Condensation with Inert Gases

An inert gas-vapour mixture saturated with condensing vapours has to be extracted independent of the condenser design. If there is only one kind of vapour, then the saturation quantity can be calculated easily with the equation  

M is the molecular weight, p is the partial pressure, and m the mass flow rate. The index T stands for the inert gas and V for vapour. 

An example can best illustrate the influence the condensation conditions have on the specification of the vacuum pump. 

Steam is to condense at a vacuum of 60 mbar. This corresponds to a saturated steam temperature of 36 C. The steam to be condensed contains 10 kg h of air. The condenser should be suitable to cool the air, together with the included steam down to 30 C. The question is now, how much steam-air mixture has still to be extracted by a vacuum pump. The steam partial pressure of a saturated mixture with 30°Cispy = 42.4 mbar (= saturated steam pressure at 30 C). The partial pressure of the inert gas is then the difference between the total pressure and the 

the saturation quantity of steam is calculated with Equation 2.1  

---

Condensation with Inert Gases 17 Figure 2.2 Container with weightless piston. 

A three-necked 250-mL flask with magnetic stirrer, reflux condenser (with inert-gas bypass and bubbler), and dropping funnel is charged with a solution of bis(l,5-cyclooctanediylboryl)monoselenide (22.39 g, 69.8 mmol) in pentane... 

In a 250-mL flask (with magnetic stirrer, inside thermometer tube, and reflux condenser with inert-gas bypass and bubbler) a stirred mixture of bis(l,5-cyclooctanediylboryl)monoselenide (BSeB) (10.65 g, 33.2 mmol) and black selenium powder (2.62 g, 33.2 mmol) in mesitylene (120 mL) is heated 2 h at... 

Figure 2.14 Temperature profile in a condenser with inert gas.

Figure 3.11. Condenser pressure control with inert gas.

At — 20°C, the reflux condenser and the dropping funnel are replaced under a countercurrent inert gas flow with a stopper and a sintered glass funnel (250 mL, medium porosity), which is connected to a 1-L round-bottomed flask. The funnel and flask each bear a lateral stopcock (see Fig. 1) and have previously been evacuated and filled with inert gas five times. The filtration as well as the washings (3 x 15-mL portions of cold monoglyme) are carried out at — 78 °C under reduced pressure and as rapidly as possible. Both flasks at the ends of the frit are replaced with socket caps under inert gas flow via the stopcocks of the frit (corresponding to HI and H2 in Fig. 1). The frit is evacuated at room temperature for S min and refilled with inert gas three times. This drying operation is interrupted as soon as the slightest reddish color of the substance becomes visible. Yield 8.4 g (75%). 

Fullarton and Schlunder (1983) investigated the process of diffusional distillation for separating liquid mixtures of azeotropic composition. The process is shown schematically in Figure 8.8. A liquid mixture is evaporated at a temperature below its boiling point, diffuses through a vapor space filled with inert gas and condenses at a lower temperature. The inert gas functions as a selective filter that allows preferential passage of those components that diffuse more quickly. Thus, the condensed liquid has a composition different from that of the original mixture. 

Regeneration can be carried out with hot inert gas, but steam is usually preferred if the solvent is not miscible with water. Steam condenses in the bed, raising the temperature of the solid and providing the energy for desorption. The solvent is condensed, separated from the water, and perhaps dried before reuse. The bed may then be cooled and dried with inert gas, but is is not necessary to lower the entire bed to ambient temperature. If some water vapor can be tolerated... 

To prepare tetraethyldiboroxane from diethylhydroxyborane using triethylborane, a 1-L three-necked flask is equipped with a magnetic stirrer, thermometer, 250-mL dropping funnel, and reflux condenser. The temperature of the reflux-condenser coolant should be 3-5°. Evaporation losses of ethylboranes are avoided under these conditions. The apparatus is evacuated (10 3 torr), filled with inert gas, then charged with 232 g (2.37 mole) triethylborane. 

A 1 -L two-necked flask is equipped with magnetic stirrer, thermometer, a 100-mL dropping funnel, and a reflux condenser which is connected to a gas clock. The apparatus is evacuated (10-3 torr) and then filled with inert gas (argon or nitrogen). Water-free methanol, 64.8 g (2.02 mole), is added dropwise at 10-15° in 5.5 hr to a stirred mixture of 196.1 g (2.0 mole) triethylborane and 0.4 g 2,2-dimethylpropanoic acid.t Approximately 43 L ethane (STP) is evolved. After stirring for a further 5 hr at room temperature (cooling to 20°) a total of 48,4 L (99%) ethane has been evolved. The product mixture is fractionated (15-cm column) at atmospheric pressure to give 3.6 g forerun (bp = 54-83°) and 186.1 g (93%) pure product with bp = 88-89°. 

Tetrahydrofuran is dried by refluxing over Na/K and finally distilling from sodium tetraethylaluminate. The apparatus consists of a 500-mL three-necked flask equipped with an internal thermometer, a magnetic stirrer, and a reflux condenser capped with an inert gas (pure N2, argon) bypass. The apparatus is evacuated and then filled with inert gas. 

A 1-L apparatus consisting of a three-necked flask with a magnetic stirrer is fitted with a jacket for an inside thermometer and a reflux condenser capped with a bypass for inert gas and a bubbler, connected with a gasometer (for measuring the amount of the evolved gas). The whole apparatus is evacuated, then filled with inert gas (Ar, N2) and charged with oxygen-free, dry mesitylene (about 300 mL), elemental sulfur (6.78 g, 212 mmol), and (9H-9-BBN)2 t (52.5 g, 212 mmol). 

Equipment for hydride reactions must be scrupulously dry before use. This includes valve bonnets, outlets to gages, vent lines, and traps. The atmosphere should contain less than 1% oxygen by analysis. Purging with inert gas (carbon dioxide is not inert ) is excellent. The hydride is added through an entrance lock for bags or by a hopper whose connecting valve and pipe can be purged. Reactors should be heated or cooled with oil or Dowtherm, even for condensers. 

A solution of 21 g of SDS in 700 mL of deoxygenated water was prepared. N-4-Butylphenylacrylamide (0.444 g) was dissolved in this solution followed by 20.6 g of acrylamide. The resulting solution was carefully transferred to a 1-L Morton-style resin kettle fitted with a chilled water condenser, thermometer, inert gas sparger, and mechanical stirrer. The temperature was adjusted to 50 °C and polymerization was initiated by the addition of 1.47 mg of K2S2O8. After stirring for 1.5 h at 50 2 C, a 100-mL portion of the viscous solution was poured slowly into 3 L of methanol. The precipitated polymer was then masticated in with methanol in a blender (Waring), filtered, and dried under vacuum at 30 °C. The yield of polymer was 0.86 g (28.7%). After 16 h, the solution was diluted with 600 mL of distilled water and a 200-mL ahquot was removed. The polymer was isolated to yield 2.94 g (98.0%). 

Although the tank in ballast voyage is filled with inert gas saturated with water vapor, the water vapor on condensation absorbs oxides of sulfur, carbon, and nitrogen to form various acids that attack the steel. 

The temperature differences AT at each point in the condenser are smaller than for the condensation of inert gas free pure vapour. Particularly at the end of the condenser (after the main amount of condensation, heat is dissipated), the condensation temperature drops to very low values. It can easily be seen that in these cases, it is very important to run the coolant in counterflow to the condensing vapour. Sometimes, such condensers are constructed with a special under-cooling section where the remaining inert gas-vapour mixture is forced to flow to the coldest place of the condenser. Installations of the most diverse forms are made, in order to achieve this purpose. However, in such installations, dead corners can form when the flow is not directed properly. There the inert gas collects and blocks the vapour away from the heat exchange surface, so that parts of the surface remain unused. 

Russian scientists have extensively investigated the carbon detonation products from explosives, as described in references 56 thru 60. They exploded mixtures of TNT and RDX in explosive chambers with inert gas. They collected the solid products, which were 8 to 9 percent of the initial mass of the explosive. They have been able to obtain up to 80% of the solid product as diamond powder with an average particle diameter of 4 nanometers. Larger diamond particles were obtained which are made up of Svelded 4 nanometer particles. From electrical conductivity measurements they found that the carbon production was completed in 0.2 to 0.5 microseconds . They studied the formation of carbon using isotopic carbon methods and found that the condensed carbon isotopic ratio was the same as in the initial explosive. They report producing about a ton of industrial diamonds a year from explosives. 

Also identified in Figure 1.3 are utility streams. Utilities are needed services that are available at the plant. Chemical plants are provided with a range of central utilities that include electricity, conpressed air, cooling water, refrigerated water, steam, condensate return, inert gas for blanketing, chemical sewer, waste water treatment, and flares. A list of the common services is given in Table 1.3. which also provides a guide for the identification of process streams. 

---