Costs hydrocarbon separation methods

Supercritical fluid extraction (SFE) is a suitable process for many separation problems. The regeneration of the supercritical fluid is as important as the extraction step itself Therefore this paper presents a method to do this in a more isobaric way than the customary pressure reduction regeneration. For the example of soil remediation we have investigated the activated carbon regeneration of supercritical carbon dioxide loaded with the low-volatile polycyclic aromatic hydrocarbon (PAH) pyrene. Characteristics of supercritical fluid extraction for soil remediation are elevated temperatures and pressures up to 370 K and 300 bar. For this reason adsorption isotherms of pyrene on activated carbon up to these conditions are measured first. Subsequently this method is used to regenerate carbon dioxide in a closed solvent cycle plant with a 4 1 extractor. An economic analysis using these results indicate that the soil remediation costs will decrease for about 20 - 30 % by means of an activated carbon adsorber. 

A mixture of hydrocarbons such as petroleum does not boil at a single, sharply defined temperature. Instead, as such a mixture is heated, the compounds with lower boiling points (the most volatile) boil off first, and as the temperature increases, more and more of the material vaporizes. The existence of a boiling-point range permits components of a mixture to be separated by distillation (see discussion in Section 11.6). The earliest petroleum distillation was a simple batch process The crude oil was heated in a still, the volatile fractions were removed at the top and condensed to gasoline, and the still was cleaned for another batch. Modern petroleum refineries use much more sophisticated and efficient distillation methods, in which crude oil is added continuously and fractions of different volatility are tapped off at various points up and down the distillation column (Fig. 7.5). To save on energy costs, heat exchangers capture the heat liberated from condensation of the liquid products. 

An efficient method of reclaiming vulcanized scrap was developed about 1900, involving digestion of the scrap with NaOH plus a hydrocarbon softener. This separated the cotton insertions from the rubber and partially reversed the effect of vulcanization. Use of reclaim has long been an important adjunct to the industry, especially for low-cost, high-volume products. 

For many years, one of the most common methods for performing analytical separations on complex environmental, pharmaceutical, food, and petroleum samples was based on extraction of bulk samples with hydrocarbon or chlorinated organic solvents using a Soxhiet extractor. Unfortunately, liquid extractions frequently fail to meet several of the ideal criteria listed in the previous paragraph. They usually require several hours or more to achieve satisfactory recoveries of analytes, and sometimes never do. The solvent costs are often high. The solution of the recovered analyte is often so dilute that a concentration step must follow the extraction. Analyte degradation-or loss as well as atmospheric pollution may accom )any this concentration step. 

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