Investigation of Nanoporous Superalloy Membranes for the Production of Nanoemulsions
Premix membrane emulsification is a gentle process for producing nanoemulsions, i.e., for pharmaceutical purposes. The operating time of common membranes is short today, because of their fragility, membrane fouling and poor cleanability. In contrast, superalloy membranes are cleansable because of their high mechanical strength as well as high chemical and thermal resistances and therefore, could achieve clearly longer operating times. Their usability for premix membrane emulsification is investigated in this study. Different flow rates of the premix emulsion were tested up to 21 cycles with a small-scale extruder, three different nanoporous superalloy membrane structures have been tested in comparison to a common polymer membrane. Varying the two-phase-structure ( - and 0-phase) of superalloy bulk material through thermal or thermo-mechanical treatments and chemical extraction of either one of the phases, different membrane microstructures could be obtained. These membranes differ in pore size, pore structure, and porosity, resulting in different flow resistances, droplet sizes and droplet size distributions in the investigated premix membrane emulsification process. Emulsions with droplet sizes in the desired range of 100 to 500 nm and with acceptable droplet size distributions were achieved. Data display an improved process stability for superalloy membranes, however, special attention needs to be paid towards narrow droplet size distributions.