Spent sulfuric acid products

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. 

Spent Sulfuric Field. Spent sulfuric acid recovered from petrochemical and refinery processes can be fed to a high temperature furnace at 870—1260°C, where it is transformed kito sulfur dioxide, water, and other gaseous products. After suitable scmbbkig and drykig, the gases are passed to a conventional contact sulfuric acid plant (263). 

By-Product Calcium Sulfate. There are many iadustrial chemical processes that produce by-product calcium sulfate in one of its forms. Whereas the most common is the neutralization of spent sulfuric acid, many of those processes do not produce a commercially useful by-product because of contaminants, particle size, or volume produced. There are, however, six chemical processes that do produce sufficient volume to have potential commercial value. Each is named after its chemical process. 

These three steps all produce significant amounts of waste. First, as discussed earlier, the nitration process results in the production of spent sulfuric acid. In the past the company had been able to sell much of this material to the coke and steel industries but declining demand meant that the acid now required disposing of, at additional cost. At the time green catalytic nitration technology was becoming available with clay, zeolite and lanthanide catalysts all providing possible alternatives to the use of sulfuric acid (see below). Improved selectivity to the desired para-isomer is an added benefit of some of these catalytic systems. However on the... 

Other sources of sulfur dioxide are flue gases and spent sulfuric acid. Sulfur dioxide may be recovered from stack gases in smelting or power plants. Similarly, SO2 can be generated from spent sulfuric acid recovered from oil refineries. The spent acid is burned in a high temperature furnace above 900°C to form sulfur dioxide, water, and gaseous products. 

The sulfate process has traditionally used batch ore digestion, in which concentrated sulfuric acid is reacted with ilmenite. This reaction is very violent and causes the entrainment of sulfur oxides (SOA) and sulfuric acid in large amounts of water vapor. In an effort to reduce the particulate emissions, scrubbers have been installed at most plants, but these, in turn, have necessitated the treatment of large quantities of scrubbing liquid before discharge. Other waste-disposal problem products are spent sulfuric acid and copperas (FeS04-7H20). 

Production of pure sulfuric acid from contaminated spent sulfuric acid catalyst is almost always done near the source of the spent acid - to minimize forward and return acid shipping distance. 

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.

This is the most important inorganic by-product formed during production of p-anisic aldehyde from p-cresol via the intermediate product p-cresyl-methyl ether (PCME). Manganese dioxide Mn02 (80-82%) in presence of sulfuric acid (80%) converts PCME to p-anisic aldehyde and a by-product stream rich in manganese sulfate and excess spent sulfuric acid used in the oxidation reaction as shown below ... 

Direct continuous reaction of SOs with benzene, highly successful in the case of dimethyl ether as described above, is not practical because of high sulfone formation. Indirect continuous reaction with SOs by a procedure stated to yield no sulfone has, however, been achieved by the method developed by Dennis and Bull. This process is based upon an observation made by the former that, in the presence of sulfuric acid, benzene will dissolve 2-3 per cent of its own volume of benzenesulfonic acid. This process is also designed to operate in continuous countercurrent flow in a cascade system, benzene being introduced at the bottom and a benzene solution of the sulfonic acid overflowing from the top. Concentrated sulfuric acid is added continuously at the top, and spent sulfuric acid (77 per cent) is removed at the bottom of the reactor. The spent acid may be fortified to original strength with SO3 for reuse, and the benzene is recycled after the product sulfonic acid has been extracted from it with water. This procedure is, in theory, the most efficient possible, since benzenesulfonic acid is, in... 

Subsequently, instead of the sodium salt, the free sulfonic acid [149] is precipitated by addition of sulfuric acid or recycled mother liquor, followed by cooling. The mother liquor, which remains after filtering off the product, can be supplied directly to existing plants for regeneration of spent sulfuric acid. 

Occasionally, spent sulfuric acid from petroleum refineries, petrochemical plants, and soap factories can be used for ammonium sulfate production if impurities do not cause insurmountable frothing or corrosion problems or render the product unacceptable. If the acid is too badly contaminated, it may be more expedient to burn off the impurities in a specially designed furnace and to produce fresh acid for ammoniation. 

Spent Sulfuric Acid. The sulfuric acid used to dry chlorine gas becomes a waste product. The discussion in Section 9.1.4.1 shows that the quantity of waste acid generated is inversely related to the difference between the concentrations of feed acid and waste acid. Production of a more dilute waste acid means generation of less waste product. This is constrained by the ability of the drying system to produce chlorine gas of satisfactory quality, the increasing corrosivity of the chlorine-containing acid, and the method of disposal of the waste acid. 

In multiple-tube boilers (usually horizontal) the fire may be on the tube side. As long as the fire tubes are kept submerged in water, the tubes do not overheat. Boilers of this type are widely used in the regeneration of spent sulfuric acid, and in the production of elemental sulfur from hydrogen sulfide. 

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