A Soxhlet extraction process for preparing low-crystallinity TiO 2 and by-product ammonium sulfate

Abstract

The present invention discloses a Soxhlet extraction process for preparing low-crystallinity TiO2 and by-producing ammonium sulfate. Using inexpensive intermediate metatitanic acid (TiO2·xH2O·ySO3) in sulfuric acid process titanium dioxide production as the titanium source, ammonia water as the sulfur leaching agent, the Soxhlet extraction method is used to neutralize and separate the entrained sulfur in industrial metatitanic acid, and then low-crystallinity TiO2 is obtained by low-temperature calcination and dehydration. This low-crystallinity TiO2 has a loose crystal structure, which is more conducive to the inorganic titanium source requirements of materials such as titanium lithium batteries, titanium lithium ion sieves, and potassium titanate whiskers. This process can synchronize the operations of ammonia-sulfur neutralization, entrained sulfur leaching, and product ammonium sulfate separation, greatly reducing the calcination temperature for the conversion of metatitanic acid to TiO2, thus saving thermal energy. At the same time, ammonium sulfate can be by-produced and there is theoretically no pollutant emission.

Description

Technical Field

[0001] The present invention belongs to the field of extraction, and particularly relates to a Soxhlet extraction process for preparing low-crystallinity TiO 2 and by-product ammonium sulfate. Background Art

[0002] Titanium-oxygen-containing materials are new high-tech materials with wide uses, important values and scientific and technological prospects, such as titanium-based whiskers, titanium-lithium electrodes, titanium lithium ion sieves and other materials. The synthesis of titanium-based whiskers usually consists of "sintering - ion exchange - secondary heat treatment". For example, TiO 2 and K 2 CO 3 generate K 2 Ti 4 O 9 through high-temperature solid-phase reaction. After the hydration process, part or all of the potassium ions are exchanged in water or acid solution, and after secondary heat treatment, various potassium titanate whisker materials can be prepared respectively. Spinel-type lithium titanate (Li 4 Ti 5 O 12 ) is a "zero-strain" material with advantages such as stable charge-discharge voltage platform, excellent cycling performance, and low cost, and is a very important electrode material in the lithium-ion battery industry. Titanium lithium ion sieve has a high saturated exchange capacity and cycling stability for lithium ions. Its preparation mainly involves appropriately treating the precursor with an eluent. The most common precursors for titanium lithium ion sieve are Li 2 TiO 3 (metatitanic acid type) and Li 4 Ti 5 O 12 (spinel type). Currently, one of the important methods for industrial production of such titanium-containing materials is the high-temperature solid-phase synthesis method, which has the advantages of low equipment requirements, simple process operation, and low cost. This method mostly uses pigment-type anatase TiO 2 , rutile TiO 2 in the current titanium dioxide industry as the titanium source raw materials.

[0003] Currently in the chemical industry, sulfuric acid process titanium white is an important source of large-scale and industrial pigment-type titanium dioxide. The intermediate product of this process is metatitanic acid (TiO 2 ·xH 2 O·ySO 3 ), which is the precipitate formed by the hydrolysis reaction of titanium oxysulfate in the "black titanium liquid" (a viscous aqueous solution composed of titanium oxysulfate, ferrous sulfate, free sulfuric acid, etc.), and can be considered as amorphous TiO 2 doped with "entrapped sulfur" and a small amount of anatase-type TiO 2Hydrate. After the metatitanic acid is washed to remove acid and iron, it is dehydrated at about 200-600 °C during the calcination process, and sulfur decomposition gradually occurs at about 600-850 °C. The TiO 2 crystal structure transformation is as follows: metatitanic acid → amorphous TiO 2 → anatase TiO 2 → rutile TiO 2 . In fact, the current TiO 2 production is mainly oriented towards pigment performance, that is, titanium dioxide type TiO 2 , and a high-crystallinity anatase or higher crystal structure must be required to exhibit excellent pigment performance. Moreover, the current process must be carried out at a high temperature of about 800 °C or above to realize the "entrained sulfur" in metatitanic acid to decompose and overflow in the form of SO 3 or SO 2 gas. Amorphous or low-crystallinity TiO 2 does not have pigment performance, but it can fully meet the titanium source requirements of materials such as titanium lithium batteries, titanium lithium ion sieves, and potassium titanate whiskers, and the loose crystal structure is more conducive to the high-temperature solid-phase reaction synthesis of such titanium materials. Summary of the Invention

[0004] The present invention uses the low-cost intermediate metatitanic acid in the sulfuric acid process titanium dioxide industry as the titanium source and ammonia water as the sulfur leaching agent, and uses the Soxhlet extraction method to neutralize, leach, and separate the entrained sulfur in industrial metatitanic acid, and then obtains low-crystallinity TiO through low-temperature calcination dehydration 2 , and ammonium sulfate can be by-produced at the same time. This low-crystallinity TiO 2 product is different from the current anatase-type and rutile-type titanium dioxide-based TiO 2 oriented towards pigment performance, and has a loose crystal structure, which is more conducive to the inorganic titanium source requirements of materials such as titanium lithium batteries, titanium lithium ion sieves, and potassium titanate whiskers; this process can realize the synchronous operation of ammonia-sulfur neutralization, entrained sulfur leaching, and product ammonium sulfate separation; greatly reduce the calcination temperature of the metatitanic acid → TiO 2 transformation, thus saving heat energy; and ammonium sulfate can be by-produced, and there is theoretically no pollutant emission.

[0005] The present invention is realized through the following technical solutions:

[0006] A Soxhlet extraction process for preparing low-crystallinity TiO 2 and by-producing ammonium sulfate, comprising the following steps:

[0007] (1) Take the intermediate metatitanic acid from the "second washing" section in the production of sulfuric acid process titanium dioxide and wash it again, and control the Fe ion concentration in the washing filtrate ≤ 10 ppm; dry the washed metatitanic acid at 105 °C to a powdery state without obvious moisture; this process can remove a small amount of free sulfuric acid, but it is difficult to remove the "entrained sulfur".

[0008] (2) Add 50 g of metatitanic acid powder into the filter paper cylinder of the Soxhlet extractor. Divide 300 g of ammonia water (mass fraction 20%) into two parts. Slowly add one part into the Soxhlet extractor to submerge the metatitanic acid powder, but the liquid level should be lower than the top of the siphon tube. Add the remaining ammonia water into the flask of the Soxhlet extractor.

[0009] (3) Heat under reflux for 6 hours;

[0010] During this process, the ammonia water evaporates, condenses and drips onto the metatitanic acid material. The metatitanic acid is mixed with sulfur and NH 3 to undergo a neutralization reaction to form ammonium sulfate, which is "stripped" from the metatitanic acid "skeleton", that is, the leaching process of sulfur-containing impurities.

[0011] TiO 2 ·xH 2 O·ySO 3 + NH 3 ·nH 2 O → TiO 2 ·zH 2 O + (NH 4 ) 2 SO 4 + tH 2 O (Equation 1)

[0012] When the liquid level of ammonia water in the extractor is higher than the siphon tube, the product ammonium sulfate is carried and sucked to the bottom of the kettle by the ammonia water. Since ammonium sulfate cannot evaporate, it is retained in the ammonia water at the bottom of the kettle, and the ammonia water continues to be evaporated, condensed and dripped onto the metatitanic acid to continue the reaction.

[0013] The above process is repeated cyclically, and the product ammonium sulfate is periodically removed from the reaction system, which greatly promotes the forward progress of the chemical reaction and the effectiveness of leaching sulfur-containing impurities from the metatitanic acid skeleton. This operation realizes the synchronous progress of the ammonia-sulfur neutralization reaction, the leaching of sulfur-containing impurities, and the separation of the product ammonium sulfate. The final products are the metatitanic acid wetted by ammonia water in the extractor and the ammonia water containing ammonium sulfate at the bottom of the kettle.

[0014] (4) Remove the metatitanic acid wetted by ammonia water and heat it to 105 °C. The ammonia water is evaporated, condensed and collected for reuse; calcine the dried metatitanic acid, and after cooling, it is the low-crystallinity TiO 2 product.

[0015] TiO 2 ·zH 2 O → TiO 2 (low crystallinity) + zH 2 O (Equation 2)

[0016] Furthermore, in step (1), vacuum filtration and washing are carried out with demineralized water at 40 °C to 50 °C, and the Fe ion concentration in the washing filtrate is controlled to be ≤ 10 ppm (determined by sulfosalicylic acid spectrophotometry).

[0017] Further, the dripping rate of the ammonia water reflux is 5 ml / min.

[0018] Further, the metatitanic acid after drying is calcined at 350 °C for 3 hours to dehydrate.

[0019] The beneficial effects of the present invention are as follows:

[0020] 1. The low-crystallinity TiO prepared by the present invention 2 is different from the currently mainstream anatase and rutile titanium dioxide-based TiO with pigment performance as the guide 2 , and has a looser crystal structure, which is more suitable for the inorganic titanium source requirements of materials such as titanium lithium batteries, titanium lithium ion sieves, and potassium titanate whiskers.

[0021] 2. For the anatase and rutile titanium dioxide-based TiO used in the above industry 2 , due to the desulfurization requirement, the calcination temperature is usually higher than 800 °C. After the metatitanic acid is leached with ammonia water to remove the included sulfur, the calcination temperature of the metatitanic acid can be reduced to 300-400 °C to complete dehydration and then become the product, greatly reducing the energy consumption.

[0022] 3. The Soxhlet extraction method of the present invention can simultaneously realize the neutralization reaction, the leaching of the included sulfur, and the separation of ammonium sulfate. Since ammonium sulfate is removed synchronously, the washing operation of the metatitanic acid filter cake after leaching the included sulfur is reduced, saving washing water.

[0023] 4. In the present invention, the included sulfur is immediately stripped from the "skeleton" of the metatitanic acid, and the product ammonium sulfate is periodically siphoned to the bottom of the kettle. The removal of the product ammonium sulfate promotes the forward progress of the chemical reaction and the sulfur leaching efficiency.

[0024] 5. The ammonia-containing tail gas in operations such as Soxhlet extraction and drying is absorbed by sulfuric acid, and the ammonia water in the bottom liquid of the kettle is combined and neutralized to ammonium sulfate. By vacuum distillation, by-product ammonium sulfate can be obtained, and theoretically no pollutants are generated. Description of the Drawings

[0025] Figure 1 is the Soxhlet process diagram for leaching the included sulfur in metatitanic acid with ammonia water;

[0026] Figure 2 is the TG analysis diagram of metatitanic acid before and after leaching the included sulfur;

[0027] Figure 3 is the XRD pattern of the bottom liquid crystal product;

[0028] Figure 4 Low-crystallinity TiO 2 Comparison diagram of the XRD patterns of the product. Specific Embodiments

[0029] To enable those skilled in the art to better understand the solution of the present invention and make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with embodiments.

[0030] Example 1

[0031] A Soxhlet extraction process for preparing low-crystallinity TiO 2 and by-product ammonium sulfate, comprising the following steps:

[0032] 1. Take the intermediate metatitanic acid from the "second washing" section in titanium dioxide production by the sulfuric acid method and wash it again. Vacuum filter and wash it with demineralized water at 40°C - 50°C, and control the Fe ion concentration in the washing filtrate ≤ 10 ppm (determined by sulfosalicylic acid spectrophotometry); dry the washed metatitanic acid at 105°C until it becomes a powdery state without obvious moisture.

[0033] 2. Add the above 50 g of metatitanic acid powder into the filter paper cylinder of the Soxhlet extractor. Divide 300 g of ammonia water (mass fraction 20%) into two parts. Slowly add one part into the Soxhlet extractor to submerge the metatitanic acid powder but the liquid level is lower than the top of the siphon tube, and add the remaining ammonia water into the flask of the Soxhlet extractor.

[0034] 3. Install a condensing reflux device, an anti-ammonia tail gas escape device (using 25% sulfuric acid as the absorption liquid) and the whole set of extraction devices. Control the heating to boiling and the reflux intensity, and the dripping rate of ammonia water reflux is about 5 ml / min, lasting for about 6 hours.

[0035] TiO 2 ·xH 2 O·ySO 3 + NH 3 ·nH 2 O → TiO 2 ·zH 2 O + (NH 4 ) 2 SO 4 + tH 2 O (Equation 1)

[0036] 4. Remove the ammonia water-soaked metatitanic acid and heat it to 105°C. The ammonia water is evaporated, condensed and collected for reuse. Calcinate the dried metatitanic acid at 350°C for 3 hours to dehydrate, and after cooling, it is the low-crystallinity TiO 2 product.

[0037] TiO 2 ·zH 2 O → TiO 2 (low crystallinity) + zH 2 O (Equation 2)

[0038] 5. Combine the recycled ammonia water and the bottom liquid of the kettle, and conduct the next operation of leaching sulfur impurities from metatitanic acid.

[0039] To verify the product situation, the following analysis and tests were carried out:

[0040] 1. Thermogravimetric analysis (TG) was carried out on the 105°C dried metatitanic acid with unextracted sulfur impurities and the 105°C dried metatitanic acid with extracted sulfur impurities. The results are as Figure 2 shown: The metatitanic acid without extracted sulfur impurities needs to be calcined at ~800°C to complete dehydration and sulfur decomposition. In the present invention, the calcination temperature can be reduced to ~350°C to obtain low-crystallinity titanium oxide.

[0041] 2. Without adding sulfuric acid for neutralization, directly evaporate and crystallize the loaded bottom liquid of the kettle, and conduct X-ray diffraction analysis (XRD) on the crystals. As Figure 3 shown, it is shown that the product is indeed (NH 4 ) 2 SO 4 crystals (PDF97-005-2383).

[0042] 3. Content analysis and comparison were carried out on the products obtained by directly calcining the metatitanic acid without extracted sulfur impurities at 350°C and the products obtained by calcining at 350°C after extracting sulfur impurities (the product of the present invention, low-crystallinity TiO 2 ). As shown in Table 1. It shows that the sulfur impurities in the original metatitanic acid are basically removed, the TiO 2 content of the product is greater than 99%, and the S content is less than 0.5‰ (GB / T 1706-2006 Titanium Dioxide Pigment - 7.1 Determination of Titanium Dioxide Content - Aluminum Reduction Method, Infrared Carbon-Sulfur Analyzer).

[0043] Table 1 TiO 2 and S contents of each material

[0044] Sample Calcination product of unextracted sulfur-included metatitanic acid at 350 °C Calcination of metatitanic acid after extracting sulfur-included matter (product of the present invention) at 350 °C <![CDATA[TiO 2 , %]]> 88.21 99.25 S,％ 1.791 0.042

[0045] 4. X-ray diffraction comparative analysis was carried out on the 105°C dried metatitanic acid with unextracted sulfur impurities, the low-crystallinity titanium oxide obtained by calcining at 350°C after extracting sulfur impurities (the product of the present invention), and the titanium oxide samples of anatase titanium dioxide on the market. As Figure 4 shown.

[0046] The low-crystallinity titanium oxide product prepared in the present invention ( Figure 4 , Sample No. 2) has X-ray diffraction peaks that are almost "bread-shaped peaks" and the diffraction intensity is slightly stronger than that of the intermediate product metatitanic acid, but much lower than that of the anatase TiO 2 products on the current market that are oriented towards pigment performance. It shows that the product prepared in the present invention is low-crystallinity TiO 2 , and may be amorphous TiO 2 doped with a small amount of anatase TiO 2 .

Claims

1. A Soxhlet extraction process for preparing low-crystallinity TiO 2 and by-product ammonium sulfate It is characterized in that it includes the following steps: (1) Take the intermediate metatitanic acid in the "second washing" section of sulfuric acid process titanium dioxide production and wash it again, controlling the Fe ion concentration in the washing filtrate to ≤ 10 ppm; Dry the washed metatitanic acid at 105 °C until it becomes powdery; (2) Add 50 g of metatitanic acid powder into the filter paper cylinder of the Soxhlet extractor. Divide 300 g of ammonia water into two parts. Slowly add one part into the Soxhlet extractor to submerge the metatitanic acid powder but the liquid level is lower than the top of the siphon tube, and add the remaining ammonia water into the flask of the Soxhlet extractor; (3) Heat and reflux for 6 hours; (4) Remove the ammonia-wetted metatitanic acid and heat it to 105 °C. The ammonia water is evaporated, condensed, collected, and reused. Calcinate the dried metatitanic acid at a low temperature, and after cooling, it is the low-crystallinity TiO 2 product.

2. A Soxhlet extraction process for preparing low-crystallinity TiO 2 and by-product ammonium sulfate It is characterized in that the dried metatitanic acid is calcined at 350 °C for 3 hours to dehydrate.

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