Titanium dioxide superfine grinding process with superheated steam as working medium

Abstract

The invention relates to the technical field of powder processing, and particularly discloses a titanium dioxide superfine grinding process with superheated steam as a working medium. Comprising the following steps: 1, mechanically crushing crude titanium dioxide to obtain a titanium dioxide primary product; 2, carrying out organic surface coating treatment on the titanium dioxide primary product, filtering, and carrying out flash evaporation drying to obtain a titanium dioxide base material; step 3, feeding the titanium dioxide base material to carry out superfine grinding, and meanwhile, carrying out primary organic treatment by using an organic treatment agent; step 4, discharging the material with qualified particle size from the flat jet mill; step 5, introducing qualified titanium dioxide into a cyclone separator, and adding the organic treating agent for the second time at the same time; and 6, separating the titanium dioxide product through a cyclone separator. The technical problems that in the prior art, an organic treating agent is added in a titanium dioxide airflow crushing process using superheated steam as a working medium, after titanium dioxide particles are coated with the organic treating agent, the particles still possibly break, the broken surfaces are not coated, and the coating completeness is insufficient are solved.

Description

TECHNICAL FIELD

[0001] The application relates to the powder processing technical field, and particularly discloses a titanium dioxide ultrafine grinding process taking superheated steam as a working medium. BACKGROUND

[0002] Titanium dioxide is also known as titanium dioxide (TiO2); titanium dioxide has three kinds of crystals: plate titanium type, sharp titanium type and rutile type. The plate titanium type is unstable and has no industrial utilization value, the sharp titanium type (Anatase) is simply referred to as A type and the rutile type (Rutile) is simply referred to as R type, both of which have stable crystal lattices and are important inorganic pigments and functional materials. Compared with other pigments, titanium dioxide has superior whiteness, tinting strength, hiding power, weather resistance, heat resistance and chemical stability. Therefore, the titanium dioxide is widely applied to the industries of coatings, plastics, papermaking, printing ink, chemical fiber, rubber and cosmetics.

[0003] But the production process of sulfuric acid method titanium dioxide contains calcination process, just calcined out of titanium dioxide is the aggregate or sintering of uneven particle size, can not be used as a pigment, need subsequent crushing treatment, the initial mechanical crushing of titanium dioxide particle size in D50 ≤ 20 μm (about 200 mesh), still can not reach the use of pigment requirements, therefore, after mechanical crushing, further need to further micronization of titanium dioxide to nano level of fine powder. Current titanium dioxide micronization mainly rely on two kinds of process route of air jet milling technology and mechanical grinding technology: mechanical grinding process: the mechanical extrusion of hammer type or ball mill equipment to achieve the crushing of materials, limited by the screen aperture and mechanical heating, the fineness is difficult to break through 10 μm, and the high temperature generated by mechanical friction is easy to cause the crystal transformation of rutile titanium dioxide; Therefore, gradually eliminated. Air jet milling process: using gas as working medium, the material is broken by high-speed airflow impact; Traditional use compressed air as working medium, but the material after compressed air crushing exists the problem of electrostatic agglomeration: the material particles are charged again under the action of compressed air, and the heterogeneous charge adsorption leads to the agglomeration of finished product, which affects the fineness and dispersibility. Therefore, the industry is to use superheated steam as working medium for crushing. Such as the patent with publication number: CN107115945B discloses a method for processing nano talc powder by high temperature and high pressure steam jet mill. It is to use high temperature and high pressure steam as working medium for crushing, which has very significant advantages in reducing energy consumption and processing crushing strength. And overcome the dehydration, drying and material easy agglomeration and other shortcomings of wet production of nano talc powder process. But titanium dioxide is too small, need to add organic treatment agent to improve its dispersibility, therefore, will add organic treatment agent in air jet milling process, usually, the organic treatment agent is accompanied by raw materials into the air jet milling equipment, but the titanium dioxide solid semi-finished powder itself exists agglomeration, mutual adhesion, how to ensure the full mixing of organic treatment agent and gas powder base has been a major technical problem faced by titanium dioxide factory, therefore, the industry appears to add organic treatment agent to superheated steam, using superheated steam to premix the organic treatment agent, such as the patent with publication number: CN106497146B discloses a method and equipment for air jet milling of titanium dioxide, which is also using superheated steam as working medium, in addition to using superheated steam as working medium to crush titanium dioxide, also set organic treatment agent feeding pipe on the superheated steam pipeline to realize the premixing of organic treatment agent and superheated steam, improve the uniform mixing degree of organic treatment agent and material in the air jet milling process.

[0004] Although the above patent technology can complete the titanium dioxide crushing and solve the mixing problem of the organic treatment agent and the semi-solid titanium dioxide, since the organic treatment agent is brought by the superheated steam, the organic treatment agent is quickly mixed with the titanium dioxide particles and coated on the titanium dioxide particles under the action of the steam pressure when the superheated steam just contacts the titanium dioxide particles, but since the titanium dioxide is still in the airflow crushing process, the particles can be further broken in the high-speed rotation process, and the new surface of the newly broken particles is not coated with the organic treatment agent, resulting in that the final titanium dioxide product is not fully coated with the organic treatment agent and the coating completeness is insufficient. SUMMARY

[0005] The purpose of the present application is to provide a titanium dioxide ultrafine crushing process using superheated steam as the working medium, so as to solve the technical problem that in the existing technology using superheated steam as the working medium, the titanium dioxide particles can be broken after being coated with the organic treatment agent, the new surface of the broken particles is not coated with the organic treatment agent, resulting in that the final titanium dioxide product is not fully coated with the organic treatment agent and the coating completeness is insufficient.

[0006] In order to solve the above problems, the technical scheme adopted by the present application is as follows: a titanium dioxide ultrafine crushing process using superheated steam as the working medium, comprising the following steps: Step 1, mechanically crushing the coarse titanium dioxide sinter obtained by rotary kiln sintering, the particle size of the mechanically crushed material is 15-20 μm, and a titanium dioxide primary product is obtained; Step 2, after the titanium dioxide primary product is subjected to organic surface coating treatment, filtration and flash drying, a titanium dioxide base material is obtained; Step 3, the titanium dioxide base material is sent into a flat airflow crusher for ultrafine crushing, and a metered amount of organic treatment agent is added for the first time through an organic treatment agent feeding pipe arranged on the superheated steam pipeline; the material crushed to a qualified particle size in the flat airflow crusher is guided into the center discharge pipe of the crusher by the centripetal airflow and discharged from the flat airflow crusher, and the coarse powder falls back to the crushing chamber under the centrifugal force for crushing; Step 4, the ultrafine particle size titanium dioxide of qualified particle size is guided into a powder cyclone separator through the discharge pipe, and a metered amount of organic treatment agent is added for the second time through an organic treatment agent feeding pipe arranged on the discharge pipe pipeline; Step 5, the steam and the titanium dioxide product are separated by the cyclone separator.

[0007] The beneficial effects of the present embodiment are as follows: 1. In existing titanium dioxide airflow milling processes using superheated steam as the working fluid, organic treatment agents are added. After the organic treatment agent coats the titanium dioxide particles, the particles may still break. The new surfaces of the broken particles do not have the organic treatment agent, resulting in incomplete coating and insufficient coating integrity on the final titanium dioxide product. This application divides the organic treatment machine into two stages. A metered amount of organic treatment agent is first added through an organic treatment agent feed pipe installed on the superheated steam pipeline, ensuring thorough mixing between the organic treatment machine and the titanium dioxide, completing the initial coating. After milling, a second metered amount of organic treatment agent is added through an organic treatment agent feed pipe installed on the discharge pipeline. Since most of the titanium dioxide particles are already coated with organic treatment agent after the first addition, the coating integrity is improved on the new cross-sections of the particles being milled further during the milling process.

[0008] Furthermore, the mechanical crushing in step 1 is a three-stage crushing process involving a jaw crusher, a roller mill, and a sand mill.

[0009] Furthermore, the discharge particle size of the jaw crusher is controlled to be less than or equal to 10 mm, and the discharge particle size of the roller mill is controlled to be 40–60 μm.

[0010] Furthermore, in step 2, the initial titanium dioxide product is subjected to an organic surface coating treatment using a wet precipitation coating process.

[0011] Furthermore, in step 2, the surface treatment agent for organically coating the titanium dioxide raw material is any one of aluminum sulfate, sodium aluminate, or sodium aluminate.

[0012] Furthermore, the first organic treatment agent added is a dispersible organic treatment agent that inhibits agglomeration, and the second organic treatment agent added is a hydrophobic organic treatment agent that performs final surface modification and improves flowability.

[0013] Furthermore, the dispersible organic treatment agent is any one of sodium polyacrylate, polycarboxylic acid ether superplasticizer, and modified phosphate ester, and the hydrophobic organic treatment agent is any one of aminopropyltriethoxysilane, glycidoxypropyltrimethoxysilane, and methacryloxypropyltrimethoxysilane.

[0014] Furthermore, the ratio of the first addition to the second addition of the organic treatment agent is 8:2.

[0015] Attached image description.

[0016] Figure 1 This is a process flow diagram of the present invention.

[0017] Detailed implementation method.

[0018] Further details are explained in the following by specific embodiments.

[0019] The embodiments are illustrated in the accompanying drawings, of which: Figure 1 Methodology: Step 1: Mechanical pulverization of coarse titanium dioxide sinter from rotary kiln sintering, the particle size of the mechanically pulverized material is 15-20 μm, to obtain titanium dioxide powder primary product; Step 2: After organic surface coating treatment, filtration and flash drying of the titanium dioxide powder primary product, a titanium dioxide powder base material is obtained; Step 3: The titanium dioxide powder base material is fed into a flat jet mill for ultrafine pulverization, and a metered amount of organic treatment agent is added for the first time through the organic treatment agent feeding pipe provided on the superheated steam pipeline; the material pulverized to the qualified particle size in the flat jet mill is guided into the center discharge pipe of the flat jet mill by the centripetal airflow and discharged from the flat jet mill, and the coarse powder falls back to the pulverization chamber under the centrifugal force for pulverization; Step 4: The ultrafine particle size titanium dioxide powder of qualified particle size is guided into the powder cyclone separator through the discharge pipe, and a metered amount of organic treatment agent is added for the second time through the organic treatment agent feeding pipe provided on the discharge pipe pipeline; Step 5: Steam and titanium dioxide powder product are separated by the cyclone separator.

[0020] Example 1 Step 1: Mechanical pulverization of coarse titanium dioxide sinter from rotary kiln sintering, the particle size of the mechanically pulverized material is 15-20 μm, to obtain titanium dioxide powder primary product; Raw material source and properties: coarse TiO2 sintered block from high-temperature sintering in a rotary kiln, in rutile form, with a small amount of unreacted TiCl4 residue, alkali metal salts (such as NaCl, MgCl2, and carbonaceous residues. Its physical form is a hard agglomerate with a Mohs hardness of about 6-7.

[0021] Mechanical pulverization includes three-stage pulverization, coarse titanium dioxide sinter is sequentially pulverized by a jaw crusher, a roller mill, and a sand mill to break the large coarse titanium dioxide sinter to an average particle size D50 = 18 μm titanium dioxide powder primary product (allowable fluctuation range 15-20 μm). The particle size distribution is required to be narrow to avoid excessive pulverization leading to increased energy consumption and subsequent dispersion difficulties.

[0022] ​Specific three-stage crushing adopts a "jaw crusher + roller mill + sand mill" three-stage crushing system: the sintered coarse titanium dioxide is put into the jaw crusher for crushing, and the particle size of the jaw crusher is controlled to be ≤10 mm; primary mechanical crushing is completed. The roller mill uses a high-pressure roller mill, and the coarse titanium dioxide after primary mechanical crushing is put in, and the controller output particle size is between 40-60 pm; secondary mechanical crushing is completed, and the coarse titanium dioxide after secondary mechanical crushing is already coarse titanium dioxide powder. The coarse titanium dioxide powder is configured into a 40-50 wt% suspension and put into the sand mill for tertiary mechanical crushing. When preparing, soft water (conductivity ≤10 ps / cm) is required; the zirconium beads of the sand mill are 1.8 mm, the filling rate is 85%, and the rotation speed is 3000 r / min; it is crushed to below 5 pm. The process monitoring: the online laser particle size instrument monitors the particle size of the three-stage outlet in real time; the automatic feedback control system is set to adjust the rotation speed, pressure, and grinding wheel frequency of the first two stages of mechanical grinding to maintain stable particle size output.

[0023] Step 2: Organic surface coating treatment → filtration → flash drying (base preparation).

[0024] (1) The titanium dioxide slurry after sand milling is directly subjected to the first coating treatment of the organic treatment agent to improve the dispersibility of the titanium dioxide; so as to be easily dispersed to a particle size of 5 pm in the air flow crushing and collide. The surface treatment agent includes any one of aluminum sulfate, sodium metaaluminate, and sodium aluminate; sodium metaaluminate is used in this embodiment, and the organic auxiliary agent is sodium polyacrylate (PAAS) or sodium hexametaphosphate; the coating process adopts wet precipitation coating: the titanium dioxide slurry after sand milling is a suspension with a concentration of 40-50 wt%, which can be directly subjected to the coating process; the titanium dioxide slurry is adjusted to 9.0-10.0 with ammonia water; sodium polyacrylate (PAAS) or sodium hexametaphosphate is added in an amount of 0.2-0.5%; the titanium dioxide in the titanium dioxide slurry is uniformly dispersed, and the coating precursor solution (sodium metaaluminate (5-10 wt%) and a precipitating agent (such as H2SO4 / NaOH) are added dropwise, the reaction time is 1.5-2.5 hours (key for densification of the film layer), and the stirring speed is 200-300 rpm (to avoid vortex-induced agglomeration.

[0025] (2) The filtration and dehydration are selected from a full-automatic compartment filter press (PP material filter plate, corrosion-resistant) or a disc vacuum filter; the filtration precision is ≤1 pm, and the moisture content of the filter cake is controlled to be 20-25%. The washing requirements are: multi-stage countercurrent washing (at least three times) to remove free Na⁺ and Cl⁻ ions; the washing endpoint standard is: conductivity <50 ps / cm (detection of the washing water).

[0026] (3) The selected rotary flash dryer (model XSG-1000 or above) is used for flash drying, the hot air temperature is 280-350℃, the inlet air speed is ≥25 m / s; the main shaft rotation speed is 200-400 rpm, the shear strength is controllable; the drying time is <30 seconds, to avoid local overheating causing crystal transformation or organic matter decomposition. The product index: the outlet moisture is ≤0.5 wt%; the agglomerates are fully broken, the D50 is not more than 1.5 times of the original slurry state.

[0027] After drying, the titanium dioxide base material is obtained. The "titanium dioxide base material" formed in this stage is a key intermediate for functional improvement in the entire process, and its surface chemical state directly affects the performance grade of the final product.

[0028] Step 3: Flat airflow crushing + real-time organic treatment agent injection (ultrafine crushing coupling functional modification).

[0034] The crushing principle of the flat airflow crusher: two high-speed jets collide to achieve particle-to-particle impact crushing; the particle motion trajectory is affected by centrifugal force and centripetal airflow: qualified fine powder (0.2-0.5μmm) is guided by the centripetal airflow to move to the center of the crusher and is sucked into the discharge pipe by the negative pressure in the discharge pipe; coarse particles are thrown to the outer wall by centrifugal force and fall back to continue crushing in the crusher, forming an internal circulation. Target particle size control: product D50 = 0.2-0.5μm, D90 ≤0.5μm (meeting the requirements of high-end rutile titanium dioxide for coatings).

[0030] The cavity material of the flat airflow crusher: ceramic coating or zirconia lining to prevent metal contamination; working pressure: 0.8-1.2MPa (overheated steam as working medium).

[0031] The organic treatment agent is added simultaneously during the crushing process, which is the first addition. A special metering pump + atomizing nozzle is installed on the overheated steam pipeline about 1 meter before entering the crushing chamber to continuously meter the addition of the organic additive; the first addition of the high-dispersion treatment agent to inhibit agglomeration should select polyacrylic acid sodium salt, polycarboxylic acid ether superplasticizer, modified phosphate, etc.; polyacrylic acid sodium salt is selected in this embodiment, and the addition amount is 0.3-1.0% of the mass of titanium dioxide. It is worth noting that since it is added to the overheated steam, high-boiling-point, thermally stable organic treatment agents should be selected.

[0032] The metering pump uses a high-precision gear pump, and the flow control precision is ±1%; the addition timing: starts synchronously with the start of the crushing and stops 1 minute before the end. The nozzle selects a gas-assisted two-fluid atomizing nozzle, and the droplet diameter is <50 pm. The mechanism of action: the newly broken surface has high surface energy, which is easy to adsorb organic molecules to form "in-situ coating"; inhibits the re-agglomeration of nanoparticles, improves the crushing efficiency (reduces energy consumption by 10-15%); forms a steric hindrance effect, which is beneficial to the later dispersion.

[0033] Studies have shown that the introduction of surfactants in jet milling can significantly reduce the absolute value of the Zeta potential of the powder, while increasing the repulsive potential barrier under the Hamaker constant, thereby achieving stable dispersion.

[0034] Step 4: Secondary dosing of the discharge path, and the qualified titanium dioxide product is obtained by separation.

[0035] The fine titanium dioxide particles crushed in the flat jet mill are sucked into the discharge pipe under the action of the centripetal airflow and the negative pressure of the discharge pipe, and are pumped into the cyclone separator.

[0036] The second organic treatment agent is injected on the discharge pipe line before reaching the cyclone separator. A second organic treatment agent inlet is provided about 0.5 m downstream of the central discharge pipe; the pipe is made of stainless steel 316L material, equipped with a T-shaped mixer to promote uniform mixing; a Venturi pipe section is installed before the feeding point to use negative pressure to assist the suction of the second added organic treatment agent. The second added organic treatment agent is aminopropyltriethoxysilane, epoxypropoxypropyltrimethoxysilane, methacryloyloxypropyltrimethoxysilane, etc., and in this embodiment, methacryloyloxypropyltrimethoxysilane is selected, the addition amount is 0.2-0.5% of titanium dioxide, and the microcrystalline wax emulsion is 0.1-0.3%. The addition method is: sprayed after pre-dilution into a 10% ethanol solution; reaction temperature condition: steam afterheat from crushing; contact time: ≥10 seconds, sufficient to complete the condensation reaction (Si-OR→ Si-O-Ti).

[0037] The original once-added organic treatment agent is divided into two times in this application, and there are many types of titanium dioxide organic treatment agents, which can be divided into two times according to the type, the first time in the inlet pipe line of the superheated steam, mainly adding auxiliary crushing, inhibiting agglomeration, and pre-coating dispersant; the second time in the pipe line of the discharge pipe line, mainly adding surface finishing, improving flowability, and moisture-proof hydrophobic agent (such as: silane).

[0038] Cyclone separator system design (gas-solid separation and energy recovery) system composition: two-stage series cyclone separator + bag dust collector; material: inner wall sprayed with polytetrafluoroethylene (PTFE) anti-sticking coating; separation efficiency: ≥99.5% for particles above 0.1 pm.

[0039] Steam treatment: exhaust gas contains trace dust and organic volatile matter; subsequent access to condenser (shell and tube, cooling water 15℃) to recover moisture and part of the organic solvent; tail gas is adsorbed by activated carbon or RTO incineration to meet the emission standard (in line with GB 31571-2015 standard).

[0040] Product collection: bottom star-shaped discharge valve connected to nitrogen-sealed screw conveyor, sent to ton bag packaging area; inert atmosphere operation throughout (O2<3%), to prevent dust explosion risk.

[0041] Example 2 Example 2 differs from Example 1 in that the organic treatment agent to be added is dispersed and hydrophobic pre-mixed into a composite treatment agent, added in two times, the ratio of the first addition amount to the second addition amount being 8:2.

[0042] The above is only an embodiment of the present application, and the common knowledge of specific structures and properties in the scheme is not described in detail. It should be noted that for those skilled in the art, without departing from the structure of the present application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the present application, which will not affect the effect and practicality of the patent. The protection scope claimed in this application should be subject to the content of its claims, and the specific implementation mode and the like recorded in the specification can be used to explain the content of the claims.

Claims

1. A titanium dioxide ultrafine grinding process using superheated steam as the working medium, characterized in that: The method comprises the following steps: ​ Step 1, mechanically crushing the coarse titanium dioxide sinter of rotary kiln sintering, the particle size of the mechanically crushed material being 15-20 μm, to obtain titanium dioxide powder primary product; Step 2, after organic surface coating treatment, filtration and flash drying of the titanium dioxide powder primary product, obtaining titanium dioxide powder base material; Step 3, feeding the titanium dioxide powder base material into a flat jet mill for ultrafine crushing, and adding a metered amount of organic treatment agent for the first time through an organic treatment agent feeding pipe arranged on the superheated steam pipeline; the material crushed to a qualified particle size in the flat jet mill is guided into the center discharge pipe of the flat jet mill by centripetal airflow and discharged from the flat jet mill, and the coarse powder falls back to the crushing chamber under the centrifugal force for crushing; Step 4, the ultrafine particle size titanium dioxide powder of qualified particle size is guided into a powder cyclone separator through the discharge pipe, and a metered amount of organic treatment agent is added for the second time through an organic treatment agent feeding pipe arranged on the discharge pipe pipeline; steam and titanium dioxide powder product are separated by the cyclone separator.

2. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 1, characterized in that: The mechanical crushing in step 1 is three-stage crushing through a jaw crusher, a roller mill and a sand mill in sequence.

3. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 2, characterized in that: The discharge particle size of the jaw crusher is controlled to be less than or equal to 10 mm, and the discharge particle size of the roller mill is controlled to be 40-60 μm.

4. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 1, characterized in that: The organic surface coating treatment of the titanium dioxide powder primary product in step 2 adopts a wet precipitation coating process.

5. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 4, characterized in that: The surface treatment agent for the organic surface coating treatment of the titanium dioxide powder primary product in step 2 is any one of aluminum sulfate, sodium metaaluminate and sodium aluminate.

6. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 1, characterized in that: The first added organic treatment agent is a dispersion type organic treatment agent for inhibiting agglomeration, and the second added organic treatment agent is a hydrophobic type organic treatment agent for surface finishing, improving flowability.

7. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 6, characterized in that: The dispersion type organic treatment agent is any one of polyacrylic acid sodium salt, polycarboxylic acid ether superplasticizer and modified phosphate ester, and the hydrophobic type organic treatment agent is any one of aminopropyl triethoxysilane, epoxypropoxypropyl trimethoxysilane and methacryloxypropyl trimethoxysilane.

8. The titanium dioxide ultrafine pulverization process with superheated steam as the working medium according to claim 1, characterized in that: The ratio of the first added amount of the organic treatment agent to the second added amount is 8:2.

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