Benzene stripping

The resulting benzene strips or extracts frequently will not tolerate storage even in the frozen state. 

The benzene strip or extract solutions are evaporated nearly to dryness in 500-ml. standard-taper Erlenmeyer flasks on 3 units of a 6-unit variable heat extraction apparatus hot plate (see Figure 1). Evaporation is hastened by directing a jet of air at the surface of the benzene, gentle enough to avoid spattering when maintained 0.5 inch above the surface of the liquid. The benzene vapors are removed through a manifold connected to the house vacuum. On this apparatus 250 ml. of sample can be reduced to a volume of about 5 ml. in 10 minutes. 

Screening methods are available for analysis of benzene in feces and urine (Ghoos et al. 1994) and body fluids (Schuberth 1994). Both employ analysis by capillary GC with an ion trap detector (ITD). Benzene in urine has been determined by trapping benzene stripped from the urine on a Carbotrap tube, followed by thermal desorption GC/flame ionization detection (FID). The detection limit is 50 ng/L and the average recovery is approximately 82% (Ghittori et al. 1993). Benzene in urine has also been determined using headspace analysis with capillary GC/photoionization detection (PID). The detection limit is 40 ng/L (Kok and Ong 1994). 

Extractive separation of As. Evaporate a sample, containing not more than 60 pg of As, almost to dryness, with HNO3 or H2SO4 (the solution must not contain halide ions). To the cooled solution, add 10 ml of As-free cone. HCl and 2 drops ofl% KI solution. Mix and allow to solution to stand for 5 min, then transfer it to a separating funnel and shake with three 5-ml portions of benzene. Strip the combined extracts with two 5-ml portions of water. 

The theoretical minimum air requirement at equilibrium to strip aromatic-contaminated water can be calculated from the Henry s Law constant. Thus, at 68°F benzene stripping requires 69 SCFM of air, toluene... 

In general, the sulfolane extraction unit consists of four basic parts extractor, extractive stripper, extract recovery column, and water—wash tower. The hydrocarbon feed is first contacted with sulfolane in the extractor, where the aromatics and some light nonaromatics dissolve in the sulfolane. The rich solvent then passes to the extractive stripper where the light nonaromatics are stripped. The bottom stream, which consists of sulfolane and aromatic components, and which at this point is essentiaHy free of nonaromatics, enters the recovery column where the aromatics are removed. The sulfolane is returned to the extractor. The non aromatic raffinate obtained initially from the extractor is contacted with water in the wash tower to remove dissolved sulfolane, which is subsequently recovered in the extract recovery column. Benzene and toluene recoveries in the process are routinely greater than 99%, and xylene recoveries exceed 95%. 

Polypropylene-derived branched alkyl (0 2) benzene (BAB) has been batch sulfonated using 60—70% oleum in Hquid SO2 solvent at temperatures of — 1 to —8°C, with SO2 serving as a self-refrigerant and viscosity reducer in the process. After sulfonation and digestion, SO2 is stripped, recovered, and recycled (256). 

The acid wash test consists of shaking a mixture of 96% sulfuric acid with benzene and comparing the color of the (lower) acid layer with a set of color standards. Other quaUtative tests include those for SO2 and H2S determination. The copper strip corrosion test indicates the presence of acidic or corrosive sulfur impurities. The test for thiophene is colorimetric. 

Some catalysts exposed to air stripping off-gas were subject to deactivation. However, using a catalytic oxidizer at a U.S. Coast Guard faciUty (Traverse City, Mich.) for the destmction of benzene, toluene, and xylene stripped from the groundwater, the catalytic oxidization unit operated at 260 to 315°C, and was able to achieve 90% destmction efficiency (see Groundwatermonitoring). 

The condition defined by equation (8) is met by adjustment of (Qg(3)) nd (T(3)). The pressures at the second stripping flow inlet and that of the outlet for solute (C) must be made equal, or close to equal, to prevent cross-flow. Scott and Maggs [7] designed a three stage moving bed system, similar to that described above, to extract pure benzene from coal gas. Coal gas contains a range of saturated aliphatic hydrocarbons, alkenes, naphthenes and aromatics. In the above theory the saturated aliphatic hydrocarbons, alkenes and naphthenes are represented by solute (A). 

The main product, benzene, is represented by solute (B), and the high boiling aromatics are represented by solute (C) (toluene and xylenes). The analysis of the products they obtained are shown in Figure 12. The material stripped form the top section (section (1)) is seen to contain the alkanes, alkenes and naphthenes and very little benzene. The product stripped from the center section appears to be virtually pure benzene. The product from section (3) contained toluene, the xylenes and thiophen which elutes close to benzene. The thiophen, however, was only eliminated at the expense of some loss of benzene to the lower stripping section. Although the system works well it proved experimentally difficult to set up and maintain under constant operating conditions. The problems arose largely from the need to adjust the pressures that must prevent cross-flow. The system as described would be virtually impossible to operate with a liquid mobile phase. 

The product of a second step is the methyl aceloacelic ester enamine of N-2-amino-2-(1,4-cyclohexadienyl)acelic acid sodium salt. 306 mg D-2-amino-2-(1,4-cyclohexadienyl)-acelic acid (2.00 mmol) are dissolved by warming in a solution of 108 mg of NaOCHj (2.00 mmol) in 4.3 ml reagent grade MeOH. 255 mg (0.24 ml, 2.20 mmol) methyl ace-loacelale are added and the mixture refluxed for 45 minutes. The MeOH Is almost totally stripped off in vacuo. Five milliliters benzene are added and distilled off to a small residual volume. The addition and distillation of benzene is repealed to insure complete removal of the MeOH and water. The product crystallizes out overnight from a small residual volume of benzene. It is filtered off, washed with benzene, and dried in vacuo. 

A benzene-toluene mixture is to be separated in a tower packed with 1-in. fieri saddles. The feed is 55.2 mol% (liquid feed, saturated), and an overhead of 90 mol% benzene, and bottoms of not more than 24 mol% benzene is desired. Using the data of Ref. 51 plotted in Figure 9-98, determine the number of transfer units in the rectifying and stripping sections using a reflux ratio (reflux to product, L/B) = 1.35. 

Should pure olefin be used for alkylation (Shell process), the organic phase consists of benzene, LAB, and heavy alkylate and is fractionally distilled, after which the remaining HF is usually removed by stripping. When using olefin as a solution in paraffin (Pacol and Hiils process) for alkylation, the organic phase contains additional large quantities of paraffin which have to be separated out by distillation and used again in the production of olefin. 

The excess benzene is distilled over a column and used as recycled benzene in the alkylation. In the bottom of the stripping section of the column the raw alkylates, consisting of LAB, heavy alkylate, and excess paraffin, are separated. This mixture is fed to a second column in which the excess paraffin is separated off. The actual purification of the LAB follows in a third column. The bottom product, heavy alkylate, consisting mainly of dialkylbenzene is also separated. Heavy alkylates are used in various applications. Both the paraffin and the LAB column are operated under vacuum. 

FIG. 17 Alkylation of benzene with n-chloroparaffins. R, reactor ST, settling tank SC, stripping column C, condensor V, vessel. 

Preliminary purification of a starting band contaminated with plant oil should be performed by predevelopment with a nonpolar solvent such as benzene or n-heptane, delivered from the eluent container. Weakly retained ballast substances (e.g., lipids) move with the solvent to the edge of the adsorbent layer, covering the glass plate where the volatile solvent evaporates. The contaminants can then be removed (scraped out with the adsorbent) from the layer or adsorbed on the strip of blotting paper placed on the upper edge of the layer. 

Choice of Solvent. As indicated by Averell and Norris (1), and independently confirmed by the authors, technical benzene is a superior stripping solvent for parathion residues. It is almost completely miscible with technical grade parathion at room temperatures, it is universally available and low in cost, it is readily volatile, it fails to contribute to storage decomposition (6), it is a good solvent for plant oils and waxes, and it is immiscible with water. On the other hand, benzene is highly flammable and its vapors are very toxic to human beings, especially as a chronic toxicant even in small doses. 

The substrate was Valencia orange leaves, with 2500 leaves per sample selected in a carefully prescribed manner (4). The trees involved were field sprayed in a conventional manner with 4 pounds of a 25% wettable powder of parathion, then sampled after 7 days and again after 11 days. Each sample was mixed thoroughly and subsampled into 125-leaf units in 2-quart Mason jars. To all units were added 250 ml. of benzene each, and they were sealed, stripped for various lengths of time, then restripped with fresh benzene, again for various lengths of time. The strip solutions were analyzed in the usual manner. 

Benzene is the best single solvent for stripping or extracting the contained parathion. 

Leaves are stripped for 30 minutes in the usual 2-quart wide-mouthed Mason jars. Instead of a waxed paper gasket, however, 2 squares of No. 300 M.S.T. cellophane topped by a square of white nylon are used, as the benzene would disintegrate the wax paper during this longer stripping period. The entire 250 ml. of benzene are added at once, the... 

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