J. de Graauw

Extraction of metal ions from waste water. Modelling of the mass transfer in a supportedliquid-membrane process

Abstract The use of liquid ion exchangers in a supported liquid membrane process with two capillary membrane modules seems an attractive technique for the extraction of metal ions from waste water. This paper presents a mass transfer model for the extraction of copper ions with LIX 84 that may easily be extended to describe the extraction of other metal ions. The effect of the hydrogen and copper ion concentrations on the copper flux through the membrane was measured for the diffusion and for a reaction-limited case to determine the rate parameters in the mass transfer model. The regeneration of the liquid ion exchanger (carrier) was found to be slow compared with the formation of the chelate complex. It is shown that the extraction experiments can be simulated by using the proposed mass transfer model.

A corrugation geometry based model for efficiency of structured distillation packing

Abstract Although the structured packing is a well established gas–liquid contacting device, the understanding of its function is insufficient and often leads to poor exploitation of the available phase separating potential. This is a consequence of a rather superficial approach to modelling the packing performance through the years resulting in a lack of information on the nature and extent of interaction between counter-currently flowing gas and liquid phases and the micro and macro geometry of a rather ordered structure with a pronounced flow discontinuity at the transition among packing elements. This paper addresses the relation between the fluid-dynamics imposed by packing geometry and the mass transfer efficiency, and introduces a performance prediction method which does not require packing specific constants to describe mass transfer coefficients of phases.

Eutectic freeze crystallization : Application to process streams and waste water purification

Abstract Two case studies are presented using eutectic freeze crystallization (EFC) as an alternative for evaporative crystallization: a 7.8 ton day −1 35 w% aqueous sodium nitrate and a 24 ton day −1 12 w% copper sulfate stream. The proposed crystallizer is a cooled disk column crystallizer (CDCC), using indirect cooling for heat transfer. In single stage operation, the formed ice crystals are used to pre-cool the feed stream. A two stage refrigeration unit utilizes the formed ice crystals in the condensation of refrigerant. Expressed as a thermal equivalent energy requirement, EFC requires 1282 kJ kg −1 NaNO 3 and 1037 kJ kg −1 CuSO 4 ·5H 2 O. Compared to conventional multi-step evaporation, the energy reductions are 30% for sodium nitrate and 65% for copper sulfate.

Extraction of flavors from milk fat with supercritical carbon dioxide

Abstract Next to triglycerides, milk fat contains a large number of components (lactones, ketones, aldehydes) that provide milk fat with its characteristic flavor. In this study, supercritical carbon dioxide has been found to be a good solvent for the extraction of these flavor components from milk fat. Concentration factors varying from 20 to 50 have been measured at carbon dioxide densities of 600 to 700 kg/m3 and extraction temperatures between 40 to 50 °C. It has been observed that, if the the flavor extract is produced in two steps, these flavor components could be concentrated 500 to possibly 1000 times. The height equivalent to a theoretical equilibrium stage in the extraction column used, filled with 5-mm steel raschig rings, appeared to be approximately 20 cm.

Experimental Studies on the Interaction Between the Initial Liquid Distribution and the Performance of Structured Packings

Abstract Distillation and hydraulic test data are reported which give insight into the effect of the quality of initial liquid distribution on the performance of two corrugated sheet metal structured packings, differing considerably in surface area and texture. As expected, the packing with the larger surface (Montz-Pak BS-450) is more sensitive to initial liquid maldistribution. From the packing with smaller surface (Ralu-Pak 250 YC) a good performance may be expected even with only 40 drip points/sq m.

Gas distribution in large-diameter packed columns

Abstract The aim of the present work was to determine the extent of gas maldistribution in large-diameter columns containing corrugated-sheet structured packings. A large-diameter column simulator has been designed for this purpose (cross section, 3 m × 0.5 m; packed bed height, 4.4 m) with 15 independent inlets for gas, allowing the introduction of diverse initial distribution profiles. The gas velocity profiles leaving the top of the packed bed are discussed in terms of lateral spreading and observed effects of gas load, liquid load and the height of the packed bed.

Axial dispersion in packed fiber beds

Abstract The application of fibrous sorbent materials in gas and liquid separations as an alternative to conventional granular sorbents has attracted increased attention over the last decade. Though axial dispersion of flow in granular beds has been investigated extensively, published experimental data concerning the dispersion phenomena in porous fiber beds are sparse. The study presented involves the experimental determination of axial dispersion for water flow in packed beds of randomly aligned fibers, using a tracer pulse response technique. The influence of the bed properties (fiber diameter, bed void fraction) and the flow velocity on the dispersion coefficient was determined. The measured Bodenstein numbers vary between 0.001 and 0.1. the experimental results are compared with predicted values obtained from a theoretical model, based on isotropic fiber structures, showing substantial disagreement between the experimental and predicted values attributed to inhomogeneities of the fiber structure. The effect of inhomogeneities is similar for various types of random fiber structure. An empirical correlation for the axial dispersion coefficient for water flow in random fiber structures is presented.

Modelling and measurement of gas flow distribution in corrugated sheet structured packings

Abstract A mathematical model and calculation procedure are developed for the gas flow distribution in channels formed between tightly packed, corrugated, unperforated metal sheets. The model is a discrete cell model based on averaged mass, momentum and energy balance equations for each of numerous crossings of gas flow channels, with characteristic friction factors for gas inlet, bulk zone and wall zone as model parameters, which can be easily obtained from pressure drop measurements for each type and size of structured packing. The model enables prediction of velocity profiles leaving an element or packing layer consisting of segments of unperforated, structured packing. It is also suited for perforated packings which under operating (wetted) conditions function as a closed surface packing.

Separation of Alkanes and Aromatics with Supercritical C2H6, CO2, CCIF3, and CHF3

Abstract A study on the separation of alkanes and aromatics with supercritical ethane, carbon dioxide, monochlorotrifluoromethane, and trifluoromethane is presented. It appears that only with solvents that have a low dipole moment, such as ethane and carbon dioxide, can reasonable solubilities in the vapor phase be obtained. These low dipole moment solvents will separate alkanes and aromatics mainly on the basis of their difference in vapor pressure rather than on their difference in chemical structure. Therefore, supercritical solvents can only be used for specific applications where alkanes and aromatics have to be separated on the basis of their difference in vapor pressure.

A novel apparatus for countercurrent sorption separation processes using fibrous sorbents

This paper discusses a technical feasibility study on continuous countercurrent sorption equipment using mechanically transported fibrous sorbent materials such as fiber beds and open-cell foam. A pilot unit was developed and tested and the apparatus performed adequately. Under the conditions applied, the separation efficiency of the appartus is limited by the mechanical properties and structure of the currently available fibrous sorbent materials.