High-purity rhodium triiodide and preparation method thereof

Abstract

The invention relates to the technical field of precious metal compound synthesis, in particular to high-purity rhodium triiodide and a preparation method thereof.The preparation method comprises the following steps that solid rhodium trichloride is put into a reaction kettle, the temperature is increased, ozone is introduced, when reaction tail gas is absorbed by silver nitrate and no white precipitate is generated, reaction continues for 1-1.5 h, and rhodium oxide powder is obtained; washing the rhodium oxide powder until no white precipitate exists after the washing solution is mixed with the silver nitrate solution, adding hydriodic acid and an initiator into rhodium oxide, heating and refluxing, and reacting for 4-6 hours to obtain black crystal powder; and washing and drying the black crystal powder to obtain the high-purity rhodium triiodide. According to the method, the chlorine element in the solid rhodium trichloride is oxidized into chlorine gas through ozone, so that the chlorine element in the raw material is removed, and the problem that chlorine ions in the final product exceed the standard is avoided. A hydriodic acid solution is adopted to react with rhodium oxide, no metal impurities or other substances are introduced in the reaction process, and the content of chloride ions in the high-purity rhodium triiodide prepared by the method is 1-5 ppm.

Description

Technical Field

[0001] This invention relates to the field of precious metal compound synthesis technology, specifically to a high-purity rhodium triiodide and its preparation method. Background Technology

[0002] Rhodium triiodide, a highly valuable rhodium compound, exhibits unique and crucial applications in numerous fields. In catalysis, it serves as a highly efficient catalyst for various organic chemical reactions, particularly in specific hydrogenation, dehydrogenation, and redox reactions, significantly improving reaction rates and selectivity while reducing reaction condition requirements. This has played a vital role in promoting the development of industries such as fine chemicals and petrochemicals. For example, rhodium triiodide is widely used as a catalyst in the carbonylation synthesis of acetic acid, acetic anhydride, and ethylene glycol. In electronic materials, rhodium triiodide can be used to prepare functional materials with special electrical properties, providing crucial raw material support for the miniaturization and high performance of electronic devices. In analytical chemistry, it also serves as a sensitive detection reagent for the quantitative and qualitative analysis of specific substances.

[0003] However, existing methods for preparing rhodium triiodide have many problems, severely restricting its large-scale production and widespread application. From the perspective of process complexity, traditional methods often involve multiple cumbersome steps and strict control of reaction conditions. For example, some traditional methods first electrolyze elemental rhodium in hydrochloric acid solution, then separate and purify it to obtain rhodium trichloride solution, followed by the addition of a certain concentration of potassium iodide solution, stirring and heating, washing and filtering to obtain rhodium triiodide. The entire process is complex, increasing production costs and reducing efficiency. Another example is the preparation method proposed in patent publication number "DD290865A5," which reacts an aqueous solution of hexachlororhodium salt such as Na3RhCl6 with an aqueous solution of potassium iodide or sodium iodide to obtain trivalent rhodium iodide under certain conditions; however, the reaction conditions in this method are difficult to control.

[0004] From the perspective of product quality and purity, existing methods for preparing rhodium triiodide suffer from problems such as unstable product quality, low rhodium yield, and low purity. Traditional methods involve numerous processing steps, easily leading to product quality fluctuations, and generate a large amount of byproducts and waste during the reaction, reducing the yield and purity of the target product, rhodium triiodide. Furthermore, numerous domestic and international patents clearly indicate that chloride ions cause significant catalyst loss during the use of rhodium triiodide preparation catalysts. Rhodium triiodide prepared by traditional methods often has a high chloride content, severely affecting its performance. This is particularly true in applications requiring extremely high purity, such as the methanol carbonylation to acetic acid production; high chloride content in rhodium triiodide catalysts leads to decreased catalyst performance, shortened lifespan, and increased production costs. Summary of the Invention

[0005] To address the problems of low rhodium triiodide yield, low purity, and high chlorine content in the existing technologies, this invention provides a high-purity rhodium triiodide and its preparation method.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A method for preparing high-purity rhodium triiodide includes the following steps:

[0008] S1: Place solid rhodium trichloride into a reaction vessel, heat it, and introduce ozone. When no white precipitate is produced after the reaction tail gas is absorbed by silver nitrate, continue the reaction for 1-1.5 hours to obtain rhodium oxide powder.

[0009] S2: Wash the rhodium oxide powder until no white precipitate is formed after mixing the washing solution with the silver nitrate solution. Add hydroiodic acid and an initiator to the rhodium oxide, heat under reflux, and react for 4-6 hours to obtain a black crystalline powder.

[0010] S3: Wash and dry the black crystalline powder obtained in S2 to obtain high-purity rhodium triiodide.

[0011] Further, in S1, the temperature is raised to 400-500℃, and the reaction pressure is 0.1-0.2MPa; the rhodium trichloride contains 36-39% rhodium, and the ozone purity is >99.5%.

[0012] Further, in S2, the reflux temperature is 80-95℃; the molar ratio of the added hydroiodic acid to rhodium oxide is 6-8, and the molar ratio of the added initiator to rhodium oxide is 0.01-0.03; the concentration of the silver nitrate solution is 10-15%, the concentration of the hydroiodic acid is 55-60%, and the initiator includes liquid bromine with a purity >99.5%.

[0013] Furthermore, in S3, a vacuum drying oven is used for drying. The pressure of the vacuum drying oven is -0.08-0 MPa, the drying temperature is 40-60℃, and the drying time is 6-8 hours.

[0014] This invention also includes the following technical solutions:

[0015] A high-purity rhodium triiodide prepared using the above-described method.

[0016] Furthermore, the high-purity rhodium triiodide has a purity >99.95%, a chloride ion content of 1-5 ppm, and a yield of 98.2-98.5%.

[0017] The present invention relates to the following reaction mechanism:

[0018] 2RhCl3 + O3 → Rh2O3 + 3Cl2↑

[0019] Rh₂O₃ + 6HI → 2RhI₃↓ + 3H₂O

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This invention provides a high-purity rhodium triiodide and its preparation method. The method first uses ozone to oxidize the chlorine in solid rhodium trichloride into chlorine gas, simultaneously generating rhodium trioxide, thus removing chlorine from the raw materials and avoiding excessive chloride ion content in the final product. The reaction endpoint is determined by observing the absence of a white precipitate after absorption of the reaction tail gas with silver nitrate, ensuring complete conversion of rhodium trichloride to rhodium oxide. The rhodium oxide powder is then washed until no chloride ion residue remains, further reducing the chlorine content in the raw materials. The rhodium oxide is reacted with hydroiodic acid solution. This reaction is a complete acidolysis reaction of metal oxides, with no side reactions occurring. The hydroiodic acid solution acts as both a reactant and a solvent, preventing the introduction of any metal impurities or other substances during the reaction, thus improving product yield and ensuring product purity. The high-purity rhodium triiodide prepared by this method has a chloride ion content of 1-5 ppm. Attached Figure Description

[0022] The embodiments of the present invention will be further described below with reference to the accompanying drawings, wherein:

[0023] Figure 1 A process flow diagram for the preparation of rhodium triiodide is shown. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0025] Example 1

[0026] A method for preparing high-purity rhodium triiodide includes the following steps:

[0027] S1: Place solid rhodium trichloride into a reactor equipped with inlet and outlet gas pipelines, open the inlet and outlet gas valves and gradually heat to 400℃, adjust the outlet valve opening to make the internal pressure of the reactor 0.1MPa; introduce ozone to react, and when no white precipitate is produced after the reaction tail gas is absorbed by silver nitrate, continue the reaction for 1 hour, then stop heating and cool to room temperature to obtain rhodium oxide powder.

[0028] S2: Wash rhodium oxide powder with deionized water until no white precipitate is formed after mixing the washing solution with silver nitrate solution. Add hydroiodic acid and liquid bromine to rhodium oxide. The molar ratio of hydroiodic acid to rhodium oxide is 6, and the molar ratio of liquid bromine to rhodium oxide is 0.01. Reflux at 80°C for 4 hours to obtain black crystalline powder.

[0029] S3: The black crystalline powder obtained in S2 was washed and dried in a vacuum drying oven at 40°C for 8 hours. The pressure inside the vacuum drying oven was -0.08 MPa, to obtain high-purity rhodium triiodide.

[0030] Example 2

[0031] A method for preparing high-purity rhodium triiodide includes the following steps:

[0032] S1: Place solid rhodium trichloride into a reactor equipped with inlet and outlet gas pipelines, open the inlet and outlet gas valves and gradually raise the temperature to 500℃, adjust the outlet valve opening to make the internal pressure of the reactor 0.2MPa; introduce ozone to react, and when no white precipitate is produced after the reaction tail gas is absorbed by silver nitrate, continue the reaction for 0.5h, then stop heating and cool to room temperature to obtain rhodium oxide powder.

[0033] S2: Wash the rhodium oxide powder with deionized water until no white precipitate is formed after mixing the washing liquid with silver nitrate solution. Add hydroiodic acid and liquid bromine to the rhodium oxide. The molar ratio of hydroiodic acid to rhodium oxide is 8, and the molar ratio of liquid bromine to rhodium oxide is 0.03. Reflux at 95°C for 6 hours to obtain black crystalline powder.

[0034] S3: The black crystalline powder obtained in S2 is washed and dried in a vacuum drying oven at 60°C for 6 hours at a pressure of 0 MPa to obtain high-purity rhodium triiodide.

[0035] Example 3

[0036] A method for preparing high-purity rhodium triiodide includes the following steps:

[0037] S1: Place solid rhodium trichloride into a reactor equipped with inlet and outlet gas pipelines, open the inlet and outlet gas valves and gradually raise the temperature to 450℃, adjust the outlet valve opening to make the internal pressure of the reactor 0.15MPa; introduce ozone to react, and when no white precipitate is produced after the reaction tail gas is absorbed by silver nitrate, continue the reaction for 0.8h, then stop heating and cool to room temperature to obtain rhodium oxide powder.

[0038] S2: Wash the rhodium oxide powder with deionized water until no white precipitate is formed after mixing the washing liquid with silver nitrate solution. Add hydroiodic acid and liquid bromine to the rhodium oxide. The molar ratio of hydroiodic acid to rhodium oxide is 7, and the molar ratio of liquid bromine to rhodium oxide is 0.02. Reflux at 85°C for 5 hours to obtain black crystalline powder.

[0039] S3: The black crystalline powder obtained in S2 is washed and dried in a vacuum drying oven at 50°C for 7 hours. The pressure inside the vacuum drying oven is -0.05 MPa to obtain high-purity rhodium triiodide.

[0040] Comparative Example 1

[0041] A method for preparing high-purity rhodium triiodide includes the following steps:

[0042] S1: Rhodium trichloride aqueous solution and hydroiodic acid are mixed and reacted under microwave radiation of 150W to obtain a solution containing rhodium triiodide;

[0043] S2: Ozone is continuously bubbled into the solution containing rhodium triiodide obtained in step S1 to carry out the reaction at a temperature of 50°C. The reaction is stopped when the color of the solution no longer deepens.

[0044] S3: After filtering the ozone-treated solution containing rhodium triiodide from step S2, wash it with an organic solvent and dry it to obtain high-purity rhodium triiodide.

[0045] The yields and analytical results of the products obtained from the above embodiments and comparative examples are shown in Table 1.

[0046] Table 1 Product Yield and Detection Analysis Results

[0047] Yield (%) Rhodium content (%) purity(%) Chlorine content (ppm) Example 1 98.2 21.25 ＞99.95 3ppm Example 2 98.5 21.23 ＞99.95 5ppm Example 3 98.3 21.24 ＞99.95 1ppm Comparative Example 1 99.35 21.18 ＞99.9 10ppm

[0048] The high-purity rhodium triiodide product prepared in the above embodiments was tested by ICP-OES, and the test results are shown in Table 2. It fully meets the requirements of the rhodium triiodide industry standard.

[0049] Table 2. Analysis results of rhodium triiodide samples / % (mass fraction)

[0050]

[0051] This invention provides a high-purity rhodium triiodide and its preparation method. The method first uses ozone to oxidize the chlorine in solid rhodium trichloride into chlorine gas, simultaneously generating rhodium trioxide, thus removing chlorine from the raw materials and avoiding excessive chloride ion content in the final product. The reaction endpoint is determined by observing the absence of a white precipitate after absorption of the reaction tail gas with silver nitrate, ensuring complete conversion of rhodium trichloride to rhodium oxide. The rhodium oxide powder is then washed until no chloride ion residue remains, further reducing the chlorine content in the raw materials. The rhodium oxide is reacted with hydroiodic acid solution. This reaction is a complete acidolysis reaction of metal oxides, with no side reactions occurring. The hydroiodic acid solution acts as both a reactant and a solvent, preventing the introduction of any metal impurities or other substances during the reaction, thus improving product yield and ensuring product purity. The high-purity rhodium triiodide prepared by this method has a chloride ion content of 1-5 ppm.

[0052] The foregoing descriptions have outlined some exemplary embodiments of the present invention. It is understood that these embodiments are merely illustrative and do not constitute a limitation on the scope of protection of the present invention. Features in these embodiments can be rearranged in suitable ways, and the resulting solutions remain within the scope of protection claimed by the present invention. All other embodiments obtained by those skilled in the art based on the foregoing embodiments without inventive effort, i.e., all modifications, equivalent substitutions, and improvements made within the spirit and principles of this application, fall within the scope of protection claimed by the present invention.

Claims

1. A method for preparing high-purity rhodium triiodide, characterized in that, Includes the following steps: S1: Place solid rhodium trichloride into a reaction vessel, heat it, and introduce ozone. When no white precipitate is produced after the reaction tail gas is absorbed by silver nitrate, continue the reaction for 1-1.5 hours to obtain rhodium oxide powder. S2: Wash the rhodium oxide powder until no white precipitate is formed after mixing the washing solution with the silver nitrate solution. Add hydroiodic acid and an initiator to the rhodium oxide, heat under reflux, and react for 4-6 hours to obtain a black crystalline powder. S3: Wash and dry the black crystalline powder obtained in S2 to obtain high-purity rhodium triiodide.

2. The method for preparing high-purity rhodium triiodide according to claim 1, characterized in that, In S1, the temperature is raised to 400-500℃, and the reaction pressure is 0.1-0.2MPa; the rhodium trichloride contains 36-39% rhodium, and the ozone purity is >99.5%.

3. The method for preparing high-purity rhodium triiodide according to claim 1, characterized in that, In S2, the reflux temperature is 80-95℃; the molar ratio of the added hydroiodic acid to rhodium oxide is 6-8, and the molar ratio of the added initiator to rhodium oxide is 0.01-0.03; the concentration of the silver nitrate solution is 10-15%, the concentration of the hydroiodic acid is 55-60%, and the initiator includes liquid bromine with a purity >99.5%.

4. The method for preparing high-purity rhodium triiodide according to claim 1, characterized in that, In S3, a vacuum drying oven is used for drying. The pressure of the vacuum drying oven is -0.08-0 MPa, the drying temperature is 40-60℃, and the drying time is 6-8 hours.

5. A high-purity rhodium triiodide prepared by any one of the high-purity rhodium triiodide preparation methods according to claims 1-4.

6. The high-purity rhodium triiodide according to claim 5, characterized in that, The high-purity rhodium triiodide has a purity >99.95%, a chloride ion content of 1-5 ppm, and a yield of 98.2-98.5%.

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