In this blog post, we will look at the scientific principle behind how oxygen permeable membranes selectively separate oxygen from a mixture of gases and their applications.
Oxygen is essential for life. Without oxygen, living organisms cannot breathe and survive. Oxygen is not only important for living organisms, but also for industry and medicine. In particular, the demand for oxygen continues to grow in high-tech fields such as space exploration. Astronauts use oxygen to operate life support systems, and oxygen is used as a key component in atmospheric regeneration systems. In the future, oxygen will also be an essential resource when building facilities for humans to live on planets such as Mars and the Moon.
As such, oxygen is the most produced chemical substance in the world, with more than 100 million tons produced annually. The oxygen used in industry and medicine is not the oxygen found in the atmosphere, but high-purity oxygen. To obtain high-purity oxygen, oxygen must be extracted from a mixture of gases. Oxygen permeation membranes were developed for this purpose. When a mixture of gases is passed around this membrane, a remarkable phenomenon occurs in which only oxygen escapes.
To understand how this phenomenon occurs, we first need to look at the material of the oxygen permeation membrane. The solid we commonly think of appears to be densely packed with atoms, but in reality, the shape of the atoms creates empty spaces in between. If we assume that atoms are spherical and place several spheres of the same size next to each other, we can see that they cannot completely cover all the space.
Other atoms can fill these empty spaces, and these atoms are called interstitial atoms. However, not all atoms can fill these empty spaces. If the size of an atom is larger than the space between atoms, it cannot enter. Pauling experimentally summarized these principles.
He published these laws, which are known as Pauling’s laws. Among them, two laws are the most important. The first is the size issue mentioned earlier, and the second is the rule regarding the electrons possessed by atoms. When interstitial atoms enter empty spaces, they take the form of ions. Ions refer to a state different from that of atoms in terms of the number of electrons they have. If there are many electrons, they become anions, and if there are few electrons, they become cations. When the charge of the intruding atom is offset by the ion charge of the atoms surrounding the empty space, the intruding atom can exist stably.
So, what kind of material is used for oxygen permeable membranes? The most important property is that the membrane must allow only oxygen to pass through.
Based on Pauling’s law, we began searching for substances that could have oxygen as the only intruder atom, and as a result, oxygen permeable membranes were developed. So how does oxygen from a mixture of gases enter one side of the membrane and become an intruder atom, and then exit the other side? The answer to this question can be found in the phenomenon of diffusion.
Diffusion is a phenomenon in which molecules or atoms move from a place of high concentration to a place of low concentration when a concentration difference occurs within a certain space. In an oxygen-permeable membrane, the oxygen concentration is high on the mixed gas side and low on the opposite side, so oxygen atoms pass through the membrane due to the concentration difference. At this time, the oxygen atoms are transformed into intruding atoms and move inside the membrane.
In mixed gases, oxygen exists in the form of molecules, but inside oxygen-permeable membranes, only oxygen atoms can move, so the molecules must be broken down into atoms. To do this, a thin layer of a substance such as platinum is applied to the surface of the membrane to induce a surface reaction that breaks down the oxygen molecules.
After passing through the membrane, the split oxygen atoms recombine into molecules to form pure oxygen. The movement of oxygen molecules can be summarized as follows. First, oxygen molecules in the mixed gas are split into two oxygen atoms at the surface of the membrane. These atoms then move into the empty space inside the membrane and diffuse to the other side due to the difference in concentration.
Finally, they recombine into oxygen molecules on the other side of the membrane. In this way, the oxygen in the mixed gas is separated into its pure form.
Pure oxygen produced through this process is used in the steel industry for metallurgy, metal welding, and cutting, and in the medical field to promote metabolism and aid recovery in patients. Oxygen is also likely to play an important role in future energy production and storage technologies. Oxygen plays an essential role in clean energy technologies such as hydrogen energy, and research in this field will contribute to building an environmentally friendly society in the future. As such, pure oxygen is expected to have a wide range of applications in industries such as manufacturing, medicine, space, and renewable energy. With the development of oxygen permeable membranes, humanity will continue to expand the range of applications for oxygen, and the possibilities are endless.
