Pure Gas Values Research Articles

Transport of organic vapors through poly(1-trimethylsilyl-1-propyne)

Poly(1-trimethylsilyl-1-propyne) [PTMSP], a high-free-volume glassy polymer, has the highest gas permeability of any known synthetic polymer. In contrast to conventional, low-free-volume, glassy polymers, PTMSP is more permeable to large, condensable organic vapors than to permanent gases. The organic-vapor/permanent-gas selectivity of PTMSP based on pure gas measurements is low. In organic-vapor/permanent-gas mixtures, however, the selectivity of PTMSP is much higher because the permeability of the permanent gas is reduced dramatically by the presence of the organic vapor. For example, in n-butane/methane mixtures, as little as 2 mol% n-butane (relative n-butane pressure 0.16) lowers the methane permeability 10-fold from the pure methane permeability. The result is that PTMSP shows a mixed-gas n-butane/methane selectivity of 30. This selectivity is the highest ever observed for this mixture and is completely unexpected for a glassy polymer. In addition, the gas mixture n-butane permeability of PTMSP is considerably higher than that of any known polymer, including polydimethylsiloxane, the most vapor-permeable rubber known. PTMSP also shows high mixed-gas selectivities and vapor permeabilities for the separation of chlorofluorocarbons from nitrogen. The unusual vapor permeation properties of PTMSP result from its very high free volume - more than 20% of the total volume of the material. The free volume elements appear to be connected, forming the equivalent of a finely microporous material. The large amount of condensable organic vapor sorbed into this finely porous structure causes partial blocking of the small free-volume elements, reducing the permeabilities of the noncondensable permanent gases from their pure gas values.

Penetrant-plasticized permeation in polymethylmethacrylate

Pure and mixed gas permeation of CO 2 and C 2H 4 in PMMA have been measured. Carbon dioxide permeability and CO 2/C 2H 4 selectivity for the mixture is significantly lower than estimates based on pure gas permeabilities. At 15 atm, CO 2 permeability is reduced from 0.71 barrer to 0.41 barrer. CO 2/C 2H 4 selectivity calculated from pure gas values yields a value of 185 while the actual selectivity in the mixture is 80. Analysis of these data reveal that competitive sorption effects are responsible for the large depression in CO 2 permeability. Available information indicates that specific interactions between CO 2 and the ester moiety in PMMA are responsible for large increases in the diffusivity of C 2H 4 in PMMA. The increase in C 2H 4 diffusivity causes a two-fold increase in permeability further accentuating the selectivity drop caused by the reduction in CO 2 permeability. This study indicates that specific interactions play an important role in penetrant-induced plasticization.

Gas-induced plasticization and the permselectivity of poly(tetrabromophenolphthalein terephthalate) to a mixture of carbon dioxide and methane

Despite its rigid backbone, poly(tetrabromophenolphtaleine terephtalate)'s permeability at 35°C to either pure carbon dioxide or pure ethane showed a minimum at ∼10 atm when measured as a function of the gas pressure. The normalized diffusion coefficient, D(c)/D(c=0), of ethane increased more than 60 times over a small concentration range (∼3.5 w%), reflecting the effects of «gas-induced plasticization». Moreover, the mixed-gas permeabilities of carbon dioxide were much less than the corresponding pure-gas values at the same partial pressures. There also was not an upturn in the mixed-gas CO 2 permeability when the partial pressure of carbon dioxide was raised up to 15 atm.

Der Entwicklungsstand der Hochtemperatur‐Verbrennung und Rauchgasreinigungstechnik — dargestellt an zwei laufenden Bauvorhaben

AbstractState of development of high‐temperature combustion and flue gas purification — illustrated for two current construction projects. The state of the art in rotary furnace combustion plant is described with the aid of two current construction projects for a chemical plant and for a publicly accessible plant. The concepts of the plant are adapted to the waste material to be disposed of, the energy utilisation system, and disposal of the residual materials. Data for the chemical plant indicate higher concentrations and fluctuations in the flue gas constituents. Flue gas scrubbing is accomplished here by quenching, passage, through two rotary scrubbers, and wet electrofiltration. Scrubber liquid is passed to a company purification plant. In the other case, no waste water may occur. A two‐field electrofilter and a two‐stage milk of lime washer are employed. Washing liquid is passed to a waste water treatment unit with vacuum evaporation. Special process engineering measures are necessary to maintain pure gas values even in cases of pronounced concentration fluctuations. Household and special waste incineration are discussed increasingly from the viewpoint of NOx reduction. Possible developments of SCR processes up to use of activated charcoal final purification stages are considered.

Effects of hydrogen impurities on shock structure and stability in ionizing monatomic gases. Part 1. Argon

At shock Mach numbers Ms ∼ 16 in pure argon with initial pressures p0 ∼ 5 torr and final electron number densities ne ∼ 1017 cm−3, the translational shock front in a 10 x 18 cm hypervelocity shock tube develops sinusoidal instabilities which affect the entire shock structure including the ionization relaxation region, the electron-cascade front and the final quasi-equilibrium state. By adding a small amount of hydrogen (∼ 0·5% of the initial pressure), the entire flow is stabilized. However, the relaxation length for ionization is drastically reduced to about one-third of its pure-gas value. Using the familiar two-step collisional model coupled with radiation-energy loss and the appropriate chemical reactions, it was possible to deduce from dual-wavelength interferometric measurements a precise value for the argon-argon collisional excitation cross-section SAr Ar* = 1·0 x 10−19 cm2/eV with or without the presence of a hydrogen impurity. The reason for the success of hydrogen, and not other gases, in bringing about stabilized shock waves is not clear. It was also found that the electron-cascade front approached the translational-shock front near the shock-tube wall. This effect appears to be independent of the wall material and is not affected by the evolution of adsorbed water vapour from the walls or by water vapour added deliberately to the test gas. The sinusoidal instabilities investigated here may offer some important clues to the abatement of instabilities that lead to detonation and explosions.

Effects of hydrogen impurities on shock structure and stability in ionizing monatomic gases: 2. Krypton

At shock Mach numbers [Formula: see text] in pure krypton, at initial pressures p0 ~ 5 Torr, and final electron number densities ne ~ 1017 cm−3, the translational shock front in a 10 cm × 18 cm hypervelocity shock tube develops sinusoidal instabilities which affect the entire shock structure including the ionization relaxation region, the electron-cascade front and the final quasi-equilibrium state. By adding a small amount of hydrogen (~0.5% of the initial pressure), the entire flow is stabilized. However, the relaxation length for ionization is drastically reduced to about one half of its pure-gas value. Unlike argon the stability appears to diminish with the addition of hydrogen beyond about 0.5%. Using the familiar two-step collisional model coupled with radiation-energy loss and the appropriate chemical reactions, it was possible from dual-wavelength interferometric measurements to deduce a more precise value for the krypton–krypton collision excitation cross-section, S*Kr–Kr = 1.2 × 10−19 cm2/eV, with or without the presence of hydrogen impurities. The reason for the success of hydrogen, and not other gases, in bringing about stabilized Shock waves in argon and krypton is not clear. It was also found that the electron-cascade front approached closely to the translational-shock front with increasing proximity to the shock-tube wall. This effect appears independent of the wall material and is not affected by the evolution of adsorbed water vapour from the walls or by water added deliberately to the test gas. The sinusoidal instabilities investigated here may offer some important clues to the abatement of instabilities that lead to detonations and explosions.