Organic and Third Phase in HNO3/TBP/n-Dodecane System: No Reverse Micelles

The composition and speciation of the organic and third phases in the system HNO3/TBP (tri-n-butyl phosphate)/n-dodecane have been examined by a combination of gravimetric, Karl Fischer analysis, chemical analysis, FTIR, and 31P NMR spectroscopy, with particular emphasis on the transition from the two-phase to the three-phase region. Phase densities indicate that third-phase formation takes place for initial aqueous HNO3 concentrations above 15 M, while the results from the stoichiometric analysis imply that the organic and third phases are characterized by two distinct species, namely the mono-solvate TBP⋅HNO3 and the hemi-solvate TBP⋅2HNO3, respectively. Furthermore, the 31P NMR spectra of organic and third phase show no significant chemical differences at the phosphorus centers, suggesting that the second HNO3 molecule in the third phase is bound to HNO3 rather than TBP. The third-phase FTIR spectra reveal stronger vibrational absorption bands at 1028, 1310, 1653, and 3200–3500 cm−1, reflecting higher concentrations of H2O, HNO3, and TBP. The molecular dynamics simulation data predict structures in accord with the spectroscopically identified speciation, indicating inequivalent HNO3 molecules in the third phase. The predicted structures of the organic and third phases are more akin to microemulsion networks rather than the distinct, reverse micelles assumed in previous studies. H2O appears to be present as a disordered hydrogen-bonded solvate stabilizing the polar TBP/HNO3 aggregates in the organic matrix, and not as a strongly bound hydrate species in aggregates with defined stoichiometry

Single Polymer Chain Surface Area as a Descriptor for Rapid Screening of Microporous Polymers for Gas Adsorption

The presented work shows that a qualitative assessment of the trends in surface area in a given microporous polymer family can be obtained by analyzing the properties of a single polymer chain. We analyzed the properties of polymers of intrinsic microporosity (PIMs) that contain imide groups (known as PIM-PIs) and obtained the surface area of available PIM-PIs and proposed some hypothetical structures that can result in higher surface areas and potentially more favourable properties for adsorption. The advantage of the proposed method is that it allows for a rapid screening of potential monomers avoiding the need to perform computationally expensive calculations

The behaviour of tributyl phosphate in an organic diluent

Tributyl phosphate (TBP) is used as a complexing agent in the Plutonium Uranium Extraction (PUREX) liquid-liquid phase extraction process for recovering uranium and plutonium from spent nuclear reactor fuel. Here, we address the molecular and microstructure of the organic phases involved in the extraction process, using molecular dynamics to show that when TBP is mixed with a paraffinic diluent, the TBP self-assembles into a bi-continuous phase. The underlying self-association of TBP is driven by intermolecular interaction between its polar groups, resulting in butyl moieties radiating out into the organic solvent. Simulation predicts a TBP diffusion constant that is anomalously low compared to what might normally be expected for its size; experimental nuclear magnetic resonance (NMR) studies also indicate an extremely low diffusion constant, consistent with a molecular aggregation model. Simulation of TBP at an oil/water interface shows the formation of a bilayer system at low TBP concentrations. At higher concentrations, a bulk bi-continuous structure is observed linking to this surface bilayer. We suggest that this structure may be intimately connected with the surprisingly rapid kinetics of the interfacial mass transport of uranium and plutonium from the aqueous to the organic phase in the PUREX process