The spent acid

After separation of the nitroglycerine, the following remain in the spent acid nitroglycerine, dinitroglycerine, mixed esters of sulphuric and nitric arid. The two latter esters react slowly with the nitric arid contained in the waste arid to form further nitroglycerine, which floats on the surface of the arid. 

There is a further method of obtaining nitroglycerine from the spent acid if the main product is separated immediately after nitrating. Nitration is commonly performed at the temperature of 25 - 30°C. The waste acid is cooled after nitration is complete, to the temperature of 15°C or less, and as a result a part of the nitroglycerine which was dissolved in the acid is separated. 

The amount of nitroglycerine recovered from the spent arid amounts to about 2% of the total output. 

The separation rate of this supplementary yield of nitroglycerine depends not only on the velocity of the additional reaction of esterification, but also on the purity of the glycerine used and the purity of the mixed arid. It should be borne in 

The supplementary separation is carried on in a special building. Several days supply of spent add is collected in special lead tanks (settlers) each having a capacity sufficient to hold the add collected from a full-day s nitration. Nitroglycerine collected on the surface of the acid may be removed in various ways by means of an aluminium spoon (the old system) or by displacing the contents of the tank from below with the waste add (the combined process, p. 95). The handling of waste acid free from nitroglycerine is not wholly safe, since more nitroglycerine may still separate out. 

Safety diagram of acidic nitroglycerine, according to Oehman et al. [27]. For comparison, nitroglycol is also indicated. 

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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. 

Liquid Effluents. Recycling of acid, soda, and zinc have long been necessary economically, and the acid—soda reaction product, sodium sulfate, is extracted and sold into other sectors of the chemical industry. Acid recovery usually involves the degassing, filtering, and evaporative concentration of the spent acid leaving the spinning machines. Excess sodium sulfate is removed by crystallization and then dehydrated before sale. Traces of zinc that escape recovery are removable from the main Hquid effluent stream to the extent that practically all the zinc can now be retained in the process. 

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). 

The H2SO4 concentration is controlled above 90% to provide the optimum activity and selectivity. Purity is maintained by the withdrawal of system acid and replacement with fresh 98% acid. The spent acid is returned to an acid manufacturiag plant for reprocessiag. 

Spent acid burning is actually a misnomer, for such acids are decomposed to SO2 and H2O at high temperatures in an endothermic reaction. Excess water in the acid is also vaporized. Acid decomposition and water vaporization require considerable heat. Any organic compounds present in the spent acid oxidize to produce some of the required heat. To supply the additional heat required, auxiUary fuels, eg, oil or gas, must be burned. When available, sulfur and H2S are excellent auxiUary fuels. 

The purified ziac solution is fed to the electrolyte recirculating stream at a rate that holds the composition of the electrolyte constant, commonly ranging from 100—200 g H2SO4 and 45—70 g Zn/L. Continuous monitoring of the density and conductivity of the spent acid aids ia control. This is important siace the range of acidity is narrow for maximum current efficiency at any given current density. 

Petroleum. Citric acid is added to hydrochloric acid solutions in acidising limestone formations. Citric acid prevents the formation of ferric hydroxide gel in the spent acid solution by chelating the ferric ions present. Formation of the gel would plug the pores, preventing the flow of oil to the producer well (123—127). 

The wash water and the spent acid from all the pre-treatment tanks is also transferred to the effluent treatment plant for further treatment. Spent passivation liquor from the passivation tank is a strong waste and it may be provided with a separate pipeline to the effluent treatment plant, as shown in Figure A13.12. 

The first vessel in the blowdown system is therefore an acid-hydrocarbon separator. This drum is provided with a pump to transfer disengaged acid to the spent acid tank. Disengaged liquid hydrocarbon is preferably pumped back to the process, or to slop storage or a regular non-condensible lowdown drum. The vented vapor stream from the acid-hydrocarbon separator is bubbled through a layer of caustic soda solution in a neutralizing drum and is then routed to the flare header. To avoid corrosion in the special acid blowdown system, no releases which may contain water or alkaline solutions are routed into it. 

The mass was allowed to settle for 15 minutes, and the oil separated from the spent acid in the same manner as in the manuf of NG. The sepd oil was washed, first with w at 40°, then with aq soda soln, also at 40°, and finally with w. The yield was about 100kg of oil contg 16.32 to 16.36% N. In Italy, yields as high as... 

Acid compns for practical nitrations must be formulated in such a manner that the spent acid must ... 

It is obvious that the nitrated product must be separated from the acid in equil with it (spent acid). If the product and the spent acid form two immiscible liq phases, eg, NG, EGDN, or molten TNT, separation is effected by gravity or centrifuging. If the product and spent acid form a solid and a liq phase, eg PA, NC or PETN, separation is effected by centrifuging (PA NC) or filtration (PETN). If the nitration is carried in the vapor phase (NM), separation is effected by distillation... 

To keep product yield at a maximum it is important that the solubility of product in the spent acid be kept to a minimum. This also facilitates removal of traces of product from the spent acid so that it can be either fortified and reused, reused to make lower nitro compds, or neutralized and discharged as non-polluting waste material... 

HNO3 in the spent acid. The vertical line corresponds to the mole ratio of H20/H2S04 to form the mo no hydrate H2SO4.H2O. Note that the max HNO3 solubility for each curve occurs dose to this vertical line. It is clear that both water content and HN03 content of the spent acid should be kept low in order to minimize HN03 solubility in the NG... 

In both stages, turbulent flow of the impinging streams is very desirable. The spent acid of the second stage, upon separation of the TNT, is fortified with aq nitric acid and is reused as the nitrating acid for the first stage... 

The NG-acid emulsion enters a cooling system immediately after leaving the injector and the temp of 45-50° is maintained for only about half a second. During the next 80—90 secs the mixt is cooled to 15° In the following 30 secs the NG is separated from the spent acid... 

A continuous centrifugal separator separates NG from the spent acid. The centrifuge operates at 3200 rpm. For a unit with a capacity of 2500 /hr the quantity of NG in the separator bowl during operation is only 3.5 kg. The separated acid-free NG is emulsified immediately by a wash-jet to form a non-expl mixt and is removed continuously from the separator house to the NG wash-and-weigh house... 

Composition of the nitrating mixture, % Composition of the spent acid, % Cellulose to acid ratio 1 j Nitrogen content of nitrocellulose. %... 

The spent acid compn is 12.6/70.8/16.6 nitric acid/sulfuric acid/water, or 83.4% total acid and 15.1% nitric acid based on total acid. The total heat of reaction AHt = AHn + AHj where AHn is the heat of nitration, ie, the heat of... 

The spent acid from trinitration has also been the cause of several disasters, although it had been considered safe to handle. The most noteworthy example of this occurred in the Reinsdorf factory in Germany in 1935. The hot spent acid flowed down to open iron tanks, where, as the liquid cooled, a mixture of di- and tri-nitrotoluenes rose to the surface. It was skimmed off from time to time and transferred to a washing tank, where it was washed with water. On skimming, a rubber glove and a sheif left bn the brim of the tank with some... 

A method which appears to be essentially equivalent to the best ABL method was patented by Brennecke (Ref 10) who claims better utilization of the spent acid and solvent and better yield in a repetitive, step-wise procedure. Another modification patented by Rolewicz et al (Ref 12) utilizes mixed acid and methylene chloride extrn and appears to be little different from the above methods, except that the nitric acid is made oxide-free. A method of obtaining 98.4% pure Petrin from its mixts with PETN and PE dinitrate is claimed by Brennecke (Ref 16)... 

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... 

Upon completion, the spent acid solution should be neutralized and pumped to a suitable disposal point. The boiler should be thoroughly rinsed and all sludge washed out. 

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