Benzene extraction, petroleum recovery

Toluene (300 mL) was added to (i-PrO)2TiCl2 (1.40 g. 5.9 mmol), the chiral diol (above equation, 3.12 g, 5.9 mmol) and 4 A molecular sieves (powder, 3.0 g) at 0 C and the mixture stirred for 30 min. The acrylamide 43 (R = Me 10.0 g, 71 mmol) in petroleum ether (200 mL) was added. Subsequently, a petroleum ether soln (100 mL) of ketene dimethyl thioacetal (44 10.0 g, 83 mmol) was added and the mixture stirred at 0 C for 1 h. The reaction was quenched by adding pi I 7 phosphate buffer and inorganic materials removed by filtration. The organic materials were extracted with EtOAc and the extracts washed with brine and dried (Na,S04). After evaporation of the solvent, the crude product was purified by eolumn chromatography yield 14.8 g (80%). Optically pure 45 was obtained by two recrystallizations from benzene/hexane (80% recovery) mp 90.5 92.0 C. 

Most papers dealing with phenolic acid HPLC analysis in herbs describe only simple liquid extraction without the hydrolysis step. Acetone, methanol, or alcoholic-water or acetone-water mixtures are applied. Very rarely, pure water is used as the extraction solvent. " It was found that the extraction recoveries for water extracts are often lower in comparison to alcoholic-water mixtures, especially when the simultaneous separation of polar and less polar phenolic acids has been performed. Sometimes, the control of pH can improve the recovery. If necessary, n-hexane, chloroform, diethyl ether, benzene-acetone, petroleum ether, or other less polar solvents are recommended for removing interfering compounds. The extraction is usually performed by refluxing the samples for a specific time in a Soxhlet apparatus, with simple mechanical or magnetic stirring of the sample with the extraction solvent, or by plant sample maceration. The application of an ultrasonic bath for the liquid extraction has also become popular in recent years. The hydrolysis steps have also been recommended for medicinal species preparation, especially when other phenolic compounds are also analyzed simultaneously with phenolic acids in herbs. 

The inflammable solvents most frequently used for reaction media, extraction or recrystallisation are diethyl ether, petroleum ether (b.p. 40-60° and higher ranges), carbon disulphide, acetone, methyl and ethyl alcohols, di-Mo-propyl ether, benzene, and toluene. Special precautions must be taken in handling these (and other equivalent) solvents if the danger of Are is to be more or less completely eliminated. It is advisable to have, if possible, a special bench in the laboratory devoted entirely to the recovery or distillation of these solvents no flames are permitted on this bench. 

Large-scale recovery of light oil was commercialized in England, Germany, and the United States toward the end of the nineteenth century (151). Industrial coal-tar production dates from the earliest operation of coal-gas faciUties. The principal bulk commodities derived from coal tar are wood-preserving oils, road tars, industrial pitches, and coke. Naphthalene is obtained from tar oils by crystallization, tar acids are derived by extraction of tar oils with caustic, and tar bases by extraction with sulfuric acid. Coal tars generally contain less than 1% benzene and toluene, and may contain up to 1% xylene. The total U.S. production of BTX from coke-oven operations is insignificant compared to petroleum product consumptions. 

Walker et al. [114] examined several methods and solvents for use in the extraction of petroleum hydrocarbons from estuarine water and sediments, during an in situ study of petroleum degradation in sea water. The use of hexane, benzene and chloroform as solvents is discussed and compared, and quantitative and qualitative differences were determined by analysis using low-resolution computerised mass spectrometry. Using these data, and data obtained following the total recovery of petroleum hydrocarbons, it is concluded that benzene or benzene-methanol azeotrope are the most effective solvents. 

The impact of the extraction conditions using various solvents on the recoveries has never been studied in detail, and the results have never been compared. The introduction of modern extraction methods, such as microwave-assisted extraction, supercritical fluid extraction, and solid-phase extraction, probably will improve the efficiency of extraction, even in the instance of unstable pigments and pigment mixtures. The majority of TLC separations were carried out on traditional silica layers. As the chemical structures and, consequently, the retention characteristics of pigments are highly different, a wide variety of eluent systems has been employed for their separation, consisting of light petroleum, ethyl formate, ethyl acetate, benzene, toluene, chloroform, methanol, n-butanol, formic or acetic acid, and so forth. 

Soil samples were extracted first with a 0.05 N CaCl2-acelone mixture, and later with n-hexane and benzene or chloroform. The presence of the CaCl2 prevented the appearance of disturbing coextractives. This procedure resulted in 92-98% recovery. HCH and dilor were separated on Silufol plates in n-hexane, the a-thiodane and -isomer in petroleum ether, and pyrethroids, OP, and OC insecticides in various n-hexane-acetone mixtures (20) (Table 10). 

---