Liquid–Liquid Phase Behavior of Diesel/Biofuel Blends: Ternary Mixtures of n-Hexadecane, 2,2,4,4,6,8,8-Heptamethylnonane, and Ethanol and the Binary Subsystems

Abstract

Mixtures of n-hexadecane and 2,2,4,4,6,8,8-heptamethylnonane are common diesel fuel surrogates. This paper describes a systematic investigation of the liquid−liquid phase behavior of the ternary mixtures of the normal alkane nhexadecane and its isomer 2,2,4,4,6,8,8-heptamethylnonane (both C n H 2n+2 ; n = 16) with ethanol as a model system of surrogate fuels. By applying the cloud point method in the temperature range of T = 240−330 K at ambient pressure (p = 1013 mbar), the complete liquid−liquid phase diagram is obtained. The binary mixtures of the alcohol with both isomeric alkanes show partial miscibility with upper critical solution points. The behavior of the ternary mixtures is examined by investigating the quasi-binary subsystems of mixtures of the alcohol with mixtures of the two isomers for various fixed mole ratios. By changing the ratio of the different isomers, the region of the phase diagram of the alcohol mixture with the n-alkane is gradually shifted toward lower temperatures when adding the branched isomer toward the phase diagram of the binary mixture of the alcohol with the isomeric compound. The general shape of the phase bodies of the pseudobinaries, predefined by the ratio of the isomeric components, shows only a slight change. For the numerical analysis of the measured phase behavior of the pseudobinary mixtures, concepts are used that are applied for binary solutions presuming Ising criticality. A master curve is obtained when applying the corresponding state principle on the binary and the pseudobinary mixtures. Superposition of the different results allows for a comprehensive description of the liquid−liquid phase behavior, and it estimates the loci of critical line and tie lines. The limits of the range of validity of the descriptions are determined by the appearance of solid phases, which are also reported here. This study is expected to establish a basis for optimizing blends of petrochemical fuels and fuels from renewable sources.

Liquid–Liquid Phase Behavior of Ternary Mixtures: n-Dodecane, n-Hexadecane, and Ethanol

“…The ethanolic binary systems form highly nonideal mixtures with highly asymmetric phase diagrams, similar as other fluid mixtures of polar or ionic with nonpolar or weakly polar components. ,,, Note, ideal mixing behavior is found for mixtures of alkane isomers or alkanes with comparable chain length, , thus almost ideal mixing behavior is expected for C 12 and C 16 mixtures. The present mixtures do not show a significant change of the shape of the phase diagrams, in accordance to the ternary mixtures of ethanol with C 16 isomers …”

“…The coefficients obtained with eq are also useful to compare the ternary systems with the binaries. We have recently proposed the effective carbon numbers for characterizing hydrocarbon mixtures, based on UCSTs of binary n -alkane/ethanol mixtures . The dependency of UCSTs of ethanolic mixtures of the different n -alkanes on the chain length n of the alkyl chain of the normal alkanes can be described by the polynomial …”

“…As suggested in the pioneering work of the last century, ,,, the data do also allow for charting the isobaric temperature–composition phase prism of the ternary C 16 /C 12 /ethanol mixture (Figure ). Estimated tie lines as well as the occurrence of a precipitate where observed or described in prior work (red dashed lines) are included there. With the exception of the binary mixtures of C 16 /ethanol and C 12 /ethanol, best to our knowledge, no data are available in the literature.…”

“…As figured out in the past, this setting allows for the determination of LLE in a temperature range of T = (230–430) K at ambient pressure ( p = 1013 mbar/1.013 × 10 5 Pa). ,, Liquid baths with a high temperature stability (δ T = ±0.03 K)here only water filled baths are of relevanceallow together with DKD (Deutscher Kalibrierdienst) calibrated Pt-100 thermometers (Kelvimat 4323, Burster, Gernsbach, Germany; accuracy Δ T = ±0.02 K) a precise temperature control. Cloud points were determined visually, ,, so that the optical limitations which were described in ref , , and − can be handled appropriately . The repeatability of measurements of T cloud is limited by the appearance of supercooling, difficulties of the visual detection of the phase separation caused by the almost equal refractive indices of the coexisting phases and, therefore, a vanishing turbidity during demixing.…”

“…The experimental schedule follows the systematic needed for an effective determination of ternary phase diagrams. − Following the concepts described in a recent study, a set of pseudobinary mixtures with ethanol was characterized. The ratio of the amounts of C 12 and C 16 (i.e., the mole fraction of C 16 for binary mixtures of C 16 and C 12 : x C16 (C 16 –C 12 )) are fixed to values of x C16 (C 16 –C 12 ) = 0.25, 0.5, and 0.75 in order to mimic n -alkanes with alkyl chain lengths of 13, 14, and 15.…”