Propane/propylene separation by pressure swing adsorption: sorbent comparison and multiplicity of cyclic steady states

• Published in: Chemical engineering science 2002-04, Vol.57 (7), p.1139-1149
• Main Authors: Rege, Salil U., Yang, Ralph T.
• Format: Article
• Language: English
• Subjects: Adsorption; AlPO 4-14; Applied sciences; Chemical engineering; Chemistry; Exact sciences and technology; General and physical chemistry; Multiplicity of cyclic steady states; Pressure swing adsorption; Propane/propylene separation; Solid-gas interface; Surface physical chemistry; π-Complexation
• ISSN: 0009-2509; 1873-4405
• DOI: 10.1016/S0009-2509(01)00440-7

The separation of propane/propylene mixtures is an important yet difficult separation. Two types of adsorbents, namely a π-complexation sorbent (AgNO 3/SiO 2), and a steric (based on size exclusion) sorbent (AlPO 4-14), were previously proposed to be highly effective materials for C 3H 6/C 3H 8 separation using a vacuum pressure swing adsorption (PSA) cycle. In this work, high pressure C 3H 6 and C 3H 8 adsorption isotherms have been measured for the AgNO 3/SiO 2. The performance of the AgNO 3/SiO 2 sorbent has been compared with that of AlPO 4-14 by simulating a four-step PSA cycle with two different grades of feed. The adsorption step was carried out at 7 atm while desorption was conducted at either 1 or 0.2 atm . It was found that although both sorbents provided more than 99% product purity at reasonably high recovery, the performance of AgNO 3/SiO 2 was better than the AlPO 4-14 sorbent. The advantage of performing adsorption at a superatmospheric pressure was that the olefin product could be obtained at a higher pressure than that possible with a vacuum-swing cycle. For C 3H 6/C 3H 8 separation using AlPO 4-14 sorbent, multiplicity of cyclic steady states was observed under certain operating conditions. One unstable and two stable steady states were observed within these regions for identical cycle conditions depending upon the initial temperature or sorbate concentration in the PSA bed at startup. The exact initial bed temperature and concentration at which there was a switch in the stable steady states was identified.