CS264248B1 - Process for preparing double manganese-magnesium cyclo-tetraphosphates - Google Patents

Abstract

A method for synthesizing double cycling manganese-magnesium tetraphosphates c-Mn2_xMg? P4Oi2, where x £ (0; 2) consists of calcination mixtures of oxide, hydroxide, sodium carbonate, or manganese carbonate and magnesium carbonate and phosphoric acid at a rate heating is less than 45 ° C / min, to temperature 260 ° C to 895 ° C and tension in the calcination area water vapor above 20 kPa.

Description

The invention relates to a process for the preparation of double manganese-magnesium cyclo-tetraphosphates.

The manganese-magnesium _double cyclo-tetraphosphates are represented by the formula c-Mn _{2 x} Mg _x P ₄₀ 12, where x can range from near zero to close to two. These compounds are characterized by high thermal and chemical stability and their use can be as hygienically and ecologically harmless special pigments or in various high-temperature materials or for agrochemical purposes. The only method so far disclosed is to crystallize them from a cooling melt containing phosphate anions in the necessary amounts together with manganese and magnesium cations. However, this process for the preparation of double manganese-magnesium cyclo-tetraphosphates is particularly suitable for preparative laboratory purposes. Thus, very pure products can be prepared, but this method is of little use for a wider technological application to produce products for pigmentary or agrochemical purposes that do not require completely pure products. Indeed, this method has high energy requirements, since it is necessary to transfer the starting mixture to the melt at high temperatures, and it must then be allowed to cool in a controlled manner (under constant heating). Technological implementation of this method is also complicated by the necessity of providing a dry atmosphere or vacuum in the melt space.

These drawbacks are overcome by a process for the preparation of double manganato-magnesium manganese-magnesium phosphates of the formula c-Mn _{2 x} Mg _x P ₄ O 12, where x can range from near zero to close to two according to the invention. that the manganese oxide, hydroxide, or carbonate together with the oxide, hydroxide, hydroxide-carbonate, or magnesium carbonate in an Mn / Mg ratio corresponding to the (2-x) / x molar ratio is calcined with phosphoric acid in the starting mixture, wherein the amount of phosphate anions with respect to divalent cations, the molar ratio P ₂ O ₅ / (Mn + Mg) is equal to 0.9 to 1.4, preferably 1 to 1.05, the starting mixture being prepared by reacting the manganese and magnesium compounds with phosphoric acid, preferably a concentration of 30 to 85 wt. % H ₃ PO ₄ , and the starting mixture is preferably allowed to continue to react for at least 1 hour, preferably with stirring, and then started to heat at less than 45 ° C / min, preferably at 1 to 10 ° C / min, to a temperature of 260 ° C to 895 ° C, preferably a temperature of 300 to 750 ° C, wherein the water vapor pressure in the calcination space is higher than 20 kPa, preferably 60 to 100 kPa.

The ratio of the manganese and magnesium compounds in the starting mixture is chosen according to the requirement for the manganese magnesium cation content of the product. The content of magnesium cations (x) may range from values close to zero to values close to two. A value of zero or two cannot be used, since then it would not be a double product, but a pure di-magnesium tetraphosphate. The amount of phosphoric acid in the starting mixture, expressed as the molar ratio P ₂ O ₅ / (Mn + Mg), would be best to use exactly by stoichiometry (i.e., said ratio equal to one) when using completely pure raw materials. However, according to the purity of the phosphoric acid used (the content of metal ions therein) and the purity of the manganese and magnesium raw materials (metal admixtures), the ratio should be adjusted within the range of 0.9 to 1.4, more preferred if the phosphate anions are in excess 1 to 1.05) than their significant deficiency compared to stoichiometry. The concentration of phosphoric acid is lower from the point of view of controlling the condensation rollers and hence the yield and purity of the product; however, this lower concentration causes an increase in the energy requirement for the evaporation of excess water and increases the volume of increase in the starting mixture, which moreover has the character of a slurry. Its calcination then presents technical problems, as opposed to calcination of a smaller volume mixture, which would be in the form of a solid or pasty, which results when a phosphoric acid concentration in the preferred range of 30 to 85 wt.% Is used. %. Allowing the mixture containing phosphate, manganese, and magnesium ions to react freely for at least 1 hour is advantageous in order to sufficiently conduct the initial reaction of the starting manganese and calcium compounds with phosphoric acid; this is a neutralization reaction using hydroxides or, in particular, a decomposition reaction of the carbonates, since the released carbon dioxide and the resulting loosening of the mixture would complicate the calcination itself. Therefore, mixing of the mixture is also preferred. The heating of the mixture at a rate of less than 45 ° C / min is chosen so that the individual dehydration and condensation reactions gradually taking place in the mixture can occur at (or near) the temperatures at which they occur as slowly as possible and thereby with the highest yield. Otherwise, unwanted cleavage of the intermediates would result in the release of the phosphorous component, which would then condense separately into polyphosphoric acids and thereby contaminate the main product and reduce its yield. When selecting a very low heating rate, a disproportionate increase in product preparation time and thus a certain increase in material and energy requirements is to be expected. In addition, it will be more difficult in this case to maintain sufficient water vapor pressure in the calcined mixture space and thereby prevent the possible breakdown of the intermediates. The lower limit of calcination temperature (260 ° C) is given by the temperature of the gradual formation of the first particles of double manganese magnesium manganese magnesium cyclophosphates. The upper limit of the calcination temperature region (895 ° C) is related to the thermal stability of double cyclo-tetraphosphates, which melt non-congruently above this temperature. A preferred calcination temperature in the range of 300 ° C to 750 ° C is due to the fact that the double cyclo-tetraphosphates are already formed at a temperature above 300 ° C at a sufficiently rapid rate and the initially formed amorphous products are converted to microcrystals which are use, in its most suitable form. The upper limit of this preferred temperature range (750 ° C) is given by the fact that at this temperature the double cyclotetaphosphate formation reactions have already taken place (if advantageous heating rates have been used), even at higher water vapor pressures in the calcination space. Maintaining a water vapor pressure in the space of the calcined mixture greater than 20 kPa is necessary to prevent the formation of undesirable by-products of condensation and to prevent cleavage and separate condensation of the phosphorus component. The water vapor present somewhat slows down the condensation reactions, allows them to be more quantitative, and also prevents the formation of undesired non-porous crusts on the surface of the calcined mixture particles, which would prevent the quantitative course of the dehydration reactions. It is advantageous to maintain the water vapor pressure above 60 kPa, when its action is sufficient in said direction. The upper limit for the advantageous vapor pressure in the space of the calcined mixture - 100 kPa - is given above all by the necessity of increased constructional, material and energy demands on the calcining device and the calcination line, when using higher pressures than atmospheric pressure. In addition, increased braking of the condensation and dehydration reactions due to a water vapor pressure above 100 kPa would again disproportionately prolong the product preparation time.

The process of the invention further comprises treating the product with a hydrochloric, sulfuric, nitric or phosphoric acid, preferably a concentration of 0.5 to 10% by weight, after curing. This operation is performed as ev. Purification of the obtained product in its pure form. The action of said acids removes all unwanted by-products and ev. residues of the starting mixture which thus pass into solution. Double manganese-magnesium cyclo-tetraphosphates resist the action of these acids. If the double cyclotetraphosphates are prepared for use for pigmentary or agrochemical purposes, and in particular if they are prepared under the preferred conditions of the invention, such purification is not required.

The process makes it possible to prepare double manganese-magnesium cyclotrophosphates under technologically feasible conditions, with a sufficient yield and with a sufficient purity of the products. It also allows the use of lower quality raw materials - diluted and less pure phosphoric acid and less pure manganese compounds. Under the conditions of preparation of the product according to the invention,

Claims (2)

A process for the preparation of double manganato-magnesium manganese-magnesium phosphate (c-Mn _{2 x x} Mg _x P ₄ O ₁₂ ) wherein x may range from zero to two according to the invention, characterized in that: The carbon monoxide, hydroxide, or manganese carbonate, together with the oxide, hydroxide, and carbon dioxide of the present invention as preferred, can produce almost pure products. If less pure products are obtained, they can be purified by the process according to the invention. The following is an example of a process for the preparation of double manganese-magnesium cyclo-tetraphosphates according to the invention. Example 1 100 g of manganese oxide (containing 77% Mn) and 141.93 g of a slurry of magnesium hydroxide (containing 24% Mg) were mixed with 862 g of phosphoric acid. concentration of 65% H3PO4 and allowed to react spontaneously with stirring for 3 hours. The mixture was then heated at 5 ° C / min to 580 ° C for 3 hours at this temperature. The water vapor pressure in the space of the calcined mixture was maintained at 85 to 95 kPa. 583 g of a product was obtained which contained 95% of double manganese-magnesium manganese-magnesium phosphate double-phase of the formula cMnMgP _{40 12} . Example 2 100 g of manganese carbonate (containing 48% Mn) and 24.4 g of magnesium carbonate (containing 29% Mg) were carefully mixed with 577 g of 40 wt% phosphoric acid. % H3PO4 and allowed to react spontaneously with occasional stirring. The mixture was then heated at a rate of 8 ° C / min to 540 ° C for 2 hours at this temperature. The water vapor pressure in the space of the calcined mixture was maintained at 75 to 85 kPa. 250 g of product were obtained, which was further purified by leaching with 3% hydrochloric acid. % HCl. After washing with water and drying at 150 [deg.] C., 245 g of product were obtained with a content of 97.5% c-Mn < + > Example 3 50 g of manganese carbonate (containing 48% Mn) and 133 g of slurry of magnesium hydroxide (containing 24% Mg) were carefully mixed with 433 g of 80 wt% phosphoric acid. % H3PO4 and allowed to react spontaneously with occasional stirring. The mixture was then heated at 4 ° C / min to 500 ° C for 3 hours at this temperature. The water vapor pressure in the space of the calcined mixture was maintained at 80 to 90 kPa. 339.6 g of product were obtained, which contained 96% of double manganese-magnesium manganese-magnesium _{phosphate dibasic} c-Mn _{O 15} Mg ₁₅ P _{4 O 12} . OF THE INVENTION tannic or calcium carbonate in a ratio of Mn / Mg corresponding to the molar ratio of (2-x) / x is calcined with phosphoric acid in the starting mixture, wherein the amount of phosphate anions to divalent cations corresponds to molar ratio P ₂ O ₅ / (Mn + Mg ) of from 1 to 1.05, the starting mixture being prepared by treating the manganese and magnesium compounds with phosphoric acid, preferably a concentration of 30 to 85 wt. . % H 3 PO 4 and the starting mixture is preferably allowed to continue to react for at least 1 hour, preferably with stirring, and then heated at a rate of less than 45 ° C / min, preferably at a rate of 1 to 8 ° C / min, to a temperature of 260 ° C to 895 ° C, preferably to a temperature of 300 to 750 ° C, wherein the water vapor pressure in the calcination space is higher than 20 kPa, preferably 60 to 100 kPa. Method according to claim 1, characterized in that the product after calcination is treated with hydrochloric, sulfuric, nitric or phosphoric acid, preferably a concentration by weight of 0.5 to 10%.