Marko Laakkonen

Vapour–liquid equilibrium for the 1-butene + methanol, + ethanol, + 2-propanol, + 2-butanol and + 2-methyl-2-propanol systems at 326 K

An automated static total pressure measurement apparatus was used to measure isothermal vapor−liquid equilibria for five binary systems:  trans-2-butene + methanol, + ethanol, + 2-propanol, + 2-butanol, and + 2-methyl-2-propanol at 332.3 K. Error analysis of the measured results has been presented. All systems exhibited positive deviation from Raoults law. The trans-2-butene + methanol and trans-2-butene + ethanol systems showed azeotropic behavior.

Modelling fermenters with CFD

Abstract Agitated gas-liquid reactors are widely used in the biochemical industry. In aerobic fermenters the dissolution of oxygen to the fermentation broth is impportant for the efficient operation of the reactor. In order to make accurate designs for bioreactors the local reaction and mass transfer conditions need to be modelled in detail. To validate the simulation results, experimental information is needed, but it is difficult to acquire from industrial fermenters. An alternative is to validate phenomenological models against experiments with a simple model system. The validated models can then be used to simulate industrial scale fermenters. A mixture of a transparent xanthan gum and additives was used as a shear-thinning model system to study hydrodynamics in gassed 14 and 200 dm3 stirred laboratory vessels. Physical properties, bubble size distributions, mixing energy and gas hold-up were measured. The used mixing intensities (0.1-3 W/kg) and gas feeds (0.1-1 vvm) are in line with industrial operating conditions. A Eulerian Computational Fluid Dynamics (CFD) simulation of a 70 m3 industrial fermenter was made. The measured physical properties of 0.25 w-% aqueous xanthan solution and a bubble size of 2 mm were used. Gas-liquid mass transfer was modelled with two-film theory and simplified Maxwell-Stefan multicomponent diffusion. Xanthan gum bioreaction kinetics was included in the simulation. Local mass transfer and bioreaction were modelled, spreads of gaseous NH3 and an aqueous nutrient were also simulated. The developed reactor model allows the identification of potential problem areas in fermenters.

CFD modelling of local bubble size distributions in agitated gas-liquid vessels - verification against experiments

Abstract Gas-liquid reactors and mixing units are widely used in chemical, biochemical, petroleum and mining industries. Understanding of turbulent gas-liquid phenomena is still very limited, but basic physical laws that control these phenomena are known. Population balance models incorporated into Computational Fluid Dynamics (CFD) offer a fundamental way for modelling mass transfer in inhomogeneous stirred reactors. Time-averaged bubble size distributions (BSD) were measured from several locations at various aeration rates and stirring speeds in a 13.8 dm 3 vessel for CO 2 - n-butanol and air - distilled water systems. Parameters of the bubble breakage and coalescence models were fitted against experimental BSDs in a relatively simple multiblock model. The fitted breakage and coalescence models were then incorporated to the CFD-code. Euler-Euler approach and sliding grid technique with multiple bubble size groups was used. The CFD simulation results were compared to the corresponding experimental local BSDs to evaluate the accuracy of the fitted model. With the breakage and coalescence models and CFD it was possible to predict local BSDs when vessel scale was changed. The CFD simulation results show physically reasonable behaviour with varying levels of agitation and gas feed, when compared to the visual observations and experimental results. The validated bubble breakage and coalescence with the CFD offer a reliable tool for the simulation of agitated gas-liquid vessels.