Kerry M. Dooley

Effects of pretreatments on state of gallium and aromatization activity of gallium/ZSM-5 catalysts

Abstract Additional evidence is presented for the role of gallium reduction in preparing active Ga/ZSM-5 catalysts for alkane aromatization. The gallium in ion-exchanged ZSM-5, both with and without additional Ga 2 O 3 , can be reduced to Ga + , in the former case up to a limit determined by the number of anionic framework sites. An ion-exchanged, reduced catalyst exhibits similar redox behavior, and is as active for propane aromatization, as catalysts prepared from purely physical mixtures of Ga 2 O 3 and H-ZSM-5. Although reduction generates dispersed, active gallium species in zeolite channels, it is shown that for ethane dehydrogenation to aromatics the reduced (with hydrogen) Ga/ZSM-5 catalysts are not as active or selective as are materials which have been substantially reoxidized either by air or by traces of oxygen in inert gases. A combination of thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) studies has been used to confirm that rapid reoxidation takes place at 550°C. However, the reoxidation does not regenerate β-Ga 2 O 3 , but rather a higher energy, dispersed Ga 3+ which appears to be optimal for production of aromatics from ethane. This form of Ga 3+ is stable under reaction conditio

Gallium-loaded zeolites for light paraffin aromatization : evidence for exchanged gallium cation active centers

Abstract It is shown that certain metal-loaded zeolites (e.g., Ga-MFI) initially prepared as separate metal-containing and zeolite phases are reducible, resulting in solid-state transfer of the metal to the zeolite. The final material is similar to those initially prepared as ‘unsegregated’ by methods such as aqueous impregnation. Reduction occurs either through appropriate pretreatment or onstream in certain hydrocarbon reactions. First, preparation methods leading to one or the other type of material are examined. Then it is shown that reduced catalysts give far higher ratios of dehydrogenation to cracking rates (for alkanes) than either segregated or unsegregated but unreduced systems. The product distributions of the propane reaction at low partial pressure and low conversion are also reviewed, and new data presented for unsegregated, reduced catalysts. There are great differences in the distribution obtained using reduced 1/1 metal/A1 catalysts from corresponding distributions for the H-form zeolites or for segregated systems. The differences suggest a mechanism which may be entirely independent of catalysis by protons.

Ignition and Combustion of Boron Nanoparticles in Ethanol Spray Flame

Biofuels such as ethanol have lower energy density than conventional petroleum-based fuels; therefore, enhancing their energy density by addition of higher-energy-density components is an attractive option. Boron is considered to be a good choice as a fuel additive because it has almost the highest volumetric heating value among potentially suitable additives. The present study deals with an experimental investigation of boron combustion in an ethanol spray flame. Measurements have been made of the emission of the intermediate suboxide BO2 using spectroscopy and chemiluminescence imaging with interference filters. The size, surface structure, and chemical composition of the injected boron nanopowders were characterized by x-ray diffraction, porosimetry, thermogravimetric analysis, and scanning electron microscopy. The postburn particles were also characterized by x-ray diffraction and thermogravimetric analysis. The effects of boron nanoparticles on the hydrocarbon combustion in terms of heat releasewere determined usingCHchemiluminescence and temperaturemeasurements. The chemiluminescence and spectroscopic signatures indicate that boron underwent combustion and simultaneously increased the CH-radical emission and flame temperatures. The x-ray diffraction and thermogravimetric analysis measurements of the particles collected at the exhaust indicate that complete conversion of the boron was achieved. The effect of particle size on the combustion of the boron nanoparticles was examined, comparing small commercial particles to sintered particles. A demonstrable size effect was observed with the larger particles, which exhibited their initial BO2 signatures at distances further above the dump plane, indicating greater ignition delay times.

A facile approach to fabricate porous nanocomposite gels based on partially hydrolyzed polyacrylamide and cellulose nanocrystals for adsorbing methylene blue at low concentrations

Porous nanocomposite gels were fabricated by a facile method consisting of the electrospinning and subsequent heat treatment based on partially hydrolyzed polyacrylamide (HPAM) of ultra-high molecular weight, with cellulose nanocrystals (CNCs) as crosslinker. The effects of three electrospinning parameters (i.e., solution concentration, composition of solvent mixture, and CNC loading level) on morphology and diameter of electrospun fibers were systematically investigated. The swelling properties of porous gels and their application in the removal of methylene blue dye (as a compound representative of contaminants) were evaluated. Electrospun fiber morphologies without beads, branches, and ribbons were achieved by optimizing the electrospinning solutions. The thermal crosslinking between HPAM and CNCs was realized through esterification, rendering the product nanocomposite membranes insoluble in water. Electrospun fibers of approximately 220 nm in diameter comprised the 3D porous nanocomposite gels, with porosity greater than 50%. The porous nanocomposite gels displayed a rapid swelling rate and an efficient adsorption capacity in removing methylene blue at low concentrations from aqueous solutions.

Thermal analysis of adsorbed propanamines for the characterization of GaMFI zeolites

Gallium-containing forms of MFI zeolite have been subjected to adsorption of 1- and 2-propanamine, and the results of subsequent thermal treatment have been analyzed and compared to literature reports for propanamines adsorbed on proton forms of MFI. Zeolitic gallium cations show completely different behavior from zeolitic protons, including a propanamine decomposition mechanism which is different from Hofmann elimination. In this mechanism NH3 is desorbed at temperatures as much as 160 K below that of HMFI. Major differences in the decomposition chemistry of the two amines were also observed when Ga cations were present.

Supercritical carbon dioxide extraction of a phenolic mixture from an aqueous waste stream

Supercritical C02 can be used to remove contaminants from aqueous streams. Generally, the literature reports only pure contaminant distribution coefficients (K values). In a more realistic situation, however, more than one contaminant can be expected to be present in water. In order to study the effect of cosolubility, we have measured the distribution coefficients when a mixture of four contaminants — phenol, m-cresol, p-chlorophenol, and benzene — were present in water. No effect of cosolubility on the distribution coefficients has been found for this system. However, these results along with recently available data1 for a different mixture of contaminants have been analyzed to show that both strong solute-solute interactions and high relative volatilities need to act together if one contaminant is to act as an entrainer ano another contaminant.

Proton‐poor, gallium‐ and indium‐loaded zeolite dehydrogenation catalysts

The catalytic (propane dehydrocyclization) and reduction behaviors of near 1:1 cation (Ga, In)/framework‐Al MFI zeolites were examined under conditions where the materials were initially either in fully protonated or zero−protonated states. Reductions at appropriate temperatures proceeded up to ∼100% exchange of protons for reduced univalent cations. Further aqueous exchange of alkali (K+>) or alkaline earth (Ba2+) cations increased the selectivity for dehydrogenation reactions at little or no sacrifice in overall activity.

Measurement and modeling of supercritical carbon dioxide extraction of phenol from water

Abstract An equilibrium flow apparatus for measuring phase equilibria in systems containing liquids and super-critical fluids is described. Saturated vapor and liquid compositions and K values are determined with this apparatus for the ternary system of CO2, phenol, and water. The results are accurately modeled using a perturbation theory-based equation-of-state (EOS) — the Carnahan-Starling-DeSantis-Redlich-Kwong (CSDRK) EOS. Differences with K values previously reported in the literature are discussed.

Algae attachment on carbonated cements in fresh and brackish waters - preliminary results

Abstract In order to evaluate the usefulness of different cements as substrates for artificial reefs, we have performed preliminary tests of both conventional and pH-neutral molded cements for attachment of microalgae populations. Neutrality was achieved by molding in the presence of carbon dioxide. It was verified through analysis of carbonate and hydroxide content and measurement of contact pH. Algae attachment tests were conducted at both brackish and freshwater conditions. We have found pH-neutral materials to which microalgae readily attach. These include silica-enriched (pozzolanic) cements, but also blast-furnace slag and fly ash, which are also silica-rich, and mixtures of these with Portland cement. In most cases the pH-neutralized, carbonated cements outperformed the conventional materials in rate of algae attachment, in some cases by wide margins. The high pH, conventional cements preferentially attached barnacles in brackish water. There was no evidence of weight loss in any of the test specimens.

Paraffin isomerization and disproportionation catalyzed by Pd-loaded fluorided mordenites

Fluorided, Pd-loaded ({approximately}1.1 wt% Pd) mordenites, with 8, 12, 28, and 100% replacement of {minus}OH groups, were synthesized from H-mordenite. These materials were characterized by IR, XRD, SEM, the adsorption of N{sub 2} and 2-methylpentane, and their activity for paraffin reactions. Except in the case of 100% nominal fluoridation, the fluorided mordenites retained their crystallinity, displayed enhanced acid strengths and adsorption capacities for paraffinic hydrocarbons, and were catalytically active (at 533-573 K and {approximately}0.1 bar hydrocarbon partial pressure) for the transformation of n-butane to isobutane and products of both higher and lower molecular weights. The presence of a small amount of isobutene in the feed greatly accelerated these transformations and increase yields to the pentane isomers. The primary reactions were apparently acid-catalyzed, with the role of Pd confined to activity maintenance. The mildly fluorided zeolites in some cases proved more active overall than the parent zeolites H-mordenite and Pd-mordenite and were especially selective for the formation of the pentane isomers, apparently through a combination of disproportionation reactions and secondary alkylation reactions involving light hydrocarbon primary products.