The depth of nanocrystallites of pyrocarbon deposition in pores of ultrafiltration membranes and its influence on their efficiency

Scanning electron microscopy and energy dispersion spectrometry were used to determine the depth of the deposition of pyrocarbon nanocrystals (PNCs) on the pore surface of TRUMEM inorganic ultrafiltration membranes (D _pore = 50 nm) depending on the pressure of the gas subjected to pyrolysis (methane). It was shown that, while the deposition of PNCs occurred over the whole pore length equal to the selective layer thickness (20 μm) at 4.9 kPa methane pressure, an increase in pressure to 40.0 kPa decreased the deposition depth to 5.0 μm. Simultaneously, the λ/D ratio decreased from 94 to 11. At a pressure increased to 100.0 kPa, the depth of PNC deposition was ～1.5 μm (λ/D = 5). Changes in the depth of PNC deposition and the λ/D ratio depending on pressure were similar in character and could be described by exponential dependences. With PNCs deposited ～1.5 nm deep (100 kPa), membranes with pore size 8–17 nm were obtained. Their efficiency, for instance, for ethanol, was 50–75% of that of the initial membranes. The diameter of pores decreased by 3–6 times.