Solubility and mass transfer of hydrogen in light cycle oil and vacuum gas oil

A comprehensive understanding of the mass transfer characteristics of hydrogen in petroleum distillates is crucial for optimizing the hydrogenation process. In this study, we investigated hydrogen solubility (S) and volumetric liquid-side mass transfer coefficients (kLa) in light cycle oil (LCO) and vacuum gas oil (VGO) using a modified dynamic pressure-step method. We defined kLa*S/2 as the average mass transfer rate to quantitatively compare mass transfer rates and obtained relative dissolved hydrogen concentration-relative time of hydrogen dissolution (SD-tD) curves by normalizing the data to further investigate variations in mass transfer. Our results indicated that temperature and pressure are major factors promoting hydrogen solubility in both distillates, while temperature and stirring speed significantly influence the hydrogen dissolution rate. The higher polyaromatic composition and greater viscosity of VGO resulted in lower hydrogen solubility and mass transfer rates compared to LCO. Considering the effect of temperature on the molar heat of dissolution, the hydrogen solubility calculated using Henry's constant correlated well with the experimental values. Furthermore, we proposed a multi-parameter correlation to predict kLa values. The average mass transfer rate of both distillates increased with temperature, pressure, and stirring speed, with VGO showing a greater dependence on temperature. The SD-tD curves indicated that the relative mass transfer rate was not affected by pressure and stirring speed at a given temperature and that the mass transfer rate variation for LCO was more influenced by temperature.