Experimental Research Of Deep Eutectic Solvents For NH₃ Uptake

Ammonia（NH₃）is a widely used basic chemical raw material,which is often used in the preparation of fertilizers,plastics and many fine chemical products.The manufacture and utilization of NH₃usually causes the emission of exhaust gas containing NH₃.As a typical poisonous gas,NH₃participates in the formation of acid rain and haze in the atmosphere through complex chemical and physical processes,which seriously affects economic development and human health.Therefore,the capture of NH₃can not only solve the problem of atmospheric pollution effectively,but also realize the recycling o resource of resource,which possesses great economic value and social significance.The key of NH₃capture to technology is the development of new absorbents with excellent performance.Altough water and acidic solutions can efficenty capture NH₃,they troubles with the inorganic ammonia salts and diluent aqueous ammonia.The use of ILs for NH₃capture is not preferred from the viewpoints of practical application due to their high price and complex synthetic routes,Deep eutectic solvents（DESs）can provide new selection for NH₃capture due to their serials of good properties similar with ILs,availability of raw materials,simple preparation and lowpresent paper,several sets of new DES systems have been constructed and used in the experimental study on NH₃absorption,with the main contents as follows:Common choline chloride-based DESs were formed with Choline chloride（Ch Cl）as a hydrogen bond acceptor（HBA）and 1,3-propanediol,1,4-butanediol,2,3-butanediol and trifluoroacetamide（TA）as hydrogen bond donors（HBD）.The solubilities of NH₃in these choline chloride-based DES at 303.15～333.15 K and 0～550.0 k Pa were determined by using isochoric saturation method.By model correlation of the experiment data,the Henry constant Hm and the standard Gibbs free energyΔ_disG⁰and the enthalpy of dissolutionΔ_disH⁰and dissolution entropyΔ_disS⁰were obtained.The results showed that Ch Cl-1,4-butanediol system had the best absorption effect on NH_3,and the process of NH₃absorption by Ch Cl-based DES was a spontaneous exothermic process.Glycerol（Gly）,a typical triol from biodiesel by-product,has the characteristics of large quantity,low price,good biocompatibility and high boiling point.In this thesis,the NH₃dissolution behavior in glycerin and its derivatives（DL-1,2-isopropyl glycerol,glycerol formal,and 3-methoxy-1,2-propanediol）were systematically investigated using experimental determination,model correlation,spectrum analysis and quantitative calculation.The results demonstrated that the dissolution of NH₃is a spontaneous and exthomic process,with the hydroxyl groups in glycerin and its derivatives asis the main binding site for dissolving NH₃.In order to reduce the viscosity of glycerin,pyrazole（Py）was introduced as HBA to construct non-ionic glycerin-pyrazole DES.The solubility data at 293.15-313.15 K for 0-400.0 k Pa NH₃and 0-600.0 k Pa CO₂were determined and correlated in glycerol-pyrazole DESs.The results show that the addition of pyrazole can greatly reduce the viscosity of glycerol,for example,the viscosity of Gly-Py（1:1）DES（101 m Pa?s）,is much lower than that of pure glycerol（645 m Pa?s）at 303 K;the maximum absorption capacity of NH₃in the glycerol-pyrazole DES achieves 5.561mol?kg^-1at 293 K and normal pressure,and the ideal selectivity of NH₃/CO₂is 259.In order to obtain DES with high mass transfer rate and large NH₃absorption capacity,protonated guanidinium isothiocyanate（GI）was introduced as HBA and paired with acetamide（AT）as HBD to prepare a series of low viscosity GI-AT DES.Furthermore,the research on NH₃uptake and separation in the GI-AT DES were carried.It was found that the absorption capacity of NH₃at normal pressure is 3.762mol?kg^-1,the ideal selectivity of NH₃/CO₂is as high as 130;the enthalpy change of NH₃absorption process is less than 25 k J?mol^-1;the absorption process is reversible and the recycling performance is satisfactory.GI-AT DES has the potential in the practical industrial application.