High-pressure Permeation Research Articles

Supercritical CO2 permeation in glassy polyimide membranes

The high-pressure permeation and sorption behavior of supercritical carbon dioxide (sc-CO2) in glassy Matrimid® 5218 polymer membranes were extensively investigated. The effect of pressure (0–120 bar) and temperature (25–55 °C) was examined. The observations were related to the intrinsic membrane properties, plasticization phenomena and the CO2 fluid properties. The phase transition from gaseous (-like sc) CO2 to liquid (-like sc) CO2 has the largest influence on the CO2 fluid properties and therefore was found to have the most influence on the CO2 sorption and CO2 permeability. The CO2 sorption was directly dependent on the CO2 density in the liquid (-like sc) regime. The CO2 permeability of Matrimid® 5218 showed typical CO2-induced plasticization behavior in the gaseous (-like sc) CO2 regime. When entering the liquid (-like sc) CO2 regime, the extent of plasticization was found to be independent of the applied feed pressure in this regime. The membranes showed strong hysteresis with pressure. The permeation history of the membrane thus has a large influence on the time-dependent permeability behavior. Clearly, the CO2 permeability behavior at these high pressures in glassy Matrimid® 5218 is determined by a combination of the CO2 fluid density and plasticization phenomena.

Synthesis of tubular ZIF-8 membranes for propylene/propane separation under high-pressure

ZIF-8 membrane-based separation of propylene/propane is attractive for reducing the energy and cost of the conventional cryogenic distillation. However, the high-pressure permeation results are rarely reported on the tubular ZIF-8 membranes. In this work, high-quality ZIF-8 membranes were successfully fabricated on the tubular ceramic support. The coating of a PDMS layer can significantly improve the quality and reproducibility of as-synthesized membranes. The effect of permeating temperature (35–100 °C) and feeding pressure (1~6 bar) as well as the feeding compositions on the C3H6/C3H8 separation performance are carefully investigated. The C3H6/C3H8 permeation manners (with or without sweep gas, and under vacuum) on the tubular ZIF-8 membrane are also compared. Concentration polarization is only obviously existed when no sweep gas is used.

Hybrid FSC membrane for CO2 removal from natural gas: Experimental, process simulation, and economic feasibility analysis

The novel fixed‐site‐carrier (FSC) membranes were prepared by coating carbon nanotubes reinforced polyvinylamine/polyvinyl alcohol selective layer on top of ultrafiltration polysulfone support. Small pilot‐scale modules with membrane area of 110–330 cm2 were tested with high pressure permeation rig. The prepared hybrid FSC membranes show high CO2 permeance of 0.084–0.218 m3 (STP)/(m2 h bar) with CO2/CH4 selectivity of 17.9–34.7 at different feed pressures up to 40 bar for a 10% CO2 feed gas. Operating parameters of feed pressure, flow rate, and CO2 concentration were found to significantly influence membrane performance. HYSYS simulation integrated with ChemBrane and cost estimation was conducted to evaluate techno‐economic feasibility of a membrane process for natural gas (NG) sweetening. Simulation results indicated that the developed FSC membranes could be a promising candidate for CO2 removal from low CO2 concentration (10%) NGs with a low NG sweetening cost of 5.73E−3 $/Nm3 sweet NG produced. © 2014 American Institute of Chemical Engineers AIChE J 60: 4174–4184, 2014

Permeability, diffusivity and solubility of carbon dioxide in fluoropolymers: an experimental and modeling study

Carbon dioxide has successfully been used as an alternative refrigerant in many applications, replacing chlorofluoro- and hydrofluorocarbons (CFCs and HFCs), due to its negligible ozone depletion and significantly lower global warming potential. However, the use of carbon dioxide as a refrigerant requires a refrigeration cycle with greater extremes of pressure, placing greater demands on the plant’s seals and packings. The integrity of the refrigeration system (it should release as little refrigerant as possible to the atmosphere) depends crucially on the material used for the seals and packings. Using a high-pressure permeation cell, the permeability and diffusivity of carbon dioxide were measured in several polymers used as packing and sealing materials. These were the fluoropolymers PTFE, FKM and TFM, both pure and containing glass, graphite, Ekonol and polysulfone as additives. The solubility coefficient of carbon dioxide in these polymers was then obtained as the ratio of the measured permeability and diffusivity data. Measurements were carried out over a pressure range of 45–50 bar and a temperature range of 40–80 °C. The solubility of carbon dioxide in the polymers is then modeled with the Simplified Perturbed Chain – Statistical Associating Fluid Theory (sPC-SAFT) equation of state. Pure component parameters were determined using an extrapolation method based on the lower molecular weight monomer and available density data for the polymers. In the case of copolymers, mixing rules were used to determine parameters. Carbon dioxide solubility can be accurately correlated to the measured data with the sPC-SAFT equation of state using a temperature–independent binary interaction parameter.

Microstructure, strength and CO2 separation characteristics of α-alumina supported γ-alumina thin film membrane

In this work, a mesoporous γ-Al2O3 membrane was synthesised on an α-Al2O3 substrate by a sol–gel dip coating process. The membranes were characterised using SEM, field emission SEM, X-ray diffractometry and N2 adsorption/desorption measurements (Brunauer–Emmett–Teller analyses). The characterisation results revealed that a flawless γ-alumina membrane layer with 3·5 μm thickness and 2·1 nm average pore size was achieved. Subsequent separation tests indicated that CO2 could be separated from N2 by the mesoporous γ-Al2O3 membrane. In spite of the difficulties of the separation, the optimised microstructure achieved for the prepared membrane led to desirable and regular permeation behaviour. It was also observed that separation could be more efficient in high pressure permeation conditions. The prepared substrate fulfilled the required strength and permeability for the thin γ-Al2O3 membrane film under these conditions. Accordingly, an optimised completely ceramic membrane structure, applicable for CO2 separation applications, was achieved.

Preparation, characterization and microstructural optimization of a thin γ-alumina membrane on a porous stainless steel substrate

► A mesoporous γ-Al 2 O 3 membrane was synthesized on conventional α-Al 2 O 3 substrates. ► γ-Al 2 O 3 membrane was potential for CO 2 separation at high pressure test conditions. ► Thus, it was required to provide the membrane layer with more strength. ► α-Alumina substrate was substituted with porous stainless steel. ► A stainless steel supported α-Al 2 O 3 membrane with better properties was synthesized. In this work, a supported mesoporous (MEP) γ-Al 2 O 3 membrane was synthesized on conventional α-Al 2 O 3 substrates by sol–gel dip coating process. In the following, the preparation of a novel metallic–ceramic composite membrane was studied, which incorporated desirable properties of both ceramic membrane and porous metallic substrate. For this purpose, mesoporous alumina membrane layer was developed on a porous 316L stainless steel substrate. The substrate was prepared by loose powder sintering and modified by soaking–rolling and fast drying method. The prepared membranes were characterized using scanning electron microscope (SEM), field emission scanning electron microscope (FESEM), X-ray diffractometer (XRD) and N 2 -adsorption/desorption measurements (BET analyses). The results revealed that a defect-free γ-alumina membrane with 2.1 nm average pore size can be produced. Permeation tests with N 2 gas revealed that the stainless steel substrate had 40 times more permeability than conventionally used alumina support. Additionally, single gas permeation of γ-alumina membrane for CO 2 and N 2 was compared. It was observed that CO 2 could be separated from N 2 by the MEP γ-Al 2 O 3 membrane in high pressure permeation condition, where stainless steel presents superior mechanical strength than alumina as a substrate.

A new method for calculating the specific surface area of porous metal foams

Porosity and pore diameter are two elementary parameters that are easy to be measured for porous materials. A new method is proposed for calculating the specific surface area of porous metal foams based on a mathematical relationship between this area and the porosity and pore diameter. Using this method, the specific surface areas of metal foams prepared by different methods, namely electrodeposition and high-pressure permeation casting, are successfully calculated. The results indicate that the present model can accurately describe experimental data.

Characterization of the surface layer due to oxygen for the hydrogen related C–SiC films

The films containing C and about 80%SiC were deposited by R F. magnetron sputtering followed with argon ion beam bombardment to enhance the adhere strength of the substrate and then were introduced hydrogen by using hydrogen ion irradiation or high pressure permeation techniques. XPS was used to investigate the sub-surface of these C–SiC films. The results show that, apart from carbon adsorbing hydrogen, carbon–hydrogen, SiC and Si 1− x C x , contamination by oxygen reacting with Si and C in the films was apparent. Further reaction with hydrogen to form C y –Si–O–H on the sub-surface of the C–SiC films was also shown. Calculation of the concentrations of the different configurations based on Ghosh model shows that different x values in Si 1− x C x and different y values in C y –Si–O–H can be obtained due to different hydrogen introduction methods.

Study in the oxygen contamination on the surface of CSiC films

AbstractCSiC films were prepared with an ion‐mixing technology and then introduced with hydrogen by using hydrogen ion irradiation or high‐pressure permeation. It is found that the surfaces of the CSiC films are always covered by contamination oxygen. XPS was used to analyze the behavior of the contamination oxygen on the surfaces of the CSiC films before and after hydrogen introduction. The results show that apart from the adsorbed top layer‐containing contaminations like oxygen, carbon, and oxyhydrogen species, the oxygen can react with elements of films and hydrogen. Different carbon–oxygen–hydrogen configurations and CSiO or CSiOH on the subsurfaces can be formed with different hydrogen introduction methods. Also, the thicknesses of these species‐related oxygen on the subsurface of CSiC films are estimated in this article. Copyright © 2009 John Wiley & Sons, Ltd.

Crosslinked mixed matrix membranes for the purification of natural gas: Effects of sieve surface modification

Crosslinked polymer–zeolite “mixed matrix” membranes potentially offer both outstanding separation properties and swelling resistance for the purification of natural gas. This paper describes the dispersion of SSZ-13, a CO 2/CH 4 size-discriminating zeolite, in a crosslinkable polymer, 3:2 6FDA-DAM-DABA chemically modified with 1,3-propane diol (PDMC polymer). Pure crosslinked dense film membranes formed with this polymer have proven resistant to CO 2 swelling when crosslinked in a previous study. Earlier studies have shown the polymer–zeolite interface to be crucial in the successful formation of these hybrid materials. Several techniques for modifying the polymer–zeolite interface of crosslinked mixed matrix membranes are described in this study. These techniques seek to optimize adhesion between the dispersed phase and continuous matrix to provide membrane properties that transcend Robeson's tradeoff upper bound curve between permeability and selectivity. Crosslinked mixed matrix membranes are analyzed via low pressure permeation studies (pure and mixed gas) and compared with the well-known Maxwell Model in addition to Robeson's upper bound curve. High pressure permeation experiments are also conducted to prove the stability of crosslinked mixed matrix membranes in the presence of aggressive CO 2 feeds. The resulting crosslinked mixed matrix membranes have the ability to separate CO 2 from CH 4 more effectively than traditional pure polymer membranes, while also providing needed membrane stability in the presence of aggressive CO 2-contaminated natural gas streams.

Deuterium-Tritium Beta-Layering Within a National Ignition Facility Scale Polymer Target in the LANL Cryogenic Pressure Loader

Beta-layering, the process of beta-decay heat-driven mass redistribution, has been demonstrated in a deuterium-tritium (D-T)-filled polymer sphere of the type required for fusion ignition experiments at the National Ignition Facility. This is the first report, to the best of the authors’ knowledge, of a D-T layer formed in a permeation-filled sphere. The 2-mm-diam sphere was filled with D-T by permeation; cooled to cryogenic temperatures while in the high-pressure permeation vessel; and, while cold, removed to an optical axis where the D-T was frozen, melted, and beta-layered in a series of experiments over several weeks’ time. This work was performed in the Los Alamos National Laboratory cryogenic pressure loader system. The beta-layering time constant was 24.0 ± 2.5 min, less than the theoretical value of 26.8 min, and not showing the significant increase due to build-up of 3He often observed in beta-layered samples. Supercooling of the liquid D-T was observed. Neither the polymer target nor its tenting material showed visual signs of degradation after 5 weeks of exposure to D-T. Small external thermal gradients were used to shift the D-T material back and forth within the sphere.

The Accurate Measurement of Elevated Pressure Gas Permeation through Polymers Based on New Specimen Geometries

Knowledge of high pressure (HP) gas permeation rates is essential for designing thermoplastic-based flexible pipes for offshore oil and gas production. An effect which masks the permeation flow associated with normal HP gas permeation test procedures used for testing engineering thermoplastics at MERL and elsewhere has been illustrated herein by laboratory testing at medium pressures. HP permeation tests conventionally use porous steel sinters as supports for test samples, which are now seen to reduce measured rates; hence calculated associated permeation coefficients are diminished correspondingly. These coefficients are used for prediction purposes of permeation rates at other, service-related, conditions, which in turn will be affected by the error arising from sinters during testing. It has been possible to make these observations because situations have been identified where testing of unsupported samples, allowing free escape of permeated gas, could be carried out at medium pressures (∼70 bar). However, another factor also applies; normal thermoplastic samples cut from the walls of flexible pipe lining materials and used for HP permeation work, whether flat or “curvidisc” samples, are invariably sealed with O-rings etc in such a way that edge regions exist – and these will absorb some of the permeating species, thus again affecting measured rates. In quantifying such effects, some finite element analysis modelling has been used to provide valuable information, highlighting deficiencies in the current permeation test procedure, to suggest tentatively the degree of correction required. In summary, for the systems measured (involving plasticised PVDF (pPVDF) and methane at 70 bar), reductions in permeation rate brought about by the sinter support during laboratory testing mean that the permeation coefficient obtained by the normal means of testing and calculation should in reality be increased by a factor of 1.8. Moreover, even for unsupported pPVDF permeation tests, the coefficient should also be increased by another ca two thirds, to allow for a combination of outer edge sample effects and the need to reach absolute equilibrium. Hence the overall correction factor for the coefficient applying when using sinters is apparently nearer three. In a validation exercise which also leads to an improved test procedure, initial work was conducted with a novel sample based on a conical section, an arrangement needing no sinter support and possessing no edge regions; a test at medium pressure shows directly an increase in the coefficient obtained of more than two compared with testing an unsupported curvidisc possessing edge regions. However, considerable sealing difficulties exist; when solved, this geometry has the potential of operating at genuine high pressures, to lead to near-absolute measurements of HP permeation coefficients. In applying a similar approach to the performance of flexible pipes in service – which is much associated with HP gas permeation – a small simulation of armour windings of the type which support their thermoplastic liners has been found also to reduce rates, for analogous reasons. Here, the effect is beneicial to pipe users, as support windings reduce the unsupported permeation rate by 70%. Additionally, an equation giving a single permeation coefficient for a sample (or component) having a temperature gradient occurring across it has been developed and validated by laboratory testing.

Observed non-linearity of Darcy-permeability in compacted fine pigment structures

Liquid permeability was measured on a range of porous samples, using a specially-constructed high pressure permeation cell. The samples consisted of compacted fine isotropic mineral pigment—calcium carbonate—compressed over a range of compaction pressures. These samples have pore diameters typically (number basis) finer than 0.1 μm. The porosities and the pore size distributions of the samples have been determined by means of mercury porosimetry. The permeability of these fine-pore network systems is seen under certain conditions not to obey the well-known linearity of the Darcy relation as a function of applied liquid pressure differential. A considerable pressure–flux hysteresis is observed following saturation by imbibition. Furthermore, it is seen that there is no direct linear correlation between permeability and porosity despite the use of a constant pigment particle size distribution and, hence, skeletal size distribution. The measured permeability displays a local maximum at a fractional porosity of approximately 0.26 with a further distinct drop at around 0.27. Interestingly, this phenomenon is also confirmed using a computer-based porous network simulator which provides a relative permeability based on matching the mercury percolation data. Taking into account the effects of earlier-proposed mechanisms of preferred pathway flow and film flow during imbibition, it is postulated that some pores remain unfilled during imbibition and saturation prior to the permeability study, such that there remains entrapped air or vapour phase in microscopic ganglia. This air does not dissolve in the aliphatic mineral oil used in the experiments. Structures with a delineated pore-throat structure will probably lead generally to observed non-linear phenomena within the range of dimensions studied here, which can have implications, amongst others, for microscopic filtration, catalysis and absorption phenomena.

Development of the Los Alamos National Laboratory Cryogenic Pressure Loader

Targets for inertial fusion research and ignition at OMEGA, the National Ignition Facility, LMJ, and future facilities rely on beta-radiation-driven layering of spherical cryogenic DT ice layers contained within plastic or metal shells. Plastic shells will be permeation filled at room temperature then cooled to cryogenic temperatures before removal of the overpressure. The cryogenic pressure loader (CPL) was recently developed at Los Alamos National Laboratory as a testbed for studying the filling and layering of plastic target shells with DT. A technical description of the CPL is provided. The CPL consists of a cryostat, which contains a high-pressure permeation cell, and has optical access for investigating beta layering. The cryostat is housed within a tritium glovebox that contains manifolds for supplying high-pressure DT. The CPL shares some design elements with the cryogenic target handling system at the OMEGA facility to allow testing of tritium issues related to that system. The CPL has the capability to fill plastic targets by permeation to pressures up to 100 MPa and to cool them to 15 K. The CPL will accommodate a range of targets and may be modified for future experiments.

Formation and characterization of polyamide membranes via interfacial polymerization

The formation of plyamide membranes via the interfacial polymerization (IP) of m-phenylenediamine (MPD) in water with trimesoyl chloride (TMC) in hexane or heptane is studied using two novel measurement techniques: light relfection and pendant-drop tensiometry. These techniques permit obtaining real-time data on effects of TMC and MPD concentration as well as reaction time on the IP membrane-formation process. The structure of the IP membranes is studied using scanning electron microscopy (SEM) and their performance is assessed via high pressure permeation measurements. These studies indicate that for very small TMC concentrations (<0.01 wt%) the IP process is diffusion controlled in the organic layer. for higher TMC concentrations appropriate to commercial practice, the IP process is MPD-diffusion controlled in the IP film layer. Although under typical IP reaction conditions (MPD ≈2 wt%, TMC ≈0.1 wt%), the IP reaction is nearly instantaneous, the growth of the IP film thickness becomes self-limiting on a longer time scale (<40 s) owing to the inability of the two reactants to interpenetrate after sufficient densification has occurred toward the organic side of the IP film. However, the IP film properties continue to change long after (300 s) the IP film growth becomes self-limiting presumably because of additional cross-linking. The light-reflection, pendant-drop tensiometry, SEM, and permeation measurements provide complementary supporting information on the IP membrane-formation process. In particular, these studies clearly indicate that the reactant concentrations and reaction time can be optimized to achieve improved rejection and permeation-flux properties. These studies also indicate that the light-reflection and pendant-drop-tensiometry measurement techniques provide very useful tools for studying the very rapid IP membrane-formation process.

Explosive Decompression in Elastomers Internal blistering and fracturing in rubbers after high pressure exposure to gases

When elastomers are exposed to gas at high pressures, the gas enters the elastomers by solution and diffusion processes. If the pressure is removed rapidly, the system becomes supersaturated and gas comes quickly out of solution, causing blistering and fracture of the elastomer (so-called explosive decompression). Factors and some theory involved in the gas ingress and decompression stages are discussed. Data are presented from high pressure permeation measurements, showing deviations from simple predictions, and explosive decompression experiments, showing several forms of failure. Important parameters are seen to be the solubility coefficient of gas in elastomer at the actual pressure, and moduli and tearing energy of the elastomer. However the situation remains one of extreme complexity.