Ultrahigh-Purity Vanadyl Petroporphyrins

Petroporphyrins contribute to many of the challenges encountered when producing, transporting, and refining heavy crude oil and bitumen. They are the source of heavy metals that poison catalysts and may facilitate the aggregation, deposition, and emulsion formation exhibited by asphaltenes. Here, they are extracted and enriched to ultrahigh purities from several sources: an Athabasca bitumen, a Canadian northern tier crude oil, and a North American heavy crude oil. Our motivation is to produce usable quantities that can be characterized and used in model studies to understand the molecular structure of asphaltenes and to probe asphaltene–petroporphyrin intermolecular interactions, in the bulk and at interfaces. Extraction is performed in a Soxhlet apparatus. The porphyrin-rich extract is then further purified using extrography (on silica-packed columns) and chromatography (on alumina-packed columns). The process yields purified petroporphyrins in unprecedented quantities (>100 mg). These purified petroporphyrins can be further refined to ultrahigh purities (>85% petroporphyrin by weight) using temperature and centrifugation to fractionate them into more and less soluble fractions. Petroporphyrins are characterized by ultraviolet–visible spectroscopy, X-ray fluorescence spectroscopy, and mass spectrometry (time of flight and Fourier transform ion cyclotron resonance). The majority of the petroporphyrins are simple etioporphyrin (407 nm Soret band) or deoxophylloerythroetioporphyrin (410 nm Soret band) types, but some are more functionalized compounds with highly broadened and shifted Soret bands

Heat Capacity Studies of Surface Water Confined on Cassiterite (SnO₂) Nanoparticles

Heat capacities have been measured on a series of 2, 6, 11, and 20 nm SnO₂ nanoparticles with varying amounts of surface water as well as on a bulk parent material, in the temperature range from 2 to 300 K. By subtracting the heat capacity values for 2 nm SnO₂ samples with different water contents, we calculated the heat capacity contribution of the anhydrous lattice and found that the lattice heat capacity of the nanoparticle is the same as that of the bulk material within experimental error. This is further confirmation that, for several systems, once one accounts properly for the heat capacity of adsorbed water there is no measurable excess lattice heat capacity related to particle size. Using this result, we have calculated the heat capacities of confined water on the surfaces of the various SnO₂ nanoparticles and found the water behavior to be generally similar to that of bulk ice, although with some differences in detail. The heat capacity of confined water on these same SnO₂ nanoparticles calculated from inelastic neutron scattering spectra and those determined calorimetrically agree within experimental error at temperatures below 200 K

Influence of Particle Size and Water Coverage on the Thermodynamic Properties of Water Confined on the Surface of SnO₂ Cassiterite Nanoparticles

Inelastic neutron scattering (INS) data for SnO₂ nanoparticles of three different sizes and varying hydration levels are presented. Data were recorded on five nanoparticle samples that had the following compositions: 2 nm SnO₂<b>·</b>0.82H₂O, 6 nm SnO₂<b>·</b>0.055H₂O, 6 nm SnO₂<b>·</b>0.095H₂O, 20 nm SnO₂<b>·</b>0.072H₂O, and 20 nm SnO₂<b>·</b>0.092H₂O. The isochoric heat capacity and vibrational entropy values at 298 K for the water confined on the surface of these nanoparticles were calculated from the vibrational density of states that were extracted from the INS data. This study has shown that the hydration level of the SnO₂ nanoparticles influences the thermodynamic properties of the water layers and, most importantly, that there appears to be a critical size limit for SnO₂ between 2 and 6 nm below which the particle size also affects these properties and above which it does not. These results have been compared with those for isostructural rutile-TiO₂ nanoparticles [TiO₂<b>·</b>0.22H₂O and TiO₂<b>·</b>0.37H₂O], which indicated that water on the surface of TiO₂ nanoparticles is more tightly bound and experiences a greater degree of restricted motion with respect to water on the surface of SnO₂ nanoparticles. This is believed to be a consequence of the difference in chemical composition, and hence surface properties, of these metal oxide nanoparticles