Simultaneous Catalytic Hydrolysis Of HCN And COS By Zn-Ni-Al Hydrotalcite-like Compounds

Phosphorus chemical industry is one of the pillar industries in Yunnan Province.At present,the annual output of yellow phosphorus in China has reached to 800,000 tons.A large amount of CO?about 85⁹5%?exists in yellow phosphorus tail gas,which is a kind of raw material gas?such as C1chemical industry?for industrial resource utilization.However,yellow phosphorus tail gas also contains impurity gases,such as HCN and COS.They are toxic gases,which are harmful to the ecological environment and corrode production equipment.Meanwhile,they also affect the recovery and utilization of CO in yellow phosphorus tail gas.In the yellow phosphorus tail gas,HCN content is 100³50 mg/m³ and COS content is 700¹000mg/m³.In order to protect the ecological environment,reduce the industrial production cost and make full use of resources,HCN and COS must be removed.Catalytic hydrolysis has the advantages of high stability,less side reactions and simple operation.Moreover,there is water vapor in the yellow phosphorus tail gas,which can be directly used for hydrolysis reaction.At present,the research on simultaneous catalytic hydrolysis of HCN and COS is still immature in the world.Therefore,it is important to develop catalysts that can remove HCN and COS from yellow phosphorus tail gas.According to the characteristics of yellow phosphorus tail gas,hydrotalcite-like compounds were used as catalysts for the simultaneous catalytic hydrolysis of HCN and COS.The reasons affecting the catalytic hydrolysis activity and process were investigated by characterization methods.The main research contents include:?1?A series of Zn-Ni-Al hydrotalcite-like compounds were prepared by coprecipitation method for simultaneous catalytic hydrolysis of HCN and COS.The influence of preparation conditions?such as metal content ratio,rare earth metals species,rare earth metal content,pH value of solution,crystallization temperature and calcination temperature?on simultaneous catalytic hydrolysis of HCN and COS were systematically studied.?2?The influence of experimental reaction conditions?reaction temperature,inlet gas concentration,relative humidity and reaction space velocity?on the efficiency of simultaneous catalytic hydrolysis of HCN and COS.?3?A series of hydrotalcite-like catalysts were characterized and analyzed by BET,XRD,XPS,FTIR,TG/DTA and so on.The mechanism of catalytic hydrolysis reaction was studied through analyzing the changes before and after catalyst deactivation.The specific research conclusions are as follows:?1?The influences of different preparation conditions on the simultaneous catalytic hydrolysis of HCN and COS were investigated.From the experimental results of removing HCN and COS,the catalyst?n?Zn?/n?Ni?=1/3,rare earth metal was Ce,n?Al?/n?Ce?=50,solution pH=10,crystallization temperature of 50?after calcining at 350?for 3h in N₂atmosphere?has superior activity for the simultaneous catalytic hydrolysis of HCN and COS.The best effect of the prepared optimal catalyst on simultaneous removal of HCN and COS was that over 90%of HCN and COS removal rates can be maintained for 600min and 630min respectively.The results showed that the metal content mainly affected the pore structure of hydrotalcite-like materials.The addition of appropriate rare earth metal Ce was helpful to stabilize the layered structure of hydrotalcite-like compounds and reduced the presence of oxygen-containing functional groups.Appropriate alkaline strength of the solution was conducive to higher activity and better crystallinity of the catalyst.Crystallization temperature could affect the formation rate of stable structure of the catalyst,which affected the formation of stable crystal structure of the catalyst.The roasting temperature mainly affected the content of volatile components in the catalyst and the intact state of the hydrotalcite-like pore structure.?2?The influences of different reaction conditions on the activity of simultaneous catalytic hydrolysis of HCN and COS by Zn-Ni-Al hydrotalcite-like compounds were investigated.The reaction conditions such as reaction temperature,inlet gas concentration,relative humidity and space velocity were investigated.The experimental results under different reaction conditions show that:the optimum reaction conditions are:71.3mg/m³ HCN,634 mg/m³ COS,reaction temperature 175?,relative humidity60%,space velocity 20000 h^-1,under which the catalyst has the highest activity.When the reaction temperature was too low,the activity of catalyst was not fully activated,and the reaction temperature was too high,it would promote the formation of metal salts and accelerate the poisoning of catalyst.With the increased of inlet gas concentration,the number of active sites per unit volume of gas decreased,which led to the reduction of catalytic effect.Excessive relative humidity led to the occupancy of active sites by hydrogen peroxide and the formation of more metal salts,which decreased the activity of catalysts,but anhydrous was not conducive to the catalytic hydrolysis.With the continuous increased of reaction space velocity,the catalytic activity of the catalyst for simultaneous hydrolysis of HCN and COS continued to decrease.?3?The concentration of outlet gas and the change of product were investigated,and the characterizations of Zn-Ni-Al hydrotalcite-like compounds before and after deactivation were characterized by BET and XPS.The experimental results verified that the simultaneous removal of HCN and COS by Zn-Ni-Al hydrotalcite-like compounds was a catalytic hydrolysis reaction.Meanwhile,the catalytic hydrolysis products of HCN and COS were gases,such as NH₃ and H₂S.They could react further.Furthermore,the generated metal salt could adhere to the surface of the catalyst,gradually leading to the poisoning and deactivation of the catalyst.