Patented June 11, 1935 2004.809 UNITED STATES PATENT OFFICE

y 2,004.809 STABLZNG BY DROGEN PERoxIDE SOU TON'S WITH PYROPOSPORC; ACD PLUS A T N COMPOUND Harvey N. Gilbert and Joseph S. Reichert, Niagara Falls, N.Y., assignors to E. I. duPont de Nemours & Company, Inc., Wilmington, Del, a corporation of Delaware No Drawing. Application December 1, 1932, Serial No. 645,324 13 Claims. (CL 23-251) This invention relates to the stabilization of example iron and copper salts. A few inorganic hydrogen peroxide solutions and more specifical stabilizers have advantages over organic stabiliz ly to the stabilization of the high concentration ers including the following: (1) colorless (2) acid hydrogen peroxide solutions as commonly odorless (3) better stabilizing action at high 5 transported. temperatures (4) less decrease in stabilizing is In general it should be stated that hydrogen effectiveness for long storage periods (9-12 peroxide Solutions are of two kinds. The first months) at room temperature. are those which are of a relatively high concen The object of this invention is to provide a sta tration, i. e. about 10 volume concentration or bilizer without the undesirable properties for 0 higher, and which are kept in acid condition in acidified hydrogen peroxide solutions and more 0 Order to have a maximum stability. Secondly particularly for hydrogen peroxide solutions of a the more dilute, alkaline hydrogen peroxide so concentration as ordinarily shipped in com lutions as are commonly used in bleaching, i. e. merce, i. e. about 10 volume concentration or about one volume concentration. higher, and to provide thereby high concentra For bleaching purposes it has been found more tion peroxide solutions which can be shipped and 15. Satisfactory to operate with solutions which are stored for relatively long periods without serious of an alkaline nature, since the alkalies assist losses. A further object is to provide a stabil in removing various impurities. Such alkaline izer which is effective at both ordinary and high . Solutions, however, are more unstable than the temperatures. . 20 acid solutions and hence, it has been common We have discovered that a compound made by 20 practice to add various stabilizers to the alkaline heating orthophosphoric acid and stannous chlo Solution to prevent undue loss of peroxide. In ride together is an excellent stabilizer for con this case, however, we are dealing with the first centrated acid hydrogen peroxide Solutions. So type of peroxide solutions. lutions of peroxide stabilized with this compound In the production of acidic hydrogen peroxide are colorless, odorless and show a marked stabil- 25 Solutions it has been found usually impractical ity at room temperature and also at a tempera to completely remove the last traces of the im ture of 100° C. By stabilizing hydrogen peroxide purities which accelerate the decomposition of solutions with this tin-pyrophosphate compound peroxide. . It has, therefore, been desirable to we obtain the stabilizing effect of the tin con 30 add stabilizers to these solutions in order to re pounds and the pyrophosphate ion. 30 tard the decomposition of peroxide by these In carrying out the present invention a small traces of impurities or particles of dirt or other amount of this pyrophosphoric acid-tin compound active decomposition catalysts which may be in is added to hydrogen peroxide solutions of vari troduced into the solution in handling or use. ous concentrations. For the sake of simplicity 35 Many organic stabilizers are very effective in in the following examples, the amount of the sta- 35 retarding the decomposition of impure acidic bilizer added is expressed in a contracted form, hydrogen peroxide and their use adds very little for example 0.2 g. HaP2O7--5 mg. Sn/liter. This to the peroxide production costs. However, or means that we have added thereto an amount ganic stabilizers have undesirable properties. of a stabilizer prepared by heating tin chloride 40 Materials such as salicylic acid form colored so and orthophosphoric such that an equivalent of 40 lutions if there are traces of iron salts present 0.2 grams of pyrophosphoric acid and 5 milli in the bleach bath in which the peroxide is sub grams of tin as a tin compound have been added Sequently used or the peroxide solution itself to a liter of the peroxide solution. Such an ex may become colored due to the oxidation of these pression is made necessary because the exact 45 Organic materials such as acetanilide. Further composition of this tin-pyrophosphate stabilizer .45 more, organic stabilizers are decomposed if the is not known and the proportions of tin and pyro Concentrated peroxide solutions are heated and phosphate can be varied. thereby lose their stabilizing properties. Inorganic materials are in general not as ef Ecample I 50 fective as organic materials in retarding the de Toportions of freshly prepared commercial hy- 50 composition of peroxide solutions. Furthermore drogen peroxide solution of 100 volume strength there are only a few inorganic compounds which was added 0.2g. HAP2O--5 mg. Sn/liter of sta are efficient stabilizers for peroxide solutions; in bilizer. The pH of the unstabilized sample was fact many inorganic materials are active cata about 3.5, and the pH of the stabilized samples 55 lysts for the decomposition of peroxides, as for was about 2.0. All samples were maintained at 55 2 2,004.809 a constant temperature of 32° C. and the rate composition losses were determined. The results of oxygen evolution was measured. From these of these experiments are given in the following measuremnts the losses in volume concentration table: equivalent to the loss over a period of 30 days were calculated. The results of this experiment Wolume concen appear in the following table: tration loss S. s: Sample equivalent to at 100°C, for 100 volume H2O2 80 listgage "fior Unstabilized 100 stabilized with volume O 0.2 g. HP01-5 loss in volume Ing. Sinfliter. vol 174 vol. HO stabilized with 0.5g. O concentration IPO7 - 5 mg. Sn------0.26 2.3 equivalent to 30 uine concentraiwa 162 vol. H2O stabilizedw HP207 - 5 mg. Sn------0.20 1.7 329Estorage C. at storageES5'E, at 32°C. 174 vol. H2O2 unstabilized.------2.0 ------162 vol. H2O, unstabilized.------1.9 ------s ------5.7 0. 5 2------6.8 0. This experiment shows that the decomposition losses in 162 and 174 vol. hydrogen peroxide sta These results show that pyrophosphoric-tin bilized with our pyrophosphoric acid-tin stabi stabilizer is a very effective stabilizer at ordi lizer are only about one tenth of the loss occur 20 nary temperatures. The losses of this stabilized ring in unstabilized perOxide solutions of the 20 peroxide as compared with the losses in the same same strength when stored at 32° C. for 30 days. peroxide unstabilized are in the ratio of approxi This stabilizer is effective in keeping the decom mately l;30. In other words, addition of this position losses low at 100° C. stabilizer to the unstabilized peroxide increases Eacample IV its stability almost 30 times. 25 Eacample II To determine the effect of the hydrogen ion concentration on the stability of peroxide Solu To portions of freshly prepared hydrogen per tions, we have taken 100 volume peroxide and oxide of 100 volume strength and normal com stabilizing it with 0.2g. of HAP2O7--5 mg. Sn/liter 30 mercial acidity Was added pyrophosphate-tin and have adjusted the pH of samples so sta 30 stabilizer in such quantity that the amount of bilized at 2, 3, 4, 5, 6 and 6.5 respectively. All pyrophosphate remained constant and the amount samples were maintained at a constant tempera of tin present varied from 0 to 0.2g. These sam ture of 32° C. and the rate of oxygen evolution was measured. From these measurements the 35 ples were heated at 100° C. for 16 hours and the 35 OSS determined. The following results were ob losses in volume concentration equivalent to the tained: loss over a period of 30 days were calculated. The results of this experiment are given in the foll Per cent loss lowing table: when heated at O 100 Wo. HO with OO C. for 16 00 vol. HaOa stabiliaed with 0.2g. 40 hours HAP2O7--5 mg. Sn per liter

------1.5 g. HP,07--0.2g. Sn/liter.----. Wolune concea ------: g. IPO --0.01.g. Sinfilter. tration loss 8------53. EPO7--0.002 g. Sinfilter------pH equivalent to 45 4------1. 5g. IPO7--no Sinfliter------4i 30days' storage 45 at 32° O. We have found that small amounts of this sta bilizer containing from 0.2 grams to 0.002 grams Sn/liter increased the stability of the peroxide 50 from 4% to more than 20 times depending upon 50 the amount of tin present as compared with the Same peroxide stabilized with only pyrophosphoric acid. By increasing the amount of tin present We have found from this experiment that py from 0.002 g. to 0.2 g. per liter we were able, as rophosphate-tin stabilizer is most effective in so 55 shown in Example II, to decrease the volume loss lutions in which the pH is maintained below 5. 55 of the peroxide solution when heated for 16 hours It should be noted that the losses in peroxide in at 100° C. from 9.i vol. to 1.4 vol. crease six or sevenfold when the pH of a solution We prefer to use about 0.2 grams of pyrophos is increased from 5 to 6. We prefer to keep the phoric acid--0.005 g. of tin per liter for we have pH between 1.5 and 3.0 when using the stabilizer 60 found that this gives sufficient stabilization for in concentrated peroxide solutions although it is commercial uses. On the other hand, we have readily apparent from the above example that the used as high as 1.5 g. HaP2O7+0.2 g. Sn/liter and stabilizer has some effect even at a pH of as high have obtained the same desirable results. as 6.5. One method of preparing Our pyrophosphoric 65 Eacample III acid-tin stabilizer is to dissolve 2.5 grams of SnCl2.2H2O in 500 grams of 85% orthophosphoric To portions of freshly prepared commercial acid (H3PO4) and heat gradually to 300° C. and hydrogen peroxide of 162 and 174 volume strength then hold the temperature at 300° C. for 1 hour. was added pyrophosphate-tin stabilizer equiva In carrying out this experiment, it was observed 70 lent to 0.5 g. H4P2O7+5 mg. Sn/liter. The rate that the temperature rises fast until water begins of decomposition at 32° C. was determined for to boil off. After boiling starts, the temperature samples of stabilized and unstabilized peroxide rises slowly while the water and HCl is boiling. and the decomposition equivalent to storage at off. After the water has been boiled off, the tem 32 C. for 30 days was computed. Other samples perature rises rapidly up to the maximum. The , 75. were stored at 100° C. for 16 hours and the de temperature is maintained at the maximum for 5 2,004,809 3 the desired heating period, that is until the loss acid-tin compound equivalent to 0.2 grams in weight of HaPO4--SnCl2.2H2O mixture is about HAP2O7--0.005, grams tin per liter and adjusting 20%. the acidity to a pH of below 6.5. Other batches of stabilizer have been Success 5. Method of stabilizing hydrogen peroxide so fully prepared with a maximum temperature of lutions comprising adding thereto pyrophosphoric 250° C. and 350° C. The time of heating at the acid-tin Compound equivalent to 0.2 grams maximum temperature has been varied from 0 to HAP2O7+0.005 grams tin per liter and adjusting 4 hours. When a maximum temperature of above the pH to between 1.5 and 3.0. 300° C. is used care must be taken not to heat 6. Method of stabilizing 100 vol. hydrogen 0 too fast or too long, otherwise the tin will be pre peroxide Solution comprising adding thereto O cipitated out. The results obtained from various pyrophosphoric acid-tin compound equivalent to batches of stabilizer are given in the following 0.2 grams HAP2O7-0.005 grams tin per liter and table: adjusting the acidity of said solution to a pH of between 1.5 and 3.0. 5 Wol. 7. Method of stabilizing 100 to 174 vols. hydro 5 COC gen peroxide Solution comprising adding thereto equiva-loss First2V2 pyrophosphoric acid-tin compound equivalent to Samplepieng He- EAt WeightPO4. SnCl2.2H2OWeight storagelent to 100°loss atC. 0.2 grams HAP2O7-0.005 grams tin per liter and C. Br. weight at for 16 adjusting the acidity of said solution to a pH

32° C. hours of between 1.5 and 3.0. 20 for 30 20 days 8. A stable homogeneous peroxide solution con taining pyrophosphoric acid-tin compound with 8 500 g 2.5 g. ... 4 6.4 the acidity adjusted to a pH of below 6.5. 8 500 g 2.5 g. 0.7 5. 9. A stable homogeneous hydrogen peroxide 0 500 g 2.5 g. 0.9 6.1 6500 g 2.5 g. 0.8 6.5 solution ... containing pyrophosphoric acid-tin 25 O 500 g 2.5 g. 1. 6.6 compound with the acidity adjusted to a pH of below 6.5. It is readily apparent from the results found 10. A stable homogeneous hydrogen peroxide that the pyrophosphate-tin stabilizer can be pre solution containing stabilizing amounts of pyro 30 pared under a wide range of temperature and phosphoric acid-tin compound equivalent to less 30 heating conditions. We prefer to prepare Our than 1.5 grams HAP2O7-0.2 g. tin per liter and stabilizer according to the method of Example 3 with the acidity of the solution adjusted to a above. pH of between 1.5 and 3.0. This stabilizer is also satisfactory for retarding 11. A stable homogeneous hydrogen peroxide 35 the decomposition of acid peroxide solutions of solution containing stabilizing amounts of pyro higher and also of lower peroxide concentrations phosphoric acid-tin compound equivalent to less than that of the specific examples shown herein. than 1.5 grams HAP2O7-0.2 grams tin per liter We cairn: and with the acidity of the solution adjusted to a 1. Method of stabilizing peroxide solutions pH of below 6.5. - 40 comprising adding thereto a pyrophosphoric, 12. A stable homogeneous hydrogen peroxide . acid-tin compound. solution containing pyrophosphoric acid-tin con 2. Method of stabilizing hydrogen peroxide so pound equivalent to 0.2 grams HaP2O7-0.005 lutions comprising adding thereto pyrophosphoric grams tin per liter and with the acidity of the acid-tin compound. v. solution adjusted to a pH of between 1.5 and 3.0. 3. Method of stabilizing hydrogen peroxide so 13. A stable homogeneous 100 to 74 volune 45 lutions comprising adding thereto stabilizing hydrogen peroxide solution containing pyrophos amounts of pyrophosphoric acid-tin compound phoric acid-tin compound equivalent to 0-2 grains equivalent to less than 1.5 grams HaP2O7-02 HaP2O7-0.005 grams tin per liter and with the grains tin per liter, and adjusting the acidity of acidity of the solution adjusted to between 50 said solution to a pH of less than 6.5. - 5 and 3.0. 4. Method of stabilizing hydrogen peroxide so HARVEY IN. GLBERT, lutions comprising adding theretopyrophosphoric JOSEPB. S. RECBER