Xylene, a group of isomeric aromatic hydrocarbons, is a widely used solvent in various industrial applications. The density of xylene isomers, including o-xylene, m-xylene, and p-xylene, is a critical physical property that plays a crucial role in the design and optimization of these processes. This comprehensive guide delves into the intricacies of xylene density, providing a wealth of technical details and practical insights for physics students and professionals alike.
Understanding Xylene Density: The Fundamentals
Xylene density, measured in kilograms per cubic meter (kg/m³), is a measure of the mass of a given volume of the xylene compound. This property is influenced by factors such as temperature, pressure, and the specific isomeric composition of the xylene mixture. Knowing the precise density of xylene is essential for various applications, including:
- Chemical Processing: Accurate density values are crucial for the design and operation of chemical reactors, distillation columns, and other process equipment used in the production of xylene-based products.
- Solvent Applications: The density of xylene determines its solvency power and compatibility with other materials, making it a crucial parameter in formulating paints, coatings, inks, and adhesives.
- Transportation and Storage: Xylene density is essential for calculating the volume and weight of xylene shipments, ensuring safe and efficient transportation and storage.
- Environmental Monitoring: Xylene density data is used in the assessment and modeling of environmental impacts, such as the fate and transport of xylene in soil and groundwater.
Xylene Isomers and Their Densities
Xylene is a collective term that encompasses three distinct isomers: o-xylene, m-xylene, and p-xylene. Each isomer has its own unique density characteristics, which are essential to understand for various applications.
o-Xylene Density
o-Xylene, also known as ortho-xylene, is the most dense of the three xylene isomers. The density of o-xylene at different temperatures is as follows:
| Temperature (K) | Density (kg/m³) |
|---|---|
| 288.15 (15°C) | 746.76 – 884.09 |
| 303.15 (30°C) | 883.91 |
| 308.15 (35°C) | 79.9 ± 9.42 – 149.750 |
| 313.15 (40°C) | 149.480 – 149.466 |
| 318.15 (45°C) | 149.210 – 149.480 |
m-Xylene Density
m-Xylene, or meta-xylene, has a slightly lower density compared to o-xylene. The density of m-xylene can be found in various sources, and it is essential to consult these references for accurate values at different temperatures.
p-Xylene Density
p-Xylene, or para-xylene, is the least dense of the three xylene isomers. Similar to m-xylene, the density of p-xylene can be found in literature and should be consulted for specific applications.
Factors Influencing Xylene Density
The density of xylene isomers is influenced by several factors, including temperature, pressure, and the specific composition of the xylene mixture. Understanding these factors is crucial for accurately predicting and applying xylene density in various industrial processes.
Temperature Effect on Xylene Density
As the temperature of xylene increases, its density generally decreases. This is due to the thermal expansion of the xylene molecules, which causes them to occupy a larger volume at higher temperatures. The relationship between temperature and xylene density can be expressed using the following formula:
ρ = ρ₀ / (1 + α(T – T₀))
Where:
– ρ is the density of xylene at the desired temperature (kg/m³)
– ρ₀ is the density of xylene at the reference temperature T₀ (kg/m³)
– α is the thermal expansion coefficient of xylene (K⁻¹)
– T is the desired temperature (K)
– T₀ is the reference temperature (K)
By using this formula, you can calculate the density of xylene at any given temperature, provided that you have the reference density and the thermal expansion coefficient.
Pressure Effect on Xylene Density
The density of xylene is also influenced by pressure, although the effect is generally less significant compared to the temperature effect. As the pressure increases, the density of xylene slightly increases due to the compression of the xylene molecules. The relationship between pressure and xylene density can be expressed using the following formula:
ρ = ρ₀ / (1 – (P – P₀) / K)
Where:
– ρ is the density of xylene at the desired pressure (kg/m³)
– ρ₀ is the density of xylene at the reference pressure P₀ (kg/m³)
– P is the desired pressure (Pa)
– P₀ is the reference pressure (Pa)
– K is the bulk modulus of xylene (Pa)
By using this formula, you can calculate the density of xylene at any given pressure, provided that you have the reference density, the reference pressure, and the bulk modulus of xylene.
Xylene Mixture Composition Effect on Density
The density of a xylene mixture is also influenced by the relative proportions of the three xylene isomers (o-xylene, m-xylene, and p-xylene). The overall density of the mixture can be calculated using the following formula:
ρ = Σ(xi × ρi)
Where:
– ρ is the density of the xylene mixture (kg/m³)
– xi is the mole fraction of the i-th xylene isomer
– ρi is the density of the i-th xylene isomer (kg/m³)
By using this formula, you can determine the density of a xylene mixture based on the known densities and mole fractions of the individual xylene isomers.
Practical Applications of Xylene Density
The precise knowledge of xylene density is crucial in various industrial applications, including:
- Chemical Process Design: Xylene density data is used in the design and optimization of chemical reactors, distillation columns, and other process equipment to ensure efficient and safe operation.
- Solvent Formulations: The density of xylene is a key parameter in the development of paints, coatings, inks, and adhesives, as it affects the solvency, viscosity, and compatibility of the formulations.
- Transportation and Storage: Xylene density is used to calculate the volume and weight of xylene shipments, enabling efficient and safe transportation and storage.
- Environmental Monitoring: Xylene density data is essential for modeling the fate and transport of xylene in the environment, such as in soil and groundwater contamination studies.
Numerical Examples and Calculations
To illustrate the practical application of xylene density, let’s consider the following examples:
Example 1: Calculating the Density of a Xylene Mixture
Suppose a xylene mixture contains the following mole fractions of the three isomers:
– o-Xylene: 0.4
– m-Xylene: 0.3
– p-Xylene: 0.3
Given the following densities of the individual isomers at 25°C:
– o-Xylene: 880 kg/m³
– m-Xylene: 860 kg/m³
– p-Xylene: 856 kg/m³
Calculate the density of the xylene mixture at 25°C.
Solution:
Using the formula for the density of a xylene mixture:
ρ = Σ(xi × ρi)
ρ = (0.4 × 880) + (0.3 × 860) + (0.3 × 856)
ρ = 352 + 258 + 256.8
ρ = 866.8 kg/m³
Therefore, the density of the xylene mixture at 25°C is 866.8 kg/m³.
Example 2: Calculating the Density of o-Xylene at a Different Temperature
Suppose the density of o-xylene at 15°C is 884.09 kg/m³. Calculate the density of o-xylene at 40°C, given that the thermal expansion coefficient of o-xylene is 1.05 × 10⁻³ K⁻¹.
Solution:
Using the formula for the temperature effect on xylene density:
ρ = ρ₀ / (1 + α(T – T₀))
ρ = 884.09 / (1 + 1.05 × 10⁻³ × (313.15 – 288.15))
ρ = 884.09 / (1 + 1.05 × 10⁻³ × 25)
ρ = 884.09 / 1.02625
ρ = 861.12 kg/m³
Therefore, the density of o-xylene at 40°C is 861.12 kg/m³.
These examples demonstrate how to apply the formulas and principles discussed in this guide to calculate the density of xylene isomers and mixtures under different conditions.
Conclusion
The density of xylene isomers is a critical physical property that plays a crucial role in various industrial applications, from chemical processing to environmental monitoring. This comprehensive guide has provided a detailed exploration of the fundamentals of xylene density, including the characteristics of individual isomers, the factors influencing density, and practical applications of this knowledge.
By understanding the intricacies of xylene density, physics students and professionals can optimize industrial processes, develop effective solvent formulations, and ensure safe transportation and storage of xylene-based products. The numerical examples and calculations presented in this guide further illustrate the practical application of xylene density data, empowering readers to confidently tackle real-world challenges in their respective fields.
References
- TOXICOLOGICAL PROFILE FOR XYLENE, Agency for Toxic Substances and Disease Registry (ATSDR)
- Chemical Properties of o-Xylene (CAS 95-47-6), Cheméo
- A review of environmental and occupational exposure to xylene and its health effects, National Center for Biotechnology Information (NCBI)
- Handbook of Chemistry and Physics, CRC Press
- Perry’s Chemical Engineers’ Handbook, McGraw-Hill Education
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