Description

History

Xylol was first isolated in 1850 by Auguste Cahours, a French chemist, from wood tar. The name “Xylol” comes from the Greek word “Xylol,” meaning wood, reflecting its source. Initially derived from coal tar, xylene’s significance grew with the development of petroleum refining and the petrochemical industry. By the mid-20th century, xylene became a critical industrial solvent and chemical intermediate, especially as the demand for synthetic fibers, plastics, and other petrochemical products increased.

Properties

1. Physical Properties

• Appearance: dimethyl benzene is a clear, colorless liquid with an aromatic odor that resembles sweet or paint-like smells. Due to this characteristic odor, it is easily recognizable, even in small concentrations.
• Density: Xylene has a density of around 0.86 g/cm³, making it less dense than water. This property enables dimethyl benzene to float when mixed with water, making separation easier in certain industrial processes.
• Boiling Point: The boiling points of dimethyl benzene isomers vary slightly. Ortho-xylene boils at approximately 144°C (291°F), meta-dimethyl benzene at around 139°C (282°F), and para-xylene at about 138°C (280°F). These boiling points are relatively high, contributing to dimethyl benzene’s effectiveness as a solvent in applications requiring slow evaporation.
• Melting Point: dimethyl benzene has low melting points, with o-xylene melting at -25°C (-13°F), m-xylene at -47.9°C (-54.2°F), and p-xylene at 13.3°C (55.9°F). The melting point differences affect how each isomer behaves under varying temperature conditions.
• Solubility: dimethyl benzene is practically insoluble in water, with a solubility of about 0.2 g/L at 25°C, but it is highly soluble in most organic solvents such as ethanol, ether, acetone, and benzene. This makes it an ideal solvent for dissolving various organic compounds.
• Viscosity and Volatility: Xylene has a moderate viscosity, making it flow easily. Its moderate volatility means it evaporates slower than lighter solvents like acetone or ethanol, providing more extended working times in applications like painting and coating.

2. Chemical Properties

• Molecular Formula and Weight: The chemical formula for xylene is C₆H₄(CH₃)₂, with a molecular weight of approximately 106.16 g/mol. The structure consists of a benzene ring with two methyl groups attached, and the position of these methyl groups determines the specific isomer (ortho, meta, or para).
• Flammability: Xylene is highly flammable, with a flash point ranging between 25°C to 30°C (77°F to 86°F), depending on the isomer. This means it can easily ignite when exposed to an open flame or spark. Its flammable nature requires careful handling and storage, especially in industrial settings.
• Reactivity: dimethyl benzene is relatively stable under normal conditions but can react with strong oxidizing agents such as nitric acid, sulfuric acid, or chlorine, leading to potentially hazardous situations. It can undergo substitution reactions typical of aromatic compounds, such as halogenation, nitration, and sulfonation, where one of the hydrogen atoms on the benzene ring is replaced by another atom or group.
• Hydrophobic Nature: As a non-polar compound, xylene is hydrophobic, meaning it does not mix with water. This characteristic allows xylene to effectively dissolve non-polar substances such as oils, fats, and resins, making it an excellent solvent in various industrial applications.

Various Grades

Ortho-Xylene (o-Xylene)

o-dimethyl benzene, among the commercially important dimethyl benzene isomers, exhibits a molecular structure in which two methyl groups are fixed on adjacent carbon atoms of a benzene ring. Due to this unique molecular structure, properties that make it suitable for specific applications in industry are conferred on the molecule. The most significant use of ortho-xylene involves the manufacture of phthalic anhydride, which is a very important intermediate for producing plasticizers, unsaturated polyester resins, and alkyd resins. Application fields of phthalic anhydride also vary from flexible PVC to dyes and pigments. Paints, coatings, and plastics downstream industries keep the demand for o-dimethyl benzene high since it serves as a feedstock in the manufacture of phthalic anhydride.

Meta-Xylene (m-Xylene)

The m-xylene molecule is one such isomer in which two methyl groups are attached to the benzene ring, separated by one carbon atom. This positioning affects its chemical reactivity and is useful in the preparation of isophthalic acid. It is an important chemical in the preparations of alkyd and polyester resins, used in a wide variety of coating and adhesive applications. The resins made from isophthalic acid show higher durability and flexibility with great chemical resistance for high-performance paints, coatings, and sealants. M-xylene also acts as a solvent in the rubber, leather, and printing industries due to its excellent dissolving properties besides being an active feedstock in resin production.

Para-Xylene (p-Xylene)

Among the dimethyl benzene isomers, para-xylene, or p-xylene, is perhaps the most important commercially. The two methyl groups of p-xylene lie opposite to each other on the benzene ring. This confers structural and property differences that enable p-xylene to act as the principal feedstock for both purified terephthalic acid (PTA) and dimethyl terephthalate (DMT). These are simple feedstocks in the manufacture of polyethylene terephthalate, a versatile polymer used in the manufacture of polyester fibers, plastic bottles, packaging materials, and varieties of films. The growing demand for PET within the packaging, textile, and beverage industries makes p-xylene vital feedstock, thus continuing to spur growth within the industries that depend on polyester-based products.

Mixed Xylene

Mixed xylene is a mixture of all three xylene isomers including o-xylene, m-xylene, and p-xylene along with ethylbenzene. The resultant mixture possesses solvent properties that are useful for a wide range of industrial applications. It finds extensive use in the paint and coating industry as a solvent due to its ability to dissolve a wide variety of resin types and its excellent drying properties. Mixed xylene is used as a solvent in the rubber industry in the processing of rubber and the adhesives and sealants industry as a diluent for adjustment of viscosity. In gasoline, mixed xylene is added as a blending agent to increase the octane level, thus contributing toward fuel efficiency.

High Purity Xylene

High-purity xylene, frequently with a higher content of one isomer, usually para-xylene, is used in industries in which the highest purity of the chemical is demanded. Consequently, high-purity p-xylene remains indispensable to the polyester industry in the manufacture of PTA and DMT for the production of PET of the best quality. Demand for high-purity xylene is related, therefore, to industries that want products of high precision, as are required for the manufacture of synthetic fibers and materials of package and high-grade plastics.

In all, different grades of xylene are applied to a wide variety of areas. Ortho-xylene is used in the production of phthalic anhydride, which is mainly utilized in plastics and coatings. Meta-xylene is quite important in resin production, especially in high-performance coatings. Because para-xylene can be applied in the production of PET, it therefore becomes indispensable in textiles and packaging, while mixed xylene is a versatile solvent. High-purity xylene addresses those industries where quality and consistency are paramount. This understanding of the different grades assists in ascertaining the right type of xylene for many industrial applications.

Application and uses

1. Paints, Coatings, and Inks Industry

Xylene generally acts as a solvent in paint and coating industries due to its ability to dissolve resins, binders, and pigments very efficiently. It can assure uniform consistency of paint or coating-smoothness and resistance. Xylene’s slow evaporation rate ensures that paint does not dry too quickly, thereby avoiding imperfections like brush marks or irregular layers. Xylene is considered suitable for high-quality applications such as automotive paints, marine coatings, and industrial protective coatings where flawless finishing is required. Xylene is used as a solvent in printing applications, particularly in ink formulation that needs to dry very quickly onto the surfaces of plastics, metals, or glass to produce bright and lasting prints.

2. Adhesives and Sealants Production

Xylene finds its applications in the adhesive and sealant industries. Its ability to dissolve a wide range of polymers, resins, and elastomers turns xylene indispensable in the production of many kinds of adhesives, including rubber-based, contact, and pressure-sensitive adhesives. Examples include adhesives with xylene used in construction and automotive industries that have strong and durable bonds and can be used for bonding metals, plastics, and other materials. It adjusts the viscosity in sealants and improves the flow properties of the sealers so that the application can take place properly; it promotes the adhesion of the sealant to appropriate surfaces. This is especially helpful where waterproofing or tight seals are required, for example, in windows, doors, and structural joints.

3. Rubber Industry Applications

Xylene is used as a solvent in the rubber industry, especially in large amounts in both natural and synthetic rubber processing. In general, xylene plays a vital role in the production process of rubber products by breaking down raw rubber to achieve good moldability, shape, and extrusion into any desired shapes. This process is indispensable in the manufacture of tires, hoses, belts, gaskets, and rubberized coatings. Xylene also acts as a dispersing agent for rubber chemicals, allowing them to distribute uniformly within the compound. This provides improved characteristics such as elasticity, resistance to tensile strength, abrasion resistance, and heat resistance, all of which are crucial in terms of the durability and performance of a rubber product.

4. Leather Industry Utilization

Xylene is used in the leather industry for degreasing in the course of preparation and finishing hides. It simply dissolves oils, fats, and other contaminants on the surface of leather, preparing them for other processes. Xylene helps to apply dyes, finishes, and coatings to give a uniform color penetration and even luster. That explains the importance, especially in high-quality leather item production, like shoes, bags, jackets, and upholstery, where aspects such as appearance and texture are crucial.

5. Chemical Manufacturing and Intermediates

Xylene is a basic feedstock for the production of many key chemicals, and among these, the most valuable commercially is para-xylene. The major uses of para-xylene are in the manufacture of PTA and DMT, both of which are key building blocks for the production of PET. Major uses of PET include the production of polyester fibers for use in textiles, plastic bottles, food packaging, and films. This makes xylene a principal feedstock for the manufacture of a wide assortment of polyester products, from apparel and fabrics to beverage bottles. Ortho-xylene is mainly used in the production of phthalic anhydride, which is a feedstock for plasticizers used to provide flexibility to PVC products and in the production of dyes, pigments, and some alkyd resins.

6. Fuel Additive and Blending Agent in Gasoline

Another critical application of xylene involves the addition into fuel, particularly in the enhancement of gasoline quality. Mixing xylene into gasoline increases its octane rating, which is essentially a way of describing a fuel’s resistance to knocking or pinging during combustion. This improves engine performance and overall fuel economy because such resistance to knocking provides better efficiency. Due to the high energy content of xylene, its inclusion as a reformulated gasoline additive ensures excellent performance and contributes toward a more regulated requirement for cleaner-burning fuels. It is also applied as internal fuel for small engines, like those in chainsaws, outboard motors, and lawnmowers, where only high-octane fuels could serve best for such machinery.

7. Cleaning Agent and Industrial Degreaser

Xylene’s strong solvency makes it effective in cleaning and degreasing heavy grease, oils, wax, and adhesives from machineries, equipment, and parts across different industries. Applications in the cleaning of engines, carburetors, and transmission parts in automotive industries ensure that any residues are removed from components that may hamper their performance. It is also used in paint shops to clean printing rollers, tools, and brushes so the paint does not dry or the ink accumulates. This cleaning aspect makes xylene important and helpful in maintaining equipment efficiency and longevity.

8. Laboratory and Medical Applications

Xylene has many other important uses at the laboratory level during tissue preparation for histology and pathology examination by microscopy. During the processing of tissue, xylene is used to remove the alcohol and dissolve the paraffin wax, making tissues transparent-a process known as clearing that good staining will be enabled and the specimen will also be seen under the microscope. This is important in the diagnosis of diseases, including cancers, where it enables pathologists to investigate the morphology of tissues and cells. Xylene is also used as a solvent in the preparation of many chemical reagents and solutions and thus finds wide applications in many laboratory procedures.

9. Resin and Plastic Production

Xylene is highly used in the manufacture of resins, such as polyester, alkyd, and epoxy resins used in paints, varnishes, and coatings. The polyester resins made with xylene-based intermediates have been finding extensive use in reinforced plastics, laminates, and fiberglass applications for industries like automobiles and marine. Xylene-modified alkyd resins find application in quality paints and enamels which can boast of good gloss, hardness, and weather resistance. For resin production, xylene is used; it is important in quality, durability, and performance for the final products.

Packing

Bulk Transport:

For large industrial operations, xylene is transported in tank trucks, railcars, or ISO containers.

Drums:

Commonly available in 55-gallon steel drums, which are suitable for medium-scale usage in various industries.

Cans:

Smaller quantities are packed in 1-gallon or 5-gallon metal cans, making them manageable for smaller businesses and laboratories.

Bottles:

Laboratory-grade xylene is often packed in glass or high-density polyethylene (HDPE) bottles, available in various sizes to meet the needs of scientific research and medical applications.

 

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