Ana Martín-Calvo

Effect of air humidity on the removal of carbon tetrachloride from air using Cu–BTC metal–organic framework

We have used interatomic potential-based simulations to study the removal of carbon tetrachloride from air at 298 K, using Cu-BTC metal organic framework. We have developed new sets of Lennard-Jones parameters that accurately describe the vapour-liquid equilibrium curves of carbon tetrachloride and the main components from air (oxygen, nitrogen, and argon). Using these parameters we performed Monte Carlo simulations for the following systems: (a) single component adsorption of carbon tetrachloride, oxygen, nitrogen, and argon molecules, (b) binary Ar/CCl(4), O(2)/CCl(4), and N(2)/CCl(4) mixtures with bulk gas compositions 99 : 1 and 99.9 : 0.1, (c) ternary O(2)/N(2)/Ar mixtures with both, equimolar and 21 : 78 : 1 bulk gas composition, (d) quaternary mixture formed by 0.1% of CCl(4) pollutant, 20.979% O(2), 77.922% N(2), and 0.999% Ar, and (e) five-component mixtures corresponding to 0.1% of CCl(4) pollutant in air with relative humidity ranging from 0 to 100%. The carbon tetrachloride adsorption selectivity and the self-diffusivity and preferential sitting of the different molecules in the structure are studied for all the systems.

Enantioselective Adsorption in Achiral Zeolites

Minority excluded: If mixtures of chiral compounds are adsorbed in Al-substituted MFI zeolite containing nonframework cations, a process occurs that ultimately might be used for enantioseparation. If one enantiomer is present in excess it will organize the nearby cations, which in turn influence all other cations through long-range interaction, such that all adsorption sites become effectively chiral. This suppresses the minority enantiomer.

Adsorption of hydrogen sulphide on Metal-Organic Frameworks

Three new sets of interatomic potentials to model hydrogen sulphide (H2S) have been fitted. One of them is a 3-sites potential (which we named 3S) and the other two are 5-sites potentials (which we named 5S and 5Sd). The molecular dipole of the 3S and 5S potentials is 1.43 D, which is the value usually employed for H2S potentials, while the dipole of the 5Sd is the dipole measured experimentally for the H2S molecule, circa 0.974 D. The interatomic potentials parameters were obtained by fitting the experimental vapour-liquid equilibrium, vapour pressure and liquid density curves. The potential parameters fitted so far for H2S have been obtained applying long-range corrections to the Lennard–Jones energy. For that reason, when a cut and shift of the Lennard–Jones potentials is applied they do not yield the correct results. We employed a cut and shift of the Lennard–Jones potentials in the fitting procedure, which facilitates the use of the new potentials to model H2S adsorption on systems such as Metal-Organics Frameworks (MOFs). We have employed the newly developed potentials to study the adsorption of H2S on Cu-BTC, MIL-47 and IRMOF-1 and the results agree with the available electronic structures calculations. All calculations (both quantum and interatomic potential-based) predict that H2S does not bind to the Cu atoms in Cu-BTC.

Intensified Biobutanol Recovery by using Zeolites with Complementary Selectivity.

A vapor-phase adsorptive recovery process is proposed as an alternative way to isolate biobutanol from acetone-butanol-ethanol (ABE) fermentation media, offering several advantages compared to liquid phase separation. The effect of water, which is still present in large quantities in the vapor phase, on the adsorption of the organics could be minimized by using hydrophobic zeolites. Shape-selective all-silica zeolites CHA and LTA were prepared and evaluated with single-component isotherms and breakthrough experiments. These zeolites show opposite selectivities; adsorption of ethanol is favorable on all-silica CHA, whereas the LTA topology has a clear preference for butanol. The molecular sieving properties of both zeolites allow easy elimination of acetone from the mixture. The molecular interaction mechanisms are studied by density functional theory (DFT) simulations. The effects of mixture composition, humidity and total pressure of the vapor stream on the selectivity and separation behavior are investigated. Desorption profiles are studied to maximize butanol purity and recovery. The combination of LTA with CHA-type zeolites (Si-CHA or SAPO-34) in sequential adsorption columns with alternating adsorption and desorption steps allows butanol to be recovered in unpreceded purity and yield. A butanol purity of 99.7 mol % could be obtained at nearly complete butanol recovery, demonstrating the effectiveness of this technique for biobutanol separation processes.