Hans-Jörg Bart

Phosphate removal from wastewater by model-La(III) zeolite adsorbents

Phosphorus is one of the primary nutrients which leads to eutrophication and accelerates aging process in enclosed water bodies. Because of the poor phosphorus selectivity of other adsorbents, the novel La(III)-modified zeolite adsorbent (LZA) was prepared by modifying 90 nm zeolite with lanthanide to selectively remove phosphate in the presence of various omnipresent anions, such as sulfates, bicarbonates, and chlorides. Through batch and fixed bed operation, the following optimum conditions were obtained: concentration of lanthanum chloride solution 0.05 mol/L; solid/liquor ratio 1/25; pH 10; calcination temperature 550 degree C time 1 h. The value of the Freundlich model constants Kf and 1/n were found to be 16.76 mg/L and 0.2209, respectively. In addition, when calculated at pH 6.0, distribution coefficient K(D) could be as high as 36.6. Furthermore, in the alkaline pH range, solution of 0.8 mol/L NaCl was used to regenerate the saturated LZA, which could reach the high regeneration efficiency as high as 100%. Because of the good selectivity and regenerability of LZA, it might serve as a potential way for advanced phosphate removal from the sewage containing other anions.

New approach in the modelling of the extraction equilibrium of zinc with bis-(2-ethylhexyl) phosphoric acid

Abstract The extraction equilibrium of the possible test system for reactive extraction zinc sulphate/bis (2-ethylhexyl)-phosphoric acid (D2EHPA)/n-heptane was studied at 25°C. The results from slope analysis, computer modelling and quantitative FT-IR spectroscopy have been compared. The computer program SXLSQA was used for modelling the equilibrium taking into account the non-ideality of both phases, based on the Pitzer approach for the aqueous phase and the regular solution theory of Hildebrand/Scott for calculating organic phase activity coefficients. The three methods employed provide the same result: that the dominating zinc complex in the organic phase is ZnR 2 (RH). Some analytical improvements have been carried out, such as purification of D2EHPA, a purity determination method for D2EHPA, an analytical method for the determination of D2EHPA concentration in aqueous solutions. Fr-IR has also been used to illustrate the role of water in the formation of the organic metal complexes. While in the extraction of nickel an appreciable amount of water is co-extracted, the extraction of zinc does not show the same behaviour.

Numerical simulation of extraction columns using a drop population model

Abstract The drop population balance model describes the drop size distribution and the mass distribution of the solute in a liquid-liquid extraction column. It accounts for drop interactions (like breakage and coalescence) and the axial transport in the colunm, considering the phase inlets as point sources. Both integro-differential equations are discretized by utilizing Galerkins method. This leads to a coupled, nonlinear, dominantly hyperbolic system of conservation laws with additional drop interaction terms. We apply a diagonally implicit space-time discretization in conservative form to this system of PDEs.

LLECMOD: A Bivariate Population Balance Simulation Tool for Liquid- Liquid Extraction Columns

The population balance equation finds many applications in modelling poly-dispersed systems arising in many engineering applications such as aerosols dynamics, crystallization, precipitation, granulation, liquid-liquid, gas-liquid, combustion processes and microbial systems. The population balance lays down a modern approach for modelling the complex discrete behaviour of such systems. Due to the industrial importance of liquid-liquid extraction columns for the separation of many chemicals that are not amenable for separation by distillation, a Windows based program called LLECMOD is developed. Due to the multivariate nature of the population of droplets in liquid -liquid extraction columns (with respect to size and solute concentration), a spatially distributed population balance equation is developed. The basis of LLECMOD depends on modern numerical algorithms that couples the computational fluid dynamics and population balances. To avoid the solution of the momentum balance equations (for the continuous and discrete phases), experimen- tal correlations are used for the estimation of the turbulent energy dissipation and the slip velocities of the moving droplets along with interaction frequencies of breakage and coalescence. The design of LLECMOD is flexible in such a way that allows the user to define droplet terminal velocity, energy dissipation, axial dispersion, breakage and coalescence frequen- cies and the other internal geometrical details of the column. The user input dialog makes the LLECMOD a user-friendly program that enables the user to select the simulation parameters and functions easily. The program is reinforced by a pa- rameter estimation package for the droplet coalescence models. The scale-up and simulation of agitated extraction col- umns based on the populations balanced model leads to the main application of the simulation tool.

KINETICS OF ESTERIFICATION OF ACETIC ACID WITH PROPYL ALCOHOL BY HETEROGENEOUS CATALYSIS

Kinetic data on the esterification of acetic acid with propyl alcohol catalyzed by the ion exchange resin DOWEX MONOSPHERE 650 C have been obtained using a stirred batch reactor. It was checked if there is an influence of pore diffusion and film resistance on the reaction rate when varying reaction temperature, initial molar ratios, and amount of resin. The possible mechanisms of reaction were mathematically treated using the theories of Langmuir-Hinshelwood and Rideal-Eley. Taking the nonideal behavior of the system acetic acid, propyl alcohol, propyl acetate, and water into account, all calculations were realized with activities using the UNIQUAC-equation. By using the experimental results in a process of model discrimination the best kinetic parameter set was found out by the aid of the commercial software package SIMUSOLV. The resulting data of rate constants and the experimental determined equilibrium constants served as a basis for the calculation of the thermodynamic parameters of esterification, as reaction enthalpy, reaction entropy, and activation enthalpies.

Investigating the process of liquid-liquid extraction by means of computational fluid dynamics

Abstract Liquid-liquid two-phase flow in extraction columns of the rotating disc contactor type is analysed using the multi-dimensional computational fluid dynamics (CFD) technique. Euler-Euler and Euler-Lagrange models are employed to give insight into the global flow structure and to analyse the turbulence related dispersion processes. Laser-Doppler velocity measurements are used to check the Euler-Euler results while a measured residence time distribution allows the assessment of the Euler-Lagrange approach. The results give rise to the expectation that CFD will become an accepted design tool in chemical engineering.

Continuous Chromatographic Separation of Fructose, Mannitol and Sorbitol

Abstract The separation of mixtures of fructose, mannitol and sorbitol by continuous annular chromatography on Dowex 50W-X8 has been investigated. Distribution and mass transfer coefficients of the three substances were obtained by batch chromatography. The influence of feed concentration and flow rate on these parameters were discussed. The separation was simulated numerically and compared with experimental data. With this procedure, the separation of mixtures of fructose, mannitol and sorbitol by continuous annular chromatography (CAC) was calculated in advance, using only batch data. Additionally, the influence of rotation rate, column loading, eluent flow rate and feed concentration on the resolution of the individual peaks were investigated. With these results, the operation parameters for an industrial application of the CAC for this separation problem were determined.

Microkinetics and reaction equilibria in the system ZnSO4/D2EHPA/isododecane

Abstract Studies have been made on the kinetics of zinc extraction for the ZnSO 4 /D2EHPA/isododecane system which is being considered as a Recommended Liquid–Liquid Extraction Test System by the European Federation of Chemical Engineering (EFCE) Working Party on Distillation, Absorption and Extraction. A constant interfacial cell has been used to determine the chemical rate-controlling parameters at 25°C. Additionally, correlations for the system properties such as density, viscosity and interfacial tension have been developed as well as a correlation for the distribution coefficient. A rigorous equilibrium model based on chemical potential theory serves as a frame for the microkinetic formulation. The heterogeneous mass transfer is controlled at low zinc concentrations by two slow reversible interfacial reactions. The adsorption of the interfacial solutes is considered with the Langmuir law. It could be shown that neither complex stoichiometry, equilibria nor microkinetic constants will depend on a chosen aliphatic diluent, when the model formulation is expressed in activities.

Modelling of solvent extraction equilibria of Zn (II) from sulfate solutions with bis-(2-ethylhexyl)-phosphoric acid

Abstract The distribution of Zn(II) between aqueous sulfate solutions and n-dodecane solutions of bis-(2-ethylhexyl)-phosphoric acid (D2EHPA) has been measured in the range of an initial aqueous Zn(II) concentration from 1.5 × 10 −3 to 1.5 × 10 −1 M . The ionic strength I , for several experiments carried out, was adjusted to a constant value by using Na 2 SO 4 , for I =0.1−3. The data obtained were used to find a way of calculating the equilibrium distribution over a large concentration range. In this case, for the chemical reaction between the reactive extractant D2EHPA and the bivalent metal cation Zn (II), the stoichiometry changes from 2 to 1.5 for high D2EHPA loading conditions. A model was developed, based on the law of mass action, which enables the prediction of extraction equilibria for a given system over a large range of parameters such as ionic strength, pH, D2EHPA and zinc concentrations for known initial concentrations of the components of the system.

Influence of morphology and rheology on the production characteristics of the basidiomycete Cyathus striatus

The influence of the pellet morphology of the basidiomycete Cyathus striatus on the production of the antibiotics striatals A, B, and C was investigated. The main operating parameters in fermenters of different sizes were the tip speed and the volumetric power input. Different methods were developed for quantification of morphological characteristics. The apparent viscosity of the suspension was measured with a cylinder rheometer. Sediment density was measured with a sedimentation apparatus. Particle size distributions were recorded with an image analysis system. By means of the presented measuring methods, morphological characteristics could be determined and enabled an early assessment of the fermentation course and the antibiotics production. During the exponential growth phase of the fungus the relative sediment height correlated with the biomass concentration. The pellet morphology at this stage influenced the later production of striatals. The yield of the striatals was markedly influenced by pellet size and sediment density. Since these morphological characteristics determine the rheological properties of the culture the measurement of the apparent viscosity of the culture in the production phase allowed predictions of the production yield.