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The air available in nature consists of a mixture of pure gases. These gases always contain individual atoms (like noble gases) or atomic gas (as neon), or compound molecules containing a variety of atoms (like carbon dioxide). Each of these gases has its applications. Also, each gas must be separated from the mixture and converted into its pure form for further usage. This article explains the manufacture of pure gases from a mix of pure gases.
What is Gas?
Gas is one of the three forms of matter, other than the liquid and solid state. It has no definite shape or volume. It takes the shape of a vessel or container in which it is present. Gases can be of any of the types listed below.
Pure gases
Mixed gases
Compound gases
What are Pure Gases?
Pure gases consist of individual atoms or a mixture of noble gases and other atomic gases. They can be elements with many atoms, or a single compound.
Examples of pure gases
Some examples of Pure gases are:
Acetylene
Oxygen
Acetylene
Acetylene is a tasteless, colourless and odourless gaseous element discovered in 1836 by Edmund Davy, a scientist and chemistry professor. This gas is used widely for various industrial applications. Acetylene is odourless and colourless in its pure form. If this gas is used without safety measures, it can be dangerous as it could explode.
Applications of Acetylene
This gas is used in many areas, such as,
Welding
Cutting
Chemical production
Metallurgical heating
In glass industry
Production of Acetylene
This gas is produced by mixing the raw materials Calcium Carbide (CaC2) and water in the Acetylene gas plant. Calcium Carbide is prepared by mixing lime and coke in a blast furnace, which is formulated as shown below:
CaC₂+ 2H₂O 🠆 C₂H₂+Ca(OH)₂
where,
C₂H₂ 🠆 Acetylene
Ca(OH)₂ 🠆 Carbon Hydroxide
This experimental setup to produce acetylene is shown in the figure below.
The step-by-step manufacturing process of generating acetylene is explained below with a block diagram.
The process is initiated by sending Calcium Carbide into the hoover.
Next, water and C₂H₂ are mixed, and acetylene, along with heat and calcium hydroxide, gets formed instantly. Calcium Carbide is added in small quantities each time after the pressure drops inside the generator to sustain the pressure in the reaction.
The heat produced during this process is controlled or minimised by passing this acetylene into a cooling condenser surrounded by water pipes.
Water is removed from this stream using an ammonia scrubber, which lowers the temperature of the acetylene stream.
A medium pressure drier with calcium chloride is also used to remove most of the moisture present in the stream.
Further, to remove any impurities in the stream like Arsine and Phosphine, the dried acetylene is passed through a special purifier and is removed from the gas. This step can be avoided if the desired product is Industrial Acetylene.
The gas is then passed into a sequence of high-pressure driers used to remove any oil and moisture.
Acetylene is finally compressed into a cylinder containing acetone and porous monolithic mass filler. The ratio of acetone and acetylene is always constant. However, it can vary according to the cylinder size.
This air compressor helps in the functioning of the acetone pump, slurry pump and actuated ball valves.
Oxygen
Oxygen is a tasteless, colourless and odourless gaseous element that belongs to the Chalcogen group of the periodic table. It is highly reactive and easily forms oxides and other compounds as it is a good oxidising agent. It is the third-largest element in the universe after hydrogen and helium.
Manufacture of Oxygen
Oxygen can be manufactured using many techniques. One simple and natural technique is photosynthesis.
Generation of Oxygen through Photosynthesis
During photosynthesis, plants absorb Carbon dioxide and water from soil and air. Water molecules are oxidised inside the plant cells, and electrons are lost, whereas Carbon dioxide is reduced, and the gain of electrons is seen. Then, CO2 is converted into oxygen and released into the air.
The photosynthesis is explained through the following equation.
6CO₂+6H₂O🠆C₆H₁₂O₆+6O₂
where,
CO₂ is carbon dioxide
H₂O is water
C₆H₁₂O₆ is carbohydrate
Generation of Oxygen through Cryogenic Distillation Method
This is the most commonly used method to generate oxygen. It was developed by Carl Von Linde in 1895. In this process, oxygen is separated from argon, nitrogen and other elements. This method is said to produce about 99% of pure oxygen. The term Cryogenic relates to lower temperatures, and distillation refers to methods of separating the elements in a mixture based on the boiling points of the elements.
The block diagram of the Cryogenic distillation of air is shown below:
The step-by-step manufacturing process of oxygen is explained below.
Pre-treatment
Compressing and cooling the incoming air
Carbon dioxide removal
Heat transfer
Air distillation
Pre-treatment
This process involves passing air through filters and purifying them.
This filtered air is compressed and passed into several intercoolers, which cools the air.
This is an important step where all the Carbon dioxide that is present in the air must be removed completely before it is passed into the downstream unit as they may clog the equipment, damaging them when they freeze at low temperatures.
Heat Transfer and Cooling the Air
Filtered air is fed through a heat exchange component as shown above, where it is cooled and further passed into the other units.
Air Distillation
It is the final step in the oxygen manufacturing procedure.
Nitrogen is separated using a distillation column (usually one for Nitrogen).
Two distillation columns are also used in cases when the gas is to be very pure.
Oxygen separation also requires two distillation columns where the first column is maintained at high pressure and the second at low pressure.
To remove argon from oxygen, we use a side stream and remove it.
