D3.3 – REPORT ON 3RD GENERATION OF ADVANCED PVDF MEMBRANES FOR MD

This deliverable provides an update on the results obtained on the development (CNR) and characterization (UNICAL and CNR) of the third generation of membranes prepared with green solvents and of specific coatings to enhance their performance in Membrane Distillation (MD). This approach foresees continuous follow-up of the activities in membrane preparation, coating procedures and characterization, in the perspective of developing sustainable membranes suitable for MD processes. The first deliverable (D3.1) focused on the preparation of different poly (vinylidene fluoride) (PVDF) flat sheet membranes using γ-Valerolactone (GVL) as a bio-based and greener solvent, obtaining a pore size ranging from 0.1 μm to 1 μm. It also identified the PVDF membrane with a mean flow pore size of 0.2 μm for the first surface functionalization by dip-coating deposition with hybrid organic/inorganic solution coatings (AFAS coating was finally chosen) - first generation of membranes. A commercial PVDF 0.2 μm membrane (GVS Company) was also coated with the same material. The results confirmed a significant enhancement of the hydrophobicity for both coated membranes (contact angle around 170° with the AFAS coating), together with an improvement of the repellency of the industrial “Rinsing” wastewater provided by GVS (γ=32 mN/m), for which the AFAS coating showed a contact angle of about 140°. When tested in a Direct Contact Membrane Distillation (DCMD) lab set-up with deionised water, all membranes were quite stable in time. Nevertheless, coated membranes showed a reduction of flux with respect to uncoated ones, probably due to a partial occlusion of the pores, together with the lower porosity. In particular, a flux of 1.6 and 3.8 kg/m2h was registered for the 0.2 μm PGVL (prepared with the green solvent) and GVS (commercial) coated membranes, respectively. To increase the permeate flux, the second deliverable (D3.2) focused on GVS and CNR-ITM membranes with larger pore sizes (approximately 0.45 and 0.8 microns), as second generation of membranes. A hybrid organic/inorganic AFAS coating was selected and deposited on the membrane surface by dip coating. From the DCMD experiment results, GVS membranes exhibited an increase in flux with pore size (as expected), whereas PGVL membranes showed the opposite trend, likely due to traces of PVPK17 in the polymeric matrix. Preliminary results on PGVL0.5 membranes (prepared without PVP) demonstrated an improvement in flux (around 7.5 kg/m²h) compared to the corresponding PGVL membrane prepared with PVP (around 5 kg/m2h). Regarding the coated membranes, although they showed a decrease in flux compared to the uncoated ones, these fluxes were still higher than those recorded for the 0.2 μm coated membranes (first generation). Green membranes with pore sizes ranging from 0.2 to 0.5 μm were the focus of the third generation of membranes (D3.3), to reduce wetting risk over the time. For further enhancing flux (by reducing thickness), but also mechanical stability, these membranes were cast on GVS non-woven support (Sanko support). In particular, the main goals of the work carried out were: 1.To complete the characterization of the second generation PVDF membranes (deliverable D3.2) (UNICAL and CNR); 2. To produce and scale-up unsupported PGVL0.5 coated membranes - 21 x 21 cm (CNR-ITM and CNR-ISSMC); 3. To produce and scale-up supported PGVL0.2 and PGVL0.5 coated membranes (using the GVS support) - 21 x 21 cm - (CNR-ITM and CNR-ISSMC); 4. To scale-up the coating on the commercial GVS0.2 and GVS0.45 membranes - 21 x 21 cm – (CNR-ISSMC); 5. To characterize the third generation of membranes (UNICAL and CNR); 6. To carry out Air Gap Membrane Distillation (AGMD) tests on scaled and coated membranes with GVS rinsing water and CWT module (UNICAL).