The cooking gas is the LPG (Liquefied petroleum gas), but this acronym can also mean Pressurized Liquid Gas. These names indicate the origin and some characteristics of cooking gas, that is, its origin is oil; it is liquid inside the gas cylinder; and is subjected to high pressures. But let's explain all this in more detail.
O oil refinement through fractional distillation it originates several fractions that have wide commercial use. Among these fractions, there is LPG, which is composed of propane gases (hydrocarbon with three carbon atoms) and butane (a hydrocarbon with four carbon atoms).
H3C CH2 CH3 H3C CH2 CH2 CH3
Propane Butane
Propane and butane gases are the main components of cooking gas, being highly flammable, odorless and colorless. But if they don't smell, why do we immediately smell a distinctive odor when cooking gas is leaking?
In fact, this smell that we smell is neither propane nor butane, but rather sulfur substances (thiocompounds or sulfur compounds), more specifically from the group of thiols, also called mercaptans. These substances that are added to cooking gas have an extremely unpleasant odor and can be readily detected by the consumer even at low concentrations. This alert reduces the risk of accidents. Commonly used thiols are ethanethiol, butan-1-thiol and 1,1-dimethylethanethiol. They are shown below:
CH3
│
H3C CH2 ─ SH H3C CH2 CH2 ─ SH H3C C ─ SH
ethanethiol butan-1-thiol │
CH3
1,1-dimethylethanethiol
Another fraction that is even the lightest fraction obtained in oil refining is thenatural gas. It can also be used in some cases as cooking gas in homes and industries with specific installation. Natural gas is composed of hydrocarbons of 1 to 2 carbon atoms, mainly the methane (CH4), which can appear in an abundance of 70% to 99%. Other components are: ethane (C2H6), from 0.5% to 7%, in addition to inorganic substances such as H2S, CO2, no2, He etc.
Molecules that are part of the cooking gas composition (butane, methane, propane and ethane, respectively)
LPG gas does not contain inorganic substances such as those mentioned. Another difference is that, unlike LPG that comes in cylinders, natural gas is distributed by concessionaires (piped or street gas).
But we have another question: After all, cooking gas is it liquid or gaseous?
Under ambient conditions, cooking gas components (propane and butane) are in a gaseous state. But inside the cylinder made of steel, this gas is subjected to a very high pressure, which causes it to liquefy, that is, to pass from the gaseous state to the liquid (hence the name Pressurized Liquid Gas). That's why, if you shake the gas cylinder, you'll feel a liquid inside. This can be easily seen on clear lighters.
Liquid inside transparent lighter
This change in the state of aggregation is explained because, when substances are in a gaseous state, the particles (atoms or molecules) are far apart from each other. However, as the pressure increases, these particles come closer together. The closer they are, the more the substance will tend to become a liquid and then a solid.
Particle spacing in physical states.
However, it is not 100% of the cylinder volume that is filled with this liquid. In fact, there is at most 85% of the propane and butane gases in the liquid state and at least 15% of the vapors of these gases. This procedure is performed for safety reasons in order to prevent the pressure on the gas from being too great and it from exploding. Thus, when it comes out of the cylinder and is used on the stove, it returns to a gaseous state because the pressure has decreased.
In fact, they are liquids that are present inside the gas cylinders.
By Jennifer Fogaça
Graduated in Chemistry
Source: Brazil School - https://brasilescola.uol.com.br/quimica/composicao-gas-cozinha.htm