Cold condensation

An interesting and novel use of a soHd desiccant, the reduction of cold condensate corrosion in automotive exhaust systems, illustrates a hybrid closed—open system. Internal corrosion occurs in mufflers when the water vapor in the exhaust condenses after the engine is turned off and the muffler cools. Carbon dioxide dissolves in the condensate to form an acidic soup. In an essentially closed static drying step, an acid- and heat-resistant desiccant located in the muffler adsorbs water vapor from the exhaust gas as it cools to prevent formation of corrosive acidic condensate. When the engine is restarted, the system becomes open, and the desiccant is regenerated by the hot exhaust gas to be ready for the next cooldown step (19). 

Wania F, Mackay D (1993) Global fractionation and cold condensation of low volatility organochlorine compounds in polar regions. Ambio 22 10-18 Wania F, Mackay D (1995) A global distribution model for perstitent organic chemicals. The Science of the Total Environment 160/161 211-232... 

Cold condensate Cold condensate (organic) (inorganic)... 

The separate stepwise condensation of the products from Fe-LTFT and Fe-HTFT synthesis produces streams of different carbon number distributions that serve as feeds to the oil refinery (Figure 18.4).30 It is consequently not necessary to employ an atmospheric distillation unit as the first step in the refinery. The stepwise condensation products from Fe-LTFT are reactor wax (liquid at LTFT conditions), hot condensate (>100°C), cold condensate (produced by condensation with the aqueous product and then phase separated), and tail gas (typically C4 and lighter). The stepwise condensation products from Fe-HTFT are decanted oil (liquid at 145°C 1.6 MPa), light oil (produced by condensation with the aqueous product and then phase separated), and tail gas. 

On the day of the incident, a pump that supplied hot lean oil to a large heat exchanger on the absorber column tripped. A chart recorder that should have indicated the upset was out of ink. The temperature in the exchanger dropped because of cold condensate flowing through the tubes. After several hours, two supervisors discovered the problem and restored hot lean oil flow to the exchanger to warm it up. This act was car-... 

An obvious correlation between polar and alpine environments is the decrease in temperature with increasing latitude or elevation. This temperature change leads to a shift in environmental phase distribution equilibria - i.e. a chemical moves from the atmosphere to terrestrial surfaces, including direct deposition to surface waters, but also to snowpack and soils from which movement into surface and groundwater is possible. This process has been termed cold condensation but should more correctly be called cold-trapping because the contaminants are not actually condensing. 

The tower overhead vapor, shown in Fig. 13.6, condenses to a liquid on the outside of the cold condenser tubes. The liquid drips off the tubes. These droplets of liquid are in close contact with the saturated vapor in the condenser shell. This means that the liquid is in equilibrium with the vapor. The condensed liquid is therefore, initially, at its bubble-point temperature. This liquid accumulates in the bottom of the condenser s shell. The submerged tubes then must subcool this liquid. Part of the surface area of the condenser is hence devoted to subcooling liquid, and part is devoted to condensing vapor. 

Fig. 2. Heat-input methods Tor freeze-drying processes la) conduction, tb) radiation, (cl microwave. CC = cold condenser RHS = radiam-heat device...

The correct inlet temperature for the deaerator is obtained by mixing the hot condensate downstream of the preheater with cold condensate. This inlet temperature is maintained by a temperature controller around the preheater, which detects the mixed condensate s inlet temperature to the deaerator and is set at a little lower (15°F [8°C]) than the boiling temperature. 

The two water concentrations (temperate and Arctic) are similar, even though the air concentration in the Arctic is an order of magnitude less than temperate air. This temperature driven phenomenon that favours chemical partitioning to surfaces is commonly known as the cold condensation effect and has resulted in the worrying rise in persistent organic pollutants in the polar environments. 

The reaction of atomic carbon with A -methylpyrrole 1020 at 77 K generates the A -methyl-3-dehydropyridinium ylide 1021, novel reactive intermediate (Scheme 198), which can be trapped with added hydrogen halides or carbon dioxide <1997JA5091>. The intermediacy of ylide 1021 in the 77 K cocondensation of arc generated carbon with pyrrole 1020 is implied by the fact that addition of methanolic HCl to the cold condensate generates the A -methylpyridinium ion 1023. 

The carbonyl compound, an alcohol, and an acid are dissolved in benzene. As the mixture is heated, the carbonyl compound is converted to the acetal with water as a by-product. Benzene and water co-distill from the reaction mixture. When the hot vapors reach the cold condenser, they condense, forming a liquid that then collects in the glass tube below. Water, the more dense liquid, forms the lower layer, so that as it collects, it can be drained through the stopcock into a flask. In this way, water can be removed from a reaction mixture, driving the equilibrium. 

Indeed, Dachs et al. (2002) demonstrated, using a combination of field measurements of atmospheric PCBs, PCDDs, and PCDFs, and remote sensing data of ocean temperatirre, wind speed and chlorophyll, that deposition in mid-high latitudes is driven by sinking marine particulate matter, rather than by cold condensation. However, the relative contribution of this process is highly dependent on the physical chemical properties of the POPs under consideration. 

As demonstrated in the first experiment, sublimation can occur readily at atmospheric pressure. For substances with lower vapor pressures vacuum sublimation is used. At very low pressure the sublimation becomes very similar to molecular distillation, where the molecule leaves the warm solid and passes unobstructed to a cold condensing surface and condenses in the form of a solid. 

Because of the relatively high melting point of the solvent (23-26°C), it is not advisable to put the condenser directly on the flask. With the addition funnel between the flask and the condenser, most of the tert-butyl alcohol is condensed as a liquid and does not collect as a solid on the cold condenser. 

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