Experimental Investigation Of Ammonium Phosphate Absorbing Ammonia In The Production Of Hydrogen Cyanide

Andrussow method is the most widely used in the production of hydrogen cyanide with natural gas for raw material.But the conversion rate of ammonia was only 60%,therefore,the recycling of ammonia is a problem that must be solved.The treatment of mixed tail gas mainly uses concentrated sulfuric acid to wash the gas,recycling ammonia,removing water and producing ammonium sulfate,but this process has low economic revenue.The price of raw materials by sulfuric acid and ammonium sulfate market have a great influence on economic benefits,and the technique can not recover the excess ammonia.The paper propose a new process to absorb ammonium of mixed gas by ammonium phosphate absorbing ammonia process.Anhydrous ammonia can be produced with unconverted ammonia in this process and anhydrous ammonia can be reused as reactant.The process also achieves the recycling of the absorption solution and greatly saves the cost.The paper firstly analyzes the main chemical reaction in liquid phase,reaction equilibrium constant,the material conservation and charge conservation in the system of HCN-NH3-?NH4?2HPO4-NH4H2PO4.The thermodynamic state of the liquid phase electrolyte system was described by the Electrolyte-NRTL activity coefficient model.On a self built experimental platform,gas-liquid equilibrium experiment has been carried out.Gas-liquid equilibrium data of system was obtained by the absorption experiment.The correlation equation for P_NH3H3 and T?mole ratio R of N₃/H₃PO₄ was builded.In the condition of laboratory,temperature 40?-50?,the concentration of absorbing liquid 1.2-3.2 mol/L,the ratio of liquid to gas L/G 3 L/m³-13 L/m³ and initial ammonia concentration 10 g/m³-30g/m³ are studied.The results showed that partial pressure of ammonia can produce the mutation point when NH₄H₂PO₄ is converted to?NH₄?₂HPO₄ in the absorption process of NH₃.The pH value is over 7 and the absorption rate of NH₃ decreases at this time.HCN will dissolve in large amounts.When pH<7,HCN does not react with the components in the absorption solution and produces a small amount of ionization.In the absorption solution,NH₃ exists in NH₄H₂PO₄ and?NH₄?₂HPO₄ two level equilibrium.Therefore,when pH<7,corresponding larger R value can be used as the control point of the absorption tower.When the molar ratio of R was unchanged,the partial pressure of ammonia in the gas phase was decreased with the increase of the concentration of ammonium phosphate.When the gas phase ammonia gas pressure is in common,the molar ratio of R increased with the increase of the concentration of the absorption solution.Results show that the suitable conditions are as following:temperature 50?,the concentration of absorbing liquid 2.1 mol/L,the ratio of liquid to gas L/G is 11 L/m³.At this time,the liquid rich molar ratio is controlled at about 1.53.