Study On Rigidity/Flexibility Of Zeolitic Imidazolate Framework-8 And Its Application In Propylene/Propane Separation

Propylene/propane separation is mainly achieved by cryogenic distillation in industry,but this separation technology is really high energy-consumed.Adsorption and membrane separation are considered to have great potential to replace cryogenic distillation.Among numerous materials,porous Metal-Organic Frameworks(MOFs)have attracted much attention from researchers due to their large surface area,adjustable pore size and high controllability.However,the influence of MOF structures on its gas separation performance is not clear now.In this paper,rigid and flexible zeolite imidazole frameworks(ZIF-8)powders were prepared,and the influence of ZIF-8 framework rigidity/flexibility on its propylene/propane adsorption and separation behavior was studied.The specific research contents of this paper are as follows:(1)Using an external electric field to lead the lattice distortion of ZIF-8,and the rigid ZIF-8 powder was prepared under an external electric field,while the flexible ZIF-8 powder is prepared without the electric field.Gas adsorption tests on rigid and flexible ZIF-8 show that the flexible ZIF-8 has a slightly larger adsorption capacity at close to atmospheric pressure.We especially pay attention to C3H6/C3H8 adsorption behavior of rigid/flexible ZIF-8.They have a slight difference in the thermodynamic adsorption behavior of C3H6/C3H8,while they have an obvious difference in the adsorption kinetics of C3H6/C3H8.The diffusion of C3H8 is inhibited in rigid ZIF-8,so it can achieve higher kinetic selectivity of C3H6/C3H8.By comparative experiments,we found the framework rigidity/flexibility of ZIF-8 influences its adsorption behavior,which provides some guidance for rigid/flexible MOF applying in gas separation.(2)Take advantage of high C3H6/C3H8 kinetics adsorption selectivity of rigid ZIF-8,we used it to mix with polysulfone(PSF)to prepare mixed matrix membranes(MMMs)for C3H6/C3H8 separation.Firstly,the mixing behavior of ZIF-8 with different sizes was investigated,and it was found that large ZIF-8 particles can prepare the MMMs with ZIF-8provided the main transmission path.The C3H6/C3H8 separation performance tests showed that the increase of ZIF-8 loading improved C3H6 permeability and C3H6/C3H8 selectivity simultaneously.The 30wt% ZIF-8/PSF MMM shows a high C3H6/C3H8 selectivity among polymer membranes and other MMMs.In addition,ZIF-8/PSF MMMs also show long-term operation stability and plasticizing resistance.