Silica gel beds

Reversed-phase silica gel column Place a cotton wool plug at the bottom of a glass chromatography column. Pack 5 g of reversed-phase silica gel slurried with a solvent mixture of n-hexane-benzene-methanol (80 20 0.4, v/v/v) into the glass column. Place an anhydrous sodium sulfate layer about 1 -cm thick above and below the silica gel bed Bell jar-type filtering apparatus Buchner funnel, 11-cm i.d. 

Centrifuge tube with ground stopper 100-mL Glass chromatography column 400 x 15-mm i.d. with a stopcock Column preparation A silica gel column is prepared by packing a slurry of silica gel (10 g) in n-hexane-ethyl acetate (9 1, v/v) solvent mixture into a glass chromatography column. About a 1-cm layer of anhydrous sodium sulfate is placed above and below the silica gel bed... 

Using a medium size filter funnel, add enough silica gel to the depth of about 1.5 covered with sand. Prewash the silica gel with methylene chloride (CH2CI2) under suction, discarding the filtrate. Add the reaction mixture and flush with CH2CI2. Dicyclohexylurea remains at the top of the silica gel bed. 

Prepare the lipid for chromatography by dissolving 50 to 75 mg of crude lipid in a minimum of hexane (5 to 10 mL). Open the stopcock and allow excess solvent to drain from the column until the level of solvent just reaches the top of the silica gel column. Very carefully add the solution of crude lipid to the top of the column. This should be done by using a Pasteur pipet and allowing drops of the solution to run down the inside of the glass column to the top of the silica gel bed. It is important not to disturb the top of the silica gel column. After addition of the lipid solution, begin to collect a fraction from the bottom of the column into a 25-mL Erlen meyer flask. Set the flow rate to about 2 drops per second. When the level of solution in the column reaches the top of the silica gel, turn off the stop-... 

In the pilot plant, a stream of oxygen containing 2 weight % ozone left the ozone generator, was cooled, and was fed to the silica gel beds. Evacuation and... 

Step 2. Desorb ozone in a stream of carrier gas, letting the relatively small amount of oxygen blown out initially from the silica gel bed contaminate the carrier gas. 

Step 1. Adsorb ozone on silica gel from the stream of oxygen plus ozone, first purging the relatively small amount of carrier gas blown out initially from the silica gel bed through an ozone decomposition catalyst to the atmosphere (or to a gas holder if the carrier gas is valuable), then recycling the oxygen back to the ozonizer. 

The optimum operating temperature for the silica gel beds would have to be selected after a cost study for each individual case. 

Undiluted ozone at a pressure somewhat below atmospheric (depending on the silica gel loading) may be obtained by pumping ozone off the silica gel. By keeping the ozone gas at a low pressure, gas phase explosions may be avoided. If the ozone is to be used in a chemical reaction, the reactor might be placed between the silica gel beds and the vacuum pump. 

In a typical resolntion procednre, the rac-TH(3C.HCl (3.199 kg, 91.6% w/w) and K2CO3 are slurried under reflux in EtOH (58.6 L) for 8 h. After cooling to room temperature, the suspension is filtered and the resulting ethanolic solntion of the free base (rac-THpC) is percolated through a silica gel bed (5.15 kg). The silica gel is washed with EtOH (4.16 L). Both ethanolic solutions of rac-THpC are pooled together and concentrated nntil a concentration of 1 g rac-THpC per 26 mL EtOH is obtained. To that ethanolic solntion is added (5)-(+)-camphorsulfonic acid (2.135 kg, 1 equiv). The reaction mixtnre (snspension) is refluxed for 2 h and stirred for another 2 h at room temperature. The crystals are filtered, washed with EtOH (4.6 L), and dried between 40 to 50°C under reduced pressure to yield the diastereomeric salt (5)-TH[3C.(S)-CSA (1.849 kg, 39.1%, 82.8% d.e.). 

The absolute determination of the moisture content of gases can be carried out by the absorption method (allowing gas to flow through a silica-gel bed or allowing it to be absorbed by methanol and then determining the water content by Karl-Fischer titration, for example). A detailed description of these and other special methods are given in Refs. [3,7]. 

From the earliest days of industrial-scale air separation, this issue had been dealt with by chemical means. Typically, carbon dioxide was removed from the feed air using lime or caustic soda. Water was removed using caustic potash. The bed used for these purposes was replaced when expended the expended beds were either disposed of or regenerated (40). Later, activated alumina and/or silica gel beds were used to remove water from the feed air. 

NATCO reports the use of hollow fibre bundles of cellulose triacetate in an EOR application in Texas (USA) at a scale 100MMSCFD (3 OOOOOOmVday) of gas since 1994 [14], Pre-treatment includes chilling to remove heavy hydrocarbons and then dehydration by silica gel beds. An expansion of this facility to 200MMSCFD (6000000mVday) was planned in 2005. 

The complete system is shown in Fig. 5. Before the gas enters the silica-gel beds, more methane has been condensed and frozen out in a tank in the liquid-nitrogen bath. Conversion to 50/50 ortho-parahydrogen is also made in the liquid-nitrogen bath, thereby conserving refrigeration in the liquefier conversion section. 

The heat produced by the combustion of sulphur can be utilized in boilers to generate steam for melting the sulphur or for steam supply purposes around the plant or to heat ambient air required for regenerating the silica gel beds used for drying process air to a dew-point of about - 60°C. 

Calculate the amount of water removed in the silica gel bed drier (air with a dew point of -60 C contains 0.009 gram water per kg dry air). 

Raw extracts in hexane solution are concentrated by rotary evaporation under reduced pressure below room temperature to < 1 mL in a conical flask. The concentrate is transferred to a silica gel chromatography column. The mass ratio of extracted organic matter to silica gel should be 1 100 or less. Four fractions of increasing polarity are eluted with two silica gel bed volumes each of n-hexane, n-hexane plus 20 % dichloromethane, dichloro-methane and methanol. The eluates are concentrated by rotary evaporation under reduced pressure below room temperature to < 1 mL. Further concentration may be achieved by blowing a slow stream of purified nitrogen over the pre-concentrated sample solution inside a suitable ampoule. 

When the column is packed, remove the septum from the top of the column and maintain a gentle flow of inert gas over the silica gel using the side-arm stopcock. Place a 3 mm layer of 50-100 pm mesh sand on the flat top of the silica gel bed. Check the column. If there are air bubbles or cracks in the column, start again. Replace the septum on the top of the column. 

What is the length of the silica gel bed needed if benzene breaks through as a square wave at 90 minutes Employ an equilibrium nondispersive mode of operation of the bed being saturated by a trace gas. If the length... 

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