Volumetric instruments

Nitrogen adsorption was performed at -196 °C in a Micromeritics ASAP 2010 volumetric instrument. The samples were outgassed at 80 °C prior to the adsorption measurement until a 3.10 3 Torr static vacuum was reached. The surface area was calculated by the Brunauer-Emmett-Teller (BET) method. Micropore volume and external surface area were evaluated by the alpha-S method using a standard isotherm measured on Aerosil 200 fumed silica [8]. Powder X-ray diffraction (XRD) patterns of samples dried at 80 °C were collected at room temperature on a Broker AXS D-8 diffractometer with Cu Ka radiation. Thermogravimetric analysis was carried out in air flow with heating rate 10 °C min"1 up to 900 °C in a Netzsch TG 209 C thermal balance. SEM micrographs were recorded on a Hitachi S4500 microscope. 

Gasometric methods have long been practiced because of their simplicity and accuracy. For a long time however, these methods have been performed only on a macro or semimicro scale. (A remarkable fact van Leeuwenhoek tried to measure blood gas on a true ultramicro scale in 1692 see Letter No. 72.) Manometric methods are preferred instead of volumetric methods because of their greater accuracy. A volumetric instrument for gasometry on ultramicro scale (samples of 20 [xl) nevertheless was developed by Lazarow (LI, L2) and according to the author, the reproducibility for CO2 determination in serum is better than 1 vol % (L3). 

Nitrogen sorption isotherms of ZSM-5 zeolites were measured with a Micromeritics ASAP 2020 volumetric instrument at - 196 °C. In order to attain a sufficient accuracy in the accumulation of the sorption data, this instrument was equipped with pressure transducers covering the 133 Pa, 1.33 and 133 kPa ranges. Prior to the sorption measurements, all samples were degassed at 250 °C for at least 24 h until a pressure of 10 Pa was attained. 

Figure 1 Equipment used for a manual titration. (A) Transfer pipette (B) burette (C) information provided on volumetric glassware (D) conical or Erlenmeyer flask (normally 250 or 100 cm ) (E) burette reader. (Reproduced with permission from Belcher etal. (1970) and Rudolf Brand and Co. Working tMth Volumetric Instruments. Wertheim Brand.)...

Volumetry or, preferably Manometry , cp. Sect. 2.1, is the oldest method to investigate sorption of gases in solids. Early experiments had already been performed by C. W. Scheele (1777), Chappuis (1881), W. Ostwald (1905) and J. Langmuir (1912), [1.1]. Some of these experiments were designed to determine the volume of geometrically complicated objects like cauliflower or sea-urchins. A special instrument for this purpose was designed by R. W. Pohl about 1940 and was called a volumimeter [2.1]. It served as a prototype of many of today s volumetric instruments. 

As we here are mainly interested in adsorption measurement techniques for industrial purposes, i. e. at elevated pressures (and temperatures), we restrict this chapter to volumetric instruments which on principle can do this for pure sorptive gases (N = 1), Sect. 2. Thermovolumetric measurements, i. e. volumetric/manometric measurements at high temperatures (300 K - 700 K) are considered in Sect. 3. In Section 4 volumetric-chromatographic measurements for multi-component gases (N>1), are considered as mixture gas adsorption is becoming more and more important for a growing number of industrial gas separation processes. In Section 5 we discuss combined volumetric-calorimetric measurements performed in a gas sensor calorimeter (GSC). Finally pros and cons of volumetry/manometry will be discussed in Sect 6, and a hst of symbols. Sect. 7, and references will be given at the end of the chapter. 

In order to measure simultaneously the mass and the enthalpy of an adsorbed phase, the adsorption vessel in the volumetric instrument. Fig. 2.1, has to be replaced by a calorimeter vessel. Traditionally this vessel is... 

Figure 10.1. Basic configuration of the volumetric instrumentation for measuring the gas adsorbed onto the surface of a sample of powder.

It is important to note that, in ejq)erimental work involving glassware, correction factors for the expansion of the vessel itself should also be considered. The corrections in volume of the solution as a result of the expansion can be found elsewhere. The coefficients of expansion of glasses used for volumetric instruments are generally considered to vary from 0.000023 to 0.000028. ... 

For calculation of the volumetric flow rate only the cross section area of the pipe is to be known. In order to give flow under standard conditions the temperature and pressure must be measured, and for conversion to mass flow the composition or density of the gas must be determined. These process parameters are often monitored by calibrated instrumentation. 

Balances, volumetric flasks, pipets, and ovens are standard pieces of laboratory instrumentation and equipment that are routinely used in almost all analytical work. You should be familiar with the proper use of this equipment. You also should be familiar with how to prepare a stock solution of known concentration, and how to prepare a dilute solution from a stock solution. 

To ensure that S eas is determined accurately, we calibrate the equipment or instrument used to obtain the signal. Balances are calibrated using standard weights. When necessary, we can also correct for the buoyancy of air. Volumetric glassware can be calibrated by measuring the mass of water contained or delivered and using the density of water to calculate the true volume. Most instruments have calibration standards suggested by the manufacturer. 

A turbine flowmeter consists of a straight flow tube containing a turbine which is free to rotate on a shaft supported by one or more bearings and located on the centerline of the tube. Means are provided for magnetic detection of the rotational speed, which is proportional to the volumetric flow rate. Its use is generally restric ted to clean, noncorrosive fluids. Additional information on construction, operation, range, and accuracy can be obtained from Holzbock (Instruments for Measurement and Control, 2d ed., Reinhold, New York, 1962, pp. 155-162). For performance characteristics of these meters with liquids, see Shafer,y. Basic Eng., 84,471-485 (December 1962) or May, Chem. Eng., 78(5), 105-108 (1971) and for the effect of density and Reynolds number when used in gas flowmetering, see Lee and Evans, y. Basic Eng., 82, 1043-1057 (December 1965). 

Velocity and Volumetric Flow Rate The U.S. EPA has published Method 2 as a reference method for determining stack-gas velocity and volumetric flow rate. At several designated sampling points, which represent equal portions of the stack volume (areas in the stack), the velocity and temperature are measured with instrumentation shown in Fig. 25-27. 

The flow that is shown in these figures is the instrument flow measured as m/s in the measuring tube. Multiplied with the flow cross-section of 5.59 cm, this gives the volumetric flow in the 2.67-cm diameter flow tube. Using a different catalyst basket or measuring tube will change this ratio. The volumetric flow is the same in the basket. Because the small basket has a 3.15 cm diameter and 7.79 cm cross-section, the linear velocity will be 5.59/7.79 = 0.72 fraction of that in the tube. 

Standard instrument control and pacing signals are generally acceptable for common feeder system operation. Volumetric and gravimetric feeders are usually adaptable to operation from any standard instrument signals. 

When solution must be pumped, consideration should be given to use of holding tanks between the dry feed system and feed pumps, and the solution water supply should be controlled to prevent excessive dilution. The dry feeders may be started and stopped by tank level probes. Variable-control metering pumps can then transfer the alum stock solution to the point of application without further dilution. Means should be provided for calibration of the chemical feeders. Volumetric feeders may be mounted on platform scales. Belt feeders should include a sample chute and box to catch samples for checking actual delivery with set delivery. Gravimetric feeders are usually furnished with totalizers only. Remote instrumentation is frequently used with gravimetric equipment, but seldom used with volumetric equipment. 

I = complex impedance, B = conductivity bridge, C = capillary viscometer, P = pycnometer or dilatometer, V = volumetric glassware, I = instrument, U = method unknown... 

Stock solutions of approximately 1 mg mL were prepared by dissolving the appropriate amounts of the analytical standards in acetonitrile. Working standard solutions for fortification were prepared in volumetric flasks by appropriate dilutions of the stock solutions for each analyte or combination of analytes. During analysis, SCA is converted to DMS and HMS is derivatized therefore, the analytical standard solutions for quantitation and instrument calibration contained sulfentrazone, DMS and derivatized HMS. A measured volume of a standard solution containing sulfentrazone, DMS and HMS (prepared from stock solutions) was derivatized simultaneously with the samples. 

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