Hydrate phase equilibrium conditions for the simulated landfill gas (LFG) of methane and carbon dioxide (50 mol% methane, 50 mol% carbon dioxide) were investigated with the pressure range of (1.90 to 13.83) MPa and temperature range of (280.0 to 288.3) K at (0.050, 0.170, 0.340, and 0.394) mass fraction (w) of tetrabutylammonium nitrate (TBANO(3)). The phase boundary between liquid-vapor-hydrate (L-V-H) phases and liquid-vapor (L-V) phases was determined by employing an isochoric pressure-search method. The phase equilibrium data measured showed that TBANO3 appeared a remarkable promotion effect at w(TBANO3) = 0.394, corresponding to TBANO(3) center dot 26H(2)O, but inhibition effect at w(TBANO3) = (0.050, or 0.170) on the semiclathrate hydrate formation. In addition, the application of TBANO(3) at 0.340 mass fraction, corresponding to TBANO(3) center dot 32H(2)O, displayed promotion effect at lower pressures (below 6.38 MPa) and inhibition effect at higher pressures (above 6.38 MPa). (C) 2013 Elsevier Ltd. All rights reserved.