Vicente I. Águeda

Adsorption and Diffusion Parameters of Methane and Nitrogen on Microwave-Synthesized ETS-4

ETS-4 is a titanium silicate developed by Engelhard Corporation, which possesses a small pore network, the size of which can be reduced by heat treatment to improve its kinetic selectivity in nitrogen/methane separation. Most of the reported studies about ETS-4 employ crystals synthesized with conventional heating. Furthermore, information available on the adsorption properties of ETS-4, especially the diffusion properties, is scarce. In this work, Na-ETS-4 crystals have been synthesized by microwave heating and have been exchanged with strontium to obtain Sr-ETS-4 using also microwave heating. This method for obtaining the strontium form of ETS-4 has not been reported before. Both materials have been dehydrated to reduce their pore size. The adsorption and diffusion parameters of nitrogen and methane on these materials, which have not been measured for microwave-synthesized ETS-4 up to the present date, have been estimated by modeling the desorption breakthrough curves of both gases using a fixed bed of ETS-4 crystals. The kinetic selectivity of nitrogen over methane at 298 K of microwave-synthesized Sr-ETS-4 is 26. This value is higher than the maxima reported in the literature for this material.

Adsorption of indole and benzothiophene over zeolites with faujasite structure

This work addresses the adsorption of indole and benzothiophene as model heteroring compounds of nitrogen and sulfur impurities, present in liquid fuels like gasoline and diesel, over zeolites with faujasite structure. It has been studied the influence of the Si/Al molar ratio, the exchanged cation and the presence of toluene considered as a model aromatic compound present in liquid fuels. Cristallinity (by XRD), exchange level (XRF), and basic properties (CO 2 TPD) of different adsorbents have also been determined. The Si/Al molar ratio and the alkali cation exchanged have a big influence on the selective adsorption of indole and benzothiophene. Competitive adsorptives present in fuels, such as toluene, affect to the selectivity to benzothiophene adsorption rather than the corresponding to indole. Thermogravimetric analysis of the spent adsorbents shows a strong indole adsorption. Finally, a comparative study between nitrogen and sulfur adsorption confirms that nitrogen compounds could be selectively removed from fuels.

Microwave synthesis of Sr-ETS-4 and evaluation of its molecular sieving properties in the nitrogen/methane separation

This work addresses the synthesis of the Na-ETS-4 titanosilicate, and the subsequent transformation into Sr-ETS-4 by ion exchange, using microwave radiation as the heating source for both processes, instead of the conventional method. The crystallization kinetics and the ion exchange degree obtained with microwave and conventional synthesis have been compared. The molecular sieving properties of the microwave synthesized Sr-ETS-4 in the nitrogen/methane separation have been evaluated by studying the adsorption and desorption of nitrogen and methane in a fixed bed of Sr-ETS-4 crystals. The nitrogen/methane equilibrium selectivity was 6 approximately, confirming the molecular sieving effect of the studied material.

Desulphurization of fuels by liquid adsorption onto mesoporous materials

This work addresses the desulphurization of several commercial fuels using mesoporous materials as selective adsorbents. The influence of the pore size and the chemical composition of the adsorbent has been studied. Mesoporous materials based on Al, P and Si showed higher desulphurization levels than mesoporous SBA-15. Heavy fuels such as gas oil can be deeper desulphurized than naphtha or kerosene. The chemical composition and the pore diameter have a slight effect on the desulphurization rates. Heavy fuels desulphurization by adsorption seems to follow a physisorption mechanism. In this case adsorbate-adsorbent interactions decrease with temperature yielding lower desulphurization levels. On the other hand, diffusivities into the pores increase with temperature, compensating the previous effect. Regeneration experiments by solvent displacement showed that methanol, and dimethylformamide (DMF) could be used as adsorbent regeneration agents.

Modeling the Regeneration of a Polymeric Resin Column Saturated with Ethanol by Air Purge and External Heating

In this work, the regeneration of a polymeric resin column saturated with ethanol with air purge and external heating has been studied. A theoretical model is proposed for describing the mass and heat transfers in the system, and it has been validated with experimental data. This model can be used for simulating the regeneration step in a concentration-thermal swing adsorption process for fuel-grade ethanol production. The model has been used to analyze the process dynamic behavior, and to compare the performance of the regeneration step using external heating and hot air purge.

Air Regeneration of a Silicalite Column Loaded with Ethanol: Modelling and Energy Estimation

Concentration-thermal swing adsorption (CTSA) using an ethanol-selective adsorbent can be an attractive option to reduce the energy costs associated with the separation of ethanol from water. In this process, ethanol regeneration is the only step with significant energy consumption, in which the adsorbent column saturated with liquid ethanol is purged with a hot inert gas to recover ethanol by condensation. Despite many showing interest in applying CTSA, the method has received little attention in the open literature, and consequently little information is available about its energy requirement. In this work, we experimentally measured the regeneration dynamics of a heated silicalite column saturated with liquid ethanol by air purge using different column wall temperatures and purge gas flow rates. Using a theoretical model based on conservation equations, the mass and heat transfer kinetics in this process are adequately reproduced. The proposed model has been used to estimate the overall energy requirement of the ethanol vapourization/desorption and the subsequent condensation processes.

Modelling the Desorption of Ethanol from an Externally Heated Saturated Activated Carbon Column by Purging with Air

The desorption of ethanol from an externally heated column loaded with activated carbon and purged with air has been studied. The column was initially saturated with liquid ethanol. This process simulates the regeneration step in a concentration-swing/thermal-swing adsorption process for the production of fuel-grade ethanol. A theoretical model was developed for describing the mass- and heat-transfer kinetics of the process. Validation of the model was achieved by comparing its predictions with experimental data, employing initial column temperatures between 298 K and 395 K and air flow rates between 1.6 × 10−6 m3/s and 11.3 × 10−6 m3/s. Experimentally measured adsorption isotherms of ethanol from ethanol/air gas mixtures onto activated carbon, as well as the regeneration column dynamics, are reported.

Modelling of the separation of normal paraffins from kerosene fractions by a simulated moving bed process

Linear paraffins are widely used in the manufacturing of industrial and domestic detergents. Some adsorbents selectively separate these linear hydrocarbons by adsorption from petroleum feedstocks. LTA molecular sieves (5A zeolite) adsorb linear paraffins while excluding the rest of the components of kerosene (branched hydrocarbons and aromatics). Equilibrium and kinetic parameters are available in the literature for light paraffins in the vapour phase, however, there is scarce information concerning high molecular weight paraffins in liquid phase, especially at the operating conditions of commercial processes. In a previous work, the equilibrium and kinetics of high molecular weight n-paraffins C5, C10, C14 and C18 were studied for the adsorption in liquid phase on 5A zeolite. The aim of this work is to study the equilibrium and kinetics of n-paraffins C12 and C16, as well as mixtures of n-paraffins C10, C12 and C14 in the same conditions. n-pentane has been included in the study as it is mainly used as desorbent in the cyclic simulated moving bed (SMB) commercial process. Pure component isotherms were obtained, as well as a multicomponent isotherm. By comparing them, it was observed that selectivities are significantly lower in mixtures (for example, selectivity towards C14 with respect to C12 is lowered from 2.84 for pure paraffins to 1.05 for mixtures). A theoretical model has been developed to describe the column adsorption dynamics of the studied systems. The model has been included in an SMB simulation program (SMBSIM), and the model prediction has been validated by comparison with the separation performance data reported for a commercial SMB unit that separates normal paraffins from a hydrotreated kerosene fraction The model predicts the separation of linear paraffins with 99.2% purity and 96.3% recovery (5% error obtained for n-paraffin concentration in the extract and non-adsorptives in the raffinate).