The separationofolefin–paraffinmixturesisoneofthemostimportantandexpensiveprocessesin petrochemicalindustries.Inthisresearch,theperformanceofcelluloseacetate–silicananocomposite membranesintheseparationofethylene/ethaneandpropylene/propanehasbeenstudied.Silica nanoparticleswerepreparedviahydrolysisoftetraethoxysilane(TEOS).Membraneswerepreparedby the solution-castingmethod.ThepreparedmembraneswerecharacterizedusingFT-IR,SEMandTGA analyses.Puregaspermeationexperimentswereperformedbytheconstantvolume/variablepressure methodat2barfeedabsolutepressureand35 1C. Theresultsshowedthepermeabilityofethyleneand propyleneincreasedfrom0.052barrerand0.046barrerinpurecelluloseacetateto0.11and0.098 barrerinthecompositemembranecontaining30wt%silicaparticles,respectively.Thecomparisonof the selectivitiesofC2H4/C2H6 and C3H6/C3H8 indicates anincreasefrom2.16and2.55inpurecellulose acetateto4.07and6.12incompositemembranecontaining30wt%silicaparticles.Thediffusion coefficientsofpreparedhybridmembranesweredeterminedbythetimelagmethod.Thesolubility coefficientwascalculatedindirectlyfrompermeabilityanddiffusivitycoefficients.Theresultsshowed an increaseinthesolubilitycoefficientandadecreaseinthediffusioncoefficientofgaseswhile increasingthesilicamassfraction.Toinvestigatethepossibleplasticizationphenomena,theeffectof feed pressureongaspermeabilityandO2/N2 selectivity,beforeandafterexposureofmembraneswith propylene,wasstudied.Theresultsshowednoplasticizationeffectsupto8barfeedpressure.

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