NB/SH/T 0918-2015 Determination of acidity of solid catalysts — Ammonia chemisorption method

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Card type: Test method

1. Method number / full title / English title / replacement relationship

• Standard number: NB/SH/T 0918—2015
• Chinese title: Determination of acidity of solid catalysts — Ammonia chemisorption method
• English title: Standard test method for determination of catalyst acidity by ammonia chemisorption
• Replacement relationship: This standard is first published (not provided in the available source as replacing other standards)
• Adoption relationship: Modified adoption by redrafting method of ASTM D4824-13 "Standard method for determination of catalyst acidity by ammonia chemisorption"
• Main technical differences from ASTM D4824-13 (listed in the source):
  • Delete the referenced standard ASTM D3766 in clause 2, retain the definition of acidity related to ASTM D3766 in clause 3 terms and definitions of the standard, delete the symbol content of clause 3.2, and express its content in relevant places of the standard
  • Add a note under clause 8.2, supplementing that when valve V₅ and valve V₆ are both connected to samples, the two samples need to be independently measured according to the test procedure and calculated separately
  • Change the test temperature from Kelvin temperature to Celsius temperature, and modify formula (2) and formula (3) accordingly
  • In the standard, for atmospheric pressure only retain the expression of standard atmospheric pressure, and modify formula (4) accordingly
• Publication/implementation: published on 2015-10-27, implemented on 2016-03-01
• Issuing authority: National Energy Administration
• Drafting organization: Petrochemical Research Institute of PetroChina Company Limited
• Main drafters: Zhang Chunguang, Xiao Zhanmin, Liang Yingchun, Wang Chunyan
• Secretariat: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Proposed by: China Petrochemical Corporation

2. Scope of application and non-applicability

• Scope of application: This standard specifies a measurement method for determining the acidity of catalysts and catalyst carriers by ammonia chemisorption, where the amount of chemisorbed ammonia is obtained by a static volumetric measurement system. This standard is applicable to the determination of the acidity of solid catalysts or carriers.
• Non-applicability: no explicit non-applicability clause is provided in the available source.
• Method application (clause 5): Ammonia chemisorption is used to evaluate the acidity of catalyst materials and conformity with specifications, and can be used for catalyst production control, catalyst evaluation, and catalyst research and development.

3. Method principle

First, the catalyst is heated and degassed in vacuum to remove gas adsorbed on the sample surface. Then, the catalyst is placed in an excess ammonia atmosphere for chemisorption, and the remaining ammonia is condensed out with a cold trap containing liquid nitrogen. The amount of chemisorbed ammonia can be obtained by calculating the difference between the amount of ammonia before the catalyst is placed and the amount of ammonia recovered by the liquid nitrogen cold trap, and then the acidity can be obtained by calculation.

4. Reagents and materials (purity / preparation)

• 7.1 Nitrogen: purity not lower than 99.8% (the source source-text extraction is "purity not ... 8%", which in context is suspected to be 99.8%, requires confirmation against the source standard (source-text extraction))
• 7.2 Ammonia: purity not lower than 99.8% (the source source-text extraction is "purity not lower ... 8%", requires confirmation against the source standard (source-text extraction)); ammonia needs to flow through a drying tube
• 7.3 Liquid nitrogen
• Drying tube packing: 3A molecular sieve or BaO (the source source-text extraction is "Ba0", requires confirmation against the source standard (source-text extraction))

5. Instruments and equipment

• 6.1 Figure 1 gives a schematic diagram of a typical instrument. The instrument can be constructed of glass or metal and can be operated manually or automatically.
• 6.1.1 System: in the absence of a sample, the pressure can reach and be maintained at 0.01 Pa (the source source-text extraction is "0.01 Pao", requires confirmation against the source standard (source-text extraction))
• 6.1.2 Expansion vessel: volume (Vₐ) is between 300 cm³ and 500 cm³, with an error within 0.01 cm³. Volume Vₐ is defined as the volume between flow regulating valve V₁ and valve V₆, including pressure measuring device 2 and the ammonia condensation return line. A smaller-volume expansion vessel is intended for materials with low specific surface area or small particle size.
• 6.1.3 Pressure measuring device 1: measuring range is 0 Pa to 1.34×10⁵ Pa, measurement accuracy is 0.1 Pa (the source source-text extraction is "1.34×10° Pa", requires confirmation against the source standard (source-text extraction))
• 6.1.4 Pressure measuring device 2: measuring range is 0 Pa to 3.3×10⁴ Pa, measurement accuracy is 10 Pa (the source source-text extraction is "3.3×10* Pa", requires confirmation against the source standard (source-text extraction))
• 6.1.5 Valve (Vₐ): connects the ammonia source and the expansion vessel
• 6.1.6 Sample tube: volume is 5 cm³ to 25 cm³; the sample tube can be connected to the apparatus through a standard sleeve joint, a glass sealed joint, or a ferrule-type joint
• 6.1.7 Dewar flask: holds liquid nitrogen, used to immerse the expansion vessel containing ammonia (the source source-text extraction is "dead flask", requires confirmation against the source standard (source-text extraction))
• 6.1.8 Thermometer or thermocouple (T₁): used to measure the temperature of the expansion vessel. If the constant temperature of the expansion vessel is higher than the surrounding environment, this temperature may not be recorded
• 6.1.9 Heating mantle or small heating furnace: used to heat the sample tube
• 6.1.10 Balance: readability is 0.1 mg
• 6.1.11 Thermometer or thermocouple (T₂): used to measure the temperature of the sample tube
• 6.1.12 Cold trap: used to condense ammonia in the vacuum system
• 6.1.13 Drying tube: used to dry ammonia; the packing can be 3A molecular sieve or BaO

6. Recommended operating conditions

• Sample pretreatment degassing temperature: 400 °C (8.1.5, 8.1.6)
• Degassing time: at least 3 h, degassing may be about 12 h (8.1.6)
• Degassing pressure: not exceeding 0.1 Pa (8.1.6)
• Adsorption temperature: 175 °C ± 1 °C (8.2.1, 8.2.6)
• Ammonia pressure (during adsorption): 13 kPa to 20 kPa (8.2.2, the source source-text extraction is "13 KPa to 20k", requires confirmation against the source standard (source-text extraction))
• Time for sample exposure to excess ammonia: 30 min (8.2.6)
• Condensation time: 2 h (8.2.7)
• Evacuation time: usually 2 min is relatively sufficient (8.2.4)
• Heating rate: if air humidity exceeds 5%, it is recommended that the heating rate not exceed a certain value (the source source-text extraction is "/mir", the specific value is not provided in the available source, requires confirmation against the source standard (source-text extraction))

7. Sampling and sample preparation

• 8.1.1 Weigh the mass of the sample tube to the nearest 0.1 mg, and record it as W₁, then place about 2 g of sample into the sample tube.
• 8.1.2 Install the sample tube on the apparatus.
• 8.1.3 Open the sample tube connection valves; the valves may be opened either sequentially or simultaneously (the source source-text extraction has missing characters, requires confirmation against the source standard (source-text extraction)).
• 8.1.4 Slowly open the valve connected to the vacuum system while monitoring the pressure drop rate to avoid too rapid a pressure drop, because too rapid a pressure drop will cause additional loss of powdered sample.
• 8.1.5 Place a heating mantle or heating furnace on the outside of the sample tube, and raise the sample temperature to 400 °C.
  • Note: If the air humidity exceeds 5%, special precautions should be taken to avoid sudden spattering of the powdered sample. It is recommended that the heating rate in such an environment not exceed a certain value (the source source-text extraction is "/mir", the specific value is not provided in the available source, requires confirmation against the source standard (source-text extraction)).
• 8.1.6 Continue degassing at a temperature of 400 °C for at least 3 h, with degassing pressure not exceeding 0.1 Pa; degassing may be about 12 h.
  • Note: For general samples, determine the pretreatment temperature as 400 °C, but for some samples that decompose or sinter at a temperature of 400 °C, a lower pretreatment temperature is required, and the pretreatment temperature needs to be stated in the test report.

8. Analytical procedure

• 8.2 Determination of ammonia adsorption amount
  • Note: If valve V₅ and valve V₆ are both connected to samples, the two samples need to be independently measured according to the steps of 8.2.1 to 8.2.10 and calculated separately.
• 8.2.1 After degassing is completed, lower the sample temperature to 175 °C.
• 8.2.2 Close shut-off valve V₁ to separate the sample from the expansion vessel, and allow ammonia to enter the expansion vessel through valve Vₐ. Assume a certain amount of chemisorption (the source source-text extraction is "cm³/g", the specific expression requires confirmation against the source standard (source-text extraction)), and introduce sufficient ammonia to ensure that during contact with ammonia, the ammonia pressure is 13 kPa to 20 kPa.
• 8.2.3 Close ammonia valve Vₐ, immerse the expansion vessel in liquid nitrogen, and condense ammonia into the expansion vessel.
• 8.2.4 After ammonia condensation, close sample tube connection valve V₅ and valve V₆, open valve V₇, and evacuate uncondensed impurity gas. (Generally, 2 min is a relatively sufficient evacuation time.)
• 8.2.5 After evacuating the uncondensed impurity gas, close valve V₇ leading to vacuum, and remove the liquid nitrogen from the expansion vessel so that ammonia can expand into the expansion vessel. At this time, measure pressure P₁ and temperature T₁.
• 8.2.6 Close the valve to the vacuum V₇, open valve V₁, then open valve V₅ or valve V₆, and expose the sample to excess ammonia 30 min. The sample temperature should be maintained at 175 °C ± 1 °C.
• 8.2.7 After ammonia adsorption through 30 min, immerse the expansion vessel again in liquid nitrogen 2 h to recondense the ammonia.
• 8.2.8 After this period of condensation, close valve V₁, thereby separating the sample tube from the expansion vessel. If, near the end of the condensation stage, the pressure is not less than 10 Pa, it indicates that the system is leaking, and the test needs to be carried out again. Remove the liquid nitrogen and allow the ammonia to expand into the expansion vessel. If the system is not leaking, no condensed substance will remain, and at this time pressure P₂ and temperature T₂ can be measured.
• 8.2.9 Remove the heating jacket or heating furnace wire from the sample tube, and cool to ambient temperature. Refill the sample tube with nitrogen to atmospheric pressure or slightly above atmospheric pressure. Close the sample tube connection valve V₅ and valve V₆.
• 8.2.10 Remove the sample tube from the equipment and weigh it. Record mass W₂, accurate to 0.1 mg.
  • Note: If a standard sleeve joint is used, care must be taken to remove grease during weighing.

9. Qualitative and Quantitative Determination and Calculation Formulas

• 9.1 Calculate the amount of sample adsorbing ammonia according to formula (1):
  • Wₐ = W₂ − W₁ (1)
  • Where:
    • Wₐ——the amount of sample adsorbing ammonia, in grams (g);
    • W₁——mass of the sample tube, in grams (g);
    • W₂——sum of the mass of the sample adsorbing ammonia and the sample tube, in grams (g).
• 9.2 Calculate the pressures P₁ᵣ and P₂ᵣ at standard temperature according to formula (2) and formula (3):
  • P₁ᵣ = P₁ × 273 / (T₁ + 273) (2)
  • P₂ᵣ = P₂ × 273 / (T₂ + 273) (3)
  • Where:
    • P₁ᵣ——initial ammonia pressure converted to standard temperature, in pascals (Pa);
    • P₂ᵣ——final ammonia pressure converted to standard temperature, in pascals (Pa);
    • P₁——initial ammonia pressure, in pascals (Pa);
    • P₂——final ammonia pressure, in pascals (Pa);
    • T₁——temperature of the expansion vessel at the initial pressure, in degrees Celsius (°C);
    • T₂——temperature of the expansion vessel at the final pressure, in degrees Celsius (°C).
• 9.3 Calculate the adsorption volume Vₐds according to formula (4):
  • Vₐds = Vₐ × (P₁ᵣ − P₂ᵣ) / 1.013 × 10⁵ (4)
  • Where:
    • Vₐds—— the volume of adsorbed ammonia converted to standard conditions, in cubic centimeters (cm³);
    • Vₐ——corrected ammonia expansion volume, in cubic centimeters (cm³).
• 9.4 Calculate acidity A according to formula (5):
  • A = Vₐds / Wₐ (5)
  • Where:
    • A—— acidity of the sample, in cubic centimeters per gram (cm³/g).
• Term definition (3.1): acidity acidity refers to the ratio of the amount of adsorbed ammonia to the sample mass after the catalyst or support has saturated chemically adsorbed ammonia, expressed as cm³/g (the source text source-text extraction is "cm2/g"; combined with the formula units it should be cm³/g, requires confirmation against the source standard (source-text extraction)). Note: The amount of ammonia needs to be converted to standard atmospheric pressure gas volume.

10. Precision

• Four independent catalyst samples were taken in nine different laboratories to carry out repeatability and reproducibility tests for acidity determination, and inconsistent experimental data were removed according to standard ASTM E691, and the precision of this standard was obtained after detailed analysis. Judge the reliability of test results according to the following provisions (95% confidence level):
• 11.1.1 Repeatability (r): For continuous determinations of the same sample by the same operator, using the same instrument, under the same operating conditions, the difference between the two test results obtained shall not exceed the requirement of the value calculated by formula (6):
  • r = 0.10X (6)
  • Where: X—— the average of the two test results.
• 11.1.2 Reproducibility (R): In different laboratories, by different operators using different instruments, the same sample is determined according to the same test method, and the difference between the two single, independent test results obtained shall not exceed the requirement of the value calculated by formula (7):
  • R = 0.30X (7)
• 11.2 Bias: The bias of this standard has not yet been determined.

11. Report

• 10.1 The report shall include the sample pretreatment temperature, degassing temperature, and the temperature at which the sample fully adsorbs ammonia.
• 10.2 The results given in the report shall be in cubic centimeters per gram (cm³/g), accurate to 0.01 cm³/g.

12. Referenced Documents

• ASTM E 691 Procedure for conducting interlaboratory studies to determine the precision of test methods (Practice for Conducting an Interlaboratory Study to Determine the Precision of a Test Method)
• Note: This standard uses the redrafting method to modify and adopt ASTM D4824-13, but that standard is not listed in Chapter 2 normative referenced documents.

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference for Questions and Answers