Thomas Stephen Farris

Calcined hydrotalcites for the catalytic decomposition of N2O in simulated process streams

Various hydrotalcite based catalysts were prepared for testing for the catalytic decomposition of N2O. CoAl, NiAl, Co/PdAl, Co/RhAl, and Co/MgAL substituted hydrotalcites and CoLaAl hydroxides offer very good activity at modest temperatures. Precalcination of these materials at ca. 450–500°C, which destroys the hydrotalcite phase, is necessary for optimum activity and life. For Co substituted hydrotalcites, the optimal ratio of Co/Al is 3.0. The temperature for 50% conversion of N2O of these calcined cobalt hydrotalcites is ca. 75°C lower than for the previous highly active Co-ZSM-5. These calcined cobalt hydrotalcite materials display sustained life at temperatures in excess of 670°C in an O2 rich, wet stream with high levels of N2O [10%]. Excess O2 does not seriously impact N2O decomposition, but the combination of both water vapor and O2 does reduce activity by ca. 50%.

Preparation of carbon molecular sieves, I. Two-step hydrocarbon deposition with a single hydrocarbon

Abstract A process is described for preparing a carbon molecular sieve that is suitable for the kinetic separation of gases, such as oxygen from nitrogen. The process involves modifying a carbon support, having a majority of micropores with an effective pore size of about 4.5 to 20 A, using a two-step process in which the sieve is contacted with two different concentrations of a volatile carbon-containing organic compound. The concentration of the carbon-containing compound used in the first step is larger than that in the second step, so that the pore openings of the micropores of the support are narrowed successively in two distinct steps without excessively filling the micropores themselves.

The unusual hydrothermal stability of Co-ZSM-5

Abstract We wish to report that cobalt exchanged ZSM-5 has remarkably high hydrothermal stability, especially in comparison to Cu-ZSM-5. Calcination of Co-ZSM-5 in 2% water vapor at 750°C for a period of 99 h has a modest effect upon its activity for nitrous oxide decomposition. Treatment of Cu-ZSM-5 under the same conditions dramatically reduces the performance of the copper exchanged zeolite.

Granular carbon molecular sieves

Abstract Any future carbon molecular sieve (CMS) for use in the commercial production of N2 should have a high volumetric O2 equilibrium capacity. We developed a procedure for producing a high capacity coconut shell char that can be converted into a high capacity CMS for air separation. Granules of coconut shell char are heated in flowing inert gas at about 2 to 12°C per minute to a peak temperature of 775° to 900°C. After holding from 1 to 8 hours, the char is cooled in an inert gas atmosphere. The granular char thus produced has an oxygen capacity in excess of 8.0 cc/cc. Contacting the char with an oxidizing atmosphere containing CO2, H2O, or O2 at 650° to 900°C increases the O2 capacity to greater than 9.0 cc/cc. The coconut shell char can be converted to a CMS by treatment with a volatile carbon-containing organic compound that, when pyrolyzed, deposits carbon within the interior of the carbon granules. The granular CMS thus produced can be used in a nitrogen pressure swing adsorption column without the need for pelletization.

LIQUID-PHASE CATALYTIC HYDROGENATION USING PALLADIUM ALLOY MEMBRANES

Abstract The hydrogenation of several liquid alkenes was studied over Pd/Ru alloy membranes in either metal or glass membrane reactors. For cyclohexene, cyclo-octadiene, and octadecene as liquids, conversions of ca. 2–5% were common in contrast to the facile conversion of acetylenic alcohols.

Membrane Catalysis Over Palladium and its Alloys

Abstract Dense palladium metal membranes offer one approach to developing permselective membrane catalysts which offer a long term opportunity for reducing unit operations while enhancing product selectivities. We report the use of palladium and palladium alloys in the form of spirals or foils as both membranes and catalysts for several model hydrogenation reactions. The substrates investigated include: ethylene, butadiene, toluene, and cyclohexene with respect to critical process issues such as membrane life, reactor stability and productivity, optimum reactor temperatures, and membrane composition. Two reactor designs were used to evaluate hydrogenations performed in the liquid or vapor phase. The performance of these reactors as they relate to current difficulties in this field will be discussed.

Carbon-based oxygen selective desiccants for use in nitrogen PSA

Abstract Techniques for the production of composite oxygen selective adsorbents are disclosed. These adsorbents are comprised of a carbon molecular sieve (CMS) which is kinetically selective for the adsorption of oxygen over nitrogen and an agent for the sorption of water such as LiCl or SiO2. The adsorption properties of the composite adsorbents and results obtained from pressure swing adsorption (PSA) process testing are presented. The composite adsorbents improve the nitrogen PSA process performance (recovery and productivity) over the use of conventional desiccants which do not exhibit oxygen selectivity. Using a standard nitrogen PSA process cycle, replacement of conventional inorganic desiccants like alumina with the current CMS-based desiccants improved air recovery 2 to 4 percentage points and increased nitrogen productivity 15 to 20% at 70°F and a nitrogen purity of 99.5%.

Simultaneous exchange and extrusion of metal exchanged zeolites

Abstract We wish to report that simple combination of an aqueous transition metal salt, alumina, and the ammonium form of the zeolite can be readily extruded, and upon calcination to 650°C, the resulting extrudate as a catalyst behaves similarly to catalysts prepared by the traditional, more complex, stepwise approach using multiple, aqueous ion exchanges followed by extrusion and calcination.