J.R. Alvarez

Mass transfer correlations in membrane extraction: Analysis of Wilson-plot methodology

Mass transfer correlations have been obtained for the past eight decades by the Wilson-plot method which has proved to be suitable for systems operating in steady-state conditions and where the only variable is the fluid velocity. In this work, this methodology is evaluated by using a membrane extraction process with a hollow-fiber membrane contactor as a case study. Taking into consideration the currently available mathematical tools, alternative methods to obtain mass transfer correlations are proposed and discussed. The proposed one-step calculation methodology proved to be a most suitable approach, leading to a drastic reduction in the errors associated with the estimated parameters. Additionally, improvements were observed when accounting for the partition coefficient variation.

Recovery of phenol from aqueous solutions using hollow fibre contactors

The purpose of this study is to characterise recovery of phenol from an aqueous solution using a hydrophobic polypropylene membrane contactor. The effects of temperature and hydrodynamics on the overall mass transfer coefficient were determined. Integration of the extraction and stripping stages was also carried out thereby allowing removal of more than 99% of the original phenol, while the organic phase is simultaneously regenerated.

A comparative study of reverse osmosis and freeze concentration for the removal of valeric acid from wastewaters

Abstract The recovery of valeric (n-pentanoic) acid from a synthetic aqueous solution simulating a wastewater stream in nylon manufacturing has been carried out using freeze concentration and reverse osmosis as separation processes. The concentration of valeric acid in aqueous solutions was in the range of 0.5–25 g/L. Reverse osmosis was carried out at 20 and 40°C and at a transmembrane pressure in the range of 1.3 to 6.0 MPa. The feed flow rate was 2 m/s in all the experiments. Although no membrane fouling was observed under the experimental conditions tested, a strong interaction of the acid with the membrane was noticeable. Rejections of the order of 90% were observed at 20°C, while values below even 50% were found at 40°C. The optimum performance for freeze concentration was determined, the best conditions being −10°C of subcooling temperature and 1012 kg/hm of feed flow. A model based on the heat transfer balance allows to predict the rate of ice crystallization. An economic analysis reveals that although freeze concentration consumes as much as five times the energy of reverse osmosis, which is compensated by the high costs of membrane replacement in reverse osmosis.

Removal of valeric acid from wastewaters by membrane contactors

Membrane contactors, providing a non-dispersive extraction technique, were used for the removal of valeric (n-pentanoic) acid from synthetic aqueous solutions simulating an industrial wastewater from polymer manufacturing. Amberlite LA-2 (secondary amine) in toluene was chosen as the extraction system. Equilibrium conditions were determined and mechanistically modelled for different extractant concentrations allowing the further calculation of mass transfer coefficients. The influence of the hydrodynamics of both the aqueous and organic phases on the overall mass transfer coefficient, calculated through two proposed methods, was studied. The integration of extraction and backextraction was also carried out, allowing a further acid removal with lower extractant concentrations.

Electrodialysis in the separation of dilute aqueous solutions of sulfuric and nitric acids

Abstract Dilute aqueous mixtures of sulfuric and nitric acids were electrodialyzed with the aim to separate and concentrate both acids. The stack was fitted with heterogeneous or homogeneous membranes, the former untreated, the latter with a low transport number of bivalent anions. Changes in concentration were analyzed in terms of the normalized concentration C * = C/C ° as a function of the relative mass concentration of the slower ion in the diluate, X dS = C dS /( C dS + C dN ). The results show that such a separation is possible and more efficient with treated membranes.

Extractive ultrafiltration for the removal of valeric acid

The removal of valeric acid (pentanoic acid) from aqueous solutions in the range of 0.01 to 0.7 wt%, using amines (Alamine 336 and Amberlite LA-2) and tributyl phosphate at 25°C as extractants, was carried out by extractive ultrafiltration, a combination of solvent extraction and membrane filtration. Several diluents were used in the preliminary solvent extraction tests. A tubular, ceramic, ultrafiltration membrane was used in all the membrane filtration experiments. Extraction results showed that Amberlite LA-2 and tributyl phosphate are the best extractants from those tested, but only the system with the amine shows a high degree of extraction, when using the extractive ultrafiltration technique. A more detailed study of the extractive ultrafiltration of valeric acid with Amberlite LA-2 in toluene as diluent was carried out. Permeation rates and extraction behaviour were studied under the following conditions: at total recirculation, with permeate removal and continuous operation of the system.