Sulphite 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. 

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. 

In industrial practice, losses of crude TNT in the sulphitation process amount from 6 to 8%. Out of this 2%-3. 5% is ascribed to the loss of a- trinitrotoluene and 3.5-4.5% to that of unsymmetrical isomers and other impurities, such as tetrani-tromethane (p. 339) and trinitrobenzene which is easily soluble in sodium sulphite, forming addition products. 

The suspension of crystals in sodium sulphite solution is pumped upwards by a rotary pump to a vacuum filter through a small tank in which the suspension is diluted with water. After the TNT has been separated from the liquor it is washed with cold water until its pink colour, produced during the sulphitation process, disappears. The aluminium filter plate in the filter bowl should be covered with linen cloth, which in turn is covered with a layer of pine, granulated TNT. 

For further purification molten TNT and hot water in equal volumes are run into a cast iron tank of 15 m3 capacity, where the TNT is emulsified by vigorous stirring. The emulsion is cooled to 74-76°C and treated with a 25% solution of sodium sulphite, used in such a proportion as to obtain a final concentration of sodium sulphite in the mixture of 2.5%. During the sulphitation process 5-6% of trinitro compounds and 0.2-0.3% of tetranitromethane (calculated on the TNT) go into solution. 

Samuelson O (1948) A contribution to the chemistry of the sulphite process III A comparison between the sulphur content and the amount of sulphomc acid groups in hgnosulphomc acid Sven Kem Tidskr 60 128-130... 

Samuelson O, Westhn A (1947) Chemistry of the sulphite process Sven Papperstidn 50 149-154... 

Ammoniacal Sellite (ammonium-sodium sulphite) process introduced by the West Virginia Ordnance Works of General Chemical Co.,... 

The alkaline Sellite (sodium sulphite) process of Hercules Powder Co. 

Conventional sulphite pulping processes use aqueous solutions of sulphur dioxide at various pH levels. Sulphite solutions differ in their content of sulphur dioxide, bisulphite ions and sulphite ions, as shown in Figure 13.9. At a low pH of between 1 and 2 the sulphite liquor contains about 50% sulphurous acid and bisulphite ions respectively at a pH of 4 to 5 it contains approximately 100% bisulphite ions and at a pH of 8 to 10 it consists almost entirely of sulphite ions. When allowance is made for chemical charge, it is the pH and the relative amounts of bisulphite and sulphite ions that chiefly control the mode of pulping. In the original acid sulphite process... 

The production of juices for the direct manufacture of white sugar requires a more thorough elimination of non-sucrose compounds. This is achieved in the sulphitation process by the addition of milk of lime and sulphur dioxide and removal of calcium sulphite. 

Pulping of hgnocellulosic materials results in fibres termed pulps. Pulping of wood can generally be divided into mechanical and chemical pulping or mixtures of both types. In chemical pulping, nowadays the alkaline Kraft sulphate pulp process is predominant compared to the sulphite process. 

Lignosulphonate is a by-product of the sulphite process in the manufacturing of pulp (see Chapter 10). It is a corrqtlex mixture of small-to-moderate-size pol5miers and oligomers bearing sulphonate groups, which display a strong polyelectrolyte character and are often used to deflocculate clay-based muds. 

Marches, J. 1953. Clarification of cane juices by means of the sulphitation process. In Principles of Sugar Technology (P. Honig, ed.). Elsevier Publishing Co., New York, pp. 582-654. 

This process description comes from a reference plant which is a highly integrated into a compound of chemical plants. Totally free of chlorine (TFC) bleached pulp is manufactured via the sulphite process route and immediately fed to the viscose production plant. Furthermore, a paper production plant (which is not integrated in the production of pulp), a waste incineration plant as well as some minor chemical companies are situated at the same site. 

The sodium sulphite process yields good results. On fractional distillation not more tnan 25 per cent, should distil below 185 and at least 55 per cent, to 65 per cent, should distil over 200 , a considerable fraction—40 per cent, to 50 per cent.—being obtained from 220 to 230 . 

In the sulphite process the wood is digested with an acid solution of sulphur dioxide and an alkali or alkaline earth bisulphite. 

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