Volatile compound enrichment from water

In the case of pervaporation of dissolved volatile organic compounds (VOCs) from water, the magnitude of the concentration polarization effect is a function of the enrichment factor. The selectivity of pervaporation membranes to different VOCs varies widely, so the intrinsic enrichment and the magnitude of concentration polarization effects depend strongly on the solute. Table 4.2 shows experimentally measured enrichment values for a series of dilute VOC solutions treated with silicone rubber membranes in spiral-wound modules [15], When these values are superimposed on the Wijmans plot as shown in Figure 4.12, the concentration polarization modulus varies from 1.0, that is, no concentration polarization, for isopropanol, to 0.1 for trichloroethane, which has an enrichment of 5700. 

The purge-and-trap method (see Section 6.4) is a common method to enrich volatile organic compounds from water samples. In your apparatus, you purge a 1 L water sample with a gas (air) volume flow of 1.5 L gas per minute at a temperature of 25°C. The compounds that you are interested in include tetrachloroethene, chlorobenzene and methyl-t-butylether (MTBE). Calculate the time required to purge 90% of each compound from the water. Any comments How much time would you save if you would increase the temperature from 25°C to 35°C What could be a problem when raising the temperature too much You can find all necessary data in Appendix C and in Table 6.3. 

Volatile Compounds in Thalli Culture. A large mass of clean thalli culture, regenerated from protoplasts of U. pertusa, was obtained by cultivation in Provasoli s enriched sea water containing antibiotics (56). The essential oil was prepared from the thalli culture by a simultaneous distillation extraction (SDE) procedure (57). The yield of the essential oil was 8.0 X 10-3% (cf. 4.2 X 10-3% for the field fronds). Twenty-three of the volatile compounds in the oil were identified by GC and GC-MS (Table IV). The major characteristic compounds were long-chain fatty aldehydes as in the oil from the field fronds mainly -pentadecanal, (Z, Z, Z)-7,10,12-hexadecatrienal, (Z)-8-heptadecenal, (Z, Z)-8, 11-heptadecadienal, and (Z, Z, Z)-8, 11, 14-heptadecatrienal. They accounted for ca 40% of the oil and were considered to have the... 

Beiner et al. tested the collecting capacity of several metal compounds for some volatile sulfur substances. They noted high enrichment rates and good selectivity for silver sulfide. It was used in combination with membrane extraction, thermodesorption, and GC-MS to analyze sulfides, thiols, and tetrahydrothiophene from water samples. Detection limits down to the lower ng/1 range were achieved. The disadvantages of the method are the experimental equipment, the long analysis times, and displacement reactions between the matrix and analytes on the sorbent s surface. 

Fluorine compounds from fluorite (fluorspar, CaF2) are used in water treatment (to suppress dental caries) and to make fluoropolymers (such as Teflon), lubricants, and refrigerants. Molten cryolite (Na3AlF6) is essential as a solvent for Al203 in the electrolytic production of aluminum metal, while the isotopic enrichment of uranium for nuclear power reactors is usually achieved by diffusion or gas centrifugation of volatile UF6. 

As reviewed above, enzymatic decarboxylation plays an important role in organic syntheses, especially in the synthesis of enantiomerically enriched compounds. The choice of enzymes and/or microorganisms strongly depends on (1) the nature of the substrate, in terms of solubility in water and/or organic solvent, and volatility (2) the ease of purification of the products from byproducts, unreacted starting materials, and reagents and (3) the accessibility of precursors as well as that of the enzymes and microorganisms required. 

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