Wetting packing

Column Chromatography. The substances to be purified are usually placed on the top of the column and the solvent is run down the column. Fractions are collected and checked for compounds using TLC (UV and/or other means of visualisation). The adsorbent for chromatography can be packed dry and solvents to be used for chromatography are used to equilibrate the adsorbent by flushing the column several times until equilibration is achieved. Alternatively, the column containing the adsorbent is packed wet (slurry method) and pressure is applied at the top of the column until the column is well packed (i.e. the adsorbent is settled). 

A solution of about 300 mg of 25-hydroxyprecholecalciferol prepared as described above in 5 ml of chloroform is heated for 3% hours at 70°-75°C under Nj in a sealed flask. The solvent is evaporated and the residue is chromatographed through a 60 g column containing TLC grade Florisil, 150-200 mesh packed wet with 35% ethyl acetate in Skellysolve B hex-... 

Alternatively, as described in U.S. Patent 3,341,557, 6-dehydro-17-methyltestosterone may be used as the starting material. A mixture of 0.4 g of cuprous chloride, 20 ml of 4 M methylmagnesium bromide in ether and 60 ml of redistilled tetrahydrofuran was stirred and cooled in an ice bath during the addition of a mixture of 2.0 g of 6-dehydro-l 7-methyl-testosterone, 60 ml of redistilled tetrahydrofuran and 0.2 g of cuprous chloride. The ice bath was removed and stirring was continued for four hours. Ice and water were then carefully added, the solution acidified with 3N hydrochloric acid and extracted several times with ether. The combined ether extracts were washed with a brine-sodium carbonate solution, brine and then dried over anhydrous magnesium sulfate, filtered and then poured over a 75-g column of magnesium silicate (Florisil) packed wet with hexanes (Skellysolve B). The column was eluted with 250 ml of hexanes, 0.5 liter of 2% acetone, two liters of 4% acetone and 3.5 liters of 6% acetone in hexanes. 

Packing Wetting Rates Related to Pacldng Material Surface... 

Figure 9-43. Fraction packing wetted. Used by permission of Shul-man, H. L., Uiiich, C. F., Prouix, A. Z., etnd Zimmerman, J. O., A.I.Ch.E. Jour., V. 1, No. 2 (1955) p. 253 ail rights reserved.

All foods must be clean on entry. Some, such as fish, leaf vegetables and some fruits, may be washed and left wet. Fish will tend to dry out and lose its fresh appearance, so it is packed wet or given a sprinkling of ice chips to keep the surface moist. 

If very low liquid rates have to be used, outside the range of FLV given in Figure 11.44, the packing wetting rate should be checked to make sure it is above the minimum recommended by the packing manufacturer. 

This paste is packed wet into tbin>walled paper tubes, ocoinally a-bout -i diameter by 1" long, with the fingers or a spatula, with i-inch length of stiff black match inserted neerly its full length into tbe composition before it dries. Tbe stars must be dried until quite hard, which nay take a full week at room temperature. 

The solutions are transferred to the reaction kettle through metered tubes, and the precipitated lead azide is washed and either filtered and dried or packed wet for shipment. In some countries the practice is to introduce the azide into detonators or explosive trains only at the place of manufacture in other countries, notably the U.S.A., transportation is permitted, and the packed azide may be stored and used in detonators or fuze trains at distant locations. However, while such peripheral practices and associated equipment are important, it is the control exercised during the metathesis in the kettle that affects the product and, more importantly, introduces subtle differences that make one form of lead azide different from another in performance characteristics, if not in gross physical appearance. Therefore, the emphasis of the present discussion will be on the reaction kettles and their associated equipment, and the following section will emphasize the control on the metathesis. 

The column of Example 2.12 is packed randomly with spherical glass beads 3.5 mm in diameter. The water is now supplied as a fine mist that flows down through the packed bed at a flow rate just enough to replace the water lost by vaporization and to keep the surface of the packing wet. Under these conditions, it may be assumed that equation (2-90) applies. 

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