Dead space liquid volume

An important point in analytical distillation is to use a stUl head having as low a dead space as possible. By dead space that volume of liquid is denoted which is retained above the column in the stUl head instead of taking part further in the countercurrent process. The automat ic column heads for the partition of vapour or... 

The method is described in Section 4-4.5. It is important to ensure that the dead spaces (gas volumes between the liquid surface and the exit gas concentration detector) are deconvoluted from the measured response. Gas-phase RTD has been measured by Hanhart et al. (1963) and Gal-or and Resnick (1966) and is often in between the ideal limits of plug flow and perfectly backmixed. 

A number of potential sources of error must be taken into account. In the volumetric method the following items need attention (a) constancy of the level of liquid nitrogen (b) depth of immersion of the sample bulb ( S cm) (c) temperature of sample (monitoring with vapour pressure thermometer close to sample bulb) (d) purity of adsorptive (preferably 99-9 per cent) (e) temperature of gas volumes (doser, dead space), controlled to 01 C. 

There is a minor anomaly in the retention-ume distribution curve in Fig. 6. starling at r 1.2tp. This is caused by a small amount of liquid following a second flow path longer than the mainstream flow. This minor flowstream probably exited the upper spreader through the vent and then used the dead space for separation purposes, reducing the inactive volume of this vessel. 

Left Five-stage gas compressor Right Single-stage liquid pump Vh, Stroke volume Vr dead space Apa pressure amplitude per stage... 

The total accessible pore volume may be measured by the amount of adsorbate at the saturation pressure of the adsorptive, calculated as liquid volume, provided the adsorption on the external surface can be neglected or can be evaluated. The accessible pore volume may be different for molecules of different sizes. A method which is not subject to the effect of the external surface is the determination of the dead space by means of a non-sorbable gas (normally helium) in conjunction with the determination of the bulk volume of the adsorbent by means of a non-wetting liquid or by geometrical measurements. 

Thus in addition to the data required to determine the surface excess amount (cf. Section 3.3.1), one needs to know dQKV (the heat exchanged reversibly during each adsorption step) and Vc (the volume - dead space - of that part of the adsorption bulb which is located within the calorimetric detector (cf. Figure 3.15). Vc is evaluated by liquid weighing or by geometrical considerations and corrected for the sample volume. 

A successful sampling valve is that due to Pratt and Purnell (Fig. 58) . A dead-space sample is first withdrawn, followed by a reacted sample. Cundall et claim a better valve is the push-pull type (Fig. 59), a variation of the valve used on some commercial glc instruments. For sample injections after fractionation, a constant volume and manometer is employed for gases, and precision microlitre syringes for liquids. 

In all the volumetric methods the basic principles are the same. The adsorbate is degassed under vacuum to remove surface contamination. Helium is next admitted into a burette of known volume and its pressure and temperature measured so that the amount at STP can be calculated. The sample tube is immersed in liquid nitrogen and helium admitted. The residual amount in the burette is determined and the amount expanded into the sample tube determined. Since helium does not adsorb on to the solid, this volume is termed the dead space volume and it is found to be linearly dependent on pressure, l e helium is removed and the procedure repeated with nitrogen. When the nitrogen expands into the sample tube, it splits into thi parts, residual in the burette, dead space which can be calculated from the previously found dead space factor, and adsorbed. The process is repeated at increasing pressures and the amount adsorbed determined as a function of relative pressure. 

Tap 4 is opened allowing the gas to expand into the sample tube, which is immersed in the liquid nitrogen bath to a fixed, constant level, and the pressure noted at each of the burette volumes. The data are recorded in Table 2.3. The dead space factor (Q) is ... 

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