At one time, people might consider oxygen a human right. But the pandemic has revealed that access to oxygen – in its pure form, for medical use – is a luxury in most low- and middle-income countries.
Getting access to pure oxygen for medical procedures is a complex, expensive and often very dangerous business. The current situation in India is a crude reminder of this issue. The second wave of Covid-19 hit the country hard, with the total number of deaths just above the 2,000,000 mark. Oxygen is in short supply.
Due to the current state of emergency, Indian citizens turned to the black market to buy oxygen far above its regular price.
This is partly due to the way oxygen is produced, stored and transported around the world. That̵
Oxygen is mostly obtained from liquefied air. Engineers turn the air we breathe into a liquid using a combination of processes that cool the gases as they condense. Once they have liquefied the mixture, they use distillation – the same process used to make whiskey and gin – to separate the air into its various components, the oxygen between them.
This process requires huge amounts of energy and huge industrial facilities, so it is limited to only a few areas in the world, most of them in the global north. Liquid oxygen must be stored and transported under high pressure, creating serious logistical problems and safety concerns – oxygen is really explosive.
This means that the main obstacle to oxygen production are precisely the cylinders. The United States relies on heavy tubes to transport oxygen under pressure. In Europe, transport takes place mainly through liquid oxygen, which is transported to large tanks. For lower-income countries, the distribution is in bottles.
But the oxygen cylinder market is in the corner of only a handful of chemical companies. The use of bottles also adds another layer of safety considerations, as their proper handling requires several precautions and proper training. Therefore, developing countries lack both the infrastructure needed to produce liquid oxygen and that can be easily and cheaply transported to a hospital.
From the air
Another way to “prepare” oxygen is to use concentrators, devices that selectively remove nitrogen – the gas that makes up 78% of our atmosphere – using a series of membranes, porous materials and filters. They began production in the mid-1970s and the technology is very well established.
These devices convert air into a stream enriched with oxygen gas, usually over 95% (the rest is formed mainly by argon). This is usually good enough for respirators and fans. The advantage of the concentrator is that it can be manufactured as a small device to be used in hospitals or nursing homes. There are currently commercial hubs, but they are expensive and difficult to manufacture in developing countries.
That’s why scientists like me are looking for solutions. My team is studying new types of materials that store and emit gases, some of which offer potentially affordable solutions for devices such as oxygen concentrators. We develop two main types of materials – zeolites (crystals of silicon, aluminum and oxygen) and metal-organic frames. Both are highly porous materials. You can think of them as miniature mushrooms the size of a molecule.
Like mushrooms, these porous materials absorb more liquids than you would intuitively imagine. Although the millions of pores in zeolites and metal-organic frames may appear small, their overall surface is monumental. In fact, one gram of some record metal-organic frames have an area of over 7,000 square meters.
Small amounts of zeolites and organometallic structures can store huge amounts of liquids, often gases, and they have been used for gas storage, purification, carbon capture, and water collection.
Some of my team, in partnership with Cambridge Precision Engineering and the Center for Global Equality, began researching whether they could be used to store oxygen. We have developed an initial prototype that works. We hope to have a final prototype in two months and then we will have to seek medical approval.
How is it done
The principle is quite simple. We have an aluminum cylinder full of porous materials and air flow circulates through it. This purifies oxygen to 95% – the rest being mostly argon. Nitrogen is trapped in the zeolite due to the way the electric charge is distributed to the nitrogen atoms, which means that it interacts more strongly with the electric field of the zeolite. Oxygen and argon are not.
Therefore, nitrogen remains trapped inside the millions of small pores and we empty them later after storing our oxygen.
We typically commercialize our porous materials through Immaterial, a branch of the University of Cambridge. Yet making huge profits from selling oxygen in a pandemic seemed immoral. For example, in Africa, oxygen is five times more expensive than in Europe and the United States. Therefore, our team and Immaterial have partnered with other scientists in Cambridge to create the Oxygen and Fan System Initiative to improve and manufacture affordable oxygen procedures.
We hope the benefits of a low-cost oxygen concentrator outlive the pandemic. Oxygen supply is key to treating childhood pneumonia and chronic lung disease – both conditions that kill more people worldwide than AIDS or malaria. Everyone needs to have access to oxygen and technology like ours can one day help ensure that access.
David Firen-Jimenez is a reader in molecular engineering at the University of Cambridge.
This article first appeared in The Conversation.