D3.2 – REPORT ON 2ND GENERATION OF ADVANCED PVDF MEMBRANES FOR MD

This deliverable provides an update on the results obtained in the second semester of 2023 on the development (CNR) and characterization (UNICAL and CNR) 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 membranes 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). 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°. However, the results in terms of permeate flux (using deionized water as a feed) in Direct Contact Membrane Distillation (DCMD) processes for coated membranes showed a significant reduction of flux with respect to uncoated ones, probably due to partial occlusion of the pores, together with a lower porosity. Considering that in the MD pilot the Air Gap Membrane Distillation (AGMD) configuration will be used, which is characterised by a lower flux with respect to the DCMD, to obtain higher fluxes for the second generation of membranes, both GVS and CNR-ITM membranes of bigger pore size (around 0.45 and 0.8 micron) were coated. In particular, main goals of this deliverable were: 1. To replicate the preparation of PVDF membranes with larger pores (from 0.45 μm to 0.8 μm), using GVL as a greener solvent via phase inversion at CNR-ITM; 2. To functionalize both prepared GVL and commercial GVS PVDF membranes (0.45 μm and 0.8 μm pore size) using AFAS solution by dip-coating deposition at CNR-ISSMC; 3. To characterize the membranes coated and uncoated at UNICAL and CNR-ITM; 4. To carry out at CNR-ITM DCMD characterization tests (with deionised water as feed) on the produced PVDF membranes, specifically: • PVDF membranes prepared by CNR-ITM; • PVDF membranes supplied by GVS Company; • PVDF membranes (CNR-ITM) coated following the procedure developed at CNR-ISSMC; • PVDF membranes (GVS) coated following the procedure developed at CNR-ISSMC.