Browsing by Author "Nicolau, Marco"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- Modeling adsorption equilibria of xylene isomers in a microporous metal–organic frameworkPublication . Bárcia, Patrick da Silva; Nicolau, Marco; Gallegos, José; Chen, Banglin; Rodrigues, Alírio; Silva, José A.C.Single and multicomponent adsorption equilibria of xylene isomers: o-xylene (o-x), m-xylene (m-x), pxylene (p-x) and ethylbenzene (eb) was investigated on the three dimensional microporous metal–organic framework Zn(BDC)(Dabco)0.5 (BDC = 1,4-benzenedicarboxylate, Dabco = 1,4-diazabicyclo[2.2.2]-octane), MOF 1, in the range of temperatures between 398 and 448 K and partial pressures up to 0.1 bar. The equilibrium data show that a significant amount (around 34 g/100gads at 398 K) of xylene isomers can be adsorbed in MOF 1. The affinity to the adsorbent measured by the Henry’s constants to decreases in the order o-x > m-x > eb > p-x for all temperatures. The zero coverage adsorption enthalpies are all similar and range from 77.4 (eb) to 79.8 kJ/mol (o-x). The Dual-Site Langmuir model (DSL) was used for the interpretation and correlation of the experimental data. The parameters obtained from the pure component isotherms fitting were also used to predict the multicomponent equilibrium data by an extended DSL model. A good agreement was obtained between the predictions and the experimental data. It was also demonstrated that the DSL model is also capable to explain the increase in the isosteric heat of sorption with increasing coverage.
- Separação dos Isómeros de Xileno em Metal-Organic Frameworks - MOFsPublication . Nicolau, Marco; Silva, José A.C.A separação dos isómeros de xileno é um problema clássico da indústria petroquímica devido à sua ligação directa à produção de PET. A destilação é uma das formas possíveis de remover o o-xileno, mas falha para os restantes alquilaromáticos devido aos pontos de ebulição serem muito próximos. Além da cristalização, a qual possui uma pobre eficiência, a adsorção é largamente usada, sendo operado industrialmente em leito móvel simulado (SMB). Como adsorventes nesses processos são usados os zeólitos X e Y, permutados com catiões, tal como o Na+, K+ e Ba2+. Os metal-organic frameworks (MOFs) são uma nova classe de materiais cristalinos e recebem actualmente bastante interesse devido às suas potencialidades para serem aplicados como adsorventes. O carácter maioritariamente orgânico da superfície interna dos MOFs oferece um potencial sem precedentes para melhorar e ajustar a afinidade para adsorbatos aromáticos. Este trabalho representa um dos primeiros estudos acerca do uso de MOFs na separação por adsorção em fase gasosa dos isómeros de xileno. Neste trabalho, apresenta-se um estudo detalhado do equilíbrio de adsorção mono- e multicomponente dos isómeros de xileno e do etilbenzeno no MOF Zn(BDC)(Dabco)0:5. Os resultados obtidos, indicam que o MOF em estudo apresenta duas categorias de sítios activos de adsorção e que a forma como as moléculas se empacotam na estrutura microporosa do sólido pode ser determinante na separação. Além da baixa selectividade, o valor elevado das entalpias de adsorção, comparativamente aos zeólitos, é prejudicial do ponto de vista da operação de processos adsorptivos. The separation of mixed C8 alkylaromatic compounds is one of the most challenging issues in the chemical industry because of its direct link with PET manufacture. Distillation is only feasible for the removal of o-xylene; it fails for the other C8 alkylaromatic compounds because of the similarity of their boiling points. Besides crystallization, which has a poor efficiency, adsorption is widely used and is operated industrially in simulated moving bed processes. Zeolites X and Y exchanged with cations such as Na+, K+ e Ba2+ are used in such processes. Metal-organic frameworks (MOFs) are a new class of microporous crystalline materials and currently receive much attention in regard to adsorption applications. The mainly organic character of the inner surface of MOFs offers unprecedented potential for enhancing and fine-tuning the affinity for aromatic adsorbates. This work represents one of the first uses of MOFs in the separation by adsorption of xylene isomers under vapor conditions. This work reports a detailed experimental study of single and multicomponent adsorption equilibrium of xylene isomers and ethylbenzene in the MOF Zn (BDC)(Dabco)0:5. The results arising from this study lead us to conclude that the MOF has two categories of adsorption sites and that the stacking of the molecules in the microporous structure is crucial in the separation. Besides the poor selectivity, the high value of the adsorption enthalpy of aromatics in this MOF, in comparison to zeolites, is not beneficial with respect to the operation of adsorption processes.
- Single- and multicomponent vapor-phase adsorption of xylene isomers and ethylbenzene in a microporous metal-organic fameworkPublication . Nicolau, Marco; Bárcia, Patrick da Silva; Gallegos, José; Silva, José A.C.; Rodrigues, Alírio; Chen, BanglinVapor-phase adsorption of the C8 alkylaromatic components p-xylene (p-x), m-xylene (m-x), o-xylene (o-x), and ethylbenzene (eb) on the three-dimensional rnicroporous metal-organic framework (MOF) Zn(BDC)-(Dabco)(0.5) (BDC = 1,4-benzenedicarboxylate, Dabco = 1,4-diazabicyclo[2.2.2]octane) was investigated. Single- and multicomponent fixed-bed experiments were carried out at temperatures ranging from 125 to 175 degrees C and total hydrocarbon pressures up to 0.10 bar. At high pressure, the adsorption capacity for all the components varies from 35 to 26 g/100 g(ads) at 125 and 175 degrees C. Henry's constants are slightly different for all C8 alkylaromatics, except for o-xylene, which is significantly higher. The adsorption enthalpies at zero coverage for the different isomers ranges from 77.40 (eb) to 79.84 kJ/mol (o-x), indicating that the C8 alkylaromatics have comparable interactions with the framework at the low coverage, On the basis of binary and quaternary breakthrough experiments performed at different hydrocarbon pressures and temperatures, MOF Zn(BDC)(Dabco)(0.5) was realized for the efficient and feasible separation of o-xylene from other C8 alkylaromatic components with the selectivity up to 1.88 because of the stronger interactions between o-xylene molecules and the framework and their differential pore-filling and molecular-packing effects confined within nanopores of MOFs.