Chemical Looping Decomposition Of Ammonium Chloride And Ammonium Sulfate

Ammonium chloride(NH4Cl)and ammonium sulfate[(NH4)2SO4]are undesired by-products in the production of soda ash and caprolactam respectively.How to convert these by-products into resources has become a burning problem.A feasible solution is to recover the ammonia nitrogen of the ammonium chloride and ammonium sulfate,which can not only economize the investment and consumption of the synthetic ammonia plant for related enterprises,but also eliminate the overproduction of the ammonium by-product.In addition,because the synthetic ammonia is no longer consumed in the soda ash industry which can become a net process of large-scale conversion of carbon dioxide(CO2),providing a new scheme for the resource utilization of greenhouse gas CO2.It is an effective way to use chemical looping technologies to recover the ammonia nitrogen resource.By the action of chemical looping carriers,the decomposition process of ammonium chloride can be divided into two sub-reactions named "releasing NH3 reaction" and "releasing HCl reaction" respectively.In the releasing NH3 reaction,the HCl is fixed by the carrier and the NH3 which can be recycled to the soda ash unit is released;in the releasing HCl reaction,the carrier is regenerated and the HCl which can be used as the cheap chlorine source of vinyl chloride industry is released.Similarly,the decomposition process of ammonium sulfate can be divided into two sub-reactions named "releasing NH3 reaction" and "releasing SO2 reaction" respectively.The ammonia obtained from the releasing NH3 reaction can be recycled to the caprolactam unit,while the sulfur dioxide obtained from the releasing SO2 reaction can be used to produce sulfuric acid which can also be recycled to the caprolactam unit as the catalyst of Beckmann rearrangement reaction.In this work,systematic chemical engineering research was carried out on chemical looping decomposition of ammonium chloride and ammonium sulfate,aiming to achieve industrialization of the above process,injecting vitality into the development of soda ash and caprolactam industry,and laying an experimental foundation for the large-scale conversion of CO2 into soda ash.The research content includes the following aspects:1.The kinetic mechanism of releasing NH3 and releasing HCl reaction in the chemical looping decomposition of ammonium chloride with magnesium oxide as carrier was studied in a fixed bed reactor by isothermal method.The effect of temperature,particle size,molar ratio and water pressure on the reaction rate were quantitatively investigated.The results show that the mechanism of the releasing NH3 reaction is random nucleation-rapid growth mechanism with an apparent activation energy of 50.27 kJ/mol.The mechanism function of the releasing HCl reaction is two-dimensional interfacial reaction with an apparent activation energy of 65.00 kJ/mol.The specific surface area of magnesium oxide plays a key role in both reactions.The reaction rate of releasing HCl reaction is proportional to the molar fraction of steam in gas phase.2.A new type of velocity changed fluidized bed reactor concept was proposed for the strong endothermic property of the chemical looping decomposition of ammonium chloride.Based on this concept,a monolithic cross-flow heat transfer decomposer was specifically designed for the decomposition of ammonium chloride.The decomposition reactor was preliminarily designed and calculated for the annual production scale of 10,000 tons.The designed decomposition temperature of the releasing HCl section was 600?,while the releasing NH3 section was 300?,and the required volume flow rate of flue gas was 1.36 m3/s.The total heat exchange area of the reactor was 210m2.In addition,the numerical calculation method was adopted to optimize the heat load distribution of the reactor by adjusting the wall thickness.After the optimization,the releasing NH3 and the releasing HCI section were all operated near the design temperature,and the conversion rate was around 0.99;Finally,the two-fluid model based on kinetic theory of granular flow was used to simulate the velocity changed fluidized process,and the axial and radial flow structures of conventional fluidized bed and velocity changed fluidized bed were compared.3.The releasing NH3 reaction in the chemical looping decomposition process was systematically studied.Firstly,the non-isothermal kinetics of the ammonium sulfate decomposition was studied.The decomposition process of ammonium sulfate can be divided into three stages and the corresponding activation energy are 96.47?79.47 and 98.30 kJ/mol respectively.The carriers were evaluated by the recycling rates of ammonia,illustrated that calcium oxide and iron oxide carriers can almost accomplish the full recovery of ammonia,while ferric oxide can not.The releasing kinetics of magnesium oxide and calcium oxide mixed with ammonium sulfate were studied in a fixed bed reactor.The decomposition process of magnesium oxide can be divided into two steps and the corresponding activation energy are 87.31 and 113.65 kJ/mol respectively,while the activation energy of calcium oxide is 88.10 kJ/mol.The feasibility of using calcium oxide as carrier to distillate the ammonia in ammonium sulfate was explored.The experimental results show that the ammonia can be full recovered by wet method.The dry method and wet method used for ammonia recovery were compared and three chemical looping process for ammonium sulfate decomposition were proposed.4.A thermodynamic model for the CaS04-(NH4)2S04-NH3-H20 quaternary system with the asymmetric E-NRTL activity coefficient model was developed to understand the thermodynamic behavior.The modeling works involved the data fitting of binary solubility,osmotic coefficient,enthalpy of solution and heat capacity data,as well as ternary solubility data.It was shown that the model could predict the solubility of ammonia and calcium sulfate in aqueous ammonium sulfate solution with temperature range from 0 to 160? and pressure up to 1.0 MPa.Furthermore,the constructed model for the quaternary system was proved to be reliable for predicting the phase transition behavior of solid CaS04 in the electrolyte mixtures of(NH4)2S04-NH3-H20 solution.For the regeneration process of NH3 from ammonium sulfate,this work offered a reliable model for the reactor design and process optimization.