Recovery of Acid Heat as Steam

The acid cooling described in Section 24.7 is straightforward and efficient but it doesn t make use of hot acid s energy. 

Recent acid plants rectify this by recovering much of the acid s heat as steam (for electricity production etc.). All major acid plant designers are working on this technology (Friedman and Friedman, 2004). 

A second key feature of Fig. 24.7 s version of the process is its double packed bed H2SO4 making tower - through which  

The bottom packed bed is fed with slightly diluted return acid from the heat-from-acid boiler. H2O in the acid reacts with ascending SO3 gas to form H2SO4 by Reaction (1.2). Input acid composition and flowrate are controlled to give hot (-485 K) acid boiler feed, Fig. 24.7. 

The top packed bed is fed with cool acid from the final H2SO4 making tower. Its principal purpose is to absorb H2S04(g), H20(g) and 803(g) rising from the bottom 

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In a 500 ml. three-necked flask, fitted with a reflux condenser and mechanical stirrer, place 121 g. (126-5 ml.) of dimethylaniline, 45 g. of 40 per cent, formaldehyde solution and 0 -5 g. of sulphanilic acid. Heat the mixture under reflux with vigorous stirring for 8 hours. No visible change in the reaction mixture occurs. After 8 hours, remove a test portion of the pale yellow emulsion with a pipette or dropper and allow it to cool. The oil should solidify completely and upon boiling it should not smell appreciably of dimethylaniline if this is not the case, heat for a longer period. When the reaction is complete, steam distil (Fig. II, 41, i) the mixture until no more formaldehyde and dimethylaniline passes over only a few drops of dimethylaniline should distil. As soon as the distillate is free from dimethylaniline, pour the residue into excess of cold water when the base immediately solidifies. Decant the water and wash the crystalline solid thoroughly with water to remove the residual formaldehyde. Finally melt the solid under water and allow it to solidify. A hard yellowish-white crystalline cake of crude base, m,p. 80-90°, is obtained in almost quantitative yield. RecrystaUise from 250 ml. of alcohol the recovery of pure pp -tetramethyldiaminodiphenylmethane, m.p. 89-90°, is about 90 per cent. 

Essentially all the ammonium sulfate fertilizer used in the United States is by-product material. By-product from the acid scmbbing of coke oven gas is one source. A larger source is as by-product ammonium sulfate solution from the production of caprolactam (qv) and acrylonitrile, (qv) which are synthetic fiber intermediates. A third but lesser source is from the ammoniation of spent sulfuric acid from other processes. In the recovery of by-product crystals from each of these sources, the crystallization usually is carried out in steam-heated sa turator—crystallizers. Characteristically, crystallizer product is of a particle size about 90% finer than 16 mesh (ca 1 mm dia), which is too small for satisfactory dry blending with granular fertilizer materials. Crystals of this size are suitable, however, as a feed material to mixed fertilizer granulation plants, and this is the main fertilizer outlet for by-product ammonium sulfate. 

Benzyl phthalimide. Grind together 53 g. of finely-powdered, anhydrous potassium carbonate and 147 g. of phthalimide (Section IV,169) in a glass mortar, transfer the mixture to a 750 ml. round-bottomed flask, and treat it with 252 g. (230 ml.) of redistilled benzyl chloride. Heat in an oil bath at 190° under a reflux condenser for 3 hours. Whilst the mixture is still hot, remove the excess of benzyl chloride by steam distillation. The benzyl phthalimide commences to crystallise near the end of the steam distillation. At this point, cool the mixture rapidly with vigorous stirring so that the solid is obtained in a fine state of division. Filter the solid with suction on a Buchner funnel, wash well with water and drain as completely as possible then wash once with 200 ml. of 60 per cent, ethanol and drain again. The yield of crude product, m.p. 100-110°, is 180 g. Recrystallise from glacial acetic acid to obtain pure benzyl phthalimide, m.p. 116° the recovery is about 80 per cent. 

D. 2,6-Dibromoaniline. In a 2-1. flask, equipped with a two-holed stopper carrying an exit tube to a condenser and an entrance tube for steam, 50 g. of crude 3,5-dibromosulfanilamide (Notes 17 and 18) and 250 ml. (5 ml./g.) of 70% sulfuric acid are heated in an oil bath when the temperature of the bath reaches 175— 180°, steam is passed rapidly through the mixture (Note 19). The hydrolysis is continued in this way for 2 hours small amounts of the dibromoaniline distil (Note 20). The bath is then allowed to cool to 105-110°. At this temperature the main mass of the product is steam-distilled. The slightly colored 2,6-dibromoaniline melts at 84-86° and weighs 25-30 g. (66-79% based on 3,5-dibromosulfanilamide) (Note 21). It may be purified by recrystallization from 70% alcohol (7 ml./g.) after recrystallization the product is obtained as long colorless needles which melt at 87-88°. The recovery is 85-90%. 

Several ion-exchange methods are also known that offer efficient recovery of lithium from its ores. In such processes, ore is heated with an acid, or its sodium or potassium salt, at moderate temperatures between 100 to 350°C. Often an aqueous solution of sodium or potassium salt such as sodium carbonate is employed which is heated with the ground ore in a steam autoclave. Lithium ions are liberated into aqueous solution from the silicate complex, exchanging hydrogen, sodium or potassium ions. 

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