Control of product quality plays a crucial role in petrochemical industries. In this paper, we propose a new strategy to control the quality of purified terephthalic acid (PTA) product. In this approach, the PTA quality is controlled by monitoring the concentration of the main impurity in the hydropurification process, which is 4-carboxybenzaldehyde (4-CBA) in the crude terephthalic acid (CTA) powder. To attain the research objectives, a dynamic dispersion model is developed in the face of catalyst deactivation, considering the vital operating parameters. The CTA powder streams with low and high 4-CBA concentrations can be effectively used through a proper (and controlled) mixing procedure. This strategy can be applied by controlling the ratio of the mass flowrates of the two streams, having high and low concentrations. The positive effect of H2 partial pressure on the system performance can be implemented by a small decrease in reactor temperature. Off-spec PTA powder can be used with the CTA powder having a high 4-CBA concentration. Increasing temperature accelerates the reduction rate of the Pd/C catalyst surface area, leading to an unfavorable sintering phenomenon. The decreased activity of Pd/C catalyst is in good agreement with the normalized ratio of decrease in the surface area of pure Pd with increasing temperature.