Non-oxidative propane dehydrogenation (PDH) is an on-purpose propylene production process increasingly practiced to fill the gap between propylene demand and production. The reaction is thermodynamically limited, and single-pass propane conversion of commercial PDH reactors are often below 50%. Membrane reactors can debottleneck propylene production by PDH. By selectively removing the hydrogen product, membrane reactors can enhance the single-pass propane conversion above the equilibrium conversion according to Le Chatelier's principle. High membrane hydrogen permeance and hydrogen/propane selectivity are desired for PDH membrane reactors. While many polymer membranes can give outstanding hydrogen/propane selectivity at room temperature, inorganic membranes such as carbon molecular sieve (CMS) membranes must be used for PDH membrane reactors due to the aggressive high-temperature reaction condition (450-650 °C) required to activate PDH catalysts.
In this talk, we will present hydrogen/propane separation in novel composite CMS hollow fiber membranes made by pyrolysis of dual-layer sheath/core precursor hollow fibers. Engineering the core layer chemistry gave nearly defect-free dual-layer precursor hollow fibers. This allowed the formation of defect-free composite CMS hollow fiber membranes without precursor pre-treatment. The composite CMS hollow fiber membranes showed hydrogen permeance over 400 GPU and hydrogen/propane ideal selectivity around 1000 at room-temperature permeation. High-temperature permeation (200 to 500 °C) of a hydrogen/propane mixture was investigated using the constant-volume method. The results show that the composite CMS hollow fiber membrane was able to provide attractive hydrogen permeance and hydrogen/propane selectivity under realistic PDH reaction conditions.
