Phebe on a bench that shows how high sea-levels are expected to rise due to climate change. Phebe's review of adsorption-based post-combustion CO2 capture shows one way we can reduce CO2 and so reduce climate change.

Adsorption-based post-combustion CO2 capture review by Phebe L. Bonilla Prado

Congratulations to our Phebe Linette Bonilla Prado for publishing a review of adsorption-based post-combustion CO2 capture.

You can find Phebe’s review here: Experimental studies, molecular simulation and process modelling\simulation of adsorption-based post-combustion carbon capture for power plants: A state-of-the-art review.

We asked Phebe to explain the importance of the paper to us.

Why is your adsorption-based post-combustion CO2 capture review useful for sustainability?

One of the most important actions we can take to mitigate the effects of climate change is to reduce our CO2 emissions. CO2 is a greenhouse gas that is important because it helps regulate the temperature of the planet. However, if there is more in the atmosphere than required, the temperature starts to increase, affecting climate.

Most human activities generate CO2 emissions, including transportation, construction, agriculture and power generation. And we have reached a point in which ecosystems cannot regulate the amount of CO2. So we need to reduce our emissions.

There are many things we can do to reduce them. But one of the most important is to capture the CO2 we generate before it gets released. If we find ways to reduce our emissions we will be able to transition to a more sustainable society.

Can you outline the most important idea in your review?

Our paper provides an overview of efforts to improve adsorption-based post-combustion CO2 capture, so that it is an attractive alternative to chemical absorption.

We present the different approaches to improve this technology, such as process modelling and optimisation, molecular simulation and experiments.

Plus we provide an overview of the different materials studied so far for adsorption and projects using this technology. We highlight what scientists have learnt from these projects and studies, and what challenges lie ahead to make adsorption competitive.

Can you explain what carbon capture/CCUS is and why we need it?

“CCUS” refers to the technologies we can use to capture, use and store CO2.

These technologies are important because they will allow us to significantly reduce our emissions while at the same time, allowing us to continue activities in sectors such as cement and steel production or power generation.

Within CCUS technologies, capturing CO2 is the most expensive. Currently, it is commercially done using chemical solvents. However, it is expensive because of the energy required to regenerate the solvents, and some of them are corrosive and volatile.

That is why the scientific community is looking for alternative capture processes.

What is adsorption-based post-combustion carbon capture?

Let’s break down this question. “Carbon capture” refers to the fact that we want to “trap” or “capture” the CO2.

To do it, we need to define the source of the CO2 we want to capture. Are they emissions from a point source or do we want to capture CO2 already in the atmosphere? Both are feasible, but each option has its advantages and disadvantages.

Currently, it is cheaper to capture the CO2 before it is released into the atmosphere. So, if we look for processes that release significant amounts of CO2, we can see that many involve the combustion of a fuel containing carbon, such as coal, biomass or gas.

“Post-combustion” refers to the fact that the CO2 will be captured after the combustion of the fuel. Interestingly, there are other technologies that can separate the carbon from the fuel before it is burned, but these fall into the “pre-combustion” category.

Finally, we get back to “adsorption-based”. This refers to how you are going to capture the CO2. The most common approach is to use chemical solvents which absorb the CO2 molecules. In contrast, adsorption-based uses solid materials, or adsorbents, onto which the CO2 molecules get attached.

What’s the difference between absorption and adsorption?

When you eat a biscuit, you absorb it into your body. After you eat it, the biscuit is no longer a biscuit. It changes into energy and other things.

On the other hand, if you put the same biscuit on your hand, it might get sticky or crumbly, but you cannot absorb it. It stays on your hand’s surface.

With CO2 something similar happens. Chemical solvents react with the CO2 and they transform together, whereas solid adsorbents only trap the CO2, like a sponge. This is part of the reason we are looking into it as an alternative to absorption.

It is easier to take the CO2 out of the solid adsorbents than from the chemical solvents. It requires less energy, and thus, has the potential to be cheaper.

More on carbon capture at the Grantham Centre

Why scientists should think like policy makers: Interview with Gloria Mensah. Grantham Scholar Gloria Mensah explains how the rise and fall of carbon capture technology on the UK government’s agenda reveals lessons for all sustainability researchers.

Molecular Simulation of Post-combustion Carbon Capture using Hydrotalcites. Phebe publishes paper on how molecular simulations can provide information about hydrotalcites and their interaction with CO2.

The main photo is of Phebe in Copenhagen on a tall bench that shows the height which it would have to be if the sea level increases due to climate change as expected.