SU814855A1 - Method of producing sodium polyphosphate - Google Patents

Description

one

This invention relates to a process for the preparation of phosphoric salts, in particular glassy polyphosphates of the Graham salt type.

A known method of producing condensed glassy alkaline phosphates by heating monophosphates at a temperature of 5 ° C above the melting point and the subsequent cooling of the melt formed is introduced into water or an aqueous solution of inorganic salts with simultaneous granulation. The high molecular weight phosphate content is 95.1% l.

The closest to the proposed technical essence is the method of obtaining sodium polyphosphate of the Graham salt type, including melting of sodium orthophosphate for 40-60 minutes with subsequent cooling of the melt at a rate of 45-85 K / min with a layer thickness of 5-2 O mm 2.

The disadvantage of this method is the long duration of calcination to obtain a homogeneous melt and an insufficiently high content of high molecular weight linear phosphates, about 94%.

The inventive chain is a reduction in process time and an increase in quality by increasing the content of high molecular weight linear phosphates in the product.

The goal is achieved by the proposed method of producing sodium polyphosphate, including heating sodium orthophosphate first in a spray dryer in the presence of urea at 15 ° -3OO ° C, and then at 65 ° -9OO ° C, followed by cooling at a rate of 10 ° -12 ° deg / min with a layer thickness 1-4 mm.

The method is carried out as follows.

The stock solution of monosodium phosphate containing 0.5–3 wt.% Carbamide is dried in a spray dryer at a temperature of 15 ° C; 1; then, the resulting dry product is sent to a conditioning furnace, where it is melted at a temperature C, and then The resulting melt is cooled at a rate of 8 ° -12 ° C / min on the Bodoochlazhim rolls rotating in opposite directions with a thickness of the melt layer of 1-4 mm. Decontamination of the original pacTBcf) a first in the spray gun allows intensive evaporation of the main amount of moisture, including the constitutional one. Subsequent melting and clarification in a polymerization furnace (removal of air bubbles and moisture) does not require a long time. This increases the productivity of the furnace and the amount of linear, high molecular weight phosphates, since their content is inversely related to the amount of moisture in the water. The introduction of urea in an amount of less than 0.5 wt.% Does not provide an increase in the rate of dehydration of the solution of one-substituted sodium phosphate. The content of urea more than 3 wt.% Irrational, since the increase in the rate of dehydration is negligible. Drying in the spray dryer is carried out in the range of 150-ZOO C, since at temperatures below 15 ° C the product adheres to the walls of the dryer, which makes its operation impossible. An increase in temperature above 30 ° C is inexpedient, since the required degree of dehydration has been achieved and will only lead to sintering of the product, which will complicate its transportation. Drying in the spray dryer provides intensive removal of the main amount of moisture, which will ultimately lead to a reduction in the residence time of the product in the polymerization furnace. Further calcination and melting of dry product is carried out in a bath of a polymerization furnace at a temperature of 65 ° -90 ° C, heated by flue gases. The lower limit of the temperature range is selected based on the melting point of 628 ° C. An increase in temperature above 9OO ° C leads to intensive evaporation from the melt, which causes a decrease in the content of the main substance — high molecular linear phosphates and severe destruction of the furnace refractory material. hail / min does not provide a greater conjugation of high-molecular phosphates, but an increase in the rate of more than 12o hail / min 8 54 is impractical because the increase in the content of these phosphates is not significant. but The thickness of the melt layer of 1–4 mm was chosen in order to ensure the .Jy quasi th cooling rate. Next, the melt from the polymerization cure is directed to the water-cooled rolls. Example 1. 500 g of a 50% solution of a monosubstituted sodium orthophosphate with a carbamide content of 7.5 g (which is 1.5 wt.% Based on the weight of the solution) are taken and sent to a vertical spray dryer for drying. The product is heated to a temperature and then melted in a polymerization furnace at 650 ° C, melting is carried out for the time required to completely melt the product and clarify the melt, and then the product is cooled on water cooled rolls rotating in opposite directions. at a speed of 8 ° C / min with a layer thickness of 4 mm. The cooled glassy product contains 204.6 g (96%) of high molecular weight sodium phosphate, the remainder being molecular phosphate. PRI mme R 2. The same operations as. and in example 1, but taking carbamide 15 g (3%), the product is heated to a temperature of 250 ° C, melted at a temperature of 75 ° C, cooled at a rate of 1OO degree / min with a layer thickness of 1 mm. The cooled glassy product contains 208 g (98%) of high molecular weight sodium phosphate, the rest is low molecular weight phosphate. Example 3. The same operations as in example 1, but taking carbamide 1O g (2%), the product is heated to temperature ZOO ° C, melted at a temperature cooled at a speed of 120 deg / min with a layer thickness of 2 mm. The cooled glassy product contains 206 g (97%) of high molecular weight plibjx sodium phosphates, the rest is low molecular weight sodium phosphate, the rest is low molecular weight phosphate. As follows from the above examples, the introduction of carbamide into the initial solution of the monosubstituted sodium orthophosphate and carrying out the process in two stages ensures its intensification due to a higher degree of dehydration of the monosubstituted orthophosphate at the drying stage and shortening the melting time of the second station.

The higher cooling rate of the melt in the thin layer compared to the prototype ensures its intensive cooling, which causes a high content of high molecular weight sodium linear phosphate in the finished product, which determine its complexing properties at the application stage.

Thus, the proposed technical solution ensures the intensification of the process twice and the improvement of the quality of the product.

Claims (2)

1. A method of producing sodium polyphosphate comprising melting sodium orthophosphate with a subsequent cooling of the melt. characterized in that, in order to reduce the process time and increase high molecular weight linear phosphates in the product, prior to melting, sodium orthophosphate mixed with urea is heated in a drying oven at 15 ° -3OO ° C, melting is carried out at 650900 ° C, and cooling is carried out at a rate 8O-120 degrees / min with a layer thickness of 14 mm. 2. The method according to claim 1, about tl and h and y - y and with the fact that urea is introduced in an amount of 0, 5-3 wt.%, Sources of information taken into account in the examination 1. Van Weser. Phosphorus and its compounds, M., 1962, p. 593. 2. USSR author's certificate M 64725O, cl. C O1 B 25 / 4O, 1977.