Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation. 2. Low-Relative-Volatility Binary Mixtures with Heavy Entrainer.

All former studies reported that the separation of the low relative volatility binary mixture by using a heavy entrainer in a batch rectifier imposed the obligatory withdrawal of the most volatile original component. In this paper, we demonstrate that this does not always happen and that the product sequence can be unambiguously determined from the sole analysis of thermodynamic properties of residue curve maps and the occurrence of unidistribution lines and univolatility lines, following the general feasibility criterion enounced in part I for the separation of azeotropic mixtures using heavy or light entrainers. For low relative volatility mixtures, the original component having an intermediate boiling temperature can be also drawn as the first distillate product. Cases concerning 94% of statistically occuring zeotropic ternary mixtures are investigated, allowing to define the product sequence without any previous calculation of the liquid composition profile inside the column. Preliminary feasibility results are confirmed by computing maps of extractive and rectifying liquid composition profiles using a simplified mass balance. Final validation is done via rigourous simulation using ProSim Batch software

Fischer-tropsch synthesis: Differences observed in local atomic structure and selectivity with pd compared to typical promoters (Pt, Re, Ru) of Co/Al <inf>2</inf>O <inf>3</inf> catalysts

Pd was examined as a promoter for Fischer- Tropsch synthesis, and its effects on cobalt oxide reduction and product selectivities relative to commonly used promoters (i.e., Pt, Re, and Ru) at atomically equivalent levels were compared. Pd was identified to promote cobalt oxide reduction to even lower temperatures than Pt and Ru. However, Pd addition deleteriously affected product selectivity, and a clear shift to favor light products was observed. XANES analysis of an activated model catalyst revealed that Pd was in the reduced state. Local atomic structure was examined by EXAFS. Unlike Pt, Re, and Ru promoters, where previous investigations by groups such as Dr. Guczi's and ours have only observed coordination of the promoter with cobalt, Pd displayed both direct coordination to Co as well as other Pd atoms. The results suggest that this feature may be responsible for the measurably higher light gas selectivities observed. © Springer Science+Business Media, LLC 2012

Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation. 4. Azeotropic Mixtures with Intermediate Boiling Entrainer

This paper shows how knowledge of the univolatility and nidistribution line location and residue curve analysis help to assess the feasibility of batch extractive rectifying or stripping distillation of azeotropic mixtures by using an intermediate boiling entrainer. We consider five minimum boiling (minT) azeotropic mixtures AB with entrainer E, namely, acetone−heptane with benzene, methanol−toluene with triethylamine, methyl acetate−cyclohexane with carbon tetrachloride, dichloromethane−ethanol with acetone, and ethyl acetate−heptane with benzene; and one maximum boiling (maxT) azeotropic mixture, namely, chloroform−ethyl acetate with either 2-chlorobutane, isobutylchloride, bromopropane, or bromochloromethane. All ternary diagrams A−B−E belong to the 1.0-1b class, for which all three possible univolatility, !AB, !BE, and !AE, and unidistribution lines, KA, KB, and KE can exist. With application of the general feasibility criterion of Rodriguez-Donis et al. (Ind. Eng. Chem. Res. 2009, 48 (7), 3544−3559), both azeotropic components, A and B, accomplish the criterion, and they can be recovered, A in an extractive rectifier and B in an extractive stripper. The process efficiency of each alternative depends strongly on the location of the !AB univolatility line interception with the triangle edge, and also depends on the !BE (!AE) in the minT (maxT) case and of the unidistribution line KE closeness to the (E−B) (A−E) edge. Besides, choice of the rectification of A instead of the stripping of B is set by the ratio of !AE/!BE, the ratio of relative volatility variation of the binary mixtures between A or B and E

Morphology Changes of Co Catalyst Nanoparticles at the Onset of Fischer-Tropsch Synthesis

Cobalt nanoparticles play an important role as catalysts for the Fischer–Tropsch synthesis, which is an attractive route for production of synthetic fuels. It is of particular interest to understand the varying conversion rate during the first hours after introducing synthesis gas (H2 and CO) to the system. To this end, several in situ characterization studies have previously been done on both idealized model systems and commercially relevant catalyst nanoparticles, using bulk techniques, such as X-ray powder diffraction and X-ray absorption spectroscopy. Since catalysis takes place at the surface of the cobalt particles, it is important to develop methods to gain surface-specific structural information under realistic processing conditions. We addressed this challenge using small-angle X-ray scattering (SAXS), a technique exploiting the penetrating nature of X-rays to provide information about particle morphology during in situ experiments. Simultaneous wide-angle X-ray scattering was used for monitoring the reduction from oxide to catalytically active metal cobalt, and anomalous SAXS was used for distinguishing the cobalt particles from the other phases present. After introducing the synthesis gas, we found that the slope of the scattered intensity in the Porod region increased significantly, while the scattering invariant remained essentially constant, indicating a change in the shape or surface structure of the particles. Shape- and surface change models are discussed in light of the experimental results, leading to an improved understanding of catalytic nanoparticles

Thermodynamic Insights on the Feasibility of Homogeneous Batch Extractive Distillation. 1. Azeotropic Mixtures with Heavy Entrainer.

Feasibility assessment of batch homogeneous extractive distillation for the separation of an A-B mixture feeding entrainer E traditionally relies on the systematic computation of rectifying and extractive composition profile maps under various reflux ratio and entrainer flowrate conditions. This is a well-settled methodology for determining the product sequence and the corresponding column configuration. However, we show that all related literature examples can be simply explained by using thermodynamic insights of residue curve maps, in particular, the unidistribution and univolatility curves. A general feasibility criterion at infinite reflux is proposed and finite reflux operation is also discussed. Illustration is provided for the most common cases, namely the separation with a heavy entrainer of minimum boiling (class 1.0-1a) and maximum boiling azeotropes (class 1.0-2). New cases not published so far are presented and operating conditions are also discussed. These results demonstrate the obligatory incorporation of the univolatility lines for explaining the unexpected behaviour of some particular ternary mixtures to be separated by the homogeneous extractive distillation proces