Selective Water Adsorption Research Articles

Economically Scalable Cu-based MOFs: Vital Role of Structural Integrity towards Selectivity on Azeotropic Ethanol Dehydration.

A facile, green, and economical method for the scalable synthesis of hydrophilic copper-triazole metal-organic frameworks (Cu-trz) is demonstrated. Numerous open metal sites within the highly crystalline porous structure of Cu-trz are generated through mild thermal activation, enabling its application in liquid-phase ethanol dehydration under ambient conditions. The frameworks with distinct crystallinity and particle sizes were achieved by modifying the synthesis process. The high crystallinity of the framework plays an exclusive role in enhancing water adsorption capacity. With selective water adsorption comparable to commercial zeolite 3A, Cu-trz MOF emerges as a promising candidate for cost-effective water-ethanol separation.

Biogas upgrading by intensified methanation (SESaR): Reaction plus water adsorption - desorption cycles with Ni-Fe/Al2O3 catalyst and LTA 5A zeolite

This work is conducted within the framework of the Power to Gas (PtG) technologies, focusing on the topic of “biogas upgrading”. The objective is to enhance the CH4 content of biogas streams by utilizing the CO2 present in these streams through the Sabatier reaction, thereby producing a renewable alternative to natural (fossil) gas. Referred to as “SESaR”(Sorption Enhanced Sabatier Reaction), this process employs a catalytic fixed-bed reactor, featuring selective water adsorption using LTA 5A zeolites, as an innovative approach to traditional methanation reactors. The catalyst used comprises Ni-Fe (7.5:2.5 wt/wt) as the active metallic phase supported on γ-Al2O3. Experimental work has been divided in two sets of trials. The first set focuses on the hydrogenation of CO2 as single reactant (H2 also supplied in the inlet with 4:1 = H2:CO2 molar ratio). The second set of experiments was carried out with a synthetic gas mixture representative of a sweetened biogas stream (molar ratio CH4:CO2 = 7:3). Maximum intensification behavior for CO2 conversion was found at 350 °C, also showing that CH4 presence in the inlet gas has negligible influence on the conversion of CO2. Selectivity to CO is minimized at temperatures exceeding 300 °C and remains constant after three consecutive cycles of methanation, water adsorption, and desorption. The Fe-Ni catalyst has demonstrated sustained performance throughout the experimental cycles, exhibiting no significant loss of activity.

Electrically Tunable Reactivity of Substrate-Supported Cobalt Oxide Nanocrystals.

First-row transition metal oxides are promising materials for catalyzing the oxygen evolution reaction. Surface sensitive techniques provide a unique perspective allowing the study of the structure, adsorption sites, and reactivity of catalysts at the atomic scale, which furnishes rationalization and improves the design of highly efficient catalytic materials. Here, a scanning probe microscopy study complemented by density functional theory on the structural and electronic properties of CoO nanoislands grown on Au(111) is reported. Two distinct phases are observed: The most extended displays a Moiré pattern (α-region), while the less abundant is 1Co:1Au coincidental (β-region). As a result of the surface registry, in the β-region the oxide adlayer is compressed by 9%, increasing the unoccupied local density of states and enhancing the selective water adsorption at low temperature through a cobalt inversion mechanism. Tip-induced voltage pulses irreversibly transform α- into β-regions, thus opening avenues to modify the structure and reactivity of transition metal oxides by external stimuli like electric fields.

CO2 methanation in a Ni-Fe based catalyst fixed bed reactor enhanced by selective water adsorption with LTA zeolites (Sorption Enhanced Sabatier Reaction – SESaR)

A Fixed-Bed reactor improved by selective water adsorption LTA zeolites is proposed as an alternative to the conventional methanation reactors. This reactor produces methane from renewable H2 (i.e. surplus electricity) and high CO2 concentration sources, as could be municipal wastes derived biogas (30%v CO2 + 70%v CH4). As catalyst, a supported (g-Al2O3) Ni-Fe (7.5:2.5 wt/wt) was chosen.

Víctor D Mercader - CO2 methanation in a Ni-Fe based catalyst fixed bed reactor enhanced by selective water adsorption with LTA zeolites (Sorption Enhanced Sabatier Reaction) - SESaR

Víctor D Mercader - CO2 methanation in a Ni-Fe based catalyst fixed bed reactor enhanced by selective water adsorption with LTA zeolites (Sorption Enhanced Sabatier Reaction) - SESaR

Mirror twin boundaries in MoSe2 monolayers as one dimensional nanotemplates for selective water adsorption.

Water adsorption on transition metal dichalcogenides and other 2D materials is generally governed by weak van der Waals interactions. This results in a hydrophobic character of the basal planes, and defects may play a significant role in water adsorption and water cluster nucleation. However, there is a lack of detailed experimental investigations on water adsorption on defective 2D materials. Here, by combining low-temperature scanning tunneling microscopy (STM) experiments and density functional theory (DFT) calculations, we study in that context the well-defined mirror twin boundary (MTB) networks separating mirror-grains in 2D MoSe2. These MTBs are dangling bond-free extended crystal modifications with metallic electronic states embedded in the 2D semiconducting matrix of MoSe2. Our DFT calculations indicate that molecular water also interacts similarly weak with these MTBs as with the defect-free basal plane of MoSe2. However, in low temperature STM experiments, nanoscopic water structures are observed that selectively decorate the MTB network. This localized adsorption of water is facilitated by functionalization of the MTBs by hydroxyls formed by dissociated water. Hydroxyls may form by dissociating of water at undercoordinated defects or adsorbing of radicals from the gas phase in the UHV chamber. Our DFT analysis indicates that the metallic MTBs adsorb these radicals much stronger than on the basal plane due to charge transfer from the metallic states into the molecular orbitals of the OH groups. Once the MTBs are functionalized with hydroxyls, molecular water can attach to them, forming water channels along the MTBs. This study demonstrates the role metallic defect states play in the adsorption of water even in the absence of unsaturated bonds that have been so far considered to be crucial for adsorption of hydroxyls or water.

Atomically Precise Titanium–Oxo Nanotube with Selective Water Adsorption and Semiconductive Behaviors

We report the first example of carbon nanotube (CNT)-like assembly of the titanium (Ti) framework, Ti oxo inorganic cluster (Ti6O6) hexagonal rings into a titanium oxide (Ti–O) nanotube, prepared b...

Adsorption/heat exchanger (HEX) reactor for simultaneous DME and hydrogen production: A theoretical investigation

Heat exchanger (HEX) reactor is recognized as one of the most promising configurations for production of DME and hydrogen, simultaneously. In the current study, dehydration of methanol to DME is carried out in exothermic side, which is a fixed bed reactor assisted by regenerative zeolite 4A particles and coupled with benzene synthesis in endothermic side. The mathematical modeling results prove that selective water adsorption from direct DME synthesis leads to an intensification of DME production compared to non-adsorbent configuration as well as conventional one. Furthermore, the simulation results represent 336.52 ton/day enhancement in the hydrogen production rate in comparison with non-adsorbent configuration using the same catalyst loading and duty. Finally, the effects of main operating variables are considered on DME molar flow rate and cyclohexane conversion. The results suggest that the coupling of these reactions in the presence of zeolite 4A adsorbent could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the novel reactor.

Front Cover: Mild Upgrading of Bio‐Crude Pyrolysis Oil: A Concept Based on Bio‐Based Alcohols with Selective Water Adsorption (Energy Technol. 7/2018)

Front Cover: Mild Upgrading of Bio‐Crude Pyrolysis Oil: A Concept Based on Bio‐Based Alcohols with Selective Water Adsorption (Energy Technol. 7/2018)

Mild Upgrading of Bio-Crude Pyrolysis Oil: A Concept Based on Bio-Based Alcohols with Selective Water Adsorption

Biocrude pyrolysis oil is obtained by a process called fast-pyrolysis, in which almost any organic-based feedstock is thermally processed at moderate temperatures, in the range of 400–600 °C, in the absence of oxygen at short residence times. After condensing the vapors in a cooling tray, a dark-brown bioliquid is obtained. The quality of the thus obtained fast pyrolysis oil has some barriers for its direct use as transportation fuel. Low caloric value, high viscosity, and corrosion are the major challenges for its implementation in conventional engines. There have been sustained efforts to improve the quality of the oil. In this Communication we are reporting a concept on improving the acidic properties by means of a combined catalysis and adsorption approach. We found that fast pyrolysis oil can be upgraded through alcoholysis using n-butanol and tetrahydrofurfuryl alcohol, which are biomass-derived bulk chemicals. The reaction is acid catalyzed whereas water is continuously separated from the condensate mixture through molecular sieve adsorption. Under optimal conditions, the ultimate acidity and water content of the upgraded product are negligible.

Sorption enhanced process by integrated heat-exchanger reactor assisted by fluidization concept for methanol synthesis

Coupling reactor has been identified as one of the most promising configurations for simultaneous production of methanol and hydrogen; as well stabilizing the atmospheric greenhouse gases level. In this work, methanol synthesis is carried out in exothermic side, which is a fluidized-bed reactor with in-situ water adsorption and supplies the necessary heat for the dehydrogenation of cyclohexane in endothermic side. Simulation results show that selective water adsorption from methanol synthesis in Fluidized bed Sorption Enhanced Thermally Coupled Reactor (FSE-TCR) leads to a considerable intensification of methanol production compared to zero solid mass ratio condition. Subsequently, a multi-objective optimization of FSE-TCR is conducted using the NSGA-II algorithm, and Pareto optimal frontiers are obtained in two cases including the maximum methanol production rate and selectivity. The Shannon’s Entropy, LINMAP, and TOPSIS methods as three decision making approaches are used to select the final solution of Pareto front. The optimization results enhance about 214.3 and 280.5tonday−1 methanol production rate and CO2 removal rate, respectively, based TOPSIS methods in comparison with the conventional methanol configuration. Furthermore, the optimization results represent 6.88tonday−1 enhancement in hydrogen production rate in comparison with the non-optimized configuration using the same catalyst loading and duty.

Reversible Water-Induced Structural and Magnetic Transformations and Selective Water Adsorption Properties of Poly(manganese 1,1′-ferrocenediyl-bis(H-phosphinate))

A flexible and hydrolytically stable metal–organic framework [Mn(H2O)2(Fc(PHOO)2)·2H2O]n has been synthesized using ferrocene-based ligand bearing phosphinic groups (Fc(PHOOH)2 = 1,1′-ferrocenediyl-bis(H-phosphinic acid)). In this compound manganese atoms are bound by phosphinate fragments to give infinite chains, and the latter are interconnected by ferrocene groups to form two-dimensional coordination polymer. The elimination of both coordinated and lattice water molecules during heating up to 150 °C produced the compound, which is nonporous for nitrogen, but can selectively adsorb water over methanol and other solvents at 298 K. The reversible structural transformation during adsorption/desorption of water is also reflected in a change of magnetic properties of the metal–organic framework.

Anhydrous ethanol recovery from wet air in TSA systems – Equilibrium and column studies

An experimental and theoretical study of two combined temperature swing adsorption (TSA) systems for the recovery of anhydrous ethanol from wet air using activated carbon Sorbonorit 4 (ACS4) and zeolite molecular sieve 3A (ZMS3A) are developed. Adsorption isotherms of ethanol and water vapors on ACS4 and ZMS3A in the temperature range of 20–140°C and water from liquid ethanol on ZMS3A at temperatures of 20–60°C were measured. The data were analyzed using multi-temperature Toth, Sips, hybrid Langmuir-Sips, inhomogeneous DA and the excess surface work models. The results demonstrate selective water adsorption on ZMS3A with higher adsorption capacity in the liquid (28.02mol/kg) than in the gas phase (10.67mol/kg), and higher adsorption of ethanol (7.21mol/kg) than water vapor on ACS4 up to relative pressure 0.6. The influence of the inlet concentration in the gas (2.8–8.4g/m3 for ethanol) and liquid phase (45–141kg/m3 for water–ethanol mixture) on the adsorption dynamic was studied in two fixed-bed columns with ACS4 and ZMS3A. The characteristic parameters of breakthrough curves and maximum temperature rise in the column were determined. The Thomas model was successfully employed to predict the breakthrough curves for both gas and liquid phase. The energy requirement for ethanol electrothermal desorption from ACS4 bed (151–235kJ/mol) was lower than for hot purge gas regeneration of wet ZMS3A bed (423kJ/mol). These values were several times larger than the isosteric heat of adsorption (13–71kJ/mol) which represents minimum energy requirement for desorption.

Highly selective water adsorption in a lanthanum metal-organic framework.

We present a new metal-organic framework (MOF) built from lanthanum and pyrazine-2,5-dicarboxylate (pyzdc) ions. This MOF, [La(pyzdc)1.5(H2O)2]⋅2 H2O, is microporous, with 1D channels that easily accommodate water molecules. Its framework is highly robust to dehydration/hydration cycles. Unusually for a MOF, it also features a high hydrothermal stability. This makes it an ideal candidate for air drying as well as for separating water/alcohol mixtures. The ability of the activated MOF to adsorb water selectively was evaluated by means of thermogravimetric analysis, powder and single-crystal X-ray diffraction and adsorption studies, indicating a maximum uptake of 1.2 mmol g(-1) MOF. These results are in agreement with the microporous structure, which permits only water molecules to enter the channels (alcohols, including methanol, are simply too large). Transient breakthrough simulations using water/methanol mixtures confirm that such mixtures can be separated cleanly using this new MOF.

Separation of ethanol/water azeotrope using compound starch-based adsorbents

Comparing breakthrough cures of five starch-based materials experimentally prepared for ethanol dehydration, a compound adsorptive agent ZSG-1 was formulated with high adsorption capacity, low energy and material cost. The selective water adsorption was conducted in a fixed-bed absorber packed with ZSG-1 to find the optimum conditions yielding 99.7wt% anhydrous ethanol with high efficiency. The adsorption kinetics is well described by Bohart–Adams equation. The adsorption heat, ΔHabs, was calculated to be −3.16×104Jmol−1 from retention data by inverse gas chromatography. Results suggested that water entrapment in ZSG-1 is a exothermic and physisorption process. Also, ZSG-1 is recyclable for on-site multiple-use and then adapt for upstream fermentation process after saturation, avoiding pollution through disposal.

Selective water adsorption from aqueous ethanol-containing vapours by phillipsite-rich volcanic tuffs

The use of Neapolitan yellow tuff (NYT), a phillipsite/chabazite-containing volcaniclastic rock, rich in phillipsite, is proposed for an inexpensive dehydration process of ethanol vapours. NYT selective water adsorption kinetics was investigated both in a continuous microbalance apparatus and in laboratory-scale fixed-bed columns. The influence of operational parameters such as tuff grain dimensions, column temperature and pressure, volumetric flow-rate and partial pressure of adsorbates was studied. A preliminary study on the fluid dynamics of the column is also described. Finally, evidence is reported that a partial, but economical bed regeneration can be attained at the column working temperature by simply flushing the system with dry nitrogen.

逆浸透用膜材料に関する研究 ＩＩＩ 酢酸セルロース（水蒸気吸着および透過機構）

The effects of membrane preparation variables on the reverse osmosis properties of cellulose acetate membrane have been investigated by water vapor sorption. Dependence of isotherm on the annealing temperature was not observed in casting conditions of one minute solvent evaporation and of annealing temperature of 60-80°C. This may indicate that the primary membrane structure is formed in the evaporation step and the dense layer is thin. The membrane prepared from Eastman 398-3 was more porous than one prepared from Wako Pure Chemicals. Reverse osmosis properties of cellulose membrane was discussed, based on the selective water adsorption on cellulose in the amorphous region, and a crevasse-like structure model was proposed. By using this model, a good agreement was obtained between the experimental and the calculated data.