Preferential permeability of methanol into water using polysilicone and poly(1-trimethylsilyl-1-propyne) membranes

The permeation of initially pure methanol into >95% relative humidity air has been demonstrated with three membranes, supported poly(1-trimethylsilyl-1-propyne) (PTMSP), supported poly(dimethylsiloxane) (PDMS), and a 125-μm polysilicone film. Although fundamentally similar to pervaporation, the arrangement entailed small scale (∼1 cm2) membrane dispensing of methanol with water counterdiffusion. Volumetric readings over time, final concentration measurements, and subsequent parameter fitting to a derived first-order mathematical model revealed high selectivities – 8.4, 10.3, and 8.3 for the respective membranes – for delivery of methanol versus uptake of water. These selectivities represented factors of 1.5, 1.9, and 1.5 beyond the relative saturation vapor pressures of methanol and water, perhaps, as a result of a favorable inhibition of water counterdiffusion by methanol permeation. Initial methanol permeation rates of 380, 730, and 260 g/h m2 were also estimated. A transport mechanism adjustment is suspected with PTMSP because of a slightly more rapid permeation rate decrease than indicated by the model. The experimental arrangement and mathematical model provide a new general framework for evaluation of membranes and designs for potential dispensing applications.