PX is the abbreviation of p-xylene
1. Physical and chemical constants of substances:
National standard number 33535
Si Nuo. 106-42-3
Chinese name 1, 4- xylene
English name 1, 4- xylene; para-xylene
para-xylene
The molecular formula is c8 h10; ; The appearance and properties of C6H4(CH3)2 is a colorless and transparent liquid with an odor similar to toluene.
Molecular weight 106. 17 vapor pressure 1. 16kPa/25℃ Flash point: 25℃
Melting point 13.3℃ Boiling point: 138.4℃ Soluble, insoluble in water, miscible in most organic solvents such as ethanol, ether and chloroform.
Density Relative density (water =1) 0.86; The relative density (air = 1)3.66 is relatively stable.
Danger sign 7 (flammable liquid) is mainly used as raw material for synthesizing polyester fiber, resin, paint, dye and pesticide.
2. Impact on the environment:
I. Health hazards
Invasion route: inhalation, ingestion and percutaneous absorption.
Health hazard: Xylene can irritate eyes and upper respiratory tract, and can anesthetize central nervous system at high concentration.
Acute poisoning: Inhalation of high-concentration nuclear weapons in a short time can cause obvious irritation to eyes and upper respiratory tract, congestion of conjunctiva and pharynx, dizziness, nausea, vomiting, chest tightness, weakness of limbs, confusion and stumbling gait. In severe cases, restlessness, convulsions or coma may occur, and some of them may have hysterical attacks.
Chronic effects: long-term exposure to neurasthenia syndrome, irregular menstruation of female workers, dry skin, chapped skin and dermatitis of workers.
Second, toxicological data and environmental behavior.
Toxicity: low toxicity.
Acute toxicity: LD505000mg/kg (taken orally by rats); LC50 19747mg/kg, 4h (inhaled by rats).
Irritation: human eyes: 200ppm, causing irritation. Percutaneous rabbit: 500 mg (24 hours), moderately irritating.
Subacute and chronic toxicity: Rats and rabbits inhaled 5000mg/m3 for 8 hours/day for 55 days, resulting in eye irritation, fatigue, ataxia, slight decrease of red blood cells and white blood cells, bone marrow hyperplasia and 3% ~ 4% megakaryocytes.
Mutagenicity: cytogenetic analysis: Saccharomyces cerevisiae 1mmol/ tube.
Reproductive toxicity: The lowest toxic concentration (TDL0) of rats in 24 hours (taking medicine on the 9th ~14th day of pregnancy) is 19 mg/m3, which causes abnormal musculoskeletal development.
Pollution source: Xylene is an important chemical raw material. Wastewater and waste gas from organic synthesis, synthetic rubber, paint and dye, synthetic fiber, petroleum processing, pharmacy and cellulose, as well as unsealed production equipment and ventilation in the workshop are the main sources of xylene in the environment. Overturning, leakage and fire during transportation and storage can also cause accidental pollution accidents.
Metabolic degradation: in humans and animals, except for 3% ~ 6% inhaled xylene, all three isomers of xylene are metabolized into corresponding benzoic acid (60% o-xylene and 80% ~ 90% m-xylene), and then these acids react with glucuronic acid and glycine. In this process, a large amount of o-benzoic acid is combined with glucuronic acid, while p-benzoic acid is almost completely combined with glycine to generate corresponding methylhippuric acid, which is excreted. At the same time, a small amount of corresponding xylenol (phenol) and 3- hydroxy -2- methylbenzoic acid hydride may be formed (less than 2%).
Residue and accumulation: In occupational contact, xylene mainly enters the body through respiratory tract. For all isomers of xylene, the vapor absorbed by the lung is the same, the total amount is 60% ~ 70%, and this absorption amount is relatively constant during the whole contact period. Xylene solution can penetrate the whole skin with an average absorption rate of 2.25? 0? 8g/(cm3 min) (range 0.7 ~ 4.3? 0? 8g/(cm3 min)) was absorbed, and the transdermal absorption of xylene vapor was negligible compared with direct contact with liquid. The retention and accumulation of xylene is not serious. As we said above, in the presence of NADP (transferase II) and NAD (transferase I), xylene entering human body can generate methylbenzoic acid, and then combine with glycine to generate methylhippuric acid, which is almost completely excreted in 18 hours. Even the 3% ~ 6% xylene remaining in the lungs after inhalation is exhaled within 3 hours after contact (half-life is 0.5 ~ 1 hour). The residual detection of xylene exposure is mainly to determine the content of methylhippuric acid in urine, and it is also suggested to determine the content of xylene in our gas or blood, but the result of the latter is often inaccurate. Because methylhippuric acid does not exist naturally in urine, and because it is almost a residual xylene metabolite, it is the best confirmation of xylene contact test to determine its existence. Xylene can exist in drinking water for a long time. When the concentration of xylene in tap water is 5mg/L, its odor intensity is equivalent to grade 5, and the unique odor of xylene will disappear after 7 ~ 8 days. When the odor intensity is level 3, it takes 4 to 5 days. The odor of xylene in river water is kept for a short time, which is related to the initial concentration, and can generally be kept for 3 to 5 days.
Migration and transformation: Xylene is mainly made from crude oil in petrochemical process. It is widely used as a diluent for pigments and paints, and as a solvent for printing, rubber and leather industries. As cleaning agents and degreasing agents, components of aviation fuel, raw materials and intermediates in chemical factories and synthetic fiber industries, and coating and impregnating materials for fabric and paper. Xylene can be discharged into the atmosphere through mechanical exhaust and ventilation equipment, causing pollution. The amount of xylene discharged into the atmosphere by an oil refinery is as high as 1 3.18 ~145g/h, and xylene can enter the water body with the wastewater discharged by its production and use units, producing1ton of xylene, and the general discharge contains 300 ~1000. Because xylene has a strong volatilization tendency in aqueous solution, it can be considered that xylene is not a persistent pollutant in surface water. Xylene can also be biodegraded in the environment, but the speed of this process is much lower than that of volatilization. Xylene volatilized into the air may also be photolyzed, which is the main migration and transformation process.
Xylene is excreted from human body through exhalation and metabolites very quickly, and almost all of it is excreted within 18 hours after contact stops, so xylene can exist in drinking water for a long time. Because xylene is volatile in aqueous solution, it can be considered not to be a persistent pollutant in surface water. Xylene can also be biodegraded and chemically degraded in the environment, but its speed is much lower than that of volatilization, and xylene volatilized into the air can be photolyzed. It can react with oxidant, and high concentration gas will explode when mixed with air. Xylene has a moderate burning hazard. Because its steam is heavier than air, the flame spreads along the ground when burning. Xylene is volatile, and the scene of the accident will be filled with its special fragrance. Xylene dumped into water can float on the water surface or be distributed on the water surface as oil, which can cause the death of fish and aquatic organisms.
Hazard characteristics: flammable, and its vapor can form an explosive mixture with air. Fire and high temperature can cause combustion and explosion. Can react strongly with oxidant. The flow velocity is too fast, which is easy to generate and accumulate static electricity. Its vapor is heavier than air, and it can spread to a considerable distance at a lower place, which will lead to tempering when it meets an open flame.
Combustion (decomposition) products: carbon monoxide and carbon dioxide.
3. The field emergency monitoring method:
Gas detection tube method; Portable gas chromatograph; Water quality detection tube method
Rapid detection tube method "Emergency monitoring and treatment technology of sudden environmental pollution accidents" edited by Wan Bentai.
Gas rapid measuring tube (produced by Beijing Labor Insurance Institute and Doelger Company of Germany)
4. Laboratory monitoring methods:
Source categories of monitoring methods
Gas chromatography GB 1 1890-89 water quality
Gas chromatography GB/T 14677-93 Air
Gas chromatography without pump sampling WS/T 153- 1999 Workplace air
Handbook of gas chromatography for testing, analysis and evaluation of solid waste.
Chromatography/mass spectrometry EPA524.2 American water quality
5. Environmental standards:
The maximum allowable concentration of harmful substances in the air of China (TJ36-79) workshop is 100mg/m3 (xylene).
The maximum allowable concentration of harmful substances in the air of China (TJ36-79) residential area is 0.30mg/m3 (initial value, xylene).
China (GB 16297- 1996) Comprehensive Emission Standard for Air Pollutants (Xylene) ① Maximum allowable emission concentration (mg/m3):
70 (Table 2); 90 (table 1)
② Maximum allowable discharge rate (kg/hour):
Secondary 1.0 ~ 10 (Table 2); 1.2 ~ 12 (table 1)
Grade iii 1.5 ~ 15 (table 2); 1.8 ~ 18 (table 1)
③ Monitoring concentration limit of unorganized emission: 1.2mg/m3 (Table 2); 1 .5mg/m3 (table1)
The maximum allowable concentration of harmful substances in drinking water sources in China (to be promulgated soon) is 0.5mg/L (xylene).
China (GHZB 1- 1999) surface water environmental quality standard (specific values of Class I, II and III waters) is 0.5mg/L (xylene).
China (GB8978- 1996) Integrated Wastewater Discharge Standard Grade I: 0.4 mg/L.
Grade II: 0.6 mg/L.
Grade iii: 1.0mg/L/L
6. Emergency treatment and disposal methods:
First, the emergency treatment of leakage
Quickly evacuate the personnel in the leaked and polluted area to a safe area, isolate them, and strictly restrict access. Cut off the fire. It is recommended that emergency personnel wear self-contained positive pressure breathing apparatus and fire protection clothing. Cut off the source of leakage as much as possible to prevent it from entering confined spaces such as sewers and flood discharge ditches. Small amount of leakage: absorbed by activated carbon or other inert substances. You can also brush the emulsion made of incombustible dispersant and put it into the wastewater system after dilution. A large number of water leaks: build a dike or dig a pit to accommodate; Cover with foam to suppress evaporation. Use explosion-proof pump to transfer it to tank car or special collector, and recycle it or transport it to waste disposal site for treatment. Quickly collect the soil contaminated by xylene and move it to a safe place. Strengthen ventilation along the ground in the polluted area, evaporate residual liquid and eliminate steam. Quickly build a dam to cut off the polluted water flow, and use fences to limit the diffusion of xylene on the water surface.
Second, the protective measures
Respiratory system protection: When the air concentration is high, wear a filter gas mask (half mask). Air respirator is recommended for emergency rescue or evacuation.
Eye protection: Wear chemical safety glasses.
Physical protection: wear anti-virus infiltration overalls.
Hand protection: wear rubber gloves.
Others: Smoking and eating are prohibited in the workplace. After work, take a shower and change clothes. Maintain good hygiene habits.
Third, first aid measures.
Skin contact: take off contaminated clothes and rinse skin thoroughly with soapy water and clean water.
Eye contact: Lift eyelids and rinse with running water or normal saline. See a doctor.
Inhalation: leave the scene quickly and go to a place with fresh air. Keep the respiratory tract unobstructed. If you have difficulty breathing, give oxygen. If breathing stops, give artificial respiration immediately. See a doctor.
Intake: Drink enough water to induce vomiting. See a doctor.
Fire extinguishing method: spray water to cool the container, and if possible, move the container from the fire to an open place. Extinguishing agent: foam, carbon dioxide, dry powder, sand. thank you