An ashing method for an organochromium catalyst and its application

Abstract

This invention provides an ashing method for organochromium catalysts, comprising the following steps: a mixture of an ashing aid and the organochromium catalyst is reacted in a sealed oxygen-containing atmosphere under the synergistic effect of microwaves and high frequency, with the temperature programmed to <350°C, to completely ashing the organic matter in the organochromium catalyst; wherein the ashing aid is selected from nitrates; and the reaction pressure is less than 20.0 MPa. This invention, by ashing under the combined action of an ashing aid and high frequency with microwaves, effectively and completely removes organic matter from organochromium catalysts at low temperatures. This method overcomes the shortcomings of existing organochromium catalysts, which suffer from volatilization losses during conventional ashing or wet digestion treatments. It offers advantages such as a wide range of sample amounts, high accuracy, and suitability for the analysis and detection of chromium and other elements in different organochromium catalysts.

Description

Technical Field

[0001] This invention relates to the field of ashing technology, and in particular to an ashing method and application of an organic chromium catalyst. Background Technology

[0002] Chromium-based catalysts, as the main catalysts in ethylene polymerization, were first proposed for use in ethylene polymerization processes by Phillips Petroleum Company in the early 1950s. Subsequently, Univation introduced a new generation of chromium-based catalysts. Due to their simple preparation methods and high catalytic activity, chromium-based catalysts have been a research hotspot in the field of olefin polymerization since their inception. Currently, nearly half of the products in high-density polyethylene production are obtained using supported chromium-based catalysts. Supported chromium-based catalysts generally include inorganic chromium-based (chromium oxide-based) and organic chromium-based catalysts. Inorganic chromium-based catalysts mainly consist of inorganic chromium salts and chromium oxides; organic chromium-based catalysts utilize chromium atoms to coordinate and form organic catalysts, thus exhibiting good adaptability, high catalytic activity, and high stability.

[0003] In recent years, with the updating of ethylene polymerization processes and the development of new products, many modified chromium-based catalysts have emerged to meet higher demands and overcome the shortcomings of existing chromium-based catalysts. For example, compounds containing elements such as aluminum, magnesium, titanium, zirconium, and fluorine are added as modifiers during catalyst preparation; or different organometallic compounds (alkylates of aluminum, zinc, magnesium, lithium, boron, etc.) are added as co-catalysts during the polymerization process of chromium-based catalysts, thereby directly altering the polymer's properties. Since the different ratios of chromium salts, metal oxides, and co-catalysts during the synthesis of supported chromium-based ethylene polymerization catalysts directly affect the catalyst's activity, effective analysis of the chromium content and other metal or non-metal elements in chromium-based catalysts can fully assess the catalyst's performance, providing technical support for the development of chromium-based catalysts. This is crucial for the development of new polyolefin products.

[0004] Currently, numerous analytical methods exist for the analysis of metal elements in chromium-based ethylene polymerization catalysts, such as ICP-AES internal standard method, chemical analysis method-ferrous ammonium sulfate method, iodometric method, microwave digestion-inductively coupled plasma mass spectrometry (ICP-AES), etc. In other words, most existing pretreatment techniques employ microwave digestion and chemical methods to treat organic chromium-based samples, followed by analysis using ICP-AES. Microwave digestion involves rapidly digesting the sample in a sealed container by increasing temperature and pressure. During microwave digestion, a gradual temperature increase is generally used to avoid excessively vigorous reactions in high-organic-content samples, which could lead to gas release from the digestion vessel, potentially causing significant sample overflow and loss. Furthermore, continuous heating time should not exceed 10 minutes; excessively high temperatures can soften the vessel and cause accidents. Therefore, the parameter adjustments of the microwave digester have a significant impact on the digestion effect and analytical results. Inappropriate parameter settings may lead to incomplete digestion or the generation of interfering substances.

[0005] Given the current situation where existing supported organic chromium catalysts have high chromium content and a wide variety of supported and modified elements, microwave digestion methods are no longer sufficient in terms of applicability. In particular, for the determination of volatile elements such as boron and fluorine, the use of microwave digestion still carries the risk of volatilization loss and the defect of incomplete digestion of high-concentration elements.

[0006] Ashing is a method that uses high temperatures to remove organic matter from a sample. The remaining ash is dissolved in acid and used as the sample solution for analysis. Traditional ashing involves dehydrating and carbonizing the organic sample at high temperatures (450–850°C). Under the influence of oxygen in the air, the organic matter undergoes complete oxidative decomposition, breaking C / C bonds. The generated carbon dioxide, water, and other gases evaporate. Simultaneously, many non-volatile components in the sample are converted into monomers, oxides, or heat-resistant salts. The remaining inorganic matter is dissolved in hydrochloric acid or nitric acid for analysis. However, under high-temperature conditions, mercury, lead, cadmium, tin, and selenium are easily lost through volatilization, making traditional ashing unsuitable for analyzing the content of metallic elements. Low-temperature ashing involves heating organic matter to below 400°C (generally <100–400°C) to decompose it into inorganic substances and carbon. The carbon is then mixed with other inorganic substances to obtain an ash-like substance, such as plasma low-temperature ashing. However, during the low-temperature ashing process, organic matter may not be completely ashed, or may even remain on the container wall and cannot be extracted; or volatile components may volatilize, leading to inaccurate element detection in organic chromium catalysts.

[0007] For example, Chinese patent document CN110808210A discloses a plasma processing method and a plasma ashing apparatus. After plasma etching using a mask with a boron-containing amorphous carbon film, plasma is used to selectively remove the amorphous carbon film from a silicon nitride film, a silicon oxide film, or a tungsten film. The method includes a removal step using plasma generated from a mixture of O2 and CH3F gases to remove the amorphous carbon film. In this plasma ashing method for removing boron-containing amorphous carbon films using plasma, both the removal rate of the boron-containing amorphous carbon film and the suppression of lateral etching towards the trench sidewall layer can be achieved. However, this method is not suitable for processing organochromium catalysts.

[0008] Chinese patent document CN 114664630 A discloses a plasma rapid ashing system and method, including an electronic control system, a furnace body, and a gas filling and exhaust system. The gas filling and exhaust system is connected to the furnace body. A microwave generating system and a temperature detection module are installed inside the furnace body, both of which are connected to the electronic control system. The furnace body includes a furnace frame, a furnace shell, and a base. The base is located inside the furnace shell. A furnace door is located at the inlet of the furnace shell, and a gas filling pipe and an exhaust pipe are located at the outlet of the furnace shell. Both the exhaust pipe and the gas filling pipe are connected to the gas filling and exhaust system. A gas filling sealing valve is installed on the gas filling pipe, and an exhaust sealing valve is installed on the exhaust pipe. However, this method is not suitable for the treatment of organochromium catalysts.

[0009] The standard HG / T 5762-2020, "Analytical Method for Chemical Composition of Chromium-Based Ethylene Polymerization Catalysts," proposes a wet digestion method using nitric acid and hydrofluoric acid on a hot plate to treat chromium-based ethylene polymerization catalysts. After complete dissolution, the catalysts are transferred to volumetric flasks for analysis. This method is suitable for determining the Cr, Ti, and Al content in the catalysts; however, the wet open digestion process carries the risk of elemental volatilization loss.

[0010] To address the shortcomings of existing ashing techniques and wet digestion methods, and considering the characteristics of supported organochromium catalysts, this study aims to develop a treatment method for organochromium catalysts that offers high ashing efficiency, good adaptability, high accuracy, and avoids volatilization loss. This method is of great significance for the development of chromium catalysts and allows for the detection of their elements. Summary of the Invention

[0011] The purpose of this invention is to provide an ashing method for organochromium catalysts. By ashing with an ashing aid and high-frequency synergistic microwave plasma, organic matter in the organochromium catalyst can be effectively and completely removed at low temperatures. The resulting inorganic chromium compounds and other metal and non-metal compounds are easily dissolved by acid and leave the ashing device without remaining there. Inductively coupled plasma atomic emission spectrometry (ICP-AES) is then used for analysis. This method overcomes the shortcomings of existing organochromium catalysts, which suffer from volatilization losses during conventional ashing or wet digestion processes. It offers advantages such as a wide range of sample volumes, high accuracy, and suitability for the analysis and detection of chromium and other elements in various organochromium catalysts.

[0012] To achieve the above objectives, the present invention provides the following technical solution:

[0013] An ashing method for an organochromium catalyst includes the following steps:

[0014] The mixture of ashing aid and organochromium catalyst is reacted in a closed oxygen-containing atmosphere under the synergistic effect of microwave and high frequency, with the temperature programmed to <350°C, so as to completely ashing the organic matter in the organochromium catalyst.

[0015] The ashing aid is selected from nitrates; the reaction pressure is less than 20.0 MPa.

[0016] Optionally, in the ashing method of the organochromium catalyst provided by the present invention, the mass ratio of the organochromium catalyst to the ashing aid is (1-10):1.

[0017] Optionally, in the ashing method for the organochromium catalyst provided by the present invention, the ashing aid is selected from any one of KNO3, NaNO3, Ca(NO3)2, and Zn(NO3)2, and the ashing aid does not contain the element to be measured subsequently. In addition, the spectral interference of the introduced new element on the element to be measured when the element is measured by inductively coupled plasma atomic emission spectrometry should be considered to avoid the elements having similar or overlapping wavelengths. Specifically, the ashing aid can be determined according to the actual component to be measured in the organochromium catalyst.

[0018] Optionally, in the ashing method of the organic chromium catalyst provided by the present invention, the frequency of the high frequency is 40-200 kHz and the output power is 0.5-2.0 kW.

[0019] Optionally, in the ashing method for the organic chromium-based catalyst provided by the present invention, the microwave frequency is 2450MHz and the output power is 0.1 to 6.0KW.

[0020] The specific operating parameters for high frequency and microwave can be adjusted according to the requirements of different samples.

[0021] Optionally, in the ashing method of the organochromium catalyst provided by the present invention, the programmed temperature rise includes two stages; the first stage is to heat from room temperature to T1 and hold for 5 to 10 minutes; the second stage is to heat from T1 to T2 and hold for 15 to 30 minutes; T1 = 150 to 180°C, T2 = 200 to 280°C.

[0022] Optionally, in the ashing method of the organochromium catalyst provided by the present invention, the programmed temperature rise includes three stages: the first stage is to heat from room temperature to T1 and hold for 5 to 10 minutes; the second stage is to heat from T1 to T2 and hold for 5 to 10 minutes; the third stage is to heat from T2 to T3 and hold for 15 to 30 minutes; T1 = 70 to 90°C, T2 = 150 to 170°C, and T3 = 280 to 300°C.

[0023] Optionally, in the ashing method for the organic chromium-based catalyst provided by the present invention, after the programmed heating is completed, the process further includes turning off the microwave and the high frequency, and cooling from T2 to room temperature.

[0024] The rates of the above-mentioned temperature ramp-up and cooling processes are not specifically limited, as long as the organic matter in the organochromium catalyst is completely ashed. The recommended rates for the above-mentioned temperature ramp-up and cooling processes are 8-12 °C / min. The specific settings of T1 and T2 during the temperature ramp-up process can be based on the decomposition temperature and thermal weight loss of the sample measured by the simultaneous thermal analyzer, and the melting point of the sample measured by the differential scanning calorimeter.

[0025] Optionally, the ashing method for the organic chromium-based catalyst provided by this invention is carried out in an ashing furnace equipped with a fiber optic temperature sensor. By using fiber optic temperature control, it is not affected by microwave field interference, and the measurement accuracy is high, with good safety. When microwave and high frequency are not activated, the temperature control range of the ashing furnace equipped with the fiber optic temperature sensor is 0 to 1000℃, the temperature control accuracy is ±0.5℃, and the heating and cooling rate is 0.01 to 99.99℃ / min.

[0026] The present invention also provides a method for determining the elemental content in an organochromium catalyst, including the step of obtaining ash by the above-mentioned ashing method of the organochromium catalyst.

[0027] Optionally, the method for determining the elemental content in an organochromium catalyst provided by the present invention further includes the step of dissolving and adjusting the volume of the ash with acid, and then measuring it using an inductively coupled plasma atomic emission spectrometer; the element is selected from at least one of chromium, titanium, magnesium, aluminum, zinc, zirconium and boron.

[0028] Compared with the prior art, the present invention has the following advantages:

[0029] Beneficial Effect 1: The ashing method for the organic chromium-based catalyst provided by this invention, through the synergistic effect of ashing aids, high frequency and microwave, ashing the organic matter in the organic chromium-based catalyst at low temperature in a closed oxygen-containing atmosphere, can prevent the loss of some volatile elements and improve the sample ashing efficiency, while effectively preventing the retention problem of the sample during the ashing process. At the same time, it can make the analyte form a more stable inorganic salt and be easier to transfer, thus avoiding the problems of volatilization and transfer loss in sample processing.

[0030] Beneficial Effect 2: The ashing method for organic chromium catalysts provided by this invention achieves efficient and lossless processing of supported organic chromium catalyst samples, satisfying the requirement for accurate determination of chromium and other elements in the samples. Attached Figure Description

[0031] Figure 1 This is a melting point analysis diagram of the organic chromium catalyst (Cat-1) in Example 1 of the present invention;

[0032] Figure 2 This is an analytical graph showing the decomposition temperature and thermal weight loss of the organic chromium catalyst (Cat-1) in Example 1 of the present invention;

[0033] Figure 3 This is a melting point analysis diagram of the organic chromium catalyst (Cat-4) in Example 2 of the present invention;

[0034] Figure 4 This is an analytical graph showing the decomposition temperature and thermal weight loss of the organic chromium catalyst (Cat-4) in Example 2 of the present invention;

[0035] Figure 5 This is a melting point analysis diagram of the organic chromium catalyst (Cat-5) in Example 3 of the present invention;

[0036] Figure 6 This is an analytical graph showing the decomposition temperature and thermal weight loss of the organic chromium catalyst (Cat-5) in Example 3 of the present invention. Detailed Implementation

[0037] The present invention will now be described in detail through embodiments. It should be noted that the following embodiments are only for further illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0038] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0039] Simultaneous thermal analyzer, Netzsch STA409PC, Germany, ozone atmosphere, 10 mL / min, to determine decomposition temperature and thermal weight loss;

[0040] Differential scanning calorimetry (DSC250, TA Instruments, USA) was used to determine the melting point.

[0041] Inductively coupled plasma atomic emission spectrometry (ICP-AES), PE Corporation AVI500, USA, was used to determine elemental concentrations (the instrument results are automatically retained to five significant digits);

[0042] Muffle furnace, Beijing Labtech Instrument Co., Ltd., room temperature ~ 1050℃, temperature sensitivity ±1℃;

[0043] Quartz crucible, 30 mL, with quartz lid.

[0044] Ashing furnace, room temperature to 400℃, temperature sensitivity ±0.5℃, ozone atmosphere.

[0045] Dissolve the residual sample in the sample dish by adding about 5-10 mL of 2%-5% dilute nitric acid or dilute hydrochloric acid, and place it on a hot plate at a low temperature of 120-150°C. After dissolution, transfer the solution to a 100 mL volumetric flask with 2%-5% dilute nitric acid or dilute hydrochloric acid and make up to volume before measurement. The measuring instrument used is ICP-AES.

[0046] The organometallic standards used in the spiking recovery test were: chromium isooctanoate, 10% (m / m); titanate, 5% (m / m); alkyl magnesium, 5% (m / m); methylaluminum, 5% (m / m); diethylzinc, 5% (m / m); zirconium isooctanoate, 2% (m / m); and diborane, 2% (m / m).

[0047] Example 1

[0048] This embodiment provides an ashing method for an organochromium catalyst (Cat-1, Cat-2, and Cat-3, which are the same type of chromium catalyst with the same type of supported elements). The metals supported in the organochromium catalyst are zinc and zirconium. The ashing method includes the following steps:

[0049] (1) Investigation of ashing temperature

[0050] The melting point of Cat-1 was determined using a differential scanning calorimeter, such as Figure 1 As shown. By Figure 1 It is known that the melting point of Cat-1 is approximately 160℃.

[0051] The decomposition temperature and pyrogravimetric analysis of Cat-1 were performed using a simultaneous thermal analyzer, and the results are as follows: Figure 2 As shown. By Figure 2It can be seen that Cat-1 exhibits three stages of mass change, with mass decreases occurring at 160℃, 257℃, and 505℃. 160℃ is precisely the melting point of Cat-1. Further heating to 257℃ initiates the decomposition of organic matter in Cat-1. Continuing to heat to 505℃ results in the greatest weight loss from heat, after which the mass remains unchanged, indicating complete decomposition of organic matter in Cat-1. Based on these temperature points, the ashing temperature and ashing time of Cat-1 were investigated.

[0052] Five parallel Cat-1 samples were weighed, each weighed accurately to three decimal places (0.5 g). Each sample was mixed thoroughly with approximately 0.1 g of ashing aid Ca(NO3)2. The samples were then ashed in an oxygen atmosphere using an ashing furnace under different programmed temperature rise conditions, with the combined effects of microwave and high frequency. The specific operation is as follows:

[0053] The well-mixed sample and ashing aid mixture was placed in a quartz crucible and covered with a quartz lid. The crucible containing the sample was then placed in an ashing furnace. The vacuum pump was started to evacuate the furnace. Microwave and high-frequency equipment were then activated, and oxygen was introduced to maintain a system pressure of 5.0 MPa. The microwave frequency was 2450 MHz with an output power of 0.1 kW; the high-frequency equipment was set to 200 kHz with an output power of 2.0 kW. A programmed temperature rise was then initiated.

[0054] The samples were heated from room temperature to 160℃ at a rate of 10℃ / min and held at 160℃ for 10 min. Then, the temperatures were increased from 160℃ to 180℃, 200℃, 230℃, 260℃, and 280℃ at a rate of 10℃ / min for ashing experiments. The completeness of ashing was observed. The ash samples obtained from ashing at different temperatures were dissolved using the method described above and analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific results are shown in Table 1-1.

[0055] Table 1-1 Results of Ashing Temperature Investigation in the Second Stage

[0056]

[0057]

[0058] Over-ashing of the sample can lead to carbonization. Carbonized samples require decarbonization at 550–700℃ to obtain ash, but this temperature range is too high and results in elemental volatilization losses. This method uses an ashing aid and microwave-assisted high-frequency ashing in an ion atmosphere to promote ashing. During the heating process, the organic macromolecular chains break down, forming small C and H molecules that are removed through volatilization. Chromium reacts with the ashing aid to form stable chromium nitrate. Based on the data in Table 1-1 above, the final temperature program parameters for the Cat-1 sample are shown in Table 1-2 below.

[0059] Table 1-2 Temperature rise procedure for ashing

[0060] step Temperature / °C Speed ​​ / (°C / min) Hold time / min 1 Room temperature ~160°C 10 10 2 160～260 10 30 3 260°C to room temperature 10 25

[0061] (2) Comparative test between ordinary ashing method and the ashing method of the present invention

[0062] Two sets of parallel Cat-1 samples were accurately weighed and ashed according to the following method (each method was performed three times in parallel). The ash content was measured by inductively coupled plasma atomic emission spectrometry after acid dissolution treatment as described above. The specific results are shown in Tables 1-3 below.

[0063] Conventional ashing method: The sample was ashed at a fixed temperature using a traditional method. 0.5 g of Cat-1 sample (accurate to three decimal places) was accurately weighed and placed in a quartz crucible. Based on the thermal analysis results above, 505 °C was selected as the conventional ashing temperature. The quartz crucible containing the sample was placed in a muffle furnace under air atmosphere, and the temperature was increased from room temperature to 505 °C at a rate of 20 °C / min. Heating was maintained at 505 °C for 4 hours, followed by natural cooling. 5 mL of 5% dilute nitric acid was added to the ashed sample, and the sample was dissolved at a low temperature of 135 °C on a hot plate. After dissolution, the solution was transferred to a 100 mL volumetric flask and diluted to volume for analysis. The analysis was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0064] The ashing method of this invention is as follows: Accurately weigh 0.5g (accurate to three decimal places) of Cat-1 sample and mix it evenly with 0.1g of ashing aid Ca(NO3)2. Place the mixture in a quartz crucible and cover it with a quartz lid. Place the crucible in an ashing furnace, start the vacuum pump to evacuate the furnace, and then start the microwave and high-frequency aerator. Oxygen is introduced to control the system pressure at 5.0 MPa. The microwave frequency is 2450 MHz with an output power of 0.1 kW; the high-frequency aerator frequency is 200 kHz with an output power of 2.0 kW. A programmed temperature rise is performed using the temperature rise program shown in Table 1-2. After ashing and cooling, add 5 mL of 5% dilute nitric acid to the sample and dissolve it at a low temperature of 135°C on a hot plate. After dissolution, transfer the solution to a 100 mL volumetric flask and make up to volume before analysis. Analyze the sample using an inductively coupled plasma atomic emission spectrometer under the same conditions.

[0065] Table 1-3 Comparison of conventional ashing method and the ashing method of the present invention

[0066]

[0067] (3) Repeatability test

[0068] Five parallel samples of each of Cat-1, Cat-2 and Cat-3 were accurately weighed and ashed according to the ashing method of the present invention in step (2) above. The five parallel samples of each sample were tested and the analysis results are shown in Tables 1-4.

[0069] Table 1-4 Repeatability Tests (n=5)

[0070]

[0071]

[0072] As can be seen from the data in the table above, the relative standard deviations of the repeatability tests for Cr, Zn, and Zr elements are all less than 3.5%, indicating that the ashing method of the organic chromium catalyst provided by this invention has good repeatability.

[0073] (4) Spike recovery test

[0074] Four parallel samples of Cat-1 were accurately weighed, and three of them were spiked with each element. Since the content of the main elements was different, organic standards containing Cr, Zn and Zr were used to spike them separately. Then, they were ashed and tested according to the ashing method of the present invention in step (2) above. The analysis results are shown in Tables 1-5.

[0075] Table 1-5 Spike Recovery Tests

[0076]

[0077]

[0078] As can be seen from the data in the table above, the recovery rates of Cr, Zn, and Zr elements in the spiked recovery test are all between 95% and 105%, indicating that the ashing method of the organic chromium catalyst provided by this invention has good accuracy.

[0079] Example 2

[0080] This embodiment provides an ashing method for an organochromium catalyst (Cat-4) supported on titanium, magnesium, aluminum, and boron. The ashing method includes the following steps:

[0081] (1) Investigation of ashing temperature

[0082] The melting point of Cat-4 was determined using a differential scanning calorimeter, such as Figure 3 As shown. By Figure 3 It is known that Cat-2 has multiple melting points, approximately 66℃, 103℃, 135℃, 156℃ and 209℃.

[0083] The decomposition temperature and thermal weight loss of Cat-4 were tested using a simultaneous thermal analyzer, and the results are as follows: Figure 4 As shown. By Figure 4 It can be seen that Cat-4 exhibits multiple stages of mass change, with mass reduction occurring at 79℃, 130℃, 177℃, 219℃, 295℃, 562℃, 703℃, and 829℃. This multi-stage temperature change is due to the presence of various components in the sample. The temperatures of 79℃, 130℃, 177℃, and 219℃ represent approximately the time before the sample reaches its melting point. Further heating to 295℃ causes the organic matter in the sample to begin decomposing. Continuing to 562℃ results in further weight loss, with carbon content being removed. Further heating to 703℃ and 829℃ still results in weight loss, possibly due to the volatilization of a small amount of inorganic components. After this point, the mass remains unchanged, with a total weight loss of approximately 50%, indicating complete decomposition of the organic matter. Based on these temperature points, the ashing temperature and ashing time of Cat-4 were investigated.

[0084] Five parallel Cat-4 samples were weighed, with each sample accurately weighed 0.5g (accurate to three decimal places). Each sample was mixed thoroughly with 0.5g of ashing aid Zn(NO3)2. The samples were then ashed in an oxygen atmosphere using an ashing furnace under different programmed temperature rises and the combined effects of microwave and high frequency. The specific operation is as follows:

[0085] The well-mixed sample and ashing aid mixture was placed in a quartz crucible and covered with a quartz lid. The crucible containing the sample was then placed in an ashing furnace. A vacuum pump was started to evacuate the furnace. Microwave and high-frequency equipment were then activated, and oxygen was introduced to maintain a system pressure of 10.0 MPa. The microwave frequency was 2450 MHz with an output power of 3.5 kW; the high-frequency equipment was set to 100 kHz with an output power of 1.5 kW. A programmed temperature rise was then initiated.

[0086] The samples were heated from room temperature to 80℃ at a rate of 10℃ / min and held at 80℃ for 5 min. Then, the temperatures were increased from 80℃ to 180℃, 200℃, 230℃, 260℃, and 290℃ at a rate of 10℃ / min for ashing experiments. The completeness of ashing was observed. The ash samples obtained from ashing at different temperatures were dissolved using the method described above and analyzed using inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific results are shown in Table 2-1.

[0087] Table 2-1 Results of Ashing Temperature Investigation in the Second Stage

[0088]

[0089]

[0090] Based on the data in Table 1-2 above, the final temperature program parameters for the Cat-2 sample are shown in Table 2-2 below.

[0091] Table 2-2 Ashing Procedure

[0092] step Temperature / °C Speed ​​ / (°C / min) Hold time / min 1 Room temperature ~80 10 5 2 80～160 10 5 3 160～290 10 30 4 290°C to room temperature 10 25

[0093] (2) Comparative test between ordinary ashing method and the ashing method of the present invention

[0094] Two sets of parallel Cat-4 samples were accurately weighed and ashed according to the following method (each method was performed three times in parallel). The ash content was measured by inductively coupled plasma atomic emission spectrometry after acid dissolution treatment as described above. The specific results are shown in Table 2-3 below.

[0095] Conventional ashing method: The sample was ashed at a fixed temperature using a traditional method. 0.5 g of Cat-4 sample (accurate to three decimal places) was accurately weighed and placed in a quartz crucible. Based on the thermal analysis results above, 555 °C was selected as the conventional ashing temperature. The crucible containing the sample was placed in a muffle furnace under air atmosphere, and the temperature was increased from room temperature to 505 °C at a rate of 20 °C / min. Heating at 505 °C was maintained for 4 hours, followed by natural cooling. 5 mL of 5% dilute nitric acid was added to the ashed sample, and the sample was dissolved at a low temperature of 135 °C on a hot plate. After dissolution, the solution was transferred to a 100 mL volumetric flask and diluted to volume for analysis. The analysis was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0096] The ashing method of this invention is as follows: Accurately weigh 0.5g (accurate to three decimal places) of Cat-4 sample and mix it evenly with 0.5g of ashing aid Zn(NO3)2. Place the mixture in a quartz crucible and cover it with a quartz lid. Place the crucible in an ashing furnace, start the vacuum pump to evacuate the furnace, and then start the microwave and high-frequency circuits. Oxygen is introduced to control the system pressure at 10.0 MPa. The microwave frequency is 2450 MHz with an output power of 3.5 kW; the high-frequency circuit is 100 kHz with an output power of 1.5 kW. A programmed temperature rise is performed using the temperature rise program shown in Table 1-2. After cooling, add 5 mL of 5% dilute nitric acid to the ashing sample and dissolve it at a low temperature of 135°C on a hot plate. After dissolution, transfer the solution to a 100 mL volumetric flask and dilute to volume for analysis. Analyze the sample using an inductively coupled plasma atomic emission spectrometer under the same conditions.

[0097] Table 2-3 Comparison of conventional ashing method and the ashing method of the present invention

[0098]

[0099] (3) Repeatability test

[0100] Five parallel samples of Cat-4 were weighed and ashed according to the ashing method of the present invention in step (2) above. The ash obtained after ashing was processed and tested in the aforementioned manner. The sample was tested 5 times, and the analysis results are shown in Table 2-4.

[0101] Table 2-4 Repeatability Tests (n=5)

[0102]

[0103]

[0104] As can be seen from the data in the table above, the relative standard deviations of the repeatability tests for Cr, Ti, Mg, Al, and B elements are all less than 4.5%, indicating that the ashing method of the organic chromium catalyst provided by this invention has good repeatability.

[0105] (4) Spike recovery test

[0106] Four parallel samples of Cat-4 were accurately weighed, and three of them were spiked with each element. Since the content of the main elements was different, organic standards containing Cr, Ti, Mg, Al and B were used to spike them separately. Then, they were ashed and tested according to the ashing method of the present invention in step (2) above. The analysis results are shown in Tables 1-5.

[0107] Table 2-5 Spike Recovery Test

[0108]

[0109]

[0110] As can be seen from the data in the table above, the recovery rates of Cr, Ti, Mg, Al and B elements in the spiked recovery test are all between 95% and 105%, indicating that the ashing method of the organic chromium catalyst provided by the present invention has good accuracy.

[0111] Example 3

[0112] This embodiment provides an ashing method for an organochromium catalyst (Cat-5) supported on titanium and zirconium. The ashing method includes the following steps:

[0113] (1) Investigation of ashing temperature

[0114] The melting point of Cat-5 was determined using a differential scanning calorimeter, such as Figure 5 As shown. By Figure 5It is known that the melting point of Cat-1 is approximately 112℃.

[0115] The decomposition temperature and thermal weight loss of Cat-5 were tested using a simultaneous thermal analyzer, and the results are as follows: Figure 6 As shown. By Figure 6 It can be seen that Cat-5 exhibits three stages of mass change, with mass decreases occurring at 212℃, 322℃, and 444℃. 82.5℃ is the initial decomposition temperature of Cat-5. Further heating to 212℃ and 322℃ initiates the decomposition of different organic components in Cat-5. Upon reaching 444℃, Cat-5 experiences the greatest weight loss, after which its mass remains unchanged, indicating complete decomposition of the organic matter. Based on these temperature points, the ashing temperature and ashing time of Cat-5 were investigated.

[0116] Five parallel Cat-5 samples were weighed, each weighed accurately to three decimal places (0.5g). Each sample was mixed thoroughly with approximately 0.05g of ashing aid NaNO3. The samples were then ashed in an oxygen atmosphere using an ashing furnace under different programmed temperature rise conditions, with the combined effects of microwave and high frequency. The specific operation is as follows:

[0117] The well-mixed sample and ashing aid mixture was placed in a quartz crucible and covered with a quartz lid. The crucible containing the sample was then placed in an ashing furnace. The vacuum pump was started to evacuate the furnace. Microwave and high-frequency equipment were then activated, and oxygen was introduced to maintain a system pressure of 20.0 MPa. The microwave frequency was 2450 MHz with an output power of 6.0 kW; the high-frequency equipment was set to 40 kHz with an output power of 0.5 kW. A programmed temperature rise was then initiated.

[0118] The samples were heated from room temperature to 82.5℃ at a rate of 10℃ / min and held at 82.5℃ for 5 min. Then, the temperature was increased from 82.5℃ to near the melting point, 115℃, and held for 5 min. The temperature was then further increased from 115℃ to 180℃, 200℃, 220℃, 240℃, and 260℃, and held for a certain time for ashing tests. The completeness of ashing was observed. The ash samples obtained from ashing at different temperatures were dissolved using the above method and measured using inductively coupled plasma atomic emission spectrometry (ICP-AES). The specific results are shown in Table 3-1.

[0119] Table 3-1 Results of Ashing Temperature Investigation in the Second Stage

[0120]

[0121]

[0122] This method promotes ashing in an ion atmosphere using an ashing aid and microwave-assisted high-frequency ashing. During the heating process, the organic macromolecular chains of the sample break down, forming small C and H molecules that are removed through volatilization. Chromium metal undergoes a displacement reaction with the ashing aid, forming stable chromium nitrate. Based on the data in Table 3-1 above, the final temperature program parameters for the Cat-5 sample are shown in Table 3-2 below.

[0123] Table 3-2 Temperature rise procedure for ashing

[0124] step Temperature / °C Speed ​​ / (°C / min) Hold time / min 1 Room temperature ~82 10 5 2 82～115 10 5 3 115～260 10 30 4 260°C to room temperature 10 25

[0125] (2) Comparative test between ordinary ashing method and the ashing method of the present invention

[0126] Two sets of parallel Cat-5 samples were accurately weighed and ashed according to the following method (each method was performed three times in parallel). The ash content was measured by inductively coupled plasma atomic emission spectrometry after acid dissolution treatment as described above. The specific results are shown in Table 3-3 below.

[0127] Conventional ashing method: The sample was ashed at a fixed temperature using a traditional method. 0.5 g of Cat-5 sample (accurate to three decimal places) was accurately weighed and placed in a quartz crucible. Based on the thermal analysis results above, 505 °C was selected as the conventional ashing temperature. The quartz crucible containing the sample was placed in a muffle furnace under air atmosphere, and the temperature was increased from room temperature to 505 °C at a rate of 20 °C / min. Heating was maintained at 505 °C for 4 hours, followed by natural cooling. 5 mL of 5% dilute nitric acid was added to the ashed sample, and the mixture was dissolved at a low temperature of 135 °C on a hot plate. After dissolution, the solution was transferred to a 100 mL volumetric flask and diluted to volume for analysis. The analysis was performed using inductively coupled plasma atomic emission spectrometry (ICP-AES).

[0128] The ashing method of this invention is as follows: Accurately weigh 0.5g (accurate to three decimal places) of Cat-5 sample and mix it evenly with 0.05g of ashing aid NaNO3. Place the mixture in a quartz crucible and cover it with a quartz lid. Place the crucible in an ashing furnace, start the vacuum pump to evacuate the furnace, and then start the microwave and high-frequency ablation. Oxygen is introduced to control the system pressure at 20MPa. The microwave frequency is 2450MHz with an output power of 6.0KW; the high-frequency ablation frequency is 40kHz with an output power of 0.5KW. A programmed temperature rise is performed using the temperature rise program in Table 3-2. After ashing and cooling, add 5mL of 5% dilute nitric acid to the sample and dissolve it at a low temperature of 135℃ on a hot plate. After dissolution, transfer the solution to a 100mL volumetric flask and make up to volume for analysis. Analyze the sample using an inductively coupled plasma atomic emission spectrometer under the same conditions.

[0129] Table 3-3 Comparison of conventional ashing method and the ashing method of the present invention

[0130]

[0131] (3) Repeatability test

[0132] Five parallel samples of Cat-5 were weighed and ashed according to the ashing method of the present invention in step (2) above. The ash obtained after ashing was processed and tested as described above. The test was repeated 5 times for each sample. The analysis results are shown in Table 3-4.

[0133] Table 3-4 Repeatability Tests (n=5)

[0134]

[0135]

[0136] As can be seen from the data in the table above, the relative standard deviations of the repeatability tests for Cr, Ti, and Zr elements are all less than 5.0%, indicating that the ashing method of the organic chromium catalyst provided by this invention has good repeatability.

[0137] (4) Spike recovery test

[0138] Four parallel samples of Cat-5 were accurately weighed, and three of them were spiked with each element. Since the content of the main elements was different, organic standards containing Cr, Ti and Zr were used to spike them separately. Then, they were ashed and tested according to the ashing method of the present invention in step (2) above. The analysis results are shown in Table 3-5.

[0139] Table 3-5 Spike Recovery Test

[0140]

[0141] As can be seen from the data in the table above, the recovery rates of Cr, Ti and Zr elements in the spiked recovery test are all between 95% and 105%, indicating that the ashing method of the organic chromium catalyst provided by the present invention has good accuracy.

[0142] Of course, the present invention may have other various embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art can make various corresponding changes and modifications according to the present invention, but these corresponding changes and modifications should all fall within the protection scope of the claims of the present invention.

Claims

1. A method for ashing an organochromium catalyst, characterized in that, Includes the following steps: The mixture of ashing aid and organochromium catalyst is reacted in a closed oxygen-containing atmosphere under the synergistic effect of microwave and high frequency, with the temperature programmed to <350°C, so as to completely ashing the organic matter in the organochromium catalyst. The ashing aid is selected from nitrates; the reaction pressure is less than 20.0 MPa. The high frequency is 40~200kHz, and the output power is 0.5~2.0kW; The microwave has a frequency of 2450 MHz and an output power of 0.1~6.0KW; The programmed temperature rise includes two stages; the first stage is to raise the temperature from room temperature to T1 and hold it for 5-10 minutes; the second stage is to raise the temperature from T1 to T2 and hold it for 15-30 minutes; T1 = 150-180℃, T2 = 200-280℃; The programmed temperature rise includes three stages: the first stage is from room temperature to T1 and held for 5-10 minutes; the second stage is from T1 to T2 and held for 5-10 minutes; the third stage is from T2 to T3 and held for 15-30 minutes; T1 = 70-90℃, T2 = 150-170℃, T3 = 280-300℃.

2. The ashing method as described in claim 1, characterized in that, The mass ratio of the organic chromium catalyst to the ashing aid is (1~10):

1.

3. The ashing method as described in claim 1, characterized in that, The ashing aid is selected from any one of KNO3, NaNO3, Ca(NO3)2, and Zn(NO3)2.

4. The ashing method as described in claim 1, characterized in that, After the program's heating phase ends, it also includes a process of shutting down the microwave and the high frequency, and then cooling down to room temperature from T2.

5. A method for determining the elemental content in an organochromium catalyst, characterized in that, The step of obtaining ash includes the ashing method of the organochromium catalyst according to any one of claims 1-4.

6. The method for determining the elemental content in an organochromium catalyst as described in claim 5, characterized in that, The method also includes the step of dissolving and adjusting the volume of the ash with acid, and then measuring it using an inductively coupled plasma atomic emission spectrometer; the element is selected from at least one of chromium, titanium, magnesium, aluminum, zinc, zirconium and boron.

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