[Chemical Knowledge]：The nature and use of mixed xylene, upstream and downstream raw materials, storage methods, and the harm of mixed xylene to human body.

Properties of Mixed Xylene

Mixed xylene (Mixed Xylene) is an aromatic hydrocarbon, mainly composed of o-xylene (o-Xylene), m-xylene (m-Xylene) and p-xylene (p-Xylene) and ethylbenzene. Its physical properties include colorless transparent liquid, with aromatic odor, volatile and insoluble in water, but soluble in most organic solvents. Mixed xylenes have a density of about 0.86g/cm³, a boiling point range of 137°C to 143°C, and a flash point of about 27°C. In terms of chemical properties, mixed xylene has the typical reactivity of aromatic hydrocarbons, and can undergo substitution reactions and oxidation reactions with halogen, nitric acid, sulfuric acid, etc.

Use of mixed xylene

mixed xylene is widely used in chemical production and is an important intermediate for many chemical products. Its main uses include:

1. solvent mixed xylene is an excellent solvent, which is widely used in the preparation of paints, coatings, inks and adhesives. Its good solubility enables it to dissolve a variety of organic substances, enhancing the uniformity and stability of the product.
2. chemical raw materials mixed xylene is the raw material for the production of para-xylene (p-Xylene) and ortho-xylene (o-Xylene). Paraxylene is a key feedstock for the production of terephthalic acid (PTA), an important material for the manufacture of polyester fibers and plastics. Ortho-xylene is used to produce phthalic anhydride, which is an important component of plastic plasticizers.
3. fuel additive as a fuel additive with high octane number, mixed xylene can improve the antiknock and combustion efficiency of gasoline.

Upstream feed of mixed xylene

the production of mixed xylenes depends on the petroleum and petrochemical industry, and its upstream raw materials mainly include crude oil and toluene. The main components of mixed xylenes can be obtained by catalytic reforming and catalytic cracking in petroleum refining processes. The specific process includes:

1. catalytic reforming: The naphtha (mainly C7-C8 hydrocarbons) in the reformer is reformed under the action of a catalyst to produce reformed gasoline rich in aromatics, including a large amount of mixed xylene.
2. catalytic cracking: The heavy oil is cracked by the cracking unit to produce lighter hydrocarbons, which contain a certain amount of mixed xylene components.

Downstream products of mixed xylene

there are a wide variety of downstream products for mixed xylenes, including:

1. terephthalic acid (PTA) this is an important raw material for the production of polyethylene terephthalate (PET). PET is widely used in the manufacture of plastic bottles, films and synthetic fibers.
2. Phthalic anhydride (PA): Mainly used in the production of plastic plasticizers, alkyd resins and unsaturated polyester resins.
3. Solvents and Thinners: Used as a solvent and thinner in industries such as coatings, inks and adhesives to improve product performance.

Storage Method of Mixed Xylene

due to the volatile and flammable nature of mixed xylenes, their storage requires special attention to safety precautions:

1. container Selection: Special steel or aluminum storage tanks should be used, these materials have good corrosion resistance to mixed xylene. Tanks shall be provided with sealing covers to prevent volatilization and leakage.
2. Environmental requirements: The storage area should be well ventilated, away from fire sources, heat sources and oxidants. At the same time, should be equipped with fire prevention facilities, such as fire extinguishers and fire isolation belt.
3. Temperature control: The storage temperature should be kept within the appropriate range to avoid excessive temperature leading to increased volatilization of mixed xylene, and at the same time to prevent crystallization or solidification caused by low temperature.

Safety and environmental protection

it is necessary to pay attention to the potential safety and environmental protection problems during the use and storage of mixed xylene. Inhalation of high concentrations of mixed xylene vapor may cause harm to human health, such as headache, dizziness, nausea and other symptoms. Long-term exposure may lead to chronic toxicity that damages the nervous system, liver, and kidneys. Therefore, personal protective measures should be taken during operation, such as wearing gas masks and gloves, and ensuring that the workplace is well ventilated.

From an environmental point of view, the volatile organic compounds (VOC) emissions of mixed xylene have a negative impact on air quality, and their emissions should be minimized. The disposal of waste shall comply with relevant laws and regulations to avoid environmental pollution.

Conclusion

as an important chemical raw material and solvent, mixed xylene has broad application prospects. Its production depends on the petrochemical process, the upstream and downstream industrial chain extension is rich. Every link from production to use to storage requires strict safety and environmental protection measures to ensure personal safety and environmental protection. In the future, with the progress of science and technology and the improvement of environmental protection awareness, the application of mixed xylene will be continuously optimized, and the relevant industrial chain will be more perfect.