Water thermal dissociation

The reason for the poor conversion efficiency to synthetic fuels is the high energy cost in liberating hydrogen from water (thermal dissociation, electroly-... 

An excess of acetic acid is usually added before heating in order to repress the hydrolysis (and also the thermal dissociation) of the ammonium acetate, thus preventing the escape of ammonia. The excess of acetic acid, together with the water, is removed by slow fractional distillation. The method is rarely used except for the preparation of acetamide. 

Water-soluble peroxide salts, such as ammonium or sodium persulfate, are the usual initiators. The initiating species is the sulfate radical anion generated from either the thermal or redox cleavage of the persulfate anion. The thermal dissociation of the persulfate anion, which is a first-order process at constant temperature (106), can be greatly accelerated by the addition of certain reducing agents or small amounts of polyvalent metal salts, or both (87). By using redox initiator systems, rapid polymerizations are possible at much lower temperatures (25—60°C) than are practical with a thermally initiated system (75—90°C). 

The TG and DTG curves of Figure 12 show that melamine polyphosphate undergoes a complex degradation process between 330-650 C. In step 3 of the DTG curve (max. rate 390 C), water, ammonia and melamine are evolved. In this step the thermal behaviour of polyphosphate is somewhat similar to that of the sulphate in the same range of temperature (300-400 0. Indeed evolution of melamine indicates that thermal dissociation of polyphosphate giving free melamine takes place above 330 C. However, evaporation of melamine competes with its condensation as shown by evolution of ammonia. 

Thermal dissociation produces ammonia, carbon dioxide, and water reacts with metal salts forming their formates oxidized by strong oxidants forming carbon dioxide, water, and oxides of nitrogen. 

Thallium oxide also can he prepared hy thermal dissociation of thallium hydroxide, TlOH or thallium carbonate, TI2CO3. Thallium oxide dissolves in water forming thallous hydroxide, TlOH. It reacts with carbon dioxide to form thallous carbonate, TI2CO3. 

Figure 11.44 is a schematic diagram of one LIF instrument (Stevens et al., 1994 Brune et al., 1998). An air-cooled copper-vapor laser pumps a dye laser whose output at 616 nm is doubled to generate the 308-nm exciting radiation. An OH reference cell in which OH is generated from the thermal dissociation of water... 

Powder Formation. Metallic powders can be formed by any number of techniques, including the reduction of corresponding oxides and salts, the thermal dissociation of metal compounds, electrolysis, atomization, gas-phase synthesis or decomposition, or mechanical attrition. The atomization method is the one most commonly used, because it can produce powders from alloys as well as from pure metals. In the atomization process, a molten metal is forced through an orifice and the stream is broken up with a jet of water or gas. The molten metal forms droplets to minimize the surface area, which solidify very rapidly. Currently, iron-nickel-molybdenum alloys, stainless steels, tool steels, nickel alloys, titanium alloys, and aluminum alloys, as well as many pure metals, are manufactured by atomization processes. 

Thermal Dissociation of Nitrogen(IV) Oxide. Use two communicating flasks filled with nitrogen(IV) oxide for this experiment (Fig. 46). Immerse flask 1 into a beaker filled with snow or crushed ice, and flask 2 into a beaker with water. Heat the latter and watch the change in the colour of the gas in both flasks. Extract the flasks from the beakers. How does the colour of the gas change ... 

It is pertinent at this point to refer briefly to the sources of quinone methides, though these have been reviewed (B-74M122400). The general approach used in chroman syntheses involves the thermal elimination of HX from an -substituted phenol. Commonly the eliminated molecules are water, methanol or dimethylamine (287 X = OH, OMe, NMe2, respectively). However, these methods are not entirely suitable because the eliminated molecules may promote side reactions. In the case of 1,2-naphthoquinone 1-methide, the thermal dissociation of the spirodimer (288) is a better source than the other methods. Its formation represents another example of dimerization by a [4+2]-cycloaddition, since it is prepared by heating l-dimethylaminomethyl-2-naphthol in dodecane or xylene with careful exclusion of moisture (73JCS(P1)120,81CJC2223). 

Strong oxidation as well as reduction reactions have been observed due to generation of IT and OH radicals. The main primary chemical process in the sonolysis of water is the thermal dissociation of water to hydrogen atoms and hydroxyl radicals ... 

Combined EPR and spin-trapping studies showed that solvent vapor and ambient gases (e.g., air) decompose to atoms or free radicals in the gaseous bubble interior. Water vapor is thermally dissociated into OH radicals, H atoms, and O atoms. The latter interconvert with OH radicals at the high pressures in the cavity and recombine in the cooler interfacial region to form Oz and H2Oz. The power dependence in the sonolytic transformation of a phenolic aqueous solution was found to be the first order. 

There is also a paper on the use of platinum in high temperature gas thermometry during the 19th century112 and there are brief discussions of some aspects of the early developments of microcalorimetry in France,113 and the thermal dissociation of water.114... 

It is more easily observed at higher temperature, because with rise of temperature the position of the equilibrium moves in favour of a higher proportion of dissociated molecules. In 1847 4 Grove noticed the formation of some free hydrogen and oxygen when platinum, heated almost to fusion, was dropped into water, the experiment being repeated by Deville 5 a little later, with an even more decisive result. The main difficulties in detecting the thermal dissociation are the smallness of its... 

Electrochemical water splitting, generating H2 and O2 at separate electrodes, largely circumvents the gas recombination and high temperature limitations occurring in thermal hydrogen processes. Thus a hybrid of thermal dissociation and elec-... 

Kogan has calculated that, at a pressure of 0.05 bar, water dissociation is barely discernible at 2000 K.1 By increasing the temperature to 2500 K, 25% of water vapor dissociates at the same pressure. A further increase in temperature to 2800 K under constant pressure causes 55% of the vapor to dissociate.1 These basic facts indicate the difficulties that must be overcome in the development of a practical hydrogen production by solar thermal water splitting ... 

As mentioned earlier, direct thermal dissociation of water requires temperatures above approximately 2500 K. Since there are not yet technical solutions to the materials problems, the possibility of splitting water instead, by various reaction sequences, has been probed. Historically, the reaction of reactive metals and reactive metal hydrides with water or acid was the standard way of producing pure hydrogen in small quantities. These reactions involved sodium metal with water to form hydrogen or zinc metal with hydrochloric acid or calcium hydride with water. All these... 

Aquaconversion A process for converting heavy crude petroleum oils and residues into lighter products, which are more easily converted into more valuable products in oil refineries. Intended for use at the well head rather than the oil refinery. Three steps are involved thermal dissociation of aromatics, dissociation of water giving hydrogen atoms, and addition of these hydrogen atoms to the aromatic fragments to prevent their association. Developed by Foster Wheeler USA Corporation, Intevep, and UOP from 1998. First commercialized in Curacao, Peru, in 1996. 

Adsorption of methyl mercaptan in moist conditions was performed on numerous samples of activated cartons of various origins. Methyl mercaptan adsorption was tested by a dynamic method. The amount of products of surface reaction was evaluated using thermal analysis. The results revealed that the main product of oxidation, dimethyl disulfide, is adsorbed in pores smaller than SO A. There is apparent competition for adsorption sites between water (moist conditions) and dimethyl disulfi. The comp ition is won by the latter molecule due to its strong adsorption in the carbon pore system. Althou dimethyl disulfide has to compete with water for the adsorption sites it can not be formed in a significant quantity without water. Water facilitates dissociation of methyl mercaptan and thus ensures the efficient removal process. 

Studies of the rate of approach to the water gas equilibrium from the H2 + CO2 side have been made by Tingey [433], Kochubei and Moin [434] and others using tubular flow reactors at temperatures around 1000 K. Such measurements rely on the thermal dissociation of hydrogen for their radical concentrations, and in the absence of measurements of these the systems are not regarded as sufficiently well defined for a valid determination of fe 2 3. 

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