Hydrocarbon separation is an energy-intensive process that is currently dominated by thermal distillation
1. Membrane techniques without phase changes can offer an energy-efficient alternative, but require membranes which are (i) stable in organic solvents; (ii) capable of enriching permeate streams in selected crude oil molecules; and (iii) have high permeance. While membranes have been widely utilized for sea water desalination and gas separation, it remains challenging to apply them in large-scale oil fractionation processes due to a lack of materials which are stable and selective in hydrocarbon liquids. Polymers of intrinsic microporosity (PIMs) and epoxysilicone have been used for processing non-polar liquids in organic solvent nanofiltration (OSN), and have been sucessfuldue to the hydrophobic nature of these materials. However, they can becomesignificantly swollen and plasticized in organic solvents, which hinders their application in separating small liquid hydrocarbon molecules. To overcome this issue, rigid PIM-like membranes were fabricated from spirocyclic polymers with aryl-N-aryl linkage. By locking the interconnectivity, the membranes demonstrated class-based separations of light crude oil molecules, but this was coupled with a penalty of low permeance due to the thick separation layer created from spin coating technique. By contrast, interfacial polymerization has been widely used to fabricate ultrathin polyamide and polyester films as the selective layer in thin film composite (TFC) membranes, enabling high solvent transport rates and an enduring separation performance in OSN. However, the hydrophilic nature of polyamide and polyester networks leads to limited permeance (typically below 5 L.m
-2.h
-1.bar
-1) of non-polar solvents such as toluene. Therefore, hydrophobic ultrathin nanofilms with high permeances are of great interest for hydrocarbon separations.
In this work, we synthesized multiblock oligomer amines, which comprised a central amine segment with two hydrophobic oligomer blocks, and used them to fabricate hydrophobic polyamide nanofilms by interfacial polymerization from self-assembled vesicles. These polyamide nanofilms provide transport of hydrophobic liquids more than 100 times faster than that of conventional hydrophilic counterparts. In the fractionation of light crude oil, manipulation of the film thickness down to ~10 nanometers achieves permeance one order of magnitude higher than that of current state-of-the-art hydrophobic membranes while retaining comparable size- and class-based separation. This high permeance can markedly reduce plant footprint, which expands the potential for using membranes made of ultrathin nanofilms in crude oil fractionation.
