Benzene is an organic chemical compound; it is a colourless and a highly flammable liquid. It has a sweet smell and is an aromatic compound also known as an Arene. However it is used under strict conditions because it is carcinogenic. It is an important substance used primarily in industry to produce styrene for plastics, and is used as a solvent and precursor.
Structure and Formula
The molecular formula for Benzene is; C6H6. The structure of the aromatic hydrocarbon consists of alternating carbon double bonds, which has a continuous pi bond. The electrons between the C-C bonds are distributed evenly between the six Carbon atoms. In order to represent the nature of the delocalized electrons, Benzene can be shown simply as a circle inside a hexagon and is the simplest arene. The arrangement of six carbon atoms in aromatic compounds is known as a benzene ring.http://csrchem2005.bootsglobal.com/library/benzene.gifhttp://stpatschem11.files.wordpress.com/2010/05/benzene.jpg
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Its characteristic properties are that it is a colourless liquid, which is highly flammable. It has a molar mass of 78.11 g/mol and is less dense than water with a density of 0.8765 g/cm3. The melting point of the substance is 5.5 oC (279K) and has a boiling point of 80.1 oC (353K).
Arenes and Phenols Characteristic Properties
Arenes and Phenols are based on the Benzene ring; the structure of Phenol is shown below. Phenols have a hydroxyl group added onto a Benzene ring of C6H6. Phenols structure is C6H6OH, and is a crystal solid. Phenol has a molar mass of 94.11 g/mol and has a density of 1.07g/cm3. Its melting point is 40.5 °C, 314 K and has a boiling point of 181.7 °C, 455 K; It is used as a precursor to materials and is mildly acidic. However it has the potential to cause burns.
File:Phenol chemical structure.png
Benzene has many advantages and uses; these mainly lie with industrial products and processes. In motor vehicles Benzene is used as a fuel additive. This substance increases the fuels octane rating and reduces knocking. Increasing the octane rating means that the fuel burns in a more controlled manner as supposed to uncontrolled explosions. Meanwhile the reduce in knocking means that the air/fuel mixture combusts correctly in response to the ignition, by the spark plug and the air/fuel mixture will not explode outside the normal combustion cycle.
Other advantages to Benzene are that it can be used to produce styrene which is used to make polymers. Other derivatives include phenol and cyclohexane, phenol being used for resins and adhesives, while cyclohexane used for the production of nylon. Phenols are used to make rubber, lubricants, dyes, detergents, drugs, explosives and pesticides. Due to the health risks of Benzene a substitute called Toluene can be used, which has similar solvent properties, but is less toxic.
Benzene's main disadvantage is its reaction to humans. Benzene is carcinogenic; this means that it is an agent that causes cancer. Low levels of Benzene can cause dizziness, drowsiness, increased heart rate, headaches and tremors. Benzene has been infamously linked with many birth defects and rare cases of diseases. Health and safety factors must be consulted when interacting with Benzene, which means regulations, must be met by businesses in industry.
The use of Benzene in pesticides poses a threat to humans and animals. Benzene based pesticides are used to treat the soil, leafs, bulbs and crops of fruit and vegetable. The reaction to the small quantities of Benzene in the food can result in skin and mucous membrane irritations. The irritation of the mucous membrane occurs around the eyes and in the nose. Wildlife is also threatened; mainly to fish Pentachloronitrobenzene is highly toxic. People are liable to benzene exposure through cigarettes. These account for the highest number of exposures of benzene. Cigarettes produce benzene when they are lit. Approximately 50-150 micrograms of Benzene is produced per cigarette.
Benzene is produced in some soft drinks, while being stored. Sodium benzoate and potassium benzoate form benzene. Heat, light and shelf life can affect the rate at which benzene is formed. Benzene can be exposed as a vapor; these can come from detergents, glues and paints. Benzene is considered to be carcinogenic at concentration of 0.1% and greater.
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How is Benzene is used in industry?
Different products which use benzene are paint strippers. Benzene is used because it is a solvent, which breaks down the adhesion of the paint making it weak and allowing it to be removed.
Benzene when used as a fuel additive for car engines, reduces knocking and increases octane rating, typically Benzene is being used much less due to its carcinogenic properties, therefore only 0.62% of Benzene is used in these type of products.
Xylene comes from is a mixture of three structural isomers of the aromatic hydrocarbon dimethylbenzene, it is used in permanent markers, it is used as it acts as a solvent, in this product, it dissolves a layer of the surface allowing the ink to adhere.
Benzene used extensively in the rubber industry. Car tires, shoes and other synthetic rubber products are common. Styrene is used to make these products which is comes from Benzene. It has always been used as a feedstock for synthetic rubbers. Typically a concentration of 0.5% of Benzene is used in rubber.
4.2 The Friedel Crafts alkylation of Benzene
The alkylation process causes Benzene C6H6 to react with an Aluminium Chloride or an Iron Chloride catalyst. This forms Toluene (C6H5CH3) + Hydro-Chloric Acid (HCL).
In this case of Benzene, a methyl group is substituted into the Benzene ring. A hydrogen atom is replaced by the methyl group. Benzene reacts with a Chloroalkane alongside an Aliminium Chloride catalyst. This product that is formed is methylbenzene also known as Toluene.
Aluminium Chloride catalyst is a strong Lewis acid and an electrophile. The electrophile accepts electrons from the chloroalkane a nucleophile. The Alimnium chloride accepts the lone chloride which forms Al4- at the same time the CH3+ is formed. The Al4- in the reaction removes the hydrogen atom from the Benzene ring; the catalyst is naturally not used up, so is present at the end of the reaction.http://www.chemguide.co.uk/mechanisms/elsub/alkylm1.GIF
Producing a Phenol
In order to produce Phenol for industrial purposes, Cumene is produced in the gas phase of the Friedel crafts alkylation of Benzene. Cumene partially oxidizes using the Hock Rearrangement:
C6H5CH(CH3)2 + O2 → C6H5OH + (CH3)2CO
4.3 Coking process of petrochemicals
Coking is the process of transforming very heavy resid into gasoline diesel fuel and petroleum coke.
There are two main types of coking, these are delayed coking and fluidic coking, there is also flexi-coking process but is not used in industry.
Delayed Coking process
The use of the delayed coker cracks the heavy and long chain resid into coker gas oil and petroleum coke. The act of thermo-cracking increases the hydrogen to carbon ratio by carbon rejection.
Preheat resid feed which provides condensing of coke drum vapors by introducing the feed to the bottom of the main fractionators.
The coke drum feed is heated by fired heaters. As cracking continues in the drum, gas, oil is converted into vapor which then separate from the liquid and solids. Only the drum vapor is sent to a fractionation column where it is separated into the different boiling point fractions. Solid coke is sent to a porous drum which allows the coke to pass through. All solids and uncracked resid produced from the vapor and liquid remain in the drum.
After the drum is filled with solidified coke, the mixture from the furnace is switched to a second drum. While the second drum is filling, the first drum undergoes steaming to further reduce hydrocarbon content of the petroleum coke, and then water is added to cool it. When the drums are full of coke in the bottom and top areas, the solid petroleum coke is then separated from the coke drum via hydro jetting, where it falls into a pit, where it can be kept in storage.
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Fluidic Coker Process
The fluidic process is used to convert low value resid to valuable products such as coker gas oil including Naphtha and Diesel. The act of thermo-cracking increases the hydrogen to carbon ratio by carbon rejection in a continuous process.
Resid feed is heated, and then the coke particles are scrubbed. This provides condensing of the reactor vapors, by interacting the oil feed and the scrubber. The vaporized resid is atomized into liquid coke; this is then ready for thermo-cracking which happens on the particle surface. Coke particles that exit the reactor are undergone by steam stripping this removes the remaining liquid hydrocarbons. Some of the coke is burned in order to produce heat for the reactor, substoichiometric air is used in this process. Lastly the vapors from the scrubber exit to the fractionators where it is heated in desirable boiling point fractions.