444a Propane/propylene Separation: From Molecular Scale to Process

Alirio E. Rodrigues¹, Miguel Granato², Pedro Sa Gomes², and Nabil Lamia². (1) Laboratory of Separation and Reaction Engineering, University of Porto - Faculty of Engineering, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Porto, Portugal, (2) LSRE, Dept Chem Eng, UNiv Porto, University of Porto - Faculty of Engineering, Rua Dr. Roberto Frias s/n, 4200-465 Porto, Porto, Portugal

Propane/propylene separation is an energy intensive separation currently done by distillation with consumption of 1.5 MWh/ton propylene in cryogenic distilllation units which can be lowered to 0.3 MWh/ton in well heat integrated units.

Alternative technologies studied in our laboratory include Vacuum Swing Adsorption (VSA) and Simulated Moving Bed in gas phase. In VSA zeolite 4A or 13X have been used in processes controlled by crystal diffusion and macropore diffusion, respectively.

In the case of SMB process the adsorbent chosen was zeolite 13 X. The desorbent was either isobutane or butene-1.

The experimental methodology was the following: measurement of single component adsorption equilibrium isotherms; measurement of binary equilibria; fixed bed dynamics. This was coupled with modeling and simulation of SMB allowing the design and determination of operating conditions.

Molecular simulation studies of propane, propylene and isobutane (or butene-1) were carried out and they are a tool to look for better desorbents.

A recently developed force field for adsorption of linear alkanes in the sodium form of FAU is applied to reproduce experimental data for propylene adsorption in 13X zeolites by fitting LJ parameters between the sp2-hybridized bond of propylene and the other atoms for this system. Similar methodology was extend for the adsorption of isobutane.

References:

A.E. Rodrigues et al. Method of separating propylene in mixture with propane by adsorption in simulated moving bed, WO 2008/012410 A1, 31 January 2008

A.E. Rodrigues et al, Procédé de séparation du propylène en mélange avec du propane par adsorption en lit mobile simulé, French patent application No 06 06827, 24/07/ 2006

M. Granato, T. Vlught and A.E. Rodrigues, “Molecular Simulation of Propane/Propylene Adsorption in Zeolite 13X”, Ind Eng Chem Res, 46, 7239-7245 (2007)

N. Lamia, Luc Wolff , P. Sa Gomes , C. A. Grande, and A.E. Rodrigues, “Propane / Propylene Separation by Simulated Moving Bed I. Adsorption of Propane, Propylene and Isobutane in Pellets of 13X Zeolite”, Separation Science and Technology, 42, 2539-2566 (2007)