Carlos Téllez

High Flux Thin Film Nanocomposite Membranes Based on Metal–Organic Frameworks for Organic Solvent Nanofiltration

Thin-film nanocomposite membranes containing a range of 50-150 nm metal-organic framework (MOF) nanoparticles [ZIF-8, MIL-53(Al), NH2-MIL-53(Al) and MIL-101(Cr)] in a polyamide (PA) thin film layer were synthesized via in situ interfacial polymerization on top of cross-linked polyimide porous supports. MOF nanoparticles were homogeneously dispersed in the organic phase containing trimesoyl chloride prior to the interfacial reaction, and their subsequent presence in the PA layer formed was inferred by a combination of contact angle measurements, FT-IR spectroscopy, SEM, EDX, XPS, and TEM. Membrane performance in organic solvent nanofiltration was evaluated on the basis of methanol (MeOH) and tetrahydrofuran (THF) permeances and rejection of styrene oligomers (PS). The effect of different post-treatments and MOF loadings on the membrane performance was also investigated. MeOH and THF permeance increased when MOFs were embedded into the PA layer, whereas the rejection remained higher than 90% (molecular weight cutoff of less than 232 and 295 g·mol(-1) for MeOH and THF, respectively) in all membranes. Moreover, permeance enhancement increased with increasing pore size and porosity of the MOF used as filler. The incorporation of nanosized MIL-101(Cr), with the largest pore size of 3.4 nm, led to an exceptional increase in permeance, from 1.5 to 3.9 and from 1.7 to 11.1 L·m(-2)·h(-1)·bar(-1) for MeOH/PS and THF/PS, respectively.

Combination of MOFs and Zeolites for Mixed-Matrix Membranes

Mixed-matrix membranes (MMMs) were prepared by combinations of two different kinds of porous fillers [metal-organic frameworks (MOFs) HKUST-1 and ZIF-8, and zeolite silicalite-1] and polysulfone. In the search for filler synergy, the MMMs were applied to the separation of CO(2)/N(2), CO(2)/CH(4), O(2)/N(2), and H(2)/CH(4) mixtures and we found important selectivity improvements with the HKUST-1-silicalite-1 system (CO(2)/CH(4) and CO(2)/N(2) separation factors of 22.4 and 38.0 with CO(2) permeabilities of 8.9 and 8.4 Barrer, respectively).

Mesoporous silica sphere-polysulfone mixed matrix membranes for gas separation.

A series of mixed matrix membranes were prepared comprising polysulfone Udel matrix and ordered mesoporous silica spheres as filler with loadings varying between 0 and 32 wt %. The interaction between the filler and the polymer was studied by scanning and transmission electron microscopy, thermogravimetry, differential scanning calorimetry and dynamic mechanical analyses, N2 porosity, X-ray photoelectron spectrometry, and attenuated total reflectance Fourier transform infrared spectroscopy. All these characterizations allowed us to infer an optimum interaction based on both the penetration of the polymer chains into the mesoporosity of the silica spheres and the establishment of hydrogen bondings between the hydroxyl-rich surface and the aryl ether groups of the polymer. An optimum loading of 8 wt % was found in terms of H2/CH4 separation performance. In addition, the optimum membrane was tested for CO2/N2 separation.

Metal Organic Framework Crystals in Mixed-Matrix Membranes: Impact of the Filler Morphology on the Gas Separation Performance

Mixed-matrix membranes (MMMs) comprising NH2-MIL-53(Al) and Matrimid® or 6FDA-DAM have been investigated. The MOF loading has been varied between 5 and 20 wt%, while NH2-MIL-53(Al) with three different morphologies: nanoparticles, nanorods and microneedles have been dispersed in Matrimid®. The synthesized membranes have been tested in the separation of CO2 from CH4 in an equimolar mixture. At 3 bar and 298 K for 8 wt% MOF loading, incorporation of NH2-MIL-53(Al) nanoparticles leads to the largest improvement compared to nanorods and microneedles. The incorporation of the best performing filler, i.e. NH2-MIL-53(Al) nanoparticles, to the highly permeable 6FDA-DAM has a larger effect, and the CO2 permeability increased up to 85 % with slightly lower selectivities for 20 wt% MOF loading. Specifically, these membranes have a permeability of 660 Barrer with CO2/CH4 separation factor of 28, leading to a performance very close to the Robeson limit of 2008. Furthermore, a new non-destructive technique based on Raman spectroscopy mapping is introduced to assess the homogeneity of the filler dispersion in the polymer matrix. The MOF contribution can be calculated by modelling the spectra. The determined homogeneity of the MOF filler distribution in the polymer is confirmed by FIB-SEM analysis.

Sonocrystallization of zeolitic imidazolate frameworks (ZIF-7, ZIF-8, ZIF-11 and ZIF-20)

Zeolitic imidazolate frameworks ZIF-7, ZIF-8, ZIF-11 and ZIF-20 have been synthesized by sonocrystallization. In general, crystals obtained at lower temperatures and shorter times are smaller and have a narrower size distribution than those achieved by conventional solvothermal synthesis. Moreover, crystallization curves have been calculated from the XRD patterns and the Gualtieris model has been applied to simulate the extent of crystallization as a function of time. According to the parameters calculated, for ZIF-8 the nucleation rate controls the synthesis reaction, while for ZIF-11 and ZIF-20 both growth and nucleation rates are similar.

Accelerating the Controlled Synthesis of Metal–Organic Frameworks by a Microfluidic Approach: A Nanoliter Continuous Reactor

Segmented microfluidics was applied to the ultrafast crystallization of dicarboxylate based MIL-88B type metal-organic frameworks (MOFs; Fe-MIL-88B-NH2, Fe-MIL-88B, and Fe-MIL-88B-Br). Particular attention was paid to the influence of the temperature, residence time, and slug volume on the size and crystal size distribution of the MOFs. Average sizes in the 90-900 nm range with relatively narrow crystal size distributions were obtained with residence times as short as 20 s depending on the MOF type and synthesis conditions.

Preparation of mordenite membranes for pervaporation of water-ethanol mixtures

Abstract A mordenite membrane was synthesized on a ceramic tubular support by seeded hydrothermal synthesis andtested in the dehydration of a water/ethanol mixture by pervaporation. The influence of synthesis conditions (timeand gel composition) on the water/ethanol separation factor and water flux was investigated. Typical membranesyielded a water/ethanol separation factor of 150, at a water flux of 0.2 kg/m 2 ·h. The XRD patterns showed thatmordenite was the only zeolite material present in the membrane. Keywords: Zeolite membrane; Pervaporation; Zeolite synthesis; Mordenite; Alcohol dehydration 1. Introduction Zeolite membranes are widely used in a varietyof applications, such as separation processes,catalytic reactors and sensors. Separations of aze-otropic and close-boiling liquids mixtures and thedewatering of organic solvents, such as alcohols(methanol, ethanol…) by pervaporation usingzeolite membranes are examples of relativelyrecent developments. While polymeric membraneshave been commercially developed for theseprocesses, their use is limited because their lowthermal and chemical stability [1]. Microporousinorganic membranes (silica, zeolites, etc.) havebeen presented as an alternative to broaden thefield of membrane application. In particular, thearea of zeolite membrane has been the subject ofintense research during the last years and severalreviews about the subject have been published

Beyond the H2/CO2 upper bound: one-step crystallization and separation of nano-sized ZIF-11 by centrifugation and its application in mixed matrix membranes

The synthesis of nano-sized ZIF-11 with an average size of 36 ± 6 nm is reported. This material has been named nano-zeolitic imidazolate framework-11 (nZIF-11). It has the same chemical composition and thermal stability and analogous H2 and CO2 adsorption properties to the conventional microcrystalline ZIF-11 (i.e. 1.9 ± 0.9 μm). nZIF-11 has been obtained following the centrifugation route, typically used for solid separation, as a fast new technique (pioneering for MOFs) for obtaining nanomaterials where the temperature, time and rotation speed can easily be controlled. Compared to the traditional synthesis consisting of stirring + separation, the reaction time was lowered from several hours to a few minutes when using this centrifugation synthesis technique. Employing the same reaction time (2, 5 or 10 min), micro-sized ZIF-11 was obtained using the traditional synthesis while nano-scale ZIF-11 was achieved only by using centrifugation synthesis. The small particle size obtained for nZIF-11 allowed the use of the wet MOF sample as a colloidal suspension stable in chloroform. This helped to prepare mixed matrix membranes (MMMs) by direct addition of the membrane polymer (polyimide Matrimid®) to the colloidal suspension, avoiding particle agglomeration resulting from drying. The MMMs were tested for H2/CO2 separation, improving the pure polymer membrane performance, with permeation values of 95.9 Barrer of H2 and a H2/CO2 separation selectivity of 4.4 at 35 °C. When measured at 200 °C, these values increased to 535 Barrer and 9.1.

Insight into the crystal synthesis, activation and application of ZIF-20

The crystallization of the zeolitic imidazolate framework ZIF-20 has been tuned from the point of view of crystal size and aggregation by using rotation and seeding with a previously prepared material. In addition, the activation of ZIF-20 by solvent extraction has been found to be in correlation with the relative permittivity of the solvent. High permittivity solvents (acetone and methanol) extract more guest dimethylformamide but amorphize the structure, while those with low permittivity (n-pentane and chloroform) preserve the crystallinity of ZIF-20. The dispersion in commercial polysulfone of the small synthesized ZIF-20 particles obtained with low aggregation results in an improved O2-selective mixed matrix membrane (O2 permeability and O2/N2 selectivity being 1.0 (±0.0) Barrer and 6.7 (±0.5), respectively).

Use of zeolite membrane reactors for selectivity enhancement: application to the liquid-phase oligomerization of i-butene

Abstract This work investigates the use of a zeolite membrane reactor (ZMR) in the liquid-phase oligomerization of i -butene. The membrane was used for the selective removal of i -octene from the reaction environment, thus reducing the formation of unwanted C 12 and C 16 hydrocarbons. MFI (silicalite) membranes prepared by secondary growth on stainless steel porous tubes were used for this purpose, given the non-polar nature of the compounds to be separated. Preliminary non-reactive tests demonstrated the capability of the membrane to separate i -octene from i -butene and from C 12 and C 16 hydrocarbons. Reaction experiments were then carried out over an acid resin catalyst bed located on the membrane tube side. The ZMR produced a very significant increase in the selectivity, and as a consequence also in the yield of i -octenes (intermediate product in the oligomerization of i -butene), compared to a conventional fixed bed reactor (FBR).