Vegetable fat hydrogenation in supercritical-fluid solvents: Melting behavior analysis by DSC and NMR

The melting behavior of six fat samples hydrogenated on Pd catalysts (uniform 2% Pd/C and eggshell 0.5% Pd/Al2O3) in supercritical dimethylether (DME) or propane as reaction solvents was investigated. Hydrogenation was carried out at 484 K, with pressures between 20 and 28 MPa and a molar hydrogen content ranging from 4 to 9%, and using a continuous internal-recycle reactor. The melting and crystallization behavior of the hydrogenated products was characterized by differential scanning calorimetry (DSC) and nuclear magnetic resonance (NMR), which allowed the determination of solid fat content (SFC). DSC values were generally higher than NMR values. Melting behavior is one of the most important characteristics of edible fats and margarines as it has an impact on their organoleptic properties. These are strongly affected by supercritical-fluid (SCF) processing, so readjustment is necessary. The results obtained show that supercritical hydrogenation on the eggshell 0.5% Pd/Al2O3 catalyst in supercritical DME leads to an improved melting profile of the hydrogenated products compared with uniform 2% Pd/C catalyst in propane. In addition, supercritical conditions have a greater influence on melting behavior than conventional hydrogenation.