A premembrane comprising polybenzimidazole and aromatic polyester for deacidification, wherein said polybenzimidazole is selected from the formula I or II (i) wherein, R belongs to the tetraamine monomer having structure III(a)-III(f) and R' is from dicarboxylic acid as shown in structure IV: wherein, R 1, R 2 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 containing alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups and X can be any of the following: -CH 2 -, -O-, -SO 2 -, -C(CH 3) 2 -, -C(CF 3) 2 -, -C(Ph) 2 -, -CH 3 C(Ph)-, -CH 3 C(isopropyl)-, -CH 3 C(t-butyl)-, -CH 3 C(n-propyl)-, -CH 3 C(ethyl)- or any other C 1-24 containing alkyl or aryl groups, HOOC-(C k H m X n)-COOH IV where, k = 1-30 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring such as pyridine, pyrazine, furan, quinoline or thiophene groups as straight chain, branched, cyclic, aromatic or combination of these; X = O, N, S, halogen or combination thereof, n = 0-10 and m = appropriate numbers of hydrogen; (ii) the aromatic polyester has structural formula V wherein, R" is derived from phenolphthalein or its derivatives as shown in formula VI and R''' is from dicarboxylic acid as shown in IV: wherein R 1, R 2, R 3, R 4 = H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups. (i) wherein, R belongs to the tetraamine monomer having structure III(a)-III(f) and R' is from dicarboxylic acid as shown in structure IV: wherein, R 1, R 2 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 containing alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups, wherein, R 1, R 2, R 3, R 4 is selected from a group consisting of H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups and X can be any of the following: -CH 2 -, -O-, -SO 2 -, -C(CH 3) 2 -, -C(CF 3) 2 -, -C(Ph) 2 -, -CH 3 C(Ph)-, -CH 3 C(isopropyl)-, -CH 3 C(t-butyl)-, -CH 3 C(n-propyl)-, -CH 3 C(ethyl)- or any other C 1-24 containing alkyl or aryl groups, HOOC-(C k H m X n)-COOH IV where, k = 1-30 containing alkyl, aryl, aromatic ring, arylene, alkylene, arylene-ether or heterocyclic ring such as pyridine, pyrazine, furan, quinoline or thiophene groups as straight chain, branched, cyclic, aromatic or combination of these; X = O, N, S, halogen or combination thereof, n = 0-10 and m = appropriate numbers of hydrogen; (ii) the aromatic polyester has structural formula V wherein, R" is derived from phenolphthalein or its derivatives as shown in formula VI and R''' is from dicarboxylic acid as shown in IV: wherein R 1, R 2, R 3, R 4 = H, CH 3, CF 3, F, Cl, Br, I, NO 2 or C 1-24 alkyl or aryl groups.