Preparation and Gas Separation Performance of Thermally Rearranged Membranes Containing Isomerized Naphthalene Ring Structures
Two kinds of novel diamine monomers containing naphthalene rings,1,5-bis(4-amino-5-hydroxyphenoxy)naphthalene(NDBAP)and 1,6-bis(4-amino-5-hydroxyphenoxy)naphthalene(NDBPA)were firstly synthesized.Then,six kinds of polyimide(PI)membranes and the corresponding thermally rearranged(TR)membranes were separately prepared by the solution polymerization of the two diamines and three kinds of dianhydrides,followed by thermal imidization and further thermal treatment at 450 ℃.The testing results show that the obtained six kinds of PI membranes exhibit excellent thermal properties,with higher glass transition temperatures around 350 ℃.After further thermal treatment,the gas separation performance of the TR membranes is significantly improved compared to the original PI membrane.The gas permeability coefficients of the TR(NDBAP-6FDA)for H2,CO2,O2,and N2 are 268.4 Barrer,249.32 Barrer,56.7 Barrer and 7.87 Barrer,respectively.The ideal selectivities of CO2/N2,O2/N2 and H2/N2 are 31.67,7.21 and 34.1 respectively,beyond 2008 Robeson upper limit of O2/N2.However,the H2,CO2,O2 and N2 permeabilities of the TR(NDBPA-6FDA)are 220.4 Barrer,210.32 Barrer,32.34 Barrer and 5.62 Barrer.The selectivities of CO2/N2,O2/N2 and H2/N2 reach 37.42,5.75 and 39.22 respectively,close to 2008 Robeson upper limit of O2/N2.Therefore,1,5-substituted NDBAP can increase the gas permeabilities of the TR membranes more effectively than 1,6-substituted NDBPA.
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