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A detailed kinetic model was proposed to analyze experimental data obtained from indole hydrodenitrogenation (HDN) over γ-Al2O3 and amorphous silica-alumina (ASA)-supported NiMo catalysts. The goal was to investigate the support acidity effects on indole HDN and compare with a recent study on quinoline HDN. Similarly to quinoline HDN, indole HDN occurred via hydrogenation of the aromatic ring, followed by N-ring opening and exocyclic C-N bond breaking. The high support acidity of NiMo(P)/ASA exhibited a promoting effect for N-removal steps and adsorption of nitrogen compounds. However, in contrast to quinoline HDN, it did not clearly induce a positive effect for the hydrogenation step. The acidic function of ASA also favored the formation of byproducts such as toluene, cyclohexane, dimer, and trimer of indole. Catalytic conversion of a quinoline and indole mixture revealed a strong inhibiting effect of quinoline on indole HDN, whereas the inhibiting effect of indole on quinoline HDN was weak. The inhibition was weaker over NiMo(P)/Al2O3 than over NiMo(P)/ASA. This result is in agreement with a relative ranking of apparent adsorption constants of quinoline, indole, and their products on NiMo(P)/Al2O3 and ASA. [ABSTRACT FROM AUTHOR]

The adsorption processes for postcombustion CO2 capture are usually based on a temperature or vacuum swing (TSA or VSA). In the present contribution an alternative concept is presented, which is based on the regeneration of the solid sorbent (an immobilized amine) by a purge gas, low pressure vapor, under almost isothermal conditions. Because of the close to isothermal operation, the process consumes significantly less thermal and mechanical energy than conventional TSA and VSA processes, respectively. We present a rough design of such an isothermal concentration swing process based on a simplified, analytical model of a 2-step PSA (pressure swing adsorption) process. The analytical model allows a definition of the range of operating conditions that lead to the best compromise between energy consumption and productivity (size and number of the adsorbers). Moreover, it is possible to define the equilibrium and mass transfer properties of the ideal solid sorbent. The feasibility of the concentration swing process was finally validated by numerical simulations of a full PSA cycle under adiabatic conditions. [ABSTRACT FROM AUTHOR]

In silico screening of CO2 adsorbents is a very powerful method for preselecting the most promising porous solids for experimental studies. Because of increased computational power, it is now possible to investigate a large number of adsorbents in a fairly short time. However, it remains difficult to rationalize structure-performance correlations because the complexity of such porous materials cannot be reduced to a few simple descriptors. In this paper, we present a different approach that was applied to the design of an optimal adsorbent for CO2 separation from gas mixtures. A CO2-CH4 mixture was used as the feed. We constructed a simplified model of the porous material by adopting a spherical pore geometry. From the dispersion-repulsion point of view, the spherical pore was modeled by homogeneously distributed Lennard-Jones sites. Besides, a charge distribution was introduced to mimic the electrostatic behavior. The selected charge distribution is constituted of negative charges homogeneously distributed over the surface of the pore. The total negative charge is counterbalanced by eight positive discrete charges placed on the corners of the cube inscribed in the sphere. This model can be characterized by two main descriptors: the pore size and the cation charge. For this model, the adsorbate-adsorbent interaction potential due to electrostatic and dispersion-repulsion interactions was determined. Then, the Henry constants of CO2 and CH4 are calculated from statistical thermodynamics and substituted in the Ruthven statistical model, which allows calculation of the binary adsorption isotherms. Finally, the adsorbed quantities are used to estimate the performance indexes of the pressure swing adsorption (PSA) process, such as the working capacity and separation factor. We show how these two parameters depend on the pore size and cation charge. For a medium-pressure PSA process, the optimal adsorbent has a large pore volume and is highly charged, which provides high working capacity and selectivity. The high cationic charge allows one to efficiently fill the large pore volume and assures high CO2 selectivity. [ABSTRACT FROM AUTHOR]

Thechoice of an appropriate adsorbent for CO2separationby pressure-swing adsorption remains a field of intense research.In this work, several FAU and LTA zeolites with different Na contents(Si/Al ratios) are studied for the separation of CO2frommixtures of CO2, CO, and CH4by means of breakthroughexperiments. The breakthrough experiments were carried out between1 and 5 bar at 303 K using two feed mixtures: 50/50 (v/v) CO2/CH4and 75/15/15 (v/v/v) CO2/CH4/CO. The most polar zeolites, i.e., those with high Na content, exhibitthe highest adsorption capacity and selectivity for CO2, but their regeneration is difficult; hence, their working capacityis low. The opposite is true for the least polar zeolites, i.e., thosewith low Na content. In order to quantify the trade-off between theselectivity and working capacity, the Ruthven statistical model (RSM)was used. It satisfactorily reproduced the experimental trends. We,therefore, used the RSM to identify the properties of the adsorbentthat lead to an optimal compromise between the working capacity andseparation factor. The critical parameter is the concentration ofextraframework cations, which, in turn, depends on the framework chargeof the zeolites FAU and LTA. The optimal trade-off zone is definedin terms of the Henry constant of CO2(KCO2). It is found that this zone is placedbetween KCO2= 5 × 10–3and 50 × 10–3molecules·bar–1·Å–3. This interval correspondsto a heat of adsorption of CO2at zero coverage between27 and 32 kJ·mol–1. In our study, this optimalrange of Henry constants was achieved for the zeolites Na-USY, SAPO-37,LTA (Si/Al = 5), and EMC-1. [ABSTRACT FROM AUTHOR]

The separation of paraffin isomers is a very importanttopic inthe petrochemical industry. Zeolite 5A is industrially used to sievealkane isomers, but its pore size does not allow the separation ofmonobranched and dibranched alkanes by a kinetic mechanism. In thispublication, we compare three ZIF materials in the separation of C6-paraffinisomers: ZIF-8, ZIF-76, and a new material called IM-22. The performanceof the materials is evaluated by a breakthrough curve of binary mixturesof n-hexane, 3-methylpentane, and 2,2-dimethylbutane.We show that ZIF-8 is a very attractive alternative to zeolite 5Abecause it exhibits a high (kinetic) selectivity for the adsorptionof linear alkanes and at the same time a high adsorption capacity.The new material IM-22, a ZIF with CHAtopology, seemsto be particularly suited for the separation of mono- and dibranchedparaffin isomers. [ABSTRACT FROM AUTHOR]