Natural gas is a major energy source worldwide used for electricity generation, heating, and industrial processes. Extracted from deep underground reservoirs, it consists of a mixture of gases. The main ingredient in natural gas, and the reason it functions effectively as a fuel, is the gaseous hydrocarbon known as methane.
Methane The Core Ingredient
Methane is the simplest organic molecule, identified by the chemical formula CH4. It consists of one carbon atom bonded to four hydrogen atoms, making it the lightest and most abundant hydrocarbon found in raw natural gas. This simple structure contributes directly to the fuel’s high energy yield during combustion.
Raw natural gas streams typically contain a high percentage of methane, ranging from approximately 70% to over 90% by volume, depending on the geologic source. When this gas is burned, the clean, efficient reaction primarily produces heat, carbon dioxide, and water vapor. This combustion process is why methane is considered a cleaner-burning fuel compared to more complex hydrocarbons like oil or coal.
The physical properties of methane make it suitable for pipeline transport and consumer use. In its pure state, methane is a colorless and odorless gas that is significantly lighter than air, meaning it dissipates quickly when released. It remains a gas at standard temperatures and pressures, which allows for efficient transport through extensive pipeline networks as a vapor.
Methane’s high energy content per unit of mass is a measure of its efficiency as a fuel. It releases a greater amount of energy than any other hydrocarbon when burned. This makes methane a highly effective energy carrier for industrial furnaces, power plants, and residential appliances. The natural gas industry focuses on separating this core ingredient from the other components mixed with it in the reservoir.
The Supporting Gases and Impurities
While methane is the dominant molecule, raw natural gas is a complex mixture that contains several other hydrocarbons and non-hydrocarbon impurities. These other components are generally grouped into two major categories that must be addressed during processing. The first group consists of heavier hydrocarbons, often referred to as Natural Gas Liquids (NGLs), which are valuable byproducts.
Natural Gas Liquids (NGLs) include ethane (C2H6), propane (C3H8), and various butanes (C4H10). These molecules are separated because they have higher heating values and are useful as feedstocks for the petrochemical industry. Ethane is a primary raw material for producing ethylene, which is used to make plastics. Propane and butane are liquefied and sold as Liquefied Petroleum Gas (LPG) for heating and cooking.
The second group includes non-hydrocarbon impurities, which must be removed for safety and to prevent pipeline corrosion. These impurities include water vapor, which can freeze or form corrosive hydrates inside pipes, and non-combustible gases like nitrogen (N2) and carbon dioxide (CO2). Carbon dioxide is a common diluent that lowers the heating value of the gas.
The most problematic impurities are the toxic and corrosive “acid gases,” specifically hydrogen sulfide (H2S). Gas containing significant amounts of hydrogen sulfide is termed “sour gas,” posing a health hazard and causing equipment deterioration. The presence of these acid gases and other contaminants necessitates a rigorous refining process before the gas can be transported and sold to consumers.
Refining the Ingredient for Safe Use
The raw gas mixture extracted from the earth must undergo processing to meet the strict “pipeline quality” specifications required for safe distribution. This refining process isolates the methane and removes all undesirable components. The initial step typically involves separating any free liquids, such as water and hydrocarbon condensate, directly at or near the wellhead.
Following separation, the gas moves to a processing plant for acid gas removal, often called “sweetening,” to eliminate corrosive H2S and CO2. This is frequently accomplished using an amine treating process, where acidic components are chemically absorbed into a liquid solution. The gas must then be dehydrated to remove remaining water vapor, preventing the formation of ice or hydrates in the transmission lines.
Natural Gas Liquids are stripped from the methane stream using cryogenic expansion, which lowers the temperature. This causes the heavier NGLs to condense into a liquid state, allowing separation from the gaseous methane. This extraction step ensures the final pipeline gas is almost pure methane, providing a consistent heating value for the end-user.
The final step before the gas enters the distribution network is odorization. Because pure methane is odorless and colorless, a chemical called mercaptan is added in trace amounts. This additive gives the gas its rotten-egg smell, serving as a safety mechanism to allow consumers to detect dangerous leaks. The product delivered to homes and businesses is a refined stream of methane, confirming its status as the main ingredient.