Adsorption equilibria of alkane-α, ω-diols (propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, and hexane-1,6-diol) from aqueous solution onto an all-silica zeolite of the type mordenite framework inverted (MFI, also known as silicalite-1) are obtained by simulations and experiments at T = 323 K and also for pentane-1,5-diol (C5) at 348 and 383 K. After an initial slow rise, isotherms at T = 323 K exhibit steep changes in loading, reaching saturation at 10, 9, 8, and 7 molec/uc as the number of carbon atoms of the diols increases from 3 to 6. The abrupt change in loading corresponds to a minimum in the free energy of adsorption (from vapor to zeolite) that is associated with a rapid rise in the number of hydrogen bonds per sorbate molecule due to the formation of large clusters. For C5 at low loading, the centers-of-mass primarily occupy the channel intersections with oxygens oriented along the straight channels where intermolecular hydrogen bonds are formed. At saturation loading, the C5 centers-of-mass instead occupy the straight and zig-zag channels, and nearly all C5 molecules are involved in a percolating hydrogen-bonding network (this also occurs for C6). With increasing temperature, the C5 isotherm decreases in steepness as the minimum in free energy of adsorption decreases in depth and a less-ordered structure of the adsorbed molecules results in a lower number of diol-diol hydrogen bonds. However, the C5 isotherm does not shift significantly in concentration of the adsorption onset, as the free energies of solvation and adsorption increase by similar and compensating amounts. At T = 323 and 348 K, the steep change for the C5 adsorption isotherm is found to be a phase transition (as indicated by a bimodal distribution of unit cell occupancies at intermediate loading) from a less-dense phase with only small hydrogen-bonded clusters to an ordered solid phase with loadings of 8 molec/uc. At T = 383 K, the sorbates are less ordered, the distribution of occupancies becomes unimodal at intermediate loading, and the loading rises more gradually with concentration. Several different enhanced sampling methods are utilized for these simulations.

direct synthesis of high-aspect-ratio microporous zeolite nanosheets and the use of such nanosheets in separation membranes are described.

b‐oriented silicalite‐1 membranes on porous silica supports were synthesized using gel‐free secondary growth. The porous silica supports were made by pressing crushed quartz fibers followed by sintering and polishing, and further modified by slip‐coating three layers of Stöber silica particles (1000, 350, and 50 nm). The b‐oriented seed layers were prepared by rubbing silicalite‐1 particles (2 μm × 0.8 μm × 3 μm along a‐, b‐, and c‐axis, respectively) after depositing a polymeric layer on the support. After silicalite‐1 seed deposition, a final coating of spherical silica particles was applied. Well‐intergrown, μm‐thick, b‐oriented membranes were obtained, which, after calcination, exhibited ethanol permselectivity in ethanol/water mixture pervaporation. At 60°C and for ∼5 wt % ethanol/water mixtures, the best membrane exhibited overall pervaporation separation factor of 85 (corresponding to membrane intrinsic selectivity of 7.7) and total flux of 2.1 kg/(m2·h). This performance is comparable to the best performing MFI membranes reported in the literature. © 2015 American Institute of Chemical Engineers AIChE J, 62: 556–563, 2016

The latest developments in zeolite membranes are reviewed, with an emphasis on the synthesis techniques, including seed assembly and secondary growth methods. This review also discusses the current industrial applications of zeolite membranes, the feasibility of their use in membrane reactors and their hydrothermal stability. Finally, zeolite membranes are compared with metal-organic framework (MOF) membranes and the latest advancements in MOF and mixed matrix membranes are highlighted.

Process design and techno-economic evaluation of glucose isomerization on Sn-Beta require reliable catalytic reaction rate expressions and kinetic constants. Here, the isomerization of sugars (glucose, fructose and mannose) in water using Sn-Beta is investigated at various temperatures ranging from 70 to 130°C. It is shown that the catalyst deactivates during the course of the reaction. A phenomenological model that describes the isomerization reaction in the presence of deactivation is developed and the corresponding kinetic constants are estimated from experimental data.

Spatially well-distributed copper-zinc oxides supported on mesoporous silica (SBA-15 and commercial silica gel) showed high adsorption capacity for hydrogen sulfide (as high as 80 mgS/g(sorbent)) and stability during cyclic adsorption-regeneration process. (C) 2014 Elsevier Inc. All rights reserved.

Journal Article Probing Structure-Property Relationship of Active Metal Nanoparticles on Mesoporous Silica Sorbent Get access Prashant Kumar, Prashant Kumar Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, MN Search for other works by this author on: Oxford Academic Google Scholar Jong Seok Jeong, Jong Seok Jeong Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, MN Search for other works by this author on: Oxford Academic Google Scholar Bahman Elyassi, Bahman Elyassi Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, MN Search for other works by this author on: Oxford Academic Google Scholar Nafiseh Rajabbeigi, Nafiseh Rajabbeigi Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, MN Search for other works by this author on: Oxford Academic Google Scholar Michael Tsapatsis, Michael Tsapatsis Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, MN Search for other works by this author on: Oxford Academic Google Scholar K Andre Mkhoya K Andre Mkhoya Department of Chemical Engineering & Materials Science, University of Minnesota, Minneapolis, MN Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 20, Issue S3, 1 August 2014, Pages 464–465, https://doi.org/10.1017/S1431927614004048 Published: 27 August 2014

Steam stability of MCM-22 and its all siliceous analogue, ITQ-1, with MWW structure was investigated in a mixture of water vapor and nitrogen (95 mol% H2O, 5 mol% N-2) at 10 barg pressure and two different temperatures of 600 degrees C and 350 degrees C for a period of 84 days. Further, the effect of calcination temperature and silicon tetrachloride (SiCl4) treatment on the steam stability of ITQ-1 was studied. Behavior of these zeolites was monitored in 21-day intervals using XRD, SEM, TEM, Si-29 solid-state NMR, nitrogen and argon adsorption analyses. It was found that structural defects adversely affected the steam stability of the zeolites but SiCl4 treatment was effective to enhance the zeolite resistance to water vapor attack. It was observed that long-term steaming can generate holes in the crystals along with some amorphization; however, it also generated highly homogeneous short range order in the crystals. (C) 2014 Elsevier Inc. All rights reserved.

Highly crystalline exfoliated MFI-nanosheets can pave the way for large-scale deployment of sub-500-nm zeolite membranes due to their processing and packing advantages. Exfoliated MFI-nanosheets prepared by melt compounding contain a large amount of polymer and unexfoliated particles which are detrimental to the fabrication of ultrathin zeolite membranes. Complete removal of polystyrene from the nanosheet suspension in toluene is demonstrated by centrifugation of the suspension across chlorobenzene as confirmed by thermogravimetric analysis (TGA) data and transmission electron microscopy (TEM) images. Rate-zonal centrifugation in a nonlinear density gradient fractionated exfoliated MFI-nanosheets from unexfoliated particles. The purified nanosheets were highly crystalline as indicated by high-resolution TEM (HRTEM) and electron diffraction (ED). Coating of purified MFI-nanosheets on a smooth α- alumina support, fabricated by filtration of α- alumina suspension, led to a compact, b-oriented, 80-nm-thick film. A mild hydrothermal treatment of the film led to a 200-nm-thick membrane, which demonstrated molecular sieving properties. © 2013 American Institute of Chemical Engineers AIChE J , 59: 3458–3467, 2013

Hydrogen-permselective asymmetric silicon carbide (SiC) membranes were prepared in this study by incorporating highly porous SiC nanofibers into the membrane structure using a sacrificial interlayer-based technique. The resulting membranes were characterized with permeation studies, nitrogen adsorption experiments, and electron microscopy analysis. Their characteristics were compared with those of SiC membranes prepared with the same approach but making use, instead, of fine, nonporous SiC powders as fillers.

Thin zeolite films are attractive for a wide range of applications, including molecular sieve membranes, catalytic membrane reactors, permeation barriers, and low-dielectric-constant materials. Synthesis of thin zeolite films using high-aspect-ratio zeolite nanosheets is desirable because of the packing and processing advantages of the nanosheets over isotropic zeolite nanoparticles. Attempts to obtain a dispersed suspension of zeolite nanosheets via exfoliation of their lamellar precursors have been hampered because of their structure deterioration and morphological damage (fragmentation, curling, and aggregation). We demonstrated the synthesis and structure determination of highly crystalline nanosheets of zeolite frameworks MWW and MFI. The purity and morphological integrity of these nanosheets allow them to pack well on porous supports, facilitating the fabrication of molecular sieve membranes.

Silicon carbide nanofibers were fabricated by immersion of anodized aluminum oxide templates in allyl-hydridopolycarbosilane (AHPCS) solutions, and subsequent pyrolysis at 750°C. The technique offers better control on the final morphology of the nanofibers, hence resolving some of the fabrication difficulties encountered in the past. The effect of polystyrene – the pore former – on the formation of the nanofibers in the confined channels of the templates was studied. Low concentrations of polystyrene in the AHPCS solution resulted in ellipsoidal hollow regions inside the SiC nanofibers, whereas high concentrations resulted in the formation of some hollow fibers. The fibers prepared by adding polystyrene possessed higher surface areas than those without polystyrene. The morphology and surface area of the SiC nanofibers were studied using the SEM, TEM, and BET analyses.

A novel method is presented based on the use of sacrificial interlayers for the preparation of nanoporous silicon carbide membranes. It involves periodic and alternate coatings of polystyrene sacrificial interlayers and silicon carbide pre-ceramic layers on the top of slip-casted tubular silicon carbide supports. Membranes prepared by this technique exhibit single gas ideal separation factors of helium and hydrogen over argon in the ranges 176–465 and 101–258, respectively, with permeances that are typically two to three times higher than those of silicon carbide membranes prepared previously by the more conventional techniques. Mixed-gas experiments with the same membranes indicate separation factors as high as 117 for an equimolar H2/CH4 mixture. We speculate that the improved membrane characteristics are due to the sacrificial interlayers filling the pores in the underlying structure and preventing their blockage by the pre-ceramic polymer. The new method has good promise for application to the preparation of a variety of other inorganic microporous membranes.

SiC microporous membranes were prepared by the pyrolysis of thin allyl-hydridopolycarbosilane (AHPCS) films coated, using a combination of slip-casting and dip-coating techniques, on tubular silicon carbide macroporous supports. Combining slip-casting with dip-coating significantly improved the reproducibility in preparing high quality membranes. The membranes prepared, so far, exhibited an ideal H2/CO2 selectivity in the range of 42–96, and a H2/CH4 ideal selectivity in the range of 29–78. Separation factors measured with the same membranes, using equimolar binary mixtures of H2 in CO2 and H2 in CH4, were similar to the ideal selectivity values. Steam stability experiments with the membranes lasting 21 days, using an equimolar flowing mixture of He/H2O at 200°C, indicated some initial decline in the permeance of He, after which the permeance became stable at these conditions.