Xylene Isomerization over Beta Zeolites in Liquid Phase

An experimental study of xylene isomers interconversion (isomerization) kinetics was conducted to gain a deeper insight into the field. Two beta zeolites with SiO₂/Al₂O₃ ratio of 35 (BEA35) and 38 (BEA38) were used as catalysts for the performed experiments. The isomerization reactions were carried out under the following conditions: 513, 493, 473, and 453 K at 2.1 MPa in liquid phase. It was verified that all reactions were in the kinetic-controlled regime. Kinetic constants were estimated with four different models; two of them were based on the xylene isomerization thermodynamic equilibrium from the literature. The linear reaction scheme, which does not consider the direct conversion between <i>p-</i> and <i>o-</i>xylene, presented a better fit to the experimental values. Higher conversion of <i>p-</i>xylene was observed when compared with the conversion of the other two isomers. This may be attributed to its smaller molecular size. BEA35 presented better performance due to its higher amount of Brønsted acid sites. Finally, activation energies over the two catalysts, estimated through Arrhenius equation, presented similar values

Stability of an Al-Fumarate MOF and Its Potential for CO₂ Capture from Wet Stream

In this work, a new aluminum fumarate MOF was investigated regarding its water stability and CO₂ adsorption in the presence and absence of water. The adsorption equilibrium isotherms were measured at 303, 323, and 348 K for CO₂ and at 288 and 313 K for water vapor. Water vapor adsorption isotherms are type IV and were fit using the Langmuir-Ising model. The adsorption capacity of CO₂ at 303 K and 1.0 bar was 2.1 mmol/g and remained constant after exposure to humidity and regeneration. The isosteric heats of adsorption were 21 and 44 kJ/mol for CO₂ and H₂O, respectively. Fixed bed experiments were performed at 303 K to determine breakthrough curves of CO₂, water vapor, and the CO₂/water vapor mixture. Binary breakthrough indicated a reduction of only 17% in CO₂ adsorption capacity for a stream with 14% RH. The remarkable stability of this MOF suits it for such applications as CO₂ capture and thermal storage with water

Toward Understanding the Influence of Ethylbenzene in <i>p</i>-Xylene Selectivity of the Porous Titanium Amino Terephthalate MIL-125(Ti): Adsorption Equilibrium and Separation of Xylene Isomers

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 <i>n</i>-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 <i>n</i>-heptane as the eluent. MIL-125­(Ti) is a <i>para</i>-selective material suitable at low concentrations to separate <i>p</i>-xylene from the other xylene isomers. Pulse experiments indicate a separation factor of 1.3 for <i>p</i>-xylene over <i>o</i>-xylene and <i>m</i>-xylene, while breakthrough experiments using a diluted ternary mixture lead to selectivity values of 1.5 and 1.6 for <i>p</i>-xylene over <i>m</i>-xylene and <i>o</i>-xylene, respectively. Introduction of ethylbenzene in the mixture results however in a decrease of the selectivity