As interest in polyethylene terephthalate (PET) recycling grows, research into PET hydrogenolysis has expanded, yet reactor design studies remain limited. This work presents a mathematical model for a three-phase slurry bubble column reactor, chosen for its suitability in high-pressure and viscous conditions. Using hydrodynamic correlations and a GPU-based optimization solver, the model simulates and optimizes reactor performance. Results reveal that viscosity, influenced by polymer molecular weight and solvent ratio, critically impacts PET conversion rates. Catalyst size and feed proportion also significantly affect conversion via changes in axial dispersion, mass transfer, and reaction kinetics. These findings underscore the importance of optimizing viscosity and other reactor parameters to improve the efficiency of PET hydrogenolysis, supporting more effective industrial recycling strategies.