Glycols solvent desorption

Glycol ether and glycol ether acetate vapours in air Lab method using charcoal adsorbent tubes, solvent desorption and gas chromatography 21... 

Different techniques using sampling on appropriate adsorption media followed by solvent desorption or thermodesorption and GC-analysis are suitable for the quantitative determination of glycols in indoor air. 

Waste-Gas Purification by Scrubbing with Glycol Ethers [35]. In the pharmaceutical industry, certain waste-gas streams are purified by scrubbing with glycol ethers. The solvent mixture produced on desorption contains ca. 16 components that are impossible to separate. 

The elution of the organic compounds collected involves extraction by a solvent (displacement) or thermal desorption. Pentane, CS2 and benzyl alcohol are generally used as extraction solvents. CS2 is very suitable for activated charcoal, but cannot be used with polymeric materials, such as Tenax or Amberlite XAD, because decomposition occurs. As a result of displacement with solvents, the sample is extensively diluted, which can lead to problems with the detection limits on mass spectrometric detection. With solvents additional contamination can occur. The extracts are usually applied as solutions. The readily automated static headspace technique can also be used for sample injection. This procedure has also proved to be effective for desorption using polar solvents, such as benzyl alcohol or ethylene glycol monophenyl ether (1% solution in water, Krebs, 1991). 

Since the equilibrium constant is a function of temperature, absorber and stripper desigas must take into account temperature changes that occur as a result of absoqition (or desorption) of components. Zawacki et al. (1981) report using heats of absorption values of 150, 180, and 1,000 Btu/lb for CO2, H2S, and H2O, respectively, for calculating the temperature rise due to absorption in two different solvents (N-formyl morpholine and the dimethyl ether of tetraeth-ylene glycol). They also assumed tray efficiencies of 15 to 20% for absorption in these solvents, and estimated that 50 to 60 actual trays would represent practical column heights. 

The use of physical absorption to remove V(X)s from exhaust air streams has found limited application. In Germany, where the limits for solvents in air were reduced to 20 mg/m as of Jan. 1, 1989, one plant has been built to absorb 10-200 g/m dichloromethane from a 30 m /h air stream at ambient temperature using tetraethylene glycol dimethyl ether as the absorbent. Absorption is accomplished in a countercurrent spray column. Desorption occurs in an electrically heated column at 100°-130°C and 80-100 millibar pressure. The operation requires 11 kW power and 5 m /h cooling water (Anon., 1989). 

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