Abstract
•The first case of retrofitting of extractive distillation units by pervaporation membranes.•A new, energy optimized, graphic-assisted iterative design of extractive distillation systems.•Even medium-low performance membranes can produce energetically advantageous retrofittings.•The Pervaporation Index Analysis gives an incorrect prediction of membrane performances.1Contributed equally to this work.
In the context of the production of n-butyl acetate, acetic acid or ethyl acetate from methyl acetate, a pervaporation module was employed in order to retrofit the extractive distillation unit used to recover methyl acetate from a methanol/methyl acetate industrial waste stream. The PolyAl TypM1® membrane (from PolyAn™) was first tested using a wide feed concentration range (11–90mol% methanol) and three temperatures (30, 36, 44°C). Then, it was compared with other commercial membranes reported in literature (at 40–45°C) at the methanol/methyl acetate azeotropic composition, resulting in a medium/low separation factor and with the highest flux. This ensured the simulation of a very challenging condition for the retrofitting from an energetic point of view (i.e., for moderate or low separation factor membranes: the higher the flux, the higher the process energy requirement).
The retrofitting permits to avoid the use of a solvent during azeotropic separation. Moreover, during comparison of the retrofitted hybrid pervaporation-distillation unit with the source industrial extractive distillation unit, an overall energy saving up to ∼38% was demonstrated (∼23% when only the energy consumed by the heaters is taken into account).
In addition, major hydraulic modifications could be avoided employing structured packing and membranes of higher separation factors.