Production of diesel fuel from polyolefins by pyrolysis

Increasing consumption of plastics has demanded to seek new solutions for the treatment of
accumulating waste. Pyrolysis is a chemical recycling method in which plastics are thermally
degraded to more valuable products such as chemicals or fuels. The quality of pyrolysis
products depends on many factors such as process conditions, reactor type and the quality
of feedstock. Plastics are typically originated from the same feedstock as conventional fuels
which makes them a desirable choice for pyrolysis treatment. However, they produce a wide
spectrum of degradation products and can contain detrimental impurities that produce
harmful compounds. With certain process choices and the utilization of catalyst, plastic can
be converted to diesel range fuel. Catalyst with low acidity and high porosity is better suited
to produce larger molecular compounds. The product can be further processed by various
upgrading methods such as distillation, hydrogenation and the use of additives.
The objective of the thesis was to find a route to convert polyolefins to diesel range fuel by
pyrolysis. Experimental series was performed with a lab-scale batch reactor in order to seek
the most promising catalyst and optimal process conditions. The catalysts tested were ZSM5, montmorillonite and γ-alumina. The temperature was varied in a range of 500–550 °C.
Based on the results, montmorillonite catalyst was chosen to be used in a larger, fluidizedbed unit in temperature range of 475–575 °C. GC/MS, GC/FID and simulated distillation
were done to all products.
The results showed that the catalyst shifts the product distribution towards lighter fraction.
Average liquid yield was 75 wt.%. ZSM-5 catalyst produced high amount of gases and
aromatic components. Montmorillonite and γ-alumina produced mainly liquid in a carbon
length range of <C10 and C11–C21. Simulated distillation revealed that around 40 wt.% of the
product was in a range of <C10. In fluidization-bed unit average liquid yield was 70 wt.%.
Aliphatic content was 4-5 times higher than aromatic. The proportion of lighter components
(<C10) accounted 30 wt.% in average. The yield for diesel range fuel increased at lower
temperatures based on the simulated distillation. Montmorillonite catalyst yielded
promising results and could be a potential candidate for future experiments.