Capturing carbon gases with cost-efficient slurry

Carbon dioxide has a bad reputation these days – perhaps deservedly so, as it is one of the main culprits behind global warming.

Carbon dioxide has a bad reputation these days – perhaps deservedly so, as it is one of the main culprits behind global warming.

Although global CO2 emissions continue to increase, the European Union’s share of emissions has declined by 19 per cent from their levels in 1990.

But to limit the increase in average global temperature to 2°C, Europe will have to further curtail its emissions, and the rest of the world will have to follow.

Business as usual is no longer an option, says a report by the Intergovernmental Panel on Climate Change published last Saturday.

The report alarmingly concludes that continued emissions will increase “the likelihood of severe, pervasive, and irreversible impacts for people and ecosystems”.

There are many ways to curb greenhouse gas emissions. A stagnating economy can be one of them, as we have seen in Europe in the past years.

Replacing petrocarbons such as oil, petrol or natural gas with renewable alternatives such as solar, wind, or water power would be a more desirable approach, which is able to provide us with a long-term solution.

Such strategies, however, will take time, and it is certain that our activities will continue to produce significant amounts of greenhouse gas emissions.

Just think of cement production, which presently accounts for more than 5 per cent of global CO2 emissions.

With no carbon-neutral alternatives in sight, other solutions will be needed to keep industrial CO2 emissions out of the atmosphere. Recycling CO2 is one alternative; storing it underground is another.

Ultimately, carbon capture and storage is the only realistic solution we can rely on to decrease greenhouse gas emissions without turning the global economy on its head, since it is estimated to add only US$30 (Dh110) a barrel of oil.

But CO2 is not isolated; it comes bundled with other gases. Therefore, whether we decide to reuse CO2 from

industrial emissions or to store it underground, we first need an effective way to capture and extract it from the other, less pernicious gases.

Carbon capture, or the retention of CO2 before it escapes smoke stacks and enters the atmosphere, is already practised around the world.

Typically, these sites use liquids that bind CO2 when flue gases are bubbled through them in a process known as amine scrubbing.

Then the solution is regenerated, releasing pure CO2.

But this approach has yet to be perfected. The vast amount of energy required to release CO2 from the liquid makes it inefficient.

As an alternative, researchers have focused on replacing the liquid with powders.

Thanks to greater control over the interactions between the gas and the powder, releasing CO2 could be made much less costly.

But although liquids can be efficiently pumped, transporting powders can be a mess. Just imagine walking around with a plate full of baby powder.

Working with a team of researchers from the University of California, Berkeley and Peking University, we recently developed a carbon-capture technique that brings together the best of both worlds.

It binds CO2 in a way that allows it to be released again with a low-energy input, and uses a substrate that can be pumped through pipes much like water.

Rather than using a pure liquid or a pure powder, our approach uses a slurry, a viscous, honey-like substance that is made up of a mix of liquid glycol and a porous powder called ZIF-8.

This powder is composed of so-called metal-organic frameworks, which are metal atoms that are connected to a three-dimensional structure with organic linkers.

One of the reasons this approach is so effective lies in the design of the porous powder. Its pores are just the right size to capture CO2 but too small to let the glycol in the slurry enter.

And because of the properties of the powder, CO2 can be released without having to spend excessive amounts of energy.

What happens with the captured CO2 is another story. At current test sites, it is being pumped into deep geological storage sites such as depleted oil fields, where it can be stored away safely for long periods of time.

A new chemical industry is taking shape as an alternative to the petrochemical industry.

Instead of using fossil fuels as a source of carbon, this new field seeks to recycle captured carbon and use it as a high-value chemical compound.

Professor Berend Smit is the director of the Energy Centre and the director of the Laboratory of Molecular Simulation at the Ecole Polytechnique Federale de Lausanne in Switzerland.

Published: November 8, 2014 04:00 AM


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