Preparation process of phosphorus ammonium slurry and application thereof in compound fertilizer

Abstract

The application belongs to the technical field of phosphorus ammonium and fertilizer, and provides a preparation process of phosphorus ammonium slurry and application of the phosphorus ammonium slurry in compound fertilizer.The preparation process comprises the following steps: S1, measuring and adding phosphoric acid and gaseous ammonia into a neutralization reactor to obtain a neutralization slurry; S2, adding a composite modified dispersant into the neutralization slurry obtained in S1 and uniformly mixing to obtain the phosphorus ammonium slurry; and the phosphorus ammonium slurry is subjected to gravity sedimentation treatment at 87-90 DEG C.The composite modified dispersant is composed of polyacrylamide, starch-sodium hexametaphosphate modifier and maleic anhydride-styrene-butyl acrylate copolymer, the mass of the polyacrylamide is 0.23-0.25% of the mass of the neutralization slurry, the mass of the starch-sodium hexametaphosphate modifier is 0.33-0.34% of the mass of the neutralization slurry, and the mass of the maleic anhydride-styrene-butyl acrylate copolymer is 0.03-0.04% of the mass of the neutralization slurry.The application effectively improves the sedimentation speed of the prepared phosphorus ammonium slurry, so as to shorten the sedimentation time and operation cycle.

Description

Technical Field

[0001] This invention belongs to the field of ammonium phosphate and fertilizer technology, and in particular relates to a preparation process of ammonium phosphate slurry and its application in compound fertilizer. Background Technology

[0002] Non-ferrous smelting and deep processing enterprises generate a large amount of phosphoric acid during production. To further process this byproduct phosphoric acid into marketable products, they often choose to initiate compound fertilizer projects. These projects neutralize metered phosphoric acid and ammonia gas in a forced circulation reactor, producing monoammonium phosphate (MAP) and byproducts, resulting in MAP slurry. MAP is an important chemical fertilizer. Because my country's phosphate rock resources are mostly medium- and low-grade ores, the resulting MAP slurry contains many impurities, primarily iron, aluminum, and magnesium, mainly water-insoluble compounds such as aluminum iron phosphate gel [(Al,Fe)PO4·nH2O]. These water-insoluble compounds often exist as fine crystals or amorphous, irregular solid phases, frequently in a colloidal state, leading to increased viscosity and decreased fluidity of the MAP slurry. This affects the solid-liquid separation characteristics of the MAP slurry, making the production of industrial-grade MAP difficult.

[0003] The widespread application of industrial-grade ammonium phosphate can bring significant economic benefits to enterprises. However, effectively removing water-insoluble compound impurities from ammonium phosphate slurry is a key technology in the purification and production of industrial-grade ammonium phosphate. Existing technologies utilize gravity to separate solid-liquid mixtures of ammonium phosphate slurry; the greater the settling velocity, the shorter the required settling time, which not only reduces costs but also significantly shortens the operation cycle. It is known that within a certain range, as the temperature of the ammonium phosphate slurry increases, its viscosity decreases, the intermolecular interactions weaken, and the settling velocity accelerates.

[0004] When the temperature rises too high, although the viscosity of the ammonium phosphate slurry decreases with increasing temperature, at the same time, the hydrodynamic interaction caused by the disturbance of the local velocity of the surrounding liquid by the solid particles, as well as the thermodynamic interaction caused by the Brownian motion of the particles and their interaction with each other, increases. The Brownian motion causes the solid particles to shift from their original positions, ultimately leading to a decrease in the settling velocity. Summary of the Invention

[0005] To address the aforementioned problems, this invention proposes a preparation process for ammonium phosphate slurry and its application in compound fertilizers, which further effectively improves the settling speed of the prepared ammonium phosphate slurry, thereby shortening the settling time and operation cycle.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a process for preparing ammonium phosphate slurry, comprising the following steps: S1. Phosphoric acid and ammonia gas are metered and added to the neutralization reactor to obtain a neutralized slurry; S2. Add the composite modified dispersant to the neutralized slurry obtained in S1, mix well, and the ammonium phosphate slurry is obtained. The ammonium phosphate slurry was subjected to gravity settling treatment at 87-90℃; The composite modified dispersant is composed of polyacrylamide, a starch-sodium hexametaphosphate modifier, and a maleic anhydride-styrene-butyl acrylate copolymer. The mass of the polyacrylamide is 0.23-0.25% of the mass of the neutralizing slurry, the mass of the starch-sodium hexametaphosphate modifier is 0.33-0.34% of the mass of the neutralizing slurry, and the mass of the maleic anhydride-styrene-butyl acrylate copolymer is 0.03-0.04% of the mass of the neutralizing slurry.

[0007] Furthermore, the preparation method of the starch-sodium hexametaphosphate modified product is as follows: A1. Mix cassava starch and water in a mass ratio of 1:1 to obtain a starch solution; A2. Adjust the pH of the starch solution obtained in A1 to 9.5-10, add sodium hexametaphosphate (sodium hexametaphosphate) at a mass of 1.3-1.4 times that of cassava starch, and stir the mixture in a constant temperature water bath at 54-58℃ to obtain the starch-sodium hexametaphosphate modified product.

[0008] Furthermore, in A2, the pH value of the starch solution is adjusted using anhydrous sodium carbonate.

[0009] Furthermore, in A2, the stirring speed is 270-300 r / min, and the stirring time is 3-3.2 h.

[0010] Furthermore, the preparation method of the maleic anhydride-styrene-butyl acrylate copolymer is as follows: B1. Add 30g styrene (St), 9.5-10.5g maleic anhydride (MAH), 9.5-10.5g butyl acrylate (BA), 0.24-0.27g benzoyl peroxide (BPO) and 100mL toluene to a 250mL three-necked flask equipped with a reflux condenser, stirrer and thermometer. Heat and stir to dissolve, then heat to polymerize and obtain a precipitate. B2. The precipitate obtained in B1 is first dissolved in butanone, then precipitated with toluene. This purification process is repeated several times. After filtration, the purified product is obtained and then vacuum dried to constant weight to obtain the maleic anhydride-styrene-butyl acrylate copolymer.

[0011] Furthermore, in B1, the heating is carried out in a constant temperature water bath at 50±2℃.

[0012] Furthermore, in B1, the specific operation of the heating polymerization reaction is as follows: first, heat to 75±2℃ and react for 5.5-6 hours, then heat to 90±2℃ and continue the reaction for 2.5-3 hours.

[0013] Furthermore, in B2, the drying temperature is 80±2℃.

[0014] Furthermore, the water content of the neutralized slurry is 66-70 wt%.

[0015] Secondly, the present invention provides an application of the ammonium phosphate slurry prepared by the above-mentioned preparation process in compound fertilizer.

[0016] Compared with the prior art, the present invention has the following beneficial effects: In the preparation of ammonium phosphate slurry in this invention, a composite modified dispersant (polyacrylamide, starch-sodium hexametaphosphate modifier, and maleic anhydride-styrene-butyl acrylate copolymer) is added. Polyacrylamide itself can reduce the frictional resistance between slurries. After the sodium hexametaphosphate in the starch-sodium hexametaphosphate modifier combines with starch, the phosphate groups in its molecules can still dissociate into a large number of negative charges in water, which are adsorbed onto the surface of positively charged impurity particles, making the particle surface negatively charged. The particles repel each other due to the same charge, preventing aggregation. Furthermore, the degradation of starch fragments can form physical isolation, providing stronger mechanical barrier ability, enhancing the steric hindrance effect, and weakening Brownian motion interference. This further improves the slurry flowability and creates more favorable conditions for particle sedimentation.

[0017] The molecular structure of maleic anhydride-styrene-butyl acrylate copolymer contains anchoring groups and solvation chains. The anchoring groups can form multi-point anchoring with the surface of impurity particles, inhibiting particle displacement caused by Brownian motion. The solvation chains extend in the dispersion medium, forming a protective layer and enhancing the steric hindrance effect. This weakens or even offsets the negative impact caused by the increased thermodynamic interaction when the temperature is further increased (e.g., from 80℃ to 88℃). Thus, it synergistically increases the heating temperature threshold while simultaneously increasing the gravity settling velocity of the ammonium phosphate slurry. Attached Figure Description

[0018] Figure 1 This is a comparative trend chart of gravity settling test (settling velocity) data of ammonium phosphate slurry in Example 1 and Comparative Examples 1-3 of the present invention. Figure 2 This is a comparative trend chart of gravity settling test (settling velocity) data of ammonium phosphate slurry in Examples 1, 2, 4 and 5 of the present invention. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Unless otherwise specified, all raw materials used in the embodiments / comparative examples of this invention are commercially available.

[0021] The preparation method of the starch-sodium hexametaphosphate modified product involved in the embodiments / comparative examples of this invention is as follows: A1. Mix cassava starch and water at a mass ratio of 1:1 to obtain a starch solution. Specific procedures: Accurately weigh 100.00g of cassava starch and 100.00g of deionized water using an electronic balance; slowly add the cassava starch to the beaker containing the deionized water, stirring gently with a glass rod while adding to initially disperse the starch. After adding all the starch, start the stirrer and stir at a low speed of 130 rpm for 15 minutes to ensure the cassava starch is fully mixed with the water to form a uniform starch solution, avoiding clumping; after stirring, a uniformly dispersed starch solution is obtained.

[0022] A2. Adjust the pH of the starch solution obtained in A1 to 9.8 with anhydrous sodium carbonate, add sodium hexametaphosphate (1.35 times the mass of cassava starch), and stir the mixture in a constant temperature water bath at about 56℃ at a speed of 280 r / min for 3 hours to obtain the starch-sodium hexametaphosphate modified product. Specific procedures: The initial pH of the starch solution obtained in A1 was measured using a pH meter. Anhydrous sodium carbonate granules were slowly added while continuously stirring with a glass rod, and the pH was monitored in real time to adjust the pH of the starch solution to 9.8. Based on the mass of the cassava starch, sodium hexametaphosphate was accurately weighed, with a mass 1.35 times the mass of the cassava starch, i.e., 135.00 g of sodium hexametaphosphate. This sodium hexametaphosphate was then slowly added to the pH-adjusted starch solution, with continuous stirring to ensure uniform dispersion. After the addition was complete, a mixture was obtained. The beaker containing the mixture was placed in a constant temperature water bath (set to 56.0℃ with a temperature control accuracy of ±0.5℃). After the temperature stabilized at the set value, the mixture was stirred at 280 r / min for 3 hours. Stirring and water bath heating were then stopped, and the beaker was removed to obtain the starch-sodium hexametaphosphate modified product.

[0023] Among them, the cassava starch is food grade; the anhydrous sodium carbonate is industrial grade and was purchased from Henan Mingzhixin Chemical Products Co., Ltd.; and the sodium hexametaphosphate (superior grade) was purchased from Jinan Zesheng Chemical Co., Ltd.

[0024] The preparation method of the maleic anhydride-styrene-butyl acrylate copolymer involved in the embodiments / comparative examples of this invention is as follows: B1. Add 30g styrene (St), 10g maleic anhydride (MAH), 10g butyl acrylate (BA), 0.26g benzoyl peroxide (BPO) and 100mL toluene to a three-necked flask equipped with a reflux condenser, stirrer and thermometer. Heat and stir in a constant temperature water bath at about 50°C to dissolve. Then raise the temperature to 75°C and react for 5.5h. Then raise the temperature to 90°C and continue to react for 3.0h to obtain a precipitate.

[0025] B2. The precipitate obtained in B1 is first dissolved in methyl ethyl ketone and then precipitated with toluene. This purification process is repeated three times. After filtration, the purified product is obtained and then dried under vacuum (-0.09 MPa) (80℃) to constant weight to obtain maleic anhydride-styrene-butyl acrylate copolymer.

[0026] Styrene (St) and butyl acrylate (BA) were purchased from Jinan Anqi Chemical Co., Ltd.; maleic anhydride (MAH) and benzoyl peroxide (BPO) were purchased from Jinan Shuangying Chemical Co., Ltd.

[0027] Other specific details of the embodiments / comparative examples of the present invention are as follows.

[0028] Example 1: This example provides a process for preparing ammonium phosphate slurry, specifically including the following steps: S1. Phosphoric acid and ammonia gas (purity ≥99.5%) are separately metered and added to a neutralization reactor (forced circulation reactor) for neutralization. The degree of neutralization is 1.0, resulting in a neutralized slurry. The water content of the neutralized slurry is 68.3 wt%. This step is existing technology and will not be described further here.

[0029] S2. Add a composite modified dispersant to the neutralized slurry obtained in S1. This composite modified dispersant is composed of polyacrylamide, a starch-sodium hexametaphosphate modifier, and a maleic anhydride-styrene-butyl acrylate copolymer. Specifically, add polyacrylamide, starch-sodium hexametaphosphate modifier, and maleic anhydride-styrene-butyl acrylate copolymer to the neutralized slurry obtained in S1. The mass of polyacrylamide is 0.24% of the mass of the neutralized slurry, and the mass of starch-sodium hexametaphosphate modifier is 0.24% of the mass of the neutralized slurry. 335% (in this modified material, the mass ratio of starch, water, and sodium hexametaphosphate is 1:1:1.35. Correspondingly, in the neutralizing slurry, the mass of starch is 0.1% of the mass of the neutralizing slurry, the mass of water is 0.1% of the mass of the neutralizing slurry, and the mass of sodium hexametaphosphate is 0.135% of the mass of the neutralizing slurry. The sum of the masses of the three is consistent with the mass of the modified material), the mass of maleic anhydride-styrene-butyl acrylate copolymer is 0.035% of the mass of the neutralizing slurry; mix well to obtain ammonium phosphate slurry.

[0030] The ammonium phosphate slurry was heated to 88°C and subjected to gravity settling at 88°C.

[0031] Example 2: This example provides a process for preparing ammonium phosphate slurry, specifically including the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0032] S2. Add a composite modified dispersant to the neutralized slurry obtained in S1. This composite modified dispersant is composed of polyacrylamide, a modified starch-sodium hexametaphosphate, and a maleic anhydride-styrene-butyl acrylate copolymer. Specifically, add polyacrylamide, a modified starch-sodium hexametaphosphate, and a maleic anhydride-styrene-butyl acrylate copolymer to the neutralized slurry obtained in S1. The mass of polyacrylamide is 0.23% of the mass of the neutralized slurry, the mass of the modified starch-sodium hexametaphosphate is 0.33% of the mass of the neutralized slurry, and the mass of the maleic anhydride-styrene-butyl acrylate copolymer is 0.03% of the mass of the neutralized slurry. Mix well to obtain ammonium phosphate slurry.

[0033] The ammonium phosphate slurry was heated to 87°C and subjected to gravity settling at 87°C.

[0034] Example 3: This example provides a process for preparing ammonium phosphate slurry, specifically including the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0035] S2. Add a composite modified dispersant to the neutralized slurry obtained in S1. This composite modified dispersant is composed of polyacrylamide, a modified starch-sodium hexametaphosphate, and a maleic anhydride-styrene-butyl acrylate copolymer. Specifically, add polyacrylamide, a modified starch-sodium hexametaphosphate, and a maleic anhydride-styrene-butyl acrylate copolymer to the neutralized slurry obtained in S1. The mass of polyacrylamide is 0.25% of the mass of the neutralized slurry, the mass of the modified starch-sodium hexametaphosphate is 0.34% of the mass of the neutralized slurry, and the mass of the maleic anhydride-styrene-butyl acrylate copolymer is 0.04% of the mass of the neutralized slurry. Mix well to obtain ammonium phosphate slurry.

[0036] The ammonium phosphate slurry was heated to 90°C and subjected to gravity settling at 90°C.

[0037] In other embodiments, evaporation concentration technology can also be used. Process route: Phosphoric acid and ammonia are metered into the neutralization reactor to generate a neutralized slurry, while simultaneously flashing steam. This steam, combined with the flash steam from the first-effect evaporation, serves as the heat source for the second- and third-effect heaters. The neutralized slurry drawn from the neutralization reactor sequentially enters the third-effect, second-effect, and first-effect evaporation concentration systems, reducing the moisture content of the concentrated slurry to 25 wt%. The slurry is heated using a shell-and-tube stainless steel heater, and the circulating pump is a mixed-flow, high-flow, low-head, energy-saving circulating pump, equipped with a Class I energy-efficient motor. The predicted parameters for flash steam and live steam in each effect during the triple-effect evaporation concentration process are shown in Table 1 below.

[0038] Table 1. Steam Parameters for Triple-Effect Concentrator Process

[0039] The final flash steam generated by the triple-effect steam generator enters the mixing condenser to heat the circulating water, which serves as the heat source for liquid ammonia evaporation. Finally, the residual heat is utilized. After being cooled, the circulating water is used again as makeup water for the mixing condenser.

[0040] After sedimentation / concentration, the slurry is pumped into the company's existing spray drying tower via a high-pressure plunger pump. The high-pressure plunger pump uses a variable-speed motor. The spray drying tower uses hot air drying, with air heating employing a new type of aluminum alloy plate steam heater. The heat source is 0.5 MPaG saturated steam, and the inlet air is heated using steam condensate to recover waste heat from steam condensation. The ammonium phosphate product obtained from spray drying is mostly in powder or fine granule form and can be used directly as fertilizer or in the production of compound fertilizers.

[0041] Comparative Example 1: The difference between this comparative example and Example 1 is that: in the preparation of the ammonium phosphate slurry, maleic anhydride-styrene-butyl acrylate copolymer is not added, and 0.335% by mass of starch-sodium hexametaphosphate modifier in the neutralized slurry is replaced with 0.135% by mass of sodium hexametaphosphate in the neutralized slurry; the heating temperature of the ammonium phosphate slurry is reduced to 80°C, and gravity sedimentation treatment is performed at 80°C.

[0042] Specifically, a process for preparing an ammonium phosphate slurry includes the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0043] S2. Add polyacrylamide and sodium hexametaphosphate to the neutralized slurry obtained in S1; the mass of polyacrylamide is 0.24% of the mass of the neutralized slurry, and the mass of sodium hexametaphosphate is 0.135% of the mass of the neutralized slurry; mix well to obtain ammonium phosphate slurry.

[0044] The ammonium phosphate slurry was heated to 80°C and subjected to gravity settling at 80°C.

[0045] Comparative Example 2: The difference between this comparative example and Example 1 is that maleic anhydride-styrene-butyl acrylate copolymer is not added in the preparation of the ammonium phosphate slurry, and 0.335% by weight of starch-sodium hexametaphosphate modifier in the neutralized slurry is replaced with 0.135% by weight of sodium hexametaphosphate in the neutralized slurry.

[0046] Specifically, a process for preparing an ammonium phosphate slurry includes the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0047] S2. Add polyacrylamide and sodium hexametaphosphate to the neutralized slurry obtained in S1; the mass of polyacrylamide is 0.24% of the mass of the neutralized slurry, and the mass of sodium hexametaphosphate is 0.135% of the mass of the neutralized slurry; mix well to obtain ammonium phosphate slurry.

[0048] The ammonium phosphate slurry was heated to 88°C and subjected to gravity settling at 88°C.

[0049] Comparative Example 3: The difference between this comparative example and Example 1 is that the heating temperature of the ammonium phosphate slurry is reduced to 80°C, and gravity sedimentation treatment is carried out at 80°C.

[0050] Specifically, a process for preparing an ammonium phosphate slurry includes the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0051] S2. Add a composite modified dispersant to the neutralized slurry obtained in S1. This composite modified dispersant is composed of polyacrylamide, a modified starch-sodium hexametaphosphate, and a maleic anhydride-styrene-butyl acrylate copolymer. Specifically, add polyacrylamide, a modified starch-sodium hexametaphosphate, and a maleic anhydride-styrene-butyl acrylate copolymer to the neutralized slurry obtained in S1. The mass of polyacrylamide is 0.24% of the mass of the neutralized slurry, the mass of the modified starch-sodium hexametaphosphate is 0.335% of the mass of the neutralized slurry, and the mass of the maleic anhydride-styrene-butyl acrylate copolymer is 0.035% of the mass of the neutralized slurry. Mix well to obtain ammonium phosphate slurry.

[0052] The ammonium phosphate slurry was heated to 80°C and subjected to gravity settling at 80°C.

[0053] Comparative Example 4: The difference between this comparative example and Example 1 is that maleic anhydride-styrene-butyl acrylate copolymer is not added in the preparation of the ammonium phosphate slurry.

[0054] Specifically, a process for preparing an ammonium phosphate slurry includes the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0055] S2. Add polyacrylamide and starch-sodium hexametaphosphate modifier to the neutralized slurry obtained in S1; the mass of polyacrylamide is 0.24% of the mass of the neutralized slurry, and the mass of starch-sodium hexametaphosphate modifier is 0.335% of the mass of the neutralized slurry; mix well to obtain ammonium phosphate slurry.

[0056] The ammonium phosphate slurry was heated to 88°C and subjected to gravity settling at 88°C.

[0057] Comparative Example 5: The difference between this comparative example and Example 1 is that in the preparation of the ammonium phosphate slurry, 0.335% by mass of the starch-sodium hexametaphosphate modifier in the neutralized slurry was replaced with 0.135% by mass of sodium hexametaphosphate in the neutralized slurry.

[0058] Specifically, a process for preparing an ammonium phosphate slurry includes the following steps: S1. Same as in Example 1, a neutralized slurry was obtained; the water content of the neutralized slurry was 68.3 wt%.

[0059] S2. Add polyacrylamide, sodium hexametaphosphate, and maleic anhydride-styrene-butyl acrylate copolymer to the neutralized slurry obtained in S1; the mass of polyacrylamide is 0.24% of the mass of the neutralized slurry, the mass of sodium hexametaphosphate is 0.135% of the mass of the neutralized slurry, and the mass of maleic anhydride-styrene-butyl acrylate copolymer is 0.035% of the mass of the neutralized slurry; mix well to obtain ammonium phosphate slurry.

[0060] The ammonium phosphate slurry was heated to 88°C and subjected to gravity settling at 88°C.

[0061] Experimental Example: Experimental Subjects and Items: Gravity sedimentation tests were conducted on the ammonium phosphate slurries prepared in Examples 1-3 and Comparative Examples 1-5 at corresponding temperatures; gravity sedimentation is a process of separating solid-liquid mixtures by means of gravity.

[0062] Experimental method: 400g of ammonium phosphate slurry for each test object was measured using an electronic balance, placed in a beaker, and heated to the corresponding test temperature; it was then quickly stirred and poured into a 500mL measuring cylinder and allowed to stand. At the same time, a stopwatch was started and the height h (mm) of the clarified liquid layer falling in different time periods t (1 min, 2 min, 3 min, 4 min, 5 min, 6 min) was recorded; the settling velocity v (mm / min) was calculated; the calculation formula is v=h / t.

[0063] Experimental results: see Table 2.

[0064] Table 2. Experimental Data

[0065] Results Analysis: Combining the data in Table 2 and... Figures 1-2 The analysis focused on Example 1 and Comparative Examples 1-5: Specifically, comparing Comparative Example 1 and Comparative Example 2, it can be seen that compared to Comparative Example 1, which was heated to 80℃ and then subjected to gravity settling, Comparative Example 2, which was heated to 88℃ and then subjected to gravity settling, resulted in a decrease in the settling rate. This indicates that the temperature (80℃→88℃) was raised too high, which in turn led to a decrease in the gravity settling rate of the ammonium phosphate slurry.

[0066] This is mainly because when the temperature rises too high, although the viscosity of the ammonium phosphate slurry decreases with increasing temperature, at the same time, the hydrodynamic interaction caused by the disturbance of the local velocity of the surrounding liquid by the solid particles, as well as the thermodynamic interaction caused by the Brownian motion of the particles and their interaction with each other, increases. The Brownian motion causes the solid particles to shift from their original positions, ultimately leading to a decrease in the settling velocity.

[0067] Specifically, by comparing Comparative Example 1 and Comparative Example 3, it can be seen that, compared to Comparative Example 1 which uses polyacrylamide and sodium hexametaphosphate, Comparative Example 3 which uses the composite modified dispersant of the present invention (polyacrylamide, starch-sodium hexametaphosphate modifier and maleic anhydride-styrene-butyl acrylate copolymer), results in an increased gravity settling velocity of the ammonium phosphate slurry.

[0068] Specifically, comparing Comparative Examples 2 and 4, it can be seen that, compared to Comparative Example 2 which used polyacrylamide and sodium hexametaphosphate, Comparative Example 4, which used polyacrylamide and a starch-sodium hexametaphosphate modifier, resulted in an improved settling velocity. This indicates that replacing sodium hexametaphosphate with the starch-sodium hexametaphosphate modifier can increase the gravity settling velocity of ammonium phosphate slurry.

[0069] Specifically, comparing Comparative Example 2 and Comparative Example 5, it can be seen that compared to Comparative Example 2 which uses polyacrylamide and sodium hexametaphosphate, Comparative Example 5, by introducing maleic anhydride-styrene-butyl acrylate copolymer, resulted in an increased settling velocity. This indicates that introducing maleic anhydride-styrene-butyl acrylate copolymer can also improve the gravity settling velocity of ammonium phosphate slurry.

[0070] In comparison with Example 1, it can be seen that when sodium hexametaphosphate is replaced with starch-sodium hexametaphosphate modifier, and maleic anhydride-styrene-butyl acrylate copolymer is introduced, the two can produce a synergistic effect, which can synergistically improve the gravity settling speed of ammonium phosphate slurry.

[0071] Furthermore, compared to Comparative Example 3, which was heated to 80°C and then subjected to gravity settling, Example 1 increased the heating temperature to 88°C and then subjected to gravity settling. As a result, the gravity settling rate of the ammonium phosphate slurry was further increased. This indicates that the simultaneous presence of both (replacing sodium hexametaphosphate with a starch-sodium hexametaphosphate modifier and introducing maleic anhydride-styrene-butyl acrylate copolymer) can increase the heating temperature threshold.

[0072] Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for preparing ammonium phosphate slurry, characterized in that, Includes the following steps: S1. Phosphoric acid and ammonia gas are metered and added to the neutralization reactor to obtain a neutralized slurry; S2. Add the composite modified dispersant to the neutralized slurry obtained in S1, mix well, and the ammonium phosphate slurry is obtained. The ammonium phosphate slurry was subjected to gravity settling treatment at 87-90℃; The composite modified dispersant is composed of polyacrylamide, a starch-sodium hexametaphosphate modifier, and a maleic anhydride-styrene-butyl acrylate copolymer. The mass of the polyacrylamide is 0.23-0.25% of the mass of the neutralizing slurry, the mass of the starch-sodium hexametaphosphate modifier is 0.33-0.34% of the mass of the neutralizing slurry, and the mass of the maleic anhydride-styrene-butyl acrylate copolymer is 0.03-0.04% of the mass of the neutralizing slurry.

2. The preparation process of ammonium phosphate slurry according to claim 1, characterized in that, The preparation method of the starch-sodium hexametaphosphate modified product is as follows: A1. Mix cassava starch and water in a mass ratio of 1:1 to obtain a starch solution; A2. Adjust the pH of the starch solution obtained in A1 to 9.5-10, add sodium hexametaphosphate (sodium hexametaphosphate) with a mass of 1.3-1.4 times that of cassava starch, and stir the mixture at 54-58℃ to obtain the final product.

3. The preparation process of ammonium phosphate slurry according to claim 2, characterized in that, In A2, the pH value of the starch solution is adjusted using anhydrous sodium carbonate.

4. The preparation process of ammonium phosphate slurry according to claim 2, characterized in that, In A2, the stirring speed is 270-300 r / min, and the stirring time is 3-3.2 h.

5. The preparation process of ammonium phosphate slurry according to claim 1, characterized in that, The preparation method of the maleic anhydride-styrene-butyl acrylate copolymer is as follows: B1. Add 30g styrene, 9.5-10.5g maleic anhydride, 9.5-10.5g butyl acrylate, 0.24-0.27g benzoyl peroxide and 100mL toluene to a three-necked flask, heat and stir to dissolve, then heat to polymerize and obtain a precipitate. B2. Dissolve the precipitate obtained in B1 with butanone, then precipitate it with toluene. Repeat the purification process several times, filter, and vacuum dry to constant weight to obtain the final product.

6. The preparation process of ammonium phosphate slurry according to claim 5, characterized in that, In B1, the heating is carried out in a constant temperature water bath at 50±2℃.

7. The preparation process of ammonium phosphate slurry according to claim 5, characterized in that, In B1, the specific operation of the heating polymerization reaction is as follows: first, heat to 75±2℃ and react for 5.5-6 hours, then heat to 90±2℃ and continue the reaction for 2.5-3 hours.

8. The preparation process of ammonium phosphate slurry according to claim 5, characterized in that, In B2, the drying temperature is 80±2℃.

9. The preparation process of ammonium phosphate slurry according to claim 1, characterized in that, The neutralized slurry has a water content of 66-70 wt%.

10. The application of a phosphate slurry prepared by the preparation process according to any one of claims 1 to 9 in compound fertilizer.

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