Microwave digestion solution and microwave digestion method for high-purity alumina-based catalyst

Abstract

The invention discloses a microwave digestion solution and a microwave digestion method for a high-purity alumina-based catalyst, and relates to the technical field of substance determination methods. The microwave digestion method comprises the following steps: placing a pretreated sample in a polytetrafluoroethylene cup, adding a microwave digestion solution, sealing and placing in a microwave digestion instrument for digestion, and determining the element content of the obtained digestion solution by adopting an inductively coupled plasma atomic emission spectrometry method, the volume ratio of hydrochloric acid to nitric acid to water in the microwave digestion solution is (5-3): (3-5): 1. On one hand, product consistency and effectiveness and stability of a detection result can be ensured, and introduction of exogenous pollution is avoided; on the other hand, digestion is rapid, consumption of manpower, material resources, time, reagents and the like is saved, efficiency can be effectively improved, and the method is suitable for synchronous treatment and detection analysis of large-batch samples in the actual operation process.

Description

Technical Field

[0001] The present invention relates to the technical field of substance determination methods, and particularly relates to a microwave digestion solution and a microwave digestion method for a high-purity alumina-based catalyst. Background Art

[0002] The key active component of the alumina-based catalyst is usually the noble metal palladium, which is widely used in the pyrolysis gasoline hydrogenation reaction device in daily life, and the carrier is a multi-morphological alumina with a relatively complex structure. Since the price of the noble metal palladium is relatively expensive, the selection of the digestion solution is crucial in the process of transferring the noble metal palladium from the solid catalyst.

[0003] Generally, strong acids are required to digest high-purity alumina. However, the digestion with a single type of strong acid has disadvantages such as low efficiency, long reaction time, and incomplete digestion effect. Although the conventional phosphoric acid-sulfuric acid digestion solution system can digest most multi-morphological aluminas, the operation is dangerous during the heating process, the acid gas leaks severely, and the viscosity of the acid solution system is relatively high, which will have a certain impact on the subsequent elemental result analysis. Moreover, the above methods cannot ensure the complete dissolution of multi-morphological alumina and the accurate determination of elements.

[0004] Therefore, it is of great significance to establish a full-process SOP method from sample preparation → digestion → detection with high efficiency, low consumption, and batch accurate detection of element content for the actual process production quality assessment and cost control. Summary of the Invention

[0005] To solve the problems of the prior art, the present invention provides a microwave digestion solution and a microwave digestion method for a high-purity alumina-based catalyst, which can achieve the complete digestion of the high-purity alumina-based catalyst and reduce the consumption to a certain extent during the determination of metal elements and other trace elements, so as to control the product quality and process technology cost, and has the advantages of high efficiency, low consumption, accurate detection, and high safety factor.

[0006] To achieve the above object, the technical solutions adopted by the present invention include: The present invention provides a microwave digestion solution for a high-purity alumina-based catalyst, and the volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 5-3: 3-5: 1.

[0007] Optionally, the volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 3: 5: 1.

[0008] Optionally, the volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 4: 4: 1.

[0009] Optionally, the volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 5: 3: 1.

[0010] The present invention also provides a microwave digestion method for a high-purity alumina-based catalyst. The microwave digestion method includes: placing the pretreated sample in a polytetrafluoroethylene cup, adding a microwave digestion solution, sealing it and placing it in a microwave digester for digestion, and measuring the element content of the obtained digestion solution by inductively coupled plasma atomic emission spectrometry; The volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 5 - 3: 3 - 5: 1.

[0011] Optionally, the set conditions for the digestion adopt a three-stage gradient temperature increase.

[0012] Optionally, the set conditions for the digestion include: under the condition of ≥20 psia, first keep the temperature at 120 - 140 °C for 2 - 5 min, then keep the temperature at 150 - 170 °C for 2 - 5 min, and then keep the temperature at 180 - 220 °C for 8 - 30 min.

[0013] Optionally, the set conditions for the digestion include: under the condition of 20 psia, first keep the temperature at 120 °C for 2 min, then keep the temperature at 150 °C for 2 min, and then keep the temperature at 180 °C for 10 min.

[0014] Optionally, the set conditions for the digestion include: under the condition of 20 psia, first keep the temperature at 120 °C for 2 min, then keep the temperature at 150 °C for 2 min, and then keep the temperature at 180 °C for 8 min.

[0015] Optionally, the set conditions for the digestion include: under the condition of 20 psia, first keep the temperature at 120 °C for 5 min, then keep the temperature at 150 °C for 5 min, and then keep the temperature at 220 °C for 30 min.

[0016] Optionally, the set conditions for the digestion include: under the condition of 20 psia, first keep the temperature at 120 °C for 5 min, then keep the temperature at 150 °C for 5 min, and then keep the temperature at 200 °C for 30 min.

[0017] Optionally, the set conditions for the digestion include: under the condition of 20 psia, first keep the temperature at 120 °C for 5 min, then keep the temperature at 150 °C for 5 min, and then keep the temperature at 180 °C for 20 min.

[0018] Optionally, the mass-to-volume ratio of the pretreated sample to the microwave digestion solution is 0.05 - 0.125 g: 9 mL, preferably 0.1 g: 9 mL.

[0019] Optionally, the element is palladium or ruthenium.

[0020] Optionally, the pretreatment includes sampling the sample by the quartering method and mixing it evenly, and grinding the sample into a uniform powder with an agate mortar.

[0021] Optionally, the particle size of the pretreated sample < 50 μm.

[0022] The beneficial effects of the present invention include: The present invention uses the inductively coupled plasma atomic emission spectrometry (ICP-AES) method to detect the data of the spike recovery experiment of precious metal elements in the sample, and the recovery rate reaches 86.85% - 99.43%. It is proved that the digestion solution adopted by the present invention can completely digest the high-purity alumina-based catalyst under the condition of gradient heating, and accurately determine the precious metal elements therein, forming a stable and reliable sample evaluation mechanism.

[0023] On the one hand, the present invention can ensure the product consistency, the effectiveness and stability of the detection results, and avoid the introduction of exogenous pollution; on the other hand, it can quickly digest, save the consumption of manpower, material resources, time, reagents, etc., effectively improve the efficiency, and is suitable for the synchronous processing and detection analysis of a large number of samples in the actual operation process. At the same time, the reaction is carried out in a closed space with gradient heating, avoiding violent reactions, effectively reducing the operation risk, ensuring safety, and having obvious advantages compared with the traditional digestion method. Specific embodiments

[0024] The present invention uses water, hydrochloric acid and nitric acid in a combined ratio, which can greatly improve the digestion efficiency and effectively avoid the occurrence of existing problems. Especially for the high-purity alumina-based palladium catalyst, dissolving requires specific types and concentrations of acids. Through the optimization of the experimental process, the acid solution ratio is determined, and the activity of the reaction system is adjusted to avoid the passivation of the precious metal surface caused by a strong acid environment. While ensuring the complete dissolution of the alumina matrix, the efficient release of palladium is realized, ensuring the accuracy, effectiveness and stability of the detection results.

[0025] The present invention uses guaranteed reagent grade reagents and secondary water, which can effectively avoid the introduction of impurity interference and effectively improve the accuracy of detection, especially suitable for the treatment of high-purity samples. The samples of the present invention are ground in an agate mortar to ensure the uniform distribution of nanoscale Pd active sites, with the particle size controlled < 50 μm, increasing the contact area of the digestion reaction and accelerating the completion of the reaction.

[0026] The digestion solution of the present invention does not need secondary dilution / acid adjustment, and is directly compatible with plasma excitation, effectively combining the advantages of high sensitivity and simultaneous multi-element detection of ICP-AES to achieve the purpose of improving the analysis efficiency. The detection limit of palladium element can be as low as 0.05 μg / g, and the recovery rate is 86.85% - 99.43%.

[0027] The present invention completes the premixing of the acid solution in a polytetrafluoroethylene cup, and the whole microwave digestion reaction is completed in a closed space, reducing the loss of volatile components, having a high safety factor, greatly reducing the acid gas leakage in the conventional digestion process and effectively improving the safety of the operation.

[0028] During the digestion of the present invention, the sample structure is pre-activated by a first-stage temperature increase, the main reaction is initiated by a second-stage temperature increase, and the decomposition of the remaining refractory components is completed by a third-stage temperature increase. The total time consumption is short, and the time is greatly shortened compared with the traditional method. Moreover, the staged temperature control can effectively avoid the pressure increase caused by the sudden reaction of the sample, further ensuring safety.

[0029] The palladium catalyst described in the present invention is any high-purity alumina-based palladium catalyst purchased from the market.

[0030] The ruthenium catalyst described in the present invention is any high-purity alumina-based ruthenium catalyst purchased from the market.

[0031] The quartering sampling method described in the present invention, also called the coning and quartering method, refers to a sample reduction operation method in which each sample is piled into a uniform conical shape, pressed into a frustum of a cone, and then divided into four equal parts by a cross-shaped frame.

[0032] The following further elaborates on the present invention in conjunction with embodiments. The following embodiments can enable those of ordinary skill in the art to more comprehensively understand the present invention, but do not limit the present invention in any way.

[0033] Example 1 0.1 g of the palladium catalyst was sampled and mixed evenly by the quartering method, ground into a powder in an agate mortar with a particle size <50 μm. The ground sample was placed in a polytetrafluoroethylene cup, and microwave digestion solution was added. It was sealed and placed in a microwave digester. The microwave digestion solution consisted of 3 mL of hydrochloric acid, 5 mL of nitric acid, and 1 mL of secondary water. The set conditions for microwave digestion were: under 20 psia, first hold at 120 °C for 2 min, then hold at 150 °C for 2 min, and then hold at 180 °C for 10 min. The experimental results showed that the sample in this example could be completely dissolved, and through the spike recovery experiment and ICP-AES detection method for verification, it could meet the expected target requirements. The spike recovery rate of palladium element is shown in Table 1.

[0034] Example 2 The difference from Example 1 was that the component ratio in the microwave digestion solution was changed, as shown in Table 2 specifically. The experimental results showed that the sample in this example could be completely dissolved, and through the spike recovery experiment and ICP-AES detection method for verification, it could meet the expected target requirements. The spike recovery rate of palladium element is shown in Table 2.

[0035] Example 3 The difference from Example 1 was that the heating time and temperature at each stage in the microwave digestion set conditions were changed, as shown in Table 3 specifically. The experimental results showed that the sample in this example could be completely dissolved, and through the spike recovery experiment and ICP-AES detection method for verification, it could meet the expected target requirements. The spike recovery rate of palladium element is shown in Table 3.

[0036] Example 4 Different from Example 1, a ruthenium catalyst was used. The experimental results show that the sample of this example can be completely dissolved, and through the spike recovery experiment and ICP-AES detection method for verification, it can meet the expected target requirements. The spike recovery rate of ruthenium element is shown in Table 4.

[0037] Example 5 Different from Example 1, the weight of the sample after pretreatment was changed. The experimental results show that the sample of this example can be completely dissolved, and through the spike recovery experiment and ICP-AES detection method for verification, it can meet the expected target requirements. The spike recovery rate of palladium element is shown in Table 5.

[0038] Example 6 Different from Example 1, the sample particle size was >50 μm. The experimental results show that through the spike recovery experiment and ICP-AES detection method for verification, the palladium recovery rate of the sample in this example was <80%. When the sample particle size was >50 μm, the sample could not be completely dissolved. Therefore, to accelerate the completion of the reaction, increase the reaction contact area, and ensure the accuracy and effectiveness of the results, the particle size of the sample of the present invention should be controlled <50 μm after being treated with an agate mortar.

[0039] Comparative Example 1 Different from Example 1, the microwave digestion consisted of 1 mL of secondary water, 6 mL of hydrochloric acid, and 2 mL of nitric acid. The experimental results show that the sample of this example can be completely dissolved, but through the spike recovery experiment and ICP-AES detection method for verification, it could not meet the expected target requirements. The spike recovery rate of palladium element is shown in Table 6.

[0040]

[0041] Comparative Example 2 Different from Example 1, the component ratio of the microwave digestion solution was 1 mL of secondary water, 2 mL of hydrochloric acid, 6 mL of nitric acid or 1 mL of secondary water, 1 mL of hydrochloric acid, 7 mL of nitric acid. The experimental results show that the sample of this comparative example could not be completely dissolved.

[0042] Comparative Example 3

[0043] The microwave digestion of this comparative example consisted of 1 mL of secondary water, 4 mL of hydrochloric acid, and 4 mL of nitric acid, but different from Example 2, the set condition of the microwave digestion was to directly heat up to 200 °C and keep warm for 14 min. The experimental results show that the sample of this comparative example could not be completely dissolved.

[0044] Although specific aspects of the invention have been explained and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. Accordingly, the appended claims are intended to cover all such changes and modifications that fall within the scope of the invention.

Claims

1. A microwave digestion solution of a high-purity alumina-based catalyst, characterized in that: The volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 5-3:3-5:

1.

2. The microwave digestion solution according to claim 1, characterized in that: The volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 3:5:

1.

3. A microwave digestion method for high-purity alumina-based catalysts, characterized in that: The microwave digestion method comprises: placing the pretreated sample in a polytetrafluoroethylene cup, adding a microwave digestion solution, sealing and placing the sample in a microwave digestion instrument for digestion, and determining the element content of the obtained digestion solution by using an inductively coupled plasma atomic emission spectrometry method; The volume ratio of each component in the microwave digestion solution is hydrochloric acid: nitric acid: water = 5~3:3~5:

1.

4. The microwave digestion method according to claim 3, characterized in that: The set conditions for the digestion adopt a three-stage gradient temperature increase.

5. The microwave digestion method according to claim 3 or 4, characterized in that: The digestion setting conditions include: under the condition of pressure ≥ 20psia, first keep warm at 120-140°C for 2-5min, then keep warm at 150-170°C for 2-5min, and then keep warm at 180-220°C for 8-30min.

6. The microwave digestion method according to any one of claims 3 to 5, characterized in that: The digestion setting conditions include: under 20 psia conditions, first keep warm at 120° C. for 2 minutes, then keep warm at 150° C. for 2 minutes, and then keep warm at 180° C. for 10 minutes.

7. The microwave digestion method according to any one of claims 3 to 6, characterized in that: The mass volume ratio of the pretreated sample to the microwave digestion solution is 0.05-0.125 g:9 mL, preferably 0.1 g:9 mL.

8. The microwave digestion method according to any one of claims 3 to 7, characterized in that: The element is palladium or ruthenium.

9. The microwave digestion method according to any one of claims 3 to 8, characterized in that: The pretreatment comprises sampling and mixing the samples uniformly by using the quartering method, and grinding the samples into uniform powder by using an agate mortar.

10. The microwave digestion method according to any one of claims 3 to 9, characterized in that: The particle size of the sample after the pretreatment is less than 50 μm.

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