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Dominguez I.,University of Vigo | Gonzalez E.J.,LSRE Laboratory of Separation and Reaction Engineering | Palomar J.,Autonomous University of Madrid | Dominguez A.,University of Vigo
Journal of Chemical Thermodynamics | Year: 2014

Separation of aromatic and aliphatic hydrocarbons is a complex process in the petrochemical industry due to overlapping boiling points and azeotrope formation. In this paper, liquid extraction of aromatic compounds (toluene and ethylbenzene) from aliphatic compounds (hexane and cyclohexene) using ionic liquids (1-butyl-3-methylimidazolium methylsulfate, BMimMSO4, 1-propyl-3-methylimidazolium bis{trifluoromethylsulfonyl}imide, PMimNTf 2, and 1-butyl-3-methylimidazolium bis{trifluoromethylsulfonyl}imide, BMimNTf2) as solvent was studied. (Liquid + liquid) equilibrium (ELL) data for the ternary systems {hexane (1) + ethylbenzene (2) + BMimMSO 4, or BMimNTf2, or PMimNTf2 (3)}, {hexane (1) + toluene (2) + BMimMSO4 (3)} and {cyclohexene (1) + ethylbenzene (2) + BMimMSO4 (3)} were experimentally determined at T = 298.15 K and atmospheric pressure. Moreover, an analysis of the influence of the structure of each compound on the phase behavior was also carried out. The ability of the studied ILs to separate aromatic from aliphatic compounds was evaluated in terms of the solute distribution ratio, β, and the selectivity, S. The Non Random Two-Liquid (NRTL) and UNIversal QUAsiChemical (UNIQUAC) thermodynamic models were used to correlate the experimental LLE data. Furthermore, the COnductor-like Screening MOdel for Real Solvents (COSMO-RS) was applied to predict the (liquid + liquid) equilibrium. The suitability of this model to describe the phase behavior of the studied mixtures was evaluated comparing the experimental and calculated data. © 2013 Elsevier Ltd. All rights reserved.


Calvar N.,LSRE Laboratory of Separation and Reaction Engineering | Dominguez I.,University of Vigo | Gomez E.,University of Vigo | Palomar J.,Autonomous University of Madrid | Dominguez A.,University of Vigo
Journal of Chemical Thermodynamics | Year: 2013

For the study of the separation of benzene or toluene from octane, nonane and cyclooctane, the ionic liquids 1-butyl-3-methylimidazolium methylsulfate, BMimMSO4, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, BMimNTf2, were used as solvents. The (liquid + liquid) equilibria of the ternary systems {octane, or nonane, or (cyclooctane + benzene + BMimMSO4)}, and {(nonane + toluene + BMimMSO4) or BMimNTf2} at T = 298.15 K were determined, and an analysis of the influence of the structure of each compound was carried out. Besides, the experimental data have been compared with literature data with sulfolane as solvent. The experimental results obtained have been correlated using NRTL and UNIQUAC models. Finally, COSMO-RS has been used to predict the (liquid + liquid) equilibrium of the systems studied. The differences between the predicted and experimental values were used to evaluate the ability of the COSMO-RS model to describe the impact of the structure of the alkane, aromatic and ionic liquid on the (liquid + liquid) equilibria. © 2013 Elsevier Ltd. All rights reserved.


Garrido N.M.,LSRE Laboratory of Separation and Reaction Engineering | Garrido N.M.,Institute of Physical Chemistry | Jorge M.,LSRE Laboratory of Separation and Reaction Engineering | Queimada A.J.,LSRE Laboratory of Separation and Reaction Engineering | And 3 more authors.
Fluid Phase Equilibria | Year: 2010

In the present work, molecular dynamics calculations of the Gibbs energy of hydration of 10 different substituted barbiturates in SPC/E water were performed using thermodynamic integration. Given that experimental determination of the Gibbs hydration energy for this class of compounds is currently unfeasible, computer simulations appear as the only alternative for the estimation of this important quantity. Several simulation parameters are discussed and optimized based on calculations for barbituric acid. It is concluded that accounting for electrostatic interactions with the Reaction-Field method can be up to two times faster than with Particle-Mesh-Ewald method, without loss of accuracy. Different number of solvent molecules and simulation lengths were also tested. Lennard-Jones and electrostatic contributions were scaled down to zero in an independent way. It is shown that the electrostatic contribution is dominant (representing approximately 90% of the total Gibbs energy of hydration) and that barbiturate intra-molecular interactions cannot be neglected. The importance of the electrostatic contribution is attributed to the formation of hydrogen bonds between the barbiturates and water, which play an important role in the solvation process. The influence of the different substituents and their contribution to the Gibbs energy of hydration was assessed. Finally, the Lennard-Jones contributions and the total hydration Gibbs energy can both be correlated against molecular weight or partition coefficient data for mono- and di-substituted barbiturates. © 2009 Elsevier B.V. All rights reserved.


Silva B.,University of Porto | Ribeiro A.M.,University of Porto | Chang J.-S.,Korea Research Institute of Chemical Technology | Loureiro J.M.,LSRE Laboratory of Separation and Reaction Engineering | Rodrigues A.E.,University of Porto
Separations Division 2013 - Core Programming Area at the 2013 AIChE Annual Meeting: Global Challenges for Engineering a Sustainable Future | Year: 2013

Hydrogen is one of the most important industrial and potential chemicals, used in many applications, such as hydrocracking, hydrogenation of oils and in the production of methanol and ammonia. Moreover, due to environmental concerns hydrogen has increasingly received attention as it is a promising energy source for electrical power generation and transportation fuel (Ribeiro et al., 2009). Therefore, the demand of hydrogen is continuously increasing with the resulting worldwide attention and research motivation for advances in the field of hydrogen production and purification. Nowadays, the catalytic reforming of natural gas combined with a water gas shift reaction step is the main and the most cost-effective process for hydrogen production at a commercial scale (Sircar et al., 1999). The hydrogen production by steam methane reforming (SMR) originates a hydrogen stream containing several impurities, such as water vapor, CH4, CO2, N2 and CO. The use of hydrogen in fuel cell applications requires a high purity (99.99+%), which is attained by removing these impurities (Ribeiro et al., 2008). The commercial technology that is widely used for hydrogen purification and separation from steam methane reforming is pressure swing adsorption (PSA) (Ruthven et al., 1994). Several studies have been done focusing on PSA processes for hydrogen separation and purification (Yang and Lee, 1998; Park et al., 2000; Huang et al., 2008; Lopes et al., 2011; You et al., 2012). A new class of adsorbents named Metal Organic Frameworks (MOFs) represents an excellent alternative to the conventional materials used so far (Silva et al., 2012). The diversity in the configurations of these materials results from co-ordination between inorganic metal atoms and organic ligands or linkers, to form highly porous network structures (Chowdhury et al., 2012; Dasgupta et al., 2012). The use of MOFs is advantageous compared to the utilization of zeolites, since their skeleton accepts almost all the cations of the periodic table (Ferey et al., 2011). Among the different MOFs, CuBTC is one of the few materials that have already commercial availability. This material is composed of copper dimers coordinated to the oxygen atoms of benzene-1,3,5-tricarboxylate (BTC) linkers, forming a regular porous network with a large surface area (BET surface area up to 1600 m2/g), high pore volume, high chemical stability and Lewis acidity (Plaza et al., 2012). Because of these features, this material has a high potential for applications in the field of adsorption, such as gas separation and gas storage (Min Wang et al., 2002; Dathe et al., 2005; Millward and Yaghi, 2005). In this work, hydrogen purification from mixtures that also contain CO2, CO, CH4, and N2 was performed by PSA with CuBTC as adsorbent (supplied by KRICT). First, the equilibrium adsorption of each pure gas was measured in a magnetic suspension microbalance (Rubotherm, Germany). Second, single component, binary and ternary fixed-bed adsorption experiments were carried out. At the beginning of a breakthrough experiment, a stainless steel column filled with CuBTC and equipped with thermocouples, started to be fed with the gas mixture. During the adsorption and desorption steps, the temperature histories and the molar flow rate were recorded. Additionally, samples were collected in the loops of a multi-port valve for subsequent determination of the molar composition of the exit gas in the gas chromatograph. The same column, employed for the fixed-bed breakthrough curves described above, was used for PSA experiments. A PSA cycle of four elementary steps was performed. The PSA cycle started with the co-current pressurization with feed, followed by feed, blowdown and purge steps. In the purge step, a stream of pure hydrogen was used countercurrently at low pressure to regenerate the column. The mathematical modelling of a multicomponent adsorption in a fixed bed involves the material, momentum and energy balances that govern the process, taking into account axial dispersion and mass transfer resistances. The mathematical model developed was applied for the simulation of the breakthrough experiments. This fixed-bed model establishes the basic procedure to simulate adsorption-based cyclic processes. The modeling of a PSA unit involves the same conservation equations used for the fixed-bed simulations coupled with the appropriate boundary conditions for each step. The previously developed model was validated against the results obtained in breakthrough experiments and PSA tests. The results of the breakthrough experiments showed that the mathematical model describes well the dynamics of the adsorption processes that take place in the fixed bed. The adsorption and desorption showed a good fitting with the simulation results, since the molar fraction, molar flow rate and temperature histories were well predicted by the model. The typical roll-up that appears in multicomponent fixed bed adsorption is also observed and well predicted by the model. The increase of the molar flow rate of the adsorbed gases observed when the desorption step begins was well described by the model. The experimental pressure and temperature histories for all PSA experiments were well predicted by the model. The composition and the molar flow rate of each gas in the different experiments were generally well fitted by the model. In terms of PSA experiments with ternary mixtures, the best performance was achieved for a mixture with 78 % H2, 18 % CO2 and 3 % CH4 and a total cycle time of 516 s: 262 s, 62 s and 192 s for pressurization + feed, blowdown and purge steps, respectively. For this non-optimized cycle, a hydrogen purity of 99.97 % was attained, with a recovery of 45.76 % and a productivity of 6.86 mol.kg-1.h-1 (simulation results). In conclusion, this work demonstrates that the mathematical model developed is a powerful tool for the prediction of PSA experiments, which can save time and money, reducing the number of required experiments.


Oliveira E.L.G.,LSRE Laboratory of Separation and Reaction Engineering | Grande C.A.,LSRE Laboratory of Separation and Reaction Engineering | Rodrigues A.E.,LSRE Laboratory of Separation and Reaction Engineering
Chemical Engineering Science | Year: 2010

In this work we have studied the performance of catalyst extrudates of Ni-Al2O3 promoted with potassium for steam methane reforming. The most interesting property of this catalyst is the presence of large pores (average diameter of 8×10-4 m) to reduce diffusional limitations. We have determined the true kinetics using catalyst powder in the temperature range covering 757-804 K. Furthermore, experiments using a fixed bed filled with extrudates were performed in the temperature range covering 701-800 K at constant methane/steam ratio for different feed flowrates. In the true kinetic experiments using catalyst powder it was observed that this catalyst has a very high CO2 selectivity against CO. The conversion of the catalyst is smaller than other commercial materials due to the smaller content of Ni (10%). Experiments using catalyst extrudates showed that the reaction suffers from strong mass and heat limitations: diffusion of reactants/products and heat transfer in the gas/solid interface. The presence of large pores has an important contribution in decreasing the resistance to mass transfer in particles with 1.1×10-2 m diameter. At 800 K and 2 bar the effectiveness factor was about 0.43 for the steam methane reforming reaction and 0.41 for the global reaction. © 2009 Elsevier Ltd. All rights reserved.


Calvar N.,LSRE Laboratory of Separation and Reaction Engineering | Gomez E.,University of Vigo | Dominguez A.,University of Vigo | Macedo E.A.,LSRE Laboratory of Separation and Reaction Engineering
Fluid Phase Equilibria | Year: 2012

The osmotic and activity coefficients and vapor pressures of binary mixtures containing the alcohols 1-propanol, 2-propanol, 1-butanol, 2-butanol and 1-pentanol and the ionic liquid 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, C6MimNTf2, were determined at T=323.15K using the vapor pressure osmometry technique. The experimental osmotic coefficients were correlated using the Extended Pitzer model of Archer and the MNRTL model, obtaining standard deviations lower than 0.020 and 0.049, respectively. The mean molal activity coefficients and the excess Gibbs free energy for the studied mixtures were calculated from the parameters of the Extended Pitzer model of Archer. Besides the effect of the alkyl-chain of the alcohol and the position of the alcohol group, the effect of the alkyl-side chain of the cation of the ionic liquid can be assessed comparing the experimental results with those previously obtained for imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids with different alkyl-side chain lengths. © 2011 Elsevier B.V.


Calvar N.,LSRE Laboratory of Separation and Reaction Engineering | Dominguez I.,University of Vigo | Gomez E.,University of Vigo | Dominguez A.,University of Vigo
Chemical Engineering Journal | Year: 2011

Binary mixtures of hydrocarbon+aromatic compounds are usually separated using conventional organic volatiles, and to avoid the use of these compounds, the ionic liquids are gaining importance to substitute them. To study the influence of the structure of the different compounds on the separation, we have carried out the liquid-liquid equilibrium of ternary systems containing binary mixtures of hydrocarbon+aromatic compounds and ionic liquids, namely hexane or heptane or cyclohexene+benzene+BMimMSO4, hexane or cyclohexane+benzene+BMimNTf2 and hexane+toluene+BMimNTf2 at 298.15K and atmospheric pressure, and the obtained experimental data have been correlated using NRTL and UNIQUAC models. The comparison of the phase behavior of the different systems studied has allowed us to analyze the influence of the anion of the ionic liquid, the chain length of the aliphatic and the lack of substituent (side chain) in the aromatic compound on the phase equilibria and on the separation ability of these ionic liquids. © 2011 Elsevier B.V.


Pinho L.X.,LSRE Laboratory of Separation and Reaction Engineering | Azevedo J.,CIIMAR – Interdisciplinary Center of Marine and Environmental | Vasconcelos V.M.,CIIMAR – Interdisciplinary Center of Marine and Environmental | Vasconcelos V.M.,University of Porto | And 2 more authors.
Journal of Advanced Oxidation Technologies | Year: 2012

In this study, it is reported the destruction of Microcystis aeruginosa and the toxin microcystin-LR (MC-LR) by photolysis and TiO 2 photocatalysis in a lab-scale prototype using artificial UV light and at pilot-scale plant using natural solar radiation, as UV photon source. TiO 2 photocatalysis showed to be effective in the destruction of M aeruginosa (∼ 5-log order decrease) and in the degradation of the MC-LR released into the aqueous solutions, in the short reaction period of 5-15 min, even at extremely high concentrations. The photocatalytic process can be considered as a viable alternative for disinfection of contaminated water by cyanobacteria, especially in countries with high solar insolation. However, the use of UV light or sunlight alone, as well as TiO 2 in dark is not sufficient to achieve complete elimination of cells and degradation of MC-LR in full-scale water treatment. © 2012 Science & Technology Network, Inc.


Vilar V.J.P.,LSRE Laboratory of Separation and Reaction Engineering | Vilar V.J.P.,University of Porto | Capelo S.M.S.,LSRE Laboratory of Separation and Reaction Engineering | Capelo S.M.S.,University of Porto | And 4 more authors.
Catalysis Today | Year: 2011

A solar photo-Fenton process, without iron addition, is proposed for the decontamination of a landfill leachate in a pilot plant with CPCs, after a preliminary pre-treatment in aerated and non-aerated lagoons. The solar photo-Fenton reaction leads to 60% mineralization (DOCfinal = 1200 mg L-1) and 90% reduction of aromatic content of the leachate after 5 sunny clear days (165 kJUV L-1), consuming 275 mM of H2O2. Photo-Fenton kinetics comprises a "lag period" after the acidification until approximately 68.7 kJUV L-1 in which less oxidized compounds are converted into more oxidized ones but without significant CO2 release, followed by a first-order kinetic behaviour (k = 0.007 L kJUV -1, r0 = 20.2 mg kJUV -1) until 136 kJUV L-1, with a H2O2 consumption rate in both periods of kH2O2=2.1mmolH2O2kJUV-1. According to activated sludge respirometry and Zahn-Wellens biodegradability tests, BOD5/COD ratio, polyphenols concentration and COS (carbon oxidation state), the biodegradability of the leachate was enhanced during the photo-Fenton treatment. From the kinetic results, the optimal amount of UV solar energy required for photo-treatment to reach a biodegradable effluent is 100 kJUV L-1 (10.5 h of photo-Fenton at a constant solar UV power of 30 W m-2), consuming 180 mM of H2O2 when used in excess, which means almost 40% mineralization of the leachate, 82% reduction of polyphenols concentration and 83% reduction of aromatic content. © 2010 Elsevier B.V. All rights reserved.


Calvar N.,LSRE Laboratory of Separation and Reaction Engineering | Gomez E.,University of Vigo | Dominguez A.,University of Vigo | MacEdo E.A.,LSRE Laboratory of Separation and Reaction Engineering
Journal of Chemical Thermodynamics | Year: 2011

The osmotic and activity coefficients and vapour pressures of binary mixtures containing 1-propanol, or 2-propanol and imidazolium-based ionic liquids with bis(trifluoromethylsulfonyl)imide as anion (1-ethyl-3- methylimidazolium bis(trifluoromethylsulfonyl)imide, C2MimNTf 2, 1-methyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide, C3MimNTf2, and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, C4MimNTf2) were determined at T = 323.15 K using the vapour pressure osmometry technique. The experimental osmotic coefficients were correlated using the extended Pitzer model modified by Archer and the MNRTL model, obtaining standard deviations lower than 0.033 and 0.064, respectively. The mean molal activity coefficients and the excess Gibbs free energy for the mixtures studied were calculated from the parameters of the extended Pitzer model modified by Archer. Besides the effect of the alkyl-chain of the cation, the effect of the anion can be assessed comparing the experimental results with those previously obtained for imidazolium ionic liquids with sulphate anions. © 2011 Elsevier Ltd. All rights reserved.

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