Sulphur trioxide, decomposition

Sulphur-based cycles, such as the sulphur-iodine cycle, take full advantage of the range of temperatures at which the VHTR provides heat. In particular, the oxygen generation step (sulphur trioxide decomposition) requires very high temperature heat (typically T > 800°C), which can only be... 

The situation that was described in the previous accident happened again and even twice, with o-nitrotoluene and p-nitrotoluene during their sulphonation. Oleum containing 24% sulphur trioxide had been added to o-nitrotoiuene at 32 C. The reaction went out of control and caused the 2 I reactor to break and a very large volume of carbonised compound to be ejected (this was probably due to the decomposition of the sulphonic acid formed) ... 

A Fischer reagent had been made with pyridine, iodine, sulphur trioxide and formamide, instead of methanol. The bottle detonated after being stored for a couple of months. The authors put it down to the decomposition of formamide into ammonia and carbon oxide, which created the overpressure that caused the bottle to detonate. 

This product is a pale yellow hygroscopic solid, which can be kept unchanged for months. It gives off oxygen, iodine, and sulphur trioxide at about 120°, but at 190° the residue still retains some sulphur trioxide. The compound I204.3S0, dissolves in a large quantity of water with decomposition, forming iodine, iodic and sulphuric acids. It forms a yellow soln. in well-cooled alcohol, and the alcoholic soln. on evaporation at... 

According to H. Rose,47 dry powdered ammonium chloride at 0° absorbs the vapour of sulphur trioxide without decomposition, forming a hard mass which, when heated, first develops hydrogen chloride, and forms ammonium sulphate— it has been suggested that the product may be ammonium chloropyro-sulphate, NH4.0.S205C1. With carbon monoxide at a red heat, C. Stammer observed no changes, but with calcium carbide, R. Salvadori obtained calcium chloride, nitrogen, ammonia, carbon, and a series of hydrocarbons—methane, ethylene, and acetylene. 

It attacks glass at a red heat, giving silicon tetrafluoride and sulphur trioxide. Carbon and boron are without action on the gas at a red heat, but sodium at a temperature considerably above the melting-point causes gradual decomposition with absorption. Hydrogen sulphide, aided by heat, attacks both thionyl and sulphuryl fluorides, inducing decomposition.1... 

When passed through a red-hot tube the vapour is almost entirely decomposed into sulphur dioxide, sulphur trioxide and chlorine. Vapour density determinations at various temperatures, and analyses of the decomposition products, indicate that decomposition proceeds according to the equations 8... 

When heated strongly, the vapour of chlorosulphonic acid undergoes decomposition into sulphur trioxide and hydrogen chloride 14 or, at... 

Chemical Properties.—Pyrosulphuric acid, whether pure or mixed with excess of sulphuric acid1 or sulphur trioxide, readily undergoes decomposition into sulphuric acid and the trioxide indeed, the fumes evolved at the ordinary temperature are due to vaporisation of the trioxide from the molten acid or its solution in sulphuric acid. On heating the acid, sulphur trioxide is expelled until the mixture of sulphuric acid and water of minimum vapour pressure (98-3 per cent, sulphuric acid) remains. It is owing to this behaviour that pyrosulphuric acid and fuming sulphuric acids in general have no definite and constant boiling temperature. 

When heated strongly, for instance above 450° C., the pyrosulphates undergo decomposition into sulphur trioxide and the corresponding normal sulphate. The sodium salt, which melts at 400-9° C.,8 exhibits appreciable dissociation at about 460° C. In contact with moist air or... 

At very high temperatures the sulphates of metals such as copper, zinc, iron, aluminium and chromium tend to lose sulphur trioxide (largely in the form of sulphur dioxide and oxygen) and to give residues of the corresponding oxides.7 Calcium sulphate is stable up to 1300° C., above which temperature it melts and immediately undergoes almost complete decomposition with abundant evolution of fumes.8 Very slight decomposition has been observed with barium sulphate at 1300° C.9... 

The perdisulphates of the alkali metals and ammonium crystallise in the anhydrous condition and when heated alone undergo decomposition with formation of sulphate, sulphur trioxide and oxygen ... 

The ammonium salt is less stable than the potassium salt. Rapid decomposition does not take place even in the presence of 10 per cent, of organic matter.5 Barium and lead perdisulphates contain water of crystallisation and therefore on decomposition yield sulphuric acid in place of sulphur trioxide. The perdisulphates of the heavier metals also form additive compounds with ammonia, for example ZnS2Og. 4NH3 and CdS208.6NH3, and even with organic bases.6... 

Nitrosulphonic Anhydride, S208(N02)2.—Nitrosulphonic anhydride, or nitrous-pyrosulphuric anhydride (the choice of name depending on the view entertained as to the structure of the NOa-group), is formed during the decomposition of nitrosulphonic acid by heat (p. 248),a but it may more conveniently be obtained by the action of dry nitric oxide on sulphur trioxide 8... 

As would be expected from a substance of this nature, water causes rapid decomposition into sulphuric acid and the decomposition products of nitrous acid, whilst sulphuric acid dissolves the substance with formation of nitrosulphonic acid, which crystallises on cooling. With sulphur trioxide the anhydride yields a stable complex of composition 2(S2N209).S03.1 Gaseous ammonia causes the anhydride to melt and decompose slowly with formation of nitrogen and ammonium hydrogen sulphate ... 

The second step, common to all sulphur processes, is the result of two successive reactions. As sulphuric acid is vaporised (ca 650 K) and superheated (ca 900 K), it spontaneously decomposes into water and sulphur trioxide. The following decomposition occurs by heating the vapour to high temperatures (> 1000 K) in the presence of a catalyst to produce oxygen and sulphur dioxide. 

Concentrated sulphur acid evaporation and dehydration is performed in a group of two heat exchangers with important exchange surface (up to 1 340 m2) (HX-208). The S03/S02 decomposition reactor (HX-209) is a set of five reactors with two reactive zones. The first one, with a temperature of 875 K requires a platinum catalyst and the second one an iron-oxide catalyst. The operating temperature in the second zone increases up to 1125 K. Due to operating conditions (temperature, chemical composition), these three devices require a nickel-iron-chromium alloy. Then sulphur trioxide recombination reactor consists of a packed column (HX-210). Required investment for S03 conversion is estimated about EUR(08) 508.6 M. 

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