Goran N. Jovanovic

Dechlorination of p-chlorophenol on a Pd/Fe catalyst in a magnetically stabilized fluidized bed; implications for sludge and liquid remediation

p-Chlorophenol is dechlorinated using a Pd/Fe bimetallic micro-size catalyst in a magnetically stabilized fluidized bed (MSFB) reactor. The catalyst is used in both powder form (dc=7 μm) and entrapped in alginate beads (db=2.0 mm). The dechlorination reaction is performed in aqueous solution containing p-chlorophenol with and without the presence of soil particles (20% w/w). Several important operating parameters involved in this complex chemical process are studied: Pd/Fe weight ratio, the extent of palladization or the ratio of Pd (Fe) interface area to the amount of chlorine to be removed, system pH, and dissolved O2. Important process resistances including formation of Fe(OH)2, Fe(OH)3, and hydrogen gas bubbles, which are dependent on the mentioned operating parameters, are identified for accurate representation of the overall reaction kinetics. Pseudo first-order kinetics (k=3.81±0.08 m3/kg min) with first order deactivation of catalyst (kd=0.12 1/min) are found to excellently represent dechlorination chemical reaction. Once the chemical kinetics were defined, the active Pd/Fe catalyst was entrapped in alginate beads for use in a magnetically stabilized fluidized bed. Diffusion constraints (De=8.0×10-10 m2/s) through the bead material (1.5% alginate +98.5% H2O) are not severe and are reported as being approximately 85–90% of the diffusivity measured in water (Shishido et al., Chem. Engng. Res. Design: Trans. Inst. Chem. Eng. 73(6), 719–725, 1995; Oyaas et al., 1995a Biotechnol. Bioengng 47, 492–500). It can be further moderated by decreasing the size of the beads and by using a nano size Pd/Fe catalyst particles (Wang and Zhang, 1997). Overall, the Pd/Fe bimetallic catalyst has been shown to effectively dechlorinate p-chlorophenol both as a powder and entrapped in 2 mm alginate beads. Integration of the catalyst entrapped in the beads with the MSFB introduces a novel method for the treatment of difficult to handle materials, and toxic compounds. The MSFB and alginate beads are shown to be an excellent engineering platform which can be implemented in a variety of catalytic and non-catalytic liquid-solid reaction processes.

Experimental and Theoretical Analysis of Tubular Membrane Aeration for Mammalian Cell Bioreactors

A combination of experimental and theoretical approaches was used to characterize the dynamics of oxygen transfer in a membrane‐aerated bioreactor. Pressure profiles along the length of the membrane at varying entrance and exit pressures were determined by actual experimental measurements, unlike most previous studies that have relied solely on theoretical descriptions of the pressure profile in the tubing. The mass transfer coefficient, kLa, was also determined under these conditions and was found to be essentially independent of tubing exit pressure. Measurement of the tubing pressure profile coupled with estimation of kLa allowed for computation of the oxygen transfer rate (OTR) along the length of the tubing. A mathematical model that incorporated friction pressure loss and losses due to tubing bending was developed to describe the pressure and hence OTR characteristics of membrane‐aerated systems. The applicability of the model was verified by testing it on experimentally measured pressure data, and in all cases the model accurately described experimental data. When tubing properties are known, the mathematical model presented in this study allows for a priori estimation of OTR profiles along the length of the tubing. This information is vital for optimal design and scale‐up of membrane‐aerated bioreactors for mammalian cell culture.

Performance of demulsions: entrainment problems in solvent extraction

Abstract A method for predicting performance of demulsions involves the relationship between the phase separation operation/method and the secondary liquid-liquid contact system, taking into account limitations of the equipment or plant capacity and maximal permitted content of residual emulsion or wanted sensitivity. This work conveys the knowledge organization or the process synthesis, main objective of which is to enable a choice in and design of the phase separation method, equipment and/or plant conception. The particular problem considered in this paper is the process synthesis in treatment of entrainment in liquid-liquid extraction. The experimental results obtained in the pilot plant for uranium recovery from wet phosphoric acid were used as the comparable source.

Porous cobalt spheres for high temperature gradient magnetically assisted fluidized beds.

Porous metallic cobalt spheres have been prepared as high temperature capable media for employment in gradient magnetically assisted fluidization and filtration technologies. Cobalt impregnated alginate beads are first formed by extrusion of an aqueous suspension of Co3O4 into a Co(II) chloride solution. The organic polymer is thermally decomposed yielding cobalt oxide spheres, followed by reduction to the metallic state, and densification. Cobalt beads have been produced with porosities ranging between 10 and 50%, depending upon sintering conditions. The product media have been characterized by scanning electron microscopy (SEM), nitrogen adsorption porosimetry, and vibrating sample magnetometry.

Magnetically Assisted Gasification of Solid Waste

A variety of techniques, including supercritical water oxidation, fluidized bed combustion, and microwave incineration have been applied to the destruction of solid wastes produced in regenerative life support systems supporting long duration manned missions. Among potential problems which still deserve attention are the need for operation in a variety of gravitational environments, and the requirement for improved methods of presenting concentrated solids to the reactor. Significant improvements in these areas are made possible through employment of the magnetically assisted gasification process. In this paper, magnetic methods are described for manipulating the degree of consolidation or fluidization of granular ferromagnetic media, for application in a gravity independent three step solid waste destruction process. Solids are first concentrated from an aqueous slurry using a depth filter in which the particles of filtration media are stratified according to size and consolidated for maximum filtration efficiency using magnetic forces. The organic material within the entrapped solids is destroyed by a combination of pyrolysis, isomerization, and oxidation reactions in a fluidized bed reactor. Finally, inorganic solids are removed by reverse-flow fluidization and collected on a downstream filter.

Preparation of metallic cobalt and cobalt-barium titanate spheres as high temperature media for magnetically stabilized fluidized bed reactors.

Fluidized bed reactors are extremely efficient when mass transfer limitations dominate global reaction rates, such as in combustion or incineration [1, 2]. Because fluidized beds operate using a balance between direct fluid dynamic forces and the gravitational restoring force, the maximum mass transfer rates for a given reactor configuration are limited by gravity. This limitation has been overcome using magnetic fields acting upon magnetically susceptible fluidization media to augment the force of gravity [3–7]. However, the use of magnetically stabilized fluidized beds in high temperature reactions has been limited by the lack of suitable media. Three magnetic properties are required to obtain suitable media: high magnetic susceptibility, high Curie temperature, and low coercivity. Cobalt, with a Curie temperature of 1121 ◦C, meets these requirements. We have investigated the preparation of two forms of cobalt containing spherical fluidization media: metallic cobalt, and cobalt impregnated barium titanate. Novel ferromagnetic media including cobalt impregnated barium titanate and metallic cobalt spheres have been prepared for high temperature application in magnetically stabilized fluidized beds. Spherical polymeric beads were initially formed by gelation of an alginateprecursor oxide suspension. Water was then eliminated from the hydrous gel at low temperature and the organic polymer was removed by oxidation in air. The temperature was then raised and the firing atmosphere changed to a reducing mixture containing hydrogen. Under these conditions, cobalt oxide was first reduced to the metallic form, and at a sufficiently high temperature, densification occurred via sintering. Cobalt impregnated barium titanate was prepared by intimately mixing BaCO3, TiO2, MgSO4, SiO2, and Co3O4 in a ball mill using zirconium oxide milling media, with molar ratios corresponding to one mole of Ba0.95Mg0.05TiO3, 0.064 moles of TiO2, 0.311 moles of Co, and 0.0207 moles of SiO2. The excess TiO2 and SiO2 form a low melting eutectic, predominately BaTiSi2O7, which melts at 1245 ◦C and acts as a sintering aide. The cobalt content corresponds to 10% (w/w) of the resulting BaTiO3. The oxides, carbonates, and sulfates were initially added to 1.4 times their weight

Urea separation in flat-plate microchannel hemodialyzer; experiment and modeling

Two flat-plate microchannel hemodialyzers were constructed consisting of two identical laminae separated by a 20[μm] thick ultrafiltration membrane (Gambro AN69). Each lamina contains a parallel array of microchannels 100[μm] deep, 200[μm] wide, and 5.6[cm] or 9.9[cm] in length respectively. Urea was removed from the aqueous stream containing 1.0[g] urea per liter de-ionized water in the blood side, by countercurrent contact with pure de-ionized water in the dialysate side of the flat-plate hemodialyzer. In all cases volumetric flow rate of water in the dialysate side was equal or less than the volumetric flow rate in the blood side, which is in large contrast to commercial applications of hollow-fiber hemodialyzers where dialysate flow is severalfold larger than blood flow rate. A three-dimensional finite volume mass transport model, built entirely from the first principles with no adjustable parameters, was written in FORTRAN. The results of the mathematical model excellently predict experimental results. The fractional removals of urea predicted by the model are within 2.7%–11% of experimentally obtained values for different blood and dialysate velocities/flow rates in microchannels, and for different transmembrane pressures. The overall mass transfer coefficient was calculated using the urea outlet concentrations obtained at various average velocities (1.0–5.0[cm/s]) in the blood and dialysate, and two nominal transmembrane pressures (∆Ptm = 0 and 10,000.[Pa]). Overall mass transfer coefficients obtained experimentally ranged from 0.068 to 0.14 [cm/min]. The numerical model predicted an average overall mass transfer coefficient of 0.08 [cm/min]. This value is 60% higher than those found in commercial dialyzers (~0.05[cm/min]).

The effect of interparticle forces on fluidization regimes in the magnetized fluidized beds

This paper investigated the influence of interparticle forces on the quality of fluidization in a magnetically stabilized fluidized bed (MSFB), where we can “artificially” create interparticle forces (Fattr) of any magnitude by applying an external magnetic field to ferromagnetic particles. A theoretical model was proposed which predicts the transition point from a homogeneous to a heterogeneous fluidization as a function of the magnitude of the interparticle force and other physical characteristics of both particles and fluids that are usually observed in fluidizationρp, ρf,μ, dp, ε). The concept of the elastic wave velocity, Ue, and the continuity wave velocity, Uε, was introduced. In particular, the interparticle force manipulated by an externally applied magnetic field was taken into account in addition to a general consideration of a conventional fluidized bed. Bubbles form in a bed when the continuity wave velocity becomes faster than the elastic wave velocity. The simulation demonstrated the proposed model could predict the transition point of fluidization regime with reasonable accuracy.

Preparation and evaluation of PEO-coated materials for a microchannel hemodialyzer

The marked increase in surface-to-volume ratio associated with microscale devices for hemodialysis leads to problems with hemocompatibility and blood flow distribution that are more challenging to manage than those encountered at the conventional scale. In this work stable surface modifications with pendant polyethylene oxide (PEO) chains were produced on polydimethylsiloxane (PDMS), polycarbonate microchannel, and polyacrylonitrile membrane materials used in construction of microchannel hemodialyzer test articles. PEO layers were prepared by radiolytic grafting of PEO-polybutadiene-PEO (PEO-PB-PEO) triblock polymers to the material surfaces. Protein repulsion was evaluated by measurement of surface-bound enzyme activity following contact of uncoated and PEO-coated surfaces with β-galactosidase. Protein adsorption was decreased on PEO-coated polycarbonate and PDMS materials to about 20% of the level recorded on the uncoated materials. Neither the triblocks nor the irradiation process was observed to have any effect on protein interaction with the polyacrylonitrile membrane, or its permeability to urea. This approach holds promise as a means for in situ application of safe, efficacious coatings to microfluidic devices for blood processing that will ensure good hemocompatibility and blood flow distribution, with no adverse effects on mass transfer.

Sensitive-cell-based fish chromatophore biosensor

A sensitive biosensor (cytosensor) has been developed based on color changes in the toxin-sensitive colored living cells of fish. These chromatophores are highly sensitive to the presence of many known and unknown toxins produced by microbial pathogens and undergo visible color changes in a dose-dependent manner. The chromatophores are immobilized and maintained in a viable state while potential pathogens multiply and fish cell-microbe interactions are monitored. Low power LED lighting is used to illuminate the chromatophores which are magnified using standard optical lenses and imaged onto a CCD array. Reaction to toxins is detected by observing changes is the total area of color in the cells. These fish chromatophores are quite sensitive to cholera toxin, Staphococcus alpha toxin, and Bordatella pertussis toxin. Numerous other toxic chemical and biological agents besides bacterial toxins also cause readily detectable color effects in chromatophores. The ability of the chromatophore cell-based biosensor to distinguish between different bacterial pathogens was examined. Toxin producing strains of Salmonella enteritis, Vibrio parahaemolyticus, and Bacillus cereus induced movement of pigmented organelles in the chromatophore cells and this movement was measured by changes in the optical density over time. Each bacterial pathogen elicited this measurable response in a distinctive and signature fashion. These results suggest a chromatophore cell-based biosensor assay may be applicable for the detection and identification of virulence activities associated with certain air-, food-, and water-borne bacterial pathogens.