Abstract: The study is been conducted to understand the different techniques to separate nitrogen from atmospheric air. Separation of nitrogen takes place by following techniques: Cryogenic air separation, Pressure swing adsorption and Membrane separation technique. Cryogenic air separation operates at a very low temperature, which uses the principle of rectification to separate nitrogen at a very high purity (99.999%). Pressure swing adsorption rely on the fact that higher the pressure, more the gas is adsorbed which results in high purity (95-99.99%) of nitrogen. Membrane separation technology is the process that uses hollow fibre membranes to separate the constituent gases in air, which gives the purity in the range of 93%-99.5%. After the comparative study, it is understood that membrane separation technique is the most efficient technology based on the cost, purity, flexibility in terms of adjusting the purity, maintenance, availability; it operates without heating and therefore uses less energy than conventional thermal separation processes. Different step designs of membrane separation techniques are discussed. A Process Flow Diagram and Piping Instrumentation Diagram is been added for single step membrane separation technique. Keywords: Atmospheric air, nitrogen, Cryogenic air separation, Pressure swing adsorption, Membrane separation technique.