Method for optimizing ammonium fluoride and ammonium chloride doped ammonium sulfate crystallization by using nucleation activation energy

Abstract

The invention relates to a method for optimizing ammonium fluoride and ammonium chloride doped ammonium sulfate crystallization by using nucleation activation energy, and belongs to the technical field of industrial crystallization optimization. According to the method, the solubility of the ammonium sulfate solution and a metastable region are associated with a classical 3D nucleation model to obtain the nucleation activation energy of ammonium sulfate, and the optimal mass ratio of the doping agents ammonium fluoride to ammonium chloride is determined according to the strength of the nucleation activation energy; adjusting the doping amount of ammonium fluoride and ammonium chloride in the ammonium sulfate solution according to the optimal doping mass ratio of ammonium fluoride and ammonium chloride, and performing evaporative crystallization at the crystallization temperature determined according to the width of a metastable region of the ammonium sulfate solution to obtain ammonium sulfate crystals with large average particle size and uniform particle size distribution. According to the method, the ammonium sulfate crystallization process can be efficiently optimized, and high-quality ammonium sulfate crystals are obtained.

Description

Technical Field

[0001] This invention relates to a method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy, belonging to the field of industrial crystallization optimization technology. Background Technology

[0002] Ammonium sulfate, an important nitrogen fertilizer in agriculture, is commonly used in crop fertilization to improve crop quality and yield. Ammonia desulfurization technology efficiently treats SO2 while yielding ammonium sulfate as a byproduct, which has high economic value. However, to remove substances such as arsenic, zinc, and lead, 2%–3% of chlorides such as CaCl2 are often added to the sintering mixture in steel plants, leading to volatile chlorides entering the flue gas. Furthermore, hydrogen fluoride, silicon tetrafluoride, and small amounts of fluorine-containing dust in the sintering flue gas are absorbed, accumulated, and enriched in the desulfurization slurry. This not only causes equipment corrosion and the combination of metal ions on equipment surfaces to form soluble fluorides and chlorides that enter the mother liquor, introducing more metal ions, but also combines with NH4+. + The formation of NH4F and NH4Cl leads to changes in the crystallization rate, crystal quality, and crystal particle size of the byproduct ammonium sulfate. This causes irreversible damage to the equipment and reduces the amount and average particle size of ammonium sulfate crystals, resulting in a significant decrease in the utilization rate of ammonium sulfate. Summary of the Invention

[0003] This invention addresses the problem of unstable ammonium sulfate crystal quality caused by the mixing of ammonium fluoride and ammonium chloride in existing ammonium sulfate mother liquor. It proposes an optimized ammonium sulfate crystallization method that utilizes nucleation activation energy to optimize the doping of ammonium fluoride and ammonium chloride. In ammonium sulfate solution, excessive ammonium chloride content results in a large aspect ratio of ammonium sulfate crystals, making them highly prone to breakage. Conversely, excessive ammonium fluoride content leads to insufficient ammonium sulfate crystal yield, significantly reducing the utilization rate of the ammonium sulfate mother liquor. This invention, through design and calculation, obtains the optimal synergistic mass ratio of ammonium fluoride and ammonium chloride, adjusting the doping amounts of ammonium fluoride and ammonium chloride in ammonium sulfate to effectively solve the problems of poor ammonium sulfate crystal quality, small crystal particle size, and low ammonium sulfate utilization rate caused by the mixing of ammonium fluoride and ammonium chloride in existing ammonium sulfate mother liquor.

[0004] A method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy, the specific steps of which are as follows: S1. Using pure water as the solvent, the molar solubility X of ammonium sulfate at different saturation temperatures T0 was determined under different ammonium fluoride and ammonium chloride doping mass ratios. The enthalpy of dissolution and entropy of dissolution were calculated using the Van't Hoff equation. S2. Cool the ammonium sulfate saturated solution at saturation temperature T0 to the nucleation temperature T1 at a preset cooling rate, and calculate the maximum undercooling ΔT. max That is, the width of the metastable region; S3. Based on saturation temperature T0, molar solubility X, enthalpy of dissolution, entropy of dissolution, temperature T1, and metastable region width ΔTmax By linear fitting, the nucleation activation energy is obtained, and the optimal doping mass ratio of ammonium fluoride and ammonium chloride is determined based on the minimum nucleation activation energy. S4. Adjust the doping amount of ammonium fluoride and ammonium chloride in the ammonium sulfate solution according to the optimal doping mass ratio of ammonium fluoride and ammonium chloride. Evaporate and crystallize at a crystallization temperature determined according to the metastable region width of the ammonium sulfate solution (selecting a crystallization temperature with a moderate metastable region width that allows for good controllability of the ammonium sulfate crystallization process and the formation of uniform large-particle-size ammonium sulfate crystals based on literature and experimental test results) to obtain ammonium sulfate crystals. Calculate the average particle size and particle size variation coefficient of the ammonium sulfate crystals.

[0005] Preferably, in step S1, the total doping mass of ammonium fluoride and ammonium chloride is 4.5% to 6.0% of the mass of ammonium sulfate.

[0006] Preferably, the method for calculating the enthalpy of dissolution and the entropy of dissolution in step S1 specifically includes: S11. At a saturation temperature T0, the masses of (NH4)2SO4, NH4F, NH4Cl and pure water in a saturated mixed aqueous solution of ammonium sulfate are denoted as m1, m2, m3 and m4, respectively, and the molar masses of (NH4)2SO4, NH4F, NH4Cl and pure water are denoted as M1, M2, M3 and M4, respectively. S12. Calculate the molar solubility X of ammonium sulfate in a saturated aqueous solution at saturation temperature T0: ; In the formula, m1, m2, m3, and m4 represent the masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g; M1, M2, M3, and M4 represent the molar masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g / mol. S13. Calculate the enthalpy of dissolution and entropy of dissolution using the Van'tHoff equation; the Van'tHoff equation is as follows: ; In the formula, X is the molar solubility of ammonium sulfate at saturation temperature T0, and ΔH s ΔS is the enthalpy of solubility of ammonium sulfate, J / mol; s R is the entropy of solute ammonium sulfate, J / K·mol; T0 is the saturation temperature, K; R G The gas constant is 8.314 J / K·mol.

[0007] The width of the metastable region ΔT of S2. max The calculation formula is: ; In the formula, ΔTmax T0 is the width of the metastable region, T1 is the saturation temperature, and T1 is the nucleation temperature.

[0008] Preferably, the S3. ammonium sulfate nucleation rate J is related to the supersaturation S max The calculation method specifically includes: S31. Will By performing a linear fit with lnR, the slope F of the fitted line is obtained; S32. ln(F) 1 / 2 ) and T0 -1 Perform linear fitting to obtain the slope of the fitted line, and calculate the nucleation activation energy E of ammonium sulfate. sat .

[0009] More preferably, the formula for calculating the ammonium sulfate nucleation rate J is: ; in, ; ; In the formula, A is the nucleation kinetics-related constant, m -3 / h; B is the given kernel shape parameter; T0 is the saturation temperature; T nuc The nucleation temperature; c0 and c nuc Temperatures T0 and T are respectively nuc The concentration of ammonium sulfate in the solute is given in mol / L; γ is the solid-liquid interfacial energy in mJ / m 2 ;k B Boltzmann constant, 1.38 × 10⁻⁶ -23 J / K; Ω is the molecular volume, m 3 .

[0010] More preferably, based on the ammonium sulfate nucleation rate J, we can obtain Linear relationship with lnR: ; in, ; ; Get the parameter ln(F) 1 / 2 ) and T0 -1 Linear relationship between them: ; In the formula, F and -F1 represent the intercept and slope of the linear fit, respectively; R is the cooling rate; R G ε is the gas constant, 8.314 J / (mol·K); Esat is the nucleation activation energy.

[0011] Preferably, the average particle size of the ammonium sulfate crystals is calculated using the following formula: ; in, ; In the formula The average crystal size is in mm. To screen for the mass fraction of grade i, %; L i The average particle size of the i-th sieve is in mm; i The standard aperture for sieve grade i is in mm.

[0012] Preferably, the formula for calculating the coefficient of variation of the particle size of the ammonium sulfate crystals is: ; In the formula, The standard deviation is represented by MS, which is the intermediate particle size value, i.e., the sieve aperture size corresponding to a cumulative mass fraction of 50% when sieving, in mm.

[0013] The beneficial effects of this invention are: (1) This invention uses the solubility of ammonium sulfate solution and the width of the metastable region to design and calculate the thermodynamics and nucleation kinetics of ammonium sulfate, and obtains the nucleation activation energy of ammonium sulfate with different synergistic ratios of ammonium fluoride and ammonium chloride. The synergistic doping mass ratio of ammonium fluoride and ammonium chloride with the lowest nucleation activation energy is selected as the optimal doping crystallization condition. The strength of the nucleation activation energy reflects the ease of ammonium sulfate nucleation. The lower the nucleation activation energy, the easier it is for ammonium sulfate to nucleate. (2) The present invention crystallizes under the optimal mass ratio of ammonium fluoride and ammonium chloride co-doping, which can obtain ammonium sulfate crystals with larger average particle size, better crystal morphology and more concentrated particle size distribution, and can also reduce equipment corrosion and other problems. If the ammonium chloride content is too high, the length-to-width ratio of the ammonium sulfate crystals will be too large, and the ammonium sulfate crystals will be very easy to break. If the ammonium fluoride content is too high, the amount of ammonium sulfate crystallization will be too low, and the utilization rate of ammonium sulfate mother liquor will be greatly reduced. Attached Figure Description

[0014] Figure 1 Example 1: The (T0 / ΔT) of (NH4)2SO4 under different NH4F to NH4Cl mixing ratios with a total ammonium fluoride and ammonium chloride doping of 4.5%. max ) 2 Curves showing the logarithmic variation of lnR with cooling rate; (a): undoped, (b): NH4F:NH4Cl=1:1, (c): NH4F:NH4Cl=1:2, (d): NH4F:NH4Cl=1:3, (e): NH4F:NH4Cl=2:1, (f): NH4F:NH4Cl=3:1; Figure 2 For Example 1, with a total doping of 4.5% ammonium fluoride and ammonium chloride, the ln(F) calculated by classical 3D nucleation theory is... 1 / 2 ) and T0-1 Fit a linear graph; Figure 3 This is a SEM image of crystallization under the optimal mass ratio of ammonium fluoride and ammonium chloride co-doping in Example 1 (NH4F:NH4Cl=2:1). Figure 4 This is a SEM image of ammonium sulfate crystals co-doped with ammonium fluoride and ammonium chloride, as shown in Comparative Example 1. Figure 5 Example 2: (T0 / ΔT) of (NH4)2SO4 under different NH4F to NH4Cl mixing ratios with a total ammonium fluoride and ammonium chloride doping of 5.0%. max ) 2 Curves showing the logarithmic variation of lnR with cooling rate; (a): undoped, (b): NH4F:NH4Cl=1:1, (c): NH4F:NH4Cl=1:2, (d): NH4F:NH4Cl=1:3, (e): NH4F:NH4Cl=2:1, (f): NH4F:NH4Cl=3:1; Figure 6 The ln(F) calculated by classical 3D nucleation theory under a total doping of 5.0% ammonium fluoride and ammonium chloride in Example 2 is... 1 / 2 ) and T0 -1 Fit a linear graph; Figure 7 Example 3: (T0 / ΔT) of (NH4)2SO4 under different NH4F to NH4Cl mixing ratios with a total ammonium fluoride and ammonium chloride doping of 6.0%. max ) 2 Curves showing the logarithmic variation of lnR with cooling rate; (a): undoped, (b): NH4F:NH4Cl=1:1, (c): NH4F:NH4Cl=1:2, (d): NH4F:NH4Cl=1:3, (e): NH4F:NH4Cl=2:1, (f): NH4F:NH4Cl=3:1; Figure 8 The ln(F) calculated by classical 3D nucleation theory under a total doping of 6.0% ammonium fluoride and ammonium chloride in Example 3 is... 1 / 2 ) and T0 -1 Fit a linear graph. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the content described.

[0016] Example 1: A method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy, the specific steps of which are as follows: S1. Using pure water as the solvent, determine the molar solubility X of ammonium sulfate at different saturation temperatures T0 under different ammonium fluoride to ammonium chloride doping mass ratios (1:1, 1:2, 1:3, 2:1, 3:1). Calculate the enthalpy of dissolution ΔH using the Van't Hoff equation. s and solubility entropy ΔS s (See Table 1); In this embodiment, the total doping mass of ammonium fluoride and ammonium chloride is 4.5% of the mass of ammonium sulfate; The methods for calculating the enthalpy of dissolution and the entropy of dissolution specifically include: S11. At a saturation temperature T0, the masses of (NH4)2SO4, NH4F, NH4Cl and pure water in a saturated mixed aqueous solution of ammonium sulfate are denoted as m1, m2, m3 and m4, respectively, and the molar masses of (NH4)2SO4, NH4F, NH4Cl and pure water are denoted as M1, M2, M3 and M4, respectively. S12. Calculate the molar solubility X of ammonium sulfate in a saturated aqueous solution at saturation temperature T0: ; In the formula, m1, m2, m3, and m4 represent the masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g; M1, M2, M3, and M4 represent the molar masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g / mol. S13. Calculate the enthalpy of dissolution and entropy of dissolution using the Van'tHoff equation; the Van'tHoff equation is as follows: ; In the formula, X is the molar solubility of ammonium sulfate at saturation temperature T0, and ΔH s ΔS is the enthalpy of solubility of ammonium sulfate, J / mol; s R is the entropy of solute ammonium sulfate, J / K·mol; T0 is the saturation temperature, K; R G The gas constant is 8.314 J / K·mol; Table 1. Molar solubility X of ammonium sulfate at different saturation temperatures T0 and enthalpy of dissolution ΔH for different addition amounts. s , solubility entropy ΔS s ; S2. Cool the ammonium sulfate saturated solution at saturation temperature T0 to the nucleation temperature T1 at a preset cooling rate (12K / h, 18K / h, 24K / h, and 30K / h are selected for ease of subsequent statistical calculations), and calculate the maximum undercooling ΔT. max This refers to the width of the metastable region (see Table 2); the width of the metastable region ΔT max The calculation formula is: ; In the formula, ΔT max T0 is the width of the metastable region, T1 is the saturation temperature, and T1 is the nucleation temperature. Table 2. Nucleation temperature T1 and metastable region width ΔT at different cooling rates. max ; S3. Based on saturation temperature T0, molar solubility X, enthalpy of dissolution, entropy of dissolution, temperature T1, and metastable region width ΔT max The nucleation activation energy was obtained through linear fitting (see Table 3). Based on the minimum nucleation activation energy, the optimal doping mass ratio of ammonium fluoride and ammonium chloride was determined. The nucleation rate J of ammonium sulfate was related to the supersaturation S. max The calculation method specifically includes: S31. Will Linear fitting with lnR (see) Figure 1 ), to obtain the slope F of the fitted line; S32. ln(F) 1 / 2 ) and T0 -1 Perform linear fitting (see) Figure 2 The slope of the fitted straight line was obtained, and the activation energy E of ammonium sulfate nucleation was calculated. sat ; The formula for calculating the ammonium sulfate nucleation rate J is: ; in, ; ; In the formula, A is the nucleation kinetics-related constant, m -3 / h; B is the given kernel shape parameter; T0 is the saturation temperature; T nuc The nucleation temperature; c0 and c nuc Temperatures T0 and T are respectively nuc The concentration of ammonium sulfate in the solute is given in mol / L; γ is the solid-liquid interfacial energy in mJ / m 2 ;k B Boltzmann constant, 1.38 × 10⁻⁶ -23 J / K; Ω is the molecular volume, m 3 ; Based on the ammonium sulfate nucleation rate J, we can obtain Linear relationship with lnR: ; in, ; ; Get the parameter ln(F) 1 / 2 ) and T0-1 Linear relationship between them: ; In the formula, F and -F1 represent the intercept and slope of the linear fit, respectively; R is the cooling rate; R G ε is the gas constant, 8.314 J / (mol·K); Esat is the nucleation activation energy; Table 3. F, F1, ln(F) under different mixing ratios of ammonium sulfate with NH4F and NH4Cl in this embodiment. 1 / 2 ) and nucleation activation energy E sat ; Table 3 shows that when the mass ratio of ammonium fluoride to ammonium chloride is 2:1, the nucleation activation energy E sat The lowest is 46.225 kJ·mol -1 Therefore, the optimal doping mass ratio of ammonium fluoride to ammonium chloride is 2:1; S4. Adjust the doping amount of ammonium fluoride and ammonium chloride in the ammonium sulfate solution according to the optimal doping mass ratio of ammonium fluoride and ammonium chloride (the total doping mass of ammonium fluoride and ammonium chloride is 4.5% of the mass of ammonium sulfate, and the doping mass ratio of ammonium fluoride and ammonium chloride is 2:1). Evaporate and crystallize at the crystallization temperature (60℃) determined according to the metastable region width of the ammonium sulfate solution (based on the metastable region test results obtained from literature and experiments, the metastable region width is moderate at a temperature of 60℃, which makes the ammonium sulfate crystallization process more controllable and conducive to the formation of uniform large-size crystals). Obtain ammonium sulfate crystals and calculate the average particle size and particle size variation coefficient CV of the ammonium sulfate crystals. The formula for calculating the average particle size of the ammonium sulfate crystals is: ; in, ; In the formula The average crystal size is in mm. To screen for the mass fraction of grade i, %; L i The average particle size of the i-th sieve is in mm; i The standard aperture for screening grade i is in mm; The formula for calculating the coefficient of variation (CV) of the ammonium sulfate crystals is: ; In the formula, The standard deviation is represented by MS, which is the intermediate particle size value, i.e., the sieve aperture size corresponding to a cumulative mass fraction of 50%, in mm. In this embodiment, when the doping mass ratio of ammonium fluoride to ammonium chloride is 2:1, the SEM image of the ammonium sulfate crystals is shown below. Figure 3 ,from Figure 3It can be seen that as the proportion of ammonium fluoride increases, the metastable region of the ammonium sulfate solution widens, and the ammonium sulfate solution remains in a metastable state. This allows for the accumulation of more solute during crystal growth, resulting in more stable and regular crystal growth and larger crystal grains. Simultaneously, F... - It can participate in crystallization modification, accelerate crystal nucleus formation and growth, and the resulting crystals are relatively regular hexahedrons; In this embodiment, the average particle size of the ammonium sulfate crystals is 0.902 mm, and the coefficient of variation (CV) is 119.787.

[0017] Comparative Example 1: The doping amounts of ammonium fluoride and ammonium chloride in the ammonium sulfate solution were adjusted (the total doping mass of ammonium fluoride and ammonium chloride was 4.5% of the mass of ammonium sulfate, and the doping mass ratio of ammonium fluoride to ammonium chloride was 1:1, 1:2, 1:3, 2:1, and 3:1). The appropriate crystallization temperature was determined based on the metastable region width of the ammonium sulfate solution, and evaporation crystallization was carried out at 60℃ to obtain ammonium sulfate crystals. The average particle size and particle size variation coefficient CV of the ammonium sulfate crystals were statistically analyzed (see Table 4). SEM images of ammonium sulfate crystals with doping mass ratios of ammonium fluoride and ammonium chloride of 1:1 and 1:3 in this comparative example are shown below. Figure 4 Compared to Example 1 Figure 3 , Figure 4 Ammonium sulfate crystals are plate-shaped with a large length-to-width ratio and are accompanied by shorter, finer crystals around the edges, indicating that the crystallization is not very stable and is easily broken. When the proportion of ammonium chloride is high, the ammonium sulfate crystals are long columnar, which makes them more prone to collisions and affects the crystallization state. Table 4. Average particle size and coefficient of variation (CV) of ammonium sulfate crystals from Example 1 and this comparative example. ; Table 4 shows that as the proportion of ammonium chloride increases, the average particle size of ammonium sulfate first increases and then decreases, while the CV value first decreases and then increases. As the proportion of ammonium fluoride increases, the average particle size of ammonium sulfate increases, the CV value increases, and the particle size distribution becomes more concentrated. When the ratio of ammonium fluoride to ammonium chloride reaches 2:1, ammonium sulfate can obtain crystals with a larger average particle size, a smaller CV value, and a more concentrated particle size distribution.

[0018] Example 2: A method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy, the specific steps of which are as follows: S1. Using pure water as the solvent, determine the molar solubility X of ammonium sulfate at different saturation temperatures T0 under different ammonium fluoride to ammonium chloride doping mass ratios (1:1, 1:2, 1:3, 2:1, 3:1). Calculate the enthalpy of dissolution ΔH using the Van't Hoff equation. s and solubility entropy ΔS s (See Table 5); In this embodiment, the total doping mass of ammonium fluoride and ammonium chloride is 5.0% of the mass of ammonium sulfate; The methods for calculating the enthalpy of dissolution and the entropy of dissolution specifically include: S11. At a saturation temperature T0, the masses of (NH4)2SO4, NH4F, NH4Cl and pure water in a saturated mixed aqueous solution of ammonium sulfate are denoted as m1, m2, m3 and m4, respectively, and the molar masses of (NH4)2SO4, NH4F, NH4Cl and pure water are denoted as M1, M2, M3 and M4, respectively. S12. Calculate the molar solubility X of ammonium sulfate in a saturated aqueous solution at saturation temperature T0: ; In the formula, m1, m2, m3, and m4 represent the masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g; M1, M2, M3, and M4 represent the molar masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g / mol. S13. Calculate the enthalpy of dissolution and entropy of dissolution using the Van'tHoff equation; the Van'tHoff equation is as follows: ; In the formula, X is the molar solubility of ammonium sulfate at saturation temperature T0, and ΔH s ΔS is the enthalpy of solubility of ammonium sulfate, J / mol; s R is the entropy of solute ammonium sulfate, J / K·mol; T0 is the saturation temperature, K; R G The gas constant is 8.314 J / K·mol; Table 5. Molar solubility X of ammonium sulfate at different saturation temperatures T0 and enthalpy of dissolution ΔH for different addition amounts. s , solubility entropy ΔS s ; S2. Cool the ammonium sulfate saturated solution at saturation temperature T0 to the nucleation temperature T1 at a preset cooling rate (12K / h, 18K / h, 24K / h, and 30K / h are selected for ease of subsequent statistical calculations), and calculate the maximum undercooling ΔT. max This refers to the metastable region width (see Table 6); the metastable region width ΔT max The calculation formula is: ; In the formula, ΔT max T0 is the width of the metastable region, T1 is the saturation temperature, and T1 is the nucleation temperature. Table 6. Nucleation temperature T1 and metastable region width ΔT at different cooling rates. max ; S3. Based on saturation temperature T0, molar solubility X, enthalpy of dissolution, entropy of dissolution, temperature T1, and metastable region width ΔT max The nucleation activation energy was obtained through linear fitting (see Table 7). Based on the minimum nucleation activation energy, the optimal doping mass ratio of ammonium fluoride and ammonium chloride was determined. The nucleation rate J of ammonium sulfate was related to the supersaturation S. max The calculation method specifically includes: S31. Will Linear fitting with lnR (see) Figure 5 ), to obtain the slope F of the fitted line; S32. ln(F) 1 / 2 ) and T0 -1 Perform linear fitting (see) Figure 6 The slope of the fitted straight line was obtained, and the nucleation activation energy E was obtained. sat ; The formula for calculating the ammonium sulfate nucleation rate J is: ; in, ; ; In the formula, A is the nucleation kinetics-related constant, m -3 / h; B is the given kernel shape parameter; T0 is the saturation temperature; T nuc The nucleation temperature; c0 and c nuc Temperatures T0 and T are respectively nuc The concentration of ammonium sulfate in the solute is given in mol / L; γ is the solid-liquid interfacial energy in mJ / m 2 ;k B Boltzmann constant, 1.38 × 10⁻⁶ -23 J / K; Ω is the molecular volume, m 3 ; Based on the ammonium sulfate nucleation rate J, we can obtain Linear relationship with lnR: ; in, ; ; Get the parameter ln(F) 1 / 2 ) and T0 -1 Linear relationship between them: ; In the formula, F and -F1 represent the intercept and slope of the linear fit, respectively; R is the cooling rate; R G ε is the gas constant, 8.314 J / (mol·K); Esat is the nucleation activation energy; Table 7. F, F1, ln(F) for different NH4F to NH4Cl mixing ratios of ammonium sulfate in this embodiment. 1 / 2 ) and nucleation activation energy E sat ; Table 7 shows that when the mass ratio of ammonium fluoride to ammonium chloride is 2:1, the nucleation activation energy E sat The lowest is 39.157 kJ·mol -1 Therefore, the optimal doping mass ratio of ammonium fluoride to ammonium chloride is 2:1; S4. Adjust the doping amount of ammonium fluoride and ammonium chloride in the ammonium sulfate solution according to the optimal doping mass ratio of ammonium fluoride and ammonium chloride (the total doping mass of ammonium fluoride and ammonium chloride is 5% of the mass of ammonium sulfate, and the doping mass ratio of ammonium fluoride and ammonium chloride is 2:1). Evaporate and crystallize at the crystallization temperature (60℃) determined according to the metastable region width of the ammonium sulfate solution to obtain ammonium sulfate crystals. Calculate the average particle size and particle size variation coefficient CV of the ammonium sulfate crystals. The formula for calculating the average particle size of the ammonium sulfate crystals is: ; in, ; In the formula The average crystal size is in mm. To screen for the mass fraction of grade i, %; L i The average particle size of the i-th sieve is in mm; i The standard aperture for screening grade i is in mm; The formula for calculating the coefficient of variation (CV) of the ammonium sulfate crystals is: ; In the formula, The standard deviation is represented by MS, which is the intermediate particle size value, i.e., the sieve aperture size corresponding to a cumulative mass fraction of 50%, in mm. In this embodiment, the average particle size of the ammonium sulfate crystals is 0.896 mm, and the coefficient of variation (CV) is 120.113.

[0019] Comparative Example 2: The doping amounts of ammonium fluoride and ammonium chloride in the ammonium sulfate solution were adjusted (the total doping mass of ammonium fluoride and ammonium chloride was 5% of the mass of ammonium sulfate, and the doping mass ratio of ammonium fluoride to ammonium chloride was 1:1, 1:2, 1:3, 2:1, and 3:1). Based on the metastable region width of the ammonium sulfate solution, a suitable crystallization temperature was determined, and evaporation crystallization was carried out at 60℃ to obtain ammonium sulfate crystals. The average particle size and particle size variation coefficient CV of the ammonium sulfate crystals were statistically analyzed (see Table 8). Table 8. Average particle size and coefficient of variation (CV) of ammonium sulfate crystals from Example 1 and this comparative example. ; Table 8 shows that as the proportion of ammonium chloride increases, the average particle size of ammonium sulfate first increases and then decreases, while the CV value first decreases and then increases. As the proportion of ammonium fluoride increases, the average particle size of ammonium sulfate increases, the CV value increases, and the particle size distribution becomes more concentrated. When the ratio of ammonium fluoride to ammonium chloride reaches 2:1, ammonium sulfate can obtain crystals with a larger average particle size, a smaller CV value, and a more concentrated particle size distribution.

[0020] Example 3: A method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy, the specific steps of which are as follows: S1. Using pure water as the solvent, determine the molar solubility X of ammonium sulfate at different saturation temperatures T0 under different ammonium fluoride to ammonium chloride doping mass ratios (1:1, 1:2, 1:3, 2:1, 3:1). Calculate the enthalpy of dissolution ΔH using the Van't Hoff equation. s and solubility entropy ΔS s (See Table 9); In this embodiment, the total doping mass of ammonium fluoride and ammonium chloride is 6.0% of the mass of ammonium sulfate; The methods for calculating the enthalpy of dissolution and the entropy of dissolution specifically include: S11. At a saturation temperature T0, the masses of (NH4)2SO4, NH4F, NH4Cl and pure water in a saturated mixed aqueous solution of ammonium sulfate are denoted as m1, m2, m3 and m4, respectively, and the molar masses of (NH4)2SO4, NH4F, NH4Cl and pure water are denoted as M1, M2, M3 and M4, respectively. S12. Calculate the molar solubility X of ammonium sulfate in a saturated aqueous solution at saturation temperature T0: ; In the formula, m1, m2, m3, and m4 represent the masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g; M1, M2, M3, and M4 represent the molar masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g / mol. S13. Calculate the enthalpy of dissolution and entropy of dissolution using the Van'tHoff equation; the Van'tHoff equation is as follows: ; In the formula, X is the molar solubility of ammonium sulfate at saturation temperature T0, and ΔH s ΔS is the enthalpy of solubility of ammonium sulfate, J / mol; s R is the entropy of solute ammonium sulfate, J / K·mol; T0 is the saturation temperature, K; R G The gas constant is 8.314 J / K·mol; Table 9. Molar solubility X of ammonium sulfate at different saturation temperatures T0 and enthalpy of dissolution ΔH for different addition amounts. s , solubility entropy ΔS s ; S2. Cool the ammonium sulfate saturated solution at saturation temperature T0 to the nucleation temperature T1 at a preset cooling rate (12K / h, 18K / h, 24K / h, and 30K / h are selected for ease of subsequent statistical calculations), and calculate the maximum undercooling ΔT. max This refers to the metastable region width (see Table 10); the metastable region width ΔT max The calculation formula is: ; In the formula, ΔT max T0 is the width of the metastable region, T1 is the saturation temperature, and T1 is the nucleation temperature. Table 10. Nucleation temperature T1 and metastable region width ΔT at different cooling rates. max ; S3. Based on saturation temperature T0, molar solubility X, enthalpy of dissolution, entropy of dissolution, temperature T1, and metastable region width ΔT max The nucleation activation energy was obtained through linear fitting (see Table 11). The optimal doping mass ratio of ammonium fluoride and ammonium chloride was determined based on the minimum nucleation activation energy. The nucleation rate J of ammonium sulfate is related to the supersaturation S. max The calculation method specifically includes: S31. Will Linear fitting with lnR (see) Figure 7 ), to obtain the slope F of the fitted line; S32. ln(F) 1 / 2 ) and T0 -1 Perform linear fitting (see) Figure 8 The slope of the fitted straight line was obtained, and the activation energy E of ammonium sulfate nucleation was calculated. sat ; The formula for calculating the ammonium sulfate nucleation rate J is: ; in, ; ; In the formula, A is the nucleation kinetics-related constant, m -3 / h; B is the given kernel shape parameter; T0 is the saturation temperature; T nuc The nucleation temperature; c0 and c nuc Temperatures T0 and T are respectively nuc The concentration of ammonium sulfate in the solute is given in mol / L; γ is the solid-liquid interfacial energy in mJ / m2 ;k B Boltzmann constant, 1.38 × 10⁻⁶ -23 J / K; Ω is the molecular volume, m 3 ; Based on the ammonium sulfate nucleation rate J, we can obtain Linear relationship with lnR: ; in, ; ; Get the parameter ln(F) 1 / 2 ) and T0 -1 Linear relationship between them: ; In the formula, F and -F1 represent the intercept and slope of the linear fit, respectively; R is the cooling rate; R G ε is the gas constant, 8.314 J / (mol·K); Esat is the nucleation activation energy; Table 11. F, F1, ln(F) under different mixing ratios of ammonium sulfate with NH4F and NH4Cl in this embodiment. 1 / 2 ) and nucleation activation energy E sat ; Table 11 shows that when the mass ratio of ammonium fluoride to ammonium chloride is 2:1, the nucleation activation energy E sat The lowest is 36.30 kJ·mol -1 Therefore, the optimal doping mass ratio of ammonium fluoride to ammonium chloride is 2:1; S4. Adjust the doping amount of ammonium fluoride and ammonium chloride in the ammonium sulfate solution according to the optimal doping mass ratio of ammonium fluoride and ammonium chloride (the total doping mass of ammonium fluoride and ammonium chloride is 6.0% of the mass of ammonium sulfate, and the doping mass ratio of ammonium fluoride and ammonium chloride is 2:1). Evaporate and crystallize at the crystallization temperature (60℃) determined according to the metastable region width of the ammonium sulfate solution to obtain ammonium sulfate crystals. Calculate the average particle size and particle size variation coefficient CV of the ammonium sulfate crystals. The formula for calculating the average particle size of the ammonium sulfate crystals is: ; in, ; In the formula The average crystal size is in mm. To screen for the mass fraction of grade i, %; L i The average particle size of the i-th sieve is in mm; i The standard aperture for screening grade i is in mm; The formula for calculating the coefficient of variation (CV) of the ammonium sulfate crystals is: ; In the formula, The standard deviation is represented by MS, which is the intermediate particle size value, i.e., the sieve aperture size corresponding to a cumulative mass fraction of 50%, in mm. In this embodiment, the average particle size of the ammonium sulfate crystals is 0.884 mm, and the coefficient of variation (CV) is 119.895.

[0021] Comparative Example 3: The doping amounts of ammonium fluoride and ammonium chloride in the ammonium sulfate solution were adjusted (the total doping mass of ammonium fluoride and ammonium chloride was 6% of the mass of ammonium sulfate, and the doping mass ratio of ammonium fluoride to ammonium chloride was 1:1, 1:2, 1:3, 2:1, and 3:1). The appropriate crystallization temperature was determined based on the metastable region width of the ammonium sulfate solution, and evaporation crystallization was carried out at 60℃ to obtain ammonium sulfate crystals. The average particle size and particle size variation coefficient CV of the ammonium sulfate crystals were statistically analyzed (see Table 12). Table 12 Average particle size and coefficient of variation (CV) of ammonium sulfate crystals from Example 1 and this comparative example. ; Table 2 shows that as the proportion of ammonium chloride increases, the average particle size of ammonium sulfate first increases and then decreases, while the CV value first decreases and then increases. As the proportion of ammonium fluoride increases, the average particle size of ammonium sulfate increases, the CV value increases, and the particle size distribution becomes more concentrated. When the ratio of ammonium fluoride to ammonium chloride reaches 2:1, ammonium sulfate can obtain crystals with a larger average particle size, a smaller CV value, and a more concentrated particle size distribution. Comparing Examples 1, 2, and 3, it can be seen that the nucleation activation energy changes with the total doping amount of ammonium fluoride and ammonium chloride, but the overall trend is the same. For both, a doping ratio of 2:1 for ammonium fluoride and ammonium chloride is the better choice. Furthermore, subsequent evaporation and crystallization experiments have verified that when the doping ratio of ammonium fluoride and ammonium chloride is 2:1, both can obtain higher crystallization yield, larger average particle size, and more concentrated particle size distribution.

[0022] The specific embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy, characterized in that, The specific steps are as follows: S1. Using pure water as the solvent, the molar solubility X of ammonium sulfate at different saturation temperatures T0 was determined under different ammonium fluoride and ammonium chloride doping mass ratios. The enthalpy of dissolution and entropy of dissolution were calculated using the Van't Hoff equation. S2. Cool the ammonium sulfate saturated solution at saturation temperature T0 to the nucleation temperature T1 at a preset cooling rate, and calculate the maximum undercooling ΔT. max That is, the width of the metastable region; S3. Based on saturation temperature T0, molar solubility X, enthalpy of dissolution, entropy of dissolution, temperature T1, and metastable region width ΔT max The nucleation activation energy was obtained through linear fitting, and the optimal doping mass ratio of ammonium fluoride and ammonium chloride was determined based on the minimum nucleation activation energy. S4. Adjust the doping amounts of ammonium fluoride and ammonium chloride in the ammonium sulfate solution according to the optimal doping mass ratio of ammonium fluoride and ammonium chloride. Evaporate and crystallize at the crystallization temperature determined according to the metastable region width of the ammonium sulfate solution to obtain ammonium sulfate crystals. Calculate the average particle size and particle size variation coefficient of the ammonium sulfate crystals.

2. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 1, characterized in that: Step S1. The total doping mass of ammonium fluoride and ammonium chloride is 4.5% to 6.0% of the mass of ammonium sulfate.

3. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 1, characterized in that: Step S1. The calculation method for enthalpy of dissolution and entropy of dissolution specifically includes: S11. At a saturation temperature T0, the masses of (NH4)2SO4, NH4F, NH4Cl and pure water in a saturated mixed aqueous solution of ammonium sulfate are denoted as m1, m2, m3 and m4, respectively, and the molar masses of (NH4)2SO4, NH4F, NH4Cl and pure water are denoted as M1, M2, M3 and M4, respectively. S12. Calculate the molar solubility X of ammonium sulfate in a saturated aqueous solution at saturation temperature T0: ； In the formula, m1, m2, m3, and m4 represent the masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g; M1, M2, M3, and M4 represent the molar masses of (NH4)2SO4, NH4F, NH4Cl, and the solvent pure water, respectively, in g / mol. S13. Calculate the enthalpy of dissolution and entropy of dissolution using the Van'tHoff equation; the Van'tHoff equation is as follows: ； In the formula, X is the molar solubility of ammonium sulfate at saturation temperature T0, and ΔH s ΔS is the enthalpy of solubility of ammonium sulfate, J / mol; s R is the entropy of solute ammonium sulfate, J / K·mol; T0 is the saturation temperature, K; R G The gas constant is 8.314 J / K·mol.

4. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 1, characterized in that: S2. Mesostable region width ΔT max The calculation formula is: ； In the formula, ΔT max T0 is the width of the metastable region, T1 is the saturation temperature, and T1 is the nucleation temperature.

5. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 1, characterized in that: S3. Nucleation rate of ammonium sulfate J and supersaturation S max The calculation method specifically includes: S31. Will By performing a linear fit with lnR, the slope F of the fitted line is obtained; S32. ln(F) 1 / 2 ) and T0 -1 Perform linear fitting to obtain the slope of the fitted line, and calculate the activation energy E of ammonium sulfate nucleation. sat .

6. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 5, characterized in that: The formula for calculating the ammonium sulfate nucleation rate J is: ； in, ; ； In the formula, A is the nucleation kinetics-related constant, m -3 / h; B is the given kernel shape parameter; T0 is the saturation temperature; T nuc The nucleation temperature; c0 and c nuc Temperatures T0 and T are respectively nuc The concentration of ammonium sulfate in the solute is given in mol / L; γ is the solid-liquid interfacial energy in mJ / m 2 ;k B Boltzmann constant, 1.38 × 10⁻⁶ -23 J / K; Ω is the molecular volume, m 3 .

7. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 6, characterized in that: Based on the ammonium sulfate nucleation rate J, we can obtain Linear relationship with lnR: ； in, ; ； Get the parameter ln(F) 1 / 2 ) and T0 -1 Linear relationship between them: ； In the formula, F and -F1 represent the intercept and slope of the linear fit, respectively; R is the cooling rate; R G ε is the gas constant, 8.314 J / (mol·K); Esat is the nucleation activation energy.

8. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 1, characterized in that: The formula for calculating the average particle size of the ammonium sulfate crystals is: ； in, ; In the formula The average crystal size is in mm. To screen for the mass fraction of grade i, %; L i The average particle size of the i-th sieve is in mm; i The standard aperture for sieve grade i is in mm.

9. The method for optimizing the crystallization of ammonium sulfate doped with ammonium fluoride and ammonium chloride using nucleation activation energy according to claim 1, characterized in that: The formula for calculating the coefficient of variation (CV) of the ammonium sulfate crystals is: ； In the formula, CV is the particle size variation coefficient; The standard deviation is represented by MS, which is the intermediate particle size value, i.e., the sieve aperture size that corresponds to a cumulative mass fraction of 50% when sieving, in mm.

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