Solvent vapour drying

This experiment requires less time than the former, for the paper strip comes into equilibrium with the solvent vapour much more rapidly, and can then be inserted into the solvent without intermediate drying. 

During stoving in convection-type box ovens, drying can be delayed (as it can on air drying when the ventilation is insufficient, e.g. in a ship s hold) if the vents are closed too far, or if the coated articles are too closely packed. In the latter case there may even be trouble caused by solvent wash, i.e. redissolution of the uncured film by stagnant solvent vapours, which occurs mostly on surfaces near the top of the oven. This can lead to the establishment of practically unprotected areas. 

After the samples have been applied and dried, the plate is placed in a tank that contains the solvent (0.5-1 cm deep). It is particularly important when using volatile solvents that the atmosphere of the tank is saturated with solvent vapour. This prevents both evaporation from the surface of the plate and alteration to the composition of the solvent due to the loss of volatile components. 

Figure 16.32. Flowsheet for drying polypropylene by fluidising with a hot stream of solvent vapour— ...

Dry-cleaning machines are usually provided with a centrifugal pump to force the liquid through a filter, and with a blower to move and filter the solvent vapour phase also. After the cleaning cycle, the solvent is drained from the cleaning chamber and may be reused, provided that the level of dissolved contaminants is not approaching saturation, otherwise it is regenerated by distillation or cleaned by mechanical filtration. 

For instance, aromatic solvent vapours were determined with polyurethane MIPs combined with SAW transducers [124]. That is, first, the hydrophilic quartz surface of SAW was hydrophobized with NW-dimethylaminotrimethylsilane. Then a solution for polymerization was prepared by mixing functional monomers, such as 4,4 -dihydroxydiphenyldimethylmethane, 4,4 -diisocyanatodiphenylmethane and 30% 2,4,4 -triisocyanatodiphenylmethane, with the 1,3,5-trihydroxybenzene crosslinker in the ethyl acetate or ethanol template used also as the solvent for polymerization. Subsequently, the hydrophobized resonator surface was spin-coated with an aliquot of this solution. Finally, the free-radical polymerization has been initiated thermally to form a polyurethane MIP film. The desired vapour concentration and relative humidity of the analyte were achieved by mixing dry air and saturated steam with solvent vapours generated with thermoregulated bubblers. 

However, the most frequently used system is trace enrichment in a short LC column or SPE precolumn. The column is usually filled with C18 or PLRP-S and dried with nitrogen prior to elution. The analytes are eluted with an organic solvent, usually ethyl acetate, which is injected into the gas chromatograph through an on-column interface by a retention gap. In the chromatograph there is also a retaining precolumn, to minimize losses of the most volatile compounds, an analytical column and, between the precolumn and the analytical column, a solvent vapour exit (SVE) to eliminate the vapour (Figure 13.18). 

The toluene solution of the product of hydrolytic condensation with pH of the nonaqueous solution not lower than 5 and the nonvolatile content of 40 3% is sent for completion into collector 14 the toluene solution of the product of hydrolytic condensation with pH of the nonaqueous solution lower than 5 and the nonvolatile content of less than 37% is sent into tank 15 for additional flushing and partial distillation of the solvent. The additional flushing in the tank is carried out with the solution of sodium chloride (like the second flushing) then the contents of the tank are heated to 40-60 °C and held for 2-10 hours. The bottom layer, the settling products, is poured off and collected in collector 16. Then a vacuum is created in the tank (the residual pressure is 0.05-0.07 MPa) and the solvent is partially distilled (until the nonvolatile content is 40+3%). The distilled solvent vapours are condensed in cooler 17 and collected in collector 18. If the moisture content is above 1.5%, the solvent is sent into collector 16 for subsequent additional drying. The toluene solution of polymethylsilsesquioxane is poured from receptacle 14 or tank 15 into balancing tank 19, where several batches of varnish are mixed and balanced. The finished varnish is analysed to determine the nonvolatile content, pH of the nonaqueous solution, viscosity and gelatinisation time. 

For many routine reactions involving Grignard reagents in diethyl ether, the solvent vapour forms a protective blanket over the solution (cf. Ref. [5]), and drying tubes are adequate to exclude moisture. Nevertheless, the use of closed systems with inert atmospheres is recommended even for preparative work, and for physicochemical studies, where traces of alkoxides may have significant effects, it may be necessary to employ vacuum line techniques, rigorously purified atmospheres in glove boxes, and the like. The cheapest form of inert atmosphere is white spot ... 

Selenium and tellurium The elements are present as selenite and tellurite in dilute nitric acid solution. The mixture is spotted upon paper and dried thoroughly in the air. The solvent is dry n-butyl alcohol containing 4 per cent (v/v) of dry methanol. The atmosphere in the separation vessel is saturated with respect to the solvent vapour and the relative humidity is also maintained at 50 per cent by means of a saturated solution of calcium nitrate. The solvent is allowed to diffuse 8-10 cm down the strip (c. 2 hours). After evaporation of the solvent, the strip is sprayed with 0 5m tin(II) chloride in dilute hydrochloric acid. The tellurium is indicated by a black band (RF 0 1) and the selenium as an orange band (RF 0 5). It is possible to detect 1-5 pg of Se in the presence of 1 mg of Te by this method (see also Fig. VI.5g). 

The development tank for plates of (2 cm x 5 cm) a clean, dry beaker (100 mL) covered with a watch-glass is ideal. The eluting solvent should be about 3 mm deep and filter paper should be placed in the tank to saturate the tank atmosphere with solvent vapour (Fig. 32.11). 

To calibrate the instrument requires only that a known amount of each alkane be introduced into the instrument. For alkane numbers above 14 (and explosive compounds) this is best done by the three step process depicted in Figure 5. A glass tube is attached to the inlet and a known amount of alkanes dissolved in methanol are injected. A short drying (step 2) removes the volatile solvent vapours but leaves the semi-volatile alkanes (or explosives) attached to the walls of the tube. The final step is to heat the tube to vapourize the semi-volatiles and then collect them in the preconcentrator trap of the zNose . 

According to Viguid and Spitz [75], both a chemical and a physical factor determine whether or not a spray process can be classified as chemical vapour deposition. Processes that may occur with increasing temperature arc shown schematically [75] in Fig. 16. In process A the droplets reach the substrate, the solvent vapourizes and leaves a dry deposit which will react and form a film. 

Solvent drying by adsorption cannot be made into a continuous process easily and is usually a single bed batch process or a twin bed with one bed on stream while the other is being regenerated. Since the solvent wets the adsorbent a considerable amount of solvent vapour is generated while the water is desorbed and the effluent air or gas needs to be passed through an AC (or similar) bed. 

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