Chemical composition of the crust

The crust of the earth composed of three principal types of rocks igneous, sedimentary and metamorphic. The 8 elements make up almost 99% of the earth’s crust.

Oxygen is the most abundant element by weight and accounts for more than 90% of the volume of the crust. Next in the sequence is silicon.

In the most abundant element’s list, everyday common elements like carbon, cooper, zinc and nitrogen do not appear among the 10 most abundant elements.

Chemical Composition of the atmosphere

The hydrosphere is composed of water, along with snow and ice. There is about 273 liters of water for each square cm of the earth’s surface. Of this water, 286.4 liters if ocean. 0.1 litres is freshwater and 4.5 litres is ice & snow. The earth’s atmosphere, is made up of a number of gases, which are

The N2 in the air, control the O2 in the air, as O2 is very reactive. Without N2, everything will be burning in the atmosphere. N2 also helps in plant growth & protein formation. CO2 is utilized by the plants to prepare food during the photosynthesis. Water vapour controls the evaporation of water from the bodies of plants & animals. Air is also required for burning and combustion. O2 is essential for respiration. The amount of O2, N2 and CO2 remains the same.

Petroleum and Natural Gas

The chemical composition of all petroleum or rock oil is principally hydrocarbons, although a few sulfur-containing and oxygen-containing compounds are usually present; the sulfur content varies from about 0.1 to 5 percent. Petroleum contains gaseous, liquid, and solid elements. The consistency of petroleum varies from liquid as thin as gasoline to liquid so thick that it will barely pour. Small quantities of gaseous compounds are usually dissolved in the liquid; when larger quantities of these compounds are present, the petroleum deposit is associated with a deposit of natural gas (see Gases, Fuel).

Three broad classes of crude petroleum exist: the paraffin types, the asphaltic types, and the mixed-base types. The paraffin types are composed of molecules in which the number of hydrogen atoms is always two more than twice the number of carbon atoms. The characteristic molecules in the asphaltic types are naphthenes, composed of twice as many hydrogen atoms as carbon atoms. In the mixed-base groups are both paraffin hydrocarbons and naphthenes

Formation

Petroleum is formed under the earth’s surface by the decomposition of marine organisms. The remains of tiny organisms that live in the sea—and, to a lesser extent, those of land organisms that are carried down to the sea in rivers and of plants that grow on the ocean bottoms—are enmeshed with the fine sands and silts that settle to the bottom in quiet sea basins. Such deposits, which are rich in organic materials, become the source rocks for the generation of crude oil. The process began many millions of years ago with the development of abundant life, and it continues to this day. The sediments grow thicker and sink into the seafloor under their own weight. As additional deposits pile up, the pressure on the ones below increases several thousand times, and the temperature rises by several hundred degrees. The mud and sand harden into shale and sandstone; carbonate precipitates and skeletal shells harden into limestone; and the remains of the dead organisms are transformed into crude oil and natural gas.

Once the petroleum forms, it flows upward in the earth’s crust because it has a lower density than the brines that saturate the interstices of the shales, sands, and carbonate rocks that constitute the crust of the earth. The crude oil and natural gas rise into the microscopic pores of the coarser sediments lying above. Frequently, the rising material encounters an impermeable shale or dense layer of rock that prevents further migration; the oil has become trapped, and a reservoir of petroleum is formed. A significant amount of the upward-migrating oil, however, does not encounter impermeable rock but instead flows out at the surface of the earth or onto the ocean floor. Surface deposits also include bituminous lakes and escaping natural gas.

Refining

Once oil has been produced from an oil field, it is treated with chemicals and heat to remove water and solids, and the natural gas is separated. The oil is then stored in a tank, or battery of tanks, and later transported to a refinery by truck, railroad tank car, barge, or pipeline. Large oil fields all have direct outlets to major, common-carrier pipelines.

Basic Distillation

The basic refining tool is the distillation unit. Crude oil begins to vaporize at a temperature somewhat less than that required to boil water. Hydrocarbons with the lowest molecular weight vaporize at the lowest temperatures, whereas successively higher temperatures are required to distill larger molecules. The first material to be distilled from crude oil is the gasoline fraction, followed in turn by naphtha and then by kerosene. The residue in the kettle, in the old still refineries, was then treated with caustic and sulfuric acid, and finally steam distilled thereafter. Lubricants and distillate fuel oils were obtained from the upper regions and waxes and asphalt from the lower regions of the distillation apparatus. In the later 19th century the gasoline and naphtha fractions were actually considered a nuisance because little need for them existed, and the demand for kerosene also began to decline because of the growing production of electricity and the use of electric lights. With the introduction of the automobile, however, the demand for gasoline suddenly burgeoned, and the need for greater supplies of crude oil increased accordingly.

Alternatives

In light of the reserves available and the dismal projections, it is apparent that alternative energy sources will be required to sustain the civilized societies of the world in the future. The options are indeed few, however, when the massive energy requirements of the industrial world come to be appreciated. Commercial oil shale recovery and the production of a synthetic crude oil have yet to be demonstrated successfully, and serious questions exist as to the competitiveness of production costs and production volumes that can be achieved by these potential new sources.

The various problems and potentials involved in such alternative sources as geothermal energy, solar energy, and nuclear energy are discussed in see Energy Supply, World. One of the alternative fuel that is capable of supplying the huge energy need of today’s world is coal, the availability of which in the U.S. and elsewhere throughout the world is well established. Associated with its projected increased utilization would be an increase in the use of coal-based electrical power to do more and more of the chores of industrialized nations. Adequate safeguards can perhaps be set on its use by modern engineering technology, with little increase in capital and operating costs. The last large-scale use of petroleum may thus occur before the end of the 20th century.

Use of ethanol as a blend and biofuels is catching pace nowadays.

Gaseous Fuels

Coal Gas

The most important coal-gasification processes aim chiefly at production of so-called pipeline quality gas, which is reasonably interchangeable with natural gas. Gas from coal, besides having pumping and heating specifications, must meet strict limits on content of carbon monoxide, sulfur, inert gases, and water. To meet these standards, most coal-gasification processes culminate with gas cleanup and methanation operations. Various hydrogasification processes, in which hydrogen reacts directly with coal to form methane, are used today; these processes bypass the indirect step of producing synthesis gas, hydrogen and carbon monoxide, before an upgrading yields methane. Other coal-gas processes include the carbon dioxide acceptor process, employing the lime-bearing material dolomite, and the molten salt process. These processes work indirectly to produce synthesis gas first. Other gases manufactured formerly from coal and coke, such as illumination gas and coke-oven gas, are of little or no importance today.

Producer and Blast-Furnace Gases

Producer gas is a form of water gas, a term applied to steam-process gases. It is made by burning low-grade fuel (such as lignite or bituminous coal) in a closed vessel, called a producer, while passing a continuous stream of steam and air through the producer. Because of the air present in the producer, the resulting gas is approximately 50 percent incombustible nitrogen and is low in fuel value, having only about 28 percent the heating value of coke-oven gas.

Blast-furnace gas, which results from the interaction of limestone, iron ore, and carbon in blast furnaces, has some heating value because of its carbon monoxide content but contains about 60 percent nitrogen. Enormous quantities are produced during the operation of furnaces. Most of this gas is consumed in heating the air blast and driving the compressors for the blast. The heating value of blast-furnace gas is about 16 percent of that of coke-oven gas. For a discussion of oil gas, made by the pyrolysis of petroleum hydrocarbons.

Natural Gas

A certain amount of natural gas almost always occurs in connection with oil deposits and is brought to the surface together with the oil when a well is drilled. Such gas is called casing-head gas. Certain wells, however, yield only natural gas.

Natural gas contains valuable organic elements that are important raw materials of the natural-gasoline and chemical industries. Before natural gas is used as fuel, heavy hydrocarbons such as butane, propane, and natural gasoline are extracted as liquids. The remaining gas constitutes so-called dry gas, which is piped to domestic and industrial consumers for use as fuels; dry gas, devoid of butane and propane, also occurs in nature. Composed of the lighter hydrocarbons methane and ethane, dry gas is used also in the manufacture of plastics, drugs, and dyes. Natural gas contains about 80% methane and 10% ethane, while rest is the other hydrocarbon gases. It is utilised as a domestic cooking gas, which is compressed and filled as liquefied petroleum gas (LPG) in the cylinders.

LPG

The Liquefied Petroleum Gas (LPG) is essentially liquid butane or propane (obtained from natural gas) or butane propane mix (obtained during refining of gas or cracked gas). The fuel is highly volatile, gaseous under ordinary atmospheric situations, highly combustible and forms an explosive mixture with air. To detect the gas leakage, a strong smelling substance (odorous organic sulphides known as mercaptans) are added. Except domestic use, the LPG can be utilised in agricultural, food processing, textile, metal and ceramic purposes. The compressed natural gas can be utilized as engine fuel for vehicles and trucks.

Gobar Gas

This gas is obtained by the gobar, which is subjected to anaerobic fermentation by a culture of microorganisms in closed tanks. The gas thus formed is mainly methane and CO2.The optimum temperature for the reaction is 35-55C.The residue is a excellent manure for the plant’s growth.

Performance of fuel

An octane rating scale has been developed to compare the performance of different mixtures of gasolines that might be used in automobile engines. A poor fuel such as heptanes, has been given an octane rating of zero while iso-octane has been given a rating of 100 on the octane scale and is known as the best fuel.

Octane number of a fuel is the percentage by volume of iso-octane in a mixture of iso-octane and the normal heptane that is equal to the fuel in knock characteristics under specified test conditions.

Chemical compounds are frequently added to petrol, to increase its efficiency as an engine fuel. One such additive is tetra ethyl lead. Organic phosphates are also introduced as additives.

Fuel cells

Fuel cells convert the energy of a fuel directly to electricity and supposed to be more efficient than the other methods of electricity generation.These electrical cells convert the energy from the combustion of fuels such as hydrogen, carbon monoxide or methane directly into electricity.A fuel cell uses the reaction of hydrogen with oxygen to from water and to supply electric power.The fuel cells can supply the electricity as long as reactants are supplied. So far 60-70 percent efficient fuel cells have been developed.

Fuel cells are free from pollution, and work is going on to reproduce electricity from fuel cells on commercial scale.