Method for removing phosgene in titanium tetrachloride

Abstract

The invention belongs to the field of titanium chemical industry, and particularly relates to a method for removing phosgene in titanium tetrachloride, which comprises the following steps: a chlorination process: mixing a titanium-containing oxide and a carbonaceous reducing agent, pouring into a chlorination reaction furnace, heating to 700-725 DEG C, and carrying out chlorination reaction to obtain crude titanium tetrachloride; a rectification process: introducing the crude titanium tetrachloride into a rectification tower for rectification, and controlling the ratio of the distillate of the rectification tower to the feed amount to be 30-50% to obtain fine titanium tetrachloride; stirring and heating, namely introducing the fine titanium tetrachloride into a stirring and heating tank, heating and stirring to remove phosgene, and controlling the heating temperature to be 20-25 DEG C and the stirring time to be 5-10 minutes to obtain a titanium tetrachloride product and tail gas; and a tail gas treatment process: enabling the tail gas to pass through an alkali liquor absorption tower to absorb residual phosgene. According to the method, phosgene in titanium tetrachloride is efficiently removed by controlling the chlorination reaction temperature, rectification parameters and heating and stirring parameters.

Description

Technical Field

[0001] The invention belongs to the field of titanium chemical industry, and particularly relates to a method for removing phosgene from titanium tetrachloride. Background Art

[0002] Phosgene, also known as carbonyl chloride, has a chemical formula of COCl2. It is a colorless gas that is highly toxic and has a smell similar to moldy hay or rotten fruit. Phosgene has a strong reactivity and can participate in a variety of organic synthesis reactions, such as being used to make polyurethane materials and polycarbonates. However, inhaling a certain amount of it can cause serious damage to the respiratory tract and endanger human health.

[0003] Titanium tetrachloride is an important intermediate carrier for the production of titanium sponge and titanium dioxide, which is mainly obtained by the reaction of chlorine and titanium oxide. During the production process, phosgene will be generated by adding carbonaceous reducing agents at high temperatures, and phosgene will enter the product titanium tetrachloride. If phosgene and other carbon-containing organic matter cannot be removed efficiently, it will be enriched in the metal titanium sponge product with a 4-fold content, resulting in an excessively high carbon content, which seriously affects the quality of the titanium sponge product.

[0004] Therefore, it is necessary to develop a method for efficiently removing phosgene from titanium tetrachloride. Summary of the invention

[0005] In view of this, the present invention proposes a method for removing phosgene from titanium tetrachloride, aiming to efficiently remove phosgene from titanium tetrachloride by controlling chlorination reaction temperature, distillation parameters and heating and stirring parameters.

[0006] In order to solve at least one of the above technical problems, the present invention adopts the following technical solution: According to the present invention, a method for removing phosgene from titanium tetrachloride is provided, comprising: a chlorination step, mixing titanium-containing oxide and a carbonaceous reducing agent, pouring the mixture into a chlorination reaction furnace, heating to 700-725° C. for chlorination reaction, and obtaining crude titanium tetrachloride; a rectification step, introducing the crude titanium tetrachloride into a rectification tower for rectification, controlling the ratio of the distillate of the rectification tower to the feed amount to be 30%-50%, and obtaining refined titanium tetrachloride; a stirring and heating step, introducing the refined titanium tetrachloride into a stirring and heating tank for heating and stirring to remove phosgene, controlling the heating temperature to be 20-25° C., and the stirring time to be 5-10 minutes, and obtaining a titanium tetrachloride product and tail gas; and a tail gas treatment step, passing the tail gas through an alkali liquid absorption tower to absorb residual phosgene.

[0007] According to one embodiment of the present invention, in the chlorination process, the heating temperature is controlled to be 720°C.

[0008] According to one embodiment of the present invention, the chlorination process comprises: separating and condensing the gas generated by the chlorination reaction to obtain liquid crude titanium tetrachloride.

[0009] According to one embodiment of the present invention, in the distillation process, the ratio of the distillate from the distillation tower to the feed amount is controlled to be 50%.

[0010] According to one embodiment of the present invention, in the distillation process, the reflux pipe temperature is controlled to be 75-90°C.

[0011] According to one embodiment of the present invention, in the distillation process, the tower top pressure is controlled to be less than 2 kPa.

[0012] According to one embodiment of the present invention, in the stirring and heating step, the stirring time is controlled to be 10 minutes.

[0013] According to one embodiment of the present invention, in the tail gas treatment process, NaOH alkaline solution is used to treat the tail gas to generate sodium chloride and sodium carbonate.

[0014] According to one embodiment of the present invention, the sodium chloride generated in the tail gas treatment process is dried and then returned to the chlorination furnace for use as molten salt.

[0015] According to one embodiment of the present invention, the sodium carbonate generated in the tail gas treatment process is acidified and dried before being returned to the chlorination furnace for use as molten salt.

[0016] By adopting the above technical solution, the present invention has at least one of the following advantages compared with the prior art: 1. According to the method of the present invention, phosgene in titanium tetrachloride can be efficiently removed by controlling the chlorination reaction temperature, distillation parameters and heating and stirring parameters, without modifying existing equipment, with low cost and convenient operation; 2. According to the method of the present invention, the sodium chloride and sodium carbonate obtained after the tail gas treatment are processed and then returned to the chlorination furnace for use as molten salt, thereby realizing the reuse of resources; 3. In the titanium tetrachloride product prepared by the method of the present invention, the titanium tetrachloride content is higher than 99.99%, and the phosgene content is controlled below 0.0001%, which is effectively removed. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other embodiments can be obtained based on these drawings without paying creative work.

[0018] Figure 1 A flow chart of a method for removing phosgene from titanium tetrachloride according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0019] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0020] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are only illustrative. Although only a few embodiments are described in detail in the present invention, it is easy for those skilled in the art to appreciate that multiple modifications are feasible without actually departing from the teaching of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other replacements, modifications, changes and deletions may be made to the design, operating conditions and parameters of the following exemplary embodiments.

[0021] In the process of chlorine and titanium oxide reacting to produce titanium tetrachloride, if there is a carbonaceous reducing agent and certain specific conditions in the system, phosgene will be produced. For example, in the reaction of preparing titanium tetrachloride with chlorine and titanium oxide as the main reactants, carbonaceous reducing agents such as petroleum coke are usually added. Under high temperature conditions, chlorine first reacts with carbon to produce chlorinated carbon intermediates, such as CCl4, CCl3, etc. Under the influence of high temperature and catalyst conditions, these chlorinated carbon intermediates will further react with chlorine or other active substances, resulting in the breaking and rearrangement of the carbon-chlorine bond, thereby producing phosgene. For example, CCl4 can decompose at high temperature to produce phosgene and chlorine. The reaction equation is CCl4→COCl2+Cl2.

[0022] According to the present invention, a method for removing phosgene in the process of preparing titanium tetrachloride is provided, such as Figure 1 As shown, the overall process includes the following steps: In the chlorination process, titanium oxide and a carbonaceous reducing agent are mixed and poured into a chlorination reaction furnace, heated to 700-725°C for chlorination reaction to obtain crude titanium tetrachloride; In a distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, and the ratio of the distillate to the feed amount of the distillation tower is controlled to be 30% to 50% to obtain refined titanium tetrachloride; In the stirring and heating process, the refined titanium tetrachloride is introduced into the stirring and heating tank for heating and stirring to remove phosgene, the heating temperature is controlled at 20-25°C, the stirring time is 5-10 minutes, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through an alkaline solution absorption tower to absorb residual phosgene.

[0023] In the chlorination process, the raw materials must first be pretreated, that is, titanium oxide and a suitable reducing agent must be fully mixed to ensure that the two can be in good contact and synergistic reaction in the subsequent reaction. Titanium dioxide is usually used as a titanium source, and petroleum coke is used as a carbonaceous reducing agent. The carbonaceous reducing agent can play a reducing role in the reaction and help achieve the conversion of titanium oxide to titanium tetrachloride. Secondly, the pretreated raw materials are put into a special chlorination reaction furnace and heated to a high temperature. Chlorine is then introduced into the furnace. Under high temperature conditions, chlorine and titanium oxide undergo a complex chemical reaction under the action of a carbonaceous reducing agent. Taking titanium dioxide as an example, the main reaction equation is TiO2+2C+2Cl2→TiCl4+2CO, generating titanium tetrachloride gas and by-product gases such as carbon monoxide and phosgene. In the prior art, the chlorination reaction temperature is generally around 800°C~1100°C. However, the higher the chlorination reaction temperature, the phosgene content in titanium tetrachloride will also increase. The present invention effectively inhibits the generation of phosgene and further reduces the phosgene content by controlling the temperature of the molten salt chlorination furnace to be less than 725°C, for example, 700-725°C. In a preferred embodiment of the present invention, the temperature of the molten salt chlorination furnace is controlled at 720°C.

[0024] In the embodiment of the present invention, in the chlorination process, the gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride. Specifically, after the mixed gas generated by the reaction is discharged from the chlorination reaction furnace, it will first enter the preliminary separation device, and by using the differences in physical properties such as boiling points of different gases, some solid particle impurities and some high-boiling-point, easily condensable impurity gases carried therein are removed by cooling, filtering, etc., so that the gas entering the distillation process later is relatively pure.

[0025] The distillation process is to separate and purify titanium tetrachloride by utilizing the obvious difference in boiling point between titanium tetrachloride and other impurities such as a small amount of unreacted chlorine, hydrogen chloride, other metal chlorides and by-products of the reaction. Specifically, the crude titanium tetrachloride that has been initially separated is introduced into a distillation tower, where the mixed gas is partially vaporized and partially condensed multiple times in the tower by controlling the temperature, pressure and other conditions. Titanium tetrachloride with a low boiling point will preferentially vaporize and move upward, and after repeated separation and purification on multiple layers of tower plates, it will eventually be extracted from the top of the tower in a relatively high-purity gaseous form, and then condensed into liquid titanium tetrachloride for collection; while impurities with higher boiling points will remain at the bottom of the tower or be separated and discharged at a suitable location to achieve the refinement of titanium tetrachloride. In the distillation process, the ratio of the reflux flow rate to the product flow rate extracted from the top of the tower is called the reflux ratio. In the embodiment of the present invention, controlling the reflux ratio to 30% to 50% allows the gas and liquid to fully contact and exchange substances on the tower plate for multiple times, and can effectively leave trace impurities such as other metal chlorides that have not reacted completely and a small amount of hydrogen chloride in the titanium tetrachloride in the liquid phase through repeated distillation and separation processes, and discharge them with the bottom effluent, thereby significantly improving the purity of the refined titanium tetrachloride product extracted from the top of the tower. At the same time, the reflux pipe temperature is controlled to 75 to 90°C to ensure that phosgene exists in the titanium tetrachloride in the form of gas phase. The top pressure of the tower is controlled to be less than 2kPa in conjunction with the distillation process, and the phosgene content in the product is stable; ensuring that the discharge path of gaseous organic impurities is unobstructed.

[0026] In the stirring and heating process, the refined titanium tetrachloride containing phosgene is introduced into the stirring and heating tank, a pipeline interface is opened on the upper part of the tank body, the tank body temperature is controlled at 20-25°C, and the stirring time is 5-10 minutes, preferably 10 minutes, to ensure that phosgene can be smoothly evaporated from the titanium tetrachloride to obtain titanium tetrachloride products and tail gas. Those skilled in the art can further process the refined titanium tetrachloride in this process according to actual working conditions, such as blending in the stirring and heating tank, adding specific additives, and other operations.

[0027] The tail gas discharged from the stirring and heating tank contains the unreacted chlorine gas discharged from the chlorination reaction furnace during the entire production process, the generated carbon dioxide, phosgene and other by-product gases, and a small amount of gas containing chlorine and acidic substances emitted from the distillation process and other links. The tail gas is passed through an alkali liquid absorption tower to absorb the residual phosgene. In an embodiment of the present invention, NaOH alkali liquid can be used to treat the tail gas. The tail gas is fully contacted with the sodium hydroxide solution, and a chemical reaction occurs: Cl2+2NaOH→NaCl+NaClO+H2O, COCl2+4NaOH=Na2CO3+2NaCl+2H2O, converting chlorine into harmless salt substances, such as sodium chloride and sodium carbonate. Further, the sodium chloride generated in the tail gas treatment process is dried and then returned to the chlorination furnace for use as molten salt, and the generated sodium carbonate is acidified and dried and then returned to the chlorination furnace for use as molten salt.

[0028] The following are specific embodiments of the method for removing phosgene from titanium tetrachloride according to the present invention and its specific process parameters.

[0029] Example 1 In the method for removing phosgene from titanium tetrachloride of this embodiment, the following steps are included: In the chlorination process, titanium dioxide and petroleum coke are mixed and poured into a chlorination reaction furnace, heated to 720°C for chlorination reaction, and the gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride; In the distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, the reflux ratio is controlled to be 50%, the reflux pipe temperature is controlled to be 80°C, and the tower top pressure is controlled to be 2kPa to obtain refined titanium tetrachloride; In the stirring and heating step, the refined titanium tetrachloride is introduced into the stirring and heating tank and heated and stirred to remove the phosgene, the heating temperature is controlled to be 25° C., the stirring time is 10 min, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through a NaOH alkaline solution absorption tower to absorb residual phosgene. The generated sodium chloride is dried and then returned to the chlorination furnace for use as molten salt. The generated sodium carbonate is acidified and dried and then returned to the chlorination furnace for use as molten salt. The titanium tetrachloride product obtained by using this embodiment has a titanium tetrachloride content of 99.99% and a phosgene content of 0.0001%.

[0030] Example 2 In the method for removing phosgene from titanium tetrachloride of this embodiment, the following steps are included: In the chlorination process, titanium dioxide and petroleum coke are mixed and poured into a chlorination reaction furnace, heated to 725°C for chlorination reaction, and the gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride; In the distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, the reflux ratio is controlled at 30%, the reflux pipe temperature is controlled at 90°C, and the tower top pressure is controlled at 1.5 kPa to obtain refined titanium tetrachloride; In the stirring and heating step, the refined titanium tetrachloride is introduced into the stirring and heating tank and heated and stirred to remove the phosgene, the heating temperature is controlled to be 25° C., the stirring time is 5 min, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through a NaOH alkaline solution absorption tower to absorb residual phosgene. The generated sodium chloride is dried and then returned to the chlorination furnace for use as molten salt. The generated sodium carbonate is acidified and dried and then returned to the chlorination furnace for use as molten salt. The titanium tetrachloride product obtained by using this embodiment has a titanium tetrachloride content of 99.98% and a phosgene content of 0.0012%.

[0031] Example 3 In the method for removing phosgene from titanium tetrachloride of this embodiment, the following steps are included: In the chlorination process, titanium dioxide and petroleum coke are mixed and poured into a chlorination reaction furnace, heated to 710°C for chlorination reaction, and the gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride; In the distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, the reflux ratio is controlled to be 40%, the reflux pipe temperature is controlled to be 75° C., and the tower top pressure is controlled to be 1.9 kPa to obtain refined titanium tetrachloride; In the stirring and heating step, the refined titanium tetrachloride is introduced into the stirring and heating tank and heated and stirred to remove the phosgene, the heating temperature is controlled to be 22° C., the stirring time is 8 min, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through a NaOH alkaline solution absorption tower to absorb residual phosgene. The generated sodium chloride is dried and then returned to the chlorination furnace for use as molten salt. The generated sodium carbonate is acidified and dried and then returned to the chlorination furnace for use as molten salt. The titanium tetrachloride product obtained by using this embodiment has a titanium tetrachloride content of 99.98% and a phosgene content of 0.0010%.

[0032] Example 4 In the method for removing phosgene from titanium tetrachloride of this embodiment, the following steps are included: In the chlorination process, titanium dioxide and petroleum coke are mixed and poured into a chlorination reaction furnace, heated to 710°C for chlorination reaction, and the gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride; In the distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, the reflux ratio is controlled to be 35, the reflux pipe temperature is controlled to be 85° C., and the tower top pressure is controlled to be 1.7 kPa to obtain refined titanium tetrachloride; In the stirring and heating step, the refined titanium tetrachloride is introduced into the stirring and heating tank and heated and stirred to remove the phosgene, the heating temperature is controlled to be 22° C., the stirring time is 7 minutes, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through a NaOH alkaline solution absorption tower to absorb residual phosgene. The generated sodium chloride is dried and then returned to the chlorination furnace for use as molten salt. The generated sodium carbonate is acidified and dried and then returned to the chlorination furnace for use as molten salt. The titanium tetrachloride product obtained by using this embodiment has a titanium tetrachloride content of 99.98% and a phosgene content of 0.0013%.

[0033] Example 5 In the method for removing phosgene from titanium tetrachloride of this embodiment, the following steps are included: In the chlorination process, titanium dioxide and petroleum coke are mixed and poured into a chlorination reaction furnace, heated to 715°C for chlorination reaction, and the gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride; In the distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, the reflux ratio is controlled to be 45, the reflux pipe temperature is controlled to be 90° C., and the tower top pressure is controlled to be 1.9 kPa to obtain refined titanium tetrachloride; In the stirring and heating step, the refined titanium tetrachloride is introduced into the stirring and heating tank and heated and stirred to remove the phosgene, the heating temperature is controlled to be 24° C., the stirring time is 6 minutes, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through a NaOH alkaline solution absorption tower to absorb residual phosgene. The generated sodium chloride is dried and then returned to the chlorination furnace for use as molten salt. The generated sodium carbonate is acidified and dried and then returned to the chlorination furnace for use as molten salt. The titanium tetrachloride product obtained by using this embodiment has a titanium tetrachloride content of 99.98% and a phosgene content of 0.0009%.

[0034] The experiments described in Examples 1-5 show that in the titanium tetrachloride product prepared by the method for removing phosgene from titanium tetrachloride of the present invention, the titanium tetrachloride content is higher than 99.98%, and the phosgene content is controlled below 0.0015%, and is effectively removed.

[0035] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0036] The above-mentioned embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application shall be subject to the attached claims.

Claims

1. A method for removing phosgene from titanium tetrachloride, characterized in that: include: In the chlorination process, the titanium-containing oxide is mixed with a carbonaceous reducing agent and poured into a chlorination reaction furnace, heated to 700-725°C for chlorination reaction to obtain crude titanium tetrachloride; In a distillation step, crude titanium tetrachloride is introduced into a distillation tower for distillation, and the ratio of the distillate to the feed amount of the distillation tower is controlled to be 30% to 50% to obtain refined titanium tetrachloride; In the stirring and heating process, the refined titanium tetrachloride is introduced into the stirring and heating tank for heating and stirring to remove phosgene, the heating temperature is controlled to be 20-25°C, the stirring time is 5-10 minutes, and the titanium tetrachloride product and tail gas are obtained; In the tail gas treatment process, the tail gas is passed through an alkaline solution absorption tower to absorb residual phosgene.

2. The method according to claim 1, characterized in that In the chlorination step, the heating temperature is controlled to be 720°C.

3. The method according to claim 1, characterized in that The chlorination process comprises: The gas generated by the chlorination reaction is initially separated by a separation device to obtain crude titanium tetrachloride.

4. The method according to claim 1, characterized in that In the distillation process, the ratio of the distillate from the distillation tower to the feed amount is controlled to be 50%.

5. The method according to claim 4, characterized in that In the distillation process, the reflux pipe temperature is controlled to be 75-90°C.

6. The method according to claim 5, characterized in that In the distillation step, the tower top pressure is controlled to be less than 2 kPa.

7. The method according to claim 1, characterized in that In the stirring and heating process, the stirring time is controlled to be 10 minutes.

8. The method according to claim 1, characterized in that: In the tail gas treatment process, NaOH alkali solution is used to treat the tail gas to generate sodium chloride and sodium carbonate.

9. The method according to claim 8, characterized in that The sodium chloride generated in the tail gas treatment process is dried and then returned to the chlorination furnace for use as molten salt.

10. The method according to claim 8, characterized in that The sodium carbonate generated in the tail gas treatment process is acidified and dried and then returned to the chlorination furnace for use as molten salt.

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