Steven Ray Auvil

Elucidating the mechanism(s) of gas transport in poly[1-(trimethylsilyl)-1-propyne] (PTMSP) membranes

Abstract Gas permeabilities in poly[1-(trimethylsilyl)-1-propyne] (PTMSP) are orders of magnitude larger than in other glassy polymers such gas polycarbonate. Based on solubility, permeability and other data, it is concluded that fast diffusion (and not a large solubility) is responsible; and that the polymer has ∼25 vol% of voids which may be linked through chain-to-chain gaps at least ∼3 A wide, suggesting that PTMSP may be“microporous”. Further evidence for the connectivity of microvoids in PTMSP is offered by mixture permeation results. The permeability of a light gas such as He or N 2 is drastically reduced by the co-permeation of a more strongly sorbing and/or more condensable species such as SF 6 . The extent of this light gas rejection is within the scope of mixture permeation under the pore transport model — via competitive adsorption/surface-diffusion and pore blocking — but appears to exceed expectations based on the dual-mode sorption model — which tacitly takes the microvoids to be not connected.

Mass transfer in carbon molecular sieves—an interpretation of Langmuir kinetics

Abstract In this paper, the Langmuir kinetics rate expression, which has gained currency in modeling O 2 /N 2 mass transfer in carbon molecular sieve adsorbents, is derived, starting from “surface barrier” model of diffusion under a chemical potential gradient; this provides a physical basis for the use of mass-action rate laws to describe diffusion processes.

Membrane/cryogenic hybrid scheme for argon production from air

Abstract A novel membrane/cryogenic hybrid scheme is presented wherein crude argon from a cryogenic air separation unit is fed to an oxygen selective membrane unit to remove a substantial portion of the oxygen. The oxygen enriched permeate from the membrane unit is returned to the crude argon distillation column of the cryogenic air separation process. The non-permeate stream is enriched in argon and can be further purified in a catalytic unit to produce an oxygen-free argon stream. The proposed process makes use of the synergy between the two separation units whereby, the cryogenic unit offers high recovery and the membrane provides purification leading to improved argon recoveries at higher argon concentrations. Calculations show that this process, in conjunction with an oxygen removal catalytic process, provides an economical alternative for the production of pure argon as compared to the conventional process using just a cryogenic unit and a catalytic unit to remove oxygen.

Membrane/cryogenic hybrid processes for hydrogen purification

Abstract Membrane gas separation processes, while becoming more widespread, suffer from inherent limitations in their use. Combining membranes with other gas separation processes has been found to be an effective means of overcoming these limitations. A combination of hybrid process comprising a membrane unit with a cryogenic process has been found of value for producing hydrogen from a rather dilute source such as FCC off-gas. The success of the hybrid stems from the use of each component part of the process in its region of greatest efficiency. The judicious combination of processes leads to an overall process that is not only more efficient than either of the component processes, but more cost-effective as well.

Summary: Societal risk criteria and pipelines

The selection of appropriate risk criteria for pipelines depends upon the objective of the analysis. This article describes options for pipeline risk assessment (F‐N and individual risk analyses); the descriptions include objectives, methods, and criteria. Methods that compare pipeline to fixed facility risk have the advantage of facilitating appropriate allocation of risk reduction resources. This article is a summary of a more detailed article from a recent Global Congress. It also references other PSP articles that cover risk analyses and criteria.