Preparation And Performance Of PPENK Composite Membranes For Pervaporation

Pervaporation membrane separation technology of aromatic/aliphatic hydrocarbons has significant advantages in separating organic azeotropes and organic mixtures with similar boiling points,so it is valuable in petrochemical industry and green production.The composite membranes with pore-filling structure were prepared by means of atmospheric dielectric barrier discharge(DBD)plasma syn-irradiation grafting technology.The effects of pore size and distribution of the ultrafiltration membranes and preparation conditions on the structure and morphology of the composite membranes,and the separation performance of aromatic/aliphatic hydrocarbons was studied.Finally,the molecular dynamics simulation was used to explain the causes of these effects.Firstly,the ultrafiltration membrane was prepared by the poly(phthalazinone ether nitrile ketone)s containing phthalazinone moieties(PPENK),which was used as the support layer of the composite membrane.The composite membrane was prepared by methods of atmospheric dielectric barrier discharge(DBD)plasma and syn-irradiation grafting to graft poly(ethylene glycol)methacrylate(PEO500OHMA)in pores of and onto the surface of the ultrafiltration membrane.And then,the effects of pore size and distribution of ultrafiltration membranes,coating concentration of monomer solution and coating temperature on the separation performance of the composite membranes was investigated.The ultrafiltration membranes and composite membranes were characterized by Fourier transform infrared spectroscopy(FTIR)and field emission scanning electron microscopy(FESEM).The reasons showed that PPENK ultrafiltration membrane with pore size of about 15 nm was used as the base membrane to prepare the composite membrane,which had the best separation performance for toluene/n-heptane.The selectivity of the membrane was 6.85,the permeation flux for toluene and n-heptane were 1379 gpu and 202 gpu,respectively.At 45 ~oC,when the concentration of monomer solution increased from 0.30 mol/L to 0.75 mol/L,the selectivity of the composite membrane increased first and then decreased,reaching the maximum at 0.45mol/L.Besides,the thickness of the graft layer of the composite membrane did not increase with the increasing of the concentration of monomer aqueous solution,and it increased first and then decreased as same as the change of the separation performance,reaching the maximum at 0.45 mol/L.When the coating concentration was 0.45 mol/L and the coating temperature rose from 30 ~oC to 60 ~oC,the selectivity of the obtained composite membranes for toluene/n-heptane decreased,and the thickness of the graft layer decreased with the increasing of the coating temperature.Finally,through characterization and analysis of the viscosity and surface tension of monomer aqueous solution and contact angle of UF membrane,combined with molecular dynamics simulation technology,this paper attempts to explain the reasons of the above experimental results by the diffusion process of PEO500OHMA macromonomer in solution.The results showed that the diffusion coefficient of PEO500OHMA increased first and then decreased at 45 ~oC,reaching the maximum at 0.45 mol/L,when the concentration increased from 0.30 mol/L to 0.75 mol/L.Besides,the diffusion coefficient of PEO500OHMA decreased gradually with the increasing of temperature from 30 ~oC to 60 ~oC,when concentration was 0.45 mol/L.These changes were consistent with the variation of the thickness of the graft layer and separation performance of the composite membrane with the monomer coating concentration and temperature.Therefore,it could be concluded that the diffusion of monomers was an important parameter for the preparation of pore-filling composite membranes.