Mixed matrix membranes transport mechanism

Figure 7.3 Schematic representation of the transport mechanism through mixed matrix membranes with (a) conventional and (b) high aspect ratio permeable particles.

Gas separation membranes combining the desirable gas transport properties of molecular sieving media and the attractive mechanical and low cost properties of polymers are considered. A fundamental analysis of predicted mixed matrix membrane performance based on intrinsic molecular sieve and polymer matrix gas transport properties is discussed. This assists in proper materials selection for the given gas separation. In addition, to explore the practical applications of this concept, this paper describes the experimental incorporation of 4A zeolites and carbon molecular sieves in a Matrimid matrix with subsequent characterization of the gas transport properties. There is a discrepancy between the predicted and the observed permeabilities of O2/N2 in the mixed matrix membranes. This discrepancy is analyzed. Some conclusions are drawn and directions for further investigations are given. 

Of the three important technologies currently being pursued for CO2 capture, namely liquid absorption, solid adsorption [5], and membrane separations [6], membrane-based separation is promising since it is more energy efficient, mechanically simple and easy to scale-up with a smaller footprint. Polymeric, inorganic (silica, zeolite etc.), mixed matrix, and facilitated transport membranes are currently being investigated for this application [7]. 

Nicotera et al. investigated the behavior of water confined in recast NAFION and in NAFION-clay hybrids membranes using PFGSE NMR and spin—lattice relaxation time Tj, and concluded that the transport mechanism is influenced from the dimensions of the dispersed platelets and mainly from the type of nanocomposites formed upon mixing the clay particles with the polymer matrix. Compared to pure NAFION, the water uptake and the water diffusion of the hybrid membranes are increased, with the exception of the Kunipia-NAFION composite [83]. 

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