Ueber condensation von dekamethylendiamin mit aldehyden und ket...

Thesis (doctoral)--

Etude de la condensation des amines aromatiques primaires avec.

Thesis (doctoral)--

Condensation on and evaporation from a rotating flat-disk wiped-film evaporator.

Mode of access: Internet.

Microcanonical temperature for a classical field: Application to Bose-Einstein condensation

We show that the projected Gross-Pitaevskii equation (PGPE) can be mapped exactly onto Hamilton's equations of motion for classical position and momentum variables. Making use of this mapping, we adapt techniques developed in statistical mechanics to calculate the temperature and chemical potential of a classical Bose field in the microcanonical ensemble. We apply the method to simulations of the PGPE, which can be used to represent the highly occupied modes of Bose condensed gases at finite temperature. The method is rigorous, valid beyond the realms of perturbation theory, and agrees with an earlier method of temperature measurement for the same system. Using this method we show that the critical temperature for condensation in a homogeneous Bose gas on a lattice with a uv cutoff increases with the interaction strength. We discuss how to determine the temperature shift for the Bose gas in the continuum limit using this type of calculation, and obtain a result in agreement with more sophisticated Monte Carlo simulations. We also consider the behavior of the specific heat.

Improvement of the Derjaguin-Broekhoff-de Boer theory for capillary condensation/evaporation of nitrogen in mesoporous systems and its implications for pore size analysis of MCM-41 silicas and related materials

In this work, we propose an improvement of the classical Derjaguin-Broekhoff-de Boer (DBdB) theory for capillary condensation/evaporation in mesoporous systems. The primary idea of this improvement is to employ the Gibbs-Tolman-Koenig-Buff equation to predict the surface tension changes in mesopores. In addition, the statistical film thickness (so-called t-curve) evaluated accurately on the basis of the adsorption isotherms measured for the MCM-41 materials is used instead of the originally proposed t-curve (to take into account the excess of the chemical potential due to the surface forces). It is shown that the aforementioned modifications of the original DBdB theory have significant implications for the pore size analysis of mesoporous solids. To verify our improvement of the DBdB pore size analysis method (IDBdB), a series of the calcined MCM-41 samples, which are well-defined materials with hexagonally ordered cylindrical mesopores, were used for the evaluation of the pore size distributions. The correlation of the IDBdB method with the empirically calibrated Kruk-Jaroniec-Sayari (KJS) relationship is very good in the range of small mesopores. So, a major advantage of the IDBdB method is its applicability for small mesopores as well as for the mesopore range beyond that established by the KJS calibration, i.e., for mesopore radii greater than similar to4.5 nm. The comparison of the IDBdB results with experimental data reported by Kruk and Jaroniec for capillary condensation/evaporation as well as with the results from nonlocal density functional theory developed by Neimark et al. clearly justifies our approach. Note that the proposed improvement of the classical DBdB method preserves its original simplicity and simultaneously ensures a significant improvement of the pore size analysis, which is confirmed by the independent estimation of the mean pore size by the powder X-ray diffraction method.

Self-condensation of a thiazole-peptide bearing a 21-membered loop into a library of giant macrocycles with multiple orthogonal loops

Tetrapeptide analogue H-[Glu-Ser-Lys(Thz)]-OH, containing a turn-inducing thiazole constraint, was used as a template to produce a 21-membered structurally characterized loop by linking Glu and Lys side chains with a Val-Ile dipeptide. This template was oligomerized in one pot to a library (cyclo-[1](n), n = 2-10) of giant symmetrical macrocycles (up to 120-membered rings), fused to 2-10 appended loops that were carried intact through multiple oligomerization (chain extension) and cyclization (chain terminating) reactions of the template. A three-dimensional solution structure for cyclo-[1](3) shows all three appended loops projecting from the same face of the macrocycle. This is a promising approach to separating pepticle motifs over large distances.

Organic reactions in ionic liquids:ionic liquids ethylammonium nitrate promoted Knoevenagel condensation of aromatic aldehydes with active methylene compounds

The Knoevenagel condensation of aromatic aldehydes with active methylene compounds proceeded efficiently in a reusable ionic liquid, ethylammonium nitrate, at room temperature in the absence of any catalyst with high yields.

Organic reactions in ionic liquids: Ionic liquid-promoted three-component condensation of benzotriazole with aldehyde and alcohol

1-(alpha-Alkoxyalkyl)benzotriazoles are readily synthesized from three-component condensation of benzotriazole with aldehyde and alcohol in ionic liquid [Bmim]PF6.

Organic reactions in ionic liquids:Ionic liquid promoted Knoevenagel condensation of aromatic aldehydes with (2-thio)barbituric acid

The Knoevenagel condensation of aromatic aldehydes with (2-thio)barbituric acid proceeded efficiently in reusable ionic liquids, EAN, BmimBF4, and BmimPF6 at room temperature in the absence of any catalyst with high yields.

Organic reactions in ionic liquids: Knoevenagel condensation catalyzed by ethylenediammonium diacetate

The moisture and air stable ionic liquids 1-butyl-3-methylimidazonium tetrafluoroborate [bmim]BF4 and 1-butyl-3-methylimidazonium hexafluorophosphate [bmim]PF6 were used as ‘green' recyclable alternatives to volatile organic solvents (VOCs) for ethylenediammonium diacetate (EDDA) catalyzed Knoevenagel condensation between aldehydes or ketones with active methylene compounds. Both aldehydes and ketones gave satisfactory results. The ionic liquids containing catalyst EDDA were recycled several times with no decreases in yields and reaction rates. In the case of 2-hydroxybenzaldehyde, the reactions led to the formation of 3-substituted coumarins under standard reaction conditions.

Reentrant condensation of proteins in solution induced by multivalent counterions

Negatively charged globular proteins in solution undergo a condensation upon adding trivalent counterions between two critical concentrations C* and C**, C*condensation behavior above C** is caused by short-ranged electrostatic interactions between multivalent cations and acidic residues, mechanistically different from the case of DNA. Small-angle x-ray scattering indicates a short-ranged attraction between counterion-bound proteins near C* and C**. Monte Carlo simulations (under these strong electrostatic coupling conditions) support an effective inversion of charge on surface side chains through binding of the multivalent counterions.

Eulerian model for the condensation of pyrolysis vapors in a water condenser

The paper presents the simulation of the pyrolysis vapors condensation process using an Eulerian approach. The condensable volatiles produced by the fast pyrolysis of biomass in a 100 g/h bubbling fluidized bed reactor are condensed in a water cooled condenser. The vapors enter the condenser at 500 °C, and the water temperature is 15 °C. The properties of the vapor phase are calculated according to the mole fraction of its individual compounds. The saturated vapor pressure is calculated for the vapor mixture using a corresponding states correlation and assuming that the mixture of the condensable compounds behave as a pure fluid. Fluent 6.3 has been used as the simulation platform, while the condensation model has been incorporated to the main code using an external user defined function. © 2011 American Chemical Society.

A hydrothermally stable transition alumina by condensation-enhanced self-assembly and pyrolysis crystallization:application in the steam reforming of methane

The preparation of a steam-based hydrothermally stable transition alumina is reported. The gel was derived from a synthetic sol-gel route where Al-tri-sec-butoxide is hydrolysed in the presence of a non-ionic surfactant (EO20PO70EO20), HCl as the catalyst and water (H2O/Al = 6); the condensation was enhanced by treating the hydrolysed gel with tetrabutylammonium hydroxide (TBAOH), after which it was dried at 60 °C by solvent evaporation. The so-obtained mesophase was crystallized under argon at 1200 °C (1 h) producing a transition alumina containing δ/α, and possibly θ, alumina phases. Due to its surface acidity, the pyrolysis conditions transform the block copolymer into a cross-linked char structure that embeds the alumina crystallites. Calcination at 650 °C generates a fully porous material by burning the char; a residual carbon of 0.2 wt.% was found, attributed to the formation of surface (oxy)carbides. As a result, this route produces a transition alumina formed by nanoparticles of about 30 nm in size on average, having surface areas in the range of 59-76 m2 g-1 with well-defined mesopores centered at 14 nm. The material withstands steam at 900 °C with a relative surface area rate loss lower than those reported for δ-aluminas, the state-of-the-art MSU-X γ-alumina and other pure γ-aluminas. The hydrothermal stability was confirmed under relevant CH4 steam reforming conditions after adding Ni; a much lower surface area decay and higher CH4 conversion compared to a state-of-the-art MSU-X based Ni catalyst were observed. Two effects are important in explaining the properties of such an alumina: the char protects the particles against sintering, however, the dominant effect is provided by the TBAOH treatment that makes the mesophase more resistant to coarsening and sintering. This journal is © the Partner Organisations 2014.

Condensation-enhanced self-assembly as a route to high surface area α-aluminas

High surface area nanosized α-alumina has been obtained by thermally treating a sol-gel-derived mesophase at 1200 C; the mesophase was synthesized by a sol-gel route involving evaporation induced self-assembly (EISA) of a hydrolyzed gel from Al-tri-sec-butoxide in s-BuOH in the presence of a nonionic surfactant (EO20PO70EO20), HCl as catalyst, and water (H2O/Al = 6). The activated material renders moderate surface areas of about 8.4-10 m2 g-1, associated with significant crystallite coarsening. The key aspect to produce smaller crystallites is making the mesophase more resistant to coarsening. This was achieved by enhancing the condensation step by treating the hydrolyzed gel with tetrabutyl ammonium hydroxide (TBAOH) before evaporation. The characteristics of the mesophase indicate condensation of the primary particles with less AlO5 unsaturated sites, at the expense of a lower solid yield due to small crystallites dissolution. The activated TBAOH condensed EISA material is composed of α-alumina aggregated crystallites of about 60-100 nm, and the material possesses surface areas ranging from 16 to 24 m2 g -1 due to the improved resistance to coarsening. At least two aspects are suggested to play a role in this. The worm-hole morphology of the mesophase aggregates yields high particle coordination, which favors densification rather than coarsening. Furthermore, the decrease of the AlO5 defect sites by the TBAOH condensation makes the mesophase less reactive and consequently more resistant to coarsening. © 2013 American Chemical Society.