A catalyst for preparing chlorine by catalytic oxidation of hydrogen chloride and a preparation method and application thereof

Abstract

The application discloses a catalyst for preparing chlorine by catalytic oxidation of hydrogen chloride, which comprises a titanium dioxide carrier and an active component distributed on the titanium dioxide carrier, wherein the active component is a ruthenium species particle, and a titanium oxide shell layer is uniformly wrapped on the surface of the ruthenium species particle. The application further discloses a preparation method of the catalyst, which comprises the following steps: adding Ru / TiO2 into an inducer solution, heating and stirring overnight, and drying the obtained precipitate to obtain Ru / TiO2-A, wherein the inducer is selected from one or more of melamine, urea and dopamine; and calcining the Ru / TiO2-A in a nitrogen atmosphere, an air atmosphere and an oxygen atmosphere in sequence to obtain the catalyst. The application further discloses application of the catalyst in catalytic oxidation of hydrogen chloride to prepare chlorine. The catalyst provided by the application effectively alleviates the problems of high-temperature agglomeration and poor stability of the active component ruthenium species, and exhibits more excellent catalytic performance and stability when applied in catalytic oxidation of hydrogen chloride to prepare chlorine.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, and in particular to a catalyst for the catalytic oxidation of hydrogen chloride to produce chlorine, its preparation method, and its application. Background Technology

[0002] The large amounts of hydrogen chloride produced annually by many industries, including polyurethane, chlor-alkali, organic fluorine, pesticides, and pharmaceuticals, have become a common problem restricting their development.

[0003] Currently, byproduct hydrogen chloride is mostly processed into crude hydrochloric acid for sale or treated as waste, resulting in low utilization and environmental unfriendliness. If the large quantities of industrially produced and difficult-to-treat byproduct hydrogen chloride could be directly converted into chlorine gas for reuse, achieving a closed-loop cycle of chlorine and zero emissions in the reaction process, it would not only solve the problem of hydrogen chloride surplus in related industries but also meet the ever-increasing industrial demand for chlorine to a certain extent, promoting the healthy development of emerging industries and the optimization and upgrading of the chlor-alkali industry.

[0004] The preparation of chlorine from hydrogen chloride is mainly achieved through three processes: electrolysis, direct oxidation, and catalytic oxidation. Catalytic oxidation has advantages such as low energy consumption, ease of operation, and high single-pass conversion rate, and is currently being widely studied.

[0005] The core of the catalytic oxidation of hydrogen chloride to chlorine lies in the development of catalysts. Ruthenium-based catalysts exhibit high reactivity at relatively low reaction temperatures, with titanium dioxide-supported ruthenium-based catalysts showing the best performance. However, the large amount of heat released during this reaction leads to the agglomeration and sintering of the active components, resulting in a loss of activity. Therefore, solving the problem of high-temperature agglomeration and sintering of the active ruthenium species is crucial for improving the stability of ruthenium-based catalysts.

[0006] Currently, the methods used to solve this problem include: Chinese Patent CN116078379A discloses a titanium diboride ceramic-supported ruthenium catalyst with high density. The material prepared by this method undergoes plastic deformation of the grains under continuous high temperature and high pressure, further filling the pores and obtaining higher density, which to a certain extent ensures hardness and stability. Moreover, the plastic deformation of the grains also results in the grain morphology being mainly irregular near-spherical with a large number of dislocation structures, thereby changing the surface roughness of the support to a certain extent. The unevenness of the support surface can hinder the sintering of ruthenium into sheets, thereby improving the activity and stability of the catalyst; and Chinese Patent CN112536032A discloses a high-temperature sintering resistant catalyst for the production of chlorine by chlorination and hydrogenation and its preparation method. The high-temperature sintering resistant catalyst is composed of a tin-doped titanium dioxide support and highly dispersed ruthenium dioxide nanoparticle active components. Doping the titanium dioxide support with tin can enhance the interaction between the ruthenium dioxide nanoparticle active components and the support, thereby improving the catalyst's resistance to high-temperature sintering. Summary of the Invention

[0007] The purpose of this invention is to provide a catalyst for the catalytic oxidation of hydrogen chloride to produce chlorine, which effectively alleviates the problems of high-temperature agglomeration and poor stability of the active component ruthenium species. This invention also provides the application of the above catalyst in the catalytic oxidation of hydrogen chloride to produce chlorine, which exhibits superior catalytic performance in this catalytic reaction.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A catalyst for the catalytic oxidation of hydrogen chloride to produce chlorine gas, the catalyst comprising a titanium dioxide support and an active component distributed on the titanium dioxide support, wherein the active component is ruthenium species particles, and the surface of the ruthenium species particles is coated with a titanium oxide shell.

[0010] To address the challenge of the significant heat released during the hydrogen chlorination-hydrogenation reaction, which leads to the agglomeration and sintering of the active ruthenium species and subsequent deactivation, this invention provides a ruthenium-based catalyst supported on coated titanium dioxide. This catalyst possesses a unique coated structure, where a titanium oxide shell is coated onto the surface of ruthenium species particles distributed on a support. This titanium oxide shell is a non-sealed shell with gas channels: firstly, reactant gases can contact the encapsulated ruthenium species through these channels, exerting a catalytic effect, while reaction products can diffuse out through the gas channels; secondly, the titanium oxide shell's encapsulation of the active component creates physical isolation between the ruthenium species particles, providing a spatial confinement effect and enhancing interfacial interactions, effectively limiting the agglomeration of the active component during the reaction (and mitigating the agglomeration and sintering of the active component particles during the reaction).

[0011] Preferably, the active component is ruthenium oxide, with ruthenium accounting for 0.1–5.0 wt% of the total catalyst mass; the titanium oxide shell has gas channels, and the thickness of the titanium oxide shell is 0.1–10 nm. More preferably, ruthenium accounts for 0.5–3.0 wt% of the total catalyst mass. At this active component mass content, the active sites are sufficient for the catalytic oxidation reaction of hydrogen chloride and oxygen.

[0012] Preferably, the titanium dioxide is rutile titanium dioxide.

[0013] This invention also provides a method for preparing a catalyst for the catalytic oxidation of hydrogen chloride to chlorine, the method comprising:

[0014] (1) Add Ru / TiO2 with titanium dioxide as carrier and ruthenium as active component to an inducing agent solution, heat and stir overnight, dry the resulting precipitate to obtain Ru / TiO2-A, wherein the inducing agent is selected from one or more of melamine, urea and dopamine;

[0015] (2) The Ru / TiO2-A obtained in step (1) is calcined in nitrogen atmosphere, air atmosphere and oxygen atmosphere in sequence to obtain RuO2 / TiO2 with a coated structure, which is used as a catalyst.

[0016] The above-mentioned inducer can induce the formation of TiO in a high-temperature atmosphere. x The shell can encapsulate the active component ruthenium species particles, preventing the ruthenium species from growing and thus maintaining good dispersion of the active component during the reaction.

[0017] Preferably, the preparation method specifically includes:

[0018] (1) Add Ru / TiO2 with titanium dioxide as carrier and ruthenium as active component to an inducing agent solution and heat and stir overnight at a temperature of 20-90°C. Centrifuge the precipitate obtained, wash it with deionized water, and dry it overnight at 40-90°C to obtain Ru / TiO2-A. The inducing agent is selected from one or more of melamine, urea, and dopamine.

[0019] (2) The Ru / TiO2-A obtained in step (1) is calcined in a nitrogen atmosphere for 1 to 8 hours, wherein the calcination temperature is 500 to 800℃ and the heating rate is 1 to 10℃ / min, to obtain Ru / TiO2-B.

[0020] (3) The Ru / TiO2-B obtained in step (2) is calcined in air for 1 to 10 hours, wherein the calcination temperature is 500 to 900℃ and the heating rate is 1 to 10℃ / min, to obtain the coated structure Ru / TiO2-C.

[0021] (4) The Ru / TiO2-C obtained in step (3) is calcined in an oxygen atmosphere for 1 to 10 hours, wherein the calcination temperature is 300 to 500°C and the heating rate is 1 to 10°C / min, to obtain RuO2 / TiO2 with a coating structure.

[0022] Preferably, the inducer is melamine or urea, which is more conducive to improving the stability of the catalyst.

[0023] In step (3), Ru / TiO2-B is placed in a high-temperature oxidizing atmosphere, where the inducing agent can induce the TiO2 support to encapsulate Ru particles, forming TiO2. x Shell layer. Preferably, the calcination temperature in step (3) is 700–800°C. This is more conducive to improving the stability of the catalyst.

[0024] This invention also provides an application of the above-mentioned catalyst in the catalytic oxidation of hydrogen chloride to produce chlorine gas. The method for catalytic oxidation of hydrogen chloride to produce chlorine gas is as follows: hydrogen chloride and oxygen react with the catalyst to obtain chlorine gas. Specifically, hydrogen chloride and oxygen contact the active components through the gas channels of the titanium oxide shell, and the chlorine gas diffuses out through the gas channels of the titanium oxide shell.

[0025] The method further includes activating the catalyst before the contact reaction. The catalyst is activated by raising the temperature from room temperature to 100-200°C in a nitrogen atmosphere at a heating rate of 1-20°C / min, and then raising it to the reaction temperature at a heating rate of 0.5-5°C / min.

[0026] In step (2), the volume ratio of hydrogen chloride to oxygen is 1:(0.5-6), and the reaction temperature is 200-400°C. Preferably, the reaction temperature is 300-375°C.

[0027] In step (2), a reaction dilution gas is introduced, wherein the reaction dilution gas is nitrogen.

[0028] The ruthenium-based catalyst supported on coated titanium dioxide is packed in a fixed-bed reactor, which can be a Hastelloy tube.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The catalyst provided by this invention forms physical isolation by encapsulating the active components with a titanium oxide shell, which has a spatial confinement effect and enhances interfacial interactions, effectively limiting the aggregation and loss of active components caused by the heat of reaction during the reaction process.

[0031] Compared with traditional supported ruthenium-based catalysts, the catalyst provided by this invention effectively alleviates the problems of high-temperature agglomeration and poor stability of the active component ruthenium species, and exhibits superior catalytic performance in the catalytic oxidation of hydrogen chloride to chlorine. Attached Figure Description

[0032] Figure 1 Model diagrams of the catalyst obtained by the preparation example of the present invention and the conventional catalyst are given;

[0033] Figure 2 TEM characterization images of the catalysts obtained in the preparation examples of this invention are provided. Detailed Implementation

[0034] The present invention will be further described below with reference to specific embodiments, but the invention is not limited to these specific embodiments. Those skilled in the art should recognize that the present invention covers all alternatives, improvements, and equivalents that may be included within the scope of the claims.

[0035] Catalyst Preparation Examples

[0036] The present invention provides a method for preparing a coated catalyst for the catalytic oxidation of hydrogen chloride, comprising the following steps:

[0037] (1) Preparation of Ru / TiO2

[0038] Ru / TiO2 was prepared using a chemical reduction method.

[0039] (1-1) Prepare a ruthenium chloride solution according to the ruthenium loading, add sodium citrate in an equal mass ratio, and mix thoroughly by ultrasonication;

[0040] (1-2) Weigh 10g of TiO2 powder and add it to the solution obtained in (1-1) above;

[0041] (1-3) Add sodium borohydride (sodium borohydride and noble metal molar ratio of 4:1) to the solution obtained in (1-2) above and stir;

[0042] (1-4) The mixed solution obtained in (1-3) above is heated in an oil bath, cooled to room temperature, filtered, washed and dried to obtain Ru / TiO2 catalyst.

[0043] In step (1), the oil bath heating time is 1-10 hours, the heating temperature is 60-120℃, and the drying temperature is preferably 60-120℃. Chemical reduction is a conventional technique in this field and will not be described in detail here.

[0044] (2) Preparation of RuO2 / TiO2 coated structures;

[0045] (2-1) Preparation of inducing agent solution: Add the inducing agent to 25ml of deionized water, wherein the concentration of the inducing agent is 1-10mg / ml, and the inducing agent is one or more of melamine, urea, and dopamine;

[0046] (2-2) Add 0.1g Ru / TiO2 to the above inducing agent solution, heat and stir overnight, wherein the heating temperature is 20-90℃, the obtained precipitate is centrifuged and washed with deionized water, and dried overnight at 40-90℃ to obtain Ru / TiO2-A;

[0047] (2-3) The Ru / TiO2-A obtained in (2-2) was calcined in a nitrogen atmosphere for 3 h, wherein the calcination temperature was 500-800℃ and the heating rate was 5℃ / min, to obtain Ru / TiO2-B.

[0048] (2-4) The Ru / TiO2-B obtained in (2-3) was calcined in air for 3 hours, wherein the calcination temperature was 500-900℃ and the heating rate was 5℃ / min, to obtain the coated structure Ru / TiO2-C.

[0049] (2-5) The Ru / TiO2-C obtained in (2-4) was calcined in an oxygen atmosphere for 2 hours, wherein the calcination temperature was 300-500℃ and the heating rate was 5℃ / min, to obtain RuO2 / TiO2 with a coating structure.

[0050] The table below shows the results of different catalysts prepared under different inducing agents, Ru loading, air calcination temperatures, etc., as detailed in Table 1:

[0051] Table 1 Different catalysts obtained under different reaction conditions

[0052]

[0053]

[0054] The catalyst obtained by the above preparation method is used for catalytic oxidation to prepare chlorine gas.

[0055] The model diagram of the prepared catalyst is shown below. Figure 1 As shown: The titanium oxide shell encapsulates the ruthenium species particles distributed on the titanium dioxide support, forming a physical isolation between the ruthenium species particles. The titanium oxide shell also has gas channels, through which the reaction gases (HCl and O2) can contact the active component ruthenium species encapsulated within, and the reaction product (Cl2) can diffuse out through the gas channels.

[0056] TEM characterization of catalyst R-3 is as follows Figure 2 As shown, the titanium oxide shell can effectively encapsulate ruthenium species particles.

[0057] Examples 1-20 illustrate the catalytic oxidation of hydrogen chloride to chlorine using the catalysts prepared in the aforementioned examples.

[0058] Reaction temperature 300–400℃, reaction space velocity 40,000 h⁻¹ -1 The volume ratio of HCl to O2 was 1:(0.5-6), and the dilution gas was nitrogen. The catalyst was packed in a fixed-bed reactor, which was a Hastelloy tube with an outer diameter of 20 mm and an inner diameter of 10 mm. The catalyst loading was 1 g. Samples were taken for analysis after 2 hours and 24 hours of reaction. The products were analyzed by iodometric titration and acid-base neutralization titration. The product analysis results of each embodiment are shown in Table 2.

[0059] Table 2. Product analysis results for each embodiment.

[0060]

[0061]

[0062] As shown in Table 2, compared with Examples 3 and 13-16, the catalyst effect was best at a reaction temperature of 350°C. Compared with Examples 3 and 17-20, the effect was best when the volume ratio of HCl to O2 was 1:2. Compared with Examples 1-12, the catalyst effect was best when urea and ruthenium loading were 2%.

[0063] Comparative Examples 1-3

[0064] The operation of this comparative example is the same as in Example 3, except that the catalyst is a conventional supported RuO2 / TiO2, i.e., a catalyst formed by RuO2 supported and exposed on TiO2. The experimental results are shown in Table 3:

[0065] Table 3. Product analysis results for each embodiment.

[0066]

[0067] Table 3 shows that, compared with the activity of traditional RuO2 / TiO2 catalysts, the catalyst of the present invention exhibits a smaller decrease in activity after 24 hours of reaction. The R-3 catalyst, with the best activity, shows only a 2% decrease in feed conversion rate after 24 hours, while the traditional RuO2 / TiO2 catalyst shows a 41% decrease under the same reaction conditions. At reaction temperatures of 325℃ and 375℃, the feed conversion rates decrease by 30% and 48%, respectively. Clearly, the catalyst of the present invention has superior stability, which is of great significance for its industrial application in the catalytic oxidation of hydrogen chloride to chlorine. The higher initial conversion rate of the traditional RuO2 / TiO2 catalyst compared to the catalyst of the present invention is due to the TiO2 layer on the surface of the catalyst of the present invention. x This is due to the partial coverage of active sites.

Claims

1. A catalyst for the catalytic oxidation of hydrogen chloride to produce chlorine, characterized in that, The catalyst comprises a titanium dioxide support and an active component distributed on the titanium dioxide support. The active component is ruthenium species particles, and the surface of each ruthenium species particle is coated with a titanium oxide shell.

2. The catalyst according to claim 1, characterized in that, The active component is ruthenium oxide, with ruthenium accounting for 0.1 to 5.0 wt% of the total mass of the catalyst; the titanium oxide shell has gas channels, and the thickness of the titanium oxide shell is 0.1 to 10 nm.

3. The catalyst according to claim 2, characterized in that, The ruthenium element accounts for 0.5 wt% to 3.0 wt% of the total mass of the catalyst.

4. The catalyst according to claim 1, characterized in that, The titanium dioxide is rutile titanium dioxide.

5. A method for preparing the catalyst according to any one of claims 1-4, characterized in that, The preparation method includes: (1) Add Ru / TiO2 with titanium dioxide as carrier and ruthenium as active component to an inducing agent solution, heat and stir overnight, dry the resulting precipitate to obtain Ru / TiO2-A, wherein the inducing agent is selected from one or more of melamine, urea and dopamine; (2) The Ru / TiO2-A obtained in step (1) is calcined in nitrogen atmosphere, air atmosphere and oxygen atmosphere in sequence to obtain RuO2 / TiO2 with a coating structure as a catalyst.

6. The method for preparing the catalyst according to claim 5, characterized in that, The preparation method includes: (1) Add Ru / TiO2 with titanium dioxide as carrier and ruthenium as active component to an inducing agent solution and heat and stir overnight at a temperature of 20-90°C. Centrifuge the obtained precipitate, wash it with deionized water, and dry it overnight at 40-90°C to obtain Ru / TiO2-A. (2) The Ru / TiO2-A obtained in step (1) is calcined in a nitrogen atmosphere for 1 to 8 hours, wherein the calcination temperature is 500 to 800℃ and the heating rate is 1 to 10℃ / min, to obtain Ru / TiO2-B; (3) The Ru / TiO2-B obtained in step (2) is calcined in air atmosphere for 1 to 8 hours, wherein the calcination temperature is 500 to 900℃ and the heating rate is 1 to 10℃ / min, to obtain the coated structure Ru / TiO2-C. (4) The Ru / TiO2-C obtained in step (3) is calcined in an oxygen atmosphere for 1 to 8 hours, wherein the calcination temperature is 300 to 500°C and the heating rate is 1 to 10°C / min, to obtain RuO2 / TiO2 with a coating structure.

7. The application of the catalyst according to any one of claims 1-4 in the catalytic oxidation of hydrogen chloride to produce chlorine gas, characterized in that, The method for preparing chlorine by catalytic oxidation of hydrogen chloride is as follows: hydrogen chloride and oxygen react with a catalyst to obtain chlorine; wherein, hydrogen chloride and oxygen contact the active components through the gas channels of the titanium oxide shell, and the chlorine diffuses out through the gas channels of the titanium oxide shell.

8. The application according to claim 7, characterized in that, The method includes activating the catalyst before the contact reaction. The catalyst is activated by raising the temperature from room temperature to 100-200°C in a nitrogen atmosphere at a heating rate of 1-20°C / min, and then raising the temperature to the reaction temperature at a heating rate of 0.5-5°C / min.

9. The application according to claim 7, characterized in that, The volume ratio of hydrogen chloride to oxygen is 1:(0.5-6), and the reaction temperature is 300-400℃.

10. The application according to claim 9, characterized in that, The reaction temperature is 300–375°C.

Images