Vast underground deposits of liquid hydrocarbons, mainly alkanes, are found it many regions of the catch. These are often locked under the dome-shaped imperious rock. When drilled out of the mine, the oily mixture of hydrocarbons in its crude form is called Petroleum (Latin, Petra= rock, oleum =oil), or Crude Oil. Accompanying the reservoirs of petroleum is Natural Gas, consisting of gaseous hydrocarbons, largely methane.
The origin of petroleum lies in plants and animals which lived on earth and in sea many millions of years ago. These organisms died and their remains became buried under the earth. Due to the bacterial decomposition and under the action of earth’s heat and pressure, these remains were converted to liquid hydrocarbons, the petroleum. The gaseous hydrocarbons that were produced, constituted the natural gas.
Today petroleum and natural gas rank as the main sources of our fuel and the bulk of organic chemicals used in market. With the rapid development of automobile and aircraft industry, and the petrochemicals that have shot up into prominence in 1960s, the rate of consumption of petroleum has become fast indeed. According to the present estimates, 80% of the world’s petroleum will be exhausted by the year 2025.
As at present, America is the biggest producer of petroleum, with is production of about 50% of
the world’s output. However, the largest oil fields are located in Saudi Arabia and Kuwait is estimated
that (USA has less than 10% of the world’s crude oil reserves, whereas the Middle East and Eastern
Countries possess over 60%
COMPOSITION AND USES OF NATURAL GAS.
The gas found above the petroleum deposits in mines or by itself, is referred to us Natural Gas
It is a mixture of low molecular weight alkanes. It is composed primarily of methane (30%), ethane
(13%), pro pane (3%), butane (1%), C5 to C8, alkanes (0 5%) and nitrogen (1.3%).
The natural gas is used as domestic fuel for heating and cooking. For this purpose, the hydrocarbon’s from C3, to C8, are removed as liquids by compression or ”solvent absorption’. The Remaining gad consisting of methane and ethane (also nitrogen) is compressed in steel cylinders and sold as Bottle: Gas. In large towns, compressed natural gas is distributed by pipelines. The natural gas has currently become a important tow material for several industrial organic chemicals. The prominent among these are ethylene, methyl alcohol, acetylene, and ammonia Ethylene and acetylene in turn are used for synthesising u spectrum of their derivatives.
COMPOSITION OF PETROLEUM.
Petroleum is an extremely complex mixture made up of hundreds of compounds, mostly hydrocarbons. It consists of alkanes, eycloalkanes, and aromatic hydrocarbons. Besides, there are present small amounts of sulphur and nitrogen compounds. The ratio of the various components much depends on the origin of the oil.
(30-70%). Petroleum contains straight chain alkanes (n-alkuncs) of well over 30 carbon atoms. Also present are many branched isomers (methyl n-alkanes) in the range C6-C8.
(16-64%). The cycloalkanes commonly present in petroleum are:
(8-15%). The cheif aromatic components of petroleum are:
S, N, O Compounds.
The sulphur compounds present to the extents of 6% include mercaptans (R-SH) and sulphides (R-S-R). The Nitrogen compounds are alkylpyridines, quinolines and pyrroles. The oxygen compounds found include alcohols, phenols and resins.
Petroleum usually occurs at moderate depths, sometimes 5,000 feet or more deep. The oil is found in porous
strata beneath the impervious rock (Fig. 10.13). It is often associated with natural gas which exerts pressure on the oil surface and drives it out with great velocity through natural openings.
In case of artificial mining, mines are bored in the upper crust. When the oil pocket is pierced, the gas pressure forces the out. As the gas pressure subsides or when there is nо gas, air pressure is applied to raise the oil from well.
The oil obtained from the mine is conveyed by a system of pipe-lines to a distant place and distilled. The distillation is not carried out on the spot so that the inflammable natural gas or other dissolved gases may not catch fire and thus damage the whole mine.
Petroleum as it comes from the ground is a rather viscous and highly coloured liquid. It often possesses unpleasant odour which is largely due to the presence of sulphur compounds in it. Technically it is called Crude Oil.
Crude oil consists chiefly of mixture of alkanes boiling between a wide range, say 0°C and 400°C
and as such it is unsuitable for most technical purposes. If, however, the oil is subjected to fractional
distillation, it can be separated into a number of fractions clash of which has a technical name and finds
use in industry. The process of dividing petroleum into fractions with different boiling ranges and free
from undesirable impurities, is termed Refining.
The distillation of petroleum is carried in a tubular furnace with a tall steel fractionating column (build). The crude oil is pumped continuously through heated pipes and flashed into the fractionating column. The vapours of the oil as they rise up the fractionating column, become cooler and condense at the shelves at various heights. The highest boiling fraction condenses, at the bottom and the Lowest booking fraction at the top. The uncondensed gases escape along with the gasoline.
vapours at the head of the column. Outlets are provided in the side of the column it suitable heights
to withdraw a number of fractions, the actual number of fractions and their boiling point ranges
depending on the source of the petroleum and the trade demand shows the composition
and uses of the main petroleum fractions.