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Benzene (chemical formula C)
6
H
6
It is an aromatic hydrocarbon. It is flammable, volatile, pungent and colorless liquid at room temperature. Benzene is highly toxic, on October 27, 2017, the World Health Organization's International Agency for Research on Cancer published a preliminary list of carcinogens for reference, benzene in the list of class 1 carcinogens.
[1]
Benzene is the simplest aromatic hydrocarbon, insoluble in water, easily soluble in organic solvents, itself can also be used as an organic solvent. Benzene is the basic raw material of petrochemical industry, and its output and production technology level is the symbol of the development level of national petrochemical industry. The benzene ring system is called the benzene ring, which is the simplest aromatic ring. The structure of benzene molecule after removing a grain of hydrogen is called phenyl group, which is expressed by Ph; Thus benzene can also be expressed as PhH.
[2]
- Chinese name
- benzene [3]
- Foreign name
- Benzene, benzol
- alias
- Benzoic oil
- Chemical formula
- C 6 H 6 [3]
- Molecular weight
- 78.11 [3]
- CAS login number
- 43-71-2 [3]
- EINECS login number
- 200-753-7 [3]
- Melting point
- 5.5 ℃ [3]
- Boiling point
- 80.1 ℃ [3]
- Water solubility
- Slightly soluble (0.17g / 100g) [4] (0.17g/100g)
- density
- 0.88 g/cm³ [3]
- Flash point
- -11 ℃ [3]
- should
- Used as spices, dyes, plastics, medicine, explosives, rubber and so on
- Security description
- S36/37; S45; S53
- Risk description
- R11; R36/38; R45; R46; R48/23/24/25; R65 [5]
- UN Dangerous Goods number
- 1114/1115 [5]
- Molar mass
- 78.11 g/mol [3]
- Ignition temperature (℃)
- 560
- Explosion limit (%)
- 8.0 [5]
- Lower explosive limit (%)
- 1.2 [5]
- solubility
- Insoluble in water, soluble in ethanol, ether, acetone and other organic solvents.
- Refractive index (25 ℃)
- 1.49794
- Viscosity (mPa·s,
- 0.6010
catalogue
- 1Brief history of research
- 2Material structure
- 3Physical property
- 4Chemical property
- ▪Substitution reaction
- ▪Halogenation reaction
- ▪Nitration reaction
- ▪Sulfonation reaction
- ▪The Fouckek reaction
- ▪Blanc chloromethylation reaction
- ▪Gattermann-Koch reaction
- ▪Addition reaction
- ▪Oxidation reaction
- ▪Reduction reaction
- ▪Coordination reaction
- ▪photoisomerization
- ▪other
- 5Molecular structure data
- 6Computational chemical data
- 7Related substance
- ▪derivate
- ▪The main isomer
- 8Preparation method
- ▪Extracted from coal tar
- ▪Extracted from petroleum
- ▪Alkane aromatization
- ▪Steam cracking
- ▪Aromatics separation
- ▪Toluene dealkylation
- ▪Toluene thermal dealkylation
- ▪Other methods
- 9Application field
- 10Security risk
- ▪Health hazard
- ▪Safety measure
- ▪Fire extinguishing method
- ▪Relevant laws and regulations
- ▪Exposure limit
- ▪Clinical manifestations of acute benzene poisoning
- ▪First aid treatment
- 11Toxicological data
- ▪Acute toxicity
- ▪irritability
Benzene was first discovered in 1825 by the English scientist Michael Faraday (1791-1867). At the beginning of the 19th century, the United Kingdom and other European countries, the city lighting has been widespread use of gas. After gas is prepared from the raw materials used to produce gas, an oily liquid remains that has long been neglected. Faraday was the first scientist to become interested in this oily liquid. He separated this oily liquid by distillation and produced another liquid, which was actually benzene. Faraday referred to this liquid as a "heavy carbon compound of hydrogen."
Kekule double bond oscillation model
Kekul
In 1834, German scientist Ernst Mitscherlich (i.e., Ernst Mitscherlich, 1794-1863)
[6]
By distilling a mixture of benzoic acid and lime, a liquid identical to Faraday's was obtained and named benzene. After the correct molecular and valence concepts in organic chemistry were established, the French chemist Gerhardt (Charles Frederic Gerhardt, 1816-1856)
[7]
The relative molecular mass of benzene is 78 and the molecular formula is C
6
H
6
. The relative amount of carbon in benzene molecules was so high that chemists were surprised. Chemists have encountered difficulties in determining the structural formula for benzene: such a large ratio of carbon to hydrogen indicates that benzene is a highly unsaturated compound, but it does not have the typical unsaturated compounds should be prone to addition reactions.
[8]
Austrian chemist Lochmitt (i.e. Johann Jasef Loschmidt)
[9]
In his book Chemical Investigations (1861), he drew the cyclic chemical structures of 121 benzene and other aromatic compounds. German chemist Friedrich August Kekule von Stradonitz (1829-1896)
[11] 10 -
Having also read the book, in a letter to his students dated January 4, 1862, Lochmet's description of molecular structure was confusing. However, Lochmet drew the benzene ring as a circle.
Kekule was a highly imaginative scholar who developed the important theory that carbon tetrad and carbon atoms can be connected into chains. For the structure of benzene, after analyzing a large number of experimental facts, he believes that this is a very stable "nucleus", the bond between the six carbon atoms is very firm, and the arrangement is very compact, and it can be connected with other carbon atoms to form aromatic compounds. So Kekule focused on the "core" of these six carbon atoms. After proposing a variety of open chain structures but rejecting them one by one because they were inconsistent with the experimental results, in 1865 he finally realized that the form of closed chain was the key to solving the molecular structure of benzene.
Kekule's understanding of the ring structure of benzene molecules has been an interesting story in the history of chemistry. In 1890, at a conference held in Berlin's city Hall to celebrate the 25th anniversary of Kekule's discovery of the benzene ring structure, he said it came from a dream. One night, when he was teaching at Ghent University in Belgium, he dozed off in his study and saw spinning carbon atoms again. The long chain of carbon atoms coiled and curled like a snake, and suddenly a snake caught hold of its tail and spun around. He woke up like an electric shock, worked through another busy night sorting out the benzene ring structure hypothesis. In response, Kekule said: "We should dream! ... Then we can discover the truth... But let us not declare our dreams before sober reason has examined them." It should be noted that it is no accident that Kekule was able to take inspiration from his dreams and successfully put forward important structural theories.
However, in 1992, John H. Wotiz (1919-2001), a professor of chemistry at Southern Illinois University, wrote in his book The Kekule Mystery, The book "The Kekuleriddle, a Challenge to Chemists and Psychologists" questions Kekuleriddle's role in the construction of the benzene ring structure. As early as 1854, the French chemist Laurent (Auguste Laurent, 1807-1853) had drawn the molecular structure of benzene into a hexagonal ring structure in his book Chemical Methods. Votiz also found in Kekule's archives a letter he had written to his German publisher on July 4, 1854, in which he offered to translate Laurene's book from French into German. This suggests that Kekule has read and is familiar with Lauren's book. However, Kekule did not mention Laurene's work on the structure of the benzene ring in his paper, only Laurene's other work.
[3]
[8]
Benzene's benzene ring structure gives it special aromaticity. Benzene ring is the simplest aromatic ring, consisting of six carbon atoms forming a six-membered ring, each carbon atom is connected to a group of groups, the six groups of benzene are hydrogen atoms.
Benzene is not a rotaene with alternating single and double bonds, and the bonding between atoms is not a discontinuous alternating single and double bond, but a cloud of delocalized π electrons.
Benzene is A flat molecule with 12 atoms in the same plane, 6 carbons and 6 hydrogens equal, and the C-H bond length is 1.08 A and the C-C bond length is 1.40 A, which is between the single and double bond lengths. All bond angles of the molecule are 120°, indicating that the carbon atoms all adopt sp
2
Hybrid. So each carbon atom is left with a p orbital perpendicular to the molecular plane, and each of those orbitals has an electron. The six orbitals overlap to form a delocalized large Π bond (π
6
6
The resonance formula shown in the figure below is now believed to be the reason why the benzene ring is very stable, and also directly makes the benzene ring aromatic.
[12]
From the perspective of molecular orbital theory, it can be assumed that the six p orbitals of benzene interact to form six Π molecular orbitals, where ψ
1
, ψ
2
, ψ
3
It's the lower energy bonding orbital, ψ
4
, ψ
5
, ψ
6
It's a higher energy antibonding orbital. Bits of
2
, ψ
3
Sum ψ
4
, ψ
5
It's two degenerate orbitals. The electron cloud distribution of benzene in the ground state is the result of the superposition of the three bonding orbitals, so the electron cloud is evenly distributed on the benzene ring and the ring atoms, forming a closed electron cloud. It is the source of the ring current generated by benzene molecules in magnetic fields.
12 - [13]
Benzene has a boiling point of 80.1 ℃ and a melting point of 5.5 ℃. It is colorless, transparent, aromatic and volatile at room temperature. Benzene has a lower density than water, with a density of 0.88 g/cm
3
But its molecular mass is higher than that of water. Benzene is insoluble in water
[4]
1 liter of water dissolves up to 1.8 grams of benzene; However, benzene is a good organic solvent and has a strong ability to dissolve organic molecules and some non-polar inorganic molecules.
[14]
Benzene can be azeotized with water, boiling point 69.25 ℃, containing benzene 91.2%, in the reaction of water generation often benzene distillation, in order to distillate water.
The saturated vapor pressure between 10 and 1500 mmHg can be calculated according to Antoine's equation:
The unit of P is mmHg, the unit of t is ℃, A = 6.91210, B = 1214.645, C = 221.205.
There are roughly three kinds of chemical reactions that benzene participates in: one is the substitution reaction between other groups and hydrogen atoms on the benzene ring; One is the addition reaction on the benzene ring (note: the benzene ring has no carbon-carbon double bond, but a unique bond between a single bond and a double bond); One is universal combustion (oxidation reaction) (which does not discolor acidic potassium permanganate).
[15]
Under certain conditions, the hydrogen atoms on the benzene ring can be replaced by halogens, nitro, sulfonic acid groups, hydrocarbon groups, etc., to form the corresponding derivatives. Due to the different substituents and the different positions and quantities of hydrogen atoms, isomers of different quantities and structures can be formed.
The electron cloud density of benzene ring is high, so most of the substitutions in benzene ring are electrophilic substitutions. Electrophilic substitution reaction is a typical reaction of aromatic rings. When benzene substituents undergo electrophilic substitution, the position of the second substituent is related to the type of the original substituent.
[15]
The general formula for the halogenation of benzene can be written as:
In the reaction process, halogen molecules are heterolysis under the combined action of benzene and catalyst, X
+
Attack the benzene ring, X
-
It binds to the catalyst.
Take bromine as an example, the liquid bromine and benzene are mixed, bromine is dissolved in benzene, forming a reddish-brown liquid, no reaction occurs, when the iron filings are added, under the catalysis of the generated iron bromide, bromine and benzene react, the mixture is slightly boiling, the reaction exothermic red brown bromine steam is generated, and the condensed gas appears white fog (HBr) when it meets the air. Catalytic process:
After the reaction, the mixture is poured into cold water, and the reddish-brown oily liquid (dissolved with bromine) is sunk to the bottom, and the colorless liquid bromobenzene is obtained after washing with dilute lye.
In the industry, benzene halogenates with chlorine and bromine substitutes are the most important.
[15]
Nitrobenzene can be formed by benzene and nitric acid in the presence of concentrated sulfuric acid as catalyst
Nitrification is a strong exothermic reaction, easily forming a substitute, but further reaction is slower. Among them, concentrated sulfuric acid as a catalyst, heated to 50~60 degrees Celsius reaction, if heated to 70~80 degrees Celsius benzene will occur sulfonation reaction with sulfuric acid, so the general use of water bath heating method for temperature control. When the benzene ring is connected with a nitro group, the nitro group can inhibit the further nitrification of benzene, and the nitro group is the passivation group.
[15]
Benzene sulfonic acid can be sulfonated into benzene sulfonic acid by fuming sulfuric acid or concentrated sulfuric acid at a higher temperature (70~80 ℃).
After the introduction of a sulfonic acid group on the benzene ring, the reaction ability is reduced, and it is not easy to further sulfonate, and higher temperatures are required to introduce the second and third sulfonic acid groups. This shows that nitro and sulfonic acid groups are passivating groups, that is, groups that prevent the re-electrophilic substitution.
[15]
In AlCl
3
When catalyzed, benzene can also react with alcohols, alkenes and halogenated hydrocarbons, and the hydrogen atoms in the benzene ring are replaced by alkyls to form alkyl benzene. This reaction is called alkylation reaction, also known as Fourier alkylation reaction. For example, alkylate with ethylene to form ethylbenzene:
During the reaction, the R group may be rearranged: for example, 1-chloropropane reacts with benzene to form isopropylbenzene, because the free radical always tends to a stable configuration.
Under the catalysis of strong sulfuric acid, benzene reacts with an acyl halide or carboxylic anhydride, and the hydrogen atoms in the benzene ring are replaced by acyl groups to form acyl benzene. The reaction conditions are similar to alkylation reactions, which are called Fouck-K reactions. For example, the reaction with acetyl chloride:
chloromethylation can be prepared by the reaction of benzene with formaldehyde and hydrogen chloride in the presence of anhydrous zinc chloride. This reaction is called chloromethylation and is an important method for introducing substituents into aromatic rings.
Under pressure or under the catalysis of cuprous chloride, benzene or other aromatic compounds react with carbon monoxide and hydrogen chloride to produce aromatic aldehydes, which is called Gattermann-Koch reaction.
Although benzene ring is very stable, but under certain conditions can also occur double bond addition reaction. Benzene can produce cyclohexane, usually by catalytic hydrogenation with nickel as catalyst, but the reaction is extremely difficult.
In addition, the reaction of benzene to hexachlorocyclohexane (BHC) can be obtained by the addition of benzene and chlorine gas under the condition of ultraviolet irradiation. The reaction belongs to the addition reaction of benzene and free radicals.
[15]
Benzene, like any other hydrocarbon, burns. When oxygen is sufficient, the products are carbon dioxide and water. But when burned in air, the flame is bright and has thick black smoke. This is due to the large mass fraction of carbon in benzene.
Benzene itself cannot be mixed with acidic KMnO
4
The solution reaction, however, can make acidic KMnO after the benzene ring is connected with C directly to H
4
The solution faded.
[15]
Benzene can also be oxidized by ozone under certain circumstances, and the product is glyoxal. This reaction can be seen as the ozonation of cyclic polyolefins formed after the delocalization of benzene electrons.
Under normal conditions, benzene cannot be oxidized by strong oxidants. However, in the presence of catalysts such as molybdenum oxide, benzene can be selectively oxidized to maleic anhydride by reacting with oxygen in the air. This is one of the few reactions that can destroy benzene's six-membered ring system.
Australian chemist A. J. Birch found that alkali metals (sodium, potassium or lithium) react with aromatic compounds in A mixture of liquid ammonia and alcohol (ethanol, isopropyl alcohol or secondary butanol), and the benzene ring can be reduced to 1, 4-cyclohexene compounds, the reaction is called Birch reduction.
Benzene and substituted benzene can form π complexes with transition metals. For example, titanium vapor is mixed with benzene vapor and cooled to -196 ℃ with liquid nitrogen to obtain benzene complexes of titanium.
Benzene can be converted into Dewar benzene under strong light conditions: the nature of Dewar benzene is very active (benzene itself is a stable aromatic state, the energy is very low, and to become Dewar benzene requires a lot of light energy, so Dewar benzene energy is very high, unstable).
Under the action of the laser, it can be converted into a more active prism alkane: prism alkane presents a three-dimensional state, resulting in carbon atoms sp
3
π bonds formed by hybrid orbitals have a larger mutual repulsion, so they are more unstable.
[15]
Benzene at high temperature, with iron, copper, nickel as catalyst, can undergo condensation reaction to form biphenyls. In the presence of zinc chloride with formaldehyde and hypochlorous acid, alkyl metallides such as chloromethyl benzene and sodium ethyl can be formed. Neutralizing magnesium with tetrahydrofuran, chlorobenzene, or bromobenzene produces a phenyl Grignard reagent.
Benzene will not react with potassium permanganate and fade, and only extraction will occur when mixed with bromic water, and in benzene and its derivatives, potassium permanganate can fade only when the carbon atom connected with the benzene ring is connected with hydrogen in the substituent group on the benzene ring side chain (essentially oxidation reaction). This also applies to aromatic hydrocarbons (if there is an unsaturated bond on the substituent, it must be able to react with potassium permanganate to fade). Note: 1. Only carbon atoms connected to the benzene ring on the substituent; 2. The carbon atom will bond with the hydrogen atom.
For bromine water, benzene and benzene derivatives and saturated aromatic hydrocarbons can only be extracted (provided that there are no unsaturated bonds on the substituents, otherwise the addition reaction will still occur).
[15]
1, molar refractive index: 26.25
2. Molar volume (cm
3
/mol) : 89.4
3. Isotropic specific volume (90.2K) : 207.2
4, surface tension (dyne/cm) : 28.8
5, polarizability (10-24cm
3
) : 10.40
[3]
1. Reference value for calculating hydrophobic parameters (XlogP) : None
2. Number of hydrogen bond donors :0
3. Number of hydrogen bond receptors :0
4. Number of rotatable chemical bonds :0
5. Number of tautomers: None
6. Topological molecular polar surface area 0
7. Number of heavy atoms :6
8. Surface charge :0
9. Complexity :15.5
10. Number of isotope atoms :0
11. Determine the number of protonic centers :0
12. Number of uncertain atomic stereocentes :0
13. Determine the number of chemical bond structure centers :0
14. Number of uncertain chemical bond stereocenter :0
15. Number of covalent bond units :1
[3]
1. Substituted benzene:
Alkyl substitutions: toluene, xylene (p-xylene, m-xylene, o-xylene), styrene, phenylacetylene, ethylbenzene
Group substitution: phenol, benzoic acid, acetophenone, benzoquinone (p-benzoquinone, o-benzoquinone)
Halogenated: chlorobenzene, bromobenzene
Multiple mixed group substitution: 2,4, 6-trinitrotoluene (TNT)
2. Polycyclic aromatic hydrocarbons: biphenyls and terphenyls
3. Dense aromatic hydrocarbons: naphthalene, anthracene, phenanthrene, indene, fluorene, acenaphthene and azulene
[16]
The main isomer of benzene
Benzene can be obtained by incomplete combustion of materials with a high carbon content. Benzene is produced in nature by volcanic eruptions and forest fires. Benzene is also found in cigarette smoke. Benzene is the main component of coal tar obtained by coal distillation.
Until World War II, benzene was a by-product of the coking process of the steel industry. This method can only extract 1 kilogram of benzene from 1 ton of coal. After 1950, with the increasing demand for benzene in industry, especially in the growing plastics industry, the process of producing benzene from petroleum came into being. Since the 21st century, most of the world's benzene has come from petrochemical industry. The three most important processes for the industrial production of benzene are catalytic reforming, hydrodealkylation of toluene and steam cracking.
The light tar produced in the coking process of coal contains a large amount of benzene. This is how benzene was originally produced. The generated coal tar and gas are passed through the washing and absorption equipment together, and the coal tar with high boiling point is used as the washing and absorption agent to recover the coal tar in the gas, and the crude benzene and other high boiling fraction are obtained after distillation. Industrial grade benzene can be obtained by refining crude benzene. The purity of benzene obtained by this method is relatively low, and the environmental pollution is serious, and the process is relatively backward.
[17]
Crude oil contains a small amount of benzene, and the extraction of benzene from petroleum products is the most widely used preparation method.
[17]
The process by which aliphatic hydrocarbons are formed into rings and dehydrogenated to form aromatic hydrocarbons. It was developed during the Second World War.
At 500-525 ° C and 8-50 atmospheres of pressure, various aliphatic hydrocarbons with boiling points between 60-200 ° C are converted to benzene and other aromatic hydrocarbons by dehydrogenation and cyclization via platinum-rhenium catalysts. After the aromatic hydrocarbon product is extracted from the mixture, benzene is separated by distillation. These fractions can also be used as high octane gasoline.
[18]
Steam cracking is a process of producing olefin from low molecular alkanes such as ethane, propane or butane, as well as petroleum components such as naphtha and heavy diesel. One of its by-products, cracked gasoline, is rich in benzene and can be fractionated to produce benzene and other components. Cracked gasoline can also be mixed with other hydrocarbons as an additive to gasoline.
About 40-60% of benzene in cracked gasoline, but also contains diolefin and styrene and other unsaturated components, these impurities in the storage process easy to further reaction into polymer gum. Therefore, it is necessary to first go through the hydrotreatment process to remove these impurities and sulfides in the cracked gasoline, and then carry out appropriate separation to obtain benzene products.
The components of benzene-containing fractions obtained from different methods are very complex and difficult to be effective by ordinary separation methods. Generally, liquid-liquid extraction with solvents or extraction distillation is used to separate aromatics, and then benzene, toluene and xylene are separated by general separation methods. There are a variety of separation methods depending on the solvent and technology used.
Udex method: Jointly developed by Dow Chemical Company and UOP Company in 1950, it initially used diethylene glycol ether as a solvent, and later improved to triethylene glycol ether and tetraethylene glycol ether as a solvent, and the process used a multi-stage ascending channel extractor. The yield of benzene is 100%.
Sulfolane process: Developed by Shell, patented by UOP. The solvent is sulfolane, and the extraction is carried out by rotary extraction tower. The product needs to be treated with clay. The yield of benzene was 99.9%.
[19]
Arosolvan method: Developed by the Federal German company Lurgi in 1962. The solvent is N-methylpyrrolidone (NMP), and in order to increase the yield, sometimes 10-20% glycol ether is added. With the specially designed Mechnes extractor, the yield of benzene is 99.9%.
IFP method: Developed by the French Institute of Petroleum Chemistry in 1967. Aqueous dimethyl sulfoxide was used as solvent and back extraction was carried out with butane in a turntable column. The yield of benzene was 99.9%.
Formex process: Developed in 1971 by the Italian company SNAM and the LRSR Petroleum Processing Division. Morpholine or N-formylmorpholine was used as solvent in a turntable column. The total yield of aromatic hydrocarbons was 98.8%, and the yield of benzene was 100%.
Any of a class of hydrocarbons containing one or more benzene rings, belonging to an aromatic hydrocarbon.
[18]
Benzene can be prepared by catalytic hydrodealkylation of toluene or thermal dealkylation without catalyst. The feedstock may be toluene and its mixture with xylene, or fractions containing benzene and other alkyl aromatics and non-aromatics.
Catalytic hydrodealkylation of toluene
With chromium, molybdenum or platinum oxide as a catalyst, under the conditions of 500-600 ℃ high temperature and 40-60 atmospheres, toluene and hydrogen can be mixed to produce benzene, this process is called hydrodealkylation. If the temperature is higher, the catalyst can be omitted. The reaction follows the following equation:
According to the different catalyst and process conditions, there are many process methods
The Hydeal process was developed by Ashiand & refing and UOP in 1961. 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℃, the pressure is 3.43-3.92 MPa. The theoretical yield of benzene is 98%, the purity is above 99.98%, and the quality is better than that of benzene produced by Udex method.
Detol process, developed by Houdry. Alumina and magnesium oxide were used as catalysts, the reaction temperature was 540-650 ℃, the reaction pressure was 0.69-5.4 MPa, and the raw material was mainly carbon-7-carbon-9 aromatics. The theoretical yield of benzene is 97% and the purity is 99.97%.
Pyrotol process, developed by Air products and chemicals and Houdry. It is suitable for producing benzene from ethylene by-product cracked gasoline. The catalyst was alumina-chromium oxide, the reaction temperature was 600-650 ℃, the pressure was 0.49-5.4MPa.
Benzene can be prepared by dealkylation of toluene under high temperature hydrogen without catalyst. The reaction is exothermic and a variety of processes have been developed in response to different problems encountered.
The MHC hydrodealkylation process was developed by Mitsubishi Petrochemical and Chiyoda Construction in 1967. Raw materials can be made of pure alkyl benzene such as toluene, containing aromatic fractions within 30% of non-aromatic fractions. The operating temperature is 500-800 ℃, 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 by Hydrocarbon Research and Atlantic Richfield in 1962. The raw materials are toluene, xylene, hydrocracked gasoline and reformed oil. The reaction temperature was controlled from different parts of the reactor, such as hydrogen. The reaction temperature was 600-760 ℃, the pressure was 3.43-6.85 MPa, the hydrogen/hydrocarbon ratio was 1-5, and the residence time was 5-30 seconds. The selectivity is 95% and the yield is 96-100%.
Toluene disproportionation and alkyl transfer: With the increase of xylene consumption, toluene disproportionation and alkyl transfer technologies that can simultaneously increase xylene production were developed in late 1960.
This reaction is a reversible reaction, according to the use of catalyst, process conditions, raw materials and different processes.
1.LTD liquid phase toluene disproportionation process, the United States Mobil Chemical company developed in 1971, the use of non-metallic zeolite or molecular sieve catalyst, reaction temperature 260-315 ℃, the reactor using liquid phase adiabatic fixed bed, raw material for toluene, conversion rate of more than 99%.
Alkyl transfer
2.Tatoray process, developed by Toray Company and UOP Company in 1969, uses toluene and mixed carbon-9 aromatics as raw materials, the catalyst is mercerized zeolite, the reaction temperature is 350-530 ℃, the pressure is 2.94 MPa, the hydrogen/hydrocarbon ratio is 5:12, and the adiabatic fixed bed reactor is adopted. The conversion rate of one way is above 40%, the yield is above 95%. 90% selectivity, the product is a mixture of benzene and xylene.
Xylene plas process: Developed by Atlantic Richfield and Engelhard in the United States. Rare earth Y-type molecular sieve was used as catalyst, the reactor was a vapor phase moving bed, the reaction temperature was 471-491 ℃, normal pressure.
3.TOLD process, Japan Mitsubishi Gas Chemical Company developed in 1968, hydrofluoric acid-boron fluoride catalyst, reaction temperature 60-120 ℃, low pressure liquid phase. It is corrosive.
[20]
In addition, benzene can also be obtained by acetylene trimerization, but the yield is very low.
As early as 1920, benzene has been a common solvent in industry, mainly for metal degreasing. Benzene is toxic, and the human body can directly contact the solvent production process has not used benzene as a solvent.
Benzene can be used as a gasoline additive because it has the effect of reducing knock. Before the introduction of tetraethyl lead in 1950, all antiknock agents were benzene. But now that the leaded gasoline has faded, benzene has returned. Benzene has an adverse effect on the human body, the underground water quality is also polluted, European and American countries limit the content of benzene in gasoline shall not exceed 1%. In 2011, the U.S. Environmental Protection Agency tightened restrictions again, lowering the benzene limit in gasoline to 0.62 percent.
[16]
The most important use of benzene in the industry is to do chemical raw materials, the main uses are as follows:
1. Used as an important raw material for synthetic dyes, synthetic rubber, synthetic resins, synthetic fibers, synthetic grains, plastics, medicine, pesticides, photographic film and petrochemical products. This product has good solubility, so it is widely used as adhesives and industrial solvents such as: varnish, nitro fiber paint thinner, paint remover, lubricating oil, grease, wax, celluloid, resin, artificial leather and other solvents.
2. Standard sample for measuring refractive index. It can be used as a solvent and cleaning agent for precision optical instruments, electronics industry, organic synthesis, etc.
3. Used as an analytical reagent. If used as solvent, chromatographic analysis of standard substances.
4. Cosmetic solvents. It is mainly used as a thinner for cosmetics such as nail polish to accelerate drying and hardening, and to improve the solubility of skin film components such as resins.
5. Used as a solvent and synthetic benzene derivatives, spices, dyes, plastics, medicine, explosives, rubber, etc.
[21]
Benzene is volatile and diffuses easily when exposed to air. Human and animal inhalation or skin contact of a large amount of benzene into the body, can cause acute and chronic benzene poisoning, benzene has a stimulating effect on the skin, mucous membranes. Some studies have reported that benzene poisoning is caused in part by the conversion of benzene into phenol in the body.
Benzene can paralyze the central nervous system and cause acute poisoning. In severe cases, headache, nausea, vomiting, confusion, loss of consciousness, coma, convulsions and other symptoms, and in severe cases, death due to central system paralysis. A small amount of benzene can also cause drowsiness, dizziness, rapid heart rate, headache, shaking, confusion, confusion and other phenomena. Ingestion of foods containing too much benzene can cause symptoms such as vomiting, stomach pain, dizziness, insomnia, convulsions, rapid heart rate and even death. Inhaling 20,000 ppm of benzene vapor for 5 to 10 minutes can be fatal.
[22-23]
Long-term exposure to benzene can cause great damage to the blood, cause chronic poisoning, and cause neurasthenic syndrome. Benzene can damage bone marrow, reduce the number of red blood cells, white blood cells, and platelets, and make chromosome aberration, resulting in leukemia, and even aplastic anemia. Benzene can cause excessive bleeding, which suppresses the function of the immune system and allows disease to take hold. Studies have reported that the incubation period of benzene in the body can be as long as 12 to 15 years.
[22]
When a woman inhales too much benzene, it can cause irregular menstruation for months and shrink the ovaries. The effects of benzene on fetal development and male fertility are not well understood. Inhalation of benzene in pregnant animals can lead to weight loss in young, delayed bone development, and bone marrow damage.
[23]
Benzene has an irritating effect on skin and mucous membrane. The International Center for Research on Cancer (IARC) has identified it as a carcinogen.
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Store in low temperature and ventilated place, away from fire and heat sources. And oxidizer, edible chemicals equal storage. Do not use tools that may cause sparks.
Flammability: flammable
Fire extinguishing agent: foam, dry powder, carbon dioxide, sand. Extinguishing with water is ineffective.
According to the Indoor Air Quality Standard (GB/T 18883-2022)
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, benzene ≤0.03 mg/m
3
According to the Code for Indoor Environmental Pollution Control of Civil Building Projects (GB 50325-2020), Class I civil building projects (residential buildings, hospitals, elderly buildings, kindergartens, school classrooms and other civil building projects) : benzene ≤ 0.06mg /m
3
Class II civil construction projects (offices, shops, hotels, cultural and entertainment places, libraries, stadiums, exhibition halls, gymnasiums, public transport waiting rooms, restaurants, barber shops and other civil construction projects) : benzene ≤ 0.09mg /m
3
China PC-TWA: 6 mg/m
3
; PC-STEL: 10 mg/m
3
American ACGIH 10 ppm, 32 mg/m
3
TWA: OSHA 1 ppm， 3.2 mg/m
3
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Metabolism: Benzene enters the human body mainly through respiratory inhalation (47-80%), gastrointestinal and skin absorption. A portion of benzene can be excreted in the urine, but the unexcreted benzene is first oxidized by oxygen molecules in the liver under the action of cytochrome P450 monooxygenase to epoxide benzene (7-oxabicyclic [4.1.0] hept-2, 4-diene). Benzene epoxide is in balance with its rearrangement product oxacycloheptatriene, which is a toxic intermediate produced during benzene metabolism. Then there are three metabolic pathways: binding with glutathione to produce phenylmercaptouric acid; Continue to metabolise into phenol, catechol, hydroquinone, pyrogallol, o-quinone, p-quinone, etc., and excreted in the form of glucosidic acid or sulfate conjugate; And oxidized to hexadienedioic acid. Ethanol and toluene can reduce the toxicity of benzene.
Benzene metabolites enter the cell, combined with deoxyribonucleic acid (DNA) in the nucleus, will make chromosome changes, such as some breaks, some combination, which is cancerous (figurative, is mutated, because the chromosome is genetic material, it controls the structure of the cell and life activities, etc.), long-term, it will cause cancer.
1, mild poisoning may have headache, dizziness, tears, dry throat, cough, nausea and vomiting, abdominal pain, diarrhea, gait instability; Skin, nail and mucous membrane purple, acute conjunctivitis, tinnitus, photophobia, palpitation and pale face and other symptoms.
2, moderate and severe intoxication, in addition to the above symptoms of aggravation, lethargy, slow reaction, trance, etc., may also be rapid coma, pulse tachycardia, blood pressure drop, systemic skin, mucous membrane cyanosis, rapid breathing, convulsions, muscle tremors, some patients can also appear agitation, euphoria, delirium and peripheral nerve damage, and even dyspnea, shock.
1, inhalation of poison, patients should be quickly moved to fresh air, take off contaminated clothes, loosen all clothes and neck, chest buttons. Belt, so that it lies still, if there is dirt in the mouth and nose, it should be removed immediately to ensure normal lung ventilation and smooth breathing. And pay attention to keep your body warm.
2, oral poisoning should use 0.005 g/ml activated carbon suspension or 0.02 g/ml sodium bicarbonate solution to wash the stomach to induce vomiting, and then take cathartic and diuretic drugs to speed up the excretion of toxins in the body and reduce the absorption of toxins.
3, skin poisoning, should change the contaminated clothes and shoes and socks, with soapy water and water repeatedly wash the skin and hair.
4, coma, convulsive patients, should be removed as soon as possible to keep the airway smooth, by the special escort hospital treatment.
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LD50:1800 mg/kg (rat transoral); 4700 mg/kg (mouse oral); 8272 mg/kg (rabbit percutaneous)
LC50：31900 mg/m
3
(Rat inhalation, 7 h)
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Rabbit percutaneous: 500 mg (24 h), moderate irritation.
Rabbit transocular: 2 mg (24 h), severe stimulation.
3.3 Subacute and chronic toxicity
Rabbits inhaled 10 mg/m
3
A few days to a few weeks, causing a decrease in white blood cells and a relative increase in the percentage of lymphocytes. Hematopoietic system changes in chronically poisoned animals, serious bone marrow dysplasia.
DNA inhibition: human leukocyte 2200 μmol/L. Sister chromatid exchange: human lymphocytes 200μmol/L. Cytogenetic analysis: Human inhalation 125 ppm (1a). Somatic mutation: Human lymphocyte 1 gm/L.
The minimum toxic dose (TCLo) of 5 ppm was inhaled 6 to 15 days after pregnancy, resulting in malformation of the blood and lymphatic system (including spleen and bone marrow). The mice were given the lowest toxic dose (TDLo) of 219 mg/kg in the abdominal cavity, resulting in developmental malformations of the blood and lymphatic systems and hepatobiliary duct systems.
IARC Carcinogenicity Review: G1, Confirmed human carcinogen.
The minimum inhalation toxic concentration (TCLo) in rats was 15 ppm/24 h (7-14 d of gestation), resulting in increased post-implantation mortality and abnormal skeletal muscle development.
LC50:45 mg/L (24 h) (goldfish); 20 mg/L (24-48 h) (bluegill sunfish); 27 mg/L (96 h) (small Longarm shrimp);
LC100:12.8 mmol/L (24 h) (Tetrahymena pyriformis);
LD100:34 mg/L (24 h) (bluegill sunfish);
TLm: 36 mg/L (24~96 h) (guppies, soft water)
Aerobic biodegradation (h) : 120~384
Anaerobic biodegradation (h) : 2688~17280
Aqueous photodissociation half-life (h) : 2808~16152
The maximum wavelength range of photolysis light absorption (nm) : 239~268
Photooxidation half-life (h) in water: 50.1~501
Bioenrichment: BCF: 3.5 (Anguilla japonica); 4.4 (Atlantic herring); 4.3 (Goldfish)
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Store in a cool, ventilated warehouse. Keep away from fire and heat. The temperature of the reservoir should not exceed 30 ℃. Keep the container sealed. It should be stored separately from oxidants and edible chemicals, and should not be mixed. Explosion-proof lighting and ventilation facilities are adopted. Do not use mechanical equipment and tools that are prone to spark. The storage area should be equipped with leak emergency treatment equipment and suitable containment materials.
[3]
Closed operation to enhance ventilation. Operators must be specially trained and strictly abide by the operating procedures. It is recommended that operators wear a self-priming filter gas mask (half mask), chemical safety protective glasses, protective work clothes, and rubber oil-resistant gloves. Keep away from fire and heat. No smoking in the workplace. Use explosion-proof ventilation systems and equipment. Prevents steam from leaking into the workplace air. Avoid contact with oxidants. When filling, the flow rate should be controlled, and there is a grounding device to prevent static accumulation. When handling, light loading and unloading should be done to prevent damage to packaging and containers. Equipped with the corresponding variety and quantity of fire equipment and leakage emergency treatment equipment. Empty containers may have harmful residues.
[3]
Gas chromatography and high performance liquid chromatography can detect the benzene content in various products. The purity of benzene is generally determined by the freezing point method.
For the detection of trace benzene in the air, it can be absorbed by volatile organic solvents such as methylsilicone oil or low molecular weight polymers, and then analyzed by chromatography; Or use colorimetric analysis; The air containing benzene can also be deeply frozen, the benzene is frozen, and then the solution of iron sulfate and hydrogen peroxide is added to obtain a yellowish brown or black precipitate, and then dissolved with nitric acid, and then analyzed by colorimetric method. Or directly absorb benzene in the air with nitric acid, nitrate into m-dinitrobenzene, and then titrate with titanium dichloride solution, or use m-xylene prepared methyl ethyl ketone base solution colorimetric quantification.
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