This work reports the preparation and characterization of biomass-derived renewable microporous carbon nanoparticles obtained by microwave-assisted hydrothermal carbonization (MAHC), following by physical activation, of assai stone waste. Conventional routes (i.e. carbonization in furnace and chemical activation) was also investigated. The highest yield provided by MAHC combined with CO2 as activating agent resulted in nano carbons with surface area of 1100 m(2)/g and a very narrow pore size distribution with a micropore volume of 0.45 cm(3)/g. Owing to the excellent combination of microporosity and high bulk density (0.89 g/cm(3)). The biomass-derived carbon shows great potential to be used as adsorbent for natural gas storage. Indeed, high pressure methane adsorption isotherm in volumetric basis revealed an uptake value of 140 V(STP)/V at 25 degrees C and 4 MPa.