The gas transport and separation properties of polymers have been successfully exploited in commercial ventures. Industrial applications employing membrane processes range from production of pure gases to barrier coatings for protection against environmental elements. Membrane separations are simple, energy efficient processes, which can be economically competitive with traditional separation technologies. Membrane separation and permeation characteristics for a particular mixed gas system is typically calculated from single-component transport parameters, namely, diffusion coefficients and solubility constants. In certain gas systems involving gaseous or vapor mixtures, where mass transport is affected by coupling effects or competition between penetrants for unrelaxed free volume, such calculations can lead to erroneous estimates of the membrane separation efficiency. Attempts to study the true transport phenomena effective during mixed gas permeation through membranes have been restricted due to experimental limitations. Also, the absence of rigorous theoretical models hinders the complete understanding of the transport phenomena. The current research involved design and development of an experimental set-up for observing mixed gas permeation through non-porous membranes with real time resolution. The technique employs a gas chromatograph as the selective detector for monitoring the variation in gas concentration, as the gases permeate through the membrane. The same set-up can also be used for conducting single gas permeation experiments. The novelty in the experimental set-up is the In-line sampling interface, used for injection of permeate gases in the GC without introducing any leaks in the permeate volume. Also, a novel data cropping technique is used to elucidate the transport properties of gases through membranes under mixed gas permeation conditions. Mixed gas feed concentration studies performed on a rubbery polymer (PDMS: poly dimethyl siloxane) showed no coupling effects. However, with a glassy polymer (NEW TPI: thermoplastic polyimide), the synergistic effects of gases is observed to play a major role in altering the gas transport and separation properties of the membrane. / Ph. D.

Natural gas is among the most dominant resources to provide energy supplies and Saudi Arabia ranks among the top 5 producers worldwide. However, prior to use of methane, natural gas has to be treated to remove other feed gas components, such as H2O, CO2, H2S, N2 and C2+ hydrocarbons. Most NG fields in KSA contain about 10 mol% carbon dioxide that has to be reduced to less than 2 mol% for pipeline delivery. The conventional unit operations for natural gas separations, that is, molecular sieves, amine absorption, cryogenic distillation, and turbo expansion exhibit some disadvantages in terms of economics, operational flexibility or system footprint. One of the most attractive alternative is membrane technology in either standalone- or hybrid system configuration. Currently, the only two membrane materials used in industrial natural gas applications are cellulose acetate and polyimide, which have moderate permeability and fairly low selectivity when tested under realistic industrial conditions. The goal for future research is to develop unique polymeric membranes, which can at least partially replace conventional gas processing in future natural gas projects. This will support global economics and specifically the economy of Saudi Arabia. Newly developed polymeric materials must meet certain criteria to be used on a commercial scale. These criteria include: (i) high permeability and selectivity, (ii) processability into thin films, (iii) mechanical and thermal stability, and (iv) chemical stability against feed gas components. This project focused on the removal of carbon dioxide from natural gas by developing and characterizing functionalized aromatic polyimide membrane materials that exhibit very high selectivity under aggressive mixed-gas conditions. 6FDA-DAR demonstrated a mixed-gas CO2/CH4 selectivity of 78 at a CO2 partial pressure of 10 bar with no pronounced indication of plasticization. Combining hydroxyl- and carboxyl groups in a miscible polyimide blend led to mixed-gas CO2/CH4 selectivity of 100 with no aging and no plasticization effects. This burgeoning membrane material has very high potential in large-scale natural gas separations with the best overall performance of any type developed to date.

Efficient propylene and propane separation is a major challenge in the modern chemical industry. With current separation methods being highly energy-intensive, there is a pressing need to find alternative green technology. Membrane separation emerged as a promising candidate for propylene and propane separation. Their small footprint, low cost, reliability, and environmental friendliness give membrane separation systems a competitive edge in the race towards sustainable development. The continuous advancements in material science created avenues for new membrane materials such as carbon molecular sieve (CMS) membranes which exhibit exceptional gas separation performances for challenging applications due to their strong size-sieving capabilities. In this work, a carbon molecular sieve (CMS) membrane derived from a polymer of intrinsic microporosity (TPE-PIM) has been investigated for propylene/propane separation made by pyrolysis at 400, 450, 500, 550, 600, 650, and 700 ºC. TPE-PIM-derived CMS films showed excellent pure and mixed-gas permeability and selectivity, exceeding the upper bound limits for propylene and propane. Observed in this work was the presence of an optimal pyrolysis temperature at 600 ºC, where the film showed the best performance with a permeability of 41.6 Barrer and a selectivity of 197 based on pure-gas measurements but dropping to 34 Barrer and selectivity of 33 under equimolar mixed-gas conditions. Such performance could be attributed to the unique internal structural changes that occurred during the pyrolysis. In addition, propane permeability though the CMS films was slow and required long times to reach steady-state values. Such slow kinetics illustrates the molecular sieving capabilities of CMS membranes for bigger and more condensable gases. Several characterization techniques have been performed on the films to confirm CMS formation and showcase deeper molecular structure insights. X-ray diffraction of all TPE-PIM films showed a broad spectrum at each peak due to the material’s amorphous nature. Diffraction patterns also revealed a gradual peak shift for the (002) plane towards smaller values closer to that of pure graphite. Raman spectra showed the characteristic D and G peaks for carbon films prepared at 500 ºC and above. FTIR analysis was also performed to investigate the potential formation of triazine crosslinks in the thermally treated samples, but no conclusive results were obtained.

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.

The goal of this project was to understand and model the performance of hybrid inorganic-organic membranes under realistic operating conditions for hydrocarbon gas/vapor separation, using butane isomers as the model vapors and a hybrid membrane of 6FDA-DAM-5A as an advanced separation system. To achieve the set goal, three objectives were laid out. The first objective was to determine the factors affecting separation performance in dense neat polymer. One main concern was plasticization. High temperature annealing has been reported as an effect means of suppressing plasticization. A study on the effect of annealing temperature was performed by analyzing data acquired via sorption and permeation measurements. Based on the findings from this study, a suitable annealing temperature was determined. Another factor studied was the effect of operating temperature. In deciding a suitable operating temperature, factors such as its possible effect on plasticization as well as reducing heating/cooling cost in industrial application were considered. Based on the knowledge that industrial applications of this membrane would involve mixture separation, the second objective was to understand and model the complexity of a mixed gas system. This was investigated via permeation measurements using three feed compositions. An interesting transport behavior was observed in the mixed gas system, which to the best of our knowledge, has not been observed in other mixed gas systems involving smaller penetrants. This mixed gas transport behavior presented a challenge in predictability using well-established transport models. Two hypotheses were made to explain the observed transport behavior, which led to the development of a new model termed the HHF model and the introduction of a fitting parameter termed the CAUFFV fit. Both the HHF model and CAUFFV fit showed better agreement with experimental data than the well-established mixed gas transport model. The final objective was to explore the use of mixed matrix membranes as a means of improving the separation performance of this system. A major challenge with the fabrication of good mixed matrix membranes was the adhesion of the zeolite particle with the polymer. This was addressed via sieve surface modification through a Grignard treatment process. Although a Grignard treatment procedure existed, there was a challenge of reproducibility of the treatment. This challenge was addressed by exploring the relationship between the sieves and the solvent used in the treatment, and taking advantage of this relationship in the Grignard treatment process. This study helped identify a suitable solvent, which allowed for successful and reproducible treatment of commercial LTA sieves; however, treatment of lab-made sieves continues to prove challenging. Based on improved understanding of the Grignard treatment reaction mechanism, modifications were made to the existing Grignard treatment procedure, resulting in the introduction of a "simplified" Grignard treatment procedure. The new procedure requires less control over the reaction process, thus making it more attractive for industrial application. Permeation measurements were made using mixed matrix membranes in both single and mixed gas systems. Selectivity enhancements were observed under both single and mixed gas systems using sieve loadings of 25 and 30wt%. The Maxwell model was used to make predictions of mixed matrix membrane performance. Although the experimental results were not in exact agreement with Maxwell predictions, the observed selectivity enhancement was very encouraging and shows potential for future application. Recommendations were made for future study of this system.

Die vorliegende Arbeit beschäftigt sich nach der Analyse und Optimierung der Stromzuführungen auf Flüssigstickstoff-Temperaturniveau, hauptsächlich mit der Untersuchung einer Gemisch-Stickstoff-Kaskade als Kälteversorgungssystem eines resistiven HTSL-Kurzschlussstrombegrenzers. Unter einem Kurzschlussstrombegrenzer versteht man einen veränderlichen elektrischen Widerstand, welcher, gegebenenfalls in Serie mit konventionellen, mechanischen Stromunterbrechern, direkt in den zu schützenden Stromkreis eingebaut ist. Als veränderlicher elektrischer Widerstand kann z.B. ein supraleitendes Element verwendet werden. Im normalen Betriebsfall setzt dieser dem fließenden Strom praktisch keinen Widerstand entgegen. Die Dimensionierung wird so gewählt, dass im Falle eines Überstroms ein rascher Übergang in den normalleitenden Zustand erfolgt. Durch den nun vorhandenen Widerstand wird der Stromfluss sehr effektiv begrenzt, bis beispielsweise nachgeschaltete mechanische Schutzeinrichtungen ansprechen. Sobald dies erfolgt ist, kann der Supraleiter regenerieren und in den Ausgangszustand zurückkehren. Die Verwendung von HTSL-Material als Supraleiter erscheint hier höchst vorteilhaft, da damit ein Arbeiten auf Flüssigstickstoff-Temperaturniveau erlaubt wird. Ein entscheidender Punkt für die erfolgreiche Einführung der HTSL-FCL ist die Bereitstellung einer geeigneten Kälteversorgung. Dies kann entweder durch regelmäßiges Nachfühlen mit flüssigem Stickstoff oder durch den Einsatz einer Kältemaschine zur Stickstoffrekondensation realisiert werden. Beim Einsatz einer Kältemaschine hat man einen von der Stickstoffnachlieferung unabhängigen Betrieb mit geschlossenem Kühlsystem. Die Energiedissipation in dem HTSL-Element selbst ist unter Normalbedingungen vernachlässigbar klein. Für die Auslegung des Kühlsystems ist von Bedeutung, dass der größte Teil der Wärmelast durch die metallischen Stromzuführungen verursacht wird. Die Auslegung des Kühlsystems muss sich daher an der thermodynamischen Analyse der Stromzuführungen orientieren. Das Ziel dieser Arbeit bestand in der Analyse von Kühlmethoden für solche Stromzuführungen hinsichtlich ihrer Effektivität und Wirtschaftlichkeit. Ein neues Kühlsystem auf der Basis einer Gemisch-Stickstoff-Kaskade wird vorgeschlagen als Alternative zu den derzeit in Frage kommenden Kühltechniken. Es wurde folgende Vorgehensweise gewählt: 1. Verschiedene Kühlmethoden zur Kühlung von SZF werden aufgeführt und thermodynamisch bewertet. 2. Kühlsysteme, basierend auf einer Gemisch-Stickstoff-Kaskade, werden vorgeschlagen und deren Charakteristika mittels numerischer Simulation bestimmt. 3. Ein auf der Basis einer Gemisch-Kältemaschine gebauter Stickstoffverflüssiger wird in Betrieb genommen und getestet. 4. Die Funktion und die Effektivität der Gemisch-Stickstoff-Kaskade zur Kühlung der Stromzuführungen werden bewertet. 5. Zugehörige Kühlsysteme auf der Basis verschiedener Kühltechniken werden analysiert 6. In einer Wirtschaftlichkeitsbetrachtung werden die Kühlsysteme einander gegenübergestellt Insgesamt kann als Ergebnis festgehalten werden, dass der Einsatz der vorgestellten Gemisch-Stickstoff-Kaskadenanlagen zur Kälteversorgung im vorgestellten Anwendungsfall eine durchaus wettbewerbsfähige, voraussichtlich sogar überlegene Alternative zu den sonst verfügbaren Methoden darstellt.

Die vorliegende Arbeit beschäftigt sich nach der Analyse und Optimierung der Stromzuführungen auf Flüssigstickstoff-Temperaturniveau, hauptsächlich mit der Untersuchung einer Gemisch-Stickstoff-Kaskade als Kälteversorgungssystem eines resistiven HTSL-Kurzschlussstrombegrenzers. Unter einem Kurzschlussstrombegrenzer versteht man einen veränderlichen elektrischen Widerstand, welcher, gegebenenfalls in Serie mit konventionellen, mechanischen Stromunterbrechern, direkt in den zu schützenden Stromkreis eingebaut ist. Als veränderlicher elektrischer Widerstand kann z.B. ein supraleitendes Element verwendet werden. Im normalen Betriebsfall setzt dieser dem fließenden Strom praktisch keinen Widerstand entgegen. Die Dimensionierung wird so gewählt, dass im Falle eines Überstroms ein rascher Übergang in den normalleitenden Zustand erfolgt. Durch den nun vorhandenen Widerstand wird der Stromfluss sehr effektiv begrenzt, bis beispielsweise nachgeschaltete mechanische Schutzeinrichtungen ansprechen. Sobald dies erfolgt ist, kann der Supraleiter regenerieren und in den Ausgangszustand zurückkehren. Die Verwendung von HTSL-Material als Supraleiter erscheint hier höchst vorteilhaft, da damit ein Arbeiten auf Flüssigstickstoff-Temperaturniveau erlaubt wird. Ein entscheidender Punkt für die erfolgreiche Einführung der HTSL-FCL ist die Bereitstellung einer geeigneten Kälteversorgung. Dies kann entweder durch regelmäßiges Nachfühlen mit flüssigem Stickstoff oder durch den Einsatz einer Kältemaschine zur Stickstoffrekondensation realisiert werden. Beim Einsatz einer Kältemaschine hat man einen von der Stickstoffnachlieferung unabhängigen Betrieb mit geschlossenem Kühlsystem. Die Energiedissipation in dem HTSL-Element selbst ist unter Normalbedingungen vernachlässigbar klein. Für die Auslegung des Kühlsystems ist von Bedeutung, dass der größte Teil der Wärmelast durch die metallischen Stromzuführungen verursacht wird. Die Auslegung des Kühlsystems muss sich daher an der thermodynamischen Analyse der Stromzuführungen orientieren. Das Ziel dieser Arbeit bestand in der Analyse von Kühlmethoden für solche Stromzuführungen hinsichtlich ihrer Effektivität und Wirtschaftlichkeit. Ein neues Kühlsystem auf der Basis einer Gemisch-Stickstoff-Kaskade wird vorgeschlagen als Alternative zu den derzeit in Frage kommenden Kühltechniken. Es wurde folgende Vorgehensweise gewählt: 1. Verschiedene Kühlmethoden zur Kühlung von SZF werden aufgeführt und thermodynamisch bewertet. 2. Kühlsysteme, basierend auf einer Gemisch-Stickstoff-Kaskade, werden vorgeschlagen und deren Charakteristika mittels numerischer Simulation bestimmt. 3. Ein auf der Basis einer Gemisch-Kältemaschine gebauter Stickstoffverflüssiger wird in Betrieb genommen und getestet. 4. Die Funktion und die Effektivität der Gemisch-Stickstoff-Kaskade zur Kühlung der Stromzuführungen werden bewertet. 5. Zugehörige Kühlsysteme auf der Basis verschiedener Kühltechniken werden analysiert 6. In einer Wirtschaftlichkeitsbetrachtung werden die Kühlsysteme einander gegenübergestellt Insgesamt kann als Ergebnis festgehalten werden, dass der Einsatz der vorgestellten Gemisch-Stickstoff-Kaskadenanlagen zur Kälteversorgung im vorgestellten Anwendungsfall eine durchaus wettbewerbsfähige, voraussichtlich sogar überlegene Alternative zu den sonst verfügbaren Methoden darstellt.