Polyimides and their derivatives for gas separation applications

High performance polymers are of interest for high temperature gas separations, especially for the sequestration of carbon dioxide. A new family of high performance imide polymers (VTEC, RBI Inc.) has been identified as a material class containing the potential building blocks needed for a successful membrane capture material. The VTEC polyimides possess the desired thermal properties (up to 500 °C) and are robust and flexible even after multiple thermal cycles (up to 400 °C). A critical variable when working with the glassy polymers is their moisture content. It has been found that water entrapped within the polymer matrix (either as hydration molecules attached to salts in the polymer, left over solvent, or physisorbed) can also cause the polymer to change dramatically. Additionally presence of molecular water in the polymer’s void volume has been validated through Positron Annihilation Lifetime (PAL) spectroscopy. In this presentation, polymer characterization and gas-separation testing results will be discussed

CO2 Separation Using Thermally Optimized Membranes: A Comprehensive Project Report (2000 - 2007)

This is a complete (Fiscal Years 2000–2006) collection of the Idaho National Laboratory’s (INL) research and development contributions to the project, “CO2 Separation Using Thermally Optimized Membranes.” The INL scientific contribution to the project has varied due to the fluctuations in funding from year to year. The focus of the project was polybenzimidazole (PBI) membranes and developing PBI compounds (both substitution and blends) that provide good film formation and gas separation membranes. The underlying problem with PBI is its poor solubility in common solvents. Typically, PBI is dissolved in “aggressive” solvents, like N,N-dimethylacetamide (DMAc) and N methylpyrrolidone (NMP). The INL FY-03 research was directed toward making soluble N-substituted PBI polymers, where INL was very successful. Many different types of modified PBI polymers were synthesized; however, film formation proved to be a big problem with both unsubstituted and N-substituted PBIs. Therefore, INL researchers directed their attention to using plasticizers or additives to make the membranes more stable and workable. During the course of these studies, other high-performance polymers (like polyamides and polyimides) were found to be better materials, which could be used either by themselves or blends with PBI. These alternative high-performance polymers provided the best pathway forward for soluble high-temperature polymers with good stable film formation properties. At present, the VTEC polyimides (product of RBI, Inc.) are the best film formers that exhibit high-temperature resistance. INL’s gas testing results show VTEC polyimides have very good gas selectivities for both H2/CO2 and CO2/CH4. Overall, these high-performance polymers pointed towards new research areas where INL has gained a greater understanding of polymer film formation and gas separation. These studies are making possible a direct approach to stable polymer-based high-temperature gas separation membranes. This report is separated into several sections due to the complexity of the research and the variation with the development of better high-temperature, gas separation membranes. Several fiscal years are combined because the research and development efforts within those areas crossed fiscal year boundaries

Constraint methods for determining pathways and free energy of activated processes

Activated processes from chemical reactions up to conformational transitions of large biomolecules are hampered by barriers which are overcome only by the input of some free energy of activation. Hence, the characteristic and rate-determining barrier regions are not sufficiently sampled by usual simulation techniques. Constraints on a reaction coordinate r have turned out to be a suitable means to explore difficult pathways without changing potential function, energy or temperature. For a dense sequence of values of r, the corresponding sequence of simulations provides a pathway for the process. As only one coordinate among thousands is fixed during each simulation, the pathway essentially reflects the system's internal dynamics. From mean forces the free energy profile can be calculated to obtain reaction rates and insight in the reaction mechanism. In the last decade, theoretical tools and computing capacity have been developed to a degree where simulations give impressive qualitative insight in the processes at quantitative agreement with experiments. Here, we give an introduction to reaction pathways and coordinates, and develop the theory of free energy as the potential of mean force. We clarify the connection between mean force and constraint force which is the central quantity evaluated, and discuss the mass metric tensor correction. Well-behaved coordinates without tensor correction are considered. We discuss the theoretical background and practical implementation on the example of the reaction coordinate of targeted molecular dynamics simulation. Finally, we compare applications of constraint methods and other techniques developed for the same purpose, and discuss the limits of the approach

The History of Makassan Trepang Fishing and Trade

The Malayan term trepang describes a variety of edible holothurians commonly known as sea cucumbers. Although found in temperate and tropical marine waters all over the world, the centre of species diversity and abundance are the shallow coastal waters of Island Southeast Asia. For at least 300 years, trepang has been a highly priced commodity in the Chinese market. Originally, its fishing and trade was a specialized business, centred on the town of Makassar in South Sulawesi (Indonesia). The rise of trepang fishing in the 17th century added valuable export merchandize to the rich shallow seas surrounding the islands of Southeast Asia. This enabled local communities to become part of large trading networks and greatly supported their economic development. In this article, we follow Makassan trepang fishing and trading from its beginning until the industrialization of the fishery and worldwide depletion of sea cucumbers in the 20th century. Thereby, we identify a number of characteristics which trepang fishing shares with the exploitation of other marine resources, including (1) a strong influence of international markets, (2) the role of patron-client relationships which heavily influence the resource selection, and (3) the roving-bandit-syndrome, where fishermen exploit local stocks of valuable resources until they are depleted, and then move to another area. We suggest that understanding the similarities and differences between historical and recent exploitation of marine resources is an important step towards effective management solutions

Positron Annihilation Spectroscopy of High Performance Polymer Films under CO2 Pressure

Positron annihilation Lifetime and Doppler broadening measurements are reported for six polymer films as a function of carbon dioxide absolute pressure ranging from 0 to 45 psi. Since the polymer films were thin and did not absorb all positrons, corrections were made in the lifetime analysis for the absorption of positrons in the positron source and sample holder using the Monte Carlo transport code MCNP. Different polymers are found to behave differently. Some polymers studied form positronium and some, such as the polyimide structures, do not. For those samples that form positronium an interpretation in terms of free volume is possible; for those that don’t form positronium, further work is needed to determine how best to describe the behavior in terms of the bulk positron annihilation parameters. Some polymers exhibit changes in positron lifetime and intensity under CO2 pressure which may be described by the Henry or Langmuir sorption models, while the positron response of other polymers is rather insensitive to the CO2 pressure. The results demonstrate the usefulness of positron annihilation spectroscopy in investigating the sorption of CO2 into various polymers at pressures up to about 3 atm

Correlations of Polyimides and Blended Polyimides for High Temperature Gas Separations

High performance polymers are of interest for high temperature gas separations, especially for the sequestration of carbon dioxide. A new family of high performance imide polymers has been identified as a successful membrane capture material. VTEC polyimides possess desired thermal properties (up to 500 °C) along with being robust and flexible even after multiple thermal cycles (up to 400 °C). Polyimides (PI) are excellent materials for high selectivity for smaller kinetic diameter gases such as H2 and CO2; however, they have low fluxes. We blended small amounts of different polymers with VTEC polyimide, which changes the fluxes. Another critical problem when working with glassy polymers is their moisture content. It has been found that water entrapped within the polymer matrix (left over from the solvent, or physisorbed) can also cause the polymer to change dramatically. Additionally presence of molecular water in the polymer’s void volume has been validated through Positron Annihilation Lifetime (PAL) spectroscopy. In this presentation, polymer characterization and gas-separation testing results will be discussed

Operational space weather service for GNSS precise positioning

The ionospheric plasma can significantly influence the propagation of radio waves and the ionospheric disturbances are capable of causing range errors, rapid phase and amplitude fluctuations (radio scintillations) of satellite signals that may lead to degradation of the system performance, its accuracy and reliability. The cause of such disturbances should be sought in the processes originating in the Sun. Numerous studies on these phenomena have been already carried out at a broad international level, in order to measure/estimate these space weather induced effects, to forecast them, and to understand and mitigate their impact on present-day technological systems. <P style="line-height: 20px;"> SWIPPA (Space Weather Impact on Precise Positioning Applications) is a pilot project jointly supported by the German Aerospace Centre (DLR) and the European Space Agency (ESA). The project aims at establishing, operating, and evaluating a specific space-weather monitoring service that can possibly lead to improving current positioning applications based on Global Navigation Satellite Systems (GNSS). This space weather service provides GNSS users with essential expert information delivered in the form of several products - maps of TEC values, TEC spatial and temporal gradients, alerts for ongoing/oncoming ionosphere disturbances, etc

On developing a new ionospheric perturbation index for space weather operations

To better and faster quantify the strength and impact of the ionospheric perturbations, we propose a new index for operational use in communication/navigation systems. Presented here is the analysis of selected events of strong disturbances observed with techniques based on Global Navigation Satellite Systems (GNSS) in order to show some insufficiencies when using existing geomagnetic indices. We found that the GNSS Total Electron Content (TEC) measurements and/or derivatives are outstanding candidates for defining a new ionospheric perturbation index, more specialised and therefore more effective. It is believed that the standardization and usage of the proposed perturbation index, together with other indices of similar nature, can prove helpful in reducing the space weather impact on the GNSS-based navigation and positioning