Adsorption Science & Technology

Hybrid silicas bearing octadecylsilane ligands and Lewis acid centres were synthesized by grafting and sol-gel methods. In grafting, Cp₂ZrCl₂ was employed, while ZrCl₄ was used in the sol-gel method. A very low grafted metal content (ca. 0.1 wt% Zr/SiO₂) was achieved, with the carbon percentage being dependent on the grafting time. However, a much higher Zr content (up to 20.5 wt% Zr/SiO₂) and carbon content (up to 49.3%) was obtained by the sol-gel method. The surface concentration of alkyl groups varied between 0.2 and 2.8 μmol/m². The solids were characterized by infrared spectroscopy (IR), ultraviolet diffuse reflectance spectroscopy (DRS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and nitrogen adsorption. The behaviour of the phases towards the adsorption of acetaminophen was evaluated. Two phases showed a higher retention capacity than that exhibited by the commercial octadecyl phase. Recovery results remained between 70% and 100%.

The purpose of this study was to investigate the adsorption of two Basic dyes, i.e. Basic Blue 3 (BB3) and Basic Orange 2 (BO2), onto Sphagnum Magellanicum peat. The equilibrium studies were carried out at 30°C and 45°C, respectively. The equilibrium experimental results were fitted to the Langmuir model to obtain the characteristic parameters. The maximum sorption capacities for each dye were 41 mg/g for BB3 and 92 mg/g for BO2. The magnitude of the a_L parameter increased with temperature for both dyes. The batch kinetic studies of Basic dye adsorption onto peat considered the effect of the initial concentrations of the dyes and the peat dosage. The models fitted were first order (Lagergren equation), pseudo-second order (chemisorption mechanism) and intra-particle diffusion. For all the systems studied, the pseudo-second-order model provided the best correlation. The intra-particle diffusion model provided good correlations over the intermediate and final steps of the adsorption process.

We report some conceptual and numerical results for a single-column chromatographic process analogous to a simulated moving bed (SMB) with asynchronous port switching. It is shown that the periodic state of the multi-column SMB unit is reproduced by a one-column chromatograph in which the part of its outlet stream that is not recovered as product is recycled back to the column with a lag of (N – 1)τ time units, where N and τ are, respectively, the number of columns and the switching interval of the equivalent SMB unit. This requirement holds true regardless of the port configuration or operational scheme of the analogous multi-column unit. The proposed one-column chromatographic process is a more compact, less expensive and simpler-to-operate alternative to the SMB. By changing the operation of the single-column chromatograph from the classical synchronous port switching to an optimized asynchronous Varicol mode, it is shown that one can easily compensate for a less perfect operation of the plug-flow device that implements the recycle lag.

A basic investigation of the removal of Cd(II) and Zn(II) ions from aqueous solutions by Sargassum sp. and NaY zeolite was conducted at room temperature under batch conditions. The results obtained indicated that, for both sorbents, cadmium and zinc ion uptake could be described by the Langmuir adsorption model. The kinetics of the biosorption process followed a pseudo-second-order model, whereas equilibrium in the ion-exchange process was attained so rapidly that the data obtained could not be modelled. The maximum uptake capacities of the sorbents studied were 120 mg/g biomass and 108 mg/g zeolite for cadmium ions and 45.5 mg/g biomass and 70 mg/g zeolite for zinc ions, respectively. This can be considered an excellent result compared with conventional adsorbent materials. Thus Sargassum sp. and NaY zeolite have a great potential for removing cadmium and zinc ions, especially when the concentrations of these ions are low as in wastewater stream samples.

Industrial effluents discharged into aquatic bodies without proper treatment have contributed to the increasing pollution of water by heavy metals. The development of efficient processes for the treatment of industrial effluents is becoming more and more vital since legislation concerning the disposal of metal-contaminated effluents is becoming ever more rigorous.

In the present work, the adsorption of Cd(II) and Ni(II) ions by chelate-impregnated clays has been examined. Montmorillonite K10, an acid-treated industrial clay purchased from Fluka Chemicals, was impregnated with di(2-ethylhexyl)phosphoric acid (D₂EHPA), sodium diethyldithiocarbamate (DDTC) and the disodium salt of iminodiacetic acid (IDA). We have investigated the sorption process from both the static (batch) and kinetic viewpoint, and have studied the influence of pH and temperature on the process. It was observed that the clays exhibited rapid adsorption capabilities and that those impregnated with IDA and DDTC had a high efficiency in the removal of Cd(II) and Ni(II) ions.

New integrated schemes combining membrane permeation and pressure swing adsorption (PSA) have been developed for gas separation. By using the membrane as a pre-bulk separation unit and coupling it to the intrinsically dynamic periodic operation of the PSA, the separation performance of the hybrid scheme is enhanced with respect to that of the two stand-alone units. Instead of constant-composition regular feed, the PSA is fed with a mixture which is progressively enriched in the more adsorbed component during the pressurization and high-pressure adsorption steps of the cycle. This results in sharper concentration fronts.

The hybrid scheme detailed here has been applied successfully to the bulk separation of an 30:70 mol% CO₂/N₂ mixture over activated carbon. Process performance is reported in terms of product recovery and purity at cyclic steady state. Numerical simulations were validated by experimental work on a composite membrane and a laboratory-scale PSA unit. For the examples studied, product purity and recovery for the hybrid process were increased by 23% and 58% for CO₂, and by 14% and 5% for N₂, compared to an equivalent stand-alone PSA.