Continuous coating method for titanium dioxide

Abstract

The invention relates to the technical field of titanium dioxide production, and discloses a titanium dioxide continuous coating method which comprises the following steps: S1, obtaining various production parameters; s2, enabling the pretreated titanium dioxide slurry to sequentially flow through n multi-stage series coating tank groups corresponding to the n coating agents, wherein each multi-stage series coating tank group comprises m coating tanks which are connected in series, the volumes of the coating tanks are gradually increased along the flowing direction of the slurry, and each coating tank is provided with a stirring kettle; s3, monitoring the pH value and temperature of the titanium dioxide slurry of each coating tank, and dynamically controlling by adjusting the flow of a pH regulator and the flow of steam; and S4, then the materials enter a terminal pH adjusting multi-stage tank group, the coated titanium dioxide slurry is adjusted to the terminal pH, coating of the materials is completed, the next unit operation is waited, and the problems that in the prior art, an intermittent coating process is unstable in batch and poor in coating uniformity are solved.

Description

Technical Field

[0001] The invention relates to the technical field of titanium dioxide production, and in particular to a titanium dioxide continuous coating method. Background Art

[0002] Titanium dioxide, a white pigment, is widely used in coatings, plastics, inks, and other fields. Untreated titanium dioxide has numerous hydroxyl groups on its surface, resulting in high polarity and prone to agglomeration and sedimentation in organic media. This results in poor dispersibility and dispersion stability. Furthermore, due to inherent lattice defects, untreated titanium dioxide also suffers from poor weatherability and chemical stability. Therefore, titanium dioxide is typically coated on the surface to improve its weatherability and other application properties. The quality of the coating directly impacts the final application performance of the titanium dioxide product. For example, the prior art patent for a continuous titanium dioxide coating method, published as CN119331435A, illustrates this approach. Different coating agents are continuously fed into corresponding coating tanks. Although this patent utilizes internal baffles within the coating tanks to extend the material flow path, back-mixing, short-circuiting of unreacted material, and dead zones within the same continuous stirred tank can still occur. This can lead to self-nucleation of the coating agent, poor coating uniformity, and inconsistent batch quality. Summary of the Invention

[0003] The present invention aims to provide a continuous coating method for titanium dioxide to solve the problems of unstable batches and poor coating uniformity in the intermittent coating process of the prior art.

[0004] To achieve the above object, the present invention adopts the following technical solution: a titanium dioxide continuous coating method, comprising the following steps:

[0005] S1: Obtain various production parameters;

[0006] S2: The pretreated titanium dioxide slurry flows sequentially through n multi-stage series coating tank groups corresponding to n types of coating agents, each multi-stage series coating tank group comprises m coating tanks connected in series and having a stirred tank, the volume of which gradually increases with the flow direction of the slurry;

[0007] S3: Monitor the pH value and temperature of the titanium dioxide slurry in each coating tank, and dynamically control it by adjusting the pH regulator flow and steam flow;

[0008] S4: The material then enters the terminal pH adjustment multi-stage tank group to adjust the coated titanium dioxide slurry to the terminal pH. The material completes the coating and waits for the next unit operation.

[0009] The beneficial effects of this program are:

[0010] 1. Ensure that the titanium dioxide slurry is fully reacted.

[0011] Since titanium dioxide is prone to photocatalysis and unstable performance when exposed to acid and alkali, it is often necessary to include one or more layers of other materials on the surface of titanium dioxide particles to protect and improve its performance. In order to increase the single production capacity, the existing technology often stirs and coats in a large coating tank. The volume of the coating tank is usually designed to be 50-200m 3 , a velocity gradient dead zone is easily formed in a large coating tank. For example, the part close to the stirring paddle can be fully stirred, and the flow rate decreases away from the stirring end. It is difficult for the titanium dioxide slurry in this part to react fully, resulting in uneven contact between the titanium dioxide particles and the coating agent, and the coefficient of variation (CV value) of the coating layer thickness is as high as 10%-15%; in this technical solution, the titanium dioxide slurry is pretreated and then passed into a multi-stage series coating tank group for coating. Each multi-stage series coating tank group contains m stirring kettle coating tanks connected in series and the volume gradually increases with the flow direction of the slurry. The titanium dioxide slurry in this technical solution reacts multiple times in multiple coating tanks instead of reacting once in the same large coating tank. The first-stage coating tank of each multi-stage series coating tank group can play a preliminary mixing role and fully react in the subsequent coating tanks. This staged and graded coating method effectively avoids the dead zone problem caused by a large-volume single coating tank, ensuring that the titanium dioxide particles can evenly contact the coating agent, thereby achieving higher coating uniformity and reducing the CV value.

[0012] 2. Improve production efficiency.

[0013] The commonly used processing technology in the existing technology is a single batch intermittent coating mode, that is, according to each coating stage, the corresponding coating agent is added, and the pH and temperature are adjusted. After the reaction is sufficient, the next coating agent is added and the reaction is continued. The complete process of a single batch takes more than 12 hours. If a multi-component composite coating is used, the total time can be extended to more than 24 hours, and the production efficiency is low. In this technical solution, continuous coating is carried out through multiple connected tank groups instead of multiple coatings in the same tank. Therefore, the titanium dioxide slurry can be continuously passed through and subjected to the multi-stage series coating tank group. The corresponding coating process can carry out continuous production to reduce waiting time and thus improve production efficiency; at the same time, the volume of the coating tanks in series in each multi-stage coating tank group gradually increases with the flow direction, so that the residence time of the titanium dioxide slurry in the smaller coating tank is shorter, and the reaction time in the larger coating tank is longer, shortening the overall material backmixing and material short-circuiting, making the residence time distribution closer to the plug flow (PFR), ensuring that the titanium dioxide slurry is fully stirred in the small coating tank and stays longer in the larger coating tank for full reaction, avoiding the backmixing situation of the traditional process.

[0014] 3. Batch products have high stability.

[0015] Through the above settings and real-time monitoring of the pH value and temperature of the titanium dioxide slurry in the coating tanks at all levels, and dynamic control by adjusting the pH regulator flow and steam flow, combined with precise temperature control under sufficient reaction and stirring, it can be ensured that the titanium dioxide produced by the above process has high stability.

[0016] 4. Reduce waste.

[0017] The existing technology requires cleaning the reaction tank each time the single batch intermittent coating mode is switched, resulting in 5%-8% residual raw material loss. In this technical solution, continuous production can ensure that the materials in each tank group are in a uniform state, which can reduce the frequency of cleaning to a certain extent and thus reduce waste.

[0018] Preferably, as an improvement, the volume of the coated tank of each series-connected coated tank group in S2 satisfies the following formula:

[0019]

[0020] Where: n is the number of the n-th coating agent, m is the number of the coating tank of the n-th coating level m;

[0021]

[0022] Where: The volume of the mth-level coating tank of the nth type of coating, in m 3 ; Q0 is the flow rate of titanium dioxide slurry after sand grinding, unit is L / h; Q w is the desalted water flow rate, in L / h; Q v is the steam mass flow rate, in kg / h; ρ is the density of water, in kg / L; Q n is the flow rate of the nth coating agent, in L / h; q n is the flow rate of the nth coating pH regulator, in L / h; It is the flow time in the tank of m-level of the n-th coating, in hours.

[0023] The beneficial effects are: the volume of each coating tank comprehensively considers multiple flow factors, including titanium dioxide flow, desalted water flow, steam flow, coating agent flow, pH adjuster flow, etc., so that the volume of each coating tank is consistent with the actual material flow and reaction requirements. The volume of each coating tank is accurately calculated according to the flow and residence time of the material, ensuring that the titanium dioxide and the coating agent can fully react in each coating tank, and ensuring that in each reaction stage, the titanium dioxide can fully contact the coating agent, thereby forming a uniform coating layer.

[0024] Preferably, as an improvement, when the titanium dioxide slurry processed in the previous step in S2 enters the next multi-stage series coating tank group, the titanium dioxide slurry enters from above the first-stage coating tank of the n-th coating tank group, and the titanium dioxide slurry discharged from below the first-stage coating tank of the n-th coating tank group is input from below the second-stage coating tank of the n-th coating tank group and discharged from above the tank until it is discharged from above the m-th coating tank of the n-th coating tank group.

[0025] The beneficial effect is: the above-mentioned setting avoids the possibility that the material may enter directly from the top of the coating tank under the action of gravity and be quickly discharged from the bottom, resulting in some materials not being fully in contact with the coating agent, insufficient or uneven reaction causing material short-circuiting. By adjusting the flow direction of the material, the problem of the material being discharged after only a very short residence time in the coating tank or without sufficient reaction is avoided, ensuring that the titanium dioxide particles are in full contact with the coating agent in each coating tank, avoiding incomplete reaction or uneven layers. At the same time, the first coating tank is only used to fully mix and temperature-regulate the raw materials, and entering from the top can help ensure processing efficiency.

[0026] Preferably, as an improvement, the coating agent flow rate Q n Calculated according to the following formula:

[0027]

[0028] Where: Q n is the flow rate of the nth coating agent, C0 is the initial concentration of titanium dioxide slurry, X n % is the mass fraction of the coating, C n is the concentration of the coating agent.

[0029] The beneficial effect is that by calculating the flow rate of each coating agent according to the initial concentration of titanium dioxide, the coating agent concentration and the coating mass fraction, the accurate addition of the coating agent can be ensured to avoid excess or deficiency.

[0030] Preferably, as an improvement, there is a process pH adjustment multi-stage tank between the multi-stage series coating tank groups, and the process pH adjustment multi-stage tank includes c pH adjustment tanks connected in series and whose volumes gradually increase with the slurry flow direction.

[0031] The beneficial effect is: through the above setting, when the pH requirements between different coating agent processes are quite different, the process pH adjustment multi-stage tank can be set between different processes according to the needs, so that the material entering the next process meets the requirements and can fully react.

[0032] Preferably, as an improvement, the volume calculation formula of the terminal pH adjustment multi-stage tank group is:

[0033]

[0034] Where: Q is the total flow rate of the coating material, unit is L / h; It is the residence time of the material in the pH adjustment tank of stage c, in h.

[0035] The beneficial effect is: by connecting multiple pH adjustment tanks in series and controlling different residence times in each tank, the pH value of titanium dioxide can be adjusted gradually and accurately, thereby ensuring the stability of pH changes during the coating process.

[0036] Preferably, as an improvement, a heat exchanger (16) is provided between the multi-stage series-connected coating tank groups for temperature regulation.

[0037] The beneficial effect is that when a multi-layer coating process is carried out, different coating processes require different temperatures, and the temperature of the material entering the next coating process can be adjusted by setting a heat exchanger.

[0038] Preferably, as an improvement, the coating agent in S2 is a zirconium-aluminum coating agent combination, including:

[0039] The first coating agent: S2 includes three coating agents, the first coating agent is a zirconium-based compound with a concentration of 0.1%-1.5%, the second coating agent is an aluminum coating agent with a concentration of 0.5%-1.5%, and the third coating agent is an aluminum coating agent with a concentration of 0.5%-1.5%. The three multi-stage series coating tanks all include three coating tanks. The pH control range of the multi-stage series coating tank corresponding to the first coating agent is 2-4, the pH control range of the multi-stage series coating tank corresponding to the second coating agent is 3-5, and the pH control range of the multi-stage series coating tank corresponding to the third coating agent is 8-10.

[0040] The beneficial effect is that different coating agents act in sequence to form a multi-layer composite coating structure, thereby improving the resistance to photocatalysis and weathering resistance.

[0041] Preferably, as an improvement, S2 includes three coating agents, the first coating agent is a silicon-based coating agent with a concentration of 0.1%-1.5%, the second coating agent is an aluminum coating agent with a concentration of 1.5%-3.5%, and the two multi-stage series coating tanks each include three coating tanks. The pH control range of the multi-stage series coating tank corresponding to the first coating agent is 3.5-5, and the pH control range of the multi-stage series coating tank corresponding to the second coating agent is 3-5.

[0042] The beneficial effects are: different coating agents act in sequence to form a multi-layer composite coating structure, which improves the resistance to photocatalysis and weathering, and improves the resistance to acid and alkali corrosion.

[0043] Preferably, as an improvement, the real-time temperature range of the slurry of the multi-stage series coating tank group corresponding to the first coating agent and the process pH adjustment multi-stage tank is 80°C-90°C; the real-time temperature range of the slurry of the multi-stage series coating tank group corresponding to the first coating agent and the terminal pH adjustment multi-stage tank group is 60°C-70°C; a heat exchanger (16) is used between the process pH adjustment multi-stage tank and the multi-stage series coating tank group corresponding to the second coating agent for cooling.

[0044] The beneficial effect is that the above setting takes into account the requirements of coating reaction rate and film quality, meets the temperature requirements of different coating processes through the heat exchanger, and realizes energy-saving, uniform and stable continuous composite coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Figure 1 Schematic diagram of a dynamic mixing tank and a multi-stage first coating tank according to an embodiment of the present invention;

[0046] Figure 2 This is a schematic diagram of a multi-stage second coating tank according to an embodiment of the present invention;

[0047] Figure 3 This is a schematic diagram of a multi-stage third coating tank according to an embodiment of the present invention;

[0048] Figure 4 This is a schematic diagram of a multi-stage terminal pH adjustment tank according to an embodiment of the present invention;

[0049] Figure 5 This is a schematic diagram of a multi-stage process pH adjustment tank according to an embodiment of the present invention;

[0050] Figure 6 Schematic diagram of a multi-stage second coating tank containing a heat exchanger according to an embodiment of the present invention;

[0051] Figure 7 Titanium dioxide TEM processed by continuous silicon-aluminum coating process;

[0052] Figure 8 TEM of titanium dioxide treated by intermittent silicon-aluminum coating process.

[0053] The figure marks in the drawings of the specification include: dynamic mixing tank 1, first coating agent primary tank 2, first coating agent secondary tank 3, first coating agent tertiary tank 4, second coating agent primary tank 5, second coating agent secondary tank 6, second coating agent tertiary tank 7, third coating agent primary tank 8, third coating agent secondary tank 9, third coating agent tertiary tank 10, process pH adjustment primary tank 11, process pH adjustment secondary tank 12, process pH adjustment tertiary tank 13, terminal pH adjustment primary tank 14, terminal pH adjustment secondary tank 15, terminal pH adjustment tertiary tank 16, heat exchanger 17. DETAILED DESCRIPTION

[0054] The following is further described in detail through specific implementation methods and examples: The titanium dioxide continuous coating method includes the following steps:

[0055] S1: Obtain various production parameters, including the initial concentration C0 of titanium dioxide slurry sanding, the concentration C0 of titanium dioxide slurry before coating t , the number of coating agents n, the concentration of each coating agent C n , coating mass fraction of each coating agent X n %, curing time of each coating agent t n , pH of each coating stage and concentration of pH regulator of each coating stage, terminal pH and terminal aging time t z , titanium dioxide slurry flow rate after sand grinding Q0, desalted water flow rate Q W , steam flow Q v , the flow rate of each coating agent Q n , pH regulator flow rate of each coating q n , the number of coated tanks n*m, the volume of each coated tank and the volume V of the dynamic coating tank d .

[0056] S2: According to Figure 1 In the form of titanium dioxide slurry flow Q0, desalted water flow Q w , steam flow Q v Titanium dioxide slurry, desalted water and heating steam are continuously transported into the dynamic mixing tank 1 to dilute and heat the titanium dioxide slurry; the diluted titanium dioxide slurry flows through the multi-stage series coating tank group corresponding to n coating agents in sequence, and each multi-stage series coating tank group contains m stirred tank coating tanks connected in series and the volume gradually increases with the flow direction of the slurry. Specifically, the diluted and heated titanium dioxide slurry is discharged from the bottom of the dynamic mixing tank 1 and transported to the The first coating agent level 1 tank 2 is filled with the first coating agent and the first coating pH regulator. The first coating agent and the first coating pH regulator are simultaneously transported to the first coating agent level 1 tank 2 according to the first coating agent flow rate Q1 and the first coating pH regulator flow rate. The material flows in the first coating agent level 1 tank 2 for a time of up to After that, the continuous discharge flow volume is The material flows in the first coating agent secondary tank 3 for a time of After that, it is continuously discharged into the first coating agent tertiary tank 10, and the above steps are followed until the flow of all m coating tanks in the first coating process is completed.

[0057] according to Figure 2 In the form of, then the material is continuously discharged to the volume The second coating agent first-level tank 5 is continuously fed with the second coating agent and the second coating pH regulator according to the second coating agent flow rate Q2 and the second coating pH regulator flow rate; the material flows in the second coating agent first-level tank 5 for a time period of up to After that, the continuous discharge flow volume is The above steps are followed in the second coating agent secondary tank 6 until all n coating agents are added. The materials are fully mixed and reacted during the flow of the coating tanks. Several multi-stage pH adjustment tanks can be set between different coating agent processes. The multi-stage pH adjustment tanks include c pH adjustment tanks connected in series, with the volume gradually increasing with the direction of slurry flow. With this arrangement, when the pH requirements of different coating agent processes vary significantly, multi-stage pH adjustment tanks can be set between different processes as needed to ensure that the materials entering the next process meet the requirements and can fully react.

[0058] When the titanium dioxide slurry processed in the previous step in S2 enters the next coating process, the titanium dioxide slurry enters from the top of the first coating tank of the nth coating tank group, and the titanium dioxide slurry discharged from the bottom of the first coating tank of the nth coating tank group is input from the bottom of the second coating tank of the nth coating tank group and discharged from the top of the tank, and so on, it is input from the bottom of the next coating tank and discharged from the top. Specifically, taking the first coating agent first-level tank 2 as an example, the diluted and heated titanium dioxide slurry, the first coating agent and the first coating pH regulator are transported from the top of the first coating agent first-level tank 2 to the first coating agent first-level tank 2, and the flow time in the first coating agent first-level tank 2 reaches The material is discharged from the bottom of the first coating agent first tank 2 and continuously input from the bottom of the first coating agent second tank 3. Figure 2 In the form of the first coating agent secondary tank 3, the flow time reaches The material is discharged from the top of the first coating agent secondary tank 3 and continuously input from the bottom of the first coating agent tertiary tank 4. Figure 3 In the form of the first coating agent three-stage tank 4, the flow time reaches The material is discharged from the top of the first coating agent three-stage tank 4 and continuously input from the top of the second coating agent one-stage tank 5. In the same coating process, the material is always input from the bottom and discharged from the top after the first-stage coating tank. The above arrangement avoids the possibility that the material may enter the coating tank directly from the top and be quickly discharged from the bottom under the action of gravity, resulting in some materials not being fully in contact with the coating agent, and the material short-circuiting caused by insufficient or uneven reaction. By adjusting the flow direction of the material, the problem of the material being discharged after only a very short residence time in the coating tank or without sufficient reaction is avoided, ensuring that the titanium dioxide particles are in full contact with the coating agent in each coating tank, avoiding incomplete reaction or uneven layers. At the same time, the first coating tank is only used to fully mix the raw materials and adjust the temperature. Entering from the top can help ensure processing efficiency.

[0059] The volume of the coated tank of each series coated tank group in S2 satisfies the following formula:

[0060]

[0061] Where: n is the number of the nth coating agent, m is the number of the coating tank of the nth coating and mth level;

[0062]

[0063] Where: The volume of the mth-level coated tank of the nth coating, in m 3 ; Q0 is the flow rate of titanium dioxide slurry after sand grinding, unit is L / h; Q w is the desalted water flow rate, in L / h; Q v is the steam mass flow rate, in kg / h; ρ is the density of water, in kg / L; Q n is the flow rate of the nth coating agent, in L / h; q n is the flow rate of pH regulator for the nth coating, in L / h; It is the flow time in the tank of the nth coating and the mth level, in hours.

[0064] The volume of each coating tank is consistent with the actual material flow and reaction requirements. The volume of each coating tank is accurately calculated based on the material flow and residence time, ensuring that titanium dioxide and the coating agent can fully react in each coating tank. It can ensure that titanium dioxide can fully contact with the coating agent in each reaction stage, thereby forming a uniform coating layer. The tank volume calculated by the above formula is 50-200m smaller than that of the traditional process. 3 The volume of the tank is larger, and stirring, temperature control and pH adjustment in a smaller tank are more accurate and uniform to ensure that the materials can fully react.

[0065] The coating agent flow rate is calculated according to the following formula:

[0066]

[0067] Where: Q n is the flow rate of the nth coating agent, C0 is the initial concentration of titanium dioxide slurry, X n % is the mass fraction of the coating, C n is the coating agent concentration.

[0068] In order to make the structure simple, reliable and easy to assemble, the preferred embodiment adopted by the present invention is that a heat exchanger 17 is provided between different coating agent processes for temperature regulation. When performing a multi-layer coating process, the temperature required by different coating processes is different. The heat exchanger 17 can be set to adjust the temperature of the material entering the next coating process.

[0069] S3: Real-time monitoring of the pH value and temperature of the titanium dioxide slurry in each level of coating tanks, and dynamic control by adjusting the pH regulator flow and steam flow;

[0070] S4: The material then flows to the terminal pH adjustment multi-stage tank group, and the coated titanium dioxide slurry is adjusted to the terminal pH. The material then completes the coating and is input into the storage tank to wait for the next unit operation. In order to make the structure simple, reliable, and easy to assemble, the preferred embodiment adopted by the present invention is that the terminal pH adjustment multi-stage tank group is a 2-4 stage continuous feeding reaction tank, such as Figure 1-Figure 3 As shown, the material and pH regulator enter continuously from the top of the first-level pH tank and stay in the first-level pH regulating tank. After a certain time, it is continuously discharged from the bottom of the first-level pH tank and continuously input from the bottom of the second-level pH adjustment tank, and stays in the second-level pH adjustment tank. After a certain time, it is continuously discharged from the top of the secondary pH tank and input from the bottom of the tertiary pH adjustment tank, where it stays. After a certain period of time, it is continuously discharged from the top of the three-stage pH tank.

[0071] The volume calculation formula of the terminal pH adjustment multi-stage tank group is:

[0072]

[0073] Where: Q is the total flow rate of the coating material, unit is L / h; It is the residence time of the material in the pH adjustment tank of stage c, in h.

[0074] By connecting multiple pH adjustment tanks in series and controlling the different residence times in each tank, the pH value of titanium dioxide can be adjusted gradually and accurately, thereby ensuring the stability of pH changes during the coating process.

[0075] Since titanium dioxide is prone to photocatalysis and unstable performance when exposed to acid and alkali, it is often necessary to include one or more layers of other materials on the surface of titanium dioxide particles to protect and improve its performance. In order to increase the single production capacity, the existing technology often stirs and coats in a large coating tank. The volume of the coating tank is usually designed to be 50-200m 3 , it is easy to form a velocity gradient dead zone in a large coating tank. For example, the area close to the stirring paddle can be fully stirred, and the flow rate decreases away from the stirring end. It is difficult for the titanium dioxide slurry in this part to fully react, resulting in uneven contact between the titanium dioxide particles and the coating agent, and the coefficient of variation (CV value) of the coating layer thickness is as high as 10%-15%; In this technical solution, the titanium dioxide slurry, desalted water, and steam are continuously input into a dynamic mixing tank for preliminary dilution and heating, and then the titanium dioxide slurry is passed into a multi-stage series coating tank group for coating, and each multi-stage series coating tank group is coated. Containing m stirred tank coating tanks connected in series and with a volume gradually increasing with the flow direction of the slurry, the titanium dioxide slurry in this technical solution reacts multiple times in multiple coating tanks instead of reacting once in the same large coating tank. The first-stage coating tank of each multi-stage series coating tank group can play a preliminary mixing role and fully react in the subsequent coating tanks. This staged and graded coating method effectively avoids the dead zone problem caused by a single large-volume coating tank, ensuring that the titanium dioxide particles can evenly contact the coating agent, thereby achieving higher coating uniformity and reducing the CV value.

[0076] The commonly used processing technology in the prior art is a single batch intermittent coating mode, that is, according to each coating stage, the corresponding coating agent is added, and the pH and temperature are adjusted. After the reaction is sufficient, the next coating agent is added and the reaction is continued. The complete process of a single batch takes more than 12 hours. If a multi-component composite coating is used, the total time can be extended to more than 24 hours, and the production efficiency is low. In this technical solution, continuous coating is performed through multiple connected tank groups instead of multiple coatings in the same tank. Therefore, the titanium dioxide slurry can be continuously introduced and reacted in the multi-stage series coating tank group. The coating process can carry out continuous production to reduce waiting time and thus improve production efficiency; at the same time, the volume of the coating tanks in series in each multi-stage coating tank group gradually increases with the flow direction, so that the residence time of the titanium dioxide slurry in the smaller coating tank is shorter, and the reaction time in the larger coating tank is longer, shortening the overall material backmixing and material short-circuiting, making the residence time distribution closer to the plug flow (PFR), ensuring that the titanium dioxide slurry is fully stirred in the small coating tank and stays longer in the larger coating tank for full reaction, avoiding the backmixing situation of the traditional process.

[0077] Through the above-mentioned setup and real-time monitoring of the pH and temperature of the titanium dioxide slurry in each level of coating tanks, and dynamic control by adjusting the pH regulator flow and steam flow, combined with precise temperature control under sufficient reaction and stirring, it is possible to ensure that the titanium dioxide produced by the above process has high stability. The existing single-batch intermittent coating mode requires cleaning the reaction tank each time it switches, resulting in 5%-8% residual raw material loss. In this technical solution, through continuous production, the material in each tank group is kept in a uniform state, which can reduce the frequency of cleaning to a certain extent and thus reduce waste.

[0078] When using zirconium aluminum coating, the specific steps are as follows:

[0079] S1: Medium titanium dioxide is coated with zirconium aluminum. The frosted titanium dioxide slurry can be from sulfuric acid process titanium dioxide or chloride process titanium dioxide. Its initial concentration C0 is 350-550g / L. The concentration of titanium dioxide slurry before coating C t The concentration of the coating agent is 250-350 g / L, and the number of coating agents is 3.

[0080] S2: The first coating agent is a zirconium-based coating agent, which can be zirconium sulfate, zirconium oxychloride, etc. The concentration C1 is 0.1%-1.5%, the pH control range is 2-4, and the residence time of the first coating agent in the first tank 2 is The residence time of the first coating agent in the secondary tank 3 is 0.1-0.3h The residence time of the first coating agent in the third tank is 0.2-0.4h 0.4-0.6h;

[0081] The second coating agent is aluminum coating agent, which can be aluminum sulfate, aluminum chloride, sodium aluminate, etc., with a concentration of C2 of 0.5%-1.5%, a pH control range of 3-5, and a residence time of the second coating agent in the first tank 5. The residence time of the second coating agent in the secondary tank 6 is 0.3-0.5h The residence time of the second coating agent in the third tank 7 is 0.5-0.7h 0.9-1.1h;

[0082] The third coating agent is an aluminum coating agent, which uses sodium metaaluminate, potassium metaaluminate, etc. The concentration C3 is 0.5%-1.5%, the pH control range is 8-10, and the residence time of the third coating agent in the first tank 8 is 2 hours. The residence time of the third coating agent in the secondary tank 9 is 0.3-0.5h The residence time of the third coating agent in the third tank is 0.5-0.7h. 0.9-1.1h;

[0083] S3: The real-time temperature range of the slurry during the coating process of each coating tank and the terminal pH adjustment tank is 60℃-70℃, and steam is used for heating;

[0084] S4: Terminal pH control range 6-8, terminal pH adjustment first-stage tank 14 residence time 0.3-0.5h, terminal pH adjustment secondary tank 15 residence time The residence time of the terminal pH adjustment tertiary tank is 0.5-0.7h. 0.9-1.1h; the residence time t of dynamic mixing tank 1 d 0.4-0.6h.

[0085] When using silicon aluminum coating, the specific steps are as follows:

[0086] S1: The titanium dioxide is coated with silicon-aluminum film. The frosted titanium dioxide slurry can be from sulfuric acid process titanium dioxide or chloride process titanium dioxide. Its initial concentration C0 is 350-550g / L; the concentration of titanium dioxide slurry before coating C t is 250-350g / L; the number of coating agents is 2.

[0087] S2: The first coating agent is a silicon-based coating agent, such as sodium silicate, orthosilicic acid, etc., with a concentration C1 of 0.5%-1.5%. The residence time of the first coating agent in the first tank 2 is The residence time of the first coating agent in the secondary tank 3 is 0.1-0.3h The residence time of the first coating agent in the third tank is 0.2-0.4h 0.4-0.6h;

[0088] The material then flows to the process pH adjustment multi-stage tank. In the process pH adjustment process, the pH adjuster used is dilute hydrochloric acid with a concentration of 5%-30%. The pH control range is 3.5-5. The residence time of the material in the process pH adjustment first-stage tank 11 is The residence time of the process pH adjustment secondary tank 12 is 0.4-0.6h The pH of the process is adjusted to the residence time of the third tank 13, which is 0.7-0.9h. 0.9-1.1h.

[0089] The second coating agent used is aluminum coating agent, which can be aluminum sulfate, aluminum chloride, sodium aluminate, etc. The concentration C2 is 1.5%-3.5%, the pH control range is 3-5, and the residence time of the second coating agent in the first tank is 5. The residence time of the second coating agent in the secondary tank 6 is 0.4-0.6h The residence time of the second coating agent in the third tank 7 is 0.7-0.8h 0.9-1.1h.

[0090] S3: The real-time slurry temperature range of the dynamic mixing tank 1, the first coating multi-stage tank, and the process pH adjustment multi-stage tank is 80°C-90°C; all are heated by steam; the real-time slurry temperature range of the first coating multi-stage tank and the terminal pH adjustment multi-stage tank is 60°C-70°C; a heat exchanger 17 is used between the process pH adjustment third-stage tank 13 and the second coating agent first-stage tank 5 for cooling;

[0091] S4: Terminal pH control range 6-8, terminal pH adjustment first-stage tank 14 residence time 0.3-0.5h, terminal pH adjustment secondary tank 15 residence time The residence time of the terminal pH adjustment tertiary tank is 0.5-0.7h. 0.9-1.1h; the residence time t of dynamic mixing tank 1 d 0.4-0.6h.

[0092] Example 1:

[0093] S1: This embodiment adopts Figure 1 、 Figure 2 、 Figure 3 、 Figure 4 The multi-stage continuous stirred tank coating tank shown in the figure continuously coats the frosted titanium dioxide, wherein the dynamic mixing tank 1 has a volume of 5m 3 The volumes of the first coating agent first-level tank 2, the first coating agent second-level tank 3 and the first coating agent third-level tank 4 are 2m 3 , 3m 3 , 5m 3 The volumes of the second coating agent first-level tank 5, the second coating agent second-level tank 6 and the second coating agent third-level tank 7 are 5m 3 , 8m 3 、10m 3 The volume of the third coating agent first-level tank 8, the third coating agent second-level tank 9 and the third coating agent third-level tank 10 are 5m 3 , 8m 3 、10m 3 The volume of the terminal pH adjustment first-stage tank 14, the terminal pH adjustment second-stage tank 15 and the terminal pH adjustment third-stage tank 16 are 5m 3 , 8m 3 、10m 3 , the specific steps are as follows:

[0094] S2: In this embodiment, titanium dioxide is coated with zirconium-aluminum film, and the designed production capacity is 50 tons / day. First, the frosted titanium dioxide slurry, high-temperature steam and desalted water are continuously fed into the dynamic mixing tank 1, and are fully mixed in the dynamic mixing tank 1. Then, the titanium dioxide slurry is mixed from the bottom of the dynamic mixing tank 1 according to the pressure. Figure 1The first coating agent is continuously output to the first coating agent first tank 2, the first coating agent second tank 3 and the first coating agent third tank 4 in series order. After completing the first coating process, Figure 2 The second coating agent first-stage tank 5, the second coating agent second-stage tank 6 and the second coating agent third-stage tank 7 are continuously passed through in series order. After the second coating process is completed, the second coating agent is continuously passed through in series order. Figure 3 The product passes through the third coating agent primary tank 8, the third coating agent secondary tank 9 and the third coating agent tertiary tank 10 in series sequence to complete the third coating process.

[0095] S2.1: Dynamic mixing tank 1 process:

[0096] After frosting, the titanium dioxide slurry is 500g / L, the flow rate Q0 is 4200L / h, and the desalted water flow rate Q w =2800L / h, steam flow Q v =700kg / h, residence time t0 of dynamic mixing tank 1 = 0.5h, temperature control range is 60-65℃;

[0097] S2.2: First coating process (zirconium coating):

[0098] Coating agent type: zirconyl chloride, coating concentration X1% = 0.35%, Q1 = 7.4L / h, pH regulator is 10% hydrochloric acid, pH control range is 2.5-3.5, the three-stage tank residence time is: The temperature control range is 60-65℃;

[0099] S2.3: Second coating process (acid aluminum coating):

[0100] Coating agent type: sodium metaaluminate, coating concentration X2% = 1.15%, Q1 = 24.2L / h, pH regulator is 10% hydrochloric acid, pH control range is 4.0-4.5, the three-stage tank residence time is: The temperature control range is 60-65℃;

[0101] S2.4: The third coating process (alkali aluminum coating):

[0102] Coating agent type: sodium metaaluminate, coating concentration X3% = 1.35%, Q1 = 17L / h, pH regulator is 10% hydrochloric acid, pH control range is 9.5-10, the three-stage tank residence time is: The temperature control range is 60-65℃.

[0103] S3: Real-time monitoring of the pH value and temperature of the titanium dioxide slurry in each level of coating tanks, and dynamic control by adjusting the pH regulator flow and steam flow.

[0104] S4: According to Figure 4The pH regulator is 10% hydrochloric acid, and the pH control range is 7.0-7.5. The residence time of the three-stage tank is as follows: The temperature is controlled in the range of 60-65℃ to complete the final coating.

[0105] Example 2

[0106] S1: This embodiment adopts Figure 1 、 Figure 5 、 Figure 6 、 Figure 4 The multi-stage continuous stirred tank coating tank shown in the figure continuously coats the frosted titanium dioxide, wherein the dynamic mixing tank 1 has a volume of 5m 3 The volumes of the first coating agent first-level tank 2, the first coating agent second-level tank 3 and the first coating agent third-level tank 4 are 2m 3 , 3m 3 , 5m 3 The volumes of the second coating agent first-level tank 5, the second coating agent second-level tank 6 and the second coating agent third-level tank 7 are 5m 3 , 8m 3 、10m 3 The volumes of process pH adjustment first-stage tank 11, process pH adjustment second-stage tank 12 and process pH adjustment third-stage tank 13 are 5m 3 , 8m 3 、10m 3 The volume of the terminal pH adjustment first-stage tank 14, the terminal pH adjustment second-stage tank 15 and the terminal pH adjustment third-stage tank 16 are 5m 3 , 8m 3 、10m 3 ;

[0107] S2: In this embodiment, titanium dioxide is coated with silicon-aluminum film, and the designed production capacity is 40 tons / day. First, the frosted titanium dioxide slurry, high-temperature steam and desalted water are continuously input into the dynamic mixing tank 1, and are fully mixed in the dynamic mixing tank 1. Then, the titanium dioxide slurry is mixed from the bottom of the dynamic mixing tank 1 according to the pressure. Figure 1 The first coating agent is continuously output to the first coating agent first tank 2, the first coating agent second tank 3 and the first coating agent third tank 4 in series order. After completing the first coating process, Figure 5 The series sequence continuously passes through the heat exchanger 17, the process pH adjustment first tank 11, the process pH adjustment second tank 12 and the process pH adjustment third tank 13. After the process pH adjustment is completed, the Figure 2 The second coating agent passes through the second coating agent primary tank 5, the second coating agent secondary tank 6 and the second coating agent tertiary tank 7 in series sequence to complete the second coating process.

[0108] S2.1: Dynamic mixing tank 1 process:

[0109] After frosting, the titanium dioxide slurry is 450g / L, the flow rate Q0 is 4000L / h, and the desalted water flow rate Q w =1000L / h, steam flow Q v =600kg / h, residence time t0 of dynamic mixing tank 1 = 0.5h, temperature control range is 80-85℃;

[0110] S2.2: First coating process (silicon coating):

[0111] Coating agent type: sodium silicate, coating concentration X1% = 1.1%, Q1 = 19.8 L / h, only pH is monitored, no pH regulator is added, and the residence time of the three-stage tank is: The temperature control range is 80-85℃;

[0112] S2.3: Process pH control technology:

[0113] The pH regulator is 10% hydrochloric acid, the pH control range is 4.0-4.5, and the residence time of the three-stage tank is: The temperature control range is 80-65℃;

[0114] S2.4: Second coating process (acid aluminum coating):

[0115] Coating agent type: sodium metaaluminate, concentration X2% = 3.0%, Q2 = 54L / h, pH regulator is 10% hydrochloric acid, pH control range is 4.0-4.5, the three-stage tank residence time is: The temperature control range is 60-65℃.

[0116] S3: Real-time monitoring of the pH value and temperature of the titanium dioxide slurry in each level of coating tanks, and dynamic control by adjusting the pH regulator flow and steam flow.

[0117] S4: According to Figure 4 The pH regulator is 10% sodium hydroxide, and the pH control range is 6.5-7.0. The residence time of the three-stage tank is as follows: The temperature is controlled in the range of 60-65℃ to complete the final coating. The titanium dioxide TEM of the continuous silicon-aluminum coating is as follows: Figure 7 .

[0118] Comparative Example 1

[0119] An intermittent silicon-aluminum coating process is used: the sand-milled slurry is poured into a coating tank, the slurry concentration is adjusted to 250-350 g / L with desalted water, and heated to 50-60°C; a quantitative zirconium coating agent is added, and the reaction is carried out for 30-60 minutes at a pH of 2.5-3.5 and a stirring rate of 100-200 rpm; the first aluminum source is added, the pH is adjusted to 4.5-5.5, and the reaction is carried out for 1-2 hours; the second aluminum source (such as sodium metaaluminate) is added, the pH is adjusted to 8.5-9.5, and the reaction is carried out for 2-3 hours; the pH is finally adjusted to 6.5-7.5 and the reaction is carried out. After the coating is completed, the process is transferred to the next step. The TEM results of titanium dioxide obtained through the above process are as follows: Figure 8 shown.

[0120] It can be seen from the above images that the above-mentioned embodiments of the present invention achieve the following technical effects: compared with the existing technology, the method provided by this application has good coating uniformity, is fully wrapped on the surface of titanium dioxide particles, has small quality differences between batches, and has high continuous production efficiency.

[0121] The above are only embodiments of the present invention, and common knowledge such as the specific technical solutions and / or characteristics in the solutions are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A method for continuous coating of titanium dioxide, characterized by: The following steps are involved: S1: Obtain various production parameters; S2: The pretreated titanium dioxide slurry flows sequentially through n multi-stage series coating tank groups corresponding to n types of coating agents, each multi-stage series coating tank group comprises m coating tanks connected in series and having a stirred tank, the volume of which gradually increases with the flow direction of the slurry; S3: Monitor the pH value and temperature of the titanium dioxide slurry in each coating tank, and dynamically control it by adjusting the pH regulator flow and steam flow; S4: The material then enters the terminal pH adjustment multi-stage tank group to adjust the coated titanium dioxide slurry to the terminal pH. The material completes the coating and waits for the next unit operation.

2. The method for continuous coating of titanium dioxide according to claim 1, wherein: The volume of the coated tank of each multi-stage series coated tank group in S2 satisfies the following formula: Where: n is the number of the nth coating agent, m is the number of the coating tank of the nth coating agent and mth grade; Where: The volume of the mth-level coating tank of the nth type of coating, in m 3 ; Q0 is the flow rate of titanium dioxide slurry after sand grinding, unit is L / h; Q w is the desalted water flow rate, in L / h; Q v is the steam mass flow rate, in kg / h; ρ is the density of water, in kg / L; Q n is the flow rate of the nth coating agent, in L / h; q n is the flow rate of the nth coating pH regulator, in L / h; It is the flow time in the tank of m-level of the n-th coating, in hours.

3. The method for continuous coating of titanium dioxide according to claim 1, characterized in that: When the titanium dioxide slurry processed in the previous step in S2 enters the next multi-stage series coating tank group, the titanium dioxide slurry enters from the top of the first-stage coating tank of the n-th coating tank group. After being discharged from the bottom of the first-stage coating tank of the n-th coating tank group, the titanium dioxide slurry is input from the bottom of the second-stage coating tank of the n-th coating tank group and discharged from the top of the tank until it is discharged from the top of the m-th coating tank of the n-th coating tank group.

4. The method for continuous coating of titanium dioxide according to claim 1, wherein: Coating agent flow rate Q n Calculated according to the following formula: Where: Q n is the flow rate of the nth coating agent, C0 is the initial concentration of titanium dioxide slurry, X n % is the mass fraction of the coating, C n is the coating agent concentration.

5. The method for continuous coating of titanium dioxide according to claim 1, characterized in that: There is also a process pH adjustment multi-stage tank between the multi-stage series coating tank groups. The process pH adjustment multi-stage tank includes c pH adjustment tanks connected in series and whose volumes gradually increase with the slurry flow direction.

6. The method for continuous coating of titanium dioxide according to claim 1, characterized in that: The volume calculation formula of the terminal pH adjustment multi-stage tank group is: Where: Q is the total flow rate of the coating material, unit is L / h; It is the residence time of the material in the pH adjustment tank of stage c, in h.

7. The method for continuous coating of titanium dioxide according to claim 1, characterized in that: There is also a heat exchanger (17) between the multi-stage series-connected coating tank groups for temperature regulation.

8. The method for continuous coating of titanium dioxide according to claim 1, characterized in that: S2 includes three coating agents, the first coating agent is a zirconium-based compound with a concentration of 0.1%-1.5%, the second coating agent is an aluminum coating agent with a concentration of 0.5%-1.5%, and the third coating agent is an aluminum coating agent with a concentration of 0.5%-1.5%. The three multi-stage series coating tanks all include three coating tanks. The pH control range of the multi-stage series coating tank corresponding to the first coating agent is 2-4, the pH control range of the multi-stage series coating tank corresponding to the second coating agent is 3-5, and the pH control range of the multi-stage series coating tank corresponding to the third coating agent is 8-10.

9. The method for continuous coating of titanium dioxide according to claim 5, characterized in that: S2 includes three coating agents, the first coating agent is a silicon-based coating agent with a concentration of 0.1%-1.5%, the second coating agent is an aluminum coating agent with a concentration of 1.5%-3.5%, and the two multi-stage series coating tanks each include three coating tanks. The pH control range of the multi-stage series coating tank corresponding to the first coating agent is 3.5-5, and the pH control range of the multi-stage series coating tank corresponding to the second coating agent is 3-5.

10. The method for continuous coating of titanium dioxide according to claim 9, characterized in that: The real-time temperature range of the slurry in the multi-stage series coating tank group corresponding to the first coating agent and the process pH adjustment multi-stage tank is 80°C-90°C; the real-time temperature range of the slurry in the multi-stage series coating tank group corresponding to the first coating agent and the terminal pH adjustment multi-stage tank group is 60°C-70°C; a heat exchanger (17) is used between the process pH adjustment multi-stage tank and the multi-stage series coating tank group corresponding to the second coating agent for cooling.

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