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WO1998047814A1 - Procede de cristallisation de solution aux fins de la production de phosphates acides a solubilite non congruente par incorporation d'une solution de lavage a base de sel phosphate - Google Patents

Procede de cristallisation de solution aux fins de la production de phosphates acides a solubilite non congruente par incorporation d'une solution de lavage a base de sel phosphate Download PDF

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WO1998047814A1
WO1998047814A1 PCT/US1998/008140 US9808140W WO9847814A1 WO 1998047814 A1 WO1998047814 A1 WO 1998047814A1 US 9808140 W US9808140 W US 9808140W WO 9847814 A1 WO9847814 A1 WO 9847814A1
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phosphate
solution
crystals
incongruently
soluble acid
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David R. Gard
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Solutia Inc
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Solutia Inc
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/30—Alkali metal phosphates
    • C01B25/301—Preparation from liquid orthophosphoric acid or from an acid solution or suspension of orthophosphates
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/32—Phosphates of magnesium, calcium, strontium, or barium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • C01B25/451—Phosphates containing plural metal, or metal and ammonium containing metal and ammonium

Definitions

  • This invention relates to a method for producing incongruently-soluble acid phosphates. More particularly, this invention relates to a method for producing incongruently-soluble acid phosphates in a solution crystallization process by incorporating a phosphate solution wash to improve the recovery, the purity, and physical properties of the resulting finished product.
  • salts may be classified as being either congruently-soluble or incongruently-soluble.
  • a congruently-soluble salt dissolves in water to yield a solution which contains the ions present in the same proportion as in the salt.
  • a saturated solution of a congruently-soluble salt is in equilibrium with the salt itself.
  • a congruently-soluble salt can be identified in an aqueous phase diagram by the intersection of the salt-water line with the two-phase envelope of the salt.
  • Another example of a congruently-soluble salt is monopotassium phosphate, KH 2 PO 4 .
  • an incongruently-soluble salt undergoes a disproportionation reaction as it dissolves.
  • An example is the acidulant hemipotassium phosphate (HKP), expressed as KH 5 (PO 4 ).
  • HKP acidulant hemipotassium phosphate
  • the system at equilibrium consists of a solution (more acidic than HKP) in equilibrium with solid monopotassium phosphate, KH 2 PO 4 .
  • incongruently-soluble phosphates One method of producing incongruently-soluble phosphates is crystallization from solution.
  • An incongruently-soluble salt cannot be prepared by crystallization from a solution having the same ionic ratio as the salt itself.
  • an incongruently-soluble salt is necessarily prepared by crystallization from a solution having a different ionic ratio as the salt. The ratio of ions and the concentration are adjusted such that the overall composition is supersaturated with respect to the desired salt.
  • the compositions yielding incongruently-soluble salts by crystallization from solutions can be determined from a phase diagram of the appropriate system. A slurry is thereby produced wherein the solid phase is the crystallized phosphate salt.
  • the ion ratio and the concentration required to crystallize an incongruently-soluble salt can be determined from an aqueous phase diagram representing the salt.
  • the ion source may be (but is not limited to) phosphoric acid and the appropriate base or bases. Supersaturation may be achieved through cooling, evaporation of water, etc.
  • the phosphate is recovered from the slurry through a solid-liquid separation technique such as centrifugation or filtration. The separation process generally leaves an amount of mother liquor entrained with the crystals.
  • the entrained mother liquor, having a composition different than that of the product salt, may adversely impact the chemical and physical properties of the phosphate.
  • the mother liquor for salts such as HKP and SALP contain phosphoric acid (free acid).
  • the presence of phosphoric acid can adversely impact the purity and the physical properties of the product crystals, including the hygroscopicity, handling characteristics, and fiowability. It is therefore necessary to remove as much of the entrained mother liquor containing free phosphoric acid as possible from the crystals.
  • the mother liquor is generally removed from the solids by washing. Drying the crystals alone is insufficient for the removal of free acid.
  • washing techniques to remove the mother liquor from the solids include the use of either water, a saturated solution, or a phosphoric-miscible organic solvent.
  • Washing the solids with water during or immediately after the separation step may result in a disproportionation reaction of incongruently-soluble solids with the water.
  • the product crystals may therefore be contaminated with phosphoric acid or more basic phosphate compounds.
  • Water washing may not sufficiently reduce the phosphoric acid content (free acid) because of the reaction of the incongruently-soluble salt with the water wash to generate additional phosphoric acid.
  • the salt is highly soluble, water washing of the separated salts results in low recoveries of the solids because of the dissolution of the salt.
  • U.S. Patent No. 4,329,326 discloses the use of a saturated monoammonium phosphate solution for washing monoammonium phosphate crystals.
  • the monoammonium phosphate is a congruently-soluble compound which will not disproportionate upon dissolution. Therefore, washing with an aqueous monoammonium phosphate solution does not introduce impurities, does not reduce recovery of the solids, and does not undergo reaction with the solids.
  • the monoammonium phosphate solution which is entrained in the washed cake is converted to solid monoammonium phosphate upon subsequent drying.
  • the crystallization mother liquor is the saturated solution of the salt. Washing with a saturated solution of the salt, as in U.S. Patent No. 4,329,326, therefore does not constitute a wash since the washed solids would have essentially the same quantity and composition of entrained mother liquor as the unwashed solids.
  • the saturated solution wash would be of a different ionic ratio than the crystals and impurities would therefore be introduced upon subsequent drying.
  • the saturated wash solution would contain a high level of free acid and would therefore be ineffective in removing free acid.
  • a novel method for producing incongruently-soluble acid phosphates in a solution crystallization process by incorporating a phosphate wash solution improves the product purity by removing entrained free acid from the surface of the crystals. Furthermore, the method of the present invention results in significantly higher product recoveries compared to conventional crystal washing techniques.
  • the method of the present invention generally involves washing incongruently-soluble acid phosphate crystals produced in a solution crystallization process. The crystals are formed in a reaction slurry and then separated from the solution. Some of the solution remains on the crystal surface in the form of entrained phosphoric acid or free acid. The entrained free acid must be removed in order to maintain product purity.
  • the method of the present invention utilizes a phosphate solution wash to displace the entrained free acid from the crystal surface.
  • the phosphate solution generally has a common metal ion with the incongruently soluble acid phosphate to reduce impurities introduced into the process.
  • the phosphate solution is passed over the wet crystals and displaces the entrained free acid without dissolving a significant amount of the crystals.
  • the phosphate solution used for washing in accordance with this invention may contain phosphoric acid as well as a salt such as e.g., monosodium phosphate or monopotassium phosphate.
  • a salt such as e.g., monosodium phosphate or monopotassium phosphate.
  • this invention also includes the use of phosphoric acid solution as a wash (common ion is hydrogen).
  • a phosphoric acid wash would be used at a lower concentration than the free acid content of the entrained mother liquor in order to reduce the free acid content.
  • the entrained mother liquor in a SALP wet cake may typically be 62% P 2 O 5 ; washing with a phosphoric acid having a concentration below 62% P 2 O5 may substantially reduce the free acid content of the washed cake as the entrained wash has a lower density and viscosity than the mother liquor which it displaces.
  • the present invention includes a process for producing mixed cation, incongruently-soluble acid phosphates.
  • the process involves the formation of an acidic solution having a molar excess of phosphorus over the theoretically required amount to form the specific mixed cation phosphate.
  • the process eliminates the formation of intermediate phases of the mixed cation phosphate thus eliminating additional processing steps and resulting in improved production rates and better control of crystallization.
  • the crystals are then washed with a phosphate solution in accordance with the present invention.
  • a phosphate wash solution is utilized upon separation of the incongruently-soluble acid phosphate crystals from the reaction slurry.
  • the wash removes entrained free acid from the crystal surface. The removal of the entrained free acid from the crystal surface reduces the hygroscopicity and improves the product purity and physical properties of the incongruently-soluble acid phosphate.
  • a phosphate wash solution wash reduces the amount of incongruently-soluble acid phosphate crystals that dissolve upon washing.
  • Fig. 1 is a graph comparing the moisture pick up, in weight percent, over time for HKP crystals washed with water and HKP crystals washed with monopotassium phosphate;
  • Fig. 2 is a graph illustrating the effect of varying K/P mole ratios in the wash solution on the free acid content of the finished crystals
  • Fig. 3 is a graph indicating the effect of varying K/P mole ratios in the wash solution on the K/P mole ratio of the finished crystal;
  • Fig. 4 is a graph illustrating the impact of the wash to wet cake ratio on the percent cake recovery after washing.
  • Fig. 5 is a graph illustrating the effect of increasing wash to wet cake ratios on the free acid content of SALP crystals.
  • incongruently-soluble acid phosphates prepared by crystallization from solution
  • the phosphate wash solution minimizes the reaction of the incongruently- soluble acid phosphate with the water from the wash solution.
  • the present invention also contemplates a solution crystallization process for producing mixed cation, incongruently-soluble phosphates.
  • the method of the present invention involves production of solid incongruently-soluble acid phosphates which may, for example, be used in food products.
  • the method of the present invention is suitable for use with incongruently- soluble compounds generally selected from the group consisting of hemipotassium phosphate, hemisodium phosphate, sodium aluminum phosphate, potassium aluminum phosphate, monocalcium phosphate, calcium potassium phosphate, or calcium ammonium phosphate.
  • the sodium aluminum phosphate compounds are generally expressed as Na3Al 2 H 15 (PO 4 ) 8 NaAl3H ] (PO ) 8 , NaAl3H j 4 (PO 4 ) 8 *4H 2 O.
  • Other incongruent-soluble phosphates may also be produced in accordance with the present inventive process.
  • Hemipotassium phosphate is a discrete equilibrium solid present in a concentrated acid portion of an aqueous potassium phosphate system. The compound is present at least over the temperature range of 0-50 °C, with no hydrates present over this range. The compound is highly soluble in water and decomposes to monopotassium phosphate and phosphoric acid.
  • Hemipotassium phosphate is in equilibrium with liquid at approximately 47 wt% P 2 O 5 and 13 wt% K 2 O to 57 wt% P 2 O 5 and 7 wt% K 2 O at 25°C.
  • the solubility of the compound increases with increasing temperatures.
  • the incongruently-soluble acid phosphates may be prepared by crystallization from aqueous solution.
  • the process generally involves making a reaction mixture of a phosphate containing compound and a metal containing compound at the appropriate metal to phosphorus ratio. Conventional sources of the metal and P 2 O 5 are suitable for use with the present invention.
  • the reaction mixture is then crystallized to form a handleable slurry with a significant yield i.e., usually containing about 20-50 wt% solids.
  • the solids are separated from solution and further processed before being collected. [(See refs.: B. Wendrow and K. A. Kobe, Chem.Rev. 54, 891 (1954); J. Myl and Z.Solc, Coll. Czech Chem. Comm.25,2414 (I960)].
  • the desired percent K 2 O and percent P2O5 f° r me reaction mixture are determined in accordance with a K 2 O-P 2 O5-H O phase diagram to yield 25-50% undissolved solids at about 25-30°C.
  • the desired potassium to phosphorus ratio for hemipotassium phosphate is dependent upon the temperature, but is about 0.19 to 0.45 at 25 °C.
  • the sources of potassium and phosphorus include, but are not limited to, potassium hydroxide, monopotassium phosphate, phosphoric acid.
  • a typical reaction may include 45% KOH and 85%
  • H3PO Mother liquor recycled from a solid/liquid separation step may also be used as a source of potassium and phosphorus. Temperatures while mixing the reactants may be considerably hotter (>80°C) than the final crystallization temperature.
  • the reaction mixture is crystallized to form a slurry.
  • the incongruently-soluble acid phosphates can be crystallized from solution provided the overall composition of the reaction mixture is within the phase envelope for the metal phosphate mixture.
  • an approximate composition range, at 25 °C, is 51-55 wt% P O 5 to 11-15 wt% K 2 O which yields approximately 20-50% solids.
  • Crystallization of the incongruently-soluble acid phosphate will occur when the solution becomes supersaturated, for example, through cooling or evaporation. The appearance of crystals does not typically occur spontaneously when the solubility limit is exceeded.
  • Crystallization may be initiated by seeding the mixture with previously produced crystals or with an unfiltered slurry from a previous reaction mixture. In general, seeding is accomplished by adding about 1 to 10 parts by weight of slurry to 100 parts total reaction mass. Alternatively, seeding may be accomplished by adding about 0.1 to 5 parts by weight of crystals to 100 parts total reaction mass. The seeding occurs at a temperature where the system is supersaturated. The addition of crystals at higher temperatures may result in the dissolution of the crystals.
  • a mixed cation, incongruently-soluble phosphates may be produced through a solution crystallization method.
  • the process generally involves the formation of a reaction mixture having a different mixed cation to phosphorus ratio than theoretically required by the stoichiometry of the finished incongruently-soluble phosphate crystals.
  • Conventional processes utilize drying a reaction mixture close to theoretical ratio requirement and may involve making an intermediate phase product to obtain a solid.
  • the intermediate phase product requires additional processing in order to achieve the desired finished crystal.
  • the present inventive process is capable of producing the desired finished product from a reaction mixture having a higher concentration of phosphorus.
  • the crystallization of mixed metal phosphates from solution is accomplished by preparing a composition which lies within a two phase envelope for the desired crystal form.
  • Phase diagrams for four component systems, such as mixed cation phosphate salts, are generally not available. Therefore, practical ranges for the components and temperatures are established through equilibrium experimentation.
  • the overall composition of the system must lie within the phase envelope of the desired solid phase (crystal).
  • the solution crystallization method of the present invention utilizes a reaction mixture having an excess molar amount of phosphorus that is still within the phase envelope of the desired incongruently-soluble crystals. Excess molar amounts of phosphorus in the reaction mixture are capable of producing the desired incongruently-soluble phosphate directly from solution without first forming intermediate phases of the salt.
  • a sodium aluminum phosphate expressed as Na3Al 2 H j 5 (PO 4 ) 8
  • a sodium aluminum phosphate may be crystallized at a temperature of about 80 °C when the reaction mixture has an approximate composition range of: 57-65% P O 5 , 0.05 to 0.2 Al 2 O 3 / P 2 O 5 mole ratio, and 1 to 4 Na O/Al 2 O 3 mole ratio.
  • the composition ranges for the crystallization of other mixed cation, incongruently-soluble phosphates at specific temperatures are generally determined through equilibrium experiments.
  • the process involves the formation of a reaction mixture containing source compounds for the desired mixed metal cations. Additionally, the phosphorus source, such as phosphoric acid, is added to the reaction mixture. Water may also be present in the reaction mixture.
  • the phosphorus source such as phosphoric acid
  • An adjustment in the amount of water in the reaction mixture may be necessary in order to crystallize the incongruently-soluble phosphate.
  • the adjustment may involve either the addition of water or the evaporation of water from the system.
  • Temperature limitations for evaporation may be necessary in order to prevent the formation or crystallization of an undesirable phase of mixed cation crystals or to minimize corrosion of the equipment.
  • the temperature of the reaction mixture may be maintained by introducing sweep air across the surface of the reaction mixture.
  • seed crystals may be introduced into the reaction mixture to facilitate crystallization.
  • the seed crystals can be introduced during the evaporation step or anytime thereafter. The time at which the seeding occurs may have an impact upon the finished crystal size. Seeding during the evaporation step initiates nucleation under a relatively low degree of super saturation which favors growth of a fewer number of large crystals. If seeding is initiated later in the process, the reaction mixture is more supersaturated which favors nucleation over growth. Thus, smaller crystals are generated.
  • the mixed cation reaction mixture is cooled to further crystallize the incongruently-soluble phosphate.
  • the resulting crystals are separated from the slurry utilizing conventional liquid/solid separation techniques and equipment.
  • the use of an excess amount of phosphoric acid in the reaction mixture results in an acidic slurry.
  • the separated crystals will have a high amount of entrained free acid on the crystal surface. Washing the crystals during the separation step or immediately thereafter is necessary to enhance the physical properties of the finished crystals. Washing is therefore accomplished in accordance with the present invention through the use of a phosphate solution having a common ion (metal or hydrogen ion) with the mixed cation, incongruently-soluble phosphate.
  • SALP sodium aluminum phosphate
  • a solution crystallization process for the compound may be initiated by forming a reaction mixture of phosphoric acid and alumina trihydrate in excess water. The mixture is heated to about 80 °C until the alumina is completely dissolved. Sodium hydroxide is then introduced over time into the reaction mixture. The temperature of the reaction mixture increases to about 115°C during the addition of the sodium hydroxide.
  • a composition of the reaction mixture which is suitable for producing the phase of SALP expressed as Na 3 Al 2 H 15 (PO 4 ) 8 is: 61-64% P 2 O 5 , 0.08 to 0.1 Al 2 O3. P 2 O5 mole ratio, and 1.5 to 1.6 Na 2 O/Al 2 O3 mole ratio.
  • Other sodium, aluminum, and phosphorus sources may be suitable for practicing the method of the present invention.
  • the excess water in the reaction mixture is evaporated by heating the mixture to a temperature no greater than about 130 °C while utilizing sweep air to maintain the temperature. Seed crystals are added part way through the evaporation step to induce crystallization.
  • the concentrated slurry is then cooled to a temperature between 70-90 °C for crystal growth. The crystals are then separated from the slurry and washed with the process of the present invention.
  • the crystallization of all incongruently-soluble phosphates results in phosphate crystals having relatively large particles which are well suited for separation from the reaction slurry.
  • the separation of the crystals is preferably accomplished through either filtration or centrifugation.
  • other separation techniques are suitable for use in with the present inventive process.
  • the metal to phosphorus mole ratio of the reaction slurry can enhance the separation of the crystals from the slurry.
  • a mole ratio at the higher end of the 0.19 to 0.32 potassium to phosphorus range will result in a mother liquor with a lower P 2 O 5 content and lower viscosity which improves the ability to remove the mother liquor from the crystals during the separation step of the process.
  • the separated crystals in the form of a moist cake, generally have about 1.5 to about 15 percent entrained free acid depending upon the solution crystallization process utilized in forming the crystals.
  • the entrained free acid is in the form of P 2 O5-
  • the washing or displacement of the entrained free acid is important in recovering a dry, non-hygroscopic product. Washing with water to displace the entrained free acid is not desirable because of the solubility of the incongruently- soluble phosphate or reaction of water with the salt. A water wash will therefore result in a lower recovery of product or an impure product. Furthermore, the product will have a relatively high free acid content.
  • rapid washing of the cake with a phosphate solution displaces the entrained free acid or acidic mother liquor with reduced dissolution of, and reaction with, the highly soluble acid phosphate.
  • the phosphate solution generally has a common ion with the incongruently-soluble phosphate crystal. The washing must occur rapidly to retard dissolution of the phosphate crystal. The washing is performed using conventional equipment during the separation step or immediately thereafter.
  • the wash solution may be a saturated solution in order to minimize the amount of water.
  • Examples of the phosphate wash solutions for washing sodium aluminum phosphate include solutions of monosodium phosphate, mixtures of monosodium phosphate with either phosphoric acid or disodium phosphate, or phosphoric acid solutions.
  • Examples of the phosphate wash solutions for washing hemipotassium phosphate include solutions of monopotassium phosphate, mixtures of monopotassium phosphate with either phosphoric acid or dipotassium phosphate, or phosphoric acid solutions. These examples are illustrative and the invention is not to be limited by these examples.
  • the metal to phosphorus mole ratio utilized in the wash solution is generally about 0.50 to about
  • the wash rate to wet cake ratio used in the method of the present invention is generally about 0.1 to about 1.0. Higher ratios may result in the dissolution of crystals while lower ratios result in the incomplete removal or displacement of entrained free acid.
  • a preferred solution wash to wet cake ratio for hemipotassium phosphate is about 0.15 to about 0.5.
  • a wash solution of saturated potassium phosphate may be utilized.
  • the mole ratio of the wash solution is about 0.5 to about
  • the washed cake is dried to remove water from the saturated solution remaining on the surface of the crystal.
  • Conventional drying techniques and equipment are suitable for practicing the method of the present invention.
  • the drying temperature is selected to efficiently achieve the removal of water without degrading the crystals.
  • the excess solution is removed by heating the cake to temperatures less than about 100°C, with a preferred drying range of about 80-95 °C.
  • the incongruently-soluble phosphates exhibit about a 2% to 10% weight loss during the drying step.
  • the free acid content on the surface of the crystal product will also decrease during the drying step.
  • the decrease in entrained free acid is due to the washed wet cake having some dissolved congruently-soluble phosphate and phosphoric acid on the crystal surface. Upon drying, the congruently soluble phosphate and the phosphoric acid react to form more incongruently-soluble acid phosphate.
  • the finished product is a dried crystalline incongruently-soluble acid phosphate.
  • the product has a free acid content of less than about 1.0%.
  • the hygroscopicity of the product is dependent upon the free acid content.
  • a reduced free acid content on the crystal surface reduces the amount of moisture pick up by the crystals over time.
  • the method of the present invention results in greater than 50% recovery of the incongruently-soluble acid phosphate crystals from the separated cake.
  • the recovered product With hemipotassium phosphate, the recovered product has a mean particle size of about 200-350 microns.
  • Recovered sodium aluminum phosphates have a mean particle size from about 60 to about 95 microns.
  • hemipotassium phosphate samples were prepared in order to demonstrate the method of the present invention. Each sample was prepared by reacting approximately 34 grams of 45% KOH and approximately 86 grams of 85% H3PO The solution was then heated to evaporate approximately 20 grams of H 2 0. The solution, of approximately 100 grams, contains 13 weight percent K 2 O and 53 weight percent P 2 O $ Approximately 1.7 grams of a hemipotassium potassium phosphate reaction slurry from a previous reaction was added to the solution as seed crystal while stirring the solution maintained at 40 °C. The solution was then cooled to 25 °C to facilitate the precipitation of hemipotassium phosphate crystals. The reaction slurry was then vacuumed filtered to obtain approximately a 30 gram filter cake.
  • the wet filter cake was then sprayed evenly with either 15 grams of saturated monopotassium solution at 25 °C or water at 25 °C while still under vacuum. The washed cake was then dried at 80°-95°C to remove the saturated solution remaining on the surface of the crystals.
  • the finished product was identified as hemipotassium phosphate by titration to determine the appropriate potassium to phosphorus mole ratio, which was approximately 0.5.
  • the entrained free acid remaining on the surface of the crystal was determined by extracting a 5-10 gram sample of the hemipotassium phosphate in 100 milliliters of ethyl acetate while stirring for eight minutes. The ethyl acetate phase was separated by filtration and a portion titrated break-to-break with 0.1 N NaOH. The free acid was reported as wt% P O 5
  • the extracted solids were then utilized to determine the potassium to phosphorus mole ratio of the compound. The results are indicated in Table I.
  • the particle size measurements of the finished product were determined on a Coulter LS 130 particle size analyzer.
  • the sample was suspended in air as a dry powder.
  • the mean particle size for the samples were generally between 200 and 340 microns.
  • the hygroscopicity of a solution washed sample and a water washed sample, produced in accordance with the present example, were determined by subjecting the samples to a controlled atmosphere at 58% relative humidity and 25 °C. The surface area was determined for each sample in order to normalize the rate of moisture pick-up. The samples were maintained in the controlled atmosphere for over 24 hrs. The moisture pick-up, in weight percent, of the phosphate salt solution washed sample was less than the moisture pick-up of the water washed sample after
  • Figure 1 is a graph of the moisture pick-up (weight percent) over time for both of the samples. The curve connecting the measured points was fitted utilizing a third order polynomial.
  • a hemipotassium phosphate solution was produced by reacting 561 grams of 45%) potassium hydroxide with 1391 grams of 85% phosphoric acid. Excess water was evaporated from the mixture by heating the solution until it reached a final weight of 1629 grams. The composition of the finished solution was 13 weight percent K 2 O and 53 weight percent P O5 with a K/P ratio of about 0.37. The hot solution was divided into different portions. Each sample was then allowed to cool to 55 °C, upon which about 1 gram of HKP seed crystals were added to the solution to initiate crystallization. The solution was then cooled to 25 °C to form about 60 grams of crystals per 100 ml of solution.
  • the samples were vacuum filtered in coarse frit Buchner funnels for several minutes until most of the liquid was removed. A wash of saturated monopotassium phosphate solution at 25 °C was distributed over the cake while vacuum was applied. The wash K/P ratio was varied for each sample. The wash per wet cake ratio was 0.17 ml wash per gram wet cake. The cake was then dried in an oven at 90 °C. The dried cake was then weighed and analyzed for free acid content and K/P mole ratio.
  • FIG. 2 is an illustration of the weight percent free acid plotted for wash solution with various K/P mole ratios. The graph generally indicates that free acid content appears to be minimized at a wash K/P ratio of about 1.0.
  • Figure 3 is a plot of the K/P mole ratio of the finished product for solution washes having various K/P mole ratios. The graph indicates that higher wash ratios result in higher metal to phosphorus mole ratios in the finished product.
  • a Hemipotassium phosphate solution was produced by the reaction procedure described in Examples 5-9.
  • the sample size during washing with the phosphate salt solution was larger than Examples 5-9 in order to demonstrate the impact of the wash on a larger crystal mass.
  • Hemipotassium phosphate crystals in solution were filtered on a 350 mm Buchner Filter while being washed with 54.6 grams of 1.0 K/P mole ratio solution of monopotassium phosphate.
  • the wet cake had a free acid content of 2.3% (as wt% P 2 O 5 ).
  • the ratio of MKP wash per weight of wet cake was 0.19. Sixty-nine percent of the cake was recovered upon washing.
  • Example 10 The sample was split into a 104 gram portion (Example 10) and a 69 gram portion (Example 11) for drying.
  • Example 10 Each washed cake example was dried by blowing hot air over the solids in a rotating can (to simulate a rotary drier). The bed temperature during drying was about 102-104°C for each example.
  • the K/P mole ratio and free acid content for each example was determined.
  • Example 10 had a K/P mole ratio of 0.54 and a free acid content of 0.31 wt% P 2 O 5 .
  • Example 11 had a K/P mole ratio of 0.53 and a free acid content of 0.2 wt% P 2 O 5 .
  • Hemipotassium phosphate sample were produced, filtered, and washed in a similar manner as described in Examples 5-9.
  • the samples were washed with a monopotassium phosphate solution at various wash to wet cake ratios.
  • the results are listed in Table III.
  • Fig. 4 is a graph of the percent cake recovery versus the wash to wet cake ratio. The results indicate that the percent recovery of finished crystals decreases with increasing wash to wet cake ratios. Additionally, the results indicate that a high wash to wet cake ratio may change the finished product K/P ratio (Example 17).
  • Sodium aluminum phosphate samples were prepared in order to demonstrate the solution crystallization and phosphate salt solution wash methods of the present invention.
  • a reaction flask containing 517 grams of 85% phosphoric acid and 30 grams of alumina trihydrate, Al 2 O 3 *3H 2 O was agitated and heated to a temperature of about 60°C.
  • the alumina trihydrate dissolved within 45 to 60 minutes as the temperature was increased up to 82 °C.
  • 48 grams of 50% sodium hydroxide was added over 6 to 8 minutes with the use of a peristaltic pump.
  • the reaction components resulted in a reaction mixture having a molar ratio of 2 moles Al: 3 moles Na: 22 moles of P.
  • the temperature of the solution was increased to about 115°C. Sweep air was then introduced at a rate of 20-25 SCFH over the reaction surface while the solution is heated to evaporate water. After the evaporation of 30 to 40 grams of water, crystallization was initiated by adding 10 grams of sodium aluminum phosphate from a previous sample as seed crystals. The evaporation of water continued until 65 to 80 grams was removed and the reaction temperature reached 115°C to l25°C.
  • reaction slurry was cooled to 80 °C and held at that temperature for one hour.
  • Slurry samples of 30 ml each, were removed and vacuum filtered at 80°C on 60 ml coarse frit glass filters. The vacuum was applied until little additional liquid was removed from the underside of the filter. The filtered cake was at a bed depth of about ' ⁇ inch. Each sample was then weighed and recorded.
  • Each sample of filtered crystals was then washed with either water, a 40%) monosodium phosphate solution, or a 40% phosphoric acid solution.
  • the wash solution for each sample was applied to the crystals through a wash bottle while the sample was vacuum filtered.
  • the solution was applied in a sweeping motion in order to contact the entire surface area of the cake.
  • the wash liquid was filtered through the cake after 30 to 45 seconds.
  • the cake was then weighed a second time to determine the percent of cake lost during washing.
  • the resulting crystals exhibited a mean particle size ranging from 60 to 95 microns.
  • the ratio of wet cake to wash solution was varied for different samples. Additionally, the monosodium phosphate concentration and the sodium to phosphorus ratio of the wash were varied to determine the impact on the free acid content and recovery of the finished sodium aluminum phosphate crystals.
  • the washing results with the 40%) monosodium phosphate solution, the 40%) phosphoric acid, and water are listed in Table IV.
  • the results indicate that the free acid content of the samples washed with monosodium phosphate is significantly lower than the free acid content of the samples washed with either water or phosphoric acid.
  • Examples 18-23 indicate a preferred free acid content on the finished sodium aluminum phosphate crystals, expressed as Na 3 Al 2 H j 5 (PO 4 ) 8 , of less than about 1.0% (P 2 O 5 ).
  • Examples 18-23 indicate a more preferred free acid content on the finished sodium aluminum phosphate of less than about 0.5% (P 2 O 5 ).
  • the samples washed with monosodium phosphate had lower cake losses than the samples washed with phosphoric acid or water.
  • Table VI represents the results of varying the sodium to phosphorus (Na/P) ratio of the 40%) monosodium phosphate wash.
  • the free acid content was the lowest at a Na/P ratio of about 1.
  • the table indicates that the percent cake loss decreased with increasing sodium to phosphorus ratios in the wash.
  • a reaction flask containing 775.5g of 85.7% phosphoric acid and 45.8g alumina trihydrate was agitated and heated to about 68°C to dissolve the alumina.
  • 71.5 Ig of 50%) sodium hydroxide was added over 6 to 8 minutes, resulting in a solution with a Al 2 O3.
  • the solution was heated under an air sweep (20 SCFH) to evaporate water. 15.0g of sodium aluminum phosphate was added as seed crystal upon the evaporation of 36g water.
  • the final temperature rose to 128°C and the final weight 786.4g (total water evaporated about 121.4g), resulting in a final P 2 O 5 concentration of about 62.4 wt%.
  • the reaction slurry was cooled to 80°C and held at that temperature for one hour. The mean particle size was 93 micron.
  • the reaction slurry was separated at 80°C into roughly three equal portions and each portion was vacuum filtered. The wet cake represented approximately 27%) of the reaction slurry by weight. Each portion was washed with either water, 40%) phosphoric acid, or 40%) MSP solution. The washed cakes were dried at 106°C.
  • Calcium carbonate was added to 24.01 g of each washed and dried sample at a level to neutralize 0.5% free acid in excess of the measured free acid content (neutralization to monocalcium phosphate).
  • Silica was added to each sample as a flow conditioner. The materials are mixed while milling in a small coffee grinder and redried at 106°C for one hour. The final material of example 44 had the lowest tendency towards caking upon storage.
  • the pick up of moisture from the atmosphere for 4 g samples after 24 hr at 75%> relative humidity and ambient temperature are as follows.
  • Example 44 The phosphoric acid-washed sample (Example 44) is the least hygroscopic while the water-washed sample (Example 45) is the most hygroscopic.
  • Example 46 The phosphoric acid-washed sample (Example 44) is the least hygroscopic while the water-washed sample (Example 45) is the most hygroscopic.
  • a reaction flask containing 625.4g of 86.4%) phosphoric acid and 37.4g alumina trihydrate was agitated and heated to about 65°C to dissolve the alumina.
  • the solution was heated under an air sweep (5 SCFH) to evaporate water.
  • 0.5g of sodium aluminum phosphate was added as seed crystal upon the evaporation of ⁇ 23g water.
  • the reaction slurry was cooled to 120°C and held at that temperature for one hour. The mean particle size was 102 micron.
  • the 499g of the reaction slurry was vacuum filtered yielding lOOg of wet cake.
  • the cake was washed with 75.5g of 80%> phosphoric acid at a rate of ⁇ 30ml/min.
  • the free acid content after washing and drying was 5.07 wt% (as P 2 O 5 ).

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Abstract

L'invention a trait à un procédé de production de phosphates acides de métal alcalin à solubilité non congruente dans le cadre d'un processus de cristallisation de solution par incorporation d'une solution de lavage à base de phosphate. Cette solution accroît la pureté du produit en enlevant l'acide libre captif de la surface des cristaux de phosphate à solubilité non congruente. Le lavage améliore ainsi les propriétés physiques des cristaux, notamment leur capacité hygrométrique et leurs caractéristiques de manoeuvrabilité. Cette solution de lavage au phosphate réduit de manière significative la quantité de cristaux dissous au cours de l'étape de lavage et, partant, facilite la récupération et ce, en comparaison des résultats obtenus au moyen des techniques habituelles de lavage de cristaux. L'invention porte, de surcroît, sur une technique de cristallisation de solution aux fins de la production de cristaux de phosphate à solubilité non congruente à cation mixte. Le procédé fait intervenir un mélange réactionnel dont le volume molaire théorique de phosphore nécessaire au sel phosphate à solubilité non congruente est excédentaire. La surface du cristal est alors débarrassée de l'acide libre captif du volume excédentaire de phosphore à l'aide d'une solution à base de phosphate.
PCT/US1998/008140 1997-04-23 1998-04-23 Procede de cristallisation de solution aux fins de la production de phosphates acides a solubilite non congruente par incorporation d'une solution de lavage a base de sel phosphate Ceased WO1998047814A1 (fr)

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AU71493/98A AU7149398A (en) 1997-04-23 1998-04-23 Solution crystallization process for the production of incongruently-soluble acid phosphates by incorporating phosphate salt solution wash

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Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2011110212A1 (fr) 2010-03-08 2011-09-15 Prayon S.A. Composition comprenant de l'hémipotassium phosphate.
EP2004574B1 (fr) 2006-03-09 2016-03-02 Rotem Amfert Negev Ltd. Compositions d'engrais solides, fluides, solubles et solubilisantes et leur préparation
EP2867160A4 (fr) * 2012-06-28 2016-05-25 Rotem Amfert Negev Ltd Procédé continu de fabrication d'un engrais granulaire neutre p/k
CN115849318A (zh) * 2022-12-26 2023-03-28 施可丰化工股份有限公司 一种全水溶粉状磷酸二氢钾的生产工艺
CN116514083A (zh) * 2023-05-09 2023-08-01 上海沃凯生物技术有限公司 医用高透明度无水磷酸氢二钾的生产工艺
CN116573656A (zh) * 2023-06-09 2023-08-11 广东盛祥新材料科技有限公司 一种基于高扬程热水泵的碳酸锂洗涤工艺

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FR659360A (fr) * 1928-09-05 1929-06-27 Ig Farbenindustrie Ag Procédé pour l'obtention d'orthophosphates alcalins
FR710343A (fr) * 1930-03-04 1931-08-21 Metallgesellschaft Ag Procédé pour la préparation de phosphates alcalins primaires, convenant par exemple comme engrais, à partir de combinaisons phosphorées de métaux, en particulier de phosphure de fer
FR720577A (fr) * 1930-08-01 1932-02-22 Scient & D Entpr S Ind Soc Et Procédé pour la préparation de phosphates monoalcalins
DE971182C (de) * 1950-02-21 1958-12-24 Metallgesellschaft Ag Verfahren zur Herstellung von phosphorsauren Salzen
US3411872A (en) * 1967-07-24 1968-11-19 Stauffer Chemical Co Method of producing nonhygroscopic sodium aluminum phosphate
ES395802A1 (es) * 1971-10-07 1973-12-01 Cros Sa Procedimiento de preparacion de sales potasicas yno amoni- cas de acidos fosforicos y polifosforicos.
EP0031803A2 (fr) * 1979-12-26 1981-07-08 FMC Corporation Méthode de production de phosphate cristallin de sodium et d'aluminium
WO1997009270A1 (fr) * 1995-09-08 1997-03-13 Monsanto Company Procede de preparation de phosphate hemipotassique

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FR659360A (fr) * 1928-09-05 1929-06-27 Ig Farbenindustrie Ag Procédé pour l'obtention d'orthophosphates alcalins
FR710343A (fr) * 1930-03-04 1931-08-21 Metallgesellschaft Ag Procédé pour la préparation de phosphates alcalins primaires, convenant par exemple comme engrais, à partir de combinaisons phosphorées de métaux, en particulier de phosphure de fer
FR720577A (fr) * 1930-08-01 1932-02-22 Scient & D Entpr S Ind Soc Et Procédé pour la préparation de phosphates monoalcalins
DE971182C (de) * 1950-02-21 1958-12-24 Metallgesellschaft Ag Verfahren zur Herstellung von phosphorsauren Salzen
US3411872A (en) * 1967-07-24 1968-11-19 Stauffer Chemical Co Method of producing nonhygroscopic sodium aluminum phosphate
ES395802A1 (es) * 1971-10-07 1973-12-01 Cros Sa Procedimiento de preparacion de sales potasicas yno amoni- cas de acidos fosforicos y polifosforicos.
EP0031803A2 (fr) * 1979-12-26 1981-07-08 FMC Corporation Méthode de production de phosphate cristallin de sodium et d'aluminium
WO1997009270A1 (fr) * 1995-09-08 1997-03-13 Monsanto Company Procede de preparation de phosphate hemipotassique

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CHEMICAL ABSTRACTS, vol. 82, no. 9, 3 March 1975, Columbus, Ohio, US; abstract no. 56672f, SOCIEDAD ANON. CROS: "Potassium and/or ammonium salts of phosphoric and polyphosphoric acids" XP002074041 *

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP2004574B1 (fr) 2006-03-09 2016-03-02 Rotem Amfert Negev Ltd. Compositions d'engrais solides, fluides, solubles et solubilisantes et leur préparation
WO2011110212A1 (fr) 2010-03-08 2011-09-15 Prayon S.A. Composition comprenant de l'hémipotassium phosphate.
EP2867160A4 (fr) * 2012-06-28 2016-05-25 Rotem Amfert Negev Ltd Procédé continu de fabrication d'un engrais granulaire neutre p/k
RU2633569C2 (ru) * 2012-06-28 2017-10-13 Ротем Амферт Негев Лтд. Непрерывный способ производства нейтрального гранулированного фосфорно-калийного (р/к) удобрения
CN115849318A (zh) * 2022-12-26 2023-03-28 施可丰化工股份有限公司 一种全水溶粉状磷酸二氢钾的生产工艺
CN116514083A (zh) * 2023-05-09 2023-08-01 上海沃凯生物技术有限公司 医用高透明度无水磷酸氢二钾的生产工艺
CN116573656A (zh) * 2023-06-09 2023-08-11 广东盛祥新材料科技有限公司 一种基于高扬程热水泵的碳酸锂洗涤工艺
CN116573656B (zh) * 2023-06-09 2023-11-24 广东盛祥新材料科技有限公司 一种基于高扬程热水泵的碳酸锂洗涤工艺

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