CA1070084A - Continuous crystallization process for preparing sodium carbonate peroxide - Google Patents
Continuous crystallization process for preparing sodium carbonate peroxideInfo
- Publication number
- CA1070084A CA1070084A CA256,866A CA256866A CA1070084A CA 1070084 A CA1070084 A CA 1070084A CA 256866 A CA256866 A CA 256866A CA 1070084 A CA1070084 A CA 1070084A
- Authority
- CA
- Canada
- Prior art keywords
- sodium carbonate
- peroxide
- solution
- carbonate solution
- hydrogen peroxide
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D9/00—Crystallisation
- B01D9/0018—Evaporation of components of the mixture to be separated
-
- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
- C01B15/055—Peroxyhydrates; Peroxyacids or salts thereof
- C01B15/10—Peroxyhydrates; Peroxyacids or salts thereof containing carbon
- C01B15/103—Peroxyhydrates; Peroxyacids or salts thereof containing carbon containing only alkali metals as metals
Abstract
CONTINUOUS CRYSTALLIZATION PROCESS FOR PREPARING SODIUM
CARBONATE PEROXIDE
ABSTRACT:
A continuous crystallization process for producing stable high bulk density sodium carbonate peroxide hav-ing a uniform particle size distribution by reacting an aqueous hydrogen peroxide solution and a purified sodium carbonate solution to maintain the sodium carbonate per-oxide concentration above its solution saturation limit while evaporating water in a molar ratio of about 1.5 to about 15.0 moles of water per mole of sodium carbonate peroxide produced.
CARBONATE PEROXIDE
ABSTRACT:
A continuous crystallization process for producing stable high bulk density sodium carbonate peroxide hav-ing a uniform particle size distribution by reacting an aqueous hydrogen peroxide solution and a purified sodium carbonate solution to maintain the sodium carbonate per-oxide concentration above its solution saturation limit while evaporating water in a molar ratio of about 1.5 to about 15.0 moles of water per mole of sodium carbonate peroxide produced.
Description
~o7~ FMC 1648 This invention relates to a continuous crystalliza-tion process for producing stable high bulk density sodium carbonate peroxide having uniform particle size distribution.
Sodium carbonate peroxide is a crystalline compound having the formula 2Na2CO3 3H2O2 ~Jhich is capable of re-leasing hydrogen peroxide in aqueous solution. Because of this property, sodium carbonate peroxide is useful as a bleaching agent in detergent formulations. Much of the recent work with sodium carbonate peroxide has focused on improved methods of production.
It is well known that sodium carbonate peroxide may be prepared by reacting hydrogen peroxide with sodium carbonate alone or in the presence of a stabilizer either in batch or continuous processes. An exemplary process for producing sodium carbonate peroxide is described in United States Patent No. 2,986,448. hccording to this process an aqueous mixture of hydrogen peroxide and so-dium carbonate are reacted in a crystallization zone at a temperature not above about 5C. After a reaction pe-riod of at least four hours, a slurry of sodium carbonate peroxide crystals is formed which is removed from the crystallization zone, filtered, and then dried to produce the sodium carbonate peroxide product. The filtered ; mother liquor containing dissolved sodium carbonate per-oxide is subjected to rapid flash evaporation under such ' , . '' .~
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conditions that excess water is removed from the system.
The resulting mixture of mother liquor and small crystals formed by evaporation is recycled to the crystallization zone.
Although the process of this Urlited ~tates patent is generally satisfactoryl it is objectionable for a number of reasons: 1) the crystallizer requires costly external cooling means; 2) large amounts of water, approaching 34 or more moles of water per mole of product, must be re-moved from the system in the flash evaporator necessi-tating the use of external heating means which add con-siderably to plant design costs and operating overhead;
and 3) the in place formation of large arnounts of magne-sium silicate during crystallization cause excessive nucleation resulting in a large proportion of very fine crystals.
A continuous crystallization process for producing stable high bulk density sodium carbonate peroxide having a uniform particle size distribution is made possible according to the present invention by:
a) continuously introducing a fresh aqueous solu-tion of hydrogen peroxide and a purified sodium carbonate solution to a crystallization zone;
b) reacting the aqueous solution of hydrogen per-oxide and the purified sodium carbonate solution in the crystallization zone in a manner which maintains the ~.
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sodium carbonate peroxide concentration above its solu-tion saturation limit, at a temperature of about 15 to about 30C, at a pH value fro~ about 10.2 to about 11.5, for a residence time of about 0.5 to about 15 hours;
c) evaporating water from the crystalliza~ion zone : in a molar ratio of about 1.5 to about 15.0 moles of water per mole of sodium carbonate peroxide produced;
d) removing from the cry.~tallization zone a slurry containing sodium carbonate peroxide crystals;
10e) separating the crystals from the crystallizer slurry, drying the sodium carbonate peroxide and recovering sodium carbonate peroxide having a bulk density between 0.90 and 1.00 g/cc;
f) treating mother liquor separated from the afore-said filtration to decompose hydrogen peroxide;
g) adding fresh sodium oarbonate to the treated mother liquor in sufficient amounts to prepare a 25% to ~ .
33% by weight sodium carbonate solution; and ..
h) purifying the sodium carbonate solution and em- .
ploying said purified sodium carbonate solution in step (a).
In carrying out the process of the invention, hydro-gen pero~ide and sodium carbonate are reacted in an es~
sentially 3:2 molar ratio. The hydrogen peroxide is intro~
duced directly into the crystallization zone in the form of an aqueous solution containing 50 to 90%, and preferably ;.
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70~ by weight hydrogen peroxide.
The sodium carbonate is added as a saturated aqueous solution, previously purified to remove iron and other transition metal contaminants which catalyze hydrogen peroxide decomposition. The sodium oarbonate solution is prepared by dissolving any commercially available sodium carbonate, preferably anhydrous or monohydrate crystalline, in recycled mother liquor in sufficient amounts to prepare a 25% to 33% by weight sodium c-arbo-nate solution. Puri~ication of the mother liquor to re-move iron and other transition metal contaminants prior to dissolving the sodium carbonate therein is not neces-sary. After the sodium carbonate solution is prepared it must be purified to remove the iron and other tran-sition metal contaminants before entering the crystal-lization zone. Purification of the sodium carbonate solution i3 conveniently achieved by the addition of 100 to 2,000 parts per million (ppm) (based on the weight of the sodium carbonate solution) magnesium oxide or a solu-ble magnesium salt, such as magnesium chloride ancl mag-nesium sulfate, which materials absorb the iron and other transition metals from the solution. Other soluble salts may also be used, such as calcium and zinc salts. The resulting solids are removed by filtration and the puri-fied sodium carbonate solution is then passed to the crystallization zone. The temperature of the sodium 4 ~
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carbonate solution passed to the crystallization zone must be at least 27C, and preferably between 40 and 100C and most preferably between 50 and 600C, to prevent the formation of solid sodium carbonate decahydrate in the feed system. If sodium carbonate decahydrate is formed in the feed system, i~
precipitates from the sodium carbonate solution, and thus ad versely alters the reactant molar ratio of sodiu~ carbonate ; and hydrogen peroxide in the crystallization zone.
The reaction between sodium carbonate and hydrogen peroxide to prepare sodium carbonate peroxide is extremely fast, requiring only a few seconds for the sodium carbonate peroxide to remain in a super~aturated state, whereafter crystallization occurs. Once the supersaturated state is reached, the hydrogen peroxide solution and purified sodium carbonate solutions are introduced into the crystal-lization zone at a sufficient rate to continually maintain the sodium carbonate peroxide concentration above its solution saturation level in the reaction mixture. By employing this procedurel maximum product formation and recovery are achieved without evaporating more than 1.5 to 15.0 moles of water per mole of sodium carbonate per-oxide produced.
The reaction temperature and associated pressure in the crystallizer are maintained at about 15 to about 30C 9 at 10 to 30 mm Hg and preferably at about 21 to about 25C
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at 15 to 19 mm Hg. The selection of a specific temperature and associated pressure during crystallization i8 essential to maintain the sodium carbonate p~roxide ~oncentration above the solution saturation limit while evaporating water from the crystallizer at a molar ratio of about 1.5 to about 15.0 moles, and preferably about 2.5 to about 9.0 moles of water per mole of sodium carbonate peroxide pro duced. Evaporation of this amount of water also controls ; the reaction temperature by removing the heat of crystal-lization resulting from the reaction of sodium carbonate and hydrogen peroxide. The resultant sodium carbonate peroxide slurry concentration in the crystallizer is about 10% to 40~ by weight solids and preferably 20% to 28~ by weight solids.
Lower temperatures and pressures, that is about 5C
at about 5 mm Hg, are not recommended since more expensive vacuum generating equipment and larger crystallizers are required. Higher temperatures and pressures, that is about 35C at about ~0 mm Hg~ are not recommended since greater hydrogen peroxide decomposition losses would result.
The crystallizer is operated for a residence time of 0.5 to 15 hours, and pre~erably 1 to 8 hours. Residence times of less than 0.5 hours result in excessive nucle-ation causing a substantial decrease in average crystal size. Residence times longer than 15 hours will result in excessive hydrogen peroxide decomposition, thus decreas-.
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ing product yield. The residence time is defined as the total weight of solids in the crystallizer divid~d by the production rate of solids per unit time.
The crystallizer is operated at a pH value of about 10.2 to about 11.5, and preferably 10.5 to 10.8. When the crystallizer is operated at a pH value above about 11.2, a 1 to 3g by weight sodium hydroxide solution i9 employed to adjust the pH. While it has been noted that operating the crystallizer at a pH value around 11.2 tends to reduce hydrogen peroxide decomposition, the process of this invention is more economical when the mother liquor has a pH value between 10.5 and 10.8.
Large crystals of sodium carbonate peroxide are continuously withdrawn from the crystallizer as a crystallizer mother liquor slurry containing about 10% to 40% by weight, and preferably 20% to 28% by weight, sodium carbonate peroxide solids. The mother liquor also con- -tains 10% to 30% by weight, and preferably 15% to 19%
by weight, sodium carbonate; and 1~ to 6~ by weight, and preferably 1.5% to 2.5~ by weight, hydrogen peroxide.
If the sodium carbonate concentration in the mother liquor is greater than about 30~ by weight when the crystallizer is operated at about 30C, a solid phase of sodium carbonate decahydrate is formed. Likewise, if the sodium carbonate concentration in the mo-ther liquor is greater than about 20~ by weight when the .
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crystallizer is operated at the preferred temperatures between 21 and 25C, a solid phase of sodium carbonate decahydrate is formed. Formation of the solid phase is not desirable since it dilutes the actiYe oxygen con-tent of the final product and because it cau~es exce~Ai~e nucleation in the crystalli2er, thus producing smaller size crystals.
The sodium carbonate peroxide crystals are removed from the mother liquor by conventional separation means and then rapidly dried to remove excess moisture by conventional means, such as tray, rotary, belt, or fluid bed driers.
The resulting sodium carbonate peroxide crystals produced according to this invention unexpectedly have a high bulk density, a high stability, and a uniform particle size distribution. These properties are extremely desirable since the crystals can be easily separated ~rom solution, easily dried, and are less friable so they can be handled easily without breakage and without objection-
Sodium carbonate peroxide is a crystalline compound having the formula 2Na2CO3 3H2O2 ~Jhich is capable of re-leasing hydrogen peroxide in aqueous solution. Because of this property, sodium carbonate peroxide is useful as a bleaching agent in detergent formulations. Much of the recent work with sodium carbonate peroxide has focused on improved methods of production.
It is well known that sodium carbonate peroxide may be prepared by reacting hydrogen peroxide with sodium carbonate alone or in the presence of a stabilizer either in batch or continuous processes. An exemplary process for producing sodium carbonate peroxide is described in United States Patent No. 2,986,448. hccording to this process an aqueous mixture of hydrogen peroxide and so-dium carbonate are reacted in a crystallization zone at a temperature not above about 5C. After a reaction pe-riod of at least four hours, a slurry of sodium carbonate peroxide crystals is formed which is removed from the crystallization zone, filtered, and then dried to produce the sodium carbonate peroxide product. The filtered ; mother liquor containing dissolved sodium carbonate per-oxide is subjected to rapid flash evaporation under such ' , . '' .~
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conditions that excess water is removed from the system.
The resulting mixture of mother liquor and small crystals formed by evaporation is recycled to the crystallization zone.
Although the process of this Urlited ~tates patent is generally satisfactoryl it is objectionable for a number of reasons: 1) the crystallizer requires costly external cooling means; 2) large amounts of water, approaching 34 or more moles of water per mole of product, must be re-moved from the system in the flash evaporator necessi-tating the use of external heating means which add con-siderably to plant design costs and operating overhead;
and 3) the in place formation of large arnounts of magne-sium silicate during crystallization cause excessive nucleation resulting in a large proportion of very fine crystals.
A continuous crystallization process for producing stable high bulk density sodium carbonate peroxide having a uniform particle size distribution is made possible according to the present invention by:
a) continuously introducing a fresh aqueous solu-tion of hydrogen peroxide and a purified sodium carbonate solution to a crystallization zone;
b) reacting the aqueous solution of hydrogen per-oxide and the purified sodium carbonate solution in the crystallization zone in a manner which maintains the ~.
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sodium carbonate peroxide concentration above its solu-tion saturation limit, at a temperature of about 15 to about 30C, at a pH value fro~ about 10.2 to about 11.5, for a residence time of about 0.5 to about 15 hours;
c) evaporating water from the crystalliza~ion zone : in a molar ratio of about 1.5 to about 15.0 moles of water per mole of sodium carbonate peroxide produced;
d) removing from the cry.~tallization zone a slurry containing sodium carbonate peroxide crystals;
10e) separating the crystals from the crystallizer slurry, drying the sodium carbonate peroxide and recovering sodium carbonate peroxide having a bulk density between 0.90 and 1.00 g/cc;
f) treating mother liquor separated from the afore-said filtration to decompose hydrogen peroxide;
g) adding fresh sodium oarbonate to the treated mother liquor in sufficient amounts to prepare a 25% to ~ .
33% by weight sodium carbonate solution; and ..
h) purifying the sodium carbonate solution and em- .
ploying said purified sodium carbonate solution in step (a).
In carrying out the process of the invention, hydro-gen pero~ide and sodium carbonate are reacted in an es~
sentially 3:2 molar ratio. The hydrogen peroxide is intro~
duced directly into the crystallization zone in the form of an aqueous solution containing 50 to 90%, and preferably ;.
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70~ by weight hydrogen peroxide.
The sodium carbonate is added as a saturated aqueous solution, previously purified to remove iron and other transition metal contaminants which catalyze hydrogen peroxide decomposition. The sodium oarbonate solution is prepared by dissolving any commercially available sodium carbonate, preferably anhydrous or monohydrate crystalline, in recycled mother liquor in sufficient amounts to prepare a 25% to 33% by weight sodium c-arbo-nate solution. Puri~ication of the mother liquor to re-move iron and other transition metal contaminants prior to dissolving the sodium carbonate therein is not neces-sary. After the sodium carbonate solution is prepared it must be purified to remove the iron and other tran-sition metal contaminants before entering the crystal-lization zone. Purification of the sodium carbonate solution i3 conveniently achieved by the addition of 100 to 2,000 parts per million (ppm) (based on the weight of the sodium carbonate solution) magnesium oxide or a solu-ble magnesium salt, such as magnesium chloride ancl mag-nesium sulfate, which materials absorb the iron and other transition metals from the solution. Other soluble salts may also be used, such as calcium and zinc salts. The resulting solids are removed by filtration and the puri-fied sodium carbonate solution is then passed to the crystallization zone. The temperature of the sodium 4 ~
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carbonate solution passed to the crystallization zone must be at least 27C, and preferably between 40 and 100C and most preferably between 50 and 600C, to prevent the formation of solid sodium carbonate decahydrate in the feed system. If sodium carbonate decahydrate is formed in the feed system, i~
precipitates from the sodium carbonate solution, and thus ad versely alters the reactant molar ratio of sodiu~ carbonate ; and hydrogen peroxide in the crystallization zone.
The reaction between sodium carbonate and hydrogen peroxide to prepare sodium carbonate peroxide is extremely fast, requiring only a few seconds for the sodium carbonate peroxide to remain in a super~aturated state, whereafter crystallization occurs. Once the supersaturated state is reached, the hydrogen peroxide solution and purified sodium carbonate solutions are introduced into the crystal-lization zone at a sufficient rate to continually maintain the sodium carbonate peroxide concentration above its solution saturation level in the reaction mixture. By employing this procedurel maximum product formation and recovery are achieved without evaporating more than 1.5 to 15.0 moles of water per mole of sodium carbonate per-oxide produced.
The reaction temperature and associated pressure in the crystallizer are maintained at about 15 to about 30C 9 at 10 to 30 mm Hg and preferably at about 21 to about 25C
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at 15 to 19 mm Hg. The selection of a specific temperature and associated pressure during crystallization i8 essential to maintain the sodium carbonate p~roxide ~oncentration above the solution saturation limit while evaporating water from the crystallizer at a molar ratio of about 1.5 to about 15.0 moles, and preferably about 2.5 to about 9.0 moles of water per mole of sodium carbonate peroxide pro duced. Evaporation of this amount of water also controls ; the reaction temperature by removing the heat of crystal-lization resulting from the reaction of sodium carbonate and hydrogen peroxide. The resultant sodium carbonate peroxide slurry concentration in the crystallizer is about 10% to 40~ by weight solids and preferably 20% to 28~ by weight solids.
Lower temperatures and pressures, that is about 5C
at about 5 mm Hg, are not recommended since more expensive vacuum generating equipment and larger crystallizers are required. Higher temperatures and pressures, that is about 35C at about ~0 mm Hg~ are not recommended since greater hydrogen peroxide decomposition losses would result.
The crystallizer is operated for a residence time of 0.5 to 15 hours, and pre~erably 1 to 8 hours. Residence times of less than 0.5 hours result in excessive nucle-ation causing a substantial decrease in average crystal size. Residence times longer than 15 hours will result in excessive hydrogen peroxide decomposition, thus decreas-.
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ing product yield. The residence time is defined as the total weight of solids in the crystallizer divid~d by the production rate of solids per unit time.
The crystallizer is operated at a pH value of about 10.2 to about 11.5, and preferably 10.5 to 10.8. When the crystallizer is operated at a pH value above about 11.2, a 1 to 3g by weight sodium hydroxide solution i9 employed to adjust the pH. While it has been noted that operating the crystallizer at a pH value around 11.2 tends to reduce hydrogen peroxide decomposition, the process of this invention is more economical when the mother liquor has a pH value between 10.5 and 10.8.
Large crystals of sodium carbonate peroxide are continuously withdrawn from the crystallizer as a crystallizer mother liquor slurry containing about 10% to 40% by weight, and preferably 20% to 28% by weight, sodium carbonate peroxide solids. The mother liquor also con- -tains 10% to 30% by weight, and preferably 15% to 19%
by weight, sodium carbonate; and 1~ to 6~ by weight, and preferably 1.5% to 2.5~ by weight, hydrogen peroxide.
If the sodium carbonate concentration in the mother liquor is greater than about 30~ by weight when the crystallizer is operated at about 30C, a solid phase of sodium carbonate decahydrate is formed. Likewise, if the sodium carbonate concentration in the mo-ther liquor is greater than about 20~ by weight when the .
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crystallizer is operated at the preferred temperatures between 21 and 25C, a solid phase of sodium carbonate decahydrate is formed. Formation of the solid phase is not desirable since it dilutes the actiYe oxygen con-tent of the final product and because it cau~es exce~Ai~e nucleation in the crystalli2er, thus producing smaller size crystals.
The sodium carbonate peroxide crystals are removed from the mother liquor by conventional separation means and then rapidly dried to remove excess moisture by conventional means, such as tray, rotary, belt, or fluid bed driers.
The resulting sodium carbonate peroxide crystals produced according to this invention unexpectedly have a high bulk density, a high stability, and a uniform particle size distribution. These properties are extremely desirable since the crystals can be easily separated ~rom solution, easily dried, and are less friable so they can be handled easily without breakage and without objection-
2~ able dusting. These crystal properties also decrease thesegregating tendencies of the crystals when used in commer-oial formulations having similar bulk densities, which is commercially important. Furthermore, the consistent formation of a sodium carbonate peroxide product with uniform particle size distribution permits a commercial operation to continuously produce a consistently good .
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~(:J'7~ 4 ; product without property fluctuation. In addition, the crystals produced have high active oxygen contents, that is at least 15.00~ actiYe oxygen with 15.28~ being the theoretical maximum active oxygen content.
The term high bulk density as used herein re~ers to sodium carbonate peroxide crystals having bulk densities between 0.9 and 1.0 g/cc and pre~erably between 0.91 and o.g8 g/cc. The term uniform particle size distribution refers to the uniformity or conA~istency of the sodium carbonate crystal particle size distribution produced during crystallization in relation to time, that is, the crystals having uni~orm particle size distributions during the entire crystallization process wherein at least 50% of the crystals are ~50 mesh size, (U.S. Standard Sieve ~ Series A.S.T.M. - E-11-61).
- The resulting mother liquor contains the dissolved sodium carbonate and hydrogen peroxide. This liquor can-not be directly recycled to the crystallizer since it contains reactant impurities and transition metal impurities.
~0 Likewise, the liquor cannot be directly employed as a water source to prepare thq sodium carbonate solution, since upon addition of sodium carbona~e to this liquor, it will react with the remaining hydrogen peroxide resulting in excessive foaming and heat evolution. Accordingly, the residual hydrogen peroxide present in the mother liquor is decomposed and the mother liquor is then recharged .
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-, . . ' .' :' , with additional sodium carbonate ancl purified as herein-above described. Hydrogen peroxide decomposition can be achieved by conventional procedures, such as by the addi tion of conventional hydrogen peroxide decomposition ; agents. Preferably, the mother liquor is sub~ected to a heat treatment, for example by passing steam through the mother liquor and thereby raising the temperature of the mother liquor to a point where hydrogen peroxide is rapidly decomposed, such as between 40 and 70~C for a few minutes.
The drawing shows a flow sheet of one embodiment of the process of the invention carried out in a continuous manner. According to this scheme, an aqueous hydrogen peroxide solution of 70~ by weight concentration is fed through line 4 from supply tank 2 into conventional draft-tube crystallizer 6 provided with an agitator which is ro-tated at a speed to maintain the solids content uniformly dispersed in crystallizer 6. (Other types of crystallizers may be employed, such as an Oslo-type crystallizer). A
purified sodium carbonate solution is fed through line 8 from supply tank 10 into crystallizer 6 or optionally fed through line 12 into the fines loop. The sodium carbonate solution and the hydrogen peroxide solution are fed simul-taneously at a rate sufficient to maintain the resultant sodium carbonate peroxide concentration above its solution saturation level. The hydrogen peroxide and sodium carbonate .-~ . .
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. , are generally employed in molar ratios of about 3:2.
The reaction mixture in crystallizer 6 is held with agitation at a temperature of about 21 to about 25C for at least 0.5 hours to prepare a 20 to 28~ by ~eight ~qlurry of sodium carbonate peroxide crystals. Crystallizer 6 is preferably maintained at a reduced pressure of 15 to 19 mm Hg by means of a conventional vacuum system whereby water is removed by evaporation through line 14 at a molar ratio of 2.5 to about 9.0 moles of water per mole of sodium carbonate peroxide prepared. Oxygen formed by hydrogen peroxide decomposition in the crystallizer is also removed through line 14. Suspended sodium carbonate peroxide fines are removed from crystallizer 6 reaction chamber by conveying line 16 and passed through heat ex-changer 18 which aids in the dissolution of the fines and provides heat for evaporation of water; this heated solu-tion is returned to the bottom of crystallizer 6.
Large crystals of sodium carbonate peroxide are continuously withdrawn from crystallizer 6 through line 20 as crystallizer mother liquor slurry, preferably .~ containing 20% to 28% by weight solids in a mother liquor containing 15% to 19% by weight sodium carbonate and 1.5 to 2.5% by weight hydrogen peroxide. The slurry is fed into centrifuge 22 whereby crystallizer mother liquor is removed from the crystals, thereby reducing the moisture content of the crystals to about 2 to 10%. Centrifuge 22 ~' .
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may be replaced with conventional rotary filters or filter presses. The centrifuged cry~tals are passed through line 24 into drier 26 whereby the crystals may be conveniently dried at a Semperature of about 40 to 600C to obtain a dry sodium carbonate peroxide product containing less than 0.2% by weight moi~ture.
Crystallizer mother liquor removed from centrifuge 22 is fed through line 28 into mother liquor tank 30. The mother liquor containing the dissolved sodium carbonate and hydrogen peroxide and minor amounts of remaining sodium carbonate peroxide crystals is fed through line 32 into liquid-solid separator 34 or alternately passed directly to hydrogen peroxide decomposition tank 38 through line 36. Liquid-solid separator 34 iS a conventional means for separating liquids and solids, such as hydroclone.
A high weight percent solids stream, second slurry, con-taining 50g to 90g by weight sodium carbonate peroxide crystals is withdrawn through line 40 and returned into crystallizer 6. The resultant mother liquor stream is withdrawn through line 36 and fed into hydrogen peroxide decomposition tank 38. The mother liquor is held in tank 38 at about 40 to 50C for a sufficient time to decompose all of the residual hydrogen peroxide to water and oxygen.
; Decomposed liquor from hydrogen peroxide decomposition tank 38 is fed through line 42 into sodium carbonate make-up . , . : - .- . ; , ~
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tank 44. Sodium carbonate, in preferably anhydrous or monohydrate crystalline form, is introduced through line 46 into make~up tank 44 in sufficient amounts to prepare a 25% to 33~ by weight sodium carbonate solution. If necessary, water can also be added through line ~8. In addition, 100 to 29000 ppm magnesium oxide or a soluble magnesium salt is added through line 50 to the solution in make-up tank 44.
After being treated with the magnesium compound, the solution is transferred from make up tank 44 through line 52 to filter 54, where solids containing magnesium, iron and other transition metals are removed through line 56 and discarded. The filtered solution is withdrawn through line 58 and fed into storage tank 10 where the purified sodium carbonate solution is temporari.ly stored before being fed to crystallizer 6.
The following example is given to further illustrate the invention. All proportions throughout the example and the specification are by weight unless otherwise specified.
Example A 70% by weight solution of hydrogen peroxide was reaoted with a 28% by weight purified sodium carbonate solution in a crystallizer in such proportions that the resulting mixture continuously contained about 175 grams/
liter of sodium carbonate and about 25 grams/liter of hydro~
gen peroxide. The sodium carbonate solution was prepared :
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by dissolving anhydrous sodium carbonate in a recycled mother liquor which had been heated t;o about 50C to de-compose all of its hydrogen peroxide content, treated with 1,000 ppm magnesium oxide, and filtered. The resulting purified sodium carbonate solution contained less then 1 ppm iron and trace amounts of other transition metals.
The crystallizer was operated at a pH of 10.8, 22.5C, a pressure of 15 mm Hg, a 7-hour residence time, wi~h a fines destruction loop and a solids concentration of 28~. About 12 moles of water per mole of sodium carbonate peroxide produced was continuously removed from the crystallizer.
The slurry was removed from the crystallizer and centri-fuged. The resultant sodium carbonate peroxide crystals containing about 5~ by weight water were dried in a fluid bed drier to prepare a sodium carbonate peroxlde product.
The product consisted of individual crystals in the shape of hexagonal prisms with a particle size distribution of about 27% +40 mesh; 36% -40-~50 mesh; 29% -50~70 mesh; and 8% -70 mesh (U.S. Standard sieve). The product had a bulk density of 0.95 g/cc, an active oxygen content of 15.18%
by weight, and a moisture content of less than 0.2~ by weight.
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~(:J'7~ 4 ; product without property fluctuation. In addition, the crystals produced have high active oxygen contents, that is at least 15.00~ actiYe oxygen with 15.28~ being the theoretical maximum active oxygen content.
The term high bulk density as used herein re~ers to sodium carbonate peroxide crystals having bulk densities between 0.9 and 1.0 g/cc and pre~erably between 0.91 and o.g8 g/cc. The term uniform particle size distribution refers to the uniformity or conA~istency of the sodium carbonate crystal particle size distribution produced during crystallization in relation to time, that is, the crystals having uni~orm particle size distributions during the entire crystallization process wherein at least 50% of the crystals are ~50 mesh size, (U.S. Standard Sieve ~ Series A.S.T.M. - E-11-61).
- The resulting mother liquor contains the dissolved sodium carbonate and hydrogen peroxide. This liquor can-not be directly recycled to the crystallizer since it contains reactant impurities and transition metal impurities.
~0 Likewise, the liquor cannot be directly employed as a water source to prepare thq sodium carbonate solution, since upon addition of sodium carbona~e to this liquor, it will react with the remaining hydrogen peroxide resulting in excessive foaming and heat evolution. Accordingly, the residual hydrogen peroxide present in the mother liquor is decomposed and the mother liquor is then recharged .
_ 9 _ .
. . -.
-, . . ' .' :' , with additional sodium carbonate ancl purified as herein-above described. Hydrogen peroxide decomposition can be achieved by conventional procedures, such as by the addi tion of conventional hydrogen peroxide decomposition ; agents. Preferably, the mother liquor is sub~ected to a heat treatment, for example by passing steam through the mother liquor and thereby raising the temperature of the mother liquor to a point where hydrogen peroxide is rapidly decomposed, such as between 40 and 70~C for a few minutes.
The drawing shows a flow sheet of one embodiment of the process of the invention carried out in a continuous manner. According to this scheme, an aqueous hydrogen peroxide solution of 70~ by weight concentration is fed through line 4 from supply tank 2 into conventional draft-tube crystallizer 6 provided with an agitator which is ro-tated at a speed to maintain the solids content uniformly dispersed in crystallizer 6. (Other types of crystallizers may be employed, such as an Oslo-type crystallizer). A
purified sodium carbonate solution is fed through line 8 from supply tank 10 into crystallizer 6 or optionally fed through line 12 into the fines loop. The sodium carbonate solution and the hydrogen peroxide solution are fed simul-taneously at a rate sufficient to maintain the resultant sodium carbonate peroxide concentration above its solution saturation level. The hydrogen peroxide and sodium carbonate .-~ . .
. . : , ,. . ,~
. ... - :
, . . . , ,............ . .- ..
.. . . .. . : .
.
, .
::
.: , - . . . . . .. .
.. . .
. , are generally employed in molar ratios of about 3:2.
The reaction mixture in crystallizer 6 is held with agitation at a temperature of about 21 to about 25C for at least 0.5 hours to prepare a 20 to 28~ by ~eight ~qlurry of sodium carbonate peroxide crystals. Crystallizer 6 is preferably maintained at a reduced pressure of 15 to 19 mm Hg by means of a conventional vacuum system whereby water is removed by evaporation through line 14 at a molar ratio of 2.5 to about 9.0 moles of water per mole of sodium carbonate peroxide prepared. Oxygen formed by hydrogen peroxide decomposition in the crystallizer is also removed through line 14. Suspended sodium carbonate peroxide fines are removed from crystallizer 6 reaction chamber by conveying line 16 and passed through heat ex-changer 18 which aids in the dissolution of the fines and provides heat for evaporation of water; this heated solu-tion is returned to the bottom of crystallizer 6.
Large crystals of sodium carbonate peroxide are continuously withdrawn from crystallizer 6 through line 20 as crystallizer mother liquor slurry, preferably .~ containing 20% to 28% by weight solids in a mother liquor containing 15% to 19% by weight sodium carbonate and 1.5 to 2.5% by weight hydrogen peroxide. The slurry is fed into centrifuge 22 whereby crystallizer mother liquor is removed from the crystals, thereby reducing the moisture content of the crystals to about 2 to 10%. Centrifuge 22 ~' .
:, . : , , : '' .
,' . ' . .
~ ........ , . ~ , . ~, ,,.: . ' ': ' :
:: , ~ , ., . ~ . ' . :
. ~
~7~
may be replaced with conventional rotary filters or filter presses. The centrifuged cry~tals are passed through line 24 into drier 26 whereby the crystals may be conveniently dried at a Semperature of about 40 to 600C to obtain a dry sodium carbonate peroxide product containing less than 0.2% by weight moi~ture.
Crystallizer mother liquor removed from centrifuge 22 is fed through line 28 into mother liquor tank 30. The mother liquor containing the dissolved sodium carbonate and hydrogen peroxide and minor amounts of remaining sodium carbonate peroxide crystals is fed through line 32 into liquid-solid separator 34 or alternately passed directly to hydrogen peroxide decomposition tank 38 through line 36. Liquid-solid separator 34 iS a conventional means for separating liquids and solids, such as hydroclone.
A high weight percent solids stream, second slurry, con-taining 50g to 90g by weight sodium carbonate peroxide crystals is withdrawn through line 40 and returned into crystallizer 6. The resultant mother liquor stream is withdrawn through line 36 and fed into hydrogen peroxide decomposition tank 38. The mother liquor is held in tank 38 at about 40 to 50C for a sufficient time to decompose all of the residual hydrogen peroxide to water and oxygen.
; Decomposed liquor from hydrogen peroxide decomposition tank 38 is fed through line 42 into sodium carbonate make-up . , . : - .- . ; , ~
. .
' ., . ... . .. ~
~7~
tank 44. Sodium carbonate, in preferably anhydrous or monohydrate crystalline form, is introduced through line 46 into make~up tank 44 in sufficient amounts to prepare a 25% to 33~ by weight sodium carbonate solution. If necessary, water can also be added through line ~8. In addition, 100 to 29000 ppm magnesium oxide or a soluble magnesium salt is added through line 50 to the solution in make-up tank 44.
After being treated with the magnesium compound, the solution is transferred from make up tank 44 through line 52 to filter 54, where solids containing magnesium, iron and other transition metals are removed through line 56 and discarded. The filtered solution is withdrawn through line 58 and fed into storage tank 10 where the purified sodium carbonate solution is temporari.ly stored before being fed to crystallizer 6.
The following example is given to further illustrate the invention. All proportions throughout the example and the specification are by weight unless otherwise specified.
Example A 70% by weight solution of hydrogen peroxide was reaoted with a 28% by weight purified sodium carbonate solution in a crystallizer in such proportions that the resulting mixture continuously contained about 175 grams/
liter of sodium carbonate and about 25 grams/liter of hydro~
gen peroxide. The sodium carbonate solution was prepared :
~ - 13 -.
,. : ' , ,: - ' - . .
, . . :
~701~3~
by dissolving anhydrous sodium carbonate in a recycled mother liquor which had been heated t;o about 50C to de-compose all of its hydrogen peroxide content, treated with 1,000 ppm magnesium oxide, and filtered. The resulting purified sodium carbonate solution contained less then 1 ppm iron and trace amounts of other transition metals.
The crystallizer was operated at a pH of 10.8, 22.5C, a pressure of 15 mm Hg, a 7-hour residence time, wi~h a fines destruction loop and a solids concentration of 28~. About 12 moles of water per mole of sodium carbonate peroxide produced was continuously removed from the crystallizer.
The slurry was removed from the crystallizer and centri-fuged. The resultant sodium carbonate peroxide crystals containing about 5~ by weight water were dried in a fluid bed drier to prepare a sodium carbonate peroxlde product.
The product consisted of individual crystals in the shape of hexagonal prisms with a particle size distribution of about 27% +40 mesh; 36% -40-~50 mesh; 29% -50~70 mesh; and 8% -70 mesh (U.S. Standard sieve). The product had a bulk density of 0.95 g/cc, an active oxygen content of 15.18%
by weight, and a moisture content of less than 0.2~ by weight.
,':' ~'.
;
,:
.. . . . ~ , . . . . . : . . :, -' ' ' ' ' : ' , ~ ' ' ' , . '
Claims (9)
1. A continuous crystallization process for the production of stable high bulk density sodium carbonate peroxide having a uniform particle size distribution, characterized by:
a) continuously introducing a fresh aqueous solution containing 50%, to 90% by weight hydrogen peroxide and a purified sodium carbonate solution to a crystalli-zation zone;
b) reacting the aqueous solution of hydrogen peroxide and the purified sodium carbonate solution in the crystallization zone in a manner which prevents the formation of a solid phase of sodium carbonate decahydrate and which maintains the sodium carbonate peroxide concen-tration above its solution saturation limit, at a temper-ature of 15° to 30°C at a pressure of 10 to 30 mm Hg, at a pH value from 10.2 to 11.5, for a residence time of 0.5 to 15 hours;
c) evaporating water from the crystallization zone in a molar ratio of 1.5 to 15.0 moles of water per mole of sodium carbonate peroxide produced;
d) removing from the crystallization zone a slurry containing sodium carbonate peroxide crystals;
e) separating the crystal from the crystal-lizer slurry, drying the sodium carbonate peroxide and recovering sodium carbonate peroxide having a bulk den sity between 0.90 and 1.00 g/cc;
f) treating mother liquor separated from the aforesaid filtration to decompose hydrogen peroxide;
g) adding fresh sodium carbonate to the treated mother liquor in sufficient amounts to prepare a 25% to 33%
by weight sodium carbonate solution having a temperature of at least 27°C; and h) purifying the sodium carbonate solution to remove iron and other transition metal contaminants and em-ploying said purified sodium carbonate solution in step (a).
a) continuously introducing a fresh aqueous solution containing 50%, to 90% by weight hydrogen peroxide and a purified sodium carbonate solution to a crystalli-zation zone;
b) reacting the aqueous solution of hydrogen peroxide and the purified sodium carbonate solution in the crystallization zone in a manner which prevents the formation of a solid phase of sodium carbonate decahydrate and which maintains the sodium carbonate peroxide concen-tration above its solution saturation limit, at a temper-ature of 15° to 30°C at a pressure of 10 to 30 mm Hg, at a pH value from 10.2 to 11.5, for a residence time of 0.5 to 15 hours;
c) evaporating water from the crystallization zone in a molar ratio of 1.5 to 15.0 moles of water per mole of sodium carbonate peroxide produced;
d) removing from the crystallization zone a slurry containing sodium carbonate peroxide crystals;
e) separating the crystal from the crystal-lizer slurry, drying the sodium carbonate peroxide and recovering sodium carbonate peroxide having a bulk den sity between 0.90 and 1.00 g/cc;
f) treating mother liquor separated from the aforesaid filtration to decompose hydrogen peroxide;
g) adding fresh sodium carbonate to the treated mother liquor in sufficient amounts to prepare a 25% to 33%
by weight sodium carbonate solution having a temperature of at least 27°C; and h) purifying the sodium carbonate solution to remove iron and other transition metal contaminants and em-ploying said purified sodium carbonate solution in step (a).
2. The process of claim 1, characterized in that the reaction is at a temperature of 21° to 25°C, at a pH value of 10.5 to 10.8, for a residence time of 1 to 8 hours.
3. The process of claim 1, characterized in that 2.5 to 9.0 moles of water per mole of sodium carbonate peroxide is evaporated from the crystallization zone.
4. The process of claim 1, characterized by: sepa-rating the crystals from the crystallizer slurry according to step (e); removing from the separated mother liquor of step (e) a second slurry containing 50% to 90% by weight sodium carbonate peroxide crystals; treating the resulting mother liquor to decompose hydrogen peroxide; and returning the second slurry to the crystallization zone.
5. The process of claim 1, characterized by: con-tacting the sodium carbonate solution of step (h) with 100 to 2,000 ppm magnesium oxide or a soluble magnesium salt based on the weight of the sodium carbonate solution;
filtering the sodium carbonate solution, and passing the resultant purified sodium carbonate solution to the crys-tallization zone.
filtering the sodium carbonate solution, and passing the resultant purified sodium carbonate solution to the crys-tallization zone.
6. The process of claim 1, characterized in that the sodium carbonate peroxide product has a bulk density between 0.91 and 0.98 g/cc, an active oxygen content of at least 15.00%, and a particle size distribution of at least 50%
+50 mesh, U.S. Standard Sieve Series ASTM - E-11-61.
+50 mesh, U.S. Standard Sieve Series ASTM - E-11-61.
7. The process of claim 1, step (a) characterized in that the sodium carbonate solution has a temperature of at least 27°C.
8. The process of claim 1, step (a) characterized in that the sodium carbonate solution has a temperature between 40 and 100°C.
9. The process of claim 1, step (a) characterized in that the sodium carbonate solution has a temperature between 50 and 60°C.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US59618775A | 1975-07-15 | 1975-07-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1070084A true CA1070084A (en) | 1980-01-22 |
Family
ID=24386306
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA256,866A Expired CA1070084A (en) | 1975-07-15 | 1976-07-13 | Continuous crystallization process for preparing sodium carbonate peroxide |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5220999A (en) |
| BE (1) | BE844167A (en) |
| CA (1) | CA1070084A (en) |
| DE (1) | DE2631917A1 (en) |
| ES (1) | ES449815A1 (en) |
| FR (1) | FR2318112A1 (en) |
| IT (1) | IT1062528B (en) |
| NL (1) | NL7607869A (en) |
| SE (1) | SE7608054L (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5906660A (en) * | 1994-09-22 | 1999-05-25 | Solvay Interox (Societe Anonyme) | Process for the manufacture of persalt particles |
| US6340452B1 (en) | 1996-03-19 | 2002-01-22 | Solvay | Sodium percarbonate and process for producing it |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE3163044D1 (en) * | 1980-05-15 | 1984-05-17 | Interox Chemicals Ltd | The production of alkali metal or alkaline earth metal peroxides and peroxides when so produced |
| JPS5751102A (en) * | 1980-09-09 | 1982-03-25 | Mitsubishi Gas Chem Co Inc | Preparation of high-quality sodium percarbonate |
| IT1142023B (en) * | 1981-07-20 | 1986-10-08 | Montedison Spa | PROCEDURE FOR THE PREPARATION OF SODIUM PERCARBONATE |
| JPS58195594U (en) * | 1982-06-21 | 1983-12-26 | 有限会社荻野工業所 | toilet paper stocker |
| US4966762A (en) * | 1988-10-06 | 1990-10-30 | Fmc Corporation | Process for manufacturing a soda ash peroxygen carrier |
| IT1276685B1 (en) * | 1995-06-08 | 1997-11-03 | Ausimont Spa | PROCESS FOR THE PRODUCTION OF SODIUM PERCARBONATE IN GRANULAR FORM |
-
1976
- 1976-07-13 CA CA256,866A patent/CA1070084A/en not_active Expired
- 1976-07-14 IT IT25324/76A patent/IT1062528B/en active
- 1976-07-14 ES ES449815A patent/ES449815A1/en not_active Expired
- 1976-07-15 SE SE7608054A patent/SE7608054L/en unknown
- 1976-07-15 JP JP51083592A patent/JPS5220999A/en active Pending
- 1976-07-15 DE DE19762631917 patent/DE2631917A1/en active Pending
- 1976-07-15 BE BE168947A patent/BE844167A/en unknown
- 1976-07-15 NL NL7607869A patent/NL7607869A/en unknown
- 1976-07-15 FR FR7621627A patent/FR2318112A1/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5906660A (en) * | 1994-09-22 | 1999-05-25 | Solvay Interox (Societe Anonyme) | Process for the manufacture of persalt particles |
| US6267934B1 (en) | 1994-09-22 | 2001-07-31 | Solvay Interox (Société Anonyme) | Process for the manufacture of persalt particles |
| US6340452B1 (en) | 1996-03-19 | 2002-01-22 | Solvay | Sodium percarbonate and process for producing it |
Also Published As
| Publication number | Publication date |
|---|---|
| SE7608054L (en) | 1977-01-16 |
| JPS5220999A (en) | 1977-02-17 |
| BE844167A (en) | 1977-01-17 |
| ES449815A1 (en) | 1977-08-01 |
| FR2318112A1 (en) | 1977-02-11 |
| IT1062528B (en) | 1984-10-20 |
| NL7607869A (en) | 1977-01-18 |
| DE2631917A1 (en) | 1977-02-03 |
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