Master-Arbeit Univ. St. Gallen, 2007.

Thesis (doctoral)--Universität St. Gallen, 2009.

Zugl.: Sankt Gallen, Univ., Diss.

Polymers with intrinsic microporosity (PIMs) showed the potential to provide highly permeable and highly selective membranes for gas separation applications with the ability to fine-tune their properties for better performance. The concept of microporosity was extended to the polyimides by using kinked, contorted and stable structures to obtain high gas performance combined with excellent solution-processability, high thermal stability, and a unique platform for a wide range of possible modifications and tunability. Thus, studying the structure-property relationships is a critical key to develop advanced materials that can replace the commercially available membranes like cellulose acetate and Matrimid. Importantly, in the microporous polyimides (PIM-PIs) system, varying the type of the side chains appended to the diamines or dianhydrides impacts polymeric membrane properties, and in turn, gas separation performance. In this dissertation, we have examined the effect of ring substitutes, incorporated into novel polyimides backbones, on polymer properties and gas separation performance. The choice of side group can induce subtle changes in material properties and molecular interactions between the polymeric chains and affect the pore-size distribution, chain packing and yielding distinct combination between gas permeability and permselectivity. We have shown that the effect of tertiary amine groups, in polyimide structures, on the CO2 solubility is marginal but it can control the chain packing. However, introducing bromine groups on the polymer backbone can boost the O2 permeability and O2/N2 selectivity and perform better than the commercially available membranes. BCBr4-SBIDA demonstrated the same O2/N2 selectivity relative to cellulose acetate but approximately 10-fold higher gas permeability. Combining high selectivity with good permeability was achieved by a newly designed carboxyl-functionalized homopolymer (6FDA-TrMPD) with CO2 permeability of 144 barrer and CO2/CH4 selectivity of 45. The new W-shaped CANAL diamines, prepared by one-step synthesis, were used as microporosity generators in polyimides and revealed promising gas transport performance with the same selectivity relative to cellulose acetate by 23-fold higher permeability (CANAL-PI-3-MeNH2). Therefore, developing advanced polymers for membrane-based gas separation can be obtained by an ideal combination between kinked monomers, side chains, and stable materials.

ABSTRACT Heaves is triggered by exposure to dust and its components, such as endotoxin, and is characterized by clinical signs such as coughing, decreased exercise tolerance, difficulty breathing and abnormal lung sounds which are due to bronchoconstriction and accumulation of neutrophils in the airways. Pulmonary intravascular macrophages (PIMs) are believed to increase horses sensitivity to endotoxemia-induced lung inflammation. The first objective of this study was to investigate a hitherto unknown role of PIMs in equine heaves. I used mouldy hay (MH) to induce heaves and gadolinium chloride (GC) to deplete PIMs in order to compare responses between non-treated and GC-treated heaves horses. A modified randomized crossover study (2X2 factorial) was conducted in which mares (N=9) were exposed to 4 different treatments: alfalfa cubes (Cb), alfalfa cubes + GC (Cb-GC), mouldy hay (MH) and MH + GC (MH-GC). Each treatment was followed by broncholaveolar lavage (BAL). MH was fed for 7 days to induce heaves followed by Cb for 21 days to achieve remission, whereas the treatments in which heaves was not induced (Cb; Cb-GC), the cubes were fed prior to the BAL and for 14 days after the BAL to allow recovery from the BAL procedure. BAL fluids were processed to investigate total cell, neutrophil and alveolar macrophage concentrations. In addition, TNFá protein levels as well as TNFá, IL-8, and TLR4 mRNA expression in BAL cells were assessed in order to infer on their activation state.<p> Data showed higher concentration of dust (3X), endotoxin (20X), and endotoxin per milligram of dust (7X) in MH compared to the Cb environment. Clinical scores and neutrophil concentrations in BAL were higher when mares received MH compared to MH and GC (MH-GC). Real time reverse transcriptase PCR revealed a significant lower expression of IL-8 and TLR4 mRNA in BAL cells from MH-GC mares compared to MH. TNFá mRNA expression as well as protein concentration were not affected by the different treatments. In vitro secondary LPS challenge significantly increased IL-8 mRNA expression in cells from MH treatment compared to without LPS, but not in the MH-GC treatment. TLR4 expression was not affected by the secondary challenge. Although secondary LPS challenge increased expression of TNFá mRNA and protein, the differences among treatment groups were not meaningful. In conclusion, PIM depletion attenuates clinical scores, migration of inflammatory cells into the alveolar space and expression of pro-inflammatory molecules in BAL cells of heaves horses.<p> The observations on the role of PIMs in heaves in horses prompted me to examine the occurrence of PIMs in human lungs. I found a trend for higher numbers of septal macrophages in autopsied lungs from human patients who died of non-pulmonary pathologies compared to those having either COPD or asthma. If these septal macrophages indeed represent the PIMs, this finding is contrary to existing belief that humans, unlike horses, do not have PIMs.

ABSTRACT Heaves is triggered by exposure to dust and its components, such as endotoxin, and is characterized by clinical signs such as coughing, decreased exercise tolerance, difficulty breathing and abnormal lung sounds which are due to bronchoconstriction and accumulation of neutrophils in the airways. Pulmonary intravascular macrophages (PIMs) are believed to increase horses sensitivity to endotoxemia-induced lung inflammation. The first objective of this study was to investigate a hitherto unknown role of PIMs in equine heaves. I used mouldy hay (MH) to induce heaves and gadolinium chloride (GC) to deplete PIMs in order to compare responses between non-treated and GC-treated heaves horses. A modified randomized crossover study (2X2 factorial) was conducted in which mares (N=9) were exposed to 4 different treatments: alfalfa cubes (Cb), alfalfa cubes + GC (Cb-GC), mouldy hay (MH) and MH + GC (MH-GC). Each treatment was followed by broncholaveolar lavage (BAL). MH was fed for 7 days to induce heaves followed by Cb for 21 days to achieve remission, whereas the treatments in which heaves was not induced (Cb; Cb-GC), the cubes were fed prior to the BAL and for 14 days after the BAL to allow recovery from the BAL procedure. BAL fluids were processed to investigate total cell, neutrophil and alveolar macrophage concentrations. In addition, TNFá protein levels as well as TNFá, IL-8, and TLR4 mRNA expression in BAL cells were assessed in order to infer on their activation state.<p> Data showed higher concentration of dust (3X), endotoxin (20X), and endotoxin per milligram of dust (7X) in MH compared to the Cb environment. Clinical scores and neutrophil concentrations in BAL were higher when mares received MH compared to MH and GC (MH-GC). Real time reverse transcriptase PCR revealed a significant lower expression of IL-8 and TLR4 mRNA in BAL cells from MH-GC mares compared to MH. TNFá mRNA expression as well as protein concentration were not affected by the different treatments. In vitro secondary LPS challenge significantly increased IL-8 mRNA expression in cells from MH treatment compared to without LPS, but not in the MH-GC treatment. TLR4 expression was not affected by the secondary challenge. Although secondary LPS challenge increased expression of TNFá mRNA and protein, the differences among treatment groups were not meaningful. In conclusion, PIM depletion attenuates clinical scores, migration of inflammatory cells into the alveolar space and expression of pro-inflammatory molecules in BAL cells of heaves horses.<p> The observations on the role of PIMs in heaves in horses prompted me to examine the occurrence of PIMs in human lungs. I found a trend for higher numbers of septal macrophages in autopsied lungs from human patients who died of non-pulmonary pathologies compared to those having either COPD or asthma. If these septal macrophages indeed represent the PIMs, this finding is contrary to existing belief that humans, unlike horses, do not have PIMs.

This Thesis investigates computationally the behaviour of two novel microporous materials,organic molecules of intrinsic microporosity (OMIMs) and polymers of intrinsic microporosity(PIMs). OMIMs and PIMs are organic amorphous materials, which achieve microporosityby packing inefficiently. The design of amorphous materials is challenging because their self-assembly process is not known. Predictive molecular simulations can help in recognising thefeatures that affect the properties of these materials, and guiding in the design of new structures with desired performances. OMIMs are highly concave shaped molecules, consisting of a core and a series of termini, which provide the geometry and the general chemical environment of these structures, respectively. PIMs are polymers consisting of fundamental units such as stiff segments and contortionsites, which form either linear or network like porous structures. While chronologically olderthan OMIMs, they share with them a common design philosophy. This Thesis is presented in alternative format, and the results, consisting of five journal articles,can be divided into three main parts. The first part focuses on recognising a reliable method to generate representative models ofOMIMs. Different computational protocols and molecular mechanics descriptions were investigated; the development of the utilised simulation protocol was based on comparison of several simulation methods and force fields to experimental wide angle X-ray scattering (WAXS) patterns. Our work suggests that OMIMs can be described successfully by both PCFF and UFF; the final packed material can be generated using a 21-step compression-decompression molecular dynamics protocol, previously developed to generate virtual model of PIMs. The examination of the simulated structures has provided a deeper understanding of the features that affect the packing behaviour of this class of materials, suggesting that OMIMs have a greater microporosity when the molecules are the most shape-persistent, which required rigid structures and bulky end groups. The adsorption behaviour described by different generic force fields (Dreiding, OPLS and UFF) was also investigated to guide on the selection of the solid-fluid interactions when modelling OMIMs, for future comparison with experimental data. Our results suggest that very strong interactions between argon adsorbate and OMIM-based framework are described by UFF, while the weakest adsorbent is obtained using OPLS force field. The second part of the research focuses on assessing the effect that different termini’s chemistry and bulkiness have over the packing behaviour, adsorption properties and solubility of the OMIMs. The microporous frameworks generated by two selected families of cruciform OMIMs (benzene and naphthalene- based) were investigated with respect to their packing behaviour, porosity and adsorption properties. Our analysis suggests that the final density of the material, as well as the surface area and pore volume, depend on the ending group’s bulkiness. Bulkier molecules lead to materials with lower densities, but it was found that the adsorption behaviour is not just related to the material’s density, but also to the pore size and shape, which are determined by the way the molecules pack. The relationship between adsorption capacity and physical properties was analysed and the role of surface area, free volume and enthalpic interaction was used to identify different adsorption regimes. It was found that the uptake of argon at low pressure is proportional to the strength of the adsorbent-adsorbate interaction while at moderate pressure it is dependent on the free volume and surface area. The dissolution of three cruciform OMIMs was investigated in dichloromethane, ethyl acetateand toluene. Direct interface molecular dynamics simulations showed that the solubility process consists of two steps; the diffusion of the solvent in the OMIM-rich phase, and the departure of the OMIMs in the solvent bulk. We proposed a simple model to represent this mechanism. Furthermore, results from infinite dilution simulations show that the solvent-OMIMs interactions can be related to the chemistry of the OMIMs and to the solvent’s properties. We found that, in general, increasing the length of the OMIM’s arm affects negatively the solubility of the material, while adding bulky alkyl groups favours the interaction with the solvent molecules. The third part concentrates on the characterisation of PIMs and their application as CO2 adsorbent. Properties of four polymers of intrinsic microporosity containing Tröger’s base units were assessed for CO2 capture experimentally and computationally. Structural properties included average pore size, pore size distribution, surface area, and accessible pore volume, whereas thermodynamic properties focused on density, CO2 sorption isotherms, and enthalpies of adsorption. It was found that the shape of the contortion site plays a more important role than the polymer density when assessing the capacity of the material, and that the presence of a Tröger base unit only slightly affects the amount adsorbed at low pressures, but it does not have any significant influence on the enthalpy of adsorption fingerprint. A comparison of the materials studied with those reported in the literature allowed us to propose a set of guidelines for the design of polymers for CO2 capture applications.

Ethylene is the most important organic molecule with regard to production volume. Therefore, the energy spent in its separation processes, based on old-fashioned distillation, takes approx. 33% of total operating costs. Membranes do not require significant thermal energy input; therefore, membrane processes may separate hydrocarbons cheaply and just as reliably as distillation columns. Olefin/paraffin separations are the future targets of commercial membrane applications, provided high-performing materials become available at reasonable prices. This thesis addresses the development of advanced carbon molecular sieve (CMS) membranes derived from intrinsically microporous polymers (PIMs). Chronologically, Chapter 4 of this work reports the evaluation of PIMs as potential ethylene/ethane selective materials, while Chapters 5 to 7 propose PIMs as carbonization precursors. The gravimetric sorption studies conducted in this work regarding both the polymers and their heated-derivatives revealed that this separation is entirely controlled by diffusion differences. The pristine polymers examined in this study presented BET surface areas from 80 to 720 m2g-1. Furthermore, the effect of using bromine-substituted PIM-polyimides elucidated a boost in ethylene permeability, but with a significant drop in selectivity. The hydroxyl functionalization of PIM-polyimides was confirmed as a valuable strategy to increase selectivity. Functionalized PMDA-HSBF is the most selective polyimide of intrinsic microporosity known to date (= 5.1) due to its hydrogen-bonded matrix. In spite of their novelty, pristine PIMs based on the spirobisindane moiety were not tight enough to distinguish between the 0.2 Å difference in diameter of the ethylene/ethane molecules. Therefore, they did not surpass the upper bound limit performance of known polymeric membranes. Nevertheless, the carbons derived from these polymers were excellent ethylene/ethane sieves by virtue of their narrow and tight pore distribution around the 3.6- 4.4 Å range. PIM-based carbons were typically 10 times more permeable than their corresponding low free-volume analogues treated after the weight-loss of the sample reached a plateau. Furthermore, carbons derived from PIM-6FDA-OH and PIM-6FDA at 800 ºC were as ethylene separating efficient as their lower free-volume counterparts. The pore sintering mechanism that takes place above 600 ºC during the carbonization procedure of these films reduced the entropic freedom of the molecules, as was observed from separation factors of up to 25 under pure-gas conditions and 2 bar of pressure— The best performing CMS membranes reported to date for ethylene/ethane separation. The mixed-gas separation of 1:1 binary ethylene/ethane mixtures revealed a significant decrease of the pure-gas measurements due to a carbon matrix dilation effect. This localized ultramicroporous dilation caused the ethane permeation rate to increase monotonically as the pressure rose to realistic operating values. Nevertheless, the CMS obtained from PIM-6FDA and PIM-6FDA-OH surpassed any diffusion-controlled polymer or carbon that has been reported to date.

The entire world including Saudi Arabia is dependent on natural gas to provide new energy supplies for the future. Conventional ways for gas separation are expensive, and, hence, it is very important to reduce the cost and lower the energy consumption. Membrane technology is a relatively new separation process for natural gas purification with large growth potential, specifically for off-shore applications. The economics of any membrane separation process depend primarily on the intrinsic gas permeation properties of the membrane materials. All current commercial membranes for natural gas separation are made from polymers, which have several drawbacks, including low permeability, moderate selectivity, and poor stability in acid gas and hydrocarbon environments. The recent development of polymeric materials called “polymers of intrinsic microporosity” (PIMs) provide a new class of high-performance membrane materials that are anticipated to be used in natural gas separation processes including, but not limited to, acid gas removal and separation of hydrocarbons from methane. PIM-7 is an excellent example of a material from the PIMs series for gas separation. It was selected for this work since it has not been extensively tested for its gas permeation properties to date. Specifically, sorption and mixed-gas permeation data were not available for PIM-7 prior to this work. Sorption isotherms of N2, O2, CH4, CO2, C2H6, C3H8 and n-C4H10 were determined over a range of pressures at 35 oC for PIM-7 using a custom-designed dual-volume pressure decay system. Condensable hydrocarbon gases, such as C3H8 and n-C4H10, show significantly higher solubility than the other less condensable gas of the test series due to their high affinity to the polymer matrix. Dual-mode sorption model parameters were determined from the sorption isotherms. Henry’s law solubility, Langmuir capacity constant and the affinity constant increased with gas condensability. Permeability coefficients of He, H2, N2, O2, CH4, CO2, C2H6, C3H8 and n-C4H10 were measured at 35 oC and 2 atm feed pressure using a home-made constant-volume/variable pressure pure-gas permeation system. Hydrocarbon-induced plasticization of PIM-7 was confirmed by measuring the permeability coefficients of C3H8 and n-C4H10 as function of pressure at 35 oC. Diffusion coefficients were calculated from the permeability and solubility data at 2 atm for all penetrants tested and as function of pressure for C3H8 and n-C4H10; the values for C3 and C4 increased significantly with pressure because of plasticization. Physical aging was studied by measuring the permeability coefficients of a number of gases in fresh and aged films. Mixed-gas permeation tests were performed for a feed mixture of 2 vol% n-butane and 98 vol% methane. Based on BET surface area measurements using N2 as a probe molecule, PIM-7 is a microporous polymer (S = 690 m2/g) and it was expected to exhibit selectivity for n-butane over methane, as previously observed for other microporous polymers, such as PIM-1 and PTMSP. Surprisingly, PIM-7 is more permeable to methane than n-butane and exhibits a mixed-gas methane/n-butane selectivity of up to 2.3. This result indicates that the micropore size in PIM-7 is smaller than that in other PIMs materials. Consequently, PIM-7 is not a suitable candidate membrane material for separation of higher hydrocarbons from methane.

Gas separation membranes are proving to be a sustainable method to mitigate climate change given the rising energy demand. Polymers of intrinsic microporosity (PIMs) have emerged as a novel material class for such application. Physical aging is a major concern for the growth and commercialization of these glassy polymers. Several factors play an important role in determining the effects of physical aging for a PIM film; one important parameter is its thickness. Gas transport properties of PIM-Trip-TB films of thicknesses between 20-150 µm were monitored over 150 days for physical aging and its dependence on film thickness. Over this period, thicker films had generally higher permeability, and thinner films aged faster. Although fresh films showed higher selectivity during the initial tests, no correlation was found between film thickness and selectivity after aging. In addition, physical aging was more severe and independent of film thickness for larger-sized gases. Film storing environment affected the physical aging of multiply tested samples significantly, whereas films which were not tested periodically showed very minimal aging. A more systematic approach is required to fully analyze and comprehend factors yielding this phenomenon.