Paulo F. M. Correia

Recovery of 2-chlorophenol from aqueous solutions by emulsion liquid membranes: batch experimental studies and modelling

Abstract A study of 2-chlorophenol recovery by emulsion liquid membranes was undergone. The effect of several permeation variables such as membrane phase composition, internal reagent concentration, solute concentration, permeation stirring speed, temperature, permeation time and phase ratios between membrane phase and internal phase and also between external phase and internal phase on 2-chlorophenol permeation was studied. The most relevant of these parameters were permeation stirring speed, temperature and phase ratio between external phase and internal phase. Advancing front model was applied to these parameters and described the experimental results.

A comparison of models for 2-chlorophenol recovery from aqueous solutions by emulsion liquid membranes

Advancing front model and three reversible reaction models were applied to describe 2-chlorophenol permeation from aqueous solutions by emulsion liquid membranes. Similar results were obtained in most cases by using either of the reversible reaction models. Also differences between reversible reaction and the advancing front model were shown to be within experimental error in most cases (with the exception of low temperature permeation data) meaning that the role of reversibility of the chemical reaction between internal phase reagent and 2-chlorophenol can be considered negligible. Both advancing front and reversible reaction models can be used with a reasonably accuracy as estimates of 2-chlorophenol permeation for design purposes.

Salt Effects on the Recovery of Phenol by Liquid‐Liquid Extraction with Cyanex 923

Abstract In this work, the effect of salt addition on the recovery of phenol from a 46 g/L aqueous solution simulating a phenolic resin plant effluent by liquid‐liquid extraction at 298 K has been studied by using an organic phase containing 0.6 M Cyanex 923 extractant in ShellSol T. Addition of sodium sulfate, potassium nitrate, and sodium chloride to the aqueous phase was tested and sodium chloride was selected. Based on the obtained results, a study of phenol recovery process was undergone by taking advantage of the salting‐out effect. Equilibrium curves are presented for liquid‐liquid extraction with and without salt addition to the aqueous phase. An integrated process involving salting‐out and liquid‐liquid extraction was proposed. The stripping concentrates can be reused for phenolic resin production.

A Study on the Selective Recovery of Phenol and Formaldehyde from Phenolic Resin Plant Effluents by Liquid‐Liquid Extraction

Abstract The selective recovery of phenol and formaldehyde from a phenolic resin plant effluent by liquid‐liquid extraction has been studied. The selective recovery of phenol was achieved by using an organic phase containing Cyanex 923 extractant in an aliphatic diluent. Equilibrium curves are presented for both the extraction and the stripping. The stripping concentrate can be reused for phenolic resin production. The results of the extraction equilibrium showed that for a mole ratio (Cyanex 923)total/(PhOH)total higher than 0.6, the complex PhOH·Cyanex 923 is the predominant species. When the ratio values are lower than 0.6, the main species are the phenol in the aqueous phase and the complexes 2PhOH·Cyanex 923 and 4PhOH·Cyanex 923. Formaldehyde recovery was also tested by applying liquid‐liquid extraction with 1‐decanol. Equilibrium curves are presented for both extraction and stripping. An integrated liquid‐liquid extraction process was proposed involving the sequential recovery of phenol and formaldehyde from the phenolic resin plant wastewater.

Tannery Waste Treatment: Leaching, Filtration and Cake Dewatering Using a Membrane Filter Press (a Pilot Plant Study)

Abstract In Alcanena (Portugal) the waste water treatment plant (WWTP) receives tannery waste, after a pretreatment for sulphides and the tanning exhaust baths have been sent to a recovery unit and the municipal waste water from Alcanena residential area. Physical, chemical, and biological treatment processes are involved, and the end products are sludge of ∼71% moisture containing mainly organic matter, sulfides, iron, chromium, and other metals. The sludge is dumped, after stabilization, in a specially designed hazardous waste landfill. In this study, tannery mixed sludge (from chemical and biological treatments) was leached and filtered. Leaching was carried out using sulfuric acid (pH 0.5) to release residual sulfides and metals from the slurry. Hydrogen sulfide (H2S) was flushed out into an oxidation trap (hypochlorite/alkaline tank) in which H2S transforms to soluble sulfate. The acidified sludge was fed into a membrane filter press where it was filtered, acid‐washed, water–washed, membrane‐squeezed, and vacuum‐dried reaching lower moisture levels (20–30%). The process cycle is approximately 101–137 min in our experiments; however, from this work, a cycle of 90 min to produce cakes with 0.9 cm thickness in the industrial scale through cutting some operational time, reaching final moisture of ∼20% at the end of the dewatering cycle, can be estimated. Filtration was carried out at different feed pressure (3–5 bar) with and without diatomite precoating. The effect of different amounts of diatomite body‐feed was studied. Specific cake resistance, α, was found to increase with the increase in feed pressure and to decrease with diatomite precoating and the increased amounts of diatomite body feed. Cake washing was accomplished using 0.05 M H2SO4 (acid washing), to remove residual metals, followed by water washing, to remove cake acidity. Cake dewatering via membrane squeezing was applied using hot water (65°C), and cake moisture was dropped from ∼71% before squeezing to 42% after squeezing. With vacuum application over the hot cakes, for 30 min, cake moisture decreased to ∼20% for cakes with an average thickness of 0.9 cm. Cake chemical analysis showed chromium levels lower than 1000 mg/kg (the maximum Cr concentration allowed by the Portuguese legislation in a solid residue for use in agricultural soil). In addition, produced cake (without diatomite body feed) has a calorific value of 11,000 kJ/kg and accordingly it can be used as a source of energy.