Showing papers on "Gas separation published in 2000"

Recovery of CO2 from Flue Gas Using Gas Hydrate: Thermodynamic Verification through Phase Equilibrium Measurements

Abstract: The main purpose of this study was to develop a new hydrate-based gas separation (HBGS) process especially for recovering CO2 from flue gas. Temperature and pressure conditions for hydrate formation have been closely examined at the various CO2 concentrations of flue gases. Tetrahydrofuran (THF) chosen as a hydrate promoter can also participate in forming hydrates and produces a mixed hydrate together with CO2. The hydrate stability region was greatly expanded by using THF for lowering the equilibrium formation pressure. To confirm thermodynamic validity of the HBGS process, the three-phase equilibria of hydrate, liquid, and vapor were measured for the systems comprising CO2, N2 and water with or without THF in the temperature range of 272−295 K. In addition, two phase equilibria of hydrate and vapor were experimentally investigated for the same systems at several temperatures. Through close examination of the overall experimental results, it was firmly verified that the HBGS process makes it possible to ...

Factors Controlling Successful Formation of Mixed-Matrix Gas Separation Materials

Abstract: Prior work has suggested simple guidelines for matching transport characteristics of materials to form high-performance mixed-matrix materials for gas separation. Such materials comprise a dispersion of molecular sieving particles in a properly selected matrix polymer phase. Recent work has shown that these simple criteria are necessary but not sufficient to achieve the desired properties. The analysis presented here shows the need to optimize the transport properties of the interfacial region, i.e., the region between the bulk polymer and dispersed sieve phases. Guided by the need to optimize both the transport properties of the interfacial region and the matrix material selection criteria noted above, a new paradigm is recommended for matrix phase selection. The practicality of the paradigm is validated by the formation of mixed-matrix membranes with an appropriate polymer and sieve. These materials lead to the attractive predicted performances at low loading. For success at higher loading a zeolite “pr...

Recent advances in gas separation by microporous ceramic membranes

Abstract: Section Headings: Preface Fundamentals and Sorption of Micropores Modeling of Sorption and Diffusion in Microporous Membranes Recent Advances in Microporous Membrane Preparation Gas Separation Applications

Membrane separation processes

Abstract: The group of membrane processes is one of the numerous unit operation systems for separation. Within the separation processes, membranes play a more and more important role. Nowadays membranes are considered as strong competitors of “classical”, conventional separation techniques. Some types of separation processes, including membranes are summarised in Tab. 1 The separation methods are classified in terms of the physico-chemical properties of the compounds to be separated 1,2. It can be seen that membrane.process(es) can be found in almost every class. Table 1 Separation processes based on physico-chemical properties Physico-chemical property Separation process size sieving,filtration,microfiltration,ultrafiltration nanofiltration,dialysis,gas separation,gel chromatography charge ion exchange,electrodialysiselectrophoresis,diffusion dialysis boiling point distillation,membrane distillation freezing point crystallization,srio-filtration density centrifugation,sedimentation magnetic nature magneto-separations affinity extraction,adsorption,absorption,reverse osmosis,gas separation,pervaporation,affinity chromatography chemical nature complexation,liquid membranes

Composites and composite membranes

Abstract: The invention relates to a composite or a composite membrane consisting of an ionomer and of an inorganic optionally functionalized phyllosilicate. The isomer can be: (a) a cation exchanger polymer; (b) an anion exchanger polymer; (c) a polymer containing both anion exchanger groupings as well as cation exchanger groupings on the polymer chain; (d) a blend consisting of (a) and (b), whereby the mixture ratio can range from 100 % (a) to 100 % (b). The blend can be ionically and even covalently cross-linked. The inorganic constituents can be selected from the group of the phyllosilicates or tectosilicates. The use of bentonites and zeolites are generally preferred in special montomorillonite. The mixture ratio isomer:bentonite ranges from 99:1 to 30:70. The invention also relates to the application of the composites/composite membranes: as proton conductors in membrane fuel cells (H2 fuel cells PEFC, direct methanol fuel cells DMFC) at temperatures greater than 100 °C; in (electro)membrane separation methods such as dialysis, diffusion dialysis, gas separation, pervaporation, perstraction and in microfiltration and ultrafiltration, particularly due to their antifouling properties, and; as catalytic membranes in catalytic membrane reactors.

Porous gas permeable material for gas separation

Abstract: A gas separator, a method for producing the gas separator, and a method for separating gases based on a property of inelasticity of the gases. The inventive gas separator is a permeable porous material for separating a mixture of gases by selectable pore size exclusion, comprising pores formed with at least one nanostructured compound. In other words, the inventive porous material can be used to separate a mixture of gases based upon the different working diameter of each of the gases. By selecting specific nanostructured compounds, the porous material can be tailored to contain pores of a predetermined size which allow gases having a working diameter smaller than the size of the pores to pass through the material while preventing the passage of gases having a working diameter greater than the size of the pores.

New Polyimides for Gas Separation. 2. Polyimides Derived from Substituted Catechol Bis(etherphthalic anhydride)s

Abstract: A new synthetic procedure was elaborated allowing for the preparation of aromatic dianhydrides. Methyl- and/or tert-butylcatechols were silylated at the OH groups and the resulting bistrimethylsilyl derivatives were used as nucleophilic reaction partners for 4-chloro- or 4-nitro-N-phenylphthalimides. The bis(o-etherphthalimides) were transformed into the corresponding bis(o-etherphthalic anhydrides) (six known ones, two new ones). For comparison, a trimethyl substituted bis(p-etherphthalic anhydride) was prepared using the same route. These dianhydrides were polycondensed with aromatic diamines such as 1,3-diamino-2,4,6-tetramethylbenzene, 1,4-diamino-2,3,5,6-tetramethylbenzene, 3,3‘-dimethoxybenzidine, 3,3‘,5,5‘-tetramethylbenzidine, or 2,2-bis(4-aminophenyl)hexafluoropropane. In total, 21 polyimides were isolated and characterized. The permeabilities and apparent diffusion coefficients of the pure gases He, H2, N2, O2, CO2, and CH4 were measured for 12 selected polyimides in a time-lag apparatus at feed...

Gas Transport Properties of Novel Cardo Poly(aryl ether ketone)s with Pendant Alkyl Groups

Abstract: Gas transport of hydrogen, oxygen, nitrogen, carbon dioxide, and methane in four cardo poly(aryl ether ketone)s containing different alkyl substituents on the phenyl ring has been examined from 30 to 100 degrees C. The permeability, diffusivity, solubility, and their temperature dependency were studied by correlations with gas shape, size, and critical temperature as well as polymeric structural factors including glass transition, secondary transition, cohesive energy density, and free volume. The bulky, stiff cardo and alkyl groups in tetramethyl-substituted TMPEK-C resulted in increased H-2 permeability (by 55%) and H-2/N-2 permselectivity (by 106%) relative to bisphenol A polysulfone (PSF). Moreover, the weak dependence of gas transport on temperature in TMPEK-C made it maintain high permselectivities (alpha(H2/N2) in 68.3 and alpha(O2/N2) in 5.71) up to 100 degrees C, exhibiting potential for high-temperature gas separation applications.

Comparison of sorbents and isotherm models for NH3-gas separation by adsorption

Abstract: Adsorption equilibrium isotherms of ammonia gas were measured at temperatures between 298 and 393 K on 13X zeolite, 4A zeolite, alumina, silica gel, and activated carbon. The applicability of these sorbents to ammonia gas separation was compared based on equilibrium data. In the pressure range of 1 to 100 kPa activated carbon has its highest working capacity (5.5 mmol·g−1) at 298 K, and the working capacity drops rapidly with temperature, reaching its lowest point at 393 K. The two zeolites provide almost the same working capacity, 3.0–3.5 mmol·g−1, over the entire temperature range. Silica gel and alumina showed low working capacities. The experimental equilibrium data were fitted to 16 different isotherm models, with accuracy and reliability statistically evaluated. The Langmuir–Freundlich model with the van't Hoff equation for the equilibrium constant and with a thermal expansion equation for the saturation sorbate concentration provided the most accurate fit for the 13X and 4A zeolites. This model was also very accurate for the alumina and silica gel data, even though the Dubinin–Astakhov model gave slightly higher predictions. The Henry and vacancy solution models provided the best fit for activated carbon.

Gas separation using C3+ hydrocarbon-resistant membranes

Abstract: A process for separating a gas from a gas mixture containing the gas and a C3+ hydrocarbon vapor, using gas-separation membranes selective for the gas over the C3+ hydrocarbon vapor. The membranes use a selective layer made from a polymer having repeating units of a fluorinated polymer, and demonstrate good resistance to plasticization by the organic components in the gas mixture under treatment, and good recovery after exposure to liquid aromatic hydrocarbons.

Nonequilibrium molecular dynamics simulation of transport and separation of gases in carbon nanopores. II. Binary and ternary mixtures and comparison with the experimental data

Abstract: We present the results of extensive nonequilibrium molecular dynamics simulations of transport and separation characteristics of binary and ternary gas mixtures consisting of CO2, CH4, and H2 through a carbon nanopore, in the presence of an external chemical potential gradient. The gas molecules are represented as Lennard-Jones (LJ) hard spheres. The effect of the various factors, such as the temperature, feed composition, and the pore size, on the transport, adsorption, and separation characteristics is investigated in detail. The simulations’ predictions are compared with experimental data obtained with a carbon molecular-sieve membrane. In some cases, there is good agreement between the predictions and the experimental data, while in other cases the simulations’ results and the data do not agree. Possible causes for the (dis)agreement are discussed, including the crucial interplay between two main factors in gas separation in a pore space, namely, adsorption on the pores’ walls versus the morphology (the pores’ interconnectivity and size distribution) of the porous material. Improved models are thus suggested.

Gas separation using organic-vapor-resistant membranes

Abstract: A process for separating a gas from a gas mixture containing an organic compound gas or vapor, using gas-separation membranes selective for the gas over the organic compound. The membranes use a selective layer made from a polymer having repeating units of a fluorinated cyclic structure of an at least 5-member ring, and demonstrate good resistance to plasticization by the organic components in the gas mixture under treatment.

Pressure swing adsorption with axial or centrifugal compression machinery

Abstract: A gas separation system for separating a feed gas mixture into a first component of the gas mixture and a second component of the gas mixture includes an adsorbent bed assembly and an axial or centrifugal compression machine. The adsorbent bed assembly includes a number of flow paths for receiving adsorbent material therein for preferentially adsorbing the first gas component in response to increasing pressure in the flow paths in comparison to the second gas component. Each flow path includes a pair of opposite ends and a valve communicating with each opposite end for controlling a flow of the feed gas mixture through the flow paths. Preferably, the compression machine consists of a gas turbine including a number of pressure inlet and outlet ports coupled to the valves for exposing each flow path to a number of different pressures between an upper pressure and a lower pressure for separating the first gas component from the second gas component.

Epitaxial thin films

Abstract: Epitatial thin films for use as buffer layers for high temperature superconductors, electrolytes in solid oxide fuel cells (SOFC), gas separation membranes or dielectric material in electronic devices, are disclosed. By using CCVD, CACVD or any other suitable deposition process, epitaxial films having pore-free, ideal grain boundaries, and dense structure can be formed. Several different types of materials are disclosed for use as buffer layers in high temperature superconductors. In addition, the use of epitaxial thin films for electrolytes and electrode formation in SOFCs results in densification for pore-free and ideal gain boundary/interface microstructure. Gas separation membranes for the production of oxygen and hydrogen are also disclosed. These semipermeable membranes are formed by high-quality, dense, gas-tight, pinhole free sub-micro scale layers of mixed-conducting oxides on porous ceramic substrates. Epitaxial thin films as dielectric material in capacitors are also taught herein. Capacitors are utilized according to their capacitance values which are dependent on their physical structure and dielectric permittivity. The epitaxial thin films of the current invention form low-loss dielectric layers with extremely high permittivity. This high permittivity allows for the formation of capacitors that can have their capacitance adjusted by applying a DC bias between their electrodes.