Process for the preparation of a powder comprising one or more complexing agent salts

Abstract

A process for the preparation of a powder comprising one or more complexing agent salts of the general formula ##STR00001##
comprises atomizing an aqueous solution comprising the one or more complexing agent salts in the presence of a crystalline fine dust of the same complexing agent salts and a drying step, wherein the concentration of the one or more complexing agent salt is from 10 to 80% by weight, based on the total weight of the aqueous solution, with an upper limit for the average particle diameter of the crystalline fine dust which is lower by at least a factor of 2 than the lower limit of the average particle diameter of the powder obtained after the process, and the fraction of the crystalline fine dust is from 0.1 to 20% by weight, based on the weight of the powder obtained after the process.

Claims

1. A process for preparing a powder comprising at least one methylglycine-N,N diacetic acid complexing agent salt of formula (I): ##STR00009## wherein R is ##STR00010## and R is methyl; M is, independently, hydrogen, an alkali metal, an alkaline earth metal, ammonium or a substituted ammonium in corresponding stoichiometric amounts, provided that at least one M is not hydrogen; comprising: (a) atomizing an aqueous solution comprising a first complexing agent salt of formula (I) in the presence of a crystalline fine dust of a second complexing agent salt of formula (I), to produce a powder, and (b) drying the powder, wherein a concentration of the first complexing agent salt in the aqueous solution is from 10 to 80% by weight, based on a total weight of the aqueous solution; an upper limit for an average particle diameter of the crystalline fine dust is lower by at least a factor of 2 than a lower limit of an average particle diameter of the powder obtained by the process; a fraction of the crystalline fine dust is from 0.1 to 20% by weight, based on a weight of the powder obtained in the process; and the residual moisture of the powder after drying is 6.5 to 14% by weight.

2. The process of claim 1, wherein the drying occurs in a spray-tower.

3. The process of claim 1, wherein the drying is a spray-granulation in which, during the atomizing, the aqueous solution is sprayed into a fluidized bed comprising granules of the complexing agent salt of formula (I).

4. The process of claim 2, wherein, in the spray-tower, a fluidized bed is integrated and an agglomerating spray-drying occurs.

5. The process of claim 1, wherein the drying is a spray-agglomeration carried out in a mixer with agitated internals, to give an agglomerate which is then fully dried in a further apparatus.

6. The process of claim 1, wherein the aqueous solution comprises ca. 30 to 50% by weight of the complexing agent salt, and is concentrated in a process upstream of the spray-drying process in a heat exchanger or a thin-film evaporator to ca. 55 to 80% by weight of the complexing agent salt, based on the total weight of the aqueous solution.

7. The process of claim 1, wherein the drying occurs at a pressure in the range from 0.1 bar absolute to 10 bar absolute.

8. The process of claim 1, wherein a residence time of the drying is in a range from 10 seconds up to 1 h.

9. The process of claim 1, wherein the first complexing agent salt of formula (I) and the second complexing agent salt of formula (I) are the same.

10. The process of claim 1, wherein the first complexing agent salt of formula (I) and the second complexing agent salt of formula (I) are different.

11. The process of claim 9, wherein at least one M is an alkali metal.

12. The process of claim 11, wherein each M is an alkali metal, and each M is the same alkali metal.

13. The process of claim 12, wherein M is sodium and wherein the process produces a methylglycine-N,N-diacetic acid trisodium salt powder with a degree of crystallinity of 30% comprising a first crystalline modification with the d values stated below in Angstrms at the diffraction angles 2-theta in : TABLE-US-00003 2-theta () d value (Angstrms) 8.4 10.5 9.5 9.3 11.1 8.0 13.2 6.7 13.9 6.35 15.8 5.6 16.5 5.36 16.84 5.26 17.34 5.11 17.67 5.02 18.92 4.69 20.29 4.37 21.71 4.09 22.3 3.98 23.09 3.85 24.74 3.59 25.36 3.51 27.04 3.29 28.28 3.15 29.63 3.01 30.09 2.97 and/or a second crystalline modification with the d values in Angstroms at the respective diffraction angles 2-theta in in the X-ray powder diffractogram corresponding to the table below: TABLE-US-00004 2-theta () d value (Angstrms) 8.2 10.80 10.5 8.40 15.55 5.70 16.47 5.38 17.09 5.18 18.10 4.90 18.82 4.71 21.00 4.23 21.35 4.16 22.64 3.92 23.69 3.75 24.73 3.60 26.75 3.33 28.93 3.08 29.88 2.99 31.46 2.84 31.88 2.80.

14. The process of claim 1, wherein the process produces a methylglycine-N,N-diacetic acid trisodium salt powder with a degree of crystallinity of 70%.

15. The process of claim 1, wherein the process produces a methylglycine-N,N-diacetic acid trisodium salt powder that is crystalline.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) A more complete appreciation of the disclosure and many of the attendant features thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:

(2) FIG. 1 shows an X-ray diffractogram for the powder obtained according to working example 1 (for comparison).

(3) FIG. 2 shows X-ray diffractograms for powders obtained in Example 2.

(4) FIG. 3 shows X-ray diffractograms for powders obtained in Example 3.

(5) FIG. 4 shows X-ray diffractograms for powders obtained in Example 4.

(6) If the spray-drying process carried out is a spray-granulation, then powders are obtained which often have an average particle diameter in the range from about 200 to 2000 m. Accordingly, it is necessary to use crystalline fine dust for which the permissible upper limit for the average particle diameter is at most 100 m.

(7) According to the invention, the weight fraction for the addition of crystalline fine dust in the spray-drying process is in the range from about 0.1 to 20% by weight, based on the weight of the powder obtained after the process, preferably about 4 to 10% by weight, based on the total weight of the powder obtained after the process.

(8) Preferably, the starting material used is an aqueous solution which is obtained by the corresponding synthesis and which comprises ca. 30 to 50% by weight of the one or more complexing agent salts, and which is concentrated in a process step connected upstream of the spray-drying process in a heat exchanger or a thin-film evaporator to ca. 55 to 80% by weight of complexing agent salts, based on the total weight of the aqueous solution.

(9) The one or more complexing agent salts correspond to the general formula

(10) ##STR00006##

(11) in which R is hydrogen or one of the groups

(12) ##STR00007##

(13) where R is hydrogen, a C.sub.1-C.sub.12-alkyl radical or a (CH.sub.2).sub.qCOOM radical where q=1 to 5 n and m are in each case an integer from 0 to 5 and R is hydrogen or a C.sub.1-C.sub.12-alkyl radical or a C.sub.2-C.sub.12-alkenyl radical which may be additionally substituted by up to 5 hydroxyl groups, or one of the groups

(14) ##STR00008##

(15) in which o and p are in each case an integer from 0 to 5, and

(16) M, independently of the others, is hydrogen, alkali metal, alkaline earth metal, ammonium or substituted ammonium in the corresponding stoichiometric amounts.

(17) These are preferably derivatives of glycine-N,N-diacetic acid or derivatives of glutamine-N,N-diacetic acid. Preference is also given to derivatives of ethylenediaminetriacetic acid or of nitrilotriacetic acid.

(18) Particularly preferred derivatives of glycine-N,N-diacetic acid are alkali metal salts of methylglycine-N,N-diacetic acid, referred to below as MGDA.

(19) The drying step of the spray-drying process is preferably carried out at a pressure in the range from about 0.1 bar absolute to 10 bar absolute, in particular at a pressure in the range from about 0.8 bar absolute to 2 bar absolute.

(20) The residence time in the drying step is preferably in a range from about 10 seconds up to 1 h.

(21) The invention also provides a formulation comprising the powder obtained according to the process described above, or an aqueous solution of the same, as complexing agent for alkaline earth metal ions and heavy metal ions in the amounts customary for this, besides other customary constituents of such formulations.

(22) The formulations may in particular be detergents and cleaner formulations.

(23) The invention also further provides the use of a powder obtained by the above process for producing compression agglomerates, and also the use of the compression agglomerates for use in solid cleaners.

(24) The above cleaners may in particular be intended for automatic dishwashers. In particular, these may be tablets for dishwashers.

(25) The spray-drying process according to the invention can also be carried out with mixtures of one or more complexing agent salts and further substances. Further substances are to be understood in particular as meaning auxiliaries and additives customarily used in the detergents and cleaners industry. For example, surfactants, polymers, inorganic salts, and/or citrates can be used. For use in the field of machine dishwashing, for example inorganic salts, such as carbonates, sulfates, phosphates, silicates; organic salts such as citrates; polymers, such as polycarboxylates or sulfonated polymers or phosphonates are suitable. As a result of mixtures of this type, the production process for producing detergents and cleaners can be designed more simply.

(26) The powders obtained by the above process can in particular also be used in mixtures with customary auxiliaries and additives.

(27) According to the process of the invention, it is possible in particular to obtain a methylglycine-N,N-diacetic acid trisodium salt powder with a degree of crystallinity of 30% comprising a first crystalline modification with the d values stated below in Angstroms at the diffraction angles 2-theta in :

(28) TABLE-US-00001 2-theta () d value (Angstrms) 8.4 10.5 9.5 9.3 11.1 8.0 13.2 6.7 13.9 6.35 15.8 5.6 16.5 5.36 16.84 5.26 17.34 5.11 17.67 5.02 18.92 4.69 20.29 4.37 21.71 4.09 22.3 3.98 23.09 3.85 24.74 3.59 25.36 3.51 27.04 3.29 28.28 3.15 29.63 3.01 30.09 2.97

(29) and/or a second crystalline modification with the d values in Angstrms at the respective diffraction angles 2-theta in in the X-ray powder diffractogram corresponding to the table below:

(30) TABLE-US-00002 2-theta () d value (Angstrms) 8.2 10.80 10.5 8.40 15.55 5.70 16.47 5.38 17.09 5.18 18.10 4.90 18.82 4.71 21.00 4.23 21.35 4.16 22.64 3.92 23.69 3.75 24.73 3.60 26.75 3.33 28.93 3.08 29.88 2.99 31.46 2.84 31.88 2.80

(31) The invention is illustrated in more detail below by reference to a drawing and working examples.

(32) In the drawing specifically:

(33) FIG. 1 shows an X-ray diffractogram for the powder obtained according to working example 1 (for comparison),

(34) FIGS. 2 to 4 show X-ray diffractograms for powders obtained in each case according to working examples 2 to 4 (according to the invention).

(35) Here, in the figures, the abscissa shows the diffraction angle 2-theta in , and the ordinate shows the measured intensity, in counts (pulses) (dimensionless).

(36) The X-ray powder diffractometer measurements were carried out on a D8 Advance diffractometer from Bruker AXS (Karlsruhe). In reflection with CuK -radiation was measured with a variable diaphragm adjustment on the primary side and on the secondary side. The measurement range was 2 to 80 2-theta, the step width 0.01 and the measurement time per angle step 3.6 seconds.

(37) The degree of crystallinity was ascertained from the X-ray powder diffractograms in a known manner by, as usual, determining the surface fraction of the crystalline phase and of the amorphous phase and using these to calculate the degree of crystallinity, CD, as the ratio of the area of the crystalline phase, I.sub.c, to the total area, consisting of the area of the amorphous phase, I.sub.a, and the area of the crystalline phase, I.sub.c:
CD==I.sub.c/(I.sub.c+I.sub.a).

(38) The determination of the degree of crystallinity can be carried out in particular using a software program, for example the software program TOPAS from Bruker AXS.

(39) For this, firstly an amorphous sample is measured and the linear course is fitted in a profile fit with the help of six individual lines. The line positions of these lines and their half-widths are then fixed and these values are saved as amorphous phase.

(40) For the sample to be measured for which the degree of crystallinity is to be determined, the surface fraction of the crystalline phase and the surface fraction of the amorphous phase is then determined and the degree of crystallinity CD is calculated therefrom in accordance with the formula given above.

(41) The amorphous phase is used as defined above.

(42) The crystalline phase can likewise be defined via its individual line positions analogously to the amorphous phase, or by reference to the following lattice constants, as so-called (hkl) phase (a=33.63, b=11.36 and c=6.20 and space group Pbcm), where the lattice parameters are variables which can be freely refined. The background is fitted as polynomial of the 1st degree.

(43) The program TOPAS calculates the optimal fit between measured diffractogram and the theoretical diffractogram consisting of amorphous and crystalline phase.

WORKING EXAMPLES

Working Example 1 (for Comparison)

Classic Spray-Drying without the Addition of Crystalline Fine Dust

(44) A quantitative stream of 60 kg/h of an aqueous solution of Na3-MGDA with a solids content of 40% was evaporated in a plate heat exchanger evaporator (heating area 1.7 m.sup.2) to a solids content of 59% and separated in a separating container. The evaporation was carried out at a wall temperature of 152 C. (steam heating) and at a pressure of 2.5 bar abs in the separator.

(45) The evaporated solution was metered into the downstream piston membrane pump at a temperature of ca. 128 C. using a gear pump and sprayed into a spray-tower using a single-material nozzle.

(46) The spray-tower had a diameter of 800 mm and a length of 12 m. The spray-tower was operated with a quantity of air of 1400 kg/h and a gas inlet temperature of 160 C. The product outlet temperature was 127 C. and the solids content of the dry product 94.1%. The product was separated out via a 2-point discharge (directly at the spray-tower and at the downstream filter).

(47) The product prepared in this way was a pourable powder. The bulk density was 529 kg/m.sup.3. X-ray structural analysis shows that the product is amorphous.

(48) The storage behavior of this sample was evaluated in a desiccator test. For this, a 3 g sample is stored in an open weighing cup in a desiccator at 20 C. and a relative atmospheric humidity of 76% over a period of 144 hours. The mass increase of the sample is then ascertained and the pourability of the sample is evaluated. The mass increase was 27.1% and the sample had started to dissolve, i.e. it was wet and no longer pourable.

Working Example 2 (According to the Invention)

Spray-Tower with the Addition of Crystalline Fine Dust

(49) A quantitative stream of 75 kg/h of an aqueous solution of Na3-MGDA with a solids content of 40% was evaporated in a plate heat exchanger evaporator (heating area 1.7 m.sup.2) to a solids content of 60% and separated in a separating container. The evaporation was carried out at a wall temperature of 156 C. (steam heating) and at a pressure of 2.5 bar abs in the separator.

(50) The evaporated solution was metered into the downstream piston membrane pump at a temperature of ca. 130 C. using a gear pump and sprayed into a spray-tower using a single-material nozzle.

(51) The spray-tower had a diameter of 800 mm and a length of 12 m. The spray-tower was operated with a quantity of air of 1400 kg/h and a gas inlet temperature of 202 C. A mass stream of 4 kg/h of crystalline fine dust Na3-MGDA was blown into the spray-tower by means of an injector. The product outlet temperature was 99 C. and the solids content of the dry product 90.2%. The product was separated out via a 2-point discharge (directly at the spray-tower and at the downstream filter).

(52) The product prepared in this way was a pourable powder. The bulk density was 568 kg/m.sup.3. X-ray structural analysis shows that the product is crystalline.

(53) The storage behavior of this sample was evaluated in a desiccator test. For this, a 3 g sample is stored in an open weighing cup in a desiccator at 20 C. and a relative atmospheric humidity of 76% over a period of 144 hours. The mass increase in the sample is then ascertained and the pourability of the sample is evaluated. The mass increase was 20.4% and the sample was only slightly caked and could be converted again to the pourable state by gentle tapping.

Working Example 3 (According to the Invention)

Agglomerating Spray-Drying in a Spray-Tower with Integrated Fluidized Bed (Fluidized Spray Dryer (FSD))

(54) 500 g of a 41% strength aqueous Na3-MGDA solution with a total solids content of 46% by weight was diluted with 150 g of deionized water. The solution was then stirred in a glass flask with stirrer at room temperature and then fed to a spray dryer with integrated fluidized bed on the laboratory scale, with introduction of drying air at 130 C., an inlet air temperature of the fluidized bed of 110 C. and atomized via a two-material nozzle. In the first phase of the drying process, the liquid droplets were dried, with formation of the granulation seeds in the bed. The bed temperature was then reduced in order to initiate the granulation phase, during which the granulation cores were agglomerated with feed solution. The resulting granules were removed continuously from the spray dryer. Granulation of the solution was carried out in a range for the bed temperature between 64 C. and 74 C. The product had a residual moisture of 6.5% by weight, a high bulk density of 700 kg/m.sup.3 and was very readily pourable. After 144 hours in the desiccator at 20 C. and a relative humidity of 76%, the product remained pourable, the X-ray diffractogram (FIG. 3) indicated a crystalline fraction of 70%.

Working Example 4 (According to the Invention)

Spray-Granulation with the Addition of Crystalline Fine Dust

(55) Aqueous Na3-MGDA solution with a solids content of 48.8% was spray-granulated on a continuously operated laboratory spray-fluidized-bed. The conical fluidized bed with a diameter at the bottom of 150 mm and at the top of 300 mm had internal hose filters and a pneumatic atomization nozzle, with which spraying was achieved into the fluidized bed from below. The fluidized bed was operated with 55 Nm.sup.3/h of nitrogen, an inlet temperature of 140 C. and a fluidized-bed temperature of 79 C. Na3-MGDA spray granules from previous experiments were introduced as initial charge into the fluidized bed. Over a period of 1.92 hours, an amount of 6.03 kg of solution in total was sprayed in. For this, the pneumatic atomization nozzle was operated with 4.7 Nm.sup.3/h of nitrogen at room temperature and at a pressure of 3.3 bar (absolute). Solid was discharged from the fluidized bed via a screw such that the level of the fluidized bed remained constant. The discharged solid was sieved out every 30 minutes. 46.8% of the discharged particles were in the particle size range from 355 to 1250 m. The bulk density of this fraction was 778 kg/m.sup.3 and its water content was 11.8 mass %. The sieved out fines fraction of less than 355 m was returned to the fluidized bed every 30 minutes.

(56) The product prepared in this way was flowable granules. X-ray structural analysis shows that the product comprises crystals of the first modification defined above and is 71% crystalline.

(57) The storage behavior of this sample was evaluated in the desiccator test. For this, a 3 g sample is stored in an open weighing cup in the desiccator at 20 C. and a relative atmospheric humidity of 76% over a period of 144 hours. The mass increase of the sample is then ascertained and the pourability of the sample is evaluated. The mass increase was 25.8% and the sample was only slightly caked and could be converted again to the pourable state by gentle tapping.