Sulfuric acid method titanium dioxide hydrolysis seed crystal, titanium dioxide and preparation method of titanium dioxide

Abstract

The invention discloses a sulfuric acid method titanium dioxide hydrolysis seed crystal, titanium dioxide and a preparation method thereof. The preparation method comprises the following steps: 1, respectively preheating a titanyl sulfate solution and an alkali solution; step 2, introducing the preheated titanyl sulfate solution and alkali solution into a micro-channel reactor at a flow rate of 5-15 mL / min, and reacting for 2-10 min at a temperature of 85-95 DEG C to prepare a seed crystal; and step 3, cooling the seed crystal prepared in the step 2. The titanium dioxide prepared by the method is uniform and controllable in particle size, and the process is simple and easy to implement. The titanium dioxide prepared by using the seed crystal is pigment-grade titanium dioxide, the D90 of the titanium dioxide is 0.5-0.6 mu m, the L * of the titanium dioxide is 98.70-98.75, the b * of the titanium dioxide is 1.40-1.55, and the lightening power of the titanium dioxide is 110-115%.

Description

Technical Field

[0001] The invention relates to the field of titanium dioxide, in particular to a sulfuric acid method titanium dioxide hydrolysis seed, titanium dioxide and a preparation method thereof. Background Art

[0002] The hydrolysis process of titanium dioxide production is to add a certain number and size of seeds to make the titanium liquid hydrolyze at a certain temperature. The number and quality of the seeds determine the composition of the hydrolysis precipitate and the performance of the final product. Therefore, it is very important to form a good crystallization center. To prepare titanic acid with an appropriate particle size and a certain composition, a certain number of ideal crystallization center seeds with a certain composition must be prepared in the titanium liquid before hydrolysis in order to correctly induce the hydrolysis. This will not only greatly accelerate the hydrolysis rate, but also make the hydrolysis reaction more complete, and high-quality titanium dioxide can be obtained.

[0003] The process of seed crystal preparation can be divided into two stages: the first stage is the formation of crystal nuclei, and the second stage is crystal growth.

[0004] The nucleus formation rate V1 has the following relationship with the solubility of the crystal and the supersaturation of the solution:

[0005] V1=K1(CS) / S (1)

[0006] C is the concentration of the precipitated substance, S is its solubility, so CS is the supersaturation, CS / S is the relative supersaturation, and K1 is the proportional constant. From formula (1), it can be seen that the greater the concentration C and the smaller the solubility S, the faster the nucleus formation rate.

[0007] The relationship between the crystal nucleus growth rate V2 and the supersaturation of the solution is as follows:

[0008] V2=K2D(CS) (2)

[0009] D is the diffusion coefficient of the solute molecule; CS is the supersaturation; K2 is the proportional constant. From this formula, we can see that V2 is also proportional to the supersaturation, but V2 is less affected by CS than V1. In the condensation process, V1 and V2 are interrelated. When the nucleation rate V1 is much greater than the crystal growth rate V2, a large number of crystal nuclei will be formed in the solution, so the dispersion of the obtained particles is large, which is conducive to the formation of sol; when the nucleation rate V1 is much smaller than the crystal growth rate V2, the obtained crystal nuclei are less, and the crystal growth rate is very fast, so the particles can grow and produce precipitation. Therefore, the dispersion of the particles is proportional to V1 and inversely proportional to V2, that is, proportional to V1 / V2.

[0010] According to the "nucleation diffusion control" model, under normal conditions, the generation of new nuclei and the growth of existing nuclei proceed simultaneously, so the final particles are formed by the growth of nuclei formed at different times. If you want to control monodisperse nuclei, you must control the supersaturation of the solute to be slightly higher than the nucleation concentration so that all nuclei are formed in a very short time. After the nuclei are formed, the solution concentration quickly drops below the nucleation concentration, so no new nuclei are generated, but the concentration is still slightly higher than the saturation, so the existing nuclei can grow slowly at the same speed due to diffusion. In order to ensure the uniformity of the preparation of the nuclei, the percentage of the maximum component of a certain particle size can be increased by controlling the seed preparation process, that is, the uniformity of the nuclei can be improved.

[0011] The Chinese patent with publication number CN107857298B discloses a method for preparing high-activity seed crystals by hydrolyzing titanium sulfate liquid, comprising the following steps: A. taking the hydrolyzed titanium sulfate liquid and placing it in a preheating tank and preheating it to 50-65°C, wherein the TiO2 concentration of the hydrolyzed titanium sulfate liquid is 195-205g / L; 3+ 1.0-3.0g / L (in terms of TiO2); effective acid and total TiO2 concentration ratio F1.70-1.85; Fe / TiO2 0.26-0.31; solid content <30mg / L; stability ≥500; B. preheat the alkali solution to 50-65°C, and control the concentration of the alkali solution after preheating to 8.0-8.5%; C. add the hydrolyzed titanium sulfate solution to the alkali solution within 1-4 minutes, and control the temperature of the seed titanium sulfate solution at 40-60°C after the reaction is completed; D. dilute and control the TiO2 concentration in the seed titanium sulfate solution to 30-160g / L. The seed crystals prepared by the method of this scheme have uneven coarse and fine particles. The crystal seeds are formed in different reaction concentration systems. The hydrolyzed titanium sulfate solution is added to the alkali solution within 1-4 minutes. The initial crystal seeds are formed in the reaction system with low titanium sulfate solution concentration and high alkali concentration. With the continuous addition of alkali solution, the crystal seeds continue to form. The crystal seeds formed earlier continue to grow, and the crystal seeds formed later are in the system with high titanium sulfate solution concentration and low alkali concentration. The growth time of the crystal seeds formed later is short. The titanium solution concentration and alkali concentration of the crystal seeds formed at different stages are different, the growth time is different, and the particle size is also different, which causes the prepared crystal seeds to have uneven particle size.

[0012] The commonly used method for preparing hydrolysis seeds is to add titanyl sulfate into an alkali tank at a controlled time and react by stirring in a reaction vessel. It is difficult to ensure uniform heating in this traditional reaction equipment, and the formation and growth of crystal nuclei usually occur simultaneously. The particle size of the obtained titanium dioxide is either large or small, the uniformity is poor, and the reproducibility between batches is poor. Summary of the invention

[0013] The technical problem to be solved by the present invention is to provide a sulfuric acid method titanium dioxide hydrolysis seed, titanium dioxide and a preparation method thereof, in view of the deficiencies in the prior art. The titanium dioxide prepared by the method has uniform particle size, suitable size and simple and easy process.

[0014] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0015] A method for preparing hydrolysis crystal seeds of titanium dioxide by sulfuric acid process comprises the following steps: 1, preheating a titanyl sulfate solution and an alkaline solution respectively; 2, reacting the preheated titanyl sulfate solution and the alkaline solution to prepare crystal seeds; 3, cooling the crystal seeds prepared in step 2; and 2, introducing the titanyl sulfate solution and the alkaline solution into a microchannel reactor at a flow rate of 5-15 mL / min, and reacting at a temperature of 85-95° C. for 2-10 min to prepare crystal seeds.

[0016] In step 2, the temperature of the reactants in the microchannel reactor is 85-95° C. At this temperature, the seed crystals prepared by the reaction of titanyl sulfate solution and alkaline solution have the best activity.

[0017] Preferably, the reaction temperature in step 2 is 85-90°C and the reaction time is 2-5min. If the reaction flow rate is too fast and the reaction time is too short, a large number of seed crystals will be generated in a very short time, resulting in a rapid decrease in supersaturation in the solution. Since too many seed crystals are formed and the distance between the particles is too close, a semisolid gel is easily formed. If the reaction flow rate is too slow and the reaction time is too long, the crystal nuclei are products of different stages, and the crystal nuclei grow while forming, resulting in a wide particle size distribution. The effect of using a microchannel reactor is lost.

[0018] In a preferred embodiment of the present invention, the weight ratio of the titanyl sulfate solution to the alkaline solution in step 2 is 3-6.

[0019] The reaction formula of titanyl sulfate and sodium hydroxide is: TiOSO4+NaOH=H4TiO4+Na2SO4. The seed crystal is represented by the chemical formula H4TiO4 (orthotitanic acid). This weight ratio is to ensure the number of seed crystals prepared and the activity of the seed crystals. If the weight ratio is too high, the amount of alkali is small, and the number of seed crystals prepared is small. If the weight ratio is too small, the stability of the prepared seed crystals is poor and they are prone to early hydrolysis. The total titanium of the seed crystal refers to the concentration of titanium dioxide in the seed crystal solution. In terms of the solution stability of the seed crystal, the higher the total titanium of the seed crystal, the higher the stability of the seed crystal. Under the same conditions, the lower the titanium-alkali ratio and the lower the concentration of the seed crystal, the lower the stability of the seed crystal and the worse the activity of the seed crystal.

[0020] In a preferred embodiment of the present invention, the flow rate of the titanyl sulfate solution in step 2 is 5-15 mL / min, and the flow rate of the alkaline solution is 2.5-10 mL / s.

[0021] In a preferred embodiment of the present invention, the inner diameter of the channel of the microchannel reactor in step 2 is 2-5 mm; preferably, the channel includes a plurality of U-shaped connecting parts.

[0022] The channel material of the microchannel reactor is stainless steel lined with polytetrafluoroethylene or heat-resistant glass.

[0023] In a preferred embodiment of the present invention, the preheating temperature of the titanyl sulfate solution and the alkaline solution in step 1 is 65-85°C; preferably, the preheating temperature of the titanyl sulfate solution and the alkaline solution in step 1 is 70-85°C.

[0024] In step 1, the stirring effect must be ensured when the titanyl sulfate and the alkaline solution are heated to ensure that the titanyl sulfate and the alkaline solution are heated evenly; the preheating temperature is 65-85° C. If the temperature is too high, the stability of the titanyl sulfate will be reduced; if the temperature is too low, the reaction time of the titanyl sulfate solution and the alkaline solution in the microchannel reactor will be affected, because the reaction temperature of the microchannel reactor is 85-95° C. If the preheating temperature is too low, it will take a long time to heat up in the reactor to reach the reaction temperature, which will inevitably affect the quality of the prepared seed crystals.

[0025] In a preferred embodiment of the present invention, in step 3, the seed crystals obtained in step 2 are cooled to below 80°C.

[0026] The seed crystals prepared in step 3 need to be cooled to below 80°C after leaving the microchannel reactor to prevent the seed crystals from continuing to grow at high temperatures. In addition, the titanyl sulfate solution will form new seed crystals or hydrolyze in the presence of seed crystals, which is not conducive to preparing seed crystals with uniform particle size.

[0027] In a preferred embodiment of the present invention, the mass concentration of the titanyl sulfate solution in step 1 is 160-220 g / L, the acidity is 1.80-2.0, the trivalent titanium (in terms of TiO2) is 1-3 g / L, the iron-titanium ratio (Fe / TiO2) is 0.2-0.3, the stability is ≥500 mL, and it is clarified.

[0028] The titanyl sulfate described in step 1 is obtained by acid hydrolysis of ore in the production of titanium dioxide by the sulfuric acid process.

[0029] The above indicators are to ensure the quality of titanyl sulfate. If the quality of titanyl sulfate solution cannot be guaranteed, it will affect the quality of seed crystal preparation. If the acidity is too low, the stability of titanium liquid will be reduced, early hydrolysis will occur easily, the particle size distribution of prepared seed crystals will be wide, and the activity of seed crystals will be poor; if the concentration of titanyl sulfate is too low, the stability of titanium liquid will also be affected.

[0030] 100 mL of titanium liquid can be poured into a Buchner funnel lined with filter paper with a diameter of 9 cm. After filtering, 100 mL of water is added. The filter paper is white without yellow spots, and a clear titanyl sulfate solution is obtained.

[0031] Preferably, the alkaline solution in step 1 is one or more of NaOH, KOH, LiOH, Na2CO3, NH3.H2O solution; preferably, the weight concentration of the alkaline solution is 5-10%.

[0032] When the concentration of the alkaline solution is too low, the reaction rate of titanyl sulfate and the alkaline solution is too slow, and the prepared seed crystal particle size is coarse. When the concentration of the alkaline solution is too high, the reaction rate of titanyl sulfate and the alkaline solution is too fast, and the prepared seed crystal particle size is small.

[0033] The invention also discloses a hydrolysis seed prepared according to the method for preparing the hydrolysis seed of titanium dioxide by sulfuric acid process.

[0034] The present invention also discloses a method for preparing titanium dioxide, which comprises adding the hydrolysis seeds to a titanyl sulfate solution in proportion for hydrolysis, and obtaining titanium dioxide through impurity removal, doping, calcination and pulverization; preferably, the weight ratio of the hydrolysis seeds to the titanyl sulfate solution is (1.5-2.5):100.

[0035] The preparation method of titanium dioxide specifically includes the following contents:

[0036] (1) Put titanium liquid into a four-necked flask, add hydrolysis seed crystals, the amount of seed crystals added is 1.5-2.5% by weight of TiO2, stir for 10-20 minutes, heat to boiling, stop heating for 30-40 minutes when the hydrolysis titanium liquid has turned blue-gray, heat again to a second boiling, keep warm for 3-4 hours, and the hydrolysis is completed.

[0037] (2) Washing: Filter the hydrolyzed material with a Buchner funnel and add deionized water to wash for 20-40 minutes.

[0038] (3) Bleaching: Pulp the washed material and heat it to 60-70°C, add 0.3-0.4% (calculated as TiO2) of organic reducing agent CXA, and keep it warm for 1-1.5 hours.

[0039] (4) Secondary washing: The bleached material is filtered with a Buchner funnel and washed with deionized water. The material is tested with hydrogen peroxide and potassium thiocyanate and is colorless, indicating that the material is clean.

[0040] (5) Salt Treatment: The second washed material is pulped, and salt treatment agents of 0.4-0.5% KOH, 0.02-0.1% phosphoric acid, and 0.15-0.1% ZnO (calculated as TiO2) are added respectively, stirred for 30-60 minutes, filtered, and dried at 100°C.

[0041] (6) Calcination: The dried material is placed in a muffle furnace and calcined at 800-900° C. for 1-2 hours.

[0042] (7) Grinding and crushing: The calcined sample is crushed by a universal grinder.

[0043] The present invention also discloses a titanium dioxide prepared according to the titanium dioxide preparation method, wherein the titanium dioxide is a pigment grade titanium dioxide, preferably, the D90 of the titanium dioxide is 0.5-0.6 μm, and the D50 is 0.3-0.4 μm; further preferably, the L * 98.70~98.75, b * The chromatic abatement power is 110-115%.

[0044] The present invention changes the reaction container from a traditional reaction tank to a microchannel reactor.

[0045] A microchannel reactor is a small reaction system manufactured by micromachining and precision machining technology. The microchannels for fluid flow are small in size, the diffusion distance of the reactants is greatly shortened, and the mixing time can be greatly reduced. Since the reactants have the advantages of short residence time and high mixing intensity, the reactants can be fully mixed in a short time during the flow process. The microchannel reactor has a large specific surface area, high heat exchange efficiency, and the reactants are heated evenly. The reaction process is carried out in a microchannel reactor in a continuous flow manner.

[0046] Titanyl sulfate reacts with alkali to prepare seed crystals. The particle size and particle size distribution of the seed crystals are related to the supersaturation distribution of the system solution. The supersaturation is generated by the reaction of titanyl sulfate and alkali. The reaction process is closely related to micro-mixing, that is, the rate of supersaturation generation depends on the micro-mixing rate. It can be seen from the crystallization kinetics that the nucleation rate of the precipitation reaction is nonlinear, and a small change in supersaturation will cause a large change in the nucleation rate, resulting in difficult to control particle size distribution and poor reproducibility between batches. The advantage of using a micro-channel reactor to prepare seed crystals is that the supersaturation generated by the reaction of titanyl sulfate and alkali is stable, and the particle size of the prepared seed crystals is uniform.

[0047] Compared with the prior art, the present invention has the following beneficial effects: (1) the titanium dioxide prepared by the method of the present invention has uniform and controllable particle size, and D90 is 0.5-0.6 μm; (2) a microchannel reactor is used to prepare hydrolysis seeds, and the high heat transfer rate of the microchannel reactor is utilized to ensure that the reaction temperature quickly reaches uniformity; (3) titanyl sulfate and alkali solution are used as raw materials to prepare hydrolysis seeds, and the titanyl sulfate solution reacts quickly with the alkali solution to prepare the seeds, and the seeds are kept uniformly growing, thereby obtaining seeds with uniform particle size; (4) by controlling the reaction of titanyl sulfate and the alkali solution in the microchannel reactor, the reaction of the seeds with the alkali solution is controlled to obtain a uniform particle size seed; and (5) controlling the supersaturation of orthotitanic acid (seeds) generated by the reaction of titanyl sulfate and alkaline solution to be slightly higher than the nucleation (seed preparation) concentration, so that all the seeds are formed in a very short time. After the seeds are formed, the solution concentration quickly drops to below the nucleation (seed preparation) concentration, and no new seeds are generated. In order to ensure the uniformity of the seed preparation, the percentage of the maximum component of a certain particle size is increased, that is, the uniformity of the seed is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 This is a particle size diagram of titanium dioxide prepared in Example 1 of the present invention.

[0049] Figure 2 This is a particle size diagram of titanium dioxide prepared in Example 2 of the present invention.

[0050] Figure 3 This is a particle size diagram of titanium dioxide prepared in Comparative Example 1 of the present invention.

[0051] Figure 4 This is a particle size diagram of titanium dioxide prepared in Comparative Example 2 of the present invention.

[0052] Figure 5 This is a photo of the microchannel reactor used in Example 1 of the present invention.

[0053] Figure 6 This is a schematic diagram of the principle of the microchannel reactor used in Example 1 of the present invention.

[0054] Figure 7 This is a schematic diagram of the overall structure of the microchannel reactor used in Example 1 of the present invention.

[0055] Among them, 1-beaker, 2-water bath, 3-pump, 4-microchannel reactor, 5-beaker, 41-U-shaped connecting part. DETAILED DESCRIPTION

[0056] The following will describe the implementation scheme of the present invention in detail with reference to a specific embodiment of the alkaline solution, taking NaOH as an example.

[0057] Example 1

[0058] 1. Take 100 mL of titanyl sulfate solution with a total titanium concentration of 220 g / L, an acid ratio of 1.80, a trivalent titanium of 1.0, a titanium-iron ratio of 0.2, and a stability of 500 mL, and pour it into a 200 mL glass beaker. At the same time, take 53.3 g of sodium hydroxide solution with an alkali weight concentration of 10% into a 100 mL glass beaker and preheat them to 65 °C.

[0059] 2. The microchannel reactor used in Example 1 is as follows Figure 5-7 As shown. The preheated titanyl sulfate solution was pumped into the microchannel reactor from the inlet at a flow rate of 15 mL / min by an axial flow pump, and the preheated alkali solution was pumped into the microchannel reactor from another inlet at a flow rate of 7 mL / min by an axial flow pump. The reaction time was 2 minutes. The reaction temperature was 90°C.

[0060] 3. The titanyl sulfate solution and alkaline solution reactants enter a glass beaker placed in an ice water tank from the outlet of the microchannel reactor.

[0061] 4. (1) Put the titanium liquid into a four-necked flask, add hydrolysis seeds, the amount of seeds is 1.5% by weight of TiO2, stir for 10 minutes, raise the temperature to boiling, stop heating for 30 minutes when the hydrolysis titanium liquid has turned blue-gray, raise the temperature again to a second boiling, keep warm for 3 hours, and the hydrolysis is completed.

[0062] (2) Washing: Filter the hydrolyzed material using a Buchner funnel and add deionized water to wash for 20 minutes.

[0063] (3) Bleaching: The temperature of the washed material was raised to 60°C, 0.3% (in terms of TiO2) of organic reducing agent CXA was added, and the temperature was kept for 1 hour.

[0064] (4) Secondary washing: The bleached material is filtered with a Buchner funnel and washed with deionized water. The material is tested with hydrogen peroxide and potassium thiocyanate and is colorless, indicating that the material is clean.

[0065] (5) Salt Treatment: The second washed material was pulped, and salt treatment agents 0.4% KOH, 0.02% phosphoric acid, and 0.15% ZnO (calculated as TiO2) were added respectively, stirred for 30 minutes, filtered, and dried at 100°C.

[0066] (6) Calcination: The dried material was placed in a muffle furnace and calcined at 890° C. for 1 hour.

[0067] (7) Grinding and crushing. The calcined sample was crushed by universal pulverizer. The particle size of titanium dioxide was measured by laser particle size analyzer, and the product quality index was measured by whiteness meter: L: 98.72b: 1.53, decolorizing power: 110%. (Data see Table 1)

[0068] Example 2

[0069] 1. Take 100mL of titanyl sulfate solution with a total titanium concentration of 160g / L, an acid ratio of 2.0, a trivalent titanium of 3.0, a titanium-iron ratio of 0.3, and a stability of 500mL in a 200mL glass beaker, and at the same time take 53.3g of sodium hydroxide solution with an alkali weight concentration of 5% in a 100mL glass beaker. Preheat them to 85℃ respectively.

[0070] 2. The preheated titanyl sulfate solution was pumped into the microchannel reactor from the inlet at a flow rate of 5 mL / min by an axial flow pump, and the preheated alkaline solution was pumped into the microchannel reactor from the other inlet at a flow rate of 2.5 mL / s by an axial flow pump. The reaction time was 5 min. The reaction temperature was 85°C.

[0071] 3. Titanyl sulfate solution and alkaline solution reactants enter a glass beaker with a cooling system from the microchannel reaction product outlet.

[0072] 4. (1) Put the titanium liquid into a four-necked flask, add the hydrolysis seed crystals, add the seed crystals according to the weight ratio of TiO2 2.5%, stir for 10 minutes, heat to boiling, stop heating for 30 minutes when the hydrolysis titanium liquid has turned blue-gray, heat to boiling again, keep warm for 3 hours, and the hydrolysis is completed. Take a small amount of the hydrolysis material and use a laser particle size analyzer to detect the particle size of the metatitanic acid.

[0073] (2) Washing: Filter the hydrolyzed material using a Buchner funnel and add deionized water to wash for 20 minutes.

[0074] (3) Bleaching: The temperature of the washed material was raised to 65°C, 0.35% (in terms of TiO2) of organic reducing agent CXA was added, and the temperature was kept for 1 hour.

[0075] (4) Secondary washing: The bleached material is filtered with a Buchner funnel and washed with deionized water. The material is tested with hydrogen peroxide and potassium thiocyanate and is colorless, indicating that the material is clean.

[0076] (5) Salt Treatment: The second washed material was pulped, and salt treatment agents 0.45% KOH, 0.025% phosphoric acid, and 0.20% ZnO (calculated as TiO2) were added respectively, stirred for 30 minutes, filtered, and dried at 100°C.

[0077] (6) Calcination: The dried material was placed in a muffle furnace and calcined at 890° C. for 1 hour.

[0078] (7) Grinding and crushing. The calcined sample was crushed by universal grinding. The particle size of titanium dioxide was measured by laser particle size analyzer, and the product quality index was measured by whiteness meter: L: 98.73b: 1.49, decolorizing power: 110%. (Data see Table 1)

[0079] Comparative Example 1

[0080] 1. Take 100mL of titanyl sulfate solution with a total titanium concentration of 220g / L, an acid ratio of 1.80, a trivalent titanium of 1.0, a titanium-iron ratio of 0.2, and a stability of 500mL in a 200mL glass beaker, and at the same time take 53.3g of sodium hydroxide solution with an alkali weight concentration of 10% in a 300mL glass beaker. Preheat them to 65℃ respectively.

[0081] 2. Pour the titanyl sulfate solution into the sodium hydroxide solution beaker within 5 minutes, maintain the reaction temperature at 85°C, and mature for 2 minutes to prepare seed crystals.

[0082] 3. (1) Put titanium liquid into a four-necked flask, add hydrolysis seed crystals, the amount of seed crystals added is 1.5% by weight of TiO2, stir for 10 minutes, raise the temperature to boiling, stop heating for 30 minutes when the hydrolysis titanium liquid has turned blue-gray, raise the temperature again to a second boiling, keep warm for 3 hours, and the hydrolysis is completed.

[0083] (2) Washing: Filter the hydrolyzed material using a Buchner funnel and add deionized water to wash for 20 minutes.

[0084] (3) Bleaching: The temperature of the washed material was raised to 60°C, 0.3% (in terms of TiO2) of organic reducing agent CXA was added, and the temperature was kept for 1 hour.

[0085] (4) Secondary washing: The bleached material is filtered with a Buchner funnel and washed with deionized water. The material is tested with hydrogen peroxide and potassium thiocyanate and is colorless, indicating that the material is clean.

[0086] (5) Salt Treatment: The second washed material was pulped, and salt treatment agents 0.4% KOH, 0.02% phosphoric acid, and 0.15% ZnO (calculated as TiO2) were added respectively, stirred for 30 minutes, filtered, and dried at 100°C.

[0087] (6) Calcination: The dried material was placed in a muffle furnace and calcined at 920° C. for 1 hour.

[0088] (7) Grinding and crushing. The calcined sample was crushed by universal grinding. The particle size of titanium dioxide was measured by laser particle size analyzer, and the product quality index was measured by whiteness meter: L: 98.65b: 1.68, decolorizing power: 105%. (Data see Table 1)

[0089] Comparative Example 2

[0090] 1. Take 100mL of titanyl sulfate solution with a total titanium concentration of 160g / L, an acid ratio of 1.80, a trivalent titanium of 1.0, a titanium-iron ratio of 0.2, and a stability of 500mL in a 200mL glass beaker, and at the same time take 53.3g of sodium hydroxide solution with an alkali weight concentration of 5% in a 300mL glass beaker. Preheat them to 85℃ respectively.

[0091] 2. Pour the titanyl sulfate solution into the sodium hydroxide solution beaker within 5 minutes, maintain the reaction temperature at 95°C, and mature for 5 minutes to prepare seed crystals.

[0092] 3. (1) Put the titanium liquid into a four-necked flask, add the hydrolysis seed crystals, add the seed crystals according to the weight ratio of TiO2 2.5%, stir for 10 minutes, heat to boiling, stop heating for 30 minutes when the hydrolysis titanium liquid has turned blue-gray, heat to boiling again, keep warm for 3 hours, and the hydrolysis is completed. Take a small amount of the hydrolysis material and use a laser particle size analyzer to detect the particle size of the metatitanic acid.

[0093] (2) Washing: Filter the hydrolyzed material using a Buchner funnel and add deionized water to wash for 20 minutes.

[0094] (3) Bleaching: The temperature of the washed material was raised to 65°C, 0.35% (in terms of TiO2) of organic reducing agent CXA was added, and the temperature was kept for 1 hour.

[0095] (4) Secondary washing: The bleached material is filtered with a Buchner funnel and washed with deionized water. The material is tested with hydrogen peroxide and potassium thiocyanate and is colorless, indicating that the material is clean.

[0096] (5) Salt Treatment: The second washed material was pulped, and salt treatment agents 0.45% KOH, 0.025% phosphoric acid, and 0.20% ZnO (calculated as TiO2) were added respectively, stirred for 30 minutes, filtered, and dried at 100°C.

[0097] (6) Calcination: The dried material was placed in a muffle furnace and calcined at 890° C. for 1 hour.

[0098] (7) Grinding and crushing. The calcined sample was crushed by universal grinding. The particle size of titanium dioxide was measured by laser particle size analyzer, and the product quality index was measured by whiteness meter: L: 98.63b: 1.75, decolorizing power: 105%. (Data see Table 1)

[0099] The particle size of titanium dioxide obtained by the above method is shown in the figure Figure 1-4 The particle size and color of titanium dioxide are shown in Table 1.

[0100] Table 1 Particle size and color of titanium dioxide obtained in Example 1-2 and Comparative Example 1-2

[0101]

[0102] The hydrolysis seed crystals prepared by the microchannel reactor in Example 1 and Example 2 have uniform particle sizes, and the titanium dioxide prepared by this method has uniform particle sizes and small diameter-to-width ratios of 0.85 and 0.82, respectively. The L value is high, the b value is low, the blue phase is biased, and the tinting power is high. The hydrolysis seed crystals prepared by the universal reaction tank are formed at different times, and the particle sizes are different. The titanium dioxide prepared by this method has a wide particle size distribution, a large diameter-to-width ratio of 1.91, a low L value, a high b value, and a yellow phase.

[0103] from Figures 1 to 4 It can be seen that the apparent D50 is about 0.34 μm, but in Example 1 ( Figure 1 )D10 is 0.251 μm, D90 is 0.547 μm; Example 2 ( Figure 2 ) D10 is 0.263 μm, and D90 is 0.546 μm. It can be seen that the particle size distribution of Example 1 and Example 2 is narrow and the particle size is uniform.

[0104] Comparative Example 1 Figure 3 )D10 is 0.140μm, D90 is 0.807μm; Comparative Example 2 ( Figure 4 )D10 is 0.187 μm, D90 is 0.847 μm; the particle size distribution of Comparative Examples 1 and 2 is relatively wide and presents a multi-modal distribution, and the particle size distribution is uneven.

[0105] The seed crystals prepared by the present invention have uniform particle size. The seed crystals are prepared by reacting TiO2 in titanyl sulfate with an alkali, and the seed crystals are prepared by a micro-pass reactor. The formed seed crystals are always a system in which the titanium liquid and the alkali reaction concentration are the same. And after the seed crystals are formed, they can grow uniformly, and the prepared seed crystals have uniform particle size. The hydrolysis of titanium liquid uses the seed crystal as the crystallization center. Through the seed crystal with uniform particle size, the particle size of the hydrolyzed metatitanic acid prepared by the hydrolysis of titanium liquid is very uniform, and the final titanium dioxide particle size is evenly distributed, narrowly distributed, and has a small diameter-to-width ratio. The smaller the diameter-to-width ratio of the particle size, the more uniform the particle size distribution.

[0106] The seed crystals prepared by the Chinese patent of CN107857298B are uneven in size. The seed crystals are formed in different reaction concentration systems. The hydrolyzed titanium sulfate solution is added to the alkali solution within 1-4 minutes. The initial seed crystals are formed in a reaction system with low titanium sulfate solution concentration and high alkali concentration. With the continuous addition of alkali solution, the seed crystals continue to form. The first seed crystals continue to grow, and the seed crystals formed later are in a system with high titanium sulfate solution concentration and low alkali concentration. The time for the seed crystals formed later to grow is short. The titanium solution concentration and alkali concentration of the seed crystals formed at different stages are different, and the growth time is different, and the size of the particle size is also different, which causes the uneven size of the seed crystals prepared. The hydrolyzed titanium solution takes the seed crystal as the crystallization center, and the seed crystal particle size distribution is uneven. The hydrolyzed metatitanic acid particle size is uneven, and the final titanium dioxide particle size is uneven.

Claims

1. A method for preparing hydrolysis seed crystals of titanium dioxide by sulfuric acid process, comprising step 1, preheating a titanyl sulfate solution and an alkaline solution respectively; step 2, reacting the preheated titanyl sulfate solution and the alkaline solution to obtain seed crystals; step 3, cooling the seed crystals obtained in step 2; characterized in that Step 2: introducing the titanyl sulfate solution and the alkaline solution into a microchannel reactor at a flow rate of 5-15 mL / min, and reacting at a temperature of 85-95° C. for 2-10 min to prepare seed crystals.

2. The method for preparing sulfuric acid titanium dioxide hydrolysis seed crystals according to claim 1, characterized in that: The weight ratio of the titanyl sulfate solution to the alkaline solution in step 2 is 3-6.

3. The method for preparing sulfuric acid titanium dioxide hydrolysis seed crystals according to claim 2, characterized in that: In step 2, the flow rate of the titanyl sulfate solution is 5-15 mL / min, and the flow rate of the alkaline solution is 2.5-10 mL / s.

4. The method for preparing sulfuric acid titanium dioxide hydrolysis seed crystals according to claim 1, characterized in that: The inner diameter of the channel of the microchannel reactor in step 2 is 2-5 mm; preferably, the channel includes a plurality of U-shaped connecting parts (41).

5. The method for preparing sulfuric acid process titanium dioxide hydrolysis seed crystals according to claim 1, characterized in that: The preheating temperature of the titanyl sulfate solution and the alkaline solution in step 1 is 65-85°C; preferably, the preheating temperature of the titanyl sulfate solution and the alkaline solution in step 1 is 70-85°C.

6. The method for preparing sulfuric acid titanium dioxide hydrolysis seed crystals according to any one of claims 1 to 5, characterized in that: In step 3, the seed crystals prepared in step 2 are cooled to below 80°C.

7. The method for preparing sulfuric acid titanium dioxide hydrolysis seed crystals according to any one of claims 1 to 5, characterized in that: The mass concentration of the titanyl sulfate solution in step 1 is 160-220 g / L, the acidity is 1.80-2.0, the trivalent titanium (in terms of TiO2) is 1-3 g / L, the iron-titanium ratio (Fe / TiO2) is 0.2-0.3, the stability is ≥500 mL, and it is clarified.

8. A hydrolysis seed crystal obtained by the method for preparing hydrolysis seed crystals of titanium dioxide by sulfuric acid process according to any one of claims 1 to 7.

9. A method for preparing titanium dioxide, characterized in that: The hydrolysis seeds in claim 8 are added to titanyl sulfate solution in proportion for hydrolysis, and titanium dioxide is obtained by removing impurities, doping, calcining and pulverizing; preferably, the weight ratio of the hydrolysis seeds to the titanyl sulfate solution is (1.5-2.5):

100.

10. A titanium dioxide prepared according to the method for preparing titanium dioxide according to claim 9, characterized in that: The titanium dioxide is a pigment grade titanium dioxide. Preferably, the D90 of the titanium dioxide is 0.5 to 0.6 μm, and the D50 is 0.3 to 0.4 μm. Further preferably, the L * 98.70~98.75, b * The chromatic abatement power is 110-115%.

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