JP2002507957A - Soluble acidic polyphosphate and apparatus for producing the same - Google Patents

Abstract

(57) [Summary] The present invention relates to the present invention, wherein the Na / P ratio is 0.3 to 0.6, the P ₂ O ₅ content is more than 77% by mass, the Na ₂ O content is less than 20%, and the residual water content is less than 20%. Is a method for producing a soluble acidic polyphosphate having a mean chain length of 3 to 10%, wherein an aqueous solution of the phosphate is dried at 400 to 600 ° C. to form a linear polyphosphate having an average chain length of 10 to 30. At a temperature of between 30 and 180 minutes, cooling the melt while forming a glassy product, while maintaining the water vapor pressure of the atmosphere in contact with the melt during melting at 0.1-0.5 bar. It is characterized by the following. The invention further relates to the polyphosphates produced by this method and their use.

Description

The present invention relates to a soluble acidic polyphosphate having a high P ₂ O ₅ content and a method for producing the same. A suitable device to enable this is described. Polyphosphates acidic than 1 corresponds to the Na ₂ O content of less than 30% by weight to the skilled person, in particular a sodium / phosphorus molar ratio of less than 0.9, further 2-10 generally in the solid state It is understood to be a polyphosphate containing water by weight. The water content is mainly based on the presence of free phosphate hydroxyl groups. A further degree of polymerization is used to characterize this phosphate which is characterized by a linear and a cyclic structure. Due to the high content of free hydroxyl groups, this phosphate solution is very strongly acidic. These acidic groups can essentially be further polymerized by releasing water, which subsequently crosslinks via the PO ₄ tetrahedron, resulting in a spatially crosslinked, significantly less water-free structure. This structure with low Na ₂ O and water content in this case is called ultraphosphate. An important feature is the remarkably low solubility in water, since it dissolves in smaller units only by hydrolysis. The conditions under which cross-linking and concomitant ultraphosphate binding occur in sodium polyphosphates with a Na / P ratio of less than 0.9 are: a) high melting temperatures and b) low water vapor pressure (A. Winkler und E. Thilo). , Z. anorg. Allg. Chemie2 98S. 302-315 (1959)). The relevance of the construction of sodium acid phosphate glass and the manufacturing conditions that depend on chemical analysis is further shown in Westman et al., Canadian Journal of Chemistry Vol. 27, 1959, 1764-1775. Furthermore, it has been found that certain compositions of acidic polyphosphates convert to crystalline products upon prolonged heat treatment of the melt. Thus, an aqueous solution of NaH (PO ₃ ) ₂ dries and melts at a temperature of 400 ° C., converts to a crystalline solid after a long heat treatment at about 300 ° C., from which it is understood that this solid is a cyclic trimetaphosphate. You. This product dissolves very slowly in water. The mixture corresponding to the composition of Na ₂ H (PO ₃ ) ₃ is converted at 300 ° C. into fibrous crystals which are poorly soluble in water and contain long-chain polyphosphates by X-ray spectrum (Griffith, ACS 1954, S 5892). Another crystal form corresponds to the formula Na ₃ H (PO ₃ ) ₄ , which is obtained by heating to 600 ° C. and heat treating at 350 ° C. for 12 hours. This product is also not soluble in water (Griffith, ACS 1956, 3867-3870 and U.S. Pat. No. 2,774,672). German Patent No. 4,128,124 describes acidic polyphosphates as additives or molten salts for the preparation of cheese. The polyphosphate is prepared by melting from monosodium phosphate and phosphoric acid or sodium hydroxide solution and phosphoric acid in a suitable mixing ratio directly at 400-500 ° C. with a residence time of 20 minutes to 2 hours, the final product being formed. The composition of the product is determined by the melting temperature, residence time and Na / P ratio. General manufacturing conditions are set forth in the aforementioned U.S. Pat. No. 2,774,672. The polyphosphate should have stability and storage properties. P ₂ O ₅ content is 7 3-77 wt%, Na ₂ O content is 20 to 25 mass%, residual water content is 2 to 3 wt%. Therefore, the Na / P ratio is 0.6 to 0.8. The solubility of these products is about 90 minutes, which is too long for intended use as molten salts and stabilizers, especially in the cheese industry. Dissolution times of less than 30 minutes, advantageously less than 20 minutes, are preferred for the required processing time. In order to use phosphates as foods, especially to produce melt cheese, these polyphosphates must have a number of properties or functions: a) The polyphosphate must be a solid powder that is easy to handle. The powder has b) a high solubility, in particular less than 30 minutes, preferably less than 20 minutes, to dissolve in water; c) a good complexing capacity for alkaline earth metals, especially calcium and magnesium. D) exhibits good buffering action in the acidic range, especially for use, for example, in salad dressings and mayonnaise; e) preservative action (number of bacteria per volume and quantity) during the storage time of the finished cheese F) shows a stabilizing effect on other additives, especially vitamin C. According to DE 4128124, weakly acidic polyphosphates having a Na / P ratio of from 0.8 to 0.6 were conventionally used for this purpose, but they did not show satisfactory dissolution properties. . According to conventional explanations, the amount of ultraphosphate was considered to be too high due to rapid dissolution. Therefore, there is a problem of finding a solid, soluble and acidic polyphosphate having a small amount of a crosslinked structure (ultraphosphate) and finding a production method thereof. Surprisingly, a strongly acidic polyphosphate (1% solution below pH 2) with a Na / P ratio of 0.3 to 0.6 is applied under suitable conditions to about 10 to 30, preferably 20 to 30, It has been found that it can be converted into the form of an average length chain with ₃ PO ₃ units, which has, to a lesser extent, crosslinks known from the literature and is already described in the literature (Na ₂ H ₂ PO ₃ ) ₄ Has no ring structure or metaphosphate structure. The chains of this average length surprisingly have a very high dissolution rate, with a dissolution time of about 10/10% by weight being achieved in an advantageous manner. The chain structure closes off most of the acidic groups, so that these polymers are significantly less acidic than the analyzed content of phosphoric acid. However, this compound can be slowly hydrolyzed and, to this extent, exert a strong buffering action. On the other hand, the polymer structure can form complexes with divalent ions, in particular magnesium and calcium ions, thus preventing their precipitation as sparingly soluble phosphates. Furthermore, this polyphosphate is shown to be a surprisingly good stabilizer. It has an easy bactericidal action against bacteria and especially fungi. Unlike previous methods had to be determined by end group titration chain length polyphosphates a tedious task, the chain length of polyphosphates and degree of crosslinking by using a modern ³¹ P-NMR method, poly By dissolving the phosphates in deuterium oxide and recording the resonance signals of the various phosphate groups during or shortly after the dissolution step, i.e. before significant hydrolysis has begun and before changing the results, it is very easy to do so. Can be determined. The terminal phosphate group has a resonance at -6 ppm to -12 ppm, the central phosphate group in the chain has a resonance frequency of -18 ppm to -24 ppm, and the cyclic phosphate is -23 ppm (trimethaphosphate) or -21 ppm (tetrametaphosphate). The signal for free orthophosphate is found to be 0 ± 2 ppm depending on the acidity in this situation. The water content of the product, which in this case determines the majority of the bound water, is generally determined by determination of the loss on ignition at 600-800 ° C., with zinc oxide being added in each case and acid polyphosphate being determined. Avoid loss of P ₂ O _{5 in} case. To determine the dissolution rate, a turbidity photometer Dr. Lange, model LTP5 and a stirrer Heidolph with a KPG blade stirrer for a 50 ml flask of Glaswerke Wertheim No. 3855, model RZ R2000 (with a tachometer )It was used. To carry out the test, 5 g each of the polyphosphates in the measuring cuvette of the photometer are mixed with 45 ml of water and stirred at a speed of 500 min ^-1 . After the scheduled measurement time (5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes and 60 minutes), the stirrer was taken out and the turbidity was measured. To avoid this step should be performed as fast as possible. The turbidity measured by TE / F is visually evaluated by the following equation. TE / F1-2 = clear TE / F2-10 = opal TE / F10-15 = low turbidity TE / F15-20 = turbidity TE / F> 20 = strong turbidity An aqueous solution consisting of phosphoric acid and a sodium phosphate or sodium hydroxide solution having a water content of 3-0.6 and up to about 20% is pre-dried and the mixture is placed in a suitable oven for a period of 60-120 minutes 400-600. It is manufactured by melting gradually by heating to a temperature of ° C. As another parameter, the steam pressure over the melt is reduced to 0.1 by passing moist air corresponding to the case of a continuous process or by adapting the amount of water to be evaporated to the furnace volume, for example in a muffle furnace. Adjust to 1-0.5 bar. After a short cooling step, the melt is cooled to room temperature in a water-free atmosphere and ground to a fineness of powder. Products with a Na / P ratio of less than 0.3 can no longer be ground or hardened at room temperature. From the following tests, the desired chain product with an average chain length of 10 to 30 having a dissolution rate of up to 20 minutes is achieved at a melting temperature of 400 to 550 ° C. and a residence time of 60 to 120 minutes. I can understand that. At temperatures higher than 550 ° C. and reaction times longer than 180 minutes, the chain length increases by more than 30, with a corresponding increase in the dissolution rate and the cyclic phosphate content, and thus the product is useful for the purposes of the present invention. Not very suitable. Optimal adjustment of the chain length in the range of about 20 to 25 can be achieved by adjusting the water vapor pressure above the melt to 0.2 to 0.3 bar. Example 1 In a muffle furnace which can be heated to a temperature of the measurement 400 to 800 ° C. reaction temperature _{(Heraeus MR70E), NaH 2 PO} 4 as a solution in a platinum shell (1.1 mol), H ₃ PO ₄ (industrial One solution, each consisting of 114.4 g and about 29.5 g (2.2 mol) of water, is gradually warmed up, thereby avoiding splashing of the solution. The results of the test are listed in the table below. As shown in Table 1, the solubility after 20 minutes at a melting temperature of 400 to 500 ° C is excellent. At the same time, as expected, the hygroscopicity increases. At the same water vapor pressure, as the temperature increases, the loss on ignition decreases, the average degree of condensation and the amount of cyclic phosphate increase corresponding to Table 2, resulting in a corresponding decrease in solubility. The designations P1 to P50 indicate the corresponding chain lengths determined by analysis. Table 3 shows that the average chain length is significantly increased at a temperature of 500 ° C. at very long residence times or at higher temperatures at short residence times, which is indicated by a reduced ignition loss. The corresponding strongly crosslinked products are no longer sufficiently soluble for use according to the invention. Example In 2 other studies, varying the feed rate to produce a Na ₂ O / P ₂ O ₅ molar ratio of 0.5 corresponds to the formula _{NaHP 2 O 5 · H 2 O} . As shown in Table 4, this product is not significantly different from the product according to Example 1 in its composition. The increase in acidity increases only the hygroscopicity, and the solubility obviously decreases somewhat due to the increase in crosslinking. Example 3 Continuous production in a tube furnace 13.8 kg of an 85% industrial H ₃ PO ₄ solution are previously charged in a quartz reactor with stirrer and cooler, and 5.9 kg of a 49.2% sodium hydroxide solution are taken from the boiling point. Add slowly with stirring to maintain low temperature. 19 kg of a phosphate solution having a Na ₂ O / P ₂ O ₅ ratio of 0.533 and a density of 1.61 are obtained. Said phosphate solution is continuously charged into the melting furnace according to FIG. 1 via a membrane metering pump whose piston working volume and cycle cycle are adjustable. As can be seen from the drawing, a quartz tube 3 of 880 cm in length and 55 cm in diameter is present as a reaction vessel in the tubular furnace 1 (in this case an F500 Gero company with a total length of 750 cm and a heating zone of 500 cm is used). Scraped by milling of graphite rod, has an area 256 cm ² and volume 1024Cm ^3, the melting tank 2 is a quartz tube which is inclined slightly, which can be reduced to 256 cm ³ by inserting the fitting wedge optionally the volume It is embedded (external graphite can use silicon carbide as material, while the other ceramic material is partially corroded by the phosphate melt). Phosphate solution is fed in at a feed rate of 300 g / h via conduit 4, and the produced melt exits continuously via conduit 5 at the end of the melting tank 2 by means of a gradient and via cooled rollers 6 Solidifies into a glass. The obtained phosphate glass is crushed by a scraper 7 while excluding air and moisture, and is intermediately stored in a container 8 and then crushed into powder. The inlet zone of the quartz tube 1a is preheated to 100 ° C and the original reaction zone 1b is adjusted to 650-675 ° C, with a melt temperature of 515-560 ° C. To adjust the steam pressure, a stream of 10 liters per minute of nitrogen is passed through the apparatus continuously via conduit 9, the nitrogen stream being introduced at 150 mbar by introducing warm water at 60 ° C. in the washing apparatus 10. Adjusted to steam pressure. The results of this test are shown in Table 5 below. It is shown that at melt temperatures up to 530 ° C., an optimum solubility can be achieved, corresponding to a chain length of about 20-30.

────────────────────────────────────────────────── ─── Continuation of front page    (81) Designated country EP (AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, I T, LU, MC, NL, PT, SE), OA (BF, BJ , CF, CG, CI, CM, GA, GN, ML, MR, NE, SN, TD, TG), AP (GH, GM, KE, L S, MW, SD, SZ, UG, ZW), EA (AM, AZ) , BY, KG, KZ, MD, RU, TJ, TM), AL , AM, AT, AU, AZ, BA, BB, BG, BR, BY, CA, CH, CN, CU, CZ, DE, DK, E E, ES, FI, GB, GE, HU, IL, IS, JP , KE, KG, KP, KR, KZ, LC, LK, LR, LS, LT, LU, LV, MD, MG, MK, MN, M W, MX, NO, NZ, PL, PT, RO, RU, SD , SE, SG, SI, SK, TJ, TM, TR, TT, UA, UG, US, UZ, VN (72) Inventor Alexander Maurer             Germany Mannheim Kochel             Seeweg 1 (72) Inventor Friedrich Var             Germany Mannheim im Wo             Filbell 61

Claims (1)

[Claims] 1. An Na / P ratio of 0.3 to 0.6, P ₂ O ₅ content of more than 77 wt% Na ₂ O content is less than 20%, the acid soluble residual water content of 3-10% In the method for producing a polyphosphate, an aqueous solution of the phosphate is dried and melted at a temperature of 400 to 600 ° C. for 30 to 180 minutes to form a chain polyphosphate having an average chain length of 10 to 30. Cooling the melt while forming a glassy product, while maintaining the steam pressure of the atmosphere in contact with the melt during melting at 0.1 to 0.5 bar. A method for producing phosphate. 2. The method of claim 1 wherein the Na / P ratio is greater than 0.5 and less than 0.6. 3. 3. The method of claim 1 wherein the phosphate solution is formed by mixing aqueous phosphoric acid with a sodium phosphate or sodium hydroxide solution. 4. The treatment step is carried out continuously in a tube furnace, wherein the phosphate solution in the melt channel passes through the furnace and the steam pressure is adjusted by introducing an inert gas containing a corresponding amount of steam. 4. The method according to any one of 1 to 3. 5. Melting temperature is 450 to 550 ° C., the method of any one of claims 1 to 4, phosphate chain has a length of 20-30 PO ₃ units. 6. A polyphosphate produced by the method according to any one of claims 1 to 5. 7. Use of the polyphosphate according to claim 6 as a molten salt and a stabilizer in melt cheese. 8. a) a tubular furnace (1), which b) has a lining consisting of a quartz tube (3) in the quartz tube c) a feed tube (4) for phosphate and a melt of phosphate A melting vessel (2) having a discharge pipe (5) for mounting the melt at a slight angle to allow the flow of the melt, and d) a steam supply pipe (9). An apparatus for continuously producing the acidic polyphosphate according to any one of 1 to 6. 9. 9. Apparatus according to claim 8, wherein cooling rollers (6) are present for the outgoing polyphosphate melt and the phosphate glass formed is crushed via a scraper (7) and conveyed to a storage vessel (8). .