Spent sulfuric acid compositions

Table 5.1. Compositions (mass%) of spent sulfuric acids from two chemical processes. Both processes use sulfuric acid as catalyst. The acid becomes contaminated with water, hydrocarbons, and other chemicals during use. It is made into new sulfuric acid as described in Fig. 5.1.

Derivation The spent black liquor from the pulping process is concentrated until the sodium salts (soaps) of the various acids separate out and are skimmed off. These are acidified by sulfuric acid. Composition and properties vary widely, but average 35—40% rosin acids, 50-60% fatty acids. 

Table 5.1 shows the compositions of two spent acids. Both are made into new, strong sulfuric acid as described in Fig. 5.1. 

Fig. 4 4. Lines of constant nitrogen for nitrocellulose prepared in mixed acid. The dashed lines are lines of constant degree of nitration, namely, 3, 6, 7, 9, 10, 11, 12, and 13 per cent N. These lines are almost parallel to the lines of constant water concentration except in the regions of high sulfuric acid concentration at the lower right-hand comer. The zone of technical nitration is also indicated. The choice of composition for technical nitration in this concentration area is probably dictated by the economics of the recovery of spent acids. F. D, MileSf Cellulose Nitrate Interscience PublisherSf Inc., p. 66, 1955.)...

By using cycle acid to dissolve the naphthalene to be nitrated and then proceeding with the nitration in the usual way, the operating steps are as follows The naphthalene—1,280 lb—is suspended, in 4,500 lb of dilute sulfuric acid or spent acid containing about 65 per cent H2SO4. The whole is thoroughly stirred, and 2,350 lb of mixed acid of the following composition is slowly added ... 

Sulfuric acid is used in huge tonnages by the chemical and metallurgical industries, yielding even larger quantities of spent acid, which has to be distilled to recover the H2SO4. An initial guide is provided in Table 7.3, which lists the pertinent vapor-liquid compositions. 

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