Effect of top layer swelling on the oxygen/nitrogen separation by surface modified polyurethane membranes

• Published in: Journal of membrane science Vol. 141; no. 2; pp. 255 - 264
• Main Authors: Chen, Shih-Hsiung, Wu, Tung-Hsing, Ruaan, Ruoh-Chyu, Lai, Juin-Yih
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.04.1998; Elsevier
• Subjects: Applied sciences; Cobalt chelating; Ethylenediamine; Exact sciences and technology; Exchange resins and membranes; Forms of application and semi-finished materials; Gas separations; Plasma treatment; Polymer industry, paints, wood; Polyurethane membrane; Technology of polymers; Polyurethane membrane; Ethylenediamine; Cobalt chelating; Gas separations; Plasma treatment; Cobalt Complexes; Complexation; Plasma; Oxygen; Nitrogen; Experimental study; Property processing relationship; Surface treatment; Polyurethane elastomer; Diamine; Gas permeability; Selective permeability; Membrane
• ISSN: 0376-7388; 1873-3123
• DOI: 10.1016/S0376-7388(97)00316-5

Cobalt(II) was chelated on the surface of a hydroxyl terminated polybutadiene (HTPB) based polyurethane (PU) membrane. The surface of a HTPB based PU membrane was first modified by ethylenediamine (EA) plasma. The cobalt chelated membrane was prepared by immersing the plasma treated membrane into a cobalt(II)/formamide solution for various length of time. For a fair comparison, the untreated and plasma treated membranes were also immersed in formamide solution. The gas transport properties of all three membranes were compared. Without solvent immersion, the O 2/N 2 selectivity increased from 2.6 to 3.1 after EA plasma treatment. But the permeability decreased from 0.88 GPU to 0.35 GPU. The selectivity was further improved to 4.4 by immersing the plasma treated membrane in a solution of CoCl 2·6H 2O/formamide for 1 h, but the permeability decreased to 0.23 GPU. The solvent immersion had little effect on the transport properties of the untreated membrane. But the transport properties of the plasma treated and cobalt chelated membranes were greatly affected by the formamide immersion. The oxygen and nitrogen permeabilities of the modified top layers could be calculated from a series model for composite membranes. It was found that both the permeability and selectivity of the top layer of the plasma treated membrane increased with the solvent immersing time. For the top layer of the cobalt chelated membrane, the gas permeability first decreased after 1 h immersion and then increased after further immersion in CoCl 2·6H 2O/formamide solution. The selectivity of cobalt chelated membrane increased as the gas permeability decreased and vice versa. These results implied that the EA grafting enhanced the O 2/N 2 selectivity by increasing its oxygen affinity but the cobalt chelating increased the O 2/N 2 selectivity by enhancing the size sieving effect.