Page 171 - CW E-Magazine (18-6-2024)

Special Report

rivers and coastlines and 1.7-mt is then significantly expanding this route is needed to optimise the process at the
transported to the ocean. Assigning an the low rate of waste collection. Over commercial scale.
economic value to this material has the longer term, there is a fundamental
the potential create a market and thus question about the continued growth The advantage of this approach is
reduce plastic waste in the environment. rate of plastic production. Significantly that it could potentially integrate with
Early-stage research has demonstrated reducing plastic production could act as existing steam crackers and down-
potential for recycling plastic from the a limiting factor on the amount that can stream facilities. Olefins, the backbone
marine environment. Improving recyc- be used a feedstock for chemicals but of much of the chemical industry, are
ling rates could greatly increase the would ultimately also reduce demand produced directly from fractions of
availability of plastic waste as a feed- on total feedstock requirements – whilst the pyrolysis liquid without passing
stock, as well as reduce demand for having further benefits for emissions through an intermediate, such as metha-
primary chemical production and virgin and the environment. Alongside collec- nol. A disadvantage is the formation
fossil feedstock input. This would tion and waste management challenges, of lighter and heavier fractions, which
reduce competition pressure for alter- there are further pressing research need reprocessing. Catalytic pyrolysis
native chemical feedstocks to produce needs to improve the viability of plastic is being explored as a way of increas-
polymers. However, polymer reuse waste as a chemical feedstock. ing the selectivity of the process. How-
(apart from mechanical recycling) is ever, it is not yet commercially possible
currently mostly very energy-intensive – Chemical recycling is already com- to use pyrolysis oil in steam crackers at
leading to high associated emissions, mercially feasible using PET but is any significant scale, as the amount of
if powered by fossil energy. much less well established for other plastic pyrolysis oil that can be fed into
materials. Further understanding of the a steam cracker is less than 10%.
This is a further challenge to con- non-mechanical recycling mechanisms,
sider when comparing the sustainability development of catalysts and processes, CO as a feedstock for chemicals
2
or emissions intensity of virgin fossil and assessment of yield, energy con-
feedstock-derived products to chemi- sumption and sustainability are needed Sources of CO 2
cally recycled feedstocks. To signifi- to evaluate the material and energy Point sources of CO and direct air
2
cantly reduce emissions and environ- efficiency in comparison to the cur- capture (DAC) of atmospheric CO are
2
mental issues associated with plastic rent production of virgin plastics using the two main potential sources of CO
2
production, whilst providing an alter- fossil fuels. An increasing uptake of that could be used as a feedstock for
native source of carbon for chemicals chemical recycling would require chemicals. These are both a form of
compared to virgin fossil carbon, recyc- investment into a greater level of waste carbon capture and utilisation (CCU).
ling rates will have to significantly separation, advanced chemical recycling
expand – with some estimating a poten- infrastructure, and asset modification. Point sources of CO 2
tial required recycling rate of between Point sources of CO are typically
2
70 – 90% 109,110,111. This is a vast Gasification to syngas offers the found at large industrial facilities that
increase on present recycling rates and possibility of building longer chain emit waste CO . Examples include
2
would require significant policy inter- molecules via methanol synthesis and power stations, cement and steel fac-
vention and system redesign. then methanol-to-olefins or Fischer- tories, chemical manufacturing like
Tropsch to straight chain hydrocarbons ammonia production, paper and waste
Challenges and future research via syngas. Improving and optimising incinerators, and brewing or bio-
needs the selectivity of the process presents ethanol production plants. The precise
The utilisation of waste plastics an opportunity for further research. ratio of CO in these emissions varies.
2
for conversion into chemicals is now For example, cement emissions com-
the focus of intensive research, lead- There may be routes that do not prise 75-90% CO , whilst natural gas
2
ing to new ideas about processing require waste type separation, which is power stations emissions are just 4-5%.
routes. However, challenges persist. one of the main challenges with waste
In the short to medium term, the plas- management. Liquefaction of solid The purity of the CO is important
2
tic waste stream could be a promising wastes containing both biogenic and for any subsequent chemical produc-
feedstock for the substitution of virgin recycled carbon, is currently being tion. Coupling these processes with
fossil carbon, as it is available in signi- scaled up via demonstration units capture provides an opportunity both
ficant quantities. A major challenge to worldwide, but further research is to concentrate and purify the waste

Chemical Weekly June 18, 2024 171

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