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Ethylene is one of the most widely produced chemical products in the world. The ethylene industry is at the core of the petrochemical sector, with ethylene-based products accounting for over 75% of all petrochemical products, thus playing an important role in the national economy. Around the world, ethylene production is regarded as one of the important indicators to measure the level of development in the petrochemical industry. 1 Application areas: In the industrial sector, its main uses are as follows: Ethylene is a crucial basic raw material for the organic chemical industry; it is primarily used in the production of polyethylene, ethylene-propylene rubber, polyvinyl chloride, etc ； One of the most basic raw materials in the petrochemical industry. In terms of synthetic materials, they are widely used in the production of polyethylene, vinyl chloride and polyvinyl chloride, ethylbenzene, styrene and polystyrene, as well as ethylene-propylene rubber, among others ； In organic synthesis, it is widely used for synthesizing various basic organic raw materials, such as ethanol, ethylene oxide, ethylene glycol, acetaldehyde, acetic acid, propionaldehyde, propionic acid, and their derivatives ； Through halogenation, chloroethylene, chloroethane, and bromoethane can be produced ； Through aggregation, α-olefins can be produced, which are then used to manufacture higher alcohols, alkylbenzenes, and other compounds ； Primarily used as a standard gas for analytical instruments in petrochemical enterprises ； Ethylene is used as an environmentally friendly ripening gas for fruits such as navel oranges, tangerines, and bananas ； Ethylene is used in pharmaceutical synthesis and the production of advanced materials. In the ecological field, the “triple response of ethylene”: ① Inhibition of stem elongation growth ； ②Promote the thickening of stems and roots ； ③Promotes lateral growth of the stem. Treating the stems of etiolated seedlings with ethylene can thicken the stems and cause the petioles to grow upward. Since ethylene can promote the synthesis of RNA and proteins, and it can increase the permeability of cell membranes in higher plants thereby accelerating respiration, when the ethylene level in fruits rises, the already synthesized auxins can be broken down by enzymes within the plant or by external light, further facilitating the conversion of organic substances and accelerating ripening. Soaking underripe fruits such as tomatoes, apples, pears, bananas, and persimmons in a solution of ethylene glycol can significantly accelerate their ripening. Ethylene also plays a role in promoting organ abscission and aging. Ethylene plays an important role in the abscission of flowers, leaves, and fruits. Ethylene can also promote flowering and the differentiation of female flowers in certain plants (such as cucurbits), as well as induce the exudation of latex from rubber trees, lacquer trees, etc. Ethylene can also induce the formation of adventitious roots from cuttings, promote root growth and differentiation, break dormancy in seeds and buds, and induce the secretion of secondary substances. 2 Overview of Safety Hazards: Routes of exposure: Inhalation. Health hazards: It has a strong ** effect. Acute poisoning: Inhaling high concentrations of ethylene can immediately cause loss of consciousness, without an obvious excitation phase; however, recovery occurs quickly after inhaling fresh air. It has mild irritation to the eyes and respiratory mucosa. Liquid ethylene can cause frostbite to the skin. Chronic effects: Prolonged exposure can cause dizziness, general discomfort, fatigue, and difficulty concentrating. A few individuals have gastrointestinal dysfunction. Environmental hazards: Harmful to the environment; can cause pollution of water bodies, soil, and the atmosphere. Flame and explosion hazard: Flammable. First aid measures: Skin contact: Do not apply any ointments in case of frostbite, and do not use hot water. Cover with a clean, dry dressing and seek medical treatment. Eye contact: Immediately lift the eyelids and rinse thoroughly with plenty of flowing water or saline for at least 30 minutes. Seek medical attention. Inhalation: Quickly move to a place with fresh air. Keep the airways clear. If there is difficulty breathing, administer oxygen. If breathing stops, perform artificial respiration immediately. Seek medical attention. Ingestion: Drink plenty of warm water and induce vomiting. Seek medical attention. Fire prevention measures. Hazardous characteristics: Flammable; when mixed with air, it can form an explosive mixture. In contact with open flames, high heat, or oxidizing agents, there is a risk of combustion and explosion. It undergoes violent chemical reactions when in contact with fluorine, chlorine, etc. Harmful combustion products: carbon monoxide. Fire extinguishing method: Cut off the gas supply. If the gas supply cannot be cut off, it is not permitted to extinguish the flame at the leak site. Use water spray to cool the container; if possible, move the container away from the fire to an open area. Extinguishing agents: foam, carbon dioxide, dry chemical. In an emergency, promptly evacuate personnel from the leak-contaminated area to a upwind location, and isolate the area while strictly restricting access. Cut off the source of fire. It is recommended that emergency responders wear self-contained positive-pressure breathing apparatus and anti-static work clothing. Seal the source of the leak as much as possible. Ensure proper ventilation to accelerate diffusion. Diluted with spray water. If possible, use an exhaust fan to send the leaked gas to an open area, or install appropriate burners to burn it off. Leaking containers must be properly handled, repaired, and inspected before being used again. 3. Precautions for handling and storage: Perform operations in a sealed environment with adequate ventilation. Operators must receive specialized training and strictly adhere to the operating procedures. It is recommended that operators wear anti-static work clothes. Stay away from flames and heat sources; smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Prevent gas from leaking into the workplace air. Avoid contact with oxidizers and halogens. During transfer, cylinders and containers must be grounded and bonded to prevent the generation of static electricity. Handle with care during transportation to prevent damage to the cylinder and its accessories. Equipped with appropriate types and quantities of fire-fighting equipment and emergency response devices for leaks. Storage precautions: Store in a cool, well-ventilated warehouse. Keep away from flames and heat sources. The storage temperature should not exceed 30°C. It should be stored separately from oxidizers and halogens; mixed storage is strictly prohibited. Use explosion-proof lighting and ventilation facilities. The use of mechanical equipment and tools prone to generating sparks is prohibited. The storage area should be equipped with emergency equipment for handling leaks. 4 Current Development Status Although China’s ethylene industry has developed rapidly and occupies a pivotal position in the global ethylene market, there are still some unavoidable risks. Firstly, market competition risks. Ethylene producers in the Middle East mainly use ethane as a raw material for producing ethylene. The cost of ethane in this region is very low; even after adding transportation costs, it remains much lower than in the United States, Western Europe, and other parts of the world, including China, giving them considerable competitive advantages. The large influx of cheap downstream Middle Eastern ethylene products such as polyethylene and ethylene glycol into the Asia-Pacific and Chinese markets will surely pose a serious threat to the related products in our country’s market. Secondly, environmental protection risks. There is a certain degree of environmental pollution in the industrial production of ethylene, but with today’s environmental protection technologies, its production still causes some level of pollution to the atmosphere and water bodies. As new projects come online one after another and China introduces stricter environmental protection standards in the future, higher demands will be placed on ethylene manufacturers regarding environmental protection measures. As a result, these companies face the risk of increased operating costs due to higher expenses related to environmental control. There is also the risk of oil imports. The large-scale construction of ethylene plants has also increased the demand for oils used in the chemical industry. Just as China faces constraints due to a petroleum shortage, the development of its petrochemical industry also encounters resource limitations; domestic crude oil production has remained around 200 million tons, which is far below the rate of growth in oil demand. With the future development of the ethylene industry, the shortage of oils for use in the chemical industry will become increasingly prominent. Propylene: Propylene is a fundamental raw material for the three major synthetic materials. It is primarily used in the production of polypropylene, acrylonitrile, isopropanol, acetone, and propylene oxide, among others. Propylene is a colorless gas with a slight sweet taste at room temperature. Freezing point: -185.3°C, boiling point: -47.4°C. It is slightly **reactive, and decomposes completely at 815°C and 101.325 kPa. Flammable; the explosion limit is 2%–11%. It is insoluble in water but soluble in organic solvents; it is a substance with low toxicity. 1 Its main uses are in the production of acrylonitrile, propylene oxide, propylene, etc. It is used to produce a variety of important organic chemical raw materials, as well as synthetic resins, synthetic rubbers, and various fine chemicals. Propylene is most widely used in the production of polypropylene; in addition, it can be used to manufacture acrylonitrile, isopropanol, phenol and propyl/butyl/octyl alcohols, acrylic acid and its esters, as well as propylene oxide and propylene glycol, epichlorohydrin and synthetic glycerin. 2 Safety precautions – Overview of hazards: Health hazards: This product is a simple asphyxiant and a mild ** agent. Acute poisoning: Inhalation of propylene by humans can cause loss of consciousness; at a concentration of 15%, it takes 30 minutes ； At 24%, it takes 3 minutes ； At 35%–40%, it takes 20 seconds ； When it exceeds 40%, it takes only 6 seconds and causes vomiting. Chronic effects: Prolonged exposure can cause dizziness, fatigue, general discomfort, and difficulty concentrating. In some individuals, gastrointestinal function becomes disordered. Environmental hazards: Harmful to the environment; can cause pollution of water bodies, soil, and the atmosphere. Flame and explosion hazard: This product is flammable. First aid measures: Inhaling: Quickly move the affected person to a place with fresh air. Keep the airways clear. If there is difficulty breathing, administer oxygen. If breathing stops, perform artificial respiration immediately. Seek medical attention. Fire prevention measures. Hazardous characteristics: Flammable; when mixed with air, it can form an explosive mixture. There is a risk of combustion and explosion in the presence of heat sources and open flames. It reacts violently with nitrogen dioxide, dinitrogen tetroxide, nitrous oxide, etc., and undergoes intense reactions upon contact with other oxidizing agents. Gases are heavier than air and can spread over considerable distances at lower levels; they will catch fire and ignite when exposed to a source of flame. Harmful combustion products: carbon monoxide, carbon dioxide. Fire extinguishing method: Cut off the gas supply. If the gas supply cannot be cut off, it is not permitted to extinguish the flame at the leak site. Use water spray to cool the container; if possible, move the container away from the fire to an open area. Extinguishing agents: fogged water, foam, carbon dioxide, dry powder. Personal protective measures are necessary; high concentrations of propylene have **harmful effects** on humans, while lower concentrations can cause irritation to the eyes and skin. Propylene and air can form explosive mixtures, with an explosion limit of 2.0% to 11% (by volume). Leaks of liquid or gaseous propylene pose a risk of fire and explosion. Respiratory protection: No special protection is generally required, but it is recommended to wear a self-priming filter-type respirator (half-mask) in special situations. Eye protection: No special protection is generally required, but chemical safety goggles can be worn in cases of high-concentration exposure. Body protection: Wear anti-static work clothing. Hand protection: Wear general-purpose protective gloves. Other protections: Smoking is strictly prohibited at the work site. Avoid prolonged and repeated exposure. When entering tanks, confined spaces, or other areas with high concentrations, supervision must be provided. In the event of a leak, emergency measures involve quickly evacuating people from the contaminated area to areas upwind, isolating the zone, and strictly restricting access. Cut off the source of fire. It is recommended that emergency responders wear self-contained positive-pressure breathing apparatus and anti-static work clothing. Seal the source of the leak as much as possible. Cover areas such as sewers near the leak site with industrial coverings or adsorbents/sorbents to prevent gases from entering. Ensure proper ventilation to accelerate diffusion. Diluted and dissolved with spray water. Construct dikes or dig pits to contain the large amount of wastewater generated. If possible, use an exhaust fan to send the leaked gas to an open area, or install appropriate burners to burn it off. Leaking containers must be properly handled, repaired, and inspected before being used again. 3 Precautions for handling, storage, and transportation: Operate in a sealed environment with adequate ventilation. Operators must receive specialized training and strictly adhere to the operating procedures. Stay away from flames and heat sources; smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Prevent gas from leaking into the workplace air. Avoid contact with oxidizers and acids. During transfer, cylinders and containers must be grounded and bonded to prevent the generation of static electricity. Handle with care during transportation to prevent damage to the cylinder and its accessories. Equipped with appropriate types and quantities of fire-fighting equipment and emergency response devices for leaks. Storage precautions: Store in a cool, well-ventilated warehouse. Keep away from flames and heat sources. The storage temperature should not exceed 30°C. It should be stored separately from oxidizers and acids; mixed storage is strictly prohibited. Use explosion-proof lighting and ventilation facilities. The use of mechanical equipment and tools prone to generating sparks is prohibited. The storage area should be equipped with emergency equipment for handling leaks. Transportation precautions: For railway transportation of this product, it must be shipped in tank cars provided by the enterprises that handle pressurized liquefied gas, and approval from the relevant authorities is required prior to shipment. When transporting cylinders, it is necessary to wear the safety cap on the cylinder. Gas cylinders should generally be placed flat, with their openings facing the same direction; they must not be crossed ； The height must not exceed the vehicle’s guardrail, and it should be secured with wooden wedges to prevent rolling. Transport vehicles should be equipped with fire-fighting equipment of the appropriate type and quantity during transportation. The exhaust pipes of the vehicles used to transport this item must be equipped with flame arrestors, and the use of mechanical equipment and tools that may generate sparks for loading and unloading is prohibited. Mixing or transporting together with oxidizers, acids, etc. is strictly prohibited. During summer, transportation should take place in the morning and evening to avoid exposure to sunlight. When making stops en route, stay away from sources of fire and heat. When transporting by road, follow the designated routes and do not stop in residential areas or densely populated zones. Sliding is prohibited during railway transportation. 4 Industrial production: Over 90% of the total propylene production in Western Europe and Japan comes from hydrocarbon cracking, while the remainder comes from refinery gas. The United States aims to increase gasoline production, with propylene derived from hydrocarbon cracking accounting for only 54% and propylene from refinery gas accounting for 45%. Furthermore, the emergence of new methods such as propane catalytic dehydrogenation to produce propylene also represents a potential industrial source of propylene. Refinery gas recovery: A certain amount of propylene is present in the refinery gas generated as a by-product of processes such as catalytic cracking, thermal cracking, and petroleum coking in oil refineries. Among them, the propylene produced in the catalytic cracking process accounts for over 90% of the total propylene in refinery gas; its amount depends on the specifications of the feedstock, the type of catalyst, and the cracking operation conditions, generally ranging from 2% to 5% of the feedstock. When processing refinery gas to recover propylene, the oil absorption method or low-temperature distillation is generally used to separate the propylene and propane fractions from light hydrocarbons such as methane and ethane, followed by precise distillation to obtain propylene (see color illustration). Since the propylene and propane fractions in refinery gas contain no methylacetylene or methacrylene, catalytic hydrogenation is not required; polymer-grade propylene can be obtained by simply removing impurities such as water and sulfides. The propylene concentration in refinery gas is low, making the absorption method more economical than low-temperature distillation. Separation of hydrocarbons from pyrolysis gas: Hydrocarbon pyrolysis produces large amounts of propylene alongside ethylene. Propylene production is related to the properties of the raw materials and the conditions of the cracking process, and it generally accounts for 40% to 70% of the ethylene production. The propylene content in the pyrolysis gas ranges from 15% to 25%, and it can be separated using either oil absorption or deep freezing methods. From the perspectives of product quality and energy consumption, deep freezing separation is the preferred method for large-scale olefin production facilities (see Deep Freezing Separation of Pyrolysis Gas). Propane catalytic dehydrogenation: In the 1980s, Mexico built the world’s first large-scale facility for producing propylene through propane catalytic dehydrogenation using the Hudlery process, with an annual production capacity of 350 kt. Propane dehydrogenation typically employs catalysts that are supported on Al2O3 or MeAl2O4 spinels; these catalysts can be either precious metals such as platinum, iridium, and rhodium, or non-precious metals such as chromium, nickel, and zinc. The reaction temperature ranges from 550 to 650°C, and the process is carried out under slightly negative pressure, using fixed-bed, fluidized-bed, or moving-bed reactors. The selectivity for producing propylene is generally over 90%. The overall yield of propylene production via catalytic dehydrogenation of propane ranges from 73% to 77%, resulting in cost savings for the plant. Therefore, in areas where large amounts of propane are obtained from refinery gas and natural gas, using this method offers high economic benefits. Coal liquefaction involves the production of ethylene and propylene through steam cracking of hydrocarbons obtained from the direct liquefaction of coal; this approach is currently not economically viable in countries with a developed petrochemical industry. However, coal reserves are much more abundant than those of oil and natural gas, and under special circumstances it can also serve as a viable source for obtaining propylene. Benzene (C6H6) is a colorless, sweet-tasting transparent liquid at room temperature, with a strong aromatic odor. Benzene is flammable, toxic, and a carcinogen as well. Benzene is a hydrocarbon and also the simplest aromatic compound. It is insoluble in water, soluble in organic solvents, and can also be used as an organic solvent itself. Benzene is a basic raw material in the petrochemical industry. The production volume of benzene and the technological level of its production are **one of the indicators of the development level of the petrochemical industry**. The ring system in benzene is called the benzene ring, and it is the simplest aromatic ring. The structure of benzene with one hydrogen atom removed is called phenyl, denoted by Ph. Therefore, benzene can also be represented as PhH. 1 Industrial uses: As early as the 1920s, benzene was already a commonly used solvent in industry, primarily for metal degreasing. Due to the toxicity of benzene, it is no longer used as a solvent in the production processes where solvents come into direct contact with the human body. Benzene can act as a detonation inhibitor and thus serve as an additive for gasoline. Before the use of tetraethyl lead in the 1950s, all antiknock agents were benzene. However, with the phasing out of leaded gasoline, benzene was reintroduced. Due to the adverse effects of benzene on the human body and its contamination of groundwater quality, Europe and the United States **require that the benzene content in gasoline not exceed 1%. The most important industrial use of benzene is as a chemical raw material. Benzene can be used to synthesize a series of benzene derivatives. A series of compounds derived from benzene through substitution reactions, addition reactions, oxidation reactions, etc., can be used as raw materials for producing plastics, rubbers, fibers, dyes, detergents, pesticides, and more. About 10% of benzene is used as a basic raw material for manufacturing benzene-based intermediates. Benzene and ethylene react to form ethylbenzene, which can be used to produce styrene for plastics ； Benzene and propylene react to form isopropylbenzene, which can be used in the isopropylbenzene process to produce phenol for making resins and adhesives ； Cyclohexane for nylon production ； Synthesis of maleic anhydride ； Used for producing aniline*** ； Various chlorobenzenes widely used in pesticides ； Various alkylbenzenes used in the production of detergents and additives ； Synthesize chemical products such as hydroquinone and anthraquinones. 2 Safety protection and health hazards: Due to benzene’s high volatility, it spreads easily when exposed to air. When humans and animals inhale or come into skin contact with large amounts of benzene, it can cause acute and chronic benzene poisoning. Some studies have shown that part of the cause of benzene poisoning is the formation of phenol in the body from benzene. Special note: (1) Prolonged inhalation can damage the nervous system, while acute poisoning can cause nerve spasms, even coma and death. (2) A large proportion of leukemia patients have a history of exposure to benzene and its derivatives. Studies have shown that Mayan blue has a strong adsorption capacity for benzene derivatives, and it can be used to remove benzene from the air. The AQ air purification spray can break down benzene in the air into carbohydrates. Safety measures should be stored in a cool, well-ventilated area, away from sources of fire and heat. Store separately from oxidizers, food chemicals, etc. The use of tools that can generate sparks is prohibited. Fire extinguishing method: Flammability: Flammable. Extinguishing agents: Foam, dry powder, carbon dioxide, sand. Using water to extinguish the fire is ineffective. First aid measures: 1. For those poisoned by inhalation, the patient should be quickly moved to a place with fresh air; contaminated clothing should be removed, and all buttons on the clothing as well as those on the neck and chest should be undone. Use a belt to keep it in a resting position; if there is any dirt in the mouth and nose, it should be removed immediately to ensure proper lung ventilation and smooth breathing. And make sure to keep your body warm. 2. In cases of oral poisoning, gastric lavage should be performed using a 0.005 solution of activated carbon or a 0.02 solution of sodium bicarbonate to induce vomiting; thereafter, laxatives and diuretics should be administered to accelerate the elimination of toxins from the body and reduce their absorption. 3. In cases of skin poisoning, remove the contaminated clothes, shoes, and socks; then wash the skin and hair repeatedly with soapy water and clean water. 4. In cases of patients with coma or convulsions, foreign objects in the mouth should be removed as soon as possible to keep the airway unobstructed, and they must be escorted to the hospital by a dedicated person for treatment. 3. Precautions for handling and storage: Operate in a sealed environment and ensure adequate ventilation. Operators must receive specialized training and strictly adhere to the operating procedures. It is recommended that operators wear self-priming filter-type gas masks (half-masks), chemical safety goggles, protective clothing resistant to toxic substances, and oil-resistant rubber gloves. Stay away from flames and heat sources; smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Prevent vapor from leaking into the workplace air. Avoid contact with oxidizers. During filling, the flow rate should be controlled, and a grounding device should be in place to prevent static electricity buildup. Handle with care during transportation to prevent damage to the packaging and containers. Equipped with appropriate types and quantities of fire-fighting equipment and emergency response devices for leaks. Empty containers may still contain harmful substances. Storage precautions: Store in a cool, well-ventilated warehouse. Keep away from flames and heat sources. The storage temperature should not exceed 30°C. Keep the container sealed. It should be stored separately from oxidizers and food chemicals; mixed storage is strictly prohibited. Use explosion-proof lighting and ventilation facilities. The use of mechanical equipment and tools prone to generating sparks is prohibited. The storage area should be equipped with emergency spill response equipment and appropriate containment materials. 4 Industrially, benzene can be obtained through the incomplete combustion of substances with a high carbon content. In nature, both volcanic eruptions and forest fires can produce benzene. Benzene is also present in cigarette smoke. In coal tar obtained from coal carbonization, benzene is the main component. Until World War II, benzene was still a by-product of the coking process in the steel industry. This method can only extract 1 kilogram of benzene from 1 ton of coal. After the 1950s, as the industrial demand for benzene increased—particularly in the rapidly growing plastics industry—processes for producing benzene from petroleum came into existence. Since the 21st century, most of the benzene in the world has come from the petrochemical industry. The three most important processes for industrial benzene production are catalytic reforming, toluene hydrodealkylation, and steam cracking. Light tar extracted from coal tar, which is produced during the coal coking process, contains large amounts of benzene. This was the original method for producing benzene. The resulting coal tar and gas are passed together through washing and absorption equipment, using high-boiling-point coal tar as a washing and absorbing agent to recover coal tar from the gas; after distillation, crude benzene and other high-boiling-point fractions are obtained. Industrial-grade benzene can be obtained by refining crude benzene. The purity of benzene obtained by this method is relatively low, it causes severe environmental pollution, and the process is rather outdated. Benzene is present in crude oil in small amounts; extracting benzene from petroleum products is the most widely used method of preparation. Alkane aromatization reforming refers here to the process of cyclizing aliphatic hydrocarbons and dehydrogenating them to form aromatic hydrocarbons. This is a technique that developed during World War II. At 500–525°C and 8–50 atmospheres of pressure, various aliphatic hydrocarbons with boiling points between 60–200°C are converted into benzene and other aromatic hydrocarbons through dehydration and cyclization using a platinum-rhodium catalyst. After extracting the aromatic hydrocarbon products from the mixture, benzene is separated through distillation. These fractions can also be used as high-octane gasoline. Steam cracking is a process by which olefins are produced from low-molecular-weight alkanes such as ethane, propane, or butane, as well as petroleum components like naphtha and heavy diesel. One of its by-products, pyrolysis gasoline, is rich in benzene, from which benzene and various other components can be distilled out. Pyrolyzed gasoline can also be mixed with other hydrocarbons as an additive for gasoline. Benzene accounts for about 40-60% of pyrolysis gasoline; it also contains dienes and other unsaturated compounds such as styrene. These impurities are prone to further reacting during storage to form high-molecular-weight gums. Therefore, a hydrogenation process must first be carried out to remove these impurities and sulfides from the pyrolysis gasoline, followed by appropriate separation to obtain benzene products. The separation of aromatics from benzene-containing fractions obtained by different methods involves components that are highly complex; conventional separation techniques are not effective in such cases. Generally, solvent-based liquid-liquid extraction or extractive distillation is used to separate the aromatics, followed by the use of conventional separation methods to isolate benzene, toluene, and xylene. There are also various separation methods depending on the solvent and technique used. Udex process: Developed jointly by Dow Chemical Company and UOP in 1950, it initially used diethylene glycol ether as a solvent; later, triethylene glycol ether and tetraethylene glycol ether were used as solvents, with a multouocomer extractor being employed in the process. The yield of benzene was 100%. Suifolane process: Developed by Shell Netherlands, with the patent held by UOP. Sulfolane is used as the solvent, and a rotary extractor tower is employed for extraction; the product requires treatment with clay. The yield of benzene was 99.9%. Arosolvan method: Developed in 1962 by the German company Lurgi. The solvent is N-methylpyrrolidone (NMP); to improve the yield, 10-20% ethylene glycol ether is sometimes added as well. Using a specially designed Mechnes extractor, the yield of benzene is 99.9%. IFP method: Developed by the French Institute of Petrochemistry in 1967. Anhydrous dimethyl sulfoxide is used as the solvent, and butane is employed for back-extraction; a rotary drum tower is used in this process. The yield of benzene was 99.9%. Formex method: Developed in 1971 by the Italian company SNAM and its LRSR oil processing division. Morpholine or N-formylmorpholine is used as the solvent, with a rotary tower. The total yield of aromatic hydrocarbons was 98.8%, with the yield of benzene being 100%. A class of hydrocarbons containing one or more benzene rings, belonging to aromatic hydrocarbons. Toluene dealkylation is used to produce benzene from toluene; this can be achieved through catalytic hydrogenation dealkylation or thermal dealkylation without a catalyst. The raw material can be toluene, mixtures of toluene and xylene, or fractions containing benzene as well as other alkyl aromatics and non-aromatics. In toluene catalytic hydrogenodealkylation, catalysts such as chromium, molybdenum, or platinum oxide are used; at high temperatures of 500–600°C and pressures of 40–60 atmospheres, a mixture of toluene and hydrogen is used to produce benzene, a process known as hydrogenodealkylation. If the temperature is higher, the catalyst can be omitted. The reaction proceeds according to the following equation: Ph-CH3 + H2 → PhH + CH4. There are various process methods depending on the catalyst used and the process conditions. The Hydeal process was developed in 1961 by Ashiand & Refing and UOP. The raw materials can be reformed oil, hydrocracked gasoline, toluene, carbon 6–carbon 8 mixed aromatics, dealkylated coal tar, etc. The catalyst is alumina-chromium oxide, the reaction temperature is 600–650°C, and the pressure is 3.43–3.92 MPa. The theoretical yield of benzene is 98%, with a purity of over 99.98%, resulting in a higher quality than benzene produced by the Udex method. The Detol method, developed by Houdry Company. Alumina and magnesium oxide are used as catalysts, the reaction temperature ranges from 540–650°C, the reaction pressure is between 0.69–5.4 MPa, and the raw materials are mainly carbon 7–carbon 9 aromatics. The theoretical yield of benzene is 97%, with a purity that can reach 99.97%. The Pyrotol method was developed by Air Products and Chemicals and Houdry Company. Suitable for producing benzene from ethylene-derived pyrolysis gasoline. The catalyst is alumina-chromium oxide, the reaction temperature is 600–650°C, and the pressure is 0.49–5.4 MPa. The Bextol process, developed by Shell. The BASF method, developed by BASF Corporation. The Unidak process, developed by UOP. Thermal dealkylation of toluene: Toluene can be dealkylated to produce benzene at high temperatures in a hydrogen stream, without the need for a catalyst. The reaction is exothermic, and various process methods have been developed to address the different problems that arise. The MHC hydrodealkylation process was developed in 1967 by Mitsubishi Petrochemical Corporation and Chiyoda Construction Company in Japan. The raw material can be pure alkylbenzenes such as toluene, or aromatic fractions containing no more than 30% non-aromatic compounds. The operating temperature is 500–800°C, the operating pressure is 0.98 MPa, and the hydrogen/hydrocarbon ratio is 1–10. Process selectivity: 97–99% (mol), product purity: 99.99%. The HDA hydrodealkylation process was developed in 1962 by the American companies Hydrocarbon Research and Atlantic Richfield. The raw materials used are toluene, xylene, hydrocracked gasoline, and reformed oil. The reaction temperature is controlled using hydrogen from different parts of the reactor; it ranges from 600 to 760°C, the pressure is between 3.43 and 6.85 MPa, the hydrogen/hydrocarbon ratio is 1 to 5, and the residence time is 5 to 30 seconds. Selectivity 95%, yield 96-100%. The Sun process was developed by Sun Oil Company; the THD process was developed by Gulf Research and Development Company; the Monsanto process was developed by Monsanto Company. Toluene disproportionation and transalkylation: As the demand for xylene increased, toluene disproportionation and transalkylation technologies were developed in the late 1960s to increase xylene production simultaneously. This reaction is reversible, and different process routes exist depending on the catalyst used, process conditions, and raw materials. The LTD liquid-phase toluene disproportionation process was developed by Mobil Chemicals in the United States in 1971; it uses non-metallic zeolite or molecular sieve catalysts, with a reaction temperature of 260–315°C. The reactor is of the liquid-phase adiabatic fixed-bed type, and toluene is used as the feedstock, achieving a conversion rate of over 99%. The Tatoray process was developed by Toray Industries and UOP in Japan in 1969; it uses toluene and mixed carbon 9-aromatic hydrocarbons as feedstocks, with mordenite as the catalyst. The reaction temperature ranges from 350–530°C, the pressure is 2.94 MPa, and the hydrogen/hydrocarbon ratio is 5–12. An adiabatic fixed-bed reactor is employed, resulting in a single-pass conversion rate of over 40%, a yield of over 95%, and a selectivity of 90%; the product is a mixture of benzene and xylene. The xylene plas process: developed by the American companies Atlantic Richfield and Engelhard. A rare earth Y-type molecular sieve is used as a catalyst, the reactor is a gas-phase moving bed, the reaction temperature is 471–491°C, and the pressure is at atmospheric level. The TOLD process was developed by Mitsubishi Gas Chemical Company in Japan in 1968; it uses a hydrofluoric acid-boron fluoride catalyst, with a reaction temperature of 60–120°C and operates in a low-pressure liquid phase. It is somewhat corrosive. Other methods: Additionally, benzene can also be obtained through the polymerization of acetylene, but the yield is very low. Toluene is a colorless, clear liquid. It has a benzene-like odor. It has strong refractive power. It is miscible with ethanol, ether, propane, chloroform, carbon disulfide, and glacial acetic acid, and is very slightly soluble in water. Relative density 0.866. Freezing point: -95°C. Boiling point: 110.6°C. Refractive index: 1.4967. Flash point (closed cup) 4.4°C. Flammable. Steam can form explosive mixtures with air, with an explosion limit of 1.2% to 7.0% (by volume). Low toxicity; median lethal dose (rats, oral) is 5000 mg/kg. High-concentration gases are **toxic**. It is irritating. 1. Industrial uses: Toluene is widely used as a solvent and an additive in high-octane gasoline. It is also an important raw material for the organic chemical industry. However, compared to benzene and xylene, which are obtained from both coal and petroleum, its current production volume is relatively excessive. Therefore, a considerable amount of toluene is used for dealkylation to produce benzene or for disproportionation to produce xylene. A series of toluene-derived intermediates are widely used in dyes ； Pharmaceuticals ； Pesticides ； Fire** ； Additives ； The production of fine chemicals such as spices is also used in the synthetic materials industry. Chlorobenzyl obtained by side-chain chlorination of toluene ； Dichlorobenzene and trichlorobenzene, including their derivatives benzyl alcohol ； Benzaldehyde and benzoyl chloride (which are also generally obtained by the photochlorination of benzoic acid) are used in pharmaceuticals ； Pesticides ； Dyes are widely used, especially in the synthesis of fragrances. The ring-chlorinated products of toluene are pesticides ； Pharmaceuticals ； Intermediates for dyes. The oxidation of toluene yields benzoic acid, an important food preservative (its sodium salt is primarily used) as well as an intermediate in organic synthesis. Intermediates obtained by sulfonation of toluene and its derivatives, including p-toluenesulfonic acid and its sodium salt ； CLT acid ； Toluene-2,4-disulfonic acid ； Benzaldehyde-2,4-disulfonic acid ； Toluenesulfonyl chloride and similar substances, used as additives in detergents and as anti-caking agents in fertilizers ； organic pigments ； Pharmaceuticals ； Production of dyes. A large number of intermediates are obtained by the nitration of toluene. Many end products can be derived from it, among which are polyurethane products ； Dyes and organic pigments ； Rubber additives ； Pharmaceuticals ； **These aspects are the most important. 2 Overview of Safety Hazards Due to the high volatility of benzene, it spreads easily when exposed to air. When humans and animals inhale or come into skin contact with large amounts of benzene, it can cause acute and chronic benzene poisoning. Some studies have shown that part of the cause of benzene poisoning is the formation of phenol in the body from benzene. Health hazards: It is irritating to the skin and mucous membranes, and has an **effect on the central nervous system. Acute poisoning: Inhaling high concentrations of this substance over a short period of time can cause significant irritation of the eyes and upper respiratory tract, congestion of the conjunctiva and throat, dizziness, headache, nausea, vomiting, chest tightness, weakness in the limbs, unsteady gait, and confusion. Severe cases may present with restlessness, convulsions, and coma. Chronic poisoning: Prolonged exposure can lead to neurasthenia syndrome, hepatomegaly, and abnormal menstruation in female workers. Dry skin, chapping, dermatitis. Environmental hazards: It poses serious threats to the environment, causing pollution to the air, water environments, and water sources. Fire and explosion hazard: This product is flammable and irritating. First aid measures: Skin contact: Remove contaminated clothing and thoroughly wash the skin with soapy water and clean water. Eye contact: Lift the eyelids and rinse with flowing water or saline. Seek medical attention. Inhalation: Quickly move to a place with fresh air. Keep the airways clear. If there is difficulty breathing, administer oxygen. If breathing stops, perform artificial respiration immediately. Seek medical attention. Ingestion: Drink plenty of warm water and induce vomiting. Seek medical attention. Fire-fighting measures: Hazardous properties: Flammable; its vapors can form explosive mixtures with air, and combustion and explosion can occur in the presence of open flames or high heat. It reacts violently with oxidizers. Too high a flow rate can easily generate and accumulate static electricity. Its vapor is heavier than air, allowing it to spread over considerable distances at lower levels; it will catch fire and reignite when exposed to a source of flame. Harmful combustion products: carbon monoxide, carbon dioxide. Fire extinguishing method: Spray water to cool the container; if possible, move the container away from the fire to an open area. If a container in a fire has changed color or sounds are coming from its safety pressure relief device, it must be evacuated immediately. Extinguishing agents: foam, dry powder, carbon dioxide, sand. Using water to extinguish the fire is ineffective. Emergency response to leaks: Immediate evacuation of people from the area contaminated by the leak to a safe zone, along with isolation of that area and strict restriction on access. Cut off the source of fire. It is recommended that emergency responders wear self-contained positive-pressure breathing apparatus and protective clothing. Seal the source of the leak as much as possible. Prevent entry into confined spaces such as sewers and drainage ditches. Minor leaks: Absorb with activated carbon or other inert materials. It can also be brushed with an emulsion made from non-flammable dispersants; the cleaning solution, after being diluted, is then discharged into the wastewater system. Large-scale leakage: Build dikes or dig pits to contain it. Cover with foam to reduce vapor damage. Transfer to a tank truck or specialized collector using an explosion-proof pump, and recycle it or transport it to a waste disposal facility for disposal. 3. Precautions for handling and storage: Operate in a sealed environment and ensure adequate ventilation. Operators must receive specialized training and strictly adhere to the operating procedures. It is recommended that operators wear self-priming filter-type gas masks (half-masks), chemical safety goggles, protective clothing resistant to toxic substances, and oil-resistant rubber gloves. Stay away from flames and heat sources; smoking is strictly prohibited in the workplace. Use explosion-proof ventilation systems and equipment. Prevent vapor from leaking into the workplace air. Avoid contact with oxidizers. During filling, the flow rate should be controlled, and a grounding device should be in place to prevent static electricity buildup. Handle with care during transportation to prevent damage to the packaging and containers. Equipped with appropriate types and quantities of fire-fighting equipment and emergency response devices for leaks. Empty containers may still contain harmful substances. Storage precautions: Store in a cool, well-ventilated warehouse. Keep away from flames and heat sources. The storage temperature should not exceed 30°C. Keep the container sealed. It should be stored separately from oxidizers; mixed storage is strictly prohibited. Use explosion-proof lighting and ventilation facilities. The use of mechanical equipment and tools prone to generating sparks is prohibited. The storage area should be equipped with emergency spill response equipment and appropriate containment materials.