Terms Of Molar Fraction Research Articles

Pyrolysis of n-octane at very low concentration and low temperature

Hydrocarbon pyrolysis concerns many different fields (petroleum geochemistry, refinery, fuel thermal stability, pyrocarbon deposition, etc.). It is therefore studied in a wide variety of temperature–pressure experimental conditions, which strongly affect the chemistry of hydrocarbons cracking.An experimental study of the pyrolysis of n-octane has been performed at very low reactant concentration (1mbar diluted in inert gas−total pressure 1500mbar−molar fraction 0.07%) in a closed reactor, at temperatures ranging between 350°C and 450°C, and reaction time from 1h to 70h. The major products of the reaction are 1-alkenes (C2H4 to C7H14), methane and ethane; other alkanes (C3H8 to C6H14) are minor products. At 450°C and 4h, the conversion is close to 9% and we observe, in terms of molar fractions:C2H4 >C3H6≈CH4>C4H8>C5H10>C6H12≈C2H6>C7H14These experimental results are very different from those of the thermal decomposition of n-alkanes at the same low temperature but at high pressure. In particular, the cracking stoichiometric equations (for example: C8H18=C6H14+C2H4) are not observed since alkanes (except methane and ethane) are in very low quantities. This can be explained by the very low concentration of reactant which limits the bimolecular reactions. In our conditions, the radicals decompose several times by beta-scissions of CC bonds when it is possible (unimolecular reaction), rather than react by H-transfers (metathesis) with the reactant (bimolecular reaction) which produce alkanes. A detailed free radical mechanism (184 reactions, 16 molecules and 18 radicals— mechanism available as Supplementary material) allows modeling the experimental results.

A Radio Frequency Sensor For Measurement Of Small Dielectric Property Changes

We propose a sensitive radio frequency (RF) sensor for the measurement of small dielectric property changes. Interference is used to cancel parasitic background signals to improve sensitivity. The device consists of two Wilkinson power dividers, a 180 degree reversephase and an in-phase CPW (coplanar waveguide)-slotline back-toback balun. The small dielectric property changes between de-ionize water and two sets of primary alcohol-water mixtures with different concentrations in terms of molar fractions are measured with clear sensing and identification. The sensor offers almost thirteen times greater sensitivity than conventional transmission lines. Experimental results also show that the lowest detection limit for the molarity of primary alcohol is about 0.25% across the sensitive sensor. Compared with microwave soil moisture sensors the proposed RF device is more sensitive.

Bayesian analysis of systems with random chemical composition: renormalization-group approach to Dirichlet distributions and the statistical theory of dilution.

We investigate the statistical properties of systems with random chemical composition and try to obtain a theoretical derivation of the self-similar Dirichlet distribution, which is used empirically in molecular biology, environmental chemistry, and geochemistry. We consider a system made up of many chemical species and assume that the statistical distribution of the abundance of each chemical species in the system is the result of a succession of a variable number of random dilution events, which can be described by using the renormalization-group theory. A Bayesian approach is used for evaluating the probability density of the chemical composition of the system in terms of the probability densities of the abundances of the different chemical species. We show that for large cascades of dilution events, the probability density of the composition vector of the system is given by a self-similar probability density of the Dirichlet type. We also give an alternative formal derivation for the Dirichlet law based on the maximum entropy approach, by assuming that the average values of the chemical potentials of different species, expressed in terms of molar fractions, are constant. Although the maximum entropy approach leads formally to the Dirichlet distribution, it does not clarify the physical origin of the Dirichlet statistics and has serious limitations. The random theory of dilution provides a physical picture for the emergence of Dirichlet statistics and makes it possible to investigate its validity range. We discuss the implications of our theory in molecular biology, geochemistry, and environmental science.

Determination of Self-Association Equilibrium Constants of Ethanol by FTIR Spectroscopy

The self-association of ethanol diluted in CCl4 has been studied by IR spectroscopy. Three OH stretching bands were assigned to monomers, linear dimers, and linear multimers. The self-association was described with two equilibrium constants, one for the formation of dimers, K2, the other for the formation of multimers, KA. These equilibrium constants were determined for ethanol concentration ranging from 0.19 to 0.76 mol L-1 by using a method developed by Coggeshall and Saier. At T = 25 °C, K2 was found to be equal to 1.08 L mol-1 in terms of molar concentration or 18.4 in terms of molar fraction; KA was found to be equal to 3.52 L mol-1 in terms of molar concentration or 60.0 in terms of molar fraction. The enthalpy of formation for K2 was found to be equal to −4.61 kcal mol-1 and to −4.15 kcal mol-1 for KA.

Densities and viscosities of binary solutions containing butylamine, benzylamine, and water

Densities and viscosities of the binary mixtures compared of butylamine, benzylamine, and water are measured at 303.15, 313.15, and 323.15 K over the entire molar fraction range. The excess volume and viscosity deviation are calculated from the experimental data and correlated by a Redlich-Kister-type equation in terms of molar fraction. McAllister's models are also used to correlate the kinematic viscosities

Densities and viscosities of 2-butanone/dibutyl ether, 2-picoline/2-butanone, and 2-picoline/water mixtures

Densities and viscosities of the binary mixtures including 2-butanone/dibutyl ether, 2-picoline/2-butatone, and 2-picoline/water are measured at 303.15, 313.15, and 323.15 K over the entire molar fraction range. The excess volumes, viscosities, and Gibbs energies of activation of flow are calculated from the experimental data, and are correlated by a Redlich-Kister-type function in terms of molar fraction. McAllister's three-body and four-body interaction models are also used to correlate the kinematic viscosities