Binary N-heptane Research Articles

The effect of molecular structures of alkylbenzenes on ignition characteristics of binary n-heptane blends

Alkylbenzenes are major aromatic constituents of real transportation fuels and important surrogate components. In this study, the structural impact of nine alkylbenzenes on their ignition characteristics is experimentally and computationally investigated with particular emphasis on the blending effect with significantly more reactive normal alkanes. Experimental comparisons of mono-alkylbenzenes (toluene, ethylbenzene, n-propylbenzene, iso-propylbenzene) from a modified CFR engine showed that the difference in pure alkylbenzene reactivity significantly diminished when blended with n-heptane, as the strength of the radical scavenging effect of all three alkylbenzenes is similar. Among C8H10 isomers, the reactivity of pure ethylbenzene and o-xylene and their blends with n-heptane showed a complex competing effect between the difference in CH bond energy and the existence of intermediate/low-temperature chemistry caused by adjacent methyl pairs. A similar structural impact was also observed for C9H12 isomers and their blends with n-heptane, while the influence of CH bond energy was more noticeable than C8H10 molecules. Kinetic simulations of the alkylbenzene/n-heptane blends highlighted the effect caused by adjacent methyl pairs that is referred to as the “ortho effect”. Analysis of ethylbenzene and o-xylene showed that o-xylene's intermediate/low-temperature pathways initiated by benzylperoxy radical – benzylhydroperoxide isomerization (RO2 – QOOH) produce additional active radicals such as OH and CH2O, which accelerates the oxidation chemistry of more reactive n-heptane. This study provides knowledge on the blending effect of alkylbenzene compounds with n-heptane on their ignition characteristics that is useful to develop surrogates that can better mimic the reactivity of real fuels.

Ionic liquids as entrainers for the separation of aromatic–aliphatic hydrocarbon mixtures by extractive distillation

The conceptual engineering of a new process proposed for the aromatic–aliphatic separation from naphtha has been developed based on extractive distillation using the 1-ethyl-3-methyl imidazolium dycianamide [EMIM][DCA] ionic liquid as entrainer. Process designs and simulations have been carried out with a computer-aided methodology recently developed in our group that integrates molecular modeling and process simulation via COSMO-based thermodynamic models in Aspen Plus. The computational analysis has been performed for two different multicomponent real-like naphtha models: a low aromatic content naphtha (10wt%) and a naphtha with a high aromatic content (90wt%). A sensitivity analysis with 8200 different extractive distillation column designs has been carried out varying the ionic liquid solvent to feed ratio, reflux ratio, number of stages and feed stage, in order to optimize the column design minimizing the reboiler duty and maximizing the throughput. In the low aromatic content naphtha, the results show that similar separation efficiencies to liquid–liquid extraction may be achieved by extractive distillation, requiring lower solvent to feed ratios but higher energy consumptions. For the high aromatic content naphtha, good separation performance is obtained with a significant reduction of the energy required per ton of naphtha fed to the system in comparison with the separation by liquid–liquid extraction. To evaluate the behavior of the process simulator using COSMOSAC, the classical NRTL thermodynamic model, fitted using experimental vapor–liquid and liquid–liquid data, was used to simulate the extractive distillation process for a simpler binary n-heptane–toluene mixture. Similar results are obtained using COSMOSAC and NRTL models for this binary aromatic–aliphatic mixture indicating the reliability of the COSMOSAC-based simulations of more complex multicomponent naphtha separation.

Estimation of the number of polar molecules in a solvate shell of a fluorescent probe 4-dimethylaminochalcone

The fluorescence decay kinetics has been studied in different parts of the emission spectrum of diluted solutions of a membrane fluorescent probe, 4-dimethylaminochalcone, in a binary n-heptane + acetone solvent with the volume fractions of polar and nonpolar components of the latter varying in a wide range. It has been shown that the fluorescence of these solutions has a significantly heterogeneous character, which is indicative of the presence of several types of solvate complexes with controllable ratios of components (1: 1, 1: 2, 1: 3, etc.) in the studied systems. Based on a quantitative analysis of the mentioned kinetic dependences, a model has been proposed in which these data can serve as a source of information about statistical features of the structure of solvate shells of polar dye molecules in an excited electronic state. This information can in turn be used to obtain new biophysical data.

Volumetric properties of the binary mixture n-heptane+ethylbenzene mixtures at high temperatures and high pressures

New experimental data on the density of three (0.2393, 0.4856 and 0.7390 mole fraction of ethylbenzene) binary n-heptane+ethylbenzene mixtures have been measured with a constant-volume piezometer immersed in a precision liquid thermostat. These new experimental data covering a temperature range from 306 to 527 K and a pressure range of 0.1 to 11 MPa. The experimental data reported here have an uncertainty less than 0.06% for the density, 0.05% for the pressure, 15 mK for the temperature, and 0.012% for the concentration. Excess molar volumes were derived using measured values of density for the mixtures and for the pure components calculated with reference equation of state for n-heptane (Span and Wagner, 2003) and for the pure ethylbenzene (Frenkel et al., 2005). The derived values of excess molar volumes at atmospheric pressure were compared with the values reported by other authors in the literature. The effect of pressure on the excess molar volumes was studied.

Separation of close-boiling hydrocarbons with silicalite zeolite membranes

The permeation behaviour of n-heptane, isooctane and n-hexane vapours through continuous silicalite zeolite membranes on porous alumina supports has been investigated between 359 and 523 K. Pure isooctane, n-heptane and n-hexane have similar permeances. In the presence of n-heptane and n-hexane, in both binary and ternary mixtures, however, the isooctane permeance decreases by a factor of up to ca. 50, whereas the n-heptane and n-hexane permeances are almost the same as the pure component permeances. Thus, separation selectivities for n-heptane–isooctane as high as 138 were obtained at 373 K in ternary mixtures with n-hexane, but such separations cannot be predicted from the pure gas permeances. Selectivity is a strong function of temperature, and lower selectivities were obtained above and below 373 K for the ternary mixture. The highest selectivity of 57 for a binary n-heptane–isooctane mixture was obtained at 359 K, and selectivity decreased with increasing temperature. The permeances of all compounds in the mixtures increase with temperature.

Zeolite-in-metal membranes: preparation and testing

By galvanic metal deposition, silicalite crystals have been embedded in silver or nickel foils; the resulting composites are self-supporting high-temperature membranes (thermally stable up to 650 K) and have been tested by permeation/pervaporation studies of a binary n-heptane–toluene mixture; a separation factor αtol/n-C7ca. 4 ± 1.5 is found over a wide temperature range.

Spectrofluorometric Probe Method for Examining Preferential Solvation in Binary Solvent Mixtures

A spectrofluorometric method is developed to examine preferential solvation of a probe molecule dissolved in binary solvent mixtures. The method assumes that the solvational sphere around every fluorophore is solvated by only one type of solvent component and that each solvated fluorophore contributes to the measured emission intensity. Expressions derived from the model are illustrated with the use of observed fluorescence emission behavior of 3,4-dihydrobenzo[ghilperylene dissolved in binary n-heptane + 1,4-dioxane and dibutyl ether + acetonitrile solvent mixtures, which were measured as part of the present study.

Viscosity coefficients of binary n-heptane+n-alkane mixtures

Abstract New absolute measurements of the viscosity of n-decane and binary mixtures of n-heptane with n-decane are presented. The measurements, performed in a vibrating-wire instrument, cover a temperature range 290–330 K and pressures up to 70 MPa. The concentrations studied are 40 and 70% by weight of n-heptane. The overall uncertainty in the reported viscosity data is estimated to be ±0.5%. The present measurements together with other n-heptane+n-alkane viscosity and thermal conductivity measurements, are used to develop a consistent semiempirical scheme for the correlation and prediction of these mixture properties from those of the pure components.

Application of Bloomfield and Dewan relationship to the excess viscosity of binary mixtures heptane + nonylbenzene versus pressure and temperature

Abstract The excess viscosity of the binary n-heptane + nonylbenzene has been measured versus pressure (P < 400 bar) and temperature (40°C < T < 80°C) with a falling-body viscometer. The 105 experimental values were adjusted by means of the Bloomfield-Dewan relationship and the Flory's theory without using any adjustable parameter. The average absolute deviation observed on the mixture viscosity is quite good: 5.7%.