Sulphur impurities

The commas in this schematic indicate that the carbon and sulphur impurities reside within the same phase as the iron. 

The reaction products are chemicals that commonly occur in the hypochlorite solution, which is an advantage over using a sodium sulphite solution as an absorption medium, for example, as its use would entail removal of sulphuric impurities. 

The effect of sulphur on the activity profile is shown in Figure 2. The sulphur poisoning arises from sulphur impurities found in the synthesis gas, which is derived from coal. Sulphur is a common F-T catalyst poison [2,11] and it is apparent from the results that the top portion of the reactor is acting as a guard bed" to remove this impurity. The finding that sulphur is only found to be present in the top section of the catalyst bed has been observed previously for F-T and related catalysts [12-15]. 

Kepen Any of several sulphur compounds, liver-colored, made by fueing sulfur or a sulphide with an alkali metal compound or metallic oxide as hepar antlmonii Umpure antimony and potassium sulphide heoer calcis Ccelcium sulphide) heoer eulphurus or liver of sulphur (impure potassium suli lde). 

Sulphur impurities (0.007-0.013% S) in the low alloyed forging steel (0.38 Cr, 0.71 Ni, 0.62 Mo, 0.22 C) lead to increased corrosion fatigue rates in high purity water (45 pS/cm, 8 pg/1 O2) at 149 °C and 260 °C [42]. The addition of oxygen containing water shifts the corrosion potential above -250 mVscE and increases the crack rate by a factor of four. Determination of the area fractions of sulphide inclusions on fracture surfaces led to the conclusion that below a value of0.006% sulphur the corrosion fatigue susceptibility is very low (see also [43]). 

Before this treatment, the cassiterite content of the ore is increased by removing impurities such as clay, by washing and by roasting which drives off oxides of arsenic and sulphur. The crude tin obtained is often contaminated with iron and other metals. It is, therefore, remelted on an inclined hearth the easily fusible tin melts away, leaving behind the less fusible impurities. The molten tin is finally stirred to bring it into intimate contact with air. Any remaining metal impurities are thereby oxidised to form a scum tin dross ) on the surface and this can be skimmed off Very pure tin can be obtained by zone refining. 

Crude lead contains traces of a number of metals. The desilvering of lead is considered later under silver (Chapter 14). Other metallic impurities are removed by remelting under controlled conditions when arsenic and antimony form a scum of lead(II) arsenate and antimonate on the surface while copper forms an infusible alloy which also takes up any sulphur, and also appears on the surface. The removal of bismuth, a valuable by-product, from lead is accomplished by making the crude lead the anode in an electrolytic bath consisting of a solution of lead in fluorosilicic acid. Gelatin is added so that a smooth coherent deposit of lead is obtained on the pure lead cathode when the current is passed. The impurities here (i.e. all other metals) form a sludge in the electrolytic bath and are not deposited on the cathode. 

Since arsenic is often found in nature associated with sulphide ores, sulphur dioxide obtained by this method may contain some arsenic(III) oxide as impurity, and in certain processes this is a distinct disadvantage. 

In all the above methods, the sulphur dioxide obtained is impure. Dust is removed by first allowing the gases to expand, when some dust settles, then by passage through electrostatic precipitators and finally by washing with water. Water is removed by concentrated sulphuric acid which is kept in use until its concentration falls to 94%. 

Petroleum Available in fractions of b.p. 40-60°, 60-80°, 80-100°, 100-120° yy Frequently called light petroleum or petrol ether. Unless specially purified, contains sulphur derivatives, etc.y as impurities. 

Liquids are occasionally purified by removing impurities as constant-boiling mixtures, or by shaking with concentrated sulphuric acid and subsequently separating the dried liquid from the acid the second method is therefore limited to liquids which are insoluble in, and chemically unaffected by, the strong acid e.g., benzene, anhydrous chloral). 

Impure aldehydes and ketones are sometimes purified by conversion into the corresponding oximes, and the latter after recrystallisation are then hydrolysed by boiling with dilute sulphuric acid ... 

This type of extraction depends upon the use of a reagent which reacts chemically with the compound to be extracted, and is generally employed either to remove small amounts of impurities in an organic compound or to separate the components of a mixture. Examples of such reagents include dilute (5 per cent.) aqueous sodium or potassium hydroxide solution, 5 or 10 per cent, sodium carbonate solution, saturated sodium bicarbonate solution (ca. 5 per cent.), dilute hydrochloric or sulphuric acid, and concentrated sulphuric acid. 

Dilute hydrochloric or sulphuric acid finds application in the extraction of basic substances from mixtures or in the removal of basic impurities. The dilute acid converts the base e.g., ammonia, amines, etc.) into a water-soluble salt e.g., ammonium chloride, amine hydrochloride). Thus traces of aniline may be separated from impure acetanilide by shaking with dilute hydrochloric acid the aniline is converted into the soluble salt (aniline hydrochloride) whilst the acetanilide remains unaffected. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

Nitrobenzene. Nitrobenzene, of analytical reagent quality, is satisfactory for most purposes. The technical product may contain dinitrobenzene and other impurities, whilst the recovered solvent may be contaminated with aniline. Most of the impurities may be removed by steam distillation after the addition of dilute sulphuric acid the nitrobenzene in the distillate is separated, dried with calcium chloride and distilled. The pure substance has b.p. 210°/760 mm. and m.p. 5 -7°. 

The sulphuric acid treatment removes high-boiling impurities which are not easily separated by distillation. 

Esterification with cycloaliphatic alcohols is comparatively easy when the alcohol is saturated with hydrogen chloride and treated with excess of the acid, but a very impure ester results from the use of sulphuric acid as a catalyst, for example ... 

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