United States Patent (19) [11] 3,927,189 Jayawant (45) Dec. 16, 1975 54 METHOD FOR MAKING PEROXYDSULFURIC ACID AND SALTS OTHER PUBLICATIONS THEREOF Price, “Per-Acids and Their Salts,' Longmans, Green 75 Inventor: Madhusudan D. Jayawant, & Co., London, 1912, p. 22. Hockessin, Del. Primary Examiner-Earl C. Thomas 73 Assignee: E. I. Du Pont de Nemours & Co., Wilmington, Del. (22 Filed: Apr. 12, 1974 57 ABSTRACT A non-electrolytic process for making peroxydisulfuric 21 Appl. No.: 460,610 acid by the reaction of sulfur trioxide with peroxy monosulfuric acid and/or hydrogen peroxide under (52) U.S. Cl. ................................................ 423/513 defined conditions by which quite high yields of per (51 int. Cl.’.................... C01B 15/06; COB 15/08 oxydisulfuric acid are obtained. Ammonium, alkali 58 Field of Search............................. 4231513, 52 metal and alkaline earth metal salts of peroxydisul furic acid are produced by treating the acid with the 56) References Cited corresponding hydroxide, oxide, sulfate or carbonate. FOREIGN PATENTS ORAPPLICATIONS 7 Claims, No Drawings 967,951 8/1964 United Kingdom................. 4231513 3,927,189 1. 2 up to about 5% by weight peroxydisulfuric acid is ob METHOD FOR MAKNG PEROXYDSULFURC tained as an unwanted byproduct in the manufacture of ACID AND SALTS THEREOF peroxymonosulfuric acid by reaction of concentrated hydrogen peroxide and oleum. Leaver et al. in U.S. Pat. BACKGROUND OF THE INVENTION No. 3,351,426 disclose that a mixture of hydrogen per 1. Field of the Invention oxide, bisulfates and peroxymonosulfates is converted The invention relates to the manufacture of peroxy to peroxydisulfates upon heating to 75-300°C. under disulfuric acid by the reaction of sulfur trioxide with peroxymonosulfuric acid and/or hydrogen peroxide vacuum. Similarly to the D'Addieco et al. patent cited and also to the manufacture of certain metal salts of O above, U.K. Pat. No. 967,951 to Marshall discloses that peroxydisulfuric acid. 0-30.5 mole % peroxydisulfuric acid may result from 2. Description of the Prior Art the reaction of concentrated hydrogen peroxide and Peroxydisulfuric acid, sometimes known as Mar gaseous sulfur trioxide at 20-50°C. shall's acid, is a white crystalline solid having a melting The invention therefore provides a process by which point of 65°C. It is, of course, a quite active and rather 15 peroxydisulfuric acid (PODISA) can be made nonelec unstable oxidizing agent containing 8.2% by weight ac trolytically in economically quite high yields and in tive oxygen. Because of its relative instability and mois such form that the acid itself may be used directly for ture sensitivity, peroxydisulfuric acid is seldom iso the preparation of the many useful salts thereof. lated. Instead, it is synthesized and used in solutions More particularly, the invention provides a process chiefly as an intermediate to make hydrogen peroxide. 20 for making peroxydisulfuric acid comprising the steps Heretofore, peroxydisulfuric acid has been made al of most entirely by electrolysis of sulfuric acid, as follows: a. forming a dispersion of sulfur trioxide and active ox ygen precursors in which the ratio by weight of sulfur 25 lectrical trioxide to the sum of the weight of the active oxygen 2HSO El H.S.O. + H. precursors and any water present corresponds to from about X - 0.015A - 0.0046B to about 1.5X, Furthermore, as mentioned above, essentially the only wherein X is defined by the relationship (0.00264A - use of the acid has been as an intermediate in the man 0.03741B -- 4.4434), wherein A is the 96 by weight ufacture of hydrogen peroxide, viz.: hydrogen peroxide and B is the % by weight peroxy monosulfuric acid, the basis of the above relation HSO + HO - HSOs -- HSO, ships being predicated upon the sum of the weight of HSO + HO HO -- HSO, the active oxygen precursors and any water which is However, the corresponding salts of peroxydisulfuric 35 present; and acid are used extensively in industry as polymerization b. maintaining the dispersion in the liquid phase at a catalysts, laboratory oxidizing reagents, for soap and temperature no higher than about 45°C. until the ac fat bleaching, oxidation of dyestuffs, treatment of metal tive oxygen distribution of the final reactant mixture surfaces and as maturing agents for wheat flour. Of the therefrom is less than about 67 mole % active oxygen many salts of peroxydisulfuric acid, ammonium, so 40 precursors and more than about 33 mole % peroxydi dium and potassium are by far the most widely used. Of sulfuric acid. particular importance is the use of potassium peroxydi sulfate as a free radical initiator for the polymerization DEFINITIONS of wide variety of monomers, but especially as a com The term “active oxygen' (A.O.) as used herein ponent of redox catalyst systems and as promotor for 45 means the available oxygen, expressed in terms of the polymerization of styrene-butadiene monomer sys atomic oxygen having a gram equivalent weight of tems. In this latter use, the salt is customarily referred 8.00, contained in peroxidic compounds such as perox to rather ambiguously as "potassium persulfate.' ides, perborates, percarbonates, persulfates and the Nevertheless, these important derivatives of peroxy disulfuric acid have notheretofore been made from the 50 like. The A.O. value is a measure of the oxidizing peroxydisulfuric acid, but from ancillary materials. For power of such compounds. Thus, pure HO has an example, ammonium peroxydisulfate is made by anodic A.O. content of 47.0% by weight. electrolysis of ammonium bisulfate and potassium per The terms “active oxygen distribution' as used oxydisulfate is made by the addition of potassium bisul herein means the distribution on a molar basis of the fate or potassium hydroxide to the ammonium peroxy 55 components of the reaction mixture containing active disulfate electrolysis liquors described above. Thus, as oxygen in a given system. Within the context of the in a practical matter, the manufacture of peroxydisulfuric vention active oxygen distribution (A.O. Distribution) acid and its salts has been limited to electrolytic pro would be limited to the molar proportions of the hydro CeSSS gen peroxide, peroxymonosulfuric acid and peroxydi To a substantial degree, the previous lack of indus 60 sulfuric acid contained in the system in question. trial interest in peroxydisulfuric acid (also often re The term "active oxygen precursors' as used herein ferred to as perdisulfuric acid) is reflected in the pub refers to peroxymonosulfuric acid or hydrogen perox lished literature. For example, in Jones, W. N., Inor ide or to mixtures of the two. ganic Chemistry, Blakiston Co., 1947, pp. 418-19. The The term "dispersion" as used herein refers to liquid reaction of hydrogen peroxide and sulfur trioxide to 65 dispersions including both homogeneous dispersions form peroxydisulfuric acid is disclosed broadly without such as solutions and non-homogeneous dispersions reference to reaction conditions or yields. In U.S. Pat. such as solid/liquid, liquid/liquid and gas/liquid mix No. 2,926,998 to D'Addieco et al., it is disclosed that tures and combinations of such type of dispersions. 3,927,189 3 4 precursors in the aqueous solution used. Thus, if the DETAILED DESCRIPTION OF THE INVENTION amount of water in the reaction system is high, as when The process of the invention proceeds according to quite dilute active oxygen precursor solutions are used, the following described basic reaction: the SO:active oxygen precursor ratio must be consid - SO3 + H2SO (2 H2SOs erably higher than when more concentrated active oxy Notwithstanding the fact that the basic reaction pro gen precursor solutions are used. In particular it has ceeds from the peroxymonosulfuric acid (POMOSA), been found that peroxydisulfuric acid is produced with because of the rather low stability of this material, economical yield and stability if the weight ratio of it will, as a practical matter, be preferred to carry out added SO to the sum of weights of active oxygen pre the reaction concurrently with the preparation o f 10 cursors and water, if any, corresponds to from about X fresh POMOSA from hydrogen peroxide and sulfur - 0.015A - 0.0046B to about 1.5X, wherein X is de trioxide, as follows: fined by the relationship (0.00264A - 0.03741B + HO, +SO HSOs 4.4434), wherein A is the weight percent of hydrogen HSO - SO HSOs peroxide and B is the weight percent of peroxymono HO -- 2SO HSO 5 sulfuric acid in the dispersion of hydrogen peroxide, In carrying out the above-noted reactions, either 100% hydrogen peroxide or aqueous solutions thereof peroxymonosulfuric acid and water, if any. may be used. As a matter of general practice, aqueous Because the reactions used here take place in the liq peroxide solutions containing 10-90 percent by weight uid phase or at a gas-liquid interface, it is apparent that and preferably 35-90 percent by weight hydrogen per the pressure of reaction is not a significant operating oxide will be used since they are more economical and variable except as it may affect the fugacity of the SOa are readily available in commercial quantities. It is pre gas and thus the efficiency of the process as regards ferred that the hydrogen peroxide be stabilized to re SO utilization. Therefore, to reduce SO losses, it is duce decomposition in handling and storage with hy preferred to operate the process of the invention at a drogen peroxide stabilizers such as ethylenediamine 25 pressure of one atmosphere or higher. tetraacetic acid, diethylenetriamine pentaacetic acid, Though the temperature of the process is not critical sodium stannate, ammonium nitrate, organic phospho in the sense of mere operability, it is nevertheless im nates and magnesium compounds. portant that the process be run at a temperature no Though hydrogen peroxide and/or peroxymonosulfu higher than about 45°C, and preferably 35°C, to main ric acid are the preferred starting materials for carrying 30 tain good PODISA yields.