Mixed xylene, also known as mixed xylenes or xylene mixed isomers, is a commercial C8 aromatic hydrocarbon mixture widely used as an industrial solvent and chemical raw material. Its physical properties, including density, boiling point, flash point, molecular weight, specific gravity, viscosity, vapor pressure, and water solubility, are important for understanding its performance in different applications.
Because mixed xylene is a mixture rather than a single pure compound, its physical properties can vary slightly depending on composition, grade, temperature, and manufacturing process.
This guide explains the key physical properties of mixed xylene and how they affect its behavior and applications.
1. What Is Mixed Xylene?
Mixed xylene is a mixture of C8 aromatic hydrocarbons with CAS No. 1330-20-7 and the molecular formula C₈H₁₀.
Commercial mixed xylene generally contains three xylene isomers:
- m-Xylene
- p-Xylene
- o-Xylene
It may also contain ethylbenzene and small amounts of other aromatic or non-aromatic components, depending on the production source and specification.
Unlike pure xylene isomers, mixed xylene does not have one fixed set of physical properties. Its composition can influence its boiling range, density, flash point, evaporation behavior, and other characteristics.
2. Mixed Xylene Molecular Weight and Chemical Formula
The molecular weight of mixed xylene is approximately 106.16 g/mol, and its molecular formula is C₈H₁₀.
The three xylene isomers and ethylbenzene have the same molecular formula and molecular weight because they are structural isomers.
| Property | Typical Value |
|---|---|
| Chemical formula | C₈H₁₀ |
| Molecular weight | 106.16 g/mol |
| CAS No. | 1330-20-7 |
Molecular weight is a useful basic property for chemical calculations, but it does not indicate the exact composition of a commercial mixed xylene product.
3. Mixed Xylene Density
Mixed xylene density is typically around 0.86–0.87 g/cm³, although the exact value depends on temperature and composition.
For example, reference data may report approximately 0.864 g/cm³ at 20 °C, while commercial specifications can show values around 0.870 g/cm³ at 15 °C.
| Property | Typical Reference |
|---|---|
| Density at 20 °C | ~0.864 g/cm³ |
| Density at 15 °C | ~0.870 g/cm³ |
| General range | ~0.86–0.87 g/cm³ |
The difference between density values at different temperatures is expected because liquid density changes with temperature.
Why Does Mixed Xylene Density Matter?
Density affects:
- Mass-to-volume conversion
- Solvent blending
- Tank and container calculations
- Formulation calculations
- Liquid handling
When comparing density values, the measurement temperature should always be considered.
4. Mixed Xylene Specific Gravity
Mixed xylene specific gravity is generally around 0.86–0.87.
Specific gravity is a dimensionless ratio comparing the density of a substance with the density of water under a specified reference condition.
| Property | Typical Value |
|---|---|
| Density | ~0.86–0.87 g/cm³ |
| Specific gravity | ~0.86–0.87 |
Because mixed xylene has a specific gravity below 1, it is less dense than water.
Although density and specific gravity are closely related, they should not be treated as identical measurements because density has units while specific gravity is dimensionless.
5. What Is the Boiling Point of Mixed Xylene?
One of the most important physical properties of mixed xylene is its boiling behavior.
Unlike a pure compound, mixed xylene does not have one single boiling point. Because it contains several components, it is normally described by a boiling range or distillation range.
Commercial reference values are commonly around 136–145 °C, depending on product composition and grade.
| Property | Typical Reference |
|---|---|
| Boiling range | ~136–145 °C |
| Initial boiling point | ~136 °C |
| Upper boiling range | ~145 °C |
The boiling behavior is influenced by the proportions of ethylbenzene and the different xylene isomers.
Approximate boiling points of the major components are:
| Component | Approx. Boiling Point |
|---|---|
| Ethylbenzene | 136 °C |
| p-Xylene | 138 °C |
| m-Xylene | 139 °C |
| o-Xylene | 144 °C |
This relatively narrow distillation range contributes to the use of mixed xylene as a medium-evaporation aromatic solvent.
6. Mixed Xylene Boiling Point and Evaporation
The mixed xylene boiling point is closely related to its evaporation behavior.
A higher-boiling solvent generally evaporates more slowly than highly volatile solvents such as acetone or ethyl acetate.
Mixed xylene's relatively moderate boiling range can provide useful evaporation characteristics in:
- Paints and coatings
- Printing inks
- Adhesives
- Rubber processing
- Industrial cleaning
- Solvent formulations
The actual evaporation behavior depends not only on boiling range but also on temperature, formulation, airflow, and the composition of the solvent mixture.
7. Mixed Xylene Flash Point
The mixed xylene flash point is generally in the low-to-mid 20 °C range for many commercial grades.
Reference values commonly fall around 23–27 °C, although the exact value can vary according to composition and test method.
| Property | Typical Reference |
|---|---|
| Flash point | ~23–27 °C |
| Physical state at room temperature | Liquid |
| Flammability | Flammable |
The flash point is the lowest temperature at which a liquid can produce enough vapor to form an ignitable mixture with air under specified test conditions.
Why Is Flash Point Important?
Flash point provides information about the fire and ignition characteristics of a solvent.
For mixed xylene, the relatively low flash point means that appropriate ventilation, ignition-source control, and safe handling practices are important during industrial use.
The exact flash point should be determined from the applicable specification or SDS for the particular product.
8. Mixed Xylene Viscosity
Mixed xylene viscosity is relatively low compared with many industrial liquids.
A commercial reference may report a kinematic viscosity of less than approximately 0.9 mm²/s at 20 °C, although the exact value depends on grade and measurement conditions.
Low viscosity allows mixed xylene to flow easily and mix efficiently with many organic materials.
This property is useful in applications such as:
- Coatings
- Printing inks
- Cleaning formulations
- Solvent blending
- Chemical processing
Viscosity is temperature-dependent, so a viscosity value should always be considered together with its measurement temperature.
9. Mixed Xylene Vapor Pressure
Vapor pressure describes how readily a liquid forms vapor at a given temperature.
Commercial xylene reference data commonly show vapor pressure in the approximate range of 0.8–1.2 kPa at 20 °C, depending on composition and grade.
Vapor pressure affects:
- Evaporation rate
- VOC emissions
- Solvent drying
- Storage behavior
- Ventilation requirements
As temperature increases, the vapor pressure of mixed xylene also increases, resulting in faster vapor formation.
10. Mixed Xylene Solubility in Water
Mixed xylene is only slightly soluble in water.
A commonly cited reference value is approximately 106 mg/L at 25 °C, although reported solubility can vary depending on composition and test conditions.
Its low water solubility is related to its hydrophobic aromatic structure.
This property makes mixed xylene suitable for applications requiring an organic aromatic solvent with limited water miscibility.
Mixed xylene can dissolve or mix readily with many organic solvents, while its interaction with water is comparatively limited.
11. Mixed Xylene Melting Point
Mixed xylene does not have one universal melting point because it is a mixture of several components.
The individual xylene isomers have significantly different melting points:
| Component | Approx. Melting Point |
|---|---|
| m-Xylene | −47.8 °C |
| o-Xylene | −25.2 °C |
| p-Xylene | 13.2 °C |
The relatively high melting point of p-xylene compared with the other isomers illustrates why the composition of mixed xylene can influence its low-temperature behavior.
For commercial mixed xylene, the freezing or melting behavior should therefore be considered product-specific rather than represented by one universal number.
12. Mixed Xylene Refractive Index
The mixed xylene refractive index can be used as a laboratory or quality-control parameter.
Because mixed xylene contains multiple components, its refractive index can vary slightly with composition and temperature.
Refractive index can be useful for:
- Laboratory identification
- Batch comparison
- Quality control
- Solvent composition monitoring
However, it is generally less important than density, distillation range, and flash point for understanding the basic industrial behavior of mixed xylene.
13. Summary of Mixed Xylene Physical Properties
The following table summarizes the main physical properties of mixed xylene:
| Property | Typical Reference Value |
|---|---|
| Chemical formula | C₈H₁₀ |
| Molecular weight | 106.16 g/mol |
| CAS No. | 1330-20-7 |
| Density | ~0.86–0.87 g/cm³ |
| Specific gravity | ~0.86–0.87 |
| Boiling range | ~136–145 °C |
| Flash point | ~23–27 °C |
| Kinematic viscosity | <~0.9 mm²/s at 20 °C* |
| Vapor pressure | ~0.8–1.2 kPa at 20 °C* |
| Water solubility | ~106 mg/L at 25 °C* |
| Appearance | Colorless liquid |
*Reference values can vary according to composition, temperature, test method, and commercial grade.
14. Why Do Mixed Xylene Physical Properties Vary?
Unlike pure chemical compounds, commercial mixed xylene is a variable-composition mixture.
Its physical properties can therefore be affected by:
Composition
The relative amounts of m-xylene, p-xylene, o-xylene, ethylbenzene, and other components can change the overall physical properties.
Temperature
Density, vapor pressure, viscosity, and other properties are temperature-dependent.
Product Grade
Different commercial grades can have different specifications and distillation characteristics.
Manufacturing Source
The production process and feedstock can influence the composition of the final xylene mixture.
For this reason, published reference values should be treated as typical ranges rather than universal specifications.
15. Mixed Xylene Applications Related to Its Physical Properties
The physical properties of mixed xylene help explain its widespread use as an industrial solvent.
Paints and Coatings
Its aromatic solvency and moderate evaporation behavior make mixed xylene useful in various paints, coatings, primers, and industrial formulations.
Printing Inks
Its solvency and evaporation characteristics can support selected printing ink formulations.
Adhesives and Sealants
Mixed xylene can dissolve or dilute certain resins and polymer systems used in adhesives and sealants.
Rubber and Chemical Processing
Its organic solvency and low viscosity make it useful in selected rubber and chemical-processing applications.
Industrial Cleaning
Mixed xylene can dissolve many oils, resins, coatings, and other organic residues, making it useful for certain industrial cleaning applications.
The suitability of mixed xylene depends on the specific formulation and required solvent properties.
16. Mixed Xylene vs. Individual Xylene Isomers
Mixed xylene should be distinguished from individual xylene isomers.
| Product | Main Characteristic |
|---|---|
| Mixed Xylene | Mixture of several C8 aromatic components |
| m-Xylene | Pure xylene isomer |
| p-Xylene | Pure xylene isomer |
| o-Xylene | Pure xylene isomer |
The individual isomers have different boiling points, melting points, and other physical properties.
For example, p-xylene has a substantially higher melting point than m-xylene, while o-xylene has a higher boiling point than the other two xylene isomers.
Therefore, physical-property data for pure xylene isomers should not automatically be used as specifications for mixed xylene.
17. Frequently Asked Questions About Mixed Xylene Physical Properties
What is the boiling point of mixed xylene?
Mixed xylene is normally described by a boiling or distillation range rather than one fixed boiling point. Commercial reference values are commonly around 136–145 °C, depending on composition and grade.
What is the density of mixed xylene?
Mixed xylene typically has a density of approximately 0.86–0.87 g/cm³. The exact value depends on temperature and composition.
What is mixed xylene specific gravity?
Mixed xylene generally has a specific gravity of approximately 0.86–0.87.
What is the flash point of mixed xylene?
The flash point is commonly in the 23–27 °C range for commercial reference grades, although the exact value depends on composition and test method.
What is the molecular weight of mixed xylene?
The molecular weight of mixed xylene is approximately 106.16 g/mol, with the molecular formula C₈H₁₀.
What is mixed xylene viscosity?
Mixed xylene has relatively low viscosity. A commercial reference value can be below approximately 0.9 mm²/s at 20 °C, depending on grade and measurement conditions.
Is mixed xylene soluble in water?
Mixed xylene has low water solubility. A commonly cited reference value is approximately 106 mg/L at 25 °C, although the exact value varies with composition.
Does mixed xylene have a fixed melting point?
No. Because mixed xylene is a mixture, it does not have one universal melting point. Its low-temperature behavior depends on the proportions of its components.
Why do mixed xylene properties vary between suppliers?
Commercial mixed xylene can have different compositions and specifications. As a result, properties such as density, boiling range, flash point, viscosity, and vapor pressure can vary slightly between products.
18. Conclusion
The key physical properties of mixed xylene include its density, molecular weight, boiling range, flash point, specific gravity, viscosity, vapor pressure, water solubility, melting behavior, and refractive index.
Among these properties, density, boiling range, flash point, and evaporation behavior are particularly useful for understanding how mixed xylene performs as an industrial aromatic solvent.
Because mixed xylene is a variable-composition mixture rather than a pure compound, its physical properties should generally be expressed as typical values or ranges rather than universal constants.
Understanding these properties helps users select the appropriate mixed xylene grade for applications such as paints and coatings, printing inks, adhesives, rubber processing, chemical manufacturing, and industrial cleaning.
