Chemistry of inorganic compounds – Sulfur or compound thereof – Oxygen containing
Reexamination Certificate
1996-01-22
2002-04-09
Griffin, Steven P. (Department: 1754)
Chemistry of inorganic compounds
Sulfur or compound thereof
Oxygen containing
C423S521000
Reexamination Certificate
active
06368570
ABSTRACT:
TECHNICAL FIELD
The invention is in the field of producing Caro's acid by reaction of hydrogen peroxide and sulfuric acid in a controlled and effective manner.
BACKGROUND ART
Caro's acid, H
2
SO
5
, is also known as peroxymonosulfuric acid. It is a strong oxidizing compound which has been used in many applications including purification of cyanide-containing effluents by conversion of their cyanides into non-toxic derivatives. Caro's acid is usually produced by reacting sulfuric acid with hydrogen peroxide to produce an equilibrium mixture of Caro's acid containing peroxymonosulfuric acid, sulfuric acid, hydrogen peroxide and water. However, since the Caro's acid is not stable for long periods it must be made and immediately used on site or quickly cooled and stored by refrigeration. In general, the Caro's acid is manufactured on site only as needed to avoid storing any excess amounts.
One procedure for producing Caro's acid is set forth in U.S. Pat. No. 3,900,555 by using an apparatus described in U.S. Pat. No. 3,939,072 for mixing the sulfuric acid and hydrogen peroxide and cooling the mixture with a water-cooled jacket to prevent overheating of the reactants and premature decomposition of the monoperoxysulfuric acid product. These patents teach the use of the monoperoxysulfuric acid product for treating waste aqueous effluents from an electroplating plant containing cyanide ions while simultaneously adding an alkali in amounts suitable to maintain the solution at pH 9.
Another procedure is set forth in U.S. Pat. No. 4,915,849 where the Caro's acid is used to treat cyanide-containing effluents from an ore-processing plant. The Caro's acid is manufactured by reacting sulfuric acid with hydrogen peroxide in proportions corresponding to between 0.01 and 0.5 moles of sulfuric acid per mole of hydrogen peroxide. The resulting acid is then added to the cyanide-containing effluent simultaneous with aqueous lime or sodium hydroxide mixtures in order to maintain the effluent at the preferred pH of between 9.5 and 11.5.
PCT Publication No. WO 92/07791, a published patent application of Lane et al, teaches the production of peroxymonosulfuric acid by introducing a hydrogen peroxide solution into a stream of sulfuric acid flowing through a reaction chamber, the H
2
O
2
introduction being intermediate the sulfuric acid inlet and the reaction mixture outlet. Both the hydrogen peroxide solution and sulfuric acid are introduced under pressure into the closed tubular reaction chamber of the invention. In the reaction chamber, the through-put per minute of the reaction chamber is at least about 20 times its internal volume measured between the inlet for the hydrogen peroxide and the outlet.
Another PCT application, Publication No. WO 92/11200 to McDonogh et al. teaches the use of substoichiometric amounts of sulfuric acid to avoid the need to neutralize part of the acid for some applications. However, the conversion of hydrogen peroxide to Caro's acid is too low to be economical for most large scale applications.
U.S. Pat. Nos. 5,439,663 and 5,470,564, incorporated herein by reference are both to Manganaro et al.; both teach processes for preparing Caro's acid by reacting sulfuric acid having a concentration of at least about 85% by weight and hydrogen peroxide having a concentration of at least about 50% by weight by weight, wherein the sulfuric acid and hydrogen peroxide are fed through separate feed lines into a funneling zone open to the atmosphere, the feed lines having air gaps between their ends and the funneling zone; continuing to introduce the sulfuric acid and the hydrogen peroxide into the funneling zone to flow and mix within the funneling zone, passing the resulting mixture by gravity flow into one end of a reaction zone whose size permits a pressure drop which is at least 8 times the theoretical pressure drop for such reaction zone and removing a mixture containing Caro's acid from the exit end of the reaction zone. Although the process eliminates many problems of the prior art, particularly safety problems, decomposition within the funneling zone is undesirable and results in an increased pressure drop in the reactor, resulting in the high pressure drop therein and lowering the throughput. These two patents are very valuable in that they disclose how to eliminate two important safety problems inherent in prior processes; contamination of the hydrogen peroxide feed tanks, and the overflow or rupture of reaction vessels caused by uncontrolled decomposition.
It has been the custom in the industry to isolate the storage tank of hydrogen peroxide from the reactor where Caro's acid is produced by means of an intermediate tank (sometimes called a “break” tank) to interrupt the stored hydrogen peroxide source from the line delivering hydrogen peroxide to the Caro's acid generator. The peroxide from the storage tank is passed by pump means or by gravity into the top of an intermediate tank to a given level in the intermediate tank without requiring a direct liquid connection between the peroxide in the intermediate tank and the line flowing from the storage tank. This assures that any contamination which may back up from the Caro's acid generator into the intermediate tank will not be able to enter the hydrogen peroxide storage tank.
DISCLOSURE OF THE INVENTION
We have now found a process for producing Caro's acid by introducing hydrogen peroxide having a concentration of at least 50% by weight through a first feed line into a first reactor conduit open to the atmosphere and introducing sulfuric acid having a concentration of at least 85% by weight through a second feed line into a second reactor conduit open to the atmosphere, proportionally adjusting the rate of flow of the hydrogen peroxide into the first reactor conduit and of the sulfuric acid into the second reactor conduit to maintain the desired mole ratio and to provide a hydrostatic head of hydrogen peroxide and of sulfuric acid, thereby independently introducing the hydrogen peroxide from the first reactor conduit and the sulfuric acid from the second reactor conduit by gravity into a baffled, plug flow mixing reactor without substantial premixing of the sulfuric acid and the hydrogen peroxide, and removing a Caro's acid reaction mixture from the exit end of the plug flow mixing reactor.
In carrying out the present process, the Caro's acid is produced by reacting sulfuric acid and hydrogen peroxide together, without substantial premixing. The reaction is essentially adiabatic so that the heat evolved increases the rate formation of the Caro's acid. A very simple and desirable method of discharging the hydrogen peroxide and sulfuric acid from the feel lines into the reactor conduits is for the inlets of the hydrogen peroxide and sulfuric acid reactor conduits to be each expanded, optionally in a cylindrical shape or in a conical shape (funnel form) as taught in U.S. Pat. Nos. 5,439,663 and 5,470,564 so that none of the reaction mixture can overflow and enter into the feed lines of either the hydrogen peroxide and/or sulfuric acid. The ends of the reactor conduits located downstream from the inlets direct the solutions without substantial premixing directly into the baffled, mixing reactor, desirably a pipe-like or tube reactor the baffles convert the energy of the flowing fluid to promote mixing. Most preferably a commercial static mixer such as those available from Koch Engineering Corporation. The mixing reactor may be either vertically oriented, horizontally oriented or any skew angle intermediate these two extremes and is fed by gravity from the reactor conduits. Normally static mixers contain several mixing elements which will ensure a complete mixing and reaction of the two reagents. A very desirable embodiment is for the reactor conduits to be in the form of a single “funnel form” partitioned vertically into a first reactor conduit and a second reactor conduit, the partition reaching to the baffled portion of the mixing rea
FMC Corporation
FMC Corporation
Griffin Steven P.
Vanoy Timothy C
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