Spent acid decomposition production

Metallurgical (smelter) plants and spent acid decomposition plants usually produce acid of good (low) color because the SO2 feed gases ate extensively purified prior to use. In some cases, however, and particularly at lead smelters, sufficient amounts of organic flotation agents are volatilized from sulfide ores to form brown or black acid. Such acid can be used in many applications, particularly for fertilizer production, without significant problems arising. 

Water-rich acids (e.g., methyl methacrylate production spent acid) often have part of their water vacuum-evaporated before they are sent to the H2SO4 decomposition furnace (De Dietrich, 2012 Outotec, 2008). This decreases ... 

Thermal decomposition of spent acids, eg, sulfuric acid, is required as an intermediate step at temperatures sufficientiy high to completely consume the organic contaminants by combustion temperatures above 1000°C are required. Concentrated acid can be made from the sulfur oxides. Spent acid is sprayed into a vertical combustion chamber, where the energy required to heat and vaporize the feed and support these endothermic reactions is suppHed by complete combustion of fuel oil plus added sulfur, if further acid production is desired. High feed rates of up to 30 t/d of uniform spent acid droplets are attained with a single rotary atomizer and decomposition rates of ca 400 t/d are possible (98). 

A considerable amount of nitrous acid is present in the spent acid. /J-Nitroethyl nitrate is feebly acidic and dissolves in dilute alkali solutions with a yellow color. It is not sufficiently stable for use in commercial explosives. On digestion with warm water or on slow distillation with steam it undergoes a decomposition or sort of hydrolysis whereby nitrous acid and other materials are produced. Numerous patents have been issued for processes of procuring pure nitroglycol from the Kekule oil. One hundred parts of the last-named material yield about 40 parts of nitroglycol, and the economic success of the Process depends upon the recovery of valuable by-products from the 0-nitroethyl nitrate which is destroyed. ... 

Fig. 5.1. Spent sulfuric acid regeneration flowsheet. H2S04(f) in the contaminated spent acid is decomposed to S02(g), 02(g) and H20(g) in a mildly oxidizing, 1300 K fuel fired furnace. The furnace offgas (6-14 volume% S02, 2 volume% 02, remainder N2, H20, C02) is cooled, cleaned and dried. It is then sent to catalytic S02 + Vi02 —> S03 oxidation and H2S04 making, Eqn. (1.2). Air is added just before dehydration (top right) to provide 02 for catalytic S02 oxidation. Molten sulfur is often burnt as fuel in the decomposition furnace. It provides heat for H2S04 decomposition and S02 for additional H2S04 production. Tables 5.2 and 5.3 give details of industrial operations.

Heat for this reaction is mainly provided by burning molten sulfur and other fuels with preheated air (occasionally oxygen-enriched) and the 02 from Reaction (5.1). A small amount of heat is obtained from oxidizing the spent acid s hydrocarbons. Sulfur burning has the advantages that it increases S02 concentration in decomposition furnace offgas and H2S04 production rate. 

Sulfonation of LAB. The sulfonation of alkylbenzenes leads to sulfonic acid tyre product, which is then neutralized with a base such as sodium hydroxide to produce sodium alkylbenzene sulfonate. The sulfonation reaction is highly exothermic and instantaneous. An efficient reactor heat removal system is used to prevent the decomposition of the resultant sulfonic acid. The sulfonation reaction takes place by using oleum (SO3H2SO4) or sulfur trioxide (SO3). Although, the oleum sulfonation requires relatively inexpensive equipment, the oleum process has major disadvantages compared to sulfur trioxide. The need for spent acid stream disposal and the potential corrosion owing to sulfuric acid generation increased the problems related to oleum process [1]. 

However the methods being used at present for the manufacture of nitroglycerine, such as batch combined process (Vol. II, p, 95) and all continuous processes (Vol. II, p. 97) require that spent acid be dealt with correctly. Originally primitive arrangements were in use consisting in distillation of nitric acid and careful decomposition of organic products dissolved in the spent acids. 

Subba Rao pointed out the case of hydrolytic reactions in the spent acid, followed by oxidation. They found formic, oxalic and inesoxalic acid among the decomposition products,... 

The organic solvent is recovered for reuse in the production plant. Excess sulfuric acid mother liquor is conveyed via the internal piping system for spent acid to the existing sulfuric acid plant, where concentration, decomposition to sulfur dioxide, and oxidation to sulfur trioxide occur. Sulfur trioxide is then withdrawn and fed to the sulfonation reaction through piping. 

When working up the products from dinitration, the reaction mixture is settled and separated into a dinitrotoluene-rich stream and a spent-acid stream. The dini-trotoluene stream is refined by alkali washing and crystallization. The isomer composition is 20% 2,6-dinitrotoluene, 76% 2,4-dinitrotoluene, 0.6% 3,5-dinitrotoluene and small quantities of 2,5-dinitrotoluene (80/20 DNT). The yield from dinitration is around 96 to 98% the commercial product has a crystallizing point of 55 to 58 °C. The decomposition of dinitrotoluenes at higher temperatures is highly exothermic, and hence they should not be stored at a temperature exceeding 75 °C. 

Current processes for the manufacture of trinitrotoluene (TNT) produce atmospheric and water pollution that is only partly relieved by mechanical clean-up methods. TNT is currently produced from toluene by successive mono-, di-, and trinitrations with mixed aqueous nitric and sulfuric acids in the first two steps and anhydrous mixed acid in the last. Each stage in the current process is conducted at elevated temperatures, and side reactions in the overall process directly produce thousands of pounds of oxides of nitrogen, sulfuric acid aerosols, and volatile nitro organic products (such as tetranitromethane and nitroaro-matics). These pollutants derive from the thermal decomposition of the aqueous nitric acid solutions, from oxidative side reactions that produce as many as 40 by-product compounds, and from formation of unsymmetrlcal "meta" Isomers. Since symmetrical TNT is inevitably accompanied by meta isomers as well as oxidation products, the crude material is treated with sodium sulfite solutions to remove the undesirable Isomers and nitroaromatics by derivatization. The spent sulfite solution, known as "red water, is then disposed of by combustion to an inorganic ash. Itself a disposal problem. 

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