Atsushi Morisato

Nanostructured poly(4-methyl-2-pentyne)/silica hybrid membranes for gas separation☆

The separation of hydrocarbons from permanent gases is of considerable importance in the chemical industry. Poly(1-trimethylsilyl-1-propyne) [PTMSP] is extremely permeable to hydrocarbons and has high hydrocarbon/ permanent gas selectivity. However, the poor chemical resistance of this material limits its use as a membrane for industrial applications. To overcome this problem, we studied an alternative acetylene-based polymer, poly(4-methyl-2-pentyne) [PMP], which exhibits much better chemical resistance than PTMSP. Several types of non-porous, nano-sized, fumed silica fillers were incorporated in PMP to manipulate the molecular polymer chain packing. The pure-and mixed-gas permeation properties of the PMP/silica hybrid membranes were studied. The gas permeability and the hydrocarbon/permanent-gas selectivity increased simultaneously with increasing filler content. The n-butane/ methane selectivity was 13 for pure PMP, but increased to 26 for 45 wt% silica-filled PMP. In addition, the n-butane permeability also increased 3–4 fold. Therefore, the silica-filled hybrid PMP membrane showed completely opposite gas permeation behavior to that of conventional polymers filled with non-porous inorganic nanoparticles.

Hydrocarbon/hydrogen mixed gas permeation in poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and PTMSP/PPP blends

The gas permeation properties of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and blends of PTMSP and PPP have been determined with hydrocarbon/hydrogen mixtures. For a glassy polymer, PTMSP has unusual gas permeation properties which result from its very high free volume. Transport in PPP is similar to that observed in conventional, low-free-volume glassy polymers. In experiments with n-butane/hydrogen gas mixtures, PTMSP and PTMSP/PPP blend membranes were more permeable to n-butane than to hydrogen. PPP, on the other hand, was more permeable to hydrogen than to n-butane. As the PTMSP composition in the blend increased from 0 to 100%, n-butane permeability increased by a factor of 2600, and n-butane/hydrogen selectivity increased from 0.4 to 24. Thus, both hydrocarbon permeability and hydrocarbon/hydrogen selectivity increase with the PTMSP content in the blend. The selectivities measured with gas mixtures were markedly higher than selectivities calculated from the corresponding ratio of pure gas permeabilities. The difference between mixed gas and pure gas selectivity becomes more pronounced as the PTMSP content in the blend increases. The mixed gas selectivities are higher than pure gas selectivities because the hydrogen permeability in the mixture is much lower than the pure hydrogen permeability. For example, the hydrogen permeability in PTMSP decreased by a factor of 20 as the relative propane pressure (p/psat) in propane/hydrogen mixtures increased from 0 to 0.8. This marked reduction in permanent gas permeability in the presence of a more condensable hydrocarbon component is reminiscent of blocking of permanent gas transport in microporous materials by preferential sorption of the condensable component in the pores. The permeability of PTMSP to a five-component hydrocarbon/hydrogen mixture, similar to that found in refinery waste gas, was determined and compared with published permeation results for a 6-A microporous carbon membrane. PTMSP exhibited lower selectivities than those of the carbon membrane, but permeability coefficients in PTMSP were nearly three orders of magnitude higher.

Gas separation properties of aromatic polyamides containing hexafluoroisopropylidene groups

Abstract The synthesis and gas transport properties of aromatic polyisophthalamides (PIPAs), based on isophthaloyl chloride derivatives bearing pendent groups and hexafluoroisopropylidene (6F) linkages in the main chain, are reported and compared with properties of a similar series of PIPAs containing sulfonyl (SO2) rather than 6F in the main chain. All of those polymers exhibit high glass transitions temperatures. The polymers containing 6F groups were markedly more permeable and somewhat less selective than their sulfonyl analogs. Polymers containing a t-butyl pendent group at the 5 position of the isophthaloyl linkage were much more permeable than those bearing only a hydrogen atom at this position, although a strong decrease in permselectivity accompanied the large increase in permeability. CO2/CH4 solubility selectivity values of the 6F-containing polymers were similar to values reported for other polymetric and non-polymeric organic materials with similar concentrations of polar carbonyl linkages. In contrast, the CO2/CH4 solubility selectivity in SO2-containing variants of these polymers was substantially lower than expected based on total polar group concentration. The low CO2/CH4 solubility selectivity is believed to be related to the extremely efficient chain packing in the SO2-containing polymers, which may lead to strong amide-amide linkage interaction, thereby inhibiting carbonyl groups in the amide linkage from interactions with CO2 molecules to increase CO2/CH4 solubility selectivity.

Long‐term permeation properties of poly(1‐trimethylsilyl‐1‐propyne) membranes in hydrocarbon—Vapor environment

Poly(1-trimethylsilyl-1-propyne) (PTMSP), a high free-volume glassy di-substituted polyacetylene, has the highest gas permeabilities of all known polymers. The high gas permeabilities in PTMSP result from its very high excess free volume and connectivity of free volume elements. Permeability coefficients of permanent gases in PTMSP decrease dramatically over time due to loss of excess free volume. The effects of aging on gas permeability and selectivity of PTMSP membranes continuously exposed to a 2 mol % n-butane/98 mol % hydrogen mixture over a period of 47 days are reported. The permeation properties of PTMSP membranes are quite stable when the polymer is continuously exposed to a gas mixture containing a highly sorbing organic vapor such af n-butane. The n-butane/hydrogen selectivity was essentially constant for the 47-day test period at a value of 29, or 88% of the initial value of the as-cast film of 33. Condensable gases such as n-butane may serve as a “filler” in the nonequilibrium free volume of the polymer, thereby preserving the high level of excess free volume.

Transport properties of PA12-PTMO/AgBF4 solid polymer electrolyte membranes for olefin/paraffin separation

Abstract A rubbery nylon-12/tetramethylene oxide block copolymer (PA12-PTMO) was used as a polymeric matrix material for silver tetrafluoroborate (AgBF 4 ) based solid polymer electrolyte membranes. Ethane sorption uptake of PA12-PTMO/AgBF 4 increased linearly with increasing feed pressure. Moreover, the ethane sorption capacity decreased by increasing the AgBF 4 concentration in the polymer electrolyte. Ethylene sorption of pure PA12-PTMO also followed Henrys law. On the other hand, the ethylene sorption isotherms of PA12-PTMO/AgBF 4 showed a completely different behavior. As the silver concentration increased in the polymer electrolyte membranes, the sorption isotherms showed a dual-mode sorption behavior. The initial sorption enhancement provides clear evidence of complex formation between ethylene and silver ions. Mixed-gas permeation studies performed with dry ethylene/ethane mixture demonstrated that PA12-PTMO/AgBF 4 composite membranes exhibited good stability. In a 14-day test period, the ethylene/ethane selectivity of this membrane decreased from 25–20. This performance is far better than that of any polymeric membrane for ethylene/ethane separation. The decline in membrane performance occurred only during the first 3 days of operation; thereafter, the membrane showed excellent long-term stability.

Pure hydrocarbon sorption properties of poly(1-trimethylsilyl-1-propyne) (PTMSP), poly(1-phenyl-1-propyne) (PPP), and PTMSP/PPP blends

Propane and n-butane sorption in blends of poly(1-trimethylsilyl-1-propyne) (PTMSP) and poly(1-phenyl-1-propyne) (PPP) have been determined. Solubilities of propane and n-butane increased as the PTMSP content in the blends increased. This result is consistent with the higher free volume of PTMSP-rich blends and the better thermodynamic compatibility between PTMSP and these hydrocarbons. Propane and n-butane sorption isotherms were well described by the dual-mode model for sorption in glassy polymers. PTMSP/PPP blends are strongly phase-separated, heterogeneous materials. A noninteracting domain model developed for sorption in phase-separated glassy polymer blends suggests that sorption in the Henrys law regions (i.e., the equilibrium, dense phase of the blends) is consistent with the model. However, Langmuir capacity parameters in the blends are lower than predicted from the domain model, suggesting that the amount of nonequilibrium excess free volume associated with the Langmuir sites depends on blend composition.