**3. Natural gas as a clean energy source**

Natural gas is a homogeneous mixture, having variable proportions of hydrocarbons. The general composition of natural gas includes methane (CH4) constituting the major part, and it generally ranges from 55 to 98% in volume, ethane (C2H6), propane (C3H8), and other heavy constituents. There is a growing interest in the use of natural gases as an alternative source of energy especially because it is clean. Its thermal efficiency is higher than that of other fuels, and it produces mainly CO2 and water vapor. The emissions of CO2 are 25–30% lower than that generated from fuel-oil and 40–50% lower than coal per unit of produced energy [2]. As regards its use as a fuel, natural gas has many advantages. These include reduction in post combustion contaminants, reduction in maintenance costs compared with other fuels, reduction in suspended solid particles, which are associated with combustion of gasoline, absence of sulfur and sulfur dioxide (SO2) emissions, which are typical contaminants from transportation vehicles. Compared with liquid fuels, the emissions from natural gas vehicle combustion are 76% less in carbon monoxide, 75% less in nitrogen compounds, 88% less in hydrocarbons, and 30% less in carbon dioxide [2]. Furthermore, the physiochemical properties of natural gas enable the use of catalysts for the combustion of gases, obtaining excellent results and minimizing emissions. In spite of the numerous advantages associated with the use of natural gas as a fuel over other forms of hydrocarbon fuels, its efficiency and economics in storage and transportation have constituted a major barrier to its usage. This could be attributed to its low energy density (heat of combustion/ volume) at standard temperature and pressure conditions [2].
