Chemical Composition of Petroleum
Petroleum is a complex mixture of hydrocarbons that occur in the sedimentary rocks in the form of gases (natural gas), liquids (crude oil), semisolids (bitumen), or solids (wax or asphaltite).
The hydrocarbons in crude oil are mostly paraffin , naphthene, olefin and various aromatic hydrocarbons while the other organic compounds contain nitrogen, oxygen and sulfur, and trace amounts of metals such as iron, nickel, copper and vanadium.
A- Hydrocarbons components :
1- Paraffins are also called alkanes and have the general formula of CnH2n+2, where n is the number of carbon atoms. Paraffins from C1 to C40 usually appear in crude oil and represent up to 20% of crude by volume. Since paraffins are fully saturated (no double bond), they are stable and remain unchanged over long periods of geological time. Paraffins are found in different formula as follows:
a- Normal /or series paraffins:
The hydrocarbon chain is straight, example n butane mean n = 4 = carbon atoms ( C4H10 ). The properties of normal paraffins are:
High molecular weight.•
High boiling point.•
Low octane• number.
b- Branch /or iso paraffins:
The hydrocarbon chain is branched, example iso butane mean n = 4 = carbon atoms ( C4H10 ). The properties of branch paraffins are:
Low boiling point.•
High octane number therefore is• favorite in cars fuel.
The common in crude oil is one branch and less tow branches.•
2- Olefins are another series of noncyclic hydrocarbons but they are unsaturated and have at least one double bond between carbon-carbon atoms. Compounds with one double bond are called monoolefins or alkenes. Monoolefins have a general formula of CnH2n.
Olefins are uncommon in crude oils due to their reactivity with hydrogen that makes them saturated; however, they can be produced in refineries through cracking reactions.
3- Naphthenes or cycloalkanes or cycloparaffins are ring or cyclic saturated hydrocarbons with the general formula of CnH2n. Cyclopentane (C5H10), cyclohexane (C6H12), and their derivatives such as n-alkylcyclopentanes are normally found in crude oils.
Thermodynamic studies show that naphthene rings with five and six carbon atoms are the most stable naphthenic hydrocarbons. The content of cycloparaffins in petroleum may vary up to 60%.
4- Aromatics are an important series of hydrocarbons found in almost every petroleum mixture from any part of the world. Aromatics are cyclic but unsaturated hydrocarbons that begin with benzene molecule (C6H6) and contain carbon-carbon double bonds.
Some of the common aromatics found in petroleum and crude oils are benzene and its derivatives with attached methyl, ethyl, propyl, or higher alkyl groups. This series of aromatics is called alkylbenzenes and have a general formula of CnH2n-6 (where n ? 6).
B- Non hydrocarbons components :
The non hydrocarbon components are caused :
1- Corrosion.
2- Break down in the refinery operation.
The non hydrocarbon components are divided to :
I- Sulphur components :
It is the most important one that increase as the density increased. The types of sulphur components in the petroleum are :
i- Hydrogen Sulphide H- S- H ( or H2S )
ii- Mercaptance : H- S- R , where R is Alkyl ( H- S- CH3 ) .
iii- Sulphides :
* Aliphatic sulphide : R- S- R
* Cyclo sulphide :
Disadvantages of sulphur components:
1- Corrosion the metal parts of the engine.
2- Reduce octane number.
3- Reduce oxidation resistance.
4- Solids deposition.
II- Oxygen components :
These compounds increase with increasing the ( b.p. = boiling point ) of the fraction. The types of oxygen components in the petroleum are :
i- Acidic oxygen components:
III- Nitrogen components :
More asphaltic crudes will contain N2 compounds. They usually tolerate up to 0.25 wt%.
Disadvantages:
1- Can poison catalysts.
2- Increased carbon residue .
3- Decreased API.
Types of nitrogen components in the petroleum :
IV- Metallic components :
Disadvantages :
1- Affected on catalyst activity.
2- Coke formation.
3- Reduced the yield of the gasoline.
4- Form ash deposits-power generation plants.
5- Corrosion.
Types of metallic components in the petroleum :
1- Organic metallic ( Iron Fe , Nickel Ni , Vanadium V , Cadmium Cd).
2- Soap metallic ( Magnesium Mg , Calcium Ca , ….. ).
3- Salt metallic ( Na+ , Ba2+ , .... ).
VI- Brine water :
Water molecules are suspension in crude oil with extremely high
concentrations of dissolved salt ions nearly 300 – 300 000 ppm . The ions are divided to types:
1- Positive ions ( Na+ , Ba2+ , Mg2+ , Al3+ , ……… ) .
2- Negative ions ( Cl- , Br-, SO42- , I- , …….. ) .
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .
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