Separation of olefin/paraffin is an energy-intensive and difficult separation process in petrochemical industry. Energy-efficient adsorption process is considered as a promising alternative to the traditional cryogenic distillation for separating olefin/paraffin mixtures. In this work, we explored the feasibility of adsorptive separation of olefin/paraffin mixtures using a magnesium-based metal-organic framework, Mg-MOF-74. Adsorption equilibria and kinetics of ethane, ethylene, propane, and propylene on a Mg-MOF-74 adsorbent were determined at 278, 298, and 318 K and pressures up to 100 kPa. A dual-site Sips model was used to correlate the adsorption equilibrium data, and a micropore diffusion model was applied to extract the diffusivities from the adsorption kinetics data. A grand canonical Monte Carlo simulation was conducted to calculate the adsorption isotherms and to elucidate the adsorption mechanisms. The simulation results showed that all four adsorbate molecules are preferentially adsorbed on the open metal sites where each metal site binds one adsorbate molecule. Propylene and propane have a stronger affinity to the Mg-MOF-74 adsorbent than ethane and ethylene because of their significant dipole moments. Adsorption equilibrium selectivity, combined equilibrium and kinetic selectivity, and adsorbent selection parameter for pressure swing adsorption processes were estimated. The relatively high values of adsorption selectivity suggest that it is feasible to separate ethylene/ethane, propylene/propane, and propylene/ethylene pairs in a vacuum swing adsorption process using Mg-MOF-74 as an adsorbent.

Synthetic, structural, spectroscopic and aging studies conclusively show that the main colorant of historical iron gall ink (IGI) is an amorphous form of Fe(III) gallate• xH 2 O (x = ∼1.5−3.2). Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spectroscopy, XRD, X-ray photoelectron spectroscopy, and Mossbauer spectroscopy confirm the relationship between the model and authentic samples. These studies settle controversy in the cultural heritage field, where an alternative structure for Fe(III) gallate has been commonly cited.P rior to the 20th century, historical iron gall ink (IGI) was by far the most common writing material of the western world, and a plethora of recipes from which to produce the ubiquitous dark, brown-black ink can be found starting from at least the Middle Ages. This ink has been used to pen many of the most important documents and drawings in human history, including unique, hand-written works such as Thomas Jefferson's original draft of the Declaration of Independence, Abraham Lincoln's first draft of the Emancipation Proclamation, and Beethoven's original scores. While the virtue of IGI lies in its relative permanence, the great vice of this medium lies in its well-known tendency to degrade paper and parchment substrates. 1−7 Despite its historical importance, there is little consensus on the chemical structure or composition of the iron-gallate complex, the main species responsible for the color of the IGI. We describe here a series of synthetic, structural, spectroscopic, and aging studies, which unequivocally demonstrate that the primary colorant in IGI is an amorphous form of an octahedral Fe(III) gallate metal organic framework structure that has previously been described by Wunderlich 8−10 and Feller. 11 Unlike the majority of prior studies, we use authentic IGI precursors to prepare both crystalline and amorphous forms of the IGI precipitate and study the crystal-to-amorphous transition by way of XRD, thermal gravimetric analysis (TGA), IR and Raman, Mossbauer, and X-ray photoelectron spectroscopy (XPS). Spectroscopic comparisons with historical documents prove the relevance of the synthetic crystalline and amorphous forms of the model IGI materials to those found in the authentic manuscripts.

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We report the high strain-rate response of a spiropyran (SP) mechanophore in poly(methylmethacrylate). Previous work on this system has demonstrated a reversible bond scission in the SP under local tensile force, converting it to a fluorescent merocyanine form. A Hopkinson bar was used to apply fast compressive loads at rates from 10 2 to 10 4 s 21 , resulting in significant activation of the SP near fracture surfaces. However, comparison with a similar thermochromic SP reveals that much of the observed activation likely arises from thermal effects during high-rate fracture. These results show the importance of a thermally active control system in distinguishing mechanochromic response during high-rate loading. Microscale fluorescence mapping of the fracture surfaces using a confocal Raman microspectrometer suggests that some distinct mechanical activation may be occurring in craze-like regions during fibril rupture. The thermal response of the SP is useful in its own right for characterizing plastic heating regions during dynamic fracture.

Oxidation of ligand-protected aluminum clusters: an ab-initio molecular dynamics study. "J. Chem. Phys. 140, 104313 (2014 We report Car-Parrinello molecular dynamics simulations of the oxidation of ligand-protected aluminum clusters that form a prototypical cluster-assembled material. These clusters contain a small aluminum core surrounded by a monolayer of organic ligand. The aromatic cyclopentadienyl ligands form a strong bond with surface Al atoms, giving rise to an organometallic cluster that crystallizes into a low-symmetry solid and is briefly stable in air before oxidizing. Our calculations of isolated aluminum/cyclopentadienyl clusters reacting with oxygen show minimal reaction between the ligand and O 2 molecules at simulation temperatures of 500 and 1000 K. In all cases, the reaction pathway involves O 2 diffusing through the ligand barrier, splitting into atomic oxygen upon contact with the aluminum, and forming an oxide cluster with aluminum/ligand bonds still largely intact. Loss of individual aluminum-ligand units, as expected from unimolecular decomposition calculations, is not observed except following significant oxidation. These calculations highlight the role of the ligand in providing a steric barrier against oxidizers and in maintaining the large aluminum surface area of the solid-state cluster material. [http://dx

Temperature-dependent vapor pressures of solid explosives and their byproducts are calculated to an accuracy of 0.32 log units using a modified form of the conductor-like screening model for real solvents (COSMO-RS). Accurate predictions for solids within COSMO-RS require correction for the free energy of fusion as well as other effects such as van der Waals interactions. Limited experimental data on explosives is available to determine these corrections, and thus we have extended the COSMO-RS model by introducing a quantitative structure−property relationship to estimate a lumped correction factor using only information from standard quantum chemistry calculations. This modification improves the COSMO-RS estimate of ambient vapor pressure by more than 1 order of magnitude for a range of nitrogen-rich explosives and their derivatives, bringing the theoretical predictions to within typical experimental error bars for vapor pressure measurements. The estimated temperature dependence of these vapor pressures also agrees well with available experimental data, which is particularly important for estimating environmental transport and gas evolution for buried explosives or environmentally contaminated locations. This technique is then used to predict vapor pressures for a number of explosives and degradation products for which experimental data is not readily available.