Formation of bed agglomeration in a fluidized multi-waste incinerator

A case study was carried out to investigate the bed agglomeration observed in a fluidized bed incinerator when burning blends of three wastes (carbon soot, biosludge and fuel oil). Several instrumental approaches were employed (i.e. XRF, SEM, XRD, and ICP-AES) to identify the bed materials (fresh sand and degrader sand) and clinkers formed in the full-scale incinerator tests. Several elements (V, Al, S, Na, Fe, Ni, P, and Cl), which normally are associated with the formation of low melting point compounds, were found in the waste blends at high content levels. The clinker bridges were identified to be associated with Al, Fe, V, K, Na, S, Ni, and Si elements.The effects of temperature and blending ratio were investigated in a muffle furnace. Carbon soot is believed to be more susceptible to the clinker formation than the other two fuels. Thermodynamic multi-phase multi-component equilibrium calculations predict that the main low melting point species could be Al₂(SO₄)₃, Fe₂(SO₄)₃, Na₂SO₄, NaCl, Na₂SiO₃ and V₂O₅. This information is useful to understand the chemistry of clinker formation. Also, it helps to develop methods for the control and possible elimination of the agglomeration problem for the design fuels.     

Rigid-particle toughening of glassy polymers

The nature of the toughening of glassy polymers by rigid particles was investigated by using aligned assemblages of spherical glass particles. The particles were aligned by an electric field in a photopolymerizable monomer, which was polymerized while the field was still being applied. These materials were fractured with the aligned particle strings in three orientations with respect to the crack plane and propagation direction. The fracture toughness and fracture energy of these and of random arrangements of particles (formed without the electric field) were all higher than of the matrix alone. The increases were compared with predictions from processes on or in the immediate vicinity of the fracture plane and from those away from the fracture plane. The increases were inconsistent with those predicted by on-fracture plane processes as represented by crack pinning and bowing. But the increases did correlate with the size of the process zones, which could extend more than 100 μm away from the fracture plane. Detailed calculations showed that the increase in fracture energy arose almost completely from off-fracture plane processes of particle-matrix debonding and the accompanying local inelastic deformation of the matrix around the particles.     

Oscillatory behaviour during the oxidation of methane over palladium metal catalysts

Oscillatory reactions over palladium foil and wire catalysts during the oxidation of methane have been investigated over a wide range of reaction temperatures and argon/methane/oxygen feed gas compositions. Characterisation of the catalyst has also been carried out using scanning electron microscopy (SEM) techniques, which revealed the presence of a porous surface. This suggested that the metal surface has undergone a change since the reaction commenced, and using X-ray powder diffraction (XRD) techniques the palladium phase was shown to be the dominant phase present. Hysteresis phenomena were observed in the activity of the reaction as the temperature was cycled up and down, showing that the metal surface was continually changing throughout the reaction. The activation energies of the reaction during the high reactivity mode, PdO, and low reactivity mode, Pd, were also calculated. Oscillation rates were observed to depend on the dominant surface. Oscillations were frequent when the high reactivity mode was dominant while the activation energy of this mode was found to be low. When the low reactivity mode was dominant, the oscillations were slower and the activation energy was three times larger. The results obtained imply that the behaviour of the palladium surface, switching back and forth from the reduced state to the oxidised state, is responsible for the oscillatory behaviour seen in this system.     

Flow patterns in granulating systems

Particle flow patterns were investigated for wet granulation and dry powder mixing in ploughshare mixers using Positron Emission Particle Tracking (PEPT). In a 4-l mixer, calcium carbonate with mean size 45 μm was granulated using a 50 wt.% solution of glycerol and water as binding fluid, and particle movement was followed using a 600-μm calcium hydroxy-phosphate tracer particle. In a 20-l mixer, dry powder flow was studied using a 600-μm resin bead tracer particle to simulate the bulk polypropylene powder with mean size 600 μm. Important differences were seen between particle flow patterns for wet and dry systems. Particle speed relative to blade speed was lower in the wet system than in the dry system, with the ratios of average particle speed to blade tip speed for all experiments in the range 0.01–0.25. In the axial plane, the same particle motion was observed around each blade; this provides a significant advance for modelling flow in ploughshare mixers. For the future, a detailed understanding of the local velocity, acceleration and density variations around a plough blade will reveal the effects of flow patterns in granulating systems on the resultant distribution of granular product attributes such as size, density and strength.     

Microstructure Development in Reactive-Templated Grain Growth of Bi1/2Na1/2TiO3-Based Ceramics: Template and Formulation Effects

"Reactive-templated grain growth" (RTGG) processing of Bi_1/2Na_1/2TiO₃ (BNT)-based ceramics is reported. Molten salt synthesis was used to prepare platelike (∼0.2 μm × 5 μm × 5 μm) Ruddlesden–Popper (Sr₃Ti₂O₇ (ST)) and Aurivillius (BaBi₂Nb₂O₉ (BBN)) phases which were used as "templates" in studies of RTGG with BNT-based matrixes. A "citrate-gel" route was designed to produce intimately mixed, fine-grain matrixes for these studies. The analytical techniques used were powder X-ray diffraction and microstructural examination of dry-pressed and fired compacts. For mixtures templated with BBN, single-phase perovskite readily formed, and an initially heterogeneous microstructure evolved toward a dense assemblage of anisometric, micrometer-scale grains. Perovskite formation was more sluggish in the mixtures templated with ST, and the final sintered microstructure featured larger, porous grains in an equiaxed, micrometer-scale matrix. A qualitative model, which examined the excess constituents in the matrix after formation of stoichiometric ABO₃ perovskite, is proposed to explain the observations. The model predicted an excess of Na₂O and TiO₂ in the matrix in the case of BBN templates and only excess TiO₂ in the case of ST templates. The results indicate that careful examination of matrix and template chemistry could be important in the selection of systems for RTGG processing.     

Surfactant behavior and its influence on the viscosity of associative thickeners solutions, thickened latex dispersions, and waterborne latex coatings

Surfactants, varying in their chemical composition and hydrophobic behavior, are used in the formulation of a waterborne coating. These differences influence their aggregation in micellar structures, their interaction with associative thickeners, and in particular, the synergies present in their competitive adsorptions on the disperse phases in a waterborne coating. Adsorption of HEUR thickeners on latexes and the ability of surfactants to displace them from those surfaces is an important variable in the dispersion’s viscosity. With large particle latexes, viscosity increases arise primarily from the network built through the interaction of HEURs with surfactants in the aqueous phase. Fluorescence is used to verify the mechanism by which surfactants enhance associative thickener viscosities. That is best achieved with nonionic surfactants, because of their synergies with large hydrophobe HEURs at low concentration. With decreasing latex particle size the adsorbed species is an important contributor to the dispersion’s viscosity through its contribution to the latex’s effective volume fraction increase and when the size of the adsorbed HEUR is matched to the separation distances of the latex at 0.25 volume fraction. Achieving controlled shear-thinning behavior in small particle size latex paints with the economic constraints on the amount of HEUR required to obtain 90 KU viscosities are discussed. Presented at the 80th Annual Meeting of the Federation of Societies for Coatings Technology, October 30–November 1, 2002, in New Orleans, LA. Polymer and Coatings Dept., Fargo, ND 58103.     

Elucidation of the miniemulsion stabilization mechanism and polymerization kinetics

Styrene/hexadecane miniemulsions were polymerized at 50°C using a redox initiator. The miniemulsions and their corresponding latexes were characterized in terms of size, polymerization rate, and surface properties. The resulting data were analyzed to elucidate the miniemulsion stabilization and polymerization mechanisms. It was found that the free surfactant concentration exceeded the critical micelle concentration when large amounts of surfactant (60 mM sodium lauryl sulfate) were used, resulting in simultaneous micellar and droplet nucleation. Most surfactant was on the surface of the droplets (85%) or particles (95%). The fractional surface coverage was proportional to the surfactant concentration to the 0.55 power. Using a particle diameter equation, the number of particles was calculated to be proportional to the surfactant concentration to the 1.35 power. Through direct particle size measurements, a power of 1.38 was confirmed. The rate of polymerization was determined by reaction calorimetry to be proportional to the number of particles to the 0.59 power, in contrast to classical Smith–Ewart kinetics for conventional emulsions (1.0 power). The average number of radicals per particle was estimated from the rate and number data, and varied with the particle diameter to the 0.97 power. The observed kinetic dependencies were validated through an extension of Smith–Ewart theory. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3987–3993, 2003     

NMR Studies of Diffusion-Coherence Phenomena in Red Cell Suspensions: Current Status

Pulsed field-gradient spin-echo (PGSE) nuclear magnetic resonance (NMR) diffusion experiments conducted on some heterogeneous systems have been observed to show periodicities in the data. These “coherence patterns” are manifest in the normalized PGSE signal intensities as a function of the spatial wave vector q in so-called q-space plots. The sample that to our knowledge best reveals these coherence patterns is suspensions of red blood cells (RBC). The origin of these patterns and their mathematical and physical underpinnings are now well established. We have used computer simulations of molecular diffusion in lattices of RBC and other cells to aid in the interpretation and analysis of the corresponding experimental data. The aim of this review is to present the current status of NMR q-space studies of RBC suspensions that show the diffusion-coherence effect.     

Enzyme‐catalyzed hydrolysis of poly(ethylene terephthalate) cyclic trimer

Oligoesters present in poly(ethylene terephthalate) fibers are commonly extracted from the fiber during processing, such as aqueous‐based dyeing. Aqueous, insoluble oligoesters, particularly cyclic trimers that precipitate on processing machinery and on the fiber surface are difficult to remove under benign conditions. Reported is a new method for the efficient removal of cyclic trimer by enzyme‐catalyzed hydrolysis. Almost complete hydrolysis of trimer was accomplished at pH 8 and 60°C. Effects of time, agitation, surfactant, and enzyme and trimer concentrations on the efficiency of hydrolysis are reported. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2545–2552, 2003     

Coupling hydrothermal liquefaction and aqueous phase reforming for integrated production of biocrude and renewable H2

Lignin-rich stream from lignocellulosic ethanol production was converted into biocrude by continuous hydrothermal liquefaction (HTL) while hydrogen was produced by aqueous phase reforming (APR) of the HTL aqueous by-product. The effects of Na₂CO₃ and NaOH were investigated both in terms of processability of the feedstock as well as yield and composition of the obtained products. A maximum biocrude yield of 27 wt% was reached in the NaOH-catalyzed runs. A relevant amount of dissolved phenolics were detected in the co-produced aqueous phase (AP), and removed by liquid–liquid extraction using butyl acetate or diethyl ether, preserving the APR catalyst stability and reaching an hydrogen yield up to 146 mmol H₂ L⁻¹ AP. Preliminary mass balances integrating HTL and APR showed that the hydrogen provided by APR may account for up to 46% of the hydrogen amount theoretically required for upgrading the HTL biocrude, thus significantly improving the process performance and sustainability.