João C. Santos

Toward Understanding the Influence of Ethylbenzene in p-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 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.

Selective Liquid Phase Adsorption and Separation of ortho-Xylene with the Microporous MIL-53(Al)

Metal-organic framework MIL-53(Al) pellets were tested for the selective adsorption and separation of xylene isomers, in liquid phase and using n-heptane as eluent. The objective of this work is to assess relevant data for a posterior xylene isomers separation process design. In order to complete this study, single and multi-component breakthrough experiments were performed at 313 K, in the presence of n-heptane. MIL-53(Al) presented a preference for o-xylene over m-xylene and p-xylene in all experiments. The selectivities of 2.0 were obtained for o-xylene over m-xylene and over p-xylene. It is concluded that MIL-53(Al) may be used for separating o-xylene from the other xylene isomers, using n-heptane as desorbent. Supplemental materials are available for this article. Go to the publishers online edition of Separation Science & Technology to view the free supplemental file.

Gas-phase simulated moving bed: Propane/propylene separation on 13X zeolite

In the last years several studies were carried out in order to separate gas mixtures by SMB technology; however, this technology has never been implemented on an industrial scale. In the present work, a gas phase SMB bench unit was built and tested for the separation of propane and propylene mixtures, using 13X zeolite extrudates as adsorbent and isobutane as desorbent. Three experiments were performed to separate propane/propylene by gas phase SMB in the bench scale unit with a 4-2-2 configuration, i.e., open loop circuit by suppressing section IV (desorbent regeneration followed by a recycle). Consequently, all the experiments were conducted using an external supply of pure isobutane as desorbent. Parameters such as switching time, extract and raffinate stream flow rates were changed to improve the efficiency of the process. Experimental results have shown that it is feasible to separate propylene from propane by gas phase SMB at a bench scale and that this process is a potential candidate to replace the conventional technologies for the propane/propylene separation. The performance parameters obtained are very promising for future development of this technology, since propylene was obtained in the extract stream with a purity of 99.93%, a recovery of 99.51%, and a productivity of [Formula: see text] . Propane was obtained in the raffinate stream with a purity of 98.10%, a recovery of 99.73% and a productivity of [Formula: see text] . The success of the above mentioned bench scale tests is a big step for the future implementation of this technology in a larger scale.

Syngas Stoichiometric Adjustment for Methanol Production and Co-Capture of Carbon Dioxide by Pressure Swing Adsorption

Methanol is an important raw material in industry and is commonly produced from syngas. The stoichiometric ratio (H2–CO2)/(CO + CO2) of the methanol synthesis reactor feed stream must be adjusted to approximately 2.1. In this study, the replacement of the solvent unit within a coal to methanol process by a pressure swing adsorption (PSA) unit is proposed. The PSA produces a hydrogen enriched stream, to adjust the stoichiometric ratio of the methanol feed stream, and simultaneously captures the carbon dioxide for future sequestration. The feed flow rate is sub divided into eight 4-bed PSA units, operated with a defined phase lag between them in order to flatten the products (composition and flow rate) oscillations. The results show that the stoichiometric adjustment is possible and that oscillations on the products flow rate and composition are reduced to less than 3%. A carbon dioxide stream of 95.15% is obtained with a recovery of 94.2% and a productivity of 82.7 mol CO2/kg/day. The power consumption of the global process is 119.7 MW, which includes the requirements for the rinse stream (64.4 MW) and the compression of the CO2 product to 110 bar for sequestration (55.3 MW).

Surface B-splines fitting for speeding up the simulation of adsorption processes with IAS model

Abstract The ideal adsorbed solution theory (IAS) is commonly used in process simulation for predicting multicomponent adsorption equilibrium. However, this model requires a significant computational effort which translates in time consuming simulations. A methodology using surface B-splines fitting was developed for speeding the prediction of the multicomponent equilibrium with IAS theory. As a case study, a breakthrough of an enantiomer bi-component mixture in a fixed bed was simulated and a speed-up of 57.9% was achieved while maintaining the accuracy of IAS multicomponent equilibrium prediction.

Simulated Moving Bed Reactor

The simulated moving bed reactor (SMBR), an important chromatographic reactor, is addressed in this chapter. The SMBR mathematical model, considering external and internal mass-transfer resistances and variable velocity due to change of liquid composition, is shown. An analytical solution for linear SMBR in the presence of mass-transfer resistances, based on the steady-state equivalent true moving bed reactor analogy, is also presented. This solution allows a fast evaluation of the linear SMBR performance for different conditions. The required steps to implement an SMBR-based process, fundamental data acquisition and validation, are highlighted using the green solvent ethyl lactate as a case study. The performance of this reactor for acetals production is also discussed. For all the studied compounds, the SMBR exhibits high conversion and high productivity at moderate temperatures, but also a significant desorbent consumption, which might be reduced by using new materials with lower water affinity.

Gas-Phase Simulated Moving Bed

In this chapter, two methods are proposed for the design of a gas-phase simulated moving bed: by making use of the equilibrium theory or by mathematical modeling and computer simulation. A mathematical model of a gas-phase SMB unit is presented, comprising mass and energy balances and a mass-transfer model that describes these phenomena at macropore and micropore levels. The separation region for the test case separation—propane/propylene—was determined with 13X zeolite as adsorbent and isobutane as desorbent using both design methodologies, and the advantages of each method are addressed.