Chemistry - Various Raw Materials

Natural Gas, Coal

Fossil fuels and many other raw materials are the remains of plants and animals which lived millions of years ago. They are composed of hydrocarbons, so we call them fossil carbon compounds. Fossil fuels and other raw materials can occur as solids, usually in stratified layers of earth. Or, these materials can be liquids, as with oil. Natural gas, which is found in underground caves in often great quantities, occurs sometimes in kilometre-wide supply. Because coal is usually deposited near the surface of the Earth, it was the first fossil fuel to be used as an energy provider by our distant ancestors. Oil and natural gas have gained their importance as fuels mostly as raw materials for industry, and that in more recent times.

Coal is a flammable material made from the remains of plants and other organic substances, which during millions of years of geological history has been charred, or carbonised, to a brown or black colour in a sedimentary layer. Coal can be divided into various kinds based on its degree of carbonisation: brown, black and anthracite.

While brown coal contains about 60-70% carbon and has a relatively high water content, with ash matter and bitumen making up around (asi 7-20% ), hard, black coal is much richer in carbon (75-92% ), while being lower in water content, ash and bitumen. This makes it more expensive, of course. Anthracite is coal with a high degree of carbonisation (containing more than 91.5% carbon). Its water and ash content are negligible.

Carbonisation, or charring, is a process by which fossilised compounds become coal. In the process of this long-term geochemical change, plant material (cellulose and lignite) are transformed into peat, then to brown coal, hard coal and anthracite. One of the prerequisites for carbonisation is a large amount of matter containing carbon. A damp environment is also needed, as is a moderate climate. The organic material has to be covered with a thick layer of mineral sediment (in a depression in the earth). Carbonisation begins at high temperature and pressure in the absence of air, leading to the decrease of the concentrations of hydrogen and oxygen in the material. On the other hand, the relative concentration of carbon in the material increases.

The degree of carbonisation in a material rises from peat material, to brown coal, to black coal, to anthracite.

The various types of coal, with their differing degrees of carbonisation, have variable heat, or calorific, value, with the least amount in peat. Calorific value is the amount of heat energy which is released when 1 kg of material is burned. The calorific value of the individual fossil fuels is given in units of kilojoules per kilogram (KJ/kg)

wood 16 800 KJ/kg

peat 16 380 KJ/kg

brown coal 21 000 KJ/kg

black coal 34 860 KJ/kg

anthracite up to 36 120 KJ/kg

benzene 44 520 KJ/kg

Coal is used in a number of industrial processes, and in households, mostly as a fuel.

Natural gas is a naturally-occurring gas which is often found in caverns in the earth, often together with oil. Natural gas can also be found in porous layers of sand. Natural gas is a mixture of gases composed mostly of methane. Other gases which can be found in natural gas are other hydrocarbons (ethane, propane, butane), nitrogen, hydrogen, water and helium. It is formed by the transformation of fossil compounds by long geological processes. Natural gas can be won by digging natural gas wells. Natural gas need not be taken from the surface of the earth, because the internal pressure of the layer where it is found is sufficient to push it up to the surface of the earth. It is used today as a propulsion and heating material. It is also widely used in many chemical processes.

Oil, Fossil Fuels and Raw Materials

Composition and Uses of Oil and Natural Gas

Oil begins to be formed when microorganisms decompose plant and animal matter in the absence of air. This previously organic material is amassed thousands of meters below the surface of the Earth, in porous caverns in sedimentary rock formations. Oil is a brown to black liquid. It is more or less viscous, thanks to its chemical composition. Oil is a mixture of materials, but it is primarily composed of normal or cyclic hydrocarbons (up to 80-90% ) and water (10-14% ). Oil can be burned when it is in its liquid state, as a heating oil, but it is also a raw material in the production of other fuels, lubricants, paraffins and bitumens. Besides these uses, it is a geochemical raw material which is used in other special processes which produce various powders, plastics and synthetic fibres, among others.

Separation of Individual Oil Fractions Using Distillation

Oil is composed of a mixture of linear and cyclic hydrocarbons. These can be separated by taking advantage of their different boiling points, using distillation to separate the components. When oil is heated, its fractions, or components, with the lowest boiling point vaporise first. If the distillation is carried out gradually and slowly, a fraction can be cooled, and the gas will condense. In this way, one liquid fraction can be isolated, and this fraction should be fairly pure. This separation of the individual fractions of oil is called a fractional distillation. Of course, each individual fraction separated contains a mixture of materials. Each mixture has its own special uses as well.

Approximate Boiling Point (° C) Fraction Uses

500 bitumen asphalt products, freeway materials

From a practical point of view, fractional distillation means that when oil is heated, it vaporises, its fumes rising up a column from its liquid origin in the bottom of the column to the top. These fumes are horizontally divided into individual columns. The temperature of each fraction decreases as the column rises away from the original liquid material. The fractions condense and can be divided out. Before a fractional distillation of oil is carried out, the original oil sample must be cleaned, which means removing the salts it contains, and removing any water which might be present.

Mineral Oils and Motor Oil

Fuels contain alkanes and cyclic hydrocarbons in their liquid form, with two main groups which can be distinguished. Motor oils are products with low boiling points (30-200° C). These can be used in the propulsion systems of Otto motors. Diesel oil is separated from a boiling fraction at temperatures of 200-300° C. It is used in diesel motors and has a higher burning temperature than petrol. When the fuel is completely burned, water and carbon dioxide are produced. If there is insufficient oxygen available during the burning process, carbon monoxide, a very poisonous and reactive gas, is produced. The release of excessive carbon monoxide into the air can result in problems in the atmosphere. To help solve this problem, modern cars are equipped with catalytic converters, in order to decrease the amount of carbon monoxide and other harmful gases into the atmosphere. Catalytic converters change carbon monoxide into the less harmful carbon dioxide, as well as transforming harmful nitrogen oxides into less harmful compounds.

Environmental Consequences of Burning Fossil Fuels

Besides water, carbon dioxide is formed when fossil fuels are burned. This gas is released into the atmosphere. Atmospheric concentration of carbon dioxide rises, and the result is the we have to be concerned about possible changes to the Earth's climate. Carbon dioxide is not the only harmful gas released in burning reactions: Nitrogen-containing oxides and sulphur oxides are also released. The latter are easily dissolved in water, which makes them a main ingredient in rain, which falls on both land and water, acidifying our environment and bringing even more consequences to bear. The burning of fossil carbon sources, then, has significant effects on the Earth's climate, nature, agriculture and of course, our health. The use of alternative sources of energy, therefore, is the only possible answer to this dilemma. Only in this way can the negative effects of the release of these harmful gases be limited. Another possibility, of course, is using less energy, especially that derived from fossil fuels.

The significance of the above-mentioned alternative sources of energy has grown and continues to grow, on the one hand because of the pollution of our environment which is the result of the burning of fossil fuels. Not to be underestimated, however, is the reasoning that the stocks of these fuels are bound to be used up at some point in the not so distant future. Fossil fuels are one type of exhaustible energy source. There is only a certain amount of fossil fuels found on Earth; once this amount is gone, there is no way to produce more. As these stocks are used up, it will become more and more important to generate the energy humanity needs from alternative sources which can be regenerated and can therefore be used in a practically unlimited way. Wind energy, solar energy, hydroelectric energy and geothermic energy are only some of the possibilities.

Carboxylic Acids and Eesters

Nomenclature of Carboxylic Acids

Carboxylic acids are organic acids which contain a functional carboxylic group (-COOH). Aliphatic, saturated monocarboxylic acids which contain one carboxylic group in the molecule form a homologous group with the general chemical formula (CnH2a+1COOH). In naming of these acids, the compound name of the corresponding alkane is taken as an adjective, with the name of the acid added on. The first acids in the homologous group carry their traditional names:

formic acid (HCOOH)

acetic acid (CH3COOH)

propionate acid (CH3CH2COOH)

butyl acid (CH3CH2CH2COOH)

When the salts of carboxylic acids are named, the base name of the corresponding alkane is taken and an -ate suffix is added to the end. The cation of the salt is indicated by an adjective of the name of the element.

The hydrocarbon portion of the molecule of carboxylic acids is named according to how the corresponding alkane would be named. This is characterised by the main symbol of the carboxylic acid - for example the carboxylic group (-COOH), which is the functional group.

Physical Properties and Reactivity

Molecules of carboxylic acid are polar. The carboxylic groups contained on the molecules form hydrogen bonds with neighbouring molecules. Thanks to these weak intermolecular forces, carboxylic acids have high melting and boiling points. With increasing size of the hydrocarbon rest of the molecule, the polar character of the functional group is masked by the non-polar character of the hydrocarbon chain. The first homologous members of the series are liquids which are soluble in water. As the series continues, however, its members become solid at room temperature, and begin dissolving in non-polar solvents. Because of their acidic character, carboxylic acids form salts with impure metals.

The acid reactions which take place among carboxylic acids are caused to a great degree by the presence of their carboxylic group. Its oxygen atom increases the polar character of bonds formed with oxygen and hydrogen, making it very easy for it to release an electron - to form a carboxylic ion.

Acetic Acid

Acetic acid is the base ingredient of common table vinegar. Acetic acid is a clear liquid with an acrid odour. It is corrosive, and combined with indicators, it reacts in an acidic manner. Concentrated acetic acid is known as icy acetic acid, because below 16.6° C, its melting point, it hardens into a metal-like structure. Acetic acid is easily soluble in water and ethanol. When it is reacted with impure metals, hydrogen, metal salts and acetic acids known as octanes (acetates) are formed. Acetic acid is used in the food service industry. It is used as a preservative in the production of some groceries.

In industry, acetic acids are used to produce acetic acid esters. These are good solvents. In addition, acetic acids can be used in the production of plastics, artificial silks, some medicines and paints and other colourings.

The acids which are found in vinegar are produced with the help of the bacteria found in alcoholic wine. This reaction has as its mechanism the oxidation of ethanol by oxygen contained in the air, to acetic acid. This process is called acetic fermentation.

bacteria

CH3CH2OH + O2 ¾ ¾ ¾ ® CH3COOH + H2O

Ethanol acetic acid

Production of Esters and their Reactivity

Esters are produced when carboxylic acids are allowed to react with alcohols. Esters have the functional group -COO-. Water is also produced as a by-product in the reaction which produces esters.This is a reversible reaction, sometimes also called an equilibrium reaction. The break-up of an ester (reversible reaction) is called the hydrolysis of an ester. The synthesis of an ester is a multi-step reaction, with additions and eliminations included.

Significance of Esters

One of esters' most distinguishing characteristics is their intense odour, similar in some cases to fruits and other plants. For this reason, they are often used in the food service industry, especially in the production of certain delicacies or additives which tend to intensify some tastes in foods. Esters are good solvents. They are ingredients in some glues and paints. In the production of an ester from an acid derived from an alkane bonded to glycerin (glycerol), fats and oils are produced. The oils contain

unsaturated carboxylic acids of ester glycerin. The fats contain saturated acids. Waxes are esters of higher aliphatic alkanols with carboxylic acids. They have 16-32 carbon atoms in each molecule. Fats and oils are very significant for living organisms, because important materials necessary for living systems can dissolve in them.