CONICET | Buscador de Institutos y Recursos Humanos

The present work demonstrates the potential of oil/n-hexane miscella separation from alocal factory via a hybrid nanofiltration-evaporation process. In the membrane separation,solvent resistance nanofiltration (SRNF) membranes lab-made of polyvinylidene fluoride(PVDF) as support, poly-dimethylsiloxane (SI) or cellulose acetate (CA) as coating materialsand a commercial composite membrane were used. To perform this study, a representa-tive spiral-wound (SW) module made-up with the membranes previously mentioned wasemployed. For miscella mass transfer through the SW module, a plug-cross-mixing flow(PCMF) model was used. From experimental miscella permselectivity data at T = 30◦C andp = 20 bar, an analytical final expression of mass balance was obtained which correlatedthe retentate oil concentration with the membrane area. The multistage process of suchmembranes was integrated by a number of single-stage in series. In the multistage mem-brane performance evaluation, several restrictions were imposed on the model consideringthe operational conditions of the local factory that uses an evaporation and steam strippingprocess. Seven stage (total membrane area 702 m2) using PVDF-10% SI membrane gave thebest oil/n-hexane separation effectiveness. From this, a hybrid SRNF-evaporation processwas proposed in which the selected membrane multistage process replaced the first andthe second evaporators. The permeate stream rich in n-hexane (90.5 w%) was fed to thesection of the expeller in which the oil was depleted, and the retentate stream enriched inoil (86.7 w%) was pumped to the third-stage evaporator and strippers, where the oil wasconcentrated to >99 w%. The overall energy demand was significantly reduced (≈50%) andthere was around 60% less consumption of cooling water and steam by the SRNF-assistedprocesses in comparison with the conventional factory evaporation process.

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