Langmuir-Blodgett, gas-separation membranes

• Main Author: Bruinsma, Paul Joseph
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1994
• Subjects: Chemical engineering; Chemistry; Physical chemistry; Polymer chemistry; Polymers
• ISBN: 9798208044575

Novel asymmetric composite membranes were fabricated by transferring monolayers onto porous support membranes. Langmuir-Blodgett (LB) films are attractive for gas-separation membranes because uniformity and extreme thinness (about 0.1 $\mu$m) of the films promise high mass-transfer rates. By bridging over the holes of the porous support, the LB multilayer acts as a selective barrier to gas diffusion. While nitrogen is relatively inert, carbon dioxide tends to have a high solubility in polymers and the difference in the permeabilities of the two gases was used to characterize solution-diffusion permeation of carbon dioxide in the LB films. The films were also characterized by elevated temperature infrared spectroscopy to correlate permeability changes with changes in molecular ordering. This work consists of three studies. A preformed polymer, consisting of alkyl tails and flexible hydrophilic-spacer groups, was used to bridge the pores. The main chain spacer groups allowed increased packing of the alkyl tails and contained tertiary amines that could facilitate diffusion of acid gases. The carbon dioxide permeability increased at 35$\sp\circ$C due to irreversible disordering of the alkyl tails. Membranes exposed to hydrogen sulfide showed an irreversible decrease in carbon dioxide permeabilities. Permeation studies were also made on LB films with ferric stearate and ferric complexes. Ferric ions in the monolayer undergo a condensation reaction to form an inorganic polymer network, enabling bridging of the pores in the support. Ferric stearate LB films greatly reduced the permeability through the membrane. Above 65$\sp\circ$C, there was a time-dependent permeability increase. Gas permeation through ferric stearate occurred by Knudsen diffusion. LB films selective for carbon dioxide over nitrogen were made by co-depositing poly(-2-vinylpyridine) with ferric stearate and with the ferric salt of poly(maleic anhydride 1-octadecene). Finally, permeation and infrared spectroscopy studies were made of a gegenion of arachidic acid and poly(ethyleneimine). The alkyl tails of the fatty acid were oriented with the surface normal and were hexagonally packed. At elevated temperatures, the tails and the carboxylate head groups disordered continuously with temperature away from the surface normal. Correlated with the disordering was a sharp increase in the carbon dioxide permeability while that of nitrogen increased only moderately.