Mass flow measurement packed column

For measuring the inert species, some of which are present in the majority of gases, the thermal-conductivity detector (TCD) is often the detector of choice for gas analyses. Since the TCD is a concentration detector and its sensitivity is lower than that of mass-flow detectors such as the flame-ionization detector (FID), relatively high concentrations of compounds in the carrier gas are needed. This means that packed columns, with their high loadability, are still quite popular for such analyses. 

Whereas in the example just described the sample amount was about 50 mg, a similar procedure developed by another group 129) started with 4 g polyethylene copolymer. The sample was applied as a dilute solution in xylene and precipitated by very slow cooling (1.5 K/h) onto the Chromosorb P packing of a 500 x 127 mm column. The first separation was temperature-rising elution fractionation at a flow-rate of 20 ml/min and a Unear temperature increase by 8 K/h. The MMD of the fractions was measured by SEC at 145 °C in o-dichlorobenzene at 0.7 ml/min flow rate. The column set included a pair of bimodal columns 100 A and 1000 A plus a 4000 A column. The apparatus was equipped with an IR detector. The experimental data is computed to show the distribution of short-chain branching and of molar mass simultaneously. 

The residence-time distribution in the liquid phase of a cocurrent-upflow fixed-bed column was measured at two different flow rates. The column diameter was 5.1 cm and the packing diameter was 0.38 cm. The bed void fraction was 0.354 and the mass flow rate was 50.4 g s l. The RTD data at two axial positions (which were 91 cm apart in Run 1 and 152 cm apart in Run 2) are summarized in Table 3-2. Using the method of moments, estimate the mean residence time and the Peclet number for these two runs. If one assumes that the backmixing characteristics are independent of the distance between two measuring points, what is the effect of gas flow rate on the mean residence time of liquid and the Peclet number Hovv does the measured and the predicted RTD at the downstream positions compare in both cases ... 

The reported study on gas-liquid interphase mass transfer for upward cocurrent gas-liquid flow is fairly extensive. Mashelkar and Sharma19 examined the gas-liquid mass-transfer coefficient (both gas side and liquid side) and effective interfacial area for cocurrent upflow through 6.6-, 10-, and 20-cm columns packed with a variety of packings. The absorption of carbon dioxide in a variety of electrolytic and ronelectrolytic solutions was measured. The results showed that the introduction of gas at high nozzle velocities (>20,000 cm s ) resulted in a substantial increase in the overall mass-transfer coefficient. Packed bubble-columns gave some improvement in the mass-transfer characteristics over those in an unpacked bubble-column, particularly at lower superficial gas velocities. The value of the effective interfacial area decreased very significantly when there was a substantial decrease in the superficial gas velocity as the gas traversed the column. The volumetric gas-liquid mass-transfer coefficient increased with the superficial gas velocity. 

A set of ternary mass transfer experiments was carried out by Toor and Sebulsky (1961b) and Modine (1963) in a wetted-wall column and also in a packed column. These authors measured the simultaneous rates of transfer between a vapor-gas mixture containing acetone, benzene, and nitrogen or helium, and a binary liquid mixture of acetone and benzene. Vapor and liquid streams were in cocurrent flow in the wetted-wall column and in countercurrent flow in the packed column. Their experimental results show that diffusional interaction effects were significant in the vapor phase, especially for the experiments with helium in the wetted wall column. 

In this chapter, all of the process flow rates were considered to be constrained by zero flow and the maximum flow allowable by the valve size and span of the flow measurement. The main column constraint because of flooding is associated with the vapor traffic and pressure drop across the trays or packing in the distillation column. The mass transfer rate limit for stripping light key impurity from the bottoms stream was presented. The mass transfer rate limit for absorbing heavy key impurity from the overhead vapor stream was also presented. 

For compounds eluting between dotriacontane and hexatriacontane, the 2 in the above equation was changed to a 4 to calculate indices between 3200 and 3600. The C34 hydrocarbon standard was not available. The chromatograph used was a Hewlett-Packard (HP) 5890 Series II model attached to an HP 5988 mass spectrometer, which was used to verify the identity of the spectral peaks used to produce the data presented here. The column used was an HPl capillary column with an inside diameter of 0.2 mm and a 0.33 micron film thickness of methyl silicone stationary phase. The carrier gas was helium at a flow rate of 0.9 ml/min. All measurements were made with isothermal temperature programs. The data are presented as Kovats indices followed by the column temperatures, in degrees Centigrade, used to produce the data. To reproduce the results presented in this book, the same temperature, stationary phase, carrier gas, gas flow rate, and column dimensions should be used. The Kovats indices presented here cannot be compared with indices measured with a packed column. A table of retention indices appears in Appendix E. 

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