Natural Gas Storage on Activated Carbon

Natural gas is a good fuel for internal combustion engines, but its low energy density is a significant drawback. The energy density can be increased by adsorption on a high surface area activated carbon. But with usage, some of the constituents in the natural gas composition accumulate on the carbon and reduce its adsorptivity. The adsorption-desorption of natural gas on 9LXC activated carbon was investigated to 100 cycles at 21 °C and pressures of up to 12 MPa. The decrease in the capacity, G, as a function of the number of cycles, N, was found to follow the empirical correlation:G/G_o = 1 − 0.085Log (N). Analysis of the activated carbon after 100 cycles showed accumulation of C₄. and higher hydrocarbons but not of C₂ and C₃. For automotive applications, activated carbon appears practical in a narrow pressure range, centering around 7 MPa (1000 psig). The preferred storage is at a pressure of 17 MPa or higher, without the use of activated carbons.