M/p-Xylene

The prepared MAC adsorbents were tested for benzene, toluene, 0-, m-, p-xylene, methanol, ethanol, iso-propanol, and MEK. The modified content of all MACs was 5wt% with respect to AC. The specific surface areas and amounts of VOC adsorbed of MACs prepared in this study are shown in Table 1. The amounts of VOC adsorbed on 5wt%-MAC with acids and alkali show a similar tendency. However, the amount of VOC adsorbed on 5wt%-PA/AC was relatively large in spite of the decrease of specific surface area excepting in case of o-xylene, m-xylene, and MEK. This suggests that the adsorption of relatively large molecules such as 0-xylene, m-xylene, and MEK was suppressed, while that of small molecules was enhanced. It can be therefore speculated that the phosphoric acid narrowed the micropores but changed the chemical nature of surface to adsorb the organic materials strongly. 

Note Normally inhibited with 8-12 ppm 4-7er7-butylcatechol to prevent polymerization. According to Chevron Phillips Company (March 2002), 99.93% styrene contains the following components (ppm) benzene (<1), toluene (<1), ethylbenzene (50), a-meth ylstyrene (175), m + p-xylene (120), o-xylene (125), isopropylbenzene (100), / -propylbenzene (60), m + p-ethyltoluene (20), vinyltoluene (10), phenylacetylene (50), m + p-divinylbenzene (<10), o-divinylbenzene (<5), aldehydes as benzaldehyde (15), and peroxides as benzoyl-peroxides (5). 

Thomas and Delfino (1991) equilibrated contaminant-free groundwater collected from Gainesville, FT with individual fractions of three individual petroleum products at 24-25 °C for 24 h. The aqueous phase was analyzed for organic compounds via U.S. EPA approved test method 602. Average m-i-p-xylene concentrations reported in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were 8.611, 0.658, and 0.228 mg/L, respectively. When the authors analyzed the aqueous-phase via U.S. EPA approved test method 610, average m+p-xylene concentrations in water-soluble fractions of unleaded gasoline, kerosene, and diesel fuel were lower, i.e., 6.068, 0.360, and 0.222 mg/L, respectively. 

Based on laboratory analysis of 7 coal tar samples, m+p-xylene concentrations ranged from ND to 6,000 ppm (EPRl, 1990). Detected in 1-yr aged coal tar film and bulk coal tar at concentrations of 260 and 830 mg/kg, respectively (Nelson et ah, 1996). A high-temperature coal tar contained xylene at an average concentration of 0.03 wt % (McNeil, 1983). 

It was Interesting to study the nucleatlon and growth behaviour of crystals during pressure application, or under a steady pressurized state In a supersaturated condition. So, they were studied with p-xylene crystals from m-, p-xylene mixture by means of In-sltu observation. And some results have been presented both on nucleatlon (2) and on growth behaviour (3) elsewhere, which were related to supersaturation pressure and p-xylene concentration. 

Figure 3. Isothermic phase diagram of m, p-xylene mixture.

In one patented process (19) a m-p-xylene fraction is produced from xylene mixtures by distillation, and is subsequently cooled to about —70° F. to produce p-xylene crystals, which are removed in high purity by filtering or centrifuging. The yield of p-xylene is limited by eutectic formation with m-xylene. As the mixture behaves as an ideal solution, the yield and temperature level can be calculated from the thermodynamic properties of xylenes, which were reported by Kravchenko (12). 

The ultimate in xylene separation is claimed, however, by Hetzner (10), who first distills the mixture to remove o-xylene by taking m-p-xylene and ethylbenzene overhead in a column having about 35 to 60 theoretical plates. It is reported that concentrates containing up to 97% o-xylene have been produced by this process. The m-xylene, p-xylene, and ethylbenzene mixture is selectively sulfonated to remove m-xylene. In this operation, 2 moles of Sulfuric acid (96 to 98%) are added per mole of m-xylene in the mixture to be treated. After separation, the aqueous layer is hydrolyzed at 250° to 300° F. to recover a concentrate containing 90% or more m-xylene. The hydrocarbon layer is cooled to produce p-xylene crystals, which are separated by filtration or centrifugation. The 85 to 90% p-xylene concentrate is reprocessed to recover a final product containing 96% p-xylene. The mother liquor from the p-xylene crystallization contains impure ethylbenzene and is rejected from the system. 

The experimental setup of the SSM is shown in Fig. 19.12a. The temporal increase of the aqueous concentration of four diesel fuel components (benzene, m/p-xylene, naphthalene) is given in Figs. 19.126 to d. Relevant physicochemical properties are summarized in Table 19.3. Note that the two isomers m- and /7-xylene exhibit virtually the same properties, and are, therefore, considered together. 

Figure 19.12 (a) Experimental setup to determine the exchange dynamics of a combined NAPL-water system using the slow stirring method (SSM). (6) - (d) Measured and calculated aqueous concentrations of benzene m/p-xylene and naphthalene. The solid lines give the result of the linear bottleneck exchange model with an aqueous boundary layer thickness of 8bl = 2.4 x 1CT2 cm = 240 pm (adapted from Schluep et al., 2000). 

For m/p-xylene and naphthalene the aqueous equilibrium concentration (reached after about 2 days) agrees well with the calculated value, Ciw/NAPL. However, for benzene the measured value lies about 10% below the calculated equilibrium concentration (410 pg L-1). This discrepancy will be explained below (Answer d). 

Newspaper, Newspaper journal Toluene, o-,m-,p-xylene, a-/P-pinene, 2 limonene, aliphatic hydrocarbons (C10-C20)... 

Aromatic hydrocarbons Benzene, toluene, ethylbenzene, propylbenzene, 1,3,5-trimethylbenzene, 1,2,4-trimethylbenzene, 1,2,3-trimethylbenzene, tert-butylbenzene, o,m,p-xylene, p-cymene, styrene, alpha-methylstyrene, naphthalene, methylnaphthalene... 

The capillary column should be able to resolve 2-methylpentane from the methanol solvent front (when gasoline in soil is to be determined) and ethylbenzene from m/p-xylene. A 30 m x 0.53 mm ID x 1.0 pm film fused silica capillary column, such as DB-5, SPB-5, AT-5, or equivalent should give adequate separation. Columns with other dimensions can also be used. A longer column, e.g., Rtx 502.2 (105 m x 0.53 mm x 0.3 pm) gives excellent resolution, but with a longer analysis time. 

Hydrocarbons Ethyl cyclohexane, heptane, octane, toluene, o-, m- p-xylene... 

As illustrated by Table 3 aromatic compounds such as toluene, benzene, 0, m, p-xylenes and ethyl benzene are important pollutants in urban air. These compounds comprise a substantial fraction of automotive fuel and its use results in substantial emissions of aromatic compounds into urban atmo-... 

Reaction of monocyclic aromatics with O3 and NO3 radicals is generally very slow and unimportant. Atmospheric degradation of aromatics is initiated by OH radical attack. The kinetics of the reaction of OH radicals with aromatic compounds are well established [65]. As seen from Table 2 the fife-time of aromatics with respect to reaction with OH is typically a few days or less. Reaction proceeds by addition to the ring and H-atom abstraction from either the substituent groups or possibly from the ring C - H sites. In all cases the addition channel is dominant. For benzene, toluene, 0, m, p-xylene, and ethyl benzene the H-atom abstraction pathway accounts for 5-10% of the overall reaction [15], the remaining 90-95% proceeds via addition. For toluene ka/(ka + h,) = 0.07 [15,65]. 

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