Sulphur dioxide manufacture

On the industrial scale it is produced in large quantities for the manufacture of sulphuric acid and the production methods are dealt with later. It was once estimated that more than 4 000 000 tons of sulphur dioxide a year entered the atmosphere of Britain from the burning of coal and oil. 

It is extensively used industrially as a catalyst, notably in the oxidation of sulphur dioxide to the trioxide in sulphuric acid manufacture. It is an essentially acidic oxide, dissolving in alkalis to give vanadates however, addition of acid converts the anionic vanadate species to cationic species, by processes which are very complex, but which overall amount to the following ... 

Sulphur dioxide is used as a preservative for beer, wine and meats in the production of sulphites and hydrosulphites in solvent extraction of lubricating oils as a general bleaching agent for oils and foods in sulphite pulp manufacture in the cellulose and paper industries and for disinfection and fumigation. 

Sulphuric acid is an important industrial chemical. It has been said that the output of sulphuric acid is a measure of the wealth of a country, as it is used in the manufacture of fertilisers, detergents, pigments and fibres, amongst many other products. In the first stage of the process, sulphur is burned to produce sulphur dioxide. 

So far, no reference has been made to the presence of more than one phase in the reactor. Many important chemicals are manufactured by processes in which gases react on the surface of solid catalysts. Examples include ammonia synthesis, the oxidation of sulphur dioxide to sulphur trioxide, the oxidation of naphthalene to phthalic anhydride and the manufacture of methanol from carbon monoxide and hydrogen. These reactions, and many others, are carried out in tubular reactors containing a fixed bed of catalyst which may be either a single deep bed or a number of parallel tubes packed with catalyst pellets. The latter arrangement is used, for exjimple, in the oxidation of ethene to oxiran (ethylene oxide)... 

The titre of the Karl Fischer reagent varies with time because of the instability of the solutions. For this reason, manufacturers usually sell the Karl Fischer reagent in two different containers one containing a mixture of sulphur dioxide, methanol and a base, the other containing a solution of either iodine or iodide. The contents are generally mixed a few days before use of the reagent. 

Amongst other applications may be mentioned the use of free sulphur in the manufacture of Ultramarine and the occasional conversion of the element into thiosulphates (sec p. 193), sulphurous acid or sulphur dioxide (p. 103) and sulphuric acid (p. 150). 

The use of zinc blende and mixed zinc ores as a convenient source of sulphur dioxide for sulphuric acid manufacture has been advocated. The residue from the roasting is often more valuable than in the case of pyrites, but the roasting process is more troublesome and the presence of fluorspar in the blende exerts a deteriorating influence on the lead chambers.2... 

Liquid sulphur dioxide finds occasional use as a refrigerating liquid for the manufacture of ice and as a solvent for the extraction of fats and oils from bones and other waste animal matter. It is also employed in the refining of natural petroleum, owing to its property of dissolving aromatic and other heavy hydrocarbons which are present in petroleum distillates.1 When the distillate is shaken with liquid sulphur dioxide at a low temperature, separation into two layers occurs, one of which is the sulphur dioxide solution, the other the purified distillate containing paraffin hydrocarbons and naphthenes, which remain unaffected. 

The gas is used in various chemical industries. For example, it forms an intermediate stage in the production of sulphuric acid and of sulphites it is also applied in the preparation of chemical substances such as selenium, tellurium, quinol, etc. To some extent sulphur dioxide finds application for fire-prevention and -extinguishing, and much is used in the form of alkali sulphite in the production of wood pulp for paper and artificial silk manufacture. 

Extraction.—(1) From Pyrites.—In the oxidation of the pyrites (or other sulphur mineral) for the formation of sulphur dioxide in the manufacture of sulphuric acid, foreign elements like arsenic and selenium also undergo oxidation and pass ofC as vapours with the sulphur dioxide. The selenium dioxide produced in this manner their suffers more or less complete reduction by the sulphur dioxide, when finely divided selenium separates, mainly in the lead chambers, as a red, amorphous powder, accompanied possibly by some of the greyish-black form a portion of the dioxide is also found in the Glover tower acid. The amount of selenium in the chamber mud depends, of course, on the nature of the pyrites relatively large quantities of compounds of arsenic, zinc, tin, lead, iron, copper or mercury are always present, arising almost entirely from impurities in the pyrites. 

Bleaching. It is often necessary in the manufacture of lacquer nitrocellulose to remove all traces of coloured substances by bleaching. One method consists in oxidizing with potassium permanganate in the proportion of 1 kg KMn04 to 100 kg of lacquer nitrocellulose in the presence of a little sulphuric acid. After the reaction is over the nitrocellulose is rinsed with water, and the brown colour of manganese dioxide is removed by the action of sulphur dioxide or sodium sulphite. 

There are several methods of manufacturing is on a commercial scale, for instance the calcination of oxalic add blended with potassium chloride, treatment of sodium chlorite with chlorine, or of sodium chlorate with sulphur dioxide in the presence of concentrated sulphuric add. Chlorine dioxide is utilized as a strong bleaching agent for cellulose, paper, flour, oils and such like, as well as a solvent for removing lignin from wood pulp. 

There are particular problems in the manufacture of non-carbonated RTD beverages that are not aseptically packed. These relate to microbial contamination. Products that have no carbon dioxide in their head space are particularly vulnerable to contamination by moulds and certain types of bacterial infection. For many years it was possible to control such potential contamination by the use of low levels of sulphur dioxide (50 ppm). Changes in European Preservative Regulations now make the use of this preservative in RTD formulations (but not dilutables) illegal unless it is carried over from a fruit component, when up to 20 ppm SO2 may be present. Even at this level, the gaseous preservative is rapidly lost and is quickly ineffective. 

The importance of the manufacture of sulphuric acid has caused a great amount of study to be made of the equilibrium between sulphur dioxide, oxygen, and sulphur trioxide, and the validity of the law of molecular concentrations, as applied to this reaction, has been put to a rigid test. 

Chlorine dioxide can also be manufactured by introducing a gaseous mixture of sulphur dioxide and air into a solution of sodium chlorate and sulphuric acid... 

Oxidation is extremely important both from a scientific and a practical point of view. Without oxidation life would not exist. In the chemical industry, too, oxidation is probably the most important process. A major example is the combustion of fossil fuels. This process is usually uncatalyzed, but sophisticated catalytic processes do exist. Examples in the inorganic industry are the oxidation of sulphur dioxide and ammonia in the manufacture of sulphuric acid and nitric acid, respectively. In the petrochemical industry many catalytic synthesis processes are carried out, for example the production of ethylene and propene epoxide, phthalic acid anhydride. An example which has recently also become important is the catalytic combustion of hydrocarbons in flue gases. Table 5.2 gives a list of examples of oxidation catalysis in industry [93]. 

The chief commercial use of pyrites (including marcasite) is in the manufacture of sulphuric acid.5 The pyrites, on being roasted in air, yields sulphur dioxide and a residue of ferric oxide. Thus —... 

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