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Applied Chemistry and Physics
Published in Robert A. Burke, Applied Chemistry and Physics, 2020
The next aromatic hydrocarbon discussed is xylene, also known as dimethylbenzene. Xylol, and Xylenes. It is a clear liquid with a TLV of 100 ppm, and it is nonpolar and immiscible with water. It is a moderate fire risk, with a flammable range of 0.9%–7% in air. The boiling point is between 281°F and 292°F (138°C–144°C), depending on the mixture. The flash point ranges from 81°F to 90°F (27°C), and the ignition temperature ranges from 867°F to 984°F (463°C–528°C). Xylene is a commercial mixture of the three isomers: meta-xylene, para-xylene and ortho-xylene (Figure 3.56), (Figure 3.57), (Figure 3.58). The last member of the benzene family is styrene (Figure 3.59). It is, however, quite different from the other members of the aromatic family. Styrene is a monomer used in the manufacture of polystyrene. It has a vinyl radical attached to the benzene ring. The double bond in the vinyl radical is reactive. Reaction can occur with the oxygen in the air, with an oxidizer, or it can self-react in storage.
Catalytic Applications of Zeolites in Industrial Processes
Published in Subhash Bhatia, Zeolite Catalysis: Principles and Applications, 2020
The largest petrochemical application of zeolites is in the ZSM-5-catalyzed xylene isomerization processes. The principal source of xylene is the product from catalytic reformers. The objective is to convert C8 aromatic streams which contain about 20% ethylbenzene, 20% o-xylene, 40% m-xylene, and 20% p-xylene from reformers or pyrolysis gasoline units to equilibrium mixtures of xylenes from which the most valuable product, p-xylene, can then be separated. Typically these C8 streams which contain 20% ethylbenzene are costly to be separated by distillation. In a conventional process scheme, p-xylene is removed either by low temperature crystallization or molecular sieve adsorption, e.g., UOP’s Parex process. To increase the yields of the more desirable p- and o-isomers, various isomerization processes have been designed.
Reprotoxic and Endocrine Substances
Published in Małgorzata Pośniak, Emerging Chemical Risks in the Work Environment, 2020
Katarzyna Miranowicz-Dzierżawska
Technical xylene is a mixture of xylene isomers, containing 44–70% of m-xylene and approx. 20% each of p-xylene and o-xylene. The mixture often contains 6–10% of ethylbenzene. Xylene is mostly used for fuel enhancement, as solvents for paints, varnishes, glues, resins, and as a cleaning and degreasing agent in organic synthesis. In experimental studies on mice administered a dose 2,060 mg/kg of xylene per day between day 6 and day 15 of gestation, a significant increase in the incidence of cleft palate and lower birth weight was found in the fetuses. Delayed jaw ossification was found in fetuses of pregnant Wistar rat females, exposed to xylene vapors with a concentration of 870 mg/m3 6 h per day between day 4 and day 21 of gestation. The offspring of mothers exposed to xylene had a slightly larger body mass and less developed motor skills (especially the female offspring). A dose of 3,100 mg/kg per day of xylene has caused a 30% mortality rate of the fetuses [Ligocka 2007].
Probabilistic health risk assessment of occupational exposure to BTEX in a paint manufacturing plant using Monte-Carlo simulation
Published in Human and Ecological Risk Assessment: An International Journal, 2023
Maedeh Hosseinzadeh, Rasoul Hemmatjo, Zahra Moutab Sahihazar, Sadjad Galvani, Mohammad Hajaghazadeh
BTEX compounds are commonly used in industry as chemical intermediates, solvents, and adhesives (Davidson et al. 2021).The USEPA classified BTEX compounds as hazardous air pollutants (USEPA 2022a). Benzene is the most toxic member of the BTEX family that, with prolonged exposure, may increase the risk of leukemia and aplastic anemia in humans (Hazrati et al. 2016). Prolonged exposure to toluene and ethylbenzene can have adverse effects on the central nervous system (CNS), leading to brain disorders and eye irritations (Behnami et al. 2023). Xylene exposure can lead to harmful health outcomes such as respiratory tract problems, irritation of the eyes, nose, and throat, and damage to the nervous system (McKenzie et al. 2012). The International Agency for Research on Cancer (IARC) has classified benzene as a human carcinogen in Group 1 and ethylbenzene as known or probable human carcinogens in Group 2 A or 2B (IARC 2018). Therefore, it is crucial to understand the level of BTEX compounds in a workplace and determine their associated health risks.
Volatile organic compounds in carpet manufacturing plants: Exposure levels and probabilistic risk assessment using Monte-Carlo simulations
Published in Human and Ecological Risk Assessment: An International Journal, 2022
Amir Hossein Khoshakhlagh, Simone Morais
Benzene, toluene, ethylbenzene, and xylene (BTEX) are mono-aromatic volatile organic compounds and specifically four solvent heavily applied in industry as chemical intermediates, solvents, and adhesives (Davidson et al. 2021). BTEX are significant constituents of air pollution, which is the fifth main risk factor for premature death in the world (Davidson et al. 2021). The type and severity of potential human health effects depend on the amount of BTEX, the exposure length time, and the specific BTEX toxicity (Leusch and Bartkow 2010; Masih et al. 2016). BTEX have been identified as toxic, carcinogenic and mutagenic hazardous air pollutants. The international agency for research on cancer (IARC) and the 14th report of the national toxicology program of U.S. department of health and human services on carcinogens have categorized benzene, toluene, ethylbenzene and xylenes as class 1 (carcinogen to humans), class D (no carcinogen), group B2 (likely carcinogen to humans) and class D (no carcinogen), respectively (Lan and Binh 2012; Marć et al. 2014; Masih et al. 2016). Many detrimental health effects have been related to inhalation exposure to benzene such as anemia, non-lymphocytic and myeloid leukemia, and also, several immunological effects (McKenzie et al. 2012). The main impact of toluene is on the brain and nervous system, with symptoms of fatigue and drowsiness (Dorsey 2000; Pourabdian et al. 2020). Also, exposure of toluene affects premature delivery, and neurobehavioral and reproductive system (Fan et al. 2012; Dehghani et al. 2019). Adverse health effects of xylene include eyes, nose and throat irritation, breathing problems and nervous system damage (McKenzie et al. 2012). Although, the evidence determined the carcinogenicity of toluene and xylene at higher concentration levels in animal experiments, the IARC and the United States environmental protection agency (U.S.EPA) have not classified toluene and xylene as carcinogenic to humans (Masih et al. 2016; Dehghani et al. 2022). Acute exposure to ethylbenzene affects respiratory system including throat irritation and chest constriction and nervous system such as dizziness; there is no document about chronic toxic effects of ethylbenzene in human, but histopathological changes in the liver and kidney of experimental animals have been found (Taylor 2010).