Accelerating Net Zero

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ACCELERATING NET ZERO

Role

of CCUS in

Net Zero

Transition

Prof. Rajnish Kumar

Department of Chemical Engineering,

IIT Madras

hile role of renewables, solar, wind, hydro/waves,

hydrogen etc. including nuclear would ensure a cleaner

future. Current energy need, and proposed GDP growth

in many parts of the world could not be achieved without

ensuring implementation of CCUS. In general, people

around the world are aware of the effect of rising CO2 in the atmosphere

and resulting global warming. Prime challenge for the scientific

community is to educate people that the scale at which CCUS has to be

implemented has no parallel in the history of human kind. Significant

effort is required to identify a solution which is not only economical but

also sustainable at the scale it has to be delivered.

In 2023, not a single electricity producing commercial plant around the

world has been able to demonstrate CCUS in its entirety.

CCUS is essentially a three-step process, the first step is to capture the

carbon dioxide at its source;

1. Point source capture (or separation) of CO2 from its associated

gases (mostly N2, as the other toxic gases which are at a much lower

concentration has already been captured) from industries like steel

manufacturing, cement manufacturing, electricity production etc.

For CO2 capture the most mature process is use of mono-ethanol amine

(MEA, or a derivative of this molecule) for CO2 capture. An alternate route

which uses solid adsorbent/absorbent like, carbon nanotubes (CNT), metal

organic framework (MoF) etc. has not been proven at this scale. Some

Innovative solutions also exists (hydrates, ionic liquids etc.) which are being

tested at lab/pilot scale. If one talks about the most mature process which

utilizes a chemical solvent (like MEA) to capture CO2 from its associated

gases, the biggest challenge is in recycling and regeneration of MEA,

assuming that the corrosion issues could be handled appropriately. Some

of the major concerns are regeneration cost, loss of active material during

regeneration, and significantly large losses of water from cooling towers

and other operations. If one talks about CNT, and MoF like materials for

CO2 capture, corrosion is not an issue, however, generation of such

material itself at such a scale is a big challenge. MEA based processes are

being implemented for demonstration around the world, with a typical cost

of USD 30-50 per ton of CO2 captured. This only captures the process cost

of CO2 capture from using MEA based solvent. However, if one looks at the

raw material (i.e. MEA itself) it has its own CO2 footprint. MEA is produced

from reacting ammonia and ethylene oxide, thus, production of these two

chemicals should also be decarbonised and the cost of the same should

appropriately be added in the overall CO2 capture cost.

Direct air capture (DAC) is a technology which many believes is a way

to go, the proponent of this approach takes a futuristic view. It is argued

that producing fossil fuels and capturing CO2 from its utilization is an

endless trap, rather one should stop using fossil fuels all together! This

approach ensures no anthropogenic CO2 emission into the atmosphere (at

least not from use of fossil fuel). Sometime in future when there is no CO2

emission from point source, DAC would ensure that all the CO2 which has

been emitted by humans (so far) could be captured directly from air, and

its concentration could be brought down to 350-400 PPM level. However,

capture of PPM level CO2 from a gas stream is not going to be trivial, and

this process could be prohibitively expensive, current cost is close to 200

USD per ton for captured CO2. Further, the material/chemical required to

capture PPM level CO2 (from air) is currently quiet immature, and actual

cost of the process will not be evident unless one does a proper life cycle

analysis of this approach.

The second step in CCUS involves utilization of captured CO2.

Here one has to realise that an electricity production plant or a cement

manufacturing unit produces tonnes of CO2 every day!

2. Transporting the captured, relatively purer CO2 (which comes

from step 1) to the utilisation site where CO2 could be processed (with a

hydrogen rich source, or H2) and converted to a liquid chemicals. Some of

the typical chemicals are methanol, dimethyl ether, formic acid, aviation

fuels etc.

However, if one looks

at the raw material

(i.e. MEA itself) it has

its own CO2 footprint.

MEA is produced from

reacting ammonia

and ethylene oxide,

thus, production of

these two chemicals

should also be

decarbonised and

the cost of the same

should appropriately

be added in the overall

CO2 capture cost

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