Carbon dioxide sequestration is one of many mitigation tools available to help reduce carbon dioxide emissions while other disposal/repurposing methods are being investigated. Geologic sequestration is the most stable option for long-term storage of carbon dioxide (CO2), with significant CO2 trapping occurring through mineralization within the first 20-50 years. A fiber optic based monitoring system has been proposed to provide real time concentrations of CO2 at various points throughout the geologic formation. The proposed sensor is sensitive to the refractive index (RI) of substances in direct contact with the sensing component. As RI is a measurement of light propagating through a bulk medium relative to light propagating through a vacuum, the extraction of the effects of any specific component of that medium to the RI remains very difficult. Therefore, a requirement for a selective barrier to be able to prevent confounding substances from being in contact with the sensor and specifically isolate CO2 is necessary. As such a method to evaluate the performance of the selective element of the sensor was investigated. Polybenzimidazole (PBI) and VTEC polyimide (PI) 1388 are high performance polymers with good selectivity for CO2 used in high temperature gas separations. These polymers were spin coated onto a glass substrate and cured to form ultra-thin (>10 μm) membranes for gas separation. At a range of pressures (0.14 –0.41 MPa) and a set temperature of 24.2±0.8 °C, intrinsic permeabilities to CO2 and nitrogen (N2) were investigated as they are the gases of highest prevalence in underground aquifers. Preliminary RI testing for proof of concept has yielded promising results when the sensor is exposed exclusively to CO2 or N2. However, the use of both PBI and VTEC PI in these trials resulted in CO2 selectivities of 0.72 to 0.87 and 0.33 to 0.63 respectively, for corresponding feed pressures of 0.14 to 0.41 MPa. This indicates that both of the polymers are more selective for N2 and should not be used in CO2 sensing applications as confounding gas permeants, specifically N2, will interfere with the sensing element. / Graduate / 0428 / 0495 / 0542 / ben.t.davies@gmail.com

This research aimed to develop new composite membranes using a polymer of intrinsic microporosity (PIM-1) and metal organic frameworks (MOFs) for use in gas separations. PIM-1 was successfully synthesised using the high temperature method (40 min, 160 oC) and the resulting polymer was cast into membranes. PIM-1 membranes were chemically modified by reacting hexamethylenediamine (HMDA) with the nitrile group of PIM-1 to form HMDA-modified PIM-1 membranes. Surfaces of PIM-1 membranes were also modified by basic hydrolysis to form amide-modified PIM-1 membranes. These polymer materials were characterized by different techniques (GPC, NMR, ATR-IR, TGA, Elemental analysis and nitrogen sorption analysis). In addition, eight MOF materials [MIL-101(Cr), ED-g-MIL-101(Cr), TEPA-g-MIL-101(Cr), MIL-101(Cr)-NH2, MIL-101(Al)-NH2, UiO-66(Zr), UiO-66-NH2 and UiO-66(COOH)2] were successfully synthesized. They were chosen due to having high surface areas and large porosity. These MOF compounds were characterized using PXRD, SEM, TGA, and low pressure N2.Successful PIM-1/MOF MMMs were fabricated utilising PIM-1 and the MOFs outlined above with various loadings. The highest MOF loading achieved was 28.6 wt. %, apart from MIL-101(Cr)-NH2, for which it was 23.1 wt. %, and MIL-101(Al)-NH2, for which it was 19.8 wt. %. The morphology of MMMs was characterized by scanning electron microscopy (SEM), proving the dispersion of MOF fillers. Novel PIM-1 supported MOF membranes were successfully prepared by depositing ZIF-8 and HKUST-1 layers on the surfaces of unmodified and modified PIM-1 membranes. These materials were characterized using PXRD, SEM, ATR-IR and SEM-EDX. Gas permeation properties of the MOF/PIM-1 MMMs and PIM-1 supported MOF membranes were determined using a time lag method. Most MMMs tested showed an increase in the permeability and stable selectivity as the MOF amount was increased. However, this was not true for MIL-101(Al)-NH2, where the permeability and selectivity decreased. In contrast, PIM-1 supported ZIF-8 and HKUST-1 membranes caused a sharp decrease in the permeability and increase in the selectivity.

Este trabalho tem por objetivo avaliar a viabilidade técnica de processos de separação de gás carbônico em correntes de gases de combustão. Neste sentido, a separação por meio de membranas e por criogenia são avaliadas por meio de simulação de sistemas. As propostas envolvendo membranas avaliam arranjos de membranas em série, os quais são otimizados para condições de maior fluxo permeado e maior beneficio econômico. A corrente de alimentação é de 5 kmol/s e as respectivas frações molares de CO2 e N2 que compõem esta corrente são 0,15 e 0,85. Os resultados obtidos da otimização, para um arranjo de três membranas em série de polyimida de 9000 m² de área superficial, foram uma corrente de permeado de 443,1 mol/s de CO2 a 41,6%, correspondendo a aproximadamente 59% do CO2 da corrente de alimentação. Já com um arranjo de 6 membranas de 9000 m², onde a função objetivo é o maior lucro, foi selecionado o material kapton e a quantidade de CO2 separada é 161,12 mol/s, cuja concentração na mistura é de 79%, e a função objetivo tem um valor de 24.405,30 €/ano. Na outra parte do trabalho, propõe-se e avalia-se um ciclo para o aproveitamento da disponibilidade térmica na regasificação do gás natural líquido, para liquefação de CO2. Obtém-se como resultando em CO2 líquido com fração molar igual a 94%. Este processo consta de uma corrente proveniente da combustão completa de 1 mol/s de metano, contendo 1 mol/s de CO2 e 7,52 mol/s de N2. Esta corrente é comprimida e resfriada até atingir a pressão de 4000 kPa e 25 °C, posteriormente uma membrana enriquece a corrente de gases de combustão, que novamente é comprimida e resfriada até se obter a condensação e separação do CO2. Realiza-se o cálculo de equilíbrio líquido-vapor da mistura utilizando as equações de Peng-Robinson e a regra de mistura de Van der Waals no software VRTherm. A vazão molar do CO2 líquido obtida é de 0,3207 mol/s na concentração declarada. A intensidade energética do processo é de 1,135 kWh/kg de CO2 liquefeito. / The objective of this work is to evaluate the technical feasibility of carbon dioxide separation processes of flue gases streams. In this way, separation processes due membrane and cryogenics are evaluated by system simulation. The systems using membranes evaluates setup of those membranes in series, these setups are optimized for the largest permeate molar flow and the largest economic profit. The feed stream is a 5 kmol/s CO2 – N2 mixture, with molar fraction of 0.15 and 0.85 respectively. The result obtained from the optimization for a setup of three polyimide membranes of 9000 m² is a permeate stream of 443.1 mol/s with CO2 at 41.6%, corresponding to aproximadely 59% of the CO2 contained in the feed stream. When a setup of six 9000 m² membranes is analyzed using an objective function that results in the largest profit, kapton was selected as the material for the membranes. The quantity of CO2 captured is 161.12 mol/s, at 79% of concentration in the mixture, and the objective function has a value of 24,405.30 €/year. The second part of this work, proposes and evaluates a cycle that takes the thermal availability of the regasification of liquid natural gas in advantage for CO2 liquefaction. The product of the cycle is liquid CO2, with a molar fraction of 0.94. The process is fed with a stream that comes from the stoichiometric combustion of 1 mol/s of methane, that stream is composed by 1 mol/s of CO2 and 7.52 mol/s of N2. The stream is then compressed up to the pressure of 4000 kPa and cooled down to 25 °C. After that a membrane concentrates the CO2 in one stream, which is again compressed and cooled down until the condensation of CO2 is achieved. Calculations of liquid – vapor are performed with the Peng- Robinson’s equations and the Van der Waals mixture rule using the software VRTherm. The molar flow rate of liquid CO2 obtained is of 0.3207 mol/s in the concentration mentioned before. The energy intensity of the process is of 1.135 kWh/kg of liquid CO2.

Zeolite membranes are formed as a thin zeolitic layer on the supports. They are usually synthesized by hydrothermal methods in batch systems. In this study, MFI and SAPO-34 type zeolite membranes were produced on macroporous tubular alumina supports in a recirculating flow system at elevated temperatures for the first time in the literature. During the synthesis, the synthesis mixture is flown between the reservoir and the membrane module which includes the support material. The synthesis temperatures were 180&deg / C and 220&deg / C, and the corresponding system pressures were approximately 20 and 30 bars for MFI and SAPO-34, respectively. The CH4 and n-C4H10 single gas permeances were measured through MFI membranes and the performance of membranes was investigated in the separation of equimolar CH4/n-C4H10 mixtures. The best MFI membrane had a CH4 single gas permeance of 1.45x10-6 mol/m2-s-Pa and CH4/n-C4H10 ideal selectivity of 35 at 25oC. The membranes preferentially permeated n-C4H10 in the separation of mixtures. The n-C4H10/CH4 separation selectivity was 43.6 with a total permeance of approximately 0.8x10-6 mol/m2-s-Pa at 25oC. The ideal selectivities of CO2/CH4 of SAPO-34 membrane synthesized in stagnant medium were 227, and &gt / 1000 at 220 and 200oC, respectively. Formation of amorphous structure and the additional secondary phases (impurities) were observed on SAPO-34 membranes synthesized in recirculating flow system. The results showed that it is possible to produce SAPO-34 and high quality MFI membranes by a recirculating flow system operating at elevated temperature.

Robust industrially relevant membranes for CO₂ removal from aggressive natural gas feed streams were developed and characterized. Asymmetric hollow fiber membranes with defect-free selective skin layers on an optimized porous support substructure were successfully spun and subsequently stabilized by covalent crosslinking within the economical membrane formation process. Thermal treatment conditions, which promote sufficient crosslinking without introducing defects or undesired substructure resistance, were identified. It was found that crosslinking improves membrane efficiency and plasticization resistance as well as mechanical strength of fibers. The capability to maintain attractive separation performance under realistic operating conditions and durability against deleterious impurities suggests that the crosslinked fibers have great potential for use in diverse aggressive applications, even beyond the CO₂/CH₄ example explored in this work.

Polymeric membranes have been essential to increasing the efficiency of membrane separation processes. The viability of membrane systems for industrial gas applications lies in the tolerance of such membranes to contamination. While membrane contamination from volatile species can be addressed using purge streams and heat treatment, contamination from non-volatile hydrocarbons can cause a significant decline in membrane permselectivity. This study was focused on the characterization and remediation of cellulose acetate (CA) hollow fibre membranes contaminated by heavy hydrocarbons. CA membranes have a moderate resistance against performance decline from hydrocarbons found in natural gas. Hollow fibre CA membranes were coated with motor oil lubricant to simulate heavy hydrocarbon contamination from large-scale gas compressors and industrial feed streams, and remediation of the CA fibres was conducted using solvent extraction methods. The permeabilities of the membranes to carbon dioxide, helium, hydrogen, methane, nitrogen and oxygen were measured at pressures 300 – 1500kPa and at temperatures 25° – 50°C. It was shown that even a thin layer of oil on the membrane surface can result in substantial losses in membrane performance, with faster permeating gases (e.g. He and H₂) suffering the worst losses. Solvent exchange, in which the membrane was washed using a series of solutions of varying organic content, was unable to remediate the membrane effectively, while the removal of the heavy hydrocarbons by a direct cyclohexane rinse was found to work well to restore the membrane performance.

Developing new membrane morphologies and modifying the existing membrane materials are required to obtain membranes with improved gas separation performances. The incorporation of zeolites and low molecular-weight additives (LMWA) into polymers are investigated as alternatives to modify the permselective properties of polymer membranes. In this study, these two alternatives were applied together to improve the separation performance of a polymeric membrane. The polycarbonate (PC) chain characteristics was altered by incorporating p-nitroaniline (pNA) as a LMWA and the PC membrane morphology was modified by introducing zeolite 4A particles as fillers. For this purpose, pure PC and PC/pNA dense homogenous membranes, and PC/zeolite 4A and PC/pNA/zeolite 4A mixed matrix membranes (MMM) were prepared by solvent-evaporation method using dichloromethane as the solvent. The pNA and zeolite 4A concentrations in the casting solutions were changed between 1-5% (w/w) and 5-30% (w/w), respectively. Membranes were characterized by SEM, DSC, and single gas permeability measurements of N2, H2, O2, CH4 and CO2. They were also tested for their binary gas separation performances with CO2/CH4, CO2/N2 and H2/CH4 mixtures at different feed gas compositions. DSC analysis of the membranes showed that, incorporation of zeolite 4A particles into PC/pNA increased the glass transition temperatures, Tg, but incorporation of them to pure PC had no effect on the Tg, suggesting that pNA was a necessary agent for interaction between zeolite 4A and PC matrix. The ideal selectivities increased in the order of pure PC, PC/zeolite 4A MMMs and PC/pNA/zeolite 4A MMMs despite a loss in the permeabilities with respect to pure PC. A significant improvement was achieved in selectivities when the PC/pNA/zeolite 4A MMMs were prepared with pNA concentrations of 1 % and 2 % (w/w) and with a zeolite loading of 20 % (w/w). The H2/CH4 and CO2/CH4 selectivities of PC/pNA (1%)/zeolite 4A (20%) membrane were 121.3 and 51.8, respectively, which were three times higher than those of pure PC membrane. Binary gas separation performance of the membranes showed that separation selectivities of pure PC and PC/pNA homogenous membranes were nearly the same as the ideal selectivities regardless of the feed gas composition. On the other hand, for PC/zeolite 4A and PC/pNA/zeolite 4A MMMs, the separation selectivities were always lower than the respective ideal selectivities for all binary gas mixtures, and demonstrated a strong feed composition dependency indicating the importance of gas-membrane matrix interactions in MMMs. For CO2/CH4 binary gas mixture, when the CO2 concentration in the feed increased to 50 %, the selectivities decreased from 31.9 to 23.2 and 48.5 to 22.2 for PC/zeolite 4A (20%) and PC/pNA (2%)/zeolite 4A (20%) MMMs, respectively. In conclusion, high performance PC based MMMs were prepared by blending PC with small amounts of pNA and introducing zeolite 4A particles. The prepared membranes showed promising results to separate industrially important gas mixtures depending on the feed gas compositions.

ABSTRACT EFFECT OF PREPARATION AND OPERATION PARAMETERS ON PERFORMANCE OF POLYETHERSULFONE BASED MIXED MATRIX GAS SEPARATION MEMBRANES Karatay, Elif M.Sc., Department of Chemical Engineering Supervisor : Prof. Dr. Levent Yilmaz Co-supervisor : Assoc. Prof. Dr. Halil Kalip&ccedil / ilar August 2009, 126 pages Membrane processes have been considered as promising alternatives to other competing technologies in gas separation industry. Developing new membrane morphologies are required to improve the gas permeation properties of the membranes. Mixed matrix membranes composing of polymer matrices and distributed inorganic/organic particles are among the promising, developing membrane materials. In this study, the effect of low molecular weight additive (LMWA) type and concentration on the gas separation performance of neat polyethersulfone (PES) membranes and zeolite SAPO-34 containing PES based mixed matrix membranes was investigated. Membranes were prepared by solvent evaporation method and annealed above the glass transition temperature (Tg) of PES in order to remove the residual solvent and erase the thermal history. They were characterized by single gas permeability measurements of H2, CO2, and CH4 as well as scanning electron microscopy (SEM), thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Various LMWAs were added to the neat PES membrane at a concentration of 4 wt %. Regardless of the type, all of the LMWAs had an anti-plasticization effect on PES gas permeation properties. 2-Hydroxy 5-Methyl Aniline, HMA, was selected among the other LMWAs for parametric study on the concentration effect of this additive. The incorporation of SAPO-34 to PES membranes increased the permeabilities of all gases with a slight loss in selectivities. However, the addition of HMA to PES/SAPO-34 membranes increased the ideal selectivities well above the ideal selectivities of PES/HMA membranes, while keeping the permeabilities of all the gases above the permeabilities of both pure PES and PES/HMA membranes.

Mixed matrix membranes (MMMs) have gained importance because they combine the desirable properties of the polymers and the organic/inorganic filler materials and they may have a very big potential. In this study polyethersulfone (PES) was used as polymeric material, and Zeolitic Imidazolate Framework-8 (ZIF-8) was used as porous filler material, and 2-hydroxy 5-methyl aniline(HMA), was used as a third component in membrane formulation. In this study, ZIF-8 crystals were synthesized with varying particle sizes, and a novel recycling methodology was developed to improve the efficiency of ZIF-8 production. ZIF-8 nano-crystals were synthesized by a 1-hour stirring method at room temperature and characterized by X-ray diffractometer, scanning electron microscopy (SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS) and thermal gravimetric analysis (TGA). In order to investigate the effect of ZIF-8 loading on the membrane performance, different types of membranes were prepared with varying amounts of ZIF-8 between 10-60% (w/w). Moreover, ternary mixed matrix membranes were synthesized consisting of different amounts of ZIF-8 between 10-30% (w/w) and HMA 1-10% (w/w). Gas transport properties of the membranes were investigated by single gas permeation experiments of H2, CO2 and CH4 at 3 bar feed pressure. In order to investigate the effect of feed pressure on the gas transport properties of the membranes, single gas experiments were conducted on 3, 6, 8, 10 and 12 bar feed pressures. Moreover, binary gas permeation experiments of CO2/CH4 pair were conducted through selected membranes at 3 bar and 12 bar feed pressures. In addition to gas permeation experiments, the morphology and thermal characteristics of the membranes were characterized by SEM, TGA and differential scanning calorimetry (DSC) analysis. The incorporation of ZIF-8 crystals into continuous PES matrix resulted in high performance gas separation membranes. The permeabilities of all studied gases increased with ZIF-8 loading while the ideal selectivities showed a slight decrease compared to neat PES membrane. Highly reproducible and repeatable results were obtained up to 30 % w/w ZIF-8 loading, while membrane formulation reproducibility was decreased for higher ZIF-8 contents (&gt / 30 w/w %). Addition of HMA improved the gas separation performances of the binary membranes significantly by decreasing permeabilities and increasing ideal selectivities. PES/ZIF-8(%20)/HMA(%7) membrane has the best separation performance for all gases among the ternary membranes. When 7 w/w % HMA was added to PES/ZIF-8(%20) membrane, H2 permeability decreased from 26.3 to 13.7 barrer, while H2/CH4 ideal selectivity increased from 61.8 to 103.7. Increasing feed pressures appreciably increased the separation performances of all membranes. While the H2 permeability is pressure independent, the CO2 and CH4 permeabilities were reduced with increasing feed pressures and the highest selectivity improvement was observed in H2/CH4 pair for all membrane compositions. For instance, when the feed pressure was increased from 3 bar to 12 bar, the percentage improvements in ideal selectivities through PES/ZIF-8(%10)/HMA(%4) membrane were calculated as 26, 69, 113 % for the H2/CO2, CO2/CH4 and H2/CH4 gas pairs / respectively. This results show that working at higher feed pressures will be more advantageous for separation of the studied gas pairs. The ideal selectivities and the separation factors were equal to each other for all membrane compositions both for 3 and 12 bar operating pressures.

We examined the effect of the pore dimension of zeolites on the separation of gas mixtures using atomistic simulation methods. We studied two categories of the zeolites with small pores: pore modified silicalite for H₂/CH₄separation and small pore silica zeolites for CO₂/CH₄separation. The effect of pore modification of silicalite on the H₂/CH₄separation was examined. Under some degrees of surface modification, the CH₄flux was reduced much more than the H₂flux, resulting in high ideal selectivities. The use of small pore zeolites for CO₂/CH₄separations was studied. In DDR, we showed that CO₂diffusion rates are only weakly affected by the presence of CH₄, even though the latter molecules diffuse very slowly. Consequently, therefore, the permeance of CO₂in the equimolar mixtures is similar to the permeance for pure CO₂, while the CH₄permeance in the mixture is greatly reduced relatively to the pure component permeance. The calculated CO₂/CH₄separation selectivities are higher than 100 for a wide range of feed pressure, indicating excellent separation capabilities of DDR based membranes. Inspired by the observation in DDR we also examined the separation capabilities of 10 additional pure silica small pore zeolites for CO₂/CH₄separations. From these considerations, we predict that SAS, MTF and RWR will exhibit high separation selectivities because of their very high adsorption selectivities for CO₂over CH₄. CHA and IHW, which have similar pore structures to DDR, showed comparable separation selectivities to DDR because of large differences in the diffusion rates of CO₂and CH₄.