Showing papers on "Gas separation published in 2002"

Future directions of membrane gas separation technology

Abstract: During the past 20 years, sales of membrane gas separation equipment have grown to become a $150 million/year business. More than 90% of this business involves the separation of noncondensable gases: nitrogen from air; carbon dioxide from methane; and hydrogen from nitrogen, argon, or methane. However, a much larger potential market for membrane gas separation lies in separating mixtures containing condensable gases such as the C3+ hydrocarbons from methane or hydrogen, propylene from propane, and n-butane from isobutane. These applications require the development of new membranes and processes. In this review, the existing gas separation applications are surveyed, and the expected growth of these and potential new applications of gas separation membranes over the next 20 years are described. The improvements in gas separation technology needed to produce these changes in the membrane industry are also discussed.

The Effects of Crosslinking Chemistry on CO2 Plasticization of Polyimide Gas Separation Membranes

Abstract: To suppress undesirable plasticization effects in CO2/CH4 separations, crosslinkable 6FDA-based copolyimides were synthesized by using 3,5-diaminobenzoic acid (DABA) as one of two diamine monomers. DABA contains a carboxylic acid group that can be used to crosslink the polymer chains with ethylene glycol and aluminum acetylacetonate. These chemistries were compared for effectiveness in suppressing CO2 plasticization on the basis of pure CO2 permeation and sorption data up to 800 psia. The time and pressure dependencies of permeation and sorption were analyzed to characterize the plasticization phenomenon and how it can be controlled by covalent crosslinking. Mixed-gas permeation data are reported up to a total feed pressure of 850 psia for the separation of 50:50 CO2/CH4 mixtures at 35 °C. Selectivity losses with increasing feed pressure are modeled to further understand the effects of plasticization, dual-mode sorption, gas-phase nonidealities, and bulk flow on membrane performance. Additionally, a short...

Mixed matrix membrane materials with glassy polymers. Part 2

Abstract: Analysis presented in Part 1 of this paper indicated the importance of optimization of the transport properties of the interfacial region to achieve ideal mixed matrix materials. This insight is used in this paper to guide mixed matrix material formation with more conventional gas separation polymers. Conventional gas separation materials are rigid, and, as seen earlier, lead to the formation of an undesirable interphase under conventional casting techniques. We show in this study that if flexibility can be maintained during membrane formation with a polymer that interacts favorably with the sieve, successful mixed matrix materials result, even with rigid polymeric materials. Flexibility during membrane formation can be achieved by formation of films at temperatures close to the glass transition temperature of the polymer. Moreover, combination of chemical coupling and flexibility during membrane formation produces even more significant improvements in membrane performance. This approach leads to the formation of mixed matrix material with transport properties exceeding the upper bound currently achieved by conventional membrane materials. Another approach to form successful mixed matrix materials involves tailoring the interface by use of integral chemical linkages that are intrinsically part of the chain backbone. Such linkages appear to tighten the interface sufficiently to prevent “nonselective leakage” along the interface. This approach is demonstrated by directly bonding a reactive polymer onto the sieve surface under proper processing conditions.

Metallic Hydrides I: Hydrogen Storage and Other Gas- Phase Applications

Abstract: A brief survey is given of the various classes of metal alloys and compounds that are suitable for hydrogen-storage and energy-conversion applications. Comparisons are made of relevant properties including hydrogen absorption and desorption pressures, total and reversible hydrogen-storage capacity, reaction-rate kinetics, initial activation requirements, susceptibility to contamination, and durability during long-term thermal cycling. Selected applications are hydrogen storage as a fuel, gas separation and purification, thermal switches, and sorption cryocoolers.

Membrane-assisted fluid separation apparatus and method

Abstract: This present invention relates to a fluid separation module adapted to separate a given fluid mixture into permeate and retentate portions using bundles of hollow fiber membranes. The membranes may be composed of different kinds of membranes depending on the application being used to separate the fluid mixture. The fluid separation module may be used to separate fluid mixtures by a number of different processes, including but not limited to, pervaporation, vapour permeation, membrane distillation (both vacuum membrane distillation and direct contact membrane distillation), ultra filtration, microfiltration, nanofiltration, reverse osmosis, membrane stripping and gas separation. The present invention also provides an internal heat recovery process applied in association with those fluid separation applications where separation takes place by evaporation through the membrane of a large portion of the feed into permeate. Desalination and contaminated water purification by means of vacuum membrane distillation are just two examples where the internal heat recovery process may be applied. In these two examples, large portions of the feed are separated by membranes into a high purity water permeate stream by evaporation through the membranes and into a retentate stream containing a higher concentration of dissolved components than present in the feed. In this process the permeate vapour that is extracted from the fluid separation module is compressed by an external compressor to increase the temperature of the vapour higher than the temperature of the feed entering the separation module. Heat from the permeate vapour at the elevated temperature is transferred back to the incoming feed fluid mixture entering the fluid separation module in a condenser/heat exchange.

Process for making hollow fiber mixed matrix membranes

Abstract: Isopycnic or asymmetric mixed matrix hollow fiber membranes for gas separation can be made by a continuous spinning process. Mixed matrix membranes are characterized by a continuous phase of selectively gas permeable polymer in which are uniformly dispersed discrete absorbent particles such as molecular sieves that also have selectivity enhancing properties. The fibers can be monolithic in which the fiber wall is entirely mixed matrix, or composite in which an active mixed matrix layer is positioned adjacent to a supporting substrate layer. The novel mixed matrix hollow fiber membranes provide higher selectivity than dense film membranes of the continuous phase polymer. A monofunctional organosilicon compounds can be used to treat the zeolite in order to achieve compatibility between sieve and polymer.

Pressure swing adsorption gas separation method and apparatus

Abstract: The present invention is a gas separator for separating a gas mixture into a product gas. The gas separator has an adsorbent bed including a separation chamber with first and second ports and a molecular sieve material contained in the separation chamber. A first pumping chamber is connected to the first port. A first valve regulates flow of the gas mixture between the first port and first pumping chamber. A first piston is located in the first pumping chamber. A second pumping chamber is connected to the second port. A second valve regulates flow of the product gas between the second port and second pumping chamber. A second piston is located in the second pumping chamber. A drive system coordinates operation of the first and second pistons and first and second valves in a cycle including pressurization gas shift and depressurization stages.

Preparation of FAU type zeolite membranes by electrophoretic deposition and their separation properties

Abstract: A novel method using electrophoretic deposition (EPD) is proposed for the preparation of dense FAU type zeolite membranes. The precursor membranes deposited through EPD were transformed into continuous bodies without interparticle pores by hydrothermal treatment in reaction mixtures with molar ratio Na2O∶Al2O3∶SiO2∶H2O = 8∶1∶12∶360. It was found that the densification of the precursor membranes during the hydrothermal treatment was achieved via two reaction routes; one was crystal growth of FAU type zeolite seeds and the other was generation of FAU type zeolite particles in the interparticle pores from the reaction mixtures. The thus prepared FAU type zeolite self-supported membranes exhibited high performances with a selectivity of 20 in CO2/N2 gas separation.

Gas Separation Properties of Polymers Containing Fluorene Moieties

Abstract: Polymers containing fluorene moieties are interesting because of their potential applications as photoelectronic materials and as gas separation membranes. In this work, the gas transport properties of two novel poly(arylene ether)s, one containing diphenylfluorene (FBP) and 2,6-bis(trifluoromethylphenylene)pyridine (6FPPr) groups and the other containing FBP and 2,5-bis(3-trifluoromethylphenylene)thiophene (6FPT) groups in the main chain, were investigated. The influence of temperature on permeability, diffusivity, and selectivity is reported at temperatures from 30 to 65 °C. Activation energies of permeation and diffusion for He, H2, CO2, O2, N2, and CH4 were obtained for the diphenylfluorene-containing polymers. It was found that the two FBP-containing poly(arylene ether)s studied here show higher gas permeabilities than most of the reported FBP-containing polymer membranes. A comparison revealed that the replacement of the thiophenylidene group with the pyridinylidene has an obvious influence on the g...

Radial adsorption gas separation apparatus and method of use

Abstract: An apparatus includes a vessel and a radial adsorption bed within the vessel and either an axial adsorption bed for a storage tank within the inner diameter of the radial adsorption bed. In one example, the radial adsorption bed surrounds an axial adsorption bed. A process that can be conducted in the vessel includes directing a gas mixture across the radial adsorption bed, thereby causing adsorption of at least a portion of a gas component present in the gas mixture and producing partially purified product. The partially purified gas is directed through the axial adsorption bed, thereby causing further purification of the partially purified gas and producing product gas. In another example, the radial adsorption bed surrounds a storage tank. The storage tank can be employed to store a gas generated or used in a separation process conducted in the radial adsorption bed. For instance, the storage tank can be employed to store product gas or void gas generated in a vacuum/pressure swing adsorption process.

Gas separation using organic-vapor-resistant membranes in conjunction with organic-vapor-selective membranes

Abstract: A process for treating a gas mixture containing at least an organic compound gas or vapor and a second gas, such as natural gas, refinery off-gas or air The process uses two sequential membrane separation steps, one using membrane selective for the organic compound over the second gas, the other selective for the second gas over the organic vapor The second-gas-selective 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 The membrane steps can be combined in either order

Enrichment of Methane concentration via separation of gases using vortex tubes

Abstract: The objective of this work was to determine if a vortex tube can be used as a gas separation device. A vortex tube is a simple mechanical device that has no moving parts. It separates a compressed inlet fluid into two streams, one hot and the other cold. There are a variety of theories to explain this separation. It has been hypothesized that a mixture of compressed gases flown into the vortex tube may separate into individual gas streams by virtue of differential centrifugal forces acting on them. During previous studies by others, conflicting results have been obtained using this hypothesis. Further study of the gas separation process in a vortex tube was carried out. An attempt has been made to separte methane and nitrogen gases using vortex tubes. This particular separation or the resulting enrichment of Methane concentration has applications in the mining industry. Methane is emitted in an underground coal mine. It leaks from the coal seams and is extremely hazardous for workers because of its high explosivity in air. A conventional but costly means of circumventing this problem is methane drainage before mining. Yet another effective method is to blow large amounts of air through the mine to locally dilute methane concentration. The mixture of methane and air is directly passed into the atmosphere. There are advantages to separating methane from air at the ventilation exhaust of the mine. First, methane being a greenhouse gas has strict EPA emission standards, and second, methane can be directly used for generating power. In this experimental work, a laboratory size setup was used to investigate the feasibility of using a fixed geometry vortex tube for separating methane and nitrogen from a mixture. It was found that there was partial gas separation leading to a higher concentration of methane at one exit in comparison to the inlet and a lower concentration at the other exit.