Desorption Of Ethanol Research Articles

Creep Behaviors during and after Drying and Microstructures after Drying of Wood Swollen by Water, Methanol and Ethanol

To investigate the relationship between microstructures of wood and the physical and mechanical properties, creep behaviors during and after drying and microstructures after drying of wood swollen by water, methanol and ethanol were studied in this report. Results obtained were as follows. 1) Creeps for every swollen wood during drying were greater than immediately after drying, and much greater than after conditioned at the before and after contents. Wood samples with greater degree of creep during and immediately after drying were; methanol-swollen wood, ethanol-swollen wood and water-swollen wood when similar amount of content were changed. 2) Similar degree of creep occurred during drying despite drying rate. Degree of creep immediately after drying depended on drying rate and elapsed time after drying. 3) Larger amount of micropores existed in wood after desorption of methanol and ethanol than in wood after desorption of water when vacuum-dried at 110°C. 4) One and a half times as much as greater creep occurred during drying for liquid mixtures (water : methanol = 0.2 : 0.8, water : ethanol = 0.8 : 0.2) swollen wood than for water-swollen wood. Accordingly, it was considered that different swollen states of wood produced different wood microstructures during and after drying.

Reaction network and kinetic analysis of ethanol steam reforming over a Ru/Al 2O 3 catalyst

Ethanol steam reforming, a potential technology of hydrogen production for fuel cell application, has attracted great research attention recently. Because ethanol can be produced from biomass cheaply, using bioethanol with large excess of water as the direct feed of steam reforming is believed to be a promising technology to produce hydrogen for fuel cells. Although various catalyst systems were used for ethanol steam reforming, detailed reaction kinetics was not investigated thoroughly. In the analysis of heterogeneous catalytic kinetics, reaction mechanism including adsorption step of reactants, reaction step of the adsorbed species, and desorption step of the products were usually proposed. Then a suitable rate determining step was assumed to allow the derivation of the rate equation as a function of reactant and/or product concentrations. In this study, the general rate equations for cyclic reaction networks with multiple pathways were applied to derive the rate equation and hydrogen yield equation for ethanol steam reforming. The derived rate and yield equations were used to analyze the kinetic data of Vaidya and Rodrigues. The results showed that the experimental ethanol conversions and hydrogen yield ratios at varying space times and reaction temperatures could be satisfactorily predicted by the model equations. The rate controlling steps are water reaction with the adsorbed ethanol, water reaction with the adsorbed acetaldehyde, and CO desorption. Furthermore, for temperature lower than 923 K, the overall reaction is also controlled by desorption of ethanol and desorption of acetaldehyde; for temperature higher than 923 K, the overall reaction is also controlled by the dehydrogenation of the adsorbed ethanol. The averaged activation energy of three sequential reaction steps was found to be 110 kJ/mol, compared with the overall activation energy 96 ± 17 kJ/mol determined by Vaidya and Rodrigues.

(100) facets of γ-Al2O3: The Active Surfaces for Alcohol Dehydration Reactions

Temperature programmed desorption (TPD) of ethanol, as well as ethanol and methanol dehydration reactions were studied on γ-Al2O3 in order to identify the active catalytic sites for alcohol dehydration reactions. Two high temperature (>473 K) desorption features were observed following ethanol adsorption. Samples calcined at T ≤ 473 K displayed a desorption feature in the 523–533 K temperature range, while those calcined at T ≥ 673 K showed a single desorption feature at 498 K. These two high temperature desorption features correspond to the exclusive formation of ethylene on the Lewis (498 K) and Bronsted acidic (~525 K) sites. The amount of ethylene formed under conditions where the competition between water and ethanol for adsorption sites is minimized is identical over the two surfaces. Furthermore, a nearly 1-to-1 correlation between the number of under-coordinated Al3+ ions on the (100) facets of γ-Al2O3 and the number of ethylene molecules formed in the ethanol TPD experiments on samples calcined at T ≥ 673 K was found. Titration of the penta-coordinate Al3+ sites on the (100) facets of γ-Al2O3 by BaO completely eliminated the methanol dehydration reaction activity. These results demonstrate that in alcohol dehydration reactions on γ-Al2O3, the (100) facets are the active catalytic surfaces. The observed activities can be linked to the same Al3+ ions on both hydrated and dehydrated surfaces: penta-coordinate Al3+ ions (Lewis acid sites), and their corresponding –OH groups (Bronsted acid sites), depending on the calcination temperature. Temperature-programmed desorption of ethanol, as well as steady state dehydration reactions of ethanol and methanol, indicate that the (100) facets are the primary active surfaces of γ-Al2O3. The active centers on both the hydroxylated and dehydroxylated (100) facets are related to the coordinatively unsaturated Al3+ ions

A TPD-MS study of the adsorption of ethanol/cyclohexane mixture on activated carbons

The adsorption of ethanol/cyclohexane binary mixtures on different types of activated carbons was studied in this work by temperature programmed desorption coupled with mass spectroscopy (TPD-MS). The texture, morphology and surface chemistry of the carbons were evaluated by N2 adsorption, scanning electron microscopy (SEM) and TPD-MS techniques. The ethanol and cyclohexane TPD-MS desorption profiles showed that specific interactions between the carbon material and the adsorbate are involved during the adsorption. Most of the activated carbons adsorb strongly ethanol on the surface, leading to desorption temperatures above 100 °C. Only one carbon exhibits an affinity for cyclohexane. These observations were correlated to the different surface chemistry of the materials.

Implementing chemical functionality into oriented films of metal–organic frameworks on self-assembled monolayers

The generation of thin films of oriented functionalized metal–organic frameworks (MOFs) on self-assembled monolayers was achieved via direct growth from solution. Specifically, the direct growth from solvothermally pretreated synthesis solutions of two different MOF structures with amino functionality was investigated: the flexible framework structure NH2–Fe–MIL-88B and the mesoporous MOF NH2–Fe–MIL-101 with its remarkably large unit cell. Both MOF structures can be grown in a highly oriented fashion on self-assembled monolayers of 16-mercaptohexadecanoic acid on gold. With the help of a quartz crystal microbalance we demonstrate that the introduction of amino groups into the framework strongly affects the host–guest interactions towards ethanol molecules: thin films of NH2–Fe–MIL-88B show a significantly higher uptake of ethanol than unfunctionalized Fe–MIL-88B films. In situXRD experiments during sorption of ethanol showed that the amino group does have an impact on the cell parameters of the structure, but the flexibility (“breathing”) during ad- and desorption of ethanol is similar for the functionalized and the unfunctionalized structures. It is anticipated that the implementation of chemical functionalities into oriented MOF films will lead to selective host–guest interactions that are of key importance for chemical sensing and other applications.

Modelling the Desorption of Ethanol from an Externally Heated Saturated Activated Carbon Column by Purging with Air

The desorption of ethanol from an externally heated column loaded with activated carbon and purged with air has been studied. The column was initially saturated with liquid ethanol. This process simulates the regeneration step in a concentration-swing/thermal-swing adsorption process for the production of fuel-grade ethanol. A theoretical model was developed for describing the mass- and heat-transfer kinetics of the process. Validation of the model was achieved by comparing its predictions with experimental data, employing initial column temperatures between 298 K and 395 K and air flow rates between 1.6 × 10-6 m3/s and 11.3 × 10-6 m3/s. Experimentally measured adsorption isotherms of ethanol from ethanol/air gas mixtures onto activated carbon, as well as the regeneration column dynamics, are reported.

Water and ethanol desorption in the flexible metal organic frameworks, MIL-53 (Cr, Fe), investigated by complex impedance spectrocopy and density functional theory calculations

The breathing behaviour of MIL-53(Cr) and MIL-53(Fe) upon water and ethanol desorption has been investigated by combining complementary experimental techniques including ThermoGravimetry Analysis (TGA), Differential Scanning Calorimetry (DSC) and Complex Impedance Spectroscopy (CIS). It was shown that two stages of solvent departure are involved in the desorption process, as revealed by (i) a change of the weight loss gradient in the TGA curve, (ii) the existence of a second endothermic peak in the DSC signal and (iii) a sudden drop and/or profile change of the ac conductivity in CIS. All these features are observed around a typical temperature T(c), for which the framework contractions, caused by the solvent desorption, occur. Moreover, it is shown that these modifications are more pronounced when the magnitude of the breathing is higher, as illustrated by the comparison of the water/MIL-53(Cr), ethanol/MIL-53(Cr) and water/MIL-53(Fe) systems. CIS data were further analyzed in the light of DFT calculations which provided the preferential arrangements of the molecules within the pores and the resulting host/guest interactions. It could then be proposed that (i) the polarization conductivity results from the local re-orientation of the μ(2)-OH dipoles bonded to the metal atom from the hybrid solid, i.e. Fe or Cr, and (ii) that dc conductivity, which can be ascribed to a proton propagation via a Grotthus mechanism, is favoured when the solvent molecules form strong hydrogen bonds between each other.

Mechanistic Aspects of the Ethanol Steam Reforming Reaction for Hydrogen Production on Pt, Ni, and PtNi Catalysts Supported on γ-Al2O3

Mechanistic aspects of ethanol steam reforming on Pt, Ni, and PtNi catalysts supported on gamma-Al(2)O(3) are investigated from the analysis of adsorbed species and gas phase products formed on catalysts during temperature-programmed desorption of ethanol and during ethanol steam reforming reaction. DRIFTS-MS analyses of ethanol decomposition and ethanol steam reforming reactions show that PtNi and Ni catalysts are more stable than the Pt monometallic counterpart. Ethanol TPD results on Ni, Pt, and NiPt catalysts point to ethanol dehydrogenation and acetaldehyde decomposition as the first reaction pathways of ethanol steam reforming over the studied catalysts. The active sites responsible for the acetaldehyde decomposition are easily deactivated in the first minutes on-stream by carbon deposits. For Ni and PtNi catalysts, a second reaction pathway, consisting in the decomposition of acetate intermediates formed over the surface of alumina support, becomes the main reaction pathway operating in steam reforming of ethanol once the acetaldehyde decomposition pathway is deactivated. Taking into account the differences observed in the mechanism of ethanol decomposition, the better stability observed for PtNi catalyst is proposed to be related with a cooperative effect between Pt and Ni activities together with the enhanced ability of Ni to gasify the methyl groups formed by decomposition of acetate species. On the contrary, monometallic catalysts are believed to dehydrogenate these methyl groups forming coke that leads to deactivation of metal particles.

NO x Reduction by Ethanol on Pd/Sulphated Zirconia

The NO reduction by ethanol was studied on palladium catalyst supported on sulphated zirconia. Temperature programmed desorption of NO and ethanol (TPD) and temperature programmed surface reaction (TPSR) analyses as well as catalytic tests in reducing and oxidizing conditions (O2 presence), besides diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) showed the formation of intermediate species during the reaction, such as ethoxy species that reacted forming ethylene. Besides dehydrogenate formed adsorbed acetate species, which than decompose and/or react with hydroxyls of the support. The sulphated zirconia support increased the acid sites with the formation of strong Bronsted sites, favoring the formation of ethoxy species. Acetate species also react with NO adsorbed on Pd forming N2, N2O, CO and CO2. The excess of O2 favored ethanol oxidation to CO2, consequently less ethanol was available to react with NOx.

Development of a detailed surface mechanism for the selective catalytic reduction of NO x with ethanol on silver alumina catalyst

Ethanol selective catalytic reduction (SCR) of NO x on silver alumina catalyst is a promising technology in reducing NO x from Diesel engines. In particular, experimental results show that using ethanol reductant on low loading silver alumina catalyst can result in greater than 90% of NO x reduction over a wide temperature range. Even though this technology has been demonstrated experimentally, there is no known detailed surface model to describe the ethanol SCR process. In this work, a detailed surface mechanism with 35 irreversible reactions has been developed by critically reviewing literature data on ethanol SCR and by performing Surface Perfectly Stirred Reactor (SPSR) simulations. Using the new surface SCR mechanism along with validated ethanol gas phase chemistry from LLNL, the cause of the inactivity of ethanol SCR at temperatures above 500 °C is found to be the desorption of NO and ethanol rather than gas phase ethanol oxidation. Predictions with the new ethanol SCR mechanism agree well with the experimental NO x conversion. However, further improvement on the model is needed to improve predictions involving the hydrocarbon species.

Fixed-bed adsorption performance of oil palm shell-based activated carbon for removal of 2,4,6-trichlorophenol

This study investigated the adsorption potential of oil palm shell-based activated carbon to remove 2,4,6-trichlorophenol from aqueous solution using fixed-bed adsorption column. The effects of 2,4,6-trichlorophenol inlet concentration, feed flow rate and activated carbon bed height on the breakthrough characteristics of the adsorption system were determined. The regeneration efficiency of the oil palm shell-based activated carbon was evaluated using ethanol desorption technique. Through ethanol desorption, 96.25% of the adsorption sites could be recovered from the regenerated activated carbon.

NO x reduction by ethanol on Pd/zeolites-effect of oxygen

The reduction of NO by ethanol on palladium catalysts supported on NaZSM-5 and HZSM-5 zeolites was studied. Temperature programmed techniques, such as desorption of ethanol, NO and surface reaction (TPSR) analyses, besides NH3 (NH3–TPD), as well as, FTIR after pyridine adsorption were used to accomplish reaction products and surface properties. Results show that NaZSM5 and HZSM5 present different amounts of Lewis and Bronsted acid sites, which affect strongly the carbon product distribution, but not the nitrogen selectivity. NO reaction with ethanol in the presence of oxygen occurs only over the metal and is independent of the acid sites.

Ethanol Steam Reforming over Pt Catalysts Supported on CexZr1−xO2 Prepared via a Glycine Nitrate Process

Hydrogen production for application to proton exchange membrane fuel cells (PEMFCs) has been a focus of investigation globally. Ethanol as a H2 source benefits from the ready availability of infrastructure and environmental benignity in comparison with those of other hydrocarbon fuels. Thus, H2 production from ethanol has gained much attention worldwide. In this work, H2 production from ethanol steam reforming (ESR) was investigated over Pt catalysts supported on CexZr1−xO2 (x = 0.2, 0.4, 0.6, or 0.8) developed via a glycine nitrate process. The supports or catalysts were characterized by low temperature N2 physical adsorption, powder X-ray diffraction (XRD), transmission electron microscopy (TEM), H2 temperature-programmed reduction, temperature-programmed desorption of ethanol, and catalytic performance measurements for ESR at 350–550 °C. Initial catalyst stability was also investigated. The results indicated that Pt/CexZr1−xO2 catalysts were highly active for ESR at lower temperatures, only yielding H2, CO, CH4, and CO2 as products. However, selectivity to CH4 was found around 50.0% at 350–400 °C, while selectivity of products at 450–550 °C was found close to thermodynamic control values, indirectly suggesting that ethanol first dehydrogenates on the metallic surface and then aldehyde undergoes decarbonylation, forming CO and CH4. The function of steam was to establish thermodynamic equilibria for methane steam reforming and water gas shift reactions. The high activity and good initial stability made the catalysts suitable for application to portable power generation by using a PEMFC combined with a solid oxide fuel cell or a methane internal combustion engine for capturing the energy in methane.

High yield hydrogen production from low CO selectivity ethanol steam reforming over modified Ni/Y 2O 3 catalysts at low temperature for fuel cell application

Ethanol–water mixtures were converted directly into H 2 with 67.6% yield and >98% conversion by catalytic steam reforming at 350 °C over modified Ni/Y 2O 3 catalysts heat treated at 500 °C. XRD was used to test the structure and calculate the grain sizes of the samples with different scan rates. The initial reaction kinetics of ethanol over modified and unmodified Ni/Y 2O 3 catalysts were studied by steady state reaction and a first-order reaction with respect to ethanol was found. TPD was used to analyze mechanism of ethanol desorption over Ni/Y 2O 3 catalyst. Rapid vaporization, efficiency tube reactor and catalyst were used so that homogeneous reactions producing carbon, acetaldehyde, and carbon monoxide could be minimized. And even no CO detective measured during the first 49 h reforming test on the modified catalyst Ni/Y 2O 3. This process has great potential for low cost H 2 generation in fuel cells for small portable applications where liquid fuel storage is essential and where systems must be small, simple, and robust.

The adsorption and desorption of ethanol ices from a model grain surface

Reflection absorption infrared spectroscopy (RAIRS) and temperature programed desorption (TPD) have been used to probe the adsorption and desorption of ethanol on highly ordered pyrolytic graphite (HOPG) at 98 K. RAIR spectra for ethanol show that it forms physisorbed multilayers on the surface at 98 K. Annealing multilayer ethanol ices (exposures >50 L) beyond 120 K gives rise to a change in morphology before crystallization within the ice occurs. TPD shows that ethanol adsorbs and desorbs molecularly on the HOPG surface and shows four different species in desorption. At low coverage, desorption of monolayer ethanol is observed and is described by first-order kinetics. With increasing coverage, a second TPD peak is observed at a lower temperature, which is assigned to an ethanol bilayer. When the coverage is further increased, a second multilayer, less strongly bound to the underlying ethanol ice film, is observed. This peak dominates the TPD spectra with increasing coverage and is characterized by fractional-order kinetics and a desorption energy of 56.3+/-1.7 kJ mol(-1). At exposures exceeding 50 L, formation of crystalline ethanol is also observed as a high temperature shoulder on the TPD spectrum at 160 K.

Effects of potassium on the adsorption and dissociation pathways of methanol and ethanol on Mo 2C/Mo(1 0 0)

The adsorption, desorption and dissociation of methanol and ethanol on K-dosed Mo 2C/Mo(1 0 0) have been investigated by work function, thermal desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). The adsorption of both molecules at 100 K caused a significant decrease in the work function of the Mo 2C/Mo(1 0 0) surface suggesting an electron donation from the O lone pair to carbide surface. Potassium additive stabilized the adsorbed alcohols, and converted a fraction of them to an irreversibly bonded surface species, which decomposed only at higher temperatures, 450–500 K, to yield H 2, CO and CH 4(CH 3OH) and H 2, CO, acetaldehyde and ethylene (C 2H 5OH). From the coincident desorption of major products, H 2, CO and K, we inferred the existence of surface compounds between alcohols and potassium on Mo 2C/Mo(1 0 0) surface. Analysis of the HREEL spectra of the adsorbed layers suggested that the scission of O–H bond is the primary step in the decompositions of alcohols and we can count with the formation of very stable CH 3O–K and C 2H 5O–K surface species at high potassium coverage. In addition, we can also reckon with the rupture of C–O bonds producing adsorbed CH 3 and C 2H 5 species.

Surface reactivity of zinc-modified hydroxyapatite

Surface reactivity of hydroxyapatite (Hap), Ca 10(PO 4) 6(OH) 2, and zinc-Hap was evaluated using temperature-programmed desorption (TPD) of ethanol and diffuse reflectance infrared spectroscopy (DRIFTS). Hap was prepared by the precipitation method and the Zn-based catalysts were prepared by the ionic exchange method (ZnHap troc) and by zinc oxide deposition (ZnHap dep). X-ray diffraction (XRD) results have shown the Ca 2+ substitution by Zn 2+ ions for the catalyst prepared by ionic exchange method and a zinc oxide formation as a segregated phase after zinc deposition. TPD-ethanol analyses showed that Hap has catalytic activity to ethanol decomposition and low surface acidity. DRIFTS results showed ethoxide species formation at the surface of ZnHap troc, which undergoes transformation into acetate and carbonate species with increasing temperature. The catalyst prepared through the ionic exchange method (ZnHap troc) showed high selectivity to the ethanol dehydrogenation reaction.

Adsorption and Reaction of Ethanol on ZnO Nanowires

The surface reaction of ethanol on ZnO nanowires was studied by temperature-programmed desorption (TPD). Desorption products of ethanol from ZnO nanowires were examined as function of temperature and exposure. During heating of the sample up to 900 K, ethanol, ethylene, and hydrogen molecules are desorbed as the main desorption products. Molecular desorption of ethanol was observed at 145 K from physisorbed layers. A higher desorption energy was observed for chemisorbed ethanol desorbing at 250−275 K. As decomposition products of ethanol on the ZnO nanowire surface, ethylene and hydrogen desorbed at 517 and 523 K, respectively. A reaction model is suggested for the surface decomposition of ethanol on ZnO nanowires.

Sorption and desorption parameters of water or ethanol in light‐cured dental dimethacrylate resins

AbstractTwo cycles of sorption/desorption of water or ethanol by light‐cured dental resins of bisphenol A glycol dimethacrylate (Bis‐GMA), bisphenol A ethoxylated dimethacrylate (Bis‐EMA) urethane dimethacrylate (UDMA) triethylene glycol dimethacrylate and decanediol dimethacrylate (D3MA) were studied. The experimental curves mt = f(t) taken for the first water sorption by poly‐Bis‐GMA, poly‐Bis‐EMA and poly‐UDMA showed a maximum. A maximum was also observed in the curve obtained for first sorption of ethanol by poly‐Bis‐GMA. In all other cases, the curves for sorption or desorption of water or ethanol showed Fickian behavior. The experimental data obtained for first sorption of water or ethanol were perfectly fitted to a new proposed equation, which predicts water or ethanol sorption with simultaneous extraction of unreacted the monomer. This equation gave us the possibility for the determination of the diffusion coefficient of the extraction of the unreacted Bis‐GMA during the water and ethanol sorption, as well as the diffusion coefficient of the extraction of the unreacted Bis‐EMA and UDMA during the water sorption. The maximum water or ethanol absorbed at equilibrium and the diffusion coefficient are determined from the second sorption/desorption cycle during which the extraction of the monomer is negligible. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Decomposition and Aromatization of Ethanol on ZSM-Based Catalysts

The adsorption, desorption, and reactions of ethanol have been investigated on pure and promoted ZSM-5 catalysts. FTIR spectroscopy indicated the formation of a strongly bonded ethoxy species on ZSM-5(80) at 300 K. TPD experiments following the adsorption of ethanol on both ZSM-5 and Mo2C/ZSM-5 have shown desorption profiles corresponding to unreacted ethanol and decomposition products (H2O, H2, CH3CHO, C4H10O, and C2H4). The main reaction pathway of ethanol on pure ZSM-5 is the dehydration reaction yielding ethylene, small amounts of hydrocarbons, and aromatics. Deposition of different additives, such as Mo2C, ZnO, and Ga2O3 on zeolite, greatly promoted the formation of benzene and toluene at 773-973 K, very likely by catalyzing the aromatization of ethylene formed in the dehydration process of ethanol. Separate studies of the reaction of ethylene revealed that the previous additives markedly enhanced the selectivity and the yield of aromatics on ZSM-5.