Pressure packed column

Pesticide analysis in water can be simplified considerably if a single short column (20-mm X 4.0-mm ID) is used. Use of the short column (high-pressure packed column) permits baseline separation of over 20 analytes. The column can be reused for some 20 real samples without any decrease in performance. 

Single short, high-pressure packed columns coupled with MS or tandem MS detection permits the rapid trace-level determination and identification of environmental pollutants in water samples. Using an ACPI interface, a mixture of 17 pesticides, including OPPs, can be successfully used to identify pesticides at the level of 0.1 yug/L in tap water (93,94). 

Pig. 22. Schematic representation of typical pressure drop as a function of superficial gas velocity, expressed in terms of G = /9q tiQ, in packed columns. O, Dry packing , low Hquid flow rate I, higher Hquid flow rate. The points do not correspond to actual experimental data, but represent examples. 

Fig. 24. Generalized method using log scales for estimating packed column flooding and pressure drop, AP, in kPa/m g = gravitational constant, 9.81 m/s t = kinematic viscosity in mm /s (= cSt) E, G have units of kg/(m s) are in kg/m and the packing factor, F, in can be found in...

There are notable cases where plate columns have been converted to packed columns to gain advantage of the low pressure drop exacted from the vapor stream. More recently the packings have been largely of the stmctured type. Illustrative of this is the trend toward the use of stmctured packing in ethylbenzene—styrene fractionators, some of which have diameters of 10 m or higher. 

Temperature-sensitive mixtures are to be separated. To avoid decomposition and/or polymerization, vacuum operation may then be necessary. The smaller liqmd holdup and pressure drop theoretical stage of a packed column may be particularly desirable. 

Selection of Equipment Packed columns usually are chosen for very corrosive materials, for liquids that foam badly, for either small-or large-diameter towers involving veiy low allowable pressure drops, and for small-scale operations requiring diameters of less than 0.6 m (2 ft). The type of packing is selected on the basis of resistance to corrosion, mechanical strength, capacity for handling the required flows, mass-transfer efficiency, and cost. Economic factors are discussed later in this sec tion. 

Example 13 Packed Column Pressure Drop Air and water are flowing coiinterciirrently through a bed of 2-inch metal Pali rings. The air mass velocity is 2.03 kg/s-m (1500 Ihs/hr-fd), and the liquid mass velocity is 12.20 kg/s-m (9000 Ihs/hr-fr). Calculate the pressure drop hy the generalized pres-... 

Determination of pressure drop through the column (for packed columns, correlations dependent of packing type, column-operating data, and physical properties of the constituents involved are available to estimate the pressure drop through the packing for plate columns, the pressure drop per plate is obtained and multiplied by the number of plates)... 

In preparing any of the above for use in columns, the dry powder is evacuated, then mixed under reduced pressure with water or the appropriate buffer solution. Alternatively it is stirred gently with the solution until all air bubbles are removed. Because some of the wet powders change volumes reversibly with alteration of pH or ionic strength (see above), it is imperative to make allowances when packing columns (see above) in order to avoid overflowing of packing when the pH or salt concentrations are altered. 

Washed with 10% (vol) aqueous H2SO4 (three times), 10% aqueous KOH (three times), and then with water until neutral. Dried with MgS04 and fractionally distd from CaH2 through a glass helices-packed column under reduced pressure. 

Fractionally distd below ISmm pressure, using packed column and taking precautions to avoid absorption of water. 

Perchlorobutadiene [87-68-3] M 260.8, b 144.1"/100mm, 210-212"/760mm, d 1.683, n 1.5556. Washed with four or five 1/lOth volumes of MeOH (or until the yellow colour has been extracted), then stirred for 2h with H2SO4, washed with distilled water until neutral and filtered through a column of P2O5. Distd under reduced pressure through a packed column. [Rytner and Bauer J Am Chem Soc 82 298 I 960.]... 

Propargyl alcohol (2-propyn-l-ol) [107-19-7] M 56.1, b 54 /57mm, 113.6 /760mm, d 0.947, n 1.432. Commercial material contains a stabiliser. An aqueous soln of propargyl alcohol can be concentrated by azeotropic distn with butanol or butyl acetate. Dried with K2CO3 and distd under reduced pressure, in the presence of about 1% succinic acid, through a glass helices-packed column. 

Biphenylyl diphenyl phosphate [132-29-6] M 302.4, n l.5925. Vacuum distd, then percolated through an alumina column. Passed through a packed column maintained at 150° to remove residual traces of volatile materials by a counter-current stream of nitrogen at reduced pressure. [Dobry and Keller J Phys Chem 61 1448 1957.]... 

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