The authors' claim is that it is cheaper than other catalytic methods that have been explored/invented to depolymerize PET into TPA monomers. These qualitative cost estimates are based on the reaction conditions (temperature, solvent, other reactants (in this case, humid air)) and the unit operations involved in the downstream separation processes that isolate the TPA product from unreacted PET. The largest hurdle that precludes widespread deployment of technologies for PET recycling, as well as those for most other plastics, occurs (way) upstream of the reaction and separation train. The highest cost is related to collecting and sorting used PET bottles and TPA-derived textiles.
Mechanical recycling or any flavor of chemical recycling (pyrolysis, hydrolysis, etc.) all suffer from the same hurdle. If the target product of the recycling process is a TPA-derived plastic (be it for clothing or soda bottles), then mechanical recycling is usually cheaper, since it produces a product that only needs to be reshaped and remolded to give shirts or jugs. Chemical recycling converts PET into its constitutive monomers, and to (re)produce a TPA-derived plastic from the monomers requires a not inexpensive (re)polymerization step, in addition to reshaping and remolding.
Chemists, even highly regarded ones like Tobin Marks, are less interested in "solving" the PET recycling issue and more interested in the fundamental chemistry involved in chemical recycling. Issues of Green Chemistry (or blurbs in phys.org) are not the appropriate reading materials to get insight into costs, scale-up, etc.. Very few, if any, academic journals are focused on such matters, and rightly so, in my opinion.
Jet fuel is comprised mostly of hydrocarbons with 8 to 16 C atoms, and a large fraction of these hydrocarbons are straight-chain alkanes.
Combustion of dodecane (a C12 straight-chain alkane) makes 12 CO2 molecules. A 747 jet consumes about 4 L of jet fuel per second when in flight. Based on the density and molecular weight of dodecane and the stoichiometry of its combustion reaction, you'd arrive at something like 0.01 ton of CO2 emitted per second of flight time.
Membranes segregate mixtures of molecules into their individual components. This segregation typically requires pore diffusion and relies on the sizes of the molecules being distinct; the size of the pores within the membrane is chosen so that small molecules (e.g., Helium) can pass through it while larger ones (e.g., Neon) cannot. The behavior of these graphene-based membranes does not follow this typical train-of-thought; water and helium are of similar size, yet these membranes allow facile permeation of water but blocks entirely the passage of He.
This is because these membranes do not rely on pore diffusion to segregate the molecules. Water permeates through these graphene-based membranes through an entirely different mechanism that relies on the intermolecular interactions between water molecules (i.e., hydrogen bonded networks of water). One He molecule does not interact strongly with another He molecule, and He molecules do not interact strongly with graphene. Water molecules, however, interact strongly not only with other water molecules but with graphene surfaces. This discrepancy in the intermoleculer and fluid-surface interactions is what fundamentally gives rise to this "strange" behavior of these graphene-based membranes.
Mechanical recycling or any flavor of chemical recycling (pyrolysis, hydrolysis, etc.) all suffer from the same hurdle. If the target product of the recycling process is a TPA-derived plastic (be it for clothing or soda bottles), then mechanical recycling is usually cheaper, since it produces a product that only needs to be reshaped and remolded to give shirts or jugs. Chemical recycling converts PET into its constitutive monomers, and to (re)produce a TPA-derived plastic from the monomers requires a not inexpensive (re)polymerization step, in addition to reshaping and remolding.
Chemists, even highly regarded ones like Tobin Marks, are less interested in "solving" the PET recycling issue and more interested in the fundamental chemistry involved in chemical recycling. Issues of Green Chemistry (or blurbs in phys.org) are not the appropriate reading materials to get insight into costs, scale-up, etc.. Very few, if any, academic journals are focused on such matters, and rightly so, in my opinion.