Quick Answer
The density of p-xylene (paraxylene, CAS 106-42-3) is approximately 0.861 g/cm³ at 20°C (68°F) and 0.857 g/cm³ at 25°C (77°F) under atmospheric pressure. Because liquids expand when heated, the density of p-xylene gradually decreases as temperature increases.
This property is important for chemical storage, transportation, tank volume calculations, process design, and quality control in the petrochemical industry.
| Property | Value |
|---|---|
| Chemical Name | p-Xylene (Paraxylene) |
| CAS Number | 106-42-3 |
| Molecular Formula | C₈H₁₀ |
| Molecular Weight | 106.17 g/mol |
| Density (20°C) | 0.861 g/cm³ |
| Density (25°C) | 0.857 g/cm³ |
| Density (kg/m³, 20°C) | 861 kg/m³ |
| Physical State | Colorless Liquid |
| Boiling Point | 138.35°C |
| Melting Point | 13.2°C |
| Flash Point | 25°C (Closed Cup) |
What Is p-Xylene?
P-Xylene (also known as paraxylene) is one of the three xylene isomers and an important aromatic hydrocarbon produced during petroleum refining and catalytic reforming. It is the primary feedstock for manufacturing Purified Terephthalic Acid (PTA), which is subsequently converted into Polyethylene Terephthalate (PET) for polyester fibers, plastic bottles, films, and engineering plastics.
Today, more than 95% of global p-xylene production is consumed in the PTA/PET value chain, making it one of the world's most important petrochemical intermediates.
Density of p-Xylene at Different Temperatures
Like most organic liquids, the density of p-xylene decreases as temperature increases because thermal expansion causes molecules to occupy a larger volume.
The following values are commonly used for engineering calculations and laboratory reference.
| Temperature | Density (g/cm³) | Density (kg/m³) |
|---|---|---|
| 0°C | 0.878 | 878 |
| 10°C | 0.869 | 869 |
| 20°C | 0.861 | 861 |
| 25°C | 0.857 | 857 |
| 30°C | 0.853 | 853 |
| 40°C | 0.845 | 845 |
Note: Actual density values may vary slightly depending on measurement methods and purity. Always refer to the product's Certificate of Analysis (COA) or Safety Data Sheet (SDS) for precise specifications.
Why Does the Density of p-Xylene Change with Temperature?
The density of p-xylene decreases as temperature rises because its molecules move farther apart due to thermal expansion. While the mass remains constant, the liquid occupies a larger volume, resulting in a lower density.
This behavior is common for aromatic hydrocarbons and is an important consideration in:
- Storage tank volume calculations
- Pipeline flow measurements
- Pump sizing
- Bulk chemical transportation
- Industrial process engineering
For accurate inventory management and custody transfer, density should always be referenced at a specified temperature, typically 20°C or 25°C.
Is p-Xylene Heavier Than Water?
No.
P-xylene has a density of approximately 0.861 g/cm³, which is significantly lower than the density of water (1.000 g/cm³ at 4°C). Therefore, p-xylene floats on water if the two liquids are mixed.
Density Comparison with Other Xylene Isomers
Although o-xylene, m-xylene, and p-xylene have the same molecular formula (C₈H₁₀), their molecular structures result in slightly different physical properties.
| Compound | Density (20°C) |
|---|---|
| o-Xylene | 0.880 g/cm³ |
| m-Xylene | 0.864 g/cm³ |
| p-Xylene | 0.861 g/cm³ |
These differences influence separation processes, solvent applications, and industrial handling.
Industrial Applications of p-Xylene
Production of Purified Terephthalic Acid (PTA)
The largest application of p-xylene is the oxidation process used to manufacture Purified Terephthalic Acid (PTA).
PTA is an essential intermediate for producing Polyethylene Terephthalate (PET).
PET is widely used for:
- Polyester fibers
- Beverage bottles
- Food packaging
- Packaging films
- Engineering plastics
More than 95% of global p-xylene demand originates from this production chain.
Polyester Manufacturing
Through PTA, p-xylene supports the production of numerous polyester products, including:
- Textile fibers
- Industrial yarns
- Tire cord
- PET resin
- Packaging films
- Engineering plastics
Production of Benzoic Acid
P-xylene is also used as a feedstock for manufacturing benzoic acid, an important intermediate in chemical synthesis.
Benzoic acid is widely applied in:
- Food preservatives
- Pharmaceutical formulations
- Plastic additives
- Chemical intermediates
Intermediate for p-Tolualdehyde
P-xylene is an important raw material for producing p-tolualdehyde, which is further used in:
- Agrochemicals
- Pharmaceutical intermediates
- Fragrances
- Dyes and pigments
- Specialty chemicals
Storage and Handling Considerations
Because p-xylene is a flammable organic solvent, it should be stored in tightly closed containers in a cool, dry, and well-ventilated area away from heat, sparks, and open flames.
Recommended storage conditions include:
- Store below 30°C whenever possible
- Keep containers tightly sealed
- Avoid strong oxidizing agents
- Use explosion-proof equipment
- Follow applicable local safety regulations
Frequently Asked Questions
What is the density of p-xylene at 20°C?
The density of p-xylene at 20°C is approximately 0.861 g/cm³ (861 kg/m³).
What is the density of p-xylene at 25°C?
At 25°C, the density decreases slightly to approximately 0.857 g/cm³ because of thermal expansion.
Why does p-xylene density decrease as temperature increases?
As temperature rises, molecules move farther apart, increasing volume while mass remains unchanged. Consequently, the density decreases.
Is p-xylene soluble in water?
No. P-xylene has very low water solubility and is considered practically insoluble in water.
Where is p-xylene mainly used?
P-xylene is primarily used to produce Purified Terephthalic Acid (PTA), which is further converted into Polyethylene Terephthalate (PET) for polyester fibers, beverage bottles, films, and engineering plastics.
