The diffusion of methane in inorganic membrane pores under Knudsen conditions: the kinetics and depth of pyrocarbon deposition and its influence on transport properties

Abstract

The kinetics of the topochemical reaction of methane dehydrogenation was studied using TRUMEM ultrafiltration membranes (TiO2 + Cr2O3 on porous steel, the size of transport pores 50 nm). The depth of the deposition of pyrocarbon nanocrystallites (PNC) into pores was determined. The depth of PNC deposition was estimated using scanning electron microscopy and high-resolution energy-dispersion spectrometry. The deposition of PNC at a 4.9 kPa methane pressure in the reaction zone created Knudsen conditions for methane diffusion in pores. The deposition of PNC therefore occurred over the whole area of pore surfaces. Studies of the kinetics of PNC formation on the surface of pores showed that reaction rate V and its constant k substantially depended on reaction duration. The influence of PNC deposition on the electrosurface properties and permeability of the membranes to ethanol and dodecane was studied. After the deposition of PNC with Lc = 1.0–1.1 nm on the surface of pores, the ζ-potential and surface charge density (σ) decreased; simultaneously, the efficiency with respect to ethanol increased.