Polymers for gas separations: the next decade

Membranes for gas separation

This is part of a larger study that addresses the question of whether site-specific sorption of organic compounds takes place in soil organic matter (SOM). Competitive sorption is one indication that such interactions may take place. Competitive sorption was tested between atrazine (AT) and other co-solutes in water suspensions of natural and model sorbents. The co-solutes included several s-triazine analogs, a substituted benzene analog (5-chloro-1,3-dimethoxybenzene), and a dissimilar compound, trichloroethene (TCE). The sorbents included a mineral soil (3% OM), a peat soil (93% OM), soil humic acid particles (99% OM), rubbery polymers (polyethylene, cellulose, chitin), a glassy polymer [poly(2,6-diphenyl-p-phenylene oxide)], and a mesoporous silica gel. The rubbery polymers afforded linear single-solute isotherms and no competition, both consistent with ideal (Henry's law) partition sorption. The other sorbents, including the glassy polymer, gave nonlinear single-solute isotherms and significant compet...

Competitive Sorption between Atrazine and Other Organic Compounds in Soils and Model Sorbents

Transport in non-porous polymeric membranes is based on the so-called ‘solution–diffusion’ concept [1,2]. This model, formulated in the 19th century, is grounded in the works of J. K. Mitchell [3], T. Graham [4] and S. von Wroblewski [5], who demonstrated that the presence of microscopic open pores or capillaries was not a prerequisite for mass transfer through polymeric films (or septa as they were referred to), such as natural rubber. First, Graham in 1829 [4], and then Mitchell in 1831 [3], noted that gases were capable of permeating through non-porous rubber films and that this process was related to gas dissolution and diffusion in the polymeric materials. The currently accepted interpretation of such experiments was given several decades later by Graham [4] (this and other articles from the early history of membrane science have been reproduced, in part, in a special issue of the Journal of Membrane Science) [6]. Because he did not find a monotonic correlation between the rates of transport and the known gas phase diffusion coefficients of the penetrant molecules, Graham concluded that the process of permeation comprised two stages: sorption of gas by the rubber ‘that must depend upon a kind of chemical affinity’ and diffusion of the sorbed gas molecules [4]. The sorbed gas, as he wrote, ‘comes to evaporate . . . . and reappears as gas on the other side of the membrane. Such evaporation is the same into vacuum and into another gas, being equally gas-diffusion in both circumstances’ [4]. Empirical observations of the pressure and thickness dependence of the steady-state gas permeation rate or flux, N, led von Wroblewski [5] to propose the following relation:

Transport of Gases and Vapors in Glassy and Rubbery Polymers

The solution and transport behaviour of low molecular weight substances in polymeric materials is a topic of interest for many fields of science and technology. The importance and relevance of such behaviour has become more apparent in recent years with the accelerating development of separation membrane systems, highly impermeable or selectively permeable packaging or barrier films, and the overall increase in the use of polymeric materials for diverse applications with consequent exposure to various environmental agents.

G. S. Huvard

Papers

Energetics of gas sorption in glassy polymers