Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Patent
1992-10-23
1994-05-03
Straub, Gary P.
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
423522, 423523, 423525, 423531, 423DIG2, 423265, 252407, 208 13, C01B 1790
Patent
active
053086007
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
The present invention relates to a process for conditioning waste sulfuric acid, which is prone to precipitation of tars or resins, by means of emulsifiers.
In many chemical processes, a sulfuric acid laden with water, organic or inorganic materials, such as nitro compounds, sulfonic acids, mineral salts, nitric acid or hydrogen chloride, arises as a waste product. The content of such waste sulfuric acid fluctuates within wide limits. For example, it can arise as thin acid of 5 to 60% by weight of H.sub.2 SO.sub.4 or as a waste acid of 60 to 80% by weight of H.sub.2 SO.sub.4. A plurality of processes are known for concentrating such contaminated waste sulfuric acid by evaporation of the water content. The method, according to which the evaporation is carried out, depends as a rule on the content of the waste sulfuric acid. For example, waste acid of 60 to 80% by weight of H.sub.2 SO.sub.4 can be concentrated by the Pauling process to give 95 to 96% by weight H.sub.2 SO.sub.4. More highly diluted sulfuric acid can be evaporated in a circulation evaporator (Winnacker-Kuchler, Chemische Technologie [Chemical Technology], volume 2 (1982), pages 61 to 71). Waste acid laden with organic materials can also be processed by thermal cracking, but this involves a very high energy consumption (loc. cit. pages 23 to 25).
Waste sulfuric acid must as a rule be transported or stored before or during processing. This is made considerably more difficult or even impossible if a solid or highly viscous phase separates out of the waste sulfuric acid. Thus, pipes can be blocked by precipitated resins or tars, or vessels can be filled up to such an extent that their functioning is greatly impeded. Other parts of the equipment for reprocessing, such as heat exchangers, can also be impaired in their functioning by deposits, in particular by resin or tar precipitates taken along in the waste sulfuric acid.
Such troublesome precipitates can in principle be separated off by filtration, but precisely resins or tars easily cause blockage of the filter apparatus (German Offenlegungsschrift 2,450,255). Moreover, renewed precipitation after a filtration is frequently observed.
Particularly in the nitration of reactive aromatics such as naphthalene or acenaphthene, varying quantities of resins are also frequently formed in addition to the desired nitro compounds (Houben-Weyl, Methoden der organ. Chemie [Methods of organic chemistry], 4th edition, volume 10/1 (1971), pages 492 and 496). The waste sulfuric acid thus obtained tends to secrete so-called nitration resins, whereby reprocessing is made much more difficult. Frequently, within only a few hours, such a large quantity of resin precipitates from the waste sulfuric acid that the pipes and vessels foul up. Nitration processes, such as are listed, for example, in Houben-Weyl, Methoden der organ. Chemie [Methods of organic chemistry], 4th edition, volume 10/1 (1971), page 663, likewise lead to such waste sulfuric acids which cause problems.
These so-called nitration resins can also arise as undesired by-products in nitrations in highly concentrated nitric acid (German Offenlegungsschrift 2,338,479) and cause deposits.
Admittedly, the deposits in the pipes, tanks or equipment items can as a rule be removed by washing with a solvent, but this represents an additional process step. Furthermore, the contaminated solvents thus arising must likewise also be reprocessed.
It is known to condition waste sulfuric acid by treatment with activated carbon, i.e. to render it stable for storage, transport and reprocessing. A disadvantage of this process is the high cost of procuring the fresh activated carbon and disposing of the spent activated carbon. Moreover, waste sulfuric acid treated in this way frequently deposits impurities again, even after a short time.
In addition, a number of processes for eliminating the impurities from the said waste sulfuric acids by treatment with oxidizing agents have been described (German Offenlegungsschrift 2,404,613 and German Offenlegungsschrift 2,450
REFERENCES:
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patent: 2198686 (1940-04-01), Watson
patent: 3372009 (1968-03-01), Waldmann
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patent: 4409000 (1983-10-01), LeSuer
Fritsche-Lang Wolfram
Lorke Horst
von Plessen Helmold
Hoechst Aktiengesellschaft
Straub Gary P.
Vanoy Timothy C.
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