Significance and Use

This gas adsorption method complements the X-ray procedure of Test Method D3906. This test method will be useful to laboratories that do not have X-ray diffractometers. Each test method can be calibrated by use of an appropriate series of mechanical mixtures to provide what may be termed percent zeolite. If there is disorder in the zeolite, the adsorption method will yield higher values than the X-ray method. The reverse will be true if some zeolite pores (micropores) are blocked or filled.

Scope

This test method covers the determination of total surface area and mesopore area. From these results are calculated the zeolite area and micropore volume of a zeolite containing catalyst. The micropore volume is related to the percent zeolite in the catalyst. The zeolite area, a number related to the surface area within the zeolite pores, may also be calculated. Zeolite area, however, is difficult to interpret in physical terms because of the manner in which nitrogen molecules pack within the zeolite.

Summary of Test Method

The volume of nitrogen gas adsorbed by the catalyst at liquid nitrogen temperature is measured at various lowpressure levels by the catalyst sample at liquid nitrogen temperature. This is done by measuring pressure differentials resulting from introducing a fixed volume of nitrogen to the degassed catalyst in the test apparatus. This procedure is the same as Test Method D3663, that gives total surface area, but extends the pressure range to permit calculation of micropore volume and matrix surface area, by the t-plot method. Zeolite area is the difference between total area and matrix area.

Apparatus

6.1 Aschematic diagram of the apparatus is shown in Fig. 1. It may be constructed of glass or of metal. It has the following features:

6.1.1 Distribution or Dosing Manifold, having a volume between 18 cm3 and 40 cm3, (Vd), known to the nearest 0.05 cm3. This volume is defined as the volume between the stopcocks or valves and includes the pressure gauge.

6.1.2 Vacuum System, with a pump capable of attaining pressures below 4 × 10-3 hPa (3 × 10-3 torr). This can include a vacuum gauge (not shown in Fig. 1). Access to the distribution manifold is through the valve V.

6.1.3 Pressure Sensing Devices or Pressure Transducer, capable of measurements to the nearest 0.1 torr sensitivity in the range from 0 torr to 1000 torr (1 torr = 133.3 Pa).

6.1.4 Valve (H), from the helium supply to the distribution manifold.

6.1.5 Valve (N), from the nitrogen supply to the distribution manifold.

6.1.6 The connection between the sample tube and the S valve can be a standard-taper glass joint, a glass-to-glass seal, or a compression fitting.

6.1.7 Extra Volume (EV) Bulb, if employed, may be attached through valve EV. Its volume (Vx) should be 100 cm3 to 150 cm3, known to the nearest 0.05 cm3. Vx includes the volume of the stopcock bore in the glass apparatus. It is preferred that this volume be held at the same temperature as that of the distribution manifold.

NOTE 1—Modern commercial instruments automatically adjust the amounts dosed in order to produce data points at user-selected target pressures. Hence, the use of an EV bulb is optional. They may also include additional Pressure Transducers in addition to the one shown in Fig. 1.

6.2 Sample Tubes, with volumes from 5 cm3 to 25 cm3 depending on the application. Markings should be placed on the sample tubes about 30 mm to 50 mm below the connectors to indicate the desired liquid nitrogen level if automatic control of liquid nitrogen level is not available.

NOTE 2—Some instruments can analyze multiple samples simultaneously and may use sample tubes with volumes outside of the range specified in this test method.

6.3 Heating Mantles or Small Furnaces. 

6.4 Dewar Flasks.

6.5 Laboratory Balance, with 0.1 mg (10-7 kg) sensitivity.

6.6 Thermometer or Thermocouple, for measuring the temperature of the distribution manifold, T1'(i) or T2'(i), in degrees Celsius or T1(i) or T2(i) in kelvin.

6.6.1 The manifold may be thermostated at a particular temperature, a few degrees above ambient, to obviate the necessity of recording this temperature at each reading.

6.7 Pressure Saturation Tube from which P0 values may be measured directly, or Thermometer or Thermocouple, for measuring the temperature of the liquid nitrogen bath Ts(i) in kelvins from which P0 values may be derived.

6.8 Thermometer or Thermocouple, for measuring the temperature of the EV bulb, Tx'(i), if different from T1'(i) or T2'(i).

6.9 Sample Preparation Unit (not shown) for degassing the sample(s) prior to analysis. Can be integral to the surface area apparatus or can be a separate external unit.

6.9.1 The Sample Preparation Unit may be equipped with a cold trap to improve elimination of evolved moisture from the vacuum system.

*Contact us (sales@goldapp.com.cn) to get this downloaded PDF*