Gas-liquid mass transfer in three-phase fluidized beds with viscous pseudoplastic liquids

Liquid phase volumetric mass transfer coefficients for oxygen were determined in three-phase fluidized beds of 8 mm glass spheres fluidized by a cocurrent flow of air and pseudoplastic polysaccharide solutions (carboxymethyl cellulose, xanthan). A semi-theoretical relation for the effective shear rate was suggested. The mass transfer coefficients could be correlated, together with literature data for particle diameters of 3 mm and 5 mm in other liquids, using the terminal velocity as the particle-specific property.     

Bioreaktoren — derzeitiger Stand und erkennbare Entwicklungen

Bioreactors – State of the art and recognizable future developments. Industrial biotechnological processes, which require monoseptic conditions, are currently performed largely batchwise in stirred tank reactors. A broad-based exploitation of the potential of biotechnology, i.e. both in the production of commodity biologicals/chemicals and in the manufacture of products of the ?new”? biotechnology, requires, for economic and technological reasons, continuous processes and other reactor configurations, which permit increased biomass concentrations by cell retention or immobilization, and integration of work-up operations.     

Model studies on the mechanism of endotoxin adsorption on flat-sheet microfiltration membrane adsorbers

The adsorption of endotoxin from E.coli O 111:B₄ and bovine serum albumin on membrane adsorbers with the ligands polymyxin B, L-histidine, deoxycholate, poly(L-lysine), poly(ethyleneimine) and diethylaminoethyl was studied under equilibrium and dynamic conditions. Apparent association constants varied between 30 and 30 000 mL/mg for endotoxin, whereas with BSA only approximately 1 mL/mg was found on average. With all ligands a reduction of the removal efficiency was experienced in the presence of BSA, which was used as model protein. Detailed analysis of the influence of BSA on the association constants as well as the equilibrium and dynamic capacities of endotoxin adsorption demonstrated that endotoxin and BSA molecules recognize distinct binding centres on the membrane adsorbers. Competition for binding sites plays a less important role than assumed so far. It is concluded that interactions of endotoxin with protein molecules in solutions are limiting endotoxin clearance from protein solutions. With net-positively charged proteins, electrostatic interactions yield protein-endotoxin complexes. Net-negatively charged proteins attract endotoxin by the mediation of calcium ions that are derived from endotoxin micelles and vesicles. In the latter case, endotoxin clearance can be significantly improved by the addition of EDTA.