| Summary: |
There is an increasing demand for in-situ high purity oxygen (>99%) production. Nowadays the oxygen with this purity is essentially produced by
cryogenic distillation. Due to the same adsorption capacity of oxygen and argon in traditional zeolites, the conventional PSA (pressure swing adsorption) units are only able to produce 95% of oxygen and 5% of argon. However, the recent development of a new adsorbent (AgLiLSX type adsorbent) by Air Products and Chemicals, Inc. (US 6432170 B1), which adsorbs more argon than oxygen, gives way to the development of new PSA cycles for the production of high purity oxygen directly from air. Air Products filed a patent one year later (2003) reporting an oxygen recovery of 5% for producing 99% oxygen (US 6544318). Preliminary studies conducted in our lab indicate, however, that this recovery can be largely increased optimizing the PSA unit for using this new adsorbent. The recovery targeted for producing 99% of oxygen is 15%. This is essentially the aim of the present project.
There has been an increase of the publications regarding new PSA cycles. On the last 3 years several patents were issued and several scientific papers were published. One of the targets of this renewed interest in PSA is the production of high purity oxygen using a technology that considers two PSA units in series. Despite some advantages of this approach, namely the higher oxygen recovery, the technology involved is more complex, needing e.g. two compressors instead of just one as the present approach. The technology based on the new AgLiLSX adsorbent is then more suitable for small-scale production of oxygen.
In-situ oxygen production has many potential applications such as in the medical field for being used in campaign hospitals or in hospitals in remote places (the oxygen purity required for surgeries is 99% in USA and 99.5% in Europe), for supplying welding systems and in the energy field for feeding fuel cells. Increasing the oxygen partial pressu  |
Summary
There is an increasing demand for in-situ high purity oxygen (>99%) production. Nowadays the oxygen with this purity is essentially produced by
cryogenic distillation. Due to the same adsorption capacity of oxygen and argon in traditional zeolites, the conventional PSA (pressure swing adsorption) units are only able to produce 95% of oxygen and 5% of argon. However, the recent development of a new adsorbent (AgLiLSX type adsorbent) by Air Products and Chemicals, Inc. (US 6432170 B1), which adsorbs more argon than oxygen, gives way to the development of new PSA cycles for the production of high purity oxygen directly from air. Air Products filed a patent one year later (2003) reporting an oxygen recovery of 5% for producing 99% oxygen (US 6544318). Preliminary studies conducted in our lab indicate, however, that this recovery can be largely increased optimizing the PSA unit for using this new adsorbent. The recovery targeted for producing 99% of oxygen is 15%. This is essentially the aim of the present project.
There has been an increase of the publications regarding new PSA cycles. On the last 3 years several patents were issued and several scientific papers were published. One of the targets of this renewed interest in PSA is the production of high purity oxygen using a technology that considers two PSA units in series. Despite some advantages of this approach, namely the higher oxygen recovery, the technology involved is more complex, needing e.g. two compressors instead of just one as the present approach. The technology based on the new AgLiLSX adsorbent is then more suitable for small-scale production of oxygen.
In-situ oxygen production has many potential applications such as in the medical field for being used in campaign hospitals or in hospitals in remote places (the oxygen purity required for surgeries is 99% in USA and 99.5% in Europe), for supplying welding systems and in the energy field for feeding fuel cells. Increasing the oxygen partial pressure in the cathode will result in the increase of the electromotive force produced by the fuel cell. This can be achieved either by increasing the pressure of the oxidizing gas, compressing the feed stream, or by increasing the oxygen content of this stream. The use of enriched oxygen is particularly important for the use of fuel cells on commercial airplanes. DLR-Stuttgart (Deutsches Zentrum fur Luft- und Raumfahrt e.V.) is working together with Air Bus on the development of high performing fuel cells, based on phosphoric acid proton exchange membranes, for powering all the electric systems of these airplanes.
Our research laboratory (LEPAE) developed recently a powerful tool for modelling PSA processes. Our simulator is now being used in a development project funded by Air Products (HPSA-5236).
With the present project, this powerful tool will be improved for taking into account new phenomena and new adsorption cycles and will be used on the search for an optimised PSA cycle using the new AgLiLSX adsorbent.
The contamination of the adsorbents that will be studied in this project is amazingly absent from the scientific publications, despite its practical up-most interest. The contaminants carbon dioxide and water vapour are present in the ambient air fed to the adsorption unit and adsorb almost irreversibly in the zeolite. For small scale systems air dryers can not be used and the decrease with time of the oxygen purity is almost inevitable. The complete replacement of the zeolite is often required.
For units producing high purity oxygen and for the applications mentioned before, |