The balanced chemical equation for this is:
C3H8 + 5 O2 --> 3 CO2 + 4 H2O
So we can see that for every 1 mole of C3H8, 2219.9 kJ of energy is released. Hence the total number of moles of C3H8 required is:
moles C3H8 = 2.45×10^6 kJ / (2219.9 kJ / mol)
moles C3H8 = 1103.65 mol
The molar mass of C3H8 is 44.1 g/mol, therefore the mass is:
mass C3H8 = 1103.65 mol * 44.1 g/mol
mass C3H8 = 48,671.11 grams = 48.67 kg