Using spent acids

In sulfonation units, sulfuric acid discharges can in fact be profitably reclaimed if they are relatively concentrated and if they have strong free acidity. However, the fact that they carry considerable associated COD pollution must be remembered. As an illustration, the following example of analysis is presented  

Experience shows that the layer of sprung acids forms in 15 min to a few hours and almost always in the upper part of a test tube. This is due to the difference in real specific gravities or to assisted flotation promoted by the amount of H S and CO2 degassing into the atmosphere, something that would not happen in a pressurized vessel. 

Sedimentation of viscous blacfc products has been seen (third phase) with very concentrated caustic (COD 100 g H) containing over 10 gd of total sulfur. It has been attributed to tars and polymers, but can also be concomitant with the ptecipitation of Na2SO,(, whose saturation is sometimes exceeded (see paragraph 4.2.1.2.D). 

Foaming can also be observed. It can be substantial if acidification is fast, but does not hinder the run if acidification is gradual for about fifteen minutes. 

The pH must also be checked during laboratory tests. H-rough a pH of 4 is sufficient in theory, in fact the lower the pH the better the oil separation (Table 41) and mercaptan hydrolysis (Table 42). 

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At the Bobingen factory hexamine dinitrate is prepared by the action of 50% nitric acid on hexamine at a temperature below 15°C, using spent acid from the nitration of pentaerythritol. NH4N03-HN03 is obtained by the reaction of equi-molecular amounts of ammonium nitrate and concentrated nitric acid. 

Spent process baths can also be reused for other purposes. A common example is to use spent acid or alkaline cleaners for pH adjustment during industrial waste treatment. Typically, these cleaners are dumped when contaminants exceed an acceptable level. However, these solutions remain acidic or alkaline enough to act as pH adjusters. Alkaline cleaners, for instance, can be used in chrome reduction treatment. Since spent cleaners often contain high concentrations of metals, they should not be used for final pH adjustments, however. 

Rearick etal. (1997)ieportedapilot run of re-using spent acid/reactive dye bath. The color shade obtained by the reclaimed dye bath was approximately 20% lighter than with the original formulation. It was assumed that shade adjustment efforts failed due to the interference of high levels of magnesium or siUca and/or peroxide in the bath. 

During my Cleveland years, I also continued and extended my studies in nitration, which I started in the early 1950s in Hungary. Conventional nitration of aromatic compounds uses mixed acid (mixture of nitric acid and sulfuric acid). The water formed in the reaetion dilutes the acid, and spent aeid disposal is beeoming a serious environ-... 

To solve some of the environmental problems of mixed-acid nitration, we were able to replaee sulfuric acid with solid superacid catalysts. This allowed us to develop a novel, clean, azeotropic nitration of aromatics with nitric acid over solid perfluorinated sulfonic acid catalysts (Nafion-H). The water formed is continuously azeotroped off by an excess of aromatics, thus preventing dilution of acid. Because the disposal of spent acids of nitration represents a serious environmental problem, the use of solid aeid eatalysts is a significant improvement. 

The Biazzi continuous process is also used. The reactants are continuously fed to a series of nitrators at 15—20°C followed by separation of the PETN, water washing, solution in acetone at 50°C, neutralization with gaseous ammonia, and precipitation by dilution with water. The overall yield is more than 95%. The acetone and the spent acid are readily recovered. 

The electrowinning process developed by Ginatta (34) has been purchased by M.A. Industries (Atlanta, Georgia), and the process is available for licensing (qv). MA Industries have also developed a process to upgrade the polypropylene chips from the battery breaking operation to pellets for use by the plastics industry. Additionally, East Penn (Lyons Station, Pennsylvania), has developed a solvent-extraction process to purify the spent acid from lead—acid batteries and use the purified acid in battery production (35). 

Because sulfur suppHes, either as elemental sulfur or by-product sulfuric acid, have grown owiag to iacreased environmental awareness, demand for sulfur has decreased ia some consuming iadustries for the same reason. Industries such as titanium dioxide productions, which traditionally utilized sulfuric acid, have concerted to more environmentally friendly processes. In addition, many consumers who contiaue to use sulfuric acid are puttiag an emphasis on regenerating or recycling spent acid. 

In general, plants using SO2 gas derived from metallic sulfides, spent acids, or gypsum anhydrite purify the gas stream before drying it by cold, ie, wet, gas purification. Various equipment combinations including humidification towers, reverse jet scmbbers, packed gas cooling towers, impingement tray columns and electrostatic precipitators are used to clean the gas. 

Spent Acid or Burning. Burners for spent acid or hydrogen sulfide are generally similar to those used for elemental sulfur. There are, however, a few critical differences. Special types of nozzles are required both for H2S, a gaseous fuel, and for the corrosive and viscous spent acids. In a few cases, spent acids maybe so viscous that only a spinning cup can satisfactorily atomize them. Because combustion of H2S is highly exothermic, carehil design is necessary to avoid excessive temperatures. 

In drying towers of sulfur-burning plants, mesh pads or inertial impaction-type mist eliminators are usually adequate. High efficiency mist eliminators are usually used in drying towers of spent acid or metallurgical plants. 

In the gas cleaning sections of spent acid or metaUurgical sulfuric acid plants, the weak acid scmbbing circuit is typicaUy handled by plastic or glass fiber reinforced plastic (ERP) pipe. The contaminants in weak acid usuaUy vary too greatly to aUow use of an economical aUoy. 

Oxygen-enriched air is sometimes used in spent acid decomposition furnaces to increase furnace capacity. Use of oxygen-enriched air reduces the amount of inerts in the gas stream in the furnace and gas purification equipment. This permits higher SO2 throughput and helps both the heat and water... 

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. 

E. O. Jones and K. L. Kensington, Spent acid recovery using WFDdprocess system, ACS meeting, Chicago, HI., Aug. 19, 1993. 

Raw material input to petroleum refineries is primarily crude oil however, petroleum refineries use and generate an enormous number of chemicals, many of which leave the facilities as discharges of air emissions, wastewater, or solid waste. Pollutants generated typically include VOCs, carbon monoxide (CO), sulfur oxides (SOJ, nitrogen oxides (NOJ, particulates, ammonia (NH3), hydrogen sulfide (HjS) metals, spent acids, and numerous toxic organic compounds. 

Typical nitrating acid and spent acid compns used in the manufacture of selected high expls are shown in Table 2... 

Sources of thermochemical data for such calculations are Vol 7, H38 Lff Heat Effects — Data for Common Explosives NBS Circular 500 (Ref 39a) Cox Pilcher (Ref 89) and the studies of Rhodes Nelson (Ref 24b) and McKinley Brown (Ref 28a) on mixed acids As an example of such a calculation we will compute the heat evolution and temp rise occurring during the mixed acid nitration of glycerol to NG. We will assume that a typical 50/50 nitric acid/sulfuric acid MA is used and that the MA/glycerol ratio is 5/1. Further assumptions are that all the glycerol is converted to NG, and that the heats of soln of NG in die. spent acid, and of spent acid in the NG, are negligibly small (cf discussion of these effects by the writer in Ref 51). The net reaction is then ... 

Nearly insoi in w, easily sol in ale, eth, et ac, benz gelatinizes NC. Can be prepd by the nitration of ], 3-propanediol with mixed nitric-sulfuric acid, as described by Naoum (Ref 4) and Blechta (Ref 3). The nitration requires a lower temp than that used for nitrating glycerin, because the central methylene group is readily oxidized at a higher temp. A temp between 0-10° is recommended since decompn is possible even at 15°, while at 20° yel fumes are evolved. Separating the product from the spent acid occurs with ease at 10°. From lOOp of... 

Proteins, Nitrated. Proteinaceous or albuminoid materials (glue, bones, hides, leather, hair, feathers, etc) can be nitrated in a two-stage process to yield expl yel oils. Thus, glue is treated first with 3.6 pts by wt of 66°Be sulfuric acid and 2.7 pts of 36°Be nitric acid. The resultant oil is sepd from the heavier spent acid and nitrated further with 3 pts of oleum and 2.6 pts of 36°BS nitric acid. Both nitrations are conducted at 15—20°, and never above 40°. The resulting oily expl can be used alone or mixed with other materials... 

Most LAB is sulfonated using thin-film S03 technology. In this process no spent acid is produced because the S03 reacts almost stoichiometrically with LAB. High-quality LAS slurry with low color and a low level of Na2S04 can be produced. Sulfonation of LAB yields predominantly the para isomer [14]. 

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