How does an oxygen permeable membrane selectively extract oxygen from a mixture of gases?

Oxygen is an essential resource not only for life support, but also for industry, medicine, space exploration, and many other applications. Oxygen permeation membrane technology selectively isolates oxygen from mixed gases, with invasive atoms and diffusion playing a key role in the process.

 

Oxygen is an essential substance for life. It is not only important for living organisms, but also for industrial and medical applications. In particular, the demand for oxygen in high-tech fields such as space exploration continues to grow. Astronauts rely on oxygen to run their life support systems, and oxygen is a key component of atmospheric regeneration systems. In the future, oxygen will also be an essential resource when building human settlements on planets like Mars and the Moon.
As such, oxygen is the most produced chemical 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. In order to obtain high-purity oxygen, it is necessary to extract only oxygen from a mixture of gases. This is what oxygen permeation membranes are designed for. When a mixture of gases flows around this membrane, a curious phenomenon occurs: only oxygen escapes.
To understand how this happens, we first need to take a look inside the material of the oxygen permeation membrane. The way we usually think of solids is that they look like a tightly packed row of atoms with no gaps, but in reality, the shape of the atoms creates gaps in the middle. If we assume a spherical model of the atoms and glue several spheres of the same size next to each other, we can see that not all the space can be covered perfectly. Other atoms can fit into these spaces, and these atoms are called interstitial atoms.
However, not all atoms can fit into these spaces. If the size of the atom that wants to fit into the space between the atoms is larger than the space, it cannot. Pauling was the first person to organize some of these principles experimentally. He published these laws, which are known as Pauling”s laws. Two of them are the most important. The first is the size issue we mentioned earlier, and the second is the rule about the number of electrons an atom has. When an invading atom enters an empty space, it takes the form of an ion. An ion is a state that differs from the number of electrons an atom has, with more electrons making it an anion and less making it a cation. An invading atom can exist stably when the charge of the invading atom is offset by the ionic charge of the atoms surrounding the empty space.
So what are the materials used in oxygen-permeable membranes? The most important property is that the membrane should only allow oxygen to pass through. Inspired by Fouling’s law, we started looking for materials that can only have oxygen as an invading atom, and oxygen-permeable membranes were developed. So, how does oxygen in a mixed gas get into one side of the membrane, become an invading atom, and come out the other side?
The answer to this question can be found in the phenomenon of diffusion. Diffusion is the movement of molecules or atoms from a higher concentration to a lower concentration in a given space when a concentration difference occurs. In an oxygen-permeable membrane, the oxygen concentration is high on the gas side of the membrane and low on the other side, so oxygen atoms will pass through the membrane due to the concentration difference. At this time, the oxygen atoms are transformed into invasive atoms and move inside the membrane.
In mixed gases, oxygen exists in the form of molecules, but inside an oxygen-permeable membrane, only oxygen atoms can move, so the molecules must be split into atoms. To do this, the surface of the membrane is covered with a thin layer of a material such as platinum to induce a surface reaction that splits the oxygen molecules. After the split oxygen atoms pass through the membrane, they recombine back into molecules to form pure oxygen.
Here’s how the oxygen molecules move through the membrane Initially, an oxygen molecule in the gas mixture splits into two oxygen atoms at the surface of the membrane. These atoms then migrate to the empty space inside the membrane and diffuse through the membrane to the other side due to the concentration difference. Finally, they recombine back into oxygen molecules on the other side of the membrane. This is how the oxygen in the gas mixture is separated into its pure form.
This pure oxygen is used in the steel industry for metallurgy, welding and cutting metals, and in the medical field to help patients recover by boosting their metabolism. It 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 area will contribute to building an environmentally friendly future society. The applications of pure, aggregated oxygen are expected to be very broad, ranging from industrial, medical, and space applications to renewable energy. With the development of oxygen-permeable membranes, mankind will be able to utilize oxygen more and more, and the possibilities are endless.