What is Acrylonitrile?
Acrylonitrile (CH2=CHCN) is a representative unsaturated nitrile organic compound. At room temperature and pressure, it is a colorless, transparent, free-flowing liquid with a distinctive pungent odor similar to bitter almonds or pyridine.
- Core Chemical Characteristics:
High Flammability and Explosion Hazard: Acrylonitrile is not only highly flammable, but its flash point is also only -1°C (open cup). Its vapor has a wide explosive limit range (3.05% ~ 17.0% by volume), making it highly susceptible to deflagration even at low concentrations. - High Chemical Reactivity: Due to the presence of carbon-carbon double bonds and cyano groups, it exhibits extremely high chemical reactivity. It readily undergoes spontaneous exothermic polymerization reactions when exposed to light, heat, or contact with strong alkalis or peroxides, potentially leading to container rupture. Therefore, polymerization inhibitors (such as hydroquinone) are typically added during industrial storage.
- Secondary toxicity: When acrylonitrile burns or decomposes at high temperatures, it releases highly toxic hydrogen cyanide gas and nitrogen oxides, significantly increasing the difficulty of rescue operations and the risk of casualties at fire scenes.
Main applications in which industries?
Acrylonitrile is hailed as one of the “pillars” of the organic synthesis industry, with an extremely long industrial chain covering multiple fields from basic chemicals to high-tech materials:
- Synthetic fibers (acrylic fibers): Approximately half of acrylonitrile is used to produce polyacrylonitrile fiber (commonly known as “artificial wool”), widely used in clothing, carpets, and industrial filter cloths.
- High-performance plastics (ABS/SAN): ABS resin, produced by copolymerizing acrylonitrile with butadiene and styrene, has excellent impact resistance and weather resistance, making it a core raw material for household appliance housings, automotive dashboards, and toys.
- Synthetic rubber (nitrile butadiene rubber): NBR, produced by copolymerizing acrylonitrile with butadiene, has excellent oil resistance and is widely used in the manufacture of oil hoses, sealing rings, and protective gloves.
- Advanced technology (carbon fiber): Polyacrylonitrile is the main precursor for manufacturing high-performance carbon fiber (PAN-based). Carbon fiber, with its lightweight and high strength, is indispensable in aerospace, wind turbine blades, and high-end sporting goods.
- Fine Chemicals: Used in the synthesis of acrylamide (a raw material for water purification agents), L-monosodium glutamate (MSG), and various pharmaceutical intermediates.
Health Hazards and Safety of Acrylonitrile
Acrylonitrile is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC) of the World Health Organization. Its toxic effects are diverse and insidious:
- Acute Toxicity: Acrylonitrile is highly toxic and can enter the human body through the respiratory tract, digestive tract, and skin. During metabolism, acrylonitrile releases cyanide ions, inhibiting the activity of cellular respiratory enzymes and leading to tissue hypoxia.
- Skin and Mucous Membrane Damage: Direct contact with the liquid can cause significant chemical burns. Due to its high permeability, even after washing, subcutaneous tissue may continue to be damaged.
- Nervous System Damage: Long-term exposure to low concentrations can lead to significant neurotic symptoms, such as intractable insomnia, memory loss, and autonomic nervous system dysfunction.
Why Install Acrylonitrile Alarms?
Given acrylonitrile’s dual properties of being flammable and explosive as well as highly toxic, installing automated alarm systems is a mandatory requirement for industrial safety.
Alarm System Composition and Functions
An acrylonitrile alarm system typically includes a gas detector (front end) and an alarm control unit (back end):
- Multi-level Alarm: The system usually has two alarm levels. When the concentration reaches the first level (usually targeting occupational exposure limits), personnel are alerted to take protective measures; when it reaches the second level (targeting the lower explosive limit or acute poisoning limit), the system is activated.
- Interlocking: The alarm can automatically activate explosion-proof exhaust fans to reduce noise or forcibly close the supply pipeline shut-off valves via relay signals, cutting off the hazard source at its origin.
Core Working Principle
Currently, mainstream acrylonitrile detection uses electrochemical sensors or photoionization sensors (PID):
- Electrochemical Method: After the gas enters the sensor, a redox reaction occurs on the sensing electrode, generating a tiny current proportional to the gas concentration. This method has good selectivity and is suitable for monitoring low concentrations of toxicity.
- PID Method: Utilizes high-energy ultraviolet light to ionize acrylonitrile molecules, exhibiting extreme sensitivity to trace leaks (ppb level), making it suitable for high-precision environmental monitoring.
Usage and Maintenance Precautions
Usage Guidelines
- Location: The detector should be installed near potential leak sources (e.g., pump areas, valves, loading/unloading platforms). Since acrylonitrile vapor is heavier than air, the detector should be installed at a height of 0.3m to 0.6m above the ground.
- Explosion-proof Check: Ensure the alarm has explosion-proof certification and that the casing is properly grounded to prevent static electricity buildup.
- Prohibited Operations: Never disassemble the probe while it is powered on. Never directly impact the sensor with high-concentration gases, as this may cause sensor poisoning and failure.
Maintenance
- Regular Calibration: Sensors exhibit natural drift; standard gas calibration should be performed every 6 or 12 months to ensure data accuracy.
- Filter Cleaning: Industrial environments are dusty; regularly clean the dust cover at the detector’s air inlet to prevent blockage and response lag.
- Lifespan management: The electrolyte inside the electrochemical sensor will gradually be depleted, and its lifespan is usually 2-3 years. After that, the core components must be replaced.
