Patented Jan. 14, 1936 2,027,838 UNITED STATES PATENT OFFICE 202,838. sTABILIZING HYDROGENPEROXDE solu TONS WITH PYROPHOSPORIC ACD Joseph S. Reichert, Niagara Falls, N.Y., assignor to E. I. du Pont de Nemours & Company, Inc., Wilmington, Del, a corporation of Delaware 49 No Drawing. Application September 12, 1932, Seria No. 632,796 8 Claims. (CI. 23-251) This invention relates to the stabilization of shipped in commerce, i.e. about 10-volume or hydrogen peroxide solutions and more specifi-. higher, and to provide a high concentration per cally to the stabilization of the high concentra oxide solution which can be shipped and stored tion acid hydrogen peroxide Solution as COm for relatively long periods without serious losses. monly transported. I have discovered that pyrophosphoric acid is In general it should be stated that hydrogen an excellent stabilizer for hydrogen peroxide sor peroxide solutions are of two kinds, the first lutions of the nature described above. By stabil those which are transported and which are usu izing hydrogen peroxide solutions with pyropros ally of relatively high concentrations, e. g. 10 phoric acid, the combined stabilizing effect of voluné or stronger, and which have been acidi the hydrogen ion and the pyrophosphate ion is 10 10 fied in Order to have maximum stability, and obtained. Hydrogen peroxide solutions stabilized secondly, the more dilute, alkaline hydrogen per with pyrophosphoric acid show only very small Oxide Solutions, losses when stored for long periods of time even bleaching purposes.as . .are . commonly used for at temperatures higher than the normal storage 5 For bleaching purposes it has been found more temperature. Satisfactory to operate with solutions which are In carrying out the present invention, a Small 5 of an alkaline nature, since the alkalies assist amount, for example, 0.025 to 1.5 grams or more in removing various impurities. Such alkaline of pyrophosphoric acid is dissolved per liter of solutions, however, are more unstable than the hydrogen peroxide Solution to be stabilized. If 20 acid Solutions and hence, it has been the common the peroxide solution is not at the optimum acid 20 practice to add various stabilizers to the alkaline ity for stabilization, the pH is adjusted to the solution to prevent undue loss of peroxide. proper value by acids or alkalies as required. Acidified hydrogen peroxide solutions, how The results thereby obtained are shown in the ever, are more stable than the alkaline solutions following examples: 25 and it is therefore preferred that for transpor Eacample tation and storage purposes the solutions be of an acid character. However, merely acidifying To portions of freshly prepared commercial the peroxide with a mineral acid does not im . hydrogen peroxide solution of 100-volume. part Sufficient stability for transportation and strength, varying amounts of pyrophosphoric 30 storage purposes. Certain additional stabilizers acid were added. The acidity of the peroxide was so haye been proposed for Such acid, relatively high adjusted after adding the pyrophosphoric acid concentration, peroxide solutions but they have to a pH of about 2. been of an unsatisfactory nature for several rea These portions were stored at a constant tem sons. Many organic stabilizers are very effective perature of 32° C. for a period of three months, 35 in retarding the decomposition of impure hydro-. together with other portions containing no sta gen peroxide and their use adds very little to the bilizer. During this time, at intervals of 30 days, peroxide production costs. However, organic the solutions were analyzed to determine the loss stabilizers have undesirable properties. Mate in volume concentration. The results appear in rials such as salieylic acid or acetanilide form the following table: 40 colored solutions if there are traces of iron salts - 10 in the bleach bath in which the peroxide is sub sequently used, or the peroxide solution itself Volume loss during storage at 32° C. may become colored, due to the oxidation of Concentration of PO these organic stabilizers. Furthermore, organic 30 days 60 days 90 days 45 stabilizers are decomposed if the concentrated None.------32. 53. (5 peroxide solutions are heated or allowed to stand 0.7 gram per liter.-- 2. 4. for long periods and thereby lose their stabiliz 1.5 grams periter. 2. 3 ing properties. Inorganic stabilizers are, in general, not as ef These results indicate that pyrophosphoric acid 50 fective as Organic stabilizers. The solubility of added in small amounts has a marked stabilizing 50 many inorganic compounds in strong acid per effect on acid hydrogen peroxide solutions, and oxide solutions is small so that either cloudy also that additions of 0.7 gram per liter or more solutions are obtained, or it is impossible to in tend to produce low losses for periods of over 2 troduce enough stabilizer. Many inorganic ma months at 32 C. . terials as for example, ferric chloride, cause acid Eacample II 55 65 peroxide solutions to decompose rapidly. The object of this invention is to provide a To portions of freshly prepared commercial hy stabilizer for acidified hydrogen peroxide solu drogen peroxide solution of 100-volume strength tions and more particularly for a hydrogen per an equivalent to 0.4 gram per liter of pyrophos oxide solution of a concentration as ordinarily phoric acid as NaPao.10H2O was added. The so 2. 2,027,888 pH was adjusted to 4.3 after the addition of the peroxide solution a salt of the acid, for example, NaPO7.10H2O, alkali metal pyrophosphate or alkali metal acid This portion and a portion of unstabilized hy pyrophosphates, together with sufficient of a drogen peroxide were stored at a temperature of strong acid to acidify the solution, or, pyrophos 5 32' C. for 30 days. At the end of this storage phoric acid itself may be added to the acid solu period both samples were analyzed for the loss tion. in volume concentration. The results appear in fam aware that it has been previously pro the following table: - posed to stabilize bleach liquors over a pH range of 7-10 with an alkali pyrophosphate. Here, 0 Wolume loss however, the beneficial effect of pyrophosphoric 0 Concentration of HPO E.g.store acid is not secured because care is taken to main for 60 days tain the solution within the definitely alkaline pH range of 7-10. Thus, the stabilizer is not py rophosphoric acid but is an alkaline salt of the acid. 15 There are four alkali pyrophosphates of vary The results of this experiment show the effec ing acidity: NaPOt, Na2HPaOt, Na2HP2O, and tiveness of Small amounts of HAP2O7 as a stabilizer NaH2Pao. Computations from ionization data for hydrogen peroxide solutions. indicate that the last three of this group have 20 a pH (in water solutions) below 7, and that the 20 Ecample III pH of Na4P2O7 is above 7. In the case of COm To Samples of 50-volume impure grade hydrogen mercial hydrogen peroxide solutions containing peroxide, sodiurn pyrophosphate equivalent to 0.5 ionic impurities, I do not know the exact state gram per liter was added, and the solution ad of ionization, but I have found that effectiveness - 25 justed to a pH of 5 with HaSO4 or NaOH. Other of my pyrophosphoric acid stabilizer is due to 25 . Samples of the same peroxide containing no sta pyrophosphate ions in the presence of hydrogen bilizer Were adjusted to a pH or 5 and tested with . ions, and, further, that alkali metal ions which the stabilized samples. All samples were main are undoubtedly present in, for example, hydro tained at a constant temperature of 32 C. and gen peroxide solutions of pH 5 have no stabiliz the rate of oxygen evolution was measured. From ing action on hydrogen peroxide solutions. Thus, 30 these measurements the losses in volume concen the effectiveness of this stabilizer can only be tration equivalent to the loss over a period of 30 secured in solutions which are acid," i.e. have a days were calculated. These results appear in pH of less than 7. 35 the following table: I have found pyrophosphoric acid to be of - special utility in stabilizing hydrogen peroxide 35 Equivalent Solutions for storage purposes at Ordinary tene 30 day, 32° C. Concentration of NaPOr.10Hso volume con peratures. I find it of considerable utility when centration used in combination with other stabilizers which loss also have a specific effect in stabilizing hydrogen peroxide at relatively high temperatures. . 40 Non------The exact amount of pyrophosphoric acid 0.5 gram periter (equivalent to 0.2 grams PO). needed to Secure maximum stability will vary over a wide range dependent on several factors These results indicate that HaPaO produced by Such as impurities in the peroxide and other dis 45 adding NaPaO7 to an acid hydrogen peroxide so Solved natter. I have used as little as 0.025 45 lution, is an effective stabilizer in impure grades gram per liter and up to 1.5 grams per liter, but of peroxide solutions. do not wish to be limited in the amount to be Example V illustrates the influence of hydro added because of the variations found. gen ion concentration on the effectiveness of my As shown in the foregoing, the effectiveness 50 stabilizer. of pyrophosphoric acid as a stabilizer exists in 50 Eacample IV acid solutions, and in general, the best results A series of 00-volume hydrogen peroxide solu are secured with pyrophosphoric acid alone when tions having varying degrees of acidity were pre the stability of the solution lies in the pH range 55 pared and 0.66 gran per liter of pyrophosphoric of about .5-4.5. However, I have found pyro acid was dissolved in a portion of each solution, phosphoric acid alone effectively stabilizes hy 55 These solutions were tested as in Example drogen peroxide solutions over the pH range with the following results: between 1 and substantial neutrality. Hence, in this specification, and in the appended claims, when the pH is defined as being between 1 and 7, it means up to but not including 7. While the 60. most effective range for pyrophosphoric acid alone is between about 1.5 and 4.5, when pyro phosphoric acid is used in combination with other stabilizers, the most effective pH range may be altered. Thus, with solutions of tin com 65 pounds as disclosed and claimed in my co-pend ing application, S. N. 572,721, fled Nov. 2, 1931, Patent No. 1,958,204, May 8, 1934, the most-effec i tive pH range is between about 3.5 and 6. Fur. thermore, the most suitable pH of the peroxide 70 A convenient method of securing the pyrophos solutions and the exact amount of pyrophos phoric acid is by heating 85% orthophosphoric phoric acid to be used for any specified lot of .acid to a loss in weight of about 20%. Peroxide solutions must be adjusted in accord The stabilizing action of pyrophosphoric acid ance with other variables such as impurities pres 75 may thus be secured by adding to the hydrogen ent in peroxide solutions, the nature of storage 76 2,097,888 3 0.025 gram to 1.5 grams per liter of solution, and Ör shipping containers, And the storage condi then adjusting the acidity of said solution to tions. pH value of between 1 and 7. What1. A method is claimed of stabilising is, a hydrogen peroxide 5. A process for preparing a stable solution of solution which comprises adding thereto a sta hydrogen peroxide which comprises the steps of bilizer which consists of a small amount of a adding to the hydrogen peroxide solution a sta pyrophosphate, and then adjusting the acidity of bilizer which consists of a pyrophosphate in an said solution to a pH of between 1 and 7. amount chemically equivalent to from 0.025 2. A method of stabilizing a solution of hydro gram to 1.5 grams of pyrophosphoric acid per O gen peroxide which comprises adding thereto a liter, and then adjusting the acidity of the solu- 10 stabilizer which consists of a small amount of tion to a pH value of between 1.5 and 4.5. pyrophosphoric acid, and then adjusting the 6. A homogeneous, stable solution of hydrogen ity, said solution to a p value of between peroxide of an acidity equivalent to a pH value and 7. of less than 6 which contains as a stabilizer a 6 3. A method of preparing a stable, low residue, small amount of pyrophosphoric acid. . 100 volume solution of hydrogen peroxide which 7. A homogeneous, stable solution of hydrogen comprises adding to the hydrogen peroxide solu peroxide of an acidity equivalent to a pH value of between 1 and which contains, as a stabi tion a stabilizer which consists of pyrophosphoric lizer, pyrophosphoric acid in an amount ranging acid in amounts, ranging from 0.025 gram to 15 from 0.025 gram to 1.5 grams per liter. 90 grams per liter of solution, and then adjusting 8. A homogeneous, stable solution of hydrogen the acidity of said solution to a pH value of peroxide of an acidity equivalent to a pH value between and 7. of between 1.5 and 4.5 which contains as a sta 1004. volumeA method solution of preparing of hydrogen a stable, peroxide low residue, which bilizer pyrophosphoric acid in an amount ranging comprises the steps of adding to the hydrogen from 0.25 gram to 1.5 grams periter. peroxide solution a stabilizer which consists of pyrophosphoric acid in an amount ranging from JoSEPH. S. REICHERT. Certificate of Correction January 14, 1936. Patent No. 2,027,838. JOSEPH S. REICHERT It is hereby certified that error appears in the printed specification of the above . . numbered patent requiring correction as follows: Page 2, first column, lines 59 to 63, inclusive, under Example IV, strike out the heading to the table and insert instead the following: Equivalent30Day Volume Concentration Loss Hydrogen on Concentration (pH) Unstabilized Solutions Stabilized Solutions and that the said Letters Patent should be read with this correction therein that the sameSigned may conform and sealed to the this record 25th dayof the of caseFebruary, in the A.Patent D. 1936. Office. (sRAL) LESLIE FRAZER, Acting Commissioner of Patents. Certificate of correction Patent No. 2,027,838. January 14, 1936. JOSEPH S. REICHERT It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 2, first column lines 59 to 63, inclusive, under Example IV, strike out the heading to the table and insert instead the following: Equivalent 30 Day Volume Concentration Loss Bydrogen Ion Concentration (pH) --- Unstabilized Solutions Stabilized Bolutions and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. Signed and sealed this 25th day of February, A. D. 1936. s.At LESLIE FRAZIER, Acting Commissioner of Patents.