BY DAVID BOTT

There is much talk of “decarbonisation” these days, and you could be forgiven for thinking this means eliminating carbon from all human activities. But there are lots of things that need carbon to exist. The chemistry of carbon is unique and nature relies on it for many things. Carbon has direct influence on conditions for life on our planet, whether or not you factor in the specific needs of human beings! And we depend on carbon chemistry for life too – our bodies burn carbon based fuels ourselves (grains, vegetables and meat are all carbon based materials).

We have also depended for millennia on carbon-based materials as clothing (skins, cotton and wool), housing (wood and thatch), and much more – until about 6000 BC when we started using inorganic materials (metals!) as well. With the birth of the oil age in the late 19th century, we started to make synthetic materials, initially striving to reproduce the properties of the natural materials we were used to – polyester was a cotton like material, polyamides were meant to be like silk, polyacrylonitrile was similar to wool in properties. In healthcare we started making naturally occurring therapies (like aspirin and morphine) at scale using synthetic chemistry. As we understood the relationships between chemical structure and properties during the 19th century, we moved on to more complex chemical structures. We cannot get away from carbon because so many planetary systems depend on it, so getting it rid of it altogether is not really an option!

So, what do we mean when we say “decarbonisation”?

The problem is not with carbon dioxide as such, but with the amount we have put into the ecosphere over the last 150 years or so years and the effect it is having on the climate.

In the past there was a lot more carbon than we currently have in the atmosphere – somewhere between 15-30 times as much – but then life wasn’t the same in the Mesozoic period – evidence suggests the average global temperature was 10-15 degrees higher, so species like us would probably not have survived. Over the intervening 150,000,000 years, a variety of natural processes absorbed and sequestered that carbon in rocks, coal, oil and gas. But coal, oil and gas are an easily available source of energy, and their extraction has powered progress over the last 200 years! And when we burn them, the carbon that was previously safety locked up in the ground goes back into the atmosphere.

So what is the problem?

The amount of carbon dioxide we have generated over the last 150 years can be found in the atmosphere, the oceans and on land. This is the product of the coal, oil and gas we have extracted and burnt over the same time period. The problem is that the Earth’s climate cannot cope with this increase, and we need to stop.

Here is how it all adds up:

Atmosphere – Since the beginning of the industrial revolution, the amount of carbon dioxide in the atmosphere has increased from around 2.2 to 3.3 trillion tonnes – meaning we have added about 1.1 trillion tonnes.

Oceans – There is a lot of focus on carbon dioxide in the atmosphere and the impact it has on climate, but carbon dioxide is also absorbed by the oceans, where it also has an impact – the water becomes more acidic and damages marine ecosystems. For every tonne of carbon dioxide in the atmosphere there is about 0.75 of a tonne in the oceans. This means there is probably about 800 billion tonnes in the oceans.

Land – There is also work that indicates that about 8.3 billion tonnes of plastic waste have been produced since 1950 – roughly equivalent to 26 billion tonnes of carbon dioxide. Since plastics account for about 30% of the petrochemical products stream, we can work out that 87 billion tonnes of carbon dioxide from the use of oil and gas as a feedstock is also in the ecosphere.

Total – This means we can estimate that we have put about 1.99 trillion tonnes of carbon dioxide into the ecosphere since we started using coal, oil and gas as a source of energy.

The amount that we find in the ecosphere is almost identical to the amount extracted from the geosphere over this time period. Evidence that this is a man-made effect can be seen by comparing this number to the 2.2 trillion tonnes of carbon dioxide equivalent that industry records show the coal, oil and gas industries have extracted from the planet over the last 150 years. The small difference is probably due to the accuracy of the figures, which have been collected over 150 years!

We often fall into the trap of differentiating between fossil carbon and biogenic carbon, as if biogenic carbon is acceptable, but we have been putting fossil carbon into the atmosphere for so long that it makes up about 35% of the carbon in the atmosphere and has therefore been absorbed by plants and will make up roughly the same fraction of what we call biomass! This means that 35% of the biogenic carbon is really second generation fossil carbon. This becomes important when one source is favoured over another by regulations.

The goal is not to stop using carbon – it is to stop taking it out of the ground and putting it into the ecosphere!

If the various government promises to achieve Net Zero are kept and we do manage to stop using fossil carbon as a fuel by 2050, where will we get the carbon we use as a chemical feedstock that we have come to rely on as the source of materials such as plastics, fertilisers, packaging, clothing, digital devices, medical equipment, detergents or tyres? Currently we use about 2.6 billion tonnes of carbon dioxide equivalent a year to make a wide variety of things – through a “petrochemical” supply chain. We cannot “decarbonise” that without inventing new materials to deliver all of the products, but we can “defossilise” it – which means we stop using virgin fossil carbon as its feedstock.

Where will the carbon come from then?

There are three sources of carbon (biomass, recycled plastics/oils/solvents and carbon capture and utilisation) widely touted as replacements for all that fossil carbon. All are essentially recycling previously used carbon. They tend to get framed as competitors for the role, but if you analyse the amounts available, the likely costs of using them, and the timescales needed to get them to the right scale it looks like we will need them all!

Back to Nature

Biomass refers to using biological sources for the raw materials – wood, crops, animals and bacteria are good examples. Advocates rightly point out that many synthetic materials are clones of natural materials. They tend to forget that society moved to synthetic analogues because there wasn’t enough to satisfy societies needs in terms of volume and price, but global supply chains were less sophisticated back then.

However, from the generally accepted numbers, there would be enough raw materials – the planet produces about 50 billion tonnes of biomass a year – of which about 14 tonnes is produced by man. Of that, it is estimated that about 1.8 billion tonnes of “waste” is produced a year – mainly cellulosic. This produced in farms and food processing plants. Of the biomass that goes to food, we waste about 30-40%, so can add another 1.6 billion tonnes, but this is produced in restaurants and houses, so collection might be expensive! And finally, we have the waste we humans and our animals directly produce. Estimates vary but are usually about 500 million tonnes of human waste and almost 3 billion tonnes from farm animals! There would be enough carbon in biomass to satisfy the requirements, but the logistics of collecting it might be a challenge (and probably involve the generation of more carbon dioxide – there is always a trade-off where transport is involved). Also, biological processes can often be slow and less atom efficient than the currently used chemical processes, but this can be accommodated by appropriate systems design.

Nevertheless, the use of biomass as a feedstock for chemicals is already here and growing in scale.

Second time around

All the carbon that currently goes out in the form of products could form the basis of a different recycling route – often called “chemcycling”. Here the previously used plastics, oils and solvents can be partially broken down into reactive chemical species like those used in the manufacture of the original products. This is usually done with heat, and so costs energy. It also often uses solvents or extra chemistry. Given the range of materials that will make up the input, there will probably need to be a sorting process at the front end. And, like the waste biomass, the input materials will be collected from geographically distributed sites, so will need to be transported to plants where the recycling will take place (with the potential carbon dioxide emissions as a result).

Mining the problem

Finally, we could use the largest source of carbon already in the ecosphere – the carbon dioxide we have been putting into the atmosphere. With its current concentration of about 0.05%, it is a daunting task. However, we can “practice” how to make it work with a higher concentration (often 10-15%) – when we burn things, we produce a gas stream with a higher concentration of carbon dioxide and send it up a chimney or flue. We will probably go on burning things for a few years yet and using them as a source of carbon will not only moderate the amount we put into the atmosphere in the short term, but also enable us to refine the technology so that we can one day we can remove carbon dioxide from the atmosphere and reverse the damage we have done to the climate – although sadly it would take hundreds of years to do so.

Are we there yet?

All three routes to providing a non-virgin fossil source of carbon are being worked on already. However, they are all at such a small scale it is difficult to judge their efficiencies and effectiveness.

• Biomass is probably the most technologically advanced, but scaling-up the processes and addressing the collection and logistics issues are important challenges that need to be overcome.
• Recycling the “second generation” carbon cannot supply enough – it is limited by the efficiencies and costs of all the processes from collection to chemical recycling but can probably contribute a sizable fraction of the requirement.
• Carbon Capture and Utilisation (CCU) is the least well advanced but with a roadmap to Direct Air Capture (DAC) (the slightly different name for capturing the carbon dioxide direct from the atmosphere) offers the most compelling argument for investment – if DAC can be made to work commercially, it can be used to remediate the atmosphere. Net zero targets aim to take us back to 1990 levels of carbon dioxide in the atmosphere by eliminating the use of fossil fuels. Depending on the scale and speed at which DAC can be implemented, it might be possible to get back to pre-Industrial Revolution atmospheric carbon dioxide levels in several hundred years!

Carbon Capture (CC) has rather had its reputation tarnished by the pervasive suggestion that it can be used to capture (and store) carbon dioxide so effectively we can go on using fossil fuels for many years. Most analysts outside the oil and gas industry do not see how the maths works!

All of the routes are years away from making a major contribution to replacing the volume of carbon based feedstocks used to make the wide variety of products (and the market is growing at over 5% per year, which means that it will double in size every 12 or so years). We need to start soon and grow quickly to make any meaningful impact.

Written by David Bott, Director of Innovation at SCI and originally published on Linkedin