Condensation directed

Miblimation The volatilization of a solid substance into the vapour phase without passing through the liquid phase. Also used to describe the process of purification in which the vapour is condensed directly from the vapour phase to a solid (on a cold-finger often cooled by refrigerant). In the latter case this substance may melt during the initial vaporization. Used for purification. 

It is clear that if the vapour at a pressure below the triple point is reduced sufficiently in temperature, it will condense directly to the solid form, or, sublimation will ensue. In order that a solid may pass directly... 

Benzal derivatives. Primary aromatic amines generally condense directly with benzaldehyde to form benzal derivatives (Schiff s bases or anils) ... 

Recovery system SheU-and-tiibe condenser Shell-and-tiibe condenser Direct-contact condenser Shell-and-tiibe condenser... 

The experimental conditions for the syntheses starting from acid chlorides of hydroxamic acids and from nitrile oxides are somewhat different. In the former case the other component of the reaction is organometallic, usually an organomagnesium derivative of an acetylene or, less frequently, a sodium enolate of a /8-diketone. Nitrile oxides condense directly with unsaturated compounds. 

Latentiation of ampicillin can also be achieved by tying up the proximate amino and amide functions as an acetone aminal. Inclusion of acetone in the reaction mixture allows 6-APA to be condensed directly with the acid chloride from 24. There is thus obtained directly the prodrug hetacillin (34). Although this compound has little antibiotic activity in its own right, it hydrolyzes to ampicillin in the body. The p-hydroxy derivative amoxycillin (35) shows somewhat better oral activity. A similar sequence using formaldehyde gives metampicillin (36). °... 

One of the drawbacks of thermal cracking in an FCC is that a high percentage of the olefins formed during intermediate reactions polymerize and condense directly to coke. 

On a single-evaporator flooded system, a float valve can be fitted which will pass any drained liquid from the condenser direct to the evaporator. The action is the same as that of a steam trap. The float chamber is at condenser pressure and the control is termed a high-pressure float (Figure 8.3). 

N2 and CO2 have triple points that are well below room temperature. Although both are gases at room temperature and pressure, they behave differently when cooled at P = 1 atm. Molecular nitrogen liquefies at 77.4 K and then solidifies at 63.3 K, whereas carbon dioxide condenses directly to the solid phase at 195 K. This difference in behavior arises because the triple point of CO2, unlike the triple points of H2 O and N2, occurs at a pressure greater than one atmosphere. The phase diagram of CO2 shows that at a pressure of one atmosphere, there is no temperature at which the liquid phase is stable. 

This section covers the design of shell and tube exchangers used as condensers. Direct contact condensers are discussed in Section 12.13. 

If the degree of superheat is large, it will be necessary to divide the temperature profile into sections and determine the mean temperature difference and heat-transfer coefficient separately for each section. If the tube wall temperature is below the dew point of the vapour, liquid will condense directly from the vapour on to the tubes. In these circumstances it has been found that the heat-transfer coefficient in the superheating section is close to the value for condensation and can be taken as the same. So, where the amount of superheating is not too excessive, say less than 25 per cent of the latent heat load, and the outlet coolant temperature is well below the vapour dew point, the sensible heat load for desuperheating can be lumped with the latent heat load. The total heat-transfer area required can then be calculated using a mean temperature difference based on the saturation temperature (not the superheat temperature) and the estimated condensate film heat-transfer coefficient. 

Dining the reduction of iridium hexafluoride, osmium hexafluoride or rhenium hexafluoride with silicon to the pentafluorides, the hexafluorides must not be condensed directly onto undiluted silicon powder, or explosions may result [1]. The same is true for molybdenum hexafluoride and uranium hexafluoride [2],... 

Fig. 11. Sugar aldehydes condensed directly on pyrrole derivatives by Lindsey s chemistry.

Volatile substances of which the vapours, on cooling, condense directly to crystals without passing through the liquid phase are sometimes advantageously purified by sublimation, particularly when solubility relations render recrystallisation difficult. The purification of iodine is a well-known case in point. In organic chemistry this process is particularly suitable for quinones. 

Caution. Metal hexafluorides should not be condensed directly onto dry silicon powder. Explosions can occur. 

The temperatures of appearance of various solid phases as a cooling solar gas condenses are illustrated in Figure 7.1. This particular condensation calculation was performed at a pressure of 10 4 atm (thought to be appropriate for parts of the nebula). It is important to note that not every mineral in the sequence actually condenses directly from the vapor. Instead, some minerals form by reaction of previously condensed solids with the vapor. For example, FeS forms by reaction of already condensed Fe metal with sulfur in the gas phase, and olivine first condenses as the magnesium end member forsterite and then becomes progressively more iron-rich by reaction with vapor as temperature decreases. 

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