Biomass is a renewable resource capable of producing activated carbons and high quality fuels. Current technologies of biomass conversion can be divided in biological, biochemical and thermochemical processes. A combination of chemical and physical activation processes was performed to obtain an activated carbon from elephant grass. Elephant grass (Pennisetum Purpureum) is a promising source of renewable energy, due to its fast growth, disease resistance, adaptability and easy propagation. The elephant grass was chemically activated with NaOH and H3PO4, afterward the impregnated biomass was washed to neutral pH and pyrolysed in a screw reactor at 500 °C with 33 minutes of residence time. The activated carbon produced in this process was physically activated with CO2 in a fixed-bed tubular reactor at 800 °C and 900 °C. The results showed an activated carbon with high surface area (until 1260 m2.g-1) and microporous structure, which is suitable for the separation of CO2 and CH4 gases.