Giovanni Golemme

Gas permeation properties of phenylene oxide polymers

Abstract Gas permeability (Pi) and diffusion (Di) coefficients in respect to several gases (H2, O2, N2, CO, CO2, CH4) have been measured for poly(2,6-dimethylphenylene oxide) (PMPO), poly(2,6-diphenylphenylene oxide) (PPPO), and phenylene oxide copolymers containing methyl, phenyl, and allyl radicals as side groups. X-ray diffraction study shows that both homopolymers are semicrystalline materials, whereas all the copolymers are completely amorphous. The results show that a replacement of methyl by phenyl groups in PMPO/PPPO pair is accompanied by decrease in the P values. A transition from semicrystalline PMPO to amorphous copolymers results in a decrease in permeability and solubility coefficients and not in a growth of these parameters as can be expected on the basis of the behavior of other semicrystalline polymers (e.g. polyolefins). It is supposed that the crystallites of PMPO, and possibly of PPPO are packed loosely and, hence, take part in sorption and gas transport. This assumption is in agreement with numerous X-ray data as well as the results of positron annihilation study of these polymers.

Simulation of CO2 hydrogenation with CH3OH removal in a zeolite membrane reactor

A thermodynamic analysis of the CO2 hydrogenation to methanol where competitive reactions take place is presented for a membrane reactor (MR) where methanol was selectively removed. A non-isothermal mathematical model was written to simulate a micro-porous MR. Zeolite membranes with different values of the CH3OH and H2O permeances were considered in the MR modelling. The effect of temperature, pressure and species permeation on the conversion, selectivity and yield was analysed. A higher CO2 conversion and CH3OH selectivity can be reached by the use of an MR. An increased CH3OH yield allows to reduce the consumption of reactant and also to operate at lower pressures and higher temperatures, a fact, which favours the kinetics reducing the residence time and the reactor volume. The MR with the highest CH3OH/H2O permeance ratio resulted in better selectivity and yield of CH3OH with respect to the other MR characterised by a higher conversion.

Preparation and characterization of high-performance dehydrating pervaporation alginate membranes

In a previous work, sodium alginate dense membranes demonstrated a good combination of selectivity and permeation flux for dehydrating organic solvents by pervaporation. In this article, the pervaporation performances of alginate composite membranes has been investigated to find out the best condition of membrane formation and the optimum operating conditions. Some ultrafiltration membranes made of poly-(vinylidene fluoride), polyacrylonitrile, and hydrolyzed polyacrylonitrile—either commercially available or prepared in our laboratories—were used as supports for the composite membranes. Sodium alginate dense membranes, modified through ion exchange of sodium with multivalent metal ions (such as Al3+, Cr3+, Fe3+, and Mg2+) have also been prepared, and their permselectivities have been tested for the water–ethanol mixture. An interesting stability of the modified membranes in long-term operation is expected.

Amine-functionalized SBA-15 in poly(styrene-b-butadiene-b-styrene) (SBS) yields permeable and selective nanostructured membranes for gas separation

New nanostructured hybrid membranes for gas separation have been prepared and characterized for the first time in the literature by using a block copolymer, poly(styrene-b-butadiene-b-styrene) (SBS), and aminated SBA-15. Short mesopore channels, platelet SBA-15 particles with a high surface density of 3-aminopropyl grafts (3.8 nm−2) and modest surface area reduction (45%) were prepared, characterized and used as a filler. The gas transport characterization of the hybrid membranes indicates that with a 10 wt% content of aminated filler, outstanding performances in terms of selectivity and permeability for the CH4/N2 and the CO2/N2 gas pairs can be obtained. In particular, the CH4/N2 ideal selectivity of 7.3 is higher than the values of the existing block co-polymers used for this separation and of mixed matrix membranes described to date in the literature. Membranes with such a high separation factor may enable the exploitation of natural gas with high N2 content and increase the amount of methane that can be economically recovered. The combination of the CO2/N2 ideal selectivity of 53 with a CO2 permeability of 173 Barrer demonstrates that the new hybrid membranes prepared in this study deserve further attention as a practical commercial solution also for the post-combustion capture of carbon dioxide. Finally, the small and flat particles dispersed in the polymer lend themselves to the fabrication of thin industrial membranes with enhanced productivity.

Dynamical homeotropic and planar alignments of chromonic liquid crystals

We report on our latest studies on alignment of chromonic liquid crystals, a special class of molecules which recently attracted the attention of researchers. In particular, we show a detailed study of planar anchoring of disodium cromoglycate (DSCG) and, for the first time in the literature, a stable homeotropic alignment, achieved using a surface property of the alignment layer, i.e. the hydrophobicity. Excellent candidates from this point of view are pure polybutadiene (PB) and polydimethylsiloxane (PDMS). In fact, for the former the homeotropic anchoring stabilizes after one day, while for the latter stabilization occurs soon after cooling from the isotropic phase. After a long time both types of alignments (planar and homeotropic) evolve into thermodynamically stable configurations, i.e. ribbon structures. An explanation of the behaviour is given.

Self‐diffusion measurements of organic molecules in PDMS and water in sodium alginate membranes

The self-diffusion of some organic molecules in silicone rubber and of water and water-ethanol mixtures in sodium alginate membranes was investigated to obtain information on the transport behavior in these systems. The temperature dependence of self-diffusion was examined by the pulsed field gradient NMR technique. The experimental data confirm the homogeneous amorphous nature of PDMS and the affinity of silicone rubber to apolar solvents. The interrelations between solvent and polymer structures of the sodium alginate membrane varying the temperature have been obtained using differential scanning calorimetric. The results have been compared with the trend of self-diffusion coefficients, and structure modifications of the membranes have been evidenced. The overall results confirm the potentialities of the technique used in measuring transport parameter in polymeric membranes.

Membrane Operations for Industrial Applications

A resource-intensive industrial development, particularly in some Asian countries, characterized the last century. Its main causes can be ascribed to the significant elongation of life expectation, and to the overall increase in the standards characterizing the quality of life. The drawback of these positive aspects is the emergence of problems related to the industrial development: water stress, the environmental pollution, and the increase of CO2 emissions into the atmosphere.

Synthesis and gas sorption behaviour of ZIF-90 with large pore volume

Stoichiometric triethylamine in methanol produces sub-micron ZIF-90 in 98% yield with the largest gas uptakes ever measured. Micropore volume and surface area are compatible with an empty pore network and with crystallographic data, but the occurrence of crystal defects, such as missing ligands or Zn2+ ions, although improbable, can not be ruled out.