Open cooling system sampling

For most open cooling systems, the samples that will need to be taken most regularly will include the recirculating cooling water and the immediate makeup water source(s). If the makeup is a blend of waters or has been subjected to pretreatment processes that can alter its natural characteristics, such as softening, additional samples will need to be taken, albeit probably less frequently. 

After the chromium (II) chloride solution has been transferred to flask B, the flow of ammonia through the reaction vessel should be started. The ammonia delivery tube should approach but not dip below the liquid level in flask B. If tank ammonia is used, the tank should be opened carefully to avoid spattering of liquids by a sudden burst of gas. If ammonia is to be generated, the ammonium sulfate solution should be added carefully to the potassium hydroxide in flask C. It may be necessary to cool flask C with ice at first, then to warm the generator later in order to maintain a reasonably constant flow of ammonia. The use of tank ammonia avoids these problems. If zinc was used in the reduction, a precipitate of zinc hydroxide forms first and redissolves. The violet-blue solution stirred at 0° is saturated with ammonia, then a 2- to 3-g. sample of the platinum catalyst is added rapidly to flask B. A strong countercurrent of nitrogen is used to prevent entrance of air into the system when the catalyst is added. The reaction mixture is allowed to stir for one hour while the flask is cooled with ice. 

Fig. 23.3. Variation in C02 fugacity in a computer simulation of sampling, cooling, and then reheating a hypothetical geothermal fluid. Bold line shows path followed when system is held closed. Fine lines show effects of an open system in which fluid is allowed to degas C02 as it cools.

As a second experiment, let us simulate the sampling of the same fluid as an open system. This time, we allow it to effervesce CO2 as we bring it to the surface and let it cool. We start as before, but include a slide command to vary CO2 fugacity from its initial value to one, corresponding to the fugacity of this gas in the atmosphere. The procedure (starting anew in react) is... 

When a PTV instead of a classic injector was utilized in the analysis of penicillin residues, the sensitivity and the precision of the analysis were markedly improved (45). With the cooled PTV injector, some microliters could be injected, and the split-splitless mode allowed solvent venting at low injector temperatures with open slit in a first step, and quantitative transfer of volatile or derivatized drugs by a freely selected linear heat-up rate between 2-12 C/s in the splitless mode in the second step. Sensitivity could be enhanced by multiple injections before heat-up. Nonvolatile components of a sample did not contaminate the chromatographic system, since they accumulated in the glass vaporization tube, which could be changed easily. 

The mixture in the autoclave is homogeneous. This was insured by keeping the Magne Drive stirrer always at a steady 1500 r.p.m. It was experimentally proved that even distribution of coal and tetralin in the autoclave is a fair assumption because the fraction extracted from the last portion of mixture, which remained in the autoclave and was taken after the system cooled to room temperature and the autoclave was opened, was found to be very close to the yield obtained from the last sample taken from the system through the sample lines at reaction temperature. 

A 2.0-g. sample of powdered dicobalt octacarbonyl is placed in a 25-ml. glass reactor in a nitrogen-filled glove bag. The reactor is evacuated then 5 g. of trichlorosilane is condensed from the vacuum system into the reactor which has been cooled to —196°. The Teflon stopcock is closed, the reaction vessel allowed to warm to room temperature, and then the reactants are permitted to stand for 24 hours. Cool the reactor to —42° (diethyl ketone slush), open the Teflon stopcock, and remove the excess silane and noncondensable substances into the vacuum system with pumping. The remaining dry, solid material is then transferred in a nitrogen (or carbon monoxide) filled glove bag to a sublimation apparatus. The solid is then sublimed in vacuo... 

Figure 10-8. Equipment needed for lyophilization or freeze drying small samples, (a) The unit is cooled and evacnated by means of a self-contained refrigeration system and vacuum pump. Sample vessels are inserted into the rubber nozzles and the valve (little white knobs) opened for each nozzle that contains a vessel, (b, c) The units are evacuated by connecting them to a mechanical vacuum pump (connection indicated by arrows) and... 

The MHS-10 system uses an open quartz optical cell of which both ends are provided with graphite rings for cooling. The cell is normally placed in an air-acetylene flame but for convenience electrothermal heating was applied. Efficient mixing of reagent and sample solution are obtained by the conical shape of the reaction vessel and the deep immersion of the reductant inlet tube in the sample solution. No stirrer is provided. 

A vacuum of from 4-6 torr (0.53 - 0.80 kPa) is common, and the heat loss by the subliming water usually will keep the material frozen. During small-scale laboratory operations the sample holders are left in the open air, but in large-scale commercial applications, heat must be applied to provide the sublimation energy at the rate Just below that required to keep the material frozen. To sublime 1 g of ice at 0 C requires 666 calories (2.78 kJ). This heat is provided by warm-water trays placed under the sample trays, by radiation from heated walls surrounding the sample trays, or by microwave warming. Sublimation from commercial warm water-heated trays occurs at the rate of 0.1-1.0 kg HjO/hr/m. Few systems are cooled below -30 °F, because the vapor pressure is then too low for rapid sublimation. 

Close the valve between vacuum system and the filling apparatus. Open the valve of the sample container, and cool the lower tip of the cell container with liquid nitrogen. Continue until approximately 1 ml of cyclooctane has sublimated into the tip. Close the connecting valve. 

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