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Chemical Name: p-Xylene
Common Names: para-Xylene, PX
Chemical Formula: C8H10
CAS Number: 106-42-3
Appearance: Clear, colorless liquid with an aromatic odor
Relevant Uses: PX stands as a major ingredient in the production of terephthalic acid and dimethyl terephthalate, both of which carry heavy weight in polyester manufacturing. Processing plants and labs use it for various synthesis chains, leveraging its properties for both fuels and plastics.
Main Hazards: Flammable liquid and vapor; toxic by inhalation, skin absorption, and ingestion; skin, eye, and respiratory tract irritation
GHS Classification: Flammable Liquid Category 3; Acute Toxicity: Oral, Inhalation, Dermal; Skin and Eye Irritant
Signal Word: Warning
Precautionary Statements: Avoid heat, open flames, sparks—anything that might cause ignition. Long exposure can damage nervous system function and lead to headaches, dizziness, or even unconsciousness in extreme cases. Short-term exposure irritates respiratory passages and can burn eyes and skin.
Chemical Composition: Pure p-Xylene (above 95%), presence of structural isomers like o-xylene and m-xylene in trace amounts, along with the potential for tiny amounts of ethylbenzene.
Percentages: p-Xylene content in technical-grade samples typically runs from 95-99%; impurities make up the balance.
Inhalation: Remove the person to fresh air, keep at rest, support breathing if needed; symptoms like breathing difficulty, coughing, dizziness can hit fast.
Skin Contact: Remove contaminated clothes and wash exposed skin thoroughly with soap and water. PX can really dry out and chap skin—watch for irritation.
Eye Contact: Rinse eyes thoroughly with water for several minutes, lifting eyelids; seek medical attention for persistent irritation.
Ingestion: Avoid making the person vomit; rinse mouth and seek medical help as soon as possible.
Extinguishing Media: Use foam, dry chemical, or carbon dioxide for fire-fighting. Water spray can knock down vapors, but don’t aim direct streams onto the burning liquid.
Special Hazards: Vapors spread fast, slide along surfaces, and can flash back to sources of ignition outside the immediate area. Burning PX throws off carbon monoxide and other toxic gases.
Protective Equipment: Fire-fighters face risks of toxic smoke and run-off—full turnout gear and self-contained breathing apparatus are a must in these conditions.
Personal Protection: Keep unauthorized people away, ventilate area, use protective clothing, gloves, goggles, chemical-resistant boots, and face protection.
Spill Response: Stop leak if safe. Dike large spills to contain, soak up small spills with inert material, and use grounded, spark-proof tools. Ventilation is key—PX vapor sinks and pools in low spots.
Environmental Considerations: Avoid letting PX spill into drains, rivers, or soil. Keep runoff out of storm sewers and waterways.
Safe Handling: Work in ventilated spaces, keep PX containers tightly sealed, and never smoke or use spark-producing equipment nearby. Static sparks happen easily—use proper grounding and bonding.
Storage Conditions: Store in cool, dry, well-ventilated area away from direct heat or sunlight, sources of ignition, oxidizing agents, acids, or halogens. Metallic containers serve best, with regular checking for leaks or corrosion.
Exposure Limits: Occupational exposure limits for airborne PX have been set by authorities like OSHA and ACGIH; permissible values typically fall in the 100 ppm range for an 8-hour TWA.
Ventilation: General ventilation draws vapor away, but localized extraction over open containers or process points brings concentrations down where people breathe.
Personal Protection: Chemical-resistant gloves (like nitrile or neoprene), splash-resistant goggles, long sleeves, and, in case of high vapor, respirators (approved for organic vapors) help cut individual risk.
Hygiene Measures: Wash hands and face after exposure, before eating, drinking, or smoking.
Form: Clear, mobile liquid
Odor: Sweet, aromatic smell—some pick it up around 0.5 ppm
Boiling Point: About 138 °C
Melting Point: 13.2 °C
Flash Point: 27 °C (closed cup)
Vapor Pressure: About 9 mm Hg at 20 °C
Density: About 0.86 g/cm3 at 20 °C
Solubility: Insoluble in water, mixes with organic solvents such as ethanol and ether
Auto-ignition Temperature: 528 °C
Flammable Limits: Lower: about 1.1% vol; Upper: about 7% vol (in air)
Chemical Stability: PX normally sits stable under regular temperature and pressure, but strong heat or spark wakes up reactivity, risking fire or explosion.
Reactivity: Strong oxidizers and acids set off violent reactions, so those chemicals stay far away from PX stores.
Hazardous Decomposition Products: Fires and decomposition throw off carbon monoxide, carbon dioxide, and a soup of irritant fumes.
Polymerization: Not known to polymerize under normal conditions.
Acute Effects: Inhaling PX vapor irritates respiratory tracts, causes headaches, drowsiness, and can even switch to unconsciousness with high exposure. Swallowing can be toxic and lead to lung injury if aspirated. Direct skin contact leads to dryness, redness, and irritation.
Chronic Exposure: Long-term exposure moves into nervous system issues—memory, coordination, and fatigue problems reported among industrial workers. Prolonged skin exposure builds up dermatitis.
Routes of Exposure: Inhalation, skin contact, ingestion; less commonly through eyes.
Carcinogenicity: Major agencies like IARC classify PX as not classifiable regarding carcinogenicity to humans.
Aquatic Toxicity: PX rides as toxic to fish and aquatic invertebrates. Spills into water put stress on ecosystems, hit gill function, and disrupt growth rates in multiple species.
Persistence and Degradation: PX breaks down slowly in soil or water, with microbial action driving most of the degradation process. Rapid air evaporation helps some, but the risk sticks until full breakdown.
Bioaccumulation: Low to moderate risk—PX doesn’t hang in tissues as long as heavier hydrocarbons, but repeated releases keep levels heightened in polluted environments.
Soil Mobility: High volatility lets PX escape soil, but portion sticks with organic matter long enough to pose risk of groundwater migration.
Waste Management: PX disposal calls for strict controls—incineration in a chemical incinerator with afterburner and scrubber ensures full breakdown. Unused and contaminated PX ranks as hazardous waste—special permits and handlers required.
Drain/Sewer Disposal: Direct dumping into sewer, stormwater or natural environments breaks regulations and brings stiff penalties.
Empty Containers: Don’t reuse—even small residues of vapor or liquid can spark fire or harm health. Containers need triple rinsing and professional handling for final disposal.
Transportation Mode: Trucks, trains, vessels carry PX in bulk or drum containers. PX travels under combustible liquid classification.
Proper Shipping Name: Para-xylene
UN Number: 1302
Hazard Class: 3 (Flammable liquids)
Packing Group: III
Transport Precautions: Secure drums or tanks tightly; keep away from heat, sources of ignition, and incompatible materials during transport; spill kits and fire extinguishers must ride with shipments.
Occupational Exposure: Regulated by agencies like OSHA and ACGIH. Permissible exposure limits require posting in workspaces.
Environmental Regulation: Classified as a hazardous air pollutant under US Clean Air Act and is covered by rules for handling, storage, and accidental release prevention.
Chemical Reporting: Inclusion in community right-to-know inventories, reporting required under several international and national chemical safety programs.
Labeling: Any container or shipping drum must carry clear hazard labels, including flammability, toxicity, and required PPE guidance.
REACH/CLP: For regions using European regulations, PX follows standards on classification, labeling, and reporting to authorities.
