Publications

Abstract not provided.

In this study the separation capabilities of silicalite and the titanosilicate molecular sieve ETS-10 for binary mixtures of hydrogen/methane and hydrogen/carbon dioxide were evaluated by equilibrium molecular simulation techniques. This is the first molecular simulation study that presents mixture adsorption isotherms of these components in silicalite and ETS-10, and determines selectivities based on the simulation results. Grand Canonical Monte Carlo (GCMC) simulations were carried out for pure components and binary mixtures for hydrogen/carbon dioxide and hydrogen/methane at 298 K to determine pure and mixture adsorption isotherms. The pure and mixture adsorption isotherms were calculated up to pressures of approximately 2000 bar. The results of this study indicate that the separation of hydrogen from methane or from carbon dioxide in silicalite would be successful, since hydrogen in a 50% bulk mixture does not adsorb unless the pressure is very high, on the order of 500 bar. In contrast, in ETS-10, hydrogen in a 50% bulk mixture adsorbs at a pressure near 10 bar. Simulations of adsorption in ETS-10 show at low, intermediate and high pressures a higher selectivity for the separation of carbon dioxide from hydrogen than the separation of methane from hydrogen. Simulations of adsorption in silicalite show a higher selectivity for the separation of carbon dioxide from hydrogen than the methane/hydrogen separation at high pressures only. Analysis of isosteric heat of adsorption information indicates that silicalite is energetically homogeneous with the adsorbates. In contrast, ETS-10 has energetic heterogeneity, as shown by the decrease of the heat of adsorption with increasing loading. © 2006 Elsevier B.V. All rights reserved.

MFI zeolite membranes have been synthesized on tubular α-alumina substrates to investigate the separation of p-xylene (PX) from m-xylene (MX) and o-xylene (OX) in binary, ternary, and simulated multicomponent mixtures in wide ranges of feed pressure and operating temperature. The results demonstrate that separation of PX from MX and OX through the MFI membranes relies primarily on shape-selectivity when the xylene sorption level in the zeolite is sufficiently low. For an eight-component mixture containing hydrogen, methane, benzene, toluene, ethylbenzene, PX, MX, and OX, a PX/(MX + OX) selectivity of 7.71 with a PX flux of 6.8 × 10-6 mol/(m2 s) was obtained at 250 °C and atmospheric feed pressure. The addition of a small quantity of nonane to the multicomponent mixture caused drastic decreases in the fluxes of aromatic components and the PX separation factor because of the preferential adsorption of nonane in the zeolite channels. The nanoscale intercrystalline pores also caused serious decline in the PX separation factor. A new method of online membrane modification by carbonization of 1,3,5-triisopropylbenzene in the feed stream was found to be effective for reducing the intercrystalline pores and improving the PX separation. © 2006 Elsevier B.V. All rights reserved.

Abstract not provided.

Alkylation reactions of benzene with propylene using heterogeneous catalysts H+-β zeolite, MCM-22, and ZSM-5 were studied for their affinity for cumene production. This work focused on the gas-phase reaction using different crystalline catalysts at several temperatures and amounts of reactants using both batch and continuous fixed-bed reactors. The properties of baseline commercial H+ -β catalysts versus versions modified with Ga, La, and Pt were studied. Quantitative analysis of product mixture was performed by gas chromatography. For the batch reactor, β-zeolite produced the highest cumene yield and selectivity of 72% and 92%, respectively, at 225°C. At this temperature, a benzene:propylene dilution of 7:1 molar ratio was the optimum. For the continuous system, cumene production is favored at lower space velocities, higher benzene-to-propylene ratio, and temperatures close to 225°C. Ga modification of the H+-β zeolite significantly enhanced cumene yield in the continuous fixed-bed reactor at 225°C, from 27% of the unmodified β-zeolite to 36% for the Ga-modified one. The life span of modified β-catalysts was studied in the fixed-bed reactor for the first eight hours of reaction. Copyright © Taylor & Francis Group, LLC.

Abstract not provided.

Materials in the La{sub 0.1}Sr{sub 0.9}Co{sub 1-y}MnyO{sub 3-{delta}} (LSCM) family are potentially useful as ceramic membranes for high-temperature oxygen separations. A series of LSCM samples was synthesized by solid state methods and characterized by powder X-ray diffraction, thermogravimetric analysis, and four-probe conductivity. The materials were indexed in the cubic Pm-3m space group. TGA data implied that LSCM can reversibly absorb and desorb oxygen versus temperature and partial oxygen pressure, while powder diffraction data showed that the material maintained the cubic perovskite structure. Preliminary four-probe conductivity measurements signify p-type semiconducting behavior.

Abstract not provided.

The conclusions of this paper are: (1) Adsorption/desorption on bulk unmodified zeolites showed isoprene adsorbed by zeolite-L and n-pentane adsorbed by zeolite-Y and ZSM-5; (2) Bulk carbonization is used to passivate zeolite activity toward organic adsorption/decomposition; (3) Based on the bulk modified zeolite separation results, we have determined that the MFI type has the most potential for isoprene enrichment; (4) Modified MFI type membrane are jointly made by Sandia and the Univ. of Colorado. Separation experiments are performed by Goodyear Chemical; (5) Isoprene/n-pentane separations have been demonstrated by using both zeolite membranes and modified bulk zeolites at various temperatures on the Goodyear Pilot-scale unit; and (6) Target zeolite membrane separations values of 6.7% isoprene enrichment have been established by economic analysis calculations by Burns & McDonnell.

We have synthesized defect-free aluminosilicate and silicalite zeolite thin films supported on commercially available alpha and gamma alumina disk substrates. We have also built a permeation unit that can test both pure and mixed gases from room temperature to 250 C. Results indicate fluxes on the order of 10{sup -6} to 10{sup -7} mole/(m{sup 2}Pa sec) and excellent separation values for H{sub 2} or CO{sub 2}. For the Al/Si membrane: H{sub 2}/N{sub 2} {ge} 61, H{sub 2}/CO{sub 2} {ge} 80, H{sub 2}/CH{sub 4} = 7, CH{sub 4}/CO{sub 2} {ge} 11; for the TPA/Si membrane: H{sub 2}/N{sub 2} {ge} 61, H{sub 2}/CO{sub 2} {ge} 80, H{sub 2}/CH{sub 4} = 7, CH{sub 4}/CO{sub 2} {ge} 11. Our data show that we can use the adsorption ability plus the effective pore diameter of the zeolite to 'tune' the selectivity of the membrane. Another avenue of research is into bulk novel molecular sieve materials, with the goal of 'tuning' pore sizes to molecular sieving needs. A novel crystalline 12-ring microporous gallophosphate material is described.

Abstract not provided.

Abstract not provided.

A series of amorphous silicate materials with the general formula Na{sub x+2y}M{sub x}{sup 3+}Si{sub 1-x}O{sub 2+y}(M{sup 3+} = Al, Mn, Fe, Y) were studied. Samples were synthesized by a precipitation reaction at room temperature. The results indicate that the ion-exchange capacity (IEC) decreases as follows: Al > Fe > Mn > Y. Additionally, the IEC increases with increasing aluminum concentration. Structural studies show that the relative amount of octahedrally coordinated aluminum increases with increasing Al content, as does the total amount of AlO{sub 4} species increases. The data suggest that the IEC value of these amorphous aluminosilicates is dependent on the tetrahedrally coordinated aluminum. Regeneration of the Al-silicate with acetic acid does not decrease the IEC significantly.

Abstract not provided.

An environmentally friendly method and materials study for desalinating inland brackish waters (i.e., coal bed methane produced waters) using a set of ion-exchange materials is presented. This desalination process effectively removes anions and cations in separate steps with minimal caustic waste generation. The anion-exchange material, hydrotalcite (HTC), exhibits an ion-exchange capacity (IEC) of {approx} 3 mequiv g{sup -1}. The cation-exchange material, an amorphous aluminosilicate permutite-like material, (Na{sub x+2y}Al{sub x}Si{sub 1-x}O{sub 2+y}), has an IEC of {approx}2.5 mequiv g{sup -1}. These ion-exchange materials were studied and optimized because of their specific ion-exchange capacity for the ions of interest and their ability to function in the temperature and pH regions necessary for cost and energy effectiveness. Room temperature, minimum pressure column studies (once-pass through) on simulant brackish water (total dissolved solids (TDS) = 2222 ppm) resulted in water containing TDS = 25 ppm. A second once-pass through column study on actual produced water (TDS = {approx}11,000) with a high carbonate concentration used an additional lime softening step and resulted in a decreased TDS of 600 ppm.

Abstract not provided.

The enthalpies of formation of hydrotalcite-like phases containing Mg and Al and intercalated with NO{sub 3}{sup -}, Cl{sup -}, I{sup -}, ReO{sub 4}{sup -}, or CO{sub 3}{sup 2-} were determined using high-temperature oxide melt and room-temperature acid solution calorimetry. The relative stability of phases bearing the various anions was gauged by comparing the enthalpy of formation from the single-cation components ({Delta}{sub f}H{sup scc}). Trends relating {Delta}{sub f}H{sup scc} to the nature of intercalating anions (halides, NO{sub 3}{sup -}, and CO{sub 3}{sup 2-}) show small stabilization from the mechanical mixtures of single-cation components. The aim of this study was to relate the enthalpy of formation to the nature of interlayer bonding in hydrotalcite-like compounds (HTLCs) bearing various anions, to uncover trends in the relative aqueous solubilities of these phases. The entropy of formation of these compounds was estimated using an approximation based on third-law entropy measurements for the compound Mg{sub 0.74}Al{sub 0.26}(OH){sub 2}(CO{sub 3}){sub 0.13} {center_dot} 0.39H{sub 2}O which were performed in a previous study. This approximation for the third-law entropy was combined with the enthalpy data from our calorimetric measurements performed in this work in order to calculate the standard-state free energy of formation for the HTLCs. The solubility products for the compounds investigated in this study were calculated from these free energies of formation and were used in geochemical calculations. The results of these calculations support our previous hypothesis that carbonate-intercalated HTLCs are less soluble than phases bearing other anions such as nitrates and halides. We suspect that the solubilities of HTLCs bearing anions other than carbonate may correspond to the solubilities of single-cation phases bearing the same anions.

Efficient and environmentally sound methods of producing hydrogen are of great importance to the US as it progresses toward the H2 economy. Current studies are investigating the use of high temperature systems driven by nuclear and/or solar energy to drive thermochemical cycles for H2 production. These processes are advantageous since they do not produce greenhouse gas emissions that are a result of hydrogen production from electrolysis or hydrocarbon reformation. Double-substituted perovskites, A1-xSrxCo1-yBy O3-δ (A = Y, La; B = Fe, Ni, Cr, Mn) were synthesized for use as ceramic high-temperature oxygen separation membranes. The materials have promising oxygen sorption properties and were structurally robust under varying temperatures and atmospheres. Post-TGA powder diffraction patterns revealed no structural changes after the temperature and gas treatments, demonstrating the robustness of the material. The most promising material was the La0.1Sr0.9Co1-xMnx O3-δ perovskite. The oxygen sorption properties increased with increasing Mn doping.

The need for fresh water has increased exponentially during the last several decades due to the continuous growth of human population and industrial and agricultural activities. Yet existing resources are limited often because of their high salinity. This unfavorable situation requires the development of new, long-term strategies and alternative technologies for desalination of saline waters presently not being used to supply the population growth occurring in arid regions. We have developed a novel environmentally friendly method for desalinating inland brackish waters. This process can be applied to either brackish ground water or produced waters (i.e., coal-bed methane or oil and gas produced waters). Using a set of ion exchange and sorption materials, our process effectively removes anions and cations in separate steps. The ion exchange materials were chosen because of their specific selectivity for ions of interest, and for their ability to work in the temperature and pH regions necessary for cost and energy effectiveness. For anion exchange, we have focused on hydrotalcite (HTC), a layered hydroxide similar to clay in structure. For cation exchange, we have developed an amorphous silica material that has enhanced cation (in particular Na{sup +}) selectivity. In the case of produced waters with high concentrations of Ca{sup 2+}, a lime softening step is included.

Conclusions of this paper are: (1) Adsorption/desorption on bulk unmodified zeolites showed isoprene adsorbed by zeolite-L and n-pentane adsorbed by zeolite-Y and ZSM-5; (2) Bulk carbonization is used to passivate zeolite activity toward organic adsorption/decomposition; (3) Based on the bulk modified zeolite separation results, we have determined that the MFI type has the most potential for isoprene enrichment; (4) Modified MFI type membranes are jointly made by Sandia and the Univ. of Colorado. Separation experiments are performed by Goodyear Chemical; (5) Isoprene/n-pentane separations have been demonstrated by using both zeolite membranes and modified bulk zeolites at various temperatures on the Goodyear Pilot-scale unit; and (6) Target zeolite membrane separations values of 6.7% isoprene enrichment have been established by economic analysis calculations by Burns & McDonnell.

Abstract not provided.

Abstract not provided.

A family of microporous phases with compositions Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-x}(OH){sub x} {center_dot} H{sub 2}O (0 {le} x {le} 0.4) transform to Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-0.5x} perovskites upon heating. In this study, we have measured the enthalpies of formation of the microporous phases and their corresponding perovskites from the constituent oxides and from the elements by drop solution calorimetry in 3Na{sub 2}O {center_dot} 4MoO{sub 3} solvent at 974 K. As Ti/Nb increases, the enthalpies of formation for the microporous phases become less exothermic up to x = {approx}0.2 but then more exothermic thereafter. In contrast, the formation enthalpies for the corresponding perovskites become less exothermic across the series. The energetic disparity between the two series can be attributed to their different mechanisms of ionic substitutions: Nb{sup 5+} + O{sup 2-} {yields} Ti{sup 4+} + OH{sup -} for the microporous phases and Nb{sup 5+} {yields} Ti{sup 4+} + 0.5 V{sub O}** for the perovskites. From the calorimetric data for the two series, the enthalpies of the dehydration reaction, Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-x}(OH){sub x} {center_dot} H{sub 2}O {yields} Na{sub 2}Nb{sub 2-x}Ti{sub x}O{sub 6-0.5X} + H{sub 2}O, have been derived, and their implications for phase stability at the synthesis conditions are discussed.

This project will attempt to develop a new family of inorganic crystalline porous materials under IMF that will lead to improvement of energy efficiency and productivity via improved separations. Initially this project will be focused on materials for the separation of linear from branched hydrocarbons. However, it is anticipated that the results will provide the basis of knowledge to enable this technology to be applied toward additional hydrocarbon and chemical separations. Industrial involvement from Goodyear and Burns & McDonnell provides needed direction for solving real industrial problems, which will find application throughout the US chemical and petroleum industries.

There is a great need for robust, defect-free, highly selective molecular sieve (zeolite) thin film membranes for light gas molecule separations in hydrogen fuel production from CH{sub 4} or H{sub 2}O sources. In particular, we are interested in (1) separating and isolating H{sub 2} from H{sub 2}O and CH{sub 4}, CO, CO{sub 2}, O{sub 2}, N{sub 2} gases; (2) water management in PEMs and (3) as a replacement for expensive Pt catalysts needed for PEMs. Current hydrogen separation membranes are based on Pd alloys or on chemically and mechanically unstable organic polymer membranes. The use of molecular sieves brings a stable (chemically and mechanically stable) inorganic matrix to the membrane [1-3]. The crystalline frameworks have 'tunable' pores that are capable of size exclusion separations. The frameworks are made of inorganic oxides (e.g., silicates, aluminosilicates, and phosphates) that bring different charge and electrostatic attraction forces to the separation media. The resultant materials have high separation abilities plus inherent thermal stability over 600 C and chemical stability. Furthermore, the crystallographically defined (<1 {angstrom} deviation) pore sizes and shapes allow for size exclusion of very similarly sized molecules. In contrast, organic polymer membranes are successful based on diffusion separations, not size exclusion. We envision the impact of positive results from this project in the near term with hydrocarbon fuels, and long term with biomass fuels. There is a great need for robust, defect-free, highly selective molecular sieve (zeolite) thin film membranes for light gas molecule separations in hydrogen fuel production from CH{sub 4} or H{sub 2}O sources. They contain an inherent chemical, thermal and mechanical stability not found in conventional membrane materials. Our goal is to utilize those zeolitic qualities in membranes for the separation of light gases, and to eventually partner with industry to commercialize the membranes. To date, we have successfully: (1) Demonstrated (through synthesis, characterization and permeation testing) both the ability to synthesize defect-free zeolitic membranes and use them as size selective gas separation membranes; these include aluminosilicates and silicates; (2) Built and operated our in-house light gas permeation unit; we have amended it to enable testing of H{sub 2}S gases, mixed gases and at high temperatures. We are initiating further modification by designing and building an upgraded unit that will allow for temperatures up to 500 C, steady-state vs. pressure driven permeation, and mixed gas resolution through GC/MS analysis; (3) Have shown in preliminary experiments high selectivity for H{sub 2} from binary and industrially-relevant mixed gas streams under low operating pressures of 16 psig; (4) Synthesized membranes on commercially available oxide and composite disks (this is in addition to successes we have in synthesizing zeolitic membranes to tubular supports [9]); and (5) Signed a non-disclosure agreement with industrial partner G. E. Dolbear & Associates, Inc., and have ongoing agreements with Pall Corporation for in-kind support supplies and interest in scale-up for commercialization.