Equilibrium in the Catalytic Condensation of Carboxylic Acids with Methyl Ketones to 1,3-Diketones and the Origin of the Reketonization Effect

Acetone is the expected ketone product of an acetic acid decarboxylative ketonization reaction with metal oxide catalysts used in the industrial production of ketones and for biofuel upgrade. Decarboxylative cross-ketonization of a mixture of acetic and isobutyric acids yields highly valued unsymmetrical methyl isopropyl ketone (MIPK) along with two less valuable symmetrical ketones, acetone and diisopropyl ketone (DIPK). We describe a side reaction of isobutyric acid with acetone yielding the cross-ketone MIPK with monoclinic zirconia and anatase titania catalysts in the absence of acetic acid. We call it a reketonization reaction because acetone is deconstructed and used for the construction of MIPK. Isotopic labeling of the isobutyric acid’s carboxyl group shows that it is the exclusive supplier of the carbonyl group of MIPK, while acetone provides only methyl group for MIPK construction. More branched ketones, MIPK or DIPK, are less reactive in their reketonization with carboxylic acids. The proposed mechanism of reketonization supported by density functional theory (DFT) computations starts with acetone enolization and proceeds via its condensation with surface isobutyrate to a β-diketone similar to β-keto acid formation in the decarboxylative ketonization of acids. Decomposition of unsymmetrical β-diketones with water (or methanol) by the retrocondensation reaction under the same conditions over metal oxides yields two pairs of ketones and acids (or esters in the case of methanol) and proceeds much faster compared to their formation. The major direction yields thermodynamically more stable products—more substituted ketones. DFT calculations predict even a larger fraction of the thermodynamically preferred pair of products. The difference is explained by some degree of a kinetic control in the opposite direction. Reketonization has lower reaction rates compared to regular ketonization. Still, a high extent of reketonization occurs unnoticeably during the decarboxylative ketonization of acetic acid as the result of the acetone reaction with acetic acid. This degenerate reaction is the major cause of the inhibition by acetone of its own rate of formation from acetic acid at high conversions

Thermodynamic Small Scales in Transcritical Turbulent Jets

This article is a technical note, so it does not have an abstrac

The origin of the spurious iron spread in the globular cluster NGC 3201

NGC 3201 is a globular cluster suspected to have an intrinsic spread in the iron content. We re-analysed a sample of 21 cluster stars observed with UVES-FLAMES at the Very Large Telescope and for which Simmerer et al. found a 0.4 dex wide [Fe/H] distribution with a metal-poor tail. We confirmed that when spectroscopic gravities are adopted, the derived [Fe/H] distribution spans ~0.4 dex. On the other hand, when photometric gravities are used, the metallicity distribution from Fe I lines remains large, while that derived from Fe II lines is narrow and compatible with no iron spread. We demonstrate that the metal-poor component claimed by Simmerer et al. is composed by asymptotic giant branch stars that could be affected by non local thermodynamical equilibrium effects driven by iron overionization. This leads to a decrease of the Fe I abundance, while leaving the Fe II abundance unaltered. A similar finding has been already found in asymptotic giant branch stars of the globular clusters M5 and 47 Tucanae. We conclude that NGC 3201 is a normal cluster, with no evidence of intrinsic iron spread.Comment: Accepted for publication by ApJ, 7 pages, 4 figure

Mixing and non-premixed combustion at supercritical pressures

This thesis is devoted to the numerical investigation of mixing and non- premixed combustion of cryogenic propellants at supercritical pressures. These severe conditions are commonly encountered in high pressure combustion chambers, such as those of liquid-fueled rocket engines (LRE), and lead to significant deviations from the ideal gas thermodynamic behavior of the reacting mixtures. The non-premixed laminar flame structure of liquid oxygen (LOx) and methane or liquid natural gas (LNG) mixtures, a recently proposed LRE propellants com- bination, is investigated by means of a general fluid unsteady flamelet solver. Real gas effects are analyzed on prototypical unsteady flame phenomena such as autoignition and re-ignition/quenching caused by strain perturbations. Such effects influence different flame regions depending on pressure, as well as the critical strain values that a laminar flame can sustain before quenching occurs. Moreover the flame structure is also influenced by the composition of the LNG, in particular the early stage soot precursors production and oxidation. In order to shed light on real gas mixing, a low-Mach approximation for real gas reacting mixtures is presented. A single species non-reacting real gas model is implemented in a highly scalable spectral element computational fluid dynamic (CFD) code with state of the art thermodynamic and transport properties. Transcritical and supercritical planar temporal jets, are chosen as representative test cases for investigating high-pressure mixing by means of direct numerical simulations. The pseudo-boiling phenomenon, occurring in transcritical flows, significantly influences the jet development, mitigating the development of shear layer instabilities and leading to a liquid-like jet break-up. Moreover pseudo-boiling is confined in a narrow spatial region suggesting particular care in the turbulent combustion modeling of non-premixed flames when transcritical thermodynamic conditions are encountered. The results of the present thesis, its physical insights as well as the modeling considerations involved, can be of support in the development of future CFD tools capable of simulating real engine operative conditions and configurations

Agricultural information and FM radio: acceptability of the combination in Tennessee

The overall objective of this study is to determine as far as possible from the data available whether agriculture has a place in FM broadcasting in Tennessee. This study has, in addition, several specific objectives: (1) to determine what the attitude of FM radio station program directors is in working with Extension subject matter material and Extension agents, (2) to determine what the attitude of Extension agents is in working with FM radio stations, (3) to determine what types of audiences own FM radio receivers and listen to FM radio stations, (4) to determine what Extension has to offer that these audiences might desire; e.g. commercial agricultural information, home economics, gardening, insect control, etc., and (5) to determine if Extension has a role in FM broadcasting and, if so, what is its role

Analysis of the Cramer classification scheme for oral systemic toxicity - implications for its implementation in Toxtree

In the application of the Threshold of Toxicological Concern (TTC) concept to non-cancer endpoints, the decision tree proposed by Cramer, Ford and Hall in 1978, commonly referred to as the Cramer scheme, is probably the most widely used approach for classifying and ranking chemicals according to their expected level of oral systemic toxicity. The decision tree categorises chemicals, mainly on the basis of chemical structure and reactivity, into three classes indicating a high (Class III), medium (Class II) or low (Class I) level of concern. Each Cramer class is associated with a specified human exposure level, below which chemicals are considered to present a negligible risk to human health. In the absence of experimental hazard data, these exposure threshold (TTC) values have formed the basis of priority setting in the risk assessment process. To facilitate the application of the TTC approach, the original Cramer scheme, and an extended version, have been implemented in Toxtree, a freely available software tool for predicting toxicological effects and mechanisms of action. Building on previous work by Patlewicz and coworkers, this report provides some suggestions for improving the Cramer scheme based on a review of the scientific literature, a survey of Toxtree users, and an analysis of lists of body and food components incorporated in Toxtree.JRC.DG.I.6-Systems toxicolog

Investigating the spatial variability of the time-scaling properties in Italian seismicity

International audienceSignificant power-law long-range correlated structures have been identified in the Italian seismicity from 1983 to 2003. We performed the Allan Factor Analysis and the Detrended Fluctuation Analysis on both the full and the aftershock-depleted seismic data, extracted by the INGV (National Institute of Geophysics and Volcanology) instrumental catalog.Our findings suggest that (i) the time-scaling behaviour characterizes mainly the Apennine chain; (ii) the time-correlated behaviour of the seismicity is persistent, and this implies that the dynamics underlying the seismic phenomenology is characterized by the presence of "positive feedback mechanisms"; (iii) significant time correlation is not simply related with the mainshock/aftershock mechanisms

Towards an Unsteady/Flamelet Progress Variable method for non-premixed turbulent combustion at supercritical pressures

Combustion devices operating at elevated pressures, such as liquid rocket engines (LRE), are usually characterized by supercritical thermodynamic conditions. Propellants injected into the combustion cham- ber experience real fluid effects on both their mixing and combustion. Transition through super-criticality implies abrupt variations in thermochemical properties which, together with chemical reactions and high turbulent levels introduce spatial and temporal scales that make these processes impractical to be simulated directly. Reynolds-Averaged Navier-Stokes (RANS) and Large Eddies Simulation (LES) equipped with suitable turbulent combustion modeling are therefore mandatory to attempt numerical simulation on real- istic length scales. In the present work, the building blocks for extending the unsteady/flamelet progress variable approach for turbulent combustion modeling to supercritical non-premixed turbulent flames are presented. Such approach requires a large number of unsteady supercritical laminar flamelet solutions at supercritical pressures, usually referred as flame structures, to be preliminarily established by solving the flamelet equations with suitable real fluid thermodynamics. Given such unsteady flame structures, flamelet libraries can then be generated for all thermochemical quantities. The explicit dependence on flamelet time is usually eliminated using mixture fraction, reaction progress parameter, and maximum scalar dissipation rate as independent flamelet parameters. Real fluid thermodynamics used for such unsteady supercritical laminar flamelet solutions, is taken into account by means of a computationally efficient cubic equation of state. In order to have a better handling of real gas mixtures, the real gas equation of state is written in a comprehensive three-parameter fashion. A priori analysis at supercritical pressures of transient flame structures is performed in order to study how solutions populate the flamelet state space which is usually characterized by the S-shape diagram representing a collection of steady solutions. High-pressure condi- tions ranging from 60 to 300 bar are chosen as representative of a methane/liquid-oxygen rocket engine operating condition

Multiple populations in the old and massive Small Magellanic Cloud globular cluster NGC121

We used a combination of optical and near-UV Hubble Space Telescope photometry and FLAMES/ESO-VLT high-resolution spectroscopy to characterize the stellar content of the old and massive globular cluster (GC) NGC121 in the Small Magellanic Cloud (SMC). We report on the detection of multiple stellar populations, the first case in the SMC stellar cluster system. This result enforces the emerging scenario in which the presence of multiple stellar populations is a distinctive-feature of old and massive GCs regardless of the environment, as far as the light element distribution is concerned. We find that second population (SG) stars are more centrally concentrated than first (FG) ones. More interestingly, at odds with what typically observed in Galactic GCs, we find that NGC121 is the only cluster so far to be dominated by FG stars that account for more than 65% of the total cluster mass. In the framework where GCs were born with a 90-95% of FG stars, this observational finding would suggest that either NGC121 experienced a milder stellar mass-loss with respect to Galactic GCs or it formed a smaller fraction of SG stars.Comment: 25 pages, 7 figures, 3 tables; accepted for publication in Ap

Multifractal variability in geoelectrical signals and correlations with seismicity: a study case in southern Italy

International audienceMultifractal fluctuations in the time dynamics of geoelectrical data, recorded in a seismic area of southern Italy, have been revealed using the Multifractal Detrended Fluctuation Analysis (MF-DFA), which allows to detect multifractality in nonstationary signals. Our findings show that the geoelectrical time series, recorded in the seismic area of southern Apennine Chain (Italy), is multifractal. The time evolution of the multifractality suggests that the multifractal degree increases prior the occurrence of earthquakes. This study aims to propose another approach to investigate the complex dynamics of earthquake-related geoelectrical signals