Showing papers on "Gas separation published in 2007"

Synthesis and Performance of Polymerizable Room-Temperature Ionic Liquids as Gas Separation Membranes

Abstract: Room-temperature ionic liquids (RTILs) with polymerizable groups can be readily converted into solid, dense poly(RTILs) for use as gas separation membranes. A series of RTIL monomers with varying length n-alkyl substituents were synthesized and converted into polymer films. These membranes were tested for their performance in separations involving CO2, N2, and CH4. CO2 permeability was observed to increase in a nonlinear fashion as the n-alkyl substituent was lengthened. CO2/N2 separation performance was relatively unaffected as CO2 permeability increased. Plotting the performance of these membranes on a “Robeson plot” for CO2/N2 shows that first-generation poly(RTILs) “hug” the “upper bound” of the chart, indicating that they perform as well or better than many other polymers for this separation. The CO2/CH4 separation is less impressive when compared to other polymer membranes on a “Robeson plot”, but poly(RTILs) perform as well or better than molten RTILs do in bulk fluid gas absorptions for that gas p...

A Mesh‐Adjustable Molecular Sieve for General Use in Gas Separation

Abstract: Gas separation using molecular sieves (MSs) is a environmentally benign, energy-conserving alternative to traditional separation processes, such as distillation and absorption. When using zeolite MSs, an accurate one-on-one match between the mesh size and the separation need is essential. However, when the size disparity of the two gases to be separated is small, a MS with the optimum mesh size is not always readily available. A mismatch inevitably leads to an inefficient separation. Recently, titanosilicate was shown to possess superior flexibility over that of traditional zeolites; a few MSs with discrete mesh sizes were made based on the degree of dehydration of this material at various temperatures. Nevertheless, a MS with more than one mesh size has never been made in the past. Herein, we report the design, synthesis, and application of a novel mesh-adjustable molecular sieve (MAMS-1) that possesses an infinite number of mesh sizes. MAMS-1 is based on a metal–organic framework (MOF), compounds known for their dynamic porous properties. However, the concept of a MAMS has never appeared in the literature prior to the present work. MAMS-1 represents a MOF-based MS whose mesh can be adjusted continuously. The mesh range of MAMS-1 falls between 2.9 and 5.0 5, which covers the size range of almost all commercially important gas separations. When the temperature is precisely controlled, any mesh size within this range can be accurately attained. Gas separations such as those of N2/O2 and N2/CH4, which are normally difficult to achieve, are readily attainable by using MAMS-1. In principle, by precise temperature control, any two gases with a size difference can be separated by a MAMS. MOFs have attracted a great deal of attention because of their unique structures 7] and potential applications in catalysis, separation, and gas storage. In particular, flexible MOFs have caught enormous attention lately. Numerous studies have indicated that the key to constructing a flexible MOF lies in the utilization of weak interactions, such as hydrogen bonding, p–p stacking, and hydrophobic interaction, in addition to strong covalent and coordinative bonding. Flexible MOFs based on hydrogen bonding have been widely studied, but those originating from p–p stacking and hydrophobic interaction have rarely been explored. To make a MAMS, two factors must be taken into account: the material must have permanent porosity to hold gas molecules, and the pores must be flexible. The former usually requires strong bonds, while the latter implies weak interactions in the framework. These two seemingly irreconcilable prerequisites for a MAMS can be met simultaneously by using a graphitic structure, in which atoms in each layer are connected covalently but the layers are held together by weak interactions. One approach to such a graphitic MOF is to apply an amphiphilic ligand that consists of hydrophobic and hydrophilic ends, similar to a surfactant, but with the hydrophilic end functionalized. The functional group at the hydrophilic end of the ligand will bind metal ions/clusters, and the structure will propagate into a 2D layer. Two layers of ligands will sandwich a metal-ion/cluster layer, thus giving rise to a trilayer, and these trilayers will pack through van der Waals interaction. The ligand adopted for the aforementioned purposes is 5tert-butyl-1,3-benzenedicarboxylate (bbdc), which was previously used in our laboratory to build a micelle-like cuboctahedral cage to adjust the solubility of a 24-molybdenum cluster. Recently, it was also used in a zinc microporous MOF. In fact, solvothermal reaction between H2(bbdc) and Ni(NO3)2 in H2O/ethylene glycol in a Teflon-lined autoclave afforded such a graphitic structure, [Ni8(5-bbdc)6(m3-OH)4] (designated MAMS-1 for convenience). Desolvated MAMS1 demonstrates temperature-induced molecular-gating effects in which the size of the gates can be tuned continuously from 2.9 to 5.0 5 for the first time. Commercially relevant gas separations, such as those of H2/N2, H2/CO, N2/O2, N2/CH4, CH4/C2H4, and C2H4/C3H6, can be achieved by MAMS-1. In principle, by precise temperature control, any mesh size within this range can be achieved. In fact, all the pairs of gases listed above have been separated by using MAMS-1. Single-crystal X-ray analysis revealed that MAMS-1 contains an octanickel [Ni8(m3-OH)4] cluster as one of the two secondary building units (SBUs; Figure 1a), the other being the bbdc ligand. The eight octahedral Ni atoms are divided into four pairs by a twofold axis through the center of the cluster. Ni1 binds five carboxylate O atoms from four bbdc ligands and one m3-OH group. Ni2 is coordinated by three carboxylate O atoms and three m3-OH groups. Ni3 is bound to four carboxylate O atoms, one m3-OH group, and an aqua [*] S. Ma, Dr. D. Sun, Dr. X.-S. Wang, Prof. Dr. H.-C. Zhou Department of Chemistry and Biochemistry Miami University Oxford, OH 45056 (USA) Fax: (+01)513-529-8091 E-mail: zhouh@muohio.edu

Gas separation type showerhead

Abstract: Provided is a gas separation type showerhead for effective energy supply. The gas separation type showerhead includes: a gas supply module to which a first gas and a second gas are separately supplied; a gas separation module in which the supplied first and second gases are separately dispersed; and a gas injection module which is a multi-hollow cathode having a plurality of holes and in which the first and second gases separately dispersed are ionized in the holes to be commonly dispersed.

Microporous metal-organic frameworks with high gas sorption and separation capacity

Abstract: The design, synthesis, and structural characterization of two microporous metal-organic framework structures, [M(bdc)(ted)0.5]·2DMF-0.2H 2 O (M=Zn (1), Cu (2); H2bdc=1,4-benzenedicarboxylic acid; ted=triethylenediamine; DMF: N,N-dimethylformamide) is reported. The pore characteristics and gas sorption properties of these compounds are investigated at cryogenic temperatures, room temperature, and higher temperatures by experimentally measuring argon, hydrogen, and selected hydrocarbon adsorption/desorption isotherms. These studies show that both compounds are highly porous with a pore volume of 0.65 (1) and 0.52 cm 3 g -1 (2). The amount of the hydrogen uptake, 2.1 wt % (1) and 1.8 wt % (2) at 77 K (1 atm; 1 atm =101 325 Pa), places them among the group of metal-organic frameworks (MOFs) having the highest H 2 sorption capacity. [Zn(bdc)(ted) 0.5 ]·2 DMF·0.2 H 2 O adsorbs a very large amount of hydrocarbons, including methanol, ethanol, dimethylether (DME), n-hexane, cyclohexane, and benzene, giving the highest sorption values among all metal-organic based porous materials reported to date. In addition, these materials hold great promise for gas separation.

Industrial Gas Handbook: Gas Separation and Purification

Abstract: Drawing on Frank G. Kerry's more than 60 years of experience as a practicing engineer, the Industrial Gas Handbook: Gas Separation and Purification provides from-the-trenches advice that helps practicing engineers master and advance in the field. It offers detailed discussions and up-to-date approaches to process cycles for cryogenic separation of

Scalable Fabrication of Carbon Nanotube/Polymer Nanocomposite Membranes for High Flux Gas Transport

Abstract: We present a simple, fast, and practical route to vertically align carbon nanotubes on a porous support using a combination of self-assembly and filtration methods. The advantage of this approach is that it can be easily scaled up to large surface areas, allowing the fabrication of membranes for practical gas separation applications. The gas transport properties of thus constructed nanotube/polymer nanocomposite membranes are analogous to those of carbon nanotube membranes grown by chemical vapor deposition. This paper shows the first data for transport of gas mixtures through carbon nanotube membranes. The permeation of gas mixtures through the membranes exhibits different properties than those observed using single-gas experiments, confirming that non-Knudsen transport occurs.

Solvent properties of functionalized ionic liquids for CO2 absorption

Abstract: Ionic liquids can be used as solvents for gas absorption operations in order to improve the process economy and general efficiency of gas separations. This work investigates solvent properties of ionic liquids and compares them to amine solutions used for absorption of carbon dioxide (CO2). The CO2 solubility into six different room temperature ionic liquids (RTILs) was measured at temperatures between 298 K and 343 K and pressures up to about 1 MPa. The RTILs used were: [bmim]+[BF4]−, [bmim]+[DCA]−, and four imidazolium-based ionic liquids paired with [DCA] and [BF4], in which the cation was functionalized with either a primary, tertiary amine or a hydroxyl group. The density, viscosity and surface tension of the studied RTILs were measured at temperatures ranging from 293 K up to 363 K. The results showed that CO2 absorption behaviour was influenced by the functionalized chains appended to the RTILs cation. A chemical enhancement of the CO2 absorption was observed when functionalized RTILs were used as absorption solvents. It was possible to increase the ionic liquid volumetric gas load almost threefold by attaching functional groups to the ionic liquid, whereas for the traditional amine solutions the maximum gas load is stoichiometrically limited.

SO2 gas separation using supported ionic liquid membranes.

Abstract: Measurements of permeability of sulfur dioxide (SO2) in five imidazolium-based ionic liquids supported on the polyethersulfone microfiltration membranes at temperatures from 25 to 45 °C and atmospheric pressure indicate that under the same conditions, the SO2 selectivity of separations using supported ionic liquid membranes are 9−19 times that of CO2.

Matrimid®/MgO mixed matrix membranes for pervaporation

Abstract: For the first time, porous Magnesium oxide (MgO) particles have been applied to generate mixed matrix membranes (MMM) for the dehydration of iso-propanol by pervaporation. A modified membrane fabrication procedure has been developed to prepare membranes with higher separation efficiency. FESEM and DSC characterizations confirm that the MMMs produced have intimate polymer/particle interface; the nanosize crystallites on MgO surface may interfere with the polymer chain packing and induce chains rigidification upon the particle surface. It is observed that Matrimid 1 / MgO MMMs generally have higher selectivity, but lower permeability relative to the neat Matrimid 1 dense membrane. The highest selectivity is obtained with MMM containing 15 wt. % MgO. The selective sorption and diffusion of water in the MgO particles, and the polymer/particle interface properties combine to lead to the earlier phenomena. The investigation on the effect of feed water composition on the pervaporation performance reveals that the addition of MgO can show the selectivity-enhancing effects if the feed water concentration is lower than 30 wt. %. In the dehydration of isopropanol aqueous solution with 10 wt. % water, the selectivity of the MMMs is around 2,000, which is more than twice of 900 of neat polymeric membrane. This makes MMMs extremely suitable for breaking the azeotrops of water/iso-propanol. Gas permeation tests are also conducted using O2 and N2 to determine the microscopic structure of the MMMs, and to investigate the relationship between pervaporation and gas separation performance. 2007 American Institute of Chemical Engineers AIChE J, 53: 1745–1757, 2007

Integrated vacuum absorption steam cycle gas separation

Abstract: Methods and systems for separating a targeted gas from a gas stream emitted from a power plant. The gas stream is brought into contact with an absorption solution to preferentially absorb the targeted gas to be separated from the gas stream so that an absorbed gas is present within the absorption solution. This provides a gas-rich solution, which is introduced into a stripper. Low pressure exhaust steam from a low pressure steam turbine of the power plant is injected into the stripper with the gas-rich solution. The absorbed gas from the gas-rich solution is stripped in the stripper using the injected low pressure steam to provide a gas stream containing the targeted gas. The stripper is at or near vacuum. Water vapor in a gas stream from the stripper is condensed in a condenser operating at a pressure lower than the stripper to concentrate the targeted gas. Condensed water is separated from the concentrated targeted gas.

Gas permeation properties of polyamide membrane prepared by interfacial polymerization

Abstract: Interfacial polymerization technique has been widely employed to prepare reverse osmosis (RO) and nanofiltration (NF) membranes. The present study explores the possibility of preparing a polyamide membrane by interfacial polymerization and its utilization for the separation of CO2 and H2S from CH4. A novel ultraporous substrate of polysulfone (PSF) was prepared by phase inversion technique from a solution containing 18% PSF and 4% propionic acid in dimethyl formamide (DMF) solvent. Thin film composite (TFC) polyamide membrane was synthesized on PSF substrate from the reaction between meta-phenylene diamine in an aqueous media and isophthaloyl chloride in hexane. The membrane prepared was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) to study intermolecular interactions, crystallinity, thermal stability and surface morphology, respectively. Gas permeabilities of pure CO2, H2S, CH4, O2, and N2 gases were measured using the indigenously built permeation cell incorporated into a high-pressure gas separation manifold. At the feed pressure of 1 MPa, the membrane exhibited permeances of 15.2 GPU for CO2 and 51.6 GPU for H2S with selectivities of 14.4 and 49.1 for CO2/CH4 and H2S/CH4 systems, respectively. The observed N2 permeance of 0.95 GPU was close to that of CH4. The corresponding O2 permeance was 5.13 GPU with a reasonably high O2/N2 selectivity of 5.4. The effect of feed pressure on polyamide membrane performance was examined. Further, molecular dynamics (MD) simulations were employed to compute the cohesive energy density (CED), solubility parameter (δ) and sorption of CO2, H2S, CH4, O2, and N2 gases in polyamide membrane to corroborate theoretical study with experimentally determined gas transport properties.