Andreas Pfennig

Determination of a coalescence parameter from batch-settling experiments

Abstract Until today, neither measurements nor theory are able to describe the complex processes at the interface that occur during coalescence in liquid–liquid dispersions in a detailed way. With the model presented in this study, it is possible to characterize coalescence processes with a single integral coalescence parameter. This parameter is obtained from a simple batch-settling experiment. If experimental data are evaluated based on this model, it is ensured that the parameter is independent of the experimental equipment, mixing intensity and volume fraction of the dispersed phase. Furthermore, the drop size in the dense-packed zone can be determined with this model.

Mass transfer by free and forced convection from single spherical liquid drops

Abstract Numerical simulations of the mass-transfer of droplet in a continuous phase were done for a conjugate problem. The effect of free and combined convection on the mass transfer was investigated by solving the governing equations using the finite element method. The results show that the mass transfer depends very strongly on the flow conditions. The effect of free convection on mass transfer at high Reynolds number is small. The mass transfer by the combined free and forced convection for a rising drop was found to be smaller than that for a falling drop. The simulation was limited to Re c ⩽20.

Thermodynamics of aqueous poly(ethylene glycol)-dextran two-phase systems using the consistent osmotic virial equation

Abstract In this work we present a thermodynamic model for the prediction of the liquid-liquid phase behavior of aqueous poly(ethylene glycol) (PEG) - dextran two-phase systems. The model is based on the McMillan-Mayer solution theory (1945) and results in thermodynamically consistent expressions for the chemical potentials of the solutes derived from the osmotic virial equation (COVE). Applying the COVE, we have examined the predictability using a complete and reliable data- base of liquid-liquid equilibrium (LLE) and vapor-liquid equilibrium (VLE) data. As a result of this examination, we were able to demonstrate the essential influence of the molecular-weight distribution of polydisperse polymers on the LLE predictions. Accounting for the polydispersity in our calculations, the prediction of the compositions as well as the molecular-weight distributions in the coexisting phases is in good agreement with our experimental results, as illustrated for the system PEG 3000 + dextran 110000 + water at 293.15 K. It should be stressed, that these calculations are true predictions, since the LLE were calculated using model parameters determined from VLE measurements alone.

Consistent view of electrolytes in aqueous two-phase systems.

The effects of electrolytes in aqueous two-phase systems are investigated. It is shown that macroscopic and molecular models give a consistent view of electrolytes at interfaces. The electrostatic potential difference delta psi between coexisting phases is a common property at interfaces even though the phases are strictly electroneutral and delta psi can not be measured. It is shown how delta psi can be quantified under controlled conditions. Additionally, a molecular picture is presented based on computer simulations.

Synthesis and Application of Carbonated Fatty Acid Esters from Carbon Dioxide Including a Life Cycle Analysis

Carbon dioxide can be used in various ways as a cheap C1 source. However, the utilization of CO2 requires energy or energy-rich reagents, which leads to further emissions, and therefore, diminishes the CO2-saving potential. Therefore, life cycle assessment (LCA) is required for each process that uses CO2 to provide valid data for CO2 savings. Carbon dioxide can be incorporated into epoxidized fatty acid esters to provide the corresponding carbonates. A robust catalytic process was developed based on simple halide salts in combination with a phase-transfer catalyst. The CO2-saving potential was determined by comparing the carbonates as a plasticizer with an established phthalate-based plasticizer. Although CO2 savings of up to 80 % were achieved, most of the savings arose from indirect effects and not from CO2 utilization. Furthermore, other categories have been analyzed in the LCA. The use of biobased material has a variety of impacts on categories such as eutrophication and marine toxicity. Therefore, the benefits of biobased materials have to be evaluated carefully for each case. Finally, interesting properties as plasticizers were obtained with the carbonates. The volatility and water extraction could be improved relative to the epoxidized system.

Measurement and Representation of Ternary Vapour-Liquid-Liquid-Equilibria

Abstract For the design of separation processes in systems showing azeotropic behaviour and two liquid phases, VLLE data must be represented with high accuracy. The ternary system ethanol/water/cyclohexane has been investigated for model development. The static method of p ( x , T ) measurement was applied to evaluate VLE of this highly non-ideal system which exhibits a wide miscibility gap. The tie-lines and the LL coexistence curve were determined by analysing samples of two liquid phases in equilibrium. The vapour composition of the heterogeneous azeotrope was determined by analysis of the head product of a rectification at infinite reflux ratio. To obtain full thermodynamic information on multicomponent VLE from p ( x , T ) measurement, a consistent description of the excess Gibbs energy of the liquid phase is required. The experimental data were described consistently, facilitating a modification of the NRTL equation with considerably increased flexibility in the ternary region.

A Critical Review of the Application of Drop-Population Balances for the Design of Solvent Extraction Columns: I. Concept of Solving Drop-Population Balances and Modelling Breakage and Coalescence

Population-balances are a powerful method to predict the population behavior of drops in chemical-engineering equipment such as solvent extraction columns. In such columns a complex interaction of different phenomena, namely drop sedimentation, mass transfer, drop breakage and coalescence as well as axial dispersion occurs. In this article the concept of drop-population balances is discussed in detail as well as possible solution methods. Also, a critical review of existing models accounting for breakage and coalescence taking place in extraction columns is presented. Future parts of this series will be devoted to modelling mass-transfer and sedimentation as well as on application of single-drop based modelling.

Analysis of the electrostatic potential difference in aqueous polymer two-phase systems

Experimental partition coefficients of two ionic dyes in two-phase systems water + poly(ethylene glycol) 3000 + dextran 500000 containing various salts are presented. Based on these data unambiguous information on the electrostatic potential differences induced by the salts is obtained. To achieve this goal the model proposed by Albertsson (1986) is applied to systems containing mixed salts to account for an ionic impurity present in the polymer samples. With both dyes the value of ΔϕNa2SO4 − ΔϕNaCl = 4.7 mV at salt concentrations up to 50 mmol kg−1 is obtained. Also the partition coefficients of the salts are predicted in agreement with the experiment. These results indicate that up to a salt concentration of approximately 50 mmol kg−1 the Albertsson model can be applied. Above this concentration limit, the basic two-phase system is altered and the model predictions are severely in error.

Development of a model for the Description of Intra-diffusion in Homogeneous Liquid Lennard - Jones Mixtures

A model for calculation of intra-diffusion coefficients of homogeneous liquid 1-centre Lennard–Jones (LJ) mixtures is proposed. As starting point for deriving this model we have chosen the model of Liu et al. [Chem. Eng. Sci. 53, (1998), 2403–2422] suggested for calculation of the self-diffusion coefficients of pure LJ model fluids. This model was extended to liquid mixtures by introducing suitable combining and mixing rules for description of different characteristics of the mixture components. The five parameters of the model were determined from data obtained by molecular-dynamics (MD) simulations performed in this work. To generate a database for intra-diffusion coefficients the method of optimal experiment design is employed. This method is applied to plan simulations in such a way as to obtain optimal estimates of the model parameters. The parameters were determined based on the range of temperatures 90 < T<350 K and mass densities 200 < ρ M<2580 kg/m3 with the total average absolute deviation of 5.56%. The suggested model was tested on the data available in literature concerning intra-diffusivities of 1-centre LJ liquid mixtures. The prediction accuracy of 42 data points is 13.08%. Further work will be directed at further optimisation of model structure and model parameters.

GEQUAC, an excess Gibbs energy model describing associating and nonassociating liquid mixtures by a new model concept for functional groups

Abstract The physically founded excess Gibbs energy model, GEQUAC, allows the description of excess properties for associating as well as nonassociating liquid mixtures. This is achieved by explicitly accounting for different poles of molecular surface between which strong interactions take place in a mixture. In previous work, the model concept and the subsequent model equation were tested against results of Monte-Carlo computer simulations and proved the ability to describe gE, hE and TsE of ketone+n-alkane and n-alcohol+n-alkane mixtures. This work provides model parameters fitted to binary isothermal VLE and hE data for the mixtures butanone+n-heptane, 1-butanol+n-heptane and butanone+1-butanol as a first step in application. The model parameters show physical relevance and are used for prediction of isothermal VLE and hE data (own measurements) at 323 K of the ternary mixture butanone+n-heptane+1-butanol.