Molecular-scale effects of additives on the nucleation, growth and crystal properties of long-chain alkyl methyl-esters

Biodiesel is a diesel-related fuel manufactured from vegetable oils, recycled grease,
or animal fats. It is technically competitive with, or offers technical advantages when
compared to, conventional diesel fuel. However, the freezing and gelling behaviour
of many biodiesel formulations are potentially limiting their applications. It is known
that the use of additives is an efficient way to improve the cold flow properties of
formulated, so it is very important to clarify the mechanism and effect of additives.
Molecular cluster modelling work has been explored to study the effect of additives
on crystallization temperature, meta-stable zone width and solubility. A new method
has been developed for the prediction of crystallisability through the comparison of
structural variability of molecular clusters of pure naphthalene, pure biphenyl, and
naphthalene in the presence of biphenyl and vice versa. The approach has been
validated through the experimental determination of crystallization temperatures and
meta-stable zone width.
The predicted growth morphologies of methyl stearate have been derived through
attachment energy calculations and the resulting surface chemistry of the
morphological habit faces characterized. Molecular simulations using grid search
methods combined with experimental observed images were used to investigate the
solvent-mediated effect on crystal habits of methyl stearate.
Tubidometric studies employing a 100ml batch crystallizer operating in a polythermal
mode confirmed the change of crystallization temperature and the meta-stable zone
width of methyl stearate with or without additives. Related crash-cooling studies
enabled the characterization of crystallization kinetics with or without additives
through examination of set paints as a function of supersaturation.