At Creare, new technology is often built on experience gained in previous projects that then leads us into neighboring areas with related problems. This is exactly the situation with our work in the area of gas separation. We began by developing a cryogenic distillation technology to improve aircraft safety and operability, then branched into gas separation for advanced space launch vehicles, and further expanded into biomedical applications using molecular sieves, ceramic membranes, and semi-permeable membranes.

In the early stages of our gas separation work, we developed a system which separated air into oxygen and nitrogen. The focus of that first project was on-board systems for large military aircraft, and used a reverse-Brayton cryocooler coupled to a compact cryogenic distillation column. Advanced mass transfer techniques were developed so that the distillation column would fit under the floor of the aircraft and yet still operate correctly, given that the local gravitational vector changes during aircraft maneuvers. Our gas separation system development must often meet extreme constraints of a given application and we utilize novel techniques in thermodynamics, heat and mass transfer, advanced materials, multiphase cryogenic flow, and system design and fabrication.

In this military aircraft application, the separated nitrogen provides an increased level of safety by reducing fuel tank explosions; the nitrogen displaces the oxygen in the gas space located above the fuel in the partially empty tanks. The separated oxygen is used for air crew life support, medevac patient breathing, and special operations which require oxygen pre-breathe.

In follow-on projects, we adapted this technology for commercial aircraft, where the inerting fuel tanks also present a serious risk. We designed two approaches for on-board gas separation for commercial aircraft. The first for large aircraft was based on cryogenic air separation technology which requires less bleed air and less power at similar system weight and size. The second was a compact, lightweight nitrogen generating system for smaller aircraft using advanced semi-permeable membranes to separate the gases. The second system uses a compact, electrically driven centrifugal compressor with long-life foil bearings so that it can operate independently from engine bleed air, which is often in short supply on small transport aircraft.

Our next advance in gas separation technology supported the development of advanced space launch vehicles. The Horizontal Take-off Horizontal Landing (HTHL) aerospace plane concept is a two-stage vehicle designed to collect oxygen from air during subsonic flight, then liquefy and use the oxygen to combust liquid hydrogen for propulsion to orbit. This onboard oxygen generation dramatically reduces the spacecraft weight and enables much larger payloads to earth orbit.

As a world leader in compact, airborne cryogenic distillation systems, Creare was called upon to design critical components in the novel Rotational Fractional Distillation Unit (RFDU). The RFDU provides centrifugal force hundreds of times greater than normal gravity which enables much higher flow rates than a normal vertical distillation column. The RFDU occupies approximately two orders of magnitude less volume than a conventional cryogenic distillation column of similar capacity and product purity. Liquid hydrogen cools incoming air and drives the distillation and oxygen liquefaction processes; the vaporized hydrogen then powers the vehicle. One hundred thousand lbm of liquid hydrogen can be used to produce almost one million pounds of liquid oxygen in about two hours. We designed innovative structured packing for the column to enhance mass transfer while reducing pressure drop. We also designed compact heat exchangers for high-temperature and cryogenic service, including a heat exchanger that employs catalysts that enable para-to-ortho hydrogen conversion to maximize the cooling available from the liquid hydrogen.

Naturally we have also applied our expertise in gas separation to problems in bioengineering. We developed a hybrid system that uses a molecular sieve to separate oxygen from air and a reverse-Brayton cryocooler to liquefy the oxygen for medevac purposes. We also miniaturized our cryogenic distillation systems, intended for aircraft, to produce liquid oxygen needed for Home Oxygen Therapy (HOT). With over a million HOT users in the United States – a number that is growing – liquid oxygen is the preferred delivery method for mobile patients because it provides a compact, lightweight, long-lasting source of oxygen. However, existing liquid oxygen systems must be refilled from liquid oxygen dewars, too expensive for most patients. Creare’s innovation is a compact, low-power, low-cost system that resides in the patient’s home and generates liquid oxygen from air, eliminating the need for liquid oxygen storage reservoirs and the cumbersome re-supply infrastructure.

In a variation of the home oxygen therapy delivery system, Creare developed a Ceramic Oxygen Generating System (COGS). Most patients who use in situ oxygen generating systems rely on molecular sieve oxygen generator technology, which is noisy, expensive, heavy, and unreliable. Creare’s COGS is a solid state device consisting of an oxygen-conducting ceramic membrane across which oxygen ions flow when a differential voltage is applied. The COGS does not require a compressor, and provides oxygen of greater than 99% purity with improved reliability and cost. Our breakthrough technology in this project was the development of a technique to produce a ceramic membrane that could operate at the required high temperature, but thin enough to conduct oxygen efficiently.

We have also used our gas separation expertise for gas recycling of rare and expensive noble gas isotopes, 3He and 129Xe. Both gases are highly effective imaging agents for high-resolution MRI of lungs and airways, but their extremely limited availability and high cost make recovery of these gases for reuse critical. We have been able to demonstrate high recovery rates at very high purity.

And finally, we are also using molecular sieve technology and cryogenic trapping to recycle xenon for other medical purposes. Laboratory testing has shown that xenon has the potential to greatly reduce brain damage in stroke victims. However, the cost of delivering xenon to stroke patients would be prohibitive if it were simply exhaled into the atmosphere. To reduce the cost of xenon for this application, Creare is developing a portable xenon delivery apparatus for emergency medical teams. The device supplies neuroprotective xenon gas and captures it from exhaled breath for later purification and re-use.

We expect that the future of gas separation work at Creare will continue to evolve, and we look forward to more opportunities to make a positive difference in our world.

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