| Ionic liquids have been widely used in the field of gas separation owing to their negligible volatility,remarkable solubility,excellent thermal stability and structure designability.The research of ammonia?NH3?separation and recovery ionic liquids has aroused widespread concern in academia,but some problems can not be ignored,such as lower NH3 absorption performance in conventional ionic liquids,complex synthesis route of some functional ionic liquids and the NH3 absorption performance still can not meet the industrial demands.Considering the single functionalized site and requirements for improving NH3 absorption,a new strategy by simultaneously introducing two functionalized sites into ionic liquids was proposed.A series of dual-functionalized protic ionic liquids?DPILs?with both weak acidic protons and hydroxyl groups were designed and prepared for NH3 separation and recovery.In this work,the physical properties,NH3 absorption performance,NH3 selectivity,recyclability of DPILs were studied systematically.Further,the interaction mechanism between the DPILs and NH3 as well as the thermodynamic properties of NH3 absorption process were studied and analyzed in order to provide new strategies for the design of novel ionic liquids,which can be governed the NH3-containing tail gases in industry.The main innovative work and results are as follows:?1?A series of imidazolium-based and pyridinium-based DPILs were designed and prepared,and their structures were characterized by NMR and IR.The results showed that the structures of the preparation DPILs are consistent with that of the target ionic liquids,and all exhibited a good thermal stability.?2?Four imidazolium-based DPILs[CnOHim]X?n=1,2;X=[NTf2]-,[BF4]-,[SCN]-?were used to investigate the effect of anions,the length of side chain in cations,temperatures and pressures on the NH3 absorption performance.The selectivity of NH3/CO2,NH3/N2 and the recyclability of NH3 absorption process were also studied.The results indicated that the imidazolium-based DPILs show a remarkable NH3 solubility,and the NH3 solubility in[Et OHim][NTf2]was 3.11 mol NH3/mol IL at 313.15 K and atmospheric pressure,which is superior to any non-metallic ionic liquids reported so far.Moreover,the NH3 mass solubility in[Et OHim][BF4]and[Et OHim][SCN]can reach 0.210 and 0.221 g NH3/g IL,which are the highest value of all the ionic liquids ever reported under the same conditions.?3?Based on the characteristic analysis of NH3 absorption curve in imidazolium-based DPILs,the NH3 absorption in DPILs can be divided into two processes:chemical reaction and physical dissolution.Taking[Et OHim][NTf2]as an example,the in-situ FTIR spectra and 1H NMR of the process of NH3 absorption in[Et OHim][NTf2]were measured.The results indicated that there is a strong physicochemical interaction between DPILs and NH3 and the week acidic protons and hydroxyl groups play a key role in the NH3 absorption.Meanwhile,quantum chemical calculations were further applied to calculate the interaction energies between NH3 and[Et OHim][NTf2].The results reflected the week acidic protons interact with NH3 mainly through both a chemical reaction and hydrogen bonding,while the hydroxyl groups through a hydrogen bonding.In summary,that DPILs absorbed NH3 mainly through the synergistically physicochemical interaction between NH3 and dual-functionalized sites,which provides guidance for the design of novel ionic liquids.?4?In this work,seven kinds of pyridinium-based DPILs[2/4-CnOHPy]X?n=0,1,2;X=[NTf2]-,[SCN]-,[NO3]-?were applied to measure the NH3 solubility under different temperatures and pressures.The NH3 absorption isotherms in DPILs were fitted by the reaction equilibrium thermodynamic model?RETM?and obtained the thermodynamic properties,such as molar Gibbs free energy??rGm?,molar reaction enthalpy??rHm?,molar reaction entropy??rSm?etc.The analysis showed that the molar reaction enthalpy is the main driving force for NH3 absorption in DPILs,which has important reference significance for industrial NH3 separation process. |
PDF Full Text Request