A method for preparing palladium nitrate at room temperature and a preparation system thereof

Abstract

The present application embodiment provides a method for preparing palladium nitrate at room temperature and its preparation system, it is related to the technical field of palladium nitrate preparation method, the method including: step S1, aqua regia dissolution-oxidation to obtain H2PdCl6 solution, step S2, ultrasonic reduction of high-valent state palladium liquid to obtain high-activity palladium powder, step S3, buffer washing: the high-activity palladium powder obtained by step S2 is filtered and washed, 1-2 times are washed with a pH maintenance agent of 0.50%-2%, and then washed to neutrality with deionized water of 40°C-50°C; step S4, normal temperature peracid segmented dissolution of palladium powder: a certain amount of nitric acid is weighed according to the concentration required for palladium nitrate, and step S3 is then washed to neutral high-activity palladium powder by weight, and sufficient nitric acid is segmented and fully stirred for dissolution. This program does not need to add nitric acid separately, and the palladium nitrate concentration obtained is higher.

Description

Technical Field

[0001] The present application relates to the technical field of palladium nitrate preparation methods, and in particular to a method for preparing palladium nitrate at room temperature and a preparation system thereof. Background Art

[0002] Palladium nitrate is widely used in many fields. For example, it is used as a precursor for automobile exhaust purification catalysts, as an intermediate synthesis catalyst and as a coupling catalyst in the pharmaceutical industry. In the electronics industry, it is used to manufacture electronic components such as capacitors and printed circuit boards. In the field of environmental protection, it can purify wastewater and exhaust gas, and remove harmful organic pollutants and heavy metal ions.

[0003] Common methods for preparing palladium nitrate solutions primarily include direct dissolution, where palladium powder with a purity of ≥99.95% is dissolved directly in nitric acid. However, variations in the control conditions during the reduction, drying, and storage processes of the palladium powder can lead to dense particle size and surface oxidation, resulting in only partial or no dissolution of the palladium powder. Furthermore, this method requires continuous heating at high temperatures for 5-8 hours. This sustained high temperature results in poor stability of the prepared palladium nitrate and prone to precipitation. Another common preparation method involves dissolving the palladium nitrate in nitric acid with an additive. This method also suffers from the same issue of poor stability due to heating and can introduce other impurities (such as chloride ions), poisoning the subsequently prepared catalyst and significantly reducing its catalytic activity. These issues result in low palladium utilization and poor quality of the resulting palladium nitrate. Summary of the Invention

[0004] The purpose of the present invention is to provide a method and system for preparing palladium nitrate at room temperature, so as to solve the problems existing in the existing palladium nitrate preparation methods, such as low palladium utilization, poor stability of palladium nitrate, and catalyst poisoning caused by the introduction of impurity ions. The specific technical solution is as follows:

[0005] In a first aspect of the present application, a method for preparing palladium nitrate at room temperature is provided, comprising:

[0006] Step S1, aqua regia dissolution: take a certain amount of palladium powder, add aqua regia to dissolve it at a liquid-solid ratio of 4-6:1, after the dissolution is completed, concentrate and remove the nitrate until no yellow smoke is generated by adding hydrochloric acid, and the removal of nitrate is completed. Slowly add 70℃-90℃ deionized water to the solution after removing the nitrate and continue to concentrate the volume to remove the acid. When the volume reduction is the same as the amount of deionized water added, repeat the operation 2-3 times, and the removal of acid is completed. Add an oxidant to remove Pd 2+ Oxidation to Pd 4+ , obtaining H2PdCl6 solution;

[0007] Step S2, ultrasonic reduction of the high-valent palladium solution: neutralizing the HPdCl solution obtained in step S1 with an alkali solution to adjust the pH value of the solution to 8-13, placing the neutralized solution in an ultrasonic reactor, and adding a reducing agent under stirring to carry out reduction until no reaction occurs after the addition of the reducing agent and the solution becomes transparent and colorless, thereby completing the reduction and obtaining a high-activity palladium powder;

[0008] Step S3, buffer washing: filtering and washing the high-activity palladium powder obtained in step S2, washing it 1-2 times with a 0.50%-2% pH maintaining agent, and then washing it with deionized water at 40°C-50°C until it becomes neutral;

[0009] Step S4, dissolving the palladium powder in a peracid solution at room temperature: weighing a certain amount of nitric acid according to the required concentration of palladium nitrate, and then dividing the high-activity palladium powder washed to neutrality in step S3 into 3-4 equal parts by weight, adding the weighed quantitative nitric acid to the first part of the high-activity palladium powder, stirring thoroughly to dissolve it, observing the reaction process, and after the reaction is completed, adding the second part of the high-activity palladium powder to the solution, stirring thoroughly to dissolve it, and then adding the third and fourth parts of the high-activity palladium powder in sequence and repeating the above operation.

[0010] Optionally, the oxidant in step S1 includes hydrogen peroxide, sodium chlorate, or sodium hypochlorite.

[0011] Optionally, the reducing agent in step S2 includes hydrazine hydrate or formic acid.

[0012] Optionally, the alkali in step S2 includes sodium hydroxide or potassium hydroxide.

[0013] Optionally, the pH maintaining agent in step S3 includes sodium hydroxide or potassium hydroxide.

[0014] Optionally, step S3 and step S4 are continuous steps, and the time for step S3 and step S4 is less than or equal to 12 hours.

[0015] In a second aspect of the present application, a preparation system for preparing palladium nitrate at room temperature is also provided. The system comprises:

[0016] The first reaction kettle and heating device, ultrasonic reduction and filtering device and palladium nitrate dissolving device;

[0017] The outer layer of the first reactor is provided with a hollow layer, the hollow layer is connected to the heating device, and heat-conducting oil / water circulates in the hollow layer to control the temperature regulation of the aqua regia dissolution, nitrate removal, acid removal and neutralization processes;

[0018] The ultrasonic reduction and filtration device includes: a second reaction kettle for reducing high-activity palladium powder, an ultrasonic reactor, a first sensor and a second sensor for controlling the addition of reducing agent and cooling by spraying cold water, a titanium filter plate and a filter bottle, and a gravity sensing device is provided at the bottom of the filter bottle;

[0019] The palladium nitrate dissolving device comprises a first-level palladium nitrate reactor, a second-level palladium nitrate reactor, and a third-level palladium nitrate reactor. The palladium nitrate reactors at each level are fixedly linked to a turntable, and a gravity sensing device is provided at the bottom of each level of the palladium nitrate reactor. The installation height of the palladium nitrate reactors at each level on the turntable is sequentially reduced so that the palladium nitrate solution is transferred between the palladium nitrate reactors at each level by gravity.

[0020] Optionally, a feeding port is provided at the top of the first reactor, a circulation inlet and a circulation outlet are symmetrically provided at both ends of the first reactor, the circulation inlet and the circulation outlet are connected to the hollow layer, a stirring blade is fixedly installed inside the first reactor, and a unloading switch is provided at the bottom of the first reactor.

[0021] Optionally, a first feed switch is provided at the top of the second reactor, a glass pipe is installed between the first feed switch and the unloading switch, both ends of the glass pipe are connected to the first reactor and the second reactor respectively, a second feed switch is installed at one end of the second reactor, one end of the second feed switch passes through the second reactor and extends into the interior, a first feed port is provided at one end of the second feed switch, a first stirring paddle is symmetrically provided below the first feed port, and the first stirring paddle is fixedly connected to the inner wall of the second reactor;

[0022] The second reactor is fixedly connected to the ultrasonic reactor. A connecting portion is provided at the bottom of the second reactor, which is flexibly connected to the titanium plate funnel. A discharge switch for controlling the solution from the second reactor into the titanium plate funnel is provided above the connecting portion. A titanium filter plate is fixedly installed in the titanium plate funnel. A rubber plug is provided below the titanium plate funnel so that the titanium plate funnel is flexibly connected to the filter bottle through the rubber plug. An air extraction hole is provided at one end of the filter bottle, which is connected to an external filtration device.

[0023] A second feed inlet is provided at the top of the second reactor, and the second feed inlet is in the shape of a shower. A switch is provided at the upper end of the second feed inlet, and the switch is used to control the cold water in the water tank to enter the second reactor through the second feed inlet. A first sensor is provided below the second feed inlet, and a second sensor is provided below the first sensor. Both the first sensor and the second sensor are fixedly connected to the second reactor;

[0024] The filter bottle is fixedly connected to the turntable, and a water outlet is provided at the bottom of the filter bottle, which is connected to the waste liquid recovery area through a hose.

[0025] Optionally, a first base is fixed at the bottom end of the first-level palladium nitrate reactor, the first base is fixedly connected to the turntable, a second stirring paddle is provided in the first-level palladium nitrate reactor, a first discharge port is provided at one end of the first-level palladium nitrate reactor, the first discharge port is communicated with the third feed port of the second-level palladium nitrate reactor through a glass tube, a second base is fixed at the bottom end of the second-level palladium nitrate reactor, the second base is fixedly connected to the turntable, a third stirring paddle is provided in the second-level palladium nitrate reactor, the second base is lower than the first base, a second discharge port is provided at one end of the second-level palladium nitrate reactor, the second discharge port is communicated with the tertiary palladium nitrate reactor through a glass tube, and a fourth stirring paddle is provided in the tertiary palladium nitrate reactor.

[0026] Beneficial effects of this application:

[0027] The present invention provides a method for preparing palladium nitrate at room temperature, which adopts a method of dissolving in aqua regia - neutralizing palladium solution in high valence state - ultrasonically reducing high-activity palladium powder - and dissolving in peracid at room temperature. The palladium powder is dissolved in aqua regia and then steamed at high temperature for a long time, such as driving out nitrate and acid. The palladium ions in the solution are all divalent. By adding an oxidant, the Pd 2+ Oxidation to Pd 4+ , neutralize the high-valent palladium liquid. The Pd(OH)4 generated during the neutralization process is unstable and forms easily soluble compounds under alkaline conditions, thereby reducing the amount of precipitation generated and reducing the problem of encapsulation caused by precipitation during the reduction process. The neutralized liquid is ultrasonically reduced to obtain high-activity palladium powder. Adding ultrasound during the reduction process can inhibit particle agglomeration and break up the Pd(OH)4 generated during the neutralization process. After a period of ultrasound, a reducing agent is added. The reduced palladium powder has a small particle size and does not stick to the wall, and no metal loss occurs during the process. The high-activity palladium powder obtained by ultrasonic reduction is prepared into palladium nitrate by a peracid segmented dissolution method. The palladium powder dissolution reaction is rapid and the reaction is complete in only 0.5 hours. No additional nitric acid needs to be added, and the resulting palladium nitrate has a high concentration. Moreover, the palladium powder is dissolved at room temperature, and the resulting palladium nitrate is stable in nature. No precipitation is produced after long-term observation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art.

[0029] Figure 1 This is a flow chart of a method for preparing palladium nitrate at room temperature in this application;

[0030] Figure 2 This is a flow chart for preparing palladium nitrate by direct dissolution in nitric acid;

[0031] Figure 3 Flow chart for the preparation of palladium nitrate by the auxiliary dissolution method;

[0032] Figure 4 This is a schematic diagram of the structure of a preparation system for preparing palladium nitrate at room temperature in this application;

[0033] In the figure, 1, first reactor; 2, feeding port; 3, circulation inlet; 4, circulation outlet; 5, hollow layer; 6, stirring blade; 7, discharge switch; 8, first feed switch; 9, second feed switch; 10, first feed port; 11, first stirring paddle; 12, ultrasonic reactor; 13, first sensor; 14, second sensor; 15, switch; 16, second feed port; 17, discharge switch; 18, titanium filter plate; 19, air extraction hole; 2 0. Water outlet; 21. Hose; 22. First-stage palladium nitrate reactor; 23. First base; 24. Second stirring paddle; 25. First discharge port; 26. Third feed port; 27. Second-stage palladium nitrate reactor; 28. Second base; 29. ​​Third stirring paddle; 30. Second discharge port; 31. Third-stage palladium nitrate reactor; 32. Fourth stirring paddle; 33. Second reactor; 34. Filter flask; 35. Titanium plate funnel; 36. Turntable; 37. Connecting part. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] In order to solve the problems in the prior art, the present application provides a method for preparing palladium nitrate at room temperature and a preparation system thereof, so as to solve the problems existing in the existing palladium nitrate preparation method, such as low palladium utilization, poor stability of palladium nitrate, and catalyst poisoning caused by the introduction of impurity ions.

[0036] The following first introduces a method for preparing palladium nitrate at room temperature provided in an embodiment of the present application.

[0037] like Figure 1 As shown, the present invention provides a method for preparing palladium nitrate at room temperature, which may include the following steps:

[0038] Step S1, aqua regia dissolution: take a certain amount of palladium powder, add aqua regia to dissolve it at a liquid-solid ratio of 4-6:1, after the dissolution is completed, concentrate and remove the nitrate until no yellow smoke is generated by adding hydrochloric acid, and the removal of nitrate is completed. Slowly add 70℃-90℃ deionized water to the solution after removing the nitrate and continue to concentrate the volume to remove the acid. When the volume reduction is the same as the amount of deionized water added, repeat the operation 2-3 times, and the removal of acid is completed. Add an oxidant to remove Pd 2+ Oxidation to Pd 4+, obtaining H2PdCl6 solution. Wherein, the oxidant includes hydrogen peroxide, sodium chlorate, and sodium hypochlorite.

[0039] Step S2, ultrasonic reduction of the high-valent palladium solution: The HPdCl solution obtained in step S1 is neutralized with an alkali solution to adjust the pH of the solution to 8-13. The neutralized solution is placed in an ultrasonic reactor and, under stirring, a reducing agent is added for reduction until no reaction occurs after the reducing agent is added and the solution becomes transparent and colorless, thereby completing the reduction and obtaining a high-activity palladium powder. The reducing agent includes hydrazine hydrate or formic acid, and the alkali includes sodium hydroxide or potassium hydroxide.

[0040] Step S3, buffer washing: The high-activity palladium powder obtained in step S2 is filtered and washed, washed 1-2 times with a 0.50%-2% pH maintaining agent, and then washed with deionized water at 40°C-50°C until neutral. The pH maintaining agent includes sodium hydroxide and potassium hydroxide.

[0041] Step S4, dissolving palladium powder in a peracid solution at room temperature: Weigh a certain amount of nitric acid according to the concentration required for palladium nitrate, then divide the high-activity palladium powder washed to neutrality in step S3 into 3-4 equal parts by weight, add the weighed quantitative nitric acid to the first part of the high-activity palladium powder, stir thoroughly to dissolve it, observe the reaction process, and after the reaction is completed, add the second part of the high-activity palladium powder to the solution, stir thoroughly to dissolve it, and then add the third and fourth parts of the high-activity palladium powder in sequence and repeat the above operation. Wherein, step S3 and step S4 are continuous steps, and the time of step S3 and step S4 is less than or equal to 12 hours.

[0042] In order to clarify the advancement and innovation of the technology of the present invention and make the technical features of the present invention easier to understand, further explanation is given in conjunction with specific examples. Example 1

[0043] Step S1, aqua regia dissolution: take 50g of palladium powder, add aqua regia to dissolve it at a liquid-solid ratio of 4:1, after the dissolution is completed, concentrate and remove nitrate until no yellow smoke is generated by adding hydrochloric acid, and the removal of nitrate is completed. Slowly add 70℃ deionized water to the solution after removing nitrate and continue to concentrate the volume to remove acid. When the volume reduction is the same as the amount of deionized water added, repeat the operation twice, and the removal of acid is completed. Add oxidant to remove Pd 2+ Oxidation to Pd 4+ , obtaining H2PdCl6 solution;

[0044] Step S2, ultrasonic reduction of the high-valent palladium solution: the HPdCl solution obtained in step S1 is neutralized with a 20% NaOH solution, and the pH value of the solution is adjusted to 8. The neutralized solution is placed in an ultrasonic reactor, and hydrazine hydrate is added under stirring to carry out reduction until no reaction occurs after the addition of the reducing agent and the solution becomes transparent and colorless, thereby completing the reduction and obtaining a high-activity palladium powder;

[0045] Step S3, buffer washing: filtering and washing the high-activity palladium powder obtained in step S2. The washing process is first washed once with 0.50% pH maintaining agent, and then washed with 40°C deionized water until neutral;

[0046] Step S4, dissolving palladium powder in a peracid solution at room temperature: the theoretical amount of 65% nitric acid required for 50g of palladium powder is 121g, 182g of nitric acid is weighed according to 1.5 times the theoretical amount, and the high-activity palladium powder washed to neutrality is divided into 3 equal parts by weight, each 16.66g, and the weighed 182g of nitric acid is added to the first portion of 16.66g of ultra-high activity palladium powder, stirred thoroughly to dissolve, and the reaction process is observed. After the reaction is completed, the solution is added with a second portion of 16.66g of high-activity palladium powder, stirred thoroughly to dissolve, and finally added to the last portion of 16.66g of palladium powder to fully dissolve, and the reaction is completed. Example 2

[0047] Step S1, aqua regia dissolution: take 100g of palladium powder, add aqua regia to dissolve according to the liquid-solid ratio of 5:1, after the dissolution is completed, concentrate and drive out the nitrate until no yellow smoke is generated by adding hydrochloric acid, and the nitrate is driven out. Slowly add 80℃ deionized water to the solution after the nitrate is driven out and continue to concentrate the volume to drive out the acid. When the volume reduction is the same as the deionized water added, repeat the operation 3 times, and the acid is driven out. Add an oxidant to Pd 2+ Oxidation to Pd 4+ , obtaining H2PdCl6 solution;

[0048] Step S2, ultrasonic reduction of the high-valent palladium solution: The HPdCl solution obtained in step 2 is neutralized with a 20% NaOH solution, and the pH of the solution is adjusted to 10. The neutralized solution is placed in an ultrasonic reactor, and hydrazine hydrate is added under stirring to carry out reduction until no reaction occurs after the addition of the reducing agent and the solution becomes transparent and colorless, thereby completing the reduction and obtaining a highly active palladium powder.

[0049] Step S3, buffer washing: filtering and washing the high-activity palladium powder. The washing process is first washed twice with a 1% pH maintaining agent, and then washed with 45°C deionized water until neutral;

[0050] Step S4, dissolving palladium powder in a peracid solution at room temperature: The theoretical amount of 65% nitric acid required for 100 g of palladium powder is 242.86 g. 364.30 g of nitric acid is weighed, which is 1.5 times the theoretical amount. The high-activity palladium powder washed to neutrality is then divided into three equal portions by weight, each weighing 33.33 g. The weighed 364.30 g of nitric acid is added to the first portion of 33.33 g of high-activity palladium powder, stirred thoroughly to dissolve, and the reaction process is observed. After the reaction is completed, the second portion of 33.33 g of high-activity palladium powder is added to the solution, stirred thoroughly to dissolve, and finally the final portion of 33.33 g of palladium powder is added and dissolved. The reaction is completed. Example 3

[0051] Step S1, aqua regia dissolution: take 500g of palladium powder, add aqua regia to dissolve according to the liquid-solid ratio of 6:1, after the dissolution is completed, concentrate and drive out the nitrate until no yellow smoke is generated by adding hydrochloric acid, and the nitrate is driven out. Slowly add 90℃ deionized water to the solution after the nitrate is driven out and continue to concentrate the volume to drive out the acid. When the volume reduction is the same as the deionized water added, repeat the operation 4 times, and the acid is driven out. Add an oxidant to Pd 2+ Oxidation to Pd 4+ , obtaining H2PdCl6 solution;

[0052] Step S2, ultrasonic reduction of the high-valent palladium solution: The HPdCl solution obtained in step 2 is neutralized with a 20% NaOH solution, and the pH of the solution is adjusted to 13. The neutralized solution is placed in an ultrasonic reactor, and hydrazine hydrate is added under stirring to carry out reduction until no reaction occurs after the addition of the reducing agent and the solution becomes transparent and colorless, thereby completing the reduction and obtaining a high-activity palladium powder;

[0053] Step S3, buffer washing: filtering and washing the high-activity palladium powder. The washing process is first washed four times with a 2% pH maintaining agent, and then washed with 50°C deionized water until neutral;

[0054] Step S4, dissolving palladium powder in sections with peracid at room temperature: the theoretical amount of 65% nitric acid required for 500g of palladium powder is 1214g, 1822g of nitric acid is weighed according to 1.5 times the theoretical amount, and the high-activity palladium powder washed to neutrality is divided into 4 equal parts by weight, each 125g, and the weighed 1822g of nitric acid is added to the first portion of 125g of ultra-high activity palladium powder, stirred thoroughly to dissolve it, and the reaction process is observed. After the reaction is completed, the solution is added to the second portion of 125g of high-activity palladium powder, stirred thoroughly to dissolve, and after the reaction is completed, the solution is added to the third portion of 125g of high-activity palladium powder, and finally added to the last portion of 125g of palladium powder to fully dissolve, and the reaction is completed. Example 4

[0055] Step S1, aqua regia dissolution: Take a certain amount of palladium powder, add aqua regia to dissolve it at a liquid-solid ratio of 4:1. Add hydrochloric acid to the reactor and heat it to a slight boil, stop heating, add palladium powder, start stirring, slowly add nitric acid in small amounts several times, and the total amount of nitric acid added is 300mL. After all the palladium powder is dissolved, concentrate the solution volume to 1500mL, slowly add hydrochloric acid to drive out the nitric acid, until no yellow smoke is produced by adding hydrochloric acid. Slowly add 70°C deionized water to the solution after driving out the nitric acid, concentrate the solution volume, and repeat the operation twice when the volume reduction is the same as the deionized water added. After the acid is driven out, add 50mL of hydrogen peroxide to Pd 2+ Oxidation to Pd 4+ , and obtain H2PdCl6 solution.

[0056] Step S2, ultrasonic reduction of the high-valent palladium solution: Neutralize the H2PdCl6 solution with a 20% NaOH solution, performing the operation in small amounts and multiple times to avoid overheating the solution, and adjust the pH value of the solution to 8. Place the neutralized solution in an ultrasonic reactor, start stirring, and slowly add 300 mL of hydrazine hydrate dropwise. The reaction temperature is 40°C and the reaction time is 1 hour to obtain a highly active palladium powder.

[0057] Step S3, buffer washing: the high-activity palladium powder is first washed once with a 0.50% sodium hydroxide solution, soaked in a funnel at room temperature for 10 minutes, filtered, and then washed with deionized water at 40°C until neutral.

[0058] Step S4, staged dissolution of palladium powder with superacid at room temperature: Weigh nitric acid according to the desired concentration of palladium nitrate and divide 500g of palladium powder into three portions, each containing 166.66g. Add sufficient nitric acid (theoretical amount: 396.22g, actual excess: 3 times, i.e., 1188.66g, volume: 837ml, liquid-to-solid ratio: 1.67:1) to the first portion of palladium powder. The reaction is exothermic. Once the first stage reaction is complete and the solution temperature is suitable, add the second portion of palladium powder. Repeat this process until the palladium powder is completely dissolved. Example 5

[0059] Step S1, aqua regia dissolution: Take a certain amount of palladium powder and dissolve it in aqua regia at a liquid-to-solid ratio of 6:1. The operation is similar to Example 4, adjusting the rate of nitric acid addition according to the intensity of the reaction. The nitric acid removal procedure is the same. Slowly add 90°C deionized water to the solution after nitric acid removal. Repeat this process three times until the volume reduction is equal to the amount of deionized water added. After the acid removal is complete, add the oxidizing agent palladium ion oxide to obtain an HPdCl solution.

[0060] Step S2, ultrasonic reduction of high-valent palladium solution: adjust the pH value of the H2PdCl6 solution to 13 with alkaline solution, add a reducing agent in an ultrasonic reactor for reduction, and other operations are similar to those in Example 4.

[0061] Step S3, buffer washing: washing twice with 2% sodium hydroxide solution, and then washing with deionized water at 40°C-50°C until neutral.

[0062] Step S4, dissolving palladium powder in sections using peracid at room temperature: Divide the palladium powder into 4 parts, and dissolve the palladium powder in sections at room temperature according to the calculated amount of nitric acid to obtain a palladium nitrate solution.

[0063] The method for preparing precious metal compounds at room temperature employed in this application allows for rapid palladium powder dissolution reaction, requiring only 0.5 hours for complete reaction, eliminating the need for additional nitric acid. The resulting palladium nitrate has a high concentration. Furthermore, the palladium powder is dissolved at room temperature, resulting in stable palladium nitrate with no precipitation observed over long periods of time.

[0064] For example, the present application sets up a comparative group, using the direct dissolution method in nitric acid and the dissolution method adding an auxiliary agent to nitric acid to prepare palladium nitrate solution, and compares them with the method of the present application. The comparison content includes the dissolution rate of palladium, the stability of palladium nitrate solution (observing whether precipitation occurs), the impurity ion content in the solution (such as chloride ion content), and the catalytic activity of the catalyst prepared using the prepared palladium nitrate as a precursor (testing indicators such as conversion rate and selectivity through specific catalytic reactions). The data of the comparative test are collated and analyzed, and presented in the form of charts to intuitively demonstrate the advantages of the method of the present application.

[0065] Nitric acid direct dissolution method

[0066] like Figure 2 As shown, 50g of palladium powder is placed in a beaker and 1.5 times the theoretical amount of nitric acid is added. The beaker is placed in an electric furnace and heated at 200°C. During the heating process, the amount of nitric acid in the beaker is observed. When the amount of yellow smoke escaping decreases, additional nitric acid is added to ensure that the reaction can proceed. After 3 hours of reaction, the reaction is stopped, filtered and dried, and the filter residue is weighed. The filter residue is placed in this beaker and dissolved repeatedly. Repeat the dissolution three times, filter, and weigh the filter residue to calculate the dissolution rate of palladium powder and the amount of nitric acid used.

[0067] Auxiliary agent dissolution method

[0068] like Figure 3 As shown, 50g of palladium powder is placed in a beaker and 1.5 times the theoretical amount of nitric acid is added. The beaker is placed on an electric furnace and heated at 80°C. After the solution reaches the temperature, hydrochloric acid is added to the beaker in small portions to help dissolve the palladium powder. The consumption of the reagents during the dissolution process is observed, and the required reagents are added at any time until the palladium powder is completely dissolved by visual observation. The reaction is terminated, filtered, and the filter residue is weighed. The filtrate is a palladium nitrate solution containing chloride ions. The chloride ions in the solution need to be driven out. Concentrated nitric acid can partially oxidize the chloride ions to generate chlorine gas at high temperature, but the temperature conditions must be strictly controlled to avoid decomposition of the palladium nitrate.

[0069] 3. This application

[0070] Place 50g of palladium powder in a beaker. Add 200mL of hydrochloric acid to the beaker and heat on an electric stove set to 90°C until it is slightly boiling. Add nitric acid to the beaker in small amounts and repeatedly until the palladium powder is completely dissolved. Concentrate the solution to remove the nitric acid and acid. Add 20mL of hydrogen peroxide dropwise to the resulting chloropalladic acid solution for oxidation. Neutralize the solution with 20% sodium hydroxide solution to a pH of 8-13. Place the neutralized solution in an ultrasonic reactor and add hydrazine hydrate dropwise until the solution becomes colorless, completing the reduction. Filter and wash the resulting ultra-high-activity palladium powder. Due to the unstable nature of palladium, rinse with deionized water at approximately 50°C until neutral. Calculate the amount of nitric acid required to dissolve 50g of palladium powder, divide the ultra-high activity palladium powder into 3 portions, each 16.6g, add 1.2 times the theoretical amount of nitric acid used for 50g of palladium powder to 16.6g of palladium powder, and after the reaction is completed, pour the second portion of palladium powder into the solution until all the palladium powder is dissolved.

[0071] The palladium nitrate obtained by the three preparation methods was analyzed in terms of dissolution rate, direct utilization rate, impurity elements and compound stability.

[0072] Table test results

[0073]

[0074] As can be seen from the table, the dissolution rate of palladium powder after repeated dissolution of palladium powder in nitric acid is only 75.32%. The solution is filtered, bottled and fixed to volume, and the direct utilization rate is 74.69%. The palladium nitrate solution obtained by repeated dissolution and the high concentration of nitrate in the solution lead to low activity of the prepared catalyst, the most important manifestation of which is the increase in the initial reaction temperature. In addition, the concentration of palladium nitrate is low, and if a high concentration solution is required, it needs to be evaporated and concentrated. After 24h and 48h of observation, a small amount of precipitation is produced in the obtained solution, and the precipitate is insoluble.

[0075] The additive dissolution method achieves high palladium powder dissolution rates and direct utilization rates. However, the chloride ion concentration in the solution after chlorine removal can still reach 0.5%, far exceeding the standard requirement. This makes chlorine removal challenging and the process difficult to operate. Furthermore, this method requires prolonged, high-temperature heating, resulting in unstable palladium nitrate and prone to precipitation. The presence of chloride ions in the solution primarily affects the catalyst in the following ways.

[0076] ① Active site coverage and poisoning

[0077] Chloride ions tend to adsorb onto the active sites of palladium, competing with reactants (such as hydrogen or organic matter) for binding, resulting in reduced catalytic activity. For example, in applications such as automotive exhaust catalysis, chloride ions can poison precious metal catalysts, significantly reducing redox activity.

[0078] ② Decreased catalyst structural stability

[0079] The introduction of chloride ions during the preparation of palladium nitrate will destroy the dispersion of palladium and affect the uniformity of the supported catalyst.

[0080] ③ Side reactions and equipment corrosion

[0081] Chloride ions can participate in side reactions at high temperatures or in acidic environments, generating HCl gas and accelerating corrosion in reactors or pipelines. In certain reactions, such as hydrogenation, chloride ions can alter the reaction pathway and reduce the selectivity of the target product.

[0082] The present invention utilizes a high-activity palladium powder dissolution method at room temperature, achieving dissolution rates of 99.99% and direct dissolution rates of 99.89%. The peracid-based dissolution method allows for rapid dissolution of the palladium powder, requiring only 0.5 hours for complete reaction. This method eliminates the need for additional nitric acid, resulting in a high concentration of palladium nitrate. Furthermore, the palladium powder is dissolved at room temperature, resulting in stable palladium nitrate with no precipitation observed over time.

[0083] Compared with the embodiment of the above method, the embodiment of the present application provides a preparation system for preparing palladium nitrate at room temperature, such as Figure 4 As shown, the system may include:

[0084] The first reaction kettle 1 and the heating device, ultrasonic reduction and filtering device and palladium nitrate dissolving device;

[0085] The outer layer of the first reactor 1 is provided with a hollow layer 5, which is connected to the heating device, and heat-conducting oil / water circulates in the hollow layer to control the temperature regulation of the aqua regia dissolution, nitrate removal, acid removal and neutralization processes;

[0086] The ultrasonic reduction and filtration device includes: a second reactor 33 for reducing high-activity palladium powder, an ultrasonic reactor 12, a first sensor 13 and a second sensor 14 for controlling the addition of reducing agent and cooling by cold water spraying, a titanium filter plate 18 and a filter bottle 34, and a gravity sensing device is provided at the bottom of the filter bottle 34; illustratively, the gravity sensing device may include a gravity sensor, etc.

[0087] The palladium nitrate dissolving device includes a first-level palladium nitrate reactor 22, a second-level palladium nitrate reactor 27, and a third-level palladium nitrate reactor 31. The palladium nitrate reactors at each level are fixedly linked to a turntable 36, and a gravity sensing device is provided at the bottom of each level of the palladium nitrate reactor. The installation height of the palladium nitrate reactors at each level on the turntable 36 is successively reduced to utilize gravity to transfer the palladium nitrate solution between the palladium nitrate reactors at each level.

[0088] Optionally, a feeding port 2 is provided at the top of the first reactor 1, and a circulation inlet 3 and a circulation outlet 4 are symmetrically provided at both ends of the first reactor 1. The circulation inlet 3 and the circulation outlet 4 are connected to the hollow layer 5. A stirring blade 6 is fixedly installed inside the first reactor 1, and a discharge switch 7 is provided at the bottom of the first reactor 1.

[0089] Optionally, a first feed switch 8 is provided at the top of the second reactor 33, a glass pipe is installed between the first feed switch 8 and the unloading switch 7, the two ends of the glass pipe are respectively connected to the first reactor 1 and the second reactor 33, a second feed switch 9 is installed at one end of the second reactor 33, one end of the second feed switch 9 passes through the second reactor 33 and extends to the interior, a first feed port 10 is provided at one end of the second feed switch 9, a first stirring paddle 11 is symmetrically provided below the first feed port 10, and the first stirring paddle 11 is fixedly connected to the inner wall of the second reactor 33;

[0090] The second reactor 33 is fixedly connected to the ultrasonic reactor 12. A connecting portion 37 is provided at the bottom of the second reactor 33. The connecting portion 37 is operatively connected to the titanium plate funnel 35. A discharge switch 17 for controlling the flow of the solution from the second reactor 33 into the titanium plate funnel 35 is provided above the connecting portion 37. A titanium filter plate 18 is fixedly installed in the titanium plate funnel 35. A rubber plug is provided below the titanium plate funnel 35 so that the titanium plate funnel 35 is operatively connected to the filter bottle 34 via the rubber plug. An air extraction hole 19 is provided at one end of the filter bottle 34, and the air extraction hole 19 is connected to an external filtration device.

[0091] A second feed port 16 is provided at the top of the second reactor 33. The second feed port 16 is in the shape of a shower head. A switch 15 is provided at the upper end of the second feed port 16. The switch 15 is used to control the cold water in the water tank to enter the second reactor 33 through the second feed port 16. A first sensor 13 is provided below the second feed port 16. A second sensor 14 is provided below the first sensor 13. Both the first sensor 13 and the second sensor 14 are fixedly connected to the second reactor 33.

[0092] The filter bottle 34 is fixedly connected to the turntable 36 . A water outlet 20 is provided at the bottom of the filter bottle 34 . The water outlet 20 is connected to the waste liquid recovery area through a hose 21 .

[0093] Optionally, the bottom end of the first-level palladium nitrate reactor 22 is fixed with a first base 23, the first base 23 is fixedly connected to the turntable 36, a second stirring paddle 24 is provided in the first-level palladium nitrate reactor 22, one end of the first-level palladium nitrate reactor 22 is provided with a first discharge port 25, the first discharge port 25 is communicated with the third feed port 26 of the second-level palladium nitrate reactor 27 through a glass tube, the bottom end of the second-level palladium nitrate reactor 27 is fixed with a second base 28, the second base 28 is fixedly connected to the turntable 36, a third stirring paddle 29 is provided in the second-level palladium nitrate reactor 27, the second base 28 is lower than the first base 23, one end of the second-level palladium nitrate reactor 27 is provided with a second discharge port 30, the second discharge port 30 is communicated with the third-level palladium nitrate reactor 31 through a glass tube, and a fourth stirring paddle 32 is provided in the third-level palladium nitrate reactor 31.

[0094] For example, in the embodiments of this application:

[0095] Aqua regia dissolution - nitric acid chase - acid chase - neutralization: hydrochloric acid is added to the first reactor 1 through the feed port 2. The outer layer of the first reactor 1 is also provided with a hollow layer 5. The two ends of the first reactor 1 are symmetrically provided with a circulation inlet 3 and a circulation outlet 4. The circulation inlet 3 and the circulation outlet 4 are connected to the hollow layer 5. Thermal oil / water is entered through the circulation inlet 3 and then flows into the thermal oil heating device through the circulation outlet 4 to ensure that the thermal oil / water in the hollow layer 5 is maintained at the temperature required for the reaction. Hydrochloric acid is added to the first reactor 1 and heated to a slight boil. The thermal oil / water is emptied and the stirring blade 6 is turned on. The palladium powder to be reacted is added to the first reactor 1 through the feed port 2. The required nitric acid is then slowly added to the first reactor through the feed port 2. During the process, pay attention to the degree of reaction and adjust the speed of adding nitric acid at any time. After the palladium powder is completely dissolved, the thermal oil / water is turned on for heating, and the nitric acid is concentrated and chased. The generated gas escapes through the feed port 2. After the nitrate removal is completed, hot deionized water is added to the solution, and heating is continued to concentrate the solution volume. The boiling point of hydrochloric acid is lower than that of deionized water to reduce the amount of hydrochloric acid in the solution. After the acid removal is completed, hydrogen peroxide is added dropwise to the solution to oxidize the divalent palladium to tetravalent palladium. After the completion, the heat transfer oil / water in the hollow layer 5 is drained and the solution is cooled naturally. When the temperature is about to reach 60-70°C, cold water is introduced into the hollow layer 5 through the circulation inlet 3 and then discharged through the circulation outlet 4 to realize cold water circulation and rapidly cool the solution. After the temperature drops to room temperature, alkali solution is added for neutralization. The neutralization process is a large exothermic process. The solution is cooled in time by the cold water circulation, which can ensure both operational efficiency and the stability of the ions in the solution.

[0096] Ultrasonic reduction-washing-filtration: After neutralization, the discharge switch 7 and the first feed switch 8 are opened, and the neutralized solution enters the second reactor 33, which is made of titanium. After the solution enters, the first stirring paddle 11 located on the reactor wall is turned on to stir the solution. Then the ultrasonic reactor 12 is turned on. When the second sensor 14 does not detect the solution, the second feed switch 9 is opened, and the reducing agent is slowly added through the first feed port 10. Because this process is relatively violent, when the second sensor 14 detects the solution, the second feed switch 9 is closed, and the reducing agent addition is stopped. When the first sensor 13 detects the solution, the switch 15 is opened, and cold water enters through the second feed port 16 to lower the reaction temperature and slow the reaction rate. The second feed port 16 is designed in a shower shape, so that the cold water contacts the reaction interface with a larger spray area, thereby rapidly reducing the reaction rate. After the reduction is completed, the ultrasonic reactor 12, the first stirring paddle 11, the first sensor 13, and the second sensor 14 are closed in sequence. Connect the titanium plate funnel 35 to the second reactor 33. 37 is the connection, and 18 is the titanium filter plate. The titanium filter plate has numerous micropores with a diameter of 1 μm, allowing direct filtration without filter paper. Connect the filter flask 34 to the titanium plate funnel 35. The funnel is fitted with a rubber stopper. Connect the air extraction port 19 to the filtration equipment. Open the discharge valve 17 to begin filtration. After draining the solution, disconnect the air extraction port 19 from the filtration equipment. Add hot deionized water at approximately 60°C (the first pass should be at a pH of approximately 10 to maintain the pH during reduction and prevent incomplete reduction, ensuring complete reduction) to the second reactor 33 through the first feed port 10. Thoroughly mix with the reduced high-activity palladium powder. After soaking for a period of time, connect the air extraction port 19 to the filtration equipment and drain the wash water. The wash solution then enters the waste liquid collection area through a hose 21 connected to the outlet 20 at the bottom of the filter flask 34. Repeat this process eight times to clean the sodium ions from the high-activity palladium powder. After cleaning, disconnect the titanium plate funnel 35 from the filter bottle 34, rotate the turntable 36 to place the first-level palladium nitrate reactor 22 below the titanium plate funnel 35, and the first-level palladium nitrate reactor 22 is provided with a first base 23 to ensure that the first-level palladium nitrate reactor 22 is in the highest position (relative to the second-level palladium nitrate reactor and the third-level palladium nitrate reactor), and transfer one-third of the material to the first-level palladium nitrate reactor 22; continue to rotate the turntable 36, place the second-level palladium nitrate reactor 27 below the titanium plate funnel 35, and provide the second base 28 at the bottom of the second-level palladium nitrate reactor 27 so that its height is lower than the first-level palladium nitrate reactor 22 and higher than the third-level palladium nitrate reactor 31, and another one-third of the material enters the second-level palladium nitrate reactor 27, continue to rotate the turntable, place the third-level palladium nitrate reactor 31 below the titanium plate funnel 35, and all the remaining materials are added to the third-level palladium nitrate reactor 31, and the third-level palladium nitrate reactor 31 is directly fixed on the turntable 36.

[0097] Nitric acid dissolution: open the second stirring paddle 24 in the first-level palladium nitrate reactor 22, add nitric acid to the first-level palladium nitrate reactor 22 (the amount of nitric acid at this time is the total amount of nitric acid used), observe the reaction process, and after the reaction is completely completed, immediately open the first discharge port 25 and the third feed port 26, turn on the third stirring paddle 29, and use the effect of gravity to allow the palladium nitrate solution to enter the second-level palladium nitrate reactor 27. Similarly, after the reaction is completed, the solution enters the third-level palladium nitrate reactor 31 until the reaction is completely completed to obtain a high-concentration palladium nitrate solution.

[0098] The first-stage palladium nitrate reaction kettle 22 , the second-stage palladium nitrate reaction kettle 27 , the third-stage palladium nitrate reaction kettle 31 , and the filter bottle 34 are all fixed on the turntable 36 .

[0099] It should be noted that, in this document, relational terms such as first and second, etc., are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply the existence of any such actual relationship or order between these entities or operations. Moreover, the terms "comprises," "comprising," or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article, or device comprising a series of elements includes not only those elements, but also other elements not explicitly listed, or elements inherent to such process, method, article, or device. In the absence of further limitations, an element defined by the phrase "comprising a ..." does not exclude the presence of other identical elements in the process, method, article, or device comprising the element.

[0100] Each embodiment in this specification is described in a related manner. Similar portions between the embodiments can be referred to in conjunction with each other. Each embodiment focuses on the differences from other embodiments. In particular, the device embodiments are generally similar to the method embodiments, so their description is relatively simple. For related portions, refer to the description of the method embodiments.

[0101] The above description is only a preferred embodiment of the present application and is not intended to limit the scope of protection of the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application are included in the scope of protection of the present application.

Claims

1. A method for preparing palladium nitrate at room temperature, characterized in that, include: Step S1, aqua regia dissolution: take a certain amount of palladium powder, add aqua regia to dissolve it at a liquid-solid ratio of 4-6:1, after the dissolution is completed, concentrate and remove the nitrate until no yellow smoke is generated by adding hydrochloric acid, and the removal of nitrate is completed. Slowly add 70℃-90℃ deionized water to the solution after removing the nitrate and continue to concentrate the volume to remove the acid. When the volume reduction is the same as the amount of deionized water added, repeat the operation 2-3 times, and the removal of acid is completed. Add an oxidant to remove Pd 2+ Oxidation to Pd 4+ , obtaining H2PdCl6 solution; Step S2, ultrasonic reduction of the high-valent palladium solution: neutralizing the HPdCl solution obtained in step S1 with an alkali solution to adjust the pH value of the solution to 8-13, placing the neutralized solution in an ultrasonic reactor, and adding a reducing agent under stirring to carry out reduction until no reaction occurs after the addition of the reducing agent and the solution becomes transparent and colorless, thereby completing the reduction and obtaining a high-activity palladium powder; Step S3, buffer washing: filtering and washing the high-activity palladium powder obtained in step S2, washing it 1-2 times with a 0.50%-2% pH maintaining agent, and then washing it with deionized water at 40°C-50°C until it becomes neutral; Step S4, dissolving the palladium powder in a peracid solution at room temperature: weighing a certain amount of nitric acid according to the concentration required for palladium nitrate, and then dividing the high-activity palladium powder washed to neutrality in step S3 into 3-4 equal parts by weight, adding the weighed quantitative nitric acid to the first part of the high-activity palladium powder, stirring thoroughly to dissolve it, and observing the reaction process. After the reaction is completed, the second part of the high-activity palladium powder is added to the solution, stirring thoroughly to dissolve it, and then the third and fourth parts of the high-activity palladium powder are added in sequence and the above operation is repeated; The preparation system for implementing the above method comprises: a first reaction kettle (1) and a heating device, an ultrasonic reduction and filtering device, and a palladium nitrate dissolving device; The outer layer of the first reactor (1) is provided with a hollow layer (5), the hollow layer (5) is connected to the heating device, and heat-conducting oil / water circulates in the hollow layer to control the temperature regulation of the aqua regia dissolution, nitrate removal, acid removal and neutralization processes; The ultrasonic reduction and filtration device comprises: a second reaction kettle (33) for reducing high-activity palladium powder, an ultrasonic reactor (12), a first sensor (13) and a second sensor (14) for controlling the addition of a reducing agent and cooling by spraying cold water, a titanium filter plate (18), and a filter bottle (34), wherein a gravity sensing device is provided at the bottom of the filter bottle (34); The palladium nitrate dissolving device comprises a first-stage palladium nitrate reactor (22), a second-stage palladium nitrate reactor (27), and a third-stage palladium nitrate reactor (31). Each palladium nitrate reactor is fixedly connected to a turntable (36), and a gravity sensing device is provided at the bottom of each palladium nitrate reactor. The installation height of each palladium nitrate reactor on the turntable (36) is successively reduced, so that the palladium nitrate solution is transferred between the palladium nitrate reactors of each stage by utilizing gravity.

2. The method according to claim 1, characterized in that The oxidant in step S1 includes hydrogen peroxide, sodium chlorate, and sodium hypochlorite.

3. The method according to claim 1, characterized in that The reducing agent in step S2 includes hydrazine hydrate and formic acid.

4. The method according to claim 1, wherein The alkali in step S2 includes sodium hydroxide and potassium hydroxide.

5. The method according to claim 1, wherein The pH maintaining agent in step S3 includes sodium hydroxide and potassium hydroxide.

6. The method according to claim 1, characterized in that Step S3 and step S4 are continuous steps, and the time for step S3 and step S4 is less than or equal to 12 hours.

7. The method according to claim 1, characterized in that The top of the first reactor (1) is provided with a feeding port (2), and both ends of the first reactor (1) are symmetrically provided with a circulation inlet (3) and a circulation outlet (4), the circulation inlet (3) and the circulation outlet (4) are connected to the hollow layer (5), a stirring blade (6) is fixedly installed inside the first reactor (1), and a discharge switch (7) is provided at the bottom of the first reactor (1).

8. The method according to claim 1, characterized in that A first feed switch (8) is provided at the top of the second reactor (33), a glass pipe is installed between the first feed switch (8) and the discharge switch (7), and both ends of the glass pipe are connected to the first reactor (1) and the second reactor (33) respectively. A second feed switch (9) is installed at one end of the second reactor (33), and one end of the second feed switch (9) passes through the second reactor (33) and extends to the interior. A first feed port (10) is provided at one end of the second feed switch (9), and a first stirring paddle (11) is symmetrically provided below the first feed port (10), and the first stirring paddle (11) is fixedly connected to the inner wall of the second reactor (33); The second reactor (33) is fixedly connected to the ultrasonic reactor (12), a connecting portion (37) is provided at the bottom of the second reactor (33), the connecting portion (37) is operatively connected to the titanium plate funnel (35), a discharge switch (17) for controlling the solution from the second reactor (33) into the titanium plate funnel (35) is provided above the connecting portion (37), a titanium filter plate (18) is fixedly installed in the titanium plate funnel (35), a rubber plug is provided below the titanium plate funnel (35), so that the titanium plate funnel (35) is operatively connected to the filter bottle (34) through the rubber plug, and an air extraction hole (19) is provided at one end of the filter bottle (34), and the air extraction hole (19) is connected to an external filtration device; A second feed port (16) is provided at the top of the second reactor (33), and the second feed port (16) is in the shape of a shower. A switch (15) is provided at the upper end of the second feed port (16), and the switch (15) is used to control the cold water in the water tank to enter the second reactor (33) through the second feed port (16). A first sensor (13) is provided below the second feed port (16), and a second sensor (14) is provided below the first sensor (13). Both the first sensor (13) and the second sensor (14) are fixedly connected to the second reactor (33); The filter bottle (34) is fixedly connected to the turntable (36). A water outlet (20) is provided at the bottom of the filter bottle (34). The water outlet (20) is connected to the waste liquid recovery area through a hose (21).

9. The method according to claim 1, characterized in that A first base (23) is fixed at the bottom end of the first palladium nitrate reactor (22), and the first base (23) is fixedly connected to the turntable (36). A second stirring paddle (24) is provided in the first palladium nitrate reactor (22). A first discharge port (25) is provided at one end of the first palladium nitrate reactor (22), and the first discharge port (25) is communicated with a third feed port (26) of the second palladium nitrate reactor (27) through a glass tube. A second base (28) is fixed at the bottom end of the second palladium nitrate reactor (27), and the second base (28) is fixedly connected to the turntable (36). A third stirring paddle (29) is provided in the second palladium nitrate reactor (27), and the second base (28) is lower than the first base (23). A second discharge port (30) is provided at one end of the second palladium nitrate reactor (27), and the second discharge port (30) is communicated with a third palladium nitrate reactor (31) through a glass tube. A fourth stirring paddle (32) is provided in the third palladium nitrate reactor (31).

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