4th International Symposium “Molecular Order and Mobility in Polymer Systems”. St.Petersburg, June 3-7, 2002.


POLYIMIDE LANGMUIR-BLODGETT LAYERS IN GAS SEPARATING COMPOSITE MEMBRANES

 

G.A.Polotskaya*, V.P.Sklizkova*, S.I.Goloudina**, V.M.Pasyuta**, V.V.Luchinin**, I.V.Gofman*, V.V.Kudryavtsev*

 

*Institute of Macromolecular Compounds, Russian Academy of Sciences,

Bolshoy pr.31, St.Petersburg 199004, Russia.

**St.Petersburg State Electrotechnical University, ul. Prof. Popova 5, St.Petersburg 197333, Russia.

 

Aromatic polyimides are promising membrane material for gas separation because of their unique permselectivity in combination with high chemical resistance and thermal stability. Their application as homogeneous membranes is limited by relatively low gas permeability. Two-layer composite membranes make it possible to use polymers with high selectivity but low permeability in thin active layers ensuring their effective productivity in gas separation. Several attempts to use Langmuir-Blodgett (LB) films as active layers of composite membranes for gas separation have been published but sutisfactory permselectivity has rarely been achieved.

In the present work composite membranes containing polyimide LB ultra-thin film (~30 layers) deposited on a support surface (38.5 cm2) were obtained and studied. The LB ultra-thin film was formed from polyamic acid tert-amine salt which was synthesized by reaction of dianhydride of 3,3’,4,4’-biphenyltetracarboxylic acid and o-tolidine and subsequent neutralization by O,O’,O’’-trihexadecanoyltriethanolamine. Polyphenylene oxide (PPO) films with a known gas separation properties were used as a support. An imidization was carried out by thermal treatment of LB/PPO composite membranes.

Gas transport properties were measured on a chromatography installation with a diffusion type cell for membranes by air (O2 and N2 mixture) or He transmission at 30oC and a partial pressure of 1 bar.

The LB/PPO membrane was analyzed in terms of the resistance model of gas transport through a composite membrane. According to the law of successive resistance, the overall resistance of two-layer LB/PPO membrane to gas flow is comprised of the sum of its layers resistances. Since resistances of the LB/PPO membrane and the PPO support are known, the resistance of the LB film can be calculated. It was established that the contribution of LB film is the principal factor for selective separation of gas mixtures by LB/PPO membrane (a O2/N2=8.5).


G.A.Polotskaya, V.P.Sklizkova, S.I.Goloudina, V.M.Pasyuta, V.V.Luchinin, I.V.Gofman, V.V.Kudryavtsev. Polyimide Langmuir-Blodgett layers in gas separating composite membranes // 4th International Symposium “Molecular Order and Mobility in Polymer Systems”. St.Petersburg, June 3-7, 2002, p. 125


 

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