Aircraft fuel tank flammability reduction methods and systems and air separation methods using membranes

An air separation method comprising:

• feeding pressurized air into a filter containing a hollow fiber membrane, contaminants in the pressurized air including hydrocarbons containing six or more carbon atoms and the hollow fiber membrane exhibiting a property of resisting degradation due to exposure to the hydrocarbons;
• contacting the hollow fiber membrane with the air feed, permeating oxygen and nitrogen from the air feed through the membrane, and producing filtered air from the filter as a result of the membrane removing hydrocarbons containing six or more carbon atoms, the filter exhibiting a pressure drop across the membrane of less than 5 pounds/inch2 (psi);
• and
• feeding the filtered air into an air separation module (ASM) containing a hollow fiber membrane and producing nitrogen-enriched air from the air separation module, the ASM hollow fiber membrane exhibits a susceptibility to degradation from exposure to hydrocarbons containing six or more carbon atoms.

An aircraft fuel tank flammability reduction system comprising:

• a source for air;
• a filter configured to receive air feed from the air source;
• a membrane in the filter, the membrane being configured to permeate oxygen and nitrogen from the air feed through the membrane at a pressure drop across the membrane of less than 5 pounds/inch2 (psi) and to produce filtered air from the filter as a result of the membrane removing hydrocarbons containing six or more carbon atoms;
• an air separation module (ASM) configured to receive filtered air from the filter and to produce nitrogen-enriched air from the air separation module;
• and
• a fuel tank on board the aircraft and configured to receive the nitrogen-enriched air.