Electrospun hierarchical fibrous composite membrane for pomegranate juice concentration using osmotic membrane distillation

A dual-layered hierarchical fibrous composite (HFC) membrane with poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) as a thin active layer and poly(ethylene terephthalate) (PET) as a thick support layer was fabricated through electrospinning process. The membrane was tested for the concentration of clarified pomegranate juice through the osmotic membrane distillation (OMD) process. Experimental data showed that the transmembrane water flux until 8.621 ± 0.235 kg.m−2. h−1 was achieved at 25 ± 1 °C, which is about 4-fold higher than most of the reported work. The juice was successfully concentrated to 51.3 ± 0.052°Bx in a total time of 25.5 h. Membrane hydrophobicity analysis showed that the contact angle of the membrane dropped from 143.7°±3° to 120.1°±3°, while the liquid entry pressure decreased from 28.0 ± 1.8–25.0 ± 1.7 kPa, after the completion of the OMD process. Detailed morphology analysis depicted that pore blockage occurred due to the gel layer formation when the juice viscosity increased exponentially during the final stages of OMD process. Gel layer formation along with random fouling spots were found to be the main cause of drop in water vapor flux. However, simple washing of the membrane with deionized water effectively cleaned the fouling areas and removed the gel layer from the pores of the membrane. The first-ever application of dual-layered electrospun HFC membrane in the OMD concentration of pomegranate juice thus displayed a satisfactory performance, benefiting from the unique structures of the HFC membrane having the minimized mass transfer resistance and durable antifouling performance.