CHEMISTRY  TOPIC: PETROLEUM - 1
By Kingsley Idiagbor,B.Sc (Hons), PGDCs, NCE, MNSM
The word "Petroleum" is derived from the Greek words "petros" (rock) and "oleum" (oil). Therefore, petroleum literally means "rock oil". It is synonymous with crude oil. Crude Oil This is a dark, greenish-brown and viscous liquid. It is formed when the remains of marine organisms are subjected to high temperature and pressure over millions of years. Crude oil is associated with stratified or sedimentary rock where it is trapped along with natural gas. The rocks surrounding the so-called "oil-trap" are impervious and non-porous. The gas is made to burn off, during the extraction of the crude oil, in what is known asgas flaring. The crude oil is extracted by drilling very deep holes into the earth crust using rotary rig supported by derrick. The crude oil is pumped out and sent to oil refineries through pipelines or by using oil tankers. Refining of Crude Oil Crude oil is a complex mixture of hydrocarbons, mostly alkanes. These hydrocarbons have boiling points close to one another and must undergo fractional distillation in the oil Refineries. The products of the distillation are called fractions which in turn contains several compounds that fall within a given boiling point range. Below is a table showing the various refined fractions and their different uses:
| Fraction | Approx. boiling pt
range | carbon atom
number | Uses | | Petroleum gas | < 40oC | 1-4 | Fuels for homes
and industries | | Naphtha/Ligroin | 40oC-175oC | 5-7 | organic solvents | Gasolene-PMS
(Petrol) | 175oC-250oC | 4-10 | Automobile &generator fuels; organic solvent | Kerosene
-DPK | 250oC-340oC | 11-18 | Fuel for lighting & heating
fuel for modern jet engines | Diesel
-AGO | 340oC-400oC | 12-23 | Fuel for diesel engines & farm machinery;fuel for heavy duty vehicles like trailers & tankers | Fuel oils/Lubricating wax
& grease | 400oC-500oC | >20 | As lubricant;
Used in making Petroleum jelly (e.g. Vaseline®),candles and polish | | Bitumen | > 500oC | > 35 | Residue used for surfacing roofs and roads |
Beyond Refining Process Of the refined fractions, gasoline (petrol) or PMS (Premium Motor Spirit) is probably the most demanded and popular fuel. However, it makes up less than 30% of the fractions. It is economical to convert some of the less desirable fractions with higher boiling points to lower boiling ones. This is possible through the process of cracking. CRACKING This is the splitting up of larger molecules of less desirable hydrocarbons (usually alkanes) to smaller and more desirable ones by heating. The products are mostly simpler alkanes and alkenes. TYPES OF CRACKING Thermal Cracking: The less volatile fractions like diesel or kerosene are heated to temperature of well over 650oC to form smaller chain alkanes and alkenes (predominantly etherne). Sometimes, hydrogen gas may be evolved, too. C11H24---->C6H14+ C3H6+ C2H4 Catalytic Cracking: The less desirable and non-volatile fractions of the crude oil like diesel are heated along with finely divided silica-alumina gel catalyst. This is called catalytic cracking. It is relatively more controllable than thermal cracking. Secondly, the process does not only increase the quantity of petrol but gives petrol of higher quality, as well. Back |Next
Copyright ©Kingsley Idiagbor | 5 September 2005- All rights reserved. No part of this article may be reproduced, transmitted or stored in electronic retrieval system without first obtaining permission from theownerof the copyright. Violators of this copyright notice are liable to civil action under the applicable Federal Laws ||| | | 
