Process for producing crystalline DTPMP
10590153 · 2020-03-17
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Abstract
The present invention relates to crystallizates of the pure aminoalkylenephosphonic acid DTPMP in three crystal polymorphs and to a process for obtaining solid crystalline DTPMP by a preferably one-stage crystallization from an aqueous product mixture comprising DTPMP, wherein the process comprises the following process steps: (a) introducing seed crystals comprising DTPMP into an aqueous crude product comprising DTPMP with a total proportion in the range from 10 to 65 percent by mass up to a suspension density in the range from 1% to 25%; (b) introducing kinetic energy into the aqueous crude product to precipitate a crystallizate containing DTPMP as pure acid with a total content of at least 75% by mass; and (c) removing the crystallizate formed from the aqueous crude product by sedimentation and/or filtration, such that DTPMP is obtained as a solid end product in the form of a crystallizate.
Claims
1. Crystallisate of the pure acid diethylenetriamine penta(methylenephosphonic acid) (DTPMP) of the general formula (I) or a tautomeric form thereof: ##STR00003## wherein n is a number between 0 and 2, and wherein the crystallisate has at least one crystal modification selected from , and , wherein the crystal modification comprises the following characteristic reflections in the X-ray diffraction diagram, measured with Cu-K.sub. radiation: TABLE-US-00025 2 d 6.8 13.00 17.9 5.0 20.2 4.40 22.2 4.00 22.5 3.95 23.0 3.86 23.1 3.84 25.0 3.6. wherein the crystal modification comprises the following characteristic reflections in the X-ray diffraction diagram, measured with Cu-K.sub. radiation: TABLE-US-00026 2 d 6.7 13.17 18.6 4.77 19.6 4.5 20.0 4.4 22.1 4.0 22.5 3.9 23.0 3.9 24.8 3.6 25.2 3.5, and wherein the crystal modification comprises the following characteristic reflections in the X-ray diffraction diagram, measured with Cu-K.sub. radiation: TABLE-US-00027 2 d 13.0 6.8 17.9 4.9 22.0 4.0 22.4 4.0 23.1 3.8 23.3 3.8 25.1 3.6 26.1 3.4.
2. A process for obtaining solid crystalline diethylenetriamine penta(methylenephosphonic acid) (DTPMP) as the pure acid of the general formula (I) according to claim 1 or a tautomeric form thereof from an aqueous crude product containing DTPMP at a pH of less than 4, comprising the following steps: a. introducing seed crystals comprising DTPMP into an aqueous crude product containing DTPMP with a total fraction in the range of from 10 to 65% by mass, up to a suspension density in the range of from 1 to 25%, b. inputting kinetic energy into the aqueous crude product, whereby a crystallisate containing DTPMP as the pure acid in a total content of at least 75% by mass precipitates, and c. separating the crystallisate from the aqueous crude product by sedimentation and/or filtration.
3. The process according to claim 2, wherein the aqueous crude product contains impurities in the form of secondary products and/or unreacted educts.
4. The process according to claim 2, wherein the input of kinetic energy takes place in the form of stirring and/or shaking and/or ultrasound treatment.
5. The process according to claim 2, wherein the aqueous crude product for the obtainment of solid has a temperature in the range of from 25 to 85 C.
6. The process according to claim 2, wherein a separated crystallisate has a content of dry matter of at least 65%.
7. The process according to claim 2, wherein the process comprises at least one isothermal process stage in which the temperature difference in the aqueous crude product is constant over a defined period of the input of kinetic energy.
8. The process according to claim 7, wherein the temperature of the aqueous crude product is reduced with a temperature profile of from 1 to 7 K per day between the defined period of two isothermal process stages.
9. The process according to claim 2, wherein the process is completed in a quasi-continuous operation.
10. The process according to claim 2, wherein the aqueous crude product for the obtainment of solid comprises a strong acid in the range of from 1 to 4.5% by mass.
11. A method for purifying a water-containing crude product containing diethylenetriamine penta(methylenephosphonic acid) (DTPMP) in a total content of at least 10% by mass, said method comprising performing the processing according to claim 2 in order to purify said water-containing crude product containing DTPMP in a total content of at least 10% by mass.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
(1) The invention is to be described in greater detail by means of the following figures and embodiments, without limiting the invention thereto.
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EXAMPLES
Example 1Isothermal Procedure
(17) A starting amount of 4.5 kg of slurry, containing 40% by mass DTPMP and 3% by mass chloride in water, is placed in a double-walled 5-litre stirred tank reactor having a 14 cm anchor agitator. Seeding was carried out with 0.2 kg of solid containing 85% by mass DTPMP and 0.1% by mass chloride and having a main particle size of 20 m. A calculated initial suspension density of 4% by mass was obtained. Precipitation took place at a constant stirring speed of 150 rpm.
(18) A temperature profile is specified during the quasi-continuous process, whereby the temperature of the aqueous solution is first increased continuously over a period of 18 hours to a temperature of 58 C. and then the temperature is cooled continuously over a period of 72 hours by 1 K per 8 hours to a temperature of 46 C. and then kept constant for 70 hours. Samples of the slurry were removed at various times, and both the solution and the suspended solid were tested for their contents of DTPMP and chloride.
(19) TABLE-US-00004 Suspension DTPMP Chloride DTPMP Chloride Tem- density solution solution solid solid Test perature [% by [% by [% by [% by [% by time [ C.] mass] mass] mass] mass] mass] 0.5 58 14 38.9 3.0 55.2 2.1 18 58 16 39.6 3.1 53.1 2.2 24 58 16 38.9 3.1 54.3 2.2 42 55 21 39.2 3.1 53.2 2.2 48 54 21 39.8 3.2 52 2.3 66 51 30 36.3 3.2 50.8 2.4 72 50 33 37.5 3.2 52.6 2.4 90 46 44 34.3 3.4 49.5 2.4 96 46 48 33.9 3.4 48.8 2.5 115 46 59 31.8 3.6 47.4 2.5 140 46 67 29.6 3.7 49 2.6 161 46 73 29 3.9 45.8 2.6
(20) Separation of the crystallisate from the aqueous solution takes place in a filtering centrifuge having a perforated drum with a filtering area of 235 cm.sup.2 and at a centrifugation speed of 6500 rpm for 2 minutes. This centrifugation speed of 6500 rpm corresponds to a separating capacity of 3500 g. Three washing operations with washing water (corresponding to half the amount of solid, divided into 3 equal amounts) are then carried out. Finally, the separated crystallisate is dried for 5 minutes at a centrifugation speed of 10,000 rpm. This centrifugation speed of 10,000 rpm corresponds to a separating capacity of 8400 g.
(21) The particle sizes of the DTPMP crystallisates are determined by means of a laser diffraction particle size analyser LS 13 320/Beckmann Coulter at a wavelength of 780 nm.
(22) TABLE-US-00005 Mean [m] 60 d.sub.10 [m] 17 d.sub.90 [m] 113
(23) For characterising the breadth of a particle size distribution, the d.sub.10 and the d.sub.90 value are used in addition to the d.sub.50 value. The d.sub.50 value (mean) indicates the mean particle diameter, that is to say that exactly 50% of the particles are larger than or smaller than the indicated particle diameter, and is called the main particle size in the following. The d.sub.10 value refers to the particle diameter at which 10% of the particles are smaller than this limit value.
(24) Correspondingly, the d.sub.90 value indicates a particle diameter at which 90% of the particles are smaller than the indicated limit value.
(25) The crystallisates of the isolated solid have a cutter shape with an edge length of from 50 to 120 m, a width of from 10 to 50 m and a thickness in the range of from 1 to 5 m (cf.
(26) Following the test, the contents of DTPMP and chloride in the individual components were determined by complexometric titration and by argentometric titration, respectively.
(27) TABLE-US-00006 DTPMP Chloride Amount obtained, content content based on the [% by [% by amount of slurry mass] mass] Slurry 4.5 [kg] 40 3 Solid unwashed 34 [% by mass] 83.6 0.6 Solid washed 23 [% by mass] 87.2 0.1 Filtrate 65 [% by mass] 26.9 3.8 Washing water 29 [% by mass] 12.1 1.5
Example 2Continuous Procedure
(28) For continuous long-term production in the state over a total period of 8 weeks on an industrial scale, a starting amount of 10 kg of slurry, containing 40% by mass DTPMP and 3% by mass chloride in water, is placed in a 10-litre stirred tank reactor having an 11 cm propeller mixer. Seeding is carried out once by the introduction of 2 kg of solid containing 85% by mass DTPMP and 0.1% by mass chloride and characterised by a main particle size of 35 m. A calculated initial suspension density of 14% by mass is obtained. Precipitation takes place at a constant temperature of 40 C. and at a constant stirring speed of 280 rpm.
(29) During quasi-continuous long-term production, 2.5 kg of suspension are removed every 12 hours, the amount removed being replaced by the addition of an identical amount of fresh suspension (40% by mass DTPMP and 3% by mass chloride). Depending on the time at which the samples are removed, the suspension density, determined gravimetrically by means of centrifugation at 6500 rpm/2 minutes, is from 30 to 45%. This centrifugation speed of 6500 rpm corresponds to a separating capacity of 3500 g.
(30) The crystallisate is separated from the amount of slurry removed in a filtering centrifuge having a perforated drum with a filtering area of 235 cm.sup.2 and at a centrifugation speed of 6500 rpm for 2 minutes. This centrifugation speed of 6500 rpm corresponds to a separating capacity of 3500 g. Three washing operations with washing water (corresponding to half the amount of solid, divided into 3 equal amounts) are then carried out. Finally, the separated crystallisate is dried for 5 minutes at a centrifugation speed of 10,000 rpm. This centrifugation speed of 10,000 rpm corresponds to a separating capacity of 8400 g.
(31) The particle sizes of the DTPMP crystallisates are determined by means of a laser diffraction particle size analyser LS 13 320/Beckmann Coulter at a wavelength of 780 nm. The crystallisates of the isolated solid have a lance shape with an edge length of from 50 to 100 m, a width of from 10 to 50 m and a thickness in the range of from 1 to 5 m (cf.
(32) TABLE-US-00007 d.sub.50 [m] 50 d.sub.10 [m] 10 d.sub.90 [m] 95
(33) Following the test, the contents of DTPMP and chloride in the individual components were determined analogously to Example 1.
Example 3Influence of Seeding and Kinetic Energy Input
(34) In order to determine the influences of seeding and kinetic energy input on the stirring speed and the space-time yield (amount of crystallisate formed per crystallisation volume and per unit time), the tests described below were carried out as follows.
(35) A 250 ml screw-top jar clamped in a stand and provided with a perforated lid in order to reduce evaporative losses was equipped with a propeller mixer having a 4 cm stirring member driven by a stirring mechanism. The test setup was operated at room temperature in a fume cupboard.
(36) An aqueous solution comprising 25% by mass DTPMP was used as the slurry. The solid DTPMP acid used to prepare the slurry had, upon initial weighing, a content of 49.6% by mass DTPMP acid, 1.7% by mass chloride and 0.2% by mass orthophosphate as well as a main particle size of 15 m. This material was also used as the seed material. For seeding the slurry, the amount of solid DTPMP acid specified for the test was made into a suspension in a few millilitres of the slurry and introduced into the precipitation vessel by means of a pipette. The amount used was calculated as g of seed material per 100 g of slurry.
(37) The progress of crystallisation is determined by repeated measurements (according to the following table) of the DTPMP content in the filtrate.
(38) In order to determine the DTPMP content remaining in the slurry, samples were removed via a 45 m syringe filter and analysed by means of complexometric titration.
Result
(39) As shown in the following table, the combination of high stirring speed PLUS a large amount of seed material in test 1-1 results in the quickest depletion of the mother liquor and thus produces the greatest yield of crystallisate per unit time.
(40) Tests 2-1 and 3-1 here demonstrate that stirring, that is to say the input of kinetic energy, is the dominant factor. At a constantly high stirring speed, tests 1-1, 2-1 and 3-1 show a clear advantage for the larger amounts of seed material.
(41) TABLE-US-00008 Test no. 1-1 2-1 2-3 3-1 3-2 3-3 Seed amount 5 0.5 0.5 0.1 0.1 0.1 [% by mass] Resulting initial 2.4 0.25 0.25 0.05 0.05 0.05 suspension density [% by mass] Stirring [rpm] 160 160 0 160 40 0 DTPMP DTPMP in the DTPMP in DTPMP in DTPMP in DTPMP in in the Run filtrate the filtrate the filtrate the filtrate the filtrate filtrate time [% by [% by [% by [% by [% by [% by [h] mass] mass] mass] mass] mass] mass] 0 25.0 25.0 25.0 25.0 25.0 25.0 2 25.0 4 23.6 23.6 15 7.5 18.4 16 10.5 21 14.6 17.1 19.8 23 7.5 8.8 14.4 24 15.4 19.7 26 13.7 28 13.9 19.6 39 7.1 40 7.4 8.6 46 8.6 47 7.5 7.4 63 6.9 64 7.2 7.4 69 10.8 7.7 17.8 71 6.9 7.6 7.1 94 17.1 99 16.8 140 6.7 165 15.0
Example 4Process for the Production of the Crystal Modification, Isothermal at 70 C. and 60 C.
(42) A starting amount of 2 kg of slurry, containing 55% by mass DTPMP, 3.9% by mass chloride and 0.7% by mass ortho-phosphate, is placed in a double-walled 3-litre stirred reactor having a 14 cm anchor agitator. Seeding was carried out once with 140 g (about 7% by mass) of crystallisate of the crystal modification comprising 82.5% by mass DTPMP and 0.09% by mass chloride and having a main particle size of 50 m. Precipitation took place at a constant stirring speed of 180 rpm.
(43) The quasi-continuous process is left isothermal over a period of 19 days. The crystallisation is first left at a constant initial temperature of 70 C. for 7 days and then the temperature is lowered to 60 C. and left for a remaining period of 12 days. The matured crystallisate is separated from the aqueous solution in a filtering centrifuge having a perforated drum with a filtering area of 235 cm.sup.2 and at a centrifugation speed of 6800 rpm for 2 minutes. This centrifugation speed of 6500 rpm corresponds to a separating capacity of 3500 g. Three washing operations with washing water (corresponding to half the amount of solid, divided into 3 equal amounts) are then carried out. Finally, the separated crystallisate is dried for 5 minutes at a centrifugation speed of 10,000 rpm. This centrifugation speed of 10,000 rpm corresponds to a separating capacity of 8400 g.
(44) The suspension density, that is to say the solids content of the suspension in % by mass, is determined gravimetrically via a benchtop centrifuge in 12 ml vials at 6500 rpm. This centrifugation speed of 6500 rpm corresponds to a separating capacity of 3500 g.
(45) Analytical values during isothermal procedure at 70 C.:
(46) TABLE-US-00009 Chloride DTPMP Chloride fraction content content in DTPMP [% by [% by [% by Amount mass] mass] mass] [g] Filtrate 49.8 2.69 5.2 789 Solid unwashed 90.9 0.28 0.31 1290 Solid washed 93.8 0.06 0.06 941
(47) Analytical values during isothermal procedure at 60 C.:
(48) TABLE-US-00010 Chloride DTPMP Chloride fraction content content in DTPMP [% by [% by [% by Amount mass] mass] mass] [g] Filtrate 48.7 2.94 6.03 511 Solid unwashed 89.8 0.4 0.45 1470 Solid washed 92.8 0.03 0.03 895
(49) The particle size of the DTPMP crystallisates is then determined by means of a laser diffraction particle size analyser LS 13 320/Beckmann Coulter at a wavelength of 780 nm. The average growth rate (in [m/h]) of the crystallisates was determined for an isothermal procedure at 70 C. as 0.15.
(50) TABLE-US-00011 Start End d.sub.50 [m] 50 68 d.sub.10 [m] 22 39 d.sub.90 [m] 88 103
(51) For characterising the breadth of a particle size distribution, the d.sub.10 and the d.sub.90 value are used in addition to the d.sub.50 value. The d.sub.50 so value (mean) indicates the mean particle diameter, that is to say that exactly 50% of the particles are larger than or smaller than the indicated particle diameter, and is called the main particle size in the following. The d.sub.10 value refers to the particle diameter at which 10% of the particles are smaller than this limit value. Correspondingly, the d.sub.90 value indicates a particle diameter at which 90% of the particles are smaller than the indicated limit value.
(52) Because of the small specific surface area of crystallisates of the crystal modification, both tests, 60 C. and 70 C., for obtaining the crystal modification advantageously yield, even without washing, very pure solids which, as a result of the low residual moisture contents of <10% by mass, can be dried significantly more efficiently than is the case with the other crystal forms. When the filter cake of crystallisates of the crystal modification is washed analogously to examples 5 and 6, residual moisture and impurities can advantageously be reduced further.
(53) The powder diffractogram calculated from the structural data of a single-crystal structure analysis of the crystal modification by means of PowderCell software (Bundesanstalt fr Materialforschung und-prfung Berlin) is shown in
(54) TABLE-US-00012 TABLE 3 Characteristic reflections of crystallisates of the crystal modification Crystal modification 2 d Rel. intensity 8.939 9.8849 33.80% 10.652 8.2986 12.80% 11.673 7.5753 13.50% 13.008 6.8005 48.10% 16.280 5.4403 16.40% 17.914 4.9476 37.20% 20.128 4.408 27.70% 21.768 4.0794 17.00% 21.960 4.0443 39.20% 22.432 3.9602 100.00% 23.113 3.845 64.40% 23.311 3.8128 44.90% 25.058 3.5508 92.60% 26.131 3.4704 36.00% 26.909 3.3107 20.50%
Example 5Process for the Production of the Crystal Modification
(55) A starting amount of 24.3 kg of slurry, as detailed in the following table, is placed in a pilot plant having a 10-litre stirred tank reactor and an 11 cm propeller mixer. Seeding is carried out with 2.4 kg % by mass DTPMP crystallisates of the crystal modification comprising 50% by mass DTPMP, 1.5% by mass chloride and having a main particle size of 20 m, at a reaction temperature of 30 C. A calculated initial suspension density of 5% by mass is obtained. Precipitation is carried out at a constant stirring speed of 170 rpm.
(56) The suspension density, that is to say the solids content of the suspension in % by mass, is determined gravimetrically via a benchtop centrifuge in 12 ml vials at 6500 rpm/5 minutes. This centrifugation speed of 6500 rpm corresponds to a separating capacity of 3500 g.
(57) After a test duration of 15.5 hours, the solid is separated from the liquid via a porcelain suction filter (50 mbar, on filter paper), the unwashed solid and the filtrate having the contents of DTPMP, chloride and ortho-phosphate indicated in the following table.
(58) TABLE-US-00013 Chloride Ortho- DTPMP Chloride fraction phosphate content content in DTPMP content Amount [% by [% by [% by [% by [kg] mass] mass] mass] mass] Slurry 24.3 46.5 3.3 7.1 0.6 Solid unwashed 8.5 59.5 2.6 4.4 0.4 Filtrate: 15.8 32.8 3.8 11.6 0.5
(59) As the suspension density increases, the thin crystal plates increasingly rub together and are thereby destroyed mechanically. This leads to new nuclei, so that the suspension density increases further as they heal. As a result, no further significant crystal growth is observed, but the crystals remain at crystal sizes of about 20 m. These small crystal sizes, combined with the plate form typical for crystal form A, result in high specific surface areas. This leads to extremely high residual moisture contents and losses due to washing.
(60) The grain growth to be observed by means of laser diffraction on a macroscopic scale takes place primarily via the formation of agglomerates (see
(61) A two-step process appears to be expedient here. The solid precipitated and separated off by filtration in the first step is dissolved again, without being washed, and recrystallised in a second step in a mother liquor which is now purer and, on account of its higher purity, advantageously less supersaturated. After filtration, this solid is washed and shows significantly better purification. However, the high content of residual moisture of >60% by mass disadvantageously remains. Should this material be dried energy-efficiently at temperatures >60 C., it forms aggregates by rolling up or even begins to dissolve in the residual moisture. In order to counteract this, it is necessary to carry out drying beforehand to residual moisture contents <40% by mass with significantly lower energy inputs, that is to say at temperatures of about 40 C.
(62) This dependency is shown by the following example for determining the drying behaviour of crystallisates in dependence on residual moisture and product purity.
(63) A DTPMP solid isolated by recrystallisation is characterised by residues of adhering mother liquor via the quality parameters listed in the following table. Determination of the residual moisture content by means of a halogen dryer HB 43 S/Mettler Toledo is carried out isothermally at the indicated temperature using the shutoff criterion 4 (AK4=mean weight loss is <1 mg per 90 seconds):
(64) TABLE-US-00014 DTPMP Chloride PO4 inorg. H3PO3 Residual [% by [% by [% by [% by moisture mass] mass] mass] mass] 130 C. AK4 unwashed 47.7 1.8 0.13 3 45.6 sample
(65) After a purification step, which consists in suspending the solid in water and then separating it off by means of a filtering centrifuge, the following quality criteria are obtained:
(66) TABLE-US-00015 DTPMP Chloride PO4 inorg. H3PO3 Residual [% by [% by [% by [% by moisture mass] mass] mass] mass] 130 C. AK4 washed 50.9 0.7 0.15 1.5 44.8 sample
(67) The adhering residual moisture is removed stepwise from these solid samples in a rotary evaporator at 40 C. and 5 mbar vacuum, so that a series of samples with decreasing residual moisture content is prepared from each of the two purity grades (unwashed and washed).
(68) TABLE-US-00016 Unwashed Residual moisture Washed Residual moisture sample no. [% by mass] sample no. [% by mass] 1 53 1 51 2 47 2 47 3 36 3 40 4 32 4 36 5 26 5 31 6 14 6 24 7 11 7 19
(69) 4 ml borosilicate vials are filled with this sample material and the filling level is adjusted to of the height of the glass by gentle tapping. In order to minimise evaporative losses, the screw cap of each vial is additionally sealed with a polyethylene film. All the samples are shaken in parallel in a tempering block on a heating and cooling shaker ThermoTwister comfort/Quantifoil Instruments GmbH for a defined period at a defined temperature and then assessed visually. Classification is made according to the following points system:
(70) 5 points=sample unchanged
(71) 4 points=sample compacted/started to dissolve
(72) 3 points=sample visibly started to dissolve
(73) 2 points=sample cloudy highly viscous solution
(74) 1 point=sample dissolved to clear solution
(75) The following two tables compile the observations made at the end of each tempering step, photographs (see
(76) TABLE-US-00017 Table of samples of unwashed quality: Test duration [h] 24 24 24 24 24 24 5 5 5 5 5 5 Temperature [ C.] 35 40 45 50 55 60 65 70 75 80 85 90 51 [% by mass] residual moisture 5 5 5 5 5 2 1 1 1 1 1 1 47 [% by mass] residual moisture 5 5 5 5 5 3 1 1 1 1 1 1 40 [% by mass] residual moisture 5 5 5 5 5 3 1 1 1 1 1 1 36 [% by mass] residual moisture 5 5 5 5 5 3 1 1 1 1 1 1 31 [% by mass] residual moisture 5 5 5 5 4 3 1 1 1 1 1 1 24 [% by mass] residual moisture 5 5 5 4 4 3 2 1 1 1 1 1 19 [% by mass] residual moisture 5 5 5 5 5 4 2 2 2 2 2 2
(77) TABLE-US-00018 Table of samples of washed quality: Test duration [h] 24 24 24 24 24 24 5 5 5 5 5 5 Temperature [ C.] 35 40 45 50 55 60 65 70 75 80 85 90 53 [% by mass] residual moisture 5 5 5 5 5 3 1 1 1 1 1 1 47 [% by mass] residual moisture 5 5 5 5 5 5 3 1 1 1 1 1 36 [% by mass] residual moisture 5 5 5 5 5 5 3 1 1 1 1 1 32 [% by mass] residual moisture 5 5 5 5 5 5 4 3 3 2 2 2 26 [% by mass] residual moisture 5 5 5 5 4 5 4 3 3 2 2 2 14 [% by mass] residual moisture 5 5 5 5 5 5 5 5 5 5 5 5 11 [% by mass] residual moisture 5 5 5 5 5 5 5 5 5 5 5 5
(78) The photographs of the samples taken at the end of each tempering step show very clearly that samples with high residual moisture contents and at the same time low purity compact at only low temperatures and dissolve partially or even completely in their own residual moisture. This property makes economical process management, that is to say high production yields by the input of a large amount of drying energy, significantly more difficult. DTPMP solid qualities with less than 0.7% chloride and less than 40% residual moisture, on the other hand, are found to be advantageous in terms of their drying behaviour.
(79) The X-ray diffraction diagram, recorded with Cu-K.sub.1 radiation, of the crystal modification according to the invention is shown in
(80) TABLE-US-00019 TABLE 1 Characteristic reflections of crystallisates of the crystal modification 2 d Rel. intensity 6.796 12.99626 38.00% 12.534 7.05661 21.70% 12.937 6.83779 24.10% 17.9 4.9513 35.60% 18.641 4.75618 26.50% 18.981 4.67183 22.00% 20.152 4.40287 41.00% 20.94 4.23896 27.60% 21.276 4.17267 10.20% 21.854 4.06371 21.30% 22.229 3.99591 45.80% 22.52 3.94501 100.00% 23.031 3.85863 72.60% 23.119 3.84415 39.10% 25 3.55902 64.30%
Example 6Process for the Production of the Crystal Modification
(81) A starting amount of 4.49 kg of slurry, containing 38.9% by mass DTPMP and 3.0% by mass chloride, is placed in a double-walled 5-litre stirred tank reactor having a 14 cm anchor agitator. Seeding was carried out once with 0.2 kg of crystallisate of the crystal modification comprising 85% by mass DTPMP and 0.1% by mass chloride and having a main particle size of 30 m. A calculated initial suspension density of 3.6% by mass was obtained. Precipitation took place at a constant stirring speed of 150 rpm.
(82) The process is left isothermal for a period of 3 days. The crystallisation is first left at a constant initial temperature of 58 C. for 24 hours and then the temperature is lowered continuously to 46 C. with a temperature profile of about 1 K per 6 hours and left for a remaining period of 71 hours. The matured crystallisate is separated from the aqueous solution in a filtering centrifuge having a perforated drum with a filtering area of 235 cm.sup.2 and at a centrifugation speed of 6800 rpm for 2 minutes. This centrifugation speed of 6800 rpm corresponds to a separating capacity of 3500 g. Three washing operations with washing water (corresponding to half the amount of solid, divided into 3 equal amounts) are then carried out. Finally, the separated crystallisate is dried for 5 minutes at a centrifugation speed of 10,000 rpm. This centrifugation speed of 10,000 rpm corresponds to a separating capacity of 8400 g.
(83) TABLE-US-00020 Chloride DTPMP Chloride in DTPMP Amount [% by [% by [% by [g] weight] weight] weight] Slurry 4492 38.9 3.0 7.7 Solid unwashed 1509 83.6 0.6 0.7 Solid washed 1x 85.4 0.36 0.4 Solid washed 2x 86.0 0.3 0.4 Solid washed 3x 1017 87.2 0.09 0.1 Filtrate: 2915 26.9 3.8 14.1 Washing water: 1312 12.1 1.54 12.7
(84) The particle size of the DTPMP crystallisates is then determined by means of a laser diffraction particle size analyser LS 13 320/Beckmann Coulter at a wavelength of 780 nm.
(85) TABLE-US-00021 End d.sub.50 [m] 60 d.sub.10 [m] 17 d.sub.90 [m] 113
(86) The determination of the average particle size at the end of the test is carried out by means of a microscope and Olympus visualisation software (cf.
(87) TABLE-US-00022 Length [m] 50-120 Width [m] 10-50 Thickness [m] 1-5
(88) Crystallisates of the crystal modification can be obtained with comparable yields and degrees of purification over a wide temperature range. Cooling crystallisation requires low cooling rates in order to avoid supersaturation. An isothermal reduction of supersaturation is possible both in the upper existence range of the crystal modification and in the lower existence range of the crystal modification.
(89) The X-ray diffraction diagram, recorded with Cu-K.sub.1 radiation, of the crystal modification according to the invention is shown in
(90) TABLE-US-00023 TABLE 2 Characteristic reflections of crystallisates of the crystal modification 2 d Rel. intensity 6.707 13.1694 41.30% 12.464 7.09618 33.30% 13.512 6.54779 22.10% 14.553 6.08179 32.50% 18.596 4.76749 43.80% 18.894 4.69305 29.40% 19.614 4.52231 36.50% 20.02 4.43159 39.80% 20.854 4.25612 32.00% 21.204 4.18675 27.70% 22.12 4.01534 65.10% 22.522 3.94466 79.10% 22.988 3.86569 76.80% 24.8 3.58726 50.60% 25.166 3.53581 35.70%
Example 7Thermal Analysis of the Crystals
(91) In a drying cabinet, crystallisates of the , and crystal modification are pre-dried at 80 C. for 24 hours to residual moisture contents of <10% by mass. Thermogravimetric analysis is carried out by placing the samples in a platinum crucible under a heating regime of 30 C. to 230 C. with a constant heating rate of 1.0 K/min in a TG/DTA 220 (Seiko Instruments). Melting of the samples in a temperature range between 130 and 140 C. is detectable thermooptically (
(92) By means of DSC/TG coupled IR gas analysis (
Example 8Determination of the Hygroscopicity
(93) In order to determine the hygroscopicity, solid samples were stored in 25 ml glass beakers in a desiccator under constant humidity. Via a saturated magnesium nitrate solution with precipitate (about precipitate in of the solution), a relative humidity of 55% by mass becomes established at 222 C. The water absorption of the samples was determined gravimetrically once daily over a period of 12 days as the difference in mass (see
(94) Two spray-dried powders were tested as comparison with crystallisate samples of the crystallisates of the , and crystal modification.
(95) A DTPMP synthesis product having the quality parameters from Table 4 used as the starting slurry for the crystallisation was spray dried with a Bchi-Mini Spray Dryer B-290.
(96) The second spray-dried powder was obtained from re-dissolved crystallisate of the crystal modification and thus showed the same low degree of impurity as the crystallisate of the crystal modification.
(97) The composition of the samples used and the relative water absorption [in % by mass] are to be found in Table 4 below.
(98) TABLE-US-00024 Sum (H3PO4 + Relative H3PO3)/ Chloride/ Bulk water DTPMP DTPMP density absorption Product % by mass % by mass [g/ml] % by mass/day amorphous powder 6.5 3.5 0.27 0.40 from spray drying of an unpurified DTPMP synthesis product amorphous powder 3.3 1.3 0.27 0.29 from spray drying of a DTPMP acid purified by recrystallisation Crystal form , 3.3 1.3 0.36 0.03 purified quality Crystal form , 1.1 0.3 0.49 0.04 purified quality Crystal form , 0.95 0.05 0.59 0.003 purified quality
(99) A clear differentiation is possible after only a short time. Spray-dried powders of the unpurified DTPMP synthesis product (amorphous structure) exhibit the greatest hygroscopicity. The DTPMP quality purified by recrystallisation and spray dried (amorphous structure) exhibits a lower water absorption capacity than the unpurified crude product while having the same very high specific surface area.
(100) By contrast, the crystallisates of crystal modification , or according to the invention are distinguished by consistently low water absorption, crystal form exhibiting by far the lowest hygroscopicity. This appears to be due to the compact, cuboid crystal form, which results in a high purification success and low hygroscopicity.
Example 9Hygroscopicity of Acid and Salts
(101) In a further test, the influence of the degree of neutralisation of the phosphonic acid DTPMP on the hygroscopicity was studied, on account of its industrial relevance, especially the sodium salts. To that end, 10 g of sample were stored in four crystallisation dishes of equal size in a desiccator under constant humidity. Via a saturated magnesium nitrate solution with precipitate (about precipitate in of the solution), about 55% by weight humidity is established at 22 C. The water absorption of the samples was determined gravimetrically twice daily over a period of 22 days as the difference in mass (see
(102) A crystallisate of the crystal modification with a foreign acid content of 3.8% by weight chloride and in total 6.6% by weight H.sub.3PO.sub.4 and H.sub.3PO.sub.3 per 100% by mass DTPMP was dissolved again. Portions were neutralised with sodium hydroxide solution to pH (1% strength)=1.7 for the Na.sub.0.5-DTPMP salt, pH (1% strength)=2.1 for the Na.sub.3-DTPMP salt and pH (1% strength)=6.6 for the Na.sub.7-DTPMP salt. These aqueous solutions were spray dried using a Bchi-Mini Spray Dryer B-290.
(103) After only half the test time, the powder samples neutralised to pH 7 are visibly contracting to form a block. After 22 days, the powdered structure of the DTPMP acid is still recognisable, the sample of the Na.sub.7 salt has liquefied.
(104) This shows that, with the same, low degree of impurity, solids of DTPMP acid are stable to storage, while this is not the case for the sodium salts of DTPMP.