Guest desorption procedures for s-PS clathrate samples, leading to formation and regeneration of the nanoporous delta phase, are compared. An extraction procedure, based on supercritical carbon dioxide, allows an easy and fast recovery of the guest molecules operating under relatively mild conditions (90-200 bar, 40 degrees C) and generates a completely empty delta form, also starting from the most stable s-PS clathrate forms. In agreement with a previously proposed crystal structure of the nanoporous delta form, X-ray diffraction patterns of delta form powders obtained by this procedure do not show the peak, which is reduced but still apparent in samples extracted with previous procedures based on boiling solvents.