Kinetic Study Of Microwave Enhanced Mercury Desorption For The Regeneration Of Spent Activated Carbon Supported Mercuric Chloride Catalysts

A novel microwave enhanced mercury desorption process was proposed for the regeneration of the spent activated carbon supported mercuric chloride catalysts. The mercury species desorption kinetics were investigated in detail by TG experiments, the overall apparent activation energy of 128.4 kJ/mol, the main reaction activation energy of 95.84 kJ/mol and the adsorption energy of 32.56 kJ/mol were confirmed with the combination of the model-free method and the DMol(3) DFT module of Materials Studio package. The thermal desorption of HgCl2 and Hg2Cl2 were mainly between 473 K and 670 K, and the dominant mechanism for the desorption process was determined as second-order-model by the model-fitting method and the Z(alpha) master-plot method. Furthermore, the microwave enhancement degree of 26.36% was proved by the microwave heating experiment for the mercury desorption within 1500 s at 673 K, and the mercury content was significantly reduced from 19500 mg/kg to 149 mg/kg, which met the requirement of US land disposal restrictions (<260 mg/kg). Moreover, the preliminary activation of the spent activated carbon after microwave heating was demonstrated from the results of XRD, SEM and nitrogen adsorption analysis. Meanwhile, the HgCl2 solution with the concentration of 40-50 g/L could be effectively prepared by the water leaching of the condensate of mercury species, which could be used to regenerate the catalyst by soaking adsorption with activated carbon after microwave heating. Finally, a novel microwave enhanced mercury desorption process was proposed, which can synchronous realize the harmless and recovery of the spent activated carbon supported mercuric chloride catalysts.