Nanoscale crystals of cyclotrimethylenetrinitramine (RDX) were produced by Rapid Expansion of Supercritical Solutions (RESS). The experiments were performed by expansion of supercritical solutions of RDX in carbon dioxide through sapphire nozzles (ID: 100 and 150 mm) at pressures of 15.0 -29.5 MPa and temperatures of 343 -348 K. Recrystallized particles were characterized by Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction, HPLC and melting point analysis. The process produced particles with a mean size in the range 110 -220 nm and a narrow size distribution. The product was crystalline as determined by X-ray diffraction. The effect of process conditions (T, P, nozzle diameter) on the crystal size distribution was determined.

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Membrane distillation was suggested for the regeneration of volatile inorganic acids (hydrochloric and nitric acids) from the metal pickling solutions using hydrophobic porous and nonporous asymmetric membranes. The investigations were performed with a flat-sheet commercial microfiltration membrane based on tetrafluoroethylene/vinylidenefluoride copolymer MFF-2 and with a plasma-modified commercial asymmetric gas separation membrane based on poly(vinyltrimethyl silane) (PVTMS). The influence of acid concentration (varying over a wide concentration range from 0.01 to 7.0 N) and the feed temperature (T h = 313–333 K) on the transmembrane flux and selectivity was studied. It was shown that the concentrating of volatile inorganic acids in the feed using a porous MFF-2 membrane is effective up to 1.0 N concentration. Plasma-modified PVTMS membrane was used for the separation of feed solutions with higher acid content up to 7.0 N. It was established that the plasma treatment essentially increases the hydrophilic properties of PVTMS membrane surface.

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