A system for generating liquid oxygen (LOX) for portable use by a patient includes a patient portable unit configured to store LOX and deliver gaseous oxygen (GOX) to the patient, and a mobile base unit configured to generate LOX by cryogenic separation of air and deliver the generated LOX to the patient portable unit. The mobile base unit includes a compressor that receives and pressurizes air, a purifier that removes impurities from the pressurized air, a heat exchanger that cools the purified air, a cryocooler that further cools the air to cryogenic temperatures, and a distillation unit that separates the cryogenic air into multiple products, including LOX and one or more cold byproducts. The separated LOX is communicated toward storage, and at least one of the cold byproducts is passed through the heat exchanger to facilitate heat transfer from incoming purified air to the at least one cold byproduct in order to cool the purified air.
