HCN Removal By Coupling Catalytic Hydrolysis And Oxidation On Modified Activated Carbon In Yellow Phosphorus Tail Gas

Hydrogen cyanide (HCN) is a typical unconventional poisonous gas which has a smell off bitter almond in industrial tail gases. The HCN is included in the pollution gas which produced in the process of Yellow phosphorus generation, the concentration of it is about 150～400 ppm.In this paper, based on the comparision of the HCN purification method at home and abroad. A method of coupling catalytic hydrolysis and oxidation for HCN removal by metal-modified activated carbon was studied.Activated carbons (AC) is a good catalyst support due to its high surface area and complex pore structure, it also has a rich source, cheap price and the modification method is manifold. Therefore, activated carbon is employed as the catalyst support to study the coupling catalytic hydrolysis and oxidation for HCN removal. Firstly, the coupling catalytic properties of single transition metal modified activated carbon was studied.The results showed that impregnation of metal oxides on the activated carbon significantly enhanced the removal capacity for HCN. Among the different kinds of metal-modified catalysts, AC-Cu exhibited the highest catalytic activity. The AC-Cu catalyst showed>98% conversion of HCN at 250-350 ℃. The selectivity of N2 in the conversion of HCN reached to 48.8% at 300 ℃. Therefore, Cu was chosen as the metal species for further study. Reaction temperature, oxygen concentration, relative humidity and calcination temperature can greatly influence the catalytic activity. In particular, the reaction temperature was determined to be a crucial factor.In order to broden the reaction temperature window of AC, the sulfonated phthalocyanine cobalt and rare earth element Ce were prepared to further modified AC-Cu. The modified catalyst was then characterized. The activity stability of AC-Cu and AC-Cu-CoPcS-Ce was studied. Both catalysts have good activity stability, AC-Cu-CoPcS-Ce catalyst has more advantages because of the lower temperature of catalytic activity.The detailed characterization of the catalyst was performed using X-ray diffraction (XRD), inductively coupled plasma-atomic emission spectroscopy (ICP-AES), Brunauer-Emmett-Teller (BET), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and temperature programmed desorption (TPD). The Cu 2p XPS spectra and XRD patterns indicated that CuO was formed as an active species for the catalytic removal of HCN. The possible reaction mechanism was then speculated based on the products and characterization. Presumably, HCN hydrolysis and HCN oxidation are related to each other and promote mutually. The HCN hydrolysis produces NH3 and CO, and the HCN oxidation produces N2, NOx, and N2O. NH3 could be further oxidated by O2 to format N2 selectivitily. At the same time, the NH3 and NOx, generated during HCN hydrolysis and oxidation occured a further reaction, thus HCN can be removed completely.