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 of 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. With temperature substan out the method of the invention, it will be apparent to tially above these, products yields are reduced substan those skilled in the art that other peroxidic compounds tially. The lower operating temperature limit is that at capable of forming either hydrogen peroxide or perox which any of the reactants or intermediate reaction ymonosulfuric acid may be used as well. Examples of products are solidified and/or precipitated from the re such compounds are potassium monopersulfate dis 35 action mixture. In general, this minimum operating solved in water and treated with free HSO, and sodium temperature at which all the reactants are in the liquid perborate which upon treatment with HSO, forms free (or gaseous) phase will lie above the freezing point of any of the reactants, particularly the water. Since no H.O.The sulfur... ' trioxide reactant can be provided for the especial advantages attend the use of lower tempera reaction in either gaseous or liquid form or in associa 40 tures (e.g., 0°C), it will ordinarily be preferred to use tion with sulfuric acid as commercially available ole temperatures which are nearly ambient (ca. 20°C). ums. Though in gaseous form pure sulfur trioxide can It will be noted that any water present in the active be used, it will ordinarily be preferred to use suitable oxygen precursors does not partake in the formation of mixtures with gases which are inert to the active oxygen H2SOs. It does not however, absorb SO to form HSO reactant. By this means, polymerization of the SOa is 45 for which reason the amount of SOs in the reaction. reduced. Suitable inert gases for this purpose include mixture is adjusted upward in response to higher dilu nitrogen, oxygen, air, or their mixtures. It is likewise tions of active oxygen precursors in the system. preferred that the sulfur trioxide be stabilized to reduce In carrying out the process of the invention, the reac freezing and polymer formation. Thus, most of the sul tion may be carried out batchwise, intermittantly or fur trioxide useful for the process will be stabilized by SO continuously as may be desired. However, it is impor means of such materials as phosphoric acid, tin com tant that the SOs be added to the active oxygen precur pounds, boron oxide, phosgene, SiCl, Na2SiF6, di sors or that they be mixed simultaneously to avoid ad methyl phthalate, methylated chlorosilanes, dimethyl verse equilibrium conditions. Thus, gaseous SO will be sulfate, SnCl4, etc. bubbled through the active oxygen precursors, or liquid The relative initial amounts of peroxymonosulfuric 55 SO3 or oleum will be added to the active oxygen pre acid, sulfur trioxide and hydrogen peroxide are gov cursor with stirring to minimize localized areas in erned by the above-referred basic reactions. Thus, it is which there are high concentrations of SO vis-a-vis ac preferred that the mol ratio of SOs to HO, be at least tive oxygen precursors. 2 and the mol ratio of SO to HSOs be at least 1 in When the process is run on an intermittant basis, it is order to obtain optimum yields of product. It has also 60 possible to encounter an active oxygen precursor dis been found that the SO:HO, and SOHSOs ratios persion containing H2O2, HSOs, HSOs, HSO, and should not be too high lest substantial product instabil some free SO3. Water may be absent in such a system. ity arise. r In this case, the amount of additional SOs to be mixed In this latter regard, it has been found that the opti with the above dispersion to convert the HSOs and mum ratio of SOa to the active oxygen precursors de 65 H2O, into H2SOs will be equal to the amount calcu pends substantially upon the extent to which water is lated from the suitable "X" value of the general for present in the system. In most instances, this is an in mula, less the total amount of free SOs initially present verse function of the concentration of active oxygen in the active oxygen dispersion. 3,927,189 5 6 The central product of the process of the invention, crop yield of this product based on starting H2SOs was POSISA, is present in the reaction mixture in disper 78 percent of the theoretical. sion with POMOSA and any unreacted HO, and reac tant carriers such as water and sulfuric acid. PODISA, EXAMPLE 3 which is a white crystalline solid, can be readily sepa 5 Gaseous SOa carried by dry N, gas was bubbled into rated from the reaction mixture by lowering the tem 95.7 g of peroxymonosulfuric acid containing 66.2% perature of the reaction mixture to below about 20°C at HSOs, 3.9% HO, 8.8% HO and 21.1% HSO4. The which temperature PODISA is precipitated from solu reaction temperature was maintained at 15-20°C. The tion. However, because of relative instability of this total amount of SOs required according to the general product, it will usually be either left in the reaction mix 10 formula was 100 g (1.24 moles). When about 100g of ture or redissolved in water for subsequent use. SO were added to the reaction mixture, there was for It has been found that several quite important salts of mation of solid in the reaction mixture and there was PODISA can be made directly from the reaction mix temperature rise of about 7°C due to heat of crystalliza ture. In particular, ammonium, alkali metal and alka tion of HSOs. The reaction was stopped. The weight line earth metal salts may be prepared by adding the 15 of the batch was 196 g and the active oxygen analysis of corresponding carbonate, hydroxide, oxide or sulfate the reaction mixture was 37.2% HS2O8, 7.4% HSOs, thereeof to PODSA in solution. Of the alkaline earth 0.2% HO. This amounted to 73.0 mol %, HSOs, 24.7 metal salts, the calcium and magnesium salts are of mol % H2SOs and 2.2 mol % H.O. principal interest at this time. The ammonium, sodium The yield of H2S2O3 from HSOs -- H2O2 was 87.9 and potassium salts are, as mentioned previously, of 20 percent of theory. substantial commerical importance. In the foregoing example, from values of A = 4.94 The PODISA salts are readily prepared by addition of and B = 83.9, X was determined to be 1.32. Thus, the the above-described metallic compounds to either the weight ratio of sulfur trioxide to the total weight of ac reaction mixture or to solutions of the essentially pure tive oxygen precursors and water was 1.0X. acid. In the former case, because both POMOSA and 25 the salts thereof are quite soluble in water and because EXAMPLE 4 the corresponding PODISA salts are relatively less sol This example describes the formation of HSOs from uble, the PODISA salts are readily precipitated in crys H2O2. talline form and may be easily separated from the reac 30 Stabilized, liquid SO was added to 48.2 g of 70.6% tion mixture by such methods as filtration, centrifuga Albone hydrogen peroxide (one mol); 116 ml (216 g, tion, decantation and the like. 2.70 mols) of SO were added in about six hours. (SOs The invention can be more thoroughly understood by required according to calculations - 2.79 mols.) The reference to the following examples: reaction temperature was 15-3°C. 35 The final product weighed 264 g and showed 61.4% EXAMPLE 1. HSOs, 4.75% HSOs and 0.25% H.O.; the active oxy Gaseous SOs carried by dry N, gas was slowly bub gen distribution was 84.6 mol % HSO 11.1 mol % bled in 100 g of peroxymonosulfuric (HSOs) acid solu HaSO and 4.3 mol % H.O. The yield of HSOs from tion containing 71.3% HSOs, 16.2% HSO, 3.4% HO, HO, was 94% of theory. and 9.9% HO. The reaction temperature was main 40 In the foregoing example, from values of A=70.6 and tained at 20-25°C. After about 4% hours of SO treat B=0, X was determined to be 4.63. Thus, the weight ment, the reaction was stopped and the reaction mix ratio of sulfur trioxide to the total weight of active oxy ture analyzed. The analysis was: 18.3% HSOs, 12.4% gen precursors and water was 0.97X. HSO, 0.3% H.O., 62.02% HSO, 6.98% HO. The ac EXAMPLE 5 tive oxygen (A.O.) distribution was: 44.5 mol % 45 HSO, 51.3 mol % HSOs, and 4.2 mol % HO. The This reaction exemplifies the effects of excess SO on weightincrease in the batch due to SOs was 70.4 grams. HSOs stability. In the foregoing example, from values of A = 4.0 and To 48.2 g of 70.6% HO, (one mol) was added drop B = 84.3, X was determined to be 1.3. Thus, the weight wise freshly distilled liquid SOs. The amount of SOs cal ratio of sulfur trioxide to the total weight of active oxy 50 culated to give optimum yield of stable HSOs was gen precursors and water was 0.54X. 2.786 mols (223 g). Instead, 290 g of SOs was added over a period of about three hours. When SO added EXAMPLE 2 was about 193g, there was separation of solid in the re One hundred twenty grams of the reaction product of action mixture. When SO3 was continued, there ap Example 1 containing 18.3% HSOs was added slowly 55 peared distinct change in the reaction mixture. At to 250 ml of ice cold distilled water. The temperature about 270 g SOs, there was continuous bubbling in the was maintained at 0°-5°C. To this was added dropwise, reaction mixture without any (exothermic) tempera with stirring, at 0°-5°C 50.7 wt % KOH solution. Solid ture change. After adding 290 g of SOs, the reaction precipitate began to appear when 33.4 g of KOH solu mixture was set aside for about 17 hours at room tem tion was added. KOH addition was stopped, the reac 60 perature and analyzed. It contained no active oxygen tion mixture stirred for 42 hour and solid filtered off. due to H2O, HSO5 or H2SOs, showing total decompo The solid was then washed with two ice cold (50 ml) sition. water washes and one (50 ml) absolute ethanol wash. As against this, the HSOspreparation of Example 4, The product was dried in a forced air oven at room when analyzed after keeping for about 17 hours at temperature overnight. 65 room temperature, showed 62.4% HSOs. There was The ary product weighed 24.1 g and showed an ac thus no loss of H2SOs content of the reaction. tive oxygen content of 6.0 percent. X-ray crystallo In the foregoing example, from values of A = 70.6 graphic analysis confirmed it to be KSOs. The first and B = 0, X was determined to be 4.63. Thus, the 3,927, 189 7 8 weight ratios of sulfur trioxide to the total weight of ac 4. Add 10 ml of 50% KI solution. tive oxygen precursors and water was 1.3X. 5. Add about 4 g (NH4)2SO, and stir to dissolve. 6. Add 1 ml of 2% ammonium molybdate solution. EXAMPLES 6, 7, 8 7. Stopper the flask and heat on water bath (cau Peroxydisulfuric acid was prepared by adding liquid, 5 tion) to 50°C and keep for 10 minutes. stabilized SOa to hydrogen peroxide. It will be noted 8. Cool the flask to room temperature and titrate the that in these examples of the weight ratio of SOs to the liberated iodine against 0.1 N sodium thiosulfate. total weight of active oxygen precursors and water was 9. Record thiosulfate titer as D. about 1.0X. A ratio of from about 0.7X to about 1.1X is preferred for economic reasons. The following are 10 Calculations details of reaction conditions and results. W = Sample wt for titration A (g) TABLE 1 Reaction H2O2 SO Yield Based Temp. Concen. 3. on Reacted Ex. 4°C mo % by Wit Used mols g HO, 6 35 70.6 48.2 2.79 223 68.9 7 25 1. 70.6 48.2 2.83 226 84. 8 5 .25 20 42.4 2.48 199 90. Final Product A.O. DISTRIBUTION Weight Ratio of SO to (mol%) Total Weight of Active Ex. H2S2O HSOs H2O, A B X Oxygen Precursors & HO 6 68.4 303 13 70.6 0 4.63 OOX 7 86.2 138 O 70.6 0 4.63 OX 8 76.1 23.9 O 20.0 0 4.5 .04X

W = Sample wt for titration D (g) ANALYTICAL PROCEDURE A ml = 0.1 N NaOH titer (for HSO) In the foregoing examples, the procedure used for 30 B ml - 0.1 N ceric sulfate titer (for HO) analysis of reaction mixtures was as follows: C ml = 0.1 N NaS0 titer (for HSOs) Analysis of HSO, H.O., HSOs and the total of D ml = 0.1 N NaSOs titer (for total peroxygen) H2O, HSOs and HSOs was performed by a series of four titrations in the precise sequence shown. D X W. 35 D ml = converted D = D Titration A (Analysis of HSO) 1. Accurately add about 0.2-0.3 g (5–8 drops) of (A+B+ - D x 0.49 sample (weighed by difference) to a 500 ml beaker %6 HSHSO W containing about 150 ml of slurry of washed cracked BX 0.17 ice. Stir the mixture. 40 % Ho, - - - 2. Add 3 drops of methyl red indicator and titrate with 0.1 N NaOH to yellow or colorless end point. Cx 0.57 3. Record O. 1 N NaOH titer as A. % Ho, - - - (D - (B+C) x 0.97 Titration A (Analysis of H.O.) 45 % HSO = W 1. Immediately take the above titrated solution and % HO = 100 - (% H2SO -- % HO +% HSO -- % HSO) add 10 ml of 20% w/w HSO. It will turn pink. 2. Add one drop of ferroin indicator and titrate with 0.1 N Ce(SO) until color changes from orange to ei If there is excess free SOs in the system, negative ther colorless or faint blue. (Do not add excess ceric 50 numbers are obtained for % water. In this case the solution as it may interfere with the titration A). water content is zero and the SO content is 3. Record ceric titer as B. 80 X (%HSO -- %HO. - %HSO +%HSO - 100) Titration A (Analysis of H2SOs) % SO = - - - 1. Add immediately to the above titrated solution 10 55 ml of 25% KI and titrate with 0.1 N NaSO until the The above calculations are based on 0.1N titrants in color starts to fade. Then add 1 ml 1% starch solution all titrations. and continue titration until the blue-black disappears. I claim: The final color will be yellow-orange. 1. A method for making peroxydisulfuric acid com 2. Record thiosulfate titer as C. 60 prising the steps a. forming a dispersion of sulfur trioxide and active Titration D (Analysis of total HO, HSOs and HSOs) oxygen precursors selected from the group consist 1. Start with a fresh sample. ing of hydrogen peroxide, peroxymonosulfuric acid 2. Add an accurately weighed amount of about and mixtures thereof in which the ratio by weight 0.2-0.3 g (5-8 drops) of sample to 150 ml slurry of 65 of the sulfur trioxide to the sum of the weight of the washed cracked ice in a 500 ml Erlenmeyer flask with active oxygen precursors and any water present stopper. Stir the mixture. corresponds to from about X-0.015A - 0.0046B 3. Add 10 ml 20% HSO. to about 1.5X, wherein X is defined by the relation 3,927, 189 9 10 ship (0.00264A - 0.03741B + 4.4434), wherein A group consisting of the carbonates, hydroxides, oxides is the % by weight hydrogen peroxide B is the % by and sulfates of a cation selected from the group consist weight peroxymonosulfuric acid, the basis of the ing of ammonium, alkali metals and alkaline earthmet above relationships being predicated upon the sum als. of the weight of the active oxygen precursors and 5 4. The method of claim 3 in which the compound any water which is present; and (b) maintaining the added to the reaction mixtures is an hydroxide. dispersion in the liquid phase at a temperature no 5. The method of claim 3 in which the compound higher than about 45°C until the active oxygen dis added to the reaction mixture is a carbonate. tribution of the final reactant mixture therefrom is less than about 67 mole % active oxygen precursors 10 6. The method of claim 3 in which a salt of peroxydi and more than about 33 mole % peroxydisulfuric sulfuric acid is recovered from the reaction mixture by acid. precipitation of the salt from the reaction mixture. 2. The method of claim 1 in which the ratio by weight 7. The method of claim 1 in which the peroxydisulfu of sulfur trioxide to the sum of the weights of the active ric acid is recovered from the reaction mixture by low oxygen precursors and any water present corresponds 15 ering the temperature of the reaction mixture to below to from about 0.7X to about 1.1X. about 20°C, thus precipitating the acid from the reac 3. The method of claim 1 in which a salt of peroxydi tion mixture, and separating the precipitated acid from sulfuric acid is prepared from the reaction mixture by the reaction mixture. addition thereto of a compound selected from the ck k - k sk 20

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