In the bulk, catalyzed polymerization of propene in an industrial-scale recycle reactor, propane is an important contaminant, and for this reason it is necessary to remove it from the reaction medium in order to maintain high process productivities. In a typical industrial operation, unreacted propene/propane mixtures are purged from the recycle stream and vented to a flare, causing a significant negative impact on the process economics. Despite the potential economic advantages that membrane-based propene recovery may represent industrially, a comprehensive analysis based on a detailed mathematical model of the system is not available yet. The main purpose of this study is presenting a mathematical model to simulate the separation of propene/propane mixtures in a polymerization system using membrane modules. The model developed takes into account two extreme levels of macromixing that may be observed in the permeation module (namely, perfect mixing and plug flow), the diffusion of the gaseous mixture through the polymeric membrane, and the effect of operational variables such as temperature, pressure, flow rates, composition, and membrane area on the separation performance. It is shown that polyimide-based membranes, such as 6FDA-TMPPD (2,2-bis(3,4-decarboxyphenyl)hexafluoropropane dianhydride and 2,3,5,6-tetramethyl-1,4-phenylenediamine), may be used in permeation modules to deliver up to 5% gains in the effective propene concentration at the reactor feed, therefore increasing significantly the reactor productivity. An economic analysis shows that an economic gain of up to U.S.$1.5 million per year per polymerization plant may be attained.