Sulphate process

Alternatively cellulose is produced from wood via wood pulp. A number of processes are used in which the overall effect is the removal of the bulk of the non-cellulosic matter. The most widely used are the sulphite process, which uses a solution of calcium bisulphite and sulphur dioxide, the soda process using sodium hydroxide and the sulphate process using a solution of sodium hydroxide and sodium sulphide. (The term sulphate process is used since sodium sulphate is the source of the sulphide.) For chemical purposes the sulphite process is most commonly used. As normally prepared these pulps contain about 88-90% alpha-cellulose but this may be increased by alkaline purification and bleaching. 

Sulphate process. The ilmenite is reacted with sulphuric acid giving titanium sulphate and ferric oxide. After separation of ferric oxide, addition of alkali allows precipitation of hydrous titanium dioxide. The washed precipitate is calcined in a rotary kiln to render titanium dioxide. The nucleation and calcination conditions determine the crystalline structure of titanium dioxide (e.g. rutile or anatase). 

There are now two processes in widespread use for making titanium dioxide pigments. In the sulphate process, finely ground ilmenite is digested in sulphuric acid and the iron is reduced and separated as iron(II) sulphate. The titanium(IV) sulphate is hydrolysed by steam to a hydrous oxide, which is thoroughly washed to remove soluble impurities and finally calcined at a temperature of about 1000 °C to give the anatase form of titanium dioxide. 

The separation of cellulose from the wood is carried out by one of three methods the soda process, the sulphate process, and the sulphite process. Nitration cellulose is prepared chiefly by the sulphite and sulphate methods. 

The sulphate process consists in kiering pieces of wood in a solution composed of sodium hydroxide, sodium sulphide and sodium carbonate in a 65 15 20 ratio. The concentration of the solution is 10-12% of NaOH. Boiling at a temperature of 170-175°C under pressure lasts about 6 hr, of which 3 hr are required for heating, the other 3 hr being the kiering proper. Cellulose is then separated from the lye, washed with water, bleached, and subjected to final purification. The lye is condensed, evaporated to dryness, then sodium sulphate is added, and the whole is calcined. The sodium sulphate is thus reduced to sodium sulphide. Unchanged sulphate and the excess of carbonate are removed by addition of milk of lime. 

Potassium hydroxide, KOH.—The hydroxide can be prepared by methods similar to those employed for the corresponding sodium derivative. The chief processes are the electrolysis of the chloride, and the interaction of the carbonate or sulphate11 in aqueous solution with slaked lime. In the sulphate process, evaporation of the mother-liquid yields the anhydrous hydroxide, the monohydrate, or the di-hydrate, the formation of each product depending on the concentration.12 For laboratory use, the substance can be prepared free from carbonate by a method described by Jorissen and Filippo.13... 

Figure 2c ilustrates the influence of the sulphation on the activity of NaX zeolite in the Claus reaction.The sulphation by method A results in a very high increase in the zeolite activity. NaX sulphated by method B is also more active than pure zeolite but the growth of the activity is lower than after sulphation by method A. Such a high increase of the activity is not observed for NaY sulphated samples- According to the above discussed IR and X-ray results, one can state that hydrogen sulphite and sodium sulphate species, easily formed during NaX sulphation, cause the rise in the Claus activity. Both species react with H25 (refs.2,5,6 10). The third species i.e. aluminium sulphate seems to deactivate the catalyst- This species was observed not only after sulphation process but also after the Claus reaction on pure NaX and NaY. Sulphate ions adsorb on aluminium poison the basic sites in zeolites required in the Claus reaction. 

Kraft pulping, also termed the sulphate process, is the predominant proeess for the manufacture of ehemieal pulp. The kraft process offers some erueial advantages ... 

Losses of sodium and sulphur, e.g. in pulp wash and in flue emissions, used to be made up by the addition of sodium sulphate and sodium carbonate, hence the term the sulphate process. The sodium sulphate undergoes reduction to sodium sulphide in the recovery furnace. With systems moving to total closure of chemical and water cycles, the presence of small amounts of sulphur in the wood itself and in the magnesium sulphate coming to the evaporators from the oxygen delignification plant is such that the sodium intake exceeds sulphur losses. In that case the addition of Na2S04 would result on excessive sulphidity. Hence only NaOH may be required. 

The pulp and paper industry used both the sulphite and the sulphate processes, and in the few historical sketches of its development that exist there are found some references to laboratories. ... 

The soda method was also attempted in Finland in the 1870s and early 1880s. Theodor Hoffding and another Danish engineer were involved in setting up the first two pulp mills close to Viipuri, near the eastern border. However, commercial production first started in 1886 in the Walkiakoski paper mill, a Finnish company in the western part of the country that employed the sulphate process. Due to technical setbacks, the output remained modest for many years. Paper mills in Nokia and Kuusankoski adopted the other process, sulphite pulping, in 1885, and succeeded much better. Imitators followed, and for several decades that process dominated chemical pulping in Finland. ... 

The acid concentration may be as low as 93 per cent and it is made into a slurry with the heat-treated frit, after the latter has been ground to pass a 200-mesh screen. The preferred method of carrying out the sulphation process consists of spraying the acid ore slurry as a jet on the the preheated inner surface of a mild-steel mill, at a temperature of 250-300°C. 

In the Huelva factoiy, the oldest and most common process for titanium dioxide production is used the sulphate process. This process uses concentrated sulphuric acid (H2SO4) to dissolve the titaniferous feedstocks which are milled and dried beforehand to aid the digestion process. 

Figure 1. Diagram of the sulphate process used in the Huelva factoiy The digestion reaction process can be summarized as ...

Chernet, T. (1999). Applied mineralogical studies on Australian sand ilmenite concentrate with special reference to its behavior in the sulphate process. Minerals Engineering, Vol 72. No 5,485-495. 

Pb cathode to acid sulphate Process developed by Reilly medium. Divided ccU Tar 2-i3onieT needs Pc salt... 

K Film n A chemical wood pulp made by the sulphate process, or paper or paperboard made fi om such pulp. 

In the sulphate process a solution of sodium hydroxide and sodium sulphide is used as digestor. The raw material for the sodium sulphide is sodium sulphate from which the process derives its name. 

Titanium dioxide is commercially produced by two different processes. In the sulphate process, titanium dioxide is prepared by reacting titanium ores with sulphuric acid. In the chloride process, titanium dioxide is produced by reacting titanium ores with chlorine gas. Compounds with anatas Ti02 show an outstanding bluish white color. Rutile types exhibit a creamy white [26]. 

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