Experimental procedure - gases

A similar procedure can be carried out with gases. This technique has been used with carbon dioxide as the adsorbate and nitrogen as the carrier gas (114]. Adsorbents used were y-alumina, Gasil and Degussa 

The carbon dioxide isotherm at 22 C on y-alumina was found to obey Sips equation [115], which is valid for adsorption, at low pressure, on a non-uniform surface. 

The procedure to determine V is to select the value of B to give the best fit when log V is dotted agmnst p/(p- B). 

The heat of adsorption of carbon dioxide on y-alumina decreased with increasing coverage, thus substantiating that the surface was non-uniform. The surface of Gasil silica was found to be slightly heterogeneous and that of Degussa silica was found to be 

Burevski found that the energy of adsorption for gases varied with coverage [119]. The manner in which it varied depended on the system under examination, rendering the method unsuitable for surface area determination. 

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Experimental Procedure. Gas flow was initially fed to a column approximately 2/3 full of slurry. After the gas flow rate was set, the slurry flow was started and adjusted using the calibrated volume. Flow rates were held constant during the runs, which lasted 1+5 to 75 minutes for the 12.7 cm column, and 180 minutes for the 30.5 cm column. At the end of this time, slurry samples were taken, starting at the top of the column and working down, so as not to disturb upstream conditions. All slurry ports were purged before taking a sample, and stopcocks were turned quickly to full open and full closed to prevent settling of slurry within the sample line. 

Mercury porosimetry is generally regarded as the best method available for the routine determination of pore size in the macropore and upper mesopore range. The apparatus is relatively simple in principle (though not inexpensive) and the experimental procedure is less demanding than gas adsorption measurements, in either time or skill. Perhaps on account of the simplicity of the method there is some temptation to overlook the assumptions, often tacit, that are involved, and also the potential sources of error. 

A vast amount of research has been undertaken on adsorption phenomena and the nature of solid surfaces over the fifteen years since the first edition was published, but for the most part this work has resulted in the refinement of existing theoretical principles and experimental procedures rather than in the formulation of entirely new concepts. In spite of the acknowledged weakness of its theoretical foundations, the Brunauer-Emmett-Teller (BET) method still remains the most widely used procedure for the determination of surface area similarly, methods based on the Kelvin equation are still generally applied for the computation of mesopore size distribution from gas adsorption data. However, the more recent studies, especially those carried out on well defined surfaces, have led to a clearer understanding of the scope and limitations of these methods furthermore, the growing awareness of the importance of molecular sieve carbons and zeolites has generated considerable interest in the properties of microporous solids and the mechanism of micropore filling. 

As described in Section 6.2.1., British Gas performed full-scale tests with LPG BLEVEs similar to those conducted by BASF. The experimenters measured very low overpressures firom the evaporating liquid, followed by a shock that was probably the so-called second shock, and by the pressure wave from the vapor cloud explosion (see Figure 6.6). The pressure wave firom the vapor cloud explosion probably resulted from experimental procedures involving ignition of the release. The liquid was below the superheat limit temperature at time of burst. 

Experimental Procedure. In a typical liquefaction experiment, the autoclave was charged at room temperature with Tetralin-d12, coal and deuterium gas. In E10, a rocking autoclave was used. In El9, a stirred autoclave was used with a special stirrer which conformed to the shape of the autoclave liner. 

The experimental procedure is outlined schematically in Fig. 13 a detailed description was given by Hartog et al. 37). Benzene vapor and deuterium gas, in the molar ratio of 1 18, were passed through a catalyst bed and then through a cold trap immersed in liquid nitrogen in which the hydrocarbons were frozen out. The temperature of the catalyst bed was... 

Finally, experimental procedures differing from that described in the preceding examples could also be employed for studying catalytic reactions by means of heat-flow calorimetry. In order to assess, at least qualitatively, but rapidly, the decay of the activity of a catalyst in the course of its action, the reaction mixture could be, for instance, either diluted in a carrier gas and fed continuously to the catalyst placed in the calorimeter, or injected as successive slugs in the stream of carrier gas. Calorimetric and kinetic data could therefore be recorded simultaneously, at least in favorable cases, by using flow or pulse reactors equipped with heat-flow calorimeters in place of the usual furnaces. 

Catalytic experiments were performed in a fixed bed glass tubular reactor at atmospheric pressure and at reaction temperature of 450 and 482°C for n-heptane and gas-oil, respectively. Details on the experimental procedure have already been published (7). 

Dupuy and coworkers have reported a direct gas chromatographic procedure for the examination of volatiles in vegetable oils (11). peanuts and peanut butters (12, 13), and rice and com products (14). When the procedure was appTTed to the analysis of flavor-scored samples, the instrumental data correlated well with sensory data (15, 16, 17), showing that food flavor can be measured by instrvmental means. Our present report provides additional evidence that the direct gas chromatographic method, when coupled with mass spectrometry for the identification of the compounds, can supply valid information about the flavor quality of certain food products. Such information can then be used to understand the mechanisms that affect flavor quality. Experimental Procedures... 

Unsteady State Diffusion. The apparatus, experimental procedures, and the computational procedures used to calculate the diffusion parameter D /r (where D is the diffusion coefficient and r is the diffusion path length) have been described in detail previously (6, 8). A differential experimental system was used to avoid errors caused by small temperature fluctuations. In principle, the procedure consisted of charging the sample under consideration with argon to an absolute pressure of 1204 12 torr (an equilibrium time of about 24 hours was allowed) and then measuring the unsteady state release of the gas after suddenly reducing the pressure outside the particles back to atmospheric. 

The write-up to this point is to be completed as a Prelab assignment. The experimental procedure followed is then recorded in your notebook as you proceed through the experiment. The detail should be sufficient so that a fellow student can use your notebook as a guide. You should include observations, such as color changes or gas evolution, made during the experiment. If you obtain a recorder printout of numbers, a spectrum from a spectrophotometer, or a photograph, these records must be saved and handed in with your report. 

The investigations were performed in a closed circulation reactor with a volume of 175 cm. The volume of the reactant sample was 0.3 cm. The carrier gas was helium, freed from oxygen with an Alltech Oxy-Trap. The hydrogen used in the measurements was produced by a Matheson 8326 electrolysis apparatus equipped with a Pd diffusion cell. 2-5 mg catalyst samples were used. Details on the experimental procedure were reported earlier (refs. 5,6). 

In concomitance with the displacement observed by i.r., an evolution of the catalytic activity has been observed while studying the liquid-phase epoxidation of cyclohexene in the presence of (EGDA)- Mo(VI), freshly prepared or after four months of conditioning at room temperature under inert atmosphere. As usual, the appearance of epoxide was followed by gas chromatographic analyses or by direct titration of oxirane oxygen and the disappearance of hydroperoxide was monitored by iodometric titration. In figure we report concentration-time for typical runs in ethylbenzene at 80°C obtained with the experimental procedure already described (ref. 9). It may be seen that with a freshly prepared catalyst an induction period is observed which lowers the initial catalytic activity. Our modified Michaelis-Menten type model equation (ref. 9) cannot adequately fit the kinetic curves obtained due to the absence of kinetic parameters which account for the apparent initial induction period (see Figure). 

A preliminary cycling test was performed with pure methane. It is illustrated in Fig. 3. According to the described experimental procedure, in the first cycle, the vessel is charged from vacuum to 3.5MPa at 298K. During the first discharge, when the pressure decreases from 3.5 to 0.1 MPa, around 20% of the total amount of gas adsorbed... 

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