Page 137 - CW E-Magazine (16-4-2024)

Point of View

Multiple approaches for decarbonising ethylene

production

Ethylene is important. It is the single largest olefin produced and consumed and is the starting point for a host of chemicals and
polymers. Presently, its production comes with a hefty carbon footprint that carries down the value chain in the myriad products made
from ethylene. While it is not the only carbon-intensive feedstock (ammonia – required mainly to make fertilisers – is a significant another),
its sheer volume makes the task of decarbonising its manufacture both challenging and important if the petrochemical and downstream
industries are to meet their carbon mitigation goals.

Several efforts are ongoing to achieve this. Some are incremental improvements, which though important, are unlikely to move the
needle to the extent required. But some fundamental changes are also upcoming in the way ethylene is made, and while these are nowhere
near the scale needed at present, and not all will scale up, some will make the cut.

Current routes
Ethylene is nearly entirely made by the steam cracking of hydrocarbon feedstocks – which can be ethane-rich gas (preferred) or
naphtha. These two account for about 95% of all ethylene produced today. There is an alternate route that produces ethylene from coal through
a convoluted process that goes through syngas and methanol production, but this is practiced only in China. It accounts for about 3% of
global ethylene capacity, partly due the fact that it has been commercialised only recently (around 2010), and the capital costs of these
projects are stiff, and the environmental impacts (especially, the water footprint) are considerable. A small amount of ethylene come from
other sources, including ethanol cracking (more on this latter); and as a by-product of refinery operations (fluidised catalytic cracking).

The carbon footprints of ethylene crackers vary, depending on the feedstock mix that goes into them, but broadly speaking between
1.4-1.8-tonnes of carbon dioxide (CO ) is emitted per tonne of ethylene produced. Considering global ethylene production in 2023 was
2
around 177-mt, this olefin alone represents a carbon footprint of around 260-mt of CO .
2
The approaches to lower this footprint can be broadly classified into three categories: change in the feedstock that goes into a cracker;
modifications in the process, including through electrification (with the electricity being renewable or non-fossil based); and capture of
the CO released and its sequestration.
2
Feedstock changes
As pointed out earlier, small quantities of ethylene are currently produced by the catalytic dehydrogenation of ethanol (which is
currently made from renewable resources, including sugars, starches and biomass). This technology is relatively straightforward and has
been practiced for several decades (including in India), but for commercial reasons could not be scaled up. That may be about to change.

In Brazil (which has the most cost-efficient production of sugarcane-based ethanol), petrochemicals producer Braskem has increased
ethylene capacity to feed derivative plants, producing in the main polyethylene (PE), and is attempting to hawk the bio-based polymer
at a price premium to customers keen to burnish their green credentials. In the US, speciality chemicals producer, Croda, is also going
down this route to produce ethylene oxide (EO) – a hazardous material that has onerous requirements for long-distant transportation.
Closer home, India Glycols Ltd. also produces EO in a similar manner and supplies it to a joint venture with speciality chemicals company,
Clariant, for EO derivatives, including surfactants that can be tagged with a green label much desired by companies in the home and
personal care industries.

More recently, a sustainable feedstock for ethylene crackers is coming from efforts to address the mounting problem of plastic waste.
Given the limitations of mechanical recycling – almost always the first choice to close material loops – petrochemical companies are
mooting advanced recycling, also termed as chemical recycling. Though this is not without its critics, industry proponents believe this is
a scalable solution aimed at preventing hard-to-mechanically-recycle waste from ending up in landfills or leaking uncontrollably into the
environment.

The most common chemical recycling route (and there are several) involves converting plastic waste into a hydrocarbon-containing
oil, termed pyrolysis oil, which can be upgraded and then serve as a co-feed to a naphtha cracker. The technology is still in its early stages
and there are no crackers that purely run on this waste-derived feed, but it does afford olefins with a lower carbon footprint that can be

Chemical Weekly April 16, 2024 137

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