Aromatization of hydrocarbons during thermochemical conversion of polyethylene: Investigation on the influence of steam and potassium
Examensarbete för masterexamen
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|Type: ||Examensarbete för masterexamen|
|Title: ||Aromatization of hydrocarbons during thermochemical conversion of polyethylene: Investigation on the influence of steam and potassium|
|Authors: ||Thedin, Erik|
|Abstract: ||Within the transition towards a circular economy society, a more resource-efficient
way of handling the processed carbon atoms is needed. The valorization of the generated
plastic wastes by using them as feedstock to generate new monomers could
be an adequate strategy to reach this goal. This valorization could be achieved by
thermochemical conversion (or recycling) of these wastes. During the thermochemical
conversion of plastics, the aromatization of potentially valuable hydrocarbons
occurs. If the reaction mechanism governing the formation of aromatics is known,
the process could be better optimized towards olefins production. Olefins such as
ethylene and propylene are monomers used as feedstock to produce some of the most
conventional plastics on the market, e.g. polyethylene (PE), polypropylene (PP),
and polyvinyl chloride (PVC).
In this work, the underlying reactions of aromatization during the decomposition of
PE have been reviewed, along with the impact of the addition of steam and potassium.
The review was conducted by the literature study on (1) the decomposition
of PE in a high-temperature environment; (2) the possible reactions leading towards
aromatic structures and; (3) the interactions of potassium with hydrocarbons. Based
on the literature review, a hypothesis on how interaction from the presence of potassium
and steam affect the aromatization of the hydrocarbons is formulated. Then,
through the experimental work, the potential effect of steam and potassium in the
thermochemical process was studied. The experiments showed that the gas and
aromatic yields were affected both by the presence of steam and potassium. The
addition of steam increased the overall yields, both of valuable gases and aromatics
compared to the results obtained from the experiments conducted with only nitrogen.
The addition of potassium increased the production of H2, CO, and CO2, while
the aromatic content was reduced. When solid KOH was added to the reactor the
olefin yield was reduced. But when K-enriched olivine was used, that phenomenon
was not seen, and the yield of olefins was unaffected by the potassium. However,
there are insufficient experimental data to confirm or reject the hypothesis.
Furthermore, during this work, a new lab reactor and analysis technique capable
of detecting/measuring KOH during thermochemical conversion in a fluidized bed
was developed. From preliminary experiments, differences are observed between the
UV-spectras generated by the decomposition of PE in either nitrogen, steam/nitrogen,
and steam/nitrogen environment with potassium present. However, further
research is needed to shed light upon the governing mechanism behind the observed
differences due to the presence of steam and potassium.|
|Keywords: ||Thermochemical recycling;steam cracking;pyrolysis;fluidized bed reactor;plastic waste;polyethylene;aromatization;potassium;UV-spectroscopy|
|Issue Date: ||2022|
|Publisher: ||Chalmers tekniska högskola / Institutionen för rymd-, geo- och miljövetenskap|
|Collection:||Examensarbeten för masterexamen // Master Theses|
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