A generalized expression for lag-time in the gas-phase permeation of hollow tubes

A generalized expression for the nonsteady state parameter, lag-time, has been obtained from Fick’s second law for gas-phase transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical interest: 1) diffusion controlled transport, 2) phase boundary reaction control at the inlet surface, and 3) phase boundary reaction control at the outlet surface. In all three cases the lagtime expressions were found to be inversely proportional only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were applied to experimentally obtained lag-time data for α-phase titanium and α-phase iron. Formerly with NASA-Ames Research Center, Materials Science Branch.     

Mechanism of light fading of dyes on cellophane and poly(ethylene terephthalate)

Studies of relative rates of fading of dyes and Hammett σ-value of substituents in their molecules lead to further evidence that fading of azo dyes on Cellophane and poly-(ethylene terephthalate) is probably an oxidation type of reaction. Absorption spectra of the same dye on these two substrates tend to indicate a very high state of aggregation of dyes on Cellophane as compared to that on poly(ethylene terephthalate).     

Determination of specific surface area of ferric oxide and alumina powders

Methods for measuring the surface areas of powdered solids are considered and the specific surface areas of ferric oxide and alumina powders using adsorption of stearic acid from benzene solution are determined. It has been found that the value of the specific surface area of both powders agree with the BET nitrogen gas adsorption area if it is considered that the area occupied per molecule of stearic acid on the powder surface is of the order of 60–70Ų. This finding shows that orientation of the stearic acid molecule on the solid/liquid interface takes place so that stearic acid molecules lie neither completely perpendicular nor completely parallel to the surface. Possible orientations of stearic acid chains on the surface are envisaged.     

Oxidation and Reduction in Light Fading of Dyes

Experimental evidence and published results show that when dyes are faded they are usually oxidised, probably by atmospheric oxygen. In certain systems reduction may occur, e.g. when the substrate is more readily oxidised than the dye or under anaerobic conditions in the presence of a hydrogen donor.     

Some aspects of fluidized bed combustion of paddy husk

Some agricultural wastes—for example, bagasse, paddy husk, etc.—are frequently used as fuels, paddy husk appearing, in particular, to be quite suitable for fluidized bed combustion. The conventional method of combustion of paddy husk in grate-type furnaces is slow and inefficient.

This paper reports certain aspects of the fluidized bed combustion of paddy husk. Fluidized bed combustion was carried out by feeding husk in a bed of sand particles. The unexpanded bed height was 10 cm and the size of the sand particles, 351–420 μm. The superficial velocity of the ambient fluidization air through the bed ranged from 11·1 to 22·2 m/min.

A combustion intensity of about 530 kg/h/m² of distributor area could be achieved. This is about 7·5 times higher than the maximum combustion intensity possible in a grate-type furnace per unit grate area. The efficiency of combustion, which ranged from 81 to 98 per cent was found to increase with the air flow rate. There was significant carry-over of inert sand particles from the bed under conditions of high air flow rate.

Combustion intensity increased as the bed height rose from 10 cm to 15 cm, but increased sand entrainment also occurred.     

Glass-reinforced composites based on novel oligoimide-epoxy resin system

A novel matrix resin system, viz. oligoimide-epoxy resin, has been developed to prepare glass-fibre-reinforced composites. Diaminodiphenylmethanebismaleimide-diaminodiphenylmethane (DDMBM-DDM) andp-phenylenebismaleimide-diaminodiphenylmethane (PBM-DDM) oligomers having more-NH₂ groups were prepared through Michael addition reaction. These oligoimides were used for curing commercial epoxy resin (i.e. diglycidyl ether of bisphenol A) at 120–140°C to fabricate crosslinked oligoimide-epoxy resin glass-fibre-reinforced composites without evolution of byproduct. The fabricated composites (i.e. laminates) were characterized by their chemical resistance and mechanical properties.     

Pyrolysis of coal liquids

The pyrolysis of process recycle solvent derived from Western Kentucky coal via the SRC-II coal liquefaction process was investigated to ascertain the effect of residence time and temperature on the production of olefins. The study was made using an alonized transfer line reactor operating at temperatures of 650 and 730 °C, essentially atmospheric pressure, and residence times up to 0.13 s. A comparison is made with previously published results for the pyrolysis of hydrotreated COED light and heavy coal liquids (subsequently referred to as COED light and heavy oils, respectively) derived from Western Kentucky coal and steam pyrolysis of a hydrogenated fraction of SYNTHOIL derived from Western Kentucky coal. Results indicate that in each case the preferential pyrolysis of the saturate fraction occurs under convential pyrolysis conditions. Ethylene, propylene, and methane were the dominant gas products in all cases. The liquid pyrolysates from the COED oils and SRC-II recycle solvent had lower $\text{H}\text{C}$ ratios and heating values than their respective feedstocks. Mass spectroscopic analysis of the liquid pyrolysates in each case revealed the presence of polycyclic aromatics that were not present in the individual feedstocks. This trend which increased with temperature is indicative of cyclization and/or recombination of free radicals during pyrolysis. It is therefore surmized that the yields of light olefins from primary coal liquefaction products can be improved by partially hydrogenating them prior to pyrolysis. Alternatively, sufficient hydrogen can be provided in the vicinity of cracking to suppress retrogressive reactions which lead to the formation of coke. The pyrolysis of COED oils and SRC-II recycle solvent was found to follow first-order irreversible kinetics. The activation energy for the pyrolysis of the COED light and heavy oil was found to be 76.1 and 70.85 kJ g-mol^?1, respectively.     

Single-Reference Coupled-Cluster Calculations of the Triplet Ground-State O2 Dissociation Potential

Three single-reference coupled-cluster single and double (CCSD) substitution models, CCSD + T(CCSD), CCSDT-1, and CCSD(T), exact through the fourth order of perturbation theory, are tested on the triplet ground-state dissociation potential of O₂. For the unrestricted Hartree-Fock (UHF) initial approximation, the interatomic distance region R ˜ 2.4–2.7 a.u. is problematic due to large multireference character, and beyond R ˜ 3.0 a.u. spin contamination causes difficulties. To a large extent these deficiencies are cured by the coupled-cluster treatments. Fourth-order triples as well as higher-order singles and doubles play a significant role. A more flexible basis set than DZP is important, too. None of the methods tried reproduce the experimental potential curve to the desired accuracy (2 kcal/mol). However, in a 6–311 + + G(2df, 2p) basis, the CCSD(T) model does give spectroscopic constants that are correct within 0.2 eV for the dissociation energy D_e, 70 cm⁻¹ for the harmonic vibrational frequency v_e, and 0.5 cm⁻¹ for the first anharmonicity constant v_eX_e. This model also reproduces the potential throughout the dissociative region to better than 0.2 eV. Overall CCSD + T(CCSD) is considerably less satisfactory than CCSD(T); CCSDT-1 is similar to CCSD(T) in a DZP basis, but large basis calculations proved to be too time consuming.     

Redox Isotherms for Vanadia Supported on Zirconia

Calcination of a Pt/Ba/CeO₂ catalyst at 700 °C and subsequent reduction in hydrogen, carbon monoxide or propene at 350–550 °C resulted in a considerable improvement of its NO _x storage-reduction (NSR) properties compared to those of a freshly prepared Pt/Ba/CeO₂ catalyst. This behavior is traced back to the temporary formation of BaPtO₃ perovskite which leads after reduction to well-distributed Pt particles in intimate contact with the barium-containing phases. The oxidation and reduction of platinum is reversible which can be exploited for the design of “self-regenerating” NSR-catalysts under lean (>600 °C) and rich (>400 °C) reaction conditions. The formation of the BaPtO₃-perovskite may not only be interesting for NSR-catalysis, but generally for Pt-based catalysts where a high dispersion of Pt is important.     

Palladium/Carbon Catalyzed Hydrogen Transfer Reactions using Magnesium/Water as Hydrogen Donor

Results on nonlinear phenomenon (NLP) in the liquid phase hydrogenation of methyl benzoylformate (MBF) and pyruvaldehyde dimethyl acetal (PA) on chiral Pt-cinchona catalyst are reported for the first time (enantiomeric excess 90–95%). The new data support the conclusions of the NLP studies on ethyl pyruvate (EP) and ketopantolactone (KPL). Namely, the order of the adsorption strengths of the parent cinchona alkaloids are: CD > CN > QN ~ QD and the results of the NLP measurements indirectly verify the so-called 1:1 model of enantioselection. The new data, however, call attention to a new, substrate and modifier dependent phenomenon, which necessitates further experiments for a better understanding of the mechanism of the Orito reaction.