Ethyl tert-butyl ether (ETBE) is a major biofuel mainly produced from the reaction of isobutene with a large excess of bioethanol. This ether greatly improves fuel combustion and limits the emission of toxic hydrocarbons. Moreover, thanks to its particular molecular structure, this ether does not accumulate into the environment contrary to methyl tert-butyl ether (MTBE). Nevertheless, during the industrial ETBE synthesis, this ether forms an azeotropic mixture containing 20 wt% of ethanol, which must be removed during the final purification stage. The ternary distillation process generally used for this separation is highly energy intensive. Several works have shown that the pervaporation membrane process (PV) could be a very good alternative for ETBE purification with very important energy savings. This chapter focuses on our on-going development of high performance bio-based cellulosic membranes for ETBE purification by PV. Cellulose acetate (CA) is extremely selective for ethanol removal from ETBE but its flux is very low. Different strategies for greatly improving its flux while maintaining a very high selectivity are described and the main relationships between membrane structure, morphology and properties are illustrated. In a first part, the grafting of CA by controlled radical polymerization enables to vary the length and the number of polymethacrylate grafts, inducing different copolymer morphologies and PV properties. In particular, it is shown that, for a same graft content in the bio-based membranes, the nanostructuration of the grafts plays a determining role on the separation features. The second part explores the development of purely bio-based membranes made of a CA backbone with bio-based polylactide grafts based on a controlled grafting by “click” chemistry. This strategy enables to plasticize the cellulosic membranes very efficiently and greatly improves the membrane properties. In the third part, the grafting of ionic liquids onto CA is reported as another very efficient way of inducing CA plasticization. The influence of the ionic liquid content and molecular structure is discussed to reveal the key parameters for the membrane properties. Several bio-based membranes with grafted ionic liquids have very improved pervaporation flux (up to almost 20 times that of virgin CA) and permeate ethanol only, corresponding to outstanding infinite separation factors for this challenging liquid/liquid separation.