Nanocomposite MFI-alumina and FAU-alumina Membranes: Synthesis, Characterization and Application to Paraffin Separation and CO2 Capture

Rouleau, L. Pirngruber, G. Guillou, F. Barrere-Tricca, C. Omegna, A. Valtchev, V. Pera-Titus, M. Miachon, S. Dalmon, J. A.International audienceIn this work, we report the preparation of thermally and mechanically resistant high-surface (24-cm2) nanocomposite MFI-alumina and FAUalumina membranes by pore-plugging synthesis inside the macropores of α-alumina multilayered tubular supports. The MFI membranes were prepared from a clear solution precursor mixture being able to easily penetrate into the pores of the support. The MFI membranes were evaluated in the separation of n-/i-butane mixtures. The synthesis reliability was improved by mild stirring. The most selective MFI membranes were obtained for supports with mean pore sizes of 0.2 and 0.8 μm. The MFI effective thickness could be reduced to less than 10 μm by impregnating the support with water prior to synthesis and by diluting the synthesis mixture. The best MFI membrane offered an excellent tradeoff between selectivity and permeance at 448 K, with separation factors for equimolar n-butane/i-butane mixtures up to 18 and n-butane mixture permeances as high as 0.7 μmol$\cdot$s-1$\cdot$m-2$\cdot$Pa-1.Furthermore, a novel nanocomposite FAU membrane architecture has been obtained by an original synthesis route including in situ seeding using a cold gel-like precursor mixture, followed by growth of the FAU material by hydrothermal synthesis in two steps using a clear solution of low viscosity. This new membrane showed interesting performance in the separation of an equimolar CO2/N2 mixture at 323 K, with CO2/N2 separation factors and mixture CO2 permeances up to 12 and 0.4 μmol$\cdot$s-1$\cdot$m-2$\cdot$Pa-1,respectively

Robust Pd/Al2O3 bifunctional catalyst for single reactor tandem synthesis of furan and tetrahydrofuran derivatives from furfural

In this study, we report a reusable catalytic system based on a bifunctional Pd/Al2O3 spheres to conduct the single-reactor tandem aldol condensation/crotonization reaction between furfural and methylisobutyl ketone, followed by hydrogenation, both in batch and continuous mode. In batch mode, the process achieved an overall 86 % yield of 1-(tetrahydrofuran-2-yl)-5-methylhexan-3-one at 180 °C after 9 h at (5.2 wt% furfural concentration). The reaction rate for the aldol condensation/crotonization step decreased at higher FF concentration, suggesting the inhibition of Lewis acid centers due to adsorbed FF as inferred from kinetic modeling. In continuous mode, the catalyst was operated in a dual-type fixed bed reactor and reached 55 % steady-state conversion and 60 % and 35 % selectivity to 1-(furan-2-yl)-5-methylhexan-3-one and (E)-1-(furan-2-yl)-5-methylhex-1-en-3-one, respectively, after 12 h operation at 170 °C and a weight-hourly space velocity of 0.50 h−1 at high furfural concentration (18 wt%). NH3/CO2 temperature-programmed desorption and FT-IR spectroscopy implemented with adsorbed pyridine, NH3 and CO2 were used to assess the nature, strength, density and stability of the acid and basic sites

Direct dehydration of 1,3-butanediol into butadiene over aluminosilicate catalysts

The catalytic dehydration of 1,3-butanediol into butadiene was investigated over various aluminosilicates with different SiO2/Al2O3 ratios and pore architectures. A correlation between the catalytic performance and the total number of acid sites and acid strength was established, with a better performance for lower acid site densities as inferred from combined NH3-TPD, pyridine adsorption and 27Al-NMR MAS spectroscopy. The presence of native Brønsted acid sites of medium strength was correlated to the formation of butadiene. A maximum butadiene yield of 60% was achieved at 300 °C over H-ZSM-5 with a SiO2/Al2O3 ratio of 260 with the simultaneous formation of propylene at a BD/propylene selectivity ratio of 2.5. This catalyst further exhibited a slight deactivation during a 102 h run with a decrease in the conversion from 100% to 80% due to coke deposition as evidenced by XPS and TGA-MS, resulting in a 36% loss of the specific surface area

The critical role of the operating conditions on the Fenton oxidation of 2-chlorophenol: assessment of PCDD/Fs formation

This work assesses the influence of the operating conditions H2O2dose (20 or 100% of the stoichiometric amount), temperature (20 or 70◦C), and the presence of chloride in the oxidation medium in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) during Fenton treatment of aqueous samples of 2-chlorophenol, 2-CP, one of the strongest precursor of PCDD/Fs. After 4 h of oxidation in the experiments carried out with 20% H2O2chlorinated phenoxyphenols and biphenyls, which are intermediates in PCDD/Fs formation, as well as PCDD/Fs were observed, resulting in concentrations11 times higher than in the untreated sample. Additionally, when NaCl was also present in the reaction medium, PCDD/Fs were formed at higher extent, with a total concentration 74.4 times higher than in the untreated 2-CP solution. Results depicted a preferential formation of PCDFs over PCDDs, with dominance of lower chlorinated PCDD/Fs (tetra and penta-PCDD/Fs). Besides, the formation of the most toxic PCDD/Fs congeners (2,3,7,8-PCDD/Fs) was not favored under the operating conditions used in this work.Financial support from the projects CTQ2011-25262, CTQ2008-05545 and CTQ2008-00690 (Ministerio de Economía y Competitividad – MINECO (SPAIN) and Fondo Europeo de Desarrollo Regional – FEDER) is gratefully acknowledged

Direct inference of site strength in basic solids upon CO2 adsorption: enthalpy–entropy compensation effects

The adsorption of CO2 coupled to calorimetry is a state-of-the-art technique for characterizing the basic properties of solids. In this paper, we show that the differential heat and entropy curves measured upon CO2 adsorption on a basic solid can be reasonably estimated from a single CO2 isotherm with no need for any independent heat (calorimetric) measurement. Our method relies on two important observations: (1) formulation of generalized F–H–TS thermodynamic isotherms, the former (F) being directly generated from the raw CO2 isotherms, and (2) the presence of unexpected enthalpy–entropy compensation effects upon CO2 adsorption linking the integral enthalpy and entropy of adsorption until saturation for different solids. Our thermodynamic method has been validated using a broad library of basic solids with variable site strength and heterogeneity. Finally, a new scale of basicity is proposed using the parameters fitted from the thermodynamic isotherm (free energy basis) as descriptors of basic strength. This method opens an avenue to the inference of site strength of basic solids without the need for expensive calorimeters

Thermodynamic analysis of type VI adsorption isotherms in MFI zeolites

The adsorption of aromatics and alkanes in MFI zeolites is usually characterized by a characteristic S-shaped isotherm (formally type VI) caused by the presence of different potential sorption sites (i.e., channel intersections and interiors) and by an intricate panel of sorbate−sorbate interactions. Herein we show that this behavior can be conveniently modeled through a thermodynamic formulation alternative to the classical dual-site Langmuir isotherm linking the integral free energy of adsorption relative to saturation, Ψ/RT, expressed as a Kiselev integral, with the variable Z = 1/−ln(Π), Π being the relative pressure. The model is defined by a set of parameters providing direct information about the evolution of the energy heterogeneity of the solid upon adsorption, including the phase transition zone. Unlike the Dubinin−Astakhov and Dubinin−Radushkevich isotherms, lacking thermodynamic consistency at low pressures, the present formulation converges to Henry’s law at low pressures. Moreover, the present formulation allows the generation of generalized isotherms at different temperatures in the low-pressure region without the need of introducing an “affinity coefficient”