Design And Preparation Of Ionic Materials For Light Alkyne/Alkene Separation

The separation of light alkyne/alkene is important in industry.The absorption and adsorption technologies based on liquid/solid medium show potential to be environment friendly and economical separation methods,and the key point is the development of efficient separation medium.Ionic materials are rich in functional sites with electric charges and highly designable,showing potential to recognize the small differences between the properties of alkyne/alkene,and are expected to be applied in alkyne/alkene separation.Herein,a series of new ionic materials had been designed and prepared,including ionic liquids(ILs)with strong basic hydrogen-bond and layered ionic hybrid porous materials(LIHPM)with unique dual-channel pore structures and multiple sites in confined spaces,achieving high capacity and selectivity for alkyne/alkene separation,indicating the mechanisms of the regulations in framework structure and separation performance.The main researches include:Strong basic hydrogen-bond ILs including morpholine sulfonate ILs and carboxylate ILs were designed and prepared,the solubilities of C3H4 and C3H6 were measured that the two ILs reached high C3H4 capacity and C3H4/C3H6 selectivity simultaneously.For example,the C3H4 capacity of[P4442][C5COO]reached 0.30 mol/mol at 313.1 K,which was 3 times the best solvent[DMIM][MeHPO3]previous reported;[P4442][MOPS-1]was second to[P4442][C5COO],but the C3H4/C3H6 selectivity of the former had an 28%improvement than the latter,and this type of ILs had a wider liquid range and better thermal stability(higher than 620 K).The results of hydrogenbond basicity and hydrogen-bond energy showed the hydrogen-bond interaction was the inherent mechanism of excellent C3H4 capacity in these ILs.The solubility results also indicated that these ILs had a better C3H4/C3H6 separation ability with shorter carbon chains and the lower temperature.The absorption-desorption cycles proved that the ILs had good a cyclic regeneration performance.In terms of removing trace C3H4 in C3H6,sulfone-based ligand bridged LIHPM were designed and prepared,that was rich in basic hydrogen bond sites and possessed unique intralayer and interlayer pore structures.By changing the anion,the pore sizes was fine-tuned at the sub-nanometer level.The results showed that TiFSIX-dpso2-Cu had a record high C3H4 uptake of 3.05 mmol/g at 0.01 bar,the inflection point pressure increases from GeFSIX-dpso2-Cu to SiFSIX-dpso2-Cu with different anions,due to the structure change after activation.The dynamic breakthrough tests showed that the high-purity C3H6 productivities of three materials were as high as 81.3～86.2 mmol/g,significantly better than reported materials.Five water-contained cycles proved the excellent water stability of these materials.Desorption experiments showed that the above materials can be used to produce high-purity propylene,and high-purity propyne can also be obtained through desorption,that realized the production of two high-purity gases in one process.To further improve the separation selectivity,based on the sulfone-based ligand,two new types of thioether-based ligand bridged LIHPM with smaller pore sizes and higher flexibilities were designed and prepared through the adjustment of the oxidation state and metal node,which achieved C3H6 exclusion for the first time,and also reached a sieving effect in C2H2/C2H4 separation along with higher C2H2 uptakes than current C2H4-exclusion materials.The pore structures were finetuned with the change of metal node,the GeFSIX-dps-Cu had achieved higher alkyne uptake and alkyne/alkene selectivity than GeFSIX-dps-Zn at low pressure:for example,the uptake ratio of 0.1 bar/0.9 bar C3H4/C3H6 reached 39.25,much higher than other reported porous materials.And the material had good hydrolytic and thermal stability.Further explored the internal mechanism of specific recognition for alkynes with these LIHPM.The DFT-D calculation results showed that the multi-site synergistic interaction was formed between C3H4 and the intralayer and interlayer sites of three sulfone-based materials,and the binding energy of C3H4 was significantly higher than that of propylene,which explains the strong affinity for C3H4 at low pressure and excellent C3H4/C3H6 separation performance with these materials;thioether-based materials had strong affinity for both C3H4 and C2H2,and the alkyne binding energy of GeFSIX-dps-Cu was 20%higher than GeFSIX-dps-Zn,revealed the result of a lower gate opening pressure for alkyne with GeFSIXdps-Cu in molecular level.The analysis of alkyne-loaded single crystal structure showed the binding site and the interaction mode for alkyne adsorption.In addition,the difference between the alkyne-loaded structure and activated structure clarified the mechanism of the unique guest-responsive structure change in these LIHPM.