Fuel tank system and method

A fuel system, comprising:

• a fuel tank including a gas space in the fuel tank and a liquid space in the fuel tank;
• a first fluid flow path between the gas space in the fuel tank and outside of the fuel system;
• a gas separation membrane comprising a first side in communication with the first fluid flow path and a second side, wherein the gas separation membrane has a greater permeability to water vapor and hydrocarbon vapor than to oxygen or nitrogen;
• a second fluid flow path in communication with the second side of the membrane;
• a fluid control device in fluid communication with the second fluid flow path, with the liquid space in the fuel tank and with outside of the fuel system, said fluid control device configured to provide fluid flow from the second fluid flow path to a destination selected from the liquid space in the fuel tank and the outside of the fuel system;
• and
• a prime mover in communication with the second fluid flow path, configured to move fluid on the second fluid flow path from the second side of the separation membrane to the fuel tank liquid space or to outside of the fuel system.