Sulphur ignition

Sulphur ignites at 223 C in the air. This relatively low ignition temperature is often used for firework compositions for ease of ignition. Sulphur is used as a raw material for black powder in combination with potassium nitrate and charcoal and it is also used for white smoke compositions. 

When antimony trisulphide is dropped little by little on the surface of potassium chlorate, the temperature of which raised gradually by heating, it ignites as soon as the chlorate begins to melt at about 360°C. (Realgar has the same tendency as antimony trisulphide and sulphur ignites less instantaneously as this, even at 500°C.) Therefore it may be said that antimony trisulphide is more ignitable than sulphur. 

Sulphur ignition temperature °C, appr. 246 Heat of combustion (25 °C) ... 

The sulphur ignition temperature is about 250 C (see 4.1.1.). A cold burner therefore needs preheating with combustion gas from oil or gas for 2-3 hours and to vent the wet combustion gases from a "starting stack" on the burner. After the burner brickwork is heated the preheating is stopped and the starting stack is blanked. 

When easy and logical procedures are defined there will be no need for special attention or parallel activities during the "critical" phase of production start-up. Therefore some actions are taken prematurely, in an order not exactly required at that time of the start-up procedures (example caustic scrubber recycle and caustic feed, not necessary during plant preheating, will be started in advance to accumulate sufficient excess of caustic to absorb the initial extra amount of SO2 produced during the initial start-up period after sulphur ignition). 

Follow the step by step operating procedures. Then, once the required preheating temperatures are reached (normally witiiin two hours), the plant will be ready for sulphur ignition sulphur dosing and sulphur igniter will be started, the conversion of SO2 SO3 will proceed from an initial 50% value to 98% and the sulphonation reaction with alkylbenzene will result in a partially-converted alkylbenzene sulphonic acid, to be returned to the off-spec circulation tank. 

A sulphur ignition system is used in the Ballestra design of sulphur burner. The following safeguards must be incorporated ... 

From start-up (sulphur ignition) the plant is fully computer controlled and operated for a given (pre-set) type of product and production rate. The change of product type and/or production rate is still performed by the operator and computer-assisted in terms of control and relevant process parameters. 

Volatile boron compounds burn with a green flame. If a solid borate is mixed with methanol and concentrated sulphuric acid, the volatile compound boron trimethoxide, BfOCHj j, is formed and ignition of the alcohol therefore produces a green flame ... 

Optional experiment. When all the air has been displaced, collect a test-tube of the gas over water (by appropriate inclination of the end of the delivery tube beneath the mouth of a test-tube filled with water and supported in a beaker of water). Observe the colour and odour of the gas. Ignite the test-tube of gas, and note the luminosity of the flame and the amount of carbon deposited. Pure acetylene is almost odourless the characteristic odour observed is due to traces of hydrides of phosphorus, arsenic and sulphur. 

Sulphur monochloride S2CI2 Yellowish-red oily fuming liquid with a strong odour Combustible flash point 11 8°C Ignition temp. 233°C Liquid and vapours are irritating Decomposes when contacted by water, to produce heat and toxic/corrosive fumes Do not allow water to enter containers reaction can be violent Wash down spills with flooding amounts of water... 

Another example is the determination of pure silica in an impure ignited silica residue. The latter is treated in a platinum crucible with a mixture of sulphuric and hydrofluoric acids the silica is converted into the volatile silicon tetrafluoride ... 

In all the above methods the element is weighed as the oxide, BeO, which is somewhat hygroscopic [compare aluminium(III) oxide]. The ignited residue, contained in a covered crucible, must be cooled in a desiccator containing concentrated sulphuric acid or phosphorus(V) pentoxide, and weighed immediately it has acquired the laboratory temperature. 

Cupferron. Tin (IV) (ca 150 mg in 300 mL). Add 3 g of boric acid, 2.5 mL of concentrated sulphuric acid (CARE) and finally an excess of 10 per cent aqueous solution of cupferron. Stir vigorously, filter (Whatman No. 41 or 541 filter paper) and wash the precipitate with cold water. Dry the precipitate and filter paper in a weighed crucible, ignite carefully and weigh as Sn02 (Section 11.45). 

Determination of iodate as silver iodide Discussion. Iodates are readily reduced by sulphurous acid to iodides the latter are determined by precipitation with silver nitrate solution as silver iodide, Agl. Iodates cannot be converted quantitatively into iodides by ignition, for the decomposition takes place at a temperature at which the iodide is appreciably volatile. 

Determination of perchlorate as silver chloride Discussion. Perchlorates are not reduced by iron (II) sulphate solution, sulphurous acid, or by repeated evaporation with concentrated hydrochloric acid reduction occurs, however, with titanium(III) sulphate solution. Ignition of perchlorates with ammonium... 

The reduction is avoided by first charring the paper without inflaming, and then burning off the carbon slowly at a low temperature with free access of air. If a reduced precipitate is obtained, it may be re-oxidised by treatment with sulphuric acid, followed by volatilisation of the acid and re-heating. The final ignition of the barium sulphate need not be made at a higher temperature than 600 800 °C (dull red heat). A Vitreosil or porcelain filtering crucible may be used, and the difficulty of reduction by carbon is entirely avoided. 

Ignite the filter in a platinum crucible, fuse with 2.0 g of anhydrous sodium carbonate, dissolve the melt in 40 mL of dilute sulphuric acid, and add 1 mL of sulphurous acid solution (about 6 per cent) to reduce any iron(III) salt, etc., formed in the fusion, and filter if necessary. Transfer the solution to a 100 mL graduated flask, dilute to the mark, and mix. This flask (B) contains the acid-insoluble boron. 

Sulphur suspensions in air can detonate when they are submitted to an igniting flame if their concentration lies between 35 and 1400 g/m. The air/ sulphur/carbon mixture spontaneously combuste if carbon is subjected to great heat. The combustion of sulphur under controlled conditions produces sulphur dioxide, as used in industry. 

With aluminium powder, sulphur has an extremely violent reaction, which can be explosive if an igniting flame is applied to the mixture. The flame is blinding. 

The white phosphorus/sulphur mixture either combusts or detonates when it is heated. It forms diphosphorus pentasulphide. Red phosphorus reacts with more difficulty there is a need for an ignition flame and as a result of which the mixture combusts violently. This reaction is thought to lead to tetraphosphorus trisulphide. 

In contact with aluminium, disulphur dichloride provokes the instantaneous ignition of the metal. Lithium batteries contain thionyl chloride. A large number of explosions of batteries have been explained by the violent interaction of lithium with the chloride, which was assumed to be reieased through the anode. Sodium combusts in contact with thionyl chloride vapour heated to a temperature of 300°C. Finally, sulphur dichloride gives rise to explosive mixtures on impact with sodium. 

Sulphur, hydrogen sulphide and metal sulphides also led either to the ignition of the sulphurous substance (S and H2S) or the incandescence of the mixture. Note that sulphides and cyanides are amongst the most dangerous salts in the presence of oxidants, a fact not to be ignored. 

However, 96% nitric acid is not thought to ignite phenylamine except if sulphuric acid is present. 

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