Adrian Schumpe

Gas solubilities in microbial culture media

Available information on gas solubility in microbial culture media is reviewed. Emphasis is given to oxygen and carbon dioxide solubilities. Experimental techniques which can be successfully applied to culture media are presented. All the parameters which affect gas solubilities, i.e., above all the composition of the media are thoroughly discussed. In general, gas solubilities in nutrition and cultivation media can be predicted by a log-additivity approach. To this end knowledge of the composition of the media and the solubility parameters (K1) of the individual compounds is required. For a variety of substances encountered in cultivation broths the parameters K1 for oxygen could be evaluated from literature data and are summarized in this paper. Appropriate recommendations for applying direct and indirect predictive methods are given. Cases of failure are mentioned as well.

The gas density effect on mass transfer in bubble columns with organic liquids

Gas holdups and volumetric mass transfer coefficients in organic liquids (ethanol, 1-butanol, decalin, toluene) have been measured in a bubble column (0.1 m diameter, 3 different gas spargers) at 293-343 K. Wide ranges of the gas velocity (0.01-0.21 m/s) and the gas density (0.19-46.7 kg/m 3 ) are covered. The gas density effect is found to increase with the gas density and the gas velocity. This observation is in agreement with the theory of bubble breakage by Kelvin-Helmholz instability. Considering the additional literature data, new dimensionless correlations are developed that represent 687 gas holdups in 23 different liquids with 11.2% mean error and 673 mass transfer data in 31 liquids with 13.8% mean error.

Structure and physical properties of the extracellular polysaccharide PS-P4 produced by Sphingomonas paucimobilis P4 (DSM 6418)

A new strain, Sphingomonas paucimobilis P4 (DSM 6418), was found during a screening programme for exopolysaccharide-producing bacteria. The highly viscous fermentation broth yields a polysaccharide (up to 10 kg/m3), named PS-P4, and shows thixotropic flow behaviour. In the presence of phosphate ions, PS-P4 forms aqueous gels after heating and cooling at alkaline pH. After isolation and purification of the exopolysaccharide, structural analysis by 1D and 2D 1H NMR spectroscopy and mass spectrometry was performed. The deacylated exopolysaccharide has the following repeating trisaccharide structure:-->4)-beta-D-Glcp-(1-->4)-alpha-L-Rhap-(1-->3)-beta-D- Glcp(1-->Additionally, the presence of ester-bound acetic acid, D-glyceric acid, and (R)-3-hydroxybutyric acid in the native polysaccharide was demonstrated.

Xanthan production in a plunging jet reactor

SummaryA plunging jet reactor (0.04–0.08 m3) was used for the production of the exopolysaccharide xanthan with Xanthomonas campestris. The microorganism was not affected by the pump shear force. Similar specific growth rates and xanthan space-time yields to those in other reactor types were achieved at much lower specific power input. The better oxygen sorption efficiency in the jet reactor overcompensated for the effect of poor mixing in the wall region at high xanthan concentrations.

Mass Transfer in High-Pressure Bubble Columns with Organic Liquids

Oxygen desorption from organic liquids (ethanol (96%), 1-butanol, toluene) and water into nitrogen gas has been studied with an optical sensor. Gas hold-ups and volumetric mass transfer coefficients have been determined in the pressure range of 1-10 bar. In this range both quantities are found to increase with the gas density to the power of 0.24. However, by comparison with literature data and on theoretical grounds, the gas density effect can be shown to depend on the gas velocity and on gas density itself. The effect becomes negligible at gas velocities below 0.01 m/s and at gas densities below about 0.1 kg/m 3 .

Oxygen Absorption into Stirred Emulsions of n-Alkanes

Absorption of pure oxygen into aqueous emulsions of n-heptane, n-dodecane, and n-hexadecane, respectively, has been studied at 0 to 100% oil volume fraction in a stirred tank at the stirring speed of 1000 min−1. The volumetric mass transfer coefficient, 𝑘𝐿𝑎, was evaluated from the pressure decrease under isochoric and isothermal (298.2 K) conditions. The O/W emulsions of both n-dodecane and n-hexadecane show a 𝑘𝐿𝑎 maximum at 1-2% oil fraction as reported in several previous studies. Much stronger effects never reported before were observed at high oil fractions. Particularly, all n-heptane emulsions showed higher mass-transfer coefficients than both of the pure phases. The increase is by upto a factor of 38 as compared to pure water at 50% n-heptane. The effect is tentatively interpreted by oil spreading on the bubble surface enabled by a high spreading coefficient. In W/O emulsions of n-heptane and n-dodecane 𝑘𝐿𝑎 increases with the dispersed water volume fraction; the reason for this surprising trend is not clear.

Stoffübergang in Druckblasensäulen mit organischen Flüssigkeiten

Der Gasgehalt und der Stoffubergang in Blasensaulen wurden experimentell untersucht. Die Blasenstruktur wurde mit dynamischen Entgasungsmessungen ermittelt. Dazu wird die Begasung der Blasensaule gestoppt und die Druckdifferenz im unteren Saulenabschnitt mittels Drucktransmittern verfolgt. Der Stoffubergangszahl wurde mittels Desorption von Sauerstoff ermittelt. Dabei kam eine optische Messmethode zum Einsatz, die auf Fluoreszenzloschung eines angeregten Farbstoffes beruht. Der Farbstoff wurde direkt in der Flussigkeit gelost, um die Ansprechzeit des Sensors zu minimieren. Als Flussigkeiten wurden Decalin, Ethanol, 1-Butanol, Ethylenglycol, Toluol sowie Wasser eingesetzt. Gemessen wurde in einem Temperaturbereich von 10°C bis 80°C. So konnten die Stoffparameter in folgenden Bereichen variiert werden: Viskositat: 0,401 – 31,5 mPas; Oberflachenspannung: 19,9 – 74,2 mN/m und Dichte 793 – 1117 kg/m³. Als Gase wurden Stickstoff und Helium im Druckbereich 1 – 51 bar eingesetzt. Damit kamen Gasdichten im Bereich von 0,174 – 59,47 kg/m³ zur Anwendung. Es kamen zwei Blasensaulen mit unterschiedlichen Fullhohen und Durchmessern zum Einsatz. Als Begaser wurden Einzellochbegaser, Lochplatten und Sinterplatten eingesetzt. Die Ergebnisse werden mit Korrelationen aus der Literatur verglichen.

Ozonation of Cycloalkenes Dissolved in Ethanol

The ozonation of cyclooctene and cyclododecene in ethanol was studied at 278 K in a stirred reactor with a flat gas/liquid interface. The parallel reactions with ethanol in the gas and the liquid phase had to be accounted for. At high cyclooctene concentrations, ozone transfer into the liquid phase was enhanced by up to a factor of E = 325. Due to the high ozone solubility and the high enhancement factors, up to half of the mass transfer resistance was on the gas-side. The reaction rate constant k2 is more than threefold higher for cyclooctene as compared to cyclododecene.

New Approaches for Theoretical Estimation of Mass Transfer Parameters in Both Gas-Liquid and Slurry Bubble Columns

Bubble columns (with and without suspended solids) have been used widely as chemical reactors, bioreactors and equipment for waste water treatment. The key design parameters in bubble columns are: • gas holdup; • gas-liquid interfacial area; • volumetric liquid-phase mass transfer coefficient; • gas and liquid axial dispersion coefficients; Despite the large amount of studies devoted to hydrodynamics and mass transfer in bubble columns, these topics are still far from being exhausted. One of the essential reasons for hitherto unsuccessful modeling of hydrodynamics and mass transfer in bubble columns is the unfeasibility of a unified approach to different types of liquids. A diverse approach is thus advisable to different groups of gas-liquid systems according to the nature of liquid phase used (pure liquids, aqueous or non-aqueous solutions of organic or inorganic substances, non-Newtonian fluids and their solutions) and according to the extent of bubble coalescence in the respective classes of liquids. It is also necessary to distinguish consistently between the individual regimes of bubbling pertinent to a given gas-liquid system and to conditions of the reactor performance. The mechanism of mass transfer is quite complicated. Except for the standard air-water system, no hydrodynamic or mass transfer characteristics of bubble beds can be reliably predicted or correlated at the present time. Both the interfacial area a and the volumetric liquid-phase mass transfer coefficient kLa are considered the most important design parameters and bubble columns exhibit improved values of these parameters (Wilkinson et al., 1992). For the design of a bubble column as a reactor, accurate data about bubble size distribution and hydrodynamics in bubble columns, mechanism of bubble coalescence and breakup as well as mass transfer from individual bubbles are necessary. Due to the complex nature of gas-liquid dispersion systems, the relations between the phenomena of bubble coalescence and breakup in bubble swarms and pertinent fundamental hydrodynamic parameters of bubble beds are still not thoroughly understood. The amount of gas transferred from bubbles into the liquid phase is determined by the magnitude of kLa. This coefficient is an important parameter and its knowledge is essential