Separation of Methanol/butene/mtbe Using Hybrid Distillation-membrane Processes

Distillation Residue Curve Maps (D-RCM’s) have proven to be an extremely useful graphical tool in the design and operation of both batch and continuous distillation processes. Recently submitted work by the authors has investigated the applications of Residue Curve Maps for membrane permeation systems. Such maps are referred to as M-RCM’s. This paper aims to develop a graphical tool to provide insight in sequencing combinations of unit processes in complex systems. As an example, the separation of a methanol/butene/MTBE system is investigated. MTBE is the desired product, and hence needs to be efficiently recovered from a reactor product. Difficulty arises when separating such a mixture with traditional distillation processes, because of the binary azeotropes that exist between methanol and MTBE, as well as methanol and butene. A membrane is suited for such a separation since it is not limited by relative volatility constraints. Using available data for the permeation rates of the components through a chosen membrane, the M-RCM was plotted. The M-RCM, along with column profile maps, facilitated a graphical method to select a combination of profiles to obtain the desired product(s). The method displayed can be applied to the design, as well as extended to the synthesis of hybrid processes. Maintaining an appropriate permeate pressure, it was found that crossing the distillation boundary is possible!