An inert gas generating system includes a source of a liquid hydrocarbon fuel, and a fractioning unit configured to receive a portion of the liquid hydrocarbon fuel from the source. The fractioning unit includes a perm-selective membrane configured to separate the portion of the liquid hydrocarbon fuel into substantially sulfur-free vapors and a sulfur-containing remainder. The system further includes a catalytic oxidation unit configured to receive and react the substantially sulfur-free vapors to produce an inert gas.