Aromatic hydrocarbons from water separation

Leoni [366] observed that in the extraction preconcentration of organochlo-rine insecticides and PCB s from surface and coastal waters in the presence of other pollutants such as oil, surface active substances, etc., the results obtained with an absorption column of Tenax-Celite are equivalent to those obtained with the continuous liquid-liquid extraction technique. For non-saline waters that contain solids in suspension that absorb pesticides, it may be necessary to filter the water before extraction with Tenax and then to extract the suspended solids separately. Analyses of river and estuarine sea waters, filtered before extraction, showed the effectiveness of Tenax, and the extracts obtained for pesticide analysis prove to be much less contaminated by interfering substances than corresponding extracts obtained by the liquid-liquid technique. Leoni et al. [365] showed that for the extraction of organic micro pollutants such as pesticides and aromatic polycyclic hydrocarbons from waters, the recoveries of these substances from unpolluted waters (mineral and potable waters) when added at the level of 1 xg/l averaged 90%. 

The theory and development of a solvent-extraction scheme for polynuclear aromatic hydrocarbons (PAHs) is described. The use of y-cyclodextrin (CDx) as an aqueous phase modifier makes this scheme unique since it allows for the extraction of PAHs from ether to the aqueous phase. Generally, the extraction of PAHS into water is not feasible due to the low solubility of these compounds in aqueous media. Water-soluble cyclodextrins, which act as hosts in the formation of inclusion complexes, promote this type of extraction by partitioning PAHs into the aqueous phase through the formation of complexes. The stereoselective nature of CDx inclusion-complex formation enhances the separation of different sized PAH molecules present in a mixture. For example, perylene is extracted into the aqueous phase from an organic phase anthracene-perylene mixture in the presence of CDx modifier. Extraction results for a variety of PAHs are presented, and the potential of this method for separation of more complex mixtures is discussed. 

Another variation of the preceding method is to apply HPLC to fractionate the cleaned-up aliphatic-aromatic fraction from flash colurim separation of soluble organic matter as it is performed in the Chevron laboratory, for example, as described in Reference 2. A Waters HPLC system equipped with a preparative Whatman Partisil 10 silica column (9.4 X 500 mm), a HPLC pump, and two detectors for separation monitoring (a UV and refractive index detector) are used, giving three fractions of aliphatic hydrocarbons, mono-, di-, and triaromatics and polar compounds. The hrst two fractions are eluted with hexane, whereas polar compounds are eluted with... 

Drizo A variation of the glycol process for removing water vapor from natural gas, in which the water is removed from the glycol by stripping with a hydrocarbon solvent, typically a mixture of pentanes and heavier aliphatic hydrocarbons. The process also removes aromatic hydrocarbons. Last traces of water are removed from the triethylene glycol by stripping with toluene in a separate, closed loop. Invented in 1966 by J. C. Arnold, R. L. Pearce, and H. G. Scholten at the Dow Chemical Company. Twenty units were operating in 1990. U.S. Patent 3,349,544. 

Batch Stirred Tank H2S04/Oleum Aromatic Sulfonation Processes. Low molecular weight aromatic hydrocarbons, such as benzene, toluene, xylene, and cumene, are sulfonated using molar quantities of 98—100% H2S04 in stirred glass-lined reactors. A condenser and Dean-Stark-type separator trap are installed on the reactor to provide for the azeotropic distillation and condensation of aromatic and water from the reaction, for removal of water and for recycling aromatic. Sulfone by-product is removed from the neutralized sulfonate by extraction/washing with aromatic which is recycled. 

From 50 to 100 c.c. of the distilled alcohol are diluted with water to make it of about 25% strength, the liquid being then treated with a little dilute sulphuric acid and carefully distilled through a small dry condenser. The first two or three drops of distillate are dropped on to 5 c.c. of carbon disulphide in a small separating funnel and the liquid shaken with 4-5 c.c. of 10% sodium carbonate solution. The two layers are allowed to separate and the lower one, consisting of carbon disulphide with aromatic hydrocarbons in solution, washed in a second separator with a few c.c. of water and then transferred, free from drops of water, to a small conical flask. 

FIGURE 4-4. Two approaches to the separation of polynuclear aromatics, (a) Reverse-phase separation of isomeric 4-ring polynuclear aromatics using a gradient of 70/30 (v/v) to 100/0 (v/v) acetonitrile/water as shown beneath the chromatogram. Column C,g detection at 254 nm. (b) Normal-phase separation of aromatic hydrocarbons. Column /uPorasil (silica, 10 /urn) 3.9 mm ID x 30 cm (2 columns) mobile phase hexane flow rate 8 mL/min. (Fig. 4-4b reproduced from reference 1 with permission.)... 

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