Energy-efficient polymeric gas separation membranes for a sustainable future: A review

AbstractOver the past three decades, polymeric gas separation membranes have become widely used for a variety of industrial gas separations applications. This review presents the fundamental scientific principles underpinning the operation of polymers for gas separations, including the solution-diffusion model and various structure/property relations, describes membrane fabrication technology, describes polymers believed to be used commercially for gas separations, and discusses some challenges associated with membrane materials development. A description of new classes of polymers being considered for gas separations, largely to overcome existing challenges or access applications that are not yet practiced commercially, is also provided. Some classes of polymers discussed in this review that have been the focus of much recent work include thermally rearranged (TR) polymers, polymers of intrinsic microporosity (PIMs), room-temperature ionic liquids (RTILs), perfluoropolymers, and high-performance polyimides

Dependence of physical and mechanical properties on polymer architecture for model polymer networks

Effect of architecture at nanoscale on the macroscopic properties of polymer materials has long been a field of major interest, as evidenced by inhomogeneities in networks, multimodal network topologies, etc. The primary purpose of this research is to establish the architecture-property relationship of polymer networks by studying the physical and mechanical responses of a series of topologically different PTHF networks. Monodispersed allyl-terminated PTHF precursors were synthesized through ¡°living¡± cationic polymerization and functional end-capping. Model networks of various crosslink densities and inhomogeneities levels (unimodal, bimodal and clustered) were prepared by endlinking precursors via thiol-ene reaction. Thermal characteristics, i.e., glass transition, melting point, and heat of fusion, of model PTHF networks were investigated as functions of crosslink density and inhomogeneities, which showed different dependence on these two architectural parameters. Study of freezing point depression (FPD) of solvent confined in swollen networks indicated that the size of solvent microcrystals is comparable to the mesh size formed by intercrosslink chains depending on crosslink density and inhomogeneities. Relationship between crystal size and FPD provided a good reflection of the existing architecture facts in the networks. Mechanical responses of elastic chains to uniaxial strains were studied through SANS. Spatial inhomogeneities in bimodal and clustered networks gave rise to ¡°abnormal butterfly patterns¡±, which became more pronounced as elongation ratio increases. Radii of gyration of chains were analyzed at directions parallel and perpendicular to stretching axis. Dependence of Rg on ¦Ë was compared to three rubber elasticity models and the molecular deformation mechanisms for unimodal, bimodal and clustered networks were explored. The thesis focused its last part on the investigation of evolution of free volume distribution of linear polymer (PE) subjected to uniaxial strain at various temperatures using a combination of MD, hard sphere probe method and Voronoi tessellation. Combined effects of temperature and strain on free volume were studied and mechanism of formation of large and ellipsoidal free volume voids was explored.Ph.D.Committee Chair: Karl I. Jacob; Committee Member: Anselm C. Griffin; Committee Member: C. P. Wong; Committee Member: Rina Tannenbaum; Committee Member: William J. Koros; Committee Member: Yonathan S. Thi

Periodic Solution of a Non-Smooth Double Pendulum with Unilateral Rigid Constrain

In this paper, a double pendulum model is presented with unilateral rigid constraint under harmonic excitation, which leads to be an asymmetric and non-smooth system. By introducing impact recovery matrix, modal analysis, and matrix theory, the analytical expressions of the periodic solutions for unilateral double-collision will be discussed in high-dimensional non-smooth asymmetric system. Firstly, the impact laws are classified in order to detect the existence of periodic solutions of the system. The impact recovery matrix is introduced to transform the impact laws of high-dimensional system into matrix. Furthermore, by use of modal analysis and matrix theory, an invertible transformation is constructed to obtain the parameter conditions for the existence of the impact periodic solution, which simplifies the calculation and can be easily extended to high-dimensional non-smooth system. Hence, the range of physical parameters and the restitution coefficients is calculated theoretically and non-smooth analytic expression of the periodic solution is given, which provides ideas for the study of approximate analytical solutions of high-dimensional non-smooth system. Finally, numerical simulation is carried out to obtain the impact periodic solution of the system with small angle motion

Vibration reduction in beam bridge under moving loads using nonlinear smooth and discontinuous oscillator

The coupled system of smooth and discontinuous absorber and beam bridge under moving loads is constructed in order to detect the effectiveness of smooth and discontinuous absorber. It is worth pointing out that the coupled system contains an irrational restoring force which is a barrier for conventional nonlinear techniques. Hence, the harmonic balance method and Fourier expansion are used to obtain the approximate solutions of the system. The first and the second kind of generalized complete elliptic integrals are introduced. Furthermore, using power flow approach, the performance of smooth and discontinuous absorber in vibration reduction is estimated through the input energy, the dissipated energy, and the damping efficiency. It is interesting that only depending on the value of the smoothness parameter, the efficiency parameter of vibration reduction is optimized. Therefore, smooth and discontinuous absorber can adapt itself to effectively reducing the amplitude of the vibration of the beam bridge, which provides an insight to the understanding of the applications of smooth and discontinuous oscillator in engineering and power flow characteristics in nonlinear system

Surface modification ofZIF-90 with triptycene for enhanced interfacial interaction inmixed-matrixmembranes for gas separation

Zeolite imidazole framework (ZIF-90) nanoparticles were chemically modified by grafting triptycene moieties. The modified nanoparticles were introduced into a triptycene-based polyimide as fillers to generate mixed matrix membranes (MMMs) for gas separation. The incorporation of "hook-like" triptycene moieties in both dispersed and continuous phases led to intimate contact between the two phases and thus defect-free interfacial morphology, due to the supramolecular interlocking and pi-pi stacking interaction between triptycene units presented in both phases. The filler/polymer solution showed shear thickening behavior due to such strong interfacial interaction. The separation performance of the prepared composite membranes was investigated as a function of filler loading and particle surface grafting density. Pure-gas permeation results showed that the gas permeabilities increased expectedly as the filler loading increased, with stable or improved selectivities. The reduced permeability relative to pristine polyimide film is likely due to the pore blockage of ZIF-90 upon grafting triptycene moieties on the particle surface. Reducing the grafting density of triptycene moieties led to improved permeability and selectivity suggesting good tunability of this series of new composite membranes. Overall, modification of nanofiller with hierarchical triptycene moieties offers a fundamentally new avenue for creation of composite membranes with unique properties in gas separations

The Use of Iptycenes in Rational Macromolecular Design for Gas Separation Membrane Applications

Iptycene molecules, featuring three-dimensional [2,2,2]-ring configurations with 120° contortion sites and unique internal free volume (IFV) elements, have recently been identified for their great potential in the design of polymers for gas separation membranes. Some of these novel iptycene-containing polymers have already displayed unprecedented separation performance. This review summarizes the progression of the gas separation membranes, utilizing iptycene structures over the past five years by dividing the polymers into three categories: nonladder polymers, semiladder polymers, and ladder polymers. The focus lies on examining macromolecular design strategies of these novel polymers and consequential effects on chain packing, free volume architecture, and gas transport properties to provide useful guidance on the design of new membrane materials. Finally, we provide some perspectives and future research directions for designing and utilizing iptycene-containing polymers for gas separation membranes

LFVB-BioSLAM: A Bionic SLAM System with a Light-Weight LiDAR Front End and a Bio-Inspired Visual Back End

Simultaneous localization and mapping (SLAM) is one of the crucial techniques applied in autonomous robot navigation. The majority of present popular SLAM algorithms are built within probabilistic optimization frameworks, achieving high accuracy performance at the expense of high power consumption and latency. In contrast to robots, animals are born with the capability to efficiently and robustly navigate in nature, and bionic SLAM algorithms have received increasing attention recently. Current bionic SLAM algorithms, including RatSLAM, with relatively low accuracy and robustness, tend to fail in certain challenging environments. In order to design a bionic SLAM system with a novel framework and relatively high practicality, and to facilitate the development of bionic SLAM research, in this paper we present LFVB-BioSLAM, a bionic SLAM system with a light-weight LiDAR-based front end and a bio-inspired vision-based back end. We adopt a range flow-based LiDAR odometry as the front end of the SLAM system, providing the odometry estimation for the back end, and we propose a biologically-inspired back end processing algorithm based on the monocular RGB camera, performing loop closure detection and path integration. Our method is verified through real-world experiments, and the results show that LFVB-BioSLAM outperforms RatSLAM, a vision-based bionic SLAM algorithm, and RF2O, a laser-based horizontal planar odometry algorithm, in terms of accuracy and robustness

Modeling Gas and Vapor Sorption and Swelling in Triptycene-Based Polybenzoxazole: Evidence for Entropy-Driven Sorption Behavior

The nonequilibrium lattice fluid model was used to describe and sometimes predict nitrogen, methane, carbon dioxide, ethane, and water vapor sorption at multiple temperatures (5-50 degrees C) and pressures (up to 32 atm) in novel triptycene-based polybenzoxazole (TPBO) prepared via a thermal rearrangement (TR) process from an ortho-functional polyimide precursor. The polymer lattice fluid parameters were determined using a few sorption data in the limit of infinite dilution and used to predict the solubility of nonswelling gases at several temperatures with no adjustable parameter. To calculate the solubility of swelling gases, the polymer penetrant interaction parameter was adjusted to experimental sorption data at low pressure at a reference temperature. The second adjustable parameter, that is, the swelling coefficient, was calculated at each temperature using only one experimental sorption datum at high pressure. TPBO exhibits better dimensional stability upon exposure to swelling penetrants relative to previously reported TR polymers. Finally, it was demonstrated that the larger sorption capacity exhibited by TPBO relative to iptycene-free TR polymers has a purely entropic origin

Structure Manipulation in Triptycene-Based Polyimides through Main Chain Geometry Variation and Its Effect on Gas Transport Properties

Two new triptycene-based polyimides, 6FDA-1,4-trip_<i>ortho</i> and 6FDA-2,6-trip_<i>para</i>, were synthesized to investigate the effect of varying polymer backbone geometry on chain packing and gas transport properties. Changing the imide linkage geometry from <i>para</i> to <i>ortho</i> reduced gas permeabilities by ∼48% due to more efficient chain packing of the asymmetric <i>ortho</i> structure, which is demonstrated by decreased <i>d</i>-spacing and fractional free volume. Varying the triptycene orientation from the 1,4- to 2,6-connection also caused a decrease in permeability (e.g., 29% decrease for <i>P</i>_CO2). This is likely the result of reduced chain mobility, as evidenced by increased <i>T</i>_g, and a shift in free volume distribution toward smaller cavities, as supported by smaller <i>d</i>-spacing. Physical aging studies show that the equilibrium specific volume of these isomeric polymers is similar, as evidenced by nearly identical gas transport properties exhibited by all aged samples

High-quality development of ultra-deep large gas fields in China: Challenges, strategies and proposals

Natural gas from ultra-deep reservoirs has been a major contributor for reserves boost, deliverability construction, and profits growth in natural gas industry in China. As a significant strategic domain in the future development of upstream business, the high-quality development of ultra-deep gas resources has great significance for economic benefits enhancement and sustained regional supply assurance. In this paper, based on the appraisal of development characteristics and effectiveness in the developed large ultra-deep gas fields, challenges for high quality development were indicated, which include the difficulties in structure confirm, uncertainties in reserves define and production optimization, risks of aquifer water early breakthrough and high investment of deep wells. Through indoor physical simulation experiments, reservoir characterization, performance evaluation, reservoir simulation and knowledge acquisition from analogous fields at home and abroad, the connotation and requirements for high quality development were discussed, and furthermore, strategies and proposals were thus proposed as follows: to strengthen the pre-development reservoir evaluation to define movable gas reserves and quantify rational production rate so as to avoid facility waste; to optimize both well pattern and well flow rate to achieve uniform depletion and high EUR; to continuously enhance drilling &amp; completion technologies to further reduce drilling and completion circle and cost and targeted reservoir stimulation technologies to enhance movable reserves and single-well productivity and increase the depletion of inferior reserves; and to innovate management modes to establish scientific programs and procedures for the construction, production and operation of ultra-deep gas fields and strictly control the upper limit index of production rate so as to emphasize quality benefits. In conclusion, high-quality development of ultra-deep gas fields, a hard and complex system though, will be possibly achieved only by continuous innovation of exploration and development technologies and management modes