Separation Of Nitrogen Compounds By Deep Eutectic Solvents

Highly efficient separation of nitrogen-compounds,such as ammonia,indole and carbazole,is of great significance to protect environment and develop sustainable chemical engineering process.However,some disadvantages exist in traditional separation materials,such as low separation capacity and selectivity,difficult to recycle and large pollution.In this article,ulizing the designability of structure and character of deep eutectic solvents,newly hybrid deep eutectic solvents were constructed,which have strong hydrogen bonding capacity,low volatility,environmental friendliness,simple preparation,and readily available raw materials.A new method was constructed for separation of ammonia and neutral nitrogen compounds such as carbazole and indole by deep eutectic solvents.And efficient and clean separation of nitrogen compounds was achieved,For the first time,research on absoring ammonia by deep eutectic solvents was developed.By controlling types and ratios of hydrogen bond donor/acceptor of deep eutectic solvents,hybrid deep eutectic solvents with flexible hydrogen-bond supramolecular network framework was obtained.The new solvents solves the problem that deep eutectic solvents cannot take into account the interaction strength of solvent-ammonia and the structural stability.The solubility of ammonia is as high as 0.18 g·g-1 at 313 K and 101 kPa in the hybrid deep eutectic solvent with a composition of choline chloride/resorcinol/glycerol(molar ratio 1:7:5).It is the highest mass solubility in the known low volatility solvents,and the performance does not change for at least 10 absorption-desorption cycles.At the same time,the theoretical selectivity of hybrid eutectic solvent for ammonia/carbon dioxide is as high as 142,demonstrating the potential for selective separation of ammonia and carbon dioxide.Molecular dynamic simulation and COSMOL-RS were applied to study the microstructure of hybrid deep eutectic solvent and its interaction with ammonia.It was found that abundent flexible hydrogen-bonded supramolecular network structure exists within the hybrid eutectic solvent.The reason why the hybrid deep eutectic solvent can maintain the structural stability during the ammonia absorption process is revealed.At the same time,each atom of the ammonia molecule can have strong hydrogen bonding with hybrid deep eutectic solvent,thus forming complex hydrogen bond network between the two,making the hybrid deep eutectic solvent could absorb ammonia well and can be recycled in the case of no chemical reaction.The extraction separation performance of deep eutectic solvent for the neutral nitrogen compounds indole and carbazole in simulated oil were studied.It was found that the hybrid deep eutectic solvents consisted of choline chloride,polycarboxylic acid/hydroxycarboxylic acid/sugar,and bound water can effectively remove trace carbazole and indole from the oil.And there is significant synergistic extraction effect between water molecules and choline chloride-carboxylic acid/sugar.When choline chloride/DL-malic acid/water(1:1:3)was used as extractant,the distribution coeffcients of indole and carbazole were 11.0 and 1.82 respectively,which were dozens or even several hundred times more than the extractant based on choline chloride/DL-malic acid or pure water.Furthermore,the presence of bound water can also significantly reduce the solubility of n-heptane in extractant,making the selectivity of indole/n-heptane and carbazole/n-heptane up to 8547 and 2304,respectively.Quantum chemistry calculation shows that the looser solvent structure caused by the incorporation of bound water is an important reason for the synergistic effect.