This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.
Benzene is a colourless, flammable liquid which disappears very fast and also dissolves in water too. Benzene levels are lifted by the burning of coal and oil, benzene waste and storage operations, motor vehicle exhausts and evaporation from petrol service stations. Once benzene is in the air, it reacts with different chemicals, however is usually breaks down within a few days and is spread throughout the skies and also the environment. Having benzene in water and soil will break down more slowly and is able to go through soil and through underground water. Benzene has also got bad disadvantages on the human body a lot of these cases including affects the health of humans if humans absorb benzene by the lungs or by touching it could be very.http://web.pdx.edu/~nathanh/benzene/benzene2.gif
The molecular formula is C6H6
Benzene is a colourless liquid with a characteristic odour with formula C6H6.
A closed ring with the connection of 6 carbon atoms and bonds which differ between single and double bonds.
Every single carbon atom is like a spring to a single hydrogen atom.
Benzene has a melting point of 5.5°C; it boils at the temperature of 80.1°C.
Benzene and its unoriginal are part of which are known as the important chemical group known as aromatic compounds.
Benzene is a forerunner in the making of drugs such as for e.g.; plastics, gasoline, synthetic rubber, and dyes.
What industries use Benzene?
Here is a list of 5 different industries which have the use of benzene in the industries:
- Petroleum refining industry
- Coke and coal chemical manufacturing industry
- Rubber tire manufacturing industry
- Shoe manufacturing industry
- Formula 1 car industry
What products are made from benzene?
Here is a list of 10 different products that are made via using benzene:
Varnishes and lacquer.
Solvents that are used in industry.
Gloss paint, normal paint varnish paint etc
Many different types of Detergents
Thinners that are used
Inks are used
Rubber is used
Process of benzene in Inks:
In the Rubber tire manufacturing industry the use of benzene comes into use via the production of ink printing this is when benzene becomes solvent. This thoroughly is able to keep the ink in a liquidized form so that it isn't able to get dry very quick. When ink is being used during the process of printing, fumes of benzene can be free in the workplace and in the air; these fumes are what the workers intake. Most the time, ink is given via the use of machines this ink is heated or warmed and this is what creates friction, which will allow in-fact the fumes of benzene to get away faster and into higher levels of concentrations.
Process of benzene in gasoline:
In the petroleum refining industry benzene has a 1-2% percent of gasoline used. Due to the properties of anti-knock, a vast amount of benzene-rich aromatics is mixed with gasoline so this can be replaced for alkyl lead compounds. A few of the benzene however in the fuel is found through vehicles and as of this fuel that has not been burned. However on the other hand benzene is formed as a partial combustion product of complex aromatic fuel components. Non-benzene aromatics in gasoline such as toluene, ethyl benzene, xylenes, and heavy reformate (C9+) this tends to increase exhaust benzene levels with a mild effect, per unit of aromatic content, from this about 8 percent of that of benzene is in gasoline. In exhaust hydrocarbons the amount of benzene varies generally between 3-5 percent. Anti-knock is a gasoline stabilizer which is used to lower engine knocking and to increase the fuel's octane rating. When gasoline is used in high density internal combustion engines, it has a tendency to light early, which negatively can cause a damaging "engine knocking" noise.
Friedel-Crafts alkylation involves a halide alkyl using a powerful Lewis acid catalyst and also an alkylation of an aromatic ring. As anhydrous aluminium chloride is being the catalyst right now, the alkyl group pulls at the former site of the chloride ion just like a force. The big disadvantage about this reaction is that, the product is more nucleophilic than the reactant due to the electron donating alkyl-chain.
The 2 main types of Friedel-Crafts reactions are;
This reaction is a type of something called an electro-phillic aromatic substitution. The general reaction chain is shown below.
The Friedel-Crafts Alkylation of benzene with chloromethane
Friedel-Crafts alkylation involves a halide alkyl using a powerful Lewis acid catalyst and also an alkylation of an aromatic ring. As the alkyl group pulls at each other the former site of the chloride ion the anhydrous ferric chloride behaves just like a catalyst, below shows the basic mechanism.
Mechanism for the Friedel Crafts alkylation
By looking at reaction you can tell there is a disadvantage. This disadvantage is that the product is more nucleo philic rather than the reactant; this is mainly due to the fact of the electron donating alkyl-chain. So on the other hand, hydrogen is swapped with an alkyl-chain, which gives way to the-alkylation of the molecule. On the other hand if the chlorine is not on a tertiary carbon, carbocation rearrangement the reaction will occur most definitely. The main reason being is due to the relative stability of the tertiary carbocation over the primary and secondary carbocations.
Alkylations are not restricted to alkyl halides: It is possible that with the Friedel-Crafts reactions any carbocationic intermediate such as those derived from alkenes and a protic acid, Lewis acid, enones, and epoxides. An E.G. is the synthesis of neophyl chloride from benzene and methallyl chloride
H2C=C (CH3)2CH2Cl + C6H6 â†’ C6H5C (CH3)2CH2Cl
MECHANISM FOR THE FRIEDEL-CRAFTS ALKYLATION OF BENZENE
The alkyl halide acts with the Lewis acid to form a more electrophilic C, a carbocation
Friedel-Crafts alkylation of benzene
The ° electrons of the aromatic C=C act as a nucleophile, attacking the electrophilic C+. This step removes and destroys the aromaticity giving the cyclohexadienyl cation intermediately
The proton is removed from the sp3 C bearing the alkyl- group reforms the C=C and the aromatic system, generating HCl and regenerating the lively catalyst.
By producing high octane gasoline and aromatics in petroleum refineries and petrochemical industries you can get the best out of the catalytic reforming of naphtha. The reason why the naphtha reformer is used that it has to upgrade a specific portion of the crude oil from low octane heavy naphtha which is not suitable for motor gasoline into a high octane gasoline blending component.
Industrial catalysts used in recent catalytic reforming units are consisted of gama alumina support and some metals, such as platinum, rhenium, germanium and iridium.
There are seven types of reactions that take place in the process of catalytic reforming process they are as follows;
1. Dehydrogenation 5. Hydro cracking
2. Isomerisation 6. Hydrogenolysis
3. Cyclization 7. Coke Formation.
Catalytic reforming is the form in whichlight petroleum distillates (naphtha's) are mixed with a platinum-containing catalyst during a phase where there are high temperatures and also pressures of hydrogen from 345, to for the purpose of raising the octane number of the hydrocarbon feed stream. The low octane, paraffin-rich naphtha feed is converted to a high-octane liquid product that is rich in aromatic compounds. Hydrogen and other light hydrocarbons are also produced as reaction by-products. By the use of reformate as a blending component of motor fuels, it is also a primary source of aromatics used in the petrochemical industry.
Catalytic processes were introduced in the 1940s they offered better yields and higher octanes, however still thermal processes were used first. The first catalysts were based on supported molybdenum oxide, soon platinum catalysts came into the category and they were started being used. The first platinum-based reforming process came into use in 1949. Also since the first Platinum forming unit was commercialized, designs and plans to make it much better and advance been made on the regular, mainly including including parameter optimization, catalyst formulation, equipment design, and maximization of reformate and hydrogen yields. The need to increase yields and octane led to lower pressure, higher severity operations. This also resulted in increased catalyst coking and faster deactivation rates.
The units for catalytic reforming were created as semi regenerative (SR), or fixed bed units, using Pt/alumina catalysts. Semi regenerative reforming units are periodically shut down for catalyst regeneration. This step includes burning off coke and reconditioning the catalyst's active metals. To minimize catalyst deactivation, these units are required to be operated at high pressures in the range of 2,760 to 3,450 kPa (400-500 psig). By having high hydrogen pressure decreases the coking and deactivation rates.
Primary Process Technique:
Where the catalyst is transferred from one stage to another, through a catalyst regenerator and back again. Desired reactions include: dehydrogenation of naphthenes to form aromatics; isomerization of naphthenes; de-hydrocyclization of paraffin's to form aromatics; and isomerization of paraffin's. Hydro cracking of paraffin's is undesirable due to increased light-ends make. This is where reforming reactions occur in chloride promoted fixed catalyst beds; or continuous catalyst regeneration (CCR) beds
Naphtha feed and recycle hydrogen are mixed, heated and sent through successive reactor beds.
Each pass requires heat input to drive the reactions.
Final pass effluent is separated with the hydrogen being recycled or purged for hydro treating.
Reformate product can be further processed to separate aromatic components or be used for gasoline blending.
This is a diagram of a Catalytic Reforming Process Schematic:
The liquid product stream from the separator is directed into the gasoline stabilizer unit where the LPG and gasoline streams are produced.
Before going into the catalytic reformer, HSRG goes through a procedure called hydrodesulphurization (HDS) reaction in the hydro-treatment catalyst. The process is as follows; the hydro-treated HSRG enters the reforming reactors which are semi-regenerative types which consist of three radial flow fixed bed reactors which are connected in series circuit. The table above shows that, the reformer feed is preheated first and then secondly enters the first reactor where naphthenes are dehydrogenated to aromatics.
As the process is continuing the steam of the product from the first reactor after preheating goes through the second reactor and in the same way the product stream from the second reactor after preheating enters the third reactor. So generally its process is being repeated. The Overall reforming reactions that take place in the reactors are endothermic and so there is a pre-heater installed before each reactor. The third reactor is the product stream and this enters a separator wherein a hydrogen rich gas stream is made which is then is recycled and mixed with the first reactor fresh feed. The reforming of the catalyst distribution in the reactors of the refinery was shown above in the diagram