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Zeolite Beta membranes for the separation of hexane isomers

Publication . Bárcia, Patrick da Silva; Silva, José A.C.; Gascon, Jorge; Aguado, Sónia; Ferreira, Alexandre; Rodrigues, Alírio; Kapteijn, Freek

The preparation of a-alumina supported zeolite Beta membranes was successfully achieved and sped up by exploring combinations of three seeding techniques and three synthetic methods. The surface of the membranes was completely covered by well intergrown crystals; the thickness of the zeolite layers ranged from 2 to 6 lm depending on the synthesis method used. The quality of the membranes was tested by means of pervaporation of ethanol/1,3,5-triisopropylbenzene (TIPB) mixtures together with permporometry experiments. The performance in the vapour separation of quaternary equimolar mixtures of nhexane (nHEX), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB) and 2,2-dimethylbutane (22DMB) in the range 343–443 K showed that permeate flux decreases as the branching degree increases following the order: nHEX 3MP > 23DMB > 22DMB. In the retentate, the fractions of monobranched and normal hexane decrease while the concentration of dibranched isomers is increased compared to the feed composition. The influence of the temperature in the permeation fluxes indicates the existence of an activated transport mechanism which favours the permeation of more nHEX and 3MP with regard to their dibranched isomers. The octane number (ON) of the quaternary mixture was enhanced up to 5 points with the best synthesized membrane.

2010Journal article

Open access

Separation of light naphtha for the octane upgrading of gasoline: adsorption and membrane technologies and new adsorbents

Publication . Bárcia, Patrick da Silva; Rodrigues, A.E.; Silva, José A.C.

The aim of this work is to contribute for the development of adsorption based separation processes with considerable potential for commercial application on the refining industry, namely, in the separation of high research octane number (HRON) paraffins from light naphtha fractions. The development of an adsorption process requires first a detailed knowledge of equilibria and kinetics of adsorption and their impact on the dynamic response of an adsorption column. Accordingly, we start collecting single and mixture adsorption equilibrium isotherms of C6 isomers, n-hexane (nHEX), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB), and 2,2- dimethylbutane (22DMB), from breakthrough experiments in zeolite beta. This adsorbent was selected because its pore system posses interesting characteristics for the separation of HRON dibranched C6 from their low research octane number (LRON) monobranched isomers. It was found that the sorption hierarchy in zeolite beta was most favourable towards the linear isomer and least favourable towards the dibranched ones. Zeolite beta demonstrated significant selectivity to discriminate between mono and dibranched C6 isomers, especially at low coverage. Based on an analysis of sorption events at the molecular level, a Tri-Site Langmuir model (TSL) was developed to interpret the equilibrium data with good accuracy. Sorption kinetics studied by zero-length chromatography technique allowed us to find the nature of controlling diffusion mechanism; for nHEX and 3MP macropore diffusion is controlling. For 23DMB and 22DMB, the system is governed apparently by both macropore and micropore diffusion. The dynamics of equimolar C5/C6 paraffin fractions in a fixed bed of zeolite beta was studied. Breakthrough experiments demonstrate that the sorption hierarchy is temperature-dependent. At 583 K, an enriched HRON fraction of 22DMB, iso-pentane (iPEN) and 23DMB can be selectively separated from the isomerate feed. For the case of feed mixtures with the typical composition of the hydroisomerization reactor product, the enriched fraction contains LRON n-pentane (nPEN) which decreases the octane quality of the product obtained. However, the use of a layered bed with zeolite 5A and zeolite beta can displace the nPEN from the enriched fraction, resulting in a maximum octane number of about 92.5 points. Aspen Adsim was used to simulate the dynamic behaviour of the C5/C6 fraction in a non-isothermal and non-adiabatic bed giving a good description of the set of experimental data. An optimal design of a mono/dibranched separation process can be achieved by properly tuning the operating temperature and the zeolite 5A/zeolite beta ratio on a layered fixed bed. The performance of a layered pressure swing adsorption (PSA) process for the separation of HRON paraffins from a C5/C6 light naphtha fraction is simulated using a detailed, adiabatic single column PSA model. A zeolite 5A layer is used for selective adsorption of LRON n-paraffins while a zeolite beta layer is used to reduce the concentration of the LRON 3MP in the HRON fraction. The effects of various independent process variables (zeolite 5A-to-zeolite beta ratio, purge-to-feed ratio, cycle time, depressurization mode and operating temperature) on the process performance (product RON, HRON molecules recovery, HRON purity, and process productivity) are evaluated. It is demonstrated that an optimal zeolite 5A-to-zeolite beta ratio can improve the product average RON of up to 1.0 point comparatively to existing processes using zeolite 5A only. Moreover, process simulations demonstrated that an increase of 20 K in the operating temperature results in octane gain of 0.2 RON. The study and development of membrane technologies was also included in this work as an alternative to PSA processes. The preparation of supported zeolite beta membranes was successfully achieved by exploring several combinations of seeding techniques and synthesis methods. The surface of the membranes was completely covered by well intergrown crystals. The quality of the membranes was tested by means of pervaporation of ethanol/1,3,5-triisopropylbenzene mixtures together with permporometry experiments. The performance in the vapour separation of quaternary equimolar mixtures of C6 isomers showed that permeate flux decreases as the branching degree increases following the order: nHEX>>3MP>23DMB>22DMB. In the retentate, the fractions of 3MP and nHEX decrease while the concentration of dibranched isomers is increased compared to the feed composition. The RON of the quaternary mixture was enhanced up to 5 points with the best synthesized membrane. The potential application of the novel metal-organic frameworks (MOFs) as an alternative to zeolites was also addressed. A screening study for mixtures of C6 isomers was performed in three different MOFs.The first is a rigid zirconium terephthalate UiO- 66, which possesses two types of cages of diameter 12 Å and 9 Å; the second is a chromium trimesate MIL-100(Cr), which possesses a rigid structure with giant cages accessible through 5-9 Å microporous windows; and the third is the flexible Zn2 (BDC)2(H2O)2·(DMF) (MOF-2), in which the pore system contains 1-D large channels. Multicomponent equimolar experiments show that UiO-66 exhibits inverse shape selectivity for C6 isomers, being the retention governed by the rotational freedom of the molecules in the small cages. In the MIL-100(Cr), the sorption hierarchy is similar to the one found in zeolite beta. Finally, MOF-2 exhibits extraordinary n/iso selectivity, by making use of an unusual guest-dependent dynamic behaviour to exclusively take up nHEX, while hindering the access of branched C6 isomers to the pore system.

2010Doctoral thesis

Open access

Single and multicomponent sorption of CO2, CH4 and N-2 in a microporous metal-organic framework

Publication . Bárcia, Patrick da Silva; Bastin, Laurent; Hurtado, Eric; Silva, José A.C.; Rodrigues, Alírio; Chen, Banglin

Single and multicomponent fixed-bed adsorption of CO2, N-2, and CH4 on crystals of MOF-508b has been studied in this work. Adsorption equilibrium was measured at temperatures ranging from 303 to 343 K and partial pressures up to 4.5 bar. MOF-508b is very selective for CO2 and the loadings of CH4 and N-2 are practically temperature independent. The Langmuir isotherm model provides a good representation of the equilibrium data. A dynamic model based on the LDF approximation for the mass transfer has been used to describe with good accuracy the adsorption kinetics of single, binary and ternary breakthrough curves. It was found that the intra-crystalline diffusivity for CO2 is one order of magnitude faster than for CH4 and N-2.

2008Journal article

Open access

Modeling adsorption equilibria of xylene isomers in a microporous metal–organic framework

Publication . 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.

2012Journal article

Open access

Separation of branched hexane isomers using zeolite BEA for the octane improvement of gasoline pool

Publication . Bárcia, Patrick da Silva; Silva, José A.C.; Rodrigues, Alírio

A sorption study of single, binary, ternary and quaternary mixtures of hexane (C6) isomers nhexane (nHEX), 3-methylpentane (3MP), 2,3-dimethylbutane (23DMB) and 2,2- dimethylbutane (22DMB) was performed in commercial pellets of zeolite BETA (BEA structure), covering the temperature range between 423 K and 523 K and partial pressures up to 0.3 bar. From these data, single and multicomponent adsorption equilibrium isotherms were collected. An extended tri-site Langmuir model (TSL) was developed to interpret accurately the equilibrium data, and a dynamic adsorption model was developed and tested predicting with a good accuracy the behaviour of multicomponent fixed bed experiments. At the partial pressures studied, the sorption hierarchy in the zeolite BETA is: nHEX>3MP>23DMB>22DMB. BEA structure demonstrates a significant selectivity between C6 isomers, especially at low coverage, giving a good perspective regarding future work

2007Conference paper

Open access