Completed Research
On Hydrocracking of Vacuum Residues in Slurry Reactors
Mariela Sanoja, PhD, 2012
(Thesis: University of Pittsburgh ETD)
The equilibrium solubility (C*) and liquid-side mass transfer coefficient (kLa) were measured for H2 in four liquids, two vacuum residues (A and B); and two mixtures (vacuum residue B + liquid paraffins and vacuum residue B + liquid paraffins + molten wax). The data were measured in the presence and absence of solid particles (activated carbon) in one-liter agitated autoclave operating in a gas-inducing mode. The effect of operating variables, including pressure (27.5–55 bar), temperature (423–623 K), mixing speed (20–33 Hz), and activated carbon concentration (0 - 40 wt %) on kLa and C* values were statistically investigated using the Central Composite Statistical Design technique. The kLa values were obtained using the Transient Physical Gas Absorption technique and the C* values were calculated at the thermodynamic equilibrium.
The experimental data showed that C* values of hydrogen in the four liquids increase linearly with pressure at constant temperature following Henry’s law. The C* values also increased with temperature at constant pressure and the temperature effect was modeled using an Arrhenius-type equation.
The kLa values of H2 in the four liquids strongly increased with temperature and mixing speed, and slightly increased with H2 partial pressure. The kLa values, however, decreased with increasing solid concentrations in the vacuum residues A and B. Statistical correlations and empirical correlations, using dimensionless numbers, were developed to predict kLa values of H2 in the liquids used in the presence and absence of solid particles in the gas-inducing slurry agitated reactor.
The kinetic rate constants proposed by Sanchez at al. [15] for hydrocracking of vacuum residue at 380, 400 and 420 oC were used in a simple kinetic model using a series of CSTRs to calculate the residue conversion and the VGO, distillate, naphtha and gaseous products concentrations and molar flow rates. For a series arrangements of 4-CSTRs (3-m inside diameter and 3-m height), operating at 400 oC with an LHSV of 0.33 h-1 corresponding to an inlet liquid superficial velocity of 0.99 m s-1, the residue conversion reached 91.8%. However, for the same arrangement at 400 oC with an LHSV of 1.5 h-1 corresponding to an inlet liquid superficial velocity of 4.5 m s-1, the residue conversion was only 50.36%.