Pigment-level titanium dioxide and nano-level titanium dioxide combined preparation process, preparation system and nano-level titanium dioxide

Abstract

The invention discloses a pigment-level titanium dioxide and nano-level titanium dioxide combined preparation process, a preparation system and nano-level titanium dioxide. The combined preparation process comprises the following steps: carrying out filter pressing by a first plate-and-frame filter press to obtain a filter cake I of the pigment-level titanium dioxide; carrying out filter pressing on the slurry I of the first plate-and-frame filter press to obtain a filter cake II; pulping the filter cake II and adding a dispersing agent to obtain slurry II; grinding the slurry II until D50 is stable, and then separating to obtain slurry III; and drying the slurry III to obtain the nanoscale titanium dioxide powder. According to the present invention, the nanometer titanium dioxide is separated from the pigment-grade titanium dioxide through the manner of the filter pressing washing, the pulping, the grinding, the separation and the enrichment, such that the joint production of the pigment-grade titanium dioxide and the nanometer titanium dioxide is achieved while the nanometer titanium dioxide content in the pigment-grade titanium dioxide is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of titanium dioxide production, and in particular relates to a combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide, a preparation system and nano-grade titanium dioxide. Background Art

[0002] Nano titanium dioxide has a very high specific surface area, visible light transparency, ultraviolet light absorption capacity, catalytic activity, and a variety of mature surface modification processes. It is widely used in anti-UV materials, coatings, photocatalytic catalysts, self-cleaning glass, cosmetics, inks, food packaging materials, papermaking industry, aerospace industry, lithium batteries and other fields. It shows broad market prospects in the consumer goods market, environmental protection, and maintaining ecological balance, and has great practical significance for the sustainable development of my country's ecological environment protection.

[0003] Looking at the production of titanium dioxide at home and abroad, there are two main methods: sulfuric acid method and chlorination method. These two methods have significant differences in process flow, raw material requirements, energy consumption, environmental protection, etc.

[0004] Among them, the sulfuric acid method usually uses ilmenite or artificial rutile as raw materials. The raw materials are first crushed and reacted with concentrated sulfuric acid to generate a soluble titanyl sulfate solution at high temperature, which is then hydrolyzed to form a precipitate. After filtering, washing, calcining and other steps, titanium dioxide is finally obtained. The key indicators such as the hiding power of titanium dioxide produced by the conventional sulfuric acid process are often limited by the particle size distribution of titanium dioxide. However, it is usually difficult to achieve good control of its particle size distribution within the framework of the sulfuric acid process due to the complexity of the reaction conditions, the complexity of the precipitation and hydrolysis processes, crystal growth and aggregation, the multiple sources and instability of raw materials, environmental factors, etc. Summary of the invention

[0005] The inventors found that the particle size distribution width of titanium dioxide produced by sulfuric acid method is relatively wide, and the particle size uniformity of titanium dioxide particles is poor. Figure 1 The figure shows the SEM image of titanium dioxide produced by the sulfuric acid process. Titanium dioxide produced by the sulfuric acid process is mostly used as a pigment grade. However, its process results in the presence of titanium dioxide particles that are too large and too small in addition to the titanium dioxide particles of the target particle size. Figure 2 The figure shows the relationship between the particle size of titanium dioxide and the relative scattering power. It can be seen that the relative scattering power decreases sharply as the particle size decreases.

[0006] It is very difficult to solve this problem from the perspective of the synthesis of titanium dioxide powder produced by the sulfuric acid process. This is due to many factors, such as the long process flow of titanium dioxide powder produced by the sulfuric acid process, the high number of impurities in the raw materials, and the complex control. At present, the only thing that can be done in the industry is to separate some coarse particles after grinding and return them to the sand mill for re-grinding to reduce the proportion of coarse particles in the slurry. There is no effective means for fine particles, and in fact, fine particles are more harmful. On the other hand, during the three-wash process of the pigment-grade titanium dioxide production line, some finer particles are filtered through, and the filtrate is usually collected in the CN filter, and these particles are enriched and returned to the main line to increase the yield. The particle size of these particles is significantly finer, which has a great impact on the hiding power of pigment-grade titanium dioxide, but if they are not recycled, the main line yield will be significantly affected. There is currently no good solution.

[0007] The present application aims to solve the problem that the above-mentioned sulfuric acid titanium dioxide contains both nano-grade titanium dioxide particles and large-size titanium dioxide particles, which affects the hiding power of titanium dioxide, and the problem that the current method of separating large-size titanium dioxide particles and grinding leads to an increase in the content of nano-grade titanium dioxide particles, which further affects the hiding power of titanium dioxide. The present application proposes a combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide, a preparation system, and nano-grade titanium dioxide and the system. The specific technical solutions are as follows:

[0008] The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide includes the following steps:

[0009] The first plate and frame filter press filters and washes the raw material slurry to obtain a filter cake, the purpose of which is to remove excess salt in the incoming material;

[0010] Slurrying the filter cake and adding a dispersant to obtain slurry 2;

[0011] The slurry 2 is ground until the D50 reaches the target value stably and then separated to obtain slurry 3;

[0012] The slurry is dried to obtain nano-sized titanium dioxide powder.

[0013] Furthermore, when the filter cake is slurried, the solid content of the slurry is maintained at 30%-40% based on the mass of TiO2.

[0014] Furthermore, the amount of dispersant added when the filter cake is slurried is 3‰ to 2% of the mass of TiO2.

[0015] Furthermore, the dispersant is AMP-95, one or more combinations of phosphates, sodium silicate, polyethylene glycol, PAAS, and monoisopropanolamine.

[0016] Furthermore, the slurry is ground twice using multi-stage grinding, including at least using zirconium beads with a diameter of 0.8 to 1.0 mm for primary grinding and using zirconium beads with a diameter of 0.3 to 0.4 mm for final grinding.

[0017] Furthermore, the nano-sized titanium dioxide powder obtained after drying is subjected to air flow pulverization.

[0018] Furthermore, the nano-sized titanium dioxide powder obtained after drying is subjected to air flow pulverization and is coated with an organic treatment agent.

[0019] Furthermore, the organic treatment agent comprises a combination of one or more of trimethylolpropane, neopentyl glycol, diethylene glycol, pentaerythritol, stearic acid and its derivatives, polysiloxane and its derivatives, and an organic silicon coupling agent.

[0020] In a second aspect, the present application provides a system for the combined preparation of pigment-grade titanium dioxide and nano-grade titanium dioxide, wherein the combined preparation system uses the above-mentioned combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide, and the combined preparation system comprises:

[0021] A first plate-frame filter press, wherein the first plate-frame filter press is connected to a post-grinding position or a third-wash filtrate position of a pigment-grade titanium dioxide production line;

[0022] A pulping machine, the pulping machine is arranged at the rear section of the first plate-frame filter press, and is used to pulp the filter cake obtained by washing the first plate-frame filter press to obtain slurry 2;

[0023] A grinding device, which is arranged at the rear section of the pulping machine and is used to grind the second pulp;

[0024] A continuous separation device, which is arranged at the rear section of the grinding device and is used to separate the ground slurry 2;

[0025] A second plate-frame filter press, which is arranged at the rear section of the continuous separation device and is used to enrich the separated slurry 2 that has passed the test;

[0026] The drying device is arranged at the rear section of the second plate-frame filter press and is used for drying the filter cake in the second plate-frame filter press.

[0027] Furthermore, the liquid outlet of the second plate and frame filter press is connected to the liquid inlet of the first plate and frame filter press.

[0028] In a third aspect, the present application also provides a nano-scale titanium dioxide, which is prepared by the above-mentioned combined preparation process.

[0029] The beneficial effects of the present invention are as follows: the present application separates nano titanium dioxide from pigment-grade titanium dioxide by intercepting the filter cake obtained by the first plate and frame filter press arranged at the post-grinding position or the third-wash filtrate position of the titanium dioxide production line, washing by pressure filtration, pulping, grinding, separation and then enrichment, thereby realizing the joint production of pigment-grade titanium dioxide and nano titanium dioxide and reducing the content of nano titanium dioxide in pigment-grade titanium dioxide, which is greatly helpful for improving the hiding power of pigment-grade titanium dioxide and can increase the overall added value of titanium dioxide products. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Shown is the SEM image of sulfuric acid titanium dioxide;

[0031] Figure 2 The figure shows the relationship between the particle size of titanium dioxide and the relative scattering power;

[0032] Figure 3 Shown is a process flow chart for the combined preparation of pigment-grade titanium dioxide and nano-grade titanium dioxide;

[0033] Figure 4 Shown is a block diagram of a system for the combined preparation of pigment-grade titanium dioxide and nano-grade titanium dioxide;

[0034] Figure 5 Shown is a graph of particle size control of titanium dioxide of the examples. DETAILED DESCRIPTION

[0035] In order to make the purpose, technical solution and advantages of the embodiments of the present invention more clear, the technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments.

[0036] Example

[0037] Figure 3 The flowchart of the combined preparation process of pigment grade titanium dioxide and nano grade titanium dioxide is shown, and the preparation process includes the following steps:

[0038] S1. Pumping the raw material slurry into the first plate-frame filter press for filter pressing and washing to reduce the concentration of impurity ions and obtain a filter cake; the raw material slurry can be from multiple sources such as the overflow port of the cyclone after sand milling on the pigment-grade titanium dioxide main line, the filtrate of the third wash, and the recovered material of the CN filter;

[0039] S2, beating the washed filter cake to obtain slurry 2, maintaining the solid content of the slurry at 30%-40% based on the mass of TiO2;

[0040] S3, grinding the slurry 2 until D50 stably reaches the set target value and then pumping it into the separation equipment to obtain slurry 3; the set target value is a value of 30 to 100 nm, and the specific value is determined by the market demand for the particle size of nano titanium dioxide. The separation equipment separates the slurry below and above the target value;

[0041] S4, drying the slurry 3 to obtain nano-grade titanium dioxide;

[0042] S5. The dried material is subjected to gas-powder treatment, and the gas-powder can be organically treated according to product requirements to obtain organically treated nano-grade titanium dioxide.

[0043] In step S1, the filter pressing washing pressure is 0.09 MPa, and the filtrate is washed until the conductivity range of the filtrate is less than 200 μS / cm.

[0044] Step S3 involves two key processes, one is grinding and the other is separation.

[0045] The device involved in grinding is a sand mill commonly used in the industry. Currently, zirconium beads with a diameter of 1.0 to 1.2 mm are commonly used in the industry and can only be used for grinding pigment-grade particles. However, a multi-stage grinding method is designed in this application, which at least includes the use of zirconium beads with a diameter of 0.8 to 1.0 mm for primary grinding and the use of zirconium beads with a diameter of 0.3 to 0.4 mm for final grinding. Transition grinding can be added between the primary grinding and the final grinding according to actual production needs, using zirconium beads with diameters between 0.3 to 0.4 mm and 0.8 to 1.0 mm. The primary grinding is used to initially break up larger titanium dioxide agglomerates, eliminate the agglomeration tendency of titanium dioxide, and fully disperse the titanium dioxide to a degree close to monodispersity. The final grinding is used to grind to obtain nano-scale particles less than 100 nm.

[0046] The devices involved in separation are commonly used hydrocyclones, continuous centrifuges or other devices in the industry. In the process of sulfuric acid titanium dioxide, this type of separation device is usually used to separate coarse particles that are not fully ground in the sand mill, and return them to the sand mill for re-grinding. It is not used to separate fine particles or even nanoparticles. This is because, if it is to be used for nanoparticle separation, the premise is that the raw material slurry must be fully dispersed to a degree close to monodisperse, and the huge agglomeration tendency of nanoparticles must be overcome to maintain the stability of dispersion for a considerable period of time, which is a relatively difficult task. At present, the popular pulping and dispersion method of sulfuric acid titanium dioxide is that the nano-scale particles in the obtained slurry are not fully deagglomerated, and all exist in the form of agglomerates, so titanium dioxide companies can only separate coarse particles, but not fine particles.

[0047] In the present application, in step S2, the washed filter cake is slurried to obtain slurry 2 and a dispersant is added at the same time. The amount of dispersant added is 0.3-2% by mass of TiO2, and more preferably 0.8-1.8%. If too little dispersant is added, the dispersion effect is not good enough, and if too much dispersant is added, the dispersant cannot be adsorbed on the surface of titanium dioxide and is free in the water, thereby producing side effects.

[0048] The dispersant includes AMP-95, a combination of one or more of phosphates, sodium silicate, polyethylene glycol, PAAS, and monoisopropanolamine. The preferred combination is PAAS+AMP-95, PAAS+sodium silicate. After adding the dispersant for slurrying in step S2, combined with the multi-stage grinding in step S3, the stability of the nano-scale particles in the slurry to maintain monodispersion can be maintained for a long time in the separation process, and the nano-scale titanium dioxide particles with a particle size smaller than that of pigment-grade titanium dioxide can be separated.

[0049] In step S4, the drying temperature should generally be set at 90-105°C.

[0050] In addition, in some other embodiments, an organic treatment agent is added to the dried material while performing steam powdering to enhance some properties of titanium dioxide. The organic treatment agent comprises a combination of one or more of trimethylolpropane, neopentyl glycol, diethylene glycol, pentaerythritol, stearic acid and its derivatives, polysiloxane and its derivatives, and organosilicon coupling agent. The amount of the organic treatment agent added during steam powdering is 0.3-1% of the powder.

[0051] Figure 4 Shown is a block diagram of a system for the combined preparation of pigment-grade titanium dioxide and nano-grade titanium dioxide, which includes a first plate-frame filter press, a pulping machine, a grinding device, a continuous separation device, an online particle size detection device, a second plate-frame filter press, a drying device, and a jet mill.

[0052] The first plate and frame filter press is connected to the post-grinding position or the third-wash filtrate position of the pigment-grade titanium dioxide production line, and the filter cake produced by the first plate and frame filter press can be used as the raw material required for preparing nano titanium dioxide.

[0053] The pulping machine is arranged at the rear section of the first plate-frame filter press, and is used for pulping the filter cake obtained by hydraulic filtration and washing of the filter press of the first plate-frame filter press to obtain slurry 2.

[0054] The grinding device is arranged at the rear section of the beater and is used for grinding the second slurry.

[0055] The continuous separation device is arranged at the rear section of the grinding device, and is used to separate the ground slurry 2, and at the same time uses an online particle size detection device to detect the particle size. The slurry with qualified particle size is released, and the slurry with unqualified particle size is returned to the continuous separation device for renewal and re-separation.

[0056] The second plate and frame filter press is arranged at the rear section of the continuous separation device, and is used to enrich the separated slurry 2 that passes the test.

[0057] The drying equipment is arranged at the rear section of the second plate-frame filter press and is used for drying the filter cake in the second plate-frame filter press.

[0058] The air flow mill is arranged at the rear section of the drying equipment to further micronize the dried powder.

[0059] The above-mentioned continuous separation device adopts equipment with separation effect such as leaf filter, porous ceramic membrane, membrane separation, continuous centrifuge, etc.

[0060] The liquid outlet of the second plate and frame filter press is connected to the liquid inlet of the first plate and frame filter press. The filtrate produced by the second plate and frame filter press can be used as a substitute for the desalted water of the washing liquid of the first plate and frame filter press, and at the same time plays the function of recovering the nanoparticles filtered through the second plate and frame.

[0061] like Figure 5 As shown, in this embodiment, the following nano-grade titanium dioxide can be finally obtained, and the median diameter D50 is 63 nm.

[0062] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them.

Claims

1. A combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide, characterized in that: The steps include: The raw material slurry is filtered and washed by a first plate and frame filter press to obtain a filter cake; Slurrying the filter cake and adding a dispersant to obtain slurry 2; Grind slurry 2 until D50 is stable and then separate to obtain slurry 3; The slurry is dried to obtain nano-sized titanium dioxide powder.

2. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 1, characterized in that: When the filter cake is slurried, the solid content of the slurry is maintained at 30%-40% based on the mass of TiO2.

3. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 2, characterized in that: The amount of dispersant added when the filter cake is slurried is 3‰ to 2% of the mass of TiO2.

4. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 2, characterized in that: The dispersant is AMP-95, one or more combinations of phosphates, sodium silicate, polyethylene glycol, PAAS, and monoisopropanolamine.

5. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 1, characterized in that: The slurry is ground twice using multi-stage grinding, including at least using zirconium beads with a diameter of 0.8 to 1.0 mm for primary grinding and using zirconium beads with a diameter of 0.3 to 0.4 mm for final grinding.

6. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 1, characterized in that: The nano-sized titanium dioxide powder obtained after drying is subjected to air flow pulverization.

7. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 6, characterized in that: The nano-sized titanium dioxide powder obtained after drying is subjected to air flow pulverization and an organic treatment agent is added for coating.

8. The combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to claim 7, characterized in that: The organic treatment agent comprises a combination of one or more of trimethylolpropane, neopentyl glycol, diethylene glycol, pentaerythritol, stearic acid and its derivatives, polysiloxane and its derivatives, and an organic silicon coupling agent.

9. A system for the combined preparation of pigment-grade titanium dioxide and nano-grade titanium dioxide, characterized in that: The combined preparation system uses the combined preparation process of pigment-grade titanium dioxide and nano-grade titanium dioxide according to any one of claims 1 to 8, and the combined preparation system comprises: A first plate-frame filter press, wherein the first plate-frame filter press is connected to a post-grinding position or a third-wash filtrate position of a pigment-grade titanium dioxide production line; A pulping machine, the pulping machine is arranged at the rear section of the first plate-frame filter press, and is used to pulp the filter cake obtained by washing the first plate-frame filter press to obtain slurry 2; A grinding device, which is arranged at the rear section of the pulping machine and is used to grind the second pulp; A continuous separation device, which is arranged at the rear section of the grinding device and is used to separate the ground slurry 2; A second plate-frame filter press, which is arranged at the rear section of the continuous separation device and is used to enrich the separated slurry 2 that has passed the test; the liquid outlet of the second plate-frame filter press is connected to the liquid inlet of the first plate-frame filter press; The drying device is arranged at the rear section of the second plate-frame filter press and is used for drying the filter cake in the second plate-frame filter press.

10. Nano-scale titanium dioxide, characterized in that: The nano-scale titanium dioxide is prepared by the combined preparation process of pigment-grade titanium dioxide and nano-scale titanium dioxide as described in any one of claims 1 to 8.

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