Adsorptive Purification Of Gaseous HCN Over Ni/Al Hydrotalcite-like Compounds And Their Derivate Oxides

Hydrogen cyanide (HCN) is a highly toxic and corrosive gaseous pollutant. In the process of the treatment of industrial waste gas, HCN not only causes the corrosion of the pipe and reduces the life of the equipment, but also causes the poisoning of the catalyst and increases the cost of production. Purification of HCN not only reduces the pollution of the environment but also avails the recycling of the exhaust gas. Adsorption is simple to operate and low consumption, and has better removal efficiency for industrial gas, therefore, it shows good application prospects for the HCN removal.Because of the advantages of large specific surface area and ample base sites of hydrotalcite-like compounds (LDHs), the removal efficiency of LDHs and their calcined products was studied in this paper. Mg/Al LDHs, Zn/Al LDHs, Co/Al LDHs and Ni/Al LDHs were prepared by co-precipitation method, employing the corresponding nitrate solutions and the mixed precipitants (NaOH and Na2CO3). And the corresponding calcined products were prepared by calcination in a muffle furnace. The effects of metal ratio, pH value, space velocity, water vapour, calcination temperature and reaction temperature on the HCN removal efficiency were studied. In order to investigate structure, surface profile, and physical and chemical property of adsorbents, the sorbents were characterized by XRD, FTIR, BET, XPS, SEM, EDX and CO2-TPD. Moreover, the sorption mechanism and performance of HCN by LDH and LDO were also studied. The research results were in the following sections:(1) The Ni/Al LDHs and Ni/Al LDOs prepared by co-precipitation method have good efficiency of the HCN removal. And the HCN removal efficiency over sorbents is around 90%.(2) The appropriate preparation conditions can improve HCN removal efficiency over Ni/Al LDHs and Ni/Al LDOs. The HCN removal efficiency over Ni/Al LDHs reaches up to 96% with the Ni/Al mole ratio of 3 and pH of 10. The HCN removal efficiency over Ni/Al LDOs is 92% with the Ni/Al mole ratio of 4, pH of 10 and calcination temperature of 300 ℃.(3) The influence of water vapor and reaction temperature on HCN removal efficiency over sorbents appeared regularly. The HCN removal efficiency by Ni/Al LDHs firstly increases and then decreases with the increase of reaction temperature, and decreases with the increase of the water vapor. HCN removal efficiency by Ni/Al LDOs decreases with the increase of reaction temperature, and firstly increases and then decreases with the increase of the water vapor.(4) The mechanism of action between HCN and sorbents are confirmed. According to the analysis of the XRD, XAS, FTIR and XPS spectra, the complexes, [Ni(CN)4]2-, is formed by CN" from HCN and Ni2+ from Ni/Al LDHs and Ni/Al LDOs. [Ni(CN)4]2" can enter the layer region of the Ni/Al LDH by means of anion exchange, which increases the adsorption capacity of the Ni/Al LDH. However, since Ni/Al LDO has no anion exchange but has large specific surface area, [Ni(CN)4]2" and HCN were mainly adsorbed on the surface of the Ni/Al LDO.(5) The regeneration method of Ni/AlLDHs is studied. After the regeneration process of Ni/Al LDHs (calcination-impregnation-wash-dry), the regeneration rate of LDHs comes up to 54.2%.(6) Types of dipping solution, dipping time and roasting temperature have high effects on sorbent regeneration rate. Na2CO3 and NaOH solution is conducive to the regeneration of the sorbent and regeneration rate is up to 54.2%. The long soaking time is helpful to regeneration rate of the sorbent. Compared with other calcination temperature, under the calcination condition of 300 ℃, regeneration rate of the adsorbent reaches up to 44.7%.