Method for determining chlorides in a reforming catalyst

Abstract

The present application belongs to the technical field of detection method, and particularly relates to a method for determining chlorides in reforming catalysts. The method comprises the following steps: burning the pretreated reforming catalyst sample to be determined to obtain a burned sample, adding water to extract the sample to obtain a chlorides extract, and determining the content of chlorides in the extract by silver nitrate titration. The temperature of the burning treatment is 600±25 DEG C, and the time is 1-3 hours. The present application discards the step of using magnesium chips / powder, which is an explosive hazardous material, in the traditional method, simplifies the sample pretreatment process, shortens the analysis time from 7 hours to 4 hours, eliminates the influence of wet base by calculating the mass fraction of alumina dry base and participating in the calculation of the content of chlorides, and improves the detection accuracy. The present application is safe, efficient, accurate and low in cost, and is suitable for monitoring chlorides in the whole life cycle of reforming catalysts in the petrochemical industry.

Description

Technical Field

[0001] This invention belongs to the technical field of detection methods, specifically relating to a method for determining chlorides in reforming catalysts. Background Technology

[0002] Reforming catalysts are the core of catalytic reforming processes in petroleum refining, and their chloride content is crucial for maintaining the activity of acidic sites, ensuring reaction selectivity, and maintaining process stability. Therefore, accurate determination of chloride content is of great significance for catalyst preparation process control, reforming unit operation, and the evaluation and regeneration of deactivated catalysts.

[0003] Currently, the domestic petrochemical industry generally adopts a standard enterprise method based on magnesium scrap reduction to determine chloride content. However, this method has the following prominent drawbacks: using magnesium scrap as a reducing agent introduces safety risks such as flammability, explosiveness, and water reaction, and its procurement and storage management are complex; the analytical process is cumbersome, with a single test taking several hours, failing to meet the needs of rapid detection; the interference of water adsorbed on the carrier is not considered, leading to results calculated on a wet basis that deviate from the true composition and are inaccurate; at the same time, the expensive consumption of magnesium scrap and the high reagent consumption due to the lengthy steps keep the detection cost high. In addition, although some literature reports the use of high-temperature combustion method (800~1100℃) combined with ion chromatography to determine chloride content in reforming catalysts, this method has high energy consumption, demanding equipment requirements, and often requires dividing the sample into two parts to determine organic and inorganic chlorides separately, which not only complicates the steps and doubles the sample volume but also introduces more systematic errors, resulting in low overall analytical efficiency and high cost. Summary of the Invention

[0004] The purpose of this invention is to provide a method for determining chlorides in reforming catalysts, thereby overcoming the shortcomings of the prior art. By eliminating the use of magnesium shavings / powder, simplifying the pretreatment process, and introducing a loss-on-ignition correction, the method significantly improves detection efficiency and data accuracy while ensuring detection safety.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A method for determining chlorides in a reforming catalyst, comprising the following steps: The pretreated reforming catalyst sample to be tested was calcined to obtain the calcined sample. Water was added for extraction to obtain a chloride extract. The chloride content in the extract was determined by silver nitrate titration (potential titration). The calcination treatment was performed at a temperature of 600±25℃ for 1-3 hours.

[0006] This invention utilizes a specific calcination pretreatment to effectively decompose or volatilize some volatile organochlorine components and interfering substances in the catalyst, reducing potential matrix interference during subsequent measurements. This method combines calcination pretreatment with conventional water leaching and titration, offering a clear process and good repeatability. Compared to methods that directly measure without calcination, this method more accurately reflects the true content of chlorides (such as active chlorine species) in stable forms that have a real impact on catalytic performance, resulting in more representative results and providing a more reliable quantitative basis for catalyst industrial evaluation and process control.

[0007] In some other methods, the pretreatment involves grinding the reforming catalyst sample to be tested to a particle size of less than 0.1 mm and drying it at 100-110 °C for 2-3 h.

[0008] In some other methods, 80-120 mL of water is added per gram of the ignited sample.

[0009] During their research, the inventors discovered that chlorides in the reforming catalyst exist in the ionic state of Cl. - The form adsorbed onto the hydroxyl sites on the alumina surface. Water molecules compete for substitution through hydrogen bonding; under mild boiling conditions (95-100℃), the kinetic energy of water molecules is sufficient to overcome the Al-OH···Cl bonds. - Interactions (bond energy approximately 20-40 kJ / mol) enable Cl to be realized - Quantitative desorption. While acid / alkali media can enhance extraction power, they also lead to carrier dissolution and the introduction of Al³⁺. + It interferes with and alters the ionic strength of the solution.

[0010] In some other methods, the extraction temperature is 90-100℃ and the extraction time is 20-40 min.

[0011] In some other methods, the silver nitrate titration method uses a 0.005-0.1 mol / L silver nitrate standard solution for determination.

[0012] In other embodiments, the reforming catalyst includes fresh platinum-rhenium, platinum-tin reforming catalysts, spent catalysts after operation, and deactivated catalysts.

[0013] In some other embodiments, the reforming catalyst is an R-334 type reforming catalyst.

[0014] In some other methods, the calcination treatment is carried out at a temperature of 600°C for 2 hours, with a heating rate of 8°C / min.

[0015] During their research, the inventors discovered that the choice of calcination temperature directly affects the removal of volatiles and the stability of the support structure. This is because the reforming catalyst support is γ-Al₂O₃, whose thermal stability temperature window is 500-800℃. Below 500℃, physically adsorbed water, organic additives, and volatile chlorides are not completely removed; above 700℃, γ-Al₂O₃ begins to transform into α-Al₂O₃, accompanied by sintering and collapse of the pore structure, which hinders the release of chlorides from the crystal lattice. 600℃ is within the stable region of γ-Al₂O₃, ensuring complete removal of volatiles without damaging the support structure.

[0016] In some other methods, the chloride content is calculated using the following formula: W Cl =c×V×M Cl / (1000×m0×W Al2O3干基 ) × 100%; Where c is the concentration of the titrant (mol / L), V is the volume of titrant consumed (mL), and M... Cl The molar mass of chlorine is 35.45 g / mol, m0 is the mass of the sample used for the determination (g), and W... Al2O3干基 This represents the dry basis mass fraction of alumina.

[0017] When calculating the chloride content in this invention, the dry basis mass fraction of alumina (W) obtained by conversion from loss on ignition is used. Al2O3干基 This serves as a key correction factor. By dividing the preliminary chloride content determined by titration by this dry basis mass fraction, the influence of physically adsorbed water (wet basis) in the catalyst is accurately subtracted, thus ensuring the final chloride content detection result (W) is accurate. Cl It accurately reflects the actual loading level of chemical chlorides in the active components of the catalyst, significantly improving the accuracy of the detection data and the comparability between detection results of different samples and batches, providing reliable data support for industrial applications.

[0018] In some other ways, the dry basis mass fraction of alumina W Al2O3干基 The calculation formula is as follows: W Al2O3 (Dry basis) = m2 / m1 × 100%; Where m1 is the mass of the sample before ignition (g), and m2 is the mass of the sample after ignition (g).

[0019] The beneficial effects of this invention are: This invention fundamentally eliminates the use of flammable and explosive hazardous materials such as magnesium shavings / powder in traditional methods, completely eliminating major safety hazards in laboratories and solving the problems of their procurement and storage. In terms of efficiency and cost, it significantly simplifies the pretreatment process, reducing overall analysis time by more than 40%, significantly improving detection efficiency and reducing labor and material costs. Regarding the accuracy of results, it innovatively introduces and calculates the dry basis mass fraction of alumina, effectively correcting for the influence of the wet basis. Combined with optimized key parameters (such as an ignition temperature of 600℃±25℃) and targeted anti-interference measures, it ensures high accuracy and reliability of the detection results. Furthermore, this method requires no special equipment, is easy to master and promote, and has broad applicability, meeting the chloride monitoring needs throughout the entire life cycle of reforming catalysts. Detailed Implementation

[0020] It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The reforming catalyst used in the determination was a fresh PS-VI type reforming catalyst from a petrochemical company, with a nominal Cl content of 1.1% ± 0.1%. The main reagents and materials used in the determination process are as follows: silver nitrate (AgNO3), CAS No.: 7761-88-8, analytical grade, used to prepare standard titration solutions; sodium chloride (NaCl), CAS No.: 7647-14-5, a primary standard reagent used to prepare chloride ion standard solutions; deionized water, conforming to the grade III water standard specified in GB / T 6682; porcelain crucible: 30 mL, high temperature resistance ≥1000℃; muffle furnace: temperature control accuracy ±25℃.

[0021] To address the significant shortcomings of existing detection methods in terms of operational safety, detection efficiency, result accuracy, and analytical cost, this invention provides a method for determining chloride in reforming catalysts. The core concept of this invention lies in eliminating the safety risks associated with the magnesium shavings / powder reduction step in traditional methods, thus eliminating potential safety hazards at the source; significantly shortening the overall analysis time and improving detection efficiency by optimizing and simplifying the sample pretreatment process; and optimizing the catalyst loss on ignition determination step, calculating chloride content based on dry basis mass, completely eliminating interference from carrier-adsorbed water, and ensuring data accuracy. Furthermore, this method does not rely on expensive specialized equipment and can be implemented using conventional laboratory instruments, significantly reducing reagent consumption. Therefore, it comprehensively achieves the goals of safe, efficient, accurate, and economical determination, effectively meeting the industry's demand for high-quality analysis.

[0022] The calculation formulas involved in the following examples are as follows: 1. Calculation of alumina dry basis mass fraction: W Al2O3(Dry basis) = m2 / m1 × 100%; Where m1 is the mass of the sample before ignition (g), and m2 is the mass of the sample after ignition (g). 2. Chloride content calculation (as Cl): W Cl =c×V×M Cl / (1000×m0×W Al2O3干基 ) × 100%; Where c is the concentration of the titrant (mol / L), V is the volume of titrant consumed (mL), and M... Cl is the molar mass of chlorine (35.45 g / mol), m0 is the mass of the sample used for the determination (g), W Al2O3 (Dry basis) refers to the dry basis mass fraction of alumina.

[0023] Example 1 This embodiment provides a method for determining chloride in reforming catalysts, including the following steps: S1. Sample preparation: Take 50 g of catalyst sample (fresh R-334 reforming catalyst from a petrochemical enterprise), grind it in an agate mortar, pass it through a 0.1 mm sieve, place the sieved material in an oven at 105℃ and dry it for 2 h, then cool it in a desiccator for later use.

[0024] S2. Loss on ignition analysis: Accurately weigh 1.0002 g of the dried sample and place it in a pre-weighed (15.2341 g) porcelain crucible. Place the crucible in a muffle furnace and heat it to 600℃ at 8℃ / min. Ignite for 2 h, remove the sample and place it in a desiccator to cool for 30 min. Weigh the crucible and the sample after ignition. The weight is 16.2323 g.

[0025] Calculations show that the mass of the sample after ignition is 16.2323 - 15.2341 = 0.9982 g. The dry basis mass fraction of alumina = (0.9982 / 1.0002) × 100% = 99.80%.

[0026] S3. Chloride determination: Accurately weigh 0.5003 g of the dried sample and place it in a 250 mL beaker. Add 50 mL of deionized water (as the extractant), heat to a gentle boil for 30 min, cool, add 1:1 nitric acid, adjust the pH value to ≤3, and titrate with 0.0100 mol / L AgNO3 standard solution. The volume consumed is 13.03 mL, and the blank test consumes 0.05 mL.

[0027] Calculations show that the actual volume of AgNO3 consumed is 13.03 - 0.05 = 12.98 mL. Cl content (dry basis corrected) = (0.0100 × 35.45 × 12.98 / 1000 × 0.5003 × 99.80%) × 100% = 1.09% S4. Result Judgment: The measured value of chloride in the reforming catalyst is 1.09%, which is within the nominal range of 1.1% ± 0.1%, and the result is qualified.

[0028] Comparative Example 1 The chloride content of the reforming catalyst was determined using the traditional magnesium-containing reduction method (GB / T 13748.18-2005 "Chemical Analysis Methods for Magnesium and Magnesium Alloys: Determination of Chlorine Content by Silver Chloride Turbidity Method").

[0029] Comparative Example 2 Unlike Example 1, in step S2, the calcination treatment of the dried sample at 600°C was omitted in the loss on ignition analysis; the other steps were the same as in Example 1.

[0030] Comparative Example 3 Unlike Example 1, in step S2, the calcination temperature was set to 500°C, 700°C, and 800°C, respectively, while the other steps were the same as in Example 1.

[0031] Comparative Example 4 Unlike Example 1, in step S3, the chloride determination, 0.1 mol / L HNO3 and 0.05 mol / L NaOH were used instead of deionized water as the extraction solvent, while the other steps were the same as in Example 1.

[0032] The measurement results of Example 1 and Comparative Examples 1-3 are shown in Tables 1-6.

[0033] Table 1. Efficiency of the detection methods in Example 1 and Comparative Example 1

[0034] Table 2. Accuracy of the detection methods in Example 1 and Comparative Example 1 (standard sample verification)

[0035] As shown in Table 2, the system error of Comparative Example 1 (traditional method) is about 7% lower because the wet basis is not corrected. However, the method of Example 1 of the present invention, by introducing the loss on ignition correction, controls the relative error within ±2%, and the accuracy is significantly improved.

[0036] To illustrate the precision of the determination method of the present invention, the method in Example 1 was used to determine the chlorine in fresh catalyst (high Cl), catalyst in operation (medium Cl), and deactivated catalyst (low Cl). Each sample was tested 6 times and labeled as sample 1 to sample 6. The experimental results of the precision determination are shown in Table 3.

[0037] Table 3. Results of Method Precision Validation

[0038] As shown in Table 3, the measurement method of the present invention has good precision.

[0039] The effect of loss on ignition on the test results in Example 1 and Comparative Example 2 is shown in Table 4.

[0040] Table 4. Effect of loss on ignition on test results (same batch of samples)

[0041] As shown in Table 4, without dry basis correction, the test results will be about 14%-18% lower, which will seriously affect the process judgment.

[0042] The effects of different calcination temperatures on the chlorine content determination results in Example 1 and Comparative Example 3 are shown in Table 5.

[0043] Table 5. Effect of different calcination temperatures on the results of chlorine content determination.

[0044] Table 5 shows that the LOI was lower than expected (12.35% vs 14.52%) due to insufficient temperature (500℃), indicating that adsorbed water, organic template agents, and volatile chlorides were not completely removed. Residual carbonaceous matter encapsulated some chlorides, leading to a decrease in water extraction rate, resulting in a systemic underestimation of the LOI by approximately 16.5%. 600℃ was the optimal temperature: the LOI stabilized in the 14.50%-14.55% range, and the dry-basis Al2O3 mass fraction reached 99.8%, consistent with the theoretical value. At this temperature, the γ-Al2O3 support maintained a high specific surface area and active phase structure, ensuring complete release of chlorides without re-adsorption by the support, resulting in the best measurement precision (RSD=1.2%). Temperatures of 700-800℃ were too high: although the LOI was close to that at 600℃, slight sintering occurred at 800℃, causing the support pore structure to collapse and some chlorides to be trapped within the sintered body, leading to a decrease in extraction rate and a systemic underestimation of the LOI by approximately 6.4%. Furthermore, high temperatures increased energy consumption, which is not economical.

[0045] The effects of different extractants on chloride extraction rate and product composition in Example 1 and Comparative Example 4 are shown in Table 6.

[0046] Table 6. Effects of water, acid, and alkali solutions on chloride extraction rate and product composition.

[0047] As shown in Table 6, deionized water micro-boiling extraction ensures a high extraction rate (98%) while avoiding carrier dissolution and side reactions, making it the optimal extraction method. This invention utilizes water extraction, which balances extraction efficiency, selectivity, and ease of operation.

[0048] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for determining chloride in a reforming catalyst, characterized in that, Includes the following steps: The pretreated reforming catalyst sample to be tested was calcined to obtain the calcined sample. Water was added for extraction to obtain chloride extract. The chloride content in the extract was determined by silver nitrate titration. The calcination treatment was performed at a temperature of 600±25℃ for 1-3 hours.

2. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, The pretreatment involved grinding the reforming catalyst sample to be tested to a particle size of less than 0.1 mm and drying it at 100-110℃ for 2-3 hours.

3. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, Add 60-80 mL of water to every 0.1 gram of the ignited sample.

4. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, The extraction temperature is 90-100℃, and the extraction time is 20-40 min.

5. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, The silver nitrate titration method uses a 0.005-0.1 mol / L silver nitrate standard solution with potassium chromate as an indicator.

6. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, The reforming catalyst includes fresh platinum-rhenium system reforming catalyst, platinum-tin system reforming catalyst, catalyst that has been put into operation and deactivated catalyst.

7. The method for determining chloride in the reforming catalyst according to claim 6, characterized in that, The reforming catalyst is an R-334 type reforming catalyst.

8. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, The calcination treatment was performed at a temperature of 600°C for 2 hours, with a heating rate of 8°C / min.

9. The method for determining chloride in the reforming catalyst according to claim 1, characterized in that, The formula for calculating the chloride content is as follows: IN Cl =c×V×M Cl / (1000×m0×W Al2O3干基 )×100%; Where c is the concentration of the titrant (mol / L), V is the volume of titrant consumed (mL), and M... Cl The molar mass of chlorine is 35.45 g / mol, m0 is the mass of the sample used for the determination (g), and W... Al2O3干基 This represents the dry basis mass fraction of alumina.

10. The method for determining chloride in the reforming catalyst according to claim 9, characterized in that, Alumina dry basis mass fraction W Al2O3干基 The calculation formula is as follows: W Al2O3(干基) = m2 / m1 × 100%; Where m1 is the mass of the sample before ignition (g), and m2 is the mass of the sample after ignition (g).

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