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Butane and Naphtha Hydroisomerization
Published in Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk, Petroleum Refining, 2019
Mark J. Kaiser, Arno de Klerk, James H. Gary, Glenn E. Hwerk
There are three pentane isomers: n-pentane, isopentane (2-methylbutane), and neopentane (2,2-dimethylpropane). Neopentane is practically never formed during pentane hydroisomerization, because there is no catalytic pathway that enables its formation. The only equilibrium that is of practical significance is that between n-pentane to isopentane.
A comprehensive review of geothermal energy evolution and development
Published in International Journal of Green Energy, 2019
M. Soltani, F. Moradi Kashkooli, A.R. Dehghani-Sanij, A. Nokhosteen, A. Ahmadi-Joughi, K. Gharali, S.B. Mahbaz, M.B. Dusseault
Mohan et al. (2015) used process optimization software (ASPEN Plus V7.3) for modeling an integrated gasification combined cycle (IGCC) paired with an Enhanced Geothermal System (EGS). The combined system would work by injecting the CO2 produced in the IGCC plant into a geothermal source (Dipippo 1999), and then using the super-critical CO2 in an EGS with ORC power generation to produce additional electricity. This process would symbiotically sequester CO2 and produce extra electrical energy. For a 25-year analysis, they considered the effects of four different ORC working fluids (neopentane, isopentane, n-butane and isobutane) and two different temperatures (200°C and 300°C) for the geothermal bedrock that the CO2 is injected into. The authors’ results regarding power production can be seen in Figure 20.
Application of the 2PT model to understanding entropy change in molecular coarse-graining
Published in Soft Materials, 2020
Marvin P. Bernhardt, Marco Dallavalle, Nico F. A. Van der Vegt
Figure 2 compares the radial distribution functions of the center of mass of the CG models to their atomistic reference. In most cases the CG models reproduce the radial distribution functions of the underlying atomistic system, with some prominent exceptions. The single bead mapping is particularly successful in describing the RDF of neopentane, the UA coarse-graining is effective in capturing the center of mass RDF of atomistic chloroform. As far as the dumbbell of neopentane is concerned, the heterogeneity in the bead-size affects the quality of the model. Having a molecule with tetrahedral symmetry, such as neopentane, represented as an asymmetric two bead object leads to discrepancies in the RDFs. The first peak is split into two peaks. The CH3 beads are able to come closer to each other (first peak), when compared to the much larger C4H9 beads (second peak). The mismatch between AA and single bead chloroform radial distribution functions can be attributed to the approximation of describing an anisotropic molecule with a spherically symmetric potential. For example, a chloroform () molecule has lower symmetry with respect to tetrachloromethane () and is further away from an isotropic sphere representation. That is the reason why, as shown in a previous work, the agreement between AA and CG is better in the case of tetrachloromethane.[55] The shift to the left in the radial distribution functions of some CG system suggests higher densities of the CG model. For comparison, in Table 1 the average densities of the NPT simulations are reported.
Construction of a composite-sphere model for molecules of tetrahedral symmetry
Published in Molecular Physics, 2021
Franklin Ramos, Ana Ramos, Giuseppe Pellicane, Lloyd L. Lee
Our atomistic view of a molecule where all chemical bonds are broken is in stark contrast to Lavoisier’s bonded chemical elements in a molecule with fixed proportionality and stereo-chemical structures. This fixed ratio is termed bond saturation or steric saturation. It is the basis of chemistry. The composite spheres belong to the former point of view except it adopts a careful design of the interaction forces in an attempt to re-establish the correct bonded proportion. In certain respects, it is similar to Wertheim’s TPT theory where each hard sphere is endowed with one, two, or more ‘glue spots’ on its surfaces (the outer spherical shells). In the first order TPT theory, the chemical saturation is preserved, but the bonding angles (stereo-structures) are not strictly obeyed. In the second-order theory, the angular distributions are taken into account. We achieve bond saturation in the hs-neopentane by choosing the diameters in such a way as to avoid over-saturation of the centre-carbon atom but allow the methyl groups to freely attach to it. The sizes are chosen so that the preferred geometry is the tetrahedral structure (i.e. based on the spherical order). While at the outset of this research, all future outcomes were uncertain: namely whether this strategy might work or might not work in generating steric saturation and/or the fixed bond angles. Our Monte Carlo simulations were designed to find out the limits of validity. The calculations we performed eventually showed that we obtained a high degree of pentamer formation. However, we are missing at least in two aspects for a complete chemical theory: (1) no strict adherence to the bond angles, and (2) appearance of finite concentrations of other (unwanted) oligomers (tetramers, hexamers, heptamers, etc.). The first mismatch is common to other existing ‘structural’ integral equations: as in the RISM approaches and the Wertheim theories (first-order) – i.e. lack of fidelity of stereo-chemistry. The second error does not occur with the latter two theories.