Transport of benzene

Fig. 21.2. Transport of benzene within an aerobic aquifer through which groundwater is flowing at a velocity vx of 100 m yr-1, calculated accounting for biodegradation, assuming biomass in the aquifer remains constant. Benzene recharges the aquifer at 1 mg kg-1 concentration from t = 0 to t = 2 years, after which time clean water enters the aquifer. Fine lines show transport calculated assuming the species is non-reactive, for comparison.

Fig. 21.3. Transport of benzene within an aerobic aquifer, as depicted in Figure 21.2, calculated assuming the species not only biodegrades, but sorbs to organic matter in the aquifer. Benzene in the simulation sorbs with a distribution coefficient of 0.16 x 10-3 mol (g sediment)-1, equivalent to a retardation factor R of 2. Fine lines show non-reactive case.

Fig. 21.4. Transport of benzene within an aerobic aquifer, modeled in two dimensions. Contaminated water containing 1 mg kg-1 benzene leaks into the aquifer over the course of two years, at the point indicated. As in the previous model (Fig. 21.3), the benzene is retarded by sorption to organic matter in the aquifer and attenuates due to sorption, biodegradation, and dispersive mixing. Plots were rendered using the matlab software.

Malone, R., R. Warner, J. L. Woods, and V. P. Evangelou. 1995. Transport of benzene and trichloroethylene through a landfill soil liner mixed with coal slurry. Waste Manag. Res. 12 417-428. 

Teramoto M, Matsuyama H, Nakai K, Uesaka T, and Ohnishi N. Eacilitated uphill transport of eicosapentaenoic acid ethyl ester through bulk and supported liquid membranes containing silver nitrate as carrier A new type of uphill transport. J Mem Sci, 1994 91(1-2) 209-213. Teramoto M, Matsuyama H, and Ohnishi N. Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier. J Mem Sci, 1990 50 269-278. 

Teramoto M, Matsuyama H, and Yonehara T. Selective facilitated transport of benzene across supported and flowing liquid membranes containing silver nitrate as a carrier. J Mem Sci, 1990 50 269-284. 

G. Unnikrishnan and S. Thomas, Molecular Transport of Benzene and Methyl-Substituted Benzenes into Filled Natural Rubber Sheets, Journal of Applied Polymer Science, 1996, 60, 963. 

Benzene CeHg has no action on aluminium, even as a mixture with alcohol. Aluminium equipment is used for the distillation (boiling point 80 °C), storage and transportation of benzene and its derivatives, such as toluene C6H5CH3, xylene C6H4(CH3)2, ethylbenzene C6H5C2H5, styrene C6H5C2H3 [4]. 

Various types of detector tubes have been devised. The NIOSH standard number S-311 employs a tube filled with 420—840 p.m (20/40 mesh) activated charcoal. A known volume of air is passed through the tube by either a handheld or vacuum pump. Carbon disulfide is used as the desorbing solvent and the solution is then analyzed by gc using a flame-ionization detector (88). Other adsorbents such as siUca gel and desorbents such as acetone have been employed. Passive (diffuse samplers) have also been developed. Passive samplers are useful for determining the time-weighted average (TWA) concentration of benzene vapor (89). Passive dosimeters allow permeation or diffusion-controlled mass transport across a membrane or adsorbent bed, ie, activated charcoal. The activated charcoal is removed, extracted with solvent, and analyzed by gc. Passive dosimeters with instant readout capabiUty have also been devised (85). 

The performance of various solvents can be explained with the help of the role of these solvents in the reaction. These solvents help in keeping teth benzene and hydrogen peroxide in one phase. This helps in the easy transport of both the reactants to the active sites of the catalyst. The acetonitrile, and acetone adsorption data on these catalysts (Fig. 6), suggests that acetonitrile has a greater affinity to the catalytic surface than acetone. There by acetonitrile is more effective in transporting the reactants to the catalyst active sites. At the same time, they also help the products in desorbing and vacating the active sites. 

We have also determined the delivery sites of alkylbenzenes by NMR. As already described in Section III.A, PrBe are deeply transported to the chain tail region in the bilayer core and the delivery site can be classified into category III [46]. Benzene, however, cannot deeply penetrate into the hydrophobic core, zone III, but is trapped preferentially at the interfacial site of the bilayer, zone II the delivery site can be classified into category II. Although benzene is generally considered to be hydrophobic, the delivery site of benzene determined by NMR is reasonable in the sense of the 7r-electrons with some affinity for the hydrophilic sites of the bilayer. Both drug and lipid sides of the H NMR spectra show that alkylbenzenes can deeply penetrate into the bilayer interior in the order PrBe > ethylbenzene > toluene > benzene, which is consistent with the sequence of the insolubility in water. 

First, points of release of benzene were identified petroleum refining and coke oven operations (production and extraction releases), use as a chemical intermediate (transportation, storage, use, and waste releases), use in gasoline (use-related release), and use in finished products (use-related release). Benzene also can be a contaminant of most of the derivatives made from it and its use as a solvent was substantial before health concerns arose. The complexity of the chemical systems dependent on benzene is shown in Figure 6. A list of potential releasing products appears in Table II. 

Benzene chemisorption on platinum-alumina in the range 26°-470°C has been measured in a flow system by Pitkethly and Goble (7). A small dose of benzene was injected into a stream of inert carrier gas and transported to the reactor the effluent was then sampled repeatedly and analyzed by gas-liquid chromatography. Information concerning the adsorption and desorption of benzene was obtained from the shape of the subsequent benzene concentration versus time curves. Evidence was obtained for four types of adsorption of benzene ... 

Toluene alkylation with isopropyl alcohol was chosen as the test reaction as we can follow in a detail the effect of zeolite structural parameters on the toluene conversion, selectivity to cymenes, selectivity to para-cymene, and isopropyl/n-propyl ratio. It should be stressed that toluene/isopropyl alcohol molar ratio used in the feed was 9.6, which indicates the theoretical toluene conversion around 10.4 %. As you can see from Fig. 2 conversion of toluene over SSZ-33 after 15 min of T-O-S is 21 %, which is almost two times higher than the theoretical toluene conversion for alkylation reaction. The value of toluene conversion over SSZ-33 is influenced by a high rate of toluene disproportionation. About 50 % of toluene converted is transformed into benzene and xylenes. Toluene conversion over zeolites Beta and SSZ-35 is around 12 %, which is due to a much smaller contribution of toluene disproportionation to the overall toluene conversion. A slight increase in toluene conversion over ZSM-5 zeolite is connected with the fact that desorption and transport of products in toluene alkylation with isopropyl alcohol is the rate controlling step of this reaction [9]... 

Figure 21.2 shows how in the calculation results benzene is transported through the aquifer. The pulse of benzene migrates at the rate of groundwater flow, traversing the aquifer in ten years. As a result of biodegradation by the natural microbial consortium, however, the benzene concentration decreases markedly with time, compared to the non-reacting case. 

At 1 p.m. the plant operator notices a drop in pressure in a pipeline transporting benzene. The pressure is immediately restored to 100 psig. At 2 30 p.m. a 1/4-in-diameter leak is found in the pipeline and immediately repaired. Estimate the total amount of benzene spilled. The specific gravity of benzene is 0.8794. 

Refineries and olefins plants generate the primary supplies of benzene so cyclohexane plants tend to be clustered around refining centers to save transportation costs. 

The mechanism of benzene-induced toxicity appears to involve the concerted action of several benzene metabolites. Benzene is metabolized, primarily in the liver, to a variety of hydroxylated and opened-ring products that are transported to the bone marrow, where secondary metabolism occurs. Metabolites may induce toxicity both by covalent binding to cellular macromolecules and by inducing oxidative damage. Metabolites may also inhibit stromal cells, which are necessary to support growth of differentiating and maturing marrow cells. ... 

W. F. Graydon and R. J. Stewart (41) also compared the membrane potentials with the values according to equation (46). The membrane investigated was a copolymer of p-styrene sulfonic acid and styrene crosslinked with divinyl benzene. In the large majority of cases the experimental values were lower than those according to equation (46). The smaller part of this difference could be attributed to the transport of the co-ions and was calculated roughly. The greater part was attributed to water transport. From this the transport number of water was calculated it varied from 1 to about 60. It was found that the water transport was proportional to the water content and inversely proportional to the number of crosslinks. A provisional direct measurement was effected of a water transport number. The value corresponded rather well with the indirect determination as described above. 

Estimates of daily exposure to benzene from urban or suburban air range from 180 to 1300 /ig/person/day.1112 Urban air concentrations of the other aromatic hydrocarbons are similar to those of benzene and the vast majority of exposure of the general population to these other aromatic hydrocarbons will be due to road transport or solvent-containing products rather than food. A 1995 survey of these compounds in samples from the UK Total Diet Study showed that average dietary exposures to benzene and related compounds from food in the UK are low, and very much lower than estimated exposure from active smoking of tobacco or intakes from air by urban dwellers.13 The mean dietary exposure to benzene was estimated to be in the range 0.9-2.4 /ig/person/day. 

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