Polyether-based block copolymer membranes for CO2 separation

Many environmental challenges of modern society are related to sustainable energy consumption (e.g. CH4 production and separation, CO2 sequestration and disposal, global warming) and to sustainable energy production (e.g. H2 production and separation, biofuel production by fermentation). In particular carbon dioxide separation from flue gas and natural gas is an important application in industry and attracts a significant amount of attention, as the energy sector is by far the largest contributor to the worldwide emission of CO2. Membrane technology has become very competitive, much more than the traditional separation methods, such as adsorption, cryogenic separations, distillation, etc., since offers improved performance at lower cost with increased energy efficiency and lower environmental impact [1,2]. The successful development of highly permeable and selective membranes makes a membrane-based process a viable alternative for carbon dioxide capture and storage from flue gas. Particular attention in recent years has been given to the use of membranes in a solubility-selective mode, where in more soluble gaseous species permeate preferentially through the membranes [3]. The copolymer of the PEBAX series, formed by a rigid-semicrystalline block of polyamide (Nylon12, PA-12) covalently linked to amorphous and rubbery comonomer poly(tetramethilene oxide) (PTMO) are very close to the upper bond [4] for the high selectivity for CO2/non polar gases. A successful strategy for improving CO2 is the addition of polymeric additives to this matrix polymer. Adding organic molecules with different chemical structure to a polymer matrix, generally implies a modification on the system morphology, the chemical composition and even the physico-chemical properties change, influencing the transport through the membranes [5-7]. In this sense, the classical simulation study at molecular level by using molecular dynamic simulations (MD) can powerfully support experimental studies about morphological and transport behaviour of such systems [8]. In the present work MD method has been applied for a detailed investigation of gas molecules transport through complex system of PEBAX®2533 block copolymer membranes with N-ethyl-o,p-toluenesulphonamide (KET) as additive molecules in different weight percentage. Complementary experimental and theoretical approaches give plausible explanations of the gases sorption and diffusion mechanisms, identifying a critical concentration of additive over which a significant decrease in permeability is observed.Considering that these composite membranes are solubility-selective, the decrease in the thermodynamic parameter over the critical additive concentration can be ascribed to the rearrangement and molecular segregation of the modifier inside the polymer matrix. The theoretical data, along with the experimental results, give further information about the microscopic structure and atomistic interactions between gases, PEBAX and modifiers, thus resulting in a reciprocal validation and useful correlations between MD and experimental analysis.