Dehydration Of Alcohols Research Articles

Seeding-free synthesis of oriented zeolite LTA membrane on PDI-modified support for dehydration of alcohols

ABSTRACTA seeding-free synthesis method is developed for preparation of oriented zeolite LTA membranes by using 1,4-phenylene diisocyanate (PDI) as a molecular linker. Before hydrothermal synthesis, –NCO groups are introduced with the functionalization of Al2O3 supports by PDI. A thin, well intergrown zeolite LTA membrane with a thickness of about 4.0 µm can be formed on the PDI-modified Al2O3 supports. The zeolite LTA membrane displays high pervaporation performances for dehydration of alcohols. At 90°C, the separation factor of the zeolite LTA membrane is 4480 for dehydration of 95 wt% ethanol/water mixtures, with a high water flux of 3.4 kg·m−2·h−1.

Metal-Incorporated Mesoporous Silicates: Tunable Catalytic Properties and Applications.

A relatively new class of three-dimensional ordered mesoporous silicates, KIT-6, incorporated with Earth-abundant metals such as Zr, Nb, and W (termed as M-KIT-6), show remarkable tunability of acidity and metal dispersion depending on the metal content, type, and synthetic method. The metal-incorporation is carried out using one-pot synthesis procedures that are amenable to easy scale-up. By such tuning, M-KIT-6 catalysts are shown to provide remarkable activity and selectivity in industrially-significant reactions, such as alcohol dehydration, ethylene epoxidation, and metathesis of 2-butene and ethylene. We review how the catalytic properties of M-KIT-6 materials may be tailored depending on the application to optimize performance.

Bioinspired Synthesis of Juglorubin from Juglomycin C

In this paper, the synthesis of juglorubin, a natural red dye, from juglomycin C, a plausible biogenetic precursor, is reported. Sequential intermolecular and intramolecular Michael additions of juglomycin C, oxidation, and skeletal transformation proceeded in phosphate buffer to afford an undehydrated derivative of juglorubin. Subsequent dehydration of the secondary alcohol afforded juglorubin. The one-pot synthesis of juglorubin from juglomycin C was also achieved. The photophysical properties of synthetic juglorubin and its derivatives were evaluated.

Ceria–zirconia mixed oxides: Synthetic methods and applications

ABSTRACTThe primary objective of this review was to illustrate the significance of ceria–zirconia (CZ) mixed oxides as catalysts and catalyst supports as employed for a wide variety of catalytic applications both in the liquid and gaseous phases. In particular, we were interested in bringing together the recent literature pertaining to these mixed oxides with catalysis perspective. The most prominent application of CZ mixed oxides is in three-way catalysis (TWC) as oxygen storage and release material for several years by replacing cerium dioxide as it shows better efficiency and a high thermal stability. Doping with zirconium oxide, as it is alone a non-reducible oxide, makes the CZ mixed oxide a highly reactive, thermally stable, and more reducible with elevated oxygen storage capacity (OSC) that are important for TWC applications. Apart from the TWC use, the CZ mixed oxides have a huge number of applications, as a direct component or a support, ranging from water–gas shift reaction, reforming of hydrocarbons, dehydration of alcohols, CO2 utilization, catalytic combustion of pollutants, fine chemicals production, photocatalysis, and so on. All these applications are mainly dependent on three parameters of the mixed oxides, namely, OSC or redox nature, acid–base properties, and crystalline phases. Besides, most of the applications are influenced by the physical properties such as specific surface area, pore volume, pore diameter, crystallite size, and so on. In this review, many details pertaining to the synthesis of these mixed oxides by various conventional and non-conventional methods, their characterization by several techniques, and their application for various reactions of energy and environmental significance, as reported in the literature, are assessed.

Inert competitive adsorption for the inhibition of oligomerization of alkenes during alcohol dehydration

Inert competitive adsorbents inhibit secondary undesired reactions.

Porous clay heterostructures intercalated with multicomponent pillars as catalysts for dehydration of alcohols

Abstract Montmorillonites intercalated with silica, silica-alumina, silica-titania and silica-zirconia pillars by surfactant directed method were studied as catalysts for dehydration of methanol and ethanol to dimethyl ether as well as diethyl ether and ethylene, respectively. Moreover, the samples of montmorillonite intercalated with silica pillars were doped with aluminum using template ion-exchange method. In the case of all the samples deposited metal (Al, Ti, Zr) species were present in highly dispersed forms and resulted in generation of acid sites catalytically active in dehydration of methanol and ethanol. The best catalytic results in both studied processes were obtained for the samples doped with aluminum, especially introduced by using template ion-exchange method (first time applied for deposition of metal cations into PCHs), which were more catalytically active in the process of methanol to dimethyl ether conversion than γ-Al2O3 (one of the most important commercial catalysts of this process). High catalytic activity of the aluminum doped samples was related to the nature and strength of acid sites active in the processes of alcohols dehydration.

Mixed matrix membranes with nano-sized functional UiO-66-type MOFs embedded in 6FDA-HAB/DABA polyimide for dehydration of C1-C3 alcohols via pervaporation

This study demonstrated an effective method to enhance both the normalized flux and separation factor by molecularly designing mixed matrix membranes (MMMs) consisting of porous UiO-66-NH2 nanoparticles and 6FDA-HAB/DABA polyimide. To investigate the effects of functional groups on UiO-66 particles on alcohol dehydration, MMMs containing (1) UiO-66-NH2 nanoparticles with a particle size of 80–90nm, (2) UiO-66 with a particle size of 90–110nm and (3) UiO-66-F4 with a particle size of 90–130nm were fabricated and compared for alcohol dehydration. Three alcohol dehydration systems; namely, methanol/water, ethanol/water and isopropanol/water were studied. Results showed that UiO-66-NH2 based MMMs have superior separation performance among these three MMMs because the hydrophilic amino-functional groups can facilitate water transport. Incorporation of UiO-66-NH2 nanoparticles can greatly improve both the normalized flux and separation factor simultaneously if the particle loading is within the range of 0–20wt%. Due to the good compatibility between UiO-66-NH2 particles and the 6FDA-HAB/DABA polyimide resulting from the intermolecular bonding among the amine and imide groups, the UiO-66-NH2 based MMMs exhibited stable isopropanol dehydration performance in uninterrupted 200-h tests. The excellent alcohol dehydration performance of UiO-66-NH2 based MMMs opens up their potential for alcohol dehydration via pervaporation.

Insights on the mechanism of water-alcohol separation in multilayer graphene oxide membranes: Entropic versus enthalpic factors

Experimental evidence has shown that graphene oxide (GO) can be impermeable to liquids, vapors and gases, while it allows a fast permeation of water molecules. Theoretical studies to understand the filtration mechanisms come mostly from water desalination, while very few works have been dedicated to alcohol dehydration. In this work, we have investigated the molecular level mechanism underlying the alcohol/water separation inside GO membranes. A series of Molecular Dynamics and Grand-Canonical Monte Carlo simulations were carried out to probe the ethanol/water and methanol/water separation through GO membranes composed of multiple layered graphene-based films with different interlayer distance values and number of oxygen-containing functional groups. Our results show that the size exclusion and membrane affinities are not sufficient to explain the selectivity. Besides that, the favorable water molecular arrangement inside GO 2D-channels forming a robust H-bond network and the fast water permeation are crucial for an effective separation mechanism. In other words, the separation phenomenon is not only governed by membrane affinities (enthalpic mechanisms) but mainly by the geometry and size factors (entropic mechanisms). Our findings are consistent with the available experimental data and contribute to clarify important aspects of the separation behavior of confined alcohol/water in GO membranes.

Catalytic properties of carbon nanotubes-supported heteropolyacids in isopropanol conversion

The technique of catalytic flow microreactor has been combined with the gas flow-through microcalorimetry to correlate the catalytic activity of supported heteropolyacids with both the acid strength of protons as well as the protons’ accessibility. Multiwall carbon nanotubes (CNT) were used as a support for Keggin (H3PW12O40) and Wells-Dawson (H6P2W18O62) structured heteropolyacids, in order to produce catalysts combining high acidity from the parent acids with the inherent microporosity of the support. Prior to the catalytic tests, the obtained materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) and Raman spectroscopies as well as by the nitrogen adsorption-desorption analysis (BET). The latter technique confirmed overall improved porosity of the obtained materials. Upon testing for activity in the isopropyl alcohol dehydration, the supported Wells-Dawson catalysts turned out to be superior to both the Keggin-based materials, as well as to the unsupported H6P2W18O62. It has been found that the improvement of catalytic performance in the isopropanol conversion is mostly related to the increase of the accessibility of protons, rather than to the changes in the acid strengths.

Fabrication and Characterization of Chitosan/Alginate Multilayer Composite Membrane Supported by a Porous Poly (Acrylonitrile) Substrate for Pervaporation Dehydration of Alcohol

Chitosan (CS) and alginate (Alg) are complementary in their membrane performance, but the combination of them is normally difcult to use due to their different solubilities. Layer-by-Layer deposition appears to be an effective method for improving the separation efciency of a composite membrane. In this work, the polyelectrolyte multilayer composite membranes (PEMCMs) were fabricated by depositing CS and Alg solutions alternatively onto a hydrolyzed porous poly(acrylonitrile) (PAN) substrate under a reduced pressure, as evidenced by Attenuated total reflectance Fourier transform infrared spectroscopy, contact angle and zeta potential measurement. Pervaporation results showed that the water selectivity increased while the flux decreased with the growth of CS/Alg-based polyelectrolyte layer. It was interesting that the sorption process dominated the pervaporation process when the numbers of polyelectrolyte layers were less than 7. However, the diffusion effect was more profound than the sorption effect as more than 8 polyelectrolyte layers were deposited on the PAN substrate. In particular, the prepared CS/Alg PEMCMs exhibited highly improved water selectivities towards alcohol/water mixtures, and a good compromise between flux and separation factor was observed when compared to other polyelectrolyte-based membranes. For separating 90% IPA/water mixtures at 60 oC, the (CS/Alg)4 composite membrane displayed a separation factor of 4491 and a flux of 596 g/m2.h, respectively. These results indicate that the fabricated CS/Alg composite membranes are excellent waterpermselective ones for alcohol dehydration.

Exploration of the nanostructures and separation properties of cross-linked mixed matrix membranes using multiscale modeling

A new simulation scheme was established for strategically constructing cross-linked organic-inorganic mixed matrix membrane materials. This is a multiscale method using customized programming to effectively model complicated nanostructures. The effects of hybrid fillers in the chitosan/graphene oxide composite membranes are systematically elucidated at the molecular scale. Observed from the radial distribution function analysis, the significant enhancement of the separation performance in the dehydration of alcohols can be attributed to the stabilized polymer chains and the conspicuous increase in the water adsorption from mixing with graphene oxide sheets. Results show that the simulated models agree well with the experimental works in membrane density and transfer behavior of vapor molecules, which demonstrate that the modeling tools can be applied to evaluate the performance of cross-linked mixed matrix membranes, and to design various combination of hybrid membranes.

Mechanism and kinetics of 1-dodecanol etherification over tungstated zirconia

Growing interest in finding renewable alternatives to conventional fossil fuels and petroleum-derived specialty chemicals has motivated the investigation of biomass-derived alcohols to make ethers as diesel additives or lubricants. To optimize the direct etherification of long chain alcohols in the liquid phase, it is necessary to develop an understanding of the kinetics and mechanism of etherification and dehydration reactions. In this study, tungstated zirconia was identified asa selective solid-acid catalyst for the liquid-phase etherification of 1-dodecanol. Investigations of the mechanism and kinetics of this reaction suggest that cooperation between Brønsted- and Lewis-acid sites on tungstated zirconia enhances the selectivity to ether by increasing the surface concentration of adsorbed alcohol, thereby promoting bi-molecular ether formation relative to unimolecular alcohol dehydration. The suggested rate limiting step for etherification is the formation of a CO bond between two adsorbed alcohol molecules, and the suggested rate-limiting step for dehydration is the cleavage of the CH bond of the β-carbon atom in an adsorbed alcohol. Measurements of the kinetic isotope effects for etherification and dehydration support the proposed mechanism. A microkinetic model based on the proposed mechanism for dodecanol etherification and dehydration over tungstated zirconia accurately describes the observed effects of alcohol concentration and product inhibition.

Deoxygenation of Palmitic Acid on Unsupported Transition-Metal Phosphides

Highly active bulk transition-metal phosphides (WP, MoP, and Ni2P) were synthesized for the catalytic hydrodeoxygenation of palmitic acid, hexadecanol, hexadecanal, and microalgae oil. The specific activities positively correlated with the concentration of exposed metal sites, although the relative rates changed with temperature due to activation energies varying from 57 kJ mol–1 for MoP to 142 kJ mol–1 for WP. The reduction of the fatty acid to the aldehyde occurs through a Langmuir–Hinshelwood mechanism, where the rate-determining step is the addition of the second H to the hydrocarbon. On WP, the conversion of palmitic acid proceeds via R-CH2COOH → R-CH2CHO → R-CH2CH2OH → R-CHCH2 → R-CH2CH3 (hydrodeoxygenation). Decarbonylation of the intermediate aldehyde (R-CH2COOH → R-CH2CHO → R-CH3) was an important pathway on MoP and Ni2P. Conversion via dehydration to a ketene, followed by its decarbonylation, occurred only on Ni2P. The rates of alcohol dehydration (R-CH2CH2OH → R-CHCH2) correlate with the concen...

Histological alterations in Kidney and Liver of laboratory mice following intramuscular injection of Montevipera bornmuelleri (Werner, 1898) Venom.

Histopathological changes after bites of the Montivipera bornmuelleri viper, endemic to high altitudes areas of Lebanon, have not yet been investigated. Our study focuses on histological changes and irreversible damages in the kidney and liver of white laboratory Balb/c mice that received an intramuscular injection of lyophilized venom diluted in saline solution (NaCl 0.9%). Different venom concentration doses ranging from 0.25 mg/kg to 15mg/kg in a total injection volume of 100µl was injected intramuscularly (IM) into 5 groups of mice. After dissection, observations showed no macroscopically identifiable damages in any of the organs studied. However, tissue samples from the liver and the kidney were obtained for histological studies at various time intervals following the venom injection. The histological study was carried out using the Bouin solution (fixing bath), followed by dehydration in alcohol. Paraffin-embedded sections were stained using hemalun-easine. Tissues from 6 control mice, which received only an injection of saline solution, were also examined. The common histological alterations observed microscopically in the liver and the kidney were: pycnotic nuclei, necrosis, vacuolization, cytoplasmic destruction, edema, hemorrhage and congestion of blood vessels. Moreover, inflammatory infiltration of lymphocytic cells was observed in the prevascular regions of both organs. The histological changes observed appeared within 1h and intensified with time. These changes were proportional to the dose of the venom injected into the laboratory mice. Our results on what happens in the kidney and liver of mice after injecting the venom of M. bornmuelleri had many similarities with the effect of venom of other vipers (e. g. Daboia palestinea, Bitis ssp, Bothrops moujenis etc…) observed by others authors.

Candida albicans biofilms: comparative analysis of room-temperature and cryofixation for scanning electron microscopy.

Biofilms are frequently related to invasive fungal infections and are reported to be more resistant to antifungal drugs than planktonic cells. The structural complexity of the biofilm as well as the presence of a polymeric extracellular matrix (ECM) is thought to be associated with this resistant behavior. Scanning electron microscopy (SEM) after room temperature glutaraldehyde-based fixation, have been used to study fungal biofilm structure and drug susceptibility but they usually fail to preserve the ECM and, therefore, are not an optimised methodology to understand the complexity of the fungal biofilm. Thus, in this work, we propose a comparative analysis of room-temperature and cryofixation/freeze substitution of Candida albicans biofilms for SEM observation. Our experiments showed that room-temperature fixative protocols using glutaraldehyde and osmium tetroxide prior to alcohol dehydration led to a complete extraction of the polymeric ECM of biofilms. ECM from fixative and alcohol solutions were recovered after all processing steps and these structures were characterised by biochemistry assays, transmission electron microscopy and mass spectrometry. Cryofixation techniques followed by freeze-substitution lead to a great preservation of both ECM structure and C. albicans biofilm cells, allowing the visualisation of a more reliable biofilm structure. These findings reinforce that cryofixation should be the indicated method for SEM sample preparation to study fungal biofilms as it allows the visualisation of the EMC and the exploration of the biofilm structure to its fullest, as its structural/functional role in interaction with host cells, other pathogens and for drug resistance assays.

Synthesis of ethyl α-nitro-β-trifluoromethyl acrylate and β-trifluoromethyl-substituted tryptophan analogs and their plant growth regulating activity

Ethyl α-nitro-β-trifluoromethyl acrylate was synthesized by nucleophile-catalyzed reaction of ethyl nitroacetate with excess trifluoroacetaldehyde methyl hemiacetal and subsequent dehydration of the intermediate alcohol with P2O5. The synthesized nitro olefin regioselectively reacts with the substituted indoles to give fluorinated 3-indolyl-2-nitrobutyrates, which were converted into the corresponding β-trifluoromethyl-substituted tryptophan analogs via the nitro group reduction followed by saponification of the ethoxycarbonyl group. In the step of synthesis of amino ester, the 2-methylindole derivative was resolved into diastereomers, which were transformed to the corresponding acids separately. It was found that the synthesized β-trifluoromethyltryptophans have plant-growth regulating activity apparently attributable to their metabolic transformations into substituted α-trifluoromethylindol-3-ylacetic acids.

Oxidation of ethanol on NaX zeolite modified with transition metals

NaLaX, NaX + Co, and NaPdX catalysts are synthesized by modification of NaX zeolite with transition metals (La, Co, Pd). The activity of the prepared materials in catalytic ethanol oxidation is studied in the temperature range of 423–723 K. It is shown that NaPdX and NaX + Co accelerate the reactions of partial and complete oxidation of ethanol as the temperature rises. NaLaX accelerates both intramolecular and intermolecular dehydration of alcohol. It is shown that the NaPdX (1.0% Pd) sample has the highest activity in the complete oxidation of alcohol with the formation of CO2.

Atomic layer deposition of aluminium on anatase: A solid acid catalyst with remarkable performances for alcohol dehydration

Here we reported the synthesis of Al sites with ultra-high dispersion on anatase by an atomic layer deposition (ALD) method (ALD-Al/TiO2), which exhibits Brønsted acidity and satisfactory activity in the dehydration of alcohols, a key step in the deoxygenation of biomass. More importantly, the ALD-Al/TiO2 catalyst has good stability, which is sintering-resistant and gives constant catalytic performances after treatments at high temperature.

Understanding the effect of zeolite crystal expansion/contraction on separation performance of NaA zeolite membrane: A combined experimental and molecular simulation study

Experimental measurements and molecular simulations were used to investigate the effect of adsorption-induced changes in zeolite crystal size on the separation performance of NaA zeolite membrane for dehydration of alcohols. The vapor permeation (VP) separations of water/IPA showed a dramatic decrease in selectivity due to increase of IPA flux as the feed water concentration decreased. However, in the case of water/methanol and water/ethanol mixtures, the alcohol fluxes were almost independent of the feed water concentration. Permporosimetry measurements as well as molecular simulations show that at low loading of water, NaA crystals contract slightly, while they expand at higher loadings, which significantly affects the intercrystalline defects. In addition, at low water loadings intercrystalline defects are not blocked by water adsorbed at the defect sites. Both methanol and ethanol can enter the zeolite to reduce the crystal contraction. However, isopropanol cannot enter the NaA crystal and is thus unable to mitigate the effects of low water loadings. Based on this knowledge, the presence of methanol or ethanol in the water/isopropanol mixtures with low water content was expected to improve the dehydration performance of NaA zeolite membrane. This result was also observed for the dehydration of water/other large molecular mixture. Our studies here provide an improved understanding of the permeation and separations for NaA zeolite membrane.

Flow Dehydration and Hydrogenation of Allylic Alcohols

Key words flow chemistry - dehydration - hydrogenation - solid acids - heterogeneous catalysis - allylic alcohols