Ultrapermeable benzotriptycene-based PIMs that redefine the upper bounds for CO2 separations

Gas separation by polymeric membranes is an expanding technology for a number of industrial applications such as oxygen or nitrogen separation from air (i.e. separation O2/N2) or natural gas treatment and biogas upgrading (i.e. separation CO2/CH4). However, a further enhancement of the polymer transport properties is desirable to be cost effective in comparison with the traditional separation technology currently applied for CO2 capture or removal. Up to now, only poly(trimethylsilylpropyne) (PTMSP) and few other polyacetylenes demonstrate ultrapermeability (P>20000 Barrer), but their industrial application is prohibited by their very poor gas selectivity. In this presentation, we report a series of ultrapermeable PIMs, based on benzotriptycene units, showing substantially higher selectivity than PTMSP [1]. Their extraordinary transport properties are attributable to the inefficient packing of their 2D polymeric chains which results in large interconnected pores that enhance gas permeability. We will show that the outstanding CO2/CH4 and CO2/N2 permselectivity of the whole family of benzotriptycene PIMs allows the introduction of a new upper bound to define the current state-of-the-art. The gas transport properties will be discussed in terms of permeability, diffusivity and solubility. For selected samples, a novel instrument will be used to determine not only mixed gas permeability, but also the diffusion coefficient of gas mixtures [2]. Ageing data and the effect of the temperature on the transport properties will be also discussed. Finally, we will anticipate the potential exploitation of these materials for large scale gas separation application.