Donald J. Kirwan
University of Virginia
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Featured researches published by Donald J. Kirwan.
Chemical Engineering Science | 1989
Piero M. Armenante; Donald J. Kirwan
Mass transfer to microparticles in agitated vessels was measured experimentally to establish both the turbulent and the asymptotic molecular diffusion contributions. Prior studies specifically focused on transport to microparticles, defined as those whose size is comparable to or smaller than the Kolmogoroff minimum eddy size, are limited. Further, in some cases, the earlier work that a value for the Sherwood number of less than 2 could be obtained. The asymptotic molecular diffusion contribution was experimentally measured from dissolution of 1.3- and 4-μm AgCl crystals in aqueous KCl solutions, and the exchange of Ag+ ions with 9-μm ion exchange particles. These results represent the first systematic experimental confirmation that the theoretical limit of Sherwood number=2 is valid for spherical particles suspended in stirred tanks. The turbulent contribution was determined from measurements of the transfer rate to ion exchange particles, 6 to 420 μm in diameter, in aqueous glycerol solutions. The mass transfer coefficient for microparticles can be well correlated by the expression where Re = (ed4/gs3)13. The turbulent contribution is compatible with a boundary layer model whose origin is in decaying microeddies. This equation also correlates well the reliable results on microparticles which could be found in the literature. A comparison of the proposed equation for microparticles with previous correlations for macroparticles, extrapolated into the microparticle regime, suggests that the use of macroparticle correlations for microparticles could significantly underestimate the turbulent contribution to mass transfer.
Journal of Crystal Growth | 1994
Amarjit J. Mahajan; Donald J. Kirwan
A grid mixer device (characteristic micromixing time < 3 ms) was successfully used to measure both nucleation and growth kinetics of lovastatin in 60 vol% methanol and asparagine monohydrate in 50 vol% 2-propanol at 23°C at high supersaturations but in the absence of mixing limitations. The supersaturation ratios investigated were in the range 1.25–8.8 for the lovastatin system and 1.17–4.1 for the asparagine system. When plotted according to primary nucleation theory, the induction time and nucleation rate measurements for both systems exhibited a homogeneous nucleation region at high supersaturations and a heterogeneous nucleation region at low supersaturations. The values of interfacial free energy extracted from these measurements for lovastatin (1.4–1.6 mJ/m2) and asparagine (4.5–6.1 mJ/m2) were an order-of-magnitude lower than those for inorganic salts reflecting the weaker intermolecular bonding in such biochemical solutes. The measured crystal growth rates for both solutes over the entire range of supersaturation could be represented with a power law dependence on chemical potential driving force. The kinetic orders of crystal growth were found to be 6.7 and 2.9 for lovastatin and asparagine, respectively. These unusually high kinetic orders could be represented by a polynuclear surface nucleation growth mechanism. The activation energy for the growth of lovastatin was measured as 280 kJ/mol.
Separations Technology | 1992
Giorgio Carta; Michael E. Gregory; Donald J. Kirwan; Hugo A. Massaldi
Abstract An analysis of the flow field and transport processes in a bed of permeable spherical particles for chromatography is presented. Quantitative relationships are provided to relate the intraparticle flow to the permeability of the particles and the bed properties. A theoretical development focused on the response of the bed to pulse injections of inert and linearly sorbed solutes shows how intraparticle convection enhances intraparticle transport, improving the efficiency of chromatographic operations. The theory developed is consistent with experimental results obtained for low molecular weight solutes and proteins with a commercial large-pore support. For this system, the HETP is observed to increase linearly at low flow rates, leveling off to a plateau at high flow rates when intraparticle transport becomes dominated by convection.
Biotechnology Progress | 1998
Robert P. Kasprow; Andrew Lange; Donald J. Kirwan
Complex, ill‐defined mixtures of natural origin are often used as nutrients in the production of biological products through microbial fermentation. Product yields are affected by variation in these natural products. It was desired to examine near‐infrared spectroscopy as a rapid screening tool for qualifying raw material lots. Specifically, the characterization of yeast extract was investigated. The model system consisted of a Merck & Co., Inc., microbial fermentation process. Cell mass and specific product yields are dependent upon variations in the yeast extract used in the medium. Partial least‐squares regression on the second‐derivative spectral absorbances of various yeast extracts in the ranges 1150–1380, 1554–1826, and 2100–2300 nm resulted in the development of models with multiple correlation coefficients of 0.99 for cell mass yields and 0.96 for specific product yields in large‐scale fermentations. These models could also be used to predict cell mass yields in 15 L batch fermentations and specific product yields in 2‐L shake flasks.
Chemical Engineering Communications | 2003
Neil F. Leininger; Reid Clontz; John L. Gainer; Donald J. Kirwan
Aqueous solutions of low molecular weight polypropylene and polyethylene glycol are proposed for use as novel, safe, environmentally friendly solvents. Not only are these solvents relatively nontoxic, but they are also nonvolatile, which eliminates the possibility of fugitive gaseous emissions. Many organic compounds have been found to be soluble in these polyglycol solutions; thus, they could be used as replacement solvents in various chemical processes. One use of the solvents could be as the medium for conducting chemical reactions, and this has been investigated. In particular, three classes of organic reactions, S N 1, S N 2, and Diels-Alder, have been conducted in the polyglycol solutions. Rate constants were obtained and compared to those for the traditional organic solvents. For the S N 1 reaction and the Diels-Alder reactions, the rate constants in the polyglycol solvents were greater than those found for the frequently used organic solvents.
Annals of the New York Academy of Sciences | 1984
John L. Gainer; Donald J. Kirwan
Whole cell immobilization has been the subject of numerous reviews. Most work on whole cell immobilization has involved the entrapment of the cells within gels of either polyacrylamide or carrageenan, or within c!osslinked collagen matrices. Although the entrapment method appears to allow the organisms to be maintained in an environment similar to that of free cells, the gel does introduce a significant additional mass transfer resistance. To avoid this problem, it is possible to attach cells using electrostatic and covalent coupling methods, and our work has been involved with such techniques. Since most organisms have a negative surface charge, we have studied their adsorption on positively charged ion-exchange resins. We began by studying the adsorption of a nitrogen-fixing bacterium, Azotobacter vinelandii, to such anionic resins, and found that the adsorption was faster with one particular resin, Cellex-E (Bio-Rad). It was noted that the cells are able to reproduce while adsorbed. The cells can be desorbed by increasing the ionic strength of the solution (FIG. l), and we can model the adsorption process with a Freundlich isotherm. It is particularly interesting to note that it is possible, with such adsorbed cells, to construct reactors having effective cell concentrations up to 10” per ml of reactor volume. This implies that it should be possible to construct much smaller reactors for a given conversion. A . vinelandii immobilized by electrostatic adsorption to Cellex-E maintained reproductive capacity and nitrogen fixation for more than 330 hours. Although the respiration rate was comparable for both free and immobilized cells, the nitrogen fixation rate for immobilized cells was slightly different than that for free cells, with the maximum occurring at a lower dissolved oxygen concentration. Other organisms, such as Acremonium chrysogenum and Penicillium digitatum have also been adsorbed this way, and current studies are focusing on the rate of product formation after immobilization. We have been using cyanuric chloride as a coupling agent and following an enzyme attachment procedure proposed by Kay and Lilly’ as well as one by Smith and Lenhoff.2 The method of Kay and Lilly appears to work better for yeasts, and the Smith and Lenhoff method appears to be better for bacteria. We have attached a number of bacteria and yeasts with these methods and are still developing optimum conditions for the immobilization process. Some initial observations, though, are quite interesting. We have placed immobilized cell preparations in a continuous-flow stirred reactor, and, unless the dilution rate (reciprocal of hydraulic residence time) was large, the population of free cells grew quite large. The coupled cells apparently reproduce and the results suggest that their specific growth is higher than that of free cells. In order to test the activities of only the immobilized cells, the dilution rates were increased until the free cell population was negligible in the chemostat (i.e., above the washout rate). We studied Azotobacter vinelandii and Saccharomyces cerevisiae in this way (see FIG. 2). It can be seen that the nitrogenase activity of the immobilized A . vinelandii could be maintained for over a month. The decline may or may not be related to a change in the viability of the cells, as
Chemical Engineering Communications | 1980
J.C. Ludlow; Donald J. Kirwan; John L. Gainer
This report concerns the frequency dependence of the heat transfer coefficient for water flowing in a tube. The investigation of this phenomenon was conducted in a double pipe heat exchanger in which the center stream was pulsed. The frequencies used ranged from 10 to 160 cycles per minute, and the average flow rates corresponded to a Reynolds number range of 3700 to 21,400. The data obtained indicate that pulsing can increase the individual heat transfer coefficient by as much as a factor of 5 or more, with the greatest increase occurring when the average Reynolds number is in the range typically considered as corresponding to the transition from laminar to turbulent regimes in steady flow. The percentage increase in the heat transfer coefficient also appears to be a function only of a dimensionless group which represents the frequency divided by the flow reversal frequency
Critical Reviews in Biotechnology | 1987
Lawrence C. Davis; Larry E. Erickson; G. Travis Jones; Donald J. Kirwan
(1987). Diffusion and Reaction in Root Nodules. Critical Reviews in Biotechnology: Vol. 7, No. 1, pp. 43-95.
Biotechnology Progress | 1986
W. B. Okita; Donald J. Kirwan
The production of secondary metabolites by immobilized living microorganisms was investigated by simulation techniques. The behavior of free cell and immobilized cell reactors for the production of penicillin by P. chrysogenum was compared. This system was chosen as a model system because literature data on growth and production kinetics are available. Simulation results for bioreactors containing P. chrysogenum immobilized by adsorptive techniques demonstrates a potential advantage in productivity for such reactors over conventional fed batch operation. Realization of this advantage requires an understanding of growth and product formation kinetics for immobilized cells as well as development of immobilization technology that will provide stable, high cell loadings.
Biotechnology Progress | 1985
A. C. Kirpekar; Donald J. Kirwan; R. W. Stieber
The reversion of a cephamycin C‐producing strain of Nocardia lactamdurans to a non‐producing variant under continuous culture conditions was examined at dilution rates between 0.025 and 0.045 hr−1. A model incorporating the influence of revertants, when present in the culture in significant numbers, was necessary to adequately describe the dynamics of the reversion process.