Study On Deactivation And Regeneration Of Pd/C Catalysts For PTA Hydrofining

Pd/C catalyst has been being extensively used in PTA hydrofining industry, in which the issues that are of a concern to PTA production enterprises are the deactivation causes and regeneration methods of the Pd/C catalyst.In this work, the comprehensive analysis to the deactivated Pd/C catalysts for PTA hydrofining from two typical large-scale PTA production enterprises were implemented by physio-chemical characterization techniques combined with the concrete use conditions. The main causes of the Pd/C catalysts deactivation were identified, and the optimum regeneration methods and use conditions for prolonging the use life of the Pd/C catalyst for PTA hydrofining were proposed. The study conclusions are representative. The main study results obtained are as follows:1. The main cause of Pd/C catalyst deactivation in PTA hydrofining is the covering formed by the reaction between inorganic impurities and terephthalic acid, which is temporary deactivation. The deactivation can be effectively relieved and even eliminated by water-washing and aqueous alkali-washing. The deactivated Pd/C catalyst can be regenerated by water-washing and aqueous alkali-washing, of which the latter that was better than the former may totally restore the activity of Pd/C catalyst. Specifically, the times and conditions of aqueous alkali-washing should be strictly controlled to restrain the oxidation and then dissolution of Pd in aqueous alkali. It probably also makes the deactivated Pd/C catalyst unrestored when the covering can not be removed by aqueous alkali-washing due to the comparatively strong inactivation between covering and active carbon.To improve the use situation of Pd/C catalyst the effective measures are the decrease in sources of impurities in PTA hydrofining process, reinforcing anticorrosion measures and strict controlling ash content in CTA.2. The loss and crystallite growth of Pd on the surface of Pd/C catalyst were the important causes of the Pd/C catalyst deactivation, which is permanent deactivation. The Pd loss was related to the preparation process of the active carbon carrier. In addition, the friction between catalysts due to the industrial operation conditions volatility and the scouring effect of liquid reactants on Pd/C catalysts caused also Pd loss and crystallite growth.3. The influence of the distribution of specific surface area of Pd/C catalyst on its the activity in PTA hydrofining is inapparent.