THE SPREADING OF AQUEOUS SURFACTANT SOLUTIONS ON GLASS

An investigation of the spreading behavior of drops of a number of aqueous anionic, cationic and non-ionic surfactant solutions has demonstrated, for the first-time, spreading to a maximum solid-solution contact area, and then contraction to a smaller final size. The nature and kinetics of the spreading and contraction are shown to be dependent on the type and concentration of the surfactant. Generally, the maximum contact area decreases with increasing surfactant concentration, to a minimum (or no spreading) in the vicinity of the CMC. Above the CMC, anionic and nonionic surfactant solutions spread with peripheral fingering, followed by contraction, while cationic surfactant solutions do not spread at these concentrations. The results are explained in terms of the thin primary film spreading ahead of the drop.     

AN EXPLORATORY STUDY OF A COMBINED SONIC AGGLOMERATION AND CROSSFLOW FILTRATION SYSTEM FOR HOT GAS CLEANUP

The Institute or Gas Technology has investigated a combined sonic agglomeration/crossflow filtration system to remove particles smaller than 10 microns from high-temperature, high-pressure gas streams. Sonic energy induces agglomeration so that particles can be removed in a continuously operating cross-flow filler element. Cold-model and preliminary high-temperature, high-pressure results are promising.

The objective of this investigation was to explore the potential effectiveness of sonic agglomeration, crossflow filtration, and a combination of these techniques to remove particles from high-temperature, high-pressure (HTHP) gas streams. The technique of sonic agglomeration has been known since the 1930's, and crossflow filtration has been used successfully in liquid filtration. This investigation is unique in that these two techniques were combined. Sonic energy was used to agglomerate particles to sizes large enough to be separated from the gas stream in a crossflow filter. The crossflow filter has advantages over conventional filters as a paniculate agglomerate removal system because it (1) operates continuously, (2) does not subject the fragile agglomerates to the high stress typical of inertial capture devices, and (3) can control the buildup of a filter cake when properly combined with a sonic agglomerator.

This investigation was supported by the Gas Research Institute and the Institute of Gas Technology Internal Research and Development Fund.

In this preliminary study, we found that—

? A 2-micron porosity filter must be used to achieve 98% paniculate removal from 95% of a dust-laden stream. (In the crossflow operating mode, 5% of the stream bypasses the filter.)

? When sonic agglomeration is combined with crossflow filtration, the same removal efficiency can be achieved with a 10-micron porosity filter.

? Combined sonic agglomeration/crossflow filtration removed particulates smaller than 10 microns in experiments at 265° C and 7000 kPa.

? The pressure drop across a 10-micron filter is about one-half that of a 2-micron filter, which could reduce the energy requirements for filtration.

This method of particulate removal should be applicable to many different coal reactor effluent streams, especially because it can operate at elevated temperatures and avoid gas cooling, liquid condensation, and subsequent liquid-solids separation. Preliminary estimates show that the power requirements of a combined sonic agglomerator/crossflow filter are lower than those of a crossflow filter alone, and that they are lower than or comparable with other particulate removal techniques. Additional tests are needed to establish the degree to which these benefits can be realized.     

THE SYNTHESIS AND EVOLUTION OF NETWORKS OF HEAT EXCHANGE THAT FEATURE THE MINIMUM NUMBER OF UNITS

An important problem in the design of chemical processes is that of bringing process streams from their temperatures of availability to the temperatures at which they are needed without undue cost. An important strategy for reducing the cost of doing this is heat recovery: Using the heat available from streams to be cooled to service streams to be heated.

In the absence of nonthermodynamic constraints, it is not difficult to assess the amount of heal recovery possible; and methods have been proposed (Linnhoff and Flower, 1978) that allow full heat recovery to be systematically obtained. The networks to which these methods lead are, however, more complex than necessary. Typically, therefore, those methods have been augmented with techniques for the evolutionary development of the initial network in order to simplify its structure, usually by minimizing the number of “matches” between streams.

The present work proposes a simple method for exploiting features of maximally simple networks (those that have as few “matches” as possible) in order to design, with greatly reduced effort, such a network that features a high (typically complete) degree of heat recovery. Further exploitation of those features allows a simple method of evolutionary development that makes it possible, in a very few evolutions, to improve the initial network as much as the data allow.

Unlike the other methods offered, the present ones are not hindered by the presence of nonthermodynamic constraints (practicality, safety, operability). Their generality and enhanced simplicity make them, more than any others, applicable in an industrial context. Although intended for application by hand, they lend themselves admirably to computer implementation, especially in an interactive mode.

These methods are demonstrated on the standard test examples and prove themselves powerful.     

Br⊘nsted Acid Sites in Zeolites Characterized by Multinuclear Solid-State NMR Spectroscopy

Nearly all atoms contributing to the local structure of Br?nsted acid sites in zeolites exhibit isotopes accessible for multinuclear solid-state nuclear magnetic resonance (NMR) investigations. Therefore, in the last 15 years, NMR spectroscopy has found numerous applications for the determination of the types of hydroxyl proton in zeolites, of their concentration, accessibility, and mobility, and for the characterization of their acid strength and local structure. It allows the study of the role of hydroxyl groups in the formation of adsorbate complexes and in heterogeneously catalyzed reactions. Meanwhile, NMR spectroscopy belongs to the most powerful techniques for the characterization of Br?nsted acid sites in zeolites and related materials. The basis of this success is the invention of new sample preparation techniques, external magnetic fields with high-flux densities, effective line-narrowing methods, and new two-dimensional experiments, making the detection of highly resolved solid-state NMR spectra and the separation of spectral parameters possible. This article gives a review of these techniques and a summary of the most important applications of multinuclear solid-state NMR spectroscopy for the characterization of Br?nsted acid sites in dehydrated zeolites.     

Primary and Secondary Phase Separation in CdF2-LiF-AlF3-PbF2 Glasses

Occurrence of primary and secondary phase separation in the CdF₂-LiF-AlF₃-PbF₂ glass system is observed. A primary phase separation, which is characterized by the formation of a small volume fraction of Cd-rich, Pb-deficient spheres whose size is on the order of 5μ is found to form upon cooling. A secondary phase separation initiates with precipitation of Pb-rich microspheres (about 4nm (40 Å) in diameter) in a Cd-rich matrix. The Pb-rich spheres develop with heat treatment 35°C above the glass transition temperature. They increase in volume fraction while changing composition and then grow slightly. As the material is further heat-treated, the Pb-rich regions crystallize. A pseudobinary model explaining the occurrence of both primary and secondary decomposition phenomena is presented.     

Microstructural Characterization and Fracture Toughness of Cordierite-ZrO2 Glass-Ceramics

Crystallization of an MgO-Al₂O₃-SiO₂-ZrO₂ sintered glass frit was studied. Heat treatment at 850° or 900°C caused initial crystallization of μ-cordierite and tetragonal ( t ) ZrO₂. The t -ZrO₂ crystallized with an irregular dendritic morphology and could be transformed to monoclinic ( m ) symmetry under certain conditions; the cordierite underwent the μ→α a transformation with extended annealing. Heat treatments at 1000°C caused crystallization of t -ZrO₂ rods and spheroids in an α-cordierite matrix; these ZrO₂ crystals, however, are resistant to transformation to m -ZrO₂. The beneficial effects of ZrO₂ on the fracture toughness of cordierite-based glass-ceramics are described.     

Sintering of Mullite-Containing Materials: II, Effect of Agglomeration

The sintering behavior of mullite powder compacts which contained soft and hard agglomerates was studied, The maximum density achieved depended on the size and packing of the agglomerates. Although the initial % total pore volume was kept constant, the presence of larger pores in the green compact, due to larger agglomerates, resulted in lower final densities after sintering. Densification rates were enhanced by the breakdown of agglomerates by grinding. The particle and agglomerate packing arrangements caused densification substages to occur. A schematic model is presented which agrees well with the observed experimental behavior.