Xylene* and ethylbenzene

Xylene Isomeri tion. The objective of C-8-aromatics processing is the conversion of the usual four-component feedstream (ethylbenzene and the three xylenes) into an isomerically pure xylene. Although the bulk of current demand is for xylene isomer for polyester fiber manufacture, significant markets for the other isomers exist. The primary problem is separation of the 8—40% ethylbenzene that is present in the usual feedstocks, a task that is compHcated by the closeness of the boiling points of ethylbenzene and -xylene. In addition, the equiUbrium concentrations of the xylenes present in the isomer separation train raffinate have to be reestabUshed to maximize the yield of the desired isomer. 

They reported that most of bacteria for removing benzene, toluene, ethylbenzene, and xylene (BTEX) may have a high biological activity in a weak basic environment. 

Chakraborty R, SM O Connor, E Chan, JD Coates (2005) Anaerobic degradation of benzene, tolnene, ethylbenzene, and xylene componnds by Dechloromonas strain RCB. Appl Environ Microbiol 71 8649-8655. 

Hendricks B, and 11 coauthors (2005) Dynamics of an oligotrophic bacterial aquifer community during contact with a groundwater plume contaminated with benzene, toluene, ethylbenzene, and xylenes an in situ mesocosm study. Appl Environ Microbiol 71 3815-3823. 

Benzene is one of a group of related aromatic monocyclic hydrocarbons (BTEX—benzene, toluene, ethylbenzene, and xylene), and since these are water soluble, there has been concern for their dissipation and persistence in groundwater under both aerobic and anaerobic conditions. Although aerobic growth at the expense of benzene was established many years ago, the pathway for its degradation was established only much later. The aerobic degradation of benzene by bacteria is... 

Yadav JS, CA Reddy (1993) Degradation of benzene, toluene, ethylbenzene, and xylenes (BTEX) by the lignin-degrading basidiomycete Phanerochaete chrysosporium. Appl Environ Microbiol 59 756-762. 

Morgan P, ST Lewis, RJ Watkinson (1993) Biodegradation of benzene, toluene, ethylbenzene and xylenes in gas-condensate-contaminated water. Environ Pollut 82 181-190. 

The method by whieh erude oils are expelled from souree kerogen also influences oil group eomposition. In the case of hydrothermal oils or hydrothermal bitumens, hot water ean enhanee the content of lighter aliphatie and aromatic hydrocarbons (benzene, toluene, ethylbenzene, and xylenes). Typieal hydrothermal oils have a... 

R. A. Deeb, H. Y. Hu, J. R. Hanson, K. M. Scow, and L. Alvarez-Cohen. Substrate interactions in BTEX [benzene, toluene, ethylbenzene, and xylene] and MTBE [methyl tert-butyl ether] mixtures by an MTBE-degrading isolate. Environ Sci Technol, 35(2) 312-317, 2001. 

Petroleum hydrocarbons (benzene, toluene, ethylbenzene, and xylenes—collectively BTEX), particularly benzene, are believed to pose significant health concerns, especially as they are contained in over 99% of all gasoline. However, additives such as MTBE and DIPE, which have high carbon usage rates, are not found in all gasolines and hence pose less significant health concerns. Thus, GAC is generally applicable for the removal of BTEX. 

BTEX Benzene, toluene, ethylbenzene, and xylenes (collectively)... 

The United States Environmental Protection Agency (U.S. EPA) has identified several hundred MTBE-contaminated sites that have performed treatment of soil and groundwater to remove or destroy MTBE.1 Many of these sites have also treated other fuel components, primarily benzene, toluene, ethylbenzene, and xylene (BTEX), and some have treated fuel oxygenates other than MTBE. Although others have reported about treatment technologies for MTBE cleanup,2 only limited information has been published about cleanup of other oxygenates. These oxygenates include ether compounds, such as ethyl tert-butyl ether (ETBE), tert-amyl methyl ether (TAME), diisopropyl ether (DIPE), and tert-amyl ethyl ether (TAEE), as well as alcohol compounds, such as tert-butyl alcohol (TBA), tert-amyl alcohol (TAA), ethanol, and methanol. 

The monoaromatic compounds benzene, toluene, ethylbenzene and xylene, commonly found in crude oil, are often jointly called BTEX compounds. The most harmful of these compounds is benzene, which is a known carcinogen. BTEX compounds occur naturally near natural gas and petroleum deposits and are detected in the fumes of forest fires. Most of the highly volatile BTEX compounds released by human activity originate from fuel use and end up as pollutants in the air. Inhaling BTEX-polluted air is also the greatest hazard to humans by these compounds. BTEX compounds are water-soluble, and therefore, improper handling can also cause groundwater contamination. 

Jaynes WF, Vance GF (1999) Sorption of benzene, toluene, ethylbenzene and xylene (BTEX) compounds by hectorite clays exchanged with aromatic organic cations. Clays Clay Miner 47 358-365 Johnston CT, De Oliveira MF, Teppen BJ, Sheng G, Boyd SA (2001) Spectroscopic study of nitroaromatic-smectite sorption mechanisms. Environ Sci Technol 35 4767-4772... 

Control of bioremediation of benzene, toluene ethylbenzene, and xylene 213... 

Xyloflning [Xylol refining] A process for isomerizing a petrochemical feedstock containing ethylbenzene and xylenes. The xylenes are mostly converted to the equilibrium mixture of xylenes the ethylbenzene is dealkylated to benzene and ethylene. This is a catalytic, vapor-phase process, operated at approximately 360°C. The catalyst (Encilite-1) is a ZSM-5-type zeolite in which some of the aluminum has been replaced by iron. The catalyst was developed in India in 1981, jointly by the National Chemical Laboratory and Associated Cement Companies. The process was piloted by Indian Petrochemicals Corporation in 1985 and commercialized by that company at Baroda in 1991. 

The validity of the second-order model was verified with feeds containing varying ratios of ethylbenzene and xylene. 

Environmental issues associated with the subsurface release of petroleum hydrocarbons and other organics fall into four areas (1) vapors (Figure 1.5), (2) impacted soils, (3) the presence of nonaqueous phase liquids (NAPLs), and (4) dissolved constituents (i.e., benzene, toluene, ethylbenzene, and xylenes (BTEX), and other components) in groundwater. 

Except for short-term hazards from concentrated spiUs, BTEX compounds (benzene, toluene, ethylbenzene, and xylenes) have been more frequently associated with risk to humans than with risk to nonhuman species such as fish and wildlife. This is partly because plants, fish, and birds take up only very small amounts, and because this volatile compound tends to evaporate into the atmosphere rather than persisting in surface waters or soils. However, volatiles such as this compound can pose a drinking water hazard when they accumulate in groundwater. See also BTEX entry, and entries for benzene, toluene, ethylbenzene, and xylenes. 

Petroleum refineries are a somce of hazardous and toxic air pollutants, such as BTEX compounds (benzene, toluene, ethylbenzene, and xylene). They are also a major source of criteria air pollutants particulate matter (PM), nitrogen oxides (NO t), carbon monoxide (CO), hydrogen sulfide (H2S), and sulfur oxides (SO ). 

Condensate release might be equated to the release of volatile constituents but are often named as such because of the specific constituents of the condensate, often with some reference to the gas condensate that is produced by certain petroleum and natural gas wells. However, the condensate is often restricted to the benzene, toluene, ethylbenzene, and xylenes (BTEX) family of compounds. 

To determine the concentrations of benzene, toluene, ethylbenzene, and xylenes, approved methods (e.g., EPA SW-846 8021B, SW-846 8260) are not only recommended but are insisted upon for regulatory issues. Polynuclear aromatic hydrocarbons (PAHs) may be present in condensate, and evaluation of condensate contamination should include the use of other test methods (EPA SW-846 8270, SW-846 8310) provided that the detection limits are adequate to the task of soil and groundwater protection. Generally, at least one analysis may be required for the most contaminated sample location from each source area. Condensate releases in nonsensitive areas require analysis for naphthalene only. The analysts should ensure that the method has detection limits that are appropriate for risk determinations. 

Specific contaminants that are components of total petroleum hydrocarbons, such as BTEX (benzene, toluene, ethylbenzene, and xylene), n-hexane, jet fuels, fuel oils, and mineral-based crankcase oil have been studied and a number of toxicological profiles have been developed on individual constituents and petroleum products. However, the character of the total petroleum hydrocarbons has not been studied extensively and no profiles have been developed. Although several toxicological profiles have been developed for petroleum products and for specific chemicals found in petroleum, the total petroleum hydrocarbon test results have been too nonspecific to be of real value in the assessment of its potential health effects. 

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