Designing Deep Eutectic Solvents Based On Weak Protic Acids For Ammonia Capture

As a typical toxic and harmful industrial waste gas,ammonia(NH3)is also an important chemical raw material,which has extremely important practical significance for its efficient separation and recovery.The absorption of NH3 by conventional acid or water methods often leads to problems such as high pollution,high energy consumption,large solvent loss,and high corrosivity.While ionic liquids,are limited in industrial applications due to high costs and viscosity.Therefore,the development of a new type of solvent that is efficient,stable,easy to regenerate and low-cost storage of ammonia is an urgent problem to be solved.Deep eutectic solvent(DESs)with excellent characteristics such as low volatility,controllability of acid and alkali,low cost and good thermal stability are regarded as a new type of solvent for storing NH3 with high efficiency,stability,easy regeneration and low price.Based on this,the paper firstly determined the solubility of NH3 in DESs consisting ofcholine chloride and urea.The solubility of NH3 increases almost linearly with increasing pressure,indicating it is a physical absorption process.At the same time,the thermodynamic properties of NH3 absorption in DESs are calculated by Henry's law equation.This work complements the data on the absorption of NH3 in DESs,and also proves that DESs is a kind of very promising NH3 capture solvent.NH3 is an alkaline gas,so it is important to design a moderately acidic eutectic solvent.The designs of acidic DESs can be regulated by the choice of hydrogen bond acceptor and hydrogen bond donor,as follows:The first type is phenol-based weakly acidic ternary DESs composed of choline chloride(ChCl),phenol(PhOH)and ethylene glycol(EG)in different proportions.Because of strong combination of phenol and NH3,PhOH is regarded as the key component of NH3 absorption.Studies have shown that this type of DESs has low viscosity,large absorption capacity for ammonia gas,good absorption reversibility,and high NH3/CO2 selectivity.Finally,we use the reaction thermodynamic formula to find that the enthalpy change is moderate,and further verify that this type of DESs is a type of low energy and high efficiency ammonia absorbent with great potential.The second type is based on azole-based weakly acidic ternary DESs,which are composed of three substances,ChCl,azole compounds,and ethylene glycol(EG).Among them,azole compounds include imidazole(ImZ),1,2,4-triazole(TrZ),and tetrazolium(TetrZ).The results show that these types of DESs show high NH3 absorption capcity,high NH3/CO2 selectivity,and good eh regeneration cycle.Due to the stronger acidity of TetrZ,ChCl+TetrZ+EG has a strong chemical affinity for NH3 absorption,so NH3 capacity in ChCI+TetrZ+EG is better than most previously reported absorbents/adsorbents-especially more obvious at low pressure.Furthermore,theoretical calculations were performed to gain molecular insights into the absorption of NH3 in azole-based DESs.The third type is the design of new DESs composed of azole compounds and N-methylacetamide.The azole compounds were selected from imidazole,1,2,4-triazole and tetrazolium.This type of eutectic solvent overcomes the problems of weakly acidic ternary DESs based on azoles,such as volatile,low azole content of the main absorber,and those new DESs also show good physical properties and high NH3 absorption performance.The fourth type is the design of new DESs composed of imidazole hydrochloride and glycerol.The first two works based on tetrazolium-based DESs show higher NH3 absorption capacity,but tetrazolium is more expensive than imidazole.From the perspective of cost reduction,From the perspective of cost reduction,we first react the cheap imidazole with hydrochloric acid to f-orm protonated imidazole hydrochloride(IMCl).Then,ImCl was choose to form a series of DESs with glycerolwhich is cheap and has ample hydroxyl groups.As expected,these types of DESs have achieved highly efficient absorption NH3 through the synergy with the acid-base and hydrogen bonds of NH3.The weak protonic acid-type DESs designed and synthesized in this thesis are simple to prepare,cheap,and have the advantages of high NH3 absorption capacity,fast absorption rate,and good reproducibility,which will provide a new direction for the industry to achieve efficient and low-energy ammonia separation and recovery.