Method for removing titanium tetrachloride impurity from crude vanadium oxychloride

Abstract

The invention relates to the field of preparation of high-purity products by a chlorination process, and discloses a method for removing titanium tetrachloride impurities from crude vanadium oxychloride. The method comprises the following steps: (1) stirring and mixing calcium sulfate hemihydrate whiskers serving as an impurity removal agent with vanadium oxychloride containing titanium tetrachloride impurities, and selectively adsorbing titanium tetrachloride by calcium sulfate hemihydrate; (2) filtering out the precipitate to obtain high-purity vanadium oxytrichloride; and (3) the impurity removal agent can be repeatedly used after being purged and activated by water vapor. The refining method provided by the invention has the advantages of mild reaction conditions, less loss of vanadium oxychloride, high product purity, high impurity removal efficiency, no introduction of secondary impurities, and simple impurity removal agent reactivation method.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of high-purity product preparation by chlorination method, in particular to a method for removing titanium tetrachloride impurities from crude vanadyl trichloride. BACKGROUND

[0002] As an important chemical raw material, vanadyl trichloride (VOC13) is widely used in catalysts for organic synthesis reactions, preparation of pharmaceutical intermediates, etc. High-purity vanadyl trichloride (purity ≥ 99.99 wt.%) can also be used for the preparation of high-purity vanadium pentoxide (V2O5, purity ≥ 99.99 wt.%), which is ultimately used for the production of electrolyte for large-scale energy storage devices, all-vanadium redox flow batteries.

[0003] High-purity VOC13 is generally prepared by carbon chlorination of vanadium-rich raw materials followed by further purification. The specific method is as follows: vanadium-rich raw materials (such as vanadium-containing waste catalysts, vanadium slag, etc.) are mixed with carbon sources such as petroleum coke, and then reacted with chlorine (Cl2) under certain conditions to obtain crude VOC13. The crude VOC13 contains a small amount of other chloride impurities, such as titanium tetrachloride (TiCl4), iron trichloride (FeCl3), aluminum trichloride (AlCl3), and silicon tetrachloride (SiCl4). Among them, chlorides with a large difference in boiling point from VOC13, such as FeCl3, AlCl3, and SiCl4, can be separated by distillation, while TiCl4 and other chlorides with a boiling point close to VOC13 cannot be directly removed by distillation, resulting in the inability to produce high-purity VOC13 products.

[0004] To solve this problem, the document "Selective hydrolysis of trace TiCl4 from VOCl3 for preparation of high purity V2O5, Separation and Purification Technology, 2017, 185: 196-201" proposes that a selective hydrolysis-distillation method can be used, that is, a certain amount of water is added to the crude VOCl3, heated to 80 ℃ and stirred for 15 min, and then distilled to remove TiCl4. Patent CN 202111566989.9 also uses this method to remove POCI3 impurities in crude VOCl3. However, in order to ensure complete removal of impurities, this method requires the addition of excess water mixed with VOCl3 product, which can easily cause loss of VOCl3. Patent CN 202011048310 proposes using a mixture of potassium chloride and cesium chloride as a decontaminant to complex and remove TiCl4 at a reaction temperature of 300-400 ℃, but the temperature required for gas phase reaction is high and energy consumption is large, on the other hand, chlorides have a certain solubility in VOCl3, which may cause secondary pollution to VOCl3. Therefore, a new removal technology with mild conditions, high efficiency, small vanadium loss, simple operation and no secondary pollution needs to be developed. SUMMARY

[0005] To solve the problems existing in the prior art, the present application provides a method for efficiently and selectively removing titanium tetrachloride from vanadyl trichloride using calcium sulfate hemihydrate as a decontaminant, which mainly comprises:

[0006] (1) Using calcium sulfate hemihydrate as a decontaminant, it is mixed with vanadyl trichloride containing titanium tetrachloride impurities, and the calcium sulfate hemihydrate selectively adsorbs titanium tetrachloride;

[0007] (2) After the precipitate is filtered out, high-purity vanadyl trichloride is obtained;

[0008] (3) The decontaminant can be reused after purging and water vapor activation.

[0009] Preferably, in step (1), the decontaminant is calcium sulfate hemihydrate (CaSO4·0.5H2O) in the form of whiskers. Calcium sulfate hemihydrate whisker is a single crystal fiber material with micron or nanometer size, which has a regular crystal structure, high aspect ratio and abundant surface active sites. The crystal water and sulfate ions in its structure can interact with TiCl4. Other forms (such as powder, granules) of calcium sulfate hemihydrate also have decontamination effect, but the whisker form has a larger reaction surface due to its special structure, so it has better efficiency.

[0010] Preferably, in step (1), the aspect ratio of the calcium sulfate hemihydrate whisker is selected to be 10 - 100.

[0011] Preferably, in step (1), the temperature of the mixing reaction is 60 ℃ to 80 ℃.

[0012] Preferably, in step (1), the time of the mixing reaction is 10 - 30 min.

[0013] Preferably, in step (1), the mass-volume ratio of the calcium sulfate hemihydrate to vanadyl trichloride liquid is (0.05 - 0.1) g : 1 mL.

[0014] Preferably, in step (3), the nitrogen purging temperature is 120 - 130 ℃.

[0015] Preferably, in step (3), the activating agent is water vapor.

[0016] Preferably, in step (3), the activation temperature is 130 - 150 ℃.

[0017] Preferably, in step (3), the activation pressure is 165 - 375 kPa.

[0018] Preferably, in step (3), the activation time is 0.5 - 1 h.

[0019] The basic principle of the present application is that the inventors found through a large number of experiments on various different crystal water-containing sulfates that calcium sulfate hemihydrate whiskers exhibit a much higher selective reaction / adsorption capacity for TiCl4 than for VOCl3. The possible mechanisms include: (1) TiCl4 has stronger Lewis acidity, which can hydrolyze and complex with the structural water or surface groups in calcium sulfate hemihydrate, generating stable titanium oxysulfate compounds immobilized on the surface, while VOCl3 has very low reactivity under these conditions, thereby achieving selective removal; (2) the unique crystal structure of calcium sulfate hemihydrate whiskers is more matched with the spatial configuration of TiCl4 molecules, thereby preferentially capturing TiCl4 molecules through adsorption; (3) the large specific surface area and abundant active sites of calcium sulfate hemihydrate whiskers provide sufficient reaction and adsorption interfaces.

[0020] The inventors found through experimental screening that calcium sulfate dihydrate, which is also a crystal water-containing calcium sulfate, exhibits more excellent selective reaction / adsorption capacity for TiCl4 than other crystal water-containing sulfates. However, compared with calcium sulfate hemihydrate whiskers, calcium sulfate dihydrate has poor stability, and its crystal water is more likely to be converted into free water, causing high vanadium loss rate. In addition, calcium sulfate dihydrate is in powder form, which is difficult to separate from chlorides after mixing, resulting in low filtration efficiency and also causing high vanadium loss rate.

[0021] Compared with the prior art, the refining method has the following advantages:

[0022] (1) The adsorption capacity of calcium sulfate hemihydrate on TiCl4 is much higher than that on VOCl3, the product yield is high, and the vanadium loss is small.

[0023] (2) Calcium sulfate hemihydrate is widely available and can be prepared from natural gypsum or industrial by-product gypsum. The by-product sodium chloride produced during the preparation process can be used as a chlor-alkali raw material.

[0024] (3) The impurity removal process is a simple solid-liquid mixing and separation process, without the need for complex rectification equipment and extremely high energy consumption.

[0025] (4) The impurity removal agent is an inorganic mineral material, which does not introduce new metal impurities, and the adsorbent can be regenerated and used multiple times. DETAILED DESCRIPTION

[0026] This part will combine examples to explain the specific implementation of the invention in detail.

[0027] Example 1 (intermittent stirring method)

[0028] (1) 0.5 grams of calcium sulfate hemihydrate whiskers (average diameter 1-5 μm, average length 50-100 μm) were weighed and placed in a conical flask with a stopper.

[0029] (2) 100 mL of industrial-grade VOCl3 liquid (initial TiCl4 content of 5300 ppm) was measured and added to the conical flask.

[0030] (3) The conical flask was sealed and then moved to a magnetic stirrer, and stirred at 70 ℃ and 300 rpm for 30 min.

[0031] (4) After the reaction was completed, vacuum filtration was performed through a microporous filter membrane to achieve solid-liquid separation.

[0032] (5) The filtrate (purified VOCl3) was collected and analyzed for Ti content using ICP-OES (inductively coupled plasma optical emission spectrometer).

[0033] (6) Two sets of parallel experiments were performed, and the results were averaged. The whiskers after adsorption and impurity removal were collected at 130 ℃ and purged with N2. The collected product was condensed and collected, and the mass of the collected product was calculated.

[0034] (7) The whiskers after adsorption and impurity removal were placed in a crystallization kettle and steam was introduced at a temperature of 130 ℃ and a pressure of 165 kPa for 1 h.

[0035] (8) The reactivated whiskers were repeated (1)-(6) steps to determine the VOCl3purity and to count the yield.

[0036] Example 2 (fixed bed adsorption method)

[0037] (1) The calcium sulfate hemihydrate whiskers (average diameter 1-5 μm, average length 50-100 μm) were filled into a glass adsorption column (diameter 1 cm, height 20 cm) to form an adsorption bed, and the bed was kept at 70 °C.

[0038] (2) 100 mL VOCl3liquid with an initial TiCl4content of 2400 ppm was continuously passed through the adsorption column at a flow rate of 2 mL / min.

[0039] (3) After 5 cycles, the purified VOCl3was collected, and the Ti content was analyzed by ICP-OES (inductively coupled plasma optical emission spectrometer).

[0040] (4) Two groups of parallel experiments were performed, and the results were averaged. N2was passed through the adsorption column at 130 °C to perform purging, and the VOCl3obtained by purging was collected by condensation, and the mass of the collected product was counted.

[0041] (5) The whiskers after adsorption removal of impurities were placed in a crystallization kettle, and water vapor was passed in at a temperature of 130 °C and a pressure of 165 kPa to stir and activate for 1 h.

[0042] (6) The reactivated whiskers were repeated (1)-(4) steps to determine the VOCl3purity and to count the yield.

[0043] Comparative Example 1 (calcium sulfate dihydrate as impurity removal agent)

[0044] (1) 0.5 grams of calcium sulfate dihydrate was weighed into a conical flask with a stopper.

[0045] (2) 100 mL of industrial-grade VOCl3liquid (analyzed to have an initial TiCl4content of 4700 ppm) was measured and added to the conical flask.

[0046] (3) The conical flask was sealed and then moved to a magnetic stirrer, and stirred at 300 rpm at 70 °C for 30 min.

[0047] (4) After the reaction was completed, vacuum filtration was performed by a microporous filter membrane to achieve solid-liquid separation.

[0048] (5) The filtrate (purified VOCl3) was collected, and the Ti content was analyzed by ICP-OES (inductively coupled plasma optical emission spectrometer).

[0049] (6) Two parallel experiments were conducted, and the results were averaged. The purified calcium sulfate dihydrate was purged with N2at 130 °C, and the collected VOCI3was condensed and collected. The mass of the collected product was calculated.

[0050] Comparative Example 2 (water as the impurity removal agent)

[0051] (1) 100 mL of industrial-grade VOCI3liquid (with an initial TiCl4content of 3600 ppm) was measured and added to a conical flask.

[0052] (2) Two times the required amount of distilled water for TiCl4hydrolysis was added to the conical flask. After sealing the conical flask, it was placed on a magnetic stirrer and stirred at 80 °C and 300 rpm for 30 min.

[0053] (3) After the reaction was completed, the mixed solution obtained by distillation at 130 °C was condensed (condensing medium temperature -10 ~ 20 °C) to obtain purified VOCI3. The weight was measured to calculate the vanadium loss rate.

[0054] (4) The Ti content was analyzed by ICP-OES (inductively coupled plasma emission spectrometer).

[0055] Comparative Example 3 (non-revived calcium sulfate whiskers as the impurity removal agent)

[0056] (1) The non-revived calcium sulfate dihydrate whiskers that had been adsorbed twice and purged were weighed and filled into a glass adsorption column (diameter 1 cm, height 20 cm) to form an adsorption bed. The bed was kept at 70 °C.

[0057] (2) 100 mL of VOCI3liquid with an initial TiCl4content of 3600 ppm was continuously passed through the adsorption column at a flow rate of 2 mL / min.

[0058] (3) After 5 cycles, the purified VOCI3was collected, and the Ti content was analyzed by ICP-OES (inductively coupled plasma emission spectrometer).

[0059] (4) Two parallel experiments were conducted, and the results were averaged. N2was purged in the adsorption column at 130 °C, and the collected VOCI3was condensed and collected. The mass of the collected product was calculated.

[0060] Table 1 Analysis of purified vanadous chloride product

[0061] No. VOCI3 content / wt. % TiCl4content / wt.% V loss rate / wt. % Example 1 (batch stirring method - fresh calcium sulphate hemi-hydrate whiskers) 99.995 0.005 0.56 Example 1 (batch stirring method - reactivated calcium sulphate hemi-hydrate whiskers) 99.992 0.008 0.75 Example 2 (fixed bed adsorption method - fresh calcium sulphate hemi-hydrate whiskers) 99.994 0.006 0.88 Example 2 (fixed bed adsorption method - reactivated calcium sulphate hemi-hydrate whiskers) 99.995 0.005 0.93 Comparative Example 1 (calcium sulphate di-hydrate) 99.951 0.049 2.53 Comparative Example 2 (water) 99.996 0.004 5.65 Comparative Example 3 (non-reactivated calcium sulphate whiskers) 99.865 0.135 0.23

[0062] As can be seen from the results of Table 1, the method of using the semi-hydrated calcium sulfate whisker as the impurity removing agent has good effect on removing impurities from the crude vanadyl trichloride, and high-purity vanadyl trichloride products with purity of more than 99.99wt.% can be obtained. The semi-hydrated calcium sulfate whisker after reviving after one adsorption still has relatively high adsorption level. The activity of the semi-hydrated calcium sulfate whisker without reviving is lost to some extent, so the impurity removing effect is reduced. Compared with using calcium sulfate dihydrate and water as the impurity removing agent, the V loss rate in the purification process is lower when using the semi-hydrated calcium sulfate as the impurity removing agent.

Claims

1. A process for removing titanium tetrachloride impurities from crude vanadyl trichloride, characterized by, The method comprises the following steps: (1) mixing calcium sulfate hemihydrate with vanadyl chloride as an impurity-removing agent, and the calcium sulfate hemihydrate selectively adsorbs titanium tetrachloride; (2) filtering out the precipitate to obtain high-purity vanadyl chloride; (3) the impurity-removing agent can be reused after nitrogen purging and activation of an activating agent.

2. The method of claim 1, wherein The content of titanium tetrachloride in the crude vanadyl chloride is 0.1-5.0 wt.%.

3. The method of claim 1, wherein The calcium sulfate hemihydrate in step (1) is calcium sulfate hemihydrate whiskers.

4. The method of claim 3, wherein The average diameter of the calcium sulfate hemihydrate whiskers is 0.1-10 μm, and the average length is 10-500 μm.

5. The method of claim 1, wherein The mixing mode in step (1) is stirring mixing or fixed-bed contact.

6. The method of claim 1, wherein The mixing temperature in step (1) is 50-100 ℃.

7. The method of claim 1, wherein The mixing time in step (1) is 10 min-1 h.

8. The method of claims 1 and 3, wherein The mass-volume ratio of the amount of the calcium sulfate hemihydrate to the vanadyl chloride liquid in step (1) is (0.01-0.1) g:1 mL.

9. The method of claim 1, wherein The nitrogen purging temperature in step (3) is 120-130 ℃.

10. The method of claim 1, wherein The activating agent in step (3) is water vapor.

11. The method according to claims 1 and 10, characterized in that The activation temperature in step (3) is 130-150 ℃.

12. The method of claims 1 and 10, wherein The activation pressure in step (3) is 165-375 kPa.

13. The method of claims 1, 10, 11, and 12, wherein The activation time in step (3) is 0.5-1 h.