Using MOFs to Store, Separate and Transport Gases

In this interview, AZoM talks to Professor Omar Farha of Northwestern University about metal-organic frameworks and how assist in storing, separating, and transporting gases.

What are the Current Major Challenges Associated with Storing, Separating, and Transporting Gases?

Storing and separating gases are two different issues and two different applications that we have to tackle differently. From a storage perspective, we typically look into a material that has a higher deliverable capacity. Not how much it stores, but how much we can take out of the system after storing without having to go to high pressures. High pressures cost money, and money is an issue sometimes.

A bundle of grey gas cylinders secured on yellow skids in oil and gas rig platform. (Image Credit: Opsormen/Shutterstock.com)
 

On the separation part, we are looking for materials to be stickier for certain gases or chemicals, but not others. In some cases, we make the materials sticky for the gas of choice. In other cases, we make them stickier for the impurities to remove them. The way we think about it in the laboratory and the way we use instruments to measure separations and storage is sometimes a lot different.

What Materials Have You Developed at NuMat That Take Advantage of the Properties of Different Gases?

One of the issues that people always ask is, "Can the materials we work with, metal-organic frameworks or MOFs, be commercialized?" The good news is yes. NuMat Technologies was the first company to commercialize an engineering product that is enabled with metal-organic frameworks. These materials are inside a cylinder, and we use them to store toxic gases, such as BF₃, arsine, and phosphene.

These gases are used in the electronic industry. Instead of using high pressure when there is a leak, the gas gets out of the cylinder to the outside atmosphere that can poison workers and employees.

We store these gases sub-atmospherically below one bar. That means if there is a leak in the system, the air will rush into the cylinder, but the toxic gas will not come out of the cylinder Even though we store things sub-atmospherically, we are able to store as much, if not more, than what you store in high-pressure cylinders.

This is possible in sub atmosphere because we fill these cylinders with metal-organic frameworks that are known for their high surface area. High surface area means high hot spots for those gases to interact with, and the more walls and the more surface areas you have in the cylinder, the higher the capacity. That's one of the first examples in a commercial setting to show how can you take advantage of the surface area of the MOF in a storage application.

What is the Definition of Metal-Organic Frameworks?

The materials we work with are called metal-organic frameworks, or MOFs. These materials are built from two different components. One of the building blocks is metal.

The second building block is the organic linkers. It's almost like building lego. You have different simple pieces that fit together, that in the end build very sophisticated structures.

Imagine going down to the nano-regime, and instead of dealing with legos in the centimeters. This is much smaller, but we deal with what we call self-assembly. That means putting everything in the reaction mixture, we program them in a way to find each other in a specific fashion and get one product at almost 100% healed.

Even if you have a small set of building blocks, the options and the number of possibilities become huge. However, we program them to come together in a specific manner. I cannot think of many families of materials you could do that with the way you do it with a metal-organic framework.

It’s almost like a sponge. If you look at a sponge under a microscope, you start seeing a lot of little cavities and cages. When you have a spill of water and you wipe it, all that water goes into those cages and those cavities. The only problem with a sponge is it's not uniform. It's very hard to control those cages. It's very hard to control how many of those cages lie within a small unit volume.

With MOFs, you have that control to make the cage large or small.  You can tune it on demand in a programmable way.

How Has the Instrumentation Used Helped You Achieve Your Goals in Your Research?

In research, having the right people to conduct the research is very important. It is just as important to have the instrumentations that reliably give you the appropriate answers with a good accuracy or awesome accuracy.

Here, for the typical absorption for a capacity of gases or in separation applications, we have been partnering for the last few years with Micromeritics. They have incredible hardware and they are easy to work with. That’s a very good combination.

All the instruments we have are made by Micromeritics, which is a testament to our partnership and our group's devotion to using their instrumentation.

How Do You See Gas Storage and Separation Developing in the Near Future?

The storage and separation in the future are going to be very crucial. There is two ways of taking care of energy. Either you make more of it, or you reduce the consumption of the systems. In storage and separation, what we use typically in the industry right now are very energy-intensive. Finding solutions to reduce the energy use in the storage and the separation is a crucial matter.

The materials we work on metal-organic frameworks will be used in storage and separation going forward in many sectors. NuMat Technologies proved so far in the storage area that they are able to use a metal-organic framework to store gases in the electronic industry. There is no reason why we can't use the same material in a larger-scale applications, separations, and storage.

Second, I am a believer in going forward in the future. There are new applications that will come on board that we need to find solutions for.

We need to keep making new materials and thinking about new materials. The new materials need to be able to address new challenges that we might not know yet. But once we are faced with them, we should be ready to address those challenges.

About Professor Omar Farha

Dr. Omar K. Farha is a co-founder and president of NuMat Technologies, an associate professor of chemistry at Northwestern University, and associate editor for the American Chemical Society Applied Materials & Interfaces. His research accomplishments have been recognized by several awards and honors including the Royal Society of Chemistry "Environment, Sustainability and Energy Division Early Career" Award and the American Chemical Society "The Satinder Ahuja Award for Young Investigators in Separation Science. Northwestern's Department of Chemistry also established "The Omar Farha Award for Research Leadership," which is awarded annually to a researcher in the department for stewardship, cooperation, and leadership. Omar has more than 350 peer-reviewed publications, holds 14 patents, and has been named a "Highly Cited Researcher" every year from 2014 to 2018.