Microemulsions are nanoheterogeneous, thermodynamically stable, spontaneously forming mixtures of oil and water by means of surfactants, with or without cosurfactants. The pledge to use small volumes of amphiphile molecules compared to large amounts of bulk phase modifiers in a variety of chemical and industrial processes, from enhanced oil recovery to biotechnology, fosters continuous investigation and an improved understanding of these systems. In this work, we develop a molecular thermodynamic theory for droplet-type microemulsions, both water-in-oil and oil-in-water, and provide the theoretical formulation for three-component microemulsions. Our thermodynamic model, which is based on a direct minimization of the Gibbs free energy of the total system, predicts the structural and compositional features of microemulsions. The predictions are compared with experimental data for droplet size in water-alkane-didodecyl dimethylammonium bromide systems.

MetalÀorganic framework MIL-53(Al) pellets were tested for selective adsorption and separation of xylene isomers with the aim of studying the influence of the solvent used at bulk concentrations. In this way, a set of single and multicomponent pulse experiments to measure selectivities was conducted, with iso-octane, n-hexane, and n-heptane as eluents, at 313 K. In order to complete this study, multicomponent breakthrough experiments were also performed, under the same conditions, in the presence of these three eluents, and the obtained selectivities were compared. MIL-53(Al) presented a preference for o-xylene over m-xylene and p-xylene in all experiments. The selectivity was higher when n-heptane was the eluent. For the breakthrough experiments that used nheptane as the eluent, selectivities of 2.1 were obtained for o-xylene over m-xylene and over p-xylene. It was possible to conclude that the choice of eluent influences the adsorption selectivity and capacity of the adsorbent. This could result, among other factors, from the adsorbentÀadsorbate interactions. These interactions may also occur with the eluent molecules (as an adsorbate), which influences the adsorption capacity.

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The potential of the porous crystalline titanium dicarboxylate MIL-125(Ti) in powder form was studied for the separation in liquid phase of xylene isomers and ethylbenzene (MIL stands for Materials from Institut Lavoisier). We report here a detailed experimental study consisting of binary and multi-component adsorption equilibrium of xylene isomers in MIL-125(Ti) powder at low (≤0.8 M) and bulk (≥0.8 M) concentrations. A series of multi-component breakthrough experiments was first performed using n-heptane as the eluent at 313 K, and the obtained selectivities were compared, followed by binary breakthrough experiments to determine the adsorption isotherms at 313 K, using n-heptane as the eluent. MIL-125(Ti) is a para-selective material suitable at low concentrations to separate p-xylene from the other xylene isomers. Pulse experiments indicate a separation factor of 1.3 for p-xylene over o-xylene and m-xylene, while breakthrough experiments using a diluted ternary mixture lead to selectivity values of 1.5 and 1.6 for p-xylene over m-xylene and o-xylene, respectively. Introduction of ethylbenzene in the mixture results however in a decrease of the selectivity.

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A new hybrid process for the production of o-and p-xylene is proposed to replace the traditional plant of aromatics in refineries. The proposed process comprises a simulated moving bed (SMB) unit and two crystallizers. The SMB technology as the first unit of the suggested process is applied for the separation of xylene isomers and was investigated by simulation of an industrial size unit, using experimentally measured adsorption equilibrium data on MIL-53(Al)-shaped material. The separation of p-xylene from o-xylene with m-xylene as desorbent is the key characteristic of this method. An industrial-scale SMB unit could provide extract and raffinate streams with very high purities.

The search for new adsorbents with enhanced capacity and selectivity, suitable for application on large‐scale simulated moving‐bed units for separation of p‐xylene, requires efficient, reliable, and fast adsorbent characterization methods for this specific separation. Fixed‐bed experiments were carried out under the conditions of the Parex process to evaluate a faujasite‐type zeolite as adsorbent for the separation of p‐xylene from its isomers in the proportions of the real Parex feed stream. The experimental breakthrough curves were used to evaluate the selected adsorbent in terms of nonselective and selective volumes, adsorption capacity, selectivity, and productivity, which can be applied to identify the feasible separation region for different operating conditions.