence of H 2 S exposure on sorbent performance was also examined. Although both 1,3-butadiene and 1-butene adsorption amounts were decreased by H 2 S exposure, the separation factors remained well over 100, which were still good for purification. XPS analysis revealed that Ag + in Ag-Y reacted with H 2 S to form Ag 2 S. The high selectivity for butadiene over 1-butene was indicative of the π-complexation ability of Ag 2 S. This work demonstrated that (1) an intermediate silver loading was the best for 1,3-butadiene/1butene purification and that (2) Ag-Y maintained stability against H 2 S.

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