Advanced characterization of high performing next-generation membranes for gas separation

Separation processes involve nowadays more than 15% of the total energy consumption, contributing every day to the uncontrollable increasing emission of pollutants and greenhouse gases. Nevertheless, those kinds of process have an enormous industrial relevance today, especially for CO2 removal. Recently, Mixed Matrix Membranes (MMMs) have been classified as promising materials for a new generation of membranes. MMMs consist of porous media dispersed in a polymeric matrix1; they so combine the strength points of polymers like the easy processability, the flexibility and the resistivity to the external atmosphere, with the peculiar capability of separation of the porous media. Objectives doMino is a newborn Italian project aimed to develop efficient MMM based on purposely synthesized (per-)fluorinated metal organic frameworks (F-MOFs) enabling easier, faster, and cost-effective separation of CO2 from large amounts of gases, such as post combustion flue gas (CO2/N2) and biogas (CO2/CH4) (Figure 1). All F-MOF studied in doMino are synthetized using water as solvent. Both neat polymeric matrix and F-MOFs are deeply analyzed by applying an advanced multi-technique characterization approach. Despite most classical characterization techniques aimed to evaluate, the stability and the structures of both the components of the MMMs, a key point is the study of the adsorption capacity of those materials by volumetric and microcalorimetry techniques (Figure 1). On the same time, vibrational spectroscopies (IR and Raman) can be employed to deeply investigate the structures and their modification upon gas capture. Finally, those techniques can be employed to study the combination of the crystalline porous media with the polymeric matrix, in terms of matrix-filler molecular interactions and expected improvement of capture and separation efficiency of the final membrane. Figure 1. Graphical representation of doMino's main goal and example of CO2 adsorption isotherms of some neat polymers employed in the project Expected results and significant of the work doMino concerns the synthesis and characterization of several F-MOF based on Ce, Zr and Al combined with both aromatic and aliphatic fluorinated linkers. The fluorinated backbones improve the affinity towards CO2 and allow a good hydrophobicity enhancing the stability in humid environment. Volumetric measurements coupled with IR spectra have already demonstrated the flexible behavior of some of those materials upon gas sorption. This is specifically the case of a F4_MIL53(Al) and some Ce/Zr-based metal organic frameworks containing long fluorinated chains such as optafluoroadipic acid (OFA). On the other hand, we exploit the peculiar S-shape isotherm of some F-MIL140(Ce)2. This feature not only improve the adsorption performances, but enhances the selectivity of a target molecule, favoring the separation of different components. The understanding of such peculiar features will be the basis for the synthesis of new high performing next-generation membranes developed to enable drastic reduction of the plant size, construction costs and the energy requirements for separation processes. References [1] Esposito, E. et al. Energy Environ. Sci. 12, 281-289 (2019) [2] D'Amato, R. et al. ACS Sustain. Chem. Eng. 7, 394-402 (2019)