Noncatalytic organic rearrangement using supercritical water

Abstract

Significant acceleration of Beckmam and pinacol rearrangements can be achieved by using supercritical water (scH₂O), especially just near the critical point even in the absence of any acid catalysts. A high-pressure, high-temperature flow reactor system with FTlR operable at 500°C and 50 MPa was suaxssfdy developed, wherein the non-catalytic Beckmam and pinacol rearrangements using scH₂O were carried out and monitored. It has been demonstrated that scH₂0 itself acts very effectively in the place of conventional acid catalysts for both the rearrangements. The rate of the pinacol rearrangement using scH₂O is 28,200-fold rate of that in 0.871 M HCl solution at 46.7 MPa under distillation conditions. The high rate of reaction may be attributed to a great increase in the local proton concentration around the organic reactants.     

Ion-exchange resin decomposition in supercritical water

Abstract

Using supercritical water oxidation, the cation exchange resin was decomposed fast and completely to water, carbon dioxide and sulfuric acid. While the resin decomposition yield increased with the reaction time and the amount of hydrogen peroxide added as oxidizing agent, it was constant in the resin concentration from 0.14 to 1.9 dry resin weight percent to water. More than 99% of the cation exchange resin was decomposed with hydrogen peroxide added in the amount of 7 times the stoichiometric value at 673 K and 30MPa for 30 minutes of the reaction time. The cation exchange resin is decomposed through two main reaction pathways. One has a rate controlling intermediate such as acetic acid whose decomposition rate was very slow, and the other does not have stable intermediates. The decomposition of the acetic acid is a significant factor for the complete decomposition of the resin, although it does not dominate the whole resin decomposition. A simple kinetic model that estimates the resin decomposition yield was developed.     

The formation of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles in the oxidation of aluminum by water under sub- and supercritical conditions

Massive aluminum samples were oxidized by sub- and supercritical water with the formation of (AlOOH) _n and (Al₂O₃) _n nanoparticles. The release of H₂ began at 523 K when the reagents were heated uniformly to 700 K. The time lag of the beginning of oxidation was 140 s when supercritical water was injected into a reactor with aluminum samples at 665 K and 23.1 MPa. Oxidized aluminum powders were analyzed using a transmission electron microscope. Predominantly large (300–400 nm) α-Al₂O₃ particles were formed when supercritical water was injected into a reactor with aluminum. Smaller (20–50 nm) γ-Al₂O₃ particles were also observed in samples oxidized by water vapor under temperature increase conditions. Kinetic equations describing the rate of H₂ formation in the reaction of H₂O with aluminum were obtained. Possible nanostructuring mechanisms are discussed.     

Thin film coating of photocatalytics on ultra light ceramic tile by use of supercritical fluid

Abstract

Although sol-gel method is an easy procedure to form a thin film, it's extremely difficult to coat on the surface of small size particles, fibers, and fiber ceramics, because concentration occurs by capillary phenomena and causes peeling or breakage of film.

In order to solve this problem, we use supercritical CO₂ rapid expansion from supercritical solution (RESS), nano-sized particles of TiO₂ with high intensity can be sprayed out of a nozzle, then collected on the surface of substrates, but can be absorbed into fibers or porous materials, being not interfered by viscosity of a solution.

TiO₂ sol made by hydrolysis process is set in a pressure cell and mixed together with super-critical CO₂. Controlling the pressure and the temperature, we could obtain TiO₂ sol and super critical fluid mixture, and then discharge to the substrate. At this point, Titania sol viscosity is so low that a surface wettability of the substrate becomes negligible.

By the use of the characteristics of the supercritical fluid, without constraint condition of viscosity or capillarity, this sol can penetrate into the interstices of the substance's structure.

Thus, clearing obstruction of capillary phenomena, supercritical fluid coating method shows its capability to penetrate deep into inside of entangled fiber of the three-dimensional structure so as considered to be a heat resistant filter with 95% porosity.     

Use of Organic Solvents as Additives in Inductively Coupled Argon Plasma with Atomic Emission Spectrometric Detection

Abstract

The effect of nitric acid/organic aerosols on the emission intensity of metals from the first row transition series, plus Cd and Pb was investigated. The addition of organic solvents to reference solutions diminished the aerosol mean drop size, by reducing the surface tension of the solutions. Correlation between signal intensity and BEC with the main physical characteristics (surface tension and viscosity) of the nitric acid/acetic acid and nitric acid/alcohol solutions was studied. Analytical curves (0–2.0 fig ml^?1) were evaluated using a matrix matching procedure, and detection limits indicated an improvement (ca 40%) in analytical performance as well as in linearity, sensitivity and precision.     

Research and development at rist

Abstract

The Research Institute for Solvothermal Technology (RIST) opened in September, 1997 to carry out research related to high-temperature and high-pressure fluid technology. The RIST is unique institute specialized high pressure science and technology in Japan, and probably in the world. According to government, the institute is defined as the core facility of a West-Japan creative economic development base zone.

Nowadays, RIST has developed new technologies using supercritical fluids, especially carbon dioxide and water, in areas related to the environment, such as the treatment of organic waste, the production of new materials, such as “new-carbon” substances, materials for batteries and electromagnetic wave absorption, and in the area of energy and resources, such as the conversion or the recycling of industrial plastic waste.

A review will be given on the research and development activities at RIST. It is focused on several essential results obtained in recent investigations. Progressive joint research projects with the cooperation of enterprises, universities and government will be described.     

Hydrogen bonding and clusters in supercritical methanol–water mixture by neutron diffraction with H/D substitution combined with empirical potential structure refinement modelling

ABSTRACT

Neutron diffraction measurements of H/D isotopic substitution have been performed for seven H/D substituted methanol-water mixtures of 0.3?mol fraction of methanol (x_M) under the supercritical (618?K, 100?MPa) and ambient (298?K, 0.1?MPa) conditions. The seven structure factors obtained were subjected to an empirical potential structure refinement (EPSR) modelling to derive all site-site pair correlation functions, coordination number distributions, spatial density functions, and cluster distributions. Water has a four coordinated structure in the first coordination shell under both ambient and supercritical conditions; however, the spatial density distribution of water molecules in the second coordination shell is delocalised under the supercritical condition. The mean coordination number of all atomic pairs with hydrophilic interactions decreases in the supercritical state. On the other hand, the mean coordination number of interactions between the hydrophobic part of methanol and water molecule is less sensitive to temperature. In the supercritical condition, water clusters with a wide size distribution are generated in a methanol-water mixture as well as in pure water. Since the critical temperature of a methanol-water mixture is lower than that of pure water, it can be concluded that the addition of methanol can generate fragment water clusters at a lower temperature.     

Effect of acids on the gamma-radiolysis of frozen aqueous systems of some organic compounds

Abstract

ESR spectra of γ-irradiated frozen aqueous solutions of a number of organic compounds such as alcohols, ether, acetone and tetrahydrofurans have been examined in the presence and absence of mineral acids such as H₂SO₄. The presence of the acid is found to cause an intensification of the organic radical ESR spectra as compared with the acid free solutions. Also, the presence of the organic compounds in frozen aqueous H₂SO₄ suppresses the formation of both H-atoms and SO₄ ^? radical ions. These results have been explained on the basis of reactions of the electrons and holes, or excitons, primarily formed by the action of radiation on the substrate ice.     

Data for scaling-up hydrothermal waste water treatment process

Abstract

Hydrothermal oxidation of wastes is developed as an alternative technique in order to limit the toxic end-product formation, the waste volume and the energy supply. We are now working on the transfer of this technology, and so on the determination of data for scaling-up the hydrothermal oxidation process. The main data concern the knowledge of reactive pathway, the determination of reaction kinetic and thermal parameter. Kinetic and thermal data have been determined for the hydrothermal oxidation of acetic acid as well as the reactive pathway of hydrothermal oxidation of a C, H, O, N compound, the fenuron (C₆H₅-NH-CO-N(CH₃)₂).     

Phase behavior of organic pollutants in supercritical water

Methods for analyzing, ranking, and predicting the global phase behavior and possible heterogeneous fluid equilibria in supercritical water-organic pollutant systems are discussed in terms of present-day conceptions of the global phase diagrams of binary mixtures. The phase equilibria of some classes of organic compounds (polycyclic aromatic hydrocarbons, polychlorinated biphenyls, polychlorinated dibenzodioxins and furans as well as some pesticides) in supercritical water are studied. Based on found correlations with the partition coefficient of organic substances in immiscible mixtures of octanol and water (K _OW ), we determine the binary interaction parameter k ₁₂ in a one-fluid mixture model. Analytical expressions for predicting the azeotropic states of binary mixtures are derived; the occurrence of azeotropic behavior in aqueous solutions of organic compounds is estimated. Results of calculations of phase equilibria and critical curves for earlier unstudied organic pollutants in supercritical water are described.     

Stabile Isotope in den Interaktionen von Parasiten und Wirten bei Höheren Pflanzen

Abstract

An overview is given about the δ¹³C- and δ5D-values in the organic material of hemi- and full- parasitic higher plants and of their hosts.

Hemiparasites have to direct the content of the host xylem into their tissues by lowering their water potential. They achieve this by active water secretion or by lowering the stomatal resistance. In the latter case, the intercellular CO₂-concentration in the chlorenchyme of the parasite is increased. This causes a reduction of the ¹³C-content (δ¹³C-value of the parasite more negative than of the host). The dry matter of the mistletoes is always richer in deuterium than that of the host. The reason for this fact is unknown.

In the case hemiparasites and their hosts show differences in the ¹³CO₂-discrimination during the photosynthetic CO₂-fixation, an eventual transfer of organic material from host to parasite can be checked. By this way a holoparasitic mistletoe, Tristerix aphyllus, could be demonstrated.

In contrast to mistletoes on C3-hosts, such on CAM-hosts have a lower deuterium content in the dry mass than the hosts.

Holoparasites get all their organic material from the hosts and mirror, therefore, in their δ¹³C-values those of the hosts. Their deuterium content in the organic material is always higher than the one in the host. The reason is unknown.     

Synthesis of MoO2 particles during oxidation of bulk molybdenum samples by supercritical water

It was found that bulk samples of molybdenum 〈Mo〉 are oxidized by supercritical water forming nanoparticles of monocline MoO₂. The average size of nanoparticles obtained at uniform heating of 〈Mo〉 with supercritical water was about 27 nm, and the size of agglomerates of nanoparticles was ≤ 1 μm. From time dependence of the amount of formed H₂ n _H2(t), we have determined kinetic parameters of 〈Mo〉 transition to MoO₂ particles. The dependence dn _H2/dt is characterized by the presence of two pronounced maxima. This is explained by the change of mutual diffusion of H₂ and H₂O molecules along with the growth of thickness of the layer of MoO₂ nanoparticles.     

The Spectrofluorometric Monitoring of Water Purification by Natural Alternatives

Aim: Determination of efficiency of zeolite and hydrolytic enzymes isolated from earthworms in water purification.

Methods: The autofluorescence of water was investigated by fluorescence excitation–emission matrix. The purification of water was carried out with natural zeolite and hydrolytic enzymes isolated from earthworms. These methods were applied to samples that contain ciliates that were detected with atomic force spectroscopy.

Results: The zeolite removed ammonia and partly eliminated some organic compounds. The hydrolytic enzymes were efficient in biodegrading organic compounds present in water.

Conclusion: Zeolite and enzymes are applicable in water purification.     

Inkorporation von 15N-markiertem Harnstoff in Organogene Dünge- und Abfallstoffe während der Rotte

Abstract

Eight organic fertilizers and wastes enriched with ¹⁵N labelled urea were stored at 25°C for one year. At the end of the experiment the ¹⁵N recovery rate ranged between 24 and 100%. The distributions of inorganic nitrogen (NH₄- and NO₃-N) and organic nitrogen (fulvic acids, humic acids and non extractable substances) are ascertained. Between the test materials, there are great differences in incorporation parameters.     

High pressure raman studies of GaAs/A1As superlattices: folded-acoustic phonons and resonant second-order scattering

Abstract

Materials containing light elements and characterized by a dense structure present specific physico-chemical properties.

The carbonitrides C_xN_y, and in particular C₃N₄, have attracted the attention of the scientific community during these last ten years.

The main chemical problem in the synthesis of such materials is to introduce nitrogen into the lattice, due to the strong stability of N₂.

In order to prevent nitrogen loss, the use of high pressures and the selection of nitriding media can be developed.

The present contribution describes the main results obtained through two routes:

(i) the thermal decomposition of precursors containing carbon and nitrogen under high pressure conditions (2-6GPa) (without or with nitrogen solvent)

(ii) the high pressure condensation of “organic” precursors containing carbon and nitrogen.     

Properties of MgB2 superconductor chemically treated by acetic acid

Commercial Alfa Aesar MgB₂ powder was chemically treated by acetic acid with the aim of MgO removing. Single-core MgB₂/Fe ex situ wires have been made by powder-in-tube (PIT) process using the powders treated with different acid concentration. All samples were annealed in argon at 950 °C/0.5 h. Differences in transition temperatures and critical currents of acetic acid treated MgB₂ are related to the normal state resistivity, effective carbon substitution from the organic solvent and the active area fraction (grain-connectivity).     

Organic-ligand-assisted supercritical hydrothermal synthesis of titanium oxide nanocrystals leading to perfectly dispersed titanium oxide nanoparticle in organic phase

Titanium oxide (TiO₂) nanocyrstals which are perfectly dispersed in organic solvents are synthesized by organic-ligand-assisted supercritical hydrothermal synthesis. The addition of hexaldehyde to the supercritical hydrothermal synthesis of TiO₂ leads to the in-situ surface modification, which enables the synthsized TiO₂ nanocrystals to be perfectly dispersed in iso-octane because of its hydrophobic nature. Further, the one-pot synthesis of hybrid materials results in the significant reduction of the particles size, probably due to the capping effect of hexaldehyde to suppress the particles growth.     

Submicronic particles synthesis by a supercritical way

Abstract

The chemical transformation of metallic precursors in a supercritical fluid is a new route for obtaining nanometric homogeneous powders. In this paper we present a technique to produce metal, oxide or nitride submicronic particles, with a spherical morphology and mean diameters from a few microns to a few tens of nanometers. Metallic copper, oxides (Cu₂O, Fe₃O₄, Ga₂O₃) and nitrides (Cu₃N, Fe⁴N) have been prepared. This process consists in solubilizatiw and subsequent thermal decomposition of acetylacetonates of metals in a supercritical fluid, either a mixture of CO₂/C₂H₅OH or NH₃.     

Capture of pure toxic gases through porous materials from molecular simulations

ABSTRACT

In the last three decades, the air pollution is the main problem to affect human health and the environment in China and its contaminants include SO_2, NH_3, H₂S, NO₂, NO and CO. In this work, we employed grand canonical Monte Carlo simulations to investigate the adsorption capability of metal-organic frameworks (MOFs) and covalent organic frameworks (COFs) for these toxic gases. Eighty-nine MOFs and COFs were studied, and top-10 adsorption materials were screened for each toxic gas at room temperature. Dependence of the adsorption performance on the geometry and constructed element of MOFs/COFs was determined and the adsorption conditions were optimised. The open metal sites have mainly influenced the adsorption of NH₃, H₂S, NO₂ and NO. Especially, the X-DOBDC and XMOF-74 (X = Mg, Co, Ni, Zn) series of materials containing open metal sites are all best performance for adsorption of NH₃ to illustrate the importance of electrostatic interaction. Our simulation results also showed that ZnBDC and IRMOF-13 are good candidates to capture the toxic gases NH_3, H₂S, NO₂, NO and CO. This work provides important insights in screening MOF and COF materials with satisfactory performance for toxic gas removal.     

The influence of supercritical carbon dioxide parameters on cellulose acetylization and properties of cellulose acetates

The possibility of cellulose diacetate production by direct acetylation of sulfite pulp with acetic anhydride in supercritical carbon dioxide (SC CO₂) is demonstrated. Optimum acetic anhydride to cellulose ratio and parameters of SC CO₂ are selected.