Removal of propylene from fuel-grade propane

Propane produced in refinery operations often contains substantial amounts of propylene. Propylene may cause problems through engine and injector deposits when propane is used as a motor fuel. Also, propylene is capable of polymerizing in storage, fuel lines, or vaporizers, and thus may cause plugging by gum deposits. As the use of propane expands into the motor fuel and other new markets, the removal of propylene will become increasingly more important. This manuscript reviews the most promising technologies for removal of propylene from refinery-derived propane. The only current commercially-practiced approaches are distillation and catalytic hydrogenation. Distillation is a viable technology for removal of propylene from propane, but both capital and energy costs are high, due to the very low relative volatility between the two species. Catalytic hydrogenation is straightforward, but also has a high capital cost, and the cost/availability of the continuous hydrogen production required may also be problematic. Two other approaches are very near commercialization: (1) absorption/stripping based on aqueous silver nitrate solution, and (2) pressure-swing adsorption based on zeolite molecular sieves. Membranes also show promise to provide in a single stage separation equivalent to many stages of distillation, with simple, compact, and robust equipment. Chemically selective sorbents offer even higher degrees of separation in a single stage, albeit in more complex equipment.