RU2148010C1 - Sodium tripolyphosphate production process - Google Patents

Abstract

FIELD: industrial inorganic synthesis. SUBSTANCE: sodium tripolyphosphate used in surfactant production , in flotation processes, and in oil production industry is prepared from extraction phosphoric acid and soda, process consisting in two-step neutralization of phosphoric acid to molar ratio Na₂O:P₂O₅ = 1.63-1.71. In the first step, 60-70% of soda is added and suspension is filtered to separate phosphate-fluoride sludge, which is then neutralized in presence of seed: first-step phosphate-fluoride sludge taken in amount corresponding to 0.3 to 1.5 wt parts of solid phase per 100 wt parts of the second-step suspension. To filtrate is added conditioning additive, after which filtrate is pulverized into particles of recycle mixture of orthophosphate and/or tripolyphosphate, which are dried and calcined in rotary furnaces at 100 to 450 C and then crushed to yield final product. In total, 3 to 25 wt.pts of phosphate-fluoride sludge as the first-step suspension per 100 wt.pts of the second-step suspension are used. EFFECT: intensified (by 5-15%) neutralization process. 2 cl, 1 tbl, 2 ex

Description

 The invention relates to the field of technology of inorganic substances, and in particular to a technique for producing sodium tripolyphosphate from extraction phosphoric acid and soda, a product widely used for the production of synthetic detergents in the processes of flotation, oil production, etc.

Known methods for producing sodium tripolyphosphate, including the neutralization of phosphoric acid with soda to a molar ratio of Na ₂ O: P ₂ O ₅ = 1,63- 1,71 (5: 3), dehydration of the resulting solution by evaporation and / or drying at 100-300 ^o C, thermal dehydration of a mixture of powdered or granular (1-3.5 mm) orthophosphates at 300 - 480 ^o C [E.A. Sold and others. Tripolyphosphates and their use. Minsk, "Science and Technology", 1969, p. 273-281; Pat. U.S. N 3993734, class 423- 315, C O1 B, publ. 11/23/1976]. Single-stage neutralization of phosphoric acid with soda ash is provided in the method [US Pat. U.S. N 3030180, CL 423-315, C O1 B, publ. 04/17/1962], characterized in that the solutions formed during neutralization are sprayed onto particles of a retur mixture of orthophosphates and / or tripolyphosphate in the ratio solution: retur (3-3.5): 1, followed by drying and calcination of granules in rotary kilns at a temperature 100-450 ^o C and their crushing.

 The disadvantage of these processes is the need to use expensive thermal phosphoric acid. When using extraction phosphoric acid and performing neutralization in one step, the product contains an increased amount of fluorine compounds (1-1.5% in terms of NaF) [I. L. Hoffmann, M.V. Lykov, I.P. Hudoley. "Chemical Industry", N 9, 1961, p. 620], reducing the proportion of the main component in it - tripolyphosphate [M.E. Pozin, "Technology of Mineral Salts", part 2, L, "Chemistry". 1974, p. 1081].

When processing extraction phosphoric acid to obtain a high-quality product (55-56% P ₂ O ₅ ), neutralization is carried out in two stages with separation of phosphate-fluoride sludge after each stage by filtration [M.E. Pozin, "Technology of Mineral Salts", part 2, L, "Chemistry". 1974, p. 1082; M.E. Pozin, B.A. Kopylev, R.Yu. Zinyuk. Auth. testimonial. USSR N 256741 Bull. fig. N 35, 1969], containing, along with fluorine, impurities of calcium, magnesium, aluminum, iron. To improve the consumer properties of sodium tripolyphosphate provides the introduction of various conditioning additives [E.A. Sold and others. Tripolyphosphates and their use. Minsk, "Science and Technology", 1969, p. 276], which complicates the process and increases the cost of the product.

The closest to the claimed technical essence and the achieved result is a method of producing sodium tripolyphosphate, including the neutralization of extraction phosphoric acid with soda ash to a molar ratio of Na ₂ O: P ₂ O ₅ = 1,63 - 1,71 in two stages, filtering the suspension after each neutralization steps with the separation of phosphate-fluoride sludge, the introduction of a conditioning additive (sodium pyrophosphate) into the filtrate, spraying the latter onto particles of a retur mixture of orthophosphates and / or tripolyphosphate, followed by drying and calcining the pellets in a rotary kiln at a temperature of 100-450 ^o C and crushing the desired product [A. Kuznetsov, B.D. Guller, M.A. Shapkin and others. "A method of producing sodium tripolyphosphate. Application for invention N 95 114712/25 (024627) from 08/15/1995].

 The method allows to obtain tripolyphosphate, characterized by a high dissolution rate in water and suitable for the production of compact detergents. The practical operation of this method showed, however, that the manufactured product contains a certain amount of magnesium and calcium compounds (0.15-0.35%), which cannot be completely converted to phosphate-fluoride sludge, even in conditions of prolonged implementation of the neutralization stages, i.e. e. at low intensity. The presence of alkaline earth metal compounds in sodium tripolyphosphate reduces its complexing ability.

The aim of the invention is to obtain a product with a low content of magnesium and calcium compounds (less than 0.1%), as well as the intensification of the process of neutralization of extraction phosphoric acid with soda ash and separation of phosphate-fluoride sludge. The goal is achieved by the fact that in the known method for producing sodium tripolyphosphate, which consists in neutralizing extraction phosphoric acid with soda ash to a molar ratio of Na ₂ O: P ₂ O ₅ = 1.63 -1.71 in two steps, filtering the suspension after each stage of neutralization with dividing the phosphate-fluoride sludge, introducing a conditioning additive into the filtrate, spraying the latter onto particles of a retur mixture of orthophosphates and / or tripolyphosphate, followed by drying and calcining the granules in rotary kilns at a temperature of 100-450 ^o C and crushing target product. 60-70% soda ash is introduced into the first stage and neutralization in the second stage is carried out in the presence of a seed - phosphate-fluoride sludge of the first stage, taken in an amount of 0.3-1.5 wt. including solid phase per 100 parts by weight suspensions of the second stage. While phosphate-fluoride sludge is used in the form of a suspension of the first stage, the flow rate of which corresponds to 3 to 25 wt.h. per 100 parts by weight suspensions of the second stage.

 Thus, the difference between the proposed method and the known one is that 60 - 70% soda ash is introduced into the first stage and neutralization of extraction phosphoric acid with soda at the second stage is carried out in the presence of a seed of the first stage phosphate-fluoride sludge, taken in an amount of 0.3 - 1.5 parts by weight solid phase per 100 parts by weight suspensions of the second stage. An additional difference is the use of phosphate-fluoride sludge in the form of a suspension of the first stage.

 The basis for the creation of technical elements of the novelty and usefulness of the proposed method, as well as the choice of ranges of variation of physico-chemical parameters presented in the characterizing part of the claims, were the authors performed studies on the deposition of impurity compounds of magnesium, calcium, aluminum, iron and fluorine present in the extraction phosphoric acid and excreted as it is neutralized with soda. It was found that compounds of one and a half oxides and fluorine during step-wise neutralization are released almost completely and their level in the product does not exceed thousandths of a percent. At the same time, calcium and especially magnesium compounds are prone to the formation of sufficiently stable supersaturated solutions, and for their effective isolation and obtaining a sufficiently pure product (0.02 - 0.08% of the sum of Mg and Ca) it is necessary to forcibly reduce the energy barrier and, accordingly, the induction period of onset crystallization. It was experimentally established that the nucleation of phosphate salts of magnesium and calcium in the presence of a seed (phosphate-fluoride sludge) decreases and as a result, the content of calcium and magnesium in the liquid phase of the suspension of the second stage of neutralization relatively quickly (within 30-60 minutes) reaches equilibrium values ( not more than 0.01 and 0.02% for calcium and magnesium, respectively). The research results on the basis of which the claimed ranges of seed quantities are selected are shown in table 1.

As follows from the presented data, the optimal range is the consumption of the seed, corresponding to 0.3 - 1.5 wt.h. solid phase per 100 parts by weight suspensions of the second stage. The implementation of the second stage of neutralization within 30-60 minutes provides a Me ²⁺ content in sodium tripolyphosphate equal to 0.02-0.08% with the introduction of phosphate fluoride seeds in an amount of 0.3-1.5 wt. including solid phase. Dosage reduction to 0.2 parts by weight associated with an increase in the total content (Mg + Ca) in the product up to 0.3%. In this case, additional experiments showed that increasing the exposure time of the suspension in the second stage to 180-240 minutes does not allow in this case to reduce the proportion of Me ²⁺ in Na ₅ P ₃ O _{10 to} less than 0.25%. An increase in the mass of the seed to 1.7 parts is not effective (the proportion of Me ²⁺ in the product is 0.02-0.05%, which corresponds to the values obtained when 1.5 parts by weight of the solid phase of the phosphate-fluoride sludge are introduced into the second stage first stage). Moreover, practice has shown that when dosing to the second stage 1.7 wt.h. phosphate-fluoride sludge, the filtrate increases the content of fluorion (F ^- ), due to the partial decomposition of Na ₂ SiF ₆ present in the sludge, and therefore, the proportion of polyform in the product decreases below 90%.

 As a seed can be used: 1). washed first stage sludge or 2). suspension of the first stage of neutralization, the solid phase of which is represented by phosphate fluoride slurry. In the latter case, the flow rate of the suspension of the first stage supplied to the second stage, bypassing the filter, is taking into account the ratio W: T (usually corresponding to 10-15: 1): from 0.3 • (10 + 1) to 1.5 • (15 +1), i.e. 3-25 parts by weight per 100 parts by weight suspensions of the second stage.

To specify the proposed method for producing sodium tripolyphosphate, examples of the process are given:
Example 1

10.8 t / h of extraction phosphoric acid (28% P ₂ O ₅ ) neutralize 2.3 t / h of soda (96% Na ₂ CO ₃ ). In this case, 450 m ³ / h of carbon dioxide (0.9 t) is released into the gas and 12.2 t / h of a suspension of the first stage are formed, containing 0.77 t of solid phase (L: T = 15: 1). As a result of filtration on a filter press No. 1 and washing using 1 m ³ / h of water, 2.2 t / h of wet sludge are obtained (H ₂ O - 47%, total moisture capacity 65%) and 11.1 t / h of filtrate first steps. Then it is processed for 40 minutes, 1.2 t / h of soda. At this stage, 25.0 kg / h (as a phosphate-fluoride seed) of slurry (wet cake) are also introduced from filter press No. 1. The amount of solid phase transferred is 9.0 kg, which corresponds to ~ 0.8 wt. hours per 100 parts by weight suspensions of the second stage. At the second stage, 11.83 t / h of suspension are formed, and 0.5 t / h of carbon dioxide (250 m / h) are released into the gas phase. The suspension is separated into a filter press N 2, separating 11.78 t / h of liquor (filtrate) of the second stage (molar ratio of Na ₂ O: P ₂ O ₅ - 1.67) from 0.045 t / h of sludge. 50 kg of a conditioning additive (a mixture of sodium and potassium pyrophosphates) are added to the filtrate. 11.83 t / h of solution are sprayed with compressed air onto a retur curtain (a mixture of orthophosphates and sodium tripolyphosphate) in a BGS apparatus heated by flue gases (their temperature at the inlet is 700-800 ^o C, in the veil - 250 - 350 ^o C, at the outlet of drum 180 - 230 ^o C). The dried material is sent to a rotating calcining drum heated by flue gases with a temperature of 800 - 900 ^o C at the inlet, 350 - 450 ^o C near the loading zone and 280 - 350 ^o C at the outlet of the apparatus. The calcined material is ground and 4.3 t / h of product are obtained containing 56% P ₂ O ₅ , 96% Na ₅ P ₃ O ₁₀ and 0.03% alkaline earth metal phosphate impurity in terms of Me ²⁺ .

 Example 2

13 t / h of extraction phosphoric acid (28% P ₂ O ₅ ) neutralize 2.77 t / h (96% Na ₂ CO ₃ ). In this case, 540 m ³ / h of carbon dioxide (1.08 t / h) is released and 14.7 t / h of a first-stage suspension containing 0.93 t of solid phase are formed (L: T = 15: 1). 13 t / h of suspension are filtered on a N 1 filter press, the precipitate is washed with 1.05 m / h of water and 2.35 t / h of wet sludge are obtained (H ₂ O - 47%, total moisture capacity ~ 65%) and 11.7 t / h of the filtrate of the first stage. 1.7 t / h of the suspension of the first stage, bypassing the filter, is mixed with 11.7 t / h of the filtrate of the first stage, using it as a phosphate fluoride seed (the amount of suspension corresponds to 12 parts by weight per 100 parts by weight of the suspension of the second stage of neutralization ) Next, the mixture in the second stage is treated with 1.4 t / h of soda for 45 minutes. At the same time, 0.56 t / h CO (280 m ³ / h) is released into the gas. The second stage suspension (14.2 t / h) is separated on a N 2 filter press, separating 13.86 t / h of liquor (filtrate) of the second stage (molar ratio of Na ₂ O: P ₂ O ₅ - 1.67) from 0 , 34 t / h of sludge. To the filtrate add 50 kg of conditioning agent (a mixture of sodium pyrophosphates and potassium). 13.91 t / h of the solution is sprayed with compressed air into the BGS apparatus and then sent to the calcination drum as in Example 1. After grinding, 5.2 t / h of product containing 56% P ₂ O ₅ , 96.1% Na ₅ P ₃ are obtained. O ₁₀ and 0.025% of Me ²⁺ impurities.

 Thus, the proposed method provides on the basis of extraction phosphoric acid high-quality sodium tripolyphosphate with a low content (up to 0.02%) of impurities of alkaline earth metal compounds. At the same time, the process of neutralizing phosphoric acid with soda is intensified by 5-15%.

Claims (2)

1. A method of producing sodium tripolyphosphate, including the neutralization of extraction phosphoric acid with soda ash to a molar ratio of Na ₂ O: P ₂ O ₅ = 1,63 - 1,71 in two stages, filtering the suspension after each stage of neutralization with the separation of phosphate-fluoride sludge, introduction of the conditioning additives in the filtrate, the latter on the atomization particle recycle ratio mixture of orthophosphates and / or tripolyphosphate, followed by drying and calcining the pellets in a rotary kiln at 100 - 450 ^o C and crushing the desired product, characterized in that the at ne -hand stage is introduced 60 - 70% of soda ash by weight and all its neutralization in the second stage is carried out in the presence of seed - phosphate fluoride slurry first step taken in an amount of 0.3 - 1.5 parts by weight solid phase per 100 parts by weight suspension of the second stage.  2. The method according to claim 1, characterized in that the phosphate-fluoride sludge is used in the form of a suspension of the first stage, taken in an amount of 3 to 25 wt.h. per 100 parts by weight suspensions of the second stage.

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