Fixed-Bed Adsorption Separation Of Xylene Isomers over SiO2/Silicallite-1 Core-Shell Adsorbents (original) (raw)
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Shape selective adsorption in atomistic nanopores — a study of xylene isomers in silicalite
Chemical Engineering Science, 2000
Grand Canonical Monte Carlo simulations are used to predict single component and binary mixture adsorption of p-and m-xylene in the ORTHO and PARA phases of silicalite. These predictions are compared with experimental results. Both phases adsorb pxylene selectively, the ORTHO phase manifesting stronger p-selectivity than the PARA. p-Xylene is able to access the pore space of silicalite relatively easily while m-xylene is able to access the pore space only with di$culty; this seems to be the primary reason for p-selectivity. To contrast with situations where both isomers can access the pore space with relative ease, simulations of adsorption of xylene isomers in a larger pore structure are also performed. Under such conditions we observe that the ability of each component to form ordered clusters in the pore space in#uences selectivity. Oscillations in selectivity are observed and are attributed to competition between energetic and entropic contributions to adsorption. In all cases, sorbate}sorbate interaction between the components in#uences selectivity.
Adsorbent Evaluation Based on Experimental Breakthrough Curves: Separation ofp-Xylene from C8Isomers
Chemical Engineering & Technology, 2012
The search for new adsorbents with enhanced capacity and selectivity, suitable for application on large-scale simulated moving-bed units for separation of p-xylene, requires efficient, reliable, and fast adsorbent characterization methods for this specific separation. Fixed-bed experiments were carried out under the conditions of the Parex process to evaluate a faujasite-type zeolite as adsorbent for the separation of p-xylene from its isomers in the proportions of the real Parex feed stream. The experimental breakthrough curves were used to evaluate the selected adsorbent in terms of nonselective and selective volumes, adsorption capacity, selectivity, and productivity, which can be applied to identify the feasible separation region for different operating conditions.
Journal of Membrane Science, 2009
The process optimization of p-xylene separation from p-/o-xylene binary mixture through silicalite-1 membrane using statistical design of experiments (DoE) is reported in the present study. The silicalite-1 membrane was synthesized and characterized using different analytical techniques. The effect of three important process variables, temperature (150-250 • C), p-xylene feed partial pressure (0.04-0.50 kPa) and p-xylene feed composition (0.20-0.80) on the separation performance of the membrane was studied. The response surface methodology (RSM) coupled with central composite design (CCD) was used to develop three models to correlate the effect of process variables to three responses: (i) p-xylene flux, (ii) o-xylene flux and (iii) p-/o-xylene separation factor. The most influential factor on each of the response was identified using the analysis of variance (ANOVA). The interaction between the three variables was systematically investigated based on three-dimensional response surface plots. The optimum operating condition for the process was determined by setting the optimization criteria to maximize the p-xylene flux and p-/o-xylene separation factor, and to minimize the o-xylene flux. The optimum p-xylene flux of 3.83 × 10 −6 mol/m 2 s and p-/o-xylene separation factor of 46 were obtained at a temperature of 198 • C, p-xylene feed partial pressure of 0.15 kPa and p-xylene feed composition of 0.80. The simulated values obtained from the statistical model were in agreement with the experimental results within an average error of ±2.70%. The mass transport of xylene isomers and its separation in the silicalite-1 membrane was related with the characteristics of the membrane.
Para-xylene adsorption separation process using nano-zeolite Ba-X
Chemical Engineering Research and Design, 2014
The liquid phase adsorption process was studied on nano-zeolite Ba-X for separating para-xylene from a feed mixture containing all C 8 aromatics. Nano-zeolite Ba-X with different ratios of SiO 2 /Al 2 O 3 was synthesized through hydrothermal process and ion-exchanged with barium. The product was characterized by X-ray diffraction, scanning electron microscopy (SEM), nitrogen adsorption and in situ Fourier transform infrared (FTIR) spectroscopy. The adsorption process was carried out in a breakthrough system at temperature range of 120-160 • C under 4-7 atm pressure. The influence of nano-zeolite water content on the separation process was studied. The optimization of adsorption process was also investigated by changing the operation conditions. The adsorption isotherm for all C 8 aromatic isomers and also desorbents indicated the typical Langmuir type. The selectivity factor of adsorbent for para-xylene and the adsorption capacity at saturation of the different adsorbate samples with each component from C 8 aromatic mixture were determined. It was observed that the selectivity of para-xylene increased by barium ion-exchange of cationic sites in nano-zeolite X and the adsorbent selectivity for para-xylene relative to each of meta-xylene, ortho-xylene and ethyl-benzene under the optimum conditions was found to be 7.191, 2.819 and 3.745, in the order given. It was also studied the influence of desorbent type on its selectivity for para-xylene compared to each isomer from the C 8 aromatic mixture.
Adsorbent Evaluation Based on Experimental Breakthrough Curves: Separation ofp-Xylene from C8Isomers
Chemical Engineering & Technology, 2012
The search for new adsorbents with enhanced capacity and selectivity, suitable for application on large-scale simulated moving-bed units for separation of p-xylene, requires efficient, reliable, and fast adsorbent characterization methods for this specific separation. Fixed-bed experiments were carried out under the conditions of the Parex process to evaluate a faujasite-type zeolite as adsorbent for the separation of p-xylene from its isomers in the proportions of the real Parex feed stream. The experimental breakthrough curves were used to evaluate the selected adsorbent in terms of nonselective and selective volumes, adsorption capacity, selectivity, and productivity, which can be applied to identify the feasible separation region for different operating conditions.
Xylene isomer separations by intrinsically porous molecular materials
Cell Reports Physical Science, 2021
Xylene mixtures and the three individual isomers are valuable chemical feedstocks in the chemical industry. Separation of these isomers is a pressing challenge due to their overlapping physicochemical properties. Traditional separation technologies like distillation are energy intensive and laborious and are not appropriate for sustainable development. To reduce the high energy consumption and decrease the environmental impact, adsorption by porous materials has been proposed and proven as an alternative strategy. Intrinsically porous molecular materials (IPMs) are mainly composed of organic macrocycles and cages that possess guest-accessible intrinsic cavities. They have been used for energy-intensive separations because of their high efficiency and low energy consumption. In this review, we provide a comprehensive summary of IPM-based xylene separations, as well as an overview of the challenges associated with the development of the technology and the future industrial translation of this class of materials.
The Journal of Physical Chemistry B
FT-Raman spectroscopy and temperature-programmed desorption (TPD) measurements have been used to gain information on the preferred adsorption sites for p-xylene and n-heptane adsorbed within silicalite. FT-Raman spectroscopy is used to probe the location of adsorbed p-xylene, both when pure p-xylene is adsorbed and for the binary mixtures. The TPD measurements in combination with the FT-Raman spectra are used to infer the location of the adsorbed n-heptane. The results on the preferred adsorption sites for pure adsorbates are consistent with those in the literature. The results on binary mixtures show unusual behavior at loadings of four p-xylene/three n-heptane and three p-xylene/four n-heptane molecules per unit cell. In contrast to the behavior for single component adsorption, at these loadings the n-heptane molecules preferentially occupy the straight channels of silicalite, forcing the p-xylene molecules out of their normal preferred site (the channel intersections) and into the zigzag channels. The results are of importance in understanding the performance of silicalite membranes when separating gaseous mixtures of alkanes and aromatics.
Sorption-Induced Diffusion-Selective Separation of Hydrocarbon Isomers Using Silicalite
The Journal of Physical Chemistry A, 1998
In this paper we demonstrate a new principle for separation of linear and branched (2-methyl)alkanes, in the five to seven carbon atom range, by means of permeation through a silicalite membrane. The permeation selectivity relies on subtle interplay between sorption and diffusion. The required sorption isotherms for the pure components and mixtures are generated using configurational-bias Monte Carlo (CBMC) simulations. The CBMC simulations of the mixture isotherm show a curious maximum in the loading of 2-methyl alkane; this loading decreases to almost zero with increased pressures. The high sorption selectivity for the linear alkane is due to entropic effects; the linear alkane has a higher "packing" efficiency than the branched alkane within the zeolite structure. Calculations for a 50-50 mixture of n-hexane (n-C 6 ) and 2-methylpentane (2MP), for example, show that the higher sorption selectivity for the linear alkane has the effect of enhancing the flux of n-C 6 through the silicalite membrane by up to a factor of 60 above that of 2MP. Experimental evidence to support our new separation principle is provided by permeation data of Funke et al. 2
Xylene Separation on Plate-Like SAPO-5 Zeolite Molecular Sieves
International Journal of Materials Science and Engineering, 2014
Plate-like AFI zeolite molecular sieves (SAPO-5) were synthesized and utilized for the fixed-bed separation of industrially important feedstock of xylenes isomers. The SAPO-5 crystal powders, which were synthesized using microwave heating technique together with seeds, present homogeneous porous structure (~0.73nm), particle size, as well as low aspect ratio. Adsorption experiments indicated that the sample present strong selectivity for o-xylene. Fixed bed separation of different xylene mixtures were measured experimentally and modeled using the Thomas model. It was found that the model can fit the kinetics of pure xylene and binary xylene mixtures reasonably well.
Chemical Engineering Journal, 2010
a b s t r a c t m-Xylene isomerization kinetics has been studied using acid-functionalized silicalite-1 catalytic membrane in the temperature range of 355-450 • C. Two types of catalytic membranes: (1) propylsulfonic acid-functionalized silicalite-1 membrane and (2) arenesulfonic acid-functionalized silicalite-1 membrane were synthesized on ␣-alumina support via one-step in situ hydrothermal crystallization and subsequent post-synthesis modifications. The membranes were characterized by scanning electron microscopy (SEM), ammonia temperature-programmed desorption (NH 3 -TPD) and Fourier transform infrared spectroscopy (FT-IR). Arenesulfonic acid-functionalized silicalite-1 membrane with its higher acidity gave better catalytic activity as compared to propylsulfonic acid-functionalized silicalite-1 membrane. The continuous removal of reaction products over the membrane contributed in the higher p-xylene yield. A triangular reaction scheme based on time on stream (TOS) model was used to analyze the experimental data. The simulated results were in good agreement with the experimental results, within an error less than ±5%. The estimated activation energies indicated that conversion of m-xylene to p-xylene in both acid-functionalized silicalite-1 membranes is affected by the mass transfer rate through the membrane, while conversion of m-xylene to o-xylene is controlled by the reaction rate.