Abstract
The solubility and crystallisability of a range of binary mixtures of n-hexadecane (C16H34) and n-octadecane (C18H38), as the predominant alkanes present in hydrotreated vegetable oil (HVO), from three representative fuel solutions (dodecane, toluene and kerosene) is presented. The dissolution (saturation) and crystallisation (supersaturation) points of the solutions are measured using poly-thermal methods utilising turbidometric detection over four concentrations from (192 g/l to 400 g/l). The data reveals the existence of more soluble, less stable crystal structures that form from the alkane mixtures, when compared to the stable triclinic crystal structures formed from the single solute component solutions. An increased carbon chain length results in lower solubility for all three solvents and the solvent type is not found to have any significant effect on the solid forms produced from the mixtures. van’t Hoff analysis reveals the solvent type to influence the solute solubility with the closest to ideal behaviour being dodecane followed by kerosene and toluene, respectively. This finding is further supported by the calculated dissolution enthalpies and activity coefficients, which are the lowest in dodecane followed by kerosene and toluene. Larger values of activity coefficients are observed for compositions with molar fraction (y) = 0.1, 0.5–0.7 C18H38 which reflect the complex multi-phase formation in the solutions when compared with the more simple binary melt crystallisation system.
Highlights
A global concern towards greenhouse gas emissions and their impact on the environment has led to an ever-increasing use of sustainable, bio-derived feedstocks in fuel oils
By 2020, 10% of biofuel will be shared in transport as a blend component with the traditional fossil oil according to the target set by the European Union (EU) [1]
The equilibrium solubility (Te) and supersolubility (Tc,l) temperatures obtained from extrapolation of Tdiss and The crystallisation (Tc) back to 0 °C/min are given in Tables 2–4 together with their Meta-stable zone width (MSZW) for C16H34:C18H38 binary mixtures in solution of dodecane, toluene and kerosene, respectively
Summary
A global concern towards greenhouse gas emissions and their impact on the environment has led to an ever-increasing use of sustainable, bio-derived feedstocks in fuel oils. The consequence of variance distribution of carbon number blending with 10% HVO3 into the traditional diesel [4] (Fig. 1) effects the carbon number chain distribution of the fuel fraction leading, in turn, to changes in the crystallisation behaviour and, potentially, the solid form that results. In this paper the crystallisation behaviour with respect to solubility and crystallisability of mixtures of C16H34 and C18H38 as a model system of HVO blended fuels in solution environment is investigated with the associated solid form phase behaviour which is analysed with the help of previous X-ray studies [34]. Aliphatic (dodecane), aromatic (toluene) and aliphatic-aromatic mixture (kerosene) were selected in order to gain an understanding of this behaviour when the mixed crystals are crystallised from solutions with components found in typical diesel fuel and to investigate the associated solution chemistry effects
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