This porous inner cylinder is the membrane that gives the membrane reactor its name. The membrane is a barrier that only allows certain components to pass through it. The selectivity of the membrane is controlled by its pore diameter, which can be on the order of Angstroms, for microporous layers, or on the order of microns for macroporous layers.
Membrane reactors combine reaction with separation to increase conversion.
This raises the conversion for the reaction, making the process more economical. Fogler, H. Scott. Elements of Chemical Reaction Engineering , 3rd Ed. Upper Saddle River, NJ, 1998.