Gravimetric microbalance

As alluded to earlier, in a conventional gravimetric microbalance, it is not possible to determine the true space velocity since an undeterminable, but a large amount of the feed bypasses the catalyst bed. Therefore, the conversion observed in the exit gas cannot be related to the true activity of the catalyst. To demonstrate that the plug-flow-vibration microbalance has overcome this problem we have carried out an experiment in the microbalance and in a conventional fixed bed reactor using 0.3wt%Pt-0.3wt%Re/Al203 under the same conditions 210 kPa, 750 K, = 3 and liquid-weight-hourly space... 

Conversion and coke formation during catalytic ethene oligomerization catalyzed by HZSM-5 have been investigated in the TEOM and in a conventional gravimetric microbalance under similar conditions (2). The results show that the TEOM is a powerful tool for determination of the kinetics of deactivation of catalysts, with a design that makes determination of the true space velocity (or space time) easy. The TEOM combines the advantages of the conventional microbalance with those of a fixed-bed reactor, and the same criteria can be used to check for plug flow and differential operation. 

The solubility and thermodynamic properties of various gases in [BMIM][PFg] has been determined using a gravimetric microbalance [4]. Essentially, the solubility of CO2 (particularly relevant as a carbon source) was very high, with reasonable solubilities observed for ethylene, ethane, and methane and low solubilities for oxygen, carbon monoxide, and hydrogen (H2 could not be detected). Subsequently, Henry coefficient solubility constants ofhydrogen in [BMIM][BF4] and [BMIM][PFg]... 

Historical Development. The first report concerning the use of piezoelectric resonance from a quartz crystal in a gravimetric microbalance is by J. Strutt (Lord Rayleigh), who in 1885 described a shift in resonance frequency accompanying an infinitesimal mass change in a mechanical oscillator [205]. Fundamental studies into the mass sensitivity of quartz resonators and their potential application for measuring the thickness of thin layers were reported in 1959 by Sauerbrey [203], [206]. King was the first to use a quartz microbalance QMB (in 1964) as a gas-phase... 

Isotherm measurements of methane at 298 K can be made either by a gravimetric method using a high pressure microbalance [31], or by using a volumetric method [32]. Both of these methods require correction for the nonideality of methane, but both methods result in the same isotherm for any specific adsorbent [20]. The volumetric method can also be used for measurement of total storage. Here it is not necessary to differentiate between the adsorbed phase and that remaining in the gas phase in void space and macropore volume, but simply to evaluate the total amount of methane in the adsorbent filled vessel. To obtain the maximum storage capacity for the adsorbent, it would be necessary to optimally pack the vessel. 

The main principles of instrument design are summarized in Table 9.11. In filtration, e.g. for gravimetric analysis, selection of filter material requires careful consideration in terms of strength, collection efficiency, compatibility with pump, water uptake, etc. Humidity-controlled balance rooms, microbalances and careful handling techniques are required. 

The reduction procedure described above was carried out in a static system in order to facilitate determination of the extent of reduction in situ. The reduction was monitored gravimetrically using a microbalance (Cl Electronics MK II) and volumetrically by measuring the decrease in hydrogen pressure. Total surface areas were determined by the BET method using nitrogen at 77 K. 

The total mass of particles per unit volume of air is one of the major parameters used to characterize particles in air and, along with size, is the basis of air quality standards for particulate matter (see Chapter 2). Methods of mass measurement include gravimetric methods, /3-ray attenuation, piezoelectric devices, and the oscillating microbalance. 

Experimentally, adsorption isotherms are determined by gravimetric or volumetric measurements for powders or porous adsorbents. For isolated flat surface a quartz microbalance or an ellipsometer can be applied to measure adsorption isotherms. 

Hageman et al. [3.13] calculated the absorption isotherms for recombinant bovine somatotropin (rbSt) and found 5-8 g of water in 100 g of protein, which was not only on the surface but also inside the protein molecule. Costantino et al. [3.72] estimated the water monolayer M0 (g/100 g dry protein) for various pharmaceutical proteins and for their combination with 50 wt% trehalose or mannitol as excipient. They compared three methods of calculating MQ (1) theoretical (th) from the strongly water binding residues, (2) from conventional adsorption isotherm measurements (ai) and (3) from gravimetric sorption analysis (gsa) performed with a microbalance in a humidity-controlled atmosphere. Table 3.5 summarizes the results for three proteins. The methods described can be helpful for evaluating RM data in protein formulations. 

Two different adsorbents, activated carbon Norit R 0.8 Extra (Norit N.V., The Netherlands) and molecular sieve (type 4A, Merck), were used to study tert-butylbenzene, cyclohexane, and water vapour breakthrough dynamics. Structural parameters of the carbon adsorbent were calculated from benzene vapour adsorption-desorption isotherms measured gravimetrically at 293 K using a McBain-Bakr quartz microbalance, and nitrogen adsorption-desorption isotherms recorded at 77.4 K using a Micromeritics ASAP 2405N analyzer described in detail elsewhere.22,24 Activated carbon Norit has a cylindrical... 

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