Pore Structure and Gas Diffusion Features of Ionic Liquid-Derived Carbon Membranes

In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium tricyanomethanide into the porous network of Vycor® porous glass tubes, was applied to derive the precursor Carbon/Vycor® composites. All precursors underwent a second cycle of IL infiltration/pyrolysis with the target to finetune the pore structural characteristics of the carbonaceous matter nesting inside the separation layer. The pore structural assets and evolution of the gas permeation properties and separation efficiency of the as-derived composite membranes were investigated with reference to the duration of the second infiltration step. The transport mechanisms of the permeating gases were elucidated and correlated to the structural characteristics of the supported carbon phase and the analysis of LN2 adsorption isotherms. Regarding the gas separation efficiency of the fabricated Carbon/Vycor® composite membranes, He/CO2 ideal selectivity values as high as 4.31 at 1 bar and 25 °C and 4.64 at 0.3 bar and 90 °C were achieved. In addition, the CO2/N2 ideal selectivity becomes slightly improved for longer second-impregnation times

Sorbents and separation membranes involving ionic liquid phases as precursors

Ionic Liquids (ILs) are a class of compounds composed exclusively of ions and are liquids at temperatures below to 100°C, whereas the most widely used ILs remain liquid even at ambient temperatures. These compounds are of special interest in recent years since they compile a combination of remarkable features, such as low melting points, negligible vapor pressure and ability to dissolve a plurality of components, high chemical and thermal stability and great chemical tunability. In this dissertation, porous adsorbents and separation membranes were developed utilizing ILs as precursors. Specifically, efforts were undertaken to develop liquid membranes using the method of post-synthesis modification of porous substrates with ILs and sol-gel method. In the sol-gel method the IL was one of the components of the synthetic procedures that also served as structure directing agent of the porous network in which it was trapped. In addition, ILs were used as precursors for developing porous carbon adsorbents and porous carbon membranes for gas separations. The developed porous carbons were studied with respect to the adsorption properties for various gases as well as to their catalytic properties for oxygen reduction/reaction, whereas the developed liquid and carbon membranes were evaluated for their separation properties.Τα «Ιοντικά Υγρά» είναι μια κατηγορία ενώσεων που αποτελούνται αποκλειστικά από ιόντα και είναι υγρά σε θερμοκρασίες κάτω των 100οC, ενώ τα πιο ευρέως χρησιμοποιούμενα Ιοντικά Υγρά παραμένουν υγρά ακόμα και σε θερμοκρασία περιβάλλοντος. Οι ενώσεις αυτές αποτελούν αντικείμενο ενεργούς μελέτης τα τελευταία χρόνια, εξαιτίας ενός συνδυασμού αξιοσημείωτων χαρακτηριστικών που επιδεικνύουν, όπως τα χαμηλά σημεία τήξης τους, η αμελητέα τάση ατμών τους, η ικανότητα διαλυτοποίησης-διάλυσης πληθώρας συστατικών, η υψηλή χημική και θερμική σταθερότητά τους και η ευκολία ελέγχου της χημείας τους. Στην παρούσα διδακτορική διατριβή έγινε προσπάθεια ανάπτυξης πορωδών προσροφητών και μεμβρανών διαχωρισμού με εμπλοκή προδρόμων φάσεων Ιοντικού Υγρού. Συγκεκριμένα, έγινε προσπάθεια ανάπτυξης υγρών μεμβρανών Ιοντικού Υγρού με τη μέθοδο τροποποίησης πορώδους μέσου και με τη μέθοδο διαλύματος-πηκτής. Στη δεύτερη περίπτωση το Ιοντικό Υγρό αποτελούσε συστατικό της σύνθεσης, ενώ ταυτόχρονα λειτουργούσε και ως μέσο οικοδόμησης της πορώδους δομής της μεμβράνης στην οποία και εγκλωβιζόταν. Επιπλέον, αναπτύχθηκαν πορώδεις ανθρακoύχοι προσροφητές και πορώδεις ανθρακούχες μεμβράνες διαχωρισμού με ανθρακοποίηση Ιοντικών Υγρών ως πρόδρομη ύλη. Οι ανεπτυγμένοι ανθρακούχοι προσροφητές μελετήθηκαν ως προς τις ιδιότητες προσρόφησης διαφόρων αερίων καθώς και ως προς τις καταλυτικές ιδιότητές τους για εφαρμογές αντιδράσεων αναγωγής οξυγόνου, ενώ προσδιορίστηκαν και οι ιδιότητες διαχωρισμού διαφόρων αερίων των ανεπτυγμένων υγρών και ανθρακούχων μεμβρανών

Pore Structure and Gas Diffusion Features of Ionic Liquid-Derived Carbon Membranes

In the present study, the concept of Ionic Liquid (IL)-mediated formation of carbon was applied to derive composite membranes bearing a nanoporous carbon phase within their separation layer. Thermolytic carbonization of the supported ionic liquid membranes, prepared by infiltration of the IL 1-methyl-3-butylimidazolium tricyanomethanide into the porous network of Vycor® porous glass tubes, was applied to derive the precursor Carbon/Vycor® composites. All precursors underwent a second cycle of IL infiltration/pyrolysis with the target to finetune the pore structural characteristics of the carbonaceous matter nesting inside the separation layer. The pore structural assets and evolution of the gas permeation properties and separation efficiency of the as-derived composite membranes were investigated with reference to the duration of the second infiltration step. The transport mechanisms of the permeating gases were elucidated and correlated to the structural characteristics of the supported carbon phase and the analysis of LN2 adsorption isotherms. Regarding the gas separation efficiency of the fabricated Carbon/Vycor® composite membranes, He/CO2 ideal selectivity values as high as 4.31 at 1 bar and 25 °C and 4.64 at 0.3 bar and 90 °C were achieved. In addition, the CO2/N2 ideal selectivity becomes slightly improved for longer second-impregnation times