Characteristics of HCN removal using cao at high temperatures

Experimental investigation on the removal of hydrogen cyanide (HCN) using calcium oxide (CaO) was carried out in a fixed bed reactor at temperature ranging from 300 to 1173 K, and the original HCN was produced during the pyrolysis of pyridine. Effects of temperature, volume space velocity, and initial HCN concentration on HCN removal were discussed. The results of temperature-programmed experiments show that temperature is the main factor affecting HCN removal. With the formation of CO, HCN starts to decrease from 473 K, and remains unchanged from 673 to 873 K. At 873 K, there is a further decrease in HCN without CO formation, and when temperature is higher than 1023 K, HCN is removed completely. In the isothermal experiments, CaCN² was detected at 723 K, but at higher temperatures of 923 and 1123 K, there was no CaCN² in the solid residues, and the nitrogen in the removed HCN was equal to that in the formed N². This indicates that at a lower temperature CaO is consumed to remove HCN, CaO + 2HCN f CaCN² + CO + H²; but at a higher temperature, CaO acts as a catalyst for HCN removal, 2CiHj + 2HCN f N2 + (j + 1 - k)H² + 2Ci+1H^k. The investigation on the removal efficiency shows that there is a critical temperature and a critical volume space velocity at which the HCN removal efficiency is able to reach up to 100%.